A petrogenetic model for the origin and compositional variation of the martian basaltic meteorites

Abstract

The incompatible-element abundances of the most depleted (QUE 94201-like) source region have also been calculated and provide an estimate of the composition of depleted martian mantle. The incompatible-element pattern of depleted martian mantle calculated here is very similar to the pattern estimated for depleted Earth's mantle. Melting the depleted martian mantle composition reproduces the abundances of many incompatible elements in the parental melt of QUE 94201 (e.g., Ba, Th, K, P, Hf, Zr, and heavy rare earth elements) fairly well but does not reproduce the abundances of Rb, U, Ta and light rare earth elements. The source regions for meteorites such as Shergotty are successfully modeled as mixtures of depleted martian mantle and a late stage liquid trapped in the magma ocean cumulate pile. Melting of this hybrid source yields liquids with major element abundances and incompatible-element patterns that are very similar to the Shergotty bulk rock.

Uranium–lead isotope systematics of Mars inferred from the basaltic shergottite QUE 94201

“…Pb is from Stacey and Kramers (1975) and Antarctic ice is from Vallelonga et al (2005). Borg and Draper (2003), which were calculated using data from Blichert-Toft et al (1999), Borg et al (1997;2002), Nyquist et al (1979;1995;2000;2001) and Wooden et al (1982), with the exception of Y79, which are from Borg et al (2003) and Misawa et al (2006). Calculations of µ values of shergottite and Nakhla sources are described in the text and use data from Chen and Wasserburg (1986a;1986b;1993), Misawa et al (1997), Borg et al (2005) 1986;McKenzie and O'Nions, 1991;Beattie, 1993;Ewart and Griffin, 1994;Hauri et al, 1994).…”

“…Calculations of µ values of shergottite and Nakhla sources are described in the text and use data from Chen and Wasserburg (1986a;1986b;1993), Misawa et al (1997), Borg et al (2005) 1986;McKenzie and O'Nions, 1991;Beattie, 1993;Ewart and Griffin, 1994;Hauri et al, 1994). Partition coefficients for U are: 0.0001 for olivine, 0.001 for orthopyroxene, 0.02 for clinopyroxene, 0.0001 for garnet, 0.00001 for ilmenite and 0.00001 for sulfide (from: Snyder et al, 1992;Borg and Draper, 2003 Plag = plagioclase, MgPx = Mg-rich pyroxene, FePx = Fe-rich pyroxene, Ox = oxide, Phos = phosphate, Wr = whole rock, (L) = HCl leachate, (R) = residue of HCl leachate, rej = portion of magnetically-separated mineral fraction rejected after hand-picking. a.…”

“…In models of the lunar magma ocean, mafic cumulates form a depleted mantle end-member, and late-stage trapped liquid components form an enriched mantle end-member (Snyder et al, 1992). Subsequently, Borg and Draper (2003) presented a petrologic and geochemical model for the formation of these two end- (Borg and Draper, 2003). The µ value calculated for the mafic cumulate endmember modeled as the source for QUE is 3.7.…”

“…4) Borg et al (2003) inferred that the depleted and enriched martian basalt source end-members are analogous to the compositional end-members in the lunar mantle. The lunar mantle end-members are inferred to have formed from crystallization of the lunar magma ocean (e.g., Snyder et al, 1992), and thus Borg et al (2003) proposed that the martian source end-members also formed through crystallization of a magma ocean. In models of the lunar magma ocean, mafic cumulates form a depleted mantle end-member, and late-stage trapped liquid components form an enriched mantle end-member (Snyder et al, 1992).…”

“…In contrast to QUE, Zagami has the highest initial 87 Sr/ 86 Sr ratios, lowest initial ε Nd value , and one of the most LREE-enriched REE patterns. The enormous range of incompatible trace element abundances and Sr and Nd isotopic compositions observed in the martian meteorite suite has been attributed to extreme elemental fractionation in their source regions as a result of solidification of a martian magma ocean (e.g., Borg et al, 1997;Blichert-Toft et al, 1999;Brandon et al, 2000;Borg and Draper, 2003;Borg et al, 2003). In this hypothesis, the meteorites with trace element and isotopic signatures indicative of derivation from the most depleted source regions represent differentiates of melts of early-formed magma-ocean cumulates consisting primarily of olivine and pyroxene.…”