Exhumation at orogenic indentor corners under long-term glacial conditions: Example of the St. Elias orogen, Southern Alaska
Exhumation at orogenic indentor corners under long-term glacial conditions: Example of the St. Elias orogen, Southern Alaska
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长期冰川条件下造山压痕角的折返：阿拉斯加南部圣埃利亚斯造山带的例子
DOI：
10.1016/j.tecto.2010.05.015
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发表时间：
2010
期刊：
影响因子：
2.9
通讯作者：
Aaron Berger
中科院分区：
文献类型：
--
作者：
J. Spotila;Aaron Berger
会聚板块边界的同轴弯曲，或压痕角，显示了地球上一些最有趣的变形模式，是耦合侵蚀，热弱化和应变的“动脉瘤”的典型位置。阿拉斯加的圣埃利亚斯造山带是一个小型、年轻的会聚系统，在其历史的大部分时间里一直以冰川气候为主，并表现出两个尚不清楚的突出的凹陷角。我们已经增加了40个新的磷灰石（U-Th）/He年龄已经广泛的数据集，这个造山带的低温冷却历史，以限制在这些indentor角落折返的模式。西部构造结的年龄在整个构造枢纽上有微小的变化，这表明弯曲对折返模式的影响很小，而且包括巴格利断层在内的构造从造山带核心到西南方向的俯冲带之间连接得很顺畅。山脉北侧的岩石隆起似乎朝着东部构造结稳步增加，东部构造结代表南部转换断层和西部碰撞带之间直角弯曲的顶点。根据年龄-海拔关系，可以确定岩石相对隆起带，其中，Mt. Logan Baghoff或东部构造结以北的地区，经历了比西部构造结西北部背景水平高出14.8km的岩石隆起。相对岩石隆起的凸起对称于东部压痕角的铰链。然而，在这个隆起的剥蚀率是不一样快的褶皱和冲断带的核心，并低于苏厄德冰川下的碎屑冷却年龄所暗示的。这意味着不会发生超快速（0.5毫米/年）折返的大靶心，并且年轻碎屑年龄的亚群可能来自沿着费尔韦瑟断层的狭窄压扭带。与喜马拉雅构造带不同的是，圣埃利亚斯造山带的任何一个凹陷角似乎都没有形成侵蚀-应变耦合的动脉瘤。这可能表明，在会聚造山带中，冰川侵蚀能够划分应变的程度是有限的。同样，可能存在一个贯穿右旋断层，Totschunda断层，通过东部结意味着构造，而不是表面过程，施加在这些角落的应变分配的主要控制。
Syntaxial bends in convergent plate boundaries, or indentor corners, display some of the most intriguing deformation patterns on Earth and are type localities for “aneurysms” of coupled erosion, thermal weakening, and strain. The St. Elias orogen in Alaska is a small, young convergent system that has been dominated by a glacial climate for much of its history and exhibits two prominent indentor corners that are not well understood. We have added 40 new apatite (U–Th)/He ages to the already extensive dataset for the low-temperature cooling history of this orogen to constrain the pattern of exhumation in these indentor corners. Ages from the western syntaxis show minor variation across the structural hinge, suggesting that the bend has little effect on the pattern of exhumation and that structures, including the Bagley fault, connect smoothly from the orogen core to the subduction zone to the southwest. Rock uplift on the north flank of the range appears to increase steadily towards the eastern syntaxis, which represents the apex in the right-angle bend between a transform fault in the south and the collision zone in the west. Based on age–elevation relationships, zones of relative rock uplift can be defined in which the Mt. Logan massif, or the area just north of the eastern syntaxis, experienced ∼4.8km greater rock uplift than background levels northwest of the western syntaxis. A bulge in relative rock uplift is symmetric about the hinge in the eastern indentor corner. However, rates of denudation in this bulge are not as rapid as the core of the fold and thrust belt and are lower than those implied by detrital cooling ages from beneath the Seward Glacier. This implies that a large bull's eye of ultra-rapid (∼5mm/yr) exhumation does not occur and that the subpopulation of young detrital ages may be sourced from a narrow transpressional zone along the Fairweather fault. Unlike the Himalayan syntaxes, it thus appears that an aneurysm of coupled erosion–strain has not developed in either indentor corner of the St. Elias orogen. This may indicate a limit to the degree to which glacial erosion can partition strain in convergent orogens. Similarly, the likely existence of a through-going dextral fault, the Totschunda fault, through the eastern syntaxis implies that tectonics, rather than surface processes, exerts the main control on strain partitioning in these corners.