Plumes, Plates and Porphyries

Abstract

This study developed an automated approach to understand plume and plate boundary interactions over time, investigating how flat slab and porphyry development are linked to formation mechanisms of major eastern Pacific Large Igneous Provinces (LIPs). Our method allows us to detail how the Shatsky-Hess conjugate collided with North America from 85 Ma, with the subducting front corresponding to porphyry development and matching divisions between shallow and flat slab areas. Our new formation model for the Enigma Ridge, conjugate to the Tuamotu Plateau, resolves problems for development of the Peruvian Flat Slab and the Nazca ridge, with porphyry deposits formed at the eastern tip or sides of the Enigma Ridge. We infer development of the metallogenically significant Juan Felix LIP by identifying the importance of overprinting relationships between plume trails and the potential effect of slow spreading on LIP size and note that it corresponds to the Altiplano Flat Slab, with related deposits forming between 44 Ma and 31 Ma. While deposits mainly form at the front of the flat slab or along its margins, deposits form to the north and south of the San Felix and Juan Fernandez plume trails between 36 Ma to 29 Ma. We provide an explanation for a previously unexplained set of deposits in SAM (64 to 51 Ma age), relating them to the collision of a San Felix-MOR interaction. We investigated the controversy over whether plumes may affect tectonic and metallogenic development at subduction zones or are instead suppressed or destroyed by descending flow and find that while plumes do survive relatively close interaction with a subduction zone, if they cross that zone then it takes tens of millions of years to re-establish themselves or they do not survive the interaction. Plumes identified in the geological record by non-tomographic methods, such as the Manus plume, may have either died or become temporarily suppressed by crossing a subduction zone.