Chemical Geology最新文献

{"title":"Middle Ordovician climate modulation by enhanced continental and reverse weathering: Evidence from lithium isotopes","authors":"Jena Jeong ,&nbsp;Sunhwa Bang ,&nbsp;David J. Wilson ,&nbsp;Youngsook Huh","doi":"10.1016/j.chemgeo.2025.122859","DOIUrl":"10.1016/j.chemgeo.2025.122859","url":null,"abstract":"<div><div>The Middle Ordovician represents a critical period of climate and oceanic transitions that is notable for a rapid decrease in the marine ⁸⁷Sr/⁸⁶Sr ratio, fluctuations in atmospheric CO₂ levels, and a brief warming in sea surface temperatures that interrupted a general cooling trend. To investigate the relationship between weathering processes and climate during this period, we analyzed lithium isotopes (δ⁷Li) in Middle Ordovician carbonate rocks from the Taebaeksan Basin, South Korea. We identified a pronounced ∼6 ‰ negative excursion in δ⁷Li values during the Middle Darriwilian, followed by a sustained period of low δ⁷Li values. Using a dynamic box model, we demonstrate that enhanced continental weathering, driven by Taconic arc exhumation, could have initiated the δ⁷Li decline. Concurrently, reverse weathering may have intensified, as weathering-derived element input to the ocean promoted marine authigenic clay formation. The effects of increased weathering intensity, possibly linked to a brief warming event, drove the subsequent recovery of δ⁷Li values. During the Middle to Late Darriwilian, enhanced reverse weathering – resulting from the less efficient biological Si uptake – likely reduced the isotopic fractionation between clay minerals and seawater, contributing to a secondary decline in seawater δ⁷Li values. The active reverse weathering may have played a role in stabilizing atmospheric CO₂ levels during the Middle Ordovician by counteracting the CO₂ drawdown driven by active continental weathering. Overall, our findings highlight how tectonically-driven weathering modulated global climate during the transition from the warm Early Ordovician to the cooler Late Ordovician environment.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122859"},"PeriodicalIF":3.6,"publicationDate":"2025-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144137867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stable strontium (δ88/86Sr) and calcium (δ44/40Ca) isotope fractionation in coastal groundwater and its implications for the transport of dissolved cations to the ocean","authors":"Sourav Ganguly ,&nbsp;Kousik Das ,&nbsp;Abhijit Mukherjee ,&nbsp;Ramananda Chakrabarti","doi":"10.1016/j.chemgeo.2025.122861","DOIUrl":"10.1016/j.chemgeo.2025.122861","url":null,"abstract":"<div><div>Coastal aquifers, a critical component of the land-ocean continuum, act as hotspots of fresh groundwater and seawater mixing while reactive processes further govern the elemental flux to the ocean in form of groundwater discharge. Here we report stable Sr (δ^88/86Sr) and Ca isotope (δ^44/40Ca) data for groundwater samples collected from multiple depths (14–333 mbgl) from two coastal aquifers in the Ganges River delta (Sundarbans). Significant variability is observed in δ^88/86Sr values (range 0.542 ‰) with shallow (up to 42 mbgl) aquifer samples showing high δ^88/86Sr values (up to 0.666 ‰ relative to NIST SRM987), which indicates pronounced interaction with seawater and fractionation induced by Sr removal during carbonate precipitation. The δ^44/40Ca values of these samples also show large variability (range 0.76 ‰) which loosely follows the δ^88/86Sr trend. The δ^88/86Sr-δ^44/40Ca correlation is relatively poor for shallow groundwater samples and reflects differences in fractionation mechanisms during carbonate precipitation for Sr and Ca isotopes. In contrast to the shallow aquifer samples, the deep aquifer samples display limited seawater influence. The depth-bound variability of molar Sr/Ca, δ^88/86Sr, and δ^44/40Ca suggests considerable removal of solute Sr and Ca due to secondary mineral formation, dominated by carbonates at shallower depths consistent with saturation index (SI) calculations. This study highlights that formation of secondary minerals in coastal aquifers, as inferred from stable Sr and Ca isotopes, can affect the transport of highly soluble elements like Sr and Ca from the continents to the oceans and has implications for solute geochemistry in coastal aquifers.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"689 ","pages":"Article 122861"},"PeriodicalIF":3.6,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144107271","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Trace elements and iron speciation analysis of Paleoproterozoic phyllite from the Gandarela Syncline: Implications for salinity and redox conditions in the Quadrilátero Ferrífero, Brazil","authors":"Janaina Rodrigues de Paula ,&nbsp;Wei Wei ,&nbsp;Fabricio A. Caxito ,&nbsp;Katherine N. Snihur ,&nbsp;Cody N. Lazowski ,&nbsp;Kurt O. Konhauser ,&nbsp;Erik A. Sperling ,&nbsp;Daniel S. Alessi","doi":"10.1016/j.chemgeo.2025.122839","DOIUrl":"10.1016/j.chemgeo.2025.122839","url":null,"abstract":"<div><div>The Quadrilátero Ferrífero, Brazil, is among the most significant iron ore provinces. This study utilizes geochemical proxies, including elemental paleosalinity ratios (B/Ga, Sr/Ba, S/TOC), redox-sensitive elements (RSE), and iron speciation, to investigate water mass evolution. Samples were analyzed from three drill cores and four outcrops in the Gandarela Syncline, providing new insights into the Paleoproterozoic phyllites associated with the Cauê BIF. Although metamorphism of these rocks might affect the application of the proxy, consistent directional trends in proxy results indicate a refined and/or robust paleoenvironmental reconstruction of the Minas Basin. Paleosalinity data indicate a transition from freshwater to low-brackish conditions during early sedimentation (Caraça Formation), followed by predominantly marine conditions during the deposition of the Cauê, Gandarela, and Cercadinho Formations. This model revises earlier interpretations suggesting an initial dominance of marine facies during fine sediment deposition in the Batatal Formation. Elevated concentrations of trace elements (Cu, Ni, and Zn) in carbonaceous phyllites highlight the role of microbial activity in bioproductivity before BIF deposition. Additionally, the decreasing enrichment factor _(EF) of Mo_EF/U_EF ratio and RSE concentrations toward younger rocks, coupled with variations in Fe_HR (highly reactive iron), suggest that the early basin waters were characterized by anoxic to suboxic conditions, with free O₂ likely present in surface waters. These results point to a stratified water column, featuring an oxic surface layer overlying ferruginous, anoxic water. This study advances understanding of the paleoenvironmental evolution of the Minas Basin and the depositional processes that facilitated the formation of the Quadrilátero Ferrífero's giant iron deposits. It also underscores the value of paleosalinity proxies for reconstructing environmental conditions in Paleoproterozoic systems, while also highlighting the need for more studies of how paleoenvironmental proxies behave during metamorphism.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122839"},"PeriodicalIF":3.6,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144071869","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molybdenum isotopes record slab inputs to the mantle source of late Triassic Arc Lavas, Northeast China","authors":"Zhigang Wang ,&nbsp;Hui-Dong Zhang ,&nbsp;Li-Qun Dai ,&nbsp;Zi-Fu Zhao ,&nbsp;Wei Fang","doi":"10.1016/j.chemgeo.2025.122864","DOIUrl":"10.1016/j.chemgeo.2025.122864","url":null,"abstract":"<div><div>The geochemical study of arc lavas provides an important window for the exploration of slab input into deep mantle in subduction zones. However, the classification of subduction compositions and the contribution degree that reaches the mantle are difficult to observe directly, and this recycling mechanism is still poorly understood. Here we report Mo-Sr-Nd-Hf isotope data for Late Triassic mafic rocks from Northeast China, which were products of Mongol–Okhotsk Ocean slab subduction in the Early Mesozoic. They have δ^98/95Mo values of −0.24 ‰ to 0.36 ‰, which are mostly higher than the normal mantle value of −0.20 ‰ ± 0.01 ‰. These rocks also exhibit arc-like trace element compositions and depleted whole-rock Sr-Nd-Hf isotopes, with (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7039 to 0.7043, ε_Nd(t) values of 4.0 to 8.5 and ε_Hf(t) values of 6.9 to 11.1. In addition, they also have elevated zircon ε_Hf(t) values of 7.7 to 12.7. These features, combined with high La/Sm, Th/La, Ba/La, and Ba/Th ratios, suggest that the heavy Mo isotope signatures in the arc rocks were mainly inherited from altered oceanic crust-derived aqueous solutions with minor anoxic sediment-derived melts. Therefore, the combined Mo-Sr-Nd-Hf isotopic studies in mafic igneous rocks are a powerful means to trace the geochemical fluxes in subduction zones, especially with the studies of molybdenum isotope system providing new insights into the recycling of crustal materials at the convergence plate margin.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"688 ","pages":"Article 122864"},"PeriodicalIF":3.6,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144107852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Exploring the formation mechanism of cold mineral springs in the potassic basaltic region of Wudalianchi, Northeast China","authors":"Xue Jiang ,&nbsp;Fengyu Li ,&nbsp;Yu Wang ,&nbsp;Yajie Yuan ,&nbsp;Ranran Li","doi":"10.1016/j.chemgeo.2025.122862","DOIUrl":"10.1016/j.chemgeo.2025.122862","url":null,"abstract":"<div><div>The groundwater chemistry is determined by the complex interaction between temperature-water-rock-gas. Therefore, it is a great challenge to study the formation mechanism of cold mineral spring-Erlongyan Spring, which is located in the Wudalianchi Global Geopark in Northeast China. A multiphase reactive transport model that integrated with fluid, heat transfer, and chemical reaction was employed to simulate the evolutions of water heat and water chemistry in Erlongyan Spring. Firstly, the mechanism of water migration-heat transfer was established. The low temperature rainfall penetrated into the basalt aquifer with relatively high temperature, and through heat transfer, the temperature of Erlongyan Spring reached 3.8 °C. Secondly, the source of CO₂ was determined. CO₂ from the magma chamber of the upper mantle escaped into basalt aquifers via volcanic eruption channels to participate in water evolution. By comparing the maximum weathering amount of minerals at the bottom of aquifer with or without CO₂ injection, it can be seen that the growth rate of mineral weathering in the presence of CO₂ was forsterite (411 %) &gt; ferrosilite (260 %) &gt; albite (242 %) &gt; K-feldspar (222 %) &gt; diopside (100 %). Finally, based on the coupling simulation of heat-water chemistry, the weathering and precipitation of minerals, the migration of ions at low temperature were analyzed. The presence of CO₂ enhanced the mineral weathering, but the contents of <span><math><mi>M</mi><msup><mi>g</mi><mrow><mn>2</mn><mo>+</mo></mrow></msup></math></span>, <span><math><mi>N</mi><msup><mi>a</mi><mo>+</mo></msup></math></span> and <span><math><msup><mi>K</mi><mo>+</mo></msup></math></span> in the groundwater failed to increase. The main reasons for this phenomenon were that secondary clay minerals were more likely to be generated and remain stable in cold environment, thereby consuming these ions through chemical reactions and adsorption, and reducing the release of ions into the fluid through inhibiting the mineralization of clay minerals. However, the participation of CO₂ leaded to the increase of <span><math><msub><mi>H</mi><mn>2</mn></msub><mi>S</mi><mi>i</mi><msubsup><mi>O</mi><mn>4</mn><mrow><mn>2</mn><mo>−</mo></mrow></msubsup></math></span> and <span><math><mi>C</mi><msup><mi>a</mi><mrow><mn>2</mn><mo>+</mo></mrow></msup></math></span> in groundwater, which is consistent with the actual situation (How metasilicic acid mineral water got its name and no carbonate was found in SEM observations). The cold environment, CO₂ gas and secondary clay minerals together create unique water chemistry of Erlongyan Spring. This study provides scientific guidance for predicting the response of heat-water chemistry system under changing environment and protecting rare cold mineral springs.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"689 ","pages":"Article 122862"},"PeriodicalIF":3.6,"publicationDate":"2025-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144099799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Flow paths control on spatiotemporal weathering dynamics in high-relief regions, eastern Qinghai-Tibet Plateau: Insight from dissolved Li-Sr-O isotopes","authors":"Tingting Ma ,&nbsp;Jun Zhong ,&nbsp;Si-Liang Li ,&nbsp;Sen Xu ,&nbsp;Han Luo ,&nbsp;Cong-Qiang Liu","doi":"10.1016/j.chemgeo.2025.122854","DOIUrl":"10.1016/j.chemgeo.2025.122854","url":null,"abstract":"<div><div>Mountain-building is generally acknowledged to accelerate chemical weathering of silicate rocks by reshaping geomorphology, tectonics, hydrology, and climate. Yet, the dominant driving forces of terrestrial silicate weathering remain unclear. To reveal the mechanisms of silicate weathering during mountain-building, we present hydrochemistry, water isotopes (δD and δ¹⁸O), radiogenic strontium isotopes (⁸⁷Sr/⁸⁶Sr), and lithium isotope (δ⁷Li) data of river waters from the tectonically active, fault-rich Bailong River catchment on the northeastern Qinghai-Tibet Plateau. Results show a wide spatial range of dissolved δ⁷Li values from +8.4 to +20.8 ‰ and a relatively narrow temporal range from +14.0 to +16.8 ‰. Spatially, δ⁷Li values negatively correlate with Li/Na ratios, suggesting significant Li uptake into secondary minerals. Downstream increases in δ⁷Li values corresponding with decreasing Si/(Na_sil + K) and K/(Na_sil + K) ratios (Na_sil refers to the Na concentration derived from silicate weathering) further suggest gradually enhanced secondary mineral formation and intensified weathering. We attribute these spatial variations in δ⁷Li values to changes in water flow paths that influence weathering intensity and secondary mineral formation. Specifically, longer flow paths of surface and subsurface waters in the lower reaches are facilitated by increased precipitation, greater relief, and fault-related hydrological pathways and could lead to prolonged water-rock interactions and higher δ⁷Li values. Temporally, δ⁷Li values, Li flux, silicate weathering rates, and physical erosion rates all correlate with river discharge, underscoring the influence of hydrological conditions on Li mobilization and δ⁷Li variations. Seasonal changes in water flow paths, driven by variations in precipitation and discharge, result in a δ⁷Li fluctuation of ∼2.8 ‰. During the wet season, increased discharge could extend water flow paths connected to deep groundwater and long-distance groundwater, promoting enhanced water-rock interactions and more Li incorporation into secondary minerals that lead to elevated δ⁷Li values. In contrast, shorter water flow paths (shallow groundwater) during the dry season can limit these processes, resulting in lower δ⁷Li values. Overall, these results highlight the importance role of water flow paths in regulating riverine spatiotemporal δ⁷Li variations and offer insights into modern and paleo-weathering in tectonically active regions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"689 ","pages":"Article 122854"},"PeriodicalIF":3.6,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144123304","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stable cerium isotopes as a potential new redox proxy: insight from first-principles calculations","authors":"Fang Liu ,&nbsp;Yining Zhang ,&nbsp;Yun Liu ,&nbsp;Zhaofeng Zhang ,&nbsp;Xuefang Li","doi":"10.1016/j.chemgeo.2025.122856","DOIUrl":"10.1016/j.chemgeo.2025.122856","url":null,"abstract":"<div><div>Redox fluctuation plays a key role in shaping the evolution of the atmosphere, biosphere, lithosphere and other planets in the solar system. Cerium (Ce) isotope fractionation has recently been suggested to be redox sensitive due to the high reduction potential of Ce. However, the mechanism of Ce isotope behavior is not yet clear. Therefore, we use first-principles calculations to investigate mass-dependent equilibrium Ce isotope fractionations among Ce(III) and Ce(IV) species in aqueous systems and adsorption process of surface complexes of Ce onto goethite. Our results show that the equilibrium isotope fractionation factors between Ce(III)-bearing species are relatively insignificant (mostly less than 0.14 ‰ at 25 °C). In contrast, the fractionations between Ce(III) and Ce(IV) species are significantly larger (e.g., 10³lnα_{Ce(IV)-Ce(III)} is −1.04 ‰ at 25°C), highlighting the importance of chemical bonding environment. During the adsorption onto goethite, our results show that the Ce isotope fractionation direction is opposite for Ce (III) and Ce (IV) species, respectively. Although the nuclear volume effect (NVE) induces negligible fractionation on the ¹³⁶Ce/¹⁴⁰Ce and ¹³⁸Ce/¹⁴⁰Ce ratios, it has a significant effect on the commonly used ¹⁴²Ce/¹⁴⁰Ce ratio which is opposite to that of mass dependent fractionation (MDF). The contrasting isotopic behaviors of MDF and NVE on the ¹⁴²Ce/¹⁴⁰Ce ratio result in minimum total isotopic fractionation at equilibrium. Given the lack of NVE on the ¹³⁶Ce/¹⁴⁰Ce ratio, it could be fractionated significantly under surface environments due to redox fluctuation, suggesting the strong potential of the Ce stable isotopes to serve as a valuable redox tracer.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"690 ","pages":"Article 122856"},"PeriodicalIF":3.6,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144083746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Crucial roles of local hydrothermal activities in the generation of large-scale iron formations during Mesoproterozoic tectonic quiescence","authors":"Zilong Zhou,&nbsp;Xiangkun Zhu,&nbsp;Jian Sun,&nbsp;Zhihong Li","doi":"10.1016/j.chemgeo.2025.122858","DOIUrl":"10.1016/j.chemgeo.2025.122858","url":null,"abstract":"<div><div>Iron formations (IFs), as extremely Fe-rich chemical deposits, play an important role in the global steel industry and the investigation of Precambrian ocean chemistry. However, the controlling factors of IF generation remain enigmatic, particularly during the Mesoproterozoic era when large-scale IFs are scarce. Here we report rare earth element (REE) results of a recently confirmed large-scale Mesoproterozoic-aged IF, the Jingtieshan IF in Northwest China, which could provide new insights into this issue. REE systematics is instrumental in understanding the origins of IFs and ancient ocean chemistry. However, interpretations derived from prior REE studies remain ambiguous due to the analytical challenges posed by the unusually high concentrations of Ba in the Jingtieshan IF. In this study, we present robust REE analyses using a novel method consisting of coprecipitation of REE with Fe, followed by chromatographic purification. This method enables accurate determination of REEs in samples rich in Fe and Ba matrices with ICP-MS. Our results reveal significant positive Eu anomalies (1.52–3.43) in the Jingtieshan IF, demonstrating substantial high-temperature hydrothermal contributions. Asynchronous Eu anomalies across three close IF sections formed during the same period imply that Fe was sourced from different local hydrothermal activities rather than a unified source of deep seawater upwelling. The variable Ce anomalies (0.76–1.62) and subchondritic Y/Ho ratios (18.1–28.4) indicate that the Jingtieshan IF was deposited in anoxic-suboxic waters between Mn and Fe chemoclines within a stratified ocean. Furthermore, global compilations of carbonate Ce anomalies and Fe isotope data in IFs indicate that redox conditions during the mid-Proterozoic allowed large-scale IF deposition under prevalent ferruginous oceans. Growing evidence also highlights strong hydrothermal signatures in mid-Proterozoic IFs worldwide. Collectively, these findings suggest that the scarcity of Mesoproterozoic IFs was the result of reduced hydrothermal Fe flux due to prolonged tectonic quiescence during the transition between the Columbia and Rodinia supercontinents, rather than shifts in ocean redox conditions. We emphasize that the local hydrothermal activities associated with regional rifting played a crucial role in the generation of Mesoproterozoic large-scale IFs.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"688 ","pages":"Article 122858"},"PeriodicalIF":3.6,"publicationDate":"2025-05-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144189620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deciphering multiple orogenic phases with the reactive help of monazite (Inthanon core complex, N Thailand)","authors":"Srett Santitharangkun ,&nbsp;Etienne Skrzypek ,&nbsp;Christoph A. Hauzenberger ,&nbsp;Raquel Gonzalez de Vega ,&nbsp;David Clases","doi":"10.1016/j.chemgeo.2025.122843","DOIUrl":"10.1016/j.chemgeo.2025.122843","url":null,"abstract":"<div><div>Constraining the timing of tectono-thermal events in a terrane affected by several orogenic overprints is challenging. Geochronometers sensitive to magmatic as well as low- to high-grade metamorphic reactions are required. We use the reactive accessory mineral monazite in several lithologies from the Inthanon core complex (N Thailand) to decipher the evolution of this multiply deformed and metamorphosed crustal block. We define distinct domains based on the composition and zoning of monazite and infer monazite-forming reactions using textural observations. Chemical dating by EPMA is used as a reconnaissance tool to distinguish between different age populations, followed by isotopic dating by LA-ICP-MS to assess accuracy and concordance. LA-ICP-TOF-MS mapping of complexly zoned monazite grains is used to identify domains of different ages together with zones of potentially discordant U - Pb dates.</div><div>Three age populations at ca. 240–210, 80–70 and 40–20 Ma are found in monazite from paragneiss, micaschist, orthogneiss or (meta-)granite samples. Newly grown monazite domains at ∼240 and 215 Ma (Grt ± Sil gneiss) record the prograde and retrograde parts of a medium <em>P</em> <em>-</em> <em>T</em> metamorphic loop contemporary with the Indosinian orogeny. Overgrowths formed around 80 Ma are ascribed to garnet breakdown due to an amphibolite-facies overprint during Neo-Tethyan subduction. Magmatic monazite (Bt ± Ms. orthogneiss), which formed at ca. 240 Ma, partially recrystallized at 40 Ma, indicating high-grade metamorphic conditions concurrent with the India-Eurasia collision. Locally, a younger high-<em>T</em> pulse at ca. 20 Ma triggered renewed monazite growth.</div><div>Monazite tends to (re-)grow in Ca-poor bulk compositions (metasediments) but recrystallizes in Ca-richer ones (granitoids). Our study demonstrates that monazite from diverse lithologies within a core complex has the potential to record a growth/recrystallization history spanning over 200 million years, thus helping to identify individual stages of complex tectono-thermal evolutions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"689 ","pages":"Article 122843"},"PeriodicalIF":3.6,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144088894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of clay-mineral assemblages on the B/Ga salinity proxy","authors":"Thomas J. Algeo ,&nbsp;Wei Wei ,&nbsp;Mariano N. Remírez ,&nbsp;Chaowen Wang ,&nbsp;Zhanhong Liu ,&nbsp;Geoffrey J. Gilleaudeau ,&nbsp;Jochen J. Brocks","doi":"10.1016/j.chemgeo.2025.122837","DOIUrl":"10.1016/j.chemgeo.2025.122837","url":null,"abstract":"<div><div>Boron/gallium (B/Ga) ratios have proven useful in reconstructing salinity conditions in ancient shale and marl formations. Boron is adsorbed from the watermass in proportion to its aqueous concentration, yielding sedimentary concentrations many times greater than background levels, whereas Ga is present mainly in the detrital fraction. However, the amount of B uptake by a sample depends not only on aqueous B concentrations but potentially also on the mineralogical composition of the clay fraction of the sediment, which is the main host of adsorbed B. Clay minerals have varying capacities to adsorb borate (B(OH)₄⁻), the main ionic species of boron in natural aqueous systems: highest for illite, intermediate for smectite and chlorite, and lowest for kaolinite. Thus, the salinity signal recorded by a given formation may depend on the nature of its clay-mineral assemblage. In this study, we analyzed relationships of B/Ga to clay-fraction compositions, as determined by X-ray diffraction (XRD) and geochemical (e.g., K/Al) data, for four suites of samples: (i) Modern samples from lacustrine, estuarine, coastal plain and continental shelf settings in the USA; (ii) Eocene samples from the Bohai Bay Basin of NE China; (iii) Pennsylvanian samples from the Midcontinent and Illinois basins of the USA; and (iv) Devonian samples from the Illinois Basin. Our results show that B content covaries nearly ubiquitously with total clay content, an effect explicitly compensated for by normalization of B concentration data to Ga. A key finding of our study is that, after normalization for total clay content, B/Ga ratios show no systematic relationship to any clay-mineral component in either the whole-rock or the clay-fraction data. This is good news for general application of the B/Ga paleosalinity proxy in that it suggests that the clay-mineral assemblage generally does not exert a strong influence on sediment B/Ga ratios. However, it does not preclude the existence of such influence in individual formations, and clay-fraction mineralogical analysis is a recommended auxiliary tool in paleosalinity studies. It should also be noted that all of the present study units have experienced burial heating to no higher than the oil window (∼100–180 °C), and that the influence of clay-mineral assemblages on B/Ga ratios might be manifested in other formations of greater thermal maturity. These findings will prove valuable in guiding the interpretation of elemental salinity data in future paleoenvironmental studies.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"688 ","pages":"Article 122837"},"PeriodicalIF":3.6,"publicationDate":"2025-05-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144107854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}