美国耶鲁大学Toma, Jonathan团队最新的研究发现，努那超大陆组合与19-17亿年前剪切带的碳循环有关。2024年8月20日出版的《自然—地球科学》发表了这项成果。
据了解，大约在21-18亿年前，有机碳埋藏的高峰导致了努那超大陆内部富含石墨的造山带的大量生长。然而，人们对这些造山带石墨碳的时间历史知之甚少，这限制了研究人员对造山带碳循环时间尺度的理解。
该团队人员使用铼-锇和铀-铅测年法，研究了与努那超大陆组合相关的两个北美造山带的石墨根源。它们分别是大约19.4-18.9亿年前的Taltson–Snowbird造山运动和大约18.4-17.2亿年前的Trans-Hudson造山运动。地质年代学结果表明，所研究的石墨赋存于剪切带，主要反映了约19.2- 16.7亿年前造山运动最后折返阶段热液再活化的生物碳作用。
结果表明，石墨沉积的周期为31±4个百万年，可能涉及超过2亿年间隔的5000万吨或更大规模的碳循环。与其他同时期剪切带的比较表明，后期造山作用、流体介导的石墨沉积在劳伦森和更广泛的努纳山脉带中很常见。这些发现揭示了石墨碳的大量运动是造山旋回的特有特征。
附：英文原文
Title: Nuna supercontinent assembly linked to carbon cycling in shear zones 1.9–1.7 billion years ago
Author: Toma, Jonathan, Creaser, Robert A., Card, Colin, Pana, Dinu, Dufrane, Andrew, Li, Long
Issue&Volume: 2024-08-20
Abstract: 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 approximately1.92–1.67billion 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.
DOI: 10.1038/s41561-024-01519-w
Source: https://www.nature.com/articles/s41561-024-01519-w