Quaternary calc-alkaline andesitic to dacitic lavas effusively erupted on top of about 30 km thick accreted continental crust at Methana peninsula in the western Aegean arc. We present new data of major and trace element concentrations as well as of Sr–Nd–Pb isotope ratios along with mineral compositions of Methana lavas and their mafic enclaves. The enclaves imply a parental basaltic magma and fractional crystallization processes with relatively little crustal assimilation in the deep part of the Methana magma system. The composition of amphibole in some mafic enclaves and lavas indicates deeper crystallization at ∼25 km depth close to the Moho compared with the evolved lavas that formed at <15 km depth. The presence of amphibole and low Ca contents in olivine suggest high water contents of ∼4 wt% in the primitive magmas at Methana. The compositions of andesitic and dacitic lavas reflect fractional crystallization, assimilation of sedimentary material, and magma mixing in the upper 15 km of the crust. The Methana magmas have fO₂ of FMQ + 1 to FMQ + 2 (where FMQ is the fayalite–magnetite–quartz buffer) at temperatures of 1200 to 750 °C and the fO₂ does not vary systematically from mafic to felsic compositions, suggesting that the mantle wedge was oxidized by sediment subduction. Amphibole is an important fractionating phase in the more evolved Methana magmas and causes significant changes in incompatible element ratios. Although xenocrysts and mineral compositions indicate magma mixing, the major and trace element variation implies only limited mixing between dacitic and basaltic melts.

中文翻译：

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通过大陆地壳上升期间钙碱性岩浆的化学演化：来自爱琴海弧Methana的约束

在爱琴海西部弧线的Methana半岛上，约30 km厚的增生大陆壳顶部喷发了第四纪的钙碱性和安山岩到大山熔岩。我们提供了主要和微量元素浓度以及Sr-Nd-Pb同位素比以及Methana熔岩及其镁铁质飞地的矿物成分的新数据。这些飞地暗示着Methana岩浆系统深部的一个母体玄武岩浆和部分结晶过程，地壳同化相对较少。在一些镁铁质飞地和熔岩中，闪石的组成表明，与在小于15 km的深度形成的熔岩相比，在距莫霍面约25 km的深度有更深的结晶。橄榄石中闪石的存在和低Ca的含量表明，在Methana的原始岩浆中水的含量约为4 wt％。安山和大山熔岩的成分反映了地壳上部15 km内的部分结晶，沉积物质的同化和岩浆混合。Methana岩浆有在1200至750°C的温度下FMQ + 1到FMQ + 2的f O ₂（其中FMQ是铁橄榄石-磁铁矿-石英缓冲液），f O ₂在铁镁质成分到长质成分之间没有系统地变化，表明地幔泥沙被俯冲作用氧化。角闪石是更发达的Methana岩浆中重要的分馏阶段，并导致不相容元素比率的显着变化。尽管异晶晶和矿物成分显示出岩浆混合，但主要元素和微量元素的变化暗示着高寒和玄武质熔体之间的混合有限。