Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas

Abad, Isabel; Sánchez-Gómez, Mario; Reolid, Matías; López Sánchez-Vizcaíno, Vicente

doi:10.3390/min9120748

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Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas

Isabel Abad

^1,*

Mario Sánchez-Gómez

¹,

Matías Reolid

and

Vicente López Sánchez-Vizcaíno

Departamento de Geología and CEACTierra, Universidad de Jaén, Campus Las Lagunillas s/n, 23071 Jaén, Spain

Departamento de Geología and CEACTierra, Campus Científico Tecnológico de Linares, Universidad de Jaén, 23700 Linares, Jaén, Spain

Author to whom correspondence should be addressed.

Minerals 2019, 9(12), 748; https://doi.org/10.3390/min9120748

Received: 27 September 2019 / Revised: 15 November 2019 / Accepted: 26 November 2019 / Published: 30 November 2019

(This article belongs to the Special Issue Mineral Formation in Pyrometamorphic Process)

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Abstract

A singular thermal anomaly occurred in the Molinicos Miocene, lacustrine, intramontane basin (Betic Cordillera). This gave place to vitreous vesicular materials (paralavas) and baked rocks (clinker) inside of a sequence of marly diatomites and limestones. The chemical composition of the paralavas (SiO₂ = 52–57, Al₂O₃ ≈ 20, Fe₂O₃ = 10–20, K₂O + Na₂O < 2.5, CaO < 4.5, and MgO < 1.5, % in weight), which is very different from typical igneous rocks, and their high-T mineralogy (cordierite, sillimanite, anorthite, mullite, and high-T silica polymorphs) suggest that they formed during a pyrometamorphic event. The occurrence of dry intervals in the lacustrine depositional system, the high Total Organic Carbon contents (>4% in weight) of dark clay layers and the existence of tectonic fractures give the right context for a combustion process. Short-term heating favoured the generation of paralavas, clinker and marbles. Thermodynamic modelling constrains the onset of melting at 870–920 °C for <10 MPa at equilibrium conditions. However, the presence of tridymite and/or cristobalite in clinker and paralavas and the compositional variation in both rock types suggests that the temperature at which first melting occurred ranged between 870 °C and 1260 °C due to melt fractionation processes. View Full-Text

Keywords: cordierite; clinker; combustion metamorphism; Molinicos Basin; paralava; melt fractionation; P-T pseudosection; SEM

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Abad, I.; Sánchez-Gómez, M.; Reolid, M.; López Sánchez-Vizcaíno, V. Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas. Minerals 2019, 9, 748. https://doi.org/10.3390/min9120748

AMA Style

Abad I, Sánchez-Gómez M, Reolid M, López Sánchez-Vizcaíno V. Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas. Minerals. 2019; 9(12):748. https://doi.org/10.3390/min9120748

Chicago/Turabian Style

Abad, Isabel, Mario Sánchez-Gómez, Matías Reolid, and Vicente López Sánchez-Vizcaíno. 2019. "Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas" Minerals 9, no. 12: 748. https://doi.org/10.3390/min9120748

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Pyrometamorphic Rocks in the Molinicos Basin (Betic Cordillera, SE Spain): Insights into the Generation of Cordierite Paralavas

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