Pan-African Strike-Slip Tectonics in the Sør Rondane Region, Dronning Maud Land, and Lateral Extrusion of the East African-Antarctic Orogen

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Sør Rondane occupies a key position for reconstructing the late Neoproterozoic to early Paleozoic geodynamic evolution in eastern Dronning Maud Land (DML) since it appears to be located close to the supposed intersection of the East African-Antarctic Orogen (EAAO) and the Kuunga Orogen. The western part of Sør Rondane is dominated by two distinct terranes. The amphibolite to granulite-facies NE terrane is mainly composed of metasupracrustal rocks, showing Pan-African overprint provided by new SHRIMP zircon data from metamorphic rims with ages of ca. 560 Ma. The SW terrane is subdivided by the Main Shear Zone (MSZ) into two lithothectonic units, i.e. Pan-African greenschist- to granulite-facies metamorphic rocks with ―East African‖ affinities in the N and a Rayner-age early Neoproterozoic gabbro- tonalite-trondhjemite-granodiorite (GTTG) complex with ―Indo-Antarctic‖ affinities in the S. The GTTG complex has suffered Pan-African greenschist- to lower amphibolite-facies thermal overprint but also contains large domains with only weak deformation except for its northern margin affected by the MSZ. New zircon crystallisation ages cluster around 1000-930 Ma. Oceanic affinities are reported for the GTTG terrane and its wide age range might indicate a long-lasting accretionary orogen. The MSZ is characterized by a right-lateral sense of movement and high-strain ductile deformation under peak amphibolite-facies conditions. The structure can be traced over a distance of ca. 120 km between Lågkollane in the W and Lunckeryggen in the E and reaches several hundred meters in width. The MSZ cannot be traced further to the W where it seems to terminate at the north-eastern border of the NW-SE oriented prominent magnetically defined SE DML Province. This structure may coincide with a significant dextral shear zone that runs from the Schirmacher Oasis into the region S of Sør Rondane (Schirmacher- Rondane Lineament). The SE DML Province most likely consists of Rayner-age (1000-900 Ma) crust with evidence of intense Pan-African reworking indicated by new geochronological data. The continuation of the MSZ into eastern Sør Rondane and beyond is not clear either, since it appears to terminate at a N-S oriented region with low magnetic signatures (central Sør Rondane corridor) that is possibly related to extensional tectonics. Crosscutting relationships with dated magmatic rocks bracket the activity of the MSZ between Latest Ediacaran to Cambrian times (c. 560-530 Ma). Based on new combined aeromagnetic and structural results from a four-seasons survey of the greater Sør Rondane region, we propose that the crustal structural architecture of eastern DML and is strongly influenced by N-directed (with Africa/Antarctica restored to its original position in Gondwana) lateral extrusion of the EAAO. This process was likely driven by the combination of (i) indentation of the SE DML block towards the conjugate stable Kalahari-Grunehogna cratonic foreland, (ii) extensional collapse of the previously (c. 580-550 Ma) thickened and gravitational instable crust of central DML, and (iii) large-scale tectonic escape of crustal blocks in eastern DML along major shear zones such as the Schirmacher Rondane Lineament and MSZ towards an unconstrained yet unknown region at a lateral position of the EAAO.

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XII International symposium on Antarctic Earth Sciences, 13 Jul 2015 - 17 Jul 2015, Goa.
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Ruppel, A. , Läufer, A. , Jacobs, J. , Elburg, M. , Krohne, N. , Eagles, G. , Mieth, M. , Jokat, W. , Damaske, D. and Lisker, F. (2015): Pan-African Strike-Slip Tectonics in the Sør Rondane Region, Dronning Maud Land, and Lateral Extrusion of the East African-Antarctic Orogen , XII International symposium on Antarctic Earth Sciences, Goa, 13 July 2015 - 17 July 2015 .

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