PETROGRAFíA Y GEOQUíMICA DE LAS ROCAS ANCESTRALES DEL VOLCáN NEVADO DEL RUIZ

a model of the "ruiz ancestral" stage (2 to 1 ma) at the nevado del ruiz volcano is proposed. the extension of the lava remnants of this stage covered an area of about 200 km2 and they were cartographied around the northeast-north-northwest of the present edifice of the volcano. whole-rock geochemical data of andesitic, basaltic-andesitic and dacitic samples from the different outcrops share the calcalkaline affinity with medium to high k contents. the trace elements range variation compared with sio2 suggests a fractional crystallization mechanism from the ferromagnesian minerals and the calcic plagioclase. the trace elements pattern is typical of a volcanic arc with sr, k, rb, ba y th enrichments and nb impoverishment. the ree diagram shows a smooth slope and the typical lree enrichment.