Origin of Basaltic Magmatism in the Tectonically Enigmatic High Lava Plains of Southeastern Oregon

9725166俄勒冈州中部和东南部高熔岩平原（HLP）的格伦德火山岩是独特的，因为：（1）它们位于盆岭省的西北边缘，（2）它们反映了黄石-蛇河平原省的晚第三纪和第四纪火山活动，因为西火山活动较年轻;（3）强烈的双峰式，由具大洋性的玄武岩和高硅流纹岩组成。 HLP岩浆形成的构造模式与黄石地幔柱的演化，B与晚第三纪盆岭省的形成有关的拉张背景，以及与晚第三纪盆岭省的形成有关的拉张背景有关的拉张模式，以及与晚第三纪盆岭省的形成有关的拉张模式。c）与卡斯卡迪亚俯冲带有关的弧后背景。为了区分这些模型，我们将调查一个潜在的年龄进步的趋势，在玄武岩火山作用，确定其成因联系相关的火山作用，评估地幔来源参与玄武岩浆的HLP，并确定是否地理和时间的地球化学变化是类似的黄石热点轨道。 这些问题将通过对高熔岩平原代表性地区的玄武岩进行综合野外、地质年代学和地球化学研究来回答。 选择了4个地区进行高精度~（40）Ar-~（39）Ar测年填图。 还将分析最重要的样品的主要和微量元素组成以及Sr、Nd、Pb、O和He同位素比率。

9725166 Grunder Volcanic rocks of the High Lava Plains (HLP) of central and southeastern Oregon are unique because: (1) they lie at the northwestern margin of the Basin and Range Province; (2) they mirror Late Tertiary and Quaternary volcanism of the Yellowstone-Snake River Plain Province in that silicic volcanism is younger to the west; and (3) they are strongly bimodal, being composed of basalts with oceanic affinities and high-silica rhyolites. Because of these characteristics, the HLP have been idenfied as an outstanding problem in understanding tectonism and volcanism in the western U.S. The tectonic models invoked for the formation of the HLP magmas have been associated with : a) the evolution of the Yellowstone mantle plume; b) an extensional setting related to Late Tertiary development of the Basin and Range Province; and c) a back-arc setting related to the Cascadia subduction zone. In order to discriminate among these models we will investigate a potential age-progressive trend in basaltic volcanism, determine its genetic link to the associated silicic volcanism, evaluate the mantle sources involved in the basaltic magmatism of the HLP, and determine if geographic and temporal geochemical variations are analogous to the Yellowstone hotspot track. These questions will be answered with an integrated field, geochronological and geochemical study of basalts from representative areas in the High Lava Plains. Four areas have been selected for mapping and dating by high precision 40Ar-39Ar methods. The most important samples will also be analyzed for major- and trace-element composition and Sr, Nd, Pb, O and He isotopic ratios.