The Southern Andes have been built through the stacking of crustal sheets in discrete periods during the last 100 My. The first important shortening took place in Late Cretaceous at the time of ...eastward arc expansions potentially linked to two areas of subducted slab shallowings of 200 and 800 km wide respectively. These shallowings have progressed to two smaller flat slabs in Eocene times, where rather anhydrous subducted slabs generated a discontinuous arc emplaced in the foreland area at the time of mountain building. Discrete segments of the former Late Cretaceous slab shallowings would have fallen down at this time producing early slab steepening settings where within-plate products and extensional basins developed such as in the southern Chubut Province. Then Late Oligocene times coincide with the final steepening of the broad Late Cretaceous to Eocene shallow subduction zone with the emplacement of voluminous volcanic plateaux in central Patagonia and extensional basins in the hinterland zone. Lately a long quiescence period was interrupted by the development of three Miocene shallow subduction settings more than 400 km long each, evidenced by arc expansions and associated with Andean construction. Most of these areas were extensionally reactivated in the last 5 My at the time of retraction and steepening of formerly shallow subduction zones, being associated with voluminous mantle derived materials and shallow asthenospheric injection. While some of these shallow subduction configurations could be explained by subduction of highly buoyant oceanic lithosphere related to seismic ridges, in particular those of the Aluk/Farallones and Chilean ridges, other mechanisms remain more speculative. The alternation of shallow subduction zones and their steepening in the last 100 My in the Southern Andes explain location and timing of main magmatic fluxes in the arc and retroarc areas, as well as the presence of coeval foreland mountain systems east of the Main Andes.
► The construction of the southern Andes is linked to shallow subduction settings. ► There are fast migrations/expansions of arc-derived rocks towards the foreland. ► The mountain building phases are related with expansion/migration of the arc. ► Subduction of buoyant oceanic seismic ridges is the main controlling factor.
The Southern Volcanic Zone of the Andes has a Quaternary basaltic province along the retroarc which has a unique tectonic setting. The Payenia volcanic province covers an area larger than 40,000
km
2 ...between 33°30′ and 38° South latitudes, with an estimated volcanic volume of about 8387
km
3 erupted through more than 800 volcanic centers in the last ~
2
Ma. The mainly basaltic province developed above the San Rafael Block is subdivided in three segments characterized by the Cerro Nevado, Llancanelo, Payún Matru, Tromen and Auca Mahuida volcanic fields, together with hundreds of minor monogenetic basaltic centers. The analysis of the different segments shows the formation of a common basalt plateau with intraplate signature from south to north between 2.0 and 1.7
Ma, which reached the 35°S to the north. Above this plateau monogenetic centers as Nihuil Vn. 1.433
Ma and Cerro Chato at 1.352
Ma are developed, followed by the large polygenetic center of Cerro Nevado (3980
m
a.s.l.) at 1.320
Ma. This plateau was broken by a series of normal faults that produced volcanic cone alignments such as the NNW-trending Mancha Jarilla lineament in the central part at about 1.0
Ma. Extension shifted to the eastern margin of the San Rafael Block, which concentrates tens of monogenetic centers between 0.9 and 0.7
Ma. Extension then migrated towards the foothills in the west, where many monogenetic cones were erupted through NW-trending normal faults between 0.5 and 0.435
Ma. The collapse of the large Diamante Caldera at 0.445
Ma coincides with that period. Subsequent volcanism was concentrated in (1) the Payún Matru volcanic field, with the eruption of Cerro Payén between 0.272 and 0.261
Ma; the Payún Matru shield volcano, with polygenetic eruptions at least since the last 0.233
Ma and with the caldera formation bracketed between 0.168
±
0.004
Ma and 0.082
±
0.001
Ma, followed by several eruptions until 7000
yrs, and even historical ones; and in (2) the Tromen volcano, where younger than 0.2
Ma eruptions took place and historical eruptions were reported. The understanding of these eruptions in time and space, combined with geophysical data, indicates the geometry of an important crustal attenuation beneath Payenia, associated with a hot sublithosphere. The Late Miocene uplifted San Rafael Block collapsed in the Early Pleistocene as a consequence of the steepening of the subducted slab, and the injection of hot asthenosphere produced the Quaternary Payenia volcanic province. Melts of the lower crust along the Principal Cordillera at these latitudes are responsible for the Quaternary calderas, ignimbritic flows and rhyolitic volcanism that express the crustal delamination of the Andes. The Payún Matru volcanic field concentrates this asthenospheric flow in the Present.
►Large Quaternary foreland basaltic magmatism after a period of flat-subduction. ►Basaltic floods start from the southeastern foreland to the northwestern axis of the Andes. ►Flood basalts were followed by rhyolitic caldera eruptions along the main Andes. ► Unique large Quaternary basaltic volcanic province in the Andean foreland.
Provenance of detrital sediments of the Neuquén Basin in Central Argentina was investigated using U–Pb and Lu–Hf isotopic composition of zircon grains in order to evaluate the timing of uplift of the ...southern Andes at these latitudes (36°–39°S). Samples of fluvial synorogenic deposits of the Candeleros Formation, at the base of the Neuquén Group (Upper Cretaceous), as well as from older deposits of the Rayoso and Agrio Formations (Lower Cretaceous) were investigated. A regional angular unconformity separates the Upper from the Lower Cretaceous units and is generally attributed to the onset of the foreland basin stage. The evident differences between these suites (above and below the unconformity) are clearly shown by their distinct provenance patterns, which correspond to different bedrock sources and patterns of dispersal. Detrital zircons of the Rayoso and Agrio Formations beneath the unconformity indicate provenance from the eastern foreland basement, presently exposed along the Sierras Pampeanas of central Argentina. Detrital zircon ages correspond to the Permian and Triassic Choiyoi province, the Ordovician Famatinian orogen, the Lower Cambrian–Neoproterozoic Pampean orogen, the Grenvillian age Mesoproterozoic basement and some other older sources. In contrast, detrital zircons above the unconformity, from the Candeleros Formation, have striking different prominent peaks. The pattern indicates direct derivation from the Early Cretaceous magmatic arc, probably from plutons exhumed during the Late Cretaceous deformation along the western Chilean slope of the Andean cordillera. The contrasting dispersal patterns are interpreted as a result of the uplift of the southern Central Andes at these latitudes. The youngest detrital zircons constrain the timing of uplift as being younger than 99
Ma, supporting the assumed Cenomanian age for the synorogenic deposits. This age is further constrained by fission-track data from zircons from an ash-tuff layer of the lowest parts of the Neuquén Group, which yielded ages of about 88
Ma. The Hf isotopic data indicate derivation from a juvenile mantle for the Grenvillian age zircons, which corroborates the previously assumed island arc setting. The intermediate Hf isotopic values for the Pampean age zircons indicate a transition to the extensive recycling of the continental crust for the oldest Paleoproterozoic zircons with negative values that characterize the foreland basement.
The Cretaceous-Cenozoic evolution of the Patagonian broken foreland basin system at 42–43°S in the northern Chubut province of Argentina is associated with variable retroarc phases of fold-thrust ...belt shortening, extension, and basement uplift during changes in the dynamics of oceanic slab subduction. Basement inheritance and progressive shallowing of an east-dipping subducting slab are important mechanisms of foreland partitioning, as dictated by the preexisting (pre-Andean) structural architecture and forelandward (eastward) advance of Late Cretaceous arc magmatism. Previously recognized growth strata help define the timing of fold-thrust belt shortening and retroarc basement-involved uplift, but the precise consequences for sediment routing remain poorly understood, with uncertainties in patterns of basin evolution before, during, and after shallowing and resteepening of the subducting slab.
In this study, distinctive sediment source regions and magmatic histories enable evaluation of the stratigraphic and tectonic evolution of the retroarc foreland basin using new provenance results, maximum depositional ages, and isotopic signatures from detrital zircon U-Pb geochronology and Lu-Hf geochemical analyses. A compilation of published bedrock crystallization ages and distributions of metamorphic and igneous basement rocks identify: a western source region defined by the Andean magmatic arc and associated pre-Andean basement; and an eastern source region consisting of intraplate magmatic units and the North Patagonian Massif.
We demonstrate that Aptian-Cenomanian retroarc basin fill was derived principally from the basement massif and intraplate volcanic units to the east, followed by a Late Cretaceous (Campanian-Maastrichtian) reversal in sedimentary polarity and subsequent exclusive derivation from the Andean arc and orogenic belt to the west. Late Cretaceous-Paleocene slab shallowing and arc cessation was succeeded by late Eocene–earliest Miocene extension during slab rollback and renewal of arc magmatism. Thereafter, Miocene sedimentation was closely linked to shortening in the Andean fold-thrust belt. Within the retroarc succession, new U-Pb ages provide estimates of depositional ages for Lower Cretaceous through Miocene stratigraphic units.
Finally, in addition to U-Pb provenance and chronostratigraphic constraints, zircon Hf isotopic signatures from the detrital record provide confirmation of a Cretaceous-Cenozoic history involving: (1) initial establishment of a continental magmatic arc; (2) transition from a neutral to compressive tectonic regime; (3) shallowing of the subducting slab and arc cessation during retroarc basement partitioning; (4) arc retreat and foreland basin abandonment during slab rollback (with modest extension and crustal thinning); and (5) final renewed shortening during arc rejuvenation.
•Detrital zircon U-Pb ages demonstrate Late Cretaceous reversal in sediment polarity.•Depositional ages for growth strata constrain thrust-belt and intraforeland uplift.•Hf isotopes record tectonic reorganization and overriding plate deformational mode.
This study synthesizes the tectonomagmatic evolution of the Andes between 35°30′S to 48°S with the aim to spotlight early contractional phases on Andean orogenic building and to analyze their ...potential driving processes. We examine early tectonic stages of the different fold-thrust belts that compose this Andean segment. Additionally, we analyzed the spatio-temporal magmatic arc evolution as a proxy of dynamic changes in Andean subduction during critical tectonic stages of orogenic construction. This revision proposes a hypothesis related the existence of a continuous large-scale flat subduction setting in Cretaceous times with a similar size to the present-largest flat-slab setting on earth. This potential process would have initiated diachronically in the late Early Cretaceous and achieved full development in Late Cretaceous to earliest Paleocene times, constructing a series of fold-thrust belts on the retro-arc zone from 35°30′S to 48°S. Moreover, we assess major paleogeographic changes that took place during flat-slab full development in Maastrichtian-Danian times. At this moment, an enigmatic Atlantic-derived marine flooding covered the Patagonian foreland reaching as far as the Andean foothills. Based on flexural and dynamic topography analyses, we suggest that focused dynamic subsidence at the edge of the flat-slab may explain sudden marine ingression previously linked to continental tilting and orogenic loading during a high sea level global stage. Finally, flat-subduction destabilization could have triggered massive outpouring of synextensional intraplate volcanic rocks in southern South America and the arc retraction in late Paleogene to early Neogene times.
The volcanic complex of Nevados de Chillán, located in the Southern Volcanic Zone (SVZ) of the Andes, has been active for the past 640 ± 20 ka. Its volcanic activity includes dome forming eruptions, ...explosive events, and lava flows. The most recent eruption cycle started in January 2016. We employ DInSAR time-series from Sentinel-1 data to investigate the unrest episode from January 2019 to November 2020. Two distinct periods of unrest are recognized in the time series. The first period (from January to October 2019) coincides with explosive events, dome growth inside the active crater, and a decrease in seismic activity but does not present a significant deformation. The second period (October 2019 to November 2020) is characterized by a displacement towards the sensor's line-of-sight of 100–120 mm. The observed surface deformation is compatible with an inflation source approximately 1.5 km south-southwest of the present active vent, at 5.5 ± 0.5 km depth from the surface, and with a volume change of 0.044 ± 0.014 km3. The most likely explanation for the observed inflation of Nevados de Chillan is the intrusion of magma in a reservoir feeding the current eruption cycle.
Display omitted
•DInSAR time-series from Sentinel-1 data from the latest episode of volcanic unrest.•Modeling inversion.•New injection of magma.
The Varvarco Volcanic Field (VVF) is located in the southern part of the Las Loicas Trough, as part of the Late Pliocene-Early Pleistocene rear-arc volcanic belt in the Transitional Southern Volcanic ...Zone (34.5–37°S). Its volcanic products show an elliptical distribution, elongated parallel to NW-SE main structures that regionally controlled the Las Loicas Trough. A detailed field and petrographic study was carried out to identify main lithofacies and establish its eruptive styles.
The VVF magmatic evolution is initially characterized by a voluminous explosive stage represented in the area by dense and dilute pyroclastic density currents (PDC) deposits (massive lapilli tuffs, cross-stratified lapilli tuffs and diffuse-stratified tuffs). Afterwards, it evolved into an effusive stage represented by basaltic lava flows (coherent basalts), associated with Hawaiian to Strombolian eruptive style, which constitutes most of the VVF volume. The final stage of the VVF history was linked to a stratovolcano-type activity where both effusive (coherent basalts and andesites, and rhyolitic coulees) and explosive lithofacies (such as massive lithic breccias and massive lapilli tuffs) are described. Within this stage, the uppermost effusive levels were intruded by dacitic and rhyolitic domes and basaltic dykes. Available ages allow to conclude that the VVF emplacement was developed during Plio-Pleistocene times, linked to the re-steepening of the Nazca plate, after the Late Miocene Payenia shallow subduction regime.
•The VVF is a Plio-Pleistocene rear-arc volcanic field of the Southern Volcanic Zone.•Volcanic activity initiated with PDCs during an explosive stage.•Volcanism evolved into a voluminous effusive stage represented mainly by basaltic lavas.•Finally, effusive and minor explosive stratovolcano-type activity occurred.
The Southern Central Andes developed though a complex succession of magmatic and deformational episodes, which after more than a century of studies, are still the subject of intense debate. One of ...the main controversies lies in the ambiguity regarding whether there was a single contractional phase in the Neogene or whether there were multiple contractional phases distributed over the last ∼110 My. We present 33 new K/Ar ages obtained from retroarc subvolcanic intrusives and lava flows and document their crosscutting relations with the host rock strata. These data enabled us to constrain the deformation's timing in several contractional structures along the eastern slope of the southern Central Andes ∼36.5°S. In the hinterland, the timing of compressional deformation has been constrained to the following: between Late Cretaceous and late Miocene age determined by Neogene dikes crosscutting Mesozoic folded strata; pre to syn-late Miocene determined by dikes intruded in the axial surfaces of small anticlines; and post-early Oligocene determined by folded sills. In the foreland, the timing of compressional deformation has been constrained to between the Late Cretaceous and early Oligocene by dikes crosscutting pre-deformed strata; to the post-Oligocene by folded sills; to the pre- and post-middle Eocene by Eocene to Miocene dikes crosscutting older folded strata; and to the post to syn-middle Miocene by folded lava flows. We conclude that two pre-Neogene and one Neogene contractional phases, and various retroarc magmatic events have affected this segment of the retroarc. We discuss our observations in relation to previous proposals, separating the tectonic evolution of the area into six tectonic scenarios from the late Early Cretaceous to the present.
Display omitted
•Main Neogene structures in the southern Central Andes show previous deformation.•Foreland structures show deformation between Late Cretaceous and late Eocene.•Hinterland structure shows deformation between early Oligocene and late Miocene.•Voluminous middle Eocene to the early Miocene magmatism affected the orogenic front.
Desertification of Central Patagonia began between ~14–12 Ma and therefore was not directly connected to the opening of the Drake Passage and initial conformation of the Antarctica ice cap in early ...Miocene times. Local processes, in particular the uplift of the Southern Andes, seem to have played a major role in climatic and biotic changes. We studied synorogenic strata filling a partly cannibalized foredeep between ~45° and 47°S at the latitudes of the Chile triple juction. Older synorogenic successions have yielded 18.7–16.4 Ma (U-Pb) in the western sector of the North Patagonian Cordillera corresponding to Meseta Guadal, Jeinemeni and Alto de Río Cisnes sections. This uplift was partly contemporaneous with broken foreland deformation associated with the San Bernardo fold belt to the east at 17.7–15 Ma. Younger synorogenic successions of 13.5 Ma (U-Pb), associated with a short pulse of major uplift that gave way to deposition of a thick conglomeratic succession, and subsequently finer-grained deposits of 12.3 Ma, are on the eastern Andean front in the Chalía and Guenguell sections, implying a retraction in orogenic activity, and out-of-sequence growth of the Patagonian Cordillera. Consequently, contractional deformation in this area ended after ~12 Ma, sealed by the extrusion of extensive alkali flood basalts, indicating that Neogene shortening only lasted ~6 My, ending around 6 My before the subduction of the Chile Ridge at the latitudes of Central Patagonia and 4.5 My before subduction at the southern tip of South America.
•We studied Neogene synorogenic strata in the Patagonian foredeep between 45 and 47°S•Older synorogenic successions have yielded 18.7–16.4 Ma (UPb)•Contractional deformation ended after ~12 Ma•Neogene shortening only lasted ~6 My•Neogene shortening ended 4.5 My before subduction of the Chile Ridge in South America
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