Study of the Abitagua Batholith in the Sub-Andean zone of Ecuador, using velocity models from seismic tomography

Abstract

The Abitagua Batholith is a Mid to Late Jurassic intrusive body in the Sub-Andean Zone of Ecuador. This batholith is theorized to be the source of alluvial gold in the Amazon rivers that drain from it, although due to its difficult access and location along protected areas it remains largely unexplored. This work aims to study the Abitagua Batholith using seismic velocity models that provide absolute and relative P-wave velocity and Vp/Vs ratios based on the inversion of the earthquake travel-time data recorded by the Ecuadorian survey networks RENSIG, RENAC, and ROVIG, and some stations of the Colombian Geological Service near the border with Ecuador. We use the absolute and relative P-wave velocity tomography models to describe the batholith's vertical and horizontal components. The resolution in our velocity models displays values larger than 0.8 and cover all the crust and the upper mantle to depths of seventy kilometers. We identify two velocity anomalies, possibly associated with magmatic reservoirs under the batholith that, together with hypocenter data, suggest more recent magma intrusions. We conclude that these magmatic bodies relate to potential gold-bearing intrusions, which seem to concentrate near the transition zone between the negative and positive velocity anomalies, five kilometers north of the Jatunyaku River.