Southern Puna Plateau Research Articles

Imaging a magma plumbing system from MASH zone to magma reservoir

The Puna Plateau of the Central Andes is a well-suited location to investigate the processes associated with the tectono-magmatic development of a Cordilleran system. These processes include long-lived subduction (including shallow and steep phases), substantial crustal thickening, the emplacement of large volumes of igneous rocks, and probably delamination. To elucidate the processes associated with the development of a Cordilleran system, we pair Common Conversion Point-derived receiver functions with Rayleigh wave dispersion data from Ambient Noise Tomography. The resulting high-resolution shear wave velocity model of the southern Puna Plateau reveals the details of a lithospheric-scale magma plumbing system. Slow velocities near the crust–mantle transition are interpreted as a MASH zone (a partially molten zone where mantle-derived melts interact with the lithosphere and undergo density differentiation) with ∼4–9% melt. After differentiation, less dense and presumably more felsic melts propagate to shallower depths within the crust (∼20 km below surface) and comprise vertically (∼10 km) and laterally (∼75 km) extensive slow velocity bodies that span the frontal arc and plateau interior. These large slow velocity bodies represent a partially molten mid-crust (up to 22%) where magma can further evolve to higher silica concentrations. The periodic influx of melt from the underlying MASH zone into these mid-crustal bodies may serve as a trigger to the eruption of the voluminous ignimbrites observed in the southern Puna Plateau. Many of the active tectonic processes operating along the southern Puna Plateau are thought to be analogous to the processes that formed the North American Cordillera. Thus, these results could provide insight into some of the processes associated with the development of a Cordilleran margin.

Sedimentary record of regional deformation and dynamics of the thick-skinned southern Puna Plateau, central Andes (26–27°S)

The Puna Plateau, adjacent Eastern Cordillera and the Sierras Pampeanas of the central Andes are largely characterized by thick-skinned, basement-involved deformation. The Puna Plateau hosts ∼N–S trending bedrock ranges bounded by deep-seated reverse faults and sedimentary basins. We contribute to the understanding of thick-skinned dynamics in the Puna Plateau by constraining regional kinematics of the poorly understood southern Puna Plateau through a multidisciplinary approach. On the southeastern plateau, sandstone modal composition and detrital zircon U–Pb and apatite fission-track data from Cenozoic strata indicate basin accumulation during the late Eocene to early Oligocene (∼38–28 Ma). Provenance analysis reveals the existence of a regional-scale basin covering the southern Puna Plateau during late Eocene to early Oligocene time (∼38–28 Ma) that was sourced from both the western plateau and the eastern plateau margin and had a depocenter located to the west. Petrographic and detrital zircon U–Pb data reveal erosion of proximal western and eastern sources after ∼12 Ma, in mid-late Miocene time. This indicates that the regional basin was compartmentalized into small-scale depocenters by the growth of basement-cored ranges continuing into the late Miocene (∼12–8 Ma). We suggest that the Cenozoic history of the southern Puna Plateau records the formation of a regional basin that was possibly driven by lithospheric flexure during the late Eocene to early Oligocene, before the growth of distributed basement-cored ranges starting as early as the late Oligocene.

Late Miocene upper-crustal deformation within the interior of the southern Puna Plateau, central Andes

The origin and evolution of the central Andes, a noncollisional orogenic system, have been hypothesized to evolve as a result of several dynamic processes, including formation of an eastward-propagating orogenic wedge, segmentation into rhomb-shaped basins as a result of N-S gradients in crustal shortening, reactivation of inherited deep structures, and lithospheric foundering. How these proposed processes dominate the orogen spatially and temporally is uncertain; however, constraining the timing of upper-crustal deformation is critical for investigating these models. We document the formation and deformation of the Pasto Ventura basin (NW Argentina) in the southern Puna Plateau. Through field mapping, deformation analysis, secondary ion mass spectrometry U-Pb dating of zircon from interbedded volcanic ashes, and Ar/Ar geochronology of volcanics, we show that major basin formation started ca. 11.7-10.5 Ma and continued until at least ca. 7.8 Ma. The basin underwent syndepositional faulting and folding from ca. 10 to 8 Ma. Contractional deformation in the Pasto Ventura basin ended between ca. 7.3 and 4 Ma, based on the onset of regional horizontal extension. Data from the Pasto Ventura region allow us to bridge existing data and complete a regional compilation of upper-crustal deformation for the Puna Plateau. Our analysis shows that late Miocene formation and deformation of the Pasto Ventura basin represent an important out-of-sequence contractional event in the southern Puna Plateau. While a number of geodynamic processes likely shape the evolution of the southern Puna, multidisciplinary data sets, including deformation in the Pasto Ventura basin studied here, highlight the role of the formation and detachment of a late Miocene lithospheric drip in causing the upper-crustal deformation on the southern Puna Plateau since the mid-late Miocene.

Shear wave splitting and shear wave splitting tomography of the southern Puna plateau

Fil: Calixto, Frank J.. University of Missouri-Columbia. Department of Geological Sciences; Estados Unidos

Central Andean mantle and crustal seismicity beneath the Southern Puna plateau and the northern margin of the Chilean‐Pampean flat slab

AbstractEarthquake hypocenters recorded in the Andean Southern Puna seismic array (25–28°S, 70–65°W) provide new constraints on the shape of the subducting Nazca plate beneath the Puna plateau, the transition into the Chilean‐Pampean flat slab and the thermal state of the mantle and crust. Some 270 new mantle hypocenters suggest that the subducting slab under the Puna shoals into the flat‐slab segment more abruptly and farther to the north than previously indicated. The revised geometry is consistent with the Central Volcanic Zone Incapillo caldera being the southernmost center with Pleistocene activity until reaching the southern side of the flat‐slab region. Evidence for the revised slab geometry includes three well‐defined hypocenter clusters in the Pipanaco nest (27.5–29°S, 68–66°W), which are interpreted to reflect slab‐bending stresses. A few low‐magnitude earthquakes with strongly attenuatedSwaves in the long‐recognized Antofalla teleseismic gap (25.5–27.5°S) support a continuous slab under the Southern Puna. The paucity of gap earthquakes and the presence of mafic magmas are consistent with a hot mantle wedge reflecting recent lithospheric delamination. Evidence for a hot overlaying Puna crust comes from new crustal earthquake hypocenters concentrated at depths shallower than 5 km. Two notable short‐duration swarms were recorded under the resurgent dome of the ~2 Ma back‐arc Cerro Galán caldera and the near‐arc Cerro Torta dome. New crustal earthquake focal mechanisms from 17 events in the array along with two existing mechanisms have strike slip, oblique reverse, and oblique normal solutions fitting with regional E‐W compression and N‐S extension.

Delamination of southern Puna lithosphere revealed by body wave attenuation tomography

AbstractThe southern Puna Plateau has been proposed to result from a major Pliocene delamination event that has previously been inferred from geochemical, geological, and some preliminary geophysical data. Seventy‐five seismic stations were deployed across the southern Puna Plateau in 2007–2009 by scientists from the U.S., Germany, Chile, and Argentina to test the delamination model for the region. The Puna passive seismic stations were located between 25 and 28°S. Using the seismic waveform data collected from the PUNA experiment, we employ attenuation tomography methods to resolve both compressional and shear quality factors (Qp and Qs, respectively) in the crust and uppermost mantle. The images clearly show a high‐Q Nazca slab subducting eastward beneath the Puna plateau and another high‐Q block with a westward dip beneath the Eastern Cordillera. We suggest that the latter is a piece of delaminated South American lithosphere. A significant low‐Q zone lies between the Nazca slab and the South American lithosphere and extends southward from the northern margin of the seismic array at 25°S before vanishing around 27.5°S. This low‐Q zone extends farther west in the crust and uppermost mantle at the southern end of the seismic array. The low‐Q zone reaches ~100 km depth beneath the northern part of the array but only ~50 km depth in the south. Lateral variations of the low‐Q zone reflect the possible mechanism conversion between mantle upwelling related to delamination and dehydration. The depth of the Nazca slab as defined by Q images decreases from north to south beneath the plateau, which is consistent with the steep‐flat transition of the angle of the subducting slab as defined by previous earthquake studies.

Structure of the crust and the lithosphere beneath the southern Puna plateau from teleseismic receiver functions

We present a teleseismic P and S receiver function study using data from a temporary passive-source seismic array in the southernmost Puna plateau and adjacent regions. The P receiver function images show the distribution of crustal thickness and Vp/Vs ratio for this area. Over much of the southern Puna plateau, the crustal thickness is 50–55 km, whereas to the west a thicker crust (∼60 to 75 km) is observed beneath much of the Andean volcanic arc region. From the Puna southward, there is little obvious change in the crustal thickness across the border of the plateau (south of 28°S). The crust is seen to progressively thin towards the east in the Pampean Ranges where it is 35–40 km thick. The southern Puna plateau is characterized overall by a low crustal Vp/Vs ratio (less than 1.70), implying a felsic crustal composition. An anomalously high Vp/Vs ratio of 1.87 is observed beneath the Cerro Galan volcanic center, in the region where a prominent crustal low-velocity zone identified below ∼10 km depth probably extends into the lower crust. The crustal thickness determined under the Cerro Galan area (59 km) is close to that of the rest of the southern Puna. The prominent high Vp/Vs ratio and low-velocity zone beneath the Galan region implies the presence of a zone of partial melt or a magma chamber is consistent with hypothesis calling for lithospheric delamination beneath the Galan caldera. A widespread crustal low-velocity layer observed beneath much of the southern Puna, correlates well with crustal low-velocity anomalies observed by teleseismic tomography. The lithosphere–asthenosphere boundary beneath the array can be clearly observed by both P and S receiver functions at depths of 70–90 km in agreement with previous studies suggesting a thin lithosphere beneath the high elevated plateau. The mantle transition zone discontinuities appear at expected depths.

Velocity structure beneath the southern Puna plateau: Evidence for delamination

The high elevation of the southern Puna plateau, the widespread melting of its crust, the gap in intermediate depth seismicity and the recent eruptions of ignimbrite complexes can be explained by delamination of the lithospheric mantle beneath it. To test this hypothesis, an array consisting of 73 broad band and short period seismic stations was deployed in the region for a period of 2 years starting in 2007. We inverted the data using the two plane wave approach and obtained 1‐D and 3‐D Rayleigh wave phase velocities. Our dispersion curve shows that at short periods (<70 s) the phase velocities are slightly higher than those of the Tibetan plateau and lower than those of the Anatolian plateau. At periods of 100–140 s we observe a low velocity zone that might be remnant hot asthenosphere below a flat slab (7–10 Ma). We estimate the average continental lithosphere thickness for the region to be between 100 and 130 km. Our three‐dimensional Rayleigh wave phase velocities show a high velocity anomaly at low frequencies (0.007, 0.008, and 0.009 Hz) slightly to the north of Cerro Galan. This would be consistent with the hypothesis of delamination in which a piece of lithosphere has detached and caused upwelling of hot asthenosphere, which in turn caused widespread alkaline‐collision related volcanism. This interpretation is also corroborated by our shear wave velocity model, where a high velocity anomaly beneath the northern edge of Cerro Galan at 130 km depth is interpreted as the delaminated block on top of the subducting Nazca slab.

Multi-stage Evolution of Late Neogene Mantle-derived Magmas from the Central Andes Back-arc in the Southern Puna Plateau of Argentina

Multi-stage Evolution of Late Neogene Mantle-derived Magmas from the Central Andes Back-arc in the Southern Puna Plateau of Argentina

Recent, slow normal and strike‐slip faulting in the Pasto Ventura region of the southern Puna Plateau, NW Argentina

Recent normal and strike‐slip faulting on the Puna Plateau of NW Argentina has been linked to lithospheric foundering, gravitational spreading, plate boundary forces and a decrease in crustal shortening from north to south. However, the timing, kinematics and rate of extension remain poorly constrained. We focus on the Pasto Ventura region (NW Argentina) located on the southern Puna Plateau and recent deformation (<1 Ma). Field mapping and kinematic analysis across offset volcanic cinder cones show that the overall extension direction is subhorizontal, is oriented NE‐SW to NNE‐SSW, and occurs at a slow, time‐integrated rate of 0.02 to 0.08 mm/yr since at least 0.8–0.5 Ma. A regional compilation from this study and existing data shows that recent extension across the Puna Plateau is subhorizontal but varies in azimuthal orientation dramatically. Data from the Pasto Ventura region are consistent with a number of models to explain normal and strike‐slip faulting on the Puna Plateau, all of which likely influence the region. Some role for lower lithospheric foundering through dripping appears to be seen based on the regional extension directions and ages of mafic volcanism in the southern Puna Plateau.

Recent, slow normal and strike-slip faulting in the Pasto Ventura region of the southern Puna Plateau, NW Argentina

[1] Recent normal and strike-slip faulting on the Puna Plateau of NW Argentina has been linked to lithospheric foundering, gravitational spreading, plate boundary forces and a decrease in crustal shortening from north to south. However, the timing, kinematics and rate of extension remain poorly constrained. We focus on the Pasto Ventura region (NW Argentina) located on the southern Puna Plateau and recent deformation (<1 Ma). Field mapping and kinematic analysis across offset volcanic cinder cones show that the overall extension direction is subhorizontal, is oriented NE-SW to NNE-SSW, and occurs at a slow, time-integrated rate of 0.02 to 0.08 mm/yr since at least 0.8–0.5 Ma. A regional compilation from this study and existing data shows that recent extension across the Puna Plateau is subhorizontal but varies in azimuthal orientation dramatically. Data from the Pasto Ventura region are consistent with a number of models to explain normal and strike-slip faulting on the Puna Plateau, all of which likely influence the region. Some role for lower lithospheric foundering through dripping appears to be seen based on the regional extension directions and ages of mafic volcanism in the southern Puna Plateau.

Dynamics of deformation and sedimentation in the northern Sierras Pampeanas: An integrated study of the Neogene Fiambala basin, NW Argentina

The thick-skinned Sierras Pampeanas morphotectonic domain of western and northwestern Argentina (27°S–33°S) is characterized by reverse-fault–bounded basement blocks that delimit internally deformed, Neogene sedimentary basins. Foreland-basin evolution in this part of the Andes is still not very well understood. For example, challenging questions exist as to how thick-skinned deformation develops, if there are distinct spatiotemporal trends in deformation and exhumation, how such deformation styles influence sedimentation patterns, and whether or not broken foreland basins are related to regional plate-tectonic processes, such as flat-slab subduction. The Fiambala basin of the northwestern Sierras Pampeanas is the largest of several intermontane basins in the transition to the southern margin of the Puna Plateau. This basin preserves a thick continental Neogene sequence that provides information on the dynamics of thick-skinned deformation and resulting sedimentation. The Fiambala basin contains ~4 km of fluvial-alluvial sedimentary rocks that comprise the Tamberia, Guanchin, and Punaschotter Formations. U-Pb geochronology of ashes intercalated within the Fiambala stratigraphic sequence demonstrates that these sedimentary rocks are late Miocene to Pliocene (8.2 ± 0.3 Ma to 3.05 ± 0.4 Ma) in age. Sedimentology and provenance data indicate that the source of the Tamberia Formation was located to the west of the modern western basin-bounding range. The Guanchin and Punaschotter Formations record input from local sources, including the modern basin-bounding range to the west and the southern Puna Plateau to the north, suggesting reorganization of the catchment area at ca. 5.5 Ma. The coarsening-upward trends recorded by the fluvial Tamberia and Guanchin Formations indicate enhanced tectonics and relief during sedimentation. The Punaschot-ter conglomerates record alluvial-fan sedimentation and local sources. Fault kinematic data document a contractional regime, characterized by E-W and NE-SW shortening, active throughout the middle-late Miocene and Pliocene. Furthermore, a comparison between the Fiambala basin and similar sedimentary basins in the Sierras Pampeanas (e.g., Bermejo foreland basin) and the Eastern Cordillera leads us to propose that the study area originally constituted an integral part of a continuous and more extensive foreland-basin system (thin-skinned) for much of its early history. Our data suggest coeval intrabasin deformation along strike from the Bermejo region northward to the Eastern Cordillera. The coeval change at ca. 6 Ma from a regional to more compartmentalized (thick-skinned) tectono-sedimentary environment in the regions adjacent to the Eastern Cordillera, the southern Puna margin, and other sectors within the Sierras Pampeanas domain may thus reflect a regional tectonic process related to flat subduction. Our data, combined with existing sedimentological and petrological evidence, imply that the passage from steep to flat subduction occurred synchronously from ~30°S to ~26°S.

40Ar/ 39Ar geochronology of mafic volcanism in the back-arc region of the southern Puna plateau, Argentina

Late Cenozoic back-arc mafic volcanism in the southern Puna plateau of Argentina offers insights into the state of the mantle under the world’s second largest continental plateau. Previous studies of the mafic magmas in this region proposed a scenario of mantle melting due to lithospheric delamination and/or steepening of the subducting slab. However, few of the centers have been precisely dated, which limits any geodynamic interpretation. We present results of laser incremental-heating 40Ar/ 39Ar dating of 22 back-arc centers in the southern Puna, with emphasis on the Salar de Antofalla region where volcanic activity was most intense. Three localities yielded ages between 7.3 and 7.0 Ma which, along with 2 previous 7 Ma ages, firmly establishes that back-arc activity began as early as late Miocene. Volcanism continued through the Pleistocene but the peak was in the early Pliocene. This result has important tectonic implications. If, as previously suggested, magma genesis is related to lithospheric delamination, this process was underway by the latest Miocene in the southern Puna. Furthermore, since the mafic back-arc volcanism is considered to mark a change in fault kinematics from compressional to transtensional, the new age constraints indicate that this change took place in the early Pliocene. The spatial and age distributions of the mafic centers indicate that magmatism began, and remained focussed in, a region between Salar de Antofalla and Cerro Galán. This concentration is probably structurally controlled, as it corresponds to the intersection of the NW–SE striking Archibarca lineament zone and the sets of NNE–SSW faults that run parallel to the Salar de Antofalla basin.

Twenty-five million years of silicic volcanism in the southern central volcanic zone of the Andes: Geochemistry and magma genesis of ignimbrites from 25 to 27 °S, 67 to 72 °W

Silicic volcanism in the Andean Central Volcanic Zone (CVZ) produced one of the world's largest Neogene ignimbrite provinces. The largest and best-known CVZ ignimbrites are located on the Altiplano-Puna plateau north of 24 °S. Their compositions and huge erupted volumes suggest an origin by large-scale crustal melting, and present-day geophysical anomalies in this region suggest still active zones of partial melting in the middle crust. Farther south in the CVZ, the Cerro Galán complex erupted ignimbrites in the late Miocene and Pliocene that are quite similar in volume and composition to those from north of 24 °S and they have a similar origin. However, there are a great many other, smaller ignimbrites in the southern CVZ whose compositions and geodynamic significance are poorly known. These are the subject of this paper. We present a geochemical study of 28 ignimbrite units from the southern CVZ at 25 °S to 27 °S, whose ages cover the full span of arc activity in this area, from about 25 Ma to 1 Ma. The small to medium volume ignimbrites (< 10 km 3) form valley-fill or sheet-like deposits, many of which are chemically zoned. Notwithstanding individual differences, there are several common characteristic features within the group of southern CVZ ignimbrites. By far the dominant composition is metaluminous, crystal-poor rhyolite (mean values from 236 samples: SiO 2 = 73.5 wt.%, A/CNK = 1.02, K 2O/Na 2O = 1.4). Regular major and trace element differentiation trends suggest fractionation from intermediate arc magmas and this is supported by radiogenic isotopic ratios of Sr, Nd and Pb, which show complete overlap between the silicic ignimbrites and andesite–dacites from contemporary stratovolcanoes. There are no major changes in composition of the silicic ignimbrites over the 25 Ma span of activity. We attribute minor but significant differences in isotopic composition and Nb–Ta concentration according to location in the West Cordillera (Chile) or the southern Puna plateau (Argentina) to variations in local basement compositions. The major conclusion of this study is that silicic magmas of crustal origin are rare in the CVZ south of 24 °S, and the only known example, Cerro Galán, is considerably younger than the ignimbrite “flare-up” in the Altiplano-Puna plateau region. The thermal conditions for widespread crustal melting in the Altiplano-Puna north of 24 °S are related to increased mantle heat flux caused by slab steepening and/or delamination at the base of overthickened lithosphere. These conditions have not (yet) been achieved in the southern CVZ because of the southward shallowing of slab dip and younging of compressive deformation and plateau growth.

Cenozoic orogenic growth in the Central Andes: Evidence from sedimentary rock provenance and apatite fission track thermochronology in the Fiambalá Basin, southernmost Puna Plateau margin (NW Argentina)

Intramontane sedimentary basins along the margin of continental plateaus often preserve strata that contain fundamental information regarding the pattern of orogenic growth. The sedimentary record of the clastic Miocene–Pliocene sequence deposited in the Fiambalá Basin, at the southern margin of the Puna Plateau (NW Argentina), documents the late Miocene paleodrainage evolution from headwaters to the west, towards headwaters in the ranges that constitute the border of the Puna Plateau to the north. Apatite Fission track (AFT) thermochronology of sedimentary and basement rocks show that the southern Puna Plateau was the source for the youngest, middle Miocene, detrital population detected in late Miocene rocks; and that the margin of the Puna Plateau expressed a high relief, possibly similar to or higher than at present, by late Miocene time. Cooling ages obtained from basement rocks at the southern Puna margin suggest that exhumation started in the Oligocene and continued until the middle Miocene. We interpret the basin reorganization and the creation of a high relief plateau margin to be the direct response of the source–basin system to a wholesale surface uplift event that may have occurred during the late Cenozoic in the Puna–Altiplano region. At this time coeval paleodrainage reorganization is observed not only in the Fiambalá Basin, but also in different basins along the southern and eastern Puna margin, suggesting a genetic link between the last stage of plateau formation and basin response. However, this event did not cause sufficient exhumation of basin bounding ranges to be recorded by AFT thermochronology. Our new data thus document a decoupling between late Cenozoic surface uplift and exhumation in the southern Puna Plateau. High relief achieved at the Puna margin by late Miocene time is linked to Oligocene–Miocene exhumation; no significant erosion (< 3 km) has occurred since in this arid highland.

The Late Miocene–Quaternary Antofalla volcanic complex, southern Puna, NW Argentina: Protracted history, diverse petrology, and economic potential

The Antofalla volcanic complex (AVC) is located on the southern Puna plateau of NW Argentina, ∼100 km east of the main axis of the Cordillera Occidental volcanic arc. It lies on the NW–SE Archibarca lineament, one of several transverse structures that cut across the Andes from Chile, and divert arc magmatism in SE-trending fingers across the Puna. 40Ar/ 39Ar dating of volcanic products from the AVC reveals a protracted magmatic history from 10.9 to ≤ 1.6 Ma. Initial volcanism was characterized by eruption of voluminous rhyolitic ignimbrites, deposited directly onto exposed crystalline basement and supracrustal sedimentary rocks. These rhyolites record significant geochemical evidence for crustal contamination, or derivation by crustal melting, which decreases upwards through the pyroclastic sequence. They were followed by extrusion of potassic lavas of the shoshonite–latite–trachydacite suite from 10.1 to 9.5 Ma. Subsequent magmatism (9.1–1.6 Ma) was of basaltic andesite–andesite–dacite composition, with localized, smaller volume, dacitic and rhyolitic ignimbrites. Monogenetic basaltic andesite cinder cones and lava flows were erupted in the Quaternary in response to a change to transtensional tectonics in the Puna. The volcanic sequence is interpreted to record the early development of a lower crustal MASH zone at ∼11 Ma, where mantle-derived arc magmas interacted extensively with felsic lower crustal rocks to produce evolved shoshonitic compositions, and crustal melts that erupted to form rhyolitic ignimbrites (common at this time throughout the Puna). After establishment of a steady-state MASH zone by ∼9 Ma, subsequent basaltic andesite–andesite magmas show less evidence of felsic crustal contamination, and may have developed largely by interaction with previous ultramafic–mafic fractionates of early magmas in the lower crust. More felsic dacitic magmas appear to have evolved largely by fractional crystallization from basaltic andesites and andesites, with widespread evidence of mixing and mingling between magmas of different degrees of differentiation. Some contamination by upper crustal components is also evident in these dacites, but is shown more clearly by small-volume rhyolites, some of which may again represent predominantly crustal melts. Epithermal deposits of Au and Pb–Zn–Ag occur within the AVC, apparently associated with the formation of rhyolite domes. The mineralization style is typical of other Andean volcanic centres, and may be underlain by deeper-seated porphyry-styles of mineralization. Extensive blanketing by younger lavas and limited erosion restricts exposure of these altered and mineralized sequences, however, although the potential for further discoveries beneath cover or at depth in this system appears high.

Average Pleistocene Climatic Patterns in the Southern Central Andes: Controls on Mountain Glaciation and Paleoclimate Implications

Abstract Despite elevations of 5000–6800 m, modern glaciers occur along the southern Puna Plateau and the northern Sierras Pampeanas in the southern central Andes. The modern snowline rises from 5100 m in Sierra Aconquija to 5800 m in the Puna as a result of a westward decrease in precipitation from 450 to less than 100 mm/yr. During the Pleistocene these arid highlands experienced multiple cirque and valley glaciation that likely postdate the last interglacial period, although lack of age control prevents an absolute chronology. Glaciation in the Puna and along the eastern Puna edge produced a 300‐m Pleistocene snowline (PSL) depression, while in the Sierras Pampeanas the PSL depression was at least 900 m. The greater PSL depression in the Sierras Pampeanas is best explained by a combination of cooling and increase of easterly moisture, whereas the PSL depression in the Puna appears more sensitive to moisture increases than temperature. Previously, glaciations in this region have been explained by increa...

Chronology of internal drainage development and uplift, southern Puna plateau, Argentine central Andes

Research Article| February 01, 1995 Chronology of internal drainage development and uplift, southern Puna plateau, Argentine central Andes Dirk S. Vandervoort; Dirk S. Vandervoort 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Teresa E. Jordan; Teresa E. Jordan 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Search for other works by this author on: GSW Google Scholar Peter K. Zeitler; Peter K. Zeitler 2Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015 Search for other works by this author on: GSW Google Scholar Ricardo N. Alonso Ricardo N. Alonso 3Universidad Nacional de Salta, Facultad de Ciencias Naturales, Buenos Aires 177, 4400 Salta, Argentina Search for other works by this author on: GSW Google Scholar Author and Article Information Dirk S. Vandervoort 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Teresa E. Jordan 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14853 Peter K. Zeitler 2Department of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015 Ricardo N. Alonso 3Universidad Nacional de Salta, Facultad de Ciencias Naturales, Buenos Aires 177, 4400 Salta, Argentina Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1995) 23 (2): 145–148. https://doi.org/10.1130/0091-7613(1995)023<0145:COIDDA>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Dirk S. Vandervoort, Teresa E. Jordan, Peter K. Zeitler, Ricardo N. Alonso; Chronology of internal drainage development and uplift, southern Puna plateau, Argentine central Andes. Geology 1995;; 23 (2): 145–148. doi: https://doi.org/10.1130/0091-7613(1995)023<0145:COIDDA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Fundamental to understanding the late Cenozoic evolution of the central Andes is knowledge of the age that the Puna-Altiplano plateau became a unique tectonomorphic entity within the orogen. The two attributes that define the Puna-Altiplano are (1) its average elevation of ≥3 km and (2) regions of high elevation that correspond spatially to regions with internal drainage. The chronology of plateau uplift to elevations similar to modern ones is equivocal owing to an inability to define the absolute elevation of the plateau surface through time. However, because regions of the Puna-Altiplano have nonmarine evaporites nad because such evaporites must accumulate within regions of internal drainage, the chronology of these strata elucidates when the plateau became internally drained. We show that, for the southern Puna (between lat 24° and 26°S), internal drainage was established between 14.1 and 24.2 Ma, and probably by ∼15 Ma. These results corroborate and refine other workers' inferences that the Puna-Altiplano plateau became uplifted and paleogeographically isolated from the adjacent fore arc and foreland during middle to late Miocene time. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Delamination and delamination magmatism

Lithospheric delamination is the foundering of dense lithosphere into less dense asthenosphere. The causes for this density inversion are thermal, compositional, and due to phase changes. For delamination to occur in the specific, and probably common, case where lithospheric mantle is intrinsically less dense than underlying asthenosphere due to compositional differences, a critical amount of shortening is required for the densifying effect of cooler temperature to counterbalance the effect of composition. Crustal thickening that results from shortening may result in a crustal root that, due to phase changes, becomes denser than the underlying mantle lithosphere and should delaminate with it: most of the negative buoyancy resides at the top of the mantle and the bottom of the crust. In most cases composition is not known well enough to calculate the driving energy of delamination from densities of equilibrium mineral assemblages in a lithospheric column. Poorly known kinetics of phase changes contribute additional uncertainties. In all cases however, the effects of delamination under a region are readily recognizable: rapid uplift and stress change, and profound changes in crustal and mantle-derived magmatism (a reflection of changes in thermal and compositional structure). Characteristics of delamination magmatism are exhibited in the Southern Puna Plateau, central Andes. The consequences of delamination for theories of crustal and mantle evolution remain speculative, but could be important. Recognition of delamination-related magmas in older (including Archean) orogens may be the best way to recognize past delamination events, because the magmas are among the most indelible and least ambiguous of delamination indicators.

Neotectonic deformation of the southern Puna Plateau, northwestern Argentina

Continental plateaus have been likened to pressure gauges that record the mechanical state of the lithosphere involved in mountain building. We outline the kinematic state of the southern Puna Plateau and bounding foreland provinces of the NW Argentine Andes based on surficial fault slip data and crustal seismicity. Kinematic analysis of about 350 faults, measured in a transect from the northern Sierras Pampeanas into the southern Puna, document a relatively uniform late Tertiary history of thrust faulting and vertical extension, followed by a more variable Quaternary history. During the latter, the plateau has undergone horizontal extension on strike-slip and normal faults whereas the thick-skinned foreland continues to experience thrust kinematics. The extension in the plateau, however, is not perpendicular to the trend of the Andes, but sub-parallel to it. A regional survey of all available kinematic data in the Central Andes between 12° and 32°S shows a similar style of kinematics characterizes the northern termination of the Altiplano in southern Peru and northernmost Bolivia. Although kinematic data do not exist for most of the Bolivian Altiplano, the lack of crustal earthquakes and scarcity of modern fault scarps tentatively suggest that the neotectonic activity is concentrated at both ends of the plateau. We interpret this apparent concentration in terms of an edge effect, related to along-strike narrowing topography and diminishing foreland shortening, which in turn are probably related to variations in the underlying geometry of the subducted Nazca Plate.