RT Journal Article
T1 The latest Post-Variscan fluids in the Spanish Central System: evidence from fluid inclusion and stable isotope data
A1 Martín Crespo, Tomás
A1 Delgado Huertas, Antonio
A1 Vindel, Elena
A1 López García, José Ángel
A1 Fabre, Cécile
AB The Spanish Central System has been subjected to repeated fluid incursions, which were responsible for a variety of mineralizing episodesincluding W-Sn, Cu-Zn-Pb-As-(Ag), F-Ba and barren quartz veins. These hydrothermal fluids occurred over a 200 Ma time period andthe latest hydrothermal event is recorded in barren quartz veins. This study is a multidisciplinary approach leading to the characterization ofthe hydrothermal fluids preserved in barren quartz veins, which are spatially but not temporally related to Hercynian upper crustal granites.The veins were dated by the 39 Ar/4o Ar method, and the fluids were examined using petrographic, microthermometric, chemical and isotopicmethods. Fluid inclusions in barren quartz veins indicate that two fluids were related to this hydrothermal event. The main part of the quartzveins were formed from an early low salinity « 1 wt% N aCI) H20-NaCl fluid. This fluid was trapped at around 270 ± 25 QC and 0.1-1 kbarunder sublithostatic to hydrostatic conditions. a180 (-9 to 2%0) and aD (-70 to - 34.5%0) values indicate a meteoric origin for water, withsignificant water/rock interactions. The latest H20-NaCI-CaCI2 fluid is found in two types of fluid inclusions: a primary liquid-vapour type(16-24 wt% NaCl and 1-12 wt% CaClz) and secondary hypersaline type (7-15 wt% NaCI and 21-27 wt% CaCI2). Significant Li concentrationsin this fluid were confirmed. This late Ca-bearing fluid formed quartz crystals in the central part of the veins, and was trapped at 70-140 QC, at a maximum pressure of 0.5 kbar. The low al80 (-20 to -6%0) and aD (-137 to -116%0) values suggest a meteoric origin for thisfluid, however its high salinity probably requires a source from Triassic evaporite basins located in the NE tip of the Spanish Central System.Anomalously low isotopic values have been previously reported from kaolinites of Lower Cretaceous age. Anomalous climatic conditionsduring the Cretaceous appear to be the main reason to explain this very negative meteoric water. Strong isotopic depletion in meteoric waterhas been observed in modern areas with monsoonal climates. The hydrothermal evolution of barren quartz veins in the Spanish CentralSystem is comparable to other hydrothermal Post-Variscan events in central and south-western Europe related to the opening of the NorthAtlanticduring Cretaceous time.
PB Elsevier
SN 0264-8172
YR 2002
FD 2002
LK https://hdl.handle.net/20.500.14352/58394
UL https://hdl.handle.net/20.500.14352/58394
LA eng
DS Docta Complutense
RD 15 may 2024