柴北缘造山运动中深俯冲大陆地壳多级锐钛矿的周期性:脉冲熔体的来源、时间尺度和演化

IF 1.9 3区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
Xin Chen, H. Schertl, A. Cambeses, Emma Hart, Chenggui Lin, Rongke Xu, Youye Zheng
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引用次数: 2

摘要

会聚板块边界最重要的传质过程是构造吸积和流体/熔体从生成地点释放到聚集地点。然而,关于这种深熔过程的来源、时间尺度和演化,仍然存在一些关键问题,例如,深俯冲大陆地壳的单次或多阶段深熔。为了更好地了解锐钛矿的形成过程,我们利用锆石、独居石和异时地球化学和地质年代学、全岩成分以及柴北缘吕梁山的Sr-Nd-Hf同位素分析,量化了逆行榴辉岩中多级长英质脉的形成和演化过程的时间尺度和性质。共存锆石、独居石和异长岩的U–Pb定年给出了三组年龄,分别为ca。441至435、ca。425和ca。413至409 Ma,记录了至少三次脉冲熔体。锆石形成的第一阶段不仅在阴极发光图像中没有不同锆石的振荡分带,而且其中一些锆石具有平坦的HREE和没有Eu异常,这表明它们可能在榴辉岩相条件下的深熔熔体中形成。熔体的第二和第三阶段可能发生在剥露过程中的麻粒岩和角闪石相条件下。此外,榴辉岩中的两类长英质脉显示出全岩成分(87Sr/86Sr)i、εNd(t)和εHf(t)值的广泛变化,这表明它们源于不同时期不同比例的俯冲片麻岩和榴辉岩的流体脱水部分熔融。这些发现表明,由于岩性多样性和部分熔融深度,熔体在化学和同位素特征方面存在系统性差异。因此,从源头释放的小规模熔体可以很好地解释同碰撞非均质花岗岩中全岩成分的变化、副矿物生长分区和突出的同位素变化。另一个含义是,当这些熔体逃离其邻近的形成区域时,它们沿着通道化的熔体路径迁移和混合,导致熔体-岩石和壳幔相互作用,并触发同碰撞和后碰撞岩浆作用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Cyclicity of multistage anatexis of deeply subducted continental crust during the North Qaidam orogeny: Tracing the source, timescale, and evolution of pulsed melts
The most significant mass transfer processes at a convergent plate boundary are tectonic accretion and fluids/melts released from sites of generation to sites of accumulation. However, some crucial questions remain with regards to the source, timescale, and evolution of such anatectic processes, for example, single or multistage anatexis of deeply subducted continental crust. To better understand the processes involved in anatexis, we have quantified the timescale and nature of formation and evolution processes of multistage felsic veins within retrograde eclogite using zircon, monazite, and xenotime geochemistry and geochronology, whole-rock composition, and Sr-Nd-Hf isotope analysis from the Lüliangshan, North Qaidam orogen. The U–Pb dating of coexisting zircon, monazite, and xenotime gives three groups of ages at ca. 441 to 435, ca. 425, and ca. 413 to 409 Ma, respectively, which record at least three episodes of pulsed melts. The first stage of zircon formation is characterized by not only the absence of oscillatory zoning of different zircons in cathodoluminescence images but also some of them with flat HREE and without Eu anomalies, indicating they may form in anatectic melts under eclogite-facies conditions. The second and third phases of melts may have occurred under granulite- and amphibole-facies conditions during exhumation. Furthermore, two classes of felsic veins within the eclogite show wide variations of whole-rock composition, (87Sr/86Sr)i, εNd (t), and εHf (t) values, which demonstrate that they were derived from fluid-present dehydration partial melting of different proportions of subducted gneiss and eclogite during different periods. These findings show that melts have systematic differences in chemical and isotopic signatures resulting from lithological diversity and depth of partial melting. Thus, small-scale melts released from the source can excellently explain the variability in whole-rock composition, accessory mineral growth zoning, and prominent isotope variability in syn-collisional heterogeneous granites. An additional implication is that as these melts escape their adjacent area of formation, they migrate and mix along channelized melt pathways, resulting in melt-rock and crust-mantle interaction and the triggering of syn- and post-collisional magmatism.
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来源期刊
American Journal of Science
American Journal of Science 地学-地球科学综合
CiteScore
5.80
自引率
3.40%
发文量
17
审稿时长
>12 weeks
期刊介绍: The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.
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