| Autor: |
Costa, Carlos H., Schoenbohm, Lindsay M., Brooks, Benjamin A., Gardini, Carlos E., Richard, Andrés D. |
| Zdroj: |
Tectonics; Aug2019, Vol. 38 Issue 8, p3034-3051, 18p |
| Abstrakt: |
At the latitude of 32–33°S, the orogenic front of the eastern flank of the Andes is located in the Southern Precordillera, where two major thrusts concentrate Quaternary deformation at the surface. We estimate the shortening rate for one of these, the Las Peñas thrust, for the last ~200 ka, at the site of one of the best exposures of Quaternary thrusting along the Andes. Shortening was estimated across two prominent splays of the deformation zone at the mouth of the Las Peñas River through balanced cross‐sections by using a terrace surface as a marker of cumulative deformation. Terrace ages were constrained through cosmogenic isotopes (10Be) analysis on quartz cobbles collected from the surface and three depth profiles. Results indicate a mean shortening rate across the Las Peñas thrust of 0.27 + 0.11 mm/a. Our results are lower than Holocene shortening rates (1.9–2.4 mm/a) obtained for individual splays of the Las Peñas thrust nearby. We discuss these discrepancies and implications for thrust evolution since the Late Pleistocene, in particular regarding along‐strike rate variations that highlight the complexity of the Quaternary‐active thrust deformation zone. We argue that ongoing stream incision rates largely prevail with respect to thrust activity at the study site. This observation might be connected with a recent (Holocene?) basinward shift of blind thrust activity. Key Points: Shortening rate of the Las Peñas thrust (Argentine Precordillera) is 0.27 + 0.11 mm/a for the last ~200kaThis rate is lower than Holocene shortening rates reported nearby the study siteResults highlight kinematic complexities in space and time; caution is needed for assessing slip rate with punctual data [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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