Aeromagnetic Anomalies in Central Yarlung‐Zangbo Suture Zone (Southern Tibet) and Their Geological Origins

Abstract

Two subparallel east‐west trending linear aeromagnetic anomalies are observed along the central Yarlung‐Zangbo suture zone in southern Tibet. The Yarlung‐Zangbo suture zone represents the boundary of the Eurasian and Indian plates and records the subduction of the Neo‐Tethyan oceanic slab and subsequent continental collision. The two magnetic lineaments are spatially associated with the Gangdese batholith and Xigaze ophiolites, which are separated by the Xigaze fore‐arc basin that is filled with nonmagnetic sedimentary sequences. The Mesozoic‐Cenozoic Gangdese batholith is characterized by widespread I‐type granitoids. The Xigaze ophiolites are dominated by serpentinized mantle peridotites. To investigate the geological origins and deep structures of the magnetic sources of the two magnetic lineaments, a 3‐D inversion of aeromagnetic anomaly data was undertaken. By analyzing our inversion model and further magnetic modeling, it is proposed that the Gangdese batholith has a magmatic root with higher magnetization than the exposed granitoids, indicating that the deeper part of the Gangdese batholith may contain more mafic constituents than the shallow part. The subsurface part of the Xigaze ophiolites resembles a thin slab dipping to the south, implying that the deep‐seated Xigaze ophiolites are also serpentinized and retain complete structure.

Petromagnetic Characteristics of Serpentinization and Magnetite Formation at the Zedang Ophiolite in Southern Tibet

“…The remaining S < 50% samples are weakly magnetic with lower M total values (<1 Am −1 ), similar to the Dongbo ophiolite (Li et al, 2017) and forearc samples (Figure 9b). Overall, most of the serpentinized peridotites are highly magnetized and should be a significant source of the aeromagnetic anomalies in the Zedang ophiolite and throughout the entire Yarlung‐Zangbo suture zone (Jiang et al, 2016; Wang et al, 2020).…”

“…The Yarlung‐Zangbo ophiolite belt in southern Tibet extends over 2000 km from west to east (Figure 1a) and marks the closure of the Neo‐Tethys Ocean between India and Asia during Mesozoic‐Cenozoic times (e.g., Aitchison et al, 2000; Hébert et al, 2012). Large‐scale positive aeromagnetic anomalies have been detected along this giant belt during geophysical surveys (Jiang et al, 2016; Wang et al, 2020; Yao et al, 2001), but magnetic studies of serpentinized ultramafic rocks are limited to few of the ophiolite bodies (He et al, 2014; Li et al, 2017). Here we present new data from rock magnetism, mineral chemistry, and petrographic microstructures of a suite of peridotite samples (from fresh to nearly complete serpentinization) collected from the Zedang ophiolite in the eastern part of the Yarlung‐Zangbo ophiolite belt.…”

Initial scalar lithospheric magnetic anomaly map of China and surrounding regions derived from CSES satellite data

“…It is elongated along the east-west direction and is near-parallel to the mainly east-west trending tectonic sutures due to the northsouth subduction and collision in the Himalayan-Tibetan plateau region. The aeromagnetic anomalies in southern Tibet are of relatively small spatial scales, generally along the east-west sutures and related to the magmatic arcs and ophiolites formed during the subduction and collision [37]. Their magnetic signature in southern Tibet attenuates quickly with altitude, and thus has no obvious relation to the broad satellite magnetic low.…”

Can Targeted Source Information Be Extracted From Superimposed Magnetic Anomalies?

“…The magnetic fields measured in field surveys are generated by the integrated effects of all magnetic rocks, which contain various magnetizations, magnetization directions, and distributions (Fedi & Quarta, 1998). The magnetic information of target sources recovered from the observed magnetic anomaly field is often used in geological research and mineral exploration (Li et al., 2021; Paoletti et al., 2016, 2020; Wang et al., 2020). For example, igneous rocks usually contain a range of different lithologies and distributions in horizontal and vertical directions (C. Zhang et al., 2020; Feng & Zheng, 2021; H. Zhang et al., 2020; M. Zhang et al., 2020), and large‐scale magma chambers generally form at great depth, whereas smaller‐scale stocks and dikes typically occur at shallow depth.…”