Microveins in limestones of the Oman Mountains : a structural study of the fundamental building blocks of a crack-seal-system

Crack seal is a ubiquitous process in the upper crust. It has been studied and know for a long time but it’s details are not well understood. In particular the individual events of crack seal have not been studied in great detail. In this work microveins are hypothesized to be the fundamental building blocks representing one crack-seal event and that they have a minimum opening aperture. In this study rocks from the Oman Mountains were sampled which contain a wide range of calcite veins in limestone and it was aimed to find rock samples which were devoid of veins. Many of these rock samples do not have macroscopic veins. In all these samples many microveins were found and based on a series of criteria to identify veins that belong to single crack-seal events they were selected and their properties were analyzed. The microveins typically are coarser in grain size than the surrounding matrix and based on the observed data the hypothesis that there is a minimum opening width of crack seal veins can not be rejected. The coarser grain fill is epitaxially grown inside the grain-boundary fractures in the matrix. It is proposed that these microveins represent the fundamental building blocks of crack seal and are the product of one crack seal event

Lithospheric Control on Asthenospheric Flow From the Iceland Plume: 3-D Density Modeling of the Jan Mayen-East Greenland Region, NE Atlantic

The density structure of the oceanic lithosphere north of Iceland is key for understanding the effects of the Iceland plume on the greater Jan Mayen‐East Greenland Region. We obtain the 3‐D density structure of the sediments and the crust from regional reflection and refraction seismic lines. The temperature and related density structures of the mantle between 50 and 250 km are derived from a shear wave velocity (Vs) tomography model. To assess the density between the Moho and 50‐km depth, we combine forward and inverse 3‐D gravity modeling. Beneath the Middle Kolbeinsey Ridge (MKR) region, a deep, broad negative mantle density anomaly occurs under the Kolbeinsey Ridge. It is overlain by a narrower uppermost mantle NE‐SW elongated negative density anomaly, which is increasingly displaced eastward of the spreading axis northward. It crosses the West Jan Mayen Fracture Zone and becomes weaker approaching the Mohn's spreading ridge. The effect of this anomaly is consistent with significantly shallower basement on the eastern side of the MKR. We interpret this as the result of thermal erosion of the lithosphere by hot asthenospheric flow out from the Iceland plume, possibly the main driver for several eastward jumps of the MKR during the last 5.5 Ma. The cause for the deviation of the flow may be that the West Jan Mayen Fracture Zone is easier to cross in a region where the difference in lithospheric thickness is small. That implies that the bottom lithospheric topography exerts a regional but not local influence on upper asthenospheric flow. ©2018. American Geophysical Union. All Rights Reserved

3‐D Modeling of Vertical Gravity Gradients and the Delimitation of Tectonic Boundaries: The Caribbean Oceanic Domain as a Case Study

Geophysical data acquisition in oceanic domains is challenging, implying measurements with low and/or nonhomogeneous spatial resolution. The evolution of satellite gravimetry and altimetry techniques allows testing 3‐D density models of the lithosphere, taking advantage of the high spatial resolution and homogeneous coverage of satellites. However, it is not trivial to discretise the source of the gravity field at different depths. Here, we propose a new method for inferring tectonic boundaries at the crustal level. As a novelty, instead of modeling the gravity anomalies and assuming a flat Earth approximation, we model the vertical gravity gradients (VGG) in spherical coordinates, which are especially sensitive to density contrasts in the upper layers of the Earth. To validate the methodology, the complex oceanic domain of the Caribbean region is studied, which includes different crustal domains with a tectonic history since Late Jurassic time. After defining a lithospheric starting model constrained by up‐to‐date geophysical data sets, we tested several a‐priory density distributions and selected the model with the minimum misfits with respect to the VGG calculated from the EIGEN‐6C4 data set. Additionally, the density of the crystalline crust was inferred by inverting the VGG field. Our methodology enabled us not only to refine, confirm, and/or propose tectonic boundaries in the study area but also to identify a new anomalous buoyant body, located in the South Lesser Antilles subduction zone, and high‐density bodies along the Greater, Lesser, and Leeward Antilles forearcs.Plain Language Summary: The knowledge of the density structure of the different layers that compose the solid Earth is important, for example: in the study of earthquakes, in plate tectonics reconstructions, or for the modeling of petroleum systems. These density variations affect (in small scale) the intensity of the gravity field on each point of the Earth's surface. The gravity field can be globally measured with satellites, reaching areas where the direct measurements are expensive and time consuming, such as in the ocean. In this work, we propose a new methodology with the purpose of recognizing tectonic and/or terrain limits, located in the outer most layer of the solid Earth, named crystalline crust. We calculate the gravity field of different density distributions, using four layers: seawater, sediments, crystalline crust, and mantle (a layer located below the crust), and compare the results with satellite global measurements. With our methodology it is possible to refine, confirm, and/or propose terrain limits, but additionally, we are able to estimate the average density configuration of the crystalline crust. This methodology is validated in the oceanic domain of the Caribbean, where a complex geologic history exists, due to its evolution since approximately 144 million years ago.Key Points: Vertical gravity gradients are especially sensitive to density contrasts in the upper layers of the lithosphere. We propose a new method for identifying tectonic boundaries based on the gradient's residuals and tested it in the Caribbean oceanic region. Using 3‐D lithospheric models, we forward modeled these gradients to infer the average density structure of the crystalline crust.DAAD http://dx.doi.org/10.13039/501100001655Erasmus+ http://dx.doi.org/10.13039/501100010790CEMarinFundación para la promoción de la investigación y la tecnología‐Banco de la República de ColombiaColciencias http://dx.doi.org/10.13039/10000763

Research Software Directory (as a service)

The Research Software Directory (as a service) is a content management system that is tailored to research software. Its main goal is to increase the visibility, impact and reuse of research software

Research Software Directory (as a service)

The Research Software Directory (as a service) is a content management system that is tailored to research software. Its main goal is to increase the visibility, impact and reuse of research software

Research Software Directory (as a service)

The Research Software Directory (as a service) is a content management system that is tailored to research software. Its main goal is to increase the visibility, impact and reuse of research software

Research Software Directory (as a service)

The Research Software Directory (as a service) is a content management system that is tailored to research software. Its main goal is to increase the visibility, impact and reuse of research software

Research Software Directory (as a service)

The Research Software Directory (as a service) is a content management system that is tailored to research software. Its main goal is to increase the visibility, impact and reuse of research software.Please cite this software using the information provided in this file

Research Software Directory (as a service)

The Research Software Directory (as a service) is a content management system that is tailored to research software. Its main goal is to increase the visibility, impact and reuse of research software

Interdisciplinary 3D potential field modelling of complex lithospheric structures by IGMAS+

We introduce an approach for 3D joint interpretation of potential fields and its derivatives under the condition of constraining data and information. The interactive 3D gravity and magnetic application IGMAS (Interactive Gravity and Magnetic Application System) has been around for more than 30 years, initially developed on a mainframe and then transferred to the first DOS PCs, before it was adapted to Linux in the ’90s and finally implemented as a cross-platform Java application with GUI. Since 2019 IGMAS+ is maintained and developed in the Helmholtz Centre Potsdam – GFZ German Research Centre by the staff of Section 4.5 – Basin Modelling and ID2 – eScience Centre. The core of IGMAS+ applies an analytical solution of the volume integral for the gravity and magnetic effect of a homogeneous body. It is based on the reduction of the three-folded integral to an integral over the bounding polyhedrons that are formed by triangles. Later the algorithm has been extended to cover all elements of the gravity tensor as well and the optimized storage enables fast leastsquares inversion of densities and changes to the model geometry and this flexibility makes geometry changes easy. Because of the triangular model structure of model interfaces, IGMAS can handle complex structures (multi- Z surfaces) like the overhangs of salt domes and variable densities due to voxelization. To account for the curvature of the Earth, we use spherical geometries. Therefore IGMAS+ is capable to handle models from big-scale to regional and small-scale models (meters) used in Applied Geophysics.poste