Basalts of the northern Somún Curá Plateau. Río Negro province
The basaltic Somún Curá plateau is one of the most outstanding geoforms in the northern Extrandean Patagonia; it corresponds to a Paleogene-Neogene volcanic association. The northeastern sector displays a strongly irregular outline on map view; cross sections expose a stacking of basaltic lava flows...
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2018
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00044822_v75_n3_p396_Remesal http://hdl.handle.net/20.500.12110/paper_00044822_v75_n3_p396_Remesal |
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| Sumario: | The basaltic Somún Curá plateau is one of the most outstanding geoforms in the northern Extrandean Patagonia; it corresponds to a Paleogene-Neogene volcanic association. The northeastern sector displays a strongly irregular outline on map view; cross sections expose a stacking of basaltic lava flows thinning northwards. To the south the basaltic volcanic sequence is covered by a younger basaltic to trachytic assemblage of the Alta Sierra de Somún Curá Volcanic Complex. Typical outcrop structures of inflated flows were recognized, as well as some intra-flow features (spiracles, lava tunnels). A new 40 Ar/ 39 Ar age is presented for the studied basalts which yielded 21,6 ± 0,5 Ma. Whole rock compositions correspond to subalkaline basalts and basaltic andesites, with low-to middle K. The studied flows correspond to olivine basalts, aphyric or poorly porphyric, composed of: olivine, clinopyroxene, plagioclase, Fe-Ti oxides and a glassy mesostasis. High temperature iddingsite replacements are common in olivine. A semiquantitative compositional characterization is presented for the main framework minerals. Classical textures indicating liquid immiscibility are observed in the mesostasis accompanied by partial devitrification (globules, skeletal crystals, etc.). A semiquantitative estimation of the unmixed siliceous liquid was acquired indicating a subalkaline rhyolite composition, of intermediate K 2 O content. © 2018, Asociacion Geologica Argentina. All rights reserved. |
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