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| Pampean orogeny | |
|---|---|
| Name | Pampean orogeny |
| Period | Neoproterozoic–Cambrian |
| Type | Orogeny |
| Region | Pampean region, Sierras Pampeanas, Argentina |
Pampean orogeny The Pampean orogeny was a major Paleozoic mountain-building episode affecting the Sierras de Córdoba, Sierras Pampeanas, and adjacent cratonic margins during the latest Neoproterozoic to Early Cambrian time. It involved convergence between proto-continental blocks including the Río de la Plata Craton, the Arequipa-Antofalla Craton, and exotic terranes accreted along the western margin of the Gondwana assembly. The event produced regional folding, thrusting, metamorphism, and widespread magmatism that shaped the geology of central and northwestern Argentina and influenced tectonic frameworks correlated with the Brasiliano orogeny and the Famatinian orogeny.
The orogeny occurred along the interior margin of Gondwana where the Río de la Plata Craton interacted with terranes such as Arequipa-Antofalla and the now-reconstituted Peruvian margin. Regional structures lie within the Sierras Pampeanas, Sierras de Córdoba, and the Puna fringe, adjoining basins like the Puna Basin and the Chaco Basin. Paleogeographic reconstructions link Pampean deformation to coeval events in the Famatinian belt, the Eastern Sierras Pampeanas, and correlations with the Brasiliano belts of Brazil. Key tectonic boundaries include sutures inferred from ophiolitic remnants, thrust systems, and fold belts aligned with major river catchments such as the Río de la Plata drainage.
Convergence during the late Neoproterozoic to Early Cambrian involved subduction and collision between the Río de la Plata Craton and microcontinental blocks including Arequipa-Antofalla and displaced fragments linked to the Cuyania terrane and the Precordillera. Models invoke continental arc magmatism, slab rollback, and terrane accretion comparable to processes invoked for the Famatinian orogeny and the Gondwanide orogeny. Tectonic styles ranged from thin-skinned thrusting in foreland settings adjacent to the Sierras de Córdoba to thick-skinned basement-involved deformation in the Sierras Pampeanas core, producing structures analogous to those in the Andean orogenic system. The collision modified crustal architecture, creating crustal thickening, isostatic responses, and subsequent extensional relaxation that influenced later basins such as the Mar de Plata Basin.
Sedimentary successions involved synorogenic clastic wedges derived from uplifted source areas, recorded in units equivalent to the Puncoviscana Formation and coeval strata correlated with the Sierra Grande Group. Lithologies include unmetamorphosed to low-grade metasedimentary rocks, turbidites, conglomerates, sandstones, and carbonate interbeds containing faunal assemblages comparable to Early Cambrian faunas known from the Precordillera. Stratigraphic packages preserve volcaniclastic sequences, arc-derived tuffs, and interbedded pelites that document the progression from passive margin sedimentation to active margin deposition. Detrital provenance studies link clastic inputs to the Río de la Plata Craton and recycled lithologies from the Famatinian domain.
Metamorphic grades vary from low-grade greenschist facies in peripheral basins to amphibolite facies in internal domains, with local high-pressure assemblages reported in tectonic slices resembling mini-schools of subduction-accretion complexes. Deformation style comprises tight to isoclinal folding, upright and recumbent folds, thrust nappes, crustal-scale reverse faults, and penetrative cleavage development, with regional metamorphic fabrics overprinting earlier sedimentary structures. Kinematic indicators show top-to-the-west and top-to-the-east thrust transport in juxtaposed domains, comparable to multilayer duplex systems documented in the Andes and other Paleozoic belts. Metamorphic resetting associated with intrusion of syn- and post-orogenic plutons contributed to thermochronological signatures recorded by minerals used in age dating.
Magmatic activity included calc-alkaline arc volcanism, synorogenic granitoid intrusion, and post-orogenic A-type magmatism. Plutonic complexes such as the Achala Batholith and smaller bodies crop out within the Sierras de Córdoba and Sierras Pampeanas, displaying compositional ranges from diorite to granite and associated porphyries. Geochemical signatures indicate subduction-related magma genesis transitioning to within-plate signatures during post-orogenic extension, comparable to magmatic trends documented in the coeval Famatinian arc and the Gondwanide magmatic episodes. Hydrothermal systems related to magmatism localized mineralization and altered wall rocks, producing skarn and epithermal assemblages.
Chronological control derives from U-Pb zircon dating of volcanic and plutonic rocks, SHRIMP and LA-ICP-MS analyses, and 40Ar/39Ar dating of micas and amphiboles. Key age clusters concentrate around the late Neoproterozoic to Early Cambrian interval, with zircons yielding ages broadly spanning ca. 540–520 Ma for synorogenic plutons and older inherited components tied to the Río de la Plata Craton and Grenville-age provinces. Detrital zircon spectra provide provenance and maximum depositional ages, linking sedimentation pulses to collisional timing. Thermochronologic data from fission-track and (U-Th)/He studies record exhumation during the Paleozoic and reactivation during Mesozoic–Cenozoic Andean deformation.
The orogeny and associated magmatism generated favorable conditions for base and precious metal mineralization, including deposits of copper, lead, zinc, gold, and tungsten within skarn, porphyry, and epithermal systems. Regions within the Sierras Pampeanas and adjacent belts host exploration targets exploited by national and international companies operating under Argentine mining regulations and contributing to regional economies centered in provinces such as Córdoba (province) and San Juan Province. Mineralization styles mirror metallogenic provinces comparable to those in the Andes and ancient arcs like the Famatina district, with ongoing studies by universities and geological surveys to refine exploration models.
Category:Orogenies Category:Geology of Argentina