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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Deep pooling of low degree melts and volatile fluxes at the 85 degrees E segment of the Gakkel Ridge: Evidence from olivine-hosted melt inclusions and glasses
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Deep pooling of low degree melts and volatile fluxes at the 85 degrees E segment of the Gakkel Ridge: Evidence from olivine-hosted melt inclusions and glasses

机译：Gakkel山脊85度E段的低度熔体和挥发性通量的深层汇集：来自橄榄石质熔体包裹体和玻璃的证据

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摘要

We present new analyses of volatile, major, and trace elements for a suite of glasses and melt inclusions from the 85 degrees E segment of the ultra-slow spreading Gakkel Ridge. Samples from this segment include limu o pele and glass shards, proposed to result from CO2-driven explosive activity. The major element and volatile compositions of the melt inclusions are more variable and consistently more primitive than the glass data. CO2 contents in the melt inclusions extend to higher values (167-1596 ppm) than in the co-existing glasses (187-227 ppm), indicating that the melt inclusions were trapped at greater depths. These melt inclusions record the highest CO2 melt concentrations observed for a ridge environment. Based on a vapor saturation model, we estimate that the melt inclusions were trapped between seafloor depths (similar to 4 km) and similar to 9 km below the seafloor. However, the glasses are all in equilibrium with their eruption depths, which is inconsistent with the rapid magma ascent rates expected for explosive activity. Melting conditions inferred from thermobarometry suggest relatively deep (25-40 km) and cold (1240 degrees-1325 degrees C) melting conditions, consistent with a thermal structure calculated for the Gakkel Ridge. The water contents and trace element compositions of the melt inclusions and glasses are remarkably homogeneous: this is an unexpected result for ultra-slow spreading ridges, where magma mixing is generally thought to be less efficient based on the assumption that steady-state crustal magma chambers are absent in these environments. All melts can be described by a single liquid line of descent originating from a pooled melt composition that is consistent with the aggregate melt calculated from a geodynamic model for the Gakkel Ridge. These data suggest a model in which deep, low degree melts are efficiently pooled in the upper mantle (9-20 km depth), after which crystallization commences and continues during ascent and eruption. Based on our melting model and the assumption that CO2 is perfectly incompatible, we show that the highest CO2 concentrations of the melt inclusions (similar to 1600 ppm) are consistent with the calculated CO2 concentrations of primary undegassed melts. The highest measured CO2/Nb ratio (443) of Gakkel Ridge melt inclusions predicts a mantle CO2 content of 134 ppm and would result in a global ridge flux of 2.0 x 10(12) mol CO2/yr.
机译：我们提供了来自超慢速扩展Gakkel脊85度E段的一组玻璃和熔体夹杂物的挥发性，主要和微量元素的新分析。该部分的样品包括利姆贝利和玻璃碎片，据推测是由二氧化碳驱动的爆炸活动造成的。熔融夹杂物的主要元素和挥发性成分比玻璃数据更易变且始终更加原始。与共存玻璃（187-227 ppm）中的熔体相比，熔体中的CO2含量更高（167-1596 ppm），这表明熔体中的夹杂物被捕集的深度更大。这些熔体夹杂物记录了在脊状环境中观察到的最高CO2熔体浓度。根据蒸汽饱和度模型，我们估计熔体夹杂物被困在海底深度（大约4 km）和海底以下9 km之间。但是，这些眼镜的喷发深度都处于平衡状态，这与爆炸活动预期的快速岩浆上升速率不一致。根据热压法推断出的融化条件表明，融化条件相对较深（25-40 km）和较冷（1240摄氏度至1325摄氏度），这与为Gakkel Ridge计算的热结构一致。熔体夹杂物和玻璃的水含量和微量元素组成非常均一：对于超慢扩散脊而言，这是出乎意料的结果，根据稳态地壳岩浆室的假设，通常认为岩浆混合效率较低在这些环境中不存在。所有熔体都可以通过一条单一的下降液体线来描述，该下降线源自合并的熔体成分，该熔体成分与根据Gakkel Ridge的地球动力学模型计算得出的总熔体一致。这些数据表明了一个模型，其中在上地幔（9-20 km深度）中有效地汇集了深度较低的熔体，此后结晶开始并在上升和喷发期间继续。根据我们的熔化模型和CO2完全不相容的假设，我们表明，熔体夹杂物的最高CO2浓度（约1600 ppm）与未脱气的原始熔体的CO2浓度计算值一致。 Gakkel脊熔体夹杂物的最高测量的CO2 / Nb比（443）预测地幔中的CO2含量为134 ppm，并且将导致整体脊通量为2.0 x 10（12）mol CO2 / yr。

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