Aguilera, N. G.

Alonso Alonso, Juan Luis

Bulnes Cudeiro, María Teresa

Heredia, N.

Poblet Esplugas, Josep

Rodríguez Fernández, Luis Roberto

Seggiaro, R. E.

Repositorio Institucional de la Universidad de Oviedo

The Andean Cordillera resulted from convergence
between the Nazca subducted plate and the South
American plate, and displays important variations of
structural style along-strike. An area located between
parallels 23° S and 24° S in the NW corner of
Argentina (Jujuy province) was investigated to under-
stand the transition between four different geological
provinces; from west to east they are: the thick-
skinned Eastern Cordillera, the transition between
thin-skinned Subandean Ranges (to the north) and
the thick-skinned Santa Barbara Ranges (to the south),
and the oblique rift known as Lomas de Olmedo
Trough (Fig. 1). Although six published sections close
to the study area are available (Mingramm et al., 1979;
Cahill et al., 1992; Mon and Salfity, 1995;
Drozdzewski and Mon, 1999; Rodríguez-Fernández et
al., 1999; Kley et al., 2005), some aspects still need to
be deciphered. This work aims to characterize the
main geometric and kinematic features of the struc-
tures that resulted from the Andean contraction and
previous tectonic events in this portion of the Andean
orogen, through a geological map and a transect con-
structed using both geological interpretation of satel-
lite images and field mapping.
Paleozoic to present-day kinematic evolution of the
frontal part of the Andes between parallels 23º and
24º S (Jujuy province, Argentina)
Abstract: A geological map and a transect across the thick-skinned Eastern Cordillera and the transi-
tion between the thin-skinned Subandean Ranges and the thick-skinned Santa Barbara System (all of
them NNE-SSW striking) interfered by the NE-SW trending rift called Lomas the Olmedo Trough,
at a latitude comprised between 23º S and 24° S, were constructed. The available data allowed us to
illustrate the geometry and the kinematic evolution of the structures formed during three main tecton-
ic events recorded in this region: a Cenozoic contractional event (Andean orogeny), an extensional
Cretaceous event and a Paleozoic event (?).
Keywords: contraction, extension, Andes, Eastern Cordillera, Subandean Ranges, Santa Barbara
System, Lomas de Olmedo Trough.
1Universidad Nacional de Salta, Buenos Aires 177, 4400 Salta, Argentina.
2Servicio Geológico y Minero Argentino, Avda. de Bolivia 4750, 4400 Salta, Argentina.
3Departamento de Geología, Universidad de Oviedo, C/Jesús Arias de Velasco s/n, 33005 Oviedo, Spain.
4Instituto Geológico y Minero de España, C/Ríos Rosas 23, 28003 Madrid, Spain.
5Instituto Geológico y Minero de España, C/Matemático Pedrayes 25, 33005 Oviedo, Spain.
*e-mail: raul@unsa.edu.ar, ruliseggiaro@yahoo.com.ar
R. E. SEGGIARO1, 2*, M. BULNES3, J. POBLET3, N. G. AGUILERA1, L. R. RODRÍGUEZ-FERNÁNDEZ4,
N. HEREDIA5 AND J. L. ALONSO3
Trabajos de Geología, Universidad de Oviedo, 30 : 214-220 (2010)
KINEMATIC EVOLUTION OF THE FRONTAL PART OF THE ANDES
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R. E. SEGGIARO, M. BULNES, J. POBLET, N. G. AGUILERA, L. R. RODRÍGUEZ-FERNÁNDEZ, N. HEREDIA AND J. L. ALONSO
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216
Cross-section construction
The outcrop conditions, accessibility and geological
features (Fig. 2) led us to construct three geological
sections subsequently merged into a single transect
employing the along-strike prolongation of signifi-
cant geological structures (Fig. 3). The transect relies
on surface data, except for its east end in which an
unpublished subsurface interpretation (YPF oil com-
pany) was used. Although some portions of the geo-
logical transect were constructed employing the dip
domains method and projecting faults to depth using
the available dips, the structures were modified by
hand according to the field observations and honor-
ing dip data.
Structural features
Subandean Ranges-Santa Barbara System-Lomas de
Olmedo Trough
The main structures in this portion of the
Subandean Ranges-Santa Barbara System are folds
with vertical axial surfaces (in the western part and
in the eastern boundary of the transect), and E-ver-
gent folds (in the central part). In the eastern part
there are also two major reverse faults dipping to the
west and in the western part an east dipping normal
fault. The main faults emanate from an E-directed
sole thrust, located at 20-25 km depth (deduced
from seismic data), that dips gently to the west.
From west to east the sole thrust ramps up from
Precambrian to Tertiary rocks.
The almost symmetrical anticline observed at surface
(Caimancito anticline) in the east end of the geologi-
cal transect (Fig. 3) shows a hinterland dipping
duplex at depth. A flat-bottomed syncline separates
the Caimancito anticline from the asymmetrical
Callilegua anticline. The crest and steeply E-dipping
east limb of this anticline are cut off by two reverse,
E-directed faults that dip moderately to the west. The
asymmetrical Valle Grande syncline crops out west of
the Callilegua anticline. The Valle Grande syncline
exhibits reverse faults sub-parallel to bedding in both
limbs; in the eastern limb a detachment at the base of
the Cretaceous-Eocene succession eventually ramps
up, and three imbricate thrusts merge into a detach-
ment within the upper Cambrian-Carboniferous
sequence in the western limb. These structures are
consistent with the occurrence of flexural slip. To the
west of the Valle Grande syncline, an antiformal
structure occurs, which includes a few smaller-scale,
gentle anticlines and synclines in its “flat” crest. An
almost symmetrical structure called Cianzo syncline
crops out west of the antiformal structure. The west
limb of this syncline is cut off by a normal fault
steeply dipping to the east and a reverse fault steeply
dipping to the west. The reverse fault is an E-directed
structure that ramps up from Precambrian to Tertiary
rocks, cuts off the normal fault, merges at depth with
a reverse fault whose tip is located within Cambrian-
Carboniferous rocks beneath the Cianzo syncline
hinge and is called the Main Andean Thrust (bound-
ary between the Subandean Ranges-Santa Barbara
System to the east and the Eastern Cordillera to the
west). The Cianzo syncline, together with the anti-
cline located to the west in the Eastern Cordillera, are
interpreted as fault-propagation folds related to the
Main Andean Thrust.
Eastern Cordillera
Apart from the anticline related to the Main Andean
Thrust located to the east of this province, the main
structure is interpreted as a pop-up structure formed
by imbricate thrusts directed to the east (eastern part
of the Sierra de Cajas and Quebrada de Humauaca)
and some backthrusts (central and western part of the
Sierra de Cajas) that may merge at depth.
From the Quebrada de Humahuaca to the west, the
dip of the E-directed thrusts increases progressively
westwards from shallow to steep dips, and rocks with-
in the thrust sheets are tilted but not strongly folded.
In the west side of the pop-up, the W-directed back-
thrusts dip moderately to steeply to the east and rocks
within these backthrusts are gently folded.
In the Aguilar Mine zone, a pop-up structure crops
out bounded by two moderately to steeply reverse
faults that dip and move in opposite senses, to the east
and to the west. The fault located in the east part of
the Sierra de Aguilar corresponds to the boundary
between the Eastern Cordillera to the east and the
Puna to the west.
Age of the structures
Structures developed from Paleozoic to almost present
day occur in the surveyed area. Three main tectonic
events are identified: a) a Cenozoic contractional
event that corresponds to the Andean orogeny and is
recorded by reverse faults and folds, b) an extensional
Cretaceous event involving normal faults and folds,
and c) a Paleozoic event that includes some faults.
Evidences to support the tectonic scheme presented
are discussed below.
KINEMATIC EVOLUTION OF THE FRONTAL PART OF THE ANDES 217
R. E. SEGGIARO, M. BULNES, J. POBLET, N. G. AGUILERA, L. R. RODRÍGUEZ-FERNÁNDEZ, N. HEREDIA AND J. L. ALONSO
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218
Andean contractional event
Many reverse faults and related folds involve
Cenozoic rocks pointing out that their development
occurred during the Andean orogeny (Fig. 3). Around
the Quebrada de Humahuaca (Eastern Cordillera),
Miocene-Pleistocene rocks, slightly folded, onlap
unconformably over folded Cretaceous-Eocene
deposits suggesting that Andean deformation initiat-
ed some time during the interval Eocene-Miocene.
Shallow W-dipping thrusts, also located in the
Quebrada de Humahuaca, place Mesozoic and
Tertiary rocks over hardly consolidated Quaternary
rocks (Drozdzewski and Mon, 1999; Rodríguez-
Fernández et al., 1999); this evidence, together with
earthquakes recorded around the surveyed area
(Cahill et al., 1992), indicate that tectonic activity is
still taking place.
Cretaceous extensional event
A fault that crops out at surface at the eastern portion
of the transect and offsets the east limb of the
Callilegua anticline (Subandean Ranges-Santa
Barbara System), exhibits a thick sequence of
Cretaceous deposits in the hangingwall and a much
thinner Cretaceous sequence in the footwall. This
geometry indicates that this fault was an active nor-
mal fault during Cretaceous times and that the
Cretaceous rocks consisted of syn-rift deposits. The
Cretaceous deposits in the hangingwall of this fault
thin progressively away from the fault until they dis-
appear westwards. The features of the fault and the
sedimentary record suggest a tilted fault block within
a half-graben related to a listric normal fault. The
crest of the rollover anticline, where the maximum
uplift occurred, would approximately correspond to
the crest of the present anticline in between the Valle
Grande and Cianzo synclines, where the Cretaceous-
Paleocene rocks lay on top of Paleozoic rocks and no
Cretaceous deposits occur. In addition, this fault cuts
and offsets the Miocene-Pleistocene sequence point-
ing out that it was reactivated during the Andean
orogeny. Summarizing, this fault is a Cretaceous
listric normal fault reactivated as a reverse fault during
Andean times. 
The normal, E-dipping fault in the west limb and
beneath the Cianzo syncline cuts and offsets the
whole Precambrian-Tertiary sequence. The
Cretaceous-Cenozoic rocks overly younger Paleozoic
rocks to the west block of the fault than to the east
one. The absence of part of the Ordovician, Silurian,
Devonian and Carboniferous-Permian deposits in the
footwall can be explained assuming no deposition
and/or an intense pre-Cretaceous denudation in an
uplifted fault block. The thickness of the Cretaceous
deposits is greater in the hangingwall than in the foot-
wall pointing out that this fault was an active normal
fault during Cretaceous times and that the Cretaceous
rocks consisted of syn-rift deposits. Since this fault
cuts and offsets Tertiary deposits, the simplest
hypothesis is that it was an active normal fault during
Cretaceous which was reactivated as a reverse fault
during the Andean contraction.
Paleozoic event
Within the imbricate thrust system that crops out
between the Quebrada de Humahuaca and the Sierra
de Cajas (Eastern Cordillera), small-scale faults, that
dip to the east and offset Ordovician and older rocks,
are sealed by Cretaceous deposits. This suggests that
these faults were active some time from Ordovician to
before the deposition of Cretaceous rocks.
Conclusions
The structural style of this portion of the Andean
Cordillera does not exhibit the typical features of
thick- or thin-skinned belts because multi-stage fault
reactivation during different tectonic events and set-
tings, separated by a large number of million years,
play an essential role in the configuration of the pres-
ent-day structural building. These events consisted of
contraction during Cenozoic that gave rise to the
present-day Andean Cordillera, extension during
Cretaceous responsible for the Lomas de Olmedo
Trough and Paleozoic tectonics.
Acknowledgements
We acknowledge financial support by projects CGL2005-
02233/BTE, CGL2008-03786/BTE, CGL2006-12415-C03-
02/BTE and CSD2006-0041 (Topo-Iberia) under Consolider-
Ingenio 2010 Program funded by the Spanish Ministry for
Education and Science, CGL2008-00463-E/BTE funded by the
Spanish Ministry for Science and Innovation, and CNG08-15
funded by the Asturian Ministry for Science and Education. We
would like to thank the editors of this special issue.
KINEMATIC EVOLUTION OF THE FRONTAL PART OF THE ANDES 219
R. E. SEGGIARO, M. BULNES, J. POBLET, N. G. AGUILERA, L. R. RODRÍGUEZ-FERNÁNDEZ, N. HEREDIA AND J. L. ALONSO
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220


Paleozoic to present-day kinematic evolution of the frontal part of the Andes between parallels 23º and 24º S (Jujuy province, Argentina)

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Paleozoic to present-day kinematic evolution of the frontal part of the Andes between parallels 23º and 24º S (Jujuy province, Argentina)

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