Garnet from eclogites often shows very heterogenous and extremely high hydroxyl concentration. Eight eclogite samples were selected from the Sulu ultrahigh-pressure terrane and the Sumdo high-pressure metamorphic belt (Lhasa). The mean hydroxyl concentration in pyrope-rich and almandine-rich garnet varies from 54 to 427 ppm H₂O and increases with the retrogression degree of eclogites. TEM observations reveal nanometer-sized anthophyllite exsolutions and clinochlore inclusions in water-rich domains in garnet, where anthophyllite is partly replaced by clinochlore. Because of overlapping of the infrared stretching absorption bands for structural OH in garnet and chlorite, it is impossible to exclude contribution of chlorite inclusions to the estimated hydroxyl concentration in garnet. The broad band near 3400 cm⁻¹ is attributed to molecular water and nanometer-sized chlorite inclusions. Anthophyllite exsolutions may be formed by decomposition of hydrous garnet from ultrahigh-pressure eclogites during exhumation. Significant amounts of water can be stored in garnet from massif eclogites in the forms of hydroxyl in garnet and nanometer-sized inclusions of anthophyllite and clinochlore, as well as fluid inclusions. Amphibolite facies retrograde metamorphism can significantly increase both hydroxyl concentration and water heterogeneity in garnet from massif eclogites. These nano-inclusions in garnet provide a window to trace the water cycle in subduction channels.

The relationship between the Late Ordovician–Early Silurian sedimentary system, weathering, paleoclimate, and primary productivity in the Yangzi region is not well understood. In this study, by analyzing the sedimentation cycle and major trace elements of the Youc well 2 in the southeast Sichuan Basin, the coupling relationships of weathering indicators, terrigenous debris input indicators, paleoclimate, redox condition indicators, U-Mo covariance model, Mo/TOC relationship, and paleoproductivity indicators are investigated. The results show that single-well logs delineate four third-order sedimentary sequences (SS1, SS2, SS3, and SS4), two sedimentary subfacies, and four sedimentary microfacies in the Wufeng Formation–Longmaxi Formation. The weathering degree is stronger at the bottom where the climate shifts from warm–wet to cold–dry, and the seawater is in an oxidic–anoxic–oxidic–anoxic environment. While the primary productivity and material source input decreases gradually in the middle and upper part, the climate becomes dry and cold, and the seawater is in an anoxic–oxidic environment. Thus, a rock enrichment model for the organic matter shale of the Wufeng Formation–Longmaxi Formation in southeast Sichuan has been established. This provides more information on the control factors concerning organic matter enrichment and their interactions.

Kimberlite has attracted considerable interest among geologists as the primary source of natural gem-quality diamonds. The term “transitional kimberlite” was previously introduced to categorize rocks that exhibit bulk geochemical and Sr–Nd isotopic characteristics intermediate between those of archetypal kimberlite (formerly Group-I) and orangeite (formerly Group-II). Nevertheless, the petrogenesis of transitional diamond-bearing kimberlites remains poorly understood due to limited research. The diamondiferous transitional Wafangdian kimberlite in the North China Craton (NCC) thus provides a valuable opportunity for a detailed case study. We investigated fresh hypabyssal transitional Wafangdian kimberlites using bulk-rock major and trace element geochemistry to constrain near-primary parental magma compositions and decipher their petrogenesis. Geochemical compositions identify samples affected by crustal contamination based on elevated SiO₂, Pb, heavy rare earth element (HREE) concentrations, and Sr isotopic ratios. Compositional variations among macrocrystic samples (MgO: 29.7–31.5 wt.%; SiO₂: 30.6–34.7 wt.%; CaO: 3.9–7.5 wt.%; Mg^# [atomic Mg/(Mg + Fe²⁺) × 100]: 85–88) result from substantial entrainment and partial assimilation of peridotite xenoliths (up to 35%). In contrast, variations within aphanitic samples (MgO: 24.0–29.7 wt.%; SiO₂: 27.7–30.9 wt.%; CaO: 6.0–11.8 wt.%; Mg^#: 81–85) are attributed to fractional crystallization of olivine and phlogopite (~1–32%). Based on these constraints, the near-primary parental magma composition for the Wafangdian kimberlite is estimated as ~29.7 wt.% SiO₂, ~29.7 wt.% MgO, and Mg^# 85. Trace element concentrations in the transitional Wafangdian kimberlites resemble those of archetypal kimberlites globally (e.g., Nb/U > 26, La/Nb < 1.4, Ba/Nb < 16, Th/Nb < 0.25), indicating a shared convective mantle source. However, the Wafangdian kimberlites exhibit distinct characteristics: ε_Nd(t) values ranging from −3.44 to −1.77, higher Al₂O₃ and K₂O contents, and lower Ce/Pb ratios (10–20) compared to archetypal kimberlites. These features suggest the mantle source region was profoundly influenced by deeply subducted oceanic material.