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61.
Abstract Jadeite‐bearing eclogites and associated blueschists locally crop out in a greenschist facies area at Kuldkourla, near the Akeyazhi River in the western Chinese Tianshan region, northwestern China. Garnet in these metamorphic rocks shows prograde zoning with increasing Mg and decreasing Mn from the crystal center towards the rim, and is divided into Ca‐poor/Fe‐rich core and Ca‐rich/Fe‐poor mantle parts. The garnet cores include the assemblages of (i) jadeite/omphacite (Xjd = 0.34–0.96) + barroisite/taramite; and (ii) omphacite + barroisite/pargasite, with paragonite, epidote, rutile and quartz as major phases with rare albite. The garnet mantles rarely contain inclusions of omphacite, glaucophane, epidote, rutile and quartz. Major matrix phases of the pre‐exhumation stage are omphacite, glaucophane, paragonite, rutile and quartz. These mineral parageneses give pressure (P)‐temperature (T) conditions of 0.9 GPa/390°C?1.4 GPa/560°C for the stage of the garnet core formation, 1.8 GPa/520°C for the stage of the garnet mantle formation, and 2.2 GPa/495°C‐2.4 GPa/535°C for the peak eclogite facies assemblage in the matrix. The estimated P‐T conditions and continuous changes of mineral parageneses imply a counterclockwise P‐T path which is a combination of (i) an early prograde stage of high‐pressure/low‐temperature (HP/LT) blueschist facies and/or LP/LT eclogite facies; (ii) a later prograde stage involving compression with minimal heating; and (iii) a climax‐of‐subduction stage characterized by a slight decrease of temperature with increasing pressure. The negative dP/dT of the latest subduction stage is possibly a record of the following events after a continuous subduction and ridge approach: (i) material migration within the upper part of the subducting slab, which has an inverse thermal gradient caused by ductile flow and/or slab break during subduction; and/or (ii) temporary cooling of the wedge mantle–slab interface by continuous subduction of a relatively cold slab following subduction of a hotter ridge. 相似文献
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63.
傅立叶红外光谱技术在翡翠研究中的应用 总被引:6,自引:1,他引:6
基于透射光谱的差异,用傅立叶红外光谱研究翡翠的矿物组成;分析硬玉、霓石、霓辉石和透辉石等主要矿物,以天然翡翠的特征红外光谱为依据,鉴别市售翡翠的真伪和类别(A、B货);利用红外显微镜作微区透射光谱,鉴别通常难以鉴别的有裂缝及裂缝填充物的翡翠(B货),提出了准确的无损鉴别翡翠的方法。 相似文献
64.
翡翠中的长石及其宝石学意义 总被引:4,自引:0,他引:4
显微镜观测、电子探针分析、X射线粉晶分析和红外光谱分析表明,翡翠中的长石为低温钠长石,分子式为;Na1.15[Al0.99Si2.9708],Δθ1=1.06,Δθ2=1.76,Si/Al=3.0,An和Or几乎为零。钠长石的存在对翡翠的硬度、比重、折射率有一定影响,但对透明度有较大改善,从而提高了翡翠的价值。我们还可以通过纳长石在毛料表皮上的表现,对翡翠赌石内部的透明度作出判断。 相似文献
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66.
Fluid inclusions in coesite-bearing eclogites and jadeite quartzite at Shuanghe, Dabie Shan (China) 总被引:6,自引:0,他引:6
Fluid inclusions in coesite‐bearing eclogites and jadeite quartzite at Shuanghe in Dabie Shan, East‐central China, have preserved remnants of early, prograde and/or peak metamorphic fluids, reset during post‐UHP (ultrahigh‐pressure) metamorphic uplift. Inclusions occur in several minerals (e.g. omphacite & epidote), notably as isolated, primary inclusions in quartz included in various host minerals. Two major fluid types have been identified: non‐polar fluid species (N2 or CO2) and aqueous, the latter is by far the most predominant. Aqueous fluids cover a wide range of salinity, from halite‐bearing brines to low salinity fluids. For non‐polar fluids, few N2 inclusions occur in undeformed eclogite, whereas a number of CO2‐rich inclusions have been found in microshear zones of eclogite or jadeite quartzite in close proximity to marble occurrences. The primary character of N2 and high‐salinity aqueous inclusions indicates that they are remnants from UHP metamorphic fluids and for some there is the distinct possibility that they are ultimately derived from pre‐metamorphic fluids. This conclusion is supported by the preservation, in some samples, of microdomains containing synchronous inclusions of variable salinities, which tend to relate to the chemical composition of the host crystal. Carbonic fluids may be derived from neighbouring rocks, notably marble and carbonate‐bearing metasediments, during post‐metamorphic uplift. During post‐UHP exhumation, a limited decrease of the fluid density has occurred, with formation of new sets of fluid inclusions. Fluid movements, however, remained exceedingly limited, at the scale of the enclosing crystal. 相似文献
67.
有关翡翠A、B、C货鉴定问题的讨论 总被引:1,自引:0,他引:1
翡翠A、B、C货的鉴定需要综合性的考虑,单一方法易出差错,翡翠鉴定首要任务是确定矿物组成,从而确定是否翡翠及翡翠的类型;其次确定是否有人工充填物及人工加色,从而区别A、B、C货。 相似文献
68.
红-黄色翡翠是否经过热处理,其价值相差悬殊。随着市场对红-黄色翡翠的需求增加,鉴别其是否经过热处理是目前宝玉石鉴定的难点和热点问题。通过加热实验,利用红外光谱测试技术对加热前、后的红-黄色翡翠样品的红外光谱进行对比分析。结果表明,加热前、后的红-黄色翡翠样品的红外光谱具有不同的特征,主要表现为硬玉结构中OH的四组吸收峰强弱的变化:(1)吸收峰的强变化是在3 000~4 000 cm-1之间的峰型从加热前呈U型到加热后呈V型;(2)吸收峰的弱变化则是谱线略有改变,出现3 622~3 628 cm-1或3 670 cm-1附近的吸收峰,这些特征可作为红-黄色翡翠是否经过加热处理的辅助性诊断指标。 相似文献
69.
70.
I.S. Bazhan Shin Ozawa M. Miyahara E. Ohtani K.D. Litasov 《Russian Geology and Geophysics》2017,58(1):12-19
The Novosibirsk H5/6 ordinary chondrite has signs of shock metamorphism, such as dark shock-melt veins (SMVs) crossing the chondrite host rock. The plagioclase composition grains (Ab78An14Or7) with jadeite were found in the host-rock fragments inside the SMVs. Jadeite has an unusual radial-concentric spherulite-like microtexture. The spherulite-like jadeite formed from the molten plagioclase grain under high-pressure and high-temperature conditions during an impact event. The crystallization was accompanied by sodium-potassium differentiation between coexisting jadeite and residual melt. The PT-conditions of jadeite formation were estimated to be 3-14 GPa and 1400-2150 °C. Jadeite crystallization, Na-K differentiation, and the pressure-temperature estimates of jadeite formation in the Novosibirsk chondrite are very close to those in the Chelyabinsk LL5 chondrite. The spherulite-like microtexture and jadeite-glass coexistence, most likely, point to a high cooling rate of the SMVs at the pressure release stage of the metamorphic process. 相似文献