Isotopic compositional Characteristics of Terrigenous Natural Gases in China

The C and H isotopic compositions of the methane in more than 160 gas samples from 10 basins in China are presented in this paper.The natural gases are classified as four types: biogenic gas ,bio-thermocatalytic transitional gas, gas associated with condensate oil ,and coal-type gas. The isotopic compositions of these gases closely related to the depositional basins, the types of organic matter,the stages of thermal evolution and the genetic characteristics of different gas reservoirs.Studies of the C and H isotopic compositions of terrigenous natural gases will provide valua-ble information on the prospecting and development of natural gases of different genetic types.

Dibenzofuran Series in Terrestrial Source Rocks and Crude Oils and Applications to Oil-Source Rock Correlations in the Kuche Depression of Tarim Basin, NW China

Ten series of aromatic hydrocarbon compounds (biphenyl, naphthalene, phenanthrene, anthracene, retene, chrysene, benzoanthracene, dibenzofuran, fluorene, dibenzothiophene) isolated from seven Triassic and Jurassic lacustrine mudstone samples and three swamp coal samples, as well as five crude oil samples collected in the Kuche depression of the Tarim Basin, NW China, have been analysed by GC-MS techniques. It is found that the relative abundances of dibenzofuran series are higher in the three swamp coal samples than those in the lacustrine mudstone samples. Based on the similar relative abundances of dibenzofuran series, especially dibenzofuran compound, in the TICs of aromatic hydrocarbons, crude oils from wells SA3 (K), YTK5 (E, K) and QL1 (E) are thought to have been derived predominantly from the coals of the Lower Jurassic Yangxia Formation or Middle Jurassic Kezilenuer Formation, whereas those from wells YM7 (O) and YH1 (E) were derived mainly from Triassic and Jurassic lacustrine mudstones in the Kuche depression. This is the first report about how to distinguish coal-generated oils from lacustrine mudstone-generated oils in the Kuche depression in terms of the dibenzofuran series. The present paper has enlightening and directive significance for further oil-source rock correlations and oil and/or gas exploration in the Kuche depression of the Tarim Basin.

Isotopic Geochemistry of Non-hydrocarbons in Natural Gases from the Sanshui Basin,Guangdong Province,China

This study is focused on geothermal heat flow and the origin of non-hydrocarbons in natural gases in terms of the isotope geochemical characteristics of Ar,He,CO2 and N2 in natural gases from the Sanshui Basin,Guangdong Province,China,^3He/^4He,ratios are of from the Sanshui Basin,Guangdong Province,China,^3He/^4He ratios are of (1.60-6.39)×10^-6,and ^40Ar/^36Ar ratios of 450841.The carbon isotopic composition (δ^13 C PDB)of carbon dioxide ranges from -20‰to -2‰,δ^15N (air) ratios have a wider range of -57‰-+95‰.The isotope geochemical characteristics of non-hydrocarbons indicate that He,Ar and N2 in the gas reservoirs enriched in non-hydrocarbons were derived largely from the upper mantle.Non-hydrocarbons in gaseous hydrocarbon reservoirs consist mainly of crustal radiogenic ^4He and ^40Ar and some mantle-derived He and Ar, as well as of ^13C-depleted carbon dioxide and nitrogen generated as a result of thermal decomposition of organic matter in strata.Carbon dioxide enriched in ^13C was derived largely from carbonate rocks and partially from the lower crust and upper mantle.Based on the relationship between geothermal heat flor(A)and ^3He/^4He ration in natural gases,the Q values for the area studied have been calculated.Similar Q values are reported from the upper mantle uplift area(77mWm^-2)in Huabei and the Tancheng Lujiang Rift Zone (88mWm^-2).More than 60 percent of geothermal heat flow in the Sanshui Basin may haee been derived from the upper mantle.

Palynology of Yanchang Formation of Middle and Late Triassic in Eastern Gansu Province and Its Paleoclimatic Significance

Xifeng （西峰） oilfield was recently found in the southwest of the Ordos basin. The oil source rocks are the Chang 7 Section of Yanchang （延长） Formation. In order to study the paleoclimate that controlled the formation of source rocks, a systemically palynological research on related beds in Yanchang Formation has been carried out. The core samples were analyzed with classical palynological techniques and the organic-walled sporomorphs from these samples were observed, identified and photographed under a light microscopy and a fluorescence microscopy. Abundant sporopollen were found in drilling cores from Chang 8 and Chang 7 sections, and two assemblages were distinguished： the Aratisporites-Punctatisporites assemblage and the Asseretospora-Walchiites assemblage. Their characteristics are similar to those of the assemblage of Tongchuan （铜川 ） Formation and the assemblage of Yanchang Formation in southeast Ordos basin, respectively. Their geological times are Ladinian of late Middle Triassic and Carnian of early Late Triassic, respectively. The correlation of palynoflora with their parent plants suggests the paleoclimate of eastern Gansu （甘肃） Province in the Middle and Late Triassic was warm and rainy with prosperous vegetation. The palynoflora indicated the area was in a temperate to subtropical zone then. Both the ecological types and differentiation degree curves of sporopollen indicated the period during Chang 8 and Chang 7 sections was warm and wet, and the phase accorded with large-scale lake transgression in Chang 8 Section and the largest lake area in Chang 7 Section. North China in Middle and Late Triassic was located in a warm and rainy, temperate and subtropi- cal zone. The palynofloras in Chang 8 and Chang 7 sections have the characteristics of North China flora, however they also indicate wetter and warmer climate due to their proximity to the large lakes. The period of Chang 8 to Chang 7 sections is the climax of the expansion of the lake, and the bloom of fresh algae during the period, which helped form the high-quality source rocks in Chang 7 Section.

Carbon isotopic characteristics of hydrocarbon gases from coal-measure source rocks—A thermal simulation experiment

Gaseous hydrocarbon geochemistry research through a thermal simulation experiment in combination with the natural evolution process in which natural gases were formed from coal-measure source rocks revealed that the {δ{}+{13}C-1} values of methane vary from light to heavy along with the increase of thermal evolution degree of coal-measure source rocks, and the {δ{}+{13}C-2} values of ethane range from {-28.3‰} to {-20‰} (PDB). {δ{}+{13}C-2} value was {-28‰±} (R-O={0.45%}-{0.65%}) at the lower thermal evolution stage of coal-measure source rocks. After the rocks entered the main hydrocarbon-generating stage (R-O={0.65%}-{1.50%}), {δ{}+{13}C-2} values generally varied within the range of {-26‰}-{-23‰±}; with further thermal evolution of the rocks the carbon isotopes of ethane became heavier and heavier, but generally less than -20‰.; The partial carbon isotope sequence inversion of hydrogen gases is a characteristic feature of mixing of natural gases of different origins. Under the condition of specially designated type of organic matter, hydrogen source rocks may show this phenomenon via their own evolution.; In the lower evolution stages of the rocks, it is mainly determined by organic precursors that gaseous hydrocarbons display partial inversion of the carbon isotope sequence and the carbon isotopic values of ethane are relatively low. These characteristic features also are related to the geochemical composition of primary soluble organic matter.

Helium and Argon Isotopic Composition of Cenozoic Alkali Basalts and Mantle-Derived Xenoliths from Kuandian, Liaoning Province, China

The noble gas isotopic composition and content data of 2 alkali basalts, 3 lherzolite xenoliths and one clinopyroxene megacryst from the Kuandian region have confirmed the occurrence of a fractionation of noble gases during magmatism. Light noble gases such as He and Ne are high in mobility and appear to be incompatible as compared with heavy ones (such as Kr and Xe). Therefore, light noble gases are abundant in volcanics, especially in the volcanics with bubbles; lherzolite xenoliths have relatively high heavy noble gases. The clinopyroxene megacryst has the lowest abundance of noble gases, probably due to its high P-T origin. Noble gas isotopic composition of the clinopyroxene megacryst reveals that the mantle source beneath the Kuandian area has an MORB-like reservoir with 3He/4He ratio of ～10 Ra (Ra: atmospheric 3He/4He ratio) and 40Ar/36Ar ratio of 345.6. The lherzolite xenoliths possess moderate 3He/4He ratios of 2.59-4.53 Ra, reflecting the loss of primary helium during rock deformation or metasomatism caused by enriched mantle fluids during the up-lifting. The alkali volcanics have very low 3He/4He ratios (0.47-0.61 Ra), indicating a contribution of radiogenic 4He, probably having resulted from crust contamination. Most of the samples have excess 21Ne and 22Ne as compared with atmospheric neon, but Kr and Xe isotopic compositions are indistinguishable from atmospheric values within uncertainties with only individual samples having excess 129Xe, 134Xe and 136Xe.

Genetic identification of natural gases from shallow reservoirs in some oil- and gas-bearing basins of China

Natural gases of shallow reservoirs with the carbon isotopic compositions of methane ranging from -50‰ to -60‰ (PDB) were considered as mixed gases of biogenic and thermogenic origins previously and some of them were considered as low-mature (or low temperature thermogenic) gases lately. In this paper natural gases with the carbon isotopic compositions of methane in the above range were identified using the molecular and stable carbon isotopic compositions of methane, ethane and propane. The mixed gases of biogenic and mature thermogenic origins display the characteristics of {δ{}+{13}C-1} ranging from -50‰ to -60‰, {δ{}+{13}C-2}>-35‰, Δ values ({δ{}+{13}C-3}-{δ{}+{13}C-2})< 5‰ and C-1/∑C++-2 ratios < 40. Immature to low|mature gases display the characteristics of {δ{}+{13}C-1} ranging from -50‰ to -60‰, {δ{}+{13}C-2} < -40‰, Δ values ({δ{}+{13}C-3}-{δ{}+{13}C-2}) >7‰, and C-1/∑C++-2 ratios >60.

Noble Gas Isotopic Compositions of Cobalt-rich Ferromanganese Crusts from the Western Pacific Ocean and Their Geological Implications

Noble gas isotopic compositions of various layers in three-layered （outer, porous and compact layers） cobalt-rich ferromanganese crusts and their basaltic and phosphorite substrates from the western Pacific Ocean were analyzed by using a high vacuum gas mass spectrum. The analytical results show that the noble gases in the Co-rich crusts have derived mainly from the ambient seawater, extraterrestrial grains such as interplanetary dust particles （IDPs） and wind-borne continental dust grains, and locally formation water in the submarine sediments, but different noble gases have different sources. He in the crusts derives predominantly from the extraterrestrial grains, with a negligible amount of radiogenic He from the eolian dust grains. Ar is sourced mainly from the dissolved air in the seawater and insignificantly from radiogenic Ar in the eolian continental dust grains or the formation water. Xe and Ne derive mainly from the seawater, with minor amounts of extraterrestrial Xe and Ne in the IDPs. Compared with the porous and outer layers, the compact layer has a relatively high 4He content and lower 3He/4He ratios, suggesting that marine phosphatization might have greatly modified the noble gas isotopic compositions of the crusts. Besides, the 3He/4He values of the basaltic substrates of the cobalt-rich crusts are very low and their R/R. ratios are mostly 〈0.1 R., which are similar to that of phosphorite substrates （0.087 R.）, but much lower than that of fresh submarine MORB （8.75±14 Ra） or seamount basalts （3-43 Ra）, implying that the basaltic substrates have suffered strong water/rock interaction and reacted with radiogenic ^4He and P-rich upwelling marine currents during phosphatization. The trace elements released in the basalt/seawater interaction might favor the growth of cobalt-rich crusts. The relatively low ^3He/^4He values in the seamount basalts may be used as an important exploration criterion for the cobalt-rich ferromanganese crusts.

Characteristics of the Biomarkers from Nonmarine Crude Oils in China--A Review

The present paper deals with the biomarker characteristics of crude oils and source rocks from different environments(fresh,fresh-brackish and salt waters)of nonmarine depositional basins of different ages in China.Their characters are summarized as follows:1)Souce rocks and crude oils derived from fresh-water lacustrine facies have an odd/even predominance of n-alkanes and high pristine/phytane ratios.Oils from the fresh-water lacustrine facies differ from typical marine oils in the relative contents of total steranes and terpanes,the concentrations of hopanes and organic sul-phur compounds and the values of methylphenanthrene indices and C,H,S stable isotopes.2)The source rocks and crude oils derived from saline lacustrine facies possess an even/odd predominance of n-alkanes and high phytane/pristine ratios.There are also some differences between saline lacustrine oils and freshwater lacustrine oils in the concentrations of steranes,tricyclic terpanes and organic sulphur compounds,as well as in the values of methylphenanthrene indices and C,H,S stable isotopes.3)Oils derived from fresh-brackish water lake facies differ from oils from fresh-water lacustrine or samline lacustrine environments in respect of some biomarkers.According to the various distributions of these biomarkers,a number of geochemical parameters can be applied synthetically to differentiating and identifying the nature of original depositional environments of crude oils and source rocks and that of organisms-primary source materials present in those environments.

The Influence of CO on the Carbon Isotopic Composition of CH_4 in Closed Pyrolysis Experiment With Coal

A low-mature coal (R o=0.4%, from the Manjia’er depression, Tarim Basin, China) was subjected to closed system pyrolysis, in sealed gold tubes, under isothermal temperature conditions. The carbon isotopic compositions of the pyrolyst fractions (hydrocarbon, CO 2, CO, etc.) at two temperature points (350°C and 550°C) were measured. The results showed that δ 13C CH 4 value is generally heavier at 350°C than that at 550°C, because the high abundance of CO generated at low temperature would greatly influence δ 13C CH 4 value, and the retention time of CO in gas chromatograph is close to that of CH 4. But CO is formed through chemical reaction of the oxygen-containing functional group -C=O, e.g. lactones, ketones, ether, etc. at low temperature, while CO 2 comes mainly from decarboxylization. The carbon isotopic composition of coal gas from Lanzhou Coal Gas Works was definitely different from that of thermally pyrolysed products from coal. The δ 13C CH 4 value of coal gas was abnormally heavier than δ 13C CO. At the same time, the reversed sequence ( δ 13C 1> δ 13C 2) of δ 13C 1 and δ 13C 2 happened. The bond energy of free ions generally decides the sequence of generation of hydrocarbon fractions according to the chemical structure, whereas the stability of pyrolysate fractions and their carbon isotope fractionation are affected by the C-C bond energy.

Unusual N-Alkane Distributions in Extracts from Marine Carbonate Rocks at High Levels of Maturity and Overmaturity

N\|alkanes in extracts from possible carbonate source rocks of the Lower Ordovician Majiagou Formation in the central gas field of the Shanganning Basin and the Upper Sinian Dengying Formation in the Weiyuan gas field of the Sichuan Basin, are characterized by bimodal distributions with the dominant carbon numbers in the range C\- 17 \|C\- 21 and C\- 25 \|C\- 29 . In most samples, the lower carbon number components are present in greater abundance than the higher carbon number ones. Most samples contain significant concentrations of waxy hydrocarbons(C\- 22+ ) with C\- 21- /C\- 22+ ratios between 0.50 to 3.16, and an average value of 1.34. The n\|alkanes in extracts of outcrops and shallow core samples of Upper Proterozoic and Lower Palaeozoic carbonate rocks in the western and southern parts of the North China Basin are of unimodal distributions dominated by n\|alkanes maximizing in the C\- 25 \|C\- 29 range. These extracts have very high concentrations of waxy hydrocarbons with C\- 21- /C\- 22+ ratios all <1.0, ranging from 0 14 to 0 90 and averaging 0.36. All of the extracts have a marked odd/even predominance in the high molecular weight n\|alkane range regardless of whether they are from shallow or deep cores or outcrop samples. Simulation experiments were performed using typical sapropelic\|type kerogens from the immature Sinian Lower Xiamalin Formation carbonate\|rich shales collected at Jixian, Hebei Province, North China Basin, and the contemporary microplanktonic blue\|green algae Spirulina subsala. Results indicate that the unusual distribution of n\|alkanes in the extracts of Upper Proterozoic and Lower Palaeozoic carbonate rocks possibly originated from algae in the source rocks at high levels of maturity and overmaturity.

Helium and Oxygen isotopic evidence on exchange of waters betweenthe western Pacific Ocean and the South China Sea

The composition and distribution of helium and oxygen isotopes in samples of seawater ob-tained at depths from surface to 300 m in the western Pacific Ocean (7°-26°N, 122° - 130°E) were discussed in detail. The results shaw that both δ18O and δ3He isoline extend eastward in the Pacific side of the Bashi Channel, which may suggest that the South China Sea water intrudes into the western Pacific by the Bashi Channel.

Nitrogen Contents and Isotopic Characteristics of Mesozoic and Cenozoic Granites in Northeastern China

The method of determining the nitrogen isotopic composition of granites in the northeastern part of China is described. The content and isotopic values of nitrogen released from granite samples by stepwise heating were determined as well. The results showed that the different areas of northeastern China have a great difference in nitrogen content and isotopic composition. Nitrogen released from the granites is 1.64-6.23μL/g, with the maximum at about 600℃; from rhyolite and granophyre is 108.98-755.96μL/g, with the maximum at about 900℃. It is proved that fluid is characterized by heterogeneity in the deep crust of the different areas in northeastern China. The nitrogen isotopic compositions in different ranges of temperatures are weighted. And the nitrogen isotopic values are +9.2‰ to +17.0‰, with a variation range of 7.8‰. The nitrogen isotopic ratios may have been fractionated during degassing and the fluid released from granites is the residual component.

~3He/~4He Ratios and Heat Flow in the Continental Rift-valley, Eastern China

Heat flow and the origin of helium in natural gases from fault basins of the continental rift-valley in eastern China are discussed in terms of heiium isotope geochemistry .^3He/^4He ratios in natural gases from the rift-valley range from 2.23×10^-7 to 7.21×10^-6,which are directly propor-tional to the concentration of helium and ΣNHC/ΣHC ration in natural tases.Geological and isotope geochemical data suggest that helium in natural gases consists predominantly of crustal radio-genic and upper mantle-derived helium.In a simple mixing pattern between crustal He and man-tle-derived He,mantle-derived helium in natural gases would account for 10-60%.Calculated values for heat flow (Q) range from 59.4 to 82.4mWm^-2,of which about 60 percent in the rift-valley is derived from the upper nantle.Natural helium reservoirs would be found in the areas where the up-per mantle uplifted greatly and heat flow is large in the continental rift-valley.

Thermogravimetry-differential thermal analysis coupled with chromatography as a thermal simulation experimental method and its application to gaseous hydrocarbons from different source rocks

In this paper a thermogravimetry-differential thermal analysis method coupled with chromatography (TG-DTA-GC) has been adopted to simulate the generation of gaseous hydrocarbons from different hydrocarbon source rocks such as coals, mudstones, and carbonate rocks with different maturities. The temperature programming for thermal simulation experiment is 20℃/min from ambient temperature to 700℃. As viewed from the quantities and composition of generated gaseous hydrocarbons at different temperatures, it is shown that low-mature coal has experienced the strongest exothermic reaction and the highest loss of weight in which the first exothermic peak is relatively low. Low-mature coal samples have stronger capability of generating gaseous hydrocarbons than high-mature samples. The amounts and composition of gaseous hydrocarbons generated are closely related not only to the abundance of organic carbon in source rocks, but also to the type of kerogen in the source rocks, and their thermal maturity. In the present highly mature and over-mature rock samples organic carbon, probably, has already been exhausted, so the production of gaseous hydrocarbons in large amounts is impossible. The contents of heavy components in gaseous hydrocarbons from the source rocks containing type-Ⅰand -Ⅱ kerogens are generally high; those of light components such as methane and ethane in gaseous hydrocarbons from the source rocks with Ⅲ-type kerogens are high as well. In the course of thermal simulation of carbonate rock samples, large amounts of gaseous hydrocarbons were produced in a high temperature range.

Ordovician Seawater Composition:Evidence from Fluid Inclusions in Halite

Fluid inclusions in halite can directly record the major composition of seawater,however Ordovician halite is very rare.Ordovician is a key time during the evolution history.However there are no Ordovician seawater data reported except from the data from the halite from the

Comprehensive geochemical identification of highly evolved marine carbonate rocks as hydrocarbon-source rocks as exemplified by the Ordos Basin

This study reversed the developing environments of hydrocarbon-source rocksin the Ordos Basin and evaluated carbonate rocks as hydrocarbon-source rocks and their distributionson account of the fact that China''s marine carbonate rocks as hydrocarbon-source rocks arecharacterized by intensive thermal evolution and relatively low abundance of organic matter, bytaking the Lower Paleozoic of the Ordos Basin for example and in light of the calculated enrichmentcoefficients of trace elements, the REE distribution patterns, the mathematical statistics analysisof elements and carbon isotopes and their three-dimensional diagrammatization in combination withthe necessary organic parameters. As for the Ordos Basin, TOC=0.2% is an important boundary value.Studies have shown that in the strata where TOC is greater than 0.2%, Ba is highly enriched withpositive δ^(13)C_(carb) shifts and δ^(13)C_(org) less than -28per thousand, reflecting a thighpaleo-productivity, high burial amounts of organic matter, relatively good hydrocarbon-generatingpotentiality and intensive REE fractionation. All these indicated that the settlement rates are lowand the geological conditions are good for the preservation of organic matter, hence favoring thedevelopment of hydrocarbon-source rocks. The Klimory and Wulalik formations show certainregularities in those aspects and, therefore, they can be regarded as the potential effectivehydrocarbon-source rocks. In the strata where total TOC is less than 0.2%, the contents of Ba arelow, δ^(13)C_(carb) values are mostly negative, and δ^(13)C_(org) values range from -24perthousand—-28per thousand, demonstrating low burial amounts of organic matter, poor potentialitiesof hydrocarbon generation, weak REE fractionation and rapid settlement rates. These facts showedthat most of the hydrocarbon-source rocks were formed in shallow-water, high-energy oxidizingenvironments, thus un-favoring the development of hydrocarbon-source rocks. It is feasible to makeuse of the geochemical method to comprehensively assess the highly evolved marine carbonates rocksas potential hydrocarbon-source rocks and their distributions.

Tectonic and geochemical characteristics and reserved conditions of a mantle source gas accumulation zone in eastern China

Along both sides of the Tancheng-Lujiang Fracture Zone in eastern China, a series of mantle source gas pools constitute a massive-scale tectonic accumulation zone in NNE direction, with the mantle geochemical characteristics of high concentrations of CO2 and He, high 3He/4He-40Ar/36Ar ratio system and high δ13Coo2 ratios (the mainfrequency, -3.4‰-4.6‰), showing no difference from the tectonic framework of the area. In the area, thetectonic environment is a rift formed as a result of diapiric mantle injection and crust thinning to form graben-type basins and lithospheric fractures. The mantle-derived volcanic rocks and inclusions are well-developed and a high geothermal zone (mantlesource) exists in the area. The characteristics of the three components (solid, liquid and gas) of mantle, concentrated all over the same tectonic space zone, show that the rift system is of a good tectonic environment or passage for mantle degassing and gas migration. The main types of the gas pools are volcano, fault-block, anticline, buried hill and so on, but most of them are combination traps closely related with fracture. For the mantle source gas pools, rift is an optimum tectonic region, and nearby lithospheric fracture, mantle source volcanic rocks or basement uplifts are a favourable structural location when reservoir-caprock association develops.

Reservoir-forming features of abiotic origin gas in Songliao Basin

The vertical structure of the crustal block of the Songliao Basin can be divided into upper, middle and low Earth's crust according to density. There is an about 3-km-thick low density interval between the upper crust and the middle crust. This interval may be a magma chamber accumulated in crust by 'fluid phase' which is precipitated and separated from upper mantle meltmass. The abiogenetic natural gas, other gaseous mass and hydrothermal fluids are provided to the Songliao rifted basin through crustal faults and natural earthquakes. This is a basic condition to form an abiogenetic gas reservoir in the Songliao Basin. On both flanks of the upper crust (or named basin basement) fault there are structural traps in and above the basement and unconformity surface or lateral extended sand, which contains communicated pores, as migration pathway and natural gas reservoir; up to gas reservoirs there is shale as enclosed cap rock, and the suitable arrangement of these conditions is the basic features of abiogenetic gas reservoir.

Characteristics of mantle degassing and deep-seated geological structures in different typical fault zones of China

In this paper a comprehensive tracing study is conducted on mantle degassing and deep-seated geological structures in different types of fault zones in the continent of China based on the helium isotope data, coupled with some indices such as CO2/3He, CH4/3He and 40Ar/36Ar, and geological tectonics data. There are four representative types of fault zones: (1) Lithospheric fault zones in the extensional tectonic environment are characterized by a small Earth’s crust thickness, a lower CH4/3He-high R and lower CO2/3He-high R system, the strongest mantle de- gassing, and the dominance of mantle fluid, as is represented by the Tancheng-Lujiang fault zone. (2) The lithospheric fault zones or the subduction zone in the strongly compresso-tectonic envi- ronment, for instance, the Bangonghu-Nujiang fault zone, are characterized by a huge thick Earth’s crust, with the R/Ra values within the range of 0.43―1.13, and weak mantle degassing with mantle-source helium accounting for 5%―14% of the total. (3) The deep-seated fault zones at the basinal margins of an orogenic belt are characterized by R values being on order of mag- nitude of 10?7, and the CH4/3He values, 109―1010, CO2/3He values, 106―108; as well as much weak mantle degassing. (4) The crustal fault zones in the orogenic belt, such as the Yaojie fault zone (F19), possess a high CH4/3He-low R (10?8) and high CO2/3He-low R system, with no obvi- ous sign of mantle degassing. Studies have shown that the deep-seated huge fault zones are the major channel ways for mantle degassing, the main factors controlling the intensity of mantle degassing are fault depth, tectonic environment and crust thickness; the intensity of mantle de- gassing can reflect the depth and the status of deep-seated tectonic environment of fault, while the geochemical tracing studies of gases can open up a new research approach; upwelling ac- tivity of hydrothermal fluids from the deep interior of the Earth may be one of the driving forces for the formation and evolution of the huge deep fault zones. Piedmont fault zones are the locations where deep-seated tectonic activity and crust/mantle structure are transformed, which are of great significance in understanding the mechanisms of formation of orogenic belts and basins.