Elastic Thickness, Paleo Heat Flow, and Curie Depth at the Tyrrhena Patera Highland Volcano

era Highland Volcano M. Grott and M. A. Wieczorek, German Aerospace Center, Berlin, Germany (matthias.grott@dlr.de), Institut de Physique du Globe de Paris, France Introduction: Tyrrhena Patera is a low-relief volcanic construct possessing an irregularly shaped summit caldera, and its morphology and topography is attributed to explosive volcanism related to phreatomagmatic processes. The entire construct was emplaced early in Martian history before 3.9 Ga, but subsequent activity occurred well into the Amazonian period. The caldera itself has a crater retention age of 3.3 Gyr, with limited resurfacing occurring around 1.5 Gyr [1]. A weak magnetic anomaly is associated with Tyrrhena Patera, indicating that the volcano formed in the presence of global magnetic field before magmatism demagnetized part of the crust [2]. A well localized positive free-air gravity anomaly is associated with the construct and a good correlation exists with the features topography (cp. Fig. 1). Here we use the latest gravity field model for Mars [3] expanded up to degree and order 110 to model the admittance at Tyrrhena Patera and constrain the density of the volcanic load as well as the elastic lithosphere thickness at the time of load emplacement. The improved gravity field model is above the noise level for degrees up to 95, allowing for the analysis and interpretation of small scale features such as Tyrrhena Patera. Furthermore, we derive estimates for the paleo-heat flow and Curie depths at Tyrrhena Patera assuming different carriers of the observed magnetization. Modeling: To model the observed admittance at Tyrrhena Patera we calculate the linear transfer function Ql between gravity and topography coefficients in the spherical harmonics domain using a forward model appropriate for top loading of the lithosphere [4]. Apart from the crust and mantle densities, crustal thickness, and material parameters, Ql is a function of the elastic lithosphere thickness and the load density and we invert for these parameters by fitting the modeled admittance to the observations. Tyrrhena Patera is located at 106.53E and 21.36S and we use a spherical cap localization window centered around this location to perform a localized admittance analysis. The chosen localization window has a cap diameter of θ0 = 7 and a spherical harmonic bandwidth of L = 37 was chosen, such that 99% of the gravity and topography signals are localized inside the window. In the analysis we reference the gravity field to the average planetary radius at the location of interest, which for this analysis isR = 3395.5 km. Other parameters used in the calculations are a mantle density ρm of 3500 kg m−3, a Figure 1: Topography (MarsTopo719.shape) and radial free-air gravity anomaly (MRO110b2 [3]) at Tyrrhena Patera, both referenced to a sphere of radius R = 3395.5 km and truncated at spherical harmonic degree 95. The circle indicates the location of the localization window.