Western Tethyan peridotites exposed in the European Alps show limited amounts of partial melting and mostly fertile compositions. Here we investigate the Civrari Ophiolite (northwestern Italy), which is composed of depleted spinel-harzburgites and serpentinites associated with MOR-type gabbros and basalts. The ultramafic rocks are unique amongst western Tethyan peridotites, showing homogeneous residual compositions after ~ 15% near-fractional melting, lack of pervasive melt percolation and mineral compositions that indicate high-temperature equilibration ≥ 1200 °C. Clinopyroxene chemistry records some of the lowest abundances of Na2O, Ce, and Zr/Hf amongst abyssal peridotites worldwide, suggesting that most abyssal peridotites have been affected by variable degrees of melt retention upon melting or cryptic melt percolation. Locally, cryptic MORB-like melt migration in Civrari peridotites produced orthopyroxene + plagioclase intergrowth around reacted clinopyroxene. These clinopyroxene preserve micron-scale chemical zoning indicating rapid cooling after melt crystallization. 143Nd/144Nd isotopic data indicate that Civrari mantle rocks, gabbros, and basalts are not in isotopic equilibrium. Civrari spinel-peridotites represent a highly radiogenic endmember amongst Western Tethys depleted spinel-peridotites, which together form a partial melting errochron of 273 Ma ± 24 Ma. Ancient near-fractional melting and cryptic melt–rock reaction cause variations in radiogenic εNd and εHf, leading to isotopic heterogeneity of Western Tethys mantle rocks. Such inherited signatures in mantle rocks are most likely to be preserved along (ultra-)slow-spreading systems and ocean–continent transition zones.

中文翻译：

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古代部分熔化、隐秘再肥化和特提斯地幔快速挖掘的证据（Civrari蛇绿岩，意大利西北部）

暴露于欧洲阿尔卑斯山的西特提斯橄榄岩显示出数量有限的部分熔融和主要是肥沃的成分。在这里，我们研究了 Civrari 蛇绿岩（意大利西北部），它由与 MOR 型辉长岩和玄武岩相关的耗尽的尖晶石-斜方辉石和蛇纹岩组成。超基性岩在西特提斯橄榄岩中是独一无二的，在约 15% 的近分熔融后显示出均质的残余成分，缺乏普遍的熔体渗透和矿物成分，表明高温平衡 ≥ 1200 °C。单斜辉石化学记录了全世界深海橄榄岩中 Na2O、Ce 和 Zr/Hf 的一些最低丰度，这表明大多数深海橄榄岩在熔化或隐蔽熔体渗透时受到不同程度的熔体滞留的影响。在当地，Civrari 橄榄岩中神秘的 MORB 样熔体迁移产生了正辉石 + 斜长石在反应后的单斜辉石周围的共生。这些单斜辉石保留了微米级化学分区，表明熔体结晶后快速冷却。143Nd/144Nd 同位素数据表明 Civrari 地幔岩石、辉长岩和玄武岩不处于同位素平衡。Civrari 尖晶石橄榄岩代表了西特提斯贫化尖晶石橄榄岩中的高放射成因端元，它们共同形成了 273 Ma ± 24 Ma 的部分熔融误差。古代近分次熔融和隐蔽的熔岩反应导致放射成因 εNd 和 εHf 发生变化，导致西特提斯地幔岩石的同位素非均质性。