Artículo
Paleoproterozoic P-T-d-t evolution of a gneiss with quartz-sillimanite nodules from the Azul ranges, Rio de la Plata craton, Argentina
Bianchi, Franco Denis
; Martinez, Juan Cruz
; Angeletti, Melisa
; Frisicale, Maria Cristina
; Massonne, Hans-Joachim; Dristas, Jorge Anastasio
Fecha de publicación:
03/2020
Editorial:
Elsevier Science
Revista:
Journal of South American Earth Sciences
ISSN:
0895-9811
Idioma:
Inglés
Tipo de recurso:
Artículo publicado
Clasificación temática:
Resumen
The southernmost outcrops of the ~30 km long metamorphic belt of the Azul ranges in the Rio de la Plata craton were studied in detail with special emphasis on a gneiss with quartz-sillimanite nodules. Pressure (P) - temperature (T) and T-H2O pseudosections were calculated for such a gneiss and contoured with the PERPLE_X computer software package. Remnant oriented, K-white mica laths in K-feldspar of the gneiss matrix suggest an initial metamorphic P-T path at the onset of anatexis near ~660° at 0.43 GPa and water-saturation. Peak metamorphic conditions of ~680 °C and 0.40 GPa were reached excluding garnet growth. Back-reactions in the presence of a hydrous fluid and syntectonic coaxial deformational stress (D1) produces (1) the nodules by dealkalization of K-feldspar and (2) large, roughly oriented porphyroblasts of K-white mica after sillimanite at ~650 °C and 0.38 GPa. Homogeneous compositions of this mica (3.08-3.10 Si per formula unit) are the result of retrograde conditions in the range 450-580 °C at 0.15-0.35 GPa. A ductile deformation (D2) overprinted the exhumed rocks afterward. A set of 41 U-Th-Pb ages was determined with the electron microprobe from monazite in a leucocratic sillimanite-bearing vein, a quartz-sillimanite nodule, and the quartzofeldspathic matrix of the gneiss. Two age groups could be defined: (I) 2127 ± 10 (1σ) Ma and (II) 2039 ± 3 (1σ) Ma. Group II is assigned to the peak metamorphic event, whereas group is related to the Encantadas accretionary orogeny, which provided the source material for the sedimentary protolith of the gneiss.
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Articulos(INGEOSUR)
Articulos de INST.GEOLOGICO DEL SUR
Articulos de INST.GEOLOGICO DEL SUR
Citación
Bianchi, Franco Denis; Martinez, Juan Cruz; Angeletti, Melisa; Frisicale, Maria Cristina; Massonne, Hans-Joachim ; et al.; Paleoproterozoic P-T-d-t evolution of a gneiss with quartz-sillimanite nodules from the Azul ranges, Rio de la Plata craton, Argentina; Elsevier Science; Journal of South American Earth Sciences; 98; 3-2020; 3-19; 102453
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