Dolomitisation, brecciation, and dedolomitisation occurring in fault zones
in the Variscan fold and thrust belt in the Cantabrian Zone (Northern Spain
) in three different tectonic units (Ponga, Picos de Europa and Esla) have
been investigated and compared. Cementation patterns are similar in all uni
ts: dolomite cements always predate calcite cements in brecciated limestone
(Barcaliente Fm.). Moreover, carbon and oxygen isotopic composition trends
are comparable. However, the precipitating fluids are distinct in each fau
lt zone, as evidenced by microthermometry and Raman spectroscopy. The evolu
tion of the fault zones is illustrated by the precipitation of cements from
different types of circulating fluids in several pulses. (C) 2000 Elsevier
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