Plastic flow strength of jadeite and diopside investigated by microindentation hardness tests

Microindentation hardness tests were performed on jadeite and diopside, being end members of the omphacite solid solution series. At temperatures between 300 and 750 °C, the hardness of jadeite ranges from 7.4 to 8.5 GPa, that of diopside from 4.9 to 6.1 GPa. Jadeite is significantly stronger than diopside in the low-temperature plasticity regime. Normalization of the hardness-derived yield stress with respect to the shear modulus considerably reduces the strength contrast. The normalized Peierls stress is identical for jadeite and diopside. This indicates that jadeite and diopside belong to the same isomechanical group. The hardness-derived yield stress for jadeite as well as for diopside is used to estimate flow law parameters for the low-temperature plasticity regime.     

硬玉位错滑移系及流变学特征的研究

本文所研究的硬玉采自Ｓｅｓｉａ－Ｌａｎｚｏ带（阿尔卑斯意大利段）。该带经历了高压低温榴辉岩相变质，其变质温压为５５０℃～６００℃，１．５～１．６ＧＰａ。应用透射电子镜精细研究硬玉单晶的位错特征尚属首次，研究结果表明经天然变形的硬玉单晶中，发育有大量自由位错、位错壁、亚晶粒。自由位错密度大约为１×１０８／ｃｍ２，以刃型位错为主，也发育有少量螺位错。刃位错的伯氏矢量ｂ为［００１］和［１１０］（ｂ＝７．１６Ａ；１／２（ａ＋ｂ）＝６．６Ａ）。     

缅甸硬玉岩区的硬玉化绿辉石岩

绿辉石岩是缅甸硬玉岩区一种新的岩石类型,普遍遭受多期次硬玉化.未发生硬玉化的绿辉石含较高TFeO和CaO,但较低的MgO,按化学成分分类部分已属霓石-普通辉石系列的中间相.这种绿辉石很可能是硬玉质的流体/熔体交代地幔辉石岩类的产物,与主期大规模硬玉岩的结晶、钠质-钠钙质角闪石边和钠铬辉石的形成同期或稍后,是该区第Ⅰ期的硬玉化.沿绿辉石的解理或裂隙交代并伴有充填的硬玉是在相对拉张的构造背景下形成的,是该区第Ⅱ期的硬玉化.切割早期绿辉石和硬玉的充填硬玉细脉可能是最晚一期的硬玉化.硬玉化绿辉石岩的结构与显微构造特征指示了在缅甸硬玉岩区,至少存在不少于3期的硬玉化的交代充填作用.文中讨论了硬玉化物质的可能来源,认为其可能与俯冲板片上的沉积物有密切关系.     

大别山双河和碧溪岭超高压变质岩流体包裹体研究

对大别山双河和碧溪岭含柯石英榴岩和硬玉石英岩进行了详细的流体包裹体研究。根据流体包裹体的成分和盐度的不同,可以划分出至少五种类型不同的气液包裹体;（１）Ｎ２包裹体;（３）高盐度流体包裹体;（３）ＣＯ２包裹体;（４）ＣＯ２－Ｈ２Ｏ包裹体;（５）低盐度流体包裹体。本仅见于含柯石英榴辉岩,而高盐度流体包裹体则几乎存在于所有的榴辉岩和硬玉石英岩中。ＣＯ２包裹体沿榴辉岩中微剪切带分布,或存在于强变形的硬玉石     

翡翠与相似玉石及仿制品的仪器鉴定

翡翠和相似玉石及仿制品肉眼下真假难辨,需借助仪器进行鉴定。常规仪器下的鉴定是根据其相关数据和结构特征判定;用红外光谱仪则是根据光谱图特征识别。通过常规仪器和红外光谱仪两种鉴定方式进行比较,得出红外光谱仪能更完全正确地对各类型玉石进行正确判断。     

Computer modelling of hydrogen defects in the clinopyroxenes diopside and jadeite

Atomistic computer simulation techniques have been employed to model mechanisms of hydrogen incorporation in the clinopyroxenes diopside and jadeite. Calculation of solution reaction energies for the pure phases indicates that hydrogen is most easily incorporated via the formation of [V_Si(OH)₄] ^x hydrogarnet type defects. When components of the two phases are mixed, then solution energies can become exothermic. The substitution of Al for Si in diopside and of Mg or Ca for Al in jadeite, provides favourable routes for hydrogen incorporation, with exothermic values of solution energy. Thus the amount of water present in these minerals in the Earth’s upper mantle will vary with composition. Simulation of IR frequencies associated with O–H stretching at specific defect clusters has also been carried out. An analysis of hydrogen–oxygen bond lengths gives good agreement, although comparison of experimental and calculated IR frequencies are problematic. This is partly due to the complexity of experimental spectra, but may also be due in part to deficiencies in the ability of the model to accurately describe the O–H stretching frequency.     

翡翠评估价的量化探索

由于翡翠评估本身具有现实性、市场性、预测性等特性,传统的评估方法过于依赖评估人员的经验,主观随意性大,难以保证评估结果的客观、科学、公正。针对翡翠价格与其质量因素之间的复杂、不确定关系的特性,我们提出利用特尔斐法来判定各权重之间关系,从而利用数学模型计算出各质量因素之间的权重,以减少由于评估人员主观因素造成评估结果的偏差,使评估人员运用此方法能够迅速、准确、公正的对翡翠估价前期的数据进行量化处理。     

翡翠与相似玉石及仿制品的仪器鉴定

翡翠和相似玉石及仿制品肉眼下真假难辨,需借助仪器进行鉴定。常规仪器下的鉴定是根据其相关数据和结构特征判定;用红外光谱仪则是根据光谱图特征识别。通过常规仪器和红外光谱仪两种鉴定方式进行比较,得出红外光谱仪能更完全正确地对各类型玉石进行正确判断。     

Mechanisms of OH defect incorporation in naturally occurring,hydrothermally formed diopside and jadeite

The IR spectrum of an alpine, hydrothermally formed diopside containing 17 wt ppm H₂O consists of three main OH absorption bands centred at 3647, 3464 and 3359 cm⁻¹. Jadeite from a Californian vein occurrence is characterised by bands at 3616 and 3557 cm⁻¹ and contains about 197 wt ppm H₂O. Based on the pleochroic scheme of the OH absorption bands in diopside, OH defect incorporation models are derived on the basis of fully occupied cation sites and under the assumption of M1 and M2 site vacancies; OH defects replacing O2 oxygen atoms are most common. The less pronounced OH pleochroism and the broad band absorption pattern of jadeite indicate a high degree of OH defect disordering. The pleochroic scheme of the main absorption bands at 3616 and 3557 cm⁻¹ implies partial replacement of O2 oxygen atoms by OH dipoles pointing to vacant Si sites. Under the assumption of M1 and M2 site vacancies, O1–H and O2–H defects are also derivable. OH incorporation modes assuming Si-vacancies should be considered for jadeite-rich clinopyroxenes formed in deep crust and upper mantle regions.     

A possible UHP-eclogite in the Leaota Mts. (South Carpathians) and its history from high-pressure melting to retrograde inclusion in a subduction melange

An unusual eclogite pod containing impure jadeite to omphacite pyroxene with anti-phase domain (APD) visible under the optical microscope is hosted in a medium-grade matrix in the Leaota Massif. Textural relationships support the hypothesis of garnet formation by peritectic reactions involving high-jadeite clinopyroxene, while inclusions entrapped in garnet, mainly a wide range of amphibole compositions, seemingly crystallised from a fluid phase in disequilibrium with the garnet host. Thermobarometric estimates indicate UHP, HT peak conditions (2.8–3.2 GPa, 780–840°C) inconsistent with those of the associated rocks, followed by a complicated exhumation path. The P–T-array of the retrograde path suggests syn-subduction exhumation and tectonic inclusion in a melange with a matrix derived from the accretionary wedge. Partial melting of the subducting slab, which induces tectonic weakening, may be an effective mechanism in detaching and enclosing small eclogite pods in metamorphic terrains.