Space-Time Progression of Faulting in the Northernmost Basin and Range: Implications for Crustal-Scale Processes During Extension

盆地和山脉伸展省是世界上研究大陆伸展的首选地区，因为断层正在移动，火山活动今天仍在进行。盆地和山脉省的西北部位于内华达州北部，像盆地和山脉的其他地方一样，有断层环绕的山脉和山谷，但根据地质研究，大陆地壳的上部因断层而经历的伸展要比其他地方小得多。矛盾的是，地壳作为一个整体很薄(只有28公里)，似乎与盆地和山脉的其他部分一样拉伸或变薄，或者比盆地和山脉的其他部分拉伸更多，后者平均厚度为30-35公里)。此外，伸展的年龄跨度及其与火山活动的关系，以及从这一明显的上地壳低伸展区域向盆地和山脉中向南和向东延伸较高的地区过渡的性质尚不清楚。岩浆/火山活动被认为会加热和削弱地壳，导致变薄和裂谷。然而，内华达州北部的大多数岩浆活动和火山活动发生在大约1600万年前(与蛇河-黄石火山趋势有关)，但正在进行的研究表明，伸展断裂发生在近1000万年后。这次内华达州北部伸展断裂的调查依赖于现有的和正在进行的地质现场研究，并将其汇编到数字数据库中，以更好地记录该地区断裂的分布、几何形状和时代。结合最先进的岩石和矿物地质年代学和热年代学测年，将准确地确定盆地和山脉这一部分发生的年龄或时间和伸展程度。这个新的数据库将有助于回答几个重要的问题：什么条件导致大陆变薄，以及它们的破裂和裂解？岩浆作用在地壳伸展中起什么作用？整个地壳的伸展和减薄是如何发生的？下地壳可以变薄或伸展而不依赖上地壳吗？对这些问题的回答适用于内华达州北部以外的各种地区，特别是将有助于解决有关在世界上巨大的近海大陆架上变薄的大陆壳上形成的沉积盆地的起源和演化的根本问题。

The Basin and Range extensional province is the world's premier region for the study of continental stretching as faults are moving and volcanic activity is ongoing today. The northwestern part of the Basin and Range Province, in northern Nevada, has fault-bounded mountains and valleys like elsewhere in the Basin and Range, but, based on geologic studies, the upper part of the continental crust has undergone much less extension by faulting than elsewhere. Paradoxically, the crust as a whole is thin (only 28 km) and appears to be just as stretched or thinned, or more stretched than the rest of the Basin and Range, which is on average 30-35 km thick). In addition, the age span of extension, its relationship to volcanic activity, and the nature of the transition from this region of apparent low upper crustal extension to the more highly extended areas to the south and east in the Basin and Range are not clearly known. Magmatic/volcanic activity is thought to heat and weaken the crust, leading to thinning and rifting. However, most magmatism and volcanic activity in northern Nevada occurred at about 16 million years ago (associated with the Snake River-Yellowstone volcanic trend), but ongoing studies show that extensional faulting happened almost 10 million years later.This investigation of northern Nevada extensional faulting relies on existing and ongoing geologic field studies and their compilation into a digital data base to better document the distribution, geometry and the age of faulting in the region. Combined with state-of-the-art geochronologic and thermochronologic dating of rocks and minerals, the age or time and the amount of extension that took place in this part of the Basin and Range will be determined accurately. This new data base will help answer several important questions: What conditions lead to the thinning of continents and their rupture and rifting apart? What role does magmatism play in crustal extension? How does stretching and thinning happen on the scale of the entire crust, and can the lower crust thin or stretching independently of the upper crust? Answers to these questions are applicable to a variety of regions beyond northern Nevada, and in particular, will help address fundamental questions about the origin and evolution of sedimentary basins developed on thinned continental crust of the world's vast offshore continental shelves.