T342 Basalt Weathering on Earth and Mars

Wednesday, 25 October 2017
1:30 PM - 5:30 PM
Tahoma 1

APATITE AS A RECORDER OF HYDROTHERMAL AND METASOMATIC EVENTS ON MARS

Paper number: T342-9
Program: Technical Sessions
Time: 3:30 PM – 3:45 PM

Authors

  • Yang Liu Presenting Author
    Jet Propulsion Laboratory, Pasadena, CA

Abstract

Apatite, Ca5(PO4)3(F, Cl,OH), in extraterrestrial rocks is now a key recorder of volatiles in igneous systems and an important window into volatiles in the interiors of planetary bodies. A less appreciated use of apatite in these extraterrestrial rocks is its ability to record hydrothermal and metasomatic events. Specifically, in the case of Mars that had a wet past much like Earth, we recognized that apatite can record hydrothermal and metasomatic events, like those on Earth (Howarth et al., 2016; Liu et al., 2016).

In Martian regolith breccias NWA 7034 and 7533, a significant portion of apatite grains (≤10% of apatite grains) show signs of hydrothermal alteration. These apatite grains contain clusters of sub-μm monazite [(Ce, Nd, La, Y)PO4] inclusions, and occasionally irregular, zoned merrillite inclusions (Na-merrillite in the interior to REE-merrillite toward the interface with apatite host). The apatite hosts are mainly chlorapatite, but apatite regions next to monazite and merrillite inclusions are F-rich, with compositions reaching pure fluroapatite. Cathodoluminescence (CL) images of monazite-bearing apatite grains display no igneous zonings, in contrast to zonings observed in monazite-free apatite in the same samples. The textural and compositional observations suggest that hydrothermal fluid leached REE from chlorapatite and merrillite, which then reprecipitated as monazite. Fluorine-rich apatite associated with monazite and merrillite inclusions suggest F-rich fluids were likely involved in the hydrothermal reactions. The monazite-bearing and merrillite-bearing chlorapatite, together with other evidence of hydrothermal alterations and metamorphic events in these meteorites, indicate multiple hydrothermal environments in crustal environments of Mars. Another evidence of post-crystallization alteration was observed in apatite grains in paired olivine-phyric shergottites (basaltic meteorites), LAR 06319 and 12011. Variations of Cl in apatite grains are best explained by interaction with a Cl-rich and possible water-rich fluid after crystallization (Howarth et al., 2016).

These recent observations emphasize non-trivial effects of secondary processes on apatite, and the large potential of using apatite to infer the nature of crustal fluids on Mars.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-304121

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