Collaborative Research: Characterizing and quantifying carbon sequestration processes across the Andean Convergent Margin

俯冲带是地球内部(地壳和地幔)和外部(大气和海洋)之间的界面，在那里碳和其他挥发性元素通过板块构造在陆地储集层之间活跃地移动。挥发分转移的效率控制着地球内部和外部的化学状态，包括大气成分。反过来，碳和其他挥发物在地球表面水库中的分布为地球上的生命创造了有利的条件。尽管碳很重要，但它的通量、来源和汇在俯冲相关的流体中仍然受到限制，几乎完全没有研究将其与地下生物过程联系起来。以前通过将俯冲板块的输入与弧形火山的脱气输出进行比较来估计深层碳质量平衡，两者的差异代表了输送到地球深部地幔的碳量。然而，板岩和地幔来源的碳也可以以热液矿物(如方解石、文石)的形式被封存，并通过盖层板块地壳中的微生物吸收，有效地掩盖了俯冲带输出的未知部分碳。然而，缺乏对这些关键过程的限制，限制了人们对深层碳循环整体效率的理解。该项目涉及与智利同事的实质性合作，包括一次国际研讨会，并将支持几名美国学生的工作。该项目将描述地质研究充分的安第斯汇聚边缘(ACM)沿线的矿物学和生物碳固定程度。PI假设方解石沉淀在ACM中隔离了大量的碳，特别是在中央火山带(CVZ)地壳最厚的地方。此外，该项目将测试地下微生物群落是否通过化学合成将碳隔离到生物质中，形成额外的碳汇。最后，PIS将系统地评估地球化学转化和微生物群落如何随俯冲参数(即来自板块的碳输入、上板块厚度和岩性以及板块倾角)而变化，然后可用于将结果与一系列全球收敛边缘进行比较。为了实现这些目标，PI将于2022年对CVZ进行一次实地考察，从弧前和弧内的约15个天然泉水、渗漏和烟孔中收集流体和气体样本。他们将测量所有样品中的氦和碳同位素、微生物化学合成速率以及化学合成对总微生物生物量的贡献。CVZ的结果将与ACM和全球其他趋同利润率(即中美洲)的已发布和未发布的数据集一起进行解释。如果在ACM中发现大量的地下化学和生物碳汇，这将进一步证明碳封存在汇聚边缘的上覆地壳中广泛存在。这样的发现可能会从根本上改变人们对地球表面和地幔之间深层碳循环的经典理解。该项目涉及与智利同事的实质性合作，包括一个国际研讨会，几名美国学生的工作将得到支持。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Subduction zones are the interface between Earth’s interior (crust and mantle) and exterior (atmosphere and oceans), where carbon and other volatile elements are actively moved between terrestrial reservoirs by plate tectonics. The efficiency of volatile transfer controls the chemical state of Earth’s interior and exterior, including the atmospheric composition. In turn, the distribution of carbon and other volatiles in Earth’s surface reservoirs has enabled conditions favorable for life on Earth. Despite the importance of carbon, its fluxes, sources, and sinks remain under-constrained in subduction-related fluids, with an almost complete absence of studies linking it to underground biological processes. The deep carbon mass balance has previously been estimated by comparing subducting slab inputs to arc volcano degassing outputs, with the difference representing the amount of carbon that is transported into Earth’s deep mantle. However, slab and mantle-derived carbon can also be sequestered in the form of hydrothermal minerals (e.g., calcite, aragonite) and by microbial uptake in the crust of the overriding plate, effectively masking an unknown portion of the carbon output from the subduction zone. The lack of constraints on these key processes, however, limits the understanding of the overall efficiency of the deep carbon cycle. This project involves substantive collaboration with colleagues in Chile, including an international workshop, and the work of several U.S. students will be supported.This project will characterize the extent of mineralogical and biological carbon sequestration along the geologically well-studied Andean Convergent Margin (ACM). The PIs hypothesize that calcite precipitation sequesters significant amounts of carbon in the ACM, particularly where the crust is thickest in the Central Volcanic Zone (CVZ). Furthermore, this project will test if subsurface microbial communities sequester carbon into biomass through chemosynthesis, forming an additional sink for carbon. Finally, the PIs will systematically assess how geochemical transformations and microbial communities vary as a function of subduction parameters (i.e., carbon input from the slab, upper plate thickness and lithology, as well as slab dip angle), which can then be used to compare results to a range of global convergent margins. To accomplish these goals, the PIs will conduct a field expedition to the CVZ in 2022 to collect fluid and gas samples from ~15 natural springs, seeps and fumaroles in the forearc and arc. They will measure helium and carbon isotopes, microbial chemosynthesis rates, and contributions of chemosynthesis to total microbial biomass in all samples. CVZ results will be interpreted alongside published and unpublished datasets from the ACM and other convergent margins globally (i.e., Central America). If subsurface geochemical and biological carbon sinks are found to be substantial in the ACM, it will add to growing evidence that carbon sequestration is widespread in the overlying crust of convergent margins. Such a finding could fundamentally alter the canonical understanding of deep carbon cycling between Earth’s surface and mantle. This project involves substantive collaboration with colleagues in Chile, including an international workshop, and the work of several U.S. students will be supported.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.