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When were the gabbro ring bodies of the Richat emplaced?

Asked 28 Oct 2026 by ·Part of How did the Richat Structure form?·3 answers·0·0 following
Three answers, none aheadNone is ahead yet. See what would settle it.

Where it stands

Three answers have been proposed. None is ahead on the evidence yet. Three are still possible.

Why it matters

Matton and Jébrak treated the gabbro rings as part of one Cretaceous complex of about 104 to 94 Ma⁠[1]; Abdeina and colleagues model them as sills of 230 to 200 Ma that a later intrusion domed⁠[2]. Neither has a robust age, and the answer decides whether the rings and the dome are one event or two.

Answers 3

Evidence: none yet
Still possible
Evidence: 1 for, 2 against
Still possible
Evidence: 1 for, 1 against
Still possible

What would settle it

  1. Find whether any U-Pb (zircon or baddeleyite) age on the Richat gabbros has been published since Abdeina et al. 2024, and add it as evidence.
  2. Read the full texts of Matton and Jébrak 2014 and Abdeina et al. 2024 for the field relations of the gabbros (dip of contacts, cross-cutting of bedding) and record them as evidence for or against the sill model.

History

  1. Matton et al.: matton and colleagues mapped the basalts as subvertical ring dikes, not sillsAgainst: The gabbro rings are Central Atlantic Magmatic Province sills of 230 to 200 Ma, domed about 100 million years later
  2. Matton & Jébrak: matton and Jébrak infer an age of about 104 to 94 Ma for the whole mafic-to-felsic sequenceFor: The gabbro rings belong to the same Cretaceous complex, emplaced around 104 to 94 Ma
  3. Abdeina et al.: plagioclase 40Ar/39Ar modelling places the gabbros at 230 to 200 Ma, not in the CretaceousAgainst: The gabbro rings belong to the same Cretaceous complex, emplaced around 104 to 94 Ma
  4. Abdeina et al.: matton and colleagues mapped the basalts as subvertical ring dikes, not sillsAgainst: The gabbro rings are Central Atlantic Magmatic Province sills of 230 to 200 Ma, domed about 100 million years later
  5. Abdeina et al.: the gabbros' chemistry matches the two CAMP groups best represented in north-west AfricaFor: The gabbro rings are Central Atlantic Magmatic Province sills of 230 to 200 Ma, domed about 100 million years later
  6. Session 1: raised the question, proposed three answers and found five results bearing on its answers
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