###### Abstract
The subduction zone extends from the southwestern Japan-Ryukyu Islands-Taiwan region southward to the Borneo and Palawan regions and from the Meratus Belt in southeastern Borneo to the Woyla Belt in Sumatra. The subduction zone in the northern SCS originally extended from the Baiyun Depression via the Dongsha Rise northeastward to the western part of Taiwan. [PERSON] et al. (2008) [PERSON] et al. (2008) analyzed the seismic reflection profile DPSR2002 crossing the Baiyun Depression (Figure 1, profile 2), performed the joint inversion of magnetic and gravity data, and proposed that the high-magnetic anomaly belt corresponds to volcanic rocks at depths of 2.5 to 10 km, with a density of 2.65 g/cm\({}^{3}\) and a magnetization strength of 0.7 A/m, which are products of a concealed oceanic crust subduction zone. [PERSON] et al. (2018) [PERSON] et al. (2018) [PERSON] et al. (2018) performed 2-D magnetic modeling along the OBS profile crossing the Dongsha Rise, concluding that the high-magnetic anomaly belt is associated with the root of a volcanic arc located at a depth of 18-24 km within the lower crust. These geophysical features are typically associated with subduction-related volcanic activity and mantle intrusion during continental rifting. Thus, investigating volcanic arc (subduction zone) distribution and morphology using high-magnetic anomaly belts becomes crucial for understanding the pre-Cenozoic tectonic evolution of the SCS. However, these studies mainly rely on regional magnetic anomaly characteristics and 2-D magnetic models for local places and lack the 3-D exhibition of the crustal magnetism model, limiting the comprehensive understanding of the Mesozoic volcanic arc. Figure 2: The RTP aeromagnetic anomaly map around the northern SCS (digitized from [25]). ZHU I D: Zhu I depression; PHR: Penghu Rise; TXNB: Taixinan Basin; DSR: Dongsha Rise; CSD: Chaoshan Depression; YTA: Yitong Ansha. Black lines represent the 0 m isobath. White lines outline the depressions. Three-dimensional magnetic inversion is a primary technique for revealing the 3-D magnetism structure in the subsurface and has been widely applied in fields such as deep tectonic studies and resource exploration [13; 14; 26; 27]. The 3-D magnetic inversion method based on the mixed L\({}_{\rm p}\) norm regularization (hereinafter referred to as mixed L\({}_{\rm p}\) norm inversion) is a recently developed technique [28; 29]. Compared to conventional single norm regularization inversion methods, this technique offers the advantages of more accurately delineating source boundaries, focusing on the source morphology, and providing physical-property values that are closer to the true characteristics of the source. We first investigated the mixed L\({}_{\rm p}\) norm inversion method. Then, using high-resolution reduction-to-the-pole (RTP) aeromagnetic anomaly data around the northern SCS, we constructed a reliable 3-D susceptibility model of the crust through magnetic 3-D mixed L\({}_{\rm p}\) norm inversion with the constraint of multiple deep seismic reflection profiling data. Based on the resultant model, we analyzed the crustal architecture of the Mesozoic volcanic arc, and discuss its implication on the pre-Cenozoic tectonic evolution of the SCS.