Tectonic Evolution of Death Valley

Abstract

Extension in Death Valley is interpreted as a Basin and Range extension associated with the developing Pacific-North America plate boundary in western North America (Norton 2011), or it may interpreted as the product of a pull-apart basin produced by normal faults trending NW-SE. Here we present supporting evidence that the basins produced in Death Valley are a combination of compressional tectonics related to subduction in the Cretaceous and a series of pull-apart basins produced by NW-SE trending normal faults and strike-slip faults parallel to the SE trending Furnace Creek fault and San Andreas Fault. We present evidence by focusing on the timing and tectonics of the Pahrump Group, Noonday Dolomites, Wood Canyon Fomration, Zabriskie Quartzite, Carrara Formation, and Bonanza King Formation in Death Valley and observing the structural deformation. By using methods such as measuring the trend of faults and structural geology techniques, we can make observations in the field supporting our hypothesis. We focus on the compressional tectonics during the Cretaceous and extensional tectonics during the late Cenozoic of this region.

Introduction

Death Valley is one of many desert basins between mountain ranges in the western region of North America known as the Basin and Range Province (Hunt 1975). The Basin and Range Province includes most of Nevada, western Utah, southeastern California, southern Arizona, southwestern New Mexico and northwestern Mexico with major mountain ranges such as the Snake Range, White Mountains, Panamint Range, Sandia Mountain, and the Tetons. Death Valley itself is relatively young with many a range of dominant features such salt beds, sand dunes, alluvial fans, and mountain ranges. The landscape ranges from being the lowest point in North America, 282 feet below sea level, and easily contains 11,000 feet mountain ranges. Uplift and erosion in the Cretaceous expose the thrusting and compressional tectonics occurring. Around the Miocene, extension due to strike-slip tectonics produce graben structures from detachment faults that are also seen in Death Valley.

Geologic Background

Pahrump Group
Formations deposited about 1200-800 mya (Late Proterozoic) with the three main formations composed of Crystal Springs Formation, Beck Spring Dolomite, and Kingston Peak Formation. Highly metamorphosed outcrops of this group are seen in a belt from the Panamint Mountains.

Noonday Dolomite
The Noonday Dolomite is commonly interpreted as a Neoproterozoic carbonate that formed large buildups along an ancient margin (CORSETTI 2005). It was deposited in marine basins during the Precambrian continental rifting with beds consisting mostly of silty dolomite, stilstone, and stromatolitic dolomite in the upper member and finely crystalline, laminated, and relatively pure dolomite in the lower member.

Wood Canyon Formation
The late Precambrian - Cambrian Wood Canyon Fomration three members ranging from dolomite and limestone in the upper and lower members and quartzite in the middle member. In this formation, there are minor orange-weathering silty dolomite present.

Zabriskie Quartizte
Lower Cambrian Quartzite that is mostly massive and granular. Locally in beds, it is about 6 inches to 2ft thick. Cambrian Zabriskie Quartzite contains mostly massive and granulated quartzite due to shearing.

Carrara Formation
Cambrian period deposition with nine members with alternating siliciclastic and carbonate facies.

Bonanza King Formation
Middle and Upper Cambrian deposition with dolomite and limestone members present.

Most of the beds observed in Death Valley are the beds noted above. They consist mostly of carbonates such as limestones and dolomites, or meteamorphosed carbonates such as quartzite. During the Late Precambrian to Early Cambrian, when most of the beds were deposited, western North America was a passive margin with latitudes near the equator. During this time period, deposition of carbonates were possible due to the continental shelf and passive margin, as well as the warmer climates making it ideal for reef production. Hence, fossils such as stromatolites can be found in these carbonate beds, or the carbonate platform. Over time, the accumulation and deposition of these carbonates occured on this passive margin of Western North America.

Observations

Late Precambrian to Early Cambrian

Deposition of sedimentary rocks that are easily 15km thick accumulated on the western North America during its passive margin from the Late Proterozoic to Early Paleozoic. Exposures of carbonate rocks from the Pahrump group is found on the footwall of the major detachment fault in the Mosiac Canyon. The lower part of the Mosiac Canyon also contains exposures of Noonday dolomites and laminated rocks resulting from high strain. In the upper part of Mosiac canyon, the canyon opens and major detachment faults crop out on the East above mylonitic Pahrump group. This is evident by a zone of sheared green chlorite 30m thick along with 20m of black fault gouge and 20m of overlain dolostone. The rocks on the northeast side of the valley mark the detachment, with projecting lineated shear surfaces. Evidence of irregularly folded orange-weathering Wood Canyon dolostone, Zabriskie Quartzite, and Carrara dolomite appear to be repeatedly thrusting higher up in the South. This is also evident at the Natural Bridge and Badwater basin where there are Precambrian gneiss and marble exposures in the footwall. Alongside of the Badwater fault, young fanglomerates are faulted against Neoproterozoic Noonday dolomite. The fault gouge contains extensional tensile fractures with 254o gypsum fill lineations, gouge fabrics, and Riedal shears. The Riedel shears are about 15-20o. The overall trend of the Badwater fault is E-W trending.

Miocene
We observe extensional tectonics in the lower part of Mosiac Canyon where there are laminated rocks with high strain. The rocks are laminated with evidence of feldpsar sigma prophyroclasts from shearing found within carbonate rocks. Normal conjugate faults are also found in the lower part of Mosiac Canyon. Near the Badwater basin, evidence of detachment faults are seen as the Badwater fault cuts across an alluvial fan deposit with apparent fault scarps. Mormon Point Turtlebacks have a plunging geometry with a basaltic cinder cone to the SW where part of the cone is displaced by a fault cutting across it.