Download Crustal Extension

Miocene Extension of the
Southern Death Valley Region
By Burcin Kelez & Anthony Dominguez
Introduction
In southern Death Valley normal and strike-slip faulting
associated with extensional basin formation began less than 15
Ma ago and continues today. This presentation outlines crustal
extension and it’s correlation to magmatism in the southern
Death Valley.
(Calzia et al., 2000).
Figure 1. Lithological and location map of Southern Death Valley Region
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
3000-5000 m of late Proterozoic and Paleozoic miogeoclinal deposits.
•
Most of the Proterozoic and Paleozoic rocks are intruded by Mesozoic and Tertiary
plutons.
•
All of these rocks are unconformably overlain by later Tertiary sediments, volcanic rocks,
and Quaternary alluvial deposits.
(Calzia et al., 2000)
Figure 2. Map showing approximate time of extension of crustal blocks in the Southern Death Valley
Region. FCFZ- Furnace Creek faultzone; KRHH-Kingston Range-Halloran Hills fault; SDVFZSouthern Death Valley fault zone; SHPFZ-Sheephead Pass fault zone (Calzia et al., 2000).
Crustal Extension
•
In the southern Death Valley region crustal extension is developed by a
•
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.
combination of listric faulting, planar normal faults, NW trending right
lateral SS faults, and NE trending left lateral SS faults.
(Calzia et al., 2000)
Kingston Range Detachment
Fault
• The northern segment is the Kingston Range detachment
fault. The dip is shallow at approximately 15°W. It separates
the complex faulted upper plates from the mildly unfaulted
lower plates.
• Extensional faults in the upper plate of the Kingston Range
detachment fault zone include NW trending planar, listric
normal faults and some strike slip faults as well.
• Faulting indicates that the upper plate of the Kingston Range
detachment fault was transported to the SW. This
displacement increases SW as each generation of NW
trending faults added its extension to the upper plate. (Calzia
et al., 2000)
Halloran Hills Detachment
Fault
•
The southern segment is the Halloran Hills detachment fault is
discontinuously exposed along the west side of the Mesquite
Mountains, Clark Mountains, and Mescal Range. It 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.
(Calzia et al., 2000)
Age Constraints of Crustal
Extension
I.
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)
Halloran Hills fault cuts 13.2±.04 Ma latite in the NE Silurian Hills. 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.
e)
Tacopa lake beds may date back to 7 Ma indicating large scale crustal extension in the SDV
region began 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.
(Calzia et al., 2000)
Extension Basins
Topographic expressions of the Late Cenozoic extensional basins
in SDV region
1. The Shadow Valley
2. Valjean Valley named China Ranch basin
Prave, A.R., and McMackin, M.R., 1999
Members of the Shadow Valley Basin
Member IV - youngest
East-tilted cobble to boulder fan deposits
Member III
Fluvial sandstone and conglomerate, lacustrine mudstone, and
conglomerate of volcanic clasts and the first erosional clasts of
the granite of Kingston Peak
Member II
Fanglomerate deposits that interfinger with lacustrine
sediments and rare volcanic ash
Member I - oldest
Carbonate-rich fanglomerate deposits, megabreccias of
carbonate rocks and quartzite, volcanic rocks, and minor
interbedded lacustrine limestone and siltstone
1. The Shadow Valley
Faults
NE-NW trending normal faults cut all four members
Time constraint, cross-cutting relationship
Dip angle 45-75 W, and have 0.5-3.5 km of displacement
K-Ar and 40Ar-39Ar Dating
Volcanic breccia, base of Member I : 13.1 Ma
Volcanic ash, base of Member III : 10.8 Ma
Andesite tuff breccia and biotite, in Member II : ~12.5 Ma
and ~12.3 Ma, respectively
2. Valjean Valley/China Ranch Basin
East-tilted extentional basin
27 km long by 13 km wide, along the north side of Valjean
Valley
Filled with volcanic and sedimentary rocks, named the China
Ranch beds
~ Same age as Members III and IV of the Shadow Valley Basin.
The beds are faulted and folded , their thickness are 500m –
2km.
2. Valjean Valley/China Ranch Basin
The China Ranch beds consist of
Dacite overlain by fanglomerate and lacustrine deposits.
Highly altered dacite uncomformably overlies Amargosa chaos
on the south and east side of Rainbow Mountain
Dacite yields a K-Ar age of 10.3 Ma
Magmatism
 Magmatism used for a time constraint of extension
 Magmatic rocks coeval with Late Cenozoic extension consist
of felsic to mafic plutonic & volcanic rocks in
 Kingston Range,
 Ibex Pass Volcanic field,
 Owlshead Mountains,
 Resting Spring Range, and
 Black mountains
Magmatism
Dating of volcanic and plutonic rocks in the southwestern Great
Basin:
 Plutonic can be seperated into two petrographic suites
• Older, 12-14 Ma, Kingston Peak
• Younger, 10-6.5 Ma, Black Mountains, Owlshead Mtn
 Volcanic rocks associated with rapid extension, 14-5 Ma
Conclusion
 Crustal extension began 13.4–13.1 Ma, occurs different places at
different times
 Oldest extensional fault, Kingston Range detachment fault,
occurred and diplacement increases SW
 Magmatism happened, basalt flows planar
 Fault blocks tilted ~12-9 Ma
 Westward migration of extension
 Undeformed basalt flows & lacustrine deposits suggest extension
stopped 5-7 Ma
References
Calzia, J.P., Ramo, O.T., 2000, Late Cenozoic crustal extension and magmatism.
Southern Death Valley region, California: Geologic Society of America Field
Guide 2, p. 135-164.
Prave, A.R., and McMackin, M.R., 1999, Depositional framework of mid- to late
Miocene strata, Dumont Hills and southern margin Kingston Range:
Implications for the tectonostratigraphic evolution of the southern Death
Valley region, in Special Paper 333: Cenozoic basins of the Death Valley
region, Geological Society of America, p. 259–275.
Wright, L.A., 1984, Evidence For the Westward Migration of Severe Cenozoic
Extension, Southern Great Basin, California, Geological Society of America.