1,721,022 research outputs found
Petrography 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, 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
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
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)
Amphibole-bearing metamorphic clasts in ANDRILL AND-2A core: A provenance tool to unravel the Miocene Glacial history in the Ross Embayment (western Ross Sea, Antarctica)
No full textA petrological investigation of amphibolebearing metamorphic clasts in the ANDRILL AND-2A core allows a detailed comparison with similar lithologies from potential source regions, leading to the identifi cation of three distinct provenance areas in the present-day segment of the Transantarctic Mountains between the Byrd Glacier and the Blue Glacier (Mulock-Skelton glacier area, the Britannia Range, and the Koettlitz-Blue glacier area in the Royal Society Range). A key role in the comparison is played by the wide range of Ca-amphibole compositions, type of intracrystalline zoning, mineral assemblages, and fabrics, which refl ect different bulk rocks and metamorphic conditions. Ca-amphibole compositions and zonations also offer the opportunity for the application of geothermobarometry methods, which, consistent with literature data, provide further evidence that the three provenance regions correspond to distinct metamorphic terrains with pervasive medium-pressure amphibolitegrade conditions restricted to the Britannia Range. The study contributes new insights into the depositional processes in a variety of glacial environments ranging from open marine with icebergs to distal, proximal, and subglacial settings. The results also highlight the record of two distinct glacial scenarios refl ecting either short-range (<100 km) fl uctuations of paleoglaciers in the Royal Society Range with dominant fl ows from W to E, or larger volume of ice sourced from southernmore outlet glaciers from the Skelton-Byrd glacier area with fl ow lines running N-S close to the Transantarctic Mountains front. Both scenarios demonstrate the importance of the AND-2A core to reveal a hitherto unavailable, near-fi eld record of dynamic paleoenvironmental history through the Miocene. © 2011 Geological Society of America
Amphibole-bearing metamorphic clasts in ANDRILL AND-2A core: A provenance tool to unravel the Miocene glacial history in the Ross Embayment (western Ross Sea, Antarctica)
No full textA petrological investigation of amphibole-bearing metamorphic clasts in the ANDRILL AND-2A core allows a detailed comparison with similar lithologies from potential source regions, leading to the identification of three distinct provenance areas in the present-day segment of the Transantarctic Mountains between the Byrd Glacier and the Blue Glacier (Mulock-Skelton glacier area, the Britannia Range, and the Koettlitz-Blue glacier area in the Royal Society Range). A key role in the comparison is played by the wide range of Ca-amphibole compositions, type of intracrystalline zoning, mineral assemblages, and fabrics, which reflect different bulk rocks and metamorphic conditions. Ca-amphibole compositions and zonations also offer the opportunity for the application of geothermobarometry methods, which, consistent with literature data, provide further evidence that the three provenance regions correspond to distinct metamorphic terrains with pervasive medium-pressure amphibolite-grade conditions restricted to the Britannia Range. The study contributes new insights into the depositional processes in a variety of glacial environments ranging from open marine with icebergs to distal, proximal, and subglacial settings. The results also highlight the record of two distinct glacial scenarios reflecting either short-range (<100 km) fluctuations of paleoglaciers in the Royal Society Range with dominant flows from W to E, or larger volume of ice sourced from southernmore outlet glaciers from the Skelton-Byrd glacier area with flow lines running N-S close to the Transantarctic Mountains front. Both scenarios demonstrate the importance of the AND-2A core to reveal a hitherto unavailable, near-field record of dynamic paleoenvironmental history through the Miocene
Clast 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
Integrated provenance and detrital thermochronology studies on the ANDRILL AND-2A drill core: Late Oligocene-Early Miocene exhumation of the Transantarctic Mountains (southern Victoria Land, Antarctica)
No full textDetrital apatite fission-track data combined with provenance analysis of gravel-fraction detritus are used in this study to investigate the Neogene exhumation of the West Antarctic Rift System. Samples have been collected from the upper 1000 m of the ANDRILL AND-2A drill core, which documents the Miocene history of the Victoria Land Basin. Most samples have apatites with fission-track ages between 23 and 36 Ma and gravel clasts derived from the Erebus Volcanic Province and the Transantarctic Mountains exposed along the southern Victoria Land coast. These results indicate the existence of a so far undetected Oligocene ⁄ Early Miocene exhumation phase in the region between the Blue–Koettlitz and Skelton–Mulock glaciers, suggesting the importance of fluctuation of local glaciers in the Royal Society Range and ⁄ or expansions into the McMurdo Sound of an ice sheet mainly sourced by larger outlet glaciers located further south
The record of Miocene climatic events in AND-2A drill core (Antarctica): Insights from provenance analyses of basement clasts
No full textThis paper includes the results of a detailed quantitative provenance investigation on gravel-size clasts occurring within the late Early to Late Miocene sedimentary glacimarine section recovered for the first time by the AND-2A core in the SW sector of the Ross Sea (southern McMurdo Sound, Antarctica). This period of time is of crucial interest, as it includes two of the major Cenozoic events in the global climatic evolution: the mid-Miocene climatic optimum and the middle Miocene climate transition. Petrographical and mineral chemistry data on basement clasts allow to individuate two different diagnostic clast assemblages, which clearly suggest two specific sectors of southern Victoria Land as the most likely sources: the Mulock-Skelton glacier and the Koettlitz-Blue glacier regions. Distribution patterns reveal high fluctuations of the detritus source areas throughout the investigated core interval, variations which can be interpreted as the direct result of an evolving McMurdo Sound paleogeography during the late Early to Late Miocene. Consistently with sedimentological studies, gravel-fraction clast distribution patterns clearly testify that the Antarctic ice sheet experienced a dramatic contraction at ca. 17.35 ± 0.14. Ma (likely correlated to the onset of the climatic optimum), and in a < ca. 100. ka time window passing from a glacial scenario comparable to the last glacial maximum (Phase 1) to a very dynamic glacial environment (Phase 2). Phase 2 conditions persisted through the early Middle Miocene (to ca. 14.2. Ma), when a major expansion of the Antarctic ice sheet is hypothesized, likely contemporaneously to the onset of the middle Miocene climate transition. Therefore, provenance and distribution studies of gravel-fraction clasts show that the variations of paleoenvironmental drivers characterising this period were able to exert deep transformation of the Antarctic ice sheet and reveal the methodology to be a powerful tool for the reconstruction of paleo-glacial-flow direction and paleogeographic scenarios. © 2010 Elsevier B.V
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