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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]

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]

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]

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]