Detrital-zircon age spectra have been determined for sedimentary rocks from the Delamerian orogen, southern Australia. In Neoproterozoic sedimentary rocks, patterns progressively change from Mesoproterozoic-to Neoproterozoic-dominated detritus and there are few zircons that are close to the depositional age. The base of the Cambrian Kanmantoo Group marks an abrupt change in provenance to detrital patterns dominated by Ross and Delamerian (600-500 Ma) and Grenvillean ages (1200-1000 Ma). These patterns are strikingly similar to those obtained from Lachlan fold belt sedimentary rocks, indicating that the sedimentation recorded in the Kanmantoo Group marks a change from deposition of sediments derived from the Australian cratons to those representative of the early Paleozoic Gondwana mudpile. If sedimentary rocks with zircon-provenance characteristics such as those of the Kanmantoo rocks extend under elements of the Lachlan fold belt, they would provide suitable protoliths for the S-type granites of southeastern Australia. Data Repository item 9828 contains additional material related to this article.
In the northern Flinders Ranges, Neoproterozoic and Cambrian sedimentary rocks were deformed and variably metamorphosed during the ca 500 Ma Cambro‐Ordovician Delamerian Orogeny. Balanced and restored structural sections across the northern Flinders Ranges show shortening of about 10–20%. Despite the presence of suitable evaporitic detachment horizons at the basement–cover interface, the structural style is best interpreted to be thick‐skinned involving basement with only a minor proportion of the overall shortening accommodated along stratigraphically controlled detachments. Much of the contractional deformation was localised by the inversion of former extensional faults such as the Norwest and Paralana Faults, which both controlled the deposition of Neoproterozoic cover successions. As such, both faults represent major, long‐lived structures which effectively define the present boundaries of the northern Flinders Ranges with the Gawler Craton to the west and the Curnamona Craton to the east. The most intense deformation, which resulted in exhumation of the basement along the Paralana Fault to form the Mt Painter and Babbage Inliers, coincides with extremely high heat flows related to extraordinarily high heat‐production rates in the basement rocks. High heat flow in the northern Flinders Ranges suggests that the structural style not only reflects the pre‐Delamerian basin architecture but is also a consequence of the reactivation of thermally perturbed, weakened basement.
The Kanmantoo Group is a thick and largely metamorphosed sedimentary succession that filled an isolated arcuate Cambrian basin (Kanmantoo Trough) which formed within continental Gondwana, and now lies on the southern margin of the present Australian continent. Kanmantoo Group sediments 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 fault. To the north, the basin changes to a style dominated by orthogonal extension and eventually tapers and dies out normal to the tear fault. Balanced sections show that the kinematic style and strain distribution developed during early Palaeozoic inversion was controlled by the specific architecture of the Kanmantoo Trough. Early Palaeozoic tear faulting could have linked contrasting subduction polarities along the then contiguous palaeo-Pacific margin of Gondwana. The Kanmantoo Trough is considered to have formed at a passive margin related to east-directed 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 eroded from the emergent active margin of Gondwana. The inception, localization and sedimentation in the Kanmantoo Trough reflects a complex interaction of tectonic processes along the encroaching Ross–Delamerian Orogen.
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