Georg Kleinschmidt

Structural continuity of the Ross and Delamerian orogens of Antarctica and Australia along the margin of the paleo-Pacific

The Delamerian orogen (southeast Australia) and the Wilson terrane (northern Victoria Land, Antarctica) constitute a formerly continuous lower Paleozoic fold-and-thrust belt developed along the paleo-Pacific margin of eastern Gondwana. Major folds and thrust faults in these regions, rooted in mid-crustal detachment zones, transported Cambrian-Ordovician granites and high-temperature- low-pressure metamorphic rocks divergently toward their respective western craton margins and eastern orogen margins and associated cover sequences. The structural imprints are related to the accretion of lower Paleozoic terranes at the eastern margin of the Delamerian orogen and the Wilson terrane. The continuity of the contemporaneous structure patterns in Australia and Antarctica is evidence for continuous convergent tectonism along the lower Paleozoic-Pacific margin of Gondwana.

Opposite thrust systems in northern Victoria Land, Antarctica: Imprints of Gondwana's Paleozoic accretion

Two major thrust systems with contrasting senses of displacement transect the Wilson terrane crust of northern Victoria Land, Antarctica. Along both mylonitic shear zones the central high-grade metamorphic basement is detached and thrust divergently toward the west and east over synorogenic, lower grade fore-arc and back-arc basin sedimentary rocks, respectively. Deformation was preceded by pervasive high-temperature-low-pressure metamorphism. Granites intruded the basement prekinematically and postkinematically. The structures are interpreted as results of early Paleozoic subduction of the paleo-Pacific oceanic crust under the Antarctic craton.

Late-Ross Structures in the Wilson Terrane in the Rennick Glacier Area (Northern Victoria Land, Antarctica)

Kinematic data from the Rennick Glacier area indicate the presence of two intra-Wilson Terrane late-Ross opposite-directed high-strain reverse shear systems. High-grade rocks are W- and E-ward displaced over low-grade rocks and shallow-level intrusions. The shear zones are offset in a step-like pattern suggesting the presence of ENE trending right-lateral faults. The structural pattern accounts for a relationship between the Exiles and Wilson thrusts in Oates Land, which in our opinion can be traced from the Pacific coast to the Ross Sea. The western front of the Ross Orogen towards the East Antarctic Craton is best interpreted as a broad W-vergent fold-and-thrust belt, along which the intra-Wilson Terrane arc was detached and thrust onto the craton. The shear zones related to the Exiles Thrust system represent the internal, easternmost thrusts of this belt. Based on our data in combination with recent geophysical and geochronological results, the craton-orogen boundary must be located significantly further W than previously inferred. The boundary and hence the inferred termination of the proposed fold-and-trust belt may roughly lie in the area between Mertz and Ninnis Glaciers in George V Land, taking into account a considerable amount of likely post-Ross crustal extension possibly related to the Wilkes Subglacial Basin.

Structural and Basement Evolution in the Central Schwarzwald Gneiss Complex

The Central Schwarzwald Gneiss Complex (CGC) belongs to the highly metamorphic core (“Moldanubian”) of the European Variscan orogenic belt. The prevailing lithologies are metasediments of possibly Precambrian depositional age (Wimmenauer 1980). Intercalated orthogneisses are abundant (Fig. 1). The dominant metamorphism took place under upper amphibolite facies conditions, locally reaching anatexis. Relics of eclogites and granulites occur as isolated but scattered pods within the paragneisses or form distinct chains within the basement (Fig. 1). The various lithologies underwent temporarily separate structural and metamorphic histories in space and time. As a consequence of the dominant low pressure/high temperature (LP-HT) metamorphism the segments of different crustal provenance were welded together and their previous tectonometamorphic history was somewhat blurred.

The Matusevich Fracture Zone in Oates Land, East Antarctica

The Matusevich Glacier trends 170° totally straight for more than 100 km. For this reason, a major fault was assumed along the glacier formerly. A westward directed ductile thrust system, trending 170°, was subsequently discovered in the upper Matusevich Glacier (“Exiles Thrust”). It formed under amphibolite facies conditions during the Ross Orogeny. Therefore, the course of the Matusevich Glacier was attributed to the Exiles Thrust instead of the postulated simple fault. During GANOVEX VIII/ITALANTARTIDE XV (1999/2000), the small-scale structures at the margins of the Matusevich Glacier were mapped. The most conspicuous and meaningful of these structures are cold, brittle, NW- to N-trending thrusts with slickensides, decorated with quartz fibres and uniformly SW-thrusting (−220°). They occur at the western side of the glacier (Lazarev Mts.). These structures are consistent with strike-slip tectonics along the Matusevich Glacier and could be interpreted as indicators of transpressional tectonics. Unfortunately, corresponding dextral strike-slip faults, which should strike about 170°, could not be observed directly. But 30 km to the west, 165° trending strike-slip structures are exposed at the eastern edge of Outrider Nunatak. Striations on steep fault planes indicate dextral displacement. This strike-slip tectonics produced a flower structure visible in one of the main granite-walls of Outrider Nunatak. Thus the neotectonics of westernmost Oates Land is characterized by brittle dextral strike-slip faulting, following the trend of much older Ross-age ductile thrust tectonics.