Subduction Of Paleo-Pacific Plate Research Articles

Causal sources of the significant high-amplitude magnetic anomaly zone in the northern south China Sea continental margin

The magnetic anomaly map shows an obvious NE-SW trending high-amplitude magnetic anomaly zone (NSCSMA) in the northern South China Sea (SCS) continental margin that extends from southwest Taiwan to the area at approximately 114°E and 20°N. The origin of this high-amplitude magnetic anomaly zone is important for understanding the magmatism, margin rifting, and tectonic evolution of the SCS. To gain insight into this issue, in this study, wavelet spectrum analysis, 2D magnetic modeling, and compact inversion were used to identify the causal source of the NSCSMA. Combining wavelet spectrum analysis with magnetic modeling results, we find that the depths of the major magnetic sources are not consistent along the strike of the NSCSMA (∼15 km in the east and ∼25 km in the west). The compact inversion results along five profiles across the NSCSMA also revealed two kinds of geometries (quasi-dike in the east and dome-like in the west) of the causal sources of the NSCSMA with different depths. Based on our findings and previous paleo-subduction model, we propose that the major source of the NSCSMA is serpentinized upper mantle materials associated with paleo-Pacific plate subduction.

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.

Relationship between electrical conductivity, metallogeny, and lithospheric structure in south China

The South China Block (SCB) is located at the junction of the Pacific, Eurasian, and Indo-Australian plates. Their interaction led to large-scale multi-stage mineralization in the SCB during the Mesozoic. Several regional ore-concentration areas, such as the Middle-Lower Yangtze Metallogenic Belt (MLYMB), the Qinzhou-Hangzhou Metallogenic Belt (QHMB), the Wuyishan Metallogenic Belt (WYMB), and the Nanling Metallogenic Belt (NLMB) were formed during this process. However, the dominant mineral types of these metallogenic belts are different. To study the deep mechanisms of the different metallogenic types developed in the same tectonic background at almost the same period, the magnetotelluric sounding (MT) data from 691 sites located mainly within the eastern SCB are employed to obtain a regional lithospheric 3-D resistivity model.It could be concluded from the resistivity model that deep low-resistivity anomalies and mantle upwelling channels mainly controlled almost all the Mesozoic deposits. Large-scale low-resistivity bodies extend from the crust to the upper mantle beneath the MLYMB and the QHMB, interpreted as channels of mantle-derived magma and melts/fluids containing metallogenic elements upwelling. However, the MLYMB and the QHMB have different upper crustal ore-conducting and ore-controlling structures, thus forming porphyry copper and copper-bearing tungsten deposits. Small-scale low-resistivity anomalies are invading the high-resistivity crust in the NLMB. And remelting the upper crust, mixing, and intrusion of crust-source magma, enriching tungsten-tin elements near the NLMB. Larger-scale low-resistivity anomalies exist deep in the WYMB, remelting the lower crust and resulting in the formation of porphyry copper in it. Significantly, the upper-mantle low-resistivity anomalies beneath the eastern SCB show a spatial distribution that is gradually shallowing from south to north, probably indicating that the asthenospheric materials are upwelling from south to north, corresponding with the changing progressively of magma and metallogenic activities. We propose that the lithospheric delamination and asthenospheric upwelling caused by the far-field effects of the Paleo-Pacific Plate subduction are the sources of solid magmatic activities and related metallogeny.

Co-existence of magmatic- and metamorphic-hydrothermal gold deposits in the northern margin of the North China Craton and their genetic link to Paleo-Pacific plate subduction: Insights from in-situ analyses of sulfur isotopes and trace elements

Mid-Mesozoic gold deposits, whose metallogeny was coincident with subduction of the Paleo-Pacific plate, are widely distributed in the northern margin of the North China Craton (NCC). The genesis of these deposits is currently debated with magmatic- and metamorphic-hydrothermal models. In-situ analyses of sulfur isotopes and trace elements provide an opportunity to clarify such a debate. Here, the two techniques were used to determine the trace elements and sulfur isotopes of sulfides from three mid-Mesozoic gold deposits (Jiapigou, Jinchangyu, and Jinchanggouliang) in the northern margin of NCC. The Co/Ni ratios of pyrites suggest that Jiapigou and Jinchanggouliang deposits are of magmatic-hydrothermal origin, whereas the Jinchangyu deposits receive ore-forming materials mainly from crustal-hydrothermal fluids. In addition, gold-bearing sulfides display positive (5.60 ± 1.87 ‰, SD), near-zero (−0.31 ± 1.27 ‰, SD) and negative δ34SV-CDT values (−3.84 ± 2.97 ‰, SD) in the Jiapigou, Jinchangyu, and Jinchanggouliang, respectively. The results suggest that mid-Mesozoic gold deposits in the northern margin of NCC have variable sources of sulfur and metals. The Jiapigou deposit, representative of the arc settings, received sulfur and metals mainly from the subducting ocean crust. The Jinchanggouliang deposit, representative of cratonic destruction settings, received sulfur and metals mainly from the metasomastized mantle. The Jinchangyu deposit, representative of the back-arc settings, received sulfur and metals mainly from the metamorphic basement. We infer that subduction of the Paleo-Pacific plate in the mid-Mesozoic not only led to direct metallogeny of magmatic-hydrothermal gold deposits at arc settings and cratonic destruction settings, but also triggered the release of ore-forming fluids from the basement at back-arc, favoring metallogeny of crustal-hydrothermal gold deposits. Thus, mid-Mesozoic gold deposits in the northern margin of NCC cannot be exclusively explained by a single model.

Implications of Late Triassic–Middle Jurassic detrital zircons from the southeastern margin of the South China Block for the Paleo-Pacific Plate subduction

There existed an early Mesozoic tectonic regime transformation in the South China Block (SCB). Although it was believed that this transformation was closely related to the subduction of Paleo-Pacific Plate, the process and initial time of the subduction of the Paleo-Pacific Plate have been controversial for a long time. Based on the published Upper Triassic and Middle Jurassic succession detrital zircons geochronology from the southeastern margin of the SCB, the newly obtained Late Triassic to Middle Jurassic detrital zircons Hf isotope data, and the available magmatic age data and Hf isotope data, this study discussed the subduction of the Paleo-Pacific Plate. The Hf isotope composition of zircon grains selected from the Early Mesozoic strata of the SCB, spanning from the Late Triassic to the Middle Jurassic, exhibits a consistent temporal trend with that of the Triassic–Middle Jurassic magmatic rocks. Both display a transition from negative to positive εHf(t) values, indicative of a gradually increasing contribution of mantle-derived materials from the Triassic to the Middle Jurassic. Zircon trace elements indicate that a magmatic arc appeared outside the southeastern margin of the SCB at 200–190 Ma and continued to develop into the Middle Jurassic, which may have been generated by the Paleo-Pacific Plate subduction. This study proposed that the Paleo-Pacific Plate subduction was confined to the southeastern coast of the SCB in the Late Triassic, and the subduction of the flat slab was halted by obstruction at the end of the Late Triassic. In the Early Jurassic, the Paleo-Pacific Plate began to subduction again, and arc-related magmatic rocks were formed along the coast of SCB. At the same time, due to the remote effect of the subduction of the Paleo-Pacific Plate, the weak tectonic belt existing in the Nanling area was reactivated, resulting in the Nanling area in the intraplate extensional setting. Subsequently, the continuous subduction of the Paleo-Pacific Plate led to the thickening of the crust along the SCB in the Middle Jurassic, and the Nanling area was still under in the extensional setting.

Mesozoic intra-arc basin records the tectonic transition from the Paleo-Asian Ocean to the Paleo-Pacific Ocean in northeastern Eurasia

Since the Paleozoic, the tectonic evolution of northeastern Eurasia has been dominated by the Paleo-Asian Ocean and the Paleo-Pacific Ocean tectonic domains. However, the spatiotemporal framework and the timing of tectonic transition between these two oceanic domains remain enigmatic. To address this issue, we report petrological, geochronological, and geochemical data for eight sandstone samples deposited along the convergent margin between the Northeast China terranes and the North China craton in central Jilin Province, China. The results show that these sandstones are immature graywackes with a maximum depositional age of Early Triassic (248 ± 1 Ma), and their sediments were largely derived from coeval magmatic rocks in a juvenile continental arc. According to our new results and previous studies, we identified a sedimentary basin (most likely an intra-arc or forearc basin) intimately associated with one or more continental arcs along the northeastern edge of the North China craton, and we suggest that the southwestward subduction of the Jilin-Heilongjiang Ocean in the early Mesozoic accounts for this continental arc setting. There is a distinct temporal gap between the closure of the Paleo-Asian Ocean (ca. 260 Ma) and the onset of Paleo-Pacific plate subduction (234−220 Ma), which is essentially coeval with the southwestward subduction of the Jilin-Heilongjiang Ocean between 256 Ma and 239 Ma, meaning the latter is a key link that marks the transition between these two tectonic domains.

Mesozoic structural evolution of the Northern South China Sea margin using potential field modelling

This study conducts a comprehensive geophysical inspection of the Northern South China Sea Margin (NSCSM), a complex and pivotal area for unraveling the tectonic history of Southeast China. We employ structural interpretation of the gravity and magnetic data by applying processing techniques and 2D forward modelling to delineate and subdivide the primary subsurface structures, and also to identify the sedimentary basins. Our findings reveal that the NSCSM exhibits a succession of extensional forearc basins above a heterogeneous basement, including a Mesozoic Andean-type magmatic arc and a Western Pacific-type marginal oceanic basin. It has substantial variations in crustal densities and susceptibilities across the NSCSM, reflecting its intricate geological history. The integrated interpretation of this study highlights the substantial impact of the Indosinian and Yanshanian thrusting and orogenies. These geological processes have played a significant role in deformation partitioning, leading to the development of elongated troughs and basins intersected by numerous prominent structures trending in the NE, ENE, and EW directions. The Indosinian faults provide insights into the boundary between these structures, which formed due to the Dian-Qiong Suture and the Paleo-Pacific Plate subduction. These tectonic processes have major structural trends, particularly impacting the offshore forearc region in the NE and EW directions, characterized by deep basins overlying thin crust. Our study also identifies multiple minor trends, including horse-tails and secondary fault systems of the Yanshanian origin, which inherited from the regional tectonics. These trends suggest that post-orogenic stresses and shearing have played a role in rotational and ridge jump processes during the opening and closing phases of the South China Sea (SCS). Furthermore, an uneven relationship exists between the calculated magnetic anomaly and the thickness of Cenozoic sediments, with a significant increase in sediment depth observed in the southern NSCSM compared to both crustal thickness and its heterogeneity.

Multiscale structures of crust-mantle beneath the South China block and their geodynamic implication

The South China block is an ideal location in which to study the impact of paleo-Pacific plate subduction on the upper mantle and crustal structures of the overriding plate, as well as the mechanism of lithospheric thinning. By integrating data from permanent seismic stations of the China Seismic Network and a dense seismic array at Xuefeng Mountain, this study employed P- and S-wave receiver functions (RFs) to image multiscale structures of crust-mantle across the South China block, thereby providing constraints for a comprehensive understanding of its tectonic evolution. The main findings are as follows: (1) The thickness of lithosphere and crust gradually decreases from northwest (NW) to southeast (SE). (2) Beneath the Xuefeng Mountain uplift zone, the P-to-S conversion from the 660 km discontinuity arrives earlier than that predicted from a one-dimensional model, other weak discontinuities can be traced in the upper mantle, including the lithosphere-asthenosphere boundary, the crust becomes thinner, and the Conrad discontinuity becomes deeper. Referring to previous results from tomography and geological reconstructions, we deduce that lithospheric delamination might have occurred beneath the Xuefeng Mountain uplift zone, and the delaminated lithosphere penetrated the upper mantle and reached the mantle transition zone.

Insights from Dikes for Multistage Granitic Magmatism in the Huayangchuan Uranium Polymetallic Deposit, Qinling Orogen

The Huayangchuan U-polymetallic deposit in the Qinling Orogen is a newly verified carbonatite-hosted deposit on the southern margin of the North China Craton (NCC) in Central China. Granitic magmatism is extensively developed in the Huayangchuan deposit area and is lacking analysis on the reasons for these situations; however, its ages, petrogenesis, and relationship with uranium mineralization are not well constrained. Zircon U–Pb ages for the hornblende-bearing granite porphyry and medium-fine-grained biotite granites in close proximity to carbonatite rocks are 229.8 ± 1.1 and 135.3 ± 0.6 Ma, respectively. High-K calc-alkaline series and weakly peraluminous Triassic hornblende-bearing granite porphyry are slightly enriched in light rare earth elements (LREE) with flat heavy rare earth element (HREE) patterns, enriched in Ba and Sr, and depleted in Nb, Ta, P, and Ti, i.e., geochemical characteristics similar to those of adakite-like rocks. The Early Cretaceous medium-fine-grained biotite granites are characterized by LREE enrichment and flat HREE patterns, which belong to high-K calc-alkaline series, and metaluminous belong to weakly peraluminous I-type granite, with U and large ion lithophile element (LILE) enrichment and high field strength element depletion. The high initial 87Sr/86Sr ratios and enriched Nd (εNd(t) = −10.7 to −9.5 and −19.9 to −18.9, respectively) and Hf (εHf(t) = −21.8 to −13.0 and −30.5 to −19.0, respectively) isotopes revealed that both granitic rocks from the Huayangchuan deposit mainly originated from lower crustal materials, generated by partial melting of the ancient basement materials of the Taihua Group. Triassic hornblende-bearing granite porphyry is significantly different from the mantle origin of the contemporaneous U-mineralization carbonatite. In combination with tectonic evolution, we argue that the Qinling Orogenic Belt was affected by the subduction of the North Mianlian Ocean during the Late Triassic. The ongoing northward subduction of the Yangtze Craton resulted in crustal thickening, forming large-scale Indosinian carbonatites, U-polymetallic mineralization, and contemporaneous intermediate-acid magmatism. Additionally, due to the tectonic system transformation caused by Paleo-Pacific Plate subduction, intracontinental lithosphere extension and lithospheric thinning occurred along the southern NCC margin in the Early Cretaceous. Intense magma underplating of the post-orogeny created a large number of magmatic rocks. The tremendous heat could have provided a thermal source and dynamic mechanism for the Yanshanian large-scale U-polymetallic mineralization events.

Paleo-Pacific plate subduction direction change (122−118 Ma): Insight from late kinematic plutons in the Wulian metamorphic core complex, Jiaodong Peninsula, eastern China

The late Mesozoic subduction of the paleo-Pacific plate (Izanagi plate) beneath Eurasia involved complex changes in the direction and angle of subduction, which have been controversial in recent decades. This study investigated Early Cretaceous late kinematic plutons of the Wulian metamorphic core complex that formed in the southern Jiaodong Peninsula. Based on geochemical and Sr-Nd isotopic analyses, we conclude that the granites in the Heshan (122 Ma) and Kuaijishan (118 Ma) plutons are I-type granites that formed in a back-arc extensional environment, and tensile fractures played an important role in the process of magma emplacement. Gravity anomaly inversion revealed the significant role of tension fractures in the uplift of the late kinematic plutons. Analysis of magnetic fabrics showed that the dominant plunging direction of magnetic lineation in the late kinematic plutons is NW-SE (127°−307°), while the plunging direction of the mineral stretching lineation in the wall rock is nearly E-W (102°−282°). We posit that the extensional stress field in the Jiaodong Peninsula underwent a significant transformation during the Early Cretaceous period, specifically from 135 Ma to 122 Ma, when it was dominated by a regional E-W or WNW-ESE extensional stress field. Later, from 122 Ma to 118 Ma, the stress field was controlled by a NW-SE extensional stress field. This variation in the regional stress field in the Jiaodong Peninsula indirectly indicates the changing subduction and slab rollback direction of the paleo-Pacific plate. From 135 Ma to 122 Ma, the paleo-Pacific plate subducted beneath Eurasia along a WNW-ESE direction. However, back-arc extension and slab rollback led to extensive extension in the Jiaodong Peninsula. Subsequently, the subduction direction of the paleo-Pacific plate shifted to the NW, with rollback occurring eastward at a high angle under the Jiaodong Peninsula from 122 Ma to 118 Ma. This shift resulted in extensive magmatism and widespread gold mineralization. The findings of this study offer new insights into the complex geodynamic processes that occurred during the Early Cretaceous period in the region.

Petrogenesis of Jurassic granitic rocks in South China Block: Implications for events related to subduction of Paleo-Pacific plate

Abstract Frequent magmatic intrusion and eruption during the early Yanshanian in South China formed a unique and diverse igneous rock assemblage, mainly comprising granite, rhyolite, and some basic rocks. Nevertheless, the tectonic regime responsible for the formation of these granitic rocks remains controversial. The comprehensive available data suggest that the Jurassic granitic rocks formed during the period from 180 to 145 Ma, with an age peak at ca. 160 Ma. Jurassic rocks are predominantly concentrated in Wuyi, southern Hunan, northeast Guangdong, and southern Jiangxi, followed by the eastern Guangxi-western Guangdong areas, mainly including I-, S-, and A-type granites, and a few I–S transformation-type granites. These granitic rocks invariably exhibit enrichment in Rb, Th, U, and Pb, while Ba, Nb, Sr, P, and Ti are depleted, and variable Eu/Eu* ratios. The whole-rock Sr–Nd isotopic and zircon Hf isotopic compositions show that the Jurassic granitic rocks are mainly recirculation products of Paleo-Mesoproterozoic rocks, as well as the mantle-derived magma, which played a major role in the formation process. Among them, the granites in eastern Guangxi-western Guangdong and Northeast Guangdong areas display higher ε Nd(t) and ε Hf(t) values, suggesting a relatively larger contribution from mantle-derived materials. Based on the comprehensive regional geological data, we interpret that these Jurassic granitic rocks as a product of lithosphere extensional-thinning, tectonic-magmatic interaction formed during the process of flat-slab subduction.

Petrogenesis and Tectonic Setting of Early Cretaceous A-Type Granite from the Southern Great Xing’an Range, Northeastern China: Geochronological, Geochemical, and Hf Isotopic Evidence

The southern Great Xing’an Range is located in the eastern Central Asian Orogenic Belt, where voluminous igneous rocks developed during the Late Mesozoic period. The east slope of the southern Great Xing’an Range has been the topic of numerous debates on the level of influence of the Mongol-Okhotsk and the Paleo-Pacific regimes in the Late Mesozoic period. Therefore, this area is a suitable region in which to study the temporal changes in magma sources and tectono-magmatic evolution. In this paper, whole-rock geochemical data, zircon U-Pb geochronology, and zircon Hf isotope studies were carried out on the granitoids in the east slope area of the southern Great Xing’an Range. LA-ICP-MS zircon U-Pb dating revealed the ages of four granitoid samples: 135.0 ± 0.6 Ma, 130.7 ± 1.4 Ma, 130.4 ± 1.0 Ma, and 127.6 ± 0.8 Ma, respectively. The Hf isotope values 176Hf/177Hf = 0.282751–0.283015, εHf (t) = +2.0~+11.5, and T2DM = 583~1442 Ma suggest that the magma was generated by partial melting of Meso- and Neoproterozoic accreted and thickened low crust. The whole-rock geochemical data implied that these granitoids are A-type granite and their formation is closely linked to the subduction of the Paleo-Pacific Ocean plate. These geochemical, isotopic, and geochronological data suggest that the Early Cretaceous magmatism in the east slope area of the southern Great Xing’an Range formed in an extensional back-arc tectonic setting associated with the slab roll-back of the Paleo-Pacific plate subduction.

Accelerated subduction of the western Pacific Plate promotes the intracontinental uplift and magmatism in late Jurassic South China

Widespread fold and thrust belt and magmatism that occurred in the Mesozoic South China Block (SCB) have generated much debate on their dynamic mechanism related to the western Pacific Plate. Unlike a delayed Andean orogen, the SCB contains large areas of magmatic rocks coinciding with the absence of Upper Jurassic strata, which is not consistent with a flat-slab subduction geometry, and no consensus model has been suggested. To obtain more general insight into the effects of paleo-Pacific Plate subduction on the SCB, thermal-fluid-solid simulations of the subduction process are conducted. The models involved varied subduction rates and lithospheric viscosities to investigate their effect on the subduction style, mantle flow and overriding plate deformation. Low-rate subduction easily forms a subduction geometry with a higher angle, while high-rate subduction causes the slab to break off and drip downward. Fast subduction produces a quasi-horizontal mantle flow and a poloidal flow at the front of the mantle wedge, whereas slow subduction produces two poloidal flows developed on both sides of the subducting slab. The strain tensor of the overriding plate coincides well with the gradient of the horizontal mantle flow rate. A high subduction rate and low lithospheric viscosity promote the deformation of the overriding plate and are further attributed to mantle flow. Combining these results with global plate reconstructions, we find that accelerated subduction of the paleo-Pacific Plate resulted in the Late Jurassic uplift of the SCB. The low viscosity of the overriding plate caused by multiphase orogenic deformation promoted the thinning of the lithosphere due to induced mantle flow, which was associated with the intrusion of magmas and foundering of the subducted slab in a compressional regime. At the end of the Late Jurassic, subduction-induced mantle flow transformed from westward to eastward. Concurrently, the subducted slab began to steepen, and widespread Cretaceous magmatism occurred.

Petrogenesis of the Mesozoic granitoids from the Yuanlinzi Sn-Cu deposit, Northeast China: Implications for Cu-rich Sn mineralization

Granite-related hydrothermal Sn deposits are commonly expected to contain little or no Cu because Cu and Sn have markedly different geochemical properties. However, examples of Sn deposits rich in Cu are well-known in many Sn belts worldwide. So far, the magmatic processes of ore-related rocks and genesis of Cu-rich Sn deposits remain controversial. The newly discovered Yuanlinzi Sn-Cu deposit is located in the southern Great Xing’an Range (SGXR), Northeast China. It is a typical Cu-rich Sn deposit in the SGXR. This contribution reports new cassiterite and zircon U-Pb ages, geochemical compositions, and Sr-Nd isotopic data for the granitoids in the Yuanlinzi deposit to decipher the genesis of Cu-rich Sn deposit. Cassiterite U-Pb dating reveals that the Sn mineralization at Yuanlinzi was formed at ∼ 138 Ma. Zircon U-Pb dating of the granitoids yielded two age clusters: Early Triassic (247.6–246.3 Ma) for the granodiorite, and Early Cretaceous (145.3–141.9 Ma) for the granites, including K-feldspar granite (145.3 ± 0.5 Ma), granite porphyry (143.6 ± 0.9 Ma), fine-grained granite (142.8 ± 1.1 Ma) and albite granite (141.9 ± 1.3 Ma). The Early Cretaceous granites have geochemical affinities for A-type granites, for example, A/CNK = 0.98–1.07, high TFeO/(TFeO + MgO) ratios, total alkali (Na2O + K2O), and Ga/Al ratios. The Early Triassic granodiorite have relatively low (87Sr/86Sr)i values of 0.7034–0.7041, whereas the Early Cretaceous granite has slightly variable and higher (87Sr/86Sr)i values, varying from 0.7020 to 0.7065. The Early Triassic granodiorite and Early Cretaceous granites have similar bulk-rock εNd (t) values and TDM2 ages, ranging from + 1.89 to + 3.53 and 732 to 845 Ma, respectively. The geochemical data and Sr-Nd isotopes indicate that the Early Cretaceous granites were derived from partial melting of the juvenile middle-upper crust. This study further suggests that the 145.3–141.9 Ma granites are associated with back-arc extension environment during the low-angle subduction of Paleo-Pacific plate. In addition, the whole-rock and zircon compositions show that the Cu-Sn magma is characterized by relatively oxidized and less evolved features compared to the Cu-poor Sn deposits in the region. The rapid increase of oxygen fugacity of the latest episode of the Early Cretaceous magma is supposed to have initiated by the injection of mafic magma, which supported the Cu source for the deposit. Our studies suggest that the Cu-bearing mafic magma/fluid injection plays a key role on the formation of Cu-rich Sn deposit.

Diachronous slab-driven Early Cretaceous crustal extension and pulsed magmatic response in southeastern China: Insight from A-type granite and related rocks

The Late Mesozoic magmatic belt in southeastern (SE) China, stretching over 1300 km, resulted from southwestward subduction of the paleo-Pacific plate. Our study focuses on the origin of Early Cretaceous syenite and A-type granite in SE China, utilizing zircon U-Pb and Hf isotopic analyses, bulk-rock compositions, and Nd-Hf isotopic compositions. Findings indicate that ∼ 142 Ma silica-unsaturated syenites in the southwest form through small degrees of partial melting of the metasomatized lithospheric mantle, while ∼ 142 Ma A-type granites originate from partial melting of juvenile felsic rocks. The ∼ 130 Ma A-type granites in the northeast result from mixing of ancient crustal-derived magma and mantle-derived magma. The southwest and northeast regions display distinct magmatic histories, with flare-ups and lulls occurring at different times. These variations suggest diverse extensional and compressional histories. A spatially migrating extensional regime is observed from the southwest (∼147 Ma) to the northeast (∼120 Ma) of SE China. Magmatic flare-ups in the southwest involve reworking juvenile crust, while in the northeast, they modify ancient crust, likely related to paleo-Pacific plate subduction and northeastward slab rollback. Slab subduction rate correlates strongly with observed geological events, indicating diachronous crustal extension, magmatic flare-ups, and lulls during ca. 147–110 Ma due to northeastward slab rollback and changing subduction rate.

Early Cretaceous magmatism in the northern Gyeonggi Massif and the northcentral Yeongnam Massif, Korean Peninsula: Its implications for the Cretaceous tectonic evolution of the Northeast Asia

Most Cretaceous igneous rocks in the northeastern North China Cratons (NCC) and southeastern South China Cratons (SCC) in Northeast Asia are interpreted to have formed in the extensional tectonic environment caused by subducted slab roll-back. On the other hand, the Cretaceous magmatism in the proto-Southwest Japan was confirmed to have occurred in the compressional state produced by the paleo-Pacific plate subduction. The granitoids and enclaves in the northern Gyeonggi Massif intruded at ca. 110–109 Ma and 112 Ma respectively, and the granite and pyroclastic rock in the northcentral Yeongnam Massif were formed at 106 Ma and 103 Ma respectively. The enclaves in the Ganghwa area which located in northern Gyeonggi Massif have high whole-rock Sr isotope composition (0.70748–0.71181) and low whole-rock εNd(t) (−14 to −15) value and low zircon εHf(t) (−19.2 to −14.7) values with enrichment of LILE, suggesting their origin from enriched lithospheric mantle metasomatized by subducted slab sediment. The Early Cretaceous granitoids on the northern Gyeonggi and northcentral Yeongnam massifs have adakite like geochemical composition which are derived from the lower crust instead of subducted oceanic crust derived melt. The geochemical features of the Early Cretaceous igneous rocks in the Korean Peninsula including the study area imply that the Early Cretaceous magmatism on the Korean Peninsula mainly occurred in the extension regime caused by slab roll-back of the paleo-Pacific plate as in the NCC. On the other hand, the igneous rocks formed at 80–66 Ma in the Korean Peninsula have geochemical characteristics similar to that in the Cretaceous igneous rocks in proto-Southwest Japan, indicating that the 80–66 Ma magmatism in the Korean Peninsula were produced by the subduction of the paleo-Pacific plate. The Cretaceous igneous rocks in the northeastern NCC and on the Korean Peninsula show a southeastward-younging trend from 145 Ma to 80 Ma, indicating that southeastward slab roll-back had started at 145 Ma and continued until 80 Ma. Arc-related igneous activity occurred from 116 Ma in southwestern Japan and propagated northward, resulting arc related magmatism in the northern margin of proto-southwestern Japan and the southeastern margin of the Korean Peninsula at 80–66 Ma.

Early to Middle Jurassic (ca. 182–164 Ma) fractionated granitoids in the Korean Peninsula: Implication for the tectonomagmatic history of East Asia

The Jurassic granitoids (200–164 Ma) are distributed in the Korean Peninsula due to the Paleo-Pacific plate subduction. Early Jurassic (200–182 Ma) granitoids are mainly distributed in the southern Korean Peninsula. By contrast, Early to Middle Jurassic (182–164 Ma) granitoids are distributed in the central Korean Peninsula. In this study, we report detailed petrology, zircon U–Pb ages, and whole-rock geochemistry from the Seoul–Uijeongbu and Pocheon–Gimhwa pluton units in the central Korean Peninsula. The Seoul–Uijeongbu unit is dominated by biotite granite, with minor porphyritic biotite and garnet-biotite granite while the Pocheon–Gimhwa unit consists of biotite granite and porphyritic biotite granite, garnet-biotite granite, and two-mica granite. Zircon U–Pb age from those granites gives 180–167 Ma. The granitoids in the Pocheon-Gimhwa unit formed through fractional crystallization from biotite granite and porphyritic biotite granite to garnet-biotite granite, and two-mica granite based on gradually decreasing their Nb/Ta, Zr/Hf, and Eu/Eu* ratios. The strongly fractionated granitoids are garnet-biotite granite and two-mica granite. The LILE enrichment, Ta–Nb, Sr–P, and Eu–Ti troughs, and Ba depletion in most granitoids are similar to those of granitoids due to the subduction in the arc environment. Thus, these Jurassic granitoids (180–167 Ma) are mainly peraluminous granites with moderate crystal fractionation corresponding to I-type granite. Alkali feldspar granite associated with ore mineralization occurs in the Gwanaksan pluton from the southwestern Seoul–Uijeongbu unit. The alkali feldspar granite displays distinct negative Eu anomaly with high contents of Rb, Hf, Cs, and Nb compared with other granites. These characteristics imply that alkali feldspar granite experienced strong hydrothermal activity leading to feldspar ore mineralization compared to the other granites. The formation of a wide range of moderately evolved peraluminous granitoids is presumed to be related to rapid flat-subduction during 182–164 Ma, and the mineralization-related alkali feldspar granite indicates the termination of Jurassic granitoid magmatism in the central Korean Peninsula.

Crustal and upper mantle structure beneath SE China from joint analysis of receiver functions and Rayleigh-wave dispersion

SUMMARY Various geodynamic models, such as a mantle plume, lithospheric delamination and the subduction of palaeo-Pacific Plate, have been proposed to account for the Mesozoic magmatic activity and related mineralization in SE China. However, previous seismic velocity models are insufficient in resolution to constrain the accompanying crust–mantle interactions, which limits our understanding of the deep geodynamic processes responsible for the Mesozoic magmatism in SE China. In this study, we construct a new 3-D shear wave velocity model of the crust and upper mantle beneath SE China using joint inversion of receiver functions and Rayleigh-wave dispersion. We also determine the crustal thicknesses and Vp/Vs ratios by H–k stacking of receiver functions. Compared to the western Cathaysia Block, the coastal volcanic-intrusive belt (CVIB) southeast of the Zhenghe-Dapu Fault shows relatively high-velocity anomalies in the lower crust and high Vp/Vs ratios, indicating significant underplating of mafic material beneath the CVIB. Furthermore, it is noticeable that the asthenospheric low-velocity anomalies are stronger beneath the CVIB than beneath the interior of SE China, suggesting a southeastward increase in the intensity of asthenospheric upwelling and partial melting, which was likely responsible for the strong volcanism and the inferred mafic underplating beneath the CVIB. Our observations provide new evidence and more details for the northwestward subduction and subsequent rollback of the palaeo-Pacific Plate causing the Late Mesozoic magmatism in SE China.

Fluid evolution and genesis of the Sankuanggou Fe[sbnd]Cu skarn deposit, Duobaoshan ore field, Northeast China: Evidence from fluid inclusions and H-O-S-Pb isotopes

The Sankuanggou FeCu skarn deposit is located in the Duobaoshan ore field in the northern Great Xing'an Range, Notheast China. The ore bodies occurred in the skarn of the contact zone between the Yanshanian granodiorite and the middle Ordovician Duobaoshan Formation marble. According to the field investigations and mineral crosscutting relationships, five paragenetic stages were identified: the anhydrous skarn (Stage I); hydrous skarn (Stage II); chalcopyrite-pyrite-quartz-molybdenite (Stage III); sphalerite-quartz stage (Stage IV) and quartz-calcite (Stage V). In the Stage I and II, the assemblage of fluid inclusions (FIs) in quartz is characterized by the development of daughter mineral-bearing three-phase FIs (S-type), vapor-rich two-phase aqueous FIs (LV-type) and liquid-rich two-phase aqueous FIs (VL-type). VL- and LV-type FIs were found in the Stage III quartz, whereas only VL-type FIs were present in the Stage IV quartz and Stage V calcite. The homogeneous temperatures of the FIs in Stages I to V were 364–495, 295–405, 243–360 and 135–207 °C, respectively, with salinities of 4.16–58.42, 4.17–47.99, 3.37–14.2, 1.03–11.11 and 3.53–8.4 wt% NaCl eqv., respectively. In general, the ore-forming fluids changed from high-temperature NaCl-H2O system fluids, that contained negligible amounts of CO2 and CH4 and exhibited obvious boiling, to a medium- to low-temperature and low-salinity NaCl–H2O system with fluid mixing. According to the HO isotopic analysis of Stages I and II (δ18OH2O = 0.3–6.3 ‰, δ18D = −112.6 to −79.9 ‰), the ore-forming fluid was identified as magmatic fluid. In contrast, the δ18OH2O and δ18D values in Stages III and IV gradually decreased (δ18OH2O = −9.6 to −2.3 ‰, δ18D = −133.1 to −118.9 ‰), implying a gradual meteoric water input into the fluid. The S isotopic analysis (δ34S range from −4 to −0.8 ‰) revealed that S mainly originates from the magma during the mineralization process. Further, the Pb isotopic (208Pb/204Pb = 37.64–38.725, 207Pb/204Pb = 15.45–15.606 and 206Pb/204Pb = 18.115 to 19.786) investigations indicated that the ore-forming materials of this deposit are derived from the crust-mantle mixing. Based on the previously reported geochronologic and geodynamic data, we can conclude that the Sankuanggou deposit is a typical FeCu skarn deposit and formed during the Early Jurassic Paleo-Pacific Plate subduction.