Mesozoic rock suites along western Philippines: Exposed proto-South China Sea fragments?

An ancient oceanic crustal leading edge east of mainland Asia, the proto-South China Sea crust, must have existed during the Mesozoic based on tectonic reconstructions that accounted for the presence of subducted slabs in the lower mantle and the exposed oceanic lithospheric fragments strewn in the Philippine and Bornean regions. Along the western seaboard of the Philippine archipelago, numerous Mesozoic ophiolites and associated lithologies do not appear to be genetically associated with the younger Paleogene-Neogene ocean basins that currently surround the islands. New sedimentological, paleomagnetic, paleontological, and isotopic age data that we generated are presented here, in combination with our previous results and those of others, to reassess the geological make-up of the western Philippine island arc system. We believe that the oceanic lithospheric fragments, associated melanges, and sedimentary rocks in this region are exhumed slivers of the proto-South China Sea ocean plate

Slab rollback and microcontinent subduction in the evolution of the Zambales Ophiolite Complex (Philippines) : A review

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

Interpretation of Ground Magnetic Data in Suyoc, Mankayan Mineral District, Philippines

Ground magnetic surveys conducted in Suyoc, Mankayan, Benguet led to the delineation of features related to epithermal and porphyry copper targets in the area. High reduced to equator (RTE) anomalies are observed in areas with epithermal mineralization. The high RTE anomalies are attributed to hydrothermally altered rock with quartz veins. The previously recognized porphyry copper prospect in Palasaan (Mohong Hill) is characterized by low RTE anomaly surrounded by a high RTE anomaly. One explanation for this signature is the possible presence of a magnetic core and the destruction or absence of magnetite in the alteration haloes at the periphery of a porphyry prospect. Areas such as Mangga and Liten exhibit the same magnetic signatures. This distinct magnetic pattern coupled with observed alteration and mineralization signatures led to the interpretation of prospective blind porphyry deposits in these localities. Results of the study reveal the applicability of ground magnetic data in characterizing and extracting a potential area of mineralized zones at a regional scale

Bouguer Anomaly of Central Cebu, Philippines

Cebu Island in Central Philippines consists of a Cretaceous basement complex capped by mostly Tertiary sedimentary units. Recent mapping conducted in Central Cebu revealed limited exposures of lithologies, especially those comprising the basement complex. The gravity method was utilized to generate Bouguer anomaly maps for Central Cebu. These geophysical maps provide the first images of the subsurface extent of the basement units. A prominent nearly circular gravity anomaly high is consistently observed in the Bouguer anomaly maps coinciding with the location of dense basement and intrusive rocks. However, field mapping revealed the very limited surface exposure of these units. The gravity highs recognized in the residual anomaly maps may correspond to the larger extent of the intrusive units at depth. The broad gravity high observed in the regional anomaly map may define the extent of the subsurface distribution of the Cretaceous basement complex

Mineralization parameters and exploration targeting for gold- copper deposits in the Baguio (Luzon) and Pacific Cordillera (Mindanao) Mineral Districts, Philippines: A review

The Baguio Mineral District in Luzon, Philippines is known to host several world-class epithermal gold – porphyry copper deposits. The interplay of tectonic setting, magma composition, structural control and hydrothermal systems contributed to the generation of these deposits. Ridge subduction (Scarborough seamount) resulting to flat subduction and a transpressional regime could also be related to the formation of epithermal gold - porphyry copper deposits in Baguio. Subduction processes leading to the formation of calc-alkaline rocks associated with high water pressure, oxygen fugacity and late sulfur saturation are almost always associated with the gold-copper deposits in the district. Compared to the Baguio Mineral District, less exploration work, mine development and production were done in the Pacific Cordillera Mineral District, Mindanao in southern Philippines. It is worth noting, however, that both mineral districts show similarities and overlapping features in terms of geological, geophysical and geochemical characteristics. This leads one to conclude that the Pacific Cordillera Mineral District has ore deposits waiting to be discovered

Slab rollback and microcontinent subduction in the evolution of the Zambales Ophiolite Complex (Philippines): A review

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