TIMING AND TECTONIC SIGNIFICANCE OF LATE ARCHEAN, SINISTRAL STRIKE-SLIP DEFORMATION IN THE CENTRAL PILBARA STRUCTURAL CORRIDOR, PILBARA CRATON, WESTERN-AUSTRALIA

A north-south striking zone of sinistral strike-slip shear (20 x 100 k m) and associated folding and thrusting within the central part of the Pilbara Craton is described. This zone, referred to herein as the Cen tral Pilbara Structural Corridor (CPSC), was formed during regional D3 deformation and overprints two earlier sets of structures associated with granitoid doming. It is bound to the west by a continuous, north- south striking, curviplanar fault at greenschist-facies. In the east i t is bound by a series of NE-SW striking fault segments located along sheared fold limbs, and by a kilometre-wide zone of amphibolite-facies mylonite within the western margin of the Shaw Batholith. Faults vary from narrow, high-level, brittle structures and retrograde breccia zo nes in the north; to broader, more ductile structures with S/C mylonit ic foliations in the south, suggesting a southerly increase in exhumat ion. A set of kilometre-scale, en-echelon folds with NE-SW striking, u pright axial planes and NE-plunging axes characterize the interior of the CPSC and are wholly contained within the bounding faults, thus ind icating coeval development with faulting during sinistral wrenching (s igma(1) = NW-SE). Strike-slip deformation in the CPSC is interpreted t o have resulted from northwesterly indentation of Shaw Batholith (and contiguous rocks to the east). Westerly-directed tectonic escape of th e Strelley Granite laccolith and associated supracrustal rocks from in between Shaw Batholith and North Pole Dome, was followed by ramping u p the concave eastern margin of the Yule Batholith and eastward tiltin g during the transition from westerly to northerly displacement. Conti nued northward translation of the Strelley Granite at the leading edge of the system was terminated by constriction between the Carlindi Bat holith and the North Pole Dome. Trailing greenstone successions were c rumpled into a series of NE-trending, en-echelon folds and related fau lts. Kinematic evidence and structural geometry indicate that sediment s of the Lalla Rookh Basin (De Grey Group) were deposited in advance o f the north-moving Strelley Granite within a basin bounded by faults o f opposite displacement. rather than in a pull-apart basin as previous ly suggested. The age of the D3 deformation is indicated by resetting of the Ar-Ar and Rb-Sr isotopic: systems to ca. 2950 Ma in the Western Shaw region, and by U-Pb ages of syn-kinematic granitoid rocks. (C) 1 998 Elsevier Science B.V.