Two major tectonic processes can be identified to have controlled mantle exhumation and the subsequent evolution predating the location of the deformation and magmatic activity into a mature oceanic spreading center. One process is controlled by downward concave detachment faults that are interpreted to be responsible for the exhumation of mantle rocks resulting in the formation of the OCT. A second process is manifested by widespread normal faulting that postdates mantle exhumation. This second event (late Aptian/early Albian) predates unit B and seems to be linked to a major magmatic event that is distributed throughout the southern North Atlantic and may be linked to a plate tectonic reorganization. This event is responsible for the tectonometamorphic evolution that is well documented in the more oceanward parts of the OCT in unit A on the Newfoundland margin, and time-equivalent sedimentary breccias drilled at basement highs in the OCT off Iberia. In the following, we discuss the significance of these two episodes and how they are recorded in the sedimentary architecture of the deep Iberia-Newfoundland margins.
4.2.1. Mantle Exhumation (Late Valanginian to Late Aptian)
 Manatschal et al.  proposed, based on a kinematic inversion of the LG12 section, that the crust was already thinned to less than 10 km by Tithonian time and that the geometry of the faults active during final rifting changed from upward to downward concave (for a more detailed discussion, see also Manatschal ). On the basis of the detailed mapping of the sediments in SIAP, we are now able to demonstrate how the transition from upward to downward concave faults during final rifting is documented by the sedimentary architecture. Figure 10 illustrates the reconstructed LG12 and CAM144 sections for the onset of final rifting dated as Tithonian (150–145 Ma), the end of the deposition of subunit A2, and the base of unit B (late Aptian to early Albian) that represents the end of tectonic activity and is related to the Atlantic Ocean opening between Iberia and Newfoundland.
Figure 10. Temporal and spatial evolution of sediment deposition in the SIAP inferred from the structural restoration of the LG12 and CAM144 seismic sections.
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 The prefaulting stage is constrained in the SIAP by Tithonian limestones and claystones showing outer shelf environments drilled at ODP sites 901, 1065 and 1069 [Wilson et al., 2001; Urquhart, 2001]. The fact that shallow water limestones of Tithonian age were also drilled at ODP Site 639 at the Deep Galicia margin further to the north suggests that Tithonian age sediments were deposited across the entire future distal margin, forming a large platform. The occurrence of such a shallow water platform shows that before Tithonian time the future distal margin was little affected by high-angle faulting, despite the strong evidence that the crust was by that time already thinned to less than 10 km [Manatschal et al., 2001].
 The mantle exhumation stage is difficult to date, but based on the available drilling results, final rifting seems to be associated with strong subsidence and exhumation processes. A major deepening of the basin from a restricted shelf environment during Tithonian to an open marine, outer shelf to upper slope environment of less than 1500 m water deep is documented by the nannofossil chalk bed drilled at Site 1069 over a basement high [Urquhart, 2001]. Higher subsidence rates can be expected for the adjacent fault-bounded basins. The evidence for exhumation along detachment faults is mainly documented by drilling at sites 900, 1067 and 1068 over Hobby High [Manatschal et al., 2001]. On the basis of structural observations and 40Ar/39Ar ages, it was proposed that the rocks drilled at sites 900, 1067 and 1068 were exhumed along a downward concave fault toward the seafloor. During exhumation the tectonized basement drilled at sites 900 and 1067 acted as source for the sedimentary breccia drilled at Site 1068. These basement clasts were deposited within a sedimentary matrix dated as Valanginian to Barremian (∼140–125 Ma) [Manatschal et al., 2001]. The tectonic overprint of the sedimentary breccia toward its contact to the underlying mantle [Wilson et al., 2001, Figure 17] suggests that the sedimentary breccia was deposited onto the active HHD detachment. Activity along this fault occurred around 137 Ma (late Valanginian), which is the time when the basement rocks drilled at sites 900 and 1067 were cooled below 150°C.
 The temporal and spatial evolution of final rifting is also documented in the sedimentary architecture of unit A in the LG12 and CAM144 sections. The major features that can be observed are that subunits A1 and A2 form well-imaged growth structures in basins III and IV in the CAM section whereas such structures are neither observed in the adjacent basins I and II in CAM144 nor in the LG12 sections. In these sections, the time-equivalent reflections are parallel and flat and onlap onto the adjacent basement highs. These observations, illustrated in Figure 10, can be explained by a migration of deformation from the east to the west, i.e., from more continentward parts toward the future ocean, and from south to north, i.e., parallel to the propagation of the ocean.
 Dating the migration of deformation based on growth structures is, however, hampered by the observation that growth structures are only valuable indicators for syntectonic deposition in classical rift basins bounded by high-angle faults. In the SIAP, we argue that such classical high-angle normal faults can evolve along-strike into low-angle top basement detachment faults. Therefore the apparent migration of rift activity toward the north may be an artefact reflecting the changing mode of deformation from upward to downward concave faults along strike rather than dating the age of active faulting. For the LG12 section, Manatschal  proposed that high-angle upward concave faults develop, through time, into downward concave faults [see Manatschal, 2004, Figure 13]. Such a development would imply that structures that are active, at a given time along the margin, overprint each other in sections perpendicular to the margin. This observation explains the link between the spatial and temporal evolution of structures documented in the 3-D sedimentary architecture of deep margins and shows that there is a strong link between fault geometry, basin architecture and sedimentary structures.
4.2.2. OCT Morphotectonic Evolution (Late Aptian–Early Albian)
 A comparison of the sedimentary breccias drilled at sites 897 and 899 and dated as Aptian with those drilled at Site 1277 on the conjugate Newfoundland margin shows that they share many similarities. A key observation is that they contain mafic clasts, derived from EMORB and alkaline magmas. Dating of EMORB igneous rocks at sites 1070 and 1277 gave ages similar to those expected from the accretion age of the underlying crust [Beard et al., 2002]. Alkaline igneous rocks forming magmatic veins at Site 1277 and sills at Site 1276 gave ages of 113 ± 2 Ma and younger [Jagoutz et al., 2007]. Thus the magmatic system that affected the OCT is complex and polyphase. Because at Site 1277, the breccias contain clasts of the alkaline magmas dated as early Albian and are onlapped by unit B which is Albian to Cenomanian in age, the age of the highs must coincide with or postdate the emplacement of alkaline magmas and predate the onset of deposition of unit B. That dates the formation of the highs as late Aptian to early Albian (∼112 Ma). Although no evidence for the uplift of highs is observed in seismic sections from the OCT in the SIAP (unit A is too thin to be imaged in seismic sections), on the conjugate Newfoundland margin there are geometrical relationships between units A and B that support such a late Aptian/early Albian event: Between sites 1276 and 1277 in the Newfoundland margin, unit A presents continentward tilted reflections that are onlapped by reflections belonging to unit B (Figure 1c). Although the overall mechanism of tilting is not yet understood, the fact that the breakaways of successive faults are more elevated going oceanward may indicate that this event is associated with a large-scale up-warping of the previously exhumed and accreted mantle lithosphere.
 On the basis of the mapped sediment architecture and stratigraphic ages obtained for units A and B and suggesting that M3 (128 Ma) dates the onset of seafloor spreading, we envisage the following tectonomagmatic evolution (Figure 11). After exhumation leading to the formation of a wide zone of exhumed mantle (136 to 128 Ma), accretion of oceanic crust started at 128 Ma and continued for about 10 m.y. Seafloor spreading during this initial stage is documented by magnetic anomalies M3 to M0 and the formation of EMORB basalts that were sampled as clasts in mass flows at sites 897, 899 and 1277. During the final deposition of unit A, deformation spread out over previously accreted oceanic crust to cover a region more than 200 km wide overall, suggesting a transient reduction or even cessation of seafloor spreading activity at the ridge. The reason for the delocalization of the deformation is not yet understood, but it seems that it occurred during or shortly before a major magmatic event that is documented throughout the southern North Atlantic. Local evidence for such an event are (1) sills that were drilled at Site 1276 coincide on the Newfoundland side with a strong reflection (the U reflection) that is also observed in the SIAP; (2) the thermal perturbation that is recorded by 40Ar/39Ar cooling ages on plagioclase in 128 Ma old gabbros drilled at Site 1070 (the age of 110.3 ± 1.1 Ma, interpreted as a cooling age is younger than the overlying sediments and cannot be interpreted as a simple cooling related to exhumation); and (3) the occurrence of Aptian mass flows drilled and seismically imaged on several highs. Thus our observations suggest that the morphotectonic phase leading to the basement topography observed in the OCT of the Iberia-Newfoundland margin is related to a major tectonomagmatic event that may be, in turn, linked to a major plate tectonic reorganization. Tucholke et al.  called this event the “Aptian event” and interpreted it as resulting from the final separation of subcontinental lithosphere due to the rising asthenosphere initiating seafloor spreading. Further research is necessary to better understand the nature of this event.
Figure 11. A conceptual model illustrating the temporal and spatial evolution of continental breakup in the Iberia-Newfoundland margins.
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