FORMATION AND REACTIVATION OF THE CAMBRIAN KANMANTOO TROUGH, SE AUSTRALIA - IMPLICATIONS FOR EARLY PALEOZOIC TECTONICS AT EASTERN GONDWANA PLATE MARGIN

The Kanmantoo Group is a thick and largely metamorphosed sedimentary s uccession that filled an isolated arcuate Cambrian basin (Kanmantoo Tr ough) which formed within continental Gondwana, and now lies on the so uthern margin of the present Australian continent. Kanmantoo Group sed iments unconformably overlie Neoproterozoic and older Cambrian rocks. We consider that the geometry of the southern part of this trough was influenced by strike-slip movement along an intra-continental tear fau lt. To the north, the basin changes to a style dominated by orthogonal extension and eventually tapers and dies out normal to the teal fault . Balanced sections show that the kinematic style and strain distribut ion developed during early Palaeozoic inversion was controlled by the specific architecture of the Kanmantoo Trough. Early Palaeozoic tear f aulting could have linked contrasting subduction polarities along the then contiguous palaeo-Pacific margin of Gondwana. The Kanmantoo Troug h is considered to have formed at a passive margin related to east-dir ected subduction in what is now the Australian continent. In contrast, west-directed subduction formed an active margin at contiguous parts of current Antarctica. Kanmantoo Group sediments were derived from the south by erosion of a Grenvillean province mixed with sediments erode d from the emergent active margin of Gondwana. The inception, localiza tion and sedimentation in the Kanmantoo Trough reflects a complex inte raction of tectonic processes along the encroaching Ross-Delamerian Or ogen.