Recycling of ancient sub-oceanic mantle in the Neo-Tethyan asthenosphere: Evidence from major and trace elements and Hf-Os isotopes of the Kop Mountain ophiolite, NE Turkey
Recycling of ancient sub-oceanic mantle in the Neo-Tethyan asthenosphere: Evidence from major and trace elements and Hf-Os isotopes of the Kop Mountain ophiolite, NE Turkey
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新特提斯软流圈中古代海底地幔的再循环：来自土耳其东北部科普山蛇绿岩的主量元素和微量元素以及铪锇同位素的证据
DOI：
10.1016/j.gca.2021.08.003
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发表时间：
2021
影响因子：
5
通讯作者：
Lin Yin-Zheng
中科院分区：
文献类型：
--
作者：
Liu Tong;Wu Fu-Yuan;Liu Chuan-Zhou;Zhu Di-Cheng;Lin Yin-Zheng
由于大陆、次弧或次大洋地幔域和俯冲洋壳及远洋沉积物的再循环，古代和现代大洋之下的软流圈具有高度的非均匀性。这些“老”地幔域的识别和鉴别对于认识洋壳的形成和蛇绿岩的构造背景具有重要意义。本文报道了新特提斯西部科普山蛇绿岩地幔橄榄岩的Re-Os和Lu-Hf同位素组成。这些橄榄岩的全岩和矿物成分与深海橄榄岩相当。单斜辉石的微量元素建模表明，他们受到无水熔融，在这方面的岩石是从俯冲带橄榄岩区分。Re-Os和Lu-Hf同位素组成进一步表明，这些地幔橄榄岩经历了1.52Ga或之前的古老熔融萃取和侏罗纪熔融交代作用。因此，科普山地幔橄榄岩代表古老的亚洋地幔域回收到新特提斯软流圈，经历早期熔融耗尽，然后被夹带在新特提斯海岭轴。我们的研究结果，与其他蛇绿岩发表的数据，表明新特提斯蛇绿岩的Os同位素分布是相同的全球深海橄榄岩，表明类似的熔融历史。新特提斯软流圈是高度不均匀的，可能有许多回收大陆，弧下和亚洋地幔输入。软流圈中的古老地幔的再循环可能是现代和蛇绿洋壳中异常成分的产生的另一种解释，如富钾熔岩，富集洋中脊玄武岩和弧形玄武岩。利用玄武岩地球化学数据区分构造环境（即，因此，应谨慎接近蛇绿岩的洋中脊或俯冲带。
The asthenosphere beneath both ancient and modern oceans is highly heterogeneous owing to the recycling of continental, sub-arc, or sub-oceanic mantle domains and subducted oceanic crust and pelagic sediments. The identification and discrimination of those “old” mantle domains are important for understanding of the generation of oceanic crust and the tectonic setting of ophiolites. Here we report geochemical data including Re–Os and Lu–Hf isotopic compositions for mantle peridotites from the Kop Mountain ophiolite in the western Neo-Tethys. These peridotites have whole-rock and mineral compositions comparable with those of abyssal peridotites. Trace element modeling of clinopyroxenes indicates that they were subjected to anhydrous melting, and in this respect the rocks are distinguishable from supra-subduction zone peridotites. Re–Os and Lu–Hf isotopic compositions further indicate that these mantle peridotites underwent ancient (at or before 1.52 Ga) melt extraction and Jurassic melt metasomatism. The Kop Mountain mantle peridotites thus represent ancient sub-oceanic mantle domains recycled into the Neo-Tethyan asthenosphere, undergoing earlier melt depletion before being entrained at the Neo-Tethyan ridge axis. Our results, together with data published for other ophiolites, indicate that the Os isotopic distribution of the Neo-Tethyan ophiolites is identical to that of global abyssal peridotites, suggesting similar melting histories. The Neo-Tethyan asthenosphere was highly heterogeneous, probably with numerous recycled continental, sub-arc, and sub-oceanic mantle inputs. The recycling of ancient mantle in the asthenosphere could be an alternative explanation for the generation of anomalous compositions in both modern and ophiolitic oceanic crusts such as K-rich lavas, enriched mid-ocean ridge basalts, and arc-like basalts. The use of basalt geochemical data to discriminate between tectonic settings (i.e., mid-ocean ridge or supra-subduction zone) of ophiolites should thus be approached with caution.