Jiao Liao Ji Belt Research Articles

Tectonic evolution of the Dadongcha Formation, Ji'an group, Qinghe area, Tonghua, NE China: Implications from geochronological and geochemical evidence of metapelites

The Jiao–Liao–Ji Belt (JLJB) is an important Paleoproterozoic orogenic belt that has been a focus of research to understand the Precambrian evolution of the North China Craton (NCC). The widespread Paleoproterozoic Ji’an group, which was exposed in the northern margin of JLJB, is the key to solving controversies in the tectonic setting of this special belt. An intensive study on metamorphic reactions, zircon U–Pb ages, mineral thermobarometry, geochemistry, and quantitative phase equilibria modeling (pressure–temperature pseudosections) of typical metapelites from the Dadongcha Formation of the Ji’an group provides important insight to understand the tectonic setting and processes of the Paleoproterozoic JLJB. The analyzed metapelites are exposed in Toudao and Qinghe towns in NE China, include garnet–biotite schist, garnet–biotite–plagioclase gneiss, garnet–sillimanite–cordierite–biotite gneiss, and hypersthene-spinel–cordierite–biotite gneiss. Garnets contain mineral inclusions such as sillimanite, biotite, feldspar, and quartz and retain the typical cordierite reactive edge structures. The protoliths of metapelites are sets of claystone or miscellaneous sandstone with an average chemical composition that is close to that of the upper continental crust (UCC). Chemical Index of Alteration (CIA) and Index of Compositional Variability (ICV) values suggest a high degree of weathering of their sources and low compositional maturity of clastic sediments. The chondrite-normalized rare earth element (REE) pattern of analyzed samples displays characteristics of medium fractionation in light and heavy REEs, and strong enrichment in light REEs. The primitive mantle-normalized trace element pattern shows enrichment of large ion lithophile elements (LILEs) such as Ba, and the content of high field strength elements (HFSEs) such as Zr and Hf is relatively low; furthermore, Nb, Ta, P, and Ti are distinctly depleted. The emphasis is on the metamorphism of metapelites, which shows a clockwise P–T path. In combination with zircon U–Pb dating, a general evolution model for the metapelites was drawn. The metapelites were formed in an active continental margin environment where the evolved island arcs developed around 1.95–2.02 Ga, then were involved in the collision between the Longgang and Langrim blocks in the eastern part of the NCC, and returned to the surface after undergoing regional metamorphism with widespread anatexis around 1.8–1.95 Ga.

Paleoproterozoic Adakitic Rocks in Qingchengzi District, Northeastern Jiao-Liao-Ji Belt: Implications for Petrogenesis and Tectonism

Herein, zircon U-Pb geochronology, Lu-Hf isotopes, and whole-rock major and trace element geochemistry are presented for two Palaeoproterozoic granitic rocks in Qingchengzi district, northeastern Jiao-Liao-Ji Belt (JLJB). These new geochronological and geochemical data provide reference clues for exploring the petrogenesis and tectonic setting of Paleoproterozoic magmatic rocks in the Qingchengzi district, which further constrain the tectonic nature of the JLJB. Our zircon U-Pb dating denotes that the Paleoproterozoic magmatic events in the Qingchengzi district were emplaced at ~2163 Ma and ~1854 Ma, represented by granite porphyry and biotite granite, respectively. Geochemically, these Palaeoproterozoic rocks are characterized by high Sr (760–842 ppm), SiO2 (69.72–70.89 wt.%), and Al2O3 (15.53–16.78 wt.%) contents, low Y (2.1–9.0 ppm) and Yb (0.25–0.80 ppm) contents, which indicate an adakite affinity. Combined with Hf isotopic composition (εHf(t) = −1.5~+4.8; TDM2 = 3109~2560 Ma), we believe that the Paleoproterozoic adakitic magma originated from partial melting of the thickened lower crust material in the Meso-Neoarchean. Moreover, these rocks are enriched in light rare earth elements and large ion lithophilic elements (e.g., K, Rb, and Cs), and depleted in heavy rare earth elements and high field strength elements (e.g., Nb and Ta). These features are similar to magmatic rocks formed in an arc environment (either island arc or active continental margin) and are not consistent with an intraplate/intracontinental environment. According to this study and previous research results, we conclude that the arc–continent collision model is conducive to the Paleoproterozoic tectonic attribute of the JLJB, and the oceanic crust subduction between the Namgrim and Longgang blocks may have induced the widespread occurrence of magmatic events in the region.

Geochemistry of two types of Palaeoproterozoic granites, and zircon U–Pb dating, and Lu–Hf isotopic characteristics in the Kuandian area within the Jiao‐Liao‐Ji Belt: Implications for regional tectonic setting

Palaeoproterozoic granites accompanied with granulite‐facies gneisses can be recognized in the Kuandian area, northern Jiao‐Liao‐Ji Belt (JLJB). This study highlights two episodes of Palaeoproterozoic magmatism, identified by granites and biotite monzogranitic gneisses herein. Zircon grains from biotite monzogranitic gneiss with homogeneous oscillatory zoning yielded a U–Pb age of 2,153 ± 16 Ma, in accordance with the age of zircon cores from the monzogranitic gneiss. Zircon grains from the two granites yielded upper intercept ages of 1,892 ± 38 Ma and 1,859 ± 36 Ma respectively. Monzogranitic gneiss samples are enriched in Th, Rb, Pb, U, and REE, but depleted in Sr and P. They have high 1,000 × Ga/Al ratios versus Zr, Ce, Nb, Y contents, which are usually interpreted as the features of classical A‐type granite that originated in a lithospheric extension setting. The ~1.89–1.86 Ga granite samples have relatively high Al, Rb, Th, U and low Sr, Zr, and Hf contents. These features, combined with the observation of minor apatite grains under the microscope are similar with the I‐type granites. In situ zircon Lu–Hf isotopic analyses revealed that ~1.89–1.86 Ga granite had a similar range and TDM2 ages with the monzogranitic gneiss, but with much lower εHf(t) values. The monzogranitic gneiss may have originated from an Archean crust, while the later granite may be derived from melting of the partial melting of the monzogranitic gneiss or the Archean crust that generated the monzogranitic gneiss. The ~1.89–1.86 Ga granites, together with the coeval S‐type granites in the JLJB, represent an orogeny process that may involve a Palaeoproterozoic subduction.

Paleoproterozoic postcollisional metamorphic and igneous activities in the Jinan area of the Jiao-Liao-Ji Belt in the North China Craton and their tectonic implications

The Jiao-Liao-Ji Belt (JLJB) is a Paleoproterozoic collisional belt between the Longgang Block in the northeastern North China Craton and the Nangrim Massif on the Korean Peninsula. The Jinan area, located in the northeastern JLJB, was intruded by monzogranite at 2151 ± 6 Ma and then intruded again by porphyritic granites at 1842 ± 5 Ma in a postcollisional tectonic setting. The monzogranite and an associated gabbro were metamorphosed into metamonzogranite and metabasite at 1868 ± 11 Ma–1846 ± 3 Ma. Pelitic granulites occur together with the porphyritic granites. The pelitic granulites have peak metamorphic mineral assemblages of garnet + biotite + plagioclase + K-feldspar + sillimanite + quartz + ilmenite and underwent retrograde metamorphism, as evidenced by the presence of cordierite and muscovite. Pseudosection analysis of the granulites yields peak metamorphic conditions of ~8.5–7 kbar and 800–760 °C, and conventional geothermobarometry analysis of garnet rims and adjacent minerals yields retrograde metamorphic conditions of ~5–3.5 kbar and 740–680 °C. Dating of monazite from the two granulites demonstrates that peak metamorphism occurred between 1840 ± 2 Ma and 1847 ± 4 Ma. These results, together with the findings of previous studies, indicate that in the Liaodong and Jinan areas of the JLJB, igneous and metamorphic activities occurred together at ~1.85 Ga in a postcollisional tectonic setting, suggesting that collision between the Longgang Block and the Nangrim Massif occurred before ~1.85 Ga.

Location of the tectonic boundary between the Paleoproterozoic Jiao–Liao–Ji Belt and the Archean Longgang Block in the Lianshanguan area, northeastern China

The tectonic evolution of the Paleoproterozoic Jiao–Liao–Ji Belt, which is located in the North China Craton in northeastern China, is the subject of ongoing debate. Most previous studies on this belt have been based on traditional geological methods, with most of the data being obtained from the surface, leading to uncertainties regarding the deep geological structure of the belt. This has restricted our understanding of the tectonic character and development of the belt; however, this limitation could be overcome by geophysical studies. Here, we analyze and interpret newly collected rock physical property data (density, magnetic susceptibility, and resistivity) and non-seismic geophysical data (gravity, magnetic, and magnetotelluric sounding data) for the Lianshanguan area to infer the location, configuration, and nature of the tectonic boundary between the Paleoproterozoic Jiao–Liao–Ji Belt and the Archean Longgang Block. The Lianshanguan rock mass, which belongs to the Archean Longgang Block, shows a weak gravity anomaly (0–6 mGal) and high resistivity (103.6–104 Ω·m). The area south of the Lianshanguan rock mass consists of the Paleoproterozoic Liaohe Group and displays an intermediate magnetic anomaly (0–200 nT) and low resistivity (10–102.5 Ω·m). We therefore infer that the tectonic boundary of the Jiao–Liao–Ji Belt is located along the southern margin of the Lianshanguan intrusion. We also show that the tectonic boundary in the Eastern Liaoning–Southern Jilin area trends E–W and extends from Shuangtaling through Lianshanguan, Caohecheng, Balidianzi, and to Guaimozi. The boundary between the Longgang Block and the Jiao–Liao–Ji Belt dips predominantly to the south, suggesting an extensional tectonic regime during the Paleoproterozoic time.

Geochronology and geochemistry of the palaeoproterozoic mafic dikes in the Jiaobei terrane: implications for tectonic evolution of the Jiao-Liao-Ji Belt, eastern North China Craton

ABSTRACT The palaeoproterozoic tectonic/geodynamic evolution of the Jiao-Liao-Ji Belt (JLJB), one of the three representative palaeoproterozoic tectonic units in the North China Craton (NCC), remains controversial. The palaeoproterozoic mafic dikes sampled in the Jiaobei terrane, situated in the southern segment of the JLJB, could provide significant evidence for the JLJB’s evolution. Their LA-ICP-MS zircon U-Pb dating data show that these dikes were emplaced at the period of ~2175 Ma. They have relatively low SiO2 contents and relatively high contents of Al2O3, MgO, Cr, and Ni. Further, they exhibit high field strength elements (HFSE) (e.g. Nb and Ta) depletion and weak Eu anomalies. Also, they show limited initial 87Sr/86Sr ratios (0.700478–0.705069) and low ɛNd(t) values (−2.07 to −0.09) with model ages (TDM1) of 2722–2967 Ma. The magmatic crystal zircons yielded low ɛHf(t) values of −9.22 ~ −3.82 relative to the corresponding Hf model ages of 2627–2870 Ma. These geochemical characteristics of the dikes indicate that they originated via 5–10% partial melting of the North China Craton’s enriched lithospheric mantle within the spinel stability field. In combination with contemporaneous A-type granites, mafic rocks, and other meta-volcanic associations, palaeoproterozoic Jiaobei mafic dikes formed in a back-arc extensional tectonic setting. This further indicates that the JLJB experienced back-arc extending triggered by slab rollback of subducted oceanic plate at ~2175 Ma ago. This study reports new evidence regarding the evolution of Precambrian tectonics of the North China Craton.

Discovery of kyanite in typically cordierite/sillimanite-bearing low- to medium-pressure pelitic granulites from the Jiaobei terrain, North China Craton

The pelitic granulites along the Paleoproterozoic Jiao-Liao-Ji belt (JLJB) are dominated by cordierite/sillimanite-bearing low- to medium-pressure (LMP) conditions. Recent studies have recognized a few typical high-pressure (HP) pelitic granulites without retrograde cordierite from the Jiaobei terrane, the southern part of the JLJB. The relationship between the dominant LMP and rare HP pelitic granulites is not well constrained, and whether the LMP types are retrograde products of the HP ones remains uncertain. This uncertainty precludes a full understanding of the original spatial distribution of HP pelitic granulites and the tectonic affinity of the JLJB. We identify in this study for the first time, relict kyanite and the mineral assemblage of kyanite + K-feldspar + rutile + garnet from typically cordierite/sillimanite-bearing LMP pelitic granulites within the Jiaobei terrane. Integrated results from petrology, pseudosection modeling, geothermobarometry, and zircon and monazite U-Pb geochronology suggest that these LMP pelitic granulites experienced an earlier HP granulite-facies metamorphism possibly at ~1.95 Ga, with minimum P-T conditions of 13–14 kbar and 860–870 °C. Subsequently, these rocks underwent near isothermal decompression to 4–7 kbar and >840 °C, followed by isobaric cooling to ~600 °C and 4–6 kbar. The decompression and cooling triggered LMP granulite-facies retrogression at ~1.85 Ga that eclipsed the earlier HP granulite-facies records. The clockwise P-T-t path defined is consistent with those reported from typical HP pelitic and mafic granulites elsewhere in the Jiaobei terrane. The results confirm that at least some portions of the typically cordierite/sillimanite-bearing LMP pelitic granulites are retrograded from the HP types. This greatly expands the spatial distribution of HP pelitic granulites and suggests a linear HP granulite-facies metamorphic belt within the Jiaobei terrane. The linear distribution of HP pelitic granulites whose protoliths are sedimentary rocks from Earth’s surface and the consistent clockwise P-T-t paths require Paleoproterozoic subduction, collision, and exhumation processes similar to those operating in modern plate tectonics. Our results from the JLJB thus provide new metamorphic constraints on the nature of Paleoproterozoic plate tectonics, and have implications for other Precambrian high-grade terranes worldwide where pelitic granulites are dominated by LMP types.

Synchronous A-type and adakitic granitic magmatism at ca. 2.2 Ga in the Jiao–Liao–Ji belt, North China Craton: Implications for rifting triggered by lithospheric delamination

The Jiao–Liao–Ji belt (JLJB) underwent back-arc or intra-continental rifting during the early Palaeoproterozoic but the underlying mechanism remains unclear. To address this issue, this study focuses on the petrogenesis of widespread Palaeoproterozoic granitoids on Liaodong Peninsula, China. Zircon U–Pb dating and geochemical and Hf isotopic data suggest that these granitoids were formed at ca. 2.2 Ga and they can be divided into A-type and adakitic granites. The A-type granites have relatively high SiO2, K2O, Zr, Ga, Nb and Y contents, and low CaO, MgO, Al2O3 and Sr contents. Based on these characteristics, εHf(t) values (−0.8 to +2.8) and TDM2 ages (2797–2569 Ma), the A-type granites are inferred to be derived from Neoarchaean tonalite–trondhjemite–granodiorites in a rift setting. In contrast, the coeval adakitic granites have relatively high Na2O, Al2O3 and Sr contents and high Sr/Y and LaN/YbN ratios, but low MgO, Ni, Yb and Y contents, suggesting a magma source with garnet but no plagioclase in the residue beneath thickened lower crust. Their variable εHf(t) values (−8.5 to +6.9) and TDM2 ages (3276–2305 Ma) indicate that the adakitic magmas were mainly generated by the partial melting of Meso–Neoarchaean crust. The co-existence of contemporaneous ca. 2.2 Ga adakitic and A-type granites provides evidence that the JLJB underwent regional rifting in the Palaeoproterozoic, most likely due to delamination of a thickened lithosphere, as follows. (1) In the Neoarchaean, the lower crust of the Longgang Block underwent granulite- and/or eclogite-facies metamorphism due to continuous thickening, which resulted in increasing lower crustal density. (2) The thickened lower crust became unstable and delaminated at ca. 2.2 Ga. Asthenospheric upwelling following this lithospheric delamination triggered the thinning of the overlying lithosphere. The upper crust and remnant thickened lower crust were partially melted to form the A-type and adakitic granites, respectively. The rifting likely resulted in the separation of the Longgang and Nangrim blocks, prior to their amalgamation in the late Palaeoproterozoic to form the JLJB.

Detrital zircon U-Pb geochronology and Hf isotopes of the Liaohe Group, Jiao-Liao-Ji Belt: Implications for the Paleoproterozoic tectonic evolution

The Jiao-Liao-Ji Belt (JLJB) is one of the most important Paleoproterozoic orogenic belts, which is intervening between the Longgang and Nangrim-Liaonan blocks. The Liaohe Group is an important research subject for understanding the Paleoproterozoic tectonic setting and evolution of the JLJB. However, the relationship of depositional spatial and chronological distributions between the North and South Liaohe groups are still under debates. In this paper, we present geochronological and zircon Lu-Hf isotopic results of meta-sedimentary rocks from the Liaohe Group to decipher their provenance depositional ages and environment, as well as their tectonic significance on the JLJB. The detrital zircons from the corresponding formations, including the Li’eryu, Gaojiayu and Dashiqiao formations of the North and South Liaohe groups, show similarities in age patterns and Hf isotopic compositions. The detrital zircons from the Li’eryu Formation of the two groups display unimodal 207Pb/206Pb age peaks at ca. 2.2–2.1 Ga. On the other hand, detrital zircons from the Gaojiayu and Dashiqiao formations of the two groups, yield two dominating age peaks at ca. 2.2–2.1 and ~2.5 Ga. In summary, all detrital zircons with age peaks at ca. 2.2–2.1 Ga, have εHf(t) value of −6.99 to +9.41 and two-stage Hf depleted mantle ages (TDM2 model ages) of 3143 to 2137 Ma. The ~2.5 Ga detrital zircons however, have εHf(t) value and TDM2 model ages which widely range from −9.37 to +10.13 and from 349 to 2367 Ma, respectively. Geochronological results indicate that ca. 2.2–2.1 Ga zircons were derived from the Liaoji granitoids. The adjacent basement rocks of the Longgang and Liaonan-Nangrim blocks provide the major sources to detrital zircons that yield an age peak at ~2.5 Ga. Combined with previous studies, the new geochronological data suggest that the protoliths of the corresponding formations of the North and South Liaohe groups deposited their detritus progressively in a back-arc basin. The Liaoji granitoids are the main sources providing detritus for the Li’eryu Formation. Subsequently, clastic sediments transported from the Longgang and Liaonan blocks, as well as from the Liaoji granitoids, were successively deposited and provided sources to the Gaojiayu and Dashiqiao formations.

Metamorphic P–T evolution and tectonic implications of pelitic granulites in the Ji’an area, northeastern Jiao–Liao–Ji Belt, North China Craton

The Ji’an area in the Jiao–Liao–Ji Belt of the North China Craton contains garnet-cordierite-sillimanite pelitic granulites that preserve representative metamorphic reaction textures. Petrographic observations and quantitative phase equilibria modeling indicate clockwise P–T paths with near-isothermal decompression and decompressional cooling following the peak metamorphism. The peak metamorphic assemblage was garnet + biotite + K-feldspar + plagioclase + sillimanite + quartz + ilmenite + magnetite with P–T conditions of 9–11 kbar and 830–880 °C. The ensuing post-peak near-isothermal decompressional assemblage was garnet + biotite + cordierite + K-feldspar + plagioclase + quartz ± sillimanite ± magnetite ± ilmenite with P–T conditions of 4.5–7.5 kbar and 810–900 °C, and this assemblage was characterized by large amounts of matrix cordierite due to the biotite decompressional dehydration melting reaction of Bt + Sil + Qz ± Pl → Crd + Kfs ± Ilm + Melt. LA–ICP–MS U–Pb analyses of detrital and metamorphic zircons in the sillimanite–garnet–cordierite pelitic granulites yielded a protolith age of ~2000 Ma and a late Paleoproterozoic metamorphic age of 1890–1870 Ma. Moreover, LA–ICP–MS U–Pb dating of monazites revealed a similar metamorphic age of 1880–1840 Ma. It had been suggested in the earlier literature that the metapelitic rocks from the Ji’an area reached the amphibolite-facies with a counterclockwise P–T path. However, our results indicate a clockwise P–T path and a granulite-facies metamorphism. We find that granulite-facies metamorphism was widespread throughout the Jiao–Liao–Ji Belt, as at Ji’an, Southern Liaohe, Jiaobei, and Bengbu, and the clockwise P–T paths and similar metamorphic ages obtained for all those areas indicate that the granulite-facies metamorphism within the Jiao–Liao–Ji Belt was a response to Paleoproterozoic continent–continent subduction and the collision of the Longgang and Nangrim blocks of the North China Craton during the peak metamorphic stage, followed by post-collisional exhumation in the post-peak decompressional stage.

A unique Paleoproterozoic HP–UHT metamorphic event recorded by the Bengbu mafic granulites in the southwestern Jiao–Liao–Ji Belt, North China Craton

The Wuhe Complex in the Bengbu area of the Jiao–Liao–Ji Belt, southeast North China Craton, contains garnet-bearing mafic granulites that have undergone high-pressure (HP) and ultrahigh-temperature (UHT) metamorphism. These granulites also experienced partial melting and occur as lenses within marbles. Petrographic observations and quantitative phase equilibria modeling reveal clockwise P–T paths, involving an inferred HP stage followed by decompressional, medium-pressure, granulite-facies metamorphism and subsequent cooling. The HP assemblage of garnet + clinopyroxene + plagioclase + K-feldspar ± amphibole ± quartz ± rutile indicates P–T conditions of 840–980 °C and 12–17 kbar. This was followed by post-peak, near-isothermal decompression with the development of orthopyroxene + clinopyroxene + plagioclase + K-feldspar + garnet + amphibole + ilmenite at 850–960 °C and 7–10 kbar, resulting in the development of orthopyroxene rims on resorbed garnet. Pyroxene and ternary feldspar thermometry yielded high temperatures of ~1150 °C and 1055–1087 °C at 10 kbar, respectively, which constrain the minimum crystallization temperatures of the igneous protoliths. The host and lamellae of the pyroxene and ternary feldspar are relict magmatic minerals/textures that survived metamorphism due to the silica-undersaturated bulk-rock conditions. Zr-in-rutile thermometry yielded temperatures of ~935 °C and 800 °C, with the former being consistent with the predicted peak metamorphic temperatures. Small amounts of melts (up to 5%) were generated during decompression of the Bengbu mafic granulites. The generated partial melts were mainly (quartz) monzonite at 900–920 °C, and the silica contents of the melts were controlled by the quartz stability field in P–T pseudosections. The partial melts were enriched in Na and strongly depleted in Fe–Mg at the peak pressure of ~14 kbar and 920 °C, and later evolved to Fe–Mg-rich and high-K compositions during decompression. The melt compositions in the studied rocks are similar when the pressures reached ~9 kbar. The modal proportion of amphibole increased as the melt H2O content decreased at lower pressures, indicating that the limited H2O remaining in the host rocks was consumed to produce amphibole. U–Pb geochronology of zircon containing inclusions of clinopyroxene, plagioclase, and apatite constrains the timing of metamorphism to 1930–1840 Ma, as is the case for HP granulites from Shandong, Liaoning, and southern Jilin in the central and northeastern Jiao–Liao–Ji Belt. The Wuhe HP–UHT mafic granulites were ultimately sourced from upwelling asthenosphere-derived magma at ~2.1 Ga, which intruded and crystallized at shallower depths. The igneous protoliths were then buried to middle–lower crustal levels and experienced HP–UHT granulite-facies metamorphism and partial melting at 1.95–1.90 Ga related to continental subduction and overthickening. The HP–UHT mafic granulites were rapidly exhumed at ~1.85 Ga and generated small volumes of (quartz) monzonite during decompression. The newly discovered Paleoproterozoic HP–UHT mafic granulites associated with partial melting suggest that the continent materials were deeply subducted to the lower crustal levels and that additional heating was not involved. The finding of the HP–UHT granulites, together with the widespread distributions of the granulite-facies metamorphic rocks and the determination of the clockwise P–T–t paths, reveal that the Paleoproterozoic Jiao–Liao–Ji orogenic belt extends at least 1000 km, starting from southern Jilin, passing through the southeastern Liaoning and Jiaobei terranes, and elongating to the Bengbu area in Anhui.

Paleoproterozoic Granitoids on Liaodong Peninsula, North China Craton

Paleoproterozoic granitoids are an important constituent of the Jiao–Liao–Ji Belt (JLJB). The spatial‐temporal distribution and types of Paleoproterozoic granitoids are closely related to the evolution of the JLJB. In this paper, we review the field occurrence, petrography, geochronology, and geochemistry of Paleoproterozoic granitoids on Liaodong Peninsula, northeast China. The Paleoproterozoic granitoids can be divided into pre‐tectonic (∼2.15 Ga; peak age=2.18 Ga) and post‐tectonic (∼1.85 Ga) granitoids. The pre‐tectonic granitoids are magnetite and hornblende–biotite monzogranites and granodiorites. Pre‐tectonic monzogranites are widespread in the JLJB and have A2‐type affinities. In contrast, pre‐tectonic granodiorites are only present in the Simenzi area and have adakitic affinities. The post‐tectonic granitoids consist of porphyritic monzogranite, syenite, diorite, granodiorite, quartz monzonite, monzogranite, and granitic pegmatite, which are adakitic rocks and I‐, S‐, and A2‐type granitoids. The assemblage of pre‐tectonic A2‐type granitoids and adakitic rocks indicates the initial tectonic setting of the JLJB was a continental back‐arc basin. The assemblage of post‐tectonic adakitic rocks and I‐, S‐, and A2‐type granitoids indicates a post‐collisional setting. The 2.20–2.15 Ga A2‐type granitoids and adakitic rocks were associated with the initial stage of back‐arc extension, and the peak of back‐arc extension is inferred from the subsequent (2.15–2.10 Ga) mafic intrusive activity. The ∼1.90 Ga adakitic rocks mark the beginning of the post‐collisional stage, which was followed by the intrusion of low‐temperature S‐ and I‐type granitoids. High‐ to low‐pressure granitoids (S‐type) were generated during the peak of post‐collisional lithospheric delamination and asthenospheric upwelling. The emplacement of later granitic pegmatites occurred during the waning of the orogeny.

Paleoproterozoic SEDEX-type stratiform mineralization overprinted by Mesozoic vein-type mineralization in the Qingchengzi Pb-Zn deposit, Northeastern China

The Qingchengzi Pb–Zn deposit is located in the northeastern Jiao–Liao–Ji Belt (JLJB), North China Craton (NCC). Field observation and age dating indicate that the deposit was formed from Paleoproterozoic sedimentary exhalative (SEDEX) stratiform mineralization overprinted by Late Triassic hydrothermal vein-type mineralization. Five types of fluid inclusions (FIs) are identified in the quartz grains, based on petrography and laser Raman spectroscopy: liquid-rich two-phase (type 1), vapor-rich two-phase (type 2), CO2-bearing (types 3a and 3b), and CO2-pure (type 4). Quartz from the SEDEX stratiform ores contains only type 1 FIs, and hydrogen-oxygen isotopic compositions indicate that the ore-forming fluids were magmatic water-derived. The ore-forming fluids were likely of medium-temperatures and low-salinity, and belonged to a NaCl–H2O hydrothermal system. Quartz from the vein-types contains all five types of FIs, and the ore-forming fluids may have belonged to a medium-temperature, low-salinity NaCl–H2O–CO2 hydrothermal system. Hydrogen-oxygen isotopes indicate that the vein-type ore-forming fluids were derived from magmatic-meteoric mixed source. Rare-earth element (REE) and sulfur-lead isotopic compositions indicate that ore-forming materials of the SEDEX stratiform mineralization were derived from the wall-rocks and magma, wheres those of the vein-type mineralization were derived from Late Triassic granitic magma, wall-rocks, and the Paleoproterozoic SEDEX ores.Based on field geological and geochronological data, we propose the following regional metallogenic model: (1) SEDEX mineralization occurred during the Paleoproterozoic post-collisional extension in the JLJB; (2) vein-type mineralization was generated by the north-dipping subduction of the Yangtze Craton beneath the NCC, which led to continent-continent collision and slab break-off in the Late Triassic.

Formation and evolution of Paleoproterozoic orogenic belt in southern Jilin, Jiao–Liao–Ji Belt, North China Craton: Constraints from geophysics

The tectonic setting and depositional environments of the Laoling and Ji’an groups in the northeastern Jiao–Liao–Ji Belt, northeastern China, are controversial. These Paleoproterozoic stratigraphic units are exposed sporadically (in Baishan and Tonghua) beneath a thick cover of Quaternary basalts, meaning that only limited information can be obtained by traditional geological methods. Therefore, using geophysical techniques in this region is pertinent. Here we present new data on the petrophysical properties (density, magnetic susceptibility, and specific resistivity) obtained from 2D cross-gradient joint inversion profiles. The results allow us to establish the relationships between the Laoling and Ji’an groups, interpret the tectonic setting of deposition, and locate the subsurface margins of the Jiao–Liao–Ji Belt. Petrophysical parameters from the Dataishan Formation (density of 2.58 g/cm3, zero magnetic susceptibility, and specific resistance of 103.04 Ω m) indicate that these rocks were derived predominantly from the Longgang Block in the north. For the Zhenzhumen Formation, the petrophysical parameters (high density, weak magnetic susceptibility, and high specific resistivity) are consistent with deposition in a passive margin that received detrital material sediments from the Longgang Block and the Liaoji granitoids. The Mayihe and Huangchagou formations (intermediate to high density, strong magnetic susceptibility, and intermediate specific resistivity) were deposited closer to a magmatic arc, with the detritus derived from the Liaoji granitoids. The low to intermediate density, stronger magnetic susceptibility, and intermediate specific resistivity of the Huashan–Linjiang, Dalizi, and Dadongcha formations indicate that these rocks were deposited in a pre-orogenic setting, with the detritus derived from the Longgang Block, Liaoji granitoids, and other felsic igneous rocks. Based on the geophysical profiles, we conclude that the Jiao–Liao–Ji Belt extends under Quaternary basalt, from Linjiang to Baishan, and eastward towards North Korea. Two basin-controlling faults (F1 and F2) represent the northern and eastern boundaries between the Longgang Block and the Jiao–Liao–Ji Belt. We interpret geophysical anomalies and variations in the petrophysical parameters in the context of subduction and collision processes.

Petrogenesis and tectonic implications of two types of Liaoji granitoid in the Jiao–Liao–Ji Belt, North China Craton

Two types of granitoid (monzogranite and granodiorite) are recognized within the Paleoproterozoic Liaoji granitoids of the Jiao–Liao–Ji Belt (JLJB) in the Hupiyu and Simenzi areas, North China Craton. We conducted zircon U–Pb geochronological, geochemical, and Hf isotopic analyses of these granitoids. Zircon U–Pb dating indicates an emplacement age of 2180 ± 14 Ma for the monzogranite (Hupiyu granitoids) and ages of 2130 ± 24 and 2173 ± 11 Ma for the Fangjiaweizi and Dadingzi granodiorites at Simenzi, respectively. The Hupiyu monzogranite samples are enriched in Zr, Ga, and Y, and depleted in Nb and Ti. Low Nb/Y ratios and high Zr saturation temperatures (849–884 °C) indicate that the Hupiyu monzogranites have an affinity with A2-subtype granitoids. The Fangjiaweizi and Dadingzi granodiorites have high Sr/Y and low K2O/Na2O ratios, indicating an affinity with adakitic rocks. Geochemical compositions and wide variation in εHf(t) values suggest that the monzogranites and granodiorites were derived from thinned and thickened lower crust, respectively, and that magmatism was accompanied by input of mantle material. This study represents the first identification of pre-tectonic adakitic rocks in the JLJB. The assemblage of pre-tectonic A2-type granitoids and adakitic rocks indicates a continental back-arc basin as the initial tectonic setting of the JLJB. These new data, combined with results of previous studies, support an arc–continent collision model for the JLJB.

Paleoproterozoic transition in tectonic regime recorded by the Eastern Block of the North China Craton: evidence from detrital zircons of the Langzishan Formation, Jiao-Liao-Ji Belt

ABSTRACTThe Eastern Block of the North China Craton records Paleoproterozoic oceanic plate subduction, the opening and subsequent closure of a back-arc basin, and a following collisional orogenic event to generate the Jiao-Liao-Ji Belt (JLJB). However, the processes involved in the initiation of subduction remain unclear. This study presents U–Pb age and trace elemental data for detrital zircons from the Langzishan Formation, the lowermost sedimentary unit within the JLJB, to constrain the provenance, depositional age, and depositional environment of this formation as well as the processes involved in the Paleoproterozoic transition in tectonic regime recorded by the Eastern Block. The U–Pb ages of these detrital zircons yield one major age peak at ca. 2529, and three minor age peaks at ca. 2700, ca. 2347, and ca. 2198 Ma. Provenance analysis indicates that the Langzishan Formation was derived from basement rocks in the Longgang Block with minor contributions from early magmatic rocks within the JLJB. Detrital zircon age contribution further suggests that the deposition of the Langzishan Formation was in a passive continental margin and commenced no earlier than 2205 Ma. Combining with previous research on the widespread distribution of magmatic and sedimentary rocks that formed in convergent settings in this area, this study suggests that the Eastern Block records a transition in tectonic regime at ~2205–2170 Ma, from passive continental margin to active continental margin settings, most likely as a result of the re-initiation of global plate tectonic cycling during the early history of the Earth.

Paleoproterozoic (2.0–1.97 Ga) subduction-related magmatism on the north–central margin of the Yeongnam Massif, Korean Peninsula, and its tectonic implications for reconstruction of the Columbia supercontinent

The Muju area, located on the north–central margin of the Yeongnam Massif, mainly consists of Precambrian orthogneisses (granitic, leucogranitic, augen and dioritic gneisses) with minor migmatite. Zircon U–Pb dating indicates that the protoliths of the orthogneisses intruded at ca. 2.00–1.97 Ga and were metamorphosed at ca. 1.87–1.86 Ga. Magmatic zircon grains within the orthogneisses have positive to negative εHf(t) values (−7.63 to +3.3) and a Neoarchean two-stage model age (TDM2 = 2.78 Ga), indicating that the protoliths of most of the orthogneisses may have been derived from Archean crustal material. The results of geochemical analysis indicate that the protoliths of the orthogneisses formed by partial melting of metagraywacke and mafic igneous rocks in an arc-related tectonic setting. The intrusion ages and geochemical data of the Paleoproterozoic orthogneisses in the study area match well with those of Paleoproterozoic (ca. 2.00–1.97 Ga) orthogneisses in the northeastern Yeongnam Massif, indicating the presence of regional Paleoproterozoic subduction zones along the northern margin of the Yeongnam Massif at ca. 2.00–1.97 Ga. Meanwhile, ca. 2.00–1.97 Ga subduction-related magmatism has not been reported from the northern Gyeonggi and Nangrim Massifs in the Korean Peninsula or the Jiao–Liao–Ji belt in the eastern North China Craton, indicating that the Yeongnam Massif may not be correlatable with the northern Gyeonggi and Nangrim Massifs or the Jiao–Liao–Ji belt. The Yeongnam Massif may be correlated with the Cathaysia Block in the South China Craton and may have been located near Laurentia and the Siberian Craton within the Columbia supercontinent.

Palaeoproterozoic tectonic evolution of the Jiao–Liao–Ji Belt, North China Craton: Geochemical and isotopic evidence from ca. 2.17 Ga felsic tuff

The Palaeoproterozoic tectonic evolution of the Jiao–Liao–Ji Belt (JLJB) in the North China Craton remains controversial, particularly in the absence of adequate evidence for oceanic plate subduction. Here, we report SHRIMP U–Pb zircon ages, whole‐rock geochemistry, and Sm–Nd isotope data on felsic tuffs from the Anshan–Helan–Lianshanguang area in the Liaodong Peninsula which provides important insights into the early tectonic evolution of the JLJB. The zircon SHRIMP U–Pb ages suggest formation of the tuffs crystallized at ca. 2.17 Ga, which coincide with the crystallization of the voluminous Liaoji granitoids in this belt. The felsic tuffs show calc‐alkaline features and are characterized by a wide range of SiO2 (61.89–72.55 wt.%), MgO (1.35–5.80 wt.%), Cr (36.0–67.8 ppm) and Ni (5.88–28.8 ppm) contents, and low TiO2 (0.42–0.64 wt.%) and total Fe2O3 (2.14–5.64 wt.%) concentrations. They also display enrichment in LREE and depletion in Nb, Ta, and Ti similar to the features of continental arc andesites. Their wide variation in whole‐rock εNd(t) (−2.6 to +3.4) combined with the synchronous magmatic activity in this region suggests that they were derived from mixing of mafic (e.g., those in the Liaohe suite) and felsic (e.g., the Liaoji granitoids) magmas, followed by fractional crystallization. In view of the widespread distribution of magmatism, including the Helan felsic tuffs and Liaoji granitoids, and the synchronous sedimentary rocks in the Liaodong Peninsula, we propose that the evolution of the JLJB involved an initial back‐arc extension stage, followed by arc‐continent collision.

Relics of a Paleoproterozoic orogen: New petrological, phase equilibria and geochronological studies on high-pressure pelitic granulites from the Pingdu-Laiyang areas, southwest of the Jiaobei terrane, North China Craton

High-pressure (HP) pelitic granulites have been used as important targets in evaluating ancient geodynamic processes similar to subduction, collision and exhumation operating in modern plate tectonics. In this contribution, relic HP pelitic granulites were identified from the Pingdu-Laiyang areas of the Jiaobei terrane that are dominated by low- to medium-pressure (LMP) pelitic granulites, suggesting their linear distribution and that at least some of LMP types should be retrograde products of the HP pelitic granulites. Their metamorphic P-T-t paths were traced by integrated methods of petrographic observation, mineral chemistry, P-T-X pseudosection modeling, Zr-in-rutile thermometry, and zircon and monazite geochronology. These HP pelitic granulites record consistent clockwise P-T-t paths that are manifested by similar peak metamorphism of high-pressure granulite-facies, with P-T conditions of P > 13 kbar, T > 850 °C possibly during 1950–1900 Ma, followed by near isothermal decompression (ITD) to mid-crustal level at 1900–1850 Ma and subsequent near isobaric cooling (IBC) to low temperature during 1850–1800 Ma. The consistent clockwise P-T-t paths and linear distribution of HP pelitic granulites explicitly indicate a sequence of geodynamic processes similar to modern-style plate tectonics must have operated during formation of the Paleoproterozoic Jiao-Liao-Ji belt (JLJB). These include a process similar to subduction that brought sedimentary precursors of HP pelitic granulites down, which was followed by continental orogeny during 1950–1900 Ma, leading to crustal thickening (40–50 km) and high-pressure granulite-facies metamorphism, and a post-orogenic collapse during 1900–1800 Ma that resulted in exhumation and cooling of HP granulites along ITD and IBC paths. Therefore, it is argued that ancient HP pelitic granulites can be regarded as relics of orogen and ascertain tectonic interpretation of the dominated LMP pelitic granulites in the same Precambrian metamorphic terranes. Notably, the apparent thermal gradients estimated from peak metamorphism are 15–20 °C/km, much higher than those of typical products in Phanerozoic plate tectonics, and the HP pelitic granulites that contain well-preserved kyanite probably require relatively high exhumation rates during ITD to middle crustal level. These seem to mark the differences in thermal regimes and tectonic mechanisms between Paleoproterozoic and Phanerozoic collisional orogenic systems.

Lithotectonic elements of Archean basement on the Liaodong Peninsula and its vicinity, North China Craton, China

The Liaodong Peninsula, in the northeastern part of the Eastern Block in the North China Craton, China, consists of lithologic units from Archean to Cenozoic in age. The basement rocks consist of widespread amphibolite- to granulite-facies Archean supracrustal assemblages and granitoid gneisses, as well as Paleoproterozoic volcano-sedimentary successions that were intruded by granitic–mafic complexes, and then metamorphosed under greenschist- to amphibolite-facies conditions. The basement rocks are overlain by thick Mesoproterozoic–Cenozoic sedimentary sequences. A synthesis of the available petrological and geochronological data allowed us to establish a geological framework for the Precambrian basement on the Liaodong Peninsula and its vicinity. The basement can be subdivided into three tectonic units: the Neoarchean Liaonan Block, the Eo–Neoarchean Longgang Block, and the intervening Paleoproterozoic Jiao–Liao–Ji Belt. In this paper we delineate the characteristics of an Archean tectonothermal event, and in a companion paper we examine the Paleoproterozoic lithotectonic assemblages. Rock samples of the Hadean eon are rare worldwide, but Hadean zircons have been identified in rocks of the Liaodong Peninsula, and they provide one of the oldest known mineralogical records on Earth. The Archean gneisses in the Liaonan Block are dominated by quartz dioritic–granodioritic gneisses that were emplaced between 2.55 and 2.44 Ga, and these rocks later underwent a lower-amphibolite-facies metamorphism. On the other hand, the Archean basement in the Longgang Block is dominated by TTG (tonalitic–trondhjemitic–granodioritic) and granitic gneisses, charnockites, and small amounts of supracrustal sequences with much older protolith ages of up to 3.85 Ga, and these rocks have undergone amphibolite- to granulite-facies metamorphism. Post-tectonic magmatism (ca. 2.5 Ga) marked the end of the Archean tectonothermal event in the Eastern Block of the North China Craton.