Evidence for a two-phase Palmer Land event from crosscutting structural relationships and emplacement timing of the Lassiter Coast Intrusive Suite, Antarctic Peninsula: Implications for mid-Cretaceous Southern Ocean plate configuration

New analysis of the relationships between geological structural data and radiometric ages for the Lassiter Coast Intrusive Suite indicate that the collisional mid-Cretaceous Palmer Land Event orogeny in the Antarctic Peninsula has had two kinematic phases, forming an intersection orocline, one of which can be related to Cretaceous Southern Ocean plate motions. Both are compressional phases along the Eastern Palmer Land Shear Zone: Phase 1 occurred at ~107 Ma with a principal paleostrain axis of 341°, and is best expressed in southern Palmer Land although evident elsewhere on the Antarctic Peninsula; Phase 2 occurred at ~103 Ma with a principal paleostrain axis of 259.5°, but is confined to between 68°S and 74°S. A peak in Lassiter Coast Intrusive Suite magma emplacement rate was coeval with Phase 1, whereas Phase 2 may have coincided with a lull. During Phase 1, the allochthonous Central and Western Domain terranes may have been transported to the Gondwana margin, represented by the para-autochthonous Eastern Domain, on board the Phoenix plate or on board the South American plate. The variable provenance indicators from the Central and Western terranes can be cited to support either, or a combination, of these scenarios. The convergence direction evident from Phase 2 structures cannot easily be reproduced in regional plate kinematic models. This, and the localized evidence for superposition of Phase 2 structures on Phase 1 structures suggests that Phase 2 is unlikely to have occurred solely in response to changes in the kinematics of the large plates considered.

Details