Resumo

TORO TORO, Luz Mary; ALVARAN-ECHEVERRI, Mauricio  e  BORRERO-PENA, Carlos Alberto. ADAKITE-LIKE ROCKS AT THE SOUTH-EAST OF MANIZALES: PETROGENETIC AND GEOCHEMICAL CHARACTERISTICS. bol.geol. [online]. 2008, vol.30, n.2, pp.49-60. ISSN 0120-0283.

To the southeast of Manizales city, in Gallinazo area, there are a series of aligned hills such as: Gallinazo, Amazonas, Sabinas, La Oliva and La Negra, corresponding to volcanic and sub-volcanic rocks of andesitic and dacitic composition respectively, geochemical data present characteristic of adakitic rocks. Both, volcanic and sub-volcanic rocks presents high SiO₂ concentration (63,87-70,15%), Al₂O₃ (14,18-16,83%), low Y concentration (11,20-27 ppm) and Yb (0,94-1,93 ppm); strong enrichment in Light Rare Earth Elements(LREE) and highly incompatible elements (Rb, Ba), except for Sr which presents low contents and negative anomaly of Nb-Ta, characteristic that distinguish also the calcoalkaline magmas. Geochemical pattern of LREE and multielements show a strong fractionation ((La/Yb)n>8) with typical low content of (Yb ≤ 1.8 ppm , Y ≤ 18 ppm). In this work authors propose SE Manizales adakita-like rocks were generated by subducted basaltic slab melting with some minimum peridotitic mantelic wedge contamination. Genesis and geochemical characteristics of these rocks open the possibility to find Au-Cu porphyry mineralizations and epithermal gold deposits in this area due to their highly oxidixing potential.

Palavras-chave : adakita-like rocks; subduction; volcanic rocks.

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