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首页> 外文期刊>Contributions to Mineralogy and Petrology >Formation of low-delta O-18 magmas of the Kangerlussuaq Intrusion by addition of water derived from dehydration of foundered basaltic roof rocks
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Formation of low-delta O-18 magmas of the Kangerlussuaq Intrusion by addition of water derived from dehydration of foundered basaltic roof rocks

机译：通过添加枯萎的玄武岩顶板岩石脱水产生的水，形成康格鲁苏瓦火山岩低三角O-18岩浆

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The Kangerlussuaq Intrusion in East Greenland is concentrically zoned from quartz nordmarkite (quartz syenite) at the margin, through pulaskite, to foyaite (nepheline syenite) in the centre, with no apparent intrusive contacts. The delta O-18 values of coexisting minerals are consistent with oxygen isotope equilibrium at magmatic temperatures. Most of the intrusion formed from low-delta O-18 magma; magma delta O-18 values generally increased upwards from about 3.3 % in the quartz nordmarkites to 5.6 % in the foyaites. The lowest magma delta O-18 value of about -1.0 % is from the upper part of the nordmarkites, where there is a high concentration of foundered basaltic xenoliths (stoped from the roof of the intrusion). The amphiboles in the syenites have delta D values that range from those typical of hydrous mantle-derived minerals to much lower values (-86 to -157 %), as do whole-rock samples of xenolith and country rock (-125 to -148 %). The low magma delta O-18 and dD values are consistent with continuous incorporation, exchange and upward escape of low-delta O-18 and dD fluids released from stoped basaltic roof material. Mass balance suggests that the integrated amount of water involved was 7 wt% of the volume of the magma, but locally reached 30 wt% water. The requirement for large amounts of water with low delta O-18 value is satisfied only if the foundered basalt contained most of its water in cavities as opposed to hydrous minerals. Even with this requirement, the volume of stoped basalt would have been equal to the volume of the magma. Repeated recharge of the residual magma with progressively less contaminated silica undersaturated melt resulted in a gradual shift across the low-pressure thermal divide. Crystallisation was suppressed by the depression of the liquidus due to water saturation of the residual magma (pH(2)O similar to 1 kbar).
机译：东格陵兰的Kangerlussuaq侵入带同心地带，从边缘的石英nordmarkite（石英正长岩）穿过白云母到中心的foyaite（霞石正长岩），没有明显的侵入接触。共存矿物的δO-18值与岩浆温度下的氧同位素平衡相符。大部分入侵是由低三角洲O-18岩浆形成的。岩浆三角洲O-18值通常从石英nordmarkite中的约3.3％上升到foyaites中的5.6％。最低的岩浆三角洲O-18值约为-1.0％，是在北部高锰矿的上部，那里有高浓度的沉没玄武岩异岩（从侵入岩顶部停止）。正弦岩中的闪石的δD值范围从典型的含水地幔矿物到低得多的值（-86至-157％），异种石和乡村岩石的全岩样品也是如此（-125至-148） ％）。低岩浆三角洲O-18和dD值与从停止的玄武质屋面材料释放的低三角洲O-18和dD流体的持续掺入，交换和向上逸出是一致的。质量平衡表明，所涉及的水总量为岩浆体积的7 wt％，但局部达到30 wt％。仅当枯萎的玄武岩的大部分水都在空腔中而不是含水矿物时，才能满足对大量低O-18值水的需求。即使有这个要求，玄武岩的体积也将等于岩浆的体积。残留岩浆的反复充填，并逐渐减少了污染程度较低的二氧化硅欠饱和熔体，从而导致低压热分度逐渐变化。由于残余岩浆的水饱和度（pH（2）O类似于1 kbar），液相线的下降抑制了结晶的产生。

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