Implications for Proterozoic plate margin evolution from geophysical analysis and crustal-scale modeling within the western Gawler Craton, Australia

Complexly deformed late Archean to Mesoproterozoic rocks of the western Gawler Craton are poorly exposed, thus reducing the ability to extract meaningful geological, structural and tectonic information. This study focuses on shear zone analysis via a constrained integration of qualitative aeromagnetic and Bouguer gravity data interpretation with quantitative two-dimensional forward modeling. This integration provides a means to interpret the crustal architecture as well as constrain a sequence of events, which aid the interpretation of a tectonic history for the western Gawler Craton. Results indicate a polyphase shearing history dominated by a crustal-scale array of predominantly west-dipping shear zones. The initiation of ∼ east–west trending SZ1 structures was likely coincident with ca. 1750–1720 Ma crustal extension, high heat flow and deposition on thinned areas of Archean crust with the development of a dense, possibly underplated lower crustal component. SZ1-R2 dextral transpressional movements reactivated SZ1 during the ca. 1720–1670 Ma Kimban Orogeny, which is interpreted to record collision between the Gawler Craton and the North Australian Craton. During this event basins marginal to, and in the interior of the Archean crustal block of the western Gawler Craton were inverted and the dense lower crust was vertically offset, causing some of the long wavelength (∼ 30–50 km) Bouguer gravity anomalies presently observed. Shear zone activity is constrained until ca. 1680 Ma during which time subduction rollback established a new arc position at the southern margin of the Archean crust with magmatism persisting until ca. 1670 Ma. SZ3 structures overprint and offset the interpreted axis of the Kimban Orogeny within the Archean crust. These structures record a major phase of crustal-scale sinistral strike-slip movement associated with ∼ north–south shortening between ca. 1630 and 1540 Ma prior to their reactivation at ca. 1450 Ma. This SZ3-R4 reactivation is interpreted to cause southwest-directed crustal transport, which was focused as west-side-up movements internal to the Archean continent, whereas dextral strike-slip was focused at a major rheological boundary between thick Archean crust to the south and thick Paleoproterozoic basins to the north.