Geology of southeast Bohol, central Philippines: Accretion and sedimentation in a marginal basin

Abstract

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.

Growth of the Maritime Continent and its possible contribution to recurring Ice Ages

“…Crustal shortening and thickening within Mindanao [Pubellier et al, 1991Sajona et al, 1994Sajona et al, , 2000 and across smaller islands of the Philippines have elevated these regions [e.g., Faustino et al, 2003;Travaglio et al, 1978]. Palawan, however, seems to have emerged by middle Miocene time (between~15 and 10 Ma) [e.g., Holloway, 1982;Rangin and Silver, 1991].…”

Geology, Geochemistry and U-Pb SHRIMP Age of the Tacloban Ophiolite Complex, Leyte Island (Central Philippines): Implications for the Existence and Extent of the Proto-Philippine Sea Plate

“…reported that pillow basalts from the basement of Cebu record strong subductionrelated signatures. Farther east, the Southeastern Bohol Ophiolite Complex is overlain by cherts containing Early Cretaceous radiolarian and foraminiferal assemblages (Faustino et al, 2003). This ophiolite complex also displays geochemical patterns similar to those observed in SSZ-related oceanic basins (Yumul et al, 2001).…”

Geochemical and Geophysical Characteristics of the Balud Ophiolitic Complex (BOC), Masbate Island, Philippines: Implications for its Generation, Evolution and Emplacement

“…Previous works on Central Philippine ophiolites and ophiolitic sequences show these discrete crust-mantle slices to be of supra-subduction affinity [e.g., Tacloban, Samar, Malitbog, Southeast Bohol, Cebu] (e.g., Barretto et al 2000;Faustino et al 2003;Tamayo et al 2004;Suerte et al 2005;. Apart from the Oligocene Amnay Ophiolite in Mindoro which has the ocean island basalts (OIB) or enriched mid-oceanic ridge basalts (EMORB) component in addition to its transitional island arc tholeiite -N-MORB geochemistry (Jumawan et al 1998;Perez et al 2013), the general observation is that ophiolites in the central Philippines were generated with variable degrees of subduction influences (e.g., Faustino et al 2006;Dimalanta et al 2009;Yumul et al 2013).…”