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Geological Society, London, Special Publications; 2004; v. 226; p. 289-312;
DOI: 10.1144/GSL.SP.2004.226.01.16
© 2004 Geological Society of London

Cenozoic-Present

Geology of the Zamboanga Peninsula, Mindanao, Philippines: an enigmatic South China continental fragment?

Graciano P. Yumul, Jr1,2, Carla B. Dimalanta1, Rodolfo A. Tamayo , Jr1, Rene C. Maury3, Herve Bellon3, Mireille Polvé4, Victor B. Maglambayan1, Cliff L. Querubin1,5 & Joseph Cotten3

1 National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City, Philippines rwg{at}i-next.net
2 Philippine Council for Industry and Energy Research & Development, Department of Science and Technology, Bicutan, Taguig, Metro Manila, Philippines
3 UMR 6538, Université de Bretagne Occidentale, 6, Avenue Le Gorgeu, B.P. 809, 29285 Brest Cedex, France
4 UMR 5563, Université Paul Sabatier, 38, Rue des 36 Ponts, 31400 Toulouse, France
5 Geosciences Division, Mines and Geosciences Bureau-IX, Zamboanga City, Mindanao, Philippines

Mindanao Island in the southern Philippines is made up of two blocks: the island-arc-related eastern-central Mindanao block and the continental Zamboanga Peninsula, which contains several ophiolitic bodies and mélanges. The Middle Miocene Siayan-Sindangan Suture Zone represents the tectonic boundary between the island-arc and continental blocks. A Middle Miocene age of collision is interpreted from the unconformity between the Late Miocene Motibot Formation and the underlying Middle Miocene Gunyan Mélange, which serves as basement to the suture zone. The Middle Miocene Siayan-Sindangan Suture Zone was formerly a subduction zone complex that was reactivated as a sinistral strikeslip fault following the collision of eastern-central Mindanao with the Zamboanga Peninsula. New 40K-40Ar whole-rock dating of lava flows from the Zamboanga Peninsula has revealed Middle to Late Miocene ages, which is consistent with the possible existence of an Early Miocene Sulu Trench. The possibility that the Zamboanga Peninsula could be part of the Palawan microcontinental block has been forwarded by previous workers, due to their similarity in stratigraphy, geological structure and metamorphic rock suites. The Palawan microcontinental block separated from southern China during the opening of the South China Sea in Oligo-Miocene times. If indeed the Zamboanga Peninsula was once part of Palawan, it represents the southernmost part of the rifted southeastern China continental margin.