GLACIAL GEOCHRONOLOGY TRANSECTING A TROPICAL MOUNTAIN RANGE, THE CORDILLERA BLANCA OF NORTHERN PERU

The high relief landscape of the Cordillera Blanca of northern Peru preserves a rich record of glaciation back to at least MIS 10. By combining new high-resolution mapping, new cosmogenic exposure ages from the eastern side of the range, and existing chronologic data from the western side of the range, we present an interpretation of paleoglacier extents spanning the ~200km-long range. This range is unique and well-suited for paleoclimate studies as it trends ~north-south and experiences east-west gradients in precipitation, bedrock type, and local tectonic setting. The range is bound on the west side by the active crustal-scale Cordillera Blanca Detachment Fault that offsets Holocene moraines. U-shape valleys carved into granitic bedrock characterize the western drainages, while the eastern side of the range is more typically characterized by V-shaped valleys, is underlain mainly by metasedimentary bedrock, and is not bound by an active tectonic structure. Both sides of the range host paleoglacier deposits, the most well-preserved of which have been mapped and dated by previous workers. However, new high-resolution satellite imagery has enabled us to view unmapped denuded glacial deposits on both sides of the range that suggest much more extensive paleoglaciers than previously documented. To supplement remote mapping, we mapped and sampled moraines specifically on the eastern side of the range in order to look at the distribution of paleoglaciers across gradients. Our ¹⁰Be chronology from moraine crest boulders resolve the position of paleoglacires during the LIA, mid-Holocene, early Holocene, Younger Dryas, Antarctic Cold Reversal, Last Glacial Maximum, MIS 4, MIS 6, and MIS 8 revealing a picture of paleoglaciers distributed throughout the range at approximately the same periods of time. However, the paleoglaciers have varying geometries and extents, potentially reflecting differences in catchment morphology and precipitation. New high-resolution mapping reveals a picture of dynamic paleoglaciers that regularly abutted and/or cross-cut each other as well as much more extensive ice advances than previously articulated.