Adakitic lavas in the Central Luzon back-arc region, Philippines: lower crust partial melting products?

Abstract

Volcanism in the back-arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side-main volcanic arc igneous rocks. The back-arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite-like geochemical characteristics of these back-arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet-bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc-trench gap region slab melts.

Early Cretaceous arc volcanic suite in Cebu Island, Central Philippines and its implications on paleo-Pacific plate subduction: Constraints from geochemistry, zircon U–Pb geochronology and Lu–Hf isotopes

“…Cenozoic volcanic rocks ranging in composition from tholeiitic through calc-alkaline to shoshonitic types erupted in the Philippines arc system (Maury et al, 1998;Polve et al, 2007) which also include some adakitic rocks and Nb-enriched basalts (Jego et al, 2005;Sajona et al, 1996;Yumul et al, 2000a). In contrast, the Cretaceous suite is mainly associated with ophiolites or ophiolitic rocks, showing tholeiitic affinities (e.g., Dimalanta et al, 2006;Suerte et al, 2005;Yumul, 2003; A C C E P T E D M A N U S C R I P T Yumul et al, 2001).…”

Tomographic evidence for a slab tear induced by fossil ridge subduction at Manila Trench, South China Sea

“…Equivalent examples of older plates producing adakites are found in New Zealand's South Island (Reay and Parkinson 1997), Costa Rica (Johnston and Thorkelson 1997), and Kamchatka Peninsula and the Aleutian Islands (Yogodzinski et al 2001). The adakites in Northern and Central Luzon, associated with the eastward subduction of the SCS slab (34-17 Ma), have previously been interpreted as originating from partial melting of the lower Luzon crust (Yumul et al 2000;Bellon and Yumul 2001). In our interpretation of the seismic velocity results, slab tear along the fossil ridge produces low-velocity zones from the surface to 200 km depth (red-outlined regions in Figure 10(B-D)), which are associated with hot mantle flowing upwards and producing partial melting of the edge of the slab and lower crust.…”

Gold solubility in arc magmas: Experimental determination of the effect of sulfur at 1000 °C and 0.4 GPa

“…Recent (<20 Ma) magmatism in the North Luzon arc is linked to the current subduction of the South China Sea plate along the Manila Trench, and produces a range of arc rocks (Sajona and Maury, 1998;Prouteau et al, 2000;Yumul et al, 2000; Major elements and sulfur in anhydrous double-melting quenched glasses (starting materials; see text) were measured by EPMA in Taipei, Taiwan (IES, Academia Sinica). Oxides and totals are in wt.%, with uncertainties presented as once the standard error of the mean (±1r) for the n replicate measurements.…”