The impact of depositional environment and tectonic evolution on coalbed methane occurrence in West Henan, China

A deeper understanding of the mechanisms by which geological factors(depositional environment and tectonic evolution) control the occurrence of coalbed methane(CBM) is important for the utilization of CBM resources via surface-drilled wells and the elimination of coal-methane outbursts, the latter of which is a key issue for coal mine safety. Based on drill core data, high-pressure isothermal adsorption experiments, scanning electron microscopy experiments, mercury intrusion porosimetry, and X-ray diffraction experiments, the impact of the depositional environment and tectonic evolution on CBM occurrence of the II-1 coal seam of the Shanxi Formation in West Henan was analyzed. Results showed that the depositional environment led to the epigenetic erosion of tidal flat coal-accumulating structures by shallow-delta distributary channel strata. This resulted in the replacement of the original mudstonesandy mudstone coal seam immediate roof with fine-to-medium grained sandstones, reducing methane storage capacity. Epigenetic erosion by the depositional environment also increased coal body ash content(from 6.9% to 21.4%) and mineral content, filling the cleat system and reducing porosity, reducing methane storage capacity. The maximum methane adsorption capacity of the coal body reduced from35.7 cm3/g to 30.30 cm3/g, and Langmuir pressure decreased from 1.39 MPa to 0.909 MPa. Hence, the methane adsorption capacity of the coal body decreased while its capacity for methane desorption increased. Owing to the tectonic evolution of West Henan, tectonically deformed coal is common; as it evolves from primary cataclastic coal to granulitic coal, the angle of the diffraction peak increases, d002 decreases, and La, Lc, and Nc increase; these traits are generally consistent with dynamic metamorphism.This is accompanied by increases in the total pore volume and specific surface area of the coal body, further increasing the capacity for methane storage. Increases in micropore volume and specific surface area also increase the ability of the coal body to adsorb methane.

Huanggang Intrusive Complexin Northern Tongbai Area:Island-Arc Tectonic Environment and Its Geological Significance

The Huanggang intrusive complex in northern Tongbai area was formed in Early Paleozoic. It mainly consists of ultra basic, basic, intermediate and acid rocks, dominated by intermediate and basic rocks. The complex belongs to calc alkaline series. Geochemical characteristics of major and trace elements show that the complex was derived from the fractional crystallization of co source magma. It is suggested that the complex was formed in island arc tectonic environment and was closely related to the northward subduction of the Erlangping back arc basin. Thus, the subduction of the back arc basin can induce the island arc type magmatism similar to the one formed in the setting of ocean plate subduction.

Research on the Tectonic Environment and Seismogenic Mechanism of the 1927 Gulang Great Earthquake with M=8.0

In this paper, we discussed the seismotectonic environment of the deep-seated and shallowcrust and seismological and geological model caused the 1927 Gulang great earthquake, basedon the recent research concerning about the active fault, surface rupture, fault planesolution, seismic activity, as well as the deep geophysical exploration data analysis in theepicentral area.The result shows that the 1927 Gulang great earthquake was caused by NE-SW-strikingcompressional thrusting. It was a latest event occurred in the reverse fault-folding belt thatdeveloped along the intracrustal decollement.

Sequence Stratigraphy and Tectonic Environment of the Chartai Group,Inner Mongolia

The Middle Proterozoic Chartai Group separated by two unconformities consists of three depositional se-quences: the Shujigou Formation-Zenglongchang Formation (DS Ⅰ), the Agulugou Formation (DS Ⅱ), andthe Liuhongwan Formation (DS Ⅲ). The carbonate platform and back-platform basin are the basic environ-ment model of the Chartai Group. The syndepositional faults on the oceanward side of the carbonate platformand large-scale slumping in the soft sediments are important marks of facies tracts. The newly establishedZenglongchan uplifting, an epeirogenetic uplifting, plays an important role in the formation of thepalaeogeographic framework of the Chartai Group. The stratigraphic correlation between the Chartai Groupand the Bayan Obo Group is made for the first time by using sequence stratigraphic principle and model estab-lished by P.R. Vail. The Chartai Group, which was deposited on the northern passive continental margin of theNorth China platfom, represents the platform cover.

Tectonic Environments of the Yan-Liao Rift during Earth's Middle Age(1.7～0.75 Ga): Evidence from Mafic Dyke Swarms in Eastern Hebei, North China

During the past decade,generations of Precambrian mafic dykes/sills have been investigated and revealed in the North China Craton(NCC).Researchers identified more than 20 episodes of Precambrian dyke swarms,

GRANITOIDS,VOLCANIC ROCKS AND CHERTS FROM NORTH ALTYN TAGH,NW CHINA: IMPLICATION FOR THE TECTONIC ENVIRONMENT DISCRIMINATION

Granitoids,volcanic rocks and cherts,mainly of early Paleozoic,in northern Altyn Tagh(Fig.1) are analyzed here for the purpose of the determination of the tectonic environments and their development since Early Paleozoic.(1) Granitoids\ The collection of 128 main\|element petrochemical data from North Altyn Tagh area shows that most of the granitoids here are granites and granodiorites of calc\|alkaline series.They consist mainly of metaluminous and peraluminous in Shand’s index,and only one of them,which belongs to Mesozoic,is peralkaline.Most of the granitoids plot in the IAG+CAG+CCG fields in the Maniar and Piccoli’s diagrams (1989) for tectonic discrimination of granitoids.IAG (Island arc granitoids)and CAG (Continental arc granitoids) can be distinguished for Early and Late Paleozoic granitoids,and maybe some CCG (Continental collision granitoids) for Early Paleozoic.Granitoids of Mesozoic and Cenozoic inherited the characteristics of those of Paleozoic.Destructive active plate margin (pre\|plate collision)and Anatectic magmatism(syn\|orogenic,S\|type granites)are distinguished (Fig.2)for Paleozoic granitoids using de la Roche R 1\| R 2 multicationic diagram (Batchelor and Bowden,1985).Mesozoic and Cenozoic granitoids inherited the characteristics of Anatectic magmatism (syn\|orogenic)of these early ones,and post\|orogenic(A\|type)granites occurred in Mesozoic.The mechanism for magma formation is mainly partial melting.

Tectonic environment and cause of earthquakes in the Three Gorges reservoir area

Seismotectonics in the Three Gorges reservoir area is investigated by using the P-wave tomography with earthquakes that occurred before the impoundment of the reservoir. The result indicates that most of these events occurred in or around the velocity-gradient belts between high-velocity and low-velocity anomalies. These belts have similar characteristics to buried-fauh zones. Stresses generated by movement of partially molten upper-mantle materials and thermal stress may have jointly contributed to the seismic activities along the faults and such buried faults, and possibly activated new earthquake ruptures.

Geochemical discrimination of the geotectonic environment of basaltic-andesitic volcanic rocks associated with the Laochang polymetallic ore deposit at Lancang, Yunnan

The Laochang polymetallic ore deposit at Lancang is one of the well known ancient ore deposits associated with volcanic rocks in the Sanjiang (Tri-river) region of Southwest China. Volcanic rocks are dominated by alkali basalt and trachyte basalt. There has long been a controversy on the environment of formation of basalts. Some scholars hold that the basalts were formed in a continental environment, some thought they were formed in an oceanic environment and others considered that the basalts were emplaced in a back-arc basin. This study focuses on the geochemical characteristics of the basalts on the basis of their major elements, REEs and trace elements. At the same time, strongly incompatible elements such as Ta, Th and Hf and their ratios were used to differentiate the geotectonic settings of basalts. The results showed that the basalts in the region studied were formed in a continental rift environment.

Coal forming environments and their relationship to tectonic activity in the Cévennes Stephanian coal basin

Coal forming environments in the tectonically controlled intermontane Stephanian Cévennes coal basin (Massif central, France) show a complex interelationship between structural and sedimentological features. The study of the general structural features and the geometry of the coal beds developed during the different stages in the evolution of the basin, and the spatial relation of the lithofacial units to the early tectonic activities, lead the authors to suggest the following model. The synsedimentary faults that occurred as both intrabasinal and marginal faults controlled not only the spatial distribution, shape and thickness of the detrital rock units and coal seams, but also caused the inversion of the tectonic style. The marginal faults exercised important controls on the geometry of the basin and the distribution of lithofacial units. However due to the subsidence of the central part of the basin and the depocenter, and the to differences in the timing and intensity of the displacement the coal enrichment zones shifted both vertically and laterally. This eventually resulted in the inversion of the whole tectonic framework from semi graben through graben to a new semi graben. The style and rate of the tectonic movement and basin filling that occurred in the Stephanian Cévennes coal basin were in turn closely linked with the tectonic movement in the surrounding area. Therefore the authors propose that the environment and processes of coal formation in this basin are closely linked to its tectonic evolution.

Tectonic Environments of Cenozoic Volcanic Rocks in China and Characteristics of the Source Regions in the Mantle

Extensive volcanism is one of the important features of Cenozoic geology in China.Based on temporal-spatial distribution,the volcanism was associated with three major different geological settings:1)the continental rift basalts in Northeast and North China;2)the tension-fault basalts on the continental margins of Southeast China; and 3) the collision-zone high-K volcanics in the Qinghai-Xizang Plateau and its vicinities.The characteristics of 'depletion in the south and enrichment in the north'of the China continental mantle are strongly supported by isotopic evidence.The Cenozoic continental cal characters,into the following geochemical provinces:1)the depleted mantle in South China;2)the primary mantle in Northeast and NorthChina; 3)the hybrid and transi-tional mantle in the region of Shandong ,Anhui,Jiangsu and northern Zhejiang;4)the depleted mantle around the Bohai Bay and the Lower Liaohe River;5)the K-metasomatic enriched mantle in the northern part of Northeast China;and 6)the re-cycled enriched mantle in the ancient subduction zone in the Qinghai-Xizang Plateau and its surround-ings.These geochemical characteristics on a regional scale must be a reflection of the nature of lithosphere evolution.

Coal Deformation, Metamorphism and Tectonic Environment in Xinhua, Hunan

This article discusses in detail chemical composition, molecular structure, microstructure phenomena, estimate of the palaeo-stress, paleo-temperature and the strain rate to deepen the knowledge for the correlation of coal deformation and metamorphism with structural environment in Xinhua Hunan by coal quality analysis, XRD and SEM methods, which provide dependable theoretical foundation for coal resource exploitation and utilization. The results show that 1) d002 value of six coal samples is from 3.36 to 3.39 nm, coal resolved itself into aphanitic graphite with the increase of coal rank during coalification, which is characterized by graphite flakes, and the crystallite size is from 50 nm to 250 nm;A certain degree of 3R-structure content is increases and the crystallite size is extend with the coalification process, but RH-structure content is decreased;2) the tectonic environment of research area belongs to the ductile-brittle deformation, which was characterized by low temperature, low stress, high strain rate;3) Tianlongshan magmatic intrusion provided heat source, its side-extrusion made the molecules structure of coal ordering, distance between layers decreased, finally it caused the formation of aphanitic graphite.

Geochemistry of Neogene Mudrocks from Sitakund Anticline, Bengal Basin: Implications for Provenance, Weathering, Tectonic Setting and Depositional Environment

Geochemical analysis of Neogene mudrocks from Sitakund anticline, Chittagong Tripura Fold Belt (CTFB), Bengal Basin, Bangladesh, was deployed to delineate the provenance, tectonics and depositional environments. Representative samples went through mineralogical and geochemical analysis concerning major, trace and rare earth element analysis. Rigaku ZSX Primus and NITON XL3t 800 XRF instruments were utilized for the determination of major and trace elements. The experiment results reveal that the Neogene mudrocks are rich in silica having concentration of 58.10% to 62.60% with an average of 59.90%. Therefore, the geochemical response from the experiments apparently proved the existence of the active continental margin setting for the Neogene mudrocks. Different concentrations and ratios of major oxides satisfy that the mudrocks were derived from felsic source rocks. In addition, chemical index of alteration (CIA) values for the Neogene mudrocks vary from 67.81 to 77.57 with an average 74.41 indicating significant weathering at the source areas. Moreover, U/Th, Cu/Zn, Ni/Co and V/Cr ratios designate that the mudrocks were deposited in oxidizing depositional environment.

Petrochemistry ,Chronology and Tectonic Setting of Strong Peraluminous Anatectic Granitoids in Yunkai Orogenic Belt , Western Guangdong Province ,China

Arguments persist on the genesis and ages for the banded-augen （rapakivi） anatectic granitoids （charnockite） extensively outcropped in the Yunkai （云开） region, western Guangdong （广东） Province. Their petrochemistry, SHRIMP dating, deformational and metamorphic structure were studled. The results show that most granitoids are A/CNK〉1. 1, CaO/Na2O= 0. 62-1. 61 （average 0.94〉0.3）, Al2O3/TiO2 =16.6-60.6 （average 23.68）, depleted high field strong elements Ta, Nb, Zr, strong peraluminous high-K calcalkaline and calcalkaline granitoids in the post-collisional tectonic environment of a subduction-collision orogenic belt in an active-continental margin. The temperatures of charnockite and gneissic garnet-bearing biotite monzonitic granite are obviously higher than those of banded-augen （rapakivi） biotite monzonitic granite, and charnockite and gneissic garnet-bearing biotite monzonitic granite with the evolutional characteristics of A-type granites. The forming ages from banded-augen （rapakivi） biotite monzonitic granite to charnockite and gneissic garnet-bearing biotite monzonitic granite, whose crystallizing zircon SHRIMP ages are （465±10） Ma, （467±10 ） Ma, （435±11 ） Ma and （413±8） Ma, respectively, become younger. This shows that there was an oceaniccontinental subduction-collision and post-collisional extension-delamination-underplating between the Yangtze and Cathaysia plates during the Caledonian, and the granitoids experienced compressional uplift and extensional exhumation during the lndosinian. This provides important evidence of subduction collision of the Yangtze plate to the Cathaysia plate during the Caledonian in South China.

Upper crustal velocity and seismogenic environment of the M7.0 Jiuzhaigou earthquake region in Sichuan, China

On August 8,2017,a magnitude 7.0 earthquake occurred in Jiuzhaigou County,Sichuan Province,China.The deep seismogenic environment and potential seismic risk in the eastern margin of Tibetan Plateau have once again attracted the close attention of seismologists and scholars at home and abroad.The post-earthquake scientific investigation could not identify noticeable surface rupture zones in the affected area;the complex tectonic background and the reason(s)for the frequent seismicity in the Jiuzhaigou earthquake region are unclear.In order to reveal the characteristics of the deep medium and the seismogenic environment of the M7.0 Jiuzhaigou earthquake region,and to interpret the tectonic background and genesis of the seismicity comprehensively,in this paper,we have reviewed all available observation data recorded by the regional digital seismic networks and large-scale,dense mobile seismic array(China Array)for the northern section of the North-South Seismic Belt around Jiuzhaigou earthquake region.Using double-difference seismic tomography method to invert the three-dimensional P-wave velocity structure characteristics of the upper crust around the Jiuzhaigou earthquake region,we have analyzed and discussed such scientific questions as the relationship between the velocity structure characteristics and seismicity in the Jiuzhaigou earthquake region,its deep tectonic environment,and the ongoing seismic risk in this region.We report that:the P-wave velocity structure of the upper crust around the Jiuzhaigoug earthquake region exhibits obvious lateral inhomogeneity;the distribution characteristics of the shallow P-wave velocity structure are closely related to surface geological structure and formation lithology;the M7.0 Jiuzhaigou earthquake sequence is closely related to the velocity structure of the upper crust;the mainshock of the M7.0 earthquake occurred in the upper crust;the inhomogeneous variation of the velocity structure of the Jiuzhaigou earthquake area and its surrounding medium appears to be the deep structural factor controlling the spatial distribution of the mainshock and its sequence.The 3D P-wave velocity structure also suggests that the crustal low-velocity layer of northeastern SGB(Songpan-GarzêBlock)stretches into MSM(Minshan Mountain),and migrates to the northeast,but the tendency to emerge as a shallow layer is impeded by the high-velocity zone of Nanping Nappe tectonics and the Bikou Block.Our results reveal an uneven distribution of high-and low-velocity structures around the Tazang segment of the East Kunlun fault zone.Given that the rupture caused by the Jiuzhaigou earthquake has enhanced the stress fields at both ends of the seismogenic fault,it is very important to stay vigilant to possible seismic hazards in the large seismic gap at the Maqu-Maqên segment of the East Kunlun fault zone.

Geochemical characteristics of the Permian marine mudstone and constraints on its provenance and paleoenvironment in the Fenghai area,Fujian Province, southeastern China

Permian marine strata have gradually become a research focus in the world.The marine strata of the Late Permian Dalong Formation(P3d)in the Fenghai area,Fujian Province,have become more and more important as their geochemical characteristics record important geological information and are a good indicator for recovering and reconstructing the paleosedimentary environments and tectonic attributes.The major elements,trace elements and rare earth elements were analyzed by XRF and ICP-MS,respectively.Based on the results of detailed field geological surveys,profile measurements as well as typical sample collection,the tectonic setting and provenance of Permian marine mudstone were comprehensively discussed.The results showed that the Dalong Formation(P3d)was deposited in an active continental margin tectonic environment as revealed by the relation between Fe2O3 + MgO and TiO2 and Al2O3/SiO2.The fingerprint characteristics of Mn,Fe,Co,Ni and REE and the ratio of U/Th,V/Cr,Sr/Ba,(La/Yb)N and V/(V +Ni)indicated that the sedimentary provenance was mainly derived from potassium feldspar,followed by muscovite.Sedimentary water bodies showed a gradually decreasing depositional rate trend,water depth gradually shallowing and paleo-salinity and productivity gradually increasing.Moreover,since transient delamination occurred during sedimentary processes,sedimentary water bodies showed obvious neritic characteristics.It was consistent with the results revealed by lithological and geochemical characteristics.Calcareous mudstone and siltstone transitioned into fine sandstone from bottom to top,indicating paleo-water bodies became shallow.The research results provided good reference and guidance for understanding Permian paleo-sedimentary environments and tectonic attributes of the Yong’an area,Fujian Province,southeastern China.

Deep Structures in China and Its Adjacent Areas: Plate Tectonics and Its Metallogenic Significance

This paper proposes a new tectonic pattern of the deep-seated structures in China and its adjacent areas (including the T - A - B system of the Ryukyu Islands). This is based on studies of the gravity field and gravity inversion coupled with the summation of the most recent achievements in geophysical studies. From a plate-tectonic point of view, the metallogenic characteristics and their indications at depth, as well as relevant geophysical-geological characteristics of four tectonic environments of the Chinese continent are analysed, and a classification of composite metallogenic provinces and belts and prediction of metallogenic prospects are made. The author extends the Kunlun-Qilian-Qinling tectonic belt to the T-A-B system of the Ryukyu Islands through the NW deep boundary of the Hangzhou Bay, and also proposes the following basic views' the migration and superposition of tectonic environments led to the formation of a composite metallogenic system; the change in the tectonic environment resulted in the superposition of various types of mineral deposits; seismic activities and metallogeny are mutually inducing factors. These views will be helpful to a discussion on the tectonic environments and metallogenic regularities.

Geochemistry and Tectonic Significance of Chlorite Amphibolite in Nanfen BIF, Benxi Area, Northeastern China

Benxi area, Northeastern China, is the main distribution area of Archean BIF-hosted iron deposits in China. In this area, Nanfen iron deposit is well known as the largest open-pit iron deposit not only in China but also in Asia. So far, the tectonic nature during Archean BIF formation period in Benxi area has been long disputed and the tectonic setting of Nanfen BIF had not been found. In this study, the geochemical characters of chlorite amphibolites closely associated with BIF have been investigated for the tectonic environment of Nanfen BIF. Chlortie amphibolites show the geochemical affinity to the back-arc basin basalt (BABB), indicating that the tectonic environment of Nanfen BIF is the back-arc basin. In conjunction with geological evidence of other BIFs at Benxi area, it is identified that BIF in Benxi area might be formed in the subduction-related back-arc basin, which provides a favorable sedimentary environment of Algoma-type BIF.

Geological division of gas in the Pingdingshan mine area based on its tectonic dynamics characteristics

In this paper,we used tectonic dynamics theories to study the tectonic evolution characteristics of the Pingdingshan mine area,and analyzed the impact of tectonic progressive control on gas occurrence.The study results are as follows:the Pingdingshan mine area has been mainly controlled by multiple squeezing and shearing actions of the Qinling orogenic belt since early and middle Yanshan,forming the tectonic control characteristics of master control in two directions,namely NWW trending and NNE trending;the NWW trending structure is dominated by squeezing and shearing,while the NNE trending structure is dominated by tension.Progressively controlled by the structure,the gas occurrence presents partition and zonation,i.e.compared with the western structure,the eastern NWW-NW trending structure of the mine area is more highly developed,resulting in the mine area gas occurrence distribution characteristics are distinct in the east while indistinct in the west.Based on this,the mine area can be divided into the following two geological dynamic areas:the western half of mine area,namely the Guodishan fault control area,where the NW-SE trending synchronous tension action suffered by the northeast side(footwall) is relatively strong,and compared with the southwest side(hanging wall),its coal and gas outburst seriousness is weak;and the eastern half of mine area,namely the NWW-NW thrust nappe fracture fold control area,which is a serious area of coal and gas outburst,in particular the axial area of the Likou syncline is the intersection compound and combination position of the NW and NE trending structures,a tectonic concentrated area,and the gas pressure and content here are the largest.

GENERAL CHARACTER OF MULTISTAGES OFMETALLOGENESIS FOR MICRO-MESOTHERMAL GOLD DEPOSITS:EXAMPLES FROM ZHANG-BALING TECTONIC BELT,ANHUI,CHINA

In Zhangbaling Tectonic Belt,two types of mineralization,auriferous quartz veins and alter- ation halos,can observed within many deposits.The pressure of metallogenesis of auriferous al- teration halos ismuch higher than thatof quartz vein,thetemperatures ofmetallogeneses ofthese two types of orebodies are don’tthe same Geochemistry study indicates thatboth ofthem are mi- cro- mesothermal deposits related to Yanshanian granites.The results of proton microprobe analy- sis of sulphides from the gold deposits in the area show that the“invisible” gold existed in sul- phides is in the form ofmicro inclusions,and the concentration of“invisible” gold in sulphidemin- erals within quartz vein is poorerthan thatfrom alteration halos.Field observation shows thatthe structural modality of the fractures controlling the orebodies of auriferous quartz vein is different from thatof the auriferous alteration zones.The fracture controlling the orebodies of auriferous alteration halos is compress- shearfracture,auriferous quartzvein is controlled by extensive fault. The alteration halos crosscut by auriferous quartz vein.The wallrocks of the former altered strongly and developed alteration zones well.The wallrocks of auriferous quartz vein altered slightly.The results of tectonogeochemical study shows that the concentration of associated met- allogenesis elements and intensity of alteration are positively correlated with tectonic deformation strength for auriferous alteration halos.Itindicates that it is probably a general character for mi- cro- mesothermal gold deposits due to the multistages of metallogeneses took place.The tectonic environmentis the most important fact determining the mechanism of fluid flow and precipitationof gold,and then the types of mineralization and modes of gold.