Olivine-rich lavas in the Margi area, Cyprus, are part of the boninitic Upper Pillow Lava series of the Troodos ophiolite. Re-Os isotope compositions of both whole rock and olivine phenocrysts of these lavas have been measured to determine the initial Os/Os isotope compositions of the primary boninitic magma. The Margi lavas have high and variable whole rock Re-Os isotope compositions (Re/Os: 1.060–8.613; Os/Os: 0.1307–0.1599), with (Sr/Sr) (0.705936 ± 0.001021), ε(90 Ma) (5.6 ± 2.5), and δO (8.59 ± 0.38 ‰). In contrast, olivine phenocrysts, which host spinel and melt inclusions, have low and constant Os/Os from 0.1301 to 0.1336 and low Re/Os from 0.1350 to 1.557. Initial Os/Os of these olivine phenocrysts (0.1300 ± 0.0041) is lower than that of whole rock (0.1373 ± 0.0135). These facts indicate that the olivine phenocrysts faithfully record initial Os/Os of the primary boninitic magmas, which are comparable to the Os/Os of primitive mantle, whereas whole rock Re-Os isotopes have been affected by secondary processes after olivine crystallization. Further geochemical modeling indicates that, although Os can be mobilized during slab dehydration, the contribution of crustal Os is insufficient to significantly raise the Os/Os of the mantle wedge in a nascent subduction zone. Overall, our findings provide new insights about Os recycling in the early stages of subduction.

中文翻译：

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蛇绿质砗磲岩揭示新生俯冲带地壳 Os 的再循环

塞浦路斯 Margi 地区富含橄榄石的熔岩是特罗多斯蛇绿岩胶质上枕熔岩系列的一部分。测量了这些熔岩的整个岩石和橄榄石斑晶的铼-锇同位素组成，以确定原生胶质岩浆的初始锇/锇同位素组成。 Margi 熔岩具有高且可变的全岩 Re-Os 同位素组成（Re/Os：1.060–8.613；Os/Os：0.1307–0.1599），其中（Sr/Sr）（0.705936 ± 0.001021），ε（90 Ma）（ 5.6 ± 2.5) 和 δ18O (8.59 ± 0.38 ‰)。相比之下，含有尖晶石和熔体包裹体的橄榄石斑晶具有 0.1301 至 0.1336 的低且恒定的 Os/Os 和 0.1350 至 1.557 的低 Re/Os。这些橄榄石斑晶的初始 Os/Os (0.1300 ± 0.0041) 低于整个岩石的初始 Os/Os (0.1373 ± 0.0135)。这些事实表明，橄榄石斑晶忠实地记录了原生胶质岩浆的初始Os/Os，与原始地幔的Os/Os相当，而全岩Re-Os同位素受到了橄榄石结晶后次生过程的影响。进一步的地球化学模拟表明，尽管在板片脱水过程中Os可以被动员，但地壳Os的贡献不足以显着提高新生俯冲带中地幔楔的Os/Os。总的来说，我们的研究结果为俯冲早期阶段的骨回收提供了新的见解。