Re-Os Systematics in Proterozoic Anorthosite Complexes

元古代斜长岩杂岩中的Re-Os系统学

• 批准号: 0106874
• 负责人: Judith Hannah
• 金额: $ 19.5万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0106874&HistoricalAwards=false
• 关键词: Re; Os; Systematics; Proterozoic; Anorthosite

HannahEAR-0106874The magma source for Proterozoic massif-type anorthosite complexes and the origin of massive sulfide bodies found in some of those complexes remain unresolved problems. We propose that rhenium-osmium (Re-Os) concentrations and Os isotope ratios for oxides, sulfides, and silicates from two well-studied anorthosite suites will shed light on these issues. Most models based on geochemical data suggest that anorthosite complexes are derived from mantle melts that pond and fractionate at the base of the crust, and are then variably contaminated by crustal materials during ascent. Considerations from phase equilibria, however, suggest that parental magmas are derived by partial melting of a gabbroic source, presumably in the lower crust. Os isotope ratios, which are particularly sensitive indicators of crustal melting or assimilation, should help discriminate between competing models. High the initial 187Os/188Os ratios in sulfides from Proterozoic anorthosite complexes suggest dominance of crustal Os. It is unclear, however, whether the crustal Os was acquired by selective volatilization and incorporation of crustal sulfide, wholesale assimilation of bulk crust, or derivation of parental melts by partial melting of a crustal gabbroic source. We will compare Os isotopic data from two systems - the apparently sulfide-free Laramie Anorthosite Complex in Wyoming, and the sulfide-bearing Hakefjorden Complex in SW Sweden - to estimate the most likely source for the sulfides and their contained metals. The results could offer an exploration tool for distinguishing sulfide-poor and sulfide-rich systems.

元古宙杂岩体的岩浆来源和某些杂岩体中块状硫化物体的成因至今仍是一个悬而未决的问题。 我们建议，锇（铼-锇）的浓度和Os同位素比值的氧化物，硫化物，硅酸盐从两个研究良好的斜长岩套件将揭示这些问题。 基于地球化学数据的大多数模型表明，斜长岩复合体来自地幔熔体，这些熔体在地壳底部形成池和破裂，然后在上升过程中被地壳物质污染。 然而，相平衡的考虑表明，母岩浆来自辉长岩源的部分熔融，大概在下地壳。 锇同位素比值是地壳熔化或同化的特别敏感的指标，应该有助于区分竞争模型。 高的初始187 Os/188 Os比值的硫化物从元古宙斜长岩杂岩建议占主导地位的地壳Os。目前还不清楚，但是，是否获得了地壳Os的选择性挥发和纳入地壳硫化物，批发同化散装地壳，或衍生的母体熔体的部分熔融的地壳辉长岩源。 我们将比较来自两个系统的Os同位素数据--怀俄明州的明显不含硫化物的拉勒米斜长岩复合体和瑞典西南部的含硫化物的哈克峡湾复合体--以估计硫化物及其所含金属的最可能来源。 研究结果可为区分贫硫和富硫体系提供一种勘探工具。