U-Pb ages from the Harts Range, central Australia: evidence for early Ordovician extension and constraints on Carboniferous metamorphism

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb analyses of monazite and zircon from the Harts Range indicate the southeastern Arunta Inlier ha s been affected by two major Palaeozoic tectonothermal events. During the e arly Ordovician (467 +/- 8 Ma), regional deformation produced a sub-horizon tal upper amphibolite-facies (greater than or equal to 700 degrees C and 7 kbar) shear fabric that overprinted c. 800 degrees C migmatitic assemblages . In the intracratonic Amadeus Basin south of the Harts Range region, subsi dence rates increased in the early Ordovician with the accumulation of east erly, and southerly, derived mature sediments. This is contrary to what wou ld be expected if deformation in the Harts Range region occurred in a compr essional setting, and suggests that the early Ordovician deformation may ha ve occurred in an extensional intraplate setting. The terrain remained at d epth until the mid-Carboniferous when up to 20 km of exhumation occurred du ring the latter stages of the intracratonic Devonian to Carboniferous (400- 300 Ma) Alice Springs Orogeny. Monazite U-Pb data indicates the structurall y lowest parts of the terrain were at c. 6 bar and greater than or equal to c. 600 degrees C at 343 +/- 8 Ma, and subsequently underwent high-temperat ure decompression, resulting in overprinting of the kyanite-grade assemblag es with sillimanite-bearing assemblages during south-directed thrusting. Du ring exhumation, pegmatite emplaced in the southeastern Harts Range at 330 +/- 6 Ma (zircon U-Pb) was strongly deformed at temperatures around 560 deg rees C and depths around 15 km. The U-Pb data from the Harts Range indicate that the record of intraplate deformation in central Australia was more co mplex than previously thought.