Late Jurassic Volcanism Deduced from Geochemical,Geochronological,and Sr-Nd-Hf Isotopic Composition Characteristics of the Nanyuan Formation,South China

The Nanyuan Formation contains information related to the Mesozoic tectonic transformation.In this study,three representative profiles were surveyed from the Nanyuan Formation,and multiple analyses were conducted.Zircon U-Pb dating yielded their ages as approximately 158–146 Ma.The volcanic rocks are enriched in Rb,Th,U,K,and Pb and depleted in Nb,Ta,P,and Ti,implying their affinity for I-type granites.TheεNd(t)values(-8.3 to-6.0),^(87)Sr/^(86)Sr)i values(0.7077–0.7094)of the volcanic rock,andεHf(t)values(-8.71 to 0.12)of the Mesozoic zircons suggest that the Nanyuan Formation magma originated in the lower crust with the involvement of depleted mantle materials.The parent rocks of the rhyolitic and dacitic volcanic rocks formed by partial melting of basement rocks in South China and the andesitic volcanic rocks were derived from partial melting of the metasomatites generated by slab-mantle interaction.The fractional crystallization also played an important role in later stage.Discrimination diagrams of the volcanic rocks indicated that they formed in a volcanic arc environment.Combined with previous data,the Nanyuan Formation recorded subduction of the Paleo-Pacific Plate before regional tectonic transformation.The compressive stress field endured until the end of the Late Jurassic.

Intentional introduction of Artemia sinica(Anostraca) in the high-altitude Tibetan lake Dangxiong Co:the new population and consequences for the environment and for humans

The imbalance between supply and demand of Artemia cysts in China and around the world is increasing now.Salt lakes in Tibet may contribute to the solution of the problem.In Northern Tibet there are 26 saline lakes whose salinity and temperature may support Artemia survival at an altitude of 4 000–5 100 m.We found Artemia in 15 of these lakes.The saline lakes with Artemia populations mainly belong to the shallow basin lakes,and the majority of these lakes are small in area.The total area of lakes without Artemia is more than 1 000 km 2.Lake Dangxiong Co(Co means lake in Tibet) was chosen for the intentional introduction of Artemia sinica.In 2004,850 g of A.sinica cysts,originating from Qinghai,were introduced in the lake.Surveys in 2006–2014 showed that the average abundance of Artemia adults in the lake gradually increased from 20 ind./m 3 in 2006 to 1950 ind./m 3 in 2013.We assume that two subpopulations of A.sinica,separated by depth,may exist in the lake.The new Artemia population caused an increase in the number of species of phytoplankton and heterotrophic protozoa with a decrease of their total abundance.Water transparency also increased.Dominance in phytoplankton passed from cyanobacteria to diatoms.Changes occurred not only in the lake ecosystem;the number of water birds using the lakes also dramatically increased.Preliminary calculations showed that is it possible to harvest at least about 150 t cysts per year from the lake as well as 3.2 thousand tons of frozen or 350 t of dried biomass of adult Artemia.

Helium Isotope Geochemistry of Ultrahigh-Pressure Metamorphic Eclogites From the Dabie-Sulu Terrane in East China

The 3He/4He ratios of most eclogites from the Dabie-Sulu terrane range from 0.056 to 0.67 Ra; the data points fall into the mixing part of the crust and the mantle in the 3He-4He diagram. The 3He/4He ratios of eclogites are obviously correlated with the types of their surrounding rocks. The helium isotope composition of the eclogites from the Bixiling complex possesses characters of mantle-derived rocks with the 3He/4He ratio being 5.6 Ra. The 4He concentration of the eclogites exhibits visible inverse correlation with the δ18O value of the quartz in the eclogites from the Sulu area. The δ18O values of the eclogites change synchronously with those of the country rocks. Those results suggest that protoliths of the eclogites were basic-ultrabasic rock bodies or veins intruding into the continental crust in the early stage; strong exchange and hybridization between the basic-ultrabasic rocks and continental rocks and the atmospheric water during the intrusion led to abrupt increase of the 3He/4He ratios, δ18O values and Nd(0) values of the intrusive bodies or veins, which show characters of continental rocks. This indicates that the eclogites are autochthonous.

Advances in Research of Mineral Chemistry of Magmatic and Hydrothermal Biotites

Biotite is an important hydrated ferromagnesian silicate mineral in igneous rocks and porphyry deposits.The determination of chemical compositions of biotite plays an important role in both igneous petrology and ore forming processes.This paper summarizes research results of magmatic and hydrothermal biotites exemplified by the Lakange porphyry Cu–Mo deposit and the Qulong porphyry Cu deposit in the Gangdese porphyry–skarn metallogenic belt,Tibet.Biotite mineral chemistry can provide critical insights into classification,geothermometer,geothermobarometry,oxygen fugacity,petrogenesis and tectonic setting,evaluating magmatic-hydrothermal process by halogen and halogen fugacity ratios,and distinguishing between barren and mineralized rocks.Biotite provides the latest mineralogical evidence on metallogenic prognosis and prospecting evaluation for porphyry Cu polymetallic deposits or magmatic hydrothermal deposits.

Fluid Evolution and Ore-forming Processes of the Jiama Cu Deposit, Tibet： Evidence from Fluid Inclusions

The Jiama deposit is a large copper deposit in Tibet. Mineralization occurs in three different host rocks： skarn, hornfels and porphyry. A detailed fluid inclusion study was conducted for veins in the different host rocks to investigate the relationship between fluid evolution and ore-forming processes. Based on examination of cores from 36 drill holes, three types of veins （A, B and D） were identified in the porphyries, four types （I, II, III and IV） in the skarn, and three （a, b and c） in the hornfels. The crosscutting relationships of the veins and that of the host rocks suggest two hydrothermal stages, one early and one late stage. Fluid inclusions indicate that the Jiama hydrothermal fluid system underwent at least two episodes of fluid boiling. The first boiling event occurred during the early hydrothermal stage, as recorded by fluid inclusions hosted in type A veins in the porphyries, type a veins in the hornfels, and wollastonite in the skarns. This fluid boiling event was associated with relatively weak mineralization. The second boiling event occurred in the late hydrothermal stage, as determined from fluid inclusions hosted in type B and D veins in the porphyries, type I to IV veins in the skarns, and type b and c veins in the hornfels. This late boiling event, together with mixing with meteoric water, was responsible for more than 90% of the metal accumulation in the deposit. The first boiling only occurred in the central part of the deposit and the second boiling event took place across an entire interlayered structural zone between hornfels and marble. A spatial zoning of ore-elements is evident, and appears to be related to different migration pathways and precipitation temperatures of Cu, Mo, Pb, Zn, Au and Ag.

Diamond and Recycled Mantle:A New Perspective——Introduction of IGCP 649 Project

The IGCP 649 project entitled ＂Diamonds and Recycled Mantle＂was approved by UNESCO and IUGS in March 2015.This project is led by an international team of researchers,including Prof.Yang Jingsui of Institute of Geology of CAGS（China）.

Time Sequence of Himalayan Endogenetic Mineralization on the East Side of the Qinghai-Tibet Plateau

Among the endogenetic deposits in the Sanjiang area and at the west margin of the Yangtze platform, Himalayan deposits are the most important and contribute a large proportion of the resources of superlarge deposits. Among the controlled resources of this region, 84% of copper resources, 67% of Pb-Zn, 31% of Ag, 77% of gold and 24% of tin come from Himalayan deposits on the east side of the Qinghai-Tibet plateau. Himalayan endogenetic mineralization shows a relatively complete sequence evolution in the Sanjiang area and on the west margin of the Yangtze platform. Mineralization is manifested by gold deposits related to K-rich lamprophyre, REE deposits related to alkalic complexes and Cu-Au-polymetallic deposits related to alkaline porphyry. Six sequences of mineralization evolution since 65 Ma B.P. in the Sanjiang area and on the west side of the Yangtze platform can be recognized. Himalayan endogenetic mineralization on the east side of the Qinghai-Tibet plateau reached its peak before the Oligocene, corresponding to episodes I and II of the intracontinental orogenic cycle. Afterwards, mineralization waned obviously.

Late Cretaceous Adakitic Granites of the Southeastern Tibetan Plateau: Garnet Fractional Crystallization of Arc-Like Magmas at the Thickened Neo-Tethyan Continental Margin

The tectonic setting of Cretaceous granitoids in the southeastern Tibet Plateau,east of the Eastern Himalaya Syntax,is debated.Exploration and mining of the Laba Mo–Cu porphyry-type deposit in the area has revealed Late Cretaceous granites.New and previously published zircon U–Pb dating indicate that the Laba granite crystallized at 89–85 Ma.Bulk-rock geochemistry,Sr–Nd isotopic data and in situ zircon Hf isotopic data indicate that the granite is adakitic and was formed by partial melting of thickened lower crust.The Ca,Fe,and Al contents decrease with increasing SiO2 content.These and other geochemical characteristics indicate that fractional crystallization of garnet under high-pressure conditions resulted in the adakitic nature of the Laba granite.Cretaceous granitoids are widespread throughout the Tibetan Plateau including its southeastern area,forming an intact curved belt along the southern margin of Eurasia.This belt is curved due to indenting by the Indian continent during Cenozoic,but strikes parallel to both the Indus–Yarlung suture zone and the Main Frontal Thrust belt.It is therefore likely that Cretaceous granitoids in both the Gangdese and southeastern Tibetan Plateau areas resulted from subduction of Neo-Tethyan lithosphere.

The Sachakou Deposit in West Kunlun of Xinjiang: A Pb-Zn Polymetallic Deposit Associated with Magmatic Metasomatism of Carbonate Rock

Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It belongs to the West Kunlun orogenic belt on the northwest edge of the Qinghai-Tibet Plateau and is connected to the Sanjiang orogenic belt to the south （Spurlin et al., 2005）. In recent years, a series of Pb-Zn mineralized spots and deposits have been discovered in this area one after another, which is called the Huoshaoyun ore concentration area. Among them, the Sachakou Pb-Zn deposit has reserves up to140 Mt, which has reached a large scale. However, the study on the genesis of deposits in this area has only just begun. This work studied the genesis ofthis Pb-Zn deposit in order to provide new ideas for the genesis of regional deposits and regional prospecting.

Laser ablation in situ U-Pb dating and its application to diagenesis-porosity evolution of carbonate reservoirs

Through the development and calibration of a reference material which is 209.8 Ma old using a newly-developed Laser Ablation(LA)Multi-Collector Inductively Coupled Plasma Mass Spectrometry(MC-ICP-MS)technique,we successfully overcome the difficulty in sampling and dating ultra-low U-Pb ancient marine carbonates,which was previously untenable by isotope dilution(ID)methods.We developed the LA-MC-ICP-MS in situ U-Pb dating technique for ancient marine carbonates for the study of diagenesis-porosity evolution history in Sinian Dengying Formation,Sichuan Basin.By systematically dating of dolomitic cements from vugs,matrix pores and fractures,we found that the burial and diagenetic process of dolomite reservoirs in Sinian Dengying Formation was characterized by progressive filling-up of primary pores and epigenic dissolution vugs.The filling of vugs happened in three stages,early Caledonian,late Hercynian-Indosinian and Yanshanian-Himalayan,while the filling of matrix pores mainly took place in early Caledonian.The unfilled residual vugs,pores and fractures constitute the main reservoir sapce.Based on the above knowledge,we established the diagenesis-porosity evolution history of the dolomite reservoir in Sinian Dengying Formation,Sichuan Basin.These findings are highly consistent with the tectonic-burial and basin thermal histories of the study area.Our study confirmed the reliability of this in situ U-Pb dating technique,which provides an effective way for the investigation of diagenesis-porosity evolution history and evaluation of porosity in ancient marine carbonate reservoirs before hydrocarbon migration.

Building a scientific and ecological earth–on an important field of geo-science:Geo-environment and construction engineering effect

This paper explores the 12 aspects of geo-environment and construction engineering, including the earth evolution, the structure of geological bodies, the comprehensive utilization of resources, the geo-environmental effect, the engineering construction, the sustainable development and, etc. This paper presents that the good environment could only be created through the conservation and efficient utilization of resources, the joint efforts of disaster prevention and mitigation, as well as the avoidance of adverse environmental effect caused by human activities. This paper concludes that, to build a scientific and ecological earth, the development laws of geo-science must be learnt.

Origin of Halite in the Lanping–Simao Basin,Southeastern Tibetan Plateau,China:Evidence from Sr and Cl Isotopes

The Lanping−Simao Basin is located on the southeastern Tibetan Plateau,China,and contains massive evaporites.The origin of evaporites in the basin has been hotly debated because of the strong transformation by tectonic movement.Forty halite samples from borehole MK-3 in the Mengyejing area of the basin were collected and analyzed using XRD,Cl-Sr isotopes and chemical compositions to trace the origin of the evaporites in the basin.The Br×10^(3)/Cl ratios of the halite samples are between 0 and 0.55,most of which are synchronized with the law of seawater evaporation and at the stage of halite precipitation from seawater,indicating that the evaporites are mainly of marine origin.The^(87)Sr/^(86)Sr ratios range from 0.707489 to 0.711279;after correction,the^(87)Sr/^(86)Sr 145 Ma ratios range from 0.704721 to 0.707611,equivalent with the 87Sr/86Sr ratios of seawater at 145 Ma,indicating a marine origin.The decay of 87Rb in the evaporite during deposition,change of the depositional environment and the unsealed environment at a later period resulted in the present^(87)Sr/^(86)Sr ratios of some samples being high.The δ^(37)Cl value compositions range from−0.38‰to 0.83‰,which is consistent with the δ^(37)Cl value composition of the world marine halite(−0.6‰to 0.4‰),further confirming that seawater is the main origin.In addition,the high δ^(37)Cl value of some samples at the boundary of the upper and lower evaporite layers might be related to the influence of δ^(37)Cl-rich brine and the incomplete dissolution of the halite.

Meso-Cenozoic Mineralization Pattern in the Continent of China

Based on the complex structure and material resources, the complex geological setting of the Mesozoic-Cenozoic continent of China controlled four kinds of dynamic mechanisms of the continental tectonic-mineralization pattern, i.e. the dynamic mechanisms related to (1) underthrusting or collision, (2) activation of old tectonic belts or activity of new tectonic belts, (3) upwelling of mantle material and heat, and (4) interaction between the atmosphere, hydrosphere, biosphere and lithosphere. The four dynamic factors are related to and interact with each other; and the mantle-crust interaction leads to the regular time-space zonation of endogenetic deposits on a regional scale. The Meso-Cenozoic mineralization pattern in China can be outlined as the network tectono-metallogenic pattern constructed by NNE- and E-W-trending tectonics in eastern China, and multi-layer ring tectono-metallogenic pattern in the Qinghai-Tibet plateau and its northern and eastern neighbouring areas.

Geothermal-type Lithium Resources in Southern Xizang,China

High-temperature geothermal water has abundant lithium(Li)resources,and research on the development and utilization of geothermal-type lithium resources around the world are increasing.The Qinghai–Tibetan Plateau contains huge geothermal resources;especially,Li-rich geothermal resources in southern Xizang,southwestern China,are widely developed.The Li-rich geothermal spots in Xizang are mainly distributed on both sides and to the south of the Yarlung Zangbo suture zone.Such resources are often found in the intensely active high-temperature Li-rich geothermal fields and,compared with other Li-rich geothermal fields around the world,the Li-rich geothermal fluid in the Xizang Plateau,southern Xizang is characterized by good quality:the highest reported Li concentration is up to 239 mg/L;the Mg/Li ratio is extremely low and ranges from 0.03 to 1.48 for most of the Li-rich geothermal fluid;the Li/TDS value is relatively high and ranges from 0.25–1.14%compared to Zhabuye Li-rich salt lake(0.19%)and Salar de Uyuni(Bolivia)(0.08–0.31%).Continuous discharge has been stable for at least several decades,and some of them reach industrial grades of salt lake brine(32.74 mg/L).In addition,elements such as boron(B),caesium(Cs),and rubidium(Rb)are rich and can be comprehensively utilized.Based on still-incomplete statistics,there are at least 16 large-scale Li-rich hot springs with lithium concentration of 20 mg/L or more.The total discharge of lithium metal is about 4300 tons per year,equivalent to 25,686 tons of lithium carbonate.Drilling data has shown that the depth is promising and there is a lack of volcanism(non-volcanic geothermal system).With a background of the partial-melting lower crust caused by the collision of the Indo-Asia continent and based on a comprehensive analysis of the tectonic background of southern Xizang and previous geological,geophysical,and geothermal research,deep molten magma seems to provide a stable heat source for the high-temperature Li-rich geothermal field.The Li-rich parent geothermal fluid rushes to the surface to form hot springs along the extensively developed tectonic fault zones in southern Xizang;some of the Li-rich fluid flows in to form Li-rich salt lakes.However,most of the Li-rich geothermal fluid is remitted to seasonal rivers and has not been effectively exploited,resulting in great waste.With the continuous advance of lithium extraction technologies in Li-rich geothermal fluid,the lithium resource in geothermal water is promising as a new geothermal type of mineral deposit,which can be effectively exploited.This is the first study to undertake a longitudinal analysis on the characteristics,distribution and scale,origin and utilization prospects of Li-rich geothermal resources in southern Xizang,research that will contribute to a deeper understanding of Li-rich geothermal resources in the area and attract attention to these resources in China.

Microbial Mats in Tibetan Hot Springs and their Contributions to the Cesium-bearing Geyserite Ore Formation

Microbial mats, mainly dominated by filamentous algae Calothrix and Oscillatoria, are well developed in Tibetan hot springs. A great number of fossil microorganisms, which existed as algae lamination in thermal depositional cesium-bearing geyserite in this area, are identified as Calothrix and Oscillatoria through microexamination and culture experiments. These microbial mats show the ability to accumulate cesium from spring water to the extent of cesium concentration of 0.46-1.03% cell dry weight, 900 times higher than that in water, and capture large numbers of cesium-bearing opal grain. Silicon dioxide colloid in spring water replaces and fills with the organism and deposits on it to form algae laminated geyserite after dehydration and congelation. Cesium in the microbial mats and opal grain is then reserved in the geyserite. Eventually, cesium-bearing algae laminated geyserite is formed. Study on cesium distribution in geyserite also shows that cesium content in algae lamination, especially in heavily compacted algae lamination, is higher than in the opal layer. For geyserite with no algae lamination or other organism structure, which is generally formed in spring water with low silicon content, cesium accumulation and cesium-bearing opal grain assembled by the microbial mats are also indispensable. After the microbial mats accumulating cesium from spring water, silicon dioxide colloid poorly replaces and fills with the organism to form opal grain-bearing tremellose microbial mats. The shape and structure of the organisms are then destroyed, resulting in cesium-bearing geyserite with no algae lamination structure after dehydration and congelation. It is then concluded that microbial mats in the spring area contribute to the enrichment of cesium in the formation of cesium-bearing geyserite, and a biological genesis of the geyserite, besides of the physical and chemical genesis, is likely.

Orbital and Millennial-Scale Climate Variability over the Past 76 ka in the Western Tarim Basin, Northwest China

Paleoclimate changes during the last glacial in the arid central Asia are not as well understood as the monsoon-dominated areas of Asia. Here we report a 75-m-long sediment core over past 120 kyr based on astronomical tuning combined with the optically stimulated luminescence(OSL) dating in the Kashi depression of the western Tarim Basin, Northwest China. Analysis of grain size and highresolution gamma ray(GR) logs from the KT11 borehole across the last glacial period yields a climate history for the Tarim Basin which reflects the variations of its temperature and the hydrological cycles. Comparison of these records with north hemisphere summer insolation, the Greenland ice core temperature, stalagmites and the loess from the nearby region indicates that the deposits in the fluvio-lacustrine system of the Kashi depression responded to climate change at the Younger Dryas(YD), six Heinrich cooling events and the Dansgaard-Oeschger cycles. Our work indicates that the alternations between warm-humid and cold-dry climates were prevalent in the western Tarim Basin during the last glacial period, showing an in-phase pattern with the climate variations of the East Asian Monsoon, controlled ultimately by precession and North Atlantic Ocean climate variability on orbital-millennial time scales.

Zircon U-Pb and geochemical analyses for leucocratic intrusive rocks in pillow lavas in the Danfeng Group,north Qinling Mountains,China

Field observation showed that there are many irregular leucocratic intrusive rocks in pillow lavas in the Danfeng Group in the Xiaowangjian area, north Qinling orogenic belt. Photomicrographs indicated that the protoliths of those altered leucocratic intrusive rocks are dioritic rocks. Geochemical analyses showed that pillow lavas have a range of SiO2 from 47.35% to 51.20%, low abundance of TiO2 from 0.97% to 1.72%, and percentages of MgO (MgO#=41―49). Chondrite-normalized REE patterns of pillow lavas are even, indicative of a weak differentiation between LREE and HREE (La/YbN=1.52―0.99). N-MORB-normalized trace element abundances showed that pillow lavas are enriched in incompatible elements (e.g., K, Rb, and Ba). Leucocratic intrusive rocks in pillow lavas have a wide range of SiO2 from 53.85%―67.20%, low abundances of TiO2 from 0.51%―1.10%, and MgO (MgO#=40―51), and higher percentages of Al2O3 (13.32%―16.62%) and concentration of Sr (342-539 μg/g), ratios of Na2O/K2O (2―7) and Sr/Y (17―28). Chondrite-normalized REE patterns of leucocratic intrusive rocks showed highly differentiation between LREE and HREE (La/YbN=12.26―19.41). N-MORB-normalized trace element abundances showed that leucocratic intrusive rocks are enriched in incompatible elements (e.g., K, Rb, and Ba), and significantly depleted in HFSE (e.g., Nb, Ta, Zr and Ti), indicative of a relationship to subduction. Isotopically, leucocratic intrusive rocks have a similar εNd(t) (+7.45―+13.14) to that of MORB (+8.8―+9.7), which indicates that those leucocratic intrusive rocks sourced from depleted mantle most likely. SHRIMP U-Pb analyses for zircon showed that those leucocratic intrusive rocks were formed at 442±7 Ma, yielding an age of subduction in the early Paleozoic in the north Qinling orogenic belt.

Porphyry mineralization in the Tethyan orogen

The Tethyan metallogenic domain(TMD),as one of the three major domains in the world,extends over 10000 km from east to west,and has developed several world-class metallogenic belts,such as the Gangdese porphyry Cu belt,the Sanjiang metallogenic belt,the Iran porphyry Cu belt,the Pakistan porphyry Cu belt,the southeastern European epithermal gold deposit belt,and the Southeast Asian Sn belt.The formation and evolution of the TMD is mainly controlled by the multi-stage subduction of Tethys oceanic slabs,the opening and closing of several small ocean basins,and continent-continent collision.The Tethys oceans include the Proto-Tethys(Cambrian-Silurian),Paleo-Tethys(Carbonaceous-Triassic)and Neo-Tethys(Jurassic to Cretaceous),which in turn are formed by rifting from the Gondwana land at different times in different micro-continents.With a series of geological processes such as oceanic opening and closing,continental collision and post-collisional reworking with intraplate deformation,various types of ore deposits are developed in the TMD,including porphyry deposits,epithermal deposits,VMS deposits,chromite deposits,Sn deposits and orogenic gold deposits.The metallogenic processes of the TMD can be categorized into three stages.(1)Oceanic subduction:With the subduction of the oceanic slab and dehydration of basalt and sediments,the asthenospheric mantle was metasomatized with preliminary enrichment in metals under oxidized condition.(2)Continental subduction:Continental collision induced partial melting of the mantle wedge enriched the metals and water in mafic melts,which ascended from subarc depths to the lower crust,locally to the shallow crust for hydrothermal mineralization.(3)Post-collisional reworking:Partial melting of the mafic intrusives in the lower crust produced felsic melts under oxidized and water-rich conditions,which underwent crystal fractionation and transferred water and metals into hydrothermal fluids for mineralization.The large-scale porphyry mineralization in the TMD mainly occurs in the Miocene,which is an important scientific issue worthy of further study in the future.How is the metal enriched in the processes of gradual maturity of the crust,and how does large-scale mineralization occur in a collisional orogen where there is no subduction and dehydration of oceanic slabs anymore to supply S and Cl?These are still important questions in the study of porphyry mineralization in the Tethyan orogen.The application of hyperspectral and mineralogical studies of alteration assemblages is beneficial for prospecting and exploration in the TMD.