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Early Cambrian magmatic arc flanked by an inverted Cambrian sedimentary basin in the Wilson Terrane of East Antarctica

By E Armadillo, F Ferraccioli and P Balbi

Abstract

The Ross Orogen, in East Antarctica, is linke d to Cambro-Ordovician subduction and terrane accretion processes along the paleo-Pacific active margin of Gondwana. Geological investigations within the partially exposed basement rocks of Northern Victoria Land (NVL) have revealed several major terrane bounding and intra-terrane faul ts that were active during the Ross Orogen. However, considerable uncertainty remains regard ing the deeper crustal architecture and tectonic evolution of the innermost Wilson Terrane (WT), the closest recognised tectonic domain to the East Antarctic Craton. Here we compile and an alyse enhanced aeromagnetic and gravity anomaly images from NVL to the Wilkes Subglacial Basin (WSB) to provide new geophysical constraints on the crustal architecture and the tect onic and magmatic evolution of the WT. Aeromagnetic imaging delineates a major fault system flanking the eastern margin of the Wilkes Subglacial Basin, which connects to the previously interpreted Prince Albert Fault System to the south. Contrary to previous interp retations, however, this fault syst em is distinct and lies west of the Exiles Thrust fault system. Magnetic mode lling indicates that much larger and thicker batholiths were emplaced along this fault system , compared to the thinner sheet-like granitoid bodies emplaced along the late-Ross Exiles Thrust fault system. Zircon U–Pb dating over small exposures of gabbro-diorites within the Prince Al bert Mountains to the south lead us to propose that this part of the magmatic arc was emplac ed in a dominantly transtensional setting along a major pre-existing fault or suture zone during an earlier phase of subduction (>520 Ma or older), compared to the intrusions exposed further to the east. Long-wavelength magnetic lows and residual Bouguer gravity highs over the central Wi lson Terrane further to the east are interpreted with the aid of two-dimensional modelling as refl ecting several-km thick inverted sedimentary basins of inferred early Cambrian age. Tectonic inve rsion likely occurred along major thrust faults, formed in a dominantly transpressional late stage of the Ross Orogen. Overall, our interpretations provide new geophysical evidence in support of a long-lived and composite WT that experienced magmatic arc migration and basin inversion in re sponse to changes in the geometry and dynamics of the subduction system, much like several modern subduction systems

Year: 2014
OAI identifier: oai:iris.unige.it:11567/856337
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