The Mechanism and Dynamics of N‐S Rifting in Southern Tibet: Insight From 3‐D Thermomechanical Modeling

Pang, Yajin; Zhang, Huai; Gerya, Taras; Liao, Jie; Cheng, Hui

doi:10.1002/2017jb014011

Cited by 23 publications

(21 citation statements)

References 68 publications

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“…According to Anderson's “standard” relationship between stress and fault types (Simpson, 1997), this stress pattern may induce localized E‐W extensions and N‐S directed normal faults, as observed in the graben zone. This correlates well with the numerical simulation experiments for central Tibet (Pang et al, 2018) that show a weak lower crust giving rise to the E‐W opening of the graben systems. In a similar manner as in the eastern Tibet (H. Dong et al, 2016), these local E‐W extensions would accumulate and produce the eastward surface velocity field (Gan et al, 2007).…”

Section: Discussionsupporting

confidence: 90%

“…The southern part of the Lhasa block experienced widespread basaltic to andesitic magmatism during early Cenozoic times. Aside from calc-alkaline volcanism, the Lhasa block has been characterized with potassic and ultrapotassic intrusions since the Oligocene (Nomade et al, 2004). Those intrusions are believed to be related to metasomatism in the lower crust or lithospheric mantle, which suggests convective thinning or removal of mantle lithosphere (C. Liu et al, 2011).…”

Section: Tectonic Scenariosmentioning

confidence: 99%

“…Those intrusions are believed to be related to metasomatism in the lower crust or lithospheric mantle, which suggests convective thinning or removal of mantle lithosphere (C. Liu et al, 2011). Curiously, the strike-slip zone near the BNS is barren in Cenozoic magmatism, with almost no samples after the Miocene (Nomade et al, 2004), whereas the normal fault zone in the Qiangtang terrane is again characterized with younger volcanism since the Pliocene (Q. Wang et al, 2016).…”

Section: Tectonic Scenariosmentioning

confidence: 99%

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Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

et al. 2020

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The ongoing India-Asia collision since the Paleogene created the Tibetan Plateau, the most prominent elevated plateau on our planet. This convergence also contributed to the formation of two distinct types of active surface deformation of the plateau, namely, north-south trending normal fault systems and "conjugate" strike-slip fault systems. The tectonics and geodynamic mechanism(s) behind this curious combination are still unclear, despite numerous theories proposed over past decades. Here we present a new three-dimensional, lithospheric-scale, electrical conductivity model with unprecedented resolution of the central part of Tibetan Plateau derived from the SINOPROBE magnetotelluric array data set and discuss its inferences related to this question. Our model reveals contrasting conductivity structures corresponding to the surface deformation patterns, namely, highly conductive lower crustal anomalies beneath the graben systems in the Lhasa and Qiangtang terranes and moderately resistive crustal features in the strike-slip region near Bangong-Nujiang Suture Zone. With the help of experimentally calibrated constraints between conductivity and melt fraction, the conductivity model and the inferred lateral viscosity distribution together suggest a weak lower crust beneath the graben regions, compared to a stronger crustal rheology associated with the strike-slip zone. Here we expand the previously proposed "extensional extrusion" tectonic model in central Tibet to interpret our conductivity model and other geophysical/geodesic observations. The weak rheology under a N-S directed primary stress may have caused the east-west extension of the graben regions, which further aides the eastward extrusion of the conjugate strike-slip zone and eventually shapes the surface deformation of central Tibetan Plateau into its current, complex pattern. Plain Language Summary The collision between the Indian and Asian continents built the Tibetan Plateau, the highest plateau in the world. This active collision also formed distinctly different types of large-scale geological structures on the plateau surface. Among the most important features on the plateau, the origin of the N-S directed normal (or spreading) fault zones in two regions named Lhasa and Qiangtang, and the NW/SE directed slip fault zones between these two regions are still unclear. In order to understand the generation of those structures, we use a geophysical imaging method called magnetotellurics to measure the naturally occurring electromagnetic waves in the earth. We model and analyze these magnetotellurics data to obtain the deep structure beneath those surface structures, using sophisticated computer codes. We find that the two dominant but different types of those structures are most likely due to the different strengths of the deep crust. This strength difference can lead to a mechanical stress contrast, which further builds the distinctly different surface structures. These kinds of deep physical structure differences have not been detected for the area bef...

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Section: Discussionsupporting

confidence: 90%

Section: Tectonic Scenariosmentioning

confidence: 99%

Section: Tectonic Scenariosmentioning

confidence: 99%

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Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

et al. 2020

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“…Previous geodynamic simulations of lower crustal deformation in Tibet have primarily focused on estimating the viscosity required to generate observed topographic relief 15 and gradients 13 along 2D profiles, or full 3-D time-dependent thermomechanical derivation of viscosity with assumed flow laws and temperature gradients 20 – 22 to assess the effects of crustal thickness and viscosity variations and required driving forces in generating both topographic features and continental subduction 23 – 25 . Since 2D simulations neglect flow in and out of the third dimension and thermomechanical simulations derive strength distributions rather than test a given hypothetical distribution determined from geophysical data, neither approach addresses the lithospheric wide influence of an assumed lower crustal strength.…”

Section: Introductionmentioning

confidence: 99%

Normal faulting and viscous buckling in the Tibetan Plateau induced by a weak lower crust

Bischoff

Flesch

2018

Nat Commun

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Flow of weak lower crust has been invoked to reconcile observed topographic gradients, uniform elevations, slow seismic velocity, and high conductivity measured in the Tibetan Plateau, with viscosity estimates of 1016–1021 Pa·s. Here we investigate the dynamic response resulting from a range of lower crust viscosities in a 3-D lithospheric-scale geodynamic simulation of the India–Eurasia collision zone to determine bounds of physically viable lower crustal strengths. We show that thickening of the plateau is accommodated through viscous buckling of the upper crust in response to lower crustal flow for a lower crustal viscosity on the order of 1020 Pa·s. This generates two east–west trending bands of surface subsidence and dilatation consistent with observed normal faulting and estimates of vertical velocity. These results suggest viscous buckling of the upper crust, induced by lower crustal flow from gravitational pressure gradients due to high topography, is responsible for the observed extension in Tibet.

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“…It is worth noting that most large earthquakes occur within the boundaries of these two channels (Bao et al, 2015), which corroborates our finding that the formation of large‐scale shear zones require/promote a weak and flowing middle/lower crust. Indeed, other numerical models also show that a weak middle to lower crust is required for the development of the N‐S rifting systems in southern Tibet (Pang et al, 2018), as well as for the development of a wide plateau (Chen et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

Lower Crustal Rheology Controls the Development of Large Offset Strike‐Slip Faults During the Himalayan‐Tibetan Orogeny

Yang

Kaus

et al. 2020

Geophysical Research Letters

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The mechanism of crustal deformation and the development of large offset strike-slip faults during continental collision, such as the India-Eurasia zone, remains poorly understood. Previous mechanical models were simplified which are either (quasi-)2-D approximations or made the a priori assumption that the rheology of the lithosphere was either purely viscous (distributed deformation) or purely localized. Here we present three-dimensional visco-elasto-plastic thermo-mechanical simulations, which can produce both distributed and highly localized deformation, to investigate crustal deformation during continental indentation. Our results show that large-scale shear zones develop as a result of frictional plasticity, which have many similarities with observed shear zones. Yet localized deformation requires both a strong upper crust (>10 22 Pa•s) and a moderately weak middle/lower crust (~10 20 Pa•s) in Tibet. The brittle shear zones in our models develop low viscosity zones directly beneath them, consistent with geological observations of exhumed faults, and geophysical observations across active faults. Plain Language Summary Large offset strike-slip faults are one of the key surface features of continental collision, such as in Tibet. These narrow belts of strike-slip faults accommodate strong deformation, and deciphering their mechanism of formation helps to understand the complex dynamics of India-Eurasia collision. Yet previous models developed to address this either assumed simplified rheologies or employed low numerical resolutions that is insufficient to simulate the spontaneous formation of localized zones. Here, we present high-resolution 3-D visco-elasto-plastic thermo-mechanical models that simulate the formation of large-scale strike-slip faults during Indian indentation, while also taking distributed deformation into account. Our simulations show that a combination of a strong upper crust and a moderately weak middle/lower crust produces faults that are, to first order, consistent with observed ones in the Tibet region. Localized deformation usually initiates at the brittle-ductile transition, and a weak middle/lower crust facilitates subsequent shear localization such that the shear zones cut through the whole crust. The craton-like strong terranes can sustain large stresses and initiate large offset faults along their boundaries.

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The Mechanism and Dynamics of N‐S Rifting in Southern Tibet: Insight From 3‐D Thermomechanical Modeling

Cited by 23 publications

References 68 publications

Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

Shaping the Surface Deformation of Central and South Tibetan Plateau: Insights From Magnetotelluric Array Data

Normal faulting and viscous buckling in the Tibetan Plateau induced by a weak lower crust

Lower Crustal Rheology Controls the Development of Large Offset Strike‐Slip Faults During the Himalayan‐Tibetan Orogeny

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