The Moho beneath western Tibet: Shear zones and eclogitization in the lower crust

Zhang, Zhongjie; Wang, Yanghua; Houseman, Gregory A.; Xu, Tao; Zhen-bin, WU; Yuan, Xiaohui; Chen, Yun; Tian, Xiaobo; Bai, Zhiming; Teng, Jun

doi:10.1016/j.epsl.2014.10.022

Cited by 78 publications

(97 citation statements)

References 49 publications

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“…As Chun & Yoshii (1977) first observed, the fundamental mode Rayleigh wave crustal Airy phase has a minimum at ∼35 s, a significantly longer period than that observed for most regions of the continents. In western Tibet, the depth of the Moho defined from receiver function studies (Wittlinger et al 2004;Rai et al 2006;Zhang et al 2014;Gilligan et al 2015) agrees well with the depth of the steepest gradient in increasing shear velocity in our surface-wavederived model (Fig. 4).…”

Section: Determining the Crust And Uppermost Mantle Structuresupporting

confidence: 71%

Lateral variations in the crustal structure of the Indo–Eurasian collision zone

Gilligan

2018

Geophysical Journal International

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S U M M A R YThe processes involved in continental collisions remain contested, yet knowledge of these processes is crucial to improving our understanding of how some of the most dramatic features on the Earth have formed. As the largest and highest orogenic plateau on the Earth today, Tibet is an excellent natural laboratory for investigating collisional processes. To understand the development of the Tibetan Plateau, we need to understand the crustal structure beneath both Tibet and the Indian Plate. Building on previous work, we measure new group velocity dispersion curves using data from regional earthquakes (4424 paths) and ambient noise data (5696 paths), and use these to obtain new fundamental mode Rayleigh wave group velocity maps for periods from 5 to 70 s for a region including Tibet, Pakistan and India. The dense path coverage at the shortest periods, due to the inclusion of ambient noise measurements, allows features of up to 100 km scale to be resolved in some areas of the collision zone, providing one of the highest resolution models of the crust and uppermost mantle across this region. We invert the Rayleigh wave group velocity maps for shear wave velocity structure to 120 km depth and construct a 3-D velocity model for the crust and uppermost mantle of the Indo-Eurasian collision zone. We use this 3-D model to map the lateral variations in the crust and in the nature of the crust-mantle transition (Moho) across the Indo-Eurasian collision zone. The Moho occurs at lower shear velocities below northeastern Tibet than it does beneath western and southern Tibet and below India. The east-west difference across Tibet is particularly apparent in the elevated velocities observed west of 84• E at depths exceeding 90 km. This suggests that Indian lithosphere underlies the whole of the Plateau in the west, but possibly not in the east. At depths of 20-40 km our crustal model shows the existence of a pervasive mid-crustal low velocity layer (∼10% decrease in velocity, V s < 3.4 km s −1 ) throughout all of Tibet, as well as beneath the Pamirs, but not below India. The thickness of this layer, the lowest velocity in the layer and the degree of velocity reduction vary across the region. Combining our Rayleigh wave observations with previously published Love wave dispersion measurements, we find that the low velocity layer has a radial anisotropic signature with V sh > V sv . The characteristics of the low velocity layer are supportive of deformation occurring through ductile flow in the mid-crust.

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Section: Determining the Crust And Uppermost Mantle Structuresupporting

confidence: 71%

Lateral variations in the crustal structure of the Indo–Eurasian collision zone

Gilligan

2018

Geophysical Journal International

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“…However in this case, Moho deformation should be observed beneath the Frontal and Principal Cordillera as observed in other orogens (e.g. Giese et al, 1999;Zangh et al, 2014). Also, because our structure would drive Cuyanian material to the west, under the Chilenia terrane, it would be difficult to explain the abnormally thick crust observed beneath the Central Precordillera.…”

Section: The Cuyania-chilenia Terrane Boundarymentioning

confidence: 84%

High-resolution images above the Pampean flat slab of Argentina (31–32°S) from local receiver functions: Implications on regional tectonics

Ammirati

Lujan

Alvarado

et al. 2016

Earth and Planetary Science Letters

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In the flat slab region of the South Central Andes (∼31-32 • S), geological observations suggest that the regional crustal structure is inherited from the accretion of different terranes during the Ordovician. These structures were later reactivated, first in extension during the Triassic and later in compression during the Andean uplift since the Miocene. Seismological observations confirmed that those fault structures extend to depth with décollement levels that accommodate current crustal shortening in the region. In order to get better insight on the regional tectonics we computed higher frequency receiver functions (RF) from local slab seismicity of intermediate ∼100 km depth. Using a common conversion point (CCP) stacking method we obtained cross sections showing high vertical resolution crustal structure at the transition between the Precordillera and the Frontal Cordillera. In addition we performed a joint inversion of our high frequency RFs with surface wave data from ambient noise tomography allowing us to constrain absolute seismic wave velocities. Our higher resolution images reveal more structural details down to a depth of 80 km and laterally over the flat slab in good agreement with previous studies. Our results help to better identify very shallow discontinuities in seismic velocities. Recent petrological analyses combined with our high-resolution RF structure correlates with a crustal mafic composition and partial eclogitization in the lower crust. We observe a shift in the crustal structure between the Precordillera (east) and the Frontal Cordillera (west). Regional seismicity and previously determined focal mechanisms superimposed over our images indicate this shifting is a thrust structure extending down to a depth of 40 km. Our results suggest the presence of a master fault between the Cuyania (Western Precordillera) and Chilenia (Frontal Cordillera) terranes that probably accommodates the crustal deformation in the Pampean flat slab region since the Late Ordovician.

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“…2). The stations were installed and operated by the Institute of Geology and Geophysics of the Chinese Academy of Sciences during the time period of 11/2011-11/2013 (Zhang et al, 2014). The profile, which is named as TW-80, traversed the Himalayan, Lhasa, and Qiangtang Blocks, which are separated by lithospheric suture zones (Taylor and Yin, 2009).…”

Section: Methodsmentioning

confidence: 99%

“…The existence of such flow is a debated issue (e.g., Tapponnier et al, 2001;Royden et al, 2008;Zhao et al, 2013;Zhang et al, 2014). The NE-SW oriented crustal anisotropy revealed by both the Pms and XKS phases provides additional support for the existence of such a flow, which is considered as the main cause for the uplift and growth of the Tibetan Plateau (Royden et al, 2008).…”

Section: Geodynamic Implicationsmentioning

confidence: 96%