Grenvillian‐aged orogenesis in the Palaeoproterozoic Gascoyne Complex, Western Australia: 1030–950 Ma reworking of the Proterozoic Capricorn Orogen

Abstract

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.

The Australo-Antarctic Columbia to Gondwana transition

“…The Capricorn Orogen preserves several intraplate tectonic events, however. These include the high temperature, magmatism dominated, and possibly extensional Mangaroon Orogeny from 1680 to 1620 Ma (Sheppard et al, 2005); the prolonged Mutherbukin Tectonic Event from 1385 to 1200 Ma, characterised by shearing and metamorphism, but lacking magmatism (Johnson et al, 2011b), and the relatively minor and locally restricted Edmundian Orogeny from 1040 to 955 Ma (Sheppard et al, 2007). Between these orogenic events the Capricorn Orogen saw several basin forming events between 1620 and 1465 Ma (Edmund Basin) and ca.…”

Spatio-temporal evolution of the Satpura Mountain Belt of India: A comparison with the Capricorn Orogen of Western Australia and implication for evolution of the supercontinent Columbia

“…5) has a history of evolution for 800e1000 Ma that comprises repeated basin formation, magmatism and orogeny in the Wilson cycle of PaleoproterozoiceMesoproterozoic age (Tyler and Thorne, 1990). Four discrete Paleoproterozoic orogenic events at 2215e2145 Ma (Opthalmian Orogeny), 2005e1960 Ma (Glenburgh orogeny), 1830e1780 Ma (Capricorn Orogeny) and 1680e1620 Ma (Mangaroon orogeny) and a single Mesoproterozoic to Neoproterozoic Edmundian orogeny (1070e755 Ma) have been recorded from the Capricorn Orogen (Cawood and Tyler, 2004;Sheppard et al, 2004Sheppard et al, , 2007.…”

The role of radiogenic heat in prolonged intraplate reworking: The Capricorn Orogen explained?

“…Subsequent episodes of tectonic reactivation resulted in deformation, metamorphism, and sedimentation, with little or no magmatism (Fig. 2), as exemplified by the Mutherbukin Tectonic Event (1320-1170 Ma; Korhonen et al, 2015), the Edmundian Orogeny (1030-955 Ma; Martin and Thorne, 2004;Sheppard et al, 2007), and the c. 570 Ma Mulka Tectonic Event. This protracted tectonomagmatic history has produced a stratified crustal profile (Fig.…”

“…Deep crustal seismic imaging shows that the batholith ranges in thickness from ∼1.8 km in the center of the Mutherbukin Zone to ∼11.5 km at its northern contact where it is truncated by the Ti Tree Shear Zone ( Fig. 1b; Johnson et al, 2013b), a long-lived crustal-scale structure with evidence for fault reactivation as recently as the Neoproterozoic (Sheppard et al, 2007). The batholith has a concave basal contact with the underlying basement, which suggests that it has been folded after emplacement.…”