Collaborative Research: Quantifying CO2 Fluxes Along the Himalayan Arc

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该团队最近的工作表明，喜马拉雅山脉前缘主中央冲断层带附近主要河谷的地热泉是二氧化碳的重要来源。到目前为止，我们已经表明，这种来源的二氧化碳超过消耗的二氧化碳化学风化在大纳拉亚尼盆地的尼泊尔中部。研究人员提出，这种大的CO2通量的来源是变质脱碳酸盐和脱羧反应，发生在喜马拉雅山脉前缘下的俯冲小喜马拉雅沉积物中。至少在喜马拉雅山的这一地区，碳酸盐-硅酸盐循环的CO2净通量是非常积极的，与人们普遍认为的喜马拉雅山是一个重要的CO2 sink.Investigators建议解决两个问题：1）他们将从地热站点采样流体，气体和沉淀物，并使用DIC，CO2（g）和CaCO 3（CaCO 3）的组合#948; 13 C数据来改善对近地表脱气程度的限制。他们认为，他们目前的估计太低，因为我们以前无法限制这一过程中低#948; 13 CDIC弹簧。他们的假设是，低#948; 13 CDIC地热系统的脱气程度与他们在高#948; 13 CDIC温泉中估计的相似，即大约90%，同位素组成的差异是由不同的深层CO2来源造成的。结合多相#948; 13 C数据将使他们能够定量测试这一假设。2)他们只有来自喜马拉雅山200公里长的部分的数据，目前还不清楚他们来自尼泊尔中部的数据对更大区域的代表性如何。他们假设，地热通量的热量和CO2随折返率而变化。他们将通过对印度西北部Sutlej山谷的地热通量进行类似的估计来测试这一假设，那里的热计时数据表明，尼泊尔中部的挖掘率约为一半。或者，他们可能会发现没有特殊的关系，这将表明CO2通量更多地取决于俯冲的总体速率或在适当的P-T窗口中经历变质作用的沉积物岩性的局部变化。无论结果如何，来自印度西北部的数据将使他们能够解决喜马拉雅地热系统中CO2通量沿走向不均匀的问题，并大大提高对整体碳平衡的估计。科学价值：该项目解决了全球碳循环中的一个主要问题：主要造山事件和硅酸盐-碳酸盐循环之间的关系是什么。喜马拉雅变质通量抵消或超过CO2风化消耗的想法是新颖的和潜在的变革，直接挑战了地球科学中广泛持有的范式。更广泛的影响：这是一个主要研究型大学（康奈尔大学）和本科院校（惠顿学院）之间的合作提案。他们将涉及本科生和研究生广泛的领域和实验室工作。该项目将为这两个机构及其在法国CRPG的国际合作者提供出色的教育和培训机会。他们还将与一个结合美国和尼泊尔学生的学习计划密切互动。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Recent work by this team shows that geothermal springs in major river valleys near the Main Central Thrust zone of the Himalayan front are significant sources of carbon dioxide. To date we have shown that this source of CO2 exceeds the consumption of CO2 by chemical weathering in the large Narayani basin of central Nepal. Investigators have proposed that the source of this large CO2 flux is metamorphic decarbonation and decarboxylation reactions which take place in the subducted Lesser Himalyan sediments beneath the Himalayan front. In at least this region of the Himalaya, the net flux of CO2 from the carbonate-silicate cycle is strongly positive, in contrast to the widely held view that the Himalaya are an important CO2 sink.Investigators propose to address two issues: 1) they will sample fluids, gasses and precipitates from geothermal sites and use the combined δ 13C data from DIC, CO2(g), and travertine (CaCO3) to improve constraints on the extent of near-surface degassing. They believe that their current estimates are too low because of our previous inability to constrain this process in low δ13CDIC springs. Their hypothesis is that the extent of degassing in the low δ13CDIC geothermal systems is similar to what they have estimated in the high δ13CDIC springs, i.e. roughly 90%, and that the difference in isotopic composition is caused by different deep sources of CO2. Combined multi-phase δ13C data will allow them to quantitatively test this hypothesis. 2) They only have data from a 200 km-long section of the Himalaya, and it is unclear how representative their data from central Nepal are for the larger region. They hypothesize that geothermal fluxes of heat and CO2 vary with exhumation rate. They will test this hypothesis by developing a similar estimate of geothermal flux in the Sutlej valley of NW India, where thermochronometric data suggests exhumation rates about one half of those in central Nepal. Alternatively they may find that there is no particular relation, and that would suggest CO2 fluxes are more dependent on the overall rate of subduction or local variations in the lithology of sediments undergoing metamorphism in the appropriate P-T window. Regardless of the outcome, data from NW India will allow them to address the issue of along-strike heterogeneity of the CO2 flux in Himalayan geothermal systems and greatly improve estimates of the overall carbon balance.Scientific merit: the project addresses a major issue in the global carbon cycle: what is the relationship between major orogenic events and the silicate-carbonate cycle. The idea that Himalayan metamorphic fluxes offset or exceed weathering consumption of CO2 is novel and potentially transformative, as directly challenges a widely held paradigm in Earth Sciences.Broader impacts: this is a collaborative proposal between a major research university (Cornell) and an undergraduate institution (Wheaton College). They will involve undergraduate and graduate students extensively in the field and laboratory work. The project will provide outstanding opportunities for education and training between the two institutions and their international collaborators at the CRPG, France. They will also interact closely with a study program that combines US and Nepali students.