Late Quaternary Activity of the La Rinconada Fault Zone, San Juan, Argentina

Abstract

Most of the permanent deformation in the Pampean Flat slab segment of the central Andes is taken up at the Andean Orogenic Front in Argentina, a narrow zone between the Eastern Precordillera and Sierras Pampeanas that comprises one of the world's most seismically active thrust zones. Active faults and folds in the region have been extensively mapped but still largely lack information on style and rates of deformation, which is essential for understanding the distribution of regional strain and estimating the seismic potential of individual faults. Structural, geomorphic, and 36 Cl cosmogenic radionuclide surface exposure age methods are used to focus on key sites along the 30-km-long La Rinconada Fault Zone in this region of west-central Argentina, which is~15 km away from the highly populated (~500,000) city of San Juan, to define a late Quaternary average shortening rate of 0.41 ± 0.01 mm/year. This slip rate is the same order of magnitude, but slightly lower than nearby similar east dipping Eastern Precordillera faults including the La Laja and Las Tapias Faults. Relatively low slip rates are interpreted as being a consequence of distributed deformation between the latitude of the La Rinconada Fault Zone (31 and 32°S), as compared to between latitudes 32 to 33°S where deformation appears to be focused on fewer structures, including the Las Peñas and La Cal Thrust Faults. The La Rinconada Fault Zone is capable of generating earthquakes of M w 6.6-7.2, but further investigations are required to determine timing and recurrence intervals of discrete events.

Assessing Quaternary Shortening Rates at an Andean Frontal Thrust (32°30′S), Argentina

“…Hedrick et al () identified alluvial surfaces as old as ~181 +/‐ 29 ka at the Loma Negra fan complex west of the city of San Juan, and ~212 +/‐ 37 ka at the Rinconada‐Carpinteria complex ~25 km to the south of San Juan. Similar results (153.5 +14.6/‐13.7 ka), have been reported by Rimando et al () also for the Rinconada‐Carpintería area. Along the El Tigre fault to the northwest, Siame et al () dated a ~180 +/‐ 38 ka fan, as well as two older surfaces ranging up to ~670 ka.…”

Late Quaternary Intraplate Deformation Defined by the Las Chacras Fault Zone, West‐Central Argentina

“…Assuming zero erosion could be justified by the observed ubiquity of desert varnish, which is an indication of high degree of surface preservation (e.g., Jakica et al, 2011;Rimando et al, 2019). Furthermore, zero erosion has also been assumed in other slip rate studies employing cosmogenic dating in several sites along the Precordillera and the Sierras Pampeanas (Costa et al, 2019;Hedrick et al, 2013;Rimando et al, 2019;Schmidt et al, 2011a;Siame et al, 2002). Alluvial surfaces are more likely than not to have a component of inherited nuclide concentration (e.g., Anderson, Repka, & Dick, 1996;Blisniuk et al, 2012;Brocard et al, 2003;Lal, 1991;Repka et al, 1997).…”

“…Compared to the thin-skinned structures in the west (e.g., Las Peñas, La Rinconada, and Las Tapias faults, Figure 1; Costa et al, 2019;Siame et al, 2002, and references therein;Rimando et al, 2019), little is known about the rates of movement of most of the basement-cored uplifts of the Sierras Pampeanas. These structures create significant relief in the retroarc region of Argentina (Costa, 2019).…”

“…Well-localized seismicity in the Argentinian side is from Linkimer et al (2020), which used two temporary seismological networks: the SIEMBRA (SIerras Pampeanas Experiment using a Multicomponent BRoadband Array; between 2007 and 2009, and the ESP (Eastern Sierras Pampeanas) array between 2008 and 2010 (Gilbert, 2008); blue and red circles indicate overriding plate and subducting slab seismicity, respectively. AOF-Andean orogenic front, VZP-Villicum-Zonda-Pedernal Fault, PdPW-Western Pie de Palo Fault, PdPE-Eastern Pie de Palo, VF-Valle Fértil Fault, LCFZ-Las Chacras Fault Zone, SLSMU-Sierras de Los Llanos, Sierras de las Minas and Ulapes Fault, P-Pocho Fault, SC-Sierra Chica Fault Zone (modified from Rimando et al, 2019).…”

10Be surface exposure dating reveals unexpected high deformation rates in the central Andean wedge interior

“…Long‐term deformation and erosion rates across the Precordillera and adjacent provinces based on own estimated and previously published data (Bohon, Schoenbohm, Brooks, & Costa, 2008; Rimando et al., 2019; Schmidt et al, 2011; Schoenbohm et al., 2013; Siame, Bellier, Sébrier, & Araujo, 2005; Siame et al., 1997, 2002). Black and blue circles represent vertical slip rates and shortening rates, respectively.…”