Late Paleo–Mesoproterozoic plate margin deformation in the southern Gawler Craton: Insights from structural and aeromagnetic analysis

Abstract: The integration of structural analysis of outcrop and aeromagnetic interpretation has revealed a complex tectonic evolution for the southern Gawler Craton that reflects the regional tectonic signal during the late Paleo- to early Mesoproterozoic. Results suggest that exposures at Yarlbrinda Hill comprise the margin of a highly deformed St Peter Suite pluton emplaced within the southwestern Gawler Craton at ca. 1611 Ma. D1 at outcrop records east- to northeast-directed ductile thrusting. Regionally, this deformation overprints north–south trending dextral Yarlbrinda Shear Zone fabrics within ca. 1622 Ma St Peter Suite granite and ca. 1690–1670 Ma Tunkillia Suite granite. Progressive east to northeast directed thrust movements led to exhumation of the deformed ca. 1611 Ma granite. D2 deformation is recorded by the brittle reactivation of first generation mylonitic fabrics, accompanied by cataclasis, alteration and pseudotachylite development. D3 records a switch to ∼northwest–southeast shortening, which led to the folding and tear faulting of the D1–2 shear zone. A switch to extension and subsequent rotations of the principle stress axes led to Hiltaba Suite granite emplacement and contemporaneous faulting under ∼east–west extension during D4 and west–northwest–east–southeast extension during D5. Deformation of ca. 1622 Ma St Peter Suite granite is consistent with movement on the Yarlbrinda Shear Zone and requires the St Peter Suite to have been emplaced into or adjacent to the ca. 1690–1670 Ma Tunkillia Suite prior to shear zone activity and on the overriding plate during subduction. D1–D3 deformation is constrained by the emplacement of ca. 1580 Ma Hiltaba Suite granite and correlates with the Wartakan Orogeny in the southeastern Gawler Craton and the Olarian Orogeny in the Curnamona Province. A ∼52° disparity between the shortening directions in these respective areas suggests different degrees of Mesoproterozoic rotation, which likely aided the formation of an intervening basin province, the remnants of which are presently preserved in the Mount Painter Inlier. The record of convergent deformation is geochronologically constrained to a ∼30 Myr period and places this region of the central Gawler Craton near a late Paleoproterozoic convergent plate margin prior to a period of transient extension beginning at ca. 1580 Ma. The continental scale signal of tectonic events can be recognized at the outcrop scale highlighting the importance of detailed outcrop studies in sparsely exposed areas. [Copyright &y& Elsevier]