青藏高原巴塘断裂带地震滑坡危险性预测研究

全新世以来青藏高原东部巴塘断裂带活动强烈,地形地貌和地质构造复杂,历史地震频发,并诱发大量滑坡灾害。基于巴塘断裂带地震滑坡长期防控的需要,在分析区域地质灾害成灾背景和发育分布特征的基础上,采用Newmark模型完成了巴塘断裂带50年超越概率10%的潜在地震滑坡危险性预测评价,并完成地震滑坡危险性区划。结果表明：巴塘断裂带及其临近的金沙江断裂带区域、金沙江及其支流沿岸具有较高的潜在地震滑坡危险性,地震滑坡危险区具有沿断裂带和大江大河等峡谷区分布的总体趋势,受活动断裂和地形地貌影响显著;距离断层越近、坡度越大的斜坡,地震滑坡危险性越高;规划建设中的川藏铁路经巴塘县德达乡、白玉县沙马乡,向西北延伸,跨越金沙江,可以穿越较少的地震滑坡危险区,金沙江水电工程规划建设需加强潜在地震滑坡危害研判及防控。巴塘断裂带潜在地震滑坡危险性评价结果可为区域城镇开发和重大工程规划建设的地震滑坡长期防控提供科学参考。     

The Olmsted fault zone, southernmost Illinois: A key to understanding seismic hazard in the northern new Madrid seismic zone

Geological deformation in the northern New Madrid seismic zone, near Olmsted, Illinois (USA), is analyzed using integrated compressional-wave (P) and horizontally polarized-wave (SH) seismic reflection and regional and dedicated borehole information. Seismic hazards are of special concern because of strategic facilities (e.g., lock and dam sites and chemical plants on the Ohio River near its confluence with the Mississippi River) and because of alluvial soils subject to high amplification of earthquake shock. We use an integrated approach starting with lower resolution, but deeper penetration, P-wave reflection profiles to identify displacement of Paleozoic bedrock. Higher resolution, but shallower penetration, SH-wave images show deformation that has propagated upward from bedrock faults into Pleistocene loess. We have mapped an intricate zone more than 8 km wide of high-angle faults in Mississippi embayment sediments localized over Paleozoic bedrock faults that trend north to northeast, parallel to the Ohio River. These faults align with the pattern of epicenters in the New Madrid seismic zone. Normal and reverse offsets along with positive flower structures imply a component of strike-slip; the current stress regime favors right-lateral slip on northeast-trending faults. The largest fault, the Olmsted fault, underwent principal displacement near the end of the Cretaceous Period 65 to 70 million years ago. Strata of this age (dated via fossil pollen) thicken greatly on the downthrown side of the Olmsted fault into a locally subsiding basin. Small offsets of Tertiary and Quaternary strata are evident on high-resolution SH-wave seismic profiles. Our results imply recent reactivation and possible future seismic activity in a critical area of the New Madrid seismic zone. This integrated approach provides a strategy for evaluating shallow seismic hazard-related targets for engineering concerns.     

Probabilistic seismic hazard assessment for the Horn of Africa based on seismotectonic regionalisation

A probabilistic seismic hazard analysis (PSHA) for the Horn of Africa is presented. Our seismicity database consists of a revised and up-to-date regional catalogue compiled from different agencies, checked for completeness with respect to time and homogenized with respect to magnitude (M_s). The seismic source zones are based on our present day knowledge of the regional seismotectonics. Among the results we present regional hazard maps for 0.01 annual probability for intensity and Peak Ground Acceleration (PGA) and hazard curves and response spectra for six economical significant sites within the region. The model uncertainties with respect to seismicity are analysed in a novel approach and form part of a sensitivity analysis that quantifies our PSHA modelling uncertainties.

For 0.01 annual probability we find randomly oriented horizontal PGA that exceed just 0.2 g and MM-scale intensity VIII in the Afar depression and southern Sudan. Uncertainties amount to 20% g PGA in some cases, mainly due to attenuation uncertainties. Intensity uncertainties seldom exceed 0.5 intensity units. Relatively large seismic hazard is found for Djibouti (VIII for 0.01 annual probability), slightly lower for the port of Massawa (between VII and VIII for 0.01 annual probability) and low for the port of Assab (between VI and VII for 0.01 annual probability).     

Seismic hazard analysis for critical infrastructures in California

California is in a highly seismically active region, and structures must be designed and constructed to withstand earthquakes. Seismic hazard analysis to estimate realistic earthquake ground motions and surface fault rupture offsets is done for various mitigation measures. The best policy is to avoid constructing structures crossing seismogenic faults. Because earthquake timings are unpredictable within our current understanding, the best method is time-invariant deterministic seismic hazard analysis (DHSA) to assess effects from the largest single earthquake called Maximum Credible Earthquake (MCEs) expected from seismogenic faults. Time-dependent hazard estimates such as those arrived at through probabilistic seismic hazard analysis (PSHA) are inherently unreliable. Hazard analyses based on MCEs have been in continuous use for the design and construction of highways and bridges in California for over 30 years.

This paper presents an alternative to other methods of analysis, e.g., Abrahamson (2000) [Abrahamson, N.A., 2000. State of the practice of seismic hazard evaluation. Melbourne: proceedings of GeoEng, 2000].     

Analysis of input data and seismic hazard assessment for the low seismicity area ‘Belgium,The Netherlands and NW Germany’

From the earthquake catalogue of the region of interest 2–8°E, 49–52°N, only events with intensity > 3 are considered. The fore/aftershocks and the induced seismicity are removed. The completeness and other properties of the remaining data set are investigated. The seismic data, as well as the geological, tectonic, and other geophysical data of the area are used for the determination of the seismotectonic zones. For each zone, the cumulative intensity-frequency relation (taking into account the completeness of the catalogue), the attenuation depending on the direction, the upper bound of intensity and the average depth are calculated. When the seismic activity is changing within a zone, this zone is divided into subzones with an almost constant activity and a b value equal to the value of the whole zone. When necessary for each subzone, a different attenuation coefficient can be used, to take into account more regional effects. Then the seismic hazard is assessed with the modified McGuire program. Annual probability versus intensity for several sites and hazard intensity and probability maps are calculated. Finally, an error discussion of the whole procedure for one test site is given.     

Tectonic stress,seismicity, and seismic hazard in the southeastern Carpathians

Intermediate-depth earthquakes in the Vrancea region occur in response to stress generation due to descending lithosphere beneath the southeastern Carpathians. In this article, tectonic stress and seismicity are analyzed in the region on the basis of a vast body of observations. We show a correlation between the location of intermediate-depth earthquakes and the predicted localization of maximum shear stress in the lithosphere. A probabilistic seismic hazard assessment (PSHA) for the region is presented in terms of various ground motion parameters on the utilization of Fourier amplitude spectra used in engineering practice and risk assessment (peak ground acceleration, response spectra amplitude, and seismic intensity). We review the PSHA carried out in the region, and present new PSHA results for the eastern and southern parts of Romania. Our seismic hazard assessment is based on the information about the features of earthquake ground motion excitation, seismic wave propagation (attenuation), and site effect in the region. Spectral models and characteristics of site-response on earthquake ground motions are obtained from the regional ground motion data including several hundred records of small and large earthquakes. Results of the probabilistic seismic hazard assessment are consistent with the features of observed earthquake effects in the southeastern Carpathians and show that geological factors play an important part in the distribution of the earthquake ground motion parameters.     

郯庐断裂带苏鲁界地应力积累特征及地震危险性研究

郯庐断裂带是中国东部重要的地质构造带和地震活动带,苏、鲁交界部位的地震活动性和强震危险性一直引人瞩目,1668年发生过郯城8.5级大地震。为了解郯庐断裂带苏鲁界现今地应力环境与地震发展趋势,应用水压致裂法在该区开展了一个钻孔的原地应力测量工作,同时参考前人利用钻孔崩落法与声发射法获取的中国大陆科学钻探(CCSD)主孔301～5047m深度范围内的地应力数据,揭示了研究区地应力状态。利用库伦破裂准则、Byerlee定律以及断层摩擦参数μ_m分析研究该地区的地应力积累水平,评估断层发生滑动的可能性。结果表明:水压致裂法测点在75.74～191.04m深度范围内最小水平主应力的量值为3.68～13.15MPa,最大水平主应力的量值为4.02～19.40MPa。CCSD主孔在1269～5047m深度范围内最小水平主应力的量值为25.3～122.0MPa,最大水平主应力的量值为41.4～166.4MPa;分析地应力结构,发现自地表至660m的范围内,σ_Hσ_hσ_v,为逆断层地应力状态,660m以下表现为σ_Hσ_vσ_h,为走滑断层地应力状态。综合分析断层摩擦参数μ_m,郯庐断裂带苏鲁交界处尚未达到断层失稳的临界地应力状态。     

SHRIMP U–Pb zircon dating of the Neoproterozoic Penglai Group and Archean gneisses from the Jiaobei Terrane, North China, and their tectonic implications

Archean basement gneisses and supracrustal rocks, together with Neoproterozoic (Sinian) metasedimentary rocks (the Penglai Group) occur in the Jiaobei Terrane at the southeastern margin of the North China Craton. SHRIMP U–Pb zircon dating of an Archean TTG gneiss gave an age of 2541 ± 5 Ma, whereas metasedimentary rocks from the Neoproterozoic Penglai Group yielded a range in zircon ages from 2.9 to 1.8 Ga. The zircons can be broadly divided into three age populations, at: 2.0–1.8 Ga, 2.45–2.1 Ga and >2.5 Ga. Detrital zircon grains with ages >2.6 Ga are few in number and there are none with ages <1.8 Ga. These results indicate that most of the detrital material comes from a Paleoproterozoic source, most likely from the Jianshan and Fenzishan groups, with some material coming from Archean gneisses in the Jiaobei Terrane. An age of 1866 ± 4 Ma for amphibolite-facies hornblende–plagioclase gneiss, forming part of a supracrustal sequence within the Archean TTG gneiss, indicates Late Paleoproterozoic metamorphism. Both the Archean gneiss complex and Penglai metasedimentary rocks resemble previously described components of the Jiao-Liao-Ji orogenic belt and suggest that the Jiaobei Terrane has a North China Craton affinity; they also suggest that the time of collision along the Jiao-Liao-Ji Belt was at 1865 Ma.     

Late Pliocene–recent tectonic setting for the Tianchi volcanic zone, Changbai Mountains, northeast China

Mafic volcanic rocks have erupted in the Tianchi volcanic zone, Changbai Mountains, northeast China, since late Pliocene time. The zone formed in an extensional environment during early-middle Cenozoic time, and in a compressional environment during late Cenozoic. Crustal thickness (about 40 km) in the Changbai Mountains is larger than the regional average of 34–36 km to the northwest and southeast. The conduit for magma upwelling was not coincident with the NE-striking regional faults, but seem to be confined to a deep-seated NW–WNW-striking fault zone. Since the late Pliocene, the Tianchi volcanic zone was subjected to crustal uplift within an intracontinental, weakly compressional environment (with minor WNW–ESE shearing) related to the westward subduction of the West Pacific plate. The nature of this volcanism is not typical of active, subduction-related continental margin volcanism. The magmatic evolutionary process evolved from trachybasalt through basaltic trachyandesite, trachyte, and pantellerite.     

Microseismic activity in the Hellenic Volcanic Arc, Greece, with emphasis on the seismotectonic setting of the Santorini–Amorgos zone

The volcanic arc of the Hellenic subduction zone with its four volcanic centers is of major relevance when evaluating the seismovolcanic hazard for the Aegean region. We present results from a 22-station temporary seismic network (CYCNET) in the central Hellenic Volcanic Arc (HVA). CYCNET recordings allow to analyze the level and spatio-temporal evolution of microseismic activity in this region for the first time. A total of 2175 events recorded between September 2002 and July 2004 are analyzed using statistical methods, cluster analysis and relative relocation techniques. We identify distinct regions with significantly varying spatio-temporal behavior of microseismicity. A large portion of the seismic activity within the upper crust is associated with the presence of islands representing horst structures that were generated during the major Oligocene extensional phase. In contrast, the central part of the Cyclades metamorphic core complex remains aseismic considering our magnitude threshold of 1.8 except one spot where events occur swarm-like and with highly similar waveforms.The highest activity in the study area was identified along the SW–NE striking Santorini–Amorgos zone. Within this zone the submarine Columbo volcano exhibits strong temporal variations of seismic activity on a high background level. This activity is interpreted to be directly linked to the magma reservoir and therein the migration of magma and fluids towards the surface. NE of Columbo where no volcanic activity has yet been reported we observe a similar seismicity pattern with small-scaled activity spots that might represent local pathways of upward migrating fluids or even developing volcanic activity within this zone of crustal weakness. In contrast, the Santorini and Milos volcanic complexes do not show significant temporal variations and low to moderate background activity, respectively. Relating our results to the distribution of historical earthquakes and the GPS-derived horizontal velocity field we conclude that the Santorini–Amorgos zone is presently in the state of right-lateral transtension reflecting a major structural boundary of the volcanic arc subdividing it into a seismically and volcanically quiet western and an active eastern part.     

Oligo-Miocene shearing along the Ailao Shan–Red River shear zone: Constraints from structural analysis and zircon U/Pb geochronology of magmatic rocks in the Diancang Shan massif, SE Tibet, China

The left-lateral strike-slip shearing along the Ailao Shan–Red River (ASRR) shear zone in the Southeastern Tibet, China, has been widely advocated to be a result of the Indian–Eurasian plate collision and post-collisional processes. The Diancang Shan (DCS) massif, which occurs at the northwestern extension of the Ailao Shan massif, is a typical high-grade metamorphic complex aligned along the ASRR tectonic belt. Structural and microstructural analysis of the plutonic intrusions in the DCS revealed different types of granitic intrusions spatially confined to the shear zone and temporally related to the left-lateral shearing along the ASRR shear zone in the DCS massif. The combined structural and geochronological results of SHRIMP-II and LA-ICP-MS zircon U/Pb isotopic dating have revealed successive magmatic intrusions and crystallization related to the Oligo-Miocene shearing in the DCS massif. The pre-, early- and syn-kinematic emplacements are linked to regional high-temperature deformation (lower amphibolite facies) at relatively deep crustal levels. The zircon U/Pb geochronological results suggest that the left-lateral ductile shearing along the ASRR shear zone was initiated at ca. 31 Ma, culminated between ca. 27 and 21 Ma resulting in high-temperature metamorphic conditions and slowed down at ca. 20 Ma at relatively low-temperatures.     

华北地块北缘中元古界几个重要不整合面的地质特征及构造意义

华北地块北缘中元古代沉积层序中出现多个沉积间断和不整合面。此次研究对其中5个不整合面进行了野外考察,分析了它们的地质特征和空间分布,认为它们与不同的地质过程有关。大红峪组底部不整合面是早期裂谷盆地演化为被动大陆边缘的记录,属于裂解不整合面性质;高于庄组底部和杨庄组底部的不整合面是海平面变化造成被动大陆边缘内部高地沉积间断和海岸超覆沉积的结果;铁岭组顶部不整合面可能与弧后环境发生挤压抬升有关;下马岭组沉积后的抬升可能是相邻大陆地块碰撞作用的产物。华北地块北缘中元古代层序中不整合面的形成与Columbia和Rodinia超大陆的形成和裂解过程密切相关。     

Spatial variations in the similarity of earthquake populations: The case of the 1997 Colfiorito–Sellano (northern Apennines, Italy) seismic sequence

The spatial properties of events in the 1997 Colfiorito–Sellano seismic sequence (Northern Apennines, Italy) were investigated using coherence, a parameter derived from seismic moment tensors that quantifies the kinematic similarity between focal mechanisms. The 1997 Colfiorito–Sellano seismic sequence predominantly consists of normal faulting earthquakes, with a few strike-slip and reverse faulting episodes. This kinematic heterogeneity is possibly related to the contemporaneous activity of two different sets of faults: NW–SE normal faults and NNE–SSW sub-vertical faults, the latter inherited from the previous Miocene compressional phase. The study used two independently-derived data sets of the same seismic sequence characterized by a different number of events and by different precision of spatial localisation. Their statistical significances, assessed through a reshuffling procedure, reveal that data sets with at least some hundreds of events and good positional precision are required to obtain significant results through coherence analysis. Results from the better quality data set indicate that this seismic sequence is characterized by a rapid decrease in the kinematic similarity between earthquake pairs within 2 km of separation, particularly along directions sub-perpendicular to the normal fault strike. The decrease rate seems to be controlled by the geometric characteristics of the normal faults, given that the mean along-dip distance between fault segments is 2 km. In proximity to pre-existing tectonic lineaments the relative abundance of strike-slip and reverse faults tends to decrease the kinematic similarity between events but does not influence the coherence decrease rate. The presence of mixed focal mechanisms (normal, reverse and strike-slip) in a single seismic phase implies that mixed fault types are not restricted to polyphase tectonic histories: such heterogeneous kinematics during a single phase may be induced by the presence of inherited discontinuities.     

Geochronological framework and Pb, Sr isotope geochemistry of the Qingchengzi Pb–Zn–Ag–Au orefield, Northeastern China

The Qingchengzi orefield in northeastern China, is a concentration of several Pb–Zn, Ag, and Au ore deposits. A combination of geochronological and Pb, Sr isotopic investigations was conducted. Zircon SHRIMP U–Pb ages of 225.3 ± 1.8 Ma and 184.5 ± 1.6 Ma were obtained for the Xinling and Yaojiagou granites, respectively. By step-dissolution Rb–Sr dating, ages of 221 ± 12 Ma and 138.7 ± 4.1 Ma were obtained for the sphalerite of the Zhenzigou Zn–Pb deposit and pyrargyrite of the Ag ore in the Gaojiabaozi Ag deposit, respectively. Pb isotopic ratios of the Ag ore at Gaojiabaozi (²⁰⁶Pb/²⁰⁴Pb = 18.38 to 18.53) are higher than those of the Pb–Zn ores (²⁰⁶Pb/²⁰⁴Pb = 17.66 to 17.96; Chen et al. [Chen, J.F., Yu, G., Xue, C.J., Qian, H., He, J.F., Xing, Z., Zhang, X., 2005. Pb isotope geochemistry of lead, zinc, gold and silver deposit clustered region, Liaodong rift zone, northeastern China. Science in China Series D 48, 467–476.]). Triassic granites show low Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb = 17.12 to 17.41, ²⁰⁷Pb/²⁰⁴Pb = 15.47 to 15.54, ²⁰⁸Pb/²⁰⁴Pb = 37.51 to 37.89) and metamorphic rocks of the Liaohe Group have high ratios (²⁰⁶Pb/²⁰⁴Pb = 18.20 to 24.28 and 18.32 to 20.06, ²⁰⁷Pb/²⁰⁴Pb = 15.69 to 16.44 and 15.66 to 15.98, ²⁰⁸Pb/²⁰⁴Pb = 37.29 to 38.61 and 38.69 to 40.00 for the marble of the Dashiqiao Formation and schist of the Gaixian Formation, respectively).Magmatic activities at Qingchengzi and in adjacent regions took place in three stages, and each contained several magmatic pulses: ca. 220 to 225 Ma and 211 to 216 Ma in the Triassic; 179 to 185 Ma, 163 to 168 Ma, 155 Ma and 149 Ma in the Jurassic, as well as ca. 140 to 130 Ma in the Early Cretaceous. The Triassic magmatism was part of the Triassic magmatic belt along the northern margin of the North China Craton produced in a post-collisional extensional setting, and granites in it formed by crustal melting induced by mantle magma. The Jurassic and Early Cretaceous magmatism was related to the lithospheric delamination in eastern China. The Triassic is the most important metallogenic stage at Qingchengzi. The Pb–Zn deposits, the Pb–Zn–Ag ore at Gaojiabaozi, and the gold deposits were all formed in this stage. They are temporally and spatially associated with the Triassic magmatic activity. Mineralization is very weak in the Jurassic. Ag ore at Gaojiabaozi was formed in the Early Cretaceous, which is suggested by the young Rb–Sr isochron age, field relations, and significantly different Pb isotopic ratios between the Pb–Zn–Ag and Ag ores. Pb isotopic compositions of the Pb–Zn ores suggest binary mixing for the source of the deposits. The magmatic end-member is the Triassic granites and the other metamorphic rocks of the Liaohe Group. Slightly different proportions of the two end-members, or an involvement of materials from hidden Cretaceous granites with slightly different Pb isotopic ratios, is postulated to interpret the difference of Pb isotopic compositions between the Pb–Zn–(Ag) and Ag ores. Sr isotopic ratios support this conclusion. At the western part of the Qingchengzi orefield, hydrothermal fluid driven by the heat provided by the now exposed Triassic granites deposited ore-forming materials in the low and middle horizons of the marbles of the Dashiqiao Formation near the intrusions to form mesothermal Zn–Pb deposits. In the eastern part, hydrothermal fluids associated with deep, hidden Triassic intrusions moved upward along a regional fault over a long distance and then deposited the ore-forming materials to form epithermal Au and Pb–Zn–Ag ores. Young magmatic activities are all represented by dykes across the entire orefield, suggesting that the corresponding main intrusion bodies are situated in the deep part of the crust. Among these, only intrusions with age of ca. 140 Ma might have released sufficient amounts of fluid to be responsible for the formation of the Ag ore at Gaojiabaozi.Our age results support previous conclusions that sphalerite can provide a reliable Rb–Sr age as long as the fluid inclusion phase is effectively separated from the “sulfide” phase. Our work suggests that the separation can be achieved by a step-resolution technique. Moreover, we suggest that pyrargyrite is a promising mineral for Rb–Sr isochron dating.     

Structural and stratigraphical constraints on the kinematics history of the Southern Tan–Lu Fault Zone during the Mesozoic Anhui Province, China

The Tan–Lu Fault Zone (TLFZ) extends in a NNE–SSW direction for more than 2000 km in Eastern China. It has been considered either as a major sinistral strike-slip fault, as a suture zone or as a normal fault. We have conducted a structural analysis of the southern segment of this fault zone (STLFZ) in the Anhui Province. The ages (Triassic to Palaeocene) of the formations affected by the faults have been re-appraised taking into account recent stratigraphical studies to better constraint the ages of the successive stages of the kinematics of the STLFZ. Subsequently, the kinematics of the faults is presented in terms of strain/stress fields by inversion of the striated fault set data. Finally, the data are discussed in the light of the results obtained by previous workers.We propose the following history of the STLFZ kinematics during the Mesozoic. At the time of collision, a  NNE orientated Tan–Lu margin probably connected two margins located north of the Dabie and Sulu collision belts. During the Middle–Late Triassic, the SCB has been obliquely subducted below the NCB along this margin which has acted as a compressional transfer zone between the Dabie and Sulu continental subduction zones. The STLFZ has been initiated during the Early Jurassic and has acted as a sinistral transform fault during the Jurassic, following which the NCB/SCB collision stopped. A  NW-trending extension related to metamorphic domes was active during the basal Early Cretaceous ( 135–130 Ma); it has been followed by a NW–SE compression and a NE–SW tension during the middle–late Early Cretaceous ( 127 to  105 Ma, possibly  95 Ma); at that time the TLFZ was a sinistral transcurrent fault within the eastern part of the Asian continent. During the Late Cretaceous–Palaeocene, the STLFZ was a normal fault zone under a WNW–ESE tension.     

Genesis of the Xiuwenghala Gold Deposit in the Beishan Orogen,Northwest China: Evidence from Geology,Fluid Inclusion,and H–O–S–Pb Isotopes

The Xiuwenghala gold deposit is located in the Beishan Orogen of the southern Central Asian Orogenic Belt. The vein/lenticular gold orebodies are controlled by Northeast‐trending faults and are hosted mainly in the brecciated/altered tuff and rhyolite porphyry of the Lower Carboniferous Baishan Formation. Metallic minerals include mainly pyrite and minor chalcopyrite, arsenopyrite, galena, and sphalerite, whilst nonmetallic minerals include quartz, chalcedony, sericite, chlorite, and calcite. Hydrothermal alterations consist of silicic, sericite, chlorite, and carbonate. Alteration/mineralization processes comprise three stages: pre‐ore silicic alteration (Stage I), syn‐ore quartz‐chalcedony‐polymetallic sulfide mineralization (Stage II), and post‐ore quartz‐calcite veining (Stage III). Fluid inclusions (FIs) in quartz and calcite are dominated by L‐type with minor V‐type and lack any daughter mineral‐bearing or CO₂‐rich/‐bearing inclusions. From Stages I to III, the FIs homogenized at 240–260°C, 220–250°C, and 150–190°C, with corresponding salinities of 2.9–10.9, 3.2–11.1, and 2.9–11.9 wt.% NaCl eqv., respectively. The mineralization depth at Xiuwenghala is estimated to be relatively shallow (<1 km). FI results indicate that the ore‐forming fluids belong to a low to medium‐temperature, low‐salinity, and low‐density NaCl‐H₂O system. The values decrease from Stage I to III (3.7‰, 1.7–2.4‰, and ?1.7 to 0.9‰, respectively), and a similar trend is found for their values (?104 to ?90‰, ?126 to ?86‰, and ?130 to ?106‰, respectively). This indicates that the fluid source gradually evolved from magmatic to meteoric. δ³⁴S values of the hydrothermal pyrites (?3.0 to 0.0‰; avg. ?1.1‰) resemble those of typical magmatic/mantle‐derived sulfides. Pyrite Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb = 18.409–18.767, ²⁰⁷Pb/²⁰⁴Pb = 15.600–15.715, ²⁰⁸Pb^/204Pb = 38.173–38.654) are similar to those of the (sub)volcanic ore host, indicating that the origin of ore‐forming material was mainly the upper crustal (sub)volcanic rocks. Integrating evidence from geology, FIs, and H–O–S–Pb isotopes, we suggest that Xiuwenghala is best classified as a low‐sulfidation epithermal gold deposit.     

Geochemistry and Nd–Sr isotopic studies of Late Mesozoic granitoids in the southeastern Hubei Province, Middle–Lower Yangtze River belt, Eastern China: Petrogenesis and tectonic setting

A geochemical and isotopic study was carried out for the Mesozoic Yangxin, Tieshan and Echeng granitoid batholiths in the southeastern Hubei Province, eastern China, in order to constrain their petrogenesis and tectonic setting. These granitoids dominantly consist of quartz diorite, monzonite and granite. They are characterized by SiO₂ and Na₂O compositions of between 54.6 and 76.6 wt.%, and 2.9 to 5.6 wt.%, respectively, enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), and relative depletion in Y (concentrations ranging from 5.17 to 29.3 ppm) and Yb (0.34–2.83 ppm), with the majority of the granitoids being geochemically similar to high-SiO₂ adakites (HSA). Their initial Nd (ε_Nd = − 12.5 to − 6.1) and Sr ((⁸⁷Sr/⁸⁶Sr)_i = 0.7054–0.7085) isotopic compositions, however, distinguish them from adakites produced by partial melting of subducted slab and those produced by partial melting of the lower crust of the Yangtze Craton in the Late Mesozoic. The granitoid batholiths in the southeastern Hubei Province exhibit very low MgO ranging from 0.09 to 2.19 wt.% with an average of 0.96 wt.%, and large variations in negative to positive Eu anomalies (Eu/Eu = 0.22–1.4), especially the Tieshan granites and Yangxin granite porphyry (Eu/Eu = 0.22–0.73). Geochemical and Nd–Sr isotopic data demonstrate that these granitoids originated as partial melts of an enriched mantle source that experienced significant contamination of lower crust materials and fractional crystallization during magma ascent. Late Mesozoic granitoids in the southeastern Hubei Province of the Middle–Lower Yangtze River belt were dominantly emplaced in an extensional tectonic regime, in response to basaltic underplating, which was followed by lithospheric thinning during the early Cretaceous.     

Lithogeochemical,Re–Os and U–Pb Geochronological,Hf–Lu and S–Pb Isotope Data of the Ga'erqiong‐Galale Cu–Au Ore‐Concentrated Area: Evidence for the Late Cretaceous Magmatism and Metallogenic Event in the Bangong‐Nujiang Suture Zone,Northwestern Tibet,China

The Ga'erqiong‐Galale skarn–porphyry copper–gold ore‐concentrated area is located in the western part of the Bangong‐Nujiang suture zone north of the Lhasa Terrane. This paper conducted a systematic study on the magmatism and metallogenic effect in the ore‐concentrated area using techniques of isotopic geochronology, isotopic geochemistry and lithogeochemistry. According to the results, the crystallization age of quartz diorite (ore‐forming mother rock) in the Ga'erqiong deposit is 87.1 ± 0.4 Ma, which is later than the age of granodiorite (ore‐forming mother rock) in the Galale deposit (88.1 ± 1.0 Ma). The crystallization age of granite porphyry (GE granite porphyry) in the Ga'erqiong deposit is 83.2 ± 0.7 Ma, which is later than the age of granite porphyry (GL granite porphyry) in the Galale deposit (84.7 ± 0.8 Ma).The quartz diorite, granodiorite, GE granite porphyry and GL granite porphyry both main shows positive ε_Hf(t) values, suggesting that the magmatic source of the main intrusions in the ore‐concentrated area has the characteristics of mantle source region. The Re–Os isochron age of molybdenite in the Ga'erqiong district is 86.9 ± 0.5 Ma, which is later than the mineralization age of the Galale district (88.6 ± 0.6 Ma). The main intrusive rocks in the ore‐concentrated area have similar lithogeochemical characteristics, for they both show the relative enrichment in large‐ion lithophile elements(LILE: Rb, Ba, K, etc.), more mobile highly incompatible lithophile elements(HILE: U, Th) and relatively depleted in high field strength elements (HFSE: Nb, Ta, Zr, Hf, etc.), and show the characteristics of magmatic arc. The studies on the metal sulfides' S and Pb isotopes and Re content of molybdenite indicate that the metallogenic materials of the deposits in the ore‐concentrated area mainly come from the mantle source with minor crustal source contamination. Based on the regional tectonic evolution process, this paper points out that the Ga'erqiong‐Galale copper–gold ore‐concentrated area is the typical product of the Late Cretaceous magmatism and metallogenic event in the collision stage of the Bangong‐Nujiang suture zone.     

Halogen elements as indicator of deep-seated orebodies in the Chadong As–Ag–Au deposit, western Guangdong, China

Halogen elements play an important role in the metallogenesis of metallic ore deposits and are involved in the whole process of remobilization, transport and precipitation of metallic elements. However, with the exception of fluorine, which, as a component of fluorite and mica minerals, can be occasionally concentrated in ores, Cl, Br and I are hard to enrich in the ores. Investigations have found that the halogen elements tend to diffuse toward country rocks with the development of hydrothermal alteration in the process of their involvement in metallogenesis, especially during the post-ore stage when extensive halogen diffusion halos over orebodies would be formed. Such halogen element diffusion halos over the Chadong As–Ag–Au deposit extend as widely as 200 m. The largest diffusion extent is for I and the diffusion halos of Br are most noticeable 50–130 m away from the orebodies. In areas of ore exposure and the strongly altered zone, the Cl, Br and I contents are close to those of the strata with a V-shaped distribution pattern in the periphery of the mining district. Comparatively speaking, in going away from the altered zone, the major metallic elements Au and Ag in the deposit tend to decrease suddenly to their normal contents in the strata. This variation feature of halogen elements can be used as geochemical indicators for exploring concealed orebodies at depth. In the Chadong ore deposit, halogen element anomalies can be used to predict concealed orebodies at the depth range of 0–200 m.