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61.
62.
Jan Marten Huizenga Alexandra Crossingham Fanus Viljoen 《Comptes Rendus Geoscience》2012,344(2):67-76
Previous research has shown that the Kaapvaal lithospheric mantle is generally reduced and characterised by a decreasing redox state with increasing depth. As a consequence, C-O-H fluids in the Kaapvaal lithospheric mantle are dominated by H2O, CH4, and C2H6. Thermodynamic calculations demonstrate that diamond precipitation from such a fluid during ascend is possible as it is exposed to a more oxidised environment and both CH4 and C2H6 are oxidised. However, the calculations also demonstrate that the diamond precipitation potential from such a fluid decreases when: (1) the mantle is either more reduced or oxidised compared to the Kaapvaal mantle, or (2) the change in temperature with pressure is smaller compared to that of the Kaapvaal mantle. Therefore, the presence of reduced mantle fluid species and a generally decreasing oxygen fugacity with increasing depth do not necessarily warrant diamond precipitation from a rising reduced fluid. 相似文献
63.
S. K. Simakov 《Contributions to Mineralogy and Petrology》2006,151(3):282-296
Pressure–Temperature-
conditions and fluid compositions estimated for mineral parageneses from inclusions in diamonds, diamond-bearing and diamond-free
xenoliths using a garnet–clinopyroxene–silica oxygen barometer data indicate that the upper mantle is zoned, with a relatively
oxidized lithosphere and a reduced asthenosphere. Calculations in the C–O–H system indicate that eclogite inclusions within
diamonds and xenoliths have formed mainly in equilibrium with water-rich fluids. 相似文献
64.
从岩筒地质特征、组成岩石和矿物的成因类型,对岩浆源区温压条件作出判断,并与含金刚石金伯利岩筒对比,认为该区火山角砾岩筒不完全具备金刚石成矿温压条件。 相似文献
65.
辽南50号金伯利岩管金刚石的包裹体类型一直被认为是以超镁铁岩组合为主。最近,在同一岩管中发现一颗金刚石中有两种组合类型矿物共生:橄榄石,为超镁铁岩型;石榴石,绿辉石,为榴辉岩型组合。化学成分分析还表明,同一矿物的不同颗粒化学成分没有明显变化。根据石榴石与绿辉石的共生组合关系,钙、镁和铁之间的交换,计算其平衡温度为1203℃,压力为5×10 ̄9Pa。超镁铁岩与榴辉岩包裹体共生,表明该金刚石成生环境的复杂性。很可能是地幔动力学过程或者是幔源岩浆多期多相导致金刚石成生环境的迅速变化。 相似文献
66.
西藏罗布莎橄榄岩与中国大陆科学钻探主孔(CCSD-MH)榴辉岩中金刚石的红外特征初探 总被引:5,自引:1,他引:4
大别苏鲁超高压变质带上的大陆科学钻探主孔(CCSD-MH)中榴辉岩中的金刚石形成于大陆深俯冲作用过程,西藏雅鲁藏布江缝合带罗布莎蛇绿岩铬铁矿中的金刚石来自深部地幔,两者的形成背景和机制可能不同.本文对两地的金刚石样品开展了傅立叶变换红外光谱(FT-IR)定性分析.结果表明,西藏罗布莎金刚石样品为ⅠaA型;而CCSD-MH金刚石为ⅠaAB型,既表明其杂质氮的聚集形式和演化路径上存在着差异.红外光谱特征不仅仅表明两者属天然金刚石常见类型,并且超高压变质带中的金刚石形成时间可能更久远. 相似文献
67.
The popularity of the work Guns, germs and steel (GGS) has served to bring the question of human–environment connections once again to the forefront of popular thought. We assert that the recent success of GGS represents both a persistence of environmental determinist logic and a contemporary trend that privileges the environment as the primary influence on human–environment relationships. The historical development of the human–environment field is reviewed from the cultural and political ecology (CAPE) perspective, with particular attention to illustrating the varying emphasis between humans and their environment. GGS is situated within this developing field through a critical analysis of the arguments and methods forwarded by Jared Diamond. The book is found to mirror earlier environmental determinism by failing to take into account many of the advances in human–environmental thought since the early twentieth century. Its popular success suggests the pitfalls of failures to acknowledge the complex, intertwined and indivisible relationship that exists among humans and their environment. Furthermore, there is evidence that the environmental determinism espoused in GGS has caught the attention of international development policymakers potentially influencing future outlays of aid and assistance to the developing world. These conclusions raise cautionary flags against repeating past theoretical mistakes by accepting simplistic, causal explanations based largely on a deterministic conception of the natural environment. 相似文献
68.
Sonja Aulbach Steven B. Shirey Thomas Stachel Steven Creighton Karlis Muehlenbachs Jeff W. Harris 《Contributions to Mineralogy and Petrology》2009,157(4):525-540
Sulfide inclusions in diamonds from the 90-Ma Jagersfontein kimberlite, intruded into the southern margin of the Kaapvaal
Craton, were analyzed for their Re–Os isotope systematics to constrain the ages and petrogenesis of their host diamonds. The
latter have δ13C ranging between −3.5 and −9.8‰ and nitrogen aggregation states (from pure Type IaA up to 51% total N as B centers) corresponding
to time/temperature history deep within the subcontinental lithospheric mantle. Most sulfides are Ni-poor ([Ni + Co]/Fe = 0.05–0.25
for 15 of 17 inclusions), have elevated Cu/[Fe + Ni + Co] ratios (0.02–0.36) and elemental Re–Os ratios between 0.5 and 46
(12 of 14 inclusions) typical of eclogitic to more pyroxenitic mantle sources. Re–Os isotope systematics indicate two generations
of diamonds: (1) those on a 1.7 Ga age array with initial 187Os/188Os (187Os/188Osi) of 0.46 ± 0.07 and (2) those on a 1.1 Ga array with 187Os/188Osi of 0.30 ± 0.11. The radiogenic initial Os isotopic composition for both generations of diamond suggests that components with
high time-integrated Re–Os are involved, potentially by remobilization of ancient subducted oceanic crust and hybridization
of peridotite. A single sulfide with higher Os and Ni content but significantly lower 187Os/188Os hosted in a diamond with less aggregated N may represent part of a late generation of peridotitic diamonds. The paucity
of peridotitic sulfide inclusions in diamonds from Jagersfontein and other kimberlites from the Kaapvaal craton contrasts
with an overall high relative abundance of diamonds with peridotitic silicate inclusions. This may relate to extreme depletion
and sulfur exhaustion during formation of the Kaapvaal cratonic root, with the consequence that in peridotites, sulfide-included
diamonds could only form during later re-introduction of sulfur. 相似文献
69.
70.
利用数字摄像和计算机技术,对金钢石的粒径等参数进行了测试,对数据的分析揭示了金刚石粒径,等效短径和平均网径之间的内在关系,提出了以平均网径为基础,建立金刚石粒径标准的方法。 相似文献