Supra-subduction igneous formations of the Char ophiolite belt, East Kazakhstan
Supra-subduction igneous formations of the Char ophiolite belt, East Kazakhstan
复制标题
DOI：
10.1016/j.gr.2018.04.001
复制
发表时间：
2018-07
影响因子：
6.1
通讯作者：
I. Safonova;T. Komiya;R. Romer;V. Simonov;R. Seltmann;S. Rudnev;S. Yamamoto;M. Sun
中科院分区：
文献类型：
--
作者：
I. Safonova;T. Komiya;R. Romer;V. Simonov;R. Seltmann;S. Rudnev;S. Yamamoto;M. Sun
关于中亚造山带（CAOB）西部的古亚洲洋（PAO）最终发育的构造概念存在广泛的争议，主要是由于年代学和地球化学资料的缺乏。本文介绍了东哈萨克斯坦火成岩带长英质火成岩的U-Pb锆石定年和详细的地球化学（主微量元素、Sr、Nd和Pb同位素）研究结果。新的数据揭示了该地区PAO的最后阶段。火成岩组合包括基性至长英质火山岩及其深成岩变种。泥盆纪和早石炭世U-Pb锆石年龄与前人报道的洋源沉积岩微古生物年龄相符。根据主要元素组成，岩石属于拉斑岩系和拉斑岩-钙碱性过渡型火成岩系。它们具有低TiO2（平均0.7 wt%）和中等富集的轻稀土元素（LREE）至扁平球粒陨石归一化稀土模式（Lan= 3.5 ~ 34.6,La/Smn= 0.8 ~ 4.6,La/Ybn= 0.6 ~ 9.1）的特征。原始地幔归一化多元素谱在Nb处有明显的波谷（Nb/Lapm= 0.1 ~ 0.38;Nb/Thpm= 0.04 ~ 0.6）。大部分样品的ε ndt值在+2.9 ~ +8.8之间，206pb /204Pb比值在~18.0 ~ ~19.7之间。Nb-Yb体系的微量元素和同位素数据以及地球化学模拟结果表明，尖晶石稳定场中存在强枯竭地幔源的高度熔融。斜辉石（cpx）单矿物测温和基于cpx携带的熔体包裹体组成的计算表明，较年轻样品的熔体在12,6 - 3 km深度和地下条件下在较低温度下结晶（低于1170 °С），而较老样品在较高温度下（高达1193 °С）在6 - 3 km深度结晶。我们的新数据表明，在哈萨克斯坦大陆活动边缘的古亚洲洋伊尔吉什-再山分支中，至少有两个洋内弧的碎片，分别是中泥盆世和早石炭世。
There is a wide range of controversial tectonic concepts for the final development of the Paleo-Asian Ocean (PAO) in the western Central Asian Orogenic Belt (CAOB), largely due to scarcity of geochronological and geochemical data. Our paper presents first results of U-Pb zircon dating and detailed geochemical studies (major and trace elements, Sr, Nd and Pb isotopes) of subduction-related mafic to felsic igneous rocks of the Char ophiolite belt (East Kazakhstan). The new data shed light on the final stage of the PAO in this region. The igneous assemblages comprise mafic to felsic volcanic rocks and their plutonic varieties. The rocks yield Devonian and early Carboniferous U-Pb zircon ages, which match the previously reported micropaleontological ages of sedimentary rocks of oceanic origin. According to major element composition, the rocks belong to the tholeiitic and tholeiitic to calc-alkaline transitional igneous series. They are characterized by low TiO2(0.7 wt% in average) and moderately enriched light rare-earth element (LREE) to flat chondrite normalized REE patterns (Lan= 3.5–34.6, La/Smn= 0.8–4.6, La/Ybn= 0.6–9.1). Primitive mantle normalized multi-element spectra show distinct troughs at Nb (Nb/Lapm= 0.1–0.38; Nb/Thpm= 0.04–0.6). Most of the samples have positive εNdtvalues ranging from +2.9 to +8.8 and206Pb/204Pb ratios ranging from ~18.0 to ~19.7. The trace element and isotope data and the results of geochemical modeling in the Nb-Yb system suggest high degrees of melting of a strongly depleted mantle source in the spinel stability field. Clinopyroxene (cpx) monomineral thermometry and the calculations based on the composition of cpx hosted melt inclusions suggest that the melts from which the younger samples were derived crystallized at lower temperatures (below 1170 °С) at depths of 12, 6–3 km and in subsurface conditions, while the older samples derived at higher temperatures (up to 1193 °С) crystallized at a depth from 6 to 3 km. Our new data show that the Char ophiolite belt hosts fragments of at least two intra-oceanic arcs, middle Devonian and Early Carboniferous, which existed in the Irtysh-Zaisan branch of the Paleo-Asian Ocean, at the active margin of the Kazakhstan continent.