Thermal constraints on crustal rare gas release and migration: Evidence from Alpine fluid inclusions

doi:10.1016/0016-7037(94)90337-9

Geochimica et Cosmochimica Acta

Volume 58, Issue 20, October 1994, Pages 4333-4348

https://doi.org/10.1016/0016-7037(94)90337-9 Get rights and content

Abstract

The Palfris marl of the Helvetic Alpine Nappes contains four distinct vein fill generations. CH₄-rich gas is found in abundant fluid inclusions within these carbonate veins, while free CH₄ gas has also been produced from exploratory boreholes through this formation. The stable isotope and helium, neon, and argon isotopic composition of these fluids has been determined. A constant radiogenic ⁴⁰Ar concentration of 1.25 ± 0.13 (1σ) ppm in these differently sited fluids requires an intimate association between the ⁴⁰Ar_rad source and the hydrocarbon phase. This can only be reasonably explained if the ⁴⁰Ar_rad was input into the hydrocarbon phase during hydrocarbon generation, migration, or storage prior to entrapment in the fluid inclusions. Stable isotope results constrain the maturity of hydrocarbon production, while fluid inclusion formation pressures and temperatures record values of up to 2.5 kbars and 250°C. These values place limits on the range of thermal conditions in which the hydrocarbon/⁴⁰Ar_rad relationship was established.

All fluids within inclusions also contain radiogenic $^{4} He^{40} Ar$ values at predicted crustal production ratios. These observations provide the first evidence that both ⁴He_rad and ⁴⁰Ar_rad can be quantitatively released on a regional scale bounded by the thermal conditions required to produce the hydrocarbon phase and the conditions under which the fluid inclusions were formed (T = 190–250°C). These results require that negligible quantities of excess ⁴⁰Ar_rad, decoupled from ⁴He_rad, have been released into this system. Given the wide array of mechanisms which can potentially cause decoupling of these two species, this result provides an important constraint on the role of these processes within the sedimentary fluid regime. In contrast, the free borehole gas contains excess radiogenic ⁴He and ²¹Ne, relative to ⁴⁰Ar_rad, in proportions which can be accounted for by local production and subsequent diffusion from the surrounding marl. The latter pattern is consistent with rare gas migration in lower temperature environments. A conceptual model which considers both diffusional and metamorphic release of helium and argon, and the ability of the surrounding fluid regime to transport the rare gases from their respective mineral production sites, is consistent with both these results and data from regional rare gas studies.

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^∗: Present address: Department of Geological Sciences, The University of Michigan, Ann Arbor, MI 48109-1063, USA.

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Thermal constraints on crustal rare gas release and migration: Evidence from Alpine fluid inclusions

Abstract

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Chem. Geol.

J. Hydrol.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Appl. Geochem.

Geochim. Cosmochim. Acta

Chem. Geol.

Geochim. Cosmochim. Acta

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Chem. Geol.

The isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers

Chem. Geol.

Rare gas systematics: Formation of the atmosphere, evolution and structure of the Earth's mantle

Earth Planet. Sci. Lett.

He, Ne and Ar isotopes as tracers in crustal fluids

The use of natural He, Ne and Ar isotopes as constraints on hydrocarbon transport

Diagenese und schwache metamorphose in den sedimentären abfolgen der Zentralschweizer Alpen (Vier-wäldstatter See, Urirotstock)

Eclogae Geol. Helv.

Tonmineralogische und sedimentpetrographische Untersuchungen in der untersten Kreide des östlichen Helvetikums

Schweiz Mineral. Petrogr. Mitt.

Fazielle entwicklung und paläogeographische rekonstruktion des helvetischen schelfs während der untersten Kreide in der Zentral- und Ostschweiz

Eclogae Geol. Helv.

Metamorphic fluids: evidence from fluid inclusions

Fluid Inclusions in Vein Samples from Boreholes at Wellenberg, Switzerland: NAGRA Internal Report

WLB: Sondierbohrung SB1—Bohrloch-geophysik. Zusammenfassung der Rohdaten: NAGRA Internal Report

The movement and entrapment of fluids in the subsurface

J. Geol. Soc. London