Density, temperature, and composition of the North American lithosphere—New insights from a joint analysis of seismic, gravity, and mineral physics data: 1. Density structure of the crust and upper mantle

Abstract

We introduce a new method to construct integrated 3-D models of density, temperature, and compositional variations of the crust and upper mantle based on a combined analysis of gravity, seismic, and tomography data with mineral physics constraints. The new technique is applied to North America. In the first stage, we remove the effect of the crust from the observed gravity field and topography, using a new crustal model (NACr2014). In the second step, the residual mantle gravity field and residual topography are inverted to obtain a 3-D density model of the upper mantle. The inversion technique accounts for the notion that these fields are controlled by the same factors but in a different way, e.g., depending on depth and horizontal dimension. This enables us to locate the position of principal density anomalies in the upper mantle. Afterward, we estimate the thermal contribution to the density structure by inverting two tomography models for temperature (NA07 and SL2013sv), assuming a laterally and vertically uniform ''fertile'' mantle composition. Both models show the cold internal part and the hot western margin of the continent, while in some Proterozoic regions (e.g., Grenville province) NA07 at a depth of 100 km is >200 C colder than SL2013sv. After removing this effect from the total mantle anomalies, the residual ''compositional'' fields are obtained. Some features of the composition density distribution, which are invisible in the seismic tomography data, are detected for the first time in the upper mantle. These results serve as a basis for the second part of the study, in which we improve the thermal and compositional models by applying an iterative approach to account for the effect of composition on the thermal model.

Density structure and isostasy of the lithosphere in Egypt and their relation to seismicity

“…In this section we describe a general approach for the integrative analysis of gravity and other geophysical data that was developed and applied previously for Europe, North America, and some parts of Asia (Kaban et al, , 2014a(Kaban et al, , 2016a. All details on the methods and datasets used will be provided in the following sections.…”

“…Therefore, the identification of density variations in the crust and upper mantle is challenging and this problem cannot be solved by a particular geophysical method alone. Recent efforts have aimed at integrating multiple geophysical and petrological datasets into a common interpretation framework (e.g., Fullea et al, 2009;Gradmann et al, 2013;Kaban and Mooney, 2001;Kaban et al, 2014a).…”

Density, temperature, and composition of the North American lithosphere—New insights from a joint analysis of seismic, gravity, and mineral physics data: 2. Thermal and compositional model of the upper mantle

“…Therefore, an infinite number of solutions can be obtained, besides the preferred one. In Part 1 [ Kaban et al ., ], we have presented a newly developed inversion technique that jointly utilizes gravity and seismic tomography data to simultaneously estimate thermal and compositional density heterogeneity in the upper mantle. To test this technique, we chose as a study area the North American (NA) continent (10°N by 85°N and 170°W by 50°W), which is composed of a mosaic of tectonic provinces of different age (Figure ).…”

“…In Kaban et al . [], we first computed mantle gravity anomalies and residual topography by estimating the gravity effect of the crust. The latter was evaluated using as input NACr14, the most recent NA crustal model, providing thickness and average velocity of the three layers that comprise the crystalline crust [ Tesauro et al ., ].…”

“…Successively, we inverted for temperature of the upper mantle the regional NA07 [ Bedle and van der Lee , ] and the global SL2013sv [ Schaeffer and Lebedev , ] tomography models, based on similar data and assumptions in order to evaluate possible discrepancies due to using different tomography data. In fact, as discussed before [ Kaban et al ., ], the amplitudes of the seismic anomalies may differ significantly for various seismic tomographic models depending on the method used. In the inversion for mantle density, we used a uniform composition representative of a “fertile” mantle, affected by a small amount of melt extraction.…”