GEOLOGICAL CHARACTERISTICS AND FORMING ORIGIN OF ULTRAMAFIC ROCKS (SERPENTINITE) OF HIEP ĐUC COMPLEX

Abstract

Serpentinite of Hiep Đuc complex has been determined and described in project of geological mapping in 1/ 500,000 scale and arranged in hyperbazite formation with MgO/ FeO > 6 (Huynh Trung et all, 1980). They are lens, sheet in shape, with small crops. They injected along tectonic line (rift) with longitudinal direction or subparallel direction. They do not cause thermal - exomorphism for surrounding rocks and named as non root – protrusion. Petrography composition are mainly olivinite, lherzolite (chemical composition) rich in MgO (32–37%). The serpentinite bodies distributed mainly in rift zone. This zone displays spilite and ultramafic, mafic formations of Ngoc Hoi complex of early Paleozoic age. Serpentinite formations of Hiep Duc complex are not common magmatic origin of spilite, pyroxenite, gabbro formations which mentioned. Association of these formations formed Kontum ophiolite assemblage of early Paleozoic age, which can be compared with ophiolite assemblage of Alpine-type.Petro-geochemical characteristic of serpentinite are like composition of upper mantle, alpinotype hyperbazite and oceanic floor. During early Paleozoic, they were compressed and protruded from deep crush. Kontum massif was formed in late Proterozoic, and separated into microplates by tectonic line in which the serpentinite bodies of Hiep Duc complex protruded.