Open thread

I’m so busy finalizing the manuscript of my book that I can’t find the bandwidth for my accustomed fortnightly post today. There won’t be one in two weeks, either. Next post will be on 6 December. In the meantime, the comments are open so we can talk to ourselves for the rest of the month. (“Did you even know you have selves you can talk to?” Bob Weir reputedly told the audience at a Grateful Dead show as they took a technical break.)

The photo is a fine specimen of mariposite rock from the Carson Hill quarry in Angels Camp. This popular landscaping stone is shot with a green chromian variant of the metamorphic mica mineral phengite. Portions of the deposit are worked for gold as part of California’s continuing gold crawl. The specimen is a recent addition to the rock garden at Lake Merritt.

What’s up with you?

One Response to “Open thread”

  1. Pat Flaherty Says:

    I’m rereading McPhee’s Assembling California and note that it was published in 1993 – which is already 24 years ago and things can, and sometimes do, change fast. I mean, a lot of the story consists of the fundamentals of plate tectonics, which was new in 1978 when McPhee began the series and that hasn’t changed but to what extent does maybe not the science but the scientific phenomenology need to be added to or amended?

    E.g. McPhee writes that, here in the middle of the state opposite (east of) the Bay Area, California consists of three island arcs that accreted and added to the state in a westerly direction, the last of which is the Smartville Block. Vastly intruded upon by the Sierra Nevada batholith that is. How up-to-date are the three island arcs part? That is, the terranes that have added to (created) California over time?

    [McPhee was strongly guided by the late Eldridge Moores, whose ideas were well argued but have not been universally accepted. As far as I know, the evidence of three island arcs is still considered clear, but there’s no consensus on which direction subduction took place as they were emplaced on the continent. Fortunately, all of those rocks are older than anything in the Oakland Hills, so I’ve been content to ignore them. — Andrew]

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