Aleutian Earthquake
Wednesday, 19. December 2007, 16:54:55
I haven’t blogged about earthquakes for some time. They get a lot of attention in the news anyway, because of their destructive character. There is more to earthquakes than destruction, however, and I always want to see them in a plate tectonic perspective. Most earthquakes occur at plate boundaries, and to strike a more positive economic note, a large number of metal deposits are associated with plate boundary environments.
A large earthquake, magnitude 7.2, rattled Alaska's Aleutian Islands on 19 December 2007, but didn’t receive much attention outside Alaska, as there were no reports of any damages or injuries, and a tsunami warning was cancelled early for Alaska's coasts after officials determined waves from the earthquake posed no widespread destructive threat.
The Aleutian Islands are a chain - or volcanic arc - of more than 300 islands that extend southwestward from Alaska into the northern Pacific Ocean. The Aleutian arc extends approximately 2,500 kilometres along the southern edge of the Bering Sea and Alaskan mainland. The Aleutian arc is the result of subduction of the Pacific Plate beneath the North American Plate. The 3,400-kilometer-long Aleutian trench that extends from the northern end of the Kamchatka trench to the Gulf of Alaska marks the boundary between the two plates. The Aleutian arc is a typical oceanic arc of most subduction zones. The angle of dip of the descending lithosphere, which is Pacific Plate, along much of the Aleutian trench is near 45 degree.
A book about the tectonic history and metal deposits in the area called Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera and prepared in collaboration with Alaska Division of Geological and Geophysical Surveys, Geological Survey of Canada, Russian Academy of Sciences, Russian Ministry of Natural Resources, is freely available on the internet as as a 429-page PDF file (14.2 MB). Otherwise books like this cost me a fortune, so I really enjoy getting it for free.
The map below from the book cover shows the major present-day metallogenic and tectonic elements for the Circum-North Pacific and geographic names for major regions.
The major metallogenic belts (marked in red) are (1) the Kuril (KU) metallogenic belt, which is hosted in the Kuril volcanic-plutonic belt (part of Northeast Asia arc); (2) the Alaska Peninsula and Aleutian Islands (AP) metallogenic belt that contains granitic-magmatism-related deposits and is hosted in the Aleutian volcanic belt (part of Aleutian-Wrangell arc); and (3) the Owl Creek (OC) metallogenic belt, which is hosted in the Cascade volcanic-plutonic belt (part of Cascade arc).
Let me quote this from the book’s conclusions:
The Phanerozoic metallogenic and tectonic evolution of the Circum-North Pacific can be explained as a succession of arcs and tectonically paired subduction zones that formed along the margins of the Northeast Asian and North American plates above the subducting oceanic lithosphere of mainly the Mongol-Okhotsk, Cache Creek, ancestral Pacific, and Pacific Oceans. In both Northeast Asia and in the North American Cordillera, most of the arcs formed in island arcs near continental margins or along the continental margins. With respect to Northeast Asia and North America, the paleolocations of those arcs, which occur oceanward of coeval accretionary complexes, are highly suspect in the Paleozoic but are successively less so in the Mesozoic.
• http://www.foxnews.com/story/0,2933,317408,00.html
• http://pubs.usgs.gov/pp/pp1697/
A large earthquake, magnitude 7.2, rattled Alaska's Aleutian Islands on 19 December 2007, but didn’t receive much attention outside Alaska, as there were no reports of any damages or injuries, and a tsunami warning was cancelled early for Alaska's coasts after officials determined waves from the earthquake posed no widespread destructive threat.
The Aleutian Islands are a chain - or volcanic arc - of more than 300 islands that extend southwestward from Alaska into the northern Pacific Ocean. The Aleutian arc extends approximately 2,500 kilometres along the southern edge of the Bering Sea and Alaskan mainland. The Aleutian arc is the result of subduction of the Pacific Plate beneath the North American Plate. The 3,400-kilometer-long Aleutian trench that extends from the northern end of the Kamchatka trench to the Gulf of Alaska marks the boundary between the two plates. The Aleutian arc is a typical oceanic arc of most subduction zones. The angle of dip of the descending lithosphere, which is Pacific Plate, along much of the Aleutian trench is near 45 degree.A book about the tectonic history and metal deposits in the area called Metallogenesis and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera and prepared in collaboration with Alaska Division of Geological and Geophysical Surveys, Geological Survey of Canada, Russian Academy of Sciences, Russian Ministry of Natural Resources, is freely available on the internet as as a 429-page PDF file (14.2 MB). Otherwise books like this cost me a fortune, so I really enjoy getting it for free.
The map below from the book cover shows the major present-day metallogenic and tectonic elements for the Circum-North Pacific and geographic names for major regions.
The major metallogenic belts (marked in red) are (1) the Kuril (KU) metallogenic belt, which is hosted in the Kuril volcanic-plutonic belt (part of Northeast Asia arc); (2) the Alaska Peninsula and Aleutian Islands (AP) metallogenic belt that contains granitic-magmatism-related deposits and is hosted in the Aleutian volcanic belt (part of Aleutian-Wrangell arc); and (3) the Owl Creek (OC) metallogenic belt, which is hosted in the Cascade volcanic-plutonic belt (part of Cascade arc).
Let me quote this from the book’s conclusions:
The Phanerozoic metallogenic and tectonic evolution of the Circum-North Pacific can be explained as a succession of arcs and tectonically paired subduction zones that formed along the margins of the Northeast Asian and North American plates above the subducting oceanic lithosphere of mainly the Mongol-Okhotsk, Cache Creek, ancestral Pacific, and Pacific Oceans. In both Northeast Asia and in the North American Cordillera, most of the arcs formed in island arcs near continental margins or along the continental margins. With respect to Northeast Asia and North America, the paleolocations of those arcs, which occur oceanward of coeval accretionary complexes, are highly suspect in the Paleozoic but are successively less so in the Mesozoic.
• http://www.foxnews.com/story/0,2933,317408,00.html
• http://pubs.usgs.gov/pp/pp1697/
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