Re-Os Isotopic Systematics Accompanying the Conversion of Organic-Rich, Pelitic Country Rocks to Hornfels, Magma Contamination and Sulfide Ore-Genesis, Duluth Complex

由于幔源玄武岩部分熔体中Re相对于Os的富集，以及地壳岩石的高Re/Os比值，Re/Os同位素体系已被证明是评价壳幔源基性岩浆动态相互作用过程的敏感示踪剂。在乡村岩石污染评价中，稀土-氧同位素体系作为岩石学示踪剂的应用取决于对污染岩石中开放或封闭系统行为的正确评价，以及火成岩或富硫化物矿石结晶后稀土和氧的不动性。本项目将评价富有机质沉积岩中Re、Os的分布和同位素特征，接触变质和角岩转化过程中Re、Os同位素特征的变化，以及由于围岩同化或释放的流体相而产生的含硫化物火成岩中Re、Os同位素的变化。德卢斯杂岩和元古代乡村岩石的地质背景为通过接触变质脱水和基性岩浆对乡村岩石的同化作用来追踪Re-Os体系的演化提供了极好的机会。在巴氏铜镍矿床区域存在受地壳污染和未受污染的辉长岩和橄榄岩，系统的Re-Os分析将允许对同位素变化的原因进行深入评估，这些同位素变化可能是由于变质和热液作用在乡村岩石中产生的，以及与硅酸盐岩浆与硫化物岩浆比例变化有关的岩浆作用。

9814204RipleyBecause of the enrichment of Re relative to Os in mantle-derived, basaltic partial melts, and the high Re/Os ratio of crustal rocks, the Re/Os isotopic system has proven to be a sensitive tracer in the evaluation of dynamic interaction processes between crust and mantle-derived mafic magmas. In the assessment of country rock contamination the application of the Re-Os isotopic system as a petrologic tracer is dependent upon the proper evaluation of open- or closed-system behavior in the contaminant rock, and immobility of Re and Os after crystallization of the igneous rock or sulfide-rich ore material. This project will evaluate the distribution and isotopic characteristics of Re and Os in organic-rich sedimentary rocks, changes in isotopic characteristics during contact metamorphism and conversion of these rocks to hornfels, and isotopic variation found in sulfide-bearing igneous rocks produced as a result of assimilation of country rocks or a released fluid phase. The geologic setting of the Duluth Complex and Proterozoic country rocks presents an excellent opportunity to trace the evolution of the Re-Os system through the processes of contact metamorphism and dehydration, and assimilation of country rocks by mafic magma. Both crustally-contaminated and uncontaminated gabbroic and troctolitic rocks are present in the area of the Babbitt Cu-Ni deposit, and systematic Re-Os analyses will permit an in-depth evaluation of the causes of isotopic variability that may originate as a result of metamorphic and hydrothermal processes in the country rocks, and magmatic processes related to changes in the ratio of silicate magma to sulfide magma.