Abstract The Posht-e-Badam Block in Central Iran likely formed part of the Neoproterozoic Arabian-Nubian Shield (ANS). However, its Phanerozoic history is not well constrained. Zircon U Pb ages, Hf isotopic compositions and whole-rock geochemistry of igneous rocks from the Bafq district were determined to constrain their source and tectonomagmatic evolution. Two magmatic cycles are identified; early Paleozoic events associated with the Cadomian Orogeny resulting from Proto-Tethys subduction beneath the northern margin of Gondwana, and Cenozoic volcanism related to the Alpine-Himalayan Orogeny and closure of Neo-Tethys. The main plutonic and volcanic rocks record early Cambrian ages. The Zarigan, Narigan and Chahcholeh granitoids, volcanic rocks of the lower Cambrian volcano-sedimentary unit (CVSU) and the Zarigan gabbro have remarkably similar ages of 536 to 528 Ma. The Zarigan and Chahcholeh granitoids and volcanic rocks of the CVSU have positive eHf(t) values of 1.4 to 9.3, with Hf model ages (Hf-TDMc) of 715–1034 Ma. They are mostly A2-types, although some samples show affinity to A1- and I-types, suggesting an asthenospheric mantle source, modified by various amounts of crustal assimilation. The Narigan granite records eHf(t) values of −3.8 - 3.1, with Hf-TDMc of 970 to 1255 Ma and displays I-type characteristics, formed through mixing of mantle-derived melts with predominantly Neoproterozoic crust. All rocks were generated in a post-collisional setting. The Esfordy syenite and mafic dikes are younger and essentially coeval, with weighted mean ages of 457 ± 5 Ma and 451–448 Ma, respectively. The Esfordy syenite has A1-type characteristics, indicating possible derivation in an intraplate rift environment and was likely plume-related. The mafic dikes have OIB-like characteristics. Mafic rocks related to closure of Neo-Tethys include the ca. 23 Ma Bahabad diorite that records eHf(t) values of −16.8 to 10.1 (Hf-TDMc = 241–283 Ma) and an OIB-like signature, indicating assimilation of crustal material by asthenospheric mantle-derived melt.

中文翻译：

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Posht-e-Badam 地块岩浆岩的锆石 U-Pb-Hf 同位素和全岩地球化学：伊朗中部构造岩浆演化的关键

摘要 伊朗中部的 Posht-e-Badam 地块可能是新元古代阿拉伯-努比亚地盾 (ANS) 的一部分。然而，它的显生宙历史并没有受到很好的限制。确定了 Bafq 地区火成岩的锆石 U Pb 年龄、Hf 同位素组成和全岩地球化学，以限制它们的来源和构造岩浆演化。确定了两个岩浆旋回；早期古生代事件与冈瓦纳北缘下原始特提斯俯冲导致的卡多米造山运动有关，以及与高山-喜马拉雅造山运动和新特提斯闭合有关的新生代火山活动。主要的深成岩和火山岩记录了早寒武纪时代。Zarigan、Narigan 和 Chahcholeh 花岗岩，下寒武统火山-沉积单元（CVSU）和扎里甘辉长岩的火山岩年龄非常相似，为 536 至 528 Ma。CVSU 的 Zarigan 和 Chahcholeh 花岗岩和火山岩具有 1.4 至 9.3 的正 eHf(t) 值，Hf 模型年龄 (Hf-TDMc) 为 715-1034 Ma。它们大多是 A2 型，尽管一些样品显示出对 A1 型和 I 型的亲和力，表明软流圈地幔来源，被不同程度的地壳同化所改变。Narigan 花岗岩记录的 eHf(t) 值为 -3.8 - 3.1，Hf-TDMc 为 970 至 1255 Ma，显示 I 型特征，由地幔衍生的熔体与主要是新元古代地壳混合形成。所有岩石都是在碰撞后环境中生成的。Esfordy 正长岩和镁铁质岩脉更年轻，基本上是同时代的，加权平均年龄分别为 457 ± 5 Ma 和 451-448 Ma。Esfordy 正长岩具有 A1 型特征，表明可能来源于板内裂谷环境，并且可能与羽流有关。基性岩脉具有类似 OIB 的特征。与新特提斯洋闭合有关的基性岩包括约。23 Ma 巴哈巴德闪长岩，记录 eHf(t) 值为 -16.8 至 10.1（Hf-TDMc = 241-283 Ma）和类似 OIB 的特征，表明软流圈地幔衍生的熔体对地壳物质的同化作用。