Chemical Geology最新文献

{"title":"Multistage formation and geochemical response of pipe-morphology cold seep carbonate in the Qiongdongnan Basin, northern South China Sea","authors":"Jing Zhao ,&nbsp;Xuewan Wu ,&nbsp;Wei Zhang ,&nbsp;Zhifeng Wan ,&nbsp;Yifei Dong ,&nbsp;Xi Xiao ,&nbsp;Yang Wu ,&nbsp;Xiaoyu Wu ,&nbsp;Junxi Feng ,&nbsp;Qianyong Liang","doi":"10.1016/j.chemgeo.2024.122524","DOIUrl":"10.1016/j.chemgeo.2024.122524","url":null,"abstract":"<div><div>Cold seep carbonates are commonly used to record the nature of seepage, including fluid sources, diagenetic environments, and variations in seepage activity. However, the relationship between diagenetic environments and trace element enrichment in dynamic environments is poorly understood. Pipe-morphology cold seep carbonates form from outside to inside in methane seeps and record variations in elements and isotopes over time, which can be used to reconstruct diagenetic environments and fluid dynamics. In this work, we analysed the mineral compositions, carbon and oxygen (C<img>O) isotopes and major and trace element contents in different areas of pipe-morphology cold seep carbonate collected from the Qiongdongnan Basin in different growth directions. The cold seep carbonate exhibits changes from high-magnesian calcite (HMC) to aragonite and then to HMC, indicating that it has undergone changes in the sedimentary environment inside the fluid migration pathway. On the basis of these findings, the formation of this pipe-morphology cold seep carbonate is divided into three stages. The low δ¹³C values (from −36.13 ‰ to −32.18 ‰) indicate anaerobic oxidation of methane during carbonate formation. The response of δ¹³C to changes in the methane flux is not obvious. The gradual increase in δ¹⁸O from the outer to the inner portions suggests that the methane flux affected δ¹⁸O. The samples have relatively high enrichment factors (EFs) of molybdenum (Mo) and high molybdenum/uranium (Mo/U) ratios. The U_EF values show an increasing trend from the outer to the inner portions, whereas the changes in Mo_EF, Cd_EF and V_EF are not obvious. However, Mo_EF, Cd_EF, and V_EF all have good correlations with Mn/Al and Fe/Al, indicating that the particulate shuttle process significantly impacts the enrichment of Mo, Cd, and V. We concluded that the enrichment of U is influenced by the methane flux, whereas the enrichment of Mo, Cd and V is unrelated to methane dynamics. This study provides insights into the behaviour of the methane flux and seawater, redox-sensitive trace element contents and changes in the sedimentary environment and plays an essential role in understanding the activities of cold seeps in dynamic environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122524"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815919","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":"Single quartz δ18O: A new frontier in detrital provenance analysis (Bengal Fan, IODP Expedition 354)","authors":"Mara Limonta ,&nbsp;Christian France-Lanord ,&nbsp;Albert Galy ,&nbsp;Andrey Gurenko ,&nbsp;Nordine Bouden ,&nbsp;Eduardo Garzanti","doi":"10.1016/j.chemgeo.2024.122525","DOIUrl":"10.1016/j.chemgeo.2024.122525","url":null,"abstract":"<div><div>Quartz is the most abundant mineral in sediments and sedimentary rocks but efforts to reliably identify its provenance have been only partially fruitful so far. Even advanced methods such as cathodo-luminescence, Raman spectroscopy, synchrotron X-ray absorption spectroscopy, and laser ablation spectrometry have led to limited success. This article demonstrates how the δ¹⁸O of detrital quartz provides useful additional insight. The oxygen-isotope signature primarily depends on source rocks and their formation conditions, being highly different for different crustal sources and highest for carbonate rocks.</div><div>This study illustrates a new protocol to analyze δ¹⁸O signatures of single quartz grains and shows how provenance from magmatic, metamorphic, or sedimentary domains can be discriminated. In each sand sample from rivers draining exclusively a single Himalayan tectonic domain (e.g., Trans-Himalaya, Greater Himalaya, Lesser Himalaya, and Tethys Himalaya), ∼200 quartz grains were analyzed by ion microprobe LG-SIMS (Large Geometry Secondary Ion Mass Spectrometry) to characterize their oxygen-isotope variability. In each turbidite sample collected from the Bengal Fan during IODP Expedition 354, ∼150 quartz grains were analyzed next to quantify the relative contribution of each Himalayan domain. This allowed us to complement data obtained with other bulk-sediment to single-mineral approaches, thus enhancing provenance resolution and highlight the erosional evolution of the Himalayan-Tibetan orogen through time.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122525"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858013","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Re-Os isotopic evidence for ancient melt depletion in refertilized Neo-Tethyan suboceanic mantle domain","authors":"Yang Xu ,&nbsp;Chuan-Zhou Liu ,&nbsp;Chang Zhang ,&nbsp;Tong Liu","doi":"10.1016/j.chemgeo.2024.122520","DOIUrl":"10.1016/j.chemgeo.2024.122520","url":null,"abstract":"<div><div>Ancient mantle domains with unradiogenic Os isotopes have been well documented in the Yarlung-Tsangpo ophiolites (YTO), southern Tibet. Nonetheless, previous Os isotope studies have yielded relatively young <em>Re</em>-depletion model (T_RD) ages of &lt;1.0 Ga for mantle peridotites of the Zedong ophiolite in the eastern segment of the YTO. In this study, a comprehensive petrological and geochemical study has been conducted on a suite of mantle samples including harzburgites, lherzolites and one pyroxenite. Our results indicate that the Zedong harzburgites have been subjected to low to moderate degrees (∼6–20 %) of partial melting and late-stage melt-rock interaction with basaltic melts. In contrast, both lherzolites and pyroxenite were generated by melt refertilization. The Zedong lherzolites display flat patterns of highly siderophile elements (HSE; Os, Ir, Ru, Pt, Pd, Re), whereas the harzburgites show depletion in Pt, Pd and Re relative to Os, Ir and Ru. The <em>Re</em>-Os isotopes of the Zedong lherzolites have been modified by melt refertilization and thus cannot provide reliable age information. Three Zedong harzburgites with the lowest Pd_N/Ir_N and Re_N/Ir_N ratios have the least radiogenic ¹⁸⁷Os/¹⁸⁸Os of 0.11497–0.11537, giving the old T_RD ages of 1.89–1.98 Ga. These ages are considerably older than previously reported T_RD ages for the Zedong peridotites (&lt; 1.0 Ga), but comparable to the oldest T_RD age for the Luobusa peridotites. This supports the occurrence of similarly old mantle domains in both Zedong and Luobusa ophiolites in the eastern part of the YTO. The Zedong pyroxenite has a radiogenic ¹⁸⁷Os/¹⁸⁸Os ratio of 0.158 that is similar to the ¹⁸⁷Os/¹⁸⁸Os ratios (0.156–0.180) of previously reported for the YTO pyroxenites, which can be explained by selective assimilation of interstitial sulfides during the percolation of migrating melts through the mantle lithosphere. Grain boundary sulfides may play a significant role in the high ¹⁸⁷Os/¹⁸⁸Os of the YTO pyroxenites.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122520"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142777462","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":"Extreme rare earth element (REE) enrichment during weathering recorded in saprolites from South Carolina","authors":"Utpalendu Haldar ,&nbsp;Ramananda Chakrabarti ,&nbsp;Roberta L. Rudnick","doi":"10.1016/j.chemgeo.2024.122553","DOIUrl":"10.1016/j.chemgeo.2024.122553","url":null,"abstract":"<div><div>Rare earth elements (REE) and other trace element concentrations as well as ¹⁴³Nd/¹⁴⁴Nd and ⁸⁷Sr/⁸⁶Sr in saprolites developed on the Cayce metadiabase dike, South Carolina, document extreme REE mobilization during chemical weathering and enrichment of REE on clays. Saprolites display a bimodal distribution in their total REE concentrations (ΣREE) and light-REE (LREE)/heavy-REE (HREE) ratios. Shallower (0–6 m depth), Group I, saprolites have high ΣREE (up to 2633 ppm) with enrichment of LREE &gt; MREE &gt; HREE. Group II saprolites, at &gt;6 m depth, have lower ΣREE (45–67 ppm) and relatively flat LREE/HREE, similar to the unweathered metadiabase. Group I saprolites are more weathered (chemical index of alteration (CIA) values of 87–95), than the Group II saprolites (CIA = 46–88, with most &lt;55). Mass balance calculations using ¹⁴³Nd/¹⁴⁴Nd rules out significant input of dust to the weathering profile, which is consistent with the lack of depth-dependent variation in ε_Nd. Weathering and REE enrichment occurred through a three-stage process. Stage 1 involved regional weathering during which saprolites developed on both the metadiabase dike and Liberty Hill granite country rock. During this stage, breakdown of LREE-rich accessory minerals (e.g., titanite) in the granite released REE and radiogenic Sr to weathering fluids that penetrated the metadiabase where these elements were adsorbed onto clays, consistent with their Nd and Sr isotopic compositions. The kaolinite/smectite (K/S) ratio in Group II saprolites negatively correlates with Sm/Nd and positively with Y/Ho and Rb/Sr ratios indicating preferential adsorption of lighter REE (e.g., Nd), Y, and Rb by kaolinites; no trends are seen in Group I saprolites, suggesting that these samples were overprinted by later events that did not impact the Group II saprolites. Stage 2 involved replacement of smectite veins by siderite in the entire saprolite at high pH and under reducing conditions such as found in swamps, which did not affect the adsorbed REE in the clays. In stage 3, siderite dissolution under acidic and oxidized conditions at the shallowest depths (upper 2 m) led to the formation of Fe³⁺-smectite and LREE mobilization; this REE-bearing fluid percolated downwards where the REE were adsorbed onto clays to develop a REE-enriched zone locally in the upper 6 m (within the Group I saprolites). Carbonates may have also acted as depositional ligands and induced REE precipitation. This study shows that REE can be extremely mobile during chemical weathering under specific conditions and may be deposited onto secondary clay minerals like kaolinites, which absorb REE, particularly LREE, leading to local enrichments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122553"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815831","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":"Ca-Sr-Nd isotopic signatures of mid-ocean ridge basalts from the Central Indian Ridge and implications for recycled materials in the Indian Ocean mantle domain","authors":"Hongli Zhu ,&nbsp;Yujie Shan ,&nbsp;Renqiang Liao ,&nbsp;Lipeng Zhang ,&nbsp;Jianghong Deng ,&nbsp;Congying Li ,&nbsp;Long Du ,&nbsp;Zhaofeng Zhang ,&nbsp;Weidong Sun","doi":"10.1016/j.chemgeo.2024.122546","DOIUrl":"10.1016/j.chemgeo.2024.122546","url":null,"abstract":"<div><div>Mid-ocean ridge basalts (MORBs) from the Indian Ocean have been demonstrated to have more enriched radiogenic isotopic compositions than MORBs from the Pacific and Atlantic Oceans. However, the origin of such anomaly is still under debate. To better constrain the genesis of the isotopic anomaly observed in Indian MORBs, we present a systematic Ca-Sr-Nd isotopic study of a suite of MORBs from the Central Indian Ridge (CIR) between 19 and 20°S and the adjacent Gasitao Ridge. The δ^44/40Ca values of these MORBs vary from 0.70 to 0.89 ‰, most of which are similar to those of reported Pacific and Atlantic MORBs. However, some samples from the northern part of the studied CIR region showed slightly lower δ^44/40Ca values than the average of the reported Pacific and Atlantic MORBs. Notably, these δ^44/40Ca values are correlated with Sr<img>Nd isotopic ratios, which extend from the depleted MORB mantle to a component with lower δ^44/40Ca and more enriched Sr<img>Nd isotopic compositions, suggesting the presence of an enriched component in the source of these Indian MORBs. Recent studies have proposed that lower continental crust has similar δ^44/40Ca values to the estimated Bulk Silicate Earth, indicating that the low δ^44/40Ca signatures of some Indian MORBs are unlikely to be produced by delaminated lower continental crust. Garnet in the residue and recycled carbonate-rich marine sediments with oceanic crust can cause lower δ^44/40Ca signatures in mantle-derived rocks. However, trace element ratios and our model calculations suggest that these two factors can hardly induce the correlated Ca-Sr-Nd trends in these Indian MORBs. Instead, recently reported subcontinental lithospheric mantle xenoliths that experienced silicate and/or carbonatite metasomatism, which also show low δ^44/40Ca and enriched Sr<img>Nd isotopic compositions, correspond with the correlated Ca-Sr-Nd trends in the studied Indian MORBs. Moreover, ancient metasomatized subcontinental lithospheric mantle materials have been observed in abyssal peridotites from the Southwest Indian Ridge. Therefore, delaminated subcontinental lithospheric mantle maybe the most likely cause of the Ca-Sr-Nd isotopic anomaly in Indian MORBs. Our study suggests that combined Ca-Sr-Nd isotopes can be treated as potential tracers to the genesis of mantle heterogeneity.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122546"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815875","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":"A comprehensive and consistent mineral dissolution rate database: Part III: Non-silicate minerals including carbonate, sulfate, phosphate, halide, and oxy-hydroxide minerals","authors":"Eric H. Oelkers ,&nbsp;Mouadh Addassi","doi":"10.1016/j.chemgeo.2024.122528","DOIUrl":"10.1016/j.chemgeo.2024.122528","url":null,"abstract":"<div><div>This paper describes the creation of a consistent database of the far-from-equilibrium dissolution rates in aqueous fluids of the major non-silicate minerals including carbonates, sulfates, phosphates, oxides and hydroxides. This work, based on the regression of available dissolution rate data normalized to their BET surface area as a function of pH and temperature, was performed using equations described in Heřmanská et al. (2022, 2023). For carbonate minerals, an additional term was added to account for the slowing of rates in response to increasing aqueous bicarbonate and carbonate concentration. All rate equations have been incorporated into a computer accessible database allowing for the direct application of these rates to assess the temporal evolution of chemical mass transfer in laboratory and field-based systems. It is anticipated that such applications will lead to further advances in our understanding the reaction rates of individual minerals and of natural water-rock interaction in the future.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122528"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858011","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":"Investigating pressure effects of Ti and Zr partitioning into zircon, quartz, and rutile at crustal temperatures","authors":"Heather M. Kirkpatrick ,&nbsp;Dustin Trail ,&nbsp;T. Mark Harrison ,&nbsp;Elizabeth A. Bell","doi":"10.1016/j.chemgeo.2024.122518","DOIUrl":"10.1016/j.chemgeo.2024.122518","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The dependency of Ti partitioning between quartz and zircon on the activity of TiO&lt;sub&gt;2&lt;/sub&gt; and Zr partitioning between zircon and rutile on the activity of ZrO&lt;sub&gt;2&lt;/sub&gt; suggest that an intercalibration among the three minerals (i.e., concentration information from all three phases in the same experiment) could reduce propagated errors when using multiple systems simultaneously. Experiments were undertaken to assess pressure effects in Ti and Zr partitioning in the zircon-quartz-rutile system and intercalibration of the three phases at low concentrations (down to ∼20 ppm). Analysis of small crystals (down to ∼8 μm) was possible due to the high spatial resolution of the CAMECA &lt;em&gt;ims&lt;/em&gt;1290 ion microprobe. Regressions for pressure-temperature-phase domains for experiments between 800 and 1000 °C and 10 and 15 kbar array about the initial calibration data providing confidence in their merit despite recent criticisms. Ti and Zr partitioning into quartz, rutile, and zircon can be quantified as:&lt;span&gt;&lt;span&gt;&lt;span&gt;&lt;math&gt;&lt;mo&gt;log&lt;/mo&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mi&gt;Ti&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;in&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;quartz&lt;/mi&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;log&lt;/mo&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;msubsup&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;Si&lt;/mi&gt;&lt;msub&gt;&lt;mi&gt;O&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;α&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;quartz&lt;/mi&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;6.71&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;0.11&lt;/mn&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mn&gt;383&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mi&gt;K&lt;/mi&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;/mfrac&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;0.122&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;0.07&lt;/mn&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;0.00197&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;0.00024&lt;/mn&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;msup&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;span&gt;&lt;span&gt;&lt;span&gt;&lt;math&gt;&lt;mo&gt;log&lt;/mo&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mi&gt;Zr&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;in&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;rutile&lt;/mi&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mo&gt;log&lt;/mo&gt;&lt;msubsup&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;msub&gt;&lt;mi&gt;iO&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;α&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;quartz&lt;/mi&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;7.39&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;0.21&lt;/mn&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mn&gt;4262&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;220&lt;/mn&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;T&lt;/mi&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mi&gt;K&lt;/mi&gt;&lt;/mfenced&gt;&lt;/mrow&gt;&lt;/mfrac&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;0.021&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;0.0051&lt;/mn&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mi&gt;P&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;&lt;/span&gt;&lt;/span&gt;&lt;/div&gt;&lt;div&gt;and&lt;span&gt;&lt;span&gt;&lt;span&gt;&lt;math&gt;&lt;mo&gt;log&lt;/mo&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mi&gt;Ti&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;in&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;zircon&lt;/mi&gt;&lt;/mrow&gt;&lt;/mfenced&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;mi&gt;log&lt;/mi&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;msubsup&gt;&lt;mi&gt;a&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;msub&gt;&lt;mi&gt;iO&lt;/mi&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;α&lt;/mi&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;quartz&lt;/mi&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mn&gt;4147&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mfenced&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;mn&gt;555&lt;/mn&gt;&lt;/mrow&gt;&lt;/mf","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122518"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815832","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":"Grassland woody encroachment alters subsurface mineral weathering and groundwater composition in a carbonate system","authors":"Christa Anhold ,&nbsp;Camden Hatley ,&nbsp;Eresay Alcantar-Velasquez ,&nbsp;Rachel M. Keen ,&nbsp;Kayalvizhi Sadayappan ,&nbsp;Karla M. Jarecke ,&nbsp;Pamela L. Sullivan ,&nbsp;Jesse B. Nippert ,&nbsp;Li Li ,&nbsp;G.L. Macpherson ,&nbsp;Matthew F. Kirk","doi":"10.1016/j.chemgeo.2024.122522","DOIUrl":"10.1016/j.chemgeo.2024.122522","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Displacement of grasses by woody plants (woody encroachment) is occurring in grasslands worldwide. Previous studies indicate that encroachment can alter subsurface carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) concentrations and mineral weathering, though these impacts are still poorly understood. To address this knowledge gap, we sampled groundwater and stream water every three weeks during the 2022 water year from two watersheds at Konza Prairie Biological Station, a native tallgrass prairie underlain by limestone and mudrock units in Kansas, USA. Amounts of woody encroachment differ between the watersheds primarily because of differences in fire frequency. One watershed is burned annually and contains 6 % and 45 % woody plant coverage in its upland and riparian areas, respectively, whereas the other is burned every four years and contains 28 % and 74 % woody plant coverage, respectively. We expected to find higher CO&lt;sub&gt;2&lt;/sub&gt; levels in the more encroached watershed, assuming the deep roots of woody plants increase inputs of CO&lt;sub&gt;2&lt;/sub&gt; to bedrock. However, we found the opposite. Our results indicate that groundwater from a single limestone aquifer contained an average of 1.4 mM CO&lt;sub&gt;2&lt;/sub&gt; in the less encroached watershed and 1.0 mM CO&lt;sub&gt;2&lt;/sub&gt; in the more encroached watershed. Similarly, stream water CO&lt;sub&gt;2&lt;/sub&gt; concentrations at the outlet of the less encroached watershed (0.25 mM) were more than twice that of the more encroached watershed (0.12 mM) on average. Despite these differences in CO&lt;sub&gt;2&lt;/sub&gt; concentration, amounts of mineral weathering per liter of groundwater differed little between watersheds. We hypothesize that encroachment is causing differences in CO&lt;sub&gt;2&lt;/sub&gt; concentrations between watersheds by decreasing the proportion of mineral weathering that occurs under conditions that are open with respect to CO&lt;sub&gt;2&lt;/sub&gt; exchange. During open-system weathering, dissolved CO&lt;sub&gt;2&lt;/sub&gt; consumed by weathering reactions can be replaced from an adjacent gas phase, allowing CO&lt;sub&gt;2&lt;/sub&gt; concentrations to remain elevated as weathering progresses. In contrast, during closed-system weathering, CO&lt;sub&gt;2&lt;/sub&gt; is not replaced and decreases in concentration as weathering progresses. If weathering primarily occurs under open-system conditions within the study area soils, which are unsaturated, and closed-system conditions within the underlying bedrock, where pores are more commonly saturated, then woody encroachment has the potential to decrease the proportion of open-system weathering by increasing soil permeability and thus decreasing soil water residence times. This hypothesis is consistent with our findings and implies that a shortening of soil water residence time with woody encroachment lowers the proportion of CO&lt;sub&gt;2&lt;/sub&gt; delivered from the soil to the subsurface and creates a more aggressive weathering engine at depth and along deeper flow paths. Encroachment may also be altering soil CO&lt;sub&gt;2&lt;/sub&gt; production an","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122522"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815833","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":"Application of Ni, Cu and Fe isotopes as indicators of ore genesis - New insights from the epigenetic-hydrothermal Rajapalot AuCo prospect, Finnish Lapland","authors":"J. Tepsell ,&nbsp;Y. Lahaye ,&nbsp;F. Molnár ,&nbsp;O.T. Rämö ,&nbsp;N. Cook","doi":"10.1016/j.chemgeo.2024.122513","DOIUrl":"10.1016/j.chemgeo.2024.122513","url":null,"abstract":"<div><div>Application of stable transition metal isotopes as indicators of ore genesis is becoming more popular, yet the fractionation mechanisms and isotopic distribution in these unconventional systems remain poorly understood. In this study, we present an analysis of sulphide Ni, Cu and Fe isotopes measured from solution using multicollector ICP-MS. The data were collected from the dominant sulphide phases in the Raja prospect within the epigenetic-hydrothermal Rajapalot Au<img>Co deposit, Finnish Lapland. Our main goal was to gain new information on the systematics and behaviour of the isotopes in high-temperature ore-forming environments, with implications for ore genesis. The Raja prospect is hosted by a Paleoproterozoic volcanic-sedimentary sequence and was formed by multi-stage hydrothermal processes during the Svecofennian orogeny. Pyrite shows significant variation in δ⁵⁶Fe (-2.08 to +3.29 ‰), including the heaviest iron isotopes thus far observed in natural pyrite. The δ⁵⁶Fe values in pyrrhotite vary less (-0.74 to +0.80 ‰) but are unusually heavy compared to those of magmatic pyrrhotite. δ⁵⁶Fe in chalcopyrite ranges from +0.10 to +1.45 ‰, δ⁶⁰Ni in pyrrhotite from -1.03 to +0.18 ‰, and δ⁶⁵Cu in chalcopyrite from -0.30 to +0.23 ‰. The δ⁵⁶Fe values in co-existing sulphide phases suggest both equilibrium and kinetic fractionation effects. The extreme Fe fractionation in pyrite implies that kinetic fractionation played a major role in the precipitation of isotopically light pyrite. Moreover, inheritance of low δ⁵⁶Fe values from a pyrrhotite precursor is likely. The heavy Fe isotopic composition of some of the pyrrhotite and pyrite is probably the result of preferential leaching of light isotopes by late hydrothermal fluids.</div><div>Systematic correlations between the composition of the examined isotope systems, Co and Au concentrations, and textural features link the sulphide isotopes to multi-stage ore formation. Gradual trends in the isotope compositions suggest Rayleigh fractionation. Early Co deposition is attributed to isotopically heavy fluid, probably derived from a sedimentary formation with abundant iron oxides. The isotopically lighter Au mineralising fluids point to a separate fluid source, probably involving evolved granites. The late hydrothermal Au-carrying fluids overprinted the early Co mineralisation forming Au<img>Co enriched zones. Our study highlights the potential of multiple isotope systematics in sulphides as a useful diagnostic tool for tracing mineralisation processes in and source regions of hydrothermal Au and Co.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122513"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142777461","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The role of scavenging and early diagenesis in controlling hydrothermal fluxes into the ocean along the Endeavour segment of the Juan de Fuca ridge","authors":"Isabelle Beaupré-Olsen ,&nbsp;Steve Mihaly ,&nbsp;Hannah Robutka ,&nbsp;Jody Spence ,&nbsp;Kathryn M. Gillis ,&nbsp;Laurence A. Coogan","doi":"10.1016/j.chemgeo.2025.122675","DOIUrl":"10.1016/j.chemgeo.2025.122675","url":null,"abstract":"<div><div>Mixing of high-temperature hydrothermal vent fluids with seawater leads to the precipitation of a large fraction of the non-conservative element load and scavenging of elements from seawater onto the particles formed. This substantially modifies hydrothermal fluxes into the ocean relative to the flux across the seafloor at vents. However, the particles formed in the plume are rarely in equilibrium within the uppermost sediments, and scavenged elements may be loosely bound to particle surfaces, meaning that the net flux from the ocean can be readily modified by processes operating during early diagenesis. Using bulk geochemistry, and progressive leaching experiments, we characterize sediments from around the Endeavour segment of the Juan de Fuca ridge to investigate scavenging and early diagenetic processes. Changes in bulk sediment composition with distance from the ridge (e.g., decreases in Fe/Ti) support a decreased hydrothermal input off-axis. Bulk-sediment and leachate data are interpreted as indicating substantial scavenging of elements such as P, V, Cr and REEs as previously suggested, with different elements scavenged with different efficiencies in different parts of the plume. Correlations of these elements with Fe in the HCl leachates, suggests their uptake is associated with Fe-oxyhydroxides. Water column scavenging is overprinted by fluxes associated with benthic scavenging for V and REE. In contrast, early diagenesis leads to complete loss of scavenged P back to the ocean. Leaching the samples with NaOH and acetic acid provides evidence for recrystallization of reactive (biogenic and hydrothermal) silica and CaCO₃ during early diagenesis in all locations. The fraction of Fe and Mn leached by 1 M HCl in 1 h versus 24 h, and the amount leached in 24 h, vary systematically; these data can be explained by progressive recrystallization of hydrothermally-derived Fe and Mn minerals during early diagenesis. These early diagenetic reactions release almost all hydrothermally-derived Mn back into the ocean, while Fe remains largely fixed in the sediment. Large-scale loss of Co, Zn, Mo, Ag and Cd also occurs during early diagenesis, with some evidence As, Pb and U are also lost. In deeper, more reducing, sediments there is uptake of As, Mo, Ag, Cd and U, presumably via diffusion through the shallow oxic sediments. Such diagenetic processes mean that the net fluxes of elements into and out of the ocean associated with hydrothermal systems differ from those estimated from studies of either vent fluids or hydrothermal plumes.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122675"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143369703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}