Collaborative Research: Rates of Carbonate Formation in the Samail Ophiolite, Oman: Implications of Ultramafic Weathering for the Carbon Cycle

在过去的几年里，相当多的注意力集中在碳捕获和储存，以减少人为输入的大气CO2。一个建议的缓解方案是在构造暴露的地幔岩（或橄榄岩）的化学风化过程中增加CO2气体向稳定的固体碳酸盐矿物的转化。虽然橄榄岩的天然碳酸化是常见的，但其速率以及通过这种风化机制吸收CO2的速率知之甚少。确定橄榄岩碳酸化的自然速率是理解这一潜在的重要影响的关键？水槽？在全球碳循环中。天然橄榄岩碳酸化速率也是一个重要的参数，但在评价利用人工增强的橄榄岩原位蚀变来减轻人类输入大气CO2的累积的可行性时，其约束性很差。阿曼Samail蛇绿岩是世界上规模最大、出露程度最好的蛇绿岩之一，是研究地幔橄榄岩天然碳储量的理想天然实验室。研究小组选择并仔细绘制了八个地点，其中包括暴露碳酸盐脉、碳酸盐矿床的道路开挖，以及一个位于天然橄榄岩风化表面并含有丰富碳酸盐脉的地点。该工作计划包括使用两种独立的放射性测年技术确定碳酸盐的年龄：14 C（约50，000年的碳酸盐）和238 U-230 Th（约350，000年的碳酸盐）。此外，他们将确定宿主地幔橄榄岩的暴露年龄，以检验碳酸盐风化主要发生在与侵蚀速率保持同步的薄风化层中的假设。该项目构成了博士学位。MIT/WHOI联合项目学生Evelyn Mervine的论文研究。提高对超镁铁岩中天然碳酸盐形成的认识将有助于在超镁铁岩中开发CO2捕获和储存，以抵消人为CO2排放并减缓全球气候变化。

In the last few years, considerable attention has been focused on carbon capture and storage to mitigate anthropogenic input of atmospheric CO2. One proposed option for mitigation is to increase conversion of CO2 gas to stable, solid carbonate minerals during chemical weathering of tectonically exposed mantle rock (or peridotite). While natural carbonation of peridotite is commonly observed, its rate, and therefore the rate of CO2 uptake via this weathering mechanism, is poorly known. Determining the natural rate of peridotite carbonation is critical for understanding the influence of this potentially important ?sink? in the global carbon cycle. The natural peridotite carbonation rate is also an essential, but poorly constrained, parameter in calculations evaluating the viability of using artificially-enhanced, in situ alteration of peridotite to mitigate the buildup of anthropogenic input to atmospheric CO2.The primary objective of this research is to determine natural carbonation rates of exposed mantle peridotites. The Samail Ophiolite, Oman, is one of the largest and best-exposed ophiolites in the world, and hence is an ideal natural laboratory for investigating natural carbon storage in mantle peridotites. The research team has selected and carefully mapped eight sites that include roadcuts exposing carbonate veins, travertine deposits, and one site located on the natural peridotite weathering surface and containing abundant carbonate veins. The work plan consists of determining the ages of carbonates using two independent radiogenic dating techniques: 14C (for carbonates as old as ~50,000 years) and 238U-230Th (for carbonates as old as ~350,000 years). In addition, they will determine exposure ages for the host mantle peridotite to test the hypothesis that carbonate weathering primarily occurs in a thin weathering horizon that keeps pace with erosion rates. This project constitutes the Ph.D. thesis research for MIT/WHOI Joint Program student Evelyn Mervine. An improved understanding of natural carbonate formation in ultramafic rocks will aid efforts to develop CO2 capture and storage in ultramafic rocks to offset anthropogenic CO2 emissions and mitigate global climate change.