The curious case of the rock at Venera 8

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

The surface rock composition measured by gamma (γ)-ray spectrometry at the Venera 8 landing site has anomalously high Th (6.5 ± 2.2 ppm) and U (2.2 ± 0.7 ppm) concentrations with respect to the material analyzed at other landing sites (Vega 1, Vega 2, Venera 9, Venera 10). A calculated bulk rock composition of Venera 8, constrained by the measured Th, U and K2O (4.0 ± 1.2 wt%) contents, is similar to silicic to intermediate rocks (diorite/granodiorite) that are typical of terrestrial convergent margins (magnesian, calc-alkalic). In this study, major and trace elemental modeling is applied in order to determine if the calculated whole rock composition of Venera 8 can be derived from a parental magma composition similar to Venusian basalt. The modeling results indicate that polybaric fractional crystallization of a hydrous (H2O = 0.4 wt%) and relatively oxidizing (ΔFMQ + 0.7) parental composition similar to Venera 14 basalt can yield residual silicic liquids that match the calculated Venera 8 whole rock composition. The measured Th and U concentrations can also be reproduced within the data uncertainty. Although Venus lacks modern Earth-style plate tectonics, magnesian, calc-alkalic compositions are common within Archean greenstone belts and some rift settings (Haida Gwaii). Consequently, it is possible that the Venera 8 probe encountered a fragment of crust that resembles a terrestrial greenstone belt.

Original languageEnglish
Pages (from-to)50-61
Number of pages12
JournalIcarus
Volume321
DOIs
Publication statusPublished - 2019 Mar 15

Fingerprint

rocks
rock
greenstone belt
landing sites
basalt
gamma ray spectrometry
convergent margin
diorite
Venus
plate tectonics
fractional crystallization
granodiorite
modeling
plates (tectonics)
Archean
Venus (planet)
magma
probe
crust
margins

Keywords

  • Greenstone belt
  • Proto-continental crust
  • Silicic rock
  • Venera 8
  • Venus

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The curious case of the rock at Venera 8. / Shellnutt, J. Gregory.

In: Icarus, Vol. 321, 15.03.2019, p. 50-61.

Research output: Contribution to journalArticle

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