MIDDLE ORDOVICIAN HIGH PT METAMORPHIC ROCKS IN EASTERN AUSTRALIA - EVIDENCE FROM K-AR AGES

Phengite, separated from a metagabbro, three blueschist, and one metabasite that occur as blocks in serpentinite melange in the New England Fold Belt, eastern Australia, has yielded K-Ar ages of 465 - 480 Ma, significantly older than the age of most components of the belt. The schists and metabasite contain either glaucophane and/or crossite intergrown with the phengite, providing the first conclusive evidence for early Paleozoic subduction accretion associated with the east Gondwana margin. The tectonic affinity of the blocks is uncertain. They and other small early Paleozoic convergent margin elements in the New England Fold Belt may be allochthonous remnants of an are system accreted in the Devonian or Carboniferous, or they may be related to early Paleozoic convergent margin components found farther inboard in the Paleozoic fold belts of eastern Australia.