ROCAS CON AFINIDAD ADAKITICA AL SUR-ESTE DE MANIZALES: RASGOS PETROGENETICOS Y GEOQUIMICOS
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Universidad Industrial de Santander
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Al sureste de la ciudad de Manizales, en el sector de Gallinazo, se presentan una serie de cerros alineados: Gallinazo, Amazonas, Sabinas, La Oliva y La Negra, correspondientes a rocas volcánicas y sub-volcánicas de composición andesítica y dacítica respectivamente, con características geoquímicas similares a las de rocas adakíticas.
Ambos tipos de rocas tienen altos contenidos de SiO2 (63,87- 70,15%) y Al2O3 (14,18-16,83%), bajos contenidos en Y (11,20-27 ppm) e Yb (0,94-1,93 ppm), fuerte enriquecimiento en tierras raras livianas (LREE) y en elementos altamente incompatibles (Rb, Ba), con excepción del Sr, el cual presenta bajo contenido, y anomalía negativa de Nb-Ta, características que de igual manera distinguen a los magmas calcoalcalinos. En general, los patrones de tierras raras y multielementos son muestran un fuerte fraccionamiento ((La/Yb)N>8) con los típicos bajos contenidos de (Yb ≤ 1.8 ppm, Y ≤ 18 ppm).
Se propone que estas rocas con signatura adakítica fueron generadas por la fusión de la placa subducida de composición basáltica y con una leve participación de cuña mantélica. El origen y las características geoquímicas de estas rocas abre la posibilidad de encontrar mineralizaciones de tipo pórfdo con Au-Cu y epitermales de Au en la zona debido a su potencial áltamente oxidante.
Palabras Claves: adakitas, subducción, rocas volcánicas, Manizales, Colombia. |
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. Keywords: adakita-like rocks, subduction, volcanic rocks, Manizales, Colombia.
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. Keywords: adakita-like rocks, subduction, volcanic rocks, Manizales, Colombia.