Yakutat Block
Encyclopedia
The Yakutat Block is a terrane
in the process of accreting
to the North American continent along the south central coast of Alaska
. It has been displaced about 600 km northward since the Cenozoic
along the Queen Charlotte-Fairweather fault system.
The Yakutat Block is bounded on the northeast by the Fairweather Fault, and on the north by a system of thrust and possibly strike-slip faults in the Chugach Mountains
and St. Elias Mountains. The Yakutat Block is bounded on its southwest side by an as yet undefined underwater geologic feature known as the Transition Zone. Global Positioning System
(GPS) measurements indicate that the Yakutat block has a distinctive velocity relative to both the Pacific Plate
and the North American Plate
. Thus it appears to be a terrane in the process of accreting rather than a block already sutured on to the Pacific or North American plate.
Relative to North America, the Yakutat Block moves at a rate of about 45 mm/yr to the north northwest, along the Fairweather fault. There is about 20 mm/yr of contraction between the Yakutat block and the Pacific plate, which is probably accommodated on an offshore structure. South of Yakutat Bay, the boundary between the Yakutat block and the North American plate is once again along the Fairweather Fault. North of Yakutat Bay, between Yakutat Bay and the Copper River/Wrangell Mountains region, about 40 mm/yr of contraction is taken up by compression, accommodated by faults within the continental crust. The convergence rate is among the highest in the world within continental crust, surpassing even that which is occurring between the Indo-Australian Plate
and the Eurasian Plate
which is lifting the Himalayas
.
Terrane
A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...
in the process of accreting
Accretion (geology)
Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...
to the North American continent along the south central coast of Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
. It has been displaced about 600 km northward since the Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
along the Queen Charlotte-Fairweather fault system.
The Yakutat Block is bounded on the northeast by the Fairweather Fault, and on the north by a system of thrust and possibly strike-slip faults in the Chugach Mountains
Chugach Mountains
The Chugach Mountains of southern Alaska are the northernmost of the several mountain ranges that make up the Pacific Coast Ranges of the western edge of North America. The range is about 500 km long, running generally east-west. Its highest point is Mount Marcus Baker, at , but most of its...
and St. Elias Mountains. The Yakutat Block is bounded on its southwest side by an as yet undefined underwater geologic feature known as the Transition Zone. Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
(GPS) measurements indicate that the Yakutat block has a distinctive velocity relative to both the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
and the North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...
. Thus it appears to be a terrane in the process of accreting rather than a block already sutured on to the Pacific or North American plate.
Relative to North America, the Yakutat Block moves at a rate of about 45 mm/yr to the north northwest, along the Fairweather fault. There is about 20 mm/yr of contraction between the Yakutat block and the Pacific plate, which is probably accommodated on an offshore structure. South of Yakutat Bay, the boundary between the Yakutat block and the North American plate is once again along the Fairweather Fault. North of Yakutat Bay, between Yakutat Bay and the Copper River/Wrangell Mountains region, about 40 mm/yr of contraction is taken up by compression, accommodated by faults within the continental crust. The convergence rate is among the highest in the world within continental crust, surpassing even that which is occurring between the Indo-Australian Plate
Indo-Australian Plate
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
and the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
which is lifting the Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
.