Abstract:Cenozoic ultrapotassic volcanic rocks which are widely distributed in Lhasa block of southern Qinghai-Tibetan Plateau were mainly erupted between 25 Ma and 10 Ma. These ultrapotassic volcanic rocks have typical lamproite characteristics such as high SiO2, MgO, K2O and TiO2, low Al2O3 and Na2O, and high K2O/Na2O ratios. Their high abundances of incompatible trace elements like large ion lithophile elements (LILE) and light rare earth elements (LREE) also reach the extreme levels typical of lamproites. The lamproites show high radiogenic 87Sr/86Sr and low unradiogenic 143Nd/144Nd, low 206Pb/204Pb, and elevated radiogenic 207Pb/204Pb and 208Pb/204Pb ratios. Geochemical and Sr-Nd-Pb isotopic characteristics of these ultrapotassic volcanic rocks in Lhasa block suggest that they were probably derived from a phlogopite-bearing enriched mantle source related closely to metasomatism during earlier subduction events. The ultrapotassic rocks in southern Tibet may imply the uplift and extension of Tibetan plateau after the collision of Indian plate and Eurasian plate. Meanwhile, there are a number of N-S grabens (rifts) mostly formed in 23～8 Ma in Lhasa block, which might have cut the lower crust or lithosphere into the depth, suggesting the extension of southern Tibet in Miocene. Furthermore, these ultrapotassic volcanic rocks are coincident with N-S grabens (rifts) in space and time. In addition, the tectonic activities in western Lhasa block (such as Karakorum fault) in 17 Ma and in eastern Lhasa block (such as Jiali fault and Red River-Ailao Mountain fault zone) in 23～17 Ma imply that at about 20±3 Ma the tectonic stress field in southern and southern-eastern parts of Qinghai-Tibetan Plateau underwent a considerable change from the NS-trending compression to the EW-trending extension. Combined with contemporary adakitic rocks along the Yarlung Zangbo suture, the authors hold that the northward subducted Indian lithospheric mantle might have experienced break-off beneath the Lhasa block along the Yarlung Zangbo suture in early Miocene, which caused the upward and lateral migration of the asthenosphere material under the Indian lithospheric mantle along the slab window. The upward and lateral migration of the asthenosphere material led to the rapid uplift of southern Qinghai-Tibetan Plateau as well as the eastward movement of the thickened crust, which further resulted in the EW-trending extensional deformation (23～8 Ma) of the widely distributed N-S grabens (rifts) and the eruption of the ultrapotassic magma(25～10 Ma).

Abstract:Quite a few lamprophyre dikes are developed in the Daping gold ore district, mostly associated with quartz veins. Petrochemically, SiO2 content, MgO content and K2O/Na2O ratios are 44.86%～54.10%, 5.84%～13.52% and 0.56～2.09, respectively, suggesting a shoshonite series; rocks of the lamprophyre dikes are enriched with large-ion lithosphile elements (Sr, U, Rb, Ba) and LREE and depleted in high-field-strength elements (Ta, Nb, Ti), assume “TNT" negative anomalies of Ta, Nb and Ti, and have δEu values of 0.72～1.36, with indistinct negative Eu anomalies; 87Sr/86Sr ratios are in the range of 0.7066～0.7074 (0.7071 on average)，higher than the modern value of original mantle (0.7045)；143Nd/144Nd ratios are 0.5124～0.5125 (averagely 0.5124)，lower than the modern value of original mantle (0.512638)；εNd values range from -2.5 to -4.6 (averaging -3.98). Nb/Ta ratios vary in the range of 48.96～82.58 (averaging 62.99 )， much higher than the value of original mantle (17.5±2.0)； Zr/Hf ratios are in the range of 20.45～47.53 (averaging 39.57)， slightly higher than the value of original mantle (36.27±2.0)； Nb/Ta and Zr/Hf ratios are much higher than the values of the continental crust (11 and 33), respectively. It is thus thought that the source rock of the lamprophyre is an early subducting oceanic crust or an enriched mantle which might have been metasomatized by the enriched fluids released from the dehydration of the root matter in the orogenic belt. The magma was formed in a post-collision intraplate environment and was mixed with small amounts of crustal matter as it intruded upward. Whether in time, space or mechanism, the lamprophyre dikes in the Daping ore district must have had a close genetic relationship with big tectonic events in the Jingshajiang-Ailaoshan tectonic belt.

Abstract:Magmatic rocks of Early Cretaceous Zenong Group are extensively developed in the Gangdise belt of Tibet, and the genesis of these rocks has given rise to much controversy. In view of this, the authors sampled and analyzed systematically felsic volcanic rocks of Zenong Group in Coqen area of Gangdise orogenic belt. The results show that magmatic rocks of Zenong Group are characterized by high SiO2 content, relative enrichment of LREE and evident enrichment of LILE, Rb, Ba, Th and U, depletion of such HFS elements as Nb and Ta, and the appearance of Sr negative anomalies, with isotopic features of high Sr (0.70789～0.71017) and low Nd (-3.4～-9.3). They are aluminum-oversaturated (A/CNK=1.09～1.17) and geochemically similar to the crustal magma. In the diagram of εNd（t）－（87Sr/86Sr）i, all the samples fall in the No.4 quadrant and are distributed around the mixture line of the upper crust and the Yarlung Zangbo River MORB-type depleted crust, suggesting the existence of fairly abundant upper crust matters and the participation of small amounts of mantlematerials. Moreover, magmatic rocks of Zenong Group are extensively distributed almost in the whole region. The diagram of La/Sm-La indicates that the felsic magmatic rocks of Zenong Group are probably different partial melting products from the same magma source. The felsic magmatic rocks are greatly enriched in LREE and have a spidergram very similar to that of the upper continental crust. The tectonic-setting discrimination diagram of trace elements implies that magmatic rocks of Zenong Group were formed in a island-arc tectonic setting. Based on previous research results and the latest 1∶250000 regional geological survey, the authors hold that the felsic magmatic rocks of Zenong Group might be products of the dehydration and remelting of the crustal materials caused mainly by the heat of the mantle basic magma with the participation of some mantle materials. The tectonic setting of the magmatic rocks of Zenong Group was probably associated with the southward subduction of the Bangong Lake-Nujiang River Tethys oceanic crust.

Abstract:During the migration of basaltic magma through the lithosphere mantle, the interaction between melt and peridotite inevitably took place and led to the compositional variation of the lithosphere mantle. Mantle peridotite and its disaggregated minerals such as olivine (Ol), clinopyroxene (Cpx) and orthorpyroxene (Opx) xenocrysts were captured by the Cenozoic basalt in Hannuoba. The xenocrysts usually have the reaction rim structure, which provides important information about the melt-xenolith interaction during the migration of basaltic magma through the lithosphere mantle. The xenocrysts in basalt are on the whole perfectly round, embayed or serrated in shape and have characteristic reaction rim structure which distinguishes them from relatively euhedral and small phenocrysts in basalt. Based on microscopic petrographic observations and electron microprobe analyses of xenocrysts and their reaction rims, this paper deals tentatively with the melt-xenolith interaction. The rims of Ol and Cpx xenocrysts show similar compositional variations from the Mg-rich core to the Ferich rim. The composition of the outer part of the reaction rim tends to be close to the composition of the phenocryst in basalt. Olivine composition changes from the core (Fo 88～90) to the rim (Fo 68～72). Clinopyroxene composition changes from Mg#90 to Mg#74, with the corresponding variation of diopside in the core to salite in the rim. Usually, the reaction rim of Opx with double-layered structure consists of Ol+Cpx+Glass. The composition of Ol and Cpx in the Opx reaction rim is rich in Fe relative to its mantle counterpart. Meanwhile, the reaction rim minerals will become richer in Fe and poorer in Mg with the Opx xenocrysts approaching the host basalt. The glass constituent rich in silicon and alkali (the content of SiO2, Al2O3, Na2O and K2O is respectively 64%～67%, 18%～19%, 5%～7% and 6%～9%) in the Opx reaction rim offers important information concerning the origin of Si- and alkali-rich melt inclusions present in mantle minerals in eastern China. It is thought that Si- and alkali-rich melt might have resulted from the reaction between basaltic magma and Opx in peridotite, i.e., the reaction basaltic magma (Si-poor melt)+Opx→ Si-rich melt+Ol+Cpx. It is also found that the variation of color and composition of the spinel (Sp) in one peridotite xenolith is related to temperature: when the temperature rises, the content of Cr in Sp increases, so does Al in melt. The preservation of the reaction rim structure or disequilibrium structure in xenocrysts implies rapid uprising of the host basalt. The extensive melt-xenolith interaction inevitably changed the properties of the lithosphere mantle.

Abstract:The Qian'an iron mine is one of the large-sized metamorphic sedimentary iron mines in China. As the ore-bearing metamorphic rocks here are of Precambrian hypometamorphic ones, the minerals in the existent rocks have been deformed,[HJ] metamorphosed and recrystallized several times, resulting in the extreme complexity of the rock microstructure. In order to have a better understanding of the fabric of the deformed rocks, the authors employed EBSD (electron backscatter diffraction) to analyze the samples in the study area. With the help of Channel 5 developed by HKL Co., the authors processed all the data collected and drew the corresponding magnetite polo figures and quartz polo figures. Quartz optical axes, which exist in gneiss and granulite, are basically consistent with the direction of foliation in hand specimen and are also in the same direction or at the small-angle intersection with the elongated direction and wave extinction of quartz under microscope. The analysis shows that the characteristics of magnetite do not show a preferred orientation, while the internal fabric of quartz in deformed rock does. Furthermore, the authors have also obtained the information concerning the conditions during the structural deformation. Most polo figures reflect a circumstance of medium to medium-high temperature, whereas a small number of figures suggest the composition of medium-low temperature deformation. In combination with the knowledge of deformation partitioning which belongs to the deformation field, the authors believe that different minerals in the solid rock such as quartz, feldspar and garnet have different mechanical strength and ductile shear deformation conditions, and such differences would contribute to partition deformation between the light-color deformed quartz and the high mechanical strength magnetite.

Abstract:In order to probe into the dynamic mechanism of the oolitic limestone under the deep burial condition, the authors designed a high-pressure pump controlled device to simulate the process of dolomitization. The dolomitization experiment on oolitic limestone was conducted under the 40 MPa comparative lithostatic pressure and 150℃ geothermal temperature (equivalent to the condition of 4000 m deep burial) for 15 days. The results show that the rock structure was slightly changed, the content of Ca2+, the main component of the tail liquid, increased from 0 mg/L to 337 mg/L, and Mg2+ decreased to 2380 mg/L. Meanwhile, electron microprobe analyses show that the content of CaO in solid sample decreased from 61.000% to 60.830%, while the content of MgO increased from 0.296% to 0.350%. It is considered that the main elements Ca and Mg in solid and liquid samples experienced growth-and-decline changes before and after the reaction. An integrated comparative analysis was conducted by means of microscope observation, scanning electron microscope, stereoscopic microscope, electron microprobe analysis and X-ray diffraction analysis. Although the experiment failed to produce dolomitization, the result could provide constraints and experimental data support for further understanding of the conditions of dolomitization.

Abstract:Extensive crustal extension existent in northeast Asian continent since Late Mesozoic has resulted in the formation of one of the world's largest extensional provinces. Metamorphic core complexes (MCCs) from Lake Baikal to the southern margin of North China constitute a typical extensional phenomenon in this province. The duration and mechanism of such large-scale crustal extension, especially the mechanism of the extension as to whether the stretching took place simultaneously in this region or it was gradually expanded, deserve further research. Obviously the precise chronological limit of the beginning of each metamorphic core complex is an effective means to solve this problem. Syn-tectonic mylonitized granite (vein) is an ideal symbol body for studying the kinematics, dynamics and chronology of the metamorphic core complexes, and is also an important object for determining the structural features and deformation time. Southern Liaoning was a rather intense and typical lithospheric thinning and destruction area in North China Craton during Late Mesozoic, with the formation of the Liaonan metamorphic core complex serving as one of the marks. The authors tentatively studied the deformation features and zircon SHRIMP U-Pb geochronology of the mylonitized granite vein exposed in the Jinzhou detachment fault of the Liaonan MCC, with the purpose of providing new evidence for constraint on the ductile detachment time. The vein intruded into Archean mylonitic biotite plagioclase gneiss along the mylonitic foliation of the wall rock and underwent a strong extensional ductile shear deformation together with the wall rocks. Field observations and micro-structural analysis show that the vein is syn-kinematic. Fry's finite strain measurements of feldspars show that the sample's Flinn K values is 0.83, Lodυvalues is 0.09, and strain intensity (Es) is 0.71, indicating that the mylonite is dominated by plane strain. The kinematic vorticity number (Wk) is 0.89, implying that the deformation is dominated by simple shear. SHRIMP U-Pb dating of the magmatic zircon from the mylonitized granite vein yields an age of 129±2 Ma (n=10, MSWD=1.6), suggesting that the vein was emplaced in Early Cretaceous. Recent researches have shown that the Liaonan MCC resulted from regional and lithosphere thinning in the North China Craton in Late Mesozoic. The formation of the Jinzhou detachment fault and the uplift on its eastern side are the major indicator of the turning point of the tectonic regime from contraction to extension. In combination with the results obtained by the authors, it is suggested that the Jinzhou detachment fault started its ductile shearing at least at 129±2 Ma and the tectonic regime changed from contraction to extension at this time.

Abstract:The Shoushan stone is a unique carving stone in China, with long history and great reputation. The authors studied the mineralogical characteristics of Gaoshan stones and Kengtou stones from Shoushan, Fujian Province, by means of microhardness tester, hydrostatic weighing method, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic absorption spectrophotometer and environmental scanning electron microscopy (ESEM). The study probed into the differences between Gaoshan stones and Kengtou stones in the aspects of hardness, specific gravity, mineral composition, chemical composition and microstructure characteristics, with a discussion on the factors affecting the color and transparency of Shoushan stones. The results indicate that the samples collected in this study all belong to kaolinite group Shoushan stones. Their data are similar in hardness and specific gravity. As for mineral composition, their main minerals are alike while their auxiliary minerals have some slight differences. According to XRD and FTIR, the kaolinite group can be found in Gaoshan stones while the proportion of dickite is much higher than that of other stones, and the main minerals in the Kengtou stone are dickite and nacrite, with some transitional minerals like dickite-kaolinite and dickite-nacrite. The authors hold that the structures of dickites in some Kengtou stones were somewhat changed under some reactions in later periods. According to whole-rock chemical analyses, Fe is the main trace element contributing to dark Shoushan stones. ESEM photographs reveal that the particle sizes and degrees of crystallization of minerals are associated with the transparency of stones, and the directionality of mineral particles is one of the main factors causing the ‘cracking' during the carving of Shoushan stones, and hence carving on the well-orien-tated faces should be avoided.

Abstract:In the past decades, significant advances have been made in the research on Re-Os isotopes. Re and Os can be concentrated from various organic-rich geologic samples, and hence the study of the Re-Os isotopic system in these samples has become a new hot spot in the field of isotope geochemistry. The organic matter, which is contained in organic-rich sedimentary rocks, is capable of absorbing and enriching Re and Os from the seawater. With the diagenesis of these organic-rich sedimentary rocks, the Re-Os isotopic system becomes closed, and the isotopic timing begins. If the hydrocarbon source rock becomes maturated, Re and Os would move with the organic hydrocarbon, and the Re-Os isotopic system could attain re-equilibrium. This paper deals with the principles of Re-Os isotopic system applied to various organic-rich geological samples such as black shale, oil shale, asphalt, schungite, oil and coal. Moreover, the potential disturbances of the weathering-leaching and the hydrocarbon maturation to the closure of Re-Os isotopic system are analyzed. In the aspect of practical application, several cases are cited to illustrate the significance of this isotopic system in the organic-rich system with the purpose of understanding such systems as environmental evolution, metallogenic process and hydrocarbon generation and accumulation. In order to help geologists and chemical analysts employ this isotopic system effectively, this paper has summed up the sampling and digesting methods for different samples. The Re-Os isotopic system in organic-rich geological samples should become a powerful tool in geological researches, but some problems remain to be solved in the near future.

Abstract:Lithium has two stable isotopes, 7Li and 6Li, which have the biggest relative mass difference among all isotope pairs except for hydrogen-deuterium. Its potential for mass-dependent fractionation is thus obvious. Unlike the better established light stable isotopic systems (e.g. C, O, S), Li is a trace cation and does not form an integral part of the hydrological, atmospheric or biological cycle. Hence measurements of Li isotopes are likely to provide information rather different from data obtained from more commonly used isotope systems. Lithium isotope is regarded as a potential trace element because Li has many favorable characteristics, such as moderate incompatibility during mantle melting, high mobility in hydrous fluids and a strong isotopic fractionation at low temperatures, which make this trace element a powerful tracer for recycled materials in the mantle. In recent years，studies of Li and its isotopes in the solid earth have been rapidly increasing in number, as there exists great interest in determining the usefulness of the Li isotope system in tracing crust-mantle recycling. Lithium isotopes can be strongly fractionated under different conditions, with δ7Li values ranging from +32‰ in sea water to very low in eclogites（-35‰）, which are interpreted as analogs of the dehydrated oceanic crust. Because Li is a fluid-mobile element, it has been held that heavy seawater Li incorporated into altered oceanic crust would move from the slab into the mantle wedge together with other fluid-mobile elements during subduction zone metamorphism and ultimately manifested itself again in island arc lavas. However, studies of island arcs show that Li is decoupled from other fluid-mobile elements, and most island arc lavas (+2‰～+6‰) have δ7Li indis tinguishable from δ7Li of MORB. Several models have been proposed to explain the Li isotopic composition of lavas, such as fluid filtering and fluid-mantle wedge mixing. Thus, the isotopic composition of recycled Li remains a matter of speculation in the subduction zone.

Abstract:Chlorinated hydrocarbons (CHs) are widespread organic contaminants in the groundwater system. Among them, trichloroethylene (TCE) is most common. Since TCE is a typical DNAPL (dense non-aqueous phase liquids), it tends to migrate downward into the groundwater system where pools exist. During the migration of trichloroethylene in the vadose zone, soil sorption plays an important role in determining its mobilization, transportation and accommodation. Soil organic matter (SOM) and soil minerals are two major sorbents in the vadose zone which strongly affect sorption behaviors of organic contaminants. Based on batch experiments, the authors studied the adsorption behaviors of trichloroethylene (TCE) in four simulated mineral samples with different ratios of silica to kaolinite (representing respectively primary minerals and clay minerals) and six soil samples with different ratios of total organic matter (TOC) to clay minerals which were collected at different depths of the vadose soil profile. Instead of employing the isolation procedure of SOM which might cause changes in physicochemical properties of SOM, the sorption behaviors of TCE in SOM were predicted by the comparison between soil samples and simulated soil mineral samples. The results obtained show that both the sorption isotherm of soils and that of minerals fit Langmuir sorption model. The maximum sorption capacity of pure kaolinite is nearly 200 μg/kg, while that of pure silica is only about 15 μg/kg. The maximum sorption capacity of clay minerals is almost 13 times as lager as that of primary minerals. The clay minerals contribute most of the sorption capacity of soil minerals, while the primary minerals only present negligible sorption of TCE. The content of TOC is the key factor affecting the sorption of TCE in soils, as the sorption capacity of TCE in SOM is several orders of magnitude larger than that in clay minerals, which accounts for the positive correlation between the content of TOC and the soil sorption capacity. The ratio of TOC to clay minerals is another factor affecting the sorption behaviors of TCE in soils. Soil with lower ratios of TOC to clay minerals would produce higher Koc values. SOM has been reported to be intimately associated with the clay mineral fraction and widely distributed in the environment in the form of organo-clay complexes. The thickness of SOM coating on clay minerals decreases with the decrease of the ratio of TOC to clay minerals on the uniform organo-clay complexes, and the molecular layers close to the mineral surface may take a more compacted form due to the attractive power of mineral surface. Any SOM layer beyond this compacted region may be relatively intensely expanded as the attractive force becomes weaker with the increasing distance from the mineral surface. Therefore, the proportion of the bound SOM in the condensed form would be relatively high at the lower ratio of TOC to clay minerals. Soil with lower ratios of TOC to clay mineral is likely to produce higher Koc values indicating an increasing affinity of TCE for the soil, which suggests that organo-mineral complexes potentially play an important role in regulating the accessibility and distribution of sorption sites for organic chemicals, and are thus important in the study of sorption mechanism.