Geology of Sabtang Island and Reconnaissance Geology of Batan, Itbayat and Ivuhos Islands Batanes Province, Philippines

J.D. Dianala, J.W. Carag, J.P. Domingo, R.N. Eco, C. Lit, T.M. Herrero, R. Leuterio,
S.J. Probst, J. Rimando, P.L. Tolentino, A.M. Villareal, 
S. Catane, A.G. Fernando, A. Peleo-Alampay

National Institute of Geological Sciences, University of the Philippines, 
Diliman, Quezon City 1101



Information about the geology of the islands in Batanes is limited, with Batan Island being the most extensively studied due to the presence of the active Iraya Volcano near the densely populated town of Basco. A geologic survey was done to delineate the rock units present in Sabtang Island, and to confirm reported rock units present in Ivuhos and Itbayat Islands. At least three geologic units were observed in Sabtang, herein proposed to be named as:Chavayan Volcanic Complex, Sabtang Breccia and Savidug Limestone. The Chavayan Volcanic Complex is composed of andesite flows and diorite plugs, which are unconformably overlain by theSabtang Breccia, which are thick sequences of volcanic breccia with minor tuffites and basaltic lava flows. Majority of the clasts in the breccia reveal breadcrust structures indicating direct input of sediments from volcanic eruptions. The youngest unit in Sabtang Island is the sub-horizontal to gently dipping Savidug Limestone, which unconformably overlies the volcanic complex and breccia. Recent volcanic deposits were observed only in Itbayat and Batan. The rock unitsin Sabtang reveal a history of significant submarine volcanicactivity prior to uplift and quiescence, followed by deposition of limestones.

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