DYNAMIC PROCESSES CONTROLLING DEVELOPMENT OF RIFTED BASINS
Peter A. Ziegler
Geological-Palaeontological Institute, University of Basel, Bernoullistr. 32,
4065 Basel, Switzerland
Lithospheric extension, controlling the development of rifted basins, is driven by the combination of plateboundary
forces, frictional forces exerted on the base of the lithosphere by the convecting asthenosphere
and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system.
Although mantle plumes are not a primary driving force of rifting, they play an important secondary role by
weakening the lithosphere and by controlling the level of rift-related volcanic activity. A distinction between
“active” and “passive” rifting is only conditionally justified.
Extension of the lithosphere, depending on its rate and magnitude and the potential temperature of the
asthenosphere, can cause by adiabatic decompression partial melting of the lower lithosphere and upper
asthenosphere. The level and timing of volcanic activity is highly variable in rift systems. The lack of
volcanic activity implies “passive” rifting. An initial “passive” rifting stage can be followed by a more
“active” one during which magmatism plays an increasingly important role. Magmatic destabilization of the
Moho may account for the frequently observed discrepancy between upper and lower crustal extensionfactors.
Combined with evidence for thermal thinning of the mantle-lithosphere, this suggest that the volume
of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models.
The structural style of rifts is controlled by the rheological structure of the lithosphere, the availability of
crustal discontinuities which can be tensionally reactivated, the mode (orthogonal or oblique) and amount of
extension, and the lithological composition of pre- and syn-rift sediments. Simple-shear extension prevails
in rifts... [continues]
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