187Re-187Os, 190Pt-186Os, 34S/32S Isotopic Systematics of the Subcontinental Mantle of the Western United States

美国西部次大陆地幔的 187Re-187Os、190Pt-186Os、34S/32S 同位素系统学

• 批准号: 9804909
• 负责人: Richard Walker
• 金额: $ 14.4万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-01 至 2000-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9804909&HistoricalAwards=false
• 关键词: 187Re; 187Os; 190Pt; 186Os; 34S

9804909Walker The timing of melt extraction in the subcontinental lithospheric mantle (SCLM) underlying regions of Proterozoic and Phanerozoic crust in the western United States is largely unknown. Distinctions between metasomatism of the SCLM via fluids and melts derived from subducting slabs, and the processes resulting in formation of OIB-type mantle domains, remain unclear. As a first step to alleviate some of the ambiguity, recent investigations have identified several compositional parameters that are unique to subduction-related metasomatism. These include high oxygen fugacities relative to oceanic and cratonic mantle, suprachondritic 187Os/188Os, and heavy 34S/32S. Some OIB-type mantle domains may have suprachondritic 186Os/188Os ratios. Therefore, these data combined with other geochemical parameters may discern between subduction zone metasomatism and OIB-type compositional enrichments within the SCLM. To address the timing of melting and the processes that modified the SCLM associated with Proterozoic and Phanerozoic crust, we will obtain 187Re-187Os, 190Pt-186Os and 34S/32S isotopic data on mantle xenoliths from the western United States. We will use negative thermal ionization mass spectrometry to obtain Os isotopic data. Bulk rock S isotopic data will be obtained using gas source mass spectrometry, and in situ S isotopes will be obtained by secondary ionization mass spectrometry.

[804909]美国西部元古宙和显生宙地壳下伏的次大陆岩石圈地幔（SCLM）熔体萃取的时间在很大程度上是未知的。由俯冲板块产生的流体和熔体导致的SCLM交代作用，以及导致obb型地幔域形成的过程之间的区别尚不清楚。为了减轻这种模糊性，最近的研究已经确定了俯冲相关交代作用特有的几个成分参数。这些特征包括相对于海洋和克拉通地幔的高氧逸度，超球粒质187o / 188o，以及重的34S/32S。某些obb型地幔域可能具有超球粒性的186o / 188o比值。因此，这些数据与其他地球化学参数相结合，可以区分俯冲带交代作用和大陆架内obb型成分富集。为了解决熔融时间和与元古宙和显生宙地壳相关的SCLM的修改过程，我们将获得美国西部地幔捕虏体的187Re-187Os， 190Pt-186Os和34S/32S同位素数据。我们将使用负热电离质谱法获得Os同位素数据。块状岩石S同位素数据将采用气源质谱法获得，原位S同位素数据将采用二次电离质谱法获得。