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Mafic and Ultramafic Rock Association in the East Arc of Sulawesi
R. Soeria Atmadja, J.P. Golightly & B.N. Wahju
Abstract. The East Arc (East and South-East Arms) of Sulawesi is largely occupied by a huge complex of ultramafic rocks of presumably late Mesozoic to early Tertiary age. The ultramafic rocks of Sulawesi are closely associated with small masses of gabbroic rocks. The ultramafic complex takes the form of discontinuous belts which can be traced from the eastern-most part of the Eastern Arm west-ward curving to the South-East following the Structural trend of the South-East Arm. The complex is made up chiefly of harzburgite, lherzolite, with some dunite and pyroxenite. Over most parts of the investigated area, these rocks have been serpentinized to variable degrees. Dikes and small intrusive bodies of gabbroic and dioritic composition have been encountered in many places within this belt. This rock assemblage is characterized by irregularity in form and distribution. The purpose of this paper is to bring up-to-date what is known on the petrology and tectonic setting of the mafic and ultramafic rocks in the light of new available data and current theories, the present preliminary study is mainly based upon petrographic data, and field relations obtained from recent geological exploration activities and mapping by P.T. International Niekel Indonesia.