Origin and Formation Process of Gabbro and Diorite Xenoliths in the Northern Part of Uromieh-Dokhtar Magmatic Belt, NW Iran: Constraints from Mineral and Whole-Rock Chemistries

IF 1.5 4区 地球科学 Q2 GEOLOGY
Journal of Geology Pub Date : 2020-02-06 DOI:10.1086/707325
A. Khezerlou, M. Grégoire, N. Amel, M. Moayyed, A. Jahangiri, Mohammad Kilzi
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引用次数: 1

Abstract

Gabbro and diorite xenoliths occur within the alkaline trachyandesites in the northern part of Uromieh-Dokhtar magmatic belt (NW Iran). The host volcanic rocks are located on the upper Miocene sediments; therefore, they are probably Plio-Quaternary in age. The texture of xenoliths is granular, and the gabbro xenoliths are classified into two groups based on their petrographic characteristics and mineral chemistry. Based on chemical analyses, xenoliths show a subalkaline to slightly alkaline magmatic trend. Thermobarometric results indicate that gabbro and diorite xenoliths formed within the middle crustal level. All xenolith samples are light rare earth elements (LREEs) enriched and depleted in Ta, Zr, and Nb. These features can be explained by the subduction of the Neotethys. The LREE enrichment as well as negative Th, Ti, Nb, and Zr anomalies and positive Pb anomaly are in agreement with an origin through partial melting of an enriched mantle previously affected by metasomatism processes linked to mantle wedge-derived melts (fluids). Different REE concentration levels and patterns for Group 1 gabbro, Group 2 gabbro, and diorite xenoliths point out that their parental melts were not the same. Those forming the Group 1 gabbro xenoliths originated from melting of garnet mantle lherzolite, whereas the parental melts from Group 2 gabbro and diorite xenoliths originated from melting of spinel-garnet mantle lherzolite. The 86Sr/87Sr and 143Nd/144Nd ratios and chemical composition of minerals are different for host volcanic rocks and xenoliths; therefore, we may conclude that the parental melts of the different groups of xenoliths and host volcanic rocks differ in composition.
伊朗Uromieh-Dokhtar岩浆带北部辉长岩和闪长岩捕虏体的成因和形成过程:矿物化学和全岩化学的约束
辉长岩和闪长岩包体产于伊朗西北部乌洛米耶-多克塔尔岩浆带北部碱性粗面岩中。寄主火山岩位于中新统上部沉积物中;因此,它们的年龄可能为上第四纪。捕虏体结构为颗粒状,根据岩石学特征和矿物化学特征将辉长岩捕虏体分为两类。化学分析表明,捕虏体具有亚碱性-微碱性岩浆倾向。热压测量结果表明,辉长岩和闪长岩包体形成于地壳中部。所有捕虏体样品均为轻稀土元素(lree),富集Ta、Zr和Nb。这些特征可以用新特提斯的俯冲作用来解释。LREE富集以及负Th、Ti、Nb、Zr异常和正Pb异常与富集地幔部分熔融形成的成因一致,富集地幔部分熔融与地幔楔源熔融(流体)相关的交代作用有关。第1组辉长岩、第2组辉长岩和闪长岩包体的稀土元素含量和模式不同,说明它们的母熔体不相同。第1组辉长岩捕虏体主要形成于石榴石幔辉长岩的熔融,第2组辉长岩和闪长岩捕虏体的母熔体主要形成于尖晶石-石榴石幔辉长岩的熔融。寄主火山岩和捕虏体的86Sr/87Sr和143Nd/144Nd比值及矿物化学组成不同;因此,我们可以得出结论,不同种类的捕虏体和寄主火山岩的母熔体在组成上是不同的。
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来源期刊
Journal of Geology
Journal of Geology 地学-地质学
CiteScore
3.50
自引率
5.60%
发文量
0
审稿时长
3 months
期刊介绍: One of the oldest journals in geology, The Journal of Geology has since 1893 promoted the systematic philosophical and fundamental study of geology. The Journal publishes original research across a broad range of subfields in geology, including geophysics, geochemistry, sedimentology, geomorphology, petrology, plate tectonics, volcanology, structural geology, mineralogy, and planetary sciences. Many of its articles have wide appeal for geologists, present research of topical relevance, and offer new geological insights through the application of innovative approaches and methods.
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