Emplacement and rheomorphic deformation of a large, lava-like rhyolitic ignimbrite: Grey's Landing, southern Idaho
Emplacement and rheomorphic deformation of a large, lava-like rhyolitic ignimbrite: Grey's Landing, southern Idaho
复制标题
DOI：
10.1130/b30167.1
复制
发表时间：
2011-03
影响因子：
4.9
通讯作者：
G. Andrews;M. Branney
中科院分区：
文献类型：
--
作者：
G. Andrews;M. Branney
中新世Grey 9 s登陆熔结凝灰岩达到70米厚，覆盖至少400平方公里的蛇河平原的中部地区。它表现出特别强烈的焊接和流变变形，虽然部分是共晶的，但大部分是熔岩状的，有流动带，没有火焰。一个几乎无处不在的渗透流分层，与发达的伸长线理，折叠成小的叶内紧等斜和鞘褶皱，这是再折叠的上部较大的褶皱。结构和运动学分析表明，焊接和早期变形发生在沉积过程中，从一个非常热的（≤1000 °C），高质量流量的火山碎屑密度流，向西流过地堑断层景观。由于热颗粒沉积，他们迅速凝集和合并，并在一个近水平的韧性剪切带靠近电流-沉积界面进行非共轴剪切。剪切带被解释为小于2米厚。它产生和变形的流变组构，它向上迁移与上升的电流沉积界面在加积过程中，使它短暂地影响所有级别的厚熔结凝灰岩。变形是渐进的，在异重流消散之后，粘性扩展和下坡流继续，并涉及越来越厚的部分。这将流动带和F1叶内等斜带折叠成更大的鞘褶皱，并在熔结凝灰岩顶部附近形成更直立的周斜带。我们证明，结构和运动学分析可以阐明侵位历史的流变熔结凝灰岩。
The Miocene Grey9s Landing ignimbrite reaches 70 m thick and covers at least 400 km 2 in the central region of the Snake River Plain. It shows particularly intense welding and rheomorphic deformation, and although parts are eutaxitic, most is lava-like with flow-banding and no fiamme. A near-ubiquitous penetrative flow lamination, associated with a well-developed elongation lineation, is folded into small intrafolial tight to isoclinal oblique and sheath folds, which are refolded by larger folds in the upper parts. Structural and kinematic analysis reveals that welding and early deformation occurred rapidly during deposition from a very hot (≤1000 °C), high-mass-flux pyroclastic density current that flowed westward across a graben-faulted landscape. As hot particles were deposited, they rapidly agglutinated and coalesced, and underwent noncoaxial shear in a subhorizontal ductile shear zone close to the current-deposit interface. The shear zone is interpreted to have been less than 2 m thick. It produced and deformed the rheomorphic fabric, and it migrated upward with the rising current-deposit interface during aggradation, so that it transiently affected all levels of the resultant thick ignimbrite. Deformation was progressive, and after the density current had dissipated, viscous spreading and downslope flow continued and involved an increasingly thick portion of the sheet. This folded the flow banding and F 1 intrafolial isoclines into larger sheath folds, and into more upright periclines near the top of the ignimbrite. We demonstrate that structural and kinematic analysis can elucidate the emplacement history of rheomorphic ignimbrites.