Ultramafic Pseudotachylytes

A Rosetta Stone for Seismogenic Processes in the Upper Mantle

Abstract

 This paper reviews research on ultramafic pseudotachylytes. Shand coined the name pseudotachylyte in 1916 from his studies on enigmatic vein networks developed in Precambrian granitic rocks, South Africa. Ultramafic pseudotachylyte was first reported from Balmuccia peridotite, N. Italy in 1995. Significant research progress has been made on researching this controversial rock type, coupled with advances in rock mechanics, rock rheology, and seismology. The difficulty and complexity of the studying ultramafic pseudotachylytes is analyzed referring mainly to case studies on the Balmuccia ultramafic pseudotachylytes. It is emphasized that studies of ultramafic pseudotachylytes are closely linked to understanding the mechanics of deep earthquakes occurring in the upper mantle, and also to understanding physicochemical behavior under the extreme conditions that may occur at very sites where seismic waves are generated.