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The Sulu orogenic belt, formed by the collision between Sino‐Korean and South China blocks, has important geological implications due to its unique tectonic setting. To understand the deep crustal structure of the extension of the Sulu orogenic belt in the Yellow Sea, we presented a 220‐km long active‐source ocean‐bottom seismometer wide‐angle reflection/refraction profile across the Yellow Sea. The obtained P‐wave velocity structure exhibits significant horizontal and vertical variations. The middle and upper crustal regions of the north beneath the survey line exhibit a higher velocity and larger thickness than those of the south, whereas the opposite is the case with the lower crust. The lower crustal high‐velocity zone in the Northern Depression of the South Yellow Sea Basin is a manifestation of the mantle material upwelling and accretion to the lower crust. Magmatic intrusions occurred along the faults and formed a high‐velocity zone in the middle and upper crusts. Due to undulating Moho interface and varying crustal velocities, the Qingdao–Rongcheng fault is identified as a fault in the Sulu orogenic belt without the significance of tectonic zoning. This study shows that the Sino‐Korean Block, Sulu orogenic belt and South China Block are bounded by the Jimo–Muping faults (an extension to the sea), Qianliyan fault and deep fault of the South Yellow Sea. Furthermore, the Sulu orogenic belt may have been formed by the northward subduction of the South China Block beneath the Sino‐Korean Block during the Indosinian orogeny to the east of the Shandong Peninsula. [ABSTRACT FROM AUTHOR]

Lamprophyre is one of the most important probes to understand the enrichment and depletion processes of the lithospheric evolution. Determining the age and petrogenesis of lamprophyres could provide critical data for deducing the timing and process of lithospheric revolution of the Sulu Orogenic Belt (SOB) and North China Craton (NCC). In this study, the Taolin lamprophyre in SOB was delineated by zircon U–Pb dating with the ages of 126 Ma. This lamprophyre is characterized by high contents of SiO2 and total alkali contents (Na2O + K2O), low Mg# value, low contents of total Fe2O3, MgO, and compatible elements, enriched in LREE and LILE but strong depleted in HFSE, as well as enriched Sr–Nd and depleted Pb isotope compositions (87Sr/86Sr(i) = 0.707757 to 0.708048, εNd(t) = – 13.0 to – 12.7, 206Pb/204Pb(t) ratios of 16.934 to 17.000, 207Pb/204Pb(t) of 15.435 to 15.442, and 208Pb/204Pb(t) of 37.682 to 37.706). Interpretations of whole-rock elemental data suggest the Taolin lamprophyre was derived from 1% to 5% partial melting of spinel peridotite; and MELTS modelling indicates fractional crystallization of ~16.7% orthopyroxene and ~16.6% clinopyroxene under 1.5 Gbar. Based on the analyses of Neoproterozoic relic zircons and Sr–Nd–Pb isotopic components of the Taolin lamprophyre and adjacent lamprophyres, we put forwards that there are several subducted crustal materials were trapped into the SOB lithospheric mantle, and the magma source of these lamprophyres might have experienced metasomatic processes not only by the hydrous fluids derived from the subducting Paleo–Pacific oceanic crust in the Jurassic, but also by melts derived from partial melting of the subducting South China continental crust in the Triassic. A geodynamic trigger for generation of the Taolin lamprophyre is proposed to be related to lithospheric thinning coupled with asthenospheric upwelling beneath the North China Craton. [ABSTRACT FROM AUTHOR]

In order to make a new breakthrough in the exploration of crystalline graphite deposits in northern Jiangsu, it is of great significance to study the metallogenic law and prospecting model of typical graphite deposits in the Sulu orogenic belt ( Jiangsu section). By summarizing the geological and geophysical characteristics of Shuanghu graphite deposit, combined with the study of its metallogenic model and key prospecting elements, the prospecting prediction model was summarized. The research shows that the Shuanghu graphite ore body occurs in a set of marble granulite quartzite of the amphibolite marble formation of the East China Sea complex in a layered and lenticular shape. The ore bearing lithology is graphite quartzite and graphite containing marble, which is formed by multistage regional metamorphism. Shuanghu graphite mine is a regional sedimentary metamorphic crystalline graphite mine. The occurrence, scale and shape of ore (chemical) body are controlled by marble, which is not only the ore bearing parent rock, but also the ore bearing surrounding rock. The graphite mineralized body is basically consistent with the anomaly of low resistance and high polarization. On this basis, a geological geophysical prospecting prediction model is established. It can be seen that IP measurement near the ore bearing strata is a method to quickly determine the prospecting prospect [ABSTRACT FROM AUTHOR]

The Lingshan Island scientific drill confirms that two episodes (Laiyang period and Qingshan period) of rifting developed in the central Sulu orogenic belt (SOB) in Late Mesozoic. With a set of methods including fieldwork, drilling, core logging, zircon U-Pb dating and whole rock geochemistry applied, the age, the depositional sequence and the deep dynamic mechanisms of rift evolution were unraveled. The stratigraphic sequence of the Laiyang-Qingshan Groups on Lingshan Island was composed of two different rifting sequences: (1) Laiyang Group (147–125 Ma), which consists of deep-water gravity flow deposits with interlayers of intermediate volcanic rocks; and (2) Lower Qingshan Group (125–119 Ma), which unconformably overlies the former sequence and contains subaerial volcanic deposits and terrestrial deposits. The tectonic environment changed during the evolution of these two episodes of rifting: the rift was in a NNW-SSE extensional environment in the Laiyang period and showed the typical passive rifting character that "lithospheric extension and rifting preceded volcanism". The passive rifting period was ended by a short WNW-ESE compression at about 125 Ma. After that, the tectonic environment transferred to a strong NW-SE extensional environment and the rifting evolved into a volcanic arc basin in the Qingshan period. The igneous rocks are shoshonitic to high-K calc-alkaline trachyandesites to trachytes with a few intercalated lamprophyres and a rhyolite. The geochemical characteristics of the igneous rocks indicate that they are mantle-derived melts with a metasomatized mantle source and/or crustal contamination. In addition, an increased thinning of the lithosphere happened during the rifting episodes. The low-angle subduction of the Paleo-Pacific plate in the Jurassic weakened the thickened SOB lithospheric mantle. The rollback of the subducting plate started in late Jurassic to early Cretaceous, and the SOB lithospheric mantle was delaminated synchronously because of the gravity collapse. Thus, this caused passive rifting in the Laiyang period. Thereafter, the rollback and trench retreat of the high-angle subducting Paleo-Pacific plate would have achieved its climax, resulting in the strong regional extension. Passive rifting was ended by the crustal uplift caused by asthenospheric upwelling beneath the rift. The lower crust was heated by the upwelling asthenosphere and partially melted to form felsic melts, which were emplaced upwards and erupted explosively. The rift evolved into a volcanic arc basin in the Qingshan period and showed some characteristics of active rifting. Above all, a passive rifting in the Laiyang period and a volcanic arc basin in the Qingshan period developed successively in the Lingshan Island area (the central SOB). This records the transfer of the study area from the Paleo-Tethys tectonic domain to the circum-Pacific tectonic domain. The delamination of SOB lithospheric mantle and the upwelling of asthenospheric material were the deep dynamic mechanisms driving the development and evolution of two rift episodes. Additionally, the rift development was controlled remotely by the subduction of the Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

Unlike stable cratons elsewhere in the world, the lithosphere is strongly thinned in the east of both the North China Craton (NCC) and the Yangtze Craton (YZC) compared with the west. We deployed four active-source onshore-offshore wide-angle seismic survey lines in the eastern NCC and YZC from 2010 to 2016 with the aim of revealing the mechanism of lithospheric thinning and the process of the collision between the NCC and YZC. We obtained high-resolution crustal P-wave velocity models for the eastern NCC and YZC based on seismic forward modeling, travel-time tomography, and finite-difference wave-field modeling. Based on our integrated geophysical study and previous work, we propose a five-stage model for the collision between the YZC and NCC, with different dominant geodynamic mechanisms in each stage. Our collision model shows that lithospheric thinning in the eastern NCC and YZC is a consequence of the NCC-YZC collision and subduction of the Pacific plate.

The Jiaonan uplift and its adjacent areas (JUAA) are the result of collision and amalgamation of the North China plate and Yangtze plate. In this area, the tectonic environment is complex and crustal deformation is strong. However, detailed and in-depth study of the upper crustal structure and medium properties in the JUAA has not previously been performed. The high-resolution three-dimensional crustal velocity structure of the JUAA is helpful to analyze the characteristics of the crustal structure in this area and is important for evaluating the tectonic environment and medium properties of the JUAA. We obtained the three-dimensional crustal velocity structure in the JUAA using the double-difference seismic tomography technique, and found that the Rizhao area and the sea areas to its southwest in the Jiaonan uplift are characterized by a high-velocity structure, and that most of the high-velocity anomaly area is located in the sea area. The crustal velocity values of the southern end of the Yishu fault zone are also high. The high crustal velocity anomaly areas in the JUAA are considered to be caused by the upwelling of mantle material. The velocity structure of the upper crust beneath the depression structures shows notable low-velocity anomalies, which are closely related to loose sediments in the depression structures. The existence of abnormally high-velocity and low-velocity structures in the Jiaonan uplift indicates that there are substantial differences in the properties of the crustal media in the Jiaonan uplift. Crust-mantle interaction in the Jiaonan uplift is mainly concentrated in the Rizhao area and sea areas to its southwest. [ABSTRACT FROM AUTHOR]

The Wulian complex is located on the northern margin of the Sulu orogenic belt, and was formed by collision between the North China Craton (NCC) to the north and South China Craton (SCC) to the south. It consists of the metasedimentary Wulian Group, gneissic granite and meta-diorite. The U–Pb analyses for the detrital zircons from the Wulian Group exhibit one predominant age population of 2600–2400 Ma with a peak at c. 2.5 Ga and several secondary age populations of > 3000, 3000–2800, 2800–2600, 2200–2000, 1900–1800, 1500–1300 and 1250–950 Ma; some metamorphic zircons have metamorphic ages of c. 2.7, 2.55–2.45, 2.1–2.0 and 1.95–1.80 Ga, which are consistent with magmatic-metamorphic events in the SCC. Additionally, the Wulian Group was intruded by the gneissic granite and meta-diorite at c. 0.76 Ga, attributed to Neoproterozoic syn-rifting bimodal magmatic activity in the SCC and derived from partial melting of Archaean continental crust and depleted mantle, respectively. The Wulian Group therefore has tectonic affinity to the SCC and was mainly sourced from the SCC. The detrital zircons have positive and negative ϵHf(t) values, indicating that their source rocks were derived from reworking of both ancient and juvenile crustal rocks. The major early Precambrian crustal growth took place during c. 3.4–2.5 Ga with a dominant peak at 2.96 Ga and several secondary peaks at 3.27, 2.74 and 2.52 Ga. The two oldest zircons with ages of 3307 and 3347 Ma record the recycling of ancient continental crust (> 3.35 Ga) and crustal growth prior to c. 3.95 Ga in the SCC. [ABSTRACT FROM AUTHOR]

Lamprophyre dykes that crosscut different types of ultrahigh pressure (UHP) metamorphic rocks are widely distributed in the Triassic Sulu UHP orogenic belt. Although abundant studies have been performed on these dykes, their origin and petrogenesis remain topics of controversy. This study presents the results of a detailed field-based study of petrology, whole-rock geochemistry and zircon U-Pb and Lu-Hf isotopes on lamprophyre dykes exposed in the central Sulu UHP zone, aiming at shedding lights on their petrogenesis and providing clues on the geological evolution of eastern continental China during the Cretaceous. The lamprophyres are typically porphyritic, with phenocrysts dominantly composed of amphibole and clinopyroxene set in a lamprophyric matrix. The dykes have moderate SiO2 (47.70 wt.%–60.44 wt.%), variably high MgO (2.58 wt.%–8.28 wt.%) and Fe2O3T (4.88 wt.%–9.26 wt.%) contents with high Mg# of 49–66. Geochemically, they have enriched light rare earth element (REE) and flat heavy REE patterns ((La/Gd)N=5.14–10.56; (Dy/Yb)N=1.43–1.54) with negligible Eu anomalies (Eu/Eu*=0.83–1.10), and they show enrichment in large ion lithophile elements (e.g., Ba and K) but depletion in high-field strength elements (e.g., Nb, Ti and P). In-situ zircon U-Pb geochronology reveals that the lamprophyres have concordant ages of 120–115 Ma, demonstrating that the dykes emplaced in the Early Cretaceous. These zircons have εHf(t) values ranging from −26.0 to −11.0. Inherited zircons that occur in the dykes are dated to be Neoproterozoic, in line with the protolith ages of their host (i.e., the UHP rocks). An integration of these data allows us to propose that the lamprophyres were generated during the Cretaceous, by melting of subcontinental lithospheric mantle-derived metasomatite with enriched chemical compositions underneath the North China Craton. The metasomatite was formed mainly by peridotite-fluid/melt reactions, with the fluids/melts mainly liberated from subducted Yangtze continental crust during the Triassic. Regional extension, lithospheric thinning and mantle upwelling caused by rollback of the subducted paleo-Pacific plate is considered to account for the generation of the lamprophyres as well as the extensive arc-like magmatic rocks in eastern continental China during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Post-orogenic alkaline intrusions from the Sulu Orogenic Belt of eastern North China Craton consist of A-type granites. In this study, we report U–Pb zircon ages, geochemical data, Sr–Nd–Pb, and zircon Hf isotopic data for these rocks. The LA-ICP-MS U–Pb zircon analyses yield consistent ages ranging from 127.1 ± 2.4 to 119.5 ± 4.8 Ma for four samples. The alkaline rocks are characterized by high total alkalis (K2O + Na2O = 8.32–10.11 wt%), light rare-earth element enrichment, and heavy rare-earth element depletion, with a wide range (La/Yb)N values (20–48), moderate negative Eu anomalies (Eu/Eu* = 0.50–0.74), enrichment in large-ion lithophile elements (LILEs, i.e., Rb, Th, U and Pb), and depletion in Ba, Sr and high field strength elements (HFSEs, i.e., Nb, Ta, and Ti), high (87Sr/86Sr)i ranging from 0.708 to 0.7089, low εNd (t) values from −19.4 to −16.8, (206Pb/204Pb)i = 16.751 – 16.935, (207Pb/204Pb)i = 15.381−15.535, (208Pb/204Pb)i = 37.472–37.838, negative εHf (t) values between −21.3 and −25.7 for the magmatic zircons, and larger TDM2 model ages from 2.5 to 2.8 Ga. These results suggest that the rocks were derived from a common enriched lithospheric mantle source that was metasomatized by foundered lower crustal eclogitic materials before magma generation. Furthermore, the geochemical and isotopic feature implies that the primary magma of these rocks originated through partial melting of ancient lithospheric mantle that was variably hybridized by melts derived from lower crust eclogite. These rocks in this study may have been generated by subsequent fractionation of potassium feldspar, plagioclase, ilmenite, and/or rutile. However, negligible crustal contamination occurred during the diagenesis process. [ABSTRACT FROM AUTHOR]

A major and trace element, Sr–Nd–Hf isotope, and zircon U–Pb geochronology study was conducted on Early Cretaceous volcanic rocks from the northern margin of the Sulu orogenic belt in Shandong Province, eastern China. These results constrain the petrogenesis of the volcanic rocks and provide important insights into the significance of crust–mantle interaction. The rocks comprise high‐K basaltic andesite, shoshonites, latites, high‐K dacites, and high‐K rhyolites. U–Pb zircon dating of four representative samples of latite, two high‐K dacites, and high‐K rhyolite indicates that these rocks formed from 126 to 122 Ma. The volcanic rocks are characterized by high K2O (2.04–6.70 wt.%) and total alkalis (Na2O + K2O; 5.3–10.9 wt.%) that plot within the field for shoshonitic rocks. All the rocks are enriched in light rare earth and large‐ion lithophile elements (e.g., Rb, Th, U, and K) and are depleted in high‐field‐strength elements (e.g., Nb, Ta, and Ti). The rocks have high initial 87Sr/86Sr ratios (0.706760–0.708898), low εNd(t) values (−19.5 to −12.5), and negative εHf(t) values (−31.3 to −19.7), similar to the Early Cretaceous Jiaodong mafic dikes and intermediate–mafic volcanic rocks. These geochemical and isotopic characteristics indicate that the volcanic rocks formed through simultaneous fractional crystallization and crustal assimilation of a basaltic magma derived from metasomatized mantle. The metasomatized mantle source might have been produced by the recycling of subducted Yangtze Craton crust into the ancient lithospheric mantle of the North China Craton. [ABSTRACT FROM AUTHOR]

The basal conglomerates ('Linsishan Conglomerate', LC, herein) are exposed discontinuously along the northern part of the Sulu Orogenic Belt (SOB) and the southern part of the Jiaobei Terrane. Studying these conglomerates can offer key constrains for the formation age of the Jiaolai Basin and improve our understanding of the uplift and erosional histories of the SOB and Jiaobei Terrane, which are still in great controversy. In Huangyadi section, the LC is characterized as debris-flow deposits, channel deposits, and sheet-flow deposits. However, in Shanjiao section, the LC is changed to sheet-flow and sieve deposits, as well as debris-flow and channel deposits. These deposit characteristics indicate an unstable tectonic setting during initial opening stage of the basin. Based on the data of conglomerate component, palaeocurrent, and debris zircons ages, it can be inferred that the sediments in the Laiyang region were sourced from the Jiaobei Terrane and Northern Sulu Orogenic Belt (NSOB), and the sediments in the Zhucheng and Wulian regions were derived from the Jiaobei Terrane and the Southern Sulu Orogenic Belt (SSOB). Besides, the sediments in the Haiyang and Jimo regions were provided by the NSOB and SSOB, respectively. The significant SHRIMP U-Pb ages of a tuff developing in the LC has been obtained, indicating that 149 ± 2.5 Ma is the oldest age constraint for the Jiaolai Basin. In addition, our result shows that the Latest Jurassic (ca. 149 Ma) may be a critical time; before this time, the Jiaobei Terrane and the SOB experienced a rapid uplift with minimal uplift velocity (~0.9 km/Ma); since then, the Orogen began to collapse and a series of basins formed rapidly in its core, which indicate the tectonic stress regime of the Dabie-Sulu Orogen varied from compressional stress to tensile stress. [ABSTRACT FROM AUTHOR]

This study presents data of in-situ mineral major and trace element chemistry, whole-rock major and trace element and Sr-Nd isotope geochemistry, as well as zircon U-Pb dating and Lu-Hf isotope studies of andesite dykes from the Sulu orogenic belt of eastern China to evaluate their petrogenesis and thus to provide insights into crust-mantle interactions in a tectonic terrane that underwent continental subduction and was then overprinted by oceanic subduction. The andesites mainly comprise plagioclase, hornblende, clinopyroxene and magnetite as phenocrysts that are embedded in a groundmass of fine-grained quartz and K-feldspar, with minor amounts of biotite, magnetite, titanite, apatite and zircon. They possess intermediate concentrations of SiO2 (54.97-62.24 wt.%), Na2O + K2O (6.35-7.24 wt.%) and MgO (3.37-7.12 wt.%) with high Mg# values [Mg# = 100 × Mg/(Mg + Fe2+) molar] of 54-64, and are characterized by arc-like trace element patterns that are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) but depleted in high field strength elements (HFSE). The hornblende and clinopyroxene phenocrysts exhibit enrichment in Th and U but an obvious depletion of HFSE. The andesites have high initial 87Sr/86Sr ratios of 0.7073-0.7086 and negative ɛNd(t) values of −15.7 to −14.4 for whole-rock, and newly crystallized magmatic zircons show negative ɛHf(t) values of −27.0 to −17.6. U-Pb dating on syn-magmatic zircons yields consistent ages of 124 ± 2 to 116 ± 1 Ma, indicating eruption of the andesitic lavas during the Early Cretaceous. Inherited zircons are present and yield Neoproterozoic, Paleoproterozoic and Archean U-Pb ages. Taking into account all these geochemical and geochronological data, and the compositional features of contemporaneously formed mafic-andesitic igneous rocks from the Sulu belt and the adjacent continental crust of the North China Craton, we propose that the andesites crystallized from primary andesitic magmas derived from partial melting of enriched metasomatites in the subcontinental lithospheric mantle. The enriched metasomatites are inferred to be formed by a two-step process: firstly by crust-mantle interactions during the Triassic collisional orogeny and secondly by a subsequent modification by fluids/melts that mainly derive from seafloor sediments during subduction of the paleo-Pacific plate in eastern Asia. Slab rollback of the subducted paleo-Pacific slab and concomitant asthenosphere upwelling are an appropriate geodynamic mechanism for the generation of extensive arc-like magmatism during the Early Cretaceous in the Sulu belt. [ABSTRACT FROM AUTHOR]

Refertilization of depleted peridotites widely occurs in lithospheric mantle but is poorly understood in a continental subduction channel. The Sulu orogenic belt is a typical ultra-high pressure (UHP) terrane formed by continental subduction and collision. To understand the complex metasomatic processes on peridotites during continental subduction, we combined detailed petrographic and geochemical studies for fertile garnet lherzolites (Chijiadian) from the Sulu UHP terrane, as well as refractory peridotites (Xugou and Lijiatun) for comparison. The fertile garnet lherzolites (Chijiadian) are not residues of low-degree partial melting, but they formed from refertilization processes during peak-UHP metamorphic stages (garnet-facies) in a continental subduction channel, as reflected by abundant clinopyroxene (12 vol%) and garnet (12 vol%), low bulk-rock Mg# of 91 and high Al 2 O 3 of 2.4–3.3 wt%. Garnet, clinopyroxene, and orthopyroxene display secondary poikilitic textures and often contain early phases of olivine, spinel, and garnet inclusions, indicating later precipitation of these minerals into depleted peridotite protoliths. The clinopyroxenes show enrichment of large ion lithophile elements (LILE) and high 87Sr/86Sr of 0.7061–0.7084. The estimated pressure-temperature are 720–770 °C at 4.4–4.8 GPa, consistent with previous constraints on UHP conditions. These features suggest strong refertilization processes at UP-UHP conditions (garnet-facies) in continental subduction channels. The metasomatic agents for refertilization would be basaltic-intermediate melts which incorporated continental materials. Similarly, Xugou harzburgites and Lijiatun dunites also record the subducted continental signatures with enrichment of LILE and high Sr isotopes on clinopyroxenes (87Sr/86Sr: 0.7050 to 0.7065). However, Xugou harzburgites and Lijiatun dunites overall do not display the same typical refertilization features as for Chijiadian, as reflected by low abundances of clinopyroxene and high Mg# of 92–93. Consequently, continental subduction could lead to diverse types of metasomatism of refractory peridotites, including refertilization at UP-UHP metamorphic stages in subduction channels, as in other tectonic settings. • Secondary garnet lherzolites formed from refertilization at high-pressure condition in the subduction channel. • Continental subduction could lead to diverse types of metasomatism. • Continental subduction also drives the formation of refertilized lherzolites as other tectonic settings. [ABSTRACT FROM AUTHOR]

As a minor phase, kyanite has been repeatedly shown to have experienced ultrahigh pressure (UHP) metamorphism together with its host eclogites. Thus, it could play some role in transporting water into the deep earth. Here we present a detailed investigation of water concentrations of kyanite, and for reference, of garnet and omphacite from four Maobei eclogites in the Sulu orogenic belt, eastern China. Fourier transform infrared (FTIR) measurements show that kyanites, garnets, and omphacites all have distinct hydroxyl absorption bands due to OH groups bound in their crystal structure. The FTIR profile analyses on ten grains from different samples reveal a homogeneous distribution of water across kyanite, suggesting insignificant water loss during exhumation. The calculated water concentrations in kyanite (21 wt ppm-41 wt ppm) are comparable to those reported previously for kyanite from various geological occurrences when using the most recent calibration. They are however much lower compared with those in garnet (46 wt ppm-83 wt ppm) and omphacite (302 wt ppm-548 wt ppm) from the Maobei eclogites. This implies that kyanite is not a major water carrier in eclogites considering its low volume fraction and contributes negligibly to transport water into the deep mantle accompanying subducted oceanic crust until its possible transformation to AlSiOOH. [ABSTRACT FROM AUTHOR]

The Sulu Orogenic Belt in eastern China has experienced a multistage tectonic evolutionary history. However, its geological evolution has not yet been corroborated by sufficient direct evidence from basement rocks. Chaolian Island on the Qianliyan Uplift provides an opportunity to study the formation and evolution of the Sulu Orogenic Belt using direct geochronological and geochemical evidence. We determined that the characteristic mineral assemblage in the study region is quartz + K-feldspar + perthite + biotite + muscovite. The samples are silica- (SiO2 = 72.8%–75.8%) and alkali-rich (ALK(Na2O+K2O) = 8.7%–9.3%), with high iron-magnesium ratios (FeO /(FeO +MgO) = 0.92–0.96) and low CaO and MgO concentrations. Furthermore, they are rich in large-ion lithophile elements K, Rb, Ba, and U, but depleted in high field strength elements Nb, Ta, and Zr. They exhibit high Ga/Al values (Ga × 104/Al = 3.33–3.74) and significant fractionation between light and heavy rare earth elements. The samples are A-type granites. In the discrimination diagrams for granite genesis types, the samples plotted in the post-orogenic A2-type granite region. Secondary ion mass spectrometer (SIMS) zircon U–Pb dating results indicated that the granitic gneiss formed ~782.6–802.3 Ma (Middle Neoproterozoic), consistent with the timing of the breakup of the Rodinia supercontinent on the northeastern margin of the Yangtze Plate. Comparing geochemical characteristics and zircon U–Pb ages of the A-type granitic gneisses of the Sulu Orogenic Belt, the Qianliyan Uplift appears to be an extension of the belt across the ocean and is affiliated with the Yangtze Plate. The granitic gneiss on Chaolian Island is related to the formation of a mantle superplume during the breakup of Rodinia, and the northeastern margin of the Yangtze Plate during the Middle Neoproterozoic was located in a back-arc extension setting induced by the subduction of oceanic plates. [ABSTRACT FROM AUTHOR]

The operation of early plate tectonics is evidenced by belt-like occurrences of some Neoarchean–Paleoproterozoic (ca. 2.7–1.8 Ga) high-grade basement rocks in ancient continental blocks. Studies on the continental evolution of the North China Craton defined Paleoproterozoic mobile/orogenic belts in this continental block, which are usually regarded as solid evidence for the operation of plate tectonics during the Paleoproterozoic. However, if considering subsequent tectonic overprinting, then whether the current occurrences of these mobile belts can represent the primary tectonic geometry remains unclear. The high-grade Jiaobei Terrane is centrally located within one such Paleoproterozoic mobile belt, namely the Jiao–Liao–Ji mobile belt of the eastern North China Craton. Archean–Paleoproterozoic basement rocks are well preserved in this terrane and its multiple episodes of metamorphism are similar in age with those of the other Paleoproterozoic mobile belts of the craton. Additionally, Phanerozoic tectonothermal overprinting in this terrane also widely influenced much of the whole North China Craton. Most importantly, the basement rocks occurring in different regions of this terrane exhibit different metamorphic grades. Therefore, this terrane is ideal for identifying how the high-grade basement components, after repeated episodes of exhumation, were finally emplaced on the surface in the Phanerozoic. The Archean–Paleoproterozoic lithologies of the Jiaobei Terrane mainly consist of Archean tonalite–trondhjemite–granodiorite gneisses (TTGs) and Paleoproterozoic meta-volcanosedimentary rocks, as well as a small amount of Paleoproterozoic granitoids. The Archean TTGs occupy the central part of the Jiaobei Terrane and exhibit three episodes of magmatism at ca. 2.9 Ga, ca. 2.7 Ga, and ca. 2.5 Ga, respectively. The Paleoproterozoic meta-volcanosedimentary sequences are further divided into the Jingshan Group and the Fenzishan Group, which mainly occur in the southern and northern margins of the Archean gneisses, respectively. Despite this division, both groups have similar protoliths and geochronological frameworks. The Jiaobei Terrane was subjected to two episodes of high-grade metamorphism during the Neoarchean (ca. 2.57–2.46 Ga) and the Paleoproterozoic (ca. 1.98–1.78 Ga). Although the Neoarchean metamorphism has been identified in many places of the Jiaobei Terrane, its geological implications are equivocal because of pervasive and strong Paleoproterozoic metamorphic overprints. The Paleoproterozoic high-grade metamorphism greatly influenced the whole terrane, and pelitic and mafic granulites have been reported along the southern margin of the high-grade metamorphic terrane bordering the North Sulu ultrahigh-pressure (UHP) belt. The metamorphic pressure and temperature conditions and the pressure-temperature (P–T) paths of these granulites are comparable to those of the Phanerozoic, indicating that the continental crust has maintained similar thermal and mechanical characteristics since at least the Paleoproterozoic in certain tectonic settings. A synthesis of previous studies in combination with new petrographic observations reveals clear spatial variations in the metamorphic grade for the Paleoproterozoic metamorphism in the Jiaobei Terrane, with granulite-facies rocks occurring only along the southern margin and the metamorphic grade gradually changing to amphibolite and greenschist facies towards the north. Even though the amphibolite and granulite facies rocks show distinct mineral assemblages, their metamorphic geochronology and metamorphic reaction textures (especially the symplectite around garnet grains) observed in the thinsection are strikingly similar. Therefore, we infer that these rocks showing different metamorphic grades represent a cross-section of the continental crust, with the granulites representing lower crustal components and the amphibolites representing exposed rocks of the shallower crustal levels. The strike direction of the variable metamorphic grades is notably subparallel with the North Sulu orogenic belt. The early Precambrian basement rocks along the southern Jiaobei Terrane and within the Phanerozoic fault zone also show Permo–Triassic metamorphic overprinting associated with the Sulu UHP orogenesis. The spatial variations in metamorphic grade as well as the Permo–Triassic overprint, thus, imply that the final emplacement of Jiaobei Terrane basement components was related to the continental collision process between the North China and South China cratons. Therefore, the belt-like occurrences of the Paleoproterozoic granulites in this region should not be regarded as representing the primary tectonic geometry of the Paleoproterozoic orogenic belt. This inference based on the Jiaobei Terrane should also apply to other high-grade terranes of the North China Craton considering that basement rocks are more often exposed in high-elevation regions caused by Phanerozoic tectonothermal events. [ABSTRACT FROM AUTHOR]

Processes related to the subduction of the South China Block beneath the North China Block and collision of the two blocks along the Qingling–Dabie–Sulu Orogenic Belt have been well studied. Different tectonic models have been proposed based on time constraints of metamorphism and magmatism and the uplift and exhumation of the HP–UHP metamorphic belt. However, propagation of the foreland thrust belt during the collision along the eastern North China Block has not been well documented, leading to a weak understanding of the collision process. The Liaodong Peninsula, 200–300 km northeast of the Sulu Orogenic Belt, is an essential area for the study of the foreland thrust belt. The rocks of the peninsula record at least three deformation events during the Mesozoic: D 1 NW–SE folds and thrust faults that were strongly overprinted by D 2 NE–SW thrusts and folds and D 3 large-scale regional extensional structures. According to detailed geological investigation and tectonic stress reconstruction using striations and dolomite twins, seven imbricate fold–thrust units in the Pulandian, Guiyunhua and Qingchengzi areas of Liaodong Peninsula were defined as representing the D 1 deformation. Together with thrust units in the southernmost part of Liaodong Peninsula and on the northern Jiaodong Peninsula, a top-to-the-NE propagated fold–thrust belt is proposed for the eastern North China Block. U Pb ages of zircons from three post-tectonic dyke samples in the Qingchengzi area, combined with previous geochronological results, constrain the D 1 deformation at 249–224 Ma. We suggest that the collision of the South China and North China blocks along the Sulu Orogenic Belt and the subduction of the South China Block beneath the North China Block resulted in NE–SW compression, formation of a detachment fault in the deep crust, and propagation of a fold–thrust belt toward the NE in the upper plate along the eastern margin of the North China Block. [Display omitted] • Middle-Late Triassic fold-thrust belts with top-to-the-NW kinematics were distinguished in Liaodong Peninsula. • New and previous age results constrain the fold-thrust deformation at 249–224 Ma. • The collision between the NCB and SCB is proposed to result in the propagation of foreland thrust belt in northeast China. [ABSTRACT FROM AUTHOR]

Recent studies have documented marine turbidites with syn-sedimentary deformation features in the central Sulu orogenic belt of eastern China. These units preserve essential information on the Late Mesozoic evolution of the Sulu orogenic belt. Referred to as the Baxiandun Formation, the turbidites exhibit similar lithologic characteristics to nearby units such as the Lingshandao Formation that have been well studied even though precise geochronologic constraints are lacking for a more precise correlation. This study reports detrital zircon U Pb age data that correlate the Baxiandun Formation turbidites of the central Sulu orogenic belt to the Early Cretaceous Lingshandao Formation. We also report Al-in-hornblende emplacement depth estimates for granitic intrusions of the Sulu orogenic belt's Laoshan mountain. A sharp contact between the Laoshan granites and the marine Baxiandun Formation indicates that the Baxiandun basin rapidly subsided to the emplacement depth of the Laoshan plutons. Lateral correlation among the marine turbidites, the Lingshandao and Baxiandun Formations, combined with information established by previous studies indicates initiation of transpressional tectonics at 122–121 Ma. Transpression ceased with the emplacement of the Laoshan granites, whose A1-type composition indicates a return to extensional tectonics at ca. 111 Ma. [ABSTRACT FROM AUTHOR]

Widespread Late Mesozoic igneous events in northern China have been intensively investigated over the past decades and provide evidence for regional lithospheric thinning. The underlying mechanism causing lithospheric thinning remains unclear however. This study reports U–Pb zircon ages, geochemical data and isotopic ratios for Cretaceous igneous units from the central Sulu orogenic belt as it occurs in the Shandong Peninsula. LA-ICP-MS U–Pb analyses of magmatic zircons identified a relatively restricted population of ages ranging from 123 ± 2 Ma to 120 ± 2 Ma from four representative samples of igneous units in the study area. Geochemical analysis of the samples revealed LREE and LILE enrichment, HREE depletion, high initial 87 Sr/ 86 Sr values ranging from 0.7040 to 0.7096, and low negative ε Nd ( t ) values from −22.0 to −12.2. The data suggest lamprophyres derived separately from heterogeneous mantle inputs, which experienced crust–mantle interaction, andesitic porphyrites and syenogranites derived from enriched lithospheric mantle and rhyolites derived from partial melting of an ancient crustal component. Assimilation and fractionation processes did not contribute to lamprophyre formation, but did play an important role in generating andesitic porphyrites, syenogranites and rhyolites. The petrogenetic history of these rocks indicates intensive lithospheric thinning of the upper mantle and lower crust beneath the Sulu orogenic belt at 123–120 Ma. Given the timing and regional tectonic framework in which these units formed, thinning was likely caused by an abrupt change in the direction of the subducting Pacific plate. [ABSTRACT FROM AUTHOR]

Abstract: Detailed mineralogical and geochemical studies have been carried out on a suite of pyroxenite xenoliths captured in a late Mesozoic basaltic dike from Junan, eastern Shandong, which is tectonically situated in the Sulu ultrahigh pressure orogenic belt. Two types of pyroxenites, namely websterite and garnet pyroxenite were identified according to their mineral assemblages. The equilibrium temperatures (828–935°C) of websterite and garnet pyroxenite xenoliths, falling within the temperature range of lower crustal xenoliths, suggest that they were derived from the lower crust rather than the lithospheric mantle. The websterite xenoliths are characterized by higher MgO and lower Al2O3; their convex upward REE patterns, along with lower concentrations of highly incompatible elements indicate that they were high pressure cumulates. Their extremely unradiogenic Nd and radiogenic Sr isotopic compositions imply the contribution of crustal materials to their sources. It is suggested that the precursor melts of websterite xenoliths were derived from a mantle source which had been intensely modified by the subducted lower continental crust of the Yangtze craton following the collision with the North China craton in the Triassic. The compositional features of garnet pyroxenites also suggest their cumulative origin, however, the sharp contrast in trace element concentrations and Sr–Nd isotopic compositions with those of websterite xenoliths indicate they have different precursor melts. Their Sr and Nd isotopic compositions are consistent with the suggestion that their precursor melts were derived from an enriched lithospheric mantle which had been metasomatized by melts released from the Proto-Tethyan oceanic crust which was subducted into the mantle prior to the subduction of continental crust of Yangtze craton. The occurrence of websterite and garnet pyroxenite xenoliths provide evidence that the lithospheric mantle of the North China craton had been significantly modified by the recycled oceanic and continental crust resulting from the collision between the Yangtze craton and the North China craton. [Copyright &y& Elsevier]

Combined with field studies, microscopic observations, and EBSD fabric analysis, we defined a possible Early Cretaceous metamorphic core complex (MCC) in the Wulian (五莲) area along the Sulu (苏鲁) orogenic belt in eastern China. The MCC is of typical Cordilleran type with five elements: (1) a master detachment fault and sheared rocks beneath it, a lower plate of crystalline rocks with (2) middle crust metamorphic rocks, (3) syn-kinematic plutons, (4) an upper plate of weakly deformed Proterozoic metamorphic rocks, and (5) Cretaceous volcanic-sedimentary rocks in the supradetachment basin. Some postkinematic incursions cut across the master detachment fault zone and two plates. In the upper plate, Zhucheng (诸城) Basin basement consists of the Proterozoic Fenzishan (粉子山) Group, Jinning period granite (762-834 Ma). The supradetachment basin above the Proterozoic rocks is filled with the Early Cretaceous Laiyang (莱阳) (∼135-125 Ma) and Qingshan (青山) groups (120-105 Ma), as well as the Late Cretaceous Wangshi (王氏) Group (85-65 Ma). The detachment fault zone is developed at the base and margin of the superposed basin. Pseudotachylite and micro breccia layers located at the top of the detachment fault. Stretching lineation and foliation are well developed in the ductile shear belt in the detachment faults. The stretching lineation indicates a transport direction of nearly east to west on the whole, while the foliations trend WNW, WSW, and SE. Protomylonite, mylonite, and ultramylonite are universally developed in the faults, transitioning to mylonitic gneiss, and finally to gneiss downward. Microstructure and quartz preferred orientation show that the mylonites formed at high greenschist facies to low greenschist facies as a whole. The footwall metamorphic rock series of the Wulian MCC are chiefly UHP (ultrahigh pressure) metamorphic rocks. Syntectonic rocks developed simultaneously with the Wulian MCC detachment and extension. Geological research has demonstrated that the MCC is associated with small-scale intrusive rocks developing in the vicinity of the detachment faults, for instance, dike. Geochronology results indicate that the denudation of the Wulian MCC occurred at about 135-122 Ma. Its development and exhumation was irrelevant to the Sulu UHP metamorphism zone rapid exhumation during Triassic Period but resulted from the crustal extension of North China Craton and adjacent area. [ABSTRACT FROM AUTHOR]

Abstract: The Dadian alkaline intrusive complex is located within the Sulu orogenic belt, and includes hornblende syenite, syenite, quartz syenite and syenite porphyry. All the rocks from the complex show high SiO2, K2O+Na2O and LREE and low CaO, FeOT, MgO and HFSE (Nb, Ta, P, Ti) concentrations. The Sr, Nd, and Hf isotopic compositions ((87Sr/86Sr)i =0.708505–0.70876, εNd(t)=−16.5 to −17.9, εHf(t)=−21.5 to −16.4) of the rocks fall within the compositional field of mafic dykes occurring nearby, suggesting that the Dadian alkaline complex was mainly derived from an enriched lithospheric mantle. The initial Pb compositions ((206Pb/204Pb)i =16.706–16.779, (207Pb/204Pb)i =15.427–15.450, (208Pb/204Pb)i =37.266–37.352) of the Dadian rocks are lower than those of the Yangtze lithospheric mantle, albeit similar to that reported from beneath the North China Craton, implying that the mantle source of the Dadian alkaline complex most likely belong to the North China Craton. The relatively high SiO2 and HREE contents and low Nb/Ta ratios as well as strongly negative Eu and Sr anomalies of some of the rocks from the Dadian complex suggest that crustal material was also involved in the formation of this complex and that the crustal component was probably derived through partial melting at low pressure. The high crystallization temperatures revealed by zircon saturation thermometry and low pressures suggested by Al-in-hornblende barometry indicate that the Dadian alkaline complex crystallized at high temperature and intruded into shallow crustal level. This intrusive complex does not show any relationship with post-orogenic process in the region, and its petrogenesis is inferred to be associated with the Paleo-Pacific subduction tectonics. [Copyright &y& Elsevier]

Origin of the continental-scale Tan-Lu fault zone (TLFZ), East China, remains controversial. About 550 km sinistral offset of the Dabie orogenic belt (DOB) and Sulu orogenic belt (SOB) is shown along the NE-NNE-striking TLFZ. Syn-collisional, sinistral ductile shear belts in the TLFZ have been identified. Thirteen phengite bulk separates from the mylonites were dated by the 40Ar/39Ar method. They gave cooling ages of the 198–181 Ma for the shear belts along the eastern margin of the DOB and 221–210 Ma from the western margin of the SOB. Distribution of the foreland basin deposits suggests that sinistral offset of the DOB and SOB by the TLFZ took place prior to deposition of the Upper Triassic strata. The marginal structures around the DOB and SOB support syn-collisional faulting, and indicate anticlockwise rotation of the DOB during the displacement. The folding and thrust faulting related to crustal subduction, coeval with the Tan-Lu faulting, is older than the foreland basin deposition related to the orogenic exhumation. Several lines of evidence demonstrate that the TLFZ was developed as a syn-collisional transform fault during latest Middle to earliest Late Triassic time when the DOB and SOB experienced crustal subduction of the South China Block (SCB). Eastward increase of the crustal subduction rates is believed to be responsible for the sinistral transform faulting. [ABSTRACT FROM AUTHOR]

By using data on the 1:100 000 aeromagnetic anomalies of the Sulu orogenic belt, we designed three simulated geotraverses, in which deep seismic reflection and other geophysical investigations have been completed. Based on the features of magnetism of the three profiles, and under the constraints of deep seismic reflection data, together with the magnetism of the core petrology at the Chinese Continental Scientific Drilling (CCSD) pilot-hole and areal geology, the three inversions of magnetic anomalies are carried out. The characteristics of terrane structure are presented: the rocks are mostly composed of eclogite, marble, and gneiss at the depth of 5 km. At the depth between 5 and 7 km under the surface, inverse magnetic bodies are mainly the ultra high pressure metamorphic (UHPM) rock slices containing a lot of coesite-bearing eclogite. At the depth between 7 km and the bottom of upper crust are the rocks of the gneiss, granite and granite diorite that underwent ultra high pressure metamorphic process. Middle crust (10–19 km) is mostly composed of UHPM gneiss and granite that intruded later. The rocks of acid and basic granulite dominate the lower crust. Based on the inversed results of the three simulated geotraverses, we know that the UHPM rock slices of the three profiles are dipping north, stacking each other and being uplifted to the earth’s surface, which may be the result of the North China craton’s subduction and exhumation in the Triassic. [ABSTRACT FROM AUTHOR]

The origin of ultramafic rocks, especially those in suture zones, has been a focus because they are not only important mantle sources of magma, but also provide substantial information on metamorphism and melt/fluid–peridotite interaction. Ultramafic rocks in Hujialin, in the central part of the Sulu orogen, include peridotite and pyroxenite. Although many papers on their origin and tectonic evolution have been published in the past few decades, these questions are still highly debated. Here, we present mineralogy, mineral composition, and bulk-rocks of these ultramafic rocks to evaluate their origin and tectonic evolution. The garnet clinopyroxenite is low in heavy rare-earth elements (HREE, 5.97–10.6 ppm) and has convex spoon-shaped chondrite-normalized REE patterns, suggesting the garnet formed later, and its precursor is clinopyroxenite. It is high in incompatible elements (i.e., Cs, Rb, Ba) and shows negative to positive U, Nb, and Ta anomalies, without pronounced positive Sr or Eu anomalies. Clinopyroxene in garnet clinopyroxenite contains high MgO (Mg# 0.90–0.97). The mineral chemistry and bulk-rock compositions are similar to those of reactive clinopyroxenite, suggesting that it originally formed via peridotite–melt interaction, and that such silicic and calcic melt might derive from the subducted Yangtze continent (YZC). Dunite contains olivine with high Fo (93.0–94.1), low NiO (0.11–0.29 wt.%) and MnO (≤0.1 wt.%), chromite with high Cr# (0.75–0.96), TiO2 (up to 0.88 wt.%), and Na2O (0.01–0.10 wt.%). It has negatively sloped chondrite-normalized REE patterns. Mineral chemistry and bulk rocks suggest dunite likely represent residual ancient lithosperic mantle peridotite beneath the North China Craton (NCC) that was overprinted by aqueous fluids. The lack of prograde and retrograde metamorphic minerals in dunite and irregular shaped mineral inclusions in chromite suggest dunite did not subduct to deep levels. Dunite mingled with garnet clinopyroxenite during exhumation of the latter at shallow depths. These ultramafic rocks, especially hydrated peridotite, may be important sources of Au for the Jiaodong gold province in the NCC. [ABSTRACT FROM AUTHOR]

[Display omitted] • The parent magma of the ~130 Ma Taolin intrusion was derived from melting of the Yangtze crust. • The Early Cretaceous igneous event in the Sulu orogenic belt was related to an extensional setting. • Variable protoliths and complex magmatic processes led to the diversity of felsic rocks. Early Cretaceous felsic intrusions are widely exposed in the Sulu orogenic belt (SOB), eastern China. The Taolin granitic intrusion is an example of these intrusions and mainly comprises monzogranite, syenogranite, and granite. Here we present new geochronological and geochemical data for the intrusion. The ~130 Ma Taolin intrusion belongs to normal to fractioned I-type granite and is divided into two groups based on geochemical differences. Rocks in the Daxiezhuang and Malingzhan units belong to Group 1 and have relatively low SiO 2 (61.35–69.44 wt%), high Sr/Y ratios (26.04–60.18), low εHf(t) values (−27.2 to −21.4), and old T DM2 ages (2541–2903 Ma). They also display weak to no negative Eu anomalies (Eu/Eu*=0.65–1.29). Rocks from the Shibu and Tiqiushan units belong to Group 2 and have relatively high SiO 2 (76.38–77.68 wt%), low Sr/Y ratios (0.61–12.38), high εHf(t) values (−24.3 to −17.2) and young T DM2 ages (2271–2722 Ma). They have obviously negative Eu anomalies (Eu/Eu*=0.10–0.42). The partial melting of the Yangtze continental crust at different depths led to variable elemental and isotopic compositions of magma in Group 1 and Group 2. The SOB was in an extensional environment during the Early Cretaceous, which allowed the formation of felsic magmatic rocks with low Sr, Sr/Y, and Sr/CaO values. Early Cretaceous felsic magmatic rocks in the SOB were mainly sourced from the continental crust by crustal reworking. There are diverse rock types with variable geochemical features in the SOB, which is ascribed to the heterogeneity of the continental crust and the complex evolution of felsic magma. [ABSTRACT FROM AUTHOR]

It is well known that the Dabie-Sulu orogenic belt resulted from the northward continental subduction of the South China Block (SCB) beneath the North China Block (NCB) during the Triassic. Correlating the deformation events recorded in the subducted and overriding plates is essential to understand its tectonic evolution, but related deformation is poorly documented in the overriding plate. In this contribution, we present detailed structural analysis, anisotropy of magnetic susceptibility (AMS), and geochronological data in the Linsishan unit of the Jiaobei massif, the overriding plate of the Sulu orogenic belt. The Linsishan unit preserves a significant ductile deformation characterized by NNW-, NE-, or SE-dipping foliations with NE–SW trending mineral lineations. Coupling mesoscopic and magnetic fabrics augment the NE–SW linear structures. The NE-dipping monoclinal structures with top-to-SW kinematics could be interpreted as a SW-directed thrusting, the deformation temperature of which is 350–450 °C according to the quartz c-axis fabrics. The timing of deformation is constrained to be 223–221 Ma based on 40Ar/39Ar dating of the deformed rocks and linked with a syn -collisional stage in the Sulu orogenic belt. Combining these new results with previous works, we propose a three-stage evolution model for the Sulu orogenic belt, namely (1) subducted SCB experienced ultra-high pressure (UHP) metamorphism before 230 Ma; (2) SW-directed thrusting was developed in the overriding plate, coeval with the syn -collisional exhumation of UHP rocks during 230–220 Ma; (3) post-collisional migmatization, magmatism, extension, and UHP rocks exhumation took place at 220–205 Ma. • Late Triassic SW-directed thrusting is reported in the overriding plate of Sulu belt. • New data improve our understanding of tectonic evolution of Sulu orogenic belt. • Structural and AMS data are combined to understand the geometry of gneissic domain. [ABSTRACT FROM AUTHOR]

The Sulu orogenic belt is the source of information on important magmatic events associated with the collision of the Yangtze craton and North China craton (NCC) and the destruction of the NCC during the Mesozoic in eastern China. In this study, we have, for the first time, identified a monzonitic granitic pluton. We hereby present petrological, geochemical, and zircon U-Pb-Hf-O isotopic data, shedding new light on the petrogenesis and tectonic implications for the granitic pluton in the Sulu belt. LA-ICP-MS and SHRIMP II analyses of zircon grains suggest that the monzonitic granitic pluton was crystallized in the Early Cretaceous (ca. 120 Ma). Geochemically, the granitic pluton shows sub-alkaline, high-K calc-alkaline, and metaluminous signatures, and is genetically of I-type granite, excluding the possibility of S-type granite, as evidenced by mantle-like zircon oxygen isotopic features. In addition, the pluton is enriched in light REE and large-ion lithophile elements (LILE) (e.g., La, Cs, Ba, K, and Pb), but depleted in high-field-strength elements (HFSE) (e.g., Nb, Ta, P, and Ti), suggesting an arc-related affinity. Zircon Hf isotopes (εHf(t) = −27.51~−32.35; TDM2 = 2979~3175 Ma) and mantle-like δ18O values (5.12–6.24‰) together indicate that the identified granitic pluton is derived from the partial melting (reworking) of the ancient mafic lower crustal material, with no supra-crustal material participation. Moreover, high Magnesium number (Mg# = 42–49) values and mafic micro-granular enclaves suggest that mantle-derived magma participated in the evolution of the granitic pluton in this study. Integrating the findings of this study and previous work, we propose that the Caochang granitic pluton is derived from the partial melting of the deep Yangtze basaltic lower crust during the Early Cretaceous, and that the large-scale thinning of the lithospheric mantle was the main factor that led to Early Cretaceous magmatic flare-up in the Sulu orogenic belt. [ABSTRACT FROM AUTHOR]

The Rizhao Hujialin area is located in the central Sulu ultrahigh-pressure orogenic belt, where garnet clinopyroxenite is exposed in the upper part of an ultramafic rock complex and serpentinized dunite is exposed in its lower part. Based on textural criteria, the garnet clinopyroxenites were divided into three types: Equigranular garnet, porphyroclastic garnet, and megacrystic garnet pyroxenites. The garnet clinopyroxenites have convex-upward chondrite-normalized rare earth element patterns, large positive Pb anomalies, and depletion of high-field-strength elements (e.g., Nb, Zr, and Ti), suggesting a mantle source protolith overprinted by fluid metasomatism. Petrographic, mineral chemistry, phase equilibrium modeling, and zircon U–Pb geochronology data show that the evolutionary stages of the Hujialin garnet clinopyroxenites were as follows: Stage I: formation of the magmatic protoliths; stage II: formation of megacrystic garnet pyroxenite accompanying subduction; stage III: formation of porphyroclastic or equigranular garnet clinopyroxenite with a mineral assemblage of garnet + clinopyroxene + ilmenite + humite accompanying initial exhumation at ~215.0 ± 5.7 Ma; stage IV = progressive cooling and decompression associated with the crystallization of water-bearing minerals such as clinochlore and pargasite at 206 Ma; and Stage V = late epidote amphibolite-facies retrograde metamorphism producing a mineral assemblage of garnet + clinopyroxene + amphibole + chlorite + epidote + ilmenite at ~180–174 Ma associated with fluid activity in shear–tensional fractures and/or pores. The P-T conditions of the peak metamorphism were estimated at 4.5 ± 0.5 GPa and 800 ± 50 °C. Retrograde metamorphism recorded conditions of 1.0 GPa and 710 ± 30 °C during the exhumation and cooling process. The mineral transformation from early high-Al clinopyroxene to garnet and to late diopside records the general metamorphic evolution during subduction and exhumation, respectively. One zircon U–Pb analysis presents the Palaeoproterozoic age of 1817 ± 40 Ma, which is coeval with widespread magmatic and metamorphic events in the North China Craton. [ABSTRACT FROM AUTHOR]

The Jiaodong Peninsula in North China is an important Chinese gold mining region, and deposits are mainly controlled by the northeast trending Sanshandao, Jiaojia, and Zhaoyuan–Pingdu faults. Most previous study results proposed the relationships of the known deposits, controlling faults and regional tectonics. One important tectonic belt, the Sulu Orogen, is thought to be related with mineralization and controlling faults. But debates remain concerning the orogeny boundary and tectonic process. We arranged 32 magnetotelluric stations in one line across the central and southern Jiaodong area to analyze the deep electrical structure of this orogeny. After the data collection (using Phoenix instruments) and pre-processing (Phoenix software), we carried out impedance analysis, data selection, static shift correction and three-dimensional inversion using our software. The results consequently proposed that the distribution of upwelling hydrous basaltic magma acts as conductor in the lower crust. We also proposed the boundary of the North China Block and the Sulu Orogenic Belt by the difference of electrical structure, and suggested a possible collision–coupling process. After the formation of the Jiaobei uplift and Sulu Belt in the subduction process, the tectonic regime was transformed from compression to extension indicated by the conductors. The clockwise rotation of the Yangtze Block might be carried out under the extension setting with the southern Dabie Belt acting as the stress fulcrum. [ABSTRACT FROM AUTHOR]