Geometry and kinematics of large arcuate structures formed by impingement of rigid granitoids into greenstone belts during progressive shortening

Abstract

Regional-scale arcuate structures in the central part of the Archean Yilgarn craton, Western Australia, were generated by impingement of competent granitoid blocks into less competent greenstone belts during progressive east-west shortening. Sinistral shear zones developed along northwest-trending margins of the granitoid blocks, whereas dextral shear zones developed along northeast-trending margins. In apex regions, these northeast- and northwest-trending shear zones are linked by north-trending contractional zones along which shortening was accommodated by the formation of folds and reverse faults in the greenstone belts and a coaxial flattening fabric in granitoid rocks. Lateral escape of the greenstone belts is indicated by the progressive rotation of early macroscopic folds into parallelism with the strike-slip shear zones during granitoid impingement. This recently recognized deformation style may have important tectonic implications for other Archean granite-greenstone terranes and where rock heterogeneity and competency differences are significant.