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H2O in metamorphism and unexpected behaviour in the preservation of metamorphic mineral assemblages (2001)

Guiraud, M. ; Powell, R. ; Rebay, G.

Oxford, UK : Blackwell Science Inc

Journal of metamorphic geology 19 (2001), S. 0

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ISSN: 1525-1314

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: The preservation of mineral assemblages that were fluid-present during their prograde history is primarily related to the consumption of the fluid by growth of more hydrous minerals as the retrograde history begins. The range of behaviour relating to the preservation of mineral assemblages is examined using calculated phase diagrams for fluid-saturated conditions, contoured for the H2O content of the mineral assemblage. At equilibrium, as a mineral assemblage crosses contours of decreasing H2O content along a pressure–temperature path, it dehydrates, the fluid being lost from the rock. If the assemblage crosses contours of increasing H2O content, the mineral assemblage starts to rehydrate using any fluid on its grain boundaries. When the rock has consumed its fluid, the resulting mineral assemblage is that preserved in the rock. Conditions relating to the preservation of mineral assemblages are discussed, and examples of the consequences of different pressure–temperature paths on preservation in a metapelitic and a metabasic rock composition are considered on phase diagrams calculated with thermocalc.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.0263-4929.2001.00320.x

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Digitale Medien

Calculating the long-term displacement rates of a normal fault from the high-resolution stratigraphic record (early Tethyan rifting, French Alps) (2003)

Chevalier, F. ; Guiraud, M. ; Garcia, J.-P. ; [weitere]

Oxford, UK : Blackwell Science Ltd

Terra nova 15 (2003), S. 0

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ISSN: 1365-3121

Quelle: Blackwell Publishing Journal Backfiles 1879-2005

Thema: Geologie und Paläontologie

Notizen: Displacement rates of normal faults deduced from stratigraphic data are often unreliable. Here we calculate the velocity of motion on a normal fault from the variations in accommodation potential on both sides of the fault within a high-resolution time-frame established by biostratigraphy and physical stratigraphy. Our example is the Ornon normal fault bounding the Early Jurassic Bourg-d'Oisans Basin formed during Tethyan rifting. We show that motion on the fault was discontinuous when examined at high resolution and over a long time interval. During a first interval (Hettangian to Sinemurian Arietites bucklandi zone) a low rate of displacement (=202–423 m Myr−1) coeval with diffused extensional deformation throughout the sedimentary basin is observed. A second interval of localized deformation (Early Sinemurian Caenisites turneri zone) is characterized by higher rates of displacement on the fault (1846 m Myr−1). Our results concur with recent numerical models identifying the main stages of extensional deformation.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1046/j.1365-3121.2003.00508.x

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