A simple model for the pressure preservation index of inclusions in diamond
A simple model for the pressure preservation index of inclusions in diamond
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金刚石内含物保压指数的简单模型
DOI：
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发表时间：
2003
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通讯作者：
L. Barron
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文献类型：
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作者：
L. Barron
摘要金刚石-矿物包裹体对的等体积轨迹发生在两种矿物的相对体积对压力-温度（P-T）条件变化的响应相同的地方。用该体系的简单线性模型对30种可能的包裹体矿物进行了评价。包裹体（地球表面的金刚石）上的残余压力可以通过使用等体积轨迹的斜率将金刚石形成的条件外推到0 °C来估计。残余压力可以是正的（等体积线低于地层压力），也可以是负的（等体积线高于地层压力），后者表明包裹体已经完全减压。当按照等体积斜率增加的顺序放置时，该矿物列表定义了压力保持指数（PPI）。已发表的工作证实，该模型是定量的钻石形成压力为50 Kb和定性超越。10种矿物被确定为关键的PPI指标-按PPI降序排列，它们是：透长石、柯石英、白云石、（尖晶石、石榴石、透辉石、锆石）、镁钨铁矿、尖晶石、Mg0.9Fe0.1SiO3钙钛矿。在大多数金刚石形成条件下，前三种矿物的包裹体将保持较高的残余压力，而后三种矿物将完全溶解。括号中的中心四种矿物将具有高度可变的响应，因为它们的等体积轨迹通过金刚石形成条件。初步计算表明，流体包裹体（H2O，CO2）落在或接近列表的顶部。对于地球表面含包裹体的金刚石，该模型预测：（1）残余压力;（2）包裹体在交付过程中的围压;（3）高压多晶型体的稳定性;（4）保留与放射性年龄重置;（5）适合于根据测量的残余压力确定形成条件的矿物;（6）能够稳定微金刚石包裹体的那些矿物;和（7）超临界流体保存大多数矿物中的微金刚石包裹体。
Abstract The isovolume locus for a diamond-mineral inclusion pair occurs where the relative volumes of the two minerals respond identically to changes in pressure-temperature (P-T) conditions. Thirty potential inclusion minerals have been assessed with a simple linear model of this system. The remnant pressure on the inclusion (diamond at the Earth’s surface) can be estimated by extrapolating the conditions of diamond formation to 0 °C using the slope of the isovolume locus. Remnant pressures can be positive (isovolume locus lower than formation pressure) or negative (locus higher than formation pressure), the latter indicating the inclusion has decompressed completely. When placed in order of increasing isovolume slope, this mineral list defines a pressure preservation index (PPI). Published work confirms that the model is quantitative up to diamond formation pressures of 50 Kb and qualitative beyond. Ten minerals are identified as key PPI indicators-in decreasing order of PPI they are: sanidine, coesite, dolomite, (sphene, garnet, diopside, zircon), magnesiowüstite, spinel, Mg0.9Fe0.1SiO3 perovskite. For most diamond formation conditions, inclusions of the first three minerals will retain high remnant pressures, whereas the last three will decompress completely. The central four minerals in brackets will have a highly variable response because their isovolume loci pass through diamond formation conditions. Preliminary calculations suggest that fluid inclusions (H2O, CO2) fall at or near the top of the list. For inclusion-bearing diamonds at the Earth’s surface, the model predicts: (1) remnant pressures; (2) confining pressure on inclusion during delivery; (3) the stability of high-pressure polymorphs; (4) retention vs. resetting of radiometric ages; (5) those minerals suited for determining the conditions of formation based on measured remnant pressure; (6) those minerals capable of stabilizing a microdiamond inclusion; and (7) that supercritical fluids preserve inclusions of microdiamond in most minerals.