Chief Editor:HOU Zengqian
Governing Body:China Association for Science and Technology
Organizer:Geological Society of China
start publication :1922
ISSN:ISSN 1000-9515
CN:CN 11-2001/P
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2017, 91(2):1-1.
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2017, 91(2):Ⅰ-Ⅰ.
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LI Yong , YAN Liang , SHAO Chongjian , WANG Zhengjiang , YAN Zhaokun , YU Qian , ZHOU Rongjun , LI Haibin
2017, 91(2):379-395.
Abstract:Depending on the analysis of the coeval sedimentary geometry and subsidence mechanism in the Longmen Shan foreland basin, three models about the coupling relationship between Longmen Shan uplift and foreland basin subsidence since the Indosinian have been proposed: (1) crustal shortening and its related wide wedge-shaped foreland basin, (2) crustal isostatic rebound and its related tabular foreland basin, and (3) lower crustal flow and its related narrow wedge-shaped foreland basin. Based on the narrow wedge-shaped foreland basin developed since 4 Ma, it is believed that the narrow crustal shortening and tectonic load driven by lower crustal flow is a primary driver for the present Longmen Shan uplift and the Wenchuan (Ms 8.0) earthquake.
YANG Wei , LI Jianfeng , GUO Zhaojie , Marc JOLIVET , Gloria HEILBRONN
2017, 91(2):396-413.
Abstract:The Mesozoic–Cenozoic uplift history of South Tianshan has been reconstructed in many ways using thermochronological analyses for the rocks from the eastern Kuqa Depression. The main difference in the reconstructions concerns the existence and importance of Early Cretaceous and Paleogene tectonic activities, but the existence of a Cenozoic differential uplift in the Kuqa Depression remains enigmatic. Here, we present new apatite fission-track ages obtained for 12 sandstone samples from the well-exposed Early Triassic to Quaternary sequence of the Kapushaliang section in the western Kuqa Depression. The results reveal that there were four pulses of tectonic exhumation, which occurred during the Early Cretaceous (peak ages of 112 and 105 Ma), Late Cretaceous (peak age of 67 Ma), Paleocene–Eocene (peak ages at 60, 53, and 36 Ma), and early Oligocene to late Miocene (central ages spanning 30–11 Ma and peak ages of 23 and 14 Ma), respectively. A review of geochronological and geological evidence from both the western and eastern Kuqa Depression is shown as follows. (1) The major exhumation of South TiansShan during the Early Cretaceous was possibly associated with docking of the Lhasa block with the southern margin of the Eurasian plate. (2) The Late Cretaceous uplift of the range occurred diachronically due to the far-field effects of the Kohistan-Dras Arc and Lhasa block accretion. (3) The Paleogene uplift in South Tianshan initially corresponded to the far-field effects of the India–Eurasia collision. (4) The rapid exhumation in late Cenozoic was driven by the continuous far-field effects of the collision between India and Eurasia plates. The apatite fission-track ages of 14–11 Ma suggest that late Cenozoic exhumation in the western Kuqa Depression prevailed during the middle to late Miocene, markedly later than the late Oligocene to early Miocene activity in the eastern segment. It can be hypothesized that a possible differential uplift in time occurred in the Kuqa Depression during the late Cenozoic.
LIU Qianqian , SHI Yanan , WEI Dongping , HAN Peng , CHEN Shunyun , LIU Peixun , LIU Liqiang
2017, 91(2):414-428.
Abstract:The Xianshuihe fault (XSHF) zone, characterized by intense tectonic activity, is located at the southwest boundary of the Bayan Har block, where several major earthquakes have occurred, including the 2008 Wenchuan and the 2013 Lushan earthquakes. This study analysed underground temperature sequence data for four years at seven measuring points at different depths (maximum depth: 18.9 m) in the southeastern section of the XSHF zone. High-frequency atmospheric noise was removed from the temperature sequences to obtain relatively stable temperature fields and heat fluxes near the measurement points. Our measurements show that the surrounding bedrock at (the seven stations distributed in the fault zone) had heat flux values range from ?41.0 to 206 mW/m2, with a median value of 54.3 mW/m2. The results indicate a low heat flux in the northern section of Daofu-Kangting and a relatively high heat flux in the southern section of Kangting, which is consistent with the temperature distributions of the hot springs near the fault. Furthermore, our results suggest that the heat transfer in this field results primarily from stable underground heat conduction. In addition, the underground hydrothermal activity is also an obvious factor controlling the geothermal gradient.
WU Fuyao , RAN Yongkang , XU Liangxin , CAO Jun , LI An
2017, 91(2):429-442.
Abstract:The easternmost Tian Shan lies in eastern Xinjiang, Central Asia. The South Barkol basin fault (SBF) in the northern part of the easternmost Tian Shan is a major tectonic structure in this orogenic region. The late Quaternary activity, paleoseismology, and deformation characteristics of the fault provide important clues for understanding the tectonic process of the eastern Tian Shan orogen and implementing seismic mitigation. Through interpretation of high-resolution satellite images, unmanned aerial vehicle measurements, and detailed geological and geomorphic investigations, we suggest that the fault exhibits clear left-lateral slip along its western segment. Paleoseismic trenches dug near Xiongkuer reveal evidence of six large paleoearthquakes. The four latest paleoearthquakes were dated: the oldest event occurred at 4663 BC–3839 BC. Data on the horizontal offsets along the probable 1842 Barkol earthquake coseismic rupture suggest clear multiple relationships between cumulative offsets and possible ~4 m of coseismic left-lateral slip per event. From the cumulative offsets and 14C sample ages, we suggest an average Holocene left-lateral slip rate of 2.4–2.8 mm/a on the SBF, accounting for ~80% of lateral deformation within the entire eastern Tian Shan fault system. This result is comparable with the shortening rate of 2–4 mm/a in the whole eastern Tian Shan, indicating an equal role of strike-slip tectonics and compressional tectonics in this orogen, and that the SBF may accommodate substantial lateral tectonic deformation.
WU Jiwen , HUANG Xuemeng , XIE Furen
2017, 91(2):443-454.
Abstract:The Garzê–Yushu strike-slip fault in central Tibet is the locus of strong earthquakes (M > 7). The deformation and geometry of the co-seismic surface ruptures are reflected in the surface morphology of the fault and depend on the structure of the upper crust as well as the pre-existing tectonics. Therefore, the most recent co-seismic surface ruptures along the Garzê–Yushu fault zone (Dangjiang segment) reveal the surface deformation of the central Tibetan Plateau. Remote sensing images and field investigations suggest a 85 km long surface rupture zone (striking NW-NWW), less than 50 m wide, defined by discontinuous fault scarps, right-stepping en echelon tensional cracks and left-stepping mole tracks that point to a left-lateral strike-slip fault. The gullies that cross fault scarps record systematic left-lateral offsets of 1.8 m to 5.0 m owing to the most recent earthquake, with moment magnitude of about M 7.5, in the Dangjiang segment. Geological and geomorphological features suggest that the spatial distribution of the 1738 co-seismic surface rupture zone was controlled by the pre-existing active Garzê–Yushu fault zone (Dangjiang segment). We confirm that the Garzê–Yushu fault zone, a boundary between the Bayan Har Block to the north and the Qiangtang Block to the south, accommodates the eastward extrusion of the Tibetan Plateau and generates strong earthquakes that release the strain energy owing to the relative motion between the Bayan Har and Qiangtang Blocks.
XIONG Fahui , YANG Jingsui , ROBINSON Paul T. , DILEK Yildirim , MILUSHI Ibrahim , XU Xiangzhen , ZHOU Wenda , ZHANG Zhongming , RONG He
2017, 91(2):455-468.
Abstract:Various combinations of diamond, moissanite, zircon, corundum, rutile and titanitehave been recovered from the Bulqiza chromitites. More than 10 grains of diamond have been recovered, most of which are pale yellow to reddish–orange to colorless. The grains are all 100–300 μm in size and mostly anhedral, but with a range of morphologies including elongated, octahedral and subhedral varieties. Their identification was confirmed by a characteristic shift in the Raman spectra between 1325 cm?1 and 1333 cm?1, mostly at 1331.51 cm?1 or 1326.96 cm?1. This investigation extends the occurrence of diamond and moissanite to the Bulqiza chromitites in the Eastern Mirdita Ophiolite. Integration of the mineralogical, petrological and geochemical data of the Bulqiza chromitites suggests their multi–stage formation. Magnesiochromite grains and perhaps small bodies of chromitite formed at various depths in the upper mantle, and encapsulated the ultra–high pressure, highly reduced and crustal minerals. Some oceanic crustal slabs containing the magnesiochromite and their inclusion were later trapped in suprasubduction zones, where they were modified by tholeiitic and boninitic arc magmas, thus changing the magnesiochromite compositions and depositing chromitite ores in melt channels.
LIU Jianguo , HATTORI Keiko , WANG Jian
2017, 91(2):469-485.
Abstract:High-Al chromite from the Kudi chromitites contains a wide range of mineral inclusions. They include clinopyroxene, amphibole, phlogopite, olivine, orthopyroxene, apatite, base-metal sulfides, calcite and brucite. The modal abundance of inclusions vary greatly among different grains of chromite. The common inclusions are clinopyroxene and amphibole, which occur as monomineral or polymineral associated with other minerals. The shapes of these inclusions tend to follow the growth plane of host chromite. Mineral assemblages and textures demonstrate that some inclusions (olivine, clinopyroxene) are trapped during magmatic stage, and most of the inclusions (e.g., amphibole, phlogopite) are trapped during recrystallization of chromite. Sulfide inclusions are pentlandite, chalcopyrite and cubanite. They occur either as isolated grains or together with silicate minerals, and formed from the separation of sulfide-bearing liquid from silicate magma. The parental magma of chromitites contains Al2O3 15.0wt%–16.5wt%, TiO20.30wt%–1.05wt% based on calculation with the composition of chromite, similar to parental magma of high-Al chromitites from elsewhere and the estimated melt composition is comparable with that of MORB. Considering the high-Mg olivine in disseminated chromitite and abundant hydrous inclusions, we propose that Kudi chromitites formed beneath a volcanic front during the subduction initiation of Proto-Tethys.
2017, 91(2):486-499.
Abstract:The ca. 1.5 Ga mafic intrusions in the Zhuqing area, predominantly composed of alkaline gabbroic rocks in the Kangdian region of SW China, occur as dykes or irregular small intrusions hosting Fe–Ti–V mineralization. All of the intrusions that intrude the dolomite or shales of the Mesoproterozoic Heishan Formation of the Huili Group are composed of three cyclic units from the base upward: a marginal cyclic unit, a lower cyclic unit and an upper cyclic unit. The Fe–Ti–V oxide ore bodies are hosted in the lower and upper cyclic units. The textural relationships between minerals in the intrusions suggest that titanomagnetite formed earlier than silicate grains because euhedral magnetite and ilmenite grains were enclosed in clinopyroxene and plagioclase. Both the magnetitess–ilmenitess intergrowths due to subsolidus oxidation–exsolutions and the relative higher V distribution coefficient between magnetite and silicate melts in the gabbros from the Zhuqing area are different from those of other typical Fe–Ti bearing mafic rocks, suggesting that the oxygen fugacity was low in the gabbric rocks from the Zhuqing area. This finding was further confirmed by calculations based on the compositions of magnetite and ilmenite pairs. The clinopyroxene, magnetite and ilmenite in the intrusions from the Zhuqing area had considerably lower MgO than those of other typical Fe–Ti oxide-rich complexes, suggesting that the titanomagnetite from the intrusion may have crystallized at a relatively late stage of evolution from a more evolved magma. Titanomagnetite first fractionally crystallized and subsequently settled in the lower parts of the magma chamber, where it concentrated and formed Fe–Ti–V oxide ore layers at the bases of the lower and upper cycles. Moreover, the occurrence of multiple Fe-Ti oxide layers alternating with Fe-Ti oxide-bearing silicate layers suggests that multiple pulses of magma were involved in the formation of the intrusions and related Fe-Ti-V oxide deposits in the Zhuqing area.
XIA Zhaode , XIA Mingzhe , JIANG Changyi
2017, 91(2):500-514.
Abstract:The Xingdi mafic-ultramafic intrusions occur in the northeastern margin of the Tarim craton. The Xingdi No. 3 intrusion is the smallest of four intrusions, with an exposed area of 1.7 km2, and the zircon U-Pb age of the intrusion is 752±4 Ma. The intrusion consists of gabbros, pyroxenites and peridotites, and exhibits a crystallization sequence of the main rock-forming minerals as olivine, orthopyroxene, clinopyroxene and plagioclase. Mineralization occurred at or near the boundaries of the intrusion between pyroxenites and peridotites, and appears as a layered or lenticular shape about 500 m long and 4–15 m wide. The primary sulfides have a relatively simple mineralogy dominated by pyrrhotite-pentlandite-chalcopyrite assemblages, which occur as droplet, star-like and graphic texture and locally sideronitic structures. Geochronological and geochemistry investigations suggest that the Xingdi mafic-ultramafic intrusions and coeval volcanic rock in the Kuluktag area of the Tarim craton formed in an intracontinental breakup environment. Based on the composition of the dominant rock-forming minerals and covariant relationships of other oxides versus MgO, the parental magma of the Xingdi No. 3 intrusion belongs to high-Mg tholeiitic basaltic magmas with MgO of 10.78 wt%. The Xingdi No. 3 intrusive rocks are characterized by light REE enrichment relative to heavy REE, negative Nb-Ta anomalies, low 143Nd/144Nd ratios (from 0.511183 to 0.511793) and high initial 87Sr/86Sr ratios (from 0.7051 to 0.7113). The magma was derived from the enriched-lithospheric mantle and was contaminated during emplacement. According to rock assemblages, mineralization, olivine characteristics, geochemical characteristics and mass balance, there are better copper-nickel ore prospects in the Xingdi No. 3 intrusion than in the other three intrusions in the area.
ZHU Feilin , SHI Zeming , XIONG Fuhao , NI Shijun , BAI Mei
2017, 91(2):515-529.
Abstract:Cu–Au mineralization is rare in the Jurassic–Early Tertiary batholiths related to the India–Asia collision. Geochemical analysis and U–Pb isotope chronology was carried out on Shuangbujiere biotite hornblende granodiorite from the Zedong area. Zircon grains of the biotite hornblende granodiorite show oscillatory growth zonation and have high Th/U ratios of 1.08–2.39, indicating a magmatic origin for the zircons. Geochrological test yielded a LA-ICP-MS U-Pb age of 51.5±1.0 Ma, suggesting that the emplacement age of the biotite hornblende granodiorite is Early Eocene. The Shuangbujiere biotite hornblende granodiorites have geochemical features characteristic of adakite and are associated with a calc–alkaline metaluminous I-type granite enriched in Sr, high in Mg# (49.6–54.9) and Sr/Y, and depleted in Y and Yb. These results indicate that this intrusion formation may have been associated with crustal thickening caused by the early collision of the Indian and Eurasian Plates. As the process of crustal thickening continued, the heating of the underplated basaltic magma caused the thickened lower crust amphibolite to dehydrate the melt and form a high-K calc–alkaline adakitic melt at about 848°C. Meanwhile, magma mixing of the underplated basaltic melt and high-K calc–alkaline adakitic melt formed a high-Mg# adakite representative of the sys-collisional tectonic setting.
DUAN Shigang , ZHANG Zuoheng , WANG Dachuan , LI Fengming
2017, 91(2):530-544.
Abstract:The Dabate Mo-Cu deposit is a medium-sized porphyry-type deposit in the Sailimu Lake region, western Tianshan, China. We present the geology, geochemistry and zircon U-Pb geochronology of granite porphyries from the Dabate district with the intent to constrain their tectonic setting and petrogenesis. Porphyries in the Dabate district include granite porphyry I (gray white color with large phenocrysts), granite porphyry II (pink color with small phenocrysts) and quartz porphyry. Granite porphyry II is the Cu and Mo ore-bearing granitoid in the Dabate deposit. LA-ICPMS zircon U-Pb analyses indicate that granite porphyry II was emplaced at 284.2±1.8 Ma. Granite porphyry I and II have similar geochemical features and are both highly fractionated granites: (1) They have high SiO2 content (70.93–80.18 wt% and 72.14–72.64 wt%, respectively), total alkali (7.58–8.95 wt% and 9.35–9.68 wt%, respectively), mafic index (0.95–0.98 and 0.93–0.94, respectively) and felsic index (0.79–0.94 and 0.89–0.91, respectively); (2) They are characterized by pronounced negative Eu anomaly, “seagull-style” chondrite-normalized REE patterns and “tetrad effect” of REE; (3) They are rich in Rb, K, Th, Ta, Zr, Hf, Y and REE, but depleted in Sr, P, Ti and Nb. The magma of granite porphyries in Dabate can be interpreted to have been generated by partial melting of the upper crust due to mantle-derived magma underplating in a post-collisional extensional setting.
XU Bo , HOU Zengqian , ZHENG Yuanchuan , ZHOU Ye , ZHOU Limin , YANG Yu , HAN Yanwei , ZHEN Guo , WU Changda
2017, 91(2):545-564.
Abstract:The Gangdese batholith, more than 2500 km in length, is composed mainly of Jurassic-Miocene igneous rocks. This batholith is one of the most important constituents of the Tibetan orogenesis and provides an ideal place for study of Neo-Tethyan ocean geodynamic evolution and plateau uplift. Recent studies on the Gangdese Jurassic felsic magmatism highlight its juvenile source. However, important aspects concerning the genesis of the juvenile magmatism and related deep geodynamic evolution are still unclear. Here, we report detailed petrological, geochronological, geochemical, whole-rock Sr-Nd isotopic, and in situ Sr-Hf isotopic data for a recently identified hornblende gabbro in the Dongga area, southern Lhasa sub-block. This hornblende gabbro is dominated by hornblende and plagioclase, dated at Early Jurassic (ca. 180–190 Ma), and characterized by a narrow compositional range in SiO2 (49.38wt%–52.27wt%), MgO (4.08wt%–7.00wt%), FeO (10.43wt%–11.77wt%), Na2O (2.58wt%–3.51wt%), and K2O (0.48wt%–1.53wt%). It has depleted isotopic signatures, with whole-rock (87Sr/86Sr)i ratios of 0.7033–0.7043, εNd(t) values of +4.90 to +6.99, in situ plagioclase (87Sr/86Sr)i ratios of 0.7034–0.7042, and zircon εHf(t) of +12.2 to +16.8. Our results integrated with published data suggest a model of Gangdese juvenile crustal growth by a subduction-related water-enriched mantle wedge. The hydrous partial melting of the lithosphere mantle was triggered by the dehydration of a Neo-Tethyan oceanic slab. This mafic magmatism emplaced in the middle-lower crust of intraoceanic arcs or active continental margins, leading to Jurassic juvenile crustal growth in southern Tibet.
CHEN Guochao , PEI Xianzhi , LI Ruibao , LI Zuochen , LIU Chengjun , CHEN Youxin , PEI Lei , WANG Meng , LI Xiaobing
2017, 91(2):546-580.
Abstract:The Qushi'ang granodiorite (QSG) is located at the central east of the ophiolitic melange belt in the East Kunlun Orogenic Belt (EKOB) in the northern margin of the Qinghai-Tibetan Plateau. LA-MC-ICP-MS zircon U–Pb dating suggests that the granodiorite and mafic microgranular enclaves (MMEs) crystallized 246.61±0.62 and 245.45±0.9 Ma ago, respectively. Granodiorite, porphyritic diorite, and MMEs are metaluminous and medium-K calk - alkaline series, with island-arc magma features, such as LILE enrichment and HFSE depletion. The porphyritic diorite has high Cr (13.50 ppm to 59.01 ppm), Ni (228.53 ppm to 261.29 ppm), and Mg# (46–54). Granodiorite and porphyritic diorite have similar mineral compositions and evolved major and trace elements contents, particularly Cr and Ni, both of which are significantly higher than that in granites of the same period. The crystallization age of MMEs is close to that of granodiorite, and their major and trace elements contents are in-between porphyritic diorite and granodiorite. The results suggest that the original mafic magma, which was the product of mantle melting by subduction process, intruded into the lower crust (Kuhai Rock Group), resulting in the formation of granodiorite. Countinous intrusion of mafic magma into the unconsolidated granodiorite formed MMEs and porphyritic diorite. The granodiorite reformed by late-stage strike-slip faulting tectonic event indicates that the strike-slip fault of Middle Kunlun and the collision of the Bayanhar block with East Kunlun were later than 246 Ma. Therefore, the formation of the QSG not only indicates the critical period of evolution of East Kunlun but also represents the tectonic transition from oceanic crust subduction to slab breaking.
DING Shuai , CHEN Yuchuan , TANG Juxing , ZHENG Wenbao , LIN Bin , YANG Chao
2017, 91(2):581-601.
Abstract:The Duolong area is the most important part of the Western Bangong-Nujiang Suture Zone porphyry Cu(Au) metallogenic belt, in Tibet, China. Here new detailed data are presented from LA-ICP-MS zircon U-Pb, whole-rock geochemical, and in?-situ zircon Hf isotope analyses for igneous rocks in the large Naruo deposit (2.51 Mt of Cu and 82 t of Au) which is located ~2 km NE of the Duolong (Duobuza and Bolong) super-large gold-rich porphyry copper deposit. We integrated our results with previous research of other porphyry deposits in the Duolong area and have identified the timing, geodynamic setting, and petrogenesis of the mineralization-associated magmatic events. Based on the measurements, the Duolong area porphyry Cu(Au) deposit formations are associated with Early Cretaceous intermediate-felsic magmatism, which is consistent with U-Pb zircon ages of 120 Ma. All the main intrusive rocks in the ore-concentrated area have similar lithogeochemical characteristics; they show a relative enrichment in both light rare earth elements (LREEs) and large-ion lithophile elements (LILEs: Rb, Ba, K, etc.) and relative depletion in both heavy rare earth elements (HREEs) and high field strength elements (HFSEs: Nb, Ta, Zr, Hf, etc.). Moreover, the granite porphyry shows positive εHf(t) values between 1.38–7.37 suggesting that magmas were potentially derived from the partial melting of a depleted mantle wedge that had been metasomatized by subducted slab-derived fluids or melts. This paper points out that the formation of the porphyry-epithermal Cu(Au) deposit in the Duolong area was dominated by northward subduction of the Bangongco Tethys Plate beneath the Qiangtang block in the Early Cretaceous (124–114 Ma), when the subducted oceanic crust reached 50–70 km underground and generated different degrees of phase transformation, which lead to a melt produced by dehydration of amphibole minerals, a metasomatized mantle wedge, and induced mantle partial melting that produced the magma. Those deposits occurred in a continental arc tectonic setting, which is similar to the continental margin arc environment of the ocean-continent subduction setting of the Andes metallogenic belt in South America.
LIN Bin , CHEN Yuchuan , TANG Juxing , WANG Qin , SONG Yang , YANG Chao , WANG Wenlei , HE Wen , ZHANG Lejun
2017, 91(2):602-616.
Abstract:The Tiegelongnan deposit is a newly discovered super-large porphyry-epithermal Cu-(Au) deposit in the western part of the Bangong Co-Nujiang metallogenic belt, Tibet (China). Field geology and geochronology indicate that the porphyry mineralization was closely related to the Early Cretaceous intermediate-felsic intrusions (ca. 123–120 Ma). Various epithermal ore and gangue mineral types were discovered in the middle-shallow part of the orebody, indicating the presence of epithermal mineralization at Tiegelongnan. Potassic, propylitic, phyllic and advanced argillic alteration zones were identified. 40Ar/ 39Ar dating of hydrothermal biotite (potassic zone), sericite (phyllic zone), and alunite (advanced argillic zone) in/around the ore-bearing granodiorite porphyry yielded 121.1±0.6 Ma (1σ), 120.8±0.7 Ma (1σ) and 117.9±1.6 Ma (1σ), respectively. Five hydrothermal mineralization stages were identified, of which the Stage IV pyrite was Rb-Sr dated to be 117.5±1.8 Ma (2σ), representing the end of epithermal mineralization. Field geology and geochronology suggest that both the epithermal and porphyry mineralization belong to the same magmatic-hydrothermal system. The Tiegelongnan super-large Cu-(Au) deposit may have undergone a prolonged magmatic-hydrothermal evolution, with the major mineralization event occurring at ca.120–117Ma.
Lü Jing , ZHOU Wen , XIE Runcheng , SHAN Yuming , ZHANG Chong , XU Hao
2017, 91(2):617-629.
Abstract:This work established a geological model for the 5th member of the Xujiahe Formation (X5 member) in the Xinchang gas field of the West Sichuan Depression based on the lithological, structural and depositional properties, as well as logging and well completion data and drill-core observations. Rock mechanical parameters were calculated according to rock mechanic experiments and rock mechanic interpretations from logging data. We also calculated the magnitudes and orientations of the in situ stresses based on acoustic emission tests, differential strain tests, fracturing behaviour and logging interpretations as well as anisotropy logging tests, borehole-breakout measurements and well-log data. Additionally, the present stress field of the X5 member was simulated using finite element numerical (FEM) simulation methods. The numerical simulation results indicate that the distributions of lithology and fractures are key factors that influence the present stress field. The stress field in the study area is discontinuous as a result of fractures and faults in the central and eastern areas. Stress is concentrated at the end sections and bends of faults, but dissipates with distance away from both sides of the faults. A longitudinal profile clearly demonstrates the zonality and continuity of the stress field and an increase with depth. The differential stress distribution is relatively uniform; however, large deviations occur in fracture zones.
CHEN Lan , XU Guiwen , DA Xuejuan , YI Haisheng , ZHU Zhangxiong , HUANG Zhaohui , LI Xiaogang
2017, 91(2):630-643.
Abstract:The marine oil shales of the Qiangtang Basin, northern Tibet, exposed in the Biluo Co, Tuonamu, Shenglihe and Changsheshan areas are believed to be important petroleum source rocks. This work comprehensively analyzed the carbon isotopes, trace elements, and calcareous nannofosills, ammonites and bivalves of the Biluo Co section in the Qiangtang Basin. The organic carbon isotopes show a positive excursion close to 2.17‰ (relative to PDB), which, albeit significantly smaller, may also be associated with other Early Toarcian Oceanic Anoxic Events (T-OAE) in the European epicontinental seas and the Tethyan continental margins. Coinciding with the Early Toarcian transgression, the oxygen deficiency in bottom water had led to dysoxic-anoxic conditions and deposition of black shales lacking benthic fauna. Under such condition, the redox-sensitive trace metals such as Mo, V, Ni, Cr, and U were enriched, in conjunction with high planktonic productivity of Watznaueriaceae calcareous nannofossils. Comparison of the results with the records of chemo- and biostratigraphy, as well as the palaeogeography during the Early Jurassic suggests that the anoxia linked to the Early Toarcian oceanic anoxic event was mainly caused by the high surface water temperature, sea-level rise and an increase of surface water productivity.
WANG Siqi , LIU Zhao , SHAO Jingli
2017, 91(2):644-657.
Abstract:Nyemo-Nagqu, Tibet, is rich in high-temperature geothermal resources. The geothermal fields in Yangbajain and Yangyi as well as 11 unexplored geothermal fields along the geothermal belt from Nyemo to Nagqu were systematically investigated and the hydrochemistry data were collected from the whole field. Meanwhile, H-O-C-S isotope data were obtained for the new fields, and H-O isotope data for the Yangbajain and Yangyi fields. A comparison of the Nyemo-Nagqu geothermal fields with those in the Yangbajain area shows that the types of high-temperature geothermal water are dominated by Cl-Na and Cl·HCO3-Na, while the types of medium-high-temperature geothermal water are dominated by HCO3-Na. The concentrations of Li, F, SiO2, and HBO2 in the geothermal water are positively correlated with Cl content, indicating possible mixing with magma water. The reservoir temperatures range from 90 to 270°C by geothermometers. Slight drifting of 18O was recorded at the Dongweng and Nyingzhong high-temperature geothermal fields, while more significant drifting was recorded at Gulu. The geothermal water is mainly replenished by atmospheric precipitation. The low tritium contents (<1 TU) of the geothermal water from Nyingzhong, Gulu, and Luoma indicate that it is mainly replenished by sub-modern (prior to 1952) water, while the high tritium content (8.4 TU) in Yuela implies modern water replenishment. Other geothermal fields are replenished by a mix of sub-modern fresher water. The isotopic data in this study show that the carbon and sulfur in the geothermal water originates mainly from sediment leaching, with some of the carbon and sulfur having a deep origin.
DU Guoliang , ZHANG Yongshuang , YANG Zhihua , Javed IQBAL , TONG Bin , GUO Changbao , YAO Xin , WU Ruian
2017, 91(2):658-668.
Abstract:The eastern Himalayan syntaxis is one of the most tectonically active and earthquake-prone regions on Earth where earthquake-induced geological disasters occur frequently and caused great damages. With the planning and construction of Sichuan-Tibet highway, Sichuan-Tibet railway and hydropower development on the Yarlung Zangbo River etc. in recent years, it is very important to evaluate the seismic landslide hazard of this region. In this paper, a seismic landslide hazard map is produced based on seismic geological background analysis and field investigation using Newmark method with 10% PGA exceedance probabilities in future 50 years by considering the influence of river erosion, active faults and seismic amplification for the first time. The results show that the areas prone to seismic landslides are distributed on steep slopes along the drainages and the glacier horns as well as ridges on the mountains. The seismic landslide hazard map produced in this study not only predicts the most prone seismic landslide areas in the future 50 years but also provides a reference for mitigation strategies to reduce the exposure of the new building and planning projects to seismic landslides.
DAI Shuang , DAI Wei , ZHAO Zhenbin , LUO Junhua , QIANG Lei , MA Xin , ZHANG Xianwen , XU Jianjun
2017, 91(2):669-687.
Abstract:The Altyn Tagh Fault (ATF) is the longest, lithospheric scale and strike-slip fault in East Asia. In the last three decades, multidisciplinary studies focusing on the timing, displacement of strike-slip and growth mechanics of the ATF have made great progresses. Most studies revealed that the ATF is a sinistral strike-slip and thrust fault, which underwent multiple episodes of activation. The fault is oriented NEE with a length of 1600 km, but the direction, timing of activity and magnitude of its extension eastward are still unclear. The AFT was predominately active during the Mesozoic and Cenozoic, in relation to the Mesozoic collision of the Cimmerian continent (Qiangtang and Lhasa block) and Cenozoic collision of India with Asia. The AFT strike-slipped with a left-lateral displacement of ca. 400 km during the Cenozoic and the displacement were bigger in the western segment and stronger in the early stage of fault activation. The slip-rates in the Quaternary were bigger in the middle segment than in the western and eastern segment. We roughly estimated the Mesozoic displacement as ca. 150-300 km. The latest paleomagnetic data showed that the clockwise vertical-axis rotation did not take place in the huge basins (the Tarim and Qaidam) at both side of ATF during the Cenozoic, but the rotation happened in the small basins along the ATF. This rotation may play an important role on accommodating the tectonic deformation and displacement of the ATF. Even if we have achieved consensus for many issues related to the ATF, some issues still need to be study deeply; such as: (a) the temporal and spatial coupling relationship between the collision of Cimmerian continent with Asia and the history of AFT in the Mesozoic and (b) the tectonic deformation history which records by the sediments of the basins within and at both side of AFT and was constrained by a high-resolution and accurate chronology such as magnetostratigraphy and paleomagnetic data.
WAN Hongqiong , SUN He , LIU Haiyang , XIAO Yilin
2017, 91(2):688-710.
Abstract:Subduction zones involve many complex geological processes, including the release of slab-derived fluids, fluid/rock interactions, partial melting, isotopic fractionations, elemental transporting, and crust/mantle interactions. Lithium (Li) isotopes (6Li and 7Li) have relative mass difference up to 16%, being the largest among metal elements. Thus, Li isotopes have advantage to interprete trace various geological processes. Most importantly, during crust/mantle interactions in deep subduction zones, surface materials and mantle rocks usually have distinct Li isotopic compositions. Li isotopes can be potential tracer for subduction processes, from the onset of subduction to the release of Li from subducted slabs and interaction with mantle wedge, as well as the fate of Li in slab-derived fluids and residual slabs. Moreover, the Li isotopic composition of subducting output materials can provide useful information for understanding global Li circulation. With developments in measurement and expansion of Li isotopic database, Li isotopic geochemistry will provide more inference and be a powerful tracer for understanding subduction-related processes. This work retrospected the application of Li isotopes in tracing successive subduction processes, and made some prospects for further studies of Li isotopes.
MENG Yumiao , HU Ruizhong , HUANG Xiaowen , GAO Jianfeng
2017, 91(2):711-726.
Abstract:Magnetite is a very common mineral in various types of iron deposits and some sulfide deposits. Recent studies have focused on the use of trace elements in magnetite to discriminate ore types or trace ore-forming process. Germanium is a disperse element in the crust, but sometimes is not rare in magnetite. Germanium in magnetite can be determined by laser ablation ICP-MS due to its low detection limit (0.0X ppm). In this study, we summary the Ge data of magnetite from magmatic deposits, iron formations, skarn deposits, iron oxide copper-gold deposits, and igneous derived hydrothermal deposits. Magnetite from iron formations contains relatively high Ge (up to ~250 ppm), whereas those from all other deposits mostly contains Ge less than 10 ppm, indicating that iron formations can be discriminated from other Fe deposits by Ge contents. Germanium in magmatic/hydrothermal magnetite is controlled by a few factors. Primary magma/fluid composition may be the major control of Ge in magnetite. Higher oxygen fugacity may be beneficial to Ge partition into magnetite. Sulfur fugacity and temperature may have little effect on Ge in magnetite. The enrichment mechanism of Ge in magnetite from iron formations remains unknown due to the complex ore genesis. Germanium along with other elements (Mn, Ni, Ga) and element ratios (Ge/Ga and Ge/Si raios) can distinguish different types of deposits, indicating that Ge can be used as a discriminate factor like Ti and V. Because of the availability of in situ analytical technique like laser ablation ICP-MS, in situ Ge/Si ratio of magnetite can serve as a geochemical tracer and may provide new constraints on the genesis of banded iron formations.
2017, 91(2):726-726.
Abstract:
2017, 91(2):729-729.
Abstract:
BIAN Weiwei , YANG Tianshui , SHI Yuruo , MA Yiming , JIN Jingjie , GAO Feng , PENG Wenxiao , ZHANG Shihong , WU Huaichun , LI Haiyan
2017, 91(2):737-738.
Abstract:
MABI Awei , ZHANG Mingchun , YANG Zhengxi , LI Yanlong , WEN Dengkui , LIU Xuyang
2017, 91(2):741-742.
Abstract:
ZHANG Yongsheng , PENG Yuan , SHI Lizhi , XING Enyuan , GUI Baolin , LI Kai
2017, 91(2):745-746.
Abstract:
XIAN Benzhong , LIU Jianping , DONG Yanlei , LU Zhiyong , HE Yanxin , WANG Junhui
2017, 91(2):751-752.
Abstract:
HUANG Chenjun , LIU Geyun , MA Yongsheng , LIU Bo , LIU Hongguang , SHI Kaibo
2017, 91(2):755-756.
Abstract:
2017, 91(2):758-758.
Abstract:
2017, 91(2):758-758.
Abstract:
Chief Editor:HOU Zengqian
Governing Body:China Association for Science and Technology
Organizer:Geological Society of China
start publication :1922
ISSN:ISSN 1000-9515
CN:CN 11-2001/P