Destruction Of North China Craton Research Articles

Hydrocarbon generation and migration in the Fuxin Basin during the Cretaceous evolution of the North China Craton, NE China

The extensive thinning and destruction of North China Craton (NCC) during the Early Cretaceous led to the development of numerous rift basins and petroleum systems. However, the specific relationship between NCC evolution and hydrocarbon generation and accumulation in these sedimentary basins is still unclear. In this study organic geochemistry and oil-source correlation analyses were conducted to investigate the hydrocarbons generation potential and migration pathway in the representative Fuxin Basin. Results demonstrate that the semi-deep lacustrine source rocks were developed in the Jiufotang Formation (K1jf) in the west and the upper Shahai Formation (K1sh) in the east, both of which are enriched with organic matter content and hydrocarbon generation potential of kerogen Types II to III. Based on the hierarchical cluster analysis of crude oils biomarker fingerprints, two crude oil types (A and B) were deduced. The Type A crude oil is characterized by high gammacerane, low pristane/phytane, relatively high C29 regular sterane and methylphenanthrene index, which is consistent with the K1jf biomarker characteristics in the west. Therefore, the Type A crude oil is likely generated from the K1jf source rock that accumulated in turbidite sand bodies of the K1jf and/or migrated to the K1sh reservoir through strike-slip faults. Type B crude oil is dominated by low gammacerane, moderate pristane/phytane, high C27 regular sterane and 1,2,5-trimethylnaphthalenes, which is in good agreement with the K1sh4 features. The basin simulation revealed that hydrocarbon generation of source rocks in the Jiufotang and Shahai formations was linked to a rapid subsidence of the basin, which was induced by intense extension with the NCC destruction during the Early Cretaceous. Subsequently, the rapid subduction of the Western Pacific plate during the earliest Late Cretaceous led to the development of extensive epigenetic fractures, enabling extensive hydrocarbon migration in the Fuxin Basin. This study sheds light on oil sources in sedimentary basins in an extensional setting and provides insights into the dynamic process of hydrocarbon generation and migration associated with NCC evolution.

Petrogenesis of the Zijinshan alkaline complex in Shanxi Province, western North China Craton: Mixing of melts from multiple sources

The destruction of the North China Craton (NCC) is a well‐known dynamic event in the Mesozoic, but the western NCC, with only few magmatic activities, has lacked studies so far. The Zijinshan alkaline complex, tectonically located at the western part of the NCC and the eastern edge of Ordos Block/Basin, is one of the most typical alkaline intrusions during the NCC destruction, and consists of monzonite, aegirine–augite syenite, nepheline syenite, pseudoleucite phonolite and trachyte porphyry. Geochronological, geochemical and in situ Sr–Nd–Hf isotopic analyses were performed on the various lithologies, in order to reveal the magma sources, petrogenesis and possible geodynamic processes. Zircon and titanite U–Pb dating shows that the Zijinshan complex was emplaced at ~130 Ma. The main rocks are enriched in light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs; such as Rb, Ba, K, Sr), and depleted in heavy rare earth elements (HREEs) and high‐field‐strength elements (HFSEs; such as Th, U, Nb, Ta, Ti), without negative Eu anomaly. In addition, the obviously enriched and inhomogeneous Sr–Nd isotopic components occurred among the various lithologies, implying the primary magma of Zijinshan complex may originate from a deep mixed source. Specifically, the monzonites of Zijinshan complex come from the partial melting of the enriched lithospheric mantle with participation of crustal materials. Meanwhile, the nepheline syenites and alkaline volcanics originated from the enriched lithospheric mantle mixing with the depleted asthenosphere‐derived compositions. During the NCC destruction, continuous asthenospheric upwelling resulted in several times of mixing of melts from asthenospheric mantle, lithospheric mantle and lower crust in different proportions, and then the mixed magma of each episode migrated upward to the shallow part to form the Zijinshan pluton.

Large-Scale Cretaceous Adakitic Magmatism Induced by Water-Fluxed Melting of Continental Crust during the North China Craton Destruction

ABSTRACT The mechanism behind the destabilization of the North China Craton (NCC) remains a contentious topic among researchers. Large-scale Cretaceous adakitic magmatism in the NCC offers insights into the decratonization process. This study focuses on the Huashan and Laoniushan plutons located in the Lesser Qinling on the southern margin of the NCC and compiles published data for coeval adakitic rocks to investigate the role of water in adakitic rock petrogenesis during the peak destruction of NCC. Both the Huashan and Laoniushan plutons exhibit adakitic signatures, including high Sr (193–1080 ppm), low Yb (<14.8 ppm) and Y (<1.24 ppm) concentrations, as well as high Sr/Y (18–100) and La/Yb (24–58) ratios. The zircon Hf–O isotope compositions suggest that the primary source for the Huashan and Laoniushan plutons is the mafic lower crust of NCC. Nevertheless, there are significant differences in trace element characteristics between the two plutons. Specifically, the Huashan pluton displays higher Na2O/K2O ratios, lower levels of Rb, Rb/Sr, Nb, Ta content, and a weak Eu anomaly in comparison to the Laoniushan pluton. These variations in geochemical attributes cannot be accounted for by mechanisms like mantle-derived magma mixing, crustal contamination, or fractional crystallization processes. Instead, these disparities are attributed to distinct modes of crustal anatexis, involving both water-fluxed and dehydration melting. Subsequently, we conducted thermodynamic simulations of the melting process of mafic lower crust under different pressure (0.5–1.5 GPa) and water content conditions (1–3 wt.%). The simulation results suggest that the Huashan pluton is most likely formed through water-fluxed melting in a scenario with normal crustal thickness (1 GPa). On the other hand, the Laoniushan pluton might have originated from dehydration melting under normal crustal thickness and pressure conditions. Notably, high pressure (>1.5 GPa) is not necessary for the formation of intracontinental adakitic rocks. The release of water from metasomatized lithospheric mantle and subsequent hydration of the lower continental crust triggers extensive adakitic magmatism in the NCC. These findings emphasize the significance of deep water cycling in understanding large-scale magmatic events and illuminate the decratonization mechanism.

Spatial heterogeneity of the lithospheric destruction of the North China Craton: Evidence from an extended magnetotelluric sounding profile

To study the spatial heterogeneity of the North China Craton (NCC) destruction, this paper used a magnetotelluric sounding (MT) profile that passes through almost the entire NCC from west to east. Three-dimensional inversion is used to obtain a lithospheric resistivity model of the NCC. The results show that the upper crust of the Ordos Block is characterized by high resistivity. The lower crust to the upper mantle is characterized by low resistivity. The resistivity structure below the Trans-North China Orogen (TNCO) has stratification features; The Shanxi Graben shows high-low-high-low resistivity features from the upper crust to the asthenosphere; The lithosphere of the Lüliang and Taihang uplifts show high-resistivity features, and only some local relatively low-resistivity areas appear at the crust-mantle boundary. The upper crust on both sides of the Tan-Lu Fault Zone is characterized by high resistivity, but the resistivity structures of the lower crust and the lithospheric mantle are significantly different; The lower crust and the lithospheric mantle of the Sulu Orogenic Belt on the east are characterized by high resistivity; The Luxi Uplift on the west is represented by low resistivity. We propose that the mantle low-resistivity bodies (C1 and C4) of the Western and Eastern blocks may be related to the upwelling of partial melting materials along the ancient structurally weak zones in the lithosphere. The TNCO still has a typical Archean cratonic lithosphere, and the low-resistivity body C2 may be the remnant of the subducted oceanic crust. The Tan-Lu Fault Zone is structurally weak in the Eastern Block, while its western branch is a channel for the asthenospheric upwelling. We propose that the lithosphere of the northwestern Ordos Block and the Yinchuan-Hetao area is being destructed, and the TNCO is in the initial stage of being destructed. In contrast, the lithosphere of the Eastern Block has been severely destructed. In conclusion, affected by the subduction of the paleo-Pacific plate and the collision of the Indian and Eurasian plates, the ancient structures in the NCC were reactivated in the Mesozoic and Cenozoic, resulting in the spatial heterogeneity of the NCC destruction.

Earth's one‐of‐a‐kind fault: The Tanlu fault

AbstractLarge‐scale strike‐slip faulting commonly occurs in active tectonic margins, but rarely, if ever, do large faults cut deep into ancient continental nuclei known as cratons. With thick mantle roots, cratons are considered to be the most tectonically stable portions of Earth's continental lithosphere, with an eminent exception being the relatively recent destruction of North China craton. Here, we show that from 240 to 165 Ma ago the roughly coeval continental collisions of South China to the south and Mongolia to the north ruptured the Tanlu fault within the then thick North China craton. A large ~450 km displacement mechanically induced by a ~16° intracratonic rotation along the Tanlu fault reconciles the offsets of geological piercing points and palaeomagnetic data of North China on either side of the fault. Shortly after the displacement of the only large young strike‐slip cratonic fault, the cratonic lithosphere of eastern North China collapsed.

Early Cretaceous extensional allochthons in the Taihang Shan associated with destruction of the North China Craton

Whilst geophysical exploration and petrological analyses imply that the Early Cretaceous North China Craton (NCC) destruction may have impacted the Taihang Shan in the central NCC, associated evidence indicative of contemporary upper-crustal extension is lacking. We herein investigate the formation mechanism and timing of the allochthons that consist of Mesoproterozoic to Mesozoic sedimentary rocks within the Paleoproterozoic Fuping complex in the middle Taihang Shan, based on field investigation and zircon U-Pb analysis. Our results indicate that the western boundary of the selected allochthon features wide collapsed breccias filled with synchronous Early Cretaceous (∼134 Ma) pyroclastics. These allochthons likely formed under extension along with the basement doming of the Fuping complex in response to crustal stretching in Early Cretaceous. Our results provide explicit evidence of upper-crustal extension in the Taihang Shan associated with the Early Cretaceous NCC destruction.

Linking the Jehol Biota Evolution to the Early Cretaceous Volcanism During the North China Craton Destruction: Insights From F, Cl, S, and P

AbstractThe Early Cretaceous Jehol Biota evolution has remarkable spatiotemporal correlation with the destruction of the North China craton though the coupling mechanism remains enigmatic. The craton destruction was accompanied by intense magmatic activity and the released volatiles and nutrients might have had climatic and environmental impacts on the biotic evolution. In this study, we investigated the mentioned hypothetical causal link by determining concentrations and total emissions of volatile elements (S, F, Cl) and bulk‐rock P contents of volcanic rocks that were erupted during the pre‐flourishing, flourishing and post‐flourishing stages of the Jehol Biota. Our results show that the volcanism near the flourishing stage has lower S (1,083–2,370 ppm), Cl (1,277–5,608 ppm) and higher P2O5 contents (0.48–0.84 wt.%) than that in the non‐flourishing stages with S of 1,991–3,288 ppm, Cl of 7,915–12,315 ppm and P2O5 of 0.17–0.23 wt.%. Fluorine contents in the three stages vary from 893 to 3,746 ppm. The total volatile emissions are minor in the flourishing stage (1–14 Gt S, 0.6–10 Gt Cl, 0.6–9 Gt F) but elevated in the non‐flourishing stages (2–766 Gt S, 4–1,168 Gt Cl, 1–175 Gt F). Our data suggest that regional climatic and environmental impacts of volcanism in the non‐flourishing stages probably hindered the species diversification. The high P flux released from lithospheric mantle‐derived lavas during the peak time of craton destruction might have enhanced primary productivity and contributed to the flourishing of the Jehol Biota. Our study provides insights into the relationship between the biosphere and deep geodynamic processes driven by volcanism.

Linking the Jehol Biota evolution to the Early Cretaceous volcanism during the North China craton destruction: insights from F, Cl, S, and P

Linking the Jehol Biota evolution to the Early Cretaceous volcanism during the North China craton destruction: insights from F, Cl, S, and P

Linking the Jehol Biota evolution to the Early Cretaceous volcanism during the North China craton destruction: insights from F, Cl, S, and P

Linking the Jehol Biota evolution to the Early Cretaceous volcanism during the North China craton destruction: insights from F, Cl, S, and P

Geochronology, stable isotopes and pyrite chemistry of the Cangzhuyu gold deposit in the North China Craton: Implications for gold metallogeny of Xiaoqinling

The ore genesis of gold deposits in Xiaoqinling, located in the south margin of the North China Craton (NCC), remains highly debated. Either a magmatic source or a metamorphic origin has been advocated for the ore-forming fluids. In this paper, we report new 40Ar/39Ar dating, in-situ pyrite trace elements and C-H-O isotopic data for the Cangzhuyu deposit, hosted in quartz veins within the Archaean metamorphic rocks to constrain the ore-forming processes. Four stages of mineralization and alteration can be recognized in the deposit, including Stage I: quartz-pyrite veins; Stage II: pyrite-quartz-ankerite veins; Stage III: polymetallic sulfides-ankerite-quartz veins; Stage IV: quartz-carbonate veins. Sericite from stage III gold-bearing veins has a 40Ar/39Ar plateau age of 130.7 ± 1.3 Ma, which is synchronous with the regional gold mineralization event in the Xiaoqinling district. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) trace element analysis shows that Stage I and Stage IV pyrite show similar compositions and rarely contain lattice gold. In contrast, gold mostly occur as native gold or Au-Te-Bi mineral inclusions within Stage III pyrite, which are consistent with their high Ni, Te, Bi contents. The ore-forming fluids equilibrated with ankerite have C-O isotopes of −6.6 to −4.1‰ and 8.8 to 10.8 ‰, respectively. They are consistent with H and O isotopes of sericite that δDfluid ranges from −61.1 to −60‰ and δ18Ofluid ranges from 8.2 to 7.2 ‰, implying a magmatic source. We hence suggest that the Cangzhuyu gold deposit was formed from mantle-derived magmas in a setting of the destruction of NCC and lithospheric thinning.

Lithospheric Conductors Shed Light on the Non‐Uniform Destruction of North China Craton

AbstractLow resistivity in the continental lower crust and uppermost mantle has been commonly observed in both Phanerozoic and Precambrian areas. Given different tectonic history, these conductors could be attributed to different conductive mechanisms. The North China Craton (NCC) is one of typical craton that have suffered from extensive destruction, part of which was modified by Phanerozoic tectonic‐thermal events and the others remain stable cratonic lithosphere. We here present a high‐resolution 3‐D electrical resistivity model from the inversion of magnetotelluric data collected in 183 sites of NCC. Beneath the stable craton in the north part of Ordos Block, an E‐W trending conductor extends from lower crust to uppermost mantle, which can be attributed to the concentration of sulfides/graphite emplaced through oceanic subduction during the Paleoproterozoic assembly of Columbia. The conductors beneath the Taihang Mountains and the south part of Ordos Block also reflect ancient sutures. In contrast, the conductor in mantle beneath the south part of North China Plain (SNCP) reflects an on‐going process of craton destruction relating to the subduction of the Pacific Plate in Cenozoic. The MT data, combined with seismic radial anisotropy model suggest the lower crust and uppermost mantle beneath SNCP is anisotropic. And a significant electrical anisotropic layer with the most conductive direction along N70°W and the anisotropy factor of 6.3 is revealed in the 20–70 km depth by 2‐D anisotropic inversion. We attribute the enhanced conductivity along anisotropy direction to the accumulation of melts in sills, resulting from the upwelling of asthenosphere in Cenozoic.

Characteristics of Terrestrial Heat Flow and Lithospheric Thermal Structure in Typical Intermountain Basin at the Eastern Foot of Yanshan Mountain, North China

The Yanshan area is rich in geothermal resources. However, limited research has been done on the geothermal resources of intermountain basins in the area, which restrict the exploration and development of geothermal resources. In this study, the Yanheying Basin, a typical intermountain basin located in the eastern foothills of Yanshan Mountain, is selected to perform a comprehensive analysis regarding heat flow and lithospheric thermal structure, to have a better understanding of the geothermal background and resource utilization potential of the area. The methods of deep borehole temperature logging, and rock sampling and testing were applied. With geological and geophysical data collected in the surrounding basins, the thermophysical parameters of rock formations, terrestrial heat flow and temperature distribution on a crustal-scale around the basin were analyzed. Results show that the ratio of crust heat flow to that of the mantle in the Yanheying Basin is 0.68, which falls in the range of that of the North China Plain (0.6–0.8), showing an obvious result of lithospheric thinning. The results also show that both crust and mantle heat flows in the Yanheying Basin are far lower than those of the North China Plain. it indicates that the crust of the Yanheying Basin and the entire Yanshan area has experienced a low degree of damage. That provides a piece of good thermodynamic evidence for the spatial variation of North China Craton destruction. The depth of the Curie surface in the study area is estimated to be about 24 km, which is consistent with the results of aeromagnetic data analysis. It confirms the results of lithospheric thermal structure and deep temperature distribution in the Yanheying Basin. The Yanheying Basin has certain potential for geothermal resources utilization in the depth of 2–6 km, where probably exist several carbonate thermal reservoirs with medium-temperature geothermal water. The above results can provide new insights into the geothermal research and exploration of intermountain basins in the Yanshan area.

Extensional tectonics and North China Craton destruction: Insights from the magnetic susceptibility anisotropy (AMS) of granite and metamorphic core complex

Extensional tectonics and North China Craton destruction: Insights from the magnetic susceptibility anisotropy (AMS) of granite and metamorphic core complex

Upwelling mantle plume and lithospheric delamination beneath the North China Craton

Various models have been proposed for the destruction of the Eastern North China Craton (NCC); however, it is still a highly controversial scientific issue. In this study, abundant teleseismic data recorded by permanent and temporary stations in the NCC were collected, and P-wave tomography and common conversion point (CCP) stacking of receiver functions were performed. The results from this study reveal an upwelling mantle plume and a shallow Lehmann discontinuity (or the lower boundary of a low-velocity zone) beneath the Eastern NCC. Additionally, a large-scale, plate-like high-velocity anomaly is defined under the Eastern NCC that might be related to the delamination of a lithospheric keel. Based on the above results and assessment, NCC destruction might include two causes: lithospheric keel removal or delamination and mantle plume upwelling.

Significance of crustal extension and magmatism to gold deposits beneath Jiaodong Peninsula, eastern North China Craton: Seismic evidence from receiver function imaging with a dense array

The Jiaodong Peninsula, located in the eastern North China Craton (NCC), is a key region to study the genetic linkage between large-scale gold mineralization and craton destruction. We construct a fine crustal structural image across the Jiaodong Peninsula, using teleseismic P-wave receiver function data recorded by a dense linear array of 340 short-period seismic stations. The results reveal significant similarities and differences between the eastern and the western Jiaodong Peninsula. The presence of an intracrustal low-velocity zone, and the north-dipping interfaces beneath the Jiaolai Basin imply widespread crustal extension in the whole region. In the northwest Jiaodong metallogenic belt, the identified detachment faults, small vertical velocity gradients in the upper part of the lower crust and the thick crust-mantle transition zone provide evidences for intense crustal extension in this area, probably coeval with the peak of lithospheric thinning and destruction of the eastern NCC in the Late Mesozoic. In the Muru metallogenic belt, distinct differences are found on the opposite sides of the Wulian-Yantai Fault Zone (WYFZ), in the depth and structure of the Moho, intracrustal low-velocity zone, upper crustal Vp/Vs ratios, and Bouguer gravity anomalies, indicating that the WYFZ may be a steep transcrustal fault. We propose that the coupled effects of intense crustal extension, voluminous magmatism and water released from the subducting Paleo-Pacific slab may have been responsible for the concentrated gold deposits in the northwest Jiaodong during the peak of the NCC destruction, while limited gold deposits in the Muru metallogenic belt may have been attributed to relatively weak crustal extension and steep faults.

Destruction of the North China Craton and its influence on surface geology and terrestrial biotas

The North China Craton (NCC), a major geological element of East Asia, had hehaved as a stable craton untile late Mesozoic. The NCC experiencd multiple contraction and extension in late Mesozoic, evidened by three phases of shortening and two phases of stretching. The three shortening phases occurred in the late Middle Jurassic, earliest Early Cretaceous, and latest Early Cretaceous, respectively. Crustal stretching happened in Late Jurassic and Early Cretaceous times, and was marked by large-scale magmatism and development of rift basins and metamorphic core complexes. Widespread vigorous magmatism and extensive rifting indicate the loss of the NCC stability in the Early Cretaceous. Alternating crustal contraction and extension of the NCC are attributed to the change in subduction angles of the paleo-Pacific plate, with low-angle subduction resulting in shortening and high-angle subduction leading to stretching. However, magmatism, deformation and lithospheric thinning are merely the various expressions of the NCC destruction. It is shown that deep thermal processes must have strongly altered the properties of overlying lithosphere, resulting in a change from the continental into oceanic mantle. It was the transformation of physico-chemical properties of the lithospheric mantle that destabilized the NCC. Also noticeable are occurrences of the Yanliao and Jehol biotas that evolved in the Middle-Late Jurassic and Early Cretaceous, respectively, and just coincided with the initial and peak stages of the NCC destruction. Flourishing and vanishing of the biotas appeared closely related to volcanic intensity and rift basin development in space and time, implicating a profound control of deep dynamic processes on surface paleogeography and ecosystems. Implicitly, life should have been evolving in accord with surrounding environments. Volcanism might have exerted a strong influence on prosperity and disappearance of the Yanliao and Jehol biotas, with ash fallout leading to perfect preservation of a variety of precious fossils. Also noteworthy is that biotas thrived in the period when rift basins were developing, whereas biotas died out when basins were inverted. It is still a challenge to explore the linkage of terrestrial life evolution and tectonic processes. Recent developments in geodynamic studies reveal that subduction of the western paleo-Pacific plate might have produced a unique mantle profile in late Mesozoic, with the stagnant plates in mantle transition zone being sandwiched between the lower mantle and the big mantle wedge. Extensive dehydration and decarbonization of the stagnant plates resulted in melting and metasomatism of the upper and lower parts of mantle transition zone. These processes should have played a crucial role in altering the nature of lithospheric mantle and in triggering large-scale magmatism in the crust. A big mantle wedge is thought to have developed beneath the East Asia continent during the Early Cretaceous as a result of the slab rollback and the stagnation in the mantle transition zone. The combined tectonic processes must have exerted a profound influence on both the NCC destruction and Yanliao/Jehol biotal evolution. Interdisciplinary researches will help us understand the complicated interaction of deep and surface processes and comprehend the past, present and future of our habitable planet.

40Ar/39Ar dating of basic–felsic dikes in the Sulu Orogen, Shandong Peninsula, China: Evidence for the destruction of the southeastern North China Craton

During the Early Cretaceous, the North China Craton (NCC) underwent dramatic lithospheric thinning and destruction, resulting in widespread granitic magmatism and lithospheric extension. The geochronology of basic–felsic dikes provides a unique perspective on a crustal‐extension event that was related to the NCC destruction. Previous studies usually used zircon U–Pb dating to constrain the time of dike emplacement. This method is limited in terms of dating basic dikes because the authigenic zircons are rare or absent. Additionally, recording later reheating events during multiple phases of extension that occurred in the NCC after the Mesozoic is impossible. Here, we present 40Ar/39Ar geochronological data for basic–felsic dikes in the Sulu Orogen, Shandong Peninsula, East China. Our results indicate that these dikes were emplaced between ca. 127 and 95 Ma, with only two felsic samples recording ages <100 Ma, suggesting that crust‐derived magmatism decreased after this time. Several of these dikes that were adjacent to faults also recorded a later Cretaceous reheating event, which may have been related to fault movement and magmatic activity in the deeper crust. Combined with previous research results, Cretaceous dike emplacement was contemporaneous with crustal extension and widespread magmatic activity, slightly later than the peak time of the NCC destruction, suggesting an intrinsic connection between the dikes' emplacement and NCC destruction. The crustal magma and tectonic activity are direct evidence of the craton destruction, so these age data constrain the timing of destruction in the southeastern portion of the NCC to approximately 95 Ma.

Indication from finite-frequency tomography beneath the North China Craton: The heterogeneity of craton destruction

We picked new traveltime residual datasets in three frequency bands (0.02–0.1, 0.1–0.8, and 0.8–2.0 Hz) for P-waves from 793 teleseismic events and two frequency bands (0.02–0.1 and 0.1–0.8 Hz) for S-waves from 310 teleseismic events, recorded by 389 permanent stations of the China National Seismic Network and 832 broadband stations of 10 temporary arrays deployed in the North China Craton (NCC) region. The final datasets are composed of 65628 P-arrivals and 47050 S-arrivals. Based on previous research and our team’s 2012 tomographic work, we constructed new three-dimensional P-velocity and S-velocity models of the NCC through some improvements, such as augmenting a much denser station coverage in the western NCC, considering the incident angle effect in crustal correction and using a multi-frequency joint inversion tomographic technique. The new velocity models provide several salient features, from which we draw possible inferences on regional dynamic processes. We observed high-velocity anomalies in the mantle transition zone (MTZ). Obvious morphological heterogeneities suggest buckling and/or fragmentation of the subducted Pacific slab, and some of the slab materials are visible below 660-km discontinuities. The velocity structure of the eastern NCC is dominated by small-scale lateral heterogeneities. At shallow depths, high-velocity anomalies beneath the southern part of the eastern NCC and the Yanshan region likely represent a remnant of cratonic lithosphere, which may suggest that the NCC destruction is spatially non-uniform. We also detected a high-velocity anomaly in the Sulu Orogen extending downward to ~300 km, which is seemingly controlled by the Tan-Lu Fault. The northern boundary of this anomaly spatially coincides with the Yantai-Qingdao-Wulian Fault, and is likely a remnant of the Yangtze cratonic lithosphere subducting northwestward. Significant low-velocity anomalies imaged beneath the central NCC show a spatial discordance between their northern and southern parts. The northern low-velocity anomaly extends downward to the top of MTZ with a lateral NW-SE strike, whereas the southern one tapers off at ~200–300 km. Low-velocity anomalies are present beneath the Phanerozoic orogenic belts surrounding the NCC, the Paleoproterozoic Trans-North China Orogen, and the Tan-Lu Fault. This feature not only shows excellent spatial correlation with the orogens at the surface, it also exhibits a consistent vertical continuity in a depth range of 60–250 km. This intriguing feature suggests that the collisional orogenic belts and Tan-Lu Fault are inherited weak zones, which may play a key role in craton destruction. By combining multidisciplinary results in this area, we suggest that the spatial heterogeneities associated with the NCC destruction most likely result from the combined effects of a spatially non-uniform distribution of wet upwellings triggered by the subducted Pacific slab and pre-existing weak zones in the cratonic lithosphere.

Geochemical and Sr–Nd–Pb–Hf–O isotopic compositions of the Tiezhai complex: Implications for lithosphere destruction of the North China Craton

It is generally accepted that in the Late Mesozoic, >100 km of ancient refractory lithospheric mantle beneath the eastern part of the North China Craton (NCC) was removed and replaced by young and fertile mantle material. However, the mechanisms and a tectonic model for this lithospheric destruction remain subjects of debate. To elucidate this lithospheric destruction, an investigation that included whole-rock geochemical analyses, zircon U–Pb age determinations, and in situ Hf–O isotope analyses of samples from the Tiezhai syenite porphyry and mafic rocks from western Shandong Province (the Luxi terrane) was conducted. Zircon U–Pb dates reveal that the Tiezhai syenite porphyry, gabbro, and monzonite were emplaced during the Early Cretaceous (weighted-mean 206Pb/238U ages of 130–129 Ma). Abundant Mesoarchean–Paleoproterozoic inherited zircons/cores were identified in both the syenite porphyry and the gabbro, yielding 207Pb/206Pb ages of 2.95–2.34 Ga. Both the syenite porphyry and mafic rocks are metaluminous, high-K calc-alkaline rocks enriched in large ion lithophile elements (e.g., Rb, Sr, and Ba) and light rare earth elements, and depleted in high field strength elements (e.g., Nb, Ta, and Ti) and heavy rare earth elements. The samples and have no obviously Eu anomalies. The syenite porphyry has high Sr and La contents, high Sr/Y (196–292) and (La/Yb)N (24.8–36.2) ratios, and low Y and Yb contents, similar to adakitic rocks. The Tiezhai syenite porphyry has a relatively narrow range of (87Sr/86Sr)i ratios (0.7057–0.7059), εNd(t) values (−8.9 to −6.8), and relatively high radiogenic Pb isotopic compositions [(206Pb/204Pb)i = 18.36–18.37, (207Pb/204Pb)i = 15.54–15.55, and (208Pb/204Pb)i = 38.25–38.31]. The Tiezhai mafic rocks can be divided into two groups (1 and 2) based on their whole-rock Sr, Nd, and Pb isotopic compositions. Group 1 has lower (87Sr/86Sr)i ratios than group 2 (0.7046–0.7047 vs. 0.7072–0.7096), lower radiogenic Pb isotopic compositions [(206Pb/204Pb)i = 17.68–17.71 vs. 18.08–18.12; (207Pb/204Pb)i = 15.44–15.45 vs. 15.52–15.53; (208Pb/204Pb)i = 37.72–37.98 vs. 40.17–40.60], and slightly higher εNd(t) values (−8.0 to −7.1 vs. –10.8 to −8.2). The syenite porphyry and gabbro from group 2 have similar narrow ranges of zircon rim εHf(t) values (mostly between −4 and + 2), and high zircon rim δ18O values (syenite porphyry = 6.9‰–9.0‰; gabbro = 7.7‰–9.1‰), and low inherited zircon/core δ18O values (syenite porphyry = 5.8‰–6.9‰; gabbro = 5.7‰–6.9‰). The Tiezhai mafic rocks were probably derived from partial melting of the Luxi EM1-asthenospheric mantle previously metasomatized by fluids derived from subducted oceanic crust and sediments. The melts probably assimilated ancient NCC upper crust material (~5% assimilated by group 1 mafic rocks, 20%–30% assimilated by group 2 mafic rocks) during magma ascent. The Tiezhai syenite porphyry was most likely derived from partial melting of the newly underplated thick lower crust and assimilated ~10% of the ancient NCC upper crust material during ascent. The addition of fluids derived from oceanic crust and sediments to the overlying subcontinental lithospheric mantle during subduction was an important factor contributing to lithosphere destruction in the eastern NCC. Slab rollback, together with the ridge subduction of the paleo-Pacific slab beneath the eastern NCC, is the most reasonable tectonic model for NCC destruction and formation of the Early Cretaceous large-scale magmatic rocks in the eastern NCC.

Mesozoic magmatism in the eastern North China Craton: Insights on tectonic cycles associated with progressive craton destruction

The North China Craton (NCC) provides a classic example for lithospheric thinning associated with craton destruction (or decratonization) through multiple tectonic events. The peak of craton destruction is considered to have occurred during Mesozoic, especially in Early Cretaceous, linked to the subduction/collision between the NCC and Yangtze Craton during the Triassic in the south and the Paleo-Pacific plate subduction during Early Cretaceous in the east. Here we investigate a suite of intrusive and volcanic suites including granite, gabbro, diorite, basalt, andesite, volcanic tuff, agglomerate, siliceous tuff and trachyte from the southern Yishui and Juxian domains to gain insights into the Mesozoic tectonic evolution of the eastern NCC in relation to decratonization. Zircon U-Pb data from basalt show multiple populations with xenocrystic grains ranging in age from Paleoproterozoic (2457–1940 Ma), through Neoproterozoic (896–559 Ma), to Paleozoic (442–380 Ma) and Mesozoic (204–122 Ma). Inherited grains from the granite and gabbro yield weight mean 206Pb/238U ages of 650.0 ± 13 to 773.4 ± 2.6 Ma suggesting the involvement of components from the Yangtze Craton. Magmatic zircons from diorite show weight mean 206Pb/238U ages of 121.5 ± 1.2 Ma representing the emplacement age of this rock. Magmatic zircon grains from the volcanic suite (andesite, volcanic tuff, agglomerate, siliceous tuff and trachyte), show weighted mean 206Pb/238U ages of 132.4 ± 1.4 Ma, 123.02 ± 0.71 Ma, 122.97 ± 0.69 Ma, 121.96 ± 0.49 Ma, and 124.6 ± 1.1 Ma respectively, corresponding to the timings of their eruption. The Paleoproterozoic zircon grains correspond to xenocrysts captured from the NCC basement rocks, whereas the Neoproterozoic and Paleozoic grains were inherited from the Yangtze Craton. The Late Triassic to Jurassic zircon grains can be correlated to delamination of the thickened continental crust during deep subduction of Yangtze continental crust and the continent-continent collision between NCC and the Yangtze Craton. The Early Cretaceous population can be linked to the subduction of the Paleo-Pacific plate from the east and related extensional setting. The geochemical data display significant enrichment in LREE along with negative Eu anomalies, with high Th/Ta and La/Nb ratios, negative Nb–Ta anomalies, and high concentration of LILE (K, Rb, Ba and Pb) than HFSE (Nb, Ta and Ti), suggesting subduction-related arc magmatic setting in an active continental margin. Zircon Lu-Hf data from these rocks display dominantly negative εHf(t) values ranging from −36.8 to −3.1, TDM in the range of 1105–2572 Ma, and TDMC between 1785 Ma and 3776 Ma, indicating that the magma sources involved Paleoproterozoic components with minor input of reworked Archean crust through different degrees of enrichment with crustal material and minor input from extension-related mantle melting. In conjunction with the results from previous studies in the eastern NCC, we propose that the late Paleozoic southward subduction of the Paleo-Asian Ocean, the Triassic northward subduction and collision of the Yangtze Craton with the NCC, and the Early Cretaceous westward subduction of the Paleo-Pacific plate jointly contributed to the cratonic destruction of NCC. The Paleo-Pacific plate subduction beneath the NCC (major contributing mechanism) with the slab rollback induced lithospheric extension likely facilitated back-arc spreading, asthenospheric upwelling resulting in lithospheric thinning including delamination, melting of lithosphere mantle, and underplating of the modified mantle beneath the lower crust of the NCC during the Early Cretaceous.