Experimental study on reactions between alkaline basaltic melt and orthopyroxenes: constraints on the evolution of lithospheric mantle in the North China Craton

The experimental results of the reactions between an alkaline basaltic melt and mantle orthopyroxenes under high-temperature and high-pressure conditions of 1300–1400℃ and 2.0–3.0 GPa using a six-anvil apparatus are reported in this paper.The reactions are proposed to simulate the interactions between melts from the asthenospheric mantle and the lithospheric mantle.The starting melt in the experiments was made from the alkaline basalt occurring in Fuxin,Liaoning Province,and the orthopyroxenes were separated from the mantle xenoliths in Damaping,Hebei Province.The results show that clinopyroxenes were formed in all the reactions between the alkaline basaltic melt and orthopyroxenes under the studied P–T conditions.The formation of clinopyroxene in the reaction zone is mainly controlled by dissolution–crystallization,and the chemical compositions of the reacted melt are primarily infl uenced by the diff usion eff ect.Temperature is the most important parameter controlling the reactions between the melt and orthopyroxenes,which has a direct impact on the melting of orthopyroxenes and the diff usion of chemical components in the melt.Temperature also directly controls the chemical compositions of the newly formed clinopyroxenes in the reaction zone and the reacted melt.The formation of clinopyroxenes from the reactions between the alkaline basaltic melt and orthopyroxenes can result in an increase of CaO and Al_(2)O_(3) contents in the rocks containing this mineral.Therefore,the reactions between the alkaline basaltic melt from the asthenospheric mantle and orthopyroxenes from the lithospheric mantle can lead to the evolution of lithospheric mantle in the North China Craton from refractory to fertile with relatively high CaO and Al 2 O 3 contents.In addition,the reacted melts in some runs were transformed from the starting alkaline basaltic into tholeiitic after reactions,indicating that tholeiitic magma could be generated from alkaline basaltic one via reactions between the latter and orthopyroxene.

Characteristics and main controlling factors of helium resources in the main petroliferous basins of the North China Craton

At present, the main controlling factors of helium accumulation is one of the key scientific problems restricting the exploration and development of helium reservoir. In this paper, based on the calculation results of He generation rate and the geochemical characteristics of the produced gas, both the similarities and differences between natural gas and He resources in the Bohai Bay, Ordos and the surrounding Songliao Basin are compared and analyzed, discussing the main controlling factors of helium resources in the three main petroliferous basins of the North China Craton. It is found that the three basins of Bohai Bay, Ordos and Songliao have similar characteristics of source rocks, reservoirs and cap rocks, that's why their methane resource characteristics are essentially the same. The calculated ~4He generation per cubic metamorphic crystalline basement in the three basins is roughly equivalent, which is consistent with the measured He resources, and it is believed that the ~4He of radiogenic from the crust is the main factor controlling the overall He accumulation in the three basins;there is almost no contribution of the mantle-derived CH_4, which suggests that the transport and uplift of mantle-derived ~3He carried by the present-day magmatic activities along the deep-large faults is not the main reason for the mantle-derived ~3He mixing in the basins. Combined with the results of regional volcanic and geophysical studies,it is concluded that under the background of the destruction of North China Craton, magma intrusion carried a large amount of mantle-derived material and formed basic volcanic rocks in the Bohai Bay Basin and Songliao Basin, which replenished mantle-derived ~3He for the interior of the basins, and that strong seismic activities in and around the basins also promoted the upward migration of mantle source ~3He. This study suggests that the tectonic zone with dense volcanic rocks in the Cenozoic era and a high incidence of historical strong earthquakes history may be a potential area for helium resource exploration.

Assembly, Accretion and Break-up of the Paleo-Mesoproterozoic Columbia(Nuna) Supercontinent: Records in the North China Craton

Columbia(Nuna)is a Paleo-Mesoproterozoic supercontinent that was assembled during global 2.0–1.8Ga collisional events,underwent long-lived,subductionrelated accretion at key continental margins in the period

Final-stage Southward Subduction of the Eastern Paleo-Asian Ocean:Evidence from the Middle Permian Mafic Intrusions in the Northern Margin of the North China Craton

The northern margin of the North China Craton(NCC)contains widespread Permian magmatic rocks,but the origin of these rocks remains controversial.This uncertainty hampers us from better understanding of tectonic framework and evolution of the eastern Paleo-Asian Ocean,particularly with respect to its final-stage subduction and closure time.To address these questions,this study presents petrological,zircon U-Pb geochronological,whole-rock geochemical and in situ zircon Hf isotopic data for these Permian mafic intrusions in the northern margin of the NCC.Precise zircon U-Pb dating results indicate that these mafic intrusions were emplaced in the Middle Permian(ca.260 Ma).Geochemically,the studied mafic intrusions have high MgO and transition metals element contents,with high Mg^(#) values,indicating a mantle origin.These mafic intrusions are characterized by enrichments in large ion lithophile elements(LILEs;e.g.,Rb,Ba,and K)and light rare earth elements(LREEs),and depletions in high field strength elements(HFSEs;e.g.,Nb,Ta,and Ti)and heavy rare earth elements(HREEs),indicating that they were formed in a subduction-related setting.These geochemical features,together with zircon ε_(Hf)(t)values(-1.1 to+11.2),indicate that their parental magmas were derived from partial melting of heterogeneous mantle wedge metasomatized by subduction-related fluids,with the contributions of slab sediments.The studied mafic intrusions also show wide range of major and trace elements contents,and variable Mg^(#) values,Eu and Sr anomalies,suggesting that their parental magmas had undergone variable degrees of fractional crystallization.Together with the E-W trending Permian continental arc along the northern margin of the NCC,we confirm that the generation of the Middle Permian mafic intrusions was related to southward subduction of the Paleo-Asian oceanic lithosphere beneath the NCC and the Paleo-Asian Ocean had not closed prior to the Middle Permian.

Petrogenesis of the Early Cretaceous Laojunshan monzogranite at the southern margin of the North China Craton: Constrains on the transition of the tectonic regime

1 Introduction Voluminous Mesozoic magmatic rocks containing abundant Au-Mo polymetallic mineralization resources are developed in the Xiaoqinling-Xiong’ershan district of the southern margin of the North China Craton(NCC).

LA-ICP-MS Zircon U-Pb Age of Longtou Syenite body in South Songxian County, Southern Margin of the North China Craton

Objective Indosinian magmatic rocks mainly locate in west Qinling Orogen, which are, however, extremely rare in east Qingling Orogen （Lu Xinxiang, 2000; Zhang Guowei et al., 2001; Guo Xianqing et al., 2017）. The Zhifang Huangzhuang （ZH） area in south Songxian County is located in the southern margin of the North China Craton （Fig. l a）, which is an important lndosinian alkaline magmatic occurrence including 32 syenite bodies and syenitic dykes in east Qinling Orogen. There are five syenite bodes in the ZH area, i.e., the Lang＇aogou, Mogou, Longtou, Jiaogou and Wusanggou from west to east （Fig. l b）.

Paleomagnetic Evidence for Tectonic Setting of Paleoproterozoic Dyke Swarms in the North China Craton, China

In order to investigate the tectonic setting of 1.77-1.78Ga dyke swarms emplaced into the central North China Craton(NCC),we carried out a paleomagnetic and magnetic fabric study on the well geochronologically

Late Paleoproterozoic-Neoproterozoic Multi-rifting Events Accompanied by Four Stages of Magmatism in the North China Craton and Their Geological Significance

An important Paleoproterozoic mobile belt event took place in the North China Craton(NCC),termed the Hutuo Movement.This has been interpreted as a cratonic reworking event with rifting-subduction-collision

Redox Evolution of the Lithospheric Mantle beneath the North China Craton

Objective The North China Craton （NCC） is a large Archean craton with a long geological history, yet very few studies have been carried out on the evolution of the redox conditions of its underlying mantle. Oxidation state of the mantle is critical in controlling the formation of metallic mineral deposits because metals can be readily released from the mantle to partial melt under oxidized conditions. In contrast, highly reduced and stable conditions are essential for the crystallization of diamond. The subcontinental lithospheric mantle （SCLM） beneath major cratons in the world has been stable since their formation and highly reduced in its oxidation state, but the SCLM below the NCC is different.

Magnetic Fabric Studies of Xiong'er Volcanic Rocks in Southern Margin of the North China Craton and its Implications

The Paleoproterozoic Xiong’er Group is composed of mafic to felsic volcanic rocks and minor sedimentary rocks,distributed along the southern margin of the North China craton(NCC).It is a key marker for regional

NUMERICAL MODELLING OF LITHOSPHERE EVOLUTION IN THE NORTH CHINA CRATON: THERMAL THINNING VERSUS TECTONIC EXTENSION THINNING

The boundary between lithosphere and asthenosphere essentially represents a thermal boundary (the solidus). Temperature variation across this boundary can lead to the change of lithosphere thickness. In the case of elevated temperatures in a lithospheric layer above 1 200℃, partial melting will begin and the result of that is a thinned lithosphere. The other mechanism that can also thin lithosphere is extension. Stretching during an extension event can result in a thinner and longer lithosphere. The two mechanisms above are the reason why we can alserve large variations in lithosphere thickness spatially across various continents and temporally throughout the geological history.

Late Mesozoic extensional tectonics of the Liaodong Peninsula massif:Response of crust to continental lithosphere destruction of the North China Craton

Unlike most Precambrian cratons that have thick sub-continental lithospheric roots,the Archean lithosphere beneath the North China Craton is thin (reduced from 200 km to about 80 km),and has been replaced by a geochemically juvenile lithospheric mantle.This is a unique regional geological event,which has attracted worldwide attention.In the North China Block,Late Mesozoic extensional tectonics is evident by low-angle detachment faults,syntectonic plutons bounded by ductile faults,metamorphic core complexes (MCC) and widespread Jurassic to Cretaceous half-grabens filled by continental terrigenous deposits and volcanic rocks.At a regional scale,these structures share the same NW-SE extensional direction,while maintaining their own individual kinematics.In other words,the MCC feature a top-to-the-NW sense of shear,and syntectonic plutons are typified by a top-to-the-SE shearing deformations.Geochronological results indicate that the extensional structures were formed between 130-120 Ma.These extensional events lead to magmatic rock emplacement,distributed at the footwall of the detachment faults.Two different exhumation stages can be identified based on regional structural and magmatic interpretation:a Jurassic slow or negligible exhumation and a Cretaceous fast one assisted by normal faulting.These two cooling stages correspond to distinct geodynamic processes that occurred during the Jurassic and Cretaceous.Extensional tectonics appear to have been insignificant before the Early Cretaceous,and the process may be demonstrated by partial melting of the crust.The second stage,dominated by an extensional regime,developed after ca 120 Ma,and is tentatively correlated with crustal extension caused by lithospheric removal of the North China Craton.

Late Mesozoic magmatism and tectonic evolution in the Southern margin of the North China Craton

Late Mesozoic granitic magmatism(158–112 Ma) are widespread in the southern margin of the North China Craton(NCC), contemporary with many world-class Mo-Au-Ag-Pb-Zn polymetallic deposits. There are abrupt changes in the elements and isotopic compositions of these granites at about 127 Ma. The early stage(158–128 Ma) granites show slightly or no negative Eu anomalies, large ion lithophile elements enriched and heavy REE depleted(such as Y and Yb), belonging to typical I-type granite. The late stage(126–112 Ma) granites are characterized by A-type and/or highly fractionated I-type granite, with higher contents of SiO2, K2 O, Y, Yb and Rb/Sr ratio and lower contents of Sr, δEu value and Sr/Y ratio than that of the early-stage granites.Moreover, the whole rock Nd and Hf isotopic compositions of the granites younger than 127 Ma show more depleted than those of the older one. The two stages of Late Mesozoic granites were derived from a source region of the ancient basement of the southern margin of the NCC incorporated the mantle material. The late stage(126–112 Ma) granites contain more fractions of mantle material with depleted isotopic composition than the early ones. The granites record evidence for a strong crust-mantle interaction. They formed in an intracontinental extensional setting which was related to lithospheric thinning and asthenospheric upwelling in this region, which was possibly caused by westward subduction of the Paleo-Pacific plate. 127 Ma is an critical period of the transformation of the tectonic regime.

Phase Equilibria Modeling and P-T Evolution of the Mafic Lower-Crustal Xenoliths from the Southeastern Margin of the North China Craton

The Precambrian lower crust rocks at the southeastern margin of the North China Craton （NCC） are mainly exposed as granulite xenoliths hosted by Mesozoic dioritic porphyry and metamorphic terrains in the Xuzhou-Suzhou area. Garnet amphiholites and garnet granulites are two kinds of typical lower-crustal xenoliths and were selected to reconstruct different stages of the metamorphic process. In this study, in view of multistage metamorphic evolution and reworking, phase equilibria modeling was used for the first time to better constrain peak P-T conditions of the xenoliths. Some porphyroblastic garnets have a weak zonal structure in composition with homogeneous cores and were surrounded by thin rims with an increase in XMg and a decrease in X Ca （or X Mg）- Clinopyroxene contain varying amounts of Na2O and Al2O3 as well as amphibole of TiO2, while plagioclases are different in calcium contents. Peak metamorphic P-T conditions are calculated by the smallest garnet x（g） （Fe2＋/（Fe2＋＋Mg）） contours and the smallest plagioclase ca（pl） （Ca/（Ca＋Na）） contours in NCFMASHTO （Na2O-CaO-FeO-MgO-Al2O3-SiO2- H20-TiO2-Fe2O3） system, which are consistent with those estimated by conventional geothermobarometry. The new results show that the peak and decompressional P-T conditions for the rocks are 850-900 ℃/ 1.4-1.6 GPa and 820-850 ℃/0.9-1.3 GPa, respectively, suggestive of high and middle-low pressure granulite-facies metamorphism. Combined with previous zircon U-Pb dating and conventional geothermobarometry data, it is indicated that the xenoliths experienced a clockwise P-T-t evolution with nearisothermal deeompressional process, suggestive of the Paleoproterozoic subduction-collision setting. In this regard, the studied region together with Jiao-Liao-Ji belt is further documented to make up a Paleopro- terozoic collisional orogen in the eastern block of the NCC.

Paleoproterozoic Multistage Metamorphic Ages Registered in the Precambrian Basement Rocks at the Southeastern Margin of the North China Craton and Their Geological Implications

The Precambrian basement rocks in the Bengbu and neighboring areas, located at the southeastern margin of the North China Craton, occur as granulite terrains and xenoliths in the Mesozoic dioritic porphyry.

Origin of Felsic Microgranitoid Enclaves in Granite in Zhangjiakou District,China:Implication for Process and Lifespan of Granitic Magma Chambers

Sparse felsic microgranitoid enclaves(FMEs)in the Shangshuiquan granite of the Zhangjiakou district,the north margin of the North China Craton,are fine-grained,dark-colored and exhibit subangular to subspherical shapes.They share similar mineral assemblages,chemical compositions,and zircon Hf isotope compositions to the host granite.New zircon U-Pb geochronology reveals that the FMEs crystallized at 156-153 Ma,while the Shangshuiquan granite formed at ca.146 Ma.The FEMs are,therefore,10 to 7 Ma older than the host granite.Combined with petrological evidence,we suggest that the FMEs are fragments of rapidly crystalized magmas,which were captured by the younger Shangshuiquan magma.Magmas of the FMEs and Shangshuiquan granite originated from the same reservoir.The Shangshuiquan granite is the result of small batches of magma being built up incrementally,and the FMEs belong to the earlier batches of magma.The lifespan of the Shangshuiquan magma reservoir exceeds 10 Ma.FMEs derived from cogenetic fragments have the potential to offer critical information about the formation process and timescale of granitic plutons.

Three-dimensional crustal velocity structure model of the middle-eastern north China Craton (HBCrust1.0)

Lithosphere thinning and destruction in the middle-eastern North China Craton(NCC), a region susceptible to strong earthquakes, is one of the research hotspots in solid earth science. All 42 seismic wide-angle reflection/refraction profiles have been completed in the middle-eastern NCC. We collect all the 2-D profiling results and perform gridding of the velocity and interface depth data, building a 3-D crustal velocity structure model for the middle-eastern NCC, named HBCrust1.0, by using the Kriging interpolation method. Our result shows that the first-arrival times calculated by HBCust1.0 fit well with the observations. The result demonstrates that the upper crust is the main seismogenic layer, and the brittle-ductile transition occurs at depths near interface C(the interface between upper and lower crust). The depth of interface Moho varies beneath the source area of the Tangshan earthquake, and a low-velocity structure is found to extend from the source area to the lower crust. Based on these observations, it can be inferred that stress accumulation responsible for the Tangshan earthquake may have been closely related to the migration and deformation of the mantle materials. Comparisons of the average velocities of the whole crust, the upper and the lower crust show that the average velocity of the lower crust under the central part of the North China Basin(NCB) in the east of the craton is obviously higher than the regional average. This high-velocity probably results from long-term underplating of the mantle magma.

Discovery of the Early Paleozoic Boin Sum-Ordor Sum Island Arc in the Hadamiao Gold Ore District, Inner Mongolia and its Significance to the Evolution of the Paleo-Asian Ocean

Early Paleozoic granodiorite has been identified on the northern margin of the North China craton in the east section of the central-Asian orogenic belt, which was previously known as early Indosinian in age. By using the LA-ICP-MS method, the obtained zircon U-Pb age is 445.6 2.7 Ma, which represents the crystallization age of the granodiorite. The granodiorite near the east of the large-sized Bilihe gold deposit is of the tholeiite series with low potassium. It is quasi-aluminous I-type granite, enriched in sodium （Na2 O/K2O=7.29 9.77） and magnesium （Mg # =0.51 0.67）. The ΣREE value is relatively low, obvious differentiation is shown between LREE and HREE and within LREE, and the Eu anomaly is low and negative （δEu=0.74 0.91）. In the primitive-mantle normalized spider diagrams of trace elements, the granodiorite is relatively rich in LREE and LILE （Ba, Sr, Th）, and strongly depleted in HFSE （Nb, Ta, Ti and P）, which shows features of subduction zone components （SZC）. In the discrimination diagrams of tectonic settings of granite for Rb vs. （Nb＋Y）, Rb vs. （Ya＋Ta）, La/Nb vs. Ba/Nb and Th/Nb vs. Ba/Nb, the granodiorite exhibits typical features of island arc granite. The normalized values of K and Rb are extremely low, while the values of Sr and Eu are very high, which are similar to those of island arc magma that has undergone metasomatism of fluid from the oceanic crust. The granodiorite is relatively depleted in ε Hf （t） （5.1 7.1） and low in ε Hf （t） model ages （1089 921 Ma）. In the ε Hf （t） vs. age （T） diagram, the distribution area of the granodiorite is accordant with the field of the Xing’anling-Mongolia orogenic belt, which indicates that the magmatic sources are mainly the mixture of partial melting of wedged mantle subjected to metasomatism of fluid from the oceanic crust and young substance from the crust. The granodiorite is similar to the felsic arc magma in the Damao Banner, Bate Obon, Boin Sum and Ordor Sum regions, and they altogether constitute an early Paleozoic accretionary island arc magmatic belt on the northern margin of the North China craton. A number of early Paleozoic zircons trapped in late Paleozoic intrusions in the Hadamiao and Bilihe regions and the discovery of the early Paleozoic island arc magmatic belt near the east of the Bilihe gold deposit suggest that the late Paleozoic volcanic-intrusive rocks have a basement of early Paleozoic arc accretionary complexes. This is just the evident of the multiphase subduction and accretion model of the Paleo-Asian Ocean （PAO）. Paleozoic structures and magmas on the northern margin of the North China craton are shown from south to north as the late Paleozoic Andes-type arc magmatic belt in the Inner Mongolia plateau, the Chifeng-Bayan Obo fault and the late and early Paleozoic arc magmatic belt, which shows that after the early Paleozoic arc-continent collisional orogeny and at the stage of the late Paleozoic accretionary orogeny, the PAO plate was likely to continuously pulsate and underthrust beneath the early Paleozoic island arc accretionary complex belt and its front, i.e. the North China craton. During the early Paleozoic collisional orogeny, the PAO plate might not experience large-scale breakup or delamination. The characteristics of the early Paleozoic island arc accretionary complex basement have a significant control on late Paleozoic diagenesis and metallization in the Hadamiao and Bilihe gold concentrated areas.

Summary of technology for a comprehensive geophysical exploration of gold mine in North China Craton

The North China Craton is the oldest continental block,and has suffered from large-scale lithospheric thinning and destruction,which in turn led to gold deposits in northern China.The decratonic gold deposits in the North China Craton became the most important gold deposits in China,and geophysical methods are key means to detect and discover gold deposits there.In this paper,based on the geological and petrophysical characteristics of the North China Craton,the geological model of the decratonic gold deposits is transformed into a geophysical model.At present,two methods of geophysical exploration of decratonic gold deposits are in use:rapid and efficient exploration on the scale of the ore concentration area,and large depth exploration on the scale of the deposit area.In detail,the airborne electromagnetic,magnetic and gravity methods are used to detect the shallow(1,500 m)anomaly area on the scale of the ore concentration area.Through the ground-controlled source electromagnetic and ground magnetotelluric methods,explorations for targets at significant depth(5,000 m)are carried out in the mining area.Then,taking the Liaodong ore concentration area as an example,geophysical methods are used to discover two prospecting areas around the Jianshanzi Fault in the Qingchengzi ore concentration area,Baiyun-Xiaotongjiapuzi deep prospecting area,and Qingchengzi deep prospecting area.Next,three prospecting areas are delineated around the Jixingou Fault in the Wulong mining area,Wulong deep prospecting area,Weishagou deep prospecting area,and Chang’an deep prospecting area.The anomalies in the ore concentration area and mining area are revealed by means of three-dimensional exploration methods,thereby providing technical support for the exploration of metal minerals such as decratonic gold deposits.

Early Cretaceous extensional structures in the Liaodong Peninsula:Structural associations,geochronological constraints and regional tectonic implications

Various extensional structures,e.g.,half grabens,detachment faults,and metamorphic core complexes,were formed in the Liaodong Peninsula.There are two metamorphic core complexes (mcc's) in the western part of the Peninsula,i.e.the Liaonan mcc and the Wanfu mcc.They share the same lower plate and constitute a conjugate mcc pair.The Dayingzi detachment fault system and the three half grabens are exposed in the central and eastern parts,respectively.U-Pb dating of zircons from syntectonic plutons in the lower plates of the detachment faults and volcanic rocks from half graben basins indicates that their formation spans from 135 to 106 Ma,although the individual structure may be formed at a particular stage.Despite the differences in age of formation,in the regional attitudes,and in rooting depths,the extensional structures have great similarities in their kinematics,geometrical asymmetry,and coeval tectono-magmatic activities etc.Macroscopically,the extensional structures constitute conjugate associations,but a particular one generally has asymmetric patterns.Early Cretaceous extensional structures extend from the Liaodong Peninsula to North China,Northeast China,South China,and eastern Mongolia and Transbaikal area in Russia.The extensional structures from different areas share many common features.The Liaodong Peninsula is the miniature of the East Asia with respect to the formation of extensional structures in Early Cretaceous.It is suggested that the interaction of the Izanagi Plate with Eurasia Plate is responsible for the extension of crust.The structural mobility of the lithosphere,partly attributed to the fluid flow at the depth,and detachment faulting in both the crustal and mantle lithosphere provide important constraints on the development of Early Cretaceous extensional structures in the East Asia.