Mode of opening of pull-‐apart basins

Mode of opening of pull-­‐apart basins A comparison between the continental Dead Sea Basin (Dead Sea Transform, Eastern
Mediterranean)
and the oceanic 20°N Basin (Owen Fracture Zone, NW Indian Ocean).
Perspectives for the Eastern Mediterranean strike-slip basins.
East Mediterranean Mee4ng-­‐ Cyprus, November 2014 M. Rodriguez, U. ten Brink, Z. Ben Avraham, and Owen Cruise members
(N. Chamot-Rooke, M. Fournier, P. Huchon, M. Delescluse) University of Haifa, Dr. Moses Strauss department of Geosciences
Ø What is a pull-apart basin?
Stepover configura<on & releasing bends Ø  In the initial definition by Cloos
(1968), the term of ‘pull-apart’
refers to all type of basins
observed along a strike-slip fault
Ø  Pull-apart basins form at
stepover areas along strike slip
faults, and display a large variety
of structures
Subsidence curves ($me in Myrs) Ø  Pull-apart basins are
characterized by extremely fast
subsidence
Ø  What are the mechanisms of
pull-apart basin opening? What
is the mechanism at the origin
of the fast subsidence?
Depth (km) Mode of opening : the seminal model of Mann et al.
1983
Ex. Blanco Fracture Zone, Pacific Ocean Ø Con$nuum of opening of pull-­‐apart Ø Rela$onships between pull-­‐apart dimensions and amount of rela$ve mo$on Stepover basins around Arabia A con$nental pull apart : the Dead Sea A con$nental pull apart / in a core complex field area: the North Aegean Trough An oceanic pull apart basin : the 20°N Basin along the Owen Fracture Zone Extreme subsidence in different types of lithosphere. Understanding subsidence at pull-­‐apart basins, A way to further constrain the mechanical behaviour of the lithosphere? Mode of opening of the Dead Sea
Ten Brink and Flores, JGR, 2011 Subsidence curve of the Dead Sea basin The Dead Sea Basin (132 x 16 km) Along the Levant Fault Ben Avraham et al GJI, 2008 Ø  The subsidence rate increased dras$cally between 2-­‐3 Ma Ø Considering constant the present-­‐day slip rate of the Levant Fault of 4-­‐5 mm/yr, only ~15 km of rela$ve mo$on has been accommodated Misfit between the size of the basin and the amount of rela$ve mo$on The Dimensions of a pull-­‐apart basin depend on the ini$al configura$on of the stepover Dooley & Schreurs, Tectonophysics, 2012 Mode of opening of the Dead Sea and the role of gravity driven tectonics Kashai and Croker, Tectonophysics,1988 Smit et al., Tectonophysics, 2008 The salt acts as a décollement layer The superficial structure of Dead Sea is similar to a ‘rollover’ …and is controlled by gravity-­‐driven tectonics Sandbox analog modelling The isola$on of a third block is needed to reproduce the behavior of a listric fault Ø Consistent with the dimensions of the basin Mauduit & Brun, Tectonophysics, 2008 Mode of opening of the Dead Sea : what happened at depth? Ø No moho uplift
Ø The Dead Sea is an
upper crust structure
Ø Probably a major
décollement level at the
brittle/ ductile transition
(~15-18 km)
Ø But where is the base of the upper crust that used to be below the DSB? What drives the duc$le flow? Ten Brink and Flores, JGR, 2011 Ø Several hypothesis : fluid circulation, ductile
channel flow along the Dead Sea Transform…
but what triggered the ductile flow around 2-3
Ma?
Ten Brink and Ben-­‐Avraham, Tectonics,1989 Working hypothesis on the Dead Sea Ø The Dead Sea Basin may be considered as an upper-crust scale rollover structure,
resulting from the subsidence of a third block enclosed by the stepover area
….Similar to what inferred for salt tectonics, but at the upper crust scale
Ø No major distribution of extension – extension is accommodated by the main bounding listric faults
Ø The ductile flow may be channeled towards the main bounding listric fault
Ø What triggered this ductile flow at 2-3 Ma? Coeval with Early Pleistocene climate
change
Ø High erosion rates can enhance fault slip rates (Olive et al., GRL, 2014, among many
others)
Ø Increased fault slip rates can induce shear heating processes (sensu Fleitou &
Froidevaux, 1980) at the base of the listric fault… and promote ductile flow
Ø ROLE OF TECTONIC-CLIMATE INTERACTION IN THE DEAD SEA AREA
On the other side of Arabia : the Owen Fracture Zone Main characteris<cs : Ø  800-­‐km-­‐long strike-­‐slip boundary Ø  Pure strike-­‐slip mo$on Ø  Major stepover basins Ø  Dextral offsets of the Owen Ridge, in the order of 10-­‐12 km Ø  Rate : 3 ±1 mm.yr -­‐1 Ø  Age of the OFZ : 3-­‐6 Ma-­‐old Fournier et al., EPSL, 2011 The 20°N pull-apart along the Owen Fracture Zone
The 20°N Basin (90 x 12 km) Mul$beam mapping Rodriguez et al., Tectonics, 2013 The Dead Sea Basin The 20°N pull-­‐apart basin displays a surface structure similar to the Dead Sea Basin in spite of a different rheological segng (oceanic versus con$nental)! Age of opening of the 20°N Basin
Ø  Maximal age : deac$va$on of the last channel-­‐levee system at 3.4 ± 1.2 Ma Ø  Minimal age : Onset of contourites at 2.5 ± 1 Ma Rodriguez et al., Tectonics, 2013 Age of opening at 2.4 Ma according to long distance correlaCon with an ODP Site Ø Consistent with the age of the OFZ Structural evolu$on of the 20°N pull-­‐apart Core site Rodriguez et al., Tectonics, 2013 Ø 
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At 1.8 ± 0.5 Ma, the C3 reflector indicates that the basin already reached its present-­‐day dimensions. A 90 km long basin opened in less than 1 Ma Rollover structure Gravity driven tectonics (Shale tectonics?) The structural similari$es between the DSB and the 20°N Basin are due to the dominant control of gravity driven processes. The structure of the 20°N Basin is not controlled by the rheology of the oceanic lithosphere Duc$le flow in the mantle? Lack of informa$on on the deep structure of the basin The North Aegean Trough in the Aegean Sea Ø Formed over a con$nental lithosphere previously strechted by core complex exhuma$on Ø Peculiar mechanical proper$es of the lithosphere, different from the Dead Sea area, also allowed the develoment of a large pull-­‐
apart like basin there Ø Age of the structure not well constrained (around Pliocene… )Tectonic-­‐climate interac$ons cannot explain the subsidence there…Which process may be involved? Papanikolaou et al., Mar. Geol.,2002
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