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Medellín, Colombia

El Morito basaltic Andesite unit outcrops in the converging zone of the oceanic basement of the western cordillera and the continental basement of the central mountain range, beside the Combia Formation. It is formed by basalt and basaltic andesite with porphyritic texture, it has phenocrysts of plagioclase and clinopyroxene mainly, and occasionally olivine and orthopyroxene that float on a microcrystalline matrix with a fluidal texture to phyllotaxis; they correspond to shoshonitic magma series with highest values in K2O, Na2O, P2O5 and major values in the elements Rb, Ba, Th, U, K, La, Ce, Pr, Sr, P, Nd, Zr, Sm and Eu and minor values in Ti, Y, Yb y Dy, than the calc-alkaline magmas of the Combia Formation. The age of the units of the Arco de El Botón which has shoshonitic affinity, corresponds to a range between 9 and 12.5 Ma, including the basaltic andesite of El Morito, while the ages of the units belonging to the Combia Formation are located in the range from 6 to 8.5 Ma.

Rodriguez G.,Servicio Geologico Colombiano GTR | Arango M.I.,Servicio Geologico Colombiano GTR
Boletin de Geologia | Year: 2013

The Arquia Complex appears as a strip elongated, narrow and discontinuous, consisting in amphibole - sericite schist, quartzites and gneisses alongside amphibolites and metagabbros associated with ultramafic rocks. There is located between the Cauca Almaguer and Silvia Pijao Faults, in the collision zone of metamorphic basement of the Cordillera Central and oceanic basement of the Cordillera Occidental of Colombia. The Arquia Complex has been considered as part of a "melange" which is formed for strips thins discontinuous blocks involving continental and oceanic crust parts between Cauca almaguer and San Jerónimo Faults. Geochemical analysis was performed on Arquia Complex metabasites (Sabaletas schist, Cauca river amphibole schist, Buesaco metamorphic sequence, Bugalagrande Group, Rosario Complex, Bolo azul Complex, Lisboa - Palestina schist and Santa Rosa metagabbro), corresponding to subalkaline tholeiitic basalts protolites type N-MORB with high magnesium, SiO2 between 44,24% and 53,49wt%, alkalis vs SiO2 0,03%- 0,09wt%, with Nb/Y=0,05-0,15 ratios and #Mg=45,03 - 72,34. The Arquia Complex ages are grouped into the two ranges: 100-113 Ma and 203-229 Ma. The first range (100-113 Ma) corresponded with radiometric ages obtained by K/Ar method, and coincide with the start stage of the Barroso- Sabanalarga Arc, affecting the suture zone and the two crusts, being interpreted as heating ages. The second range include ages between 203 - 229 Ma, obtained by Ar/Ar, and are interpreted as metamorphic age. These data are consistent with the age of metamorphism of the Cajamarca Complex, being this the basement of the Cordillera Central of Colombia.

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