Search

Microseismic phase detection and arrival picking are critical steps in the processing of hydraulic fracturing microseismic monitoring data. As the signal-to-noise ratios of P- and S-waves differ because of the influence of focal mechanisms, geometry, and background noise, difficulties are introduced in the effective discrimination of seismic phases and the accurate acquisition of arrivals in conventional processing methods. In this paper, we propose a method for identifying microseismic phase arrival time by comprehensively analyzing the variation of moveout curves and combining the intra-event waveform similarities with the energy ratio of multitrace signals. First, a curve-fitting formula is constructed with perforation arrivals, and event detection is achieved by adopting an energy-weighted similarity coefficient that seeks plausible fitting curves with a sliding time window in continuous microseismic recordings. Then, the P- and S-waves are separated by the fitting parameters. The known arrival time trend of the microseismic phase is employed to calculate residual time corrections. Finally, the accurate arrival results of the microseismic phases can be obtained by picking the arrivals of stacked traces. The reliability and effectiveness of the proposed method for microseismic phase detection and arrival picking were determined through tests using field data. Arrival results indicate that the proposed method can improve accuracy compared with the traditional energy ratio method.

A group of mafic dykes was discovered in the Menglianggu area, the Western Shandong Province located in the Eastern block of the North China Craton. The dykes are chlorite–actinolite schists, which commonly underwent greenschist facies metamorphism. LA-ICP-MS zircon U–Pb analysis reveals that the magmatic precursors of these dykes were emplaced at 2084 ± 15 Ma and preserved a group of ∼2.5 Ga inherited zircons, which are consistent with the monzogranitic gneisses that surround the dykes. The dyke samples are characterized by geochemical compositions that are similar to the extrusive counterparts of tholeiitic basalts and have high MgO content (Mg# values of 70–82), negative Eu anomalies (δEu = 0.55–0.60), slight light rare-earth element enrichment (La/YbN = 1.45–2.70 and Gd/YbN = 0.98–1.34), and small negative anomalies in the high-field-strength elements. They show slightly negative to positive zircon eHf (t) values (−0.26 to +3.89) and negative eNd (t) values (−4.87 to −0.53). Evidence of dyke petrogenesis suggests that they most likely derived from the partial melting of a depleted mantle source caused by asthenospheric upwelling at shallow levels in the upper mantle. They then experienced 3%–12% crustal assimilation and initial fractional crystallization of olivine, hypersthene, and plagioclase during magma ascent through the continental crust. These dykes have geochronological features that are consistent with the 2200–2000 Ma Hengling magmatic belt (HMB), which indicates that Paleoproterozoic magmatic events extended to the Western Shandong Province (the interior of the Eastern block in the North China Craton).

The Ms 8.0 Wenchuan earthquake occurred in the Longmenshan fault zone (LFZ) of the eastern margin of the Tibetan Plateau (TP). The tectonic activities in this region have been a focus of extensive studies in the past two decades. Two different models involving oblique stepwise rise and channel flow, respectively, are proposed and can be used to explain the generation of earthquakes. The oblique stepwise rise model emphasizes more about the fault of the upper crust, whereas the channel flow model concerns more about the different crustal rheological structures. Currently, because of the confirmation of geophysical data on the rheological structure of the TP, more researchers agree with the channel flow model. To investigate the generation of earthquakes in the LFZ, this study establishes a three-dimensional viscoelastic model based on the heterogeneity of the lithospheric structure and the segmentation of faults. Using ANSYS finite element software to simulate the evolution of stress and strain, the calculated results are consistent with focal mechanism solutions, fault striations, and topography. The best-fit stress field suggests that stress localization in the Longmenshan range is mainly controlled by the channel flow and fault segmentation. The differing viscosities and relative movement between the channel flow and the Sichuan Basin induce a concentration of stress in the LFZ. The stress was most concentrated in segment II, closest to the leading edge of the channel flow, and wherein the Wenchuan earthquake occurred. Additionally, the higher locking degree of segment II found before the Wenchuan earthquake induced higher stress levels at shallow depths, corresponding to higher seismic activity in segment II. Thus, the combined action of the channel flow and fault segmentation controls the distribution of stress and causes the generation of earthquakes in the LFZ.

Tectonic fractures that generally controlled by tectonic stress field, especially tensile fractures, are crucial for tight reservoirs that are characterized by low porosity and low permeability. Prediction of fracture distribution is extremely important for further exploration and development of such reservoirs. Tensile fractures are developed in the upper Bashijiqike Formation in Kuqa Depression in Northwest China. The subject of this study was the KS2 faulted fold, and the characteristics of the tensile fractures were analyzed in detail. A three-dimensional finite element elastic model of the faulted fold was constructed, and the two-factor method was applied to predict the distribution of tensile fractures in the upper Bashijiqike Formation in the faulted fold. Distributions of predicted tensile fractures reveal that positions relative to the fold axis and faults in the hinge zone both have significant influence on the distribution of tensile fractures. The predicted tensile fractures are developed in the hinge zone in the faulted fold, particularly in the area around fault tips, which is the region with the most potential for oil and gas exploration in faulted folds.

The Tan-Lu Fault Zone (TLFZ), East China, is the site of several historical M 6.5–8.0 earthquakes and remains seismically active today. Although differential kinematic and geomorphic features in the upper crust can well divide the TLFZ into several segments, many questions remain regarding the spatial distribution of the middle-large earthquakes along the active faults and what triggers earthquakes in the seismic zone. Namely, what is the relationship, if any, between the observed seismicity and the fault segmentation along the TLFZ? Here we present a three-dimensional viscoelastic finite element model to simulate the stress distribution along the TLFZ and better understand the relationship between the regional stress field and observed seismicity, with a particular emphasis on how the heterogeneous lithosphere influences earthquake initiation at different depths and along the various segments of the TLFZ. The global crustal model Crust 1.0 and structural information from regional and areal studies are utilized to infer the lithospheric viscosity structure and provide an important input to the numerical model. The model results are well supported by the geological evidence, in terms of both the observed stress field and distribution. Our results suggest ~ENE-oriented maximum principal compressive stress in East China, which are consistent with the local fault-plane solutions. The calculated maximum shear strain and rupture values at different crustal depths are consistent with the distribution of the large earthquakes, which suggest that these larger earthquakes are initiated by stress localization in the heterogeneous lithosphere along the TLFZ. Cross-sections of our calculated maximum shear strain and rupture values along the TLFZ support the initiation of large earthquakes in the middle crust, particularly along the Bohai Bozhong and Yishu segments. Furthermore, the “soft” low-velocity zone (fluid system) in the lower crust along the TLFZ provides the potential for earthquake stratification and initiation in the middle crust along the TLFZ. Our results provide strong evidence that the stress localization of the heterogeneous lithosphere in different segments of the TLFZ and the lower crustal fluid system initiate different magnitude of earthquakes in each seismic zone.

The Jiaolai Basin, to the east of the Tan-Lu Fault Zone (TLFZ), is a Cretaceous NE-trending basin in eastern North China and has a multi-episodic evolution. Different from other contemporary NW-trending en-echelon graben systems west to the TLFZ, the origin of the Jiaolai Basin (three episodes: K1l, 135–120 Ma; K2q, 120–105 Ma; K2w, 88–65 Ma) cannot be simply explained by the sinistral displacement of the TLFZ at the beginning of the Early Cretaceous (around ca. 135 Ma). The purpose of this paper is to investigate the critical factors (e.g., bounding faults, tectonic setting, stress field) driving the development of the Jiaolai Basin and constraint its evolution. Three episodes of two-dimensional finite element models were generated in order to determine the roles of the boundary conditions and to reveal the tectonic development of the basin. When compared to the calculated maximum horizontal compressive stress (σHmax) trajectories and the observed data, along with a comparison between the Von Mises Stress ( u Von ) and the depocenters of the basin, the calculated results can be well proved by the geological evidence both in stress field evolution and in the basin patterns. Our analysis show that the three episodes of the maximum principle stress trajectories changed from NE-SW (earlier Early Cretaceous, K1l) NNE-SSW (later Early Cretaceous, K1q) then E-W (Late Cretaceous, K2w). Moreover, the results show a good consistency between the u Von and the depocenters in the basin through geological cross-sections. Via models we suggest that the origin and evolution of the Jiaolai Basin were controlled by three episodes of tectonic events, (i) the reactivated bounding faults and the post-orogenic extension of the Sulu Orogen during the earlier Early Cretaceous, (ii) the lithospheric delamination of the thickened lithosphere during the later Early Cretaceous, and (iii) the likely far-field effects produced by the collision between the Kohistan-Drags arc complex and Asia during the Late Cretaceous. The Jiaolai Basin evolved from extension to pull-apart experiencing volcanic activity during the three episodes of the Cretaceous.

The East African Rift System (EARS) is thought to be an intra-continental ridge that meets the Red Sea and the Gulf of Aden at the Ethiopian Afar as the failed arm of the Afar triple junction. The geodynamics of EARS is still unclear even though several models have been proposed. One model proposes that the EARS developed in a local tensile stress field derived from far-field loads because of the pushing of oceanic ridges. Alternatively, some scientists suggest that the formation of the EARS can be explained by upwelling mantle plumes beneath the lithospheric weak zone (e.g., the Pan-African suture zone). In our study, a shell model is established to consider the Earth’s spherical curvature, the lithospheric heterogeneity of the African continent, and the coupling between the mantle plumes and the mid-ocean ridge. The results are calculated via the finite element method using ANSYS software and fit the geological evidence well. To discuss the effects of the different rock mechanical parameters and the boundary conditions, four comparative models are established with different parameters or boundary conditions. Model I ignores the heterogeneity of the African continent, Model II ignores mid-ocean spreading, Model III ignores the upwelling mantle plumes, and Model IV ignores both the heterogeneity of the African continent and the upwelling mantle plumes. Compared to these models is the original model that shows the best-fit results; this model indicates that the coupling of the upwelling mantle plumes and the mid-ocean ridge spreading causes the initial lithospheric breakup in Afar and East Africa. The extension direction and the separation of the EARS around the Tanzanian craton are attributed to the heterogeneity of the East African basement.

The Lower Jurassic low porosity and low permeability Ahe Formation is the major reservoir of Dibei Gasfield in the Kuqa Depression, Tarim Basin. Natural fractures are important spaces for storage of hydrocarbons in low permeability reservoirs and can significantly improve the fluid flow capability; therefore, predicting the location and intensity of natural fractures in the Ahe Formation are of extreme importance. In the present study, the Late Himalayan paleotectonic stress field, the period of time when the majority of natural fractures generated in the Dibei Gasfield, was simulated and investigated with a three dimensional finite element (3D FE) model, which serves as a starting point for the prediction. Based on the principle of energy conservation and simulated paleotectonic stress field, the relationship between fracture density and stress parameter was established, and hence, natural fractures in the Ahe Formation of Dibei Gasfield were predicted. The results indicated that the development and distribution of natural fractures were primarily fault-controlled. Regions with well-developed natural fractures were mainly located in fault zones and around faults. Tectonic activities and ultra-high pressures were the dominant factors for natural fractures in the Ahe Formation. Regions with higher development degree of natural fractures in the Ahe Formation usually have a larger gas production; therefore, regions among Well Y1, B3, X1 and B2 should be focused in the Dibei Gasfield.

Tectonic fractures are otherwise known as joints or fissures. The density of tectonic fractures is governed by the lithology, layer thickness and structures. The distribution and density of tectonic fractures in the Kuqa Depression in the northern Tarim Basin of Northwest China are dominantly controlled by the regional faulted fold belt. Our purpose of this paper is to analyze how folding and faulting control the development of tectonic fractures, based on outcrop and logs of drill data. In the folded tight sandstone reservoirs in the Kuqa Depression, the extensional area, transition area and shortening area have been separated by two neutral lines, which control the distribution and density of tectonic fractures in the buckle folds. From the twelve sites of field measurements, six logs of drill core data and analysis of the micro-texture of tectonic fractures, it can be deduced that the fracture development in the sub-salt faulted fold belt is related to the neutral lines and related faults. The high-density tensile fractures in the vicinity of fold hinges are more developed than in the limbs of the fold. Folding is thus the first level of control over the general pattern of fracture distribution. The fractures in the hanging wall of the thrust faults are more developed than those in the footwall. Further more, the fractures in the hinge zone and steeply tilted limbs of folds close to thrust faults are more developed than the gently tilted limbs which are far from faulting. This suggests that faulting is a secondary control over the development of local fractures within the faulted fold belt. The development of fractures related to faulted folds in the Kuqa Depression can be also divided into three episodes: pre-folding, syn-folding and post-folding, which are identified by field observation.

The Neoarchean Sonakhan Greenstone Belt, located in the northeastern fringes of Bastar Craton, Central India, is dominated by basalts, andesites, dacites, and rhyolites and also contains some basic rocks with very high MgO (up to 33.4 wt%). Chromite mineralization is present in these rocks along with the cumulates of olivine and clinopyoxenes. The rocks are classified as siliceous high-magnesium basalts (SHMB) exhibiting enriched large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the high field strength elements. Elevated Th/Yb ratios and negative Nb-Ta-Ti anomalies in the primitive mantle normalized multielement diagram indicates a significant role of subduction-related melts/fluids in their genesis. The chromites in SHMB have high Cr# (0.67–0.75) and moderate Mg# (0.11–0.5) values. Parental melt calculations in the chromites indicate that they are crystallized from an SHMB magma in an island-arc setting. A plausible model for the genesis of the rocks of Sonakhan Greenstone Belt includes initial subduction of an intraoceanic lithosphere followed by eruption of lava in an oceanic environment. Continued subduction of the slab followed by slab rollback followed by the generation of SHMB parental magma, which was introduced into the basal portions of the lithosphere in which cumulates of olivine and clinopyroxene have been developed and the chromite mineralization occurred in the inter cumulus space. Final emplacement of the magma took place in a forearc suprasubduction-zone environment with SHMB signature carrying the cumulates, which were located in the lower part of the lithosphere.

The Paleo-Mesoproterozoic Zhongtiao aulacogen in the North China Craton and Cuddapah basin in the Indian Craton, have both been interpreted as intra-continental rift formed by a mantle plume that led to the breakup of Columbia supercontinent, but the mechanism has not been completely deciphered. In this paper, the mechanism of the Zhongtiao aulacogen and Cuddapah basin related to initial breakup of Columbia has been evaluated with 2D elastic finite element models of the North China Craton and the Indian Craton. The trajectories of the horizontal maximum principal compressive stress of the best-fit model fit well with the trends of dyke swarms in the North China Craton and the Indian Craton. When the other three models generated were compared with the best-fit model, it can be found that a mantle plume beneath the Zhongtiao and Cuddapah areas played the most vital role in developing the Zhongtiao aulacogen, Cuddapah basin and initial breakup of Columbia supercontinent. The boundary subduction forces, including the northern margin of the NCC, the northwest and southwest margins of the Indian Craton are indispensable factors for the rifting and breakup, whereas the mechanical properties have little influence on these modeling results. The initial breakup of Columbia supercontinent might have been resulted from the coupling between a mantle plume upwelling and some plate tectonic forces.

Porphyroclasts have been widely used to determine the shear sense, vorticity and other kinematic parameters of shear zones. Previous studies have revealed that several factors affect the rotation angle of porphyroclasts. These studies mostly regard porphyroclasts as rigid objects or viscous deformable objects to simulate porphyroclast rotation in the upper or lower crust. However, research on how these porphyroclasts behave in the brittle-viscous transition zone is still limited. In this study, a two-dimensional viscoelastic finite element model is presented to simulate the rotation and deformation of an elastic porphyroclast embedded in a viscoelastic matrix with various mechanical parameters (Young's modulus, Poisson's ratio and viscosity coefficient) and different boundary conditions (load magnitude and load time). The modelling results demonstrate that the rotation angle of the porphyroclast is strongly influenced by the Young's modulus, Poisson's ratio and viscosity coefficient of the matrix and boundary conditions. The modelling results have a level of consistency with the natural examples of porphyroclast-matrix systems of the Taili and Tianhuang ductile shear zones of the North China Craton. These results are helpful to further explain the rotation and deformation mechanism of porphyroclasts in the brittle-viscous transition zone.

The importance of the Ordos Block, which is surrounded by different Chinese continental blocks, is well documented, but the development of the structural fractures and the stress fields within the Late Mesozoic and Cenozoic eras in this stable block (dips of the Mesozoic and Cenozoic strata are less than 3°) have been poorly studied. In this paper, two dominant groups of structural fractures with NW to EW and NNE to ENE trends are identified through field measurements and imaging log observations. The maximum principal compressive stress magnitudes and stress trajectories are calculated employing 2D finite element models (2D-FEM). Based on the displacement fields, the rotation of the Ordos Block and comparisons between the measured and the calculated stresses, it can be deduced that there are two episodes of fracture formation in the Ordos Block. The calculated orientations of maximum compressive stress in the Late Mesozoic and the Cenozoic eras are found to be WNW and NE respectively, which imply that the NW to EW trending structural fractures were developed in a Late Mesozoic stress field whereas the NNE to ENE ones were developed in a Cenozoic stress field in the block. The change in stress fields may have resulted in the change in tectonic setting from the northwestward subduction of the Izanagi Plate in the Late Mesozoic to the collision between the Indian Plate and the Eurasian Plate in the Cenozoic. The change in the Mesozoic and Cenozoic stress fields is of great significance to the further fracture prediction in fractured reservoirs, basin analyses in the Ordos Basin and research on the geodynamics of the North China Craton.

The New Madrid Seismic Zone (NMSZ) in the Midwestern United States was the site of several major M 6.8–8 earthquakes in 1811–1812, and remains seismically active. Although this region has been investigated extensively, the ultimate controls on earthquake initiation and the duration of the seismicity remain unclear. In this study, we develop a finite element model for the Central United States to conduct a series of numerical experiments with the goal of determining the impact of heterogeneity in the upper crust, the lower crust, and the mantle on earthquake nucleation and rupture processes. Regional seismic tomography data (CITE) are utilized to infer the viscosity structure of the lithosphere which provide an important input to the numerical models. Results indicate that when differential stresses build in the Central United States, the stresses accumulating beneath the Reelfoot Rift in the NMSZ are highly concentrated, whereas the stresses below the geologically similar Midcontinent Rift System are comparatively low. The numerical observations coincide with the observed distribution of seismicity throughout the region. By comparing the numerical results with three reference models, we argue that an extensive mantle low velocity zone beneath the NMSZ produces differential stress localization in the layers above. Furthermore, the relatively strong crust in this region, exhibited by high seismic velocities, enables the elevated stress to extend to the base of the ancient rift system, reactivating fossil rifting faults and therefore triggering earthquakes. These results show that, if boundary displacements are significant, the NMSZ is able to localize tectonic stresses, which may be released when faults close to failure are triggered by external processes such as melting of the Laurentide ice sheet or rapid river incision.

The East Asian continent underwent intense crustal shortening-thickening and following large-scale lithospheric extension in the late Mesozoic due to multiple plate convergence. How to respond to the multiple plate convergence in the North China Craton remains enigmatic. Here we undertaken structural measurements and fault kinematic analysis of the Kalaqin massif in the northern part of the North China Craton (NCC), together with new geochronological results, delineate two stages of intracontinental deformation in the area: (1) NE–SW-striking ductile sinistral shearing (Ds) at 150–135 Ma; and subsequent (2) NW–SE ductile–brittle extensional deformation (De) at 135–110 Ma. Based on electron-backscatter diffraction (EBSD) analysis of quartz c-axis fabric and the characteristics of dynamically recrystallized quartz and feldspar, we estimate that ductile deformation during Ds and De occurred at temperatures of 400–700 °C (i.e., greenschist–amphibolite facies conditions). Kinematic vorticity analysis shows that Ds deformation was characterized by vorticity values (Wk) of 0.72–0.87 (average = 0.793), corresponding to general shear with a dominant simple shear component. Somewhat lower vorticity values of 0.45–0.92 (average = 0.698) during De event indicate a dominant pure shear component. We suggest that Ds reflected the regional NE-striking sinistral shearing represented by the Tan-Lu Fault Zone. Combined with contemporaneous dextral transpression along the ~E–W-striking Chifeng–Kaiyuan Fault and Fengning–Longhua Fault, these structures constituted a regional conjugate strike-slip system in the northern edge of the NCC. Ds event was likely associated with the episode B of the Yanshanian movement, which might result from the subduction of the Paleo-Pacific plate beneath East Asia and the closure of the Mongol-Okhosk Ocean. The subsequent De represents the destruction of the NCC during the Early Cretaceous, which was likely influenced by the roll-back of the Paleo-Pacific plate and post-orogenic extensional collapse of the Mongol-Okhotsk belt.

The interaction of active faults as a factor affecting the mechanisms of large earthquakes has been observed in many places. Most aftershock and clustering earthquake sequences do not recur on the main seismogenic fault but are controlled by fault interactions with adjacent seismic structures. Four groups of conceptual models were generated in this study to determine how the geometry of the seismogenic faults controls the distributions of stress fields and earthquakes. The influences of the fault length ratio, center distance, overlap ratio, echelon distance and fault opening angle were considered in a 2D viscoelastic model. The results indicate that the interaction in the slipping zone is larger when collinear interacting faults are more closely positioned, with one fault lengthening. For noncollinear faults, the interaction is stronger as the inner tips pass each other, which impedes their growth after some degree of overlap. Additionally, fault interaction at the slipping zone becomes stronger as the opening angle approaches 180°. We further generated a 3D viscoelastic model of fault interactions in Central North China Block and applied the finite element method to analyze the relationship between distributions of earthquakes and fault geometry. The calculated results reveal well-matched higher stress and maximum shear strain concentrations in the southern part of the Fen-wei Graben Zone than in other zones in Central North China Block, which can be explained by the longer faults, shorter center distances, shorter overlap lengths and larger opening angles. The stress distributions and fault interactions should be considered in long-term seismic hazard assessment in these zones.

The study of Precambrian rifts, such as those found in the Tarim craton, is of great interest in the field of deep petroleum exploration as the source rocks of the rifts are depositional deep lacustrine facies. In this study, two buried rifts (Manjiaer and Wushi rifts) that may exist in the Tarim craton are identified based on the seismic profiles. Through the analysis of the outcrops and stratigraphic columns of the identified rifts, two types of rifts are classified and their evolution is divided into different stages. The evolution of the Manjiaer rift, which experiences frequent volcanic activity, can be roughly divided into three rift periods. Meanwhile, the evolution of the Wushi rift can be simply divided into two rift periods during the Nanhuan–Sinian period. A noticeably stronger activity of the Manjiaer rift in comparison with that of the Wushi rift was noted. The paleogeography of the Proterozoic Tarim craton was also reconstructed, and the prospect for deep petroleum exploration in the Tarim craton is proposed.

第七届国际岩墙会议于2016年8月在北京召开。会议的主题为“岩墙群——古地理重建的钥匙”。与会学者认为,过去10年,学术界在岩墙群和相关单元区域地质填图,以及通过大型岩墙群等大岩浆岩省进行超大陆/古大陆重建等方面取得了重要成就。另外一些方向是未来几年有发展潜力并可望取得重大进展的领域,如,1)岩墙群/岩床群(杂岩)的侵位机制;2)岩墙群的岩石成因、构造背景和地质意义;3)地外星体上的岩墙群和相关建造;4)岩墙群及相关建造和矿产资源的联系。

The Lingshan Island in Shandong Province in the eastern North China Craton, well known for the Late Mesozoic multi-scale slide-slump structures is related to paleo-earthquake. Terrigenous clastic rocks, volcanic clastic rocks and volcanic lavas are extensively exposed in the Lingshan Island and its adjacent regions of the Shandong Province, which led to fierce debates on their ages, sedimentary characteristics and tectono-sedimentary evolution. In this contribution, we present the characteristics of the Late Mesozoic stratigraphy in the Lingshan Island. Whole-rock K–Ar dating of dyke at Beilaishi and rhyolites at Laohuzui of the Lingshan Island yielded ages of 159 Ma and $$106\hbox {–}92\hbox { Ma}$$ which coincides with the Laiyang Period rifting and the Qingshan Period rifting in the Jiaolai Basin, respectively. On the basis of the analysis to the Late Mesozoic sedimentary environment of ‘flysch’ and ‘molasse’-like formations as well as tectonic stress fields reconstruction, four episodes of the tectono-sedimentary evolution were established in the Lingshan Island and its adjacent regions in the eastern North China Craton. They consist of two episodes of extensional events for the syn-rift, and two episodes of compression events for the inversion of the post-rift. The entire episodes can be summarized as follows: (1) the first syn-rift NW–SE extension in Laiyang Period can be identified by the ‘flysch’ formation (Unit 1) and by emplacement of the NE-trending dyke in the Laiyang Group. This syn-rift episode can be related to the NW–SE post-orogenic extension resulted from the gravity collapse of the thickened lithosphere along the Sulu Orogen. (2) The first post-rift NW–SE inversion, which was caused by the NW-directed subduction of Izanaqi Plate, can be well documented by the ‘X’ type conjugate joints as well as slide slump folds in Unit 1. (3) The second syn-rift NW–SE extension in Qingshan Period is characterized by rhyolite rocks (Unit 2). This syn-rift episode can be considered to be associated with lithospheric delamination of the thickened lithosphere in the eastern North China Craton. And finally, (4) the second post-rift NW–SE inversion which resulted from the subduction of the Pacific Plate under the eastern North China Craton in the NW direction at the end of the Qingshan Period is recorded by ‘molasse’-like formation (Unit 3).

Knowledge of the deformation history and dominant factors influencing the formation of sub-salt structures is necessary to understand the formation of sub-salt traps. In this study, the discrete-element method (DEM) is used to assess the deformation mechanism of sub-salt structures in the Central Kelasu fold-thrust belt of the Kuqa Depression. A series of DEM models of the Central Kelasu fold-thrust belt are constructed, the final deformation styles of the models are compared with the real structures in order to determine the fitting degree of each models, and the dominant factors influencing the formation of sub-salt structures are determined. A thin salt layer promotes the deformation in the sub-salt sequence. Salt sub-sags, basal uplifts, and pre-existing faults can also promote the deformation in the sub-salt sequence in the northern part of the models. Large deformations accumulate in pre-existing structures in the northern part of the models, and then subsequent deformations are also transmitted to the salt layer and supra-salt sequence; however, these deformations are hardly transmitted to the sub-salt sequence in the middle and southern parts of the models. Among the eight DEM models constructed in our research, the horizontal-stratum model without any initial structures showed the best fit to actual phenomena. Earlier simple structures of Mesozoic layers can be deformed into the current complex structures under compression effects in the late Himalayan period. By comparing with other regions and analyzing the deformation progress of the DEM model, the sub-salt structures in the Kuqa Depression are considered to be fold-accommodation fault structures.

The Broad Triangle Area (BTA) is a significant active seismic zone located mainly in East Asia. The Pamir-Baikal tectonic belt, North-South tectonic belt and Himalayan tectonic belt compose the three boundaries of the BTA. Previous studies suggested that the geodynamics of the BTA may be related to coupling between the Indian and Eurasian plates, yet quantitative analysis is lacking. In this study, we use the elastic finite element method in the ANSYS software to establish a spherical shell model and analyze the stress field of the model. We obtain a best-fit model that matches the geological evidence and seismicity by considering the real geological background; a series of models with different initial settings are also discussed to analyze the boundary influence on the different models. Our modeling results indicate that the India-Eurasia collision, the stable Siberia craton and the blocking effects of the Yangtze and North China cratons play the most important roles in the formation of the BTA. Crustal heterogeneity has little influence on the distribution of seismicity within the BTA. Further, the effects of subduction of the Pacific and Philippine plates may not reach the BTA area, which is different from the results of other studies.

The Bohai Sea is a Late Mesozoic-Cenozoic feature of the basin-mountain system located in eastern North China Craton (NCC). The Late Mesozoic thinning of the lithosphere signals the early destruction of the NCC. The onset of the destruction was due to the delamination of thick lithosphere of the craton, represented by the NW-trending grabens in an en-echelon arrangement west to Tanlu Fault, and by the NNE-trending grabens within the Tanlu Fault Zone. The Late Mesozoic NW-trending grabens are overprinted by structures related to the Cenozoic NE-trending pull-apart basin with very thick Mesozoic-Cenozoic sediments in the eastern NCC. C-frequency diagrams of growth faults and the extension factor (β) of four sections across the basin suggest that the extension migrated from the margin to the center of Bohai Sea, and that the Mesozoic and Cenozoic extension factors for Bohai Sea are higher than that of the margin. These evidences suggest that the greatest extension occurred in the center of Bohai Sea, which is consistent with the thinnest crust being found in the center of the sea. The extension ratios and tectonic evolution of the Bohai Sea suggest that it is the key region for the destruction of the NCC, as evidenced by the topography. However, the NCC experienced two stages of destruction with the late stage related to the tectonic regime of Northeast Asia.

Two petrologically distinct alkali feldspar syenite bodies (AFS-1 and AFS-2) from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidiomorphic texture and consists of feldspar (Or55Ab43 to Or25Ab71), ferro-pargasite/ferro-pargasite hornblende, hastingsite, pyroxene (Wo47, En5, Fs46), magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene (Wo47-50, En22-39, Fs12–31) set in a groundmass matrix of alkali feldspar (Or99Ab0.77 to Or1.33Ab98), titanite and magnetite. In comparison to AFS-1, higher elemental concentrations of Ba, Sr and ∑REE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is ∼1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.

The Mesozoic African rift system is an important continental rift system related to the Central African Shear Zone. While several geological models have been discussed, the mechanism of the Mesozoic African rift system is still unclear. One model proposed that the mechanism of the Mesozoic African rift system was inherited from the Benue Trough, which is a failed arm of the Guinea triple junction. Other models suggested that the mechanism of the Mesozoic African rift system could be clarified by the spreading of the Atlantic and weak lithospheric zones, such as the Pan-African suture zone. In this research paper, we create a shell model that considers spherical curvature, the heterogeneous structure of the African basement framework, and a combination of the upwelling St. Helena plume and seafloor spreading. The calculation of the model is solved through the finite element software ANSYS, and the modeling results match the actual geological evidence. In this study, nine other models are created with altered rock parameters or boundary constraints and compared to the original model to examine the influence of these factors. Compared to the nine comparative models, the original model best reflects the calculated results, which indicates that the coupling of the St. Helena mantle plume and ocean-ridge spreading caused the initial lithospheric rifting at ∼130 Ma and that the heterogeneities within Africa did not affect the extension direction of the rift basin but did influence the location of the rift basin.

Understanding the rock mass deformation and stress states, the fracture development and distribution are critical to a range of endeavors including oil and gas exploration and development, and geothermal reservoir characterization and management. Geomechanical modeling can be used to simulate the forming processes of faults and folds, and predict the onset of failure and the type and abundance of deformation features along with the orientations and magnitudes of stresses. This approach enables the development of forward models that incorporate realistic mechanical stratigraphy (e.g., the bed thickness, bedding planes and competence contrasts), include faults and bedding-slip surfaces as frictional sliding interfaces, reproduce the geometry of the fold structures, and allow tracking strain and stress through the whole deformation process. In this present study, we combine field observations and finite element models to calibrate the development and distribution of fractures in the fault-bend folds, and discuss the mechanical controls (e.g., the slip displacement, ramp cutoff angle, frictional coefficient of interlayers and faults) that are able to influence the development and distribution of fractures during fault-bend folding. A linear relationship between the slip displacement and the fracture damage zone, the ramp cutoff angle and the fracture damage zone, and the frictional coefficient of interlayers and faults and the fracture damage zone was established respectively based on the geomechanical modeling results. These mechanical controls mentioned above altogether contribute to influence and control the development and distribution of fractures in the fault-bend folds.

A numerical model – “rifts – plume or hot spot – drift model” – is proposed for the first time in this paper for the generation of the three regional-scale dyke swarms (the Narmada–Tapi dyke swarm, the Nasik–Pune dyke swarm and the West Coast dyke swarm) within the Deccan Large Igneous Province (LIP) on the basis of the geological evolution of Deccan LIP and the orientations of dyke swarms. The dyke swarms have been modelled with finite element method (FEM) in three stages (stages I–III) considering that there was about 20° counterclockwise rotation of the Indian subcontinent since 65 Ma. During stage I, the orientation of the horizontal maximum principal compressive stress (σ1) is ∼ENE–WSW, generating the ENE–WSW-trending Narmada–Tapi dyke swarm. In stage II, the σ1 orientations are weakly preferred in NW–SE and E–W which are in agreement with the orientations of Nasik–Pune dyke swarm. In stage III, the σ1 orientation is ∼N–S generating the nearly N–S-trending West Coast dyke swarm. The rifts, plume or hot spot and the northward counterclockwise motion of Indian subcontinent altogether contributed to the generation of Deccan LIP and its associated dyke swarms.

This paper presents the end Late Paleozoic tectonic stress field in the southern edge of Junggar Basin by interpreting stress-response structures (dykes, folds, faults with slickenside and conjugate joints). The direction of the maximum principal stress axes is interpreted to be NW–SE (about 325°), and the accommodated motion among plates is assigned as the driving force of this tectonic stress field. The average value of the stress index R ′ is about 2.09, which indicates a variation from strike-slip to compressive tectonic stress regime in the study area during the end Late Paleozoic period. The reconstruction of the tectonic field in the southern edge of Junggar Basin provides insights into the tectonic deformation processes around the southern Junggar Basin and contributes to the further understanding of basin evolution and tectonic settings during the culmination of the Paleozoic.

The fractal dimensions of folds are related to layer thickness and viscosity of the multilayer. This paper discusses how the thickness, viscosity, and anisotropic degree affect the rheological deformation of fractal folds in multilayers. The number of layers, their thicknesses, viscosities, and anisotropic degree of multilayers cooperate to affect the rheological deformation of folds, which is not controlled by a single rheological factor. A greater anisotropic degree of multilayers is favorable to develop the more complex and disharmonious fractal folds.

Remnants of 2.1–1.8 Ga orogens can be recognized in nearly every craton assembled within reconstructions of the Rodinia supercontinent, although no particular pattern of laterally extensive orogenic belts emerges. These cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early Earth history. Paleomagnetic constraints have played a limited role in many previous reconstructions of the early Precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles. The geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the Pre-Rodinian supercontinent. Some early unmetamorphosed and undeformed mafic dyke swarms in North China, Southern Peninsular India and North America share coeval age of ~ 1.85 Ga. If these continents are assembled, the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm, with a piercing point between the Cuddapah rift in South India and the Xiong'er aulacogen in North China. This suggests that the North China Craton, Indian Craton and Canadian Shield may be fragmented from the same landmass. The reconstruction of ~ 1.85 Ga giant radiating dyke swarm attempted in this paper suggests that the North China Craton, India Craton and Canadian Shield were united together to form a landmass within the Columbia supercontinent before its extension and break-up. The 1.90–1.85 Ga Andean-style North Orogenic Belt suggests that a subduction zone existed on the northern margin of the North China Craton. Wopmay Orogenic Belt developed in a 1.88–1.84 Ga continental volcano-plutonic arc, which is interpreted as the product of eastward subduction of oceanic lithosphere. The Transantarctica Orogenic Belt in East Antarctica may be another candidate to be linked with the subduction zone. The North Orogenic, Wopmay Orogenic and Transantarctica Orogenic Belts could be connected to form a continuous subduction zone. The orogenic comparison strengthens the configuration of the Columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm. The Laurentia, West Australia and East Antarctica were relatively stable from 1.85 Ga to 1.20 Ga as inferred from the data on dyke swarms, magmatism and the paleomagnetism. These continents constituted the core of the Columbia supercontinent in the Late Paleoproterozoic time. The North China Craton and Indian Craton were however separated from the Columbia supercontinent during the Mesoproterozoic time.

The 1.3– 1.2 Ga fan- shaped Mackenzie dyke swarm and other similar- aged dyke swarms in the Canadian Shield constitute the subswarms of a Late Mesoproterozoic giant radiating swarm. The Late Mesoproterozoic mafic dyke swarms in Australia and East Antarctica might constitute additional subswarms of the giant radiating dyke swarm. A possible Late Mesoproterozoic mantle plume is placed at the focal area of the giant radiating dyke swarm between North America and the landmass (West Australia– East Antarctica). This mantle plume triggered the continuous extension at ca. 1.3–1.2 Ga, which extended into much of Columbia and led to the final fragmentation of the Columbia supercontinent.