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Tectonic Evolution of the Andes of Ecuador, Peru, Bolivia and Northern

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Tectonic Evolution of the Andes of Ecuador, Peru, Bolivia and Northern CORDANI, LJ.G./ MILANI, E.J. I THOMAZ flLHO. A.ICAMPOS. D.A. TECTON IeEVOLUTION OF SOUTH AMERICA. P. 481·559 j RIO DE JANEIRO, 2000 TECTONIC EVOLUTION OF THE ANDES OF ECUADOR, PERU, BOLIVIA E. Jaillard, G. Herail, T. Monfret, E. Dfaz-Martfnez, P. Baby, A, Lavenu, and J.F. Dumont This chapterwasprepared underthe co-ordination chainisvery narrow. Thehighest average altitudeisreached ofE.[aillard. Together withG.Herail andT. Monfret,hewrote between 15°5 and 23°S, where the Altiplano ofBolivia and the Introduction. Enrique Dfaz-Martinez prepared the southernPerureaches anearly 4000 mofaverage elevation, section on the Pre-Andean evolution ofthe Central Andes. andcorresponds tothewidest partofthechain. TheAndean Again Iaillard, onthe Pre-orogenic evolution ofthe North­ Chain is usually highly asymmetric, witha steep western Central Andes. E.[aillard, P. Baby, G. Herail.A, Lavenu, and slope. and a large and complex eastern side. In Peru,the J.E Dumont wrote the texton theorogenic evolution of the distance between the trench and the hydrographic divide North-Central Andes, And, finally, [aillard dosed the variesfrom 240 to }OO km.whereas. the distancebetween manuscript with theconclusions. thehydrographic divide and the200m contourlineranges between 280 km(5°N) and about1000 kIn (Lima Transect, 8·S - 12°5). In northern Chile and Argentina (23·5),these distances become 300 krn and 500 km, respectively. Tn INTRODUCTION: southern Peru,as littleas 240 km separates the Coropuna THE PRESENT-DAY NORTH-CENTRAL Volcano (6425 m) from the Chile-Peru Trench (- 6865 m). This, together with the western location of the Andes ANDES (jON - 23°5) _ relative to theSouth American Con tinent,explains whythe riversflowing toward the Pacific Ocean do not exceed 300 TheAndean Chain isthemajormorphological feature of kmlong, whereas thoseflowing to theAtlantic Ocean reach theSouth American Continent. ThisB(){)() kmlongmountain 4000 kmlong.We haveto notetwo exceptions to this rule. beltextends alongthewestern borderoftheSouth American In Ecuador thisasymmetry disappears, duetopeculiar Plate, and can be divided into three segments of distinct tectonic history and deformational processes. Thetrench­ orientations, separated bytwomajorbends. TheNNE-SSW hydrographic divide distance roughly equalsthe distance trendingColombian-Ecuadorian segment (12°N - 5°S) is between the waterdivide and the 200 m contourline,and 2000 km long and includes part of northernmost Peru and ranges between 280and 350km. Between U·S and 24°$ easternmost Venezuela. It is separated from the Peruvian (southern Peru-Bolivia). there are two hydrographic segment by the Huancabamba Bend (Megard, 1987). Its divides, delimiting a wide, flat, endorheic basin known as northern end(eastern Venezuela) exhibits achange to anE­ the Altiplano, which coincides with the zone of highest Worientation. dueto itsconnection to theSouth Caribbean average elevation and largest widthofthe chain(fig. 1). dextral transform system. ThePeruvian segment (S·S ~ 18°5) The highest summits are usually recent or active is 2000 km long and its orientation is closeto NW-SE. It volcanoes situated on the deformed chain or on includes northern Bolivia, andisseparated from theChilean metamorphic or graniticslices uplifted by reverse faults. segments by the Arica Bend. The Chilean segment (IBCS ­ Among the former are the Cotopaxi (5897 m) and 56°5) is 4000 km long and trends N-S. Its southern tip Chimborazo volcanoes (6310 m) in Ecuador, the Coropuna exhibitsa change to an E-W direction along the Scotia (6425 m) andAmpatovolcanoes (6310 m) in Peru,andthe sinistral transform system. Sajama Volcano (6520 m) in Bolivia, nearthe Bolivia-Chile Thewidthofthe Andean Chain variesfrom250km in border. Among the latter, we may notethe mainly granitic northern Peru (5·5) or southernmost Chile (52°5 - 55°5). Cordillera Blanca in Peru,which culminates at 6768 m to as muchas 750 km in Bolivia (18°S). (Nevada Huascaran), and the metamorphic Eastern Thearea described in this chapter includes Ecuador. Cordillera ofsouthernPeru and northernBolivia (Nevado Peru, Bolivia and,therefore, northernmost Chile (Nof23°S). Illimani, 6682 m; Nevado Illampu, 6485 m). However. It includes parts ofthethreesegments described above, the deformed and uplifted sediments may also form high orientation of which played a significant role in the pre­ summits in Peru, suchas theNevado Yerupaja (6632 m) in orogenic period. the CordiJIera Huayhuash andthe Nevado Ausangate (63&4 The lowest pass of the studied area is situated in m) in southern Peru or the Cordillera de Apolobamba northernPeru(Abra dePorculla, 2300 m),a zonewhere the (Nevado Cololo, 5975 m) in Bolivia. 481 "''''''''' '-"'- ""', ~ .~ .. ..... ,! ! ,• 0 - ­ .(21 .-..._- ,........... ! ~ Eo>lom e-. , E3 - ~ r.:-::.J ~ ­ I ',:,{:JB s- ; • • • • "'u.....,·_ _ ~.._ ...__ -_~ .,---...-._..-....._-.... ­ "",.,, "" .. _---,..,., - ~--....-..-,. ..., u , ..., -,-_ .. ... "..._--­.. ' ,..,.. ~ ""'-' ! • = 1 -- "'8 -__- G _ _ - .-k:! a.-•... 0 __ , I, -•­ .0---­ -- -- 1 = 11= 1- , -- I .J,;- ""'-*F5i:0 , ~! G1'2)~- "'--[;::.­ I -- t; ! •• • r• • j .J.. - ! - - - -- I ::... • -- • I ! --._----;:' I::...•• MO'l'lHKtrudural unib and ..... Crll$t al ,t ru d u r~ -___'--",,...i"lJ"'-_"""".... __.. _- -­..__ .. ...~. _ .--.,,_ ,"'" "',,'''',,_,,''' ,.,,_ ..... "" , ,~- .......... 1""' ,. -.__.u ' , .. '.. ... -.. - < , ... ...... ",.. , ,.. ,..... _..-- _........6<l _ .~ -... "--....,--_ _.--. _ - ____,_ ~- ... .... ... .-- ,,___.-.~I.-.0<",- -, __, -. .... .. h __ .. "'__,,_pO. -" -_-...."-"'" .."'-..,""""," -w, ~"'-, .-. _... .. _, ........d.,.· "_....,"".. _ ., -.. __ -.--.. ....,.......--, ....,...._' .- " --_ ...-.~.,-_ ,__ ---.-_---_- ...... _..__.. _..-_­- ..... .. .. .......---.- ... "" ... __..., -.. -.. .. ___ ....... -,_• _ ..._ _,_ l. __ --_ __ ",,~ " ............ H _ .... "' _ 'Cool 1Joo<.,...... ..................,--. .-. --.,.. ,"'--_.- .. ,." -.... ... -_..- --*--,."" ..., - ~--_ ... ... ,_ 0- -._'*-""_.... _... ... .... '-"_._ ..--..-, _ ""'_... - ..._,- "'_,, -- -_ ••'" ..-,• •"•• _ <-, , """ ......__,." .._ w.."'... _ - ,,..,_...., _ ... - ,-,·.......- -1- ,.,. ..... z o ~ Manazo FTB) involving mainly Mesozoic sedimentary rocks. => Plate tectonic setting Cl Insouthern Peru, the EasternCordillera is thrust over the Altiplano bymeans ofSW-verging reverse faults. Longitudinal valleys, the trend ofwhich iscontrolled bythe mainAndean As first proposed byWegener early in this century, the structures, separate N of 13°5 the Eastern and Western Andean Orogeny isrelated to the convergence between the Cordilleras. 5of 13°S, theEastern andWestern Cordilleras are Pacific Ocean Plate and the SouthAmerican Continent, the more distantand areseparated bylarge valleys (13° - 14"S) latter being pushedwestwards bytheopeningoftheSouth evolving southeastwards intoanendorheic basin (Altiplano). Atlantic Ocean. We know nowadays that not only South which considerably enlarges inBolivia. America, but also the Pacific oceanic Plate moves in an Thedeformed subandean zone is muchlargerthan in absolute reference frame. SouthAmerica migratesroughly Ecuador (120to 250km) and enlarges southeastwards (Fig. westwards at a rate of 3 cm/y. Between 2"5 and 23"5, the 2). Deformation involve the Mesozoic and Tertiary Nazca Oceanic Plate migrates to the E to ENE, and the sedimentary rocks, together with their Paleozoic, convergence rate between the Nazca and South American sedimentary or metamorphic basement. The eastward plates is around8 cmly, although it seems to be lower at 0° migration ofdeformation influenced thecourse oftherivers, (Fig. 3).Thewhole Andeanmarginis,therefore, submitted which trend mainly parallel to theAndeanstructures.The to a roughly E-W convergence between the subducting eastern lowlands are made of either wide alluvial plains Nazca Plateand the SouthAmerican continental margin. receiving Quaternary sediments (northernPeru),orslightly This phenomenon is long regarded as the majorcauseof uplifted, fault-controlled zones underlainby the Brazilian the Andean Orogeny (Rutland, 1971; James, 1971). Shield (southernPeru,Bohvia). TheNEtrendingGrijalva FractureLone (GFI)located In northern Peru (7"S), where the chain is relatively between 3°S and 50S (Fig. 3) separatesthe Nazca Oceanic narrow, crustal thickness is 40 - 45 km below the Western Plate into two portions.To the N ofthe GFZ, the currently Cordillera and decreases rapidly eastwards,whereas in subducting oceanic plateis 23to 10Maold (Miocene) and southernPeru(13°5),wherethechain ismuch wider, crustal the depth of the oceanic bottom is 2800 to 3500 m below thickness reaches 65 km below the Western and Eastern sealevel. Most ofthe Ecuadorian -Colombian trenchisless Cordilleras and drastically decreases below theSubandean than 4000 m deep. The NazcaPlate is overlain bythe E-W Zone(Fukao etal., 1989). trending Carnegie aseismic ridge, which is presently The northern part of the Chilean-Bolivian segment is subducting offshore Ecuador between 0" and 2°S. The morecomplex. To the W, the 50km wideCoastal Cordillera Carnegie Ridge is regarded as formed by the Galapagos is madeof chiefly Jurassic-Early Cretaceous magmatic arc hotspot,situated about}000km Wofthe Ecuadorian coast. rocks, cut bythe majorN-StrendingAtacama wrench fault Southofthe GFZ, the subducting oceanic plateis 50to system. The Longitudinal Valley, underlain by Middle 30 Maold (Eocene - earlyOligocene) and 4000 to 5600 m Cretaceous arcrocks separates itfrom thePrecordillera. The deep. ThePeruvian-Chilean trench
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