Shrimp zircon geochronology constrains on Permian pyroclastic levels, Claromecó Basin, South West margin of Gondwana, Argentina

Abstract

Pyroclastic levels are descripted in Sierras Australes outcrops and Claromeco Basin sub-surface records, interbedded with mudrocks and coal beds in the base of the Tunas Formation sequence that correspond to the Permian South West margin of Gondwana. The pyroclastic levels classify as fine tuff. SHRIMP zircon ages obtained are 291.7 ± 2.9 Ma in the outcrop and 295.5 ± 8.0 Ma in the subsurface. These ages are consistent with other zircon SHRIMP ages of other outcrops tuff of the Tunas Formation, with Permian flora, and with tuff ages of correlated Gondwana areas, in the Paraná, Karoo and Paganzo basins. These data, in addition with other geological evidences, support a tectonically active and changing

Metamorphic evolution of the Loma Marcelo skarn within the geotectonic context of the crystalline basement of the Ventania System (Argentina)

“…On the other hand, U-Pb zircon dating of tuffs interbedded in the upper half of the top unit of the Pillahuincó Group (Tunas Formation) yielded ages of ca. 292-281 Ma (Tohver et al, 2008;Alessandretti et al, 2013;López-Gamundí et al, 2013;Arzadún et al, 2018), which allow the age of the Palaeozoic cover to be extended at least until the Early Permian.…”

Following the steps of CHIPA: Chilenia and Patagonia formed the same drift terrain that collided with the southwest Gondwana margin during the middle Paleozoic

“…This AMS axes arrangement indicates a SW-NE maximum compression direction (Tomezzoli et al, 2018; Figure 3B). From paleomagnetic studies, it emerges that these rocks bear a postectonic remagnetization carried by hematite and/or magnetite, which is located in the apparent polar wander path (APWP) of South America (Tomezzoli, 2009;Gallo et al, 2017) in the Permian position close to that of the Tunas II paleomagnetic pole (PP; Tomezzoli, 2001;Figure 3E) aged 280.8 ± 1.9 Ma (López- Gamundi et al, 2013;Arzadún et al, 2018). The fact that these rocks are carriers of a postectonic remagnetization and a tectonic magnetic fabric indicates the overlap of different coaxial deformation events, as documented by other authors (Andreis, 1979;Japas, 1989;Sellés Martínez and Quenardelle, 1992;Japas et al, 2001).…”

“…In this unit, the vegetal structure that corresponds to Glossopteris, Gangamopteris, Lycopsids, and woody tissues can be distinguished. Additionally, there are some tuff levels intercalated in the sequence, indicating the presence of pyroclastic activity in Gondwana during the early Permian, with U/Pb data of 291-280 Ma (López- Gamundi et al, 2013;Arzadún et al, 2018). The study of the Tunas Formation has accumulated knowledge spanning various scientific disciplines over the course of decades.…”

“…The shortening direction indicates that the maximum stress along this part of Gondwana came from the southwest and remained stable during the Early Carboniferous up until the Permian. The deformation propagated in a diachronous fashion eastward to the foreland, displaying signs first of a decrease and a subsequent pick up of intensity to decay again, suggesting cycles of higher and lower deformation intensity; the first one between the Sauce Grande and Bonete formations (nearly 300 to 290 Ma) and the second one in the Tunas Formation (290-276 Ma; Arzadún et al, 2018).…”

“…Furthermore, within the Pillahuincó group itself, there are differences in the intensity of the deformation, as the base is more deformed than the top (Figures 2E, F). It is not disputed that in the Sierras Australes area, the deformation attenuates in space (to the east-northeast) (Figure 2) and time (up to the Permian) (Tomezzoli, 2001;Arzadún et al, 2018). Moreover, the sequence is covered in unconformity (Cenozoic deposits).…”