In:
Bulletin de Minéralogie, PERSEE Program, Vol. 102, No. 5 ( 1979), p. 526-536
Abstract:
Fluid inclusion studies from syncinematic quartz crystals gave new insights into the fluid composition and P-T distribution of the external part of the Central Alps. Knowing the densities of methane and the minimum temperature of formation, fluid inclusions of the system CH4-H2O and CH4 have been used as geothermometers and barometers. For the regional distribution the following conclusions can be drawn : 1. Fluids trapped in inclusions define zones of different fluid composition related to the zones of metamorphism : — non-metamorphic zone : 〉 1 mol-% higher hydrocarbons, CH4, H2O, CO2, ... — low and medium grade anchizone : CH4, 〈 1 mol-% higher hydrocarbons, H2O, CO2, ... — high grade anchizone and epimetamorphic zone : H2O, CO2, ... 2. The minimum conditions of formation for mineral clefts and their quartz crystals from the low and medium grade anchizone are 200-270° C — 1,200-1,700 bar, with geothermal gradients of 25-45° C/km. 3. From the fluid inclusion studies the following minimum P-T conditions were deduced with respect to metamorphic grade : — non-metamorphic zone — low grade anchizone : T 〉 200° C — P 〉 1,200 bar — medium grade anchizone — high grade anchizone : T 〉 270° C — P 〉 1,700 bar 4. The evolution of the fluids is a product of the progressive metamorphism. But the fluids were trapped in quartz crystals towards the end of the nappe overthrust and during the uplift of the Alps (middle to final Miocene era). As rocks with fluid inclusions of higher grade metamorphism are found above rocks with fluid inclusions of lower grade metamorphism, their metamorphism must have taken place before the final transport of the nappes.
Type of Medium:
Online Resource
ISSN:
0180-9210
DOI:
10.3406/bulmi.1979.7301
Language:
French
Publisher:
PERSEE Program
Publication Date:
1979
