Noble gases preserve history of retentive continental crust in the Bravo Dome natural CO2 field, New Mexico
Noble gases preserve history of retentive continental crust in the Bravo Dome natural CO2 field, New Mexico
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DOI：
10.1016/j.epsl.2016.03.014
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发表时间：
2016-06
影响因子：
5.3
通讯作者：
K. Sathaye;A. Smye;J. Jordan;M. Hesse
中科院分区：
文献类型：
--
作者：
K. Sathaye;A. Smye;J. Jordan;M. Hesse
4He和40Ar的预算限制了固体地球和大气的化学演化。虽然从地球上脱气的4He和40Ar大部分来自大陆地壳，但脱气机制仍是学术界争论的焦点。在这里，我们通过比较美国新墨西哥州布拉沃穹顶天然二氧化碳储藏库中积累的稀有气体与下伏地壳中的放射性产物来限制地壳脱气。详细的储层地质模型被用来提供4He、40Ar、21Ne、20Ne、36Ar和84Kr的绝对丰度和地质统计不确定度。现今地壳4He和40Ar的产生率，以下简称4He⁎和40Ar⁎，是利用地壳的基底成分、地表和地幔热流以及地壳密度的地震估算得出的。在减去地幔和大气贡献后，储集层中的放射性产物不到下伏地壳中的0.02%。这明确地表明，在数千年的时间尺度上，放射性成因的惰性气体有效地保留在克拉通大陆地壳中。这也需要大约1.5GT的地幔产生的二氧化碳通过地壳迁移，而不动员地壳积累的气体。这一观察结果表明，沿着局部的裂缝网络运输。因此，惰性气体在稳定的结晶陆壳中的滞留使得浅层放射性成因气体的聚集可以记录构造历史。在布拉沃穹隆，地壳4He⁎/40Ar⁎比值是预期地壳生产比值的五分之一，记录了上古落基山造山过程中4He的优先释放，即300 Ma。
Budgets of4He and40Ar provide constraints on the chemical evolution of the solid Earth and atmosphere. Although continental crust accounts for the majority of4He and40Ar degassed from the Earth, degassing mechanisms are subject to scholarly debate. Here we provide a constraint on crustal degassing by comparing the noble gases accumulated in the Bravo Dome natural CO2reservoir, New Mexico USA, with the radiogenic production in the underlying crust. A detailed geological model of the reservoir is used to provide absolute abundances and geostatistical uncertainty of4He,40Ar,21Ne,20Ne,36Ar, and84Kr. The present-day production rate of crustal radiogenic4He and40Ar, henceforth referred to as4He⁎and40Ar⁎, is estimated using the basement composition, surface and mantle heat flow, and seismic estimates of crustal density. After subtracting mantle and atmospheric contributions, the reservoir contains less than 0.02% of the radiogenic production in the underlying crust. This shows unequivocally that radiogenic noble gases are effectively retained in cratonic continental crust over millennial timescales. This also requires that approximately 1.5 Gt of mantle derived CO2migrated through the crust without mobilizing the crustally accumulated gases. This observation suggests transport along a localized fracture network. Therefore, the retention of noble gases in stable crystalline continental crust allows shallow accumulations of radiogenic gases to record tectonic history. At Bravo Dome, the crustal4He⁎/40Ar⁎ratio is one fifth of the expected crustal production ratio, recording the preferential release of4He during the Ancestral Rocky Mountain orogeny, 300 Ma.