Fahui Xiong , Basem Zoheir , Joseph Meert , Xiangzhen Xu , Tian Qiu , Xuxuan Ma , Ibrahim Milushi , Jingsui Yang
{"title":"阿尔巴尼亚Bulqiza蛇绿岩中铬铁矿形成过程中的多阶段熔体-岩石相互作用和氧化还原演化:Mӧssbauer光谱、FeMg同位素和铬铁矿地球化学的约束","authors":"Fahui Xiong , Basem Zoheir , Joseph Meert , Xiangzhen Xu , Tian Qiu , Xuxuan Ma , Ibrahim Milushi , Jingsui Yang","doi":"10.1016/j.chemgeo.2025.122948","DOIUrl":null,"url":null,"abstract":"<div><div>Fe<img>Mg isotopes integrated with Fe<sup>3+</sup>/∑Fe data provide robust constraints on the redox state of the oceanic lithospheric mantle, as both are sensitive to oxygen fugacity and mineral–melt equilibria. Fe isotopes track valence changes, while Mg isotopes reflect melt–rock interaction during partial melting and metasomatism. Applied to ophiolites, these proxies offer detailed insights into mantle melting, melt transport, and redox evolution. The Bulqiza ophiolite massif in Albania, a major chromite-bearing ultramafic complex in the Balkans, presents an ideal natural laboratory to investigate mantle processes during the evolution of the Mesozoic Tethys Ocean. This study integrates mineral chemistry, LA-ICP-MS trace element data, Mössbauer spectroscopy, and Fe and Mg isotope analyses to reconstruct mantle compositional changes and the genesis of ultramafic assemblages.</div><div>Harzburgites and dunites from Bulqiza show high forsterite (Fo<sub>91–97</sub>) and Ni contents indicative of subsolidus equilibration between olivine and magnesiochromite. Two partial melting stages are identified: an initial ∼25 % melting forming harzburgite, followed by ∼30 % melting producing dunite and chromitite. Variations in spinel Cr# [100Cr/(Cr + Al + Fe<sup>3+</sup>)] and oxygen fugacity suggest that dunite-chromitite formation resulted from focused melt–rock interaction. Chromitites are enriched in Cr<sub>2</sub>O<sub>3</sub> (53–61 wt%) and display variable FeO (12–21 wt%), reflecting mantle source heterogeneity and dynamic melt extraction. Isotopic trends, including a negative correlation between δ<sup>26</sup>Mg and Cr# and a positive δ<sup>56</sup>Fe-δ<sup>26</sup>Mg relationship, indicate progressive melt–rock interaction and oxidation. Mössbauer spectroscopy reveals Fe<sup>3+</sup>/∑Fe ratios of 0.075–0.253 in magnesiochromite, documenting variable redox conditions during formation. Together, these data support a multistage genesis involving high-degree melting, melt percolation, and redox evolution within an upwelling asthenospheric mantle, consistent with localized mantle flow beneath a slow-spreading ridge or transform margin rather than a subduction-related setting.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122948"},"PeriodicalIF":3.6000,"publicationDate":"2025-06-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Multistage melt–rock interaction and redox evolution during chromitite formation in the Bulqiza ophiolite (Albania): Constraints from Mӧssbauer spectroscopy, FeMg isotopes and chromitite geochemistry\",\"authors\":\"Fahui Xiong , Basem Zoheir , Joseph Meert , Xiangzhen Xu , Tian Qiu , Xuxuan Ma , Ibrahim Milushi , Jingsui Yang\",\"doi\":\"10.1016/j.chemgeo.2025.122948\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><div>Fe<img>Mg isotopes integrated with Fe<sup>3+</sup>/∑Fe data provide robust constraints on the redox state of the oceanic lithospheric mantle, as both are sensitive to oxygen fugacity and mineral–melt equilibria. Fe isotopes track valence changes, while Mg isotopes reflect melt–rock interaction during partial melting and metasomatism. Applied to ophiolites, these proxies offer detailed insights into mantle melting, melt transport, and redox evolution. The Bulqiza ophiolite massif in Albania, a major chromite-bearing ultramafic complex in the Balkans, presents an ideal natural laboratory to investigate mantle processes during the evolution of the Mesozoic Tethys Ocean. This study integrates mineral chemistry, LA-ICP-MS trace element data, Mössbauer spectroscopy, and Fe and Mg isotope analyses to reconstruct mantle compositional changes and the genesis of ultramafic assemblages.</div><div>Harzburgites and dunites from Bulqiza show high forsterite (Fo<sub>91–97</sub>) and Ni contents indicative of subsolidus equilibration between olivine and magnesiochromite. Two partial melting stages are identified: an initial ∼25 % melting forming harzburgite, followed by ∼30 % melting producing dunite and chromitite. Variations in spinel Cr# [100Cr/(Cr + Al + Fe<sup>3+</sup>)] and oxygen fugacity suggest that dunite-chromitite formation resulted from focused melt–rock interaction. Chromitites are enriched in Cr<sub>2</sub>O<sub>3</sub> (53–61 wt%) and display variable FeO (12–21 wt%), reflecting mantle source heterogeneity and dynamic melt extraction. Isotopic trends, including a negative correlation between δ<sup>26</sup>Mg and Cr# and a positive δ<sup>56</sup>Fe-δ<sup>26</sup>Mg relationship, indicate progressive melt–rock interaction and oxidation. Mössbauer spectroscopy reveals Fe<sup>3+</sup>/∑Fe ratios of 0.075–0.253 in magnesiochromite, documenting variable redox conditions during formation. Together, these data support a multistage genesis involving high-degree melting, melt percolation, and redox evolution within an upwelling asthenospheric mantle, consistent with localized mantle flow beneath a slow-spreading ridge or transform margin rather than a subduction-related setting.</div></div>\",\"PeriodicalId\":9847,\"journal\":{\"name\":\"Chemical Geology\",\"volume\":\"692 \",\"pages\":\"Article 122948\"},\"PeriodicalIF\":3.6000,\"publicationDate\":\"2025-06-28\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Chemical Geology\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0009254125003389\",\"RegionNum\":2,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Chemical Geology","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0009254125003389","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Multistage melt–rock interaction and redox evolution during chromitite formation in the Bulqiza ophiolite (Albania): Constraints from Mӧssbauer spectroscopy, FeMg isotopes and chromitite geochemistry
FeMg isotopes integrated with Fe3+/∑Fe data provide robust constraints on the redox state of the oceanic lithospheric mantle, as both are sensitive to oxygen fugacity and mineral–melt equilibria. Fe isotopes track valence changes, while Mg isotopes reflect melt–rock interaction during partial melting and metasomatism. Applied to ophiolites, these proxies offer detailed insights into mantle melting, melt transport, and redox evolution. The Bulqiza ophiolite massif in Albania, a major chromite-bearing ultramafic complex in the Balkans, presents an ideal natural laboratory to investigate mantle processes during the evolution of the Mesozoic Tethys Ocean. This study integrates mineral chemistry, LA-ICP-MS trace element data, Mössbauer spectroscopy, and Fe and Mg isotope analyses to reconstruct mantle compositional changes and the genesis of ultramafic assemblages.
Harzburgites and dunites from Bulqiza show high forsterite (Fo91–97) and Ni contents indicative of subsolidus equilibration between olivine and magnesiochromite. Two partial melting stages are identified: an initial ∼25 % melting forming harzburgite, followed by ∼30 % melting producing dunite and chromitite. Variations in spinel Cr# [100Cr/(Cr + Al + Fe3+)] and oxygen fugacity suggest that dunite-chromitite formation resulted from focused melt–rock interaction. Chromitites are enriched in Cr2O3 (53–61 wt%) and display variable FeO (12–21 wt%), reflecting mantle source heterogeneity and dynamic melt extraction. Isotopic trends, including a negative correlation between δ26Mg and Cr# and a positive δ56Fe-δ26Mg relationship, indicate progressive melt–rock interaction and oxidation. Mössbauer spectroscopy reveals Fe3+/∑Fe ratios of 0.075–0.253 in magnesiochromite, documenting variable redox conditions during formation. Together, these data support a multistage genesis involving high-degree melting, melt percolation, and redox evolution within an upwelling asthenospheric mantle, consistent with localized mantle flow beneath a slow-spreading ridge or transform margin rather than a subduction-related setting.
期刊介绍:
Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry.
The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry.
Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry.
The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.