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Polarforschung

The USARP Mountains comprise two N-S-aligned mountain ranges (Daniels Range, Pomerantz Tableland) located along the western margin of the RennickGlacier inNorthernVictoria Land (NVL). Four zircon and titanite ¢ssion track (FT) ages fromgranitic samples from the PomerantzTableland fall in a common range of 369^392Ma.The apatite FTages from20GraniteHarbour Intrusive rocks sampled throughout theUSARPMountains are distinctively younger (86^270Ma); their mean track lengths (MTL) vary between11.0 and13.9mm. Six samples fromRenirie Rocks and the Kavrayskiy Hills east of theUSARPMountains have even younger, concordant apatiteFTages of 43^71Ma, andMTL of 12.2^14.0 mm.Thermal history modelling of the thermochronological data indicate that both the Daniels Range and PomerantzTableland experienced a common Phanerozoic geologic history consisting of a mid-Devonian pulse of rapid denudation, followed by a protracted denudation stage between the Carboniferous and Jurassic.This latter period of denudationwas contemporaneous with the formation of theTransantarctic Basin to the east.We consequently suggest that theUSARP Mountains were one of the major source areas for the Beacon Supergroup that formed the ¢ll of the Transantarctic Basin.Subsequent to the deposition of the Beacon sequence, the now-outcropping rocks of theUSARPMountains were buried to a maximum depth of 4.2km. A palaeogeothermal gradient of 25 8 1Ckm1was inferred at the time of maximumburial. Inversion of theTransantarctic Basin due to the breakup of Gondwana, and in response to Cenozoic rifting and uplift of theTransantarctic Mountains, has triggered the ¢nal denudation stages recorded inNVL since the Cretaceous.Thereby, the amounts of denudation increase eastward.Whereas 2.4^4.2 km of crustal unloading are recognized for theUSARPMountains since the Cretaceous,more than 4 km of denudation has occurred towards the RennickGraben alone since the Eocene.This denudationwas associatedwith major fault activities involving earlyENE^WSWtoE^W-directed extension.Related structureswere reactivated bydominant NW^SEtoNNW^SSE-oriented right-lateral shear genetically linked to the formation and inversion of the structural depression of the RennickGraben in Cenozoic times.

Polarforschung

The Indo-Burman Ranges (IBR) are a mountain range comprised of Mesozoic-Cenozoic rocks which run the length of Western Myanmar, extending into India and Bangladesh; to the west lies the Indian Ocean, and to the east lies the Central Myanmar Basin (CMB) along which the Irrawaddy River flows. The IBR are considered to be an accretionary prism, developed at the juncture of the Indian and Sunda plates, and a number of hypotheses have been proposed for their evolution. However, in order for these hypotheses to be evaluated, the timing of IBR evolution needs to be determined. We undertook a two-pronged approach to determining the timing of uplift of the IBR. (1) We present the first low-temperature thermochronological age elevation profiles of the IBR using ZFT, AFT and ZHe techniques. Our data show: a major period of exhumation occurred around the time of the Oligo-Miocene boundary; we tentatively suggest, subject to further verification, an additional period of exhumation at or before the late Eocene. (2) We carried out a detailed multi-technique provenance study of the sedimentary rocks of the IBR and Arakan Coastal region to their west, and compared data to coeval rocks of the CMB. We determined that during Eocene times, rocks of the CMB and IBR were derived from similar local provenance, that of the Myanmar arc to the east. Therefore at this time there was an open connection from arc to ocean. By contrast, by Miocene times, provenance diverged. Rocks of the CMB were deposited by a through-flowing Irrawaddy River, with detritus derived from its upland source region of the Mogok Metamorphic Belt and Cretaceous-Paleogene granites to the north. Such a provenance is not recorded in coeval rocks of the IBR, indicating that the IBR had uplifted by this time, providing a barrier to transport of material to the west. To the previously published list of viable proposals to explain the exhumation of the range, we add a new suggestion: the period of exhumation around the time of the Oligo-Miocene boundary could have been governed by a change to wedge dynamics instigated by a major increase in the thickness of the incoming Bengal Fan sediment pile.

Fission-track dating on detrital apatites from modern sands of the Po Delta is used for a provenance study of sediments in the Po River basin. Analysed samples show a fission-track grain-age distribution characterized by two prominent peaks at 7.7 Ma and 17 Ma. The youngest peak accounts for 46% of the total population of dated grains. This young component in the grain-age distribution is consistent with bedrock cooling ages observed in the Western Alps between the External Massifs and the Houiller unit, as well as in the Lepontine dome of the Central Alps and in the Miocene foredeep units of the Apennines, that overall represent only 12% of the orogenic source area. Results suggest that most of the sediment load in the last 10(2)-10(5) years was supplied by focused erosion of relatively small areas that experienced short-term erosion rates one order of magnitude higher than in the rest of the.

The Ross Sea region of the East Antarctic plate provides evidence for intraplate tectonic activity in 13 Cenozoic times. Still unresolved are the cause, timing and kinematics of this intraplate tectonism. By 14 integrating and discussing the different (kinematic and temporal) signals of Cenozoic tectonism, intraplate 15 dextral shearing is recognized as the main tectonic regime controlling the structural architecture of the Ross 16 Sea region from the Mid-Eocene (c. 40–50 Ma) onward. We speculate that propagation and persistence of this 17 tectonic regime through time constitutes a feasible seismogenetic framework to explain past and current 18 tectonism in the Ross Sea region.

In this paper we report a synthesis of the structural data collected during the WISE campaign on north Victoria Land, Antarctica. These data are integrated with the available apatite fission track data from the neighbour regions in order to place constraints to the kinematics and chronology of the brittle deformation along the western shoulder of the Wilkes Basin. Brittle faulting is consistent with the regional Cenozoic tectonic pattern of north Victoria Land and respond to the increasing phases of denudation that accompanied extension/transtension of the Rennick Graben shoulders since 40-50 Ma. The discovery of pseudotachylyte-bearing fault rocks at the Pacific termination of the Rennick Graben is also reported. The dating of the pseudotachylyte-bearing fault zone opens new perspectives for the reconstruction of the brittle tectonic evolution of the region. Results coming from these studies with the analyses of the new samples collected for the fission track dating may generate permissive kinematic and geodynamic models for the Cenozoic tectonic evolution of the entire northern Victoria Land region.