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Caltech Authors (142.336 recursos)

Repository of works by Caltech published authors.

Group = Caltech Tectonics Observatory. Indo-Asian Collision Zone

Mostrando recursos 1 - 20 de 23

  1. Thermal structure and exhumation history of the Lesser Himalaya in central Nepal

    Bollinger, L.; Avouac, J. P.; Beyssac, O.; Catlos, E. J.; Harrison, T. M.; Grove, M.; Goffé, B.; Sapkota, S.
    The Lesser Himalaya (LH) consists of metasedimentary rocks that have been scrapped off from the underthrusting Indian crust and accreted to the mountain range over the last ~20 Myr. It now forms a significant fraction of the Himalayan collisional orogen. We document the kinematics and thermal metamorphism associated with the deformation and exhumation of the LH, combining thermometric and thermochronological methods with structural geology. Peak metamorphic temperatures estimated from Raman spectroscopy of carbonaceous material decrease gradually from 520°–550°C below the Main Central Thrust zone down to less than 330°C. These temperatures describe structurally a 20°–50°C/km inverted apparent gradient. The Ar...

  2. Holocene Hydrological Changes Inferred from Alluvial Stream Entrenchment in North Tian Shan (Northwestern China)

    Poisson, Blanche; Avouac, Jean-Philippe
    We analyze the possible contribution of climate change or tectonics on fluvial incision from the study of a case example along the northern flank of Tian Shan. The rivers that exit the high range fed large alluvial fans by the end of the last glacial period. They have since deeply entrenched the piedmont by as much as 300 m. We have surveyed several terraces that were cut and abandoned during river entrenchment, providing information on intermediate positions of the riverbed during downcutting. They suggest a gradual decline in river slope during a major phase of incision throughout the Holocene. Tectonic...

  3. Magnetostratigraphy of the Yaha section, Tarim Basin (China): 11 Ma acceleration in erosion and uplift of the Tian Shan mountains

    Charreau, Julien; Gilder, Stuart; Chen, Yan; Dominguez, Stéphane; Avouac, Jean-Philippe; Sen, Sevket; Jolivet, Marc; Li, Yongan; Wang, Weiming
    We report a magnetostratigraphic and rock magnetic study of the Yaha section, located on the southern flank of the central Tian Shan mountains, Asia. Our results show a two-fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca. 11 Ma. After 11 Ma, sedimentation rate remained remarkably constant until at least 5.2 Ma. These findings are consistent with sedimentary records from other sections surrounding the Tian Shan. We conclude that uplift and erosion of the Tian Shan accelerated ca. 11 Ma, long after the onset of the collision between India and Asia, and that the...

  4. Mountain Building, Erosion, and the Seismic Cycle in the Nepal Himalaya

    Avouac, Jean-Philippe
    The Himalaya is the most impressive example on earth of an active collisional orogen. It combines rapid crustal shortening and thickening, intense denudation driven by the monsoon climate, and frequent very large earthquakes along an incomparably long and high mountain arc. It has therefore been the focus of a variety of investigations that have addressed various aspects of mountain building on various timescales. Geological and geophysical studies give some idea of the structure of the range and physical properties at depth. The long-term geological history of the range, over say several millions to a few tens of millions of years, has been documented by structural, thermo barometric, and thermo...

  5. Stress transfer and strain rate variations during the seismic cycle

    Perfettini, H.; Avouac, J.-P.
    The balance of forces implies stress transfers during the seismic cycle between the elastobrittle upper crust and the viscoelastic lower crust. This could induce observable time variations of crustal straining in the interseismic period. We simulate these variations using a one-dimensional system of springs, sliders, and dashpot loaded by a constant force. The seismogenic zone and the zone of afterslip below are modeled from rate-and-state friction. The ductile deeper fault zone is modeled from a viscous slider with Newtonian viscosity ν. The force per unit length, F, must exceed a critical value F_c to overcome friction resistance of the fault...

  6. Dynamic Processes in Extensional and Compressional Settings - Mountain Building: From Earthquakes to Geological Deformation

    Avouac, J.-P.
    Mountain ranges are the most spectacular manifestation of continental dynamics. T he fact that some mountain ranges were able to maintain their topography over tens of millions of years, while their erosion was feeding large sedimentary basins, is unambiguous evidence that tectonic forces can cause sustained uplift of subsidence of the continental crust. Geologists noticed quite early on that most mountain ranges are contractional orogens, the result of horizontal contraction of the continental crust, and that they tend to form long belts separating domains with often quite different geological history (e.g., Willis, 1891; Argand, 1924). A rapid tour of active...

  7. Thermal metamorphism in the lesser Himalaya of Nepal determined from Raman spectroscopy of carbonaceous material

    Beyssac, Olivier; Bollinger, Laurent; Avouac, Jean-Philippe; Goffé, Bruno
    The determination of metamorphic conditions is critical to the understanding of the formation of mountain belts. However, all collisional mountain belts contain large volumes of accreted sediments generally lacking metamorphic index minerals and are therefore not amenable to conventional petrologic investigations. By contrast, these units are often rich in carbonaceous material, making it possible to determine thermal metamorphism through Raman spectroscopy of carbonaceous material (RSCM method), a technique that has been recently calibrated [Beyssac et al., J. Metamorph. Geol. 20 (2002) 859–871]. The Lesser Himalaya (LH) is one of these problematic cases with a very poor mineralogy, but a key...

  8. Magnetostratigraphy and rock magnetism of the Neogene Kuitun He section (northwest China): implications for Late Cenozoic uplift of the Tianshan mountains

    Charreau, Julien; Chen, Yan; Gilder, Stuart; Dominguez, Stéphane; Avouac, Jean-Philippe; Sen, Sevket; Sun, Dongjiang; Li, Yongan; Wang, Wei-Ming
    In order to better constrain the tectonic evolution of central Asia under the influence of the India–Asia collision, we carried out a magnetostratigraphic study at the Kuitun He section, on the northern flank of the Tianshan range (northwest China). A total of 801 samples were collected from a 1559-m-thick section, which is composed mainly of fluvio-lacustrine sandstone and conglomerate. Stepwise thermal and alternating field demagnetization isolated a linear magnetization component that decays univectorally toward the origin and likely represents a primary magnetization principally carried by magnetite. From this component, 29 magnetic polarity intervals were identified. They correlate between ~3.1 and...

  9. Current shortening across the Himalayas of Nepal

    Jouanne, F.; Mugnier, J. L.; Gamond, J. F.; Le Fort, P.; Pandey, M. R.; Bollinger, L.; Flouzat, M.; Avouac, J. P.
    Underthrusting of the Indian lithosphere beneath the Himalayas occurs during the Quaternary period along a gently north-dipping main basal detachment (main Himalayan thrust: MHT), from which the southernmost emergent ramp (main frontal thrust: MFT) branches. Historical seismicity shows that slip on the MHT is frequently accommodated through M > 8 shallow earthquakes, but shows a seismic gap in western Nepal. This absence of major historical earthquakes in western Nepal can be explained either by an aseismic slip on the MHT or a long-lived elastic strain accumulation. To test these hypotheses, the present-day displacement field has been measured for a GPS...

  10. Stress buildup in the Himalaya

    Bollinger, L.; Avouac, J. P.; Cattin, R.; Pandey, M. R.
    The seismic cycle on a major fault involves long periods of elastic strain and stress accumulation, driven by aseismic ductile deformation at depth, ultimately released by sudden fault slip events. Coseismic slip distributions are generally heterogeneous with most of the energy being released in the rupture of asperities. Since, on the long term, the fault's walls generally do not accumulate any significant permanent deformation, interseismic deformation might be heterogeneous, revealing zones of focused stress buildup. The pattern of current deformation along the Himalayan arc, which is known to produce recurring devastating earthquakes, and where several seismic gaps have long been...

  11. Tectonic evolution of a continental collision zone: A thermomechanical numerical model

    Toussaint, G.; Burov, E.; Avouac, J.-P.
    We model evolution of a continent-continent collision and draw some parallels with the tectonic evolution of the Himalaya. We use a large-scale visco-plasto-elastic thermomechanical model that has a free upper surface, accounts for erosion and deposition and allows for all modes of lithospheric deformation. For quartz/olivine rheology and 60 mm/yr convergence rate, the continental subduction is stable, and the model predicts three distinct phases. During the phase 1 (120 km or 6% of shortening), deformation is characterized by back thrusting around the suture zone. Some amount of delaminated lower crust accumulates at depth. During phase 2 (120 km–420 km or...

  12. The 2005, M_w 7.6 Kashmir earthquake: Sub-pixel correlation of ASTER images and seismic waveforms analysis

    Avouac, Jean-Philippe; Ayoub, Francois; Leprince, Sébastien; Konca, Ozgun; Helmberger, Don V.
    We analyze the M_w 7.6 Kashmir earthquake of October 8, 2005, using sub-pixel correlation of ASTER images to measure ground deformation, and modeling seismic waveforms. The surface rupture is continuous over a distance of 75 km and cuts across the Hazara syntaxis reactivating the Tanda and the Muzaffarabad faults. North of Muzaffarabad the surface rupture coincides approximately with the MBT, on the southwestern flank of the syntaxis, although the two faults have opposite dip angles. The rupture terminates abruptly at the hairpin turn of the MBT showing a strong structural control. The fault offset is 4 m on average and...

  13. Plate Motion of India and Interseismic Strain in the Nepal Himalaya from GPS and DORIS Measurements

    Bettinelli, Pierre; Avouac, Jean-Philippe; Flouzat, Mireille; Jouanne, François; Bollinger, Laurent; Willis, Pascal; Chitrakar, Gyani Raja
    We analyse geodetically estimated deformation across the Nepal Himalaya in order to determine the geodetic rate of shortening between Southern Tibet and India, previously proposed to range from 12 to 21 mm yr^(−1). The dataset includes spirit-levelling data along a road going from the Indian to the Tibetan border across Central Nepal, data from the DORIS station on Everest, which has been analysed since 1993, GPS campaign measurements from surveys carried on between 1995 and 2001, as well as data from continuous GPS stations along a transect at the logitude of Kathmandu operated continuously since 1997. The GPS data were processed in International Terrestrial Reference Frame 2000 (ITRF2000), together with the...

  14. Mountain building in the Nepal Himalaya: Thermal and kinematic model

    Bollinger, L.; Henry, P.; Avouac, J. P.
    We model crustal deformation and the resulting thermal structure across the Nepal Himalaya, assuming that, since 20 Ma, shortening across the range has been primarily taken up by slip along a single thrust fault, the Main Himalayan Thrust (MHT) Fault, and that the growth of the Himalayan wedge has resulted mainly from underplating and to the development of a duplex at midcrustal depth. We show that this process can account for the inverse thermal metamorphic gradient documented throughout the Lesser Himalaya (LH), the discontinuity of peak metamorphic temperatures across the MCT, as well as the distribution of age of exhumation...

  15. Modeling the shortening history of a fault tip fold using structural and geomorphic records of deformation

    Daëron, Mathieu; Avouac, Jean-Philippe; Charreau, Julien
    We present a methodology to derive the growth history of a fault tip fold above a basal detachment. Our approach is based on modeling the stratigraphic and geomorphic records of deformation, as well as the finite structure of the fold constrained from seismic profiles. We parameterize the spatial deformation pattern using a simple formulation of the displacement field derived from sandbox experiments. Assuming a stationary spatial pattern of deformation, we simulate the gradual warping and uplift of stratigraphic and geomorphic markers, which provides an estimate of the cumulative amounts of shortening they have recorded. This approach allows modeling of isolated...

  16. Seasonal modulation of seismicity in the Himalaya of Nepal

    Bollinger, L.; Perrier, F.; Avouac, J.-P.; Sapkota, S.; Gautam, U.; Tiwari, D. R.
    For the period 1995–2000, the Nepal seismic network recorded 37 ± 8% fewer earthquakes in the summer than in the winter; for local magnitudes ML > 2 to ML > 4 the percentage increases from 31% to 63% respectively. We show the probability of observing this by chance is less than 1%. We find that most surface loading phenomena are either too small, or have the wrong polarity to enhance winter seismicity. We consider enhanced Coulomb failure caused by a pore-pressure increase at seismogenic depths as a possible mechanism. For this to enhance winter seismicity, however, we find that fluid...

  17. Seasonal variations of seismicity and geodetic strain in the Himalaya induced by surface hydrology

    Bettinelli, Pierre; Avouac, Jean-Philippe; Flouzat, Mireille; Bollinger, Laurent; Ramillien, Guillaume; Rajaure, Sudhir; Sapkota, Som
    One way to probe earthquake nucleation processes and the relation between stress buildup and seismicity is to analyze the sensitivity of seismicity to stress perturbations. Here, we report evidence for seasonal strain and stress (~ 2–4 kPa) variations in the Nepal Himalaya, induced by water storage variations which correlate with seasonal variations of seismicity. The seismicity rate is twice as high in the winter as in the summer, and correlates with stress rate variations. We infer ~ 10–20 kPa/yr interseismic stress buildup within the seismicity cluster along the high Himalaya front. Given that Earth tides exert little influence on Himalayan...

  18. Exhumation, crustal deformation, and thermal structure of the Nepal Himalaya derived from the inversion of thermochronological and thermobarometric data and modeling of the topography

    Herman, Frédéric; Copeland, Peter; Avouac, Jean‐Philippe; Bollinger, Laurent; Mahéo, Gweltaz; Le Fort, Patrick; Rai, Santaman; Foster, David; Pêcher, Arnaud; Stüwe, Kurt; Henry, Pierre
    Two end‐member kinematic models of crustal shortening across the Himalaya are currently debated: one assumes localized thrusting along a single major thrust fault, the Main Himalayan Thrust (MHT) with nonuniform underplating due to duplexing, and the other advocates for out‐of‐sequence (OOS) thrusting in addition to thrusting along the MHT and underplating. We assess these two models based on the modeling of thermochronological, thermometric, and thermobarometric data from the central Nepal Himalaya. We complement a data set compiled from the literature with 114 ^(40)Ar/^(39)Ar, 10 apatite fission track, and 5 zircon (U‐Th)/He thermochronological data. The data are predicted using a thermokinematic model (PECUBE), and the model parameters are constrained using...

  19. India-Asia collision and the Cenozoic slowdown of the Indian plate: Implications for the forces driving plate motions

    Copley, Alex; Avouac , Jean-Philippe; Royer, Jean-Yves
    The plate motion of India changed dramatically between 50 and 35 Ma, with the rate of convergence between India and Asia dropping from ~15 to ~4 cm/yr. This change is coincident with the onset of the India-Asia collision, and with a rearrangement of plate boundaries in the Indian Ocean. On the basis of a simple model for the forces exerted upon the edges of the plate and the tractions on the base of the plate, we perform force balance calculations for the precollision and postcollision configurations. We show that the observed Euler poles for the Indian plate are well explained...

  20. The Neogene Xiyu Formation, a diachronous prograding gravel wedge at front of the Tianshan: Climatic and tectonic implications

    Charreau, Julien; Gumiaux, Charles; Avouac , Jean-Philippe; Augier, Romain; Chen, Yan; Barrier, Laurie; Gilder, Stuart; Dominguez, Stéphane; Charles, Nicolas; Wang, Qingchen
    The Tarim and Junggar basins in central Asia are capped by a thick pile of conglomerates, called the Xiyu Formation, that are commonly linked to a change in climate and/or accelerated uplift near the Plio- Pleistocene boundary. In order to better understand their origin and significance, we carried out a combined structural and magnetostratigraphic study in the Quilitage syncline (southern Tianshan), where the base of the Xiyu conglomerates is observed at both sides of the syncline. A balanced cross-section shows that, even at a local-scale, the base of the Xiyu conglomerates cannot be regarded as a single continuous stratigraphic layer. On the southern flank of the...

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