| Summary: | The collision of Australia-Antarctica with western Laurentia in the late Mesoproterozoic or earlyNeoproterozoic is hypothesised marks the final assembly of the supercontinent Rodinia. Evidence formetamorphism or deformation along the eastern margin of Australia-Antarctica and the western margin ofLaurentia that might be attributed to this Rodinia-forming collision is equivocal. One of the few places ineastern Australia where Late Mesoproterozioc metamorphism is recognised is King Island- a small islandlocated approximately 100 km northwest of Tasmania. Based on its record of Late Mesoproterozoicmetamorphism, some workers interpret King Island to be a fragment of the collisional suture betweenAustralia-Antarctica and Laurentia within Rodinia. However, the tectonic setting of Late Mesoproterozoicmetamorphism on King Island has not been studied in detail and the interpretation that it reflectscollisional processes has not been demonstrated. This study presents results from recent field-based mapping on King Island and a reassessment of thepressure-temperature-time history of the Late Mesoproterozoic metamorphic event recorded here.Mesoproterozoic strata exposed on the west coast of King Island comprise sandy turbidites of the SurpriseBay Formation. The Surprise Bay Formation is intruded by a series of northeast trending dolerite dykes withMORB and within-plate basalt geochemical affinities. Probable mafic volcaniclastic rocks are locallyinterlayered with turbdites in the Surprised Bay Formation and are compositionally similar to the doleritedykes. Both the Surprise Bay Formation and dolerite dykes record deformation assigned to D1, whichproduced a subhorizontal fabric and tight recumbent folds that were subsequently rotated into an uprightposition during NeoproterozoicPaleozoic deformation. Metamorphism was pre- to syn-kinematic withrespect to D1 with the peak garnet- and andalusite-bearing assemblages equilibrating in the low-pressureamphibolite facies at ca. 1290 Ma. Integrating field and microstructural observations suggests that sedimentation, mafic magmatism,deformation, and low-pressure medium-temperature metamorphism on King Island may have beenbroadly contemporaneous. We suggest that Late Mesoproterozoic metamorphism on King Island occurredin a mature continental rift setting, where mantle upwelling and voluminous mafic magmatism drive low pressuremediumhigh-temperature metamorphism in thinned continental crust. Late Mesoproterozoictectonism on King Island may therefore to be unrelated to orogenesis associated with the assembly ofRodinia. Instead, ca. 1290 Ma rift-related metamorphism on King Island overlaps with the final stages of thebreakup of the supercontinent Nuna, which is also recorded by widespread basin formation throughoutmainland Tasmania at this time.
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