TIMING OF GRANITE EMPLACEMENT UNDER CONDITIONS OF LOW STRAIN IN THE NORTHERN TASMAN OROGENIC ZONE, AUSTRALIA

Granite plutons of the Mount Alto and Whypalla supersuites intruded up per crust in the south of the multiply deformed Silurian-Devonian Hodg kinson Province in northern Queensland, Australia, during the Early Pe rmian. Emplacement occurred under conditions of low strain, with pluto n wallrocks displaying variation in the development of country rock st ructure due to heterogeneity of deformation intensity. Pluton wallrock s contain evidence for four deformation events, with subsequent minor deformation defined by localized kinks and recumbent folds. The struct ural timing of widespread contact metamorphic cordierite porphyroblast growth, combined with pluton-wallrock histories, indicates the main s tage of granite emplacement occurred during weak contractional D-3 def ormation. Minor igneous intrusion during the contractional D-4 deforma tion is suggested by rare D-4 cordierite porphyroblast growth, present as very narrow rims on the D-3 porphyroblasts. New U-Pb zircon age da ta from the Mount Alto Supersuite overlap with crystallization ages of the nearby Whypalla Supersuite and allow tentative correlation of the deformation history of the Rumula district with that established for the central meridional Hodgkinson Province. A fundamental control on e mplacement of plutons of both the Whypalla and Mount Alto supersuites was a set of WNW-ESE-striking faults, which combined with N-S-striking bedding and faults to impart pronounced curvilinear geometries to sev eral groups of plutons. (C) 1998 Elsevier Science B.V. All rights rese rved.