I have been
taking advantage of our sunny weather by half dozing on my back deck while listening
to various of Nick Zentner’s geology podcasts.
Much of the material is new to me: either ideas that have originated
since I stopped working in the Cordillera, or – sadly – stuff I may have known
a long time ago but have thoroughly forgotten!
Either way, it has been useful, restful, and fun.
But I have a
suggestion or maybe it should be called a question. I notice that terrane maps for the most part depict
a series of extremely elongate map units.
Most, if not all, are very much longer (NW/SE) than they are wide. Obviously, some exotic material is highly
attenuated at origin: hotspot tracks for instance. However, some definitely are not; for example
many oceanic plateaus as well as various chunks of detached continental crust
such as are found between Australia and southern Asia. And how about Madagascar?
So, my question
or perhaps more accurately speculation: are we paying too little attention to
what I will call “post-docking attenuation”?
After all, interaction of various oceanic plates with western North
America has had a northward element since way back in the Mesozoic. I can visualize roughly equant exotic
terranes getting “all smeared out” by dextral faulting after they are added to
North America. Seems likely to me. What do you think?
I discovered your blog courtesy of a shout-out by Nick Zentner. This is an interesting idea. Thank you for posting it. Thank you for posting your blog.
ReplyDeleteI am also here because of Nick Zentner and happy to have found to blog hosting your musings and witticisms and other sage thoughts. Your post here is certainly one of the greatest challenges in our understanding of N.A. Cordilleran geology going forward. Many thanks for your contributions.
ReplyDeleteI think that the rocks certainly tell the story of northward migration post docking, In some cases very significant translation. We see the present day large scale translation evident on the San Andreas and Queen Charlotte- Fairweather fault zones which are continuing this long-term process. Large displacement strike slip faults are figuratively "everywhere" (in a sense), and, if the rocks were observable in a coherent mass, the story of "exotic terranes" showing displacement may be more of a normal story than we realized the 40+ years ago.
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