MATERIAL TRANSPORT IN CHANNELIZED FLUIDS-EXAMPLES FROM HIGH-TEMPERATURE SHEAR ZONES IN THE CENTRAL-EUROPEAN VARISCAN BELT

Two Variscan small scale shear zones and their precursors were analyze d to evaluate fluid-assisted chemical and physical changes. The retrog rade transformation of the Weissenstein eclogite under amphibolite fac ies conditions (Munchberg Massif/Bavaria) and the shear deformation in the Lattersberg amphibolite (Odenwald/Hesse) are accompanied by signi ficant mass transport, mainly of K, Ba, P, Sr, Zr and the LRE elements . The whole rock and mineral chemistry reveal that the active fluids d uring retrogression were alkali-rich as well as F- and/or (PO43-)-rich , and probably explain the observed 4 mobility and transport of so-cal led ''immobile'' elements such as Zr. The calculated fluid/rock ratios of the shear zones are not higher than 2-10. The comparison with retr ogressed eclogites of the Schwarzwald shows similar chemical changes a s in the Weissenstein eclogite. Additionally, the comparison with retr ogressed but minor deformed parts of the Weissenstein eclogites reveal s that the degree of chemical changes does not depend on the state of deformation. The transformation of the eclogites led to a significant volume increase of about 20%, which must imply structural consequences like pure shear ductile deformation in the surrounding rocks and exte nsional tectonics above the retrogressed rocks. The interpretation of the chemical composition of retrogressed and/or fluid ingressed metaba sic rocks must be handled with caution concerning LIL, LRE elements an d Zr.