Constraining the Timing of Evolution of Shear Zones in Two Collisional Orogens: Fusing Structural Geology and Geochronology

In recent decades, constraining the timing of shear activity has been one main topics research about tectono-metamorphic evolution orogenic belts. We present a review combined structural and geochronological approach to two major ductile regional zones, in collisional orogens: first affecting Variscan basement northern Sardinia (Italy) External Crystalline Massifs Alps (East Shear Zone; EVSZ), second deforming medium- high-grade rocks metamorphic core Himalaya (High Himalayan Discontinuity). High-resolution, texturally chemically controlled monazite geochronology applied separated zones belt allowed recognizing similar ranging between c. 340–330 300 Ma. This led better understanding EVSZ, supporting model where several branches were active according growth by linkage model. Following approach, situ U-Th-Pb analysis constrained top-to-the-S/SW shearing regional-scale High Discontinuity 28 Ma 17 Earlier exhumation hanging wall was triggered zone activity, whereas at same time, footwall still experiencing burial with increasing P-T conditions. The this fits an in-sequence tectonic for mid-crust.