alten, m., adelmann, d., kiefer, e. und gÖrler, k ... · salar del hombre muerto salar pocitos...
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DEFORMATION PROCESSES IN THE ANDESCollaborative Research Centre 267, Project D1B/B1B
Tectonic and Neotectonic Style in the Salar de Antofalla Region ofthe Southern Puna (NW Argentina)ALTEN, M., ADELMANN, D., KIEFER, E. und GÖRLER, K.Institut für Geologie, Geophysik und Geoinformatik, Freie Universität Berlin
SFB 267
Fig. 6 Detail from an aerial pic-ture. The fold-structures andthe striae-pattern
are clearly visible.WNW of the
“peninsula”
Fig. 5 Neotectonics: Detail from a land-sat-TM-scene. Striae pattern and fold-structures WNW of the “peninsula”.
Tectonic style in the northern and central Salar deAntofallaThe area is characterized by NNE/SSW to N/S striking high-anglereverse faults and thrust faults.The crystalline basement and Palaeozoicsediments are involved. The style of deformation can be interpreted as"thick-skinned tectonics" (fig. 2), as observed in the adjacent EasternCordillera and the Subandes.The vergency in the Antofalla region is pre-dominantly WNW to W, opposite to the direction of the tectonic transportin the Subandes and backthrusting is therefore assumed. In the EasternCordillera both directions of thrusting are observed.
The style of deformation depends strongly on the type of the involvedrocks.Subhorizontal and flat thrusts in the Neogene continental red bedsare common, whereas in the older sediments and metamorphites steepreverse faults prevail (fig. 3). Especially the Neogene limestones andgypsum beds reacted on the compressional forces with fold structures.
Large scale normal faults are missing, minor normal faults are especiallyfrequent on both rims of the southern Salar de Antofalla and areinterpreted as progressive step faults, triggered by gravitational effects.
The existence of strike slip faults has been proved at only few positions inthe field, but a pattern of WNW/ESE to NW/SE striking lineaments areinterpreted as sinistral lateral shifts (outside fig. 2). There is no fieldevidence for a pull apart origin of the Salar de Antofalla and the relatedSalina de Fraile basin. An interpretation as a "compressional basin"sensu C et al. (1993), M (1990) and L H (1986) ispreferred. The basin is on both sides delimited by reverse faults andoverthrusts and subdivided by someWNW/ESE to NW/SE striking strike-slip-faults.
The importance of pre-Andean (ocloyic) or Cretaceous structures for theorientation of the Cainozoic tectonics is not well understood.They mightbe a good explanation for the NNW/SSE to N/S-striking of the reversefaults and overthrusts, which seem to be inconsistent with the stress-fieldinduced by the convergence direction of the Nazca plate.
OBBOLD IALL IU EFU
Neotectonics in the area of the recent Salar de AntofallaClear cut-signs of neotectonics, as alluvial fans or young volcanoesaffected by faulting, are rare in this region and the seismic activity is low.But good evidence for the results of ongoing compressional forces arevisible in the local deformation of the actual surface of the Salar deAntofalla:
Along the western rim of the "peninsula" (fig. 7, 8) the surface of the salaris locally uplifted and demonstrates an imbricate NNE/SSW strikingstructure.This structure is also well visible as a pattern of striae in aerialand satelite pictures (fig, 5, 6).Perpendicular to the strike of this structureare channels arranged, which are filled with fine-grained sediments.These channels can be interpreted as tension fractures (fig.9).
An interpretation of this structure as a series of reversed faults result issupported by another small tilteted block (fig. 10) 8 m high and gentlydipping towards ESE.
In the adjacent part of the "peninsula" folded evaporates of a probableLate Tertiary age are outcropping showing an already advanced stage ofcompressional deformation
Further activitiesCollection of further indications of neotectonicsExamination of the significance of pre-Andean structures for the styleof Andean tectonicsKinematics analysis of the fault-systemDetermination of the tectonic deformation by balanced geologicalcross-sections3D visualisation of the tectonic structures
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References
C , P.R., D , P., G , D., R , E.A., S , E.,T , J. C., T B , J. J. & U , M. (1993):Sedimentary basins and crustal thickening. – Sediment. Geol., 86:77–89.
L H (1986):Geodynamic scenario and structural styles of Mesozoicand Cenozoic basins in China.– AAPG Bull., (4):377–395.
M , A.D. (1990):Principles of sedimentary basin analysis.– 2.ed.,XI +667 p.; (Springer).
OBBOLD AVY APAIS OSELLO ADYBAKASOVHOMAS ONDIJI IYO RREIZTIETA DE
IU EFU
IALL
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Fig. 2 Geological map and cross-section in the central part of the Salar de Antofalla area.
Fig. 9 Channel with a filling offineclastic sediments, perpen-dicular to the striking of theimbricate structures.
Fig.10 Gently ESE-dipping tilted block.
Salta
Cafayate
Tucumán
66°68°27°
25°
Antofagastade la Sierra
S a l t a
C a t a m a r c aT u c u m á n
Chi
le
Salar delHombre Muerto
SalarPocitos
Salar de Arizaro
Salinadel Fraile
Salar deAntofalla
SalarRio Grande
Geological map (fig. 2)
Fig. 1 Investigated area
Thrust fault
Thrust fault, supposed
Fault
Age (Ma)
Modern salt flats
Basaltic andesites (Pliocene)
Mid-Miocene to Pliocenesediments (Juncalito unit)
Late Eocene - Oligocenesediments (Quinuas unit)
Early Palaeozoicsediments and volcanics
Crystalline basement
Permian sediments
Early Miocene sediments(Potrero Grande unit)
Syncline
Detail of landsat-TM-scene
Position of the peninsulain cross-section
Alluvium
Vega LasQuiñoas
VegaLa Botijuela
Vega Juncalito
SalarUncal Grande
VegaOrohuasi
Sie
rra
deC
ala
last
e
Sala
r de
Anto
falla
0 2 4 6 8 10 km
389.0± 8.0
9.0 ±0.3
3.2 ±0.1
12.9 ±0.8
28.2 ±.2.4
4.6 ±0.5
9.1 ±0.3
7.3 ±1.4
7.0 ±0.3
19.0 ±0.6
620 000
714
000
07
120
000
Cross-section
5 000
4 000
3 000
2 000
1 000
0 mabovesea-level
??
Salar deAntofalla
SierraCalalaste
WNW ESE
Fig. 3 WNW-verging thrust faults at the easternrim of the salar.They are localized at the base ofa Neogene halite-series.
Fig. 4 Tertiary fan sediments in offlap-onlap-disposition, indicating syntectonic sedimenta-tion. They are in contact with upthrusted earlyPalaezoic meta-sediments.
Fig. 7 Eastern rim of the salar: In the foregrounda fold-structure; in WNW-direction follows theimbricate structure.
Fig. 8 The series of reverse faults at the surfaceof the recent salar.
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