Isotopic Studies of Hydrothermal Flow Systems Above and Below the Duluth Complex, Midcontinent Rift System, Minnesota

为了更好地理解与大陆裂谷相关的岩浆相关的热液流动系统的发展过程，计划进行详细的氧和氢同位素研究，并通过放射性成因同位素分析进行补充，其中竞争过程可能产生类似的稳定同位素特征。为期一年的初步研究表明，德卢斯杂岩上方的热液流体在北岸火山群的可渗透流动顶部和底部，并可能沿着杂岩下方元古代沉积岩的断层接触通道流动。为了更好地确定与德卢斯杂岩侵位和浅成侵入岩相关的热液循环系统的性质，计划对该杂岩的上方和下方进行额外的O和H同位素测量。同位素交换和反应的建模将基于温度约束、流动参数、水/岩比，以及平衡和动力学分馏。计划进行一些Sr、Nd和Pb同位素分析。放射性成因同位素值作为蚀变和水岩相互作用强度的函数的潜在变化也将被确定。研究结果对解释德卢斯杂岩中铂族元素矿化的可能成因具有重要意义，并有助于更好地理解世界范围内裂谷环境中地壳-岩浆的相互作用。

9614165 Ripley In order to better understand the processes involved in the development of hydrothermal flow systems associated with continental rift-related magmas, a detailed oxygen and hydrogen isotopic study is planned, to be augmented by radiogenic isotopic analyses where competing processes may have produced similar stable isotopic signatures. Results of a one-year pilot study indicate that above the Duluth Complex hydrothermal fluid flow was channeled in the North Shore Volcanic Group within permeable flow tops and bottoms, and possibly along the contact of sills within the Proterozoic sedimentary rocks below the Complex. Additional O and H isotopic measurements of sills located both above and below the Complex are planned to better define the nature of the hydrothermal circulation system association with emplacement of the Duluth Complex and hypabyssal intrusives. Modeling of isotopic exchange and reactions will be pursued based on temperature constrains, flow parameters, and water/rock ratios, and both equilibrium and kinetic fractionation. Some Sr, Nd and Pb isotopic analyses are planned. Potential variations in radiogenic isotope values as a function of alteration and intensity of water-rock interaction will also be determined. Results will be of particular significance to the interpretation of possible origins of platinum-group element mineralization in the Duluth Complex and will lead to a better understanding of crust-magma interaction in rift environments worldwide.