1. Miocene Extension of the Southern Death Valley Region By Burcin Kelez & Anthony Dominguez

2. 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).

3. Figure 1. Lithological and location map of Southern Death Valley Region

4. 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 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 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. 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. 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. All of these rocks are unconformably overlain by later Tertiary sediments, volcanic rocks, and Quaternary alluvial deposits. (Calzia et al., 2000)

5. 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; SDVFZ- Southern Death Valley fault zone; SHPFZ-Sheephead Pass fault zone (Calzia et al., 2000).

6. Crustal Extension 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. 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. 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. 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%. 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. 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. (Calzia et al., 2000)

7. 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. 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. 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) 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)

8. 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. 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. 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. 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)

9. 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)

10. Extension Basins Topographic expressions of the Late Cenozoic extensional basins in SDV region 1. 1.The Shadow Valley 2. 2.Valjean Valley named China Ranch basin

11. Prave, A.R., and McMackin, M.R., 1999

13. 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 40 Ar- 39 Ar 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 1. The Shadow Valley

14. 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

15. 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 2. Valjean Valley/China Ranch Basin

16. 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  Ibex Pass Volcanic field,  Owlshead Mountains,  Resting Spring Range, and  Black mountains

17. 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 Older, 12-14 Ma, Kingston Peak Younger, 10-6.5 Ma, Black Mountains, Owlshead Mtn Younger, 10-6.5 Ma, Black Mountains, Owlshead Mtn  Volcanic rocks associated with rapid extension, 14-5 Ma

18. 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

19. 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. References