Trans-North China Orogen Research Articles

The late-Paleoproterozoic I- and A-type granites in Lüliang Complex, North China Craton: New evidence on post-collisional extension of Trans-North China Orogen

The late-Paleoproterozoic granitoids from Lüliang Complex can provide pivotal constraints on the amalgamation process between Eastern and Western blocks of North China Craton along the Trans-North China Orogen. LA-ICP-MS zircon dating gives emplacement ages of 1854 ± 20 Ma for the Huijiazhuang granite, 1830 ± 21 Ma for the Xiyupi granite vein and 1760 ± 20 Ma for the Dacaoping porphyritic granite, respectively. The Huijiazhuang granite and Xiyupi granite dyke have variable SiO2 (66.71–74.31 wt%), high K2O (5.09–6.35 wt%), low P2O5 (0.02–0.16 wt%), Al2O3 (13.92–15.31 wt%), right inclined REE patterns with medium negative Eu anomalies, enrichment in LILE, depletion in HFSE, especially Nb, Ta, consisting to high-K I-type granite in a post-collisional setting. The Sr/Y (7.36–59.95), εNd(t) (−5.7 to −4.1) with TDM (2381 Ma to 2570 Ma) from whole rock Sm-Nd isotope and εHf(t) (−9.6 to 2.3) with TCDM (2360 Ma to 3070 Ma) from zircon Lu-Hf isotope suggest that they are produced by partial melting of slightly thickened Neoarchean-Paleoproterozoic basement materials (including both meta-sedimentary and meta-igneous rocks). The Dacaoping porphyritic granites are characterized by high SiO2 (70.83–74.30 wt%), K2O (4.84–5.60 wt%), FeOT/(FeOT + MgO) (0.86–0.92), “seagull-type” REE pattern with strong negative Eu anomaly (δEu=0.16–0.35) and higher 10000∗Ga/Al (2.99–3.36), HFSE (Zr + Nb + Ce + Y = 378–583 ppm), showing an affinity of A2-type granite. They have low Sr/Y (1.17–8.62), εNd(t) (-6.1 to -6.4) with TDM (2690 Ma to 2776 Ma) from whole rock Sm-Nd isotope and εHf(t) (-7.9 to -5.2) with TCDM (2775–2938 Ma) from zircon Lu-Hf isotope, indicating a result from the melting of thinned Neoarchean calc-alkaline intermediate basement. Taking into account the temporal-spatial distributions of late-Paleoproterozoic rocks in the Trans-North China Orogen, it suggests a post-collisional extension occurred during 1.89–1.76 Ga and the crustis thinnedvisibly since 1.82 Ga.

Structural evolution of the Paleoproterozoic Trans-North China Orogen: Evidence from the Xiaoqinling region, central China

High-grade metamorphic rocks of Archean to Paleoproterozoic age, collectively called the Taihua Complex, are well exposed in the Xiaoqinling region in the western part of the southern segment of the Trans-North China Orogen (TNCO), central China. However, the evolution of orogenic events in this part of the TNCO remains unclear. Here we present structural and zircon U–Pb data to constrain the structural evolution of the rocks in the Xiaoqinling region. The first phase of deformation (D1) produced penetrative, ductile fabrics and localized ductile shear belts, and it was accompanied by a regional high-grade metamorphism. The D1 structures were the result of WNW-directed thrusting movements that have been dated at 1863–1840 Ma, and the microstructures suggest temperatures of 600–650 °C, which correspond to the conditions of exhumation of these orogenic rocks. These data support the ca. 1.85 Ga collision model for the Western and Eastern blocks that involves the SE-directed subduction of the Western Block. The second phase of deformation (D2) produced localized E–W-striking normal shear belts, and the D2 structures provide reliable evidence for N–S extension during the late Paleoproterozoic. Intense magmatic activity accompanied this period of extension. Zircon U–Pb dating constrains the extension to the period between 1829 and 1703 Ma. Post-orogenic extension in the TNCO accounts for D2 and the associated magmatism, and orogen-parallel extension is indicated by the structures. Thus, the Paleoproterozoic structural evolution of the rocks in the Xiaoqinling region of the TNCO records orogenic processes from exhumation to post-orogenic extension.

The Fangmayu Alaskan-type ultramafic intrusion: Implications for Paleoproterozoic assembly of the North China Craton

Alaskan-type ultramafic intrusions constitute a rare suite of rocks formed in subduction-related settings and provide important insights into mantle source and geodynamic processes associated with convergent plate margins. The North China Craton (NCC) witnessed subduction-accretion-collision events in the Paleoproterozoic prior to the final cratonization, and preserve important imprints of magmatic and metasomatic processes associated with oceanic plate subduction along the margins of the amalgamated crustal blocks and within the collisional orogens. Here we investigate a suite of serpentinized dunite, serpentinite, olivine orthopyroxenite, and anthophyllite glimmerite from the Fangmayu ultramafic complex along the eastern margin of the Trans-North China Orogen (TNCO) adjacent to the Eastern Block of the NCC. We present petrology, mineral chemistry, zircon U-Pb geochronology, REE and Lu-Hf isotopes, and whole rock geochemistry including REE and PGE data with a view to investigate the magmatic and metasomatic processes in this ancient subduction zone. The lithological distribution in the Fangmayu intrusion shows concentric zoning with dunite in the core, mantled by peridotite and pyroxenite, similar to that of Alaskan-type intrusions. Mineral chemistry including spinel composition shows distinct characteristics of stratiform chromite associated with Alaskan-type ultramafic intrusions formed in an arc-related subduction environment. Phase diagram computations show that the olivine (XMg = 0.92–0.93) and orthopyroxene (XMg = 0.9–0.91) in the olivine orthopyroxenite formed at high temperature conditions (∼1200 °C), and the antigorite (XMg = 0.92–0.98) chemistry shows that serpentinization occurred at much lower temperature (∼570 °C). Zircon U-Pb data from the ultramafic suite define two distinct groups of ages: 2.3 to 2.0 Ga and ca. 1.84 Ga corresponding to magma crystallization within suprasubduction zone mantle associated with subduction, and metamorphism during continental collision and final cratonization of the NCC. The REE patterns of zircons distinguish dominant population of magmatic grains and a minor group of metasomatic grains. Zircon Lu-Hf isotope data exhibit both positive and negative εHf(t) values in the range of −8.5 to 4.4 with TDM of 2434–2714 Ma, suggesting both enriched and depleted components in the magma source. Geochemical data including PGE characteristics suggest hydrous melting of depleted mantle wedge under high temperatures and fluid pressure in a subduction-related setting. Our study on the Paleoproterozoic Alaskan-type intrusion offers insights into arc-continent and continent-continent collision within a long-lived subduction system in the North China Craton.

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.

Crustal azimuthal anisotropy in the trans-North China orogen and adjacent regions from receiver functions

The North China Craton (NCC) is an important part of eastern China. Recent studies have shown that the eastern NCC (ENCC) has undergone significant lithospheric thinning and destruction since the late Mesozoic. Destruction of the cratonic lithosphere is necessarily accompanied by crustal deformation. Therefore, a detailed crustal deformation model can provide basic observational constraints for understanding the process and mechanisms of the destruction of the NCC. In this study, we estimated the crustal azimuthal anisotropy beneath 198 broadband stations in the NCC with a joint analysis of Ps waves converted at the Moho from radial and transverse receiver function data. We also performed a harmonic analysis to test the reliability of the measured anisotropy. We obtained robust crustal azimuthal anisotropy beneath 23 stations that are mostly located on the western margin of the Bohai Bay Basin, Yin-Yan orogenic belt, and Taihang Mountains, which reflects the crustal deformation characteristics in those regions. The crustal shear wave splitting time was found to range from 0.05 s to 0.68 s, with an average value of 0.23 s, which reveals a distinct crustal anisotropy in the Trans-North China Orogen (TNCO) and its adjacent areas. Our analysis of the results suggests that the strong NW-SE tectonic extension in the late Mesozoic and Cenozoic played an important role in crustal anisotropy in this region. In addition, the E-W trending crustal anisotropy on the margin of the Bohai Bay Basin indicates an effect of the ENE-WSW trending horizontal principal compressive stress. The crustal anisotropy in the Yin-Yan orogenic belt may be an imprint of the multiple-phase shortening of a dominant N-S direction from the early-to-middle Jurassic to the Early Cretaceous. Stations in the Taihang Mountains show large splitting times and well-aligned NW-SE fast directions that correlate with those measured from SKS splitting and that are possibly related to the lithospheric modification and magmatic underplating from the Late Mesozoic to Cenozoic in this area.

Precambrian Hongqiyingzi Complex at the northern margin of the North China Craton: Its zircon U-Pb-Hf systematics, geochemistry and constraints on crustal evolution

The Precambrian Hongqiyingzi Complex (HQC) in the middle segment of the northern margin of the North China Craton (NCC) is a crucial magmatic intrusive complex offering insights into the early evolutionary history of the northern margin of the NCC. The HQC, exposed from Congli to Longhua towns in the northern Hebei Province, is mainly composed of Neoarchean quartz dioritic-tonalitic-granodioritic (DTG) gneisses and Paleoproterozoic granodiorite-monzogranite-syenogranite (GMS) intrusions. SHRIMP and LA-ICP-MS zircon dating results show that the DTG gneisses formed at 2546–2532 Ma, while the GMS intrusions were emplaced between 1870 and 1819 Ma. LA-MC-ICP-MS zircon Lu-Hf isotope analyses indicate that the Neoarchean DTG magmas were mainly derived from partial melting of juvenile crust, but the Paleoproterozoic GMS magmas originated from partial melting of the metamorphic basalts and greywackes from Neoarchean to Paleoproterozoic volcanic or related sedimentary materials.Lithological assemblages, chronological and geochemical data, petrogensis and geodynamic settings of the Neoarchean DTG and Paleoproterozoic GMS magmatism show that the HQC is most likely at the northernmost part of the Trans-North China orogen of the NCC. The Precambrian HQC thus recorded Neoarchean subduction-related arc magmatism and Paleoproterozoic post-collisional magmatism that were associated with subduction and collision at the northern margin of the NCC. These Precambrian geological units were intensively overprinted by Late Paleozoic calc-alkaline magmatism, which may be caused by southward subduction and collision of the Central Asian Orogenic Belt (CAOB) with the NCC.

Uplift of the Lüliang Mountains at ca. 5.7 Ma: Insights from provenance of the Neogene eolian red clay of the eastern Chinese Loess Plateau

The Lüliang Mountains, located at the western margin of the Trans-North China Orogen, are thought to have undergone several uplift events during the late Mesozoic and Cenozoic due to far field effects of the India–Eurasia collision and/or Pacific Plate subduction. However, the timing and mechanisms of late Cenozoic uplift of the Lüliang Mountains are not clear. Our investigation of the source characteristics of the Shilou red clay sequence, an eolian deposit on the eastern Chinese Loess Plateau adjacent to the Lüliang Mountains, provides a new understanding of the relationship between the material composition of the eolian sediment and regional tectonic activity. Grain size data for the Shilou red clay sequence reveal an abrupt increase at ca. 5.7 Ma, and UPb detrital zircon geochronology indicates that the major source areas of Shilou red clay shifted after ca. 5.7 Ma, from the Junggar Basin, western Mu Us desert, and Gobi-Alxa arid lands, to the eastern Mu Us desert and the Lüliang Mountains. Detrital zircons younger than 5.7 Ma in the Shilou red clay have similar U and Th contents to zircons from the Lüliang Mountains, indicating that the mountains acted as a proto-source for the red clay after ca. 5.7 Ma. We suggest that the influx of coarser grained sediment is due to rapid uplift of the Lüliang Mountains at ca. 5.7 Ma, and that this timing is consistent with northeastward propagation of mountain uplift in response to the India–Eurasia collision.

Geochemical constraints on genesis of Paleoproterozoic A-type granite in the south margin of North China Craton

Paleoproterozoic A-type granites are widely outcropped in the North China Craton (NCC), particularly in the Trans-North China Orogen. However, their genesis and tectonic significance remain obscure. Here we report systematic studies on geochronology and geochemical characteristics of A-type granite in Huayangchuan, south margin of the NCC. The samples are enriched in total alkali (K2O + Na2O > 8.97 wt%), and depleted in MgO (0.84–0.93 wt%), CaO (1.28–1.90 wt%) and P2O5 (0.18–0.20 wt%), with high FeOT/MgO (5.69–6.67). They are characterized by high Zr + Y + Nb + Ce values (1293–1392 ppm) and 10,000 × Ga/Al ratios (3.14–3.35), which are typical characteristics of A-type granite. The Huayangchuan A-type granite can be further classified as A1-type subgroup based on particular geochemical features, e.g., low Y/Nb (0.87–1.00) and Yb/Ta (0.88–1.10). High precision zircon U–Pb dating of the A-type granite by secondary ion mass spectrometry (SIMS) yields Paleoproterozoic 207Pb/206Pb ages of 1829.5 ± 2.5 Ma. The low zircon ɛHf(t) values (−6.97 to −10.45), along with zircon Hf model age of 2.7–2.9 Ga, indicate that the Huayangchuan A-type granite was derived from partial melting of the ancient continental crust with contribution of enriched mantle components. The low zircon δ18O composition (4.00 to 6.78‰) indicates that the zircons were crystallized from low δ18O magmas, which derived from the crust metasomatized by low δ18O mantle fluids or melts. The E-W trend A1-type granitic plutons in the NCC are generally outcropped in a rift tectonic regime, which is consistent with the development of the mantle plume in the Xiong'er district. The large volume of basaltic magmas, generated by mantle plume head, underplated the lower continental crust and formed the Huayangchuan A-type granite.

Detrital zircon U-Pb geochronology and provenance of the Sanxiatian Formation (Huade Group) in the North China Craton: Implications for the breakup of the Columbia supercontinent

The tectonic evolution and Paleoposition of the North China Craton (NCC) in the Columbia supercontinent during Mesoproterozoic is still not well constrained owing to scarce outcrops of the Mesoproterozoic geological records. Here we present detailed U-Pb geochronological study on detrital zircons and trace elemental geochemistry of the Mesoproterozoic meta-sedimentary rocks from the Sanxiatian Formation, the upper Huade Group, in the northern NCC. The youngest cluster of detrital zircons from the Sanxiatian Formation has U-Pb age peak at ∼1357 Ma, which constrains the deposition of the Sanxiatian Formation after ∼1400 Ma. We suggest a stratigraphic correlation among the Sanxiatian, Baiyinbaolage, Liuhongwan and Xiamaling formations, all of which were deposited simultaneously in the northern NCC. The small portion of ∼2530 Ma zircons possibly corresponds with the growth of juvenile crust in the NCC at the late Neoarchean. The distinct ∼1850 Ma population may have originated from the syn-and post- tectonic granites distributed in the Trans-North China Orogen (TNCO), which is related with the collision between the Western and Eastern blocks in the NCC. The ∼1750–∼1600 Ma zircon populations were also sourced from the NCC and are possibly characterized by the post-collisional magmatic events after the amalgamation of the NCC. The zircon clusters younger than 1600 Ma with peaks at ∼1575 Ma and ∼1357 Ma, were interpreted as exotic sources, while the latter possibly related with the final breakup of the supercontinent Columbia. With the compilation of the detrital zircon dataset from the North India, the West Australia, the North Australia, the Siberia blocks and the northwestern Laurentia, the final fragmentation of the supercontinent Columbia is suggested to be characterized by the separation between the NCC, the Australia or the India blocks during the late Mesoproterozoic.

Metamorphic evolution and SHRIMP U-Pb geochronology of mafic granulites with double symplectites in the Fuping metamorphic complex, middle Palaeoproterozoic Trans-North China Orogen

Garnet-bearing mafic granulites occur as lenses within TTG gneiss or metapelite in the Fuping Complex, middle Palaeoproterozoic Trans-North China Orogen. They are composed mainly of garnet, clinopyroxene, orthopyroxene, hornblende, plagioclase, quartz and accessary zircon and titanite. Four stages of metamorphic mineral assemblages have been found in these mafic granulites: (a) the prograde assemblages (M1) are inclusions preserved in the garnet porphyroblasts, including clinopyroxene, hornblende, plagioclase and quartz; (b) the metamorphic peak assemblages (M2) consist of garnet porphyroblasts plus matrix minerals clinopyroxene + orthopyroxene + hornblende + plagioclase + quartz + zircon + titanite; (c) the first retrograde assemblages (M3) are represented by clinopyroxene + orthopyroxene + plagioclase + quartz symplectites rimming the garnets; and (4) the final retrograde assemblages (M4) are hornblende + plagioclase + quartz symplectites rimming or adjacent to the garnets. The retrieved metamorphic P-T paths pass from 530–600 °C/6.5–7.0 kbar (M1) through 680–820 °C/7.2–11.7 kbar (M2) to 730–760 °C/3.2–3.9 kbar (M3) and finally to 600–640 °C/3.2–3.7 kbar (M4). All the P-T paths of the mafic granulites are clockwise, two of these even contain near isothermal decompression (ITD) and subsequent near isobaric cooling (IBC) segments. SHRIMP U-Pb dating of metamorphic zircons of the mafic granulites yields a mean weighted age of ∼1849 ± 9Ma, which is consistent with the metamorphic time of surrounding TTG gneisses. Therefore, the Fuping Complex records the collision event between the Eastern and Western Blocks of the North China Craton that led to the final assembly of this craton during the late Paleoproterozoic.

Metamorphic P–T paths and zircon u–pb ages of Paleoproterozoic metabasic dykes in eastern Hebei and northern Liaoning: Implications for the tectonic evolution of the North China Craton

Metabasic dykes are described from Qianxi (JD1462) and Qinglong (JD15158) in the eastern Hebei and Qingyuan (15Q18) in the northern Liaoning that clearly crosscut the foliation of Neoarchean tonalitic–trondhjemitic–granodioritic (TTG) gneisses and supracrustal rocks in the Longgang Block. Petrographic observations and phase modeling using THERMOCALC suggest that these metabasic dykes have experienced metamorphism of high-pressure (HP) granulite facies and amphibolite facies characteristic of clockwise P–T paths. Their peak P–T conditions were constrained to be 11.5 ± 0.6 kbar/815 ± 62 °C for sample JD1462, 8–9 kbar/570–585 °C for JD15158 and 10.7 ± 0.6 kbar/780 ± 70 °C for 15Q18, corresponding to apparent geothermal gradients of 18–19 °C/km. Zircon U–Pb dating yields metamorphic ages of ∼1.82 Ga for samples JD15158 and JD1462, interpreted to represent the peak stage of amphibolite facies and the post-peak decompression stage of HP granulite assemblage. Zircons in sample 15Q18 yield four age groups of ∼1.84 Ga, 1.94 Ga, 2.12 Ga and 2.49 Ga, interpreted to represent the ages, respectively, of the post-peak decompression stage of HP granulite assemblage, a mixed result from zircons of ∼1.84 Ga and ∼2.12 Ga, the emplacement of basic dykes, and the captured zircon grain from country TTGs. Thus, the metamorphic evolution of metabasic dykes may correlate to a crustal thickening event occurred close to 1.84–1.82 Ga, which is separated from the collision event at ∼1.95 Ga prevailed in the North China Craton. The metabasic dykes show weakly right-declined REE patterns and are depleted in Nb, Ta and Ti, inferred to represent a within-plate extensional setting at ∼2.12 Ga, consistent with the magmatic events occurred in the Trans-North China Orogen and Jiao-Liao-Ji Belt. As a consequence, the Archean Longgang Block was largely influenced by the Paleoproterozoic magmatic and metamorphic events.

Petrogenesis and tectonic implication of Paleoproterozoic granites and granulites in the Fengzhen area of North China craton

The North China Craton (NCC) is one of the oldest cratons in the world that preserves the records of many important geological events in the early evolution of the Earth. However, the early Precambrian tectonic evolution history of the NCC is still controversial. Here we report Paleoproterozoic leucogranites, garnet granites and granulites in the Fengzhen area that constitutes a junction between the Khondalite Belt and the Trans-North China Orogen (TNCO). The leucogranites have high SiO2 content (75–85wt%), and magmatic zircon U-Pb age of 2199±3 Ma. Their zircons have slightly various εHf(t) values (−0.45 to 1.41) with TDM model ages of 2.5–2.6Ga. The granites show strong LREE enrichment with La/Ybcn ratio of 12–176, and have high initial Nd isotope (εNd(t)=3.5–4.5). Most of them display positive Eu anomaly, excluding fractional crystallization contribution on the high Si feature. The leucogranite was produced by melting of Late Archean felsic TTGs (tonalite–trondhjemite–granodiorite) and addition of juvenile crust. Magmatic zircons yield the garnet granite age of 2002±3Ma. The zircons show various εHf(t) values (−5.8 to 7.1) and TDM model ages (2.1–2.6Ga). Low initial εNd(t) isotope value (−4.2 to −8.3) was determined in the granites. The granulites are high pressure metamorphic rocks with a peak pressure of 12.0±0.8 kbar, and have similar metamorphic age of 1967±10Ma to the garnet granites. This indicates that the Fengzhen area underwent 2-Ga inter-continental orogeny, in which the melting of sedimentary rock formed the garnet granites. Similarly, sodic TTG melting to form K-rich leucogranites also needs high pressure. However, the leucogranite age is obviously older than the peak metamorphic timing of continent–continent collision. This implies that the Fengzhen area may have underwent arc-continental collision at 2.2Ga.

Late Neoarchean magmatism and tectonic evolution recorded in the Dengfeng Complex in the southern segment of the Trans-North China Orogen

The Dengfeng Complex exposed in Songshan area in the southern segment of the Trans-North China Orogen (TNCO) mainly consists of Late Neoarchean tonalite-trondhjemite-granodiorite (TTG) gneiss, metadiorite and amphibolite. The Sanhuangzhai amphibolite records the earliest mafic magmatism (2658±5Ma) in the region, which is enriched in LREE and LILE with negative Nb, Ta and Ti anomalies and positive initial εNd(t) and εHf(t) values, suggested to be the remnant of an arc-related juvenile mafic crust. The Shipaihe amphibolite at the end of Neoarchean (2492±7Ma) is characterized by flat REE pattern, slightly negative Nb, Ta and Ti anomalies and positive initial εNd(t) and εHf(t) values, which is interpreted as large-degree partial melt of metasomatised mantle source in a back-arc basin. Zircon U-Pb dating shows two episodes of TTG magmatism (2.57–2.55Ga and 2.55–2.50Ga) within the Dengfeng Complex. All TTG gneisses have high SiO2 and Na2O, but low Mg#, Cr, Ni, [Yb]N and Y with high [La/Yb]N and Sr/Y. The early TTG gneiss (2.57–2.55Ga) in the eastern Songshan area has variable whole-rock Hf-Nd isotopes (εHf(t)=−2.14–4.64; εNd(t)=0.11–3.35; respectively), and its protolith is interpreted as the result of partial melting of a thickened lower crust with residual garnet and amphibole in the source. But the later TTG gneiss (2.55–2.50Ga) in the western Songshan area has depleted whole-rock Hf-Nd isotopes (εHf(t)=5.59–6.08; εNd(t)=2.42–3.86; respectively), suggesting an overall juvenile source, and its protolith is interpreted as the partial melt of flat-subducting oceanic crust. The Shipaihe metadiorite is characterized by high Mg#, Cr, Ni, Sr, Ba, highly fractionated REE patterns and strong negative Nb, Ta and Ti anomalies, resembling to sanukitoid suite, which is interpreted as the partial melt of a mantle wedge metasomatised by subduction-derived fluids/melts. Integrated geochronology and geochemical data of the Dengfeng Complex in Songshan area reveal the Late Neoarchean crustal accretion process from subduction to arc-continental collision (accretionary orogeny) followed by post-collisional extension (back-arc basin), implying an active continental margin arc environment in the southern segment of the North China Craton.

Constraints on sedimentary ages of the Chuanlinggou Formation in the Ming Tombs, Beijing, North China Craton: LA-ICP-MS and SHRIMP U–Pb dating of detrital zircons

Detrital zircons in five sedimentary samples, MC1 to MC5, from the bottom of the Chuanlinggou Formation in the Ming Tombs District, Beijing, were dated with the LA-ICP-MS and SHRIMP U–Pb methods. Age spectra of the five samples show a major peak at 2500 Ma and a secondary peak at 2000 Ma, suggesting their provenances were mainly from the crystalline basement of the North China Craton and the Trans-North China Orogen. The youngest zircon has an age of 1673 ± 44 Ma, indicating that the Chuanlinggou Formation was deposited after this age. From sample MC4 to MC5, lithology changed from a clastic rock (fine-grained sandstone) to a carbonate rock (fine-grained dolomite), suggesting that the depositional basin became progressively deeper. The age spectrum of sample MC5 shows a major peak at 2500 Ma and a secondary peak at 2000 Ma. Sample MC4, which is stratigraphically lower than sample MC5, only had one peak at 2500 Ma. We conclude that there was a transgressive event when sediments represented by MC5 was deposited, and seawater carried ca. 2000 Ma clastic materials to the basin where the Chuanlinggou Formation was deposited, leading to the addition of ca. 2000 Ma detritus. Our research indicates that the source area for the sediments became more extensive with time. We conclude that the Chuanlinggou Formation in the Ming Tombs District was deposited in a low-energy mud flat sedimentary environment in the inter-supra tidal zone because it is mainly composed of silty mudstone and fine-grained sandstone with relatively simple sedimentary structures.

Discovery of mafic granulite in the Guandishan area of the Lüliang complex, North China Craton: Age and metamorphic evolution

Mafic granulite and amphibolite occur as boudinaged lenses in felsic and metapelitic gneiss in the Guandishan area of the southern Lüliang metamorphic complex. Peak assemblages recorded by large granoblastic minerals yield pressure–temperature (P-T) conditions of 790°C and 9.4kbar in granulite and >750°C and >6.2kbar in amphibolite based on standard thermobarometric techniques. Retrogression produced fine-grained resorptive rims in garnet, symplectitic hornblende, orthopyroxene and plagioclase that record P-T conditions of 560–775°C and 2.8–7.5kbar in granulite and 740°C and 5.7kbar in amphibolite. Mineral inclusion patterns and major element zoning are consistent with aclockwise P-T path that ended with nearly isothermal decompression. Uranium-Pb dating of metamorphic zircons from the granulite and host metapelite reveal two discrete, meaningful age groups of metamorphism in the Guandishan area: most metamorphic zircon grains exhibit peak metamorphic growth at 1935–1920Ma, whereas a smaller, younger group exhibit growth during retrogression between 1860 and 1815Ma. Regional metamorphism in the Lüliang metamorphic complex was related to the amalgamation of the North China Craton along the Trans-North China Orogen between c.1.95 and 1.80Ga.

P–T–t path and tectonic significance of pelitic migmatites from the Lüliang Complex in Xiyupi area of Trans-North China Orogen, North China Craton

In order to reveal the metamorphic evolution of the Lüliang Complex, a combined study of petrography, phase equilibria modeling and zircon U–Pb dating is carried out on two mesosome of pelitic migmatites from the Jiehekou Group in the Lüliang Complex. Sample (15XYP-02) preserved the thermal peak assemblage of garnet, biotite, K-feldspar, sillimanite, quartz and ilmenite, without plagioclase. It recorded two near-isothermal decompressional indicators that rutile was moated by ilmenite and garnet was replaced by cordierite. Small plagioclase occurred in the rim of K-feldspar and garnet. Four stages (M1–M4) of metamorphic evolution have been identified based on the mineral assemblages and P–T pseudosection. It is interpreted to record pre-Tmax decompression from rutile-stability field (M1, represented by rutile relicts in matrix and biotite+sillimanite+quartz inclusions in garnet porphyroblasts) at ∼8.9kbar to the Tmax stage (M2, characterized by garnet rim with ilmenite and biotite+K-feldspar+sillimanite+quartz in matrix) of 815–838°C. The following suprasolidus post-Tmax cooling comprises M3stage (represented by appearance of cordierite in the assemblage of garnet+biotite+K-feldspar+sillimanite+ilmenite+quartz) of 780–838°C/5.0–6.3kbar and M4stage (defined by the final mineral assemblage of garnet+biotite+K-feldspar+plagioclase+sillimanite+cordierite+ilmenite+quartz) of ∼775°C/∼5.0kbar. Another sample (15XYP-21) preserved the thermal peak assemblage of garnet, biotite, plagioclase, K-feldspar, sillimanite, quartz. It also records pre-Tmax decompression from rutile-stability field at 9.0kbar to the Tmax stage of 796–821°C/6.4–7.1kbar, followed by suprasolidus post-Tmax cooling stage of 778–803°C/5.0–5.7kbar. The clockwise P–T paths are consistent with those of orogenic belt. Furthermore, the zircon U–Pb dating on mesosome and leucosome of pelitic migmatite yield metamorphic ages of 1.95Ga and 1.91Ga, respectively, in which, the former represents the early stage of cooling after Tmax, nearly close to the time of pressure peak metamorphism. Combined with those granulites in the Trans-North China Orogen, a common long-lived continent-continent collision processes was proposed, which may culminated at ∼1.95Ga and followed by a prolonged cooling process.

Crust–mantle interaction and craton destruction: evidence from Late Mesozoic plutons in the North China Craton

Late Mesozoic granitoids, widely distributed in the Yanshan Belt of the North China Craton (NCC), are important markers of cratonic destruction and lithospheric thinning. We report new petrological, geochemical, zircon U–Pb and Lu–Hf isotopic data on two late Mesozoic granitic plutons from the central NCC near the Trans-North China Orogen. We report zircon U–Pb emplacement ages of 162 – 156 Ma and 132 Ma from the Siganding and Fangshan plutons respectively, indicating Late Jurassic–Early Cretaceous magmatism. The presence of a dusty zone, and discontinuous zoning, in plagioclase phenocrysts and the occurrence of mafic microgranular enclaves in both granitoid plutons suggest mingling and mixing of felsic and basic magmas. The rocks investigated in this study show high Na 2 O + K 2 O and high Mg# (Mg# = Mg/(Fe + Mg)) and are metaluminous, with enrichment in light rare earth elements and large ion lithophile elements (Rb, Ba, U, and Sr) and depletion in high strength field elements (Th, U, Nb, Ta, P, and Ti). They also display negative εHf( t ) values and high Sr/Y ratios, comparable with adakitic rocks, suggesting that the felsic magmas of these intrusions were probably derived from the partial melting of the Palaeoproterozoic (two-stage zircon Hf-depleted model ages between 2.5 and 1.9 Ga) thickened lower crust of the NCC, whereas the mafic magma was probably derived from subcontinental lithospheric mantle. We correlate the magmatism with lithospheric thinning beneath the NCC and associated crust–mantle interaction. It is inferred that lithospheric thinning was of limited extent in Late Jurassic (162 – 156 Ma) times. The magma flare-up at around 130 Ma was produced by large-scale melting of the enriched subcontinental lithospheric mantle with development of extensive intracontinental adakitic magmatic rocks derived from thickened ancient lower continental crust with variable involvement of subcontinental lithospheric mantle. Supplementary material: Mineral assemblages and abundance, representative electron microprobe analyses, LA-ICP-MS zircon U–Pb age data and LA-MC-ICP-MS Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.3815308

Neoarchean Algoma-type banded iron formation from the Northern Shanxi, the Trans-North China Orogen: SIMS U-Pb age, origin and tectonic setting

Algoma-type BIF-hosted iron deposits in Northern Shanxi occur in Sanyangping, Baiyuli, Zhaocun and Baizhiyan. These deposits are developed in Archaean rocks and their formation was related to volcanic and sedimentary processes in small volcano-sedimentary basins. Supracrustal rocks of the Wutai Group were metamorphosed from greenschist facies to lower amphibolite facies. The BIF-hosted iron deposit in Northern Shanxi formed in the late Neoarchean, and is represented by the Zhaocun deposit that yielded a SIMS U-Pb zircon age of 2693.7±4.9Ma. The other two BIF-hosted iron deposits are represented by the Sanyangping and Baiyuli deposits that formed between 2528Ma and 2543Ma. The late Neoarchean BIF iron deposits can be considered to have formed in a magmatic arc environment. The Eu anomalies of the ore samples from Northern Shanxi show that the BIF ores formed in a hydrothermal related volcanic submarine environment, where submarine hydrothermal effluents associated with volcanic activities may have supplied the iron and silica for the Northern Shanxi BIFs. A ridge subduction model is suggested for the formation of the BIFs and their host late Neoarchean volcanic rocks, this model does not only explain the sources of silica and iron for the BIFs, but can also well explain many other geological features of the Trans-North China Orogen.

Zircon and titanite U-Pb dating of the Zhangjiawa iron skarn deposit, Luxi district, North China Craton: Implications for a craton-wide iron skarn mineralization

The North China craton hosts numerous iron skarn deposits containing more than 2600 Mt of iron ores, mostly with an average grade of >45wt% Fe, which have been among the most important source of high-grade iron ores for the last three decades in China. These deposits typically form clusters and can be roughly divided into the western and eastern belts, which are located in the middle of Trans-North China orogen and to the west of the Tan-Lu fault zone in the eastern part of North China craton, respectively. The western belt mainly consists of the southern Taihang district, as well as the Linfen and Taiyuan ore fields, whereas the eastern belt comprises the Luxi and Xu-Huai districts. The Zhangjiawa deposit in the Luxi district has proven reserves of 290 Mt at an average of 46% Fe (up to >65%). The iron mineralization occurs mainly along contact zones between the Kuangshan dioritic intrusion and middle Ordovician marine carbonate rocks that host numerous evaporite intercalations. Titanite grains from the mineralized skarn are closely intergrown with magnetite and retrograde skarn minerals including chlorite, phlogopite and minor epidote, indicating a hydrothermal origin. The titanite grains have extremely low REE contents and low Th/U ratios, consistent with their precipitation directly from hydrothermal fluids responsible for the iron mineralization. Ten hydrothermal titanite grains yield a weighted mean 206Pb/238U age of 131.0±3.9Ma (MSWD=0.1, 1σ), which is in excellent agreement with a zircon U-Pb age (130±1Ma) of the ore-related diorite. This age consistency confirms that the iron skarn mineralization is temporally and likely genetically related to the Kuangshan intrusion. Results from this study, when combined with existing isotopic age data, suggest that iron skarn mineralization and associated magmatism throughout both the eastern and western belts took place coevally between 135 and 125Ma, with a peak at ca. 130Ma. As such, those deposits may represent the world's only major Phanerozoic iron skarn concentration hosted in Precambrian cratons. The magmatism and associated iron skarn mineralization coincide temporally with the culmination of lithospheric thinning and destruction of the North China craton, implying a causal link between the two.

Late Neoarchean crust-mantle geodynamics: Evidence from Pingquan Complex of the Northern Hebei Province, North China Craton

A late Neoarchean intra-oceanic arc along the northwestern margin of Eastern Block (EB), North China Craton, provides important insights into the nature of Archean mantle sources and crust-mantle geodynamics. The Pingquan Complex and the entire Northern Hebei Province (NHB) are located in the middle part of the arc, and overlap the northern extent of the trans-North China Orogen. Zircon U-Pb isotopic age data reveal that the Pingquan Complex consists of ∼2537–2515Ma dioritic gneisses, ∼2506–2503Ma amphibolites, and ∼2491Ma quartz monzodioritic to monzogranitic gneisses, and they show dominantly positive zircon εHf(t) (−0.6 to +5.4) that are lower than coeval model depleted mantle values.Geochemical data for the Pingquan rocks and synchronous metabasalts and granitoid gneisses of Huai’an-Xuanhua and Dantazi complexes in the NHB are integrated. Except for the monzogranitic gneisses that were derived from partial melting of juvenile metagreywackes, the other rocks of the Pingquan Complex were derived from a metasomatized lithospheric mantle, and subjected to variable fractionation of clinopyroxene, hornblende and plagioclase, without significant crustal contamination. Moderately depleted zircon εHf(t), and high Sm/Hf and Nb/Ta (mostly of 1.34–3.96 and 15.50–32.58, respectively) suggest that the lithospheric mantle was enriched by subducted pelagic sediments metamorphosed to rutile-bearing eclogites before melting.Late Neoarchean crust-mantle geodynamic processes in the NHB are reconstructed. Intra-oceanic subduction initiated offshore the northwestern margin of the EB at ∼2.55Ga or earlier. Partial melting of slab basalts occurred at ∼2542–2499Ma, with the melts contaminated by mantle wedge materials forming TTGs. Meanwhile, the sub-arc lithospheric mantle was enriched by fluids and melts released from slab basalts and pelagic sediments, and partial melting of this moderately depleted mantle generated ∼2537–2503Ma diorites and basalts. Following final accretion of the arc onto the continental margin of the EB, the slab rollback/breakoff and asthenospheric mantle upwelling triggered partial melting of the metasomatized lithospheric mantle and crustal anatexis, generating ∼2491Ma quartz monzodioritic and monzogranitic rocks.Accordingly, the NHB records Neoarchean crustal growth linked to oceanic subduction and arc-continent accretion, and highlights the importance of resolving the nature of mantle sources and crust-mantle interactions in understanding Archean crustal growth and evolution.