1.4 OUtline

1. 1.4 OUtline Plates converge or scrape past each other

2. I. Tectonic plates push together at convergent boundaries • Subduction:when one oceanic plate sinks beneath another • Continental-continental collision • Continental-continental collision:occurs when 2 plates carrying continental crust push together • Both crusts are the same density, neither plate can sink beneath the other • European Alps are found where the African & European plates are colliding • Himalayas first formed when the Indian plate began colliding with the European Plate

3. B. Oceanic-Oceanic Subduction • Oceanic-oceanic subduction:occurs when 1 plate with oceanic crust sinks under another plate with oceanic crust • Two main features form at oceanic-oceanic subductions: • Deep-Ocean Trenches – most are found in the Pacific Ocean; for example at the Mariana Trench the Pacific Plate is sinking under the Philippine Plate • Island Arcs – there are chains of volcanic islands that form on the top plate, parallel to a deep ocean trench; as oceanic crust of the sinking plate melts, magma rises through the top plateExamples: Philippine Islands, Aleutian Islands

4. C. Oceanic-continental subduction • Oceanic-continental subduction:occurs when ocean crust sinks under continental crust • Deep-ocean trenches and coastal mountains form at these boundaries • Deep-Ocean Trenches – some of the world’s youngest trenches are in the eastern Pacific Ocean; for example, the Pacific Plate is sinking under the North American Plate causing underwater earthquakes • Coastal Mountains – continental crust buckles to form mountain ranges; parallel to a deep-ocean trench; some are active volcanoes

5. II. Tectonic plates scrape past each other at transform boundaries • At a transform boundary, crust is neither formed nor destroyed • As the plates move, their edges scrape & grind against each other • Transform boundaries occur mostly on the sea floor near mid-ocean ridges • They also occur on land; example: San Andreas Fault

6. III. The theory of plate tectonics helps geologists today • Theory has helped to explain Earth’s past and to predict what might happen along plate boundaries in the future • Theory of plate tectonics gives scientists a way to study & predict geologic events