Upper Proterozoic rift-related rocks in the Pensacola Mountains, Antarctica: Precursors to supercontinent breakup?

Sedimentological and structural studies in the Pensacola Mountains, Antarctica, suggest that upper Precambrian clastic sedimentary rocks of the Patuxent Formation and associated bimodal volcanic rocks formed in an intracontinental rift setting. The turbidites of the Patuxent Formation are part of a large depositional system, derived from a continental source. Interbedded pillow basalts and basaltic sills have trace and rare earth element signatures enriched relative to mid-ocean ridge basalt and similar to some rift-related tholeiitic suites. Nd and Sr isotopic values are compatible with derivation from a lithospheric mantle source in a continental setting. Associated felsic volcanic rocks have crustal trace element and isotopic characteristics. The rifting may have been a prelude to the fragmentation of a supercontinent and, according to recent hypotheses, the separation of Laurentia from Antarctica. Comparisons between the late Precambrian and Cambrian records of western North America and Antarctica suggest that, if these were conjugate margins, separation must have been Neoproterozoic rather than Cambrian in age.

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