Taking Beijing plain groundwater system as the research object,this paper collected the concerned geological and hydrogeological data.By analyzing the data,a reasonable generalization was made on the boundary conditions and aquifer structure,and a conceptual model of hydrogeology was established.On this basis,MODFLOW was used to establish a groundwater flow numerical model for Beijing plain area.In order to describe the complex aquifer structure and three-dimensional groundwater flow characteristics,the vertical section of the model was divided into 10 layers,and every layer surface was divided into 499 ×499 irregular rectangular grid,with effective 1 103 000 units in total.According to the model parameter identification and correction based on the observed data,the most calculated and observed groundwater levels have better fitting,the simulated flow field and measured flow field coincide the parameters conform with the hydrological and geological conditions,which shows this study to establish the numerical model can characterize the Beijing plain groundwater flow characteristics.
Abstract The genesis and timing of formation of the giant Bayan Obo deposit, the world's largest rare earth element (REE) deposit in the western part of the late Paleozoic northern North China continental arc (NCA), are highly controversial due to complex mineral assemblages and reported ages of mineralization. We conducted new zircon U‐Pb and 40 Ar/ 39 Ar dating of metamorphic and igneous Neoarchean to Permian mid‐to upper‐crustal rocks exhumed along a north−south corridor across the western NCA and its retroarc foreland. The results show that the mid‐ to upper‐crust of the western part of the NCA has been strongly affected by thermal modifications during arc construction in the late Paleozoic, while the retroarc foreland remained thermally stable. Our results first reveal an unusually warm upper‐crust around Bayan Obo during the late Paleozoic with high geothermal gradients of 50.0 ± 8.3 to 88.3 ± 8.3°C/km and strong thermal modification of the upper‐crust during arc construction. This unusually warm upper‐crust and high geothermal gradients resulted in intensive thermal perturbations and recrystallization of REE‐bearing minerals in the Bayan Obo deposit, as well as formation of high‐grade REE ores and complete or partial resetting (U‐)Th‐Pb isotopic systems of REE minerals. Our identification of the unusually warm upper‐crust and high geothermal gradients in the western part of the NCA provides important constraints on genesis, timing and thermal modification of the giant Bayan Obo deposit, as well as other REE deposits with complex isotopic ages.
Jurassic coal-bearing strata are widely distributed in the North China Craton (NCC) and other areas of northern China. These coal-bearing strata were previously considered to be Early–Middle Jurassic in age based on plant fossils, particularly the fossil assemblage of Coniopteris–Phoenicopsis. Since coal-bearing strata are interbedded with volcanic units in the basins of the Yanshan Fold-and-Thrust Belt (YFTB), northern NCC, isotopic dating of the volcanic units can therefore provide age constraints on the coal-bearing strata and the Coniopteris‒Phoenicopsis assemblage. In this paper, we performed a systematic geological survey and present the results of zircon U–Pb dating of the volcanic units and a pluton in typical basins of the YFTB. These data, combined with the results of previous studies, indicate that the ages of the Nandaling/Xinglonggou, Haifanggou, Jiulongshan, and Tiaojishan/Lanqi formations are 180–168, 169–161, 161–157, and 161–153 Ma, respectively. The ages of the interbedded coal-bearing Yaopo and Beipiao formations are constrained to be 169–161 and 177–169 Ma, respectively. Our results demonstrate that both the coal-bearing strata and the Coniopteris‒Phoenicopsis assemblage are Middle Jurassic in age, which is younger than that previously considered. This fossil assemblage plays a critical role in age constraints on the Jurassic coal-bearing strata. The refinement of its age permits a more precise dating of the coal-bearing strata, especially in northwestern China, where datable interbedded volcanic units are lacking. Stratigraphical framework for the Jurassic strata of Yanshan region is established.The fossil assemblage of Coniopteris‒Phoenicopsis occurred in Middle Jurassic.The Jurassic coal-bearing strata in northern China are mainly Middle Jurassic.
Abstract Records of the Lomagundi–Jatuli Event (LJE) are well preserved globally, but high δ 13 C carb carbonates have not been identified in the North China Craton (NCC). Our results on ~ 3–4 km thick carbonates from the newly confirmed Palaeoproterozoic successions in Fanhe Basin in the northeastern NCC show that the ~2.20–2.06 Ga carbonates have positive carbon isotope excursion and those deposited after 2.06 Ga have normal carbon isotope. Specially, carbonates from the Daposhan Formation have δ 13 C carb values of 10.2‰–11.8‰, which is the largest positive carbon isotope excursion in the NCC. The ~2.20–2.06 Ga carbonates in Fanhe Basin have similar δ 13 C carb values as those contemporaneously deposited in other cratons and their δ 13 C carb values exhibit a decreasing trend from ~2.20 Ga to 2.06 Ga. Our identification of carbonates with high positive δ 13 C carb values in Fanhe Basin not only casts new lights on records of the LJE in the NCC, but also provides important constraints on global significance of the positive δ 13 C carb excursion of LJE.
Research Article| January 01, 2009 Contrasting Late Carboniferous and Late Permian–Middle Triassic intrusive suites from the northern margin of the North China craton: Geochronology, petrogenesis, and tectonic implications Shuan-Hong Zhang; Shuan-Hong Zhang † 1Key Laboratory of Crustal Deformation and Processes, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China, and Beijing SHRIMP Center, Chinese Academy of Geological Sciences, Beijing 100037, China †E-mail: tozhangshuanhong@163.com. Search for other works by this author on: GSW Google Scholar Yue Zhao; Yue Zhao 2Key Laboratory of Crustal Deformation and Processes, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Biao Song; Biao Song 3Beijing SHRIMP Center, Chinese Academy of Geological Sciences, Beijing 100037, China Search for other works by this author on: GSW Google Scholar Jian-Min Hu; Jian-Min Hu 4Key Laboratory of Crustal Deformation and Processes, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Shu-Wen Liu; Shu-Wen Liu 5Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China Search for other works by this author on: GSW Google Scholar Yue-Heng Yang; Yue-Heng Yang 6State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Fu-Kun Chen; Fu-Kun Chen 6State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Xiao-Ming Liu; Xiao-Ming Liu 7State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China Search for other works by this author on: GSW Google Scholar Jian Liu Jian Liu 8Key Laboratory of Crustal Deformation and Processes, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (1-2): 181–200. https://doi.org/10.1130/B26157.1 Article history received: 24 Nov 2006 rev-recd: 12 Oct 2007 accepted: 13 Nov 2007 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Shuan-Hong Zhang, Yue Zhao, Biao Song, Jian-Min Hu, Shu-Wen Liu, Yue-Heng Yang, Fu-Kun Chen, Xiao-Ming Liu, Jian Liu; Contrasting Late Carboniferous and Late Permian–Middle Triassic intrusive suites from the northern margin of the North China craton: Geochronology, petrogenesis, and tectonic implications. GSA Bulletin 2009;; 121 (1-2): 181–200. doi: https://doi.org/10.1130/B26157.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Two contrasting intrusive suites have been identified from the northern margin of the North China craton: a Late Carboniferous dioritegranodiorite suite mainly made up of quartz diorite, diorite, granodiorite, tonalite, and hornblende gabbro, and a Late Permian–Middle Triassic suite of granitoid intrusions consisting of monzogranite, syenogranite, and quartz monzonite. Plutons from the Late Carboniferous suite exhibit variable SiO2 contents and calc-alkaline or high-K calc-alkaline, metaluminous geochemical features. Most have low negative whole-rock ϵNd(T) values (where T is the crystallization age) of −17.1 to −11.5 and zircon ϵHf(T) values of −38.3 to −11.2, indicating that they were derived mainly from anatectic melting of the ancient lower crust with some involvement of mantle materials. However, an older pluton in the suite exhibits higher ϵNd(T) values of −11.5 to −9.9, Nd model ages of 1.82–1.64 Ga, lower initial 87Sr/86Sr ratios of 0.7046–0.7048, and it contains some zircon grains that are characterized by high negative to positive zircon ϵHf(T) values of −8.7 to 1.2, indicating strong involvement of juvenile materials derived from the lithospheric mantle. The Late Carboniferous plutons are interpreted as subduction-related and to have been emplaced in an Andean-style continental-margin arc during the southward subduction of the paleo–Asian oceanic plate beneath the North China craton. Rocks from the Late Permian–Middle Triassic intrusive suite display geochemical signatures ranging from highly fractionated I-type to A-type. They exhibit higher zircon ϵHf(T) values of −14.9 to −6.7, whole-rock ϵNd(T) values of −10.6 to −8.8, and younger Hf and Nd model ages than most of the Late Carboniferous plutons, indicating that they could have been produced by extreme fractional crystallization of hybrid magmas resulted from mixing of coeval mantle- and crust-derived melts. They are interpreted as postcollisional/postorogenic granitoids linked to lithospheric extension and asthenosphere upwelling due to slab break-off and subsequent sinking after final collision and suturing of the Mongolian arc terranes with the North China craton. These two contrasting intrusive suites suggest that the final closure of the paleo–Asian Ocean and collision between the Mongolian arc terranes and the North China craton occurred during the Late Permian, and these events were followed by postcollisional/postorogenic extension, large-volume magmatism, and significant continental growth. No significant syncollisional crustal thickening, high-pressure metamorphism, or S-type granitoid magmatism occurred during the collision process. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Comparisons of large igneous provinces (LIPs) and black shales from different cratons can provide important constraints on Precambrian paleogeographic reconstructions and a better understanding of the environmental effects of large-scale volcanic events. A comparison of intraplate mafic events mostly interpreted as LIPs or portions of LIPs (LIP fragments/remnants due to continental breakup or erosion) from the North China Craton (NCC) and North Australian Craton (NAC) shows good correlation in the age range from 1800 Ma to 1300 Ma, and four robust age matches at ca. 1790–1770 Ma, ca. 1730 Ma, ca. 1680–1670 Ma and ca. 1320 Ma have been identified. Most notably, the coeval ca. 1320 Ma Yanliao LIP in the eastern-northern NCC and the Derim Derim-Galiwinku LIP in the NAC are also characterized by similar field occurences and dominantly subalkaline tholeiitic basalts and intraplate geochemical compositions, and are interpreted as portions of the same LIP, separated by continental breakup. Subsequent to 1300 Ma, the NCC and NAC exhibit very different magmatic histories, indicating that separation of these two cratons occurred, likely subsequent to the ca. 1320 Ma LIP event. A comparison of Paleo-Mesoproterozoic black shales from the NCC and NAC provides further evidence for close connections between these regions during this period. Black shales of the Chuanlianggou Formation in the northern NCC and the Cuizhuang Formation in the southern NCC were deposited in the age range ca. 1650–1635 Ma and can be correlated with ca. 1640–1635 Ma black shales in the Barney Creek Formation of the NAC. Deposition of black shales within the Xiamaling Formation in the NCC and the Velkerri and Kyalla formations of the McArthur Basin in the NAC occurred synchronously at ca. 1380–1360 Ma. Our results from matching of LIP ages and black shales combined with paleomagnetic data show that the northern–northeastern margin of the NCC was connected to the northern margin of the NAC from ca. 1800 Ma to 1300 Ma. This long-lived late Paleoproterozoic to mid-Mesoproterozoic connection lasted for at least 500 million years until separation of the NCC from the NAC between ca. 1320 and ca. 1230–1220 Ma.
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