Multi-scale analysis of Proterozoic shear zones: An integrated structural and geophysical study

摘要

Structural mapping of poorly exposed shear zone outcrops is integrated with the analysis of aero-magnetic and Bouguer gravity data to develop a multi-scale kinematic and relative overprinting chronology for the Palaeoproterozoic Tallacootra Shear Zone, Australia. D_2 mylonitic fabrics at outcrop record Kimban-aged (ca. 1730-1690 Ma) N-S shortening and correlate with SZ_1 movements. Overprinting D_3 sinistral shear zones record the partitioning of near-ideal simple shear and initiated Riedel to regional-scale SZ_2 strike-slip on the Tallacootra Shear Zone (SZ_2). Previously undocumented NE-SW extension led to the emplacement of aplite dykes into the shear zone and can be correlated to the (ca. 1595-1575 Ma) Hiltaba magmatic event. D_4 dextral transpression during the (ca. 1470-1450 Ma) Coorabie Orogeny reactivated the Tallacootra Shear Zone (SZ_(2-R4)) exhuming lower crust of the northwestern Fowler Domain within a positive flower structure. This latest shear zone movement is related to a system of west-dipping shear zones that penetrate the crust and sole into a lithospheric detachment indicating wholesale crustal shortening. These methods demonstrate the value of integrating multi-scale structural analyses for the study of shear zones with limited exposure.