Gondwana Research, V 6, No. 4, p p . 595-605. 0 2003 International Association for Gondwana Research, Japan. ISSN: 1342-937X

Pan-African Alkali Granitoids from the S0r Rondane Mountains, East Antarctica

Zilong Lilj **, Yoshiaki Tainosho3, Jun-ichi Kirnura4, Kazuyuki Shiraishi5 and Masaaki Owada6

Department of Earth Sciences, Zhejiang University, 38 Zheda Road, Hangzhou 310027, I! R. China, E-mail: zilongliOhotmail.com Graduate School of Science and Technology, Kobe University, Nada, Kobe 657-8501, Japan Faculty of Human Development, Kobe University, Nada, Kobe 657-8507, Japan Department of Geology, Shimane University, Nishikawatsu 1060, Matsue 690-8504, Japan National Institute of Polar Research, Kaga 1-chome, Itabashi-ku, Tokyo 173-8515, Japan Department of Earth Sciences, University of Yamaguchi, Yamaguchi 753-8512, Japan

E-mail: zilongliOhotmail.com * Corresponding author: Department of Earth Sciences, Zhejiang University, 38 Zheda Road, Hangzhou 310027, P. R. China,

(Manilscript received April 26, 2003; accepted June 29,2003)

Abstract

Alkali granitoids (500-550 MP) representing a prominent Pan-African magmatic event are widcly distributed in thc S@r Rondanc Mountains, Dronning Maud Land, East Antarctica. Geochemically, they are granitic to syenitic in composition and show an alkaline affinity of A-type granites. They are characterized by high K,O+Na,O (7-13 wt%) and K,O/Na,O (1-2), low to intermediate Mg#, wide ranges of SiO, (45-78 wt%), Sr (20-6500 ppm) and Ba (40-13000 ppm) and have Nb and Ti depletion in thc primitive mantle normalized diagram. The granitoids are subdivided into Group I granites, Group I1 granites, Lunckeryggen Syenitic Complex and MefJell Plutonic Complex. The Group I granites have higher Mg#, Sr/Ba, S r n , ( L a m ) , and LREE/HREE, lower A/CNK, CREE and initial 87Sr/87Sr ratios and lack Eu anomalies compared to those with negative Eu anomalies in the Group I1 granites. The syenitic rocks from the Mcfjcll Plutonic Complex are higher in alkali, Ga, Zr, Ba, and have lower Mg#, Rb, Sr, Nb, Y, F and LREE/HREE with positivc Eu anomaly, whereas the granites from the MefJell Plutonic Complex have high LREE/HREE ratios with negative Eu anomaly. The Lunckeryggen sycnitic rocks have intermediate Mg#, higher YO, P,O,, TiO,, Fe,O,/FeO, Ba, Sr/Y and LREE/HREE ratios with lack of Eu anomalies and are lower in A1,0,, Ga, Y, Nb and Rb/Sr ratios. Based on chcmical characteristics combined with isotopic data, we suggest that the Lunckeryggen syenitic body and Group I granitic bodies may be derived from the mantle-derived hot basic magma by fractional crystallization with minor assimilation. We also suggest that the Group I1 granites may bc dcrivcd from assimilation with crustal rocks to varing degrees and then fractional crystallization in higher crustal levels (ACF model). The Mefjell Plutonic Complex seems to bc derived from a heterogcnetic magma source compared with other granitoids from the SOr Rondanc Mountains. The syenitic rocks in the MefJell Plutonic complex have a unique source (iron-enriched) and have a chemical affinity with the charnockites in Gjekvikjella and western Muhlig-HofmannfJella, but not like the Yamato syenites in adjacent areas.

Key words: Pan-African alkali granitoids, chemical characteristics, petrogenesis, S0r Rondane Mountains, East Antarctica.

Smr Rondane Mountains. More recently, early Paleozoic magmatism has drawn attention for its significance on source materials, magmatic process, F-bearing fluid component in biotite and association with the formation of Gondwanaland (Li et al., 2001b; Li, 2002; Li et al., 2003). The Mefjell Plutonic Complex is considered separately from the volcanic-arc granites because it mainly consists of syenite and granite and has a different chemical

Introduction

The Smr Rondane Mountains, East Antarctica have a well-documented magmatic history with ages of 900-1000 and 500-550 Ma. Several geologists (Sakiyama et al., 1988; Takahashi et al., 1990; Tainosho et al., 1992,1993) have carried out geological and geochemical studies on late Proterozoic and early Paleozoic plutonic rocks in the

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596 Z.-L. LI ET AL.

composition (Li et al., 2001a) compared to the Dufek granites and Lunckeryggen granites. Li et al. (2001b) argued two possibilities for petrogenesis of the volcanic- arc type granites and within-plate type granites. Due to problems with terminology of within-plate type granites having Nb depletion in the primitive mantle normalized diagram, we presently grouped the early Paleozoic granitoids into the four groups: Group I granites, Group I1 granites, Mefjell Plutonic Complex and Lunckeryggen Syenitic Complex. The Group I granites and the Group I1 granites respectively correspond to the division of the volcanic-arc type granites and the within-plate type granites (Li et al., 2001b). The Group I granites include the Dufek grani tes and Lunckeryggen granites, whereas the Group I1 granites include the Austkampane granites, Pingvinane granites, Rogerstoppane granites and Vikinghogda granites. The Pan-African magmatism in the S0r Rondone Mountains provide important information on the magmatism during the evolution of Gondwanaland. In this paper, we present characteristics, address possible petrogenesis of Pan-African alkali granitoids in the S0r Rondane Mountains and compare sycnitic rocks from the S0r Rondane Mountains with those from adjacent areas.

Regional Geology

The SOr Rondane Mountains (22"E to 28"E, 71.5"s to 72 .55) in Dronning Maud Land, East Antarctica (Fig.l), mainly consist of late Meso-Proterozoic greenschist- to granulite-facies metamorphic rocks, and early Paleozoic granitoids with minor mafic dykes (Kojima and Shiraishi, 1986; Sakiyama et al., 1988; Takahashi et al., 1990; Shiraishi et al., 1991; Shiraishi and Kagami, 1992; Grew et al., 1992; Osanai et al., 1992; Tainosho et al., 1992, 1993; Araltawa et al., 1994; Ikeda and Shiraishi, 1998). On the basis of metamorphic grade, the region can be divided into two terranes: an amphibolite- to granulite- facies northeastern terrane and an epidote amphibolite- to greenschist-facies southwestern terrane. The S0r Rondane Suture Zone separates the two terranes, and the Main Shear Zone cuts the southwestern terrane (Osanai et al., 1996). Granulite facies rocks formed at 750-850°C and 7-8 kbar for non-mylonitized gneisses and at 530-630°C and 5-5.5 kbar for mylonitized gneisses (Asami et al., 1992).

Two widely distributed episodes of late Proterozoic and early Paleozoic plutonism were divided on the basis of the ages of 900-1000 Ma and 500-550 Ma by the whole- rock Rb-Sr isochron, Sm-Nd and SHRIMP U-Pb zircon method (Takahashi et al., 1990; Tainosho et al., 1992; Shiraishi and Kagami, 1992 and Shiraishi et al., 1996).

The Nils Larsen Tonalite is exposed in the southern part of the S0r Rondane Mountains, and is affected by regional mylonitization with greenschist to epidote amphibolite facies metamorphic condition (Kojima and Shiraishi, 1986). The Lunckeryggen Syenitic Complex intruded into the Nils Larsen Tonalite and was intruded by the Lunckeryggen granites (Sakiyama et al., 1988). The Mefjell Plutonic Complex intruded into two metamorphic terranes. It is intruded by tonalite and diorite dykes. Geochronological data for early Paleozoic granitoids are shown in table 1. Isotopic data indicate that initial 87Sr/86Sr ratios are lower (0.7037 and 0.7050) in the Group I granites, wide range with slightly higher values (0.7035 to 0.7302) in the Group I1 granites and 0.7056 in the Mefjell Plutonic Complex (Table 1).

Petrography The Mefjell Plutonic Complex

The Mefjell Plutonic Complex is exposed in a 7x10 km2 area and consists of syenitic rocks and granites. Field relationship between the syenitic rocks and granites is not clear because of a lack of outcrops. The syenitic rocks are composed of K-feldspar (50-70%), plagioclase (15-30%), quartz (2-lo%), mafic minerals of clinopyroxene (1-5%), hornblende (l-8%) and biotite (1-5%) with apatite, zircon, titanite and ilmenite with or without relic olivine (95-98% fayalite component). The granite is mainly composed of K-feldspar (30-60%), plagioclase (20-35%), quartz (20-35%), and biotite (1-5%) with or without hornblende.

The Lunckeryggen Syenitic Complex

The Lunckeryggen Syenitic Complex occurs in the central part of the Lunckeryggen area and is composed of layered syenite, melanocratic syenite and quartz syenite (Sakiyama et al., 1988). Small dykes of the fine-grained melanocratic syenite intrude into the layered syenite. Medium- to fine- grained quartz syenites intrude into the layered syenite and the melanocratic syenite. The layered syenite is mainly composed of K-feldspar (70-90%), amphibole (5-20%) and clinopyroxene (1-5%) with accessory biotite, titanium, apatite, zircon and magnetite. Melanocratic syenite has a much higher modal composition of mafic minerals than the layered syenite though they have similar mineral assemblages. The quartz syenite contains K-feldspar, plagioclase, quartz, amphibole and accessory titanite, apatite, zircon, allanite and magnetite with or without biotite. Interstitial fluorite is rarely present.

The Group I granites

The Dufek grani te is exposed in an area of approximately 10x10 km2 (Fig. 1). The granite is a massive and consists of medium-grained biotite granite with fine-

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PAN-AFRICAN GRANITOIDS FROM THE S0R RONDANE MOUNTAINS 597

Fig. 1. Simplified geological map of the SOr Rondane Mountains (modified from Shiraishi et a]., 1997). The Group I granites are: DG-Dufek granites and LG-Lunckeryggen granites. The Group I1 granites are: AG-Austkampane granites, PG-Pingvinane granites, VG-Vikingh~gda granites and RG-Rogerstoppane granites. MPC-Mefjell Plutonic Complex; LSC-Lunckeryggen Syenitic Complex; MSZ- Main Shear Zone; SRS-S0r Rondane Suture Zone.

grained biotite granite. The medium-grained biotite granite consists of plagioclase (25-40%), K-feldspar (30-55%), quartz (16-45%) and biotite (0.5-4%) with accessory titanite, apatite, zircon and Fe-Ti oxides with or without muscovite (Table 1). Greenish yellow biotite is mostly interstitial to K-feldspar. The fine-grained granite contains hornblende, which is subordinate to biotite and forms elongate prismatic crystals interstitial to K-feldspar.

The Lunckeryggen granite is exposed in an area of 6x6 km2 in the southern part of the Lunckeryggen area. It is composed of coarse-grained biotite granite and hornblende-biotite granite. The coarse-grained granite is composed of quartz (20-35%), K-feldspar (30-55%), plagioclase (25-38%) and biotite (1-5%) with or without hornblende. Accessory minerals include titanite, apatite, zircon, magnetite and occasionally fluorite.

Table 1. Summarv of neolonical. mineralonical. neochronolonical and initial Sr ratio characteristics of early Paleozoic nranitoids.

Plutons Host rocks Mineralogical assemblages Age (Ma) Sri faults

(inferred) grade gneiss

(inferred) high-grade gneiss

Group I granites Dufek sz intermediate- Kfs+Pl+QtzkHbl+Bt&Flt 528+.31a.b 0.7037220.00029

Lunckeryggen SZ intermediate to Kfs+Pl+QtziHbl+Bti-Flt 525231” 0.7050410.00025

Austkampane - granulite facies gneiss’ Kfs + P1+ Qtz2 Hbl+ Bt +.Grt+Ms Group I1 granites Pingvinane MSZ high-grade gneiss Kfs+Pl+Qtz+Hbl+Cpx+Bt 510”, 500‘ 0.70345-0.70680

Rogerstoppane MSZ high-grade gneiss Kfs+ PI + Qtz?Hbl+Bt r Grt+Ms 0.7302“

Vikinghprgda MSZ high-grade gneiss Kfs+Pl+Qtz+BtkMs 525” 0.7067-0.7184 Lunckeryggen Syenitic Complex MSZ intermediate to

Mefjell Plutonic Complex MSZ intermediate to

Notes: SZ: Suture zone; MSZ: Main shear zone; SRS: S0r Rondane suture zone; ’: Sapphire-bearing gneiss; a: Rb-Sr whole-rock isotopic data (Tainosho et al., 1992; Takahashi et al., 1990; Arakawa et al., 1994); b: 519k98 Ma of the Dufek granites (whole-rock) and Sm-Nd isotopic data from Arakawa et al. (1994); and <: K-Ar biotite isotopic analysis (Takigami and Funaki, 1991). Kfs: K-feldspar, P1: plagioclase, Qtz: quartz, Hbl: hornblende, Bt: biotite, Cpx: clinopyroxene, Ah: allanite, Ttn: titanite, Ap: apatite, Zrn: zircon, Grt: garnet, Mag: magnetite, Ilm: ilmenite, Ep: epidote, Ms: muscovite and Flt: fluorite.

high-grade gneiss Kfs +PI + Qtz + Hbl+ Cpx? Bt +Mt 496-500’ -

and SRS high-grade gneiss Kfs + P1+ Qtz? Hbl? Cpx+ Bt + Ilm +. 01 506 543” 0.7056

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598 Z:L. LI ET AL.

The Group I1 granites

The Austkampane granite is exposed in the eastern part of Austkampanc and has a foliation defined by biotite and hornblende. It consists of quartz (16-45%), plagioclase (25-55%), K-feldspar (25-45%), hornblende and biotite (0.5-5%) with accessory zircon, apatite, titanite and ilmenite.

The Pingvinane granite displays a weak schistosity parallel to the host gneissosity near contacts, but the central part of this granite is massive. The equigranular coarse-grained biotite hornblende granite is composed of K-feldspar (35-55%), quartz (20-45%), plagioclase (20-45%), hornblende and biotite (2-So/o) with or without clinopyroxene. Accessory minerals are titanite, apatite, zircon and Fe-Ti oxides.

The Rogerstoppane granite occurs a t the southern end of Rogerstoppane. Its gneissosity is parallel to the host gneiss. The granite consists mainly of plagioclase (25-40%), quartz (18-40%), K-feldspar (30-50%), biotite (1-5%) and hornblende with accessory allanite, epidote, zircon, apatite and Fe-Ti oxides with or without garnet.

Table 2. Rcprescntative chemical compositions of biotite from granitoids.

The Vikinghmgda granite intrudes into basic schists and has a gneissosity with many xenoliths of host gneisses in it. It consists of quartz (25-40%), plagioclase (20-40%), K-feldspar (25-45%), biotite (1-5%) and muscovite with accessory titanite, apatite, zircon and Fe-Ti oxides.

Analytical Methods Chemical analyses of minerals were obtained using a

JEOL-8900M electron probe microanalyzer a t the Venture Business Laboratory of Kobe University. Element determinations were carried out using a beam diameter of 3pm, an accelerating energy of 15 kV, a probe current of 12 nA and a counting time of 20 s for each element analyzed except for F and C1, where a counting time of 100 s and 50 s respectively were applied. For fluorine and chlorine analyses, natural pure fluorite (CaF,) and a granular aggregate of halite crystal (NaC1) were used as standards. A more detailed description of analytical conditions is presented in Li et al. (2003).

Major and trace elements were analyzed by XRF (Rigaku 3270E) at Kobe University using the analytical

Plutons MPC LSC Group I granitcs Group I1 granites MG MS DG LG AG PG RG VG

Sample No. 1 2 3 4 5 6 7 8 9 Point No. 6 2 11 20 3 12 25 34 30 SiO, (wt%) 34.32 34.50 32.78 37.63 38.38 35.18 34.78 33.61 44.91 TiO;

FcOt MnO

CaO Na,O

F CI Cr203

A403

MgO

K,*

1.92 13.96 34.53

0.35 1.21 0.32 0.02 7.98 0.03 0.25 0.00

4.25 13.70 35.75

0.31 1.04 0.25 0.05 4.96 0.13 0.01 0.00

1.53 10.35 16.39 0.26

15.34 0.11 0.08

11.48 3.11 0.06 0.06

0.00 14.62 18.18 0.07

13.25 0.03 0.10 9.43 2.37 0.10 0.00

1.36 15.22 17.38 0.32

12.12 0.02 0.12

10.35 2.04 0.09 0.00

3.27 18.63 26.49

0.27 5.14 0.00 0.01 5.55 0.48 0.09 0.00

3.53 13.09 36.57

0.34 0.65 0.20 0.03 4.75 0.76 0.44 0.00

0.06 15.28 30.91 0.07 2.61 0.00 0.04

11.14 0.34 0.08 0.00

0.00 26.49 6.49 0.10 1.67 0.03 0.19 12.50 0.41 0.01 0.00

Total wt?h 94.89 94.95 91.55 95.78 97.40 95.11 95.14 94.14 92.80 0 = 2 2 Si 5.692 5.630 5.525 5.820 5.811 5.458 5.748 5.633 6.464 A1 2.729 2.635 2.056 2.665 2.716 3.407 2.550 3.018 4.494 Ti 0.240 0.522 0.194 0.000 0.155 0.382 0.439 0.008 0.000 Fe 4.308 4.389 2.078 2.115 1.979 3.091 4.546 3.897 0.703 Mn 0.049 0.043 0.037 0.009 0.041 0.035 0.048 0.010 0.012 Mg 0.299 0.253 3.854 3.055 2.736 1.189 0.160 0.652 0.358 Ca 0.057 0.044 0.020 0.005 0.003 0.000 0.035 0.000 0.005 Na 0.006 0.016 0.026 0.030 0.035 0.003 0.010 0.013 0.053 K 1.689 1.033 2.468 1.860 1.999 1.098 1.001 2.382 2.295 Total 15.070 14.564 16.258 15.558 15.474 14.663 14.536 15.613 14.385 F 0.016 0.067 1.657 1.159 0.977 0.235 0.397 0.180 0.187 c1 0.070 0.003 0.017 0.026 0.023 0.024 0.123 0.023 0.002 OH 3.914 3.930 2.325 2.815 3.000 3.741 3.480 3.797 3.811

Mg/(Mg+Fc) 0.065 0.055 0.650 0.591 0.580 0.278 0.034 0.143 0.338 F/(F + C1+ OH) 0.004 0.017 0.414 0.290 0.244 0.059 0.099 0.045 0.047 Note: Calculating method for F and C1 is based on stoichiometry; MG and MS: the syenitic rocks and granites from the Mefjell Plutonic Complex

respectively; the other symbols as in figure 1. Sample No.1: B90012402A, 2: B90012504, 3: 85011453A2, 4: B90012303B, 5: B90011902A, 6: B90010807, 7: B90011406, 8: B90012310D and 9: B90017C5B.

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PAN-AFRICAN GRANITOIDS FROM THE SOR RONDANE MOUNTAINS 599

methods of Yamamoto et al. (1997). Rare earth elements were determined by ICP-MS at Shimane University. Trace element analyses were carried out using solution ICP-MS, following the methods described by Kimura et al. (1995). Representative major, trace and rare earth elements of early Paleozoic granitoids are listed in Table 3.

Mineral Chemistry

Biotite

Representative chemical analyses and structural formulae of biotite are given in Table 2. The XMg of biotites among Group I and Group I1 granites from the Mefjell Plutonic Complex and the Lunckerygen Syenitic Complex show variation from 0.48-0.69,0.13-0.38,0.05-0.33 and 0.61- 0.72 (Fig. 2). The Group I granites and the Lunckeryggen syenitic rocks have higher F/(OH+F+Cl) ratios of 0.20- 0.42 and low C1 contents. However, biotites from the Group I1 granites have lower fluorine values ranging from <1.15 wt.% and chlorine values of <0.60 wt.%. On the other hand, the Mefjell Plutonic Complex has a much lower F of <0.12 wt.% and C1 contents (<0.3 wt.%) in biotite.

Hornblende

Hornblendes from the Group I granites have MgO contents of 7.80-12.68 wt.% and fluorine contents of 0.45-1.22 wt.%, however the Group I1 granites have lower MgO contents of 0.89-1.60 wt.% and F of 0.20-0.38 wt.%. The rocks from the Mefjell Plutonic Complex have <0.13 wt.% in F and 0.05-0.28 in M@(Mg+Fe) ratio (15 samples), whereas the Lunckryggen syenitic rocks have 0.68-1.50

Annite Siderophyllite FegSi6 Fe5Si5

0

h

Group I granite A LG

DG

Group I1 granit 0 AG

0 PG

V RG

A VG

+ MPC

* LS

6 5

Phlogopite Si Eastonite Mg6sk1 MS5.55

Fig. 2. Si vs. Mg/(Mg+Fe) plot in biotite from early Paleozoic granitoids. The symbols are the same as in figure 1.

wt.% in F and 0.63-0.65 in Mg/(Mg+Fe) ratio. Hornblendes from the Group I1 granites have high A1,0, contents in comparison to common anorogenic granites (Anderson, 1983).

Feldspars

Anorthite contents of plagioclase in the Group I1 granites (Anl, in core to An, a t rim) are lower than those in the Group I granites (An33 in core to Anl8 at rim in zoned crystals). The composition of plagioclase in the syenitic rocks from the Mefjell Plutonic Complex ranges from An,, in core to An, at rim. Chemical compositions of K-feldspar are Or88.98Ab2-12 among early Paleozoic granitoids.

Geochemistry

Mefjell Plutonic Complex

The syenitic rocks and granites from the Mefjell Plutonic Complex are 66-57 wt.% and 70-75 wt.% in SiO, respectively. The rocks are syenite and alkaline rocks in the SiO, vs. Na,O+K,O plot (Fig. 3) and belong to A-type granite in AFM diagram (Fig. 4). In the Harker diagram (Fig. 5), SiO, has a good negative correlation with FeO, TiO,, MgO, CaO, P,O, and Ba. The syenitic rocks are metaluminous, high in alkaline (10-11 wt.%), higher Na,O (4-5 wt.%), A1,0,, Ga, Zr (847 ppm, mean value of 12 samples) and Ba, K20/Na,0 and FeOJ(FeOt+MgO) ratios (ca. 0.85), and lower Mg#, CaO, Fe,O,/FeO, P20,, Rb, Sr, Nb, Y and F whereas the granites are metaluminous and have higher Fe,O,/FeO, Ga/Al, and lower Mg, F, Y, Nb and Rb (Table 3). In the Y vs. Nb and Rb vs. (Y+Nb) plots (Pearce et al., 1984), all of the syenitic rocks fall into the field of volcanic-arc granite (Tainosho et al., 1992).

The syenitic rocks from the Mefjell Plutonic Complex show moderate CREE amounts of 106.60-274.67 ppm with positive Eu anomalies of Eu/Eu”= 1.25-4.99, moderate to weak LREE/HREE ratios of (La/Lu), = 4.72- 9.34 and concave shape in HREE pattern (Fig. 6). This REE pattern implies that the syenitic rocks from the Mefjell Plutonic Complex differ distinctly from those of other early Paleozoic granitoid rocks as well as the Yamato syenites (Zhao et al., 1995). The granites from the Mefjell Plutonic Complex have distinct characters of La/Sm, La/Yb, (La/Yb), and LREE/HREE ratios (54.70-74.70) with negative Eu anomaly compared to those of the syenitic rocks from the same complex.

Lunckeryggen Syenitic Complex

The Lunckeryggen syenitic rocks have 43-59 wt.% in SiO,, intermediate Mg#, higher K20, P,O,, TiO,, CaO, Ba, Fe,O,/FeO and Sr/Y ratios, but are poor in A1,0,, Ga, Y,

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600 Z.-L. LI ET AL

Table 3. Representative major, trace and rare earth elements of the early Paleozoic granitoids.

Plutons Mefjell Plutonic Complex Lunckeryggen Syenitic Complex Group I granites Group I1 granites Rock types syenite granite LS QS MS LG DG AG PG VG RG Sample No. S91012002C S91012301C B86012103A S91010702B 85012009A S870331-4G 1 2 3 4 5 6

SiO, (wt%) 57.26 57.99 72.52 58.36 60.33 53.06 72.14 73.32 74.18 65.48 77.15 72.61 TiO, 0.80 0.84 0.38 1.30 1.05 1.23 0.44 0.22 0.18 0.62 0.08 0.17 A 4 0 3 15.62 16.27 14.16 14.95 16.10 12.64 13.67 14.90 14.92 17.19 12.15 13.47 Fe,O,(T) 10.54 9.72 2.80 7.89 6.21 6.68 2.63 1.74 1.16 3.65 1.05 2.43 MnO 0.08 0.09 0.00 0.00 0.05 0.00 0.03 0.02 0.02 0.04 0.02 0.04 MgO 0.40 0.59 0.55 1.62 1.05 5.97 0.91 0.36 0.32 1.18 0.11 0.28 CaO 3.55 3.66 1.18 2.71 3.84 7.14 2.10 1.63 1.13 3.48 0.45 1.19 Na,O 4.11 4.09 3.09 2.89 4.04 1.53 3.96 4.60 3.76 5.17 3.72 4.30

5.87 6.03 5.76 9.14 6.57 8.21 3.45 3.69 5.04 2.40 4.67 3.83 0.29 0.29 0.11 0.46 0.22 2.04 0.20 0.07 0.09 0.58 0.00 0.03 P-0,

K,O

Ba (ppm) Rb Sr Zr Nb Y Ga F La c c Pr Nd Sm Eu Gd Tb DY Ho Er Tm Yb Lu

52 47 208 267

13 4 20 15 24 21

21.95 18.20 51.26 39.92 6.68 5.25 29.98 23.19 6.24 4.50 5.77 5.27 5.43 4.03 0.75 0.52 4.01 2.85 0.75 0.52 1.94 1.38 0.29 0.22 2.17 1.70 0.36 0.29

320 60 188 64 570 97 24 4 21 22 18

< 10 168.90 29.23 318.00 65.12 34.35 8.50 119.50 36.31 15.08 7.28 1.34 2.56 10.90 6.12 1.06 0.75 4.86 3.62 0.76 0.56 1.88 1.20 0.27 0.15 2.02 0.90 0.35 0.14

Total 98.52 99.57 100.55 99.32 99.46 98.5 99.53 100.55 100.80 99.79 99.40 98.35 C.I.P.W. norms 9 5.50 4.97 29.30 1.73 5.06 0.00 30.75 28.45 30.13 18.68 36.73 30.56 or 35.21 35.79 33.85 54.38 39.84 49.26 20.48 21.69 29.55 14.21 27.76 23.01 ab 35.30 34.76 26.00 24.62 35.08 13.14 33.67 38.71 31.56 43.84 31.67 37.00 an 6.94 8.26 5.11 0.83 6.56 3.42 9.15 7.59 4.98 13.50 2.25 5.80 di 2.18 3.18 0.00 3.99 5.79 11.41 0.00 0.00 0.00 0.00 0.00 0.00 wo 1.17 1.71 0.00 2.14 3.11 6.12 0.00 0.00 0.00 0.00 0.00 0.00 en 1.01 1.48 0.00 1.85 2.68 5.29 0.00 0.00 0.00 0.00 0.00 0.00 hY 0.00 0.00 1.36 2.21 0.00 4.17 2.28 0.89 0.79 2.95 0.28 0.71 en 0.00 0.00 1.36 2.21 0.00 4.17 2.28 0.89 0.79 2.95 0.28 0.71 il 0.17 0.19 0.00 0.00 0.11 0.00 0.06 0.04 0.04 0.09 0.04 0.09 hm 10.70 9.76 2.78 7.94 4.32 6.78 2.64 1.73 1.15 3.66 1.06 2.47 tn 1.77 1.82 0.00 3.21 2.50 3.06 0.00 0.00 0.00 0.00 0.00 0.00 ru 0.00 0.00 0.38 0.00 0.00 0.00 0.41 0.20 0.16 0.58 0.06 0.13 aP 0.68 0.67 0.25 1.07 0.52 4.80 0.47 0.16 0.21 1.35 0.00 0.07

D.I. 76.01 75.52 89.16 80.74 79.98 62.40 84.91 88.85 91.25 76.73 96.16 90.57 6300 865 1315 530 2226 128 4221 140 2350 60 21

1500 136.80 302.90 36.18 134.90 20.62 5.25 15.17 1.73 8.30 1.41 3.51 0.53 3.43 0.48

210

3 78 10 32 14

97.71 189.60 22.24 89.09 17.30 5.28 14.64 1.72 8.43 1.32 3.01 0.39 2.47 0.33

155 617 7.6 9.5 21 0.5 96.4 91.6 7.8 28 4.1 0.9 2.6 0.4 1.4 0.3 0.7 0.1 0.6 0.1 9.5

97 170 971 128 8.4 3.8 7.8 16.7 22 19 0.7 0.3 46.2 26.3 74.9 47 6.6 4.4 26.9 18.8 4 4.4 0.9 0.8 2.4 3.5 0.3 0.6 1.1 2.5 0.2 0.5 0.6 1.4 0.1 0.2 0.5 1.2 0.1 0.2 7.8 16.7

131 291 25 57.2 28 1.5

114.8 238.1 26.2 127.2 24.9 3.5 16.4 2.3 9.4 1.8 4.8 0.7 3.7 0.6 57.2

90 34 49.6 57 24 2.9 30.1 56.2 5.9 25.7 6 0.2 5.3 1.1 7 1.9 6.9 1.3 9.2 1.7 57

80 45 64.4 121.5 26 2.7 15.3 40.1 4.8 26.4 10.5 1 12.7 2.7 16 3.9 12.1 1.9 11.4 1.8

121.5 Mg# 7.0 10.7 5.7 28.9 33.1 63.9 40.7 29.1 35.3 9.7 13.5 16.2 K,O/Na,O 1.4 1.5 1.2 3.2 1.6 5.4 0.9 0.8 1.3 1.7 0.9 0.7 A/CNK 0.8 0.8 1 .o 0.8 0.8 0.5 0.97 1.03 1.09 0.92 1.04 0.97 Sr/Ba 0.2 0.4 0.71 0.74 0.24 0.13 0.27 0.01 WRb 0.1 0.1 0.1 0.0 0.0 0.0 0.02 0.04 0.03 0.05 0.04 0.04 Ga/AI 2.9 2.4 2.5 2.3 2.0 2.9 2.79 2.41 3.71 4.06 3.54 CREE (ppm) 137.6 107.8 679.3 162.4 671.2 453.5 244.5 172.6 128.5 631.6 215.5 282.1 LREE/HREE 70.1 70.1 29.7 248.4 387.4 349.9 36.76 29.92 9.99 13.38 3.6 1.55 Eu/Eu”, 3.0 3.7 0.3 1.1 0.9 1.0 0.79 0.82 0.6 0.5 0.11 0.26 (La/Yb), 6.8 7.2 56.5 21.9 27.0 26.7 108.57 62.44 14.81 20.97 2.21 0.91 Notes: Sample No.1: B90011902A, 2: B90012305A, 3: B90011107B, 4: B90011305D, 5: B90011703A, 6: B90012310C, D.I.=q+ab+or; Fe,O,(T):

as total of Fe,O,, Mg# = 100*(Mg0/40.30)/(Mg0/40.30+Fe,O3(T)*O.9/71.85), and chondrite normalized REE data after Taylor and McLennan (1985). LS: layered syenite, QS: quartz syenite, MS: melanosyenite, and the other symbols are as in figure 1.

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PAN-AFRICAN GRANITOIDS FROM THE S0R RONDANE MOUNTAINS 60 1

16 /

0 35 I 40 45 50 55 60 65 70 75 80

Si02 (wt%)

Fig. 3. Chemical classification diagram of Cox et al. (1979) for early Paleozoic granitoids. The symbols are the same as in figure 2.

Nb and Rb/Sr ratios. In the Harker diagram (Fig. 5), TiO,, FeOt, MnO, MgO and P,O, have negative correlation with SO,, however K,O and A1,0, have significant positive correlation with SiO,. The Lunckeryggen syenitic rocks have the highest fluorine contents (up to 5500 ppm) among the early Paleozoic granitoids. These rocks have high Sr contents (1000-6500 ppm) and have similar Nb depletion (Fig. 7) in the primitive mantle normalized diagram, compared with the syenitic rocks from the Mefjell Plutonic Complex and Yamato Mountains, though they have different anomalies in Sr, P and Zr contents. From layered syenite to melanocratic syenite

p, /

A-type pni$ Igmous cksmoclute i

Nay3+Kp &go

Fig. 4. AFM diagram for the early Paleozoic granitoids. The fields of the A-type granites, igneous charnockites and I-type granites are from Kilpatrick and Ellis (1992) and the field of the Yamato syenite is from Zhao et al. (1995). The symbols are the same as in figure 2.

and quartz syenite, the syenitic rocks show parallel REE patterns and a gradually increasing CREE trend. They have high LREE/HREE ratios and a lack of Eu anomalies in the chondrite normalized REE diagram (Fig. 6).

Group I granites and Group I1 granites

Both the Group I granites and Group I1 granites have a range of SiO, from 64.25 to 79.38 wt.%, high K,O+Na,O concentrations of 6.80-11.40 wt.%. They fall in the alkaline field in the diagram of Cox et al. (1979) (Fig. 3). The Group I granites and Group I1 granites are comparable with A-type granites of Kilpatrick and Ellis (1992). Detailed geochemical features are presented in Li et al. (2001b).

Discussion

Petrogenesis deduced from geochemical characteristics in the alkali granitoids

Diversity of REE patterns and Eu anomalies occurring in the early Paleozoic granitoids indicates heterogenetic source materials and/or different magma processes. In the chondrite-normalized REE diagram, varied REE patterns in the Austkampane granite show lack of variation in LREE/HREE ratios, increasing CREE (284.0 + 573.3 ppm) and more fractionation of plagioclase from melt, then decreasing XREE (118.25 ppm) and weak fractionation of plagioclase with increasing differentiation (66 .94 j73 .62 wt.% in SiO,), indicates fractional crystallization and fractionation of accessory minerals played important roles. The Pingvinane granite however, has distinct REE patterns that show no variation in LREE/HREE ratios, a decreasing trend of CREE and large variation of Eu/Eu” ratios with increase in differentiation (65.28 -+ 68.23 wt.% of SiO,). Furthermore, Eu anomalies (chondrite normalized) varied from 0.119 to 0.499. As suggested by Li et al. (2001b), the geochemical and isotopic features indicate two possibilities of petrogenesis for the Group I granites and Group I1 granites. We favor the interpretation that fractional crystallization of the source materials is a more important process to form the Group I granites.

Petersen (1980) explained the mechanism for the formation of the Kleivan granite from charnockite (moderate LREE fraction with positive Eu anomaly) to hornblende granite (high LREE with negative Eu anomaly) in southwest Norway. In the Mefjell Plutonic Complex, the syenitic rocks have moderate (La/Yb),, and the granites have positive Eu anomaly and high (Lam), ratios with negative Eu anomaly. This reflects that they are derived from different source materials or formed as such

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602 Z:L. L1 ET AL.

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12

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0

8

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\$ ** t

CaO (wt%;

K,O (wt%

A

I I I I I I

40 50 GO 70 80

S i 0 2 (wt%)

2.5

2.0

1.5

1 .o

0.5

MnO (wt%)

0.2 t

0.1

0.0 20

16

12

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4

Q

Na,O (wt%

0-

S i 0 2 (wt%)

15000

10000

5000

0 6000

5000

4000

3000

2000

1000 0

400

300

200

I00

0

20

0

* *

* * " t * * * * * .

* A . " "

*

4

3

2

1

0

50

40

30

20

10

0 6000

5000

4000

3000

2000 1000

0

800

600

400

200

0

P,O, (wt%)

A

40 50 60 70 80 40 50 GO 70 80

S i 0 2 (wt%) S i 0 2 (wt%)

Fig. 5. Harker diagram of (a) SiO, vs. major elements, and (b) SiO, vs. trace elements for early Paleozoic granitoid samples. Symbols are the same as in figure 2.

by successive stages of differentiation. If the syenitic rocks and granites are derived from the same magma source and undergo successive stages of differentiation, the model of differentiation by Petersen (1980) can account for varied REE patterns of the syenitic rocks and granites from the Mefjell Plutonic Complex, because they have similar varied trend of REE patterns.

In the Lunckeryggen Syenitic Complex, parallel REE patterns and a gradually increasing CREE trend, high LREE/HREE ratios and a lack of Eu anomalies in the chondrite normalized REE diagram may support magmatic process of fractional crystallization (Fig. 6). Furthermore, the Lunckeryggen Syenitic Complex has a similar geological affinity with the Group I granites, though the Group I granites shows much higher felsic.

Biotites from the Group I granites and Lunckeryggen syenitic rocks have higher SiO,, F contents, and kg, lower TiO, and log (f,<,J/(f,J ratios compared to the Group I1 granites and Mefjell Plutonic Complex. This reflects change in fluid composition in source materials and/or varied magma processes (Li et al., 2003).

Based on field occurrence, petrography, chemical characteristics combined with isotopic data, as well as wide occurrence of basic dykes after intrusion of early Paleozoic granitoids, we suggest that the mantle-derived, hot basic magma entering into lower crustal or upper mantle level was metasomatised with subduction-related material, or was modified by subduction processes. Subduction processes usually show Nb anomaly on trace element distribution spider diagrams (Fig. 7). This magma, an altered composition, during ascent produced the Lunckeryggen syenitic body and consequently derived the Group I granitic bodies by processes of fractional crystallization with minor assimilation or mixing. The Group I1 granites may be derived from the same hot magma by assimilation with crustal rocks to varying degrees and consequently fractional crystallization in higher crustal levels (ACF model). However, the Mefjell Plutonic Complex seems to be derived from heterogeneous magma sources or through different magma processes. The syenitic rocks from the Mefjell Plutonic Complex have a unique source judging from their chemical data.

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PAN-AFRICAN GRANITOIDS FROM THE SOR RONDANE MOUNTAINS 603

Comparison of the syenitic rocks from the Smr Rondane Mountains and adjacent areas

The early Paleozoic syenitic rocks are one of the characteristic rock types in the SOr Rondane Mountains, as well as in the Yamato Mountains, East Antarctica. Geochemical data from the Lunckeryggen Syenitic Complex compared with the Mefjell Plutonic Complex (Li et al., 2001a) is different. The syenitic rocks from the Mefjell Plutonic Complex show higher values in Zr and K/Rb ratio, lower in Rb and Sr, and similar K contents (4.5-6.0 wt%) compared to the two-pyroxene syenitic rocks from the Yamato Mountains (Shiraishi et al., 1983a, 1983b). Thus, the syenitic rocks from the Mefjell Syenitic Complex seem to have distinct chemical characteristics comparable with those from the Lunckeryggen Syenitic Complex and the Yamato syenite.

Igneous charnocltites, such as from Gjelsvikjella and western Miihlig-Hofmannfjella, Antarctica, are distributed widely towards the west of the area studied. The Gjelsvikjella and western Mdhlig-Hofmannfjella igneous

charnockites, with given age of 500st24 Ma by Rb-Sr whole-rock analysis (Ohta et al., 1990), have similar formation age compared the early Paleozoic granitoids from the Smr Rondane Mountains. They also have Fe-rich mafic minerals of pyroxene, hornblende and biotite (Ohta e t al . , 1990). On the basis of similar chemical characteristics and ages, the syenitic rocks from the Mefjell Plutonic Complex may have chemical and genetic association with the charnockite suits from Gjelsvikjella and western Miihlig-Hofmannfjella.

Summary and Conclusion (1) Comparison of the four groups of the Pan-African

alkali granitoids from the S0r Rondane Mountains yielded differences in mineral and geochemical compositions. The Group I granites show some chemical characteristics similar to the Lunckeryggen Syenitic Complex. The Group I1 granites and the Mefjell Plutonic Complex have different chemical Characteristics. In addition, the chemical characteristics of the Group I1 granites and the Mefjell

1000 Group I granites Mefjell Plutonic Complex

I

Group I1 granites Lunckery ggen Sy enit ic Complex

L! I (d) l 1 1 l I I I l I I I I I l I I I I I ~ l I I I 1 1 1 1 1 1

L a c e PrNdSmEuG TbDyHoErTmYbLu L a c e PrNdSm Eu GdTbDyHoErTmYbLu

Fig. 6. Chondritc normalized REE pattcriis of early Paleozoic granitoids. Normalized valucs after Taylor and McLennan (1985). Symbols arc the same as in figurc 2.

Gondwana Rrscwch, L: 6, No. 4, 2003

604 Z.-L. LI ET AL.

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100

10

1

0.1

100

10

1

0.1

1000

100

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Primordial Mantle Normalized

Average values of Group I and Group I1 granites

Mefjell Plutonic Complex] , , , , , I f , , , j 1 1

PbRbBaThU KNbLaCe SrNd P Zr Ti Y

Fig. 7. Primitive mantle normalized (Sun and McDonough, 1989) spider diagrams for (a) the Group I granites and Group I1 granites, (b) the Mefjell Plutonic Complex, and (c) the Lunckeryggen Syenitic Complex. Symbols in figure 7a are the same as in figure 2.

Plutonic Complex are different, compared to those of the Group I granites and Lunckeryggen Syenitic Complex.

Based on geological and geochemical study, we suggest that the mantle-derived, hot basic magma produced the Lunckeryggen syenitic body and consequently derived the Group I granitic bodies by processes of fractional crystallization with minor assimilation or mixing. However, the Group I1 granites may be derived from the same hot magma by assimilation with crustal rocks and then fractional crystallization (ACF model), The Mefjell Plutonic Complex may be derived from heterogeneity of magma sources or through different magma processes.

(2) A comparison of adjacent areas indicate that the syenitic rocks from the Mefjell Plutonic Complex may have a chemical and genetic association with the charnockite suits from Gjelsvikjella and western Muhlig-Hofmannfjella. They also seem to have distinct chemical characteristics from those of the Yamato syenite.

Acknowledgments We express our sincere thanks to the geologists who

participated in JARE-26, -28, -30 and -31 for their kind permission to use their samples. Li thanks Dr. J. Jacobs (University of Bremen) and an anonymous reviewer for their critical comments and suggestions. Li also thanks Dr. Jim Gleason (Texas, USA)) for improvement of English.

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