Displaced cratonic mantle concentrates deep carbon during continental rifting
Displaced cratonic mantle concentrates deep carbon during continental rifting
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DOI：
10.1038/s41586-020-2328-3
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发表时间：
2020-06
期刊：
影响因子：
64.8
通讯作者：
J. Muirhead;T. Fischer;S. Oliva;A. Laizer;J. V. van Wijk;C. Currie;Hyunwoo Lee;E. Judd;E. Kazimoto;Y. Sano;N. Takahata;C. Tiberi;S. Foley;J. Dufek;M. Reiss;C. Ebinger
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作者：
J. Muirhead;T. Fischer;S. Oliva;A. Laizer;J. V. van Wijk;C. Currie;Hyunwoo Lee;E. Judd;E. Kazimoto;Y. Sano;N. Takahata;C. Tiberi;S. Foley;J. Dufek;M. Reiss;C. Ebinger
大陆裂谷是地幔二氧化碳（CO2）排放到地球大气中的重要来源。由于深部碳长期储存在岩石圈地幔中，裂谷CO2通量取决于控制熔融和挥发物输送的岩石圈过程。太古代和元古代岩石圈的成分和厚度差异对深部碳通量的影响尚未得到证实。在这里，我们提出，富含碳的坦桑尼亚地幔位移集中在东非裂谷系部分地区以下的深层碳。CO2和氦的来源和通量的检查超过350- 1000米长的样带之间的边界造山（纳特龙和马加迪盆地）和造山带（Balangida和马尼亚拉盆地）岩石圈从北到南。扩散CO2脱气区表现出地幔CO2通量和3 He/4 He比值随着裂谷从太古代（超高压）向元古代（造山）岩石圈的转变而增加。活跃的碳酸岩岩浆作用也发生在克拉通边缘附近。这些数据表明，厚的白垩纪岩石圈的根部横向平流到薄得多的邻近元古代岩石圈的底部，产生了一个高度集中的深部碳带。这种深层碳提取模式可能会增加某些大陆裂谷中的CO2通量，有助于控制富含碳酸盐岩浆的生产和位置。
Continental rifts are important sources of mantle carbon dioxide (CO2) emission into Earth’s atmosphere, –. Because deep carbon is stored for long periods in the lithospheric mantle, –, rift CO2flux depends on lithospheric processes that control melt and volatile transport,,. The influence of compositional and thickness differences between Archaean and Proterozoic lithosphere on deep-carbon fluxes remains untested. Here we propose that displacement of carbon-enriched Tanzanian cratonic mantle concentrates deep carbon below parts of the East African Rift System. Sources and fluxes of CO2and helium are examined over a 350-kilometre-long transect crossing the boundary between orogenic (Natron and Magadi basins) and cratonic (Balangida and Manyara basins) lithosphere from north to south. Areas of diffuse CO2degassing exhibit increasing mantle CO2flux and3He/4He ratios as the rift transitions from Archaean (cratonic) to Proterozoic (orogenic) lithosphere. Active carbonatite magmatism also occurs near the craton edge. These data indicate that advection of the root of thick Archaean lithosphere laterally to the base of the much thinner adjacent Proterozoic lithosphere creates a zone of highly concentrated deep carbon. This mode of deep-carbon extraction may increase CO2fluxes in some continental rifts, helping to control the production and location of carbonate-rich magmas.