GeoScienceWorld
Volume

Antarctica and Supercontinent Evolution

Edited by S. L. Harley, I. C. W. Fitzsimons and Y. Zhao

Abstract

Antarctica preserves a rock record that spans three and a half billion years of history and has a remarkable story to tell about the evolution of our Earth, from the hottest crustal rocks yet found in an orogenic system, to the assembly and breakup of Gondwana in the Phanerozoic. This volume highlights our improved understanding of the tectonic events that have shaped Antarctica and how these potentially relate to supercontinent assembly and fragmentation. The internal constitution of the East Antarctic Shield is assessed using information available from the basement geology and from detritus preserved as Mesozoic sediments in the Trans Antarctic Mountains. Accretionary orogenesis along the proto-Pacific margin of Antarctica is examined and the volumes of intracrustal melting compared with juvenile magma additions in these complex orogenic systems assessed. This volume demonstrates the diversity of approaches required to elucidate and understand crustal evolution and evaluate the supercontinent concept.

  1. Page 8
    Abstract
    Corresponding author (e-mail: Simon.Harley@ed.ac.uk)

    The Antarctic rock record spans some 3.5 billion years of history, and has made important contributions to our understanding of how Earth's continents assemble and disperse through time. Correlations between Antarctica and other southern continents were critical to the concept of Gondwana, the Palaeozoic supercontinent used to support early arguments for continental drift, while evidence for Proterozoic connections between Antarctica and North America led to the ‘SWEAT’ configuration (linking SW USA to East Antarctica) for an early Neoproterozoic supercontinent known as Rodinia. Antarctica also contains relicts of an older Palaeo- to Mesoproterozoic supercontinent known as Nuna, along with several Archaean fragments that belonged to one or more ‘supercratons’ in Neoarchaean times. It thus seems likely that Antarctica contains remnants of most, if not all, of Earth's supercontinents, and Antarctic research continues to provide insights into their palaeogeography and geological evolution. One area of research is the latest Neoproterozoic–Mesozoic active margin of Gondwana, preserved in Antarctica as the Ross Orogen and a number of outboard terranes that now form West Antarctica. Major episodes of magmatism, deformation and metamorphism along this palaeo-Pacific margin at 590–500 and 300–230 Ma can be linked to reduced convergence along the internal collisional orogens that formed Gondwana and Pangaea, respectively; indicating that accretionary systems are sensitive to changes in the global plate tectonic budget. Other research has focused on Grenville-age (c. 1.0 Ga) and Pan-African (c. 0.5 Ga) metamorphism in the East Antarctic Craton. These global-scale events record the amalgamation of Rodinia and Gondwana, respectively. Three coastal segments of Grenville-age metamorphism in the Indian Ocean sector of Antarctica are each linked to the c. 1.0 Ga collision between older cratons but are separated by two regions of pervasive Pan-African metamorphism ascribed to Neoproterozoic ocean closure. The tectonic setting of these events is poorly constrained given the sparse exposure, deep erosion level and likelihood that younger metamorphic events have reactivated older structures. The projection of these orogens under the ice is also controversial, but it is likely that at least one of the Pan-African orogens links up with the Shackleton Range on the palaeo-Pacific margin of the craton. Sedimentary detritus and glacial erratics at the edge of the ice sheet provide evidence for the c. 1.0 and 0.5 Ga orogenesis in the continental interior, while geophysical data reveal prominent geological boundaries under the ice, but there are insufficient data to trace these features to exposed structures of known age. Until we can resolve the subglacial geometry and tectonic setting of the c. 0.5 and 1.0 Ga metamorphism, there will be no consensus on the configuration of Rodinia, or the size and shape of the continents that existed immediately before and after this supercontinent. Given this uncertainty, it is premature to speculate on the role of Antarctica in earlier supercontinents, but it is likely that Antarctica will continue to provide important constraints when our attention shifts to these earlier events.

  2. Page 42
    Abstract
    Corresponding author (e-mail: emikhalsky@mail.ru)

    Within the Rayner Province in the Lambert Glacier area, two Proterozoic lithotectonic zones are distinguished, which differ in age and lithology. In the Fisher Zone, a significant juvenile component (ɛNd(t)=+2 to +4) is represented by mafic, intermediate and felsic plutonic and volcanic rocks; the tectonomagmatic processes were concentrated at c. 1400–1200 Ma. In the Beaver Zone, orthogneisses record multiple emplacement, metamorphism and ductile deformation at c. 1150–930 Ma. New U–Pb SHRIMP-II zircon ages (c. 1140 Ma and 1095 Ma – protolith emplacement; c. 950–850 and c. 540 Ma – metamorphism), chemical and Sm–Nd isotopic data indicate that both zones have their continuations in the eastern Amery Ice shelf coast. The Rayner Province has some geological features in common with the Albany-Fraser Orogen in Western Australia, suggesting that these regions evolved in similar tectonic environments at c. 1400–1300 Ma, followed by steady closure, from east to west, of the ocean that separated the Mawson Continent from Western Australia.

    Supplementary material: Chemical compositions of rocks, a summary of trace element ratios, a summary of published U–Pb dates, field photo views, new U–Pb analyses by SIMS SHRIMP-II and new Sm–Nd data are available at http://www.geolsoc.org.uk/SUP18621

  3. Page 66
    Abstract
    Corresponding author (e-mail: michael.flowerdew@casp.cam.ac.uk)

    New feldspar lead isotope compositions of crystalline rocks from the Indian Ocean sector of East Antarctica, in conjunction with the review of data from elsewhere within the continent and from continents formerly adjacent within Gondwana, refine boundaries and evolutionary histories of terranes previously inferred from geological mapping and complementary isotope studies. Coastal Archaean Vestfold and Napier complexes have overlapping compositions and had Pb isotopes homogenized at 2.5 Ga sourced from or within already fractionated protoliths with high and variable U–Pb. Identical compositions from the Dharwar Craton of India support a correlation with these Antarctic terranes. The Proterozoic–Palaeozoic Rayner Complex and Prydz Belt yield more radiogenic compositions and are broadly similar and strongly suggest these units correlate with parts of the Eastern Ghats Belt of India. A strikingly different signature is evident from the inboard Ruker Complex, which yielded unradiogenic compositions. This complex is unlike any unit within India or Australia, suggesting that these rocks represent exposures of an Antarctic (Crohn) Craton. Compositions from the enigmatic Rauer Terrane are consistent with a shared early history with the Ruker Complex but with a different post-Archaean evolution.

    Supplementary material: Feldspar LA-ICP-MS Pb isotope data are available at http://www.geolsoc.org.uk/SUP18622

  4. Page 80
    Abstract
    Corresponding author (e-mail: esgrew@maine.edu)

    Granulite-facies paragneisses enriched in boron and phosphorus are exposed over c. 15×5 km2 in the Larsemann Hills, Antarctica. The most widespread are biotite gneisses containing centimetre-sized prismatine crystals, but tourmaline metaquartzite and borosilicate gneisses are richest in B (676–19 700 µg/g or 0.22–6.34 wt%; B2O3). Chondrite-normalized rare-earth element (REE) patterns give two groups: (1) LaN>150, Eu*/Eu<0.4, which comprises most apatite-bearing metaquartzite and metapelite, tourmaline metaquartzite, and Fe-rich rocks (up to 2.3 wt%; P2O5); (2) LaN<150, Eu*/Eu > 0.4, which comprises most borosilicate and sodic leucogneisses (2.5–7.4wt%; Na2O). Enrichment in boron and phosphorus is attributed to premetamorphic hydrothermal alteration, either in a rifted, most likely marine basin or in a mud volcanic system located inboard of a c. 1000 Ma continental arc that was active along the leading edge of the Indo-Antarctic craton. This margin developed before collision with the Australo-Antarctic craton (c. 530 Ma) merged these rocks into Gondwana and sutured them into their present position in Antarctica. Rocks lithologically similar to those in the Larsemann Hills include prismatine-bearing granulites in the Windmill Islands, Wilkes Land, and tourmaline–quartz rocks, sodic gneisses and apatitic iron formation in the Willyama Supergroup, Broken Hill, Australia.

  5. Page 102
    Abstract
    Corresponding author (e-mail: liuxchqw@yahoo.com.cn)

    The Prince Charles Mountains (PCM)–Prydz Bay region in East Antarctica experienced the late Mesoproterozoic/early Neoproterozoic (c. 1000–900 Ma) and late Neoproterozoic/Cambrian (c. 550–500 Ma) tectonothermal events. The late Mesoproterozoic/early Neoproterozoic tectonothermal event dominates the Rayner Complex and spreads over the main part of the Prydz Belt. This event includes two episodes (or stages) of metamorphism accompanying the intrusion of syn- to post-orogenic granitoids at c. 1000–960 Ma and c. 940–900 Ma. The c. 1000–960 Ma metamorphism in the northern PCM and Mawson Coast records medium- to low-pressure granulite facies conditions accompanied by a near-isobaric cooling path, whereas the c. 940–900 Ma metamorphism in Kemp Land reaches relatively higher PT conditions followed by a near-isothermal decompression or decompressive cooling path. The late Mesoproterozoic/early Neoproterozoic orogeny (i.e. the Rayner orogeny) involved a long-lived (c. 1380–1020 Ma) magmatic accretion along continental/oceanic arcs and a protracted or two-stage collision of the Indian craton with a portion of East Antarctica, forming the Indian–Antarctic continental block independent of the Rodinia supercontinent. The late Neoproterozoic/Cambrian tectonothermal event pervasively overprinted on both Archaean–Proterozoic basements and cover sequences in the Prydz Belt. Except for high-pressure granulite boulders from the Grove Mountains, the metamorphism of most rocks records medium-pressure granulite facies conditions with a clockwise P–T path. In contrast, this event is lower grade (greenschist–amphibolite facies) and localized in the PCM. Regionally, the late Neoproterozoic/Cambrian tectonothermal event seems to have developed on the southeastern margin of the Indo-Antarctic continental block, suggesting that the major suture should be located southeastwards of the presently exposed Prydz Belt. The precise dating for different rock types reveals that the late Neoproterozoic/Cambrian orogeny (i.e. the Prydz orogeny) commenced at c. 570 Ma and lasted until c. 490 Ma, which is roughly contemporaneous with the late collisional stage of the Brasiliano/Pan-African orogenic systems in Gondwanaland. Therefore, the final assembly of the Gondwana supercontinent may have been completed by the collision of a number of cratonic blocks during the same time period.

  6. Page 120
    Abstract
    Corresponding author (e-mail: t-adachi@scs.kyushu-u.ac.jp)

    Metamorphic rocks in the central part of Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica, are classified into three types based on petrological characteristics. (i) The Austkampane area preserves c. 800 °C and 0.5–0.6 GPa peak metamorphic conditions followed by decompression and subsequent isobaric cooling and later hydration (A-type). (ii) The Brattnipene and eastern Menipa area preserve peak P–T conditions of c. 800 °C and 0.7–0.8 GPa with subsequent isobaric cooling and later hydration (B-type). (iii) The area including Lunckeryggen, southern Walnumfjella and western Menipa preserves an amphibolite–facies peak metamorphic condition with signatures of prograde metamorphism (L-type), which are typically unaffected by the retrograde hydration event. Peak granulite–facies metamorphism of A- and B-type rocks are contemporaneous at c. 640–600 Ma, but a difference in the P–T paths between these rocks can be explained by thrusting of the A-type rock unit onto the B-type rock unit. By contrast, the timing of the metamorphism of the L-type rocks is significantly younger at c. 550 Ma, possibly related to the intrusion of pegmatites and granitoids. These metamorphic records in the central part of the Sør Rondane Mountains can be a test ground for the regional tectonic processes proposed for the orogeny related to Gondwana formation.

    Supplementary material: Representative mineral compositions are listed at http://www.geolsoc.org.uk/SUP18623

  7. Page 142
    Abstract
    Corresponding author (e-mail: toshkawa@sci.ehime-u.ac.jp)

    A possible armalcolite pseudomorph has been identified in garnet–sillimanite gneiss from Skallevikshalsen, located c. 30 km NE of Rundvågshetta, in a terrane with the highest metamorphic grade in the Lützow-Holm Complex, East Antarctica. It occurs as an Fe–Mg–Ti compositional domain consisting of ilmenite, rutile and pseudorutile, partially mantled by rutile within ilmenite. The domain yields an average XMg of 0.171±0.036 exceeding by 3 wt% TiO2 from armalcolite stoichiometry, while the analysis closest to armalcolite stoichiometry has an XMg value close to 0.202. Host ilmenite with 0.4 mol% hematite is in contact with prismatic sillimanite, quartz, plagioclase and K-feldspar.

    In run products of annealing experiments performed to investigate the origin of the pseudomorph, armalcolite–ilmenite reaction coronae were developed around relict rutile in rock fragments of quartz eclogite from the Higashi-Akaishi mass of the Sanbagawa belt, central Shikoku, Japan. The experiments were carried out at 1 atm and 960–1050 °C with wüstite–magnetite buffer and imply a minimum temperature of 1290 °C for armalcolite stability when extrapolated to Skallevikshalsen pressures of 1.0 GPa. Mineral chemistry thermobarometry for Skallevikshalsen yields a metamorphic path with PT peak conditions of 0.88–1.1 GPa and 970–1050 °C, followed by retrograde metamorphism at 0.6 GPa and 780 °C, and finally metasomatic alteration at c. 630 °C. This PT path matches that for similar ultrahigh-temperature metamorphic rocks from Rundvågshetta and Sri Lanka, and is markedly lower in temperature than the unreasonable estimates based on armalcolite stability. This discrepancy is inferred to reflect chemical impurities in armalcolite that lower its minimum temperature stability by more than 200 °C.

  8. Page 176
    Abstract
    Corresponding author (e-mail: cyak@umd.edu)

    The Fosdick migmatite–granite complex of West Antarctica preserves evidence of two crustal differentiation events along a segment of the former active margin of Gondwana, one in the Devonian–Carboniferous and another in the Cretaceous. The Hf–O isotope composition of zircons from Devonian–Carboniferous granites is explained by mixing of material from two crustal sources represented by the high-grade metamorphosed equivalents of a Lower Palaeozoic turbidite sequence and a Devonian calc-alkaline plutonic suite, consistent with an interpretation that the Devonian–Carboniferous granites record crustal reworking without input from a more juvenile source. The Hf–O isotope composition of zircons from Cretaceous granites reflects those same two sources, together with a contribution from a more juvenile source that is most evident in the detachment-hosted, youngest granites. The relatively non-radiogenic ɛHf isotope characteristics of zircons from the Fosdick complex granites are similar those from the Permo-Triassic granites from the Antarctic Peninsula. However, the Fosdick complex granites contrast with coeval granites in other localities along and across the former active margin of Gondwana, including the Tasmanides of Australia and the Western Province of New Zealand, where the wider range of more radiogenic ɛHf values of zircon suggests that crustal growth through the addition of juvenile material plays a larger role in granite genesis. These new results highlight prominent arc-parallel and arc-normal variations in the mechanisms and timing of crustal reworking v. crustal growth along the former active margin of Gondwana.

    Supplementary material: Figs S1 and S2 are available at http://www.geolsoc.org.uk/SUP18625

  9. Page 218
    Abstract
    Corresponding author (e-mail: robert.schoener@lbeg.niedersachsen.de)

    Detrital zircons of eight sandstone samples from the Triassic–Early Jurassic Section Peak Formation (Victoria Group, Beacon Supergroup) in northern Victoria Land, Antarctica, were investigated by U–Pb LA–ICPMS dating. The basin was flanked by the East Antarctic craton, and by a magmatic arc at the palaeo-Pacific margin of Gondwana. It accommodated sandstones ranging from quartzo-feldspathic to volcaniclastic in composition. The detrital zircon age spectra yield pronounced concentrations at c. 190–250 Ma, 500–700 Ma and 800–1200 Ma. The proportion of Triassic–Early Jurassic zircons increases from base to top of the formation, and correlates positively with the abundance of detrital volcanic rock fragments. The youngest zircon ages are close to the stratigraphic age of each sample, indicating contemporaneous magmatic activity along the active margin of Gondwana. Igneous rocks that formed during the Ross Orogeny (c. 470–545 Ma) were a minor source only, suggesting that the Ross Orogen became progressively covered by sediments as the basin expanded. Pan-African (c. 500–700 Ma) and Grenville (c. 800–1200 Ma) age zircons may have been derived from crustal sources currently covered beneath the polar ice sheet, although recycling from Cambro-Ordovician units provides an alternative explanation.

    Supplementary material: The exact results of the age analyses of all samples are presented in Tables A1 to A8 at http://www.geolsoc.org.uk/SUP18624

Purchase Chapters

Recommended Reading