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

9614165里普利为了更好地了解与大陆裂谷有关的岩浆有关的热液流系统的发展过程，计划进行详细的氧和氢同位素研究，并通过放射性同位素分析加以补充，其中竞争过程可能产生类似的稳定同位素特征。为期一年的试点研究结果表明，上述杜卢斯复杂的热液流是在北岸火山群内的渗透流顶部和底部，并可能沿着接触的岩床在复杂的元古代沉积岩。计划对位于复合体上方和下方的岩床进行额外的O和H同位素测量，以更好地确定与杜卢斯复合体和浅成侵入岩的侵位有关的热液循环系统的性质。同位素交换和反应的建模将根据温度约束、流动参数和水/岩石比以及平衡和动力学分馏来进行。计划进行一些Sr、Nd和Pb同位素分析。还将确定放射性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。研究结果对解释杜卢斯杂岩体中铂族元素矿化的可能起源具有特别重要的意义，并将有助于更好地了解全球裂谷环境中的地壳-岩浆相互作用。

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.