3
$\begingroup$

I found spherical or globular structures, structures in basalts of a greenstone belt which underwent alteration and deformation. However, in thin section, these structures have undeformed pyroxene and olivine. Below is a field picture of the structure. Would anyone know what these structures are called and how they form?

Globular Structure in Basalt.

$\endgroup$
  • $\begingroup$ look like oxidation-reduction zones to me, but I'm not sure $\endgroup$ – haresfur Aug 2 at 3:06
  • 1
    $\begingroup$ Can you add photographs of the thin sections? $\endgroup$ – Gimelist Aug 3 at 0:41
0
$\begingroup$

These globular structures are called varioles, and there is not complete agreement as to how they are formed. The most likely theory is that the basalt has been hydrothermically altered by millions of years of water infiltration bringing in tiny amounts of other minerals, but the jury is still out.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.