GEOLOGICAL SOCIETY OF THE PHILIPPINES
| POLYPHASED DEFORMATION AND METAMORPHISM OF THE CRETACEOUS TO EOCENE SUCCESSIONS IN CENTRAL PALAWAN, PHILIPPINES |
David, S. D., Jr.*, Suzuki, S.**, Yumul, G. P., Jr.***, Roffler, R.**** and Takemura, S.*****
The deformation and metamorphism of the Cretaceous to Eocene succession in Central Palawan was studied where the general lithology is defined by mudstones and sandstones. Modal and chemical analyses of sandstones from the sequence revealed that the clasts of sandstones are derived from Palawan continental block, which was rifted from the Asian mainland. The pelitic rocks in the study area gradationally change from slaty in the west to slightly schistose to the east.
Structural analysis of the cleavage fabric revealed three stages of folding: F1, F2 and F3 phases with associated axial plane cleavages: slaty cleavage S1, crenulation cleavage S2 and crenulation cleavage S3 from the first stage to the third stage of folding. The folding also suggested that the sequence belongs to an overturned limb of large scale inclined fold with the youngest to the west.
Metamorphic grade and condition based on the crytallinity (illite crytallinity) and b0 cell parameters of K-white micas during the first stage of deformation have been determined by X-ray diffraction analysis. It shows that the overall ‘illite crystallinity (IC)’ values decrease in grade from the E to the W, while the b0 cell parameters indicate moderate-high pressure conditions.
From this study, the following tectonic history is proposed during the deformation of the Cretaceous to Eocene succession in Central Palawan:
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