Gravimetry and petrophysics for defining the intracratonic and rift basins of the western-central Africa zone.

Geophysics ◽  
2021 ◽  
pp. 1-68
Author(s):  
Francesca Maddaloni ◽  
Tommaso Pivetta ◽  
Carla Braitenberg
Keyword(s):  
Gravity Field ◽  
Central Africa ◽  
Thermal Conditions ◽  
Deep Basin ◽  
Global Gravity ◽  
Stretching Factor ◽  
Continuous Body ◽  
African Rift ◽  
Crustal Density ◽  
Sag Basin

The global gravity field obtained from the observations of the satellite GOCE offers new opportunities in defining density variations of Earth’s crust and mantle, allowing new insights into the structure of specific geologic features. The central African rift is a key feature in understanding of the dismemberment of Gondwana, and we contribute to defining the crustal density structure underlying the rift. The presence of a narrow and up to 12 km deep basin implies crustal stretching to allow the sediment to accumulate, but a key question is whether the stretching processes affected also the deeper layers of the crust or was limited to the upper crust. The study-area includes a sub-basin of the greater Chad sag-basin, which extends over a 1500 km by 1500 km, and occupies the center of North-Central Africa, shared between the countries of Chad, Sudan, Nigeria, Niger, Algeria, Libya and Cameroon. We find that the rifting affected the lower crust of the West African Rift and demonstrate evidence for a 1500 km long and several km thick magmatic crustal intrusion presumably associated with underplating and crustal thinning. We estimate that the stretching factor must be at least 1.5 and had affected the entire crust. To our knowledge, the identification of a continuous body of magmatic intrusions is new and has been only possible through the recent global gravity field. The magmatism has altered the thermal conditions from the time of emplacement on, and is relevant for the maturation of hydrocarbons present in the sediments. The timing of the magmatism is presumably tied to two pulses of volcanism documented in the rift, associated with the first post-rift phase from 96 to 88 Ma and the second post-rift phase from 23 Ma up to the Quaternary.

Evaluation of global gravity field models using shipborne free-air gravity anomalies over the Gulf of Guinea, Central Africa

Survey Review ◽  
2021 ◽  
pp. 1-11
Author(s):  
Kamto Paul Gautier ◽  
Yap Loudi ◽  
Zanga Amougou Alain ◽  
Kandé Houetchak Ludovic ◽  
Nguiya Sévérin ◽  
...  
Keyword(s):  
Gravity Field ◽  
Central Africa ◽  
Gravity Anomalies ◽  
Gulf Of Guinea ◽  
Free Air ◽  
Global Gravity ◽  
Free Air Gravity ◽  
Gravity Field Models

Combining the deep Earth and lithospheric gravity field to study the density structure of the upper mantle

2021 ◽  
Author(s):  
Bart Root ◽  
Javier Fullea ◽  
Jörg Ebbing ◽  
Zdenek Martinec
Keyword(s):  
Gravity Field ◽  
Shear Wave ◽  
Wave Velocity ◽  
Shear Wave Velocity ◽  
Field Data ◽  
Wavelength Region ◽  
Density Structure ◽  
Long Wavelength ◽  
Global Gravity ◽  
Deep Earth

<p>Global gravity field data obtained by dedicated satellite missions is used to study the density distribution of the lithosphere. Different multi-data joint inversions are using this dataset together with other geophysical data to determine the physical characteristics of the lithosphere. The gravitational signal from the deep Earth is usually removed by high-pass filtering of the model and data, or by appropriately selecting insensitive gravity components in the inversion. However, this will remove any long-wavelength signal inherent to lithosphere. A clear choice on the best-suited approach to remove the sub-lithospheric gravity signal is missing. </p><p>Another alternative is to forward model the gravitational signal of these deep situated mass anomalies and subtract it from the observed data, before the inversion. Global tomography provides shear-wave velocity distribution of the mantle, which can be transformed into density anomalies. There are difficulties in constructing a density model from this data. Tomography relies on regularisation which smoothens the image of the mantle anomalies. Also, the shear-wave anomalies need to be converted to density anomalies, with uncertain conversion factors related to temperature and composition. Understanding the sensitivity of these effects could help determining the interaction of the deep Earth and the lithosphere.</p><p>In our study the density anomalies of the mantle, as well as the effect of CMB undulations, are forward modelled into their gravitational potential field, such that they can be subtracted from gravity observations. The reduction in magnitude of the density anomalies due to the regularisation of the global tomography models is taken into account. The long-wavelength region of the density estimates is less affected by the regularisation and can be used to fix the mean conversion factor to transform shear wave velocity to density. We present different modelling approaches to add the remaining dynamic topography effect in lithosphere models. This results in new solutions of the density structure of the lithosphere that both explain seismic observations and gravimetric measurements. The introduction of these dynamic forces is a step forward in understanding how to properly use global gravity field data in joint inversions of lithosphere models.</p>

GRACE Follow-On Gravity Field Recovery from Combined Laser Ranging Interferometer and Microwave Ranging System Measurements

2021 ◽  
Author(s):  
Saniya Behzadpour ◽  
Andreas Kvas ◽  
Torsten Mayer-Gürr
Keyword(s):  
Gravity Field ◽  
Laser Ranging ◽  
Measurement Technology ◽  
Additional Measurement ◽  
Covariance Functions ◽  
Gravity Field Recovery ◽  
Global Gravity ◽  
Least Squares Adjustment ◽  
Noise Covariance ◽  
Component Estimation

<p>Besides a K-Band Ranging System (KBR), GRACE-FO carries a Laser Ranging Interferometer (LRI) as a technology demonstration to provide measurements of inter-satellite range changes. This additional measurement technology provides supplementary observations, which allow for cross-instrument diagnostics with the KBR system and, to some extent, the separation of ranging noise from other sources such as noise in the on-board accelerometer (ACC) measurements.</p><p>The aim of this study is to incorporate the two ranging systems (LRI and KBR) observations in ITSG-Grace2018 gravity field recovery. The two observation groups are combined in an iterative least-squares adjustment with variance component estimation used to determine the unknown noise covariance functions for KBR, LRI, and ACC measurements. We further compare the gravity field solutions obtained from the combined solutions to KBR-only results and discuss the differences with a focus on the global gravity field and LRI calibration parameters.</p>

GRIM5-C1: Combination solution of the global gravity field to degree and order 120

2001 ◽  
pp. 149-149
Author(s):  
Thomas Gruber ◽  
Albert Bode ◽  
Christoph Reigber ◽  
Peter Schwintzer ◽  
Georges Balmino ◽  
...  
Keyword(s):  
Gravity Field ◽  
Global Gravity

scholarly journals The combined global gravity field model XGM2019e

2020 ◽  
Vol 94 (7) ◽  
Author(s):  
P. Zingerle ◽  
R. Pail ◽  
T. Gruber ◽  
X. Oikonomidou
Keyword(s):  
Gravity Field ◽  
Field Model ◽  
Gravity Field Model ◽  
Global Gravity ◽  
Global Gravity Field Model

scholarly journals Evaluation of Gravity Data Derived from Global Gravity Field Models Using Terrestrial Gravity Data in Enugu State, Nigeria

2018 ◽  
Vol 8 (1) ◽  
pp. 145-153 ◽  
Author(s):  
O.I. Apeh ◽  
E.C. Moka ◽  
V.N. Uzodinma
Keyword(s):  
Gravity Field ◽  
Gravity Data ◽  
Gravity Anomalies ◽  
Mean Square ◽  
Bouguer Gravity ◽  
Bouguer Anomalies ◽  
The Earth ◽  
Global Gravity ◽  
Enugu State ◽  
Gravity Field Models

Abstract Spherical harmonic expansion is a commonly applied mathematical representation of the earth’s gravity field. This representation is implied by the potential coeffcients determined by using elements/parameters of the field observed on the surface of the earth and/or in space outside the earth in the spherical harmonic expansion of the field. International Centre for Gravity Earth Models (ICGEM) publishes, from time to time, Global Gravity Field Models (GGMs) that have been developed. These GGMs need evaluation with terrestrial data of different locations to ascertain their accuracy for application in those locations. In this study, Bouguer gravity anomalies derived from a total of eleven (11) recent GGMs, using sixty sample points, were evaluated by means of Root-Mean-Square difference and correlation coeficient. The Root-Mean-Square differences of the computed Bouguer anomalies from ICGEMwebsite compared to their positionally corresponding terrestrial Bouguer anomalies range from 9.530mgal to 37.113mgal. Additionally, the correlation coe_cients of the structure of the signal of the terrestrial and GGM-derived Bouguer anomalies range from 0.480 to 0.879. It was observed that GECO derived Bouguer gravity anomalies have the best signal structure relationship with the terrestrial data than the other ten GGMs. We also discovered that EIGEN-6C4 and GECO derived Bouguer anomalies have enormous potential to be used as supplements to the terrestrial Bouguer anomalies for Enugu State, Nigeria.

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