1,721,189 research outputs found
Petrography, mineral chemistry and provenance of basement clasts in the CRP-1 drillcore (Victoria Land Basin, Antarctica)
No full textPetrographical and mineral chemistry data are described for the most representative basement lithologies occurring as clasts (pebble grain-size class) from the CRP-1 drillcore. Most pebbles consist of either undeformed or foliated biotite with or without hornblende monzogranites. Other rock types include biotite with or without garnet syenogranite, biotite-hornblende granodiorite, tonalite, monzogranitic porphyries, haplogranite, quartz-monzonite (restricted to the Quaternary section), Ca-silicate rocks and biotite amphibolite (restricted to the Miocene strata). The common and ubiquitous occurrence of biotite with or without hornblende monzogranite pebbles, in both the Quaternary and Miocene sections, apparently mirrors the dominance of these rock types in the granitoid assemblages which are presently exposed in the upper Precambrian- lower Palaeozoic basement of south Victoria Land. The other CRP-1 pebble lithologies show petrographical features which consistently support a dominant supply from areas of the Transantarctic Mountains located to the west and south-west of the CRP-1 site, and they thus further corroborate a model of local provenance for the supply of basement clasts to the CRP-1 sedimentary strata
The lowP/highT metamorphic overprint in the "Gneiss Group" (Larderello geothermal field, Italy): a thermal record of the Herynian orogenic extension in the basament of southern Tuscany. In: late orogenic extension in mountain belt.
No full textPetrography and provenance of basement clasts and clast variability in CRP-3 drillcore (Victoria Land Basin, Antarctica)
No full textDistribution patterns and petrographical and mineral chemistry data are described for the most representative basement lithologies occurring as clasts in the c. 824 m thick Tertiary sedimentary sequence at the CRP-3 drillsite. These are granule to boulder grain size clasts of igneous and metamorphic rocks. Within the basement clast assemblage, granitoid pebbles are the predominant lithology. They consist of dominant grey biotite-bearing monzogranite, pink biotite-hornblende monzogranite, and biotite-bearing leucomonzogranite. Minor lithologies include: actinolite-bearing leucotonalite, microgranite, biotite-hornblende quartz-monzonitic porphryry, and foliated biotite leucomonzogranite. Metamorphic clasts include rocks of both granitic and sedimentary derivation. They include mylonitic biotite orthogneiss, with or without garnet, muscovite-bearing quartzite, sillimanite-biotite paragneiss, biotite meta-sandstone, biotite spotted schist, biotite-calcite-clinoamphibole meta-feldspathic arenite, biotite-calcite-clinozoisite meta-siltstone, biotite±clinoamphibole meta-marl, and graphite-bearing marble. As in previous CRP drillcores, the ubiquitous occurrence of biotite±hornblende monzogranite pebbles is indicative of a local provenance, closely mirroring the dominance of these lithologies in the on-shore basement, where the Cambro-Ordovician Granite Harbour Intrusive Complex forms the most extensively exposed rock unit
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
Towards 3-D petrography of glacigenic sediments: the potential of high-resolution X-ray computed tomography
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