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Luo M.,CAS Guangzhou Institute of Geochemistry | Luo M.,University of Chinese Academy of Sciences | Huang H.,CAS Guangzhou Institute of Geochemistry | Huang H.,Guangdong Geologic Survey Institute | And 4 more authors.
Journal of Geochemical Exploration | Year: 2014

Gas compositions, helium isotopic ratios, and carbon isotopic compositions of CO2 and CH4 from six gas emission sites in the Qiangtang Basin and its adjacent areas were measured in order to unravel their origins. Gas samples from the Beiluhe, the Bucha Lake, and the eastern Tuotuo River are N2-rich with N2 over 75vol.%, while the contents of CO2 and CH4 are only 3.45-20.91vol.% and 0-3.58vol.%, respectively. Relatively high CO2/3He (~9.95×1011) and CH4/3He (5.9×109-1.65×1010), and low δ13C values of CO2 (~-15.4‰) and CH4 (~-29.7‰) suggest that both CO2 and CH4 from the Bucha Lake are biotic. The S-M-L (S, M, and L represent sedimentary organic carbon, mantle, and limestone, respectively.) three-component mixing model suggests that no mantle-derived CO2 exists in these samples, which is consistent with the result that He in these gas samples is all crust-derived. CO2 in gas samples from the Beiluhe and the eastern Tuotuo River are relatively enriched in 13C of CO2 (δ13C: -8.4‰ and -5.5‰) and low CO2/3He (2.3×109 and 2.4×109) as well as CH4/3He (5.9×107 and 3.4×107) ratios. These patterns suggest that both CO2 and CH4 are abiotic, demonstrated by the S-M-L three-component mixing model displaying that more than 50% CO2 in these two sites are mantle-derived. CO2-rich gases are discovered in the southern Erdaogou Depot, the branch of Tuotuo River, and the Tanggula Mountain Depot with CO2 exceeding 96vol.%. The relatively high δ13C of CO2 (-4.2 to -7.7‰), low CO2/3He ratios (7.9×108-9.3×109), as well as the S-M-L three-component mixing model reveal that CO2 at least partially originates from the mantle source. Only one gas sample from the Tanggula Mountain Depot contains a trace amount of abiotic CH4 (CH4/3He=1.2×107) generated by abiotic reduction of mantle-derived CO2. However, the source of He is dominantly crust-derived with only 2.15-5.66% mantle-derived He. The emission of large quantity of mantle-derived CO2 is likely due to the presence of the Hoh Xil-Jinsha River suture and the Cenozoic volcanism in northern Tibet. Nevertheless, the small fraction of mantle-derived He may result from the limited degree of openness at the bottom of fault zones and possibly reflect a geological setting of strong extrusion and crustal thickening. © 2014 Elsevier B.V. Source


Huang H.-G.,Guangdong Geologic Survey Institute | Huang H.-G.,CAS Guangzhou Institute of Geochemistry | Luo M.,CAS Guangzhou Institute of Geochemistry | Zhang P.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | And 2 more authors.
Natural Gas Geoscience | Year: 2014

CO2 and CH4 play a significant role in the global climate change and carbon circulation and can be used to monitor their origin and tectonic activity. In this paper, we carried out investigations on the gas compositions, carbon isotope ratios of CO2 and CH4, and He isotope compositions from the Qiangtang Basin and its adjacent areas. Our results show gas samples from Beiluhe, Bucha Lake, and eastern Tuotuo River are N2-rich with N2 over 75%. The contents of CO2 and CH4 are only 3.45%-20.91% and 0-3.58%, respectively. CO2/3He and CH4/3He and carbon isotopic values of CO2 and CH4 suggest that both CO2 and CH4 from Bucha Lake are biotic without mantle-derived CO2 and He, whereas those of Beiluhe and eastern Tuotuo River are abiotic. Southern Erdaogou Depot, branch of Tuotuo River, and Tanggula Mountain Depot are enriched in CO2 with more than 96%. The CO2 was at least partially originated from mantle, trace amount of CH4 was abiotic and derived from mantle-derived CO2; He was primarily originated from crust with only 2.15%-5.66% of mantle-derived origin. These results show that the emitting of large quantity of mantle-derived CO2 is likely to be ascribed to the presence of Bangong Lake-Nujiang River, Hoh Xil-Jinsha River sutures and the Cenozoic volcanism in northern Tibet. Nevertheless, the estimated small fraction of mantle-derived He may result from the low opening degree at the bottom of fault zones and possibly reflect a geological setting of strong extrusion and an increase in crustal thickness. Source


Huang H.,Guangdong Geologic Survey Institute | Huang H.,CAS Guangzhou Institute of Geochemistry | Li N.,CAS Guangzhou Institute of Geochemistry | Wang Q.,CAS Guangzhou Institute of Geochemistry | Chen D.,CAS Guangzhou Institute of Geochemistry
Geotectonica et Metallogenia | Year: 2015

Fluid sources and geochemical processes involved in terrestrial mud volcanoes are of great significance for understanding the chemical processes of methane emission to the atmosphere. Mud sediments ejected from the Dushanzi mud volcano, which is located along the southern margin of the Junggar Basin, northwestern China, were collected by hand core sampling. The ionic compositions of the pore fluids, minerals and major elements of the ejected sediments and surface sediments were analyzed. The results showed that significant correlation between Cl- and Na+ in pore fluids. Relative to seawater, the mud volcano fluids have higher ratios of K+/Cl- and Mg2+/Cl- and lower ratios of Na+/Cl- and Li+/Cl-. The mud sediments are enriched in illite, chlorite and calcite but depleted in smectite relative to the host rocks of the mud volcano. The changes in the mud and pore fluids are mainly related to clay mineral dehydration. The fluids were mainly derived from ancient sedimentary low salinity pore fluids, but modified by the surface evaporation and meteoric surface water. ©, 2015, Science Press. All right reserved. Source


Li N.,CAS Guangzhou Institute of Geochemistry | Li N.,University of Chinese Academy of Sciences | Huang H.,CAS Guangzhou Institute of Geochemistry | Huang H.,Guangdong Geologic Survey Institute | Chen D.,CAS Guangzhou Institute of Geochemistry
Applied Geochemistry | Year: 2014

Understanding fluid sources, water-rock interactions and the biogeochemical processes involved in terrestrial mud volcanoes is necessary in order to predict the chemical processes most responsible for methane emissions to the atmosphere. Mud sediments ejected from the Dushanzi and Sikeshu mud volcanoes, located along the southern margin of the Junggar Basin, northwestern China, were collected by hand core sampling in order to explore whether surface and subsurface geochemical processes occur in their fluids. The ionic compositions of the pore fluids, minerals and major elements of the ejected sediments and surface sediments were analyzed. The pore fluids were mainly derived from ancient deeper sedimentary fluids which had mixed with meteoric surface water, but altered by diagenesis processes. Relative to seawater, the mud volcano pore fluids have higher ratios of Na/Cl and Li/Cl and lower ratios of K/Cl and Mg/Cl. The mud sediments are also enriched in illite, chlorite and calcite, but depleted in smectite. In addition, they are enriched in Ca and Mn, followed by Fe, Mg and P, and depleted in Si relative to the wall rocks. These chemical and mineralogical changes in the mud sediments and pore fluids are related to diagenesis processes. Clay mineral dehydration (mainly involving the conversion of smectite to illite) released large amounts of water. Ion exchange among clay minerals increased Na+ in the pore fluid. Water-rock interaction increased Fe and Mn, but decreased Si in the mud sediments. Carbonate precipitation decreased Ca2+ and Mg2+ concentrations of the pore fluid but increased Fe, Mg and P in the mud sediments. These results indicate that the mud volcanoes system is continuously recharged from deeper sedimentary sources. The difference in fluid and sediment geochemistry of the mud volcanoes can be ascribed to the different depths of the fluid and mud sources and the different diagenesis processes during the rising of fluid and mud. © 2014 Elsevier Ltd. Source


Wu G.,China University of Geosciences | Wu G.,Guangdong Geologic Survey Institute | Wang D.,Chinese Academy of Geological Sciences | Hu Y.,Guangdong Geologic Survey Institute | Wang C.,Chinese Academy of Geological Sciences
Geotectonica et Metallogenia | Year: 2014

There are many quartz vein-type tungsten polymetallic ore deposits in northern Guangdong which can be divided into two types according to their wall rocks. One type of the ore deposits is hosted in the Cambrian sandstones and coarse-grained granite while the tungsten polymetallic mineralization is closely related to the fine-grained granite, which is represented by the Miantuwo tungsten deposit. The age of fine-grain granite is dated to be 146.95±0.84 Ma/153.82±0.96 Ma, using zircon U-Pb method, while the molybdenite Re-Os isochrone and biotite Ar-Ar isochrone are 150.5±1.4 Ma and 151.0±1.2 Ma respectively, and thus the Miantuwo deposit was formed in the Late Jurassic. The other type of the ore deposits is hosted in the Devonian limestones with the Heshangtian tungsten deposit as a representative. The after type of ore deposits is different from the one aforementioned. 39Ar/40Ar dating of the micas from the Heshantian deposit shows that the mineralization age is 161.1±1.1 Ma, i.e., the deposit was also formed in the Late Jurassic. That is the quartz vein tungsten ore deposits in northern Guangdong are closely related to the Late Jurassic granites. Indosinian granites and the Devonian limestones can be the country rocks of the ore veins in northern Guangdong, and therefore, attentions should be paid to above two types of country rocks in the future explorations. Source

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