Controls on the Thermomechanical Evolution of Hyperextended Lithosphere at Magma‐Poor Rifted Margins: The Example of Espirito Santo and the Kwanza Basins. (19th November 2019)

• Record Type: Journal Article
• Authors: Lavier, L.L.; Ball, P. J.; Manatschal, G.; Heumann, M. J.; MacDonald, J.; Matt, V. J.; Schneider, C.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 20:Number 11(2019)
• Page Start: 5148
• Page End: 5176
• Publication Date: 2019-11-19
• Subjects: rifting -- margins -- hyperextension -- detachment faults -- numerical modeling -- South Atlantic; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2019GC008580
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: High‐quality, long offset seismic data from many distal rifted margins show evidence for hyper‐extended, <10‐km‐thick crust. Direct observation of such domains is challenging as they lie, at great water depth, buried beneath thick sedimentary sequences and formed by rock‐assemblages that are hydrated and geophysically indistinguishable. Only a few drill holes have penetrated basement at ultradistal rifted margins. These observations, together with outcrops of preserved analogs exposed in collisional orogens, suggest that the complex interaction of detachment faults rooted in a subhorizontal shear zone in the hyperextended crust or, in the serpentinized mantle controls the formation of the ocean continent transition. While depth‐dependent thinning controls the early phases of rifting conforming to classical rift models, we still have a superficial understanding of how normal faults and subhorizontal shear zones form and evolve during rifting and lithospheric breakup. Here we develop a rheological parameterization to simulate the formation of, and slip‐on, large offset normal faults rooted in growing brittle to ductile shear zones. The evolution of these structures leads to the creation of a hyperextended crust and eventually exhumed serpentinized mantle. We also propose a simplified formulation to simulate magmatic underplating and seafloor spreading. The resulting numerical models provide a self‐consistent picture for the evolution of magma‐poor rifted margins from initiation of rifting to seafloor spreading. The model results are compared with first‐order observations of the Kwanza and Espirito Santo conjugate margins in the South Atlantic as well as of magma‐poor margins globally. Key Points: Models of rift to seafloor spreading are consistent with first‐order observations of tectonic/thermal evolution of hyper‐extended margins We propose a new rheological formulation for the formation of shear zone in the semibrittle crust and mantle Model also highlights the progressive evolution and formation of low‐angle shear zones as rifting evolves