HR: 13:55h
AN: T33D-02    [Abstracts]
TI: The Formation of Parallel-Dipping Normal Faults on Mature Passive Margins: Insights from Numerical and Analogue Models
AU: Schreurs, G
EM: schreurs@geo.unibe.ch
AF: Institute of Geological Sciences, University of Bern, Baltzerstrasse 1, Bern, 3012, Switzerland
AU: * Buiter, S
EM: susanne.buiter@ngu.no
AF: Centre for Geodynamics, Geological Survey of Norway, Leiv Eirikssons vei 39, Trondheim, 7491, Norway
AB: Observations indicate that extension of the continental upper crust is often accommodated by arrays of normal faults. These faults can have alternating dip directions and define a horst and graben structure or they can all dip in the same direction. Arrays of parallel-dipping normal faults are, for example, observed in the extending domains of offshore Norway, the Basin and Range Province, the Galicia margin west of the Iberian Peninsula, and offshore Angola. We aim to investigate factors and mechanisms that favor the formation of an array of parallel-dipping normal faults over a sequence of horst and graben structures. We focus on the mature stages of passive margins, when gravity spreading and multiphase rifting play a role. We use numerical models and analogue experiments to study fault formation on the scale of the upper crust. The numerical experiments use two-dimensional finite element models that can achieve large deformation with free surface behavior. The analogue experiments are built of (brittle) sand and (viscous) silicone and their internal deformation is visualized in an X-ray scanner. We show that gravity spreading of brittle sediments over a weak layer, such as salt or shales, leads to the development of parallel dipping fault arrays that dip either towards or away from the ocean domain. The dip direction is controlled by the basal shear stress at the brittle-viscous interface. This basal shear stress is in turn controlled by the relative velocities of the brittle and viscous materials and thus by the slope of the layers, their thickness ratio and their rheologies.
DE: 0545 Modeling (4255)
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8122 Dynamics: gravity and tectonics
SC: Tectonophysics [T]
MN: 2007 Fall Meeting