Pub Date : 2025-09-01DOI: 10.1016/j.chemer.2025.126266
Tianxin He , Rong Liu , Qianghao Liu , Hongliang Dang , Xu Wang
Hydrothermal chimney, one of Earth's most mysterious geological events, is crucial for understanding Earth's systems and the history of life. Fine-scale studies of these events help us better understand geological processes, though their transient and complex nature presents significant challenges. Through TIMA, LA-ICP-MS in-situ elemental testing, and Sr and S isotope testing, a relatively complete picture of a carbonate chimney event in the upper section of the Bayingebi Formation in the Yin'e Basin was revealed with high precision. This event was divided into four distinct stages: the prehydrothermal eruption stage, the initial hydrothermal eruption stage, the strong hydrothermal eruption stage and the sustained hydrothermal overflow stage. The pre-hydrothermal eruption stage (Area I) indicates dominant terrigenous sedimentation in a low-energy hydrodynamic environment, with coarse-crystalline calcite enriched in Mn and depleted in K, Na, and Sr and featuring high 87Sr/86Sr values. Subsequently, a transient hydrothermal eruption initiated the deposits in Area II, marked by the appearance of thin-plate calcite and dolomite. During the strong hydrothermal eruption stage (Area III), radial pyrite intersected with calcite, and extensive dolomite precipitation occurred. The 87Sr/86Sr ratio and the δ34SV-CDT value observed may have been a result of the activities of sulfate-reducing bacteria (SRB). In the sustained hydrothermal overflow stage, the eruption intensity decreased, leading to the formation of abundant microcrystalline carbonates in Area IV. Results show regular changes in hydrothermal mineral combinations, eruption modes, material composition, depositional environments, etc., in each stage of the carbonate chimney event, which can provide important information for global lacustrine hydrothermal activity research.
{"title":"Hydrothermal carbonate chimney event from yin’ e basin: Mineralogy, geochemistry, and mode of evolution","authors":"Tianxin He , Rong Liu , Qianghao Liu , Hongliang Dang , Xu Wang","doi":"10.1016/j.chemer.2025.126266","DOIUrl":"10.1016/j.chemer.2025.126266","url":null,"abstract":"<div><div><span><span>Hydrothermal chimney, one of Earth's most mysterious geological events, is crucial for understanding Earth's systems and the history of life. Fine-scale studies of these events help us better understand geological processes, though their transient and complex nature presents significant challenges. Through TIMA, LA-ICP-MS in-situ elemental testing, and Sr and S isotope testing, a relatively complete picture of a carbonate chimney event in the upper section of the Bayingebi Formation in the Yin'e Basin was revealed with high precision. This event was divided into four distinct stages: the prehydrothermal eruption stage, the initial hydrothermal eruption stage, the strong hydrothermal eruption stage and the sustained hydrothermal overflow stage. The pre-hydrothermal eruption stage (Area I) indicates dominant terrigenous sedimentation in a low-energy hydrodynamic environment, with coarse-crystalline </span>calcite enriched in Mn and depleted in K, Na, and Sr and featuring high </span><sup>87</sup>Sr/<sup>86</sup>Sr values. Subsequently, a transient hydrothermal eruption initiated the deposits in Area II, marked by the appearance of thin-plate calcite and dolomite. During the strong hydrothermal eruption stage (Area III), radial pyrite intersected with calcite, and extensive dolomite precipitation occurred. The <sup>87</sup>Sr/<sup>86</sup>Sr ratio and the δ<sup>34</sup>S<sub>V-CDT</sub><span><span> value observed may have been a result of the activities of sulfate-reducing bacteria (SRB). In the sustained hydrothermal overflow stage, the eruption intensity decreased, leading to the formation of abundant microcrystalline carbonates in Area IV. Results show regular changes in hydrothermal mineral combinations, eruption modes, material composition, depositional environments, etc., in each stage of the carbonate chimney event, which can provide important information for global lacustrine </span>hydrothermal activity research.</span></div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126266"},"PeriodicalIF":2.9,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145060178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Ilmeno-Vishnevogorsk (IVC) and Buldym carbonatite complexes of the Southern Urals are deformed linear-type carbonatite complexes that underwent tectonic evolution as a result of accretion-collision processes and the Hercynian collision orogeny. The deposits of niobium and rare earth elements are associated with the Ural carbonatite complexes. Nb-REE ore mineralization is represented by the pyrochlore supergroup minerals, aeschynite and monazite. Their compositional evolution and connection with various phases of alkaline magmatism, pegmatite and carbonatite formation, and late postmagmatic (carbothermal) processes were studied. To determine the age and duration of the ore-forming stages, UPb dating of minerals pyrochlore supergroup phases and monazite was carried out. The pyrochlore-group minerals of the Ural carbonatite complexes are represented by calciopyrochlore, rarely natropyrochlore, and kenopyrochlore. Pyrochlore I, rich in U-(Ta), crystallizes in the earliest magmatic phases of the IVC, in the miaskites and carbonatites I of the Central Alkaline Band. In contrast, Ta-(U)-bearing pyrochlore II is formed in the later magmatic phases, in the taxitic miaskites and miaskite-pegmatites, and is present in explosive carbonatite breccias and carbonatites II of the Vishnevogorsk massif. Both varieties of pyrochlore have magmatic characteristics – oscillatory zoning, absence of vacancies in the A-site, and low Nb/Ta <80. Pyrochlore III and Sr-REE-containing pyrochlore IV – with high Nb/Ta >300 and fluorine (4–5 wt%), are formed from fluid-saturated F-containing carbonate systems in carbonatites II of the IVC miaskite intrusions and fenite halos, as well as in carbonatites III and fenites of the Buldym complex. REE minerals – aeschynite-(Ce) and monazite-(Ce) formed in the carbothermalites of the Buldym complex and in fenite halos of miaskite massifs. The morphological features and evolution of the pyrochlore composition indicate the polygenic nature of the ore process, the late low-temperature stage of which is associated not only with Nb but also with REE mineralization (aeschynite, monazite).
The results of U-Pb-dating of the pyrochlore- and monazite-group minerals make it possible to distinguish two stages of ore formation in the studied carbonatite complexes of the Southern Urals. The early stage is recorded by U-(Ta)-rich pyrochlore in carbonatites I, the Potanino deposit (378 ± 5 Ma), and can be correlated with the primary crystallization of the IVС alkaline rocks and carbonatites at the rifting stage (D3) of the forming continental margins. Whereas, the late stage is dated at ∼255–230 Ma yielded for pyrochlores II-IV of the Vishnevogorsk deposit – in taxitic miaskites, syenite- and miaskite-pegmatites, as well a
{"title":"Сomposition, evolution and age of Nb-REE mineralization in carbonatite complexes in the Ural Fold Belt: New insight into metallogenesis","authors":"I.L. Nedosekova , B.V. Belyatsky , S.V. Pribavkin , V.А. Bulatov","doi":"10.1016/j.chemer.2025.126246","DOIUrl":"10.1016/j.chemer.2025.126246","url":null,"abstract":"<div><div><span><span>The Ilmeno-Vishnevogorsk (IVC) and Buldym carbonatite complexes of the Southern Urals are deformed linear-type carbonatite complexes that underwent </span>tectonic evolution<span><span><span> as a result of accretion-collision processes and the Hercynian collision orogeny. The deposits of niobium and </span>rare earth elements are associated with the Ural carbonatite complexes. Nb-REE ore mineralization is represented by the pyrochlore supergroup minerals, aeschynite and </span>monazite<span>. Their compositional evolution and connection with various phases of alkaline magmatism, pegmatite and carbonatite formation, and late postmagmatic (carbothermal) processes were studied. To determine the age and duration of the ore-forming stages, U</span></span></span><img>Pb dating of minerals pyrochlore supergroup phases and monazite was carried out. The pyrochlore-group minerals of the Ural carbonatite complexes are represented by calciopyrochlore, rarely natropyrochlore, and kenopyrochlore. Pyrochlore <em>I</em>, rich in U-(Ta), crystallizes in the earliest magmatic phases of the IVC, in the miaskites and carbonatites I of the Central Alkaline Band. In contrast, Ta-(U)-bearing pyrochlore <em>II</em><span> is formed in the later magmatic phases, in the taxitic miaskites and miaskite-pegmatites, and is present in explosive carbonatite breccias and carbonatites II of the Vishnevogorsk massif. Both varieties of pyrochlore have magmatic characteristics – oscillatory zoning, absence of vacancies in the A-site, and low Nb/Ta <80. Pyrochlore </span><em>III</em> and Sr-REE-containing pyrochlore <em>IV</em><span> – with high Nb/Ta >300 and fluorine (4–5 wt%), are formed from fluid-saturated F-containing carbonate systems<span> in carbonatites II of the IVC miaskite intrusions and fenite halos, as well as in carbonatites III and fenites of the Buldym complex. REE minerals – aeschynite-(Ce) and monazite-(Ce) formed in the carbothermalites of the Buldym complex and in fenite halos of miaskite massifs. The morphological features and evolution of the pyrochlore composition indicate the polygenic nature of the ore process, the late low-temperature stage of which is associated not only with Nb but also with REE mineralization (aeschynite, monazite).</span></span></div><div><span>The results of U-Pb-dating of the pyrochlore- and monazite-group minerals make it possible to distinguish two stages of ore formation in the studied carbonatite complexes of the Southern Urals. The early stage is recorded by U-(Ta)-rich pyrochlore in carbonatites I, the Potanino deposit (378 ± 5 Ma), and can be correlated with the primary crystallization of the IVС alkaline rocks and carbonatites at the rifting stage (D</span><sub>3</sub><span>) of the forming continental margins. Whereas, the late stage is dated at ∼255–230 Ma yielded for pyrochlores </span><em>II-IV</em> of the Vishnevogorsk deposit – in taxitic miaskites, syenite- and miaskite-pegmatites, as well a","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126246"},"PeriodicalIF":2.9,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145060249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-22DOI: 10.1016/j.chemer.2025.126326
Ece Kırat , Halim Mutlu
The Keban PbZn deposit is located in the Elazığ district, southeastern Turkey and hosted by the Permo-Triassic/Permo-Carboniferous Keban Metamorphics and the Late Cretaceous-Paleocene Keban Magmatics. Mineralization develops as disseminated, veins and massive types of ore within alkali syenite porphyry, sericite-chlorite banded calc-schist and dolomitic limestone.
Three paragenetic stages of skarn formation and ore deposition are recognized in the Keban PbZn deposit: prograde (stage I), retrograde-sulfide (stage II), and supergene (stage III). The endoskarn forming a narrow zone is composed of grossular (Grt 1), Fe-rich grossular (Grt 2) and andradite (Grt 3) with diopside and plagioclase. The exoskarn comprises grossular (Grt 4), pyroxene and vesuvianite. Ore minerals include galena, sphalerite, chalcopyrite, magnetite, hematite, molybdenite, and pyrite accompanied in small quantities by pyrrhotite, arsenopyrite, manganese oxides, native gold, and sulfosalts. Mineral chemistry of garnets suggests that Grt 1 precipitated under a low water/rock (W/R) ratio and relatively reduced conditions. Grt 2 with strong oscillatory zoning and Grt 3 with high Fe3+ contents were formed under infiltration metasomatism with high W/R ratios. When the water–rock intereaction was decreased, Grt 4 and vesuvianite were affected by Al-bearing residual metasomatic fluids that are derived from calc-schist under reduced conditions.
Depletion of δ13C and δ18O in skarn calcites is largely controlled by hydrothermal fluid infiltration and meteoric water influx. Microthermometric measurements support that magmatic fluids comprising the stage I (473 to 572 °C; 11.9 wt% NaCl eq.) were sequentially mixed with meteoric waters of stage II (230 to 524 °C; 0.8.-6.6 wt% NaCl eq). Based on FI trapping pressures and depths of the boiling system, the mineralization developed after boiling during the retrograde stage in a shallow environment characterized by low to moderate temperatures and low salinities, within the pressure and depth range of ∼100–500 bar and < 1.5 km, respectively. δ34S values of sulfide minerals are between −8.5 and + 2.1 ‰ indicating that ore-forming fluids and metals originated principally from a magmatic-hydrothermal source. High Fe, Mn and Ga contents of sphalerites might point to deposition at low to moderate temperature conditions and trace element concentrations imply that mineralization took place at distal part of the skarn system.
{"title":"Mineralogical, fluid inclusion, and stable isotope constraints on the genesis of Keban PbZn skarn deposit, southeast Anatolia","authors":"Ece Kırat , Halim Mutlu","doi":"10.1016/j.chemer.2025.126326","DOIUrl":"10.1016/j.chemer.2025.126326","url":null,"abstract":"<div><div>The Keban Pb<img>Zn deposit is located in the Elazığ district, southeastern Turkey and hosted by the Permo-Triassic/Permo-Carboniferous Keban Metamorphics and the Late Cretaceous-Paleocene Keban Magmatics. Mineralization develops as disseminated, veins and massive types of ore within alkali syenite porphyry, sericite-chlorite banded calc-schist and dolomitic limestone.</div><div>Three paragenetic stages of skarn formation and ore deposition are recognized in the Keban Pb<img>Zn deposit: prograde (stage I), retrograde-sulfide (stage II), and supergene (stage III). The endoskarn forming a narrow zone is composed of grossular (Grt 1), Fe-rich grossular (Grt 2) and andradite (Grt 3) with diopside and plagioclase. The exoskarn comprises grossular (Grt 4), pyroxene and vesuvianite. Ore minerals include galena, sphalerite, chalcopyrite, magnetite, hematite, molybdenite, and pyrite accompanied in small quantities by pyrrhotite, arsenopyrite, manganese oxides, native gold, and sulfosalts. Mineral chemistry of garnets suggests that Grt 1 precipitated under a low water/rock (W/R) ratio and relatively reduced conditions. Grt 2 with strong oscillatory zoning and Grt 3 with high Fe<sup>3+</sup> contents were formed under infiltration metasomatism with high W/R ratios. When the water–rock intereaction was decreased, Grt 4 and vesuvianite were affected by Al-bearing residual metasomatic fluids that are derived from calc-schist under reduced conditions.</div><div>Depletion of δ<sup>13</sup>C and δ<sup>18</sup>O in skarn calcites is largely controlled by hydrothermal fluid infiltration and meteoric water influx. Microthermometric measurements support that magmatic fluids comprising the stage I (473 to 572 °C; 11.9 wt% NaCl eq.) were sequentially mixed with meteoric waters of stage II (230 to 524 °C; 0.8.-6.6 wt% NaCl eq). Based on FI trapping pressures and depths of the boiling system, the mineralization developed after boiling during the retrograde stage in a shallow environment characterized by low to moderate temperatures and low salinities, within the pressure and depth range of ∼100–500 bar and < 1.5 km, respectively. δ<sup>34</sup>S values of sulfide minerals are between −8.5 and + 2.1 ‰ indicating that ore-forming fluids and metals originated principally from a magmatic-hydrothermal source. High Fe, Mn and Ga contents of sphalerites might point to deposition at low to moderate temperature conditions and trace element concentrations imply that mineralization took place at distal part of the skarn system.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126326"},"PeriodicalIF":2.9,"publicationDate":"2025-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144912510","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-20DOI: 10.1016/j.chemer.2025.126324
Yongshun Li , Yongjun Shao , Zhongfa Liu , Ke Chen , Zhimin Huang , Shixiang You , Yang Shi
<div><div>Tin mineralization is typically associated with polymetallic systems, and the scarcity of economic magnetite–cassiterite deposits highlights the unique hydrothermal and physicochemical constraints governing their formation. The Huanggangliang deposit (135 ± 1 Ma, 180 Mt. Fe @ 38.29 %, and 0.456 Mt. Sn @ 0.29 %) is a granite-related skarn deposit and is the largest Fe<img>Sn polymetallic deposit north of the Yangtze River. Five main mining areas (SK-I–SK-V) are distributed in a SW to NE direction. The contents of cassiterite and metal sulfides gradually increase from SW to NE. However, the controlling factors remain unknown. The granular magnetite in granite (Mt-G) is disseminated, has a uniform texture and is locally oxidized to hematite. The medium- to fine-grained magnetite replaced skarn minerals such as garnets in SK-I (Mt-Ia) and SK-II (Mt-IIa), and the coarse-grained magnetite in SK-I developed more carbonate dissolution holes (Mt-Ib), along which fine-grained cassiterite grew, but all of them were virtually free of metal sulfides. In SK-V, fluorite, arsenopyrite and pyrite surround granular magnetite, and a large amount of quartz replaces granular magnetite (Mt-Vb). Fine-grained cassiterite is present in the magnetite dissolution voids, and some of the magnetite (Mt-Vc) is syngenetic with sphalerite. Large amounts of cassiterite, pyrite, chalcopyrite, arsenopyrite, and sphalerite replace massive (Mt-IIIb) or acicular magnetite (Mt-IIIc) in SK-III, and more alteration minerals (e.g., epidote and chlorite) have developed. The Ti and V contents decrease sequentially from granite to SK-I, SK-II, SK-III and SK-V, whereas the Sn content sequentially increases. The differences in the Al + Mn vs. Ti + V contents of the Huanggangliang magnetite indicate that the formation temperature of magnetite significantly varies between mining areas (higher in granite and lower in SK-V). The high Mg + Al + Si content of magnetite in SK-III and the extensive development of wall–rock alteration suggests that the SK-III mining area may have experienced the strongest fluid–rock interactions, which may be important mechanisms for the precipitation of cassiterite and metal sulfides in the SK-III mining area. The magnetite in the Huanggangliang deposit extensively replaced skarn and was later replaced by polymetallic sulfides. The texture and trace element composition of magnetite in the layered ore body (Ti + V vs. Ca + Al + Mn, Ti + V vs. Ni / (Cr + Mn)) are similar to those of typical skarn-type deposits worldwide, supporting a magmatic–hydrothermal origin. SW–NE zonation is controlled by temperature, <em>f</em>O<sub>2</sub>, and host rock reactivity. Andesite-hosted SK-I retained high <em>f</em>O<sub>2</sub>, inhibiting sulfides, whereas marble-hosted SK-III/V enabled sulfide–cassiterite deposition. Multistage Sn recycling from skarn to hydrothermal cassiterite highlights fluid chemistry and alteration as key drivers of Sn redistribution. We emphasize t
锡矿化通常与多金属体系有关，经济磁铁矿锡石矿床的稀缺性突出了其形成的独特热液和物理化学约束。黄岗梁矿床（135±1 Ma, 180 Mt. Fe @ 38.29%, 0.456 Mt. Sn @ 0.29%）为花岗岩类矽卡岩矿床，是长江以北最大的含铁多金属矿床。5个主要矿区（SK-I-SK-V）沿SW - NE方向分布。锡石和金属硫化物的含量由西南向东北逐渐增加。然而，控制因素尚不清楚。花岗岩（Mt-G）中的粒状磁铁矿呈浸染状，结构均匀，局部氧化为赤铁矿。sk - 1 （Mt-Ia）和SK-II （Mt-IIa）中的中~细粒磁铁矿取代了夕卡岩矿物石榴石等，sk - 1中粗粒磁铁矿发育较多的碳酸盐溶蚀孔（Mt-Ib），细粒锡石沿溶蚀孔生长，但几乎不含金属硫化物。SK-V中，萤石、毒砂和黄铁矿包裹着粒状磁铁矿，大量石英代替粒状磁铁矿（Mt-Vb）。磁铁矿溶蚀孔洞中存在细粒锡石，部分磁铁矿（Mt-Vc）与闪锌矿同生。SK-III中大量锡石、黄铁矿、黄铜矿、毒砂、闪锌矿取代块状（Mt-IIIb）或针状磁铁矿（Mt-IIIc），并发育较多的蚀变矿物（如绿帘石、绿泥石）。从花岗岩到SK-I、SK-II、SK-III和SK-V， Ti和V含量依次降低，而Sn含量依次增加。黄岗梁磁铁矿Al + Mn和Ti + V含量的差异表明，不同矿区磁铁矿的形成温度存在显著差异（花岗岩较高，SK-V较低）。SK-III矿区磁铁矿Mg + Al + Si含量高，围岩蚀变广泛发育，表明SK-III矿区可能经历了最强的流体-岩石相互作用，这可能是SK-III矿区锡石和金属硫化物沉淀的重要机制。黄岗梁矿床的磁铁矿广泛取代矽卡岩，后被多金属硫化物取代。层状矿体中磁铁矿的结构和微量元素组成（Ti + V vs Ca + Al + Mn, Ti + V vs Ni / (Cr + Mn)）与世界范围内典型的矽卡岩型矿床相似，支持岩浆-热液成因。SW-NE分带受温度、fO2和寄主岩石反应性控制。安山岩上的sk - 1保留了高fO2，抑制了硫化物，而大理岩上的SK-III/V则使硫化物-锡石沉积。从矽卡岩到热液锡石的多级锡再循环表明，流体化学和蚀变是锡重分配的关键驱动因素。强调锡异常磁铁矿可作为找矿的重要工具，特别是在蚀变带矿化地区。
{"title":"Metallogenic differences revealed by magnetite texture and trace element geochemistry: A case study of the Huanggangliang FeSn deposit in the southern Great Xing'an Range, NE China","authors":"Yongshun Li , Yongjun Shao , Zhongfa Liu , Ke Chen , Zhimin Huang , Shixiang You , Yang Shi","doi":"10.1016/j.chemer.2025.126324","DOIUrl":"10.1016/j.chemer.2025.126324","url":null,"abstract":"<div><div>Tin mineralization is typically associated with polymetallic systems, and the scarcity of economic magnetite–cassiterite deposits highlights the unique hydrothermal and physicochemical constraints governing their formation. The Huanggangliang deposit (135 ± 1 Ma, 180 Mt. Fe @ 38.29 %, and 0.456 Mt. Sn @ 0.29 %) is a granite-related skarn deposit and is the largest Fe<img>Sn polymetallic deposit north of the Yangtze River. Five main mining areas (SK-I–SK-V) are distributed in a SW to NE direction. The contents of cassiterite and metal sulfides gradually increase from SW to NE. However, the controlling factors remain unknown. The granular magnetite in granite (Mt-G) is disseminated, has a uniform texture and is locally oxidized to hematite. The medium- to fine-grained magnetite replaced skarn minerals such as garnets in SK-I (Mt-Ia) and SK-II (Mt-IIa), and the coarse-grained magnetite in SK-I developed more carbonate dissolution holes (Mt-Ib), along which fine-grained cassiterite grew, but all of them were virtually free of metal sulfides. In SK-V, fluorite, arsenopyrite and pyrite surround granular magnetite, and a large amount of quartz replaces granular magnetite (Mt-Vb). Fine-grained cassiterite is present in the magnetite dissolution voids, and some of the magnetite (Mt-Vc) is syngenetic with sphalerite. Large amounts of cassiterite, pyrite, chalcopyrite, arsenopyrite, and sphalerite replace massive (Mt-IIIb) or acicular magnetite (Mt-IIIc) in SK-III, and more alteration minerals (e.g., epidote and chlorite) have developed. The Ti and V contents decrease sequentially from granite to SK-I, SK-II, SK-III and SK-V, whereas the Sn content sequentially increases. The differences in the Al + Mn vs. Ti + V contents of the Huanggangliang magnetite indicate that the formation temperature of magnetite significantly varies between mining areas (higher in granite and lower in SK-V). The high Mg + Al + Si content of magnetite in SK-III and the extensive development of wall–rock alteration suggests that the SK-III mining area may have experienced the strongest fluid–rock interactions, which may be important mechanisms for the precipitation of cassiterite and metal sulfides in the SK-III mining area. The magnetite in the Huanggangliang deposit extensively replaced skarn and was later replaced by polymetallic sulfides. The texture and trace element composition of magnetite in the layered ore body (Ti + V vs. Ca + Al + Mn, Ti + V vs. Ni / (Cr + Mn)) are similar to those of typical skarn-type deposits worldwide, supporting a magmatic–hydrothermal origin. SW–NE zonation is controlled by temperature, <em>f</em>O<sub>2</sub>, and host rock reactivity. Andesite-hosted SK-I retained high <em>f</em>O<sub>2</sub>, inhibiting sulfides, whereas marble-hosted SK-III/V enabled sulfide–cassiterite deposition. Multistage Sn recycling from skarn to hydrothermal cassiterite highlights fluid chemistry and alteration as key drivers of Sn redistribution. We emphasize t","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126324"},"PeriodicalIF":2.9,"publicationDate":"2025-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144906835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The peritectic assemblage entrainment (PAE) model effectively explains variations in Fe, Mg, Ti, and Ca, as well as positive correlations of Ti and Ca with increased maficity [molar (Fe + Mg)] in mafic I-type granitic melts. This study analyzes the whole-rock elemental geochemistry and zircon U-Pb-Hf isotopes of newly identified Ordovician to Cambrian mafic-enriched I-type granites from the Guwahati region of the Shillong Plateau, northeastern India. The key geochemical features include positive correlations between Ti and maficity, along with V, Ca, and P, while molar A/CNK and maficity demonstrate a negative correlation. These patterns suggest the granites formed from the incongruent melting of hydrous ferromagnesian minerals in the crust, incorporating a peritectic assemblage of plagioclase, FeTi oxides, and clinopyroxene. The UPb zircon ages of 523 ± 4.94–473 ± 3.5 Ma demonstrate the emplacement age of the Guwahati granites. Zircon Hf isotopic analysis indicates a two-stage model age (TDM2) of 2095–2036 Ma with negative εHf(t) values between −10.66 and − 8.47. This suggests a significant contribution from Paleoproterozoic continental crust in the formation of the 473 ± 3.5 Ma Ordovician granitic magma. In comparison, the Cambrian granites, dated around 523 to 502 Ma with weighted mean 206Pb/238U age of 513 ± 36 Ma, exhibit a slightly higher TDM2 of 2098–2092 Ma and show exclusively negative εHf(t) values, ranging from −9.95 to −9.63. These findings indicate a consistent involvement of ancient crustal sources in both granite types. Consequently, it can be concluded that the Ordovician and Cambrian Guwahati granites share notable similarities in their model ages and εHf(t) values, reflecting common geological processes underlying their formation. Overall, the Guwahati granites (523–473 Ma) are linked to Pan-African tectonic activity associated with Ordovician-Cambrian arc magmatism and the tectono-thermal events following the collision of India, Australia, and Antarctica during the assembly of the Eastern Gondwana Landmasses. This process involved the melting of Paleoproterozoic basement crustal rocks.
{"title":"Geochemistry and geochronology of high-K metaluminous (I-type) Cambrian Guwahati granites from Shillong Plateau, Northeast India: Insight into petrogenesis involving peritectic assemblage entrainment (PAE) model","authors":"Dimple Doley , Gautam Sarma , Balen Bhagabaty , Santosh Kumar , Pritom Borah","doi":"10.1016/j.chemer.2025.126325","DOIUrl":"10.1016/j.chemer.2025.126325","url":null,"abstract":"<div><div>The peritectic assemblage entrainment (PAE) model effectively explains variations in Fe, Mg, Ti, and Ca, as well as positive correlations of Ti and Ca with increased maficity [molar (Fe + Mg)] in mafic I-type granitic melts. This study analyzes the whole-rock elemental geochemistry and zircon U-Pb-Hf isotopes of newly identified Ordovician to Cambrian mafic-enriched I-type granites from the Guwahati region of the Shillong Plateau, northeastern India. The key geochemical features include positive correlations between Ti and maficity, along with V, Ca, and P, while molar A/CNK and maficity demonstrate a negative correlation. These patterns suggest the granites formed from the incongruent melting of hydrous ferromagnesian minerals in the crust, incorporating a peritectic assemblage of plagioclase, Fe<img>Ti oxides, and clinopyroxene. The U<img>Pb zircon ages of 523 ± 4.94–473 ± 3.5 Ma demonstrate the emplacement age of the Guwahati granites. Zircon Hf isotopic analysis indicates a two-stage model age (T<sub>DM2</sub>) of 2095–2036 Ma with negative εHf(t) values between −10.66 and − 8.47. This suggests a significant contribution from Paleoproterozoic continental crust in the formation of the 473 ± 3.5 Ma Ordovician granitic magma. In comparison, the Cambrian granites, dated around 523 to 502 Ma with weighted mean <sup>206</sup>Pb/<sup>238</sup>U age of 513 ± 36 Ma, exhibit a slightly higher T<sub>DM2</sub> of 2098–2092 Ma and show exclusively negative εHf(t) values, ranging from −9.95 to −9.63. These findings indicate a consistent involvement of ancient crustal sources in both granite types. Consequently, it can be concluded that the Ordovician and Cambrian Guwahati granites share notable similarities in their model ages and εHf(t) values, reflecting common geological processes underlying their formation. Overall, the Guwahati granites (523–473 Ma) are linked to Pan-African tectonic activity associated with Ordovician-Cambrian arc magmatism and the tectono-thermal events following the collision of India, Australia, and Antarctica during the assembly of the Eastern Gondwana Landmasses. This process involved the melting of Paleoproterozoic basement crustal rocks.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126325"},"PeriodicalIF":2.9,"publicationDate":"2025-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144906834","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-14DOI: 10.1016/j.chemer.2025.126323
Yunfei Zhang , Lei Liu , Heng Liu , Ming Huang , Guofeng Xu , Hongyu Liu , Shuangshuang Wang , Zhilin Wen , Baoliang Huang
The Jiangnan Orogenic Belt (JOB) in the Northeastern Hunan Province (NHP), the one of the most significant regions for rare metal mineral resources in South China Block (SCB). It is renowned for abundant Li-Be-Nb-Ta granitic pegmatite deposits, However, the magmatic process of the Lianyunshan pegmatites remain poorly understood. This study focuses on various lithologies of the Lianyunshan complex pluton and pegmatite through zircon LA-ICP-MS UPb dating, whole-rock major and trace element geochemistry, and in situ trace element analyses of muscovite and apatite. These experiments offer unique insights into the mechanisms driving lithium-enriched pegmatite formation in this region. We elucidated the genesis of pegmatite and the relationship between Li-rich pegmatite and granite in Lianyunshan region. Zircon UPb dating yielded the concordia ages of 147.4 ± 0.69 Ma for biotite monzonitic granite, 145.5 ± 0.73 Ma and 144.0 ± 1.3 Ma for two-mica monzonitic granite, respectively. The whole rock geochemical analyses reveal that granites and pegmatites exhibit obvious characteristic of fractional crystallization. In situ trace element analysis for muscovite reveal Rb, Cs, Ta concentrations increase progressively but the ration of Nb/Ta, Li/Rb, K/Cs, and K/Rb decrease in sequence of BMG → TMG → pegmatite→spodumene pegmatite in Lianyunshan region. These trends indicate varying degrees of fractional crystallization, with pegmatites and spodumene pegmatites representing more evolved magmatic differentiation products. Fractional crystallization simulation using muscovite compositions supports a rayleigh fractionation process, wherein the initial granitic melt progressively evolved to form TMG, pegmatites, and ultimately spodumene pegmatites. Apatite can be divided into magmatic and hydrothermal types, both identified as fluorapatite. The rare earth element (REE) distribution patterns of apatite are consistent with whole-rock trends. However, apatite from spodumene pegmatites and some other pegmatites exhibit anomalous REE patterns. From BMG → TMG → pegmatites to spodumene pegmatites, Sr content (23–617 ppm) in apatite decreases while REE content increases (1001–3159 ppm). Apatite in TMG, and pegmatites share similar trace element characteristics, consistent with the fractionation trends observed in muscovite modeling. Apatite from pegmatites with relative lower SiO₂ content (65–70 wt%) show reduced REE concentrations and significantly elevated Eu/Eu* (0.01–0.7) and La/Yb (0.1–26) ratios. This suggests that pegmatite formation involved plagioclase decomposition and separation crystallization of HREE-enriched minerals.
{"title":"Petrogenesis of granitic pegmatite from the Lianyunshan complex, South China: Insights from apatite and muscovite chemistry","authors":"Yunfei Zhang , Lei Liu , Heng Liu , Ming Huang , Guofeng Xu , Hongyu Liu , Shuangshuang Wang , Zhilin Wen , Baoliang Huang","doi":"10.1016/j.chemer.2025.126323","DOIUrl":"10.1016/j.chemer.2025.126323","url":null,"abstract":"<div><div>The Jiangnan Orogenic Belt (JOB) in the Northeastern Hunan Province (NHP), the one of the most significant regions for rare metal mineral resources in South China Block (SCB). It is renowned for abundant Li-Be-Nb-Ta granitic pegmatite deposits, However, the magmatic process of the Lianyunshan pegmatites remain poorly understood. This study focuses on various lithologies of the Lianyunshan complex pluton and pegmatite through zircon LA-ICP-MS U<img>Pb dating, whole-rock major and trace element geochemistry, and in situ trace element analyses of muscovite and apatite. These experiments offer unique insights into the mechanisms driving lithium-enriched pegmatite formation in this region. We elucidated the genesis of pegmatite and the relationship between Li-rich pegmatite and granite in Lianyunshan region. Zircon U<img>Pb dating yielded the concordia ages of 147.4 ± 0.69 Ma for biotite monzonitic granite, 145.5 ± 0.73 Ma and 144.0 ± 1.3 Ma for two-mica monzonitic granite, respectively. The whole rock geochemical analyses reveal that granites and pegmatites exhibit obvious characteristic of fractional crystallization. In situ trace element analysis for muscovite reveal Rb, Cs, Ta concentrations increase progressively but the ration of Nb/Ta, Li/Rb, K/Cs, and K/Rb decrease in sequence of BMG → TMG → pegmatite→spodumene pegmatite in Lianyunshan region. These trends indicate varying degrees of fractional crystallization, with pegmatites and spodumene pegmatites representing more evolved magmatic differentiation products. Fractional crystallization simulation using muscovite compositions supports a rayleigh fractionation process, wherein the initial granitic melt progressively evolved to form TMG, pegmatites, and ultimately spodumene pegmatites. Apatite can be divided into magmatic and hydrothermal types, both identified as fluorapatite. The rare earth element (REE) distribution patterns of apatite are consistent with whole-rock trends. However, apatite from spodumene pegmatites and some other pegmatites exhibit anomalous REE patterns. From BMG → TMG → pegmatites to spodumene pegmatites, Sr content (23–617 ppm) in apatite decreases while REE content increases (1001–3159 ppm). Apatite in TMG, and pegmatites share similar trace element characteristics, consistent with the fractionation trends observed in muscovite modeling. Apatite from pegmatites with relative lower SiO₂ content (65–70 wt%) show reduced REE concentrations and significantly elevated Eu/Eu* (0.01–0.7) and La/Yb (0.1–26) ratios. This suggests that pegmatite formation involved plagioclase decomposition and separation crystallization of HREE-enriched minerals.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126323"},"PeriodicalIF":2.9,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144890509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-11DOI: 10.1016/j.chemer.2025.126321
Naside Merve Sutcu , Zeynep Doner , Mustafa Kumral , Ali Tugcan Unluer , Emin Ciftci
The Azıtepe meta-gabbroic intrusions, located in Alaşehir, Manisa (western Turkiye), represent part of the Late Neoproterozoic gabbroic bodies that emplaced along the northern margin of Gondwana within the central Menderes Massif, and host Fe-Ti-(V) oxide mineralization. These gabbroic intrusions generally originated from a tholeiitic mantle source, and have minimal evidence of crustal contamination, as indicated by high Nb/U (30–166.7) and Nb/Th (9.37–58.3) ratios, along with low Pb concentrations. However, the mechanisms governing vanadium (V) enrichment in such Fe–Ti–(V) systems, particularly the role of metamorphic overprinting in V redistribution, remain poorly understood. This study aims to determine the processes responsible for V enrichment in Fe–Ti–(V) oxide minerals within the Azıtepe meta-gabbroic intrusion by evaluating V partitioning and mineral hosts in relation to magmatic and metamorphic controls. The ore mineral paragenesis includes Ti-magnetite, magnetite, ilmenite, rutile, hematite, goethite, pyrite, chalcopyrite, and pyrrhotite. In this study, V mineralization is observed in oxide minerals such as magnetite, Ti-magnetite which are influenced by both magmatic crystallization and subsequent metamorphic alteration. The Azıtepe meta-gabbroic rocks generally show enrichments in Fe₂O₃(t) (10.2 to 18.5 wt%) and TiO₂ (2.04 to 6.50 wt%). The V concentrations of the studied rocks range from 355 to 473 ppm in meta-gabbros while varying between 217 and 628 ppm in amphibolites. EPMA (Electron probe microanalysis) data indicate that V is preferentially incorporated into magnetite rather than ilmenite in meta-gabbros and garnet-free amphibolites, likely due to its compatible ionic radius and charge relative to Fe3+, a behavior that supports its preferential partitioning into magnetite under moderate to high fO₂ conditions. The formation conditions of magnetite–ilmenite pairs in meta-gabbro and amphibolite samples from the study area were evaluated using EPMA-derived equilibrium data processed through the MagMin_PT software, and its application was extended to metamorphic samples in this study. The studied samples' log fO2 values (−13.7 to −28.1) may be pointed out moderately to strongly reducing conditions with textural context guiding interpretation. In garnet-bearing amphibolites, however, variations in metamorphic conditions (P, T, fO₂) and/or hydrothermal alteration may have mobilized previously magnetite-hosted V, facilitating its redistribution into silicate minerals such as garnet, chlorite, and clinozoisite. These results suggest that V enrichment in the Azıtepe meta-gabbroic rocks is primarily controlled by magmatic processes under moderately oxidizing conditions, with secondary redistribution during metamorphism, highlighting the potential of such intrusions as significant sources of Fe–Ti–V mineralization in post-collisional tectonic settings.
{"title":"Origin and evolution of vanadium (V) enrichment in Azıtepe (Alaşehir-Manisa) meta-gabbroic rocks in Menderes massif (Western Turkiye)","authors":"Naside Merve Sutcu , Zeynep Doner , Mustafa Kumral , Ali Tugcan Unluer , Emin Ciftci","doi":"10.1016/j.chemer.2025.126321","DOIUrl":"10.1016/j.chemer.2025.126321","url":null,"abstract":"<div><div>The Azıtepe meta-gabbroic intrusions, located in Alaşehir, Manisa (western Turkiye), represent part of the Late Neoproterozoic gabbroic bodies that emplaced along the northern margin of Gondwana within the central Menderes Massif, and host Fe-Ti-(V) oxide mineralization. These gabbroic intrusions generally originated from a tholeiitic mantle source, and have minimal evidence of crustal contamination, as indicated by high Nb/U (30–166.7) and Nb/Th (9.37–58.3) ratios, along with low Pb concentrations. However, the mechanisms governing vanadium (V) enrichment in such Fe–Ti–(V) systems, particularly the role of metamorphic overprinting in V redistribution, remain poorly understood. This study aims to determine the processes responsible for V enrichment in Fe–Ti–(V) oxide minerals within the Azıtepe meta-gabbroic intrusion by evaluating V partitioning and mineral hosts in relation to magmatic and metamorphic controls. The ore mineral paragenesis includes Ti-magnetite, magnetite, ilmenite, rutile, hematite, goethite, pyrite, chalcopyrite, and pyrrhotite. In this study, V mineralization is observed in oxide minerals such as magnetite, Ti-magnetite which are influenced by both magmatic crystallization and subsequent metamorphic alteration. The Azıtepe meta-gabbroic rocks generally show enrichments in Fe₂O₃<sub>(t)</sub> (10.2 to 18.5 wt%) and TiO₂ (2.04 to 6.50 wt%). The V concentrations of the studied rocks range from 355 to 473 ppm in meta-gabbros while varying between 217 and 628 ppm in amphibolites. EPMA (Electron probe microanalysis) data indicate that V is preferentially incorporated into magnetite rather than ilmenite in meta-gabbros and garnet-free amphibolites, likely due to its compatible ionic radius and charge relative to Fe<sup>3+</sup>, a behavior that supports its preferential partitioning into magnetite under moderate to high fO₂ conditions. The formation conditions of magnetite–ilmenite pairs in meta-gabbro and amphibolite samples from the study area were evaluated using EPMA-derived equilibrium data processed through the MagMin_PT software, and its application was extended to metamorphic samples in this study. The studied samples' log <em>f</em>O2 values (−13.7 to −28.1) may be pointed out moderately to strongly reducing conditions with textural context guiding interpretation. In garnet-bearing amphibolites, however, variations in metamorphic conditions (P, T, <em>f</em>O₂) and/or hydrothermal alteration may have mobilized previously magnetite-hosted V, facilitating its redistribution into silicate minerals such as garnet, chlorite, and clinozoisite. These results suggest that V enrichment in the Azıtepe meta-gabbroic rocks is primarily controlled by magmatic processes under moderately oxidizing conditions, with secondary redistribution during metamorphism, highlighting the potential of such intrusions as significant sources of Fe–Ti–V mineralization in post-collisional tectonic settings.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126321"},"PeriodicalIF":2.9,"publicationDate":"2025-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144827512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-08-09DOI: 10.1016/j.chemer.2025.126322
Awaleh Djama Iltireh , Yusuf Kağan Kadıoğlu , Yavuz Özdemir , Mohamed Osman Awaleh , Jalludin Mohamed
This research investigates the Marginal basalts in the Asal-Ghoubbet rift, a poorly understood geological feature, with the aim of clarifying magma sources and identifying the mantle reservoir responsible for forming basaltic rocks in the region. The study involved analysing major geochemical elements, rare earth elements and radiogenic isotopes of Sr, Nd and Pb from basalt samples collected in the Marginal basalts of the rift. Additionally, the mineral composition of plagioclase, olivine, pyroxene and FeTi oxides was examined using electron probe microanalysis (EPMA) on polished thin sections. Geochemical results indicate a tholeiitic composition for the Marginal basalts, with evidence of fractional crystallization driven initially by clinopyroxene and olivine, followed by plagioclase crystallization. Thermobarometric and MELTS modelling estimated magma storage depths ranging from the Moho to the upper crust. The basalt is slightly enriched in light rare earth elements (LREEs) and depleted in Heavy Rare Earth Elements (HREEs), similar to the characteristics of enriched Mid-Ocean Ridge Basalt (E-MORB) and Ocean Island Basalt (OIB). Isotopic data of Sr and Nd reveal sources that vary between the high μ mantle source (HIMU) and the dominant prevalent mantle source (PREMA). Furthermore, Pb isotopic signatures suggest an influence from an enriched mantle (EM) component, plotting between the EMI and EMII mantle reservoirs fields. Forward-melting modelling and isotopic evidence suggest that the Afar mantle plume is a significant contributor to the magma source of Marginal basalts in the Asal-Ghoubbet rift. Overall, the study enhances understanding of the magma plumbing system in this area, elucidating the process governing magma chamber evolution and the nature of the mantle reservoirs that generated these basaltic rocks.
{"title":"Petrogenesis of rift related marginal basalts from the Asal-Ghoubbet rift area, Republic of Djibouti: Implications for magma genesis and mantle source characteristics","authors":"Awaleh Djama Iltireh , Yusuf Kağan Kadıoğlu , Yavuz Özdemir , Mohamed Osman Awaleh , Jalludin Mohamed","doi":"10.1016/j.chemer.2025.126322","DOIUrl":"10.1016/j.chemer.2025.126322","url":null,"abstract":"<div><div>This research investigates the Marginal basalts in the Asal-Ghoubbet rift, a poorly understood geological feature, with the aim of clarifying magma sources and identifying the mantle reservoir responsible for forming basaltic rocks in the region. The study involved analysing major geochemical elements, rare earth elements and radiogenic isotopes of Sr, Nd and Pb from basalt samples collected in the Marginal basalts of the rift. Additionally, the mineral composition of plagioclase, olivine, pyroxene and Fe<img>Ti oxides was examined using electron probe microanalysis (EPMA) on polished thin sections. Geochemical results indicate a tholeiitic composition for the Marginal basalts, with evidence of fractional crystallization driven initially by clinopyroxene and olivine, followed by plagioclase crystallization. Thermobarometric and MELTS modelling estimated magma storage depths ranging from the Moho to the upper crust. The basalt is slightly enriched in light rare earth elements (LREEs) and depleted in Heavy Rare Earth Elements (HREEs), similar to the characteristics of enriched Mid-Ocean Ridge Basalt (<em>E</em>-MORB) and Ocean Island Basalt (OIB). Isotopic data of Sr and Nd reveal sources that vary between the high μ mantle source (HIMU) and the dominant prevalent mantle source (PREMA). Furthermore, Pb isotopic signatures suggest an influence from an enriched mantle (EM) component, plotting between the EMI and EMII mantle reservoirs fields. Forward-melting modelling and isotopic evidence suggest that the Afar mantle plume is a significant contributor to the magma source of Marginal basalts in the Asal-Ghoubbet rift. Overall, the study enhances understanding of the magma plumbing system in this area, elucidating the process governing magma chamber evolution and the nature of the mantle reservoirs that generated these basaltic rocks.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126322"},"PeriodicalIF":2.9,"publicationDate":"2025-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144841921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-31DOI: 10.1016/j.chemer.2025.126319
Marina A. Ivanova , Maria G. Krzhizhanovskaya , Sergey N. Britvin
The first CY chondrite from the Northwest Africa region was studied (NWA 4757). It is a small (5 g) fine-grained monomict microbreccia consisting of abundant matrix (∼95 vol%) and rare pseudomorphic chondrules (up to 200 μm). The meteorite has main characteristics of CY chondrites. The oxygen isotopic composition of NWA 4757 is 16O-poor (δ18O = 23.83, δ17O = 12.84, Δ17O = 0.45 to δ18O = 26.96, δ17O = 14.50, Δ17O = 0.48 ± 0.03) which is the heaviest among other CY chondrites. NWA 4757 contains abundant sulfides (∼20 vol%) and its bulk chemical composition is enriched in sulfur compared to CM chondrites like most other CY chondrites except for Dhofar 225 and Dhofar 735.
NWA 4747 was affected by very intensive aqueous alteration corresponding to petrologic type 1.0 before it was affected by thermal metamorphism. Only a few grains of unaltered olivine (Fa10) survived in NWA 4757. In contrast to other CYs, troilite from NWA 4757 are Mn-rich. The matrix is divided into light and dark types in texture and composition. The light matrix is Ca-rich, and Fe-poor compared to the dark matrix. The dehydrated phyllosilicates had serpentine composition with a low saponite content like CY2s. The presence of high-Ni metal and sulfides, chromite and ilmenite and absence of magnetite indicate that under equilibrium conditions, the redox state of the alteration system in the NWA 4757 parent body did not exceed the fugacity of the iron-wustite buffer.
After aqueous alteration NWA 4757 experienced intensive thermal metamorphism resulting in a low H2O (1.9 wt%) compared to usual CI and CM chondrites. The Fourier Transform Infrared (FT-IR) spectroscopy of the matrices of NWA 4757 and Mighei (CM2) showed that the NWA 4757 matrix is dominated by Fe-rich fine-grained olivine. According to a classification system for thermally metamorphosed hydrated carbonaceous chondrites based on X-ray Powder Diffraction (XRD) data, NWA 4757 is characterized by heating stage IV (>750 °C) like CY2s. Since calcite (and even dolomite) survived metamorphism, it should indicate that the peak temperature was not higher than 800 °C. Thus, NWA 4757 is the first CY chondrite of thermal stage IV (CY2) which had properties of extremely altered CM1 chondrite before metamorphism and suggestively should be CY2-m1.
{"title":"Metamorphism and aqueous alteration of the unusual CY carbonaceous chondrite Northwest Africa 4757","authors":"Marina A. Ivanova , Maria G. Krzhizhanovskaya , Sergey N. Britvin","doi":"10.1016/j.chemer.2025.126319","DOIUrl":"10.1016/j.chemer.2025.126319","url":null,"abstract":"<div><div>The first CY chondrite from the Northwest Africa region was studied (NWA 4757). It is a small (5 g) fine-grained monomict microbreccia consisting of abundant matrix (∼95 vol%) and rare pseudomorphic chondrules (up to 200 μm). The meteorite has main characteristics of CY chondrites. The oxygen isotopic composition of NWA 4757 is <sup>16</sup>O-poor (δ<sup>18</sup>O = 23.83, δ<sup>17</sup>O = 12.84, Δ<sup>17</sup>O = 0.45 to δ<sup>18</sup>O = 26.96, δ<sup>17</sup>O = 14.50, Δ<sup>17</sup>O = 0.48 ± 0.03) which is the heaviest among other CY chondrites. NWA 4757 contains abundant sulfides (∼20 vol%) and its bulk chemical composition is enriched in sulfur compared to CM chondrites like most other CY chondrites except for Dhofar 225 and Dhofar 735.</div><div>NWA 4747 was affected by very intensive aqueous alteration corresponding to petrologic type 1.0 before it was affected by thermal metamorphism. Only a few grains of unaltered olivine (Fa10) survived in NWA 4757. In contrast to other CYs, troilite from NWA 4757 are Mn-rich. The matrix is divided into light and dark types in texture and composition. The light matrix is Ca-rich, and Fe-poor compared to the dark matrix. The dehydrated phyllosilicates had serpentine composition with a low saponite content like CY2s. The presence of high-Ni metal and sulfides, chromite and ilmenite and absence of magnetite indicate that under equilibrium conditions, the redox state of the alteration system in the NWA 4757 parent body did not exceed the fugacity of the iron-wustite buffer.</div><div>After aqueous alteration NWA 4757 experienced intensive thermal metamorphism resulting in a low H<sub>2</sub>O (1.9 wt%) compared to usual CI and CM chondrites. The Fourier Transform Infrared (FT-IR) spectroscopy of the matrices of NWA 4757 and Mighei (CM2) showed that the NWA 4757 matrix is dominated by Fe-rich fine-grained olivine. According to a classification system for thermally metamorphosed hydrated carbonaceous chondrites based on X-ray Powder Diffraction (XRD) data, NWA 4757 is characterized by heating stage IV (>750 °C) like CY2s. Since calcite (and even dolomite) survived metamorphism, it should indicate that the peak temperature was not higher than 800 °C. Thus, NWA 4757 is the first CY chondrite of thermal stage IV (CY2) which had properties of extremely altered CM1 chondrite before metamorphism and suggestively should be CY2-m1.</div></div>","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126319"},"PeriodicalIF":2.9,"publicationDate":"2025-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144767027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-16DOI: 10.1016/j.chemer.2025.126318
M. Trieloff , E.V. Korochantseva , A.I. Buikin , J. Hopp , A.V. Korochantsev
<div><div>We performed high-resolution <sup>40</sup>Ar/<sup>39</sup>Ar dating of a suite of lunar meteorites from hot deserts: Dhofar 025, 309, 730, 733, 1442, Northwest Africa 6888, and Sayh al Uhaymir 449. The identification of terrestrial and lunar trapped argon components via isochrons allowed us to identify in situ radiogenic argon and to obtain proper chronological information. The last total reset ages of all studied samples are in the range of 3.1 to 4.2 Ga, coeval with the intense cratering period on the Moon and mare volcanism. Only Northwest Africa 6888 was totally reset <2.5 Ga ago. The most deeply buried breccia Dhofar 733 has the oldest age of 4.23 ± 0.04 Ga within this series of meteorites. Dhofar 733, 1442, and NWA 6888 were furthermore affected by recent impact events ≤1 Ga. All meteorites were irradiated by galactic cosmic rays on the surface of the Moon for several up to hundreds of Ma. A simple irradiation history is revealed for only one meteorite Dhofar 733 delivered to Earth within ~0.5 Ma. The comparison of exposure ages, solar argon abundances and partial loss of cosmogenic and radiogenic argon of lunar breccias indicates that long surface residence enhances accumulation of solar wind implanted <sup>36</sup>Ar but also diffusive gas loss, most likely by surface thermal effects as solar and/or impact heating.</div><div>The surficial regolith breccias Dhofar 025, 1442, NWA 6888, SaU 449 contain lunar trapped argon with <sup>40</sup>Ar/<sup>36</sup>Ar ratios varying from 6 to 15, while the deep-derived breccia Dhofar 730 contains argon with (<sup>40</sup>Ar/<sup>36</sup>Ar)<sub>trapped</sub> ratio of 81. This could indicate that the composition of trapped argon in lunar meteorites may depend on rock layering depth. We suggest that the final capture of gases happens during sintering and agglutination along grain boundaries caused by thermal processes accompanying shock-induced compaction. Dhofar 1442 contains two distinct lunar trapped argon components with (<sup>40</sup>Ar/<sup>36</sup>Ar)<sub>trapped</sub> ratios of 14.58 ± 0.28 and 5.5 ± 0.7 indicating that lunar meteorites may contain more than one extraterrestrial trapped component incorporated during different thermal events.</div><div>Our new <sup>40</sup>Ar/<sup>39</sup>Ar ages of lunar meteorites significantly increase the number of high- resolution plateau age spectra, providing more compelling evidence of geochronologically meaningful pre 3.9 Ga ages. The different age distribution when compared to Apollo samples that were frequently dominated by Imbrium ejecta may be related to the fact that lunar meteorites provide a more random and thus complete sampling of the lunar surface, encompassing ejecta of older large basins, thereby favoring scenarios of more continuous or episodic pre 3.9 Ga bombardments. A possible scenario leading to episodic small body disturbances and bombardments involves close stellar encounters within the massive stellar cluster in which the
{"title":"Thermal and irradiation history of lunar meteorites by the 40Ar/39Ar technique: Dhofar 025, 309, 730, 733, 1442, Northwest Africa 6888, and Sayh al Uhaymir 449","authors":"M. Trieloff , E.V. Korochantseva , A.I. Buikin , J. Hopp , A.V. Korochantsev","doi":"10.1016/j.chemer.2025.126318","DOIUrl":"10.1016/j.chemer.2025.126318","url":null,"abstract":"<div><div>We performed high-resolution <sup>40</sup>Ar/<sup>39</sup>Ar dating of a suite of lunar meteorites from hot deserts: Dhofar 025, 309, 730, 733, 1442, Northwest Africa 6888, and Sayh al Uhaymir 449. The identification of terrestrial and lunar trapped argon components via isochrons allowed us to identify in situ radiogenic argon and to obtain proper chronological information. The last total reset ages of all studied samples are in the range of 3.1 to 4.2 Ga, coeval with the intense cratering period on the Moon and mare volcanism. Only Northwest Africa 6888 was totally reset <2.5 Ga ago. The most deeply buried breccia Dhofar 733 has the oldest age of 4.23 ± 0.04 Ga within this series of meteorites. Dhofar 733, 1442, and NWA 6888 were furthermore affected by recent impact events ≤1 Ga. All meteorites were irradiated by galactic cosmic rays on the surface of the Moon for several up to hundreds of Ma. A simple irradiation history is revealed for only one meteorite Dhofar 733 delivered to Earth within ~0.5 Ma. The comparison of exposure ages, solar argon abundances and partial loss of cosmogenic and radiogenic argon of lunar breccias indicates that long surface residence enhances accumulation of solar wind implanted <sup>36</sup>Ar but also diffusive gas loss, most likely by surface thermal effects as solar and/or impact heating.</div><div>The surficial regolith breccias Dhofar 025, 1442, NWA 6888, SaU 449 contain lunar trapped argon with <sup>40</sup>Ar/<sup>36</sup>Ar ratios varying from 6 to 15, while the deep-derived breccia Dhofar 730 contains argon with (<sup>40</sup>Ar/<sup>36</sup>Ar)<sub>trapped</sub> ratio of 81. This could indicate that the composition of trapped argon in lunar meteorites may depend on rock layering depth. We suggest that the final capture of gases happens during sintering and agglutination along grain boundaries caused by thermal processes accompanying shock-induced compaction. Dhofar 1442 contains two distinct lunar trapped argon components with (<sup>40</sup>Ar/<sup>36</sup>Ar)<sub>trapped</sub> ratios of 14.58 ± 0.28 and 5.5 ± 0.7 indicating that lunar meteorites may contain more than one extraterrestrial trapped component incorporated during different thermal events.</div><div>Our new <sup>40</sup>Ar/<sup>39</sup>Ar ages of lunar meteorites significantly increase the number of high- resolution plateau age spectra, providing more compelling evidence of geochronologically meaningful pre 3.9 Ga ages. The different age distribution when compared to Apollo samples that were frequently dominated by Imbrium ejecta may be related to the fact that lunar meteorites provide a more random and thus complete sampling of the lunar surface, encompassing ejecta of older large basins, thereby favoring scenarios of more continuous or episodic pre 3.9 Ga bombardments. A possible scenario leading to episodic small body disturbances and bombardments involves close stellar encounters within the massive stellar cluster in which the","PeriodicalId":55973,"journal":{"name":"Chemie Der Erde-Geochemistry","volume":"85 3","pages":"Article 126318"},"PeriodicalIF":2.6,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144685852","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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