Characteristics of the neogene ignimbrites in the Arequipa area.

Abstract

Four ignimbritic units have filled the Arequipa Basin and outcrop around the Chachani Volcano. (1) The oldest Rio Chili ignimbrite is 13.33 Ma old; (2) the most widespread La Joya ignimbrite is 4.9 Ma old; (3) the Arequipa Airport ignimbrite (1.65 Ma) flowed from an area buried beneath Chachani; (4) the Yura Tuffs. 1.02 Ma old. are restricted to the west of Chachani. All are calc-alkaline rhyolites with plagioclase, biotite, quartz, sanidine, and opaques, but the Rio Chili and La Joya ignimbrites also contain amphibole. Trace elements of the older ignimbrites reflect stronger crustal influence. (c) 2005 Academie des sciences. Publie par Elsevier SAS. Tous droits reserves.