南菲律宾地区类埃达克岩和富铌玄武质熔岩的成因

埃达克岩（adakite)最初 是指由消减板片玄武岩物质熔融形成的富硅、富钠、高Sr/Y和La/Yb比值的弧火山熔岩。它通常产在会聚带，这个部位的年轻的、因而仍然是热的大洋板片正在发生俯冲消减。富铌的岛弦玄武央进则是吕等到高碱的镁铁质熔岩，它们相对于正常的岛弦玄武岩含有较多的高场强元素（HFSE）。这些玄武岩通常与埃达克央共生， 这一组合是直被用于论证他们的高HFSE含量是因为他们的地幔源区受到板片来源的熔体的交代。先前的区域研究结果表明，南菲律宾是埃达克岩和富铌岛孤玄武岩的一个典型产地。然而最近的详细研究显示，尽管该地区的一些岛弧火山岩是类埃达克岩的，但是它们很可能是来自地幔楔的母岩浆的分异作用的产物，而这里的地幔楔主要是受沉积来源的成分交代的，此外，菲律宾南部最典型的富铌熔岩中HFSE的富集，也很有可能是起因于似乎是西太平洋边缘特有的富集地幔组分的熔融。这些结果提出了如下问题：南菲律宾是否存在真正的板片来源的熔体？这里的富铌岛弧 熔岩是否起因于地幔楔被这种熔体交代？

The origin of some of the adakite-like and Nb-enriched lavas in southern Philippines

The term adakite was originally used to designate silica- and sodium-rich, high-Sr/Y and -La/Yb arc lava derived from melting of the basaltic portion of a subducted slab. Adakites generally occur in convergent margins where young and, thus, still hot oceanic slabs are being subducted. Niobium-enriched arc basalts are mildly- to highly-alkalic mafic lavas that contain relatively higher amount of high field-strength elements (HFSE) than normal arc lavas. These basalts commonly occur with adakites and such association has been used to argue that their unusually high HFSE content results from metasomatism of their mantle source by slab-derived melts. Previous regional studies have suggested that the southern Philippines is a type locality for both adakites and Nb-enriched arc basalts. However, more recent detailed investigations show that although some of the southern Philippine arc lavas are adakite-like, these are most likely products of magmatic differentiation of parental lavas derived from a mantle wedge metasomatized mainly by a sediment-derived component. Moreover, HFSE-enrichment in the best examples of Nb-enriched lavas in southern Philippines is most likely due to melting of enriched mantle components that appear to be ubiquitous in the western Pacific margin. These results raise the question whether there are true slab-derived melts and whether Nb-enriched arc lavas are due to metasomatism of the mantle wedge by such melts in southern Philippines.