Geological Fluid Mapping in the Tongling Area:Implications for the Paleozoic Submarine Hydrothermal System in the Middle-Lower Yangtze Metallogenic Belt,East China

The Tongling area is one of the 7 ore-cluster areas in the Middle-Lower Yangtze metallogenic belt, East China, and has tectonically undergone a long-term geologic history from the late Paleozoic continental rifting, through the Middle Triassic continent-continent collision to the Jurassic-Cretaceous intracontinental tectono-magmatic activation. The Carboniferous sedimentary-exhalative processes in the area produced widespread massive sulfides with ages of 303-321 Ma, which partly formed massive pyrite-Cu deposits, but mostly provided significant sulfur and metals to the skarn Cu mineralization associated with the Yanshanian felsic intrusions.To understand the Carboniferous submarine hydrothermal system, an area of about 1046 km^2 was chosen to carry out the geological fluid mapping. Associated with massive sulfide formation, footwall sequences 948 m to 1146 m thick, composed of the Lower Silurian-Upper Devonian sandstone, siltstone and thin-layered shale, were widely altered. This hydrothermal alteration is interpreted to reflect largescale hydrothermal fluid flow associated with the late Paleozoic crustal rifting and subsidence. Three hydrothermal alteration types, i.e., deep-level semiconformable siliclfication （S1）, fracture-controlled quartz-sericite-pyrite alteration （S2-3）, and upper-level sub-discordant quartz-sericite-chlorite alteration （D3）, were developed to form distinct zones in the mapped area. About 50-m thick semiconformable silicification zones are located at -1-km depth below massive sulfides and developed between an impermeable shale caprock （S1） and the underlying Ordovician unaltered limestone. Comparisons with modern geothermal systems suggest that the alteration zones record a sub-seafioor aquifer with the most productive hydrothermal fluid flow. Fracture-controlled quartz-sericite-pyrite alteration formed transgressive zones, which downward crosscut the semiconformable alteration zones, and upwards grade into sub-discordant alteration zones that enveloped no economic stringer- stockwork zones beneath massive sulfides. This transgressive zone likely marks an upfiow path of high- flux fluids from the hydrothermal aquifer. Lateral zonation of the sub-discordant alteration zones and their relationship to overlying massive sulfide lenses suggest lateral flows and diffusive discharging of the hydrothermal fluids in a permeable sandstone sequence. Three large-sized, 14 middle-small massive sulfide deposits, and 40 massive sulfide sites have been mapped in detail. They show regional strata- bound characters and two major styles, i.e., the layered sheet plus strata-bound stringer-style and the mound-style. Associated exhalite and chemical sedimentary rock suites include （1） anhydrite-barite, （2） jasper-chert, （3） Mg-rich mudstone-pyrite shale, （4） barite lens, （5） siderite-Fe-bearing dolomite, and （6） Mn-rich shale-mudstone, which usually comprise three sulfide-exhalite cyclic units in the area.The spatial distribution of these alteration zones （minerals） and associated massive sulfdes and exhalites, and regional variation in δ^34S of hydrothermal pyrite and in δ^18O-δ^34C of hanging wall carbonates, suggest three WNW-extending domains of fluid flow, controlled by the basement faults and syn-depositional faults. Each fluid domain appears to have at least two upflow zones, with estimated even spacing of about 5-8 km in the mapped area. The repeated appearance of sulfide-sulfate or sulfide-carbonate rhythmic units in the area suggests episodically venting of fluids through the upfiow conduits by breaking the overlying seals of the hydrothermal aquifer.

In Situ Analyses of Trace Elements, U–Pb and Lu–Hf Isotopes in Zircons from the Tongshankou Granodiorite Porphyry in Southeast Hubei Province, Middle-Lower Yangtze River Metallogenic Belt, China

The Tongshankou Cu-Mo deposit, located in southeast Hubei province, is a typical skarn–porphyry type ore deposit closely related to the Tongshankou granodiorite porphyry, characterized by a high Sr/Y ratio.Detailed in situ analyses of the trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry were performed.Scarcely any inherited zircons were observed, and the analyzed zircons yielded highly concordant results with a weighted mean 206Pb/238 U age of 143.5 ± 0.45 Ma（n=20, mean square weighted deviation was 0.75）, which was interpreted to represent the crystallization age of the Tongshankou granodiorite porphyry.The chondrite-normalized rare-earth element pattern was characterized by a slope that steeply rises from the light-group rare-earth elements（LREE） to the heavy-group rare-earth elements（HREE） with a positive Ce-anomaly and inconspicuous Eu-anomaly, which was coincident with the pattern of the zircons from the Chuquicamata West porphyry, Chile.The analyzed zircons also had relatively low 176Hf/177 Hf ratios of 0.282526–0.282604.Assuming t=143 Ma, the corresponding calculated initial Hf isotope compositions（εHf（t）） ranged from-5.6 to-2.9.The results of the in situ analysis of trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry suggest that a deep-seated process involving a thickened-crust/enriched-mantle interaction may play an important role in the generation of high Sr/Y-ratio magma and potentially in the generation of porphyry Cu-Mo systems.

Intensification of the East Asian Monsoon in Southern China at about300-400 kaBP Inferred from Eolian Deposits in the Middle-lower Reaches of the Yangtze River

In the East Asian monsoon region, eolian deposits widely distributed in the middle-lower reaches of the Yantgze River are among the best materials available for studies on Quaternary climate change in the subtropical zone of Southern China. Typical eolian deposits in this region include upper Xiashu Loess （XL） and underlying Vermiculated Red Soil （VRS） layers. In this paper, chronological and paleoclimatic studies are conducted on an eolian deposit sequence near Jiujiang （J J） city in northern Jiangxi province. A magnetostratigraphic study, combined with optically stimulated luminescence （OSL） dating, is conducted on the JJ section and provides further evidence that eolian deposits in the middle-lower reaches of the Yangtze River have been formed since the late Early Pleistocene, and that the boundary age between the XL and VRS layers is about 300-400 kaBP. In grain-size records of the JJ section, the median grain-size and content of the 〉30μn size fraction increase sharply after 300-400 kaBP, representing an East Asian winter monsoon intensification event. Further pollen analysis reveals differing pollen assemblages before and after 300-400 kaBP： there is an evident increase in plants adapted to grow in a warm humid environment after 300-400 kaBP, implying an increase in precipitation caused by intensification of the East Asian summer monsoon. Global ice volume and uplift of the Tibet Plateau （TP） are regarded as crucial factors influencing variations of the East Asian monsoon on a long-term scale. The deep-sea JlSO record, which reflects variations in global ice volume, shows no obvious change after 300-400 kaBP. Moreover, the influence of global ice volume changes on the East Asian summer and winter monsoons is inverse; the global ice volume increase （decrease） implies a strengthened （weakened） winter monsoon and weakened （strengthened） summer monsoon. We therefore interpret the coupled intensifications of the East Asian summer and winter monsoons at about 300-400 kaBP to the uplift of the TP in the Middle Pleistocene. This climate event is also documented in eolian deposits from the southern margin of the Chinese Loess Plateau （CLP） and from the desert-loess transitional belt. However, it is not recorded in the loess-paleosol sequences from the central part of the CLP, thereby indicating differing climate responses to TP uplift in different regions, which requires further study.

Discovery of Lorandite TlAsS_2 at the Distal Au-Tl Deposit in a Skarn system,Fengshan Area,Middle-Lower Yangtze River,Eastern China

Thallium has been used geochemical exploration of gold deposits. However, as an indicator element in searching for hydrothermal the T1 minerals and mineralization are rare in nature. Lorandite T1AsS2, a relatively uncommon mineral, has been dominantly discovered in some Carlin gold deposits, and minor Sb- Hg, U and Pb-Zn-Ag deposits.

Large-scale Migration of Fluids toward Foreland Basins during Collisional Orogeny: Evidence from Triassic Anhydrock Sequences and Regional Alteration in the Middle-Lower Yangtze Area

The middle-lower Yangtze area underwent a series of complex tectonic evolution, such as Hercynian extensional rifting, Indosinian foreland basining, and Yanshanian transpression-transtension, resulting in a large distinctive Cu-Fe-Au metallogenic belt. In the tectonic evolution, large-scale migration and convergence of fluids toward foreland basins induced during the collisional orogeny of the Yangtze and North China continental blocks were of vital importance for the formation of the metallogenic belt. Through geological surveys of the middle-lower Yangtze area, three lines of evidence of large-scale fluid migration are proposed: (1) The extensive dolomitic and silicic alteration penetrating Cambrian-Triassic strata generally occurs in a region sandwiched between the metallogenic belt along the Yangtze River and the Dabie orogenic belt, and in the alteration domain alternately strong and weak alteration zones extend in a NW direction and are controlled by the fault system of the Dabie orogenic belt; it might record the locus of the activities of long-distance migrating fluids. (2) The textures and structures of very thick Middle-Lower Triassic anhydrock sequences in restricted basins along the river reveal the important contribution of the convergence of regional hot brine in restricted basins and the chemical deposition or their formation. (3) Early-Middle Triassic syndepositional iron carbonate sequences and Fe-Cu-Pb-Zn massive sulfide deposits alternate with anhydrock sequences or are separated from the latter, but all of them occur in the same stratigraphic horizon and are intimately associated with each other, being the product of syndeposition of high-salinity hot brine. According to the geological surveys, combined with previous data, the authors propose a conceptual model of fluid migration-convergence and mineralization during the Dabie collisional orogeny.

Geologic,Fluid Inclusion and Stable Isotope Constraints on Mechanisms of Ore Deposition at the Datuanshan Copper Deposit,Middle-Lower Yangtze Valley,Eastern China

The Datuanshan deposit is one of the largest and most representative stratabound copper deposits in the Tongling area,the largest ore district in the Middle-Lower Yangtze River metallogenic belt.The location of the orebodies is controlled by the interlayer-slipping faults between the Triassic and Permian strata,and all the orebodies are distributed in stratiform shape around the Mesozoic quartz monzodiorite dikes.Based on field evidence and petrographic observations,four mineralization stages in the Datuanshan deposit have been identified：the skarn,early quartz-sulfide,late quartzsulfide and carbonate stages.Chalcopytite is the main copper mineral and mainly formed at the late quartz-sulfide stage.Fluid inclusions at different stages were studied for petrography,microthermometry,laser Raman spectrometry and stable isotopes.Four types of fluid inclusions,including three-phase fluid inclusions（type 1）,liquid-rich fluid inclusions（type 2）,vapour-rich fluid inclusions（type 3） and pure vapour fluid inclusions（type 4）,were observed.The minerals from the skarn,early and late quartz-sulfide stages contain all fluid inclusion types,but only type 2 fluid inclusions were observed at the carbonate stage.Petrographic observations suggest that most of the inclusions studied in this paper are likely primary.The coexistence of different types of fluid inclusions with contrasting homogenization characteristics（to the liquid and vapour phase,respectively） and similar homogenization temperatures（the modes are 440-480℃,380-400℃ and 280-320℃ for the skarn,early and late quartz-sulfide stages,respectively） in the first three stages,strongly suggests that three episodes of fluid boiling occurred during these stages,which is supported by the hydrogen isotope data.Laser Raman spectra identified CH_4 at the skarn and early quartz-sulfide stages.Combined with other geological features,the early ore-forming fluids were inferred to be under a relatively reduced environment.The CO_2 component has been identified at the late quartz-sulfide and carbonate stages,indicating that the late ore-forming fluids were under a relatively oxidized environment,probably as a result of inflow of and mixing with meteoric water.In addition,microthermometric results of fluid inclusions and H-O isotope data mdicate that the ore forming fluids were dominated by magmatic water in the early stages（skarn and early quartz-sulfide stages） and mixed with meteoric water in the late stages（late quartz-sulfide and carbonate stages）.The evidence listed above suggests that the chalcopyrite deposition in the Datuanshan deposit probably resulted from the combination of multiepisode fluid boiling and mixing of magmatic and meteoric water.

Molybdenite Re-Os,titanite and garnet U-Pb dating of the Magushan skarn Cu-Mo deposit,Xuancheng district,Middle-Lower Yangtze River Metallogenic Belt

The Magushan skarn Cu-Mo deposit is a representative example of the skarn mineralization occurring within the Xuancheng ore district of the Middle-Lower Yangtze River Metallogenic Belt of eastern China.The precise age of an ore deposit is important for understanding the timing of mineralization relative to other geological events in a region and to fully place the formation of a mineral deposit within the geological context of other processes that occur within the study area.Here,we present new molybdenite Re-Os and titanite and andradite garnet U-Pb ages for the Magushan deposit and use these data to outline possible approaches for identifying genetic relationships in geologically complex areas.The spatial and paragenetic relationships between the intrusions,alteration,and mineralization within the study area indicates that the formation of the Magushan deposit is genetically associated with the porphyritic granodiorite.However,this is not always the case,as some areas contain complexly zoned plutons with multiple phases of intrusion or mineralization may be distal from or may not have any clear spatial relationship to a pluton.This means that it may not be possible to determine whether the mineralization formed as a result of single or multiple magmatic/hydrothermal events.As such,the approaches presented in this study provide an approach that allows the identification of any geochronological relationships between mineralization and intrusive events in areas more complex than the study area.Previously published zircon U-Pb data for the mineralization-related porphyritic granodiorite in this area yielded an age of 134.2±1.2 Ma(MSWD=1.4)whereas the Re-Os dating of molybdenite from the study area yielded an isochron age of 137.7±2.5 Ma(MSWD=0.43).The timing of the mineralizing event in the study area was further examined by the dating of magmatic accessory titanite and skarn-related andradite garnet,yielding U-Pb ages of 136.3±2.5 Ma(MSWD=3.2)and 135.9±2.7 Ma(MSWD=2.5),respectively.The dating of magmatic and hydrothermal activity within the Magushan area yields ages around 136 Ma,strongly suggesting that the mineralization in this area formed as a result of the emplacement of the intrusion.The dates presented in this study also provide the first indication of the timing of mineralization within the Xuancheng district.providing evidence of a close genetic relationship between the formation of the mineralization within the Xuancheng district and the Early Cretaceous magmatism that occurred in this area.This in turn suggests that other Early Cretaceous intrusive rocks within this region are likely to be associated with mineralization and should be considered highly prospective for future mineral exploration.This study also indicates that the dating of garnet and titanite can also provide reliable geochronological data and evidence of the timing of mineralization and magmatism,respectively,in areas lacking other dateable minerals(e.g.,molybdenite)or where the relationship between mineralization and magmatism is unclear,for example in areas with multiple stages of magmatism,with complexly zoned plutons,and with distal skarn mineralization.

Impact of Water-Sediment Regulation on Variations of Amino Acids in the Middle-Lower Yellow River, China

In order to examine the impacts of water-sediment regulation on regional carbon cycling,we collected water,particulate and sediment samples from the middle-lower Yellow River in late June and early July,2015 and analyzed their specific amino acids(AA),DOC,POC,and bacteria abundance.Summarized by 14 specific AA,the total hydrolysable AA(THAA),particulate AA(PAA),and sediment AA(SAA)varied in ranges of 2.29-9.05μmol L^-1,5.22-22.96μmol L^-1,and 81.7-137.19μg g^-1 dry weight.After the regulation,dissolved free AA(DFAA)decreased by 29%while DCAA increased by 72%.These variations suggested that DFAA were further degraded,while DCAA molecules were further activated.Meanwhile,PAA increased almost 4 times as many as those before regulation,and SAA increased as well.After regulation,the amounts of bioactive amino acids(Asp,Glu and Gly)increased in THAA but decreased in PAA,with little changes in SAA.The ratios of Asp/Gly in different phases increased after regulation,indicating the AA contributions were promoted by calcareous organisms rather than by siliceous organisms.Multiple correlation analysis showed that PAA was primary representatives of AA and organic carbon,followed by DCAA and POC.Moreover,bacterial reproduction played a key role in shaping the AA compositions and properties,followed by the redox condition and acid-base balance.The results of this study provided a clear evidence for the effects of water-sediment regulation on regional biogeochemistry of organic carbon in the middle-lower Yellow River.

Cathodoluminescence and Trace Element Composition of Scheelite from the Middle-Lower Yangtze River Metallogenic Belt(MLYB): Implications for Mineralization and Exploration

The Middle-Lower Yangtze River Metallogenic Belt(MLYB)is known to contain abundant copper and iron porphyry-skarn deposits,with an increasing number of tungsten deposits and scheelite in Fe-Cu deposits being discovered in the MLYB during recent decades.The ore genesis of the newly-discovered tungsten mineralization in the MLYB is poorly understood.We investigate four sets of scheelite samples from tungsten,iron and copper deposits,using CL imaging and LA-ICP-MS techniques to reveal internal zonation patterns and trace element compositions.The REE distribution patterns of four studied deposits show varying degrees of LREE enrichment with negative Eu anomalies.The oxygen fugacity of ore-forming fluid increased in Donggushan,while the oxygen fugacity of ore-forming fluid decreased in Ruanjiawan,Guilinzheng and Gaojiabang.The scheelites from the Donggushan,Ruanjiawan,Guilinzheng and Gaojiabang deposits show enrichment in LREEs and HFSE,with Nb/La ratios ranging from 1.217 to 52.455,indicating that the four tungsten deposits are enriched in the volatile fluorine.A plot of(La/Lu)N versus Mo/δEu can be used to distinguish quartz vein type,porphyry and skarn tungsten deposits.This study demonstrates that scheelite grains can be used to infer tungsten mineralization and are effective in identifying magmatic types of tungsten deposits in prospective mining sites.

A PREDICTION ABOUT THE EFFECT OF THE BUILDING OF SHUIKOU HYDROPOWER STATION ON THE ECOLOGICAL ENVIRONMENT OF THE MIDDLE-LOWER REACHES OF THE MINJIANG RIVER

The building of Shuikou Hydropower Station in the Minjiang River is the largest one in the region of east China. Its install capacity is 1.4 million kw., and its generated energy of planning is 4.95 billion kwh each year. In accordance with a comprehensive survey of the valley of the middle-lower reaches of the Minjiang River and the characteristic of hydrography and in association with the specific type of the hydrography station, we can be sure that no harm will be done to the ecological environment when a hydropower station is built at Shuikou. Not only the deposition of silt within the reservoir must not be very serious, it is also more favorable than before for the irrigation of farmland on plains in the lower reaches of the Minjiang River and inland navigation.In addition, after the completion of the power station, the ecological environment will be the same as before both at the Minjiang River estuary and beyond it.

Flood and Waterlogging Disaster Damage Evaluation in Middle-Lower Yangtze River by 3S technology

The evaluation method, model and process for the flood and waterlogging disaster condition by GIS,RS and GPS technology and the method for setting up disaster condition database, dyke database and historical disaster damage database are presented. An index of flood damage degree(FDD) used to evaluate the relative degree of disaster loss and divide flood and waterlogging area is suggested. The value of flood damage degree can be calculated as follows :taking the various disaster losses of sample area in a base year as standard value and computing the ratios of various disaster loss values in different areas and years to the standard flood disaster loss values, then summing up the weighted ratios. The computed results are the value of flood damage degree in the every year. The macroscopic flood disaster distribution can be evaluated by the values of flood loss degree.

Tectonodynamic Adjustment of Crustal Materials in the Middle-Lower Reaches of the Yangtze River

Under the tectonodynamic process, crustal materials tend to experience two modes of adjustment: (1) structural (physical) adjustment, manifested by folding, faulting, uplifting, downwarping, etc.: (2) compositional adjustment, represented by element migration, concentration and dispersion, crystalline and dynamic differentiation of crystals, metamorphism, etc. (Yang Kaiqing. 1986; Yang Kaiqing et al., 1986). The dynamic adjustment of crustal materials in the middle-lower reaches of the Yangtze mainly occurred in the Mesozoic under the conditions of intense collision between the North China (Dabie) massif and the Yangtze massif. The structural adjustment refers to various types of deformation within the two massifs and the intensive shortening of the stratigraphic coyer of the Yangtze massif, whereas the compositional adjustment implies the structural remelting of the basement and the ore. and rock- forming processes in the two massifs.

Research and Application of Micromotional Exploration in the Middle-Lower Yangtze Metallogenic Belt of China

Micromotion is the daily tiny vibration of the earth’s surface. Micromotional exploration can use the surface wave information of micro motion to study the shallow structure of underground media. In this study, we collected microtremor data at 68 stations in the Middle-Lower Yangtze Metallogenic Belt (MLYMB) and determined the resonant frequency and obtained the distribution of sedimentary thickness in this area by using H/V spectral ratio. According to the results of H/V, the sedimentary layer in the basin is thick, and the predominant frequency of the basin is 0.05 - 0.1 Hz. There are no obvious lateral changes in the impedance interface between bedrock and sedimentary layer in this area. The basement of Tongling, Anqing and Luzhou mining areas and their adjacent areas is Kongling-Dongling type basement, which is composed of a set of metamorphic core complex. The predominant frequency is 0.05 - 0.1 Hz. The sedimentary thickness gradually thinned from 3800 m in the west to 2100 m in the East. Moreover, this article used SPAC (spatial autocorrelation) method to obtain the S-wave velocity structure of the mining area near Luzong. The SPAC method reveals that the depth of the interface between the loose sediments and the volcanic rocks is about 600 m in the study area near the Luzhou mining area in the Middle-Lower Yangtze Metallogenic Belt, and the average depth of the interface between the volcanic rock section and the intrusive complex section is about 1000 m. The thickness of the intrusive rock is more than 2500 m. Tourmaline is developed in the interior of the intrusive rock, which may have better exploration value.

Observational and Modeling Studies of Impacts of the South China Sea Monsoon on the Monsoon Rainfall in the Middle-Lower Reaches of the Yangtze River During Summer

Based on the ERA-40 and NCEP/NCAR reanalysis data,the NOAA Climate Prediction Center＇s merged analysis of precipitation（CMAP）,and the fifth-generation PSU/NCAR Mesoscale Model version 3（MM5v3）,we defined a monsoon intensity index over the East Asian tropical region and analyzed the impacts of summer（June-July） South China Sea（SCS） monsoon anomaly on monsoon precipitation over the middle-lower reaches of the Yangtze River（MLRYR） using both observational data analysis and numerical simulation methods.The results from the data analysis show that the interannual variations of the tropical monsoon over the SCS are negatively correlated with the southwesterly winds and precipitation over the MLRYR during June-July.Corresponding to stronger（weaker） tropical monsoon and precipitation,the southwesterly winds are weaker（stronger） over the MLRYR,with less（more） local precipitation.The simulation results further exhibit that when changing the SCS monsoon intensity,there are significant variations of monsoon and precipitation over the MLRYR.The simulated anomalies generally consist with the observations,which verifies the impact of the tropical monsoon on the monsoon precipitation over the MLRYR.This impact might be supported by certain physical processes.Moreover,when the tropical summer monsoon is stronger,the tropical anomalous westerly winds and positive precipitation anomalies usually maintain in the tropics and do not move northward into the MLRYR,hence the transport of water vapor toward southern China is weakened and the southwest flow and precipitation over southern China are also attenuated.On the other hand,the strengthened tropical monsoon may result in the weakening and southward shift of the western Pacific subtropical high through self-adjustment of the atmospheric circulation,leading to the weakening of the monsoon flows and precipitation over the MLRYR.

A 3D Investigation of Geological Structure and Its Relationship to Mineralization in the Nanling-Xuancheng Ore District,Middle-Lower Yangtze River Metallogenic Belt,China

The Nanling-Xuancheng ore region of Anhui Province is located in the Middle-Lower Yangtze River metallogenic belt.Insufficient exploration and research have been carried out in this newly defined ore district,although the Chating large porphyry Cu-Au deposit and a few middle-sized skarntype Cu polymetallic deposits have been discovered.In this study,we carried out high-resolution seismic reflection,magnetotelluric,gravity,and magnetic investigations,and constructed the 3 D geological structure of the uppermost crust in a depth range of 0-5 km using a comprehensive inversion of the new data constrained by previous deep-drilling data.We hence proposed some new insights to understand the mineralization processes of this district.A system of alternating ridges and valleys is suggested as the major structure pattern,composed of“two-layer structure”of the basins and“three-layer structure”of anticlines.Moreover,a conjugated fault system and its distribution features are revealed in our models,including the Jiangnan fault,Zhouwang fault,and Kunshan thrust nappe.The Jiangnan and Kunshan faults are suggested to have controlled the diagenesis and metallogenesis.Two deep concealed plutons located in Chating and Magushan are found,forming the Mesozoic diorite-felsic intrusions.These intrusions are believed to be the causes of hydrothermal deposits such as the Chating deposit and the Magushan deposit.

THE EXCESSIVE RAIN OVER THE MIDDLE-LOWER REACHES OF CHANGJIANG RIVER AND ITS RELATION TO VOLCANIC ERUPTIONS IN HISTORY

Based on the historical data of the excessivc rains ovcr the middle-lower reaches of Changjiang River in two hundred and fifty years (1651--1900) and the data of 'Very Large' volcanic eruptions (VEI≥5) in the period of 1650--1900, which are selected from the table of volcanic eruption year complied by Sim- kin et al. (198l). This paper analyses the interannual variation of various kinds of continuous rains in the historical period, as well as the relation between plum-continuous rains and waterlogging along Chang- jiang-Huaihe reaches, and between 'Very Large' volcanic cruption and continuous rains over the middle- lower reaches of Changjiang Rivex.

Mineral Deposit Model of Cu-Fe-Au Skarn System in the Edongnan Region, Eastern China

Cu and Fe skarns are the world's most abundant and largest skarn type deposits,especially in China,and Au-rich skarn deposits have received much attention in the past two decades and yet there are few papers focused on schematic mineral deposit models of Cu-Fe-Au skarn systems.Three types of Au-rich deposits are recognized in the Edongnan region,Middle-Lower Yangtze River metallogenic belt:~140 Ma Cu-Au and Au-Cu skarn deposits and distal Au-Tl deposits.137-148 Ma Cu-Fe and 130-133 Ma Fe skarn deposits are recognized in the Edongnan region.The Cu-Fe skarn deposits have a greater contribution of mantle components than the Fe skarn deposits,and the hydrothermal fluids responsible for formation of the Fe skarn deposits involved a greater contribution from evaporitic sedimentary rocks compared to Cu-Fe skarn deposits.The carbonate-hosted Au-Tl deposits in the Edongnan region are interpreted as distal products of Cu-Au skarn mineralization.A new schematic mineral deposit model of the Cu-Fe-Au skarn system is proposed to illustrate the relationship between the Cu-Fe-Au skarn mineralization,the evaporitic sedimentary rocks,and distal Au-Tl deposits.This model has important implications for the exploration for carbonate-hosted Au-Tl deposits in the more distal parts of Cu-Au skarn systems,and Fe skarn deposits with the occurrence of gypsum-bearing host sedimentary rocks in the MLYRB,and possibly elsewhere.

3-D isotropic and anisotropic tomography of P-wave travel times from the Anhui airgun experiment in the Yangtze River

The Middle-Lower Yangtze River is a typical transition region between the nearly NW-oriented Tethys and NE-trending Pacific tectonic regimes.Structures of different periods and directions overlap strongly during these processes.The NE-trending Yangtze River compound structural belt and NW-trending Tongling-Hangzhou structural belt both control the magmatic activities and distributions of the metallogenic belts in the area.Here,we obtain 3-D high-resolution isotropic and azimuthally anisotropic velocity structures at depths of 1–10 km using the first arrivals from airgun sources.The velocity maps correspond well with the tectonic structures,with high-velocity anomalies distributed in ore-concentrated districts and low-velocity anomalies distributed along the Yangtze River.The fast directions are generally consistent with the fault strike,indicating that the azimuthal anisotropy is mainly dominated by the fault and fracture trends in the upper crust.The complicated fast directions near the Luzong and Tongling ore deposits reveal complex deformations in the upper crust,which are mainly caused by the intersection of the Yangtze River compound and Tongling-Hangzhou structural belts.The magma intrusion beneath the two ore deposits(Luzong and Tongling)are connected at depths of 5–10 km.

High-resolution 3D crustal S-wave velocity structure of the MiddleLower Yangtze River Metallogenic Belt and implications for its deep geodynamic setting

The Middle-Lower Yangtze River Metallogenic Belt(MLYMB) is an important mineral resource region in China.High-resolution crustal models can provide crucial constraints to understand the ore-forming processes and geodynamic setting in this region. Using ambient seismic noise from 107 permanent and 82 portable stations in the MLYMB and the adjacent area,we present a new high-resolution 3D S-wave velocity model of this region. We first extract 5–50 s Rayleigh wave phase velocity dispersion data by calculating ambient noise cross-correlation functions(CFs) and then use the surface wave direct inversion method to invert the mixed path travel times for the 3D S-wave velocity structure. Checkerboard tests show that the horizontal resolution of the 3D S-wave velocity model is approximately 0.5°–1.0° and that the vertical resolution decreases with increasing noise and depth. Our high-resolution 3D S-wave velocity model reveals:(1) AV-shaped high-velocity zone(HVZ) is located in the lower crust and the uppermost mantle in the study region. The western branch of the HVZ passes through the Jianghan Basin,the Qinling-Dabie orogenic belt and the Nanxiang Basin. The eastern branch, which almost completely covers the main body of the MLYMB, is located near the Tanlu Fault. The low-velocity anomalies between the western and eastern branches are located in the area of the Qinling-Dabie orogenic belt.(2) High-velocity uplifts(HVUs) are common in the crust of the MLYMB,especially in the areas near the Tanlu Fault, the Changjiang Fault and the Yangxin-Changzhou Fault. The intensities of the HVUs gradually weaken from west to east. The V-shaped HVZ in the lower crust and uppermost mantle and the HVUs in the middle and lower crust likely represent cooled mantle intrusive rocks. During the Yanshanian period, fault systems formed in the MLYMB due to the convergence between the South China Plate and the North China Plate, the multiple-direction drifting of the PaleoPacific Plate and its subduction beneath the Eurasian Plate. The dehydration of the cold oceanic crust led to partial melting in the upper mantle. Temperature differences caused strong convection of the upper mantle material that underplated the lower crust and rose to near the surface along the deep fault systems. After mixing with the crustal materials, mineralization processes, such as assimilation and fractional crystallization, occurred in the MLYMB.