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Conferència "Linking petrology and lithosphere geodynamics - from oceanic ridges to cratonic basins"

Notícia | 20-05-2008

Conferència a càrrec de Nina Simon, Physics of Geological Processes, University of Oslo, Blindern, Oslo, Noruega.
SEMINARIS DE LA FACULTAT DE GEOLOGIA I L'INSTITUT DE CIÈNCIES DE LA TERRA "JAUME ALMERA"

Universitat de Barcelona (UB)
Consell Superior d'Investigacions Científiques (CSIC)

Dia: Dimarts, 20 de maig
Hora: 12:00 h.
Lloc: Sala d'actes de l'Institut "Jaume Almera"

Resum: Petrology gives us information about phase relations in rocks and how they change with varying pressure and temperature. These phase relations, i.e. the proportion of minerals and their compositions, determine the physical properties of the rock such as density, shear and bulk moduli, viscosity etc. Moreover, mineral reactions caused by changes in pressure-temperature conditions or variations in bulk composition may significantly change the volume of the rock and/or consume or release heat. While some of the interactions between thermo-mechanical processes and petrology/geochemistry have been well explored for deep mantle convection, they have been largely overlooked in quantitative modeling of lithosphere scale geodynamics.
We have investigated in detail the changes in density of the mantle in an extending lithosphere due to changes in temperature, pressure and composition. For fertile mantle at a strongly stretched continental margin, the predicted subsidence in a sedimentary basin using these petrologically sound densities differs significantly (~1000 m using a simplified one-dimensional kinematic model) from the one predicted taking only the effect of thermal expansion on density into account. Application to e.g. the hydrocarbon-bearing Vøring basin off-shore western Norway using complex thermotectono-stratigraphic basin reconstruction models confirms that large syn-rift uplift can be fitted without invoking unrealistically high temperatures if petrological densities are used.
First dynamic thermo-mechanical-petrological modeling of the formation of the oceanic lithosphere shows that the subsidence of the sea floor away from the ridge and the patterns of small scale convection underneath a mature oceanic plate may be influence by mantle phase transitions as well. Other areas where volume changing metamorphic reactions might have an important influence on the dynamic evolution of the lithosphere are intra-cratonic basins. We propose that these basins form by deepening of the crust-mantle boundary in a compressional setting. Lower crustal phase transitions lead to a densification of the lithosphere and may cause the formation of deep basins in the absence of strong extension. This scenario is explored for the 20 km deep basin underlying the Eastern Barents Sea.


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