Volcanism in the back-arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side-main volcanic arc igneous rocks. The back-arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite-like geochemical characteristics of these back-arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet-bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc-trench gap region slab melts.

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Volcanism in the back-arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side-main volcanic arc igneous rocks. The back-arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite-like geochemical characteristics of these back-arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet-bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc-trench gap region slab melts.

Recent field mapping has refined our understanding of the stratigraphy and geology of southeastern Bohol, which is composed of a Cretaceous basement complex subdivided into three distinct formations. The basal unit, a metamorphic complex named the Alicia Schist, is overthrust by the Cansiwang mélange, which is, in turn, structurally overlain by the Southeast Bohol Ophiolite Complex. The entire basement complex is overlain unconformably by a ~ 2000 m thick sequence of Lower Miocene to Pleistocene carbonate and clastic sedimentary rocks and igneous units. Newly identified lithostratigraphic units in the area include the Cansiwang mélange, a tectonic mélange interpreted as an accretionary prism, and the Lumbog Volcaniclastic Member of the Lower Miocene Carmen Formation. The Cansiwang mélange is sandwiched between the ophiolite and the metamorphic complex, suggesting that the Alicia Schist was not formed in response to emplacement of the Southeast Bohol Ophiolite Complex. The accretionary prism beneath the ophiolite complex and the presence of boninites suggest that the Southeast Bohol Ophiolite Complex was emplaced in a forearc setting. The Southeast Bohol Ophiolite Complex formed during the Early Cretaceous in a suprasubduction zone environment related to a southeast-facing arc (using present-day geographical references). The accretion of this ophiolite complex was followed by a period of erosion and then later by extensive clastic and carbonate rock deposition (Carmen Formation, Sierra Bullones Limestone and Maribojoc Limestone). The Lumbog Volcaniclastic Member and Jagna Andesite document intermittent Tertiary volcanism in southeastern Bohol.

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