Rare-metal granitic pegmatites are commonly considered to be the results of a combination of magmatic and hydrothermal processes. Although magmatic crystallization and fractionation, and magmatic-hydrothermal transition have been extensively investigated, processes involving economically valuable mineralization of rare-metals and strong fractionation of geochemical twins remain controversial. This study documents the geochemical evolution of rare‐metal mineralized pegmatites using the mineral chemistry of muscovite and columbite-group minerals (CGM) in the Dangba rare-metal granitic pegmatites, Eastern Tibet. We propose that randomly orientated growth of spodumene crystals and widespread distribution of disordered columbite-group minerals crystals mark lithium saturation in the initial melt, and a disequilibrium condition for crystallization at the Dangba No. Ⅷ dikes. Magmatic fractionation is recognized by gradually increasing ratios of alkali metals (K/Rb ratios) and Ta# (Ta/(Ta+Nb)), and is suggested to be an important factor for enrichment of rare-metals. During the magmatic-hydrothermal transition, the muscovite from metasomatism of spodumene has similar Li, Rb, and Cs with primary muscovite, but shows strong depletion of Ta, Nb, Sn, and W. Alteration of primary minerals (e.g., spodumene, alkali feldspar, and columbite-group minerals) releases these elements into the reactive media (melt/fluid) during the metasomatism, which leads to reduction of rare metals content in local pegmatites. In turn, this process is beneficial to later Ta and Nb mineralization and their fractionation. Chemical compositions of exsolved aqueous fluid depend on the mineralogy of pegmatites and partitioning behavior between melt and fluid. In addition, pervasive albitization is an exploration criteria for Li–Ta–Nb exploration in the Ke'eryin Orefield.
The Jiangjunshan and Dakalasu alkali‐feldspar granites are located in the central part of the Chinese Altay orogen. In this paper, we present detailed geochemical, zircon U–Pb, and Hf isotopic data of these granites. The Jiangjunshan and Dakalasu alkali‐feldspar granites show a high content of SiO 2 (72.05–73.27 and 69.55–71.04 wt%, respectively), total alkalis (Na 2 O + K 2 O = 8.41–8.71 and 7.24–8.66 wt%, respectively), and high‐field strength elements (Zr + Nb + Ce + Y = 400.3–482.9 and 156.7–339.3 ppm, respectively), as well as high Ga/Al ratios (10,000 × Ga/Al = 3.46–4.19 and 2.62–3.28, respectively) and depletion in Ba, Nb, Sr, and Ti, showing geochemical characteristics similar to those of A‐type granites. Zircon U–Pb dating of the Jiangjunshan and Dakalasu alkali‐feldspar granites yielded weighted mean dating 206 Pb/ 238 U ages of 268.3 ± 1.9 and 270.4 ± 1.9 Ma, respectively, indicating that these granites intruded during the Permian. The Jiangjunshan and Dakalasu alkali‐feldspar granites show highly variable zircon ε Hf ( t ) values ranging from −7.0 to +5.6, implying that these granites originated from a mixing of mantle‐derived magma with crustal materials. Our data on the Jiangjunshan and Dakalasu alkali‐feldspar granites, coupled with previous studies of Permian magmatism and metamorphism, suggest that the tectonic regime was in a postcollisional extensional environment in the Chinese Altay orogen during the Permian. Therefore, the change in stress from compression to extension and asthenospheric upwelling triggered by slab break‐off plays a significant role in the generation of Jiangjunshan and Dakalasu alkali‐feldspar granites.
Abstract Calorie restriction (CR) extends lifespan and elicits numerous effects beneficial to health and metabolism in various model organisms, but the underlying mechanisms are not completely understood. Gut microbiota has been reported to be associated with the beneficial effects of CR; however, it is unknown whether these effects of CR are causally mediated by gut microbiota. In this study, we employed an antibiotic-induced microbiota-depleted mouse model to investigate the functional role of gut microbiota in CR. Depletion of gut microbiota rendered mice resistant to CR-induced loss of body weight, accompanied by the increase in fat mass, the reduction in lean mass and the decline in metabolic rate. Depletion of gut microbiota led to increases in fasting blood glucose and cholesterol levels independent of CR. A few metabolism-modulating hormones including leptin and insulin were altered by CR and/or gut microbiota depletion. In addition, CR altered the composition of gut microbiota with significant increases in major probiotic genera such as Lactobacillus and Bifidobacterium , together with the decrease of Helicobacter . In addition, we performed fecal microbiota transplantation in mice fed with high-fat diet. Mice with transferred microbiota from calorie-restricted mice resisted high fat diet-induced obesity and exhibited metabolic improvement such as alleviated hepatic lipid accumulation. Collectively, these data indicate that CR-induced metabolic improvement especially in body weight reduction is mediated by intestinal microbiota to a certain extent.
Rare-elements granitic pegmatites are commonly considered as the results of combination between magmatic and hydrothermal processes. Although magmatic crystallization and fractionation and magmatic-hydrothermal transition (immiscibility of melt-melt and melt-fluid) have been extensively investigated, the processes involving in economically valuable mineralization of rare-elements and strong fractionation of geochemical twins remain controversial. Here, we present internal geochemical evolution during the pegmatite-forming processes with mineralogy and chemistry of muscovite and columbite-group minerals (CGM) in the Dangba rare-elements granitic pegmatites, Eastern Tibet. The pegmatites are overprinted by remarkable continuity a sequence of magmatic, magmatic-hydrothermal and hydrothermal processes. The initial pegmatite-forming melt could attain lithium saturation before its crystallization, and crystallization of spodumene and CGM commonly occurs at a disequilibrium condition. Magmatic fractionation is recognized by gradually increasing ratios of alkali metals (K/Rb, K/Cs ratios) and Ta# (Ta/(Ta+Nb)), and is suggested to be an important factor for further enrichment of rare-elements. During the magmatic-hydrothermal transition, the muscovite from metasomatism of spodumene has similar Li, Rb and Cs with primary muscovite, but shows strong depletion of Ta, Nb, Sn and W. This indicates that these elements are not enriched in the initial hydrosaline melt exsolved from the magmatic system in the Dangba pegmatites, and subsequent alteration of early crystallized primary minerals (e.g., spodumene, alkali feldspar and CGM) replenish these elements into the melt. Fluid saturation and exsolution is suggested to occur when the pegmatite-forming melt ascent along fractures to the roof of the No. Ⅷ dikes, proved by the miarolitic cavities. The chemical compositions of exsolved aqueous fluid depends on mineralogy of pegmatites and partition behavior between melt and fluid. In addition, although albitization of pegmatite results in limited Li loss, it provides an insight for Li-Ta-Nb exploration in the Ke’eryin Orefield.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)