Fig 3 - uploaded by Thomas M Will
Content may be subject to copyright.
Relic granulite-facies mineral assemblage typically

Relic granulite-facies mineral assemblage typically

Source publication
Article
Full-text available
Within the basement of the northern Wilson Terrane at Oates Coast, a very-high-grade central zone is distinguished from high-grade zones to the east and west. In the central zone, P–T estimates of 8 kbar and 800°C derive from the relic assemblage: (1) Crd+Bt+Sil+Spl+Pl+Qtz for an earlier medium-pressure granulite-facies metamorphism which is also d...

Context in source publication

Context 1
... granulite-facies relics small exsolutions of plagioclase. Rare sillimanite was found as inclusion in plagioclase or in the have been found in the migmatites ( Fig. 3). The mineral content of US-495 is Grt+Bt+Crd+ marginal parts of garnet. ...

Similar publications

Article
Full-text available
The study area is located in the northern part of the Sanandaj-Sirjan structural zone, between Daran and Aligudarz towns, near Darreh Sary village. Based on field and petrographical evidences, exposed metaplitic metamorphic rocks in this region, consist of five categories: phyllites, slates, muscovite biotite schists, garnet schists and staurolite...
Article
Full-text available
Our recent studies of metamorphism within the Fennoscandian (or Baltic) Shield area with representative sites of orogenic gold mineralization based on the scheme of mineral facies of metamorphic rocks introduced earlier inspired thorough revision of that scheme. The proposed scheme retains the commonly adopted nomenclature (prehnite-pumpellyite, gr...
Article
Full-text available
The paper briefly outlines the main features of the metamorphic evolution of some scheelite-bearing rocks outcropping in Southern Calabria and the Peloritani Mountains. The results are based on detailed microtextural analyses and geothermobarometric interpretation of the mineral assemblage. The pre-Alpine metamorphic history turns out to be complex...
Article
Full-text available
The Proterozoic Sushina Hill Complex is the only agpaitic complex, reported from India and is characterized by a eudialyte-rinkite-bearing nepheline syenite. The complex is considered a 'metamorphosed agpaitic complex'. This study describes the mineral assemblages formed during successive stages of evolution from magmatic to hydrothermal stages and...
Article
Full-text available
Two Proterozoic terranes with different metamorphic histories are distinguished from geological mapping in southwestern Wedel Jarlsberg Land: a northern greenschist facies terrane and a southern amphibolite facies terrane which has been overprinted by greenschist facies metamorphism. To better characterize the tectonothermal history of these terran...

Citations

... Metamorphic rocks in the Lanterman and Salamander ranges are also probably correlative with the Wilson Group (Talarico et al., 1998). Regional metamorphism is variable from greenschist to granulite facies, and in many areas these rocks are intimately mixed with granitoids and migmatites of the Granite Harbour batholith (Babcock et al., 1986;Schüssler et al., 1999Schüssler et al., , 2004. Despite variable and locally high-grade metamorphism, available geochronologic evidence shows that the Wilson terrane does not represent primary Archean or Paleoproterozoic crust of the East Antarctic shield (westward, the first such rocks occur in the Terre Adélie craton of Wilkes Land), but rather is a composite metasedimentary assemblage of latest Neoproterozoic to Cambrian age. ...
... Northern Victoria Land is underlain by three major late Neoproterozoic and early Paleozoic tectonic elements, as noted earlier, which are variably deformed and metamorphosed. The presence of map-scale contractional structures (mainly upright folds and thrusts), discontinuities between different metamorphic P/T types, and early to middle Paleozoic I-type plutonic suites are all indicative of a convergent-margin tectonic setting in the latest Precambrian to early Paleozoic Bradshaw et al., 1985;Gibson and Wright, 1985;Borg et al., 1987;Kleinschmidt and Tessensohn, 1987;Kleinschmidt, 1991a, 1991b;Dallmeyer and Wright, 1992;Goodge and Dallmeyer, 1996;Ricci et al., 1997;Schüssler et al., 1999). Others have stressed the role of strike-slip tectonics (Weaver et al., 1984) or proposed the accretion of allochthonous terranes (Bradshaw et al., 1985), yet numerous connections are apparent between the various tectonic elements and reflect a coherent convergent-margin architecture (see, for example, Tessensohn and Henjes-Kunst, 2005;Federico et al., 2006;Rocchi et al., 2011). ...
... Wilson Group gneisses are separated from the Bowers terrane by steeply-dipping faults and shear zones Gibson, 1984;Roland et al., 1984;Sandiford, 1985;Capponi et al., 2002), but the age and tectonic significance of these zones are controversial. In northern Victoria Land the Ross Orogeny resulted in pronounced folding of Lower Ordovician rocks in the Bowers and Robertson Bay terranes (Bradshaw et al., 1985;Gibson and Wright, 1985), in diachronous cleavage development within the Robertson Bay Group (Dallmeyer and Wright, 1992), and ductile thrusting of Wilson Group metamorphic rocks (Kleinschmidt and Tessensohn, 1987;Flöttmann and Kleinschmidt, 1991a;Schüssler et al., 1999). ...
Full-text available
Article
The Transantarctic Mountains (TAM) are one of Earth's great mountain belts and are a fundamental physiographic feature of Antarctica. They are continental-scale, traverse a wide range of latitudes, have high relief, contain a significant proportion of exposed rock on the continent, and represent a major arc of environmental and geological transition. Although the modern physiography is largely of Cenozoic origin, this major feature has persisted for hundreds of millions of years since the Neoproterozoic to the modern. Its mere existence as the planet's longest intraplate mountain belt at the transition between a thick stable craton in East Antarctica and a large extensional province in West Antarctica is a continuing enigma. The early and more cryptic tectonic evolution of the TAM includes Mesoarchean and Paleoproterozoic crust formation as part of the Columbia supercontinent, followed by Neoproterozoic rift separation from Laurentia during breakup of Rodinia. Development of an Andean-style Gondwana convergent margin resulted in a long-lived Ross orogenic cycle from the late Neoproterozoic to the early Paleozoic, succeeded by crustal stabilization and widespread denudation during early Gondwana time, and intra-cratonic and foreland-basin sedimentation during late Paleozoic and early Mesozoic development of Pangea. Voluminous mafic volcanism, sill emplacement, and layered igneous intrusion are a primary signature of hotspot-influenced Jurassic extension during Gondwana breakup. The most recent phase of TAM evolution involved tectonic uplift and exhumation related to Cenozoic extension at the inboard edge of the West Antarctic Rift System, accompanied by Neogene to modern glaciation and volcanism related to the McMurdo alkaline volcanic province. Despite the remote location and relative inaccessibility of the TAM, its underlying varied and diachronous geology provides important clues for reconstructing past supercontinents and influences the modern flow patterns of both ice and atmospheric circulation, signifying that the TAM have both continental and global importance through time.
... A still earlier age of 544 ± 4 Ma (SHRIMP U-Pb zircon data) was interpreted as the crystallization age of an S-type granite in the Daniels Range, north-western Wilson Terrane (Black and Sheraton, 1990). But the rock was identified as diatexite by Schüssler et al. (1999) and the 544 Ma zircon population is probably inherited from the sedimentary source rock . Synorogenic to post-orogenic Granite Harbour Intrusives in the Deep Freeze Range have U-Pb zircon ages of 508 to 493 Ma for the oldest, strongly foliated synkinematic granites and tonalites, and 489 to 481 Ma for the younger calc-alkaline granites and mafic dykes (Bomparola et al., 2007). ...
Full-text available
Article
The Ross-Delamerian orogenic belt was formed along the eastern side of the Australian-East Antarctic continent during west-directed subduction of the Palaeo-Pacific Ocean in the early Palaeozoic. Northern Victoria Land (NVL) in Antarctica was located at a central position of the Ross-Delamerian system. Its metamorphic basement is formed by three lithotectonic units formerly interpreted as terranes: the Wilson, Bowers and Robertson Bay terranes (from west to east). Dating of detrital zircons from 14 meta¬sedimentary samples of these terranes combined with petrographical and whole-rock geochemical studies give new insights into the stratigraphic and tectonic evolution of NVL. All samples show very similar zircon age spectra with two main intervals, a Ross/Pan-African-age interval (470–700 Ma) and a Grenville-age interval (900–1300 Ma), as well as subordinate craton-related ages dispersed over the range of ca. 1600–3500 Ma. The Ross/Pan-African-age zircon population tends to get more dominant from the Priestley Formation of the Wilson Terrane to the Molar Formation of the Bowers Terrane, and finally to the Robertson Bay Group, whereas the number of craton-related ages diminishes in this direction. A common East Antarctic source area is indicated for all analyzed samples. The Priestley Formation was deposited on the Palaeo-Pacific passive continental margin of East Gondwana in the late Neoproterozoic after Rodinia breakup. The sequence was subsequently metamorphosed and intruded by the Granite Harbour Intrusives during the Ross Orogeny. The Molar Formation of the Bowers Terrane is interpreted as a turbiditic sequence deposited in an accretionary setting on the active continental margin in the Late Cambrian during and after accretion of the Glasgow island arc allochthon. The thick, homogeneous sequence of the Robert¬son Bay Group resulted from continuous turbiditic sedimentation in an accretionary wedge in front of the Ross Orogen after docking and imbrication of the Glasgow island arc in the Early Ordovician.
... The northernmost part of the Wilson Terrane was basically investigated for the first time during the German Antarctic North Victoria Land Expeditions GANOVEX V and VII in 1988/89 and 1992/93. There, a subdivision of the crystalline basement into three different NNW–SSE trending zones was recognised: a central zone with granulite-facies gneisses and migmatites is flanked by one eastern and one western zone with gneisses which were formed under lower amphibolite-to lowest granulite-facies conditions (Schüssler, 1996; Schüssler et al., 1999 Schüssler et al., , 2004 ). The zones are confined by the prominent Wilson, Exiles, and Lazarev thrust systems ( Kleinschmidt, 1991, 1993; Läufer et al., 2006 ) except the boundary between the eastern and the central zone which is still of unclear character. ...
... Previously, monazite U–Pb isotopic data have been published from four samples collected in the central, granulite-facies zone of the Wilson Terrane. Two of them were analysed by SHRIMP (Henjes-Kunst et al., 2004), the other two by TIMS (Schüssler et al., 1999Schüssler et al., , 2004). The SHRIMP analysed samples are G8-57.4 ...
... Monazite in medium-to high-grade metapsammitic to metapelitic gneisses and migmatites from the eastern, central and western zonesSchüssler et al., 1999) and are listed inFig. 8. ...
... The northernmost part of the Wilson Terrane was basically investigated for the first time during the German Antarctic North Victoria Land Expeditions GANOVEX V andVII in 1988/89 and1992/93. There, a subdivision of the crystalline basement into three different NNW-SSE trending zones was recognised: a central zone with granulite-facies gneisses and migmatites is flanked by one eastern and one western zone with gneisses which were formed under lower amphibolite-to lowest granulite-facies conditions (Schüssler, 1996;Schüssler et al., 1999Schüssler et al., , 2004. The zones are confined by the prominent Wilson, Exiles, and Lazarev thrust systems Kleinschmidt, 1991, 1993;Läufer et al., 2006) except the boundary between the eastern and the central zone which is still of unclear character. ...
... The Th-U-Pb EMP monazite age at 486 ± 10 Ma from the garnet-cordierite diatexite sample US-501 corresponds, within error, to the U-Pb TIMS ages between 491 and 494 Ma. The 484 ± 9 Ma Th-U-Pb age from the metatexite sample US-380 corresponds to the 484-488 Ma U-Pb TIMS age reported in Schüssler et al. (1999). ...
... The northernmost part of the Wilson Terrane was basically investigated for the first time during the German Antarctic North Victoria Land Expeditions GANOVEX V andVII in 1988/89 and1992/93. There, a subdivision of the crystalline basement into three different NNW-SSE trending zones was recognised: a central zone with granulite-facies gneisses and migmatites is flanked by one eastern and one western zone with gneisses which were formed under lower amphibolite-to lowest granulite-facies conditions (Schüssler, 1996;Schüssler et al., 1999Schüssler et al., , 2004. The zones are confined by the prominent Wilson, Exiles, and Lazarev thrust systems Kleinschmidt, 1991, 1993;Läufer et al., 2006) except the boundary between the eastern and the central zone which is still of unclear character. ...
... The Th-U-Pb EMP monazite age at 486 ± 10 Ma from the garnet-cordierite diatexite sample US-501 corresponds, within error, to the U-Pb TIMS ages between 491 and 494 Ma. The 484 ± 9 Ma Th-U-Pb age from the metatexite sample US-380 corresponds to the 484-488 Ma U-Pb TIMS age reported in Schüssler et al. (1999). ...
Article
The electron microprobe (EMP) Th-U-Pb monazite bulk chemical dating method was applied to granulite-facies rocks of the Wilson Terrane in Antarctica. A combination of this method to isotopic U-Pb-SHRIMP ages for the evaluation of metamorphic processes required the analysis of reference monazites. These can be subdivided into three groups: a) Monazite with variable total Pb at constant Th (e.g. VK-1) is unsuitable for EMP data evaluation; b) Monazite with highly variable total Pb and Th, but with at least some Th/Pb approximating an apparent isochrone (e.g. MPN) is partly useful; and c) Monazite with constant Th/Pb at high Th (e.g. Madmon monazite) is best suitable for the combined approach and can be additionally used to improve the Th calibration for EMP. Study of monazite in grain mounts and in thin sections led to partly different but complementary results: Older monazites with EMP ages up to 680 Ma occur mainly in a grain mount from diatexite and metatexite and are interpreted as detrital relics. Some of these monazites show structures and mineral-chemical zonation trends resembling metasomatism by alkali-bearing fluids. A marked mobility of Th, P, Ce, Si and U is observed. The age of the metasomatic event can be bracketed between 510 and 450 Ma. Furthermore, in the grain mount and in numerous petrographic thin sections of migmatites and gneisses, the EMP Th-U-Pb and SHRIMP U-Pb monazite data uniformly signal a major metamorphic event with a medium-pressure granulite facies peak between 512 and 496 Ma. Subsequent isothermal uplift and then amphibolite-facies conditions between 488 and 466 Ma led to crystallisation of pristine monazite. The high-grade metamorphic event, related to the Ross Orogeny, can be uniformly traced more than 600 km along strike in the Wilson Terrane.
... [54] Our interpreted rapid cooling rate following the Ross Orogeny is compatible with some previous studies. While cooling rates from across Northern Victoria Land (NVL) range from 18°to 30°Myr −1 [Goodge and Dallmeyer, 1996;Schüssler et al., 1999], both Di Vincenzo et al. [1997] and Palmeri et al. [2003] argue for very fast cooling in the NVL area based on overlapping ages in high-temperature thermochronometers (consistent with our near-identical 40 Ar/ 39 Ar hornblende and biotite age peaks). ...
Full-text available
Article
The Wilkes and Aurora basins are large, low-lying sub-glacial basins that may cause areas of weakness in the overlying East Antarctic ice sheet. Previous work based on ice-rafted debris (IRD) provenance analyses found evidence for massive iceberg discharges from these areas during the late Miocene and Pliocene. Here we characterize the sediments shed from the inferred areas of weakness along this margin (94°E to 165°E) by measuring40Ar/39Ar ages of 292 individual detrital hornblende grains from eight marine sediment core locations off East Antarctica and Nd isotopic compositions of the bulk fine fraction from the same sediments. We further expand the toolbox for Antarctic IRD provenance analyses by exploring the application of 40Ar/39Ar ages of detrital biotites; biotite as an IRD tracer eliminates lithological biases imposed by only analyzing hornblendes and allows for characterization of samples with low IRD concentrations. Our data quadruples the number of detrital 40Ar/39Ar ages from this margin of East Antarctica and leads to the following conclusions: (1) Four main sectors between the Ross Sea and Prydz Bay, separated by ice drainage divides, are distinguishable based upon the combination of 40Ar/39Ar ages of detrital hornblende and biotite grains and the ɛNd of the bulk fine fraction; (2) 40Ar/39Ar biotite ages can be used as a robust provenance tracer for this part of East Antarctica; and (3) sediments shed from the coastal areas of the Aurora and Wilkes sub-glacial basins can be clearly distinguished from one another based upon their isotopic fingerprints.
... [54] Our interpreted rapid cooling rate following the Ross Orogeny is compatible with some previous studies. While cooling rates from across Northern Victoria Land (NVL) range from 18°to 30°Myr −1 [Goodge and Dallmeyer, 1996;Schüssler et al., 1999], both Di Vincenzo et al. [1997] and Palmeri et al. [2003] argue for very fast cooling in the NVL area based on overlapping ages in high-temperature thermochronometers (consistent with our near-identical 40 Ar/ 39 Ar hornblende and biotite age peaks). ...
Full-text available
Article
Understanding the evolution of the East Antarctic Ice Sheet (EAIS) is a fundamental goal in the field of paleoclimate today. Given the current and projected state of global warming, it is important to know how an ice sheet that holds over 50 m of sea-level has behaved under warmer conditions in the past. Despite the fact that over 98% of the East Antarctica continent is covered by thick (2.1 km on average) ice, the chronological characterization of glaciogenic detrital hornblende grains has been proven an excellent provenance tool in the investigation of the source areas for ice rafted detritus around Antarctica (Roy et al., 2007, Chem. Geo.). A circum-Antarctica core-top survey of Ar-Ar ages in hornblende grains demonstrates that East Antarctica can be simply divided into several sectors that correspond to modern ice divides and published geochronological evidence from sparse outcrops around the margins of the continent. Williams et al., (2010, EPSL) found evidence in ice rafted detritus layers in ODP Site 1165 from the Wilde drift off Prydz Bay for large discharges of icebergs from the Adélie and Wilkes Land coasts occurring during the late Miocene and early Pliocene. Sourcing from the Adélie and Wilkes Land coasts requires iceberg transport more than 1500 km around the Antarctic perimeter, and this is therefore evidence for massive discharges of icebergs from these sectors. In the Aurora and Wilkes Basins in these sectors, the ice sheet is grounded well below sea level, and is therefore thought to be potentially unstable under warmer conditions. Such long distant transport of sediments with distinctive sources is reminiscent of Heinrich Events in the North Atlantic. A model often invoked as the cause of these events is the collapse and retreat of ice-streams, which leads to massive discharges of icebergs, laden with sediment, into the ocean. The importance of this interpretation, if true, has led us to make more detailed studies of Quaternary sediments from the Adélie and Wilkes Land coasts as well as glaciogenic sediments throughout the Cenozoic in Prydz Bay. We will present Ar-Ar ages of detrital hornblende and biotite grains (>150 µm), as well as epsilon-Nd values measured on the terrigenous fine fraction (
... Furthermore, monazite grains from a high-grade garnet gneiss of the Wilson Terrane (Antarctica), separated from grain concentrates by heavy liquids and hand-picking, were embedded on glass and then polished. These monazites from sample US 501 with a known U-Pb zircon lower intercept age of 469 ± 8 Ma, TIMS 238 U-206 Pb monazite ages of 494 ± 4 Ma, and a K-Ar biotite age of 470 ± 5 Ma (SCHÜSSLER et al. 1999) have been analyzed. Large metamorphic monazites in the high grade metamorphic Léon samples allowed several analyses in a single grain (Figs. ...
... Although affected by considerable uncertainty on the ages when compared to SHRIMP or SIMS methods, the Th-Pb monazite in situ dating by 266 nm laser ablation and single collector quadrupole ICP-MS is a rapid and SCHÜSSLER et al. (1999) In situ Th-Pb dating of monazite by 266 nm laser ablation and ICP-MS cost-efficient method which yielded reliable results without lengthy sample preparation and access to specialized labs equipped with mass spectrometers for isotope analysis. The minimal size of the crater (35 µm) allows only an evaluation of larger monazite grains in thin sections and in grain mounts of heavy mineral separates from sediments, leucogranites and Ca-poor high-grade metamorphic metapelites or orthogneisses. ...
... Boundaries and extent of provinces in East Antarctic interior are conjectured from coastal outcrops and extrapolation from adjacent shields in Australia, India, and southern Africa. Basement age provinces defi ned by Nd isotopic data (Borg and DePaolo, 1994; Schüssler et al., 1999) are shown by heavy horizontal ruling and fi ner grid pattern. Gray region along Pacifi c margin of Austral-Antarctica shows areas of eastern Gondwana beneath which early Paleozoic lithosphere has subducted; the composite Ross-Delamerian-Lachlan orogens refl ect an active accretionary margin at the time of Gondwana amalgamation along the collisional East African and Pinjarra orogens. ...
... The older granitoids form a western, inboard belt of Cambro- Ordovician transitional S-to I-type intrusions (Granite Harbour intrusives) that are correlative with plutonic rocks of similar age throughout the Transantarctic Mountains, whereas Devono- Carboniferous I-type granitoids occur to the east (Admiralty intrusives). The presence of map-scale contractional structures, discontinuities between different metamorphic baric types, and early to middle Paleozoic plutonic suites are all indicative of a convergent-margin tectonic setting in the late Precambrian to early Paleozoic (Grew et al., 1984; Bradshaw et al., 1985; Gibson and Wright, 1985; Borg et al., 1987; Kleinschmidt and Tessensohn, 1987; Flöttmann and Kleinschmidt, 1991; Dallmeyer and Wright, 1992; Goodge and Dallmeyer, 1996; Ricci et al., 1997; Schüssler et al., 1999). Some workers have also stressed the role of strike-slip tectonics (Weaver et al., 1984) or proposed the accretion of allochthonous terranes (Bradshaw et al., 1985). ...
... Wilson Group gneisses are sepa-rated from the Bowers terrane by steeply dipping faults and shear zones (Wodzicki et al., 1982; Gibson, 1984; Roland et al., 1984; Sandiford, 1985; Capponi et al., 2002), but the age and tectonic signifi cance of these zones are controversial. In northern Victoria Land, the Ross orogeny resulted in (1) pronounced folding of Lower Ordovician rocks in the Bowers and Robertson Bay terranes (Bradshaw et al., 1985; Gibson and Wright, 1985), (2) diachronous cleavage development within the Robertson Bay Group (Dallmeyer and Wright, 1992), and (3) ductile thrusting of Wilson Group metamorphic rocks (Kleinschmidt and Tessensohn, 1987 ; Flöttmann and Kleinschmidt , 1991; Schüssler et al., 1999). Different tectonic models have been invoked to explain these early Paleozoic structural and petrologic patterns, all involving some manifestation of plate convergence. ...
Full-text available
Article
The Ross orogen of Antarctica is one of Earth's great Phanerozoic mountain belts. It is thought from igneous geochemistry, deformation patterns, and sedimenta- tion history to be the result of late Neoproterozoic and early Paleozoic plate-margin convergence between paleo-Pacifi c oceanic lithosphere and continental lithosphere represented by the composite East Antarctic shield. Convergence along this margin is contemporaneous with, and tectonically linked to, amalgamation of the Gondwana supercontinent following collapse of former ocean basins and collision along the East African orogen. Although there is general agreement about the large-scale tectonic framework of the Ross orogen, there is a great deal of remaining uncertainty regard- ing crustal province correlation, deformation kinematics, precise timing, and plate- margin paleogeography. Our uncertainty stems from (1) a fragmentary record left by younger tectonic events that have modifi ed and, in some cases, removed parts of the orogen, and (2) extensive ice cover. Because the basement geology of the Ross orogen is composed largely of metamorphic rocks, however, study of the metamorphic roots of the orogen should help to constrain tectonic setting, thermal structure, tectonic displacements, cooling history, and timing. Evidence in the metamorphic domains refl ects 60-100 million years of continental-margin subduction, which is characterized by primary magmatic crustal accretion and low-P/T magmatic-arc meta morphism, crustal thickening and high-P/T metamorphism due to convergence and oceanic-arc collision, and high-P/T metamorphism associated with seaward growth of a plate- margin accretionary system.
... In addition to speculations about the position of the boundary between the East Antarctic Craton and the Ross-orogenic belt, there has been some debate about the presence and nature of basement rocks of cratonic origin in the Ross-orogenic WT. Based on the finding of relict granulite-facies minerals in high-grade metamorphic rocks of the westernmost WT it has been argued that these rocks represent East Antarctic cratonic crust reworked in the course of the late Precambrian to early Palaeozoic Ross Orogeny (Talarico & Castelli, 1995;; see also Schüssler et al., 1999). In addition, the results of a Rb-Sr whole-rock dating study on high-grade metamorphics and related magmatites from the coastal area of Oates Land were interpreted to indicate a pre-Ross-orogenic age of parts of the basement in the northwestern WT (Adams & Roland, 2002). ...
... This was in line with the interpretation of earlier conventional U-Pb zircon ages for anatectic rocks of the Daniels Range (northwestern WT) (Sheraton et al., 1987). However, in the course later conventional and in part SHRIMP U-Pb investigations on zircon, monazite and sphene from high-grade basement rocks of the western "granulitic" belt of the WT, these results could not be verified (Black & Sheraton, 1990;Klee et al., 1990;Klee, 1995;Schüssler et al., 1999). In order to clarify the discrepancies in geochronological results for basement rocks of the western WT, a SHRIMP dating study on high-grade metamorphic rocks and undeformed intrusives from the coastal area of Oates Land was initiated. ...
... The present study was performed on high-grade metamorphic and related igneous rocks from the Wilson Hills located in the northwestern coastal area of Oates Land ("Oates Coast") ( Fig. 1) and forming part of the inboard high temperature-dominated metamorphic belt of the WT. In this area, major thrusts activated during final tectonometamorphism of the Ross Orogeny separate units with contrasting metamorphic degrees (Flöttmann & Kleinschmidt, 1991;Schüssler et al., 1999;Schüssler et al., 2004). These structures were interpreted to indicate that blocks from different crustal levels of the WT basement were tectonically exhumed to various degrees along the thrust zones during the late stage of the Ross Orogeny (Flöttmann & Kleinschmidt, 1991;Schüssler, 1996). ...
Article
High- to very-high-grade migmatitic basement rocks of the Wilson Hills area in northwestern Oates Land (Antarctica) form part of a low-pressure high-temperature belt located at the western inboard side of the Ross-orogenic Wilson Terrane. Zircon, and in part monazite, from four very-high grade migmatites (migmatitic gneisses to diatexites) and zircon from two undeformed granitic dykes from a central granulite-facies zone of the basement complex were dated by the SHRIMP U-Pb method in order to constrain the timing of metamorphic and related igneous processes and to identify possible age inheritance. Monazite from two migmatites yielded within error identical ages of 499 ± 10 Ma and 493 ± 9 Ma. Coexisting zircon gave ages of 500 ± 4 Ma and 484 ± 5 Ma for a metatexite (two age populations) and 475 ± 4 Ma for a diatexite. Zircon populations from a migmatitic gneiss and a posttectonic granitic dyke yielded well-defined ages of 488 ± 6 Ma and 482 ± 4 Ma, respectively. There is only minor evidence of age inheritance in zircons of these four samples. Zircon from two other samples (metatexite, posttectonic granitic dyke) gave scattered 206Pb-238U ages. While there is a component similar in age and in low Th/U ratio to those of the other samples, inherited components with ages up to c. 3 Ga predominate. In the metatexite, a major detrital contribution from 545 - 680 Ma old source rocks can be identified. The new age data support the model that granulite- to high- amphibolite-facies metamorphism and related igneous processes in basement rocks of northwestern Oates Land were confined to a relatively short period of time of Late Cambrian to early Ordovican age. An age of approximately 500 Ma is estimated for the Ross-orogenic granulite-facies metamorphism from consistent ages of monazite from two migmatites and of the older zircon age population in one metatexite. The variably younger zircon ages are interpreted to reflect mineral formation in the course of the post-granulite-facies metamorphic evolution, which led to a widespread high-amphibolite-facies retrogression and in part late-stage formation of ms+bi assemblages in the basement rocks and which lasted until about 465 Ma. The presence of inherited zircon components of latest Neoproterozoic to Cambrian age indicates that the high- to very-grade migmatitic basement in northwestern Oates Land originated from clastic series of Cambrian age and, therefore, may well represent the deeper-crustal equivalent of lower-grade metasedimentary series of the Wilson Terrane.