LATE PLEISTOCENE AND HOLOCENE TEPHROSTRATIGRAPHY AND CHRONOLOGY IN SOUTHERN PERU

Late Pleistocene tephras have been dated on the west flank of Nevado Sara Sara between ca. 49,200 and 44,500 yr BP, and on the south flank of Yucamane ca. 44,000 yr BP. Tephra from Coropuna was found in a soil section that yielded 14C ages of ca. 27,200-37,370 yr BP. The Misti edifice comprises a stratovolcano termed Misti 1, overlapped by two stratocones termed Misti 2 and 3 (°Ü112 ka), and a summit cone Misti 4 °Ü11 ka. Sustained explosive eruptions have delivered at least 12 pumice falls during the past ca. 50,000 years. Late-Glacial and Holocene tephras were found in various peat-bogs. Seven tephra-fall deposits from Huaynaputina, Misti, and Ubinas were deposited over the past 15,000 years. Two recent tephra-fall deposits are present around the Ticsani domes (a dacitic pumice-fall deposit of 0.4 km3 has been dated ca.11,600 yr BP; bombs and pumice preceeding the youngest dome overlie the AD 1600 Huaynaputina tephra. The recent explosive behaviour of Ubinas produced several tephra-falls, including two widespread plinian pumice falls. The pumice-fall deposit >7840 yr BP and the ca. 980 yr BP-old pumice-fall deposit have a volume >1 km3 and may be linked to the formation of the summit caldera. The peat sequence in the Sallalli peat-bog 10 km SE from the Nevado Sabancaya includes 4 tephra-fall layers: the AD 1600 Huaynaputina ash, an AD 1200-1400 Sabancaya/Ampato ash, a thin black ash probably from Misti ca. 2,370 yr BP, and a Sabancaya/Ampato ash of ca. 8,550 yr BP. Recent tephra beds were also found that were deposited : a) during the Inca Empire (Misti eruption); b) in AD 1600 Huaynaputina plinian eruption produced voluminous (12 km3) pumice-fall deposits, along wit pyroclastic flows, and surges that disrupted life ~60 km around the volcano. Persistent eruptions of Nevado Sabancaya have dispersed a small volume of ash from May 1990 until 1998 as far as 20 km towards the east.