On shearing, magmatism and regional deformation in Neoarchean granite-greenstone systems: Insights from the Yilgarn Craton

Abstract

The structure of the Neoarchean Yilgarn Craton is dominated by craton-scale high-strain zones, mostly associated with highly-deformed elongate granitic bodies and transposed greenstone belts. These shear zones developed during widespread and prolonged magmatic activity that led to a nearly complete reworking of the felsic continental crust. The spatial, temporal and genetic relationships between such a voluminous and protracted event of crustal reworking and the development of the craton-scale shear zone network are unclear. Here, we combine new structural, geophysical and geochemical data to investigate the relationship between crustal-scale shear zones and large syntectonic plutons in the Yilgarn Craton of Western Australia. We propose that Archean granite-greenstone systems may have commonly evolved through the interaction of three fundamental geological processes: (I) emplacement of large scale syntectonic plutons; (II) activity of crustal-scale shear zones; (III) pervasive, largely syn-metamorphic polyphase deformation in greenstone belts adjacent to syntectonic plutons. We propose that the concept of “Archean regional deformation event” need to be reassessed: a regional event is probably pluton- (or batholith-) size, and the structural/metamorphic evolution of adjacent greenstone belts might have proceeded quite independently and potentially in a time-transgressive way, if those belts were not spatially related to the same syntectonic pluton.