Lithologies, structure and basement-cover relationships in the schist belt of the Dom Feliciano Belt in Uruguay

Abstract

This work is the result of a multiyear effort to use field geology to describe lithologies, to establish contact relationships and to create a sketch of the tectonic evolution of the Meso-to Neoproterozoic metasedimentary successions within the Schist Belt of the Dom Feliciano Belt. This low-grade metamorphic cover rests on the high-grade metamorphic basement of the La China and Las Tetas complexes. This basement is Archean-Paleoproterozoic in age. The Schist Belt is overlapped unconformably by the Barriga Negra formation. The Lavalleja complex and the Barriga Negra formation both deformed together during the D2 deformation event (~ 570 -540 Ma), but the Barriga Negra only partially recorded the D2 transpressive event, whereas the Lavalleja complex was affected by both the D1 tangential event and the D2 event. Event D1 would have developed a fold nappe with vergence to the south. This hypothesis is supported by different structures: (i) recumbent and upright folds oriented E-W, (ii) subhorizontal mylonitic foliation in marbles (calc-schists), (iii) stretching lineations plunging towards the SW in metaconglomerates of the Las Tetas Complex, and (iv) a reworking of the subhorizontal foliation parallel to the Sarandí del Yí strike-slip shear zone.KEYWORDS: Dom Feliciano Belt; Ediacaran; Deformation; Fold nappe; Tectonic evolution. RESUMO: Este trabalho resulta de um esforço de vários anos tentando usar a geologia de campo para descrever litologias, estabelecer relações de contato e perfazer a evolução tectônica das sucessões metassedimentares, de idades meso a neoproterozoicas, que foram deformadas dentro da Faixa de Xistos do Cinturão Dom Feliciano. Essas rochas constituem uma cobertura de baixo grau que repousa em cima do embasamento de alto grau metamórfico dos complexos La China e Las Tetas. Esse embasamento é de idade paleoproterozoica-arqueana. A Faixa de

Stratigraphy and tectonic setting of the Barriga Negra Formation in Uruguay: an update

“…Sánchez Bettucci (1998) performed an extensive mapping and petrological analyses of the southern portion of de Dom Feliciano Belt amending the Lavalleja Group following the stratigraphic criteria of Midot (1984) and Preciozzi (1989), grouping three formations (i.e., Minas, Fuente del Puma and Zanja del Tigre) with intensely deformed meta-sedimentary and meta-volcanic successions. This unit, considered basement of Barriga Negra Formation, is one of the most recognized units in the region (Sánchez Bettucci & Ramos 1999, 2010b, Pazos et al 2008, Fambrini et al 2005a, Masquelin et al 2017, Oyhantçabal et al 2010, and an equivalent of the Porongos and Brusque groups from Southern Brazil (Sánchez Bettucci & Ramos 1999, Basei et al 2000, 2010b, Pazos et al 2008, Fambrini et al 2005a, Masquelin et al 2017, Oyhantçabal et al 2010. Although, some authors had published other alternative stratigraphy proposals (Gaucher 2000, Chiglino et al 2010, Blanco et al 2010, Poiré et al 2005, Pecoits et al 2016, in which the definition and interpretation of Dom Feliciano belt has been questioned (see Bossi & Gaucher 2014).…”

“…SLB: Santa Lucia Basin; LMB: Laguna Merin Basin; 1: Sarandí del Yí Shear Zone; 2: Sierra Ballena Shear Zone. Source: modified from Sánchez Bettucci et al (2010aBettucci et al ( , 2016, Rossello et al (1999Rossello et al ( , 2000, Oyhantçabal et al (2010), Preciozzi et al (1979Preciozzi et al ( , 1985 and Masquelin et al (2017).…”

“…All those new units and their interpretations (like other proposals by Aubet et al 2014, andPecoits et al 2016) should be considered alternative proposals as there are not accepted by main part of the national and regional scientific community (see: Sánchez Bettucci & Ramos 2002, Basei et al 2000, Pazos et al 2008, Rapalini & Bettucci 2008, Sánchez Bettucci et al 2010b, Oyhantçabal et al 2010, Almeida et al 2010, Fambrini et al 2005a, Núñez Demarco 2014, Oriolo et al 2016, Masquelin et al 2011, 2017.…”

“…2 and 3). As example, the Lavalleja Group is only accurately mapped in its southern half (Preciozzi et al 1981, Midot 1984, Cosarinsky 1997, Sánchez Bettucci 1998, Sánchez Bettucci & Ramos 1999, Mallmann et al 2007, and all show the geological complexity of the region, but there are only inaccurate sketches of their northern portion that vary among different authors (see Gaucher et al 2003, Rapalini & Bettucci 2008, 2010b, Oriolo et al 2016, Masquelin et al 2011, 2017, Pecoits et al 2016). Yet, despite the fact that there are published dozens of stratigraphic profiles and chemical analyses, there are no detailed maps showing the complete extension of the Arroyo del Soldado Group nor its constituent formations: there are only narrow maps in key-areas (see Fig.…”

“…The Barriga Negra Formation is one of these controversial units; it is a thick succession of reddish conglomerates, arkoses and pelites, which is assumed to be Neoproterozoic in age (e.g., Midot 1984, Fambrini et al 2005a). It has been described as it rests unconformably over its basement (Walther 1919, Midot 1984, Fambrini et al 2005a, Masquelin et al 2017, as concordant (Preciozzi & Fay 1988, Gaucher 2000 or even interbedded with it (Caorsi & Goñi 1958). Its bedding was described with regular dip around 10°-20° E (Midot 1984, Preciozzi & Fay 1988, Bossi & Navarro 1991 and 40°-45°E (McMillan 1933, Fragoso-Cesar et al 1987.…”