Boninites in many supra-subduction zone ophiolites are thought to mark the early stage of subduction. The Troodos ophiolite in Cyprus contains a variety of volcanic rocks including the lower pillow lavas and the boninite-bearing upper pillow lavas (UPL). Here we present major, trace element and Pb isotope data for melt inclusions in olivine from the UPL on the northern flank of the Troodos ophiolite. Melt inclusions hosted by high-Mg (Fo = 89.4–93.5) olivine grains have typical high-Ca boninitic compositions with high MgO (11.2–18.4 wt%) and SiO2 (51.2–55.0 wt%) and low TiO2 (0.2–0.6 wt%) contents, in line with the existence of boninites in the northern part of the ophiolite. The melt inclusions have trace element compositions similar to the Troodos boninitic lavas and can be regarded as representing the parental magma of the boninites. The boninitic magmas were derived from high-degrees of partial melting of a refractory source at 1400 °C and 1.5 GPa based on thermobarometers and phase equilibria. The melt inclusions have significantly variable Pb isotopic compositions (208Pb/206Pb = 2.059–2.122; 207Pb/206Pb = 0.828–0.862) and are enriched in fluid-mobile trace elements (e.g., U, Sr, and Pb), indicating that the refractory source was metasomatized by slab fluids. In comparison, recalculation of literature data suggests that the lower pillow lavas were derived from a less refractory and shallower source. We propose a subduction initiation model in which melting of two unique sources was needed to form the chemostratigraphy of lavas in the Troodos ophiolite.

中文翻译：

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特罗多斯蛇绿岩熔岩中的高Ca boninitic熔体包裹体和不同熔岩类型之间的遗传关系的重新评估

许多超俯冲带蛇绿岩中的 Boninites 被认为标志着俯冲的早期阶段。塞浦路斯的特罗多斯蛇绿岩包含多种火山岩，包括下枕熔岩和含钫岩的上枕熔岩 (UPL)。在这里，我们提供了来自特罗多斯蛇绿岩北侧 UPL 橄榄石中熔体包裹体的主要、微量元素和 Pb 同位素数据。由高 Mg（Fo = 89.4-93.5）橄榄石晶粒承载的熔体夹杂物具有典型的高 Ca boninitic 组成，具有高 MgO（11.2-18.4 wt%）和 SiO2（51.2-55.0 wt%）和低 TiO2（0.2-0.6 wt%） %) 含量，与蛇绿岩北部存在 boninites 一致。熔体包裹体具有与特罗多斯博尼特熔岩相似的微量元素组成，可以看作是博尼特母体岩浆的代表。基于温度气压计和相平衡，在 1400 °C 和 1.5 GPa 条件下，博尼特岩浆源自耐火材料的高度部分熔融。熔体包裹体具有显着可变的 Pb 同位素组成（208Pb/206Pb = 2.059–2.122；207Pb/206Pb = 0.828–0.862）并且富含流体移动的微量元素（例如 U、Sr 和 Pb），表明耐火材料源被板状流体交代。相比之下，对文献数据的重新计算表明，较低的枕状熔岩来自较难熔且较浅的来源。我们提出了一个俯冲起始模型，其中需要两种独特来源的熔化来形成 Troodos 蛇绿岩中熔岩的化学地层学。5 GPa 基于热气压计和相平衡。熔体包裹体具有显着可变的 Pb 同位素组成（208Pb/206Pb = 2.059–2.122；207Pb/206Pb = 0.828–0.862）并且富含流体移动的微量元素（例如 U、Sr 和 Pb），表明耐火材料源被板状流体交代。相比之下，对文献数据的重新计算表明，较低的枕状熔岩来自较难熔且较浅的来源。我们提出了一个俯冲起始模型，其中需要两种独特来源的熔化来形成 Troodos 蛇绿岩中熔岩的化学地层学。5 GPa 基于热气压计和相平衡。熔体包裹体具有显着可变的 Pb 同位素组成（208Pb/206Pb = 2.059–2.122；207Pb/206Pb = 0.828–0.862）并且富含流体移动的微量元素（例如 U、Sr 和 Pb），表明耐火材料源被板状流体交代。相比之下，对文献数据的重新计算表明，较低的枕状熔岩来自较难熔且较浅的来源。我们提出了一个俯冲起始模型，其中需要两种独特来源的熔化来形成 Troodos 蛇绿岩中熔岩的化学地层学。表明耐火源被板坯流体交代。相比之下，对文献数据的重新计算表明，较低的枕状熔岩来自较难熔且较浅的来源。我们提出了一个俯冲起始模型，其中需要两种独特来源的熔化来形成 Troodos 蛇绿岩中熔岩的化学地层学。表明耐火源被板坯流体交代。相比之下，对文献数据的重新计算表明，较低的枕状熔岩来自较难熔且较浅的来源。我们提出了一个俯冲起始模型，其中需要两种独特来源的熔化来形成 Troodos 蛇绿岩中熔岩的化学地层学。