Cammarano, Fabio

Guerri, Mattia

Tackley, Paul J.

English

Copenhagen University Research Information System

u n i ve r s i t y  o f  co pe n h ag e n  Københavns UniversitetGeophysical, petrological and mineral physics constraints on Earth’s surfacetopographyGuerri, Mattia; Cammarano, Fabio; Tackley, Paul J.Published in:Geophysical Research AbstractsPublication date:2015Document versionEarly version, also known as pre-printCitation for published version (APA):Guerri, M., Cammarano, F., & Tackley, P. J. (2015). Geophysical, petrological and mineral physics constraintson Earth’s surface topography. Geophysical Research Abstracts, 17, [6526-2].Download date: 03. Feb. 2020Geophysical Research AbstractsVol. 17, EGU2015-6526-2, 2015EGU General Assembly 2015© Author(s) 2015. CC Attribution 3.0 License.Geophysical, petrological and mineral physics constraints on Earth’ssurface topographyMattia Guerri (1), Fabio Cammarano (1), and Paul J. Tackley (2)(1) University of Copenhagen, Department of Geosciences and Natural Resource Management, Copenhagen, Denmark(mattia.guerri@ign.ku.dk), (2) Institute of Geophysics, ETH Zurich, Zurich, SwitzerlandEarth’s surface topography is controlled by isostatically compensated density variations within the lithosphere,but dynamic topography - i.e. the topography due to adjustment of surface to mantle convection - is an importantcomponent, specially at a global scale. In order to separate these two components it is fundamental to estimatecrustal and mantle density structure and rheological properties.Usually, crustal density is constrained from interpretation of available seismic data (mostly VP profiles) basedon empirical relationships such those in Brocher [2005]. Mantle density structure is inferred from seismictomography models. Constant coefficients are used to interpret seismic velocity anomalies in density anomalies.These simplified methods are unable to model the effects that pressure and temperature variations have onmineralogical assemblage and physical properties.Our approach is based on a multidisciplinary method that involves geophysical observables, mineral physics con-straints, and petrological data. Mantle density is based on the thermal interpretation of global seismic tomographymodels assuming various compositional structures, as in Cammarano et al. [2011]. We further constrain the top150 km by including heat-flow data and considering the thermal evolution of the oceanic lithosphere. Crustaldensity is calculated as in Guerri and Cammarano [2015] performing thermodynamic modeling of various averagechemical compositions proposed for the crust. The modeling, performed with the code Perple_X [Connolly,2005], relies on the thermodynamic dataset from Holland and Powell [1998]. Compressional waves velocity andcrustal layers thickness from the model CRUST 1.0 [Laske et al., 2013] offer additional constrains. The resultinglithospheric density models are tested against gravity (GOCE) data.Various crustal and mantle density models have been tested in order to ascertain the effects that uncertainties in theestimate of those features have on the modeled topography. We also test several viscosity models, either radiallysymmetric, the V1 profile from Mitrovica and Forte [2004], or more complex laterally varying structures.All the property fields are expanded in spherical harmonics, until degree 24, and implemented in the code StagYY[Tackley, 2008] to perform mantle instantaneous flow modeling and compute surface topography and gravitationalfield.Our results show the importance of constraining the crustal and mantle density structure relying on a multidisci-plinary approach that involves experimentally robust thermodynamic datasets. Crustal density field has a strongeffect on the isostatic component of topography. The models that we test, CRUST 1.0 and those in Guerri andCammarano [2015], produce strong differences in the computed isostatic topography, in the range±600 m. For thelithospheric mantle, relying on experimentally robust material properties constraints is necessary to infer a reliabledensity model that takes into account chemical heterogeneities. This approach is also fundamental to correctlyinterpret seismic models in temperature, a crucial parameter, necessary to determine the lithosphere-asthenosphereboundary, where static effects on topography leave place to dynamic ones.The comparison between results obtained with different viscosity fields, either radially symmetric or verticallyand laterally varying, shows how lateral viscosity variations affect the results, in particular the modeled geoid, atdifferent wavelengths.References:Brocher, T. M. (2005), Empirical Relations between Elastic Wavespeeds and Density in the Earth’s Crust, Bulletinof the Seismological Society of America, 95(6), 2081-2092.Cammarano, F., P. J. Tackley, and L. Boschi (2011), Seismic, petrological and geodynamical constraints onthermal and compositional structure of the upper mantle: global thermochemical models, Geophys. J. Int.Connolly, J. A. D. (2005), Computation of phase equilibria by linear programming: A tool for geodynamicmodeling and its application to subduction zone decarbonation, Earth and Planetary Science Letters (236),524-541.Guerri, M., and F. Cammarano (2015), On the effects of chemical composition, water and temperature on physicalproperties of the Earth’s continental crust, submitted to Geochemistry, Geophysics, Geosystem.Holland, T. J. B., and R. Powell (1998), An internally consistent thermodynamic data set for phases of petrologicalinterest, J. metamorphic Geol., 16(309-343).Laske, G., G. Masters, Z. Ma, and M. E. Pasyanos (2013), CRUST1.0: An updated global model of Earth’s crust,in EGU General Assembly 2013, edited, Geophysical Research Abstracts, Vienna.Mitrovica, J. X., and A. M. Forte (2004), A new inference of mantle viscosity based upon joint inversion ofconvection and glacial isostatic adjustment data, Earth and Planetary Science Letters, 225, 177-189.Tackley, P. J. (2008), Modelling compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid, Phys. Earth Planet. Int.

Geophysical, petrological and mineral physics constraints on Earth’s surface topography

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Geophysical, petrological and mineral physics constraints on Earth’s surface topography

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