Horizontal tectonic interaction of an Archean gneiss belt and greenstones, Pilbara block, Western Australia

Abstract

The Archean Pilbara block, Western Australia, is cited as a type example of a granite-greenstone terrane. New field evidence reveals that the internal structure of one of the major batholiths, the Shaw batholith, resembles an Archean gneiss belt. Greenstone intercalations within the gneiss belt can be traced into the surrounding greenstone sequence and were incorporated during subhorizontal thrusting and recumbent folding episodes. These early tectonic episodes preceded solid-state diapiric uprise of an overthickened crust. Granitic plutonism and partial melting of the sialic crust appear to have played an important role only in the later stages of the tectonic evolution of the Shaw batholith. Deformation and metamorphism are not a direct consequence of the emplacement of granitic magmas, contrary to the widely accepted magmatic model of batholith formation.