The fate of carbon subducted to mantle depths remains uncertain, yet strongly influences the distribution of terrestrial carbon on geologic timescales. Carbon fluxes into subduction zones are exceptionally high where downgoing plates contain thick sedimentary fans. This study uses volcano geochemistry to assess sedimentary carbon recycling in the high-flux Makran subduction zone, where the Arabian plate subducts northward beneath Eurasia. On the basis of strontium isotope geochemistry and ⁴⁰Ar–³⁹Ar geochronology, I show that a portion of the submarine Indus Fan entered the Makran Trench, melted and ascended as magmas that erupted in southern Afghanistan. The resulting volcano, composed primarily of carbonate minerals, formed at approximately 3.8 million years ago. The ⁸⁷Sr/⁸⁶Sr ratios of the lavas indicate that their magmatic precursors were derived from marine sediments deposited at 28.9 ± 1.4 Ma. This implies that sedimentary carbon was subducted to and returned from mantle depths in less than 27 million years, indicating that magmas can efficiently recycle sedimentary carbon from subducting slabs to the overlying plate.

俯冲到地幔深处的碳的命运仍然不确定，但强烈影响着陆地碳在地质时间尺度上的分布。进入俯冲带的碳通量异常高，其中下沉板块包含厚厚的沉积扇。这项研究使用火山地球化学来评估高通量马克兰俯冲带的沉积碳循环，阿拉伯板块在欧亚大陆下方向北俯冲。根据锶同位素地球化学和⁴⁰ Ar- ³⁹ Ar 年代学，我表明印度河扇海底的一部分进入了马克兰海沟，融化并上升为阿富汗南部喷发的岩浆。由此产生的火山主要由碳酸盐矿物组成，形成于大约 380 万年前。⁸⁷ _熔岩的Sr/ ⁸⁶ Sr 比率表明它们的岩浆前体来源于沉积在 28.9 ± 1.4 Ma 的海洋沉积物。这意味着沉积碳在不到 2700 万年的时间内俯冲到地幔深处并从地幔深处返回，表明岩浆可以有效地将沉积碳从俯冲板片循环到上覆板块。