Geologic Constraints on Landscape Evolution of the Sierra Nevada, California: Paleochannels, Magmatism and Structure

内华达山脉的年龄和隆起历史目前是地质学争论的主题。本研究项目的目标是通过三方面的研究工作，利用新生代火山和沉积岩来表征内华达山脉中部数千万年的景观演变，以确定火山作用和断层作用与构造事件的联系。首先，对古河道中保存的第三纪地层进行详细的测绘、沉积相分析和定年，以了解塞拉利昂中部景观的演变，并将其与该地区其他地区的景观进行比较。这些古河道的源头位于内华达山脉中部，其中的物质向西输送到今天的萨克拉门托山谷。保存在这些古河道中的地层提供了隆起和再切割事件的记录，这些事件可以与构造过程联系起来。该研究项目将验证这样一种观点，即塞拉中部可能发生过三次新生代隆升，这些隆升的时间可能对应于：(1)大约1500万年前弧岩浆活动的开始，(2)大约1000万年前盆地和山脉断裂的开始，以及(3)大约600万年前三联体的到来。其次，火山-火山碎屑岩和侵入岩的构造测绘和定年被用来确定内华达山脉中部山脉前断层的开始年龄、性质以及它是连续的还是偶然的。内华达山脉地块与大盆地其余部分之间的现今至第四纪位移大部分发生在内华达山脉前缘断层的沃克莱恩带（一个约150公里宽的以右侧走滑断层为主的复杂系统，目前约占太平洋-北美板块运动的20-25%）的西部边缘。第三，对内华达山脉中部新近系火山岩和侵入岩中心进行了研究，以了解第三系祖先级联弧的古地理和构造演化。特别是，该项目将探索在内华达山脉的祖先喀斯喀特弧可能发生过三个阶段的火山活动：大约在1400万至1500万年前，900万至1000万年前，以及600万至700万年前。内华达山脉是美国境内最长、最高的山脉，长期以来一直被认为是最年轻的山脉之一，在晚新生代期间，它的东部边缘的断层上有一个坚硬的块体倾斜。然而，最近的研究提出了内华达山脉更复杂的隆起历史，一些人认为这个山脉非常古老。此外，内华达山脉被认为是造山过程中一个基本过程的原型，它是通过岩石圈沉降到地幔中完成的（根部分层）。这个研究项目将提供新的数据，有助于了解这个重要的山脉，并帮助解决一些争议。此外，结果将告知断层的历史在一个人口稠密的地震活动活跃地区，里诺-布里奇波特地区。最后，该项目将使学生参与科学研究，并将促进代表性不足的群体参与地球科学。

The age and uplift history of the Sierra Nevada are currently the subjects of geologic debate The goal of this research project is to characterize the landscape evolution of the central Sierra Nevada over a time period of tens of millions of years by using Cenozoic volcanic and sedimentary rocks in order to determine linkages of volcanism and faulting to tectonic events through a three-fold research effort. First, detailed mapping, sedimentary facies analysis, and dating of Tertiary strata preserved in paleochannels are being used to understand the evolution of the central Sierran landscape and how it compares with that of the rest of the range. These paleochannels had their headwaters in central Sierra Nevada, and material within them was transported westward to the present-day Sacramento Valley. Strata preserved in these paleochannels provide a record of uplift and re-incision events that can be linked to tectonic processes. The research project will test the idea that three episodes of Cenozoic uplift may have occurred in the central Sierra and the timing of these may correspond to the: (1) onset of arc magmatism about15 million years ago, (2) onset of Basin and Range faulting about10 million years ago, and (3) arrival of the triple junction about 6 million years ago. Second, structural mapping and dating of volcanic-volcaniclastic and intrusive rocks are being used to determine the inception age of range-front faulting in the central Sierra Nevada, its nature, and whether it proceeded continuously or episodically. Much of the present-day to Quaternary displacement between the Sierra Nevada block and the rest of the Great Basin is being taken up along the western edge of the Walker Lane belt (an approximately 150 km wide complex system of dominantly right-lateral strike slip faults that currently accommodates about 20-25% of the Pacific-North America plate motion) in the range-front faults of the Sierra Nevada. Third, Neogene volcanic and intrusive rocks centers in the central Sierra Nevada are bieing investigated to understand the paleogeographic and tectonic evolution of the Tertiary Ancestral Cascades arc. In particular, the project will explore the idea that three phrases of volcanism may have occurred in the ancestral Cascades arc of the Sierra Nevada: at about 14-15 million years ago, 9-10 million years ago, and 6-7 million years ago.The Sierra Nevada is the longest and tallest mountain chain in the coterminous U.S. It has also long been considered to be among the youngest, with uplift through Late Cenozoic tilting of a rigid block about faults along its eastern margin. More recent research, however, has proposed a more complex uplift history for the Sierra Nevada, and some have argued that the range is very old. Additionally, the Sierra Nevada is considered the prototype of a fundamental process in mountain building, accomplished by foundering of lithosphere into the Earth's mantle (root delamination). This research project will provide new data that will contribute to the understanding of this important mountain range and help resolve some of these controversies. Furthermore, results will inform the history of faulting in a heavily populated area of active seismicity, the Reno-Bridgeport area. Finally, the project will engage students in scientific research and will foster participation of underrepresented groups in the earth sciences.