Could you please note the exact time of posting so previous winners know how long they need to wait ? :)

44.9 E - 24.5 S Superb giga-pressure-shadows developed around the Neoproterozoic Saririaky anorthosite body acting as a rigid inclusion in the Ampanihy ductile shear zone that developed at the eastern margin of the Graphite Sequence of SW Madagascar. At a larger scale it’s even more spectacular : this anorthosite body appears to be pulled apart from the similar Ankafotia body located 40-50 km to NNE.

(Jeff announced WoGE #121 on my site at 14:36 GMT, 04/24/08 ; this answer was posted at 3:15 GMT, 04/25/08)

Lost Geologist : Sorry I thought my CMS did include the data automagically.

Peter : Well done, did you know the image/region beforehand ? Or how did you find it ? anyway, back to you...

Oh how bad I found it within 5 minutes but was too lazy to watch the clock to post in time. :-D

Well done Peter !

Ok, ok, I’ll find something more challenging next time (if there is a next time !). Just for interest’s sake, what made it so easy to find ?

Well, first of all there aren’t that many 10km diameter, round qhite spots on the planet so beautifully situated in a shear zone. Also, the landscape on the foto seemed fairly eroded, dry but still enough water to allow green streams and sparse vegetation. Such deeply eroded landscape I find most characteristic for Africa. So I began searching African cratons and old mountain ranges. When I didn’t find this one I remembered Madagascar is basicly African, too. I might be wrong about what I wrote but that’s how I found it so fast.

I didn’t know the region beforehand, I actually haven’t seen before such a nice regional-scale pressure shadow. But I was almost sure from the very beginning that I have to look for well exposed ductile shear zones in low-topography Precambrian high-grade terrains. Given the shear zone’s orientation and the scale of view, it was pretty easy to exclude most options...

BTW, WoGE #122 is posted.

@ Lost Geologist : when I saw your question regarding the posting time, I was almost sure you’ve found it, but then wondered why you don’t post the answer for half a day...

Thnaks for the nice "lesson" in GE exploration...

cette structure a ete etudiee par JE Martelat dans sa these en 1995

Absolument. Comment croyez vous que je l’ai découverte ?

(sauf que la these de Manu Martelat, c’est 98. La structure en question a du etre decrite dans son papier a CRAS : MARTELAT J.E., VIDAL G., LARDEAUX J.M., NICOLLET C., et RAKOTONDRAZAFY R. (1995) - Images spatiales et tectonique profonde des continents : l’exemple du Sud-Ouest de Madagascar. C. R. Acad. Sci., Paris, 321, 325-332. Je ne peux pas verifier pour le moment, je n’ai pas acces au Web of Science d’ici).