Felsic intrusions facilitate mantle exhumation along detachment faults at a continent-ocean transition drilled in the Tyrrhenian Sea

Poulaki, E. M.*; 安邊 啓明   ; 他28名*

Poulaki, E. M.*; Abe, Noriaki; 28 of others*

We analyze samples from IODP Expedition 402, which occurred from Feb-April 2024 and drilled the continent-ocean transition in the Tyrrhenian Sea offshore Italy. Two drill sites comprise a sequence of (1) variably deformed granitic gneisses intercalated with ~cm-scale slivers of peridotites and basalts, and (2) a heterogeneous section of primarily serpentinized peridotites and cm-thick granitoids emplaced between the ultramafics. All peridotites are serpentinized with moderate to high alteration. The presence of both peridotites and granitoids showcases a diverse lithological and rheological heterogeneity that has not been previously observed in in-situ mantle sections. Initial observations suggest strain localization in a ~5 m-thick zone. Preliminary zircon U-Pb ages and apatite U-Pb ages constraints coupled with the microstructures require rapid exhumation after the granitoids' emplacement. Collectively, the presence of granitic gneisses within the detachment fault, as well as the young age of felsic intrusions, suggests that the weak granitoids may have accommodated the exhumation of this mantle section to the surface.