Granitoid diapirism during protracted tectonism in an Archaean granitoid-greenstone belt, Yilgarn Block, Western Australia

The Bullfinch-Parker Dome area is an Archaean granitoid-greenstone terrain in the Yilgarn Block of Western Australia affected by a complex, protracted tectonic event. The majority of the deformation history was progressive rather than multiple discrete events. Finite strain patterns and structural and metamorphic zonation suggest that deformation in the greenstones was caused by regional ENE-WSW shortening and broadly simultaneous upward movement of granitoids by solid-state diapirism and/or ballooning plutonism, rather than by core complex formation or multiple folding. Evidence for pluton-related tectonism includes the foliation trends, steeply plunging radial mineral lineations, indications of upward movement of plutons, increase of strain towards the batholith margins, concordant structures in the pluton and the surrounding rocks - such as lineation and foliation patterns - constrictional tectonics near east-west-trending granitoid-greenstone contacts, syn-to post-kinematic peak-metamorphism, contact-metamorphic zoning, and pressure differences. Metamorphism, largely of amphibolite facies, was probably related to uprise of the granitoids at moderate crustal depths (10-12 km, P=3 kbar), causing both regional and contact metamorphism as a single thermal event. Relative and absolute timing defines an overlapping sequence of metamorphism, progressive deformation and plutonism in this part of the Yilgarn Craton during the late Archaean. (C) 1997 Elsevier Science B.V.