Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p33g..01w&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P33G-01
Physics
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5480] Planetary Sciences: Solid Surface Planets / Volcanism, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The Circum-Hellas volcanic province (CHVP), with an area of >4.86 x 106 km2, is comparable in size to the Elysium volcanic province and contains some of the oldest volcanic materials on Mars. We used new studies of imaging (HRSC, THEMIS, MOC, HiRISE, CTX), multispectral (HRSC, OMEGA), topographic (MOLA) and gravity data to build on many previous studies to better understand the formation and evolution of the volcanic materials in and around the Hellas impact basin. The CHVP includes six central vent volcanoes (Tyrrhena, Hadriaca, Amphitrites, Peneus, Malea, and Pityusa Paterae) and neighboring wrinkle-ridged plains in Malea Planum, Hesperia Planum, western Prometheii Terra, and the eastern Hellas basin floor. Crater counts on THEMIS daytime-IR images show a spread in volcanic emplacement model ages between Middle- and Late-Noachian to Early- and Middle-Hesperian, in which the central vent volcanic units range from 4.0 Ga for Tyrrhena Patera to 3.6 Ga for Amphitrites Patera, and the volcanic plains units range from 3.8 Ga for Hellas floor units to 3.4 Ga for flows in SE Malea Planum. Volcanic activity most likely ceased by ~1 Ga, unlike in the Tharsis province where volcanism could have been as recent as the last few tens of million of years. Water and ice have had a significant role in the formation and modification the volcanic units in the CHVP, likely in response to obliquity-derived climate change. For example, the low slopes, well-channeled flanks, and smooth caldera floors (at tens of meters/pixel scale) of Tyrrhena, Hadriaca, and Amphitrites Paterae are indicative of volcanoes formed from poorly-consolidated pyroclastic deposits that have been modified by fluvial and aeolian erosion and deposition. Our analysis of surface materials shows that the thermal inertia decreases from north to south in the CHVP, and that there is greater dust cover on the flanks of the CHVP volcanoes than in their putative calderas. Local variations in thermal inertia in Malea Planum are likely due to variations in surface material caused by aeolian and periglacial/permafrost processes, whereas regional variations are likely due to seasonal deposition and sublimation of ice at higher latitudes. Spectral analysis of OMEGA data indicates the widespread presence of pyroxenes and/or olivine, particularly in the rims of craters that likely excavated volcanic materials. Derivation of modal mineralogies from OMEGA data show minor variations in composition across the CHVP: Olivine decreases from 11 to <5 wt% and ratios of low-calcium to total pyroxene decreases from 0.36 to 0.15 from south to north. These variations could represent differences in magma source regions for different parts of the CHVP, or difference in the degree of chemical alteration of exposed deposits with latitude.
Fergason Robin L.
Greeley Ronald
Manfredi Leon
Ody A.
Poulet François
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