Payenia Volcanic Province Research Articles

Two million years of evolution of the southern central andes retroarc, Payenia Volcanic Province, Argentina, from the study of the Cerro Nevado Volcanic Complex

New K–Ar ages, major and trace element analyses, and Sr and Nd isotopic data for the Cerro Nevado Volcanic Complex (CNVC) coupled with those previously published allow us to better document the hot thermal anomaly which affected the upper mantle beneath the Andean back-arc Payenia Volcanic Province and generated alkaline magmatism. These data, along with previously published ones from this and neighbor volcanic centers, suggest that this anomaly stagnated there, during at least the last 2 million years. Geochemical features from the CNVC basaltic magmas indicate that they were sourced within an OIB-type mantle with an EMI signature, similar to that underlying the neighboring Auca Mahuida Shield Volcano to the south, and attributed to the rise of a mantle thermal anomaly. We identify at least five events of partial melting and seven eruptive phases from 1.88 to 0.75 Ma. Continental crust contamination in the San Rafael Block crustal basement occurred coupled with fractional crystallization processes, probably in magma chambers and across several cycles, producing the trachybasaltic, trachyandesitic and trachytic magmas of the Cerro Nevado volcanic cone (1.34–1.22 Ma).

Mantle Xenoliths from Huanul Volcano (Central-West Argentina): A Poorly Depleted Mantle Source under Southern Payenia

Huanul is a shield volcano with several lava flows hosting mantle xenoliths erupted during the Pleistocene (0.84 ± 0.05 Ma). It is located in the southern part of the Payenia Volcanic Province, which is among the largest Neogene-Quaternary volcanic provinces of South America. The volcanism here has been ascribed as the northernmost expression of the back-arc volcanism of the Andean Southern Volcanic Zone. We present the first petrographic and mineral chemistry study of mantle xenoliths collected from Huanul lavas with the aim of reconstructing directly the mantle source of the Payenia Volcanic Province. Xenoliths are commonly small (<5 cm in radius) but scarcely crossed by basaltic veins. All xenoliths have a fertile lherzolitic modal composition and are equilibrated in the spinel-facies. Most of them exhibit an almost primitive-mantle geochemical affinity, characterized by slightly depleted clinopyroxene REE patterns reproducible by partial melting degrees between 0 and 4% of a PM source. Geothermobarometric P-T estimates of clinopyroxene-orthopyroxene couples form a linear trend between 10 and 24 kbar with constant increase of T from 814 to 1170 °C along a 50–60 mW/m2 geotherm. Evidences of interaction with the host basalts occur as spongy textures in clinopyroxene and reacted spinel, which tend to became more restitic in composition and show chromatographic or complete overprinting of the trace element compositions. The presence of plagioclase and calculated P-T values constrain this melt/rock reaction process between 6 and 14 kbar, during magma ascent, and fit the mantle adiabat model. Calculated melts in equilibrium with the primary clinopyroxenes do not fit the composition of the host basalt and, together with the geothermobarometric estimations, point to an asthenospheric mantle source for the magmatism in southern Payenia. The PM geochemical affinity of the xenoliths of Huanul is an extremely rare finding in the South America lithospheric mantle, which is commonly extensively refertilized by subduction-derived melts.

Relationships between Payenia volcanism and deep-seated structural controls: Insights from geophysical methods at Nevado volcanic field, Mendoza, Argentina

The Nevado Volcanic Field (NVF), in southern Mendoza foothills, is part of the Payenia Volcanic Province, a large Quaternary retro-arc volcanic area composed principally of basaltic lava flows and monogenetic volcanoes. Monogenetic volcanism location, distribution and evolution are extremely sensitive to previous rheological discontinuities or faults affecting their basement. With the aim of exploring the subsurface configuration and contributing to a better understanding of this volcanism, we analysed and interpreted aeromagnetic and gravity datasets in addition to structural and volcanic alignments information. Our results show that location of volcanism would have been mainly controlled by NW-SE trending structures. These structures would extend at least to middle crust levels. On the other hand, a secondary control might be related to crustal domains with different densities, which could have affected magma propagation to the surface, hence, controlling the spatio-temporal distribution of volcanoes. The complex interplay between these factors would be responsible for the distribution of volcanic centres. Finally, we discuss the implications of these controls concerning the tectonic stress regime contemporaneous with volcanic activity.

The Signature of Metasomatized Subcontinental Lithospheric Mantle in the Basaltic Magmatism of the Payenia Volcanic Province, Argentina

AbstractThe Payenia region of Argentina (34.5–38°S) is a large Pliocene‐Quaternary volcanic province of basaltic compositions in the Andean Cordillera foothills representing the northernmost extent of back‐arc volcanism in the Andean Southern Volcanic Zone (SVZ). Although the chemical diversity of the Payenia basalts has been characterized previously, the processes and sources responsible for such variation remain controversial. Here, we report new whole‐rock major and trace element concentrations, Sr‐, Nd‐, Hf‐, and Pb‐isotope ratios and high‐precision olivine oxygen‐isotope ratios in a suite of 35 alkaline basalts from Payenia. These lavas have major and trace elements that define a compositional range from arc‐influenced to intraplate signature. Variable crustal contamination and/or recent slab‐derived inputs inadequately account for elemental and isotopic systematics and spatial compositional variations of Payenia lavas. We present a simple forward model indicating that early metasomatism and subsequent melting of the metasomatized subcontinental lithospheric mantle (SCLM) has significantly contributed to the Payenia lava compositional range. Isotopic ingrowth calculations of radiogenic Sr, Nd, Hf, and Pb suggest that the SCLM metasomatism occurred at 50–150 Ma, consistent with the timing of the breakup of Gondwana and the development of the proto‐Pacific Andean arc. Variations in δ18Oolivine values from modeled melts indicate that the metasomatism and melting within the SCLM can fractionate oxygen isotopes even when the metasomatizing melt has MORB‐like δ18O values, providing a different explanation for the low‐δ18O signatures observed in continental arc settings.

Volcanic spherules condensed from supercritical fluids in the Payenia volcanic province, Argentina

Spherules can be formed by high-temperature processes during volcanic eruptions, lightning strikes and meteorite impacts. Here we report four different types of spherules and spheroidal particles associated with tephra deposits from two separate volcanic fields in the southern Payenia province of Argentina. These silicate and carbonate spherules represent <0.01% of the sampled material, with individual spherules <200 µm in size. Thirty particles were imaged. Only the transparent spherules are smooth, perfect spheres; other morphologies include ellipsoids and aggregated dumbbells. The spheroids are either hollow or solid. Major element analyses show that the spherules and spheroids have silica-rich, Fe-rich, carbonate and basaltic compositions. Chemical analysis of the carbonate spheroids shows some variability in the trace element content between the cores and rims, suggesting element mobility and loss towards the margins. All the analysed carbonate spheroids have elevated Sr/Y, La/Y and La/Ce ratios outside the range for sedimentary carbonates. All four spherule types are considered to be volcanic in origin, with the excess CO 2 required for the formation of the carbonate spherules potentially sourced from the basement lithologies. Based on the major and trace element analyses, we conclude that the silica-rich and carbonate spherules formed by instantaneous condensation from supercritical CO 2 -rich hydrous fluids saturated with dissolved silicates. Supplementary material : Appendix A, containing the full analytical dataset collected by electron probe microanalysis and secondary ion mass spectrometry, is available at https://doi.org/10.6084/m9.figshare.c.5108689

Volcanología y geocronología de extensos flujos basálticos neógeno cuaternarios del sureste de Payenia, centro-oeste de Argentina

The basaltic lava flows located in the southeast of Payenia Volcanic Province, Argentina, show lengths between 40 and 181 km. These flows have transversal sections characterized by external vesicular crusts that surround a massive core hosting vesiculated structures. These characteristics defined them as P-type pahoehoe flows. Based on their surface topography, 2 types of flows were determined: sheet flows and hummocky flows. The first were emplaced through inflation and lateral coalescence of lobes in the front of the flow, giving rise to flat roofs and large lateral width. The second ones exhibit a microrelief given by local inflation structures (e.g., tumuli). It is proposed that the lava flows were initially emplaced as sheet flows on low angle slopes (

Volcanology and inflation structures of an extensive basaltic lava flow in the Payenia Volcanic Province, extra-Andean back arc of Argentina

The El Puesto lava flow is located in the Payenia Volcanic Province (central-western Argentina), has a length of 70 km and is Middle Pleistocene in age (0.200±0.027 Ma). The flow shows a P-type pahoehoe structure and exhibits several inflation structures, mainly tumuli and also inflation ridges and lava rises. Lava rise pits and radial or annular clefts are common features associated with inflation structures. The gentle slope on which the flow moved (≈0.5°) allowed the lateral coalescence of lobes at the flow front and the development of an external rigid crust that insulated the liquid core. Lava tunnels are frequent and the lava tunnel named “Cueva de Halada” which is located at its medium portion is the best example of a drainage master tube which formed from the cooling of the crust around a stable inflated flow. Tumuli alignments and long inflation ridges reveal the existence of larger tunnels within the flow. Inflation structures may occur in high concentration belts that converge on a single main belt which is assigned to an anastomosed network of internal flow pathways within the main lava body. The development of inflation structures and lava tunnels require low to moderate effusion rates. An average lava supply rate of 1.8x10-4 m3/s and an inflation time of about 15 days were estimated for an average tumulus of this flow. A high and sustained supply of low viscosity lava (η’=1550 - 483 Pa s) was inferred that initially generated a sheet flow of great areal extension. The reduction in effusion rates could then allowed the development of tunnels that carried lava to the distal fronts, generating localized inflation phenomena throughout the lava flow.

El Pozo Volcanic Complex: Evolution of a group of maars, central Mendoza province, Argentina

The El Pozo Volcanic Complex, in the south-central Mendoza province, is formed by three maars, the first to be described in the Payenia Volcanic Province and one of the few examples in Argentina. The maars of El Pozo Volcanic Complex (1, 2 and 3) show large craters (0.97 km, 1.2 km and 0.96 km, respectively) and their depth is between 10 and 57 m below the pre-eruptive surface. Their deposits are described from the only outcrops that have been found, called El Pajarito and El Visitante. It was interpreted that the first maar to be formed would have been No. 2, from which only the deposits corresponding to El Pajarito (3.6 m) and the lower section of El Visitante (28 m) are preserved. We suggest that its shape is the result of lateral vent migration and coalescence of successive vents. Then, after a short break represented by the angular unconformity in the El Visitante section, the active vent would have shifted more to the W and the maar No.3 is thought to have been formed. The activity of this maar is represented in El Visitante upper section, with features resulting from the presence of water in the time of deposition. Maar No. 1 was probably active simultaneously with maar no. 3, with which coalesces but the lack of outcrops does not guarantee this affirmation. Towards the end of the eruptive cycle, depletion of water produced a change in activity from phreatomagmatic to Strombolian and effusive. This gave rise to the nested pyroclastic scoria cone, El Pozo cone, which lies in the maars' 1 and 3 craters floors. El Pozo cone is related to lava flows with a tumulus and the deposit of a lapilli-bearing tephra plume.

Crustal and Mantle Structure Beneath the Southern Payenia Volcanic Province Using Gravity and Magnetic Data

AbstractThe Auca Mahuida volcanic field lies on the southernmost Payenia Volcanic Province, one of the broadest retroarc volcanic plateaux in the southern Central Andes (~38°S). This voluminous basaltic flooding of Quaternary age was originated from a deep asthenospheric source, interpreted as a mantle plume product of changing slab dynamics. The geometry of this source is deduced from magnetotelluric data, but the limited spatial coverage of this array does not allow a detailed resolution of this anomaly. In order to present a detailed geometry of the conductive anomaly and related crustal magmatic bodies, we used multiple data sources. We combined Magnetic and Bouguer anomalies, Curie isotherm depth (Tc), Elastic Thickness (Te) and Moho depth derived from the Global Earth Magnetic Anomaly Grid (EMAG2) and terrestrial gravity measurements, all together in a holistic geophysical analysis. The magnetic data depict a nearly 200‐km‐in‐diameter circular anomaly that would correspond to a dense body according to the Bouguer anomaly. Geoid data from the Gravity Field Model (EIGEN‐6c4) have been filtered in order to isolate deeper mass influences and visualize the asthenospheric upwelling previously described from magnetotelluric data. Moho inversion yields a crustal attenuation at 36‐ to 32‐km depth coinciding with Te below 20‐km depth and a shallow Tc (≤15‐km depth) at the site where Geoid positive undulation was calculated. Finally, surface analysis allowed defining a topographic swell, compatible with the dimensions of the identified magnetic anomaly, where the main rivers deviated, potentially due to a recent base level change.

3-D crustal-scale gravity model of the San Rafael Block and Payenia volcanic province in Mendoza, Argentina

The San Rafael Block (SRB) is part of one of the main retroarc volcanic provinces in southern Central Andes in Mendoza, Argentina. This block is located in the Andean foothills between the orogenic front and foreland basement uplifts of late Miocene age. In order to analyze the geochronological evolution of the Quaternary volcanism in the region, several geologic and geophysical studies have been conducted. Nevertheless, the crust, where the SRB is located, has not been well characterized yet.Based on gravimetric and magnetic data, together with isostatic and elastic thickness analyses, we modeled the crustal structure of the area. Information obtained has allowed us to understand the crust where the SRB and the Payenia volcanic province are located. Bouguer anomalies indicate that the SRB presents higher densities to the North of Cerro Nevado and Moho calculations suggest depths for this block between 40 and 50 km. Determinations of elastic thickness would indicate that the crust supporting the San Rafael Block presents values of approximately 10 km, being enough to support the block loading. However, in the Payenia region, elastic thickness values are close to zero due to the regional temperature increase.

The temporal evolution of back-arc magmas from the Auca Mahuida shield volcano (Payenia Volcanic Province, Argentina)

In order to better constrain the temporal volcanic activity of the back-arc context in Payenia Volcanic Province (PVP, Argentina), we present new K–Ar dating, petrographic data, major and trace elements from 23 samples collected on the Auca Mahuida shield volcano. Our new data, coupled with published data, show that this volcano was built from about 1.8 to 1.0Ma during five volcanic phases, and that Auca Mahuida magmas were extracted from, at least, two slightly different OIB-type mantle sources with a low partial melting rate. The first one, containing more garnet, was located deeper in the mantle, while the second contains more spinel and was thus shallower. The high-MgO basalts (or primitive basalts) and the low-MgO basalts (or evolved basalts), produced from the deeper and shallower lherzolite mantle sources, respectively, are found within each volcanic phase, suggesting that both magmatic reservoirs were sampled during the 1Myr lifetime of the Auca Mahuida volcano. However, a slight increase of the proportion of low-MgO basalts, as well as of magmas sampled from the shallowest source, can be observed through time. Similar overall petrological characteristics found in the Pleistocene–Holocene basaltic rocks from Los Volcanes and Auca Mahuida volcano suggest that they originated from the same magmatic source. Consequently, it can be proposed that the thermal asthenospheric anomaly is probably still present beneath the PVP. Finally, our data further support the hypothesis that the injection of hot asthenosphere with an OIB mantle source signature, which was triggered by the steepening of the Nazca subducting plate, induced the production of a large volume of lavas within the PVP since 2Ma.

Payenia Quaternary flood basalts (southern Mendoza, Argentina): Geophysical constraints on their volume

The Quaternary volcanic province of Payenia is located in southern Mendoza and northern Neuquén provinces of Argentina and is characterized by a dominant basaltic composition. The volcanic province covers an area larger than 40,000 km2 and its origin and evolution has been the center of several studies. In this study we analyzed gravity data together with more accurate volcanic volumes calculations in order to investigate the subsurface structure of the Payenia volcanic province. The volume of material was calculated using digital elevation models and geographic information system (GIS) techniques to estimate the volume of material erupted and then, with those values, make an estimation of the intrusive material that could be located within the crust. The results of the calculations were compared with different 2D-sections constructed to model the gravity data and compare with the observed satellite gravity. After evaluating different models which have been generated to match both: the observed gravity data and the subsurface material calculated, we discuss those that best fit with observation. The results clearly indicate that the lithosphere is attenuated below the region.

Olivine Major and Trace Element Compositions in Southern Payenia Basalts, Argentina: Evidence for Pyroxenite–Peridotite Melt Mixing in a Back-arc Setting

Olivine major and trace element compositions from 12 basalts from the southern Payenia volcanic province in Argentina have been analyzed by electron microprobe and laser ablation inductively coupled plasma mass spectrometry. The olivines have high Fe/Mn and low Ca/Fe and many fall at the end of the global olivine array, indicating that they were formed from a pyroxene-rich source distinct from typical mantle peridotite. The olivines with the highest Fe/Mn have higher Zn/Fe, Zn and Co and lower Co/Fe than the olivines with lower Fe/Mn, also suggesting contributions from a pyroxene-rich source. Together with whole-rock radiogenic isotopes and elemental concentrations, the samples indicate mixing between two mantle sources: (1) a pyroxene-rich source with EM-1 ocean island basalt type trace element and isotope characteristics; (2) a peridotitic source with more radiogenic Pb that was metasomatized by subduction-zone fluids and/or melts. The increasing contributions from the pyroxene-rich source in the southern Payenia basalts are correlated with an increasing Fe-enrichment, which caused the olivines to have lower forsterite contents at a given Ni content. Al-in-olivine crystallization temperatures measured on olivine–spinel pairs are between 1155 and 1243°C and indicate that the magmas formed at normal upper mantle (asthenospheric) temperatures of ∼1350°C. The pyroxene-rich material is interpreted to have been brought up from the deeper parts of the upper mantle by vigorous asthenospheric upwelling caused by break-off of the Nazca slab south of Payenia during the Pliocene and roll-back of the subducting slab beneath Payenia. The pyroxene-rich mantle mixed with peridotitic metasomatized South Atlantic mantle in the mantle wedge beneath Payenia.

Emplacement history and inflation evidence of a long basaltic lava flow located in Southern Payenia Volcanic Province, Argentina

The El Corcovo lava flow, from the Huanul shield volcano in the southern Mendoza province (central-western Argentina) traveled a distance of 70km and covered a minimum area of ~415km2. The flow emplacement was controlled both by extrinsic (e.g., topography) and intrinsic (e.g., lava supply rate, lava physicochemical characteristics) factors. The distal portion of the lava flow reached the Colorado River Valley, in La Pampa Province, where it spread and then was confined by earlier river channels. Cross-sections through the flow surveyed at several localities show two vesicular layers surrounding a dense central section, where vesicles are absent or clustered in sheet-shaped and cylindrical-shaped structures. Lavas of the El Corcovo flow are alkaline basalts with low values of viscosity.The morphological and structural characteristics of the flow and the presence of landforms associated with lava accumulation are the evidence of inflation. This process involved the formation of a tabular sheet flow up to 4m of thick with a large areal extent in the proximal sectors, while at terminal sectors frontal lobes reached inflation values up to 10m. The numerous swelling structures present at these portions of the flow suggest the movement of lava in lava tubes. We propose that this aspect and the low viscosity of the lava allowed the flow travel to a great distance on a gentle slope relief.

Sr, Nd, Pb and Hf isotopic constraints on mantle sources and crustal contaminants in the Payenia volcanic province, Argentina

The presented Sr, Nd, Hf and double-spike Pb-isotopic analyses of Quaternary basalts from the Payenia volcanic province in southern Mendoza, Argentina, confirm the presence of two distinct mantle types feeding the Payenia volcanism. The southern Payenia mantle source feeding the intraplate-type Rio Colorado and Payun Matru volcanism is isotopically distinct from the northern Payenia and arc mantle source with less radiogenic Pb and lower Sr-87/Sr-86 and Hf-176/Hf-177 for a given Nd-143/Nd-144 than the northern Payenia and arc rocks. The basalts from the northern Payenia province (Nevado volcanic field) and the retroarc zone have isotopic compositions overlapping the Andean southern volcanic zone (SVZ) arc rocks and they are probably derived from the same metasomatized South Atlantic N-MORB-like mantle source. A high field strength element melting model suggests addition of similar to 1-2% upper continental crustal material to the mantle source of the Nevado basalts and the transitional SVZ arc and retroarc rocks and similar degrees of melting throughout this arc segment. A gradual depletion of the pre-metasomatic mantle source going from the backarc over the retroarc to the arc is indicated. The depletion is suggested to be caused by step-wise melt extraction due to repeated injections of subduction zone fluids and melts. The lower crustal contamination trends found in the trace element variations of basalt groups from all parts of the Payenia province are also recognized in isotopic space and the dominant isotope assimilation trends indicate lower crustal contaminants with more unradiogenic Pb, lower Nd-143/Nd-144 and Hf-176/Hf-177 and higher or similar 87Sr/86Sr as the mantle melts. These characteristics are similar to those found in lower crustal xenoliths from the northern Proterozoic Cuyania terrane, and the Payenia basalts may have been contaminated by this type of crust during passage through the lithosphere or by more recently underplated or intruded material.

Melt–peridotite reactions in upwelling eclogite bodies: Constraints from EM1-type alkaline basalts in Payenia, Argentina

The processes of magma generation in upwelling eclogite bodies of recycled lithospheric material are not fully understood but are important for our understanding and modelling of major and trace element variations in many ocean island basalts (OIB). The primitive alkaline intraplate basalts from the Payenia volcanic province (34–38 °S) in Argentina, for which Sr, Nd and double-spike Pb isotope ratios are presented, and from other north Patagonian volcanic fields may provide details of the eclogite melt–peridotite reactions taking place in the melting column of an upwelling OIB-type mantle. The isotopic composition of the uncontaminated lavas is highly restricted but the Payenia basalts fall in two distinct trace element groups termed the high and low Nb/U groups, which both have EM1-type trace element patterns but with subtle differences that cannot be explained by contamination, fractionation or simple variations in degrees of mantle melting. The difference is also clear in major elements where the low Nb/U basalts have markedly higher alkali contents but lower FeO and Ni than the high Nb/U basalts. Four melt components have been identified based on olivine fractionation corrected compositions: a low Nb/U pyroxenite melt component which is interpreted as an eclogite melt that experienced low degrees of melt–peridotite interaction, a high Nb/U pyroxenite melt component which is interpreted as an eclogite melt that experienced high degrees of melt–peridotite interaction, a low pressure peridotite melt component which contributes to most high Nb/U, Payún Matrú, Matancilla and Auca Mahuida basalts and finally, a melt component with similarities to peridotite melts contributing to many low Nb/U lavas. The high Nb/U type basalts are interpreted to have been formed from mantle with higher temperature than ambient mantle while the low Nb/U basalts may have been formed from normal temperature mantle.

Terrain characterization and structural control of the Auca Mahuida volcanism (Neuquén Basin, Argentina)

Geomorphometric parameters (slope, aspect, valley depth, and areal density of cones) derived from a moderate resolution digital elevation model with a grid spacing of 100 m are used in an attempt to interpret the tectonic/structural features related to surface deformation in the Auca Mahuida volcanic terrain (Neuquén Basin, Argentina). The Auca Mahuida (2.03–0.88 Ma) is the southernmost volcanic field of the Payenia volcanic province, in the Andean foreland. The foreland is subjected to an E–W compression related to the eastward migration of the N–S striking thrust front of the Andes. The geomorphometric analysis indicates that the Auca Mahuida consists of a basal, E–W elongated lava field with monogenic vents and a summit, polygenic, also E–W elongated, cone. A N100°E striking fault controls the southern flank of the field, which is also affected by scarps related to erosional and gravity-controlled processes. The drainage network shows a pseudo-radial pattern around the summit cone, and the Auca Mahuida's deepest valley is structurally controlled by a NNW–SSE striking fault affecting the sedimentary basement. The volcanic field lies on a NE to E dipping substratum. The areal distribution of the monogenic cones is consistent with ascent of magmas along E–W striking fractures, and with elastic models of a pressurized hole (magma chamber) subjected to an E–W compression. At Auca Mahuida, the ascent of melts from the mantle is controlled, in the overriding crust, by tectonic structures formed in response to the E–W compression of the Andes.

Payenia volcanic province, southern Mendoza, Argentina: OIB mantle upwelling in a backarc environment

The Pleistocene to Holocene Payenia volcanic province is a backarc region of 60,000km2 in Mendoza, Argentina, which is dominated by transitional to alkaline basalts and trachybasalts. We present major and trace element compositions of 139 rocks from this area of which the majority are basaltic rocks with 4 to 12wt.% MgO and 44 to 50wt.% SiO2. The southern Payenia province is dominated by intraplate basalts and the trace element patterns of the Río Colorado and Payún Matrú lavas suggest little or no influence from subducted slab components. The mantle source of these rocks is similar to some EM-1 ocean island basalts. In contrast, the magmas from the northern Payenia province and the Andean retroarc occurrences have received an important input from the subducting slab and their trace element patterns are transitional between intraplate and arc rocks. These magmas are mainly derived from another asthenospheric mantle source which may be similar to normal MORB mantle. The Nevado and Northern Segment basalts have presumably been formed above a shallowly subducting slab and the progression of volcanism from south to north and northwest along the San Rafael block likely marks the downwarping of the slab and the end of the shallow subduction period. The downwarping slab may have generated an enhanced mantle upwelling of both the intraplate and the MORB-like mantle sources.In samples from almost all parts of the Payenia province and in particular many Nevado, Llancanelo and older Payún Matrú basalts, trace element variations suggest a significant contribution from lower crustal melts, possibly up to 70% in the most extreme cases. The contaminating lower crustal rocks must have been depleted mafic rocks with a plagioclase component. The extensive melting of lower crust is probably related to the low thickness of the lithospheric mantle and preheating of the lower crust by earlier Mio-Pliocene volcanism. Rare earth element modelling of mantle melting calls for enriched source compositions and a beginning of melting within the garnet stability field for all Payenia basalts. The Río Colorado and Payún Matrú basalts indicate high solidus pressures around 3–3.1GPa which requires either a thermal or compositional mantle anomaly. The model suggests a thinner lithosphere in the western Payenia region compared to the eastern.

Geochronology of the late Pliocene to recent volcanic activity in the Payenia back-arc volcanic province, Mendoza Argentina

Abstract Eighteen samples originating from monogenetic cones and larger complexes in the back-arc Payenia volcanic province, in Mendoza Argentina, have been dated by the 40 Ar/ 39 Ar method. Groundmass and plagioclase separates give plateau ages, ranging from 20.7 ± 0.5 to 0.06 ± 0.02 Ma. Payenia has been divided into six subfields based on the new and literature radiometric ages: Payun Matru, Rio Colorado, Llancanelo, and Nevado volcanic fields, the Northern segment and the Andes retro-arc group. Fifteen samples are younger than 2.83 Ma and show correlation between geographic position and age. Eruption centres younger than 0.5 Ma are concentrated to the west of 69° W with few exceptions among new and literature data. This westward shift of activity supports the rollback theory for the subducting Nazca plate since the late Pliocene. Furthermore, a northward progression of volcanism on the San Rafael block from 2.8 Ma to around 0.5 Ma is recognized. We conclude that rollback was initiated in the southern part of Payenia in the early Pliocene and progressed >200 km northwards during the Pliocene-Pleistocene period creating conditions for hydrous magma generation beneath the eastern part of Payenia. The long lived activity of the Payun Matru complex is ascribed to the presence of a thermal anomaly in the underlying asthenosphere which could be plume-like.

Payenia volcanic province in the Southern Andes: An appraisal of an exceptional Quaternary tectonic setting

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.