Geochemical Aspects of Metapsammit Frictional Melting During Seismic Movements (By the Example of Pseudotachylytes of the Ladoga Region)

Abstract

Based on geochemical analyses of tectonic pseudotachylytes and their host rocks the features of redistribution of major, rare and rare-earth elements during seismogenic frictional melting of arkose-type metaterrigenous rocks from different-temperature zones of regional metamorphism) of Northern Ladoga region are considered. Multidirectional trends in variations of the major elements oxides contents in the triad protolith-blastocataclasite-pseudotachylyte were revealed, but a unidirectional increase of the frictional melt basicity in comparison with the protolith was established. Geochemical evidence of partial selective melting of source rocks is considered. Peculiarities of rare and rare-earth elements fractionation during transition to the melt of protolithic material, as well as during its subsequent partial crystallization are shown. The appearance of positive europium anomaly in the melt matrix of all three sampling points is noted. By changes of these elements’ concentrations in zones of pseudotachylyte substrate generation and in areas of its injection their differential mobility during frictional melting in a zone of dynamic movement is estimated.