Читать книгу Continental Rifted Margins 2 - Gwenn Peron-Pinvidic - Страница 14

Similar to the DGM, the SIAP (Figures 1.1, 1.2 and 1.4) displays a series of tilted blocks bounded by oceanward dipping normal faults that detach along the top of serpentinized mantle. The basement geology across the SIAP is well constrained by numerous seismic experiments and the presence of several ODP boreholes drilled during Legs 149 and 173 (Sawyer et al. 1994; Whitmarsh et al. 1998). Sites 901 and 1065 sampled the top of two tilted fault-blocks and recovered shallow-water clastics (Figure 1.4), believed to indicate the presence of continental basement at depth (Whitmarsh et al. 1998). Sites 1067, 900 and 1068 sampled the same block ~30 km west of Site 1065. Site 1067 recovered anorthosites, amphibolites and tonalites, and Site 900 sampled mafic granulites, all interpreted as lower crustal rocks, while Site 1068 drilled serpentinized peridotites, which were interpreted as serpentinized mantle (Whitmarsh et al. 1998). Underlying rotated blocks between Sites 1065 and 1067, the H detachment is warped up and separates Site 900 from Site 1068 (Figure 1.4), so similarly to S, H likely represents a serpentine detachment delineating the CMB (Chian et al. 1999). Cutting across and rotating the H detachment, the fault bounding the western side of Site 1068 has been interpreted as marking the development of a newly formed detachment, which has been variously termed F detachment (Krawczyk et al. 1996) and HHD detachment (Manatschal et al. 2001, pp. 405–428). F/HHD defines the top of seismic basement from this high down to a fault block drilled at Site 1069. This rider block appears to be an allochthonous continental slice (based on the recovered sediment) resting on the same peridotitic basement as the one sampled at Site 1068. Site 899 recovered serpentinite breccias intercalated with sediments, indicating the presence of a nearby serpentinized high (Whitmarsh et al. 1998), and Site 897 recovered highly sheared, partially serpentinized mantle peridotites (Sawyer et al. 1994). Finally, Site 1070, located 15 km east of the M0 magnetic anomaly (Figure 1.1), recovered serpentinized mantle rocks and gabbro.