GEOLOGICAL SOCIETY OF THE PHILIPPINES
Sedimentary Provenance and Tectonic Setting of Northwestern Panay Clastic Rocks Deduced from Major and Trace Element Geochemistry
Northwestern Panay in Central Philippines is an interesting area to study in terms of the collision between the Palawan Microcontinental Block and the Philippine Mobile Belt (Figure 1). The Buruanga Peninsula is composed of a chert-clastic-limestone sequence. The Antique Range consists of pyroclastic flow deposits that is overlain by siltstone-sandstone-shale interbeds that are lithic-rich. Results of major and trace element geochemical analyses of clastic rocks revealed two distinct compositional ranges for Northwestern Panay. The sedimentary rocks of Buruanga Peninsula can be distinctly separated from the clastic rocks of the Antique Range in terms of provenance and tectonic setting. Buruanga Peninsula samples (Saboncogon Formation) reveal compositions that belong to a continental margin tectonic setting (Figure 2a) and a more acidic to intermediate source (Figure 2b). Sedimentary rocks from the Antique Range (Lagdo Formation) have an affinity to an oceanic island arc setting (Figure 2a) with a more basic provenance (Figure 2b). Some of the Fragante Formation, which belongs to the Antique Range terrane, plots close to the Buruanga Peninsula samples. This may indicate that the Fragante Formation was also acquiring sediment input during its formation from Buruanga Peninsula. The major and trace element composition of clastic rocks from the study area agrees with previous studies that separate the Buruanga Peninsula from the Antique Range into two distinct terranes. The Buruanga Peninsula belongs to the Palawan Microcontinental Block, a continental fragment which was part of the Mesozoic East-Asia accretionary complex that drifted southeast to collide with the Philippine Mobile Belt. This is consistent with the continental margin setting and more acidic source for Buruanga Peninsula. On the other hand, the Antique Range was reported to be part of the collision zone boundary separating the Palawan Microcontinental Block and the Philippine Mobile Belt. Based on its oceanic island arc setting and basic provenance signature, the Antique Range can be interpreted to be produced by volcanism as a result of the subduction of the leading edge of the Palawan Microcontinental Block prior to collision.
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