Eastern North China Craton Research Articles

Fluid Geochemistry within the North China Craton: Spatial Variation and Genesis

The North China Craton (NCC) is a typical representative of the ancient destruction craton. Numerous studies have shown that extensive destruction of the NCC occurred in the east, whereas the western part was only partially modified. The Bohai Bay Basin is in the center of the destruction area in the eastern NCC. Chemical analyses were conducted on 122 hot spring samples taken from the eastern NCC and the Ordos Basin. The δ 2 H and δ 18 O in water, δ 13 C in CO2, and 3He/4He and 4He/20Ne ratios in gases were analyzed in combination with chemical analyses of water in the central and eastern NCC. The results showed an obvious spatial variation in chemical and isotopic compositions of the geofluids in the NCC. The average temperature of spring water in the Trans-North China Block (TNCB) and the Bohai Bay Basin was 80.74°C, far exceeding that of the Ordos Basin of 38.43°C. The average δ D in the Eastern Block (EB) and the TNCB were −79.22‰ and −84.13‰, respectively. The He isotope values in the eastern region (TNCB and EB) ranged from 0.01 to 2.52, and the rate of contribution of the mantle to He ranged from 0 to 31.38%. δ 13 C ranged from −20.7 to −6.4‰ which indicated an organic origin. The chemical compositions of the gases in the EB showed that N2 originated mainly from the atmosphere. The EB showed characteristics of a typical gas subduction zone, whereas the TNCB was found to have relatively small mantle sources. The reservoir temperatures in the Ordos Basin and the eastern NCC (EB and TNCB) calculated by the K-Mg temperature scale were 38.43°C and 80.74°C, respectively. This study demonstrated clear spatial variation in the chemical and isotopic compositions of the geofluids in the NCC, suggesting the presence of geofluids from the magmatic reservoir in the middle-lower crust and that active faults played an important role in the transport of mantle-derived components from the mantle upwards.

Geochronology and Geochemistry of Late Triassic Intrusive Rocks in the Xiuyan Area, Liaodong Peninsula, Eastern North China Craton: Petrogenesis and Implications for Lithospheric Thinning

AbstractThe timing and mechanisms of lithospheric thinning and destruction of the North China Craton (NCC) remain controversial, and the overall geodynamics of the process are poorly understood. This paper documents Late Triassic igneous rocks including monzogranite, gabbro, and diorite from the Xiuyan District on the Liaodong Peninsula in the eastern NCC, which have LA‐ICP‐MS zircon U‐Pb ages of 229.0 ± 0.4 Ma, 216.2 ± 0.9 Ma, and 210.6 ± 2.0 Ma, respectively. Monzogranite shows high‐SiO2 adakite affinity, negative ∊Hf(t) values (–20.6 to –17.9), and old TDM2 ages (3.53–3.29 Ga), suggesting that their parental magma was derived from thickened Paleoarchean mafic lower crust and minor mantle materials that were also involved their generation. Gabbro is ultrapotassic, strongly enriched in LREEs and LILEs, depleted in HFSEs, and has evolved zircon Hf isotopes with negative ∊Hf of –10.04 to –5.85 and old TDM2 ages (2.59 –2.22 Ga). These are diagnostic signatures of a crustal component, but their high contents of MgO, Cr, Co, Ni indicate that the primary magma originated from enriched mantle. Diorite is enriched in LILEs and LREEs, depleted in HFSEs (with negative Nb, Ta, and Ti anomalies), and contains negative ∊Hf(t) values (–13.64 to –11.01). Compared with the gabbro, the diorite is relatively enriched in Nb, Ta and HREEs, and also contains younger TDM2 ages (2.11–1.94 Ga), suggesting that the diorite was formed by mixing between ancient lower crust‐derived felsic magmas and asthenospheric mantle‐derived magmas. Field observations, geochronology, geochemistry, and zircon Lu‐Hf isotopes indicate that Late Triassic magmatism and tectonic activity resulted from deep subduction of the Yangtze Craton beneath the NCC in the Xiuyan area. This phase of tectonic activity was completed in the eastern NCC by the Late Triassic (216 Ma), and was subsequently followed by lithospheric thinning that began in the Late Triassic.

Lithospheric structure beneath the boundary region of North China Craton and Xing Meng Orogenic Belt from S-receiver function analysis

The boundary region of the North China Craton (NCC) and Xing-Meng Orogenic Belt (XMOB), including the northern boundary of the NCC and the southern XMOB, is the ideal area to investigate the spatially uneven lithospheric deformation and associated tectonic evolution in the boundary region of the craton and orogen. The depths and structures of the lithosphere–asthenosphere boundary (LAB) and mid-lithosphere discontinuity (MLD) are the key information to describe the nature and deformation pattern of the lithosphere, and thus can provide basic constraints on the associated tectonic processes and mechanism of the lithospheric deformation. Based on waveform data collected from 226 broadband seismic stations, high resolution spatial variations in the LAB and MLD depths were obtained by using the wave equation migration method for the S-receiver functions. The migrated images show a lateral variation in the LAB depth from 100–120 km in the northern boundary of the NCC to 120–140 km in the southern XMOB. The imaged LAB within the NCC is much shallower than that revealed by mantle xenoliths enclosed in the nearby Early Paleozoic kimberlites (~180 km), suggesting that the cratonic lithosphere of the area may have undergone significant thinning during the Phanerozoic evolution. Furthermore, a coherent MLD is identified at depths of 70–90 km beneath the northeastern NCC, which corroborates the speculation that the MLD probably existed in the eastern NCC before lithospheric destruction in the Mesozoic. The spatial variations in the LAB and MLD depths probably reflect complex lithospheric deformation and thinning around the boundary region of NCC and XMOB. The properties, including the gradient thickness and S-wave velocity contrast, of the two discontinuities further indicate that lithospheric deformation and thinning might be related to partial melting induced by the Big Mantle Wedge associated with the subducting Paleo-Pacific plate and its stagnation during the Late Mesozoic.

Thermo-mechanical destruction of Archean cratonic roots: Insights from the Mesozoic Laiyuan granitoid complex, North China Craton

Igneous complexes with diverse magmatic suites provide essential targets for investigating magma differentiation processes and crust-mantle interaction. The North China Craton (NCC) is a crucial window to gain insights into craton destruction through voluminous magmatism during the Mesozoic involving extensive crust-mantle interaction. Here we investigate the granitoid suite from the Laiyuan complex in the central NCC to constrain the magmatic evolution and petrogenetic linkages and to gain insights into the process of crust-mantle interaction related to craton destruction. The Laiyuan granitoid complex comprises syenogranite, monzogranite, quartz monzonite and monzonite with mafic magmatic enclaves (MMEs). The granitoids were formed during the Early Cretaceous (137–128 Ma) with εHf(t) values and TDMC ages ranging from −21.8 to −16.8 and 2564 to 2255 Ma, respectively. The compositional variations of the different rock types suggest distinct magmatic evolution and petrogenesis. Geochemical and isotopic data indicate that the enriched lithospheric mantle-derived mafic magmas underwent early-stage plagioclase-dominated and late-stage hornblende-dominated fractional crystallization to form the monzonites and quartz monzonites. Geochemical modeling results suggest that the magma of the MMEs originated through mixing between lithospheric mantle-derived mafic magma and crust-derived felsic magma with post-injection hybridization to generate MMEs with variable compositions. The monzogranites are classified as high-K calc-alkaline I-type granites with higher SiO2 contents (69–71 wt%) and lower Mg# (41–44) than intermediate rocks. They were generated by partial melting of the basaltic lower crust, with the addition of mafic magma from an enriched mantle. The highly fractionated syenogranites with lower Mg# (18–27) were evolved from the monzogranitic magma through plagioclase-dominated crystal removal. The adakitic affinities of the monzonites and monzogranites were generated by crystallization of mantle-derived magmas and partial melting of continental crust of normal thickness (~40 km), respectively. The bottom-up crust-mantle interaction accounts for the compositional diversity of the Laiyuan granitoids, and suggests that thermo-mechanical destruction played a dominant role in the destruction of the central NCC as compared with the continental delamination process in the eastern NCC.

Adjoint traveltime tomography unravels a scenario of horizontal mantle flow beneath the North China craton

The North China craton (NCC) was dominated by tectonic extension from late Cretaceous to Cenozoic, yet seismic studies on the relationship between crust extension and lithospheric mantle deformation are scarce. Here we present a three dimensional radially anisotropic model of NCC derived from adjoint traveltime tomography to address this issue. We find a prominent low S-wave velocity anomaly at lithospheric mantle depths beneath the Taihang Mountains, which extends eastward with a gradually decreasing amplitude. The horizontally elongated low-velocity anomaly is also featured by a distinctive positive radial anisotropy (VSH > VSV). Combining geodetic and other seismic measurements, we speculate the presence of a horizontal mantle flow beneath central and eastern NCC, which led to the extension of the overlying crust. We suggest that the rollback of Western Pacific slab likely played a pivotal role in generating the horizontal mantle flow at lithospheric depth beneath the central and eastern NCC.

Early Cretaceous basalts record the modification of the North China Craton lithospheric mantle: implications for lithospheric thinning

ABSTRACT The modification of the Archaean lithospheric mantle root beneath the eastern North China Craton (NCC) has been noticed. However, the degree of modification and the characteristics of metasomatic agents for the NCC lithospheric mantle are still unclear. Here, we compile the geochemistry and 87Sr/86Sr and 143Nd/144Nd isotope ratios of Cretaceous primitive basalts (Yixian, Sihetun, Fangcheng and Feixian) from the eastern NCC and estimate the inputs of subduction-related elements into the Archaean lithospheric mantle beneath the NCC. These basalts show primitive (high MgO, Cr and Ni contents) and arc-like geochemical features (enrichments in LILEs and depletions in HFSEs) that indicate that the mantle sources were modified by fluids related to subducted crustal materials. Substantial proportions of subduction-mobile elements (e.g. ~95% Ba and ~90% Th) transferred to the basalt sources via hydrous melts. Thus, a large volume of fluids transferred into the lithospheric mantle. The data support the model that the NCC Archaean lithospheric mantle was weakened by hydrous melts, which resulted in a fusible weakened lithospheric mantle. Preliminary lithospheric thinning was induced by the extension of the NCC resulting from trench retreat of the Paleo-Pacific plate at ~140-120 Ma. Then, decompression melting of the lithospheric mantle caused pervasive melts in the weakened lithospheric mantle, resulting in the lithospheric mantle having a low viscosity comparable to the asthenospheric mantle, which principally reduced the lithospheric mantle.

Chronological and geochemical variations of the late Mesozoic granitoids in the Taihang Mountains and middle-southern Tan-Lu Fault: Implications for lithosphere destruction of the North China Craton

In the Late Mesozoic, the North China Craton (NCC) underwent significant lithospheric thinning and destruction, especially in the eastern part, but the mechanism and timing related to this process are still contentious. The Taihang Mountains (TH) are located in the western part of the eastern NCC and the Tan-Lu Fault (TLF) is in the eastern part, which are two essential magmatic areas that reveal deep processes of magma origin. We investigated the spatial-temporal distribution of igneous rocks from these two areas to constrain the tectonic setting and magmatic sources. SHRIMP zircon U-Pb ages of the granitoids within the Fangshan pluton in northern TH area range from 136 to 128 Ma. Their <i>ε</i>_Hf(t) values and δ¹⁸O values show ranges of −27.7 to −18.5 and 6.68 to 7.26 permil, respectively. Hence, we conclude that the rocks were formed by mixing between underplating magma and the melts from the lower crust. The O-Hf isotopic compositions of six granitoid samples from the Yunmengshan complex in northern TH are also reported. In combination with previous studies, we propose that the geochemical characteristics of the magmatic rocks from the TH area had insignificant changes during late Mesozoic time, but the rocks from the TLF area varied greatly. The difference between those two areas may reflect the diverse impact of the Paleo-Pacific subduction process. The high Mg# adakitic rocks (HMA) from TLF area have higher Mg# values than the HMA rocks from TH area. Our conclusion is that the HMA rocks in the TLF area were mainly formed by delaminated lower crust interacting with mantle materials and that the Paleo-Pacific subduction had limited impact on TH magmas. Based on chronology and geochemical characteristics, we recognize three stages: 1) ∼166 to 140 Ma, multi-directional compression resulted in crustal shortening and thickening in the NCC, accompanied by regional partial melting of the crust and underplating of mafic magmas, 2) 140 to 125 Ma, the TLF underwent left-lateral strike-slip movement. Subsequent delamination of the lower crust around the fault and the NCC evolved into an extensional tectonic environment, 3) after 125 Ma, a large-scale extension of the NCC occurred likely due to stress relaxation after delamination. The TLF acted as a favorable channel for transporting mantle material and fluids, which implies that the large-scale fault zone was a key factor of the NCC lithosphere destruction.

Cretaceous basin evolution in northeast Asia: tectonic responses to the paleo-Pacific plate subduction.

ABSTRACTCretaceous rift basin evolution was an important part of the tectonic history of northeast Asia in the late Mesozoic. Three types of rift basins are identified—active, passive and wide rift basins—and they developed in different regions. Passive rift basins in the eastern North China craton are thought to be the consequence of crustal stretching and passive asthenospheric upwelling. Wide rift basins in the eastern Central Asian orogen are assumed to originate from gravitational collapse of the thickened and heated orogenic crust. Active rift basins in the northern North China craton are attributed to uprising of asthenospheric materials along a lithospheric-scale tear fault. Slab tearing of the subducting paleo-Pacific plate is postulated and well explains the spatial distribution of different types of rift basins and the eastward shifting of magmatism in the northern North China craton. The Late Cretaceous witnessed a period of mild deformation and weak magmatism, which was possibly due to kinematic variation of the paleo-Pacific plate.

Geochronology and geochemistry of Late Triassic intrusions in the Liaodong Peninsula, eastern North China Craton: implications for post-collisional lithospheric thinning

ABSTRACT Despite numerous years and avenues of investigation, the timing, evolution, and mechanism of lithospheric thinning of the North China Craton (NCC) are still highly debated. Late Triassic igneous rocks especially mantle derived mafic rocks could provide critical information related to the post-collisional lithospheric thinning of the Liaodong Peninsula in the eastern NCC. Using newly acquired geochronological data points, we determined that the intrusive rocks have emplacement ages of 219–209 Ma, which are typical of Late Triassic magmatism. The studied Qinghekou gabbros have low SiO2 (49.43–51.86 wt.%), Na2O+K2O (3.59–7.20 wt.%), high MgO (3.70–8.54 wt.%) and transition metal element contents, with Mg# values ranging from 49.2 to 69.3. While these samples are enriched in large ion lithophile elements such as Rb, Ba, and K and light rare earth elements, they are depleted in high field strength elements such as Nb, Ta, Ti, and P and heavy rare earth elements. We conclude that these gabbros samples were formed in a subduction-related tectonic setting, where the primary magmas were derived from partial melting of the lithospheric mantle that experienced metasomatism via slab-related fluids. Our Tongyuanpu granite samples have I-type granite affinity, as indicated by their high SiO2 (73.60–75.30 wt.%) and low MgO (0.08–0.32 wt.%) contents, as well as the A/CNK values of 0.99–1.25 and the zircon saturated temperature values of 757–832°C, the parental magmas for these granites were generated by partial melting of the lower crust. Combined with the spatio-temporal distribution and rock-assemblages of the Late Triassic intrusive rocks, we conclude that these rocks were formed in an extensional environment characterized by lithospheric thinning caused by lithospheric delamination after the collision between the NCC and the Yangtze Craton. Furthermore, we infer that the initial lithospheric thinning of the eastern NCC occurred during the Late Triassic.

Geodynamics of decratonization and related magmatism and mineralization in the North China Craton

The North China Craton (NCC) experienced strong destruction (i.e., decratonization) during the Mesozoic, which triggered intensive magmatism, tectonism and thermal events and formed large-scale gold and other metal deposits in the eastern part of the craton. However, how the decratonization controls the formation and distribution of large-scale of gold and other metal deposits is not very clear. Based on a large number of published data and new results, this paper systematically summarizes all the data for the rock assemblages, chronology, geochemistry and petrogenesis of Mesozoic magmatic rocks, as well as for the mineralizing ages of gold and other metal deposits and the evolution of the Mesozoic basins in the eastern NCC. The results are used to restore the extensional rates of Mesozoic to Cenozoic basins and the strike-slip distance of the Tanlu Fault, to ascertain the location of the Paleo-Pacific plate subduction zones during the Mesozoic to Cenozoic, and to reconstruct the temporal and spatial distribution of Mesozoic gold and other metal deposits and magmatic rocks in the eastern NCC. It is obtained that the magmatism and mineralization in the eastern NCC westward migrate from east to west during the Early to Middle Jurassic, but they eastward migrate from west to east during the Early Cretaceous. The metallogenesis of these deposits is genetically related to magmatism, and the magmas provided some ore-forming materials and fluids for the generation of metal deposits. The geodynamic mechanism of decratonization and related magmatism and mineralization is proposed, i.e., the westward low-angle subduction of the Paleo-Pacific slab beneath the NCC formed continental magmatic arc with plenty of porphyry Cu-Mo-Au deposits in the Jurassic, similar to the Andean continental arc in South America. The mantle wedge was metasomatized by the fluids/melts derived from the subducting slab, laying a material foundation for hydrothermal mineralization in the Early Cretaceous. While the rollback of the subducting slab with gradually increasing subduction angle and the retreat of the subduction zones during the Early Cretaceous induced strong destruction of the craton and the formation of extensive magmatic rocks and large-scale gold and other metal deposits.

Crustal deformation and dynamics of Early Cretaceous in the North China Craton

The Early Cretaceous represents a peak period of the North China Craton (NCC) destruction. A comprehensive analysis of crustal deformation during this period can reveal processes and dynamics of the destruction. The peak destruction of the NCC was associated with intense extension whose representative deformation products are metamorphic core complexes (MCCs), extensional domes and rifted basins. These MCCs occurred along both northern and southern margins of the NCC, and resulted from synchronous extension and magmatism, showing difference from the typical orogen-type MCCs in many aspects. The MCCs of the Early Cretaceous were replaced by extensional domes under relatively weak extension and uplift. In contrast to a major depression-type basin of the Early Cretaceous in the western NCC, rifted basins of the same age in the eastern NCC appeared as medium- to small-scale ones extensively. In the eastern NCC, the rifted basins north of the Bohai Bay are characterized by a feature similar to an active rift whereas those south of the Bohai present similarity to a passive rift. Various sorts of extensional structures developed during the peak destruction indicate a stable stress state of NE-SE extension over the entire central to eastern NCC, consistent with the plate margin-driven stress field. Spatial distribution of the extensional structures presents an 1800 km wide back-arc extension region in the central to eastern NCC, consistent with the Paleo-Pacific slab rollback model following flat subduction. Temporal-spatial variation of initial extension and volcanic activity during the peak period also supports the rollback model right after the flat oceanic slab. The crustal deformation evolution demonstrates that the peak destruction of the NCC took place after the B-episode compression of the Yanshan Movement of the earliest Early Cretaceous and terminated with onset of the C-episode compression of the earliest Late Cretaceous.

Late Neoarchean to Paleoproterozoic arc magmatism in the Shandong Peninsula, North China Craton and its tectonic implications

The transition in tectonic regime of our planet during the late Archean with the initiation broadly modern style subduction system is one of the major topics of interest in earth science. The North China Craton (NCC), one of the oldest cratonic nuclei in the world, preserves important records of Archean and Paleoproterozoic crustal evolution, cratonization and related geodynamic history that are important in understanding the continental growth of the early Earth. Here we investigate a suite of Archean to Paleoproterozoic rocks including hornblendite, amphibolite, gabbro, diorite, basalt, plagiogranite, granite porphyry and greenschist from Shandong Peninsula within the southwestern Jiaoliao block of the eastern NCC using zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock geochemistry. We aim to understand the timing and petrogenesis of the rock suite and its implications on the geodynamic history of the NCC. Zircon U-Pb data show 207Pb/206Pb ages in the range of 2.68–1.83 Ga, and is divided into three groups of 2.68–2.43, 2.38–1.96 and 1.95–1.83 Ga. Among these, the 2.68–2.43 Ga group confirms with the major magmatic phase during Neoarchean-Paleoproterozoic transition in the eastern NCC, whilst the other groups of 2.38–1.96 and 1.95–1.83 Ga ages might represent the Paleoproterozoic orogenic events in the NCC. Zircon Lu-Hf isotopic data display εHf(t) values ranging from −0.4 to 10.0 and TDMC of 3074–2080 Ma, which are subdivided into one group with U-Pb ages of 2672–2445 Ma characterized by εHf(t) values from −0.4 to 7.0 and TDMC of 3074–2588 Ma and another group (2134–2009 Ma) with εHf(t) values in the range of 2.8–10.0 and TDMC ranging from 2458 to 2080 Ma. These results indicate that the magmas (2672–2445 Ma group) were sourced mainly from Late Mesoarchean to Neoarchean juvenile components with minor input of reworked Mesoarchean crustal components, whereas the 2134–2009 Ma group was derived from Paleoproterozoic juvenile components. Whole-rock geochemical data of the granite porphyry and plagiogranites show typical subduction-related arc signature with the enrichment of LREEs and LILEs and depletion of HREEs and HFSEs (e.g. Nb, Ta, Ti), and mainly belong to I-type granites generated at arc-related setting. The ultramafic–mafic magmatic suite corresponds with tholeiitic to calc-alkaline series which were formed by partial melting of enriched mantle within an island arc setting in an active continental margin. In conjunction with the results from previous studies in the NCC, we correlate the 2.68–2.43 Ga ages with Late Neoarchean amalgamation of microblocks and cratonization of the NCC driven by late Neoarchean oceanic plate subduction, and the 2.38–1.83 Ga ages represent Paleoproterozoic orogenic events including the assembly of major crustal blocks in the NCC within the Paleoproterozoic supercontinent Columbia, and the final collision of these crustal blocks and cratonization.

A machine learning approach to tracking crustal thickness variations in the eastern North China Craton

The variation of crustal thickness is a critical index to reveal how the continental crust evolved over its four billion years. Generally, ratios of whole-rock trace elements, such as Sr/Y, (La/Yb)n and Ce/Y, are used to characterize crustal thicknesses. However, sometimes confusing results are obtained since there is no enough filtered data. Here, a state-of-the-art approach, based on a machine-learning algorithm, is proposed to predict crustal thickness using global major- and trace-element geochemical data of intermediate arc rocks and intraplate basalts, and their corresponding crustal thicknesses. After the validation processes, the root-mean-square error (RMSE) and the coefficient of determination (R2) score were used to evaluate the performance of the machine learning algorithm based on the learning dataset which has never been used during the training phase. The results demonstrate that the machine learning algorithm is more reliable in predicting crustal thickness than the conventional methods. The trained model predicts that the crustal thickness of the eastern North China Craton (ENCC) was ~45 km from the Late Triassic to the Early Cretaceous, but ~35 km from the Early Cretaceous, which corresponds to the paleo-elevation of 3.0 ± 1.5 km at Early Mesozoic, and decease to the present-day elevation in the ENCC. The estimates are generally consistent with the previous studies on xenoliths from the lower crust and on the paleoenvironment of the coastal mountain of the ENCC, which indicates that the lower crust of the ENCC was delaminated abruptly at the Early Cretaceous.

Nature and secular evolution of the lithospheric mantle beneath the North China Craton

The Archean mantle lithosphere beneath the North China Craton (NCC) was transformed in the Mesozoic, leading to the craton destruction. Despite the significant breakthroughs in the craton studies, lithospheric transformation mechanisms are yet to be fully understood. Compositional variations of mantle-derived rocks and xenoliths provide insights into the nature of the mantle lithosphere before and after the craton destruction. The Paleozoic lithosphere of the NCC is ∼200 km thick. It has a refractory mantle with an evolved isotopic signature. The Mesozoic mantle lithosphere was relatively fertile and highly heterogeneous. In the Cenozoic, the lithosphere in the eastern NCC is about 60–80 km thick. It has an oceanic-type mantle that is fertile in composition and depleted in the Sr-Nd isotopic signature. The Central Zone lithosphere is >100 km thick and has a double-layer mantle with an old upper layer and a new lower layer. The Western Block has a lithosphere of ∼200 km thick. The lithospheric mantle beneath the southern and northern margins and eastern part of the NCC has been transformed significantly by peridotite-melt reactions due to the multiple subductions of adjacent plates since the Paleozoic. Paleo-Pacific subduction and the associated dynamic processes significantly alter the lithosphere based on the distribution of craton destruction. The involved mechanisms include mechanical intrusion of subduction plates, melt fluid erosion, and local delamination. The lithospheric thinning of ∼120 km is relevant to the continental extension caused by subduction plate rollback and trench retreat.

The Late Jurassic extensional event in the Yanshan fold and thrust belt (North China): New insights from an integrated study of structural geology, geophysics, and geochemistry of the Siganding granitic pluton

The Yanshan fold and thrust belt (YFTB) was built up by multiple contractional events, namely the “Yanshan Movement”, which was traditionally subdivided into the “Yanshan-A” and “Yanshan-B”. In contrast with the better constraint on “Yanshan-B” (ca.140 Ma), the timing of “Yanshan-A” is still in dispute. The Middle Jurassic contraction (172–160 Ma) was widely accepted, however, whether this contraction can last into 150 Ma is still unclear. In this article, to clarify the Late Jurassic tectonic regime in the YFTB, a multidisciplinary study, including structural geology, Anisotropy of Magnetic Susceptibility (AMS), gravity modeling, geochronology, and geochemistry, has been carried out to investigate the emplacement mechanism of the Siganding pluton (ca. 161–157 Ma) in the northern Beijing area. The magma was predominantly derived from the Precambrian continental lower crust. The magnetic foliations are pluton margin-parallel and outward dipping, resembling the fabric pattern of magmatic dome. The NE-SW striking magnetic lineations and NW-SE linear feeder zones revealed by gravity modeling indicate that the emplacement of the Siganding pluton was controlled by a weak NE-SW crustal stretching interpreted as a regional tectonic extension. Considering that the Late Jurassic (164–153 Ma) NE-SW oriented extension structures are not only documented in the YFTB, but also the entire eastern NCC, hereby we propose that the “Yanshan-A” is constrained at 172–164 Ma, instead of a wide range from the Middle Jurassic to Late Jurassic (172–150 Ma) as argued by previous workers. The extension could be ascribed to the oblique subduction of the Izanagi plate.

Tectonothermal events in the central North China Craton since the Mesozoic and their tectonic implications: Constraints from low-temperature thermochronology

The North China Craton (NCC) experienced important tectonic events during the Meso-Cenozoic as implied by many geological studies. Combined with existing low-temperature thermochronological data, new apatite fission track (AFT) and zircon (UTh)/He data from the Lüliangshan and Taihangshan mountains in this study reveal that the central NCC experienced tectonothermal events during the Meso-Cenozoic, i.e., ca. 150 Ma, 110–80 Ma, 50–40 Ma and 30–20 Ma. The Late Jurassic event caused the formation of the Lüliangshan basement-involved anticline. The main folding and thrusting in the central NCC developed in the Mesozoic instead of the Cenozoic and resulted from the low-angle subduction of the Paleo-Pacific ocean plate beneath the Eurasian Plate during the Late Jurassic; and the Late Cretaceous tectonic event stopped the Early Cretaceous extension across the eastern Asia, thrusting and sinistral strike-slip faulting occurred across the central NCC, which was possibly caused by a collision along the southeastern boundary of eastern Asia. The early Cenozoic event in central NCC was coeval with an event occurring throughout eastern Asia and may have been a regional response to changes in the movement direction and velocity of the Pacific Plate, and this event may have resulted in the formation of rift basins in the eastern NCC. The whole central NCC experienced uplift during this period in isostatic readjustment to this extension.

Exhumation of Metamorphic Core Complexes through Progressive Subhorizontal Shearing, Doming, and Detachment Faulting: Insights from the Cretaceous Liaonan Metamorphic Core Complex, Eastern North China Craton

Abstract The Early Cretaceous Liaonan metamorphic core complex (MCC), eastern North China craton, provides a field setting to evaluate progressive middle-upper crustal subhorizontal shearing, doming, and detachment faulting. The MCC is bounded by a western Jinzhou detachment fault zone (JDFZ) and a southern Dongjiagou shear zone (DSZ) that were primarily suggested to be two segments of the master detachment fault zone. Integrated structural, microstructural, quartz c-axis fabrics, and fluid inclusion analysis and zircon U-Pb dating on mylonites and syn-kinematic granites along the DSZ and JDFZ reveal that the DSZ possesses deformation characteristics that are obviously different from those along the JDFZ. The DSZ is composed of a Lower Unit of sheared Archean gneisses and an Upper Unit of sheared Neoproterozoic metasedimentary rocks, between which there is an obvious tectonic discontinuity contact (TDC). Rocks from below and above the TDC possess structures and fabrics with consistent geometries and kinematics with those along the JDFZ. A metamorphic break exists between the two units that were sheared at contrasting deformation conditions. Dating of zircons from syn-kinematic granitic dikes from DSZ yields an age of ca. 134 Ma, which is similar to the ages of early shearing along the JDFZ. It is concluded that the Jinzhou and Dongjiagou faults formed parts of a detachment faulting with top-to-the WNW kinematics. Exhumation of the Liaonan MCC shearing initiation along both the JDFZ and DSZ at an early stage (ca. 133~134 Ma), subsequent progressive shearing, and doming during slow cooling and exhumation before ca. 120 Ma, followed by fast cooling and rapid exhumation of the MCC by detachment faulting along the JDFZ until ca. 107 Ma.

Constraining the density evolution during destruction of the lithospheric mantle in the eastern North China Craton

The thermoelastic properties of minerals in mantle xenoliths combined with the thermal states can provide an integrated understanding of the petrophysics of the lithospheric mantle. Here, we conducted high-pressure and high-temperature experiments on the main minerals (e.g. olivine, orthopyroxene, clinopyroxene, spinel, and garnet) in peridotite xenoliths from basalt of the eastern North China Craton (NCC) using in situ synchrotron single-crystal X-ray diffraction combined with diamond anvil cells. The pressure-temperature-volume data were fitted to the third-order Birch-Murnaghan equations of state and yielded the thermoelastic parameters that included bulk modulus, pressure and temperature derivatives, and thermal expansion coefficients. The density profiles of the eastern NCC during the destruction process since the Mesozoic are presented from the temporal and spatial aspects. The lithospheric density dramatically decreased during destruction, and high heat flow may have been a trigger. The spatially distributed density profile also provides firm evidence for lateral heterogeneities in the eastern NCC. This may suggest that the present mantle is characterized by heterogeneous destruction of the NCC.

Mantle cooling and cratonization of Archean lithosphere by continuous plate subduction: Constraints from TTGs, sanukitoids, and high-K granites, eastern North China Craton

The evolution of plate subduction styles on the Earth is coupled with its cooling history. Continuous subduction was initiated during the Neoarchean, yet its influence on mantle cooling and the cratonization of Archean lithosphere remains unclear. Successive subduction-related magmatism occurred during the late Neoarchean evolution of the Western Shandong Province granite-greenstone belt (WSP) of the North China Craton (NCC) and preserved crucial clues relating to processes and roles of regional continuous subduction. In this study, petrology, whole rock geochemistry, and zircon U–Pb–Hf isotopes are reported for late Neoarchean TTG gneisses, quartz monzodiorites, and monzogranites from the WSP. Zircon U–Pb dating reveals that the TTG gneisses, quartz monzodiorites, and monzogranites were formed at ~2561–2517 Ma, 2540–2533 Ma, and 2541–2513 Ma, respectively. The TTG gneisses with high (La/Yb)N ratios, low K2O/Na2O ratios, and low MgO contents were mainly derived from partial melting of oceanic slab material. In contrast, the quartz monzodiorites show high K2O and MgO content and high (La/Yb)N ratios, consistent with the characteristics of Archean sanukitoids, suggesting that they were the products of partial melting of mantle source metasomatized by slab-derived melts. The monzogranites with systematically high K2O, SiO2, and low MgO contents were formed by crustal reworking of regional TTGs and sedimentary rocks. Rock assemblages, geochemical features, regional field observation, and structure geology indicate prolonged (~2.56–2.49 Ga) continuous magmatism in the WSP across three northwest-trending belts (Belts A, B, and C) related to continuous subduction and slab rollback. These processes led to a tectonic transition from early compression to late extension. The final stabilization of the continental crust in the late Neoarchean in the eastern NCC was a consequence of successive mantle cooling due to regional continuous subduction recorded by subduction-related rock assemblages (i.e., adakites, sanukitoids, high-Mg basalts-andesites, and Nb-enriched basalts), the paired type of metamorphism, and the rise of alkali basalts. Secular geochemical changes of alkaline basalts outline the role of continuous subduction in dramatic mantle cooling and the final stabilization and cratonization of the eastern NCC.

Paleomagnetic insights into the Cambrian biogeographic conundrum: Did the North China craton link Laurentia and East Gondwana?

Abstract Redlichiid trilobite and small shelly fossils indicate strong ties of the North China craton (NCC) to Gondwana during the early Cambrian, while recent discoveries of the characteristic fossils of Laurentia in Wuliuan shales in the eastern NCC imply its possible connection with Laurentia during the middle Cambrian. Here we report a new paleomagnetic pole at 31.8°S, 140.4°E (radius of 95% confidence cone of paleomagnetic pole, A95, = 5.3°), obtained from the Wuliuan (ca. 505 Ma) Hsuchuang Formation, by averaging our new data and existing virtual geomagnetic poles acquired from different parts of the NCC. A positive regional tilt test and the presence of geomagnetic reversals demonstrate that the remanence was primary. The paleomagnetic data permit placing the NCC near 20°N between Laurentia and Australia at ca. 505 Ma, suggesting that the NCC may have played the role of biogeographic link between East Gondwana and Laurentia in the middle Cambrian. Low-latitudinal westward ocean currents may have facilitated faunal migrations from Laurentia to East Gondwanan blocks via the NCC as well as the newly formed tectono-paleogeographic archipelago, which likely further enhanced biological exchange in the late Cambrian.