Polygenetic mélange in the Hodgkinson goldfield, Northern Tasman Orogenic Zone

Abstract

Polygenetic melange is intercalated with multiply deformed Siluro‐Devonian shale, greywacke, clast‐in‐matrix rock, spilite and chert in the Hodgkinson goldfield of northeast Australia. Differing sedimentary facies, fold styles, veining events and melange units occur in six fault‐bounded domains. Locally coherent stratigraphic units can be traced into the melange. The chief mechanism of fragmentation in the melange was an intense domainal cleavage event which formed chlorite‐illite‐vitrinite seams. Multiple tight folding and local shale diapirism pre‐dated cleavage development and greatly contributed to desegregation and mixing. Late brittle shear zones further juxtaposed coherent phacoidal megablocks within zones of clast‐in‐matrix rock. Laminated protolith sequences aided the formation of clast‐in‐matrix rock, whereas more massive units became slabs, blocks and clasts. The rocks are of sub‐greenschist metamorphic facies, based on spilite and sandstone mineral assemblages, textures and illite crystallinit...