A Discussion on volcanism and the structure of the Earth - Cenozoic volcanism and plate-tectonic evolution of the Western United States. II. Late cenozoic
A Discussion on volcanism and the structure of the Earth - Cenozoic volcanism and plate-tectonic evolution of the Western United States. II. Late cenozoic
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DOI：
10.1098/rsta.1972.0009
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发表时间：
1972-01
期刊：
影响因子：
--
通讯作者：
R. L. Christiansen;P. Lipman
中科院分区：
文献类型：
--
作者：
R. L. Christiansen;P. Lipman
在晚新生代时期，美国西部大部分地区的火山组合及其构造环境发生了重大变化。在可以记录这种火山-构造转换的地方，早期造山和造山后以钙碱性安山岩为主的组合被基本的玄武岩火山运动所取代，这些岩石是环太平洋大陆边缘和岛弧的典型特征，伴随着区域正常和走滑断裂。这里认为基本为玄武岩的火成岩场包括：(1)玄武岩场，(2)分化的火成岩系列通常与碱性玄武岩母岩浆有关的碱性场，(3)镁铁质和硅质岩的双峰式组合，一般为玄武岩和高硅流纹岩。类似的火成岩油田也出现在世界上其他以构造伸展为特征的地区。美国西部不同地区晚新生代火山-构造转换的性质和时间从已发表的参考文献中得到了记录。这种转换始于渐新世末期的东南部，经过中新世、上新世和第四纪向西北方向移动。玄武岩火山作用、碱性火山作用或双峰式火山作用以及与之相关的内陆地区的区域延伸似乎发生在北美和两个太平洋板块之间的板块构造边界发生剧烈变化的时代。这些变化是东太平洋隆起与中第三纪大陆边缘海沟碰撞的结果，是美国板块和西太平洋板块沿着右旋转换断层系统直接接触的结果。这些板块构造的相互作用不断演化，并决定了美国西部3000万年来的火山和构造演化。
A major change in volcanic associations and their tectonic settings occurred in much of the Western United States during late Cenozoic time. Where this volcano-tectonic transition can be documented, an earlier orogenic and post-orogenic association of predominantly calc-alkalic andesitic rocks typical of circum-Pacific continental margin and island arcs was succeeded by fundamentally basaltic volcamsm which accompanied regional normal and strike-slip faulting. The igneous fields regarded here as fundamentally basaltic include: (1) basaltic fields, (2) alkalic fields in which differentiated igneous series commonly can be related to alkali-basaltic parent magmas, and (3) bimodal associations of mafic and silicic rocks, generally basalts and high-silica rhyolites. Similar igneous fields occur in other regions of the world characterized by tectonic extension. The nature and timing of the late Genozoic volcano-tectonic transition in various areas of the Western United States are documented from published references. The transition began in the southeastern part of the region in latest Oligocene time and moved northwestward through Miocene, Pliocene, and Quaternary time. The inception of basaltic, alkalic, or bimodal volcanism and associated regional extension of inland areas appears to date the times at which plate-tectonic boundaries between North America and two Pacific plates underwent drastic changes. These changes resulted from collision of the East Pacific Rise with a mid-Tertiary continental-margin trench and resulting direct contact of the American and western Pacific plates along a right-lateral transform fault system. These platetectonic interactions have evolved continuously and have determined the volcanic and tectonic evolution of the Western United States for the last 30 million years.