Petrochemical characteristics of felsic veins in mantle xenoliths from Tallante (SE Spain): an insight into activity of silicic melt within the mantle wedge
Petrochemical characteristics of felsic veins in mantle xenoliths from Tallante (SE Spain): an insight into activity of silicic melt within the mantle wedge
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DOI：
10.1017/s0263593300001061
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发表时间：
2004-03
影响因子：
1.2
通讯作者：
Y. Shimizu;S. Arai;T. Morishita;H. Yurimoto;F. Gervilla
中科院分区：
文献类型：
--
作者：
Y. Shimizu;S. Arai;T. Morishita;H. Yurimoto;F. Gervilla
对西班牙塔兰特地幔橄榄岩包体中的长英质及相关脉体进行了研究，以了解与富硅熔体行为有关的地幔楔入过程。最厚的部分为石英闪长岩岩性，主要由石英和斜长石组成，辉石、水化矿物、磷灰石、锆石和金红石为次要相。较薄的部分不含石英，主要由斜长石组成。斜方辉石总是夹在内部(斜长石±石英)和寄主橄榄岩之间，表明它是硅质过饱和熔体与橄榄石相互作用的产物。这表明足够高的熔体/围岩比能够使熔体保持其硅过饱和特性。石英闪长岩部分具有类埃达克岩的地球化学特征，但具负的Ba、Rb、Eu、Sr异常和正的Th、U异常。这些负异常表明，斜长石和水合矿物在上地幔和板片熔融带之间发生了分馏。石英闪长岩中单斜辉石的稀土元素配分模式与阿留申埃达克岩中的单斜辉石斑晶形态极为相似。但前者的稀土元素含量比后者高一个数量级，但Eu的含量呈现明显的负峰。这一特征是由于埃达克岩熔体在凝固前和凝固过程中从分馏的埃达克岩熔体中析出大量的斜长石和少量的单斜辉石所致。这种埃达克质熔体是由第三纪贝蒂克地区下方分离下沉的板岩部分熔融而成的。
ABSTRACT Felsic and related veins within mantle-derived peridotite xenoliths from Tallante, Spain, were examined in order to understand the mantle-wedge processes related to the behaviour of Si-rich melt. The thickest part of the vein has a quartz diorite lithology, and is composed mainly of quartz and plagioclase, with pyroxenes, hydrous mineral, apatite, zircon and rutile present as minor phases. The thinner parts are free of quartz and predominantly composed of plagioclase. Orthopyroxene always intervenes between the internal part (plagioclase ± quartz) and host peridotite, indicating that it is a product of interaction between silica-oversaturated melt and olivine. This indicates that a sufficiently high melt/wall rock ratio enabled the melt to retain its silicaoversaturated character. The quartz diorite part has adakite-like geochemical signatures, except for negative Ba, Rb Eu and Sr anomalies, and positive Th and U anomalies. These negative anomalies indicate that fractionation of plagioclase and hydrous minerals was achieved between the upper most mantle and the slab melting zone. The shape of the rare-earth element (REE) pattern of clinopyroxene in quartz diorite is strikingly similar to that of clinopyroxene phenocrysts from Aleutian adakites. However, the former has one order higher REE contents than the latter, except for Eu which shows a prominent negative spike. This feature was caused by the precipitation of large amounts of plagioclase and small amounts of clinopyroxene from a fractionated adakitic melt before and during solidification. This adakitic melt was produced by partial melting of a detached and sinking slab beneath the Betic area in the Tertiary.