Читать книгу Continental Rifted Margins 2 - Gwenn Peron-Pinvidic - Страница 15

The DGM faces the southeast flank of the Flemish Cap at the Newfoundland Margin (Figure 1.1a and sections SCREECH 1/ISE1 on Figure 1.2), whereas the SIAP faces the North Newfoundland Basin (Figure 1.1a and sections SCREECH 2/LG12-TGS on Figure 1.2). Palaeographic reconstructions have proposed that both the Western Iberian and the Newfoundland margins represented a pair of conjugated margins before continental breakup (e.g. Sutra et al. 2013). The final root of S observed at the DGM is incidentally believed to be currently located on the Flemish Cap (Reston et al. 2007).

A key finding of the drilling at the SIAP was the demonstration of the presence of a wide-zone of unroofed mantle (from Site 900 to 1070 and oceanward, Figure 1.4) that extends between the hyper-thinned continental crust and the first clear magnetic polarity reversals (Figure 1.1, M0), outlining the areas where seafloor spreading occurred. This observation west of Iberia has underpinned the concept of mantle unroofing on a large-scale at other rifted margins (Whitmarsh et al. 1998; Manatschal et al. 2001). It has also led to the concept of margin pair asymmetry (e.g. Pérez-Gussinyé and Reston 2001), as comparison of sections across both margin segments (Figure 1.2) clearly shows the asymmetry of the unroofed mantle (e.g. Reston 2009). The mantle extends across ~250 km within the SIAP (sections LG12-TSG, IAM-9, Figure 1.2), versus ~50 km west of the COT offshore the Northern Newfoundland Basin (section SCREECH2, Figure 1.2). Asymmetry between the margin pair also exists when considering the thickness of the continental crust: comparison between the two margins still shows a “normal” crustal thickness of ~30 km at the Flemish Cap, whereas at the Galicia Margin, the GIB and the GB are characterized by relatively thin crust, of about ~10 km (e.g. Druet et al. 2018). This asymmetry between the WIM and its Newfoundland conjugate margin has been interpreted as having developed once the crust had become completely brittle (e.g. Pérez-Gussinyé and Reston 2001; Reston 2009).