Neoproterozoic Deformation in the Radok Lake Region of the Northern Prince Charles Mountains, East Antarctica; Evidence for a Single Protracted Orogenic Event

Precambrian Research 104 (2000) 1–24 www.elsevier.com/locate/precamres

Neoproterozoic deformation in the Radok Lake region of the northern Prince Charles Mountains, east Antarctica; evidence for a single protracted orogenic event

S.D. Boger a,*, C.J. Carson b, C.J.L. Wilson a, C.M. Fanning c

a School of Earth Sciences, The Uni6ersity of Melbourne, Park6ille, Vic. 3010, Australia b Department of Geology and Geophysics, Yale Uni6ersity, New Ha6en, CT 06511, USA c Research School of Earth Sciences, The Australian National Uni6ersity, Canberra, ACT. 0200, Australia

Received 7 May 1999; accepted 14 April 2000

Abstract

Ion microprobe dating of structurally constrained felsic intrusives indicate that the rocks of the northern Prince Charles Mountains (nPCMs) were deformed during a single, long-lived Neoproterozoic tectonic event. Deformation evolved through four progressively more discrete phases in response to continuous north–south directed compression. In the study area (Radok Lake), voluminous granite intrusion occurred at 990 Ma, contemporaneous with regionally extensive magmatism, peak metamorphism, and sub-horizontal shearing and recumbent folding. Subse- quent upright folding and shear zone development occurred at 940 Ma, while new zircon growth at 900 Ma constrains a ﬁnal phase of deformation that was accommodated along low-angle mylonites and pseudotachylites. This ﬁnal period of deformation was responsible for the allochthonous emplacement of granulites over mid-amphibolite facies rocks in the nPCMs. The age constraints placed on the timing of deformation by this study preclude the high-grade reworking of the nPCMs as is postulated in some of the recent literature. Furthermore, 990–900 Ma orogenesis in the nPCMs is at least 50 Myr younger than that recognised in other previously correlated Grenville aged orogenic belts found in Australia, east Africa and other parts of the Antarctic. This distinct age difference implies that these belts are probably not correlatable, as has been previously suggested in reconstructions of the supercontinent Rodinia. © 2000 Elsevier Science B.V. All rights reserved.

Keywords: Northern Prince Charles Mountains; East Antarctica; Granulites; Rodinia; Gondwana; Orogenesis

1. Introduction (nPCMs), has traditionally been considered part of an extensive Neoproterozoic orogenic belt The margin of the east Antarctic craton, includ- (1300–900 Ma) that has been correlated with ing the northern Prince Charles Mountains metamorphic belts of similar age in India, parts of east Africa, Sri Lanka, and Australia (Fig. 1a). * Corresponding author. These belts were thought to represent a major E-mail address: s–[email protected] (S.D. Boger). accretionary system that led to the formation of

0301-9268/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S0301-9268(00)00079-6 2 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 east Gondwana during the growth and consolida- Antarctica (Zhao et al., 1992; Shiraishi et al., tion of Rodinia (Grew and Manton, 1986; Katz, 1994; Hensen and Zhou, 1995; Carson et al., 1989; Moores, 1991; Clarke et al., 1995; Rogers, 1996; Fitzsimons et al., 1997) has lead to a num- 1996). East Gondwana was thought to have then ber of authors questioning the validity of this remained intact and generally internally unde- model. Instead, it has been suggested that east formed until rifting in the Mesozoic (Yoshida et Gondwana may represent a collage of continental al., 1992). However, the more recent recognition fragments that accreted during the Palaeozoic of extensive Palaeozoic tectonism within east (Hensen and Zhou, 1997).

Fig. 1. (a) Traditional reconstruction of Rodinia at 1000 Ma showing the location of East Gondwana within this reconstruction (after Hoffman, 1991; Unrug, 1997). In these models, east Gondwana is inferred to have formed though the accretion of parts of Australia, India and east Africa along a single laterally extensive Meso-Neoproterozoic orogenic belt thought to have rimmed the east Antarctic coastline. (b) Gondwana at 500 Ma with the continents of east and west Gondwana illustrated. The position of the nPCMs is highlighted and enlarged in (c). Traditional models for the construction of Gondwana suggest that it remained intact from Rodinian times and formed a keystone onto which west Gondwana accreted. (c) Expanded section shows the gross geology of the region of interest. NC, Napier Complex; VH, Vestfold Hills; sPCMs, southern Prince Charles Mountains; RC, Rayner Complex; nPCMs, northern Prince Charles Mountains; LHB, Lu¨tzow-Holm Bay; PB, Prydz Bay. The more complicated tectonic frame work arising from the dissection of the Proterozoic mobile belt exposed in the nPCMs by Palaeozoic terrains recognised in Prydz and Lu¨tzow Holm Bays are highlighted. S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 3

The nPCMs, together with the Mawson Coast of Neoproterozoic and possible post-Proterozoic and the Rayner Complex, separate Prydz and orogenesis in the nPCMs are assessed. Lu¨tzow-Holm Bays (Fig. 1c). With the recognition of high-grade Palaeozoic tectonism within these terrains, the nPCMs has received consider- 2. Regional geologic setting able attention regarding the extent of possible Palaeozoic reworking. A number of authors have The nPCMs are exposed as a series of isolated postulated that a late Proterozoic to early inland ranges and massifs located on the western Palaeozoic accretionary belt may have linked margin of the Amery Ice Self (Fig. 2). They form Prydz and Lu¨tzow-Holm Bays (Kriegsman, 1995; part of an east–west trending orogenic belt, dom- Hensen and Zhou, 1997) effectively crossing the inated by granulite facies felsic and mafic gneisses, nPCMs–Mawson Coast–Rayner Complex re- interleaved with subordinate metasedimentary gion. Within the nPCMs, this inference has been and calc-silicate units (Crohn, 1959; Tingey, 1982, supported by Sm–Nd age data presented by 1991; McKelvey and Stephenson, 1990; Fitzsi- Hensen et al. (1997) from which they infer two mons and Thost, 1992; Thost and Hensen, 1992; significant tectonothermal events overprinting the Kamenev et al., 1993; Hand et al., 1994b). The widely recognised 1000 Ma orogen; one at sequence as a whole was intruded episodically by 800 Ma and a second at 630–500 Ma. significant volumes of granitic and charnockitic Similarly, Scrimgeour and Hand (1997) suggest magma, as well as by locally derived partial melts that the complex pressure–temperature paths ob- (Munksgaard et al., 1992; Sheraton et al., 1996; served along the eastern edge of the nPCMs Kinny et al., 1997; Zhao et al., 1997). At Beaver reflect thermal interference between two unrelated Lake (Fig. 2), the high-grade gneisses are overlain tectonic events. They infer that 1000 Ma tec- by relatively undeformed Permo-Triassic sedi- tonism is overprinted in the east by the affects ments (Crohn, 1959; Mond, 1972; Webb and of 550–500 Ma orogenesis recognised to the Fielding, 1993; Fielding and Webb, 1995, 1996; northeast in Prydz Bay. These studies contrast McLaughlin and Drinnan, 1997a,b). These are with that of Kinny et al. (1997), who argue that thought to lie in a sub-basin on the western side the lack of new zircon growth or Pb-loss discon- of the Lambert Graben, an inferred rift system cordia post-dating 1000 Ma indicate that that separates the nPCMs from the Palaeozoic late Proterozoic to early Palaeozoic tectonism in (ca. 550–500 Ma) granulite facies terrain of Prydz the nPCMs was of relatively minor importance. Bay (Ren et al., 1992; Zhao et al., 1992; Carson et This interpretation is more consistent with earlier al., 1995; Dirks and Wilson, 1995; Harley and studies from the area (Tingey, 1982, 1991; Man- Fitzsimons, 1995; Hensen and Zhou, 1995; Car- ton et al., 1992). These different hypotheses arise son et al., 1996; Fitzsimons, 1997; Fitzsimons et primarily due to a paucity of structurally well- al., 1997). To the north and west of the nPCMs, constrained geochronologic data from the the extent of the terrain is unconstrained. How- nPCMs, an issue that we have aimed to address in ever, it probably extends to at least the Mawson this study. Coast (Fig. 3), where rocks of similar age and In this paper, we refine the temporal framework grade are exposed (Young and Black, 1991; of high-grade deformation and metamorphism in Young et al., 1997), and has been tentatively the nPCMs. We describe the sequence of high- correlated with the Rayner Complex still further grade structural events recognised, and couple our to the west (Black et al., 1987). The terrain is geometric observations with structurally con- bounded in the south by exposures of older strained geochronological data obtained from fel- Meoproterozoic volcanics at Fisher Massif sic intrusives and locally derived leucosomes. New (Kamenev et al., 1993; Beliatsky et al., 1994; SHRIMP age data from four structurally con- Mikhalsky et al., 1996; Kinny et al., 1997; Laiba strained samples collected in the vicinity of Radok and Mikhalsky, 1999), and by granitic Archaean Lake are presented, and the relative contributions basement complex overlain by two or more super- 4 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

Fig. 2. Schematic map of the northern Prince Charles Mountains showing the study area, extent of outcrop and the distribution of the Proterozoic basement and Permo-Triassic strata. Localities of existing U–Pb zircon geochronolgical data are also illustrated. Data from Mt McCarthy, Loewe Massif, Mt Collins and the Fisher Massif are after Kinny et al. (1997); data from Jetty Peninsula are after Manton et al. (1992). Locality of cross-section illustrated in Fig. 3 is also shown. Insert shows the geographic position of the northern Prince Charles Mountains along the western margin of the Amery Ice Self. Mawson and Davis refer to Australian Antarctic Stations.

crustal sequences in the southern Prince Charles (Hand et al., 1994a; Nichols 1995; Scrimgeour and Mountains (Grew, 1982; Tingey, 1982, 1991; Hand, 1997). Kamenev et al., 1993). The earliest geochronological data from the Previous studies have established that the Prince Charles Mountains were reconnaissance nPCMs attained granulite facies metamorphic Rb–Sr ages obtained by Arriens (1975). Whole conditions of approximately 800°C and 6–7 kbar rock isochrons presented by Arriens (1975) yield (Fitzsimons and Thost, 1992; Fitzsimons and ages of 1000 Ma, whereas mineral dates (biotite Harley, 1994a,b; Hand et al., 1994a; Scrimgeour and muscovite) produced ages that clustered and Hand, 1997), and followed a retrograde path dominated by cooling (Fitzsimons and Harley, around 500 Ma. On the basis of these results, 1992; Thost and Hensen, 1992; Fitzsimons and Tingey (1982, 1991) suggested that high-grade Harley, 1994a,b; Stephenson and Cook, 1997). In metamorphism in the nPCMs occurred at 1000 the southern and eastern parts of the nPCMs, Ma, overprinted by a widespread but relatively these cooling trajectories are thought to be over- low-grade thermal event recorded by mica systems printed by a subsequent phase of decompression at 500 Ma. S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 5 ) for all observed structures. 3&4 is dominant. Equal area stereographic projections summarise structural data 3 shear zones, where S 3 ) and combined foliation and lineation data (D 2&3 ), fold axis (F 1 is the dominant form surface illustrated, except in D 1 and illustrate lineation (L Fig. 3. Cross-section through(bottom). the S outcrop exposure at Radok Lake showing the extent of outcrop (top) and the distribution of rock types and the observed structure 6 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

More recent conventional and SHRIMP (Sensi- Harley, 1992; Thost and Hensen, 1992), and at tive High Resolution Ion Microprobe) dating of Else Platform located approximately 75 km to the zircon has yielded results consistent with the ini- northeast (Hand et al., 1994b). An outline of the tial ages obtained by Arriens (1975). Manton et structure at Radok Lake was also presented by al. (1992) reported upper intercept ages of 1000+ McKelvey and Stephenson (1990). All previous 14/−11 Ma (orthogneiss) and 940+27/−17 Ma studies describe a pervasive layer-parallel folia- (leucogranite) from rocks outcropping at Jetty tion, folded initially into isoclinal layer-parallel Peninsula (Fig. 3). The former age is interpreted folds, which were subsequently reoriented about as dating granulite facies metamorphism (Manton upright east–west trending folds, and then trans- et al., 1992). U–Pb SHRIMP dating by Kinny et posed into east–west trending steeply dipping al. (1997) has produced ages for felsic intrusives at high-strain zones. The different fold and foliation Loewe Massif (980921 Ma), Mt Collins (9769 nomenclature used by previous authors is summa- 25, 98497 and 984912 Ma) and Mt McCarthy rized in Table 1. An identical sequence of struc- (990930 Ma). The intrusive ages from all locali- tures observed during this study is described in ties are statistically identical, and are interpreted the following. In addition, a later phase of dis- to suggest that the nPCMs experienced a wide- crete mylonitisation was recognised, and is de- spread magmatic event that occurred concurrently scribed in this paper. All structural relationships with regional high-grade metamorphism (Kinny et and orientation data are illustrated in Fig. 3, a al., 1997). schematic cross-section through the basement ex- Younger zircon and monazite ages of about posures at Radok Lake. 550–500 Ma were obtained by Manton et al.

(1992) from minor pegmatites and granites crop- 3.1. D1–2 deformation ping out at Jetty Peninsula. These are the only reported U–Pb ages younger than 940 Ma The earliest recognised fabric element is a com- from the nPCMs. They are similar to Rb–Sr posite S0/S1 fabric deﬁned by an intense and mineral isochron ages of about 480 Ma and the pervasive preferred mineral orientation, which is projected lower intercept ages of some zircon always concordant with lithological layering (S0). discordia obtained by Manton et al. (1992), both This fabric deﬁnes the dominant foliation surface of which were interpreted as reset ages associated in the nPCMs (Fitzsimons and Thost, 1992; Thost with granite and pegmatite emplacement. Else- and Hensen, 1992; Hand et al., 1994b), and char- where in the nPCMs, two-point Sm–Nd garnet- acteristically contains a well-developed east– whole rock and garnet-matrix ages from a variety northeast (ENE) trending L1 lineation (Fig. 3). of rock types form two age groupings at 800 Although overprinted by two episodes of folding and 630–550 Ma (Hensen et al., 1997). The (D2 and D3), S1 is well preserved and only weakly 800 Ma ages are more prevalent in the west of the overprinted by the development of new fabrics nPCMs, while the younger 630–550 Ma ages associated with subsequent folding. come predominantly from the east. Hensen et al. D2 resulted in the reorientation of the com-

(1997) interpreted the Sm–Nd ages as dating posite S0/S1 fabric about recumbent, isoclinal F2 high-temperature thermal events post-dating the folds. Although folding S0/S1 isoclinally, there is 980 Ma magmatism recorded by zircon. little development of an axial planar fabric.

Rather, S1 remains the predominant foliation, potentially intensiﬁed on the limbs of F2 folds, 3. Structure where its orientation is parallel to the F2 axial plane. Large-scale F2 folds were not recognised, Detailed structural studies within the nPCMs but were inferred, as mesoscale F2 isoclinal folds have previously centred upon the Aramis, Porthos are common with type-three F2 and F3 fold inter- and Athos ranges approximately 100 km to the ference patterns (Ramsay, 1967) recognised in D3 northwest of Radok Lake (Fitzsimons and low-strain zones. F2 folds form about ENE trend- S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 7

ing axes that parallel the L1 lineation (Fig. 3). The dence of this recognised at Radok Lake. Kine- formation of an L2 lineation is not recognised, matic indicators such as asymmetric F2 folds were although the development of such a lineation found on outcrop surfaces normal to the lin- cannot be precluded. If present, L2 was of the eation, while F2 and F3 (described below) are all same grade and formed parallel to and potentially coaxial, the latter event clearly having developed in response to north–south directed shortening. intensified L1 so that the two were indistinguishable. The formation of both a flat-lying foliation Furthermore, the recent work of Passchier (1997) describes the development of orthogonal lin- (S1) and recumbent fold closures (F2) is potentially consistent with ongoing dominantly sub- eation–transport direction relationships under horizontal simple shear. Indeed granulite facies non-ideal simple shear conditions, consistent with the overall deformational environment envisaged assemblages define both the S1 foliation and, for D1–2. where developed, the subtle S2 fabric. Addition- ally, F2 folding has formed coaxially with the 3.2. D3 deformation lineation (L1) (Fig. 3). Although the rotation and transposition of lithological layering (S ) into par- 0 D was responsible for the major east–west allelism with S may represent the preservation of 3 1 trending structural grain and the gross geometry an otherwise overprinted prograde history, the observed in the nPCMs. D folded the composite similarity in metamorphic grade and the coaxial 3 S /S surface (and D structures) into a series of nature of the structures suggests that a progres- 0 1 2 meso- to macroscale upright F3 fold closures (Fig. sive evolution from D1 to D2 is more likely. A 4a). Folding occurred in response to broadly similar conclusion was drawn by a number of north–south directed compression, producing a previous structural studies from the region (Fitzsi- series of ENE trending folds that are parallel to mons and Harley, 1992; Thost and Hensen, 1992; both the F2 fold axes and the L1 stretching lin- Hand et al. 1994b). eation (Fig. 3). F3 folds plunge moderately to Tectonic transport during D1–2 is inferred to shallowly, to either the ENE or WSW (Fig. 3). have been north–south directed, perpendicular to However, with ongoing shortening, the increase in the lineation orientation and the F fold axis. 2 D3 strain is accompanied by a localised decrease Although lineations are commonly inferred to in fold wavelength and an increase in D3 fold parallel the transport direction, there is no evi- plunge. A weak axial planar S3 foliation is dis-

Table 1 Summary of the nomenclature used to describe the deformational features observed throughout the northern Prince Charles Mountains

AuthorFormation of Isoclinal Steeply dippingUprightfolding Low-angle discrete regional gneissic shear zone mylonite andrecumbent formationlayeringfolding pseudotachylite formation

D3 D4D3D2D1Thisstudy 1 D SrmeuadHand (1997)D1 D2Scrimgeourand D3 D4 D1/MY1 D2Nichols(1995) D3 MY2 MY3 1 D Hne al. (1994b)D1 D1Handet D2 D2 D3 Thost and Hensen (1992) D5D1–D2–D3 D6D4D5 Fitzsimons and Thost (1992) D1–D2–D3 D4 D5 D6 D7–D8 1 D 3cevyn Stephenson D1 D2 D3McKelveyand (1990) 8 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

Fig. 4. Structural and intrusive features from Radok Lake: (a) upright west-plunging F3 antiform; (b) D3 upright high-strain zone; (c) photomicrograph of coplanar D4 pseudotachylite and mylonite; (d) reverse offset-D4 mylonite with subtle drag folding on upper surface; (e) concordant intrusive contact between syn-D2 granite (distinctive pale unit) and host lithologies (sample 9628-141); (f) orthopyroxene bearing leucosome localised within D3 boudin neck (sample 9628-73); (g) clinopyroxene bearing leucosome formed concordant with, but locally cross-cutting S0/S1 foliation within amphibolite-facies intermediate and felsic orthogneisses.

cernible in some F3 closures. However, the devel- S1. However, continued localisation of strain opment of S3 is generally restricted to the limbs of within D3 shear zones has locally overprinted the F3 folds where discrete D3 high-strain zones are gneissic S3 foliation with a mylonitic to ultramy- developed. lonitic fabric. The mylonitic fabric is deﬁned by a

D3 high-strain zones (Fig. 4b) are tens to hun- deformation-induced grain size reduction and by dreds of metres in width. Within these zones, S3 is the growth of new, lower grade metamorphic generally indistinguishable in appearance from S0/ assemblages (Hand et al., 1994a; Nichols, 1995; S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 9

Scrimgeour and Hand, 1997). In the vicinity of immediately adjacent to, the mylonite zones.

Radok Lake, D3 high-strain zones are orientated Thus, the textural evolution of the nPCMs parallel to the S3 axial surface, trending ENE and ﬁnished with the cessation of D3 and resulted in dipping steeply to the north. Elsewhere in the the preservation of granulite facies metamorphic nPCMs, some D3 high-strain zones can dip textures formed during D1–3. steeply to the south (for example, Hand et al., D4 mylonites generally trend northwest, and

1994b). The S3 foliation contains a steeply plung- form a moderately northeast and southwest dip- ing L3 stretching lineation (Fig. 3) while S–C ping conjugate set (Fig. 5). Offset marker hori- fabric relationships and offset leucosomes show zons and parasitic drag folds show reverse offset lineation-parallel, reverse kinematics. Although (Fig. 4d), while palaeostress analysis suggest that large and regionally significant features, it is un- D4 formed in response to NNE–SSW-directed likely that D high-strain zones accommodate sig- compression (Fig. 5). Offset on most mylonites is 3 B nificant movement as there are no observed or typically minor ( 2 m). However, a major flat- reported changes in metamorphic grade across lying D4 mylonite zone exposed along the western these structures. shore of Radok lake juxtaposes granulite facies gneisses over amphibolite facies interlayered felsic The accommodation of D3 strain by upright folding, then shearing along steeply dipping high- and intermediate orthogneisses (Fig. 4). The felsic strain zones is consistent with a transition during orthogneiss consists of equigranular quartz, K- feldspar and plagioclase. The intermediate or- D3 from dominantly pure shear flattening to dominantly vertically oriented simple shear. This tran- thogneisses are composed of weak to randomly orientated biotite and fine-grained quartz inter- sition is manifested by the development of an grown with coarse grained plagioclase. Euhedral intermediate non-coaxial pure shear regime in hornblende, green in hand specimen and thin which the F fold axes were rotated toward a 3 section, may occur in the matrix, although it more vertical stretching axis, reflected by the observed commonly forms a reaction rim separating the increase in F fold plunge (Fig. 6). 3 felsic and mafic bands. Sphene typically occurs along grain boundaries between biotite and il- 3.3. D deformation 4 menite, while chlorite partially to completely pseudomorphs biotite. Clinopyroxene is also lo- Deformation post-dating D3 folding and up- cally observed in the leucosomes, where it is gen- right shear zone development is characterised by erally rimmed by green hornblende. In contrast to the formation of low- to moderate-angle my- the overriding units, these rocks do not contain lonites and coplanar pseudotachylites (Fig. 4c,d). garnet, orthopyroxene or brown hornblende, or With the exception of minor drag folds, D4 my- relics thereof, minerals that are ubiquitous in the lonites do not reorient earlier high-grade fabric granulites typical of the nPCMs. They contain no elements. They form discrete localised zones of evidence of ever undergoing granulite facies meta- deformation up to 100 mm in width, typically morphism and are considered possible equivalents defined by biotite and quartz. The presence of of the lower grade rocks exposed at Fisher Massif coexisting garnet and sillimanite, and/or green to the south. Shear sense indicators suggest hornblende within some D4 mylonites, is consis- thrusting involved emplacement of the granulites tent with their formation under amphibolite facies to the south, consistent with this interpretation, conditions, at temperatures, at least initially, in whilst the juxtaposition of granulites over lower excess of 520°C (i.e. within the stability field of grade rocks at Radok lake implies that at least in sillimanite). The development of coplanar pseudo- the southern portion of the nPCMs may be al- tachylites was probably a function of strain rate lochthonous. This is an interpretation first for- (Hobbs et al., 1986), and the anhydrous nature of warded by Manton et al. (1992) to explain the the granulite facies host rocks (Camacho et al., presence of As, Mo, Be and B in post-orogenic 1995). The overprinting of earlier textural rela- hydrous pegmatites outcropping at Jetty tionships by D4 is limited to areas within, or Peninsula. 10 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

+ 206 + 207 + vidual sectioned zircons. Zr2O , Pb , Pb , 208Pb+, 238U+, 232ThO+, and 238UO+ were measured in cycles by magnetic ﬁeld switching, seven cycles per data set. Analysis of unknowns was interspersed with analyses of the standard SL13 (which has a radiogenic 206Pb/238U ratio of 0.0928) in order to monitor the differential frac- tionation between U and Pb. Radiogenic Pb compositions were determined after subtracting contemporaneous common Pb as modelled by Cumming and Richards (1975). All reported ages are based on 207Pb/ 206Pb ratios corrected for common Pb by the 204Pb technique (Compston et al., 1984, 1992). Ages presented in the text are stated with 2| conﬁdence limits.

Fig. 5. Equal area stereographic projections of mylonite plane and contained lineation data (top), and palaeostress reconstructions after the technique of Oncken (1988) (bottom), relating to D3 and D4.

4. Analytical procedure

Zircons for SHRIMP analysis were separated by standard heavy liquid and magnetic proce- dures, and then by hand picking. They were then mounted in epoxy resin discs along with fragments of zircon standard SL13. The discs were polished and Au coated before being analysed on either the SHRIMP I or SHRIMP II (sample 9628-142) ion-microprobe at the Australian Na- tional University, Canberra. Cathodoluminescent (CL) imaging was conducted to assess the internal structure of the unknown zircons from which selected zircon domains were analysed for U, Th and Pb isotopic composition. A primary beam of Fig. 6. Interpretive cartoon illustrating the evolution of the − O ions was used to sputter positive secondary strain regime during deformation in the Radok Lake area of ions from areas 25 mm in diameter from indi- the nPCMs. S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 11

5. Geochronological results rounded terminations inferred to reflect partial metamorphic resorption. 5.1. K-Feldspar granite — west wall of Radok The isotopic data for the zircons from sample lake (sample 9628-141) 9628-141 are presented in Table 2. Twenty zircon grains were analysed, of which all but two analy- 207 206 Sample 9628-141 represents one of a number ses produce a concordant mean Pb/ Pb age of granitic sheets containing quartz, pink K- of 990918 Ma (mean square of weighted devi- feldspar, minor garnet and biotite, as well as ates (MSWD=1.13)) (Fig. 8a). The discrepant accessory apatite and zircon. Equivalent granitic analyses, 3.1 and 20.1, were both highly discor- bodies at Radok lake vary in width from one to dant (61 and 50%, respectively) and are inter- several hundred metres, and are part of a suite preted as the result of partial Pb loss. The of K-feldspar granites that form the most volu- concordant age given by the remaining 18 analy- minous intrusive bodies observed in the vicinity ses is interpreted as the crystallisation age of the of Radok Lake. They occur on either side of the granite and is considered, to constrain D2,to Battye Glacier, at Fox Ridge and at Manning have occurred at 990 Ma. Massif (Fig. 2), and vary from coarse grained and megacrystic, to finer grained and equigranu- 5.2. K-Feldspar granite — west wall of Radok lar. lake (sample 9628-142) The sampled granite (sample 9628-141) forms a sheet that has concordant boundaries with the Sample 9628-142 was collected from a 1–2 m wide, coarse-grained, sub-vertically orientated surrounding host lithologies and the S0/1 foliation (Fig. 5e). It contains a well-developed layer-par- ENE-trending granitic dyke located along the allel foliation reoriented by upright folding (F3). west wall of Radok Lake (Fig. 3). The dyke The foliation within the granite does not define intruded along the axial surface of an F3 fold, is

F2 fold closures, nor were recumbent folds (F2) unfoliated, cross-cuts structures developed during recognised within, or deﬁned by, any of the F3 folding, and is offset by later D4 mylonites. granites of this generation. We therefore con- The dyke contains quartz, pink K-feldspar, mi- clude that granite emplacement did not precede nor garnet and biotite, and accessory apatite and deformation as the granites do not preserve the zircon. It is very similar in both colour and min- earliest structures recognised in their host litholo- eralogy to the more volumetrically signiﬁcant gies, but clearly pre-date D3 as they are folded pre-D3 sills (sample 9628-141) already described. by this event. Thus, these granites are interpreted The intrusion of sample 9628-142 is inferred to to have intruded synchronously with D1–2. have occurred late-syn- to post-D3 and is consid- Zircons from sample 9628-141 are orange and ered to place a minimum age on the timing of translucent, and form a subhedral to anhedral D3 fold development. population of uniform size. Average elongation Zircons from sample 9628-142 are orange ratios of 1:1–2:1 are observed for grain lengths and translucent, and are similar in appearance between 150 and 200 mm. The zircons typically to those from sample 9628-141. They form a contain 200–500 ppm U, with a Th/U ratio be- euhe-dral to subhedral population of varying tween 0.5 and 0.9. Zircons can show some inter- grain size. Zircons vary from 200 to 400 mmin nal sector zoning that occasionally mantles small length, and have length:width ratios of approxi- detrital cores (Fig. 7a), which were not analysed mately 2:1. However, longer grains with elonga- during this study. The zircons generally lack tion ratios up to 4:1 do occur. The zircons from overgrowths but, where rims do exist, they are this sample can show internal sector zoning as discontinuous, highly luminescent, and too nar- well as planar growth bands (Fig. 7c), although row for analysis (Fig. 7b). A simple igneous they mostly do not show much internal structure. origin is inferred for these zircons, with the Rare rounded detrital cores are found in some 12 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 9 Pb 206 / Pb 207 1058 59 87 888 25 103 1069991 74 83 862 52 92 89 112 943924 16943 14 103 101 916 10 102 18 97 949 25 97 9041010 83 501019 102 98 77989 88 13 95 994933 31 41 98 102 974976 25 28 95 104 1102910 132 92 17 107 U 235 / Pb 963 934 908 963 929 943 906 928 958 896 914 982 902 931 956 948 939 999 1042 955 207 99 U 238 / Pb 206 946 38 963 1003 50 94 0.0032 883 28 879 8700.0018 102 102 0.0015 941 12 941 941 45 100 Pb 206 / Pb 207 0.088 0.0704 0.036 0.0696 0.0008 921 18 921 922 22 100 0.038 0.075 0.0029 530 9 641 1055 79 50 9 U 235 / Pb 0.525 0.039 0.0711 0.0008 932 19 940 959 22 97 1.3026 0.202 0.080 0.0060 722 87 847 1191 157 61 1.477 0.8795 207 9 0.0034 0.0150 U 238 / Pb a 206 0.01 0.14086 0.0119 1.5316 0.141 0.075 0.0027 890 67 0.0l 0.1637 0.0047 1.631 0.055 0.0723 0.0011 977 26 0.01 0.16220 0.0041 1.6295 0.060 0.073 0.0018 9989 22 0.01 0.1696 0.0031 1.676 0.041 0.0717 0.0010 1010 17 0.59 0.14680 0.0046 1.3772 0.063 0.020.06 0.1558 0.1527 0.0034 1.445 0.038 0.0687 0.0008 9160.08 19 0.1572 0.0021 1.527 0.041 B 0.02 0.1627 0.0036 1.582 0.039 0.0705 0.0006 972 20 1.360.08 0.11844 0.15389 0.0030 1.58110.54 0.058 0.075 0.16136 0.0031 0.0021 1.5080 922 0.090 0.068 17 0.0022 964 17 0.02 0.1535 0.0036 1.497 0.041 0.0707 0.0009 921 20 0.190.15 0.15210 0.0081 0.15806 1.51370.20 0.0064 0.094 1.5824 0.15304 0.072 0.079 0.0090 1.4596 0.073 O.0018 913 0.109 0.069 46 0.0027 9150.06 50 0.02 0.15520.01 0.0033 0.15090.02 1.495 0.16140.07 0.00350.02 0.0033 1.486 0.034 0.1575 1.569 0.1477 0.0699 0.0034 0.0338 0.1535 0.0032 1.558 0.034 0.0714 0.0005 0.0032 1.417 0.0705 930B 0.036 0.0006 0.035 906 0.0718 0.0004 0.0696 18 985 0.0004 20 0.0008 943 925 19 888 19 970 954 18 16 980 93 13 98 B 0.380.23 0.153390.21 0.14884 0.00270.02 0.0074 1.44662.49 0.16187 1.5016 0.15724 0.049 0.0061 0.08561 0.099 0.0048 1.5833 0.068 0.0016 1.5634 0.073 0.074 0.0019 0.050 0.071 0.0027 920 0.072 894 0.0017 15 0.0005 967 908 42 941 34 881 964 27 956 58 105 490.19 101 0.22 0.1596 0.0033 0.1542 1.543 0.0052 1.522 0.046 0.0701 0.057 0.0716 0.0014 954 0.0009 925 18 29 B 0.02 0.1702 0.0121 1.790 0.181 0.0763 0.0048 1013 67 0.02 0.1632 0.0046 1.561 0.047 0.0894 0.0006 975 26

) bhpm f206 (%) Radiogenic ratiosPbTh(ppm) Ages (Ma) Concordance (%) 205 /

) ) Pb 0.00002 0.00012494 0.20 0.16355 0.0032 1.5943 0.044 0.071 0.0012 976 18 90 9490.00001233 0.02 36 0.1532 103 0.0033 1.497 0.036 0.0709 0.0006 919 19 929 955 18 96 0.00005 0.00031 0.00001 0.00011 0.00001339 0.020.00020506 0.10014 0.35 0.0083 1.6507 0.16589 0.094 0.0058 0.5540 0.075 0.072 0.0013 0.068 958 0.0019 46 989 990 310.00003 1082 9520.00001297 0.020.00001 36 8670.00005273 0.1573 90 0.09 0.00330.00004 58 1.512 0.1546 114 0.0035 0.036 1.483 0.06970.00001158 0.02 0.038 0.0006 0.0696 942 0.1509 0.0007 0.0036 19 926 1.500 935 0.050 19 920 923 0.00721 0.0014 916 17 906 102 21 21 930 101 989 39 92 0.0000 0.00011178 0.200.00014 0.000231216 0.15105 0.39 0.00640.00001 1.5048 0.16874 0.0067 0.093 1.6880 0.072 0.078 0.0029 0.072 907 0.0014 1005 36 932 37 1003 993 999 84 91 39 101 0.00011 0.00007359 0.12 0.1621 0.0050 1.548 0.053 0.0693 0.0006 968 28 949 906 25 107 0.00000 0.00002507 0.03 0.1535 0.0054 1.510 0.057 0.0713 0.0007 921 30 934 967 20 95 0.00001 0.00004321 0.07 0.1545 0.0056 1.456 0.059 0.0683 0.0009 926 32 912 878 27 106 204 Pb (ppm) 8.22286 384.1212 226 492.1284 48 0.00013 0.22 0.15783 0.0081 1.6774 0.098 0.072 0.0021 945 45 961 1000 61 95 7.51460 978.1521 49 9610 330 6916.1407 394 4.41365 849.1481 north wall of Battye Glacier UU(ppm) / — west wall of Raclok Lake west wall of Radok Lake 0.88 0.80 0.88 0.81 0.76 — — 157 0.79 35 0.00001 239 0.48 845.1 189 0.81 413.1 335 1.11 54205 0.00034 0.89 42 0.00009 229 0.62 58 0.00003 189 0.66 39 0.00080 673 1.98 76 0.00001 158169 0.84 32290 0.50 588.1 0.57 0.00000 8911.1 341291 1.03 64249 0.98 556.1 0.91 0.00001 499.1 208 1.32 283.1 299 0.07 366 0.00145 233149 0.58 6674 0.84 3114.1 0.00012 0.06 19417.1 300225 0.44 106 0.63 587.1 0.00000 359389 0.71 80 0.77 8110.1 0.00013 449204 0.70 110 0.64 5013.1 0.00001 bearing leucosome - feldspar granite feldspar granite - - K K ( ( Opx ( 196 301 340 331 371 339 2642.1285 222 0.84 231 189 342 324 340 404 675 251 4434 340 509 639 363

141 142 73 - - -

9628 9628 9628 1.1 1.1 1.1 4.1 6. 1 3.1 Sample 7.19.1 10.112.1 550.53181 640.96328 5.17.110.1 20811.112.1 322 182 2842.1 143 0.87 262 36 0.45 601.03333 0.92 53 0.00001 0.00001 500.47159 4.1 Sample 13.115.118.1 48919.120.1 405 709 2684 381 0.83 118 85 430.49124 0.54 0.04 121 0.00022 0.00012 6.18.1 540.61206 11.1 12.1 600.72260 Sample Grain.spot Th Table 2 U–Th–Pb isotopic compositions of zircons from the northern Prince Charles Mountains S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 13 125 88 9 84 40 Pb 206 / Pb 899 54 111 207 1048 741069 84 67 87 843932 551001 29 115 109 20907 103 32 99 U 235 / Pb 966 929 973 929 987 1025 903 207 9 Pb ratio; for % Concordance, 100% denotes a concordant U 206 / 238 / Pb Pb 204 206 0.0091 424 24 937 2476 98 17 9 Pb 206 / Pb 0.0704 0.0008 940 22 940 939 22 100 207 0.1620 0.044 9 U 235 / Pb 207 0.0029 1.633 0.084 0.0707 0.0024 996 16 983 950 70 105 9 U 238 / Pb 206 0.1674 0.01 0.1509 0.0041 1.562 0.053 0.0709 0.0014 958 23 955 953 40 100 0.01 0.1602 0.0043 1.584 0.049 0.0717 0.0009 958 24 964 978 27 98 0.01 0.1389 0.0079 1.517 0.136 0.0792 0.0049 839 45 937 1177 128 71 0.01 0.1461 0.0026 1.495 0.062 0.0742 0.0028 879 15 0.0l 0.1553 0.0031 1.607 0.065 0.0750 0.0025 931 17 0.01 0.17430.010.01 0.0104 0.15250.01 1.743 0.1500 0.0059 0.0044 1.558 0.107 1.433 0.0725 0.071 0.050 0.0741 0.0007 0.0693 1038 0.0015 0.0011 915 57 901 33 954 25 1044 0.22 0.1671 0.0072 1.590 0.084 0.0890 0.0018 996 40 B 0.05 0.1570 0.0040 1.523 B B 0.10 0.0879 0.0040 1.516 0.131 B B 0.32 0.1615 0.0036 1.496 0.054 0.0672 0.0017 968 20 0.040.58 0.1699B 0.0047 0.1971B 1.642B 0.0091B 1.903 0.053 0.0701 0.123 0.0700 0.0026 1011 0.0028 1160 26 49 1082 929 Pb that is common Pb; correction for common Pb was made using the measured 206

Pb f206 (%) Radiogenic ratios) Ages (Ma) Concordance (%) 205 / Pb 0.00013 0.00000443 .00062121. 89 0.000000.6829142718.1 0.00000 0.00005305 0.060.00000 0.00012497 0.1396 0.21 0.0072 1.312 0.1687 0.0057 0.077 1.898 0.0682 0.074 0.0015 0.0730 842 0.0018 41 1005 851 31 1008 874 1013 47 96 50 99 0.00002 0.000463915 0.780.00000 0.09710.00021235 0.35 0.00320.00000 0.909 0.1837 0.048 0.0102 1.732 0.0879 0.102 0.0026 597 0.0884 0.0010 19 1087 865 56 965 1021 881 80 89 31 123 204 11 0.00000 01.45254 10112.1485 216 Pb (ppm) west wall of Radok Lake UU(ppm) / — 0.55 level; f206% denotes the percentage of | 323 0.70 73 0.00004 328 0.74 7316.1 422 0.76 90 0.00003 58 0.59 11 0.00006 13939135 0.46 0.595.1 504.1 13 0.27 977.1 5648124 1.70185 17 0.01528 0.51 40510.1 60 0.79 0.00019 1.07 5713.1 107 0.00034 0.00000 135 0.45 60 0.00020 Th (ppm)Grain.spotTh ) 100 are reverse discordant. Cpx bearing leucosome ( \ 277 553 621.1 34 0.55 97 140 6780 0.00020 0.34 0.1615 0.0031 1.522 0.056 0.0684 0.0020 965 17 939 879 61 110 79 242 495 256 309

196 - Continued

9628 Uncertainties given at the 1 a 14.1 0.07461 0.1558 0.0090 1.505 0.090 0.0701 0.0008 933 50 932 830 23 100 15.117.1 450.57157 Sample analysis. Values 2.1 3.16.18.1 270.77108 170.4742 9.111.1 15.1 1242 405 560.50132 0.33 14.1 16.1 Table 2 ( 14 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 grains and have not been analysed in this study. Twelve zircons were analysed from sample Overgrowths are generally lacking. Zircons from 9628-142. All 12 analyses form a statistically sim- this sample have U contents of 200–5000 ppm ple concordant population yielding a mean 207Pb/ with a Th/U ratio of between 0.5 and 2.0. Most 206Pb age of 936914 Ma (MSWD=1.5) (Fig. grains having a ratio of 1.0. 8b). This age is interpreted to date the timing of

Fig. 7. Cathodoluminescence images of representative zircon morphologies: (a) sample 9628-141, analysis points 10.1 and 18.1; (b) sample 9628-141, analysis points 7.1, 8.1 and 9.1; (c) sample 9628-142, analysis points 5.1 and 12.1; (d) sample 9628-73, analysis points 10.1 and 11.1; (e) sample 9628-73, analysis point 12.1; (f) sample 9628-196, analyses points 13.1 and 14.1; (g) sample 9628-196, analysis points 3.1 and 4.1; (h) sample 9628-196, analysis point 11.1. S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 15

Fig. 8. U–Pb concordia diagrams showing SHRIMP data for samples from Radok Lake. 206Pb/207Pb ages are stated to 2| (95%) confidence limits, while the illustrated error ellipses reflect 1| confidence limits (68%). MSWD, Mean square of weighted deviates. Histograms show the distribution of individual analyses and highlight the single zircon population found in samples 9628-141, 9628-142 and 9628-73 compared with the two populations found in sample 9628-196.

crystallisation of the granite, and suggests D3 shear zone on the north side of the Battye Glacier folding occurred at, or prior to, 940 Ma. (Fig. 3). The leucosome is unfoliated and is localised within the neck of a boudin formed as a

5.3. Orthopyroxene-bearing leucosome — north result of D3 shearing (Fig. 4f). We infer that the wall of Battye Glacier (sample 9628-73) leucosome formed syn-D3, concurrent with formation of the high-strain zone. Leucosome forma- Sample 9628-73 is a medium-grained leucosome tion at this time is consistent with regional consisting of quartz, K-feldspar, subordinate pla- observations that suggest that extensive partial gioclase and orthopyroxene. The sample was col- melting occurred during D3, particularly within lected from within a steeply north-dipping D3 metapelitic units. 16 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

Zircons from sample 9628-73 are generally tur- attained as a result of the emplacement of the bid and pale brown to pale reddish brown in granulites over the amphibolites, the granulites colour. They form a subhedral population that either advectively heating the underlying units, or varies in length from 100 to 500 mm, with average their emplacement resulting in the net burial and length/width ratios of approximately 3:1. A Th/U subsequent heating of the underthrust units. We ratio of 0.7 is relatively consistent for all grains therefore propose a syn-D4 timing of leucosome analysed. Likewise, the U contents of the zircons formation. No equivalent leucosome development lie in a narrow range typically between 300 and occurred as a result of D4 deformation within the 600 ppm. Most zircons show growth zoning, overlying granulites. marked by subtle concentric bands of varying Zircons from sample 9628-196 are reddish luminescence (Fig. 7d). Many contain highly lu- brown, euhedral to subhedral, and vary in length minescent inclusions of apatite (Fig. 7e). Some from 150 to 450 mm. Zircons from this sample grains are overgrown by an unzoned more lu- have length/width ratios of approximately 2:1– minescent rim. However, most zircons have a 3:1, and are generally more euhedral than those simple igneous appearance and are inferred to from the previous samples. CL imaging shows have formed at the time of leucosome formation. that they also have more complicated internal The isotopic data for the zircons from sample morphologies. Most grains contain cores that are 9628-73 are presented in Table 2. All 18 analyses commonly dark and can be either homogeneous form a single concordant mean 207Pb/206Pb age of or concentrically zoned. The internal structure of 942917 Ma (MSWD=1.44) (Fig. 8c). The indi- these cores is often cross-cut by a rounded resorp- cated age for this sample is taken as the crystalli- tion surface (Fig. 7f–h), which is then overgrown sation age of the leucosome, and constrains the by euhedral, generally more luminescent rims. development of the upright high-strain zone at However, examples of poorly luminescent euhe- 940 Ma. dral rims were also observed (Fig. 7h). Highly luminescent unzoned euhedral zircons are also present, and may represent the same period of 5.4. Clinopyroxene-bearing leucosome — west zircon growth as that which formed the rims on wall of Radok lake (sample 9628-196) other zircons. The Th/U ratio of both cores and rims lies in the range 0.3 to 1.0, with most analy- Sample 9628-196 was taken from medium- to ses 0.5. There is no consistent contrast in U coarse-grained leucosome consisting of sericitised content between core and rim analyses, with con- alkali and plagioclase feldspars, quartz, clinopy- siderable overlap occurring between individual roxene and green hornblende. The leucosome oc- grains. curs within the amphibolite facies felsic and Sixteen zircon grains from sample 9628-196 intermediate orthogneisses, exposed along the were analysed, of which 15 (excluding 2.1) lie on lower cliff faces at Radok Lake (Fig. 3). The or near concordia and produce a weighted mean amphibolite facies rocks at this locality tectoni- 207Pb/206Pb age of 954938 Ma (MSWD=2.71) cally underlie the granulites that make up the bulk (Fig. 8d). However, the large MSWD indicates of the nPCMs. Leucosomes within these rocks excess statistical scatter about the mean. Mod- (including sample 9628-196) form elongate layers elling suggests that there are two distinct sub-pop- that parallel S0/1, but which also locally form ulations that are separated by a distinct age gap spurs and accumulations that cross-cut the folia- of 50 Myr (Fig. 8d). This reflects a subtle tion at high angles (Fig. 4g). We interpret leuco- difference in age obtained from core and rim some formation to have post-dated deformation, analyses. Core analyses 1.1, 3.1, 6.1, 7.1, 12.1 and probably coincident with peak metamorphism, 14.1 definite an older grouping that yields a mean which appears to post-date deformation given the 207Pb/206Pb age of 1017931 Ma (MSWD= random to weakly orientated assemblages. We 0.685), while rim analyses 4.1, 5.1, 8.1, 9.1, 10.1, suggest that peak metamorphic conditions were 11.1, 13.1 and 15.1 define a younger grouping and S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 17

207 206 9 give a mean Pb/ Pb age of 900 28 Ma tional episodes (D1 –D4) all developed during a (MSWD=0.498). We suggest that the older pop- single evolving north–south compressive orogenic ulation is inherited from the orthogneiss, and event (Fig. 10). During this time, north–south-di- record an age reﬂecting orthogneiss emplacement, rected compression shortened the terrain, through whereas the rims are considered to have formed at gradually more discrete phases of deformation. the time of leucosome development and are con- The accumulation of strain occurred in response sidered to constrain the timing of D4. If this to the same compressive stress ﬁeld. However, the interpretation is correct, felsic orthogneiss intru- style of deformation changed in response to sion occurred at 1020 Ma, and D4 occurred at changes in the orientation and magnitude of the 900 Ma. Alternatively, the zircons may repre- intermediate and stretching axes, and the relative sent a single, somewhat scattered population contribution of the components of pure and sim- sourced from the leucosome, which would imply ple shear (Fig. 6). that the time interval between D3 and D4 was very The constraints on deformation presented are short, as the ages of samples 9628-142 (D3), 9628- consistent with published structural and age data

73 (D3) and 9628-196 (D4) are all statistically available from throughout the nPCMs. The intru- identical. We prefer the ﬁrst alternative, although sion ages presented by Kinny et al. (1997) from cannot conclusively preclude the latter. felsic bodies at Loewe Massif (charnockite, 9809 21 Ma), Mt Collins (granites, 976925 and 9849 7 Ma; quartz syenite, 984912 Ma) and Mt 6. Discussion McCarthy (leucogneisses, 990930 Ma) are all statistically identical to the 990918 Ma intrusion On the basis of our geochronological results, we age obtained in this study (Fig. 9). Equivalent conclude that deformation and high-grade meta- intrusive ages of 985929 and 954912 Ma were morphism in the Radok Lake area occurred over also recorded from charnockites outcropping a period spanning approximately 90 Myr. D1 and along the Mawson Coast (Young and Black, D2 are considered progressive, a conclusion also 1991). Structurally, all of these 980 Ma intru- draw by a number of previous studies (Fitzsimons sives are inferred to predate upright folding, con- and Harley, 1992; Thost and Hensen, 1992; Hand sistent with the conclusion drawn from this study. et al. 1994b), and occurred concurrently with Furthermore, the 940+27/−17 Ma age obtained regionally extensive magmatism and peak meta- by Manton et al. (1992) from Jetty Peninsula has morphism at 990–980 Ma. The subsequent de- been interpreted by Hand et al. (1994b) to date velopment of upright folds (F3) and steeply the emplacement of a pre- to syn-F3 leucogneiss. dipping high-strain zones occurred at 940 Ma. This interpretation concurs with the results of this

These pervasive features were then overprinted by study as it also suggests that F3 folding occurred discrete mylonites and pseudotachylites that de- at about 940 Ma (Fig. 9). Finally, SHRIMP data veloped at 900 Ma. from Mt Kirkby suggests F3 folding and shear Our structural observations show that both fold zone formation occurred at 910 Ma (Carson et generations (F2 and F3) formed coaxially with L1 al., 2000), an age that is within error of the (Fig. 3), and that the resolved palaeo-transport estimates on the timing of D3 and D4 obtained directions from D3 high-strain zones and D4 my- from this study. This consistency in published age lonites are also subparallel (Fig. 5). All four data is mirrored by a remarkable consistency in events show evidence of having formed in re- the sequence and orientation of structures ob- sponse to north–south-directed compression. served throughout the nPCMs (compare Fig. 6 of Given the consistency in orientation of the Fitzsimons and Harley (1992) with Fig. 10). Thus, palaeostress ﬁeld and the relative proximity in age it is considered likely that the conclusions drawn of the four deformational events (Fig. 9), we in this study are broadly applicable over much of suggest that the recognised sequence of deforma- the nPCMs. 18 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

As well as pervasively deforming the terrain, 1994; Mikhalsky et al., 1996; Laiba and Mikhal- 990–900 Ma orogenesis in the nPCMs has em- sky, 1999). Although this can not be shown con- placed granulite facies gneisses, which form the clusively, it is noteworthy that the Fisher Massif bulk of the exposed rock in the nPCMs, over metavolcanics are intruded by a biotite granite amphibolite facies intermediate and felsic units that yielded an age of 1020 Ma (Kinny et al., that crop out in a window exposed at Radok 1997), identical to that obtained from the inher- Lake. This relationship suggests that the gran- ited zircon population obtained from sample ulites at the southern end of the nPCMs are likely 9628-196. This relationship may well be coinci- to be allochthonous, a scenario already proposed dental. However, it supports the inference that the to explain the geochemistry of post-tectonic peg- granulites of the nPCMs may tectonically overlie matite dykes on Jetty Peninsula (Manton et al., the Fisher terrain. 1992). If correct, this could imply that the amphi- The geochronological data presented here from bolite facies rocks exposed at Radok Lake are the nPCMs is readily correlated with published equivalent to the amphibolite facies metavolcanic data from the Mawson Coast (Young and Black, sequence exposed further to the south at Fisher 1991; Young et al., 1997) and Rayner Complex Massif (Kamenev et al., 1993; Beliatsky et al., (Black et al., 1987) in the east Antarctic, and the

Fig. 9. Summary of U–Pb zircon ages (both SHRIMP and conventional) from the nPCMs and Mawson Coast, superimposed with constraints on deformation in the nPCMs. S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 19

Fig. 10. Schematic block diagram illustrating the structural evolution of the Radok Lake region in the northern Prince Charles Mountains.

Eastern Ghats of India (Grew and Manton, 1986; many east Gondwana reconstructions (for exam- Paul et al., 1990; Shaw et al., 1997). All yield ple, Moores, 1991; Rogers 1996), these belts have syn-orogenic ages of between 990 and 900 Ma. In been correlated with other Meso-Neoproterozoic 20 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 belts exposed in Africa, Australia and the Antarc- 1991; Post et al., 1997), and the Bunger Hills tic to form a single laterally extensive orogenic (Sheraton et al., 1990, 1993; Black et al., 1992) of belt, thought to have extended along the coast of east Antarctica, can be correlated on the basis east Antarctica from Coats Land at the edge of that all experienced high-grade metamorphism, the Weddell Sea, through to the Albany–Fraser magmatism and deformation between 1300 and Belt of southwest Australia and into the Mus- 1050 Ma (White et al., 1999). The youngest event grave block of central Australia. However, 990– recognised in these terrains is 60 Myr older 900 Ma orogenesis recognised in the than the onset of deformation and metamorphism nPCMs–Mawson Coast–Rayner Complex–East- in the nPCMs. Likewise, the metamorphic belts ern Ghats provinces in east Antarctica and India exposed in the Maud Province of east Antarctica is signiﬁcantly younger than that recognised both (Arndt et al., 1991; Jacobs et al., 1995, 1998) and to the east and the west (Fig. 11). The orogenic the Namaqua-Natal Province of east Africa (Cor- belts exposed in the Musgrave block of central nell et al., 1996; Thomas et al., 1996; Jacobs et al., Australia (Clarke et al., 1995; White et al., 1999), 1997; Hanson et al., 1998) are correlatable, but the Albany–Fraser belt of southwest Australia older than that recognised in the nPCMs. In the (Pidgeon, 1990) and the Windmill Islands (Tingey, Maud and Namaqua-Natal Provinces, felsic vol-

Fig. 11. Tectonic map of East Antarctica and adjacent parts of Gondwana showing the Archaean-Palaeoproterozoic cratonic blocks, and Meso-Neoproterozoic and Palaeozoic orogenic belts. The disparate ages of the Meso-Neoproterozoic orogenic belts, which have been previously correlated, and the two recently recognised intervening Palaeozoic belts in Lu¨tzow-Holm Bay and Prydz Bay are illustrated. G, Gawler craton; K, Kalahari craton; sPCMs, southern Prince Charles Mountains; V, Vestford Hills; LHB, Lu¨tzow-Holm Bay; P, Prydz Bay; nPCMs, northern Prince Charles Mountains. S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 21 canism and plutonism at 1140 Ma was fol- formation of east Gondwana and Rodinia. In- lowed by high-grade deformation and metamor- stead, we suggest that these Meso-Neoroterozoic phism at 1060–1040 Ma (Arndt et al., 1991; metamorphic belts are of separate origin and were Jacobs et al., 1995, 1998). Again, tectonism in probably accreted together during the Palaeozoic these terrains ceased 50 Ma prior to the onset along orogenic belts recognised in Lu¨tzow-Holm of deformation in the nPCMs. Given the signifi- Bay and Prydz Bay. With respect to Palaeozoic cant differences in age of these previously corre- reworking of the nPCMs, we do not rule out the lated terrains, it seems unlikely that these belts possibility of later discrete stages of deformation. represent a single continuous suture. Instead, However, our results suggest that all high-grade these three terrains probably represent separate penetrative fabrics observed in the nPCMs formed fragments of disparate Meso- to Neoproterozoic during the Neoproterozoic. orogenic belts. This is consistent with the recently recognised Palaeozoic tectonism in Lu¨tzow-Holm Bay and Prydz Bay, two younger orogenic belts Acknowledgements that separate each of these different Meso- to Neoproterozoic terrains (Fig. 11). The authors would like to thank the Australian Finally, our results impact on the debate as to Antarctic Division for logistical support over the the extent of Palaeozoic reworking experienced by 1996–1997 summer. The cost of field expenses the nPCMs. The data presented in this paper and analytical time on SHRIMP I and SHRIMP constrains all high-grade deformation and meta- II was met from an ASAC grant to C.J.L.W. The morphism to have occurred during the Neopro- Australian Geological Survey Organisation are terozoic, precluding the possibility of subsequent thanked for providing air-photos, while Doug high-grade events post-dating 900 Ma. We do Thost is also thanked for his assistance and not rule out the possibility of later stages of friendship in the field. We would also like to deformation, but suggest that they were of a thank Pete Kinny and Ian Fitzsimons for thor- relatively low grade and of a discrete nature. ough and constructive reviews that greatly im- Whereas, the adjacent terrain of Prydz Bay has proved the quality of this manuscript. been pervasively reworked by an early Palaeozoic granulite facies event, equivalent high-grade deformation is not recognised in the nPCMs. References

Arndt, N.T., Todt, W., Chauvel, C., Tapfer, M., Weber, K., 7. Conclusions 1991. U–Pb zircon age and Nd isotopic composition of granitoids, charnockites and supercrustal rocks from The structural and geochronological results pre- Heimefrontjella, Antarctica. Geol. Rundschau 80, 759– 777. sented in this paper constrain the granulite facies Arriens, P., 1975. The Precambrian geochronology of Antarc- deformation and metamorphism observed in the tica. First Australian Geological Convention, Adelaide, nPCMs to have occurred between 990 and Geology Society of Australia, Abstracts, pp. 97–98. 900 Ma. During this period, north–south-di- Beliatsky, B.V., Laiba, A.A., Mikhalsky, E.V., 1994. U–Pb rected compression deformed the terrain through zircon age of metavolcanic rocks of Fisher Massif (Prince Charles Mountains, East Antarctica). Antarct. Sci. 6, 355– four progressively more discrete phases of defor- 358. mation. Implicitly, our results suggest that oroge- Black, L.P., Harley, S.L., Sun, S.S., McCulloch, M.T., 1987. nesis can be long lived, in the case of the nPCMs, The Rayner Complex of east Antarctica, complex isotopic lasting up to 90 Myr. Our results also suggest that systematics within a Proterozoic mobile belt. J. Metamor- orogenesis in the nPCMs–Mawson Coast– phic Geol. 5, 1–26. Black, L.P., Sheraton, J.W., Tingey, R.J., McCulloch, M.T., Rayner Complex–Eastern Ghats is temporally 1992. New U–Pb zircon ages from the Denman Glacier quite distinct from other Meso-Neoroterozoic area, East Antarctic, and their signiﬁcance for Gondwana metamorphic belts thought to be involved in the reconstruction. Antarct. Sci. 4, 447–460. 22 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

Camacho, A., Vernon, R.H., Fitzgerald, J.D., 1995. Large sure–temperature paths in the Proterozoic Complex of east volumes of anhydrous pseudotachylite in the Woodroffe Antarctica. In: Yoshida, Y., Kaminuma, K., Shiraishi, K. Thrust, eastern Musgrave Ranges. Aust. J. Struct. Geol. (Eds.), Recent Progress in Antarctic Earth Science. Terra 17, 371–383. Scientiﬁc Publishing Company, Tokyo, pp. 103–111. Carson, C.J., Dirks, P.H.G.M., Hand, M., Sims, J.P., Wilson, Fitzsimons, I.C.W., Harley, S.L., 1994. The inﬂuence of retro- C.J.L., 1995. Compressional and extensional tectonics in grade cation exchange on granulite P–T estimates and a low-medium pressure granulites from the Larsemann Hills, convergence technique for the recovery of peak metamor- East Antarctica. Geol. Mag. 132, 151–170. phic conditions. J. Petrol. 35, 543–576. Carson, C.J., Fanning, C.M., Wilson, C.J.L., 1996. Timing of Fitzsimons, I.C.W., Harley, S.L., 1994. Garnet coronas in the Progress Granite, Larsemann Hills, evidence for Early scapolite-wollastonite calc-silicates from East Antarctica: Palaeozoic orogenesis within the East Antarctic Shield and the application and limitations of activity corrected grids. implications for Gondwana assembly. Aust. J. Earth Sci. J. Metamorphic Geol. 12, 761–777. 43, 539–553. Fitzsimons, I.C.W., Thost, D.E., 1992. Geological relation- Carson, C.J., Boger, S.D., Fanning, C.M., Wilson, C.J.L., ships in high-grade basement gneiss of the northern Prince Thost, D. 2000. SHRIMP U–Pb geochronology from Mt Charles Mountains, East Antarctica. Aust. J. Earth Sci. 39, Kirkby, northern Prince Charles Mountains, East Antarc- 173–193. tica. Antarctic Sci. (in press). Fitzsimons, I.C.W., Kinny, P.D., Harley, S.L., 1997. Two Clarke, G.L., Sun, S.S., White, R.W., 1995. Grenville-age belts stages of zircon and monazite growth in anatectic and associated older terrains in Australia and Antarctica. leucogneiss, SHRIMP constraints on the duration and AGSO J. Aust. Geol. Geophys. 16, 25–39. intensity of Pan-African metamorphism in Prydz Bay, East Compston, W., Williams, I.S., Meyer, C., 1984. U–Pb geo- Antarctica. Terra Nova 9, 47–51. chonology of zircons from lunar breccia 73217 using a Grew, E.S., 1982. Geology of the Southern Prince Charles sensitive high mass-resolution ion microprobe. J. Geophys. Mountains, east Antarctica. In: Craddock, C. (Ed.), Antarctic Geoscience. University of Wisconsin Press, Res. 89, B525–B534. Madison, WI, pp. 473–478. Compston, W., Williams, I.S., Kirschvink, J.L., Zichao, Z., Grew, E.S., Manton, W.I., 1986. A new correlation of sap- Guogan, M., 1992. Zircon U–Pb ages for the early Cam- phirine granulites in the Indo-Antarctic metamorphic ter- brian time-scale. J. Geol. Soc. Lond. 149, 171–184. rain, late Proterozoic dates from the Eastern Ghats Cornell, D.H., Thomas, R.J., Bowring, S.A., Armstrong, Province of India. Precam. Res. 33, 123–137. R.A., Grantham, G.H., 1996. Protolith interpretation in Hand, M., Scrimgeour, I., Powell, R., Stu¨we, K., Wilson, metamorphic terranes: a back-arc environment with C.J.L., 1994. Metapelitic granulites from Jetty Peninsula, Besshi-type base metal potential for the Quha Formation, East Antarctica, formation during a single event or poly- Natal Province, South Africa. Precam. Res. 77, 243–271. metamorphism? J. Metamorphic Geol. 12, 557–573. Crohn, P.P., 1959. A contribution to the geology and glaciol- Hand, M., Scrimgeour, I., Stu¨we, K., Arne, D., Wilson, ogy of the western part of Australian Antarctic Territory. C.J.L., 1994. Geological observations in high grade mid- Aust. Bur. Miner. Res., Geol. Geophys. Bull. 52, 1–103. Proterozoic rocks from Else Platform, northern Prince Cumming, G.L., Richards, J.R., 1975. Ore lead isotopes in a Charles Mountains region, East Antarctica. Aust. J. Earth continuously changing Earth. Earth Planet. Sci. Lett. 28, Sci. 41, 311–329. 155–171. Hanson, R.E., Martin, M.W., Bowring, S.A., Munyanyiwa, Dirks, P.H.G.M., Wilson, C.J.L., 1995. Crustal Evolution of H., 1998. U–Pb zircon age for the Umkondo dolerites, the East Antarctic mobile belt in Prydz Bay, continental eastern Zimbabwe: 1.1 Ga large igneous province in south- collison at 500 Ma? Precam. Res. 75, 189–207. ern Africa–East Antarctic and possible Rodinia correla- Fielding, C.R., Webb, J.A., 1995. Sedimentology of the Per- tions. Geology 26, 1143–1146. mian Radok Conglomerate in the Beaver Lake area of Harley, S.L., Fitzsimons, I.C.W., 1995. High grade metamor- Mac Robertson Land, East Antarctica. Geol. Mag. 132, phism and deformation in the Prydz Bay region, East 51–63. Antarctica: events and regional correlations. In: Yoshida, Fielding, C.R., Webb, J.A., 1996. Facies and cyclicity of the Y., Santosh, M. (Eds.), India and Antarctica during the Late Permian Bainmedart Coal Measures in the northern Precambrian. Geology Society of India Memoir, vol. 34. Prince Charles Mountains, East Antarctica. Sedimentology pp. 73–100. 43, 295–322. Hensen, B.J., Zhou, B., 1995. A Pan-African granulite facies Fitzsimons, I.C.W., 1997. The Brattstrand Paragneiss and the metamorphic episode in Prydz Bay, Antarctica, evidence Søstrene Orthogneiss: a review of Pan-African metamor- from Sm–Nd garnet dating. Aust. J. Earth Sci. 42, 249– phism and Grenville Relics in Southern Prydz Bay. In: 258. Ricci, C.A. (Ed.), The Antarctic Region, Geological Evolu- Hensen, B.J., Zhou, B., 1997. East Gondwanaamalgamation tion and Processes. Terra Antartica Publication, Sienna, by Pan-African collision? Evidence in the Prydz Bay re- pp. 121–130. gion, east Antarctica. In: Ricci, C.A. (Ed.), The Antarctic Fitzsimons, I.C.W., Harley, S.L., 1992. Mineral reaction tex- Region, Geological Evolution and Processes. Terra tures in high grade gneisses, evidence for contrasting pres- Antarctica Publication, Siena, pp. 115–119. S.D. Boger et al. / Precambrian Research 104 (2000) 1–24 23

Hensen, B.J., Zhou, B., Thost, D.E., 1997. Recognition of McLaughlin, S., Drinnan, A.N., 1997. Fluvial sedimentology multiple high grade metamorphic events with garnet Sm– and revised statigraphy of the Triassic Flagstone Bench Nd chronology in the northern Prince Charles Mountains, Formation, northern Prince Charles Mountains, East Antarctica. In: Ricci, C.A. (Ed.), The Antarctic Region, Antarctica. Geol. Mag. 134, 781–806. Geological Evolution and Processes. Terra Antarctica Pub- Mikhalsky, E.V., Sheraton, J.W., Laiba, A.A., Beliatsky, B.V., lication, Siena, pp. 97–104. 1996. Geochemistry and origin of the Mesoproterozoic Hobbs, B.E., Ord, A., Teyssier, C., 1986. Earthquakes in the metavolcanic rocks from Fisher Massif, Prince Charles ductile regime? Pure Appl. Geophys. 124, 309–336. Mountains, East Antarctica. Antarct. Sci. 8, 85–104. Hoffman, P.F., 1991. Did the breakout of Laurenta turn Mond, A., 1972. Permian sediments of the Beaver Lake area, Gondwana inside out? Science 252, 1409–1412. Prince Charles Mountains. In: Adie, R.J. (Ed.), Antarctic Jacobs, J., Ahrendt, H., Kreutzer, H., Weber, K., 1995. K– Geology and Geophysics. Universitetsforlaget, Oslo, pp. Ar40, 40Ar–39Ar and apitite fission-track evidence for 585–589. Neoproterozoic and Mesozoic basement rejuvenation Moores, E.M., 1991. Southwest U.S.–East Antarctica events in the Heimefrontjella and Mannefallknausane (East (SWEAT) connection: a hypothesis. Geology 19, 425–428. Antarctica). Precam. Res. 75, 251–262. Munksgaard, N.C., Thost, D.e., Hensen, B.J., 1992. Geochem- Jacobs, J., Falter, M., Thomas, R.J., Kunz, J., Jessberger, istry of Proterozoic granulites from the northern Prince E.K., 1997. 40Ar–39Ar thermochronological constraints Charles Mountains, East Antarctica. Antarctic Sci. 4, 59– on the structural evolution of the Mesoproterozoic Natal 69. metamorphic province, SE Africa. Precam. Res. 86, 71–92. Nichols, G.T., 1995. The role of mylonites in the uplift of an Jacobs, J., Fanning, C.M., Henjes-Kunst, F., Olesch, M., oblique lower crustal section, East Antarctica. J. Metamor- Paech, H., 1998. Continuation of the Mozambique Belt phic Geol. 13, 223–228. Oncken, O., 1988. Aspects of the reconstruction of the stress into East Antarctica: Grenville-age metamorphism and history of a fold and thrust belt (Rhenish Massif, Federal polyphase Pan-African high-grade events in Central Dron- Republic of Germany). Tectonophysics 152, 19–40. ning Maud Land. J. Geol. 106, 385–406. Passchier, C.W., 1997. The fabric attractor. J. Struct. Geol. 19, Kamenev, E., Andronikov, A.V., Mikhalsky, E.V., Krasnikov, 113–127. N.N., Stu¨we, K., 1993. Soviet geological maps of the Paul, D.K., Ray Barman, T., McNaughton, N.J., Fletcher, Prince Charles Mountains, East Antarctic Shield. Aust. J. I.R., Potts, P.J., Ramakrishnan, N., Augustine, P.F., 1990. Earth Sci. 40, 501–517. Archean–Proterozoic evolution of Indian Charnockites: Katz, M.B., 1989. Sri Lanka–Indian eastern Ghats–east An- Isotopic and Geochemical Evidence from Granulites of the tatctica and the Australian Albany Fraser mobile belt, Eastern Ghats Belt. J. Geol. 98, 253–263. Gross geometry, age relationships, and tectonics in Pre- Pidgeon, R.T., 1990. Timing of plutonism in the Proterozoic cambrian Gondwanaland. J. Geol. 97, 646–648. Albany mobile belt, southwestern Australia. Precam. Res. Kinny, P.D., Black, L.P., Sheraton, J.W., 1997. Zircon U–Pb 47, 157–167. ages and geochemistry of igneous and metamorphic rocks Post, N.J., Hensen, B.J., Kinny, P.D., 1997. Two metamorphic in the northern Prince Charles Mountains, Antarctica. episodes during a 1340–1180 Ma convergent tectonic event AGSO J. Aust. Geol. Geophys. 16, 637–654. in the Windmill Islands, East Antarctica. In: Ricci, C.A. Kriegsman, L.M., 1995. The Pan-African event in East (Ed.), The Antarctic region, geological evolution and pro- Antarctica: a view from Sri Lanka and the Mozambique cesses. Terra Antarctica Publication, Siena, pp. 157–161. Belt. Precam. Res. 75, 263–277. Ramsay, J.G., 1967. Folding and Fracturing of Rocks. Mc- Laiba, A.A., Mikhalsky, E.V., 1999. Granitoids of the Mt. Graw Hill, New York. Willing Massif, east Antarctica: a layered intrusion in a Ren, L., Zhao, Y., Liu, X., Chen, T., 1992. Re-examination of Proterozoic mobile belt, geologic structure and chemical the metamorphic evolution of the Larsemann Hills, East composition. Petrology 7, 32–52. Antarctica. In: Yoshida, Y., Kaminuma, K., Shiraishi, K. Manton, W.I., Grew, E.S., Hoffman, J., Sheraton, J.W., 1992. (Eds.), Recent Progress in Antarctic Earth Science. Terra Granitic rocks of the Jetty Peninsula, Amery Ice Self area, Scientific Publishing Company, Tokyo, pp. 145–153. East Antarctica. In: Yoshida, Y., Kaminuma, K., Shi- Rogers, J.J.M., 1996. A history of the continents in the past raishi, K. (Eds.), Recent Progress in Antarctic Earth Sci- three billion years. J. Geol. 104, 91–107. ence. Terra Scientific Publishing Company, Tokyo, pp. Scrimgeour, I., Hand, M., 1997. A metamorphic perspective 179–189. on the Pan-African overprint in the Amery area of Mac. McKelvey, B.C., Stephenson, N.C.N., 1990. A geological re- Robertson Land, East Antarctica. Antarct. Sci. 9, 313– connaissnce of the Radok Lake area, Amery Oasis, Prince 335. Charles Mountains. Antarct. Sci. 4, 59–69. Shaw, R.K., Arima, M., Kagami, C., Fanning, C.M., Shi- McLaughlin, S., Drinnan, A.N., 1997. Revised stratigraphy of raishi, K., Motoyoshi, Y., 1997. Proterozoic Events in the the Permian Bainmedart Coal Measures, northern Prince Eastern Ghats Granulite Belt, India: Evidence from Rb– Charles Mountains, East Antarctica. Geol. Mag. 134, 335– Sr, Sm–Nd systematics, and SHRIMP dating. J. Geol. 353. 105, 645–656. 24 S.D. Boger et al. / Precambrian Research 104 (2000) 1–24

Sheraton, J.W., Black, L.P., McCulloch, M.T., Oliver, R.L., Unrug, R., 1997. Rodinia to Gondwana: the geodynamic map 1990. Age and origin of a compositionally varied mafic of Gondwana supercontinent assembly. GSA Today 7, dyke swarm in the Bunger Hills, east Antarctica. Chem. 1–6. Geol. 85, 215–246. Webb, J.A., Fielding, C.R., 1993. Permo-Triassic sedimenta- Sheraton, J.W., Tingey, R.J., Black, L.P., Oliver, R.L., 1993. tion within the Lambert Graben, northern Prince Charles Geology of the Bunger Hillsarea, Antarctica: implications Mountains, East Antarctica. In: Findlay, R.H., Unrug, R., for Gondwana reconstructions. Antarct. Sci. 5, 85–102. Banks, M.R., Veevers, J.J. (Eds.), Gondwana 8, Assembly, Sheraton, J.W., Tindle, A.G., Tingey, R.J., 1996. Geochem- Evolution and Dispersal. A.A. Balkema, Rotterdam, pp. istry, origin, and tectonic setting of granitic rocks of the 357–369. Prince Charles Mountains, Antarctica, AGSO. J. Aust. White, R.W., Clarke, G.L., Nelson, D.R., 1999. SHRIMP Geol. Geophys. 16, 345–370. U–Pb zircon dating of Grenville events in the western part Shiraishi, K., Ellis, D.J., Hiroi, Y., Fanning, C.M., Mo- of the Musgrave Complex, central Australia. J. Metamor- toyoshi, Y., Nakai, Y., 1994. Cambrian orogenic belt in phic Geol. 17, 465–481. East Antarctica and Sri Lanka: implications for Gond- wana Assembly. J.Geol. 102, 47–65. Yoshida, M., Funaki, M., Piyadasa, V.W., 1992. Proterozoic Stephenson, N.C.N., Cook, N.D.J., 1997. Metamorphic evolu- to Mesozoic East Gondwana, the juxtaposition of India, tion of calc-silicate granulites near Battye Glacier, northern Sri Lanka, and Antarctica. Tectonics 11, 381–391. Prince Charles Mountains, East Antarctica. J. Metamor- Young, D.N., Black, L.P., 1991. U–Pb zircon dating of phic Geol. 15, 361–378. Proterozoic igneous charnockites from the Mawson Coast, Thomas, R.J., Beer, C.H., Bowring, S.A., 1996. A comparitive East Antarctica. Antarct. Sci. 3, 205–216. study of the Mesoproterozoic late orogenic porphyritic Young, D.N., Zhao, J., Ellis, D.J., McCulloch, M.Y., 1997. granitoids of southwest Namaqualand and Natal, South Geochemical and Sr–Nd isotope mapping of source Africa. J. Afr. Earth Sci. 23, 485–508. provinces for the Mawson charnokites, east Antarctica: Thost, D.E., Hensen, B.J., 1992. Gneisses of the Porthos and implications for Proterozoic tectonics and Gondwana re- Athos Ranges, northern Prince Charles Mountains, East construction. Precam. Res. 86, 1–19. Antarctica, constraints on the prograde and retrograde Zhao, Y., Song, B., Wang, Y., Ren, L., Li, J., Chen, T., 1992. P–T path. In: Yoshida, Y., Kaminuma, K., Shiraishi, K. Geochonology of the late granite in the Larsmann Hills, (Eds.), Recent Progress in Antarctic Earth Science. Terra east Antarctica. In: Yoshida, Y., Kaminuma, K., Shiraishi, Scientific Publishing Company, Tokyo, pp. 93–102. K. (Eds.), Recent Progress in Antarctic Earth Science. Tingey, R.J., 1982. The geologic evolution of the Prince Terra Scientific Publishing Company, Tokyo, pp. 155–161. Charles Mountains-an Antarctic Archaean cratonic block. Zhao, Z., Ellis, D.J., Kilpatrick, J.A., McCulloch, M.T., 1997. In: Craddock, C. (Ed.), Antarctic Geoscience. University Geochemical and Sr–Nd isotopic study of charnokites and of Wisconsin Press, Madison, WI, pp. 455–464. related rocks from the northern Prince Charles Mountains, Tingey, R.J., 1991. The regional geology of Archaean and east Antarctica: implications for charnokite petrogenesis Proterozoic rocks in Antarctica. In: Tingey, R.J. (Ed.), The Geology of Antarctica. Oxford University Press, Oxford, and Proterozoic crustal evolution. Precam. Res. 81, 37–66. pp. 1–73.