A comparison of the deep structure of the Mid-Norwegian margin and the South China Sea, based on seismic interpretation

• Main Author: Lei Weiping
• Other Authors: Osmundsen Per Terje
• Format: Master Thesis
• Language: unknown
• Published: NTNU 2020
• Subjects: Greenland; East Greenland
• Online Access: https://hdl.handle.net/11250/2781607

Rifted basins are now an important type of basin that produces petroleum, especially in Atlantic margin. The study of rifting process is important for the petroleum prospecting. In this study, we focus on the Mid-Norwegian margin with the emphasis on the Møre and Vøring basin. These two basins have a long extension history after the Caledonian orogeny. The extension history can be divided into 3 main stages: Permian to Triassic, the Late Jurassic to the Early Cretaceous and the Late Cretaceous to Early Tertiary. These rifting periods are not continuous, resulting in 3 unconformities in the study area. In these three unconformities, the Base Cretaceous Unconformity is the most widely recorded in the Mid-Norwegian Margin. Actually, this unconformity represents the ending of the Late Jurassic to the Early Cretaceous rifting phase, tentatively termed as the Base Cretaceous Unconformity. In the study area, the depth of this reflector varies from less than 5 km in the drilled area to 15 km in the deep basin, which indicates different degrees of extension caused by the normal faults. Similarly, the undulation of the top basement is also very notable. Below the top basement, we also recognized some intra-basement reflectors and provided some possible interpretations. Based on the new terminology of domains and breakaway complexes, we subdivided the study area in terms of margin domains and classified major faults in terms of breakaway complexes. Most of the seismic reflection lines used in this study contain necking and distal domain, these two domains are bounded by the outer necking breakaway complex, which is considered as a typical structure in Mid-Norwegian margin. It creates a dramatical accommodation increase in its hanging wall and cuts into the lower crust and upper mantle, coupling the deformation from upper crust to upper mantle. In the distal domain, a distinct feature is the distal breakaway complex, which is the inner boundary of an area of potential tectonic unroofing. Based on this fault, the distal domain can be subdivided into hyperextended and unroofed/exhumed subdomain. In some profiles, this breakaway complex can be clearly observed, giving a strong evidence for possible mantle exhumation. Since 1990s, South China Sea has been considered as a mini Atlantic, because these two are both born in a divergent geological setting. From two sections across the Eastern subbasin and Southwestern subbasin, we find some differences between the South China Sea and East Greenland-mid-Norwegian conjugate margins. First, two sag basins, Xisha Trough and Baiyun Sag, are notable in the proximal domain. In these two sag basins, some normal faults are interpreted to incise into the mantle rocks, and they are widely considered as failed continental breakup, possibly resulting from a disappearance of geothermal source. The outer necking breakaway complex, so typical in the Mid-Norwegian margin, cannot be found in South China Sea. There, the necking domain seems to connect with the distal domain directly and the boundary of these two domains is ambiguous. The distal domain of South China Sea is very narrow and tectonic unroofing caused by low angle detachment faults has not been widely observed. We suggest that South China Sea may not have experienced exhumation or even a hyperextension stage except in two sag basins. These differences may result from different nature of lithosphere, duration of rifting and movement of related plates.