SUBMAGMATIC AND SOLID-STATE MICROSTRUCTURES IN LA TAPERA PLUTON. SAN LUIS. ARGENTINA

LOPEZ, MONICA GRACIELA; CERREDO, M.E.

Revista de la Asociacion Geologica Argetnian

Asociacion Geologica Argentina

Lugar: Buenos Aires; Año: 2001 vol. 5 p. 131 - 138

0004-4822

The Late Ordovician La Tapera Pluton (LTP) is composed of six hectometer to kilometer bodies and numerous smaller satellite outcrops, that are arranged along a NE trending belt located in the eastern half of the Sierra de San Luis. This belt is roughly parallel to the D3 axial planar foliation within the host biotite-schists. The map outlines of the largest bodies display NE fold hinges which result parallel to the mesoscopic F3 hinges in the host biotite-schists. Similar map pattern is shown by profuse pegmatite and veins (some of which are cogenetic with LTP) which are also distributed along F3 axial planes.The pluton is composed of medium-grained biotite/muscovite granodiorite-monzogranite (with minor tonalite). Synchronous deformation and magmatism is indicated by a set of magmatic, submagmatic and high-T solid-state microstructures within LTP. Evidences of magmatic flow include the alignment of angular country rock xenoliths which are generally disposed parallel to the main foliation in the host; a nonrandom orientation of submagmatic microfractures indicates that deformation was active when only a few melt percent remained in the system. Solid-state microstructures are always observed accompanying the submagmatic features and include both a high-T homogeneous deformation (fine-grained quartz-plagioclase mosaic composed of equant, strain-free grains) and medium-T heterogeneous deformational features (very thin, discontinuous microshears with impressive grain-size reduction). Therefore, deformation has been active not only during the whole span of the crystallization history but during the cooling stages.