Exploring differential erosion patterns using volcanic edifices as a proxy in South America

Abstract

Porphyry Copper Deposit (PCD) exploration faces a challenging future, since promising areas for exploration are buried. PCDs form at kilometres depth, while volcanoes are the surface expression of extensive magmatic systems. Although not all volcanoes generate PCDs, it may be that all PCDs formed under a volcanic centre. As there are no complete magmatic-volcanic profiles available, I study the distribution of the exposed magmatic-volcanic portions. In this study, I compile eruption, volcano and PCD data for the Andes and then develop a tool to identify favourable areas for finding porphyries close to the surface. This methodology, however, does not distinguish enriched from barren porphyries, nor detect the intensity of the mineralization.
My results show when exploring for PCDs, high prospectivity areas are the eroded and remaining edifices of inactive stratovolcanoes. They also show that volcano erosion and PCD exposure in the Andes depend strongly on climate. There is a negative correlation between height and more humid climate for Pre-Quaternary edifices and, as the number of volcanoes drops with wetter conditions, the numbers of mineralised deposits rise. This trend of reduced number and height of edifices continues towards extreme latitudes, as well as close to the current Chilean coastline, the Intermediate depression and Precordillera. This suggests a strong erosion gradient increasing towards the south and west of the Andes.
The Arica Bend region and the Precordillera are areas of great importance, since they reflect the greatest exhumation in the Andes by exposing mineralised intrusions, therefore it becomes enormously relevant distinguishing these regions of high-erosion (South Peruvian Cordillera) from low-erosion (Altiplano plateau). Geomorphology is a promising tool for finding PCDs, since paleosurfaces could protect and preserve mineralised intrusions, while coupled mechanisms (tectonic uplift and climate) may facilitate the exposure of PCDs by river incision or rotational landslides.

Date of Award	23 Mar 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Alison C Rust (Supervisor) & Jon D Blundy (Supervisor)