Geology of the southern Zambales Ophiolite Complex, Luzon, Philippines

Abstract

Field, geochemical and geophysical evidence show that the southern Zambales Ophiolite Complex attained its present-day configuration through the juxtapositioning of an arc terrane (San Antonio massif) to a back-arc crust (Cabangan massif). The San Antonio massif manifests island arc-related characteristics (i.e. spinel XCr [Cr/(Cr + Al)] >0.60; mostly plagioclase An92-95; pyroxene crystallizing ahead of plagioclase; orthopyroxene as an early, major crystallizing phase) which cannot be directly parental to the Cabangan massif transitional mid-ocean ridge basalt to island arc tholeiitic volcanic carapace. The two massifs are believed to be separated by a left-lateral strike-slip fault, the Subic Bay Fault Zone. Apart from the presence of highly sheared, allochthonous outcrops, the Subic Bay Fault Zone is generally defined by northwest-southeast trending magnetic and bouguer anomalies. The San Antonio massif was translated southward from the northern part of the Zambales Ophiolite Complex through the Subic Bay Fault Zone. This resulted into its suturing with the Cabangan massif and could have led to the formation of the present-day Subic Bay.

Characterization of the Angat Ophiolite: New insights from bulk major and trace element geochemistry and petrographic analysis

“…This is consistent with the (Ol)-Pl-Cpx crystallization order observed in the Angat petrography. This trend is also present in the Coto and is consistent with the (Ol)-Pl-Cpx crystallization order noted by previous studies [3,9,10]. One can observe that the trend of the Acoje in the FeOt vs. FeOt/MgO dipped earlier than the Angat and Coto.…”

“…The consistent plotting of the present study's samples in Figure 6, along with the similar crystallization order of (Ol)-Pl-Cpx [3,10], trace element ratio diagrams, and fractionating trends between the Angat and Coto, suggest that the two units may be related and formed from a similar magmatic process. Geary et al originally proposed that the Coto experienced two stages of crustal formation: an initial N-MORB dominant magmatism in possibly a large oceanic or back-arc spreading center followed by the crustal modification of incipient island arc magmatism, possibly in a proto-forearc setting [19].…”

“…(5) The Coto Block of the Zambales Ophiolite and the Angat Ophiolite may be related and formed over a mantle initially enriched by a subduction component. This conclusion is supported by the similar crystallization order of (Ol)-Pl-Cpx [3,10], consistent overlapping of plots and trends, and similar enrichment pattern range.…”

“…Also, the hooked trend of the Acoje in the Al2O3 vs. FeOt/MgO plot may suggest that the first mineral to form after the olivine was pyroxene, followed by plagioclase. This is consistent with the (Ol)-Px-Pl crystallization order observed by [9,10]. Rock type discrimination diagrams that used immobile trace elements as proxy for the conventional Na2O+K2O were utilized considering the altered state of the samples.…”