TAILIEUCHUNG - Encyclopedia of Global Resources part 97

Encyclopedia of Global Resources part 97 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the . Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 888 Organization for Economic Cooperation and Development Global Resources 5 kilometers thick and it records the products of seafloor spreading. The top kilometer is composed of pillowed basalt. Basalt is a dense black lava containing about50 percent by weight silicon dioxide formed as a result of melting of the mantle. A sequence of these basalts looks like a huge pile of black to green pillows. Pillows form when basalt lava erupts and is quenched underwater perhaps 3 kilometers or more beneath the surface. These basalt flows are fed from a system of vertical magma channels known as a sheeted dyke complex about 1 kilometer thick . The dykes are supplied magma from an underlying magma chamber which upon cooling forms gabbro about 3 kilometers thick . Gabbro is the base of the crustal section and is underlain by mantle rocks called peridotite. Although there is wide agreement that ophiolites form by seafloor spreading scientists do not agree on precisely where these form. Early ideas that ophiolites formed at true mid-ocean ridges such as the East Pacific Rise or Mid-Atlantic Ridge have been superseded by the idea that they form at convergent margins undergoing extension. A more recent idea that ophiolites for the most part represent back-arc basin crust has been challenged by the hypothesis that ophiolites form in forearc environments during the initiation of subduction zones. Ophiolites prove that processes of seafloor spreading and plate tectonics operated at the time the ophiolites formed. Therefore the record of ophiolites can be interpreted as a record of when plate tectonics occurred on Earth. Ophiolites are common in rock sequences of the following time ages 1 800 million years ago 800 to 400 million years ago and younger than 180 million years ago. Robert J. Stern See also Earth s crust Lithosphere Plate tectonics Seafloor spreading. Organization for Economic Cooperation and Development Category Organizations agencies and programs Date Establishing treaty .

TỪ KHÓA LIÊN QUAN
Đã phát hiện trình chặn quảng cáo AdBlock
Trang web này phụ thuộc vào doanh thu từ số lần hiển thị quảng cáo để tồn tại. Vui lòng tắt trình chặn quảng cáo của bạn hoặc tạm dừng tính năng chặn quảng cáo cho trang web này.