Geotectonic evolution of the West Philippine Basin: Petrological and geochemical characterization and interaction of spreading ridge with mantle plume upwelling

西菲律宾海盆是菲律宾海板块中最古老的弧后海盆。为解决该区构造-岩浆演化史上的一个悬而未决的问题，我们进行了两次科学考察航次（KR 03 -04和KR 04 -14）。多道窄波束成图综合资料揭示了西太平洋西北部复杂的地形地貌。研究区可分为两个域，并由东北-西南走向的冲绳-吕宋断裂带（OLFZ），这似乎是右偏置。OLFZ的东部区域以一系列残留的重叠扩张中心（OSC）为特征。OSC系统的发展与位于系统北部的扩张部分撤退，被逐步取消的好处，一个新的传播裂缝位于更多的sough，这意味着连续的南脊跳跃。所有观测到的传播裂谷系统都是从东向西传播的，即，远离羽流（乌尔达内塔高原）。相比之下，OLFZ的西部区域表现出相当简单的展布组构。对回收的玄武岩进行全岩Ar-Ar定年，得到了可靠的坪年龄，约为32-40 Ma，坪年龄约为10 m。y.比以前提出的年龄要小。OLFZ东部岩浆具有类似于E-MORB和/或洋岛玄武岩（OIB）的富集地球化学成分，这与形态特征相一致，并表明深源组分对岩浆成因的贡献。与此相反，OLFZ西部玄武岩的N-MORB同位素特征与印度洋MORB型地幔的Pb同位素特征一致，表明菲律宾海板块形成早期曾有印度洋MORB型软流圈地幔的参与。

The West Philippine Basin (WPB) represents the oldest back-arc basin in the Philippine Sea Plate. To address unsolved question about its tectono-magmatic evolution, we have conducted two scientific survey cruises (KR03-04 and KR04-14). Integrative data by multi-narrow beam mapping reveals the complicated morphology in the northwestern part of WPB. The study area can be divided into two domains and separated by the NE-SW trending Okinawa-Luzon Fracture Zone (OLFZ), which appears to be right-lateral offset. The eastern domain of the OLFZ is characterized by series of relict overlapping spreading center (OSC). The OSC systems developed with the spreading segment located north of the system retreating, being progressively cancelled on the benefit of a new propagating rifts located more to the sough, implying successive southward ridge jumps. All observed propagating rift systems have propagated from east to west, i.e., away from the plume (Uldaneta Plateau). By contrast, the western domain of OLFZ demonstrates rather simple spreading fabrics. Whole-rick Ar-Ar dating for recovered basalts revealed reliable plateau-ages of ~32-40 Ma, which are ~10m. y. younger than previously suggested formation ages. Lavas from eastern domain of OLFZ have enriched geochemical compositions similar to E-MORB and/or ocean island basalts (OIB), which are compatible with morphological features and suggest contribution of deep source component to magma genesis. In contrast, basalts from western domain of OLFZ bear N-MORB affinity with Pb isotopic characteristics of the Indian Ocean MORB-type mantle, suggesting involvement of Indian ocean MORB-type asthenospheric mantle during early stage of the formation of the Philippine Sea Plate.