High-density early CO2 fluids in the ultrahigh-temperature granulites of Ihouhaouene (In Ouzzal, Algeria)
High-density early CO2 fluids in the ultrahigh-temperature granulites of Ihouhaouene (In Ouzzal, Algeria)
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DOI：
10.1016/j.lithos.2006.11.009
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发表时间：
2007-07
期刊：
影响因子：
3.5
通讯作者：
M. Cuney;Y. Coulibaly;M. Boiron
中科院分区：
文献类型：
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作者：
M. Cuney;Y. Coulibaly;M. Boiron
对阿尔及利亚霍格西部下元古界麻粒岩岩石中流体包裹体的研究为高级变质过程中存在富CO2、贫H2O的流体提供了新的证据。CO2包裹体是捕获在伊侯湖新世超高温(1000℃以上)高压(10~14kbar)麻粒岩中的主要流体。显微测温和拉曼光谱测量表明，碳酸盐流体主要由CO_2组成，部分包裹体中含有少量的甲烷和氮。碳酸盐流体密度在1.18到0.57微克/厘米~3之间。最高密度记录在超密的碳质包裹体中，提供了最早圈闭的证据，它们对应于先前由矿物地质温压计确定的地区变质作用峰值的P-T条件下的流体密度。较低的碳酸盐流体密度主要是由于早期捕获的流体包裹体在退变质作用和变质地体的最终抬升过程中重新平衡的结果，但在退变事件期间仍有可能有新的碳酸盐流体流入。碳酸盐流体可在进积事件中由层间不纯大理岩中的脱碳反应原地生成，或来自于下伏基性侵入岩的CO2冲刷。含水流体的组成(0.5至30wt%氯化钠当量)和密度(1.16至0.57微克/厘米~3)变化很大。它们明显对应于变质后流体，因为它们主要赋存于微裂缝中，没有显示出与碳酸盐流体不混溶的证据，也没有观察到混合的水-碳酸盐包裹体。水流体的渗流作用与泛非构造变质事件有关。
Fluid inclusion studies in rocks from the Lower Proterozoic granulites from western Hoggar (Algeria) provide new evidence for the hypothesis that a CO2-rich, H2O-poor fluid was present during the high-grade metamorphism. CO2inclusions represent the main fluid trapped in the Ihouhaouene ultrahigh-temperature (over 1000 °C) and high-pressure (10 to 14 kbar) granulites. The microthermometric and Raman microspectrometric measurements indicate that the carbonic fluid is mainly composed of CO2with minor amounts of CH4and N2detected in some inclusions (<4 mol% CH4). Carbonic fluid densities range from 1.18 to 0.57 g/cm3. The highest densities are recorded in superdense carbonic inclusions presenting evidence of the earliest trapping and they correspond to the fluid densities expected for the P–T conditions of the peak of metamorphism in the area previously determined from mineral geothermobarometers. Lower densities of carbonic fluids mainly result from the reequilibration of earlier trapped fluid inclusions during retrograde metamorphism and final uplift of the metamorphic terrane, but a new influx of carbonic fluids during the retrograde event remains possible. Carbonic fluids can be produced in situ from decarbonation reactions in interlayered impure marbles during the prograde event or derived from CO2flushing from underlying basic intrusions. The aqueous fluids present large variations of composition (0.5 to 30 wt.% NaCl equivalent) and densities (1.16 to 0.57 g/cm3). They clearly correspond to post-metamorphic fluids because they mainly occur along microfractures, they do not show any evidence of immiscibility with the carbonic fluids and mixed aquo-carbonic inclusions have not been observed. The percolation of aqueous fluids is related to the Pan-African tectonometamorphic event.