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Unformatted text preview: Plate Boundaries Mid-Ocean Ridges Recent Earthquake Activity Active Volcanoes Tsunami Foci Oceanic Trenches P l a te B o u n d a r i e s
* Note correspondence between Subduction zones and ocean trenches subduction zones pacific plate is consumed East pacific Rise Asthenosphere * Lithospheric not static Plates are dynamic Lithospheric plates travel across and into the Asthenosphere where the plate is consumed Convection Cells Plates are dynamic because within the Earth’s mantle there are Convection Cells! Determine: 1: Rate of plate movement 2: Direction of plate movement Mantle convection Facilitated by the semi-plastic nature of the
asthenosphere Pressure Melting
- partial melting at boundary - causing thin films of liquid - serves to lubricate crystals - allows movement and deformation
melting Ice surface Edges of a skate Pressure Melting in Asthenosphere Facilitates Plasticity
Grains surrounded by fluid Actual rock exhibiting partial melting Fluid Types of Plate Boundaries
East Pacific Rise / Mid-Atlantic Ridge Zones Process Spreading, Rifting Subduction Shear A. Divergent Peru-Chilie Trench / Alps B. Convergent C. Transform San Andraes fault / Dead sea fault A. Divergent Boundaries
1. Mid-Ocean Ridge System
* S p r e a d i n g c o i n c i d e s w i th a s c e n d i n g l i m b s o f C o n v e c ti o n C e l l * U p w e l l i n g M a g m a c o n s i s ts o f M u s h * P lu m e 1 -2 k m w id e * R id g e 2 -3 k m h ig h * C e n tr a l r i f t v a l l e y d e f i n e s j u n c tu r e b e tw e e n tw o d i v e r g i n g p l a te s 2. Continent Areas Rifting causes Continents to be Split Apart and Formation of New Ocean Basins Rising Magma Plume domes and invades Rift Valley As two sides of Rift Valley are pushed apart, Magma wells up and Fills Void New Ocean Crust added equally to both Diverging plates As Crust moves away from Spreading Center, it Cools, Thickens, and becomes more Dense 4 Stage Model of Rifting Stage 1: Upwarping or Doming ▪ Continent Uplifted and Stretched ▪ Fracturing Stage 2: Rupture of Overlying Plate
▪ Rift Valley stage East African Rift zone Stage 3: New Ocean Crust Formation
▪ Linear Sea stage ▪ Examples: Red Sea and the Gulf of Aden Red Sea Gulf of Aden Stage 4: Continued Ocean Crust Development
▪ Ocean Basin Stage B. Convergent Boundaries Collision of two Plates 3 types of Convergent Boundaries depending upon Ocean versus Continental Crust Subduction: ▪ Major process at Convergent Boundary ▪ Process where by one Plate Descends beneath another ▪ Plate that is Subducted is the Older, Denser plate—Why? 1. Ocean-Continent Collision The Andes Mountains were created by the subduction of the Nazca oceanic plate beneath the South American continental plate.
Example: Nazca plate subducted beneath South America Subduction
Subduction is the process in
w h i c h a n o c e a n i c l i th o s p h e r i c p l a te i s f o r c e d d o w n w a r d i n to th e m a n tl e b e l o w a n o th e r p l a te Juan de Fuca Plate movement beneath the North
A m e r i c a n P l a te i s a n e x a m p l e o f th e s u b d u c ti o n p r o c e s s . Mt. Rainier Would you like to live in Tacoma? How about Seattle? 2. Ocean-Ocean Convergence Pacific Ocean rimmed by Island arcs…Why?
A l e u ti a n I s l a n d s 3. Continent-Continent Collision India colliding with Eurasia preceded by Ocean-Continent Convergence Long-term Subduction of Oceanic crust along with Plate undertucking has produced Himalayas and Tibetan Plateau Sutures Zones: Ural Mountains Appalachian Mts Alps Tibetan Plateau Suture GangesBrahmaputra Submarine canyon C. Transforms - Shear Zones Occur where two Plates move past one another Exist on Land San Andreas F., Dead Sea F. Exist and in the Ocean along the Mid-Ocean Ridges Formation of Transform versus Subduction Zone controlled by angle of Approach of Plates San Andreas Fault leaving land! San-Andreas fault Tomales Bay Dead Sea Fault Transform Fault between Sinai Peninsula & Arabian Plate Red Sea Ocean Transforms are called Fracture Zoes East Pacific rise These offsets (imperfect breaks in plates) cause sheer zones Hot Spots
Formation of Island Chains Pacific Trends:
A lig n m en t o f I s la n d s s h o w s P a c i f i c P l a te h a s C h a n g e d i ts D i r e c ti o n o f M o v em en t Coral Atoll Development Wake Island M a ld iv es
Future in regime of sea-level rise? ...
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This note was uploaded on 04/14/2011 for the course GEO 142 taught by Professor Fitzgereld during the Spring '11 term at BU.
- Spring '11