Funding information Japan Society for the Promotion of Science, Grant/Award Number: 17H02987 Abstract This paper addresses formation of felsic magmas in an intra-oceanic magmatic arc. New bathymetric, petrologic, geochemical, and isotopic data for Zealandia Bank and two related volcanoes in the south-central Mariana arc is presented and interpreted. These three volcanoes are remnants of an older andesitic volcano that evolved for some time and became dormant long enough for a carbonate platform to grow on its summit before reawakening as a rhyodacitic volcano. Zealandia lavas are transitional between lowand medium-K and tholeiitic and calc-alkaline suites. They define a bimodal suite with a gap of 56–58 wt% SiO2; this suggests that mafic and felsic magmas have different origins. The magmatic system is powered by mantle-derived basalts having low Zr/Y and flat rare earth element patterns. Two-pyroxene thermometry yields equilibration temperatures of 1000–1100 C for andesites and 900–1000 C for dacites. Porphyritic basalts and andesites show textures expected for fractionating magmas but mostly fine-grained felsic lavas do not. All lavas show trace element signatures expected for mantle and crustal sources that were strongly melt-depleted and enriched by subduction-related fluids and sediment melts. Sr and Nd isotopic compositions fall in the normal range of Mariana arc lavas. Felsic lavas show petrographic evidence of mixing with mafic magma. Zealandia Bank felsic magmatism supports the idea that a large midto lower-crustal felsic magma body exists beneath the south-central Mariana arc, indicating that MASH (mixing, assimilation, storage, and homogenization) zones can form beneath intra-oceanic as well as continental arcs.

中文翻译：

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西兰蒂亚火山复合体：西太平洋马里亚纳洋内弧下方下地壳“热区”的进一步证据

资金信息 日本科学促进会，资助/奖励编号：17H02987 摘要 本文讨论了洋内岩浆弧中长英质岩浆的形成。呈现并解释了西兰迪亚银行和马里亚纳中南部两座相关火山的新测深、岩石学、地球化学和同位素数据。这三座火山是一座古老的安山火山的遗迹，该火山演化了一段时间，休眠了足够长的时间，以至于碳酸盐平台在其山顶上生长，然后重新苏醒为流纹岩火山。西兰西亚熔岩在低钾和中钾以及拉斑岩和钙碱性岩套之间过渡。他们定义了一个双峰套件，其间隙为 56–58 wt% SiO2；这表明基性岩浆和长英质岩浆具有不同的来源。岩浆系统由具有低 Zr/Y 和扁平稀土元素模式的地幔衍生玄武岩提供动力。双辉石测温法得出安山岩的平衡温度为 1000–1100 C，英安岩的平衡温度为 900–1000 C。斑状玄武岩和安山岩显示出预期用于分馏岩浆的纹理，但大多数细粒长英质熔岩没有。所有熔岩都显示出预期的地幔和地壳来源的微量元素特征，这些来源被强烈的熔体消耗并被俯冲相关的流体和沉积物熔体富集。Sr 和 Nd 同位素组成属于马里亚纳弧形熔岩的正常范围。长英质熔岩显示出与镁铁质岩浆混合的岩相学证据。西兰迪亚银行长英质岩浆作用支持这样的观点，即在马里亚纳弧中南部下方存在大型中下地壳长英质岩浆体，表明 MASH（混合，