Friday, September 30, 2011
WOGE 311
Mathias has asked me to post his image for WOGE 311 here. I have no idea what the location is or what the geology of interest is, but Mathias states that the location should not be too hard to find, and that nothing fancy is required for geological information. He is not invoking the Schott rule. I will sit out this round, so I look forward to seeing who finds this.
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21.398 S, 44.739 W
ReplyDeleteA moderately dendritic drainage pattern atop E-W striking sedimentary rocks. NW of Carrancas, Brazil
More about the geology: the prominent brown unit that forms ridges in a Z pattern across this view is a NeoProterozoic phyllite unit, and it is part of an allochthonous package of metamorphosed NeoProterozoic metasediments emplaced atop a biotite schist that forms the lighter region (inside the Z). The southern portion of the Z is a southwest plunging anticline in the phyllite unit.
ReplyDeleteAlso, though the branching pattern of the drainage is somewhat dendritic, there are areas that are more trellis-like.
Details of the geology can best be seen in the southern half of a geologic map of the Lavras region found here: http://www.comig.com.br/site/content/parcerias/mapeamento_geologicoEf_sul.asp?id=17E
There's more geology there, Ron :-) For example a well-distinguishable SW-NE dextral shear zone offsetting Neoproterozoic metamorphic rocks of the Ribeira Belt just south of the São Francisco Craton.
ReplyDeleteI defer to your superior knowledge of South American geology, Peter. It's an area I have very little background in. Wish I owned some good geologic maps of the continent...
ReplyDeleteI'm probably not more knowledgeable either, Ron, just trying harder :-) My comment actually targeted your first input, but for some obscure reason my first attempt failed and got published only after your second post.
ReplyDeleteIt's always hard to tell from the written word alone, but I was being perfectly honest and magnanimous (not trying to be snarky or facetious) in deferring to Peter's superior knowledge of South American geology. It's genuinely an area where I'm sorely lacking a good intellectual background.
ReplyDeleteMy first answer was quick and incomplete in no small part because the challenge stated in no uncertain terms that this was likely to be a quickie and "nothing fancy is required for geological information". I merely took the poster(s) at their word; they didn't ask me to try hard, so I didn't.
Few of us come up with more complete or well researched geological explanations on a regular basis than Peter. My hat is off to you for that, sir! I offer no apologies for beating you to the location, though. ;-)
Congratulations Ron!
ReplyDeleteI thought this WOGE wouldn`t be too hard because it`s such a broad scale. I actually chose this beautiful Z-shaped mountains because the southwestern tip of it is where I did my first geological mapping at university, last year (I`m Brazilian, and a student, by the way). As you said, these mountains are really an allochthonous package of metasediments, mainly quartzites and muscovite schists which can also have garnet, staurolite and/or kyanite. The lighter regions are not only biotite-schists but also gneisses, with some metaultramafic lenses. As Peter correctly said, in the center of the image is in fact a transcurrent shear zone. This is the very tip of a complex nappe system that extends for over one hundred km, but whether it is part of an interference zone between the Ribeira and Brasília fold belts or only part of the Brasília fold belt is, as pretty much everything in Brazil`s geology, being discussed. Just north of the Z we already have the São Francisco Craton. It is a very beautiful location, with an incredible view. I`m glad you enjoyed it.
Let`s see now what Ron is planning for the next WOGE!
Does anybody know where the following WOGE's are?
ReplyDeleteWoGE #312 is now posted on Google+. Sorry for the delay.
ReplyDelete