ALBERT

Description: The North Patagonian Massif (NPM) area in Argentina includes a plateau of 1200 m a.s.l. (meters above sea level) average height, which is 500–700 m higher than its surrounding areas. The plateau shows no evidence of internal deformation, while the surrounding basins have been deformed during Cenozoic orogenic events. Previous works suggested that the plateau formation was caused by a lithospheric uplift event during the Paleogene. However, the causative processes responsible for the plateau origin and its current state remain speculative. To address some of these questions, we carried out 3D lithospheric-scale steady-state and transient thermal simulations of the NPM and its surroundings, as based on an existing 3D geological model of the area. Our results are indicative of a thicker and warmer lithosphere below the NPM plateau compared with its surroundings, suggesting that the plateau is still isostatically buoyant and thus explaining its present-day elevation. The transient thermal simulations agree with a heating event in the mantle during the Paleogene as the causative process leading to lithospheric uplift in the region and indicate that the thermo-mechanical effects of such an event would still be influencing the plateau evolution today. Although the elevation related to the heating would not be enough to reach the present plateau topography, we discuss other mechanisms, also connected with the mantle heating, that may have caused the observed relief. Lithosphere cooling in the plateau is ongoing, being delayed by the presence of a thick crust enriched in radiogenic minerals as compared to its sides, resulting in a thermal configuration that has yet to reach thermodynamic equilibrium.

Description: We present a 3-D lithospheric-scale data-constrained structural model covering the area of North Patagonian Massif Plateau (NPM) and its surroundings. These data are supplementary material to “Lithospheric 3D gravity modelling using upper-mantle density constraints: Towards a characterization of the crustal configuration in the North Patagonian Massif area, Argentina” (Gómez Dacal et al. 2017). The North Patagonian Massif (NPM), in central Argentina, includes a plateau of an average altitude of 1200 m.a.s.l. mostly surrounded by basins that stand between 500 to 700 m below it. Geological observations and previous works indicate that the present-day elevation of the plateau was reached in the Paleogene by a sudden uplift that did not involve noticeable deformation. To gain insight into the causes of the uplift and the geodynamic development of the area, it is necessary to characterize the present-day configuration of the lithosphere.

Description: One of the current goals of the Global Geodetic Observing System (GGOS) through the International Association of Geodesy (IAG) is the unification of the existing classical vertical datums towards the materialization of the International Height Reference System (IHRS). In order to achieve this goal, it is possible to compute the mean geopotential offset between the equipotential surface of the Earth’s gravity field realized by the conventional value Wo= 62 636 853.4 m〈sup〉2〈/sup〉s〈sup〉-2〈/sup〉 of the IHRS and the unknown geopotential value of the local vertical datum. This offset is known as the vertical datum parameter. In this study, the determination of the discrepancy between the Argentinean National Vertical Reference System 2016 (SRVN16) over the continental part of Argentina and the IHRS is presented. With this objective, the zero-height geopotential value for the Argentinean Local Vertical Datum W0LVD was determined based on two approaches: 1) Using high-quality GNSS/Levelling data and a local gravimetric geoid model; and 2) Combining orthometric heights from SRVN16 with geoid heights through a Least Squares adjustment, integrating terrestrial gravity data for a specific area in Argentina. In both approaches, the local gravimetric geoid was computed by the well-known remove-compute-restore technique and applying a Fourier representation of Stokes’ integral formula. Preliminary analysis was carried out in a flat area in Buenos Aires province due to availability of high-quality data, gravity observations and benchmarks with GNSS/Levelling-derived heights, all located near the tide gauge station used to define the Argentinean Vertical Datum.

Description: In modelling atmospheric loading effects for terrestrial gravimetry, state-of-the-art approaches take advantage of numerical weather models to account for the global 3-D distribution of air masses. Deformation effects are often computed assuming the Inverse Barometer (IB) hypothesis to be generally valid over the oceans. By a revision of the IB assumption and its consequences we show that although the seafloor is not deformed by atmospheric pressure changes, there exists a fraction of ocean mass that current modelling schemes are usually not accounting for. This causes an overestimation of the atmospheric attraction effect over oceans, even when the dynamic response of the ocean to atmospheric pressure and wind is accounted through dynamic ocean models. This signal can reach a root mean square variability of a few nm s−2, depending on the location of the station. We therefore test atmospheric and non-tidal ocean loading effects at five superconducting gravimeter (SG) stations, showing that a better representation of the residual gravity variations is found when Newtonian attraction effects due to the IB response of the ocean are correctly considered. A sliding window variance analysis shows that the main reduction takes place for periods between 5 and 10 d, even for stations far away from the oceans. Since periods of non-tidal ocean mass variability closely resemble atmospheric signals recorded by SGs, we recommend to directly incorporate both an ocean component together with the IB into services that provide weather-related corrections for terrestrial gravimetry.