ELSI Seminar

Jain Charitra
June 18, 2018


The Interplay Between Internal Dynamics and Surface Evolution on Earth and Earth-Like Planets

I use geodynamic models to study long-term planetary evolution in terms of continent generation, continental insulation and operation of plate tectonics. I developed a two-stage melting parameterisation that can self-consistently generate Archean continental crust (TTG rocks) within a global mantle convection model for Earth. In contrast to the present-day loci of crust formation around subduction zones and intra-plate tectonic settings, TTGs are formed when hydrated basalt melts at garnet-amphibolite, granulite or eclogite facies conditions. The basaltic magma is extracted from the pyrolytic mantle, it gets hydrated, and then partially melts to form continental crust. To study the growth of TTG and the geodynamic regime of early Earth, I systematically varied the ratio of intrusive (plutonic) and eruptive (volcanic) magmatism, initial core temperature, and basalt-TTG production efficiency. I will show you the modelling results and compare them with geological and !
geochemical data.

I also identified the qualitative and quantitative correlation between continents and elevated temperatures in the Earth's mantle by conducting a systematic parameter study using 2D global convection simulations with prescribed continents. In my incompressible and compressible models, I observed the general processes of downwellings bringing cold material down into the mantle along continental margins and a buildup of thermal anomalies underneath the continents. I computed the amplitude and degree of this correlation using spectral decomposition of temperature and composition fields. Using scaling laws, I quantitatively argued that this correlation decreases with increasing core temperature, number of continents, internal heating, and Rayleigh number. Additionally, I showed for the first time that the melting and crustal production events resulting from this correlation lead to voluminous volcanism. The emplacement of this basalt-eclogite material breaks the continents apart!
, thereby destroying the correlation and acting as a negative feedback.

What conditions enable a planet like Earth to host and sustain life? This question of planetary habitability is becoming increasingly relevant with the rapidly expanding catalog of extrasolar planets over the last decades. As my research agenda at ELSI, I propose an interdisciplinary study of (exo-)planetary evolution, merging methods and expertise from geophysics, geochemistry, high-pressure mineral physics, petrology, atmospheric sciences and astrophysics. I propose to make use of and extend geodynamical methods to evaluate the feasibility of plate tectonics on extrasolar terrestrial planets, especially super-Earths, and assess their habitability. The proposed parameter space is based on several habitability factors, such as the mass of the central star and its distance from the planet, the atmospheric composition, orbital stability, the presence of water and the operation of plate tectonics. Subduction-driven plate tectonics are known to play an important role in the atmo!
spheric evolution of Earth, thereby helping stabilise its climate on long-term timescales.