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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-ε Hf (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. [Display omitted] • Ancient zircon records confirmed the Mesoarchean juvenile crust in the Jiaodong. • Differences of zircons indicate a Neoproterozoic crust reactivation of Jiaodong. • Negative ε Hf (t) values confirmed few additions of subduction material to the Mesozoic crust. [ABSTRACT FROM AUTHOR]

Mafic dikes of mainly Early Cretaceous age (130–110 Ma) are widely developed on the Jiaodong Peninsula, China. Previous studies of the dikes, which have focused mainly on occurrences in the Jiaobei uplift and in the Sulu orogenic belt, have thoroughly examined their petrogenesis and geodynamic setting. This study identified four previously unknown mafic dikes (dolerite and lamprophyre) in southeastern Jiaolai basin (near Haiyang city), Jiaodong Peninsula. Detailed geochemical and geochronological analyses were conducted to determine the petrogenesis of the dikes and to infer their geodynamic setting. Zircon U–Pb dating by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) indicates that the dikes were emplaced at ~126 Ma. The dikes are characterized by low SiO2contents (44.3–52.3 wt.%), high contents of MgO (7.28–10.13 wt.%), Cr (267–652 ppm), and Ni (93–335 ppm), and high Mg#values (63–73); they are enriched in large ion lithophile elements (LILEs; Ba, K, and Sr), depleted in high field strength elements (HFSEs; Nb, Ta, P, and Ti), and are characterized by high (87Sr/86Sr)iisotope ratios (0.707226–0.708222), lowεNd(t) values (−12.3 to −13.6), and zirconεHf(t) values (−15.6 to −23.6). These features suggest that the dikes were derived from enriched subcontinent lithospheric mantle (SCLM). The wide range of Rb/Sr (0.04–0.18) and Ba/Rb (5–34) ratios, and the low and limited range of Dy/Yb (1.93–2.52) and K/Yb (5.71–11.99) ratios of the dikes indicate that the magmas originated from a low degree of partial melting of an amphibole- and phlogopite-bearing lherzolite in the spinel–garnet transition zone. The parental magma might have experienced fractionation of olivine and clinopyroxene during its ascent without significant crustal contamination. Evident depletion of Nb–Ta and Zr–Hf, low and limited range of Th/Yb ratios, elevated Ba/La ratios, constant chondritic Zr/Hf ratios, and a large range of Hf/Sm ratios further indicate that the mantle sources of the dikes were altered by carbonate-related metasomatism from subducted slab-derived fluids, which were most likely related to subduction of the Palaeo-Pacific plate during the Mesozoic. The mafic dikes in the southeastern Jiaolai basin resemble the arc-like mafic dikes in the Jiaobei terrain and the Sulu orogenic belt, and possibly indicate lithospheric thinning induced by slab rollback of the Palaeo-Pacific plate. [ABSTRACT FROM AUTHOR]

The Yemaquan skarn deposit in the northwestern part of the Qimantagh is located in the eastern Kunlun orogenic belt. The deposit is hosted in carbonate rocks, siltstones, and sandstones of the Cambrian–Ordovician Tanjianshan Group and Late Carboniferous Di'aosu Formation. These rocks are intruded by Triassic calc-alkaline granitoid that extended NW–SE. Three stages of mineralization have been identified, i.e., pre-ore stage, syn-ore stage, and post-ore stage. The prograde skarn stage, which corresponds to the pre-ore stage, is dominated by clinopyroxene and garnet. Clinopyroxene is much more abundant than garnet in the deposit and consists of three types of clinopyroxene in the deposit. In terms of the end-members diopside (CaMgSi 2 O 6 ), hedenbergite (CaFeSi 2 O 6 ), and johannsenite (CaMnSi 2 O 6 ), namely, type I (with an average composition of Di 92 Hd 7 Joh 1 ), type II (with an average of composition of Di 62 Hd 36 Joh 2 ), and type III (with an average composition of Di 24 Hd 54 Joh 22 ) occurred from the proximal intrusions to the distal wall rocks. Type I, II, and III clinopyroxenes are associated with copper–iron, iron, and zinc–lead mineralization, respectively. Garnet mostly occurred in the middle of exoskarn zonations and is associated with type II clinopyroxene. The distribution of the garnet in the skarn zonation could be explained by the stability fields of clinopyroxene, which is strongly dependent on composition. Based on mineral assemblages, the formation of type II and type III, comparative to type I clinopyroxene, is in more reduced condition in the distal skarn. Moreover sulfur isotope carried out on sulfide minerals from both the prograde and retrograde stages show a variable and wide range of δ 34 S values (− 6.9 to 4.2‰ δ 34 S), suggesting that the skarn-forming fluid may have been affected by the reduced wall rocks. The low garnet/clinopyroxene ratios observed at the deposit might be caused by the clinopyroxene composition variations and reduced wall rocks. [ABSTRACT FROM AUTHOR]

Abstract: The Guangou bauxite deposit in western Henan, China, is located in the North China Block and to the north of the North Qinling orogenic belt. The orebody is hosted within the lower member of the Carboniferous Benxi Formation, which overlies unconformably upon the Ordovician Majiagou Formation. In the lower member of the Benxi Formation, the bauxite orebody (with a diaspore–illite–anatase mineral assemblage) is sandwiched between underlying ferric clay (illite–hematite–goethite) and overlying top clay (kaolinite–quartz–goethite). According to field observations and geochemical evidence including trace- and rare-earth-element (REE) compositions, especially Zr/Hf ratios, the ferric clays were weathered from the underlying argillaceous limestones in the Majiagou Formation. During this weathering process, trace elements S, Zn, Ni, Cr, V, Sc, F, Ba, and Be are depleted; Li, Rb, and B are enriched; and Zr, Hf, Bi, Ta, Ga, Nb, and Th are relatively immobile. REEs exhibit evident differentiation with enrichment of La, Ce, Pr, and Nd and depletion of Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The bauxite formed in weak reducing, slightly basic water conditions according to the geneses of coexisting diaspore and anatase, and it was altered during the epigenetic and second exposure periods, forming kaolinite and goethite, respectively. Interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and REEs in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements. For instance, zircon, rutile, and anatase contain Zr, Hf, Nb, Ta, W, and U. Based on geochemical evidence, together with age data and chemical compositions of the detrital minerals, both distant igneous rocks in the plate margin and Paleozoic carbonates and Precambrian rocks inside North China Block provide the miscellaneous material for the bauxite ore and the top clay. [Copyright &y& Elsevier]

Abstract: The Dajia Salento-type bauxite deposit in western Guangxi is hosted within the Quaternary ferrallitic soil profile, and it formed via breaking up, weathering and oxidizing of Permian bauxite orebodies occurring as a semi-continuous layer in the upper Permian. Mineralogical analyses reveal that diaspore, hematite and kaolinite are the major minerals in bauxite ores with small amounts of anatase, chamosite, gibbsite, goethite, illite, zircon, quartz and pyrite. The ore texture and mineral assemblage reveal that the depositional/diagenetic environment of the Dajia bauxite was much close to phreatic environment. Both the ore texture and the morphology of zircon grains also indicate that most of the bauxitic soils were transported a short distance. Diaspore is suggested to be non-metamorphic in origin and mainly formed in a reducing condition of diagenetic environment, while kaolinite is the product of the in situ epigenetic replacement of alumina in diaspore by dissolved silica. Geochemical analyses indicate that Al2O3, Fe2O3, SiO2 and TiO2 are the main components of the bauxite ores and trace elements such as Zr, Hf, Nb, Ta, Th and U were enriched during the bauxitization process. Simultaneously, Zr vs. Hf and Nb vs. Ta show a high correlation. Geochemical indices such as Zr/Hf, Nb/Ta and Eu/Eu* (among others) denote that the magmatic rocks related to the Emeishan plume in western Guangxi and the carbonates in the underlying Maokou Formation provided the main sources of material for the bauxite ores. [Copyright &y& Elsevier]

Late Carboniferous bauxite is widely developed on the North China Craton (NCC), and is referred to as the "G" layer bauxite. The bauxite ores of the southern NCC are closely related to the tectonic evolution of the NCC and its neighboring North Qinling Belt (NQB) to the south. In this study, based on the geological and mineralogical observations, we used the U–Pb and Hf isotopes of detrital zircons and chemical compositions of detrital rutiles from the Gunziying and Shibanhe bauxite deposits, along the southern margin of the NCC to study the metallogenic process of bauxite ores and their tectonic implications. One and two bauxite ore layers were observed in the Gunziying and Shibanhe bauixte deposits, respectively. The bauxite ore is dominated by diaspore, illite, anatase, kaolinite, pyrite, zircon, and rutile. Analyses of detrital zircons revealed that the largest group (∼432–515 Ma, at a peak age of ∼450 Ma) is spread throughout the Late Carboniferous bauxite deposits, with εHf(t) values of −5.7–21.4, similar to the zircons from the NQB. Similarly, the detrital zircons with peak ages of ∼950 Ma and age clusters at ∼1.1 Ga, ∼1.3 Ga, and ∼1.8 Ga as well as those ranging in age from 635 to 797 Ma, also exhibited εHf(t) values similar to the zircons from the NQB. In addition, the results suggested that 62 (73%) and 75 (88.2%) of detrital rutiles showed metapelitic protoliths and amphibolite/eclogite facies temperatures, respectively, while 23 (27%) and 10 (11.8%) exhibited metamafic protoliths and granulite facies temperatures, respectively. Based on the results above, we propose that the provenance of the bauxite ores on the southern margin of the NCC is primarily from the NQB. The dominant contributors were the Neoproterozoic Kuanping Group and the Meso–Neoproterozoic Qinling Group. The Archean-Proterozoic metamorphic rocks in the paleo-uplifts of the NCC were also likely involved in the bauxite formation. A probable outline of the bauxite-formation process on the southern NCC, former weathered residuals and subsequent deposition, is proposed; and a reasonable interpretation that the NQB was accreted to the NCC in the Late Carboniferous and formed a northward lying slope basin within the NCC, is supported. Image 1 • New constraints on the source of the NCC bauxite ores are proposed. • Mainly material transport from the North Qinling and Kuanping Group. • Bauxitic formation most likely weathered residuals and deposited. • Late Paleozoic Tectonics resulted in the "G" bauxites throughout the NCC. [ABSTRACT FROM AUTHOR]

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