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Quantifying common Pb, the non‐radiogenic Pb present in a mineral independent of in situ U decay, is essential for obtaining accurate U–Pb ages in common Pb‐bearing minerals such as apatite. However, constraining the amount and composition of common Pb, as well as the timing of its entrapment, remains a persistent challenge. Common Pb in apatites may be constrained by assuming a terrestrial Pb model and measuring 204Pb, or by fitting a two‐component mixing line between radiogenic and common components. Here, we utilize an approach that combines in situ K‐feldspar Pb isotopes (a primary common Pb reference due to negligible radiogenic ingrowth) with apatite U–Pb and trace element data. This approach allows us to understand growth relationships between apatite and K‐feldspar, providing a better framework for geo‐thermochronological interpretations. Igneous or high‐grade metamorphic apatite indicates a shared common Pb reservoir with co‐existing K‐feldspar. In contrast, recrystallized, low‐grade metamorphic apatite records distinct common Pb compositions from K‐feldspar in the same rock. Although some ages derived from recrystallized apatite appear statistically significant (e.g., Mean Squared Weighted Deviation ∼1, p(χ2) ≥ 0.05) when anchored in Tera‐Wasserburg plots using K‐feldspar 207Pb/206Pbi, they can be geologically inaccurate as the common Pb composition of recrystallized apatite is demonstrably different to the primary magmatic reservoir recorded by K‐feldspar. Rather, unanchored ordinate intercepts in Tera‐Wasserburg plots may better capture secondary common Pb signatures for recrystallized apatite, constraining common Pb at the time of (re)growth. We highlight the advantages of assessing K‐feldspar‐constrained 207Pb/206Pb corrections using a multi‐proxy geochemical approach, thereby refining thermal histories within complex geological settings.

The Pearl River is one of the largest rivers entering the South China Sea, yet its initiation time remains debated, a topic we address using Pb isotopes in detrital K‐feldspar. Based on these Pb data, Eocene and Early Oligocene sandstones from the northern South China Sea are interpreted to have been supplied with sediment by proximal rivers draining the Cathaysia Block. In contrast, the Late Oligocene and Miocene sandstones are mainly derived from the western Pearl tributaries (e.g., Hongshui River), suggesting that the Pearl River had formed by the Late Oligocene. Detrital zircon data from the Beibuwan Basin previously suggested that the western tributaries flowed into this basin before being captured by the paleo‐Pearl River. These lines of evidence suggest that progressive headward erosion of the eastern Pearl River and late Oligocene integration of this large fluvial system can be linked to contemporaneous sea‐floor spreading of the South China Sea. Plain Language Summary The Pearl River is one of the largest rivers flowing into the South China Sea. However, when this river achieved its present drainage character remains debated. Here we report a comprehensive investigation of sand/sandstone provenance of the Pearl River as well as the Pearl River Mouth Basin (PRMB) using Pb isotopes measured in detrital K‐feldspar. Our results suggest that Eocene and Early Oligocene sandstones were mainly fed by proximal rivers within the Cathaysia Block, while the Late Oligocene samples are enriched in K‐feldspar grains from the Hongshui River, suggesting that the Pearl River had achieved its present character by the Late Oligocene. Early Oligocene deposits in the Beibuwan Basin share an indistinguishable detrital zircon provenance signal to that of the western tributaries of the Pearl River, indicating that the western tributaries likely flowed into the Beibuwan Basin before being captured by the paleo‐Pearl River. Taken together, this evidence suggest that progressive headward erosion of the eastern Pearl River triggered by the subsidence of PRMB and sea‐floor spreading of the South China Sea played an important role in the late Oligocene integration of this large fluvial system. Key Points Sedimentary provenance of the Pearl River and Pearl River Mouth Basin constrained using detrital K‐feldspar Pb isotopes Pb isotopic data indicate that the Pearl River achieved its present character by the Late Oligocene The opening of the South China Sea played an important role in the drainage reorganization of the Pearl River

Crystal chemical algorithms were used to estimate the chemical composition of selected mineral phases observed with the CheMin X-ray diffractometer onboard the NASA Curiosity rover in Gale crater, Mars. The sampled materials include two wind-blown soils, Rocknest and Gobabeb, six mudstones in the Yellowknife Bay formation (John Klein and Cumberland) and the Murray formation (Confidence Hills, Mojave2, and Telegraph Peak), as well as five sandstones, Windjana and the samples of the unaltered Stimson formation (Big Sky and Okoruso) and the altered Stimson formation (Greenhorn and Lubango). The major mineral phases observed with the CheMin instrument in the Gale crater include plagioclase, sanidine, P21/c and C2/c clinopyroxene, orthopyroxene, olivine, spinel, and alunite-jarosite group minerals. The plagioclase analyzed with CheMin has an overall estimated average of An40(11) with a range of An30(8) to An63(6). The soil samples, Rocknest and Gobabeb, have an average of An56(8) while the Murray, Yellowknife Bay, unaltered Stimson, and altered Stimson formations have averages of An38(2), An37(5), An45(7), and An35(6), respectively. Alkali feldspar, specifically sanidine, average composition is Or74(17) with fully disordered Al/Si. Sanidine is most abundant in the Wind-jana sample (∼26 wt% of the crystalline material) and is fully disordered with a composition of Or87(5). The P21/c clinopyroxene pigeonite observed in Gale crater has a broad compositional range {[Mg0.95(12)-1.54(17)Fe0.18(17)-1.03(9)Ca0.00-0.28(6)]Σ2Si2O6} with an overall average of Mg1.18(19)Fe0.72(7)Ca0.10(9)Si2O6. The soils have the lowest Mg and highest Fe compositions [Mg0.95(5)Fe1.02(7)Ca0.03(4)Si2O6] of all of the Gale samples. Of the remaining samples, those of the Stimson formation exhibit the highest Mg and lowest Fe [average = Mg1.45(7)Fe0.35(13)Ca0.19(6)Si2O6]. Augite, C2/c clinopyroxene, is detected in just three samples, the soil samples [average = Mg0.92(5)Ca0.72(2)Fe0.36(5)Si2O6] and Windjana (Mg1.03(7)Ca0.75(4)Fe0.21(9)Si2O6). Orthopyroxene was not detected in the soil samples and has an overall average composition of Mg0.79(6)Fe1.20(6)Ca0.01(2)Si2O6 and a range of [Mg0.69(7)-0.86(20)Fe1.14(20)-1.31(7)Ca0.00-0.04(4)]Σ2Si2O6, with Big Sky exhibiting the lowest Mg content [Mg0.69(7)Fe1.31(7)Si2O6] and Okoruso exhibiting the highest [Mg0.86(20)Fe1.14(20)Si2O6]. Appreciable olivine was observed in only three of the Gale crater samples, the soils and Windjana. Assuming no Mn or Ca, the olivine has an average composition of Mg1.19(12)Fe0.81(12)SiO4 with a range of 1.08(3) to 1.45(7) Mg apfu. The soil samples [average = Mg1.11(4)Fe0.89SiO4] are significantly less magnesian than Windjana [Mg1.35(7)Fe0.65(7)SiO4]. We assume magnetite (Fe3O4) is cation-deficient (Fe3-x∎xO4) in Gale crater samples [average = Fe2.83(5)∎0.14O4; range 2.75(5) to 2.90(5) Fe apfu], but we also report other plausible cation substitutions such as Al, Mg, and Cr that would yield equivalent unit-cell parameters. Assuming cation-deficient magnetite, the Murray formation [average = Fe2.77(2)∎0.23O4] is noticeably more cation-deficient than the other Gale samples analyzed by CheMin. Note that despite the presence of Ti-rich magnetite in martian meteorites, the unit-cell parameters of Gale magnetite do not permit significant Ti substitution. Abundant jarosite is found in only one sample, Mojave2; its estimated composition is (K0.51(12)Na0.49)(Fe2.68(7)Al0.32)(SO4)2(OH)6. In addition to providing composition and abundances of the crystalline phases, we calculate the lower limit of the abundance of X-ray amorphous material and the composition thereof for each of the samples analyzed with CheMin. Each of the CheMin samples had a significant proportion of amorphous SiO2, except Windjana that has 3.6 wt% SiO2. Excluding Windjana, the amorphous materials have an SiO2 range of 24.1 to 75.9 wt% and an average of 47.6 wt%. Windjana has the highest FeOT (total Fe content calculated as FeO) at 43.1 wt%, but most of the CheMin samples also contain appreciable Fe, with an average of 16.8 wt%. With the exception of the altered Stimson formation samples, Greenhorn and Lubango, the majority of the observed SO3 is concentrated in the amorphous component (average = 11.6 wt%). Furthermore, we provide average amorphous-component compositions for the soils and the Mount Sharp group formations, as well as the limiting element for each CheMin sample.

The formation, storage, and evolution of granitic magmas are fundamental processes driving the growth of continental crust. While traditionally attributed to crystal fractionation in high‐melt fraction magma chambers, the model invoking low‐melt fraction crystal mushes has gained wide acceptance. However, the chemical and textural impacts of crystal mush rejuvenation remain elusive and the precise petrological record is relatively poorly studied. The rapakivi K‐feldspar identified in the early Eocene monzogranitic porphyry of the Caina intrusive complex, Gangdese batholith, is an ideal candidate for investigating these issues, as feldspar can record clues to magmatic processes. Field survey, optical and mineral flake scanning observations, X‐ray fluorescence analysis, in situ Sr and mineral Sm‐Nd isotopic analyses, TESCAN integrated mineral analysis, electron probe microanalysis, and three‐dimensional crystal shape modeling were performed on the collected samples. K‐feldspars can be divided into three types based on chemical zonation: normal, reverse, and oscillatory zoning crystals. Varying isotopic signatures between the K‐feldspar and associated mantle suggest that the rapakivi texture originated in heterogeneous magmatic pulse recharge. Crystal shape modeling of the plagioclase chadacryst, mantle, and matrix plagioclase, combined with compositions, indicates that mantle plagioclase originated from the quenching of recharge magmas. We propose a model for the formation of rapakivi K‐feldspar and the rejuvenation of crystal mush. Repeated hot magma pulses recharged the mush, triggering magma convection and thermal perturbations. This process enabled the prolonged growth of K‐feldspar megacrysts, which were subsequently capped by plagioclase, resulting in the formation of the rapakivi texture.

At temperatures above about 600 °C, alkali feldspar forms a continuous solid solution between the Na and K end members. Towards lower temperatures a miscibility gap opens, and alkali feldspar of intermediate composition exsolves, forming an intergrowth of relatively more Na-rich and K-rich lamellae. During exsolution, the crystal structure usually remains coherent across the lamellar interfaces, a feature that may be preserved over geological times. Due to the compositional dependence of the lattice parameters, coherent intergrowth requires that the lamellae are elastically strained. The associated elastic strain energy counteracts exsolution, and the solvus delimiting the misciblity gap for coherent intergrowth lies below the solvus for strain free phase equilibria. To determine the coherent solvus, homogeneous gem quality alkali feldspar of intermediate composition was annealed at conditions falling into the two-phase region of the phase diagram. Thereby a coherent intergrowth of approximately 10–20 nanometers wide lamellae was produced. Lamellar compositions were determined with atom probe tomography defining points on the coherent solvus. In parallel, the coherent solvus was calculated using a thermodynamic mixing model calibrated on the same alkali feldspar as used for the exsolution experiments and accounting for the elastic strain energy associated with coherent lamellar intergrwoth. The experimentally determined and the calculated coherent solvus are in excellent agreement indicating that phase equilibria in coherent lamellar intergrowth of alkali feldspar are adequately described, providing a sound basis for the interpretation of phase relations in coherently exsolved alkali feldspar.

Groundwater is an important source for drinking water supply in hard rock terrain of Bundelkhand massif particularly in District Mahoba, Uttar Pradesh, India. An attempt has been made in this work to understand the suitability of groundwater for human consumption. The parameters like pH, electrical conductivity, total dissolved solids, alkalinity, total hardness, calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, fluoride, nitrate, copper, manganese, silver, zinc, iron and nickel were analysed to estimate the groundwater quality. The water quality index (WQI) has been applied to categorize the water quality viz: excellent, good, poor, etc. which is quite useful to infer the quality of water to the people and policy makers in the concerned area. The WQI in the study area ranges from 4.75 to 115.93. The overall WQI in the study area indicates that the groundwater is safe and potable except few localized pockets in Charkhari and Jaitpur Blocks. The Hill-Piper Trilinear diagram reveals that the groundwater of the study area falls under Na+-Cl−, mixed Ca2+-Mg2+-Cl− and Ca2+-HCO3- types. The granite-gneiss contains orthoclase feldspar and biotite minerals which after weathering yields bicarbonate and chloride rich groundwater. The correlation matrix has been created and analysed to observe their significant impetus on the assessment of groundwater quality. The current study suggests that the groundwater of the area under deteriorated water quality needs treatment before consumption and also to be protected from the perils of geogenic/anthropogenic contamination.

We quantify the metamorphic pressure-temperature (P-T) conditions for a newly discovered silica-undersaturated high-pressure granulite (HPG) from the Central Maine Terrane (CMT) in northeastern Connecticut, U.S.A. The rocks lie within the Acadian-Neoacadian orogenic belt (Devonian) and form part of the Brimfield Schist. The Brimfield and the adjacent Bigelow Brook Formation contain silica-saturated rocks that have previously been shown to have undergone ∼1000 °C metamorphism. The pressure was less well constrained at ≥ ∼1 GPa. Silica-undersaturated rocks hold underutilized potential for pinpointing peak metamorphic conditions, particularly pressure, because of their resilience to melting and the variety of refractory minerals they contain. The typical silica-undersaturated mineral assemblage is garnet + spinel + corundum + plagioclase + K-feldspar + biotite + ilmenite. Leucosomes are syenites consisting of two feldspars ± biotite. Plagioclase is commonly antiperthitic, particularly in feldspathic domains surrounding peritectic garnet; such garnet crystals reach ∼10 cm in diameter. Alkali feldspars are perthitic. The rocks contain remarkable ellipsoidal spinels as much as 5.5 cm long comprising discrete crystallographic domains hosting crystallographically oriented lamellae of a Fe-Ti phase, most likely ilmenite. Corundum is usually colorless, but can also be found as sapphire in shades of pink, purple, and blue, particularly in antiperthite-rich domains surrounding large garnets. Some sapphires are concentrically color zoned. We carried out a P-T estimation using ternary feldspar reintegration thermometry of metamorphic antiperthites together with pseudosection modeling. Samples texturally and chemically record near-eclogite facies equilibration at minimum conditions of ∼1040 °C and ∼1.8 GPa, establishing the CMT in northeastern CT as the first known HPG locality in the U.S. These results are consistent with high P2O5 levels found in garnet (0.18 wt%), Ti-in-biotite thermometry, regional sillimanite pseudomorphs after kyanite, and preliminary experimental work on melt inclusions in garnet (Ferrero et al. 2017). The leucosomes provide strong evidence that partial melting of silica-undersaturated rocks at HPG conditions can produce syenitic magmata. Strongly melt-depleted silica-undersaturated rocks may also be protoliths for garnet + spinel + corundum xenoliths reported from kimberlites. The presence of HPG gneisses demonstrates that the large-scale thrusts of the CMT sample the deepest roots of the orogenic belt (60-70 km), and perhaps even deeper subduction zone lithologies as well.

Ice formation on aerosol particles is a process of crucial importance to Earth’s climate and the environmental sciences, but it is not understood at the molecular level. This is partly because the nature of active sites, local surface features where ice growth commences, is still unclear. Here we report direct electron-microscopic observations of deposition growth of aligned ice crystals on feldspar, an atmospherically important component of mineral dust. Our molecular-scale computer simulations indicate that this alignment arises from the preferential nucleation of prismatic crystal planes of ice on high-energy (100) surface planes of feldspar. The microscopic patches of (100) surface, exposed at surface defects such as steps, cracks, and cavities, are thought to be responsible for the high ice nucleation efficacy of potassium (K)–feldspar particles.

An improved method for producing high-purity quartz (Qtz) and potassium feldspar (Kfs) concentrates was developed using various chemical reagents. Froth flotation experiments on a Qtz–Kfs mixture showed that quartz could be selectively floated from Kfs in diluted hydrofluoric acid (HF) using a frother. Similarly, feldspar could be selectively floated from quartz. Recovery rates depended on reagent choice, pH levels, HF modifier dosage, and HF conditioning time. High recoveries and good grades were achieved for both quartz and feldspar at low pH levels. Among the five collectors tested, Brij C20 showed the highest recovery when used in conjunction with HF and a frother alone and a concentrate containing 82.8% quartz was obtained at a 96% recovery rate. Good recoveries were also achieved with collectors like Duomeen C and Flotigam V4343 for floating K-feldspar, with a Kfs concentrate of 99.9% purity at a 94% recovery. Lilaflot OT 55 and Duomeen TDO were less effective. The concentration of HF was 22 kg/t, which implies an important reduction with respect to the earlier research.

A qualitative approach, including geochemical and multivariate statistical approaches, is applied to evaluate the groundwater quality and human health risk, based on analytical data of 72 samples collected from a semi-arid region of eastern Maharashtra, India. The shifting of hydrochemical type from Ca2+–Na+–HCO3- to Na+–Ca2+–Cl− type was observed along different flow paths. The main controlling processes observed from the chemical characterisation of the groundwater are water–rock interactions, dedolomitisation and reverse ion exchange. Simulation analysis (mass transfer) exposes the dissolution of dolomite, gypsum, halite, k-feldspar and CO2 down the simulated pathways. Around 77% of the total variance was observed from the first three principal component analyses. The high positive loadings of EC, TDS, Na+, K+, Ca2+, Cl−, NO3- and SO42- of PC1 revealed silicate weathering and reverse ion exchange followed by human activities as the contamination sources. The sources identified for high positive loadings on HCO3- and SO42- of PC2 are soil CO2 and human activities. The high loadings of pH and F− in PC3 revealed fluorite dissolution and calcite precipitation. The human health risk calculated for NO3- revealed that 58% and 44% of the total groundwater samples surpassed the tolerance limit for non-carcinogenic risk of 1.0 in children and adults. The human health risk assessment for fluoride showed high hazard index values in 40% and 23% of the total groundwater samples for children and adults, respectively. The study suggests some management measures for protection of groundwater resources.