Reduced and unstratified crust in CV chondrite parent body

Area of Science:

• * Planetary Science
• * Cosmochemistry
• * Petrology

Background:

• * Early Solar System thermal models predict heating and crust preservation on planetesimals.
• * Chondrites show secondary alteration phases formed by fluid-rock interaction at low temperatures (<300°C).
• * Previous studies suggested distinct physicochemical conditions for reduced and oxidized Vigarano type Carbonaceous (CV) chondrites.

Purpose of the Study:

• * To re-evaluate the classification of reduced and oxidized CV3 chondrites.
• * To investigate the formation conditions of Ca-Fe-rich secondary phases in CV3 chondrites.
• * To understand the early Solar System's hydrothermal processes.

Main Methods:

• * Thermodynamical survey of Ca-Fe-rich secondary phases in CV3 chondrites.
• * Analysis of silica activity (aSiO2) and redox conditions.
• * Petrological and geochemical examination of meteorite samples.

Main Results:

• * The classical distinction between reduced and oxidized CV chondrites is no longer valid.
• * Ca-Fe-rich secondary phases in CV3 chondrites formed under similar reduced conditions.
• * Formation occurred near the iron-magnetite redox buffer at low silica activity (log(aSiO2) < -1) and moderate temperatures (210-610°C).

Conclusions:

• * CV3 chondrites are likely fragments of an asteroid subjected to heterogeneous hydrothermal fluid percolation.
• * The 'onion shell' structure is not a mandatory requirement for CV parent body crusts.
• * This finding refines our understanding of early Solar System asteroid evolution and fluid processes.