H2OCO2 fluids supplied in alpine-type mantle peridotites: electron petrology of relic fluid inclusions in olivines
H2OCO2 fluids supplied in alpine-type mantle peridotites: electron petrology of relic fluid inclusions in olivines
复制标题
高山型地幔橄榄岩中供给的 H2OCO2 流体：橄榄石中遗迹流体包裹体的电子岩石学
DOI：
10.1016/0012-821x(87)90041-0
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发表时间：
1987
影响因子：
5.3
通讯作者：
S. Arai
中科院分区：
文献类型：
--
作者：
H. Hirai;S. Arai
提供于高山型地幔橄榄岩中的流体以流体包裹体的形式被捕获在橄榄石中，通过低温反应将其固定，并由包裹体中的矿物推断其CO_2/H_2比值。光学显微镜在几乎所有所研究的固体侵入超镁铁质杂岩(巴布亚、阿曼、特罗多斯和日本的11个阿尔卑斯型杂岩)的橄榄石中普遍观察到残留的流体包裹体。这样的络合物以固态的形式侵位到地壳中。Higashiakaishi、Horoman和Iwanai-dake三个杂岩中的橄榄石的电子显微镜研究表明，这些橄榄石中的残留流体包裹体具有独特的矿物共生体：蛇纹石+镁砂+滑石，蛇纹石+镁砂+水镁石，以及蛇纹石+水镁石，这取决于捕获流体的CO2/(H2O+CO2)比。推测流体至少部分但在某些情况下几乎全部供应给橄榄岩，当橄榄岩仍然热的时候，可能是由于以下原因：(1)包裹体分布的曲面被侵位后的蛇纹石脉切割；(2)Higashiakaishi纯橄榄岩的残留流体包裹体仅见于斑岩橄榄石中，而在Sanbagawa变质作用中重结晶的基质橄榄石中则完全不存在，目前蛇绿岩或部分高山型橄榄岩的成因模式偏向于岛弧或弧前环境。下沉大洋板块的脱水作用可能向上覆地幔楔体提供H_2O单键CO_2蒸气。捕获在这种地幔楔体中的流体包裹体可能富含H2O组分。因此，含H2O的流体包裹体可能是上地幔中重要的H2O容器，特别是在下沉洋板上方的地幔楔形边缘附近。
Fluids supplied in alpine-type mantle peridotites and trapped as fluid inclusions in olivines have been fixed by low-temperature reactions, and theirCO2/H2Oratios can be deduced from the minerals in the inclusions. Relic fluid inclusions were commonly observed by the optical microscope in olivines from almost all examined solid intrusive ultramafic complexes (Papua, Oman, Troodos and eleven alpine-type complexes of Japan). Such complexes were emplaced into the crust in a solid state. Electron microscopic studies of olivines from three complexes, Higashiakaishi, Horoman and Iwanai-dake, showed that relic fluid inclusions in these olivines have distinctive mineral parageneses: serpentine + magnesite + talc, serpentine + magnesite + brucite, and serpentine + brucite, respectively, depending on theCO2/(H2O+CO2)ratio of the trapped fluid.It is deduced that the fluids had been supplied to peridotites, at least partly, but almost wholly in some case, when the peridotites were still hot, probably at the upper mantle for the following reasons: (1) the curved surfaces along which the inclusions are distributed are cut by post-emplacement serpentine veins; (2) for the Higashiakaishi dunite, the relic fluid inclusions are exclusively found in porphyroclast olivines and are totally absent in matrix olivines recrystallized during the Sanbagawa metamorphism.Recent models on the derivation of ophiolitic or some alpine-type peridotites favor the island-arc or fore-arc settings. Dehydration of the descending oceanic slab may supply H2Osingle bondCO2vapor to the overlying mantle wedge. Fluid inclusions trapped in such mantle wedge may abound in H2O component. H2O-bearing fluid inclusions may, therefore, be important H2O containers in the upper mantle, especially near the edge of the mantle wedge above downgoing oceanic slabs.