Trace Element Characteristics Research Articles

Controls on Corundum Formation: METASOMATISM of Ultramafic Rock, NATTIVIT, South-East Greenland

Abstract The geotectonic setting for plumasite-type corundum occurrences is understudied, even though it is of importance for the understanding of trace-element patterns used for fingerprinting of ruby and sapphire. Mineral reactions related to metasomatism caused by pegmatite intrusion into ultramafic rock result in a characteristic trace element signature in corundum and thereby control its colour. The Nattivit area, Isertoq Terrane, South-East Greenland, provides a natural laboratory to investigate these mineral reactions and corundum trace element patterns given the excellent exposure of a typical plumasite-type occurrence where pegmatites intruded ultramafic rocks of different composition, namely lherzolite and dunite. The pegmatite dykes are 10 to 50 cm wide in the ultramafic rocks, whereas the adjacent alteration zone in the ultramafic rock reaches widths between 10 and 30 cm. Metasomatism resulted in desilication of the pegmatites and a decrease in Ca, Mg, K, Mn, Al and Fe away from the centre of the pegmatite dyke. Chromium, Ni, Mg, Fe, Sc, Co, V, Zn, Ti and Mn in the metasomatic reaction zones are predominantly derived from the ultramafic rock. We identify three zones with different mineral assemblages. In the lherzolite, tschermakite and biotite are formed in the centre of the reaction zone, which is followed by anorthite-rich plagioclase, hercynite, dolomite and ultimately pink corundum that occurs in the most heavily reacted part of the metasomatic reaction zone. The metasomatic reaction zones in the ultramafic rock include an intense reactionzone at direct contact to the pegmatite dyke with biotite and actinolite, and two alteration zones further away from the pegmatite dyke with enstatite, actinolite, anthophyllite, phlogopite, dolomite, sulphide, apatite and chrome-spinel. In the dunite, no biotite formed and hence, corundum contains more Fe, Mg and Ti. The plumasite-type corundum from Nattivit contains more Fe than Cr, which is typical of pink corundum hosted in mafic-ultramafic rocks. The corundum-forming reaction is dated from the pegmatite vein to 1843±4 Ma (U-Pb zircon age), which is coinciding with convergence of the Rae and North Atlantic cratons resulting in the Nagssugtoqidian Orogen. Only syn-tectonic, corundum-normative, peraluminous, calc-alkaline pegmatites of granitic to granodioritic composition that intrude into ultramafic rocks in the upper plate formed corundum in this area. The pegmatites are classified as muscovite class granitic pegmatites and intruded at upper amphibolite facies conditions. These pegmatites possible originated from partial melting of mafic granulite or a subducted oceanic plate. The formation of granitic pegmatites and related corundum mineralization in the upper plate of a collisional orogen described here is comparable to other corundum occurrences, e.g. Polar Urals, and thus is regarded as a typical geotectonic setting for plumasite-type corundum.

Characterizing the chemical composition of red coloring matter samples from the Altamira cave using synchrotron µXRF imaging

The chemical in situ study of red coloring matter from Paleolithic cave art is challenging because the same trace elements can be present both in the matter and in the calcitic support, and the two present a heterogeneous composition. In this study, thirteen red iron oxide-based coloring matter samples obtained at drip points coming from eight locations within the Techo de los Polícromos, Altamira cave (Spain), have been analyzed by highly sensitive synchrotron-induced micro-X-ray fluorescence (SR-µXRF). Our analyses improved the characterization of red Paleolithic pigments by establishing characteristic trace element patterns, additionally facilitating a comparison of the distinct representations within the cave. Furthermore, new differentiation criteria between the composition of the calcitic walls and that of the red coloring matter could be established, helping to improve future non-invasive analyses.

Chalcopyrite, sphalerite, and pyrite chemistry in stratiform sediment-hosted Cu(-Co) metallogenic districts: trace element characteristics and factors controlling polymetallic mineralization

AbstractStratiform sediment-hosted Cu deposits are significant global sources of Cu and other important metals. The Polish Kupferschiefer produces Ag, Au, Pb, Ni, Se, and Re as by-products, whereas Co is one the of most important metals in the stratiform sediment-hosted Cu-Co deposits of the Central African Copperbelt and the Namibian Dolostone Ore Formation deposit. This study combines new and published laser ablation inductively coupled plasma mass spectrometry sulfide trace element data from these stratiform sediment-hosted copper districts. All the investigated districts exhibit sulfides occurring as disseminations and within later veins. Chalcopyrite, sphalerite, and pyrite trace element contents vary significantly between the metallogenic districts as well as between different ore stages. Random Forest discriminates the stratiform sediment-hosted Cu(-Co) districts based on trace element geochemistry. High Ag and Tl in chalcopyrite is attributed to the Polish Kupferschiefer, Ga and Ge to the Katanga Copperbelt, and Zn and In to the Dolostone Ore Formation deposit. Sphalerite from the Polish Kupferschiefer and the Dolostone Ore Formation deposit can be distinguished on the basis of the Fe and Cd contents. Cobalt and As are significantly elevated in pyrite from the Katanga Copperbelt and Mn in pyrite from the Dolostone Ore Formation deposit. The trace element contents also show that the stratiform sediment-hosted Cu(-Co) deposit sulfide data cluster separately from other deposit types. The variation in sulfide trace element contents between the three investigated stratiform sediment-hosted Cu(-Co) districts suggests that sulfide chemistry is related to the geology of the host basin and the nature of the underlying basement, which includes preexisting ore occurrences.

Petrogenesis of REE-mineralized granitic plutons in central Thailand, Southeast Asian tin belt: New insights from geochemistry and zircon U–Pb geochronology

Granitic rocks including biotite granite and biotite-muscovite granite exposed in the Uthai Thani area, central Thailand are located on the main eastern and central granitic belts of Southeast Asia. The biotite granites are characterized by an equigranular texture, whereas biotite-muscovite granites exhibit a porphyritic texture with K-feldspar megacrysts. Geochemically, biotite granites show metaluminous to weakly peraluminous high-K calc-alkaline affinity, whereas biotite-muscovite granite exhibits strongly peraluminous and shoshonitic. The biotite granites and biotite-muscovite granites have trace element features consistent with formation in subduction and syn-collision settings, respectively. The pressure–temperature conditions of emplacement in biotite and biotite-muscovite granite types are 1.94–2.28 kbar/676 °C–713 °C and 1.39–2.00 kbar/669 °C–698 °C, respectively, indicating solidification in upper crustal paleo-depths. Positive εHf (t) values of zircon in the biotite granites indicate similarity to I-type granite of the Sukhothai Terrane, whereas negative εHf (t) values of zircon in the biotite-muscovite granites compare well with S-type granites form in the Inthanon zone. Zircon U–Pb geochronology indicates that biotite granites might have emplaced during the Late Triassic is related to Paleo-Tethys subduction beneath the Indochina terrane, whereas biotite-muscovite granites might have emplaced during the Late Triassic to Early Jurassic period, probably as a result of collision between the Sibumasu and the Indochina Terranes. In the Uthai Thani area, the high total REE contents and the presence of primary REE minerals in granitic rocks reflect mineralization potential with respect to light REE, together with the magmatism related to Fe-Cu and Sn mineralization along the main granite belts in Thailand.

Kyanite microstructural and microchemical characteristics reveal differences in growth, deformation and chemical modification: A case study from the Paleoproterozoic suture zone of South Harris, NW Scotland

Based on petrological association, cathodoluminescence (CL), trace element signatures and orientation relationships, two generations of kyanite are distinguished in a high temperature, high pressure garnet-biotite-aluminosilicate bearing migmatite of South Harris, NW Scotland. The migmatite shows a garnet and biotite rich domain (Grt-Bt domain) which is cut at a low angle by a dominantly coarse-grained plagioclase-quartz leucosome. In addition, a fine-grained plagioclase-quartz-kyanite domain (Plag-Qtz-Ky domain) is present intercalated with the Grt-Bt domain and subparallel to the plagioclase-quartz domain. Type 1 kyanite is coarse grained and associated with Bt clusters and garnet within the Grt-Bt domain. It grew relatively early, syn- to post-garnet growth, in a suprasolidus environment resulting in crystallographically determined oscillatory CL and trace element zoning. Grains record evidence of progressive deformation in the crystal plastic regime, where deformation is accommodated by dislocation glide, climb and deformation twinning. The dominant activated slip system is (100)<001> with minor component of <100>, while deformation twins show a ∼ 180° rotation around ∼<001> axis and a twin plane near (001). Grains appear to be impervious to deformation induced diffusion with all zoning remaining sharp despite crystal plastic deformation. Grains in direct contact with the Plag-Qtz-Ky domain show late modification of the CL and trace element signature suggesting melt-mediated interface-coupled dissolution-precipitation reaction. This modification resulted in crosscutting lobate high trace element regions and irregular rims with low Cr and V content. These rims show similar CL and trace element characteristics as Type 2 kyanite which are exclusively seen within the Plag-Qtz-Ky domain suggesting that Type 2 grains are cogenetic with Type 1 rims. Type 2 grains are finer grained than Type 1 grains and show near uniform CL and trace element distributions with rare oscillatory zoned and relatively higher Cr & V bright cores. Type 2 show either no or very localized internal deformation features. However, they exhibit a clear shape preferred orientation which coincides with a crystallographic preferred orientation where the longest shape axis is parallel to <001>. We propose that Type 2 kyanite grains underwent melt-present deformation by rigid body rotation in an externally derived melt with different trace element chemistry than the host rock. This melt thus interacted chemically by melt-mediated interface-coupled dissolution-precipitation reactions with the surrounding rocks forming the Type 1 rims.Our study shows detailed analysis of kyanite is an important tool for giving constraints on the deformation, P–T and melting history of high-grade metamorphic rocks and migmatites.

The Cambrian collision of the Yangtze Block with Gondwana: Evidence from provenance analyses

The Neoproterozoic to Paleozoic Proto-Tethys Ocean has preserved critical records of Earth’s evolutionary history. The Lower Cambrian detrital strata along the northern margin of the Yangtze Block provide valuable information for gaining insight into the evolution of the Proto-Tethys Ocean, which is important in understanding the collision between the Yangtze Block and the Gondwana assembly. Here, we present comprehensive U-Pb ages and trace elements of zircons from Lower Cambrian detrital strata in the Yangtze Block. Our results revealed prominent age peaks at 600−500 Ma and 1100−800 Ma for detrital zircons in the Cambrian strata. The trace element characteristics of the detrital zircon indicate that the source rocks were mainly intermediate-felsic magmatic suites with minor input from mafic sources. These results suggest that the detrital materials were not only supplied from the interior of the Yangtze Block but also from magmatic sources in the internal orogenic belt of Gondwana. Furthermore, the kernel density estimate plots of detrital zircon U-Pb ages indicate a stable source-sink system in the Yangtze Block during the Early Cambrian. However, our data indicate that the crustal thickness of the Yangtze Block increased significantly since ca. 526 Ma, and the cumulative characteristics of the detrital zircons indicate that the rocks were deposited in a compressional tectonic environment after ca. 526 Ma, in contrast to those during the late Neoproterozoic, which were generally deposited in an extensional tectonic environment. This transition indicates that the initial collision between the Yangtze Block and the Gondwana supercontinent might have occurred at ca. 526 Ma, marking the rapid aggregation of the northern domain of the Gondwana assembly and potentially serving as an important indicator of the closure of the Yangtze-associated Proto-Tethys Ocean. Our findings provide key insights into late Neoproterozoic−early Paleozoic ocean-land evolution.

Gemological and Trace Element Characteristics of Cassiterite from Yunling, China

Gemological and Trace Element Characteristics of Cassiterite from Yunling, China

Effects of deep magmatic degassing and shallow seawater circulation on trace element and sulfur cycling in submarine hydrothermal systems: Insights from the Shijuligou analog, North China

Limited access to modern subseafloor sulfides hampers our understanding of the link between magmatic volatile influx and the cycling of trace elements and sulfur, as well as the effect of the subsequent shallow seawater circulation on these processes. Hence, we studied a well-preserved fossil analog of submarine hydrothermal systems – the Shijuligou volcanogenic massive sulfide (VMS) deposit from the North Qilian Mountains in North China to examine variations in elements and isotopes of subseafloor sulfides vertically.The vertical distribution of trace elements in subseafloor sulfides is strongly controlled by temperature gradients and redox states during the interaction between hot fluids and seawater beneath the paleo-seafloor. While the enrichment of elements like As, Sb, and Au (median: 1335, 43.7, and 0.30 ppm, respectively, n = 21) and negative δ34S values (mean: −3.07 ‰, n = 7) of euhedral pyrites in the jasper, along with the precipitation of high sulfidation minerals (e.g., enargite), suggest the input of magmatic volatiles into hydrothermal systems. During the shallow seawater-hydrothermal circulation, pyrites in the veined and stockwork zones exhibit distinctly elevated δ34S values (up to 15.74 ‰), accompanied by increased concentrations of wall-rock-derived elements (e.g., Cu, Ni, Si, and Ti) and low-temperature-responsive elements (e.g., Pb, Zn, and Cd). Sulfur isotopes of sulfides vary significantly from the surface to the deep ore zones, ranging from −3.36 to 19.84 ‰ (mean: 9.25 ‰, n = 37). The negative δ34S values of pyrites at the paleo-seafloor are due to the addition of H2S derived from the disproportionation of magmatic SO2. The increased δ34S values of stockwork and disseminated sulfides at depth are attributed to the progressive reduction of seawater sulfates by ferrous iron released from the alteration of fresh basalts. The trace elemental and isotopic characteristics of sulfides suggest the Shujuligou VMS deposit resembles the fossil analog of immature, subduction-related submarine hydrothermal systems.

Post-collisional reworking of juvenile mafic lower crust for the petrogenesis of late Triassic adakitic rocks in the East Kunlun Orogen

The East Kunlun Orogen (EKO), a major component of the Greater Tibetan Plateau, provides an excellent natural laboratory to investigate the tectonic evolution of the Paleo-Tethys Ocean (also known as the A'nyemaqen Ocean in the EKO). We present a combined study of in situ zircon UPb ages and LuHf isotopic compositions, and whole-rock major and trace element and Sr–Nd–Hf isotopic compositions of the post-collisional Xiangjia granodiorite at the eastern end of the EKO. Zircon UPb dating indicates that the Xiangjia granodiorites were emplaced at 225.0–217.1 Ma. Relict zircon cores yield ages of 267.5–239.5 Ma. These granodiorites are calc-alkaline to high-K calc-alkaline and metaluminous to weakly peraluminous, enriched in large-ion lithophile elements and light rare earth elements, and depleted in high field strength elements (e.g., Nb and Ta) and heavy rare earth elements. They yield trace element characteristics that are typical of adakitic rocks, including high Sr (493–590 ppm) and low Yb (0.74–1.12 ppm) and Y (8.83–12.24 ppm) contents, high Sr/Y (40.47–63.64) and (La/Yb)N (11.81–30.91) ratios, and positive Eu anomalies. The UPb ages and Hf isotopic compositions of the relict zircon cores and whole-rock SrNd isotopic compositions of the Xiangjia adakitic rocks are similar to those of the mafic arc magmatic rocks formed during the subduction of the Paleo-Tethys Ocean, suggesting they originated from the reworking of juvenile mafic lower crust. Phase equilibrium modelling suggests that the contemporaneous adakitic rocks from Xiangjia and other areas in the EKO are likely the products of partial melting of the juvenile mafic arc rocks under granulite-facies conditions at 10–11 kbar and 934–951 °C, possibly related to slab break-off in a post-collisional setting.

Critical Raw Materials Supply: Challenges and Potentialities to Exploit Rare Earth Elements from Siliceous Stones and Extractive Waste

Critical raw materials (CRMs) supply is a challenge that EU countries have to face, with many thinking about domestic procurement from natural ore deposits and anthropogenic deposits (landfills and extractive waste facilities). The present research focuses on the possibilities linked to the supply of CRMs and the potential for exploiting rare earth elements (REEs), investigating a large variety of extractive waste and siliceous rocks in the Piedmont region (Northern Italy). Indeed, the recovery of REEs from the extractive waste (EW) of siliceous quarries and other siliceous ore deposits can be a valuable way to reduce supply chain risks. Starting with a review of the literature on mining activities in Piedmont and continuing with the sampling and geochemical, mineralogical, petrographic, and environmental characterization of EW facilities connected to siliceous dimension stones, of kaolinitic gneiss ore deposits, and of soils present near the investigated areas, this study shows that the degree of REEs enrichment differs depending on the sampling area (soil or EW) and lithology. The concentration of REEs in the EW at some sampling sites fulfils the indicators of industrial-grade and industrial recovery; the high cumulative production and potential market values of EW and the positive recovery effects through proven methodologies indicate a viable prospect of REE recovery from EW. However, REE recovery industrialization faces challenges such as the difficulty in achieving efficient large-scale recovery due to large regional differences in REE abundance, the mismatch between potential market value and waste annual production, etc. Nonetheless, in the future, EW from dimension stone quarries could be differentially studied and reused based on the enrichment and distribution characteristics of trace elements. The present paper shows investigation procedures undertaken to determine both CRMs potentialities and environmental issues (on the basis of literature data employed to select the more-promising areas and on sampling and characterization activities in the selected areas), together with procedures to determine the waste quantities and tentative economic values of REEs present in the investigated areas. This approach, tested on a large area (Piedmont region), is replicable and applicable to other similar case studies (at EU and non-EU levels) and offers decision makers the possibility to acquire a general overview of the potential available resources in order to decide whether and where to concentrate efforts (including economic ones) in a more detailed study to evaluate the exploitable anthropogenic deposits.

Identification of the EMII-type mantle end-member of the Kerguelen mantle plume and its implications for the initial breakup of eastern Gondwana: New constraints from the Cretaceous diabase in the Tethyan Himalaya

The breakup of eastern Gondwana during the Early Cretaceous has been well-documented. However, the relationship between Cretaceous mafic magma and the Kerguelen mantle plume has not been well-constrained. It is also unknown if the Kerguelen mantle plume in the Tethyan Himalaya played a key role in triggering the breakup of eastern Gondwana. The petrogenesis and geodynamic processes of the coeval magmatism in the Tethyan Himalaya might provide value insights into this issue. In this study, we conducted petrological, geochronological, and geochemical investigations on a recently identified diabase from the Yamdrok Lake. The diabase contains zircon grains with a U-Pb age of 138 ± 8 Ma, suggesting the emplacement at the Early Cretaceous. Geochemically, the studied samples display OIB-like trace elemental features that are enriched in light rare earth elements (LREEs) but no significant depletion in high field strength elements (HFSEs), such as Nb, Ta, and Ti. Furthermore, they have relatively uniform Sr-Nd-Pb-Hf-O isotopic compositions with initial 87Sr/86Sr ratios varying from 0.70563 to 0.70623, εNd(t) and εHf(t) values range from 0.6 to 0.8 and 1.0–2.4, respectively, whole-rock δ18O values of 6.42 ‰ to 7.50 ‰, and (208Pb/204Pb)i = 38.995 ∼ 39.285, (207Pb/204Pb)i = 15.673 ∼ 15.698, and (206Pb/204Pb)i = 18.689 ∼ 18.914, similar to an EMII-type enriched mantle. And recycled shallow continental crustal materials into the OIB-like mantle source might account for the EMII-type mantle features observed in this study. Considering the Kerguelen mantle plume locating beneath the triple junction of Australia, Antarctica, and Greater India, we propose that the mafic rocks in this study might be genetically related to the early activity or even initiation of the Kerguelen plume during the Early Cretaceous. Our study further indicates that the Kerguelen mantle plume contains EMI- and EMII-type isotopic compositions, which are characterized by geochemical complexity and variation.

The 2.03–2.02 Ga arc–back-arc mafic magmatism from the Zhongxiang Complex, northern Yangtze Block: Implications for Columbia supercontinent assembly

To better understand Paleoproterozoic tectonic processes in the Yangtze Block during the assembly of the Columbia supercontinent, an integrated geochronological and geochemical study of amphibolite facies mafic rocks exposed in the Zhongxiang Complex in the northern Yangtze Block is presented. Based on trace element and rare earth element (REE) characteristics, these mafic rocks can be divided into two coeval groups. The MORB-like mafic rocks show flat REE patterns and are enriched in large-ion lithophile elements (e.g. Rb, Ba, K, Sr). Their zircon ɛHf(t) values range from + 3.43 to + 4.90. The other mafic rocks are arc-like and have elevated REE contents and display relatively light REE enriched patterns, as well as depletion in high field strength elements (e.g. Nb, Ta, Ti). The zircon ɛHf(t) values of the latter group range from + 0.17 to + 2.68. Zircon U-Pb dating yielded a weighted mean 207Pb/206Pb age of 2029 ± 15 Ma for the MORB-like mafic rocks, and 2023 ± 14 Ma for the arc-like mafic rocks, respectively. The elemental and isotopic characteristics indicate that the MORB-like mafic rocks may be derived from a depleted asthenospheric mantle source, whereas its counterpart with arc-like signatures originated from a lithospheric mantle source. The low (La/Yb)CN (1.10–2.84) and Sm/Yb (0.99–1.29) ratios indicate that the mafic rocks are formed by partial melting of spinel lherzolite mantle. Combined with other geological observations, these mafic rocks are inferred to constitute part of a mid-Paleoproterozoic continental arc–back-arc basin system. The 2.03–2.02 Ga mafic rocks from the northern Yangtze Block indicate that the continental margin experienced subduction in response to assembly of the Columbia supercontinent.

Zircon megacrysts in alkaline lavas of the Lusatian Volcanic field (Central Europe) – petrogenetic implications of U/Pb ages, Hf isotopes and trace element characteristics

Zircon megacrysts in alkaline lavas of the Lusatian Volcanic field (Central Europe) – petrogenetic implications of U/Pb ages, Hf isotopes and trace element characteristics

Integrated assessment of trace elements in a marine ranching area based on multi-species and multi-level biomarkers: a case study in China’s national-level marine ranching demonstration area

The goal of this study was to evaluate the trace element pollution in a marine ranching area in China based on molecular responses (expression of metallothionein and antioxidant enzyme genes), and biochemical biomarkers (metallothionein content, antioxidant enzyme activities, and malonaldehyde level) in four indicator species. We collected samples of two fish (Lateolabrax maculatus and Sebastes schlegelii), one crustacean (Charybdis japonica), and one gastropod (Rapana venosa) from the western Furong Island marine ranching area and from an adjacent area in March 2022 and measured the trace element content in these indicator species as well as in the seawater and sediment. We found that the bioaccumulation characteristics of trace elements and the response patterns of biomarkers were species specific. Moreover, not every biomarker was significantly correlated with environmental trace element content. We then established two biomarker combinations indicative of trace element pollution in seawater and sediment, respectively, based on the correlation between biomarkers and trace element contents. The selected biomarkers were integrated using integrated biomarker response version 2 (IBRv2). IBRv2 values in the studied marine ranching area were lower than those in the adjacent area. Additionally, these values were consistent with the bioaccumulation of trace elements in the indicator species, the integrated trace element pollution index for seawater, and the potential risk index for sediment. These results show that this multi-biomarker and multi-species IBRv2 approach provided a comprehensive diagnosis of trace element pollution in the marine ranching area. Therefore, its application may be beneficial for marine environmental monitoring and management in view of the ecotoxicological impact of pollutants on organisms.

Fossil metasomatized and newly-accreted fertile lithospheric mantle volumes beneath the Bakony-Balaton Highland Volcanic Field (central Carpathian-Pannonian region)

This study focuses on upper mantle xenoliths from Sabar-hill (Bakony-Balaton Highland Volcanic Field), a newly discovered locality of mantle xenoliths, situated in the central Carpathian-Pannonian region (CPR). The investigated seven peridotite and one pyroxenite xenoliths record two episodes in the geochemical evolution of the local subcontinental lithospheric mantle. The moderately deformed Group I xenoliths reveal modal contents (≥9 vol% orthopyroxene), major element characteristics (depletion in Al2O3 and CaO in orthopyroxenes) and trace element features (e.g., enrichment in U, Pb and Sr in clinopyroxenes) typical in supra-subduction zones (i.e., mantle wedge) xenoliths. All these suggest that the studied xenoliths were formed by silica-rich fluid/melt - peridotitic wall rock interactions. The tectonic background to the formation of Group I xenoliths is likely linked to the subduction of an oceanic slab during the Mesozoic-Paleogene. This may have happened far from the current position of Sabar-hill, to where the lithosphere, including the metasomatized mantle volume, was transferred via plate extrusion. The less deformed, dominantly protogranular and porphyroclastic Group II xenoliths are depleted in light rare earth elements (LREE). In contrast, they are enriched in clinopyroxene (≥11 vol%), incompatible major elements (e.g., Al and Na) and heavy rare earth elements (HREE), by a minimum of four times compared to primitive mantle. All these suggest that Group II xenoliths represent a geochemically fertile mantle partition and the degree of partial melting affected this mantle section was limited (≤7% based on trace elements). Group II xenoliths have higher equilibrium temperatures (1088–1168 °C) compared to Group I xenoliths (1018–1089 °C). The lack of petrographic and geochemical evidence pointing to metasomatism-related annealing in Group II xenoliths suggests that they are derived from a greater depth. It follows that Group II xenoliths could represent prior asthenosphere volumes which recently accreted to the lithosphere. The lithospherization of the upper part of the asthenosphere may have initiated after the tectonic inversion of the region, when compressional tectonic regime beneath the CPR gradually overtook the former extensional one in the last ∼8 Ma. The high bulk structural hydroxyl content in both Group I (22–1699 ppm) and II (55–320 ppm) xenoliths is likely linked to the subduction events that took place in the CPR from the Mesozoic onwards. These events transported significant amounts of fluid (H2O) back to the upper mantle, affecting both the mantle wedge and the asthenosphere.

Why are oceanic arc basalts Ca-rich and Ni-poor? Insights from olivine-hosted melt inclusions from Kibblewhite Volcano in the Kermadec arc

Ankaramites, which are clinopyroxene-rich basalts with primitive whole-rock compositions (Mg# >65), are common in oceanic arcs and are characterized by high whole-rock CaO/Al2O3 (>1.0) ratios and olivine crystals with anomalously low nickel contents (<0.2 wt% NiO). These geochemical characteristics cannot be explained by the melting of ordinary mantle peridotite. However, their origin is critical for understanding the formation of primary magmas in oceanic arcs. Here, we investigated olivine-hosted melt inclusions (MIs) from ankaramites and magnesian andesites of the Kibblewhite Volcano in the Kermadec arc. The MIs from the ankaramites have similar major and trace element characteristics to the host rocks, indicating that the ankaramites did not result from an accumulation of mafic minerals but rather represent the primary magma in the Kibblewhite Volcano. The MIs from the magnesian andesites were hosted in forsteritic olivine xenocrysts with a wide range of NiO contents (Fo90–92; 0.13–0.39 wt% NiO) and have similar major element compositions to the ankaramites but exhibit a wide range of CaO/Al2O3 (0.85–1.54). The trace element characteristics of the MIs from the magnesian andesites do not match those of the host rocks, indicating that they are not primary melts of the magnesian andesites but primitive basaltic melts generated before the magnesian andesites formed.Interestingly, the CaO/Al2O3 ratio of MIs from the magnesian andesites was negatively correlated with the NiO content of their host olivines. This correlation suggests that the composition of the primary basaltic magmas of the Kibblewhite Volcano changed continuously from peridotite-derived to ankaramitic. This correlation could not be explained by grain-scale process, crustal anatexis, or contribution of slab-derived carbonate-rich fluids. Instead, we propose that this correlation can be explained by the interaction of the ascending primary basaltic melts with the lithospheric mantle. During melt-mantle interaction, the assimilation of clinopyroxene and fractionation of olivine and orthopyroxene caused the CaO/Al2O3 ratio to increase in the melt and the Ni content to decrease. Furthermore, because the magnesian andesites have low CaO/Al2O3 ratios and could be derived from a clinopyroxene-poor mantle lithology, the interaction between the melt and mantle may also be closely related to the origin of the magnesian andesites at Kibblewhite Volcano. This interpretation provides a new perspective on the origin of the oceanic arc ankaramites and why primary andesitic and basaltic magmas coexist in the Kibblewhite Volcano.

Impacts of Mineral Dust on Trace Element Concentrations (As, Cd, Cu, Ni and Pb) in Lichens and Soils at Lhù’ààn Mân’ (Yukon Territory, Canada)

AbstractDust is a mineral aerosol of the atmosphere that often contains trace elements such as As, Cd, and Pb. Lhù’ààn Mân’ (Kluane Lake), located in southwestern Yukon, is a region of frequent dust activity. In 2016, the lake level fell due to a dramatic decrease in inflow from glacier meltwater, and the delta of the lake became an important source of dust to surrounding ecosystems. To determine the impacts of dust deposition on vegetation and soil trace element concentrations and characteristics, we sampled the lichen Peltigera canina and soil layers at 57 sites along a deposition gradient located 1.4–33.6 km downwind from the principal dust source. Arsenic, Cd, Cu, Ni and Pb in lichens were negatively correlated with the distance away from the dust source, with the highest correlations in Ni and Pb (r2 = 0.50 and 0.48, respectively). Lichen and tree abundances were negatively impacted by dust deposition, suggesting that dust can affect ecosystem vegetation composition. Starting 8 km away from the dust source, the concentrations of As, Ni, and Pb decreased by more than 50% per km, while Cd and Cu concentrations decreased by more than 40% per km. Overall, within the sampled ecosystems, soil pH is 1.4 times higher in the first 8 km from the dust source while carbon content and nutrients are lower, which implies changes in nutrient availability and cycling in dust‐affected ecosystems.

Origin of Early Triassic Hornblende Gabbro from the Yunkai Massif, South China: Constraints from Mineral and Bulk-Rock Geochemistry

The early Triassic (~250 Ma) hornblende gabbro from the Tengxian area of Yunkai Massif, South China, contains a mineral assemblage of clinopyroxene, hornblende, biotite, plagioclase, K-feldspar and quartz and accessory apatite, and zircon and ilmenite. Based on mineral association and crystallization sequence, two generations of the mineral assemblage have been identified: clinopyroxene + plagioclase + apatite (zircon) in Generation I and ilmenite + hornblende + biotite + K-feldspar + quartz in Generation II. The high crystallization temperature (T = 999–1069 °C) of clinopyroxene and its coexistence with labradorite (An = 52–58) indicate that Generation I crystallized in a basaltic magma, while the hornblende’s relatively low crystallization temperature (T = 780–820 °C) and coexistence with K-feldspar and quartz suggest that Generation II formed in an evolved alkaline melt. The mineralogical records are likely attributed to pulsed intrusion of the late-stage evolved magma into a crystal mush, like in Generation I. The bulk-rock geochemical data include a sub-alkaline affinity, arc-type trace element features, and highly enriched Sr-Nd-Pb-Hf isotopic compositions, consistent with the isotopic records from the accessory minerals, e.g., the very high δ18O values in both zircon and apatite and significantly negative εHf(t) in zircon. The combined mineral and bulk-rock geochemical data suggest that the primary magma for the Tengxian hornblende gabbro was derived from a mantle wedge that had been metasomatized by voluminous subducted terrigenous sediment-derived melts in response to subduction of the Paleo-Tethys Ocean.

Identification of variable contributions to arc rocks by Li[sbnd]Mo and Sr–Nd–Hf–O isotope compositions: A study of the Mafan mafic rocks in the Hong'an orogen, Central China

The geochemistry of arc rocks provides a window to probe compositional variability in mantle wedge and slab-derived inputs. However, quantitative estimation of their contribution is a great challenge. Here we report an integrated study for determination of variable contributions to early Paleozoic arc plutons (the Mafan diorites and gabbros), from the northern Hong'an orogen, central China. Zircon grains from the diorites yielded crystallization age of 445 ± 3 Ma, whereas the gabbros have zircon UPb age of 432 ± 3 Ma. Although both the two mafic rocks suites exhibit typical arc-like trace element distribution patterns, they show a series of differences in stable Li–Mo–O and radiogenic Sr–Nd–Hf isotope compositions, as well as major and trace element features. Geochemically, the diorites are medium-K calc-alkaline series with high and positive whole-rock εNd(t) (+3.8 to +4.5) and zircon εHf(t) values (+12.4 to +14.3), and normal mantle-like zircon δ18O values (5.1 ± 0.2 ‰). Contrarily, the gabbros are tholeiitic and have relatively low whole-rock εNd(t) (+ 2.3 to +3.1) and zircon εHf(t) (+5.0 to +8.5) values with normal mantle-like zircon δ18O values (5.4 ± 0.3 ‰). The diorites have δ98Mo values of −0.15 to −0.03 ‰, while the gabbros have δ98Mo values of −0.28 to −0.12 ‰. These values are slightly higher than those of the mid-ocean ridge basalts (MORB) (−0.20 ± 0.01 ‰). Whereas, δ7Li values of the studied diorites (2.15–4.49 ‰) and gabbros (2.89–5.33 ‰) are mostly consistent within the range of MORB. In combination with the above results, the primary magma of diorites was inferred to be derived from 1 to 5% partial melting of depleted lithospheric mantle metasomatized by slab-derived fluid with minor sediment-derived melts. While the gabbros were suggested to be generated by 5–10% partial melting of more depleted lithospheric mantle that had undergone perhaps extra 0.3% melt extraction, which had further been metasomatized by more subducted materials. In summary, both the slab-derived components and nature of the mantle wedge sources are quantitatively constrained for the mafic rocks in the Mafan plutons. Our new data suggest that the Mafan plutons exhibited the Mariana arc-affinity and represented products of an intra-oceanic subduction system in the northern Hong'an orogen. Combined with previously published data for the early Paleozoic mafic magmatic rocks along the Qinling-Tongbai-Hong'an orogenic belt, there exists an oceanic arc in the east (Hong'an orogen) and an Andean-type continental arc in the west (Qinling-Tongbai orogen).

Application of Machine Learning to Research on Trace Elemental Characteristics of Metal Sulfides in Se-Te Bearing Deposits

This study focuses on exploring the indication and importance of selenium (Se) and tellurium (Te) in distinguishing different genetic types of ore deposits. Traditional views suggest that dispersed elements are unable to form independent deposits, but are hosted within deposits of other elements as associated elements. Based on this, the study collected trace elemental data of pyrite, sphalerite, and chalcopyrite in various types of Se-Te bearing deposits. The optimal end-elements for distinguishing different genetic type deposits were recognized by principal component analysis (PCA) and the silhouette coefficient method, and discriminant diagrams were drawn. However, support vector machine (SVM) calculation of the decision boundary shows low accuracy, revealing the limitations in binary discriminant visualization for ore deposit type discrimination. Consequently, two machine learning algorithms, random forest (RF) and SVM, were used to construct ore genetic type classification models on the basis of trace elemental data for the three types of metal sulfides. The results indicate that the RF classification model for pyrite exhibits the best performance, achieving an accuracy of 94.5% and avoiding overfitting errors. In detail, according to the feature importance analysis, Se exhibits higher Shapley Additive Explanations (SHAP) values in volcanogenic massive sulfide (VMS) and epithermal deposits, especially the latter, where Se is the most crucial distinguishing element. By comparison, Te shows a significant contribution to distinguishing Carlin-type deposits. Conversely, in porphyry- and skarn-type deposits, the contributions of Se and Te were relatively lower. In conclusion, the application of machine learning methods provides a novel approach for ore genetic type classification and discrimination research, enabling more accurate identification of ore genetic types and contributing to the exploration and development of mineral resources.