Iron-Copper-Zinc Isotopic Compositions of Andesites from the Kueishantao Hydrothermal Field off Northeastern Taiwan

The studies of iron (Fe), copper (Cu), and zinc (Zn) isotopic compositions in seafloor andesites are helpful in understanding the metal stable isotope fractionation during magma evolution. Here, the Fe, Cu, and Zn isotopic compositions of andesites from the Kueishantao hydrothermal field (KHF) off northeastern Taiwan, west Pacific, have been studied. The majority of δ56Fe values (+0.02‰ to +0.11‰) in the KHF andesites are consistent with those of MORBs (mid-ocean ridge basalts). This suggests that the Fe in the KHF andesites is mainly from a MORB-type mantle. The Fe-Cu-Zn isotopic compositions (δ56Fe +0.22‰, δ65Cu +0.16‰ to +0.64‰, and δ66Zn +0.29‰ to +0.71‰) of the KHF andesites, which are significantly different from those of the MORBs and the continental crust (CC), have a relatively wide range of Cu and Zn isotopic compositions. This is most likely to be a result of the entrainment of the sedimentary carbonate-derived components into an andesitic magma. The recycled altered rocks (higher δ56Fe, lower δ66Zn) could preferentially incorporate isotopically light Fe and heavy Zn into the magma, resulting in relative enrichment of the lighter Fe and heavier Zn isotopes in the andesites. The majority of the δ56Fe values in the KHF andesites are higher than those of the sediments and the local CC and lower than those of the subducted altered rocks, while the reverse is true for δ66Zn, suggesting that the subseafloor sediments and CC materials (lower δ56Fe, higher δ66Zn) contaminating the rising andesitic magma could preferentially incorporate isotopically heavy Fe and light Zn into the magma, resulting in relative enrichment of the heavier Fe and lighter Zn isotopes in the andesites. Thus, the characteristics of the Fe and Zn isotopes in back-arc and island-arc volcanic rocks may also be influenced by the CC and plate subduction components.

Isotopic signatures reveal zinc cycling in the natural habitat of hyperaccumulator Dichapetalum gelonioides subspecies from Malaysian Borneo

Background Some subspecies of Dichapetalum gelonioides are the only tropical woody zinc (Zn)-hyperaccumulator plants described so far and the first Zn hyperaccumulators identified to occur exclusively on non-Zn enriched 'normal' soils. The aim of this study was to investigate Zn cycling in the parent rock-soil-plant interface in the native habitats of hyperaccumulating Dichapetalum gelonioides subspecies (subsp. pilosum and subsp. sumatranum). We measured the Zn isotope ratios (δ66Zn) of Dichapetalum plant material, and associated soil and parent rock materials collected from Sabah (Malaysian Borneo). Results We found enrichment in heavy Zn isotopes in the topsoil (δ66Zn 0.13 ‰) relative to deep soil (δ66Zn -0.15 ‰) and bedrock (δ66Zn -0.90 ‰). This finding suggests that both weathering and organic matter influenced the Zn isotope pattern in the soil-plant system, with leaf litter cycling contributing significantly to enriched heavier Zn in topsoil. Within the plant, the roots were enriched in heavy Zn isotopes (δ66Zn ~ 0.60 ‰) compared to mature leaves (δ66Zn ~ 0.30 ‰), which suggests highly expressed membrane transporters in these Dichapetalum subspecies preferentially transporting lighter Zn isotopes during root-to-shoot translocation. The shoots, mature leaves and phloem tissues were enriched in heavy Zn isotopes (δ66Zn 0.34–0.70 ‰) relative to young leaves (δ66Zn 0.25 ‰). Thisindicates that phloem sources are enriched in heavy Zn isotopes relative to phloem sinks, likely because of apoplastic retention and compartmentalization in the Dichapetalum subspecies. Conclusions The findings of this study reveal Zn cycling in the rock-soil-plant continuum within the natural habitat of Zn hyperaccumulating subspecies of Dichapetalum gelonioides from Malaysian Borneo. This study broadens our understanding of the role of a tropical woody Zn hyperaccumulator plant in local Zn cycling, and highlights the important role of leaf litter recycling in the topsoil Zn budget. Within the plant, phloem plays key role in Zn accumulation and redistribution during growth and development. This study provides an improved understanding of the fate and behaviour of Zn in hyperaccumulator soil-plant systems, and these insights may be applied in the biofortification of crops with Zn.

Fingerprinting the Cretaceous-Paleogene boundary impact with Zn isotopes

Numerous geochemical anomalies exist at the K-Pg boundary that indicate the addition of extraterrestrial materials; however, none fingerprint volatilization, a key process that occurs during large bolide impacts. Stable Zn isotopes are an exceptional indicator of volatility-related processes, where partial vaporization of Zn leaves the residuum enriched in its heavy isotopes. Here, we present Zn isotope data for sedimentary rock layers of the K-Pg boundary, which display heavier Zn isotope compositions and lower Zn concentrations relative to surrounding sedimentary rocks, the carbonate platform at the impact site, and most carbonaceous chondrites. Neither volcanic events nor secondary alteration during weathering and diagenesis can explain the Zn concentration and isotope signatures present. The systematically higher Zn isotope values within the boundary layer sediments provide an isotopic fingerprint of partially evaporated material within the K-Pg boundary layer, thus earmarking Zn volatilization during impact and subsequent ejecta transport associated with an impact at the K-Pg.

Rodingitization of mafic and ultramafic rocks in ophiolites from Northern Greece, seen by non-traditional stable isotopes, such as Cu, Fe and Zn.

<p>Rodingites are metasomatic rocks, frequently found in ophiolitic complexes. They offer important information about the interaction between ultramafic-mafic rocks and metasomatizing fluids, as well as about the post-magmatic evolution of ophiolitic suites (Tsikouras et al., 2009; Hu & Santosh, 2017; Surour, 2019; Laborda-Lopez et al., 2020). Metasomatism, such as rodingitization, is a very intricate process, which depends on the mineralogy of the initial rock, the nature of the metasomatic agent, the fluid/rock ratio, the duration of metasomatism and the chemical disequilibrium at the time of metasomatism between the host rock and the metasomatic medium (Poitrasson et al., 2013). Rodingites from the Veria-Naousa and Edessa ophiolites, in Northern Greece, were geochemically analyzed and characterized by substantial overprint of primary textures. Their field observation, their neoblastic mineral assemblages and metasomatic textures reveal that they derived from ultramafic and mafic protoliths. The mineral phases in the ultramafic derived rodingites (UDR) include mainly diopside, garnet, chlorite, epidote, tremolite and Fe-Ti oxides whereas mafic derived rodingites (MDR) consist of diopside, garnet, vesuvianite, chlorite, quartz, prehnite and actinolite. The studied rodingites present δ<sup>65</sup>Cu values varying from -0.17‰ to 0.62‰ and for ultramafic and mafic parent-rocks from -0.49‰ to +0.50‰. The UDR and MDR from both ophiolites display δ<sup>66</sup>Zn range from -0.06‰ to 0.74‰ and their photoliths present a narrower range from +0.04‰ to +0.41‰. Rodingitization affects in different way UDR and MDR samples. On one hand, Cu isotope ratios are systematically heavier in rodingites compared to their respective protoliths, except for one rodingite sample that requires confirmation due to large error bar. On the other hand, Zn isotopes show enrichment in light isotopes (group 1: comprising all UDR and some MDR samples), or in heavy isotopes (group 2, only MDR samples). Intriguingly, the same protolith can lead to both group 1 and 2 rodingites, as defined here.  No mineralogical or geochemical trend can be found to understand the dual behavior of Zn stable isotopes during rodingitization so far. Fe isotopes do not show any significant fractionation of δ<sup>56</sup>Fe, ranging from +0.07‰ to +0.19‰ for the rodingites and from +0.12‰ to +0.23‰ for their protoliths, indicating that Fe isotopes are highly resistant to rodingitization. Our study shows that rodingitization enriches metasomatized samples in heavy Cu isotopes and has no impact on Fe isotopes. It remains unclear why Zn isotopes can be affected both ways.</p>