| Summary: | Several fundamental tectonic boundaries, inferred in the amalgamation of Gondwana, are largely concealed under ice in Antarctica. The hidden geology has caused considerable speculation of rock types and their age, resulting in widely spaced interpretations of the position and type of tectonic boundaries central to the Neoproterozoic unification of the East Gondwanan elements Indo-Antarctica and Australo-Antarctica. Geological-based interpretations rely heavily on (1) incomplete coastal outcrops and (2) inland rock samples and sediment brought to the coast by ancient and modern processes. Increasingly sophisticated and detailed geophysical studies provide new opportunities to constrain the sub-glacial geology, though non-unique solutions are possible and high-resolution data is spatially limited, leading to multiple additional hypothesized locations of key boundaries. We explore the controversy using time-continuous plate tectonic reconstructions in GPlates based on sparse geological, geophysical and plaeomagnetic constraints to investigate the Neoproterozoic plate motions. We propose that the amalgamation of Indo-Antarctica and Australo-Antarctica involved two key plate boundaries: (1) a subduction boundary that consumed a >1000 km wide ocean basin, linked and approximately perpendicular to (2) a sinistral transform boundary that accommodated >1000 km of strike-slip motion. In our reconstructions, subduction and arc activity along the first boundary persisted from c. 720 Ma to c. 620 Ma concurrent with activity along the strike-slip boundary. The plate motion led to continent-continent collision at c. 600 Ma. We use an extensive compilation of zircon isotopic data for grains derived from the Gamburtsev Subglacial Mountains to evaluate recent geophysical interpretations of the Neoproterozoic East Gondwana suture being located directly north of the Gamburtsev Subglacial Mountains. Our analysis demonstrates a marked change in the zircon isotopic data compilation at c. 620-600 Ma, modeled in our reconstruction as the onset of continent-continent collision between India and Antarctica. During the inferred period of subduction (720-620 Ma), zircon with positive epsilon Hf isotopic composition dominates the compilation, whereas significantly negative compositions predominate following the inferred continent collision. A lack of significant topography along the inferred strike-slip boundary and limited c. 720620 Ma zircon from the region along this boundary support the interpretation of a dominantly transform system for the second boundary. This study reconciles multiple geophysical interpretations of the ice-covered Neoproterozoic plate boundaries for the first time. The location of the proposed Gamburtsev Suture is reinforced by zircon isotopic data that supports a subduction boundary preceding continent-continent collision.
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