Geological Society of America Bulletin - University of Vermontlewebb/PNG/PNG Papers/Daczkoetal_2011_GSA.pdf · Sea (Martinez and Cochran, 1988), the Gulf of Aden (Manighetti et al.,

Geological Society of America Bulletin

doi: 10.1130/B330326.1 published online 24 June 2011;Geological Society of America Bulletin

Nathan R. Daczko, Peter Caffi and Paul Mann Papua New GuineaStructural evolution of the Dayman dome metamorphic core complex, eastern

Email alerting servicesarticles cite this article

to receive free e-mail alerts when newwww.gsapubs.org/cgi/alertsclick

SubscribeAmerica Bulletin

to subscribe to Geological Society ofwww.gsapubs.org/subscriptions/click

Permission request to contact GSAhttp://www.geosociety.org/pubs/copyrt.htm#gsaclick

official positions of the Society.citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflectpresentation of diverse opinions and positions by scientists worldwide, regardless of their race, includes a reference to the article's full citation. GSA provides this and other forums for thethe abstracts only of their articles on their own or their organization's Web site providing the posting to further education and science. This file may not be posted to any Web site, but authors may postworks and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequenttheir employment. Individual scientists are hereby granted permission, without fees or further Copyright not claimed on content prepared wholly by U.S. government employees within scope of

Notes

articles must include the digital object identifier (DOIs) and date of initial publication. priority; they are indexed by PubMed from initial publication. Citations to Advance online prior to final publication). Advance online articles are citable and establish publicationyet appeared in the paper journal (edited, typeset versions may be posted when available Advance online articles have been peer reviewed and accepted for publication but have not

Copyright © 2011 Geological Society of America

as doi:10.1130/B330326.1Geological Society of America Bulletin, published online on 24 June 2011

http://www.geosociety.org/pubs/copyrt.htm#gsa

http://gsabulletin.gsapubs.org/cgi/alerts

http://gsabulletin.gsapubs.org/subscriptions/index.ac.dtl

ABSTRACT

A shallow-dipping ductile mylonitic shear zone and concordant brittle detachment fault (Mai’iu fault) together make up the dominant geological structure that controls the orienta-tion of dip slopes on the fl anks of Mount Day-man, eastern Papuan Peninsula, Papua New Guinea. The dip slopes dip in all directions from the peak of Mount Dayman and form a domed landform that is much less dissected by streams compared to the adjacent Mount Suckling domed landform. The orientation of megacorrugations on the domed surface of Mount Dayman (footwall) is consistent with NNE-directed transport of the hanging-wall block, which is composed of low-grade undifferentiated volcanic and sedimentary rocks and minor ultramafi c rocks. Though previously documented as a thrust surface, the geometry and style of structures and map relations presented in this study indicate an extensional origin for the domed mylonitic foliation (S1) and mineral elongation linea-tion (L1). The fi eld relationships are consis-tent with the domed landform comprising the core of a metamorphic core complex. Ob-servations of dominantly NNE-trending re-gional lineaments in aerial photography and Shuttle Radar Topography Mission (SRTM) data correlate with detailed fi eld analysis of mineral elongation lineations (L1) in the main metamorphic core complex–bounding shear zone. Field relationships show a cross-cutting sequence of structures that includes: (1) ductile S2 folia with ESE-plunging blue sodic-calcic amphibole mineral elongation lineations; (2) narrow, steeply dipping duc-tile D2 shear zones; and (3) semibrittle to brittle fault zones. S-C! fabrics, asymmetric

strain shadows around porphyroclasts, and fault drag indicate a top-down-to-the-NNE sense of shear for most structures. Kinematic vorticity analysis of the highest-grade ductile deformation indicates a kinematic vorticity number (Wk) between 0.34 and 0.56, sug-gesting general shear for the early stage of deformation (D1). The NNE-directed linea-ments and L1 mineral elongation lineations are consistent with the Australia-Woodlark Eulerian pole for periods between the early Pliocene (3.6 Ma) and Pleistocene (0.52 Ma). This observation is consistent with ca. 3.3 Ma granite and monzonite intrusions that cut the mylonitic fabrics and limit the age of the mylonitic fabrics to older than 3.3 Ma on Mount Suckling. A SE-dipping sedimentary sequence (Gwoira Conglomerate) character-izes part of the hanging wall of the metamor-phic core complex. Petrography of the clasts within the sedimentary rocks indicates that metabasite rocks were the dominant source. The unit is in fault contact with the meta-basite footwall across prehnite-bearing D3 brittle fault zones.

INTRODUCTION

Low-angle normal faults and metamorphic core complexes associated with regional tec-tonic extension are globally recognized in both oceanic (e.g., Mutter and Karson, 1992; Cann et al., 1997; Blackman et al., 1998; Tucholke et al., 1998, 2008; Ohara et al., 2001; Okino et al., 2004; Drolia and DeMets, 2005) and continental crust (e.g., Davis and Coney, 1979; Davis et al., 1986; Davies and Warren, 1988, 1992; Lister and Davis, 1989; Dinter and Royden, 1993; Hill, 1994; Little et al., 2007; Gautier et al., 2008; Spencer and Ohara, 2008; Jolivet et al., 2010; Spencer 2010). The Day-man dome is situated on the Papuan Peninsula, Papua New Guinea, adjacent to the Woodlark Basin (Fig. 1A). This region is one of only six well-recognized regions worldwide that span

the transition from active continental rifting to active seafl oor spreading; the others are the Red Sea (Martinez and Cochran, 1988), the Gulf of Aden (Manighetti et al., 1997), the Tyrrhenian Sea (Jolivet et al., 1998), the Gulf of Califor-nia (Langenheim and Jachens, 2003), and the Laptev Sea (Drachev et al., 2003). High-grade lower-crustal metamorphic core complexes have been studied in eastern Papua New Guinea on the D’Entrecasteaux Islands (Fig. 1B), where rocks that formed under a large range of depth and temperature conditions have been up-lifted (Davies and Smith, 1971; Ollier and Pain, 1981; Davies and Warren, 1988; Hill et al., 1992, 1995; Baldwin et al., 1993, 2004, 2005; Baldwin and Ireland, 1995; Little et al., 2007; Monteleone et al., 2007; Webb et al., 2008). However, studies of emergent, late Quaternary coral reefs and Neogene sedimentary sections in eastern Papua New Guinea suggest that the D’Entrecasteaux Islands have been stable or subsiding for the past 0.5 m.y. (Mann and Tay-lor, 2002). The main locus of active rifting asso-ciated with rapid uplift of Holocene reefs and late Neogene sedimentary rocks is to the south-west at Goodenough Bay (Fig. 1B), near the Dayman dome (Mann and Taylor, 2002), where actively uplifting moderate- to high-pressure (P) metabasite rocks are exposed below the Owen Stanley fault system (Davies and Smith, 1974; Davies, 1980; Worthing, 1988).

Within the Woodlark spreading basin, mag-netic anomalies indicate that seafl oor vol canism has penetrated westward since formation of the basin in late Miocene time (6 Ma; Taylor et al., 1999), and eastern Papua New Guinea is arguably the only known setting on Earth where “active” subaerial metamorphic core complexes occur in the tectonic context of an actively propagating oceanic spreading ridge. This contribution presents the fi rst detailed structural and kinematic study of the actively exhuming Dayman dome. Nearly 800 struc-tural measurements and fi eld observations from metabasite rocks from the northern fl ank of the

For permission to copy, contact [email protected]© 2011 Geological Society of America

1

GSA Bulletin; Month/Month 2011; v. 1xx; no. X/X; p. 1–17; doi: 10.1130/B30326.1; 10 fi gures.

†E-mail: [email protected]§Current address: Department of Earth and Atmo-

spheric Sciences, University of Houston, Houston, Texas 77204-5007; [email protected].

Structural evolution of the Dayman dome metamorphic core complex, eastern Papua New Guinea

Nathan R. Daczko1,†, Peter Caffi 1, and Paul Mann2,§

1Geochemical Evolution and Metallogeny of Continents Australian Research Council (GEMOC ARC) National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Sydney, Australia2Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78758-4445, USA


Daczko et al.

2 Geological Society of America Bulletin, Month/Month 2010

Dayman dome (Fig. 2) outline the structural and kinematic history of the shear zones and faults. These data establish the tectonic signifi cance of and geometric relationship between the mapped structures. Measurement of kinematic vorticity (Means et al., 1980; Lister and Williams, 1983; Passchier, 1986) for the dominant L-S tectonite permits an interpretation of the fl ow regime for the shear zone, including the sense of displace-ment. Sense-of-shear indicators were analyzed to further document the movement history of the shear zone.

REGIONAL GEOLOGY

The Oligocene to Holocene tectonics of eastern Papua New Guinea continue to be controlled by the west-southwest convergence between the Pacifi c and Australia plates (Fig. 1A). Global positioning system (GPS) work by Wallace et al. (2004) has shown that the in-tervening convergent zone is characterized by micro plates, including the North Bismarck, South Bismarck, New Guinea highlands, Solo-mon Sea, and Woodlark plates (Fig. 1A). The New Britain Arc (South Bismarck plate) is rap-idly rotating in a clockwise direction as a result

of its Pliocene to recent collision with the New Guinea highlands.

In eastern Papua New Guinea, a large active fault system called the Owen Stanley fault zone separates the New Guinea highlands of the Aus-tralia plate from the Woodlark plate to the north-

east (Fig. 1A). Wallace et al. (2004) used GPS results to defi ne a pole of rotation between the two microplates across the Owen Stanley fault zone. Their pole is consistent with the geology and topography along the length of the Owen Stanley fault zone, including the elevated area

TrobriandIslands

Trobriand Basin

GI

GB

MB

NI

FI

Gwoira Conglomerate

Suckling-Dayman massifAlotau

MS

Tip ofWoodlark

Basinspreading

system

TF

Suckling-DaymanmassifAUS/WLK

0 20 40 60 80 100

km

N

Manus Trough

New Guinea Highlands

Papua NewGuinea

Aure Trough

OSFZ

Australia

WoodlarkBasin

spreadingsystem

Trobriand Trough

4°S

8°S

12°S150°E 154°E146°E142°E

10°S

New Britain TrenchNew Britain

INDO-AUSTRALIANPLATE

PACIFICPLATE

PAPP

A,G&E

A,EB&G

MountSuckling

MountDayman

A

B

North Bismarck plate

Manus Is.New Guinea Trench

South Bismarck plateKilinailau

Trench

Solomon Sea plate

Woodlarkplate

PAC/AUS

~110 mm/yr

9°S

10°S

149°E 151°E

Owen StanleyFault Zone

Figure 1. (A) Regional tectonic setting of east-ern Papua New Guinea (PNG), indicating locations discussed in the text. Background topography and bathymetry were created using GeoMapApp (www. geomapapp.org). Australia/Woodlark (AUS/WLK) pole of rotation and dashed arrows along the Owen Stanley fault zone (OSFZ) are predicted motion across the fault of the Woodlark micro plate relative to a fi xed New Guinea highlands microplate from the best-fi t model of Wallace et al. (2004). The longest arrow represents 22.5 mm relative motion per year. (B) Map of eastern Papua New Guinea and the D’Entrecasteaux Islands: GI—Good-enough, FI—Fergusson, and NI—Normanby. PP—prehnite-pumpellyite; PA—pumpellyite-actinolite; A,G&E—amphibolite, granulite and eclogite; A,EB&G—amphibolite, epi-dote blueschist and greenschist facies; TF—Trobriand fault; GB—Goodenough Bay; MB—Milne Bay; MS—Morseby Seamount. The Gwoira Conglomerate (1 km thick; Davies and Smith, 1974) is deposited onto the exposed metabasite Dayman dome and Biman dip slopes (modifi ed from Hill and Baldwin, 1993; Wallace et al., 2004; Little et al., 2007). Compilation of faults of Mio-cene to recent age is from Little et al. (2007).


Evolution of the Dayman dome, Papua New Guinea

Geological Society of America Bulletin, Month/Month 2010 3

of the Dayman dome in the footwall block of the OSFZ. Along the northern fault, their pole predicts ~20 mm/yr of convergence perpendicu-lar to the Owen Stanley fault zone north of 8°S. Adjacent to the fault in this area, there are large folds affecting Quaternary sedimentary rocks and large thrust earthquakes. Moving to the southeast along the Owen Stanley fault zone, the pole predicts 10–15 mm/yr of left-lateral strike-slip faulting, consistent with geologic evidence (Davies and Smith, 1971). In the area of the Dayman dome, motion along the Owen Stanley fault zone plate boundary is oblique-left slip and changes at the tip of the Papuan Penin-sula to ~12 mm/yr of roughly orthogonal open-ing (Wallace et al., 2004).

Most previous workers have inferred that the large metamorphic core complexes in this area are related to the extensional component of opening along this microplate boundary (Davies and Jaques, 1984; Davies and Warren, 1988; Hill, 1994; Martinez et al., 2001; Little et al., 2007; Spencer and Ohara, 2008). An unsolved enigma is the 75–100 km step in the plate bound-ary in the 1 km deep Goodenough Bay separat-ing core complexes in the D’Entrecasteaux Islands from those at the Dayman dome. The D’Entrecasteaux Islands form the direct western continuation of oceanic spreading features in the Woodlark Basin (Fig. 1B). As in the case of these island domes, the Dayman dome exhibits a broad topographic dome that is onlapped or

faulted against the coastal plain of the Papuan Peninsula (Figs. 2 and 3; Hill, 1994).

In this study, we examine the Mai’iu fault, a component of the Owen Stanley fault zone north of Mounts Suckling and Dayman that juxtaposes rocks of differing metamorphic grade (Fig. 2). The Mai’iu fault scarp extends to elevations >1000 m from the fault trace up the northern edge of the mountain range. The fault forms the northern boundary of the Goropu Metabasalt; this unit is a regionally coherent body of mafi c rocks that consists of mainly metamorphosed pillow lava and minor limestone, and constitutes much of the domed mountain range (footwall), along with minor Tertiary felsic plutonic rocks south of Mount Suckling (Fig. 2). Planktonic

MOUNTSUCKLING

KEVERIFAULT SYSTEM

ONUAM FAULT

MOUNTDAYMAN

MAI’IU FAULT

Biniguni

Pumani

MOUNTMASASORU

GWOIRA FAULT

SOLOMON SEA

GB

Undifferentiated Quaternary and TertiaryVolcanic and Sedimentary RocksUga Sandstone(sandstone, siltstone; minor conglomerate)

Gwoira Conglomerate(conglomerate, poorly sorted sandstone and siltstone)

Undifferentiated Tertiary Felsic Plutonics(granite; granodiorite, monzonite; microdiorite, micromonzonite porphyry)

Kutu Volcanics(basalt lava and pillow lava; minor tuff, limestone)

Undifferentiated Ultramafics(ultramafic rock with cumulus or tectonite fabric)

Undifferentiated Gabbro(gabbro with ophitic, allotriomorphic/hypidiomorphic or cumulus textures)

Yau Gabbro(gabbro, diorite, granophyric tonalite: prehnite-pumpellyite facies)

Goropu Metabasalt (including Bonenau Schist Member)(variably schistose meta-basalt, -dolerite, -gabbro and -limestone; hornfels)

KEY:

JURASSIC? TO CRETACEOUS{Papuan Ultramafic Belt (PUB)Gabbro and Ultramfic zones}

PLIOCENE

PLIOCENE TO HOLOCENE

UPPER MIOCENE TO PLIOCENE

UPPER CRETACEOUSTO MIDDLE EOCENE

UPPER CRETACEOUS

N

0 5 10

km0720000 40 60

60400720000 80 00

80

20

8940000N

00

20

00

0800000E

Figure 2. Geological map (Mer-cator projection) of the Suckling Dayman massif and surround-ing areas (modifi ed from Davies and Smith, 1974). GB—Good-enough Bay. Boxes near Bini-guni and Pumani show the study areas.


Daczko et al.


foraminifera recovered from weakly metamor-phosed pelagic limestone indicate a Late Creta-ceous age for the Goropu Metabasalt (Smith and Davies, 1976). The plutonic rocks are largely undated, with the exception of a preliminary laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) 206Pb-238U zir-con age of one sample of granite, dated at 3.3 ± 0.1 Ma (Caffi , 2008). The hanging wall mainly consists of nonmetamorphic undifferentiated Quaternary and Tertiary volcanic and sedimen-tary rocks and minor parts of the Papuan ultra-mafi c belt (Fig. 2), an ophiolite obducted during Paleogene arc-continent collision.

Pumpellyite-actinolite–facies assemblages reported by previous workers to contain local aragonite, lawsonite, and/or glaucophane are found at elevations greater than 2000 m in the footwall metabasite. These assemblages have been used to infer Paleogene subduction of the Late Cretaceous oceanic crust (Davies, 1980; Davies and Jaques, 1984). The assemblage in-dicates peak metamorphic pressures of 6–9.5 kbar, demonstrating exhumation of the core of the Dayman dome from depths of 20–30 km (Daczko et al., 2009). The Mai’iu fault scarp exposes greenschist-facies footwall metabasite L-S tectonite that is ~500 m thick (Davies, 1980) and overprints the pumpellyite-actinolite–facies assemblages. The L-S tectonite fabric parallels the Mai’iu fault scarp, and mineral equilibria modeling suggests that the assemblage evolved at moderate-pressure greenschist-facies condi-tions of 5.9–7.2 kbar at ~425 °C (Daczko et al., 2009). The elevation in temperature likely de-rives from juxtaposition of the metabasite rocks

against the Papuan ultramafi c belt either during obduction of the ophiolite over the meta basite rocks (Davies, 1980) or during exhumation of the metabasite rocks from beneath the ophio-lite (or likely both). However, an aim of this contribution is to demonstrate that the L-S tec-tonite is extensional in origin and forms part of a metamorphic core complex, consistent with the juxtaposition of the greenschist-facies meta-basite footwall against mainly nonmetamorphic rocks of the hanging wall. Modeling variable Fe3+ indicates that sodic-calcic blue amphibole identifi ed by Daczko et al. (2009) in minor S2 foliations in the footwall metabasite formed under a higher oxidation state compared with the S1 assemblage, probably at <4.5 kbar. These metamorphic results suggest that the dome has been exhumed from at least 20–30 km depth, and the main L-S tectonite mylonitic fabric of the Dayman dome was last active at >20 km depth and therefore records an early part of the exhumation story for the metabasite rocks.

REMOTELY SENSED STRUCTURAL INFORMATION

Aerial photography and Shuttle Radar Topog-raphy Mission (SRTM) data were examined to delineate major structures and lineaments in or-der to place the detailed fi eld work that follows into a regional context. The specifi c observa-tional aims of this analysis are to defi ne (1) re-gional lineaments that may demarcate major structures or geological boundaries, (2) areas of the Suckling-Dayman massif where the topog-raphy is controlled by the dip of shear zones (i.e.,

metabasite dip slopes), and (3) drainage patterns across the dome to compare to dip slopes and megacorrugations (very large corrugations on a fault plane) identifi ed in the SRTM data.

Aerial Photographs

Six aerial photograph stereopairs were ana-lyzed using a Topcon mirror stereoscope. Fig-ure 4 shows a mosaic of the interpretation. Gray shaded areas represent interpreted meta-basite dip slopes. Gray lines represent water-ways. Thin black lines represent lineaments commonly observed as straight streams on dip slopes. The analysis shows that the Suckling-Dayman massif may be divided into the Suck-ling and Dayman domes (Fig. 4). The Dayman dome is nearly complete in the north, having been dissected by the Gwariu and Biniguni Rivers (Fig. 4). The Nowandowan River on the southeast fl ank and the Bonua River on the south and southwest fl anks have eroded a large proportion of the southern half of the Dayman dome (Fig. 4). The Suckling dome is largely eroded, and dip slopes are limited to the east fl ank. Therefore, aerial photographs west of the Mai’iu River (Fig. 4) were not interpreted because few lineaments were observed. The Biman dip slopes east of the Dayman dome are relatively small and are restricted to the lower hills south of the Gwoira Conglomerate. A sharp topographic change from alluvium to the irregular hills of the Gwoira Conglomerate marks the location of the Gwoira fault (Fig. 4), which marks the northern boundary of the Gwoira Conglomerate.

Dayman DomeDayman Dome

GCGC

2850 m2850 m

~5 km~5 km

BiniguniBiniguni

06040605

06300627

06040605

06300627 0669

06770664

0669

06770664

Figure 3. Shuttle Radar Topog-raphy Mission (source: U.S. Geological Survey) image view looking south of the Dayman dome. A dashed line marks the Mai’iu fault, part of the Owen-Stanley fault zone. GC—Gwoira Conglomerate. Sam-ple sites discussed in text are labeled.




Gar

ana

Ck

Mai

’iu R

.

Bon

ua R

.

Now

ando

wan

R.

Yom

e C

k

Pum

ani R

.

Now

ando

wan

R.

Mai

’iu R

.

Suc

klin

gD

ome

Day

man

Dom

e

Allu

vium

Allu

vium

Allu

vium Gw

oira

Con

glom

erat

e

Bim

andi

p sl

opes

Mou

ntD

aym

an

Bin

igun

i

Pum

ani

Gwariu R.

Bou

ndar

y of

Day

man

Dom

eC

hang

e in

dip

dire

ctio

n

Sm

ooth

dip

slop

esLi

neam

ent

KE

Y:

N =

26

N =

306

N =

85

Suc

klin

gD

ome

Day

man

Dom

e

Bim

andi

p sl

opes

NN

N

N

Gwo

ira F

ault

N =

219

Day

man

Dom

eL1

3.6–

0.52

Ma

vect

or

Cur

rent

vect

or

AB

C

D

E

Biniguni R.

Dare Ck

Aro

CkYa

tap

Ck

Yug

a C

k

Am

pae

Ck

0740

000E

8920

000N

8930

000N

8910

000N

0760

000E

0780

000EN

05

km

Fig

ure

4. (A

) Mos

aic

of in

terp

rete

d ae

rial

pho

togr

aphs

show

ing

smoo

th d

ip sl

opes

wit

h lin

eam

ents

. Fin

e da

shed

line

show

s the

app

roxi

mat

e lo

cati

on w

here

the

sad

dle

betw

een

the

two

dom

es c

hang

es d

ip d

irec

tion

. Maj

or r

iver

s an

d cr

eeks

men

tion

ed in

tex

t ar

e la

bele

d ex

cept

for

B

iyaw

ap C

reek

, whi

ch is

a s

mal

l cre

ek th

at fl

ows

into

Yat

ap C

reek

. Sca

le a

nd e

asti

ng/n

orth

ing

mar

kers

are

onl

y ap

prox

imat

e, a

s th

e ae

rial

ph

otog

raph

s ar

e no

t rec

tifi e

d. (B

) Ros

e di

agra

m s

how

ing

tren

d of

min

eral

line

atio

n da

ta in

the

stud

y ar

ea o

verl

ain

wit

h th

e cu

rren

t pla

te-

mot

ion

vect

or (W

alla

ce e

t al.,

200

4) a

nd th

e 3.

6–0.

52 M

a pl

ate-

mot

ion

vect

or (T

aylo

r et

al.,

199

9). (

C–E

) Ros

e di

agra

ms

show

ing

linea

men

ts

mea

sure

d fr

om th

e ae

rial

pho

togr

aph

inte

rpre

tati

on d

ivid

ed in

to th

ree

dom

ains

and

ove

rlai

n w

ith

the

plat

e-m

otio

n ve

ctor

s fr

om B

.


Daczko et al.


Over 400 orientation measurements were taken of the lineaments observed on metabasite dip slopes of the Suckling-Dayman massif and marked on Figure 4. These were divided into three domains: Suckling dome, Dayman dome, and Biman dip slopes (Fig. 4). Lineaments of the east fl ank of the Suckling dome trend NE and SW, whereas those of the Dayman dome dominantly trend N to NNE. Minor sets of linea-ments on the Dayman dome trend E, ESE, SE, S, SW, and NW, generally downdip. Two sets of nearly orthogonal lineaments are observed on the east fl ank of the Dayman dome. Lineaments of the Biman dip slopes trend N (Fig. 4). Our data show a progression from NE orientations in the most-dissected dome (Suckling) to NNE ori-entations on the Dayman dome to N orientations on the (nascent?) Biman dip slopes (Fig. 4).

Shuttle Radar Topography Mission (SRTM) Data

The Shuttle Radar Topography Mission (SRTM) data provide a detailed digital eleva-tion model of the topography and are very use-ful because they penetrate cloud cover and thin vegetation, bypassing a key limitation of the aerial photograph analysis. Lineaments are also visible in the SRTM data that are coincident with north-draining streams (see also Spencer, 2010), even on the east-dipping fl ank of the Day-man dome (Figs. 3 and 5). A topographic profi le oriented east to west across the SRTM data for the Dayman dome shows an undulating surface of broadly spaced ridges and troughs (Fig. 5A), called megacorrugations. The analysis identifi ed three broad megacorrugations on the Dayman dome with wavelengths of ~10 km. The parallel drainage pattern across the dome is dominantly controlled by these north-trending structural megacorrugations. The corrugated topography of the megacorrugations has been accentuated by fl uvial incision of the megacorrugation troughs following subaerial exposure of the Dayman dome. A second topographic profi le oriented south to north across the SRTM data for the lower north fl ank of the Dayman dome shows the structural dip of the dip slope changing from ~21° at the base (200–600 m elevation) to ~18° slightly higher up the dome fl ank (700–1000 m elevation). These data defi ne a three-dimensional dome that is elongate east to west.

The SRTM data were also used to further explore the two sets of lineaments identifi ed in aerial photography on the east fl ank of the Day-man dome. Figures 5B–5D show the interpreta-tion of topographic lineaments on a plan-view shaded relief image (illuminated from the west) of the Dayman dome. Thin black lines repre-sent major waterways following the troughs

of the megacorrugations, whereas thick black lines represent ridges or the interpreted crests of the megacorrugations (Fig. 5C). The six mega-corrugation crests and troughs are oriented NNE (Fig. 5C). Thirty-nine orientation measurements of the lineaments on the east fl ank of the Day-man dome (Fig. 5D) fall into two main orien-tation groups: (1) a minor set oriented ESE to ENE and (2) a major set oriented NNE to N. The fi rst group trends down the dip slope of the east fl ank and is spatially concentrated on the low-ermost east fl ank, whereas the second group is oriented in a similar direction as the dominant NNE lineaments identifi ed across the major-ity of the Dayman dome in aerial photography (Fig. 4). A notable feature of the drainage pat-tern on the eastern fl ank is a stepped pattern of some streams (Fig. 5D). The steps comprise long segments oriented NE, with shorter N- to NNE-oriented segments.

FIELD RELATIONSHIPS OF THE DAYMAN DOME

The outcrops described here are within a 1–5 km walk of the villages of Pumani (AGD66 Grid Reference: 8920500N, 0770200E) and Biniguni (8929900N, 0749100E) (Figs. 2 and 3). The Goropu Metabasalt at these localities is uniform metabasite L-S tectonite mylonite (500 m thick; Davies, 1980) that defi nes a shear zone forming the dominant structure that delineates dip slopes on the fl anks of the Dayman dome. The shear zone foliation planes dip shallowly and contain a well-developed mineral elongation lineation. Low-strain areas or preexisting fabrics were not observed due to the pervasive nature of the shear zone. Rare crosscutting features include narrow ductile shear zones, veins, brittle to semibrittle faults, and mafi c dikes.

Ductile Shallowly Dipping S1 and S2

All metabasite samples of the Dayman dome examined in this study (excluding the dikes) are grayish green and contain a well-developed S1 foliation and L1 lineation. S1 is defi ned by aligned actinolite, albite, and chlorite, whereas elongate actinolite and albite grains defi ne L1 at the outcrop scale. Very rare blue amphibole is restricted and concentrated in narrow bands (up to 3 mm wide) of S2 folia oriented subparallel to S1. The metabasite samples are fi ne grained (<0.5 mm).

S1 on the east fl ank of the Dayman dome is a coarse continuous foliation that strikes NNW and dips shallowly toward the ENE (average S1 orientation is 152°/20°/ENE; Fig. 6A). S1 fo-liation planes contain a shallowly plunging L1 mineral lineation on the east fl ank that trends

NNE (average L1 orientation is 14° towards 028°). S1 foliation planes anastomose between extensional shear bands forming an S-C! fabric (Fig. 6E).

S1 on the north fl ank of the Dayman dome also defi nes a coarse continuous foliation that strikes ESE and dips shallowly toward the NNE (average S1 orientation is 106°/17°/NNE; Fig. 6B). Figure 6D shows that the S1 data mea-sured from these two study sites form part of an overall dome pattern and are therefore only representative of the particular parts of the dome visited. Albite ribbons (up to 1 mm long) are aligned with S1 in coarse-grained samples. Undulose extinction is common in albite grains. S1 foliation planes contain a shallowly plung-ing L1 mineral lineation on the north fl ank that variably trends between NNW to NE, with an average trend of NNE (average L1 orientation is 18° towards 016°). L1 mineral lineations are commonly defi ned by elongate actinolite and al-bite grains and may be defi ned by stretched vein minerals such as calcite (Fig. 6F).

Narrow bands of S2, observed on the east fl ank, also defi ne a coarse continuous foliation oriented subparallel to S1 that strikes NNE and dips shal-lowly toward the ESE (average S2 orientation is 015°/32°/ESE; Fig. 6C). The blue amphibole is a sodic-calcic ferrowinchite to ferro barrowisite (Daczko et al., 2009); it is aligned with S2 and is elongate to defi ne L2. The L2 mineral lineation on the east fl ank is shallowly plunging and trends ESE at a high angle to L1 (average L2 orienta-tion is 29° towards 105°). An oxidized iron stain-ing is associated with S2 folia. The rare S2/L2 fabric was observed in Biyawap and Aro Creeks (Fig. 4). Blue amphibole was rarely observed on the north fl ank.

Rare Narrow Steeply Dipping S2 Shear Zones

Narrow (<100 mm), steeply dipping shear zones are rare and were observed at Biniguni River and Ampae Creek (Figs. 4 and 7) on the northern fl anks of the dome. S2 in steeply dip-ping shear zones is a moderately rough folia-tion with ductile to semibrittle character. S2 in steeply dipping shear zones strikes ESE-WNW and dips steeply toward the NNE. Steeply dip-ping S2 foliation planes contain a shallowly plunging L2 mineral lineation that trends NE (15° towards 044°), distinct to L2 measured on shallowly dipping S2 planes (see previous para-graph and Fig. 6C). Steeply dipping S2 foliation planes anastomose around microlithons that preserve the S1 foliation enveloped by the S2 fo-liation. The sense of curvature and transposition of the S1 foliation into the S2 foliation indicate a top-down-to-the-NNE sense of shear (Fig. 7).




Mount DaymanMount Dayman

A BC

D

A BC

D

A B

?

V.E. = 1

V.E. = 1

C Dm

m

1000

800

600

200

400

1000 2000 3000

10000 20000m

1000

0 m

2000

3000

18°

21°

BC C D

D N

N = 9 N = 39

Mount Dayman

10 km

N

Mount Dayman

10 km

A

Figure 5. (A) Shuttle Radar Topography Mission (source: U.S. Geological Survey [USGS]) image for the Day-man dome (view looking south) showing the location of two topographic profi les. Profi le A–B shows the ridge and trough morphology of the Dayman dome surface that defi nes megacorrugations. Profi le C–D shows a prominent dip slope on the lower north fl ank of the Dayman dome that is little dissected by streams. (B) Plan-view Shuttle Radar Topography Mission (source: USGS) image for the NE fl ank of the Dayman dome. (C) Orientation of mega-corrugation ridges (bold lines) and troughs (thin lines) plotted onto a rose diagram. (D) Lineaments on the east fl ank of the Dayman dome plotted onto a rose diagram.


Daczko et al.


N

S

EW

L1 [n = 11]

S1 [n = 24]

A B

D

C!C!

S1S1

L1L1

N

S

EW

L1 [n = 189]

S1 [n = 274]

East flank North flank

E F

Avg. S1(North)

Avg. S2(East) Avg. L2

(East)

Avg. L1 (North)

Avg. S1(East)

Avg. S2(East) Avg. L2

(East)

Avg. L1(East)

C N

S

EW

L2 [n = 12]

S2 [n = 34]

East flank

Avg. S1(North)

Avg. S1(East)

Avg. L1(East)

Avg. L1 (North)N

S

EW

Dayman dome S1 [n = 41]Suckling dome S1 [n = 60]

Figure 6. Equal-area, lower-hemisphere stereograms for the two areas visited on the Dayman dome: poles to S1 and L1 data for the east (A) and north (B) fl anks. (C) Poles to shallowly dipping S2 and L2 data for the east fl ank; average orientations are given by the labeled stars. (D) Poles to S1 data compiled from the 1:250,000 Geological Series map (Davies and Smith, 1974) show a more representative range in data compared to the areas visited for this study. (E) View looking WNW of S1 foliation planes (S; dashed line) that anastomose between extensional shear bands (C!, solid line) forming an S-C! fabric. The curvature of S-planes indicates top-down-to-the-NNE sense of shear. Site 0627, Aro Creek (Fig. 4). (F) View onto S1 foliation plane of elongate and aligned vein minerals that defi ne L1 (solid line); boulder in Gwariu River (Fig. 4). Lens cap is 60 mm across.




Narrow, steeply dipping S2 shear zones contain abundant veins that are concentrated within the shear zones and are deformed by them. Though no crosscutting relationships were observed, Daczko et al. (2009) suggested that both the shallowly and steeply dipping S2 foliations were coeval on the basis of similar mineral as-semblage and chemistry.

Kinematics

We determined the sense of shear during D1 at both thin section and outcrop scale. Thin sections used to determine sense of shear were

cut parallel to the elongation lineation (L1) and perpendicular to the foliation (S1). At outcrop scale, extensional shear bands (S-C! fabrics) are common (Figs. 6E and 7A). The shear bands are spaced from ~30 mm up to 1.5 m apart. The angle between S and C! planes varies between 25° and 44° but is commonly 30°–35°. The curvature of S planes near C! planes indicates a top-to-the-NNE sense of shear (Figs. 6E and 7A). Outcrop-scale asymmetric strain shadows around porphyroclasts are rare. Yuga Creek (Fig. 4) contains 200–250-mm-long parts of the outcrop with coarse foliation enveloped by fi ne-grained foliation (Fig. 7B). The parts of the out-

crop with coarse foliation form lenticular shapes analogous to sigma mantle porphyroclasts. The asymmetry of the tails of fi ne-grained foliation indicates a top-to-the-NNE sense of shear.

Asymmetric strain shadows around porphyro-clasts were the most common kinematic in-dicator in thin section. The best examples are in sample 0677G, where large elliptical single mineral grains or mineral clusters of epidote are enveloped asymmetrically by S1 (Fig. 7C). The stair-stepping sense of the asymmetry com-monly indicates a top-to-the-NNE sense of shear. However, elliptical porphyroclasts with their long axis oriented upstream (see Kinematic

C!C!

S1S1

epep

D E

A B

C

Figure 7. (A) View looking WNW of S1 folia (S planes) that anastomose between extensional shear bands (C!-planes) spaced 1–2 m apart. Site 0630, Yatap Creek (Fig. 4). Curvature of S planes indicates top-down-to-the-NNE sense of shear. (B) View looking WNW of 200–250-mm-long lenticular-shaped parts of the outcrop with coarse foliation enveloped by fi ne-grained foliation, analogous to sigma mantle porphyro-clasts. Site 0669, Yuga Creek (Fig. 4). The asymmetry of the sigma tails indicate top-down-to-the-NNE sense of shear. Lens cap is 60 mm across. (C) Plane-polarized light photomicrograph of sigma-type asymmetric strain shadows around epidote (ep) porphyroclast, sample 0677G, Ampae Creek (Fig. 4). The asymmetry of the sigma tails indicates a top-down-to-the-NNE sense of shear. Field of view is 3.5 mm across. (D) Crossed-polarized light photomicrograph of a pyrite grain with quartz fi bers, sample 0677D, Ampae Creek (Fig. 4). The pyrite particle boundary and the matrix have separated along a surface at a high angle to the maximum instantaneous stretch. Minerals in solu-tion diffused toward the low-stress area and precipitated as quartz fi bers, indicating a top-down-to-the-NNE sense of shear. Field of view is 1.75 mm across. (E) Crossed-polarized light photomicrograph of actinolite “fi sh,” sample 0677H, Ampae Creek (Fig. 4). The tails on the actinolite fi sh indicate a top-down-to-the-NNE sense of shear. Field of view is 1.75 mm across.


Daczko et al.


Vorticity section) show the opposite sense of asymmetry and indicate a top-to-the-SSW sense of shear. This observation indicates a component of pure shear for the fl ow regime; this will be ex-plored in the section on kinematic vorticity (see following). Rare antitaxial fi brous overgrowths on pyrite porphyroclasts have grown normal to the crystal faces of the pyrite grains (Fig. 7D). Because a pyrite grain behaves rigidly relative to the surrounding ductile matrix, the pyrite par-ticle boundary and the matrix tend to separate along a surface at a high angle to the maximum instantaneous stretch. Minerals in solution dif-fuse toward the low-stress area and precipitate. Figure 7D shows quartz fi bers growing normal to the crystal faces of a pyrite grain in its strain shadow. The quartz fi bers show an asymmetry that indicates a top-to-the-NNE sense of shear. Other weakly developed kinematic indicators observed in thin section include asymmetric ac-tinolite grains (Fig. 7E) that are shaped similarly to mica fi sh. The asymmetry indicates a top-to-the-NNE sense of shear. Our determination of the sense of shear for the dominant S1-L1 fabric confi rms that the mylonite formed as an exten-sional shear zone.

Kinematic Vorticity

Vorticity is the amount of rotation that a fl ow type possesses (Means et al., 1980). The aim of kinematic vorticity analysis is to determine the ratio of pure to simple shear. The kinematic vorticity number (Wk) represents this ratio and ranges from 0 to 1, representing wholly pure shear or simple shear, respectively. Simpson and De Paor (1993) illustrated how the hyperbolic net may be used to derive the kinematic vor-ticity number. It involves determining the sense of shear as indicated by the position and direc-tion of the stair-stepping of tails on asymmetric strain shadows around porphyroclasts, coupled with measurement of the fi nite axial ratio (Rf = long axis length [x]/short axis length [z]) and inclination (") of the elliptical porphyro clasts. The initial inclination of the porphyroclasts will control whether the porphyro clasts rotate forward or backward. The fi nite axial ratio (Rf) and inclination (") are plotted onto the hyper-bolic net using different symbols for forward- versus backward-rotated porphyroclasts. The backward-rotated porphyroclasts defi ne a fi eld on the plot (Figs. 8A and 8B). The hyperbola that envelops the fi eld of backward-rotated por-phyroclasts has two asymptotes that lie parallel to the two eigenvectors of fl ow; one is paral-lel to the shear zone boundary. The cosine of the angle between the two eigenvectors is the kinematic vorticity number (Wk = cos[#]; Bobyarchick , 1986).

Potential problems with this technique in-clude: (1) a large population of grains is needed; and (2) the fi nite axial ratio data should be random and follow a normal distribution. Por-phyroclasts that are oblique or impinge on their neighbors must be rejected.

Only one sample (0677G) had enough asym-metric strain shadows around porphyroclasts to attempt the determination of the kinematic vorticity number. Two thin sections were cut parallel to lineation and perpendicular to folia-tion. Sixteen out of 30 grains and eight out of 21 grains were identifi ed as backward-rotated in

the two thin sections. The analysis determined kinematic vorticity numbers of 0.34 and 0.56 for the two thin sections (Figs. 8A and 8B). Both analyses indicate that the fl ow type that pro-duced the D1 fabrics was dominated by a strong component of pure shear (Fossen and Tikoff, 1993; Fig. 8C).

Folds and Semibrittle to Brittle Overprint

Rare gentle to open folds of the shallowly dipping S1 (interlimb angle [i] = 70°–175°) were observed at the outcrop scale (Fig. 9B).

C

Wk = 0.9

0.8

0.6

0.4

0.2

0.75

k (pure shear component)

$ (s

impl

e sh

ear

com

pone

nt)

2

4

6

8

10

2 4 6 8 100

0.56

0.34

Pure shear–dominated deformationSimple shear–dominated deformation

A

Wk = cos 70°Wk = 0.34

S1

back-rotated %

forward-rotated %

forward-rotated &forward-rotatedcomplex %–&

field ofbackwardrotation

2nd eigenvector

at 70°

B

Wk = cos 56°Wk = 0.56

S1

field ofbackwardrotation

2nd eigenvector

at 56°

Figure 8. (A–B) Plots of kine-matic vorticity data on a hyper-bolic net for two thin sections of sample 0677G. Grain types follow Simpson and De Paor (1993). (C) Plot showing paths of constant kinematic vorticity number (Wk) in simple shear ($)–pure shear (k) space for plane-strain combinations of pure and simple shear. The nonlinearity of Wk paths is a result of the fi nite strain caused by the pure shear component increasing faster than the simple shear component (from Tikoff and Fossen, 1995).




S2S2

S1S1S1S1

S1S1 S1S1

S3S3S3S3

prhprh

S3S3

epep

dyke

dyke

dyke

dyke

D

A B

C

FE

Figure 9. (A) View looking ESE of a narrow, steeply dipping S2 shear zone. Site 0664, Biniguni River (Fig. 4). The sense of curvature and transposition of S1 into S2 indicates a top-down-to-the-NNE sense of shear. Lens cap is 60 mm across. (B) View looking W of a gentle fold of S1. Site 0669, Yuga Creek (Fig. 4). (C) Plane-polarized light photomicrograph of crenulated S1, sample 0677C, Ampae Creek (Fig. 4). Field of view is 1.75 mm across. (D) View looking E of an S3 semibrittle to brittle fault zone. Site 0604, Pumani River (Fig. 4). Long handle crack hammer is 400 mm long. Inset shows a view looking E of prehnite (prh) and epidote (ep) veins in the D3 fault zone above; site 0604, Pumani River (Fig. 4). Lens cap is 60 mm across. (E) Crossed-polarized light photomicrograph of a boudinaged vein, sample 0605, Biyawap Creek. Field of view is 3.5 mm across. (F) View looking WNW of steeply dipping mafi c dikes that cut S1. Site 0664, Biniguni River (Fig. 4). Lens cap is 60 mm across.


Daczko et al.


Detailed measurements of folded S1 at Gwariu River (Fig. 4) show crenulations that plunge very shallowly toward the SE. At this location, S1 is openly folded (i = 104°) and differently oriented to elsewhere on the northern fl ank. Stereographic determination of the attitude of the fold indicates that it is gently plunging (22° towards 253°) and upright (85°). Zonal crenu-lation cleavages were mostly observed at thin section scale (Fig. 9C). The crenulations range from close to open to gentle with chevron to sinusoidal shapes. They are commonly weakly asymmetric.

A rare semibrittle to brittle overprint (D3) of the S1 and S2 foliations was observed in the Pumani River (Fig. 4) at the contact between the Gwoira Conglomerate and Goropu Metabasalt (Fig. 9D). The fault zone is ~2 m wide, dips moderately toward the SE, and is rich in veins (Fig. 9D). Extensional shear bands (S-C! fabric) indicate a top-down-to-the-SE sense of shear (Fig. 9D). Rare narrow fault zones that contain very fi ne-grained gouge also defi ne a rare semi-brittle to brittle overprint of the S1 and S2 folia-tions. The gouge is associated with an oxidized iron staining. Grain-scale faults show top-down-to-the-NNE sense of shear.

Veins and Dikes

Narrow veins (<3 mm wide) commonly con-tain calcite, less commonly quartz, and rarely epidote and prehnite. Field relationships indi-cated that the veins are common within the nar-row D2 shear zones and brittle structures (i.e., post-S1), although rare veins were observed strung out in the S1 foliation and along L1. Rare boudinage of veins was observed in sample 0605 from Biyawap Creek (Figs. 4 and 9E). Epidote and prehnite were only observed within the semibrittle to brittle structures (D3).

Rare mafi c dikes cut the S1/L1 fabric at the Biniguni River waterfall (Figs. 4 and 9F). Chilled dike margins were not evident, and the dikes are very weakly deformed (Fig. 9F). The dikes strike NW to NNW and dip moderately to steeply toward the SW. One subhorizontal mafi c sill was observed in the Gwariu River (Fig. 4), with no evidence of chilled margins. The sill obliquely truncates the S1 foliation.

DISCUSSION

Remotely Sensed Structural Data

At the broadest scale, the Suckling-Dayman massif is a twin domal shape elongated east to west that may be subdivided into the Dayman and Suckling domes. Figures 3 and 5 show the three-dimensional aspect of the dome, consistent

with fl exure not only in a north-south direction as shown in Figure 10, but also in an east-west direction. Remote-sensed structural information is diffi cult to gain from the Suckling dome due to the high degree of dissection by streams. The analysis of the Dayman dome identifi ed three broad megacorrugations on the northern fl ank of the dome oriented NNE. The megacorrugations create a scalloped range front and curved fault trace of the Mai’iu fault or vice versa. The orien-tation of the broad megacorrugations correlates with the lineaments identifi ed in aerial photog-raphy on the Dayman dome. Lineaments north-west of Mount Dayman are continuous from the base of the northern fl ank up to the saddle be-tween Mount Dayman and Mount Suckling and over the change in dip line marked on Figure 4 to be southward plunging west of Mount Day-man. These lineaments are interpreted to have developed as northward-draining creeks that incised the freshly denuded Mai’iu fault (Ollier and Pain, 1981) and then were folded during doming. Spencer (2000) provided two models to explain the development of extension-paral-lel linear drainages such as those observed on the Dayman dome. In one model, streams are guided by small, displacement-parallel grooves in a fault surface as it is uncovered, and in the other, surface hydraulic connection is main-tained between stream segments that are cut and separated by fault movement. Both processes are viable in the Dayman example, though a full analysis of linear drainage development was not the focus of this study. The strong parallelism among linear drainages, megacorrugation ridges and troughs, and mylonitic lineation is sugges-tive of a structural control on the drainage devel-opment (Spencer, 2000).

Detailed analysis of the SRTM data on the east fl ank of the Dayman dome shows a large number of streams oriented NNE to N, at a high angle to the dip slope. The unusual along-strike orientation of these streams is consistent with a structural control such as fault surface mullions, corrugations, or striations. The orientation of stepped streams is consistent with a combina-tion of typical downdip and structural controls on the fl ow direction of the streams. Lineaments directly west of Mount Dayman trend downdip, oblique to the main structural trend in the data. The observation of lineaments trending down-dip and at a high angle to the NNE to N struc-tural trend of the megacorrugations indicates that not all drainages are structurally controlled; some are controlled by the topography.

The megacorrugations and lineaments on the Dayman dome are oriented differently to the lineaments on the Suckling dome and Biman dip slopes. Although streams heavily dissect the Suckling dome, the Mai’iu River represents a

long straight segment (Fig. 4) that may be con-trolled by a Suckling dome megacorrugation oriented parallel to NE lineaments identifi ed in the aerial photography.

On the basis of the fresh nature of the Mai’iu fault scarp, we infer that the exhumation of the Dayman dome is active and therefore relates to the present-day Woodlark extensional prov-ince. The structural data may therefore be com-pared to orientations predicted by Euler poles for the extension in this area. The oldest mag-netic anomaly picked for the Woodlark Basin is anomaly 3A.1, indicating that rifting initiated prior to ca. 6 Ma well east of the study area (Taylor et al., 1999). Analysis of fracture zone orientations and magnetic anomalies identifi es two major changes in the location of the Euler poles for rifting between the Indo-Australian and Woodlark plates (Taylor et al., 1999). The Euler poles may be used to predict the orien-tation of extension within the rifting crust at a given location. The Euler poles indicate NNW-directed extension for periods younger than ca. 0.5 Ma, whereas for periods between 0.52 and 3.6 Ma, a NNE-directed extension is pre-dicted (Taylor et al., 1999). The remote-sensed data analyzed here show no evidence of NW-directed lineaments and best match the exten-sion direction predicted by the older Eulerian pole. Therefore, the exposed sections of the dome contain structures formed greater than half a million years ago. This is consistent with erosion of any young NW-directed extensional brittle fault rock that would have likely formed a carapace of brittle fault gouge overlying the ex-posed zone of ductile mylonite that now forms dip slopes with NNE-directed linear structures. Alternatively, there may have been partitioning of the deformation into fault-parallel and fault-perpendicular components.

Field Structures

The dominant structure examined in this study is a mylonite ductile shear zone with top-to-the-NNE transport. The overprinting se-quence of structures in the Dayman dome in-cludes: (1) ductile S2 folia with ESE-plunging blue sodic-calcic amphibole mineral lineations that are oriented at a high angle to the D1 trans-port direction; (2) narrow, steeply dipping duc-tile D2 shear zones; and (3) semibrittle to brittle fault zones. The structural progression records exhumation of the massif from ductile to brit-tle deformation conditions, suggesting that the ductile shear zone likely evolved into a brittle detachment fault (Mai’iu fault). The ductile na-ture of the S1/L1 fabric is inconsistent with the D1 mylonite zones controlling the exhumation of the massif all the way to the surface. Brittle




deformation (D3) during movement along the Mai’iu fault must have controlled the fi nal stages of exhumation of both the massif and mylonite zones (Davis et al., 1986; Daczko et al., 2009). The scarcity of exposed brittle fault rock associ-ated with the Mai’iu fault (e.g., D3 fault zone exposed in the Pumani River; Fig. 9D) suggests that these fault rocks, which controlled the fi nal stages of exhumation, are largely eroded. Only one large brittle fault zone was observed at the Pumani River (Fig. 9D). This zone is ~2 m thick and is located near the contact with the Gwoira Conglomerate and may be protected by the overlying sedimentary carapace. Therefore, we suggest that most, of any, brittle fault rock that existed has been eroded to expose the D1 my-lonitic rocks that were tectonically exhumed in the footwall of the Mai’iu detachment fault.

The extension direction recorded by the opening of the mafi c dikes is similar to L1 ex-tension lineations. This observation suggests that the dikes intruded under the same stress regime as that active during the development of the S1/L1 fabric. This implies that the dikes were emplaced shortly following cessation of ductile movement in the mylonitic shear zone, prior to any change in regional stress, and this is consistent with the lack of chilled margins on the dikes and limited deformation of the dikes.

The mylonitic lineations (L1) defi ne a NNE-directed transport direction and are parallel to the aerial photograph lineaments and fault sur-face megacorrugations on the Dayman dome. The L1 elongation lineations closely parallel the Woodlark-Australia spreading vector for the Pliocene to early Pleistocene (0.5–3.6 Ma), but they are not parallel to the late Pleistocene to Holocene Woodlark-Australia spreading vec-tor (<0.5 Ma; Taylor et al., 1999). This suggests that deformation in the D1 mylonite zone is older than 0.5 Ma, in the absence of any strain partitioning into fault-parallel and fault-perpen-dicular components. It is predicted that slicken-sides on brittle faults, were they better exposed, and recent movement on the Mai’iu fault would trend NNW-SSE, parallel to the late Pleisto-cene to Holocene Woodlark-Australia spreading vector. The rare 2-m-wide semibrittle to brittle overprint (D3) observed in the Pumani River at the contact between the Gwoira Conglomer-ate and Goropu Metabasalt (Fig. 9D) contains a SE-trending lineation, and two other orienta-tions of fault slickensides measured on brittle fault planes in the Gwoira Conglomerate (Dare Creek, Fig. 4) are also consistent with tectonic transport parallel to the younger Woodlark-Aus-tralia spreading vector.

Hill (1994) presented a similar structural scheme to that presented here for the bound-ing shear zones of the Goodenough, Mailolo,

and Oiatabu domes on Goodenough and Fer-gusson Islands. Her structural scheme includes (1) several-hundred-meter-thick pervasive shear zone fabrics; (2) narrow shear zones (a few tens of centimeters or a few centimeters thick) that extend for several hundred meters or less than 1 m along strike; and (3) zones of schistosity, crenulation, and brecciation. This structural scheme matches the S1/L1 mylonitic fabric, narrow D2 shear zones, and D3 brittle fault zones presented here. The mineral lineations re-ported by Hill (1994) for the numerous bound-ing shear zones on Goodenough and Fergusson Islands include sets that trend N, NE, and E, i.e., broadly similar to the L1 lineations of this study. Also similar to this study, NW-plunging mineral lineations are not reported by Hill (1994). Little et al. (2007) examined the Pro-vost Range massif (dome) on Normanby Island and documented NNE-SSW–oriented mega-corrugations and mineral lineations similar to those reported here.

The analysis of vorticity of the shear zone defor mation indicates a kinematic vorticity number (Wk) between 0.34 and 0.56, suggest-ing general shear deformation. It must be noted that this analysis is based on only one sample (0677G), since this was the only sample con-taining a suitable number of asymmetric strain shadows around porphyroclasts. This sample is representative of those containing a well-developed S1 foliation and L1 lineation, and we consider the result indicative of fl ow dur-ing the deformation event. The strong compo-nent of pure shear suggests that the shear zone evolved with a stress involving a strong over-burden component (Bailey and Eyster, 2003). Many authors have described the coexistence of coaxial and noncoaxial shear in metamorphic core complexes irrespective of their lithology or environment (Wells and Allmendinger, 1990; Wawrzenitz and Krohe, 1998; Bestmann et al., 2000; Bailey and Eyster, 2003; Little et al., 2007). Bailey and Eyster (2003) and Bestmann et al. (2000) described an evolving combination of pure and simple shear in metamorphic core complexes at different stages of uplift. Bailey and Eyster (2003) described the overall defor-mation as general shear that evolves from shear dominated by ductile pure shear early in the defor ma tion to shear dominated by brittle sim-ple shear as the load on the footwall block (i.e., the overburden) is reduced during exhumation of the core. The evolving fl ow regime may show overprinting relationships where pure shear–dominated shear zones are cut by simple shear–dominated ones (Bailey and Eyster, 2003). The high pressures recorded by metamorphic assemblages (Daczko et al., 2009) in the core suggest that the overburden would have been

very signifi cant during the early stages of shear (D1), consistent with the determination of Wk. Simple shear–dominated semibrittle to brittle fault zones most likely formed a carapace over the pure shear–dominated ductile shear zone now exposed and may include the D3 fault zone observed at the contact between the Goropu Metabasalt and Gwoira Conglomerate. The friable nature of the more brittle simple shear–dominated deformation makes these zones more susceptible to erosion and perhaps explains their limited exposure in the study area.

Geological Synthesis

The Suckling-Dayman massif is character-ized by an elongate twin dome shape that is sub-divided into the Dayman and Suckling domes. Several similarities exist between the Suckling-Dayman massif and other metamorphic core complexes: (1) a thick mylonitic ductile shear zone that juxtaposes rocks of different metamor-phic conditions, (2) elongate domed landforms of the core, (3) igneous activity associated with progressive uplift, and (4) progressive deformation from ductile to brittle conditions. These other settings also commonly show late low-angle faults overlain by unmetamorphosed rocks, and exposures of these structures (e.g., Gwoira fault) have proven to be elusive in the areas visited for this study. The D3 fault zone identifi ed may be one such structure.

Much of the Papua New Guinea literature describes the basal contact of the Papuan ultra-mafi c belt as a thrust surface (e.g., Davies, 1980), which undoubtedly it was on the basis of the juxtaposition of mantle rocks over continen-tal rocks. However, no evidence of this thrust history was observed in shear zones examined in this study, suggesting pervasive recrystalliza-tion of this boundary during later extensional deformation. The geometry and style of struc-tures and map relations presented in this study indicate an extensional origin for the mylonitic foliation (S1) and mineral lineation (L1) of the Dayman dome. This study also contradicts Davies (1980), wherein he concludes that con-vergent tectonics were the prime mechanism for elevating and folding the metabasites into the broad domed landform.

Here, we detail the geological history of the Suckling-Dayman massif and place our in-terpretations into the broader tectonic context provided by published previous research. The evolution is divided into four stages and is pre-sented as schematic cross sections (Fig. 10). The sections do not represent a single location but rather bring together observations from across the massif to compile the overall evolution of the Suckling and Dayman domes.


Daczko et al.


Stage 1: Continental crust of the Australian plate margin (including protoliths to high-tem-perature metamorphic rocks that today consti-tute much of the Owen Stanley Range and the cores of the D’Entrecasteaux Islands metamor-phic core complexes) followed Late Cretaceous oceanic crust down into a north-dipping Paleo-gene subduction system (Davies, 1980; Davies and Jaques, 1984). The resulting arc-continent collision thickened the continental crust by thrusting the Papuan ultramafi c belt over the continental rocks during the Eocene (Fig. 10, stage 1; Davies, 1980; Davies and Jaques, 1984). This led to the deep burial (>100 km) of some continental crust (Baldwin et al., 2008).

Though the exposed continental rocks were metamorphosed at high temperatures (Davies and Jaques, 1984; Davies and Warren, 1988; Hill and Baldwin, 1993; Baldwin et al., 2004), the exposed Late Cretaceous oceanic crust varies from virtually unmetamorphosed rock (e.g., Kutu volcanics; Figs. 2 and 10) through prehnite-pumpellyite facies to pumpellyite-actinolite facies (e.g., Suckling-Dayman massif ; Davies, 1980). The Late Cretaceous oceanic crust is greenschist facies immediately below the basal contact of the Papuan ultramafi c belt (Davies, 1980; Daczko et al., 2009). All meta-basite samples examined in this study come from the greenschist-facies group of rocks.

The majority of the Suckling Dayman massif is pumpellyite-actinolite–facies schist (Davies , 1980), and this assemblage indicates that the

massif has been exhumed from a depth of 20–30 km (Daczko et al., 2009). These meta-morphic assemblages are noted in Figure 10 (stage 1) at appropriate points along the buried oceanic crust.

Stage 2: The timing of subduction system suspension and transition to an extensional tec-tonic setting remains unclear. However, seafl oor spreading in the Woodlark Basin had begun by 6 Ma (Taylor et al., 1999), and Baldwin et al. (2004) reported the timing of eclogite-facies metamorphism of the buried continental crust to be 4.3 Ma, prior to its exhumation in the exten-sional setting on the D’Entrecasteaux Islands. These results indicate that extension in this re-gion began at least as early as the Pliocene.

Regardless of when extension in this region began, the development of metamorphic core complexes extends from the D’Entrecasteaux Islands through to the Papuan Peninsula (Suck-ling-Dayman massif). It is generally agreed (Davies and Jaques, 1984; Davies and Warren, 1988; Little et al., 2007; this study) that the preexisting thrust subduction boundary was reactivated in the extensional tectonic setting, such that the bounding shear zones of the meta-morphic core complexes simply reversed the previous thrust motion (note that the kinematic arrow in Fig. 10, stage 2, has reversed from Fig. 10, stage 1). Any large displacement on low-angle normal faults results in isostatic uplift and warping of the lower plate into a broad antiform in response to tectonic denudation (Spencer,

1984). This is the dominant mechanism that controls the domed shape of metamorphic core complexes and is used here to defi ne a devel-oping domed shape for the exhuming lower plate of the Suckling-Dayman massif (Fig. 10, stage 2). The analysis of SRTM data on the lowermost north fl ank of the Dayman dome identifi ed a change in dip of the metabasite dip slope from ~21° to ~18°N. This orientation matches the average S1 orientation, which dips 17°–20°N. The change in dip of the lower north fl ank identifi ed in SRTM data is consistent with doming of the massif.

The kinematic analysis of the shear zone indicates that during this early stage of uplift, the greenschist-facies metabasite rocks under-went general shear deformation with a kine-matic vorticity number (Wk) between 0.34 and 0.56. The pure shear–dominated flow may have been caused by buoyancy of continental crust from below (Fig. 10, stage 2; Little et al., 2007) and/or the weight of a thick overburden (e.g., Papuan ultramafi c belt; Fig. 10, stage 2; Martinez et al., 2001; Bailey and Eyster, 2003). The orientation of lineaments identifi ed in aerial photographs and structural megacor-rugations identifi ed in SRTM data correlates with the NNE-plunging orientation of mineral elongation lineations (L1). This NNE extension direction best matches that predicted by the old-est recorded Eulerian pole (0.52–3.6 Ma) for Woodlark Basin seafl oor spreading, indicating that the D1 deformation is older than 0.52 Ma.

' P-A

P-P

STAGE 1

30–35 km

0 km

CC

P-A

P-P

'

STAGE 2

CC

P-P 'P-A

STAGE 3

CC

Gwoira F.Onuam F.Keveri F.System

Solomon SeaCoral SeaP-P 'P-A

STAGE 4

CC

Gwoira Conglomerate

Suckling Granite andMai’iu Monzonite

Kutu Volcanics

Papuan Ultramafic Belt (PUB)

Goropu Metabasalt

Continental crust(garnet-bearing gneiss,biotite and chlorite schist)

Undifferentiated Volcanicand Sedimentary Rocks

CC

S N

Owen Stanley Fault Zone

S N

Figure 10. Schematic cross sections of the evolution of the Suckling-Dayman Massif from Paleogene arc-continent collision (stage 1) to Miocene–Pliocene to present-day conti-nental extension (stages 2–4). P-P—prehnite-pumpellyite facies; P-A—pumpellyite-actinolite facies.




The rare presence of the blue amphibole in shallowly dipping D2 shear zones is re-lated to oxidizing fl uids rather than a change in pressure-temperature conditions (Daczko et al., 2009). This interpretation may indicate that there are two types of blue amphibole in the region: (1) sodic-calcic ferrowinchite to ferro barrowisite (Daczko et al., 2009) in shear zones, and (2) glaucophane in the core of the complex (Davies, 1980) structurally beneath the shear zones. Alternatively, the “glauco-phane” optically identifi ed by Davies (1980) in the core of the complex may not necessarily in-dicate high-pressure conditions and may rather represent oxidizing conditions (Daczko et al., 2009). Further analysis of the Davies (1980) blue amphibole- and lawsonite-bearing samples is required to confi rm that the core of the com-plex experienced blueschist-facies conditions; this can be done by chemically confi rming the presence of true glaucophane. L2 defi ned by aligned blue sodic-calcic amphibole character-izes an unusual east-directed transport direction that is diffi cult to explain using the published Eulerian poles of Taylor et al. (1999). The east-directed transport direction was only observed on the east-dipping fl ank of the Dayman dome, and this observation may indicate that the dip direction of the dome shape dominated over the overall tectonic extension direction in control-ling the D2 transport direction on differently dipping fl anks of the domes. The timing of the steeply dipping narrow D2 shear zones relative to the shallowly dipping blue amphibole–bear-ing fabrics remains unclear because no cross-cutting relationships were observed. However, their ductile nature places them within the “stage 2” evolution sequence.

Stage 3: Davies (1980) reported that emer-gence of the buried oceanic crust from beneath the Papuan ultramafi c belt took place in the middle Miocene, on the basis of extensive sedi-mentary rocks to the north of the massif (Fig. 10, stage 3). Sedimentation continued into the Pliocene (Davies, 1980) with deposition of the Gwoira Conglomerate onto the north fl ank of the developing domes (Biman dip slopes in particular). Sánchez-Gómez et al. (2002), van Hinsbergen and Meulenkamp (2006), and Sen and Seyitoglu (2009) have reported the depo-sition of sediment onto the fl anks of actively exhuming metamorphic core complexes in the eastern Mediterranean. The petrography of the lithic clasts in the Gwoira Conglomerate (Caffi , 2008) suggests that they came from metabasite units, as opposed to ultramafi c sources such as the Papuan ultramafi c belt. Fluvial sediment characteristics, such as rounded and oxidized clasts, suggest that the metabasite source was subaerially exposed. The presence of shallow-

marine fossils (Caffi , 2008) indicates transgres-sion of the sea and deposition of the Gwoira Conglomerate on a newly developed shelf (Fig. 10, stage 3).

Davies and Warren (1988) reported a gravity low that may be due to a concentration of felsic material below the metabasite carapace of the Suckling-Dayman massif. The felsic material may include continental crust (as depicted in Fig. 10) and intrusions such as the granite and monzonite that intrude metabasite rocks south of Mount Suckling (Fig. 2). The felsic rock may have contributed to buoyancy-driven uplift of the massif (e.g., Davies and Smith, 1971). The granite and monzonite is undeformed, and con-tact metamorphic assemblages, including anda-lusite, suggest that it was emplaced at less than 12 km depth (Fig. 10, stage 3). A LA-ICP-MS 206Pb-238U zircon age of one sample of granite is 3.3 ± 0.1 Ma (Caffi , 2008) and indicates the cessation of greenschist-facies ductile shearing by this time.

A thinning lithosphere is generally compen-sated by a rising asthenosphere at depth, and partial melting of the rising asthenosphere may have produced the mafi c dikes that cut S1 at the Biniguni River. A rising asthenosphere is also consistent with partial melting of the deeply buried continental crust to produce the granite and monzonite units. The post-S1 timing of both the mafi c dikes and granite and monzonite units suggests that there may be a relationship between the two.

The cessation of ductile D1 and D2 deforma-tion by the time of the mafi c and felsic intru-sions implies that brittle faults and fault zones (e.g., Mai’iu fault) must have controlled the fi nal stages of exhumation of the Suckling-Dayman massif (Daczko et al., 2009). The scarcity of brittle to semibrittle fault rock such as that exposed in the D3 fault zone identifi ed at the Pumani River suggests that any brittle fault rock carapace over the ductile D1 shear zone has been largely eroded or was particularly thin. Where exposed, brittle structures display a variably oriented, but commonly downdip slick-enside lineation that rarely matches the NNW transport direction predicted by the 0–0.5 Ma Woodlark-Australia Euler pole (Taylor et al., 1999). Prehnite in the D3 mineral assemblage indicates a much lower pressure of metamor-phism (Daczko et al., 2009) and is consistent with evolution of exhumation from ductile to brittle conditions.

Stage 4: At some stage since the Pliocene deposition of the Gwoira Conglomerate, it has been tilted toward the SE. Metamorphic core complexes are typically characterized by a low-angle detachment fault that separates a footwall of ductilely deformed metamorphic and intru-

sive rocks from a hanging wall of unmetamor-phosed sedimentary units that have been tilted and displaced along normal faults. Domino-like rotation of normal faults, movement along a fault with listric geometry at depth, bowing of a low-angle fault due to footwall uplift, or a combination of all of these may have uplifted and tilted hanging-wall strata of the Gwoira Conglomerate.

Stage 4 in Figure 10 also shows the develop-ment of young faults (such as the Keveri fault system and Onuam fault), erosion of the meta-basite domes and other units to the present-day surface, and shedding of Quaternary and Tertiary sediments mainly toward the north. The lack of drainage incision of the lowermost north fl anks of the Dayman dome suggests that tectonic exhumation of the dome is continuing today.

CONCLUSIONS

New structural and remote-sensing data and fi eld observations are integrated to document the structural evolution of the Dayman dome metamorphic core complex in eastern Papua New Guinea. A mylonitic carapace with uni-directional NNE-orientated lineation and nor-mal sense of shear shows no evidence of the previous thrust history at the juxtaposition of mantle over continental rocks. These obser-vations suggest pervasive recrystallization of preexisting structures during the development of the extensional mylonitic fabrics. Striking geomorphic lineations (megacorrugations) are approximately parallel to the extension and lin-eation direction in outcrop. The Mai’iu fault has evolved from a ductile shear zone into a brittle detachment fault, and the concordant fault and mylonitic shear zone form the dominant geo-logic structure in the Dayman dome metamor-phic core complex.

ACKNOWLEDGMENTS

Australian Research Council funding to Daczko (DP0556359) provided fi nancial support to conduct this research. P.M. supported by NSF-EAR-0708105. This work began with the honor’s project of Caffi . We thank the National Research Institute, Papua New Guinea, for permission to visit and sample localities in eastern Papua New Guinea. Tim Lithgow of Summer Institute of Linguistics provided excellent helicopter logistic support to transport us between Alotau and the villages of Pumani and Biniguni. James Benson, Ainsford Arewa, and the many other kind villagers of Pumani and Biniguni are thanked for their logistic support. Critical reviews by Jon E. Spencer, Laura E. Webb, and Douwe van Hinsbergen, and the careful ed-itorial work by Dennis Brown and J. Brendan Murphy improved an earlier version of this manuscript. This study used instrumentation (and/or geochemical laboratories) funded by Australian Research Coun-cil Linkage Infrastructure, Equipment and Facilities


Daczko et al.


(ARC LIEF) and Department of Education, Science and Training (DEST) Systemic Infrastructure Grants, Macquarie University, and industry. This is contribu-tion 675 from the ARC GEMOC National Key Centre (www.es.mq.edu.au/GEMOC/) and UTIG contribu-tion number 2335.

REFERENCES CITED

Bailey, C.M., and Eyster, E.L., 2003, General shear defor-mation in Pinaleño Mountains metamorphic core com-plex, Arizona: Journal of Structural Geology, v. 25, p. 1883–1892, doi:10.1016/S0191-8141(03)00044-0.

Baldwin, S.L., and Ireland, T.R., 1995, A tale of two eras: Pliocene-Pleistocene unroofi ng of Cenozoic and Late Archean zircons from active metamorphic core com-plexes, Solomon Sea, Papua New Guinea: Geology, v. 23, p. 1023–1026, doi:10.1130/0091-7613(1995)023<1023:ATOTEP>2.3.CO;2.

Baldwin, S.L., Lister, G.S., Hill, E.J., Foster, D.A., and McDougall, I., 1993, Thermochronologic constraints on the tectonic evolution of the active metamorphic core complexes, D’Entrecasteaux Islands, Papua New Guinea: Tectonics, v. 12, p. 611–628, doi:10.1029/93TC00235.

Baldwin, S.L., Monteleone, B., Webb, L.E., Fitzgerald, P.G., Grove, M., and Hill, E.J., 2004, Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea: Nature, v. 431, p. 263–267, doi:10.1038/nature02846.

Baldwin, S.L., Webb, L.E., and Monteleone, B.D., 2005, Late Miocene–Pliocene eclogites of eastern Papua New Guinea: The youngest known HP/UHP terrane on Earth: Mitteilungen Österreichischer Mineral Gesell-schaft, v. 150, p. 16.

Baldwin, S.L., Webb, L.E., and Monteleone, B.D., 2008, Late Miocene coesite-eclogite exhumed in the Wood-lark Rift: Geology, v. 36, p. 735–738, doi:10.1130/G25144A.1.

Bestmann, M., Kunze, K., and Matthews, A., 2000, Evolu-tion of calcite marble shear zone complex on Thassos Island, Greece: Microstructural and textural fabrics and their kinematic signifi cance: Journal of Struc-tural Geology, v. 22, p. 1789–1807, doi:10.1016/S0191-8141(00)00112-7.

Blackman, D.K., Cann, J.R., Janssen, B., and Smith, D.K., 1998, Origin of extensional core complexes: Evidence from the Mid-Atlantic Ridge at Atlantis fracture zone: Journal of Geophysical Research, v. 103, p. 21,315–21,333, doi:10.1029/98JB01756.

Bobyarchick, A.R., 1986, The eigenvalues of steady fl ow in Mohr space: Tectonophysics, v. 122, p. 35–51, doi:10.1016/0040-1951(86)90157-5.

Caffi , P., 2008, Evolution of an Active Metamorphic Core Complex, Suckling-Dayman Massif, Eastern Papua New Guinea [B.Sc. (Honor’s) thesis]: Sydney, Aus-tralia: Macquarie University, 113 p.

Cann, J.R., Blackman, D.K., Smith, D.K., McAllister, E., Janssen, B., Mello, S., Avgerinos, E., Pascoe, A.R., and Escartin, J., 1997, Corrugated slip surfaces formed at ridge-transform intersections on the Mid-Atlantic Ridge: Nature, v. 385, p. 329–332, doi:10.1038/385329a0.

Daczko, N.R., Caffi , P., Halpin, J.A., and Mann, P., 2009, Exhumation of the Dayman dome metamorphic core complex, eastern Papua New Guinea: Journal of Meta-morphic Geology, v. 27, p. 405–422, doi:10.1111/j.1525-1314.2009.00825.x.

Davies, H.L., 1980, Folded thrust fault and associated meta-morphics in the Suckling–Dayman Massif, Papua New Guinea: American Journal of Science, v. 280-A, p. 171–191.

Davies, H.L., and Jaques, A.L., 1984, Emplacement of ophio-lite in Papua New Guinea, in Gass, I.G., Lippard, S.J., and Shelton, A.W., Ophiolites and oceanic lithosphere: Geological Society of London Special Publication 13, p. 341–349, doi:10.1144/GSL.SP.1984.013.01.27.

Davies, H.L., and Smith, I.E., 1971, Geology of East-ern Papua: Geological Society of America Bulletin, v. 82, p. 3299–3312, doi:10.1130/0016-7606(1971)82[3299:GOEP]2.0.CO;2.

Davies, H.L., and Smith, I.E., 1974, Tufi -Cape Nelson, Papua New Guinea, Sheets SC/55–8 and SC55-4, Geo-logical Series and Explanatory Notes: International Series: Canberra, Australian Government Publishing Service, scale 1:250,000.

Davies, H.L., and Warren, R.G., 1988, Origin of eclogite-bearing, domed, layered metamorphic complexes (“core complexes”) in the D’Entrecasteaux Islands, Papua New Guinea: Tectonics, v. 7, p. 1–21, doi:10.1029/TC007i001p00001.

Davies, H.L., and Warren, R.G., 1992, Eclogites of the D’Entrecasteaux Islands: Contributions to Mineral-ogy and Petrology, v. 112, p. 463–474, doi:10.1007/BF00310778.

Davis, G.A., Lister, G.S., and Reynolds, S.J., 1986, Struc-tural evolution of the Whipple and South Mountains shear zones, southwestern United States: Geol-ogy, v. 14, p. 7–10, doi:10.1130/0091-7613(1986)14<7:SEOTWA>2.0.CO;2.

Davis, G.H., and Coney, P.J., 1979, Geologic develop-ment of the Cordilleran metamorphic core com-plexes: Geology, v. 7, p. 120–124, doi:10.1130/0091-7613(1979)7<120:GDOTCM>2.0.CO;2.

Dinter, D.A., and Royden, L., 1993, Late Cenozoic ex-tension in northeastern Greece: Strymon Valley de-tachment system and Rhodope metamorphic core complex: Geology, v. 21, p. 45–48, doi:10.1130/0091-7613(1993)021<0045:LCEING>2.3.CO;2.

Doblas, M., Faulkner, D., Mahecha, V., Aparicio, A., Lo’pez-Ruiz, J., and Hoyos, M., 1997, Morphologi-cally ductile criteria for the sense of movement on slickenslides from an extensional detachment fault in southern Spain: Journal of Structural Geology, v. 19, p. 1045–1054, doi:10.1016/S0191-8141(97)00032-1.

Drachev, S.S., Kaul, N., and Beliaev, V.N., 2003, Eur-asia spreading basin to Laptev Shelf transition; structural pattern and heat fl ow: Geophysical Jour-nal International, v. 152, p. 688–698, doi:10.1046/j.1365-246X.2003.01882.x.

Drolia, R.K., and DeMets, C., 2005, Deformation in the dif-fuse India-Capricorn-Somalia triple junction from a multibeam and magnetic survey of the northern Central Indian Ridge, 3°S–10°S: Geochemistry, Geophysics, Geosystems, v. 6, doi:10.1029/2005GC000950.

Ferrill, D.A., Stamatakos, J.A., and Sims, D., 1999, Normal fault corrugation: Implications for growth and seismic-ity of active normal faults: Journal of Structural Geol-ogy, v. 21, p. 1027–1038, doi:10.1016/S0191-8141 (99)00017-6.

Fossen, H., and Tikoff, B., 1993, The deformation matrix for simultaneous simple shearing, pure shearing and vol-ume change, and its application to transpression-trans-tension tectonics: Journal of Structural Geology, v. 15, p. 413–422, doi:10.1016/0191-8141(93)90137-Y.

Gautier, P., Bozkurt, E., Bosse, V., Hallot, E., and Dirik, K., 2008, Coeval extensional shearing and lateral under-fl ow during Late Cretaceous core complex develop-ment in the Nigde Massif, Central Anatolia, Turkey: Tectonics, v. TC1003, doi:10.1029/2006TC002089.

Hill, E.J., 1994, Geometry and kinematics of the shear zones formed during continental extension in eastern Papua New Guinea: Journal of Structural Geology, v. 16, p. 1093–1105, doi:10.1016/0191-8141(94)90054-X.

Hill, E.J., and Baldwin, S.L., 1993, Exhumation of high-pressure metamorphic rocks during crustal extension in the D’Entrecasteaux region, Papua New Guinea: Journal of Metamorphic Geology, v. 11, p. 261–277, doi:10.1111/j.1525-1314.1993.tb00146.x.

Hill, E.J., Baldwin, S.L., and Lister, G.S., 1992, Unroof-ing of active metamorphic core complexes in the D’Entrecasteaux Islands, Papua New Guinea: Geol-ogy, v. 20, p. 907–910, doi:10.1130/0091-7613(1992)020<0907:UOAMCC>2.3.CO;2.

Hill, J., Baldwin, S.L., and Lister, G.S., 1995, Magmatism as an essential driving force for formation of active meta-morphic core complexes in eastern Papua New Guinea: Journal of Geophysical Research, v. 100, p. 10,441–10,451, doi:10.1029/94JB03329.

Jolivet, L., Faccenna, C., Goffé, B., Mattei, M., Rossetti, F., Brunet, C., Storti, F., Funiciello, R., Cadet, J.P., d’Agostino, N., and Parra, T., 1998, Midcrustal shear zones in postorogenic extension: Example from

the northern Tyrrhenian Sea: Journal of Geophysi-cal Research, v. 103, p. 12,123–12,160, doi:10.1029/97JB03616.

Jolivet, L., Lecomte, E., Huet, B., Denèle, Y., Lacombe, O., Labrousse, L., Le Pourhiet, L., and Mehl, C., 2010, The North Cycladic detachment system: Earth and Plan-etary Science Letters, v. 289, p. 87–104, doi:10.1016/j.epsl.2009.10.032.

Langenheim, V.E., and Jachens, R.C., 2003, Crustal structure of the Peninsular Ranges Batholith from magnetic data; implications for Gulf of California rifting: Geophysical Research Letters, v. 30, p. 1–4, doi:10.1029/2003GL017159.

Lister, G.S., and Davis, G.A., 1989, The origin of meta-morphic core complexes and detachment faults formed during Tertiary continental extension in the northern Colorado River regions, U.S.A.: Journal of Structural Geology, v. 11, p. 65–94, doi:10.1016/0191-8141(89)90036-9.

Lister, G.S., and Williams, P.E., 1983, The partitioning of deformation in fl owing rock masses: Tectonophysics, v. 92, p. 1–33, doi:10.1016/0040-1951(83)90083-5.

Little, T.A., Baldwin, S.L., Fitzgerald, P.G., and Monte-leone, B., 2007, Continental rifting and metamor-phic core complex formation ahead of the Woodlark spreading ridge, D’Entrecasteaux Islands, Papua New Guinea: Tectonics, v. 26, doi:10.1029/2005TC001911.

Manighetti, I., Tapponnier, P., Courtillot, V., Gruszow, S., and Gillot, P.-Y., 1997, Propagation of rifting along the Arabia-Somalia plate boundary: The Gulfs of Aden and Tadjoura: Journal of Geophysical Research, v. 102, p. 2681–2710, doi:10.1029/96JB01185.

Mann, P., and Taylor, F.W., 2002. Emergent late Quaternary coral reefs of eastern Papua New Guinea constrain the regional pattern of oceanic ridge propagation: Eos (Transactions, American Geophysical Union), v. 83, abstract T52C-1206.

Martinez, F., and Cochran, J., 1988, Structure and tectonics of the northern Red Sea: Catching a continental margin between rifting and drifting: Tectonophysics, v. 150, p. 1–31, doi:10.1016/0040-1951(88)90293-4.

Martinez, F., Goodliffe, A.M., and Taylor, B., 2001, Meta-morphic core complex formation by density inversion and lower-crust extrusion: Nature, v. 411, p. 930–934, doi:10.1038/35082042.

Means, W.D., Hobbs, B.E., Lister, G.S., and Williams, P.F., 1980, Vorticity and noncoaxiality in progressive defor-mations: Journal of Structural Geology, v. 2, p. 371–378, doi:10.1016/0191-8141(80)90024-3.

Monteleone, B.D., Baldwin, S.L., Webb, L.E., Fitz gerald, P.G., Grove, M., and Schmitt, A.K., 2007, Late Miocene–Pliocene eclogite facies metamorphism, D’Entrecasteaux Islands, SE Papua New Guinea: Journal of Metamorphic Geology, v. 25, p. 245–265, doi:10.1111/j.1525-1314.2006.00685.x.

Mutter, J.C., and Karson, J.A., 1992, Structural processes at slow-spreading ridges: Science, v. 257, p. 627–634, doi:10.1126/science.257.5070.627.

Ohara, Y., Yoshida, T., Kato, Y., and Kasuga, S., 2001, Giant megamullion in the Parece Vela backarc basin : Marine Geophysical Researches, v. 22, p. 47–61, doi:10.1023/A:1004818225642.

Okino, K., Matsuda, K., Christie, D.M., Nogi, Y., and Koi-zumi, K., 2004, Development of oceanic detachment and asymmetric spreading at the Australian-Antarctic discordance: Geochemistry, Geophysics, Geosystems, v. 5, doi:10.1029/2004GC000793.

Ollier, C.D., and Pain, C.F., 1981, Active gneiss domes in Papua New Guinea, new tectonic landforms: Zeitschrift für Geomorphologie, v. 25, p. 133–145.

Passchier, C.W., 1986, Flow in natural shear zones—The consequences of spinning fl ow regimes: Earth and Planetary Science Letters, v. 77, p. 70–80, doi:10.1016/0012-821X(86)90133-0.

Sánchez-Gómez, M., Avigad, D., and Heimann, A., 2002, Geochronology of clasts in allochthonous Miocene sedimentary sequences on Mykonos and Paros Islands: Implications for back-arc extension in the Aegean Sea: Journal of the Geological Society of London, v. 159, p. 45–60, doi:10.1144/0016-764901031.

Sen, S., and Seyitoglu, G., 2009, Magnetostratigraphy of early-middle Miocene deposits from E-W–trending




Alasehir and Büyük Menderes grabens in western Tur-key, and its tectonic implications, in van Hinsbergen, D.J.J., Edwards, M.A., and Govers, R., Collision and collapse at the Africa-Arabia-Eurasia subduction zone: Geological Society of London Special Publication 311, p. 321–342, doi:10.1144/SP311.13.

Simpson, C., and De Paor, G., 1993, Strain and kinematic analy-sis in general shear zones: Journal of Structural Geology, v. 15, p. 1–20, doi:10.1016/0191-8141(93)90075-L.

Smith, I.E., and Davies, H.L., 1976, Geology of the south-east Papuan mainland: Australian Bureau of Mineral Resources Bulletin, v. 165, p. 1–86.

Spencer, J.E., 1984, Role of tectonic denudation in warp-ing and uplift of low-angle normal faults: Geology, v. 12, p. 95–98, doi:10.1130/0091-7613(1984)12<95:ROTDIW>2.0.CO;2.

Spencer, J.E., 2000, Possible origin and signifi cance of extension-parallel drainages in Arizona’s metamor-phic core complexes: Geological Society of America Bulletin, v. 112, p. 727–735, doi:10.1130/0016-7606(2000)112<727:POASOE>2.0.CO;2.

Spencer, J.E., 2010, Structural analysis of three extensional detachment faults with data from 2000 Space-Shuttle Radar Topography Mission: GSA Today, v. 20, no. 8, p. 4–10, doi:10.1130/GSATG59A.1.

Spencer, J.E., and Ohara, Y., 2008, Magmatic and tectonic continuous casting in the circum-Pacifi c region: Ari-zona Geological Society Digest, v. 22, p. 31–53.

Taylor, B., Goodliffe, A.M., and Martinez, F., 1999, How continents break up: Insights from Papua New Guinea:

Journal of Geophysical Research, v. 104, p. 7497–7512, doi:10.1029/1998JB900115.

Tikoff, B., and Fossen, H., 1995, The limitations of three-dimensional kinematic vorticity analysis: Journal of Structural Geology, v. 17, p. 1771–1784.

Tucholke, B.E., Lin, J., and Kleinrock, M.C., 1998, Mega-mullions and mullion structure defi ning oceanic meta-morphic core complexes on the Mid-Atlantic Ridge: Journal of Geophysical Research, v. 103, p. 9857–9866, doi:10.1029/98JB00167.

Tucholke, B.E., Behn, M.D., Buck, W.R., and Lin, J., 2008, Role of melt supply in oceanic detachment faulting and formation of megamullions: Geology, v. 36, p. 455–458, doi:10.1130/G24639A.1.

Umhoefer, P.J., and Stone, K.A., 1996, Description and kine matics of the SE Loreto basin fault array, Baja Cali fornia Sur, Mexico: A positive fi eld test of oblique-rift models: Journal of Structural Geology, v. 18, p. 595–614, doi:10.1016/S0191-8141 (96)80027-7.

van Hinsbergen, D.J.J., and Meulenkamp, J.E., 2006, Neo-gene supra-detachment basin development on Crete (Greece) during exhumation of the South Aegean core complex: Basin Research, v. 18, p. 103–124, doi:10.1111/j.1365-2117.2005.00282.x.

Wallace, L.M., Stevens, C., Silver, E., McCaffrey, R., Lora-tung, W., Hasiata, S., Stanaway, R., Curley, R., Rosa, R., and Taugaloidi, J., 2004, GPS and seismological constraints on active tectonics and arc-continent col-lision in Papua New Guinea: Implications for mechan-ics of microplate rotations in a plate boundary zone:

Journal of Geophysical Research, v. 109, p. B05404, doi:10.1029/2003JB002481.

Wawrzenitz, N., and Krohe, A., 1998, Exhumation and doming of the Thasos metamorphic core complex (S Rhodope, Greece): Structural and geochronologi-cal constraints: Tectonophysics, v. 285, p. 301–332, doi:10.1016/S0040-1951(97)00276-X.

Webb, L.E., Baldwin, S.L., Little, T.A., and Fitzgerald, P.G., 2008, Can microplate rotation drive subduction inversion?: Geology, v. 36, p. 823–826, doi:10.1130/G25134A.1.

Wells, M.L., and Allmendinger, R.W., 1990, An early his-tory of pure shear in the upper plate of the Raft River metamorphic core complex: Black Pine Mountains, southern Idaho: Journal of Structural Geology, v. 12, p. 851–867, doi:10.1016/0191-8141(90)90059-8.

Worthing, M.A., 1988, Petrology and tectonic setting of blueschist facies metabasites from the Emo metamor-phics of Papua New Guinea: Australian Journal of Earth Sciences, v. 35, p. 159–168.

SCIENCE EDITOR: BRENDAN MURPHY

ASSOCIATE EDITOR: DENNIS BROWN

MANUSCRIPT RECEIVED 7 MAY 2010REVISED MANUSCRIPT RECEIVED 13 OCTOBER 2010MANUSCRIPT ACCEPTED 21 OCTOBER 2010

Printed in the USA


Documents

Geological Society of America Bulletin - University of Vermontlewebb/PNG/PNG Papers/Daczkoetal_2011_GSA.pdf · Sea (Martinez and Cochran, 1988), the Gulf of Aden (Manighetti et al.,