The tectonic significance of K/Ar illite fine-fraction ages from the San Luis Formation (Eastern Sierras Pampeanas, Argentina)

Abstract

The Sierra de San Luis forms the southern tip of the Eastern Sierras Pampeanas in central Argentina. Two narrow belts of low-grade phyllites and quartz arenites, i.e. the San Luis Formation, have accommodated part of the strain-related differential exhumation of the medium-to high-grade metamorphic domains that constitute to the basement complex of the sierra. Eleven phyllite samples were subjected to the K/Ar fine-fraction dating technique. Results are interpreted in relation to the Kübler index of the illites, which indicate epimetamorphic conditions for the majority of the samples. Obtained ages between 330 and 290 Ma cover a period of compressional tectonics in the late Mississippian (Visean/Serpukhovian boundary) followed by the subsidence during the formation of the Paganzo Basin in the provinces of La Rioja and San Luis. These tectonic movements are coincident with the Toco orogeny in northern Chile and southern Bolivia. This suggests that the older K/Ar ages document the compressional stage and that younger ages record the cooling of the basement during the subsequent extensional uplift of the basement.

Exhumation history and landscape evolution of the Sierra de San Luis (Sierras Pampeanas, Argentina) - new insights from low - temperature thermochronological data

“…This time span matches with regional tectonic processes such as the development of the Paganzo Basin (Limarino and Spalletti, 2006;Gulbranson et al, 2010) and the San Rafael Orogeny (Ramos, 1988;Kleiman and Japas, 2009;Geuna et al, 2010;Japas et al, 2013). Active deformation during basin development was accompanied by exhumation of the study area, as indicated by K-Ar fine fraction data from Wemmer et al (2011) and thermochronological data presented here (Figs. 7, 10).…”

“…14), yielding Devonian ages (380-350 Ma; Sims et al, 1998;Steenken et al, 2008) and Carbonifeous K-Ar fine fraction ages (345-299 Ma; Wemmer et al, 2011). The latter ages were taken from the San Luis Formation, represented by two belts of low-grade phyllites and quartz arenites, several kilometres to the north of the study area.…”

“…For better view geochronometers are displayed in the x-axis. K-Ar muscovite and biotite data are taken from Steenken et al (2008) and Wemmer et al (2011). Black lines indicate individual ages, bars indicate overlapping error of individual ages.…”

A late Caledonian tectono-thermal event in the Gaissa Nappe Complex, Arctic Norway: evidence from fine-fraction K‒Ar dating and illite crystallinity from the Digermulen Peninsula

“…Fine-fraction K-Ar dating has been used in a number of studies producing reliable age constraints on low-grade metamorphism (e.g. Wemmer et al 2011;Koehl et al 2018). That technique was therefore also used in this study.…”

The Capilla del Monte pluton, Sierras de Córdoba, Argentina: the easternmost Early Carboniferous magmatism in the pre-Andean SW Gondwana margin

“…On the other hand, the Tres Árboles ultramylonites have yielded much younger 40 Ar-39 Ar ages of 343 ± 5 and 341 ± 5 Ma (Whitmeyer 2008), respectively, although these were interpreted as regional cooling ages and can only be regarded as minimum estimates for the cessation of fault movement. Wemmer et al (2011) obtained K-Ar ages of 334-291 Ma for fine-grained illite from phyllites associated with shear zones in Sierra de San Luis. They considered that the ages older than 320 Ma correspond to a phase of compressional tectonism linked with the Toco orogeny that is recognized in northern Chile and southern Bolivia.…”