Chemical Geology最新文献

{"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":"Petrology of alkali gabbro from the Messum Crater, Namibia (Paranà-Etendeka Province) – Melting of metasomatized carbonated lithospheric mantle sources","authors":"S. Jung ,&nbsp;R.L. Romer ,&nbsp;J.A. Pfänder","doi":"10.1016/j.chemgeo.2024.122547","DOIUrl":"10.1016/j.chemgeo.2024.122547","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Foid gabbros (alkali gabbros) are late-stage intrusive rocks into the alkaline core of the Cretaceous Messum complex, an anorogenic ring complex belonging to the Etendeka Large Igneous Province in NW Namibia. The mineralogy of the alkali gabbros is characterized by primary olivine, clinopyroxene (Ti-augite), nepheline and plagioclase and late-stage or secondary brown Ti-amphibole and biotite plus magnetite. The bulk rock compositions resemble low-SiO&lt;sub&gt;2&lt;/sub&gt; alkaline melts with low TiO&lt;sub&gt;2&lt;/sub&gt; and K&lt;sub&gt;2&lt;/sub&gt;O/Na&lt;sub&gt;2&lt;/sub&gt;O &lt; 1. Some of them have Cr (up to 490 ppm) and Ni (up to 265 ppm) contents that approach values characteristic for primary mantle melts. The alkali gabbros are characterized by variable enrichment in incompatible trace elements (Ba: 750–1020 ppm, Zr: 131–173 ppm; Hf: 3.0–3.4 ppm, Nb: 66–90 ppm, Ta: 3.7–5.2 ppm, La: 32–43 ppm, Th: 4.0–5.5 ppm). Zr/Hf and Nb/Ta ratios are high and negatively correlated. The alkali gabbros display a small spread in initial &lt;sup&gt;87&lt;/sup&gt;Sr/&lt;sup&gt;86&lt;/sup&gt;Sr (0.7044–0.7046), εNd (+1.2 to +1.7) and Pb isotope ratios (&lt;sup&gt;206&lt;/sup&gt;Pb/&lt;sup&gt;204&lt;/sup&gt;Pb, 17.86–18.00, &lt;sup&gt;207&lt;/sup&gt;Pb/&lt;sup&gt;204&lt;/sup&gt;Pb: 15.54–15.56, &lt;sup&gt;208&lt;/sup&gt;Pb/&lt;sup&gt;204&lt;/sup&gt;Pb: 37.65–37.81). Variations of major and trace element data and Sr, Nd, and Pb isotopic compositions indicate that the more differentiated alkali gabbro samples evolved by fractional crystallization from the most mafic parent involving mainly olivine, clinopyroxene, and minor plagioclase and Fe&lt;img&gt;Ti oxides, whereas crustal contamination was negligible. In primitive mantle-normalized multi-element diagrams, alkali gabbros show depletions in Rb, Th, U, Pb, Hf, Zr and Ti and enrichments in Sr. Notably, high molar Ca/Al, high Ti/Eu, high Zr/Hf and Nb/Ta, low TiO&lt;sub&gt;2&lt;/sub&gt;, low Zr/Nb at high Nb concentrations and low Zr/Sm in samples with high Lu/Hf and low Hf/Sm point to a carbonatitic component in the source of the alkali gabbros. REE modelling suggests that the parental melts form within the garnet stability field and may be modified either by partial re-equilibration or mixing with melts generated in the spinel stability field. Application of the thermobarometer proposed by &lt;span&gt;&lt;span&gt;Lee et al. (2009)&lt;/span&gt;&lt;/span&gt; (&lt;span&gt;&lt;span&gt;Lee et al., 2009&lt;/span&gt;&lt;/span&gt;. Constraints on the depths and temperatures of basaltic magma generation on Earth, and other terrestrial planets using new thermobarometers for mafic magmas. Earth Planet. Sci. Lett. 279, 20–33.) implies generation of the most primitive alkali gabbros at ∼4.5 GPa and ∼ 1480 °C, the latter value is in agreement with previous temperature estimates using Al-in-olivine thermometry and melt inclusion studies. The Sr-Nd-Pb isotope compositions of the alkali gabbros do not overlap with those of mafic lavas attributed to the Tristan or Gough hot spot or the newly defined Doros component. Trace element and isotope data indicate derivation of the Messum alkali gabbros from a heterogeneous m","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122547"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858012","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":"Triple oxygen and hydrogen stable isotope composition of water in Murchison carbonaceous chondrite accessed by thermogravimetry-enabled laser spectroscopy","authors":"Erik J. Oerter ,&nbsp;Alexandre Garenne ,&nbsp;Miguel Cisneros ,&nbsp;George D. Cody ,&nbsp;Michael Singleton ,&nbsp;Conel M. O’D. Alexander","doi":"10.1016/j.chemgeo.2024.122557","DOIUrl":"10.1016/j.chemgeo.2024.122557","url":null,"abstract":"<div><div>We have developed the capability to measure ¹⁷O/¹⁶O in H₂O and OH⁻ of hydrous minerals by a technique using thermogravimetric analysis coupled with isotope ratio infrared spectroscopy (TGA-IRIS) on a suite of liquid water standards, terrestrial mineral standards, multi-mineral synthetic mixtures of terrestrial samples, and Murchison carbonaceous chondrite. This ¹⁷O/¹⁶O analytical capability is combined with the previously developed TGA-IRIS capability of ¹⁸O/¹⁶O, which enables us to calculate Δ`<sup>17</sup>O values. Additionally, we have made <sup>2</sup>H/<sup>1</sup>H measurements by TGA-IRIS on the suite of materials. Analyses of 328 standard water samples sealed into silver tubes (0.25 μL, 174 VSMOW and 154 GISP) analyzed over the course of three years yielded δ<sup>18</sup>O values by TGA-IRIS with precision of ±0.30 ‰, δ<sup>17</sup>O of ±0.24 ‰, Δ`¹⁷O of ±0.126 ‰, and δ²H ± 7.5 ‰ (± 1 Std. Dev.). TGA-IRIS analyses of a suite of hydrous minerals (oxy-hydroxide, mica, serpentines, sulfide, phyllosillicates) yields similar precision. TGA-IRIS analyses of the CM2 carbonaceous chondrite Murchison resulted in δ¹⁸O, δ¹⁷O, Δ`<sup>17</sup>O, and δ<sup>2</sup>H values of the H<sub>2</sub>O and/or OH<sup>−</sup> from its hydrous minerals. Δ`¹⁷O values of Murchison H₂O range from 1.034 ‰ at 350 °C, to −0.368 ‰ at 650 °C, to −1.75 ‰ at 850 °C. TGA-IRIS can generate Δ`¹⁷O values of H₂O and/or OH⁻ in hydrous materials that are well within the precision needed for the analysis of meteoritic samples, as well as samples returned from asteroids, such as Ryugu and Bennu.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122557"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142857885","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":"Mechanism of cadmium (Cd) enrichment in the soil of karst areas with high geochemical background in Southwest China","authors":"Bo Li ,&nbsp;Kun Lin ,&nbsp;Xu Liu ,&nbsp;Xudong Ma ,&nbsp;Xuezhen Li ,&nbsp;Zhiliang Wu ,&nbsp;Cheng Li ,&nbsp;Tao Yu ,&nbsp;Tiansheng Wu ,&nbsp;Zhongfang Yang","doi":"10.1016/j.chemgeo.2024.122523","DOIUrl":"10.1016/j.chemgeo.2024.122523","url":null,"abstract":"<div><div>Karst areas are formed from the dissolution of carbonate rocks and are present worldwide. The soil found in such areas is enriched in heavy metals, such as cadmium (Cd), lead (Pb) and Arsenic (As), and has geological high-background characteristics. However, this enrichment is anomalous depending on the type of bedrock, and the mechanism of enrichment has not yet been comprehensively elucidated. To explore the mechanisms of Cd enrichment in these soils, we investigated the distribution patterns and migration characteristics of Cd during the weathering and pedogenesis of carbonate rocks, and the causes of Cd enrichment and associated ecological risks were determined. The conclusions were as follows: (1) In the process of natural evolution, the boundary between the dissolution of carbonate rocks and the weathering of insoluble substances is unclear, resulting in the overlap of and interaction between the processes of dissolution-accumulation-weathering and pedogenesis. (2) In addition to the enrichment effects caused by the dissolution of carbonate rocks and the inheritance, the readsorption of insoluble substances and the retention of secondary carrier minerals are the main driving forces of Cd enrichment. (3) During the late stage of weathering of insoluble materials, soil acidification significantly promotes the Cd activation process. When the proportion of active Cd significantly increases, the ecological risk potential increases, especially in geological high-background areas rich in Cd.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122523"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815874","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}