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Timing and exhumation of eclogite facies shear zones, Musgrave Block, central Australia
Author(s) -
CAMACHO A.,
COMPSTON W.,
McCULLOCH M.,
McDOUGALL I.
Publication year - 1997
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1997.00053.x
Subject(s) - geology , eclogite , metamorphism , greenschist , shear zone , geochemistry , mylonite , metamorphic facies , petrology , granulite , gneiss , facies , metamorphic rock , seismology , geomorphology , subduction , tectonics , structural basin
Timing constraints on shear zones can provide an insight into the kinematic and exhumation evolution of metamorphic belts. In the Musgrave Block, central Australia, granulite facies gneisses have been affected, to varying degrees, by mylonitic deformation, some of which attained eclogite facies. The Davenport Shear Zone is a dominant strike‐slip system that formed at eclogite facies conditions ( T ≈650 °C and P ≈12.0 kbar). Sm–Nd mineral isochrons obtained from equilibrated high‐pressure assemblages, as well as 40 Ar– 39 Ar data, show that the eclogite and greenschist facies high‐strain overprints were coeval, at c . 550 Ma. Mylonitic processes do not appear to have reset the U–Pb system in zircon, but may have partially disturbed it. The thermal gradient in the Musgrave Block crust at c . 550 Ma was c . 16 °C km −1 and at c . 535 Ma was c . 18 °C km −1 , based on P – T estimates of eclogite and greenschist facies shear zones, respectively. These estimates are similar to present‐day geothermal gradients in many stable continental shield areas, suggesting that the region did not undergo a significant transient perturbation of the geotherm. Therefore, in the Musgrave Block, cooling subsequent to eclogite facies metamorphism appears to have been controlled by exhumation, rather than by the removal of a heat source. Estimated exhumation rates in the range 0.2 to ≥1.5 mm year −1 are comparable with other orogenic belts, rather than cratonic areas elsewhere.