Destruction of the North China Craton

A National Science Foundation of China （NSFC） major research project, Destruction of the North China Craton （NCC）, has been carried out in the past few years by Chinese scientists through an in-depth and systematic observations, experiments and theoretical analyses, with an emphasis on the spatio-temporal distribution of the NCC destruction, the structure of deep earth and shallow geological records of the craton evolution, the mechanism and dynamics of the craton destruction. From this work the foUowing conclusions can be drawn： （1） Significant spatial heterogeneity exists in the NCC lithospheric thickness and crustal structure, which constrains the scope of the NCC destruction. （2） The nature of the Paleozoic, Mesozoic and Cenozoic sub-continental lithospheric mantle （CLM） underneath the NCC is characterized in detail. In terms of water content, the late Mesozoic CLM was rich in water, but Cenozoic CLM was highly water deficient. （3） The correlation between magmatism and surface geological response confirms that the geological and tectonic evolution is governed by cratonic destruction processes. （4） Pacific subduction is the main dynamic factor that triggered the destruction of the NCC, which highlights the role of cratonic destruction in plate tectonics.

Cratonization and the Ancient North China Continent:A summary and review

Cratonization is a key geological process to form stable continental masses with a considerable scale.The Precambrian global cratonization and formation of supercratons in the world is an unrepeated event in the history of the Earth's formation and evolution.Mainly based on study of early Precambrian geology in Eastern Hebei Region and combining other Archean regions in the North China Craton (NCC),the author proposes a two-stage cratonization model of the NCC.The first stage took place at the end of Neoarchean of ～2.5 Ga (boundary time between Archean and Proterozoic),when several micro-blocks were amalgamated together with amphibolite-granulite facies metamorphism and intrusion of crustal-melting granites to form the present-scale NCC.The second cratonization event is cratonic reworking,corresponding to rifting-subduction-collision at 2.3-1.97 Ga and subsequent extension-uplifting related to upwelling mantle at 1.97-1.82 Ga,which could be linked to,respectively,assembly and breaking up of the Columbia Supercontinent.Three main Paleoproterozoic mobile belts in the NCC record that small remnant Neoarchean ocean basins and continental rift basins within the craton were opened and finally closed,and metamorphosed to greenschist-amphibolite facies at ～2.0-1.97 Ga.After that,high-grade granulite facies (HT-HP and HT-UHT) metamorphism with abnormally high heat occurred at 1.97-1.82 Ga.A metamorphism-migmatization event that includes lower crust of the NCC uplifting as a whole,intrusion of mafic dyke swarms,continental rifting and anorogenic magmatic action took place in 1.82-1.65 Ga,marking that the second cratonization of the NCC was finally accomplished and started to evolve to a period of stable continent (platform).

Wintertime N2O5 uptake coefficients over the North China Plain

The heterogeneous hydrolysis of dinitrogen pentoxide(N2O5)plays an important role in regulating NOx.The N2O5 uptake coefficient,γ(N2O5),was determined using an iterative box model that was constrained to observational data obtained in suburban Beijing from February to March 2016.The box model determined 2289 individualγ(N2O5)values that varied from<0.001 to 0.02 with an average value of 0.0046±0.0039(and a median value of 0.0032).We found the derived winterγ(N2O5)values in Beijing were relatively low as compared to values reported in previous field studies conducted during winter in Hong Kong(average value of 0.014)and the eastern U.S.coast(median value of 0.0143).In our study,field evidence of the suppression ofγ(N2O5)values due to pNO3-content,organics and the enhancement by aerosol liquid water content(ALWC)is in line with previous laboratory study results.Low ALWC,high pNO3-content,and particle morphology(inorganic core with an organic shell)accounted for the lowγ(N2O5)values in the North China Plain(NCP)during wintertime.The field-derivedγ(N2O5)values are well reproduced by a revised parameterization method,which includes the aerosol size distribution,ALWC,nitrate and organic coating,suggesting the feasibility of comprehensive parameterization in the NCP during wintertime.

SIMS U-Pb dating of rutile within eclogitic xenoliths in the Early Cretaceous adakitic rocks of the Xuzhou-Huaibei area, China: Constraints on the timing of crustal thickening of the eastern North China Craton

This paper reports the results of secondary ion mass spectrometry （SIMS） U-Pb dating of rutile within eclogitic xenoliths from the Early Cretaceous adakitic rocks in the Xuzhou-Huaibei area of China and discusses the geological significance of these new dates. The dating of rutile from pargasite-bearing eclogite and garnet clinopyroxenite （retrograde eclogite） yielded ages of 209 ± 25 and 132 ± 7 Ma, respectively. The former is consistent with the timing of the first stage of exhumation of the Dabie-Sulu orogenic belt and provides evidence of crustal thickening within the southeastern margin of the North China Cra- ton during the early Mesozoic, related to subduction and collision between the Yangtze and North China cratons. The latter age is similar to the timing of emplacement of the hosting intrusion and indicates that the rutile U-Pb system was triggered after uplifting by the intrusion of the hosting magmas. It implies that garnet clinopyroxenite was previously at the depth where the temperature was above the futile U-Pb closure temperature.

Urban structural evolution over a century in Changchun city, Northeast China

Knowledge on urban land-use change and its driving forces has vital significance in the practice of urban planning and management. However, the characteristics of historical, long-term changes and their quantitative relationships with the urban environment are still poorly understood. Based on multi-source data, including remote sensing imageries, large-scale topographic maps, historical maps, multi-temporal city maps, and other urban thematic maps, high-quality spatial information on urban land use in the built-up area of Changchun has been extracted for 1898, 1932, 1954, 1976, 1990, 2002, and 2012 by means of geographic information systems and remote sensing. We found that the land-use structure and spatial configuration has undergone tremendous alterations according to urban function in the 100-year history of Changchun city. The built-up area of Changchun expanded from 2.26 km^2 in 1898 to 328.12 km^2 in 2012, increasing about 144 times over the past century. Historically, the development of Changchun can be categorized into three stages: the initial forming stage, the old industrial development stage, and the modern metropolis development stage. Commercial and industrial land expanded rapidly following the founding of the People's Republic of China in 1949, with an increase from 1.74 km^2 in 1954 to 15.91 km^2 in 2012, and from 16.45 km^2 in 1954 to 107.05 km^2 in 2012, respectively. Although there was substantial growth in residential land use(from 1.81 km^2 in 1898 to 113.95 km^2 in 2012), the area percentage of residential land decreased continuously(from 80.09% in 1898 to 34.73% in 2012). Moreover, it was noted that the spatial configuration and structural percentage for commercial, industrial, and residential lands and others had tremendous divergences at different stages. These divergences of land-use structure occurred between the stages and were associated with social regimes and the functional orientation of urban society across the 100 years of historical development. Socio-economics, population growth, and planning policies from specific stages, especially after 1949, had strong effects on the divergence of urban structure.

Determining the key conditions for the formation of metamorphic core complexes by geodynamic modeling and insights into the destruction of North China Craton

Metamorphic core complex(MCC) is characterized by the exhumation of lower crust over a large-scale detachment fault, providing natural records for tectonic extension. MCCs are widely identified in the North China Craton(NCC), which have been intensively studied on their structural and geological characteristics. Yet, the condition for the formation of MCCs and their link with NCC destruction are still in debate. In this study, we perform numerical simulations to investigate MCC formation under extension, with a focus on the effect of crustal rheologies. Results indicate that three end-member modes of deformation may occur: the metamorphic core complex mode, the detachment fault-uplifting mode and the pure shear mode. Weaker lower crust and stronger upper crust may promote the formation of MCC. In contrast, stronger lower crust(>1.3×1021 Pa s) may prohibit the exhumation of lower crust(detachment fault-uplifting mode), while weaker upper crust(<7.8×1021 Pa s) may fail to develop detachment faults(pure shear mode). Given that cratons typically have a strong crust, we suggest that the lower crust of NCC was weakened prior to extension, which promoted the formation of MCC in a later stage under the back-arc extension.