Structural Imprints of Andaman Accretionary Prism and Its Tectonic Relation with Ophiolite Belt of Indo-Burma Ranges

Abstract

In Andaman subduction complex Indian plate is subducting towards east below Burma plate. In this subduction complex an accretionary prism comprising of Upper Cretaceous ophiolite and Eocene sediments is exposed in Andaman Islands. Map pattern and the field distribution show dismembered ophiolites occurring in different N-S trending thrust slices where the western slices have low dip (8°–10°) and the eastern slices have steep dip (65°–70°) towards east. Besides, few N-S trending back thrust and E-W trending out of sequence thrust have affected the disposition of the litho units. Oligocene-Miocene forearc sediments are exposed on both side of the accretionary prism. Eocene sediments deposited in trench slope basin have very irregular fold geometry which is due to changes to the basin floor topography during its upliftment along with ophiolite. The forearc sediments showing proximal to distal fan facies have regular fold geometry with N-S striking axial plane and very low plunge (18°–25°) either north or south. Based on the field disposition it is suggested that on land emplacement of Andaman ophiolite took place after the deposition of Oligocene-Miocene sediments. The forearc sediment was deformed during on-land emplacement of the accretionary prism. Similarity in petrographic character, age of the ophiolite, occurrence in an accretionary prism and field disposition suggest that both the ophiolite bodies of Andaman and Naga Hills of Indo Burma Ranges (IBR) represent Neotethyan crust. The ophiolites with Neotethyan crust situated in western belt of IBR have also similarity with the ophiolites of Eastern belt of IBR and on-land emplacement of IBR ophiolites took place during India-Asia/Burma plate collision in Late Miocene time.