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The orogenic front of the Mendoza Precordillera: The orogenic front of the Mendoza Precordillera: Neotectonics in the western margin Neotectonics in the western margin
of Sierras Pampeanasof Sierras Pampeanas
Victor A. RamosVictor A. RamosInstituto de Estudios Andinos Don Pablo Instituto de Estudios Andinos Don Pablo GroeberGroeber
Universidad de Buenos Aires Universidad de Buenos Aires ‐‐ CONICETCONICET
ObjectivesObjectives::
• To identify the wedge-top developed along the orogenic front between Precordillera and Sierras Pampeanas that coincides with the most active seismogenic zone of the Pampean flat-slab segment of the Central Andes.
• The wedge-top zone is characterized by active faults and growth strata, bounded to the west by the fold and thrust belt orogenic front, and to the east by the foredeep undeformed playa-lake deposits, main depocenter of the foreland basin.
• The basement structures of Sierras Pampeanas interact with the thin-skinned tectonics of the Precordillera and can be identified by their different structural trends (northeast basement structures vs. north trending Andean th t i P dill )thrusts in Precordillera).
• To caharacterize the different structural styles along the wedge-top zone and the seismogenic structures that concentrate the main crustal earthquakes along the orogenic front.
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PrecordilleraPrecordilleraFoothillsFoothills
TheThe wedgewedge--toptop
Long Long lastinglastingdeformationdeformation duringduring 10 10 My at My at thethe lowlow shorteningshorteningraterate of 0.33 mm/a.of 0.33 mm/a.
PeriodsPeriods of of slowslow upliftupliftratesrates alternatealternate withwithbasementbasement exhumationexhumationbasementbasement exhumationexhumationand and rapidrapid upliftuplift..
ChangesChanges in subin sub--sidencesidence ratesrates triggeredtriggeredbyby tectonictectonic loadingloading ofofshiftingshifting thrustthrust frontfront..
ForelandForeland BasinBasin SystemSystem
Playa-lake deposits
MuttiMutti et al. (2009)et al. (2009)
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San JuanSan JuanPie dePie dePaloPalo
CerroCerroSalinasSalinas
MontecitosMontecitosJocolíJocolí
MendozaMendoza
Río Río Las PeñasLas Peñas
JocolíJocolíForedeepForedeep
Precordillera and Sierras Precordillera and Sierras Pampeanas Interaction:Pampeanas Interaction:
•• Basement wedges with east Basement wedges with east vergence.vergence.
•• Main eastMain east--dipping fabrics of dipping fabrics of pp gpp gPampean basement controls Pampean basement controls the surface ruptures by the surface ruptures by backthrusts. backthrusts.
CominguezCominguez andand Ramos (1991)Ramos (1991)
Basement wedges
Verges et al. 2007Verges et al. 2007
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Eastern Precordillera: Sierra de Villicum thin-skinned thrust
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Main structures of Sierra de Pie de Palo
The region is seismically active as shown by the large Recent intraplate earthquakes
CauceteSan Juan L Ri dLa RinconadaVillicúmLas ChacrasBermejoMatagusanosZondaCerro Salinas...
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The San Juan earthquake of 1941
LA LAJA FAULTLA LAJA FAULT
arthquake of 1941
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Co.Co. SalinasSalinas
San San JuanJuan
JocolíJocolí FordeepFordeep
Río Las PeñasRío Las Peñas
P dill d M dP dill d M d
Cerro SalinasCerro Salinas
Precordillera de MendozaPrecordillera de Mendoza
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Precordillera of Precordillera of northernnorthern MendozaMendozaSTRUCTURAL SECTION OF OJO DE AGUASTRUCTURAL SECTION OF OJO DE AGUA
Cegarra (1997)Cegarra (1997)
SeismogenicSeismogenic zoneszonesassociatedassociated withwiththethe orogenic orogenic frontfront::
Wedge-top zone
•• La LajaLa Laja
•• Sierra de Zonda Sierra de Zonda
•• Cerro SalinasCerro Salinas
•• Río Las PeñasRío Las Peñas
Cerro La CalCerro La Cal•• Cerro La Cal Cerro La Cal
•• BorbollónBorbollón
•• MendozaMendoza
•• BarrancasBarrancas
NEOTECTONICSIn the
OROGENIC FRONT
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Neotectonic Neotectonic faultsfaults
CerroSalinas
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VergésVergés et al. (2007)et al. (2007)
DeepDeep seismicseismic reprocessingreprocessing
ComínguezComínguez and Ramos (1991)and Ramos (1991)
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Cerro Salinas
Southern sector
Seismic line 31017
VergésVergés et al. (2007)et al. (2007)
Cerro Salinas: Line 31017Cerro Salinas: Line 31017--0505
PrePre--growthgrowth
GrowthGrowthstratastrata
TobasTobasAngosturaAngostura
MetamorficMetamorficbasementbasement
ee g o tg o tstratastrata
CominguezCominguez and Ramos (1991)and Ramos (1991)
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Cerro Salinas: Line 31017Cerro Salinas: Line 31017--0505
VergésVergés et al. (2007)et al. (2007)
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South of Cerro SalinasMontecitos anticline Rinconada
Montecitos Montecitos AnticlineAnticline
• Long lasting structure of slow growth
• Late Pliocene growth strata
• Los Mogotes Fm.< 2.6 Ma
• Pleistocene growth strata
• Western flank 27ºNW to 68ºNW
Th P t f i
Costa and Cortés (2000)Costa and Cortés (2000)
• The Present surface isgently deformed
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Orogenic Orogenic frontfront
WedgeWedge--top zonetop zone Foredeep zoneForedeep zoneFTB zoneFTB zone
Bajada del río deLas Peñas
Kilometers
Sierra de las Peñas: Precordillera Orogenic front
Wedge-top zone: synorogenic Miocene deposits and Quaternary growth strata
123 MioceneMiocene depositsdeposits
4
1. Miocene synorogenic deposits thrust on Pleistocene terrace2. Miocene and early Pleistocene deposits thrust on middle Pleistocene deposits3. Miocene and middle Pleistocene deposits thrust on late Pleistocene deposits4. Miocene deposits out-of-sequence thrust on Holocene deposits
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WWEE
Sierra de las Peñas Sierra de las Peñas MainMain thrustthrust (3)(3)
HoloceneHolocenedepositsdeposits
WW EE
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OutOut--ofof--sequencesequence thrustthrust: 4: 4
MioceneMiocene depositsdeposits
HoloceneHolocene depositsdeposits
Sierra de las Peñas:
Precordillera Orogenic front (northern side)
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Sierra de las Peñas: Precordillera Orogenic front (northern side)
TT
TT
T
QuaternaryQuaternary growthgrowth sratasrata
Sierra de las Peñas: Precordillera Orogenic front (northern side)
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GrowthGrowth stratastrata
MioceneMiocene playaplaya lakelakeMioceneMiocene playaplaya--lakelakedepositsdeposits
Sierra de las Peñas: Precordillera Orogenic front (northern side)
TT
TT
T
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Sierra de las Peñas Sierra de las Peñas FaultFault (48 km (48 km longlong))Synorogenic Synorogenic topographytopography in in thethe orogenic orogenic frontfront
ThickThick PleistocenePleistocene depositsdeposits foldedfolded and and thrustthrust byby thethe olderolder synorogenic synorogenic MioceneMiocene depositsdeposits. . TheThe upperupper levelslevels are monoclinal are monoclinal foldedfolded..Vertical slip Vertical slip ratesrates: 0.9 : 0.9 toto 0.6 mm/a in 0.6 mm/a in thethe lastlast 13 13 kakaHorizontal Horizontal shorteningshortening raterate: : 2.0+0.4 mm/a 2.0+0.4 mm/a Schmidt at al. (2011)Schmidt at al. (2011)
Costa et al. (2015)Costa et al. (2015)
Cerro SalinasCerro Salinas
Precordillera Orogenic Precordillera Orogenic frontfront
WedgeWedge--top zonetop zone
Cerro Salinas: Cerro Salinas:
Río Las PeñasRío Las Peñas
Cerro La CalCerro La Cal
•• BasementBasement wedgewedge similar similar totoSierras Sierras PampenasPampenas structuresstructureswithwith westwest--vergencevergence controlledcontrolledbyby earlyearly PaleozoicPaleozoic fabricsfabrics..
Río Las Peñas:Río Las Peñas:•• InteractionInteraction of of thinthin--skinnedskinnedstructuresstructures withwith basementbasement wedgewedgeofof oppositeopposite vergencevergenceCerro La CalCerro La Cal
BarrancasBarrancas
of of oppositeopposite vergence.vergence.
Cerro La Cal Cerro La Cal toto Barrancas:Barrancas:•• East vergence East vergence basementbasement faultsfaultsassociatedassociated withwith inversioninversionof of TriassicTriassic riftsrifts..
BorbollónBorbollón
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MendozaMendoza
Co. La Cal
BarrancasBarrancas
OlgiatiOlgiati (2002)(2002)
Cerro La Cal Cerro La Cal FaultFault (31 km (31 km longlong))
• Vertical slip rate: 0.6 to 0.9 mm/a in the last 12 ka.
• It was active during the 1861 earthquake.
Schmidt at al., 2011Schmidt at al., 2011
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Cerro La Cal Active Cerro La Cal Active FaultFault (1861 (1861 earthquakeearthquake))
Cerro Cerro La CalLa Cal
Active Active faultfault
Active Active faultfault
Cerro La Cal Active Cerro La Cal Active FaultFault (1861 (1861 earthquakeearthquake))
Schmidt et al. (2011)Schmidt et al. (2011)
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Cerro La Cal Active Cerro La Cal Active FaultFault (1861 (1861 earthquakeearthquake))
SalomonSalomon et al. (2014)et al. (2014)
Cerro La Cal Active Cerro La Cal Active FaultFault (1861 (1861 earthquakeearthquake))
SalomonSalomon et al. (2014)et al. (2014)
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Cerro La Cal Active Cerro La Cal Active FaultFault in Mendoza Cityin Mendoza City
Ramos (2013)Ramos (2013)
Mendoza Mendoza EarthquakeEarthquake: ~ 7: ~ 7
City of MendozaCity of Mendoza20th. of 20th. of MarchMarch, 1861, 1861
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FallaFallaLa CalLa Cal
La Cal La Cal FaultFault
•• Active Active faultfault thatthat crossescrosses thetheCity of Mendoza.City of Mendoza.
•• ItIt isis relatedrelated toto thethe 18611861
MENDOZAMENDOZA
ItIt isis relatedrelated toto thethe 1861 1861 earthquakeearthquake..
•• 2,95 m vertical 2,95 m vertical upliftuplift alongalong 31 31 km in km in thethe lastlast 10,000 10,000 yearsyears..
•• EstimatedEstimated magnitud magnitud betweenbetween6.7 6.7 toto 7.7.
SitioFundacional
MENDOZAMENDOZA•• EstimatedEstimated shorteningshortening raterate0.920.92--0.70 mm/a in 0.70 mm/a in thethe lastlast10,000 10,000 yearsyears..
BastíasBastías et al. (1993)et al. (1993)
ConcludingConcluding remarksremarks::
• The orogenic front has different structural styles from north to south:
• At San Juan the Eastern Precordillera is a basement structure with a n west- vergence thrust: La Laja active La Laja active faultfault backthrustbackthrust..
• At Sierra de Las Peñas is dominated by tectonic inversion of a Triassicrift system: Las Peñas active Las Peñas active faultfault..
• At the city of Mendoza la Cal Fault crosses the entire city intersectingthe growth strata of Cerro la Gloria.
• The rate of shortening of the different described structures is very slow, at least in the wedge-top zone which allows the preservation of the growthstrata.
• Active faults and sedimentation characterize all the wedge-top zone, contrasting with the playa-lake facies of the undeformed foredeep zone.
and finally as Bodenbender more than 100 years ago said…
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“No es necesario asustarse por lo terremotos, ni ponerse a discutir sobre la conveniencia de trasladar la ciudad a otro sitio.
Trasladando la ciudad al poniente se la retira de una grieta para acercarla a otra. Para ampararse de estos fenómenos de la
Final Final remarksremarks
pnaturaleza no hay otro medio que el de edificar convenientemente las habitaciones”(*)
Guillermo Bodenbender, 1894.-
(It is not necessary to be frightened by the earthquakes, nor to (It is not necessary to be frightened by the earthquakes, nor to argue about the convenience of moving the city to another placeargue about the convenience of moving the city to another placeargue about the convenience of moving the city to another place.argue about the convenience of moving the city to another place.
Moving the city to the west, it is removed from a fissure to bring it Moving the city to the west, it is removed from a fissure to bring it closer to another. To guard against these phenomena of nature there is closer to another. To guard against these phenomena of nature there is no other way than to properly build the rooms)no other way than to properly build the rooms)
(*) Boletín de la Academia Nacional de Ciencias, XIV(2): 327.-
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