Xisheng Xu

Tin mineralization is commonly associated with highly evolved granites. However, not all highly evolved granitic rocks are mineralized with Sn. Comparative studies of Sn‐fertile and Sn‐barren granites can deepen our understanding of the key processes that lead to Sn enrichment in magmatic‐hydrothermal systems. Here, we present Sn isotope data of two representative granitic suites in South China: the barren Xiaoxiong volcanic‐intrusive complex and the Sn‐mineralized Yanbei granite porphyry. The Xiaoxiong complex exhibit limited Sn isotope variation with δ ^122/118 Sn _3161a values ranging from 0.14 to 0.26‰ in the second‐stage rocks and from 0.19 to 0.33‰ in the third‐stage rocks, consistent with the baseline of the upper continental crust. In contrast, the Yanbei granite porphyry display a broad δ ^122/118 Sn _3161a range (0.05–0.48‰), reflecting the combined effects of fractional crystallization under relatively low oxygen fugacity conditions and subsequent fluid activity. Fractional crystallization of plagioclase with minor biotite, and Fe‐Ti oxides under an oxygen fugacity of ΔFMQ∼0 can account for the initial increase in δ ^122/118 Sn _3161a , but only elevates Sn content by a factor of six, which is insufficient for economic mineralization. This suggests that magmatic fluid exsolution and fluid‐melt interaction are crucial for substantial Sn enrichment. Modeling results show that exsolution of a small amount of fluid (2%–6%) from highly evolved melt (with Δ ^122/118 Sn _fluid‐melt of −0.4 to −0.5‰) and that subsequent fluid‐melt interaction can explain the observed low and variable δ ^122/118 Sn _3161a values and high Sn content in late‐stage samples. This study demonstrates that Sn isotopes are effective in tracing Sn behavior during magmatic‐hydrothermal evolution in granite‐related systems.

Formation of the earliest evolved rocks on terrestrial planets remains poorly understood. The ancient Martian regolith breccia meteorite (MRB) contains feldspar-rich clasts, which could be evolved. Here, we report the first discovery of Martian sarcopside within an igneous clast (CS) of MRB. The mineral assemblage, the presence of sarcopside included in chlorapatite, and the equilibrium temperature of 774 ± 20 °C for plagioclase and alkali feldspar in clast CS collectively demonstrate that this clast crystallized from an evolved magma. A new U-Pb zircon age of 4525 ± 66 Ma places crystallization of these feldspar-bearing clasts within the first ∼100 Myr of Martian crust evolution. Furthermore, the equilibrium temperatures of all 16 two-feldspar-bearing clasts observed in small chips of MRB are < 1000 °C, and half are < 800 °C. The low equilibrium temperatures and mineral assemblages of different clasts are consistent with the interpretation that diverse evolved magmatism could have been present on early Mars. These ancient clasts provide a unique window into the timing and thermal regimes of evolved magmatism within the early Martian crust. More importantly, taken together with evidence from evolved lunar samples and asteroidal meteorites, the evolved lithologies on early Mars inferred from MRB indicate that evolved magmatism may have played an important role in the early Solar system.

The petrogenesis of metaluminous to peralkaline high-silica rhyolites in the Cretaceous Yunshan Caldera of SE China has been investigated by analysis of apatite inclusions in zircons and apatite microphenocrysts in volcanic matrices. Zircon-hosted apatite inclusions from both metaluminous and peralkaline high-silica rhyolites are strongly similar, characterized by oscillatory zoning, high light rare earth element contents (LREE2O3 3.96–12.1 wt%), Y2O3 (0.48–2.46 wt%), and variable ϵNd(t) values (−10 to +7). In contrast, apatite microphenocrysts are unzoned, have low and concentrated LREE2O3 (≤2.71 wt%) and Y2O3 (≤0.56 wt%), and display uniform ϵNd(t) values (−4.85 to −2.76 in peralkaline and −1.62 to −1.83 in metaluminous high-silica rhyolites). Integrated whole-rock geochemical, petrographic, and thermal constraints indicate that the apatite inclusions are antecrysts, which formed within an early trachytic to low-silica rhyolitic crystal mush, whereas apatite microphenocrysts are autocrysts, which crystallized from the final erupted magmas. In high-silica rhyolites, the coexistence of these two distinct apatite groups provides direct evidence that the high-silica magmas were extracted from a shallow crustal-mush source. The reduction in isotopic heterogeneity from the apatite inclusions in zircon to the apatite microphenocrysts captures the processes of melt accumulation and homogenization, leading to the formation of eruptible rhyolitic magmas. Closed-system differentiation under H2O-undersaturated, F-rich, and low-temperature conditions could be the key to the evolution of the interstitial melt of the crystal mush from metaluminous to peralkaline. Comparison between apatite inclusions and microphenocrysts minimizes the influence of mineral-specific crystallization behavior, enabling a more coherent reconstruction of magmatic system evolution. Apatite inclusions in zircon provide a robust tracer of source-region processes. However, their compositions may decouple from those of the erupted magmas, complicating their interpretation in studies of sediment provenance.

The Precambrian basement of Madagascar hosts numerous yet poorly studied chromitite occurrences. The Ranomena deposit, a representative example in the North Toamasina chromite district, is hosted within lenticular mafic–ultramafic bodies of the Betsimisaraka/Anaboriana–Manampotsy domain. The chromitites exhibit disseminated to massive textures with cumulus chromite and orthopyroxene as the primary intercumulus silicate. Chromite compositions are high-Cr (Cr# mostly >60) with elevated TiO2 (0.18–0.78 wt %) and trace element signatures (enrichments in Ti, Zn, Co, Mn, V, Sc; depletions in Ga, Ni) resembling those of stratiform chromitites. Whole-rock platinum-group element (PGE) patterns show relative enrichment in Os, Ir, Ru, and Rh over Pt and Pd, akin to the Lower Group chromitites of the Bushveld Complex. Zircons have been both identified in situ in thin sections and separated from mineral concentrates. Zircons from chromitite samples yield concordia U–Pb ages of 530.4 ± 2.2 and 525.3 ± 2.3 Ma, respectively. Their δ18O values (4.7–6.1‰) and εHf(t) values (−5.4 to +6.8) indicate variable degrees of crustal contamination. A binary mixing model suggests that the parental magmas formed from mantle-derived melts variably hybridized with crustal material (∼15–20% in the slightly earlier pulse). The Ranomena chromitites are coeval with post-collisional granitic magmatism in the central East African Orogen. We propose that they crystallized from mafic magmas generated during lithospheric delamination and asthenospheric upwelling in a post-collisional extensional setting, which may represent a previously unrecognized type of chromitite formation setting in orogenic belts.

Despite the economic importance of lithium, there is considerable disagreement over the processes that concentrate it and other rare metals in pegmatite-type lithium deposits. Two main processes have been invoked, namely extreme differentiation of a peraluminous granitic magma and direct anatexis of a sedimentary protolith. We use geochemical modeling to quantify lithium enrichment via these two processes from a study of the Jiajika lithium pegmatite field, one of the largest of its type in the world. Based on a lithium–silicon–boron–barium (Li-Si-B-Ba) isotope study involving systematic sampling along 4,211-m of core from two deep boreholes and from the regional zonation of pegmatites at outcrops, we propose a three-stage model for the formation of the pegmatite field: i) generation of a rare metal-rich melt by deep anatexis, involving ~5% partial melting of metapelitic rocks in the presence of 10 to 30% metamorphic fluid; ii) gradual enrichment of rare metals along a path of continuous magma differentiation until 75% of the initial melt had crystallized; and iii) a final stage of lithium mineralization during the escape of the water-rich magma due to the overpressures created in response to massive fluid exsolution and the extensional stress in the granite dome structure. The study provides important insights into how lithium-rich pegmatites can be targeted during exploration for pegmatite-hosted resources of lithium.

The current debate on volcanic-plutonic connection is centered on whether efficient liquid-crystal segregation dominates the evolution of a mushy reservoir to produce evolved, crystal-poor rhyolite and cumulate leftover. However, magma recharge may remarkably influence the evolution of a mushy reservoir and obscure the evidence of liquid-crystal segregation. This complexity poses a challenge to exploring the connection of volcanic-plutonic rocks. This study investigates the Qinzhou Bay granitic complex (~250–248 Ma) from South China, which contains crystal-poor (600 ± 80 MPa) and upper (~150 ± 40 and ~60 ± 20 MPa) crustal reservoirs. Variations in quartz Fe content and chlorine-rich, metaluminous melt inclusions suggest that magma hybridization with less-evolved metaluminous magmas occurred at both crustal levels. In particular, the elevated Fe contents in the quartz population that crystallized at the shallowest level (~60 ± 20 MPa) suggest that recharge magmas were directly injected into the shallowest reservoir. Deviation of the whole-rock composition from the liquid evolution trend recorded in melt inclusions suggests a combined effect of magma mixing and crystal-melt segregation processes in upper crustal reservoirs. Thermodynamic modeling and mass balance calculations suggest that the whole-rock composition of the rhyolite could be reproduced by mixing between regionally exposed dacites and segregated melts at crystallinities of 50–60% (using parental magma represented by the least-evolved melt inclusion). For the porphyry unit, thermobarometric results reveal magma storage at middle (more than 450 ± 40 to 550 ± 40 MPa) and upper (110 ± 20 to 140 ± 20 MPa) crustal levels. The small-scale oscillatory zonation of plagioclase, the pervasive resorption of quartz and alkali feldspar, and the presence of peraluminous microgranular enclaves in the porphyries suggest a recharge event of metasediment-sourced magmas, triggering reactivation and convection of the reservoir. Autoclastic and overgrowth textures of quartz, plagioclase, and alkali feldspar phenocrysts and development of columnar jointing suggest that the reactivated porphyritic magmas ascended and emplaced at ultrashallow levels (~30 ± 10 MPa). Because of the similar storage pressures, the porphyries may represent remobilized cumulates of rhyolitic magmas, whereas the texture and geochemistry of the cumulate-liquid pair were modified, a key factor rendering a cryptic connection between the rhyolite and porphyry. Alternatively, the plumbing systems feeding the rhyolite and porphyry units are horizontally independent or vertically discrete, but this circumstance is inconsistent with the same evolution trend of quartz Fe and Al contents of the rhyolite and porphyry. Our study highlights that whole-rock composition may record blended information of complex processes, and caution should be taken when whole-rock composition is used to extract information of a single process. Multi-method constraints are required to evaluate the influence of recharge processes on the modification of liquid-cumulate records, and big data analysis on the basis of geochemistry should be conducted with caution to avoid biased understanding.