Stable and clumped isotope evidence for a rapid but spatially variable surface uplift history of the Altiplano
Abstract
In order to unravel the tectonic and climatic history of a mountain range, it is critical to have data on the uplift history of the range to understand how it has evolved both temporally and spatially. The early Miocene to present paleoelevation history of the Altiplano plateau of the central Andes has been well studied over the last fifteen years (e.g., Gregory-Wodzicki, 2000; Garzione et al., 2008; Insel et al., 2012), almost exclusively at locations the northern part of the Altiplano. However, data from the rest of the Altiplano are non-existent (see Leier et al., 2013). Here we extend the record by presenting stable isotope data from the southern Altiplano. We focus on the paleoenvironmental record preserved in pedogenic carbonates from well-dated middle-late Miocene (16.3 to 7.1 Ma) sedimentary sections. These carbonates record paleo-surface conditions that offer useful proxies for elevation, including paleo-temperature (Δ47) and paleo-rainwater chemistry (δ18O). Pedogenic carbonates show a pronounced facies change at ~14-13 Ma and an increase in δ13C values from ~16 to 8 Ma, both indicative of increasing aridity. Sediment accumulation rates in the southern Altiplano also decrease substantially at ~14-13 Ma. These environmental changes are consistent with some amount of surface uplift during this period, but do not provide detailed or quantitative information. Surface paleotemperatures decreased by 14°C from 16 to 8 Ma in the southern Altiplano relative to low-elevation paleotemperatures, which remained stable through that interval. The relationship between ground temperature and surface air temperature has complexity (e.g., Peters et al., 2012; Quade et al., 2013), so we have used low-elevation temperatures as a baseline for estimating elevation. This surface temperature record indicates a surface elevation increase of 1.5×0.5 km between 16 and 13 Ma and an additional 0.5×0.5 km between 13 and 9 Ma. Paleoelevation estimates based on oxygen isotopes are similar to those based on paleotemperatures from ~16-15 Ma, but under-predict surface elevation since ~13 Ma (including the modern elevation). This result is consistent with the evaporative enrichment of oxygen isotopes in rain water and/or soil water due to arid conditions (e.g., Decelles et al., 2007). Previous surface elevation estimates from the northern Altiplano suggest that region experienced 2.5×1.0 km of surface uplift between ~11 and 6 Ma (Garzione et al., 2008). Our results from the southern Altiplano show a similar rate and magnitude of surface uplift, but occurring 7×4 Myr earlier than in the northern Altiplano. This temporal offset is also reflected by qualitative indicators of surface uplift such as climate (aridity) and sediment accumulation rate. The consistency of the paleoclimate and paleoelevation records suggests that the same mechanism(s) were responsible for the periods of rapid uplift in both parts of the Altiplano, but was active at different times in different regions. Geologically reasonable processes that fit this observed pattern of large magnitude and spatially variable surface uplift include piecemeal removal of dense lower lithosphere and lower crustal flow, possibly in a south-to-north direction.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP21D..02A
- Keywords:
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- 1041 GEOCHEMISTRY Stable isotope geochemistry;
- 8177 TECTONOPHYSICS Tectonics and climatic interactions;
- 9360 GEOGRAPHIC LOCATION South America;
- 8120 TECTONOPHYSICS Dynamics of lithosphere and mantle: general