FluidNET Abstract MSG - Sub- to supersolidus transition in the central Pyrenees: melting reactions and element transfers
Creators: name: Noor de Leijer
name: Dörte Jordan
name: Leo Kriegsman
Publisher: name: Zenodo
Year: 2023

description: Sub- to supersolidus transition in the central Pyrenees: melting reactions and element transfers

De Leijer N.J.M.1, Jordan D.A.A.2 and Kriegsman L.M.1,2*

 

1 Dept. of Earth Sciences, University of Utrecht, Heidelberglaan 8, 3584 CS, Utrecht, Netherlands

2 Dept. of Research & Education, Naturalis Biodiversity Center, Darwinweg 2, 2333 CR, Leiden, Netherlands

 

* Contact author: leo.kriegsman@naturalis.nl ; l.m.kriegsman@uu.nl

___________________________________________________________________________

Partial melting is potentially the key factor in crustal differentiation processes and in the transfer of many critical metals from the deepest continental crust to shallower levels via granitoids. These processes can be studied in deeply exposed medium- to high-grade transects (schists => migmatites => granulites) through former mountain belts. Migmatites are sites of melt production that are also affected by melt influx from deeper, granulite-dominated levels. In addition, internally and externally derived crystallizing melts commonly react with restitic units at microscale and outcrop scale, causing a retrograde overprint on the peak mineral assemblages and an extra step in element redistribution.

This project focuses on the western Lys-Caillaouas massif [1] and the adjacent Gavarnie-Héas valleys [2] in the central Pyrenees, that expose a Hercynian window below an Alpine nappe stack. The area shows the transition from medium-grade, subsolidus metasediments to supersolidus migmatites along a steep geothermal gradient. The presentation will highlight petrological details of this transition, with an emphasis on phase reactions and mass balance. Successive reactions include:

-          transition andalusite => sillimanite

-          muscovite dehydration, leading to the assemblage Bt + Sil + Qtz + Kfs ± melt

-          biotite dehydration melting producing peritectic cordierite and, locally, garnet

-          minor restite-melt back reaction

-          melt crystallization near the solidus, releasing fluids that cause retrograde reactions.

The complexities of (prograde) melt-producing and (retrograde) melt-consuming reactions [3] will be summarized in a conceptual model for melt-mediated fluid transfer and recycling at sample and outcrop scale. This model forms the basis for our current attempts at quantification of element fluxes, including trace element redistribution. The talk may also address the geochemical link between in-situ melts in the migmatites and cross-cutting cordierite-bearing (leuco-)granites.

Acknowledgements

This research contributes to the FluidNET research and training network on fluid-rock interaction in the continental crust. FluidNET ITN is funded by the EU’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 956127.

 

References:

[1] De Bresser JHP et al. (1986) Netherlands J. of Geosc. (Geologie en Mijnbouw), 65: 177-187.

[2] Dahmani A and Driouch Y (1987) Travaux du Lab. de Géologie et Tectonophysique, Univ. Paul Sabatier, Toulouse, 273 pp.

[3] Kriegsman LM and Álvarez-Valero AM (2010). Lithos, 116: 310-320.