OPHIOLITIC AND METAMORPHIC ROCKS IN THE PERCY-ISLES AND SHOALWATER BAY-REGION, NEW-ENGLAND FOLD BELT, CENTRAL QUEENSLAND

Ophiolitic and metamorphic rocks of the eastern part of the New England Fold Belt in the Shoalwater Bay region and the Percy Isles are grouped in the Marlborough and Shoalwater terranes, respectively. Marlborough terrane units occur on South Island (Percy Isles) and comprise the Northumberland Serpentinite, antigorite serpentinite with rodingite and more silicic dykes and mafic inclusions, the Chase Point Metabasalt, some 800+ metres of pillow lava, and the intervening South Island Shear Zone containing fault-bounded slices of mafic and ultramafic igneous rocks, schist, and volcaniclastic sedimentary rocks, and zones of melange. The Shoalwater terrane, an ancient subduction complex, consists of the Shoalwater Formation greenschist facies metamorphosed quartz sandstone and mudstone on North East Island and on the mainland at Arthur Point, the Townshend Formation, amphibolite-grade quartzite, schist and metabasalt an Townshend Island, and the Broome Head Metamorphics on the western side of Shoalwater Bay, upper amphibolite facies quartz-rich gneiss. With the exception of a sliver emplaced onto the western Yarrol terrane, possibly by gravity sliding, Shoalwater terrane rocks show the effects of Late Permian polyphase deformation. The Shacks Mylonite Zone along the northwest edge of the Broome Head Metamorphics marks a zone of oblique thrusting and is part of the major Stanage Fault Zone. The latter is a northeast-striking oblique-slip dextral tear fault active during Late Permian west-directed thrusting that emplaced large ultramafic sheets farther south. Marlborough terrane rocks were emplaced along the Stanage Fault Zone, probably from the are basement on which rocks of the Yarrol terrane were deposited. Structural trends and the distribution of rock units in the Shoalwater Bay-Percy Isles region are oblique to the overall structural trend of the northern New England Fold Pelt, probably due to the presence of a promontory in the convergent margin active in this region in Devonian and Carboniferous time.