167-13 Decoding Tectono-Magmatic Evolution Through Skarns: The Sidi Bou Othmane Case Study, Including Metamorphic and Metallogenic Insights

Session: Integrating Geochronology and Geochemistry to Decipher the Tectonic Evolution of Orogenic Belts

Presenting Author:

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Abstract:

The skarns of the Sidi Bou Othmane area (Jebilet, central Morocco) offer critical insights into the complex geodynamic evolution of the region. Our study of these skarns has revealed new constraints on the emplacement of granitic bodies, the polyphase deformation history, and the interplay between magmatism, metasomatism, metamorphism, and mineralization.

Using geochemical data from El Mostadi (1992) on marbles and skarns (from both prograde and retrograde stages), a mass balance analysis was conducted using the Gresens and Grant methods to assess elemental gains and losses during metasomatism. The results indicate that W-Sn mineralization is specifically associated with the second skarnification event, linked to the emplacement of a peraluminous S-type leucogranite.

Deformation in our area began with a transtensional phase (D0) that opened the basin and produced early folding. Evidence of this includes garnets in the skarns that replicate fold geometries while remaining undeformed, confirming the presence of folding during this early stage. Toward the end of D0, a granodioritic intrusion was emplaced along an extensional shear zone. This event initiated the first stage of skarnification and produced contact metamorphism under pyroxene hornfels facies conditions.

The subsequent D1 phase was compressive and involved coaxial ductile shortening, generating schistosity, boudinage, and asymmetrical folding. This stage corresponds to regional metamorphism under greenschist facies conditions.

During the D2 shearing phase, crenulation cleavage, stretching lineation, isoclinal folds, and sheared boudins developed. It is during and shortly after this phase that the leucogranite was emplaced. This second intrusion is linked to a second skarnification event, marked by the appearance of wollastonite that crosscuts idocrase, itself formed from the retrogradation of garnet from the first skarnification stage, suggesting the emplacement of a high-temperature magmatic body. This later contact metamorphism occurred under hornblende hornfels facies conditions. These metamorphic constraints are based on previously published studies; a new metamorphic investigation is currently underway.

In summary, the study of skarns has proven essential for reconstructing the tectono-magmatic evolution of the Jebilet. Future petrochronology and thermobarometry are necessary to determine whether deformation reflects discrete polyphase events or a continuous, progressive process.

Keywords: Skarn, Jebilet, Deformation, Granite Emplacement, Metasomatism, W-Sn Mineralization, Leucogranite, Granodiorite

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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