Igneous rocks in central Iran preserve proof of several episodes of Late Mesozoic–Cenozoic Neotethyan subduction, and record temporal and spatial variations from subduction to collisional geodynamic regimes that remain a subject of debate. We revisit magmatic rocks from the central Urumieh–Dokhtar magmatic arc (UDMA; 32° 30′ N to 36° 00′ N) and report new major and trace element analyses, whole-rock Sr–Nd–Pb-isotopic data and zircon U–Pb–Hf ages on plutonic rocks from the Kajan region. The data reveal magmatic pulses between 32 and 22 Ma that are represented by igneous rocks with geochemical and isotopic features resulting from melting of a metasomatized, enriched mantle. Modeling indicates the samples represent a mixture of 97% batch melt (from a source with 98.5% mantle melt +1.5% terrigenous sediment) with 3% upper continental crust. The oldest yielded age ( 32 Ma) rules out a lull in magmatism in the central UDMA between 37 and 26 Ma and speaks against distinct flare-up magmatic episodes at ∼54–37 Ma and ∼ 20–5 Ma in the frontal arc. We hypothesize that magmatism records down-going slab tearing into two pieces beneath the central to SE UDMA, which then changes the geometry and buoyancy of subducting Neotethyan lithosphere. The down-going slab remained involved in central UDMA ( rollback) during Early Miocene whilst arc retreat beneath the SE UDMA proceeded with detachment of subducted oceanic lithosphere ( break-off). We hypothesize a diachronous collision in the UDMA, first in the southeastern segments, and subsequently in the central UDMA. These findings bear important implications for the geodynamic evolution of the Zagros orogen and run counter to a model suggesting that the collision initiated in the northwest to central and propagated progressively to the southeast along the Zagros suture zone.

中文翻译：

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伊朗中部至东南部新特提斯俯冲的时空演化：来自地球化学、锆石U-Pb-Hf和Sr-Nd-Pb同位素的约束


伊朗中部的火成岩保存了晚中生代-新生代新特提斯俯冲事件的证据，并记录了从俯冲到碰撞地球动力学状态的时空变化，这些变化仍然是一个争论的话题。我们重新审视了乌鲁米耶-多赫塔尔中部岩浆弧（UDMA；北纬 32°30′ 至北纬 36°00′）的岩浆岩，并报告了新的主量元素和微量元素分析、全岩 Sr-Nd-Pb 同位素数据和锆石 U –Pb-Hf 在卡扬地区的深成岩上年龄。这些数据揭示了 32 至 22 Ma 之间的岩浆脉冲，这些脉冲由具有地球化学和同位素特征的火成岩代表，这些特征是由交代化、富集的地幔熔化产生的。模型表明，这些样本代表了 97% 批量熔体（来自 98.5% 地幔熔体 + 1.5% 陆源沉积物的来源）和 3% 上大陆地壳的混合物。最古老的产生年龄（32 Ma）排除了中央 UDMA 在 37 至 26 Ma 之间岩浆活动的平静，并反对在额弧中约 54-37 Ma 和约 20-5 Ma 发生明显的岩浆爆发事件。我们假设岩浆作用记录了东南 UDMA 中心下方向下的板片撕裂成两块，然后改变了俯冲新特提斯岩石圈的几何形状和浮力。早中新世时期，下降板块仍参与中央 UDMA（回滚），而 SE UDMA 下方的弧形退缩继续进行俯冲海洋岩石圈的分离（断裂）。我们假设 UDMA 中存在历时碰撞，首先发生在东南段，随后发生在 UDMA 中部。 这些发现对扎格罗斯造山带的地球动力学演化具有重要意义，并且与一个模型背道而驰，该模型表明碰撞从西北到中部开始，并沿着扎格罗斯缝合带逐渐向东南传播。