## 6 Discussion
### Deep Subsurface Structures from Long Wavelength Data  
The geology of crystalline basement underneath Luconia Province is poorly known due to limited high-resolution data that can be imaged to these depths. It is certain that the basement of Luconia Province was originated and equivalent to the continental fragments drifted off from the southern china during the creation of the South China Sea marginal basin [21]. In this context, the basement material for Luconia Province is similar to the basement of Dangerous Grounds and Reed Banks. Earlier interpretation by [21; 23] estimated the depths for the crystalline basement within Central Luconia (coverage area for airborne gravity and magnetic) varies from 4 to 8 km [23]. However, the structural behavior of the crystalline basement is still undiscovered.  
Through this study, the magnetic (crystalline) basement structure is revealed by the analysis of the long wavelength aeromagnetic maps. Majority of structural trends in E-W, NNW-SSE and NWW-SEE directions are interpreted on aeromagnetic maps (Table 2). These trends are not seen in structural map of [51; 52] (Figure 13B). These E-W to NWW-SEE trends interpreted on the aeromagnetic data are assumed to be reflecting the magnetic basement of Central Luconia Province The faults interpreted on the aeromagnetic mapsare expected to represent the tectonic events formed during Cretaceous- Paleocene, at the time Luconia continental shelf began to drift away from the continent of the Southern China. The NNW-SSE and NWW-SEE structural trends accommodate the variation of finite extension of the normal faults and expected to symbolize the transfer faults during the rifting stage.  
Based on similarity of the orientation, the event has high possibility to be related with the movement of older faults that oriented in NNW-SSE to NWW-SEE direction and distributed within the South East Asia (Figure 13A), either in Borneo-Sulawesi or in IndoChina Block. One of the examples is the Red River Fault (RRF) Zone which created NW and NNW striking faults interpreted on acoustic basement along Da Nang Shelf and western of Phu Khanh Basin in Vietnam [55; 56; 57]. The trend is also parallel to the Mae-Ping Fault (Shear Zone) in South Vietnam-Cambodia [58; 56] and similarly striking in the same direction with the Adang Line-Paternoster Fault in South Kalimantan-North Makassar Strait [59; 60; 61]. All these faults were formed by the Eocene.  
The E-W direction fault, as revealed from the first derivatives and analytical signals data (Figure 5D-F and Figure 6), is parallel to the southern variation of the Crocker and Rajang fold-and-thrust belt. A potential high angle fold in E-W direction is observed on the magnetic data (Figure 5) and it has never been imaged and mapped before. Both E-W structural trend and the E-W folded structure imaged by the magnetic data follow the postulated southern boundary of the Palawan and Luconia crustal block, which is otherwise obscured to the amount of contracted sedimentary material. Although this requires further investigation, the NNW-SSE, NWW-SEE and E-W striking faults interpreted on the aeromagnetic maps have potential to associate with the early neotectonics phase in the SW sub basin of the South China Sea. Areas with potential for uplifted magnetic basement or intrusive structures are featured with high amplitude airborne gravity response and low to intermediate amplitude in aeromagnetic response (marked as Area A in Figure 13C). Similarly, it still preserves the domal and anticlinal characters as seen on FTG data and are defined by good contact lineaments/ faults. Yet, the aeromagnetic response (on analytical signal) gives low amplitude. Most intensely magnetic anomalies are detected in the east of Central Luconia Province. Area A is possibly representing tip of up-thrust structure from the magnetic basement or intrusive magnetic bodies in a shallower section (Figure 13C) instead of representing the whole magnetic basement body.