Abstract:Exposed in the Lüliang area, North China, the Hangaoshan Group is dominated by terrigenous clastic deposits and bear an ideal candidate section for the stratotype of the lower Mesoproterozoic or upper Paleoproterozoic sequence, especially for the boundary between them. The determination of formation age is of great significance for understanding the Precambrian geological evolution of the North China Craton, such as emergence of the initial cover sequence of the craton, assembling and breakup of the Nuna supercontinent. To date, there are still great contro- versies on the age, subdivision, correlation and geological implication of the Hangaoshan Group. In this study, zircon U-Pb isotopes of the andesites from the Hangaoshan Group have been analyzed with SHRIMP technique, giving a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 1 769±9 Ma ( 2σ) . This is the first direct measurement of the zircon U-Pb age of the Hangaoshan Group. In addition, weighted mean ²⁰⁷Pb/²⁰⁶Pb zircon ages of the volcanic rocks in three different parts of the Xiaoliangling Formation of the same stratohorizon are 1 792±18 Ma, 1 773±19 Ma and 1 778±20 Ma, respectively, which are consistent with the age of Hangaoshan Group within the error range. Therefore, the ages of the Hangaoshan Group and Xiaoliangling Formation are determined at 1 769±9 Ma and 1 792 ~ 1 773 Ma, respectively. In combination with previous research results, formation time of the Hangaoshan Group and Xiaoliangling Formation is ca. 1 780 Ma. As regards sedimentology, the section strata of the Hangaoshan Group in Lüliang Mts area are continuous, and a horizon of andesite is stably and widly distributed in the region. So the horizon is an excellent regional isochronous marker in the central and southern part of the North China Craton. Furthermore, rift deposits and volca- nic rocks in this period occur in the western Yangtze Block, the northwestern Laurentia, northern Australia, the São Francisco, Congo and Siberian cratons, and all can be well correlated, showing the global distribution of intracontinental rift sediments during initial breakup of Nuna supercontinent in the same period. We propose here that the international Mesoproterozoic bottom boundary should be moved down, from 1.6 Ga to 1.8 Ga, and the Hangaoshan section can be used as a new candidate stratigraphic type section of the international Mesoproterozoic bottom boundary.

Abstract:The depositional age and provenance of meta-sedimentary rock series in the Jiao-Liao-Ji Belt remain fundamental issues of considerable debate. Using LA-MC-ICP MS zircon U-Pb dating and Lu-Hf isotope analytical techniques, representative rock samples, including metamorphic supracrustal rocks of the Ji’an Group, gneissic granite, porphyry granite and TTG gneiss from the Tonghua area in the northern part of the Belt were analyzed. The results show that the detrital zircon ages from metamorphic supracrustal rocks of the Ji’an Group present two dominant peaks of 2.5 Ga and 2.1 Ga. However, it is noteworthy that the detrital zircons from different metamorphic rock yield various age populations. The detrital zircon ages of the low grade metamorphic graphite-bearing leptynite concentrates at about 2.5 Ga, suggesting provenance of neoarchean magmatic unit. Detrital zircon in the high grade metamorphic rocks, such as sillimanite-garnet-cordierite gneiss, diopside gneiss and marble usually suffered alteration, and thus it is difficult to obtain reliable provenance age information. The metamorphic zircons from the Ji’an Group record three stages ages: 1.95~1.90 Ga, 1.90~1.85 Ga and 1.85~1.80 Ga. According to the relationship between metamorphic zircon and melting simulated by quantitative phase diagram, it is inferred that the first stage represents initial cooling timing of the metamorphic terrane, the second stage represents the timing of large-scale melt condensation and crystallization in the later cooling stage, and the third stage might be related to the tectonic exhumation, which led the terrane uplifting to the shallow crust. Zircons from metamorphic supracrustal rocks of the Ji’an Group show εHf(t) values of -12.40~+ 6.17 (mostly -8~-2). Two-stage Hf model ages vary from 3.0 to 2.3 Ga, showing similar source characteristics with Archean TTG gneiss and paleoproterozoic gneissic granite. The emplacement age of Archean amphibolite gneiss (TTG) in Tonghua area is determined as 2 574 ±11 Ma with zircon εHf(t) values ranging from +1.87 to +7.30, and two-stage Hf model ages of 2.89~2.60 Ga, indicating that the rock derived from partial melting of juvenile crust. The emplacement age of gneissic granite is dated as 2 104 ±18 Ma with zircon εHf(t) values of -2~+2, and the Hf model ages of 2.8~2.7 Ga, indicating derivation from partial melting of juvenile crust and ancient supracrustal rocks. The emplacement age of undeformed porphyritic granite is as about 1 888 ±8 Ma, the zircon εHf(t) values range from -5.43 to + 0.03, and the Hf model ages range from 2.7 to 2.5 Ga, indicating that it derived by melting of ancient supracrustal rocks. In general, the Jiao-Liao-Ji Belt presents characteristics of typical continental rift during 2.3~2.0 Ga followed by collision orogenic process during 1.95~1.85 Ga, implying that they might result from different tectonic thermal events.

Abstract:The Guandu Group, which has undergone high greenschist to high amphibolite facies metamorphism, is an important meta-volcanic and meta-sedimentary rock sequence in the Zanhuang Complex of the Trans-North China Orogen, North China Craton. Depositional age and provenance of the Guandu Group are vital for understanding the Neoarchean-Paleoproterozoic tectonic evolution of the Trans-North China Orogen. In this study, LA-MC-ICP-MS (laser ablation multi-collector inductively coupled plasma mass spectrometry) and TIMA (tescan inergrated mineral analyser) were used to analyze mineral inclusions, U-Pb-Hf isotope and rare earth element compositions of zircons in the biotite leptynite and quartzite in the Guandu Group. Based on the mineral inclusions, internal structure, and U-Pb ages of zircons, the concordant ²⁰⁷Pb/²⁰⁶Pb age of 2 544 Ma or 2 536 Ma in the youngest group of detrital zircons is chosen as the maximal depositional timing of the Guandu Group. Combined with the geological relationship which the Guandu Group was intruded by the Huangcha granites, it is speculated that the depositional age of the Guandu Group wasn’t Paleoproterozoic but late Neoarchean. Detrital zircon age patterns from the biotite leptynite and quartzite samples are similar and are characterized by the major peak of 2 512 Ma. Combined with the mineral inclusions and internal structure of the detrital zircons, it is suggested that the main provenance of the Guandu Group is the late Neoarchean intermediate-acid magmatic rocks. Two stage Hf isotopic model ages of detrital zircon reveals that the intensive crustal growth in the Zanhuang Complex was concentrated from 2 850 Ma to 2 700 Ma. In addition, the new and published data from the Trans-North China Orogen reveal that the zircons in the Guandu Group recorded the consistent metamorphic age of ca. 2 500 Ma, similar to other complexes in the Trans-North China Orogen, indicating that the Trans-North China Orogen also experienced an intense regional metamorphism in ca. 2 500 Ma, which may be related to the late Neoarchean initial cratonization of the North China Craton.

Abstract:The North Lhasa terrane is one of the most widely exposed areas of Precambrian rocks in the Tibetan Plateau, but the Neoproterozoic tectonic evolution of the terrane and its role in the supercontinent evolution have been controversial. Focusing on this scientific problem, this paper collects and arranges the isotopic chronology, geochemistry and isotopic geochemistry data of the Precambrian Nyainqentanglha Group in Ren Co area of the North Lhasa terrane, and finds three periods of Neoproterozoic magmatic-sedimentary-metamorphic records: ① 925 ~ 886 Ma, the rock association is MORB-type metamorphic basic rocks and metamorphic sedimentary rocks, representing the embryonic oceanic crust and associated sediments in the latest stage of continental rift; ② 822 ~ 671 Ma, mainly plagioclase amphibolites and granitic gneisses, whose protoliths are tholeiites, calc-alkaline basalts and A2-type granite, which were formed in the process of oceanic subduction together with the coeval amphibolite-facies metamorphism; ③ 658 ~ 646 Ma, including intermediate-basic intrusive and volcanic rocks and eclogite-amphibolite-facies metamorphic rocks, which jointly record the process of slab break-off in a collision zone. The above three magmatic-sedimentary-metamorphic records are consistent with the evolution of the Mozambique Ocean, corresponding to the embryonic stage, decline stage and end stage of the Wilson cycle respectively. In addition, the temporal-spatial distribution of Andean-type magmatism in the northern margin of Gondwana supercontinent are further constrained by the Ediacaran magmatic rocks in the Nyainqentanglha Group. Based on this study and previous results, we suggest that the North Lhasa terrane drifted away from Africa in the Tonian, experienced the subduction-collision processes of the Mozambique Ocean in the Cryogenian, and then located in the northern East African orogen in the Ediacaran, and influenced by the Andean-type magmatism along the Gondwanan Proto-Tethyan margin in the Ediacaran-Cambrian.

Abstract:Anatexis is the main mechanism and key geological process of continental crustal differentiation, element migration and enrichment and migmatization. The Archean basement exposed in the southern Jilin Province, in which felsic leucosome and leucogranites are extensively distributed, widely experienced amphibolite-granulite facies metamorphism and anatexis. The field geological characteristics, correlation and petrographic characteristics of the Archean metamorphic quartz diorite and associated felsic leucosome and orthopyroxene (Opx)- and amphibole (Amp)-bearing pegmatite granite occurred in Helong granite-greenstone terrane in the southern Jilin Province indicate that the metamorphic quartz diorite underwent partial melting and in-situ segregation and accumulation of melt. The integrated analyses of zircon cathodoluminescence (CL) images, in-situ U-Pb geochronology, trace elements and Hf isotope on the metamorphic quartz diorite and pegmatite granite show that they have the same types of magmatic and metamorphic recrystallized zircons, the latter is dominated by metamorphic recrystallized zircons, that the metamorphic quartz diorite has magmatic crystallization age of 2 535 ±14 Ma, and that their magmatic zircons have consistent Hf isotope composition. Their metamorphic recrystallized zircons yield consistent metamorphic ages of 2 495±22 Ma and 2 491±10 Ma, respectively, and have identical Hf isotope compositions, which are consistent with that of magmatic zircons, Th and U contents and Th/U ratios, indicating that both metamorphic recrystallized and magmatic zircons have initial crystalline zircons formed in the same magmatic source, and further demonstrating that the metamorphic quartz diorite experienced metamorphic anatexis at ca. 2.5 Ga and that the Opx- and Amp-bearing pegmatite granite derived from in-situ partial melting of the metamorphic quartz diorite, in combination of the coeval strong and extensive magmatism and amphibolite-granulite facies metamorphism with counterclockwise p-T path at the end of Neoarchean in the North China Craton as well as the southern Jilin Province, which may reflect the thermal effect of mantle material upwelling on the continental crust during formation and stabilization of the craton lithosphere.

Abstract:In order to reveal the magma mixing mechanism of the Mid-late Triassic Jiefangyingzi Pluton on the northern margin of the North China Craton, this paper carried out electron microprobe analyses of plagioclase and hornblende in host rock and mafic enclaves. The results show that the plagioclase phenocrysts in rich-phenocrysts enclaves and the edges of poor-phenocrysts enclaves develop the spike zone of increased An value. The spike zone of An value (32~46) is higher than those of the core and rim in same plagioclase grain, and the An value of the core is consistent with that of plagioclase in host rock, indicating the spike zone was the result of the mafic magma capturing and modifying the plagioclase from host rock. The core of plagioclase at the central part of poor-phenocrysts enclaves has an erosion sieve structure, and the An value of the residual part (40~47) is higher than that of the erosion part (32~36) in the core of the plagioclase grain, but generally higher than that of rim in the phenocryst and fine-grained plagioclase in the matrix (17~35), indicating the central part of the enclaves has been modified by felsic composition. On the other hand, the TiO₂ content of hornblende phenocrysts in host rocks (0.50%~1.10%) is significantly lower than that of hornblende in enclaves (1.17%~2.47%), while the TiO₂ content of fine-grained hornblende in the matrix (1.58%~2.26%) is similar to that of hornblende in enclave, indicating that there was a mixture of mafic components at the late stage of host rocks evolution. The above studies show that magma mingling on a macroscopic scale and the migration of minerals and elements of magma mixing on a microscopic scale occurred between mafic and felsic magma during the formation of Jiefangyingzi Pluton.

Abstract:Zircon is one of the important minerals for studying the early Earth evolution, because its U-Pb age, trace elements and isotopic compositions can place important constraints on the petrogenesis and even the geodynamic background of host rocks. This article summarizes the main research results obtained in the past 10 years from six aspects: mineral inclusions in zircon, trace elements, U-Pb isotope system, Lu-Hf isotope, O isotope and Si, Zr and Ti isotopes. The previous studies have suggested different mechanisms of generation of secondary mineral inclusion and the restrictions of primary mineral inclusions on the early crustal composition, the relationship between the increase of S-type granites and the transformation of tectonic system, the mechanism and recognition of radioactive Pb enrichment, the mechanism of craton stability reflected by the Lu-Hf isotope,and the determination of the primary O isotope and its restriction on the early Earth hydrosphere state. The above research results show that zirconology is an indispensable and important research method for studying the evolution and tectonic system of the early Earth crust.

Abstract:The K-rich granite took limited volumes of the continental crust in the early earth (>2.6 Ga). Studies on ancient granite will provide great evidence for revealing the geological history of the crust. In this paper, we carry detailed studies on the geology and zircon U-Th-Pb-Hf isotopic composition of the Paleoarchean granite, which is exposed in the Anshan Gongchangling area of the North China Craton (NCC). The studied Paleoarchean granite, which is occurring as an enclave in the regional large-scaled of Mesoarchean (2.9 Ga) granite with similar tectonic feature to the latter, is composed of K-feldspar (40%~60%), plagioclase (10%~30%), quartz (30%) and minor mica. Most magmatic zircons from the Paleoarchean granite have varying Th and U contents of 100×10^-6~600×10^-6 and 400×10^-6~1 500×10^-6, respectively, with relatively high Th/U ratios (0.10~0.93). 13 concordant analysis yielded meaning weighted average age of 3 337±24 Ma(MSWD=1.5), interpreted as the emplacement time of the granite. And the inherited zircons formed at 3.76~3.60 Ga. The analyzed zircon grains yielded initial ¹⁷⁶Hf/¹⁷⁷Hf_i ratios of 0.280 391~0.280 857 with Hf depleted mantle modal ages (t_DM1) of 3 856~3 327 Ma. The differences of Hf isotopic compositions suggested that ① an ancient continent nucleus with multiple magmatic records had been formed before the end of the Paleoarchean in the Anshan area; ② the stabilization of the early crust should not be synchronous during the geological history. Crustal stabilization and differentiation had been carried out locally, early before the amalgamation of the continental basement of the NCC at ~2.5 Ga.

Abstract:In this study, SHRIMP zircon U-Pb ages and whole-rock geochemical data are reported for the mid-Paleoproterozoic granitic gneisses from the Jiaobei terrane, southeastern North China Craton. Geochronological results reveal that the granitic gneisses crystallized at 2 184~2 112 Ma and underwent metamorphism at ~1.85 Ga. Although the samples collected from different areas show obvious differences in geochemical composition, they commonly have high SiO₂, Na₂O+K₂O and Zr contents, high 10 000Ga/Al values, and high zircon saturation temperatures, indicating that their protoliths have an affinity to A-type granite. Together with published data in literatures, protoliths of the mid-Paleoproterozoic granitic gneisses from the Jiaobei terrane were formed at two major stages: 2.13~2.10 Ga and 2.19~2.17 Ga. By comparison with the earlier stage granitic gneisses (2.19~2.17 Ga), the later stage granitic gneisses (2.13~2.10 Ga) show higher Zr contents and zircon saturation temperatures, and relatively higher zircon εHf(t) values. We concluded that protoliths of the 2.19~2.17 Ga granitic gneisses were formed by high-temperature dehydration melting of ~2.7 Ga and ~2.9 Ga TTG in the Jiaobei terrane, whereas protoliths of the 2.13~2.10 Ga granitic gneisses originated from partial melting of ~2.5 Ga TTG in the Jiaobei terrane at higher temperature. The differences in magma source and melting temperature of the protoliths of the two stages granitic gneisses imply that the Jiaobei terrane underwent two separate extensional tectonic events during the mid-Paleoproterozoic.

Abstract:Carbon is an important element affecting the habitability of the Earth. The carbon cycle between the surface and the deep of the Earth has a very important impact on the global climate change. Nowadays, the Earth regulates the global carbon cycle mainly through subduction and volcanism. However, there are significant differences of carbon cycle between the early Earth and the present Earth. Based on the previous research results, this paper comprehensively discusses the source of the Earth’s original carbon, the process of the Earth’s early carbon cycle and its relationship with the great oxidation event. The Earth evolved from the solar nebula through the accretion of planetesimals. Part of the carbon on the Earth comes from the initial composition of the Earth, and part is obtained through giant impacts and late veneer. During the magma ocean period at the beginning of the Earth’s formation, the differentiation between the Earth’s core and mantle made the Earth’s core enriched carbon and the mantle extremely depleted carbon; the interaction between the magma ocean and the Earth’s early atmosphere can bring atmospheric carbon into the mantle. The collision between the proto-Earth and the planetary embryo with high C/N and C/S values can increase the carbon content of the Earth. In addition, the late veneer of chondrites enriched in volatiles can also bring additional carbon to the Earth. In the early stage of plate tectonics, the geothermal gradient of ancient subduction is about 100℃ higher than the modern subduction zone. The subducted altered ocean crust and ocean floor sediments will completely decarburize through decarburization reaction or melting at very shallow depth, and only a small amount of carbon can be brought into the deep mantle by carbonated peridotite. The resulting greenhouse effect can offset the impact of early solar luminosity deficiency on surface climate. The early carbon cycle process of the Earth is closely related to the great oxidation event. The increase of CO₂ content in the atmosphere, the burial of organic matter, and the difference of subduction efficiency between inorganic carbonate and organic carbon are the key factors to form the great oxidation event.

Abstract:Podiform chromite is a very important strategic resource, and scholars have not an unified understanding of its origin. Previous studies mainly constrained the genesis of chromitite from petrology, geochemistry and geochronology. It is still deficient in systematic summary and research about the inclusion types and their implications on geological processes. According to the detailed study of different chromitite bodies, the mineral inclusions can be divided into five catagories: ① Anhydrous silicate mineral inclusions, including olivine, orthopyroxene, clinopyroxene, etc.; ② Hydrous minerals, including hornblende, chlorite, serpentine, and apatite; ③ Platinum group minerals (PGM) and sulfides, including Os-Ir alloy, Pt-Fe alloy, natural Os and natural Ir, as well as pyrite, chalcopyrite, pyrrhotite, etc.; ④ Crust source minerals, including zircon, rutile, quartz, calcium chromium garnet, etc.; ⑤ Exotic minerals, including ultra-high pressure minerals such as diamond, moissanite, coesite, and natural nickel, natural chromium, natural iron and natural titanium, etc. Through comparative studies, it is determined that they were formed in different stages, and it is preliminarily proposed that there are four stages of the formation of podiform chromitite, which are the mantle plume/mantle convection in the deep mantle, partial melting/magma crystallization differentiation of the mantle peridotite in the oceanic lithosphere, melt-rock reaction in the super subduction zone, and hydrothermal alteration/fluid modification in the later stage. It is believed that the mineral inclusions in chromitite have recorded the environmental conditions of various periods of chromite formation, and can reveal the formation process of chromitite more accurately.

Abstract:Through the structure, composition and occurrence of sillimanite, the formation process of sillimanite has been discussed and summarized in this paper. In composition, the protolith of the sillimanite-bearing metamorphic rocks is not necessarily pelite rocks, the sillimanite-rich rocks does not necessarily correspond to any pelite rocks. The Al-rich feature of the pelite is favorable for occurrence of sillimanite, but sillimanite may not occur in the rock even under appropriate metamorphic temperature and pressure condition. The differential migration of components is essential for sillimanite. The formation of sillimanite is closely related to deformation and metamorphism, especially anatexis in metamorphic rocks. Leucosome, pegmatite and granite all can evolve through metamorphism and anatexis. The key to the formation of sillimanite is the migration and leaching of alkaline(-earth) metals and their separation from sial components, resulting in the relative enrichment of Al₂O₃. Sillimanite, especially fibrolite, corresponds to the early differential deformation-metamorphism stage. In the process of component migration, the flow of solution or melt components leads to the false image of "stress orientation" of sillimanite, the aggregation of sillimanite and related minerals, and multiple evolution stages of different metamorphic minerals. Although different variants of Al₂SiO₅ have the same composition, their rock types or environments are still significantly different. On the one hand, their formation is not only controlled by temperature and pressure conditions, but also the acidity or alkalinity of the fluid or melt, which is critial in affecting the coordination state of aluminum.

Abstract:The Alxa block is a Precambrian microcontinent bounded by orogenic belts and fault zones, and its property and tectonic affinity have always been controversial. Based on the recent research data obtained by the author in the eastern Alxa block and combined with the research progress of Alxa block in recent years, it is considered that the 2.64 Ga amphibolite and ~ 2.5 Ga TTG gneiss exposed in the eastern Alxa block, and clearly indicates that Neoarchean metamorphic basement also exists in the eastern Alxa block. The zircon Hf isotopic data of these Neoarchean metamorphic rocks show that the model ages mainly range from 3.38 Ga to 2.88 Ga, which are consistent with the Hf model ages (3.4 ~ 2.6 Ga) of the Paleoproterozoic zircons from the Diebusige Complex and Bayanwulashan Complex in the eastern Alxa block. The above data indicate that the eastern Alxa block has experienced crustal growth from the Late Paleoarchean to Early Neoarchean and magmatic-metamorphic event of the ~2.5 Ga. In addition, the magmatic event of 2.3~2.0 Ga and magmatic-metamorphic events of ~1.95 Ga and ~1.85 Ga were also recorded in the Early Precambrian basements of the eastern Alxa block, similar to that of the western Alxa block and the North China Craton. Based on the similarities in the zircon chronology data and Hf isotopic compositions of the Early Precambrian basements from the Alxa block and the Khondalite belt, we proposed that the Alxa block has a similar crustal evolutionary history with the Khondalite belt, and was probably involved in the Khondalite belt as its western extension in the Paleoproterozoic.

Abstract:As a Paleoproterozoic orogenic in the North China Craton, the Jiao-Liao-Ji Belt preserves rich records of metamorphism magmatism, sedimentation and metallogeny. The p-T-t paths of the widespread high pressure granulites within this belt reveal the subduction-collision-exhumation geodynamic process. However, the timing of continental collision and subsequent extension is still controversial. In this paper, the petrography, zircon U-Pb geochronology, major trace elements and Lu-Hf isotopes of the whole rocks of the Paleoproterozoic granites in Daloufang Dandong area are systematically analyzed. The results show that the weighted average age of the magmatic zircons is 1 873~1 869 Ma, and the emplacement time of the acquired granites is Paleoproterozoic. The Daloufang Pluton mainly consists of gneissic biotite monzogranite, with characteristics of high SiO₂(72.39%~74.20%), medium Al₂O₃(14.66%~15.40%), medium CaO(1.35%~1.84%) and low MgO(0.07%~0.35%). The REE distribution curve is right-leaning with strong Eu positive anomaly. Trace elements are enriched in large ion lithophile elements such as Rb, Th, U, K, and depleted in high field strength elements such as P, Ti, etc. It is characterized by high potassium calc-alkaline series of quasi-aluminum to weak peraluminous, and has similar petrogeochemical characteristics to I-type granites. The εHf(t) values range from -1.76 to +1.45, and the two-stage model ages range from 2 607 to 2 425 Ma, indicating that the magmatic source area is not only from crustal material recycling, but also from neoarchean to Paleoproterozoic material added to the crust or the formation ofnew crust. The geochemical characteristics of late Paleoproterozoic gneisses monzogranite in Dandong area are similar to those of active continental margin arc granites related to subduction, and similar to the metamorphic age of argillaceous granulites in Ji’an area in the north. It is suggested that the Jiao-Liao-Ji Belt may have been experienced collision in the late Paleoproterozoic, which provides important constraints for the exploration of the orogeny of the Jiao-Liao-Ji Belt and the process and time limit of the post-collision extension.