The oceanic substratum of Northern Luzon: Evidence from xenoliths within Monglo adakite (the Philippines)

Abstract

International audienceA 8.65 Ma adakitic intrusive sheet exposed near Monglo village in the Baguio District of Northern Luzon contains a suite of ultramafic and mafic xenoliths including in order of abundance: spinel dunites showing typical mantle-related textures, mineral and bulk rock compositions, and serpentinites derived from them; amphibole-rich gabbros displaying incompatible element patterns similar to those of flat or moderately enriched back-arc basin basalt magmas; and amphibolites derived from metabasalts and/or metagabbros of identical affinity. A single quartz diorite xenolith carrying a similar subduction-related geochemical signature has also been sampled. One amphibolite xenolith provided a whole-rock K-Ar age of 115.6 Ma (Barremian). We attribute the origin of this suite to the sampling by ascending adakitic magmas of a Lower Cretaceous ophiolitic complex located at a depth within the 30-35 km thick Luzon crust. It could represent an equivalent of the Isabela-Aurora and Pugo-Lepanto ophiolitic massifs exposed in Northern Luzon

Metasomatic interactions between slab-derived melts and depleted mantle: Insights from xenoliths within Monglo adakite (Luzon arc, Philippines)

“…The mineral and chemical features of the Monglo dunites are in good agreement with an origin as depleted upper-mantle rocks from subduction-related lithospheric mantle (see above and Payot et al, 2007) incorporated within the ophiolitic basement of Northern Luzon. This paper aims to discuss the origin of the secondary orthopyroxene-rich and amphibole-rich metasomatic parageneses, as well as the origin of the undeformed interstitial clinopyroxene occurring in sample 01c01.…”

“…(Table 1 and Table 2) The primary (i.e. pre-metasomatic patches and veins) mineral association of the studied dunites has been already analysed by Payot et al (2007) and therefore we only recall here its main features. The olivines are highly magnesian with Mg# [= 100 Mg/Mg + Fe total ] values ranging from 89.8 to 91.2, associated to high NiO contents ranging from 0.31 to 0.39 wt.% (Table 1).…”

“…Serpentinization occurred before the incorporation of these xenoliths within the adakitic magma, as evidenced by the contact between serpentinite xenoliths and the host adakite which is typically a reaction rim of rather constant thickness (~ 0.5 mm) consisting of a coating of fibrous antigorite and amphibole (actinolite/tremolite) growing perpendicularly to the contact (see Fig. 2 of Payot et al, 2007) As lizardite/chrysotile form under relatively low-temperature conditions while antigorite is a higher-temperature serpentine (Evans, 1977), we ascribe this reaction rim to thermal metamorphism of the already serpentinized dunites by the host (serpentine-free) adakite. The gabbros display adcumulate textures, primary mineral associations and major and trace element compositions, especially flat to moderately enriched incompatible trace element patterns similar to those of gabbros derived from back-arc basin basalt (BABB) magmas .…”

Baguio Mineral District: An oceanic arc witness to the geological evolution of northern Luzon, Philippines

“…Finding coherency among the different tectonic models presented for the mineral district (Tam et al. 2005; Payot et al. 2007; Polvé et al.…”

What underlies the Philippine island arc? Clues from the Calaton Hill, Tablas island, Romblon (Central Philippines)

“…In the case of the Philippine archipelago, little is known about the lower crust, and most of the sub-arc studies have been largely dependent on mantle xenoliths hosted by erupted arc magmas (Maury et al, 1992;Arai and Kida, 2000;Arai et al, 2004;Payot et al, 2007;Gregoire et al, 2008). In this work, we report for the first time the occurrence of a metamorphic/plutonic complex composed of amphibolites, metagabbros, hornblende pyroxenites and hornblendites in Calaton Hill, Tablas island, Romblon in Central Philippines.…”