South Africa Meteorite Impact Spherule Bed [32317]

The Spherule Beds in the Barberton Greenstone Belt (BGB) of South Africa are incredibly fascinating geological features. This specimen is from spherule bed #2, which contains impact material from an early time in Earth's history: the Paleoarchean. This spherule bed is located in the Fig Tree Group, Mapepe Formation, South Africa.

Let’s delve into its intriguing origins:

1. Formation and Composition:

   • The Spherule Bed consists of multiple layers rich in spherical particles known as spherules.
   • These spherules condensed from rock vapor clouds formed due to large meteorite impacts or asteroid collisions around 3.47–3.23 billion years ago (Ga).
   • The bed contains different types of spherules:
     • Nearly pure silica spherules: Representing non-aluminous melt precursors.
     • Nearly pure phyllosilicate spherules: Derived from mostly mafic and ultramafic liquids.
     • Compositionally mixed spherules.
   • Some beds show evidence of spherule amalgamation and surface corrosion during mixing.

2. Significance:

   • Spherule Beds provides direct evidence that terrestrial bombardment by large bolides (meteorites or asteroids) did not end abruptly at 3.8 Ga.
   • The occurrence of at least eight major impact layers within an interval of approximately 240 million years suggests impact rates much higher than those in later geological periods.
   • The bed’s composition and timing coincide with the initiation of Barberton Greenstone Belt (BGB) deformation around 3.26–3.23 Ga.
   • This suggests that an impact cluster during this time may have disrupted an earlier geodynamic system and triggered the development of a contrasting, more modern plate tectonic regime.

3. Implications:

   • The Spherule Beds in the Barberton Greenstone Belt provide valuable insights into Earth’s early history, impact events, and crustal evolution.
   • They challenge the notion that large bolide impacts ceased abruptly at 3.8 Ga, indicating a gradual decline until 3.0 Ga or even later.

Location: The Mapepe Formation is part of the Fig Tree Group, situated south of the Inyoka Fault. 

There have been 17 intersections of spherule bed layers discovered so far. These layers offer a unique opportunity to study meteorite bombardment during the early Earth.

Alteration Processes: Petrographic investigations suggest that the spherule layers underwent alteration processes such as K-metasomatism, sericitization, silicification, and carbonatization.

Meteoritic Component: Siderophile element contents in bulk samples indicate significant enrichments in nickel (Ni) and iridium (Ir), similar to other Archean spherule layers. These values suggest the presence of a meteoritic component. 

Ongoing Research
Scientists continue unraveling Archean impact spherule beds' chemical composition, trace elements, and isotopic signatures. They are gradually gaining insights into Earth’s early crustal evolution and the dramatic events that shaped our planet.

Size of specimen: 30mm L X 17mm W X 11mm D; Weight: 2.39 grams; This material is from Spherule Bed #2. The macro is 3X.

Ships with a Certificate of Authenticity, tag and detailed information.

Collectors now have a rare opportunity to have a geological specimen from an Archean meteorite impact with this terrific specimen!