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[SCG42-02] Metamorphism and thermal events in the Palawan Island: evidence for a Mid-Late Miocene exhumational event.
Keywords:Palawan Continental Block, Metamorphism, Fission track dating, Collision
Palawan Island’s geology is characterised by ophiolitic series overthrusting Asian-continent affinity sedimentary and metarmophic series and limited extend granitic bodies. In this contribution we present new maximum metamorphic temperatures estimates based on Raman Spectroscopy of Carbonaceous Material, and fission-track ages constraining the timing of the main cooling event from meta-sedimentary and granitic rocks in Northern and Southern Palawan. In northern Palawan maximum metamorphic temperatures estimates of Cretaceous metasedimentary rocks range mostly between 250-300ºC but reach temperatures >400ºC close to the Peak-Bay granitic intrusion. The Capoas and Peak-Bay granite display extremely fast cooling following emplacement at ca. 13.5Ma, with apatite fission track (AFT) ages of 10.4±1.7 Ma (n=40) and 11.7±1.7Ma (n=30), suggesting emplacement at very shallow levels and/or contemporaneously to a major exhumation event. Samples from the Caramay Schist formation present a partially-reset zircon fission-track with a young population suggesting a main cooling event at 11.6±1.2Ma. Critically, two similar AFT ages of 13.1±1.6Ma (n=49) and 13.2±1.8Ma (n=35) are recorded in Eo-Miocene clastic samples (Panas and Isugod Fm.) deposited on the lower ophiolitic thrust sheet in Southern Palawan.
We interpret the island wide 11-13Ma cooling event to be the result from a major exhumation event (erosion and/or normal faulting) affecting the Proto-South China Sea subduction/collision wedge and ophiolitic thrust sheets. This result is at odds with the commonly cited Lower Miocene timing for final ophiolitic emplacement, but corresponds well with the timing of the Pagasa wedge deformation (ca.16 to 12Ma) well characterised offshore Palawan and to the widespread erosive event inferred to have happened during the formation of the Middle Miocene Unconformity (ca.12Ma).
We interpret the island wide 11-13Ma cooling event to be the result from a major exhumation event (erosion and/or normal faulting) affecting the Proto-South China Sea subduction/collision wedge and ophiolitic thrust sheets. This result is at odds with the commonly cited Lower Miocene timing for final ophiolitic emplacement, but corresponds well with the timing of the Pagasa wedge deformation (ca.16 to 12Ma) well characterised offshore Palawan and to the widespread erosive event inferred to have happened during the formation of the Middle Miocene Unconformity (ca.12Ma).