VOLCANO MADNESS: Re: [Geology2] 4.8 Ma Age for Inception of the Modern Colorado River

Thursday, December 29, 2011

Re: [Geology2] 4.8 Ma Age for Inception of the Modern Colorado River

For the laypeople here, I googled tectonic extensions, not being familiar with the term...wikipedia has a nice description: http://en.wikipedia.org/wiki/Extensional_tectonics....Allison

From: Lin Kerns <linkerns@gmail.com>
To: Geology2 <geology2@yahoogroups.com>
Sent: Thursday, December 29, 2011 10:17 AM
Subject: [Geology2] 4.8 Ma Age for Inception of the Modern Colorado River

4.8 Ma Age for Inception of the Modern Colorado River

Article Author(s):

Jon Spencer

Introduction

Arizona's Grand Canyon reveals an enormous sequence of rocks that represent more than a third of the 4.5-billion-year age of the Earth. The canyon itself, however, is quite young in comparison, with most or all canyon incision occurring over the past 5 million years according to most interpretations. Careful investigative work has refined this age determination, as reported in this brief article.

Basin and Range tectonic extension

Before arrival of the modern Colorado River, the Mojave and Sonoran Desert region of southwestern North America was subjected to severe tectonic extension. This produced the basin and range topography that we see today in southern and western Arizona, in southeastern California, and in Nevada and western Utah (the Basin and Range tectonic province). Tectonic extension and normal faulting are still occurring in much of Nevada, in the Death Valley and Owens Valley areas of California, and along the Wasatch Front in Utah. Playas and lakes are present in all of these areas because faulting lowers valley floors faster than they can be filled with sediment. When faulting and basin subsidence end, the basins will fill with sediment and drainages will spill over to eventually form integrated stream systems that end at the ocean.

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