The interpretation of geologic processes on Mars from sparse meteorite, remote sensing and rover data is influenced by knowledge gained from well-characterized terrestrial analogues. This calls for detailed study of candidate terrestrial analogues and comparison of their observable features to those encountered on the surface of Mars. We evaluated the mineralogical, geochemical, and physical properties of the Balos cove basalts (BCB) from the island of Santorini and compared them to Martian meteorites, Mars rover surface measurements, and other verified Martian analogues obtained from the International Space Analogue Rockstore (ISAR). Twenty rock samples were collected from the Balos cove area based on their freshness, integrity, and basaltic appearance in the field. Optical microscopy of BCB revealed a pilotaxitic to trachytic texture, with olivine and clinopyroxene phenocrysts in a fine groundmass of olivine, clinopyroxene, plagioclase, magnetite, and devitrified glass. All major minerals show normal zoning, including calcic plagioclase (An 78-85 at the core and An 60-76 at the rim), augite (En 36-48 Wo 41-44 Fs 11-21), and olivine (Fo 74-88). The dominant bands in the infrared-attenuated total reflectance (IR-ATR) spectra from BCB can be assigned to olivine (~875 cm-1), calcic plagioclase (~1130 cm-1), and augite (~970 cm-1). The whole-rock chemical compositions and mineralogy of the BCB are similar to published analyses of typical olivine-phyric shergottites and basalts and basaltic materials analyzed in Gusev and Gale craters on Mars. BCB porosity is in the range of 7-15 % and is similar to the porosities of the ISAR samples. Although no terrestrial rock is ever a perfect match to Martian compositions, the differences in mineralogy and geochemistry between BCB and some classes of Martian samples are relatively subtle and the basalts of Santorini are as close a match as other accepted Mars basalt analogues. The Santorini site offers excellent field logistics that, together with the petrology of the outcrop, makes it a valuable locality for testing and calibration deployments, field training, and other activities related to current and future Mars exploration.
Santorini volcano sits ~145 km above the Aegean Wadati-Benioff zone, where the African plate subducts northward beneath Eurasia. There are only a few localities in the whole Aegean where basaltic lavas primitive enough to constrain mantle processes beneath the Aegean arc can be found; in this work we analyzed one such locality, a basalt lava from the southern part of Santorini. We apply a suite of petrological tools (PRIMACALC2 and ABS5) in sequence to estimate magma chamber conditions, primary magma composition, mantle melting conditions, and slab dehydration conditions. Back-calculation modeling based on major-element chemistry yields shallow magma chamber conditions of P = 0.02 GPa, fO 2 = QFM+2, and ~1 wt.% H 2 O in the primary magma. The estimated major element composition of this primary magma then leads to estimated mantle melting conditions of 2.1 GPa, 1353°C, and F = 8%; whereas a more precise estimate derived from trace element modeling implies 1.7 GPa, 1323°C, and F = 18%. Furthermore, the trace element model implies a slab flux derived from 4.6 GPa (~150 km slab depth). The estimated slab depth, magma segregation conditions, and magma chamber depth are all consistent with seismic observations, supporting slab dehydration in the seismically imaged steep slab interval and flux melting in a relatively hot mantle wedge.
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