Subduction-related magmatic imprint of most Philippine ophiolites: implications on the early geodynamic evolution of the Philippine archipelago

Abstract

The basement complexes of the Philippine archipelago include at least 20 ophiolites and ophiolitic complexes. These complexes are characterised by volcanic sequences displaying geochemical compositions similar to those observed in MORB, transitional MORB-island arc tholeiites and arc volcanic rocks originating from modern Pacific-type oceans, back-arc basins and island arcs. Ocean island basalt-like rocks are rarely encountered in the volcanic sequences. The gabbros from the ophiolites contain clinopyroxenes and plagioclases showing a wide range of XMg and An values, respectively. Some of these gabbros exhibit mineral chemistries suggesting their derivation from basaltic liquids formed from mantle sources that underwent either high degrees of partial melting or several partial melting episodes. Moreover, some of the gabbros display a crystallization sequence where orthopyroxene and clinopyroxene appeared before plagioclase. The major element compositions of coexisting orthopyroxenes and olivines from the mantle peridotites are consistent with low to high degrees of partial melting. Accessory spinels in these peridotites display a wide range of XCr values as well with some of them above the empirical upper limit of 0.6 often observed in most modern mid-oceanic ridge (MOR) mantle rocks. Co-existing olivines and spinels from the peridotites also exhibit compositions suggesting that they lastly equilibrated under oxidizing mantle conditions. The juxtaposition of volcanic rocks showing affinities with modern MOR and island arc environments suggests that most of the volcanic sequences in Philippine ophiolites formed in subduction-related geodynamic settings. Similarly, their associated gabbros and peridotites display mineralogical characteristics and mineral chemistries consistent with their derivation from modern supra-subduction zone-like environments. Alternatively, these rocks could have, in part, evolved in a supra-subduction zone even though they originated from a MOR-like setting. A simplified scenario regarding the early geodynamic evolution of the Philippines is proposed on the basis of the geochemical signatures of the ophiolites, their ages of formation and the ages and origins of the oceanic basins actually bounding the archipelago, including basins presumed to be now totally consumed. This scenario envisages the early development of the archipelago to be largely dominated by the opening and closing of oceanic basins. Fragments of these basins provided the substratum on top of which the Cretaceous to Recent volcanic arcs of the Philippines were emplaced.

Tectonic setting of a composite terrane: A review of the Philippine island arc system

“…Majority of the suites are classified as Tethyan (Moores, 1982). Balce et al (1976) initially grouped ophiolites based on their geographic distribution (e.g., eastern belt, western belt, central belt) in the Philippines, whereas Tamayo et al (2004) assigned the ophiolite complexes in the Philippines into four belts based on age and geochemical data. Those classified are: Cretaceous sequences, Eocene complexes with strong subduction signatures, ophiolites of varied ages and ophiolite-arc components and younger sequences with weak subduction imprints which outcrop west of the West Philippine Suture Zone.…”

“…This is brought about by the unique setting that this archipelago occupies in the western Pacific region. The Philippines offers a glimpse, based on present-day landocean interactions, of what has transpired in the past (e.g., Quebral et al, 1996;Yumul, 2003, 2004;Pubellier et al, 2003aPubellier et al, , 2003bTamayo et al, 2004). Results of terrane accretion, ocean basin closure, arc formation, and indenter tectonics are some of the features recognized in this island arc system.…”

Boninite and boninite-series volcanics in northern Zambales ophiolite: Doubly-vergent subduction initiation along Philippine Sea Plate margins

“…Zambales as suggested by Encarnación et al (1993), rather it simply demonstrates that basement complexes in the Philippine Mobile Belt consists of juxtaposed geochemically distinct Eocene and Cretaceous ophiolites (ophiolite belts 1B and 1C of Tamayo et al, 2004) (Fig. 1a).…”

“…In the most 25 comprehensive petrological and geochemical study of Philippine ophiolites, Tamayo et al (2004) notes the strong subduction geochemical imprint of Zambales ophiolite and placed it as a marginal basin between Celebes Sea Basin and the western margin of the Philippine Sea Plate. The difficulty in reconstructing the Paleogene tectonic configuration of the southeast Asian region, specifically the spreading history of the oceanic domain east of Sundaland and west of the Philippine Sea Plate, stems from the fact that this region has been fully consumed along convergent margins east of southeastern 30…”

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).…”