T.I.E.S. Neogene Basin Evolution in the Las Peñas basin, Salagasta Region, Mendoza, Argentina Laura Giambiagi J. Brian Mahoney Olivia Iverson Kris Benusa Dave Kimbrough Conicet University of Wisconsin University of Wisconsin San Diego State University Mendoza, Argentina University of Wisconsin Eau Claire, WI Eau Claire, WI Eau Claire, WI San Diego, CA Argentina ABSTRACT A succession of clastic strata in the Salagasta region, northwest of Mendoza, Argentina, was deposited in DETRITAL ZIRCON GEOCHRONOLOGY the Miocene Las Peñas basin. These strata represent sediments from the Andean foreland basin unroofed by 03JBM11- Rio de los Pozos Fm. migration of the fold and thrust belt. The coarsening upward sequence and sedimentary structures indicate a 16 10 fluvial depositional environment and evolution from a distal to proximal retroarc foreland basin. (Miocene) 30 n=84 9 (Miocene) 14 (Miocene) olcanics Three detrital zircon samples were examined from the Salagasta section to determine the timing of uplift Arc Magmatism V Rio de los Pozos Fm. Arc Magmatism 8 Paramillos in the Andes at this latitude. The samples display detrital zircon populations derived from syndepositional 25 riassic) 12 R R (Permo-T 7 R e e e l l volcanism, Miocene Farallones Group, Permian Choiyoi Group, and early Paleozoic Villavicencio Fm. The Choiyoi l a a a

t 10 t t i i 20 riassic) 6 i v La Pilona Fm. v v r r r e e lowest sample contains syndepositional zircon indicating a maximum depositional age of 8.75 Ma and a major e e e (Permo-T e p b p p b b r r Choiyoi r m o m 8 m 5 o population derived from the Permian Choiyoi Group, suggesting uplift of the Cordillera Frontal at this time. o u b u b 15 ontal u b a N a a N N b b Mariño Fm. b i i The middle sample contains peaks representing syndepositional volcanism (ca 8 Ma) as well as an introduction 4 i l l Cordillera Fr l i i

6 i t t olcanics t

y V y Arc y of early Palezoic Villavencencio Fm. suggesting uplift of the Precordillera between 8.75-8 Ma. The upper 10 3 sample is dominated by a strong Miocene peak reflecting sediments from the Farallones Fm, but lacks 4 (Carboniferous-Permian) Famatinian 2 5 syndepositional volcanic sediments, suggesting derivation from the Cordillera Principal during a period of Grenville 2 waning volcanism. 1 0 0 0 A B 0 400 800 1200 1600 2000 2400 2800 3200 3600 0 100 200 300 400 500 0 20 40 60 80 100 03JMB11 03JMB11 03JMB11 PURPOSE A.) Traverse through stratigraphy of the Las Peñas basin in the Salagasta region. Yellow markers indicate sample locations. [Google This sample is from a sandy interbed within the conglomeratic Rio de los Pozos Formation. Note persistent Grenville and Famatinian peaks. Detrital zircon provenance data from synorogenic Neogene foreland basins of the southern Central Andes (28- Earth]. B.) Photo of the examined section displaying the contacts between the Neogene synorogenic sedimentary units. Major Choiyoi peak has expanded to include late Carboniferous to Permian subpopulation, which definitively attests to major uplift of the 35°S) can be utilized to constrain the timing and pattern of orogenic exhumation of the Andean system. The Cordillera Frontal. TransAndean Miocene volcanic rocks are a volumetrically significant source. Note lack of syndepositional zircon influx. Nazca plate varies in subduction angle along the continental margin and therefore strongly influences the evolution of adjacent foreland basins. The Las Peñas basin is the easternmost exposed basin associated with the flat slab segment. Basin comparisons between the flat, transitional, and normal segments will allow for a STRATIGRAPHIC SECTION 04JBM11 - Mariño Fm. (upper sample) greater understanding of the patterns involved in basin development, timing of structural deformation, and how 18 (Miocene) n=66 12 10 (Miocene) the subduction angle influences deformation. Analyzing the stratigraphy and detrital zircon geochronology of Volcanism Las Peñas Basin, Salagasta Region 16 Arc Magmatism (Miocene) the Las Peñas basin in the Salagasta region will allow for future comparisons with basins from the transitional 10 14 Arc Magmatism 8 Syndepositional R R R e e and normal subduction segments. e l l l a a a

12 t t t

8 i i i v v v r r r e e e e e e 6 p b p p b b 10 r r r m o m m o o

u (Miocene) b u b u b 6 riassic) a riassic) N a a N N b b 8 b (Permo-T Volcanics (Permo-T i i i l l l i i i 4 t t

t Choiyoi y y Choiyoi y Paramillos 6 4 Famatinian 4 enville A B Gr 2 2 2

0 0 0 0 400 800 1200 1600 2000 2400 2800 3200 3600 0 100 200 300 400 500 0 20 40 60 80 100 04JBM11 04JMB11 04JMB11

This sample is from a well-sorted fluvial sandstone of the upper Mariño Formation. Note presence of both Grenville and Famatinian populations derived from Cuyania. Robust Choiyoi Group peak suggests derivation from Cordillera Frontal. Early Miocene peak may reflect erosion of transAndean Miocene volcanic arc represented by the Paramillos Fm. Major ca 8.3 Ma peak attests to continued syndepositional volcanisim. 05JBM11 - Mariño Fm. (lower sample) 9 45 (Miocene) 50 Mendoza, riassic) n=84 (Miocene) Argentina riassic) 8 40 c Magmatism(Permo-T Volcanism Ar Choiyoi (Permo-T 40 Choiyoi 7 35 Syndepositional R R R e e e l a l 6 l a

30 a

t (Miocene) t i t i v i v r v e r 30 e e r e e e p b c Magmatism 5 p 25 b (Miocene)

Ar p b r r m o r m o m o u b olcanics u b V u b a N a N a b 20 N 4 b b i Paramillos i l i l

i 20 l i t i t y t y 15 3 y

10 2 A.) Digital elevation model of South America. Note the distinct segmentation of the Andes at the latitude 10 Grenville of Mendoza, Argentina. B.) Seismic data indicates the depth to the subducting Nazca plate and displays 5 1

0 the segmentation of the slab. 0 0 0 400 800 1200 1600 2000 2400 2800 3200 3600 0 100 200 300 400 500 0 20 40 60 80 100 05JMB11 05JBM11 05JBM11

350-220 Ma This sample is from a waterlain tuffaceous bed in the upper Mariño Formation. Small Grenville population is inferred to be derived from the Cuyania GONDWANA 490-460 Ma composite terrane. Large population of ca 250-300 Ma grains suggests derivation from Choiyoi Group of the Cordillera Frontal. Small 160-220 Ma

A La Serena R population suggests minor influx from JuraCretaceous arc of the Cordillera de la Costa. Note strong syndepositional volcanic peak (ca. 8.5 Ma). 30ºS E 30ºS L

L I

D (Upper) CHILENIA R F O Las Peñas P R C basin R O E

I N R N

T P C SYNDEPOSITIONAL VOLCANISM A

I P L R data-point error symbols are 2 A San Juan data-point error symbols are 2T C 20 L O

C R O D Maximum depositional 30 R I L D L

I E age is derived from L CUYANIA 16 L R

E A Mendoza R youngest robust data 20 A

1 C U Y O 12 cluster (n=3+) 1 Santiago B A S I N e

34ºS 34ºS e g

g 10 a a

Mariño Fm. (upper sample) t t

8 s s e e B

B mean is S a n R a f a e l 8.3 Ma 0 71ºW r a n g e 68ºW 4

04JBM1 B Mariño Fm. (lower sample) 05JBM1 Choiyoi Group outcrops 100 Km Mean = 8.3±1.0 [12%] 95% conf. Mean = 8.5±1.9 [22%] 95% conf. mean is -10 A.) Morphostructural map of the south-central Andes, highlighting the structural belts and general age 0 Wtd by data-pt errs only, 0 of 10 rej. Wtd by data-pt errs only, 0 of 11 rej. MSWD = 0.047, probability = 1.000 MSWD = 0.054, probability = 1.000 ) Upper Mariño Fm. 8.5 Ma distribution in the region (Giambaigi et al., 2008, ages from Ramos, 2006). B.) Neogene basin location map (error bars are 2T) Fm. Mariño Lower (error bars are 2R) showing the morphostructural belts and the position of depocentres in the retroarc foreland region. Contours -4 -20 illustrate the depth to the subducting slab. Note the location of the Salagasta region within the Las Peñas basin. INTERPRETATIONS Sedimentology and Stratigraphy: · The stratigraphic section displays the classic coarsening-upward succession of a rapidly prograding clastic wedge in a retro-arc foreland basin. A B C The succession consists of, from bottom to top: ú upper Mariño Fm.: medium to coarse grained sandy braided fluvial system with distinct tuffaceous intervals ú La Pilona Fm.: transitional succession consisting of a coarsening upward sequence of coarse-grained sandstone and granule to pebble conglomerate deposited in a braided fluvial to distal alluvial fan system. ú Rio de los Pozos Fm.: pebble to boulder conglomeratic unit representing medial to proximal alluvial fan system Detrital Zircon Geochronology: Ÿthe source of the Mariño Fm. yields distinct detrital zircon populations of Grenville and Famatinian age, probably representing sediment derived from the Cuyania composite terrane. PermoTriassic populations represent the Choiyoi Group, potentially indicating sediment derivation from a newly emergent Cordillera Frontal. ŸThe upper Mariño Fm. contains a robust detrital zircon population of upper Miocene age, providing a maximum depositional age of ~8.5 Ma, interpreted to represent significant syndepositional volcanism. A.) Tuff bed within fine-grained sandstones and siltstones from the Mariño Fm. and location of detrital zircon sample 05JBM11. Ÿthe coarsely conglomeratic Rio de los Pozos Fm. displays a dramatic increase in the amount of PermoTriassic Choiyoi Group detritus, including B.) Intercalated medium grained sandstone and pebble conglomerates of the La Pilona Formation that represents the transition zone a distinctive subpopulation of Carboniferous-Permian grains definitively linked to the Cordillera Frontal. The percent of TransAndean Miocene between the Mariño Fm. and the Rio de los Pozos Fm. C.) Pebble to boulder polymict, clast-supported conglomerate of the Rio de volcanic grains also significantly increases. These detrital zircon signatures, coupled with the very coarse grained nature of the formation are los Pozos Fm. D.) Thrust contact at the top of the measured section with the distinctly red, Triassic Uspallata Group structurally indicative of a major contractional pulse unroofing the Cordillera Frontal at <8.3 Ma overlying the Rio de los Pozos Fm. E.) Salagasta region, Las Peñas basin stratigraphic section.

D E ACKNOWLEDGEMENTS We would like to thank the TIES Argentina study abroad program and the Hostel Alamo for coordinating our stay in Mendoza; Mark Pecha and the helpful staff at the University of Arizona LaserChron Lab; Sam Taylor and Todd Lau for excellent geochronologic lab assistance. REFERENCES Giambiagi, L.B., Ramos, V.A., Godoy, E., Alvarez, P.P., Orts, S., 2003. Cenozoic deformation and tectonic style of the Andes, between 33° and 34° A B south latitude. Tectonics 22 (4), 1-18. Giambiagi, L.B., Tunik M.A., Ghiglione, 2001. Cenozoic tectonic evolution of the Alto Tunuyán foreland basin above the transitional zone between A.) Schematic sequence of cross sections illustrating the deformational evolution of the Andes at 33°S since flat and normal subduction segment (33°S 30'—34°S), western Argentina. Journal of South American Earth Sciences 14, 707-724. the Early Miocene. (a) Pre-Andean extensional deformation. (b) Inversion of normal faults to reverse faults. Giambiagi, L.B., Ramos, V.A., 2002. Structural evolution of the Andes in a transitional zone between flat and normal subduction (33°30'-33°45'S) (c) Generation of Aconcagua fold and thrust belt and deposition of Mariño Formation (d) Deposition of La Argentina and Chile. Journal of South American Earth Sciences 15, 101-116. Pilona and Rio de los Pozos formations. (e) Out-of-sequence thrusting in Cordillera Principal. (f) Ramos, V.A., 1999. Plate tectonic setting of the Andean Cordillera. Episodes 22 (3), 183-190. Deformation of Cuyo basin. B.) Stratigraphic section of the Neogene synorogenic deposits of the Cuyo basin Ramos, V.A., 2006. Evolution of the Argentine-Chilean Flatslab Region over the shallowly subducting Nazca Plate. Geological Society of America associated with the main tectonic events. [modified from Giambiagi et al., 2003] Field Guide 404, 1-55.