Ophiolites were identified in the westem part of Caramoan Peninsula (Lagonoy Ophiolite) and in the islands of Cagraray, Batan and Rapu-Rapu (Rapu-Rapu Ophiolite). Exposures of ophiolites are characterized by imbricated sequences of ultramafic rocks, massive and cumulate gabbros, basalt flows with pillow structures and volcaniclastics. These are unconformably overlain by Late Cretaceous volcanic arc sequence. Radiometric dating (⁴⁰K—⁴⁰Ar) of the gabbro sample in the vicinity of Lagonoy yielded an age of 112.7 +/- 3.9 million years indicating that the ophiolite in Southeastem Luzon is pre-Late Cretaceous in age. In Rapu-Rapu island, a diorite cutting the ultramafic rocks was radiometrically (⁴⁰K—⁴⁰Ar) dated as 77.1 +/- 4.6 Ma. Geochemical analyses (major and trace elements) of selected rock samples (gabbros and basalts) within the ophiolites revealed a character intermediate between an island arc (IA) and a mid - oceanic ridge (MOR) basalt.

Structural studies of the ophiolite sequences showed that they generally trend northwest - southeast and dipping to the southwest. Some outcrops are affected by metamorphism in which pillow basalts, pillow basalt breccias and coarse - grained gabbros are stretched and schistosed trending northwest - southeast and dips to the southwest, The ophiolite in Lagonoy is in apparent thrust contact with the Late Cretaceous volcanic arc sequence. Microfolds within the metamorphosed volcaniclastics indicate a northeastward displacement of the sequence. Left-lateral strike-slip faulting affected the ophiolites which might have led to the metamorphism of some parts of the sequence. Metamorphism and strike-slip faulting on the ophiolites and the overlying Late Cretaceous volcanic arc sequence were sealed by the deposition of a Middle Eocene nummulitic limestone.

Southeastwards in the islands of Cagraray, Batan and Rapu - Rapu, recent strike - slip faulting affected the ophiolites as suggested by the tectonic contact between the serpentinites and the Late Oligocene - Neogene carbonates and terrigenous sediments. These recent faults might be associated with the left-lateral strike-slip faulting along the central active portion of the Philippine Fault.

Geological and structural studies revealed that the ophiolites in Southeastem Luzon are most probably pre-Late Cretaceous in age. These ophiolites were most probably formed in an intra - arc oceanic setting and emplaced during the pre-Middle Eocene. Their emplacement might be associated to the wrench faulting activities that occurred in southeastern Luzon since the Cretaceous.