Читать книгу Continental Rifted Margins 2 - Gwenn Peron-Pinvidic - Страница 22

The WIM has historically been, and remains, at the forefront of fundamental research on the breakup and development of oceanic basins. Three ODP legs (103, 149 and 173), many geophysical campaigns, and a recent 3D seismic volume place the WIM among the best-documented continental margins. These data allowed the definition of the earliest concepts of oceanic basin development, and still today provide the foundation to the definition of the most recent models of continental breakup. They have provided a glimpse of how extension of the continental lithosphere occurs at rifted margins, demonstrating that rifting is a diachronous process across margins, and suggesting that extension focused/migrated towards the future oceanic spreading center during the rifting history. The latest concepts can be summarized through three main models (section 1.4): depth dependent stretching, cross-cutting polyphase faulting and sequential faulting.

These models imply fundamental differences in terms of the timing and mechanisms of faulting and thinning of the continental crust, of the number of fault phases involved in rifting, of the location of the locus of extension through time, of the rate, temperature and amount of magma involved during lithospheric separation. However, because of the technical, scientific and human implications in recovering direct data from deep present-day rifted margins, these models remain fundamentally unconstrained. Indeed, while the vast amount of data available West of Iberia has provided precise images of the structures of the margin, they currently miss the temporal control to understand the kinematics and the evolution of rifting processes. To provide further time constraints during rifting of the WIM, we need to sample the pre-, syn- and post-rift sediments, as well as the basement, at successive basins across the margins to determine the detailed rift history by:

1 1) characterizing the nature of the basement and the oldest synrift/prerift unit;

2 2) dating the sequences deposited during slip on the block-bounding faults above extensional detachment faults, thus recording time constraints on the slip of individual faults across the distal margin;

3 3) constraining the age and the nature of the youngest synrift units deposited after local faulting to define the mechanisms of post-faulting uplift and faulted-blocks rotation;

4 4) defining the later subsidence of the margin from discrete palaeoenvironmental data (e.g. the local CCD and depth of the bathyal sediments) obtained through the post-rift sequence.

FURTHER READING.– The above descriptions are abbreviated and often simplified. If interested in reading and learning further, the reader is referred to the following list of publications and references.

1 – General: (Biari et al. 2021; Cresswell 2018; Epin and Manatschal 2018; Gómez-Romeu 2019; King et al. 2020; Reston and McDermott 2014; Somoza et al. 2019; Sutra et al. 2013; Whiting et al. 2021).