Search

The Jiajika rare metal deposit contains the largest area of granitic pegmatite-type rare metal deposits in China. The X03 vein is an immense rare metal deposit dominated by lithium, which was found in the deposit in recent years. The contact metamorphic belt of tourmalinization and petrochemistry is widely developed in its wall rocks, and the altered rocks formed contain Li and other rare metal mineralization. In this paper, the tourmaline found in the different rocks of the Jiajika X03 vein is divided into four types: two-mica quartz schist (Tur-Ⅰ), tourmaline hornfels (Tur-Ⅱ), tourmaline-bearing granite pegmatite (Tur-Ⅲ) and spodumene-bearing granite pegmatite (Tur-Ⅳ); their in situ major element, trace element and boron isotope data are systematically studied. The results show that all tourmalines in the Jiajika X03 vein deposit belong to the alkali group, and are schorl–Oxy/Fluor–schorl, dravite–Hydroxy-dravite and foitite–Oxy foitite solid solutions, among which Tur-Ⅰ are dravite, Tur-Ⅱ are foitite of hydrothermal origin and Tur-Ⅲ and Tur-Ⅳ are schorl of magmatic origin. The boron isotope values show that the boron involved the formation process of tourmaline mainly originates from the Majingzi S-type granite, and the boron isotope variations in tourmaline are controlled by melt fluid and Rayleigh fractionation. Moreover, there is a clear correlation between the B isotope value of tourmaline and the Li, Mn, Zn, Mg, and V contents, showing that these contents in tourmaline are good indicators of the mineralization type of pegmatite.

The heterogeneous carbonate reservoir is the most important exploration target in Sichuan basin. It is challenging to identify the potential flow units in the tight carbonate reservoir. High-resolution borehole resistivity image can reveal the dissolution features such as vugs or fractures in the pay zone. Operators in Sichuan Basin have acquired lots of borehole resistivity image using water-based mud imager in key exploration wells to identify potential reservoir. The oil-based mud has become increasingly popular in exploration and development because it reduces complex drilling practices reducing drilling costs. The new generation oil-based imager is used in these new wells. The borehole resistivity image can be obtained from both OBM (oil base mud) imager and WBM (water base mud) imagers. It is important to understand the response differences through the comparisons between different borehole imaging technologies in the same wellbore. The objective of this study is to understand the responses and refine the rule of oil-based mud borehole image interpretation in tight carbonate reservoir.The operator has logged both WBM and OBM imager in the same wellbore at different times. The WBM resistivity image is acquired in water-base mud conditions in the beginning. Then drilling fluid system was changed to OBM, and 200 meters were drilled further in the borehole. Finally, the OBM imager was logged in the hole. A comparison between the WBM resistivity images and OBM resistivity images are carried out. Increased understandings of the image log responses in this vuggy or fractured carbonated reservoir were obtained.The borehole resistivity image from WBM and OBM imager is highly correlatable over most of the logging interval as they both show similar resistivity response (bright / dark) on both images for the same geologic feature. The new generation OBM resistivity imager is proven to have similar applications as the WBM resistivity could offer. In fact, the OBM borehole images has higher resolution than the WBM borehole image in most of the intervals, especially in high resistivity formations. It was found that the responses of vugs or fractures can be interpreted slightly different in some intervals. Only the unfilled vug will have resistive response in OBM image while it will be very conductive in the WBM image because it was invaded by the resistive or conductive mud. The responses of induced fractures or natural fractures will be slightly different, which is influenced by formation conditions such as Rt/Rm. The induced fracture could be conductive or resistive under different logging conditions.This case study improved the understandings of the OBM imager response in tight carbonate reservoirs. These observations can be used as a reference for borehole image interpretation in similar reservoirs.

The modern Tianshan Mountains and their surrounding basins have mainly been shaped by the far field effects of the Cenozoic India-Asia collision. However, precollision topographic evolution of the Tianshan Mountains and its impacts on the Junggar and Turpan Basins remain unclear due to the scarcity of data. Detrital zircon U-Pb dating of 14 new and 23 published samples from Permian to Neogene strata in the northern Western Tianshan Mountains, northern and southern Bogda Mountains and Central Turpan Basin, are combined with sedimentary characteristics (lithofacies, petrofacies and paleocurrent data) to investigate the temporal and spatial changes in sediment provenances. Based on the age characteristics of the source rocks in the Tianshan Mountains, the detrital zircons are divided into three groups: pre-Carboniferous zircons, mainly from the Central Tianshan Mountains; Carboniferous to Permian zircons, mainly from the North Tianshan and Bogda Mountains; and Mesozoic zircons, mainly from syn-depositional volcanic activity. The topographic evolution of the Tianshan Mountains and their relation to the Junggar and Turpan Basins can be generally divided into six stages. (1) Positive-relief Tianshan and Bogda Mountains and a rifted marine basin formed during the Early Permian to early Middle Permian following late Carboniferous orogenesis, as evidenced by interbedded alluvial fan conglomerates and postcollisional extension-related volcanic rocks along the basin margins, by marine deposits far from the basin margins and by the predominance of Carboniferous to Permian detrital zircons. (2) Fluvial to lacustrine deposits in the modern southern Junggar and Turpan Basins are characterized by abundant pre-Carboniferous zircons and consistently northward-flowing paleocurrents, indicating the submergence of the Bogda Mountains and a contiguous Junggar-Turpan continental depression basin during the late Middle Permian to the Triassic. (3) The Bogda Mountains began to uplift in the Early Jurassic, resulting in opposing paleocurrent directions, a sudden increase in sedimentary lithic detritus and the dominance of Carboniferous to Permian detrital zircons along the southern and northern margins of this range. (4) In contrast to the uplift of the Bogda Mountains, the other parts of the Tianshan Mountains experienced gradual peneplanation from the Early Jurassic to the Middle Jurassic, as confirmed by widespread fluvial to lacustrine deposits, even inside the modern Tianshan Mountains, and by the dominance of pre-Carboniferous detrital zircons. (5) The dominance of Carboniferous to Permian zircons in the southern Junggar Basin suggests the West Tianshan Mountains were uplifted during the Late Jurassic, while the dominance of pre-Carboniferous zircons in the Central Turpan Basin indicates continuous peneplanation in the Eastern Tianshan Mountains. (6) The initial shape of the Tianshan Mountains-Junggar Basin-Turpan Basin system was constructed in the Late Jurassic but was modified in the Cenozoic by the India-Asia collision, resulting in much higher Western Tianshan and Bogda Mountains, low Eastern Tianshan Mountains and well-developed foreland basins. These Cenozoic changes were recorded by the rapid cooling of apatites, the dominance of Carboniferous to Permian zircons in the southern Junggar Basin and northern Turpan Basin, and the dominance of pre-Carboniferous zircons in the Central Turpan Basin.

Zircon U Pb analyses of granitic gneisses from the gneiss domes (Xiaru, Mabja, Lhagoi Kangri, and Kangmar)within the Tethyan Himalaya and from the High Himalaya (Gyirong, Yadong, and Namche Barwa)yield that their protolith ages range from 509 Ma to 429 Ma. Similar to the Himalayan Cenozoic leucogranites, the Paleozoic granites are characterized by (1) high SiO2 (69.9–77.0 wt%), Al2O3 (12.4–16.1 wt%), K2O + Na2O (5.8–10.3 wt%) with K2O/Na2O > 1.0 and A/CNK > 1.0; (2) large variations in Rb (166–851 ppm), Sr (20–172 ppm), Ba (27–1474 ppm) and Rb/Sr ratios (1.0–38.3); (3) low degrees of LREE over HREE fractionation with (La/Yb)N

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 SiO2 + Fe2O3T, and varying contents of Al2O3, 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 δ18OV-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.

Potassic high Ba-Sr granitoids are widely distributed over collisional orogenic belts worldwide, however, their magma sources and petrogenetic processes are still debated. To better understand them, we collected a suite of Paleogene high Ba-Sr granitoids in the Jianchuan Basin, southeast Tibet. Based on the mineralogical compositions, major and trace element geochemistry, and age of formation, we subdivide them into two groups: intermediate series and granitic series. LA-MC-ICP-MS zircon U-Pb analyses show that the intermediate series crystallized at 33.8–36.9 Ma, similar to or slightly earlier than the granitic rocks with crystallization ages of 33.1–34.0 Ma. New geochemical and zircon Hf isotopic results, in combination with previous results, support an enriched mantle source for the high Ba-Sr intermediate rocks, and a mixed source of enriched mantle and lower crust for the granitic ones. We suggest that partial melting of enriched mantle with fractional crystallization of mafic minerals produced the potassic high Ba-Sr intermediate series. Meanwhile, the juvenile heat from such magma induced melting of thickened lower crustal materials which together with magma from mantle accounted for source of the granite series. The high Ba-Sr intermediate rocks have nearly identical major and trace element, and isotopic signatures as Archean sanukitoids, thus offer a potential constraint on the formation mechanism for the sanukitoids. Our study supports that the emergence of the sanukitoids requires a sediment-metasomatized mantle and thus indicates the onset of crustal recycling into the mantle.

Iron, Cu and Zn stable isotope systems are applied in constraining a variety of geochemical and environmental processes. Secondary reference materials have been developed by the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), in collaboration with other participating laboratories, comprising three solutions (CAGS-Fe, CAGS-Cu and CAGS-Zn) and one basalt (CAGS-Basalt). These materials exhibit sufficient homogeneity and stability for application in Fe, Cu and Zn isotopic ratio determinations. Reference values were determined by inter-laboratory analytical comparisons involving up to eight participating laboratories employing MC-ICP-MS techniques, based on the unweighted means of submitted results. Isotopic compositions are reported in per mil notation, based on reference materials IRMM-014 for Fe, NIST SRM 976 for Cu and IRMM-3702 for Zn. Respective reference values of CAGS-Fe, CAGS-Cu and CAGS-Zn solutions are as follows: δ56Fe = 0.83 ± 0.06 and δ57Fe = 1.20 ± 0.12, δ65Cu = 0.57 ± 0.05, and δ66Zn = -0.79 ± 0.12 and δ68Zn = -1.65 ± 0.24, respectively. Those of CAGS-Basalt are δ56Fe = 0.15 ± 0.05, δ57Fe = 0.22 ± 0.05, δ65Cu = 0.12 ± 0.07, δ66Zn = 0.17 ± 0.11, and δ68Zn = 0.34 ± 0.21 (2s).

The concentrations and isotopic geochemistry of Li are potentially useful geochemical tracers of geological processes. To fully utilize Li isotopes as geochemical tracers, it is necessary to characterize the Li isotopic compositions of the various geological reservoirs. However, the Li isotopic composition of the juvenile lower crust is currently poorly constrained. Given that lithospheric architecture of the Tibetan Plateau includes Indian upper/lower crust, Tibetan upper/lower crust and juvenile lower crust, it is necessary to determine the Li isotopic composition for each geological endmember underneath southern Tibet. Among them, the juvenile lower crust was formed directly by underplating of mantle-derived basaltic magma, which is likely to be the critical factor to control the Cu-Au mineralization in southern Tibet and is responsible for crustal thickening beneath southern Tibet. Here, we report the Li concentration and isotopic composition of the juvenile lower crust in southern Tibet. Based on whole-rock major element, trace element, and Sr–Nd–Pb isotopic data, we infer that the Yeba basalts and Gangdese gabbros were derived from partial melting of metasomatized lithospheric mantle, and have compositions similar to the juvenile lower crust. In contrast, the Dianzhong andesites and Gangdese diorites originated from partial melting of the juvenile lower crust. Therefore, these units may be considered representative of the juvenile lower crust. The juvenile lower crust has Li concentrations of 7.1–37.2 ppm (mean = 15.4 ppm), consistent with the Li concentration for the lower crust (13 ppm). Li isotopic compositions (δ7Li) vary from +0.8‰ to +6.6‰ (mean = 3.0‰), similar to values for the EMI/EMII mantle. The Li isotopic compositions of the analyzed samples were not significantly affected by alteration, metamorphism, crustal assimilation, or magmatic differentiation, and therefore represent the isotopic compositions of the juvenile lower crust. The Li systematics of the juvenile lower crust may be attributed to partial melting of subcontinental lithospheric mantle that has undergone metasomatism by Li-rich fluids derived from subducted oceanic crust and marine sediments. Our study also demonstrates near-identical Li isotopic compositions for juvenile lower crust and metasomatized lithospheric mantle, resulting from the lack of Li isotope fractionation during basalt generation and differentiation.

Early Jurassic plutonic rocks from the Central Lhasa block that range from gabbro to granite yield similar 206Pb/238U ages ranging from 187.6 Ma to 196.0 Ma. Gabbros and diorites are characterized by similar radiogenic 87Sr/86Sr(t) ratios that range from 0.7053 to 0.7060, unradiogenic eNd(t) values ranging from −4.2 to −2.5 and eHf(t) values ranging from −8.8 to −2.8. Compared with the intermediate to mafic rocks, the granites have much higher 87Sr/86Sr(t) ratios, from 0.7102 to 0.7127, and lower eNd(t) values, from −8.7 to −7.5, and eHf(t) values from −11.9 to −7.5. Elemental and isotopic data suggest that the gabbros were derived from a melt-modified subarc mantle, diorites represent derivatives produced by hornblende fractional crystallization of gabbros, and granites were generated by the melting of ancient crustal basement rocks. Combined with literature data, these results suggest that the Central Lhasa block, as well as parts of the Southern and Northern Lhasa blocks, also contains ancient crystalline basement rocks.

Titanite, one of the major accessory phases in middle to lower crustal rocks, could play an important role in shaping trace element as well as radiogenic isotope compositions in amphibolite-derived melts. Petrographic, zircon U/Pb, whole-rock element and isotope (Sr and Nd) data on a suite of leucosomes, and titanite Nd isotope compositions from the migmatitic amphibolite complex, southern Liaoning, indicate that (1) the amphibolite with a protolith age of ~2450 Ma underwent low-degree partial melting at ~160 Ma and produced two groups of leucosome; (2) these leucosomes preserved a large magnitude of Nd isotope disequilibrium with up to ~10 epsilon units of difference with respect to their sources; (3) differential dissolution of titanite during partial melting might lead to negative correlations between Nd isotope compositions and respective Ti or V contents (proxy of the amount of titanite presented). These data indicates that during low-degree partial melting of mafic rocks, titanite stays as a residue phase due to either unfavorable texture or melting (temperature or fluid) conditions and leads to the development of melts with depletion in Ti-affinity elements, REE, and a large positive shift in Nd isotope compositions. Similar to other accessory phases (e.g., zircon, apatite, and monazite) in metasedimentary sources, this contribution presents another case that could be common in high-grade metamorphic terranes in which titanite could be a key phase that controls key trace element (e.g. Nb Ta, V, and REE) budget and Nd isotope compositions in melts derived from low-pressure melting of amphibolite or mafic rocks in various tectonic environments.

Iron oxide – apatite (IOA) and skarn Fe deposits are important sources of Fe in China. During the Mesozoic, a large number of large IOA and skarn Fe deposits formed in the Middle–Lower Yangtze River Metallogenic Belt (MLYRMB) in a short period. These deposits genetically show a close spatial relationship to Triassic evaporite layers. In this study, the S isotope values of IOA deposits and Fe skarn deposits in the MLYRMB were collected and summarized. Most of the sulfides from Fe deposits have higher S isotope values (5–10‰), and the sulfates have S isotope values (17–21‰) that are similar to those of the evaporite layers (28–30‰), indicating the involvement of the evaporite layers. The effects of the evaporite layers on the mechanism of Fe ore formation are discussed. Evaporite layers are the most important oxidation barrier in the formation of Fe ores, as they can oxidize Fe2+ to Fe3+ in magmatic melts and magmatic-hydrothermal fluids, promoting Fe accumulation. Evaporite layers can also provide Na, Ca, K, Cl, and other agents of mineralization that facilitate the formation and transformation of Fe-bearing fluids and cause the deposits to display large-scale Na and Cl alterations. When sulfate from evaporite layers oxidizes Fe2+ to Fe3+, S6+ is reduced to S2−, becoming a major sulfur source for the formation of either sulfide ores or pyrite deposits after Fe mineralization. Sulfate (gypsum) from evaporite layers could be activated and transferred to the upper or side part of the ore system, forming anhydrite/gypsum ores (veins). Therefore, pyrite, anhydrite, and Fe ores often appear in single deposit.

In the Borong Gneiss Dome and Malashan Gneiss Dome within the Tethyan Himalaya, zircon U Pb ages and whole-rock geochemical data demonstrate that at least two episodes of leucogranite formed at 19.8–19.4 Ma and 18.6–18.5 Ma, respectively. Each of them contains at least two suites of granite: two-mica granite and garnet-bearing leucogranite. Although the two types of granites are characterized by distinct element geochemistry and mineral compositions, they show similar Sr-Nd-Hf isotope ratios and regular variations in the compositions of whole-rock elements. From two-mica granite to garnet-bearing leucogranite, SiO2, Na2O, Rb, Nb, and Ta contents and Rb/Sr ratios increase; in contrast, Al2O3, CaO, MgO, FeO, TiO2, Sr, Ba, Eu, Zr, U, Th, light rare earth elements (LREEs) and Sc contents, as well as Zr/Hf and Nb/Ta ratios, decrease. Such systematic variations imply that two-mica granite and garnet-bearing leucogranite are cogenetic and that two-mica granite represents the more primary melt, whereas garnet-bearing leucogranite is a more evolved melt. During granitic magma evolution, fractional crystallization induces substantial changes in the melt structure and in turn major changes in the dissolution behavior of accessory phases (e.g., zircon, monazite, and apatite) and the geochemistry of key trace elements. Such changes might be the key factors that resulted in the subordinate W-Sn-Nb-Ta-Be anomalies in the more evolved granites, which implies that the Himalayan Cenozoic leucogranites have high potential to produce economic rare metal deposits.

The Jiajika lithium (Li) deposit in Sichuan Province is the largest pegmatite-type Li deposit in China. The petrogenesis and metallogenesis of the Jiajika granitic pegmatites remain debatable. This study presents the Li isotopic compositions of two-mica granites, Li-rich and Li-poor pegmatites, and muscovites in Li-poor and Li-rich pegmatites to unravel the Li enrichment mechanism in the Jiajika deposit. The two-mica granites have a lower average δ7Li values than those of the Li-rich and Li-poor pegmatites. The Li contents of the two-mica granites are almost the same as those of the Li-poor pegmatites but are much lower than those of the Li-rich pegmatites. Muscovites in the Li-rich pegmatites have higher average Li contents and δ7Li values than those of the Li-poor pegmatites. All these results indicate the Jiajika granitic pegmatites were the final products of the extreme fractional crystallization of two-mica granitic magmas rather than direct anatectic melts, and that the Li-poor pegmatites derived from early differentiation of the two-mica granitic magmas before they evolved into Li-rich pegmatites during the late stage of magmatic differentiation. The lower average δ7Li values of the more evolved Li-rich pegmatites compared with the Li-poor pegmatites may have been caused by fluid exsolution and kinetic diffusive fractionation during melt-fluid separation. We discovered that fluid exsolution during melt-fluid separation can cause significant Li isotopic fractionation, with 7Li enriched in a H2O-poor silicate-rich melt system. Considering the crystallization ages of the two-mica granites and granitic pegmatites and other geochemical evidence (e.g., major- and trace-element compositions), the magmatic differentiation and fluid exsolution in the late stage of the granitic magma evolution together with the Li-rich surrounding strata led to the multistage enrichments in lithium, thus contributing to the formation of the Jiajika large Li deposit.

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.

The Paleo-Tethyan tectonic evolution of north-central Tibet remains controversial, particularly regarding the nature and extension of associated sutures. The Yushu melange, located in the junction part of the western Jinshajiang, the southern Jinshajiang and the Ganzi–Litang sutures, is a key area to reveal the Paleo-Tethyan tectonics of this area. This study presents new geochronological and geochemical data for the Zhimenda volcanic suite of the Yushu Melange. These rocks preserve a record of back-arc magmatism along the northern margin of the North Qiangtang Block. The Zhimenda volcanics are composed of ignimbrite, basalt, and porphyritic tuff intercalated with terrigenous clastic rocks. Zircon 206 Pb/ 238 U ages of the ignimbrites indicate they formed at ~ 254 Ma. The basalts are relatively enriched in large-ion lithophile elements and depleted in high field strength elements. Their high MgO, Ni, and Cr contents, relatively high Sm/Yb and Rb/Nb values, and positive zircon e Hf (t) and bulk e Nd (t) values suggest they were derived from the partial melting of a depleted subcontinental lithospheric mantle source metasomatized by hydrous fluids. The Zhimenda basalts are geochemically similar to back-arc basin basalts in the Okinawa Trough. They were erupted related to subduction of the Longmuco–Shuanghu Paleo-Tethyan oceanic plate beneath the North Qiangtang Block. We propose that the Yushu Melange converges with the Ganzi–Litang Suture Zone to the east, rather than with the Jinshajiang Suture Zone to the southeast, and that a huge Permian trench–arc–back-arc system developed in north-central Tibet.

The lithium isotopic compositions of adakitic rocks and K-rich volcanic rocks in southern Tibet range from + 1.3‰ to + 7.5‰ and − 4.9‰ to + 3.5‰, respectively. The subduction of the Indian Plate beneath the Lhasa Terrane means that traditional lithium isotopic compositions of various reservoirs are unable to explain the aforementioned δ7Li data. Therefore, it is necessary to determine the Li isotopic compositions of the different geological endmembers underneath southern Tibet. Here, we report the lithium isotopic composition and concentration of Indian upper and lower continental crust. On the basis of whole-rock major and trace element data and Sr–Nd–Pb isotope data, leucogranites from Luozha and Longzi are considered as representative of Indian upper crust, whereas two-mica granites from Quedang and Dala and granulites and gneisses from Nyalam are considered as representative of Indian lower crust. The Li concentration of Indian upper crust varies from 23 to 45 ppm with a mean of 34 ppm, consistent with a weighted mean Li concentration for the upper crust of 35 ± 11 ppm. In contrast, the Li abundance of Indian lower crust is estimated to be 33–84 ppm with a mean of 58 ppm, much higher than the average Li concentration for the lower crust of ~ 8 ppm because of the high modal abundance of biotite and muscovite. The Li isotopic compositions (+ 0.9‰ to + 5.6‰) of Indian upper continental crust are relatively heavy compared with the average Li isotopic composition of upper continental crust. On the other hand, the Li isotopic compositions of Indian lower continental crust (− 4.4‰ to − 0.1‰) are lighter than those of Indian upper continental crust. The isotopically heavy signature of Indian upper crust is produced by high-δ7Li fluids released from the Indian lower crust slab, whereas the lighter signature of Indian lower crust is generated by the partial melting of residual Indian lower crust slab during metamorphic dehydration of Indian lower crust.

Geochronological investigation on gneisses of granitic to leucogranitic compositions in Cuona, south Tibet, reveal that their protoliths formed at 808.8 ± 7.9–816.4 ± 3.4 Ma and 855.8 ± 7.0 Ma, respectively. Zircon rims from the granitic gneiss record a metamorphic age of 739.4 ± 4.3 Ma. Lu-Hf isotopic analyses on zircon grains with Neoproterozoic ages yield negative eHf(t) values from −9.0 to −4.2, and the corresponding two-stage Hf model ages are 1965–2228 Ma. Whole-rock geochemical data indicate that all granitic gneisses are K-riched calc-alkali series. These new data together with literature data show that (1) the Himalayan terrane experienced an episode of Neoproterozoic magmatism at 850–800 Ma; (2) the Neoproterozoic magma of granitic compositions were derived from partial melting of ancient crusts, possibly due to the thermal perturbation related with the breakup of the Rodinia supercontinent.

Recent studies in the Xiaru and Malashan gneiss dome of the Tethyan Himalaya, southern Tibet identify that Xiaru and Paiku tourmaline-bearing leucogranite dike formed at ~ 28–29 Ma. Together with ~ 28 Ma Kuday garnet-bearing leucogranites, it is demonstrated that the Himalayan orogenic belt experienced a major episode of crustal melting in the Mid-Oligocene. Geochemical data indicate that three suites of leucogranite are characterized by large variations in the major and trace element compositions as well as Sr–Nd isotope systematics, which could be explained by combined fractional crystallization and relative contributions of micas and accessory phases dissolved into a crustal melt during decompressional melting of metapelitic rocks. Documentation of Oligocene partial melting of crustal rocks could indicate that the exhumation of deep crustal rocks in the Himalayan orogenic belt could have started as early as Oligocene.

Southern Hunan Province, South China, is located in the central part of the Qin–Hang metallogenic belt and is characterized by abundant Cu–Pb–Zn and W–Sn polymetallic ore deposits. The Cu–Pb–Zn deposits are associated with Jurassic granodiorite porphyries whereas the W–Sn deposits occur within Jurassic granite porphyries. Here we present geochronologic and geochemical data for the Tongshanling Cu–(Mo)–Pb–Zn deposit and the Weijia W deposit in the district of Tongshanling, southern Hunan. Zircon U–Pb dating and molybdenite Re–Os geochronology indicate that the emplacement of the Tongshanling granodiorite porphyry and the associated Cu mineralization occurred at 162–160 Ma, slightly earlier than the formation of the Xianglinpu granite porphyry and associated W mineralization at 159–158 Ma. The Tongshanling granodiorite is high-K calc-alkaline, weakly peraluminous, and weakly fractionated with zircon e Hf (t) values of − 15.1 to − 5.6. In contrast, the Xianglinpu granite is alkaline, peraluminous, and highly fractionated, with e Hf (t) values of − 9.5 to 0.9. Our data indicate that the Tongshanling granodiorite is relatively oxidized and was formed by the partial melting of Paleoproterozoic crustal material with inputs of mafic magma which was derived from a subduction-modified lithospheric mantle. In contrast, the Xianglinpu granite porphyry is relatively reduced and was formed by direct interaction between the crust and asthenospheric mantle. The difference in magma generation and tectonics is considered to have resulted in the different types of mineralization associated with these two intrusive bodies.

Southeast China is characterized by widespread Mesozoic igneous rocks, which have drawn a great deal of attention in recent decades because of their tectonic significance and related large-scale mineralization. Among these igneous rocks, The Tangquan pluton in Southwest Fujian Province is the only adakitic pluton that has been discovered within the Cathaysian Block. It is mainly composed of a central unit of granodiorite with peripheral granodioritic porphyries. Two medium-grained granodiorite samples have zircon U-Pb ages of 162.2 ± 2.0 Ma and 163.0 ± 1.4 Ma, indicating intrusion in Middle Jurassic times. Adakite-like geochemical features of the pluton include high Sr/Y (46.7) and (La/Yb)N (25.5) values, and low Y (12.2 ppm) and Yb (1.04 ppm) abundances. All samples have low eNd(t) values (average −9.49) and high initial 87Sr/86Sr ratios (average 0.708242). These results suggest that the adakitic rocks were generated by partial melting in thickened crust. The Tangquan pluton probably formed during the extrusion collision of microcontinents within the Cathaysian Block related to subduction of the Pacific Plate, which caused crustal thickening and partial melting of Neoproterozoic crust with arc-like magmatic characteristics. Because the extrusion collision occurred between microcontinents in an intraplate (Cathaysian Block) setting, the effects of the extrusion collision were not as strongly felt as those involved in the Jiangshan-Shaoxing Fault along which numerous adakitic rocks were emplaced with related porphyry-type copper deposits. Copyright © 2016 John Wiley & Sons, Ltd.

U–Pb ages and Hf isotopic data from detrital zircons of Gaoligongshan metamorphic complex and the Carboniferous Menghong Group and igneous zircons from intrusions constrain the origin, tectonic affinity (East Gondwana), crustal evolution processes, and the properties of regional high-grade metamorphic rocks in the Tengchong block of southeastern China. Three granites intruded into the Tengchong block at ~ 72 Ma, ~ 114 Ma and ~ 122 Ma. Detrital zircons range in age from Archean to Late Ordovician for both the Carboniferous Menghong Group and the Gaoligongshan metamorphic complex. Analyses for these two units yield similar age clusters at ~ 2.5 Ga, ~ 1.6 Ga, ~ 1.17 Ga, ~ 0.95 Ga, and ~ 0.65–0.5 Ga as well as parallel Hf isotopic distributions. The protolith of the studied Gaoligongshan complex in the Tengchong block should deposit in the Late Paleozoic. Detrital zircon age distribution patterns of the Carboniferous Menghong Group and the Gaoligongshan complex show dominant younger Grenvillian age peaks at ~ 0.95 Ga, indicating the strong paleogeographic connection of the Tengchong block with the Indian margin. The Hf isotopic comparison of both detrital and igneous dated-zircon shows that the Tengchong block can be represented by the post-Archean Indian continental margin. After 250 Ma, the intensive magma events affected the region and considerable juvenile material accreted to the crust of the Tengchong block.

The Chuanlinggou Formation is the lower formation of the Changchengian System, and hosts sedimentary iron deposits (marine oolitic ironstones) of the North China Craton (NCC). To determine the age of the iron deposits, and provide insight into the crustal growth of the craton, laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)U-Pb and in situ Hf isotope analysis were performed on detrital zircon grains. Samples were taken from the roof sand-shale of the sedimentary iron deposits at Jiangjiazhai and Pangjiapbu. Overall, 186 detrital zircon grain U-Pb ages yield three major age populations, with weighted average ages of 2450 Ma, 1848 Ma, and 1765 Ma, respectively. Four younger ages from magmatic zircon grains were obtained, ranging from 1694 to 1657 Ma. Combined with observations from published studies, the results define the lower limit for the age of the Chuanlinggou Formation, and constrain the age of the sedimentary iron deposits (marine oolitic ironstone) close to 1650 Ma. The peak ages of 1848 Ma and 2450 Ma define the major collisional events of the NCC. The age of 1765 Ma can be linked to the age range of the widespread mafic dyke swarms that represent the rifting of the NCC within the Columbia supercontinent. Detrital zircon grains from the Chuanlinggou Formation form two obvious groups, with different &epsilon, Hf (t) values ranging from &minus, 1 to &minus, 8 and from +1 to +8, which correspond to the U-Pb age ranges of 1.7&ndash, 1.9 Ga and 2.3&ndash, 2.6 Ga, respectively. They have a similar two-stage Hf model age peak at 2.65&ndash, 2.85 Ga, suggesting that the source rocks for each of these events were derived from the recycling of ancient crust. The source rocks of the older group of zircon grains might be derived from juvenile crust with a short reworking period. The critical crust&ndash, mantle differentiation event might happen during the period of 2.65&ndash, 2.85 Ga, marking the most significant stage of the crustal growth in the NCC.

The Dala diabase intrusion, at the southeastern margin of the Yardoi gneiss dome, is located within the outcrop area of the ~ 132 Ma Comei Large Igneous Province (LIP), the result of initial activity of the Kerguelen plume. We present new zircon U-Pb geochronology results to show that the Dala diabase was emplaced at ~ 132 Ma and geochemical data (whole-rock element and Sr-Nd isotope ratios, zircon Hf isotopes and Fe-Ti oxide mineral chemistry) to confirm that the Dala diabase intrusion is part of the Comei LIP. The Dala diabase can be divided into a high-Mg/low-Ti series and a low-Mg/high-Ti series. The high-Mg/low-Ti series represents more primitive mafic magma compositions that we demonstrate are parental to the low-Mg/high-Ti series. Fractionation of olivine and clinopyroxene, followed by plagioclase within the low-Mg series, lead to systematic changes in concentrations of mantle compatible elements (Cr, Co, Ni, and V), REEs, HFSEs, and major elements such as Ti and P. Some Dala samples from the low-Mg/high-Ti series contain large ilmenite clusters and show extreme enrichment of Ti with elevated Ti/Y ratios, likely due to settling and accumulation of ilmenite during the magma chamber evolution. However, most samples from throughout the Comei LIP follow the Ti-evolution trend of the typical liquid line of descent (LLD) of primary OIB compositions, showing strong evidence of control of Ti contents by differentiation processes. In many other localities, however, primitive magmas are absent and observed Ti contents of evolved magmas cannot be quantitatively related to source processes. Careful examination of the petrogenetic relationship between co-existing low-Ti and high-Ti mafic rocks is essential to using observed rock chemistry to infer source composition, location, and degree of melting.

Zircon U–Pb dating and whole-rock geochemical data for Carboniferous–Permian (meta-) sedimentary sequences, igneous rocks, and Precambrian amphibolite in the eastern Xing-Meng Orogenic Belt (XMOB) were used to constrain the final stage evolution and the position of closure of the Paleo-Asian Ocean (PAO). Detrital zircons from Late Paleozoic strata range in age from Archean to Late Paleozoic, with major age groups at ~ 1.0–0.7 Ga and ~ 0.5–0.25 Ga in the northern part and at ~ 2.7–2.5 Ga, ~ 2.1–1.8 Ga, and ~ 0.5–0.25 Ga in the southern part of the XMOB. Striking changes in zircon age distribution patterns indicate inputs to these strata were separated by the Paleo-Asian Ocean (PAO) in the Late Paleozoic. The PAO closed along the Solonker–Linxi suture. The Late Paleozoic formation ages (~ 346 Ma, ~ 303 Ma, and ~ 269 Ma) of the igneous rocks with arc-like geochemical features south to the PAO, together with previously published data on the regional igneous rocks and ophiolites, indicate double-side subduction of the PAO in the Late Paleozoic.

Lithium concentrations and isotopic compositions of 38 carbonatites and associated syenites from the Maoniuping, Lizhuang, and Dalucao in western Sichuan, along with previously published and new Pb–Sr–Nd–C–O isotope data and whole-rock analyses, are used to constrain their mantle source and genesis. Carbonatites and syenites are characterized by extremely varying Li concentrations (0.8–120 ppm) and highly variable Li isotopic compositions (−4.5‰ to +10.8‰). Among them, the majority of the carbonatites and syenites have δ7Li values between +0.2‰ and +5.8‰, which overlap with the reported values for MORB and OIB; 3 carbonatites have higher δ7Li values between +8.7‰ and +10.8‰; 5 carbonatites and 4 syenites have lighter δ7Li values between −4.5‰ and −0.3‰. These highly variable δ7Li compositions could not have been produced by diffusive-driven isotopic fractionation of Li and thus may record the isotopic signature of the late Proterozoic subcontinental lithospheric mantle (SCLM). This paper demonstrates the existence of anomalous δ7Li within the late Proterozoic subcontinental lithospheric mantle, suggesting that the ancient SCLM beneath western Sichuan was modified by interaction with fluids derived from the subducted oceanic crust and marine sediments. The modeling curves of fluids derived from a dehydrated slab (ratios: AOC80–SED20 to AOC40–SED60) with a representative mantle composition can account for the majority of lithium compositional variations. Some samples with unusual Pb–Sr–Nd–O isotopic compositions and highly variable δ7Li compositions are affected by significant involvement of marine sediments in their source region, not contaminated by crustal materials. The carbonatites and syenites in western Sichuan were generated by the partial melting of subcontinental lithospheric mantle, which was metasomatized by the Li-rich fluids derived from the subducted oceanic crust and marine sediments. This melting was most likely triggered by a Cenozoic asthenospheric mantle diapir related to Indian-Asian continental collision and post- or late-collisional stress relaxation in the Oligocene.

The Baoshan block is one of the important members in the southeastern margin of the Tibetan Plateau. Cambrian to Jurassic (meta-) sedimentary strata and their metamorphic counterparts were well preserved in the eastern part of the Baoshan block. Zircon U–Pb dating, trace elements, and Hf isotope data for both the Cambrian to Jurassic (meta-) sedimentary sequences and the Lincang granite were used to deduce the provenance of sediments and crustal affinity with eastern Gondwanaland. The Lincang granite outcropped in the Fengqing area is typical S-type, with crystallization age of ~ 230 Ma and narrow range of zircon e Hf (t) values from − 15.5 to − 10. Detrital zircons from Paleozoic strata range in age from Archean to early Paleozoic, with age peaks at ~ 2.5, ~ 0.95, and ~ 0.6 Ga. Triassic age peak (~ 230 Ma) was also detected in the Jurassic strata. Detrital zircon e Hf (t) values exhibit a wide range from negative to positive for each of the four major age groups, showing the host magma of zircons from these groups have diverse sources. The Baoshan block should be along the Indian margin as the Qiangtang, Tengchong and Simao–Indochina blocks in Early Paleozoic based on the provenance analyses. Sediment inputs eroded from both the Lincang granite and the coeval igneous rocks in the Baoshan and Gongshan blocks were the dominant contributions to the Jurassic strata after the amalgation of the Baoshan and Simao–Indochina blocks. Tectonic processes linking dispersion of the Baoshan–Sibumasu terrane from the Gondwana supercontinent to the collision with the Simao–Indochina block and the deposition of the Cambrian to Jurassic sedimentary sequences were reconstructed.

A large number of Paleoproterozoic borate deposits are hosted by the lower units of a volcanic-sedimentary sequence in Liaoning Province, northeastern China, and are a major source of boron in China. The ore-bearing wall rocks in the deposits are serpentinized ultrabasic rocks and carbonates, with layered leptynites, leptites, amphibolites, and migmatites adjacent to the ore. Both the borate ores and country rocks contain tourmaline, although the country rocks have much lower abundances of the mineral. Based on in situ boron isotope measurements using laser ablation–multi-collector–inductively coupled plasma–mass spectrometry (LA–MC–ICP–MS), boron isotope data show that: (1) δ 11 B values of borate ores range from + 6.8‰ to + 13.9‰ (mean + 10.8‰); (2) tourmalines from the borate ores have δ 11 B values from + 9.5‰ to + 12.7‰; and (3) the wall rocks within the borate ores yield slightly lower δ 11 B values ranging from + 5.7‰ to + 7.6‰, and those outside the deposits from − 9.9‰ to − 5.9‰. Positive δ 11 B values in borates as well as in tourmalines inside the mining area indicate that boron in these Paleoproterozoic borate deposits was derived from marine evaporites. δ 34 S V-CDT (where V-CDT is Vienna Canyon Diablo Troilite) values of borate ores, serpentinized marbles, and anhydrites range from + 16.1‰ to + 24.7‰, whereas δ 13 C V-PDB (where V-PDB is Vienna Pee Dee Belemnite) values of marbles range from + 3.2‰ to + 5.9‰. These isotopic characteristics are interpreted to reflect formation in a marine evaporative environment. LA–MC–ICP–MS zircon weighted 207 Pb/ 206 Pb ages of leptite and serpentinized olivine basalt from the hanging wall of the borate deposits are 2139 ± 13 Ma and 2130 ± 19 Ma, respectively. Therefore, the (~ 2.2 Ga) borate deposits may have originated from marine evaporative boron-bearing sediments, which were interbedded within bimodal volcanic rocks during the early stages of development of the Liaoji rift.

Magnetite is common in many ore deposits and their host rocks, and is useful for petrogenetic studies. In the Khetri copper belt in Rajasthan Province, NW India, there are several Cu-(Au, Fe) deposits associated with extensive Cu ± Fe ± Au ± Ag ± Co ± REE ± U mineralization hosted in phyllites, schists and quartzites of the Paleoproterozoic Delhi Supergroup. Ore bodies of these deposits comprise dominantly disseminated and vein-type Cu-sulfide ores composed of chalcopyrite, pyrite, and pyrrhotite intergrown with minor magnetite. There are also Fe-oxide ores with minor or no Cu-sulfides, which are locally overprinted by the mineral assemblage of the Cu-sulfide ores. In addition to the Fe-oxide and Cu-sulfide ores, the protolith of the Delhi Supergroup includes banded iron formations (BIFs) with original magnetite preserved (i.e. magnetite-quartzites) and their sheared counterparts. In the sheared magnetite-quartzites, their magnetite and quartz are mobilized and redistributed to magnetite and quartz bands. Trace elemental compositions of magnetite from these types of ores/rocks were obtained by LA-ICP-MS. The dataset indicates that different types of magnetite have distinct concentrations of Ti, Al, Mg, Mn, V, Cr, Co, Ni, Zn, Cu, P, Ge and Ga, which are correlated to their forming environments. Magnetite grains in magnetite-quartzites have relatively high Al (800–8000 ppm), Ti (150–900 ppm) and V (300–600 ppm) contents compared to those of BIFs in other regions such as the Yilgarn Craton, Western Australia and Labrador, Canada. The high Al, Ti and V contents can be explained by precipitation of the magnetite from relatively reduced, Al–Ti-rich water possibly involving hotter, seafloor hydrothermal fluids derived from submarine mafic volcanic rocks. Magnetite in sheared magnetite-quartzites is generally irregular and re-crystallized, and has Ni, Mn, Al, Cu and P contents lower than the magnetite from the unsheared counterparts, suggesting that the shearing-related mobilization is able to extract these elements from original magnetite. However, elevated contents of Ti, V, Co, Cr, Ge and Mg of the magnetite in the sheared magnetite-quartzites can be ascribed to involvement of external hydrothermal fluids during the shearing, consistent with occurrence of some hydrothermal minerals in the samples. Compositions of magnetite from the Fe-oxide and Cu-sulfide ores are interpreted to be controlled mainly by fluid compositions and/or oxygen fugacity ( f O 2 ). Other potential controlling factors such as temperature, fluid–rock interaction and co-precipitating minerals have very limited impacts. Magnetite in the Cu-sulfide ores has higher V but lower Ni contents than that of the Fe-oxide ores, likely indicating its precipitation from relatively reduced, evolved fluids. However, it is also indicated that the two types of magnetite do not show large distinctions in terms of concentrations of most elements, suggesting that they may have precipitated from a common, evolving fluid. We propose a combination of Ge versus Ti/Al and Cr versus Co/Ni co-variation plots to discriminate different types of magnetite from the Khetri copper belt. Our work agrees well with previous studies that compositions of magnetite can be potentially useful for provenance studies, but also highlights that discrimination schemes would be more meaningful for deposits in a certain region if fluid/water chemistry and specific formation conditions reflected in compositions of magnetite are clearly understood.

Uplift of the Tibetan Plateau and related crustal shortening are key issues in understanding collisional geodynamics, and magmatic rocks that formed in this compressional setting provide clues to the processes involved. Numerous granitic porphyry dikes have been identified in the Angsai area of the northern Qiangtang block in north-central Tibet. These dikes were emplaced along NW–SE-striking reverse faults that run parallel or sub-parallel to the thrust belt, suggesting that they are syn-collisional. New LA-ICP-MS zircon 206Pb/238U and magmatic biotite 40Ar/39Ar results demonstrate that the dikes crystallized at ca. 64 Ma, and the bulk geochemistry of the dikes shows that they are adakitic, with high Sr/Y and La/Yb ratios, and low Y and Yb contents. Their low MgO, Ni, and Cr contents, along with positive zircon eHf(t) and bulk eNd(t) values, suggest that the adakitic rocks were the result of partial melting of a juvenile thickened lower crust. Our new data indicate the uplift of north-central Tibet which started as early as 64 Ma. Synthesizing available geochronological, geochemical, and structural data, it seems that the crustal shortening and uplift of the plateau is a long-lived process consisting of a rapid early stage, and a slow and more constant later stage. Collision-related magmatic activity peaked at the time of transition between those two stages.

The goal of this paper is to study the provenance of the southern Junggar Basin during the late Triassic to early Cretaceous, based on the detrital U-Pb geochronology, petrography and depositional environments. Eight sandstone samples from the Upper Triassic to Lower Cretaceous were collected for detrital zircon U-Pb dating. A total of 794 effective U-Pb ages was obtained and divided into four groups: 488–2537 Ma (basement zircons), 328–482 Ma (subduction-related magmatic zircons), 254–322 Ma (post-collisional magmatic zircons), and 135–250 Ma (syndepositional magmatic zircons). These ages relate to three stages of basin evolution. (1) From the early to middle Jurassic, Tian Shan experienced continued exhumation, accompanied by progressive southward expansion of the Junggar Basin, and a peneplain was formed by the time Xishanyao Formation was deposited. Organic-rich sediments formed in a delta environment were well-developed in the southern Junggar Basin, with source rocks gradually switching from post-collisional volcanic rocks (295–307 Ma with a peak age of 300 Ma) of the southern North Tian Shan to post-collisional volcanic rocks of the Central Tian Shan (280–320 Ma with a peak age of 316 Ma) and then to subduction-related island arc rocks (402–423 Ma with a peak age of 415 Ma) of the Central Tian Shan. (2) During deposition of the Toutunhe and Qigu Formations, large scale volcanic activities occurred along the North Tian Shan Fault. Source rocks at this time include syndepositional volcanic rocks (151–161 Ma), and post-collisional volcanic rocks (290–320 Ma) of the North Tian Shan. By the time of deposition of the Kalazha Formation, Tian Shan experienced rapid tectonic uplift, leading to rapid lake regression. Alluvial fans were well developed in the southern Junggar Basin with source rocks being the underlying sedimentary strata of the north margin of the North Tian Shan. (3) During the early Cretaceous, exhumation of the Tian Shan and lake transgression in the Junggar Basin happened again. Shallow lake sediments were developed in the southern Junggar Basin with source rocks being subduction-related volcanic rocks (339–419 Ma with a peak age of 415 Ma) of the Central Tian Shan and post-collisional volcanic rocks (254–305 Ma with a peak age of 298 Ma) of the North Tian Shan.

Banded iron formations (BIFs) are Precambrian chemical marine sedimentary formations that record major transitions of chemical composition, and oxidation–reduction state of oceans at the time of their deposition. In this paper, we report silicon and oxygen isotope compositions of a variety of BIFs from the North China Craton (NCC) in order to deduce the mechanism of their formation. Quartz in the various types of BIFs from the NCC are generally depleted in 30Si, where δ30SiNBS-28 values range from − 2.0‰ to − 0.3‰ (average, − 0.8‰), similar to δ30SiNBS-28 values measured from modern submarine black chimneys and sinters. The δ18OV-SMOW values of quartz in the BIFs are relatively high (8.1‰–21.5‰; average, 13.1‰), similar to those of siliceous rock formed by hydrothermal activities. The δ30SiNBS-28 values of quartz in magnetite bands are commonly lower than those of quartz in adjacent siliceous bands within the same sample, whereas δ18OV-SMOW values are higher in the magnetite bands. A negative correlation is observed between δ30SiNBS-28 and δ18OV-SMOW values of quartz from siliceous and magnetite bands in BIF from Fuping, Hebei Province. The isotopic compositions of silicon and oxygen of quartz in BIFs provide insights for the formation mechanisms of silicon–iron cyclothems in BIFs. After the silicon- and iron-rich hydrothermal solution was injected onto the seabed, the abrupt temperature drop caused oversaturation of silicic acid, resulting in rapid precipitation of SiO2 and deposition of siliceous layers. Ferric hydroxide was precipitated later than SiO2 because of low free-oxygen concentration in the ocean bottom. Progressive mixing of hydrothermal solution with seawater caused a continuous drop in temperature and an increase in Eh values, resulting in gradual oxidation of hydrothermal Fe2 + and deposition of iron-rich layers. In summary, each silicon–iron cyclothem marks a large-scale submarine hydrothermal exhalation. The periodic nature of these exhalations resulted in the formation of regular silicon–iron cyclothems. The widespread distribution of BIFs indicates that volcanism and submarine hydrothermal exhalation were extensive; the low δ30SiNBS-28 and high δ18O V-SMOW values of the BIFs indicate that the temperature of seawater was relatively high at the time of BIF formation, and that concentrations of Fe2 + and H4SiO4 in seawater were saturated.

Banded iron formations (BIFs) within the Lvliang region of Shanxi Province, China, are hosted by sediments of the Yuanjiacun Formation, part of the Paleoproterozoic Lvliang Group. These BIFs are located in a zone where sedimentation changed from clastic to chemical deposition, indicating that these are Superior-type BIFs. Here, we present new major, trace, and rare earth element (REE) data, along with Fe, Si, and O isotope data for the BIFs in the Yuanjiacun within the Fe deposits at Yuanjiacun, Jianshan, and Hugushan. When compared with Post Archean Australian Shale (PAAS), these BIFs are dominated by iron oxides and quartz, contain low concentrations of Al 2 O 3 , TiO 2 , trace elements, and the REE, and are light rare earth element (LREE) depleted and heavy rare earth element (HREE) enriched. The BIFs also display positive La, Y, and Eu anomalies, high Y/Ho ratios, and contain 30 Si depleted quartz, with high δ 18 O values that are similar to quartz within siliceous units formed during hydrothermal activity. These data indicate that the BIFs within the Yuanjiacun Formation were precipitated from submarine hydrothermal fluids, with only negligible detrital contribution. None of the BIF samples analyzed during this study have negative Ce anomalies, although a few have a positive Ce anomaly that may indicate that the BIFs within the Yuanjiacun Formation formed during the Great Oxidation Event (GOE) within a redox stratified ocean. The positive Ce anomalies associated with some of these BIFs are a consequence of oxidization and the formation of surficial manganese oxide that have preferentially adsorbed Ho, LREE, and Ce 4 + ; these deposits formed during reductive dissolution at the oxidation–reduction transition zone or in deeper-level reducing seawater. The loss of Ce, LREE, and Ho to seawater and the deposition of these elements with iron hydroxides caused the positive Ce anomalies observed in some of the BIF samples, although the limited oxidizing ability of surface seawater at this time meant that Y/Ho and LREE/HREE ratios were not substantially modified, unlike similar situations within stratified ocean water during the Late Paleoproterozoic. Magnetite and hematite within the BIFs in the study area contain heavy Fe isotopes ( 56 Fe values of 0.24–1.27‰) resulting from the partial oxidation and precipitation of Fe 2 + to Fe 3 + in seawater. In addition, mass-independent fractionation of sulfur isotopes within pyrite indicates that these BIFs were deposited within an oxygen-deficient ocean associated with a similarly oxygen-deficient atmosphere, even though the BIFs within the Yuanjiacun Formation formed after initiation of the GOE.

Iron oxide–apatite (IOA) deposits are an important type of iron deposit that may host large reserves of iron and other elements. The Washan deposit in the Ningwu Ore District is a classic giant IOA deposit hosted by porphyritic diorite. At Washan, four Fe mineralization stages have been identified with clear crosscutting relationships, forming four types of ores: disseminated ores, breccia ores, and magnetite–actinolite and magnetite–apatite–actinolite veins. Trace element concentrations and single-grain geochemical profiles of magnetite from the four Fe mineralization stages were obtained via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The geochemical profiles show consistent Ti, V, Mg and Al contents from cores to rims, indicating that magnetite might have crystallized quickly under relatively stable conditions in each stage. Compatible element (e.g., Co, V, Ni, and Cr) contents of the Washan magnetite are similar to those of magmatic Fe–Ti–V deposits, with high V and Ti contents, indicating a close magmatic link. Increasing Mg, Al, Mn, Ni and Ga contents and decreasing Cr content from early to late stages imply increasingly intense reactions between Fe-bearing fluids and country rocks (e.g., diorite and evaporites), which also suggests a magmatic-hydrothermal origin. We propose a new genetic model for ore formation at the Washan IOA deposit. First, an Fe-rich liquid, which may have formed via liquid immiscibility, ascended through the magma system, resulting in the disseminated ores and albite alteration in the porphyritic diorite. With cooling and crystallization of the magma, the intrusive rocks developed fractures and brecciation, which may have provided pathways for Fe-bearing fluids. After the breccia (or massive) ores formed, the pathways would have been quickly sealed by mineral precipitation. Continuous liquid immiscibility and magma crystallization may have produced similar fluids with more sedimentary material involved and its markers displayed. When the fluid pressure overcame the lithostatic pressure, the fractures that developed may have provided the necessary conduits for emplacement of the magnetite–actinolite and magnetite–actinolite–apatite veins. Subsequently, the magmatic-hydrothermal system might have remained active during cooling and differentiation, while pyrite–quartz and calcite veins formed.

Zircon is the most useful mineral for studies in U-Pb geochronology and Hf and O isotope geochemistry. Matrix effect is a major problem of the microbeam techniques such as SIMS and LA-(MC)-ICPMS. Therefore, external standardization using well-characterized natural zircon standards is fundamental for accurate microbeam measurements. While the isotopic geochronology and geochemistry laboratories equipped with microbeam analytical facilities have been increasingly established in China during the past decade, applications of the isotopic microanalysis are still limited due to shortage of available standards. We report here the Qinghu zircon as a potential new working reference for microbeam analysis of zircon U-Pb age and O-Hf isotopes. This zircon was separated from the Qinghu quartz monzonite from the western Nanling Range, Southeast China. It is fairly homogeneous in U-Pb age and Hf and O isotopes in terms of large amounts of mircobeam measurements by LA-MC-ICPMS and SIMS at the scales of 20-60 mm. SIMS measurements yield consistent 206Pb/238U age within analytical uncertainties with that obtained by ID-TIMS. Precise determinations of O isotopes by IRMS and Hf isotopes by solution MC-ICPMS are in good agreement with the statistical mean of microbeam measurements. We recommend U-Pb age of = 159.5 ± 0.2 Ma (2SE), δ 18O = 5.4‰ ± 0.2‰ (2SD) and 176Hf/177Hf = 0.283002±0.000004 (2SD) as the best reference values for the Qinghu zircon.

Numerous Neoproterozoic magmatic and metamorphic events in the Altun–Qilian–North Qaidam (AQNQ) region record Grenvillian orogenesis and amalgamation of the supercontinent Rodinia. However, the tectonothermal regimes responsible for these Neoproterozoic events and the assumed position of the AQNQ in Rodinia remain controversial. Zircon U–Pb age data show that the orthogneiss and paragneiss/schist of the AQNQ experienced concurrent magmatism and metamorphism at 895–925 Ma. Zircon Lu–Hf isotopic data indicate that the gneisses in the AQNQ have eHf (0.9 Ga) values and tDM2 (Hf) model ages ranging from −5.6 to +3.9 and 1.4 to 1.9 Ga. These data suggest that the early Neoproterozoic magma in the AQNQ was predominately derived from a late Paleoproterozoic–early Mesoproterozoic crustal source between 1.4 and 1.9 Ga, marking an important episode of crustal growth in the AQNQ. The Neoproterozoic magmatism is geochemically characterized by (1) high SiO2, K2O, and low P2O5; (2) A/CNK ratios >1.0, ranging from 1.03 to 1.09; (3) enrichment in Rb, Th and U, and depletion in Ba, Nb, Ta, Sr, Ti, and Eu. Based on the geochemical resemblance to high-K calc-alkaline I-type granite and zircon Lu–Hf isotope signatures, the Neoproterozoic magmatism in the AQNQ was probably derived from ancient mafic-intermediate igneous rocks in an active continental margin. The Neoproterozoic tectono-magmatic–metamorphic history of the AQNQ, directly associated with the South China block (SCB) and the Tarim block (TB), indicates that the AQNQ and the TB coexisted as a single block in the early Neoproterozoic, which was temporarily connected to the SCB to the north or west in Rodinia during the late stages of the Grenvillian orogeny (950–900 Ma).

The Alxa block was traditionally considered to be part of the North China Craton, but its metamorphic basement has been poorly studied. Here we present a systematic zircon U–Pb and Hf isotopic investigation on four orthogneiss samples in the Beidashan area of the western Alxa block. The petrographic and geochemical data show that these rocks are granodioritic and trondhjemitic gneisses with TTG (tonalite–trondhjemite–granodiorite) characteristics. Zircons from the TTG gneisses display typical core–rim or core–mantle–rim structures. U–Pb datings and Hf isotopic analyses reveal two distinct age populations: the Latest Neoarchean (∼2.5 Ga) and the Late Palaeoproterozoic (∼1.85 Ga). The magmatic zircon cores and metamorphic mantles (rims) of the TTG gneisses were dated at similar ages around 2.5 Ga, supporting the existence of Archean rocks in the western Alxa block. The short time interval between the Latest Neoarchean magmatism and the subsequent metamorphism suggests that they were related to the same Latest Neoarchean tectonothermal event. The ∼2.5 Ga zircons have ɛ Hf( t ) mainly between 0.8 and 5.0, T DM (Hf) model ages mainly between 2.6 and 2.8 Ga (with a peak at ∼2.7 Ga) and T DMC (Hf) model ages mainly between 2.7 and 3.0 Ga (with a peak at ∼2.8 Ga). The age of ∼1.85 Ga obtained from two trondhjemitic gneisses is interpreted as the age of the Late Paleoproterzoic high-grade metamorphism. Our combined datasets show that the TTG gneisses in the Baidashan area of the western Alxa block experienced a main 2.7–2.8 Ga crust growth, a ∼2.5 Ga magmatic–metamorphic event and a ∼1.85 Ga high-grade metamorphic event. The sequence of events is very similar to that of the other North China Craton. A Combination of the data of Paleoproterozoic metamorphic rocks in the Alxa block suggests that the Alxa block is the western extension of the Khondalite Belt rather than the Yinshan block.

SHRIMP zircon U–Pb dating of the Huangjinshan granite porphyry in the Wutai area, North China Craton (NCC) yielded concordant ages, with a weighted mean 207 Pb/ 206 Pb age of 2137 ± 9 Ma, which indicates that the granite was emplaced in the middle Paleoproterozoic. The granite porphyry is enriched in SiO 2 , REEs (except Eu), Zr, Nb, Ga, Y and Zn, and depleted in MgO, CaO, Al 2 O 3 , Sr, Ba, V, Cr and Ni, with high FeO * /MgO ratios. With the zircon saturation temperatures ranging from 856 to 895 °C and a lack on detected inherited zircon, this indicates it is a ‘hot’ A-type granite, of the type emplaced in anorogenic or extensional settings with high heat flow. Zircons in the granite porphyry have e Hf ( t ) values ranging from −1.72 to +1.84, and Hf model T DM1 ages of 2429–2554 Ma. The Hf isotopes indicate source of the granites was pre-Neoarchean continental crust mixed with mafic rocks derived from depleted mantle, or directly from the partial melting of ca. 2.5 Ga crust. Given that there are no syn-plutonic gabbro enclaves in the Huangjinshan granite porphyry, it is preferred that it originated mainly from partial melting of ca. 2.5 Ga upper crust without mixing with mantle-derived magma. 2.2–2.0 Ga volcanic and plutonic rocks, which exhibit bimodal magma characteristics emplacing in rifting setting, are abundant in the central NCC. The results presented here are further evidence for that 2.2–2.0 Ga is an important stage of Paleoproterozoic rifting in the central NCC.

In this study, we link zircon U Pb SHRIMP and LA-ICP-MS geochronology and the Lu Hf isotopic composition of eclogites and their host gneisses/schists with whole-rock geochemistry of eclogites in the Dulan area to constrain their protoliths and metamorphic relationships. U Pb dating suggests that the protolith of one of the eclogites was a Neoproterozoic mafic intrusive rock (828 ± 58 Ma) and the protolith of enclosing orthogneiss was an early-Neoproterozoic granitoid (923 ± 12 Ma). Detrital zircons from Grt-bearing mica-schists yield ages of 0.9–2.5 Ga, with a dominant range of 1.0–1.8 Ga, indicating sedimentary sources from Neoproterozoic to Neoarchean crust and a depositional age ≤ 0.9 Ga. The matching metamorphic ages of eclogites (438 ± 5 Ma, 436 ± 4 Ma) and their country rocks (Grt-bearing mica-schists: 438 ± 4 Ma, 439 ± 8 Ma; orthogneiss: 427 ± 8 Ma) indicate that all studied samples experienced coeval Early Paleozoic HP/UHP metamorphism. The U Pb ages and Hf isotopic compositions of the inherited magmatic zircon cores of an eclogite sample ( e Hf (800) = 2.6–9.2, T DM1 = 1.0–1.3 Ga, T DM2 = 1.1–1.4 Ga) suggest that the protolith may be derived from Neoproterozoic depleted mantle with variable proportions of an older crustal component. The magmatic zircon cores of the orthogneiss (e Hf (900) = − 7.3 to − 0.2; T DM2 = 1.8–2.1 Ga) suggest that the parental magma was derived from a Paleoproterozoic crustal source. Hf isotopic compositions of the detrital zircons from the metasediments (e Hf (t) = − 19.4 to + 10.6) suggest three crust formation and reworking events: (1) Archean (T DM2 = 2.7–2.9 Ga) juvenile crust reworked at ~ 2.5 Ga; (2) early Paleoproterozoic (T DM2 = 2.3–2.5 Ga) juvenile crust reworked at ~ 1.8 Ga; and (3) late Paleoproterozoic (T DM2 = 1.5–1.9 Ga) juvenile crust reworked in the Neoproterozoic. Whole-rock geochemical data suggest that the protoliths of the Dulan eclogites were probably derived from a continental rift or an incipient oceanic basin rather than a large, long-lived ocean basin. Thus, combined with field relationships, petrology, geochemistry, zircon U Pb dating and the Lu Hf isotopic analysis presented in this paper and reported from previous studies, we suggest that the Dulan eclogites and their country rocks experienced a common UHP metamorphism during Late Ordovician deep continental subduction.

The Dunhuang block, in the easternmost segment of the Tarim craton, exposes Precambrian mafic granulite and felsic gneiss. To better understand the poorly known formation and evolution of the Tarim craton, we carried out detailed field-based petrological and geochronological investigations on the major lithologies of the Dunhuang block. U–Pb dating and Hf isotopic analyses on the mafic granulite and felsic gneiss (TTG gneiss) of the Dunhuang block reveal two distinct age populations: the Latest Neoarchaean (∼2.5 Ga) and the Late Palaeoproterozoic (1.82–1.85 Ga). The zircon magmatic cores and metamorphic rims of tonalitic gneisses yield similar ages of ∼2.5 Ga, supporting the existence of Archean rocks in the Dunhuang block. The short time interval between Latest Neoarchean magmatism and high-grade metamorphism suggests that they were related to the same Latest Neoarchean tectonothermal event. The ∼2.5 Ga zircons show Hf-depleted mantle model ages between 2.55 Ga and 2.8 Ga with a peak at ∼2.7 Ga, suggesting that ∼2.7 Ga juvenile crust of the Dunhuang block was reworked during a 200–300 m.y. period at the end of the Neoarchean. The age of ∼1.85 Ga obtained from the mafic granulites and felsic gneisses is interpreted as the age of high-pressure granulite facies metamorphism. Combined with the Hf isotopic data, these data suggest that the Dunhuang block experienced ∼2.7 Ga crustal growth, a ∼2.5 Ga magmatic–metamorphic event and a 1.82–1.85 Ga (HP) granulite facies metamorphic event. This sequence of events is very similar to that of the North China Craton, implying that the evolutionary history of the Dunhuang block was consistent with that of the North China Craton from the Neoarchean to Paleoproterozoic.