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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 18, 2019 - 05:27pm PT
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Volcaniclastic breccia &...
...blueschist of the Franciscan Complex near Jenner, CA
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 20, 2019 - 09:36am PT
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Mani stones...
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mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
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Feb 20, 2019 - 08:48pm PT
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Feb 20, 2019 - 11:18pm PT
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Meta-volcaniclastic? rock near Tengboche Monastery, Khumbu region, Nepal...
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mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
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Feb 24, 2019 - 08:30am PT
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mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
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Feb 24, 2019 - 02:07pm PT
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Meta-sedimentary rocks of the Jurassic Mariposa Fm collected on Hwy 140 west of Mariposa.
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Happiegrrrl2
Trad climber
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I have one more session left to work on cutting stones before I leave Quartzsite. Finally feel like I have a basic understanding, but only that. People say it's easy to do, and maybe it is. But it's not so easy to do it well.
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mike m
Trad climber
black hills
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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High grade metamorphic olistolith in Franciscan meta-sandstone melange, Point Bonita, Marin County, CA
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mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
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I bet you can't say that real fast three times. :0)
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Minerals
Social climber
The Deli
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^^^ I see sanidine. And fiamme.
It’s cool to see small pieces of granitic or metamorphic rock in the Bishop Tuff.
Good stuff, Tradster. Thanks for the link. When I first opened the article and saw the title, I wondered if Wes was one of the authors. Sure enough.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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You can really see the Sanidine in these photos [rectangular, colorless, glassy crystals]. Some amorphous glassy blobs of quartz, too. Fiamme in the form of collapsed lithic and pumice fragments.
I just found this recent paper on precise 40Ar/39Ar age dating of single Sanidine crystals in the Bishop Tuff (BT) by incremental heating, multi-collector mass spectrometry (IH MCMS) at 764.8 ka, shortly after the Matuyama to Brunhes magnetic polarity reversal.
https://pdfs.semanticscholar.org/0347/459ec0dcc1aea7bc24254ffda9b3fef712b1.pdf
In this paper on Compositional Zoning of the Bishop Tuff,
https://academic.oup.com/petrology/article/48/5/951/1472295
they talk about the eruption taking place over a 6-day period. I'm curious what dating method that is based on that has diurnal temporal resolution. Imagine watching the eruption of the BT from the summit of Mt Dana...Mammoth Mt would probably have been too close for comfort.
EDIT: In this 1997 J. of Geology paper
https://www.journals.uchicago.edu/doi/10.1086/515937
Wilson & Hildreth describe using fall deposit chronometry (volcanic ash accumulation rates based on modern observed volcanic ash deposits), to estimate ~ 6 days for the BT deposition.
The new stratigraphic framework shows that much of the Bishop ignimbrite is intraplinian in nature, and that fall deposits and ignimbrite units previously inferred to be sequential are largely or wholly coeval.
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mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
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Beautiful no matter how it's spelt.
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Fritz
Social climber
Choss Creek, ID
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spessertine garnet on quartz.
Barite
fluorite
aquamarine & muscovite mica
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Minerals
Social climber
The Deli
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Nice texture photos, Tradster. I’m guessing that the summit of Mt. Dana might have been a bit hostile during that week – spectacular views at the beginning of day 1, although probably quite temporary views. Thanks for the three more links. I read the abstracts and saved the two PDFs. Sure is nice to be able to store papers in PDF format on a computer, rather than in file boxes full of real paper. Reminds me of a story...
When I was in school at UNR, I was downstairs in the science library one day, photocopying papers from geology journals, and had a mishap. They often bind several journal issues into one binder/book, which makes it difficult to fully open the pages, to get a photocopy of an entire page. So, as we all have done, I was pushing down on the binder to flatten the pages as I was copying, and unfortunately didn’t realize how thin the glass on the photocopy machine was. : ) Well, next thing I know... SMASH!... there goes the glass. Oooops, sh#t, I thought. There was a girl/lady sitting over at a near table, who immediately looked up when she heard the semi-loud noise, with a look of WTF? on her face, but she didn’t say a word. I went upstairs to the front desk, and told the old guy there what had happened, who then had a look of disbelief on his face, but acknowledged that it can be difficult to copy pages when they bind so many issues together. I felt bad about it at the time, but get a good laugh out of it now. : ) LOL...
Mouse, do you see the sharp contact in your second El Cap photo, which can also be seen in your first photo? The right-facing corner in your first photo is the “rivet corner” on Tribal Rite – pitch 3. The topo in the SuperTopo book has this feature drawn more accurately than the topo in the Sloan book. The feature in your second photo obviously needs no explanation.
Fritz, your quartz has parasites! Nice stuff.
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healyje
Trad climber
Portland, Oregon
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