FluidNET Science Conference Abstract - Quartz vein formation in the Agly massif, French Pyrenees: 40Ar/39Ar dating, mineral chemistry, and fluid inclusion study
Creators: name: Intan Chalid
name: Klaudia Kuiper
name: Leo Kriegsman
name: Simona Ferrando
name: Fraukje Brouwer
name: Jan R. Wijbrans
Publisher: name: Zenodo
Year: 2024

description: Quartz vein formation in the Agly massif, French Pyrenees: 40Ar/39Ar dating, mineral chemistry, and fluid inclusion study 

 

Intan Chalid1, Klaudia Kuiper1, Leo M. Kriegsman2,3, Simona Ferrando4, Fraukje Brouwer1, Jan R. Wijbrans1 

1Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081HV Amsterdam, The Netherlands (i.chalid@vu.nl)

2Naturalis Biodiversity Center, Darwinweg 2, 2333CR Leiden, The Netherlands

3Utrecht University, Princetonlaan 8A, 3584CB Utrecht, The Netherlands

4University of Torino, Via Valperga Caluso 35, 10125 Torino, Italy 

 

Post-tectonic quartz veins in the Agly massif, northeastern Pyrenees, France, have been dated as predominantly Cretaceous by 40Ar/39Ar stepwise crushing of vein quartz. Individual age spectra typically reveal high ages in the initial stages of crushing, decreasing to plateaus in the range 140 - 60 Ma. These plateaus correspond to initial 40Ar/36Ar intercepts of primary fluid inclusions ranging from 248.0 ± 8.2 to 305.4 ± 3.4, as determined in the inverse isochron plots. In two cases, we could determine the age of secondary fluid inclusions from inverse isochron analysis at 81 to 73 Ma, respectively. 

All eleven quartz vein samples exhibit characteristics indicative of formation under upper greenschist facies conditions, with diverse mineral assemblages, including subsets of alkali feldspar, plagioclase, muscovite, Mg-biotite, Fe-biotite, siderophyllite, phengite, chlorite, titanite, ilmenite, and apatite. The assemblages as observed in the veins are thought to have originated at temperatures of 500 °C.

Quartz veins from the Souanyes and Bélesta areas contain primary fluid inclusions suitable for compositional and microthermometric analysis. Fluid inclusions present in quartz of sample L.17A from Bélesta are aqueous carbonic multi-phase inclusions showing a primary distribution, i.e. they are representative of the fluid that was present during precipitation of the mineral assemblages in the vein. During microthermometric measurements, these fluid inclusions displayed metastable behavior (lacking salt re-nucleation after melting) or indicate that they underwent post-trapping modifications (salt precipitation after cooling). Sample L.58A from Souanyes revealed primary two-phase aqueous fluid inclusions. The first liquid phase is visible at temperatures ranging from -46 °C to -26 °C. Hydrohalite is the last phase to undergo melting at temperatures ranging from -7 °C to -0.8 °C, with a well-defined peak around -4 °C. Homogenization always occurs into the liquid phase at temperatures from 204.5 °C to 367.7 °C. Our data suggests that the fluid is a brine with salinity of 25.7 wt.% NaCleq. 

In summary, most quartz veins in the Agly massif formed during Cretaceous overprinting consistent with thermochronology, rather than in the retrograde part of the Hercynian metamorphic loop. The mineral composition within these veins suggests the involvement of high-salinity aqueous fluids in the upper greenschist facies, with temperatures estimated at 500 °C.

 

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 956127