RUI: Integrated Strain and Fluid Composition, Temperature and Pressure Histories of Orogens

研究人员提出了确定造山带应变、流体组成、流体温度和流体压力史的研究计划。流体和流体压力的存在被认为对各种构造现象施加强有力的控制，包括地震旋回性、增生棱镜的几何形状以及脆性和韧性岩石变形。流体运移也是岩石圈内热量和物质传递的重要因素，也是矿床形成的重要因素之一。然而，确定活跃变形区域深处流体的性质和条件仍然非常困难。即使钻探确实获得了关于流体成分、温度和压力的信息，我们也只能得到一个简短的快照，而不是一个随地质时间可能发生的流体变化的指示。从流体包裹体和稳定同位素的研究中获得了一些信息，但在大多数情况下，构造序列中静脉形成的时间和持续时间是模糊的。PI提出，对刚性物体周围纤维应变条纹中的流体包裹体和稳定同位素进行分析，是在造山运动过程中获得近乎完整的流体条件记录的最佳方法。他们对佛蒙特州和纽约塔科尼克板岩带的一些异常大的应变条纹进行了增量应变、稳定同位素和流体包裹体研究，得到了有趣的结果。数据表明，主伸长方向与流体压力和温度之间有很强的相关性。然而，他们的方法依赖于能够连续切片应变条纹，并使用石英和碳酸盐溶解的激光氟化测量共存的石英和方解石中的O同位素。这就排除了使用大多数应变条纹，因为它们要么太小，要么含有其他矿物质，如绿泥石或白云母。这种特征的稳定同位素分析变得相当困难，因为必须生产小体积的纯矿物分离物。PI建议使用离子微探针来克服这些缺点。这样做将允许在大应变条纹中前所未有的空间分辨率，并且也允许使用较小的应变条纹。他们还将能够使用具有更多矿物学多样性的应变条纹，为研究开辟新的途径。他们建议对该方法进行测试，通过对来自Taconics的异常大应变条纹的相同样品进行硅酸盐激光氟化和碳酸盐溶解稳定同位素分析以及离子微探针稳定同位素分析。随后，他们将扩大在Taconics中的地理覆盖范围，以验证应变和流体条件相互关联并受鸟山逆冲断层运动控制的假设。他们还将分析来自比利牛斯山脉和赫尔维蒂阿尔卑斯山脉的样本，这些样本具有非常简单和复杂的菌株历史。PI相信这项工作将展示这种方法的实用性，为其他工作者开辟新的途径。他们还计划让本科生参与研究，并认为这将为每年夏天的三名学生提供一次刺激而重要的研究经历。每年将有一名学生负责研究的各个方面；增量应变、流体包裹体和稳定同位素分析，与其中一位PI密切合作。拟议工作的更广泛影响包括扩大离子微探针的用途，充分利用美国国家科学基金会在高露洁购买的稳定同位素和扫描电镜仪器，让本科生参与研究，包括本科生机构的教师参与研究，以及扩大造山流体研究的可用技术。

The investigators present a plan of research aimed at determining the strain, fluid composition, fluid temperature and fluid pressure history of orogenic belts. The presence of fluids and fluid pressure are believed to exert strong controls on a variety of tectonic phenomena, including earthquake cyclicity, the geometry of accretionary prisms and both brittle and ductile rock deformation. Fluid migration is also a significant factor in the transfer of heat and matter in the lithosphere and is one of the more significant factors in the formation of mineral deposits. However, determining the nature and conditions of fluids at depth in actively deforming regions remains highly difficult. Even when drilling does yield information about fluid composition, temperature and pressure we are given only a brief snapshot rather than an indication of possible fluid variations over geologic time. Some information has been gleaned from the study of fluid inclusions and stable isotopes in veins, but the timing and duration of vein formation in a structural sequence is obscure in most cases. The PI's propose that analysis of fluid inclusions and stable isotopes in fibrous strain fringes around rigid objects is the best way to get a nearly complete record of fluid conditions over the course of orogeny. They have conducted an incremental strain, stable isotope and fluid inclusion study of some unusually large strain fringes in the Taconic slate belt of Vermont and New York, with interesting results. The data indicate a very strong correlation between the directions of principal elongation and fluid pressure and temperature. Their methods rely, however, on being able to serially section the strain fringes and measure O isotopes in coexisting quartz and calcite using laser fluorination of quartz and carbonate dissolution. This precludes using most strain fringes, because they are either too small or contain other minerals, such as chlorite or white mica. Stable isotope analyses of such features become quite difficult because pure mineral separates in small volume must be produced. The PI's propose using the ion microprobe to overcome these drawbacks. Doing so will allow unprecedented spatial resolution in large strain fringes and will allow the use of smaller strain fringes as well. They will also be able to use strain fringes with more mineralogical diversity, opening up new avenues for research. They propose performing a test of this method by conducting both silicate laser fluorination and carbonate dissolution stable isotope analyses along with ion microprobe stable isotope analyses on identical samples of unusually large strain fringes from the Taconics. Following this, they will expand their geographic coverage in the Taconics to test the hypothesis that strain and fluid conditions are inter-related and controlled by motion on the Bird Mountain thrust fault. They will also analyze samples from well studied sites in the Pyrenees and Helvetic Alps, with both very simple and complex strain histories. The PI's believe that this work will demonstrate the utility of this approach, opening new avenues to other workers. They also plan to include undergraduates in the research and contend that this will provide a stimulating and significant research experience for three students each summer. Each year one student will work on each aspect of the research; incremental strain, fluid inclusion and stable isotope analysis, working in close collaboration with one of the PI's. Broader impacts of the proposed work include expanding the utility of the ion microprobe, taking full advantage of NSF-purchased stable isotope and SEM instrumentation at Colgate, exposure of undergraduates to research, inclusion of faculty from an undergraduate institution in research and expansion of techniques available for the study of orogenic fluids.