A peak in organic carbon burial approximately 2.1–1.8 billion years ago led to the prolific growth of graphite-rich orogens internal to the supercontinent Nuna. The temporal history of graphitic carbon in such orogens, however, is poorly understood, which limits our understanding of the timescales of carbon cycling during orogenesis. Here we examine the graphitic roots of two North American (Laurentian) orogens associated with Nuna supercontinent assembly using coupled rhenium–osmium and uranium–lead dating. These are the Taltson–Snowbird orogeny, approximately 1.94–1.89 billion years ago, and the Trans-Hudson orogeny, approximately 1.84–1.72 billion years ago. The geochronology results show that the studied graphite, hosted in shear zones, predominantly reflects biogenic carbon that was hydrothermally remobilized during the final exhumation stages of orogenesis approximately 1.92–1.67 billion years ago. Our results demonstrate that graphite deposition occurred with a periodicity of 31 ± 4 million years and probably involved carbon cycling on the scale of 50 million tonnes or more over a 200 million year interval. Comparisons with other contemporaneous shear zones suggests that late-orogenic, fluid-mediated graphite deposition was common among Laurentian, and more broadly Nuna, mountain belts. These findings imply that the mass movement of graphitic carbon is an endemic feature of the orogenic cycle.

大约 2.1-18 亿年前，有机碳埋藏达到高峰，导致努纳超大陆内部富含石墨的造山带大量生长。然而，人们对此类造山带中石墨碳的时间历史知之甚少，这限制了我们对造山作用期间碳循环时间尺度的理解。在这里，我们使用铼-锇和铀-铅耦合测年法研究了与努纳超大陆组装相关的两个北美（劳伦）造山带的石墨根源。它们是大约 1.94-18.9 亿年前的塔尔森-雪鸟造山运动，以及大约 1.84-17.2 亿年前的跨哈德逊造山运动。地质年代学结果表明，所研究的石墨存在于剪切带中，主要反映了大约 1.92-16.7 亿年前造山运动最后折返阶段热液再活化的生物碳。我们的结果表明，石墨沉积发生的周期为 31 ± 4 百万年，并且可能涉及 2 亿年间隔内 5000 万吨或更多规模的碳循环。与其他同期剪切带的比较表明，造山晚期、流体介导的石墨沉积在劳伦山脉和更广泛的努纳山脉中很常见。这些发现意味着石墨碳的大规模运动是造山旋回的普遍特征。