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<p>Crustal-derived carbonatites are increasingly recognized, yet their evolutionary history remains inadequately constrained. This study integrates U–Pb geochronology of multiple minerals with element compositions and C–O isotope analyses to elucidate the temporal evolution of the Balangoda carbonatites, a recently confirmed crustal-derived body in the Highland Complex, Sri Lanka. The carbonatites, intruding high-grade metamorphic gneisses, dominate in calcite with variable amounts of phlogopite, apatite, dolomite, clinopyroxene, olivine, and spinel, and occur as coarse-grained and pegmatitic types. Calcite from both types exhibits similar δ<sup>13</sup>C values (–1.83‰ to 0.41‰) and a broader δ<sup>18</sup>O range (17.22‰ to 22.86‰) compared to Sri Lankan marbles, indicating a metamorphic carbonate protolith. In pegmatitic carbonatites, systematic decreases in δ<sup>18</sup>O and mineral inclusion abundance from blue and white to yellow calcite indicate evolving fluid conditions during protracted magma evolution. Concordia U–Pb ages of zircon (522.8 ± 9.6&#xa0;Ma) and calcite (524 ± 29&#xa0;Ma) in sample 23C-BC, along with a weighted mean <sup>207</sup>Pb/<sup>206</sup>Pb titanite age (548 ± 12&#xa0;Ma), constrain the timing of crystallization. Whereas, the younger apatite age (487.4 ± 8.5&#xa0;Ma) from the same sample records a protracted cooling history. Additional calcite ages (~ 525&#xa0;Ma) and consistent apatite ages (521.9 ± 8.4&#xa0;Ma; 515.8 ± 9.8&#xa0;Ma) corroborate this extended magmatic evolution. These multi-mineral ages are consistent with the regional high-grade metamorphism (660–500&#xa0;Ma) followed by protracted cooling to ~ 480&#xa0;Ma in the Highland Complex. This supports a model of carbonatite magma genesis through anatexis of dolomitic marbles under prolonged high-temperature metamorphism, with antiskarn processes removing dolomitic components. The Balangoda carbonatites, in conjunction with global occurrences, exemplify that long-lived generation and evolution are typical of crustal-derived carbonatites, linked closely to regional metamorphic events.</p>

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Protracted evolution of crustal-derived carbonatites in high-grade metamorphic terranes

  • 期刊论文

  • 发表日期：

    2026年3月11日

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  • Shi-Ying Wang,
  • P. L. Dharmapriya,
  • Tian-Yi Li,
  • Jing Wang,
  • Sanjeewa P. K. Malaviarachchi,
  • Ben-Xun Su

摘要

Crustal-derived carbonatites are increasingly recognized, yet their evolutionary history remains inadequately constrained. This study integrates U–Pb geochronology of multiple minerals with element compositions and C–O isotope analyses to elucidate the temporal evolution of the Balangoda carbonatites, a recently confirmed crustal-derived body in the Highland Complex, Sri Lanka. The carbonatites, intruding high-grade metamorphic gneisses, dominate in calcite with variable amounts of phlogopite, apatite, dolomite, clinopyroxene, olivine, and spinel, and occur as coarse-grained and pegmatitic types. Calcite from both types exhibits similar δ13C values (–1.83‰ to 0.41‰) and a broader δ18O range (17.22‰ to 22.86‰) compared to Sri Lankan marbles, indicating a metamorphic carbonate protolith. In pegmatitic carbonatites, systematic decreases in δ18O and mineral inclusion abundance from blue and white to yellow calcite indicate evolving fluid conditions during protracted magma evolution. Concordia U–Pb ages of zircon (522.8 ± 9.6 Ma) and calcite (524 ± 29 Ma) in sample 23C-BC, along with a weighted mean 207Pb/206Pb titanite age (548 ± 12 Ma), constrain the timing of crystallization. Whereas, the younger apatite age (487.4 ± 8.5 Ma) from the same sample records a protracted cooling history. Additional calcite ages (~ 525 Ma) and consistent apatite ages (521.9 ± 8.4 Ma; 515.8 ± 9.8 Ma) corroborate this extended magmatic evolution. These multi-mineral ages are consistent with the regional high-grade metamorphism (660–500 Ma) followed by protracted cooling to ~ 480 Ma in the Highland Complex. This supports a model of carbonatite magma genesis through anatexis of dolomitic marbles under prolonged high-temperature metamorphism, with antiskarn processes removing dolomitic components. The Balangoda carbonatites, in conjunction with global occurrences, exemplify that long-lived generation and evolution are typical of crustal-derived carbonatites, linked closely to regional metamorphic events.