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The proto-Philippine Sea Plate (pPSP) has been proposed by several authors to account for the origin of the Mesozoic supra-subduction ophiolites along the Philippine archipelago. In this paper, a comprehensive review of the ophiolites in the eastern portion of the Philippines is undertaken. Available data on the geology, ages and geochemical signatures of the oceanic lithospheric fragments in Luzon (Isabela, Lagonoy in Camarines Norte, and Rapu-Rapu island), Central Philippines (Samar, Tacloban, Malitbog and Southeast Bohol), and eastern Mindanao (Dinagat and Pujada) are presented. Characteristics of the Halmahera Ophiolite to the south of the Philippines are also reviewed for comparison. Nearly all of the crust-mantle sequences preserved along the eastern Philippines share Early to Late Cretaceous ages. The geochemical signatures of mantle and crustal sections reflect both mid-oceanic ridge and supra-subduction signatures. Although paleomagnetic information is currently limited to the Samar Ophiolite, results indicate a near-equatorial Mesozoic supra-subduction zone origin. In general, correlation of the crust-mantle sequences along the eastern edge of the Philippines reveal that they likely are fragments of the Mesozoic pPSP. Image 1 • The eastern Philippine ophiolites share Early to Late Cretaceous ages. • Geochemical signatures reveal mid-oceanic ridge to supra-subduction affinities. • Nickel, chromitite and massive sulfides are the dominant deposit types. • The eastern Philippine ophiolites are fragments of the proto-Philippine Sea Plate. [ABSTRACT FROM AUTHOR]

New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age. Radiometric dating of its plutonic and volcanic-hypabyssal rocks yielded middle Eocene ages. On the other hand, the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge – island arc affiliated Coto block of the ophiolite complex, together with isotopic age datings of its dikes and mafic cumulate rocks, also yielded Eocene ages. This offers the possibility that the Zambales Ophiolite Complex could have: (1) evolved from a Mesozoic arc (Acoje block) that split to form a Cenozoic back-arc basin (Coto block), (2) through faulting, structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or (3) through the interplay of slab rollback, slab break-off and, at a later time, collision with a microcontinent fragment, caused the formation of an island arc-related ophiolite block (Acoje) that migrated trench-ward resulting into the generation of a back-arc basin (Coto block) with a limited subduction signature. This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation. Image 1 • Multiple ages are reported for the Zambales Ophiolite Complex. • Formation involved subduction, slab rollback and continent fragment subduction. • Western seaboard of the Philippines is floored by Mesozoic lithospheric materials. [ABSTRACT FROM AUTHOR]

The impacts of land use/land cover (LULC) change and the relationship between landscape pattern and hydrologic processes in the ungauged Calumpang watershed, Batangas, Philippines were studied. LULC change from 2003 to 2008 included an increase in built-up areas (69%) and a reduction of mixed vegetation including riparian vegetation (−10%), which have significant effects on hydrology. Using the Soil and Water Assessment Tool (SWAT), significant increases in surface runoff (5%) and sediment yield (6%) and a reduction in baseflow (−11%) were shown. Spatial and temporal variations of the impacts were observed: degraded sub-basins experienced increased streamflow (up to 31%) during stormy months and reduced baseflow (up to −26%) during dry months. In contrast, improved sub-basins decreased stormflow (up to −4%), and increased baseflow (up to 5%) during dry months. Nine landscape metrics known to affect hydrology were quantified using Fragstats and were correlated with surface runoff, baseflow and sediment yield using partial least square (PLS) regression. The results indicated that increasing patch density and largest patch index of agricultural and forested landscapes, respectively, leads to a decrease in surface runoff and sediment yield while increasing baseflow. In contrast, increasing cohesion and aggregation index of agricultural and forested landscapes, respectively, results to an increase in surface runoff and sediment yield as baseflow decreases. Although more observed data is needed for validation, the relationship model produced in this study can be applied to new data or used for scenario analysis. When coupled with economic, social and political assessments, the model serves as a useful tool in formulating comprehensive watershed management and land use policies. [ABSTRACT FROM AUTHOR]