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Andes neotectonica 2010

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  1. 1. Peru: Basic Geology and some neotectonics ANDES , Nazca Subduction Below South America Typical oceanic vs continental subduction zone but why typical as soon as we dont know so much? mercredi 14 juillet 2010
  2. 2. Central ANDES = 5 countries .....Bolivia Peru Chile Argentina and Brazil.... Politics and Geology... field access....... Bolivia first, then closed, Chile and Argentina.....then no pieces of land free of instruments...thus Peru now... Peru strongest points: overview, highly variable morphologies Widest, highest :High plateau ( 4000m ) , high chain ( 6500 m), canyons (2000m).... .... Subduction seismicity ( 1960, biggest..) Arid desertic Atacama vs tropical Amazonia Thrse BOUYSSE-CASSAGNE ( Volcanoes, earthquakes ... myths and culture , Healers of the Bolivian Andes.... The good devil, mining cults , lake Titicaca ; assimilating christianism ?...) Geology , politics...culture of the Central Andes mercredi 14 juillet 2010
  3. 3. Data acquisition is going on, but Scientists are mainly discussing processes... Questions are : - how did the Andes grow ? And where first? - what is the main contribution to uplift ? Magmatic, tectonic, cimatic, distributed or focused shortening, mantle flow, lower lithospheric flow, delamination, tectonic erosion ? - what happened on the western flank ? If nothing happened ...why? - Extensional collapse ? Delamination ...See Barnes and Ehlers , 2009 The South American margin, despite a geologic history of more than 200 million years of continuous subduction, did not begin to grow high topography until ~50 million years ago. Andean geology mercredi 14 juillet 2010
  4. 4. 3900 KONOE? a.: MourrAiN BUILDINGIN THE CENTRALANDES HOW TO FORM A HIGH PLATEAU? ..,,::..-'!::...!:.-::::.?..::..',;-?':.. :.:".!..%..":i':i!'.?:."i:;!'i:"",?:?.:.:L'?..:.:";=?.'.'?':i:.:'.?! MAGMA ADDITION FOLDING REPEATED THRUSTS THERMAL EFFECTS CRUSTAL DOUBLING Fig. 9. Processeswhichcanform an extendedplateauof highaltitude (comparewith a similarfigurein Allmendinger[1986]. Thethreeon the right involve somesortof crustalshortening,while the two on the left rely onthesupplyof volcanicmaterialor heatfrombelow. Altiplano-Puna was formed there. The absenceof a back arc factorin the WesternCordillera,but doesno east,where the crustappearsto consistof P zoic sedimentaryand metamorphicrocks. T wasstudiedby FroidevauxandIsacks[1984 the CentralAndesis essentiallyin equilibriu is thatthetopographyshouldbe compensate or by the lithosphere,becauseof the sizeof t However,we think thisratherunlikelybecau asymmetry;if the easternpart is supportedb lithosphereunderneath,similarlyhot or even shouldexistunderthe WesternCordillera,le compensationof thesurfaceloadthem. We concludethata singlemechanismcann port the topographicfeaturesof the CentralA proposethattwo differentmechanismsoperat the western and easternhalves: magma ad shortening(Figure 10). A combinationof the agent which contributedto make the Centra mountain chain associatedwith a subdu existenceof high plateausof wide extentand arc basins. In the westernhalf of the Central Andes, a s of magmahasbeenaddedto the crustfrom the crustandraisingthe plateauwithoutseve geologic formations. The reason for this (10-30) and fast (about 10 cm/yr) subduc Building a Plateau Kono et al., 1989 mercredi 14 juillet 2010
  5. 5. 3D feature EW cross sections NS variations History of the subducting plate but also of the upper plate ....... I will focus on Central Andes, Northern part, in Peru ... Andean geology mercredi 14 juillet 2010
  6. 6. Central Andes Northern Andes Oceanic accreted terranes Flat Slab Short, lower Andes North South Segmented Andes mercredi 14 juillet 2010
  7. 7. !"#$%&'$"#("')&"*$+#(&!#,%*#(&!#-&*./ (0'120$"#(!"#,&(02&')"$03'#4#$+')&5)+#6&+(0'120$+#(!"#7+*2"$03'#$"2"'1#4#,%,#&8%09"!&')&,#+77:,;+*& 2

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