%0 Journal Article
%T Low-Grade Metamorphism of Permian Mafic Rocks From the Gorz¨®w Wielkopolski Block (Fore Sudetic Monocline, Nw Poland): Age and Mechanism
%A Pawet Bylina
%J Mineralogia
%@ 1899-8526
%D 2006
%I 
%R 10.2478/v10002-007-0004-y
%X The metavolcanic rocks in the Gorz¨®w Wielkopolski area (NW Poland) are andesite-basalts and andesites derived from contaminated within-plate subalkaline basalt melts. K-Ar dating of primary K-feldspar yields an extrusion age of 285¡À5 Ma. This new date suggests that these rocks may be the youngest dated Permo-Carboniferous volcanic rocks within the eastern margin of the North German Basin. Petrological and micro-thermometric data indicate that the volcanic rocks were altered by a sub-greenschist facies, metamorphic process that proceeded within temperatures and pressures ranging from 195-290¡ãC and 63-96 MPa, respectively. The major metamorphic phases, corrensite, pumpellyite, laumontite and prehnite, formed due to interaction between the original volcanic rock and low-saline Na2SO4-rich hydrothermal fluids. Numerical modelling indicates fluid flow in fractures as the most probable explanation for the low-grade hydrothermal metamorphism. Model calculations suggest that the process was of short duration, ca 140-250 years. K-Ar dating reveals three Mesozoic episodes at 121¡À2 Ma, 188-190 Ma and 149¡À4 Ma that can be ascribed to the metamorphism. These ages are similar to previously determined Mesozoic ages from altered volcanic- and clastic rocks in the North German Basin and in the Polish Basin.
%K K-Ar dating
%K hydrothermal metamorphism
%K metavolcanic rocks
%K Polish Basin
%K North German Basin
%K Mesozoic hydrothermal activity
%U http://versita.metapress.com/content/g3311511101rh625/?p=12e1be26a1cd4382b679a62ee3c4c6a0&pi=0