Episodic widespread magma underplating beneath the North China Craton in the Phanerozoic: Implications for craton destruction

A comprehensive synthesis of U–Pb geochronology and Hf isotopes of zircons from granulite/pyroxenite xenoliths entrained in Phanerozoic magmatic rocks and inherited xenocrysts from the associated lower crust rocks from various domains of the North China Craton (NCC) provides new insights into understanding the Phanerozoic evolution of the lower crust in this craton. Episodic widespread magma underplating into the ancient lower crust during Phanerozoic has been identified throughout the NCC from early Paleozoic to Cenozoic, broadly corresponding to the Caledonian, Hercynian, Indosinian, Yanshanian, and Himalayan orogenies on the circum-craton mobile belts. The early Paleozoic (410–490 Ma) ages come from xenoliths in the northern and southern margins as well as the central domain of the Eastern Block of the craton which mark the first phase of Phanerozoic magma underplating since the final cratonization of the NCC in the Paleoproterozoic. The magmatism coincided with the northward subduction of the Paleotethysian Ocean in the south and the southward subduction of the Paleoasian Ocean in the north. The subduction not only triggered magma underplating but also led to the emplacement of the diamondiferous kimberlites on the craton, marking the initiation of decratonization. The late Paleozoic event as represented by the 315 Ma garnet pyroxenite and/or lherzolite xenoliths in Hannuoba was restricted to the northern and southern margins of the craton, correlating with the arc magmatism continuous associated with the subduction of the Paleotethysian and Paleoasian Oceans and resulting in the interaction between the melts from subducted slabs and the lithospheric mantle/lower crust. The early Mesozoic event also dominantly occurred in the northern and southern margins and was related with the final closure of the Paleotethysian and Paleoasian Oceans as well as the collisional orogeny between the NCC and the Yangtze Craton. The late Mesozoic (ca. 120 Ma) was a major and widespread magmatic event which manifested throughout the NCC, associated with the geothermal overturn due to the giant south Pacific mantle plume. The Cenozoic magmatism, identified only in the dark clinopyroxenite xenoliths in the Hannuoba, was probably induced by the Himalayan movement in eastern Asia and might also have been influenced by the subduction of the Pacific Ocean to some extent. These widespread and episodic magma underplating or rejuvenation of the ancient lower crust beneath the NCC revealed by U–Pb and Hf isotope data resulted from the corresponding addition of juvenile materials from mantle to lower crust, with a mixing of the old crust with melts. The process inevitably resulted in the compositional modification of the ancient lower crust, similar to the compositional transformation from the refractory lithospheric mantle to a fertile one through the refractory peridotite — infiltrated melt reaction as revealed in the lithospheric mantle beneath the craton.     

Correlation between land-use change and greenhouse gas emissions in urban areas

Urban areas are the main sources of greenhouse gas (GHG) emissions. Previous studies have identified the effectiveness of better urban design on mitigating climate change and land-use patterns in cities as important factors in reducing GHG by local governments. However, studies documenting the link between land-use and GHG emissions are scant. Therefore, this study explores the driving forces of land-use change and GHG emission increments in urban areas and investigates their correlations. The study area, Xinzhuang, is a satellite city of Taipei that has rapidly urbanized in the past few decades. Twenty-one potential variables were selected to determine the driving forces of land-use change and GHG emission increments by binomial logistic regression based on the investigation data of national land use in 1996 and 2007. The correlation of land-use change and GHG increments was examined by Spearman rank-order analysis. Results of logistic regression analysis identified that population and its increasing density rate are main driving forces on both land-use change and GHG increments. The Spearman rank correlation matrix indicates that fluctuating urbanization level is significantly correlated with the increase of total GHG emissions, the emissions of residence, commerce, and transportation sectors in neighborhoods; and the emissions of residence and transportation sectors seem closely connected to current urbanization level. The findings suggest that relationships among land-use, urbanization, and GHG emissions in urban areas vary greatly according to residence and transportation characteristics. Land-based mitigation may provide the most viable mechanism for reducing GHG emissions through residence and transportation sectors.     

MTA固井技术在煤层气井中应用的实验研究

MTA固井技术在油气田中的运用已经取得了显著效果,能够提高二界面的抗剪切强度以及抵抗地层水对二界面的冲蚀。通过室内实验,对MTA固井技术在煤层气井中的运用进行探索。实验结果表明,MTA技术在煤层气井的固井模拟实验中,也能够有效的提高二界面的抗剪切强度,实现二界面的整体固化胶结,抵抗地层水对煤层气二界面的冲蚀,这些特点对于提高煤层气井的产能具有重要意义。作为一种施工简捷、效果显著的固井技术,MTA固井方法在煤层气井中的应用前景是极为广阔的。     

Hydrogeochemical and isotopic evidences of the groundwater regime in Datong Basin, Northern China

Datong Basin is one of the Cenozoic faulted basins in Northern China’s Shanxi province, where groundwater is the major source of water supply. The results of hydrochemical investigation show that along the groundwater flow path, from the margins to the lower-lying central parts of the basin, groundwater generally shows increases in concentrations of TDS, HCO₃ ^?, SO₄ ^2?, Cl^?, Na⁺ and Mg²⁺ (except for Ca²⁺ content). Along the basin margin, groundwater is dominantly of Ca–HCO₃ type; however, in the central parts of the basin it becomes more saline with Na–HCO₃-dominant or mixed-ion type. The medium-deep groundwater has chemical compositions similar to those of shallow groundwater, except for the local area affected by human activity. From the mountain front to the basin area, shallow groundwater concentrations of major ions increase and are commonly higher than those in medium-deep aquifers, due to intense evapotranspiration and anthropogenic contamination. Hydrolysis of aluminosilicate and silicate minerals, cation exchange and evaporation are prevailing geochemical processes occurring in the aquifers at Datong Basin. The isotopic compositions indicate that meteoric water is the main source of groundwater recharge. Evaporation is the major way of discharge of shallow groundwater. The groundwater in medium-deep aquifers may be related to regional recharges of rainwater by infiltrating along the mountain front faults, and of groundwater permeating laterally from bedrocks of the mountain range. However, in areas of groundwater depression cones, groundwater in the deep confined aquifers may be recharged by groundwater from the upper unconfined aquifer through aquitards.     

Evaluation of petroleum hydrocarbon biodegradation in shallow groundwater by hydrogeochemical indicators and C, S-isotopes

Biodegradation is one of the main natural attenuation processes in groundwater contaminated with petroleum hydrocarbons. In this work, preliminary studies have been carried out by analyzing the concentrations of total petroleum hydrocarbons (TPH), dissolved inorganic carbon (DIC), dominant terminal electron accepters or donors, as well as δ ¹³C_DIC and δ ³⁴S_SO4, to reveal the biodegradation mechanism of petroleum hydrocarbons in a contaminated site. The results show that along groundwater flow in the central line of the plume, the concentrations of electron acceptors, pH, and E _h increased but TPH and DIC decreased. The δ ¹³C_DIC values of the contaminated groundwater were in the range of ?14.02 to ?22.28 ‰_PDB and ?7.71 to 8.36 ‰_PDB, which reflected a significant depletion and enrichment of ¹³C, respectively. The increase of DIC is believed to result from the non-methanogenic and methanogenic biodegradation of petroleum hydrocarbon in groundwater. Meanwhile, from the contaminated source to the downgradient of the plume, the ³⁴S in the contaminated groundwater became more depleted. The Rayleigh model calculation confirmed the occurrence of bacterial sulfate reduction as a biodegradation pathway of the petroleum hydrocarbon in the contaminated aquifers. It was concluded that stable isotope measurements, combined with other biogeochemical measurements, can be a useful tool to prove the occurrence of the biodegradation process and to identify the dominant terminal electron-accepting process in contaminated aquifers.     

Geological features and hydrocarbon accumulation in the Xinken oil field, Tarim Basin

Recently,a large-scale Ordovician oil and gas pool has been discovered in Xinken,north of the Tarim Basin,and it has strongly heterogeneous reservoirs and complicated fluid distribution.Through analyzing oil,gas and water samples collected from this area,in combination of field production and testing data,this study reveals that the Xinken oil pool contains dominantly normal oil characterized by low viscosity,low sulphur,and high wax.It has a low content of natural gas,which presents typical characteristics of wet gas and is oil-associated gas.Oil-gas correlation shows that the oil was from the Middle-Upper Ordovician source rocks and the charge and accumulation of oil and gas took place in the Late Hercynian Period.Controlled by paleogeomorphology,sedimentary facies,ancient karstification,faults,and other factors in the Caledonian Period,the Ordovician carbonate reservoirs are dominated by dissolved pores,cavities and fractures.The reservoir body of fractures and cavities is distributed in the shape of strip and laminate along faults and excellent reservoirs are mostly in the range of 70–100 m below the top of the Yijianfang Formation.As a whole,the Xinken oil pool is a fracture-cavity pool controlled by interbedded karst reservoirs and is a complex composed of stacked karst fractures and cavities of various sizes.It contains oil in large areas horizontally,which is quasi-laminated in distribution,and the accumulation of oil and gas is controlled by the distribution and development degree of the Ordovician carbonate reservoirs.The study shows that this area has abundant resources and a great exploration potential for oil and gas.     

The Variability of the Narrow-line Seyfert 1 Galaxies from the Pan-STARRS's View

By means of the data sets from the Pan-STARRS1 survey,we have systematically examined the relationship between the variability characteristics and the physical ...