Title: Evidence of Tharsis-Radial Dike Intrusion in Southeast Alba Patera from MOLA-based Topography of Pit Crater Chains
Abstract: INTRODUCTION: Tharsis-radial graben and pit crater chains (catenae) have been interpreted as the result of igneous dike intrusions [1,2,3], which attain lengths in excess of 2000 km from the center of the Tharsis volcano–tectonic province. Based on the assumption that these Tharsis–radial graben and pit crater chains are underlain by dikes, geodynamic models of lithospheric uplift have been proposed to account for the stress state required for Tharsis–radial dike propagation [4] and the attendant magma fluxes have been estimated [2]. In this abstract, we test the fundamental assumption that Tharsis–radial pit crater chains are underlain by igneous dikes by examining Phlegethon, Acheron and Tractus Catenae on the southeast flank of Alba Patera. Following [5] we compare MOLA–based topography against standard numerical model predictions of surface deformation above buried and surface– breaking dikes and normal faults. We find that these pit crater chains have local cross–strike topographies that are consistent with origins by either dike intrusion, by normal faulting, or by a mixed–mode of dike intrusion and normal faulting, with the causative tendencies changing with position along strike of each pit crater chain (Fig. 1). CHARACTERISTIC FAULT–AND DIKE–-INDUCED TOPOGRAPHY: We employ a boundary element code [6] to establish the distinct topographic characteristics of surface–breaking and buried normal faults and dikes under natural variations in crustal strength and deformability. We vary crustal elastic modulus between 1 GPa and 60 GPa, Poisson’s ratio between 0.2 and 0.3, and the σ3 to σ1 principal stress ratio (a function of friction, cohesion and groundwater condition) between 3 and 5, with σ1 equal to lithostatic load. The average magma to crustal density ratio is 0.85. The modeled normal faults are planar and dip at 50° to 70°, and dikes dip at 70° to 90°. Pertinent results from this series of models are shown in figure 2. Through the range of tested strength and deformability parameters, the topography above a vertical dike is characteristically symmetric, while asymmetric topography is predicted above inclined dikes. The uplifted ridges on either side of the modeled dike tops have a concave-down topography. The topography around a single normal fault is shown to be characteristically asymmetric, and [5] has shown that this asymmetry can also be predicted when an antithetic fault is present within the hanging wall. The uplifted footwall is characterized by concave–up topography, while the subsided hanging wall has a characteristic concave–down topography. 250 255 260 265 270
Publication Year: 2005
Publication Date: 2005-03-01
Language: en
Type: article
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Cited By Count: 3
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