2026/01/09 by Mihai N. Ducea, Peter G. DeCelles, James B. Chapman +6
Earth and Planetary Sciences · #Geological and Geochemical Analysis #Geochemistry and Elemental Analysis #High-pressure geophysics and materials
paper · doi:10.1130/b38190.1
Abstract Here we review regional geological, petrological, geochemical, and geophysical data from the Central Andean plateau (comprising two distinct areas, the Altiplano and Puna) and its defunct North American sibling, the Nevadaplano, as well as to a lesser extent Tibet, to show that magmatism in the middle crust of orogenic plateaus plays an important role in the development of relief and high elevation and drives the mechanical behavior of these features. We show that in situ, mostly S-type melting is an intrinsic feature of plateaus and that these melts can reside in the crust for millions to tens of millions of years without freezing just below a critical melt fraction. Some of these in situ partial melt masses escape their source regions and erupt at the surface. The chemical evolution of volcanic masses produced by partial escape from these migmatites can be predicted by simple forward petrologic calculations. Extensive migmatite in sub-plateau middle crust also contributes to the mechanical weakness of plateaus and their buoyancy. In addition, magmatism from the underlying mantle wedge can further sustain the life of these extensive partial melting zones. Additional, much deeper melt accumulation zones exist close to the bottom of these thick-crusted domains, but we have much less information about their evolution and chemistry; they are probably similar to the deepest crustal root zones of the frontal arcs. We also suggest that there is a link between the ability of Li, B, Cs, and other elements to be concentrated in S-type leucogranites of the extensive migmatite blanket of the middle crust and the concentration of Li (and other metals) in brines and ultimately in the salars of the Central Andean plateau. Hydrothermal activity directly related to the present day Altiplano-Puna magma body or the recent equivalents on South America’s plateau may have leaked these incompatible elements into the former lakes that are now hosting the largest concentrations of Li on the planet.