Mathematics – Logic
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.p21b..06h&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P21B-06
Mathematics
Logic
5417 Gravitational Fields (1221), 6225 Mars, 8147 Planetary Interiors (5430, 5724, 6024), 3255 Spectral Analysis (3205, 3280)
Scientific paper
The northern lowlands cover 1/3 of Mars' surface and are a fundamental part of the geologic evolution of Mars. We examine the admittance, (ratio of gravity to topography in the spectral domain), to better constrain the timing of northern lowlands formation. Prior to this study there have been no successful estimates of elastic thickness (Te) in the lowlands (with the exception of Utopia) due to low topographic signal. We use a Cartesian multitaper approach (that has been successful for topographically eroded regions on Earth) to estimate Te for 4 lowland regions. These regions are well resolved in the gravity data, display well constrained lithospheric parameters, and topographic power spectra similar to many highlands regions. We use the latest spherical harmonic gravity field (MGS95J), carried out to degree and order 95. The field is determined globally to degree 70 (~305km), where the noise of the unconstrained solution equals the signal. Spherical harmonic coefficients for the topography were created in the same reference as the gravity. We compare the observed admittance with those predicted from lithospheric flexure models. On the basis of these comparisons, we estimate the Te required to support the observed topographic load since the time of loading. Top and bottom loading models are used to derive Te and crustal thickness or apparent depth of compensation. All 4 regions are best fit by a bottom-loading model. We obtain best fit Te estimates between 10-25km with an acceptable error range of 0-45km. These small estimates are similar to previous studies of the southern highlands and are consistent with formation in the Noachian when heat flow was high. The consistency in Te estimates between the Noachian highlands and lowlands basement suggests that both regions of the crust formed within a short time. The paucity of crustal magnetization in the lowlands is thus more likely a result of demagnetization than formation following shutdown of the dynamo. Most proposed mechanisms of lowlands formation predict low Te values, with the exception of plate tectonics, which predict a range of values in the lowlands. The bottom loading signature is also consistent with loading via a plume or plumes, or low-density mantle residuum.
Hoogenboom Trudi
Smrekar Suzanne E.
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