Abstract The Neotethyan tectonics of the Zagros orogenic belt, SW Iran remains still hotly debated in comparing with its western counterparts. One major issue concerns the timing and nature of the Sanandaj-Sirjan magmatic-metamorphic belt (SSMB), which is made predominantly of metamorphic rocks and Jurassic to Early Cretaceous large plutonic complexes. The Alvand and Qory are two largest plutonic complexes locating in north-central and southern segments, respectively, of the SSMB. Careful LA-ICP-MS U/Pb analyses of the magmatic zircons from the Alvand plutonic complex reveal a smooth spectra, along which the concordant age increase gradually from 120 to 190 Ma; while that of Qory is step-like consisting of two stages, a Jurassic and a late Early Cretaceous ones, respectively. New geochemical data, combined with zircon Lu/Hf results suggest that (1) the Alvand granitoids mostly resulted from a long-lived, successive injection of juvenile-crust-sourced magma batches without obvious fractionation crystallization (FC); but (2) the two stages granitoids of the Qory complex both generated by FC of juvenile-crust-sourced magmas; and (3) the gabbros of the Alvand complex are geochemically of E-MORB-affinity while those of the Qory complex are typical continental arc mafic rocks. Previously published petrological and 40Ar/39Ar data have identified a broken, Jurassic to Early Cretaceous high-pressure metamorphic belt to the southwest of the SSMB, which likely represents the closed, southeastern equivalent of the northern Neotethyan Ocean, north of the Taurides-Anatolia-Armenia block. Thus, the SSMB in Iran, the Kapan belt in Caucasus, and the Serbo-Macedonian belt in northern Turkey form a huge Jurassic to Early Cretaceous continental margin arc system recording northeastwards subduction of the older Northern Neotethyan Ocean beneath Eurasia. The Albian-Cenomanian ophiolites such as Koy, Kermanshah, and Neyriz in Iran represent the eastern counterpart of the younger Southern Neotethyan Ocean, south of the Taurides-Anatolia-Armenia block. During the subduction of the Old Neotethys, an intraplate transform fault likely opened and generated a slab-window beneath the Alvand region, which provided a constant energy source to steadily heat the low crust. This model satisfactorily interprets the unusual geochronological framework and geochemistry of the Alvand complex.

中文翻译：

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Sanandaj-Sirjan岩浆变质带的两个深成杂岩体记录了伊朗微板块下古老新特提斯的侏罗纪至早白垩世俯冲

摘要 伊朗西南部扎格罗斯造山带的新特提斯构造与西方造山带的对比仍存在激烈争论。一个主要问题涉及 Sanandaj-Sirjan 岩浆变质带 (SSMB) 的时间和性质，该带主要由变质岩和侏罗纪至早白垩世大型深成岩杂岩组成。Alvand 和 Qory 是两个最大的深成杂岩体，分别位于 SSMB 的中北部和南部。对 Alvand 深成杂岩岩浆锆石进行仔细的 LA-ICP-MS U/Pb 分析揭示了一个平滑的光谱，其一致年龄从 120 Ma 逐渐增加到 190 Ma；而Qory则是阶梯状，由侏罗纪和早白垩世晚期两个阶段组成。新的地球化学数据，结合锆石 Lu/Hf 结果表明 (1) Alvand 花岗岩主要来自长期连续注入的幼年地壳来源的岩浆批次, 没有明显的分馏结晶 (FC); 但 (2) 由幼年地壳来源的岩浆 FC 产生的 Qory 杂岩的两个阶段花岗岩；(3) Alvand杂岩中的辉长岩地球化学上具有E-MORB-亲和性，而Qory杂岩中的辉长岩是典型的大陆弧基性岩。先前发表的岩石学和 40Ar/39Ar 数据已经确定了 SSMB 西南部的一条破碎的侏罗纪至早白垩世高压变质带，它可能代表了陶里德斯-安纳托利亚以北的新特提斯洋北部的封闭东南部等价物。亚美尼亚块。因此，伊朗的 SSMB、高加索的 Kapan 带、和土耳其北部的塞尔维亚-马其顿带形成了一个巨大的侏罗纪到早白垩世大陆边缘弧系统，记录了欧亚大陆之下古老的北新特提斯洋向东北俯冲。Albian-Cenomanian 蛇绿岩，如伊朗的 Koy、Kermanshah 和 Neyriz，代表了 Taurides-Anatolia-Armenia 地块以南的年轻的南新特提斯洋的东部对应物。在旧新特提斯俯冲期间，一个板内转换断层可能打​​开并在 Alvand 地区下方产生了一个板状窗口，这为稳定加热低地壳提供了恒定的能源。该模型令人满意地解释了 Alvand 复合体不寻常的年代学框架和地球化学。