tag:blogger.com,1999:blog-7563205518828267408.post7308561130585756926..comments2024-01-19T08:08:23.595-08:00Comments on All of My Faults Are Stress-Related: High-pressure metamorphism before 1.7 billion years ago?Kimhttp://www.blogger.com/profile/07738706550175991130noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-7563205518828267408.post-11892921991772177462008-03-23T16:27:00.000-07:002008-03-23T16:27:00.000-07:00"The Franciscan is really an exception, rather tha..."The Franciscan is really an exception, rather than the rule, for the preservation of high-pressure metamorphic rocks"<BR/><BR/>Yeah...good thing the San Andreas transform margin came along to help preserve it!Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7563205518828267408.post-2311678305399917322008-03-23T14:06:00.000-07:002008-03-23T14:06:00.000-07:00My impression as an undergrad in the 80's was that...My impression as an undergrad in the 80's was that Precambrian geologists questioned how much modern plate tectonics could explain of their observations. There's still talk about that, but my impression is that it's the Archean, not the Proterozoic, that's the most suspect.<BR/><BR/>Warren Hamilton had a talk about the problems with applying plate tectonics to the Archean, and he got people talking in the hallway afterward. I didn't see it, though. (I was listening to a geoscience education talk, instead.)<BR/><BR/>Chris Rowan's doing paleomag on Archean rocks, though, so he's deep into Archean tectonics. And he's worked in young tectonics in New Zealand. We should bug him to blog about the Big Questions about the differences between Archean and Phanerozoic plate tectonics.<BR/><BR/>As far as high-pressure metamorphism goes, though, I think that preservation is a huge problem. (There aren't good blueschists along either of the old orogenic boundaries in New England, although there are rocks in Vermont that are thought to be a subduction complex, and I think there's about one eclogite locality in the entire Appalachians. The Norwegian ultra-high-pressure eclogites make up for the rest of the mountain belt, though!) The Franciscan is really an exception, rather than the rule, for the preservation of high-pressure metamorphic rocks.Kimhttps://www.blogger.com/profile/07738706550175991130noreply@blogger.comtag:blogger.com,1999:blog-7563205518828267408.post-6119871979826853232008-03-23T11:09:00.000-07:002008-03-23T11:09:00.000-07:00Do you think the lack of old subduction-related ro...Do you think the lack of old subduction-related rocks is essentially all about preservation (as you allude to)?<BR/><BR/>Or, does anyone in this area of study think there was something fundamentally different about plate tectonics >1 Ga or so?<BR/><BR/>This is way out of my field ... just curious.Anonymousnoreply@blogger.com