Geologic Evolution of the Argentinian Andes Department of Geology, University of Wisconsin-Eau Claire, Eau Claire, WI 54701 Brennan M. Kadulski Anne K. Gauer Elizabeth A. Balgord Crystal L. Nickel J. Brian Mahoney Bridget B. Kelly Anna C. Baker Beth J. Teutschmann Lori D. Snyder Robert L. Hooper Abstract Regional Cross Sections l Over the past 2.1 Ga the western margin of South America has been subjected to a series of a a l ip r ta c l le distinct orogenic events. Western Argentina is underlain by several northeast-trending a l 9 Ma- present s in t i o r n d terranes including, from east to west, the Sierras Pampeanas, Precordillera, Cordillera C P o r r AFTB F c Frontal, Cordillera Principal, and the Cordillera de la Costa. The following table synthesizes eo r Sierras Pampeanas the significant geologic events, style of formation, and ages of orogenesis. A Cuyo P B Basin San Juan Miocene Foreland Sediments Orogenesis Significant Geologic Events Style Age Cuyania Terrane collision Fla Ophiolite obduction, crustal 500-520 Ma t Chilenia Pampia Oc Pampean thickening and uplift, high ea Cordillera Frontal nic Slab Subduction Orogeny grade metamorphism Cordillera Costal Famatinian Arc, Cuyania Terrane collision 495-470 Ma The change from a normal subducting slab (below) to a shallow subducting slab (above) Famatinian composite terrane, and the terminates volcanism in the Central Volcanic Zone and is responsible for the uplift of the Orogeny Chillenia terrane Precordillera, Cordillera Frontal and Cordillera Principal. Sierras Pampeanas a Final amalgamation of Terrane collision 354-290 Ma l l r a a e l t l a p l Gondwanian supercontinent t i n i s c o d n r r Orogeny Gondwana extension-related Extensional o i A B r F o 25-9 Ma C c volcanism collapse Aconcagua P Cuyo e Basin r P Miocene Foreland Sediments Mesozoic-Cenozoic Episodic continental arc Andean style 150 Ma-Present Cuyania Chilenia Precordillera N Pampia Orogenesis volcanism subduction o rm a Cordillera Principal l S Mantle Wedge ub Current Andean Fold and thrust belt, Shortening, 23.8 Ma-Present du ctin g uplift and segmentation of Nazca plate transition to flat Sl ab subduction slab Geologic Excursions in Argentina (A) Pampean Orogeny Geologic Field Excursion: Argentina is an upper division geology course that explores the geology of the (D) Aconcagua Fold and Thrust Belt southern Andes and the history and culture of Argentina. The southern Andes consist of five different geologic provinces produced by four tectonic events over the past billion years, including the most recent A. Pampean Orogeny uplift of the current Andes. Over the course of the semester, we explored the geologic processes, history, Map view of the Pampean Orogeny economy and culture that have shaped Argentina. The class culminated in a two week excursion to . Argentina examining the geologic provinces of western Argentina. B. Late Neoproterozoic to Early Cambrian Subduction has started along the western edge of Gondwana; ocean floor is accreted onto the continent and a continental magmatic arc develops. The now dormant andesite volcano, Volcano Aconcagua, is active between 16 A. Pampean Orogeny and 9 Ma. When flat slab subduction initiated at 9 Ma, magmatism ceased. At this time, thrusting begins in the west and migrates to the east causing older lithologies to be E. Sierras Pampeanas C. Early to Mid-Cambrian thrust on to younger. These faults are actively thrusting eastward today. Rio de La Plata Craton (RPC) 30° 72° 71° I 70° Consumption of the oceanic crust I I µ Subducti{ ng oceanic crust I II Legend 40 Route City Pampean Terrane Magmatic arc leads to a continent - continent L Highway Volcano a I A River e n T il i t I A h N n g collision. The Pampean Terrane is C u e O a L g a r B R I Y A I l F A I a e P n L welded to the Rio de La Plata T I e s a A c e S ni a ra s L R te F F e O E n au a ñ Craton. The suture zone contains L te l u a C I t s L I E s l W I I I t I F F I a A D au u L R l lt accreted ocean floor and L t E A O B. Late Neoproterozoic to Early Cambrian (600-520 Ma) D P San Juan I C metamorphic and igneous rocks. A C Pampe{ an Collision Barreal Rio San Juan R N I n A E R L R a P L E I Mercedaria L e A D L I R R c E D 32° L Ramada 32° O R O L I D. Tertiary Block Uplifts C O D C c R i E f Initiation of flat slab tectonics in the i O R P c C Aconcagua Early Ordovician Limestones Jurassic Sediments Miocene Plutonics Tertiary causes thick and thin a C. Early to Mid-Cambrian (540-512 Ma) P Uspallata Late Ordovician Limestones Jurassic Cretaceous Sediments skinned deformation; metamorphic Mendoza Puente Triassic Plutonics Thrust Fault Zone del Cretaceous Sediments basement rocks and overlying R Inca io n M a e y n u d n o sediments are thrusted up as blocks. z Tu a io Tupungato R After a period of erosion the thin 7 sediment layers are eroded Santiago exposing the metamorphic 50 km 71° 70° basement rocks as topographic 34° Thrusted terrane before erosion massifs east of the Precordillera. E. Sierras Pampeanas Thrusted blocks of metamorphic basement are outlined in the Thrusted terrane after erosion background. D. Tertiary Block Uplifts (9 Ma) (B) Famatinian Orogeny (C) Permo-Triassic Rifting Pillow basalts from the suture zone The contact between Triassic between Chilenia and Cuyania. sedimentary rocks and Famatinian Ordovician basement rocks. Permo triassic (255-241 Ma) Magmatic Belts extensional rifting is characterized 485Ma by bimodel rhyolitic and basaltic an volcanism along the suture zone of i c as as in ar r n at c er ia Chilenia and Cuyania. As rifting a m ni Si p ni a a m proceeds, listric faults cut the a F lc Pa uy vo Precordillera Terrane generating C half grabens. Erosion fills the rift with sediments. W Collision of E Famatina 465Ma W E Cambrian and Ordovician Chilenia platform carbonates collide Collision of with the western Precordillera Cuyania margin of Terrane Gondwana during 435Ma Lacustrine Facies the Famatinian orogeny 435 Ma. Choiyoi Group Fluvial Facies The carbonate and clastic rocks that made the sedimentary cover of Chilenia when it Basalts Alluvial Fan Facies collided with Cuyania brings the Famatinian Orogeny to a close in the Middle Carboniferous. The Chilenia Terrain is now part of the Cordillera Principal..