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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]

Karstification is influenced by numerous factors, such as climate, geomorphology, and geology. Karstified areas are faced with numerous problems such as ground subsidence and groundwater vulnerability. In rapidly urbanizing areas like Cebu in the Philippines, it is imperative to know the karstification potential, especially if karst landforms are already present. We evaluated the karstification potential of central Cebu using Raster Overlay Analysis (ROA) in a geographic information system (GIS) platform. ROA uses multiple maps which represent different factors affecting karstification, such as precipitation, temperature, vegetation, elevation, slope, drainage, lineaments, and geology. These factors were then correlated with the karstification potential map using the Cell Statistics tool. ROA reveals that 17% of central Cebu has very low karstification potential, while < 65% has low to moderate karstification potential and 18% has high to very high karstification potential. High karstification potential is generally associated with high precipitation (> 2100 mm/yr), low temperature (< 24.5 °C), very dense vegetation, high elevation (> 787 masl), gentle slope (< 10°), very high lineament density (> 0.45), very low drainage density (0), and older limestone bedrock. Areas with moderate to very high karstification potential coincide with cave locations. Cell Statistics (Range) reveals that the karstification potential map is strongly correlated with precipitation and temperature, and weakly correlated with drainage density and geology. While assumed to greatly affect karstification, the weak correlation of local geology with the karstification potential is attributed to lithological heterogeneities in central Cebu. Information on an area’s karstification is beneficial to effective land use planning and reduction of karst-related hazards. [ABSTRACT FROM AUTHOR]