We describe the first occurrence of diamond-facies ultrahigh pressure metamorphism along the Gondwana-Pacific margin of the Terra Australis Orogen. Metamorphic garnet grains from Ordovician metasediments along the Clarke River Fault in northeastern Queensland contain inclusions of diamond and quartz after coesite, as well as exsolution lamellae of rutile, apatite, amphibole, and silica. These features constrain minimum pressure-temperature conditions to >3.5 gigapascals and ~860°C, although peak pressure conditions may have exceeded 5 gigapascals. On the basis of these data, we interpret the Clarke River Fault to represent a Paleozoic suture zone and at least parts of the Terra Australis Orogen to have formed through classic Wilson cycle processes. The growth of the Terra Australis Orogen during the Paleozoic is largely attributed to accretionary style tectonics. These previously unknown findings indicate that the Terra Australis Orogen was not just a simple accretionary style orogen but rather a complex system with multiple tectonic styles operating in tandem including collisional tectonics.

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<p>The Tasmanides of eastern Australia record a complex geological history. The central, and southern Tasmanides have been widely interpreted to reflect long-lived, accretionary-style convergent tectonics. The northernmost Tasmanides, which extend into north Queensland, are more poorly understood, but considered highly prospective for numerous styles of mineralization. The region contains several slices of mafic-ultramafic rocks, situated along major regional structures. The mafic-ultramafic complexes record strong, oceanic geochemical signatures, and are structurally interleaved within high grade, strongly deformed, Paleozoic basement metamorphic assemblages. Along the Clarke River Fault, the Running River Metamorphics, which host ophiolitic mafic-ultramafic rocks, also record evidence of diamond facies, ultra-high pressure (UHP) metamorphism. The discovery of diamond facies metamorphism, in conjunction with convergent margin ophiolites, suggests that the Clarke River Fault may represent a continental suture zone. This is the first indication of continent suturing in the Tasmanides, and challenges the idea that the Tasmanides, and greater Terra Australis Orogen, represent a simple accretionary system.</p>