Japan Geoscience Union Meeting 2015

Presentation information

International Session (Oral)

Symbol S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT07] New constraints on the tectonic evolution of Northeast Asia

Mon. May 25, 2015 9:00 AM - 10:45 AM A03 (APA HOTEL&RESORT TOKYO BAY MAKUHARI)

Convener:*Jonny Wu(Department of Geosciences, National Taiwan University), Kyoko Okino(Ocean Research Institute, University of Tokyo), Cedric Legendre(Institute of Earth Sciences, Academia Sinica, Taiwan), Gaku Kimura(Department of Earth and Planetary Science of the Graduate School of Science, The University of Tokyo), Chair:Jonny Wu(Department of Geosciences, National Taiwan University), Kyoko Okino(Ocean Research Institute, University of Tokyo)

9:45 AM - 10:00 AM

[SIT07-04] Temporal constraints for the tectonic development of the Philippine ophiolite belts from new zircon U-Pb ages

*Kenichiro TANI1, Jillian Aira S. Gabo2, Kenji HORIE3, Osamu ISHIZUKA4, Jenielyn Padrones5, Betchaida Payot6, Maria Luisa Tejada7, Decibel V. Faustino-Eslava8, Akira IMAI5, Shoji ARAI9, Tomokazu HOKADA3, JR., Graciano P. YUMUL10, Carla B. Dimalanta6 (1.National Museum of Nature and Science, 2.Kyushu University, 3.National Institute of Polar Research, 4.Geological Survey of Japan/AIST, 5.Akita University, 6.University of the Philippines, Diliman, 7.Japan Agency for Marine-Earth Science and Technology, 8.University of the Philippines, Los Banos, 9.Kanazawa University, 10.Apex Mining Co. Inc.)

The tectonic framework of the Philippine Islands is important in understanding how the western Pacific margin developed along the Eurasian and the Pacific Plates since the Eocene.
The basement rocks of the Philippine Islands are characterized by the presence of ophiolitic complexes exposed among the islands. Yumul (2007, Island Arc) defined four belts in the Philippine ophiolites and proposed that they progressively become younger towards west, from Early ? Late Cretaceous at the easternmost belt to Eocene - Oligocene in the west. However, most of the ophiolitic complexes have been dated by radiolarians and foraminifera in the overlying sediments and lacked reliable radiometric ages from the igneous rocks.
To precisely determine the igneous ages of the Philippine ophiolites, we have conducted SHRIMP zircon U-Pb dating of the gabbroic and leucocratic rocks collected from the ophiolitic complexes in the Philippine Islands, including those from Luzon (Zambales, Isabela, and Lagonoy ophiolites), Masbate (Balud ophiolite), Tablas (Sibuyan ophiolite), Dinagat, and Cebu.
New zircon ages show that most of the ages obtained from the northern ophiolite belts are Eocene in age, from 52 Ma to 41 Ma. These ages coincide well with the opening of the West Philippine Basin (49 ? 33 Ma, Taylor and Goodliffe, 2004, GRL), which is a backarc basin formed behind the incipient Izu-Bonin-Mariana Arc. Furthermore, geochemical data available from the igneous rocks in the eastern ophiolite belts show backarc basin basalt-like geochemical affinities (e.g. Yumul, 2007), suggesting that these ophiolites are genetically associated with the West Philippine Basin.
On the contrary, southern ophiolites are significantly older, gabbroic and leucocratic rocks that are associated with the ophiolitic complex in Cebu and gabbroic rocks in Lagonoy and Dinagat ophiolites are Jurassic to Late Cretaceous (200 - 90 Ma) in age. Similar Mesozoic arc and ophiolitic rocks have recently discovered in the Daito Ridges, currently located north of the West Philippine Basin. Such Mesozoic terranes in the Philippine Sea Plate may potentially be correlated to the Mesozoic ophiolites in the southern Philippines, before the opening of West Philippine Basin in the Eocene.