Formation of marginal seas in Southeast Asia by rifting of the Chinese and Australian continental margins and implications for the Borneo region

Abstract

With th e exception s of th e Okinawa and Ayu tJO ughs, al l th e So utheast Asian marginal seas have formed by processes other than back-arc ex tension. The Andaman Sea is an id eal example of a leaky transform system. The West Phi lipp in e Sea, Banda Sea, Celebes Sea and S ulu Sea bas in s all appear to be remnants of former oceans now trapped behind youn ger arc-trench systems. The last three may be interpreted to be related to th e post-Early Triassic rifting of the northern continental margin of Australia. The South Ch in a Sea bas in was probably fo rm ed by post- Ea rl y Cretaceous riftin g of th e continental margin of southeast China and is now trapped behi nd the Mani la arc-trench system. The riftin g of Australi a and Chin a, an d th e associated sea-floor spreadin g, carri ed continental f rag­ ments north wards and southwards respecti vely. Borneo and th e adjacent Philippines may have resulted from th e .coming together of th ese fragments to f'orm the heterogeneous basement terr ai n over and around which Cenozoic sedim ents have accumulated. The uplift of th e margin a l sea lithosphere to form ophioliti c terrains is cons ide red to have resulted from the colli sions of th e continental fragments wi th each other or with arc- trench systems.