At Radok Lake, northern Prince Charles Mountains, more than 2500 m of Permian Amery Group strata in the Beaver Lake graben are downfaulted against a Proterozoic metamorphic basement. An irregular blanket of late Cenozoic Pagodroma Tillite, up to 100 m thick, overlies the Permian strata and Proterozoic basement. The metamorphic basement comprises repeatedly deformed, high-grade felsic, mafic, aluminous and minor calc-silicate rocks derived from igneous and sedimentary precursors. Low- to medium-pressure granulite-facies metamorphism, assumed to be the ~1000 Ma event widely recorded in the East Antarctic Shield, was followed by incipient to moderate amphibolite-facies retrogression. Three folding events are recognized. Sporadic occurrences of pseudotachylite in the basement represent seismic faulting after substantial uplift and erosion. At the southern end of Radok Lake the Permian coarse alluvial fan facies, the Radok Conglomerate, is overlain disconformably by the Dart Fields Conglomerate, a basal member of the Bainmedart Coal Measures. Five kilometres along strike the deltaic Panorama Point beds, containing sideritic ironstone strata, are overlain conformably by arkosic sandstones of the basal Bainmedart Coal Measures. The Amery Group is intruded by two alnöite sills and at least five altered alkaline mafic dykes. The Pagodroma Tillite contains reworked marine microfossils and records the erosion of higher latitude Cenozoic marine sequences by an expanding ancestral Lambert Glacier.
A total of 25 samples from 82 ash layers interbedded with middle Miocene to recent diatomaceous (variably calcareous) oozes and silty clays overlying Oligocene igneous basement was recovered from Ocean Drilling Program Hole 887 A on the Patton-Murray seamount platform in the Gulf of Alaska, northeast Pacific.The ashes consist predominantly of elongate ( >5 to < 150 µm), tubular, and bubble-wall fragments probably derived from plinian eruption cloud fallout.Major element compositions determined by electron microprobe analysis of individual vitric shards are tholeiitic and bimodal, with predominant medium-K andesite and medium-to high-K rhyolite groups.There is no evidence from this sample set for consistent temporal geochemical changes.High Ba/Nb and Sm/Ti of these ash samples are similar to island-arc magmas in general.Chondrite-normalized La of 40 to 100, Yb of 15 to 30, and La/Yb of about 2 to 3 are similar to tholeiitic volcanic rock series of the Aleutian arc.A major increase in the number of ash layers with depth in the core occurs interlayered with sediments younger than 2.7 Ma.
Abstract In the coastal mountain chain of southern Victoria Land approximately 4,000 km. 2 of glacier-cut valleys and dividing ranges are almost completely ice-free, while the surrounding areas are fully glacierized. In the ice-free Wright Valley and Victoria Valley systems evidence of four glaciations is recognized. The earliest two glaciations were the most extensive; glaciers flowed eastwards from the ice plateau through the coastal ranges and cut broad valleys extending to McMurdo Sound and the Ross Sea. The moraines of these glaciations are thin and highly weathered. The third glaciation was less extensive, consisting of advances by smaller glaciers derived from the inland ice plateau, the Wilson Piedmont Glacier and névé fields in the dividing ranges. The surfaces of moraines of this glaciation are now partly covered by saline lakes, evaporite deposits and extensive areas of desert pavements strewn with ventifacts. The fourth and youngest glaciation comprised small advances by remnants of the plateau-fed valley glaciers. Thick boulder moraines of this glaciation overlie earlier deposits. During each glaciation the greatest volume of ice was derived from the inland ice plateau. The volume of ice entering the valleys was dependent on the difference in altitude between the plateau surface and subglacial rock thresholds at the valley heads. Decrease in the surface level of the inland ice plateau caused the rock thresholds to increasingly hinder the eastward flow of plateau ice until practically no ice could flow down into the valleys, thereby terminating the glaciation. Such a condition exists at the present time.
Abstract Abstract The basement complex exposed in the Wright Valley consists of more than 15,000 ft of lolded Precambrian — Lower Cambrian marbles, hornfelses, and schists (Asgard Formation), invaded by acid plutonic rocks. The plutonic rocks comprise three intrusive phases. The oldest intrusives are a strongly foliated granite-gneiss (Olympus) and a porphyritic granite (Dais), cut by pegmatite dykes and veins. The second intrusive phase consists of microdiorite (Loke) and granodiorite (Theseus) dykes intruding the metasediments, granite-gneiss, and granite. The third intrusive phase includes an undeformed homogeneous granite (Vida) containing in a few localities large bodies of amphibolite, and dense swarms of younger lamprophyre and porphyry dykes (Vanda) invading all earlier rocks. The peneplained basement surface is overlain unconformably by more than 4,000 ft of mid-Paleozoic to mid-Mesozoic sediments of the Beacon Sandstone (Group). Ferrar Dolerite sills and dykes intrude the basement complex and the Beacon Sandstone. Late Quaternary deglacierisation has left the Wright Valley ice-free for approximately 30 miles.
The Cenozoic glacial history of East Antarctica is recorded in part by the stratigraphy of the Prydz Bay—Lambert Graben region. The glacigene strata and associated erosion surfaces record at least 10 intervals of glacial advance (with accompanying erosion and sediment compaction), and more than 17 intervals of glacial retreat (enabling open marine deposition in Prydz Bay and the Lambert Graben). The number of glacial advances and retreats is considerably less than would be expected from Milankovitch frequencies due to the incomplete stratigraphic record. Large advances of the Lambert Glacier caused progradation of the continental shelf edge. At times of extreme glacial retreat, marine conditions reached > 450 km inland from the modern ice shelf edge. This review presents a partial reconstruction of Cenozoic glacial extent within Prydz Bay and the Lambert Graben that can be compared to eustatic sea-level records from the southern Australian continental margin.
Summary Large glaciers derived from the ice plateau cut through the mountain ranges of South Victoria Land to the Ross Sea. In the McMurdo Sound region some glaciers have retreated from portions of their courses leaving almost ice free "dry valleys". The general geology of one such valley, provisionally named here the Victoria Dry Valley, is discussed in detail. The original ice level of this valley was 1,000 ft to 1,200 ft higher than the present remnants of Victoria Glacier. During the summer months meltwater from remnant cirque and glacier ice accumulates as extensive lakes in the depressions of the moraine-strewn valley floor. The basement is exposed in Victoria Drjf Valley as thick uniform sheets of granite, separated by younger dolerite sills. Acidic and basic dykes antedating sill intrusion are associated with the granite basement. The petrology and field relations of the granite, dykes, and dolerite sills resemble those of similar exposures in the Kukri Hills, 30 miles to the south. It is probable that the rocks of Victoria Dry Valley forrti part of thé northern continuation of the basement complex of South Victoria Land.
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