Cenozoic Tectonic and Magmatic Evolution of the Mojave Desert: Collaborative Research Between UCB and the University of North Carolina

这是科罗拉多大学和北卡罗来纳大学合作研究加州东南部莫哈韦沙漠地区新生代镁铁质到硅质火山岩的Nd、Sr和Pb同位素和微量元素组成的研究。这项研究将利用火山岩地球化学特征的时空变化来约束该地区的构造演化模式，并研究新生代火山岩的岩浆演化方面。来自5 Ma玄武岩的地球化学数据将被用来评估该地区目前下伏的地幔的年龄、结构和组成。这项研究的结果将被用来检验根据现有的同位素数据和该地区的一些构造模型所提出的，前新生代地幔岩石圈是否已经从大陆地壳下的构造中剥离。来自较老的新生代玄武岩的地球化学数据将被用来评估发生岩石圈移动的构造环境。将获得类似的中新世中硅质火山岩的地球化学数据集，并将用于约束这些岩石的成因模型。这些岩石的同位素组成也将被用来推断下大陆地壳的地球化学方面，并确定具有不同Nd同位素特征的前寒武纪基底地体之间的任何地下边界。总体而言，这项研究将首次全面描述莫哈韦火山岩的同位素和微量元素组成，并首次尝试将这些数据应用于约束大陆岩石圈的构造模型。这项研究是NSF之前由两家PI支持的研究的结果。Glazner(UNC)将负责样品选择、岩相学和微量元素化学，Farmer(UC)将进行所有同位素测定。

This is a collaborative study between the University of Colorado and the University of North Carolina on the Nd, Sr, and Pb isotopic, and trace element compositions of Cenozoic mafic-to- silicic volcanic rocks in the Mojave Desert region of southeastern California. The study will use temporal and spatial variations in the geochemical characteristics of the volcanic rocks to constrain models of the tectonic evolution of this region, and to study aspects of the magmatic evolution of the Cenozoic volcanic rocks. Geochemical data from 5Ma basalts will be used to evaluate the age, structure, and composition of the mantle currently underlying this area. The results of this study will be used to test whether pre-Cenozoic mantle lithosphere has been tectonically removed from beneath the continental crust, as suggested by available isotopic data and as proposed in some tectonic models for this region. Geochemical data from older Cenozoic basalts will be used to assess the tectonic setting in which lithosphere removal took place. A similar geochemical data set will be obtained for Miocene intermediate-to-silicic volcanics and will be used to constrain models for the genesis of these rocks. The isotopic compositions of these rocks will also be used to infer aspects of the geochemistry of the lower continental crust, and to define any subsurface boundaries between Precambrian basement terraines with different Nd isotopic characteristics. Overall this study will represent the first comprehensive characterization of the isotope and trace element compositions of Mojave volcanic rocks, and one of the first attempts to apply such data towards constraining tectonic models of the continental lithosphere. The study represents an outgrowth from previous NSF supported research by both of the PIs. Glazner (UNC) will be responsible for sample selection, petrography and trace-element chemistry, and Farmer (UC) will carry out all isotopic determinations.