Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p34a..08n&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P34A-08
Mathematics
Logic
5416 Glaciation, 5419 Hydrology And Fluvial Processes, 5420 Impact Phenomena, Cratering (6022, 8136), 5480 Volcanism (6063, 8148, 8450), 6225 Mars
Scientific paper
In early attempts to quantify the geologic history of Mars by crater counting techniques, most of the geological units and structures came out as being rather old, in the range of billions of years with an exception of the Tharsis province, whose volcanic constructs were found to already have existed more than 3.5 Ga ago, but which showed, at least partly, signatures of relatively young (hundreds of millions of years) volcanic activity. On the other hand, most of the ages of the martian meteorites cluster at relatively young values of around 175 m.y., 300-600 m.y. and ~ 1.3 Ga, whereas very few old ages >3 Ga had also been found. The early cratering age determinations were based on the Viking image data analysis. With the new data from MGS (MOC), MEX (HRSC), and Mars Odys-sey (THEMIS), it has become clear that the apparent discrepancy between the two age sets was a se-lection effect due to the limited Viking resolution forcing to study predominantly large, old features. Significantly younger ages have been determined since on the basis of the new high-resolution im-agery with spatial resolutions in the meter to a few tens-of-meters range. In this work we report on results from investigation of a combination of HRSC, MOC and THEMIS imagery in ten regions of Mars, such as the regions of Mangala Valles, Kasei Valles, Libya Montes, Iani/Tiu/AresValles, Medusae Fossae and five more. We have in particular mapped out and analyzed for their geologic evolution and cratering ages the two large outflow channel areas, Mangala Valles and Echus Chasma/Kasei Valles. In both areas we have found multistage geological histories with mixed volcanic, fluvial, glacial, and hydrothermal activity. The new data in combination with the previous data have been analyzed by way of a refined method of cratering age extraction also giv-ing fine details of periods of resurfacing from the characteristics of the measured crater size-frequency distributions as they deviate from the production size-frequency distributions due to resur-facing effects. Our data show, in confirmation of more subtle indications over the past two years of research, that there has been volcanic and fluvial geologic activity on the martian surface at all times from >4 Ga ago until today. This activity was rather continual if to consider all ten studied regions together but with episodic temporary increases of intensity of both volcanic and fluvial and/or glacial processes at periods ~ 3.5 Ga, 1 to 1.5 Ga, 300 to 800 m.y., ~ 200 m.y. ago. The episodes we find on the martian surface in the crater size frequency analyses are well coincident with the age groups of the martian meteorites found from radiometric dating. Episodes of volcanic activity were probably initi-ating the fluvial and/or glacial activity. This explains their correlation in time.
Bazilevskiy A.
Chapman Mark
Gerhard Neukum
Jaumann Ralf
Kneissl Thomas
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