Geology of the Morteritos region, easter sector of the Cordon del

Geology of the Morteritos region, easter sector of the
Cordon del Plata, Frontal Cordillera (33°05'S), Mendoza
province, Argentina
María Celeste Fernandez ; Daniel J. Perez , Laura B. Giambiagi and Ana Lossada
IDEAN, Lab. Tectónica Andina, Dpto. Geología, FCEN, UBA;
IGEBA, Lab. Paleomagnetismo "Daniel A.Valencio", Dpto. Geología, FCEN, UBA.
*E-mail: [email protected]
Abstract. This study is focused on the tectonic and
magmatic evolution of the Morteritos region, on the eastern
side of the Cordón del Plata range, in Frontal Cordillera,
33°S. The study area is located in the southernmost part of
the modern non-volcanic “flat-slab” segment, which extends
from 28°S to 33°S, above the flat slab segment of the
subducting Nazca Plate (5°). The stratigraphy sequence
are composes by pre-Carboniferous sedimentary rocks,
Mesozoic rocks and Cenozoic units.
Plata Formations, the Rio Blanco Conglomerates of middle
Permian age, and the Permo-Triassic rhyolitic and
rhyodacitic rocks of the Choiyoi Group. It culminates with
several Cenozoic synorogenic units, associated with the
uplifting of the Main Andes Cordillera (see Figure 2 and
The study region corresponds the thick skinned thrust front
of the Cordón del Plata range. The main structure of the
region corresponds to the -"La Carrera"- fault system,
which includes three N-S trending inverse faults,
denominated from West to East: Fault I, Fault II, Fault III
(Caminos, 1965). The same ones were renamed in the
Cerro Arenal fault (Folguera et al., 2001), La Hoyada fault
(Giambiagi et al., 2011) and Cerro Médanos fault
(Folguera et al., 2001) respectively. In the study region a
new fault was inferred, denominated Los Morteritos fault.
This structure could correspond to a normal PermoTriassic fault, inverted during Cenozoic times (see Figure
Keywords: El Plata range, Complejo Metamórfico, Chilenia
Terrane, Frontal Cordillera, Mendoza, Argentina.
1 Introduction
The aim of the present contribution is to analyze the
stratigraphy and structure of Paleozoic-Mesozoic
metamorphic and volcanic rocks, and their relationship
with Paleozoic sedimentary deposits, in the eastern sector
of the Cordon del Plata. This sector comprises a major
orogenic unit with more than 6.000 meters in topographic
elevation, located on the eastern edge of the Frontal
Cordillera, Mendoza Province, Argentina. The study region
is located at 33º05'S and 69°20'W, in Morteritos creek
region (see Figure 1a-b). This area is located in the
southernmost part of the modern non-volcanic “flat-slab”
segment (Cahill e Isacks, 1992) betwen 28° and 33°S,
under which the Nazca plate forms a broad sub-horizontal
bench between 100 and 150 km (see Figure 1c). The first
geological studies in the region correspond to Stappenbeck
(1917), Groeber (1939), Polanski (1959) and Caminos
(1965); and more recent studies by Casa (2005) and
Heredia et al., (2012).
3 Tectonic evolution and discussion
The “Serie Vallecitos” unit, could probably correspond to
the deposits of a forearc basin associated to a subduction
system, related to an active margin of the inferred Chilenia
Terrane (Heredia et al. 2012). Subsequently, during the
Late Devonian, the deformation of pre-Carboniferous
sequences could be related to the collision of the Chilenia
Terrane against the western margin of Gondwana (Ramos
et al. 1984). The Gondwana cycle began with a subduction
system along the new West Gondwana margin (Ramos,
1988). In this margin, a back-arc-basin developed with
associated shallow platform sedimentation represented in
the study area by the Loma de los Morteritos and El Plata
Formations (Mpodozis and Ramos, 1989, Fernández
Seveso et al. 1993, Astini, 1996, Azcuy et al. 1999,
Charrier et al. 2007). These sequences were affected by the
San Rafael compressive phase of Early Permian age
(Caminos, 1965), which probable generated the large
numbers of folds and thrusts that affect carboniferous
deposits. In addition, associated with this deformation, the
deposition of proximal alluvial-fans facies occurred,
represented in this area by the Rio Blanco Conglomerates
deposits. During the Permo-Triassic period, the important
2 Stratigraphy and Structure
The stratigraphy sequence begins with a pre-Carboniferous
sedimentary unit, with low metamorphic grade (slaty
cleavage). This unit was assembled by Caminos (1964)
into the Precambriam- to lower Paleozoic "Metamorphic
Complex". Recently Heredia et al. (2012) grouped the
rocks belonging to the Metamorphic Complex, located on
the Northern region of the Cordon del Plata, into the “Serie
Vallecitos” and assigned them a Silurian-Devonian age.
The stratigraphic column continues with the Carboniferous
sedimentary rocks of the Loma de Los Morteritos and El
extensional event generated grabens and the extrusion of
Choiyoi Group volcanic rocks (Ramos, 1988, Llambias
and Sato, 1990). At this time, the La Hoyada and Medanos
faults would be generated (Folguera et al., 2001), and also
the Los Morteritos fault. Finally, since the Middle
Miocene, the activation of the Cerro Arenal and Medanos
faults uplifted the Cordon del Plata range. The Morteritos
fault could have been reactivated during this last period, as
well as the La Hoyada fault, although there isn't enough
data to prove this hypothesis.
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This research was supported by PIP/CONICET 638 and
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Figure 1. a-b) Location of the study area in the Cordon del Plata range (33º, 05`S), Mendoza province (orange box) and c) location in a
regional Central Andes map, contours of the Wadatti-Benioff zone; Central and South Volcanic Zones and the Flat-Slab subduction zone
(Cahill and Isacks, 1992).
Figure 2. Geologic Map of the studied area. Cordón del Plata range, Mendoza Province (33°05'S) .
Figure 3. a) outcrops details of andesitic and rhyolitic clasts rocks of Chjoiyoi Groups; b) El Plata Formation, showing the structure
detail on a fault zone; c) view of Morteritos fault, showing the tectonic contact between the volcanites of Choiyoi Group thrusted over the
Loma de Los Morteritos Formation; d) detail of the Morteritos fault.