Synorogenic extension localized by upper-crustal thickening: An example from the Late Cretaceous Nevadaplano
Synorogenic extension localized by upper-crustal thickening: An example from the Late Cretaceous Nevadaplano
复制标题
上地壳增厚导致的同生扩张：白垩纪晚期内华达普拉诺的一个例子
DOI：
10.1130/g36431.1
复制
发表时间：
2015
期刊：
影响因子：
5.8
通讯作者：
R. V. D. Fiori
中科院分区：
文献类型：
--
作者：
S. Long;S. Thomson;P. Reiners;R. V. D. Fiori
造山系统内的同步收敛伸展通常被解释为增厚地壳的重力扩展或对冲断带动力学的响应。然而，造山运动期间空间局部化伸展的过程尚未完全了解。在这里，来自美国科迪勒拉山脉的案例研究表明，局部上地壳增厚可以对同步伸展的空间位置发挥一阶控制作用。尤里卡顶峰是内华达州东部塞维尔造山带（或“内华达普拉诺”）腹地高原上一条宽 20 公里、北向背斜，有 4.5 公里的构造起伏，是由早于晚始新世火山活动的两组北向正断层造成的变形。从两个正断层下盘的古生代石英岩收集的 (U-Th)/He 和裂变径迹热年代学数据表明，晚白垩世到古新世 (75-60 Ma) 的快速冷却 (10 °C/m.y.)，我们将其解释为伸展过程中的构造折返，并且与前塞维尔冲断带的后期缩短同时发生。这个例子说明，局部上地壳增厚区域内产生的结构和地形起伏可以在造山作用期间在空间上集中伸展，并增加了越来越多的证据表明内华达普拉诺晚白垩世-古新世伸展发生在中地壳和上地壳层面。
Synconvergent extension within orogenic systems is often interpreted as gravitational spreading of thickened crust or as a response to thrust belt dynamics. However, the processes that spatially localize extension during orogenesis are not fully understood. Here, a case study from the United States Cordillera demonstrates that localized upper-crustal thickening can exert a first-order control on the spatial location of synorogenic extension. The Eureka culmination, a 20-km-wide, north-trending anticline with 4.5 km of structural relief in the hinterland plateau of the Sevier orogenic belt (or “Nevadaplano”) in eastern Nevada was deformed by two sets of north-striking normal faults that pre-date late Eocene volcanism. (U-Th)/He and fission-track thermochronology data collected from Paleozoic quartzite in the footwalls of two normal faults demonstrate rapid (10 °C/m.y.), Late Cretaceous to Paleocene (75–60 Ma) cooling, which we interpret as tectonic exhumation during extension, and which was concurrent with late-stage shortening in the frontal Sevier thrust belt. This example illustrates that structural and topographic relief generated within zones of localized upper-crustal thickening can spatially focus extension during orogenesis, and adds to a growing body of evidence that Late Cretaceous–Paleocene extension in the Nevadaplano occurred at both mid- and upper-crustal levels.