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Re-folded structure of syn-orogenic granitoids (Padrón dome, NW Iberia): Assessing rheological evolution of cooling continental crust in a collisional setting

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Díez Fernández, Rubén and Rubio Pascual, Francisco J. and Martín Parra, Luis Miguel (2019) Re-folded structure of syn-orogenic granitoids (Padrón dome, NW Iberia): Assessing rheological evolution of cooling continental crust in a collisional setting. Geoscience Frontiers, 10 (2). pp. 651-669. ISSN 1674-9871

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Official URL: https://www.sciencedirect.com/science/article/pii/S1674987118300860


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Abstract

This contribution discusses about the rheological, kinematic and dynamic frameworks necessary to produce recumbent and upright folds from syn-orogenic granitic massifs that were formed during an early stage of magma genesis related to the onset of a migmatitic dome. Syn-kinematic granitoids occurring within the high-grade infrastructure of the Padrón migmatitic dome (NW Iberia) are deformed into large-scale recumbent folds (D2) that are later affected by upright folds (D3). Petrostructural analysis of a selected area of this dome reveals that after a period of crustal thickening (D1), NNW-directed extensional flow gave way to recumbent folds and penetrative axial plane foliation (S2). Superimposed subhorizontal compression resulted in upright folds (D3). A closer view into the dynamics of the dome allows exploring the factors that may condition the nucleation of folds with contrasting geometries during progressive deformation of molten continental crust. The formation of folds affecting syn-kinematic granitoids suggests a cooling metamorphic path in migmatitic domes. Active and passive folding mechanisms require a crystallizing (cooling) magma to nucleate folds. A more competent metamorphic host inhibits fold nucleation from much less competent magmas. As it crystallizes, magma becomes more rigid (competent), and approaches viscosity values of its host. Passive folding is favored when no significant competence contrast exists between magma and host, so this folding mechanism is more likely shortly after magma genesis and emplacement. In such conditions, and under dominant subhorizontal flow accompanied by flattening (D2), passive folding would produce isoclinal recumbent geometries. Further magma cooling introduces a shift into the rheological behavior of partially molten crust. Thereon, crystallizing magma bodies would represent significant competence contrasts relative to their host. At this point, buckling is a more likely folding mechanism, and more regular, buckle folds re-fold previous structures after significant cooling. The geometry of resulting folds is upright due to dominant subhorizontal compression (D3) at this stage.


Item Type:Article
Uncontrolled Keywords:Recumbent folds, Migmatitic domes, Partial melting, Crustal-derived granitoids, Orogenic collapse, Variscan orogen
Subjects:Sciences > Geology > Geodynamics
Sciences > Geology > Petrology
ID Code:54869
Deposited On:02 Apr 2019 17:15
Last Modified:03 Apr 2019 06:55

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