Deciphering geochemical and mineralogical changes of a Miocene sedimentary basin inll, 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) Simplied 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 inll 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 inll 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 dierentiated 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 O 1 T 2 Andesite L1 a Fe-Ti-oxides L1 N 8 D + Tephrite O Basaltic 2 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 eects of dierent 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 inuence 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). Modied 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 - Specic 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 - Quantication 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 specic 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 dierent 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.