Southernmost Andes Research Articles

From rift to foreland basin: A case example from the Magallanes‐Austral basin, southernmost Andes

AbstractThis contribution characterizes primary lithologic and depositional components of the Magallanes‐Austral basin and defines infill geometries and stacking patterns from seismic and well data. An integrated seismic model is proposed for recognition of rifting, thermal sag and foreland tectono‐stratigraphic phases based on depositional geometries and its relation with the evolving deformational and geodynamic framework. Above a Middle–Late Jurassic extensional phase, evidenced by synrift depositional geometries, follow marine successions representing the subsidence thermal sag phase (Tithonian–Early Cretaceous) characterized by concordant and laterally extensive seismic reflectors. The following foreland phase is described through the evolution and lateral migration history of the foredeep depocentre and concomitant forebulge development. The foreland phase is represented by different stages characterized by asymmetric sedimentary wedges bounded by basal surfaces and/or major unconformities recording transitions from underfilled to overfilled conditions. The accumulated thickness due to lithospheric flexure reflects different foreland subsidence profile patterns across the southern depocentre of the Magallanes‐Austral basin, producing asymmetrical westward and southward thickening wedges. The first Foreland I stage (Coniacian?–Maastrichtian) is recorded as an asymmetric wedge infill, that thins cratonward, with a NW‐trending foredeep axis. The erosive basal foreland surface (BF) at its base deepens towards the west and south along the active margin of the basin, where subsidence was maximum. On top of it, along the western portion of the basin and with a source area from the north, deep‐marine slope deposits and turbiditic complexes were deposited; while on the forebulge to the east, a clastic platform developed. The Foreland II stage (early‐to‐middle Palaeocene–middle Eocene) is characterized by renewed uplift and flexure, and increasing tectonic subsidence rates, building a new clastic wedge‐shaped foreland succession next to the orogenic belt, and a well‐represented forebulge to the east. Subsequently, an extensive diachronous G7 unconformity was generated, eroding locally the previous foreland deposits towards the eastern margin. A pronounced and continuous NW‐SE trending deflection is established subtly to the east. The following Foreland III stage (middle to late‐Eocene–Oligocene) is characterized by a reduction in thrust load along the western active margin, and progradational systems towards the NE, a time during which the subsidence rate decreased and accommodation space was reduced. Deposition occurred within a wide and continuous NW‐SE trending foredeep without a marked forebulge. The top of this stage is the A1 unconformity, marking the beginning of the Foreland IV stage (early Miocene–Neogene), regarded as an overfilled basinal stage without a marked foredeep and major variations in thickness across the extent of the basin. The depositional pattern in this stage is largely conformal and tabular. The proposal model represents an evolutionary example for the internal geometry of deep‐marine foreland basin system, including variables such as tectonic load and flexural subsidence, accommodation space, sediment supply variation, and relative sea‐level fluctuations.

Comment on the paper by Buono et al. “Dynamics of degassing in evolved alkaline magmas: Petrological, experimental and theoretical insights” (Earth Science Reviews, 211 (2020), 103402)

The mountainous, glaciated island of South Georgia is the crest of one of the most isolated fragments of continental crust on Earth. It is located approximately 1700 km east of the southern termination of the Andean Cordillera of South America. The island is primarily composed of Lower Cretaceous turbidites, the infill of a marginal basin floored by stretched continental and ophiolitic crust. Remnants of a volcanic arc are preserved on offshore islands to the southwest. The Pacific hinterland of the southernmost Andes is missing in Tierra del Fuego, terminating at a submarine escarpment forming the continental margin immediately east of Cape Horn. The arc and back-arc basin infill rocks of South Georgia correspond exactly to part of the missing Cordilleran hinterland.The mechanism of transport of the South Georgia microcontinent eastward relative to South America remains obscure, but likely involved some form of ‘escape tectonics’ during mid- to Late Cretaceous counterclockwise rotation of the arc that led to closure and inversion of the marginal basin.

The Fuegian thrust-fold belt: From arc-continent collision to thrust-related deformation in the southernmost Andes

New detailed structural data from the Fuegian Andes including new ages and cross-cutting relationships with intrusive rocks, as well as an appraisal of published structural data, support that this orogen evolved as a basement-involved thrust-fold belt after initial formation in an arc-continent collision scenario. New structural data from a deformed 84 Ma intrusive indicate that structures from the collisional event in the Argentine Fuegian Andes are of Campanian age, comprising only the youngest and less intense deformation of the orogenic wedge. In the internal thrust-fold belt, these structures are cut by intrusives with new ages of 74 Ma (Ar/Ar on hornblende). The superposition of thrusts on these early structures indicates a subsequent event in which a thrust-fold belt formed since the Maastrichtian-Danian. Additional new data confirm brittle-ductile thrusting in the central belt, with thrusts joining a common upper detachment in the base of the Lower Cretaceous rocks. These thrusts formed a first-order duplex system that transferred the shortening accommodated in the foreland until the Miocene.

The Cerro Guanaco mass movements: A geophysical and morphometric approach on a megalandslide in the Fuegian Andes (Southern Patagonia)

The Fuegian Andes, in the southernmost part of South America, are characterized by a relatively young deglacial landscape, where the glacial erosive relief is strongly influenced by regional-scale geological structures, resulting in deep longitudinal valleys with steeply dipping hillslopes. The rock-slope stability response to receding ice masses and the contribution of the gravitational processes in landscape evolution of the southernmost Andes, however, have not been assessed so far. The remoteness of the region, comprising a mountainous area hardly to access and piedmont and valley floors densely covered by forest, peatbogs or water bodies might partly explain the lack of such studies. Therefore, the objective of this contribution is to document for the first time the occurrence of massive slope failures in the Fuegian Andes using a multidisciplinary approach. This involves the use of indirect methods such as applied geophysics and landscape morphometrics. The southwest-facing slope of Cerro Guanaco, near Ushuaia, hosts several slope failures, but a massive failure stands out. The morphostructural approach allowed the geometrical description of the main dimensional characteristics of the first megalandslide recognized in the Fuegian Andes, which involved almost 1,2 km3 of material. On the other hand, the geophysical data has proved valuable in estimating the depth and characteristic of the buried detachment surface. The slope failure consisted of an initial translational movement followed by secondary slides and was developed shortly after the glacier recession. The gravitational processes represent an important element in the Fuegian deglacial landscape evolution.

Ushuaia pluton: Magma diversification, emplacement and relation with regional tectonics in the southernmost Andes

The Ushuaia pluton (UP) and the Ushuaia Peninsula Andesites (UPA) are intrusive units of a Late Cretaceous rear-arc in the Southernmost Andes. We report new LA-ICP-MS zircon ages from ∼71 to 75 Ma for the UP, and of ∼84 Ma for the UPA, which allow to differentiate these two magmatic events; consistent with their distinct petrography and geochemistry. The UP is a composite, incrementally assembled pluton in upper crustal levels. Successive injections of magma batches define two main sections, each in turn constructed by several smaller pulses: an early ultramafic-mafic section consists mainly of hornblende pyroxenite, hornblendite and gabbro/diorite with reverse concentric zonation, and a later intermediate section built up mainly by monzodiorite. Mingling and layering between mafic and intermediate facies along the contact point to simultaneous emplacement at the end of one main pulse and the beginning of the other. Mineralogy and geochemistry suggest the rock sequence in the UP is cogenetic. In part it resulted by in-situ magmatic processes that included crystal-melt fractionation during injection of magma mushes, mingling, local melt segregation and mixing with crustal partial melts. The country rock is affected by penetrative ductile deformation and regional metamorphism developed during mid-Cretaceous Andean main orogenic phase. It also shows an overimposed pluton-margin parallel foliation and a post-kinematic contact metamorphic aureole. On the other hand, the UP has a concentric igneous foliation parallel to pluton margins interpreted as a primary magmatic feature. The above evidences, along with absence of subsolidus fabrics and metamorphism, indicate the pluton post-date peak regional metamorphism and ductile structures in the country rock. The new zircon ages constrain the top age of early Andean deformation, as well as the magmatic gap registered for the end of the Cretaceous, and confirm an emplacement during a recorded compressive regime that transmitted shortening to the foreland.

A 17-year Record of Meteorological Observations Across the Gran Campo Nevado Ice Cap in Southern Patagonia, Chile, Related to Synoptic Weather Types and Climate Modes

The network of long-term meteorological observations in Southernmost Patagonia is still sparse but crucial to improve our understanding of climatic variability, in particular in the more elevated and partially glaciated Southernmost Andes. Here we present a unique 17-year meteorological record (2000-2016) of four automatic weather stations across the Gran Campo Nevado Ice Cap (53$^{\circ}$S) in the Southernmost Andes (Chile) and the conventional weather station Jorge Schythe of the Instituto de la Patagonia in Punta Arenas for comparison. We revisit the relationship between in-situ observations and large-scale climate models as well as mesoscale weather patterns. For this purpose, a 37-year record of ERA Interim Reanalysis data has been used to compute a weather type classification based on a hierarchical correlation-based leader algorithm. The orographic perturbation on the predominantly westerly airflow determines the hydroclimatic response across the mountain range, leading to significant west-east gradients of precipitation, air temperature and humidity. Annual precipitation sums heavily drop within only tens of kilometers from \textasciitilde 7500 mm\,a$^{-1}$ to less than 800 mm\,a$^{-1}$. The occurrence of high precipitation events of up to 620 mm in 5 days and wet spells of up to 61 consecutive days underscore the year-around wet conditions in the Southernmost Andes. Given the strong link between large-scale circulation and orographically controlled precipitation, the synoptic-scale weather conditions largely determine the precipitation and temperature variability on all time scales. Major synoptic weather types with distinct low-pressure cells in the Weddell Sea or Bellingshausen Sea, causing a prevailing southwesterly, northwesterly or westerly airflow, determine the weather conditions in Southernmost Patagonia during 68$\%$ of the year. At Gran Campo Nevado, more than 80$\%$ of extreme precipitation events occur during the persistence of these weather types. The evolution of the El Ni\~{n}o Southern Oscillation and Antarctic Oscillation impose intra- and inter-annual precipitation and temperature variations. Positive Antarctic Oscillation phases on average are linked to an intensified westerly airflow and warmer conditions in Southernmost Patagonia. Circulation patterns with high-pressure influence leading to colder and dryer conditions in Southernmost Patagonia are more frequent during negative Antarctic Oscillation phases.

Genesis of a Holocene soil chronosequence from the southernmost Andes Mountains, Tierra del Fuego

At the southernmost Andes Mountains, the Martial cirque glacier has retreated 2km in distance and 500m in elevation since the mid-Holocene. This study examines soil properties, processes, and classification in relation to soil age and elevation. Soils were sampled at elevations from 430 to 925m a.s.l. on drifts periodically influenced by volcanic ash that represent five age classes: 5.0 to 6.0kyrBP under deciduous Nothofagus pumilio forest; 1.3 to 3.2kyrBP under N. pumilio and N. antarctica forest and tundra; 0.3 to 1.4kyrBP under tundra; 0.3KyrBPCE under tundra; and 0.007KyrBPCE under scattered lichens and mosses. The soils represent a developmental sequence on metapellitic rocks ranging from: Cryorthents, Dystrocryepts, Humicryepts, and Humicryods. In general the soils contain abundant coarse fragments, sandy loam textures, and high levels of organic C. Clays have been altered in the soils from chlorite to a hydroxyl-interlayered vermiculite and ferrihydrite. The most developed soils are very strongly acid, Al saturated, and have illuvial horizons enriched in fulvic-acid C and organic-bound forms of free Fe and Al. The following properties are highly correlated with soil age: pyrophosphate soluble iron (Fep) in the B horizon (R2=0.97), color-development equivalence in the B horizon (R2=0.87), clay content of the B horizon (R2=0.68), and fulvic-acid C in the B horizon (R2=0.65). The results of this study imply that soil formation in magellanic subantarctic forests and tundra is rapid and involves podsolization, andisolization, and humification as primary soil-forming processes.

Obsidian sources and distribution in Patagonia, southernmost South America

Obsidian artifacts occur in some of the earliest occupied late Pleistocene archaeological sites in Patagonia, such as Pilauco (∼15,500 cal BP) in south-central Chile, and Cerro Tres Tetas (∼12,100 cal BP) in Santa Cruz, Argentina, and they are very common in numerous early Holocene sites. Trace-element analysis of artifacts from these sites indicate long-distance (>300 to >1000 km) transport of obsidian from nine different sources. Two of these sources, Chaitén (CH) and Nevados de Sollipulli (NS), are associated with active Andean volcanoes in southern Chile. One, around Seno Otway (SO), occurs in the Miocene volcanic belt in the southernmost Andes. The six others, Portada Covunco (PC), Cerro de la Planicies/Lago Lolog (CP/LL), Sacanana (S), Telsen/Sierra Negra (T/SN), Pampa del Asador (PDA) and Cordillera Baguales (CB), occur east of the Andes in Argentina. Geologic ages of these obsidians range from 17.8 Ma (Sacanana) to recent (Chaitén). Obsidian from each of these sources is generally homogeneous and chemically distinct from all the other sources. Those from the Chilean Andes are subalkaline in composition, while those from the pampas of Argentina east of the Andes are alkaline and peralkaline. Chaitén obsidian occurs in marine culture sites along the Pacific coast as far as >400 km to the north and south of this volcano, and a few samples has been found >900 km to the southeast along the Atlantic coast, presumably transported there in a canoe. Green obsidian from Seno Otway was also exploited dominantly by marine cultures, but occurs as well in terrestrial hunter-gatherer sites such as Pali-Aike and Fell's caves, from which Junius Bird first reported, in 1938, prehistoric obsidian artifacts in Patagonia. Distinctive black and red-banded “tiger-striped” obsidian from Portada Covunco has also been transported >500 km east to the Atlantic coast, as well as west into Chile and to Mocha Island off the Pacific coast, perhaps because of its aesthetic appeal. Black alkaline obsidian from Pampa del Asador, which includes at least four chemically distinct types, has been distributed by terrestrial hunter-gatherers >800 km northeast to the Atlantic coast and south to Tierra del Fuego, as well as west into Chile. The wide distribution (>300 km) of obsidian from each of these nine sources, well beyond the range considered probable for direct procurement by Patagonian terrestrial hunter-gatherers (≤200 km), implies the possibility of a considerable amount of cultural interaction among the prehistoric peoples of Patagonia throughout the Holocene.

Geometry and kinematics of the Fuegian thrust-fold belt, southernmost Andes

Fil: Torres Carbonell, Pablo Juan. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina

Mars MOURA magnetometer demonstration for high-resolution mapping on terrestrial analogues

Abstract. Satellite-based magnetic measurements of Mars indicate complex and very strong magnetic anomalies, which led to an intensive and long-lasting discussion about their possible origin. To make some progress in the investigation of the origin of these anomalies the MOURA vector magnetometer was developed for in situ measurements on Mars. In this work we propose the utilisation of such an instrument for future planetary on-ground surveys. The proof of its suitability is seen through testing it on various terrestrial analogues characterised by the distinct magnetic anomalies of their basement rocks: (1) a magnetite body of EL Laco (up to +110 000 nT) and its transition to surrounding andesites ( < +2000 nT) in the northern Andes of Chile showing the highest local magnetic anomalies. The magnetite-bearing ore body has highly variable local anomalies due to its complex formation history where a significant dispersion in palaeo-orientations has been previously reported, while our vector data show relatively uniform and probably induced declinations. (2) A basaltic spatter cone of the Pali Aike volcanic field, in southern Chile, was characterised by very strong magnetic anomalies along the crater rim (up to +12 000 nT), controlled by the amount of single domain magnetites in the ground mass of the basalts. Due to their strong remanent signature, palaeo-declinations of the lavas and reorientations of collapsed blocks could be constrained by the vector data. (3) The Monturaqui meteorite crater (350 m diameter), in northern Chile, shows significant variations of its anomalies (from −2000 to > +6000 nT) in restricted areas of several square metres along its crater rim related to unexposed iron-bearing fragments of the impactor while its granitic and ignimbritic target rocks exhibit only very weak anomalies. (4) An area with several amphibolitic dykes, which cross-cut a Cretaceous granitoid in the southernmost Andes, where a decimetre-scale mapping was performed. In this case, pyrrhotite is the only magnetic carrier. It was formed during hydrothermal processes within the dykes. Very low (+40 to +120 nT) positive magnetic anomalies clearly depict the amount of 1–4 vol % pyrrhotite in these dykes, which is important as a mineralogical indicator as well as to detect associated gold and copper enrichment.

Fault kinematics of the Magallanes-Fagnano fault system, southern Chile; an example of diffuse strain and sinistral transtension along a continental transform margin

A system of left-lateral faults that separates the South American and Scotia plates, known as the Magallanes-Fagnano fault system, defines the modern tectonic setting of the southernmost Andes and is superimposed on the Late Cretaceous – Paleogene Patagonian fold-thrust belt. Fault kinematic data and crosscutting relationships from populations of thrust, strike-slip and normal faults from Peninsula Brunswick adjacent to the Magallanes-Fagnano fault system, presented herein, show kinematic and temporal relationships between thrust faults and sets of younger strike-slip and normal faults. Thrust fault kinematics are homogeneous in the study area and record subhorizontal northeast-directed shortening. Strike-slip faults record east—northeast-directed horizontal shortening, west—northwest-directed horizontal extension and form Riedel and P-shear geometries compatible with left-lateral slip on the main splay of the Magallanes-Fagnano fault system. Normal faults record north-south trending extension that is compatible with the strike-slip faults. The study area occurs in a releasing step-over between overlapping segments of the Magallanes-Fagnano fault system, which localized on antecedent sutures between basement terranes with differing geological origin. Results are consistent with regional tectonic models that suggest sinistral shearing and transtension in the southernmost Andes was contemporaneous with the onset of seafloor spreading in the Western Scotia Sea during the Early Miocene.

Tectonic models for the Patagonian orogenic curve (southernmost Andes): An appraisal based on analog experiments from the Fuegian thrust–fold belt

Tectonic models for the evolution of the Patagonian orogenic curve were evaluated using analog experiments that considered either a rotational or a non-rotational orogenic backstop, combined with a basement promontory on the foreland cratonic margin. Five different kinematic configurations were used, aiming to evaluate the influence of the Río Chico Arc as a rigid obstacle on the evolution of the Fuegian thrust–fold belt. Rotations, strains and displacement fields obtained from each analog experiment were compared with the structural geology known from the Fuegian thrust–fold belt, in order to appraise the tectonic models that are more consistent with the natural structure. The push of a counterclockwise rotational backstop, combined with the buttressing effect of a foreland promontory, seem of major importance in controlling the final structure and map-view shape of the thrust wedge.

Late Cretaceous–early Eocene counterclockwise rotation of the Fueguian Andes and evolution of the Patagonia–Antarctic Peninsula system

The southernmost Andes of Patagonia and Tierra del Fuego present a prominent arc-shaped structure: the Patagonian Bend. Whether the bending is a primary curvature or an orocline is still matter of controversy. New paleomagnetic data have been obtained south of the Beagle Channel in 39 out of 61 sites. They have been drilled in Late Jurassic and Early Cretaceous sediments and interbedded volcanics and in mid-Cretaceous to Eocene intrusives of the Fuegian Batholith. The anisotropy of magnetic susceptibility was measured at each site and the influence of magnetic fabric on the characteristic remanent magnetizations (ChRM) in plutonic rocks was corrected using inverse tensors of anisotropy of remanent magnetizations. Normal polarity secondary magnetizations with west-directed declination were obtained in the sediments and they did not pass the fold test. These characteristic directions are similar to those recorded by mid Cretaceous intrusives suggesting a remagnetization event during the normal Cretaceous superchron and describe a large (>90°) counterclockwise rotation. Late Cretaceous to Eocene rocks of the Fueguian Batholith, record decreasing counterclockwise rotations of 45° to 30°. These paleomagnetic results are interpreted as evidence of a large counterclockwise rotation of the Fueguian Andes related to the closure of the Rocas Verdes Basin and the formation of the Darwin Cordillera during the Late Cretaceous and Paleocene.The tectonic evolution of the Patagonian Bend can thus be described as the formation of a progressive arc from an oroclinal stage during the closure of the Rocas Verdes basin to a mainly primary arc during the final stages of deformation of the Magallanes fold and thrust belt. Plate reconstructions show that the Antarctic Peninsula would have formed a continuous margin with Patagonia between the Early Cretaceous and the Eocene, and acted as a non-rotational rigid block facilitating the development of the Patagonian Bend.

Unzipping the Patagonian Andes—Long-lived influence of rifting history on foreland basin evolution

The Andean Cordillera is widely considered to be one of the type examples of a convergent margin setting. In the southernmost Andes, however, rifting and volcanism predated mid-Cretaceous breakup of Gondwana and formation of the South Atlantic Ocean by up to 40 m.y. and culminated in the opening of the Rocas Verdes backarc basin east of the Mesozoic Patagonian Batholith. We present new U-Pb geochronology from the Austral sector (49°S–50°S) that indicates rift volcanism occurred between 154 and 147 Ma near the northern terminus of the basin. Available data and observations from the southern Rocas Verdes Basin indicate larger-magnitude and longer-duration extension compared to the northern basin region. The Rocas Verdes Basin underwent progressive northward propagation and opening and was later backfilled concomitantly with the opening of the southern Atlantic Ocean by north-to-south deposition within a retroarc foreland setting. The influence of the inherited tectonic fabric of the Rocas Verdes backarc basin on the subsequent foreland basin explains many unique characteristics of the Patagonian Andes, such as a protracted deep basin that formed atop the previously rifted and weakened crust. Moreover, the early rift history helps account for intraplate deformation of southernmost South America during the opening of the South Atlantic Ocean.

Magnetic signatures of the orogenic crust of the Patagonian Andes with implication for planetary exploration

The Patagonian Andes represent a good scenario of study because they have outcrops of diverse plutonic rocks representative of an orogenic crust on Earth and other planets. Furthermore, metamorphic surface rocks provide a window into deeper crustal lithologies. In such remote areas, satellite and aerial magnetic surveys could provide important geological information concerning exposed and not exposed rocks, but they integrate the magnetic anomalies in areas of kilometres. For the southernmost Andes long wavelength satellite data show clear positive magnetic anomalies (>+100nT) for the Patagonian Batholith (PB), similar as parts of the older martian crust. This integrated signal covers regions with different ages and cooling histories during magnetic reversals apart from the variability of the rocks.To investigate the complex interplay of distinct magnetic signatures at short scale, we have analysed local magnetic anomalies across this orogen at representative sites by decimeter-scale magnetic ground surveys. As expected, the investigated sites have positive and negative local anomalies. They are related to surface and subsurface rocks, and their different formation and alternation processes including geomagnetic inversions, distinct Curie depths of the magnetic carriers, intracrustal deformation among other factors. Whole rock chemistry (ranging from 45 to >80wt.% SiO2 and from 1 to 18wt.% FeOtot.), magnetic characteristics (susceptibilities, magnetic remanence and Königsberger ratios) as well as the composition and texture of the magnetic carriers have been investigated for representative rocks. Rocks of an ultramafic to granodioritic intrusive suite of the western and central PB contain titanomagnetite as major magnetic carrier. Individual magnetic signatures of these plutonic rocks reflect their single versus multidomain status, complex exolution processes with ilmenite lamella formations and the stoichiometric proportions of Cr, Fe and Ti in the oxides. At the eastern margin of the PB the investigated plutons and mafic dykes have been emplaced and equilibrated at 4–6km depth. They do not contain magnetite but include variable amounts of ferrimagnetic monoclinic C4 pyrrhotite, which was formed along fractures zones by a hydrothermal gold-bearing mineralisation. The intensity of their positive magnetic anomalies (up to +220nT) is well correlated with the amount of pyrrhotite (1–4vol.%). In all cases, high resolution ground surveys variations of the magnetic signature down to 20nT could be used to clearly distinguish different rock types on a decimeter scale. Vector magnetometer MOURA designed for martian exploration was successfully used for these surveys and provides results comparable to a commonly used caesium scalar magnetometer. This is important for near future ground surveys on Mars and the Moon.

Glacial and tectonic control on fjord morphology and sediment deposition in the Magellan region (53°S), Chile

In the Patagonian Andes erosion by temperate Pleistocene glaciers has produced a deeply incised fjord system in which glacial and non-glacial sedimentswere deposited since the Late Glacial glacier retreat. So far, fjord bathymetry and structures in the sediment infill were widely unexplored. Here we report the results of an investigation of morphology and sediment characteristics of a 250 km long fjord transect across the southernmost Andes (53°S), using multibeam and parametric echosounder data, and sediment cores. Subaquatic morphology reveals continuity of on-land tectonic lineaments mapped using field and remote sensing data. Our results indicate that glacial erosion and fjord orientation are strongly controlled by three major strike-slip fault zones. Furthermore, erosion is partly controlled by older and/or reactivated fracture zones as well as by differential resistance of the basement units to denudation. Basement morphology is regionally superimposed by Late Glacial and Holocene subaquatic moraines, which are associated to known glacier advances. The moraines preferentially occur on basement highs, which constrained the glacier flows. This suggests that the extent of glacier advances was also controlled by basement morphology. Subaquatic mass flows, fluid vent sites as well as distinct Late Glacial and Holocene sediment infills have furthermore modified fjord bathymetry. In the western fjord system close to the Strait of Magellan subaquatic terraces occur in 20 to 30 m water depth, providing an important tag for proglacial lake level during the Late Glacial.

Late Quaternary variations of the southern westerly wind belt and its influences on aquatic ecosystems and glacier extend within the southernmost Andes

The southern tip of South America is year-round influenced by the southern westerly wind belt (SWW) causing extremely high precipitation along the Chilean coast and the Andes south of 33°S with maximum values of 3000 to >10 000 mm/year within the SWW core between 49 to 55°S which is unique for temperate regions on the global scale. Due to this key position within the global atmospheric and oceanic framework we have investigated a large number of Late Quaternary climate archives during the last decade including fjord and lake sediments, peats, stalagmites and tree rings. To improve our proxy understanding in these various archives, climate as well as hydrological monitoring stations were operated since 1999. Here we present one-year monitoring data, which document the short term variability of climate and thermohaline conditions and related fertility in the fjord surface water. In this context we also analysed the interplay between palaeo-precipitation and related freshening of surface water (low nitrate and phosphate) and the terrestrial nutrient supply to the fjords during the last 5 ka BP using new salinity and productivity proxies of a fjord sediment core. Lake sediment cores and a stalagmite record document high chemical denudation rates, and metal leaching occurs on a weakly buffered granitoid basement and areas covered by acidic peaty soils. The partly climate-controlled changes in the iron and trace metal mobility have profound implications for both terrestrial and aquatic ecosystems. Based on the investigated archives we also reviewed SWW changes and regional temperature variations during the past 30 ka BP and their implication for Glacial and Holocene glacier advances.

The Scotia Arc: Genesis, Evolution, Global Significance

The Scotia arc is the eastward-closing loop of mountains and locally emergent submarine ridges extending from the southernmost Andes through the active South Sandwich volcanic arc to the Antarctic Peninsula. Its origins lie in the Jurassic initial fragmentation of Gondwana. This fragmentation involved extreme intercratonic extension, Pacificward translation of rotating crustal blocks, and an ignimbrite flare-up. Relative motion between South America, Africa, and East Antarctica during the opening of the southern ocean basins resulted in mid-Cretaceous uplift of the Pacific margin cordillera and translation of elevated crustal blocks eastward to form the North and South Scotia Ridges. The South Sandwich volcanic arc system originated in Neogene westward-directed subduction beneath oceanic crust formed between South America and Antarctica and serves as an excellent tectonic laboratory. The physiography of the entire Scotia arc region has profoundly influenced the onset and development of the Antarctic Circumpolar Current and migration of marine and terrestrial biota.

New constrains on Neoglacial glacier advances in the superhumid southernmost Andes (50-53°S) and evaluation of their control mechanism based on new plaeoclimate records and modelling

New constrains on Neoglacial glacier advances in the superhumid southernmost Andes (50-53°S) and evaluation of their control mechanism based on new plaeoclimate records and modelling

The opening of the Magellan Strait and its geodynamic implications

Terra Nova, 25, 13–20, 2013AbstractThe existence of a Neogene‐Quaternary rift system responsible for the opening of the eastern Magellan strait has been one of the more peculiar tectonic features of the southernmost Andes since its discovery more than a decade ago. However, until now there has been no explanation pinpointing the specific tectonic factors that led to the development of the rift. This work focuses on the interaction between the fault systems and the tectonic regimes that have affected Tierra del Fuego north of the South America–Scotia left lateral strike‐slip plate boundary. Due to a good match between a Jurassic extensional fault array orientation and the principal stress directions related to the strike‐slip plate boundary, we conclude that Jurassic transfer faults reactivated extensionally generating the Magellan rift system. This process was enhanced by northward continental drift, and has implications for the geodynamic behind the separation of South America from Antarctica.