Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p33b1449h&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P33B-1449
Physics
3621 Mantle Processes (1038), 3630 Experimental Mineralogy And Petrology, 5430 Interiors (8147)
Scientific paper
We have conducted high pressure experiments in order to test if there are conditions that could produce both the shergottite parent magmas and the Gusev basalts. We have determined that the shergottite parent magmas originated deep in the mantle (~14 GPa or ~1200 km) where majoritic garnet fractionation occurs. The Gusev basalt source region is at a shallower depth in the mantle (≤10 GPa or ≤800 km) where majoritic garnet is not stable. Several recent studies support the idea that the modern martian crust and mantle may have been derived through the differentiation and crystallization of a chondritic magma ocean in the planet's earliest history. Majoritic garnet fractionation must occur early on during magma ocean crystallization in order to impart a superchondritic CaO/Al2O3 ratio to the residual magma ocean liquid. This is required to account for the superchondritic CaO/Al2O3 ratios that are observed in the shergottite parent magmas. This ratio should remain comparatively unperturbed by subsequent crystallization of olivine and orthopyroxene. However, the Gusev basalts sampled on the surface of Mars by the Spirit Rover do not exhibit a superchondritic CaO/Al2O3 ratio. If these rocks are largely unaltered basaltic samples, then their compositions appear to be inconsistent with having formed from a deep, global magma ocean. We show that both the shergottite parent magmas and the Gusev basalts can be derived from mantle plumes or regional magma oceans that are produced through impact melting. Our experimental results demonstrate that both the shergottite parent magmas and the Gusev basalts (provided they are genuine magmatic liquids) can be derived through igneous processing of a chondritic mantle and that a deep, global magma ocean is an unlikely mechanism of formation.
Agee Carl B.
Draper David S.
Hutchins K. I.
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