Geodynamic evolution of Proterozoic supracrustal rocks from the northern Shackleton Range, East Antarctica

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Preliminary work to this project (Schmädicke & Will, 2006) led to the recognition of high-temperature and high-pressure metamorphism (c. 710-810 °C, 20-23 kbar) of ultramafic rocks from the northern Shackleton Range. This finding is the first evidence of eclogite-facies metamorphism in the Shackleton Range and, to our knowledge, the first description of eclogite-facies ultramafic rocks in a generally perceived Pan-African orogen. The petrology of these ultramafic rocks is best explained by them marking a suture zone within the northern Shackleton Range, which possibly traces the convergence site between East- and West-Gondwana. To date, no evidence of truly juvenile Neoproterozoic crust has been found along this postulated suture zone. Thus the geodynamic processes that led to the amalgamation of the Gondwana supercontinent remain highly speculative. Available Sm-Nd isotope data from allegedly ophiolitic mafic rocks of the Shackleton Range (Talarico et al., 1999) are not conclusive, because they yield either unrealistic young or older Proterozoic to Archean model ages. To contribute to the fundamental question of supercontinent formation towards the end of the Precambrian, we intend to focus on isotopic and geochemical techniques on selected supracrustal and basement rocks, available from a previous expedition to the Shackleton Range. This work will follow, and will be based upon, currently on-going metamorphic studies on the PT evolution of these rocks. The overall goal is to better assess the tectonic evolution of the Shackleton Range, i.e. to distinguish between Meso- and Neoproterozoic crust-forming events and to constrain both the age of the source for the various mafic protoliths and the provenance of the supracrustal country rocks. To this effect, it is planned to carry out Sm-Nd, Rb-Sr and Pb whole rock isotope analyses, Hf zircon in-situ analyses, and geochronological studies by means of Sm-Nd garnet, U-Pb single zircon and/or monazite as well as stepwise Ar-Ar hornblende dating.