scholarly journals Constraints on rock uplift in the eastern Transverse Ranges and northern Peninsular Ranges and implications for kinematics of the San Andreas fault in the Coachella Valley, California, USA

Geosphere ◽  
2020 ◽  
Vol 16 (3) ◽  
pp. 723-750
Author(s):  
James A. Spotila ◽  
Cody C. Mason ◽  
Joshua D. Valentino ◽  
William J. Cochran
Keyword(s):  
San Andreas Fault ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Fault System ◽  
Published Data ◽  
Strain Partitioning ◽  
San Bernardino Mountains ◽  
Coachella Valley ◽  
San Andreas ◽  
Peninsular Ranges

Abstract The nexus of plate-boundary deformation at the northern end of the Coachella Valley in southern California (USA) is complex on multiple levels, including rupture dynamics, slip transfer, and three-dimensional strain partitioning on nonvertical faults (including the San Andreas fault). We quantify uplift of mountain blocks in this region using geomorphology and low-temperature thermochronometry to constrain the role of long-term vertical deformation in this tectonic system. New apatite (U-Th)/He (AHe) ages confirm that the rugged San Jacinto Mountains (SJM) do not exhibit a record of rapid Neogene exhumation. In contrast, in the Little San Bernardino Mountains (LSBM), rapid exhumation over the past 5 m.y. is apparent beneath a tilted AHe partial retention zone, based on new and previously published data. Both ranges tilt away from the Coachella Valley and have experienced minimal denudation from their upper surface, based on preservation of weathered granitic erosion surfaces. We interpret rapid exhumation at 5 Ma and the gentle tilt of the erosion surface and AHe isochrons in the LSBM to have resulted from rift shoulder uplift associated with extension prior to onset of transpression in the Coachella Valley. We hypothesize that the SJM have experienced similar rift shoulder uplift, but an additional mechanism must be called upon to explain the pinnacle-like form, rugged escarpment, and topographic disequilibrium of the northernmost SJM massif. We propose that this form stems from erosional resistance of the Peninsular Ranges batholith relative to more-erodible foliated metamorphic rocks that wrap around it. Our interpretations suggest that neither the LSBM nor SJM have been significantly uplifted under the present transpressive configuration of the San Andreas fault system, but instead represent relict highs due to previous tectonic and erosional forcing.

The San Andreas Fault Zone Drilling Project: Scientific Objectives and Technological Challenges

1995 ◽  
Vol 117 (4) ◽  
pp. 263-270 ◽  
Author(s):  
S. H. Hickman ◽  
L. W. Younker ◽  
M. D. Zoback ◽  
G. A. Cooper
Keyword(s):  
Fault Zone ◽  
San Andreas Fault ◽  
Fractured Rock ◽  
Fluid Pressure ◽  
Plate Boundary ◽  
Fault System ◽  
Earthquake Activity ◽  
Scientific Drilling ◽  
San Andreas ◽  
San Andreas Fault System

We are leading a new international initiative to conduct scientific drilling within the San Andreas fault zone at depths of up to 10 km. This project is motivated by the need to understand the physical and chemical processes operating within the fault zone and to answer fundamental questions about earthquake generation along major plate-boundary faults. Through a comprehensive program of coring, fluid sampling, downhole measurements, laboratory experimentation, and long-term monitoring, we hope to obtain critical information on the structure, composition, mechanical behavior and physical state of the San Andreas fault system at depths comparable to the nucleation zones of great earthquakes. The drilling, sampling and observational requirements needed to ensure the success of this project are stringent. These include: 1) drilling stable vertical holes to depths of about 9 km in fractured rock at temperatures of up to 300°C; 2) continuous coring and completion of inclined holes branched off these vertical boreholes to intersect the fault at depths of 3, 6, and 9 km; 3) conducting sophisticated borehole geophysical measurements and fluid/rock sampling at high temperatures and pressures; and 4) instrumenting some or all of these inclined core holes for continuous monitoring of earthquake activity, fluid pressure, deformation and other parameters for periods of up to several decades. For all of these tasks, because of the overpressured clay-rich formations anticipated within the fault zone at depth, we expect to encounter difficult drilling, coring and hole-completion conditions in the region of greatest scientific interest.

scholarly journals Chlorine-36/beryllium-10 burial dating of alluvial fan sediments associated with the Mission Creek strand of the San Andreas Fault system, California, USA

2019 ◽  
Author(s):  
Greg Balco ◽  
Kimberly Blisniuk ◽  
Alan Hidy
Keyword(s):  
San Andreas Fault ◽  
Alluvial Fan ◽  
Fault System ◽  
Middle Pleistocene ◽  
Slip Rates ◽  
San Bernardino Mountains ◽  
Production Ratio ◽  
San Andreas ◽  
San Andreas Fault System ◽  
Middle And Late Pleistocene

Abstract. We apply cosmogenic-nuclide burial dating using the 36Cl-in-K-feldspar/10Be-in-quartz pair in fluvially transported granitoid clasts to determine the age of alluvial sediment displaced by the Mission Creek strand of the San Andreas Fault in southern California. Because the half-lives of 36Cl and 10Be are more different than those of the commonly used 26Al/10Be pair, 36Cl/10Be burial dating should be applicable to sediments in the range ca. 0.2–0.5 Ma that are too young to be accurately dated with the 26Al/10Be pair, and should theoretically be more precise for middle and late Pleistocene sediments in general. However, using the 36Cl/10Be pair is more complex because the 36Cl/10Be production ratio varies with the chemical composition of each sample. We use 36Cl/10Be measurements in samples of granodiorite exposed at the surface at present to validate calculations of the 36Cl/10Be production ratio in this lithology, and then apply this information to determine the burial age of alluvial clasts of the same lithology. This particular field area presents the additional obstacle to burial dating (which is not specific to the 36Cl/10Be pair, but would apply to any) that most buried alluvial clasts are derived from extremely rapidly eroding parts of the San Bernardino Mountains and have correspondingly extremely low nuclide concentrations, the majority of which most likely derives from nucleogenic (for 36Cl) and post-burial production. Although this precludes accurate burial dating of many clasts, data from surface and subsurface samples with higher nuclide concentrations, originating from lower-erosion-rate source areas, show that upper Cabezon Formation alluvium is 260 ka. This is consistent with stratigraphic age constraints as well as independent estimates of long-term fault slip rates, and highlights the potential usefulness of the 36Cl/10Be pair for dating upper and middle Pleistocene clastic sediments.

scholarly journals Chlorine-36∕beryllium-10 burial dating of alluvial fan sediments associated with the Mission Creek strand of the San Andreas Fault system, California, USA

Geochronology ◽  
2019 ◽  
Vol 1 (1) ◽  
pp. 1-16
Author(s):  
Greg Balco ◽  
Kimberly Blisniuk ◽  
Alan Hidy
Keyword(s):  
San Andreas Fault ◽  
Alluvial Fan ◽  
Fault System ◽  
Middle Pleistocene ◽  
Slip Rates ◽  
San Bernardino Mountains ◽  
Production Ratio ◽  
San Andreas ◽  
San Andreas Fault System ◽  
Middle And Late Pleistocene

Abstract. We apply cosmogenic-nuclide burial dating using the 36Cl-in-K-feldspar∕10Be-in-quartz pair in fluvially transported granitoid clasts to determine the age of alluvial sediment displaced by the Mission Creek strand of the San Andreas Fault in southern California. Because the half-lives of 36Cl and 10Be are more different than those of the commonly used 26Al∕10Be pair, 36Cl∕10Be burial dating should be applicable to sediments in the range ca. 0.2–0.5 Ma, which is too young to be accurately dated with the 26Al∕10Be pair, and should be more precise for Middle and Late Pleistocene sediments in general. However, using the 36Cl∕10Be pair is more complex because the 36Cl∕10Be production ratio varies with the chemical composition of each sample. We use 36Cl∕10Be measurements in samples of granodiorite exposed at the surface at present to validate calculations of the 36Cl∕10Be production ratio in this lithology, and then we apply this information to determine the burial age of alluvial clasts of the same lithology. This particular field area presents the additional obstacle to burial dating (which is not specific to the 36Cl∕10Be pair, but would apply to any) that most buried alluvial clasts are derived from extremely rapidly eroding parts of the San Bernardino Mountains and have correspondingly extremely low nuclide concentrations, the majority of which most likely derive from nucleogenic (for 36Cl) and post-burial production. Although this precludes accurate burial dating of many clasts, data from surface and subsurface samples with higher nuclide concentrations, originating from lower-erosion-rate source areas, show that the age of upper Cabezon Formation alluvium is 260 ka. This is consistent with stratigraphic age constraints as well as independent estimates of long-term fault slip rates, and it highlights the potential usefulness of the 36Cl∕10Be pair for dating Upper and Middle Pleistocene clastic sediments.

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