Phase equilibrium investigations of the Adirondack class basalts from the Gusev plains, Gusev crater, Mars

Abstract

Abstract-Phase equilibrium experiments have been performed on a synthetic analog of the Gusev plains basalt composition from the Spirit landing site on Mars. Near-liquidus phase relations were determined over the pressure range of 0.1 to 1.5 GPa and at temperatures from 1125 to 1390 °C in a piston cylinder apparatus and 1 atm gas mixing furnace. The composition is multiply saturated with olivine, orthopyroxene, and spinel near its liquidus at 1320 °C and 1.0 GPa, or 85 km depth on Mars, placing an upper limit constraint on the thickness of the Martian lithosphere at the time of eruption. Our experimental work suggests that the Gusev basalts are anhydrous batch melts of a primitive Martian mantle similar to the composition estimated by Dreibus and Wänke (1984). The temperature of multiple saturation indicates the persistence of high mantle potential temperatures on Mars, similar to those on the modern Earth, until at least the very latest Noachian (3.7 Ga). These high mantle temperatures would be responsible for persistent basaltic volcanism throughout the southern highlands during the first billion years of Mars's history. The source for Gusev basalts differs strongly from the source for shergottite meteorites, reinforcing the idea of the absence of global mantle convection and mixing on Mars. The existence of a relatively primitive mantle reservoir requires that at least part of the mantle underwent little modification during early planetary differentiation.

The evolution of a heterogeneous Martian mantle: Clues from K, P, Ti, Cr, and Ni variations in Gusev basalts and shergottite meteorites

“…In contrast to the shergottites, these basalts contain fewer conspicuous crystals (McSween et al, 2004;Squyres et al, 2006) and more likely represent primary melts (Monders et al, 2007) than accumulated crystal mushes. Alkali abundances are variable in Gusev basalts (from below detection limits to 1.2 wt.% K 2 O; McSween et al, 2006aMcSween et al, , 2006bMcSween et al, , 2008 over narrow ranges in SiO 2 and MgO concentrations (Fig.…”

“…The Gusev basalts originate from a separate mantle reservoir than the basaltic shergottites based on high-pressure phase equilibria studies on a synthetic analog to Adirondack, a Gusev plains basalt (Monders et al, 2007). Adirondack melt multiply saturates with olivine, orthopyroxene, and spinel near its liquidus at 1320°C and upper mantle pressures at 1.0 GPa (85 km depth).…”

Water storage and early hydrous melting of the Martian mantle

“…This composition is similar to the one proposed by Lodders and Fegley (1997) from oxygen isotope evidence. Also, the Dreibus and Wänke (1985) composition has been shown to be consistent with phase equilibria constraints from basaltic rocks at Gusev crater (Bertka and Holloway, 1994;Monders et al, 2007), and it allows a direct comparison with the work by Mé dard and Grove (2006) performed at lower pressures. Bertka and Fei (1997) have also investigated the phase equilibrium of this composition over a wide pressure range under dry conditions (e.g.…”

“…This paper presents an experimental investigation at low temperature (700-920 1C) and high pressure (4-7 GPa) of a water-saturated analog of the primitive Martian mantle (Dreibus and Wänke, 1985). This composition corresponds to the mantleþcrust Martian bulk composition and is consistent with phase relations of basaltic rocks from Gusev crater (Monders et al, 2007). The hypothesis of an accretion-driven early hydrous melting is tested in order to further our understanding of the processes by which Mars evolved to its present state.…”

“…These data are the filter through which computing models attempt to constrain accretion and differentiation processes of Mars. The post-magma ocean history of Mars has been widely investigated with experiments on a dry Martian mantle and basalt analogs (Bertka and Holloway, 1994a,b;Bertka and Fei, 1997;Agee and Draper, 2004;Musselwhite et al, 2006;Monders Minitti and Rutherford, 2007;Filiberto et al, 2008Filiberto et al, , 2010Filiberto and Treiman, 2009). However, only a limited number of studies performed on a hydrous mantle analog at experimental conditions relevant to early water storage on Mars investigated the pre-magma ocean time.…”