Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31a1700d&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31A-1700
Other
[1595] Geomagnetism And Paleomagnetism / Planetary Magnetism: All Frequencies And Wavelengths, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5440] Planetary Sciences: Solid Surface Planets / Magnetic Fields And Magnetism, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The formation of large-scale crustal magnetic anomalies in the Southern Highlands of Mars is equivocal. Though some are indeed elongated primarily in the east-west direction, initial map projections exacerbated their linear nature, leading to the hypothesis that the anomalies are equivalent to magnetic stripes due to spreading of Earth's sea floor and hence to the proposal of plate tectonics on Mars. This interpretation, however, is inconsistent with Martian geology. For instance, a plate-tectonics model predicts the anomalies should be formed in thin, oceanic crust at low elevation, but instead they are found in the thick crust of the Highlands, not in the thin crust of the Northern Lowlands. Indeed, the formation of this Crustal Dichotomy is also equivocal, with models ranging from a giant impact (or multiple smaller impacts) near either the current north or south poles, to plate tectonics-like processes, to mantle convection, either eroding the crust in the northern hemisphere or thickening the crust in the south. Recently, the idea of a giant impact in the north has been resurrected, with the proposal that the Dichotomy results from the formation of an elliptical basin by a giant impact very early in Martian history. While it may be tempting to suggest that the current, generally demagnetized state of the Northern Lowlands may be related to this impact, this linkage makes implicit assumptions about the timing of dynamo shut-off on Mars, and it neglects other demagnetization mechanisms possibly operating in the Lowlands after such an impact (e.g., later hydrothermal processing). More direct magnetic evidence for the giant impact hypothesis would come if the remanent magnetism in Southern Highlands were relatable in a unique way to the putative impact. Here, we show that the positions of many of the dominant elongated magnetic anomalies on Mars are consistent with the first ring of a multi-ring basin. The best match comes from an ellipse ~2200 km wider than the inferred boundary of the basin. This distance is the square root of 2 minus 1 of the long axis, and root-2 spacing is characteristic of the inward dipping normal faults in multi-ring basins. The constant distance of our predicted ring, as opposed to variable spacing due to the elliptical nature of the basin, is also consistent with the idea that multi-ring basins form from stress release during inward collapse of the transient crater. Because of the size of the basin, the second ring would be found in the antipodal region, where its formation is dubious and where seismic focusing from the impact has been proposed to explain the generally absent magnetic anomalies in the south polar region. The observation that the elongated magnetic anomalies on Mars mark the first ring around a basin both provides an explanation for the formation of many of the anomalies, and supports the hypothesis that the Crustal Dichotomy of Mars is the product of a giant impact that formed an elliptical basin.
Dombard Andrew J.
Johnson Clifton L.
No associations
LandOfFree
The Smoking Gun: Remanent Magnetic Anomalies on Mars and the Formation of the Crustal Dichotomy via Giant Impact does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Smoking Gun: Remanent Magnetic Anomalies on Mars and the Formation of the Crustal Dichotomy via Giant Impact, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Smoking Gun: Remanent Magnetic Anomalies on Mars and the Formation of the Crustal Dichotomy via Giant Impact will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-870186