Quantifying the Effect of Mantle Phase
Transitions and Application to the Vøring Basin, Off-Shore Norway
Nina S.C. Simon, Lars H. Rupke, and Yuri Y. Podladchikov
Physics of Geological Processes, University of Oslo, PO Box 1048 Blindern, 0316 Oslo, Norway
e-mail: [email protected]
Temperature and composition of the extending lithospheric mantle strongly influence the physical properties of the stretched lithosphere and might vary significantly during the process. The physical property that is most important for subsidence and uplift in a sedimentary basin is density. The density distribution of the lithosphere is non-linear and discontinuous due to complex mineralogy and, most importantly, phase
transitions. Lithospheric mantle enters the plagioclase stability field above ~50 km, which can cause a large decrease in density (80-100 kg/m3). The integrated change in density of the isostatic column due to the plagioclase-in
phase
transition is predominantly influenced by the aluminum and sodium contents of the mantle. The amount of subsidence caused by
phase
transitions therefore depends on the composition of the mantle, in addition to classical parameters such as the thickness of the crust, the initial geotherm and the amount of stretching. The
phase
-transition effect is most pronounced for thin crust, strong mantle thinning/upwelling and relatively fertile mantle compositions rich in aluminum and sodium, and can exceed the effect of thermal expansion. This could explain the pronounced syn-rift uplift and accelerated post-rift subsidence observed in some basins.




AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands