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Abstract The Huoqiu iron deposit is one of the few Superior-type BIF ore fields in China. To clarify the genesis of Huoqiu BIFs, we give out the geochemical and O-S isotopic data of the BIF samples and zircon Hf isotopic data of the wall-rock. The Huoqiu BIFs show dominant composition of SiO 2 + Fe 2 O 3 T, and varying contents of Al 2 O 3 , MgO, CaO, Rb, Sr, Zr and Hf, suggesting their formation mainly through chemical precipitation and incorporation of terrigenous felsic clastics. Shale-normalized rare earth element patterns of the BIF samples show the features characteristic of other Archean and Paleoproterozoic BIFs, with HREE enrichment relative to LREE, positive La and Eu anomalies, and superchondritic Y/Ho ratios comparable to modern seawater. Positive Eu anomalies are attributed to an imprint of high-temperature hydrothermal fluids. None to negative Ce anomaly shown by the BIFs imply the Huoqiu BIFs was precipitated from the mildly oxidized seawater in a nearshore setting. The quartz separated form Huoqiu BIF has δ18O V-SMOW values of 11.8‰–14.8‰, within the extent of the siliceous rocks deposited from high-temperature hydrothermal. The δ34S values of pyrite grains vary from −2.84 to +4.38‰, which is similar as the sulfur derived from mixtures between mantle fluids and sediments; The Δ33S values varied from −0.08‰ to +1.03‰, imply that the Huoqiu BIFs deposited distally from the volcanic center. The Hf model ages of these detrital zircons from the wall rock give three prominent peak at 3.1–3.0 Ga, 2.9–2.7 Ga and 2.5 Ga, respectively, it suggest that there were three episodes of the crust growth in the Huoqiu area. Integrated these data with the pioneering studies on the Huoqiu BIFs and wall rocks, we confirmed that the Huoqiu BIFs were sourced from the high-temperature hydrothermal related with the volcanics and precipitated from the mildly oxidized seawater in a nearshore setting and distally from the volcanics at 2.5 Ga. Highlights • Huoqiu BIFs sourced from hydrothermal fluids; • It precipitated from the mildly oxidized seawater; • It depoisted distally from the volcanics. [ABSTRACT FROM AUTHOR]

The Yinshan Block constitutes the northwestern segment of the North China Craton. We characterized the geochemistry, zircon U–Pb geochronology, and Hf isotopic composition of a diorite pluton in the Yinshan Block. The zircon U–Pb data yield a protolith formation age of 2535 ± 8 Ma (MSWD = 0.46), followed by recrystallization at 2465 ± 14 Ma or 2431 ± 30 Ma; the granite vein which intruded into the diorite pluton gives a formation age of 2453 ± 5 Ma (MSWD = 1.6), according with the recrystallization age of the diorite. These diorites are characterized by moderate Mg# value and MgO, Cr, and Ni content and have relatively low Sr/Y and (La/Yb)N ratios and slightly Eu anomalies and are enriched in LILEs and depletion in high field strength elements. High‐Sr + Ba granites with low K2O/Na2O characteristics are also shown by these diorites, and the εHf(t) of zircons lie between +1.3 and −7.2, imply these diorites are most likely derived from partial melting of a thickened lower crust with minor involvement of enriched mantle. These geochemical and isotopic characteristics suggest the diorite magmas derived from an accreted arc‐related rocks remelting in a low‐pressure environment along the continent margin. Hereby, we propose a supplement to the model of crustal growth and evolution in the Yinshan Block, involving subduction and collision in the Neoarchean. [ABSTRACT FROM AUTHOR]

The Huoqiu banded iron formation (BIF) iron deposits in the southeastern margin of the North China Craton (NCC) is hosted by middle-grade metamorphic Huoqiu complex. LA-ICP-MS U–Pb dating on zircons separated from the wallrock of the orebody constrains the depositional age ≤ 2.54 Ga and metamorphic age as ∼1.8 Ga. The dominant composition of SiO 2 + Fe 2 O 3 T of the BIF ores suggests their formation mainly through chemical precipitation. The widely varying contents of major elements such as Al 2 O 3 , MgO, CaO and trace elements such as Rb, Sr, Zr, Hf, Cr, Co, and Ni clearly indicate the incorporation of clastics, especially continental felsic clastics. When compared with Post-Archean Australian Shale (PAAS), the seawater-like signatures of REE distribution patterns, such as LREE depletion, positive La and Y anomalies, and superchondritic Y/Ho ratios, support the deposition in seawater. Meanwhile, the presence of strong positive Eu anomalies suggest the participation of hydrothermal fluids, which is according with the high depletion of 30 Si in Huoqiu BIFs. Magnetite and specularites within the BIFs contain heavy Fe isotopes resulting from the partial oxidation and precipitation of Fe 2+ to Fe 3+ in seawater. Integrated with geochronological and geochemical data from other Archean rocks in this area, we propose the formation of the BIFs occurred in a back-arc basin environment, and belonged to Superior-type. [ABSTRACT FROM AUTHOR]

The hornblendite complexes hosted in the Guyang granite-greenstone terrane form part of the Neoarchean basement in the Western Block of the North China Craton. In this study, we focus on the largest one from this block, previously named the Guyang komatiite, and present results from lithological, geochronological and geochemical studies. The dominant lithology in the Guyang hornblendite complex is greenschist facies hornblendite, and can be divided into clinopyroxene hornblendite (∼75%) and olivine-orthopyroxene hornblendite (∼25%). The oldest calculated Re depletion model ages ( T RD ) of these hornblendites is of 2454 Ma, and the zircon U-Pb age of the wallrock is 2480 Ma, with single-stage depleted mantle Nd model ages T DM1 (Nd) varying from 2.61 to 2.88 Ga. These data suggest that the Guyang hornblendite complexes formed during Neoarchean-Paleoproterozoic time. The hornblendites show low SiO 2 , high MgO contents and are enriched in Cr, Ni, and LREE with negative Ce anomalies and depleted in Ti, Nb and Ta. Their 187 Os/ 188 Os ratios range from 0.11145 to 0.11279, with γOs (2.5Ga) varying from −3.9 to +1.4. Geochemically, the olivine-orthopyroxene hornblendite shows little variation with typical cumulate feature. In contrast, the clinopyroxene hornblendite shows a large range of chemical variation. In the CaO vs. MgO and CaO/Al 2 O 3 vs. MgO diagrams, the clinopyroxene hornblendite shows Opx fractionation trend. Combined with lithological information, we infer that the hornblendite magma was emplaced as a crystal mush, with orthopyroxene as cumulus phase. The Os and Nd isotope composition, negative Nb, Ta, Ce anomalies, and the relationships in Th/Yb–Nb/Yb diagram suggest that the Guyang hornblendites formed from a source mantle that was modified by subduction-related melts/fluids derived from a seawater-altered basaltic slab. Compared with typical Archean komatiites, the rocks of present study show significant differences in lithological and geochemical characteristics, and thus it cannot be named as komatiite. To explain these characteristics, we propose a geodynamic model involving ridge subduction and slab window mechanism to account for the formation of the Guyang hornblendite complex. [ABSTRACT FROM AUTHOR]

A Neoarchaean sanukitoid pluton that was intruded into the base of the Guyang greenstone belt in the Yinshan Block of the North China Craton hosts a number of hornblendite enclaves. Geochemically, the pluton is characterized by high MgO, Mg#, Cr, Ni, large-ion lithophile element (LILE), and heavy rare earth element (HREE) contents and low TiO2and high-field strength element (HFSE) contents, and has relatively low Sr/Y ratios and negative Eu anomalies. Whole-rock Sr–Nd isotopic analyses indicate that it has εNd(t) values of +1.4 to +2.0. These geochemical and isotopic characteristic suggest that the sanukitoid was formed under a low-pressure and high-temperature environment by slab melting and assimilation of hornblendite enclaves. The hornblendite enclaves show high MgO, Mg#, Cr, and Ni contents, high and variable K2O, LREE, and Th contents, enrichment in LILEs and LREEs, and depletion in HFSEs. They have high Y contents and relatively low Sr/Y values, strongly negative Eu anomalies, and whole-rock εNd(t) values of +1.0 to +1.9. The geochemical and isotopic characteristics indicate that these enclaves might have been derived from a mixed source of an enriched mantle, metasomatized by melts expelled from subducted sediments in a high-temperature, low-pressure environment. To explain these characteristics, a ridge subduction model is proposed for the formation of the sanukitoid and hornblendite in the Yinshan Block in the Neoarchaean. [ABSTRACT FROM AUTHOR]

The Yinshan Block, part of the Neoarchaean basement of the Western Block of the North China Craton, is composed of granite–greenstone and granulite–charnockite complexes. We report research on a suite of charnockites from the granulite–charnockite complex and characterize their geochemistry, zircon U–Pb geochronology, and Hf isotopic composition. The charnockites can be divided into intermediate (SiO2 = 59–63 wt.%) and silicic (SiO2 = 69–71 wt.%) groups. U–Pb zircon data yield protolith formation ages of 2524 ± 4 Ma, 2533 ± 15 Ma, followed by metamorphism at 2498 ± 3 Ma, 2490 ± 11 Ma, respectively, for these groups. Although the intermediate charnockites are characterized by higher Al2O3, TiO2, Fe2O3T, MnO, MgO, CaO, P2O5, K2O, Sr, and ΣREE content than the silicic charnockites, the ages and Hf isotopic composition of zircons and REE patterns of both intermediate and silicic charnockites are remarkably consistent, which indicates that they are genetically related. These charnockites are predominantly metaluminous to slightly peraluminous, calc-alkalic to calcic, and magnesian – characteristics generally related to a subduction setting. High-Sr + Ba granites with low K2O/Na2O characteristics, shown by these charnockites, imply a mixture of mafic and felsic magmas generated from an enriched mantle + lower crust. High MgO, Ni, Cr and Mg#, low K2O/Na2O, and metaluminous to slightly peraluminous natures imply that the source rocks most likely were amphibolites. Coeval calc-alkaline magmatism and high-T granulite-facies metamorphism under low-H2O activity in the area lead us to propose a model involving mid-ocean ridge subduction within a Neoarchaean convergent margin. The arc-related rocks accreted along the continent margin, and became a barrier when the lithospheric mantle ascended through the slab window. Melt derived from the decompressing mantle mixed with melt derived from the overlying, juvenile lower crust melt, which was warmed and metamorphosed by the ascending lithospheric mantle. [ABSTRACT FROM AUTHOR]

The Yinshan Block is a unique coherent Neoarchean basement terrane of the Western Block of the North China Craton. In this paper, three Archean plutons, namely the Dajitu, Banshentu and Haolaigou plutons, have been investigated. Based on the field observations, the major difference among these plutons is that many ultramafic–mafic enclaves are enclosed in the Dajitu and Banshentu plutons, whereas none occurs in the Haolaigou pluton. Geochemically, the Dajitu and Banshentu plutons are characterized by low SiO2 contents (56–67wt%), high MgO (1.9–7.1wt%), Cr (10–947ppm), Ni (2–274ppm) and Mg# (44–64) contents, negative Nb, Ta and Ti anomalies, high large ion lithophile elements (LILEs), with no or slightly negative Eu anomalies, similar to a typical Archean sanukitoid. New geochronological data indicate that the Dajitu and Banshentu plutons were emplaced at 2523±7Ma and 2480±20Ma, with inherited ages of 2606±19Ma and 2647±19Ma, respectively. In contrast, the Haolaigou pluton shows high SiO2 (68–71wt%), MgO, Mg# (46–55), Cr, and Ni contents, negative Nb, Ta and Ti anomalies, and high LILEs, with strongly positive Eu anomalies, high Sr and Ba concentrations and Sr/Y and La/Yb ratios, and low Y and HREEs abundances. It was emplaced at 2466±15Ma, with an inherited age of 2638±21Ma. The whole-rock ɛ Nd(t) and zircon ɛ Hf(t) values of the Haolaigou pluton are positive. The whole-rock T DM(Nd) and zircon T DM1(Hf) values range between 2.6 and 2.8Ga with a peak at ∼2.7Ga, indicating that the melt was generated by the partial melting of a subducted slab interacting with the overlying mantle wedge. The Dajitu pluton has Nd and Hf isotope characteristics identical to those of the Haolaigou pluton, implying that the two plutons have similar sources. It should be noted, however, that the Dajitu pluton displays sanukitoid characteristics, which are the result of interaction with ultramafic–mafic enclaves. The whole-rock ɛ Nd(t) and zircon ɛ Hf(t) values of the Banshentu pluton are mostly negative. The whole-rock T DM(Nd) and zircon T DM1(Hf) values of the pluton range between 2.7 and 2.9Ga with a peak at ∼2.8Ga, indicating that the pluton was generated from the melting of a lower crust. The sanukitoid characteristics of the pluton resulted from interactions with an ultramafic enclave. Taken together, these results with the geochronological geochemical data for other Archean rocks in this area, suggest that the Yinshan Block experienced significant crustal growth at 2.8–2.6Ga and further crustal reworking that led to strong magmatism at ∼2.5Ga. [ABSTRACT FROM AUTHOR]

Located in the northern margin of the North China Craton (NCC), the Bayan Obo Group is composed of low-grade metamorphic clastic rocks and carbonates unconformably overlying the Archean–Paleoproterozoic basement and is famous for its hosting of the world's largest REE ore deposit. It has long been debated whether the Bayan Obo Group was correlated with the Proterozoic sedimentary records of the Xiong’er and Yanliao rifts or whether it was an analog of the Paleozoic Sailinhudong Group. In this study, we present new U–Pb data from detrital zircons which constrain the maximum depositional ages of the Dulahala and Halahuogete formations of the Bayan Obo Group as 1822 ± 9 Ma and 1710 ± 29 Ma, respectively. Our geochronological and geochemical data suggest that the major provenance of the Dulahala and Jianshan formations was the Paleoproterozoic khondalites which were deposited during 2.0–1.95 Ga and metamorphosed during 1.95–1.82 Ga, whereas the sediments of the Halahuogete and Bilute formations were derived from various sources in the NCC. Combining our data with the pioneer's researches, it appears that the northern marginal rift system of the NCC resulted from two discrete rifting events, which were probably related to the initial intra-continental extension and the final breakup of the Columbia Supercontinent. [ABSTRACT FROM AUTHOR]