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. |