GLACIAL AND PERIGLACIAL GEOMORPHOLOGY AND CHRONOLOGY IN THE NEVADO DE CHAÑI (CORDILLERA ORIENTAL OF JUJUY): IMPLICATION FOR PAST CLIMATE IN NW ARGENTINA

MARTINI, M.A.; STRELIN, J.A.; ASTINI R.A.; KAPLAN, M.R.

Heidelberg

Congreso; 22. Lateinamerika-Kolloquium 22. Coloquio sobre las Geociencias de Latinoamérica 22nd Colloquium on Latin American Earth Sciences; 2011

Heidelberg Institute of Earth Sciences, Universidad de Heidelberg

The Nevado de Chañi (24º 3? 45?? S; 65º 44? 43?? W) is one of the highest picks in northwestern Argentina (5882 m.a.s.l.). It is the summit of a N-S trending mountain range located just north of the Arid Diagonal, which separates the southern Pacific westerlies from the South American Summer Monsoon domains. This range consists of Paleozoic sedimentary and metamorphic rocks intruded by Ordovician granites. It has been broadly eroded by glaciers during the Late Pleistocene but today no glaciers exist in the area and the periglacial activity takes a main role in the development of the landscape above 4600m. The orographically-driven climate conditions, with seasonal summer wet-air masses moving from the Atlantic determine that the west side is clearly dryer and probably warmer than the east faced side. These conditions determined a greater extent of the ice-masses and a lower paleo-equilibrium line altitude on the east side during the past glaciations. Three main groups of moraines were recognized on both sides of Chañi. 62 moraine boulders were sampled from the different glacial events, ten of which were selected for a preliminary 10Be surface exposure dating. Four peat bogs were cored to obtain radiocarbon minimum ages of the deglaciation. Preliminary results of 10Be dates revels two main glaciations: one is pre-LGM (Last Glacial Maximum) and the other occurred during the late-glacial stage, before the Younger Dryes. The periglacial geomorphology is mainly represented by scree activity, giving way to solifluxion and protalus lobes formation. Special attention was presented to rock glacier formation. Active, inactive, and fossil rock glaciers were distinguished taking in account geomorphological characteristics like the frontal slope and ridge and furrows preservation. The lower limit for active and inactive/fossil rock glaciers is located above 4700m and 4500m, respectively. Cross-cutting relation with dated moraines provides the maximum age of these geomorphic features. Finally, our geomorphological and geochronological results allow us to propose a preliminary correlation with other glaciated areas in the arid Andes and the northern Cordillera Oriental and with lake transgression phases recorded on the southern Bolivian Altiplano during late Pleistocene.