Éditeur(s) : HAL CCSD Lambert Academic Publishing
Résumé : The Himalaya-Tibet system is considered as the classical case of continental collision. Nonetheless, some fundamental questions concerning its structure, as well as physical processes influencing its evolution are still pending. This book presents several advances in the subject matter. Based on new high-resolution geophysical data from the field, combined with robust imaging techniques, the structure of the collision is revealed in detail: the underplating of India beneath half of Tibet, as well as the geometry of the surface along which this happens. Various numerical modelling techniques allow to discuss physical processes at work in the collision zone, such as the rheology of the India plate whose strong mantle supports the Himalayas, or the metamorphic reactions at depth emphasizing the role of water. We recommend this book to Earth Scientists in a broader sense. While specialists in seismology or modelling can thumb technical details, all Readers can get an interdisciplinary overview of mountain building in the Himalayas, with a retrospective outlook on early day explorers and the dawn of some classical geological principles.
https://hal.archives-ouvertes.fr/hal-00854592

ISBN : 978-3838323534
hal-00854592
https://hal.archives-ouvertes.fr/hal-00854592

Éditeur(s) : HAL CCSD
Résumé : The Karakorum Fault zone (KFZ), lying in the west of the Tibetan plateau, is an important dextral strike-slip fault and the important northern geological boundary of the west Himalaya. In the AyilaRi' gyu Range-Gai Basin area lying in the southeast of the KFZ, Ar-40/Ar-39 thermochronologic analysis was performed on the syn-tectonic minerals in the, metamorphic rocks in the Karakorum ductile shear zone, with the base of petrology and deformation structure researches. According to the microstructure features, the minerals in the shear zone recorded the continuous deformation from high ( > 600 degrees C) to low temperature ( < 250 degrees C) appeared as that the nearly horizontal dextral shearing has transformed into the oblique dextral normal slip, made the greenschist facies of deformation stack oil the early medium-high temperature deformation, indicated the uplift during the slip. The thermochronologic revealed the continuous shear process from the early Miocene to 4Ma at least, which containing three rapid cooling stage: from 25 similar to 22Ma to 21 similar to 18Ma, the deformation locally stopped or slower in the, shallow high temperature shear process; from 15Ma to 12Ma, the rapid uplift of the AyilaRi' gyu Range, the initial formation of the Gar Basin together with the main deep incision of river during the strip-slip of the KFZ; since 9Ma, the AyilaRi' gyu Range has increased the rapid uplift and the Gar Basin has formed finally. According to the different levels of deformation and the dextral displacement of the surface landform with different ages, the long term slip rate and the uplift rate indicated the intense dextral strike slip and uplift associated since the late Quarternary Period.
Acta Petrologica Sinica

hal-00411572
https://hal.archives-ouvertes.fr/hal-00411572

Éditeur(s) : HAL CCSD American Geophysical Union (AGU) American Geophysical Union
Résumé : International audience
GPS data reveal that the Brahmaputra Valley has broken from the Indian Plate and rotates clockwise relative to India about a point a few hundred kilometers west of the Shillong Plateau. The GPS velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89 and 93°E rotating clockwise at 1.15°/Myr and the Assam block from 93.5°E to 97°E rotating at ≈1.13°/Myr. These two blocks are more than 120 km wide in a north-south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastward from 18 to ≈12 mm/yr and convergence between the Shillong Plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to >8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with the reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present-day convergence rates and assuming no great earthquake since 1713 A.D., is now ~5.4 m, similar to the slip reported from alluvial terraces that offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
ISSN: 0148-0227

hal-01115084
https://hal.archives-ouvertes.fr/hal-01115084
DOI : 10.1002/2014JB011196

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
The Ama Drime range located at the transition between the high Himalayan range and south Tibet is a N-S active horst that offsets the South Tibetan Detachment System (STDS). Within the horst, a paragneissic unit, possibly attributed to the upper Himalayan crystalline series, overly the lower Himalayan crystalline series Ama Drime orthogneissic unit containing large metabasite layers and pods that have experienced pressure >= 1.4 GPa. Combining structural analysis with new and published pressure-temperature (P-T) estimates as well as U-Th/Pb, Ar-39/Ar-40 and (U-Th)/He ages, the P-T-deformation-time (P-T-D-t) paths of the main units within and on both sides of the horst are reconstructed. They imply that N-S normal faults initiated prior to 11 Ma and have accounted for a total exhumation <= 0.6 GPa (22 km) that probably occurred in two phases: the first one until similar to 9 Ma and the second one since 6 to 4 Ma at a rate of similar to 1 mm/yr. In the Ama Drime unit, 1 to 1.3 GPa (37 to 48 km) of exhumation occurred after partial melting since similar to 30 Ma until similar to 13 Ma, above the Main Central Trust (MCT) and below the STDS when these two fault systems were active together. The switch from E-W (STDS) to N-S (Ama Drime horst) normal faulting between 13 and 12 Ma occurs at the time of propagation of thrusting from the MCT to the Main Boundary Thrust. These data are in favor of a wedge extrusion or thrust system rather than a crustal flow model for the building of the Himalaya. We propose that the kinematics of south Tibet Cenozoic extension phases is fundamentally driven by the direction and rate of India underthrusting.
ISSN: 0278-7407

hal-00486405
https://hal.archives-ouvertes.fr/hal-00486405
DOI : 10.1029/2009TC002551

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Our knowledge and understanding of the 3-D lithospheric structure of the Himalayas and the Tibetan Plateau is still challenging although numerous geophysical studies have been performed in the region. The GOCE satellite mission has the ambitious goal of mapping Earth's gravity field with unprecedented precision (i.e. an accuracy of 1-2 mGal for a spatial resolution of 100 km) to observe the lithosphere and upper-mantle structure. Consequently, it gives new insights in the lithospheric structure beneath the Himalayas and the Tibetan Plateau. Indeed, the GOCE gravity data now allow us to develop a new strategy for joint gravimetry-seismology inversion. Combined with teleseismic data over a large region in a joint inversion scheme, they will lead to lithospheric velocity-density models constrained in two complementary ways. We apply this joint inversion scheme to the Hi-CLIMB (Himalayan-Tibetan Continental Lithosphere during Mountain Building) seismological network which was deployed in South Tibet and the Himalayas for a 3-yr period. The large size of the network, the high quality of the seismological data and the new GOCE gravity data set allow us to image the entire lithosphere of this active area in an innovative way. We image 3-D low velocity and density structures in the middle crust that fit the location of discontinuous low S-velocity zones revealed by receiver functions in previous geophysical studies. In the deeper parts of our velocity model we image a positive anomaly interpreted to be the heterogenous Indian lithosphere vertically descending beneath the centre of the Tibetan Plateau.
ISSN: 0956-540X

hal-00858024
https://hal.archives-ouvertes.fr/hal-00858024
DOI : 10.1093/gji/ggs110

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We investigate the timing of end of motion along the South Tibet Detachment System (STDS), a major normal fault system that runs parallel to the Himalayan range for more than 1500 km. Near Dinggye (similar to 28 degrees 10'N, 87 degrees 40'E), the STD dips similar to 10 +/- 5 degrees to the North and separates Paleozoic Tethyan series from Upper Himalayan Crystalline Series (UHCS). Immediately below the STD, the UHCS is highly deformed in the STD shear zone, lineations trend NNE and the shear senses are top to the NE. In micaschist, the P-T path constrained by pseudosection and garnet chemistry, shows successive metamorphic conditions of similar to 0.6 GPa and similar to 550 degrees C and 0.5 GPa and 625 degrees C. U/Pb dating of monazites and zircons in deformed and undeformed leucogranites suggests that ductile deformation lasted until at least similar to 16 Ma but ended prior to similar to 15 Ma in the STD shear zone similar to 100 m below the detachment. Ar/Ar micas ages in the footwall span between similar to 14.6 and 13.6 Ma, indicating rapid cooling down to similar to 320 degrees C, and suggesting persistence of normal faulting, at that time. The STDS is cut and offset by the N-S trending Dinggye active normal fault which initiated prior to 11 Ma thus providing a minimum bound for the end of STDS motion. These data are interpreted as reflecting 0.3 GPa (11 km) to 0.6 GPa (22 km) of exhumation along the STDS starting prior to similar to 16 Ma, ending between 13.6 and 11 Ma. The 1000 km long stretch of the STDS east of the Gurla Mandata probably stopped almost synchronously between 13 and 11 Ma ago, coevally with a sudden switch from NNE-SSW to E-W extension at the top of the accretionary prism, with a jump of the major thrust from the lower Main Central Thrust (MCTI) to the Main Boundary Thrust (MBT), and with a change in the India and Asia convergence direction. This synchronism is probably better explained in the frame of a thrust wedge or thrust system model than a lower channel flow model. West of the Gurla Mandata the STDS appears to stop 5 to 3 Ma earlier, possibly related to local interactions with the Karakorum fault in a way that needs to be understood.
ISSN: 0012-821X

hal-00475652
https://hal.archives-ouvertes.fr/hal-00475652
DOI : 10.1016/j.epsl.2009.12.035

Éditeur(s) : HAL CCSD Himalayan Association Advance Science
Résumé : The Himalayas and the Tibetan Plateau are considered as the classical case of continental collision.
ISSN: 1727-5210

hal-00854401
https://hal.archives-ouvertes.fr/hal-00854401
DOI : 10.3126/hjs.v5i7.1267