Eastern North China Research Articles

Metallogeny of the Hunjiang basin, northeastern North China block

The Hunjiang basin in the northeastern North China block is host to a wide range of ore deposit types that are currently exploited by more than 100 past and producing mines. Extensive field and laboratory investigations were conducted to summarize the regional metallogeny, classify the different deposit types, and to place the deposits within a regional geologic and tectonic context. The Archean basement of the basin is host to magnetite deposits that have been affected by high-grade metamorphism. In addition, Proterozoic magmatic Cu-Ni deposit and orogenic Au deposits that are likely of Mesozoic age are located in the metamorphic basement rocks. Polymetallic Co-Cu and Ni-Co-Cu deposits are located in Proterozoic schists within the basin and are of pre- to syn-metamorphic origin. However, most deposits in Hunjiang basin can be related to Mesozoic igneous activity. This includes porphyry Cu and Cu-Mo deposits as well as associated skarns and carbonate replacement deposits. Economically most significant are Au deposits hosted in Proterozoic limestone and dolomite that are located distal to the Mesozoic igneous intrusive centers. This includes the White Mountain deposit near Baishan City, which contains an endowment of more than 50 tonnes Au. There are no known high-sulfidation epithermal deposits within the Hunjiang basin, which is consistent with fluid inclusion evidence demonstrating that emplacement of the porphyry intrusions occurred at significant depth below the paleosurface. Geochronological constraints indicate that Mesozoic igneous activity and associated deposit formation in the Hunjiang basin occurred as a result of Jurassic subduction processes and subsequent extension after slab rollback and lithospheric delamination under the Eastern North China Block in the Cretaceous. Future mineral exploration efforts in the Hunjiang basin should focus on the distal sedimentary rock-hosted Au deposits associated with Mesozoic intrusions, with special emphasis on the northern part of the basin where these deposits occur preferentially at the intersection of extensional faults with a vanished evaporite unit that is distinctly enriched in Fe oxides providing a chemical trap.

Petrogenesis and Geological Significance of the Quartz Monzonites in the Jinling Area, Western Shandong Province

Jinling complex pluton is a key part of the Mesozoic magmatic belt in the eastern North China Craton. However, its petrogenesis is still being debated. The Jinling complex, mainly composed of biotite diorites, hornblende diorite, augite diorites, (quartz) monzonites, and quartz diorites, is outcropped in Huashan and Heitieshan. This paper studies the zircon geochronology, zircon Hf isotope, and Sr-Nd-Pb isotope of quartz monzonites. The samples have high contents of Cr, Ni, V, Al2O3, Ba, Sr, and are enriched in LREEs, LILEs (K, Ba, Sr), depleted in HREEs, and HFSEs (Nb, Ta, Ti). The samples with captured zircons of ~2.5 Ga yield a weighted mean age of ~127 Ma, and the zircons have negative values of εHf(t) from −3.2 to −9.4 while the ratios of 208Pb/204Pb, 207Pb/204Pb, 206Pb/204Pb 37.75~38.15, 15.41~15.43, 17.59~17.98, respectively. The ratios of Th/U are from 3.77 to 3.82, while the values of μ and ω are 9.18 and from 35.72 to 36.15. Meanwhile, the ratios of 87Sr/86Sr are higher than the ones of the mantle. Geochemical and isotopic features indicate that the quartz monzonites derived from the subcontinental lithospheric mantle that probably assimilated ancient NCC upper crust materials (~15–20%) during the magma ascent in a lithospheric extension setting.

Heat Accumulation Mechanism of the Gaoyang Carbonatite Geothermal Field, Hebei Province, North China

From 2019 to 2021, we constructed two high-productivity geothermal wells with wellhead temperatures of 109.2 and 123.4°C in the Gaoyang geothermal field. Based on the two wells, it was proved that Gaoyang is a medium-temperature carbonate geothermal field with great development potential. The article reported the latest exploration achievements of deep buried hill geothermal resources in the geothermal field. The productivity of D34 and D35 geothermal wells were evaluated by James end-pressure method: the total flow of steam–water mixture was 234.59–331.92 (t/h), the dryness was 1.36–2.03%, and the single-well power generation potential was 2.10–2.55 MW. Combined with those results, the heat control factors and heat accumulation mechanism of the deep carbonatite geothermal field were confirmed. The westward subduction of the Pacific plate caused obvious damage to the eastern North China Craton and greatly reduced the thickness of the lithosphere and crust. This process facilitated the conduction of mantle-derived heat to shallow crust. Deep strike-slip faults (e.g., Maxi fault) cut through the lithosphere, leading the deep mantle-derived heat and magma to migrate into the crust. The heat accumulated from the depression with low thermal conductivity to the uplift with high thermal conductivity. Groundwater was heated up by deep cycle and convection along faults. The catchment of regional karst groundwater also had a certain effect on the heat accumulation. The Gaoyang geothermal field was formed by these factors.

Pliocene-Pleistocene evolution of the lower Yellow River in eastern North China: Constraints on the age of the Sanmen Gorge connection

The Yellow River, the second longest river in China, originates in the northeastern Tibetan Plateau, flows in a contorted square-bend-shaped path through the Loess Plateau, then enters the Fenwei Graben before discharging through the Sanmen Gorge onto the North China Plain. Prior to its connection through the Sanmen Gorge, which cuts through the drainage divide of the Hua and Taihang mountain belt, the Yellow River had been partly impounded as a large lake filling the Fenwei Graben. To help decipher the Pliocene-Pleistocene history of the development of the lower reaches of the Yellow River, we analyzed the sedimentary histories of the Fenhe sub-basin in the northeast part of the Fenwei Graben and of fluvial-lacustrine sediments in the Huangdigou (HDG) section, which is now exposed at the upstream entrance to the current Sanmen Gorge. The Fenhe sub-basin changed from lacustrine/peat deposition to fluvial gravels at ~2.5 Ma. We suggest that this sedimentary facies change indicates the establishment of a significant outflow of the former Fenwei Graben Lake through the deepening Sanmen Gorge. The continuing lowering of base-level in the Fenwei Graben, which culminated in the direct flow of the Yellow River through the Sanmen Gorge and/or fluvial inland regressive erosion, also led to headward erosion of a new paleo-Fenhe River that cut through the Fenhe sub-basin. Tectonic activity and climate shifts may have contributed to the change to the modern path of the Yellow River. • The Fenhe sub-basin changed from lacustrine/peat deposits to fluvial gravels at ~2.5 Ma. • The detrital material deposited in the Sanmenxia isthmus was mainly from local sources at ~2.5 Ma. • Tectonic activity and climate shifts may have contributed to the change to the modern path of the Yellow River.

Structural restoration of an Eo-Mesoarchean (3.8–2.9 Ga) terrane, Eastern China, dissected by the Tanlu fault zone

Ancient gneissic terranes are critical rare materials that can reveal the Earth's early crustal evolution. This paper presents reconstruction of the oldest Eo-Mesoarchean gneissic terrane (3.8–2.9 Ga) in the eastern North China Craton that was partitioned by the ENE-WSW striking Tanghe-Hanling strike-slip fault (THF). The THF is a splay off the Tanlu fault zone and has been traced for 130 km and is 1–1.5 km wide. The THF has a 28 km sinistral offset, which has been established by detailed field observation. Restoring the 28 km offset, means that: (1) A sizeable potential area is recognized for searching for more 3.8–2.9 Ga Eo-Mesoarchean rocks; (2) A large NW-striking late Archean BIF belt is correlated with another at Anshan. Our data integrate with regional structural information of the Tanlu fault zone; we suggested that the Tanlu fault zone has an eastwards-fan splay pattern geometric feature in its northern part. Accordingly, we further restore the ancient tectonic configuration of eastern Asia before the Tanlu fault zone initiation. Eo-Mesoarchean rocks and 2.7–2.9 Ga terranes cropping out in Eastern Block of the North China Craton are arranged in line with NNW-SSE strike, which is consistent with their oriented gneissic foliations.

Correlating metamorphic mineral assemblages with metamorphic ages in rocks recording multiple tectonothermal events: A case study of the Jiaobei terrane, eastern North China Craton

Interpretations of high-grade terranes recording more than one episode of metamorphism can often be problematic due to the difficulties in assigning the metamorphic conditions to the time of metamorphism. The Jiaobei terrane as a typical Precambrian metamorphic terrane in the North China Craton (NCC) records multiple high-grade metamorphic events. Resolving the timing and features of each metamorphic event can cast light on the above issue and also play a key role in understanding the geological evolution of the Jiaobei terrane and the NCC. This study reports paired U-Pb dating with in-situ trace elements and oxygen isotope compositions of metamorphic zircons in meta-mafic rocks from the Qixia area of Jiaobei terrane. The zircons develop core-rim structures with both of them exhibiting metamorphic features. Zircon rims, although widely developed, are mostly too thin for in-situ age dating. LA-ICPMS as well as SIMS zircon U-Pb analysis of zircon cores yielded metamorphic ages of ∼ 2500 Ma, whereas the rims yielded 207Pb/206Pb ages of 1915–1717 Ma. The rare earth elements (REE) patterns and δ18O values measured in the Paleoproterozoic metamorphic zircon rims are distinct from those measured in the Archean cores. Distinct features of the cores and rims imply that the garnet-bearing (high-pressure) mineral assemblages were formed during late Paleoproterozoic metamorphic event and absent during the Neoarchean event. These new geochronological data further confirm that the Jiaobei terrane records both the late Neoarchean metamorphism and the late Paleoproterozoic tectonic thermal event. Also, our study argues for the existence of global subduction network geological records in the NCC during Paleoproterozoic, rather than during Neoarchean. The influence of the overprinted late Paleoproterozoic metamorphism should be fully considered when estimating P-T conditions of the earlier tectonothermal event (Neoarchean metamorphism).

Elemental and Sr-Nd-Pb-Hf Isotope Signatures of Early Cretaceous Magmatic Rocks in the Wulian Area, Eastern Shandong: Implications for Crust-Mantle Interaction at the Edge of the Sulu Collisional Orogenic Belt

Abstract We present new whole-rock geochemical, Sr-Nd-Pb isotopic, and zircon U-Pb and Hf isotopic data for Early Cretaceous magmatic rocks (trachy-andesite, pyroxene diorite, diorite porphyrite, and dolerite) in the Wulian area of Shandong, eastern North China. These data are used to constrain the mechanism of crust-mantle interaction at the edge of the Sulu orogenic belt. The belt formed by the collision of the Yangtze Craton (YC) and the North China Craton (NCC) during the Mesozoic. New zircon U-Pb dating indicates that the magmatic rocks were formed during the Early Cretaceous (123-124 Ma). These rocks are characterized by moderate contents of SiO2 (50.0-60.0 wt.%), MgO (3.3-5.6 wt.%), Cr and Ni with low Nb/U ratios (0.8-11.8), and high La/Nb (5.2-24.5) and Ba/La ratios (12.3-38.1). They are enriched in large ion lithophile elements, depleted in high field strength elements, and are characterized by high initial 87Sr/86Sr values (0.7079-0.7088) and low εNdt (-20.6 to -14.6). The samples have relatively low initial 206Pb/204Pb (16.38-17.18), 207Pb/204Pb (15.38-15.48), and 208Pb/204Pb (37.24-37.83) values. The Sr-Nd-Pb-Hf isotopic characteristics of the samples are similar to those of mafic rocks in the Sulu orogenic belt, suggesting that they might have similar sources. It is clear that the magma source of the samples involves both crustal and mantle materials and so we propose a model for crust-mantle interaction at the edge of Sulu orogenic belt. In this model, the Yangtze plate subducted deep below the northwestern NCC during the Triassic and was trapped in the lithospheric mantle. In the early Cretaceous, lithospheric extension in combination with asthenospheric upwelling resulted in partial melting of the overlying lithospheric mantle. The magmatic rocks in the Wulian area were generated by mixing between melts of both the lithospheric mantle of the NCC and the residual lower crust of the YC. This study therefore provides significant information on crust-mantle interaction at a continental subduction zone.

Coexisting diverse P–T–t paths during Neoarchean Sagduction: Insights from numerical modeling and applications to the eastern North China Craton

The Eastern Block of the North China Craton preserves a Neoarchean greenstone-granite rock association with typical dome-and-keel structures. Metamorphic data for these rock assemblages record both anticlockwise P–T paths involving near-isobaric cooling (IBC) and clockwise paths with nearly isothermal decompression (ITD) from nearby locations leading to controversial and contradictory interpretations. To resolve the presence of coexisting diverse P–T paths, and to place them within a viable geodynamic regime, we conducted 2D thermomechanical numerical models with the initial and boundary conditions similar to that of the Neoarchean eastern North China Craton. Our model results reveal that heat transferred from the high-temperature lower boundary and crustal density inversion leads to crustal-scale sagduction that generates the observed dome-and-keel architecture and results in four major types of P–T–t paths: (1) an anticlockwise IBC-type P–T–t path in which the supracrustal rocks progressively sink to a deep crustal level through sagduction, and experience a long-lived residence followed by ambient mantle cooling without significant exhumation; (2) an clockwise ITD-type P–T–t path where the supracrustal rocks sink to the deep crust and are partly captured by upwelling felsic magmas, resulting in rapid exhumation to a middle crustal level; (3) a newly identified crescent-type P–T–t path that reveals an integrated burial-exhumation cycle characterized by an initial high dT/dP burial stage, followed by the rapid exhumation to the upper crust and extensive low dT/dP cooling; (4) a hairpin-type P–T–t path in which deeply buried supracrustal rocks experience a slow exhumation rate. The dome-and-keel architecture and P–T–t paths produced by the numerical model conform to the structural, metamorphic and geochronological data of the Eastern Block. We propose that the geological complexity of eastern China and temporally coexisting diverse P–T–t paths most likely developed under a mantle plume related crustal-scale sagduction geodynamic regime in Neoarchean.

Keel of the eastern North China craton weakened by Proterozoic large igneous provinces

ABSTRACT Cratons are the most mature parts of the continents on Earth and can remain stable for billions of years. Cratonic keels may be destroyed, for which a prime example is the eastern North China craton (NCC), which was removed during the Mesozoic. However, the critical stable state of the keel and the destroying mechanism of the rigid and buoyant cratonic roots remain enigmatic. Here, rhenium-osmium and neodymium isotope datasets from the eastern NCC open up a possible approach to reveal its evolution prior to the destruction. Two Re (rhenium) -depletion model age peaks of the peridotite xenoliths entrained by Phanerozoic basalts reconcile the ages of the large igneous provinces (LIPs) of Yanliao (ca. 1.3 Ga) and Xuhuai (ca. 0.92 Ga), respectively. This indicates that the mantle lithosphere of the eastern NCC has undergone metasomatism and growth during the emplacement of the two LIPs. The Proterozoic LIPs probably produced buoyant mantle residues that were then captured beneath thinned lithosphere regions. Such igneous processes occur at a depth of ~100 km and may induce the formation of weak zones (e.g. palaeo-mid-lithosphere discontinuity) partially within the rigid mantle lithosphere. The palaeo-weak zones might be rheologically unstable structures and probably reduced the stability of the craton, presenting as foci for potential later keel destruction. This provides evidence that LIP event may be another key factor for the intra-cratonic mantle lithosphere destruction.

Geochronological and geochemical characteristics of continental basalts of the eastern North China Craton: insights into crust–mantle interaction induced by continental subduction

Geochronological and geochemical characteristics of continental basalts of the eastern North China Craton: insights into crust–mantle interaction induced by continental subduction

Mercury isotopic compositions of the Precambrian rocks and implications for tracing mercury cycling in Earth's interior

Mercury isotopes undergo unique mass-independent fractionation (MIF) during photochemical processes on Earth's surface. Studies have observed pronounced Hg-MIF signals in sedimentary and magmatic rocks, suggesting recycling of Hg from Earth's surface systems into the lithosphere via sedimentation and magmatism. However, the isotopic signature of Hg in metamorphic rocks and the geochemical fate of Hg during metamorphism remain unclear. Precambrian basements are important components of cratons or orogenic belts on Earth. Here, we study the Hg concentration and isotopic composition of Precambrian metamorphic and sedimentary rocks from the eastern Central Asian Orogenic Belt, and North and South China cratons. Metamorphic rocks show much lower Hg contents (0.21–7.8 ppb) than sedimentary rocks (2.6–694 ppb), indicating a substantial loss of Hg during metamorphism. The lack of correlation between δ202Hg values (–2.41 to 0.18‰) and metamorphic grades indicates no systematic mass-dependent fractionation (MDF) of Hg isotopes during metamorphism. The Δ199Hg/Δ201Hg ratios of ∼ 1.0 for both metamorphic and sedimentary rocks indicate Hg was sourced from Earth's surface systems. The coupling of Hg-MIF signals between the metasedimentary rocks and the sedimentary settings of their protolith suggests no Hg-MIF during metamorphism. The negative Δ199Hg values (–0.30 to –0.02‰) in the Precambrian coastal sedimentary rocks imply the input of Hg into coastal regions via soil erosion. The positive Δ199Hg values (0.06 to 0.31‰) in the Precambrian marine sedimentary rocks suggest deposition of atmospheric Hg(II) to open oceans via wet deposition. The lack of significant Hg-MIF during metamorphism and other underground geological processes shows that Hg-MIF signals can work as a reliable tracer for indicating material cycling in Earth's interior.

EarlyCretaceous‐Cenozoicexhumation history of Luxi Terrane and adjacent areas, eastern North China Craton

The Luxi Terrane is important for understanding the large‐scale extension and lithospheric thinning in eastern North China Craton (NCC) during the Mesozoic to Cenozoic. However, the exhumation/uplift history of the whole region in comparison to its adjacent areas is still unclear. To address this issue, we compiled 892 thermochronological data using jointly Kernel density estimation and linear inversion approaches to identify the exhumation episodes and estimate the temporal and spatial variation of the exhumation rates. The results indicated that these areas all experienced three rapid exhumation episodes, throughout the Early Cretaceous (120–100 Ma), Late Cretaceous‐Palaeocene (90–60 Ma), and Eocene (50–35 Ma). While the existence of synchronous tectonic evolution, the exhumation rates are heterogeneously distributed throughout the Luxi Terrane and neighbouring areas in space and time. We suggest that tectonics may play a role in setting up the regional variation in exhumation patterns. Considering the plate reconstructions and integrating low‐temperature thermochronological studies, the Early Cretaceous rapid exhumation corresponds to extensive craton destruction, linked with the Izanagi slab rollback within a back‐arc extensional setting. The Late Cretaceous‐Palaeocene rapid exhumation is interpreted as a response to continuing craton destruction and lithospheric thinning resulting from the subduction of Izanagi‐Pacific. In the Eocene, we propose that the coupling effect of subduction of Pacific Plate and India‐Eurasia collision can trigger this cooling episode.

Late Neoarchean high-grade regional metamorphism in the eastern North China Craton: New constraints from monazite dating in northern Liaoning

Late Neoarchean tectono-thermal events in the eastern North China Craton have been comprehensively characterized in terms of mineralogy, petrology, geochemistry, metamorphic evolution, geophysics and geochronology. The Late Neoarchean metamorphic event is debated to correlate with vertical and/or horizontal tectonism, potentially an indicator as initiation of plate tectonics. With a growing number of zircon geochronological investigations, the precise timing of the Late Neoarchean metamorphic event should be questioned due to the complexity of post-Archean multiple tectono-thermal overprints. Here we demonstrate the capabilities of LA–ICP–MS U–Pb and LA–MC–ICP–MS Sm–Nd isotope measurements applied to monazite endowed with LREE-enriched geochemical peculiarities as well as zircon U–Pb–Hf isotope, to reevaluate the Late Neoarchean metamorphic event in northern Liaoning, eastern North China Craton. Monazites within the biotite two-feldspar gneiss from the Qingyuan greenstone belt are Ce-monazite in composition, with negligible amounts of the huttonite and brabantite components. The internally homogeneous and anhedral rounded granular monazites show textural equilibration in contact with plagioclase, quartz, and K-feldspar, indicating that monazite is a product of metamorphism. The apparent ages and Eu/Eu* values of monazite analyses show a positive correlation, which confirms the continuous formation of monazite and coeval feldspar during the metamorphic evolution. These metamorphic monazites yield a weighted mean 207Pb/206Pb age of 2493 ± 8 Ma and an upper intercept age of 2496 ± 8 Ma, consistent with the metamorphic zircon dates of 2492–2468 Ma. These results, along with monazite Sm–Nd isochron of 2459 Ma, thus provide a critical clue to understand the Late Neoarchean high-grade regional metamorphism in the eastern North China Craton. As a consequence, the Qingyuan greenstone belt was only partially influenced by the Paleoproterozoic tectono-thermal events, not largely as previously thought by some workers.

Kinematic history of the Tan-Lu fault zone constrained by the Late Mesozoic–Cenozoic tectono-sedimentary evolution of basins in the Luxi Block, eastern North China Craton

• The development of basins in the Luxi Block are closely related to the Tan–Lu Fault Zone. • The basins in the Luxi Block were involved in NE–SW compression (150–145 Ma), NE–SW extension (145–122 Ma) and N–S extension (63–32 Ma). • The Tan–Lu Fault Zone experienced sinistral strike-slip, normal faulting and dextral strike-slip in Late Jurassic–Paleogene. • The change from compression to extension at ∼145 Ma in the Luxi Block represents the initiation of craton destruction. The Tan–Lu fault zone (TLFZ), a lithosphere-scale fault in the eastern North China Craton (NCC), experienced multi-stage evolution characterized by alternating extension and strike-slip faulting in different tectonic setting. A series of Meso-Cenozoic sedimentary basins striking NW–SE to nearly E–W are distributed in the Luxi Block (LXB) to the west of the TLFZ. Recently, based on detailed fieldwork focusing on the sedimentary features and the boundary faults of these basins, the genetic relationship between basins and the TLFZ is disclosed in this study. The basins in the LXB were formed in the Late Jurassic–Paleogene, which were controlled by E–W and NW-SE-trending boundary faults. They were filled by the Late Jurassic fluvial coarse clastic rocks, the Early Cretaceous volcanic-clastic rocks, and the Paleogene fluvio-lacustrine sediments. Combined with the fault geochronology and paleo-stress restoration, three evolutionary stages are proposed: NE–SW compression in the Late Jurassic (150–145 Ma), NE–SW extension in the Early Cretaceous (145–122 Ma), and the N–S extension in the Paleogene (63–32 Ma), which were associated with the sinistral strike-slip faulting, extensional rifting, and dextral strike-slip faulting of the TLFZ, respectively. The basin evolution implies that the kinematic transition of the TLFZ occurred at the Earliest Cretaceous (∼145 Ma) and Early Paleogene (∼63 Ma). The tectono-transition from compression to extension in the LXB at ∼145 Ma might indicate the initiation of destruction of the NCC due to the adjustment from continental collision between the NCC and the South China Block (SCB) to back-arc extension of the Paleo-Pacific plate. The variation of extensional stress orientation in the Paleogene is interpreted to be related to the change of subduction direction of the Paleo-Pacific plate.

Structural elements and evolution of the Yangmuchuan dome: Constraints on the tectonics of the Paleoproterozoic Jiao-Liao-Ji belt in the Eastern Block of the North China Craton

The nature of assembly of the Columbia supercontinent is well-characterized by the orogenic belts that were formed during amalgamation of continental blocks. The Jiao-Liao-Ji Belt (JLJB) in the eastern North China Craton possesses complex deformation structures that exemplify the Paleoproterozoic orogeny. A series of granitic gneiss domes in the southern JLJB characterizes the structural deformation in the Paleoproterozoic orogenic belts.Located in the middle segment of the JLJB, the Yangmuchuan dome is composed of three major elements, i.e., the Liaoji granites in the core, and sheared metamorphic rocks in the mantle and outer shell. Bedding-parallel ductile shear zones and weakly deformed metamorphic rocks between them are well-preserved in the latter two elements. Structural analysis reveals that the Yangmuchuan dome mainly experienced two deformation stages (D1 and D2). The D1 deformation is characterized by pure shear-dominated deformation structures with occurrence of penetrative foliations, symmetrical boudinages, mineral lineations and rootless folds in all the rocks from the mantle and outer shell. Dominated by simple shearing, the D2 deformation is the key stage contributing to the formation of the dome structure in the area. The D2 deformation is manifested as occurrence of A-type folds, S-C fabrics, mylonitic foliation S2, mineral stretching lineation L2 in granites, and in layered rocks in the mantle and outer shell. They were superposed on and transformed, along high strain zones, D1 deformation structures. Magnetic fabrics of the Liaoji granites from the core show a generally consistent orientation with the foliations and stretching lineations in the sheared granites. LA-ICP-MS zircon U-Pb dating on syn-tectonic leucogranitic dykes indicates that the peak deformation (D2) of the Yangmuchuan dome occurred from >1887 to 1808 Ma. Geometrical and kinematic analysis from the structural, microstructural and magnetic fabric data reveal that formation of the Yangmuchuang gneiss dome resulted from dominant subhorizontal flow and subsidiary vertical flow in the middle and lower crust as the consequence of orogenic activity along the JLJB during the assembly of the Columbia supercontinent.

Formation of the Hengshanli granitic gneiss dome in the Paleoproterozoic Jiao-Liao-Ji Belt, North China Craton

A group of granitic gneiss domes that may provide constraints on the tectonic evolution of early Precambrian orogenic belts are well preserved in the LiaoJi segment (or LJOB-Liaoji orogenic belt) of the Jiao-Liao-Ji Orogenic Belt (JLJOB), eastern North China Craton. To deeply understand the genesis of the domes and how the crustal mass flowed in collisional orogenic belt, we carried out structural analysis of the Hengshanli dome in the western part of the LJOB. Detailed analyses of deformation structures, microstructures and fabrics, and geochronology of syntectonic granitic dykes demonstrate that three episodes of structural deformation contributed to the formation of the dome structure. During D1, a pure shear-dominated deformation, penetrative foliations (S1), symmetrical lenses or boudinages, intrafolial folds (F1) and mineral lineations (L1) developed in the interlayered rocks of viscosity contrasts. The D2, the WNW-ESE orientated sub-horizontal simple shear-dominated deformation, is characterized by asymmetrical A-type folds (F2), stretching lineations (L2) , mylonitic foliations (S2), localized ductile shear zones, axial planar foliations, rotated porphyroblasts, L>S tectonites and S-C fabrics that indicate high-strain simple shear deformation. A D3 brittle deformation is evidenced by E-W directed open folds (F3) by flexural folding mechanism. LA-ICP-MS U-Pb dating of zircons from the syntectonic granitic dykes reveals that the main deformation event occurred from ca. 1946 to 1844 Ma. The dating also reveals that the Liaoji granites at the core were emplaced at ca. 2147 Ma and experienced anatexis at ca. 1864 Ma and 1846 Ma. It is suggested that the mechanism of doming is a combination of middle and lower crustal sub-horizontal flow, diapirism and folding superposition. Convergent flow of remobilized magma at depth and sub-horizontal simple shearing of metasedimentary rocks triggered middle and lower crustal flow in association with diapirism during the doming. The granitic gneiss domes are the products of dominant lateral and subsidiary vertical crustal mass flow under E-W directed compressional regime in the LJOB. We suggest that the orogenic belt experienced peak deformation at ca. 1946-1844 Ma, accompanied with syntectonic metamorphism and magmatism at nearly the same time.

Linking deep CO2 outgassing to cratonic destruction.

Outgassing of carbon dioxide from the Earth's interior regulates the surface climate through deep time. Here we examine the role of cratonic destruction in mantle CO2 outgassing via collating and presenting new data for Paleozoic kimberlites, Mesozoic basaltic rocks and their mantle xenoliths from the eastern North China Craton (NCC), which underwent extensive destruction in the early Cretaceous. High Ca/Al and low Ti/Eu and δ26Mg are widely observed in lamprophyres and mantle xenoliths, which demonstrates that the cratonic lithospheric mantle (CLM) was pervasively metasomatized by recycled carbonates. Raman analysis of bubble-bearing melt inclusions shows that redox melting of the C-rich CLM produced carbonated silicate melts with high CO2 content. The enormous quantities of CO2 in these magmas, together with substantial CO2 degassing from the carbonated melt–CLM reaction and crustal heating, indicate that destruction of the eastern NCC resulted in rapid and extensive mantle CO2 emission, which partly contributed to the early Cretaceous greenhouse climate episode.

Formation of green-core clinopyroxene in continental basalts through magmatic differentiation and crustal assimilation: Insights from in-situ trace element and Pb isotopic compositions

Green-core clinopyroxene (GCPX) widely occurs in diverse magmas and various tectonic settings. Due to its special textual and compositional zonation, it is usually considered as solid evidence for involvement of exotic felsic melt and some unique geological processes (e.g., magma mixing, mantle metasomatism and recycling of foundered lower continental crust (LCC)). However, this premise is challenged by its more complicated and enigmatic origins than previously thought. To explore potential origins of GCPXs in continental basalts, here we investigate in-situ trace element and Pb isotopic compositions of the GCPXs in the Feixian and Sihetun primitive basalts from the eastern North China Craton (NCC). The results show that the Feixian GCPXs can be subdivided into three types in addition to the Sihetun GCPXs. Regardless of the types of these GCPXs, their surrounding rims are regarded as overgrowths that crystallized from the basaltic host magmas. The wide range of Mg# (67–86), trace element patterns similar to those of clinopyroxene equilibrated with the basaltic host magmas and host lava-like Pb isotopic ratios of the Feixian type-1 GCPXs suggest that they have crystallized from differentiated melts genetically related to the basaltic host magmas. Besides unradiogenic Pb isotopic ratios, the Feixian type-2, type-3 and Sihetun GCPXs are characterized trace element signatures that are identical or similar to those of clinopyroxenes in pyroxene-rich granulite, garnet-bearing granulite and feldspar-rich granulite xenoliths from the NCC, respectively, indicating their derivation from lower crustal granulite wall rocks during the ascending of the basaltic host magmas. Our work suggests that GCPXs can be simply formed through the two common magmatic processes of continental basaltic magmas (i.e., crystallization differentiation and crustal assimilation) and highlights that exotic felsic melt and unique geological processes are not additionally required despite being possible. Before using GCPXs as an indicator of specific magmatic processes, comprehensive data (e.g., trace element and isotopic compositions) should be carefully investigated for their exact origins, especially for those in continental magmas. Additionally, GCPXs may provide valuable information about the structure and composition of the lower crust and a window to unravel crustal assimilation and digestion during magma extraction and their influence on compositions of basaltic magmas.

Provenance Identification and Source-to-Sink Studies from an Intrabasinal Subaqueous Uplift in the Eocene Western Bohai Bay Basin, Eastern North China

Provenance Identification and Source-to-Sink Studies from an Intrabasinal Subaqueous Uplift in the Eocene Western Bohai Bay Basin, Eastern North China

Seismic anisotropy evidence for modified lithosphere below the Bohai Sea region, eastern North China Craton

The Bohai Sea is proposed as the center of deformation associated with destruction of the North China Craton, and its tectonic history is essential for understanding the response of craton evolution to oceanic subduction. However, interior deformation of the craton remains unclear due to a lack of high-resolution imaging in this region. Here, we present high-resolution 3-D azimuthally-anisotropic shear-wave velocity structure of the crust and uppermost mantle using direct inversion of Rayleigh-wave phase-velocity dispersion from ambient noise. The anisotropic velocity structures reveal significant consistency between the regional strain field and seismic activity in the shallow crust. The N-S fast direction and relatively high velocity anomalies observed in the uppermost mantle beneath the Tanlu fault zone, as well as prominent Moho uplift, support the conclusion that the Tanlu fault zone has facilitated lithospheric modification of the eastern North China Craton since late Mesozoic. Anisotropy images also indicate that the northern and southern Bohai Bay Basin have undergone different deformation histories. The strong and consistent azimuthal anisotropy within the uppermost mantle beneath the southern Bohai Bay Basin may originate primarily from re-orientation arrangement of the olivine induced by new lithosphere formed from rapid cooling of upwelling asthenosphere after lithosphere delamination due to the subduction of the (Paleo-) Pacific Plate.