Granitic intrusions enhance strain localization and rapid mantle exhumation along an oceanic detachment fault

Poulaki, E. M.*; Abe, Noriaki   ; 34 of others*

Serpentinization and magmatism weaken the lithosphere and facilitate mantle exhumation during magma-poor rifting and seafloor spreading. However, the competing mechanisms that control exhumation along detachment faults remain poorly constrained. IODP Expedition 402 drilled a young oceanic basin in the Tyrrhenian Sea and recovered in-situ mantle sections. Drilled cores consist of one sequence of variably deformed granitic intrusions intercalated with slivers of peridotites and basalts, and another of primarily serpentinized peridotites with heterogeneous deformation and local granitic intrusions. Geochronologic and geochemical data constrain that the granites crystallized at 4 Ma at ~7 km and rapidly exhumed to the seafloor within ~0.5 Myrs, requiring extension rates of ~2 cm/year. Structural observations show that these granites accommodated significant post-crystallization strain during exhumation and enhanced localization of detachment faulting. Stable isotopes record serpentinization temperatures of 200C, suggesting serpentinization occurred after the onset of deformation. These observations, demonstrate that felsic melts, when present, can nucleate strain localization along detachment faults and enable continental breakup and mantle exhumation.