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Geo- and thermochronological methods were applied to diorites from the Cordillera Central, Luzon, Philippines to understand their emplacement and exhumation history in the island arc mountains. Five zircon U–Pb ages range from 32.54 ± 0.70 to 6.11 ± 0.15 (2SE) Ma, indicating that dioritic magmas intruded the upper crust intermittently during Cenozoic magmatism. Five zircon fission-track (ZFT) pooled ages range from 35.63 ± 2.17 to 6.91 ± 0.36 (2SE) Ma and are generally comparable with the U–Pb ages at each locality. These results suggest that the diorites cooled rapidly below ~ 250–350 °C (i.e., through the partial annealing zone of the ZFT system), following their intrusion. On the other hand, two zircon and five apatite U-Th(-Sm)/He (ZHe and AHe) weighted mean ages, ranging from 11.71 ± 0.36 to 8.82 ± 0.26 and 9.21 ± 0.52 to 0.98 ± 0.09 (2SE) Ma, respectively, indicate a decrease in cooling rates at a lower temperature range, especially through the partial retention zone of the AHe system. This observation suggests that the ZFT ages reflect initial cooling of the dioritic magma, whereas the AHe ages reflect the cooling history associated with regional exhumation following the initial cooling phase. The spatial distribution of the AHe ages suggests that rapid exhumation of the Cordillera Central during the Quaternary resulted from the block-like uplift of the entire mountain range. [ABSTRACT FROM AUTHOR]

Offshore and ground gravity data were utilized to estimate crustal thickness across the Central Philippines where a transition from continental to island arc terrane occurs. Significant differences in gravity anomalies were observed between the Palawan Microcontinental Block (PCB) and the Philippine Mobile Belt (PMB), two major terranes that came together through arc-continent collision. Islands of the PCB (Mindoro, Tablas, Romblon, Sibuyan and western Panay), made up of an assortment of continent-derived sedimentary and igneous rocks and slivers of ophiolitic bodies, register lower Bouguer anomalies compared to that displayed by Masbate Island in the PMB. The calculated crustal thickness of this region exhibits a complex Moho topography of non-uniform depth across the collision zone with the thickest parts (∼32 km) corresponding with ophiolitic units emplaced consequent to arc-continent collision. On the other hand, relatively thinner crust (∼21 km) within the collision zone coincides with areas surmised to have undergone attenuation following intra-arc rifting. The same characteristics are observed offshore of western Mindoro and within the Marinduque Basin, areas known to have experienced crustal thinning following regional tectonic rearrangements that triggered riftings and intra-basin openings. [ABSTRACT FROM AUTHOR]