1,721,048 research outputs found
Petrography and provenance of basement clasts in CIROS-1 core, McMurdo Sound, Antarctica
No full textPetrographical, mineral chemistry and distribution data on pebble- to boulder-size clasts in the Early Miocene-Late Eocene sedimentary succession recovered at CIROS-1 drillsite (McMurdo Sound) are described here. Clasts are dominated by granitoids and dolerites, with minor occurrences of sedimentary, volcanic and metamorphic rocks. Granitoid clasts are mainly represented by deformed or undeformed biotite and biotite-hornblende monzogranites, with minor occurrences of leucogranites, porphyries and tonalites. Metamorphic rocks consist of orthogneisses and metasediments, including both medium- to high-grade and low-grade varieties. Clast distribution suggests three major episodes of erosion, which punctuate the uplift and unroofing history of the Transantarctic Mountains in Victoria Land. Erosion of cover rocks (Beacon and Ferrar Supergroups) dominates during the first and second phases (c. 702 to c. 200 mbsf), while the third erosional phase is mainly connected to the deeper unroofing of basement rocks (Granite Harbour Intrusive Complex and Koettlitz. Group; above c. 200 mbsf). The source area is identified with the Transantarctic Mountains sector adjacent to New Harbour (Dry Valleys and Royal Society blocks). All the phases are consistent with a clast provenance mainly within the Dry Valleys Block, the Royal Society Block being subordinately involved only within the earliest and latest sedimentation of the cored succession (c. 702 to c. 326 mbsf and above c. 200 mbsf)
Geology and tectono-metamorphic evolution of the Read Group, Shackleton Range: a part of the East Antarctic Craton
No full textGeological mapping and new structural observations during the 1994/95 EUROSHACK Expedition lead us to propose a new lithological subdivision of the Proterozoic Read Group, which is exposed in a tectonic window framed by the Ross-age low-grade Mount Wegener Nappe in the southern Shackleton Range. The oldest rock-units of the Read Group comprise several varieties of high-grade gneisses, ranging in composition from pelitic to quartzo-feldspathic and mafic, interlayered with minor amphibolites, Ca-silicate rocks, quartzites, marbles and serpentinites. On the basis of the petrological evidence provided by the mafic gneisses, the metamorphic evolution of these rock units includes at least three main metamorphic stages: a medium-P granulite facies stage (8 kbar, ca. 800°C) (M1), a low-P upper amphibolite to granulite facies stage (5 kbar, ca. 700 °C) (M2), and a low-P lower-amphibolite to greenschist facies stage (M3). Several distinct plutonic suites were distinguished and mapped. They range from syn-metamorphic metaluminous to peraluminous granitoids to post-tectonic swarms of peraluminous granitic dykes. The plutonic suites were emplaced mainly after M1 and throughout M2. The overall tectono-metamorphic evolution from M1 to M3 is interpreted as a continuous record of the exhumation of a thickened crust, controlled mainly by extension and triggered by voluminous magmatism in middle-Proterozoic time. Younger, Ross-age deformation and greenschist facies metamorphism occur mainly close to the contact zone with the Mount Wegener Nappe and provide evidence for reactivation of the Proterozoic Read Group associated with its incorporation, under a prevailing transpressional regime, within the Ross-age thrust-fold system of the Shackleton Range
Abrupt climatic changes: new evidence from Arctic sedimentary proxies - A proposal open to partnership
No full textThe Mertz Shear Zone (George V Land): implications for australia/Antarctica correlations and East Antarctic Craton/Ross orogen relationships
No full textRelict granulites in the Ross Orogen of northern Victoria Land (Antarctica): I - field occurrence, petrography and metamorphic evolution
No full textGranulite-facies rocks occur as mappable relies in the Wilson Terrane (northern Victoria Land), the lithotectonic unit of the Cambro-Ordovician Ross orogen closest to the East Antarctic craton. Despite the widespread amphibolite-facies overprinting of Ross age, large-scale low-strain tectonic lozenges preserve a layered unit of felsic and quartz-poor garnet+orthopyroxene+/-cordierite metasedimentary granulite, with minor, metre-thick, layers of mafic two-pyroxene granulite and rare lenses of marble. Large bodies of massive enderbite are also present and locally show discordant, intrusive contacts with respect to the layered metasedimentary sequence. Mineral assemblages, reaction textures and geothermobarometric estimates in granulite rocks point to a pre-Ross decompressional evolution from higher-pressure (P=7.7+/-0.7 kbar at T=820+/-100 degrees C) to lower-pressure (6.3+/-0.4 kbar and 830+/-50 degrees C) granulite-facies conditions. Geological and petrological data suggest that the granulite-facies rocks of the Wilson Terrane form a distinct tectonometamorphic unit very similar to other Neoproterozoic granulite-facies terrains of the East Antarctic craton. In this aspect, the occurrence of granulite-rocks within the Transantarctic Mountains strongly suggests the reactivation of the palaeo-Pacific margin of East Antarctica during the Ross orogeny
Analysis of clast lithologies from CIROS-2 core, New Harbour, Antarctica - implications for ice flow directions during Plio-Pleistocene
No full textThis paper reports and discusses the distribution, petrography and mineral chemistry of granule- to boulder-size clasts in the Early Pliocene to Quaternary sedimentary succession recovered by the CIROS-2 drill hole, located near the mouth of the Ferrar Glacier (McMurdo Sound). In the Pliocene interval (166.47-99.27 mbsf), Early Paleozoic basement granitoids (monzogranites and granodiorites) are most common, apart from the basal 13-m-thick diamictite unit, which is dominated by basalt clasts from the late Cenozoic McMurdo Volcanics. In the Pleistocene interval (99.27-0 mbsf) basement granitoids are also the most common, but are largely tonalities. Gabbros and dolerites of the Jurassic Ferrar Supergroup are a minor persistent component throughout the core. In contrast, basement metamorphic rocks and Beacon Supergroup sandstones are present only within the lowest part of the core, the former disappearing above ca. 70.20 mbsf, and the latter above ca. 99.30 mbsf. During Pliocene time, the clast assemblage is consistent with the main source of the detritus from basement rocks to the west, transported by an ancestral Ferrar Glacier through the Transantarctic Mountains, the basal basalts suggesting an invasion of Ross Sea ice into Ferrar Fjord from the south (in the area of Mount Discovery and Mount Morning volcanoes). The dominance of tonalite in Pleistocene clasts also suggests derivation from the coastal Blue Glacier area immediately to the south. The decrease in volcanic clasts from Late Pliocene time may relate to the final construction of the Mount Morning-Mount Discovery peninsula, which acted as a barrier to the northern movement of a grounded Ross Ice Shelf, whereas the appearance of the tonalite clasts suggests periods of ice flow from its present day provenance, the Blue Glacier-Miers Valley area, northward along the coast and then into Ferrar Fjord from the east. © 2005 Elsevier B.V. All rights reserved
Towards 3-D petrography of glacigenic sediments: the potential of high-resolution X-ray computed tomography
No full text'Migmatitic metasedimentary granulites from Mills Peak and Mt. Emison (Wilson Terrane, Northern Victoria Land, Antarctica): a case history of processes involved in the formation of garnet +/- orthopyroxene leucocratic segregations
No full textClast data from CRP cores (Victoria Land Basin): Implications on the uplift history of the Transantarctic Mountains
No full textThe international Cape Roberts Project drilled three holes (CRP-1, 2/2A, 3), distributed along a SE-NW trending traverse at 16-8 km from Cape Roberts in the McMurdo Sound (southern Ross Sea, Antarctica). The 3 holes comprehensively recovered an almost continuous c. 1600 m thick section of Cenozoic glacio-marine sediments at the western margin of the Victoria Land Basin (Fig. 1). At the deepest (939 metre below the sea floor, mbsf) borehole (CRP-3), the Cenozoic sediments were found to rest unconformably on Devonian age arenites of the Beacon Supergroup, indicating a total post-Jurassic offset of the CRP block of c. 3000 m with respect to the adjacent Transantarctic Mountains block south of Mackay Glacier. Clasts (granule- to boulder-grade) are a significant component throughout most of the recovered sediments, which range in lithology from diamictite/sandstone/argillite alternated sequences to conglomerate-bearing sandstone units (confined to the section below 200 mbsf in CRP-3). During all three field drilling seasons, petrological investigations on the coarser-grade clast fractions were focused on the preliminary petrographical characterization of the main litologies and their distribution and abundance throughout the core (Cape Roberts Science Team, 1998, 1999, 2000). Subsequent laboratory analysis were then carried out in order to refine the initial report dataset and highligt some preliminary interpretations about provenance and meaning of detected distribution patterns (Talarico & Sandroni, 1998; Smellie et al., 1999; Talarico et al., 2000; Brink et al., 2000; Sandroni & Talarico, subm.). Similarly to previous drillholes (MSSTS-1, CIROS-1) in the McMurdo Sound, CRP clast lithologies were found to closely reflect the lithological composition of the major onshore geological units (granitoid and metamorphic basement, Beacon Sandstone, Ferrar dolerite, Kirkpatrick basalt, McMurdo Volcanics), thus providing a sound indication of a local provenance. A number of evidence lines based on modal and petrological investigations on granitoid basement clasts (mainly biotite±hornblende, foliated or undeformed monzogranites and ubiquitously distributed) consistently support a supply from areas of the Transantartic Mountain block located to the west and south-west of the drillsites. Nevertheless the scattered occurrence of rare phyllites, apparently confined to the lower part of the CRP-3 section (below 200 mbsf), might provide some hints for a distant (>200 km) provenance from the south (Skelton Glacier-Koettlitz Glacier region). The overall distribution patterns for coarse clasts in the three CRP drillholes provide a clear evidence of an evolving provenance which can be at least partly related to the uplift/erosion history of the on shore TAM blocks west and south of the drillsites. Several erosion phases can be distinguished and a major compositional discontinuity identified at c. 307 mbsf in CRP-2/2A, with granitoid-dominated clasts (plus McMurdo Volcanic Group clasts) above and mainly Ferrar Group lithologies (dolerite, basalt) below. The tectonic meaning of this and other petrological discontinuities detected in CRP cores will be discussed in order to assess their bearing in providing further constrains on the timing and style (gradual, short-lived rapid?) uplift history of the Transantarctic Mountains in Southern Victoria Land
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