Complex origin for the south-western Zamboanga metamorphic basement complex, Western Mindanao, Philippines |
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| Authors: | Rodolfo A Tamayo JR Graciano P Yumul JR René C Maury Hervé Bellon Joseph Cotten Mireille Polvé Thierry Juteau and Cliff Querubin |
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| Institution: | UMR 6538, Universitéde Bretagne Occidentale, 6, avenue Le Gorgeu, BP 809, 29285 Brest, France, (email:;)Rushurgent Working Group, National Institute of Geological Sciences, University of the Philippines, Diliman, Quezon City 1101, The Philippines,;UMR 5563, UniversitéPaul Sabatier, 38, rue des 36 Ponts, 31400 Toulouse, France,;Mines and Geosciences Bureau, Regional Office XI, Zamboanga City, The Philippines |
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| Abstract: | Abstract Amphibolites unconformably overlain by a metasedimentary sequence of quartz-muscovite-feldspar-kyanite schists, metagraywackes and epidote-bearing amphibolites occur in the northern portion of the south-western Zamboanga metamorphic basement complex, western Mindanao. These amphibolites (here identified as the Mount Dansalan amphibolites) display relict magmatic textures inherited from cumulate gabbro protoliths. Bulk-rock major and trace-element data are consistent with this hypothesis. Together with the chemistry of relict igneous clinopyroxenes, they indicate a magmatic arc-related signature for the gabbro protoliths. Geochemical data allow us to identify various sources for the associated metasediments: the gabbro themselves for the metagraywackes and a continental basement for the quartz-muscovite-feldspar-kyanite schists. Both sources contributed to the genesis of the epidote-amphibolite metasediments. The compositions of the metamorphic mineral assemblages suggest that the rocks have undergone metamorphism at temperatures ranging from 550°C to 700°C and pressures probably in the range of 5–9 kbar. 40K–40Ar isotopic study of amphibole separates from the Mount Dansalan samples document a metamorphic event dated at 24.6 ± 1.4, 22.2 ± 1.4 and 21.2 ± 1.2 Ma. Our results are in agreement with plate tectonic models which describe the south-western Zamboanga metamorphic basement as a continental terrane. However, its evolution was not as simple as it was usually considered. In particular the basement incorporated slivers of magmatic arc crust, which cannot be unambiguously related to any of the Tertiary arcs documented in the area. |
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| Keywords: | amphibolites metamorphic basement Zamboanga peninsula |
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