Bimodal volcanism of the High Lava Plains and Northwestern Basin and Range of Oregon: Distribution and tectonic implications of age‐progressive rhyolites
Bimodal volcanism of the High Lava Plains and Northwestern Basin and Range of Oregon: Distribution and tectonic implications of age‐progressive rhyolites
复制标题
高熔岩平原和俄勒冈州西北盆地和山脉的双峰式火山活动：年龄渐进流纹岩的分布和构造意义
DOI：
--
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
R. Duncan
中科院分区：
文献类型：
--
作者：
Mark T. Ford;A. Grunder;R. Duncan
在俄勒冈州中部和东南部的高熔岩高原上，有渐新世和更年轻时期的多期火山活动。从12马到最近，火山活动是强烈的双峰几乎相等体积的玄武岩和流纹岩。其特征在于具有中等至高二氧化硅（SiO2 >72 wt. %）流纹质凝灰岩和圆顶，是年轻的西方，和广泛的拉斑玄武岩，显示没有时间模式。我们报告了18个新的40 Ar/39 Ar增量加热年龄的韵律，并建立了年龄渐进韵律的时间是去耦的玄武岩脉冲。这项工作通过将高熔岩平原（HLP）和最西北部的盆地和山脉（NWBR）流纹岩火山活动明确地联系到一个单一的年龄递进趋势中，扩展了以前的工作者。流纹岩露头和区域构造的时空关系表明，由于地壳密度越来越大而导致的沉降在火山活动更活跃的HLP内产生了大型的、主要是沉积物填充的盆地。流纹质火山作用的西北偏西的年龄进程与相对于北美板块运动的准静止地幔上涌的预期趋势相反。我们把流纹岩年龄的进展归因于地幔上涌对板块回滚和变陡的响应，这与该地区和模拟板块回滚模型下的地幔各向异性是一致的。这消除了深地幔柱参与的必要性。实验室实验研究表明，下行板的几何形状可以集中上升流或软流圈逆流到一个收缩带，导致更大的火山体积在HLP相比，NWBR。
Multiple episodes of Oligocene and younger silicic volcanism are represented in the high lava plateau of central and southeastern Oregon. From 12 Ma to Recent, volcanism is strongly bimodal with nearly equal volumes of basalt and rhyolite. It is characterized by moderate to high silica (SiO2 >72 wt. %) rhyolitic tuffs and domes that are younger to the west, and widespread, tholeiitic basalts that show no temporal pattern. We report 18 new 40Ar/39Ar incremental heating ages on rhyolites, and establish that the timing of the age‐progressive rhyolites is decoupled from basaltic pulses. This work expands on that of previous workers by clearly linking the High Lava Plains (HLP) and northwestern‐most Basin and Range (NWBR) rhyolite volcanism into a single age‐progressive trend. The spatial‐temporal relationship of the rhyolite outcrops and regional tectonics indicate that subsidence due to increasingly dense crust creates large, primarily sediment‐filled basins within the more volcanically active HLP. The west‐northwest age progression in rhyolitic volcanism is counter to the trend expected for a quasi‐stationary mantle upwelling relative to North American plate motion. We attribute the rhyolitic age progression to mantle upwelling in response to slab rollback and steepening, and this is consistent with mantle anisotropy under the region and analog slab rollback models. This removes the necessity of deep mantle plume involvement. Laboratory experimental studies indicate that the geometry of the downgoing slab can focus upwelling or asthenospheric counterflow into a constricted band, resulting in greater volcanic volumes in the HLP as compared to the NWBR.