Implications of K-Ar dating of fault gouges in NNE trending faults, Sydney region

Abstract

In this paper, we discuss the currently identified major faults in the Sydney region based on mapping of deep excavations, tunnels and outcrops. Further, we present K-Ar data obtained from illite-smectite in fault gouges that occur in several identified fault zones. Our studies have shown that major, NNE trending faults dominate the Sydney region and that ages of 122 to 134 Ma are recorded in the <2mm fraction extracted from the fault gouges. We believe these dates record an overprinting event possibly related to underplating of mafic magma associated with the early stages of the breakup of Gondwana.