<abstract xml:lang="en" xmlns="http://www.w3.org/1999/xhtml">The metavolcanic rocks in the Gorzów 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±5 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°C 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, <italic>ca</italic> 140-250 years. K-Ar dating reveals three Mesozoic episodes at 121±2 Ma, 188-190 Ma and 149±4 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.</abstract>

The metavolcanic rocks in the Gorzów 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±5 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°C 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±2 Ma, 188-190 Ma and 149±4 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.

Low-Grade Metamorphism of Permian Mafic Rocks From the Gorzów Wielkopolski Block (Fore Sudetic Monocline, Nw Poland): Age and Mechanism

Institute of Geological Sciences, Polish Academy of Sciences, ul. Twarda 51/55, 00-818 Warszawa, Poland; bylina@twarda.pan.pl

Mineralogia

The metavolcanic rocks in the Gorzów Wielkopolski area (NW Poland) are andesite-basalts and andesites derived from contaminated within-plate subalkaline basalt...

Low-Grade Metamorphism of Permian Mafic Rocks From the Gorzów Wielkopolski Block (Fore Sudetic Monocline, Nw Poland): Age and Mechanism

Published Online: Feb 05, 2007

Page range: 3 - 49

DOI: https://doi.org/10.2478/v10002-007-0004-y

Keywords
K-Ar dating, hydrothermal metamorphism, metavolcanic rocks, Polish Basin, North German Basin, Mesozoic hydrothermal activity

This content is open access.

Low-Grade Metamorphism of Permian Mafic Rocks From the Gorzów Wielkopolski Block (Fore Sudetic Monocline, Nw Poland): Age and Mechanism

Published Online: Feb 05, 2007

Page range: 3 - 49

DOI: https://doi.org/10.2478/v10002-007-0004-y

KeywordsK-Ar dating, hydrothermal metamorphism, metavolcanic rocks, Polish Basin, North German Basin, Mesozoic hydrothermal activity

This content is open access.

Keywords
K-Ar dating, hydrothermal metamorphism, metavolcanic rocks, Polish Basin, North German Basin, Mesozoic hydrothermal activity