Multiple slope failures associated with neotectonic activity in the Southern Central Andes (37º 37º30'S), Patagonia, Argentina.

PENNA, I., HERMANNS, R., NIEDERMAN, S., FOLGUERA, A.

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

GEOLOGICAL SOC AMER, INC

Año: 2011 p. 1 - 16

0016-7606

Quaternary tectonic activity in the transitionarea between the Central and PatagonianAndes is closely associated with an anomalouscluster of rockslides: 19 rockslides with volumesup to 4 × 109 m3 developed in plateaubasalts. We divided them into two groups:(A) rockslides related to neotectonic activityand (B) rockslides not related to neotectonicactivity. Thirteen rockslides, with a total volumeof ~10 km3, which lie on either folds orfaults, have been displaced parallel to thestructures and perpendicular to the valleyaxis, and they exhibit headscarps severalkilometers away from the valley axis. Most ofthem are larger than 109 m3, and are generallyof rock avalanche type with a high degreeof crushing of rocks, although local relief insome cases does not exceed 200 m. Nine rockslideswith a total volume of 8.9 km3 are relatedto folds, while four with a total volumeof 1.3 km3 are related to faults. The six rockslidesnot related to neotectonic activity have atotal volume of 0.25 km3 (of which the largestone accounts for 0.17 km3), and are rotationalslides and block topples with a low degree ofrock fragmentation, although local relief is upto 400 m. The 3He and 21Ne surface exposureages for six of these slides, as well as relativeage assessment based on stratigraphic relationwith glacial deposits and the drainage developmenton the rockslide deposit, suggest thatthe rockslide ages spread rather randomlybetween pre-glacial and mid Holocene, discardingclimatic conditions as a commontriggering factor. The absence of structuresthat can represent ideal sliding planes showsthat rock fracturing due to neotectonic activityis a major conditioning factor for failures andthat the magnitude of landslides is stronglycontrolled by the type of deformation.