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Grenvillian‐aged orogenesis in the Palaeoproterozoic Gascoyne Complex, Western Australia: 1030–950 Ma reworking of the Proterozoic Capricorn Orogen
Author(s) -
SHEPPARD S.,
RASMUSSEN B.,
MUHLING J. R.,
FARRELL T. R.,
FLETCHER I. R.
Publication year - 2007
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.1525-1314.2007.00708.x
Subject(s) - geology , metamorphism , geochemistry , orogeny , kyanite , proterozoic , pegmatite , greenschist , metamorphic facies , geochronology , andalusite , monazite , schist , metamorphic rock , petrology , zircon , facies , geomorphology , paleontology , tectonics , structural basin
In situ SHRIMP U–Pb geochronology of monazite and xenotime in pelitic schists from the central Gascoyne Complex, Western Australia, shows that greenschist to amphibolite facies metamorphism occurred between c . 1030 and c. 990 Ma. Monazite from an undeformed rare‐element pegmatite from the same belt gives a 207 Pb/ 206 Pb age of c . 950 Ma, suggesting that peak metamorphism and deformation was followed by pegmatite intrusion and coeval granite magmatism. Metamorphism in the central Gascoyne Complex was previously interpreted as Barrovian, largely based on the identification of kyanite in peak metamorphic assemblages, and has been attributed to intense crustal shortening and substantial tectonic thickening during Palaeoproterozoic continent–continent collision. However, the stable Al 2 SiO 5 polymorph has been identified in this study as andalusite rather than kyanite, and the prograde assemblages of staurolite–garnet–andalusite–biotite–muscovite–quartz indicate temperatures of 500–550 °C and pressures of 3–4 kbar. These data show that the Palaeoproterozoic Gascoyne Complex underwent an episode of Grenvillian‐aged intracontinental reworking concentrated in a NW–SE striking corridor, during the Edmundian Orogeny. Until now, the Edmundian Orogeny was thought to have involved only reactivation of structures in the Gascoyne Complex, along with deformation and very low‐ to low‐grade metamorphism of Mesoproterozoic cover rocks some time between 1070 and 755 Ma. However, we suggest that it involved regional amphibolite facies metamorphism and deformation, granite magmatism and pegmatite intrusion between c . 1030 and c . 950 Ma. Therefore, the Capricorn Orogen experienced a major phase of tectonic reworking c . 600 Myr later than previously recognized. Our results emphasize the importance of in situ geochronology integrated with petrological studies in order to link the metamorphic history of a terrane with causally related tectonic events.