EMPLACEMENT OF THE EAST SULAWESI OPHIOLITE - EVIDENCE FROM SUBOPHIOLITE METAMORPHIC ROCKS

A newly discovered high-temperature metamorphic sole at the base of th e extensive East Sulawesi Ophiolite in Sulawesi, Indonesia yields new structural and petrological data with which to constrain the emplaceme nt history. The metamorphic sole is composed of a thin sequence of gar net and epidote amphibolite and basal greenschist metaclastics. East-d ipping tectonite fabrics in the metamorphic sole amphibolite are coinc ident with those in subjacent basement mica schist and superjacent per idotite and indicate orthogonal east to west emplacement of the ophiol ite in central Sulawesi. Metabasite in the upper levels of the sole ha s MORE geochemical characteristics, was recrystallized at temperatures of about 700 degrees C and yielded K/Ar radiometric ages of approxima tely 30 Ma. Initial detachment of the ophiolite probably occurred at a ridge segment-transform intersection in a back-are basin at the south -east margin of Sundaland. Detachment closely preceded NW-directed ove rthrusting and orthogonal obduction on to the Sundaland continental ma rgin in the Oligocene. Sinistral movement on a paleo-transform boundar y, now the Lawanopo Fault, may have facilitated obduction. Although th e westernmost segments of ophiolite may represent younger, more proxim al slices of a marginal basin, those further east probably represent s uccessively older, more distal slices of underthrust Indian Ocean back -are or forearc. (C) 1998 Elsevier Science Ltd. All rights reserved.