North China Craton Research Articles

Late Neoarchean plume-induced crust-mantle interaction and crustal reworking: Evidence from the Jianping Complex, North China Craton

The Archean basement of the North China Craton (NCC) is predominantly composed of 2.6–2.5 Ga lithological assemblages, while the tectonic regime that governed the formation and evolution of these Neoarchean basement rocks has been a controversial issue. Based on field relationships, petrographical features, whole-rock chemistry and zircon Hf isotope data, diverse late Neoarchean granitoids exposed in the Jianping Complex of the NCC are categorized into TTGs, sanukitoids and potassic granites. Their petrogenesis are associated with partial melting of metabasalts, melting of metasomatized mantle, and melting of crustal lithologies including tonalite and metasediments, respectively. Zircon U-Pb results suggest that different types of Neoarchean granitoids in the Jianping Complex are nearly coeval with crystallization ages of ∼ 2.54–2.52 Ga and metamorphic ages of ∼ 2.49–2.48 Ga. New Hf isotopic data reveal that these granitoids show positive εHf(t) values, with the tonalitic gneisses of εHf(t) values closer to the depleted mantle than those of granodioritic gneiss, sanukitoids and potassic granite. This result reflects potentially more enriched source for other granitoids than the tonalitic gneisses, which is linked with increasing level of crustal-mantle interaction and crustal reworking the late Neoarchean. Integrating other evidence from geochemical, structural and metamorphic studies, it is inferred that the plume activities play an important role in the emplacement of late Neoarchean granitoids in the Jianping Complex, with TTGs formed through the partial melting of juvenile crust induced by plume activity, sanukitoids produced from melting of metasomatized mantle resulted from sagduction process, and potassic granites formed by reworking of earlier crustal lithology caused by sustained underplating of mantle material. Overall, we interpreted that the late Neoarchean crustal growth and crustal-mantle interaction in the Jianping Complex can be attributed to upwelling of mantle plume and potential sagduction process in a vertical tectonic regime.

A paradigm shift in Precambrian research driven by big data

The enigmatic nature of the Precambrian era poses ongoing challenges for researchers seeking to uncover its secrets. With the exponential growth of scientific data, there exists a vast repository of information through which these mysteries can be explored. However, this data is often derived from fragmented investigations of geological phenomena within specific disciplinary domains and limited spatiotemporal boundaries, resulting in untapped potential for extracting undiscovered knowledge. To address this limitation, the field of big data science provides a foundation for multidisciplinary research on the geological evolution of the Precambrian. By harnessing the power of large-scale data integration and analysis, valuable insights into this pivotal era in Earth's history can be revealed. This paper offers a comprehensive overview of big data types in geoscience and elucidates common analysis methods. Through a case study focused on the North China Craton (NCC), we demonstrate the application of conjoint analysis to a dataset comprising rock and mineral geochemistry data. Employing local singularity analysis and wavelet analysis on zircon age frequency and Hf isotopic time series, we reveal a persistent long-term periodicity of 800–500 million years since 3.5 billion years ago. This finding indicates a co-evolution between the NCC and the global supercontinent cycle dating back to the Archean period. To investigate the formation of the NCC, we employ machine learning-based crustal thickness evolution reconstruction, which highlights arc formation during subduction as the primary factor, with regional mantle activities playing a secondary role in the convergence. Combining spatio-temporal evolution analysis of magmatic intensity and εHf(t) values, we infer that the development of the NCC primarily resulted from a prolonged process of accretion targeting the Eastern Block (the primary continent nuclei) through the incorporation of diverse arc massifs. This examination of the NCC serves as an example of how data collection, processing, and utilization can enhance our understanding of formational and evolutionary processes, signaling a paradigm shift in Precambrian research driven by the integration of big data.

Determining the ore-forming processes of Dongshengmiao Zn-Pb-Cu deposit: Evidence from the linear discriminant analysis of pyrite geochemistry

The orogenic base metal deposits gain more and more attentions in recent years. The ore-forming fluids associated with these deposits are enriched in reduced sulfur and have low salinity. Since this kind of fluid has low affinity to transport base metals, pre-enrichment of sulfide should take place during the formation of orogenic base metal deposits. The Dongshengmiao Zn-Pb-Cu deposit, which is located in the northern margin of the North China Block, was considered as orogenic base metal deposit, and a two-stage mineralization process was proposed by previous researchers, but other researchers proposed that the Dongshengmiao is a typical sedimentary exhalative (SEDEX) deposit. Even though the tectonic environment, fluid inclusion, geochronology and isotopic geochemistry have been widely investigated in the Dongshengmiao, its genesis is still under debate, and new data or proof should be presented to decipher the genesis model of the Dongshengmiao deposit. In this study, linear discriminant analysis (LDA), one of the commonly used machine learning methods, was employed to discriminate the genesis of pyrite in the Dongshengmiao deposit based on the trace element concentrations analyzed by LA-ICP-MS. The LDA results demonstrate that nearly all the early-stage fine-grained pyrites (Py1) show the same geochemical features as the pyrites from volcanic hosted massive sulfide (VHMS), whereas most of the late-stage recrystallized pyrite (Py2) is of orogenic origin. The Mesoproterozoic submarine volcanic activities resulted in pre-enrichment of sulfide with VHMS geochemical signature in the rocks hosting Dongshengmiao deposit. The pre-enriched sulfides were subsequently remobilized during the subsequent metamorphism in the early Cretaceous, leading to the formation of giant an orogenic base metal deposit.

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.

Identify vestiges of large igneous provinces in deep time: A 0.9 Ga case from North China (Sino-Korean) craton

Large igneous provinces (LIPs) are mostly eroded in deep time; nevertheless, their plumbing systems remained in the crust and weathered materials may be traced in basins. Vestiges of the early Neoproterozoic LIPs are investigated in the North China craton. Two large doleritic sills are dated at ca. 940 Ma and ca. 890 Ma in the Pyongnam basin in Korean peninsula, which are comparable with those coeval ones in the other two basins of the Xuhuai rift. Both of them are featured by ocean island basalt-akin trace element patterns. The ca. 890 Ma sills show stronger depletion in mobile elements, and slightly higher differentiated light and heavy rare earth elements than the ca. 940 Ma sills. They are also chemically affinitive with the ca. 920 Ma Dashigou LIP, but with slightly higher MgO and total alkalis and more differentiated light and heavy rare earth elements. This may indicate a similar (plume) source with probably lower degrees of partial melting in the source region(s) in the magma chamber than the 920 Ma one. Together with the Dashigou, they comprise a cluster of LIPs from the same plume with sequential peaks at ca. 940 Ma, 920 Ma and 890 Ma. Ages of sills and the youngest detrital zircons constrain the sediments to be within 1160–940 Ma for the 940 Ma sill-hosting lower-middle section (e.g., Jikhyon-Mukchon groups) and 940–890 Ma for the 940 Ma-sill free upper section (e.g., Myoraksan Group). A synthetic dataset of all the three basins of the Xuhuai rift reveals a similar depositional age and a similar major provenance (940–900 Ma) for the black-greenish shale-featured formations (e.g., Socheong-Xingmincun-Jinshanzhai formations), which are right above the carbonates with negative inorganic carbon (Majiatun) excursion across much of the Xuhuai rift. The significant 940–900 Ma provenance is featured by zircons resemble those from the local LIPs. It is possible that the provenance was the relevant extrusive rocks of the 940–890 Ma LIPs. This further implies that the ca. 940–920 Ma Majiatun excursion is concurrent with the LIP cluster and is possibly a result of instant turbulence of carbon cycle by the LIPs.

Circum‐Cratonic Triassic Syenite Province of North China Craton Reveals Heterogeneous Lithospheric Mantle Related to Dual Subduction

AbstractSubduction‐induced metasomatism may increase heterogeneity in the subcontinental lithospheric mantle (SCLM) over time. Syenite and its relevant varieties are typically derived from the most metasomatized portions of the SCLM and thus provide a key to decipher its heterogeneity. The only circum‐cratonic syenite province in the world, the Late Triassic belt around North China craton, is unique and offers an opportunity to investigate heterogeneity of the SCLM right before its destruction in the Mesozoic. New and previous data of whole‐rock Sr‐Nd and zircon in situ Hf‐O isotopes of syenite intrusions encircling the craton indicate two distinct types of metasomatism characterized by an alteration of juvenile or ancient materials. The spatiotemporally distinct sources can be discriminated by melts from oceanic slabs subducting beneath much of North China followed by deep subduction of South China craton only in the south. This unique setting of a circum‐cratonic syenite belt proves in a single case study that subduction‐induced metasomatism may cause craton‐scale SCLM heterogeneity.

High-resolution chronostratigraphy of late Mesozoic sequences in northern North China: Implications for the linkages among intracontinental orogeny, volcanism, Jehol Biota, and Pacific plate subduction

Abstract Subduction of the paleo-Pacific plate during the late Mesozoic is thought to have been responsible for the destruction of the North China craton, manifested by intense volcanism, lithospheric deformation, and dramatic changes in surface morphology and terrestrial ecosystems. However, the timing and correlations of these consequential events remain obscure. This issue was addressed here by carrying out a high-resolution geochronologic study on the Upper Jurassic–Lower Cretaceous sequences of the Luanping basin, northern Hebei Province, China. Secondary ion mass spectrometry (SIMS) and chemical abrasion–isotope dilution–isotope ratio mass spectrometry (CA-ID-IRMS) zircon U-Pb ages from samples near the boundaries of the stratigraphic units help to redefine the chronostratigraphic framework of this basin and more importantly reveal that the second phase of the Yanshanian orogeny, representing a tectonic transition from flat to steep subduction of the paleo-Pacific plate, occurred within 0.87 ± 0.10 m.y. between 134.162 ± 0.091 Ma and 133.295 ± 0.043 Ma. Crustal extension then followed and resulted in development of rift basins and vigorous volcanism. The Jehol Biota came into being in Lower Cretaceous successions formed after ca. 130 Ma. The late Mesozoic Luanping basin therefore records how the subduction of the paleo-Pacific plate drove intracontinental orogeny, volcanism, basin development, and ecosystem evolution.

Decoding the Link Between Magmatic Cyclicity and Episodic Variation of Tectonics and Crustal Thickness in the Overriding Plate

AbstractCyclical change in subduction angle is the favorable mechanism to elucidate the cyclicity of continental arc magmatism, however, the role of episodic tectonics and variation of the lithosphere in overriding plates is much underestimated. Here we focus on structural, magnetic, and gravitational features of the Late Jurassic to Early Cretaceous granites in the Mesozoic Paleo‐Pacific arc system of the North China block. By unraveling the emplacement process and regional tectonics, we establish a three‐staged extension‐contraction cycle with crustal thickness variation controlling the magmatic flux and behavior. The Late Jurassic extension produced high‐flux crustal‐derived magma (1.87 × 103 km2/Myr), but the thick crust >45 km accumulated large granitic batholiths by multi‐feeders emplacement at the middle‐lower crust and prevented magma ascent and eruption. Subsequently, the Latest Jurassic to Earliest Cretaceous contraction resulted in the magmatic lull and thickened crust of ca. 60 km, fueling crustal material for the ensuing magmatism. In the Early Cretaceous, intense crustal extension thinned the crust to 30 km and largely enhanced the magmatic flux (3.03 × 103 km2/Myr). The magma is prone to penetrate the thin crust with an intensive eruption. A small amount of magma was stored, and the emplacement was controlled by ductile detachments or normal faults. Our model emphasizes episodic the deformation of lithosphere and associated crustal thickness variation in controlling magma production, which may shed new light in understanding the magmatic cyclicity under continuous subduction.

Mesozoic crustal reworking at different depths in the North China Craton: Insight from the coexisting Early Cretaceous high and low Sr/Y granitoids

Crustal reworking, an important part of continental evolution, can occur in cratons even though they are generally rigid and stable. However, the reworking mechanisms are still debated. Here, we present detailed zircon UPb ages, mineral compositions, major and trace elements, and Sr–Nd–Pb–Hf isotopic data for the coexisting high and low Sr/Y granitoids in the Liaodong Peninsula to decipher the reworking mechanism in the eastern North China Craton (NCC). Mafic microgranular enclaves (MMEs) are common in the studied granitoids, and both the granitoids and their MMEs have consistent emplacement ages of 128–126 Ma. The low and high Sr/Y granitoids are characterized by high-K calc-alkaline I-type granites. They are enriched in light rare earth elements (REEs) and large ion lithophile elements (e.g., Rb, K, and Pb), with depletions in high field strength elements (e.g., Nb, Ta, P, and Ti). The low Sr/Y granitoids have homogeneous Sr–Nd–Pb-Hf isotopic compositions, indistinguishable from those of their MMEs, indicating that they are of cognate origin. Their high (87Sr/86Sr)i (0.713759–0.715341), low εNd(t) and εHf(t) values (−19.2 to −18.1 and − 20.9 to −15.0, respectively), and old two-stage Nd and Hf model ages (ca. 2.50 Ga) suggest that they are derived from partial melting of the ancient lower crust at a normal crustal depth. In contrast, the high Sr/Y granitoids show more depleted heavy REEs and higher Sr/Y (21.1–80.2) and (La/Yb)N (19.2–50.2) ratios, with very low Y (≤ 12.5 ppm) and Yb (≤ 1.11 ppm) contents and negligible Eu anomalies. Their enriched and variable Sr–Nd–Pb-Hf isotopes (e.g., εNd(t) = −20.8 to −14.9, εHf(t) = −24.3 to −9.2) are distinctly different from those of their MMEs (e.g., εNd(t) = −17.6 to −13.2, εHf(t) = −20.8 to −0.3), implying a magma mixing process. These features suggest that the high Sr/Y granitoids and their MMEs are formed by mixing of the thickened ancient lower crustal and lithospheric mantle-derived magmas, with minor contributions of the asthenospheric mantle. Combined with the coeval (129–114 Ma) high-Mg adakitic and A-type granitoids, the coexisting high and low Sr/Y granitoids may indicate intensive crustal reworking at variable depths in the NCC. The reworking is attributed to the asthenosphere upwelling and lithospheric delamination induced by the rollback of the subducting Paleo-Pacific plate.

Unveiling the formation and magma transport dynamics of the Ulanqab maar volcanic cluster in the western North China Craton: Insights from 40Ar-39Ar geochronology, mineral chemistry, and Sr-Nd-Mg isotopes

The chemical composition of eastern North China Craton (NCC)'s alkaline basaltes likely influenced by subducting Pacific Plate. Nonetheless, the influence of these processes on the western craton remains uncertain due to the lack of geochemical evidence. The recent discovery of Ulanqab maar volcanic cluster (UMVC) in the western NCC has become significant research windows. However, their petrogenesis and magmatic processes remain poorly understood. In the present study, 40Ar/39Ar, whole rock and mineral geochemistry, and Sr–Nd–Mg isotope data for the UMVC in the western NCC are reported. These data reveal that the UMVC was formed during the Neogene (7.60 ± 0.04 Ma), diverging from Quaternary basalts or as part of the Hannuoba basalts (eastern Ulanqab). The UMVC rocks, featuring typical oceanic island basalts traits with moderate (87Sr/86Sr)i values (0.70487–0.70524) and εNd(t) values from −4.95 to + 0.82, likely originated from an enriched EMI-type mantle source during the mid-Proterozoic. This involved mixing melts from 30 to 50 % partial melting of garnet lherzolite and 5–15 % partial melting of garnet pyroxenite in a deep magma chamber. Crystallization of clinopyroxene and garnet in this chamber created high-Ti alkaline lavas, with limited presence in erupted lavas due to sluggish magma ascent in the profound lithospheric mantle. In shallower lithospheric mantle regions, interactions between alkaline magma and orthopyroxenite improved transport kinetics, enabling clinopyroxene and olivine crystallization under lower pressure. These magmas integrated mafic crystal mushes from accumulation chambers. The study also identified a low Mg isotope composition (δ26Mg = − 0.56 ‰ to − 0.42 ‰) in samples, suggesting a hybrid source influenced by early decarbonation in Precambrian subduction zones. This finding indicates the incorporation of Mg-rich carbonate minerals from marine sediments into the magma source, contributing to the observed variations in eastern China's alkaline basalts.

Triassic temporal and spatial migration of the provenance along the South Ordos Basin: Insights into the tectonic evolution of Eastern Palaeo‐Tethys Ocean

AbstractClarifying the role of mountain‐building processes in the filling history of large hinterland basins is an essential aspect of basin–mountain system research. We consider the case of the Triassic South Ordos Basin (SOB) to clarify these points. Located in the south‐western North China Block (NCB), the SOB which preserves the most complete Triassic deposition on the north of the Qinling Orogenic Belt (QB) is crucial for understanding the detailed tectonic processes of the QB. Sedimentological, petrological and zircon U–Pb geochronological signatures from the three parts (eastern, central and western) in the SOB indicate that the sediment source migrated both temporally and spatially. Stratigraphic correlation identified two fluvial progradational episodes from south to north in the fluvial–deltaic–lacustrine sedimentary system, one in the eastern SOB and the other in the central SOB. The Late Triassic detrital zircons in the central SOB with distinguishing Neoproterozoic ages were derived from the southern margin of the NCB and the QB. The western SOB exhibited the sediment source shifted from pre‐Triassic North Qilian Belt sedimentary cover to basement from the Middle‐to‐Late Triassic based on a zircon age transition from ca. 2000 to ca. 430 Ma. Late Triassic sediment sources also included the southern margin of the NCB and the QB. Differing provenances from east to west were also confirmed using thin section and heavy mineral analyses. Regional comparisons of zircon age distributions in the eastern SOB with published data indicate that detritus from the QB was first transported to the eastern SOB and then to the central and western SOB. Spatiotemporal changes in the sediment source and sedimentary filling transitions in the three parts of the SOB suggest that the QB underwent asynchronous uplift that began in the east during the Early Triassic and propagated westward, reaching its maximum extent in the early Late Triassic.

Geodynamic regime of the southeastern North China Craton before the Tectono-Magmatic Lull: evidence from ca. 2510 Ma and 2430 Ma igneous rocks in the Xuhuai micro-block

ABSTRACT The Tectono-Magmatic Lull (TML) refers to the period between 2.37 and 2.24 Ga when magmatic activity declined globally, the cause of which remains debated. The North China Craton (NCC), which was formed by assembling several micro-blocks in Neoarchean to Paleoproterozoic, preserves the most records of magmatism across the TML. In this contribution, we report petrological, geochemical, and zircon U-Pb-Hf isotopic data of Paleoproterozoic basement rocks from the Xuhuai (XH) micro-block in the southeastern part of the NCC, and use them to constrain the geodynamic regime at the onset of the TML. Our data reveal that the central part of the XH micro-block is mainly composed of biotite granodioritic gneiss and plagioclase amphibolite, which is divided into a ca. 2510 Ma suite of low- and medium-pressure TTGs and a ca. 2430 Ma bimodal igneous suite including high-pressure TTG and plagioclase amphibolite. Variable magmatic zircon εHf(t) values (1.9 to 7.2), Nb, Ta and Ti anomalies for the 2510 Ma TTGs indicate that the parental magma, which was involved with mantle materials, was generated in an active subduction environment in this pre-TML era. The felsic component of bimodal igneous rocks with high Na/Ta ratios (27 to 30) and stable Mg# (41 to 44) suggests their magma source region was as deep as the rutile stability field, and the delamination-derived asthenosphere mantle ascending. The influx of hot mantle induces thermal weakening and mechanical stretching of the overlying crust, leading to back-arc extension. The results of this study support the hypotheses that the NCC formed from micro-block amalgamation and the trigger of the TML could be the large-scale delamination of the lower crust into the mantle.

A combined methodology for reconstructing source-to-sink basin evolution, exemplified by the Triassic Songpan–Ganzi basin, central China

Source-to-sink evolution of a basin is a key to understand sedimentary processes, especially in a complex regional orogenic setting. Detrital zircon populations can be traced from their primary sources to their depositional settings. The resulting interpretations are enhanced by calculation of the adjacent orogen's paleoaltimetry, which provides additional insights into paleogeography. In this study, we present a combined methodology which aims to reconstruct source-to-sink evolution by the analysis of detrital zircon age distribution in sandstones, together with the calculation of paleo-elevation of surrounding orogens based on the chemical compositions of coeval magmatic rocks. We test the method using detrital zircon U–Pb geochronological data sets from the Triassic Songpan–Ganzi basin in central China, combined with whole-rock geochemical data from intermediate-composition magmatic rocks in adjacent crustal blocks. Application of the combined methodology supports a syn-collisional basin model for the formation of the Triassic Songpan-Ganzi basin in preference to a continental back-arc basin. The clastic sediments, mainly deep-marine turbidites, accumulated in a remnant Paleotethyan Ocean that was surrounded by the converging North China Block, South China Block, East Kunlun Orogenic Belt and the Qiangtang Block. The North China Block and the North Qaidam Block were major proto-sources of detrital zircons to the basin, contributing on average 12 % and 15 %, respectively. Triassic magmatic rocks in the East Kunlun and Qiangtang regions were major sources of igneous zircons, up to 68 % for the former and up to 56 % for the latter. Despite being located at a calculated elevation of ca. 4000 m, the Qinling Orogenic Belt contributed only ca. <10 % of the zircons, mostly restricted to the eastern depocenter of the basin. In contrast, supply from the North Qiangtang Block, despite its calculated lower elevation (1000–3000 m), accounts for 2–10 % of the detrital zircons in the basin, suggesting high erosion rates of this block. The minimal supply of zircons from the South China Block, restricted to 3–6 % in the central and western depocenters, is inconsistent with the zircon abundances predicted in the alternative back-arc basin model of the Songpan–Ganzi basin.

Global sea-level fall triggered Ediacaran–Cambrian unconformity in North China craton

The Great Unconformity that separates the Cambrian and the underlying Proterozoic strata has been interpreted as recording a composite of multiple diachronous unconformities, among which the Ediacaran–Cambrian unconformity represents the last stage of these erosional processes. Whilst the major denudational episode of the Great Unconformity was strictly restricted to happen before or during the Cryogenian and considered to be associated with the Rodinia supercontinent cycle and “Snowball Earth” event, the cause(s) for the relatively temporary exhumation in late Neoproterozoic remains elusive. Here we present a synthetic geochronological study for the late Ediacaran to early Cambrian strata on the southern North China craton (NCC), where the Ediacaran–Cambrian unconformity occurs. The absence of the latest Ediacaran to earliest Cambrian age zircons of these strata may suggest a significant tectonic quiescence in NCC. A similar phenomenon can also be recognized in other blocks isolated from the Gondwanaland during the late Neoproterozoic–early Cambrian interval. This world-wide Ediacaran–Cambrian unconformity thus was more likely caused by a global sea-level fall, possibly associated with the assembly of the Gondwana supercontinent during the Precambrian–Cambrian transitional period.

Detrital zircon U‐Pb geochronology and provenance of Silurian, Devonian and Permian sedimentary rocks, South Qinling: Constraints on late Palaeozoic tectonic evolution history of the Qinling Orogenic Belt

The Qinling Orogenic Belt (QOB), formed by the subduction and collision between the North China Block (NCB) and the South China Block (SCB), is a key area for exploring the tectonic process and timing of integration between the two blocks. A range of tectonic models have been proposed with regard to the subduction and collision of the QOB, but controversy in the timing and integration process still remain debatable, especially in the late Palaeozoic orogeny. The South Qinling Belt (SQB) is located between the Shangdan and Mianlue sutures, widely dispersed sediments outcropped in the SQB provide natural ground for the detrital zircon study, that could trace the sedimentary provenance and continental crustal evolution history, thus provide important evidence for the late Palaeozoic evolutionary processes in the QOB. In this study, we applied a detailed geochronological U‐Pb zircon dating of the Silurian, Devonian and Permian sedimentary rocks from the SQB. The result of the U‐Pb isotopic data shows distinct age populations at 439–474 Ma of the Silurian samples, ca. 400–490 Ma of the Devonian samples and 260–310 Ma of the Permian samples, respectively. By comparing the regional geochronological data, we sum up that the Silurian detrital zircons are mainly derived from the SQB and the northern margin of SCB (N‐SCB), the Devonian detrital zircon age populations are dominated by the North Qinling Belt (NQB) and SQB and the Permian sediments mainly stemmed from the southern margin of the North China Block (S‐NCB) and the NQB. A mutual age population of the Devonian sediments at ca. 400–490 Ma from the NQB constrains the closure of the Shangdan Ocean between the NCB and the SCB before the middle Devonian times. Ca. 260 ~ 380 Ma age population of the Permian sediments show similarities with the age data from the northern margin of the NCB, indicating an uplift event of NQB before the late Permian, and further constrains the closure of Mianlue ocean later than Permian times.

The gold mineral systems of the West Qinling orogen, central China: New insight from the Baguamiao gold deposit

The Baguamiao gold deposit is the first large deposit discovered in the West Qinling orogen in central China in the 1990 s. However, the occurrence of invisible gold in the deposit has not been reported. There is also no consensus on whether magmatic activity is involved in the gold mineralization, the style of mineralization, and the mechanism of gold precipitation. In this study, the in-situ trace elements, and chemical mapping of pyrite and pyrrhotite in the Baguamiao gold deposit were carried out for the first time. These data combined with the C-H-O isotope data of quartz, ankerite and calcite were used to determine mineralization process. In the Baguamiao gold deposit, five types of pyrite (Py0 to Py4) and pyrrhotite (Po0 to Po4) were identified, corresponding to the sedimentary-diagenetic period and four stages of mineralization (Stage I to Stage IV), respectively. From stage I to stage IV, gold mineralization in pyrite and pyrrhotite occurs as either visible or invisible crystals. The latter occurs dominantly as lattice-bound solid solutions (Au+) and is related to the content of Cu and Te. Co and Ni contents and Co/Ni ratios indicate that pyrite and pyrrhotite are magmatic-hydrothermal origin and affected by fluid-rock interaction. The change of Se and Te concentrations in pyrite and pyrrhotite indicates that oxygen fugacity (ƒO2) was increased from stage I to stage II, and then decreased during stage III and stage IV. In addition, the δ18O values of quartz, calculated δ18OH2O values of the ore-forming fluids and δ13C values range from 16.9 to 20.3 ‰, 7.7 to 12.9 ‰, and − 19.3 to + 0.2 ‰, respectively. Such isotopic signature records typical characteristics of orogenic gold deposit. The ore-forming fluid is a mixed hydrothermal solution involving metamorphic water, magmatic water, and meteoric water, and mixed with marine carbonate and sedimentary organic matter. Gold was precipitated by phase separation, fluid-rock interaction, and fluid mixing. Combined with the tectono-magmatic evolution, metamorphic deformation, and gold mineralization age of the West Qinling orogen, it can be concluded that with the closure of the Mianlue portions of the East Paleo-Tethys Ocean, the Baguamiao gold deposit was formed in the post-collisional extensional environment between the South China Block and the North China Block in the Late Triassic and is an orogenic gold deposit reference to the crustal continuum model.

Seismic evidence for collisional tectonics of the North China and Yangtze blocks in the Tongbai-Dabie orogenic belt

The Tongbai-Dabie orogenic belt was formed in the Middle to Late Triassic through continental collision between the North China Block and the Yangtze Block. To reveal the collisional tectonics of the two blocks, we apply teleseismic tomography to study the 3-D P-wave velocity structure down to 400 km depth beneath the Tongbai-Dabie orogenic belt using 37,251 first P-wave arrival times of 1423 teleseismic events recorded at 99 seismic stations in the study region. Our tomography reveals three obvious high-velocity anomalies. One is dipping southward beneath the Tongbai-Dabie orogenic belt, reflecting the southward subduction of the North China Block. The second is visible down to 100 km depth beneath the eastern Tongbai-Dabie orogenic belt, which reflects the Yangtze Block. The third appears at depths of 300–400 km, which is interpreted as the retained broke-off paleo-Tethyan oceanic slab. On the basis of our tomographic results and previous findings, we propose a two-stage subduction model showing that the Yangtze Block subducted northward in the Triassic, and then the North China Block subducted southward in the Jurassic beneath the Tongbai-Dabie orogenic belt.

Petrogenesis of two episodes of Neoarchean TTG gneisses (∼2.72 Ga and 2.56–2.54 Ga) from the Zhongtiao Mountains, North China Craton: Implications for crustal evolution

The petrogenesis of tonalite-trondhjemite-granodiorite (TTG) suites can provide key clues for the formation and evolution of continental crust. Neoarchean TTG gneisses are widely distributed in the Zhongtiao Mountains (ZTM), North China Craton (NCC). In this contribution, to better understand Neoarchean crustal evolution of the NCC, two discrete episodes of TTG gneisses (∼2.72 Ga and ∼2.56–2.54 Ga) from the ZTM are investigated. New results approve that the two episodes of TTG gneisses are all characterized by high SiO2, Na2O contents, (La/Yb)N and Sr/Y values, but low K2O/Na2O ratios. These geochemical features are similar to the Archean TTG suites and Phanerozoic high-SiO2 adakites, suggesting that they were both derived from partial melting of mafic rocks. The characteristics of trace elements (e.g., La/Yb, Sr/Y, Y/Yb, (Ho/Yb)N and Nb/Ta ratios) imply that both of them correspond to MP-TTGs, and garnet-amphibole exist in the residue phase. The ∼2.72 Ga TTGs show high Mg# values (ave. = 51), Cr (4.87–104 ppm) and Ni (6.37–55.7 ppm) contents, and negative Nb, Ta anomalies. Some high Nb/Ta ratios (up to 17.6) imply that rutile might be involved in the residual phase, which should require a higher pressure. Zircons from these rocks yield positive εHf(t) values of +4.0 ∼ +6.8 (ave. = +5.6), with two-stage Hf model ages (TDM2) of ∼2.85–2.70 Ga, indicating a juvenile basaltic crustal source. Hence, we interpret that ∼2.72 Ga TTGs in the ZTM were derived from partial melting of mafic rocks, and more likely related to subduction process. In contrast, the ∼2.56–2.54 Ga TTGs have lower Mg# values (39–54, mostly <45), Cr (6.02–22.8 ppm) and Ni (4.93–15.7 ppm) contents. They exhibit more evolved zircon Hf (average εHf(t) = +3.21) and whole-rock Nd (εNd(t) = +1.87) isotopic compositions, and their TDM2 ages are concentrated at ∼2.85–2.68 Ga. These ∼2.5 Ga TTGs in the ZTM show similar geochemical features with contemporary TTGs in the XQL, DF and EZT of the southern NCC, identical to melts from partial melting of mafic rocks under a thickened lower crust. The ∼2.5 Ga TTGs, A-type granites and mafic rocks in the ZTM jointly indicate a complicated crust-mantle process at different depths related to mantle plume activity during the late Neoarchean. Based on comparison of the spatial-temporal distribution and geochemical features of ∼2.7 Ga and ∼2.5 Ga TTGs in the NCC, we propose that Neoarchean crustal evolution of the ZTM is similar to the whole NCC, which recorded a significant crustal growth event at ∼2.7 Ga, and an important crustal reworking event associated with some juvenile crustal growth at ∼2.5 Ga.

North China as a mechanical bridge linking Pacific subduction and extrusion of the Tibetan Plateau

North China, one of the most populated regions in the world, is exposed to elevated seismic hazards and has experienced multiple M ≥ 8 earthquakes in the past 1,000 years. The recent 1976 Ms 7.8 Tangshan earthquake constitutes a vivid reminder of the tectonic activity. Yet, the tectonic origin of the regional seismic unrest remains poorly understood. Here, we use geodetic data to construct a kinematic model encompassing the North China Block (NCB) and its neighboring Amurian Block (AB) and the South China Block (SCB) to illuminate the link between lithospheric strain accumulation and seismic activity. Our analysis illuminates two east-west oriented left-lateral shear zones that decouple the AB from the NCB, the latter representing a collage of the North China Plain (NCP) and the Ordos Block (OB). Bookshelf faulting slices the NCP through a series of NNE-trending right-lateral and conjugate WNW-trending left-lateral shear zones. These shear zones drive historical and instrumental seismic activities. The NCB serves as a mechanical bridge accommodating the relative motion of the surrounding mobile tectonic units. In the far field, Pacific subduction at the Japan Trench, extrusion of the Tibetan plateau, and retreat at the Ryukyu trench cause internal strain within the NCB, leading to the frequent occurrences of destructive earthquakes.

High positive carbonate carbon isotope excursion identified in the North China Craton: Implications for the Lomagundi–Jatuli Event

AbstractRecords of the Lomagundi–Jatuli Event (LJE) are well preserved globally, but high δ13Ccarb carbonates have not been identified in the North China Craton (NCC). Our results on ~3–4 km thick carbonates from the newly confirmed Palaeoproterozoic successions in Fanhe Basin in the northeastern NCC show that the ~2.20–2.06 Ga carbonates have positive carbon isotope excursion and those deposited after 2.06 Ga have normal carbon isotope. Specially, carbonates from the Daposhan Formation have δ13Ccarb values of 10.2‰–11.8‰, which is the largest positive carbon isotope excursion in the NCC. The ~2.20–2.06 Ga carbonates in Fanhe Basin have similar δ13Ccarb values as those contemporaneously deposited in other cratons and their δ13Ccarb values exhibit a decreasing trend from ~2.20 Ga to 2.06 Ga. Our identification of carbonates with high positive δ13Ccarb values in Fanhe Basin not only casts new lights on records of the LJE in the NCC, but also provides important constraints on global significance of the positive δ13Ccarb excursion of LJE.