Qinling-Dabie Orogenic Belt Research Articles

Deformation Mechanism in Central China Revealed by Regional Earthquake Tomography

Abstract The central China region (CCN) has experienced significant deformation and complex structural arrangements. We conducted research on the deformation pattern of the CCN through the 3D velocity structure of the crust and uppermost mantle obtained via body-wave tomography. This velocity structure strongly correlates with the region’s topographic features. The relationship between velocity distributions and topography indicates that compression in the east–west direction, which can lead to crustal and mantle shortening, may play a crucial role in shaping topography. The various structures between the Qinling mountain range in the west and the Tongbai–Dabie mountain range in the east highlight distinct geological processes occurring along the Qinling–Dabie orogenic belt. In addition, we propose that reservoir water has infiltrated the crystalline basement rock layer up to 15–20 km beneath the Three Gorges Reservoir. Furthermore, the Three Gorges Dam serves as a solid foundation to prevent reservoir water from seeping downstream underground.

Compositional diversity of late Mesozoic granites rooting from the subducted crust in the Qinling–Dabie orogenic belt

Continental subduction has been identified in many orogens, such as the Alps, the Himalayas, and the Dabie; however, better understanding of the mechanism and outcome of different subduction processes remains desirable. The Qinling–Dabie orogen in Central China shows an asymmetric distribution of Triassic ultrahigh-pressure metamorphic rocks and syn- and post-tectonic granitoid plutons, thereby providing an excellent means by which to probe the diverse processes of continental subduction. Many late Mesozoic granitoid plutons that formed in post-orogenic or even anorogenic settings are widely distributed in both the Qinling and Dabie tectonic units and can be useful for studying the composition of materials beneath the crust because of their conspicuous compositional diversity. In the present study, we report zircon ages and NdHf isotopic compositions for the Shangcheng and Heyu granite plutons, which represent late Mesozoic plutons in Dabie and Qinling. When compared with those of the Shangcheng pluton, the wide range of Nd isotopic values and the slightly depleted Hf isotopic compositions of the Heyu pluton indicate that there may be juvenile crust beneath the Qinling tectonic unit that is not present beneath the southern margin of North China. The currently undetectable juvenile material in this region may be an important candidate source of the late Mesozoic magmatism and metal mineralization in the southern margin of North China. The compositional diversity of these granites, as indicated by the NdHf isotopic compositions, is attributed to the nature of the deep crust within the orogenic belt, and the magmatic origins of this region are discussed in the present study.

High-resolution 3-D lithospheric structure beneath the Qinling-Dabie orogenic belt from joint inversion of receiver functions and ambient noise

Resulting from the convergence of the Yangtze and North China Cratons, the Qinling-Dabie orogenic zone (QD) represents an important element in the central China orogenic system. To fully comprehend the craton evolution and lower crustal flow from the Tibetan Plateau, it is important to understand the crust and mantle structure of the QD. We reconstructed the three-dimensional lithospheric structure beneath the QD with high resolution using the joint inversion of receiver functions and ambient noise. Observations reveal that a high-velocity anomaly in the middle to lower crust beneath the western Qinling (WQL) orogen obstructs the eastward extension of a crustal low-velocity anomaly originating from the Tibetan Plateau. This finding provides unambiguous evidence that the WQL orogen is not crossed by eastward lower crustal flow from the Tibetan Plateau. The lithospheric mantle beneath the Weihe Rift and East Qinling orogen exhibits low-velocity characteristics, indicating that eastward asthenospheric flow from the Tibetan Plateau has caused substantial thermal-chemical erosion in the uppermost mantle beneath these regions. The results additionally indicate that the uppermost mantle high-velocity anomalies beneath the Dabie orogen is confined in a limited area and extends only to a depth of 70 km. We propose that during the Triassic, deeply subducted continental lithosphere returned into the uppermost mantle, forming the high-velocity anomalies beneath the Dabie orogen.

Three-Dimensional Electrical Structure and Metallogenic Background of the Southeastern Hubei Ore Concentration Area

The Southeastern Hubei Ore Concentration Area (SHOCA) is located in the west section of the Middle and Lower Yangtze River Metallogenic Belt in China, and it is a significant copper and iron mining region in China. Here, 117 pieces of magnetotelluric array data were used to obtain a three-dimensional resistivity model of the SHOCA and to investigate the relationship between the deep electrical features and the genesis of mineral deposits. The model shows that the Qinling-Dabie Orogenic Belt exhibits high-resistivity characteristics, representing Mesozoic granites and high-pressure to ultra-high-pressure metamorphic rocks. There are several low-resistivity anomalies in the upper crust of the SHOCA, which are connected to the widespread low-resistivity anomaly in the middle-lower crust. Near the Yangxin-Changzhou Fault, there is evidence of an electrical gradient zone. The Xiangfan-Guangji Fault, located at the south margin of the Qinling-Dabie Orogenic Belt, also exhibits distinct high- and low-resistivity boundaries at the upper crust. However, the Yangtze Fault and the Tancheng-Lujiang Fault manifest as resistivity gradient zones at the lithospheric scale. These faults are connected the low-resistivity anomaly in the middle to lower crust, possibly serving as upwelling channels of deep thermal fluids, exerting control over shallow diagenesis and mineralization processes. The low-resistivity anomaly in the middle to lower crust of the SHOCA is explained as partial melting resulting from the mixing of crustal and mantle materials. These low-resistivity anomalies play a role as source components in the mineralization system, where mineral-rich hydrothermal fluids migrate upward along intra-basin faults, exerting control over the distribution of shallow mineral deposits.

Development of a back-arc basin from initial rifting to seafloor spreading: Constraints from Paleozoic basic rocks in the North Qinling accretionary orogen, central China

The progression from initial back-arc rifting to back-arc opening in ancient orogenic collages is important for reconstructing subduction histories, constraining tectonic switching, and understanding crustal growth and evolution. However, it is difficult to constrain this transition in ancient arcs. The Qinling-Dabie orogenic belt is one of the most important orogenic belts in eastern Asia, yet the history of Paleozoic accretionary processes in this belt remains equivocal, owing to a poor understanding of back-arc opening processes in the Erlangping unit. In this study, we present whole-rock geochemical analyses of mafic dikes in the Erlangping unit, along with U-Pb ages and Hf-O isotope compositions of zircon from these dikes. Zircon secondary ion mass spectrometry (SIMS) dating of these mafic dikes yielded U-Pb ages of 453 ± 3 Ma. The mafic dikes are calc-alkaline and are characterized by high K2O contents (1.16−3.16 wt%). They have enriched ([La/Yb]N = 4.3−14.9) light rare earth elements (REEs) and relatively flat heavy REE ([Dy/Yb]N = 0.9−1.5) patterns, and they exhibit enrichment in large ion lithophile elements (LILEs) but depletion in high field strength elements (HFSEs), resembling arc-like magmatism. These mafic dikes are characterized by relatively enriched initial 87Sr/86Sr (0.7049−0.7059), chondritic to slightly radiogenic εNd(t) (−0.36 to 1.33), and radiogenic whole-rock and zircon εHf(t) (+7.2−7.6 and +7.5−7.8, respectively). The zircons have δ18O values (5.0‰ ± 0.1‰) similar to those of normal mantle zircon. Accordingly, we interpret that the mafic dikes were derived from an enriched lithospheric mantle source metasomatized by subducted Proto-Tethys (Shangdan) ocean material. In contrast, previously reported ca. 440 Ma gabbros from the Erlangping unit are tholeiitic and have lower incompatible trace-element concentrations with less enrichment in LILEs and less depletion in HFSEs than the mafic dikes presented here. Whole-rock Nd and zircon Hf isotopic compositions suggest that these Silurian gabbros were derived from partial melting of a more depleted mantle with the involvement of asthenosphere, and they have a close geochemical affinity with back-arc basin basalts. In addition, trace-element ratios and geochemical modeling suggest higher melting pressures for the mafic dikes than the gabbros. The geochemical differences show systematic variations from island-arc basalt into back-arc basin basalt types, which is consistent with the magma source evolution of the Mariana Trough. Thus, we interpret that the ca. 454 Ma mafic dikes were emplaced when the infant arc split, and they record initial back-arc rifting in the Erlangping unit, whereas the Silurian gabbros subsequently formed during the opening of the back-arc basin. Our study provides a paradigm for deciphering the evolution of back-arc basins through the study of spatiotemporal geological and geochemical variations of mafic intrusions in ancient accretionary orogens.

Thermal Evolution, Hydrocarbon Generation, and Heat Accumulation of a High Geothermal Coalfield: A Case Study of Pingdingshan Coalfield, China.

As an important energy base in central China, the Pingdingshan coalfield has abundant coal and geothermal resources. The cooperative exploration of coal and geothermal resources is significant for the comprehensive utilization of energy resources. This work collected coal-bearing samples from the Pingdingshan coalfield to investigate the tectono-thermal evolution of a high geothermal coalfield, especially the present geothermal field and hydrocarbon generation model. The geochemical results show that the Shanxi and Taiyuan source rocks have average R o values of 0.88 and 0.97%, respectively, with an average Rock-Eval T max value of 442 °C. Hydrocarbon generation of source rocks started at ∼205 Ma, with the highest rates at ∼170 Ma, reaching the maximum transformation ratio of 40-50% in the middle of the Early Cretaceous. The age and length of apatite fission tracks (AFTs) indicate that coal-bearing strata underwent significant post-depositional annealing after the Late Permian and suggest an abnormal thermal event that occurred in the Late Mesozoic. Meso-Cenozoic thermal event was mainly caused by the plutonic metamorphism of the Early Jurassic and magmatic thermal metamorphism of the Early Cretaceous, achieving a maximum paleotemperature of ∼140 °C. The magmatic thermal event resulted from the intensive post-orogenic extension of the Qinling-Dabie Orogenic Belt caused by the tectonic transition of the North and South China Plates. The present-day high geotemperature of Pingdingshan Coalfield is dominated by the horst structure caused by the regional extension of the basin-mountain system. The Cambrian limestone with a high thermal conductivity underlying coal measure collects deep heat, forming a heat accumulation center of this horst structure with a heat flow of 74 mW/m2 and a maximum temperature of ∼50 °C nowadays.

Structural boundary and deep contact relationship between the Yangtze and Cathaysia Blocks from crustal thickness gradients

The deep boundary and contact relationship between the Yangtze and Cathaysia Blocks (the major tectonic units of the Southern China Block), as well as the tectonic attributes of the Jiangnan Orogenic Belt, have remained unknown or controversial. Using data recorded by 128 portable broadband stations and 96 permanent stations, we obtained high-resolution images of crustal thickness and Poisson’s ratio in the study area. The influences of crustal anisotropy and inclined interface were eliminated by using the newly proposed receiver function H–κ–c stacking method. We then used a gradient analysis method to obtain crustal thickness gradients at the boundary of the Yangtze and Cathaysia Blocks for the first time. Our results reveal that the crustal thickness varies from >38 km in the Qinling–Dabie Orogenic Belt to <30 km east of the Tanlu Fault and Cathaysia Block. Areas with high Poisson’s ratios (>0.27) are concentrated on the flanks of the deep fault zone and the continental margin of the study area; those with low Poisson’s ratios (<0.23) are concentrated in the Jiangnan Orogenic Belt. Large crustal thickness gradients are found beneath the eastern part of the Jiujiang–Shitai buried fault (>5 km/°). Combined with the velocity structure and discontinuity characteristics at different depths, these findings suggest that the Jiujiang–Shitai fault may constitute a deep tectonic boundary dividing the Yangtze and Cathaysia Blocks on the lithospheric scale. Moreover, our results support that the Cathaysia Block subducted northwest-ward toward the southeastern margin of the Yangtze Block in the Neoproterozoic, and that the Jiujiang–Shitai buried fault and Jiangshan–Shaoxing fault are the deep and shallow crustal contact boundaries of the two Blocks, respectively; that is, the Yangtze Block overlaps the Cathaysia Block.

Analysis of the Formation Mechanism of Medium and Low-Temperature Geothermal Water in Wuhan Based on Hydrochemical Characteristics

Wuhan and its surrounding areas have obvious geothermal spring outcrops, which are unexplored potential geothermal resources. The degree of geothermal resource development in Wuhan is low, and there is a lack of systematic research on their hydrochemical characteristics and formation mechanism. The Wuhan area is bounded by the Xiang-Guang fault, the South Qinling-Dabie orogenic belt in the north, and the Yangtze landmass in the south, with Silurian and Quaternary outcrops and little bedrock outcrops. The Silurian is the main water barrier in the region, which separates the upper Triassic and Paleogene as shallow aquifers and the lower Cambrian and Ordovician as deep aquifers. Different strata are connected by a series of fault structures, which constitute Wuhan’s unique groundwater water-bearing system. Eleven geothermal water (23~52 °C) and six surface water samples (around 22 °C) were collected from the study area. The geothermal water in the study area is weakly alkaline, with a pH of 7.04~8.24. The chemical type of geothermal water is mainly deep SO42− with a higher TDS and shallow HCO3− type water with a lower TDS. Isotopic analysis indicates that atmospheric precipitation and water-rock interaction are the main ionic sources of geothermal water. The chemical composition of geothermal water is dominated by ion-exchange interactions and the dissolution of carbonates and silicates. The characteristic coefficients, correlation analysis, water chemistry type, recharge elevation, geothermal water age, reservoir temperature, and cycle depth were also analyzed. The performance was similar in the same geothermal reservoir, which could be judged as an obviously deep and shallow geothermal fluid reservoir, and the genetic conceptual model of Wuhan geothermal was preliminarily deduced. DXR-8 and DXR-9 had the best reservoir conditions, hydrodynamic conditions, rapid alternation of water bodies, and large circulation depth, which is a favorable location for geothermal resource development and will bring considerable economic and social benefits.

Mantle contribution to the generation of the giant Jinduicheng porphyry Mo deposit, Central China: New insights from combined in-situ element and isotope compositions of zircon and apatite

Identifying crust–mantle interaction is important for understanding the genesis of granite-hosted mineral deposits in post-collisional or intracontinental settings. We have used combined zircon-apatite trace element compositions, zircon HfO isotopes and apatite SrNd isotopes, which were all acquired by in-situ techniques, to evaluate the mantle contribution to the formation of a giant porphyry Mo deposit, the Jinduicheng deposit in the East Qinling–Dabie orogenic belt, Central China. Zircons from the host granites yielded a UPb age of ∼139 Ma, suggesting a post-collisional setting for the ore-related intrusion. Most magmatic zircons from the granites have Ti-in-zircon temperatures lower than 830 °C, moderate Zr/Hf ratios (25–55), and mantle-like δ18O values (peaking at ∼5.6‰), similar to typical I-type granites worldwide. The magmatic zircons have variable εHf(t) values (−26.7 to −7.2) and Ti-in-zircon temperatures (646–894 °C, peaking at ∼740 °C). The coexisting igneous apatites have initial 87Sr/86Sr ratios of 0.70694–0.71027, and variable εNd(t) values (−16.0 to −9.3), Sr contents (132–663 ppm), and Eu/Eu* values (0.12–0.47). The Sr–Nd–Hf isotopes of the apatites and zircons, along with the positive correlations between apatite Sr contents, Eu/Eu* values, and εNd(t) values, a positive correlation between Ti-in-zircon temperatures and zircon εHf(t) values, as well as mixing modeling using SrNd isotopes, suggest that at least two end-member melts were involved in the formation of the host granites: one is the ancient lower crust-derived melt, and the other is the metasomatized lithospheric mantle-derived melt, which have relatively enriched and depleted Sr–Nd–Hf isotopic compositions, respectively. We suggest that the post-collisional lithospheric thinning, asthenospheric upwelling and underplating of the mantle-derived mafic magmas may have triggered the crustal melting, magma mixing, and generation of the host granites of the Jinduicheng deposit. We postulate that, besides the heat, the metasomatized lithospheric mantle-derived magmas likely supplied additional volatiles (e.g., Cl, S), facilitating the porphyry Mo formation. Our study highlights that, combined in-situ element and isotope compositions of accessory minerals can provide multidimensional insights into petrogenetic tracing, and enhance the genetic interpretations of granites and related mineral deposits.

Influence of geological structure on the physicochemical properties and occurrence of middle-deep groundwater in Chongqing, Southwest China

Large marine sedimentary basins often contain concentrated geothermal mineral resources. Chongqing Municipality, located in the Sichuan marine sedimentary basin and the surrounding mountainous area of southwest China, is rich in thermal waters and brines. Chongqing belongs to the Middle-Upper Yangtze Tectonic Block. Previous studies have mostly been based on basin structure, but less on the whole plate structure to study the distribution and evolution of groundwater. In this paper, 78 middle-deep groundwater samples in the study area were collected to better understand the occurrence and hydrochemical evolution of middle-deep groundwater using ionic ratios, hydrogen and oxygen isotopes, and geothermometers. Tectonic stress has been transferred from SE to NW in the Jiangnan Orogenic Belt and from NE to SW in the Qinling-Dabie Orogenic Belt, making the extent of tectonic denudation and its related properties such as hydrochemical type, reservoir temperature, and maximum circulation depth trend along the same directions. Four of the water samples have Br × 103/Cl and Na/Cl molar ratios >1.5 and <0.87, respectively, indicating that they are marine metamorphic brines. The ratios of the rest of the samples are mostly distributed in a range suggesting precipitation-dissolved halite or somewhere in between. This suggests that the study area is in the denudation leaching period of the hydrogeological cycle, and the middle-deep groundwater system is still in the dynamic process of formation water (residual metamorphic paleo-seawater) of the previous hydrogeological cycle diluted in places by rainwater. A conceptual circulation model for regional middle-deep groundwater is proposed. Rainfall in the late Pleistocene infiltrated as groundwater recharge via fractures and karst valleys and circulated to deep strata driven by gravity, where it could mix with residual, paleo-evaporated seawater. Then the groundwater was heated by geothermal and chemical energy sources, mixing with shallow groundwater as it moved upward along faults toward the surface eventually to emerge from springs.

Regional lithospheric deformation beneath the East Qinling-Dabie orogenic belt based on ambient noise tomography

SUMMARY The Qinling–Dabie orogenic belt, which contain the arc-shaped Dabbashan orocline and is the world's largest belt of HP/UHP metamorphic rocks, formed by a long-term complex amalgamation process between the North China Block and the Yangtze Block. To understand the collision processes and tectonic evolution, we constructed a 3-D S-wave velocity model from the surface to a depth of ∼120 km in the eastern Qinling-Dabie orogenic belt and its adjacent region by inverting 5–70 s phase velocity dispersion data of Rayleigh waves extracted from ambient noise data. Our 3-D model reveals low velocities in the middle–lower crust and high velocities in the upper mantle beneath the orogenic belt, suggesting the delamination of the lower crust. Our results support a two-stage exhumation model for the HP/UHP rocks in the study area. First-stage exhumation was caused by the slab breaking away from the subducted Yangtze Block during the Early–Middle Triassic. Partial melting of the lithospheric mantle caused by slab breakoff-related asthenospheric upwelling weakened the lithospheric mantle beneath the orogenic belt, and continued convergence of the two continental blocks led to further thickening of the lower crust. Such processes promoted lower-crust delamination, which triggered the second-stage exhumation of the HP/UHP rocks. In the Dabbashan orocline, two deep-rooted high-velocity domes, that is, Hannan–Micang and Shennong–Huangling domes, acted as a pair of indenters during the formation stage. High-velocity lower crust was observed beneath the Dabbashan orocline. In addition, our 3-D model reveals that high-velocity lithospheric mantle extends from the Sichuan Basin to the Dabbashan orocline, with a subhorizontal distribution, providing strong support for the high-velocity lower crust. We also observed the destruction of lithospheric mantle beneath the Yangtze Block; the destruction area is bounded by the North–South Gravity Lineament, suggesting that the destruction mechanism of the Yangtze Block may be similar to the North China Block.

Decoupling of Sr-Nd Isotopic Composition Induced by Potassic Alteration in the Shapinggou Porphyry Mo Deposit of the Qinling–Dabie Orogenic Belt, China

In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even &lt; 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even &lt; −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively.

Zircon Hf[sbnd]O isotope and magma oxidation state evidence for the origin of Early Cretaceous granitoids and porphyry Mo mineralization in the Tongbai-Hong'an-Dabie orogens, Eastern China

The Tongbai-Hong'an-Dabie orogens constitute the east segment of the Qinling-Dabie orogenic belt, which host several large molybdenum deposits, with a proven reserve of over 8 million tons metal Mo. In this study, we present an integrated study of in situ zircon UPb dating and HfO isotopes, in combination with magma oxidation state estimation for the Early Cretaceous granitoids in the Tongbai-Hong'an-Dabie regions. These granitoids can be divided into three groups on the basis of zircon UPb ages, including early-stage ore-related granitoids from Mushan, Xiaofan and Wangwan deposits (143–136 Ma), ore-barren granites (136–130 Ma), and late-stage ore-related granitoids from Qian'echong, Bao'anzhai, Tangjiaping and Shapinggou deposits (130–110 Ma). Early-stage ore-barren granitoids have the lowest average εHf(t) and δ18O values of −27.1 ± 1.6 and 4.25 ± 0.63‰ as well as the oldest two-stage Hf model ages (TDM2) of ~2.8 Ga, which are roughly comparable with the inferred Dabie lower crust, indicating that they were mainly derived from the partial melting of the lower crust. Ore-forming granitoids in two stages show similar two-stage Hf model ages from 2.2 to 2.3 Ga which differ from any inferred layer of crusts, while they exhibit different zircon HfO isotope and oxygen fugacity evolutionary trends. Granitoids display decreasing average εHf(t) and δ18O values from −17.1 ± 1.9 to −27.1 ± 1.6, and 5.71 ± 0.50‰ to 4.25 ± 0.63‰, and increasing average logƒO2 values from −17.4 ± 4.5 to −6.7 ± 3.8 with a decrease in age from 143 to 130 Ma. In addition, relict zircon cores with Paleoproterozic and Archean ages were observed with εHf(t) and δ18O values analogous to those of the Kongling Complex. These characteristics suggest that the early-stage granitoids were possibly produced by the remelting of the subducted lower crust mixed with the Kongling Complex, with the involvement of reducing Mo-rich black shales in the Yangtze Block that seemingly account for the lower oxygen fugacity of ore-forming granitoids with younger two-stage Hf model ages and lead to the formation of those early-stage Mo deposits. As the increasing contributions of the lower crust in the magma source, the metallogenic gap developed from 136 to 130 Ma in the Tongbai-Hong'an-Dabie orogens. Zircon HfO isotopic compositions of ore-related granitoids increase simultaneously up to −14.2 ± 4.3 and 5.82 ± 0.33‰ respectively at a lower slope after 130 Ma. Part of zircon δ18O values is slightly higher than 6.5‰, implying the involvement of supercrustal materials. Meanwhile, magma oxygen fugacity exhibits an abrupt drop at ca. 130 Ma in the Qian'echong deposit with the lowest average logƒO2 value (−19.3 ± 4.5) and Ce4+/Ce3+ ratios (1–138), then rises quickly up to a maximum average logƒO2 value of −7.3 ± 2.3. As such, these granitoids were likely generated by mixing of a blended crustal magma, derived from the lower crust and supercrustal materials, and the mantle-derived component which also contributes to the late-stage Mo mineralization. We propose that not only the highly oxidized magma but also the continuous change of oxygen fugacity in the deep magma chamber may have positive effects on the formation of porphyry Mo deposits. Given the significant geochemical change at ca. 130 Ma instead of 125 Ma, we agree that the intensive magmatism and mineralization in the Tongbai-Hong'an-Dabie orogens are closely associated with the delamination of the thickened lower crust of the Yangtze Block, which caused the asthenosphere upwelling that provided the heat source and led to partial melting of overlaying lower crust.

Provenance of the Phuquoc Basin fill, southern Indochina: Implication for Early Cretaceous drainage patterns and basin configuration in Southeast Asia

Cretaceous basins cover large parts of mainland SE Asia. Yet, the development during the Cretaceous is poorly understood including the establishment of the Cretaceous basin configuration. Based on detrital zircon and heavy mineral analysis, this study investigates the provenance of Lower Cretaceous deposits in the Phuquoc Basin, exposed in Cambodia and SW Vietnam and extending into the Gulf of Thailand. Our results document five major zircon populations with 130–145 Ma, 145–200 Ma, 200–270 Ma, 420–470 Ma, 1800–1900 Ma ages and two subordinate 2400–2700 Ma, 750–1000 Ma age clusters. These ages resemble those of the Qinling-Dabie and the Songpan-Ganzi orogenic belts and differ from other Asian terranes. These ages suggest that the Qinling-Dabie and Songpan-Ganzi orogenic belts were major sources of sediment for the Phuquoc Basin in the Early Cretaceous. Heavy mineral compositions including the presence of almandine, often co-occurring with silimanite and epidote, suggest metamorphic and granitic constituents in the hinterland, compatible with these orogenic belts being the source.The detrital zircon age pattern of the Phuquoc Basin closely resembles the zircon ages in Khorat and the Sichuan basins, suggesting a common sediment source, and bears great similarities with mid-Cretaceous strata in the Lanping-Simao Basin. These basins share a remarkable lithostratigraphic similarity and are confined by erosion. Taken altogether, this supports that the Phuquoc, Khorat, Sichuan, and probably the Lanping-Simao basins, formed part of a Cretaceous basin covering much of central SE Asia segregated by Late Cretaceous and Cenozoic denudation and translation. The absence of 130–145 Ma and 145–200 Ma aged zircons in the Lanping-Simao Basin suggests that another drainage system sprang from the Songpan-Ganzi Orogenic Belt and fed into this basin before merging with the Qinling-Dabie Orogenic Belt drainage system south of the Sichuan Basin. The combined drainage system likely passed through the Khorat Basin before entering the Phuquoc Basin.

High-resolution lithospheric structures of the Qinling-Dabie orogenic belt: Implications for deep subduction and delamination of continental lithosphere

The Qinling-Dabie orogenic belt was formed during the collision between the North China Craton and the Yangtze Block. A large volume of the high-pressure (HP) and ultra-high-pressure (UHP) metamorphic rocks are exposed in the eastern Dabie Mountains. In order to better understand the collision processes and the exhumation mechanism of the HP/UHP rocks, we process ambient noise data recorded at stations in the Qinling-Dabie orogenic belt and surrounding areas to extract broadband Rayleigh wave dispersion curves at 8–95 s periods. Using these dispersion curves, we construct a high-resolution 3-D shear wave velocity model of the Qinling-Dabie orogenic belt and surrounding regions. Our 3-D model reveals high velocities in the uppermost mantle beneath the western Dabie Mountains and also beneath the western Qinling Mountains, suggesting the presence of remnant continental lithosphere from the past continental subduction. Low velocities in the lower crust and uppermost mantle beneath the eastern Qinling and eastern Dabie are imaged, suggesting the continental lithosphere delaminated in the past. Our 3-D model supports a two-stage exhumation model of the HP/UHP rocks in the eastern Dabie orogenic belt, in which HP/UHP rocks were first exhumed to the mid/lower crust in the first stage and were then further exhumed to the surface under the driving force of the upper mantle upwelling induced by the lithosphere delamination.

Provenance analysis of Late Triassic turbidites in the eastern Songpan–Ganzi Flysch Complex: Sedimentary record of tectonic evolution of the eastern Paleo-Tethys Ocean

The Xikang Group represents the main stratigraphic sequence of the Songpan–Ganzi complex (SGC), a flysch basin with a wide distribution and monotonous lithology. Strong tectonic deformation and accumulation of folds have led to destruction of the original sedimentary sequence and sedimentary structure of the strata, such that there exists no reasonable sedimentary model that can explain the massive flysch. Herein, we investigated in detail the sedimentary structures, paleocurrent direction, particle sizes, major and trace elements, and magmatic zircon and detrital zircon U–Pb ages of the typical sections of the Xikang Group in the eastern SGC. Our analysis led to the following findings: 1) The U–Pb zircon ages from the Galazi (215.6 ± 1.1 Ma), Sudi (214.5 ± 1.5 Ma and 221.1 ± 1.5 Ma), and Gulu (221.3 ± 1.2 Ma) plutons, which intrude the Xikang Group, and detrital zircon samples from the uppermost part of the Xinduqiao Fm. indicated the youngest mean age (YC1σ[2+]) of 222.4 ± 2.5 Ma. This in turn indicates a pre-221 Ma depositional age for the Xikang Group. 2) The provenance was derived from the North China Block and Qiangtang Terrane, Qinling–Dabie orogenic belt, South China Block, and East Kunlun–Qaidam, and the construction of the flysch in the SGC belongs to the multi-source or line source provided by the peripheral orogenic belt. 3) Trace elements suggested that the Xikang Group may have been deposited in a sedimentary basin associated with a continental island arc. 4) The sedimentary environment in this area belonged to the distal fan of a submarine, and the new sedimentation age and sedimentation rate indicate that the Carnian pluvial event may have been the trigger mechanism. 5) The formation of the flysch deposition in SGC related to the Paleo-Tethys Ocean underwent a scissor-like closure from east to west.

Spatial‐Temporal Distribution, Geological Characteristics and Ore‐Formation Controlling Factors of Major Types of Rare Metal Mineral Deposits in China

AbstractRare metals including Lithium (Li), Beryllium (Be), Rubidium (Rb), Cesium (Cs), Zirconium (Zr), Hafnium (Hf), Niobium (Nb), Tantalum (Ta), Tungsten (W) and Tin (Sn) are important critical mineral resources. In China, rare metal mineral deposits are spatially distributed mainly in the Altay and Southern Great Xingán Range regions in the Central Asian orogenic belt; in the Middle Qilian, South Qinling and East Qinling mountains regions in the Qilian–Qinling–Dabie orogenic belt; in the Western Sichuan and Bailongshan–Dahongliutan regions in the Kunlun–Songpan–Garze orogenic belt, and in the Northeastern Jiangxi, Northwestern Jiangxi, and Southern Hunan regions in South China. Major ore‐forming epochs include Indosinian (mostly 200–240 Ma, in particular in western China) and the Yanshanian (mostly 120–160 Ma, in particular in South China). In addition, Bayan Obo, Inner Mongolia, northeastern China, with a complex formation history, hosts the largest REE and Nb deposits in China. There are six major rare metal mineral deposit types in China: Highly fractionated granite; Pegmatite; Alkaline granite; Carbonatite and alkaline rock; Volcanic; and Hydrothermal types. Two further types, namely the Leptynite type and Breccia pipe type, have recently been discovered in China, and are represented by the Yushishan Nb–Ta– (Zr–Hf–REE) and the Weilasituo Li–Rb–Sn–W–Zn–Pb deposits. Several most important controlling factors for rare metal mineral deposits are discussed, including geochemical behaviors and sources of the rare metals, highly evolved magmatic fractionation, and structural controls such as the metamorphic core complex setting, with a revised conceptual model for the latter.

Three-dimensional crustal Vp and Vs structures beneath the southern segment of the Tan-Lu fault revealed by active source and earthquake data

SUMMARY The 2400-km-long Tan-Lu fault, the largest deformation zone in eastern China, plays a decisive role in the seismicity, regional tectonics and mineral deposits distributions. However, the velocity structure beneath the Tan-Lu fault, particularly in the southern segment, is poorly imaged due to the lack of local earthquakes. To obtain a high-resolution crustal structure image, we carried out an active source experiment by firing mobile airgun sources along the Yangtze River in the Anhui Province in October 2015. We manually picked 4118 P wave and 1906 Swave first arrival times from the airgun signals. We also collected 28 957 P wave and 26 257 S wave first arrival times from local earthquakes in a larger area. 3-D crustal velocity images beneath the southern segment of the Tan-Lu fault and surrounding areas are studied using traveltime tomography. Compared with the local earthquake data, the active source data provide better constraints on the upper crustal structure, which further refines the resolution of the lower-crust structure. The Vp and Vs crustal structures are consistent with the local geological settings, and earthquakes are primarily clustered near faults and are spatially correlated with low-velocity zones. Strong velocity contrasts are observed across the Tan-Lu fault zone, which is the main factor controlling local anomalies. The high Vp, Vs and Vp/Vs beneath the Qinling-Dabie orogenic belt and the Middle-Lower Yangtze River Metallogenic Belt may relate to Mesozoic lithospheric delamination and asthenospheric upwelling. These results also demonstrate that the mobile large-volume airgun sources are promising tools for 3-D crustal structure surveys.

Trace elements of pyrite and S, H, O isotopes from the Laowan gold deposit in Tongbai, Henan Province, China: implications for ore genesis

The Laowan deposit is a large gold deposit in the Qinling-Dabie orogenic belt where pyrite is the main Au-bearing mineral phase. We present results from the occurrences of gold, trace elements and sulfur isotopes of pyrite, and hydrogen and oxygen isotopes of quartz and calcite to elucidate the sources of ore-forming fluid; the genesis of pyrite and the ore-forming process. From field observations, five generations of pyrite are identified; one formed in a metamorphic-diagenetic epoch (PyI), and the others during four mineralization stages: 1) the coarse-grained pyrite-quartz stage (PyII), 2) the quartz and medium- to fine-grained pyrite stage (PyIII), 3) the polymetallic sulfide stage (PyIV), and 4) the carbonate-quartz stage (PyV). Gold mainly occurs in PyIII and PyIV. We find that Au, Ag, Pb, and Cu are incorporated into pyrite as micro-/nano-inclusions and that Co, Ni, As, and Se enter the pyrite lattice via isomorphous replacement. The Co/Ni values and Se concentrations indicate that PyI formed from metamorphic hydrothermal fluids and that pyrites (PyII, PyIII, and PyIV) from the ore-forming stages typically reflect a hydrothermal genesis involving magmatic fluid. The δ34S values of PyI (1.45 ‰–2.09‰) are similar to that of plagioclase amphibole schist, indicating that S was primarily derived from wall rock, while those of PyII, PyIII, and PyIV (3.10‰–5.55‰) suggest that S was derived from the Guishanyan Formation and the Laowan granite. The four mineralization stages show a systematic decrease in δD (from −77.1‰ to −82.8‰, −84.7‰, and −102.7‰), while the $${{\rm{\delta }}^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}$$ values showed a gradual decrease from 5.7 to 2.7‰, 1.0‰, and −1.3‰. These data show that the ore-forming fluid was similar to a mixture of magmatic and meteoric waters. Thus, we conclude that the Laowan gold deposit is related to magmatic-hydrothermal fluid.

Lithospheric structure of Hubei Province, central China, from Rayleigh wave tomography: insight into the spatial contact relationship between the Yangtze Plate and the eastern Qinling-Dabie orogenic belt

SUMMARYKnowledge about the spatial contact relationship between the Yangtze Plate and the eastern Qinling-Dabie orogenic belt can not only provide a scientific basis for the exploration of mineral resources, disaster prevention and earthquake prediction in the region, but also play an important role in reconstructing the geological process of the central orogenic belt. Hence, high-resolution lithospheric velocity model is essential to address these geological problems. In this study, using waveform data from 48 stations in Hubei Province and adjacent regions, central China, we invert for a 3-D S-wave velocity structure model of the crust and upper mantle from Rayleigh wave tomography. Our model reveals the complex subduction pattern of the Yangtze Plate to the north and the thrust-nappe tectonics of the Qinling-Dabie orogenic belt along the Mianlue suture with different scales and different deformation strengths. In addition, in the central part of Hubei Province, the local Yangtze slab has been broken into several pieces, among which the upwelling low-velocity anomalies appear. Moreover, the southern margin of the Dabie orogenic belt has undergone thrusting-nappe movement, and a series of associated structures are formed in the northern margin of the middle Yangtze platform. The contact zone between the two blocks in this area is composed of a series of thrust faults with dextrorotation slip component. Finally, based on the 3-D S-wave velocity image of Hubei Province and its vertical cross-section profiles along three different directions, three dynamic models are proposed to explain the spatial contact relationship between the Yangtze Plate and the eastern Qinling-Dabie orogenic belt in different regions.