Chemical Geology最新文献

{"title":"Magnesium isotopic evidence for intensified continental chemical weathering during the Smithian-Spathian transition","authors":"Xingyu Ma ,&nbsp;Kangjun Huang ,&nbsp;Yan Chen ,&nbsp;Yadong Sun ,&nbsp;Ying Zhou ,&nbsp;Graham A. Shields ,&nbsp;Fang Huang ,&nbsp;Genming Luo","doi":"10.1016/j.chemgeo.2025.123133","DOIUrl":"10.1016/j.chemgeo.2025.123133","url":null,"abstract":"<div><div>The Smithian-Spathian (S-S) transition (∼249.7 to 248.7 Ma) of the Early Triassic was marked by profound paleoenvironmental upheavals, including a pronounced temperature decline following the hyperthermal event in the late Smithian, a major positive excursion in carbonate carbon isotope composition (δ¹³C_carb), and a significant biotic crisis. Yet, the mechanisms and causal linkages underlying these coeval phenomena remain elusive. In this study, we present high-temporal-resolution magnesium isotope data from siliciclastic residues within carbonate rocks (δ²⁶Mg_residue), a well-established proxy for continental chemical weathering intensity, across the S-S boundary in the Waili and Jiarong sections in South China. Our results document a distinct positive δ²⁶Mg_residue shift in the lowermost Spathian in both sections, signifying intensified continental chemical weathering. This isotopic shift broadly coincides with the positive δ¹³C_carb excursion and the recovery of terrestrial ecosystems but postdates the late Smithian thermal maximum. We interpret this temporal sequence to suggest that the recovery of terrestrial ecosystems, particularly the expansion of vascular land plants, acted as a primary driver of enhanced continental chemical weathering. The resulting increase in continental chemical weathering likely amplified nutrient flux to the ocean, potentially promoting local marine anoxia and climate cooling observed in the earliest Spathian. These findings underscore the critical role of terrestrial-marine coupling in modulating Early Triassic biogeochemical feedbacks and global climate evolution.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123133"},"PeriodicalIF":3.6,"publicationDate":"2025-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145485564","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 phosphate on hexavalent chromium immobilization by ferrihydrite under light irradiation","authors":"Chaorong Chen ,&nbsp;Sailan Wang ,&nbsp;Yixuan Yang ,&nbsp;Gaofeng Wang ,&nbsp;Jing Liu ,&nbsp;Qingze Chen ,&nbsp;Fei Ge ,&nbsp;Runliang Zhu","doi":"10.1016/j.chemgeo.2025.123144","DOIUrl":"10.1016/j.chemgeo.2025.123144","url":null,"abstract":"<div><div>Ferrihydrite is an important geosorbent and catalyst that is ubiquitous in natural environments, and plays a critical role in regulating the speciation and migration of hexavalent chromium (Cr(VI)). Phosphate has a strong affinity for ferrihydrite surfaces, but it remains unclear how phosphate influences the immobilization of Cr(VI) by ferrihydrite in sunlight-influenced surface environments. Herein, the surface interactions of ferrihydrite and Cr(VI) in the presence of phosphate were studied under mercury lamp irradiation. Results showed that mercury lamp irradiation significantly attenuated the inhibitory effect of phosphate on Cr(VI) removal by ferrihydrite compared to that under dark conditions. X-ray photoelectron spectroscopic (XPS) analysis revealed that Cr(III) was the predominant chromium species immobilized on ferrihydrite surfaces. Specifically, the reduction of Cr(VI) produced CrPO₄ precipitates, whereas the released Fe(III) can also co-adsorb with phosphate (i.e., FePO₄) onto ferrihydrite surfaces. The reduction of Cr(VI) mediated by the generated Fe(II) species and photoelectrons effectively reduces the electrostatic repulsion between Cr(VI) and phosphate, thereby enhancing the immobilization of these two ions on ferrihydrite. Energy dispersive X-ray spectrometer (EDS) results provide direct quantitative evidence that mercury lamp irradiation substantially enhances the immobilization of Cr(VI) and phosphate by ferrihydrite. The above-described results account for the effect of phosphate on the light-induced coupling process of ferrihydrite reductive dissolution and Cr(VI) reductive immobilization, advancing our understanding of the geochemical cycle of Cr(VI) pollution in sunlight-influenced surface environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123144"},"PeriodicalIF":3.6,"publicationDate":"2025-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145485562","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":"Testing selenite gypsum crystals from caves for reconstructing the stable isotope composition of paleo-aquifers","authors":"Fernando Gázquez ,&nbsp;Xuefeng Wang ,&nbsp;Wuhui Duan ,&nbsp;Paolo Forti ,&nbsp;Stein-Erik Lauritzen ,&nbsp;José María Calaforra","doi":"10.1016/j.chemgeo.2025.123134","DOIUrl":"10.1016/j.chemgeo.2025.123134","url":null,"abstract":"<div><div>Selenite is a variety of gypsum (CaSO₄·2H₂O) that typically forms large, transparent prismatic crystals. In recent decades, meter-sized selenite crystals have been found in several caves worldwide. These gypsum speleothems formed underwater, in highly stable, epithermal or low-temperature aquifers. Here we investigate the U-Th ages of decimeter-sized selenite crystals from Cueva de los Cristales (Naica mine, northern Mexico) and the Giant Geode of Pulpí (Almería, southeastern Spain). Furthermore, the hydrogen and oxygen isotope compositions of gypsum hydration water measured along the crystal growth axes were used to reconstruct the isotopic evolution of the Naica and Pulpí paleo-aquifers. Extremely low uranium concentrations (&lt;2 ppb in Pulpí and &lt; 0.1 ppb in Naica) make obtaining reliable age models challenging. However, repeated independent measurements of each sample and using large sample sizes can yield reliable and accurate ages. A Naica crystal that grew over the last 31 ± 6 kyr recorded a stepwise change in the isotope composition of paleo-aquifer water, likely reflecting a shift in recharge isotopic composition (rainfall) due to Glacial–Holocene climate change in northern Mexico. A crystal from the Giant Geode of Pulpí that began growing at 191 ± 26 kyr recorded relatively constant δ²H groundwater values, likely reflecting stable climatic conditions during its formation. We critically discuss the caveats of using selenite gypsum crystals from caves as paleohydrological archives and conclude that, despite the challenges, they have strong potential for reconstructing the isotopic composition of paleo-aquifers and past rainfall.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123134"},"PeriodicalIF":3.6,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145462065","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":"Mineralogical evidence of acid mine drainage on spoil tips of the Nord Pas-de-Calais coal mining basin (Northern France): A high-resolution characterization of the black shale weathering","authors":"Yensinga Bafounga ,&nbsp;Franck Bourdelle ,&nbsp;Pauline Claisse ,&nbsp;Sandra Ventalon ,&nbsp;Annette Hofmann ,&nbsp;Emily Lloret","doi":"10.1016/j.chemgeo.2025.123132","DOIUrl":"10.1016/j.chemgeo.2025.123132","url":null,"abstract":"<div><div>The northern France is renowned for its 200 spoil tips, vestiges of coal mining during the 19th and 20th centuries. These tailings composed of Carboniferous black shales are subject to supergene conditions, leading to weathering and potential release of contaminants into the environment. However, it was long accepted that element release process did not occur in this area, and no acid mine drainage (AMD) was observable at the regional scale. Here, we conducted a detailed characterization of the primary and secondary mineral phases comprising the weathered black shales from three selected vegetated spoil tips. Through a combination of macro, micro, and nanoscale analyses (XRD, SEM, FIB, TEM, STXM-XANES), we reveal that AMD occurs on at least the first 30 cm of the entire vegetated surfaces of the spoil tips. This AMD forms an “alteration front” at the surface of the fragmented shale blocks, consisting of two distinct submicrometric layers: an inner Fe-rich layer composed of iron oxyhydroxides and a few nanometric neoformed smectite or illite/smectite, and an outer S-rich layer, featuring euhedral and anhedral jarosite, with a few rosette-like iron oxyhydroxides. Petrographic and textural signatures suggest that these two layers form independently and successively, by direct precipitation from fluids enriched with K, Fe²⁺, Fe³⁺, and S. The 2-layer structure of this alteration front indicates a sharp change in the physico-chemical conditions, in particular a decrease in pH to below 3, during the weathering process. Results also suggest element transfers to the environment; S, Fe and K are released by the shale and fixed at least temporarily at the shale surface, as well as metals and metalloids like As, Sr, Mo and Ge. By highlighting the acidification process, the formation of secondary minerals typical of AMD, and the release of elements from shale, this study sheds light on a long-term process that, although not clearly observable twenty years ago, is now visible at the spoil tips scale and whose consequences could become evident at the landscape scale in the coming decades.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123132"},"PeriodicalIF":3.6,"publicationDate":"2025-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145462064","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":"Rare earth elements (REE) as indicators of geochemical processes in permafrost systems of the Arctic Foothills, Northern Alaska","authors":"W. Brad Baxter ,&nbsp;Joseph P. Smith ,&nbsp;Thomas A. Douglas ,&nbsp;Robyn A. Barbato ,&nbsp;Shawn Gallaher ,&nbsp;Amanda J. Barker","doi":"10.1016/j.chemgeo.2025.123131","DOIUrl":"10.1016/j.chemgeo.2025.123131","url":null,"abstract":"<div><div>In permafrost environments, distinct soil thermal regimes create unique influences on pedogenic processes and hydrological systems. Rare earth elements (REE) provide utility as indicators of soil geochemical cycling that can improve our understanding of permafrost soil-hydrological systems and their change over time, yet a greater understanding of the factors governing permafrost REE distribution is needed. We assess cryogenic controls on soil REE cycling in permafrost and active layer from three pedogenic environments in the Arctic Foothills of Alaska, and REE of adjacent surface waters. Soil parent material influenced the relative REE species abundance across sites while total extractable REE varied with soil material properties. REE reservoir transfer functions revealed differences in fractionation between permafrost and active layer in middle REE of a peat-rich site, and heavy REE for two sites with higher mineral content, potentially reflecting preferred degradation of heavy REE inorganic complexes in the active layer. Each soil profile revealed accumulation of REE above the near-surface permafrost table which could serve as an important sourcing zone for suprapermafrost flow. REE (&lt;0.45 μm) of two tundra streams featured fractionation toward heavier REE that varied throughout the thaw season, likely with changing flux of species-preferred ligands driven by top-down seasonal soil thaw. Heavy REE enrichment in permafrost translated to elevated heavy REE in the surface waters of an active thermokarst, suggesting that catchment permafrost degradation may be identifiable by increased loading of heavy REE to streams at our sites. Our results demonstrate the importance of soil thermal status on influencing chemical weathering and translocation in permafrost environments and illustrate the potential utility of REE in tracking catchment permafrost stability.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123131"},"PeriodicalIF":3.6,"publicationDate":"2025-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145462097","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":"Colloidal origin of hematite in Pleistocene iron-rich sedimentary rocks from Milos Island, Greece: An analogue for Precambrian iron shuttle","authors":"Si Sun ,&nbsp;Reiner Klemd ,&nbsp;Panagiotis Voudouris","doi":"10.1016/j.chemgeo.2025.123130","DOIUrl":"10.1016/j.chemgeo.2025.123130","url":null,"abstract":"<div><div>Banded iron formations (BIFs) are critical archives of Earth's early biogeochemical cycles, yet their genesis, especially regarding the origin of hematite and associated Fe transport mechanisms, remains intensely debated. The scarcity of unmetamorphosed Phanerozoic analogues has constrained a comprehensive understanding of BIF formation. Here, we investigate Pleistocene iron-rich sedimentary rocks from the Cape Vani sedimentary basin, Milos Island, Greece, to elucidate Fe transport processes in ancient oceans. High-resolution petrographic mineralogical, and spectroscopic analyses reveal that Fe is predominantly hosted in hematite nanoparticles (ca. 0.1–0.75 μm), which often form framboidal and irregular aggregates. Mössbauer spectroscopy indicates that the hematite has magnetic hyperfine fields (46.75–50.73 T) characteristic of medium to poor crystallinity. Raman spectra further exhibit a prominent band shift ca. 650 cm⁻¹, a feature diagnostic of nanocrystalline hematite. Carbonaceous material is spatially associated with the aggregates but is absent from individual nanoparticles. The uniform sizes and morphology of the hematite particles suggest that the majority of Fe was transported as colloids. This implies a possible allochthonous origin and <em>ex situ</em> Fe-oxidation, since colloids can be transported over long distances. The aggregation and subsequent deposition of these colloids were likely facilitated by high concentrations of dissolved Si and interactions with carbonaceous materials. The prevalence of colloidally-derived hematite at Milos highlights colloidal transport as a potentially significant mechanism for iron distribution in past oceans. Consequently, the presence of hematite in ancient sediments like BIFs does not necessarily imply <em>in situ</em> Fe-oxidation or associated microbial processes. The established model for a colloidal iron shuttle capable of transporting iron across oceanic basins offers a new perspective for interpreting the genesis of BIFs and a refined understanding on the early Earth's biogeochemical cycles.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123130"},"PeriodicalIF":3.6,"publicationDate":"2025-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145448042","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":"Corrigendum to ‘Apatite and Zircon as key indicators for effusive-explosive transition in the Leningcou Volcano: Middle Triassic Volcanic activity in the East Kunlun Orogenic Belt’ [Chemical Geology 678 (2025) 122670]","authors":"Gui-Zhi Huang ,&nbsp;Chang-Qian Ma ,&nbsp;Bin Liu ,&nbsp;Zhen-Hua Xue ,&nbsp;Huai Xiong ,&nbsp;Kai-Pei Lu ,&nbsp;Quan-Cheng Lian ,&nbsp;Ke Gao ,&nbsp;Meng-Yu Zhang ,&nbsp;Si-Yu Yang","doi":"10.1016/j.chemgeo.2025.123116","DOIUrl":"10.1016/j.chemgeo.2025.123116","url":null,"abstract":"","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"697 ","pages":"Article 123116"},"PeriodicalIF":3.6,"publicationDate":"2025-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145448043","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":"Evaluating solute dynamics and methane transformation in high-elevation Rocky Mountain fens using a transporter-transformer framework","authors":"Valerie Martin ,&nbsp;Matthew Winnick ,&nbsp;Brian Saccardi ,&nbsp;Markus Bill ,&nbsp;Mark E. Conrad ,&nbsp;Rosemary W.H. Carroll ,&nbsp;Kate Maher","doi":"10.1016/j.chemgeo.2025.123129","DOIUrl":"10.1016/j.chemgeo.2025.123129","url":null,"abstract":"<div><div>Peat wetlands at high latitudes have been a key focus for geochemical and hydrologic research due to their roles in carbon storage and greenhouse gas emissions. At the local scale, fens facilitate nutrient cycling and methane production via microbial processes. At the watershed scale, their distribution and hydrologic connectivity with surface waters can substantially influence water quality. However, the role of mid-latitude montane fens in moderating watershed functions remains understudied, despite their susceptibility to pronounced redox shifts driven by high-elevation seasonal dynamics.</div><div>We conducted a comprehensive analysis of (1) base cations, (2) biologically active, redox-sensitive nutrients and metals, and (3) carbon compounds in Rocky Mountain fens and surface waters along an elevational gradient in the East River watershed (Upper Gunnison Basin, Colorado, USA). Our aim was to evaluate whether fens act as passive <em>transporters</em> or active <em>transformers</em> of these solute groups. Fen base cation chemistry was largely indistinguishable from surface water and groundwater, suggesting transport-dominated behavior controlled by bedrock lithology. In contrast, anoxic conditions in fens produced distinct redox-sensitive nutrient signatures. A quasi-linear relationship between Cl-normalized NO₃²⁻ and PO₄³⁻ in high-elevation fens and surface waters suggests a possible mixing signal originating from nutrient-enriched fen waters and more dilute surface or groundwater sources. Stable isotope data for dissolved methane, unlike conservative cations, indicate active carbon transformation via methanogenesis, with limited microbial methane oxidation.</div><div>Collectively, our study offers an integrated assessment of the aqueous geochemistry of montane fens and their potential to modulate surface water chemistry across mid-latitude alpine watersheds.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123129"},"PeriodicalIF":3.6,"publicationDate":"2025-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145447692","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":"Divergent environmental controls on branched tetraethers along precipitation gradients in soils of the Tibetan Plateau","authors":"Yanwu Duan ,&nbsp;Yuling Zhou ,&nbsp;Shuo Hao ,&nbsp;Qing Sun ,&nbsp;Josef P. Werne ,&nbsp;Aifeng Zhou ,&nbsp;Lin Chen ,&nbsp;Yuanxin Li ,&nbsp;Mengjing Li ,&nbsp;Xianyong Cao ,&nbsp;Fahu Chen","doi":"10.1016/j.chemgeo.2025.123128","DOIUrl":"10.1016/j.chemgeo.2025.123128","url":null,"abstract":"<div><div>Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are widely used for terrestrial paleotemperature reconstructions, yet their environmental controls in Tibetan Plateau (TP) soils remain debated. Here, we analyze brGDGT distributions from 68 surface soil samples spanning a broad precipitation gradient across the TP and compare them with data from 1249 globally distributed soils. Our results show that soil pH is the primary control on brGDGT abundance and distribution for TP soils. However, regional environmental responses diverge, with a consistent threshold at ∼600 mm mean annual precipitation (MAP), as revealed by both 200-mm precipitation binning and silhouette coefficient-based clustering. In drier regions (MAP &lt;600 mm; Cluster A), 6-methyl brGDGTs dominate, primarily controlled by soil pH and precipitation. In wetter regions (MAP &gt;600 mm; Cluster B), 5-methyl brGDGTs, particularly Ia, become dominant, with mean annual air temperature (MAAT) emerging as the key driver. Consistent with global soils, cyclization (CBT′) and isomerization (IBT) indices closely track soil pH, while the relative abundance of isoprenoid GDGTs to brGDGTs (R_i/b and BIT indices) show promise as proxies for aridity. Although the MBT′_5ME index correlates with MAAT, substantial deviations occur—especially in drier regions—likely reflect combined influences of precipitation, vegetation cover, seasonal bias, air–soil temperature decoupling, and potential shifts in microbial community composition. Neither regional MBT_5/6 index nor global calibrations—including Bayesian (BayMBT) and machine learning-based (FROG) models—improve MAAT reconstructions, underscoring the limitations of existing approaches in the TP region. Notably, accounting for fractional abundance variations in brGDGT methylation subgroups substantially enhances temperature sensitivity. The resulting machine learning-based Support Vector Regression (SVR) model demonstrates strong predictive power and offers great potential for temperature reconstructions in both TP soils and diverse global settings. These findings help reconcile debates over the environmental controls on brGDGTs and contribute to a refined framework for paleoclimate reconstructions across the TP.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123128"},"PeriodicalIF":3.6,"publicationDate":"2025-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145434691","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":"Aluminum control on viscosity and structure of haplogranitic melts: Implications for rhyolitic melt viscosity determination","authors":"Gabriele Giuliani ,&nbsp;Laura Calabrò ,&nbsp;Veronica Stopponi ,&nbsp;Dmitry Bondar ,&nbsp;Sumith Abeykoon ,&nbsp;Claudia Romano ,&nbsp;Donald B. Dingwell ,&nbsp;Danilo Di Genova","doi":"10.1016/j.chemgeo.2025.123127","DOIUrl":"10.1016/j.chemgeo.2025.123127","url":null,"abstract":"<div><div>Accurate determination of melt viscosity near the glass transition temperature (<em>T</em>_<em>g</em>) is critical for modeling volcanic processes, but direct measurements are often compromised by nanostructuration in natural Fe–Ti-bearing systems, especially during experimental manipulation. Differential scanning calorimetry (DSC) offers an alternative method for estimating viscosity via “shift factors” (<em>K</em>), which link enthalpy to shear relaxation (and thus shear viscosity). This is possible because DSC analysis of supercooled melts requires significantly less time than micropenetration viscometry. However, the compositional sensitivity of the shift factors is still debated, particularly in highly polymerized melts.</div><div>To address this, we investigated the role of Al₂O₃ in controlling melt viscosity and network structure using five Fe–Ti-free haplogranitic compositions: the metaluminous HPG8 base melt and four systematically modified variants with nominal composition of +2, +5, −2 and −5 wt% Al₂O₃. We combine micropenetration viscometry, DSC, and Raman spectroscopy to examine the rheological and structural response to Al₂O₃ variation.</div><div>Our results reveal a non-linear viscosity dependence on Al₂O₃ content: peraluminous melts exhibit higher viscosities and <em>T</em>_<em>g</em>, while peralkaline melts are significantly more fluid. Despite these differences, melt fragility remains constant across the compositional series.</div><div>Calibrated DSC shift factors show no correlation with the network modifier content in peralkaline melts but instead they scale with the infinite-temperature viscosity (log₁₀<em>η</em>_∞). Peralkaline melts with log₁₀<em>η</em>_∞ &gt; −3.00 show low and constant shift factors, whereas metaluminous and peraluminous melts (log₁₀<em>η</em>_∞ &lt; −3.00) yield higher values. These findings establish benchmarks for the application of the DSC shift-factor approach to estimate melt viscosity in natural, silica-rich rhyolitic melts, especially where direct measurements are hindered, thereby improving our ability to model magma rheology and eruption dynamics.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"698 ","pages":"Article 123127"},"PeriodicalIF":3.6,"publicationDate":"2025-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145441784","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}