Seafloor Spreading and Subduction Zones

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Name: ___________________________________________ Period: __________ Date: __________________ Seafloor Spreading and Subduction Zones Directions: The diagram on the reverse side depicts an area of the ocean floor where different plates are shifting due to plate tectonics. Begin by labeling the parts (draw an arrow to indicate which feature you mean). Then answer the questions below. You may use your book and whatever notes you have. I. Label the following parts: 2 oceanic plates 2 trenches 1 continental plate mid-ocean ridge 1 oceanic/continental plate transform fault (intersecting the ridge) use brackets mountains (on land) rising magma (in 2 places) island arc II. Further Analysis: 1) Identify the plate boundaries by placing a big letter “D” above the divergent boundary and placing a “C” above each convergent boundary. (Each letter should go in the dotted box.) 2) What process is taking place along the ridge? _______________________________ What process is taking place at the trenches? _______________________________ 3) During subduction, a(n) _________________ plate will sink beneath the continental plate. 4) What causes one plate to sink while another floats? 5) Using a green colored pencil, shade in the area where the youngest ocean rocks would be found with regard to seafloor spreading. Then, in blue, shade in the area of oldest ocean rock. Which of these areas (green or blue) would have the thickest sediment sitting on top of it, AND why? 6) Using a red colored pencil, color in 2 areas of lithosphere where you would find melting rock. What happens to the melted rock, and what landforms does it produce? 7) On your diagram, draw circular arrows to show the circulation of the magma beneath the mid-ocean ridge. What is the name of this process? _________________ 8) Plate tectonic motion is causing the ____________________ Ocean to expand, while the _____________________ Ocean is getting smaller. Seafloor Diagram label plate boundaries .

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or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of Th e Oceanography Society. Send all correspondence to: [email protected] or Th eOceanography PO Box 1931, Rockville, USA.Society, MD 20849-1931, or e to: [email protected] Oceanography correspondence all Society. Send of Th approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution articleis has been published in Th SPECIAL ISSUE FEATURE Oceanography Drilling the Crust Threproduction, Republication, systemmatic research. for this and teaching article copy to use in reserved. e is rights granted All OceanographyPermission Society. by 2007 eCopyright Oceanography Society. journal of Th 20, Number 1, a quarterly , Volume at Mid-Ocean Ridges An “in Depth” perspective BY BENOÎT ILDEFONSE, PETER A. RONA, AND DONNA BLACKMAN In April 1961, 13.5 m of basalts were drilled off Guadalupe In the early 1970s, almost 15 years after the fi rst Mohole Island about 240 km west of Mexico’s Baja California, to- attempt, attendees of a Penrose fi eld conference (Confer- gether with a few hundred meters of Miocene sediments, in ence Participants, 1972) formulated the concept of a layered about 3500 m of water. This fi rst-time exploit, reported by oceanic crust composed of lavas, underlain by sheeted dikes, John Steinbeck for Life magazine, aimed to be the test phase then gabbros (corresponding to the seismic layers 2A, 2B, for the considerably more ambitious Mohole project, whose and 3, respectively), which themselves overlay mantle perido- objective was to drill through the oceanic crust down to tites.
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