Modelo preliminar do geóide na província de SanJuan: Estudo de caso nos Andes

A high-resolution and high-precision detailed gravimetric geoid has been computed for San Juan province in Argentina, ranging from 27º S to 34º S in latitude and 72º'W to 65º W in longitude. The gravimetric geoid was calculated using the RTM method, a multiband spherical Stokes Fast Fourier Transformation, and the remove-restore technique for the spherical harmonic reference field and the terrain. As an external evaluation, the gravimetric quasigeoid/geoid was compared to the geoid heights obtained from 90 GPS/levelling points available for the province. Finally, a GPS-tailored local geoid, which fits the GPS observations, was computed. Keywords: Gravimetric Geoid; RTM Method; High Precision Geoid.Um geóide gravimétrico, com alta resolução e alta precisão, foi calculado para a província de San Juan na Argentina, delimitado pelos paralelos 27º S to 34º S e pelos meridianos 72º'W to 65º W. O geóide gravimétrico foi calculado usando o método RTM associado com uma transformação rápida de Fourier de múltiplas bandas sobre a função esférica de Stokes, com aplicação da técnica remove-restore para o modelo de referência do campo da gravidade e de elevação do terreno, ambos expressos em harmônicos esféricos. Como avaliação externa, o quase-geóide/geóide foi comparado com o geóide obtido de 90 pontos de nivelamento disponíveis na província e que foram ocupados também com GPS. Finalmente, foi calculado um geóide local adaptado via GPS, o qual se ajusta com as observações GPS. Palavras-chave: Geóide gravimétrico; Método RTM; Geóide de alta precisão

An embayment in the East Antarctic basement constrains the shape of the Rodinian continental margin

East Antarctic provinces lay at the heart of both Rodinian and Gondwanan supercontinents, yet poor exposure and limited geophysical data provide few constraints on the region’s tectonic evolution. The shape of the Mawson Continent, the stable nucleus of East Antarctica, is one of Antarctica’s most important, but contested features, with implications for global plate reconstructions and local tectonic models. Here we show a major marginal embayment 500–700 km wide, cuts into the East Antarctic basement in the South Pole region. This embayment, defined by new aeromagnetic and other geophysical data, truncates the Mawson Continent, which is distinct from basement provinces flanking the Weddell Sea. We favour a late Neoproterozoic rifting model for embayment formation and discuss analogies with other continental margins. The embayment and associated basement provinces help define the East Antarctic nucleus for supercontinental reconstructions, while the inherited marginal geometry likely influenced evolution of the paleo-Pacific margin of Gondwana

Exploring the Recovery Lakes region and interior Dronning Maud Land, East Antarctica, with airborne gravity, magnetic and radar measurements

Long-range airborne geophysical measurements were carried out in the ICEGRAV campaigns, covering hitherto unexplored parts of interior East Antarctica and part of the Antarctic Peninsula. The airborne surveys provided a regional coverage of gravity, magnetic and ice-penetrating radar measurements for major Dronning Maud Land ice stream systems, from the grounding lines up to the Recovery Lakes drainage basin, and filled in major data voids in Antarctic data compilations, such as AntGP for gravity data, ADMAP for magnetic data and BEDMAP2 for ice thickness data and the sub-ice topography. We present the first maps of gravity, magnetic and ice thickness data and bedrock topography for the region and show examples of bedrock topography and basal reflectivity patterns. The 2013 Recovery Lakes campaign was carried out with a British Antarctic Survey Twin Otter aircraft operating from the Halley and Belgrano II stations, as well as a remote field camp located at the Recovery subglacial Lake B site. Gravity measurements were the primary driver for the survey, with two airborne gravimeters (Lacoste and Romberg and Chekan-AM) providing measurements at an accuracy level of around 2 mGal r.m.s., supplementing GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) satellite data and confirming an excellent sub-milligal agreement between satellite and airborne data at longer wavelengths

Revealing the crustal architecture of the least understood composite craton on Earth: East Antarctica

East Antarctica hosts one of the largest Precambrian cratons on Earth. Meager coastal exposures and sediment provenance studies provide glimpses into up to 3 billion years of its geological history. Extensive ice sheet cover hampers however our knowledge of crustal architecture, and consequently the geodynamic processes responsible for the growth and amalgamation of East Antarctica have remained elusive. Here we exploit recent aerogeophysical exploration efforts to help unveil the large-scale crustal architecture of East Antarctica. We focus on three sectors of East Antarctica: the Transantarctic Mountains and Wilkes Basin area; the Recovery/Dronning Maud Land area and the Gamburtsev Province. These areas provide new insights into both the margins of the so called Mawson craton and the processes that affected its interior. A 1,900 km-long linear magnetic and gravity boundary is imaged along the western flank of the Wilkes Basin and interpreted here as a crustal-scale Paleoproterozoic suture zone (ca 1.7 Ga) that inverted a former passive margin. Two ribbon-like Archean and Paleoproterozic microcontinents were assembled during this stage, resembling modes of amalgamation of Paleoproterozoic microcontinental ribbons in Australia. The proposed Proterozoic sutures and microcontinent boundaries also influenced Neoproterozoic rifted margin and early Cambrian back-arc basins in the Wilkes Basin/Transantarctic Mountains region. In the Recovery/Dronning Maud Land region our new potential field compilations reveal a wide tract of anastomising crustal-scale shear zones, likely of Pan-African age that flank and variably deform the margins of several distinct Archean, Paleo-Mesoproterozoic and Grenvillian age crustal blocks. In the Gamburtsev Province new magnetic and gravity models provide insights into the Gamburtsev Suture (Ferraccioli et al., 2011, Nature) that separates the Ruker Province from an inferred Grenvillian-age orogenic Gamburtsev Province with remarkably thick crust (up to 60 km thick) and thick lithosphere (over 200 km thick). We suggest that a recently inferred Tonian-age accretionary belt identified in the Sor Rondane region continues further inland in the Gamburtsev Province and was likely also reactivated during Pan-African age transpression linked to Gondwana assembly

New Views of East Antarctica- from Columbia to Gondwana

East Antarctica is a keystone in the Gondwana, Rodinia and the Columbia supercontinents. Recent aerogeophysical research, augmented by satellite magnetic, gravity and seismological data is unveiling the crustal architecture of the continent. This is helping comprehend the impact of supercontinental processes such as subduction, accretion, rifting and intraplate tectonics on its evolution. A mosaic of Precambrian basement provinces is apparent in interior East Antarctica (Ferraccioli et al., 2011, Nature). A major suture separates the Archean-Neoproterozoic Ruker Province from an inferred Grenvillian-age orogenic Gamburtsev Province with remarkably thick crust (up to 60 km thick) and thick lithosphere (over 200 km thick). The age of the suturing and its linkages with supercontinental assembly is debated with both Rodinia and Gondwana candidates being proposed. Further east, magnetic highs delineate a Paleo to Mesoproterozoic Nimrod-South Pole igneous province (Goodge and Finn, 2010 JGR) that flanks a composite Mawson Continent- including the Gawler Craton of South Australia (Aitken et al., 2014 GRL). An over 1,900 km long magnetic and gravity lineament is imaged along the western flank of the Wilkes Subglacial Basin and is interpreted here as a major Paleoproterozoic suture zone linked to the collision of Laurentia and East Antarctica within Columbia. The proposed suture played a pivotal role helping localise Neoproterozoic Rodinia rifted margin evolution and forming a backstop for the Ross-Delamerian cycle of Gondwana amalgamation. Aeromagnetic and gravity imaging help determine the extent of a Keweenawan-age (ca 1.1 Ga) large igneous province in the Coats Land Block -isotopically tied with the Mid-Continent Rift System of Laurentia (Loewy et al., 2011 Geology). Imprints of Grenvillian magmatic arc accretion link together the Namaqua-Natal and Maud belts in South Africa and Dronning Maud Land within Rodinia. The aeromagnetically distinct Southeast Dronning Maud Land province (Mieth and Jokat, 2014 GR) may represent a separate 1000-900 Ma Oceanic Arc Superterrane (Jacobs et al., 2015 Prec. Res.). New geophysical views of the Shackleton Range suture lend weight to more complex collisional and indentation tectonic models for the Pan-African age assembly of Gondwan

ADMAP-2: The next-generation Antarctic magnetic anomaly map

The Antarctic Digital Magnetic Anomaly Project compiled the first international magnetic anomaly map of the Antarctic region south of 60\ubaS (ADMAP-1) some six years after its 1995 launch (Golynsky et al., 2001; Golynsky et al., 2007; von Frese et al., 2007). This magnetic anomaly compilation provided new insights into the structure and evolution of Antarctica, including its Proterozoic-Archaean cratons, Proterozoic-Palaeozoic orogens, Palaeozoic-Cenozoic magmatic arc systems, continental rift systems and rifted margins, large igneous provinces and the surrounding oceanic gateways. The international working group produced the ADMAP-1 database from more than 1.5 million line-kilometres of terrestrial, airborne, marine and satellite magnetic observations collected during the IGY 1957-58 through 1999. Since the publication of the first magnetic anomaly map, the international geomagnetic community has acquired more than 1.9 million line-km of new airborne and marine data. This implies that the amount of magnetic anomaly data over the Antarctic continent has more than doubled. These new data provide important constraints on the geology of the enigmatic Gamburtsev Subglacial Mountains and Prince Charles Mountains, Wilkes Land, Dronning Maud Land, and other largely unexplored Antarctic areas (Ferraccioli et al., 2011, Aitken et al., 2014 \u327 Mieth & Jokat, 2014, Golynsky et al., 2013). The processing of the recently acquired data involved quality assessments by careful statistical analysis of the crossover errors. All magnetic data used in the ADMAP-2 compilation were delivered as profiles, although several of them were in raw form. Some datasets were decimated or upward continued to altitudes of 4 km or higher with the higher frequency geological signals smoothed out. The line data used for the ADMAP-1 compilation were reprocessed for obvious errors and residual corrugations. The new near-surface magnetic data were corrected for the international geomagnetic reference field and diurnal effects, edited for high-frequency errors, and levelled to minimize line-correlated noise. The magnetic anomaly data collected mainly in the 21-st century clearly cannot be simply stitched together with the previous surveys. Thus, mutual levelling adjustments were required to accommodate overlaps in these surveys. The final compilation merged all the available aeromagnetic and marine grids to create the new composite grid of the Antarctic with minimal mismatch along the boundaries between the datasets. Regional coverage gaps in the composite grid will be filled with anomaly estimates constrained by both the near-surface data and satellite magnetic observations taken mainly from the CHAMP and Swarm missions. Magnetic data compilations are providing tantalizing new views into regional-scale subglacial geology and crustal architecture in interior of East and West Antarctica. The ADMAP-2 map provides a new geophysical foundation to better understand the geological structure and tectonic history of Antarctica and surrounding marine areas. In particular, it will provide improved constraints on the lithospheric transition of Antarctica to its oceanic basins, and thus enable improved interpretation of the geodynamic evolution of the Antarctic lithosphere that was a key component in the assembly and break-up of the Rodinia and Gondwana supercontinents. This work was supported by the Korea Polar Research Institute

A Reconciled Estimate of Ice-Sheet Mass Balance

We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth's polar ice sheets. We find that there is good agreement between different satellite methods-especially in Greenland and West Antarctica-and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by -142 plus or minus 49, +14 plus or minus 43, -65 plus or minus 26, and -20 plus or minus 14 gigatonnes year(sup 1), respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 plus or minus 0.20 millimeter year(sup 1) to the rate of global sea-level rise

Mass balance of the Greenland Ice Sheet from 1992 to 2018

In recent decades, the Greenland Ice Sheet has been a major contributor to global sea-level rise1,2, and it is expected to be so in the future3. Although increases in glacier flow4–6 and surface melting7–9 have been driven by oceanic10–12 and atmospheric13,14 warming, the degree and trajectory of today’s imbalance remain uncertain. Here we compare and combine 26 individual satellite measurements of changes in the ice sheet’s volume, flow and gravitational potential to produce a reconciled estimate of its mass balance. Although the ice sheet was close to a state of balance in the 1990s, annual losses have risen since then, peaking at 335 ± 62 billion tonnes per year in 2011. In all, Greenland lost 3,800 ± 339 billion tonnes of ice between 1992 and 2018, causing the mean sea level to rise by 10.6 ± 0.9 millimetres. Using three regional climate models, we show that reduced surface mass balance has driven 1,971 ± 555 billion tonnes (52%) of the ice loss owing to increased meltwater runoff. The remaining 1,827 ± 538 billion tonnes (48%) of ice loss was due to increased glacier discharge, which rose from 41 ± 37 billion tonnes per year in the 1990s to 87 ± 25 billion tonnes per year since then. Between 2013 and 2017, the total rate of ice loss slowed to 217 ± 32 billion tonnes per year, on average, as atmospheric circulation favoured cooler conditions15 and as ocean temperatures fell at the terminus of Jakobshavn Isbræ16. Cumulative ice losses from Greenland as a whole have been close to the IPCC’s predicted rates for their high-end climate warming scenario17, which forecast an additional 50 to 120 millimetres of global sea-level rise by 2100 when compared to their central estimate