Reshuffling the Columbia River Basalt chronology—Picture Gorge Basalt, the earliest- and longest-erupting formation
Reshuffling the Columbia River Basalt chronology—Picture Gorge Basalt, the earliest- and longest-erupting formation
复制标题
重新洗牌哥伦比亚河玄武岩年代——图片峡谷玄武岩，喷发最早和最长的地层
作者：
E. Cahoon;M. Streck;A. Koppers;D. Miggins
哥伦比亚河玄武岩群（CRBG）是世界上最年轻的大陆溢流玄武岩省，据推测来源于目前位于美国西北部黄石国家公园下面的深层羽状物。该省最早喷发的玄武岩有助于了解和模拟羽流撞击以及随后的玄武火山作用演化。我们探讨了图片峡玄武岩（PGB）形成的CRBG，并讨论了位置和地球化学意义的时间背景下，早期CRBG岩浆活动。我们报告新的ARGUS-VI多收集器40 Ar/39 Ar增量加热年龄从已知的PGB地点和额外的露头，我们可以地球化学分类为PGB。40 Ar/39 Ar年龄介于17.23 ± 0.04 ~ 16.06 ± 0.14 Ma之间，表明PGB比其他CRBG主相单元喷发时间更早、更长。这些年龄表明，火山活动开始在一个广泛的地区在该省的中心，这些早期熔岩的地球化学反映了地幔源，是不同的空间和时间。结合年龄与最强的弧状（但亏损）的地球化学信号的PGB CRBG单位之间表明，最浅的交代backarc状地幔被挖掘的第一个和同时，与后来的单位（Steens和Imnaha玄武岩）表现出增加的影响，一个羽状源。
The Columbia River Basalt Group (CRBG) is the world’s youngest continental flood basalt province, presumably sourced from the deep-seated plume that currently resides underneath Yellowstone National Park in the northwestern United States. The earliest-erupted basalts from this province aid in understanding and modeling plume impingement and the subsequent evolution of basaltic volcanism. We explore the Picture Gorge Basalt (PGB) formation of the CRBG, and discuss the location and geochemical significance in a temporal context of early CRBG magmatism. We report new ARGUS-VI multicollector 40Ar/39Ar incremental heating ages from known PGB localities and additional outcrops that we can geochemically classify as PGB. These 40Ar/39Ar ages range between 17.23 ± 0.04 Ma and 16.06 ± 0.14 Ma, indicating that PGB erupted earlier and for longer than other CRBG main-phase units. These ages illustrate that volcanism initiated over a broad area in the center of the province, and the geochemistry of these early lavas reflects a mantle source that is distinct both spatially and temporally. Combining ages with the strongest arc-like (but depleted) geochemical signal of PGB among CRBG units indicates that the shallowest metasomatized backarc-like mantle was tapped first and concurrently, with later units (Steens and Imnaha Basalts) showing increased influence of a plume-like source.