Eclogitization of transient crust of the Aktyuz Complex during Late Palaeozoic plate collisions in the Northern Tianshan of Kyrgyzstan
Eclogitization of transient crust of the Aktyuz Complex during Late Palaeozoic plate collisions in the Northern Tianshan of Kyrgyzstan
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DOI：
10.1016/j.gr.2013.08.018
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发表时间：
2014-11
影响因子：
6.1
通讯作者：
R. Klemd;E. Hegner;H. Bergmann;J. Pfänder;Ji‐Lei Li;F. Hentschel
中科院分区：
文献类型：
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作者：
R. Klemd;E. Hegner;H. Bergmann;J. Pfänder;Ji‐Lei Li;F. Hentschel
吉尔吉斯斯坦西天山阿克秋兹变质杂岩由高压花岗片麻岩和变质岩组成，其中包括榴辉岩在内的镁铁质高压岩性。阿克丘兹杂岩不同岩石类型的地质关系和地球化学-同位素数据被解释为陆壳碎屑，镁铁质岩石被解释为以前的岩墙。这项研究结合了Sm-ND和40Ar/39Ar矿物年龄，并对单个退变榴辉岩样品进行了P-T假剖面模拟，以揭示镁铁质高压岩石的P-T-t演化。榴辉岩经历了顺时针进动的P-T轨迹，峰期变质条件约为2.1 GPa约670℃，对应的埋藏深度约为70 km。峰后变质P-T条件表明榴辉岩等温减压，初始抬升适度，深度约40公里。石榴石、绿辉石和全岩的Sm-ND等时线年龄为462℃±17.7 Ma，解释为榴辉岩样品在650~600℃、压力为<；和1 Gpa时的冷却和退缩时间。我们认为阿克秋兹杂岩的高压岩石代表了一个古哈萨克斯坦地体的深俯冲陆壳。在变质岩(现在的副片麻岩)的折返过程中，镁铁质岩石在不同的深度和低温(<；约400℃，就已报道的样品在约462 Ma之后)与俯冲通道中更浮力的副片麻岩并置在一起。这种通道流折返模型可以解释副片麻岩和榴辉岩不同的高温岩石学和年代学历史。
The Aktyuz Metamorphic Complex in the western Tianshan Mountains of Kyrgyzstan comprises high-pressure (HP) granitic gneisses and metasediments hosting mafic HP lithologies including eclogite. Geological relationships and geochemical-isotopic data of the different rock types of the Aktyuz Complex have been interpreted as a continental crustal fragment and the mafic rocks as former dykes. This study combines Sm–Nd and40Ar/39Ar mineral ages, and P–T pseudosection modelling for a single retrogressed eclogite sample in order to shed light on the P–T–t evolution of the mafic HP rocks. The eclogite experienced a clockwise prograde P–T path with peak metamorphic conditions of ca. 2.1 GPa at ca. 670 °C, corresponding to a burial depth of ca. 70 km. The post-peak metamorphic P–T conditions suggest isothermal decompression and moderate initial uplift of the eclogite to ca. 40 km depth. A Sm–Nd isochron age of 462 ± 7 Ma for garnet, omphacite, and whole-rock is interpreted as time of cooling and retrogression of the eclogite sample below 650 to 600 °C at pressures < 1 GPa. We suggest that the HP rocks of the Aktyuz Complex represent deeply subducted continental crust of one of the Palaeo-Kazakhstan terranes. During exhumation of the metasediments (now paragneiss), the mafic rocks were juxtaposed at variable depth and at low temperature (< 400 °C, and in the case of the reported sample after ca. 462 Ma) with the more buoyant paragneisses in the subduction channel. This channel flow exhumation model can account for the different high-temperature petrological and geochronological histories of paragneiss and eclogite.