New Geologic, Radiolarian Biostratigraphic and Petrographic Results from the Buruanga Peninsula: Implications on the Arc-Continent Collision in Central Philippines

M.G.S. Asio¹ , J.A.S. Gabo¹, E.J. Marquez², K.L. Queaño³, L.R. Zamoras⁴, C.B. Dimalanta¹, G.P. Yumul Jr.⁵, L.T. Armada¹, E.G.L. Ramos¹ and R.A. Tamayo Jr.¹

¹Tectonics and Geodynamics Group – Rushurgent Working Group, National Institute of Geological Sciences, College of Science, University of the Philippines, Diliman, Quezon City
²Department of Physical Sciences and Mathematics, University of the Philippines-Manila, Padre Faura, Manila
³Mines and Geosciences Bureau, North Avenue, Quezon City; Mapua Institute of Technology
⁴Philex Mining Corporation, Pasig City
⁵Department of Science and Technology, Bicutan, Taguig City

Recent mapping in Buruanga Peninsula reveals that it consists of alternating chert-clastic sequences juxtaposed with limestone blocks. These sedimentary units are part of the oceanic plate stratigraphy, as defined by Wakita and Metcalfe (2005), which are reconstructed from accretionary complexes. The portion of the accretionary complex that was rifted during the opening of the South China Sea corresponds to what we call the North Palawan Block. This continent-derived fragment collided with the Philippine Mobile Belt in the Miocene.

Based on the oceanic plate stratigraphy defined by radiolarian biostratigraphic data, the sedimentary sequences in Buruanga Peninsula can be correlated with the Lower-Middle Jurassic chert and Middle-Upper Jurassic clastic sequences adjacent to pelagic limestone in Busuanga Island in North Palawan. The JR5-JR6 (Callovian to Oxfordian) siliceous mudstone of the Saboncogon Formation in Buruanga Peninsula correlates with the JR5-JR6 siliceous mudstone of the Guinlo Formation in the Middle Busuanga Belt. The oceanic plate stratigraphy indicates that the Buruanga Peninsula and Busuanga Island can be correlated to the Mesozoic accretion-subduction in East Asia.

In addition, the Antique Range east of the Buruanga Peninsula is composed of stratigraphic units different from those of the Buruanga Peninsula. It consists of Middle Miocene basaltic to andesitic lava flow, pyroclastic deposits, reefal limestone and arkosic sandstone. Petrographic analysis of sandstones from the Buruanga Peninsula shows that they are quartz-rich (30-85%) when compared to the quartz-poor (0-35%) sandstones of the Antique Range. The marked difference between the lithologies suggests that the two areas have different origins.

The oceanic plate stratigraphy of Buruanga Peninsula and Busuanga Island, as well as the difference in age and lithology between the Buruanga Peninsula and the Antique Range further provides evidence for the presence of two terranes in the region: the Buruanga Peninsula having a North Palawan block affinity, while the Antique Range being part of the Philippine Mobile Belt.