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Oxygen‐isotope compositions of kyanite, andalusite, prismatic sillimanite and fibrolite from the Proterozoic terrane in the Truchas Mountains, New Mexico differ from one another, suggesting that these minerals did not grow in equilibrium at the Al2SiO5 (AS) polymorph‐invariant point as previously suggested. Instead, oxygen‐isotope temperature estimates indicate that growth of kyanite, andalusite and prismatic sillimanite occurred at c. 575, 615 and 640 °C respectively. Temperature estimates reported in this paper are interpreted as those of growth for the different AS polymorphs, which are not necessarily the same as peak metamorphic temperatures for this terrane. Two distinct temperature estimates of c. 580 °C and c. 700 °C are calculated for most fibrolite samples, with two samples yielding clear evidence of quartz‐fibrolite oxygen‐isotope disequilibrium. These data indicate that locally, and potentially regionally, oxygen‐isotope disequilibrium between quartz and fibrolite may have resulted from rapid fibrolite nucleation. Pressures of mineral growth that were extrapolated from oxygen‐isotope thermometry results and calculated using petrological constraints suggest that kyanite and one generation of fibrolite grew during M1 at 5 kbar, and that andalusite, prismatic sillimanite and a second generation of fibrolite grew during M2 at 3.5 kbar. M1 and M2 therefore represent two distinct metamorphic events that occurred at different crustal levels. The ability of the AS polymorphs to retain δ18O values of crystallization make these minerals ideal to model prograde‐growth histories of mineral assemblages in metamorphic terranes and to understand more clearly the pressure–temperature histories of multiple metamorphic events. 相似文献
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涂氏磷钙石:一种磷酸盐高压相新矿物 总被引：2，自引：0，他引：2
在随州陨石冲击熔脉中发现了一种磷酸盐新矿物，它是白磷钙石的高压多形，经国际矿物协会新矿物和矿物命名委员会批准，定名为涂氏磷钙石(Tuitel)。该矿物属三方晶系，空间群为R-3m，a=5．258(1)A，c=18．727(3)A。一轴晶，正光性，ε=1．706(3)，ω=1．701(4)。化学式为(Ca2.31Mg0.29)2.80Na0.28(P1.01O4)2，简化式为Ca3(PO4)2。X射线粉晶衍射的强谱线有：2．628(100)、2．89l(80)、1．945(47)、1．730(25)和1．567(22)。根据与其共生的其他高压相矿物形成的温压条件和人工合成实验的结果，推定涂氏磷钙石形成的压力为12～23GPa，温度为l400到2000℃。该新矿物以中国矿物岩石地球化学学会的创建人和首任会长涂光炽的姓氏命名。 相似文献
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The occurrence of γ-phase, a high-pressure polymorph of olivine (α-phase), in the shock veins of Sixiangkou chondrite was
due to a greater cooling rate (> 10 000°C·s-1) in the veins. Because γ-phase partially reverted to β-phase and no back-transformation from β-phase to α-phase took place,
the shock veins of Peace River chondrite with a cooling rate of 1 000–2 000δC·s-1 contain a great amount of β-phase. In the shock veins of Mbale chondrite with a cooling rate of <500°C·s-1, the majority of γ-phase reverted to α-phase. The heat dissipation in shock veins took place after a stage of shock compression
of chondrite parent body, and the parent body was broken into fragmental pieces. Cooling rate in the shock veins constrained
the back-transformations of (Mg, Fe)2SiO4 high-pressure polymorphs.
Project of Chen and Xie supported by the National Natural Science Foundation of China (Grant No. 496720981, Natural Science
Foundation of Guangdong Province (Grant No. 960500), and the Science Foundation of Academia Sinica for the returned scholars. 相似文献
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山东南墅石墨矿是在角闪岩相区域变质作用并叠加长英质混合岩化下形成的变质矿床。本文首次定量地研究了表征石墨晶体结构完善程度的两个要素,即石墨化程度(μ)和石墨菱面体多型(R_h)含量。在此基础上,进一步分析了它们与矿石类型、变质相的相关关系。石墨晶体结构的系统研究,将为石墨的工业利用、石墨新用途的开拓和石墨矿物学的研究提供有用的资料。 相似文献