Petrochemical Investigation of the Antique Ophiolite (Philippines): Implications on Volcanogenic Massive Sulfide and Podiform Chromitite Deposits

Abstract

IntroductionVolcanogenic massive sulfides (VMS) and podiform chromitites commonly occur in ophiolite complexes. The VMS bodies are found in or near the contact of the pillow basalts and the overlying sedimentary rocks. A common feature of these deposits, particularly those relatively unaffected by tectonic deformation, is their mound-like morphology and subsurface stockwork-type mineralization, which are reminiscent of the structure of hydrothermal vents and their associated metal accumulations observed in modern mid-oceanic ridges (Hannington et al., 1995;Knott et al., 1998) and backarc basin rifts (Halbach et al., 1989;Binns and Scott, 1993). The podiform chromitites, on the other hand, occur in the transition zone dunites and residual upper mantle sequences of ophiolite complexes (Roberts, RESOURCE GEOLOGY, vol. 51, no. 2, 145-164, 2001 145 (IAB). The residual upper mantle sequence is harzburgitic and generally more depleted than the upper mantle underlying modern mid-oceanic ridges. Calculations using whole-rock and mineral compositions show that they can represent the residue of a fertile mantle source, which have undergone degrees of partial melting ranging from 9-22.5 %. Some of the mantle samples display chondrite-normalized REE and extended multi-element patterns suggesting enrichments in LREE, Rb, Sr and Zr, which are comparable to those found in fore-arc peridotites from the Izu-Bonin-Mariana (IBM) arc system. The Antique ultramafic rocks also record relatively oxidizing mantle conditions (∆log f O 2 (FMQ)=0.9-3.5). As a whole, the ophiolite probably represents an agglomeration of oceanic ridge and fore-arc crust fragments, which were juxtaposed during the Miocene collision of the PMB and the NPB. The intrusion of the serpentinites might be either coeval or subsequent to the accretion of the oceanic crust onto the fore-arc.Volcanogenic massive sulfide (VMS) deposits occur either in or near the contact between the pillow basalts and the overlying sediments or interbedded with the sediments. The morphology of the deposits, type of metals, ore texture and the nature of the host rocks suggest that the formation of the VMS bodies was similar to the accumulation of metals around and in the subsurface of hydrothermal vents observed in modern mid-oceanic ridge and back-arc basin rift settings. The podiform chromitites occur as pods and subordinate layers within totally serpentinized dunite in the residual upper mantle sequence. No large coherent chromitite deposit was found since the host dunitic rocks often occur as blocks within the serpentinites. It is difficult to evaluate the original geodynamic setting of the mineralized bodies since the chemistry of the host rocks were considerably modified by alteration during their tectonic emplacement. A preliminary conclusion for Antique is that the VMS is apparently associated with a primitive tholeiitic intermediate MORB-IAB volcanic suite, the chemistry of which is close to the calculated composition of the liquid that coexisted with the podiform chromitites.

Indenter-tectonics in the Philippines: Example from the Palawan Microcontinental Block - Philippine Mobile Belt Collision

“…2b). As a whole, the Philippine island-arc system represents a composite terrane consisting of the aseismic PCB and the seismically-active PMB (e.g., Gervasio, 1971;Tamayo et al, 2001;Ramos et al, 2005) (Fig. 1).…”

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

“…The elevated Th content and negative anomalies in Nb, Zr, and to a certain extent, Ti, are suggestive of the involvement of sediments and hydrous magmas in the generation of volcanic-hypabyssal BOC rocks (e.g., Pearce 2003;Payot et al 2011). The ages of these ophiolites, most of which are Mesozoic (e.g., Tamayo et al 2001;Suerte et al 2005;Zamoras et al 2008), also allude to their almost contemporaneous generation suggestive of a possible common origin.…”

“…(c) General comparison of lithology, age and geochemical characteristics of the ophiolites in the Central Philippines. Numbered references are as follows: (1) Rangin et al (1991), (2) Tamayo et al (2001), (3) Barretto et al (2000), (4) Faustino et al (2006), (5) Wolcke and Scholz (1988), (6) Hashimoto (1981), ( Suerte et al 2005;. The delineation of the Balud Ophiolitic Complex (BOC) in southwest Masbate, Central Philippines gives additional information that hopefully would contribute to the reconstruction and understanding of the evolution of the Philippines and this part of Southeast Asia.…”

Terrane Boundary Geophysical Signatures in Northwest Panay, Philippines: Results from Gravity, Seismic Refraction and Electrical Resistivity Investigations

“…The study area is Northwest Panay, including Buruanga Peninsula and Antique Range, which is considered as the southeastern boundary of the Central Philippines collision (Rangin et al 1989;Tamayo et al 2001;Zamoras et al 2008;Yumul et al 2009). Two distinct terranes comprise Northwest Panay: the Buruanga Peninsula and the northern part of the Antique Range (Mines and Geosciences Bureau 2004;Zamoras et al 2008;Gabo et al 2009) (Fig.…”

“…The portion of the Antique Range investigated in this study is composed of peridotites from the Late Cretaceous Antique Ophiolite Complex Tamayo et al 2001), the volcanic and clastic rocks of the Fragante Formation and sedimentary rocks of the late Middle Miocene Lagdo Formation (Fig. 2).…”