Liaohe Group Research Articles

Evaluation of Gold Geochemical Anomalies in the Liaodong Paleorift

89 Au geochemical anomalies are delineated by using 1/200000 regional geochemical exploration data. By researching regional geochemical characteristics and the relationship with the geological background, the author points out that: the main factors causing high background of Au geochemical anomalies are Gaixian and Dashiqiao formation of Liaohe group, intrusions of Mesozoic intermediate-acid intrusive rocks. The elements combination types of typical anomalies are determined by using factorial analysis,cluster analysis and other mathematical methods with the combination of elements association in typical anomalies:the composite anomaly of Baiyun gold deposits is Au-As-Sb, Maoling gold deposit is Au-As-Bi-Mo, Wulong gold deposits is Au-As-Bi-W, Xiaotongjiapuzi gold deposit is Au-As-Bi-Mo-Sb. By using multivariate statistical analysis method,62 ore-caused anomaly are preferred in 89 Au geochemical anomalies delineated. On this basis, the 62 anomalies are divided into 4 kinds of anomaly types reference to elements combination types of typical anomalies,the classification results of ore-caused anomalies are: 4 geochemical anomalies of Baiyun type,36 geochemical anomalies of Maoling type,11 geochemical anomalies of Wulong type, 11 geochemical anomalies of Xiaotongjapuzi type. According to the results, the prospecting direction is provided for the future of gold exploration.

Zircon U–Pb and Lu–Hf isotopic constraints on Archean crustal evolution in the Liaonan Complex of northeast China

The Changhai area is located in the southeastern part of the Liaonan Complex within the Eastern Block of the North China Craton (NCC) in China. Early Precambrian rocks in this area consist mainly of various types of gneisses and schists. We present cathodoluminescence images, U–Pb dates, and trace element and Hf isotope data for zircons from these rocks in order to constrain the formation and evolution of continental crust in the Liaonan Complex. Our results show that the magmatic precursors of the biotite monzonitic gneiss, granitic gneiss, garnet-bearing monzogranitic gneiss, and biotite granodioritic gneiss, that is, relatively sodium-rich gneisses in the area, were emplaced at ca. 2543Ma. Muscovite-bearing granitic gneiss, monzogranitic gneiss, and biotite granitic gneiss, that is, relatively potassium-rich gneisses in the area, were emplaced at ca. 2516Ma, whereas the sedimentary protolith(s) of the associated schists along the gneissose fabric of the gneisses were deposited after 2518Ma and metamorphosed at ca. 1885Ma. The latter age may represent the time of metamorphism of the South Liaohe Group in the Jiao–Liao–Ji Belt. Large numbers of inherited zircons with ages of 2596–2842Ma, coupled with the results of previous studies, suggest that multiple Meso- to Neoarchean magmatic events took place in the Liaonan Complex at ca. 2.84, 2.75, 2.67–2.61, 2.54, and 2.51Ga. Lu–Hf isotopic results for magmatic zircon grains with ages of 2.61–2.84Ga have positive εHf values (+2.4 to +11.3) and average continental crust model ages (TC DM) of 2.63–3.05Ga with a peak at 2.76–2.98Ga. Of the zircons with ages of ca. 2.54Ga and 2.51Ga, 94% have positive εHf values (+0.13 to +8.57, average=+3.1) and TC DM model ages of 2.53–3.06Ga, similar to those of zircons with ages of ca. 2.61–2.84Ga, suggesting that both sets of zircons were derived from partial melting of juvenile crust. However, the remaining zircons (6%) with ages of 2.54–2.51Ga and all metamorphic zircon grains with ages of ca. 1885Ma have negative εHf values of −0.12 to −3.00 and −8.8 to −15.9, respectively, and similar older TC DM model ages of 3.11–3.56Ga and 3.08–3.23Ga, respectively. These data, combined with those from previous studies of the NCC, indicate that the basement rocks of the Liaonan Complex underwent two significant juvenile crustal growth events at ca. 2.71–2.99Ga and 2.54–2.51Ga, a local reworking event at ca. 2.51Ga, and a major reworking event at 1.88Ga.

Zircon U–Pb and Lu–Hf isotopic and whole-rock geochemical constraints on the protolith and tectonic history of the Changhai metamorphic supracrustal sequence in the Jiao–Liao–Ji Belt, southeast Liaoning Province, northeast China

The Changhai metamorphic supracrustal rocks, located in the eastern–central part of the Jiao–Li–Ji Belt in the North China Craton (NCC), are composed mainly of various garnet–mica schists, along with minor quartzites and marbles. This study presents whole-rock major and trace element data, zircon U–Pb dates and Hf isotope data for these rocks in order to constrain their protolith age and provenance, and discuss the tectonic implications. Geochemical results indicate that the source rocks were mainly granitoids with a possible minor contribution from clastic sediments with an active continental margin signature. Detrital zircons have U–Pb age peaks at approximately 1887, 2174, 2552, 2765, and 3212Ma, ɛHf values of −11.1 to +13.0, and three major time windows of average continent crustal model ages (TDMC) of 2.04–2.33, 2.48–2.56, and 2.72–2.93Ga. Besides, these units also contain significant numbers of concordant metamorphic zircons that yielded a peak age of ca. 248Ma, indicating that the region was modified by an early Triassic tectono-thermal event. These results suggest that sediments of the Changhai metamorphic supracrustal rocks were mainly sourced from nearby basement granitoid rocks and, to a lesser extent, from Paleoproterozoic metamorphosed strata such as the North and South Liaohe groups. Furthermore, the source rocks of the magmatic zircons analyzed in this study appear to have originated from interaction between old continental crust and juvenile material. The youngest concordant zircon age peak at 1879Ma coincides with the timing of formation of regionally widespread granitoids, mafic igneous rocks, and metamorphism of the South Liaohe and Ji’an groups in the Jiao–Liao–Ji Belt, and suggest that the sedimentary protoliths of the Changhai metamorphic supracrustal rocks were deposited after this time. The results indicate that the Archean Liaobei–Jinan Complex in the north and the Liaonan–Nangrim Complex in the south were already a single continental block by 1887Ma, and that the Changhai metamorphic supracrustal rocks were deposited at an active continental margin.

C–O isotope geochemistry of the Dashiqiao magnesite belt, North China Craton: implications for the Great Oxidation Event and ore genesis

The worldwide 2.33−2.06 Ga unique positive δ13Ccarbexcursion has been correlated with the Great Oxidation Event (GOE). The Dashiqiao Formation in the Liaohe Group of the northeastern North China Craton formed at 2.2−2.174 Ga and hosts one of the world‐class magnesite deposits. Here we present major element and C and O isotope analyses of 22 samples from the Dashiqiao Formation and use the data to evaluate the impact of the GOE in the North China Craton, as well as the genesis of the Dashiqiao giant magnesite deposits. Six dolomitic marble samples from a ~600 m thick interval with 1.10 ± 0.04 of MgO/CaO (mol) ratios show higher δ13CPDBvalues of 0.6−1.4‰ (average 1.2 ± 0.3‰) than those of normal marine carbonates over the globe. However, they display lower δ18OSMOWof 16.4−19.5‰ (average 18.2 ± 1.1‰) as compared to their contemporaneous counterparts, suggesting that the primary carbonates in the Dashiqiao Formation should possess a positive δ13C anomaly (possibly 4.2‰) reflecting the impact of the GOE, and that the δ13C and δ18O values have been depleted in post‐sedimentation diagenesis and/or regional metamorphism. The >550 m thick magnesite layer in the studied section has MgO/CaO ratios ranging from 4.45−200.00. These rocks show δ13C and δ18O values of 0.1−0.9‰ and 9.2−16.9‰, with average values of 0.4 ± 0.2‰ and 13.3 ± 2.5‰, respectively, obviously lower than those of the underlying dolomites. The depletions of13C and18O in magnesites relative to dolomitic marbles are interpreted to be the result of hydrothermal alteration related to regional metamorphism leading to rock recrystallization and mass exchange. This interpretation is further confirmed from the hanging‐wall dolomitic marble and the veinlet‐filled magnesite from the ore layer. The former contains mega‐crystals of cylindrical talc and has δ13C of −2.6‰ and δ18O of 14.1‰, indicating that a local fluid–rock interaction between (argillaceous) dolomite and (siliceous) hydrothermal fluids poor in13C and18O resulted in the formation of talc and further depletion both in δ13C and in δ18O. The veinlet‐filled magnesite yields δ13C and δ18O values of −2.7‰ and 16.2‰, respectively, showing lower δ13C but higher δ18O than those of massive magnesite in the adjacent strata. Our observation thus strongly supports the interpretation that the massive magnesite interacted with low‐δ13C fluids which were possibly sourced from meteoric water at low temperature during post‐ore time. Thus, the formation of the Dashiqiao magnesite deposits involved primary sedimentation, diagenesis, regional metamorphism, hydrothermal replacement and local post‐ore fluid–rock interaction. Copyright © 2013 John Wiley & Sons, Ltd.

Multiple 3.8–3.1 Ga tectono-magmatic events in a newly discovered area of ancient rocks (the Shengousi Complex), Anshan, North China Craton

Near Anshan city in the North China Craton, the oldest rocks in Asia (⩾3300Ma) have been thoroughly documented at two localities (Baijiafen and Dongshan). In this paper we report the full geological context for more ancient rocks from a third Anshan locality – the polyphase migmatite Shengousi Complex. SHRIMP U–Pb zircon dating indicates a protracted tectono-magmatic history for the Shengousi Complex: The oldest recognised component is banded trondhjemitic gneiss (3773±6Ma), which is veined by strongly deformed granitic pegmatite. These occur with a second generation of trondhjemitic rocks (3454±8 and 3448±9Ma). The next generation of plutonic rocks is a composite suite of iron-enriched mafic dykes (3332±6 and 3331±8Ma) with broadly coeval felsic veins (3311±4Ma). Finally there was intrusion of monzogranite (3129±6Ma). Strong deformation has generally brought these 3773–3129Ma plutonic phases into close concordance to form banded rocks. However, locally cross-cutting relationships are preserved in small lower strain domains, that give a relative chronology agreeing with the absolute zircon U–Pb chronology. All of this complex history is recorded in a single<50m wide outcrop.Some of the<3600Ma rocks of the Shengousi Complex contain 3780–3730 and 3660–3600Ma inherited zircon xenocrysts. The stronger prominence of 3660–3600Ma components distinguishes the Shengousi Complex from the Baijiafen and Dongshan complexes, where components of this age are rarer. One possibility is that at 3660–3600Ma, the Shengousi Complex was at a deeper crustal level than the Baijiafen and Dongshan complexes, and underwent migmatisation at that time.The ∼3450Ma igneous phases discovered in the Shengousi Complex are new ages for igneous rocks in the Anshan area. The Precambrian geology of the Anshan area is thus marked by polyphase Eoarchaean orthogneisses, the newly recognised ∼3450Ma phases, widespread 3360–3300 magmatic activity, found in association with Mesoarchaean plutonic rocks and the Neoarchaean Anshan Group and Palaeoproterozoic Liaohe Group metasedimentary rocks. This shows that the geology of the Anshan area has a strong similarity with the Narryer Gneiss Complex of Western Australia, which contains the polyphase Eoarchaean Meeberrie gneisses, the 3490–3440Ma Eurada gneiss association, ∼3300Ma granites and migmatisation, and is intercalated with younger Precambrian metasedimentary rocks of different ages containing Hadean detrital zircons. No other ancient gneiss complexes in the world show such a close match in their history with the Anshan area rocks. This means that the Anshan area is prospective for locating new occurrences of Hadean crustal components intercalated with younger sedimentary rocks.

REE geochemistry of carbonates from the Guanmenshan Formation, Liaohe Group, NE Sino-Korean Craton: Implications for seawater compositional change during the Great Oxidation Event

The worldwide 2.33–2.06Ga positive δ13Ccarb excursion has been correlated with the Great Oxidation Event (GOE) and termed as the Lomagundi Event. The 2.3−1.85Ga Guanmenshan Formation in the Liaohe Group of the northeastern Sino-Korean Craton is characterized by positive δ13Ccarb excursion and is a potential candidate to evaluate the Lomagundi Event using REY (rare earth element and yttrium, REE+Y) chemical fingerprints. Here we present major and trace element analysis of 42 samples from the Guanmenshan Formation which are pure marine chemical sediments and use the data to trace the seawater composition during 2.3–1.85Ga. 15 least altered dolomicrite samples (>600m strata) have ∑REE values of 0.739–4.175ppm (2.414±1.184ppm) and the Y/Ho ratios of 34.5–56.6 (44.1±5.7). They show uniform positive LaSN/LaSN* (1.04±0.27) and GdSN/GdSN* (1.64±0.40) anomalies, and notable LREE depletions indicated by NdSN/YbSN values of 0.24–0.92 (average 0.56±0.19). These features are consistent with the geochemistry of well-oxygenated, shallow ambient seawater, and suggest that these samples provide a robust record of the primary REY signature of seawater during the Lomagundi Event. The REY patterns of 15 silicified dolomites/marbles (locally with veinlets) from the Pb–Zn mining camps in the region, with average EuCN/EuCN*=1.56±0.95, are identical to those of high-temperature hydrothermal fluids (>250°C), characterized by a flat pattern and marked positive Eu anomalies, indicating that these rocks were subjected to metasomatism by hydrothermal fluids. The Guanmenshan Formation shows average CeSN/CeSN* of 0.93±0.09 and SmCN/YbCN of >1 which are higher than those of the Archean (>2.33Ga) chemical sediments (generally <1), suggesting that the REY geochemical characteristics of the carbonates from our study area were dominantly controlled by the nature of atmosphere–hydrosphere system, such as fO2 and pCO2. The REY in the dolomicrite were mainly sourced from fluxes of solutes from terrestrial weathering, and also from seafloor hydrothermal processes on a subordinate scale. The Guanmenshan dolomicrites have EuSN/EuSN* values of 1.34–2.55, i.e. around 1.53, indicating that they were deposited during 2.33–2.06Ga, as the EuSN/EuSN*≈1.53 can be used as a proxy for the 2.33–2.06Ga marine chemical sediments. Our study shows that the Guanmenshan Formation was formed at a critical turning point in Earth history when the global atmosphere–hydrosphere system witnessed a dramatic change from reducing to oxidizing conditions.

PbSL dating of garnet and staurolite: Constraints on the Paleoproterozoic crustal evolution of the Eastern Block, North China Craton

It is well accepted that the North China Craton formed by assembly of the Eastern and Western blocks along the Trans-North China Orogen, with cratonization in the Paleoproterozoic (∼1.85 Ma). However, there is controversy about the formation of the Eastern and Western blocks themselves, especially the timing of cratonization of the Eastern Block. The Jiao-Liao-Ji orogenic belt is the most important Paleoproterozoic Orogenic belt in the Eastern Block and consists mainly of the North and South Liaohe Groups and the Liaoji Granitoids. The timing of metamorphism of the Liaohe Group is the key to understanding the evolution of the Eastern Block of the North China Craton. Because the isotope systematics of metamorphic minerals can be used to date parts of the prograde thermal histories of metamorphic belts, dating of minerals, such as garnet and staurolite has the distinct advantage that time information can be related directly to the pressure–temperature-deformation history recorded by the same mineral. In this paper we present results of precise 207Pb/ 206Pb stepwise-leaching (PbSL) dating of garnet and staurolite from the metasedimentary rocks of the south Liaohe Group. The primitive Pb and radiogenic Pb are selectively extracted from garnet and straurolite by leach steps and determined by multiple collector (MC-) ICP-MS. The garnet and staurolite record two groups of 207Pb/ 206Pb ages, at 1.93–1.91 Ga and ∼1.86 Ga, respectively. These constrain the time of peak metamorphism of the Liaohe Group during collision between the Longgang Block in the north and the Liaonan (Nangrim) Block in the south and a subsequent post-collisional event, respectively. Our data for the South Liaohe Group and previously published data for the Liaoji Granite, combined with key lithological, structural and metamorphic information, indicate that the cratonization of the Eastern Block of the North China Craton occurred at 1.93–1.91 Ga.

Paleoproterozoic positive δ 13C carb excursion in the northeastern Sino-Korean craton: Evidence of the Lomagundi Event

The 2.33–2.06 Ga positive δ 13C carb excursion, associated with environmental change and the breakup of the Kenorland or Superia supercontinent, is called the Lomagundi or Jatulian Event or Great Oxidation Event, and has been reported in many Early Precambrian cratons, but not yet in the Sino-Korean craton. The Guanmenshan Formation of the Liaohe Group occurs in the northeastern part of the Sino-Korean craton. δ 13C carb and δ 18O values in 42 samples from this formation range from 3.5–5.9‰ (V-PDB), and 15.4–24.8‰ (V-SMOW), respectively, showing a clear positive δ 13C carb excursion that characterizes the Lomagundi Event. Thirty-five of the 42 samples with less hydrothermal alteration have higher δ 13C carb and δ 18O carb values than the other 7 samples obviously affected by fluid flow, confirming that it was fluid flow that reduced the δ 13C carb and δ 18O carb values. This positive δ 13C carb excursion places deposition of the Guanmenshan Formation within the age range of 2.33–2.06 Ga.

Timing of metamorphism in the Paleoproterozoic Jiao-Liao-Ji Belt: New SHRIMP U–Pb zircon dating of granulites, gneisses and marbles of the Jiaobei massif in the North China Craton

The Paleoproterozoic Jiao-Liao-Ji Belt lies in the Eastern Block of the North China Craton, with its southern segment extending across the Bohai Sea into the Jiaobei massif. High-pressure pelitic and mafic granulites have been recently recognized in the Paleoproterozoic Jingshan Group (Jiaobei massif). New SHRIMP U–Th–Pb geochronology combined with cathodoluminescence (CL) imaging of zircon has been applied to the determination of the timing of the metamorphism of the high-temperature and high-pressure granulites and associated gneisses and marbles. Metamorphic zircons in these high-pressure granulites, gneisses and marbles occur as either single grains or overgrowth (or recrystallization) rims surrounding and truncating oscillatory-zoned magmatic zircon cores. Metamorphic zircons are all characterized by nebulous zoning or being structureless, with high luminescence and relatively low Th/U values. Metamorphic zircons from two high-pressure mafic granulites yielded 207Pb/ 206Pb ages of 1956 ± 41 Ma and 1884 ± 24 Ma. One metamorphic zircon from a garnet–sillimanite gneiss also gave an apparent 207Pb/ 206Pb age of 1939 ± 15 Ma. These results are consistent with interval of ages of c. 1.93–1.90 Ga already obtained by previous studies for the North and South Liaohe Groups and the Laoling Group in the northern segment of the Jiao-Liao-Ji Belt. Metamorphic zircons from a high-pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207Pb/ 206Pb ages of 1837 ± 8 Ma, 1821 ± 8 Ma and 1836 ± 8 Ma respectively. Two diopside–olivine–phlogopite marbles yielded weighted mean 207Pb/ 206Pb ages of 1817 ± 9 Ma and 1790 ± 6 Ma. These Paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c. 1.85 Ga produced from the Ji'an Group in the northern segment of the Jiao-Liao-Ji Belt and c. 1.86–1.80 Ga obtained for the high-pressure pelitic granulites from the Jingshan Group in the southern segment. As this metamorphic event was coeval with the emplacement of A-type granites in the Jiao-Liao-Ji Belt and its adjacent areas, it is interpreted as having resulted from a post-orogenic or anorogenic extensional event.

Geochronological framework and Pb, Sr isotope geochemistry of the Qingchengzi Pb–Zn–Ag–Au orefield, Northeastern China

The Qingchengzi orefield in northeastern China, is a concentration of several Pb–Zn, Ag, and Au ore deposits. A combination of geochronological and Pb, Sr isotopic investigations was conducted. Zircon SHRIMP U–Pb ages of 225.3 ± 1.8 Ma and 184.5 ± 1.6 Ma were obtained for the Xinling and Yaojiagou granites, respectively. By step-dissolution Rb–Sr dating, ages of 221 ± 12 Ma and 138.7 ± 4.1 Ma were obtained for the sphalerite of the Zhenzigou Zn–Pb deposit and pyrargyrite of the Ag ore in the Gaojiabaozi Ag deposit, respectively. Pb isotopic ratios of the Ag ore at Gaojiabaozi ( 206Pb/ 204Pb = 18.38 to 18.53) are higher than those of the Pb–Zn ores ( 206Pb/ 204Pb = 17.66 to 17.96; Chen et al. [Chen, J.F., Yu, G., Xue, C.J., Qian, H., He, J.F., Xing, Z., Zhang, X., 2005. Pb isotope geochemistry of lead, zinc, gold and silver deposit clustered region, Liaodong rift zone, northeastern China. Science in China Series D 48, 467–476.]). Triassic granites show low Pb isotopic ratios ( 206Pb/ 204Pb = 17.12 to 17.41, 207Pb/ 204Pb = 15.47 to 15.54, 208Pb/ 204Pb = 37.51 to 37.89) and metamorphic rocks of the Liaohe Group have high ratios ( 206Pb/ 204Pb = 18.20 to 24.28 and 18.32 to 20.06, 207Pb/ 204Pb = 15.69 to 16.44 and 15.66 to 15.98, 208Pb/ 204Pb = 37.29 to 38.61 and 38.69 to 40.00 for the marble of the Dashiqiao Formation and schist of the Gaixian Formation, respectively). Magmatic activities at Qingchengzi and in adjacent regions took place in three stages, and each contained several magmatic pulses: ca. 220 to 225 Ma and 211 to 216 Ma in the Triassic; 179 to 185 Ma, 163 to 168 Ma, 155 Ma and 149 Ma in the Jurassic, as well as ca. 140 to 130 Ma in the Early Cretaceous. The Triassic magmatism was part of the Triassic magmatic belt along the northern margin of the North China Craton produced in a post-collisional extensional setting, and granites in it formed by crustal melting induced by mantle magma. The Jurassic and Early Cretaceous magmatism was related to the lithospheric delamination in eastern China. The Triassic is the most important metallogenic stage at Qingchengzi. The Pb–Zn deposits, the Pb–Zn–Ag ore at Gaojiabaozi, and the gold deposits were all formed in this stage. They are temporally and spatially associated with the Triassic magmatic activity. Mineralization is very weak in the Jurassic. Ag ore at Gaojiabaozi was formed in the Early Cretaceous, which is suggested by the young Rb–Sr isochron age, field relations, and significantly different Pb isotopic ratios between the Pb–Zn–Ag and Ag ores. Pb isotopic compositions of the Pb–Zn ores suggest binary mixing for the source of the deposits. The magmatic end-member is the Triassic granites and the other metamorphic rocks of the Liaohe Group. Slightly different proportions of the two end-members, or an involvement of materials from hidden Cretaceous granites with slightly different Pb isotopic ratios, is postulated to interpret the difference of Pb isotopic compositions between the Pb–Zn–(Ag) and Ag ores. Sr isotopic ratios support this conclusion. At the western part of the Qingchengzi orefield, hydrothermal fluid driven by the heat provided by the now exposed Triassic granites deposited ore-forming materials in the low and middle horizons of the marbles of the Dashiqiao Formation near the intrusions to form mesothermal Zn–Pb deposits. In the eastern part, hydrothermal fluids associated with deep, hidden Triassic intrusions moved upward along a regional fault over a long distance and then deposited the ore-forming materials to form epithermal Au and Pb–Zn–Ag ores. Young magmatic activities are all represented by dykes across the entire orefield, suggesting that the corresponding main intrusion bodies are situated in the deep part of the crust. Among these, only intrusions with age of ca. 140 Ma might have released sufficient amounts of fluid to be responsible for the formation of the Ag ore at Gaojiabaozi. Our age results support previous conclusions that sphalerite can provide a reliable Rb–Sr age as long as the fluid inclusion phase is effectively separated from the “sulfide” phase. Our work suggests that the separation can be achieved by a step-resolution technique. Moreover, we suggest that pyrargyrite is a promising mineral for Rb–Sr isochron dating.

A comparison of U–Pb and Hf isotopic compositions of detrital zircons from the North and South Liaohe Groups: Constraints on the evolution of the Jiao-Liao-Ji Belt, North China Craton

The Jiao-Liao-Ji orogenic belt is one of the important Paleoproterozoic mobile belts in the North China Craton (NCC) and its central segment consists of the North and South Liaohe Groups and the Liaoji Granitoids. The North and South Liaohe Groups consist of sedimentary and volcanic successions metamorphosed from greenschist to lower amphibolite facies, and the Liaoji granitoids are divisible into 2.2–2.1 Ga (pre-tectonic) monzogranitic gneisses and 1.88–1.85 Ga (post-tectonic) porphyritic monzogranites and alkaline syenites. Combined with cathodoluminescence (CL) imaging, we report LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) U–Pb and Hf isotopic data for detrital zircons from the North and South Liaohe Groups. Zircons grains from both groups have igneous zircon cores that yielded two U–Pb age populations at 2.0–2.2 Ga (major) and ∼2.5 Ga (minor), indicating that their provenances were similarly dominated by Paleoproterozoic Liaoji Granitoids and late Archean basement rocks. Some structureless zircon rims in both groups yield concordant or upper intercept ages ∼1.9 Ga, interpreted as the peak metamorphic age of the two groups. These results suggest that both groups were deposited in the period 2.0–1.9 Ga, shortly after the emplacement of the Liaoji Granitoids. Moreover, zircons from both groups have similar Hf model age peaks ( T DM C peaks at 2.66–2.75 Ga and 2.80–3.00 Ga) and ɛHf values (−5 to +9 and −7 to +5). Based on these striking similarities, we propose that the protoliths of the North and South Groups may have formed simultaneously, and that the basement rocks underneath the two groups belong to the same Archean continental block rather than two different blocks as previously considered. The Archean basement underwent Paleoproterozoic rifting, accompanied by the emplacement of the Liaoji granitoids at 2.2–2.1 Ga and the deposition of the North and South Liaohe Groups at 2.1–1.9 Ga, and the rift was subsequently closed by ∼1.9 Ga.

SHRIMP U–Pb zircon geochronology of the Liaoji granitoids: Constraints on the evolution of the Paleoproterozoic Jiao-Liao-Ji belt in the Eastern Block of the North China Craton

The Paleoproterozoic Jiao-Liao-Ji belt lies at the eastern margin of the Eastern Block of the North China Craton and is composed mainly of the Liaohe Group and the Liaoji granitoids. The Liaoji granitoids are divisible into pre-tectonic magnetite and hornblende/biotite monzogranitic gneisses and post-tectonic or anorogenic porphyritic monzogranites and alkaline syenites. SHRIMP U–Pb zircon geochronology, combined with cathodoluminescence (CL) imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the Paleoproterozoic Jiao-Liao-Ji belt. SHRIMP U–Pb zircon analyses reveal that the pre-tectonic magnetite monzogranitic gneisses were emplaced in the period 2176–2166 Ma and metamorphosed at 1914 Ma, and the pre-tectonic hornblende/biotite monzogranitic gneisses were emplaced at 2150–2143 Ma. These data demonstrate that the pre-tectonic monzogranitic gneisses of the Liaoji granitoids were not younger than the deposition of the Liaohe Group, as previously considered, since the latter contains a large amount of 2100–2000 Ma detrital zircons. In contrast, the pre-tectonic monzogranitic gneisses of the Liaoji granitoids or similar-aged granitoids may have been an important component of the provenance for the Liaohe Group. SHRIMP U–Pb zircon analyses also reveal that the post-tectonic porphyritic monzogranites and granites in the Jiao-Liao-Ji belt were emplaced at 1875 ± 10 and 1856 ± 31 Ma, respectively, simultaneously with the emplacement of the alkaline syenites that was dated at 1857 ± 20 and 1843 ± 23 Ma. Similar post-tecotnic or anorogenic granites are not only limited to the Jiao-Liao-Ji belt, but are also found in the North and South Korea, suggesting that the ∼1.85 Ga post-tectonic or anorogenic granitic magmatic event may have occurred in both the Korean Peninsula and the Eastern Block of the North China Craton. The SHRIMP zircon ages of this study combined with lithological, structural, metamorphic and geochemical data is consistent with a rift closure model which suggests that the Archean complexes on the northern and southern sides of the Jiao-Liao-Ji belt were originally situated on a single continental block that underwent Paleoproterozoic rifting, associated with the formation of the Liaohe Group and Liaoji granitoids, and closed upon itself at ∼1.9 Ga.

LA-ICP-MS U-Pb Zircon Geochronology of the Yushulazi Group in the Eastern Block, North China Craton

The Paleoproterozoic Jiao-Liao-Ji belt in the North China craton is composed mainly of the Liaohe Group (and its equivalents) and the Liaoji Granites. They are uncomformably overlain by the sedimentary Yushulazi Group, which itself is overlain by the Neoproterozoic (0.9-0.8 Ga) Yongning Group. The Yushulazi Group has long been considered as a Proterozoic assemblage, but its depositional age has never been precisely constrained in terms of modern geochronology. Cathodoluminescence images reveal that most detrital zircon grains from this formation are characterized by concentric-oscillatory zoning, with comparatively low luminescence and high Th/U ratios, suggesting an igneous origin, whereas minor grains have structureless overgrowth or recrystallization rims that are characterized by low Th/U ratios, indicating a metamorphic origin. The results of LA-ICP-MS U-Pb zircon analyses show that the detrital zircon grains have concordant U-Pb ages of two populations—i.e., 1.05-1.37 Ga and 1.87-2.51 Ga—with an inherited zircon core giving a concordant age of 3.35 Ga. The U-Pb age range of 1.87-2.51 Ga is in good accordance with that of the Paleoproterozoic Liaohe Group and other basement rocks in the Eastern Block of the North China craton. Zircon ages of 1.05-1.31 Ga are, for the first time, reported for the Precambrian basement. The recognition of these Mesoproterozoic (1.05-1.31 Ga) igneous zircons from the Yushulazi Group indicate the existence of Grenvillian-aged magmatism in the Eastern Block of the North China craton. The Yushulazi Group must have deposited at some time between 1.05 Ga and 0.9 Ga, prior to sedimentation of the 0.9-0.8 Ga Yongning Group and it is not the upper part of the Paleoproterozoic Liaohe Group, as previously suggested.

Zircon U–Pb geochronological constraints on the Paleoproterozoic crustal evolution of the Eastern block in the North China Craton

The North China Craton (NCC) is proposed to have formed by collision between the Western and Eastern blocks at ∼1.85 Ga. However, the detailed history of the individual blocks remains unsolved. In the Eastern block, the Paleoproterozoic volcano-sedimentary rocks are mainly exposed along its eastern margin, and are referred to as the Liaohe Group in the Liaodong Peninsula of Liaoning Province and as the Guanghua, Ji’an and Laoling Groups in the Tonghua area of southern Jilin Province. The Guanghua and Ji’an Groups are characterized by the occurrence of volcanic rocks, whereas the Laoling Group is composed of clastic sediments and carbonates. Zircon U–Pb isotopic dating by LA-ICP-MS and SHRIMP methods indicates that the Guanghua and Ji’an Groups were formed between 2.1 and 2.0 Ga, but that the rocks of the Laoling Group may have formed in two episodes at 2.5–2.2 and 2.0–1.9 Ga, respectively. The present data indicate that the Ji’an, Laoling and Liaohe Groups are chaotic, without a common stratigraphy, with intense deformation making it difficult to identify original layering and contact relationships. Combined with age data from rocks intrusive into the sequence, the Paleoproterozoic tectonic evolution of the Liaoning–Jilin area can be related to collision and extension between the Liaonan block to the south and the Longgang block to the north. Extension in the Longgang block occurred at 2.12–1.98 Ga and was represented by eruption of the Guanghua mafic volcanic rocks. However, extension in the Liaonan block is expressed by 2.16–2.09 Ga A-type granites and ∼2.12–1.98 Ga volcano-sedimentary rocks of the Ji’an Group. These two blocks collided at ∼1.93–1.90 Ga, resulting in a clockwise metamorphic P– T path recorded in the N. Liaohe–Laoling Groups, followed by ∼1.85 Ga post-collisional evolution expressed by anticlockwise metamorphic P– T paths and immense granitic intrusions in the S. Liaohe–Ji’an Groups. Therefore, it is suggested that the collision between the Longgang and Liaonan in the Eastern block of the NCC occurred a little earlier than ∼1.85 Ga, when the NCC amalgamated by collision of the Western and Eastern blocks.

Are the South and North Liaohe Groups of North China Craton different exotic terranes? Nd isotope constraints

The Liaohe Group is an important Paleoproterozoic stratigraphic unit in the northeastern part of the North China Craton and is traditionally subdivided into the North and South Liaohe Groups. Associated with both the North and South Liaohe Groups are voluminous Paleoproterozoic granitoid rocks, named the Liaoji granitoids. Different tectonic models, including terrane amalgamation, continent–arc collision and rift closure, have been proposed to interpret the tectonic setting and evolution of the North and South Liaohe Groups and associated Liaoji granitoids. At the centre of the controversy between these models is whether or not the North and South Liaohe Groups developed on the same Archean basement. Nd isotopic geochemistry of the Liaoji granitoids provides important constraints on this controversial issue. The Liaoji granitoids associated with the North and South Liaohe Groups display similar ε Nd values, restricted to a narrow range from 0 to 2, implying that these granitoid rocks were derived from the same or a similar magma source. Moreover, the Liaoji granitoids associated with the North and South Liaohe Groups have similar Nd model ages ( T DM), ranging from 2.4 to 2.6 Ga, suggesting that the protoliths of the Liaoji granitoids associated with both groups may have formed simultaneously, and that the basement rocks underneath the Liaoji granitoids and associated North and South Liaohe Groups belong to the same continental block rather than two different blocks. Combining lithological, structural and geochronological considerations, we interpret the North and South Liaohe Groups as having developed on a single late Archean basement that underwent Paleoproterozoic rifting associated with the intrusion of the Liaoji granitoids and the formation of the Liaohe Group, and closed upon itself in the Paleoproterozoic.

Metallogenic Chronology of Boron Deposits in the Eastern Liaoning Paleoproterozoic Rift Zone

Lead isotopic analytic data of 30 ores gathered from the Zhuanmiao boron deposit, Wengquangou boron (iron) deposit and its Dongtaizi Ore Member constitute three isochrons, the corresponding ages of which are 1902 ± 12 Ma, 1852 ± 9 Ma and 1917 ± 48 Ma. Lead isotopic analyses of marble from the Xiquegou Member of the Qingchenzi orefield yield a Pb-Pb isochron age of 1844 ± 27 Ma. 40Ar-39Ar quick neutron activation dating of phlogopites and microclines coexisting with ore minerals in the Wengquangou boron (iron) and Zhuanmiao boron deposits shows that: (1) the phlogopite from the Wengquangou has a plateau age of 1923 ± 1.5 Ma and an isochron age of 1924 ± 2.5 Ma; (2) the microcline from the Wengquangou has the plateau age of 1407 ± 5.4 Ma and 220 ± 12 Ma and an isochron age of 1403 ± 19 Ma; (3) the phlogopites from the Zhuanmiao yield a plateau age 1918 ± 1.3 Ma and an isochron age of 1918 ± 2.9 Ma; (4) the microclines from the Zhuanmiao yield the plateau age of 1420 ± 16 Ma and 250 ± 8 Ma and an isochron age of 1425 ± 19 Ma and 269 ± 16 Ma. These ages indicate that the eastern Liaoning area happened around 1900 Ma, an important tectonomagmatic event, which is consistent with the worldwide Mid-Proterozoic tectonomagmatic event. During this period, the Proterozoic Liaohe Group was folded and underwent strong normal metamorphism, and the (hydrothermal) sedimentary boron deposits (or source beds) formed earlier were strongly superimposed by mineralization, resulting in enrichment of boron; later regional geological processes made little contribution to the formation of the boron deposits. Lead isotopic components show that the U-Pb and Th-Pb isotopic system reached homogenization in the ores whereas only the U-Pb isotopic system reached homogenization in the marble from the Xiquegou district, which indicates that the boron deposits superimposed in the studied area endured a relatively strong process of hydrothermal migmatization during the end phase of early Proterozoic metamorphism.

Re-Os dating of gold-bearing arsenopyrite of the Maoling gold deposit, Liaoning Province, Northeast China and its geological significance

The Maoling gold deposit, one of the large gold deposits in eastern Liaoning Province, NE China, is an arsenopyrite-disseminated gold deposit with a resource of approximately 25 t Au and an average Au grade of 3.2 g/t. Six arsenopyrites closely related to Au mineralization of the Maoling gold deposit are dated by Re-Os technique and define a Re-Os isochron with an age of 2316± 40 Ma, which suggests that the deposit was formed in the Paleoproterozoic era rather than in the Indosinian period as some early researchers suggested. High initial 187Os/188Os ratio of 1.32±0.48 indicates a crustal derivation of the ore-forming material of the deposit, which may be derived from rocks of the Gaixian formation of the Liaohe Group. Furthermore, the result also implies that the age of the Gaixian Formation in the Maoling district is older than 2316±40 Ma.

SHRIMP U-Pb zircon dating for lamprophyre from Liaodong Peninsula: Constraints on the initial time of Mesozoic lithosphere thinning beneath eastern China

It is undebated fact that the lithospheric mantle beneath eastern China was considerably thinned during the Mesozoic time. However, it has no adequate evidence for the exact timing when the lithosphere thinning started. The Liaodong Peninsula is located in the eastern segment of the North China Craton and is one of the important domains to explore the event of lithosphere thinning. SHRIMP U-Pb zircon dating and geochemical study were carried out for the lamprophyre dike swarm that intruded into the magnesite ore-beds in the Dashiqiao Formation of Paleoproterozoic Liaohe Group at the Huaziyu magnesite ore district, Liaodong Peninsula. The results indicate that these lamprophyre dikes were intruded in late Jurassic (155±4 Ma) and show some geochemical characteristics of potassic magmas. It is now accepted that the lithosphere thinning took place in the late Mesozoic, and the peak thinning stage occurred in early Cretaceous (130–120 Ma). Considering the potassic mafic magmatism marking the onset of the lithospheric thinning, we therefore suggest that the studied late Jurassic potassic lamprophyre dike swarm could imply that the late Jurassic is the time that lithosphere thinning started.

Late Archean to Paleoproterozoic evolution of the North China Craton: key issues revisited

A recently proposed model for the evolution of the North China Craton envisages discrete Eastern and Western Blocks that developed independently during the Archean and collided along the Trans-North China Orogen during a Paleoproterozoic orogenic event. This model has been further refined and modified by new structural, petrological and geochronological data obtained over the past few years. These new data indicate that the Western Block formed by amalgamation of the Ordos Block in the south and the Yinshan Block in the north along the east-west-trending Khondalite Belt some time before the collision of the Western and Eastern Blocks. The data also suggest that the Eastern Block underwent Paleoproterozoic rifting along its eastern continental margin in the period 2.2–1.9 Ga, and was accompanied by deposition of the Fenzishan and Jingshan Groups in Eastern Shandong, South and North Liaohe Groups in Liaoning, Laoling and Ji’an Groups in Southern Jilin, and possibly the Macheonayeong Group in North Korea. The final closure of this rift system at ∼1.9 Ga led to the formation of the Jiao-Liao-Ji Belt. In the late Archean to early Paleoproterozoic, the western margin of the Eastern Block faced a major ocean, and the east-dipping subduction beneath the western margin of the Eastern Block led to the formation of magmatic arcs that were subsequently incorporated into the Trans-North China Orogen. Continued subduction resulted in a major continent-continent collision, leading to extensive thrusting and high-pressure metamorphism. The available age data for metamorphism and deformation in the Trans-North China Orogen indicate that this collisional event occurred at about 1.85 Ga ago, resulting in the formation of the Trans-North China Orogen and final amalgamation of the North China Craton.

LA-ICP-MS U–Pb zircon ages of the Liaohe Group in the Eastern Block of the North China Craton: constraints on the evolution of the Jiao-Liao-Ji Belt

As a major lithostratigraphic unit of the Palaeoproterozoic Jiao-Liao-Ji Belt in the Eastern Block of the North China Craton, the Liaohe Group consists of an assemblage that is transitional from a lower arkose- and volcanic-rich sequence (Langzishan, Li’eryu and Gaojiayu Formations), through a middle carbonate-rich sequence (Dashiqiao Formation) to an upper argillaceous sequence (Gaixian Formation). Tectonically associated with the Liaohe Group are large volumes of granitoid rocks, named the Liaoji Granite, whose emplacement age has been dated at about 2.1–2.2 Ga. Regionally, the Liaohe Group and the associated Liaoji Granite extend along a NEE-trending belt that is flanked by 2.45–2.55 Ga basement gneisses. U–Pb zircon data and cathodoluminescence (CL) imaging are used to constrain the maximum depositional and metamorphic ages of the Liaohe Group, which are critical in understanding the tectonic setting and history of the Jiao-Liao-Ji Belt. Cathodoluminescence images reveal that most detrital zircon grains from the Liaohe Group are characterized by concentric oscillatory zoning, with comparatively low luminescence and high Th/U ratios, suggesting magmatic origin, but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low Th/U ratio, indicating metamorphic origin. Results of this study, show that the detrital zircon grains of the Langzishan Formation, the lowest sequence of the Liaohe Group, have concordant U–Pb ages ranging from 2.05 to 2.24 Ga, suggesting that the Liaohe Group was deposited at some time after 2.05 Ga. Although most overgrowth or recrystallization rims are too narrow to be analyzed, some rims yield concordant or upper intercept ages around 1.93 Ga, interpreted as the peak metamorphic age of the Liaohe Group. Detrital zircon grains from the Dashiqiao Formation in the middle sequence of the Liaohe Group have concordant U–Pb ages ranging from 2.25 to 2.53 Ga, some of which are similar to those of the basement gneisses in the area. This study indicates that the Liaohe Group was deposited after the emplacement of the Liaoji Granite, and the latter may be a major component of the provenance for the Langzishan Formation. In contrast, the protoliths of the middle sequence of the Liaohe Group were most probably derived from the basement gneisses. These new zircon ages for the Liaohe Group and recent data for the Liaoji Granite, combined with lithological, structural and metamorphic considerations, support a rifting model for the evolution of the Jiao-Liao-Ji Belt.