Significance of pseudotachylite vein systems, Giles basic/ultrabasic complex, Tomkinson Ranges, western Musgrave Block, central Australia

Abstract

Pseudotachylite vein-breccia networks and pseudotachlyites intrafoliated with mylonites occur pervasively in the Tomkinson Ranges, about 50 km south and constituting part of the hanging wall of the Woodroffe thrust. The pseudotachylites are almost exclusively confined to gabbro, anorthosite and dolerite, and are rarely seen in basic granulites, felsic granulites and granitic gneiss. Pseudotachylite is ubiquitous in steeply tilted, deformed and mylonite-intersected sectors of the Giles Complex (Hinckley Range, Kalka, Michael Hills) but was not detected in the mildly tilted and little deformed western sectors of the Giles Complex, suggesting that fusion events concentrated in deformed relatively deep crustal levels. Two principal modes of occurrence of pseudotachylite are recognised: 1) vein-breccia networks superimposed on older lithological contacts and associated with brittle fracture systems; 2) penetrative pseudotachylite laminae interleaved with mylonite along shear zones. The chemistry of the pseudotachylites, the bulk host rock composition, the rock texture and results of Laser-Raman spectroscopic analysis are discussed. -after Authors Show more