Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusm.p21d..09h&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #P21D-09
Physics
5430 Interiors (8147), 8147 Planetary Interiors (5430, 5724)
Scientific paper
The northern hemisphere lowlands of Mars cover approximately one-third of the surface of the planet. While crustal remnant magnetization is very strong in much of the Martian highlands, in contrast only a few low amplitude anomalies occur in the lowlands [Acuna et al., 1999]. The scarcity of magnetic anomalies in the lowlands remains unexplained. Crater counts for the northern lowlands basement based on analyses of high-resolution MOLA maps show that they are comparable in age to the southern highlands [Frey, 2004]. Since the basement age is so similar, it seems unlikely that the dynamo could have been active during formation of the highlands but not the lowlands. Topography and gravity measured by the Mars Global Surveyor have enabled the determination of elastic thickness (Te) estimates in the highlands [e.g. McGovern et al., 2002]. However, there have been no successful estimates in the Northern lowlands with the exception of Utopia basin [Zuber et al., 2002]. The failure is assumed due to insufficient power in the topography. Although the northern plains have clearly been eroded, we find that for selected Northern lowland regions, the power in the topography is smaller but comparable to areas of the southern highlands, previously used to obtain Te estimates. Previously, inversions based on isostatic response methods using eroded topography yielded incorrect results [Forsyth, 1985]. McKenzie and Fairhead [1997] find that Forsyths method can only be used to estimate Te where the power of the gravity from the uncompensated topography is comparable to that of the observed gravity at short wavelengths. If this condition is not satisfied, because the short-wavelength gravity is dominated by sub-surface loads and not by the topography, the estimated value of Te provides an upper bound. We use a multi-taper approach that has been successful at minimizing this bias for eroded cratons on Earth [Swain & Kirby, 2003]. In this study we perform detailed modeling of the admittance for the northern lowlands of Mars in order to estimate elastic thickness and better constrain the timing of formation of the northern lowlands. An upper bound on the elastic thickness in the northern lowlands provides insight into the timing of formation or reheating of the northern plains, which appear to have occurred after cessation of the dynamo.
Hoogenboom Trudi
Smrekar Sue
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