Abstract

BERNARDI, Mauro I; BERTOTTO, Gustavo W  and  PONCE, Alexis D. Estructuras de segregación vesiculadas alojadas en coladas basálticas pahoehoe de Payenia, provincias de Mendoza y La Pampa, Argentina: aspectos morfogenéticos y petrográficos. Rev. Asoc. Geol. Argent. [online]. 2016, vol.73, n.1, pp.50-63. ISSN 0004-4822.

Vesiculated segregation structures comprise varied geometry bodies with milimetric to metric dimensions and vesiculation values varying between 20 and 40 %, hosted within internal sector of a lava flow. These structures resulted from segregation and migration of a residual differentiated liquid generated during the crystallization of the flow. The residuum migrates towards a permeable network of crystals thanks to a gas filter-pressing mechanism. According to their micro-texture, vesiculated structures sampled from pahoehoe basaltic lava flows of Payenia Volcanic Province were classified into three subtypes: 1) aphyric coarse-grained textured; 2) aphyric fine-grained textured and 3) porphyritic to intergranular textured. The coarse-grained textures are associated with the presence of high temperature iddingsite altering olivine crystals in the host rock and the diktytaxitic texture is a common petrographic feature observed in all sampled lava flows bearing vesicular structures. These features would be indicating an important participation of fluids during the formation of the structures. Four types of structures were described: thick vesicle sheets, thin vesicle sheets, vesicle cylinders and segregation vesicles, which were grouped regarding to their morphogenesis into three categories proposed in previous works, which are based on the thickness of host lava flow. The origin of the vesicle sheets would be linked with the spreading of vesicle cylinders under a solidification front. Cooling rates are controlled by the thickness of the lava flow which in turn control the permanence or total dispersion of the cylinders.

Keywords : Vesicle cylinders; Vesicle sheets; Segregation vesicles; Basalts.

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