12:00 〜 14:00
[R8P-02] Geology and petrography of metamorphic rocks in Sibuyan Island, Romblon, Philippines
[Presentation award entry]
キーワード：schists, phyllites, Sibuyan, Romblon Island Group
Metamorphic rocks have been identified on Tablas, Romblon, and Sibuyan in the Romblon Island Group (RIG), Philippines. Collectively termed Romblon Metamorphics, these consist primarily of schists and phyllites, which are attributed by earlier works to the collision of the Palawan Microcontinental Block (PCB) and the Philippine Mobile Belt (PMB). In this work, we present new field and petrological data from metamorphic rocks exposed in Sibuyan Island to provide new insights into their petrogenesis and the P-T-D conditions that they preserve.
Phyllite outcrops of alternating quartz-rich (psammitic) and biotite-rich (pelitic) rocks are observed in northern Sibuyan island. The foliation direction of these interlayers generally dip in the southeast direction. Schist exposures on the other hand are more predominant in eastern and southwestern Sibuyan. They are also comprised of alternating dark- and light-colored layers suggesting similar protolith to the phyllites but with distinct peak metamorphic conditions. One outcrop documented near the coast in Barangay Mabini shows dark-colored schists with white prismatic feldspar porphyroblasts. This rock type dominates the exposure and is cut by dioritic leucocratic dikes that are often subparallel to the foliation of the schists.
Initial petrographic analysis of the metapelite schist and dike samples from Mabini revealed similar mineral assemblage of quartz(Qz)-feldspar(Afs)-biotite(Bt)-muscovite(Ms)-chlorite in varying abundances. Bt and Ms are the dominant minerals in schists, while Qz and Afs are more abundant in the dike samples. Foliations are observed as the preferred orientation of Qz and Afs in dikes and Bt and Ms in schist.
The dominance of Ms and Qz suggests a continent-derived protolith possibly linked to the PCB. Further petrological and geochemical analyses will be done to interpret the pressure-temperature-deformation-time (P-T-D-t) history and petrogenesis of rocks in the Sibuyan Island.
Phyllite outcrops of alternating quartz-rich (psammitic) and biotite-rich (pelitic) rocks are observed in northern Sibuyan island. The foliation direction of these interlayers generally dip in the southeast direction. Schist exposures on the other hand are more predominant in eastern and southwestern Sibuyan. They are also comprised of alternating dark- and light-colored layers suggesting similar protolith to the phyllites but with distinct peak metamorphic conditions. One outcrop documented near the coast in Barangay Mabini shows dark-colored schists with white prismatic feldspar porphyroblasts. This rock type dominates the exposure and is cut by dioritic leucocratic dikes that are often subparallel to the foliation of the schists.
Initial petrographic analysis of the metapelite schist and dike samples from Mabini revealed similar mineral assemblage of quartz(Qz)-feldspar(Afs)-biotite(Bt)-muscovite(Ms)-chlorite in varying abundances. Bt and Ms are the dominant minerals in schists, while Qz and Afs are more abundant in the dike samples. Foliations are observed as the preferred orientation of Qz and Afs in dikes and Bt and Ms in schist.
The dominance of Ms and Qz suggests a continent-derived protolith possibly linked to the PCB. Further petrological and geochemical analyses will be done to interpret the pressure-temperature-deformation-time (P-T-D-t) history and petrogenesis of rocks in the Sibuyan Island.