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Full-Text Articles in Physical Sciences and Mathematics
Exhumation Of The Southern Sierra Nevada–Eastern Tehachapi Mountains Constrained By Low-Temperature Thermochronology: Implications For The Initiation Of The Garlock Fault, Ann Blythe, N Longinotti
Exhumation Of The Southern Sierra Nevada–Eastern Tehachapi Mountains Constrained By Low-Temperature Thermochronology: Implications For The Initiation Of The Garlock Fault, Ann Blythe, N Longinotti
Ann Blythe
New apatite and zircon fission-track and apatite (U-Th)/He data from nine samples collected on a north-south transect across the southern Sierra Nevada–eastern Tehachapi Mountains constrain the cooling and exhumation history over the past ∼70 m.y. The four northernmost samples yielded zircon and apatite fission-track ages of ca. 70 Ma, indicating rapid cooling from ∼250 °C to <60 °C (6–8 km of exhumation) at that time. Four of the five southernmost samples yielded slightly younger zircon fission-track ages (57–46 Ma) and apatite fission-track ages (21–18 Ma); the fifth southern sample (from a lower elevation) yielded an apatite fission-track age of ca. 11 Ma. Eight of the nine samples yielded apatite (U-Th)/He ages; these ranged from 60 to 9 Ma, with the youngest ages from the southernmost samples. Inverse thermal history models developed from the data reveal two major stages of cooling for the area, with an initial major cooling event ending at ca. 70 Ma, followed by 50 m.y. of thermal stasis and a second major cooling event beginning at 20 Ma and continuing to the present. The data are consistent with northward-directed tilting and exhumation beginning at 20 Ma, probably as the result of north-south extension in the Mojave Desert on an early strand of the Garlock fault with down-to-the-south offset. A third minor phase of rapid exhumation beginning at ca. 10 Ma is suggested by the data; this may indicate the beginning of left-lateral slip on the Garlock fault.
Dating Of Major Normal Fault Systems Using Thermochronology: An Example From The Raft River Detachment, Basin And Range, Western United States, Michael Wells, Lawrence Snee, Ann Blythe
Dating Of Major Normal Fault Systems Using Thermochronology: An Example From The Raft River Detachment, Basin And Range, Western United States, Michael Wells, Lawrence Snee, Ann Blythe
Ann Blythe
Application of thermochronological techniques to major normal fault systems can resolve the timing of initiation and duration of extension, rates of motion on detachment faults, timing of ductile mylonite formation and passage of rocks through the crystal-plastic to brittle transition, and multiple events of extensional unroofing. Here we determine the above for the top-to-the-east Raft River detachment fault and shear zone by study of spatial gradients in 40Ar/39Ar and fission track cooling ages of footwall rocks and cooling histories and by comparison of cooling histories with deformation temperatures. Mica 40Ar/39Ar cooling ages indicate that extension-related cooling began at ∼25–20 Ma, …
Constraints On Exhumation And Extensional Faulting In Southwestern Nevada And Eastern California, U.S.A., From Zircon And Apatite Thermochronology, David Ferrill, Alan Morris, John Stamatakos, Deborah Waiting, Raymond Donelick, Ann Blythe
Constraints On Exhumation And Extensional Faulting In Southwestern Nevada And Eastern California, U.S.A., From Zircon And Apatite Thermochronology, David Ferrill, Alan Morris, John Stamatakos, Deborah Waiting, Raymond Donelick, Ann Blythe
Ann Blythe
Eastern California and southwestern Nevada represent an area of Tertiary and Quaternary extensional and dextral transtensional deformation. We used zircon and apatite fission-track thermochronology to study the distribution and timing of tectonic exhumation resulting from extensional and transtensional detachment faulting in this area. Sampling efforts were focused on Paleozoic and Precambrian clastic sedimentary and metasedimentary rocks. Sixty-nine new apatite and zircon fission-track cooling ages from 50 samples, analyzed in conjunction with published fission-track data from the region, indicate a distinct population of young (Miocene) fission-track ages and a population of irregularly distributed older (pre-Miocene) fission-track ages. Miocene (young population) fission-track …
Evolution Of The Kangmar Dome, Southern Tibet: Structural, Petrologic, And Thermochronologic Constraints, Jeffrey Lee, Bradley Hacker, William Dinklage, Yu Wang, Phillip Gans, Andrew Calvert, Ann Blythe, William Mcclelland
Evolution Of The Kangmar Dome, Southern Tibet: Structural, Petrologic, And Thermochronologic Constraints, Jeffrey Lee, Bradley Hacker, William Dinklage, Yu Wang, Phillip Gans, Andrew Calvert, Ann Blythe, William Mcclelland
Ann Blythe
Structural, thermobarometric, and thermochronologic investigations of the Kangmar Dome, southern Tibet, suggest that both extensional and contractional deformational histories are preserved within the dome. The dome is cored by an orthogneiss which is mantled by staurolite + kyanite zone metasedimentary rocks; metamorphic grade dies out up section and is defined by a series of concentric kyanite-in, staurolite-in, garnet-in, and chloritoid-in isograds. Three major deformational events, two older penetrative events and a younger doming event, are preserved. The oldest event, D1, resulted in approximately E-W trending tight to isoclinal folds of bedding with an associated moderately to steeply north dipping axial …
Mountain Building Across A Lithospheric Boundary During Arc Construction: The Cretaceous Peninsular Ranges Batholith In The Sierra San Pedro Martir Of Baja California, Mexico, K Schmidt, S Paterson, Ann Blythe, C Kopf
Mountain Building Across A Lithospheric Boundary During Arc Construction: The Cretaceous Peninsular Ranges Batholith In The Sierra San Pedro Martir Of Baja California, Mexico, K Schmidt, S Paterson, Ann Blythe, C Kopf
Ann Blythe
The Jura-Cretaceous Peninsular Ranges batholith (PRB) of Southern and Baja California contains a remarkable example of variation in crustal composition and structure across a batholith-parallel lithospheric-scale discontinuity. This lithospheric boundary between western oceanic-floored and eastern continental-floored crust influenced contractional deformation, arc magmatism, and differential exhumation of western and eastern zones in the batholith during its evolution. In the Sierra San Pedro Martir of Baja California, Mexico, a ca. 20 km wide, doubly vergent fan structure occurs across the PRB basement transition that consists of inward-dipping mylonite thrust sheets on the sides of the fan that gradually transition to a steeply-dipping …
Plio-Quaternary Exhumation History Of The Central Nepalese Himalaya: 2. Thermo-Kinematic Model Of Thermochronometer Age Prediction Model, David Whipp Jr, Todd Ehlers, Ann Blythe, Katharine Huntington, Kip Hodges, Douglas Burbank
Plio-Quaternary Exhumation History Of The Central Nepalese Himalaya: 2. Thermo-Kinematic Model Of Thermochronometer Age Prediction Model, David Whipp Jr, Todd Ehlers, Ann Blythe, Katharine Huntington, Kip Hodges, Douglas Burbank
Ann Blythe
[1] In the Himalaya and other active convergent orogens, linear relationships between thermochronometer sample age and elevation are often used to estimate long-term exhumation rates. In these regions, high-relief topography and nonvertical exhumation pathways may invalidate such one-dimensional (1-D) interpretations and lead to significant errors. To quantify these errors, we integrate apatite fission track (AFT) ages from the central Himalaya with a 3-D coupled thermokinematic model, from which sample cooling ages are predicted using a cooling-rate-dependent algorithm. By changing the slip partitioning between faults near the Main Central thrust and the Main Frontal thrust system at the Himalayan range front, …
Climate Change And Late Pliocene Acceleration Of Erosion In The Himalaya, Katharine Huntington, Ann Blythe, Kip Hodges
Climate Change And Late Pliocene Acceleration Of Erosion In The Himalaya, Katharine Huntington, Ann Blythe, Kip Hodges
Ann Blythe
Studies of active mountain ranges suggest that atmospheric and geodynamic processes may be strongly coupled through erosion — a hypothesis that has led to a debate over the relative importance of climate and far-field tectonic forcing in influencing erosion. We addressed this debate by developing the detailed long-term erosional history of a transect in the central Annapurna Range of Nepal for comparison with the climate and tectonic forcing histories of the region. Patterns of apatite fission-track and muscovite 40Ar/39Ar apparent ages with elevation indicate a five-fold increase in apparent erosion rate between 2.5 and 0.9 Ma ago. The time frame …
Climatic Forcing Of Erosion, Landscape, And Tectonics In The Bhutan Himalayas, Djordje Grujic, Isabelle Coutand, Bodo Bookhagen, Stéphane Bonnet, Ann Blythe, Chris Duncan
Climatic Forcing Of Erosion, Landscape, And Tectonics In The Bhutan Himalayas, Djordje Grujic, Isabelle Coutand, Bodo Bookhagen, Stéphane Bonnet, Ann Blythe, Chris Duncan
Ann Blythe
A fundamental objective in studies of climate-erosion-tectonics coupling is to document convincing correlation between observable indicators of these processes on the scale of a mountain range. The eastern Himalayas are a unique range to quantify the contribution of tectonics and climate to long-term erosion rates, because uniform and steady tectonics have persisted for several million years, while monsoonal precipitation patterns have varied in space and time. Specifically, the rise of the Shillong plateau, the only orographic barrier in the Himalayan foreland, has reduced the mean annual precipitation downwind in the eastern Bhutan Himalaya at the Miocene-Pliocene transition. Apatite fission-track (AFT) …
Overview Of Radiometric Ages In Three Allochthonous Belts Of Northern Venezuela: Old Ones, New Ones, And Their Impact On Regional Geology, V Sisson, H Lallemant, M Ostos, Ann Blythe, L Snee, P Copeland, J Wright, R Donelick, L Guth
Overview Of Radiometric Ages In Three Allochthonous Belts Of Northern Venezuela: Old Ones, New Ones, And Their Impact On Regional Geology, V Sisson, H Lallemant, M Ostos, Ann Blythe, L Snee, P Copeland, J Wright, R Donelick, L Guth
Ann Blythe
No abstract provided.
Constraining The Exhumation And Burial History Of The Safod Pilot Hole With Apatite Fission Track And (U-Th)/He Thermochronometry, Ann Blythe, M D’Alessio, R Bürgmann
Constraining The Exhumation And Burial History Of The Safod Pilot Hole With Apatite Fission Track And (U-Th)/He Thermochronometry, Ann Blythe, M D’Alessio, R Bürgmann
Ann Blythe
[1] The San Andreas Fault Observatory at Depth (SAFOD) pilot hole traverses the upper 2 km of a site 1.8 km west of the San Andreas fault (SAF) near Parkfield, California. In order to evaluate the burial and exhumation history of the site and its relationship to the kinematics and mechanics of the SAF, we use 15 apatite fission-track (FT) and 5 (U-Th)/He analyses from pilot hole samples to document their thermal history. Sample ages decrease with depth: FT and (U-Th)/He ages range from ∼60 and ∼31 Ma, respectively, in the upper 800 m of the hole to ∼3 and …
Decoupling Of Erosion And Precipitation In The Himalayas, D Burbank, Ann Blythe, J Putkonen, B Pratt-Sitaula, E Gabet, M Oskin, A Barros, T Ohja
Decoupling Of Erosion And Precipitation In The Himalayas, D Burbank, Ann Blythe, J Putkonen, B Pratt-Sitaula, E Gabet, M Oskin, A Barros, T Ohja
Ann Blythe
The hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1, 2, 3. Most such models invoke a 'stream-power' rule, in which either increased discharge or steeper channel slopes cause higher erosion rates. Spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain. Here we combine observations from a meteorological network across the Greater Himalaya, Nepal, along with estimates of erosion rates at geologic timescales (greater than 100,000 yr) …
Implications Of Distributed Crustal Deformation For Exhumation In A Portion Of A Transpressional Plate Boundary, Western Transverse Ranges, Southern California, Andrew Meigs, Dong Yule, Ann Blythe, Doug Burbank
Implications Of Distributed Crustal Deformation For Exhumation In A Portion Of A Transpressional Plate Boundary, Western Transverse Ranges, Southern California, Andrew Meigs, Dong Yule, Ann Blythe, Doug Burbank
Ann Blythe
Spatial and temporal patterns of exhumation are inextricably linked to patterns of crustal deformation because crustal deformation drives rock uplift. A new interpretation of a segment of the Pacific-North America transpressional plate boundary in southern California is analyzed in the context of crustal shortening, rock uplift, and exhumation. Deformation is partitioned between two structural anticlinoria formed above thrust faults that root into a mid-crustal décollement. The southern anticlinorium began growing after 5 Ma and is characterized by almost no topographic expression, rock uplift of ∼3 km, and exhumation of <1.2 km. Deposition in the Los Angeles basin on the south generally kept pace with growth of this anticlinorium. In contrast, the northern anticlinorium is younger, has a significant topographic expression, rock uplift of 2.5–4.0 km, and exhumation of ∼1.5–2 km. On-going surface uplift above the northern anticlinorium is suggested by the mismatch between the magnitude of rock uplift relative to the exhumation. These data emphasize that the distribution of deformation between faults in the upper and middle crust, crustal root formation in the lower crust, and flexural subsidence are primary controls of patterns of exhumation, which together dictate net surface uplift in active orogenic belts.
No Frictional Heat Along The San Gabriel Fault, California: Evidence From Fission-Track Thermochronology, M.A. D’Alessio, Ann Blythe, R Bu¨Rgmann
No Frictional Heat Along The San Gabriel Fault, California: Evidence From Fission-Track Thermochronology, M.A. D’Alessio, Ann Blythe, R Bu¨Rgmann
Ann Blythe
Large earthquakes generate frictional heat, and the magnitude of heating is related to the slip magnitude, the applied effective normal stress, and the frictional strength of the fault. We looked for evidence of this heating in apatite fission-track age and track-length distributions of samples from adjacent to and within the San Gabriel fault zone in southern California. The fault is thought to be an abandoned major trace of the San Andreas fault system active from 13 to 4 Ma and has since been exhumed from depths of 2–5 km. At our sample locality, as much as 40 km of total …
Cretaceous−Cenozoic History Of The Southern Tan-Lu Fault Zone: Apatite Fission-Track And Structural Constraints From The Dabie Shan (Eastern China), J Grimmer, R Jonckheere, E Enkelmann, L Ratschbacher, B Hacker, Ann Blythe, G Wagner, Q Wue, S Liu, S Dong
Cretaceous−Cenozoic History Of The Southern Tan-Lu Fault Zone: Apatite Fission-Track And Structural Constraints From The Dabie Shan (Eastern China), J Grimmer, R Jonckheere, E Enkelmann, L Ratschbacher, B Hacker, Ann Blythe, G Wagner, Q Wue, S Liu, S Dong
Ann Blythe
Apatite fission-track (AFT) and structural data outline the Late Cretaceous−Cenozoic history of the southern Tan-Lu fault zone (TLFZ), one of Asia's major faults, the Triassic–Jurassic Dabie orogen, Earth's largest track of ultrahigh-pressure rock exposure, and its foreland, the Yangtze foreland fold-thrust belt. The fission-track analyses utilized the independent (φ-), Z- and ξ-methods for age determination, which yielded within error identical ages. Ages from Triassic–Jurassic syn-orogenic foreland sediments are younger than their depositional age and thus were reset. A group of ages records rapid cooling following shallow emplacement of granitoids of the widespread latest Jurassic−Early Cretaceous “Yanshanian” magmatism. Most ages are …
Controls On The Erosion And Geomorphic Evolution Of The San Bernardino And San Gabriel Mountains, Southern California, J Spotila, M House, Ann Blythe, N Niemi, G Bank
Controls On The Erosion And Geomorphic Evolution Of The San Bernardino And San Gabriel Mountains, Southern California, J Spotila, M House, Ann Blythe, N Niemi, G Bank
Ann Blythe
No abstract provided.
Low-Temperature Thermochronology Of The San Gabriel And San Bernardino Mountains, Southern California: Constraining Structural Evolution, Ann Blythe, M House, J Spotila
Low-Temperature Thermochronology Of The San Gabriel And San Bernardino Mountains, Southern California: Constraining Structural Evolution, Ann Blythe, M House, J Spotila
Ann Blythe
No abstract provided.
Structural And Topographic Evolution Of The Central Transverse Ranges, California, From Apatite Fission- Track, (U-Th)/He And Digital Elevation Model Analyses, Ann Blythe, D Burbank, K Farley, E Fielding
Structural And Topographic Evolution Of The Central Transverse Ranges, California, From Apatite Fission- Track, (U-Th)/He And Digital Elevation Model Analyses, Ann Blythe, D Burbank, K Farley, E Fielding
Ann Blythe
No abstract provided.
Active Tectonics And Ultrahigh-Pressure Rocks, Ann Blythe
Active Tectonics And Ultrahigh-Pressure Rocks, Ann Blythe
Ann Blythe
This chapter compares modern exhumation and surface uplift rates with the rates needed for the preservation of ultrahigh pressure (UHP) metamorphic rocks. The highest recorded exhumation rates of ~ 5–10 mm/a are inferred from isotopic and fission-track analyses in the Himalaya, Southern Alps of New Zealand, and D’Entrecasteaux Islands. Similar rates (~7 mm/a) of surface uplift are measured from leveling surveys in Nepal and correlations of marine terraces in the Southern Alps. In Nepal, however, this surface uplift rate is occurring despite erosion, and the true rate of surface uplift is probably considerably higher. In restraining bends along the San …