New Detritical Ages in Basement Rocks Outcropping to the West of the Santander Massif, Colombian Andes

Abstract

The basement in the Santander Massif represents a Neo to Mesoproterozoic interior surrounded by younger rocks associated with the evolution of the Andes Mountains. In the western fringe of the Santander Massif, the basement units are comprised of Bucaramanga Gneiss and Silgará Schist. The U–Pb ages in detrital zircons from two biotite gneisses, a micaceous gneiss from the Bucaramanga gneiss and a muscovite schist from the Silgará schists were grouped as follows: (1) Terreneuvian  to Tonian ages in the Bucaramanga gneisses and the Silgará schists (537–855 Ma) interpreted as the maximum age of the deposit, (2) ages between 900 and 1300 Ma probably derived from rocks of Sunsas age; ages between 1500 and 1300 Ma indicate provenance from the province of Rondonia–San Ignacio of the Amazonian craton and (3) ages greater than 1600 Ma were interpreted as derived from the Río Negro–Juruena province of the Amazonian craton. It is important to mention that in these rocks there is a new population of magmatic zircons from 530–800 Ma with oscillatory zoning, which were interpreted as coming from the Pan–African/Brazilian orogeny for the first time in the Santander Massif. Likewise, petrographic and geochronological results suggest that the Bucaramanga Gneiss and the Silgará Schists, in the western fringe of the Santander Massif, shared a similar origin.

Keywords: Bucaramanga Gneiss, Silgará Schist, Maximum deposit age, Eastern Cordillera