Assessing Crustal Assimilation In The Petrogenesis Of Columbia River Basalt: Plagioclase 87Sr/86Sr Stratigraphy

评估富集型地幔和陆壳对大陆溢流玄武岩熔岩的相对贡献是一个长期存在的问题，因为基本上可以用相同的全岩地球化学数据来论证这两种情况。我们建议使用哥伦比亚河玄武岩组进行测试，哥伦比亚河玄武岩组是世界上研究最深入的洪泛玄武岩省。我们将使用激光烧蚀取样结合多收集电感耦合等离子体质谱(MC-ICPMS)来确定CRBG熔岩中的斜长石斑晶是否在87Sr/86Sr中表现出分带。由于斜长石是在地壳压力下从玄武岩液体中结晶出来的，这将确定岩浆在驻留于地壳(或通过地壳)过程中是否经历了锶同位素比值的变化。虽然激光消融MC-ICPMS用于原位同位素比值分析还不是一项完全成熟的技术，但斜长石中的锶已经被证明是可行的，而且相对较少的分析挑战。这项研究有可能对紫砂污染影响哥伦比亚河熔岩成分的深度进行明确的空间约束。这一结果将影响我们对该洪泛玄武岩省成因过程中地幔岩柱-岩石圈相互作用的理解。

WolffEAR-0125986Assessing the relative contributions of enriched mantle and continental crust tocontinental flood basalt lavas is a long-standing problem, because essentially the samewhole-rock geochemical data can be used to argue for either case. We propose a testusing the Columbia River Basalt Group, the best-studied flood basalt province in theworld. We shall use laser ablation sampling in combination with multicollectorinductively coupled plasma mass spectrometry (MC-ICP-MS) to establish whether or notplagioclase phenocrysts in CRBG lavas exhibit zoning in 87 Sr/ 86 Sr. Because plagioclasecrystallizes from basaltic liquids at crustal pressures, this will establish whether or not themagmas experienced changes in Sr isotope ratio during residence in (or transportthrough) the crust. While laser ablation MC-ICP-MS for in-situ isotope ratio analysis isnot yet a fully developed technique, Sr in plagioclase has been demonstrated as feasible,and presents relatively few analytical challenges. This research has the potential to placeunequivocal spatial constaints on the depth at which lithosperic contamination hasaffected the compositions of the Columbia River lavas. The results will affect ourunderstanding of mantle plume-lithosphere interactions during genesis of this flood basaltprovince.