Locating hidden terrane boundaries in East Antarctica with detrital feldspar Pb isotopes

• Main Authors: Mulder, J, Halpin, J, Daczko, N, Meffre, S, Orth, K, Thompson, J, Morrissey, L
• Format: Conference Object
• Language: English
• Published: . 2018
• Subjects: Earth Sciences; Geology; Geochronology; Antarctic; East Antarctica; Gamburtsev Subglacial Mountains; Mirny; Antarc*; Antarctica
• Online Access: http://agcc.org.au/; http://ecite.utas.edu.au/131213

The assembly of eastern Gondwana involved the amalgamation of Indo-Antarctica and Australo-Antarctica along the Kuunga orogen. The location of the suture or sutures between Indo-Antarctica and Australo-Antarctica within the Kuunga orogen remains debated as key geological relationships are concealed beneath ice. The most recent interpretation identifies the Mirny Fault as a key suture between crust of Indo-Antarctic and Australo-Antarctic affinity. However, sparse exposure of bedrock in this region precludes traditional geological characterisation of the crust on both sides this structure. Here, we test the Mirny Fault as a key suture between Indo-Antarctica and Australo-Antarctica using Pb isotopes of detrital feldspars from offshore sediments referenced to new and compiled feldspar Pb isotopic data from onshore exposures of Indo-Antarctica and Australo-Antarctica. The feldspar Pb-isotope signature of Indo-Antarctica forms a broad population with ⁰⁷Pb/⁰⁴Pb ratios of 15.516.1 and ⁰⁶Pb/⁰⁴Pb of 1719. In contrast, Australo-Antarctica has a feldspar Pb-isotope signature characterised by a tight cluster of ⁰⁷Pb/⁰⁴Pb (15.515.8) and ⁰⁶Pb/⁰⁴Pb (16.517) ratios, which is distinct from Indo-Antarctica. Locally-derived Holocene sediments offshore of the Mirny region contain detrital feldspars with Pb-isotope compositions recording a contribution from both Indo-Antarctica and Australo-Antarctica. The presence of Australo-Antarctic and Indo-Antarctic crust near the Mirny Fault supports the interpretation of this structure as a fundamental terrane boundary. We interpret the Mirny Fault as the key suture between Indo-Antarctica and Australo-Antarctica and trace this boundary into the interior of East Antarctica to connect with an inferred Gondwanan-aged suture within the Gamburtsev Subglacial Mountains.