scholarly journals Lithospheric Deformation and Active Tectonics of the NW Himalayas, Hindukush, and Tibet

Lithosphere ◽  
2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Ishtiaq A. K. Jadoon ◽  
Lin Ding ◽  
Saif-ur-Rehman K. Jadoon ◽  
Zahid I. Bhatti ◽  
Syed T. H. Shah ◽  
...  
Keyword(s):  
Crustal Deformation ◽  
Gravity Data ◽  
Active Tectonics ◽  
Ductile Deformation ◽  
Indian Plate ◽  
The Tibetan Plateau ◽  
Mantle Lithosphere ◽  
Lithospheric Deformation ◽  
Himalayan Mountain ◽  
Mountain Belts

Abstract The Himalayan Mountain System (HMS) and the Tibetan Plateau (TP) represent an active mountain belt, with continent-continent collision. Geological and geophysical (seismological modeling, seismic reflection, and gravity) data is reviewed herein for an overview of the lithospheric deformation and active tectonics of this orogen. Shallow crustal deformation with dominance of thrusting along the margins of the TP is interpreted with normal faulting in the center and strike-slip deformation with the lateral translation of blocks, over a wedge of ductile deformation. The seismicity is the linear concentration over the margins of the orogen to ~20 km depth with exception of the Hindukush and Pamir having seismicity to 300 km depth with an interpretation of sinking Indian and Asian lithospheres. The lithospheric structure is represented by mechanically weak surfaces representing décollement to 15 km depth over the basement, low-velocity zone (LVZ) at ~20 km, the Moho at ~40-82 km, and the lithosphere-asthenosphere boundary (LAB) at 130-200 km depth. The décollement, termed as the Himalayan Mountain Thrust (HMT), is inferred to be rooted at the base of the Moho in central Tibet. Along this fault, brittle crustal deformation is interpreted to ~15-20 km depth, with brittle-ductile deformation along LVZ and ductile slip with crustal duplexing along the lower crust. The mantle lithosphere of the Indian plate is inferred as duplicated with the wedging of the Asian mantle lithosphere. The active tectonics of the TP is proposed to follow the mechanics of thrusting, similar to the foreland deformation of the mountain belts and accretionary prisms.

scholarly journals The Role of Lower Crustal Rheology in Lithospheric Delamination During Orogeny

2021 ◽  
Vol 9 ◽  
Author(s):  
Lin Chen
Keyword(s):  
Lower Crust ◽  
Numerical Models ◽  
The Tibetan Plateau ◽  
Mantle Lithosphere ◽  
Laboratory Studies ◽  
Surface Uplift ◽  
Continental Lower Crust ◽  
Lower Crustal ◽  
Flow Laws

The continental lower crust is an important composition- and strength-jump layer in the lithosphere. Laboratory studies show its strength varies greatly due to a wide variety of composition. How the lower crust rheology influences the collisional orogeny remains poorly understood. Here I investigate the role of the lower crust rheology in the evolution of an orogen subject to horizontal shortening using 2D numerical models. A range of lower crustal flow laws from laboratory studies are tested to examine their effects on the styles of the accommodation of convergence. Three distinct styles are observed: 1) downwelling and subsequent delamination of orogen lithosphere mantle as a coherent slab; 2) localized thickening of orogen lithosphere; and 3) underthrusting of peripheral strong lithospheres below the orogen. Delamination occurs only if the orogen lower crust rheology is represented by the weak end-member of flow laws. The delamination is followed by partial melting of the lower crust and punctuated surface uplift confined to the orogen central region. For a moderately or extremely strong orogen lower crust, topography highs only develop on both sides of the orogen. In the Tibetan plateau, the crust has been doubly thickened but the underlying mantle lithosphere is highly heterogeneous. I suggest that the subvertical high-velocity mantle structures, as observed in southern and western Tibet, may exemplify localized delamination of the mantle lithosphere due to rheological weakening of the Tibetan lower crust.

Contributions from the detrital approach to unravelling the timing of India-Asia collision and Himalayan evolution

2021 ◽  
Author(s):  
Yani Najman ◽  
Shihu Li
Keyword(s):  
Subduction Zone ◽  
Crustal Deformation ◽  
Earth Science ◽  
Island Arc ◽  
Current Understanding ◽  
Indian Plate ◽  
Geophysical Research

<p>Knowledge of the timing of India-Asia collision and associated Tethyan closure in the region is critical to advancement of models of crustal deformation.   One of a number of methods traditionally used to constrain the time of India-Asia collision is the detrital approach. This involves determination of when Asian material first arrived on the Indian plate, with most recent estimates documenting collision at ca 60 Ma (e.g. Hu et al, Earth Science Reviews 2016). However, more recently, such data and a number of other approaches providing data previously used to determine the timing of India-Asia collision, have been controversially re-interpreted to represent collision of India with an Island arc, with terminal India-Asia collision occurring significantly later, ca 34 Ma (e.g. Aitchison et al, J. Geophysical Research 2007). Clearly, for the detrital approach to advance the debate, discrimination between Asian detritus and arc detritus is required. Such a discrimination was proposed in Najman et al (EPSL 2017), dating the timing of terminal India-Asia collision at 54 Ma. However, this evidence is far from universally accepted.  For example, such data are at variance with various palaeomagnetic studies which suggest that an oceanic Transtethyan subduction zone existed 600-2300 kms south of the Eurasian margin in the Paleocene  (e.g. Martin et al, PNAS 2020) and therefore these authors propose different explanations to explain the detrital data.  This presentation will discuss the uncertainties associated with our current understanding of the timing of India-Asia collision.</p>

Active tectonics and erosional unloading at the eastern margin of the Tibetan Plateau

2005 ◽  
Vol 2 (2) ◽  
pp. 146-154 ◽  
Author(s):  
Alexander L. Densmore ◽  
Yong Li ◽  
Michael A. Ellis ◽  
Rongjun Zhou
Keyword(s):  
Tibetan Plateau ◽  
Active Tectonics ◽  
The Tibetan Plateau ◽  
Eastern Margin ◽  
Erosional Unloading

scholarly journals The Timing of Metamorphism, Magmatism, and Cooling in the Zanskar, Garhwal, and Nepal Himalaya

1995 ◽  
Vol 11 ◽  
Author(s):  
M. P. Searle
Keyword(s):  
Hanging Wall ◽  
Crustal Thickening ◽  
Indian Plate ◽  
Eastern Himalaya ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Main Central Thrust ◽  
Southern Tibet ◽  
Peak Metamorphism ◽  
Exhumation Rates

Following India-Asia collision, which is estimated at ca. 54-50 Ma in the Ladakh-southern Tibet area, crustal thickening and timing of peak metamorphism may have been diachronous both along the Himalaya (pre-40 Ma north Pakistan; pre-31 Ma Zanskar; pre-20 Ma east Kashmir, west Garhwal; 11-4 Ma Nanga Parbat) and cross the strike of the High Himalaya, propagating S (in Zanskar SW) with time. Thrusting along the base of the High Himalayan slab (Main Central Thrust active 21-19 Ma) was synchronous with N-S (in Zanskar NE-SW) extension along the top of the slab (South Tibet Detachment Zone). Kyanite and sillimanite gneisses in the footwall formed at pressure of 8-10 kbars and depths of burial of 28-35 km, 30- 21 Ma ago, whereas anchimetamorphic sediments along the hanging wall have never been buried below ca. 5-6 km. Peak temperatures may have reached 750 on the prograde part of the P-T path. Thermobarometers can be used to constrain depths of burial assuming a continental geothermal gradient of 28-30 °C/km and a lithostatic gradient of around 3.5-3.7 km/kbar (or 0.285 kbars/km). Timing of peak metamorphism cannot yet be constrained accurately. However, we can infer cooling histories derived from thermochronometers using radiogenic isotopic systems, and thereby exhumation rates. This paper reviews all the reliable geochronological data and infers cooling histories for the Himalayan zone in Zanskar, Garhwal, and Nepal. Exhumation rates have been far greater in the High Himalayan Zone (1.4-2.1 mm/year) and southern Karakoram (1.2-1.6 mm/year) than along the zone of collision (Indus suture) or along the north Indian plate margin. The High Himalayan leucogranites span 26-14 Ma in the central Himalaya, and anatexis occurred at 21-19 Ma in Zanskar, approximately 30 Ma after the collision. The cooling histories show that significant crustal thickening, widespread metamorphism, erosion and exhumation (and therefore, possibly significant topographic elevation) occurred during the early Miocene along the central and eastern Himalaya, before the strengthening of the Indian monsoon at ca. 8 Ma, before the major change in climate and vegetation, and before the onset of E-W extension on the Tibetan plateau. Exhumation, therefore, was primarily controlled by active thrusts and normal faults, not by external factors such as climate change.

scholarly journals Kinematics and extent of the Piemont–Liguria Basin – implications for subduction processes in the Alps

Solid Earth ◽  
2021 ◽  
Vol 12 (4) ◽  
pp. 885-913
Author(s):  
Eline Le Breton ◽  
Sascha Brune ◽  
Kamil Ustaszewski ◽  
Sabin Zahirovic ◽  
Maria Seton ◽  
...  
Keyword(s):  
Late Jurassic ◽  
Significant Proportion ◽  
Western Mediterranean ◽  
Plate Motion ◽  
Distal Margin ◽  
Lithospheric Deformation ◽  
Plate Convergence ◽  
The North ◽  
Regional Tectonic ◽  
Mountain Belts

Abstract. Assessing the size of a former ocean of which only remnants are found in mountain belts is challenging but crucial to understanding subduction and exhumation processes. Here we present new constraints on the opening and width of the Piemont–Liguria (PL) Ocean, known as the Alpine Tethys together with the Valais Basin. We use a regional tectonic reconstruction of the Western Mediterranean–Alpine area, implemented into a global plate motion model with lithospheric deformation, and 2D thermo-mechanical modeling of the rifting phase to test our kinematic reconstructions for geodynamic consistency. Our model fits well with independent datasets (i.e., ages of syn-rift sediments, rift-related fault activity, and mafic rocks) and shows that, between Europe and northern Adria, the PL Basin opened in four stages: (1) rifting of the proximal continental margin in the Early Jurassic (200–180 Ma), (2) hyper-extension of the distal margin in the Early to Middle Jurassic (180–165 Ma), (3) ocean–continent transition (OCT) formation with mantle exhumation and MORB-type magmatism in the Middle–Late Jurassic (165–154 Ma), and (4) breakup and mature oceanic spreading mostly in the Late Jurassic (154–145 Ma). Spreading was slow to ultra-slow (max. 22 mm yr−1, full rate) and decreased to ∼51 mm yr−1 after 145 Ma while completely ceasing at about 130 Ma due to the motion of Iberia relative to Europe during the opening of the North Atlantic. The final width of the PL mature (“true”) oceanic crust reached a maximum of 250 km along a NW–SE transect between Europe and northwestern Adria. Plate convergence along that same transect has reached 680 km since 84 Ma (420 km between 84–35 Ma, 260 km between 35–0 Ma), which greatly exceeds the width of the ocean. We suggest that at least 63 % of the subducted and accreted material was highly thinned continental lithosphere and most of the Alpine Tethys units exhumed today derived from OCT zones. Our work highlights the significant proportion of distal rifted continental margins involved in subduction and exhumation processes and provides quantitative estimates for future geodynamic modeling and a better understanding of the Alpine Orogeny.

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