Retentivity of CO 2 in fluid inclusions in mantle minerals
Retentivity of CO 2 in fluid inclusions in mantle minerals
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DOI：
10.1127/0935-1221/2011/0023-2150
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发表时间：
2011-10
影响因子：
2.1
通讯作者：
J. Yamamoto;Kazuhiko Otsuka;H. Ohfuji;H. Ishibashi;N. Hirano;H. Kagi
中科院分区：
文献类型：
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作者：
J. Yamamoto;Kazuhiko Otsuka;H. Ohfuji;H. Ishibashi;N. Hirano;H. Kagi
为了评价地幔矿物中流体包裹体对CO2的保留能力，在常压、fO 2为10 −11 MPa、1000 °C条件下，对两个含CO2包裹体的地幔捕虏体进行了8 d的退火实验。结果表明，在任何被检查的矿物-橄榄石，斜方辉石，单斜辉石，或尖晶石的CO2包裹体的CO2密度没有显着减少。现代地幔岩包体中橄榄石中CO2包裹体的CO2密度低于辉石和尖晶石中的CO2密度。前人的研究结果表明，橄榄石中CO2的低密度是由于在上升岩浆中退火过程中，CO2包裹体周围的橄榄石发生塑性变形所致。这项研究的结果提出的变形机制，所产生的内部压力的硅酸盐矿物中的流体包裹体的基本含义。计算了含CO2包裹体矿物的应力场.结果表明，在主机周围的夹杂物的陡峭的应力梯度。矿物中的这种局部应力引起CO2包裹体周围位错密度的局部上升。斜方辉石中CO2包裹体周围位错分布稀疏，而橄榄石中CO2包裹体周围位错分布密集，说明CO2包裹体中CO2含量低是由于包体在岩浆上升过程中热处理过程中发生塑性变形，导致CO2包裹体体积膨胀所致。在这方面，恒定的CO2密度在退火实验的所有矿物是一个有趣的发现。对于橄榄石，CO2包裹体内部压力的降低或致密位错的相互作用可能抑制CO2包裹体在退火过程中的爆裂或进一步的体积膨胀。而辉石和尖晶石的CO2密度较高且相近，这反映了它们对塑性变形的抵抗能力，也表明它们中CO2包裹体作为地幔捕虏体深度探针的有效性。
To assess the capacity of fluid inclusions in mantle minerals for CO 2 retention, annealing experiments were conducted for two mantle xenoliths with CO 2 inclusions for 8 days at 1000 °C under atmospheric pressure and f O 2 of 10 −11 MPa. The results show no marked decrease in the CO 2 density of the CO 2 inclusions for any examined minerals – olivine, orthopyroxene, clinopyroxene, or spinel. The CO 2 density of CO 2 inclusions in olivine in the present mantle xenoliths is lower than that in pyroxenes or spinel. Results of previous studies indicate that the low CO 2 density in olivine is attributable to plastic deformation of olivine around CO 2 inclusions during annealing in ascending magma. Results of this study present fundamental implications for deformation mechanisms that arise from internal pressure of fluid inclusions in silicate minerals. We calculated the stress field in minerals having a CO 2 inclusion. Results show a steep stress gradient in the host around the inclusion. Such local stress in the mineral induces a local rise in the density of dislocations around the CO 2 inclusions. The orthopyroxene used for this study showed a sparse distribution of dislocations around a CO 2 inclusion, whereas olivine showed dense dislocations around CO 2 inclusions, implying that the low CO 2 density of the CO 2 inclusions in olivine results from volume expansion of the CO 2 inclusions through plastic deformation of the host mineral during annealing of the xenoliths in ascending magma. In this respect, constancy of CO 2 density during the annealing experiments for all minerals is an interesting finding. Regarding olivines, the reduction of internal pressure of the CO 2 inclusions or interaction of the dense dislocations possibly inhibits decrepitation or further volume expansion of the CO 2 inclusions during annealing experiments. However, pyroxenes and spinel show higher and similar CO 2 density, which reflects the resistance to plastic deformation and which indicates the effectiveness of CO 2 inclusions in these minerals as a depth probe for mantle xenoliths.