Aqueous fluid connectivity and chemical transport in clinopyroxene-rich rocks
Aqueous fluid connectivity and chemical transport in clinopyroxene-rich rocks
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DOI：
10.1016/0012-821x(93)90133-t
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发表时间：
1993-05
影响因子：
5.3
通讯作者：
E. Watson;A. Lupulescu
中科院分区：
文献类型：
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作者：
E. Watson;A. Lupulescu
为了评价流体辅助化学输运在深部富辉石岩石中的有效性，在90 0°-95 0°C和1.5 Gpa的压力下进行了两种类型的合成单斜辉石实验：(1)在水溶液(水NaC l、CaCl2或CO2)存在下对铁榴石(CaMg0.4Fe0.5 4Mn0.0 6Si2O6)或透辉石(CaMg0.94Fe0.0 6Si2O6)粉末进行热处理，以产生近平衡的流体/晶体二面角(θS)；(2)扩散耦合实验，将富Fe单斜辉石(铁榴石)置于一个含水圆柱体与富镁斜方辉石(透辉石)之间。还进行了无流体单斜辉石和单斜辉石晶体的“控制”扩散实验。二面角实验一致地产生了65-69°的中值表观θ值，远高于60°的夹断值，并且与添加剂氯化钠、氯化钙和二氧化碳无关。然而，在所有情况下，θ的频率分布都足够宽，足以暗示中位数两侧的真实θS的范围。毛孔边缘频繁的晶体刻面也使纹理变得复杂。用0、0.6、1.3、2.7、4.0和8.0vol%H2O(在runPandT时)进行的扩散偶实验表明，除了最富流体(8%)的偶以外，所有的偶都没有Fe=Mg互扩散。这一结果与测定结果一致，表明对于地质上真实的流体丰度，单斜辉石岩中的水流体形成孤立的(不相互连通的)孔隙。这一结论表明，在力学平衡条件下，富辉石岩石中的水流体在大于颗粒尺度的化学运移中不起作用。这一结果还允许水作为一个独立的(但被捕获的)相被深度俯冲，超出角闪石的稳定极限。
In order to assess the efficacy of fluid-assisted chemical transport in deep-seated, pyroxene-rich rocks, two types of experiment involving synthetic clinopyroxenites were performed at 900°–950°C and 1.5 GPa: (1) annealing of ferrosalite (CaMg0.4Fe0.54Mn0.06Si2O6) or diopside (CaMg0.94Fe0.06Si2O6) powder in the presence of aqueous fluids (water NaCl, CaCl2or CO2) to produce near-equilibrium fluid/crystal dihedral angles (θs), and (2) diffusion-couple experiments in which an H2O-bearing cylinder of Fe-rich clinopyroxenite (ferrosalite) was placed against one of Mg-rich clinopyroxenite (diopside). ‘Control’ diffusion experiments on fluid-free clinopyroxenite and on single clinopyroxene crystals were also carried out. The dihedral angle experiments consistently yielded median apparent θ values (i.e., in 2D section) of 65–69°, well above the ‘pinch-off’ value of 60° and independent of additives NaCl, CaCl2and CO2. In all cases, however, the θ frequency distributions were broad enough to suggest a range of real θs on either side of the median. The textures were also complicated by frequent crystal faceting at pore margins. The diffusion-couple experiments, carried out with 0, 0.6, 1.3, 2.7, 4.0 and 8.0 vol% H2O (at runPandT) showed no Fe = Mg interdiffusion for all but the most fluid-rich (8%) couple. This result is consistent with the determinations in showing that, for geologically realistic fluid abundances, aqueous fluids in clinopyroxenite form isolated (noninterconnected) pores. This conclusion implies that aqueous fluids play no role in larger-than-grain-scale chemical transport in pyroxene-rich rocks under conditions of mechanical equilibrium. The results also allow the possibility that water can be deeply subducted as a separate (but trapped) phase beyond the stability limit of amphibole.