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from article Mylonite

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Photomicrograph of greenschist-grade mylonite and ultramylonite derived from granodiorite, Borrego Springs shear zone, southern California. Half-arrows indicate right-lateral shear sense. Feldspar porphyroclasts (f), some with recrystallized tails…

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from article Marine geology

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Map showing the tectonic structure of the Earth's lithosphere, which is composed of about 10 rigid plates, each moving as a distinct unit. (After J. F. Dewey, Plate tectonics, Sci. Amer., 226(5):56–68, 1972)

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from article Marine geology

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Geology of the North Atlantic Ocean. (a) Physiographic divisions of the ocean floor. (b) Principal morphologic features along the profile between North America and Africa. (Modified from B. C. Heezen et al., GSA Spec. Pap. 65, 1959)

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from article Marine geology

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Topography of the mid-oceanic ridge. (a) Mid-Atlantic Ridge (25°N), spreading rate 2.6 cm (1.0 in.) per year. (b) East Pacific Rise (55°S), spreading rate 8.8 cm (3.5 in.) per year; sea-level rises causing transgression (arrows). 1 km = 0.6 mi.

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from article Marine geology

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Ocean depth anomalies. (a) Schema of the lithosphere, asthenosphere, and varying ocean depths away from the axis of mid-oceanic ridge spreading system. (b) Parameters used to compute adjusted crustal depths and to analyze depth-age relationships.…

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from article Marine geology

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Digitized contoured map of a 200 km (120 mi) stretch of the East Pacific Rise (Ridge) near 11°N, 104°W. The data were collected using a multibeam swath mapping system. The depth of the ridge crest varies from south to north and illustrates an…

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from article Marine geology

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Schematic cross section of a rifted continental margin. Note dramatic change in total crustal thickness across the margin, fault-bounded sedimentary basins, and large thicknesses of land-derived sediments making up the continental rise.

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from article Marine geology

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Oceanic trench and associated tectonic and morphologic features. (a) Cross section of typical island arc system showing tectonic units and terminology (after D. E. Karig and G. E. Sharma III, Subduction and accretion at trenches, Geol. Soc. Amer.…

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from article Marine geology

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Free-air gravity map of the Southern Ocean derived from analysis of SEASAT and GEOSAT altimeter data. Light areas represent positive anomalies; dark areas represent negative anomalies. Note long linear expressions of fracture zone traces. (From W.…

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from article Marine geology

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A multibeam bathymetric swath mapping system. The bottom contour chart is produced on board the vessel in real time. The width of the mapped swath depends on the specific system used but can be up to two times the water depth. Contours are given in…

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