The Pliocene-Pleistocene magmatic activity of the ^amboanga arc is linked to the southward subduction of the Oligocene-Miocene Sulu Sea back-arc basin along the Sulu Trench. The magmatic products include small amounts ofadakites datedfrom 3-8 to 0-7 Ma, abundant Nb-enriched basalts and basaltic andesites (NEB) datedfrom 2 to 1 Ma and a lone calc-alkaline potassic basaltic andesite dated at 0 4 Ma. Three kinds of NEB are distinguished: nearly primitive Mg-rich (MG) basalts displaying positive or no Nb anomalies with respect to adjacent incompatible elements and more evolved low-K (LK) and calcalkaline (CA) lavas which, despite their Nb enrichment, display negative Nb anomalies. Although the role of OIB-type mantle components has been advocated to explain the HFSE enrichment of NEB, the spatial and temporal association of these rocks with adakites suggests a petrogenetic link between them. Trace element characteristics of the NEB imply that amphibole and ilmenite might be present in their source. We suggest that these minerals could be added metasomatically to the mantle through hybridization by percolating slab melts, during which Nb and Ti are preferentially extracted from the adakitic melts. In an early stage (4-3 Ma) of the subduction of the young and hot Sulu Sea basin crust beneath the ^jimboanga peninsula, adakitic liquids formed at depths of 75-85 km. A few of them were emplaced at the surface but most were consumed through slab melt-mantle metasomatic reactions. Adakite production and emplacement continued later (<2 Ma), while the Nb-enriched mantle was brought by convection to depths that allowed its melting and the subsequent emplacement of NEB behind the adakitic front of the ^pmboanga arc

No abstract

No abstract

Abstract-We report on the major and trace element abundances of 18 diogenites, and O-isotopes for 3 of them. Our analyses extend significantly the diogenite compositional range, both in respect of Mg-rich (e.g., Meteorite Hills [MET] 00425, MgO = 31.5 wt%) and Mg-poor varieties (e.g., Dhofar 700, MgO = 23 wt%). The wide ranges of siderophile and chalcophile element abundances are well explained by the presence of inhomogeneously distributed sulfide or metal grains within the analyzed chips. The behavior of incompatible elements in diogenites is more complex, as exemplified by the diversity of their REE patterns. Apart from a few diogenite samples that contain minute amounts of phosphate, and whose incompatible element abundances are unlike the orthopyroxene ones, the range of incompatible element abundances, and particularly the range of Dy/Yb ratios in diogenites is best explained by the diversity of their parental melts. We estimate that the FeO/MgO ratios of the diogenite parental melts range from about 1.4 to 3.5 and therefore largely overlap the values obtained for non-cumulate eucrites. Our results rule out the often accepted view that all the diogenites formed from parental melts more primitive than eucrites during the crystallization of a magma ocean. Instead, they point to a more complex history, and suggest that diogenites were derived from liquids produced by the remelting of cumulates formed from the magma ocean.