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

Henri Masquelin,Elena Peel,Hernán Silva Lara,Sofía Pascual,Pablo Núñez Demarco,Rossana Muzio,Leda Sánchez Bettucci,Fernando Scaglia

doi:10.1590/2317-4889201720160119

Henri Masquelin, Elena Peel + Show 6 more

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https://doi.org/10.1590/2317-4889201720160119

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Abstract

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.

Highlights

In recent years, the number of isotopic data regarding absolute ages of the Precambrian rocks of the Dom Feliciano Belt (DFB), in Uruguay (Fig. 1), has exponentially increased (Hartmann et al 2001, Mallmann et al 2007, Oyhantçabal et al 2009, 2011a, 2011b, Gaucher et al 2011, Aubet et al 2012, Rapalini et al 2015, Peçoits et al 2016, Oriolo et al 2016a, 2016b)
The study region is divided into six detailed key areas, all located in the Schist Belt: 1, Sepultura, 2
The evidence here exposed is likely to define a regional discordance between the two units: 1. a low‐grade metamorphic Mesoproterozoic to Cryogenian succession; and 2. a medium‐grade metamorphic unit that is pre‐Neoproterozoic in age

Summary

Introduction

The number of isotopic data regarding absolute ages of the Precambrian rocks of the Dom Feliciano Belt (DFB), in Uruguay (Fig. 1), has exponentially increased (Hartmann et al 2001, Mallmann et al 2007, Oyhantçabal et al 2009, 2011a, 2011b, Gaucher et al 2011, Aubet et al 2012, Rapalini et al 2015, Peçoits et al 2016, Oriolo et al 2016a, 2016b). Geological maps of the area are scarce, several authors have coined new formations and magmatic and metamorphic complexes (e.g., Bossi & Gaucher 2014). It is unclear whether many of these really exist or are only a result of overinterpretation of these isotopic data. The physical criteria for separating basement from cover rocks are the metamorphic grade, contact relationships, cartographic limits and style differences in deformation. Many contact relationships between basement and low-grade cover successions have been neglected, and cartographic boundaries changed with each stratigraphic interpretation. A detailed structural analysis was made in small areas to build up local tectonic sketches (Rossini & Legrand 2003, Mallmann et al 2007, Scaglia et al 2007, Cabrera 2014, Silva Lara et al 2016, among others), but it was difficult to extrapolate their results to the whole study region

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