Earthquakes in the deep continental crust - insights from studies on exhumed high-pressure rocks

Abstract

SUMMARY Recent studies on two exhumed anorthositic and gabbroic high-pressure complexes in the Bergen Arcs and Western Gneiss Region of Norway demonstrate that deeply subducted dry rocks in the lowermost continental crust may resist metamorphic re-equilibration for geologically significant periods of time. This persistent metastability exercised a profound control on the mechanical properties of these rocks, as evidenced by abundant pseudo-tachylyte veins, cataclasites and fractures, documenting eclogite facies seismic failure at depths exceeding 60 km in the thickened Caledonian crust. Our observations indicate that the brittle seismogenic state of some lower crustal rocks, and their propensity to remain metamorphically metastable despite prevailing conditions of T = 600‐800 ◦ C and P = 1.5 to > 2.0 GPa, is largely controlled by