Paleo- to Mesoproterozoic sedimentary rocks in the southern margin of the North China Craton (NCC) are represented by the Ruyang and Luoyu groups. We studied the sedimentary rocks from the Yunmengshan and Beidajian formations of the Ruyang Group and the Cuizhuang and Sanjiaotang formations of the Luoyu Group. Detrital zircon grains from these formations have U–Pb age populations of 3.64–3.31 Ga, 2.96–2.86 Ga, 2.72–2.59 Ga, 2.56–2.47 Ga, 2.45–2.0 Ga, 1.99–1.85 Ga and 1.84–1.65 Ga. The geochemical features of the sedimentary rocks suggest that some of the sediments were sourced from intermediate to felsic magmatic rocks. The age groups of the detrital zircon are roughly consistent with the tectono-thermal events in the southern margin of the NCC. The Hf isotopic compositions of detrital zircon from the sedimentary rocks in Ruyang and Luoyu groups suggest that significant crustal growth and reworking of the NCC took place during the Neoarchean and early- to mid-Paleoproterozoic, while crustal reworking at the Paleoarchean and late-Paleoproterozoic, and crustal growth at the Mesoarchean. We suggest the depositional times of the Ruyang Group and Luoyu Group are constrained to no older than 1.75–1.7 Ga and 1.7–1.65 Ga, respectively. Formation of late-Paleoproterozoic basins related to the strike slip and extrusion tectonics that cross-cut the NCC during the late Paleoproterozoic (<1.75 Ga), and the late Paleoproterozoic sedimentation once isochronous developed in the southern margin of the NCC through the Taihang region of the interior NCC and linked the Yanshan–Liaoxi regions of the northern NCC.
Skarn deposits are high grade hydrothermal deposits distributed throughout the world, containing multiple mineral resources. However, the formation of skarn deposits is extremely complex, hindering our in-depth understanding of these deposits with high economic value. The Qiaomaishan Cu deposit is a typical skarn deposit located in the Liqiao-Tongshan orefield, Middle-Lower Yangtze River Metallogenic Belt (MLYRMB). This study applied numerical simulation approach to quantitatively describe the formation of copper mineralization within the Qiaomaishan skarn deposit, and explored the correlation between the surface morphology of intrusion and the formation of mineralization. This numerical model links five main processes related to ore formation within hydrothermal ore-forming system and their complex coupled relationship, namely chemical reactions, heat conduction, rock deformation, fluid migration, and materials diffusion. Results show that rough surface morphology of the intrusions is an ore controlling factor within the Qiaomaishan skarn deposit. The uneven surface of the intrusions greatly affects the time spent in cooling, thereby affecting the generation and spatial distribution of chalcopyrite. The concave part of the surface of the intrusions lives a longer cooling period (1,000~2,500 years) than the convex part (110~160 years) from 310 to 260°C, which directly causes the difference in the temporal-spatial distribution of chalcopyrite. Results also show that the factors involved in prospectivity modeling must undergo strict conditional independence analysis, and numerical simulation method can be used to effectively achieve this goal. However, there are also some problems unsolved, such as difficulties caused by lack of data and oversimplified ore-forming chemical reactions. Future development of both geological research and modification of the law of mass action will undoubtedly improve the accuracy and practicability of numerical simulation and our understanding of the Qiaomaishan as well as other skarn deposit, providing information for mineral deposit research from the perspective of computational geoscience.
Abstract The assembly of East Asia was closely linked to the closure of the Tethyan oceans. In south‐east China, the closure of the Paleo‐Tethys ocean led to a continental collision between the South China and North China blocks (SCB and NCB), forming the world renowned (ultra‐) high pressure (UHP) metamorphic belt of the Dabie‐Sulu Orogen. The region was subsequently reworked by postorogenic extensional processes. These tectonic processes likely have left lithospheric scars identifiable by seismic imaging techniques. Here we characterize seismic structures across the orogen and analyze processes related to the closure of the Paleo‐Tethys. Using cutting‐edge tomographic approaches and ambient noise dispersion data, we developed a fine‐scale crustal shear‐wave velocity model beneath key crustal domains in the region. Distinct crustal scale velocity domains are identified, corresponding to the normal Precambrian crust, slow‐velocity suture zones and fault systems, and fast‐velocity orogens, suggesting a deep root of the corresponding surface geological features. By combining recent models of active‐source, gravity and magnetotellurics, characteristic lithospheric deformation patterns such as crustal thrust systems and lithospheric wedges can be inferred, which are attributed to a northward subduction of the SCB lithosphere and the eventual continental collision after the closure of the Paleo‐Tethys Ocean.
The remains of trilobites and other species were unexpectedly discovered in a volcanic ash layer beneath the Permian–Triassic Boundary (PTB). Based on a biostratigraphic investigation of the Zhongliangshan section in Chongqing, South China, the quantity of the species gradually decreased with subsequent volcanism. This finding provides an opportunity to further understand the disappearance of trilobites and the evolution of the mass extinction event. The temporal coincidence between the volcanic eruption event and the loss of trilobites and other species supports the idea of a cause-and-effect relationship. The species remains in the ash bed appeared before the disappearance of Clarkina yini and the climax of the negative carbon isotope excursion, which implies that the onset of the mass extinction occurred at the end-Permian. The explosive volcanic events caused massive releases of CO2, toxic gases and volcanic ash and resulted in loss of habitat for certain species in the Tethys domain. This phenomenon may have led to the abrupt death of trilobites and the catastrophic collapse of biodiversity.
Ambient noise tomography based on dense linear seismic array can reflect the fine velocity structure across different tectonic framework. Since the raypaths among the stations are naturally parallel to the trend of the linear array, special optimization of the inversion method and model parameterization are need. The Bayesian-frame transdimensional inversion method is fully non-linear using high-degree-of-freedom parameter settings, further improve model resolution by using high-dimension meshing. In order to adapt to the linear layout of the array, we suggest modifying the Voronoi cell tessellation by adding a spatial priority of Voronoi kernels, thus increasing the quantity of the Voronoi cells along the array strike. This technique uses non-uniform sampling over the entire 2D space to model space to increase the convergence speed while also increasing the model's accuracy. The application to the linear array in the North China Craton verifies the resilience of our method from the images of the phase velocity and resolution tests. This approach enhances the model resolution compared to the conventional damping least squares approach, and the derived shear wave velocity under the array reveals several low-velocity anomalies in the middle and lower crust beneath the Ordos block border and its surrounding orogenic belt. The new results are compatible with the crustal structures revealed from the receiver function and electrical methods, suggesting that hat the crustal root underwent extensive reworking following cratonic destruction underneath the stable Ordos Block.
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