Collaborative Research: Quantifying CO2 Fluxes Along the Himalayan Arc

合作研究：量化喜马拉雅弧沿线的二氧化碳通量

• 批准号: 0850913
• 负责人: Matthew Evans
• 金额: $ 10.99万
• 依托单位: Wheaton College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-01 至 2012-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0850913&HistoricalAwards=false
• 关键词: Collaborative; Research; Quantifying; CO2; Fluxes

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.

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，喜马拉雅前缘主要中央冲断带附近主要河流山谷的地热泉水是二氧化碳的重要来源。到目前为止，我们已经表明，在尼泊尔中部的大纳拉亚尼盆地，这种二氧化碳的来源超过了化学风化对二氧化碳的消耗。研究人员提出，这种大的二氧化碳通量的来源是在喜马拉雅前缘下方俯冲的小喜马拉雅沉积中发生的变质脱碳和脱羧化反应。至少在喜马拉雅的这一地区，碳酸盐-硅酸盐循环产生的二氧化碳净通量是非常正的，这与普遍认为喜马拉雅是一个重要的二氧化碳汇的观点相反。研究人员建议解决两个问题：1)他们将从地热地点采集流体、气体和沉淀物的样本，并使用DIC、CO2(G)和钙华(CaCO3)的联合13C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了，因为我们之前无法将这一过程限制在低弹簧。他们的假设是，低地热系统中的脱气程度与他们在高温泉中估计的相似，即大约90%，而且同位素组成的差异是由不同的深层二氧化碳来源造成的。组合的多相13C数据将使他们能够定量检验这一假设。2)他们只有200公里长的喜马拉雅地区的数据，不清楚他们来自尼泊尔中部的数据对更大的地区有多大的代表性。他们假设热能和二氧化碳的地热通量随掘尸速度而变化。他们将通过对印度西北部萨特勒山谷的地热流量进行类似的估计来检验这一假设，那里的温度计时数据表明，挖掘遗骸的速度大约是尼泊尔中部的一半。或者，他们可能会发现两者之间没有特殊的关系，这表明二氧化碳通量更多地依赖于在适当的P-T窗口中经历变质作用的沉积物的整体俯冲速率或岩性的局部变化。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二氧化碳通量沿走向的不均一性问题，并极大地改善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：主要造山事件与硅酸盐-碳酸盐循环之间的关系。喜马拉雅变质通量抵消或超过二氧化碳风化消耗的想法是新颖的，也是潜在的变革性的，因为它直接挑战了地球科学中一个广泛接受的范式。广泛的影响：这是一个主要研究型大学(康奈尔大学)和一个本科生机构(惠顿学院)的合作提案。他们将让本科生和研究生广泛参与实地和实验室工作。该项目将为这两个机构及其在法国CRPG的国际合作伙伴之间的教育和培训提供绝佳的机会。他们还将与一个由美国和尼泊尔学生组成的学习项目密切互动。