Surface uplift and erosion of the southernmost Argentine Precordillera

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• 作者：Alina A. Walcek ; ^{aawalcek@syr.edu} ; Gregory D. Hoke ^{gdhoke@syr.edu}
• 关键词：Landscape evolution ; Neogene ; Argentina ; Geomorphology ; Surface uplift ; Cosmogenic ; Nuclide
• 刊名：Geomorphology
• 出版年：2012
• 期刊代码：31_0169555x
• 类别：soc
• 出版时间：1 June, 2012
• 卷：153-154
• 期：Complete
• 页码：156-168
• 文件大小：2666 K

摘要

The timing of uplift of the Precordillera is important for understanding the linkages, if any, between slab dynamics, shortening and topography. The study region (between 32掳 and 33掳 S latitude) lies at the southern end of the flat slab, where the subducting Nazca plate is nearly horizontal. South of the study region, subduction occurs at normal subduction angles of around 30掳 while north of the study region the slab subducts at around 5掳. We use the geomorphology of the region to date the initiation of surface uplift and the ensuing landscape adjustment. The topography of the Precordillera of the Argentine Andes consists of both remnants of a low-relief Miocene landscape developed when the region was at a lower elevation, and rapidly eroding fluvial systems that have been dissecting this surface since uplift. This study utilizes ²⁶Al and ¹⁰Be concentrations in stream sediment quartz to calculate erosion rates of the Miocene remnant paleo-landscape, as well as incision rates within the actively incising post-uplift fluvial system. The remnant landscape is eroding at < 10 m/My, while the surrounding landscape is eroding an order of magnitude faster, approaching 100 m/My. These values show the transition from a rapidly eroding system adjusting to uplift, to a system where rates of uplift approach those of erosion. We used a locally determined relationship between average upstream slope and erosion rate to model erosion across the landscape. DEM analyses of modern river profiles are used to reconstruct paleo-river profiles, which suggest an average of 1.3 km of uplift. Uplift of the southernmost Argentine Precordillera is constrained to have initiated by ~ 10 Ma, demonstrating that under the arid conditions typical of the southernmost Precordillera, millions of years are needed for a landscape to reach equilibrium.