Eocene extension in Idaho generated massive sediment floods into the Franciscan trench and into the Tyee, Great Valley, and Green River basins
Eocene extension in Idaho generated massive sediment floods into the Franciscan trench and into the Tyee, Great Valley, and Green River basins
复制标题
DOI：
10.1130/g33746.1
复制
发表时间：
2013-02
期刊：
影响因子：
5.8
通讯作者：
T. Dumitru;W. Ernst;James E. Wright;J. Wooden;R. Wells;Lucian P. Farmer;A. Kent;S. Graham
中科院分区：
文献类型：
--
作者：
T. Dumitru;W. Ernst;James E. Wright;J. Wooden;R. Wells;Lucian P. Farmer;A. Kent;S. Graham
方济会复合体吸积棱柱是在太平洋板块俯冲到北美板块西缘下方约 165 米长的时期内形成的。在此类化石俯冲复合体中，通常很难重建大陆沉积物的增生细节并评估控制增生的因素。新的碎屑锆石 U-Pb 年龄表明，方济各杂岩的大部分主要海岸带亚基代表始新世（约 53-49 Ma）期间大规模、相对短暂的近海沟沉积和增生激增。沉积物主要来自遥远的爱达荷州基岩地区，而不是附近的内华达山脉。爱达荷州碎屑还滋养了加利福尼亚州的大峡谷弧前盆地（约 53-37 Ma）、俄勒冈州沿海的 Tyee 弧前盆地（49 至约 36 Ma）以及怀俄明州的大格林河湖盆地（50-47 Ma）。爱达荷州基岩的火成体在收缩背景下跨越了 98-53 Ma；它突然被 Bitterroot、Anaconda、Clearwater 和 Priest River 变质核复合体 (53-40 Ma) 的主要伸展运动以及 Challis 火山区 (51-43 Ma) 的主要火山活动所取代。这种伸展构造运动显然使广阔的区域变形并隆起，将大量沉积物抛向西部和东南部的沉积中心。在方济各沿海带，沉积物输入的大幅增加显然引发了大规模增生的脉冲，这种脉冲最终由北美板块内部深处的大陆构造运动控制，而不是由沿板块边界本身的某些构造事件控制。
The Franciscan Complex accretionary prism was assembled during an ~165-m.y.-long period of subduction of Pacifi c Ocean plates beneath the western margin of the North American plate. In such fossil subduction complexes, it is generally diffi cult to reconstruct details of the accretion of continent-derived sediments and to evaluate the factors that controlled accretion. New detrital zircon U-Pb ages indicate that much of the major Coastal belt subunit of the Franciscan Complex represents a massive, relatively brief, surge of near-trench deposition and accretion during Eocene time (ca. 53‐49 Ma). Sediments were sourced mainly from the distant Idaho Batholith region rather than the nearby Sierra Nevada. Idaho detritus also fed the Great Valley forearc basin of California (ca. 53‐37 Ma), the Tyee forearc basin of coastal Oregon (49 to ca. 36 Ma), and the greater Green River lake basin of Wyoming (50‐47 Ma). Plutonism in the Idaho Batholith spanned 98‐53 Ma in a contractional setting; it was abruptly superseded by major extension in the Bitterroot, Anaconda, Clearwater, and Priest River metamorphic core complexes (53‐40 Ma) and by major volcanism in the Challis volcanic fi eld (51‐43 Ma). This extensional tectonism apparently deformed and uplifted a broad region, shedding voluminous sediments toward depocenters to the west and southeast. In the Franciscan Coastal belt, the major increase in sediment input apparently triggered a pulse of massive accretion, a pulse ultimately controlled by continental tectonism far within the interior of the North American plate, rather than by some tectonic event along the plate boundary itself.