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

评估富集的地幔和大陆地壳对大陆洪水玄武岩熔岩的相对贡献是一个长期存在的问题，因为基本上相同的全岩地球化学数据可以用来论证任何一种情况。我们建议使用哥伦比亚河玄武岩群进行测试，哥伦比亚河玄武岩群是世界上研究得最好的洪水玄武岩省。我们将使用激光烧蚀取样与多电感耦合等离子体质谱（MC-ICP-MS）相结合的方法来确定CRBG熔岩中的斜长石斑晶是否在87sr / 86sr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的，这将确定岩浆在停留（或通过）地壳期间是否经历了Sr同位素比值的变化。虽然激光烧蚀MC-ICP-MS用于原位同位素比分析还不是一种完全成熟的技术，但斜长石中的Sr已被证明是可行的，并且提出了相对较少的分析挑战。这项研究有可能对岩石圈污染影响哥伦比亚河熔岩组成的深度给出明确的空间限制。研究结果将影响我们对该洪水玄武岩省成因过程中地幔柱-岩石圈相互作用的认识。

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.