Niveles de cenizas volcánicas en laderas de los valles del Río Claro y Cochiguás, Quebrada Paihuano y Tres Cruces, Región de Coquimbo, Chile
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Date
2018
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Idioma
es
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Universidad Andrés Bello
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Abstract
Hacia el interior de la región de Coquimbo, en los valles de los ríos Claro y Cochiguás, quebradas Paihuano y Tres Cruces (ca. 30°S), se encuentran niveles de ceniza volcánica intercalados con depósitos coluviales, bajo una cobertura aluvial holocena. Esta zona se caracteriza por estar inmersa en un segmento de subducción plana, caracterizada por la ausencia de volcanismo en los Andes, por lo que la ocurrencia de estos depósitos es inusual. En este trabajo se realizaron análisis granulométricos, de componentes y mineralógicos de seis depósitos de cenizas volcánicas. Además, se consideraron análisis geoquímicos de elementos mayores realizados en esquirlas de vidrio volcánico. Los niveles de cenizas volcánicas están compuestos principalmente por esquirlas de vidrio de tamaños variables entre 2 – 0.063 mm (predominantemente < 125 μm) que varían entre 67 - 74% del material que las constituye. El resto de los componentes corresponden a proporciones variables de cuarzo, feldespatos, biotita y trazas de muscovita, titanita, anfíbola y sulfuros de cobre. Los feldespatos están parcialmente argilizados, algunos presentan pátinas de sulfuros de cobre, mientras que la biotita y anfíbola están levemente oxidadas. Lo anterior permite considerar que los minerales observados, en su mayoría, corresponden a material proveniente de rocas intrusivas circundantes. Considerando además la presencia de clastos de roca en los depósitos, se interpreta que los niveles de cenizas corresponden a depósitos mixtos, formados por material volcánico y accidental. El origen del vidrio volcánico estaría asociado a una erupción variable entre pliniana y freatomagmática, con desarrollo de una pluma de cenizas, que habría formado depósitos de caída en las zonas altas de los paleo valles y paleo quebradas, los que posteriormente habrían sido removilizados y depositados en su ubicación actual. Las esquirlas de vidrio tienen composición riolítica con afinidad calcoalcalina de alto potasio, característica de productos volcánicos de arco. Se destaca la semejanza composicional de éstos con los depósitos asociados al evento eruptivo de la Caldera El Diamante (ca. 34°S), por lo que en este trabajo se propone que posiblemente el material piroclástico estudiado habría recorrido ca. 470 km de distancia desde su fuente.
Towards the interior of the Coquimbo region, in the valleys of the Claro and Cochiguás rivers, Paihuano and Tres Cruces creeks, levels of volcanic ash interleaved with colluvial deposits are found, under an holocene alluvial cover. This area is characterized by being immersed in a flat-slab segment, characterized by the absence of volcanism in the Andes, so the occurrence of these deposits is unusual. In this work granulometric analysis, components and minerals of six levels of volcanic ash are performed. In addition, geochemical analyses of major elements made of volcanic shard glass were considered. The levels of volcanic ash are mainly composed of glass shard of varying sizes between 2- 0.063 mm (predominantly <125 microns) that vary between 67 - 74% of the material that constitutes them. The rest of the components correspond to variable proportions of quartz, feldars, biotite and traces of muscovite, titanite, amphibole and copper sulphides. Feldars are partially argilized, some have patina of copper sulphides, while biotite and amphibole are slightly oxidized. The above allows to consider that the minerals observed, mostly, correspond to a material coming from surrounding intrusive rocks. Also considering the presence of rock clasts in the deposits, it is interpreted that the ash levels correspond to mixed deposits, formed by volcanic and accidental material. The origin of the volcanic glass would be associated to a variable eruption between plinian and phreatomagmatic, with the development of an ash plume, that would have formed deposits of fall in the high zones of paleo valleys and paleo creeks, which later would have been remobilized and deposit in the current location. The glass shards have rhyolitic composition with high potassium calcoalkaline affinity, characteristic of arc volcanic products. The compositional similarity of these with the deposits associated with the eruptive event of Caldera El Diamante (ca.34°S) is highlighted, so in this work it is proposed that possibly the pyroclastic material studied would have travelled ca. 470 km away from tis source.
Towards the interior of the Coquimbo region, in the valleys of the Claro and Cochiguás rivers, Paihuano and Tres Cruces creeks, levels of volcanic ash interleaved with colluvial deposits are found, under an holocene alluvial cover. This area is characterized by being immersed in a flat-slab segment, characterized by the absence of volcanism in the Andes, so the occurrence of these deposits is unusual. In this work granulometric analysis, components and minerals of six levels of volcanic ash are performed. In addition, geochemical analyses of major elements made of volcanic shard glass were considered. The levels of volcanic ash are mainly composed of glass shard of varying sizes between 2- 0.063 mm (predominantly <125 microns) that vary between 67 - 74% of the material that constitutes them. The rest of the components correspond to variable proportions of quartz, feldars, biotite and traces of muscovite, titanite, amphibole and copper sulphides. Feldars are partially argilized, some have patina of copper sulphides, while biotite and amphibole are slightly oxidized. The above allows to consider that the minerals observed, mostly, correspond to a material coming from surrounding intrusive rocks. Also considering the presence of rock clasts in the deposits, it is interpreted that the ash levels correspond to mixed deposits, formed by volcanic and accidental material. The origin of the volcanic glass would be associated to a variable eruption between plinian and phreatomagmatic, with the development of an ash plume, that would have formed deposits of fall in the high zones of paleo valleys and paleo creeks, which later would have been remobilized and deposit in the current location. The glass shards have rhyolitic composition with high potassium calcoalkaline affinity, characteristic of arc volcanic products. The compositional similarity of these with the deposits associated with the eruptive event of Caldera El Diamante (ca.34°S) is highlighted, so in this work it is proposed that possibly the pyroclastic material studied would have travelled ca. 470 km away from tis source.
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Tesis (Geólogo)
Keywords
Suelos de Cenizas Volcánicas, Contaminación de Ríos, Chile, Región de Coquimbo