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

由于在地幔玄武岩部分熔体中Re相对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地壳与地幔基性岩浆相互作用动力学过程的灵敏示踪剂。在围岩污染评价中，Re-Os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体系行为的正确评价，以及火成岩或富硫化物矿物质结晶后Re和Os的不移动。该项目将评估富有机沉积岩中Re和Os的分布和同位素特征，接触变质过程中同位素特征的变化和这些岩石向角岩的转化，以及围岩同化或释放流体相产生的含硫化物火成岩中发现的同位素变化。德卢斯杂岩和元古界围岩的地质背景为追踪Re-Os系统的演化提供了一个很好的机会，通过接触变质和脱水过程，以及围岩被镁铁质岩浆同化的过程。巴比特铜镍矿床地区既有受地壳污染的辉长岩和未受污染的辉长岩和榴辉岩，系统的Re-Os分析将使我们能够深入评估可能源于围岩变质和热液作用的同位素变化的原因，以及与硅酸盐岩浆与硫化物岩浆的比率变化有关的岩浆过程。

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.