SYNTHESIS OF THE CLINOPYROXENES JOIN CAMGSI2O6-NAALSI2O6 FOR JEWELRY

Clinopyroxenes of the join CaMgSi2O6(diopside)-NaAlSi2O6 (jadeite) were synthesized in the temperature range 800-1900 degrees C and under varying pressure, 10-55 kbar. The stability regions of various compositions of diopside-jadeite have been established experimentally using different compositions of glass materials: stoichiometric composition NaAlSi2O6, 0.1CaMgSi(2)O(6)-0.9NaAlSi(2)O(6), 0.2CaMgSi(2)O(6)0.8NaAlSi(2)O(6), 0.3CaMgSi(2)O(6)-0.7NaAlSi(2)O(6), and 0.4CaMgSi(2)O(6)-0.6NaAlSi(2)O(6). Unit cell parameters of synthetic clinopyroxenes with the above compositions were determined. The physical properties, such as hardness, toughness, density, and refractive index, etc., were also measured. The results show that synthetic clinopyroxenes have the same properties as the natural one. The gem quality of diopside-jadeite clinopyroxenes was achieved by synthesised on the basis of the above experiments. Various colouring agents, such as Cr2O3, Co2O3, NiO2, Fe2O3, TiO2, MnO, CuO, and their combinations, FeO-Cr2O3, etc., were added to obtain the different colours of gem. In addition, small amounts of the rare-earth oxides, such as CeO2, Nd2O3, Sm2O3, Dy2O3, Eu2O3, Er2O3, Pr6O11, Lu2O3 and CuO-Eu2O3, Co2O3Nd2O3, etc., were also added to produce fluorescent clinopyroxenes for jewellery.

Mineral chemistry and its genetic significance of olivine in Cenozoic basalts from the South China Sea

We dredged lots of Cenozoic basalts from areas covered from the northern sub-slope to the southern sub- slope of the South China Sea. Based on the study on mineral chemistry of clinopyroxenes in these Cenozoic hasalts, this paper indicates that pyroxenes are mostly enstatite and a few of augite, sahlite and Ca-rich pyroxene. Pyroxene microlite has higher content in, Ca, Ti and Fe than pyroxene phenocryst, it may reflect that the evolution trend of host magma of pyroxene is coincidence with that of alkali rock series. The depth of magma chambers which calculated from equilibrium temperatures and pressures between clinopyroxene and melt are as follows, that of magma of tephrite is about 49km, that of magma of trachybasalt is about 25km, and that of magma of basalt is about 15km. Correspondingly, Equilibrium temperatures( K) of three types rocks mentioned above gradually decrease from 1535 1498 to 1429 to 1369. By using discriminant plot which developed from pyroxene and alkali discriminant diagram of host rock, Cenozoic basalt from the South China Sea belongs to intraplate alkali basalt. The results suggest that alkali basalt series in the study area may be the products of continuous evolution of mantle plume, which result from some physical and chemistry process including partial melting and fractional crystallization of mantle plume during the course of its ascent to the surface.

青岛晚白垩世岩石圈结构特征：劈石口晚白垩世基性脉岩及其捕虏体提供的证据

The occurrence of Late Cretaceous mafic dykes and their entrained peridotite and granulite xenoliths as well as clinopyroxene xenocrysts in the Qingdao region provide us a precious opportunity to unveil the nature and characteristics of the Late Mesozoic lithospheric mantle and lower crust beneath the Jiaodong region, and the change of the magma sources. These studies are of important and significant for understanding the lithospheric evolution in the eastern North China Craton. There were two periods of magma activities in Late Mesozoic in Qingdao Laoshan region, one was around 107Ma in the Early Cretaceous and the other around 86Ma in the Late Cretaceous according to the whole rock K-Ar age determination. The Early Cretaceous mafic dykes and the Late Cretaceous mafic dyke (i.e. Pishikou mafic dike) have completely different geochemical characteristics. The Early Cretaceous mafic dykes are enriched in LILE, strongly depleted in HFSE (Nb, Ta, Zr, Hf) and characterized by the highly radiogenic Sr and Nd isotopic compositions. These geochemical features indicate that the Early Cretaceous mafic dykes were derived from an enriched lithospheric mantle. In contrast, the Late Cretaceous mafic dyke is enriched in LILE, without HFSE depletion (Nb, Ta, Zr, Hf) and has less radiogenic Nd and Sr isotopic compositions. These geochemical features indicate that the Late Cretaceous mafic dyke was derived from the asthenosphere modified by subducted pelagic sediment contamination. The intrusive age of the Late Cretaceous mafic dyke provides further information for the termination of the lithosphere thinning for the eastern North China Crtaon. Pishikou Late Cretaceous mafic dyke contains abundant peridotitic xenoliths, granulite xenoliths and clinopyroxene xenocrysts. The peridotitic xenoliths can be divided into two types: high Mg# peridotites and low Mg# peridotites, according to their textural and mineral features. The high-Mg# peridotites have high Fo (up to 92.2) olivines and high Cr# (up to 55) spinels. The clinopyroxenes in the high# peridotites are rich in Cr2O3 and poor in Al2O3. The low-Mg# peridotites are typified by low Mg# (Fo <90) in olivines and low Cr# (Cr# <0.14) in spinels. The clinopyroxenes in the low-Mg# peridotites are rich in Al2O3 and Na2O and poor in Cr2O3. These two type peridotites have similar equilibrated temperatures of 950C-1100C. The Clinopyroxenes in the high-Mg# peridotites generally have high and variable REE contents (REE = 5.6-84 ppm) and LREE-enriched chondrite-normalized patterns ((La/Yb)N>1). In contrast, the clinopyroxenes in the low-Mg# peridotites have low REE contents (REE = 12 ppm) and LREE-depleted patterns ((La/Yb)N<1). The textural, mineral and elemental features of the low-Mg# peridotites are similar to those of the low-Mg peridotites from the Junan, representing the newly-accreted lithospheric mantle. However, the mineralogical and petrological features of the high-Mg# peridotites are similar to those of the high-Mg# peridotites from the Junan region, representing samples from the old refractory lithospheric mantle that was strongly and multiply affected by melts of different origins Late Cretaceous mafic dike in the Qingdao region also contains two types of granulite xenoliths according to the mineral constituents: the pyroxene-rich granulites and the plagioclase-rich granulites. Equilibrated temperatures calculated from the cpx-opx geothermometers are in a range of 861C - 910C for the pyroxene-rich granulites and of 847C - 890C for the plagioclase-rich granulites. The equilibrated pressure for the plagioclase-rich granulites is in a range of 9.9-11.7 kbar. Combined with the results of the peridotitic xenoliths, a 40C temperature gap exists between the peridotite and the granulite. The petrological Moho was 33~36 km at depths, broadly consistent with the seismic Moho estimated from the geophysical data. This indicates that there was no obvious crust-mantle transition zone in the Qingdao region in the Late Mesozoic. Pishikou Late Cretaceous mafic dyke entrained lots of clinopyroxene xenocrysts which are characterized by the chemical zoning. According to the zoning features, two types of clinopyroxene xenoliths can be classified, the normal zoning and the revise zoning. The normally-zoned clinopyroxene xenocrysts have LREE-depleted REE patterns in the cores. In contrast, the revisely-zoned clinopyroxenes have LREE-enriched REE patterns in the cores. According to the rim and core compositions of xenocrysts, all the rims are balanced with the host magma. Meanwhile, the origins of the cores were complicated, in which the normally-zoned clinopyroxenes were derived form the lithospheric mantle and some of the reversely-zoned clinopyroxnes were originated from the lower crust. Other revisely-zoned clinopyroxenes had experienced complex geological evolution and need to be further investigated. According to the above results, a simplified lithospheric profile has been established beneath the Qingdao region and a constraint on the nature and characteristics of the lithospheric mantle and lower crust has been made.

西秦岭新生代火山岩中的地幔捕虏体和捕虏晶研究

Western Qinling, a conjunction region of the North China Craton, the Yangtze Craton and the Tibetan Plateau, has very complicated history of geologic and tectonic evolution. Previous studies mainly focus on tectonics and petrology of volcanic rocks in the western Qinling. Therefore, little is known about the Cenozoic lithospheric mantle beneath the western Qinling. Mafic, ultramafic and/or alkaline volcanic rocks and their entrained mantle peridotitic xenoliths and xenocrysts are known as samples directly from the lithospheric mantle. Their petrological and geochemical characteristics can reflect the nature and deep processes of the lithospheric mantle. Cenozoic volcanic rocks in the western Qinling contain abundant mantle xenoliths and xenocrysts, which provide us an opportunity to probe the lithospheric mantle beneath this region and a new dimension to insight into geologic evolution. Cenozoic volcanic rocks (7-23 Ma) from the western Qinling are sparsely distributed in the Lixian-Dangchang-Xihe Counties, Gansu Province, China. Volcanic rocks contain plenty of mantle-derived xenoliths, including spinel lherzolites with subordinate wehrlite, dunite, olivine websterite, clinopyroxenite and garnet lherzolite, and few olivine, clinopyroxene and spinel xenocrysts. These peridotitic xenoliths show clear deformed textures and their major minerals show excellent orientation. Thus, these peridotites are typical deformed peridotites. Olivine xenocrysts have clearly-zoned textures. The peridotitic xenoliths can be divided into two groups based on their compositions, namely, the H-type and L-type. The H-type peridotites are characterized by high Fo (>90) in olivines in which fine-grained ones have higher Fo than the coarse grains, low CaO (<20 %) in clinopyroxenes, high Cr# (>40) in spinels and high equilibration temperatures. They may represent the refractory lithospheric mantle. In contrast, the L-type peridotites contain low Fo (<90) olivines (with lower Fo in fine-grained olivines), high CaO (>20 %) clinopyroxenes, low Cr# (<20) spinels and low equilibration temperatures. They experienced low degree of partial melting. The Cenozoic lithospheric mantle beneath the western Qinling was refractory in major element compositions based on the mineral compositions of xenoliths and xenocrysts and experienced complicated deep processes. The lithospheric mantle was modified by shear deformation due to the diapirism of asthenosphere and strong tectonic movements including the collision between North China Craton and Yangze Craton and the uplift of Tibetan Plateau, and then underwent metasomatism with a hydrous, Na, Ti and Cr enriched melt.

华北克拉通新生代玄武岩携带的地幔橄榄岩Fe同位素地球化学及含金云母地幔岩岩石学研究

In recent years, thanks to the improvement of analytical methods and the use of MC-ICP-MS, Fe isotope can be measured precisely. Fe isotope shows considerable variation both in biological and inorganic processes (from low T to high T) in nature, Therefore, Fe isotope has become one of the exciting frontier sciences and has favorable prospects of the application to the geosciences and life sciences. Based on a comprehensive review of available references in the related field, this study focuses on the development of techniques for high-precision measurement of iron isotope using MC-ICP-MS, and application of the techniques developed to study the Fe isotopes as well as major and trace element compositions of minerals (Ol, Opx, Cpx and Sp) from spinel peridotitic xenoliths from Cenozoic alkaline basalts to investigate Fe isotopic features of the lithospheric mantle beneath the North China Craton. The minerals from these xenoliths are similar to those off-cratonic peridotites world-wide, but are remarkably different from those on-cratonic peridotites and clinopyroxenes from these spinel lherzolites exhibit two types of chondrite-normalized REE patterns i.e. LREE-depleted and flat or spoon-shaped. It is noted that total abundances of REE in clinopyroxenes from these peridotites show a broad negative correlation with Cr# numbers of Cpx and Sp. The Fe isotope results show that the spinel peridotitic xenoliths have small but distinguishable Fe isotopic variations in minerals (generally Ol < Opx < Cpx) and samples, and the isotopic range in spinel is relatively large. Positive linear relationship with the ε57Fecpx/ε57Feopx ratio close to one unit has been observed between Fe isotopes of coexistent Opx and Cpx, indicating that the Cpx and Opx have generally reached Fe isotopic equilibrium. However, Fe isotopes between the Ol and Sp show apparent disequilibrium. The broadly negative correlation between mineral Fe isotopes and oxygen fugacity (fo2), metasomatic indexes such as spinel Cr#, (La/Yb) N and (La/Sm) N ratios of clinopyroxenes suggest that Fe isotopic variations in different minerals and peridotites were probably produced by melt-peridotite interaction. This study further confirms the previous observation that the lithospheric mantle has distinguishable and heterogeneous Fe isotopic variations at a scale of xenoliths. Mantle metasomatism that induces the interaction of the lithospheric mantle peridotite with metasomatic agent is a most potential mechanism for the Fe isotope fractionation in mantle peridotites. Therefore, Fe isotope could be a new and powerful tool to probe the evolution of the lithospheric mantle. We also report mineral compositions, clinopyroxene trace element concentrations and Sr-Nd isotopes for newly-discovered phlogopite-bearing spinel lherzolite and olivine clinopyroxenite xenoliths from three different localities （Hannuoba, Hebei Province; Jining Sangyitang, Inner Mongolia; Hebi, Henan Province）of the North China Craton. Systematic comparisons with phlogopite-free spinel lherzolite xenolith from the same locality reveals that the phlogopite-bearing peridotitic xenoliths have relatively higher Al2O3, CaO, Na2O, K2O, TiO2 contents and lower MgO contents than those phogopite-free counterparts. The former also has higher LREE concentrations, but relatively less radiogenic Sr-Nd isotopic ratios. This demonstrates that mantle metasomatism can not only enrich the basaltic components and trace element concentrations, but also make a decrease in Mg# of the peridotites and olivines and a relative depletion in Sr-Nd isotopes. 87Rb/86Sr-87Sr/86Sr isochrons of the phlogopite-bearing xenoliths indicate that mantle metasomatism happened in the Mesozoic and/or Cenozoic time. The metasomatic agent was derived from the asthenosphere. The result also manifests that the widespread similarity of the geochemical features such as major and trace elements and isotopic compositions in the Cenozoic lithospheric mantle beneath the North China Craton to those “oceanic” lithospheric mantle could be as a result of the ubiquitous presence of the interaction between the old refractory peridotites and the infiltrated asthenospheric melt, rather than the actually newly-accreted lithospheric mantle.

大别山硬玉石英岩带中的水

The Dabie Mountains is a collisional orogenic belt between the North China and Yantze Continental plates. It is the eastern elongation of the Tongbai and Qingling orogen, and is truncated at its east end by the Tan-Lu fault. Jadeite-quartzite belt occurs in the eastern margin of UHPMB from the Dabie Mountains. Geochemical features indicate that the protoliths of the jadeite-quartzite and associated eclogite to be supracrustal rocks. The occurrence of micro-inclusions of coesite in jadeite and garnet confirmed that the continental crust can be subducted to great depth (8 0-100km) and then exhumed rapidly with its UHP mineral signature fairly preserved. Therefore, study of UHP jadeite-quartzite provides important information on subduction of continental crustal rocks and their exhumation histories, as well as the dynamics of plate tectonic processes at convergent margins. The purpose of this paper is to investigate the presence of hydrous component in the jadeite-quartzite belt, significant natural variations in the hydrous component content of UHP minerals and to discuss the role of water in petrology, geochemistry and micro-tectonic. On the basis of our previous studies, some new geological evidences have been found in the jadeite-quartzite belt by researches on petrography, mineralogy, micro-tectonic, hydrous component content of UHP minerals and combined with the study on rheology of materials using microprob, ER, TEM. By research and analysis of these phenomenona, the results obtained are as follows: 1. The existence of fluid during ultra-high pressure metamorphic process. Jadeites, omphacite, garnet, rutile, coesite and quartz from the jadeite-quartzite belt have been investigated by Fourier transform infrared spectrometer and TEM. Results show that all of these minerals contain trace amount of water which occur as hydroxyl and free-water in these minerals. The two-type hydrous components in UHP minerals are indicated stable in the mantle-depth. The results demonstrated that these ultra-high pressure metamorphic minerals, which were derived from continental crust protoliths, they could bring water into the mantle depth during the ultra-high pressure metamorphism. The clusters of water molecules within garnet are very important evidence of the existence of fluid during ultra-high pressure metamorphic process. It indicated that the metamorphic system was not "dry"during the ultra-high pressure stage. 2.The distribution of hydrous component in UHP minerals of jadeite-quartzite. The systematic distribution of hydrous components in UHP minerals are a strong indication that water in these minerals, are controlled by some factors and that the observed variations are not of a random nature. The distribution and concentration of hydrous component is not only correlated with composition of minerals, but also a function of geological environment. Therefore, the hydrous component in the minerals can not only take important part in the UHP metamorphic fluid during subduction of continental crustal rocks, but also their hydroxyl transported water molecules with decreasing pressure during their exhumation. And these water molecules can not only promote the deformation of jadeite through hydrolytic weakening, but also may be the part of the retrograde metamorphic fluid. 3.The role of water in the deformed UHP minerals. The jadeite, omphacite, garnet are strong elongated deformation in the jadeite-quartzite from the Dabie Mountains. They are (1) they are developed strong plastic deformation; (2) developed dislocation loop, dislocation wall; (3) the existence of clusters of water molecular in the garnet; and (4) the evolution of micero-tectonic from clusters of water molecular-dislocation loop in omphacite. That indicated that the water weakening controlled the mechanism of deformed minerals. Because the data presented here are not only the existence of clusters of water molecular in the garnet, but also developed strong elongation, high density of dislocation and high aspect ratios, adding microprobe data demonstrate the studied garnet crystals no compositional zoning. Therefore, this indicates that the diffusion process of the grain boundary mobility did not take place in these garnets. On the basis of above features, we consider that it can only be explained by plastic deformation of the garnets. The clusters of water molecules present in garnet was directly associated with mechanical weakening and inducing in plastic deformation of garnet by glissile dislocations. Investigate of LPO, strain analysis, TEM indicated that these clinopyroxenes developed strong elongation, high aspect ratios, and developed dislocation loop, dislocation wall and free dislocations. These indicated that the deformation mechanism of the clinopyroxenes plastically from the Dabie Mountains is dominant dislocation creep under the condition of the UHP metamorphic conditions. There are some bubbles with dislocation loops attached to them in the omphacite crystal. The bubbles attached to the dislocation loops sometimes form a string of bubble beads and some loops are often connected to one another via a common bubble. The water present in omphacite was directly associated with hydrolitic weakening and inducing in plastic deformation of omphacite by dislocations. The role of water in brittle deformation. Using microscopy, deformation has been identified as plastic deformation and brittle deformation in UHP minerals from the Dabie Mountains. The study of micro-tectonic on these minerals shows that the brittle deformation within UHP minerals was related to local stresses. The brittle deformation is interpreted as being caused by an interaction of high fluid pressure, volume changes. The hydroxyl within UHP minerals transported water molecules with decreasing pressure due to their exhumation. However, under eclogite facies conditions, the litho-static pressure is extreme, but a high fluid pressure will reduce the effective stress and make brittle deformation possible. The role of water in prograde metamorphism. Geochemical research on jadeite-quartzite and associated eclogite show that the protoliths of these rocks are supracrustal rocks. With increasing of temperature and pressure, the chlorite, biotite, muscovite was dehydrous reaction and released hydrous component during the subduction of continental lithosphere. The supracrustal rocks were transformed UHP rocks and formed UHP facies assemblage promotely by water introduction, and was retained in UHP minerals as hydrous component. The water within UHP minerals may be one of the retrograde metamorphic fluids. Petrological research on UHP rocks of jadeite-quartzite belt shows that there was existence of local fluids during early retrograde metamorphism. That are: (1) coronal textures and symplectite around relict UHP minerls crystals formed from UHP minerls by hydration reactions; (2) coronal textures of albite around ruitle; and (3) micro-fractures in jadeite or garnet were filled symplectite of Amp + PI + Mt. That indicated that the reactions of early retrograde metamorphism dependent on fluid introduction. These fluids not only promoted retrograde reaction of UHP minerals, but also were facilitate to diffuse intergranular and promote growth in minerals. Therefore, the hydrous component in the UHP minerals can not only take important part in the UHP metamorphic fluid during subduction of continental crustal rocks, but also their hydroxyl transport water molecules with decreasing pressure and may take part in the retrograde metamorphic fluid during their exhumation. 7. The role of water in geochemistry of UHP jadeite-quartzite. Geochemical research show that there are major, trace and rare earth element geochemical variations in the jadeite-quartzite from the Changpu district of Dabie Mountains, during retrograde metamorphic processes from the jadeite-quartzite--gneiss. The elements such as SiO_2、FeO、Ba、Zr、Ga、La、Ce、PTN Nd% Sm and Eu increase gradually from the jadeite-quartzite to retrograded jadeite-quartzite and to gneiss, whilst TiO_2. Na_2CK Fe2O_3、Rb、Y、Nb、Gd、Tb、Dy、Ho、Er、Tm、Yb decrease gradually. And its fO_2 keep nearly unchanged during early retrograde metamorphism, but decreased obviously during later retrograde metamorphism. These indicate that such changes are not only controlled by element transformation between mineralogical phases, but also closely relative to fluid-rock interaction in the decompression retrograde metamorphic processes.