Turpan-Hami Basin Research Articles

Prospect Conceiving of Joint Research and Development of Shale Gas and Coalbed Methane in China

Inspired by successful development of shale gas in USA and influenced by hydrocarbon resources shortage currently, China has strengthened shale gas research and accelerated its exploration process. In order to enrich coalbed methane (CBM) and shale gas geological theory and promote their development process, this paper compared shale gas with CBM in accumulation, distribution, reservoir and production. It expatiated on the background and significance of the combined research and development, and analyzed the geological foundation and future prospects. Our investigation demonstrated that there are many sets of coal-bearing strata in Shanxi formation of Permian system in Ordos in North China, Longtan formation of Upper Permian and Xujiahe formation of Upper Triassic in Southern Yangtze region, Xishanyao formation of Middle Jurassic in Turpan-Hami Basin and Junggar Basin in Northwest China, and Shahezi formation of Cretaceous in Songliao Basin in northeast China. In these regions, shales which are interbeded with coal seams have the characters of big thickness, continuous distribution, high content of organic matter, good parent material and high maturity, accord with the basic geological conditions to format shale gas and CBM reservoir and composite gas reservoir, thus form appropriate regions and layers to carry out joint research and exploration with good prospects for development.

Geochemical characteristics of light hydrocarbons in natural gases from the Turpan-Hami Basin and identification of low-mature gas

Theoretical and practical knowledge regarding low-mature gasses is of significant importance to identifying potential natural gas resources. Light hydrocarbon parameters and C and H isotopes are useful tools to identify low-mature gas. Twenty gas samples were collected from the Turpan-Hami Basin for light hydrocarbon analyses. The results showed that the light hydrocarbon components of natural gases contain high methylcycloxane, high isoparaffin and low benzene. This implies that the gas-generating parent materials are of typical humus type and the paleoenvironment is a fresh water sedimentary environment. These features are consistent with the geological setting of the basin. Comparative studies of isoheptane, heptane, and the carbon isotopic compositions of methane in natural gases, and other maturity indices indicated that natural gases in the Turpan-Hami Basin are dominated by low-mature gas formed during the low evolution stage of Jurassic coal seams. The parent materials are of type III, and the maturation degree was in the low evolution stage. These are the fundamental characteristics of low-mature gas. Results of light hydrocarbon research provided further evidence to suggest that the Turpan-Hami Basin is a large-scale gas producer of low-mature gas in China. It is likely that this resource will play an important role in future exploration and development of low-mature gas in China.

Geochemical characteristics and possible origin of natural gas in the Taibei Depression, Turpan-Hami Basin, China

292 chemical composition data and 82 isotopic composition data of gas samples collected from the Taibei Depression of the Turpan-Hami Basin, West China, were used in the study of their origin. Non-hydrocarbon gas is poor in most samples whereas abundant nitrogen in some samples is positively correlated with δ13C1. Although methane is the main constituent, higher molecular gaseous hydrocarbons, from ethane to pentane, are detected in most samples, in accordance with the distribution of oil reservoirs. The stable carbon isotope ratios of methane, ethane and propane are defined as δ13C1: −45.5‰ to −33.5‰, δ13C2: −30.2‰ to −10.5‰, and δ13C3: 27.6‰ to −11 respectively. According to the distribution of carbon isotope ratios, 2 families of gas can be grouped, most showing normal distribution of carbon isotopes, and others having obvious heavier carbon isotopes and being of abnormal distribution. Based on the isotopic composition, the disagreement between the relationship of Δ(δ13C1-δ13C2) and δ13C2 and that of δ(δ13C1-δ13C2) and δ13C2, and the calculated Ro, there are oil-associated gas, coal-derived gas and mixture of them. Other samples with obviously heavier isotopic compositions from the Yanmuxi oilfield of the Taibei Depression have been degraded by organisms.

Oil accumulation related to migration of source kitchens in the Lukeqin structural belt, Turpan-Hami Basin, China

The Lukeqin structural belt is the main heavy oil accumulation zone in the Turpan-Hami Basin. The recent discovery of light oil in the Triassic indicates that there may be multiple source kitchens contributing to the oil accumulation. According to oil geochemical analysis and oil-source correlation, the oil in deep and shallow reservoirs of the Lukeqin Oilfield presents different physical and saturated hydrocarbon mass spectrum characteristics. The Triassic heavy oil is from the northern Upper Permian lacustrine source rocks, and the light oil represented by the Yudong-9 Well is from the northwestern Lower Jurassic coal-measure source rocks. The timing of oil charging was determined by K/Ar isotope dating, reservoir fluid inclusion analysis and the evolution history of different source rocks. In summary, the accumulation process consists of two stages. From the end of Triassic to early Jurassic, the northern Permian source kitchen generated a considerable amount of oil, which was finally degraded to heavy oil, migrated to the south and then accumulated. The northwestern Jurassic coal-measure source kitchen began to generate oil at the end of Cretaceous, while the northern source kitchen could only generate a little hydrocarbon. The heavy oil and the light oil have different source rock locations, migration directions and accumulation times. The migration of hydrocarbon source kitchens affects the distribution of heavy oil and light oil reservoirs at the present time.

A fine assessment technology for medium-high exploration degree plays

Abstract The current evaluation methods mainly focus on plays without hydrocarbon discoveries. By integrating three techniques, i.e., spatial quantitative prediction technology of hydrocarbon bearing probability, overlapping processing technology for multi-layer spatial hydrocarbon bearing probability, petroleum resources abundance fractal simulation restricted by corresponding spatial hydrocarbon bearing probability, a new fine evaluation method was put forward. This method, based on spatial grids and combining planar and vertical evaluation results, focuses on the assessment of multi-layer plays. Compared with the present methods, it has advantages such as comprehensive assessment, precise processing results, comprehensive data collection and application, exploration effectiveness. By this Method, 38 secondary structural belts in the middle-upper exploration formations in the Turpan-Hami Basin were evaluated. Favorable drilling areas in each belts were pointed out based on the spatial probability of hydrocarbon bearing. Their corresponding geological favorability index and residual oil resources revealed that the Shengbei, Huoyanshan, Lukeqin, Shanle Structural Belts are the most favorable belts for exploration.

Organic geochemistry of Carboniferous and Lower Permian source rocks, Turpan-Hami Basin, NW China

Abstract Organic geochemistry characteristics of carbonate rock and mudstone samples are reported for cores in exploration wells and outcrops in the Carboniferous and Lower Permian, Turpan-Hami Basin. Extensive analyses include organic matter abundance, kerogen type, hydrocarbon generation and thermal evolution. The mudstone is higher in organic content, ranging from 0 – 4.45% TOC, suggesting relatively good source rock potential; whereas, the carbonate rock has a maximum TOC of 0.52% and is basically non-source rock. The matrix types of both carbonate rock and mudstone are grouped into Type III (dominant) and II2 (less). The carbonate rock is a bit better quality than the mudstone in organic types. The source rock from downhole samples can be early mature to highly mature. The maturity of outcrop samples range from mature to over-mature. The lower maturity of well samples is related to the shallower depth of the samples. The higher maturity of outcrop samples may be related to the tectonic movement and high geothermal gradient. Based on characteristics of thermal evolution, more effective Carboniferous-Lower Permian source rocks are distributed in the deeper location of the sag and can generate more natural gas. The igneous/volcanic rocks are better deep reservoirs in which natural gas accumulates.

Low-mature gases and their resource potentiality

In the 80’s of last century, based on the advances in natural gas exploration practice, the concepts of bio-thermocatalytic transitional-zone gas and early thermogenetic gas were proposed, and the lower limit Ro values for the formation and accumulation of thermogenetic natural gases of industrial importance have been extended to 0.3%–0.4%. In accordance with the two-stage model established on the basis of carbon isotope fractionation involved in the formation of coal-type natural gases, the upper limit Ro values of lowly evolved natural gases should be set at 0.8%–1.0%. This is the concept of low-mature gas which is commonly accepted at the present time. The Urengoy super-large gas field in western Siberian Basin is a typical example of low-mature gas field, where low-mature gas reserves account for 20% of the globally proven natural gas reserves, and this fully indicates the importance of this kind of resources. The proven reserves of natural gases in the Turpan-Hami Basin of China are approximate to 1000×108 m3, and the thermal evolution indices of source rocks are Ro=0.4%–0.8%. The δ13C1 values of methane are mainly within the range of −44‰–39‰ (corresponding to Ro=0.6%–0.8%), and those of ethane are mainly within the range of −29‰–26‰, indicating that these natural gases should be designated to the coal-type low-mature gases. The light hydrocarbon evolution indices of natural gases also provide strong evidence suggesting that they are the coal-type low-mature gases. If so, low-mature gas in the Turpan-Hami Basin has been accumulated to such an extent as to be equivalent to the total reserves of three large-sized gas fields, and their existence is of great significance in the study and exploration of China’s low-mature gases. If it is evidenced that the source rocks of low-mature gases are related mainly to coal measures, China’s abundant lowly evolved coal series resources will provide a huge resource potentiality for the generation of low-mature gases.

The Different Characteristics and Geological Significance of Reduction Alteration of Sandstone-Type Uranium Deposits in Northwest Region of China

Based on isotope trace studies of sandstone-type uranium deposits in Dongsheng area of Ordos basin, south margin in Yili basin and Turpan-Hami basin, such as geological attitude, carbon and oxygen isotope in fluids, hydrogen and oxygen isotope, sulfur isotope in pyrite and carbon isotope in “detritus pot top gas” of mineral-bearing stratum, this paper reveals the different features of the reduction and alteration among the formation of three uranium deposits. The differences are mainly reflected on the types of organic matter and the reduction alteration scale. These differences are the main reason to cause apparent epigenetic alteration types and intensity of uranium mineralization. It is concluded that the reduction of coal bed methane dissipation from the Neopaleozoic is the main feature of Dongsheng deposit, which leads to the abroad development of green-color alteration and bleaching phenomenon. The reduction of bacteria is the main feature of Yili deposit, which leads to a small range of weaker fading alteration and much more framboidal spherules pyrited mineralization. The organic acid from dispersed coal particles in stratum is the main feature of Turpan-Hami basin deposit, which is the main reductant of the uranium deposit. According to the above-mentioned characteristics, we think that the types, characteristics, and the scale of reductant are the important factors in determining the types of uranium deposits and the differences between the scales. This recognition has an important theoretical and practical significance to research genetic types of uranium deposits and their exploration methods.

Sedimentological setting of sandstone-type uranium deposits in coal measures on the southwest margin of the Turpan-Hami Basin, China

Sandstone-type uranium deposits usually exist in coal measures. This stratigraphy study found that the Jurassic coal measures (Shuixigou Group) at the southwest margin of the Turpan-Hami Basin consist of the Badaowan, Sangonghe and Xishanyao formations, which correspond to sequences A, B and C, respectively. Sequence C can be divided into the lowstand systems tract (LST), expanding lacustrine systems tract (EST) and highstand systems tract (HST). Uranium mineralization mainly develops in sequence C, in which LST and HST are the main mineralization strata while EST is the secondary mineralization stratum. High-resolution study of depositional systems tracts indicates that the fine sediments around the boundaries of parasequences can form the confining beds of uranium metallogenetic fluid systems. Within parasequences, the braided channel sandstones and part large-scale braided distributary channel sandstones have a close relationship with strong interlayer oxidation and uranium mineralization. Periodical development of parasequences conduces to the frequent growth of large skeletal sandstones and confining beds. That is the essential reason for the complexity of uranium mineralization in depositional systems tracts. The study also found that different depositional systems lead to obvious differences in the spatial distribution structures of skeletal sandstones and confining beds. LST and HST mainly comprise braided stream depositional systems, where uranium skeletal sandstones develop and are always located in the middle and lower parts of the parasequences, while confining beds are always located in the upper part of parasequences. While EST mainly comprises braided delta depositional systems, where uranium skeletal sandstones have a relatively small scale and are always located in the middle part of parasequences, confining beds are always located in the lower and upper parts of parasequences. Thus, the study of depositional systems tracts in sequence is only suitable for the primary exploration stage of sandstone-type uranium deposits, and parasequences are the best evaluation units in the advanced exploration stage.

Observed trends of heating and cooling degree-days in Xinjiang Province, China

Global warming has the potential to impact various aspects of human society such as agriculture, construction, transportation, water resources management, power generation, and phenology. The impact on energy, especially energy consumption for heating and cooling of buildings, is very important. These influences are different in terms of space and time due to spatial and temporal variations of temperature. In this study, daily data of minimum and maximum temperature of 51 stations for 1959–2004 were used to detect annual and seasonal variations of heating and cooling degree-days in Xinjiang, China, by using the Mann–Kendall trend test and linear regression techniques. The results indicate that: (1) taking 18°C as the base temperature, annual mean heating degree-days (HDD) ranged between 2,700 and 7,973°C, and annual mean cooling degree-days (CDD) (the base temperature is 24°C) ranged between 0.4 and 792°C. CDDs are relatively low in Xinjiang; (2) autumn, winter, and annual HDDs show significant decreasing trends. Annual CDD at 23 out of 51 stations present significant increasing trends, while no remarkable positive trends can be observed at the other stations; and (3) with respect to spatial variations, Xinjiang was characterized by significant decreasing annual, winter, and autumn HDDs, and it was particularly true for the northern Xinjiang. The annual and summer CDDs in the western parts of northern Xinjiang (the edges of the Tarim Basin and the Turpan-Hami Basin) were characterized by significant increasing trends. However, no fixed spatial patterns can be identified in the variations of annual and summer CDDs. The results of this study could be useful for energy management in Xinjiang and are also helpful for better understanding of impacts of global warming on energy consumption in other countries of the world.

Possible chemical structures and biological precursors of different vitrinites in coal measure in Northwest China

Abstract Chemical structure of Jurassic vitrinites isolated from the coals in basins in NW China have been checked using solid state 13C NMR and flash pyrolysis-GC/MS. Study shows some Jurassic collodetrinites are rich in aliphatic products in pyrolysates, consisting with the high amount of methylene carbon in 13C NMR spectra. In contrast, pyrolysates of Jurassic collotelinites are rich in phenols and alkylbenzenes. Also one Pennsylvanian and one Permian vitrinite selected from the Ordos basin, NW China have been checked for comparison. The proportion of aliphatics is low in pyrolysates, and aliphatic carbon peak in 13C NMR spectrum of Permian vitrinite is mostly composed of gas-prone carbons compared with collodetrinites in those Jurassic basins. But both pyrolysis and 13C NMR data shows the Pennsylvanian vitrinite is not only gas-prone but also oil-prone. Relatively high proportion of long chain aliphatic structure of some Jurassic vitrinite in Junggar, Turpan-Hami basins may be due to the contribution of liptodetrinites, which may be included during the formation of vitrinites. And it seems that suberinite is the most possible precursor of long chain aliphatics in the structure of Jurassic collodetrinite.

Low-mature gases and typical low-mature gas fields in China

No natural gas pool of industrial importance could be formed at the low-evolution stage of organic matter. In the 1980s, on the basis of the development in exploration practice, the hypotheses of bio-thermo-catalytic transitional zone gases and early thermogenic gases were proposed. The lower-limit Ro values for the formation and accumulation of natural gases of industrial importance have been expanded to 0.3%–0.4%. In the light of the two-stage model established on the basis of carbon isotope fractionation in coal-type natural gases, the upper-limit Ro values have been set at 0.8%–1.0%. In terms of the geological practice in the low-mature gas zones and China’s main coal-type gas fields, it is feasible and proper to set the upper-limit Ro value of low-mature gases at 0.8%. Supper-large gas fields such as the Urengoy gas field in western Siberian Basin should belong to low-mature gas fields, of which the natural gas reserves account for more than 20% of the global proven reserves, providing strong evidence for the significance of such a type of resources. The proven natural gas reserves in the Turpan-Hami Basin of China have almost reached 1000 ×108 m3. The main source rocks in this area are the Jurassic Xishanyao Formation, which occurs as a suite of coal series strata. The corresponding thermal evolution indices (Ro) are mainly within the range of about 0.4%–0.8%, the δ13C1 values of methane vary between −44‰ and −39‰ (correspondingly Ro =0.6%–0.8%), and those of ethane are within the range of −29‰–−26‰, indicating that natural gases in the Turpan-Hami Basin should be designated to coal-type low-mature gases. The light hydrocarbon evolution indices of natural gases also fall within the area of low evolution while the precursor type of light hydrocarbons also shows the characteristics of the coal-type. The geological background, carbon isotopic composition and light hydrocarbon index all provide strong evidence suggesting that the proven natural gases in the Turpan-Hami Basin are low-mature gases. In China a gas field with the gas reserves reaching 300 ×108 m3 can be defined as a large gas field, and thus the proven low-mature gases in the Turpan-Hami Basin are equivalent to the reserves of three large gas fields. Its existence is of great significance in research on and exploration of low-mature gases in China.

A Comprehensive Appraisal on the Characteristics of Coal-Bed Methane Reservoir in Turpan-Hami Basin

Abstract The rich coal-bed methane resources in the Turpan-Hami Basin are mainly located in the Shisanjianfang, Hami, Shanshan, Sha'erhu, Kekeya, Kerjian, Aidinghu inclines and the Dananhu coal-bed methane reservoirs. The bigger coal-bed reservoirs are sitting at a depth of less than 1500 m. The coalbed methane generation, storage and confining conditions of the Turpan-Hami basin can be indicated by eight key parameters. They are coal-bed thickness, coal rank, missing period, permeability, Langmuir volume, rock covering ability, structural confinement and hydrodynamic sealing environment. These parameters constitute a comprehensive appraisal index system of the coal-bed methane reservoir characteristics of the Turpan-Hami basin. In these parameters, the missing period of coal-bed methane is indicated by a stratum missing intensity factor. It reflects the relative exposure period of coal series. The results of a fuzzy comprehensive judgment showed that the Shisanjianfang coal-bed methane reservoir has the best prospects for exploitation and the Sha'erhu, Shanshan, Hami coal-bed methane reservoirs are next in line.

A review of the Cu–Ni sulphide deposits in the Chinese Tianshan and Altay orogens (Xinjiang Autonomous Region, NW China): Principal characteristics and ore-forming processes

Several Cu–Ni sulphide deposits and occurrences have recently been discovered along parallel deep faults in the Chinese Tianshan and Altay orogenic belts, Xinjiang Province, NW China. The Kalatongke and several other Cu–Ni mineralized intrusions are located along the Irtysh fault, which separates the Altay orogenic belt from the Junggar basin. The Huangshan, Huangshandong, Xiangshan, Tudun, Erhongwa, Tula’ergen, and Hongling deposits occur along the Kanggurtag suture, which separates the Jueluotage orogenic belt from the Turpan-Hami (Tuha) basin. The Baishiquan, Tianyu, and Tianxiang deposits are located along the Arqikekuduke fault, which separates the Jueluotage orogenic belt from the Central Tianshan Precambrian terrane. The Poyi, Poshi, and Luodong deposits are located along the Baidiwa fault, which separates the Central Tianshan Precambrian terrane from the Beishan Paleozoic rift. Re–Os dating of Cu–Ni sulphide ores reveals that these Cu–Ni ore belts formed in a narrow age range of 298–282 Ma. This age range is about the same as those of associated intrusions and dykes dated by the SHRIMP zircon U–Pb method. Tectonic and geochronological constraints suggest that the amalgamation of continental blocks mainly occurred during the Late Carboniferous in the Central Asian orogenic belt. Large-scale hydrothermal and magmatic metallogenesis in the region occurred during post-collisional stages of Latest Carboniferous to Early Permian age. The Cu–Ni sulphide deposits are part of this metallogenic event. The Cu–Ni orthomagmatic sulphide deposits in northern Xinjiang are represented by: (1) net-textured type deposits by segregation of a Cu–Ni metal sulphide melt and (2) magma conduit type. Some mafic–ultramafic suites exhibit lithological zoning caused by strong differentiation. Stratiform orebodies are hosted by ultramafic rocks at the base of the magma chamber. Good examples are the Kalatongke, Huangshandong, and Poshi deposits. Others, such as the Xiangshan, Baishiquan, Tianyu, and Tula’ergen deposits, are hosted by magma conduits, consisting of peridotite, troctolite, and pyroxenite. These ultramafic rocks either occur within faults or are surrounded by gabbroic and dioritic intrusions. These two types of orthomagmatic Cu–Ni sulphide deposits are also distributed along the same ore belts. For instance, the differentiated sill-related Huangshandong deposit co-exists with the magma conduit type Tula’ergen deposit in the Jueluotage orogenic belt. Orthomagmatic Cu–Ni sulphide deposits in northern Xinjiang formed during post-collisional extension and are possibly related to a Late Carboniferous–Early Permian mantle plume event. The mafic–ultramafic suites and associated Cu–Ni deposits are commonly accompanied by dyke swarms and are characterized by elongated outcrops occurring along parallel E–W-trending regional faults. These mafic–ultramafic suites and accompanying dyke swarms are generally fractionated, implying that they were feeders of presently eroded flood basalts.

Basical characteristics of fluid geologic process of interlayer oxidation zone sandstone-type uranium deposit

This paper reveals the physicochemical properties such as component, formulation, genesis, tem-perature, pH, Eh, salinity and pressure of all main alteration fluid of interlayer oxidation zone sand-stone-type uranium deposits after studying the geologic process and geochemistry of internal typical sandstone-type uranium deposits such as Shihongtan deposit in the Turpan-Hami basin, 512 deposit in the Yili basin, Dongsheng deposit in the Ordos basin. The composition of fluid can be divided into two parts based on the analysis of inclusion: one can be affirmed as atmospheric water with ordinary temperature epigenesist according to the character of hydrogen and oxygen isotope of inclusion, the other is natural gas containing gaseous hydrocarbon like CH4, and CO2 as well as a little H2S, CO, H2, N2 and so on, it always contains a small quantity of hydrocarbon liquid in petroliferous basins. The fluid property of oxidation alteration zone is always oxidation alkaline, and neutrality or weak acid-weak alkaline and reducibility during the metallizing process, but at secondary reduction or deoxidization zone it becomes strong reduction alkaline. Oxygenic groundwater in the fluid is the activate and mig-ratory medium of uranium element, but the gaseous hydrocarbon like CH4 as well as H2, H2S, CO from natural gas is the important sedimentary reducer of uranium mineral; the transformation of pH,Eh in fluid environment is the main reason for the formation of uranium metallization.

Mesozoic-Cenozoic Deformation of the Central Structure Belt in the Turpan-Hami Basin, Northwest China: Tectonic Evolution of an Intracontinental Basin, Central Asia

The central structure belt (CSB) in the Turpan-Hami Basin is composed of the Huoyanshan structure and the Qiketai structure, formed in the Late Triassic—Early Jurassic, and is characterized by extensional tectonics. The thickness of strata in the hanging wall of the fault is clearly larger than that in the footwall, and a deposition center evolved in the Taibei sag where the hanging wall of the fault is located. In the Late Jurassic, collision between the Lhasa block and the Eurasia continent resulted in the transformation of the Turpan-Hami Basin from an extensional into a compressional structure, and consequently in the tectonic inversion of the CSB from an extensional normal fault in the earlier stage to a compressive thrust fault in the later stage. Tertiary collision between the Indian and Eurasian plates occurred around 55 Ma, and this Himalayan orogenic event played a profound role in shaping the Tianshan area. However, the effect of the collision on this area was delayed and culminated approximately in Late Oligocene—Early Miocene time. The CSB was strongly deformed and thrust upward as a result of this tectonic event.

Elemental Geochemistry of the Interlayer Oxidation Zone in the Shihongtan Sandstone Type Uranium Deposit, Xinjiang

Abstract According to the oxidation intensity of ore‐hosting sandstone, the interlayer oxidation zone of the Shihongtan sandstone‐type uranium deposit in the Turpan‐Hami basin can be divided into 4 geochemical subzones, namely, intensely‐oxidized, weakly‐oxidized, redox and unoxidized primary subzones. The elemental geochemical characteristics of the four subzones have been studied in detail, and the results show that U, together with other elements such as Re, Mo, Se, Sr, S, REE, Corganic etc., is enriched in the redox subzone. Re and U have similar geochemical properties in the reduction‐oxidation process. The geochemical properties of Mo and Se are similar to those of U in the reduction condition, but different from those of U in the oxidation condition. It is proposed that the ore‐hosting layers can provide a curtain mount of uranium for uranium mineralization.

Mesozoic-Cenozoic thermal history of Turpan-Hami Basin : Apatite fission track constraints

Apatite fission track dating is carried out on nine samples collected from the central part (Lianmuqin section) and from both northern and southern margins of Turpan-Hami Basin. The fission-track ages of seven Jurassic samples are distinctly younger than depositional ages. In contrast, the fission-track ages of two Cretaceous samples are older than, or as old as depositional ages. These observations indicate that the Jurassic samples have been annealed or partially annealed, whereas the Cretaceous samples have not been annealed. The further thermal modelling results show that Turpan-Hami Basin experienced a Late Cretaceous period (120-100 Ma) of tectonic uplift with rapid cooling and exhumation of sediments. The samples underwent a Cenozoic period of reburial and re-heating and were exhumed again at 10-8 Ma. Supported by the Major State Basic Research Development Program of China (Grant No. 2001CB409804) and the National Natural Science Foundation of China (Grant No. 40173001).

New Chronological Evidence for Indosinian Diagenetic Mineralization in Eastern Xinjiang, NW China

Abstract There have been conflicting ideas about the Indosinian mineralization in E. Xinjiang, a subject that has attracted many geologists' attention over a long period. Isotopic dating shows that the Shiyingtan gold deposit located on the southern margin of the Turpan-Hami basin has a quartz fluid inclusion Rb-Sr isochron age of 237±9 Ma (95% conf.); the Shuangfengshan gold deposit on the southern margin of the Junggar orogenic belt has a quartz fluid inclusion Rb-Sr isochron age of 226±21 Ma (95% conf.); the Weiya vanadium-titanium magnetite in the E. Tianshan mountains has a mineral-whole rock Sm-Nd isochron age of 220 ±30 Ma (95% conf.); the Jinwozi and Jinwozi 210 gold deposits in the E. Tianshan mountains have quartz fluid inclusion Rb-Sr isochron ages of 228±22 Ma (95% conf.) and 230±6 Ma (95% conf.), respectively; and the Xiaobaishitouquan scheelite deposit in the E. Tianshan mountains has a quartz fluid inclusion Rb-Sr isochron age of 248±7 Ma (95% conf.). The metallogenetic ages mentioned above prove the existence of Indosinian mineralization in E. Xinjiang, and the metallogenetic event might have been related to Triassic intraplate magmatic evolution, intra-continent subduction, strike-slip shoving and ductile shearing in the studied area, representing another mineralization peak after the Late Paleozoic.

Integrated Provenance Analysis of a Complex Orogenic Terrane: Mesozoic Uplift of the Bogda Shan and Inception of the Turpan-Hami Basin, NW China

We employ petrographic and advanced geochemical tech- niques to better document the evolution of the Turpan-Hami basin based on the unique geologic histories of the arc terranes that served as potential sources of Turpan-Hami deposits. First, a provenance study of Permian through Cretaceous sandstone of the Turpan-Hami basin reveals temporal and spatial changes in dominant source ter- ranes that provided detritus to the basin. Volcanic-lithic-rich Upper Permian sandstone (mean Qm 19F18Lt63 ;Q p 7Lvm89Lsm4 ;Q m 48P39K13) followed by more quartzose compositions in Triassic sandstone (mean Qm 41F19Lt40 ;Q p 20Lvm75Lsm5 ;Q m 68P21K11) indicate progressive un- roofing of the extinct northern and central Tian Shan arc terranes to the south of Turpan-Hami. A sharp change to sedimentary-lithic-rich Lower Jurassic sandstone (mean Qm 47F16Lt37 ;Q p 16Lvm42Lsm42; Qm 75P12K13) overlain by a return to volcanic-lithic-rich Middle Ju- rassic sandstone (mean Qm 39F21Lt40 ;Q p 14Lvm51Lsm35 ;Q m 65P21K14) points to the initial uplift and unroofing of the largely andesitic Bogda Shan to the north, which first shed its sedimentary cover as it emerged to become the partition between the Turpan-Hami and southern Jung- gar basins. Second, geochronological, trace-element, and Sm-Nd isotopic varia- tions among granitoids in the late Paleozoic Tian Shan orogenic belt provide a further test of Mesozoic uplift of the Bogda Shan. On the basis of previous models of crustal compositions throughout the South, Central, and North Tian Shan, Bogda Shan, and East and West Jung- gar terranes, we infer that isotopically enriched granitic cobbles (av- erage eNdi 5 20.50, n 5 6) contained in Lower Triassic deposits in the north-central Turpan-Hami basin were derived from the continen- tal crustal Central Tian Shan terrane, south of Turpan-Hami, and not from the more oceanic North Tian Shan, Bogda Shan, and East and West Junggar terranes, north of the Turpan-Hami basin. We therefore infer that the ancestral Bogda Shan had not been uplifted by the Early Triassic, and that prior to this time, a unified Junggar-Turpan-Hami basin existed during Late Permian deposition of extensive lacustrine deposits.