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Weathering crusts after granites are the most important source of heavy rare-earth elements (HREE) worldwide. Although HREE in these deposits is known to be inherited from parental rocks, the origin of HREE enrichment and the reasons why it is rare outside of China remains unclear. Here, we report the occurrence of variably organized nanoparticles of Ce-poor (

Barite is an abundant sulfate mineral in nature. Especially, the variety of morphologies of barite is often driven by the mixing of Ba-bearing hydrothermal fluid and sulfate-bearing seawater around hydrothermal chimneys. In order to better understand the factors affecting the morphology and precipitation mechanism(s) of barite in seafloor hydrothermal systems, we synthesized barite by a new method of in-situ mixing of BaCl2 and Na2SO4 solutions at 200 °C while varying Ba concentrations and ratios of Ba2+/SO42−, and at room temperature for comparison. The results show that barite synthesized by in-situ mixing of BaCl2 and Na2SO4 solutions at 200 °C forms a variety of morphologies, including rod-shaped, granular, plate-shaped, dendritic, X-shaped, and T-shaped morphologies, while room temperature barites display relatively simple, granular, or leaf-like morphologies. Thus, temperature affects barite morphology. Moreover, dendritic barite crystals only occurred at conditions where Ba2+ is in excess of SO42− at the experimental concentrations. The dendritic morphology of barite may be an important typomorphic feature of barite formed in high-temperature fluids directly mixing with excess Ba2+ relative to SO42−.

Granitoids are the dominant component of the continental crust and can be used as probes for crustal formation and evolution. The origin of granites, especially ambiguous granites with alkaline affinities emplaced in orogenic settings, however, remains controversial. Here, we report the petrology, geochronology and geochemistry of Paleoproterozoic alkali-feldspar granites associated with carbonated alkaline rocks from the Trans-North China Orogen in the North China Craton. Corundum-bearing Al-rich gneisses are associated with the granites and occasionally contain granite pockets and veinlets. The rocks have high amounts of K2O (10–14 wt%) and low CaO (0.3–2.3 wt%) contents and show metaluminous to weakly peraluminous features. Moreover, they have low levels of total REE (18–100 ppm) and show strong LREE enrichment [(La/Yb)CN = 44–128] and positive Eu anomalies (δEu = 1.6–10.2). The zircons record a U–Pb age of 1809 ± 3 Ma and eHf(t) values ranging from −3.7 to −7.1, which are consistent with those in the gneisses (1827 ± 14 Ma, eHf(t) = −3.3 to −8.4). Inherited zircons occur in both rocks and show similar ages of ∼2.0 and ∼2.1 Ga. Considerably high δ18OSMOW ratios (9.9–10.9 ‰) in the zircons and low eNd(t) values (−4.0 to −6.2) of the granites were identified. The granite was generated by partial melting of pelitic rocks instead of differentiation of mantle-derived magmas, whilst the gneiss represents the residuum. The carbonated alkaline magmas arising from the mantle provided sufficient heat for anatexis of the crust. Granitoid rocks showing alkaline affinity in orogenic belts may not be the fractionation products of mantle-derived melts but may have formed from reworked sedimentary materials.

The North China Craton (NCC) is one of the oldest cratons in the world that preserves the records of many important geological events in the early evolution of the Earth. However, the early Precambrian tectonic evolution history of the NCC is still controversial. Here we report Paleoproterozoic leucogranites, garnet granites and granulites in the Fengzhen area that constitutes a junction between the Khondalite Belt and the Trans-North China Orogen (TNCO). The leucogranites have high SiO2 content (75–85 wt%), and magmatic zircon U-Pb age of 2199 ± 3 Ma. Their zircons have slightly various eHf(t) values (−0.45 to 1.41) with TDM model ages of 2.5–2.6 Ga. The granites show strong LREE enrichment with La/Ybcn ratio of 12–176, and have high initial Nd isotope (eNd(t) = 3.5–4.5). Most of them display positive Eu anomaly, excluding fractional crystallization contribution on the high Si feature. The leucogranite was produced by melting of Late Archean felsic TTGs (tonalite–trondhjemite–granodiorite) and addition of juvenile crust. Magmatic zircons yield the garnet granite age of 2002 ± 3 Ma. The zircons show various eHf(t) values (−5.8 to 7.1) and TDM model ages (2.1–2.6 Ga). Low initial eNd(t) isotope value (−4.2 to −8.3) was determined in the granites. The granulites are high pressure metamorphic rocks with a peak pressure of 12.0 ± 0.8 kbar, and have similar metamorphic age of 1967 ± 10 Ma to the garnet granites. This indicates that the Fengzhen area underwent 2-Ga inter-continental orogeny, in which the melting of sedimentary rock formed the garnet granites. Similarly, sodic TTG melting to form K-rich leucogranites also needs high pressure. However, the leucogranite age is obviously older than the peak metamorphic timing of continent–continent collision. This implies that the Fengzhen area may have underwent arc-continental collision at 2.2 Ga.

Syenites are commonly associated with alkaline silicate rocks and carbonatites. The origin of syenites, however, remains controversial. Here, we report an intrusive suite of carbonatite–clinopyroxenite–clinopyroxene syenite complexes and granites from the Trans-North China orogen in the North China craton and present the systematic mineralogy and geochemistry of the syenites and their associated clinopyroxenites and granites. The granite has an age of 1808 ± 6 Ma and eHf(t) ranging from −5 to −8.5, which is consistent with the clinopyroxene syenite. The syenite is composed mainly of Ba–Sr-rich alkali-feldspar and clinopyroxene, and is strongly associated with the clinopyroxenite and granite. The rock exhibits a plastic flow feature in the contact zone between the clinopyroxenite and granite. In the contact zone towards the granite margin, the alkali-feldspar shows gradual decreases in Ba, Sr, and rare earth elements (REE), whereas the clinopyroxene shows good transition from diopside to hedenbergite. The syenitic clinopyroxene has variable Fe–Mg and REE contents. Differences in the compositional zoning of the alkali-feldspar and clinopyroxene were observed such that the former mineral core contains relatively lower Sr (1864 vs. 11754 ppm), Ba (8590 vs. 41504 ppm), and REE (1.0 vs. 23 ppm, ∑La–Eu) abundances than the rim, whereas the clinopyroxene shows the opposite trend [1086 vs. 847 ppm for Sr, 178 vs. 85 ppm for REE (∑La–Lu) in the core and rim, respectively]. The mineral chemistry implies the clinopyroxene syenite was formed by mixing between the mantle-derived clinopyroxenite and crust-derived granite melts. The age of rock formation is close to the metamorphism age of high-pressure granulites in the Trans-North China orogen, indicating a post-collisional setting related to the inter-continental collision of the North China craton in the Paleoproterozoic.

Carbonatites are abundant in the rare earth elements (REE), and they host the most important REE resources in the world. However, the mechanisms that concentrate these elements during carbonatitic magmatic processes are still poorly constrained. Here, we report the occurrence of apatite-hosted melt inclusions from the Ulgii Khiid carbonatites, Mongolia, and use these to reconstruct the evolution of REE concentrations and patterns in early, primary carbonatite magma. The melt inclusions consist of a varied polycrystalline assemblage of daughter minerals, including calcite, diopside, phlogopite, magnetite, pyrite, monazite, parisite, and a phosphate glass which is remarkably enriched in REE. Heating-quenching experiments show that the homogenization temperatures of the inclusions are above 1200 °C and produce three immiscible liquid phases (i.e., phosphate-, silicate-, and Fe-silicate-melt). The phosphate melt has much higher REE content than the silicate melts. We, therefore, suggest that the melt inclusions trapped a REE-, P- and silicate-enriched carbonate melt produced via carbonate-silicate liquid immiscibility. During this process, both REE and P preferentially incorporated into the carbonate melt. With subsequent crystal fractionation of REE- and P-poor carbonate and silicate minerals, the separated carbonatitic melt becomes P-REE-saturated, forming REE minerals and an immiscible REE-rich phosphate melt. The phosphate melt is highly efficient at concentrating REE during the immiscibility process and plays a crucial role in controlling the REE budget in the P-rich carbonatite magmas.

Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ26Mg values (−1.89 to −1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.