Jiao Liao Ji Belt Research Articles

Multiple mineralization events recorded in the Dahenglu Cu[sbnd]Co deposit, eastern North China Craton: Constraints from Re[sbnd]Os and U[sbnd]Pb geochronology

The formation of sediment-hosted CuCo deposits remains controversial, in part due to the lack of a precise age for CuCo mineralization. The Dahenglu deposit is located in the eastern part of the Jiao–Liao–Ji Belt (JLJB), one of the famous sedimentary–metamorphic-type CuCo deposits in China, that is mainly hosted within Palaeoproterozoic epimetamorphic rocks. The orebodies occur as stratoid, lenticular and veined forms in conformity with the carbonaceous sericite phyllite. In this study, we present new ReOs and monazite UPb geochronological data for carbonaceous sericite phyllite, and zircon UPb geochronological data for diorite porphyry associated with the deposit. The ReOs geochronology on carbonaceous rocks from the Dalizi Formation provides a direct and reliable depositional age of 1967 ± 23 Ma. The UPb analyses of metamorphic monazite intergrown with cobaltite yield an age of 1812 ± 8 Ma. Magmatic zircon UPb dating from ore-bearing diorite porphyry yields a weighted mean age of 121.8 ± 0.8 Ma. These results constrain three periods of mineralization in the Dahenglu deposit. Syngenetic sedimentary mineralization and metamorphic mineralization occurred during the Palaeoproterozoic, and magmatic–hydrothermal mineralization occurred during the Early Cretaceous. We suggest that ReOs and UPb geochronology on carbonaceous-bearing epimetamorphic rock and metamorphic monazite can serve as robust chronometers to establish the age and temporal evolution of sedimentary hosted CuCo mineralization.

Inherited zircons in Early Cretaceous dyke: Implication of growth and reworking of continental crust in the Jiaodong Peninsula

Inherited zircons from Early Cretaceous dykes across the Jiaodong Peninsula provide a means of exploring magmatic episodes. Negative Eu anomalies, high Th and U contents, and high U/Yb ratios confirmed a zircon source of ancient continental crust. Differences in mineralogy, chronology, geochemistry, and Hf isotopes showed that these inherited zircons were not brought in by the Triassic Yangtze Craton collision. Zircons within 2938–2800 Ma confirmed that the ancient crust in the Jiaobei Terrane originated from the Mesoarchean crustal growth. This crustal growth continued until the Early Paleoproterozoic and was accompanied by crustal transformation activities in the later period. After the collision of the Jiao–Liao–Ji Belt, the Jiaodong Peninsula entered a typical craton period until it was reactivated at the end of the Neoproterozoic, which was characterised by the Archean crustal transformation. During the Palaeozoic, smooth crustal thickness change with limited addition of oceanic crust material indicated the Qinling–Dabie–Sulu Orogenic Belt as a distal island arc system that slowed the impact of Paleo-Tethys subduction. There was no record of positive-εHf(t) zircons in the Jiaodong Peninsula during the Mesozoic, but the crust thickened rapidly. This confirmed that the Paleo-Pacific Plate may have directly subducted beneath the lithospheric mantle and had little contact with the lower crust. This subduction pattern released little hydrous fluid but much heat, which prompted the remodelling of the lower crust in the Mesozoic. Furthermore, the large-scale lithospheric thinning event around 120 Ma was identified as a result of the delamination of the lithospheric mantle together with lower crust.

Petrogenesis of the Early Paleoproterozoic Felsic Metavolcanic Rocks from the Liaodong Peninsula, NE China: Implications for the Tectonic Evolution of the Jiao-Liao-Ji Belt, North China Craton

The early Paleoproterozoic (ca. 2.2–2.1 Ga) tectonic evolution of the Jiao–Liao–Ji belt (JLJB) is a continuous hot topic and remains highly controversial. Two main tectonic regimes have been proposed for the JLJB, namely arc-related setting and intra-continental rift. Abundant ca. 2.2–2.1 Ga volcanic rocks were formed in the JLJB, especially in the Liaodong Peninsula. These ca. 2.2–2.1 Ga volcanic rocks therefore could host critical information for the evolution of the JLJB. In this study, we report a suit of ca. 2.2–2.1 Ga felsic metavolcanic rocks in the Liaodong Peninsula of the JLJB to provide new insights into the above issue. Zircon U-Pb dating reveals that the felsic metavolcanic rocks were erupted at 2185–2167 Ma. They have variable εHf(t) values (−0.70 to +9.69), high SiO2 (66.30–75.30 wt.%) and relatively low TiO2 (0.03–0.78 wt.%), tFe2O3 (0.55–5.03 wt.%), MgO (0.17–8.76 wt.%), Cr (9.16–67.30 ppm), Co (2.01–7.00 ppm) and Ni (3.90–25.70 ppm) contents with enrichments in light rare earth element (REE) and large ion lithophile element (LILE), and depletions in heavy REE and high field strength element (HFSE). Geochemical and isotopic results indicate that the felsic metavolcanic rocks were sourced from partial melting of ancient Archean TTG rocks and juvenile lower crustal materials. Combined with coeval A-type granites, bimodal volcanic rocks and the absence of typical arc magmatism, the most likely tectonic regime at ca. 2.2–2.1 Ga for the JLJB is an intra-continental rift.

Tectonic Evolution of the JLJB, North China Craton, Revisited: Constraints from Metamorphism, Geochemistry and Geochronology of the Ji’an Group and Related Granites

The Jiao-Liao-Ji Belt (JLJB) is the most representative Paleoproterozoic orogenic belt in the North China Craton (NCC). The sedimentation, metamorphism and magmatism of the Ji’an Group and associated granites provide significant insights into the tectonic evolution of the JLJB. In this study, we have synthesized published geochemistry and geochronology data on metasedimentary, metavolcanic and igneous rocks. According to the available data, the protoliths of the metasedimentary rocks are sets of shale, wacke, arkose, quartz sandstone and carbonate, while the protoliths of the metavolcanic rocks are calc-alkaline basalt, basaltic andesite, andesite, dacite and rhyolite. The rock assemblages indicate a transformation of the tectonic environment from a passive margin to an active continental margin following the onset of plate convergence and subduction. The A2-type gneissic granite (Qianzhuogou pluton) is formed in a subsequent back-arc basin extension setting at 2.20–2.14 Ga. The Ji’an Group was finally deposited in an active continental margin during the closure of a back-arc basin at 2.14–2.0 Ga. Then, the sediments were involved in a continent–arc–continent collision between the Longgang and Nangrim blocks at ~1.95 Ga. This process was accompanied by HP granulite-facies metamorphism at ~1.90 Ga. The subsequent exhumation and regional extension resulted in decompression melting during 1.90–1.86 Ga, producing metamorphism with an isothermal decompression clockwise P–T path. The resulting metapelites are characterized by perthite + sillimanite, and mafic granulites are characterized by orthopyroxene + clinopyroxene. The S-type porphyritic granite (Shuangcha pluton) is formed during the crustal anatexis. Meanwhile, extensive anatexis produced significant heating and triggered prograde to peak metamorphism with an anticlockwise P–T path. Cordierite-bearing symplectites around the garnet in the metapelites indicate a superposed isobaric cooling metamorphism. The ages of monazites and anatectic zircons suggest that the post-exhumation cooling occurred at 1.86–1.80 Ga. The Paleoproterozoic magmatism, sedimentation and metamorphism suggest a process of subduction back-arc basin extension and closure, collision and exhumation for the tectonic evolution of the JLJB.

Paleoproterozoic skarn mineralization events and geodynamic background in the Jiao-Liao-Ji Belt: Geological, geochemical and chronological evidence from the Daqinggou Fe–Cu polymetallic deposit in Ji'an, NE China

The Daqinggou Fe–Cu polymetallic deposit has been discovered in the Ji'an district, east of the Jiao-Liao-Ji Belt (JLJB). It consists of the Daqinggouli and Beigou ore sections, and the ore bodies are mainly magnetite ore bodies, followed by copper polymetallic ore bodies. Six metallogenic stages have been distinguished here: The dry skarn (I1), wet skarn (I2), iron oxide (I3), early quartz-sulfide (II1), late quartz-sulfide (II2), and quartz-carbonate stages (II3). There are also three types of fluid inclusions (FIs): gas-rich (W1-type), liquid-rich (W2-type), and daughter crystal (S-type) FIs. The ore-forming fluids here belong to a H2O–NaCl ± CO2 system with a medium-high temperature and medium-high salinity during the Stages I3 and II1, in addition to a H2O-NaCl system with a medium-low temperature and medium-low salinity in the Stage II2. In-situ S isotopes indicate that the Stage II1 sulfides were derived from magmatic sources, whilst the Stage II2 sulfides were derived from a mixture of magma and stratigraphic sources and Stage II3 was dominated by the sulfur source of the sedimentary strata. Additionally, the Pb isotope data reveal that the ore-forming minerals were of crustal or orogenic origin. By comparing the metallogenic elements of typical skarn deposits, we believe that the Daqinggou deposit is a calcareous skarn deposit, which originates from dimetasomatism between the microcline granite and marble of the Mayihe Formation in the Ji'an Group. The immiscibility and mixing of ore-forming fluids are the key mechanisms of metal precipitation within the deposit. Furthermore, the U-Pb ages of single zircons from microcline granites and hydrothermal apatite in the ores constrained the formation of rocks and deposit to the late Paleoproterozoic. Elemental geochemistry and zircon Hf isotope data further divided the microcline granite into I-type granite with high potassium and differentiation, originating from the partial melting of Neoarchean crustal materials in the region, which then underwent fractional crystallization. The diagenetic tectonic environment shows the characteristics of an active continental margin, which may have resulted from regional large-scale arc-continent collisions (Longgang Block and Nangrim Block), also implying the occurrence of ocean subduction during the evolution of the JLJB.

Using multiple methods to better constrain the depositional age of a meta-sedimentary succession: An example of the Laoling Group from the northeastern North China Craton

The youngest detrital zircon (DZ) or groups of zircons age is usually interpreted as the maximum depositional age (MDA) and the oldest metamorphic zircon since deposition is used to resolve the minimum depositional age of a meta-sedimentary succession. However, DZ grains with multi-cycle or fingerprinting proximal sources may cause the MDAs older than the true depositional age, whereas post-depositional resetting has the opposite effect. Here, we present DZ U-Pb, Lu-Hf isotopic and trace elemental data, supplemented by whole-rock geochemistry, from the greenschist-facies metamorphosed Laoling Group consisting of clastic and carbonate rocks in the northern margin of the Jiao-Liao-Ji belt (JLJB) in the North China Craton to investigate the use of multiple methods to constrain its true depositional age. The dominant late Neoarchean and middle Paleoproterozoic DZ age peaks from the meta-sandstones, meta-siltstone, meta-mudstone, and meta-carbonate rocks are interpreted to be sourced from the Southern Jilin Complex and the JLJB, respectively. The low Th/U ratios (<0.18) and Ce/Nd ratios (<2.5) of the 1.96–1.77 Ga metamorphic zircons, which is consistent with the monazite ages of 1.95–1.76 Ga, are used to filter the possibly altered detrital magmatic zircons and the source-normalized α-dose metrics bigger than ca. 0.8 imply a predominant first-cycle origin, therefore the true depositional age of the group is constrained at 2.08–2.03 Ga. Additionally, in consideration of the strike of the basin parallel to the boundary between the JLJB and the Longgang Block, two periods of regional extensional tectonism, bimodal provenance, and depositional age coeval with the second magmatic event in the JLJB, we suggest that the Laoling Group most likely deposited in a back-arc basin in the northern margin of the JLJB. Finally, the temporal changes of zircon Hf isotope and Eu/Eu* in zircon crustal thickness proxy, especially the coeval excursion towards more radiogenic Hf signals and crustal thinning at 2.17–2.13 Ga, is consistent with the back-arc basin opening and closure model rather than the intra-continental rift model.

Geochronology and Zircon Hf Isotope of the Paleoproterozoic Gaixian Formation in the Southeastern Liaodong Peninsula: Implication for the Tectonic Evolution of the Jiao-Liao-Ji Belt

The Jiao-Liao-Ji belt (JLJB), in the Eastern Block of the North China Craton, is a major Paleoproterozoic orogen and underwent a complicated tectonic evolution during 2.2–1.8 Ga. The Liaohe Group, an important stratigraphic unit in the JLJB, is key to understanding the complex evolution of this belt. In this paper, we present new detrital zircon U–Pb ages and Hf isotope data for meta-sedimentary rocks from the Gaixian Formation in different areas of the JLJB, in addition to compiled data for other formations of the Liaohe Group, to establish the depositional age and source of detrital materials of the group. U–Pb age results show that the age ranges of zircons from the different samples are broadly similar. The youngest zircon group is ca. 2.06 Ga, and the youngest single-grain age is ca. 2.0 Ga, constraining the depositional age of the Gaixian Formation to between 2.0 Ga and the metamorphic age of ca. 1.9 Ga. The zircon age data indicate that the provenance was primarily Archaean basement of the Nangrim Block and Paleoproterozoic volcanic rocks of the Li’eryu Formation. On the basis of the new geochronological data and results from previous studies, it is inferred that the JLJB underwent a successive process of rifting–subduction–collision, with the different formations of the Liaohe Group being deposited in different stages from rift to passive continental margin and then to active continental margin. Zircon Hf isotope data from the JLJB and adjoining Longgang and Nangrim blocks indicate that a major crustal growth event occurred at 2.9–2.5 Ga, followed by crustal growth and intense recycling of ancient crust at ca. 2.2 Ga.

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

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

Geochemistry and petrogenesis of ca. 2.1 Ga meta-mafic rocks in the central Jiao–Liao–Ji Belt, North China Craton: A consequence of intracontinental rifting or subduction?

As one of the global 2.0–1.8 Ga continent-to-continent collisional orogens that welded the Supercontinent Columbia or Nuna, the Jiao–Liao–Ji Belt (JLJB) in the North China Craton was formed through ca. 1.90–1.85 Ga collision between the Longgang and Nangrim Blocks. However, the tectonic process before the final collision remains highly controversial. Some people insisted that during 2.2–2.1 Ga the JLJB was in a back-arc area of a subduction regime. In contrast, some other people proposed that ca. 2.2–2.1 Ga represented a continental rifting stage instead of subduction. To tackle this controversy, the coeval mafic rocks and their petrogenesis become the key hints. Therefore, we implemented synthetic petrological, geochronological, geochemical, zircon Hf and the whole rock Sr–Nd isotopic studies for the newly mapped meta-mafic rocks from the central JLJB. Zircon U–Pb dating results revealed that they were emplaced at ca. 2133–2099 Ma and experienced subsequent collision-related regional metamorphism at ca. 1879–1852 Ma. Geochemically, they are sub-alkaline basalts and contain moderate SiO2 and high concentrations of MgO, total Fe2O3, Ni, and V. They are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE; e.g., Ba, Sr and K), and are depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE; e.g., Nb and Ta). Geochemical features show largely affinity to the enriched mid-ocean ridge basalts. Isotopic results show low 87Sr/86Srt ratios (low to 0.676869), positive εNd(t) values (+0.50 to +2.45) and εHf(t) values (+0.04 to +9.81). The parental magmas of ca. 2.1 Ga meta-mafic rocks were most likely derived from the partial melting of the depleted asthenospheric mantle with contamination of crustal material. Associated with the regionally developed A-type and adakitic granites, as well as the bimodal volcanic rocks throughout the JLJB, we proposed that the Longgang and Nangrim Blocks were initially broken apart through an intracontinental rifting that was triggered by delamination of an old thickened lithosphere at ca. 2.2–2.1 Ga, before they were finally collided with each other at ca. 1.90 Ga.

Petrogenesis and implications of ∼2.1 Ga Jingqishan granites in the Jiaobei Terrane, North China Craton

Widely distributed 2.2–2.1 Ga A-type granites in the North China Craton (NCC) have not only a significant role in unveiling the regional Palaeoproterozoic tectonic evolution but also crucial implications for the spatial and temporal evolution of A-type granite. This paper presents zircon U-Pb dating, geochemistry and Nd and Hf isotopes of Jingqishan Palaeoproterozoic gneissic granites from the Jiao-Liao-Ji Belt (JLJB) of the eastern NCC. The Jingqishan granites are mainly monzogranites. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb analyses of three samples yield concordant ages of 2124 ± 7 Ma, 2089 ± 11 Ma and 2088 ± 10 Ma. The Jingqishan granites are ferroan, calc-alkalic to alkali-calcic, and metaluminous-peraluminous. The high Ga/Al ratios, Zr + Nb + Y + Ce contents and Zr saturation temperatures (861 °C on average) of these granites are consistent with the features of A-type granite. The granites have εNd(t) values of −5.7 to −0.8 with two-stage Nd model ages of 2.99–2.63 Ga and zircon εHf(t) values of −7.3 to −2.9 with two-stage Hf model ages (TDM2(Hf)) of 2.94–2.61 Ga. These TDM2(Hf) ages are similar to those of ∼ 2.5 Ga Jiaobei Tonalite-Trondhjemite-Granodiorite (TTG) gneisses. Based on petrology, geochemistry and isotopic characteristics, we infer that the Jingqishan A-type granites are mainly partial melts of the Jiaobei 2.5 Ga TTGs. Combining our data with those published for 2.2–2.1 Ga JLJB granites and extensive data, we discover that both 2.1 Ga and 2.18 Ga A-type granites of the JLJB have A2-type granite characteristics and formed in a back-arc basin but were generated from the partial melting of different sources at two magmatic stages. Most 2.2–2.1 Ga A-type granites of the NCC belong to A2-type that sourced from late Achaean crustal rocks in an extensional setting.

Tectonic setting of the South Liaohe Group in the Jiao‐Liao‐Ji Belt, North China Craton: Geochemical and geochronological constraints from metasedimentary rocks

The metasedimentary rocks of the South Liaohe Group are widely distributed along the Jiao‐Liao‐Ji Belt (JLJB) in eastern Liaoning Province. It is important to understanding tectonic setting and evolution of the JLJB by determining its sediment sources and properties of the provenances, sedimentary facies, metamorphic ages, and facies. After the detailed field geological surveys and comprehensive laboratory observation, many high‐grade metapelitic rocks are identified in the South Liaohe Group. The main rock type is sillimanite‐garnet‐cordierite‐biotite plagiogneiss. The zircon U–Pb geochronology of three samples shows that these high‐grade meta‐pelitic rocks are mainly derived from the Liaoji Granites and the Archean basement. The protolith formation ages are between 2.00 and 1.93 Ga. Subsequently, these protolithes underwent high‐pressure metamorphism resulted from collisional orogeny, with peak metamorphism at ca. 1.88 Ga. Then, at 1.88–1.84 Ga, these rocks experienced the retrograde metamorphism and exhumed to the surface during crustal uplift. Geochemical data show that the protoliths are alumina‐rich claystones and graywackes with low maturity, implying near‐source sedimentation. The chemical index of alteration (CIA) values of these samples range from 60 to 80, indicating that the protoliths underwent moderate weathering. The sediment source was mainly felsic components of the upper crust, possibly with the addition of ancient sediments. Various tectonic environment discrimination diagrams combined with previous results on metamorphism and isotope chronology of these metasedimentary rocks in the JLJB indicate that the rocks in the study area originated from an active continental margin with an evolving island arc.

Petrogenesis and tectonic implications of the Paleoproterozoic Gaoliduntai plagiogranites in the Jiao–Liao–Ji Belt, North China Craton

Paleoproterozoic plagiogranites were identified in the Gaoliduntai area of the Jiao–Liao–Ji Belt (JLJB), North China Craton (NCC). We conducted a geochronological, geochemical, isotopic, and mineral chemical investigation of the plagiogranites to constrain their petrogenesis and tectonic implications. The Gaoliduntai plagiogranites yielded zircon U–Pb ages of 1802 ± 10, 1828 ± 18, and 1853 ± 11 Ma, indicating emplacement at the late Paleoproterozoic. Geochemically, They are characterized by high SiO2 and Na2O, and low K2O and TiO2 contents, with low total rare earth element (REE) concentrations. They also exhibit enrichment in light REEs and large-ion lithophile elements (e.g., Cs, Rb and Sr), and depletion in heavy REEs and high-field-strength elements (e.g., Nb and Ta). The plagiogranites show varying initial 87Sr/86Sr ratios (0.7012–0.7053), whole-rock εNd(t) values (–8.23–+1.15) and apatite εNd(t) values (–4.78–+3.30), with whole-rock 206Pb/204Pb(t) (14.223–16.733), 207Pb/204Pb(t) (15.310–15.644) and 208Pb/204Pb(t) (35.310–35.998) values, indicating a depleted mantle source modified with an enrichment component. Zircons in the plagiogranites have positive εHf(t) values (+1.0 to +6.4) and TDM2(Hf) ages of 2408–2078 Ma. Zircons δ18O compositions (2.1‰ to 4.5‰) are lower than the zircons from normal mantle but show similar features to typical plagiogranites. Furthermore, the plagioclases in these plagiogranites are albite (Ab = 95–99). These features lead us to propose that the Gaoliduntai plagiogranites formed by partial melting of high-temperature mafic oceanic crust, with contributions from delaminated crustal components. We suggest that the Paleoproterozoic Gaoliduntai plagiogranites provide evidence of the involvement of ancient oceanic crust in the tectonic evolution of the JLJB. Based on regional geological features and previous studies, we propose that the JLJB was an arc–continent collision belt during the Paleoproterozoic, and that the Gaoliduntai plagiogranites formed in an extensional tectonic setting.

Gold mobilization during prograde metamorphism of clastic sedimentary rocks: An example from the Liaohe Group in the Jiao–Liao–Ji Belt, North China Craton

Abundant gold deposits are distributed in the Jiao-Liao-Ji Belt of the North China Craton. Gold deposits, characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock, of the Jiaodong Peninsula and Liaodong Peninsula are underlain by rocks of similar geological settings characterized by uplifted blocks of metamorphosed Archean and Proterozoic rocks surrounded by relatively unmetamorphosed Mesoproterozoic rocks and Mesozoic granitoid plutons. The huge order-of-magnitude difference in reserves between the Liaodong gold province (500 t) and the Jiaodong gold province (5000 t) attract the attention of geologists. Different C–H-O-S-Pb isotopes and isotopic dating have sparked controversy over the source of the gold deposits. In this study, we conducted integrated analyses of zircon U-Pb dating, bulk-rock compositions, mineralogical compositions and high-precision gold analyses on a series of meta-clastic sedimentary rocks from the Paleoproterozoic Liaohe Group in the Jiao-Liao-Ji Belt, North China Craton, of which the Au analyses reveal Au mobilization during prograde metamorphism. In the Gaizhou Barrovian-type metamorphic zone, the bulk-rock Au contents of samples within various metamorphic zones show a monotonic decrease up-temperature, from 2.09 ppb in the chlorite zone to 0.07 ppb in the sillimanite zone. The evolution in Au content during prograde metamorphism of other formations are identical to that of the Gaixian Formation. The Au concentrations of biotite in different metamorphic zones show little variation ranging from 0.66 to 0.35 ppb, whereas the Au concentrations of muscovite in different metamorphic zones mainly decrease from 2.60 ppb in the chlorite zone to 0.57 ppb in the sillimanite zone with increasing metamorphic grade in samples without metallic sulfides. Coincidently, there is a dechlorination process in biotites during regional metamorphism. Chlorine, released by metamorphism, may have played a vital role in the migration of Au, which could absorb onto muscovite and other minerals, during prograde metamorphism. Given an Au content of 4.67 t/km3 in the chlorite zone rock approximately equivalent to the protolith, metamorphism up to upper amphibolite grade would force the rocks to release 52% of the Au in the Gaizhou Barrovian-type metamorphic zone. Taking into account previous studies in the interpretation of our results, we propose that Precambrian rocks, such as the meta-clastic sedimentary rocks of the Gaixian Formation, may have contributed considerable amounts of Au to the Liaodong gold province. The Liaohe Group releasing large amounts of Au during Paleoproterozoic metamorphism, may thus provide the primary Au enrichment for the Mesozoic gold deposits.

Petrological, whole–rock geochemical, geochronological, and Lu–Hf isotope constraints on the regional tectonic evolution of the Laoling Group in northeastern Jiao–Liao–Ji Belt, North China Craton

This study examines the original nature, tectonic setting, and evolution of Paleoproterozoic metasedimentary rocks in the Laoling Group of northern Jiao–Liao–Ji Belt (JLJB), in the northeastern margin of the Eastern Block of the North China Craton (NCC), using new petrological, whole–rock geochemical, geochronological, and Lu–Hf isotope data. The youngest detrital zircons constrain the maximum deposition age of the metasedimentary rocks to 1.97 Ga, and two metamorphic zircon age peaks correspond to 1.91 and 1.84 Ga for their metamorphism. The protoliths of the metasedimentary rocks in the Laoling Group were medium- to fine-grained clastic sediments, dominated by shale, graywacke, and claystone, with a smaller amount of sandstone, derived from Paleoproterozoic granites and coeval acidic meta-volcanic rocks, with minor contributions from Mesoarchean–Neoarchean basement rocks and Paleoproterozoic meta-mafic rocks. The protoliths of the metasedimentary rocks in the Dalizi Formation of the Laoling Group were deposited in a convergent margin setting, and subduction along the northern JLJB likely ended before ca. 1.91 Ga when the Longgang and Nangrim blocks collided. The εHf(t) values of ca. 2.14 Ga zircons mostly lie between the depletion mantle and the chondrite evolution line, coupled with extensive coeval magmatism, are consistent with the ca. 2.14 Ga significant continental crust growth in this region. An integrated study of petrology, geochemistry, metamorphic P–T paths, and tectonic evolution suggests that the JLJB experienced two metamorphic events at ca. 1.91 and 1.84 Ga.

Does the Liaoji granite represent basement in the Jiao–Liao–Ji Belt?

Lack of knowledge of the basement structure of the Paleoproterozoic Jiao–Liao–Ji Belt (JLJB) of the North China Craton has hindered understanding of the tectonic evolution of the belt and, to an extent, the entire craton. Previous studies of the JLJB were based mostly on petrological, structural, and geochemical analyses, resulting in a lack of understanding of the deep geological structure of the belt. In this study, we used a combination of geophysical and geological methods to interpret the deep geological structure of the JLJB on the basis of high-precision non-seismic geophysical data. We collected high-precision gravity, magnetic, and magnetotelluric sounding data. We also compiled data on rock physical parameters for important geological bodies, and obtained high-precision Bouguer gravity anomaly data from the China Geological Survey. We interpreted these data to visualize the subsurface distributions of geological bodies (including sedimentary and metamorphic units and intrusive rocks) in the Kuandian–Huairen area of the JLJB. We found that the Liaoji granites are developed on a large scale in the deep part of the JLJB, showing a weak gravity anomaly (−25 to −6 mGal) and high resistivity (103.5 to 106 Ω·m). These granites may have intruded along a series of normal faults at the time of the initial formation of the belt, and expanded over time. Subsequently, the low-resistivity Liaohe Group (10 to 102.5 Ω·m) was deposited on the Liaoji granite across a sedimentary contact. Therefore, the Liaoji granite forms the basement of the JLJB. The presence of extensional faults in the deep part of the JLJB suggests that the belt was also subjected to tectonic extension. The Yuejiadian–Xiaohuanggou fault to the east of Kuandian may be the boundary between the South Liaohe Group and the North Liaohe Group. The South Liaohe Group is relatively thin and tightly folded, whereas the North Liaohe Group is thicker and characterized by relatively open folds.

Geochronology and geochemical characteristics of Paleoproterozoic syn-orogenic granitoids and constraints on the geological evolution of the Jiao-Liao-Ji orogenic Belt, North China Craton

A suite of Paleoproterozoic syn-orogenic magmatism with distinctive natures in the Jiao-Liao-Ji Belt (JLJB) of North China Craton is studied, including I-type monzogranite, related quartz gabbro, S-type granites, and adakitic granites. The Caiyuan monzogranite and quartz gabbro intrusions yield zircon U-Pb ages of 1881 ± 31 Ma and 1889 ± 19 Ma, respectively. They exhibit light rare earth element enriched patterns, and are rich in Rb, Ba, and K, but depleted in Nb, Ta, and Ti. These granites have relatively low (87Sr/86Sr)i ratios of 0.701985–0.706703, εNd(t) values of −13.0 to −0.3 and dominantly negative zircon εHf(t) values. Two Siping porphyritic granite samples give U-Pb ages of 1877 ± 11 Ma and 1881 ± 11 Ma respectively. They display enriched REE patterns, characterized by high Al2O3 and A/CNK ratio (>1.1), similar to S-type granites, with high (87Sr/86Sr)i ratios up to 0.711142 and negative εNd(t) values of −8.0 to −2.2. The Wafang and Xujiapu granites intrusions yield zircon U-Pb age of 1887 ± 11.0 Ma and 1885 ± 9.7 Ma and have high Sr/Y, (La/Yb)N and strikingly positive Eu anomalies, likely belonging to adakite. The association of quartz gabbro, I-type, and S-type granites in the Caiyuan region indicate that they were derived from mafic parental magma triggered by slab subduction. Crustal materials mixed in further AFC processes of the magma, before the monzogranite and porphyritic granite crystallized. The Wafang adakitic granite was probably related to the partial melting of a thickened crust. A complex syn-orogenic evolution model is thus proposed in the Late Paleoproterozoic of the JLJB, as slab subduction and partial melting of thickened crust simultaneously occurred at ~1885 Ma.

Diversity of zircon U-Pb geochronology of meta-sedimentary rocks from the Gaixian Formation, South Liaohe Group, Jiao-Liao-Ji belt: Implications for different provenance and crustal evolution

Comprehensive studies of depositional age and source material of the Liaohe Group are significant to the tectonic evolution of the Jiao-Liao-Ji Belt (JLJB). The Gaixian Formation is widely distributed and stratigraphically defined as the uppermost formation of the Liaohe Group. However, our new work reveals that not all meta-sedimentary rocks of the Liaohe Group deposited before the late Paleoproterozoic orogeny. Based on the geochronological results, these meta-sedimentary rocks can be subdivided into two categories. Detrital zircon from the category A meta-sedimentary rocks yield U-Pb age peaks at ca. 2.50 Ga, 2.18 Ga and 2.06 Ga. The youngest age peak of ca. 2.06 Ga, together with the metamorphic age of 1.95–1.84 Ga yielded by pervious studies, indicate their depositional ages of 2.06–1.95 Ga. Compared to the category A, detrital zircon from the category B yield similar 207Pb/206Pb age peaks at ca. 2.54 Ga, ca. 2.17 Ga and ca. 2.05 Ga, but importantly also at ca. 1.87 Ga which was never observed for the category A. The late Paleoproterozoic zircon (~1.87 Ga) include magmatic cores and weakly oscillatory zoned or unzoned rims. These rims yield two age peaks of ca. 1.88 Ga and ca. 1.80 Ga, which are interpreted as inherited partial melting ages. Therefore, the category B meta-sedimentary rocks deposited at some time after ca. 1.80 Ga. These new geochronological data reveal that the category B meta-sedimentary rocks are significantly different with those from the traditional Gaixian Formation. In combination with regional stratigraphy data, it is recommended that the category B meta-sedimentary rocks should be ascribed to the Changhai Group rather than the Liaohe Group.

Geochronological and geochemical constraints on the non-ultrahigh-pressure metasedimentary blocks of North China affinity within the Sulu ultrahigh-pressure belt, eastern China, and tectonic implications

ABSTRACT The Sulu ultrahigh-pressure (UHP) belt has been proven to form by deep northward subduction of the Yangtze Block (YB) beneath the North China Block (NCB) in the Triassic. The basement rocks originated from the YB and experienced Triassic UHP metamorphism. In this contribution, we identify for the first time tens of non-UHP metasedimentary blocks enclosed in the regional UHP granitic gneiss in the Weihai terrane in the northeastern Sulu UHP belt. They are mainly composed of paragneiss, marble and calc-silicate rocks, in which UHP-related minerals have not been identified. Detrital zircons from the non-UHP metasedimentary rocks are mostly of magmatic origin and yield U-Pb ages mainly from 2842 to 1792 Ma with two clusters of 2580–2460 Ma and 1900–1800 Ma. This zircon U-Pb age spectrum is typical of the NCB but not the YB, and matches the tectonothermal/magmatic history of the southwestern end of the Jiao-Liao-Ji belt (JLJB), eastern NCB, which lies immediately adjacent to the Weihai terrane. Furthermore, their whole-rock geochemical compositions show great resemblance to those of the Paleoproterozoic metasedimentary rocks within the JLJB. In particular, metamorphic zircons from the non-UHP metasedimentary rocks indicate widespread late Triassic-early Jurassic (213–194 Ma) metamorphic overprinting of the Paleoproterozoic (1850–1820 Ma) metamorphism that characterizes the JLJB. This means that the enclosed non-UHP metasedimentary rocks with NCB signatures in the Weihai terrane were involved in the collision-subduction process during the Triassic. They have not been carried to mantle depths during deep continental subduction. These lines of evidence prompt us to establish a Triassic tectonic erosion model to explain these new discoveries and pre-existing problems along the Sulu UHP orogenic belt.

Late Paleoproterozoic crustal thickening of the Jiao–Liao–Ji belt, North China Craton: Insights from ca. 1.95–1.88 Ga syn-collisional adakitic granites

The Jiao–Liao–Ji belt (JLJB) of the North China Craton is commonly regarded to have been involved in the global-scale collisional events that led to the amalgamation of the Columbia/Nuna supercontinent during the late Paleoproterozoic. Previous studies have revealed that the JLJB underwent a high-pressure granulite-facies metamorphic event with a clockwise P–T–t path during ca. 1.95–1.90 Ga. However, few studies have examined the contemporaneous magmatism and its genetic relationship to the high-pressure granulite-facies metamorphism. In addition, the petrogenesis of the ca. 1.95–1.90 Ga magmatism and its possible constraints on the crustal-thickening process are poorly understood. Our field investigations have discovered a series of late Paleoproterozoic granitoid plutons in Liaodong Peninsula, including the Fangjiawei, Qingchengzi, Songshugou, and Shizijie plutons. Systematic analyses of geochronology, petrology, and geochemistry were conducted to constrain the formation ages, petrogenesis, and tectonic environment of these granites. Zircon U–Pb dating reveals that the granites formed during ca. 1.95–1.88 Ga, coeval with the timing of the regional prograde or peak metamorphism and collision in the JLJB. They show geochemical characteristics of typical adakites, including high Sr (393–860 ppm) contents, low Y (1.03–3.30 ppm) and Yb (0.09–0.27 ppm) contents, and relatively high Sr/Y (125–832) and LaN/YbN (9.34–33.6) ratios. Low MgO, Cr, and Ni contents and the existence of ca. 2.5–2.0 Ga inherited zircons with ancient TDM2 ages indicate that the parental magmas were generated from partial melting of a thickened lower crust. The positive correlation between Dy/Yb and La/Yb ratios and the relatively low Nb/Ta (5.1–18.9, average of 13.6) ratios all suggest that garnets, rather than amphiboles or rutiles, were the dominant phase in the residual source, indicating a melting depth of 30–50 km. Our new results, combined with previous findings, support a rifting-and-collision model whereby the JLJB underwent a transformation from early intracontinental rifting to subsequent opening and closure of an incipient ocean, with the final collision between the Longgang Block and Nangrim Block occurring at ca. 1.95–1.88 Ga with substantial crustal thickening.

Constraints of nonseismic geophysical data on the deep geological structure of the Benxi iron-ore district, Liaoning, China

Abstract The Benxi area in Liaoning Province is one of the most important iron-ore districts in China. This study uses nonseismic geophysical data (in the form of gravity–magnetic–magnetotelluric data) and based on the section modeling method to model the deep, three-dimensional geological structure of the Benxi area. Based on the modeling results and deep geological structure characteristics, the Benxi area can be divided into three first-order deep geological tectonic units. A close relationship is between tectonic unit and iron-ore concentrations. First, high-quality iron-ore deposits occur within the tectonic boundary and sedimentary boundary zone of the Jiao–Liao–Ji Belt, reflects the protective effect of sedimentary cover on the iron-bearing formation. Second, enriched iron-ore deposits are mainly developed in Mesozoic granitic intrusion zone, reflects the hydrothermal leaching of silicon in host iron-bearing formations during magma intrusion. Thus, the findings of this study have important implications for future prospecting in the Benxi iron-ore district.