Davis Strait Paleocene picrites: Products of a plume or plates?

Abstract Voluminous, subaerial, ultra-depleted, 62 Ma, primary picritic lavas lie on conjugate volcanic margins on both sides of Davis Strait separating Baffin Island and West Greenland. Temporally, these picrites erupted just prior to, and coeval with, the initiation of sea-floor spreading in Labrador Sea and Baffin Bay. Petrogenetically, the chemical characteristics of these picrites (MgO = 18–21 wt%; K 2 O = 0.01–0.20 wt%; 87 Sr/ 86 Sr i  ≈ 0.7030; eNd i  ≈ +5.2–8.6; 3 He/ 4 He ≤ 49.5R A ) are those of D-MORBs that demand derivation only by partial melting of highly incompatible-element depleted subcontinental lithospheric mantle (SCLM) at a pressure of ~ 4 GPa, followed by rapid ascent to the surface, but do not necessarily require high temperatures or high degrees of partial melting. Tectonically, these picrites formed near Paleoproterozoic suture zones in the SCLM of thick Paleoproterozoic cratonic terranes during Paleogene rifting between Greenland and North America. Structurally, the picrites are related to the major intersection of a NNW-trending lithospheric thinning under Baffin Bay and the ~E-W-trending thickened lithosphere of the Paleoproterozoic Nagssugtoqidian Fold Belt. During the late Mesozoic, ENE extension that thinned the mantle lithosphere and created normal-faulted basins. Elastic finite-element models and present-day studies of crustal extension show that the thicker Nagssugtoqidian Fold Belt underwent less thinning and extension than the Baffin Bay lithosphere. These extensional disparities occurred at the orthogonal intersection of pre-existing ~E-W-trending strike-slip faults in the thicker Nagssugtoqidian Fold Belt with the incipient spreading under Baffin Bay, and likely resulted in the formation of one or more pull-apart basins. Because the strike-slip faults are ancient suture zones, trans-tension within these suture zones easily reached depths of ~120 km, not only creating adiabatic decompression melting in the SCLM, but also forming an open pathway for the picritic melts to rapidly reach the surface. This purely tectonic model requires no spatially or temporally improbable deep mantle plume for generation of the Paleocene picrites of Davis Strait.