Geodynamic evolution of the Antarctic Peninsula during Mesozoic times and its bearing on Weddell Sea history

This review of the tectonic evolution of the Antarctic Peninsula during Mesozoic times highlights four main events; (1) Late Triassic-Late Jurassic extension, (2) Late Jurassic-Early Cretaceous dextral transpression, (3) Early Cretaceous extension and (4) mid-Cretaceous compression. Magmatism was virtually continuous during much of this period with the exception of possible breaks in the known record in Early Jurassic and Late Jurassic-Early Cretaceous times. The second of these breaks corresponded to the first compressional event. There was no apparent hiatus in the magmatic record during the mid-Cretaceous compressional event, although there was a significant change in the pattern of sedimentation in the Larsen basin on the eastern margin of the Weddell Sea at about that time. The tectonic evolution of the peninsula is compared to, and puts some constraints on, existing Weddell Sea models. The Late Triassic-Late Jurassic arc extension correlates with initial rifting in the Weddell Sea region during sinistral motion between East and West Gondwana. However, there is no known record of large-scale pre-Mid-Jurassic transcurrent deformation in the Antarctic Peninsula that would have been consistent with rotation of West Antarctic crustal blocks in the initial rifting period. The peninsula-wide Late Jurassic-Early Cretaceous compressional event may correlate with the major change in Gondwana plate motions from E-W to N-S (African reference frame) separation of East and West Gondwana. This change probably resulted in formation of an ocean-continent boundary along the northern margin of the Weddell Sea embayment and initial seafloor spreading. Geological data do not seem to support subduction of southwestern proto-Weddell Sea oceanic lithosphere beneath the eastern margin of the peninsula at that time. Cretaceous arc extension was coeval with the initial seafloor spreading phase in the Weddell Sea. Mid-Cretaceous arc compression, linked to a global increase in ocean floor spreading rates and a superplume event, correlates with a change from NE-SW to NW-SE spreading in the Weddell Sea.

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