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The geology of the Grand Teton area consists of some of the oldest rocks and one of the youngest mountain ranges in North America. The Teton Range, mostly located in Grand Teton National Park, started to grow some 9 million years ago. An older feature, Jackson Hole, is a basin that sits aside the range. The 2.5 billion year old metamorphic rocks that make up the east face of the Tetons are marine in origin and include some volcanic deposits. These same rocks are today buried deep inside Jackson Hole. Paleozoic rocks were deposited in warm shallow seas while Mesozoic deposition transitioned back and forth from marine to non-marine sediments with the Cretaceous Seaway periodically covering the area late in that era. 70 million years ago, the Laramide orogeny started to uplift western North America, erasing the seaway and creating highlands. The first part of the Teton Range was thus formed in the Eocene epoch. Large volcanic eruptions from in the Yellowstone-Absaroka area to the north left thick volcanic deposits. A series of glaciations in the Pleistocene epoch saw the introduction of large glaciers in the Teton and surrounding ranges, which at times formed part of the Canadian Ice Sheet. Moraines left by less severe ice ages impounded several lakes, including Jackson Lake. ==Precambrian deposition, metamorphism, and intrusion== Perhaps 3,000 million years ago in Precambrian time, sand, limey ooze, silt and clay were deposited in a marine trough (accurate dating is not possible, due to subsequent partial recrystallization of the resulting rock). Interbeded between these layers were volcanic deposits, probably from an island arc. These sediments were later lithified into sandstones, limestones, and various shales. These rocks were 5 to 10 miles (8 to 16 km) below the surface when orogenies (mountain-building episodes) around 2,800 to 2,700 million years ago intensely folded and metamorphosed them, creating alternating light and dark banded gneiss and schist.〔''Geology of U.S. Parklands'', page 592, "Precambrian Rocks", paragraphs 1-2〕〔''Roadside Geology of the Yellowstone Country'', page 5, paragraph 1〕 Today these rocks dominate the Teton Range with good examples easily viewable in Death Canyon and other canyons in the Teton Range. The green to black serpentine created was used by Native Americans to make bowls. Sometime around 2,500 million years ago, blobs of magma intruded into the older rock, forming plutons of granitic rock.〔''Geology of U.S. Parklands'', page 592, "Precambrian Rocks", paragraph 2〕 Extensive exposures of this rock are found in the central part of the range. About 1,300 to 1,400 million years ago in Late Precambrian, 5 to 200 foot (1.5 to 60 m) thick black diabase dikes intruded as well, forming the prominent vertical dikes seen today on the faces of Mount Moran and Middle Teton (the dike on Mount Moran is ).〔〔''Geology of National Parks'', page 566, section 3〕 Some of the large dikes can be seen from the Jenny Lake and String Lake areas. More than 700 million years elapsed between intrusion of the black dikes and deposition of the first Paleozoic sedimentary rocks. The Precambrian rocks were uplifted during this gap in the geologic record known as an unconformity; exposed to erosion they were gradually worn to a nearly featureless plain, perhaps somewhat resembling the vast flat areas in which similar Precambrian rocks are now exposed in central and eastern Canada. At the close of Precambrian time, about 600 million years ago, the plain slowly subsided and the site of the future Teton Range disappeared beneath shallow seas that were to wash across it intermittently for the next 500 million years.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Geology of the Grand Teton area」の詳細全文を読む スポンサード リンク
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