Geologic map of the Meadow Valley Mountains, Lincoln and Clark counties, Nevada
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Cited by 4 publications
References 24 publications
The role of low-angle faults in accommodating extension within the upper crust remains controversial because the existence of these faults markedly defies extant continuum theories of how crustal faults form, and once initiated, how they continue to slip. Accordingly, for many proposed examples, basic kinematic problems like slip direction, dip angle while active, and magnitude of offset are keenly debated. A well-known example is the Miocene Mormon Peak detachment and overlying Mormon Peak allochthon of southern Nevada (USA), whose origin and evolution have been debated for several decades. Here, we use geologic mapping in the Meadow Valley Mountains to help define the geometry and kinematics of emplacement of the Mormon Peak allochthon, the hanging wall of the Mormon Peak detachment. Pre-extension structural markers, inherited from the east-vergent Sevier thrust belt of Meso zoic age, are well suited to constrain the geometry and kine matics of the detachment. In this study, we add to these markers a newly mapped Sevier-age monoclinal flexure preserved in the hanging wall of the detachment. The bounding axial surfaces of the flexure can be readily matched to the base and top of the frontal Sevier thrust ramp, which is exposed in the footwall of the detachment to the east in the Mormon Mountains and Tule Springs Hills. Multiple proxies for the slip direction of the detachment, including the mean tilt direction of hanging wall fault blocks, the trend of striations measured on the fault plane, and other structural features, indicate that it is approximately S77°W (257°). Given the observed structural separation lines between the hanging wall and footwall, this slip direction indicates 12-13 km of horizontal displacement on the detachment (14-15 km net slip), lower than a previous estimate of 20-22 km, which was based on erroneous assumptions in regard to the geometry of the thrust system. Based on a new detailed map compilation of the region and recently published low-temperature thermochronologic data, palinspastic constraints also preclude earlier suggestions that the Mormon Peak allochthon is a composite of diachronously emplaced, surficial landslide deposits. Although earlier suggestions that the initiation angle of the detachment in the central Mormon Mountains is ~20°-25° remain valid, the geometry of the Sevier-age monocline in the Meadow Valley Mountains and other structural data suggest that the initial dip of the detachment steepens toward the north beneath the southernmost Clover Mountains, where the hanging wall includes kilometer-scale accumulations of volcanic and volcaniclastic strata.
The role of low-angle faults in accommodating extension within the upper crust remains controversial because the existence of these faults markedly defies extant continuum theories of how crustal faults form, and once initiated, how they continue to slip. Accordingly, for many proposed examples, basic kinematic problems like slip direction, dip angle while active, and magnitude of offset are keenly debated. A well-known example is the Miocene Mormon Peak detachment and overlying Mormon Peak allochthon of southern Nevada (USA), whose origin and evolution have been debated for several decades. Here, we use geologic mapping in the Meadow Valley Mountains to help define the geometry and kinematics of emplacement of the Mormon Peak allochthon, the hanging wall of the Mormon Peak detachment. Pre-extension structural markers, inherited from the east-vergent Sevier thrust belt of Meso zoic age, are well suited to constrain the geometry and kine matics of the detachment. In this study, we add to these markers a newly mapped Sevier-age monoclinal flexure preserved in the hanging wall of the detachment. The bounding axial surfaces of the flexure can be readily matched to the base and top of the frontal Sevier thrust ramp, which is exposed in the footwall of the detachment to the east in the Mormon Mountains and Tule Springs Hills. Multiple proxies for the slip direction of the detachment, including the mean tilt direction of hanging wall fault blocks, the trend of striations measured on the fault plane, and other structural features, indicate that it is approximately S77°W (257°). Given the observed structural separation lines between the hanging wall and footwall, this slip direction indicates 12-13 km of horizontal displacement on the detachment (14-15 km net slip), lower than a previous estimate of 20-22 km, which was based on erroneous assumptions in regard to the geometry of the thrust system. Based on a new detailed map compilation of the region and recently published low-temperature thermochronologic data, palinspastic constraints also preclude earlier suggestions that the Mormon Peak allochthon is a composite of diachronously emplaced, surficial landslide deposits. Although earlier suggestions that the initiation angle of the detachment in the central Mormon Mountains is ~20°-25° remain valid, the geometry of the Sevier-age monocline in the Meadow Valley Mountains and other structural data suggest that the initial dip of the detachment steepens toward the north beneath the southernmost Clover Mountains, where the hanging wall includes kilometer-scale accumulations of volcanic and volcaniclastic strata.
Preliminary geologic map of the Farrier Quadrangle, Clark and Lincoln Counties, Nevada
Altitude, height (h), and thickness (t) of alluvial units on the map are given in feet and inches in order for reader to directly correlate such figures with the topographic contours reading in feet; in text all measurements are in metric units as is standard except references to topographic contours are listed in feet and meters. (2) Localities described in text are indexed to the borders of the quadrangle and to the railroad site of Farrier, except that an unofficial place name, Farrier narrows, is used in reference to the conspicuous canyon of Meadow Valley Wash from 2.5 to 4.0 km north of Farrier. The structural and sedimentary basin of Meadow Valley Wash is herein informally called the Glendale basin for the small town of Glendale at the southern end of the basin in the adjacent Moapa East quadrangle. Recent terrace alluvium (Holocene) Mostly tan silt and sand, but some mainstream gray gravel exposed in low mainstream terraces; tan sandy gravel in low sidestream terraces. Unit is subdivided into mainstream (Meadow Valley Wash, Qrm) and sidestream (Farrier Wash and other sidestream) deposits. Exposed mainstream alluvium is mostly a silt and tine sand, pluvial deposit; in many places covered by or mixed with much reworked eolian sand; dark-gray mainstream gravel is not well exposed, except in the southeastern corner where the gravel is exposed in a large, low terrace (Qrmg); elsewhere, gravel probably more widely underlies the silt and sand. The recent mainstream alluvium forms terraces about 3 m high, and is inset below the young alluvial terrace (Qym) of Meadow Valley Wash ; sidestream terraces are lower but likewise inset. Depositional surface of mainstream terrace is intact, meander channel and bar and swale features are well preserved; no obvious carbonate-enriched soil or associated pavement is recognized Qrm Recent mainstream alluvium Mainstream-terrace alluvium of Meadow Valley Wash. Predominantly silt, sand, and mud and locally some intertongued gravel lenses; the fine-grained sediments were deposited either as a normal overbank, flood-plain deposit of a perennial Meadow Valley Wash, or as a special, climatic-controlled, pluvial, paludal deposit; distinction between these two processes for Meadow Valley Wash has not been studied Qrmg Recent gravel-facies of mainstream alluvium Locally exposed deposit containing abundant, well-sorted, dark-gray, coarse, mainstream gravel; mapped in southeastern corner of quadrangle Qrf Recent alluvium of Farrier Wash Tan and light-gray terrace sand and gravel of Farrier Wash Qrs Recent sidestream alluvium Tan and light gray sidestream-terrace sand and gravel Young terrace alluvium Gate Pleistocene) Tan to gray, silty to sandy gravel, and silt and sand, poorly bedded, moderately sorted; gravel mostly clast supported. Subdivided into mainstream (Meadow Valley Wash) and sidestream (Farrier Wash and other sidestream) deposits, of which the mainstream deposit commonly consists of dark-gray gravel overlain by overbank or pluvial silt, all inset in the erosional valley of Mea...
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