Estructuras discontinuas y migración de fluidos durante la evolución tectónica paleógena-neógena de los materiales del Jurásico Superior de la Cuenca del Maestrazgo: Estudio estructural, mineralógico y geoquímico

Abstract

In the western part of the Maestrat Basin (Iberian Range) dolomite and calclte hydrothermal cements fill fractures and "chimney" structures In Tithonian-Berriasian limestones. The timing of fracture cementation is considered in the context of the structural history of the Alpine Orogeny. Three generations of structures filled with carbonate cements were recognized: A) Fractures formed during the Late Eocene- Miocene compressional stage were filled with calcite cement (-8.8%o d180 and +0.8 d13C VPDB) from a fluid of uncertain origin. B) Extensional fractures and C) "pipe- haped" structures developed during the Miocene-Pliocene extensional phase, are filled with four generations of carbonate cements: i) rhombic dolomites; 2) saddle dolomite characterized by high salinity (21.5 to 23.5 % wt. eq. NaCI), high temperatures (Th 110-155BC) and isotopically light d180 ratios (-11.5 to -11.3%o VPDB); 3) calcite replacing (dedolomite) saddle and rhombic dolomite with variable d180 and d13C ratios (-12.2 to -6.8%o d180; -4.4 to +0.2%o d13C), and 4) calcite cement (110-125gC and 160-2609C), with depleted oxygen isotope ratios (-13.4 t o -10 %o d180) and positive carbon ratios (+0.1 to +1.8 %o d13C). These data indicate an hydrothermal, saline and dolomitizing fluid linked to the lixiviation of the Triassic-Liassic evaporites, followed by an input of meteoric water (dedolomitization), which evolved to hydrothermal calcite.