rapid
THICKENING AND SYNCONVERGENT EXHUMATION OF THERMALLY WEAKENED and THINNED
CRUST in the vosges
mountains
Friday, September 24
Excursion leaders: Karel Schulmann1, Jean-Bernard Edel1
and Zuzana Kratinová2
1 Ecole et Observatoire des Sciences
de la Terre, Strasbourg,; 2 Institute of Petrology
and Structural Geology,
Charles University, Praha
2 ; schulman@illite.u-strasbg.fr
The proposed field trip describes an evolution from (I) sedimentation and magmatism during back-arc extension in the southern Vosges, (II) compression leading to burial and granulite-facies metamorphism, followed by (III) exhumation, formation of dehydration melts, migmatites and late intrusive granites in the central Vosges and (IV) magmatic evolution and deformation of low-grade rocks of the Northern Vosges.
Based on U-Pb, Ar-Ar dataset and PT estimates we shall constrain this evolution to no more than 20-25 Myr. New results of structural and magnetic anisotropy susceptibility (AMS) studies from (cca. 335 Ma) high-grade gneisses, (both cca. 340 and cca. 325 Ma) granitoids and migmatites from deeply eroded Vosges orogenic root section as well as from supracrustal levels show the existence of an early high grade steep gneissosisty in the root that is parallel to steep slaty cleavage in metasediments and emplacement fabric in syntectonic granitoids in Devonian to Carboniferous basin to the south. This early compressional fabric is in the domain of hot orogenic root reworked by sub-horizontal viscous flow deformation that is connected with mechanical collapse of orogenic lid. To the north, the root is thrust over the rigid (Saxothuringian) basement along highly oblique Lalaye-Lubine shear zone. However, adjacent northerly “Saxothuringian” granitoids show fabrics that are not consistent with emplacement in compressional regime, but reveal features of gravity driven mechanical collapse of composite magma chamber. We discuss the alternations of compressional and extensional fabrics in infra- and supra-structure of orogen during very short time interval as a result of superposed far field forces generated by activity of northerly subductional zone.
Min/max participants: 13-22