New Seismic Evidence for Continental Collision During the Assembly of the Central Asian Orogenic Belt

Abstract

The Central Asian Orogenic Belt (CAOB) was formed during the termination of the Paleo‐Asian Ocean in the Paleozoic. However, the mechanism and process of the Paleo‐Asian Ocean closure and CAOB formation remain controversial. This study presents a seismic image from the northern North China Craton to southern Mongolia derived from P and S receiver function analyses of the teleseismic records from a dense array. Our observations reveal a thicker lithosphere in the southern CAOB than in the Bohai Bay basin, which suggests that this Paleozoic orogen was less affected by the lithosphere reactivation in the eastern North China Craton during the Late Mesozoic. The imaged lithosphere‐asthenosphere boundary of the southern CAOB deepens southward and reaches a greatest depth of approximately 130 km beneath the Xilinhot fault, the northern boundary of the Solonker suture zone. The Moho displays a local uplift of approximately 5 km beneath the Linxi fault, the southern boundary of the Solonker suture zone. These features imply that the Solonker suture zone is the most plausible site of the lithosphere collision between the opposing continental margins. Additionally, a southward dipping intracrustal interface, whose depth extends from ~16 km beneath the Baolidao belt to ~20 km beneath the Linxi fault, is interpreted to be associated with the subduction of the Paleo‐Asian Oceanic slab. Additionally, the absence of lithosphere‐asthenosphere boundary phases beneath the Bainaimiao arc is inferred to be caused by the upwelling of hot mantle material after assembly of the CAOB.

Crustal‐Scale Seismic Reflection Profiling Constrains How the Paleo‐Asian Ocean Was Closed

“…In addition to the Bainaimiao magmatic rocks, large volumes of arc-volcanic and plutonic rocks occur in the area extending eastward from Tugurige via Bainaimiao to central Jilin Province, constituting a magmatic arc belt with a U-Pb age ranging from ∼474 to ∼425 Ma (Xu et al, 2016). The lithosphere-asthenosphere boundary is absent beneath the Bainaimiao arc according to the receiver functional images, consistent with the conductive body in the magnetotelluric profile, indicating upwelling of mantle-derived materials within the research area (Zhang et al, 2018). A series of accretionary complexes and sporadic ophiolitic mélanges also jointly occur with the magmatic arc and comprise metamorphic peridotite, gabbro, pyroxene, basalt, and plagiogranite (Song et al, 2015;Xiao et al, 2003).…”

“…When magma intrudes from lithospheric or asthenospheric mantle sources, lighter felsic components are emplaced and remain in the upper crust, whereas denser mafic–ultramafic components pond just above the Moho, as exemplified by the reflectors beneath eastern Nevada of the North American Cordillera (Hauser et al., 1987). Considering the abundant Mesozoic granitoids exposed at the surface of the central profile (Figures 1c and 2a), the large‐scale high‐resistivity bodies between the North and South Orogenic Belts (Zhao et al., 2022), and the absence of lithosphere–asthenosphere boundary phases beneath the South Orogenic Belt in the common conversion point stacking image of the receiver function (Zhang et al., 2018), we interpreted the high‐amplitude reflector zones (red arrows marked E in Figure 2d) as representing Mesozoic magmatic rocks, consistent with the high‐velocity domain in the near‐surface velocity structures (Figure 2b) and Mesozoic granitoids exposed at the surface (Figures 1c and 2a). As the study area was influenced by southward subduction of the Mongol–Okhotsk oceanic plate and westward subduction of the Paleo‐Pacific plate (light blue arrows marked F in Figure 2d; Wu et al., 2011), the high‐amplitude Mesozoic reflectors gradually curved owing to compression from both sides.…”

Seismic Constraints on the Magmatic System Beneath the Changbaishan Volcano: Insight Into its Origin and Regional Tectonics

“…Anisotropic Rayleigh wave tomography by Liu et al () reveals that there is an observable azimuthal anisotropy with a NEE‐SWW fast direction around the crust mantle boundary beneath the Solonker suture zone, which is interpreted as a possible reflection of crust and upper mantle deformation caused by continental collision. A recently conducted P and S receiver function study implies that the Solonker suture zone is the most plausible site of the lithosphere collision between the opposing continental margins (Zhang et al, ). Therefore, we speculate that the uppermost mantle high‐velocity pattern in our images might reflect the slab remnants or deformational fabrics contributed by the final suturing of the CAOB and SKC.…”

Crust and upper mantle electrical structure of the eastern Central Asian Orogenic Belt revealed by the MT line from Zhangwu County to East Ujimqin Banner

“…For the lithospheric structure of the Xing'an Mongolia orogenic belt on the eastern CAOB, Xiong et al (2015) conducted a comprehensive geophysical profiling study, such as the deep seismic reflection profile, the wide-angle refraction/reflection profile, and the magnetotelluric survey. In terms of the seismic inversion and interpretation, scholars have done much work, including the deep seismic reflection method (Li et al 2013;Hou et al 2015), the receiver function method (Zhang et al 2014a;Zhang et al 2018), traveltime tomography method (Li et al 2011), etc. In terms of magnetotelluric (MT), and collected, processed, and interpreted data from 12 MT sites in the plate collision zones of eastern Inner Mongolia. Li et al (2014) studied an MT profile about 500 km away from our study area, and obtained that the profile was divided into two region: low resistivity widely distributed in the northern part, and high resistance in the southern part.…”