Deciphering geochemical and mineralogical changes of a Miocene sedimentary basin in ll, Mendoza province, Argentina
Hunger G.1, Moscariello A.1, Ventra D.1, Veiga G.2 1Earth and Environmental Sciences, University of Geneva, rue des Maraichers 13, 1205 Geneva, Switzerland. 2Centro de Investigaciones Geológicas, Universidad Nacional de La Plata - CONICET, Argentina contact: [email protected]
Legend Grain size A-G Chemostratigraphic units Provenance Heavy minerals (ongoing work) Principal Cordillera Frontal Cordillera Precordillera Fluvial Aeolian very ne Geochemistry and Mineralogy medium very coarse 87Sr/86Sr Th/Sc a Chile Argentina CIA MIA Clay minerals Zr/Sc 0.704 0.706 0.708 0.71 1 b Cacheuta Basin Whole-rock Others 1472 m Cacheuta peak
32° 30’ S 32° 30’ Composite section LP177 LP177 Introduction 1400 m Uspallata Aconcagua peak LP170 LP170
Costal Precordillera N Mendoza river Mogotes Fm. Cordillera del Tigre 1 LP164 LP164 5.8 Ma Frontal LP159
Aconcagua river 1472 m LP 177 Z LP159 Potrerillos Rio de los Pozos Fm. 8.7 Ma G Mendoza Legend Grain size Argentina 2 33° 05’ S LP155 LP155 Tobas La Angostura 8.9 Ma Coastal Cordillera Potrerillos LP149 Principal 9 Ma 1400 m HM sample LP149
very ne medium very coarse Mendoza La Pilona Fm. 1200 m Mendoza river P4-32 La Pilona Fm. La Pilona P4-32 AFTB 11.7 Ma source Cordon del Plata P4-31 P4-31
12.2 Ma 1300 m P4-28 +disturbances LP 173 S P4-28 Cordon del Portillo P4-25 N 1 Tupungato peak P4-25 Mapocho river Mariño Fm. N P4-16 P4-16 33° 30’ S 1200LP 170 Z m N 33° 10’ S N 1000 m F P4-12 P4-12 100 Km Santiago 5 km > 18 Ma Tunuyan 69°10’ W 69°05’ W P4-9 P4-9 Fig 1a. Location of the investigated area 5 Km Maipo river
1100 m P4-6 Fig 1b. Geological provinces of the Andean Neogene synorogenic deposits * Logged sections Ephemeral P4-6 Fig 1c. Potrerillos region, red insets: the two outcrops Fig 2. Stratigraphy of the Central Argentinian Foreland basin Alto Tunuyan Basin Tunuyan river streams
Cordillera LP 149 studied P3-18 P3-18 Upper Neogene formations Marino Formation 2 Chile 20 km Argentina P3-14 P3-14 La Pilona Formation Divisadero Largo Formation - The study area is located in the Mendoza Province of Argentina and is delimited by the Precordillera to the North and the Fron- 70° 30’ W 69° W 1000 m 700 m 800 m P4-32 P3-11 P3-11 tal Cordillera to the west (Fig 1a-b-c). This region has long been a sedimentary basin, rst during the Mesozoic rifting phase and Quaternary deposits Miocene Aconcagua Volcanic Complex Pre-Jurassic basement (Permo-Triassic Choiyoi Group, Late Paleozoic E P3-8 sedimentary rocks) P3-8 later as part of the Cenozoic Andean foreland. Pliocene-Quaternary volcanic rocks Lower Miocene volcanic rocks (Farellones Fm.) Thrust faults LP 135 S P3-6 Early paleozoic basement 900 m P3-6 Miocene-Pliocene intrusions Eocene-Oligocene volcanic rocks (Abanico Fm.) 600 m Proterozoic metamorphic rocks P3-3 P3-3 - The Mariño and La Pilona formations comprise a large part of the Neogene sediments in the Central Argentinian Foreland, weathering Neogene synorogenic deposits * Mesozoic sedimentary rocks (Triassic-Paleocene) International border Fig 11. a) Simpli ed regional geological map indicating the main geological units in Chile and Argentina between 32°30’ S and 33°45’ S. P1-17 P1-17 800 m dating from prior to 18 Ma to 9 Ma (Irigoyen et al. ,2000; Porras et al., 2016) (Fig 2.) and extending over more than 1400 m in stratigra- Based on Porras et al. (2016). b) Map of the Cacheuta Basin in ll in the studied area based on Giambiagi et al. (2015). 500 m P1-12 P1-12 600 m phy. P1-11 P1-11 The progressive evolution through stratigraphy of the whole-rock isotopic composition towards relatively more felsic sources is Marino Fm. P1-6 P1-6 gradual. For the basal part of the Mariño Formation (units A and B) the main source could be the andesites and basalts of the Abanico 700 m 400 m LP 108 S - Extensively exposed as the surface expression of folds related to Plio-Pleistocene uplift of the Precordillera. Formation in the western Principal Cordillera. P1-4 P1-4 D Units D, E and F reveal sources related to the Farellones Formation and the Aconcagua Volcanic Complex In agreement with the pro- P1-2 P1-2
gressive eastward advance of the volcanic front by approximately 50 km from the Farellones Arc in the Middle Miocene 600LP 93 Z m P1-1 P1-1 Biotite - The in ll comprises a continuous stratigraphic record of aeolian and ephemeral uvial environments developed during the uplift Sandstone from the La Pilona Formation have very variable composition, possibly reflecting a contribution from the Choiyoi Group, 300 m 400 m L36 L36 of the main Andean range in the Frontal Cordillera. However, the exact provenance of sand fraction from the La Pilona Formation is masked by the effects of Sphene L35
eolian L35 Apatite heavy-mineral concentrations (mostly Fe-Ti oxides) as placer deposits within laminae of sampled sandstones 500 m
eolian 200 m L33 L33 facies Garnet - Display of highly di erentiated facies associations and architectures L24 L24 Ultrabasic Basic Intermediate Acid Chlorite 60 m 16 10 Granite 400 m LP25 Alkaline LP25 100 m Epidote Phonolite Mariño Fm. 14 R61 200 m A LP 31 Z R61 Main goals C Rutile 12 Foidite Trachyte LP12 LP12 Tephriphonolite B 300 m Zircon
L7S Pyroxenes L8 10 Recycling 0 m L8 facies Trachyandesite C c Phonotephrite S / - Provide a detailed reconstruction of paleoenvironmental dynamics % Muscovite h 1
T Andesite L1 a 2 O Fe-Ti-oxides L1 N 8 D
+ Tephrite Basaltic 2 O B K trachyandesite Monazite LP10 E LP 9 Z LP10 6 Basanite Amphiboles - Unravel the relative roles of climate and tectonics through a high-resolution, compositional and sedimentological analysis Trachybasalt Rhyolite 200 m Basalte Spinel A F LP7 LP7 0 m 4 Others 5045 55 60 65 700 20 40 60 80 0 20 40 60 0 0.2 0.4 0.6 0.8 1 0 5 10 15 20 -6 -4 -2 0 2 4 6 Dacite La Pilona Fm. LP5 LP5 Olivine - Recognize the e ects of di erent allogenic drives on sedimentary processes and local environmental change. Picro- Basaltic- 2 Andesite Epsilon Nd basalt Basalt andesite 0.1 Tourmaline Fig 7. CIA and MIA represent ing, respectively, the chemical and mineralogical maturity of the sandstones. Clay mineral content given in area % (sum of kaolinite, illite and smectite content in the samples). The G 100 m LP213 LP213 Sub-alkaline 1 10 100 Zr/Sc CIA trend of sandstones from the La Pilona Formation is very similar to that of the clay-mineral content, suggesting an in uence of the hydrodynamic concentration of clays in the weathering index. Th/Sc, Zr/Sc 0 - Track changes in sediment provenance and relative information on magmatism and exhumation in the uplifting Andes ratios and isotopic ratios of strontium and neodymium (epsilon notation) providing information on the igneous character of the source-rocks. 35 40 45 50 55 60 65 70 75 80 LP202 LP202 Barite SiO2% Fig 13 . Th/Sc vs. Zr/Sc plot (Roser and Korsch, 1999). The arrow indi- cates the trend expected from zircon concentration by recycling LP199 LP199 Talc Fig 12 . K2O+Na2O vs. SiO2 (TAS) diagram for the nomenclature of volcanic 0 m processes. In dashed line the compositional trend from basalt to granite 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Kaolinite Weathering and maturity Evolution of the uvial-fan rocks after Le Maitre et al. (1989). Modi ed after Alarcon and Pinto (2015). proposed by Mongelli et al. (2006) Methods relatively high concentration of barite Petrography Mariño Fm. a b A CIA Qtz A Variation of the composition due to the proximity of the mountain Logging Heavy minerals (ongoing work) U-Pb dating (ongoing work) B Frontal Cordillera Kaolinite 700 m 100 range and the contribution of sediments coming from the first C strong Pyroxenes Sampling weathering Principal Cordillera Fe-Ti-oxides MIA D stages of the uplift of the Frontal Cordillera. Amphiboles
600 m 2 mm 200 µm E Illite G IWT 20-62.5 µm 62.5-125 µm 125-250 µm 250-400 µm whole-rock albite quartz clay minerals moderate A 20-62.5 µm 62.5-125 µm 125-250 µm 250-400 µm whole-rock 20-62.5 µm 62.5-125 µm 125-250 µm 250-400 µm whole-rock F 75 2 k-feld calcite unknown weathering Migration of the deformation towards the foreland. Progressive un- 500 m - Automated petrography (QEMSCAN) B 1400 on sandstone thin-sections provide complementary quantitative La Pilona Fm. 1400 1400 C Palomares Fm. data for evaluating the modal composition of sandstones roofing of Paleozoic sequences G D weak 1 400 m G, Rh weathering - Separation of zircons E - Separation by dense liquid Plg Kfs 50 Da F 50 - Dating by LA-ICP-MS Di fluvial fan Giambiagi and Ramos (2003) reported, in the cogenetic Palomares Geochemistry - Sieving: 20-400 microns G 300 m Ba, An sorting - Speci c information on provenance Formation (Alto Tunuyan Basin), the first arrival of clasts coming 1200 1200 1200 - Geochemistry of the sandstones and mudstones samples by XRF is - Quanti cation of heavy mineral used as a screening method assemblages using the QEMSCAN from the Frontal Cordillera ~ 30 km 200 m - Major and trace elements provide informations on:
Sampling sandstones from channel provenance
100 m lls and silt-/mudstones from ood Isotopes 1000 1000 plain deposits Climate Source rock 1000 - isotopic compositions of whole-rock sandstones samples at speci c 0 Kfs stratigraphif levels
L7S 0 m weathering Plg Kfs CN K Coarsening upward trend of the sandstone units showing the pro- Tectonism recycling - mixing of di erent igneous compositions Sr - Nd - Pb maturity Principal Cordillera gradation of the fluvial-fan system during the uplift of the Principal - constrain source rock composition 800 800 800 diagenesis sorting Fig 9. Mineralogical and compositional variations of the sandstones from the Mariño and La Pilona Cordillera. formations. MIA is illustrated in the Qtz-Plg-Kfs (Quartz – Plagioclase - K-feldspar) mineralogical space and CIA is illustrated in the A-CN-K (Al2O3-CaO+Na2O-K2O) compositional space. Based on The top of the Marino fm. is characterized by Nesbitt and Young (1986), Rieu et al. (2007). 2 amalgamated coarse-grained channel fills with 600 600 Tectonic setting Mariño Fm. some conglomeratic levels. The fine-grained F 600 A Increasing trend of weathering going towards to illite pole (Fig. 9), confirmed by 1 deposits are less laterally continuous B fluvial fan 100 the increase in illite content as seen in the petrographic data (QEMSCAN). Samples plot in the island arc field, and the evolution toward the top of Th C Fluvial system: amalgamated channel fills and overbank de- D the stratigraphic column shows a trend toward active continental terminal posits, with tabular geometry and increased lateral connec- D-E 400 400 400 E The data are deviated from the ideal weathering trend (IWT) probably due to a lobes margin (Fig. 3). F aeolian ~ 30 km tivity. A few interactions with aeolian deposits at the base. sandsheet ) Passive continental La Pilona Fm. progressive change in the source-rock composition. O 10 Gradual transition to more coarse-grained deposits 2 margin G
N a The Th-Sc-Zr/10 ternary diagram proposed by Bhatia and Crook (1986; / 200 200 200 O Fig. 4) is based on the study of immobile trace elements that are not This diagram allows the recognition of the primary source rock, values indicate K 2 (
o g andesitic composition. sabkha
l sensitive to remobilization during weathering, diagenesis and metamor- C erg system 1 phism. The samples from the lower part of the succession plot in the Principal Cordillera island arc field. However, samples from stratigraphic intervals overlying B D Island Arc 0 0 0 the aeolian member show higher concentrations of Th and Zr and plot 0 10 20 30 0 10 20 30 0 10 20 30 0 10 20 30 0 20 40 60 80 0 10 20 30 0 10 20 30 0 10 20 30 0 10 20 30 0 20 40 60 80 Active continental alluvial fans margin within the field of active continental margin. A Abrupt establishment of an erg system of wide geographic 0.1 The first and second dimensions (Fig. 10; PC1 and PC2 respectively) showthe 2 25 45 65 85 sandsheet extent but probably of relatively long duration. SiO2 Sc Zr/10 Overall, the evolution of the tectonic setting compositional signature importance of the weathering and maturity signals and the concentration of Development of a dune field and marginal sand sheets, induced - Heavy-minerals study based on QEMSCAN results, confirmed by conventional petrographic tools Grain-size distribution through the basin infill shows a progressive trend towards a more heavy-minerals (positive PC2). The samples follow a trend towards the weath- 1 by climatic aridification and/or shift of the main fluvial system. Fig 3. Diagram by Roser and Korsch (1986) very used for Fig 4. A: oceanic island arc, B: active continental 20-62.5 µm 62.5-125 µm 125-250 µm 250-400 µm Next step: tectonic setting classi cation. In our case the major elements mature and evolved composition. ering and maturity pole. 1400 margin, C: continental island arc, D: passive margin fluvial fan used are biased by the high amount of calcite in the samples (Bhatia and Crook 1986). - Wide range of grain-size (from 20 to 400 µm) in order to better represent the whole distribution Variability of the compsoition C - Interpretation of the grain-size distribution of the main heavy-minerals
~ 30 km Proximal Decrease in overall grain-size, channel thickness and amalgamation and thickness overall in grain-size, channel Decrease Amalgamated channel belt 1200 complexes with high connectivity. - Assemblage dominated by pyroxenes, Fe-Ti-oxides and amphiboles Classi cation of the sandstones Few/no oodplain deposits - Zircon dating for precise provenance investigation, to understand the relationships between depo-
10.0 sition in the bassin and exhumation of the Andes Mariño Fm. - Others heavy-minerals represent, in average, less than 10 %. Their variabilityiis mostly blurred placer ratio Supply / Accomodation Increasing A Fig 5. Log(Na2O/K2O) vs. log(SiO2/Al2O3) diagram Medial 1000 Principal Cordillera for the geochemical classi cation of terrigenous sabkha B Channel belt complexes separated sands proposed by Pettijohn et al. (1972) and Quartz-rich by distinctive packages of laterally ma c continuous oodplain deposits - Pyroxene very low in La Pilona Formation 0.5 C redrawn by Herron et al. (1988). alluvial fans D 1.0 ) References O E General trends: 800 2 K 2 Greywacke weathering and maturity O / F Distal - Pyroxene is decreasing Alarcon, P., Pinto, L., 2015. Neogene erosion of the Andean Cordillera in the flat-slab segment as indicated by petrography and whole-rock geochemistry from the Manantiales Foreland Basin (32°-32°30’S). Tectonophysics 639, O Litharenite 2 2 0 Few channel belt deposits with no
K 1–22. doi:10.1016/j.tecto.2014.11.001 La Pilona Fm. lateral connectivity, domination of I N a
n Bhatia, M.R., Crook, K.A.W., 1986. Trace element characteristics of graywackes and tectonic setting discimination of sedimentary basins. Contributions to Mineralogy and Petrology 92, 181–193. ( - Amphibole is increasing Subarkose 1 oddplain material c G o g fluvial fan very low pyroxene Giambiagi, L., Spagnotto, S., Moreiras, S.M., Gómez, G., Stahlschmidt, E., Mescua, J., 2015. Three-dimensional approach to understanding the relationship between the Plio-Quaternary stress field and tectonic inversion in the l r ephemeral lacustrine systems e Triassic Cuyo Basin, Argentina. Solid Earth 6, 747–763. doi:10.5194/se-6-747-2015 a 0.1 Axial uvial system 600 s high amphibole Herron, M.M., 1988. Geochemical classification of terrigenous sands and shales from core or log data. Journal of Sedimentary Petrology 58, 820–829. i -0.5 n Irigoyen, M. V, Buchan, K.L., Brown, R.L., 2000. Magnetostratigraphy of Neogene Andean foreland-basin strata, lat 33°S, Mendoza Province, Argentina. Bulletin of the Geological Society of America 112, 803–816. g Sublitharenite Quartz arenite doi:10.1130/0016-7606(2000)112<803:MONAFS>2.0.CO;2 ma Quartz-poor Fig 8. A) Generalized sedimentological trend for deposits of a uvial fan from proxi- turi terminal Le Maitre, R.W., Baterman, P., Dudek, P., Séller, J., Lameyre Le Bas, J., Sabine, P.A., Schmid, R., Sorensen, H., Streckeisen, A., Woolley, A.R., Zanettin, B., 1989. A classification of igneous rocks and glossary of terms: Recommen- ty Intermediate lobes sediment mal to distal (Weissmann et al. 2013) and change in the stratigraphic succession ~ 30 km dations of the International Union of Geological Sciences Subcommission on the Systematics of Igneous Rocks. Blackwell Scientific Publications, Oxford 193. transport from the apex to the distal part of the system (Owen et al. 2015) Mongelli, G., Critelli, S., Perri, F., Sonnino, M., Perrone, V., 2006. Sedimentary recycling, provenance and paleoweathering from chemistry and mineralogy of Mesozoic continental redbed mudrocks, Peloritani mountains, southern Fig 6. Geochemical composition and theo- isolated peaks of Fe-Ti-oxides Fe-Ti-oxides de nes the variations, but 400 -1 0.0 Italy. Geochemical Journal 40, 197–209. doi:10.2343/geochemj.40.197 0 1 1.5 2 2.5 retical quartz composition of sandstones, d Nesbitt, H.W., Young, G.M., 1996. Petrogenesis of sediments in the absence of chemical weathering: effects of abrasion and sorting on bulk composition and mineralogy. Sedimentology 43, 341–358. 0.5 0.01 0.10 1.00 10.00 ren The overal stratigraphic picture shows a gradual transition Pyroxene de nes the general trends log(SiO2/Al2O3) infered from K2O and Na2O g neral t Beginning of the fluvial-fan deposition, dominancemuddy de- Owen, A., Nichols, G.J., Hartley, A.J., Weissmann, G.S., Scuderi, L.A., 2015. Quantification of A distributive fluvial system : The Salt Wash DFS of the Morrison Formation, SW U.S.A. Journal of Sedimentary Research 85, 544–561. Na2O e from distal to proximal facies associations recording the doi:10.2110/jsr.2015.35 posits intercallated with rare channel fills. Distal environ- Pettijohn, F.J., Potter, P.E., Siever, R., 1972. Sand and sandstone. Springer US, New York, pp. 618. doi:10.2475/ajs.275.5.607 progradation/aggradation of a large fluvial-fan in semi-arid/arid Porras, H., Pinto, L., Tunik, M., Giambiagi, L., Deckart, K., 2016. Provenance of the Miocene Alto Tunuyán Basin (33°40′S, Argentina) and its implications for the evolution of the Andean Range: Insights from petrography and U–Pb ment environment during the Miocene. overall grain-size increase 200 LA–ICPMS zircon ages. Tectonophysics 690, 298–317. doi:10.1016/j.tecto.2016.09.034 The samples from the Mariño and La Pilona formations plot mostly in the greywacke field (Fig. 5) and quartz-arenite composition (Fig. 6) showing a low composi- Rieu, R., Allen, P.A., Plotze, M., Pettke, T., 2007. Compositional and mineralogical variations in a Neoproterozoic glacially influenced succession, Mirbat area, south Oman: Implications for paleoweathering conditions. Precambrian A-B Research 154, 248–265. doi:10.1016/j.precamres.2007.01.003 tional maturity consistent with their syntectonic origin (Irigoyen et al., 2000). Along the stratigraphic succession, the maturity slightly increases towards the top of Roser, B.P., Korsch, R.J., 1986. Determination of tectonic setting of sandstone-mudstone suites using SiO2 Content and K2O/Na2O ratio. The Journal of Geology 94, 635–650. doi:10.2307/30078330 Sediments are comming from the erosion of the Principal Roser, B.P., Korsch, R.J., 1999. Geochemical characterization, evolution and source of a Mesozoic accretionary wedge: the Torlesse terrane, New Zealand. Geological Magazine 136, 493–512. doi:10.1017/S0016756899003003 the Mariño Formation, with samples from the La Pilona Formation appearing more mature. Fig 10. Principal component analysis (PCA) done using the mineralogical and geochemical composi- Cordillera Weissmann, G.S., Hartley, A.J., Scuderi, L.A., Nichols, G.J., Davidson, S.K., Owen, A., Atchley, S.C., Bhattacharyya, P., Chakraborty, T., Ghosh, P., Nordt, L.C., Michel, L., Tabor, N.J., 2013. Prograding distributive fluvial systems: tion of the sandstones from the Mariño and La Pilona formations. Pole are recognized by their com- 0 geomorphic models and ancient examples. SEPM Special Pulication 131–147. doi:10.2110/sepmsp.104.16 positional associations. 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50