Ultrahigh-Pressure Metamorphic Rocks in the Bantimala Mélange Complex and Its Implication to Cretaceous Tectonics in the South Arm of Sulawesi

Abstract

Bantimala Mélange Complex is about 75 Km to the North of Makassar, the capital city of South Sulawesi Province. The presence of High-pressure Metamorphic Rocks, and Ultrahigh Pressure in the Bantimala Mélange Complex, has been known and studied by a number of geologists. Eclogite and Blue Schist are Ultrahigh, and High-pressure metamorphic rocks in the Bantimala Mélange Complex which have important significance in explaining the Cretaceous tectonics in this area. Furthermore, Bantimala Eclogite is the only Ultrahigh-pressure metamorphic rock known to be exposed in Sulawesi. The results of thin section analysis of Eclogite show the presence of Omphacite Minerals, and Coesite as an index mineral for Ultrahigh pressure metamorphic rocks. While in Blue Schist with Glaucophane Minerals are found which are partially replaced by Chlorite which indicates the presence of Poly-metamorphism as a result of retrogradation from Ultrahigh pressure to High pressure and to Medium pressure metamorphic rocks. Radiometric age dating using the Ar40/Ar39 method shows an age spectrum of 100 Ma-114 Ma (Early Cretaceous). The 114 Ma, age is interpreted as the age of Eclogite’s Ultrahigh pressure metamorphic rocks formation with respect to the peak of subduction tectonics. Whereas the age of 100 Ma before now is interpreted as the age of exhumation or collision as the end of the Cretaceous tectonic subduction in the South Arm of Sulawesi or in the East or Southeast of Sundaland.