地球内部过程 Plate Movements-Accumulating Evidence The Topography of the Sea Floor Juan de Fuca Plate Arabian Plate Pacific Plate hippie Plate ndian-Australian o Q African Pl American Antarctic Plate Direction of plate motion (sawteeth point toward Spreading ndge Transform fault 环境跑顶学 Cneinacntalgcelogu ,率
地球内部过程 • Plate Movements-Accumulating Evidence The Topography of the Sea Floor：
地球内部过程 Plate Tectonics Magnetismiii in Rocks--General Most iron-bearing minerals are at least weakly magnetic at surface temperatures Each magnetic mineral has a Curie居里 temperature, below which it remains magnetic, but above which it loses its magnetic properties. The Curie temperature varies from mineral to mineral, but it is always below the minerals melting temperature. A hot magma is therefore not magnetic, but as it cools and solidifies, and ferromagnesian 铁镁矿物 silicates and other iron-bearing minerals crystallize from it, those magnetic minerals tend to line up in the same direction. like tiny compass needles, they align themselves parallel to he lines of force of the earth's magnetic field, which run north-south, and they point to the magnetic north pole. They retain their internal magnetic orientation unless they are heated again. This is the basis for the study of paleomagnetism, fossil magnetism in rocks 环境迪顶学 minoucntalocelogu 真去率
地球内部过程 • Plate Tectonics Magnetism磁 in Rocks—General： Most iron-bearing minerals are at least weakly magnetic at surface temperatures. Each magnetic mineral has a Curie居里 temperature, below which it remains magnetic, but above which it loses its magnetic properties. The Curie temperature varies from mineral to mineral, but it is always below the mineral’s melting temperature. A hot magma is therefore not magnetic, but as it cools and solidifies, and ferromagnesian 铁镁矿物 silicates and other iron-bearing minerals crystallize from it, those magnetic minerals tend to line up in the same direction. Like tiny compass needles, they align themselves parallel to the lines of force of the earth’s magnetic field, which run north-south, and they point to the magnetic north pole. They retain their internal magnetic orientation unless they are heated again. This is the basis for the study of paleomagnetism, “fossil magnetism” in rocks
地球内部过程 Plate Tectonics always coincided with its presen ot Magnetic north however, has ng Figure 3.10 Bluewater wne ao pose Faery position. In the early 1900s farra firlf lla at Bat ine ped Bual scientists investigating the direction of magnetization of a sequence of volcanic rocks in France discovered eh gde wand some flows that appeared to be magnetized in the opposite direction 是5m from the rest: their magnetic minerals n y adteretsp: pointed south instead of north Confirmation of this discovery in many places around the world led to the suggestion in the late 1920s that the earth's magnetic field had “ flipped翻动," or reversed polarity; that is, that the north and south poles had switched转换 places. During the time those surprising rocks had crystallized, a compass needle would have pointed to the magnetic south pole, not north 环境迪顶学 minoucntalocelogu ,率
地球内部过程 • Plate Tectonics Magnetic north, however, has not always coincided with its present position. In the early 1900s, scientists investigating the direction of magnetization of a sequence of volcanic rocks in France discovered some flows that appeared to be magnetized in the opposite direction from the rest: their magnetic minerals pointed south instead of north. Confirmation of this discovery in many places around the world led to the suggestion in the late 1920s that the earth’s magnetic field had “flipped翻动,” or reversed polarity; that is, that the north and south poles had switched转换 places. During the time those surprising rocks had crystallized, a compass needle would have pointed to the magnetic south pole, not north
地球内部过程 Plate Tectonics The Topography of the Sea Floor: If South america and africa really have moved apart one might expect to see some evidence of this between them some feature or features on the sea floor to indicate the continents passage. A topographic map of the floor of the Atlantic Ocean shows an obvious ridge running north-south about ha lfway不彻底 中途 between those continents大陆间近南 北向的明显洋脊. This mid- ocean ridge might be the seams from which the two continents moved apart. Similar ridges are found on the floors of other oceans as seen in the same figure. In other places, frequently along the margins of continents, there are trenches沟堑 several kilometers deep. It remained for scientists studying the ages and magnetic properties of seafloor rocks as described below, to demonstrate the significance of the ocean ridges to plate tectonics. The trenches, too, can be explained by plate tectonics 环境迪顶学 minoucntalocelogu
地球内部过程 • Plate Tectonics The Topography of the Sea Floor： If South America and Africa really have moved apart, one might expect to see some evidence of this between them, some feature or features on the sea floor to indicate the continents’ passage. A topographic map of the floor of the Atlantic Ocean shows an obvious ridge running north-south about halfway不彻底、 中途 between those continents大陆间近南 北向的明显洋脊. This mid-ocean ridge might be the seam缝 from which the two continents moved apart. Similar ridges are found on the floors of other oceans, as seen in the same figure. In other places, frequently along the margins of continents, there are trenches沟堑 several kilometers deep . It remained for scientists studying the ages and magnetic properties of seafloor rocks, as described below, to demonstrate the significance of the ocean ridges to plate tectonics. The trenches, too, can be explained by plate tectonics
地露内部过程 Plate Tectonics The Topography of the Sea Floor: If South america and Africa really have moved apart, one might expect to see some evidence of this between them some feature or features on the sea floor to indicate the continents I Figure 3.15 Ilww Ha bites, ch A-da l passage. A topographic map of the obvious ridge running north-soule an floor of the atlantic ocean shows about halfway不彻底、中途 between those continents大陆间近南北向的明显 洋脊. This mid- ocean ridge might be the seams from which the two continents moved apart. Similar ridges are found on the floors of other oceans as seen in the same figure. In other places, frequently along the margins of continents, there are trenches沟堑 several kilometers deep. It remained magnetic properties g the ages and for scientists study s of seafloor rocks as described below. to demonstrate 3.16 Satellite image ul lake Tanganyika.in the the significance of the ocean ridges to ican rift rnt, (In this lals-caNowr image green rgwtatm appears resL) a)NASA plate tectonics. The trenches, too, can e explained by plate tectonics 环境跑顶学 Cneinacntalgcelogu ,率
地球内部过程 • Plate Tectonics The Topography of the Sea Floor： If South America and Africa really have moved apart, one might expect to see some evidence of this between them, some feature or features on the sea floor to indicate the continents’ passage. A topographic map of the floor of the Atlantic Ocean shows an obvious ridge running north-south about halfway不彻底、中途 between those continents大陆间近南北向的明显 洋脊. This mid-ocean ridge might be the seam缝 from which the two continents moved apart. Similar ridges are found on the floors of other oceans, as seen in the same figure. In other places, frequently along the margins of continents, there are trenches沟堑 several kilometers deep . It remained for scientists studying the ages and magnetic properties of seafloor rocks, as described below, to demonstrate the significance of the ocean ridges to plate tectonics. The trenches, too, can be explained by plate tectonics