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nature
climber
Tucson, AZ
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Jul 24, 2010 - 07:44pm PT
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autochthonous Donkey on the JDF.
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Mighty Hiker
climber
Vancouver, B.C.
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Jul 25, 2010 - 01:32am PT
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An interesting bit of toponymy - Kevin's favourite new word.
The area including the Strait of Juan de Fuca - that is, the Strait, plus Georgia Strait and Puget Sound - was recently renamed the Salish Sea. The Coast Salish of various sub-groups being of course the original inhabitants of much of its coasts. I don't believe that they called it the Salish Sea in pre-contact times, though.
http://en.wikipedia.org/wiki/Salish_Sea
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Hardly Visible
Social climber
Llatikcuf WA
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Jul 25, 2010 - 11:35pm PT
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Tuolumnne tradster,
Wrangellia is what I was referring to. It is interesting how long north to south it appears in that Late Cretaceous Paleogeographic reconstruction that you show in your post, it looks like a pretty substantial addition to western north America that could not have all come from 53° N. I know some geologists think that part of the Seven Devils Mtns.in northeast Oregon is Wrangellian, it wouldn’t surprise that something in California might turn out to be Wrangellian too. Along those lines I wouldn’t have a hard time believing that a sample in Alaska could have 15° ± 8° of latitudinal displacement whereas a sample from Vancouver Island might have 39° ± 6° latitudinal displacement since the accretion of Wrangellia was a long process that by no means was uniform and contemporaneous.
Here is an abstract for a study supporting substantial northward migration for at least some of Wrangellia:
Paleomagnetism of the westcoast complex and the geotectonics of the Vancouver island segment of the wrangellian subterrane
D.T.A. Symons
Department of Geology, University of Windsor Windsor, Ontario, Canada
Abstract
Paleomagnetic data from 46 sites (674 specimens) of the Westcoast Crystalline Gneiss Complex on the west coast of Vancouver Island using AF and thermal demagnetization methods yields a high blocking temperature WCB component (> 560°C) with a pole at 335°W, 66°N (δp = 4°, δm = 6°) and a lower coercivity WCA component ( 25 mT, < 500°C) with a pole at 52°W, 79°N (δp = 7°, δm = 8°). Further thermal demagnetization data from 24 sites in the Jurassic Island Intrusions also defines two high blocking temperature components. The IIA component pole is at 59°W, 79°N (δp = 7°, δm = 8°) and IIB pole at 130°W, 73°N (δp = 12°, δm = 13°). Combined with previous data from the Karmutsen Basalts and mid-Tertiary units on Vancouver Island and from the adjacent Coast Plutonic Complex, the geotectonic motions are examined for the Vancouver Island segment of the Wrangellian Subterrane of composite Terrane II of the Cordillera. The simplest hypothesis invokes relatively uniform translation for Terrane II from Upper Triassic to Eocene time producing 39° ± 6° of northward motion relative to the North American craton, combined with 40° of clockwise rotation during the Lower Tertiary.
Mind you that I’m just a rank amateur at all this so I won’t pretend to understand any of that mumbo jumbo except for the last sentence of it.
Here’s a couple of diagrams showing plate vectors of the Kula and Farallon plates off the Washington
and Oregon coast in Paleocene to early Eocene time indicating an increase in velocity and obliquity in
the subduction of the Kula plate about 59 million years ago.
Estimates for the velocity of the Kula plate during this time run somewhere between 4 to 8 inches per
year, which over the 4 million years between 59 to 55 million years the Kula plate would have moved
something a minimum of 250 miles northward.
All interesting stuff to ponder at any rate.
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neebee
Social climber
calif/texas
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Jul 25, 2010 - 11:38pm PT
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hey there say, all... thanks for the interesting share... and the alaskan quake info, too...
very interesting...
god bless...
:)
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nature
climber
Tucson, AZ
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Jul 25, 2010 - 11:42pm PT
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whoa... HV... that's way kula!
(sorry, my inner stoner is showing).
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Jingy
Social climber
Nowhere
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Jul 26, 2010 - 12:42am PT
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Based on that last image (in the original post)...........
It'd be impossible for California to drop into the ocean, right.
Seeing how it is basically be held in, and lifted, by the pacific plate.. that "IS" dropping under the North American plate...
Has anyone told the right wing about this?
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Jaybro
Social climber
Wolf City, Wyoming
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Jul 26, 2010 - 04:32am PT
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california moves west, subducting the rest....
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Topic Author's Reply - Jul 27, 2010 - 12:53am PT
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H V: thanks for posting that abstract. By progressively heating (thermal demganetization) the WC gneiss rock samples from Vancouver Is it is possible to determine the rock's original thermal remnant magnetism. The thermal demag essentially erases any weaker magnetic signals or "overprints" in the rock caused by the fact that the rock has been exposed to 10 of millions of years of the earth's magnetic field which has undergone random reversals every few 100K years. Once the sample has been "magnetically cleaned" of any overprints and the "true" thermal remnant magnetic vector is determined this vector reflects the orientation of the earth's magnetic field at the time the rock cooled. An apparent paleo pole can be determined using this palomagnetic vector.
For example, WCB component (> 560°C) with a pole at 335°W, 66°N means that the apparent paleo pole determined from the WC rocks was located near southern Finland (I think I did that correctly). Because the time-averaged magnetic field is a geocentric axial pole (i.e. roughly averages to be coincident with the rotation axis), it is not the magnetic pole that was in southern Finland but the WCB terrain that was ~33 degrees south of where it is today.
Hope this makes sense.
Here's an animation that I posted on another thread from the USGS website that shows 30 million years of movement along the San Andreas fault and its predecessors. It is a compilation of an enormous inter-disciplinary data set including paleomagnetic data from the Transverse range (watch it rotate ~ 90 degrees clockwise) and the correlation of Pinnacles to the Neenatch Fm ~ 300 km to the south. The stripes off shore are sea floor magnetic anomalies. Note that Juan de Fuca makes a cameo at the end.
http://earthquake.usgs.gov/monitoring/deformation/tectonics/western-na.mov
If you fast forward the animation in your imagination to 5 my in the future, Baja will be located adjacent to San Bernandino.
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Hardly Visible
Social climber
Llatikcuf WA
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Jul 27, 2010 - 01:45pm PT
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TT,
Thanks for the explanation, I think I got the gist of it. I'd like to watch that movie you posted a link to but alas all I get is a blank page,
probably got to have some sort of movie watching program that I'm lacking??
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Topic Author's Reply - Jul 28, 2010 - 06:03pm PT
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pre-Cook Nootka Sound bump
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Mighty Hiker
climber
Vancouver, B.C.
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Jul 28, 2010 - 07:15pm PT
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Wrangel (Vrangel) was one of the governors of Russian America, born in Estonia. He was also a scientist and explorer, and of course from a wealthy noble family.
http://en.wikipedia.org/wiki/Ferdinand_von_Wrangel
The Russians were in fact much further ahead in exploration of their northern lands and waters than those in North America.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Topic Author's Reply - Jul 28, 2010 - 07:40pm PT
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THE RUSSIAN PRESENCE IN AMERICA
by Marco Ramerini
The Russian explorers reached the Pacific through Siberia in 1639. The Tsar later sent two expeditions in 1728 and 1741 under the command of Vitus Bering and Alexei Chorikov, they discovered the Aleutian islands and Alaska. A profitable fur trade was established, Russian temporary settlements in the Aleutians and on Unalaska island began in 1770s. the first permanent outpost was built in 1784 at Three Saints Bay on Kodiak island by Gregorii Shelikhov. From there the mainland was explored, and other fur-trade centers were established. In 1786, Shelekhov set out for Russia, unsuccessfully seeking a grant to his company of monopoly of the fur trade. Shelekhov's company was the nucleus for the Russian American Company, which was formed several years after his death. By the early 1800s. Russian were exporting an average of 62000 fur pelts from North America. The first Russian Orthodox missionaries came to Alaska in 1794.
Fort Ross (named from Rossiia) was the southernmost outpost of the Russian presence in North America. The Russians remained at Fort Ross until the year 1841.
Today none of the original fort structures remain, however several buildings have been reconstructed: the first Russian Orthodox chapel south of Alaska, the stockade, and three other buildings, including the Commander’s House, which contains exhibits of the Russian-American Fur Company and the Russian occupation.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Topic Author's Reply - Jul 29, 2010 - 07:33pm PT
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The Great Cascadia Earthquake of 26 January AD 1700
Coastal field work over the past ten years by many scientists from universities and federal, state, and provincial geological surveys in northern California, Oregon, Washington, and British Columbia has uncovered overwhelming evidence of a great (moment magnitude larger than 8) earthquake or series of earthquakes about 300 years ago. The earthquake (or earthquakes) was caused by the sudden slip of the Pacific plate beneath the North America plate along the Cascadia subduction zone, a 1000-km(600-mi)-long fault that marks the landward-dipping boundary between the two tectonic plates off the coast of western North America.
Some of the most convincing and best-preserved evidence of the earthquake(s) are sand layers that cover the peaty soils of coastal lowlands. A large tsunami that was generated by sudden movements of the ocean floor during the earthquake(s) deposited the layers when it inundated the coasts bordering the fault zone. The above photo shows such a sand layer in an exposure near the mouth of the Salmon River along the central Oregon coast about 8 km (5 mi) north of Lincoln City. One of the series of tsunami surges that probably followed the earthquake by 20 minutes to several hours picked up sand from the beach or dunes as it came ashore and deposited the sand as it moved up the river valley. At the site of the photo, the sand bed covers the remains of two fire pits dug by Native Americans, perhaps not long before the tsunami. The layers are well preserved partly because much of this part of the Oregon coast permanently subsided about 0.5-1.0 m (2-3 ft.) during the earthquake. The rise in sea level produced by the subsidence allowed tidal sediments to quickly bury the sand layers, protecting them from later erosion.
http://earthquake.usgs.gov/regional/pacnw/paleo/greateq/
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Topic Author's Reply - Jul 30, 2010 - 11:39pm PT
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HV: thanks, that article really puts it all together nicely. These deep, large magnitude subduction zone earthquakes are the real devastating ones...add a tsunami and you have a real disaster on your hands. A rather ominous last sentence "a great Cascadia subduction earthquake of moment magnitude Mm = 9.2 is possible." The one that occurred in 1700 was obviously a big one.
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Amanda Knisley
Social climber
Charlotte
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Jan 17, 2011 - 07:44pm PT
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Hi, I have been researching about Juan de Fuca Ridge but I cannot figure out why there are 8 million year old rocks on the west of the ridge and not the east?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Topic Author's Reply - Jan 17, 2011 - 08:10pm PT
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Amanda: the 8+ my old oceanic crust east of the Juan de Fuca ridge has already been subducted beneath North America.
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