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This contribution is provided to complement the manuscript submitted to Geophysical Journal International by these authors. The paper is entitled Instantaneous 3D tomography-based convection beneath the Rungwe Volcanic Province, East Africa: implications for melt generation. Here we provide our instantaneous 3D tomography-based convection (TBC) model that incorporates melt generation beneath the Rungwe Volcanic Province (RVP), the southernmost volcanic center in the Western Branch of the East African Rift. The 3D TBC was simulated using the open source code ASPECT version 2.2.0. The aim of this work is to test the hypothesis that the interaction of a thermally heterogeneous asthenosphere (plume material) with the base of the lithosphere enables localization of deep melt sources beneath the Western Branch where there are sharp variations in lithospheric thickness. To test our hypothesis, we investigate sublithospheric mantle flow beneath the Rungwe Volcanic Province (RVP), which is the southernmost volcanic center in the Western Branch. We use seismically constrained lithospheric thickness and sublithospheric mantle structure to develop an instantaneous 3D thermomechanical model of tomography-based convection (TBC) with melt generation beneath the RVP using ASPECT. Shear wave velocity anomalies suggest excess temperatures reach ~250 K beneath the RVP. We use the excess temperatures to constrain parameters for melt generation beneath the RVP and find that melt generation occurs at a maximum depth of ~140 km. The TBC models reveal mantle flow patterns not evident in lithospheric modulated convection (LMC) that do not incorporate upper mantle constraints. The LMC model indicates lateral mantle flow at the base of the lithosphere over a longer interval than the TBC model, which suggests that mantle traction from LMC might be overestimated. The TBC model provides higher melt fractions with a slightly displaced melting region when compared to LMC models. Our results suggest that upwellings from a thermally heterogeneous asthenosphere distribute and localize deep melt sources beneath the Western Branch in locations where there are sharp variations in lithospheric thickness. Our TBC models demonstrate the need to incorporate upper mantle constraints in mantle convection models and have global implications in that small-scale convection models without upper mantle constraints should be interpreted with caution. The models provided are contained in the following directories : 1. TBC_1473K_0.15factor 2. TBC_1473K_0.20factor 3. TBC_1473K_0.25factor 4. TBC_1483K_0.20factor 5. TBC_1473K_0.20factor_zero_compressibility 6. TBC_litho100km_1473K_0.20factor 7. LMC_compressible_1723K 8. LMC_compressible_1733K 9. LMC_compressible_1743K The directories in (1), (2) and (3) are models of TBC with excess sublithospheric mantle temperature derived from shear wave velocity perturbations (Emry et al., 2019) and whose background temperatures are constrained with mantle potential temperatures, Tp = 1473K and velocity-density conversion factors, 0.15, 0.20 and 0.25 respectively. The directory in (3) corresponds to TBC models for Tp = 1487 K and velocity-density conversion factor of 0.20. The directory in (5) is for TBC models without compressibility in the density equation of state with Tp =1473 K and conversion factor 0.20. The directory in (6) is model of TBC with a uniform 100 km thick lithosphere with Tp = 1473K and conversion factor = 0.20. The directories in ( (7), (8) and (9) correspond to models without seismic constraints of excess sublithospheric mantle temperature. Thus are models of lithospheric modulated convection (LMC) in which the sublithospheric mantle temperatures are constrained with Tp = 1723K, 1733K and 1743 K respectively. Each of the above models (directories) include a log.txt file that contains information of the maximum melt fraction and the corresponding model time, which permit use to test the different Tp values and conversion factors in melt generation. And also to test the relative role of lithospheric thickness variations versus sublithospheric heterogeneities in upper mantle flow and melt generation beneath the RVP. The above models also include files that allow for visualization in 3D using the software VISIT or PARAVIEW. Visualization parameters include: temperature field, viscosity, density, pressure, compositional fields, mesh, and velocities. We also provide corresponding csv files of above models. Each of these csv files contain 16 columns with the following names: "velocity:0","velocity:1","velocity:2","p","T","crust","mantle_lithosphere","porosity","peridotite","density","viscosity","melt_fraction","nonadiabatic_temperature","Points:0","Points:1","Points:2". These csv files can be used to extract information from the models and plot in another software such as Generic Mapping Tools (GMT). |
