New Advances in the Deep Structure of the Pamir Plateau: A Review

The Pamir Plateau, located in the western syntaxis of the Tibetan Plateau, is a critical region for understanding continental collision dynamics and associated metallogenic processes. First, on the basis of the spherical coordinate system, Bouguer gravity anomalies were derived from satellite gravity data covering the Pamir Plateau and adjacent regions. A three‐dimensional density structure model spanning crustal to upper mantle depths (0–200 km) was subsequently inverted through an advanced three‐dimensional physical property inversion methodology. Finally, the depth of the Moho surface in the study area was calculated using an interface inversion method with variable density, which was improved on the basis of the Parker–Oldenburg formula. Our results reveal significant lateral density variations: Moho depths exhibit a mirror‐image relationship with surface topography, and steep Moho gradients align with major tectonic boundaries, indicating deep structural controls on crustal thickening and plateau uplift. The Pamir uplift was driven by crustal thickening, mantle upwelling following slab break‐off, and erosion‐isostatic feedback. Lateral extrusion of Pamir material, constrained by the rigid Tarim Basin, further shapes the plateau's asymmetric topography. High‐density anomalies at mid‐crustal depths correlate with magmatic intrusions and fault systems, providing pathways for ore‐forming fluids. The spatial associations of porphyry Cu‐Au and skarn Fe deposits with Moho depth underscore the importance of crust–mantle interactions in mineralization.

Systematical investigation of deep mantle structure beneath the Pamir Plateau, western Tian Shan and their surroundings is of great significance to understand dynamics of continental collision, intracontinental orogenesis and deformation in response to the Indo‐Eurasian collision. In this research, we imaged the mantle transition zone (MTZ) structure beneath these regions using 42,560 P‐wave receiver functions obtained from 352 seismic stations and 6,173 teleseismic events. Our results reveal significant 15–20 km depression of the 410‐km discontinuity (d410) mainly beneath the southern Kazakh Shield, which is consistent with the low‐velocity anomaly in tomographic models and thus attributed to the mantle upwelling from the MTZ, providing evidence for the fossil Tian Shan plume responsible for the Late Cretaceous‐Paleocene basaltic magmatism (74–52 Ma) at the western Tian Shan. Considering that the d410 is slightly depressed by ∼8 km beneath the western Tian Shan, deep subduction of the Tarim lithosphere is likely excluded and its subhorizontal indentation into the Tian Shan is preferred. As a result, segments of thickened Tian Shan lithosphere delaminated and accumulated near the 660‐km discontinuity (d660), which induce small‐scale upwelling across the d410 there. The d410 is depressed by ∼10–15 km beneath Tarim, which is interpreted to be caused by the mantle upwelling originating from beneath the d410. The d660 below the central Hindu Kush is extremely depressed by 25–30 km, providing direct evidence for the deep subduction of Indian lithosphere into the bottom of the MTZ and suggesting different mechanisms for continental collision between the Hindu Kush and Pamir Plateau.

Numerical simulations were conducted to determine the impact of the Tian Shan Mountains and Pamir Plateau on arid conditions over interior Asia. These topographies are crucial for the differentiation of the precipitation seasonality among the subregions in the west, east, and north of the Tian Shan Mountains and Pamir Plateau, namely, arid central Asia, the Tarim basin, and the northern plains. Before the uplift of the Tian Shan Mountains and Pamir Plateau, the precipitation seasonality over the east arid subregion was consistent with that over the west arid subregion, with maximum rainfall in spring and winter and minimum rainfall in summer. After the uplift of the Tian Shan Mountains and Pamir Plateau, the original precipitation seasonality in the west was strengthened. As the precipitation in the east arid subregion increased in summer but decreased in winter and spring, the precipitation seasonality in the east changed to peak in summer, while the precipitation in the north arid subregion showed the opposite change. The precipitation alteration corresponded well with the change of vertical motion. With the modulation of atmospheric stationary waves, the remote East Asian monsoon was also impacted. Though enhanced southerly wind blew over East Asia, the monsoon precipitation over the east coast of China and subtropical western Pacific Ocean was significantly reduced as an anticyclonic circulation appeared. The Tian Shan Mountains and Pamir Plateau also contributed to the intensification of the East Asian winter monsoon.

Eocene seawater retreat from the southwest Tarim Basin and implications for early Cenozoic tectonic evolution in the Pamir Plateau

The Pamir Plateau region of the Northwestern Tibetan Plateau forms a prominent tectonic salient, separating the Tajik and Tarim basins. However, the topographic evolution of the Pamir Plateau remains elusive, despite the key role of this region played in the retreat of the Paratethys Ocean and in aridification across Central Asia. Therefore, the SW Tarim and Tajik basins are prime locations to decipher the geological history of the Pamir Plateau. Here, we present detrital zircon U/Pb and apatite fission-track (DAFT) ages from the Keliyang section of the SW Tarim Basin. DAFT ages show that sediments had three components during the Late Cretaceous and two components since the Oligocene. Detrital zircon U/Pb ages mainly cluster between 400 and 500 Ma during the Late Cretaceous, and coincide with ages of the Songpan-Ganzi and the West Kunlun Mountains. In contrast, detrital zircon U/Pb ages in the Eocene sediments are centered at around 200–300 Ma and 40–70 Ma, with a peak at ∼45 Ma, consistent with data from the Central Pamir and the West Kunlun Mountains. The ∼45 Ma peak in detrital zircon U/Pb ages since the Eocene indicates a new sedimentary source from the Central Pamir. Non-metric multi-dimensional scaling (MDS) analyses also show that the sedimentary source was closer to the Central Pamir after the Eocene, when compared to the Late Cretaceous. The result shows a clear Eocene provenance change in the Keliyang area. Moreover, this Eocene provenance shift has been detected in previous studies, in both the Tajik and Tarim basins, suggesting that the entire Central Pamir region likely experienced quasi-simultaneous abrupt uplift and paleo-geomorphological changes during the Eocene.

Eastern China continental lithosphere thinning is a consequence of paleo-Pacific plate subduction: A review and new perspectives

Present-day crustal motion around the Pamir Plateau from GPS measurements

Snow accumulation variability at altitude of 7010 m a.s.l. in Muztag Ata Mountain in Pamir Plateau during 1958–2002

Southeast Asia is located in an important regional geodynamic intersection zone and is surrounded by inward subduction systems on three sides. It is the largest and most complicated convergent subduction system on Earth and is known as the Southeast Asia Curved Subduction System (CSS). The deep circulation and structure of the subducted slabs, especially the relic slabs within the CSS, have been an elusive scientific mystery. In this study, using an ocean bottom seismometer (OBS) array in the South China Sea in 2019-2020 and the long-term inland seismic network, we present a new seismic tomographic deep structure of the relic slabs in the CSS mantle. Both the eastern and western CSS subducting slabs exhibit high angles and pass down through the mantle transition zone (MTZ), while the southern subducting slab not only passes through MTZ but also lies flat in the lower mantle, giving rise to a very unique "dustpan"-shaped deep mantle structure. Above the "dustpan"-shaped subduction slab, a high-velocity layer located in and around the South China Sea is interpreted as a relic slab and it lies within the MTZ and continues to subduct to the north. This relic slab is broken by the low-velocity Hainan plume and may result from paleo-Pacific subduction.

<p>We present a new shear-wave velocity model of the upper mantle beneath the East Asia, ASIA2021, derived using the Automatic Multimode Inversion technique. We use waveform fits of over 1.3 million seismograms, comprising waveforms of surface waves, S and multiple S waves.  In total, data from 9351 stations and 23344 events constrain ASIA2021, which maps in detail the structure of the lithosphere and underlying mantle beneath the region. Our model reveals deep structure beneath the tectonic units that make up East Asia. It shows agreement with previous models at larger scales and, also, sharper and stronger velocity anomalies at smaller regional scales. High-velocity continent roots are mapped in detail beneath the Sichuan Basin, Tarim Basin, Ordos Block, and Siberian Craton, extending to over 200 km depths. The lack of a high-velocity continental root beneath the Eastern North China Craton (ENCC), underlain, instead, by a low-velocity anomaly, is consistent with the destruction of this Archean nucleus. Strong low-velocity anomalies are mapped within the top 100 km beneath Tibet, Pamir, Altay-Sayan area, and back-arc basins. At greater depths, ASIA2021 shows high-velocity anomalies related to the subducted and underthrusted lithosphere of India beneath Tibet and the subduction of the Pacific and other plates in the upper mantle. In the mantle transition zone (MTZ), we find high-velocity anomalies probably related to deflected subducted slabs or detached portions of ancient continent cratons. In particularly, ASIA2021 reveals separate bodies, probably originating from the Indian Plate lithosphere beneath central Tibet, with one at 100-200 km beneath Songpan-Ganzi Block (SGFB) and the other in the MTZ. A strong low-velocity anomaly extending from the surface to the lower mantle beneath Hainan volcano and South China Sea is consistent with the hypothesis of the Hainan mantle plume. The high-velocity anomaly beneath ENCC in MTZ can be interpreted as a detached Archean continent root. The Pacific Plate subducts beneath the eastern margin of Asia into the MTZ and appears to deflect and extend horizontally as far west as the Songliao Basin. The absence of major gaps in the stagnant slab is consistent with the origin of Changbaishan volcano above being related to the Big Mantle Wedge, proposed previously. The low-velocity anomalies down to ~ 700 km depth beneath the Lake Baikal area suggest a hot upwelling (mantle plume) feeding the widely distributed Cenozoic volcanoes in central and western Mongolia.</p>

This study provides new constraints on the mantle transition zone (MTZ) structure under the Tian Shan orogenic belt in the context of the double‐sided subduction of the Junggar lithosphere and the Tarim lithosphere. The 410‐ and 660‐km discontinuities bordering the MTZ under the Tian Shan and its adjacent areas are mapped by stacking 68,361 receiver functions from 4,122 events recorded by 100 broadband seismic stations. Regional and large‐scale 3‐D velocity models are used to explain the effect of the laterally heterogeneous velocity anomalies. We identify a thickened MTZ of about 9.3 km under the eastern Tian Shan and the Darbut belt. This thickening indicates a lower temperature, which is correlated with the broken‐off subducted lithosphere or the delamination of the eastern Tian Shan lithosphere. We document the thinning of the MTZ caused by the depressed 410‐km discontinuity and the uplifted 660‐km discontinuity across the Tian Shan orogenic belt, Junggar Basin and Tarim Basin. This thinning corresponds to a + 100 K thermal anomaly in the MTZ, and we suggest that it may have been produced by thermal upwelling originating from the lower mantle. The slightly thinned MTZ beneath the Altai Mountains was caused by the uplift of these two discontinuities, which is related to the high‐velocity anomalies in the upper mantle and MTZ. In contrast, the thinned MTZ below the easternmost segment of the Tian Shan orogenic belt, formed by the depression of 6.5 km for the 410‐km discontinuity may indicate the presence of small‐scale mantle upwelling.

Dehydration and earthquakes in the subducting slab: empirical link in intermediate and deep seismic zones

THE deep seismic zone associated with the Izu–Bonin arc dips at about 40° towards the south-west beneath the Dodaira Observatory, Japan (Fig. 1). At this observatory an unexplained phase with apparent velocity of 16.5 km s−1 was observed 10–20 s after the first arrival for earthquakes in the Ryukyu Islands. No corresponding phase has been found for earthquakes of different azimuths. This unexpected phase can be explained by post-critical reflection of P waves at the deep seismic zone after strong focusing by the 400-km transition zone: this zone of reflection is apparently sharp, of the order of 10 km in thickness. Typical ray diagrams are shown in the inset of Fig. 1. The ray path involves both the deep seismic zone and the 400 km transition zone.

The Tarim craton of central Asia, a stable continental block sandwiched between the Tianshan orogen and the Tibetan Plateau, has experienced significant tectonic reactivation due to the Cenozoic India‐Eurasia collision. Previous tomographic studies have identified lithospheric subduction along the Tibet‐Tarim and Tianshan‐Tarim boundaries. However, it is unclear what the fate of the subducted lithosphere is, and how much of it is subducted or detached into the mantle transition zone (MTZ). To investigate these issues, we use the recently deployed portable seismic array inside the Tarim Basin, along with stations in the surrounding regions, to estimate the structure of MTZ with receiver function analysis. Our key findings include: (a) An anomalously thickened MTZ beneath eastern Tarim, confirmed through systematic sedimentary and crustal correction tests to represent a detached cold lithospheric slab rather than near‐surface artifacts; (b) A locally thinned MTZ (∼6 km thinner than the global average) beneath central Tarim, possibly due to hot mantle upwelling potentially triggered by peripheral slab subduction; (c) Along the Tianshan orogen, MTZ thickness variations (thin in western vs. thick in central sections) resemble previous observations, while contrasting MTZ characteristics between Pamir (relatively thin) and Hindu Kush (thickened) regions suggest different slab penetration depths beneath these two regions.

Complicated thermo-chemical heterogeneity of the mantle transition zone beneath the Philippine Sea Plate revealed by SS precursors investigation