Synkinematic interplay between felsic dykes and host rock mylonitization: how magmatism assists the formation of ductile narrow shear zones in the Sierra Chica de Córdoba, Argentina. (March 2021)

• Record Type: Journal Article
• Authors: Boffadossi, M. Alejandra; Coniglio, Jorge E.; Maffini, M. Natalia; Pinotti, Lucio P.; Radice, Stefania; D'Eramo, Fernando J.; Demartis, Manuel; Muratori, M. Eugenia; Coniglio, Joaquín
• Is Part Of: Journal of South American earth sciences. Volume 106(2021)
• Publication Date: 2021-03
• Subjects: Dyking mechanisms -- Ductile narrow shear zones -- Geometric scaling-data -- Strike-slip-dominated dextral transtension -- Famatinian orogeny; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2020.103063
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: This study provides new insights about mechanisms of synkinematic interplay between dyking emplacement and ductile narrow shear zones formation in the Sierra Chica de Córdoba. A detailed analysis of structural, microstructural, geometric-scaling and geochronologic data is performed in order to demonstrate the important role that minor and meso-scale felsic dykes played in the formation of paired shear zones symmetrically from dyke contacts. This magmatism and associated deformation conspicuously overprint medium-to high grade metamorphic and igneous rocks of Pampean age. Internally, the shear zones are formed by mylonites with mineral paragenesis in the amphibolite facies and foliation planes totally concordant to dyke contacts. Low rheological contrast between igneous intrusions and host rocks, together with fast rates of magma channeling and emplacement, was responsible for a brittle mechanical regime at moderate to high temperatures (500–700 °C). Melt-filled shear fractures rapidly propagated while the host rock was being mylonitized at ductile conditions. Shear structures controlling dyke construction and mylonite formation adjust to a strike-slip dominated dextral transtensional regime. The predicted axes of finite maximum shortening (Z) and maximum extension (X) have NNE and NNW directions, respectively. Ar/Ar muscovite cooling ages determined for pegmatite dykes, yielded minimum crystallization ages between 451 ± 1 and 435 ± 3 My. These geochronological data are further supported by field structural relationships and the regional knowledge, pointing to a Famatinian age for magmatism and related narrow shear zones. This paper constitutes a new contribution reporting the occurrence of magmatism and strike-slip-dominated dextral transtension deformation in the inner foreland of the Famatinian accretionary orogen, developed in the Lower Paleozoic along the southwestern Gondwana margin. Highlights: Felsic dykes outcrop in close spatial linkage with ductile narrow shear zones. Dykes and shear zones overprint metamorphic and igneous rocks of Pampean age. Dykes emplaced through fractures in a strike-slip dominated dextral transtension regime. Dykes assisted the formation of paired shear zones along their contacts. Ar/Ar data and field evidence support a Famatinian age for dyking/shearing.