the orogenic front of the mendoza precordillera...

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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


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


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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)

QQ

TT

QQ

TT

T

QuaternaryQuaternary growthgrowth sratasrata


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GrowthGrowth stratastrata

MioceneMiocene playaplaya lakelakeMioceneMiocene playaplaya--lakelakedepositsdeposits


QQ

TT

QQ

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


Schmidt et al. (2011)Schmidt et al. (2011)

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SalomonSalomon et al. (2014)et al. (2014)


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.-

the orogenic front of the mendoza precordillera...

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