Tectonic and structural controls on the spatio-temporal distribution of giant porphyry copper deposits in the central Andes

This thesis investigates the continental-scale tectonic and structural controls governing the spatio-temporal distribution of giant porphyry copper (Cu) deposits in the central Andes during the Cenozoic. This region contains 49 known giant porphyry Cu deposits – accounting for approximately 40% of the world’s known Cu and is the type locality for Cordilleran orogenesis. Due to the importance of the central Andes for global Cu production and the availability of data and information on Andean orogenic evolution and the history of Nazca – South America plate convergence, the region provides the ideal location to explore the underlying processes that influence the formation and clustering of these economically significant deposits. This thesis explores the geodynamic and structural controls on the formation of giant porphyry Cu ± Au ± Mo deposits in the central Andes, with broader implications for the genesis of porphyry deposits worldwide.
There is a distinct spatial clustering of giant porphyry copper deposits within orogen-parallel metallogenic belts in the central Andes. Continental-scale arc-oblique structural corridors have been proposed previously by some geologists to control the spatial distribution of porphyry copper deposits in this region. Site specific case studies in southern Peru and northwest Argentina involving multi-scale field mapping and geophysical analysis, coupled with regional-scale field traverses throughout the central Andes, and published geologic mapping, reveal the presence of long-lived continental-scale structural corridors that, in surface outcrop, manifest as myriad individual fault planes that align to the orientation of lineaments observed in multi-scale geophysical data. These structural corridors, with strike lengths of hundreds of kilometers, variable widths and surface expressions, indicate the upward propagation of underlying basement weaknesses through supracrustal sequences, persisting as steep zones of enhanced permeability. These structural corridors are inferred to serve as preferential pathways for ascending hydrous magmas and fluids during major deformation events when they mechanically couple with lower crustal shear zones. A primary control on the distribution of giant porphyry copper deposits has been exerted by linear orogen-parallel structural belts, aligned with the magmatic arc, while a secondary control arises from the intersection of orogen-oblique structural corridors with these belts, leading to the localization of deposit clusters.
Uncertainties in Andean evolution and plate reconstruction models can be tested by causal inference modelling. A novel method for the assessment of conflicting tectonic models is applied through the use of time series analysis to evaluate causal dependencies between five different orogenic proxies and four conflicting plate reconstruction models for the Andes. Plate reconstruction models that exhibit numerous statistically significant causal dependencies with orogenic proxies are highlighted, permitting the inference of the most appropriate plate reconstruction model for metallogenic analysis. By quantifying causal dependencies between plate convergence processes and the development of the central Andean cordillera since the Cretaceous, feedback mechanisms between plate convergence and overriding plate orogenesis system have been identified. Rapid changes to convergence obliquity exhibit temporal precedence to upper plate orogenic processes, and convergence velocity is inferred to be causally dependent on overriding plate topographic loading. Flat slab subduction is causally dependent on decelerating convergence rate. This analysis provides a novel perspective on the dynamics of cordilleran mountain belts.
Insights from the studies into structural corridor intersections and best fitting plate tectonic model and feedback mechanisms have been integrated into a spatio-temporal prospectivity model of giant porphyry Cu deposits in the central Andes during the Cenozoic. This unifying research utilizes time series Granger causality analysis and random forests to elucidate the relationships between giant porphyry Cu deposits, geodynamic evolution and overriding plate structure in the central Andes. The findings reveal coherent and predictable tectonic sequences governing both metallogenic and non-metallogenic processes. A tectonic model, trained without a priori spatio-temporal deposit information, successfully predicts the organization of giant porphyry Cu deposits into metallogenic belts during known metallogenic epochs and correctly predicts non-metallogenic epochs. These results yield a continental-scale spatio-temporal mineralization probability model (1 Myr temporal resolution from 70-0 Ma) for the central Andes, providing novel insights into the tectonic processes that govern metallogenic epochs.
The findings of this study enhance our understanding of the clustering of giant porphyry Cu deposits in time and space. Insights from causal inference provide a new perspective for addressing uncertainties in conflicting time series models. These novel insights can be applied to spatio-temporal prospectivity modelling, providing valuable implications for exploration targeting strategies, not only in this region but also for other porphyry Cu provinces worldwide.