Linking Sedimentation in the Northern Andes to Basement Configuration, Mesozoic Extension, And Cenozoic Shortening

8/12/2019 Linking Sedimentation in the Northern Andes to Basement Configuration, Mesozoic Extension, And Cenozoic Short

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Geological Society of America Bulletin

doi: 10.1130/B30118.1published online 10 May 2010;Geological Society of America Bulletin

and Daniel F. StockliBrian K. Horton, Joel E. Saylor, Junsheng Nie, Andrs Mora, Mauricio Parra, Andrs Reyes-HarkerU-Pb ages, Eastern Cordillera, ColombiaMesozoic extension, and Cenozoic shortening: Evidence from detrital zirconLinking sedimentation in the northern Andes to basement configuration,

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ABSTRACT

Laser ablationinductively coupledplasmamass spectrometry (LA-ICP-MS)

analyses of 29 samples from the Eastern

Cordillera of Colombia reveal the origin of

northern Andean basement and patterns

of sedimentation during Paleozoic sub-

sidence, JurassicEarly Cretaceous exten-

sion, Late Cretaceous postrift subsidence,

and Cenozoic shortening and foreland-basin

evolution. U-Pb geochronological results in-

dicate that presumed Precambrian basement

is mainly a product of early Paleozoic mag-

matism (520420 Ma) potentially linked to

subduction and possible collision. Inheritedzircons provide evidence for Mesoproterozoic

tectonomagmatic events at 12001000 Ma

during Grenville-age orogenesis. Detrital

zircon U-Pb ages for Paleozoic strata show

derivation from Andean basement, syndepo-

sitional magmatic sources (420380 Ma),

and distal sources of chiefly Mesoproterozoic

basement (1650900 Ma) in the Amazonian

craton (Guyana shield) to the east or in pos-

sible continental terranes along the western

margin of South America. Sedimentation

during JurassicEarly Cretaceous rifting is

expressed in detrital zircon age spectra as

Andean basement sources, recycled Paleo-zoic contributions, and igneous sources of

CarboniferousPermian (310250 Ma) and

Late TriassicEarly Jurassic (220180 Ma)

origin. Detrital zircon provenance during

continued Cretaceous extension and postrift

thermal subsidence recorded the elimination

of Andean basement sources and increased

influence of craton-derived drainage sys-

tems providing mainly Paleoproterozoic and

Mesoproterozoic (2050950 Ma) grains. ByEocene time, zircons from the Guyana shield

(18501350 Ma) dominated the detrital

signal in the easternmost Eastern Cor-

dillera. In contrast, coeval Eocene deposits

in the axial Eastern Cordillera contain Late

CretaceousPaleocene (9055 Ma), Jurassic

(190150 Ma), and limited PermianTriassic

(280220 Ma) zircons recording initial up-

lift and exhumation of principally Mesozoic

magmatic-arc rocks to the west in the Cen-

tral Cordillera. OligoceneMiocene sand-

stones of the proximal Llanos foreland basin

document uplift-induced exhumation of theEastern Cordillera fold-thrust belt and recy-

cling of the Paleogene cover succession rich in

both arc-derived detritus (dominantly 180

40 Ma) and shield-derived sediments (mostly

1850950 Ma). Late MiocenePliocene ero-

sion into the underlying Cretaceous section

is evidenced by elimination of Mesozoic

Cenozoic zircons and increased proportions

of 1650900 Ma zircons emblematic of Cre-

taceous strata.

INTRODUCTION

The northern Andes of Colombia (Fig. 1)are distinguished from most of the Andeanorogenic belt by multiple exposures of crystal-line basement (Cordani et al., 2005; Ordez-Carmona et al., 2006), post-Paleozoic terraneaccretion events (Aspden and McCourt, 1986;Pindell et al., 1998), large-scale Mesozoic rift-ing (Cooper et al., 1995; Sarmiento-Rojas et al.,2006), and Cenozoic tectonic interactions withthe Caribbean plate (Taboada et al., 2000; Corts

et al., 2005). Whereas the Andean orogen farther south underwent large-magnitude shorten

ing along newly formed, thin-skinned, dip-slipstructures (Kley et al., 1999; McQuarrie et al.2005), the northern Andes are characterizedby low-magnitude shortening along invertedbasement-involved faults with a considerablecomponent of strike-slip deformation (Collettaet al., 1990; Corts et al., 2006; Acosta et al.2007). The distinctive geometries and kinematics of orogenesis in the northern Andes couldarguably be driven by processes contrary to theconventional Andean model of noncollisionadeformation above a single cratonward-dippingoceanic slab (e.g., Vanderhilst and Mann, 1994

Moores et al., 2002; Cediel et al., 2003; Kerand Tarney, 2005).Critical unknowns for tectonic reconstruc

tions of the northern Andes include: (1) the ageand nature of crystalline basement; (2) the roleof possible Paleozoic orogenesis; (3) the timingand extent of Mesozoic rifting; and (4) the onseand tempo of Cenozoic shortening and surfaceuplift during the Andean orogeny.

(1) Isolated exposures of crystalline basement in the Colombian Andes (Fig. 1) havebeen regarded as inliers of an integratedGrenville-aged (12001000 Ma) Mesoproterozoic basement contiguous with the Guyana

shield farther east (Kroonenberg, 1982Restrepo-Pace et al., 1997; Cordani et al.2005). Recent U-Pb ages, however, challengethis view and suggest the possible existenceof an early Paleozoic belt of magmatism anddeformation in the northern Andes (CardonaMolina et al., 2006; Chew et al., 2008).

(2) Paleozoic tectonic reconstructions havedisparately called upon noncollisional, arc collisional, and continental collisional modes o

For permission to copy, contact [email protected] 2010 Geological Society of America

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GSA Bulletin; September/October 2010; v. 122; no. 9/10; p. 14231442; doi: 10.1130/B30118.1; 10 figures; 1 table; Data Repository item 2010051.

E-mail: [email protected]

Linking sedimentation in the northern Andes to basement configuration,Mesozoic extension, and Cenozoic shortening: Evidence from

detrital zircon U-Pb ages, Eastern Cordillera, Colombia

Brian K. Horton1,, Joel E. Saylor2, Junsheng Nie2, Andrs Mora3, Mauricio Parra2, Andrs Reyes-Harker3, and

Daniel F. Stockli41Department of Geological Sciences and Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin

Austin, Texas 78712, USA2Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78712, USA3Instituto Colombiano del Petrleo, Ecopetrol, Bucaramanga,Colombia4Department of Geology, University of Kansas, Lawrence, Kansas 66045, USA

blished online May 10, 2010; doi:10.1130/B30118.1on June 3, 2010gsabulletin.gsapubs.orgDownloaded from
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Horton et al.

1424 Geological Society of America Bulletin, September/October 2010

70W75W

10N

5N

0 100 200

km

Caribbean

Nazca

0

20S

40S

Maroni-ItacainasProvince (2.21.9 Ga)

MI

Ventuari-TapajsProvince (21. 8 Ga)

VT

CA

Rio NegroJurenaProvince (1.81.5 Ga)

RNJ

RondoniaSan IgnacioProvince (1.51.3 Ga)

RO

SunssProvince (1.31.0 Ga)

SS

Garzn

SierrasPampeanasFamatina

Arc

Precordillera

Andeanbelt

Santander

ROSS

VT

VT MI

MI

Central AmazonianProvince(> 2.3 Ga)

CA

CA

RNJ

RNJ

Neoproterozoic Braslia belt

N

80W 60W

40W

ArcheanPaleoproterozoicSo Franciscocraton

ArequipaAntofalla

Precambrianbasement

Llanos

WMV

S NT M RT

SNTNDER

FLOREST

QUT M

GRZON

GU JIR

Llanos

EC

CC

WC

MV

SANTA MARTA

SANTANDER

FLORESTA

QUETAM

E

GARZ

ON

GUAJIRA

Figure 1. Map of northwestern South America depicting major tectonomorphic provinces (WCWestern Cordillera; CCCentral Cor-

dillera; MVMagdalena Valley; ECEastern Cordillera), crystalline basement exposures (shading), and locations of sandstone samples

(white circles) and granite samples (yellow circles). Inset map (lower right) shows Precambrian crustal provinces of South America and

corresponding metamorphic and igneous ages (from Cordani et al., 2000 and Chew et al., 2007).



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Detrital zircon ages from the Eastern Cordillera of Colombia

Geological Society of America Bulletin, September/October 2010 1425

orogenesis to explain pre-Andean deformationand metamorphism in the northern Andes (Pindelland Dewey, 1982; Restrepo-Pace, 1992; Dalzielet al., 1994). Similar disagreement surrounds thetiming of these episodes, with different events pro-posed for the Cambrian (Cardona Molina et al.,2006; Chew et al., 2008), OrdovicianSilurian

(Irving, 1975; Boinet et al., 1985; Cediel et al.,2003; Chew et al., 2007), Late SilurianDevonian(Campbell and Brgl, 1965; Forero Suarez,1990; Restrepo-Pace, 1992; Ordez-Carmonaet al., 2006), and PermianTriassic (Irving, 1975;McCourt et al., 1984; Cardona Molina et al.,2006; Vinasco et al., 2006).

(3) It is generally accepted that Mesozoic rift-ing affected the northern Andean domain, butthe age of initial extension, magnitude and num-ber of stretching events, and extensional basingeometries remain uncertain (Hbrard, 1985;Fabre, 1987; Kammer and Snchez, 2006; Moraet al., 2006, 2009; Sarmiento-Rojas et al., 2006;

Nivia et al., 2006). Additional problems involvethe extent of synrift magmatism and whetherextension developed in an intracontinentalrift or backarc extensional basin (Pindell andDewey, 1982; Pindell and Erikson, 1994; Cedielet al., 2003; Vsquez and Altenberger, 2005;Bayona et al., 2006).

(4) Despite a clear signal of Cenozoic An-dean shortening in Colombia, different perspec-tives persist on the timing, geometry, and causesof deformation. Estimates for the inception ofshortening range from mid-Cretaceous to Oligo-cene time (Dengo and Covey, 1993; Coney and

Evenchick, 1994; Cooper et al., 1995; Villamil,1999; Cediel et al., 2003; Corredor, 2003;Gmez et al., 2003, 2005; Corts et al., 2005;Jaimes and de Freitas, 2006; Cobbold et al.,2007; Bayona et al., 2008; Parra et al., 2009a,2009b). The orogenic architecture has beeninterpreted as a thin-skinned, ramp-flat thrustsystem above a regional dcollement that ac-commodated >150 km of east-west shortening(Dengo and Covey, 1993; Roeder and Chamber-lain, 1995) or, alternatively, a belt of basement-involved inversion structures that reactivatedMesozoic extensional structures and accommo-dated 6070 km of shortening (Colletta et al.,

1990; Cooper et al., 1995; Kammer and Mora,1999; Branquet et al., 2002; Corts et al., 2006;Mora et al., 2006).

The motivation of the present study is to im-prove regional tectonic reconstructions throughan understanding of the distribution of northernAndean sediment sources during the Phanero-zoic history of basin evolution and associateddeformation and magmatism. A secondarygoal is to expand the database concerning thetemporal and spatial configuration of base-ment rocks in the Colombian Andes. Here we

present 2669 zircon U-Pb ages generated bylaser ablationinductively coupled plasmamassspectrometry (LA-ICP-MS) analyses. Ages ofdetrital zircon grains from 26 sandstone sam-ples (15 new samples and 11 samples recentlyreported by Horton et al., 2010) of Phanerozoicclastic units (Fig. 2) shed light on the patterns

of sedimentation during Paleozoic subsidence,JurassicEarly Cretaceous extension, LateCretaceous postrift subsidence, and Cenozoicshortening and foreland-basin evolution. Ad-ditional analyses of three samples of selectedAndean crystalline basement rocks help definethe intrusion ages and inherited age signaturesfor granitic basement exposed in the EasternCordillera of Colombia.

GEOLOGIC FRAMEWORK

Regional Overview

The northern half of the South American plateencompasses Precambrian basement of the Ama-zonian craton, Cenozoic foreland basin sedi-ments, and dominantly Phanerozoic rocks of thenorthern Andes (Fig. 1). The Amazonian cratonconsists of several northwest-trending provincesthat were accreted to an Archean nucleus. Base-ment tectonic provinces (Fig. 1 inset) includethe Central Amazonia (>2300 Ma), Maroni-Itacainas (22001950 Ma), Ventuari-Tapajs(19501800 Ma), and Rio NegroJuruena(18001500 Ma) provinces (Teixeira et al., 1989;Tassinari and Macambira, 1999; Cordani et al.,

2000). The Guyana shield generally refers to thenorthern segments of these provinces situatednorth of the east-flowing Amazon River. Al-though buried by Cenozoic basin fill, the westernedge of the Guyana shield is commonly consid-ered to be contiguous with isolated basement ex-posures in the northern Andes of Colombia andVenezuela (e.g., Irving, 1975; Priem et al., 1989).

The Andean orogenic belt in Colombia con-sists of three major ranges and flanking basinsystems (Fig. 1). The Western Cordillera iscomposed of Cenozoic igneous rocks of oceanicaffinity (McCourt et al., 1984). In the CentralCordillera, JurassicCretaceous igneous rocks

heavily overprint a crystalline basement ofmixed continental and oceanic origin (Aspdenand McCourt, 1986; Aspden et al., 1987; Cedielet al., 2003). The Eastern Cordillera contains lo-calized basement exposures capped by Phanero-zoic sedimentary rocks (Fig. 2) indicative ofmarine and nonmarine sedimentation duringvaried Paleozoic tectonic conditions, Mesozoicextension, and Cenozoic shortening (Campbelland Brgl, 1965; Cooper et al., 1995; Sarmiento-Rojas et al., 2006). The depositional products ofuplift and erosion during Andean orogenesis are

preserved in the intermontane Magdalena Valleybasin between the Central Cordillera and Eastern Cordillera and in the Llanos foreland basinat the eastern edge of the orogenic belt (Gmezet al., 2003; Parra et al., 2009a).

In Colombia, Andean crystalline basemenis exposed in six main regions (Fig. 1). Isolated

basement exposures in the Eastern Cordillera(Floresta, Quetame, Garzon, and Santandemassifs) and northern coastal zone of Colombia (Sierra Nevada de Santa Marta and Guajiramassifs) consist of gneissic and granitic rocksmany exhibiting ages between ~1200 Ma and~900 Ma (Irving, 1975; Kroonenberg, 1982Priem et al., 1989; Restrepo-Pace et al., 1997Cordani et al., 2005; Cardona Molina et al.2006; Jimnez Meja et al., 2006; OrdezCarmona et al., 2006; Cardona et al., 2010)Although partially composed of accretedmaterial, the poorly understood basement othe Central Cordillera includes low- to high

grade metamorphic rocks and limited igneous rocks yielding primarily Devonian andPermian ages with possible inheritance fromMesoproterozoic and Neoproterozoic protoliths (Restrepo-Pace, 1992; Vinasco et al., 2006Restrepo et al., 2009).

Potential Sediment Sources

In considering possible contributors of clasticsediment, we briefly review the ages of different regions in northern South America. Despitelimited geochronological efforts in Colombia

sufficient data exist to characterize probablesediment source regions. We recognize the pitfalls of wholesale acceptance of previouslyreported age summaries, particularly those incorporating K-Ar and Rb-Sr data for intrusiveand metamorphic rocks that may record ageof younger cooling rather than original crystallization (e.g., Goldsmith et al., 1971; Irving1975; Boinet et al., 1985; Forero Suarez, 1990Bartok, 1993). Therefore, wherever possibleemphasis is placed on age summaries employing high-closure temperature minerals (e.g.McCourt et al., 1984; Aspden et al., 1987Restrepo-Pace, 1992; Restrepo-Pace et al.

1997; Cordani et al., 2005; Cardona Molinaet al., 2006; Ordez-Carmona et al., 2006)From these data, a schematic summary of representative ages is provided for various parts othe Guyana shield and northern Andes (Fig. 3).

The northwest-trending basement provinceof the Amazonian craton (Fig. 1) yield distinctive ages ranging from >2300 to 1500 Ma. Metamorphic ages for the Guyana shield appear tobe concentrated at 16001450, 13501250, and1100900 Ma (Priem et al., 1982, 1989; Teixeiraet al., 1989; Goldstein et al., 1997). The common

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occurrence of late Mesoproterozoic ages innorthern South America attests to Grenville-agedcollisional orogenesis and metamorphism gener-ally attributed to assembly of Rodinia (Dalziel,1991; Hoffman, 1991; Fuck et al., 2008; Li et al.,2008; Ramos, 2010). However, some studies fa-vor a more protracted Mesoproterozoic and Neo-proterozoic history of collisional orogenesis andsubsequent rifting events (de Brito Neves et al.,1999; Chew et al., 2008; Santos et al., 2008), im-plying a broader distribution of roughly 1200

600 Ma basement ages.Andean crystalline basement in the Eastern

Cordillera of Colombia contains signatures ofGrenville-aged metamorphism expressed by aconcentration of ages at 12001000 Ma withminor inheritance of early Mesoproterozoicages (Priem et al., 1989; Restrepo-Pace et al.,1997; Cordani et al., 2005; Jimnez Meja et al.,2006; Ordez-Carmona et al., 2006; Cardonaet al., 2010). Nevertheless, crosscutting rela-tionships between intrusive rocks and Paleo-zoic strata demonstrate that a lower Paleozoicage is probable for some basement rocks of the

Eastern Cordillera (Irving, 1975; Forero Suarez,1990; Ordez-Carmona et al., 2006). Support-ing evidence includes reported low-grade meta-morphism of OrdovicianSilurian age (Cedielet al., 2003; Chew et al., 2007) and igneous agesof 460410 Ma for the Santander plutonic group(Fig. 3; Goldsmith et al., 1971; Irving, 1975;Boinet et al., 1985).

The Central Cordillera of Colombia consistslargely of subduction-related magmatic arc rocksof principally Jurassic (170150 Ma), mid toLate Cretaceous (12070 Ma), and Paleogene(6040 Ma) age (Aspden et al., 1987; Restrepo-Pace, 1992). These igneous rocks intrude and

overlap a Paleozoic metamorphic belt of mostlylow- to medium-grade rocks (Cajamarca com-plex) yielding metamorphic ages concentrated at410380 Ma and 300250 Ma (McCourt et al.,1984; Ordez-Carmona et al., 2006; Vinascoet al., 2006 and references therein), with limitedsuggestions of CretaceousPaleocene metamor-phism (Restrepo et al., 2008, 2009). Additionalmagmatic episodes are represented by intrusionages of 240210 Ma (Santa Barbara batholith,Amag stock, and other granites; Irving, 1975;McCourt et al., 1984; but see Restrepo et al., 2009

BOYACAFAULT

SOAPAGAFAULT

GUAYABO

USME

LEN

CHIPAQUE

DURA

SABANATILATA

BARCO

GUADALUPE GROUP

UNE

FMEQUE

LAS JUNTAS / CQUEZA

MACANALBUENAVISTA /

CHINGAZA

CARBONERA

MIRADORREGADERA

BOGOT LOS CUERVOS

GUADUASCACHO

GIRON

RUSIA

CUCHE/FLORESTA

TIBET GUTIERREZ

GUATIQUIA

PALERMO

MONTEBEL

CONCENTRACIN

LOWER SOCHA

SAN GIL

ARCABUCO

PAJA

TIBASOSA

CONEJO

SIMIJACA

GUAVIO /BATA

PICACHO

QUETAME

MASSIF

FARALLONES

UPPER SOCHA

FLORESTA

MASSIF

C7C5

C3

C1

Axial Eastern Cordillera EasternFoothills Llanos BasinNorthern Southern

Lacustrine siltstone

Alluvial fan conglomerates

Nonmarine sandstones

Delta and coastal-plainsandstones

Nonmarine mudstones

Delta and coastal-plainmudstones

0

10

20

30

40

50

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TURONIAN

OXFORDIAN

KIMMERIDGIAN

SANTONIAN

CENOMANIAN

ALBIAN

APTIAN

BARREMIAN

HAUTERIVIAN

VALANGINIAN

BERRIASIAN

TITHONIAN

CAMPANIAN

PLEISTOCENEPLIOCENE

MIOCENE

OLIGOCENE

EOCENE

PALEOCENE

MAASTRICHTIAN

EPOCHAge(Ma)

Facies change

Angular unconformity

Shallow-marine sandstones

Shallow-marine mudstones

Shallow-marine carbonates

170

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Volcaniclastic deposits

Intermediate to acidintrusivesLow- medium-grademetamorphic rocks

Shallow-marine siliceoussiltstones/chert

Sandstone sample

MA1

08YEM01

MP175

08YEM03TO2170

12080806 (unnamed)

MP295

08TAU02

NEOGENE

PALEOGENE

LATECRETACEOUS

EARLYCRETACEOUS

LATE

JURASSIC

MIDDLE

JURASSIC

EARLY

JURASSIC

LATE

TRIASSIC

MIDDLE

TRIASSIC

PERMIAN

CARBON-

IFEROUS

DEVONIAN

PRE-

DEVONIAN

08TAU01

08YEM0708YEM05

Granite sample

RH1

FS11A

MA16

13080808

130808101308081113080812

13080807FS5GIR08151

1308080413080803

SJ4A

AM7

AM6B

MA2

11080811

MA13

Figure 2. Phanerozoic geologic column for

the Eastern Cordillera and western margin

of the Llanos basin of Colombia, providing

the stratigraphic context for 26 sandstone

samples (triangles) and three basement sam-

ples (squares). Modified from Mora et al.

(2006) and Parra et al. (2009a, 2009b).



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for an alternative interpretation), and 160 Ma and9580 Ma (Ibague batholith, Antioquia batholith,and Altavista stock; Correa et al., 2006; Ibaez-Meja et al., 2007; Villagmez et al., 2008). U-Pbdata from Vinasco et al. (2006) demonstrate in-

heritance of scattered Mesoproterozoic and Neo-proterozoic zircons, consistent with Precambrianbasement underlying the eastern flank of the Cen-tral Cordillera (e.g., Aleman and Ramos, 2000;Cardona et al., 2010).

Accreted oceanic crust of the Western Cor-dillera contains a record of nearly continuousCenozoic magmatism with peak productivityat 2510 Ma (McCourt et al., 1984; Aspdenet al., 1987). Earlier magmatism at 9580 Main the Western Cordillera was related mainly togrowth of an oceanic plateau prior to latest Cre-taceous accretion to South America (Kerr et al.,2003; Villagmez et al., 2008). Post-accretionary

uplift of the Western Cordillera occurred duringor after construction of the Central Cordillera(Gmez et al., 2003), thus precluding signifi-cant communication with Cenozoic drainagesystems in the Magdalena Valley, EasternCordillera, and Llanos basin (Villamil, 1999).Therefore, the Western Cordillera is an unlikelysource for the Phanerozoic sedimentary unitssampled in this study on the eastern flank of theorogenic belt.

Finally, in considering detrital provenance,we emphasize that the current distribution and

ages of crystalline basement and magmaticrocks (Fig. 3) do not provide a complete inven-tory of potential sediment sources. For example,terrane accretion events characterized the lateMesozoicearliest Cenozoic history of the

westernmost Colombian Andes (e.g., Aspdenand McCourt, 1986; Restrepo and Toussaint,1988; Kerr and Tarney, 2005), with possiblysignificant along-margin translation of terranes(e.g., Bayona et al., 2006). Some have also pro-posed an allochthonous origin for PrecambrianPaleozoic basement of the Central Cordilleraand parts of the Eastern Cordillera (e.g., ForeroSuarez, 1990; Cediel et al., 2003; Cardona et al.,2010). Although more work is required to deter-mine the structural boundaries and plate historiesof potential terranes, interpretations of sedimentprovenance need to be qualified by (1) the pos-sibility that basement rocks of the Central Cor-

dillera and Eastern Cordillera were not in theirpresent configuration, and (2) the potential in-fluence of former terranes that may have oncebordered the western margin of northern SouthAmerica. An additional concern involves theerosional recycling of sedimentary rocks andresulting complication of detrital age signa-tures. For Colombia, it is anticipated that manyPhanerozoic sedimentary units have undergonesome degree of reworking during the variabletectonic conditions that affected the northernAndes. The consequences of recycling are par-

ticularly relevant for periods in which a formersedimentary basin, such as the Cretaceous basinspanning the Eastern Cordillera, was exhumedand contributing sediments to younger basins.

METHODS

Samples from 26 medium-grained quartzosesandstones and three granitic intrusions in theEastern Cordillera (Table 1) were collectedprocessed, and analyzed for U-Pb geochronology by laser ablationinductively coupledplasmamass spectrometry (LA-ICP-MS) following the methods of Chang et al. (2006) andLewis et al. (2006). Zircon grains were separatedby standard density and magnetic separationtechniques, selected randomly, then mountedinto epoxy pucks that were ground and polished to expose grains. Laser spot locations o

3040 m diameter, chiefly on sufficiently widerims of zoned grains, were identified using a basemap constructed from photomicrograph and/ocathodoluminescence images. LA-ICP-MSanalyses were conducted at the GeoAnalyticaLaboratory at Washington State University ona ThermoFinnigan Element2 single-collectordouble-focusing magnetic sector ICP-MS witha New Wave Nd:YAG 213 nm (model UP-213laser ablation system. For each analytical session, the instrument was initially tuned usingNational Institute of Standards and Technology

0 500 1000 1500 2000 2500

Age (Ma)

0 500 1000 1500 2000 2500

WESTERN CORDILLERA

GUYANA SHIELD(Llanos Basin)

CARIBBEAN COAST(Santa Marta, Guajira)

EASTERN CORDILLERA(Santander)

EASTERN CORDILLERA

CENTRAL CORDILLERA

CentralAmazonia

Maroni-Itacainas

Rio NegroJuruena

Ventauri-Tapajs

inherited igneous ormetamorphic age

igneous ormetamorphic age

peak igneous ormetamorphic age

major detrital zirconage signatures(this study)

EXPLANATION

AMAZONIAN CRATON

Figure 3. Summary of previously reported isotopic ages for potential zircon sources in northwestern South Amer-

ica, with igneous and metamorphic ages derived from U-Pb and selected 40Ar/39Ar, K-Ar, and Rb-Sr results, and

inherited ages derived from U-Pb analyses of older relict grains in crystalline and/or metasedimentary samples(Goldsmith et al., 1971; Irving, 1975, McCourt et al., 1984; Boinet et al., 1985; Aspden et al., 1987; Forero Suarez,

1990; Restrepo-Pace, 1992; Drr et al., 1995; Restrepo-Pace et al., 1997; Cordani et al., 2005; Cardona-Molina

et al., 2006; Ordez-Carmona et al., 2006; Vinasco et al., 2006). Peak igneous and metamorphic ages are defined

on the basis of multiple overlapping ages. Major U-Pb age signatures of detrital zircons from this study are rep-

resented by gray vertical columns.



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Horton et al.


(NIST) 612 glass standard, with subsequentanalyses incorporating zircon age standards onceevery ~5 unknown analyses. Data were collectedunder acquisition and operational parametersoutlined by Chang et al. (2006).

U-Pb ages (GSA Data Repository Table DR11)were calculated on the basis of analytical resultsfor zircon standards Peixe (564 4 Ma; see

Chang et al., 2006) and Temora (416.8 1.1 Ma;Black et al., 2003), with corrections for time-dependent, laser-induced fractionation using theintercept method in which the initial signal (at ac-quisition time 0) was assumed to be free of time-dependent fractionation (Sylvester and Ghaderi,1997; Chang et al., 2006; Lewis et al., 2006). Ageuncertainties are reported at the 1level. As dis-cussed by Chang et al. (2006), the low intensityof the 204Pb signal consistently generates approxi-mate values near zero with exceptionally highvariation, precluding a single reliable correctionfor common Pb.

We applied filters to all analyses of detrital

zircon and magmatic zircon in order to excludegrains most likely affected by significant Pb lossand other complex time-temperature histories.We removed from consideration all grainsexhibiting >10% discordance, >5% reversediscordance, and >10% uncertainty. For inter-

pretations of provenance and granite emplace-ment, the preferred ages are 206Pb/238U agesfor grains younger than 900 Ma and 207Pb/206Pbages for grains older than 900 Ma (Table DR1[see footnote 1]). The 900 Ma boundary wasselected in order to avoid splitting clusters ofdetrital and/or inherited magmatic grain ages,notably the common spread of ages between

~1100 Ma and ~950 Ma.Analytical results for granite samples aredepicted in standard Concordia plots. Detritalzircon U-Pb age results are plotted on relativeage probability diagrams and normalized suchthat age-distribution curves for all samples con-tain the same area, allowing graphical compari-son among different samples. For sedimentaryrocks, we attempted to analyze ~100 grains persample in order to identify, at the 95% probabil-ity level, age components constituting >3% ofthe zircon population (Andersen, 2005). Mostsamples yielded 80100 ages of individual zir-con grains, and interpretations are based on age

peaks defined by three or more grains, thus re-ducing bias that may be introduced by Pb loss,inheritance, common Pb, or inaccurate ages forindividual grains.

U-Pb RESULTS

Andean Crystalline Basement

LA-ICP-MS analyses of granitic basementrocks from the Quetame and Floresta massifs(Fig. 1 and Table 1) help clarify the tectonomag-

matic history of the Eastern Cordillera. U-Pbresults for three samples of crystalline base-ment (Fig. 4) indicate CambrianOrdovicianmagmatism, with inheritance of a wide rangeof Mesoproterozoic grains. For each sample,the collection of single-crystal U-Pb ages spansseveral tens of millions of years. We report thespread of acceptable ages, recognizing that

the younger ages may be considered more rea-sonable estimates of crystallization ages, withslightly older ages representing partial inheri-tance. For comparison, weighted mean ages ofthe more concordant zircons are also reported.

In the easternmost Eastern Cordillera, agranitic sample (sample RH1) derived fromthe Quetame massif was collected as a boulderclast in a modern river, the Rio Humea, at theeastern front of the thrust belt (Fig. 1). The RioHumea exclusively drains the Quetame massif,where a granitic body (La Mina granodiorite)intrudes phyllitic rocks (Quetame Group) ofpossible Precambrian or CambrianOrdovician

age (Campbell and Brgl, 1965; Forero Suarez,1990). U-Pb results for 15 zircon grains fromthe Rio Humea granite sample show a concen-tration of 11 concordant ages from 526 12455 11 Ma (Fig. 4A). These 11 grains havea weighted mean age of 483 10 Ma (meansquare of weighted deviates [MSWD] = 4.2).The four remaining zircons yield concordantages of 992 33, 1014 33, 1344 31, and1607 30 Ma.

In the axial zone of the Eastern Cordillera,two granitic samples were collected from the

1GSA Data Repository item 2010051, Table DR1,LA-ICP-MS analyses for zircon U-Pb geochronol-ogy of the Eastern Cordillera and Llanos basin ofColombia, is available at http://www.geosociety.org/pubs/ft2010.htm or by request to [email protected].

TABLE 1. SAMPLE INFORMATION FOR SANDSTONES AND GRANITES FROM THE EASTERN CORDILLERA AND LLANOS BASIN OF COLOMBIA

noitamroFegADIelpmaSLatitude

(N)Longitude

(W)UTM (E)Easting

UTM (N)Northing

08TAU02 Late MiocenePliocene Upper Guayabo (Corneta) 5.00221 72.79504 1142235 104503708TAU01 Late MiocenePliocene Upper Guayabo (Corneta) 4.96540 72.82360 1139075 1040960MP295 5081201438990195771.3797297.4obayauGreppUenecoilPenecoiMetaL08YEM07 8208801678381166814.2769983.5obayauGrewoLenecoiMetaL08YEM05 4020901249181150634.2786904.5obayauGrewoLenecoiMetaL12080806 6551411194341158187.2777478.5tinudemannU)?(enecoiMTO2170 9149101443001120371.3712177.4)rebmeM1C(arenobraCenecoiMylraE08YEM03 5233901584081121944.2739734.5)rebmeM2C(arenobraCenecoiMylraEMP175 6657201914001152271.3778448.4)rebmeM5C(arenobraCenecoiMylraE08YEM01 9845901951871140074.2745754.5rodariMenecoEelddiM

1565501169640189356.3713990.5aredageRenecoEelddim-ylraE1AM8864501763940192236.3795090.5epuladauGsuoecaterCetaL2AM

11080811 5470411264731192638.2765768.5euqapihCsuoecaterCetaLAM6B 3625011533761164765.2751645.5enUsuoecaterCetaL

9124011651961150155.2776635.5satnuJsaLsuoecaterCylraE7MAMA13 4210401747780143682.3775859.4lanacaMsuoecaterCylraESJ4A 334789520640108266.3744284.4atsivaneuBsuoecaterCylraE13080803 5201511616141185897.2714069.5nriGcissaruJetaL13080804 9111511674141148997.2762169.5nriGcissaruJetaL13080807 4573511423041191018.2711589.5nriGcissaruJetaL-elddiM

2174311944231176188.2721318.5nriGcissaruJetaL-elddiM5SFGIR08151 2295721183890199681.3734090.7nriGcissaruJetaL-elddiMMA16 8860301778980142762.3722378.4aiuqitauGsuorefinobraC13080812 4481511537041125608.2738769.5ehcuCnainoveDetaL13080811 9502511796041158608.2787969.5ehcuCnainoveDetaL

13080810 8022511064041199808.2731179.5ehcuCnainoveDetaL13080808 PrecambrianPaleozoic (?) Floresta: Otenga granite 5.98178 72.81274 1140042 1153385FS11A PrecambrianPaleozoic (?) Floresta: Otenga granite 5.84875 72.86448 1134345 1138658RH1 PrecambrianPaleozoic (?) Quetame: La Mina granodiorite 4.38634 73.29027 1087383 976840



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Floresta massif (Fig. 1). In this region, quartzmonzonite and intermediate intrusive bodies cutlow-grade metasedimentary rocks of presumedNeoproterozoic to lower Paleozoic age (ForeroSuarez, 1990; Ulloa et al., 1998; Kammer andSnchez, 2006). U-Pb results for 15 zircongrains from a granitic sample of the Otengastock (sample FS11A) exhibit a spread of nineconcordant to slightly discordant ages from515 11 to 435 9 Ma and one slightly discor-

dant outlier at 388 4 Ma (Fig. 4B). Excludingthe outlier, the nine analyses have a weightedmean age of 482 15 Ma (MSWD = 6.5). Fiveolder grains yield concordant to slightly discor-dant ages of 726 16, 992 25, 1008 21,1140 15, and 1214 28 Ma.

A second granitic sample (sample 13080808)from the Floresta massif was analyzed in sig-nificantly greater detail. U-Pb results for 103zircon grains show a population of 45 mostlyconcordant ages from 539 7 to 422 4 Mawith one slightly discordant outlier at 359 4 Ma (Fig. 4C). Excluding the outlier, the popu-

lation of 45 grains has a weighted mean age of464.2 8.2 Ma (MSWD = 32). If grain ageswith >2% discordance are excluded, then aweighted mean age of 477 11 Ma (MSWD =28) is obtained for the 25 youngest grains. A sig-nificant population of older zircon ages, com-prising about half of all analyzed grains, occursin the 1700600 Ma range, with most ages con-centrated between 1600 Ma and 1000 Ma.

The large number of analyses for this Florestasample facilitates consideration of interceptages. If the significant grain age populationsat ~1000 Ma and ~1500 Ma (Fig. 4C) are as-sumed to represent protolith ages, two calcu-

lated chords (Fig. 4D) yield lower intercept agesof 424 14 Ma (MSWD = 11) and 448 11 Ma(MSWD = 29), respectively. The lower interceptages are regarded as minimum ages for earlyPaleozoic magmatism in the region, and may beattributed to magmatic crystallization with var-ied populations of Mesoproterozoic xenocrystsor to significant Pb loss during an early Paleo-zoic metamorphic event.

The U-Pb geochronological results for gra-nitic basement rocks are interpreted as the prod-uct of magmatism at ~520 to ~420 Ma, with

1600

1200

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0.00

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207Pb/235U

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0.05

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0.4 0.5 0.6 0.7 0.8207Pb/235U

206Pb/238U

206Pb/238U

206Pb/238U

A

B

C

Quetame massifgranitic clast(RH1)

Floresta massifOtenga granite(FS11A)

Floresta massifOtenga granite(13080808)

580

540

500

460

420

380Lower Intercepts:424 14 Ma (MSWD = 11)448 11 Ma (MSWD = 29)

D

Weighted mean age (n= 9):482 15 Ma (MSWD = 6.5)

Weighted mean age (n= 11):483 10 Ma (MSWD = 4.2)

Weighted mean age (n= 25):477 11 Ma (MSWD = 28)

Figure 4. Concordia diagrams depicting 206Pb/238U and207Pb/235U data for zircon grains from granite samples

derived from the (A) Quetame massif (La Mina grano-

diorite), and (B, C) Floresta massif (Otenga granite).

Inset figures show Concordia diagrams for major grain

age populations in each sample, including (D) potential

lower intercept ages for the Floresta massif (Otenga

granite). MSWDmean square of weighted deviates.



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Horton et al.


preferred crystallization ages of ~482 15 Ma.In this interpretation, additional younger ages,commonly discordant, may be considered aspotential products of Pb loss during late Paleo-zoic metamorphism. Inherited zircons mostly inthe 16001000 Ma age range demonstrate igne-ous reworking of an older continental crust of

Mesoproterozoic age. The U-Pb ages for inher-ited zircons cluster at 12001140 Ma and 10501000 Ma, consistent with previous studies of theAndean orogenic belt in Colombia (Kroonen-berg, 1982; Priem et al., 1989; Restrepo-Paceet al., 1997; Cordani et al., 2005; CardonaMolina et al., 2006). The preferred crystalliza-tion ages demonstrate a CambrianOrdovician,rather than Precambrian, age for Andean graniticbasement in Colombia. Despite their spatial sep-aration of ~150 km, the Floresta and Quetamemassifs yield similar ages of granite emplace-ment, attesting to the regional extent of earlyPaleozoic magmatism. Several previous studies

have also suggested early Paleozoic magmatismin Colombia (e.g., Irving, 1975; Boinet et al.,1985), with limited geochemical evidence fromthe northern Andes suggestive of a subduction-related magmatic arc (Cardona Molina et al.,2006; Chew et al., 2007, 2008). K-Ar ages of490440 Ma from similar samples in the east-ernmost Eastern Cordillera (Irving, 1975) over-lap with the ages reported here. The timing ofthis magmatism coincides with the well-knownFamatinian arc magmatism of the central Andes(Fig. 1; Rapela et al., 1998; Chew et al., 2007).Late Neoproterozoic and early Paleozoic mag-

matism also agrees with plate reconstruc-tions for the inception of subduction-relatedmagmatism along various margins of Gond-wanaland and its bordering, peri-Gondwananterranes (e.g., Keppie et al., 2003; Cawood,2005; Horton et al., 2008). Although the presentdata clearly demonstrate early Paleozoic mag-matism in the northern Andean belt, uncertaintyremains over the polarity of any subductionzone and whether arc magmatism was situatedon South American lithosphere or on separatecontinental or oceanic terranes (Restrepo-Pace,1992; Restrepo-Pace et al., 1997).

Paleozoic Sedimentary Rocks

Detrital zircon U-Pb ages identify a prov-enance record for Paleozoic clastic deposits inthe axial zone of the Eastern Cordillera. Foursamples in the region surrounding the Florestamassif and Quetame massif (Fig. 1) representmarine to nonmarine sandstones of the UpperDevonian Cuche Formation (which overlies theLower to Middle Devonian El Tibet and Florestaformations) and the Carboniferous Capas Rojasdel Valle del Guatiquia Formation (Fig. 2). Vari-

ous marine fossils, notably vertebrate fossils,constrain the ages of these units (Mojica andVillarroel, 1984; Janvier and Villarroel, 2000;Burrow et al., 2003). Structural relationshipssuggest that part of this 1- to 2-km-thick mid-Paleozoic succession may have been depositedsynchronously with upper-crustal deformation

(Kammer and Snchez, 2006).The four sandstone samples (samples13080810, 13080811, 13080812, and MA16)show relatively similar zircon age spectra(Fig. 5). Major age peaks occur at 500400and 1070940 Ma, with subordinate peaks at12501150 and 15601470 Ma (Fig. 5). Theearly Paleozoic age peaks overlap with theevidence for CambrianOrdovician magma-tism identified above for basement rocks of theEastern Cordillera (Fig. 4). The principal Pre-cambrian age peak at ~1020 Ma is comparableto age signatures in basement rocks of the East-ern Cordillera and Guyana shield (Priem et al.,

1982, 1989; Teixeira et al., 1989; Restrepo-Paceet al., 1997). The secondary Precambrian peaks(in order of decreasing abundance) at ~1175,~1240, ~1545, ~1335, and ~1485 Ma coincidewith basement and metamorphic ages fromthe western portions of the Amazonian craton,specifically the Rio NegroJuruena province(Fig. 3). Although there is upsection variabilityin the U-Pb age spectra among the four samples,few stratigraphic trends emerge. However, thetwo younger samples (samples 13080812 andMA16) show higher proportions of approxi-mately Grenville-aged zircons at 1350950 Ma

(Fig. 5). Evidence for Paleozoic syndepositionalmagmatism is provided by a minor popula-tion of Devonian-age zircon grains in the threesamples from the Devonian Cuche Formation.These grains exhibit high 232Th/238U ratios andlow 238U concentrations consistent with igneouszircon crystallization (Williams and Claesson,1987; Vavra et al., 1999; Hartmann and Santos,2004). A weighted mean age for the five young-est Cuche Formation grains provides a maxi-mum depositional age limit of 384.0 3.9 Ma(MSWD = 1.0), consistent with Frasnian (LateDevonian) fossil assemblages (Janvier andVillarroel, 2000; Burrow et al., 2003).

On the basis of the U-Pb age spectra, weinterpret two principal sediment sources forthe Eastern Cordillera during Paleozoic time:a local Andean source of the lower Paleozoicbasement identified in this study (Fig. 4) anda distal source of Mesoproterozoic and Neo-proterozoic basement rocks from the westernedge of the Guyana shield (Figs. 1 and 3) or un-specified continental blocks along the westernmargin of northern South America. For lowerPaleozoic basement, the youngest subpopu-lations of detrital zircon ages are distributed

from ~500 to ~420380 Ma (Fig. 4), suggest-ing that Andean magmatism extended moreor less continuously from Cambrian throughDevonian time. Interpretation of an additional,distal source of older basement could supportmodels in which Paleozoic sediments are de-rived either from an eastern basement shield

source (Campbell and Brgl, 1965) or frombasement blocks along the western continen-tal margin with possible origins in Laurentia,Mexico (Oaxaca), or Baltica (Forero Suarez,1990; Keppie et al., 2001; Cediel et al., 2003;Gillis et al., 2005; Cardona et al., 2010). Theincreasing amount of Grenville-aged Meso-proterozoic detritus in the higher stratigraphiclevels (Fig. 5) could be attributed to progres-sive exposure of deeper-level metamorphicrocks as cover rocks were erosionally removed.Alternatively, this stratigraphic trend couldrecord enhanced contributions from the olderbasement provinces such as those located far-

ther east within the Amazonian craton.The Guyana shield, specifically the Rio

NegroJuruena province (Figs. 1 and 3), is con-sidered a most probable source of Mesoprotero-zoic detritus that accumulated in the EasternCordillera during Paleozoic time. McCourtet al. (1984) proposed that the Guyana shieldmay also have been the ultimate sedimentsource region for the lower Paleozoic sedi-mentary protoliths of low- to moderate-grademetamorphic rocks composing the Cajamarcacomplex in the Central Cordillera. If correct,a similar source region for both the Eastern

Cordillera and Central Cordillera would sug-gest an integrated regional drainage system,conceivably as part of a neutral-stress passivemargin or backarc basin system (e.g., McCourtet al., 1984). Alternatively, the Eastern Cor-dillera may have been the site of extensionalbasins (e.g., Hossack et al., 1999; Kammer andSnchez, 2006) sourced by a combination oflower Paleozoic Andean basement and eitherdistal eastern sources in the Guyana shield ordistal western sources in accreted blocks of un-certain affinity. Although definitive geochemi-cal data are lacking, the evidence presented herefor Cambrian through Devonian magmatism

is difficult to reconcile with a passive marginsystem, leading us to prefer models involvingeither an extensional or contractional regime ina subduction-related system.

Mesozoic Sedimentary Rocks

U-Pb ages for detrital zircon grains from11 samples of Jurassic through Upper Creta-ceous sandstones record the influence of var-ied basement sources and Permian to Jurassicmagmatism. The five oldest Mesozoic samples



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are from nonmarine sandstones of the GirnFormation (Fig. 2), which contains limitedfossil assemblages that have been variably at-tributed to Early Jurassic to Early Cretaceousdeposition, with most estimates centering ona Middle Jurassic to earliest Cretaceous age(Cediel, 1968; Mojica and Kammer, 1995;Mojica et al., 1996; Sarmiento Rojas, 2001;Bayona et al., 2006; Kammer and Snchez,2006; Sarmiento-Rojas et al., 2006). Although

older Mesozoic units are present locally, the23-km-thick Girn Formation represents thelowest occurrence of widespread coarse-grainedfacies in the Mesozoic succession. Six samplesfrom the overlying 38-km-thick Cretaceousclastic section are representative of regionallyextensive marine sandstone units, including theLower Cretaceous Buenavista, Macanal, andLas Juntas formations, and the Upper Creta-ceous Chipaque Formation, Une Formation, andGuadalupe Group (Fig. 2).

The five sandstone samples from the GirnFormation show detrital zircon U-Pb age varia-

tions (Fig. 6) suggestive of spatial and temporalvariations in provenance. A single Girn sam-ple (sample GIR08151) from the northern partof the Eastern Cordillera, near the Santandermassif (Fig. 1), shows a polymodal age distri-bution with important U-Pb age peaks at 300180 (with internal peaks at 200185, 220210,and 285260), 500470, and 1050950 Ma(Fig. 6A). The older, Precambrian to earlyPaleozoic peaks are comparable to major agepeaks defined in Devonian and Carboniferoussandstones of this study (Fig. 5). The major dif-ference lies in the presence of Permian and LateTriassicEarly Jurassic zircons in the Girn

Formation. The five youngest grains from thisnorthernmost Girn sample yield a weightedmean age of 184.5 4.2 Ma (MSWD = 1.0),older than the preferred age of Girn deposi-tion but possibly synchronous with Early Juras-sic coarse-grained sedimentation adjacent tothe Santander massif (Kammer and Snchez,2006). Three additional samples of the GirnFormation (samples 13080807, 13080804, and13080803), from exposures adjacent to theFloresta massif, show a bimodal distributionof U-Pb zircon ages concentrated at 510440

0

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MA16n= 109

D

DevonianCuche Fm.

13080810n= 88

A

DevonianCuche Fm.13080811

n= 84

B

DevonianCuche Fm.13080812

n= 98

C

Age (Ma)

Number

ofanalyses

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obability

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nalyses

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tiveprobability

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elativeprobability

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600 1175

Figure 5. Age-distribution curves and age histo-

grams depicting detrital zircon U-Pb ages for four

Paleozoic sandstone samples. Plots are arranged in

stratigraphic order. (A) Devonian Cuche Formation

(sample 13080810); (B) Devonian Cuche Formation

(sample 13080811); (C) Devonian Cuche Formation

(sample 13080812); and (D) Carboniferous Guatiquia

Formation (sample MA16).



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Horton et al.


and 1070960 Ma, with subordinate peaks at12501150 and 15601430 Ma (Figs. 6C6E).However, a fourth sample from the Florestaregion (FS5) shows a highly unimodal signa-ture with ~80% of analyzed grains falling inthe ~500 to ~450 Ma age range (Fig. 6B). ThisLate CambrianOrdovician age peak corre-

sponds to the main zircon ages revealed for thelower Paleozoic granites of the Floresta massif(Fig. 4) and to the detrital age signatures of theDevonianCarboniferous succession (Fig. 5).

For Cretaceous sandstone units, zirconU-Pb age analyses demonstrate a systematicupsection shift to progressively older grains ofdominantly Mesoproterozoic and Paleoprotero-zoic age (Fig. 7). The three Lower Cretaceoussamples (Figs. 7A7C) display an assortmentof ages, including a principal age peak at 1080940 Ma and significant peaks (in order of de-creasing abundance) at 505425, 15701460,12251175, 13801280, and 17751690 Ma.

Of these, the two lowest Cretaceous samplesfrom the Buenavista Formation (sample SJ4A,Fig. 7A) and Macanal Formation (sampleMA13, Fig. 7B) show similar age spectra withmultiple peaks and dominant populations at1060960 Ma and 505425 Ma. The thirdLower Cretaceous sample, from the Las JuntasFormation (sample AM7, Fig. 7C), shows asimilar distribution of ages with a distinguishingunimodal signal at 1100920 Ma.

The detrital zircon age spectra for threeUpper Cretaceous sandstone samples (Figs.7D7F) record the elimination of the ~500

400 Ma age peak, reduction of the ~1000 Maage signal, and a pronounced increase in zirconsin the ~2050 to ~1300 Ma age range. Relativeto the Jurassic and Lower Cretaceous samples,the Upper Cretaceous Une Formation (sampleAM6B, Fig. 7D) and Chipaque Formation(sample 11080811, Fig. 7E) are distinguishedby extremely few grains younger than ~900 Maand an absence of the 500400 Ma popula-tion that typifies the older Mesozoic units.The Une and Chipaque samples are marked byprominent age peaks at 1050950, 15801350(including 15801495 and 14801350), and18501730 Ma. The youngest sample from the

Cretaceous succession, a sandstone fromthe lower Dura Formation within the Guada-lupe Group (sample MA2, Fig. 7F), showsthe reduction of the ~1000 Ma age peak to aminor subpopulation and the amplification ofthe Paleoproterozoic to early Mesoproterozoicage signal ranging between ~2060 Ma and~1300 Ma. The major age peaks include 18701760, 16001300 (including 13801300, 14401400, and 15901510), and 20601960 Ma.

We attribute the distribution of detrital zir-con ages within the Mesozoic succession of the

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JurassicGirn Fm.13080804

n= 58

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n= 110

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FS5n= 128

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n= 109

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n= 95

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1028474

884

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15251490

1245

1095

Figure 6. Age-distribution curves

and age histograms depicting

detrital zircon U-Pb ages for

five Jurassic sandstone samples.

Plots are arranged in strati-

graphic order. (A) Jurassic low-

ermost Girn Formation (sample

GIR08151); (B) Jurassic lower

Girn Formation (sample FS5);

(C) Jurassic Girn Formation

(sample 13080807); (D) Juras-

sic Girn Formation (sample

13080804); and (E) Jurassic Girn

Formation (sample 13080803).



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Eastern Cordillera to JurassicEarly Cretaceousrifting and Late Cretaceous postrift thermalsubsidence, consistent with previous interpreta-tions (e.g., Cooper et al., 1995; Sarmiento-Rojaset al., 2006). The Girn Formation (Fig. 6) con-tains a collection of grains derived from both lo-cal Andean sources and distal cratonic sources.

Local sources include CambrianOrdovicianbasement, such as that identified here for theFloresta and Quetame massifs (Fig. 4), pos-sible recycled Paleozoic strata, and igneousrocks of Permian and Late TriassicEarlyJurassic age near the Santander massif (Gold-smith et al., 1971; Irving, 1975; Aspden et al.,1987; Forero Suarez, 1990; Drr et al., 1995).In one case (sample FS5 of the Floresta region),the lowermost Girn sediments appear to havebeen derived exclusively from a single bedrockunit with a uniform zircon age distribution at500450 Ma (Fig. 6B). For the Floresta region,we suggest that the basal Girn age spectra rep-

resent sedimentation during the early stages ofextension when small, poorly integrated water-sheds in a locally uplifted footwall contributeduniform-age sediment to an adjacent exten-sional basin. A Mesozoic history of east-westextension and attendant basin evolution in theEastern Cordillera of Colombia is defined by avariety of lateral facies relationships adjacentto mapped normal faults and inverted normalfaults (Kammer and Snchez, 2006; Mora et al.,2006, 2009), as well as reported synextensionalmagmatism (Vsquez and Altenberger, 2005).Although syndepositional volcanism has been

reported previously for the Girn Formation(Kammer and Snchez, 2006; Sarmiento-Rojaset al., 2006), the U-Pb geochronological datapresented here reveal only one sample withJurassic-age zircons (Fig. 6 and Table DR1 [seefootnote 1]). This sample, the northernmostGirn sample (sample GIR08151), exhibits anage peak at 200185 Ma and is considered theresult of Early to Middle Jurassic rifting adja-cent to the Santander massif.

U-Pb ages for the Cretaceous succession(Fig. 7) reveal the disappearance of CambrianOrdovician zircons derived from Andean base-ment, a systematic decrease in Grenville-aged

basement detritus, and a corresponding in-crease in Paleoproterozoic basement signaturesonly found in eastern parts of the Guyana shield(Fig. 3). We interpret these patterns as the re-sult of elimination of Andean basement sourcesby complete sedimentary onlap and burial dur-ing a mid-Cretaceous transition from late-stagerifting to thermal subsidence. Late Cretaceousbroadening of the basin during the postrift phaseof basin evolution likely incorporated largeparts of the western Guyana shield (includingthe present-day Llanos region), leading to a

Figure 7. Age-distribution curves and

age histograms depicting detrital zircon

U-Pb ages for six Cretaceous sandstone

samples. Plots are arranged in strati-

graphic order. (A) Lower Cretaceous

Buenavista Formation (sample SJ4A);

(B) Lower Cretaceous Macanal Forma-

tion (sample MA13); (C) Lower Cre-

taceous Las Juntas Formation (sample

AM7); (D) Upper Cretaceous Une For-

mation (sample AM6B); (E) Upper Cre-

taceous Chipaque Formation (sample

11080811); and (F) Upper Cretaceous

Guadalupe Group (sample MA2).

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MA13n= 84

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Lower CretaceousLas Juntas Fm.

AM7n= 119

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11080811n= 116

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Une Fm.AM6Bn= 113

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Horton et al.


reduction in an exposed area of Grenville-agedbasement. This process also led to an increasein the relative contribution of sediment from theolder, eastern parts of the Guyana shield, wherePaleoproterozoic basement dominates (e.g.,Figs. 1 and 3). This sediment dispersal patternis consistent with upsection compositional shifts

from locally to distally derived conglomerateclasts (Mora et al., 2009) and with the easterncratonic source reported for most of the Cre-taceous section of the Eastern Cordillera andLlanos region (Cooper et al., 1995; Villamil,1999; Sarmiento-Rojas et al., 2006).

Cenozoic Sedimentary Rocks

Eleven samples of Cenozoic sandstones dis-play variations in the U-Pb age spectra (Fig. 8)that can be linked to an eastward progression ofAndean shortening and uplift. Nine samples arefrom exposures of Cenozoic basin fill along the

boundary zone between the Eastern Cordilleraand the modern Llanos foreland basin, with theremaining two samples collected from equiva-lent strata in an intermontane region of the axialEastern Cordillera (Fig. 1). The sampled clasticintervals of nonmarine, and locally marine, ori-gin have been categorized as either pre-orogenicor synorogenic, with possible derivation fromthe Central Cordillera, different parts of theEastern Cordillera, or the eastern basementshield (Cooper et al., 1995; Villamil, 1999;Bayona et al., 2008).

Detrital zircon ages for two Eocene units

show contrasting provenance in the axial zoneversus the eastern foothills of the Eastern Cor-dillera. The Regadera Formation, the oldestCenozoic unit analyzed in this study (Fig. 2),represents a major provenance change rela-tive to the underlying Cretaceous succession(Fig. 7). A sample of the Regadera sandstone(sample MA1, Fig. 8A), the oldest of the twosamples from the axial zone of the EasternCordillera, exhibits major age peaks at 9055,190150, and 12201170 Ma.

The detrital zircon age spectra for a samplefrom the Eocene Mirador Formation (sample08YEM01; Fig. 8B) in the eastern foothills

show a significant departure from the Rega-dera Formation (Fig. 8A), its lithostratigraphicequivalent in the west. The Mirador sampleyields age peaks at 18301725, 15001350,and 16001530 Ma. These ages are comparableto detrital zircon ages in the uppermost Creta-ceous section, displaying substantial overlapwith age from the Guadalupe Group (Fig. 7F),notably the correspondence of age peaks near1800 Ma, distributed ages in the ~1600 to~1300 Ma range, and the absence of statisticallysignificant populations younger than ~900 Ma.

A pronounced shift in the U-Pb age spectrais observed in stratigraphic units overlying theEocene succession in the Eastern Cordillera.A group of three sandstone samples from theOligocenelower Miocene Carbonera Forma-tion in the eastern foothills (samples MP175,08YEM03, and TO2170; Figs. 8C8E) and a

fourth sample of presumed equivalent strata inthe axial eastern Cordillera (sample 12080806;Fig. 8F) record the introduction of zircons ofJurassicPaleogene age, with multiple agesclustering in the 18040 Ma range (with indi-vidual age peaks at 6555, 5040, 155135,and 180170 Ma). These zircons of primar-ily Middle Jurassic to middle Eocene age, aswell as a Paleozoic zircon population dated at290220 Ma, contrast with the age spectra of theunderlying Cretaceous to Eocene succession inthe eastern foothills, which is nearly devoid ofgrains younger than ~400 Ma (Figs. 6 and 7). Thethree Carbonera samples are also distinguished

by consistent age peaks at 18501700 Ma andsignificantly reduced populations of Grenville-aged zircons at ~1000 Ma (Figs. 8C8E).

Detrital zircon ages for upper MiocenePliocene deposits in the proximal zone of theLlanos foreland basin (Figs. 8G8K) recordthe virtual disappearance of zircons of JurassicPaleogene age that characterize the Oligocenelower Miocene stratigraphic levels (Figs.8C8F). The five youngest samples in this study,collected from the lower Guayabo Formation(samples 08YEM05 and 08YEM07; Figs. 8Gand 8H), the upper Guayabo Formation (sample

MP295; Fig. 8I), and the Corneta Formationequivalents of the upper Guayabo Formation(08TAU01, 08TAU02; Figs. 8J and 8K), lackstatistically significant populations of zircongrains younger than 500 Ma. Instead, thesesamples show a concentration of ages between~1600 and ~900 Ma, with a strong Grenville-aged component at 1050950 Ma and older agepeaks at 16001500 and 14001300 Ma.

We interpret the substantial shifts in Ceno-zoic provenance as the product of uplift of theEastern Cordillera and eastward advance ofthe fold-thrust belt toward the Llanos forelandbasin. During the Eocene, clastic sedimenta-

tion recorded the influence of both eastern andwestern sediment source regions. In the axialEastern Cordillera, the Eocene Regadera For-mation (Fig. 8A) provides evidence for uplift-induced erosion of the magmatic-arc rockscomposing the Central Cordillera. Magmatic-arc rocks of Jurassic to Paleogene age in theCentral Cordillera (Fig. 3) provide the mostreasonable source for observed age peaks in the18040 Ma age range. Farther east, the EoceneMirador Formation (Fig. 8B) at the eastern frontof the Eastern Cordillera contains zircon age

spectra similar to the uppermost Cretaceoussection (Fig. 7F). These deposits are dominatedby Paleoproterozoic to early Mesoproterozoiczircons indicative of an eastern source in theGuyana shield, in agreement with previous in-terpretations of regional sediment dispersal pat-terns (Cooper et al., 1995; Cazier et al., 1997;

Villamil, 1999; Roure et al., 2003).U-Pb ages from the formations spanningOligoceneearly Miocene time record the ap-pearance of zircons of JurassicPaleogene age inboth the eastern foothills (Figs. 8C8E) and theaxial Eastern Cordillera (Fig. 8F). This patternmimics the first appearance of similar, JurassicPaleogene zircons observed in the Eocene Rega-dera Formation (Fig. 8A). However, rather thana direct sediment source from magmatic-arcrocks in the Central Cordillera, independent evi-dence for uplift of the western part of the East-ern Cordillera (e.g., Gmez et al., 2003) leadsus to attribute the mid-Cenozoic appearance of

the


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ofanalyses

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obability

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Upper Miocene

Pliocene upperGuayabo Fm.

08TAU01

n= 104

K

Upper Miocene


08TAU02

n= 84

J

H

Miocene (?)unnamed unit

12080806

n= 107

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Lower MioceneCarbonera C1

TO2170

n= 114

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Upper Miocenelower Guayabo Fm.

08YEM05

n= 109

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Lower Miocene

Carbonera C5MP175

n= 106

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Upper Miocene


MP295

n= 113

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Lower Miocene

Carbonera C208YEM03

n= 78

D

B

Middle EoceneMirador Fm.

08YEM01

n= 93

Lower-mid EoceneRegadera Fm.

MA1

n= 54

A

Upper Miocene

lower Guayabo Fm.08YEM07

n= 67

Age (Ma)

Age (Ma)

Figure 8. Age-distribution curves and

age histograms depicting detrital zir-

con U-Pb ages for 11 Cenozoic sand-

stone samples. Plots are arranged in

stratigraphic order. (A) lower-middle

Eocene Regadera Formation (sample

MA1); (B) middle Eocene Mirador For-

mation (sample 08YEM01); (C) lower

Miocene Carbonera Formation, C5

member (sample MP175); (D) lower


member (sample 08YEM03); (E) lower


member (sample TO2170); (F) Mio-

cene (?) unnamed unit; (G) upper

Miocene lower Guayabo Formation

(sample 08YEM05); (H) upper Mio-

cene lower Guayabo Formation (sample08YEM07); (I) upper MiocenePliocene

upper Guayabo Formation (sample

MP295); (J) upper MiocenePliocene

upper Guayabo (Corneta) Formation

(sample 08TAU01); and (K) upper

MiocenePliocene upper Guayabo (Cor-

neta) Formation (sample 08TAU02).



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Horton et al.


basement samples studied here (Fig. 4) suggestsa shared Mesoproterozoic origin for both theGuyana shield and Eastern Cordillera basement.

Additional U-Pb results for the 26 Phanero-zoic sandstone samples provide further insightsinto basement configuration, yielding the follow-ing dominant age peaks (in order of decreasing

abundance): 1050950, 500400, 12501150,16001500, and 18501750 Ma (Fig. 9). Theseage signatures suggest derivation from a com-bination of local Andean basement and distalMesoproterozoicPaleoproterozoic basementfrom either an eastern cratonic source or anaccreted continental terrane of uncertain affin-ity along the western margin of northern SouthAmerica. The detrital age peaks also attest tothe most important Mesoproterozoic and latePaleoproterozoic tectonomagmatic episodes, in-cluding Grenville-aged collisional orogenesis at~1000 Ma and ~1200 Ma and precursor events at~1550 Ma and ~1800 Ma. Although some stud-

ies of South America suggest a protracted Meso-proterozoic history of collisional orogenesisduring Rodinia assembly followed by mul-tiple rifting episodes during the Neoproterozoic(de Brito Neves et al., 1999; Chew et al., 2008;Santos et al., 2008), our study reveals ratherlimited zircons in the 900550 Ma age range.The overall age distribution identified here favorsa single Mesoproterozoic collisional assembly ofRodinia and a single event of rift-related breakupduring the Neoproterozoic (Cawood, 2005;Fuck et al., 2008; Li et al., 2008).

The similarity of inherited basement ages for

the Eastern Cordillera and Central Cordillera ofColombia could be regarded as evidence for re-gional continuity of the northern Andean base-ment or as a coincidental similarity between awestern accreted terrane and South Americanbasement. For the eastern part of the CentralCordillera, Vinasco et al. (2006) demonstratezircon U-Pb inheritance of Mesoproterozoicand Neoproterozoic zircons (500, 700, 900,and 1100 Ma), suggesting a Mesoproterozoicto lower Paleozoic basement comparable inage to basement of the Eastern Cordillera (e.g.,Cordani et al., 2005). In contrast, the western halfof the Central Cordillera is widely considered

part of an oceanic accreted terrane (Aspden andMcCourt, 1986; Restrepo and Toussaint, 1988;Cediel et al., 2003). Although the similarity ofthe eastern flank of the Central Cordillera to theEastern Cordillera does not rule out interpreta-tions of a separate continental terrane (ForeroSuarez, 1990; Restrepo-Pace, 1992; Richards,1995), it may be more compatible with minorseparation and reattachment of a Central Cor-dillera block along the western Andean margin,as argued for the Arequipa terrane of the centralAndes (e.g., Loewy et al., 2004; Ramos, 2008). Age (Ma)

0 500 1000 1500 2000 2500

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n= 500

Paleozoic4 samplesn= 379

Cretaceous6 samples

n= 627

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ability

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ty

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Figure 9. Comparative dia-

gram showing composite

U-Pb age data for detrital

zircons from all 26 samples,

with plots arranged in strati-

graphic order: (A) Paleozoic

sandstones; (B) Jurassic

sandstones; (C) Cretaceous

sandstones; (D) Eocene to

lower Miocene sandstones;

and (E) upper Miocene

Pliocene sandstones.



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Paleozoic Tectonics

Many contradictory models of noncolli-sional and collisional orogenesis attempt to ex-plain varied records of Paleozoic deformationand metamorphism in the Andes (Pindell andDewey, 1982; Restrepo-Pace, 1992; Dalziel

et al., 1994; Daziel, 1997; Lucassen and Franz,2005; Ramos, 2008). Our results clearly iden-tify Paleozoic magmatic activity in Colombia,apparently concentrated at 520420 Ma. Lim-ited geochemical data for the northern Andessuggest this magmatism may be linked to asubduction-related magmatic arc (e.g., Car-dona Molina et al., 2006; Chew et al., 2007).If the northern Andean magmatic belt was con-tinuous with the coeval, better-known Fama-tinian belt of northern Argentina and Chile~3000 km to the south (Rapela et al., 1998;Thomas and Astini, 2003), it raises the pos-sibility of regional deformation and metamor-

phism linked to early Paleozoic subduction andpossible collisional processes along the lengthof the Andean margin (Cardona Molina et al.,2006; Chew et al., 2008). Although the polarityof subduction and precise identity of oceanicplates remain poorly known, the existence ofan unambiguous CambrianOrdovician mag-matic belt that continued into Devonian time(Fig. 5) along with scattered detrital zircons ofPaleozoic age throughout Phanerozoic sand-stones (Fig. 9) suggest a protracted active mar-gin (Fig. 10A). A history of subduction alongthe western edge of South America throughout

most of the Phanerozoic (see Coira et al., 1982)would be consistent with plate reconstructionshighlighting the permanence of the Pacificocean basin (Coney, 1992; Cawood, 2005).Although the structural record is obscured byMesozoicCenozoic deformation, Paleozoicmagmatism and a possible subduction bound-ary in the northern Andes were apparentlyaccompanied by some degree of extensionalor contractional deformation (Hossack et al.,1999; Kammer and Mora, 1999; Kammer andSnchez, 2006).

Late Paleozoic collisional tectonics during as-sembly of Pangea (Fig. 10A) is expressed in the

Phanerozoic strata of the Eastern Cordillera asdetrital zircon age signals at 300250 Ma (Fig. 9).These ages correspond with a 300270 Ma pulseof metamorphism recorded in the Central Cor-dillera (McCourt et al., 1984; Vinasco et al.,2006) and are temporally distinct from subse-quent postcollisional magmatism at 240210 Ma(Irving, 1975; McCourt et al., 1984; Vinascoet al., 2006). This relatively underappreciatedphase of CarboniferousEarly Permian deforma-tion is best related to interactions of northwesternSouth America with the eastern and/or southern

margins of Laurentia (Pindell and Dewey, 1982;Restrepo-Pace, 1992; Dalziel et al., 1994), theOaxaca block of southern Mexico (Keppie andRamos, 1999; Keppie et al., 2001, 2003; Gilliset al., 2005, Li et al., 2008) and potentially Baltica(Cardona et al., 2010).

Mesozoic Extension

Although most reconstructions of thenorthern Andes invoke Mesozoic extension,uncertainty persists over the temporal andspatial distribution, role of magmatism, andoverall tectonic context. Our U-Pb resultsindicate JurassicEarly Cretaceous synrift prov-enance histories dominated by local Andeansources with a high degree of spatial variabil-ity (Fig. 10B), followed by Late Cretaceouspostrift provenance involving basin expansionand incorporation of regional cratonic sources(Fig. 10C). Coarse-grained, synrift deposits of

the Middle Jurassic to lowermost CretaceousGirn Formation display conflicting detrital zir-con age signatures (Fig. 6) at a regional scalebetween the Floresta and Santander regions andat a local scale within the Floresta region. Incontrast, the overlying Cretaceous units recordthe elimination of Andean basement sources andprogressively greater contribution of basementsignatures from the Guyana shield.

Our results provide insights on basin geom-etry and the minimum age of initial extensionbut do not provide precise constraints on themagnitude of extension (Hbrard, 1985; Fabre,

1987) and possible linkages to strike-slip defor-mation (e.g., Bayona et al., 2006). Extensionin the northern part of the Eastern Cordillera,adjacent to the Santander massif, was probablyunder way by ~185 Ma. However, Early Jurassicrifting may be limited to northern regions withLate Jurassicearliest Cretaceous extensiondominated the majority of the Eastern Cordi-llera of Colombia (e.g., Sarmiento Rojas, 2001;Sarmiento-Rojas et al., 2006). The distributionof U-Pb ages for the Jurassic to lowermost Cre-taceous section favors a series of local discon-nected extensional basins (Fig. 10B), ratherthan a single integrated rift basin (e.g., Kammer

and Snchez, 2006; Mora et al., 2006, 2009;Sarmiento-Rojas et al., 2006). Eastward onlapand basin widening during the mid- to LateCretaceous (Fig. 10C) coincide with a phaseof substantial subsidence (Sarmiento-Rojaset al., 2006). This postrift pattern is attributedto a combination of multiple stretching events,expansion of the region affected by mechani-cal rifting (Sarmiento-Rojas et al., 2006), link-age of smaller faults into master normal faults(e.g., Gawthorpe and Leeder, 2000; Mora et al.,2009), and a thermal subsidence signature simi-

lar to the classic steers head geometry (e.g.White and McKenzie, 1988).

Although Mesozoic magmatism is widelyreported for Colombia (e.g., Aspden et al.1987), the detrital zircon age spectra record nooccurrence of young (syndepositional) agesThis absence suggests an amagmatic history

of Mesozoic extension in the Eastern Cordillera, or alternatively, a genesis of chiefly nonzircon-bearing mafic magmas during extension(e.g., Vsquez and Altenberger, 2005). In eithecase, Jurassic and Cretaceous magmatism inthe Central Cordillera suggests that the Eastern Cordillera developed inboard of a magmatic arc, potentially as a backarc extensionasystem (Fig. 10B) (Pindell and Erikson, 1994Sarmiento-Rojas et al., 2006). However, the polarity of formerly subducting slabs is not welresolved, with several workers favoring a precursor west-dipping slab prior to establishmenof the Cenozoic east-dipping slab (Moores et al.

2002; Villagmez et al., 2008).Finally, the detrital zircon age spectra for the

studied Cretaceous units, with depositional ageranging from Hauterivian to early Campanian(~13580 Ma), provide no direct evidence fosyndepositional uplift in the Central Cordilleraand Eastern Cordillera of Colombia (Fig. 10C)Therefore, we suggest a Maastrichtian or earliest Cenozoic age of initial shortening-relateduplift (Fig. 10D) in both regions, consistenwith many previous authors (e.g., Van Houtenand Travis, 1968; Van Houten, 1976; Dengo andCovey, 1993; Cooper et al., 1995; Gmez et al.

2003, 2005; Bayona et al., 2008). Although thelarge distance from the Central Cordillera precludes definitive conclusions on the inceptionof shortening in the west, the lack of basemenage signatures in samples collected in closeproximity to exposed Andean basement in theFloresta and Quetame massifs requires that theyremained buried during Cretaceous time.

Cenozoic Shortening

Variations in the U-Pb age spectra for Cenozoic sandstones (Figs. 8 and 9) can be linked toan eastward progression of Andean shortening

from the Central Cordillera to the eastern fronof the fold-thrust belt along the boundary between the Eastern Cordillera and Llanos basinPreviously proposed estimates for initial shortening and exhumation in the Eastern Cordilleraare dependent on the specific location of interest but generally span a broad temporal rangefrom mid-Cretaceous to Pliocene time (Dengoand Covey, 1993; Coney and Evenchick, 1994Cooper et al., 1995; Villamil, 1999; Cediel et al.2003; Corredor, 2003; Gmez et al., 2003, 2005Corts et al., 2005; Jaimes and de Freitas, 2006



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Horton et al.


A

B

C

D

F

E

Devonian

Carboniferous

Early Permian

Late Jurassic

Early Cretaceous

Late Cretaceous

Paleocene

middle Eocene

Late Oligocene

Miocene

EasternCordillera

CentralCordillera

Llanosbasin

Guyanashield

WesternCordillera

MV

? ?

LSF GFSF

Continental collision ?

Meta-morphism

WEST EAST

Accretedoceanicterrane

Late Eocene

early Oligocene

Figure 10. Highly schematiccross sections depicting Phan-

erozoic basin evolution in the

Colombian Andes. (A) Devo-

nianCarboniferousEarly

Permian subduction and

possible backarc extension

prior to continental collision;

(B) Late JurassicEarly Cre-

taceous ri

Documents

Linking Sedimentation in the Northern Andes to Basement Configuration, Mesozoic Extension, And Cenozoic Shortening