Interaction of the Indian and Asian Plates Under the Pamir and Hindu‐Kush Regions: Insights From 3‐D Shear Wave Velocity and Anisotropic Structures. (3rd August 2020)

• Record Type: Journal Article
• Authors: Liang, Yanling; Li, Lun; Liao, Jie; Gao, Rui
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 21:Number 8(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-03
• Subjects: Pamir -- Hindu Kush -- subduction -- break‐off -- shear wave -- radial anisotropy; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009041
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: The Pamir‐Hindu‐Kush region is widely cited as a best place to study opposing continental subduction on Earth. Yet, subducting slab morphology of the Indian and Asian plates under this region remains elusive. Here we report new shear wave velocity and radial anisotropy models from Rayleigh and Love wave tomography to constrain the geometry of these two slabs. Together with previous tomographic studies, we show that the Indian slab exhibits along‐strike variation with subhorizontally underthrusting into the Pamir and high‐angle subduction under the Hindu‐Kush. We speculate that the Indian slab was probably detached and sank into the mantle transition zone under the Pamir, while break‐off process is ongoing under the Hindu‐Kush. The Asian lithospheric mantle and lower crust are inferred to be subducting southward into the North Pamir. Two opposing subducting slabs could have interacted under the Pamir, resulting in thickening crust, horizontally stretched midcrustal flow, and horizontal mantle flow. These dynamic processes could explain surface geologic observations and potentially constrain the causes of intermediate‐depth seismicity. Plain Language Summary: The Pamir‐Hindu‐Kush region, one of most remote areas with spectacular high mountains on Earth, is widely cited as a prominent site to study ongoing continental collision. It has long puzzled scientists over last decades on how these high mountains are still rising and why many huge earthquakes occur in this region. In this study, we use seismic waves generated by earthquakes to image subsurface structure down to 240 km depth. Our new images provide a rare snapshot into what is going on within deep interior under the Pamir and Hindu Kush regions. We find that the northward subducted Indian plate (which is cold and strong) was detached and sank into the deep mantle under the Pamir, while this process is still ongoing under Hindu‐Kush, responsible for the occurrence of huge deep earthquakes in this region. We also find that the less strong Asian plate is subducting southward into the Pamir. Two opposing subducting slabs could have interacted under the Pamir, resulting in thickening crust and uplift of the mountains. These dynamic processes could explain surface geologic observations and potentially constrain the causes of intermediate‐depth seismicity. Key Points: The Indian slab is imaged to be underthrusting beneath the south Pamir The Indian slab is inferred to have sank into the mantle transition zone under Pamir, while break‐off is likely ongoing under Hindu‐Kush The Asian lithospheric mantle along with its lower crust is inferred to be subducting southward into the North Pamir