Abstract

The segment of the Argentine Andes between lat. 39°10′ S. and lat. 41°20′ S. was glaciated extensively and repeatedly during the late Pleistocene; today only a few small glaciers at high altitudes are present. The former glacier consisted of an ice sheet, in places more than 1500 m thick, centered on the high Cordillera. At times the ice divide may have shifted westward, away from the present water divide, in the direction from which the glacier was principally nourished. The ice sheet separated into lobes that occupied the valleys of major east-flowing streams. The distance between the high Cordillera and the terminus of the longest lobe is about 70 km. Cirque altitudes form an orderly sequence, rising eastward in the direction of increasing temperature and aridity in today's climate.

Three bodies of glacial drift were identified: Pichileufú, El Condor, and Nahuel Huapi, in order of decreasing age and extent. Possibly the Nahuel Huapi Drift consists of two members. Small bodies of drift younger than the Nahuel Huapi Drift were not studied.

Isotopic dating has not been possible because no datable substances in, or significantly related to, the drifts were found. Comparison of the progress of weathering of granitic clasts in the zones of weathering in the drift bodies suggests that the intervals between the times of drift deposition were not long. None of the drift is believed to be older than the Wisconsin Drift in North America. The data in hand do not permit closer comparison.

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