Abstract
This paper presents the first field, geochemical and geophysical information on the recently recognized Early Cretaceous Balud Ophiolitic Complex (BOC) in the island of Masbate in the Central Philippines. Mapping of the western limb of the island revealed that only the upper crustal section of the BOC is exposed in this area. Geochemically, the pillow basalts are characterized by transitional mid-oceanic ridge basalt-island arc tholeiitic compositions. Gravity surveys yielded low Bouguer anomaly values that are consistent with the highly dismembered nature of the BOC. Short wavelength, high amplitude magnetic anomalies registered across the study area are attributed to shallow magnetic sources. This is taken to support the model that the ophiolitic complex occurs as thin crustal slivers that are not deeply-rooted in the mantle. Comparing BOC with other ophiolites in the Central Philippines, such as those in the islands of Sibuyan, Leyte and Bohol, suggests the possibility of a common or contiguous source for similarly-aged and geochemically composed crust-mantle sequences in the region.
Highlights
The Philippine archipelago has been and remains to be a complex puzzle for geoscientists trying to reconstruct its geological history
Gravity and magnetic investigations show that the Southeast Bohol Ophiolite Complex (SEBOC), Sibuyan and Tacloban ophiolites were emplaced as thin slivers of oceanic crust (e.g., Barretto et al 2000; Dimalanta et al 2006, 2009)
The volcanic sequence of the Balud Ophiolitic Complex (BOC) shows petrographic and geochemical evidence that it was generated in a supra-subduction zone environment
Summary
The Philippine archipelago has been and remains to be a complex puzzle for geoscientists trying to reconstruct its geological history. Belt 2 consists of dismembered ultramafic-mafic sequences and mélanges These early to late Cretaceous ophiolitic sequences are mainly exposed on the western side of the eastern Philippines. This includes ophiolites exposed in the islands of Masbate, Cebu, and Bohol. A newly delineated ophiolitic complex is located in southwest Masbate Island, Central Philippines Other islands comprising this region include Panay, Negros, Cebu, Bohol, Samar, Leyte, Marinduque, and the Romblon Island Group. Most of these islands are underlain by Cretaceous ophiolite and ophiolitic units (Dimalanta et al 2006).
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