Detrital sanidine dating coupled with magnetostratigraphy indicates that the Colorado River was first integrated from the Colorado Plateau to the proto-Gulf of California at least half a million years later than previously argued. In Cottonwood Valley, 40Ar/39Ar dating of a 5.37 Ma ash in pre-Colorado River axial-basin deposits plus magnetostratigraphic analyses indicate that the overlying Bouse Formation, which records arrival of the Colorado River, was deposited after the beginning of the Thvera subchron, which started at 5.24 Ma. Detrital sanidine in the Bullhead Alluvium, the first coarse-grained aggradational package of the Colorado River, indicates a maximum depositional age of 4.6 Ma for that unit in the same area. At Split Mountain Gorge, new detrital sanidine dating coupled with previously published magnetostratigraphy and detrital zircon dating of Imperial Group sediments indicate that the first Colorado River sediment arrived at the proto-Gulf of California between 4.8 and 4.63 Ma (during the C3n.2r subchron), not at 5.3 Ma as has been previously proposed. The new geochronology supports models for rapid downward integration of this continental-scale river system extending its reach from Cottonwood Valley after 5.24 Ma to the opening Gulf of California between 4.8 and 4.6 Ma. This is consistent with the previously dated 5.0-4.9 Ma Lawlor tuff interbedded in the Bouse Formation at the highest levels in the Blythe basin, which records the last filling of that basin prior to integration of the river system to the proto-Gulf of California. Additionally, the data suggest there was little or no hiatus between integration of the Colorado River, incision into the siliciclastic Bouse Formation, and initial deposition of the Bullhead Alluvium, which seems to be a response to rapid profile changes caused by integration.
Abstract The evolution of strain in nascent continental plate boundaries commonly involves distributed deformation and transitions between different styles of deformation as the plate boundary matures. Distributed NW-striking faults, many with km-scale right-lateral separation, are prevalent near Blythe, California, and have been variably interpreted to have accommodated either Middle Miocene NE-SW extension as normal faults or Late Miocene to Pliocene dextral shear as strike-slip faults. However, with poor timing and kinematic constraints, it is unclear how these faults relate to known domains of Neogene deformation and the evolution of the Pacific–NorthAmerica plate boundary. We present kinematic data (n = 642 fault planes, n = 512 slickenlines) that demonstrate that these faults dominantly dip steeply northeast; ~96% of measured faults record normal, dextral, or oblique dextral-normal kinematics that likely reflect a gradational transition between normal and dextral oblique kinematic regimes. We constrain fault timing with 11.7 Ma and 7.0 Ma 40Ar/39Ar dates of rocks cut by faults, and laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of calcite mineralized during oblique dextral faulting that demonstrates fault slip at ca. 10–7 Ma and perhaps as late as ca. 4 Ma. This Late Miocene dextral oblique faulting is best compatible with a documented regional transition from Early to Middle Miocene NE-directed extension during detachment fault slip to subsequent NW-directed dextral shear. We estimate 11–38 km of cumulative dextral slip occurred across a 50-km-wide zone from the Palen to Riverside mountains, including up to 20 km of newly documented dextral shear that may partly alleviate the regional discrepancy of cumulative dextral shear along this part of the Late Miocene Pacific–North America plate boundary.
Research Article| November 01, 2007 40Ar/39Ar and field studies of Quaternary basalts in Grand Canyon and model for carving Grand Canyon: Quantifying the interaction of river incision and normal faulting across the western edge of the Colorado Plateau Karl E. Karlstrom; Karl E. Karlstrom 1Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar Ryan S. Crow; Ryan S. Crow 1Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar Lisa Peters; Lisa Peters 2New Mexico Bureau of Geology and Mineral Technology, Geochronology Lab, 801 Leroy Place, New Mexico Institute of Technology, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar William McIntosh; William McIntosh 2New Mexico Bureau of Geology and Mineral Technology, Geochronology Lab, 801 Leroy Place, New Mexico Institute of Technology, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Jason Raucci; Jason Raucci 3Department of Geology, 4099, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for other works by this author on: GSW Google Scholar Laura J. Crossey; Laura J. Crossey 4Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA Search for other works by this author on: GSW Google Scholar Paul Umhoefer; Paul Umhoefer 5Department of Geology, 4099, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for other works by this author on: GSW Google Scholar Nelia Dunbar Nelia Dunbar 6New Mexico Bureau of Geology and Mineral Technology, Geochronology Lab, 801 Leroy Place, New Mexico Institute of Technology, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Karl E. Karlstrom 1Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA Ryan S. Crow 1Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA Lisa Peters 2New Mexico Bureau of Geology and Mineral Technology, Geochronology Lab, 801 Leroy Place, New Mexico Institute of Technology, Socorro, New Mexico 87801, USA William McIntosh 2New Mexico Bureau of Geology and Mineral Technology, Geochronology Lab, 801 Leroy Place, New Mexico Institute of Technology, Socorro, New Mexico 87801, USA Jason Raucci 3Department of Geology, 4099, Northern Arizona University, Flagstaff, Arizona 86011, USA Laura J. Crossey 4Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA Paul Umhoefer 5Department of Geology, 4099, Northern Arizona University, Flagstaff, Arizona 86011, USA Nelia Dunbar 6New Mexico Bureau of Geology and Mineral Technology, Geochronology Lab, 801 Leroy Place, New Mexico Institute of Technology, Socorro, New Mexico 87801, USA Publisher: Geological Society of America Received: 09 Mar 2007 Revision Received: 22 Jun 2007 Accepted: 25 Jun 2007 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 The Geological Society of America, Inc. GSA Bulletin (2007) 119 (11-12): 1283–1312. https://doi.org/10.1130/0016-7606(2007)119[1283:AAFSOQ]2.0.CO;2 Article history Received: 09 Mar 2007 Revision Received: 22 Jun 2007 Accepted: 25 Jun 2007 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Karl E. Karlstrom, Ryan S. Crow, Lisa Peters, William McIntosh, Jason Raucci, Laura J. Crossey, Paul Umhoefer, Nelia Dunbar; 40Ar/39Ar and field studies of Quaternary basalts in Grand Canyon and model for carving Grand Canyon: Quantifying the interaction of river incision and normal faulting across the western edge of the Colorado Plateau. GSA Bulletin 2007;; 119 (11-12): 1283–1312. doi: https://doi.org/10.1130/0016-7606(2007)119[1283:AAFSOQ]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract 40Ar/39Ar dates on basalts of Grand Canyon provide one of the best records in the world of the interplay among volcanism, differential canyon incision, and neotectonic faulting. Earlier 40K/40Ar dates indicated that Grand Canyon had been carved to essentially its present depth before 1.2 Ma. But new 40Ar/39Ar data cut this time frame approximately in half; new ages are all <723 ka, with age probability peaks at 606, 534, 348, 192, and 102 ka. Strategic sampling of basalts provides a semicontinuous record for deciphering late Quaternary incision and fault-slip rates and indicates that basalts flowed into and preserved a record of a progressively deepening bedrock canyon.The Eastern Grand Canyon block (east of Toroweap fault) has bedrock incision rates of 150–175 m/Ma over approximately the last 500 ka; western Grand Canyon block (west of Hurricane fault) has bedrock incision rates of 50–75 m/Ma over approximately the last 720 ka. Fault displacement rates are 97–106 m/Ma on the Toroweap fault (last 500–600 ka) and 70–100 m/Ma on the Hurricane fault (last 200–300 ka). As the river crosses each fault, the apparent incision rate is lowest in the immediate hanging wall, and this rate, plus the displacement rate, is sub-equal to the incision rate in the footwall. At the reach scale, variation in apparent incision rates delineates ∼100 m/Ma of cumulative relative vertical lowering of the western Grand Canyon block relative to the eastern block and 70–100 m of slip accommodated by formation of a hanging-wall anticline.Data from the Lake Mead region indicate that our refined fault-dampened incision model has operated over the last 6 Ma. Bedrock incision rate has been 20–30 m/Ma in the lower Colorado River block in the last 5.5 Ma, and displacement on the Wheeler fault has resulted in both lowering of the Lower Colorado River block and formation of a hanging-wall anticline of the 6-Ma Hualapai Limestone. In modeling long-term incision history, extrapolation of Quaternary fault displacement and incision rates linearly back 6 Ma only accounts for approximately two-thirds of eastern and approximately one-third of western Grand Canyon incision. This "incision discrepancy" for carving Grand Canyon is best explained by higher rates during early (5- to 6-Ma) incision in eastern Grand Canyon and the existence of Miocene paleocanyons in western Grand Canyon.Differential incision data provide evidence for relative vertical displacement across Neogene faults of the Colorado Plateau-Basin and Range transition, a key data set for evaluating uplift and incision models. Our data indicate that the Lower Colorado River block has lowered 25–50 m/Ma (150–300 m) relative to the western Grand Canyon block and 125–150 m/Ma (750–900 m) relative to the eastern Grand Canyon block in 6 Ma. The best model explaining the constrained reconstruction of the 5- to 6-Ma Colorado River paleoprofile, and other geologic data, is that most of the 750–900 m of relative vertical block motion that accompanied canyon incision was due to Neogene surface uplift of the Colorado Plateau. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
This paper documents a multi-stage incision and denudation history for the Little Colorado River (LCR) region of the southwestern Colorado Plateau over the past 70 Ma. The first two pulses of denudation are documented by thermochronologic data. Differential Laramide cooling of samples on the Mogollon Rim suggests carving of 70–30 Ma paleotopography by N- and E-flowing rivers whose pathways were partly controlled by strike valleys at the base of retreating Cretaceous cliffs. A second pulse of denudation is documented by apatite (U-Th)/He dates and thermal history models that indicate a broad LCR paleovalley was incised 25–15 Ma by an LCR paleoriver that flowed northwest and carved an East Kaibab paleovalley across the Kaibab uplift.
Additional details on methods, summary of previous Ar/Ar dating relevant to the timing of Colorado River integration, sample locations, and full analytical results.<br>
