###### Abstract  
The high-magnetic anomaly belt in the northern slope of the South China Sea has long been associated with a Mesozoic volcanic arc. However, its crustal architecture remains unclear, limiting the understanding of its geological implications. We assembled high-resolution reduced-to-the-pole aeromagnetic anomaly data around the northern South China Sea and then applied the 3-D magnetic inversion method based on mixed L\({}_{\text{p}}\) norm regularization, with the constraint of multiple deep seismic reflection profiling data, to obtain high-resolution 3-D crustal susceptibility model. Our model confirms that the high-magnetic anomaly belt is caused by deep-seated magnetic bodies, which, supported by borehole and seismic data, are identified as a Mesozoic volcanic arc. We found that the Mesozoic volcanic arc described by high susceptibility bodies extends northeastward from the Dongsha Rise to Taiwan Island and primarily distributes within the depth range of 20-28 km. Our findings provide important constraints for understanding the pre-Cenozoic tectonic evolution of the northern South China Sea. the area represents a highly stretched continental crust [1; 2; 3]. The northern continental margin of the SCS, including the shelf-slope region and the ocean-continent transition zone, has widely observed high-velocity layers in the lower crust, with seismic P-wave velocities ranging from 7.0 to 7.6 km/s [4; 5; 6; 7]. Multiple deep seismic reflection profiles reveal high-velocity layers co-located with Moho discontinuities [8; 9; 10; 11]. Concurrently, a series of northwest-dipping reflection signals found in the crust of the northern SCS are considered to be low-angle subduction-type thrust faults developed within the pre-Cenozoic granite basement. Additionally, petrochemical analyses of rock and mineral samples have confirmed the occurrence of large-scale Mesozoic tectonic movements in the northern SCS. The observed enrichment of fluid-mobile elements, including cesium (Cs), potassium (K), and lead (Pb), in granitic and dioritic rocks provide compelling evidence for the involvement of subduction-zone fluids, supporting the interpretation that these rocks originated in a subduction-related hydrothermal setting [12; 13; 14]. The aeromagnetic data of the northern SCS reveal a high-magnetic anomaly belt extending from the northwestern sub-basin edge through the Dongsha Rise and Taiwan Strait to the western Taiwan margin, with peak magnetic anomalies ranging from 60 to 200 nT. The origin of the high-magnetic anomaly belt in the northern SCS (Figure 2) remains a subject of ongoing debate, but most researchers believe it corresponds to a volcanic arc formed by magmatic processes related to Late Mesozoic subduction [8; 21; 22]. [PERSON] et al. (2006), [PERSON] et al. (2010), and [PERSON] et al. (2011) [8; 21; 22] utilized combined magnetic anomaly and gravity data to delineate the possible planar locations of the volcanic arc and Mesozoic subduction zone in the northern SCS. They suggested this Mesozoic subduction zone  
Figure 1: Tectonic map of the SCS and adjacent regions. 1�: [15]; 2�: [16]; 4� and 5�: [9]; 2�: [17]; 6�: [18]; 7� and 8�: [10]; 8�: [19]; 9�: [11]; 10�, 2�, and 9�: [4]; 3�: [20]; 8�: [7]. PHR: Penghu Rise; TXNB: Taixinan Basin; DSR: Dongsha Rise; CSD: Chaoshan Depression; YTA: Yitong Ansha. The Speculated volcanic arc (yellow line) follows [8]. Black rectangular box represents the extent of the study area (Figure 2). extends along the northern continental slope of the SCS from the southwestern margin of Taiwan Island via the southwestern depression of Taiwan and the southern part of the Chaoshan Depression to Yitong-Ansha islands. [PERSON] et al. (2006) [PERSON] et al. (2006) conducted a comprehensive analysis of both gravity and magnetic anomalies around the northern SCS and proposed that the subduction may have been caused by the Mesozoic Pacific plate subducting beneath the South China continent.