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Abstract: Eclogite-hosted garnet–spinel–corundum–quartz-bearing titanohematite veins and lenses (10–20cm in width) are described for the first time in the Sulu ultrahigh-pressure metamorphic terrane. Some of the lenses were aligned parallel to the foliation of the host eclogite, suggesting that they were the product of ductile deformation of one titanohematite layer. A vein composed of titanohematite+ilmenite+hematite+spinel+garnet+corundum+quartz+K-feldspar+albite was studied in detail. Ti–Fe oxides account for up to >80% and Al-rich phases for ∼15% of the total volume of this vein. Electron microprobe analyses show that the titanohematite solid solution was made up of 0.75 hematite+0.25 ilmenite. The unusual mineral assemblage of garnet+spinel+corundum+quartz implies that this vein could have experienced high temperatures (>900°C). Although the garnets showed well-defined Mg and Mn diffusion zoning in the rim as a result of the high temperature event, slight Mg and Mn growth zoning was preserved in the core. Thus, we suggest that the Sulu UHP terrane could have experienced a short-lived, high-temperature (>900°C) stage during exhumation. Garnets in the titanohematite vein were characterized by extremely low trace-element contents. Petrological and geochemical features of the veins suggest that they could be metamorphic products of igneous cumulates composed of magnetite+plagioclase±clinopyroxene. [Copyright &y& Elsevier]

Three types of carbonates have been found in the Miocene basalt in the Dongbahao area (Inner Mongolia), including wide veins and veinlets of carbonate in basalt and carbonates in peridotite xenoliths. Except for the dolomitic zonation in the basalt, all of the carbonates are calcite. Despite their different appearances, they share almost identical geochemical characteristics of low LILE (low large ion lithophile element), HFSE (high field strength element), and REE (rare earth elements) contents (ΣREE = 0.51–137 ppm); negative Ce anomalies; and low Ce/Pb ratios (0.51–74.5). Moreover, they show high δ 18 O SMOW values (20.95–22.61‰) and 87 Sr/ 86 Sr ratios (0.7087 ± 0.0003 (1σ, n = 17)). These characteristics indicate a sedimentary precursor for these carbonates. However, the occurrence and petrographic characteristics imply an igneous origin for the carbonates rather than a hypergene process. Further, the trace element compositions of the silicate melt and carbonate melt in the calcite-dolomite-silicate zonations fall on the same variation lines in the plots of Y-Ho, La-Yb, Li-Pb and Ba-Cu. It is suggested that these melts could have evolved from one magma system or could have been equilibrated. Given the partition coefficients of REEs and alkali elements (Cs, Rb, and K) between the carbonate melt and silicate melt, it can be inferred that these melts could have been formed from a primary H 2 O-Si-bearing Mg-Ca-carbonate melt by an immiscibility process at 1–3 GPa. Considering the southward subduction of the Paleo-Asian ocean along the northern margin of the North China Craton (NCC), these carbonate melts could have been derived from the melting of subducted sedimentary carbonate rocks. Interestingly, these carbonates have quite depleted carbon isotopic compositions (δ 13 C PDB = −8.23‰ to −11.76‰) but moderate δ 18 O SMOW values, implying coupled H 2 O-CO 2 degassing during subduction and/or recycling to the Earth’s surface. Low-δ 13 C PBD carbonates appearing at the global scale may suggest an underestimated path of CO 2 emission back to the atmosphere. [ABSTRACT FROM AUTHOR]

[Display omitted] • Linglong and Guojialing granitoids were strongly depleted in S and Au. • Mafic magmas underplated in Jiaodong before 130 Ma were also poor in S and Au. • Magma underplating had not enriched the Jiaodong lower crust in sulfides and Au. • The crust was unlikely to be the primary Au source of the Jiaodong gold deposits. Mantle-derived magmas widely underplated the lower crust of eastern North China Craton (NCC) during the large-scale extension in the Mesozoic. The giant Jiaodong gold deposits formed at 120 ± 5 Ma, slightly later than the extensive magma underplating. It remains poorly constrained whether the magma underplating had pre-enriched the crust in significant sulfides and gold (Au) via sulfide accumulation, facilitating subsequent regional Au mineralization in the Jiaodong. In this study, we applied high-precision methods to determine the concentrations of S, Cu, Ag, and Au in the Mesozoic mafic and felsic igneous rocks related to the Jiaodong gold deposits. The studied samples include Guojialing granodiorites (n = 7) and their coeval mafic microgranular enclaves (MMEs, n = 13), as well as two Linglong granites. The Linglong and Guojialing granitoids display no sulfides and extremely low Au concentrations, so they are unlikely to be the major Au source. The MMEs resulted from Mesozoic magma underplating and related magma mixing at ∼130 Ma. The MMEs are also free of sulfides and show remarkably low concentrations of S, Cu, Ag, and Au. The S concentrations of MMEs are far lower than those required for sulfide saturation. This indicates that the S- and Au-depleted nature of MMEs was unlikely caused by sulfide segregation of sulfide-saturated magmas but inherited from the S- and Au-poor parental magmas. Therefore, the mantle-derived mafic magmas in the Jiaodong Peninsula, which had underplated the lower crust before 130 Ma, probably have not led to the extensive sulfide accumulation and gold pre-enrichment in the deep crust. [ABSTRACT FROM AUTHOR]