Corrélations des ignimbrites néogènes du sud du Pérou - Apports des propriétés physiques et magnétiques à la compréhension des processus de mise en place et de soudure.

摘要

Correlations indicate that four ignimbrites were emplaced between middle Miocene and early Pleistocene in the Arequipa area: the Rio Chili Ignimbrite, RCI, 13.35 Ma old; the La Joya Ignimbrite, LJI, 4.83 Ma old; the Arequipa Airport Ignimbrite, AAI, 1.77 Ma old; and the Yura Tuff, YT (1.03-1.84 Ma). Geochemical and isotopic compositions displayed by the ignimbrites, can be explained by increasing magma differentiation and contamination, in two different "crustal domains". The LJI, whose Te ranged from 650 to 680°C, displays the highest welding degree as show by physical properties. The AAI high induration is the consequence of cementation by secondary vapor phase crystallisation. The low degree of anisotropy and large dispersion of AMS directions in the LJI, may reflect turbulent transport of low concentration granular flows. In contrast, the AAI records a well-defined and oriented magnetic fabric, which can be the consequence of dense pyroclastic flows. Flow directions and isopleths map, of the AAI, point to a source now buried under the Chachani volcanic complex.