The study of Neoproterozoic mafic magmatism in the western margin of the Yangtze Terrane is crucial for reconstructing the Rodinia Supercontinent. However, the origin and tectonic significance of these widespread Neoproterozoic magmatic suites remain debated. The key point of the debate lies in whether these magmatic rocks are related to subduction-related island-arc magmatism or mantle-plume-driven rifting. The Shigu and Judian Groups in northwestern Yunnan are distributed in the Shigu-Judian area, and belong to the Zhongza Terrane which was situated at the westernmost margin of the Yangtze Terrane during Neoproterozoic. Two sets of metamorphic basic rock interlayers were identified respectively in the Yangpo and Tacheng Formation of the Shigu and Judian Groups in the Weixi County area. Zircon U–Pb dating has constrained their formation ages at 867 and 796 Ma, confirming the Neoproterozoic deposition of both groups. Whole-rock geochemistry and Sr–Nd–Hf isotope analyses indicate that these volcanic rocks were derived from a mantle source that had been modified by subduction-related components (sediments or slab melts). The primary magma likely originated from a low degree of partial melting of a spinel–garnet lherzolite mantle source and subsequently underwent plagioclase and clinopyroxene fractional crystallization during ascent. The geochemical and isotopic signatures are consistent with a subduction‑modified mantle source, and with a low degree of partial melting (spinel-garnet lherzolite source) followed by fractional crystallization of plagioclase and clinopyroxene. Collectively, the Neoproterozoic mafic magmatism of the Shigu and Judian groups in the Zhongza Terrane is compatible with long-lived oceanic-lithosphere subduction beneath the Zhongza Terrane, with subduction persisting until at least 796 Ma.
Yellow cuboid diamonds are widespread in alluvial placers of the northeastern Siberian craton, but are extremely rare in kimberlite pipes. Here we present the first systematic study of 41 cuboid diamonds from the Udachnaya (n = 23) and Yubileynaya (n = 18) kimberlite pipes of the Siberian craton. The diamonds exhibit variable resorption features with overall cuboid growth patterns and belong predominantly to the rare Ib–IaA type, containing C, A, X, and Y nitrogen defects in different proportions. Udachnaya cuboid diamonds show higher nitrogen contents ( 1000–1750 ppm) and aggregation states (
Phlogopite is an important hydrous silicate that is the primary indicator of modal mantle metasomatism. The review presents a comprehensive analysis of a dataset of phlogopite compositions from mantle xenoliths in kimberlite and inclusions in natural diamonds. Variations in major- and minor- element contents are examined in relation to mineral parageneses and geodynamic settings, spanning lherzolitic and harzburgitic peridotites, eclogitic assemblages, and phlogopite-bearing metasomatites. Systematic trends in Mg#, Ti, Cr, Al contents record two main pathways: metasomatic overprinting of mantle material and contribution of crust-derived material. Mantle metasomatism tends to diminish compositional differences between micas in peridotitic and eclogitic xenoliths. The compiled dataset demonstrates that the phlogopite composition can be used as a petrogenetic and geodynamic tracer of mantle processes beneath kimberlite provinces. Examples from peridotitic and eclogitic inclusions in diamonds, mantle xenoliths, and phlogopite-bearing metasomatites underscore the diagnostic value of such approach for reconstruction of the evolution of volatile-rich mantle domains and identification of their role in kimberlite and related magmatism.
The paper presents data on the composition of condensate vapor–gas flows sampled in summertime on the surface of dumps of processing products of mining wastes. The data make it possible to assess the migration capacity of major and trace elements in the gas phase depending on the mineral composition of the anthropogenic materials and the physical and chemical characteristics of the water extracts (mobile fraction). The condensates of the vapor–gas mixture sampled above the surface of the tailings were analyzed for a wide range of chemical elements, including major elements (Ca, Mg, Na, K, Al, and Mn), metals (Cu, Zn, Pb, Cd, Co, Ni, and Ag), and metalloids (As and Sb). The concentrations of these elements in the condensates depend on both their contents in the solid waste and the amount of mobile (water-soluble) forms. Comparison of the ratios of geochemically related elements in the different phases led us to elucidate the mobility of the elements when they form volatile species. The data on the amounts of elements that migrate with the vapor–gas phase demonstrate that contrasting anomalies form in the near-surface layer of the atmosphere, and this is confirmed by the composition of the rainwater sampled at different times in the neighboring areas.
Evaporation of crystalline and liquid wollastonite from a molybdenum cell was studied by Knudsen effusion mass spectrometry in the temperature range 1751–2087 K. Molecular species typical of simple oxides and gaseous CaSiO3 were identified in the gas phase over wollastonite. Partial pressures of vapor species over wollastonite were determined for the first time. The determination of oxide activities in wollastonite made it possible to calculate the enthalpy and entropy of mixing: –38.92 ± 0.52 kJ/mol and 2.33 ± 0.29 J/(mol K), as well as the enthalpy of CaSiO3 melting at 1818 ± 7 K: 27.64 ± 0.57 kJ/mol. Based on this information, the mixing enthalpy and entropy in rankinite (Ca3Si2O7) were estimated in the temperature range 1600–1737 K: –42.63 ± 0.63 kJ/mol and 2.39 ± 0.35 J/(mol K), which are similar to the available thermochemical data. It was shown that redox interaction with the effusion cell material was mainly due to molecular oxygen, the amount of which decreased significantly compared with atomic oxygen in the absence of interaction. The behavior of wollastonite melt follows the patterns typical of other melts of compounds found in the refractory calcium–aluminum-rich inclusions in chondrites.
