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Miocene Crustal Extension in the Southern Death Valley Region.
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Introduction
In southern Death Valley normal and strike-slip faulting associated with extensional basin
formation began less than 15 Ma ago and continues today. Geologic features such as: granitic
plutons, dikes, sills, and volcanic fields are concurrent with extension (Calzia et al., 2000). This
presentation outlines crustal extension and it’s correlation to magmatism in the southern Death
Valley.
Location map. Figure 1.
Figure 1. Lithological and location map of Southern Death Valley Region
Wright et al., 1984.
1. Detailed mapping & dating of volcanic and plutonic rocks in the southwestern Great
Basin indicate that maximum crustal extension, ascribable to the Basin and Range
event, occurred at different places in different time intervals, and migrated
westward.
2. K/Ar dating of volcanic rocks. Different times of westward extension
 Kingston Range: Extension ended prior to 14 mya (million years ago).
 Resting Springs Range: Tilting post-dates 12 myo(million year old) dacitic flows & predates 9 myo rhyolitic ash-flow tuff
 Greenwater Range/Black Mountains: volcanic and sedimentary units 9-8 myo dip >60
degrees where 4-5 myo basalt flows dip gently.
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Geologic Setting.
 The southern Death Valley Region is bounded on the west by the Panamint Range and
the south by the Providence Mountains and New York Mountains. See Figure 1.
 The pre-Cenozoic stratigraphy includes Early Proterozoic cratonic rocks and Middle
Proterozoic to Paleozoic sedimentary deposits.
 The Pahrump Group, which is Middle Proterozoic, lies unconformably on the cratonic
rocks and contains about 2100 meters. It consists of the Crystal Springs Formation, Beck
Spring Dolomite, and Kingston Peak Formation. The Pahrump Group is overlain by 30005000 m of late Proterozoic and Paleozoic miogeoclinal deposits.
 The Crystal Springs is intruded by 1068 Ma and 1087 Ma diabase sills.
 Most of the Proterozoic and Paleozoic rocks are intruded by Mesozoic and Tertiary
plutons.
 All of these rocks are unconformably overlain by later Tertiary sedimentary, volcanic
rocks, and Quaternary alluvial deposits.
Crustal Extension
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In the southern Death Valley region crustal extension is developed by a combination of
listric faulting, planar normal faults, NW trending right lateral SS faults, and NE trending
left lateral SS faults.
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The normal faults dip 50˚-30˚ W and flatten out at depths not to exceed 5 km. These
depths suggest that the deposits are sliding off of cratonic rocks into Tertiary Basins
formed during extension (Calzia et al., 2000). The faults are spread more apart in the
deeper crust, 5 to 15 km, than they are in the shallow crust, less than 5 km.
Estimates of the crustal extension in the SDV region range from 30-50%.
The oldest Late Cenozoic extensional fault is the Kingston Range-Halloran Hills
detachment fault system. It defines the east boundary of the Death Valley regime and is
divided into northern and southern segments.
A. The northern segment is the Kingston Range detachment fault. It dips as much
as 15°W and separates the complexly faulted upper plates from the relatively
unfaulted lower plates. Extensional faults in the upper plate of the Kingston
Range detachment fault zone include NW trending planar and listric normal
faults. As well as NE trending steep SS faults and oblique slip faults dipping to
the SW. NE trending faults terminate at the detachment fault. Consistent tear
faults indicate that the upper plate of the Kingston Range detachment fault
were transported to the SW. That displacement increases SW as each
generation of NW trending faults added its extension to the upper plate.
Maximum horizontal displacement along the NE most faults is about 1-2 km and
cumulative horizontal displacement in the upper plate is about 6 km.
B. The southern segment is the Halloran Hills detachment fault which is
discontinuously exposed along the west side of the Mesquite Mountains, Clark
Mountains, and Mescal Range. This is best exposed at Mesquite Pass and the
Mescal Range. Regional geologic relations show that rocks in the HW were
transported 5-9 km to the SW during the last two phases of westward sliding. A
graben in the HW consist of rock avalanche deposits and blocks cut by channel
conglomerate. An allochthon of highly brecciated Paleozoic carbonate rocks are
representative of this fault. Cross cutting relations suggest the allochthon was
displaced approximately 1.5 km during at least two episodes of faulting. The
extremely brittle character of the deformation suggest that the deformation
took place during Cenozoic time.
Cross cutting relations constrain the age of crustal extension in the SDV region.
A. The Kingston Range cuts 16 Ma ash and is deformed by 12.4 Ma granite of
Kingston Peak.
B. 12.5 Ma syntectonic andesite flows are present in the upper plate of this
detachment fault.
C. The Halloran Hills detachment fault cuts a 13.4 Ma felsic sill. 13.1 Ma volcanic
breccia was deposited on the subsiding HW of this fault.
D. A low angle fault associated with the Halloran Hills fault cuts 13.2±.04 Ma latite
in the NE Silurian Hills. Sub-horizontal basalt flows (K/Ar ages of 4.48 & 5.12
Ma) and the underformed Tacopa lake beds unconformably overlie east tilted
strata related to crustal extension. Based on data the Tacopa lake beds may
date back to 7 Ma indicating large scale crustal extension in the SDV region
began south of the Kingston Range but north of the Mescal Range and Silurian
Hills between 13.4 and 13.1 Ma and migrated northward with time. Extension
stopped in this region between 5 and 7 Ma but continues west and north of the
Death Valley graben to the present day.