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Earth's Complex Complexion http://oceanusmag.whoi.edu/v42n2/dick.html Earth’s Complex Complexion Expeditions to remote oceans expose new variations in ocean crust By Henry J.B. Dick, Senior Scientist, The creation and cooling of oceanic gold and silver. So how Earth’s crust forms Geology and Geophysics Department, crust is the primary means by which heat is more than just an academic question. Woods Hole Oceanographic Institution escapes from Earth’s interior. In this dy- namic planet-scale crucible, heat, chemi- The seafloor layer cake ven as you read this, Earth’s crust is cals and minerals are transported from Several generations of scientists have Econtinually being reborn and recycled Earth’s interior to its surface. dredged rock samples from the seafloor, in a dynamic process that fundamentally Over the long haul, the process ulti- employed submarines and robots to study shapes our planet. We’re not generally mately determines Earth’s chemical make- it, and even drilled into it to learn a aware of all this action because most of it up. It affects the amount of carbon dioxide considerable amount about the shallow occurs at the seafloor, under a formidable and water in the crust, oceans, and atmo- oceanic crust. We’ve analyzed seismic watery shroud, and often in remote re- sphere, and it produces zinc, copper, and waves that penetrate and reflect off rock gions of the oceans. other mineral deposits, including some layers deep in the crust in an effort to Working in the ice-covered Arctic Ocean in 2001, scientists and crew aboard the maiden voyage of the U.S. icebreaker Healy successfully—and surprisingly—were able to perform 200 dredge operations along the Gakkel Ridge, collecting some 4,000 seafloor rock samples. 1 Oceanus Magazine • Vol. 42, No.2 • 2004 Woods Hole Oceanographic Institution • oceanusmag.whoi.edu 8 8 8 8 3 8 3 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 2 3 ˚ 8 8 5 8 8 8 ˚ 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 8 8 8 8 8 8 ˚ ˚ ˚ 2 4 ˚ 5 5 5 5 8 8 8 7 5 5 ˚ ˚ 5 ˚ 5 ˚ 5 5 ˚ ˚ 5 ˚ 5 8 5 ˚ 6 0 5 6 ˚ ˚ ˚ ˚ ˚ 5 8 8 6 6 6 6 8 ˚ ˚ ˚ ˚ ˚ ˚ 5 6 8 8 6 6 6 6 7 7 7 7 7 7 ' ' ' ˚ ˚ 7 ˚ ˚ ˚ 6 ˚ 0 ˚ ˚ ˚ 7 8 ˚ 5 1 1 0 ˚ ˚ ˚ ˚ 6 6 6 6 6 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 8 7 8 8 8 ' ' 5 2 ˚ ˚ 4 3 8 5 8 3 4 5 6 5 4 7 9 5 5 ˚ ˚ 8 8 ˚ 9 0 0 0 1 1 2 8 ˚ ˚ ˚ 1 2 ' 8 2 3 5 3 ˚ 4 4 3 4 4 5 5 1 1 2 2 ˚ ˚ ˚ ˚ ˚ ˚ 6 ˚ ˚ 8 ˚ 8 7 ˚ ˚ ˚ 5 6 7 8 9 0 1 2 3 4 5 6 ' 5 9 0 9 ˚ 3 7 3 3 2 1 3 ˚ 1 0 9 4 9 0 8 ' 4 8 6 ˚ 7 ˚ 1 0 2 5 ' 0 5 ' 5 0 5 0 5 0 5 0 5 5 0 ˚ ˚ ˚ ˚ 8 7 8 9 0 1 2 3 4 5 6 3 5 5 6 8 39 2 2 5 ˚ ˚ ˚ 8 5 3 6 6 ˚ 0 ˚ 5 ˚ ' 5 0 4 ˚ 5 1 ˚ ˚ 0 3 ˚ 0 5 ˚ 3 0 5 1 1 2 ˚ 0 ˚ ˚ 5 ˚ 2 3 ˚ 2 8 9 ˚ ˚ 3 ˚ ˚ ' 0 5 0 5 0 5 0 5 0 5 6 2 6 8 5 0 3 ˚ 5 ˚ 2 6 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 5 ˚ ˚ 4 4 ˚ ˚ ˚ 6 5 ˚ 5 ˚ ˚ 4 5 5 5 5 1 5 ˚ 4 ˚ 7 ' 4 0 3 4 ˚ ˚ 1 ' 2 4 ˚ ' 5 0 4 4 ' 2 5 7 4 ' ' ' ˚ 9 4 5 ˚ ' ' ' ' ˚ 0 3 4 4 4 ˚ ˚ ˚ ˚ ' ' ' ' ' ' ˚ ' ' ˚ ' ˚ ' ˚ ˚ ' ˚ ' ˚ ' ' ' ˚ ' ˚ ' ˚ ' ˚ ' ˚ ' ˚ ˚ ' 1 1 ' 1 ' 2 0 2 2 5 2 50 2 2 5 3 3 3 3 3 3 3 3 ˚ ˚ ˚ 6 6 6 6 ˚ 6 6 12 11 9˚ 8˚ 7˚ 6˚ 5 4 3 2 1 0 1 3 4 5 6 7 8 9 1 ' 1 ' 1 ' 1 ' 1 1 2 ' ' 2 ' 5' 86 86 86 8 ˚ 8 8 ˚ 8 8 8 9 5 ˚ Gakkel Ridge Bathymetry 0' 1 2˚ ˚ 8 1 6 2 AMORE Cruise (Aug - Oct 2001) 9 8 ˚ 4 5 The 2001 AMORE (Arctic Mid-Ocean Ridge Expedition) collected ˚ 0 ' USCGC Healy & PFS Polarstern Seabeam and Hydrosweep Data ' 05 Polar Stereographic Projection 6˚ Central Longitude: 54 9 8 1˚ 3 1 SeaBEAM sonar data to create this detailed 1,000-kilometer ˚ nautical miles 0 20 8 0 kilometers 20 0' 2 0 ˚ 6˚ 4 Depth (km) 8 5 9 ' (620-mile) bathymetric map of the Gakkel Ridge. 2 ˚ ˚ 0 2.0 3.0 4.0 5.0 6.0 10 5' ˚ 5 302 85 9 1 ˚ 8 2 ˚ ' 4 50 0 ˚ ' 85 9 0 ˚ 5' ˚ 4 85 8 8˚ 2 ˚ 3 223 5 8 ' ' 9 0 ˚ ˚ 4 85 7˚ ' 35 8 ˚ 2 85 ˚ 3 0 ' D65 ' 250 C05 0 RR11D6561 ˚ 3 D64D63 D62 85 6˚ 8 7 8 ˚ 2 ' ˚ D66 25 2 ˚ 5 85 ' 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 ˚ 8 8 8 8 8 ˚ 8 8 8 8 8 5 5 5 5 5 5 6 6 6 6 6 6 6 6 6 6 7 7 7 7 7 7 ' 7 7 ' 8 ' 8 8 8 ˚ ' ˚ ' ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 5 ˚ 5 ˚ 5 ˚ 5 ˚ ˚ 5 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 5 5 4 0 5 5 6 7 5 5 5 8 4 5 9 0 7 1 0 4 4 4 ˚ 2 3 4 5 4 4 4 ˚ 5 6 5 2 2 2 2 2 3 2 2 2 3 3 1 3 3 0 3 3 1 3 3 2 3 3 3 4 3 4 4 6 4 7 4 4 9 4 5 9 ˚ ˚ 2 ˚ ˚ ˚ ˚ ˚ 7 8 9 0 1 2 3 4 5 4 7 8 4 0 3 2 3 4 6 4 3 0 2 1 2 ˚ 1 3 ˚ 9 0 2 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 7 8 1 ˚ 4 3 6 3 8 4 0 1 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 ˚ ˚ ˚ ˚ ˚ 5 ˚ 9 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 2 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 2 ˚ ˚ ˚ 5 ˚ ˚ ˚ 1 0 ˚ ˚ ˚ ˚ ˚ 1 1 4 1 4 1 5 1 5 0 0 1 1 1 1 2 2 5 0 5 9 ' ' ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 8 ˚ ˚ 5 ˚ 5 ˚ 3 5 5 5 3 5 2 2 5 0 2 4 1 2 1 3 2 3 3 3 4 4 4 4 4 4 2 3 3 4 4 5 5 0 0 1 1 2 2 3 3 4 4 5 5 0 0 1 5 0 5 0 5 ' ' ' 3 3 3 3 3 3 4 4 4 8 ˚ 8 8 5 5 0 5 0 5 0 5 0 5 0 5 0 5 0 ' ' ' ' ' 2 2 8 5 0 5 0 5 0 5 0 5 0 5 0 5 0 5 0 ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' ' decipher its characteristics—similar to and exposed on continental margins. logical three-layer cake about 6 to 7 kilo- the way physicians use an MRI to peer From early studies, a simple picture meters (3.7 to 4.3 miles) thick. On top was below the skin. We’ve also studied emerged: It seemed the ocean crust was lava that spilled out and cooled rapidly ophiolites—isolated portions of the relatively homogenous in composition, into a glassy substance called basalt, which seafloor that tectonic forces have thrust up structure, and thickness—sort of a geo- carpeted the ocean bottom. Below were Icebreaker Ice Flows New Crust va La s Dike r Mantle Slabs Floo Gabbros Valley Mantle Rift Rock Mantle er e Lithospher Magma Chamb Flow Direc Lava New tion Rift Valley Floor Volcanic activity at mid-ocean ridges creates new seafloor crust that spreads outward to cover 70 percent of Earth’s surface. Recent expeditions have led to the discovery of an entirely new type of mid-ocean ridge. Instead of two classes of ridges—fast-spreading and slow-spreading— there is now a third, ultraslow. Ultraslow-spreading ridges, which may make up one-third of the global ocean ridge system, have distinctive characteristics. Like other mid-ocean ridges, ultraslow ridges have areas where magma rises from the mantle and erupts at the seafloor to create new ocean crust. But in between, there are also amagmatic zones, where solid slabs of mantle rock rise directly to the seafloor. 2 Oceanus Magazine • Vol. 42, No.2 • 2004 Woods Hole Oceanographic Institution • oceanusmag.whoi.edu 8 8 8 8 3 8 3 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 2 3 ˚ 8 8 5 8 8 8 ˚ 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 8 8 8 8 8 8 ˚ ˚ ˚ 2 4 ˚ 5 5 5 5 8 8 8 7 5 5 ˚ ˚ 5 ˚ 5 ˚ 5 5 ˚ ˚ 5 ˚ 5 8 5 ˚ 6 0 5 6 ˚ ˚ ˚ ˚ ˚ 5 8 8 6 6 6 6 8 ˚ ˚ ˚ ˚ ˚ ˚ 5 6 8 8 6 6 6 6 7 7 7 7 7 7 ' ' ' ˚ ˚ 7 ˚ ˚ ˚ 6 ˚ 0 ˚ ˚ ˚ 7 8 ˚ 5 1 1 0 ˚ ˚ ˚ ˚ 6 6 6 6 6 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 8 7 8 8 8 ' ' 5 2 ˚ ˚ 4 3 8 5 8 3 4 5 6 5 4 7 9 5 5 ˚ ˚ 8 8 ˚ 9 0 0 0 1 1 2 8 ˚ ˚ ˚ 1 2 ' 8 2 3 5 3 ˚ 4 4 3 4 4 5 5 1 1 2 2 ˚ ˚ ˚ ˚ ˚ ˚ 6 ˚ ˚ 8 ˚ 8 7 ˚ ˚ ˚ 5 6 7 8 9 0 1 2 3 4 5 6 ' 5 9 0 9 ˚ 3 7 3 3 2 1 3 ˚ 1 0 9 4 9 0 8 ' 4 8 6 ˚ 7 ˚ 1 0 2 5 ' 0 5 ' 5 0 5 0 5 0 5 0 5 5 0 ˚ ˚ ˚ ˚ 8 7 8 9 0 1 2 3 4 5 6 3 5 5 6 8 39 2 2 5 ˚ ˚ ˚ 8 5 3 6 6 ˚ 0 ˚ 5 ˚ ' 5 0 4 ˚ 5 1 ˚ ˚ 0 3 ˚ 0 5 ˚ 3 0 5 1 1 2 ˚ 0 ˚ ˚ 5 ˚ 2 3 ˚ 2 8 9 ˚ ˚ 3 ˚ ˚ ' 0 5 0 5 0 5 0 5 0 5 6 2 6 8 5 0 3 ˚ 5 ˚ 2 6 ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ ˚ 5 ˚ ˚ 4 4 ˚ ˚ ˚ 6 5 ˚ 5 ˚ ˚ 4 5 5 5 5 1 5 ˚ 4 ˚ 7 ' 4 0 3 4 ˚ ˚ 1 ' 2 4 ˚ ' 5 0 4 4 ' 2 5 7 4 ' ' ' ˚ 9 4 5 ˚ ' ' ' ' ˚ 0 3 4 4 4 ˚ ˚ ˚ ˚ ' ' ' ' ' ' ˚ ' ' ˚ ' ˚ ' ˚ ˚ ' ˚ ' ˚ ' ' ' ˚ ' ˚ ' ˚ ' ˚ ' ˚ ' ˚ ˚ ' 1 1 ' 1 ' 2 0 2 2 5 2 50 2 2 5 3 3 3 3 3 3 3 3 ˚ ˚ ˚ 6 6 6 6 ˚ 6 6 12 11 9˚ 8˚ 7˚ 6˚ 5 4 3 2 1 0 1 3 4 5 6 7 8 9 1 ' 1 ' 1 ' 1 ' 1 1 2 ' ' 2 ' 5' 86 86 86 8 ˚ 8 8 ˚ 8 8 8 9 5 ˚ Gakkel Ridge Bathymetry 0' 1 2˚ ˚ 8 1 6 2 AMORE Cruise (Aug - Oct 2001) 9 8 ˚ 4 5 ˚ 0 ' USCGC Healy & PFS Polarstern Seabeam and Hydrosweep Data ' 05 Polar Stereographic Projection 6˚ ˚ Central Longitude: 54 9 8 11 3 nautical miles ˚ 0 20 8 0 kilometers 20 0' 2 0 ˚ 6˚ 4 Depth (km) 8 5 9 ' 2 ˚ ˚ 0 2.0 3.0 4.0 5.0 6.0 10 5' ˚ 5 302 85 9 1 ˚ 8 2 ˚ ' 4 50 0 ˚ ' 85 9 0 ˚ 5' ˚ 4 85 8 8˚ 2 ˚ 3 223 5 8 ' ' 9 0 ˚ ˚ 4 85 ˚ The 2001 AMORE (Arctic Mid-Ocean Ridge Expedition) 7 ' 35 8 ˚ 2 85 ˚ 3 0 ' collected SeaBEAM sonar data to create this detailed 1,000- D65 ' 250 C05 0 RR11D6561 ˚ 3 D64D63 D62 85 6˚ 8 7 8 ˚ 2 kilometer (620-mile) bathymetric map of the Gakkel Ridge.
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