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8/2/2019 A Liquid Line of Descent of Jotunite - Hypersthene Monzodiorite Suite
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JOURNAL OF PETROLOGY VOLUME 39 NUMBER 3 PAGES 439468 1998
A Liquid Line of Descent of the Jotunite
(Hypersthene Monzodiorite) Suite
JACQUELINE VANDER AUWERA1, JOHN LONGHI2 ANDJEAN-CLAIR DUCHESNE1
1L.A. GEOLOGIE, PETROLOGIE ET GEOCHIMIE, UNIVERSITE DE LIEGE, B-4000 LIEGE, BELGIUM
2LAMONTDOHERTY EARTH OBSERVATORY, PALISADES, NY 10964, USA
RECEIVED JANUARY 10, 1997; REVISED TYPESCRIPT ACCEPTED SEPTEMBER 30, 1997
Proterozoic massif anorthosites are usually associated with variable INTRODUCTIONamounts of a characteristic suite of rocks ranging from a melanocratic
Proterozoic massif anorthosites are usually associatedfacies highly enriched in Fe, Ti and P ( FTP rocks) to mafic and with variable amounts of a characteristic suite of maficgranitic rocks (the jotunitecharnockite suite). Here experimental to granitic rocks. The least evolved rocks of this suite areand geochemical data on fine-grained (chilled) samples from several enriched in mafic minerals (low- and high-Ca pyroxenes,intrusions of the Rogaland Province are used to decipher their FeTi oxides, apatite), and in some cases very highpetrogenesis. Modeling of these data supports the hypothesis that concentrations of these phases give rise to melanocraticextensive fractionation of primitive jotunites can produce quartz rocks. Various names including ferrodiorite, mon-mangerites with REE concentrations in the range of jotunites, strong zonorite, jotunite, FeTiP-rich rocks ( FTP) and oxide
depletions in U, Th, Sr and Ti, and smaller to no relative depletions apatite gabbronorite have been used; however, in thisin Hf and Zr. Experimental and petrographic data indicate that study, we will refer to them by the collective term ofthe FTP rocks represent accumulations of a dense oxide jotunite (hypersthene monzodiorite). Evolved rocks of theapatitepigeonite assemblage from coexisting multisaturated jotunitic suite include mangerites (hypersthene monzonite), quartzto mangeritic liquids. The Rogaland jotuniticcharnockitic trend mangerites and charnockites (hypersthene granite). Wecorresponds to a multi-stage process of polybaric fractional crys- will refer to the suite as a whole as the jotunite suite.tallization and crystal accumulation. The early stage, in which a The origin of jotunites remains the subject of con-primitive jotunitic magma fractionates to produce an evolved jotunite, siderable debate, despite their similar textural and geo-probably took place several kilometers below the intrusion level of chemical characteristics from one anorthosite complexdikes, either in mafic chambers similar to that of the Bjerkreim to another. Several hypotheses, not mutually exclusive,Sokndal layered intrusion or in masses of crystallizing andesine have been proposed: (1) jotunites are residual liquidsanorthosite. The later stage of fractionation, which may have after anorthosite crystallization (Ashwal, 1982; Morse,involved flow differentiation, took place within the dikes themselves 1982; Wiebe, 1990; Emslie et al., 1994); (2) they are
and produced compositions ranging from evolved jotunite to mangerite the parental magmas of the andesine anorthosite suiteto quartz mangerite and charnockite. (Duchesne et al., 1974; Duchesne & Demaiffe, 1978;
Demaiffe & Hertogen, 1981); (3) they are products of
partial melting of the lower crust (Duchesne et al., 1985,
1989; Duchesne, 1990); (4) they are transitional rocks in
a comagmatic sequence from anorthosite to mangerite
(Wilmart et al., 1989; Owens et al., 1993; Duchesne &
Wilmart, 1997); (5) they are derived by fractionation of
KEY WORDS: anorthosite; experimental petrology; geochemistry; mon- mafic magmas unrelated to the anorthositic suite (Emslie,
1985); (6) they are immiscible liquids conjugate tozodiorite; Rogaland anorthosite complex
Corresponding author. Telephone:+32 4 3662253. Fax:+32 4
3662921. e-mail: [email protected] Oxford University Press 1998
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JOURNAL OF PETROLOGY VOLUME 39 NUMBER 3 MARCH 1998
mangerites (Philpotts, 1981). In this paper, we present compositional variation can be explained by a processnew experimental data on two jotunite samples from the of fractional crystallization without progressive con-same dike (the Varberg dike) in the Rogaland anorthositic tamination (Wilmart et al., 1989). However, whole-rockcomplex as well as new geochemical data (major and RbSr isotopic data from other dikes such as Lomlandtrace elements) on fine-grained (chilled) jotunitic rocks do not fit tightly to isochrons and there is considerablefrom other intrusions in the Rogaland Province. We then variation in ISr from dike to dike (07040710) thatuse these data as well as published experimental and does not correlate with other geochemical parametersgeochemical data from the literature to: (1) define a liquid (Demaiffe et al., 1986; Duchesne et al., 1989), whichline of descent extending from jotunite up to quartz taken together suggest variable contamination of multiplemangerite (or acidic rocks); (2) discuss the possible origins sources. Jotunites also form small intrusions (e.g. Eiaof rocks showing extreme concentrations of FeO, TiO2 Rekefjord: Fig. 1) as well as chilled margins to theand P2O5; and (3) develop models of major and trace Hidra and Garsaknatt leuconoritic bodies (Demaiffe &element [REE (rare earth elements), Sr, U, Th, Zr, Hf,
Hertogen, 1981) and, locally, to the BjerkreimSokndalTa, Rb, Co, Ni, Cr, Sc] fractionation within the suite.
layered intrusion (Duchesne & Hertogen, 1988; Wilson
et al., 1996). Experiments on a sample from one of these
chilled margins, the Tjorn facies [sample 80123a of
Duchesne & Hertogen (1988)], have shown the near-GEOLOGICAL SETTING ANDliquidus assemblages to be plagioclase (An49)+ olivinePETROGRAPHY(Fo64) at 5 kbar and plagioclase (An47)+ low-Ca pyroxeneThe Rogaland intrusive complex of southern Norway(En66) at 7 kbar (Vander Auwera & Longhi, 1994). The(Fig. 1) (Michot, 1960; Michot & Michot, 1969) is onecompositions of most of the Rogaland jotunitic suite formof the group of Proterozoic anorthositic provinces thatcoherent trends in variation diagrams (Fig. 2), but thehave been recognized world-wide (Ashwal, 1993). Massif-least differentiated compositions (high MgO, low K2O)type anorthosites (EgersundOgna; HalandHelleren;are chilled margin samples and form a group distinctAnaSira), leuconoritic bodies (Hidra, Garsaknatt) andfrom the rest of the dike system. In the following, wea large layered intrusion (BjerkreimSokndal: BKSK)will refer to the distinctive group of chilled margin samplesoccupy most of the surface exposure. Jotunitic rocksas primitive jotunites and to the least differentiatedmainly occur in a system of dikes and small intrusionssamples of the dike trend as evolved jotunites. In this(Duchesne et al., 1985, 1989). There are also several
latter group, most samples are chilled margins to theFeTi ore bodies within the complex (Krause & Pedall,1980; Duchesne, 1998). New UPb ages obtained from dikes (75202F, 8926, 89115, 7355).zircon and baddeleyite (Scharer et al., 1996) suggest that In this study, we took special care to select samplesemplacement of this complex occurred within
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VANDER AUWERA et al. PETROGENESIS OF JOTUNITE SUITE
Fig. 1. Schematicgeological mapof theRogaland anorthositiccomplex [after Michot & Michot (1969)and Bolle (1996)]. EGOG, EgersundOgna;HH, HalandHelleren; AS, AnaSira; H, Hidra; G, Garsaknatt; ER, EiaRekefjord; BKSK, BjerkreimSokndal, Ap, Apophysis. Numbers referto samples described in Table 1.
that is a general feature of massif anorthosites and relatedSAMPLE PREPARATION,rocks (see, e.g. Morse, 1982). However, the graphite
EXPERIMENTAL AND ANALYTICALcapsules imposed a relatively low oxygen fugacity in these
METHODS experiments, probably between FMQ (fayalitemagnetitequartz) 2 and FMQ 4 (Vander AuweraExperiments were carried out on two powdered rocks of
& Longhi, 1994), which inhibits magnetite stability. Tothe Varberg dike at LamontDoherty either in a standard aproximate the f(O2) of the jotunites and to determine1/2 inch piston cylinder apparatus or in a Deltech verticalthe effects of magnetite, which is a late-stage mineral inquenching furnace, following the methods described bythe primitive jotunites, on the liquid line of descent, weFram & Longhi (1992) and Vander Auwera & Longhialso performed a few 1 atm melting experiments in a(1994). One sample was from the chill margin (samplecontrolled COCO2 atmosphere. These were carried out75202F; VB); the other was from the melanocratic faciesat two different f(O2) values: NNO (nickelnickel oxide;(sample 75372; MEL). High-pressure experiments wereruns VB-16 and VB-17) and FMQ (run VB-6); f(O2) wasrun in graphite capsules at 5 kbar (runs VB-1 to VB-5,measured with a Ca-doped ZrO2 electrolyte cell. GoodVB-13 and VB-14 on sample VB, and runs MEL-1 toagreement was found between f(O2) determined directlyMEL-3 on sample MEL), the likely pressure of em-andf(O2) calculated by applying the Andersen & Lindsleyplacement of the Rogaland intrusive complex ( Jansen et(1988) model to the compositions of coexisting ilmeniteal., 1985; Vander Auwera & Longhi, 1994). Dry run
conditions are consistent with the relatively low f(H2O) and spinel produced in the experiments. To minimize
441
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JOURNAL OF PETROLOGY VOLUME 39 NUMBER 3 MARCH 1998
Fig. 2. Major element variation diagrams of the jotunitic suite. Data from fine-grained samples (chills), from the Tellnes dike (Wilmart, 1988;Wilmart et al., 1989) and from other localities [Grenville Province, Quebec: Owens et al. (1993); Laramie: Kolker & Lindsley (1989); Mitchell etal. (1996); Nain: Wiebe (1979); Emslie et al. (1994)] are shown for comparison. P corresponds to the average of four samples from the Puntervollfacies (FTP rocks) of the Lomland dike (Duchesne et al., 1985).
442
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VANDER AUWERA et al. PETROGENESIS OF JOTUNITE SUITE
Table 1: Sample description, location and facies of jotunites
Sample UTM grid: zone 32 VLK Intrusion
89115/ch (1) 305859 Kjervall dike crosscutting the EgersundOgna
anorthosite
78211/ch (2) 407825 Eiavatn dike crosscutting the EiaRekefjord
intrusion
8925, 8926/ch (3) 315812 dike on top of the Koldal small intrusion: 8925 is
from the central part of the dike, and 8926 from
the contact
8951/ch (4) 534615 satellite to the Tellnes dike crosscutting the
AnaSira anorthosite
7355/ch (5) 399727 EiaRekefjord intrusion
91141/ch (6), 80123a/ch (7) 273992; 354983 fine-grained margin of the BjerkreimSokndal
intrusion
75182, 7519, 75202F/ch, 75202G, 249883; 249875; 244825; 244825; 244825; Varberg dike crosscutting the EgersundOgna
75 204 , 7 520 6, 7 537 2, 782 01, 244 8 25; 244 83 8; 251 79 7; 2 43 84 1 an ort hos ite
7912(8)
7838/ch, 8034/ch (9) 550624; 554627 Fidsel dike crosscutting the Apophysis
T2/ch,T221/ch,T82/ch, 7832, 7828, 514657; 455701; 517653; 523627; 472698; Tellnes dike crosscutting the AnaSira
7252 (10) 477697 anorthosite
66175, 7536, 7533, 7534 (11) 263803; 267815; 275827; 273829 Puntervold facies (melanorites) of the Lomland
dike
7234/ch (12) 589602 fine-grained margin of the Hidra leuconoritic
body
Numbers in parentheses correspond to the localities shown in Fig. 1; /ch indicates that the sample corresponds to a chill.Duchesne & Hertogen (1988). Wilmart (1988). Duchesne et al. (1974).
iron loss in highly crystalline runs, powdered samples Major element compositions of the experimental phasesare reported in Table 3. Rims and cores of feldspars andwere pressed into disks of 6 mm diameter (bonded with
polyvinyl alcohol) and loosely wrapped in Pt wire of 0254 pyroxenes occurring in the different facies of the Varbergdike have been analyzed with the Cameca SX50 of themm diameter. Run conditions and phase assemblages are
given in Table 2. CAMST (Centre dAnalyse par Microsonde pour lesSciences de la Terre, Louvain-La-Neuve, Belgium; J.Wautier analyst). Standards included natural mineralsand synthetic compounds. Accelerating voltage was set
Analytical method at 15 kV and beam current was 20 nA with 10 s countingtimes. X-ray intensities were reduced using the CamecaAfter each experiment, the charges were mounted in
PAP correction program. Results are given in Table 4.epoxy, polished and analyzed at LamontDoherty under Mass balance between the bulk composition of thethe Camebax/Micro electron microprobe equipped withstarting material and the compositions of all phasesa wavelength dispersive system. Accelerating voltage waspresent in each run has been calculated using a least-set at 15 kV and all elements were measured for 20 s atsquares multiple regression to determine phase pro-a beam current of 25 nA, except in the case of feldspars,portions and to test if Fe and Na loss occurred in the 1phosphates, and glasses, where Na and K were measuredatm experiments. Results are given in Table 2. Na lossfirst for 30 s at 5 nA. Rims of minerals were analyzedranges from 4% up to 14% whereas Fe displays a smallwith a point beam and glasses with a defocused beam ofgain in VB-16 (6%) and a significant one in VB-17 (25%).5 m to minimize alkali loss. X-ray intensities wereThe latter experiment did not equilibrate pervasively, asreduced using the Cameca PAP correction program. Athe temperature was near the solidus and the chargecombination of mineral and glass standards were usedmelted only locally. In run VB-14, the orthopyroxenefor glass analyses whereas only mineral standards were
used for plagioclase, oxides, pyroxenes, and olivines. (opx) coefficient had a negative sign. The opx coefficient
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JOURNAL OF PETROLOGY VOLUME 39 NUMBER 3 MARCH 1998
Table 2: Experimental conditions and products
Experiment T (C) P t (h) f(O2) Products
VB-1 1150 5 kbar 25 gl
VB-2 1120 5 kbar 26 gl94 pl6
VB-3 1100 5 kbar 36 gl96 pl4
VB-4 1080 5 kbar 47 gl82 pl17 ol0.2 il0.7 ap0.1
VB-14 1078 5 kbar 66 gl61 pl30 pig6 il3 ap0.01opx 0
VB-13 1074 5 kbar 114 gl pl ol il ap pig
VB-5 1060 5 kbar 71 gl pl pig aug il ksp qtz
VB-6 1050 1 bar 125 FMQ gl50 pl30 ol7 il3 uvsp6 phosph
VB-16 1065 1 bar 46 NNO gl47 pl28 pig4 aug4 uvsp13 phosp4
VB-17 1060 1 bar 89 NNO gl30 pl33 pig4 aug9 uvsp19 phosp5
MEL-1 1130 5 kbar 23 gl
MEL-2 1110 5 kbar 18 gl99 il1
MEL-3 1090 5 kbar 25 gl90 il4 ol4 ap2
The numbers following the phase abbreviations are the weight proportions of the relevant phases present in the experiments,calculated using a weighted least-squares minimization.
was then changed to zero and its components were (An32Ab66Or2). There seems to be a correlation betweenplagioclase composition and bulk composition, as plagio-included in the other phases. This results in an increased
proportion of the remaining phases. clase displaying the lowest anorthite content (An30 insample 75206; Table 4) is associated with the bulkThe fine-grained samples of jotunites were analyzed
for major elements and some trace elements by X-ray composition showing the lowest MgO (279%) and high-est SiO2 (4929%) content observed in the samples fromfluorescence on a CGR Lambda 2020 Spectrometer at
the University of Liege (analyst G. Bologne) (Bologne & the Varberg dike (Table 5; analysis of sample 75204 is
given instead of that of sample 75206). This observationDuchesne, 1991). The other trace elements were analyzedeither on a VG elemental PQ2 Plus inductively coupled is supported by petrographic data from the Tellnes dike,
in which there is a systematic change in the feldsparplasma-mass spectrometer at the University of Liege(Vander Auwera et al., 1998) or by neutron activation at composition associated with bulk composition: jotunites
are characterized by antiperthitic plagioclase and lesserthe Pierre Sue Laboratory (CEA, Saclay, France; analystJ. L. Joron). Major and trace element data are presented K-feldspar (microperthite), mangerites contain more K-
feldspar and mesoperthite-rimmed plagioclase, whereasin Table 5.quartz mangerites display mesoperthite (Wilmart et al.,1989).
EXPERIMENTAL AND ANALYTICAL
RESULTS Experimental results
Mineral compositions At 5 kbar and 1120C plagioclase (An49) is the soleliquidus phase of VB, the chill margin sample. OlivineThe compositions of plagioclase and pyroxenes from theVarberg dike (Fig. 3) have a limited range and are similar (Fo50), ilmenite, and apatite appear approximately to-
gether at 1080C in run VB-4. The SiO2 and P2O5to those observed in jotunites from the Tellnes dike(Wilmart, 1988). In the chill margin plagioclase is not concentrations in the 1080C liquid are 460% and
274%, respectively (Table 3); these values are consistentsignificantly zoned, with cores of An33 and mantles withan average of An34. Augite, whether as lamellae or with the apatite-saturation model of Harrison & Watson
(1984). In run VB-14 at 1078C there is a drastic increaseprimary crystals, has an intermediate mg-number (049).The low-Ca pyroxene (lpyx) is orthopyroxene (Wo12Ens35) in crystallinity and olivine is replaced by pigeonite and
orthopyroxene. At a slightly lower temperature (1074C,inverted from pigeonite (Fig. 3, Table 4). In the sampleof the melanocratic facies ( MEL), the pyroxenes are VB-13) olivine reappears as a stable phase. Only the top
half of the VB-13 charge shows signs of glass and texturalsimilar to those elsewhere in the dike, but alkali feldsparis present (An06Or89) together with plagioclase equilibration. Thus the solidus probably lies within the
444
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VANDER AUWERA et al. PETROGENESIS OF JOTUNITE SUITE
Table
3:Com
posit
ionofex
perimen
talpro
ducts
Exp.
No.
Ph
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
K2O
Na2O
P2O5
F
Total
An,
Fo,
En
VB-1
4
gl
4726(34)
382(9)
1397(9)
1556(19)
306(8)
025(3)
770(3)
177(3)
328(6)
24(4)
9907
VB-2
4
gl
4762(31)
385(10)
1330(14)
1634(22)
316(3)
023(2)
747(11)
192(3)
295(11)
243(2)
9927
5
pl
5729(60)
015(2)
2752(47)
057(7)
006(1)
000
956(34)
078(5)
561(32)
000
10155
46
VB-3
4
gl
4751(26)
39(2)
1347(11)
1574(14)
316(3)
023(1)
757(5)
189(3)
317(9)
253(5)
9917
3
pl
5630(28)
014(5)
2789(47)
057(7)
007(2)
000
999(79)
062(8)
544(18)
000
10101
49
VB-4
4
gl
4600(52)
424(12)
1157(21)
1826(46)
366(7)
027(2)
780(11)
182(8)
280(1)
274(8)
9916
4
pl
585(14)
005(6)
2680(99)
052(9)
003(2)
000
88(12)
082(21)
588(55)
000
10136
43
5
ol
3418(19)
022(3)
005(1)
001(1)
4144(27)
2338(21)
051(2)
040(3)
000
002(1)
000
10021
50
4
il
005(2)
5593(4)
033(3)
000
000
4042(9)
420(6)
041(2)
019(5)
000
002(1)
000
10155
3
ap
000
000
002(3)
097(23)
018(13)
006(0)
5352(73)
008(6)
006(1)
4114(19)
185(51)
9788
VB-14
7
gl
4580(36)
416(8)
1087(8)
2017(22)
325(7)
032(3)
749(7)
204(9)
269(8)
284(7)
9963
7
pl
5960(72)
002(3)
2581(33)
039(11)
002(1)
000
724(31)
146(51)
565(31)
000
10019
38
8
pig
5093(55)
083(14)
11525)
001(1)
2625(77)
1641(44)
051(4)
419(56)
008(1)
10036
48
5
il
005(2)
5435(27)
032(2)
001(1)
000
4176(17)
339(8)
042(4)
011(5)
001(1)
10042
1
opx
5050
031
080
2946
1568
067
185
006
9933
47
4
ap
000
000
000
094(48)
020(21)
008(2)
5427(51)
003(1)
007(2)
4092(28)
193(55)
9844
VB-13
2
gl1
5024(11)
292(8)
1048(3)
1958(48)
185(4)
033(6)
652(5)
272(4)
284(32)
247(3)
9995
1
gl2
5101
261
1092
1715
159
032
732
320
307
328
10047
1
gl3
5518
233
1179
1558
139
022
512
404
468
173
10206
3
gl4
5050(87)
282(19)
1063(25)
1877(14)
176(15)
033(4)
679(46)
288(28)
291(26)
274(47)
10013
9
pl
5980(57)
006(7)
2559(33)
041(14)
002(2)
000
714(40)
152(46)
570(24)
000
10024
37
7
pig
4984(69)
079(7)
095(19)
001(1)
3089(91)
1270(60)
059(4)
442(62)
008(2)
10027
38
1
ol
3196
046
004
006
5439
1207
075
061
002
10036
28
5
il
008(2)
5317(38)
021(1)
002(2)
000
4363(27)
198(3)
043(5)
017(9)
002
9971
5
ap
000
000
005(3)
124(12)
023(1)
008(4)
5264(38)
006(1)
007(2)
4084(48)
215(20)
9736
VB-5
3
gl
6764(14)
077(11)
1485(20)
001(1)
449(13)
032(9)
004(2)
147(17)
617(77)
370(42)
031(5)
9977
445
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JOURNAL OF PETROLOGY VOLUME 39 NUMBER 3 MARCH 1998
Table
3:cont
inue
d
Exp.
No.
Ph
SiO2
TiO2
Al2O3
Cr2O3
Fe2O3
FeO
MgO
MnO
CaO
K2O
Na2O
P2O5
F
Total
An,
Fo,
En
VB-6
6
gl
5441(64)
254(6)
1218(11)
000
1416(31)
222(4)
025(3)
611(11)
292(15)
300(24)
186(6)
9965
11
pl
5904(13)
007(5)
2622(77)
000
065(20)
004(3)
000
827(92)
105(19)
546(55)
000
10080
43
5
ol
3449(51)
019(4)
013(10)
000
4281(26)
2164(32)
067(4)
052(10)
003(1)
10048
47
4
il
003(1)
469(37)
045(21)
002(2)
1265
3592(23)
326(10)
044(1)
014(6)
9981
6
uvsp
013(1)
2388(25)
223(3)
003(2)
2105
4881(61)
264(7)
047(4)
022(6)
9946
VB-16
7
gl
5669(20)
218(21)
1253(40)
003(2)
1102(12)
234(34)
022(4)
559(66)
283(30)
306(8)
165(32)
9814
12
pl
5712(17)
007(5)
2651(11)
000
056(22)
003(3)
000
89(12)
080(17)
500(58)
000
9897
47
8
pig
5076(43)
077(8)
125(22)
002(1)
199(13)
179(11)
058(3)
75(21)
011(4)
9885
52
1
aug
4957
096
170
005
1745
1550
048
1198
017
9786
46
5
uvsp
016(3)
1976(54)
246(6)
002(1)
2810
4408(53)
299(7)
050(2)
012(7)
001(1)
9820
6
phosp
000
000
011(9)
345(11)
375(4)
018(2)
4490(25)
023(23)
049(17)
4387(22)
000
9698
VB-17
5
gl
6694(73)
124(12)
1397(7)
571(21)
103(7)
010(2)
265(8)
413(20)
348(15)
057(4)
9982
9
pl
583(15)
011(6)
2652(97)
067(27)
004(4)
000
862(91)
092(22)
500(62)
000
10015
44
3
pig
5106(94)
061(21)
097(40)
002(2)
226(15)
173(16)
073(5)
62(25)
009(4)
9959
50
9
aug
5019(43)
088(15)
143(20)
002(1)
178(13)
141(10)
058(12)
141(21)
020(3)
9932
41
5
uvsp
037(25)
1641(31)
232(8)
002(1)
3507
4173(40)
257(12)
061(4)
029(11)
002(1)
9941
4
phosp
000
000
034(16)
359(10)
372(4)
022(2)
4549(30)
024(19)
046(13)
4356(61)
000
9762
MEL-1
4
gl
3659(16)
708(2)
734(4)
2705(8)
451(4)
034(3)
913(8)
062(6)
187(8)
440(7)
9893
MEL-2
5
gl
3695(37)
656(18)
713(15)
2719(39)
461(2)
037(2)
929(7)
057(4)
166(5)
451(8)
9885
4
il
004(1)
5453(25)
031(2)
001(1)
000
4135(31)
366(5)
036(1)
020(6)
000
001(1)
000
10047
MEL-3
6
gl
3956(21)
578(5)
814(8)
2566(28)
399(7)
035(2)
901(7)
061(7)
198(11)
391(8)
9898
5
ol
3319(16)
024(3)
003(1)
005(1)
4613(23)
1936(8)
053(3)
042(2)
000
002
000
9998
43
4
il
003(1)
5538(37)
029(2)
001(1)
000
4168(26)
334(4)
043(3)
015(2)
000
000
000
10131
3
ap
000
000
001(1)
146(40)
024(19)
005(2)
5378(41)
004(2)
004(1)
4121(51)
169(39)
9852
gl,glass;ol,olivine;pig,pigeonite;opx,orthopyroxene;pl,plagioclase;il,
ilmenite;uvsp,ulvospinel;aug,augite;ap,apatite;phosp,whitlockite.
Foreachphase,
theaverageofseveralanalyses
(No.
isthenumberofanalyses)isgivenandthestandarddeviationisinparen
theses.Fo[Mg
100/(Mg+
Fe)],
En[Mg
100/
(Mg+
Fe+
Ca)],
An[Ca
100
/(Ca+
Na+
K)]aregiveninatomicunits.
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Table
4:Microprobeanalysesof
the
Varberg
dikefeldsparsan
dpyroxenes
Sample:
75202F
7912
7912
75202G
75182
75182
75372
75372
75206
7820
1
Phase:
Plag
Plag
FK
Plag
Plag
FK
plag
FK
Plag
Plag
No.:
6
6
2
4
8
2
8
4
7
8
Feldspars
SiO2
6106
6089
6488
6138
6134
6433
6116
6490
6181
6090
Al2O3
2462
2478
1829
2448
2443
1840
2463
1843
2416
2466
FeO
021
018
006
015
011
008
012
005
022
010
CaO
696
715
004
665
665
006
667
011
615
701
K2O
035
036
1606
035
036
1522
040
1477
032
037
Na2O
738
728
082
743
747
093
749
114
779
730
Total
10058
10064
10015
10045
10036
9901
10048
9939
10045
10034
Si
27032
26950
29957
27160
27165
29915
27075
29983
27321
27008
Al
12842
12923
09952
12763
12751
10082
12851
10031
12586
12890
Fe
00076
00065
00025
00056
00039
00030
00045
00021
00080
00038
Ca
03300
03393
00019
03153
03153
00030
03166
00056
02914
03329
Na
06333
06246
00738
06372
06416
00836
06431
01023
06673
06273
K
00201
00204
09457
00200
00205
09027
00224
08701
00181
00211
Catsum
49783
49781
50146
49704
49730
49919
49791
49813
49755
49748
%An
3356
3446
019
3242
3227
030
3223
057
2983
3393
%Ab
6440
6346
722
6553
6564
845
6549
1046
6832
6393
%Or
204
208
9260
206
210
9125
228
8897
185
215
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Table
4:cont
inued
Sample:
75202F
75202F
7912
7912
75202G
75202G
75202G
75182
75182
75372
75372
75206
75206
78201
78201
78201
Phase:
opx
cpx
opx
cpx
opx
cpx
cpxexs.opx
cpx
opx
cpx
opx
cpx
opx
cpx
cpxexs.
No.:
4
4
4
3
7
3
1
4
3
6
4
4
4
4
2
2
Pyroxenes
SiO2
4984
5125
4969
5145
4961
5123
5098
4973
5134
4974
5113
5039
5192
5002
5114
5150
TiO2
010
014
006
016
010
021
024
010
017
012
024
007
017
011
025
023
Al2O3
059
124
058
129
071
126
133
060
116
067
131
061
119
065
133
134
Cr2O3
004
002
005
005
003
003
000
003
001
004
006
000
001
004
000
001
FeO
3793
1752
3774
1761
3714
1665
1675
3911
1828
3779
1792
3506
1536
3736
1897
1661
MgO
1169
935
1130
902
1198
946
935
1028
820
1103
879
1314
996
1165
917
959
MnO
081
039
095
040
076
041
031
084
036
082
037
092
044
082
046
034
CaO
056
2063
077
2124
080
2134
2178
087
2127
083
1981
064
2071
079
1884
2138
K2O
003
001
000
001
001
001
000
002
001
001
001
000
001
000
000
001
Na2O
001
033
000
034
000
034
034
000
033
000
034
000
037
000
037
031
Total
10161
10090
10114
10158
10114
10093
10107
10157
10113
10105
10022
10083
10025
10144
10054
10132
Si
19754
19676
19800
19653
19702
19627
19540
19840
19756
19826
19798
19849
19863
19805
19735
19631
Ti
00030
00040
00019
00046
00029
00062
00069
00031
00048
00037
00070
00020
00049
00031
00074
00067
Al
00275
00561
00270
00581
00334
00568
00602
00283
00526
00316
00597
00283
00536
00302
00607
00600
Cr
00012
00007
00016
00016
00010
00008
00000
00009
00004
00013
00018
00001
00006
00012
00001
00004
Fe
12571
05625
12575
05626
12334
05335
05368
13047
05882
12598
05803
11547
04914
12369
06126
05293
Mg
06908
05352
06712
05133
07091
05404
05341
06114
04703
06553
05072
07714
05679
06877
05275
05450
Mn
00272
00126
00321
00129
00256
00133
00100
00282
00118
00276
00120
00306
00144
00276
00150
00110
Ca
00237
08486
00327
08692
00341
08759
08943
00372
08770
00353
08220
00269
08489
00333
07785
08731
K
00015
00006
00001
00003
00006
00004
00000
00012
00005
00004
00004
00000
00005
00002
00000
00004
Na
00005
00248
00000
00255
00000
00249
00253
00000
00244
00002
00254
00004
00274
00002
00275
00230
Catsum
40081
40127
40040
40132
40101
40150
40216
39989
40055
39977
39954
39991
39957
40009
40027
40118
%En
3503
2750
3422
2639
3587
2771
2718
3130
2430
3360
2656
3950
2976
3512
2749
2799
%Fs
6376
2889
6412
2893
6240
2736
2732
6680
3039
6459
3039
5913
2575
6318
3191
2718
%Wo
120
4361
167
4469
173
4493
4551
190
4531
181
4305
137
4449
170
4060
4484
mg-no.
036
049
035
048
037
050
050
032
044
034
047
040
054
036
047
051
No.,numberofanalysespersa
mple.
exs.,cpxexsolutioninopx.
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Fig. 3. Anorthite content of plagioclase (a) and pyroxene compositions (b) [En (MgSiO3)Fs (FeSiO3)Di (CaMgSi2O6)Hd (CaFeSi2O6)quadrilateral] in the Varberg dike (Table 4) as well as in liquidus and near-liquidus experiments (VB runs) (Table 3). Numbers in the pyroxenequadrilateral are run numbers.
charge. The few areas of glass are chemically hetero- the array of phase relations in Fig. 4, we believe that thehigh-SiO2 glass in VB-5 is primarily the result of localgeneous (Table 3), and thus represent local surface equi-
librium. Mass balance calculations show that there is a equilibrium in the experimental charge where more maficdomains having a higher solidus temperature remainedprecipitous drop in percent liquid between 1080C (82%)
and 1078C (61%), so encountering the solidus a few entirely crystalline, whereas more felsic domains havinga lower solidus temperature yielded a small amount ofdegrees lower is not surprising; however, in VB-5 at
1060C, which should have been below the solidus, a high-SiO2 melt. Therefore, as with VB-13, even thoughrun VB-5 did not achieve bulk equilibrium, the liquid issmall amount of glass with 676% SiO2 was observedadjacent to K-feldspar. An explanation of these phe- probably multiply saturated nonetheless, so we have used
the VB-5 glass composition to approximate the multiplenomena can be deduced from Fig. 4, in which liquidusphase diagrams are drawn from experimental phase saturation surface of charnockitic (high-SiO2) liquids. A
second curious point is the apparent absence of olivinecompositions. In a plagioclaseilmeniteapatite pro-jection (Fig. 4a), the compositions of liquid, pigeonite, in VB-14, despite the fact that olivine is present in
runs immediately above (VB-4) and below (VB-13) thisand olivine (plus plagioclase, ilmenite, and apatite) inVB-14 are nearly coplanar, implying a thermal divide temperature. Given that the composition of the
olivine+ plagioclase+ pigeonite (+ augite, apatite,on the olivinepigeonite (+ plagioclase, ilmenite, andapatite) liquidus boundary, which in turn promotes ex- and ilmenite) pseudo-invariant point lies close to a line
from the Pl component through the VB composition, ittensive crystallization in a narrow temperature interval.Moreover, both the plagioclaseilmeniteapatite pro- is likely that a small difference in pressure between the
two runs produced a diff
erent crystallization sequence:jection (Fig. 4a) and the wollastoniteilmeniteapatiteprojection (Fig. 4b) indicate that the VB-14 liquid com- lower pressure in VB-4 (ol, no pyx) shifted the pseudo-invariant point away from the Ol component and sta-position is also close to a second thermal divide pla-
gioclasepigeonite (+ augite, apatite, and ilmenite) bilized olivine; whereas higher pressure in VB-14 shiftedthe pseudo-invariant point toward the Ol componentand a eutectic olivine+ plagioclase+ pigeonite
(+ augite+ apatite+ ilmenite). This latter thermal di- and stabilized low-Ca pyroxene. Accordingly, olivineshould be stable at the same pressure as, but at a lowervide restricts SiO2 enrichment at 5 kbar and low f(O2)
and prevents olivine-saturated liquids from ever reaching temperature than VB-14, which is what is observed inVB-13.quartz saturation. Had magnetite been stable or the
pressure lower, it is likely that the eutectic would become At 1 atm and the NNO buffer, pigeonite, augite,plagioclase, and phosphate are stable together near thea peritectic (olivine in reaction) and that liquids would
be able to breach the augitepigeonite thermal divide. solidus with the only FeTi oxide being titanomagnetite(actually ferri-ulvospinel: uvsp58mgt42 in VB-16), whereasGiven the absence of magnetite in the various runs and
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VANDER AUWERA et al. PETROGENESIS OF JOTUNITE SUITE
Fig. 4. Projections according to Longhi (1991) on the silicaolivinewollastonite plane from plagioclase, ilmenite and apatite and on the
silicaolivineplagioclase plane from wollastonite, ilmenite and apatite. In (a) and (b), 5 kbar experiments are shown; in (c) and (d), 1 barexperiments. In all diagrams except (a), the small black dots correspond to the fine-grained samples and the large stippled points to startingcompositions (VB and MEL). Low-Ca pyroxene (lpyx) composition () are from VB-13 and VB-14 in (a) and (b) and from VB-16 and VB-17in (c) and (d). In (a) and (b), VB-4 and VB-14 glasses () were used to position the ol+ plag+ lpyx boundary and the VB-5 glass providessome constraint on the sil+ lpyx+ plag (+ aug) point. In (c) and (d), the ol+ plag+ lpyx boundary has been constrained with the VB-6 ()and VB-16 () glasses whereas the VB-17 glass fixes the plag+ lpyx+ aug boundary.
at the FMQ buffer, both ilmenite and ferri-ulvospinel but not in the 1 atm experiments, suggesting that thephosphate is probably fluoroapatite in the former and(uvsp69mgt31 in VB-6) precipitate (Table 2). We presume
that olivine would be stable at higher temperatures at whitlockite in the latter. The liquidus boundaries drawnon the basis of the 1 atm experiments are shown in Fig.NNO, as it is at FMQ. Phosphate analyses (Table 3)
indicate that fluorine is present in the 5 kbar experiments 4c and d. They indicate that under moderately oxidizing
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low-pressure conditions the thermal divide involving orthopyroxene hosts and augite exsolutions (optical de-termination). The range of calculated compositions ofaugite+ low-Ca pyroxene+ plagioclase is not stablenatural pyroxenes (4859 wt % CaO) is slightly higherand that olivine is in reaction with liquid when low-Cathan the value calculated by Duchesne (1972b) for in-pyroxene is stable. Thus olivine, which is the first mafic
verted pigeonites from BKSK (3747% CaO). Thephase to crystallize in the jotunite compositions at lowvalues indicate a pressure of emplacement between 1pressure, will be replaced by low-Ca pyroxene and pla-atm and 5 kbar (Fig. 5), the latter pressure being consistentgioclase (Fig. 4d) at a peritectic reaction, and furtherwith estimates for the crystallization of the Bjerkreimfractional crystallization will drive the liquid toward silicaSokndal intrusion (Vander Auwera & Longhi, 1994).saturation, and produce SiO2 enrichment. The liquidus
Because the chill margin composition (VB) projectstopology is consistent with petrological variations ob-well into the plagioclase field in Fig. 4b and d, it is clearserved in the Tellnes orebody and its associated dikethat the chill margin is not itself a quenched liquid at(Wilmart et al., 1989) where olivine-bearing ilmenitepressures of 5 kbar or less. In the 5 kbar near-liquidusnorite contains the minerals with the most primitiverun, VB-2, plagioclase has the composition An46, whereascompositions, and other lithologies are olivine free andthe most anorthitic plagioclase in the chill margin samplegrade continuously from jotunite to mangerite to quartzis only An36. So the chill margin is not even a simplemangerite.quenched liquid. In Fig. 4b (5 kbar) the chill margin lies
Titanomagnetite is present together with ilmenite in nearly on a line between the plagioclase component andthe matrix of the Varberg dike; however, both oxidesthe pseudo-invariant point. These relations, together withhave been exsolved and subjected to strong subsolidusthe abrupt simultaneous appearance of olivine, ilmenite,reequilibration (Duchesne, 1972a), so their compositionsand apatite in the crystallization sequence, are consistentprovide no constraint on redox conditions in the dike.with the chilled margin being a multi-saturated liquid,Accordingly, we have estimated redox conditions in thelike VB-4 or -14, enriched with 1530% plagioclase bydike on the basis of experimental FeTi oxide as-weight. It should be noted that plagioclase in run VB-semblages. At 1 atm and the FMQ buffer, two FeTi14 has an average composition of An38, which is close tooxides are stable, ilm86hem14 and uvsp69mgt31, whereas atthat observed in the dike, and which supports a multi-
1 atm and the NNO buffer, only spinel precipitatessaturated liquid composition similar to that of VB-14.
(uvsp58mgt42 in VB-16; uvsp48mgt52 in VB-17). Also, pre-Alternatively, if the jotunite magma was derived by
vious work on a primitive jotunite has shown that FMQfractionation at a higher pressure where multi-saturated
1 marks the low-f(O2) stability limit for spinel in these
liquids sustain higher plagioclase components (Vandercompositions (Vander Auwera & Longhi, 1994). Thus, Auwera & Longhi, 1994), some portion of the apparentinasmuch as both spinel (magnetite) and ilmenite are
excess plagioclase component would be due to de-present in the dike, the f(O2) was probably close to the compression, and the actual liquid composition wouldFMQ buffer during crystallization.
be displaced toward the Pl component, but not as far asNatural and experimental pyroxene compositions have
the chill margin composition (Vander Auwera & Longhi,been plotted in a Al2O3 vs CaO diagram (Fig. 5) in an 1994). So, despite the fine grain size of the chill marginattempt to glean some information about the pressure of
and the absence of phenocrysts, the material flowingcrystallization of the dike. The situation is complicated
along the margins of the dikes contained some plagioclaseby inversion and exsolution in the pyroxene; however,
crystals in suspension. The more evolved compositionsthe primary pyroxene compositions are constrained to
of the fine-grained samples with higher Qtz componentslie on mixing lines between host and lamellae. Both the
do fall close to the plagioclase+ pyroxene cotectics in1 atm and 5 kbar data fall above (higher Al2O3) the Fig. 4b and d, so it is likely that the more evolved fine-mixing lines of the natural pyroxenes in Fig. 5, indicating
grained samples within the dikes closely approximateno simple relationship. Comparison of pyroxene com- liquid compositions.positions in the two 5 kbar runs suggests that the lower
Al2O3 content observed in the natural pyroxenes may
result from continued equilibration to the solidus and intoWhole-rock analysesthe subsolidus. Even so, there is no way to discriminate
between 1 atm and 5 kbar on the basis of Al 2O3 con- The fine-grained samples from the Varberg dike andcentrations. However, the experimental data suggest that various other dikes display high total Fe as FeOt (965CaO decreases systematically with increasing pressure. 1603%),TiO2 (127% up to 462%), K2O (096% up toConsequently, we have calculated the CaO concentration 424%), and P2O5 (071% up to 259%) concentrationsof the primary pigeonite from the compositions of or- together with a modest range in SiO2 (4645% up tothopyroxenes and exsolved augites in samples 78201 6041%) (Table 5, Fig. 2). In variation diagrams (Fig. 2),
the primitive jotunites form a group distinct from theand 75202G (Table 4) and the modal proportions of
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Fig. 5. Al2O3 and CaO contents of natural and experimentally obtained pyroxenes. For the experimental compositions, boxes correspond to 1SD. The calculated compositions of natural pyroxenes correspond to their compositions before exsolution (see text for explanation).
jotunites of the dike system, which define trends of are rather constant except for K. Duchesne et al. (1989)previously pointed out this feature and attributed it todecreasing FeOt, TiO2, P2O5 and CaO, and increasing
SiO2 and K2O, with decreasing MgO. Samples of jotu- the variability of the source of jotunites. Apart from theenormous variation in Th, the primitive jotunites havenites from other localities have been included in Fig. 2
for comparison. Among them, two [sample 738: Owens relatively featureless patterns in contrast to the highlyfractionated patterns of the evolved jotunites, mangeriteset al. (1993); sample EC90-216: Emslie et al. (1994)] are
very similar to the primitive jotunites of Rogaland and quartz mangerites. Primitive jotunites show small
depletions of Ta (not Nb) and Hf (but not Zr in all cases)whereas the others fall near or on the trend of the dikesystem. Nevertheless, a group of samples from Nain relative to the adjacent REE, whereas Ti shows a smallexcess as does P. Also, Sr may show a small depletion(Wiebe, 1979) and Grenville (Owens et al., 1993) define
a trend higher in CaO/MgO and lower in K 2O/MgO (80123a, 7234 in Fig. 7), where Eu shows no depletion(Fig. 6), or Sr may show no depletion (91141) where Euthan samples from the other localities. This probably
results mainly from different fractionation paths from shows a small excess. However, all the evolved jotunites,mangerites and quartz mangerites show prominent de-locality to locality (see discussion) and from accumulation
of plagioclase+mafics. This latter process can also ex- pletions in Sr relative to Ce and Nd, yet Eu anomaliesremain small and may even be positive in the quartzplain the dispersion observed in samples from the Laramie
complex (Mitchell et al., 1996) especially in the FeOt/ mangerites. The Sr depletions indicate extensive crys-tallization of plagioclase despite the evidence for pla-MgO, TiO2/MgO and P2O5/MgO diagrams.
La concentrations in the fine-grained samples and gioclase accumulation in some samples. The unexpectedbehavior of Eu is discussed below. Interestingly, P, whichother representative samples range from 15 ppm to 80
ppm (Table 5). The evolved jotunites, mangerites and shows small relative excesses in the primitive jotunites,shows larger excesses in the evolved jotunites and thenquartz mangerites (Fig. 6) are higher in total REE content
than the primitive jotunites, except the quartz mangerite little or no excess or depletion in the mangerites, andfinally prominent depletions in the quartz mangerites.7832 which is in the range of primitive jotunites. The
fine-grained samples display similar light REE (LREE) This pattern signals the onset of apatite crystallization asthe magma changes from jotunitic to mangeritic. Relativeenrichment [average (La/Yb)N = 9] except for one
sample [91141: (La/Yb)N = 4]. Eu anomalies are either depletions of NbTa become more pronounced, andpronounced relative depletions of Ti develop with differ-weakslightly negative or slightly positive (e.g.
91141)or absent. entiation, whereas relative depletions of Hf and Zr dimin-ish in the mangerites and even become slight enrichmentsIn a multielement diagram (Fig. 7), the primitive jotu-
nites display variable concentrations of several trace in the quartz mangerites, which are consistent with Ti-oxide crystallization, but not zircon. Th shows hugeelements, especially for Th, Rb, and REE (see also U in
Table 5), whereas their major element concentrations depletions relative to the LREE in all of the evolved
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Fig. 6. REE patterns of the jotunitic suite [7234 (Duchesne et al., 1974); 80123a (Duchesne & Hertogen, 1988); 7252, 7828, T82, 7832 (Wilmartet al., 1989)]. REE abundances normalized to C1 chondrite of Sun & McDonough (1989).
jotunites despite its variability in the primitive jotunites, A LIQUID LINE OF DESCENT OF THEsuggesting that the ThREE relation is a characteristic
JOTUNITE SUITE AND ORIGIN OFof the parental magma,and of the three primitive jotunites
ROCKS WITH EXTREME FeTiPonly 80123a could be parental to the evolved jotunites.Primitive jotunites also show considerable range in K2O CONTENTwith limited variation in MgO (Figs 2 and 8). These
Liquid line of descent (LLD)features suggest variable contamination of the large in-
A series of samples presented in this study display petro-trusions by country rock gneisses during emplacementgraphic features typical of chilled rocks that suggest they(Hoover, 1989; Wilson et al., 1996). For all the samplesare close to liquid compositions and thus constrain athe K/Rb ratio varies from 376 to 1535 and Zr/Hf fromliquid line of descent of the jotunitic suite under dry40 to 58. These trace elements compositions are in theconditions. Nevertheless, projection of the fine-grainedrange of those previously reported by Duchesne (1990)samples in the OlPlQtz diagram (Fig. 4) seems tofor the jotunitic suite of the Rogaland Province and areindicate that some of them are enriched in plagioclase.similar to those reported in other anorthositic complexesWe have already mentioned that the fine-grained samples[e.g. Grenville Province: Emslie et al. (1994); Laramie
Complex: Kolker et al. (1990); Mitchell et al. (1996)]. define in variation diagrams (Fig. 2) two clusters of
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Fig. 7. Multielement diagrams of the jotunitic suite [7234 (Duchesne et al., 1974); 80123a (Duchesne & Hertogen, 1988); 7252, 7828, T82,7832 (Wilmart et al., 1989)]. Abundances normalized to chondrites (Thompson, 1982).
points, one with a narrow range of intermediate MgO, Fe2+ ratio imposed by the graphite capsules; and evencorresponding to the primitive jotunites (chilled margins though the 1 atm experiments have been run at the
of large intrusions), and the other, off
set from the first, appropriate f(O2), the lower pressure increases the pro-forming linear trends ranging from evolved jotunites portion of plagioclase and olivine crystallization relativeto quartz mangerites, in which FeOt, TiO2, and CaO to pyroxene. These difficulties turn out to be relativelydecrease, whereas K2O and SiO2 increase, versus de- minor if one compares a combination of the 1 atm andcreasing MgO. These trends are repeated by samples high-pressure (5 and 7 kbar) data with the variationfrom other dikes in the Rogaland system. The com- pattern of the dikes, as illustrated in Fig. 8, where thepositions of samples from the Tellnes dike, for example, shaded areas correspond to the compositional ranges ofoverlap those from the Varberg dike and extend the the Rogaland jotunites shown in Fig. 2.trend to higher SiO2 (charnockite). Thus in Rogaland The most important feature is that the FMQ VB pointthere is an apparent discontinuity between primitive
(run VB-6) lies on or very near the dike trend in all ofjotunite and evolved jotunite, but continuous chemical
the panels (Fig. 8). The track of NNO VB is parallel tovariation from evolved jotunite, through quartz man-
the dike trend, but is offset from the dikes in the directiongerite, to charnockite.
of higher SiO2 and lower FeOt and TiO2, because of the
The experimental data obtained on the two Varberg crystallization of too high a proportion of FeTi-oxides.dike samples plus previous data on the Tjrn jotuniteThe track of 5 kbar VB follows a path of much higher(Vander Auwera & Longhi, 1994), which belongs to theFeOt and lower SiO2 than the dikes, as the reducinggroup of primitive jotunites, bring additional constraintsconditions imposed by the graphite capsules delay theon the LLD. However, some care must be taken becausecrystallization of FeTi oxides, which in turn induces anthe compositions of the experimental liquids vary byexcessive ferrous iron content in the liquid. It thus seemsequilibrium crystallization, whereas the jotunite LLDlikely that crystallization of a liquid with VB-like com-more probably results from a partially fractional crys-position at modest pressures and with f(O2) close to FMQtallization process, and also because the pressureredoxwould produce a track very close to the dike trend, andconditions of the experiments do not match those of thethat following eventual crystallization of titanomagnetitedikes. Delayed crystallization of ilmenite, the absence ofthe track would extend to high SiO2 (charnockitic) con-magnetite near the solidus, and decreased mg-number of
ferromagnesian phases all are effects of the low Fe3+/ centrations.
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Fig. 8. Comparison of experimental data (wt % oxides) on VB (75202F), MEL (75372), and TJ (Vander Auwera & Longhi, 1994) with theRogaland jotunitic trend from Fig. 2 (shaded areas).
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Comparison of the data on a primitive jotunite (TJ) Origin of the extreme concentrations of Fe,from a previous study (Vander Auwera & Longhi, 1994) Ti and P in some jotuniteswith data on the evolved jotunite (VB) from the present Jotunites characterized by very high concentrations ofstudy provides further constraints on their possible re-
FeO, TiO2 and P2O5 (FTP) have been recognized in alllationship. In all sets of experiments on TJ, TiO2 and anorthosite complexes (Ashwal, 1982; Owens & Dymek,FeOt increase with decreasing temperature until ilmenite 1992; Owens et al., 1993; McLelland et al., 1994). Emsliebecomes a liquidus phase. While plagioclase is the sole et al. (1994) and McLelland et al. (1994) have proposedcrystallizing phase, the initial TiO2 and FeOt tracks show that the unusually high FeTiP content is characteristican increase with decreasing temperature. The effect of of a liquid derived from the processes of anorthositeilmenite saturation is probably best illustrated by the TJ crystallization under reducing conditions. FTP-rich jotu-experiments run at 1 atm (FMQ 1 TJ). In this case, nites from Rogaland have been recognized in the Varbergthe maximum TiO2 concentration (~45 wt %) is reached and Lomland dikes. In the latter, they constitute theat ~4 wt % MgO. As temperature decreases further, Puntervoll facies, which passes progressively along strike
into jotunites, mangerites and quartz mangerites. AnTiO2 and FeOt decrease with MgO, whereas SiO2 in-
average of four analyses of the Puntervoll facies (Duchesnecreases. The tracks of TiO2, FeOt, and SiO2 for FMQ et al., 1985) plots on an extension of the trend of evolved1 TJ eventually all join the trend of the dike compositions:
jotunites at 39 wt % MgO (P in Fig. 2). In the VarbergFeOt and SiO2 at MgO lower than that of sample VB;dike, the transition between the FTP rocks and theTiO2 at MgO higher than VB. Crystallization of TJ atcommon jotunites is not observed in the field but thesehigher pressure will move the tracks of the FeOt andFTP rocks (e.g. MEL with 420% P2O5, 623% TiO2 andSiO2 closer to VB. If titanomagnetite were to crystallize2743% FeOt) plot with higher FeO and TiO2 thanafter ilmenite at 5 kbar, the 5 kbar tracks of both VBsimple extensions of the dike trend (Figs 2 and 8). Theand TJ would move closer to and follow the dike trend.chemical variation toward low-SiO2 compositions is moreP2O5 concentration in the liquid increases with decreasingnearly continuous in anorthosite complexes from thetemperature until phosphate crystallizes in experimentsGrenville Province (Owens & Dymek, 1992; McLellandon both TJ and VB. In the VB experiments, apatiteet al., 1994).begins to crystallize simultaneously with ilmenite and
Variation diagrams combining experimental and geo-olivine (VB-4): this liquid is probably very close to thechemical data (Fig. 8) indicate that the composition ofVarberg liquid composition (see above). The TJ datasample MEL cannot be simply explained by fractionation
also show that the early increase in P2O5 appears more from a primitive jotunite even under very reducing con-pronounced at high pressure. This pressure effect derivesditions [f(O2) in the 5 and 7 kbar TJ experiments liesfrom a greater proportion of pyroxene crystallizing rel-between FMQ 2 and FMQ 4]. Consequently, given
ative to olivine at higher pressure: olivine can incorporatethat field evidence indicates that sample MEL is co-
a small amount of P2O5 [more than low-Ca pyroxene: magmatic with VB, three alternatives are left: the FTP-see Vander Auwera & Longhi (1994)] and Mg decreases
rich jotunites may correspond to immiscible liquids con-more rapidly because of the higher Mg content of olivine.
jugate to the mangerites found in the same dikes (e.g.SiO2 decreases with temperature in TJ liquids at 7 kbar Lomland) or they can represent liquids more or lessbecause of co-crystallization of high-Si plagioclase and
heavily laden with FeTi oxides and apatite or possiblyorthopyroxene and a low proportion of ilmenite; whereas cumulates injected as a crystal mush (Ashwal, 1982).at 5 kbar SiO2 increases weakly because olivine is the The position of sample VB in the jotunitic differ-sole maficsilicate phase near the liquidus. K2O always entiation trend corresponds to the culmination of FeO tincreases and the residual experimental TJ liquids reach and TiO
2
concentrations in the jotunite trend and thusthe K2O content observed in dikes. it is the most likely candidate to plot within the im-
An important feature of Fig. 8 is thus the bridge made miscibility field (Roedder, 1979). However, the ex-between the field of primitive jotunites and the trend of perimental MEL liquid compositions (Fig. 8) trend towardevolved jotunites by liquids residual to TJ. At 57 kbar the array of evolved jotunite compositions with decreasingthe paths of the TJ liquids join the evolved jotunite trend temperature, i.e. SiO2 and K2O increase as MgO, FeO,close to the multi-saturated VB experimental liquids P2O5, and TiO2 decrease. Therefore the VB and MELthat most closely approximate the parental liquid of the compositions are not situated on opposite sides of someVarberg dike. Consequently, the apparent discontinuity immiscibility field. There is also no evidence (globules,between primitive and evolved jotunites shown in Fig. menisci) of two liquids of any kind (silicatesilicate or2 could result from a lack of exposures of this early silicateoxide) in any of the experiments. Plagioclase isfractionation stage. This process probably took place not a near-liquidus phase of the MEL composition,
nor is there any textural or petrographic evidence forbelow the intrusion level of the dikes.
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immiscibility in the dike itself. Moreover, if we assume we will present a three-stage model based on previouspetrogenetic studies of other Rogaland dikes (Duchesnethat, in the Varberg dike, the melanorite represented byet al., 1985; Wilmart et al., 1989) as well as of the BKSKsample MEL and the mangeritic composition representedlayered intrusion (Duchesne, 1978). Stage 1 of the modelby the Kungland facies (Duchesne et al., 1985) correspondinvolves fractionating a primitive jotunite, similar toto conjugate immiscible liquids, the partition coefficientsthe parental magma of BKSK (TJ: sample 80123a) toof P, Zr, REE, Ba and Sr are much lower than thoseproduce an evolved jotunite; the second stage involvesmeasured by Watson (1976). We therefore conclude thatfractionating an evolved jotunite, similar to VB to produceimmiscibility is not a relevant process for the formationa mangeritic composition; and the third stage involvesof the FTP rocks, which leaves crystal accumulationfractionating a mangeritic composition to produce quartz(perhaps achieved through flow differentiation) as themangerite.only viable mechanism to produce FTP rocks.
Variation diagrams in Fig. 8 show that subtraction ofGiven that plagioclase is texturally primitivea leuconoritic assemblage from TJ drives the residual(hypidiomorphic) in the Varberg dike and is ubiquitousliquid toward the field of evolved jotunite compositions,in the cumulates (BKSK intrusion), the absence of plagio-close to the chilled margin composition of the Varbergclase near the liquidus of the melanorite MEL is adike (VB). In the different sets of experiments on TJclear indication that the rock has accumulated non-felsic(Vander Auwera & Longhi, 1994), cumulus assemblagesminerals. However, experiments performed on the MELin equilibrium with the liquid closest to VB are: 64%sample show that its liquidus temperature (1110C) isplag+ 30% low-Ca pyroxene+ 6% ilm at 7 kbar, 74%similar to that of the chilled margin (1120C) of theplag+ 20% ol+ 2% pig+ 4% ilm at 5 kbar, and 70%Varberg dike, and is only marginally higher than theplag+ 18% ol+ 12% oxides at 1 atm and FMQ 1.temperature of the likely parental liquid (~1080C; VB-These phase proportions closely match the leuconoritic14), despite its having higher FeOt and lower SiO2. If acumulate deduced by Duchesne (1978) (74% plag+ 16%rock is a chilled suspension of a single phase in a liquid,low-Ca pyroxene+ 10% ilm) from the SrCa modelingthe liquidus temperature of the rock will be higher thanof the leuconoritic stage of BKSK, except that olivine isthe temperature at the time of accumulation and thethe major ferromagnesian phase at 5 kbar and 1 atmliquidus phase is likely to crystallize over a large tem-instead of low-Ca pyroxene. Moreover, the fraction ofperature interval. However, if several phases have ac-liquid is 047 at 5 kbar and 051 at 1 atm, which is closecumulated then there is the possibility of little or noto the value (f= 047) calculated by Duchesne (1978).increase in liquidus temperature as in the case of eutectic
The phase proportions observed in the experimentalaccumulation. Multi-phase accumulation appears to be cumulates correspond to an equilibrium crystallizationthe case for the relatively low liquidus temperature ofprocess whereas those derived for BKSK are based onMEL, and the similarity of the liquidus temperatures ofa fractional crystallization process. Nevertheless, as aVB and MEL is thus partly coincidental. Nevertheless,fractional crystallization process is more relevant for thethe situation is more complex here, as only the non-felsic
jotunitic trend discussed here, we have chosen a cotecticpart of the saturating assemblageilmenite, magnetite,leuconoritic cumulate made of 74% plag+ 16% low-Caapatite, and possibly orthopyroxeneappears to havepyroxene+ 10% ilm with f= 05 for the first stage.accumulated to form the melanocratic facies. In the
To further model the fractional crystallization processprojections (Fig. 4), though, there appears to be a dis-along the jotunitic trend, there is the possibility to useplacement of the MEL composition away from liquidssimulations based either on partition coefficients (Nielsen,saturated with the dikes assemblage not toward or-1990) or on minimization of the Gibbs free energythopyroxene, but toward the olivine component. This(Ghiorso & Sack, 1995). Nevertheless, it has been showndisparity may be attributed to Fe3+ incorporated in the
that these simulations do not predict well the saturationaccumulated FeTi oxides, but treated as Fe2+
in the of FeTi oxides (Toplis & Carroll, 1996). We haveprojections. Subtraction of this Fe will drive the projectedtherefore used mass balance calculations to further modelMEL composition toward Qtz on a line parallel to thethe major element variations in the jotunitic trend. InOlQtz join, thus increasing the proportion of or-the case of fractional crystallization, the mineral phasethopyroxene relative to olivine in the apparent ac-compositions must be in equilibrium with the startingcumulated component.liquid and this will be true for a certain amount ofcrystallization after which a new set of mineral com-positions must be selected. We assume that the parent
Major element modeling magma of the Lomland dike was close to the VarbergTo model the trace element variations in the jotunitic chilled margin (VB) and to the EiaRekefjord chill (7355)trend, we must first constrain the phase proportions and, but we must point out that these compositions are prob-
ably slightly enriched in plagioclase, so that we use parenthence, the major element variation. In the following,
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Table 6: Three-stage major element model
Calculated cumulates
Primitive jotuniteC1 = 74% plag (An43) +16% low-Ca pyrx + 10% ilm (f1 = 05, F= 05)
Evolved jotunite
C2 = 433% plag + 196% low-Ca pyrx + 85% high-Ca pyrx + 93% ilm + 113% mgt + 8% ap (f2 = 06, F= 03)
Mangerite
C3 = 469% plag + 113% low-Ca pyrx + 127% high-Ca pyrx + 28% ilm + 211% mgt + 52% ap (f3 = 067, F= 02)
Least-squares fractionation model for cumulate 2 (C2)
Mineral compositions used in fit
Evolved Mangerite Cumulate Plag Opx Cpx Ilm Mgt Apa
jotunite (An40) (mg-no. 056)(mg-no. 066)(Hem2) (Uvsp15)
SiO2 4730 5160 4055 5852 5038 5122 049 174 000
TiO2 355 241 525 000 014 042 4881 484 000
Al2O3 1370 1465 1242 2631 122 212 039 310 000
FeOt 1583 1328 1948 000 2590 1153 4471 7898 000
MgO 320 226 490 000 1862 1244 055 046 000
MnO 025 019 029 000 000 000 000 000 000
CaO 765 621 986 786 074 2034 010 011 5480
Na2O 356 396 295 650 013 065 000 000 000
K2O 170 300 035 080 000 000 000 000 000
P2O5 227 144 340 000 000 000 000 000 4170
r2 = 0086
Least-squares fractionation model for cumulate 3 (C3)
Mineral compositions used in fit
Mangerite Quartz Cumulate Plag Pig VB-16 Cpx Ilm Mgt Apa
mangerite (An30) (mg-no. 062)(mg-no. 067)(Hem0) (Uvsp31)
SiO2 5702 6571 3993 6100 5166 5106 040 122 000
TiO2 192 099 432 000 078 051 5279 1105 000
Al2O3 1416 1331 1233 2470 127 236 010 213 000
FeOt 1198 754 2191 000 2030 1151 4505 7950 000
MgO 171 065 475 000 1820 1304 131 091 000
CaO 471 256 929 610 767 2100 008 016 5679
Na2O 335 307 347 720 011 053 000 000 000
K2O 364 504 047 100 000 000 000 000 000
P2O5 105 051 259 000 000 000 000 000 4321r2 = 0057
For stage 2, the starting composition corresponds to the average of several evolved jotunites including 75202F and 7355whereas the mangerite is the average of the Kungland facies of the Lomland dike (Duchesne et al., 1985).For stage 3, the starting and final compositions are samples 7828 and 7832 of the Tellnes dike, respectively (Wilmart, 1988;Wilmart et al., 1989).
magma instead of liquid. The composition of this liquid gives Fo56 at 5 kbar (1094C). This olivine con-strains the mg-number of the pyroxenes in equilibriumparent magma is given in Table 6 (evolved jotunite).
Calculation of the virtual olivine composition, using the with that liquidand permits selection of the other minerals(plag, ilm and magnetite) in the series of BKSK cumulateFord et al. (1983) relationship, in equilibrium with that
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assemblages. Given these compositions, it is possible to of FTP rocks such as MEL indicates that it is possiblecalculate by least-squares fitting the proportions of the to accumulate large amounts of FeTi oxides from theseminerals in the cumulate which subtracted from an magmas.evolved jotunitic liquid close to VB give a mangeriticcomposition close to that of the Lomland dike (Klunglandfacies) which is also close to that of sample 78211 (27%
Constraints from trace elementsMgO). The fitting is excellent (sum of the squared residuesWe have also modeled the abundances of various trace
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Table 7: REE partition coefficients selected for the modeling
plag (1) apa,2 (2) apa,3 (3) opx (4) cpx (5) ilm (6) mgt (1)
La 013 120 145 00019 004 00023 0006
Ce 011 150 211 00035 0075 00019 0006
Pr 01 170 269 00059 0113 00016 0006
Nd 009 190 328 0013 015 00012 0006
Sm 006 200 460 0063 022 00023 0006
Eu 046 130 255 0059 02 00009 0006
Gd 0052 200 439 0069 025 0006 0006
Tb 005 190 394 011 0258 00095 0006
Dy 0048 180 348 015 0267 0013 0006
Ho 0046 168 288 02 0275 0022 0006
Er 0044 155 227 024 0283 0031 0006
Tm 0042 142 191 0315 0292 0044 0006
Yb 004 130 154 039 03 0057 0008
Lu 0038 100 138 047 03 007 0008
1, Demaiffe & Hertogen (1981); 2, see text for explanation; 3, Fujimaki (1986); 4, Dunn & Sen (1994); 5, McKay (1989) for40% Wo; 6, Nakamura et al. (1986); 2 and 3 correspond to the cumulates c2 and c3 of Table 6. Values of D not given in theliterature were extrapolated.
Table 8: Trace elements partition coefficients selected for the modeling
plag1 plag2 plag3 opx ilm apa2 apa3 cpx mgt
Sr 19 (1) 23 (1) 39 (1) 00034 (2) 14 (3) 22 (3) 009 (5)
U 034 (2) 034 (2) 034 (2) 00002 (8) 25 (12) 25 (12) 00009 (13)
Th 004 (6) 004 (6) 004 (6) 00001 (8) 009 23 19 00015 (13) 0025 (19)
Zr 0021 (2) 033 (10) 025 (14) 012 (19)
Hf 001 (7) 001 (7) 001 (7) 0004 (8) 0419 (10) 029 (15) 097 (19)
Ta 0018 (6) 0018 (6) 0018 (6) 0004 (21) 37 003 004
Rb 01 (6) 01 (6) 01 (6) 0025 (4)
Ba 038 (2 & 22) 038 (2 & 22) 038 (2 & 22) 000015 (8) 00023 (16)
Co 005 (6) 005 (6) 005 (6) 07 (8) 9 12 (4) 5 (20)
Ni 95 (8) 17 2 (17) 44 (19)
Cr 003 (7) 003 (7) 003 (7) 1 (8) 16 (11) 27 (18) 350 (11)
Sc 0015 (7) 0015 (7) 0015 (7) 2 (9) 2 (9) 4 (9) 2 (9)
(1) Duchesne (1978) and Vander Auwera et al. (1993); (2) Dunn & Sen (1994); (3) Watson & Green (1981); (4) Henderson(1982); (5) Ray et al. (1983); (6) calculated from Demaiffe & Hertogen (1981) and Duchesne et al. (1974); (7) Phinney &Morrison (1990); (8) Kennedy et al. (1993); (9) Duchesne et al. (1985); (10) McKay et al. (1986); (11) Jensen et al. (1993); (12)J. C. Duchesne, personal communication (1996); (13) Beattie (1993); (14) Johnson & Kinzler (1989); (15) Hart & Dunn (1993);(16) average of values given by Hart & Dunn (1933), Beattie (1993) and Hauri et al. (1994); (17) Steele & Lindstrom (1981);(18) average of values given by Hart & Dunn (1993) and Hauri et al. (1994); (19) Nielsen et al. (1994); (20) Horn et al. (1994);(21) Forsythe et al. (1994); (22) Duchesne & Demaiffe (1978). 1, 2 and 3 are for the three cumulates c1c3 of Table 6. Whenthe D value is not specified in a mineral, it is assumed equal to zero. Partition coefficients in italics have been calculated.
compared with the observed compositions of the different increase in the first stage and then decreases in thesubsequent stages as magnetite crystallizes. The uniformlytypes of rocks in Table 9. Sr, U, Th, Co, Ni and Cr
decrease with fractionation; Zr, Hf, Rb and Ba increase; incompatible nature of Zr and Hf suggests that zircon isnot a liquidus phase in the jotunitic suite. These resultsTa slightly increases; and, finally, Sc displays a slight
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Table 9: Comparison between observed and calculated trace element content
Primitive jotunites Evolved jotunites Mangerites Quartz mangerites
80123a Observed Calculated Observed Calculated Observed Calculated Observed
range range range range
Sr 530 382784 400 412465 377 272310 257 128211
U 010 0113 017 032 009 0118 008 0102
Th 050 0538 097 051119 063 059067 063 066087
Zr 26200 155292 51096 89558 82185 717952 119336 12511387
Hf 650 4582 1256 5411 1910 173221 2571 285325
Ta 131 08131 201 122 278 1319 395 094162
Rb 1700 5844 3221 97134 5238 34 7663 4871
Ba 46900 469801 77187 10651602 118261 15331801 164305 18421979
Co 4900 30729 4736 347569 3376 17202 2696 72115
Ni 6000 5360 1288 66161 027 014 000Cr 2800 2850 1628 2266 000 434 000 121
Sc 1380 138259 1910 815281 1769 19211 1620 16177
For each type of rock, the composition calculated using the three-stage major element model (see text for explanation) iscompared with the range observed in the fine-grained samples. In the case of the primitive jotunites, these samples are80123a, 7234, 91141; 7020 (Duchesne et al., 1974); 200/22, 259/11 (Demaiffe & Hertogen, 1981); B90, B93, B95 (Wilson et al.,1996). For the evolved jotunites, the samples are 75202F, 7355, 89115, 8925, 8926 as well as 7252 (Wilmart et al., 1989). Forthe mangerites, the samples are 7838 and 7832 (Wilmart et al. 1989).
are similar to those obtained for the Tellnes dike (Wilmart, of contamination in the various batches of the parentaljotunite magma. Although some additional con-1988; Wilmart et al., 1989). For most elements the agree-tamination during fractionation of the Varberg and Lom-ment between observed and calculated values is veryland dikes cannot be excluded, RbSr isotopic datagood, which supports the major element modelling pro-prohibit any significant contamination of the Tellnes dikeposed above. It should be noted especially that the Srduring fractionation (Wilmart et al., 1989). The sameconcentration decreases with crystallization, whereas theconclusion can also be drawn regarding the K2O evol-LREE show a small overall increase; hence the de-ution. Small variations in the K2O content of the parentalvelopment of a pronounced Sr depletion relative tomagma batches, noted by Duchesne et al. (1989), arethe LREE in the most evolved rocksa clear sign ofamplified by fractionation of a low-K cumulate. Con-plagioclase fractionation. Continuous enrichment of Hftamination of the dikes is curious because most of theand Zr smooths out the depletions of Hf and Zr relativeoutcrop of the jotunitic dikes lies within anorthositic rocksto the middle REE (MREE) in the transition from evolvedwhich are very low in K and Rb. The unsuitability ofjotunite to quartz mangerite as observed in the rocksthe anorthosite as a source of contamination for the dikes(Fig. 7). For U and Th, our calculated values increase insuggests that the dikes intruded the anorthosites alreadystage 1 and then slowly decrease in stages 2 and 3, as
contaminated.observed in the rocks, reflecting the crystallization ofapatite in stages 2 and 3, with high partition coefficientsfor these elements (Duchesne & Wilmart, 1997). Also,
the calculated Rb concentration increases as expectedDISCUSSIONwith differentiation, but, starting with 17 ppm in 80123a,
the concentrations after stages 1 and 2 are higher than Results presented here indicate that quartz mangeritesthose measured in the evolved jotunites and the man- occurring in the vicinity of anorthositic complexes can begerites. When a starting composition lower in Rb is produced by extensive fractionation of primitive jotunites.chosen, as, for example, 580 ppm in primitive jotunite Their compositions will be dependent upon the com-91141, the calculated values in stages 2 (1787 ppm) and position of the parental jotunite, but some generalizations3 (2617 ppm) are lower than the observed ranges. The are possible: such quartz mangerites will be characterizedhighly variable Rb contents of the primitive jotunites by REE concentrations in the range of jotunites with a
weak Eu anomaly that is more positive (or less negative)(Duchesne et al., 1989) probably reflect different degrees
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VANDER AUWERA et al. PETROGENESIS OF JOTUNITE SUITE
Fig. 9. Calculated REE (a) and trace elements (b) content of the evolved jotunite (L1), the mangerite (L2) and the quartz mangerite (L3) usingsample 80123a as a starting composition and the three cumulates deduced from the major element modeling (in Table 6). Partition coefficientsused in the model are given in Tables 7 and 8.
Fig. 10. Schematic representation of liquidus equilibria of ilmeniteapatitemagnetiteplagioclase saturated liquids projected onto the olivinewollastonitequartz plane. Arrows show direction of decreasing temperature; single arrows indicate cotectics; double arrows indicate reactioncurves. Shaded paths indicate lines of descent consistent with mineral assemblages as explained in text. G, Laramie and Marcy trends; Nj, Nainjotunite (ferrodiorite) trend; Ng, Nain granitoids; R, Rogaland trend (see text); I, hypothetical trend of crustal melt with intermediate composition.
than its parent; and on multi-element plots there will be of evolved compositions in the range of 5262 wt %SiO2, but a continuum in SiO2 from 62 (quartz mangerite)locally strong depletions of U, Th, Sr, and Ti with smaller
to no relative depletions of Hf and Zr. Complementary to 74% (charnockite) in the Nain Complex of Labrador.Not surprisingly, Emslie et al. (1994) ascribed their high-to the quartz mangerite will be a series of cumulates richin oxides and apatite which will form melanocratic rocks. Si compositions to partial melting of the lower crust, not
fractionation. The Nain high-Si compositions have muchRecently, Owens et al. (1993) described a broadly similarscenario for derivation of quartz mangerite from jotunite in common with the Rogaland quartz mangerites in terms
of mineralogy and trace element abundance patterns;in the Grenville Province of Quebec. These observationsdiffer in detail from those of Mitchell et al. (1996) and however, the Nain granitoids show small negative Eu
anomalies and more pronounced relative depletions ofEmslie et al. (1994). Mitchell et al. (1996) described mon-zodiorite (~jotunite) evolving to monzonite (mangerite) Sr and P, which might reflect more extensive fractionation
of plagioclase and apatite, but might also reflect partialand then monzosyenite instead of quartz monzonite(~quartz mangerite) along with the formation of com- melting of a mafic crustal source. Also, the Rogaland
quartz mangerites are found only within fractionatedplementary oxideapatite-rich rocks in the Laramie Com-plex of Wyoming. Emslie et al. (1994) observed an absence dikes or as the upper portion of a much larger jotunitic
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intrusion such as BKSK (Duchesne & Wilmart, 1997), Fe has been removed from the Ol component to formwhereas some of the Nain granitoids comprise entire an Fe3O4 (Mgt) component. Liquid lines of descent arediscrete intrusions or substantial fractions of others. Al- represented by shaded lines and FTP trends by patternedthough the difference in field relations between Rogaland areas. Because different suites probably crystallized atand Nain may be due in part to the level of exposure, different pressures the topology of the entire diagramwe cannot exclude the possibility of deriving some quartz may not be appropriate to a single pressure or com-mangerites by partial melting of the lower crust. Indeed, position (with decreasing pressure or increasing mg-num-as discussed below, there is a wide range of pressure and ber the olivine pseudo-eutectic becomes peritectic andcomposition for which fractionation of a jotunitic magma the pyroxeneplagioclase thermal divide disappears).cannot yield quartz mangerite. However, the diagram was constructed such that the local
Our conclusions on the liquid line of descent of jotu- liquidus topologies would be appropriate. The diagramnites, as well as those of Owens et al. (1993) and Mitchell shows that the plagioclase+ low-Ca pyroxene+ augiteet al. (1996), contradict those presented by McLelland et thermal maximum is stable on the aug+ lpyx liquidusal. (1994), who modeled the compositions of PTiFe- boundary and that the Wo-rich portion of the ol+ lpyxrich mafic dikes and sheets from the contact zone of the curve is even, whereas the low-Wo portion is odd andMarcy massif in the Adirondack mountains. In variation truncates the thermal ridge that crosses the lpyx liquidusdiagrams, the trends defined by these rocks show extreme
field. This configuration allows olivine to react out ofenrichments in FeOt (up to 25%), TiO2 (up to 76%), magmas along the R curve and be replaced by pigeoniteP2O5 (36%) correlated with extreme depletion in silica (lpyx); and it also allows the fractionating magma to(down to 36% SiO2). McLelland et al. (1994) admitted eventually reach silica saturationRogaland, some ofthat these rocks are likely to represent crystal-laden liquids the Grenville intrusions (Owens et al., 1993) and parts ofbut nevertheless contended that the liquid line of descent
the Adirondacks (De Waard & Romey, 1968) are ex-followed at least in part a trend of decreasing Si and
amples. The Gcurve represents magmas in which olivineincreasing P, Ti, and Fe. However, comparison with the
crystallizes after pigeonite at the pseudo-eutectic, such asdata from this study indicates that the highest Fe, Ti, P
in the Greaser Intrusion in the Laramie Complex (Mit-and lowest Si concentrations are similar to those of
chell et al., 1996) and the Marcy trend of McLelland etRogaland sample MEL, which is demonstrably a partial
al. (1994). The Nj curve [NainEmslie et al. (1994);cumulate of a multiphase liquidus assemblage (pyroxene,Maloin Ranch plutonKolker & Lindsley (1989)] is an
apatite, ilmenite, magnetite); furthermore, experimentsexample of a trend in which the liquid lies in the
show that FeOt, TiO2, and P2O5 decrease as oxides and pyroxene+ plagioclase thermal divide, so neither olivineapatite crystallize from this composition. In projectionsnor quartz crystallizes, even after extensive fractionation.
such as Fig. 4a and b, the FTP-rich model magmasAs a result, jotunitic (ferrodioritic, monzonoritic) rocks
M6M9 from McLelland et al. (1994) (Table 1) define agrade into two-pyroxene mangerites, and subsequently
trend (not shown) pointing away from the 5 kbar pseudo-into syenites. Such rocks will show a modest increase in
eutectic toward the Ol component; whereas modelSiO2 concentration because the high-Si felsic componentsmagmas M4M6 plot close to the pseudo-eutectic.increase at the expense of the low-Si mafic componentsAs explained above, the highest apparent contents ofin the residual liquids (e.g. Longhi, 1991). Because thethe Ol component may be in part a mixture ofdecrease in the Qtz component is so small along the Gpyroxene and magnetite. The presence of trend, SiO2 will also increase weakly in the residual liquidpyroxene+ oxide+ apatite+ plagioclase in M8 fol-as it progressively forms olivine-free jotunites (ferro-lowed by the initial appearance of olivine in M9 is alsodiorites), olivine-bearing mangerites, and ol syenites. Thusconsistent with a eutectic-like pseudo-inv