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The contribution to exogenic CO2 by contact metamorphism at continental arcs: A coupled model of fluid flux and metamorphic decarbonation
American Journal of Science ( IF 2.9 ) Pub Date : 2019-10-01 , DOI: 10.2475/08.2019.01
Xu Chu , Cin-Ty A. Lee , Rajdeep Dasgupta , Wenrong Cao

Recent work has suggested a possible temporal coincidence between greenhouse intervals and enhanced arc volcanism, motivating the hypothesis that magmatic and metamorphic CO2 emissions from volcanic arcs, particularly those intersecting crustal carbonates, may play a strong role in modulating the long-term carbon budget of the exogenic system. When hot fluid exsolving from arc magmas interacts with carbonate sequences on active margins, contact metamorphism releases CO2 to metasomatic fluids that transport carbon to shallow reservoirs. To estimate the magnitude of CO2 release, here we model how the infiltration of silica-saturated magmatic water into a porous medium facilitates the decarbonation reaction in contact aureoles. Analytical scalings and numerical simulations show that the propagation rate of the reaction front scales with the ratio of the infiltration flux to the mass of the rate-limiting reactant, and accordingly the CO2 flux increases linearly with the infiltration flux. This simple relationship allows for scaling to predict regional and global scale CO2 release at continental arcs if magma emplacement rate is known. Using the global rate of continental arc magma emplacement, we estimate that the present-day contact-metamorphic CO2 release range from ∼0.06 to 0.9 Tmol/yr, half-to-one orders of magnitude smaller than the field-based estimates of carbon output in modern arcs (1.5–3.5 Tmol/yr). Yet, the extrapolated CO2 release from Cretaceous continental arcs via simple infiltration-induced decarbonation is comparable to the release from mid-ocean ridges. CO2 released from continental arcs amplifies the background flux of CO2 from direct degassing of the magma, and therefore may have been key in causing the climatic greenhouse interval in the Cretaceous when there was heightened arc activity. Thus, our result supports the hypothesis that global arc flare-ups at continental margins effectively increase CO2 outgassing coinciding with green-house intervals in the geological past. The contribution by arcs to the tectonic CO2 input could be significant, which needs field-based studies to revise long-term climate models.

中文翻译:

大陆弧接触变质作用对外生二氧化碳的贡献:流体通量和变质脱碳的耦合模型

最近的工作表明,温室间隔和增强的弧火山活动之间可能存在时间重合,从而激发了以下假设:火山弧的岩浆和变质二氧化碳排放,特别是那些与地壳碳酸盐相交的二氧化碳,可能在调节火山弧的长期碳收支方面发挥重要作用。外生系统。当从弧形岩浆中溶出的热流体与活动边缘的碳酸盐层序相互作用时,接触变质作用将 CO2 释放到交代流体中,从而将碳输送到浅层储层。为了估计 CO2 释放的幅度,我们在这里模拟了二氧化硅饱和岩浆水渗透到多孔介质中如何促进接触光环中的脱碳反应。分析标度和数值模拟表明,反应前沿的传播速率与渗透通量与限速反应物质量的比例成比例,因此 CO2 通量随渗透通量线性增加。如果岩浆侵位率已知,这种简单的关系允许进行缩放以预测大陆弧的区域和全球尺度的 CO2 释放。使用全球大陆弧岩浆侵位率,我们估计当今接触变质 CO2 释放范围为 ~0.06 至 0.9 Tmol/yr,比基于现场的碳输出估计值小半到一个数量级在现代弧中(1.5-3.5 Tmol/yr)。然而,通过简单的渗透引起的脱碳作用从白垩纪大陆弧外推的 CO2 释放与大洋中脊的释放相当。大陆弧释放的 CO2 放大了岩浆直接脱气产生的 CO2 背景通量,因此可能是导致白垩纪大陆弧活动加剧时气候温室间隔的关键。因此,我们的结果支持了这样的假设,即大陆边缘的全球弧耀斑有效地增加了与过去地质时期温室间隔一致的 CO2 除气。弧对构造 CO2 输入的贡献可能很大,这需要基于实地的研究来修订长期气候模型。我们的结果支持了这样一个假设,即大陆边缘的全球电弧爆发有效地增加了与地质过去温室间隔相吻合的 CO2 释气。弧对构造 CO2 输入的贡献可能很大,这需要基于实地的研究来修订长期气候模型。我们的结果支持了这样一个假设,即大陆边缘的全球电弧爆发有效地增加了与地质过去温室间隔相吻合的 CO2 释气。弧对构造 CO2 输入的贡献可能很大,这需要基于实地的研究来修订长期气候模型。
更新日期:2019-10-01
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