Clinopyroxene with diverse origins in alkaline basalts from the western Pannonian Basin: Implications from trace element characteristics
Clinopyroxene with diverse origins in alkaline basalts from the western Pannonian Basin: Implications from trace element characteristics
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DOI：
10.1016/j.lithos.2016.06.030
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发表时间：
2016-10
期刊：
影响因子：
3.5
通讯作者：
M. Jankovics;Z. Taracsák;G. Dobosi;A. Embey-Isztin;A. Batki;S. Harangi;C. Hauzenberger
中科院分区：
文献类型：
--
作者：
M. Jankovics;Z. Taracsák;G. Dobosi;A. Embey-Isztin;A. Batki;S. Harangi;C. Hauzenberger
Pannonian盆地西部Bakony-Balaton高地火山区最年轻的喷发中心Bondoró-hegy和Füzes-tó火山渣锥的碱性玄武岩中，出现了不同来源的单斜辉石晶体，这些玄武岩中的晶体和捕虏体异常丰富。单斜辉石显示出不同的结构和分带特征，以及高度可变的主要和微量元素化学。捕虏晶、巨晶和斑晶晶体群可根据其成分差异加以区分，绿色单斜辉石核的微量元素模式显示出较大的成分变化范围，表明大多数单斜辉石都具有变质成因。其中大部分是由下地壳镁铁质麻粒岩围岩，而只有少数是岩浆成因的辉石岩（II型）堆晶岩。无色单斜辉石捕虏晶反映了研究区域下的次大陆岩石圈地幔的结构和地球化学多样性，主要代表了具有不同交代阶段特征的区域。无色和绿色巨晶在成因上相互关联，分别作为早期和晚期结晶产物结晶，来自与岩石成因相关的熔体，作为分步结晶序列的一部分。这些熔体代表较早的碱性玄武岩浆（如代表的II型捕虏体），已停止和结晶附近的壳幔边界的地幔的最上部。这作为证据表明，深岩浆系统下的单成因火山田是复杂的，涉及几个阶段的熔体生成，积累和分馏在不同的depth.We表明，原位微量元素分析是必要的，以解开的起源和关系的不同单斜辉石人口。这些研究对我们理解碱性玄武岩浆的上升历史和提供有关构成岩石圈的岩石特征的信息有重要贡献。此外，在解释全岩地球化学数据时，必须考虑到在上升的玄武岩浆中含有的外来晶体的丰度及其对寄主岩浆的污染潜力。
Clinopyroxene crystals of various origins occur in the unusually crystal- and xenolith-rich alkaline basalts of the Bondoró-hegy and the Füzes-tó scoria cone, which are the youngest eruptive centres in the Bakony-Balaton Highland Volcanic Field, western Pannonian Basin. The clinopyroxenes show diverse textural and zoning features as well as highly variable major and trace element chemistry. Xenocryst, megacryst and phenocryst crystal populations can be distinguished on the basis of their compositional differences.The trace element patterns of green clinopyroxene cores display a large range in composition and indicate that most of them have a metamorphic origin. Most of them were incorporated from lower crustal mafic granulite wall rocks, while only a few of them are of magmatic origin representing pyroxenite (Type II) cumulates. The colourless clinopyroxene xenocrysts reflect the texturally and geochemically diverse nature of the subcontinental lithospheric mantle beneath the studied area, mainly representing regions characterised by various stages of metasomatism.The colourless and green megacrysts are genetically related to each other, having crystallised as early and late crystallisation products, respectively, from petrogenetically related melts as part of a fractional crystallisation sequence. These melts represent earlier alkaline basaltic magmas (as represented by the Type II xenoliths), having stalled and crystallised near the crust–mantle boundary in the uppermost part of the mantle. This serves as evidence that the deep magmatic systems beneath monogenetic volcanic fields are complex, involving several phases of melt generation, accumulation and fractionation at variable depths.We show that in situ trace element analysis is necessary in order to unravel the origins and relationships of the diverse clinopyroxene populations. Such studies significantly contribute to our understanding of the ascent histories of alkaline basaltic magmas and provide information about the characteristics of the rocks that constitute the lithosphere. Additionally, the abundance of foreign crystals incorporated in the ascending basaltic magmas, and their potential for contamination of the host magma, must be taken into account when whole-rock geochemical data are interpreted.