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<p>Calcite veins are crucial recorders of tectonic-fluid interactions, preserving information on fracture timing and fluid evolution. This study investigates calcite veins within Carboniferous volcanic rocks near Well Pen-1 in the Junggar Basin to decipher the coupling between regional tectonic events, fluid dynamics, and diagenesis. Through comprehensive geochemical and geochronological analyses, including in-situ U-Pb dating, isotopic compositions, and fluid inclusion studies, we identify two distinct stages of calcite precipitation driven by different tectonic regimes. Stage I veins, dated to the Late Permian (257 ± 3.6&#xa0;Ma), formed contemporaneously with Late Hercynian extensional tectonics. This tectonic setting activated a volcanic-hydrothermal system. The veins’ geochemical signatures—a LREE-enriched pattern with positive Ce and Eu anomalies, high δ¹³C values (− 2.87‰ to 0.39‰), and low ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7075)—confirm their precipitation from mantle-derived fluids under relatively reducing conditions. This stage documents the direct control of extensional volcanism on the initial fluid activity in the basin. Stage II veins, dated to 137 ± 5.7&#xa0;Ma (Early Cretaceous), formed under an entirely different tectonic control: the Yanshanian transpressional regime. This intense tectonic activity reactivated fault systems, creating conduits that connected deep crustal fluids with maturing hydrocarbon source rocks. The resulting fluid mixing is recorded in the veins’ distinct geochemistry: a right-inclined REE pattern with a positive Eu but negative Ce anomaly, significantly lower δ¹³C (− 7.08‰ to − 2.14‰) and δ¹⁸O (− 12.96‰ to − 8.54‰) values, and higher ⁸⁷Sr/⁸⁶Sr ratios (0.7045 to 0.7064). These characteristics reflect the incorporation of organic matter and basinal brines, indicating precipitation from hydrocarbon-related fluid systems. In conclusion, the two vein stages provide a direct record of the basin’s tectono-fluid evolution. Stage I captures the signature of Late Hercynian volcanic-hydrothermal activity, while Stage II documents a complex fluid system during the Yanshanian orogeny, where tectonic reactivation facilitated the mixing of deep fluids with migrating hydrocarbons. This study demonstrates that calcite veins serve as an excellent archive for reconstructing how distinct tectonic events govern fluid composition, diagenetic processes, and ultimately, reservoir formation in volcanic basins.</p>

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Genetic mechanism and geological significance of calcite veins in volcanic rocks: a case study from the Carboniferous Batamayineishan Formation, Junggar Basin

  • 期刊论文

  • 发表日期：

    2026年6月22日

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  • Hanqing Liu,
  • Chunmei Dong,
  • Chengyan Lin,
  • Huoqing Gao,
  • Guoqiang Luan,
  • Lihua Ren

摘要

Calcite veins are crucial recorders of tectonic-fluid interactions, preserving information on fracture timing and fluid evolution. This study investigates calcite veins within Carboniferous volcanic rocks near Well Pen-1 in the Junggar Basin to decipher the coupling between regional tectonic events, fluid dynamics, and diagenesis. Through comprehensive geochemical and geochronological analyses, including in-situ U-Pb dating, isotopic compositions, and fluid inclusion studies, we identify two distinct stages of calcite precipitation driven by different tectonic regimes. Stage I veins, dated to the Late Permian (257 ± 3.6 Ma), formed contemporaneously with Late Hercynian extensional tectonics. This tectonic setting activated a volcanic-hydrothermal system. The veins’ geochemical signatures—a LREE-enriched pattern with positive Ce and Eu anomalies, high δ¹³C values (− 2.87‰ to 0.39‰), and low ⁸⁷Sr/⁸⁶Sr ratios (0.7033 to 0.7075)—confirm their precipitation from mantle-derived fluids under relatively reducing conditions. This stage documents the direct control of extensional volcanism on the initial fluid activity in the basin. Stage II veins, dated to 137 ± 5.7 Ma (Early Cretaceous), formed under an entirely different tectonic control: the Yanshanian transpressional regime. This intense tectonic activity reactivated fault systems, creating conduits that connected deep crustal fluids with maturing hydrocarbon source rocks. The resulting fluid mixing is recorded in the veins’ distinct geochemistry: a right-inclined REE pattern with a positive Eu but negative Ce anomaly, significantly lower δ¹³C (− 7.08‰ to − 2.14‰) and δ¹⁸O (− 12.96‰ to − 8.54‰) values, and higher ⁸⁷Sr/⁸⁶Sr ratios (0.7045 to 0.7064). These characteristics reflect the incorporation of organic matter and basinal brines, indicating precipitation from hydrocarbon-related fluid systems. In conclusion, the two vein stages provide a direct record of the basin’s tectono-fluid evolution. Stage I captures the signature of Late Hercynian volcanic-hydrothermal activity, while Stage II documents a complex fluid system during the Yanshanian orogeny, where tectonic reactivation facilitated the mixing of deep fluids with migrating hydrocarbons. This study demonstrates that calcite veins serve as an excellent archive for reconstructing how distinct tectonic events govern fluid composition, diagenetic processes, and ultimately, reservoir formation in volcanic basins.