Dolomitisation and brecciation along fault zones in the Cantabrian mountains

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 Science B.V. All rights reserved.