Horlick Mountains Research Articles

Age and significance of ‘outboard’ high-grade metamorphics and intrusives of the Ross orogen, Antarctica

We present new U–Pb zircon and 40Ar–39Ar hornblende isotopic data for gneisses and undeformed intrusions from three important and widely separated localities from the northern–eastern ‘outboard’ edge of the Ross orogen in the Queen Maud and Horlick mountains, Antarctica. U–Pb zircon analyses of gneisses that have long represented possible candidates for Precambrian cratonic crust have yielded latest Late Proterozoic to early Paleozoic ages. One paragneiss from the Fallone Nunataks, near Scott Glacier yields a 546+10.6/−18.9Ma age for its youngest zircon population, indicating a maximum latest Neoproterozoic–early Paleozoic (Ross orogeny) age for deformation and fabric development. Two orthogneisses from the Bravo Hills near Shackleton Glacier yield igneous protolith crystallization ages of 535+8.5/−8.9Ma and 517+6.9/−6.5Ma, and one orthogneiss from Woodall Peak near Ramsey Glacier yields a protolith crystallization age of 503.8+6.9/−6.5Ma. Intrusion of the orthogneiss protoliths therefore occurred concomitant with other pretectonic (deformed) subduction-related magmatic rocks associated with the early Paleozoic Queen Maud batholith. The younger limit for deformation of the paragneiss and orthogneiss protoliths is constrained by U–Pb crystallization ages of post-tectonic (undeformed) intrusions of the batholith that intrude the gneisses. These intrusions yield U–Pb crystallization ages of 503.5+6.2/−6.5Ma (post-tectonic, Woodall Peak), 498.4+8.8/−7.6Ma (post-tectonic, Bravo Hills), and 484.7±8.4Ma (syntectonic to post-tectonic, Fallone Nunataks). The younger limit for deformation is further constrained in the Bravo Hills by 40Ar–39Ar hornblende analyses that yield a metamorphic cooling age of 502±7Ma for an orthogneiss. On a regional scale, magmatism commenced by ~535Ma within the Queen Maud batholith. Deformation locally extended into the Late Cambrian to Ordovician, with several areas transitioning to post tectonic magmatism and orogenic cooling by the late Middle Cambrian to Early Ordovician possibly concomitant with phases of slab roll back along the Gondwana margin.

Geophysical studies of the West Antarctic Rift System

Geophysical studies of the West Antarctic Rift System

Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic rift system and a speculation on possible climate forcing

The Cenzoic West Antarctic rift system, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. It is bounded on one side by a spectacular 4-to 5-km-high rift-shoulder scarp (maximum bedrock relief 5 to 7 km) from northern Victoria Land-Queen Maud Mountains to the Ellsworth-Whitmore-Horlick Mountains. Jurassic tholeiites crop out with the late Cenozoic volcanic rocks along the section of the Transantarctic Mountains from northern Victoria Land to the Horlick Mountains. The Cenozoic rift shoulder diverges here from the Jurassic tholeiite trend, and the tholeiites are exposed discontinuously along the lower elevation (1-2 km) section of the Transantarctic Mountains to the Weddell Sea. Various lines of evidence, no one of which is independently conclusive, lead the authors (as others have also suggested) to interpret the following. The Transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of {approximately}1 km/m.y., most recently since mid-Pliocene time, rather than continuously at the mean rate of 100m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. The authors speculate that this uplift may have climatically forcedmore » the advance of the Antarctic ice sheet since the most recent warm period. They suggest a possible synergistic relation between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic rift system and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time.« less

Major features of the distribution of coal‐bearing deposits in Antarctica

Abstract The authors have attempted to assess the potential coal reserves of Antarctica. Several coal‐bearing sedimentary basins are located around the margins of the East Antarctic Platform. The most extensive coal‐bearing deposits, Permian and Triassic in age, are located in the Transantarctic Mountains, where they extend for 2500 km from Victoria Land to the Horlick Mountains. Another significant basin, Permian in age, is that in the Prince Charles Mountains. The authors present a detailed description of the stratigraphy of the coal‐bearing sequences in each of these major basins. Estimates of reserves are as follows: 10.8 billion tons in the Prince Charles Mountains; 6 billion tons in the Queen Alexandra Range in the Transantarctic Mountains, and 130 million tons in southern Victoria Land, also in the Transantarctic Mountains. Some information is also provided on minor coal‐bearing deposits located in the nunataks around the Weddell Sea and Filchner Ice Shelf.

Permian nonmarine bivalves from the Ohio Range, Antarctica

Compressed bivalve fossils collected from the Permian Mount Glossopteris Formation on Mount Glossopteris in the Ohio Range, Horlick Mountains, are identified and described as Palaeanodonta fischeri (Amalitsky). The bivalves are accompanied by fragmented plant material, mainly Glossopteris, and occur roughly at the same stratigraphic horizon as conchostracans on Mount Schopf 10 km to the south.

The discontinuous glacio-eustatic fall in tertiary sea level

In eastern Antarctica at latitude 86° S and 3,000 m elevation, a solifluxion layer and overlying drifts from temperature glaciers are older than the East Antarctic Ice Sheet, which built up after the glacier tongues had reached low ground. The glacial-eustatic drop in sea level eventually amounted to about 60 m by the time this ice sheet had an equilibrium profile. Land ice also covered the western Antarctic archipelago, but no more could accumulate in Antarctica until further cooling allowed “cold” shelf ice to spread, thicken, and come to ground in the former strait between eastern Antarctica and the western Antarctic archipelago. The West Antarctic Ice Sheet then built up, causing an additional drop in sea level of about 5 m. Intensely glaciated landscapes in the Horlick Mountains, now partially buried by this ice sheet, indicate a long interval of glacial erosion in eastern Antarctica before the West Antarctic Ice Sheet existed. The Greenland Ice Sheet, with less critical temperature requirements, may have formed either during this interval, causing a further drop in sea level of about 6 m, or contemporaneously with the West Antarctic Ice Sheet, resulting in a total fall at that time of about 11 m. The crucial spread of Antarctic shelf ice preceded the formation of the first North American and European ice sheets, for until then temperatures were higher than they are today. It probably marks the Pliocene-Pleistocene transition, if this is defined as the point when falling temperatures first reached today's level.

The geology and geochronology of the basement complex of the central Transantarctic Mountains

The central part of the Transantarctic Mountain chain consists of a basement complex of igneous and metamorphic rocks overlain nonconformably by sedimentary rocks of late Paleozoic age, including Permian tillites and coal measures. The basement complex is exceptionally well exposed in the Wisconsin Range of the Horlick Mountains, which are located about 500 km from the South Pole. In this area clastic metasedimentary rocks and overlying metavolcanic rocks of probable pyroclastic origin are intruded by a variety of granitic rocks of the Wisconsin Range batholith, including rapakivi granites and quartz diorites, which are in turn cut by bodies of quartz monzonite, and aplite and pegmatite dikes. The basement complex elsewhere in the central Transantarctic Mountains also includes Cambrian limestones overlain by acid volcanic pyroclastic rocks and lava flows.Age determinations by the Rb–Sr method applied to suites of total rock specimens suggest the presence of two orogenic events accompanied by intrusions of granitic plutons. The first of these occurred about 630 ± 25 m.y. ago and was accompanied by the formation of rapakivi granites. The second took place during the Ordovician Period about 480 ± 10 m.y. ago and involved the intrusion of quartz monzonite and pegmatite dikes. The metasedimentary rocks, which were intruded by both of the granitic rocks, give an apparent age of 460 ± 16 m.y., while the overlying pyroclastic unit was dated at 633 ± 13 m.y. A Precambrian age for the metasedimentary and metavolcanic rocks is consistent with the dating and the field evidence. Rhyolites from localities in the Byrd Mountains and the Long Hills were dated at 489 ± 30 and 498 ± 45 m.y. and are late Cambrian to early Ordovician in age.

Movement Directions in Late Paleozoic Glacial Rocks of the Horlick and Pensacola Mountains, Antarctica

Striae and associated structures beneath and within the Buckeye Tillite in the Ohio Range of the Horlick Mountains show that Permian(?) glaciers moved toward the west-southwest. Striae in the Wisconsin Range of the Horlicks display similar orientation, but the sense of movement could not be determined. Paleoglaciers in the Neptune Range and the Cordiner Peaks of the Pensacola Mountains moved toward the south-southwest with some dispersion. Paleocurrents flowed parallel to ice motion in the Ohio Range and in the Pensacolas, but they also flowed toward the north-northeast in the Pensacolas.

Stratigraphy of the Wisconsin Range, Horlick Mountains, Antarctica

The Wisconsin Range consists of a basement complex of granitic and metamorphic rocks unconformably overlain by about 550 meters of Upper Paleozoic sedimentary rocks. The base of the Upper Paleozoic succession is composed of the Buckeye formation, a tillite, which varies in thickness from 80 to more than 140 meters. Overlying the Buckeye formation are the Weaver and Queen Maud formations, with a combined thickness of about 455 meters, characterized by a prolific Glossopteris flora, indicative of a Permian age.

On the Relationship of Ice-Surface Topography to Bed Topography on the South Polar Plateau

AbstractIce-surface and isopachous maps, and rock-elevation maps, were prepared for the area between the South Pole and the Horlick Mountains from seismic and gravimetric measurements. Basal shear-stress was calculated from these data and surface-slope measurements at 25 sites. The mean is 0.8 bar with an areal standard deviation of 0.5 bar. Forty-five values of average basal shear stress were computed from consecutive 30 km. segments along flow lines. The mean is 0.4 bar with an areal standard deviation of 0.1 bar. These variations are too large for accurate estimates of ice-thickness variations to be made from surface-slope data alone, following Nye’s suggestion that basal shear-stress be treated as constant. From theoretical considerations Nye demonstrated that surface features of wave-length less than 40 km. should disappear within a few months unless related to bed topography. Ice and rock profiles along a 220 km. line do not show an expected theoretical relationship. Surface-elevation measurements, repeated after a 2 yr. interval. showed the surface features with wave-lengths between 5 and 40 km. to be essentially unchanged in amplitude and position. Hence these features are not adequately explained by existing theory.

On the Relationship of Ice-Surface Topography to Bed Topography on the South Polar Plateau

AbstractIce-surface and isopachous maps, and rock-elevation maps, were prepared for the area between the South Pole and the Horlick Mountains from seismic and gravimetric measurements. Basal shear-stress was calculated from these data and surface-slope measurements at 25 sites. The mean is 0.8 bar with an areal standard deviation of 0.5 bar. Forty-five values of average basal shear stress were computed from consecutive 30 km. segments along flow lines. The mean is 0.4 bar with an areal standard deviation of 0.1 bar. These variations are too large for accurate estimates of ice-thickness variations to be made from surface-slope data alone, following Nye’s suggestion that basal shear-stress be treated as constant. From theoretical considerations Nye demonstrated that surface features of wave-length less than 40 km. should disappear within a few months unless related to bed topography. Ice and rock profiles along a 220 km. line do not show an expected theoretical relationship. Surface-elevation measurements, repeated after a 2 yr. interval. showed the surface features with wave-lengths between 5 and 40 km. to be essentially unchanged in amplitude and position. Hence these features are not adequately explained by existing theory.

Probable Disintegration of Antarctica

The writer's research life has coincided fairly closely with the vast discoveries made in thi c ntury s nce he first joined the Sc tt Expedition to Antarctica in 1910. Nothing was known within the coasts of Antarctica until Scott had returned; indeed, until the end of 1904 the map merely showed a pear-shaped outline extending around the South Pole. In my first long memoir, which appeared in this Journal in 1914, I discussed generally the structure of Antarctica, and I especially stressed the resemblance between Antarctic and Australian structure ('Physiography and glacial geology of East Antarctica'; Geogr. J. 44 (1914) 365-82; 452-67; 553-71). I suggested that a broad syncline or downfold below sea level might extend from the Ross Sea to the Weddell Sea?somewhat as the Tasman Sea separated the folded New Zealand Ridge from the Horsts of Australia. Possibly this marine channel was present in midTertiary times. I have seen these suggestions to a considerable degree corroborated by the con? clusions ofthe I.G.Y. researches as seen in the recent topographic map published by the Scientific American in September 1962 (Antarctica: prepared by the American Geographical Society for the United States Antarctic Research Program, with a grant from the National Science Foundation: 1:5M. 1962). Two techniques have been developed in the Antarctic in the last thirty years? exploration by air, and echo-sounding through the ice cap. I may instance a few errors on the earlier maps. In 1914 Amundsen, as he sledged over the Ross Ice Shelf to the Pole, gave it as his opinion that 'Carmen Land' blocked my hypothetical geosyncline. This land was illusory: Scott's ship sailed over several so-called 'lands' in 1911 near Cape Adare (near d Fig. 1). Mawson found that many landfalls cited by Wilkes in 1840 were greatly out of position in this area. Wilkins, on his first flight in December 1928 charted 'Stefansson Strait' in approximately lat. 71 ? in such a position as to divide Graham Land from the Continent; this was later found to be an error. In 1940 was published in the Regionale Geologie der Erde of Leipzig (Bd. I: Die alten Kerne) my geological account of Antarctica which, though written in 1934, was more complete than anything that had been published before, and which was illustrated by a block diagram of Antarctica. In 1935 Ellsworth flew across from the Weddell Sea to the Ross Sea, and found that his 'Sentinel Range' (c) much prolonged the 'Antarctic-Andes' towards the Ross Sea. However, Byrd's aviator (Anderson) in 1936 reported that the 'Great Horst' extended for some 180 miles beyond the South Pole towards the Weddell Sea. The new sonic data reported as late as 1960 gave sonic and other inform? ation which seemed wholly to block the suggested geosyncline. The latest map, the American one discussed here, shows that the geosyncline, some 2000 miles long, and varying in width from 200 miles downwards until it narrows near the Horlick Mountains at the point marked * on Figure 1, is an actual feature. Recent soundings have shown that the Ross Shelf extends south-east for some 500 miles to the

Field Control for Antarctic Mapping

Control work of U S Geological Survey field engineers to obtain control for new scale map series; errors discovered on existing maps; USGS is compiling maps of 5 areas -- Thurston Peninsula, Sentinel Mountains, Horlick Mountains, Executive Committee Range, and McMurdo Sound; publication scale will be 1:250,000, with contour interval of 300 m; mapping is done with trimetrogon photography.

Sedimentary Rocks of the Buckeye Range, Horlick Mountains, Antarctica

In the Buckeye Range of the Horlick Mountains, 4000 feet of sedimentary rocks nonconformably overlie a granitic basement and underlie a thick diabasic sill. The sedimentary section consists of Devonian sandstone and shale (Horlick formation), Carboniferous (?) tillite (Buckeye formation), Permian (?) platy and carbonaceous shale (Discovery Ridge formation), and Permian arkose, shale, and numerous coal beds (Mount Glossopteris formation). This apparently is the first report of a Paleozoic tillite in Antarctica.

Tectonics of Antarctica: ABSTRACT

Antarctica has long been considered to consist simply of a large Precambrian shield, flanked on one side by the circum-Pacific belt of Mesozoic and Cenozoic orogeny. The great amount of geologic information obtained during recent years indicates that between shield and circum-Pacific belt are belts of Paleozoic orogeny. The continent is probably crossed by a late Precambrian and Early Cambrian miogeosyncline whose contents were metamorphosed and intruded by batholiths during the Middle (?) Cambrian. Erratics bearing Lower Cambrian pleosponges, like those characterizing the Adelaide geosyncline of South Australia, have been found in four places; K/Ar dates suggest crystallization about 500 million years ago; and the distinctive granites are remarkably similar to those of Middle Cambrian age in South Australia. This orogen crosses the Antarctic coast between 145° and 160° E., and flanks the Ross Sea and Ross Ice Shelf, and possibly Filchner Shelf and Weddell Sea, as a continuous system of high mountains. These mountains have long been termed the Great Antarctic horst, thought to be of old P ecambrian rocks; the horst concept was based on a misinterpretation of structures near McMurdo Sound, where the broad structure of the present range is anticlinal. At least in the 1,100-mile segment from Terra Nova Bay to the Horlick Mountains, the crystalline rocks are metasedimentary rocks whose structures are subparallel with the mountain system, and distinctive granitic rocks of a composite batholith. Rocks of the orogen are overlain by little-deformed Devonian to Triassic sedimentary strata. Northeastern Victoria Land, west of the Ross Sea, is composed of metasedimentary rocks, striking generally west-northwestward, whose metamorphism and intrusion by granites occurred about 350-400 million years ago. On strike across the Ross Sea, and trending toward the Weddell Sea at least to the region of 90° W., 82° S., are metasedimentary rocks intruded by distinctive granites which contain relatively large trace amounts of tin. These rocks are undated, but are unlike the Mezozoic crystallines of Palmer Peninsula; a middle Paleozoic age is likely. It may be significant that Devonian granites of eastern Australia are also relatively rich in tin. The coast between 35° and 165° E. is characterized by charnockites, granulites, and gneisses, in part polymetamorphic, and by varied younger crystalline rocks. The rocks resemble those of the Precambrian K/Ar ages. As has long been recognized, this is part of a Precambrian shield, which may extend farther toward the Weddell Sea, and which presumably extends far toward the South Pole also. The Palmer Peninsula belongs to the circum-Pacific orogen, as has long been known, and the Thurston Peninsula also may belong to it. This revised pattern of Antarctic tectonics is essentially that required by Du Toit's reassembly of the southern hemisphere continents before post-Paleozoic continental drift. End_of_Article - Last_Page 408------------