Paper No. 11
Presentation Time: 11:10 AM


WÖRNER, Gerhard, GZG, University of Göttingen, Abt. Geochemie, Goldschmidtstr. 1, Göttingen, 37077, Germany,

Our field and laboratory work since 1986 in the Central Andes involved supportive colleagues and collaborators, many students, and good friends. It has resulted in a body of work that attempts to characterize aspects of Andean magmatism through time an space over more than 1500 km and from 35 Ma to present. Magmatism in the "modern" Andes, i.e. since uplift and crustal thickening started 35 Ma ago, is initiated by voluminous plateau-forming ignimbrites. These reflect episodes of mantle and crustal melting which migrate from N to S from 25 - 10 Ma. Compositional and isotopic variation of Andean andesites, that follow the ignimbrites, reflect distinct crustal domains and different lithologies that were assimilated at conditions of increasing pressure while the crust was thickened to 70 km during Andean orogeny.

Isotope compositions of magmas and Proterozoic basement allow to estimate the proportion of juvenile to recycled crustal input (20 to 50% at 30 to 90 km3/km*Ma) and thus to constrain the role of magmatic addition to crustal thickening during the past 35 Ma to less than 10%.

The extreme climate of the Atacama desert is an ideal playground to link processes of uplift, erosion, valley incision, and sedimentation and the way these are linked to, and constrained by, the composition and age of volcanic rocks. Geological and geochronological evidence date both, fossil ignimbrite surfaces on the Western Andean slope and the onset of formation of deep canyons to around 10 Ma, which is consistent with tectonic models and sedimentary records.

On the other end of scale, the evolution of individual magma batches, their sequence and evolution in individual Andean magma systems were reconstructed from micro meter zonation features in magmatic phenocrysts, high-resolution geochronology and U-series isotope analyses.

This talk presents - on the occasion of this session - a summary of our results over the past 25 years that involved a total of 78 co-authors on > 40 publications.

I wish to extend my deep appreciation to all my colleagues, students, and friends for their support.