中国科学院广州地球化学研究所唐功建团队研究了印度-亚洲板块碰撞期间的碳循环，提供了来自西藏西北部超钾质火山所揭示的δ²⁶Mg-δ⁶⁶Zn-δ⁹⁸Mo证据。这一研究成果于2024年6月18日发表在国际顶尖学术期刊《地质学》上。

研究人员采用Mg-Zn-Mo同位素组成对西藏西北部新生代超钾质火山岩进行了研究。结果显示，Mg-Zn同位素负相关(δ²⁶Mg= -0.39‰至-0.19‰；δ⁶⁶Zn= +0.27‰至+0.36‰)，研究结合岩石圈幔源捕掳体的岩石学分析表明，超钾质岩浆来源于富含方解石和白云石的，含碳酸盐沉积物再循环富集的岩石圈地幔源区。

相对于大陆地壳的平均值(δ⁹⁸Mo=+0.10‰至+0.35‰)而言，非常低的δ⁹⁸Mo值(- 0.78‰~ 0‰)进一步表明，沉积成分来源于印度大陆地壳脱水后的俯冲。Monte Carlo模型估计，这些沉积物进入岩石圈地幔的碳(元素C)输入通量为约5.6Mt/yr，预测的CO₂排放率为约15.5Mt/yr。

研究人员认为，印度构造板块的持续俯冲作用在将大量富含碳酸盐的沉积物，引入西藏岩石圈地幔中发挥了至关重要的作用，导致大量CO₂通过碳酸盐交代作用被封存。因此，造山背景下这种富碳地幔储层的部分熔融提供了正反馈机制，可以解释印亚碰撞期间火山CO₂的高通量。研究结果强调，这些发现不仅突出了大陆俯冲、沉积物再循环和富碳熔体/流体的地幔交代作用，在西藏超古生代火山活动形成中的重要性，还揭示了深部碳循环对火山CO₂脱气的影响。

据悉，印度-亚洲大陆碰撞诱导火山气体排放，被认为在驱动新生代大气CO₂变化中发挥了重要作用，但深层碳循环如何影响火山CO₂脱气的细节尚不清楚。

附：英文原文

Title: Carbon cycling during the India-Asia collision revealed by δ²⁶Mg-δ⁶⁶Zn-δ⁹⁸Mo evidence from ultrapotassic volcanoes in NW Tibet

Author: Jian Wang, Sebastian Tappe, Qiang Wang, Jie Li, Zongqi Zou, Gong-Jian Tang

Issue&Volume: 2024-06-18

Abstract: India-Asia continental collisioninduced volcanic gas emissions are thought to have played an important role in driving Cenozoic atmospheric CO₂ variations, yet the details of how the deep carbon cycle may influence volcanic CO₂ degassing are not understood. We present a novel study employing Mg-Zn-Mo isotopic compositions of Cenozoic ultrapotassic lavas from NW Tibet. The negative Mg-Zn isotope correlation (δ²⁶Mg = 0.39‰ to 0.19‰; δ⁶⁶Zn = +0.27‰ to +0.36‰), bolstered by petrographic analysis of mantle-derived xenoliths from these lavas, demonstrates that the ultrapotassic magmas originated from a lithospheric mantle source that had been enriched by recycled carbonate-bearing sediments rich in calcite and dolomite. Very low δ⁹⁸Mo values (0.78‰ to 0‰) relative to the average continental crust (δ⁹⁸Mo = +0.10‰ to +0.35‰) further indicate that the sedimentary components were derived from the subducted Indian continental crust after its dehydration. Monte Carlo modeling estimates that the input flux of carbon (elemental C) from such sediments into the lithospheric mantle is ～5.6 Mt/yr, with a predicted CO₂ emission rate of ～15.5 Mt/yr. We suggest that the still ongoing subduction of the Indian tectonic plate has played a crucial role in introducing substantial quantities of carbonate-rich sediments into the Tibetan lithospheric mantle, leading to the sequestration of large amounts of CO₂ via carbonatite metasomatism. Hence, partial melting of such a carbon-rich mantle reservoir in an orogenic setting provides the positive feedback mechanism that can explain the high flux of volcanic CO₂ during India-Asia collision. These findings not only highlight the importance of continental subduction, sediment recycling, and mantle metasomatism by carbon-rich melts/fluids in the generation of Tibetan ultrapotassic volcanism, but they also show how the deep carbon cycle influences volcanic CO₂ degassing.

DOI: 10.1130/G52267.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G52267.1/645042/Carbon-cycling-during-the-India-Asia-collisionredirectedFrom=fulltext