Blueschist relic clinopyroxenes of Smith Island ( South Shetland Islands): their composition, origin and some tectonic implications.

Clinopyroxene porphyrocrysts thought to be relics, of igneous origin, were found in mafic blueschists of the pre-Jurassic(?) Smith Island metamorphic complex. The composition of the clinopyroxenes (low Ti-augites) and the nature of the associated lithologies, support the idea that the high P-low T metamorphics of the South Shetland Islands are at least in part composed of accreted subalkaline ocean floor or island arc basalts. The geochemical data preclude an origin involving an eclogitic or other high grade metamorphic rock. A more or less continuous belt of oceanic lithologies accreted to the margin of Gondwana during the Late Palaeozoic and/or Early Mesozoic can be postulated. -from Author