Other
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusm.p41a..07t&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #P41A-07
Other
1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 3672 Planetary Mineralogy And Petrology (5410), 5415 Erosion And Weathering, 5464 Remote Sensing, 5480 Volcanism (6063, 8148, 8450)
Scientific paper
The Mars Odyssey spacecraft gamma-ray spectrometer (GRS) is providing us with our first global database of the chemical composition of Mars. GRS has measured the concentrations of K, Th, Fe, Si, Al, Ca, Cl, and H in the upper few tens of cm at an intrinsic instrumental spatial resolution of about 500 km. The surface is compositionally heterogeneous, but summing the data into 5x5 degrees bins shows that each element has close to a normal distribution. K and Th are strongly correlated, Cl and H, and Si and Fe are weakly correlated, and Cl and Si are weakly anti-correlated. Correlations among other elements are statistically less significant. Cluster analysis on the elemental data indicates that in spite of the weak elemental correlations and normal distributions, large areas are similar to each other in composition. The clusters differ in key elemental variables, such as the concentrations of one or two elements (e.g., K, Th, and Fe) or elemental ratio (e.g., Ca/Al). We are searching for areas in which two or three elements all differ from the mean by more than one standard deviation. These areas are much smaller than those identified by cluster analysis, typically containing only several 5x5 grid points. The high Cl (0.2 to 0.8 wt%) and H2O (1.5 to 7 wt%, calculated from H concentrations) indicate the ubiquitous presence of the products of aqueous alteration. An initial (very rough) attempt to correct for such products (up to 10-15 wt% of each GRS measurement) using meteorite and landing-site data suggests that the primary igneous rocks are largely olivine basalts with a range in Fe/Mg and Al concentrations, similar to aqueously unaltered rocks reported at Gusev and Meridiani. The aqueous alteration is widespread but did not significantly affect the K/Th ratio, indicating either highly acid conditions or short wet periods. We will be able to determine the concentrations of S and U over large regions (but not be able to make maps). These elements will shed more light on the conditions of aqueous alteration on Mars.
Boynton Willam V.
Gasnault Olivier
Karunatillake Suniti
Lentz R. C.
Martel L. M.
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