South China Block Research Articles

Integrated detrital rutile and detrital zircon ages: a new perspective on the tectonic evolution of South China

Abstract Paleogeographic reconstructions are of key importance for understanding the history of continental breakups and amalgamations during the whole history of the Earth. A special case is the history of the Asian continent, which, compared to other continents, consists of several large cratons and numerous smaller continental blocks. The history of the assembly of South China remains controversial in terms of the timing, Late Neoproterozoic or Early Paleozoic, and the participating continental blocks, e.g., Yangtze, Cathaysia, India and/or Australia. Detrital rutile U-Pb dating possesses a significant potential for deciphering tectonic settings as rutile frequently crystallizes during orogenic events associated with the processes of collision and subduction. Detrital zircon U-Pb dating is a perfect instrument for identifying provenance characteristics and age characteristics of sedimentary sources. An integration of these two methods of dating offers better opportunities for reconstructing tectonic settings. This paper presents a first attempt to reconstruct the Neoproterozoic to Early Palaeozoic tectonic history and paleogeography of the whole South China Block based on U-Pb geochronology of rutile and zircon and Hf-in-zircon isotopes from Lower Jurassic Baitianba Formation sedimentary rocks of the western margin of the Yangtze Block, a major part of South China. Our obtained integrated U-Pb rutile and zircon age data show three main age populations of 960-940 Ma, 630-610 Ma and 530-520 Ma. The new U-Pb detrital rutile and zircon ages, compared with former data from Gondwana and Australia, suggest that Yangtze amalgamated with Cathaysia to form South China during the Sibao orogeny at 960-940 Ma. The detrital rutile and zircons of the new 630-610 Ma age group could have been delivered from western Australia during Late Neoproterozoic to Cambrian Paterson-Petermann orogeny. The abundant 530-520 Ma detrital rutile and zircon ages fit well the coeval zircon age populations recorded in Gondwana-derived terranes, like India and Indochina.

Metamorphism and geochronology of the Foping gneiss dome: Insights into Early Triassic collision of the Qinling Orogen, Central China

The Foping gneiss dome, which outcrops in the narrowest part of the Qinling Orogen, contains high-grade metamorphic rocks that record the collision between the North China Block (NCB) and South China Block (SCB). Herein, petrography, mineral chemistry, phase equilibria modeling and UPb geochronology are used to constrain the collision events responsible for the high-grade metamorphism and exhumation of the Foping gneiss dome. The pelitic and mafic granulites sampled from the dome reveal peak metamorphism at P/T conditions of 6.2–7.4 kbar/ 805–855 °C, and document clockwise P-T-t paths with retrograde metamorphism of amphibolite-facies at 3.4–4.7 kbar/ 605–715 °C. While the pelitic schist from the rim of this dome witnessed peak metamorphism at P/T conditions of 4.9–5.1 kbar/ 590–605 °C and retrograde metamorphism at 3.5–3.7 kbar/ 510–520 °C. UPb dating of zircon and monazite confirm ages of ∼247–240 Ma for peak metamorphism with granulite-facies, ages of ∼208–198 Ma for retrograde metamorphism. The two metamorphic stages may record the transition from crustal thickening to dome exhumation, and the age of peak metamorphism probably marks the timing of the collision between the NCB and SCB along the Qinling Orogen in the Early Triassic. The collision probably terminated in the Late Triassic. The new discovery of the Triassic metamorphic event in the Qinling, combined with previously reported collision event of the Dabie Orogen to the east, supports the idea that the continental collision between the NCB and SCB along the Qinling-Dabie Orogen was synchronous.

Late Paleozoic to Mesozoic tectonic evolution of the Qinling Orogenic Belt: Structural and geochronological constraints from the Devonian Liuling Group, eastern Qinling area, China

The Late Paleozoic to Mesozoic tectonic evolution of the Qinling Orogenic Belt is not fully understood. To address this, structural analysis and rutile U-Pb dating were performed on the Middle–Late Devonian Liuling Group located along the northern margin of the South Qinling Belt (SQB). Detailed structural analysis reveals that the Liuling Group experienced four main deformation events (D1–D4). Initial D1 deformation is characterized by intrafolial folds (F1) and a regional penetrative foliation (S1). Subsequent D2 is marked by SW-vergent asymmetric, overturned folds and related crenulation lineation (L2). D3 and D4 are represented by, respectively, nearly E-W trending open folds and NNE-SSW trending centimeter-scale kink folds, both of which slightly modify D1 and D2 structures. Taking into account published chronological data, we propose that D1 and D2 occurred at 363–349 Ma and 332–318 Ma, respectively, and were associated with NE-SW oriented shortening during continental subduction of the SQB. Our new rutile U-Pb ages of 243–240 Ma provide a lower age limit for D3 deformation, which was related to N-S oriented shortening triggered by continental collision between the South China Block (SCB) and SQB along the Mianlue Suture Zone (MLSZ). Finally, D4 deformation was associated with the far-field effects of Late Jurassic subduction of the Paleo-Pacific Plate, which generated a WNW-ESE oriented shortening. Our findings suggest that continental subduction of the SQB continued until the earliest Late Carboniferous. Subsequently, the northern margin of the SQB experienced a Triassic metamorphic overprint triggered by collision between the SCB and SQB.

Lithium isotopes track changes in continental weathering regimes across the end-Permian mass extinction in Southwest China

It has been assumed there was a massive amount of volcanic CO2 injection into the Permian-Triassic atmosphere and ocean systems, leading to rapid climatic warming and expansion of marine anoxia. However, it remains intriguing how Earth recovered from such a CO2-driven hyperthermal condition. One potential mechanism involves the negative feedback between continental silicate weathering and atmospheric CO2, which could have helped maintain habitability across the end-Permian mass extinction (EPME) interval. This process can be examined using lithium isotopes (δ7Li), which reflect the balance of physical erosion and chemical weathering, and chemical weathering indices such as the Chemical Index of Alteration (CIA), which indicates the chemical alteration of parent materials during weathering. In this study, we analyze siliciclastic sedimentary rocks from the Lopingian to Lower Triassic depositional sequences in the HK-1 drill core at the Lengqinggou section, a terrestrial coastal depositional environment in Southwest China, to reconstruct changes in continental chemical weathering intensity across the EPME. We observed a significant ∼4 ‰ positive shift in δ7Li, accompanied by a marked decrease in Li content from 26 ppm to 6 ppm. Our corrected CIA data (CIAcorr) also exhibits a considerable decrease from 94 to 59 across the EPME. The new δ7Li and CIAcorr data from the terrestrial section indicate a decrease in overall chemical weathering intensity in Southwest China, alongside an increase in physical erosion rates, suggesting a shift from a transport-limited to a kinetically limited weathering regime across the EPME. These changes in the continental weathering regime appear to be linked to active volcanic activity near the South China Block, which led to massive deforestation and the collapse of soil systems. Dramatic reductions in chemical weathering intensity may result in inefficient atmospheric CO2 consumption through silicate weathering if other climatic and tectonic conditions remain constant, potentially contribute to maintaining high global surface temperatures and prolonged marine anoxia into the Early Triassic.

Two phases of granulite-facies metamorphism superimposied on retrograde eclogite: Constraints on the early Paleozoic tectonic evolution of the Qinling Orogenic Belt, central China

Existing studies provide adequate petrological evidences on ca. 500 Ma ultra-high pressure (UHP) metamorphism in the North Qinling Orogenic Belt (NQOB) in central China, but the genesis of 470–420 Ma multi-phase granulite-facies metamorphism in the NQOB and their relationship with the ca. 500 Ma UHP metamorphism remain controversial, resulting in the early Paleozoic evolution of the Qinling Orogenic Belt (QOB) highly debatable. In this study, we present mafic granulites and host felsic gneisses with a “red-eye socket” texture from the Shuanglong area, eastern NQOB, which recorded two phases of granulite-facies metamorphism superimposing on former eclogite-facies metamorphism. The former eclogite-facies metamorphism is indicated by eclogite-facies zircon trace element patterns and 496–495 Ma zircon ages, which are the same with those of the HP–UHP eclogite-facies metamorphic rocks in NQOB. The first granulite-facies metamorphism occurred at 460–448 Ma is characterized by coarse-grained minerals in matrix. Compositions and zonings of these minerals define an anticlockwise P–T path involving a prograde stage (751–763 °C), a high-temperature peak stage (9.2 kbar and 864 °C), and a near-isobaric cooling retrograde stage (8.3 kbar and 818 °C). The second granulite-facies metamorphism occurred at 422–421 Ma is represented by coronal garnet and coexisting fine-grained mineral aggregates. Coronal garnet compositional zonings suggest a clockwise P–T path consisting of a high-pressure peak stage (9.5–11.2 kbar and 748–783 °C) and a decompressing and heating retrograde stage (9.2–9.5 kbar and 789–800 °C). Combining dating results of leucosomes in these rocks and existing data, we proposed a new model for early Paleozoic tectonic evolution of the NQOB. The North Qinling Terrane (NQT), probably separated from the South China Block (SCB) during the breakup of Rodinia, drifted northwards and underwent UHP metamorphism at 500 Ma and then rapidly exhumed to crust level. Later, the Shangdan Ocean subducted northwards beneath the exhumed NQT at 470–440 Ma, resulting in the first granulite-facies metamorphism and contemporaneous migmatization and magmatism. Finally, the closure of the Shangdan Ocean led to collision between the NQT and South Qinling Terrane/SCB and the second granulite-facies metamorphism and anatexis at 422–418 Ma.

Tectonic evolution of the early Paleozoic intraplate orogen in the South China Block: Insights from Ductile Shear Zones in North Wuyishan

The ductile shear zones within the North Wuyishan domain are key to understand the tectonic evolution of the South China Block (SCB). This study integrates a multifaceted approach, including field observations, thin section analysis, quartz electron backscatter diffraction (EBSD), zircon U-Pb dating, and mica 40Ar/39Ar dating, to elucidate the deformation history of these shear zones in North Wuyishan. The research identifies a two-stage deformation process of early Paleozoic. The initial D1 phase is marked by a top-to-SW thrusting shear, with associated felsic veins dated to the Ordovician period (447 ± 10 Ma to 459 ± 4 Ma), correlating with high-grade metamorphism and partial melting. The later D2 phase is characterized by NE-striking foliation and lineation, indicative of sinistral strike-slip shear, dated to the early Devonian (412 Ma) and early Carboniferous (∼354 Ma). The D1 phase suggests early crustal thickening and melting within the Cathaysia block, while D2 indicates a transpressional regime during post-orogenic adjustment. The geological features of the SCB, notably the absence of arc magmatism, ophiolitic mélange, and high-pressure metamorphism, comply with an intracontinental rift closure model as previously proposed. This model supports the hypothesis that the Early Paleozoic intracontinental orogeny in the SCB was likely a far-field consequence of a continental collision between the SCB-North Vietnam and South Vietnam blocks near the east Gondwana supercontinent.

Microseismicity and fault structure in the Daliangshan block within the Southeastern Tibetan Plateau

The Daliangshan block is located between the Tibetan Plateau and the South China block and has accommodated several M > 6.5 damaging earthquakes in the past ∼600 years, as well as intense tectonic deformation and complex fault structures. In this study, we analyze more than two years of continuous seismic data recorded by a recently deployed dense seismic array. We used a recently developed machine learning-based earthquake location workflow (ESPRH) to construct a high-precision earthquake catalog for the region and obtained 3539 earthquakes, which is approximately three times as many as the National Earthquake Data Center (NEDC) catalog contains. The seismicity distribution not only confirms the nature of the faults marked on the map but also delineates the detailed geometry of the unmapped faults, including the en échelon faults at the northern end of the Zemuhe Fault and the “V”-shaped conjugate fault within the Mabian Fault Zone. The Zemuhe Fault and Lianfeng Fault are prone to hosting large earthquakes according to the derived low b-value. The western side of the Daliangshan block is dominated by strike-slip faults. Combining the fault geometry presented in this paper, we observed that the fault properties on the eastern side are complex. This tectonic phenomenon is attributed to the fact that during the lateral extrusion of the southeastern edge of the Chuandian fragments, the northeastern part of the Daliangshan block was squeezed by the South China block more strongly than its southwestern part. We provide the first precise earthquake catalog for Daliangshan block, which can be used as important seismological data for regional hazard assessment and research on the southeastern (SE) margin of the Tibetan Plateau.

Contemporary crustal strain rates derived from GPS measurements in southwestern China

Surface strain rates in southwestern China can provide constraints on tectonic evolution of the Tibetan Plateau. Unfortunately, different strain rate fields were obtained from different authors although almost the same GPS data were exploited. Based on updated GPS data, in this paper, we calculate the strain rates in southwestern China using the method proposed by Zhu et al. (2005, 2006). The results confirm that the strain rates in the Sichuan Basin and the South China Block are very small, and the high values are largely concentrated along the Xianshuihe-Anninghe-Xiaojiang fault system and the Sagaing Fault. Furthermore, the highest principal strain rates are located around the eastern Himalayan syntaxis (EHS), with compressive orientations perpendicular to the strike of the Main Thrust Belt. The basic characteristic of the strain rate distribution is in accordance with the tectonic structures from the geological and geophysical investigations. In particular, the two calculated extensive deformation regions basically match the locations of normal-faulting earthquakes in the Sichuan-Yunnan Rhombic Block (SYRB), with one in N-S extension trending in the northern SYRB, and the other nearly E-W orientation in the southern SYRB. We suggest that the extensive deformation and the normal faulting earthquakes in southwestern China is mainly controlled by the lower crustal channel flow with a bend direction, rather than by gravitational spreading alone, as previous authors proposed.

Surface and Deep Structure of the Hanshan–Wuwei Basins in the Lower Yangtze Region: Implications for Mesozoic Tectonic Evolution of the South China Block

AbstractIndicating the tectonic features of the Hanshan–Wuwei basin can reconstruct the framework of the basins formed in Mesozoic and further understand the Mesozoic tectonic evolution of the South China Block. Studies on surface structure, regional stress field and deep geophysical characteristics of the Mesozoic Hanshan–Wuwei basin in Lower Yangtze region were carried out. NE–NNE trending folds and faults developed in the northern margin of the basins. The reconstruction of tectonic stress fields indicates four stress stages dominating the basins' evolution including NW–SE compression, N–S compression, NW–SE extension and NWW–SEE compression. 2D seismic profiles reveal coexistence of thrust, strike‐slip and normal faults in the basin. Combined with regional geological studies, the geodynamic processes for the formation of the Hanshan–Wuwei basin can be divided into five stages: 1) During the Late Triassic, EW trending foreland basin was formed by N–S compression; 2) From Mid‐Jurassic to Late Jurassic, continuous compression strengthened the foreland deformation and formed thrust nappes. In this stage, the integrated foreland basin was compartmentalized or fragmented, and transferred to the broken foreland basin; 3) NE‐trending sinistral strike‐slip movement at the beginning of the Early Cretaceous; 4) Regional extension resulted in normal faults and rift basins developing in the Late Cretaceous; 5) The NWW–SEE compression at the end of the Late Cretaceous caused NW sinistral strike‐slip faults to form, which partly transformed the rift basin.

Upper mantle shear velocity structure of the Cathaysia Block and surrounding areas: New insight into deep geodynamics

The Cathaysia Block (CAB) and its surrounding areas experienced intensive magmatism and mineralization in the Yanshanian period (ca. 200–90 Ma), but their mechanism and deep geodynamics are still debated. In addition, the origin and structures of the Hainan mantle plume are still unclear. To resolve these issues and investigate the large-scale lithospheric thinning and extension in the eastern South China Block, we determine a detailed 3-D S-wave velocity (Vs) model down to 700 km depth by collecting 24,190 S-wave teleseismic data recorded at 164 permanent stations and 125 portable stations deployed in the CAB and surrounding areas. Our results show that high-Vs anomalies exist separately in the study volume. Two high-Vs anomalies appear in the shallow upper mantle and the mantle transition zone, which may reflect the present thin lithosphere and the stagnant Paleo-Pacific slab, respectively. Two other high-Vs anomalies exist in the upper mantle, which may reflect the detached lithosphere and subducting slabs. In contrast, low-Vs anomalies appear widely beneath the CAB, which reflect a tilting magmatic conduit beneath the Wuyishan metallogenic belt (WYMB) and magmatic chambers beneath the Nanling metallogenic belt (NLMB). In addition, our results show that the Hainan plume has a double-layered appearance. Combining our tomographic results with previous multidisciplinary findings, we consider that (1) the subduction and rollback of the Paleo-Pacific Plate may have played different roles in the Yanshanian mineralization of the WYMB and the NLMB; (2) the double-layered appearance of the Hainan plume may be formed due to the influence of plume self-evolution dynamics and pre-existing deep structures; and (3) lithospheric delamination triggered by gravity instability may have occurred beneath the Xuefengshan Mountain in the late Mesozoic.

Provenance of the Southeastern South China Block in the Late Triassic and Initiation of Paleo-Pacific Subduction: Evidence from Detrital Zircon U-Pb Geochronology

Provenance of the Southeastern South China Block in the Late Triassic and Initiation of Paleo-Pacific Subduction: Evidence from Detrital Zircon U-Pb Geochronology

Mississippian foraminifera from the Lueyang Formation in Guozhen area, South Qinling Orogen, China

The Mianlue Suture Belt, located in the southern part of the Qinling Orogenic Belt, is a significant tectonic zone in China that formed by the collision of the South China Block with the North China Block during Triassic. The Lueyang Formation, distributed along the southern margin of the Mianlue Suture Belt, is one of the major components of the Late Paleozoic marine strata of the Mianlue Belt. Unfortunately, only a few published paleontological studies are available. This hinders the understanding of the age and sequence of this formation and the evolution of the Mianlue Ocean. Herein, we report, for the first time, at least 51 species and 25 genera of foraminifera from the Lueyang Formation at the Zhuyuanba section. The Zhuyuanba foraminiferal fauna is dominated by Eostaffella, Archaediscus, Paraarchaediscus, Omphalotis, Bradyina, Janischewskina, Endothyra and Mediocris, and possesses some stratigraphically important taxa such as Bradyina cribrostomata, Janischewskina spp. and Paraarchaediscus stilus. Two foraminiferal zones are recognized in the Lueyang Formation, ascendingly the Visean Paraarchaediscus stilus Zone and Serpukhovian Bradyina cribrostomata Zone. So, the age of the Lueyang Formation at the Zhuyuanba section is considered from Visean to Serpukhovian. This paper confirms for the first time that the Lueyang Formation contains the Visean and Serpukhovian strata, providing new paleontological evidence for understanding the evolution of the Mianlue Ocean during the Late Paleozoic.

Indosinian magmatism in NE Vietnam: Petrogenesis and geodynamic implications of Triassic mafic suites from the Song Hien region

The Song Hien region is located at the southern margin of the South China Block and includes Early–Middle Triassic mafic suites. The petrogenesis and tectonic context of these rocks are important to comprehending one of the most challenging periods in the tectonic evolution of northern Vietnam related to the South China–Indochina collision. In the present study, we provide the first systematic examination of whole-rock geochemical and SrNd isotopic compositions of mafic suites from the NE Vietnam. The studied Early–Middle Triassic suites are dominated by basalts. The rocks are enriched in LILEs, U, and Th and depleted in Nb and Ta and show a wide range of geochemical and SrNd isotopic compositions ((La/Yb)CN = 0.4–4.6; Dy/Dy⁎ = 0.7–1.3; (87Sr/86Sr)i = 0.7053–0.7125; εNd(t) = (+3.7)–(−8.0)). They all originated from shallow melting of a subduction-modified lithospheric mantle, and the compositional diversity of these basalts is attributed mainly to geochemical and Nd-isotopic heterogeneity in the mantle source. The geochemical and SrNd isotopic features of the studied mafic suites indicate a negligible contribution of the asthenospheric mantle to magma generation and differ significantly from those of the Emeishan plume-related basalts. A model in which Early–Middle Triassic mafic magmatic activity in the NE Vietnam region is the result of decompression melting driven by convective thinning of the South China mantle lithosphere during the 250–240 Ma period is discussed in the study. This period corresponds to the South China–Indochina continental collision. In the NE Vietman region, the Early–Middle Triassic syn-collisional magmatism has an important metallogenic context, controlling NiCu sulfide and Sn(Cu) mineralizations.

Shallow crustal structure of the northern Longmen Shan fault zone revealed by a dense seismic array with ambient noise analysis

The Longmen Shan (LMS) fault zone located in the southwest of China is not only the boundary tectonic zone of the Tibetan Plateau and South China block, but also an important part of the north–south seismic belt of China. To investigate the detailed crustal structure of the LMS fault zone, we deployed a dense seismic array of 151 short-period temporary stations in its northern section from March 16 to April 6, 2023. Continuous vertical component ambient noise waveforms recorded by these stations were cross-correlated for all station pairs, enabling the extraction of Rayleigh wave phase velocity dispersion curves across periods ranging from 0.5 s to 6 s. We then inverted these data to derive the crustal shear wave velocity using direct surface wave tomography. Meanwhile, a linear sub-array consisting of 54 stations and crossing the surface rupture of the 2008 Wenchuan earthquake was used to image the fault structure by applying the Transmitted Surface Wave Reverse Time Migration method (TSW-RTM). The ambient noise tomography results show that strong lateral heterogeneity exists in the shallow crust in the study area, with a high shear velocity in the northwest and a low shear velocity in the southeast. The low shear velocity is generally distributed between the Yingxiu-Beichuan fault (YBF) and the Guanxian-Jiangyou fault (GJF). The results of TSW-RTM indicate that the Wenchuan-Maoxian fault (WMF) and the YBF are both characterized with a steep dip to the northwest. Our results could serve as the important basis for the study of segmentation characteristics of the LMS fault and seismic hazard preparation and mitigation.

Driven magmatism and crustal thinning of coastal southern China in response to subduction

Abstract. The late Mesozoic igneous rocks along the coastal South China Block (SCB) exhibit complex parental sources involving a depleted mantle, subducted sediment-derived melt, and melted crust. This period aligns with the magmatic flare-up and lull in the SCB, debating with the compression or extension in coastal region. Our study employs numerical models to investigate the dynamics of the ascent of underplating magma along the Changle–Nan'ao Belt (CNB), simulating its intrusion and cooling processes while disregarding the formational background. The rheological structure of the lithospheric mantle significantly influences magma pathways, dictating the distribution of magmatism. This work reveals that the ascent of magma in the presence of faults is considerably faster than in the absence of faults, and contemporaneous magmatic melts could produce different cooling and diagenetic processes. Additionally, the influence of pre-existing magma accelerated the emplacement of underplating magma. The magma beneath the fault ascended rapidly, reaching the lower crust within 20 million years, with a cooling rate of approximately ∼ 35 °C Myr−1. Conversely, the thickened magma took 40–50 million years to ascend to the lower crust, cooling at a rate of ∼ 10 °C Myr−1. In contrast, magma without thickening and fault would take a considerably longer time to reach the lower crust. The ascent of magma formed a mush-like head, contributing to magmatic circulation beneath the crust and decreasing crustal thickness. Multiphase magmatism increases the geothermal gradient, reducing lithospheric viscosity and promoting underplating magma ascent, leading to magmatic flare-ups and lulls. Our findings suggest that the Cretaceous magmatism at different times in the coastal SCB may be associated with the effects of lithospheric faults under similar subduction conditions. Boundary compression forces delay magma ascent, while rising magma induces a significant circulation, decreasing the crustal thickness of the coastal SCB. This study provides new insights into the complex interplay of magmatic processes during subduction, emphasizing the role of lithospheric structure in shaping the temporal and spatial evolution of coastal magmatism.

Activity and motion characteristics on the southern segment of the Red River fault zone, Yunnan province, China

The longer time for recording large earthquakes on a plate boundary fault, the better that understanding of large earthquake rupture behavior and seismic hazard on the fault zone. However, large earthquakes (M ≥ 7) are rarely recorded on the boundary fault with slow slipping rate, such as the Red River fault zone (RRFZ), which is an important plate boundary fault that marks the southwestern boundary of the Yangtze platform or south China block. There have been no large earthquake records on the southern segments (including the segment in Vietnam) of the RRFZ since historical earthquake records began in 886 AD, except the 1652 Midu M 7 earthquake and the 1925 Dali M 7 earthquake on the northern segment. The southern segment of the RRFZ will not have a large earthquake in the future or as a large earthquake seismogenic zone with a long period of recurrence, remains controversial, in part because of the absence of constraints from geological evidence. This controversial seriously restricts the risk assessment of future large earthquakes on the southern segment of the RRFZ. By careful interpretations of high resolution remote sensing images, in combination with a detailed field geological and geomorphic survey, we found a series of fault valleys and bedrock outcrops from Gasha toYaojie and Yuangjiang to Hekou on the southern segment of the RRFZ. Multiple trench excavation and radiocarbon dating sample analyses show that the mid valley trace in the southern segment of the RRFZ is an active fault. Geological and geomorphic evidence from Gasha to Yaojie and Yuanjiang to Hekou indicate that the mid valley trace in the southern segment of the RRFZ exhibits dip slip and dextral strike slip motion characteristics. This result is inconsistent with those of previous studies that the mid valley trace is purely strike slip. Furthermore, trenches opened on the range front trace in the southern segment of the RRFZ in Ejia are found to still be active, differing from previous studies. Thus, the seismic hazard on the southern segment of the RRFZ should be reevaluated.

A Mid‐Crustal Channel of Positive Radial Anisotropy Beneath the Eastern South China Block From F‐J Multimodal Ambient Noise Tomography

AbstractWe investigated the crustal radial anisotropy in the eastern South China Block (ESCB) with the F‐J multimodal ambient noise tomography. Well corresponding to widespread mid‐crustal low‐velocity zones in the model, a pronounced mid‐crustal channel of positive radial anisotropy is revealed. In the Cathaysia Block, it may origin from sub‐horizontally aligned quartz induced by extension and correspond to the phase transition of to quartz. In other areas, while, it may be relevant to other well‐aligned minerals. This positive mid‐crustal radial anisotropy channel not only provides the solid evidence for dominative extensional deformation since late Mesozoic, but also may indicate an important detachment surface, contributing much to the early Mesozoic magmatism in the ESCB.

Seismic Reflection Imaging Reveals Relict Subduction Zone of the Paleo-Pacific Plate in the Northeastern South China Sea

The South China Sea (SCS) is widely accepted as an active margin that is associated with the subduction of the Paleo-Pacific plate during the Mesozoic. However, the exact location of the subduction or suture zone remains unclear. Understanding the location of the subduction zone is crucial for comprehending the Mesozoic tectonic evolution of the South China Block and the Cenozoic rifting process of the SCS. To clarify the position of the subduction zone and the influences of preexisting structures, we used a multichannel seismic reflection profile to investigate the crustal architecture. The seismic profile reveals a crustal “crocodile” structure that is interpreted as relict subduction in the Chaoshan Depression and a set of south-dipping crust-mantle reflectors related to the initial rifting in the continent–ocean transition (COT) zone. The results indicate that a Mesozoic subduction zone is located at the northeastern margin of the SCS and that preexisting structures (subduction-related structures) facilitated the rifting process. Combined with previous studies on the oceanic plateau collision-accretionary zone of the northern SCS and the Mesozoic accretionary zone in Palawan of the southern SCS, we infer that a section of the suture zone of the Paleo-Pacific plate subduction is preserved at the northeastern SCS margin and that the rifting of the SCS may have initiated at the suture zone.

Lithospheric resistivity structure of the Xuefeng Orogenic Belt and its implications for intracontinental deformation in South China

The Xuefeng Orogenic Belt (XFOB), located in the central part of the South China Block, is a typical Mesozoic intracontinental orogen in the central Jiangnan Orogenic Belt. By collecting magnetotelluric (MT) data across the XFOB, we obtained the resistivity structure of the lithosphere, which sheds light on the Mesozoic intracontinental orogenic processes in the XFOB. The resistivity structure reveals a low-resistivity body (<10 Ω∙m), beneath the XFOB, dipping southeast wards from a depth of 10 km to the bottom of the crust. This conductor is interpreted as a relic of the lower detachment zone, which coincides with low-density areas obtained from joint inversion of seismic models. It is believed to result from mineral fluids migrating along the thrust fault and squeezing sulfides into folds. Four low-resistivity bodies were identified at three extensional locations along the Jiangshan-Shaoxing Fault and at the Cili-Baojing Fault. The low-resistivity body (<10 Ω∙m) at the junction of the Shaoyang and the Hengyang Basin is located at the point where the Moho depth thins. The variation trend of the terrestrial heat flow values, with this low-resistivity body as the plate boundary, is consistent with the average variation of the terrestrial heat flow values within the block. We propose that the low-resistivity body under the Qidong-Yongzhou-Guilin fault conforms to the characteristics of the suture zone in the resistivity structure. Its existence indicates that the missing location of the Jiangshan-Shaoxing suture zone of the Yangtze and Cathaysia Block in the middle-southwest section of the South China Block is the Qidong-Yongzhou-Guilin fault. The Yangtze Block and the Hengyang Basin show high resistivity, the depth of which reaches 100 km and 40 km, respectively. Based on the resistivity model and geological data, the XFOB experienced Triassic compression, leading to basement decollement, thrusting, and nappe structures due to low-angle Paleo-Pacific Plate subduction. This compression also led to the uplift of the orogenic belt. Moreover, under the tension caused by the high-angle retreat of the Paleo-Pacific Plate, the Cretaceous extensional tectonics led to detachment along the thrust faults, forming half-graben and basin structures along the margins.

Lithospheric Folding Controls the Intracontinental Orogen of South China: Insight from Numerical Simulation

Abstract Orogenic processes worldwide have been attributed to various deformation mechanisms. However, the significance of lithospheric folding in these processes has often been overlooked and underestimated. Within the South China Block (SCB), a region marked by notable temporal and spatial variability in intracontinental deformation, the emergence of fold-and-thrust belts during the Paleozoic and Mesozoic periods has captured a scientific interest. The mechanisms governing the genesis of these belts remain a subject of debate, with no discernible subduction interface accounting for the extensive-scale fold-thrust deformation. Moreover, the SCB presents a substantial variation in lithospheric thickness, exceeding 100 km, offering a plausible mechanism for lithospheric folding. To interrogate this mechanism, we conducted lithospheric compression simulations via two-dimensional finite element methods, incorporating variable viscosity both laterally and vertically within the SCB. Our models elucidate that disparities in lithospheric strength beget distinctive deformational manifestation within the SCB. We observe that a weaker lithosphere tends to uplift, whereas a stronger lithosphere tends to subside during compression. Lithospheric strength also influences the Xuefengshan uplift and the spatial distribution of deformational features. In addition, lithospheric folding can account for crustal shortening and the presence of deep anomaly structures. A compelling correlation emerges between lithospheric folding and fluctuations in Moho depth and lithospheric thickness, suggesting its potential influence over the prolonged topographical evolution and shifts in depositional environments within the SCB. This study sheds new light on the role of lithospheric folding in the complex geodynamic history of the SCB and highlights its importance in understanding the broader context of orogenic processes worldwide.