Fluid and metal sources of the Changfagou porphyry copper deposit, southern Jilin Province, NE China: Constraints from fluid inclusions and H-O-S-Pb isotope systematics

The Changfagou copper deposit, a newly discovered porphyry deposit in the southern Jilin Province, NE China, is tectonically located on the northeastern margin of the North China Block. We recognized four types of sulfide-quartz veins at Changfagou, including quartz–K-feldspar–magnetite veins (Stage I), quartz–molybdenite–pyrite–chalcopyrite veins (Stage II), quartz–chalcopyrite–pyrite–galena–sphalerite veins (Stage III), and quartz–carbonate veins (Stage IV). Three types of fluid inclusions, including liquid-rich two-phase (L-type), vapour-rich two-phase (V-type), and daughter mineral-bearing multi–phase (S-type) inclusions, have been distinguished. The fluid inclusions in the quartz phenocrysts of the ore-hosting granite porphyry contain liquid-rich two-phase, gas-rich two-phase, and daughter mineral-bearing multi-phase fluid inclusions. Stages I, II, and III quartz contain all types of fluid inclusions, whereas only L-type inclusions can be observed in Stage IV quartz. The fluid inclusions in the quartz phenocrysts of the granite porphyry yield homogenization temperatures ranging from 282 to 586 °C and salinities ranging from 3.55% to 58.41% NaCl equiv. The fluid inclusions in the quartz of Stages I, II, III, and IV mainly homogenized at temperatures of 290 to 492 °C, 270 to 424 °C, 248 to 398 °C, and 119 to 219 °C, respectively, with salinities of 9.98–50.85 wt.% NaCl equiv, 6.30–46.37 wt.% NaCl equiv, 6.45–35.99 wt.% NaCl equiv, and 6.59–18.04 wt.% NaCl equiv, respectively. The ore–forming fluids of the Changfagou Cu deposit are therefore characterized by their high temperature and high salinity, and they belong to the H2O–NaCl–CO2 system. The δ18Ofluid values of quartz phenocrysts and vein quartz range from −9.97‰ to +6.91‰, and their δDfluid values range from −142‰ to −93‰, indicating that the early-stage ore-forming fluids mainly consisted of magmatic water that experienced the input of magmatic and meteoric water during the last stage. The δ34S values of chalcopyrite and molybdenite range from +2.2‰ to +4.3‰, with an average value of +3.17. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of granite porphyry, arsenopyrite, and pyrite range from 16.672–17.567, 15.516–15.658, and 37.210–38.733, respectively. Both the S and Pb isotopic systems indicate that the ore-forming materials were derived from mixed mantle and crustal sources. We thus proposed that multiple stages of the boiling of ore-forming fluid represented the dominant mechanism of the formation of the Changfagou Cu deposit.

Spectral and chemical characterization of gypsum-phyllosilicate association in Tiruchirapalli, South India, and its implications

Here, we present the detailed chemical and spectral characteristics of gypsum-phyllosilicate association of Karai Shale Formation in Tiruchirapalli region of the Cauvery Basin in South India. The Karai Shale Formation comprises Odiyam sandy clay and gypsiferous clay, well exposed in Karai village of Tiruchirapalli area, Tamil Nadu in South India. Gypsum is fibrous to crystalline and translucent/transparent type with fluid inclusions preserved in it. Along some cleavage planes, alteration features have been observed. Visible and near infrared (VNIR), Raman, and Fourier transform infrared techniques were used to obtain the excitation/vibration bands of mineral phases. VNIR spectroscopic analysis of the gypsum samples has shown absorption features at 560, 650, 900, 1,000, 1,200, 1,445, 1,750, 1,900, 2,200, and 2,280 nm in the electrical and vibrational range of electromagnetic radiation. VNIR results of phyllosilicate samples have shown absorption features at 1,400, 1,900, and 2,200 nm. Further, we have identified the prominent Raman bands at 417.11, 496.06, 619.85, 673.46, 1,006.75, 1,009.75, ∼1,137.44, ∼3,403, and 3,494.38 cm−1 for gypsum due to sulphate and hydroxyl ion vibrations. We propose that gypsum veins in Karai may have precipitated in the fractures formed due to pressure/forces generated by crystal growth. The combined results of chemical and spectral studies have shown that these techniques have significant potential to identify the pure/mineral associates/similar chemical compositions elsewhere. Our results definitely provide the database from a range of spectroscopic techniques to better identify similar minerals and/or mineral-associations in an extraterrestrial scenario. This study has significant implications in understanding various geological processes such as fluid-rock interactions and alteration processes involving water on the planets such as Mars.

Petrogenesis of pillow basalts in West Junggar, NW China: Constraints from geochronology, geochemistry, and Sr–Nd–Pb isotopes

West Junggar is located at the southwest margin of the Central Asian Orogenic Belt and includes Silurian pillow basalts of the Mayilashan Formation. The petrogenesis and tectonic setting of these pillow basalts are important for the understanding of the tectonic evolution and metallogeny of the West Junggar area. This paper presents geochronological, geochemical, and whole-rock Sr–Nd–Pb isotope data from the pillow basalts of the Mayilashan Formation. Zircon LA-ICP-MS U–Pb dating of a pillow basalt, which is in conformable contact with the chert, suggests that they were erupted at 437.2 ± 2.2 Ma marking the timing of generation of these rocks as Middle Silurian. Geochemically, all the pillow basalts bear the signature of ocean island basalt (OIB), and are characterized by alkaline affinity with high concentrations of TiO2 (3.28–4.12 wt.%), LILE and LREE enrichment and HREE depletion ((La/Yb)N = 5.5–7.3), with very weak Eu anomalies (Eu/Eu* = 0.96–1.06), and no obvious Nb, Ta, or Ti negative anomalies. Their Sr–Nd–Pb isotopic compositions ((87Sr/86Sr)I = 0.7037–0.7051, εNd(t) = 1.9–2.9, 206Pb/204Pbi = 17.74–18.22, 207Pb/204Pbi = 15.48–15.52, and 208Pb/204Pbi = 36.49–37.86) show Dupal-like isotopic signature of ophiolites in the southern Paleo-Asian Ocean. These characteristics indicate that the magmas were derived from a deep OIB reservoir, that is, a depleted but slightly heterogeneous asthenospheric mantle source with ~5–15% partial melting of garnet and spinel lherzolite. Our obtained results, in conjunction with previous published data, allow us to suggest that the alkaline pillow basalts formed in a seamount within an intraoceanic setting, where a larger number of seamounts with different ages occurred in the Paleo-Asian Ocean.

Tectonic setting of the Late Triassic magmatism in the Qinling Orogen: New constraints from the interplay between granite emplacement and shear zone deformation in the Shagou area

Multidisciplinary studies of the Baliping granite pluton and the Shagou shear zone (East Qinling Orogen, Central China) have been conducted to reconstruct the emplacement and deformation processes of the Baliping pluton, to explore the relationship between granite pluton and shear zone deformation, and further to constrain the tectonic setting of the Late Triassic magmatism in the Qinling Orogen which remains controversial. Zircon U–Pb geochronology studies confirmed that the Baliping granites and the protolithes of the Shagou granitic mylonites crystallized from the same magmas at ca. 221 Ma since the two nearly have the same zircon U–Pb ages and Ti–in–zircon temperatures. Meanwhile, the 210 Ma of metamorphic zircons and the 201 Ma of syntectonic granitic vein provide precise limits on the timing of synkinematic deformation in response to Late Triassic orogeny. Anisotropy of magnetic susceptibility, microstructural observation, and shape preferred orientation were combined to study the internal structures. New fabrics datasets display a high degree of coupling between the Baliping pluton and the Shagou shear zone, indicating a syntectonic emplacement of the pluton. Microstructural data suggest that the magmatic to high-temperature solid-state deformation is a continuum process in which the fabrics were mainly acquired. We propose an integrated syntectonic emplacement model of the Baliping pluton, in which the shear zone deformation (sinistral transpression) play a significant role on the emplacement of the magma by creating rooms. Emplacement of the pluton, in turn, triggers the nucleation of Shagou shear zone by providing the protoliths and the heat. On the basis of this study, we argued that the Qinling Orogen was still under the convergent setting during 221–201 Ma.

Spatial and temporal change of fractional vegetation cover in North-western China from 2000 to 2010

Northwestern China is located at the core area of The Belt and The Road at present and it once has been an essential transportation hub of the ancient Silk Road. However, the north-western part belongs to arid and semi-arid region where water resource and vegetation cover are scarce, leading to soil erosion, desertification, and environmental degradation. So it is meaningful to study fractional vegetation cover in North-western China. Vegetation MODIS data of northwestern China from 2000 to 2010 were collected, and then, the pixel dichotomy model and simple linear regression model were applied in this research. The results were as follows. First, the fractional vegetation cover was decreasing from the margin to the middle and western part and the higher value shown in the north-east part of Inner Mongolia, the south part of Shaanxi, the north-west part of Ningxia, the south-east part of Gansu, and the north-west part of Xinjiang. Second, the overall trend of fractional vegetation cover was rising during 2000 to 2010, which is clearly shown in northern Shaanxi, south-eastern Qinghai and Gansu, and also south-western Inner Mongolia. Third, fractional vegetation cover varied differently with season changes. To be more specific, the index in spring and winter was considerably low; in contrast, the index in summer and autumn was improved dramatically.

Palaeomagnetism and detrital zircon U–Pb geochronology of Cretaceous redbeds from central Tibet and tectonic implications

Understanding the magnitude of intra-Asian crustal shortening and the collision age of Lhasa–Qiangtang terranes requires quantitative constraints on the crustal motion. The key to this is defining the palaeogeography of the Tibetan Plateau, which constitutes a poorly known factor over the entire convergence history. New detrital zircon U–Pb geochronological and palaeomagnetic data from the terrestrial Abushan Formation in the Qiangtang terrane demonstrate that central Tibet was located at 27.5 ± 3.0°N during the time interval of ~111–83 Ma. Our results suggest 7.5 ± 2.9° continental shortening has occurred between central Qiangtang and Mongolia during the India–Asia convergence. Declination anomaly indicates the central Qiangtang terrane has experienced significant clockwise rotation (57.3 ± 3.9°) relative to stable Eurasia. The compilation of palaeomagnetic results since the Cretaceous reveals ~8.5° northward drift of the Lhasa terrane from 123 ± 9 to 97 ± 7 Ma and the palaeolatitudinal overlap between the Lhasa and Qiangtang terranes after ~111–103 Ma. Together with the onset age of the terrestrial Abushan Formation, our results provide the youngest timing (ca. ~111–103 Ma) for the closure of the Bangong Meso-Tethys Ocean, as well as for the final collision of the Lhasa and Qiangtang terranes.

Late Neoproterozoic–Early Palaeozoic stratigraphic succession, Western Himalaya, North Pakistan: Detrital zircon provenance and tectonic implications

This paper presents the first ever detrital zircon U–Pb–Hf isotopic study for the Late Neoproterozoic–Early Palaeozoic stratigraphic succession exposed in the Hazara Basin, Western Himalaya, North Pakistan. This time span represents the break-up of the supercontinent Rodinia and final assembly of Gondwana. The detrital record of the Late Neoproterozoic succession indicates well-mixed detritus shed from within the Indian Craton, especially the Central Indian provenance (including the Delhi Fold Belt, Aravalli Orogen, and Bundlekhand Craton). The εHf(t) values are mostly negative, and Hf TDMC ages are clustered at 2.0–2.4 Ga, which indicates the derivation from an ancient reworked crustal source. In addition, the presence of a few positive εHf(t) values in the Late Neoproterozoic sequence indicates addition of the juvenile crust that corresponds to the period of the Rodinia break-up. However, dissimilarities with detrital signatures from the Australian continent may indicate break-up of the Rodinia supercontinent and detachment of Australia from India prior to ~754 Ma, which is the depositional age of the Hazara Formation. In addition, the angular unconformity at the base of the Abbottabad Formation represents the compressional tectonics that might be associated with the Pan-African (Indo-Antarctic Craton collision with the East African Orogen during 800–700 Ma) orogeny. The presence of the metamorphism and deformation in the rocks below the unconformity supports such an event prior to deposition of the Early Palaeozoic Abbottabad Formation. Similarly, the appearance of the Pan-African detritus in the Early Palaeozoic Abbottabad Formation could be due to closure of the ocean basin between Eastern and Western Gondwana along the Mozambique Suture. This provenance change may indicate the final assembly of supercontinent Gondwana.

Geochemical characteristics and tectonic setting of the bimodal volcanic rocks in Sepikou region of eastern Tianshan

The Sepikou region is located in the eastern Bogda Mountains of the east Tianshan. The Bogda belt is mainly composed of Carboniferous strata, including the Lower Carboniferous Qijiaojing Formation (C1q), Upper Carboniferous Liushugou Formation (C2l), and Qijiagou Formation (C2qj). Here, we report the petrology, geochemistry, and geochronology of bimodal volcanic rocks from the Upper Carboniferous Liushugou Formation, which is widely distributed in the Sepikou region. The basalts, basaltic andesite, and keratophyre have similar petrochemical characteristics and exhibit the high-Na, low-K characteristics belonging to calc-alkalic rocks. These are characterized by the high abundance of K, Rb, Th, Ba, the depletion of HFSE (Nb, Ta, Zr, and Hf), and the slight depletion of Ti. Chondrite-normalized rare-earth elements (REE) patterns for basalts-keratophyre show right-leaning parallel curve clusters, together with a slight enrichment in light rare-earth elements (LREE) contents and low heavy rare-earth elements (HREE)/LREE ratios. The keratophyre exhibits slightly negative Eu anomalies. Compared with the basalts, the rhyolites have high alkali contents, slightly high ∑REE contents, low heavy rare-earth elements/LREE ratios, negative εSr(t) (−9.1 to −12.0), low 87Sr/86Sr initial ratio, highly positive εNd (t) (+5.3 to +6.4), and low Pb isotope ratios. The fractionated REE patterns with prominent negative Eu anomalies suggest they were chiefly derived from the mantle magma underplated basaltic body remelting from the depleted mantle source. The LA-ICP-MS analysis on zircons from quartz keratophyre and rhyolite yield similar ages of 314.9 ± 1.2 and 314.0 ± 1.1 Ma, respectively, suggest that the major bimodal volcanism took place in the Late Carboniferous epoch. The quartz keratophyre zircons, with the 176Hf/177Hf ratios of 0.282897–0.283097, have highly positive εHf (10.99–19.97) and depleted mantle model ages between 180 and 628 Ma. The mafic rocks were chiefly derived from the depleted mantle with the partial incorporation of crustal components. The bimodal volcanic rocks were formed under a continental rift setting. The rift experienced extension in the early period of the Early Carboniferous and its final closure arose after a late period of the Late Carboniferous.

Geochemical, zircon U–Pb–Hf, and whole-rock Sr–Nd isotopic study of Late Jurassic Sanming A-type granite in the Wuyi area, Fujian province, Southeast China

The Sanming pluton is the only Late Jurassic A-type granitic intrusion in the Wuyi area, west Fujian Province, Southeast China, and its formation has important implications for our understanding of the tectonic evolution of the region. The U–Pb ages of 157 ± 1 Ma and 159 ± 1.1 Ma were obtained for the pluton by zircon LA–ICP–MS analysis, which is interpreted to be the crystallization age of the Sanming pluton (i.e., Late Jurassic). The pluton has the geochemical characteristics of A-type granite, such as high K2O+Na2O contents (average 7.703 wt%), FeOT/(FeOT + MgO) ratios (average 0.85), and high 10,000 Ga/Al values and Zr + Nb + Ce + Y (380–446.1 ppm, average 419.2 ppm) contents, but relatively low CaO, Sr, and Eu contents. Zircon saturation temperatures range from 875 °C to 890 °C, also similar to other A-type granites. The (87Sr/86Sr)i ratios (0.707368–0.71102) and εNd(t) and εHf(t) values (−5.54 to −6.09, and −6.93 to −1.07, respectively), the 2-stage Nd model ages of 1.50–1.55 Ga, and 2-stage Hf model ages of 1.25–1.62 Ga, suggest the pluton was derived by extensive fractionation of melts containing both mantle materials and Mesoproterozoic crustal components. The Sanming A-type granitic pluton is younger than adakitic rocks in the region (162 Ma), suggesting a localized transition from compressional to intraplate extensional tectonics at 162–159 Ma, with mantle-derived material playing a crucial role in the formation of A-type granites in the Wuyi Mountain area. This tectonic transition is explained by localized rollback of the subducting Pacific plate.

Mineralogical characteristic of ductile–brittle shear zone in the Baguamiao gold deposit, Shaanxi Province: Implication for gold mineralization

The Baguamiao gold deposit in Fengxian County of Shaanxi Province is located in Fengtai polymetallic ore concentration area in the orogenic belt of West Qinling Mountain. It is a typical gold deposit under the control of brittle–ductile shear zone. The progressive deformation of brittle–ductile shear zone has been found to be closely associated with gold enrichment: the gold-bearing sulphides pyrrhotite and pyrite are distributed along blastobedding S0 in the undeformed area, they are developed along phyllitic foliation S1 (//S0) in the slightly deformed area, along mylonitic foliation (S2#S0), or S–C foliation in the highly deformed area, and they are enriched along rheological quartz vein (S2–L) and joint quartz vein (S3) in the highly deformed and the tectonic fluid area. Researches based on electron microprobe analysis and mineral–structure–geochemistry indicate that the characteristic metamorphic mineral assemblage of the brittle–ductile shear zone is albite–biotite–sericite–chlorite–quartz–ankerite, with diagenetic and metallogenic temperatures and pressures spanning from 350 to 450 °C and from 0.12 to 0.31 GPa, respectively. In addition, greenschist facies in intermediate temperature and intermediate and low-pressure environment is the metamorphic facies of shear zone in main period. A reconstruction of the palaeotemperature history, based on the biotite and chlorite compositional geothermometer, revealed an intermediate-temperature phase, a high-temperature phase, and a high-temperature critical phase. Biotitization tends to develop towards an oxidation phase, while chloritization is characterized by development towards a reduction phase, indicating large-scale gold enrichment and mineralization were accompanied by strong redox reactions in the ore-forming fluid.