Achieved best fit by using 2000m contour depth (corresponds to position halfway between shoreline and ocean basin, true edge of continents) Matching sequences of rocks and mountain chains Type, age, structural style (type and degree of deformation) Evidence for glacial activity in areas now tropical Distribution of climate-sensitive deposits Distribution of climate-sensitive fossils Patterns of magnetic anomalies on the sea floor Worldwide distribution of earthquakes and active volcanoes LECTURE 5: GLOBAL PLATE TECTONICS II 23 Feb. 2000 ASSOCIATED READING: Pinet, Chapter 2 ( text internet site ) INTERESTING INTERNET LINKS: Sea-floor spreading Hot spots and mantle plumes Earth s magnetic field and magnetic anomalies Nearly all igneous rocks and some sedimentary rocks contain particles of magnetite (Fe-oxide, magnetic) Palaeomagnetism study of Earth s ancient magnetic field, used to interpret past positions of continents Polarity/orientation of magnetic field has reversed through time Rocks like tape recorders have preserved these variations, used to date rocks (distinct patterns) Disparity between ages of oceans and continents (~4 billion years) and ocean floor (&lt;180 million years) Plate boundaries Divergent boundaries occur where two plates move away from one another Associated physiographic feature is a mid-ocean ridge Stages in the development of mid-ocean ridge indicates how ocean basins are created Upwarping Rifting Sea invades rift valley Sea floor spreading continues, ocean basin created with mid ocean ridge in the centre Variations in spreading rates affect the morphology of spreading centres Faster the spreading rate, the broader the mountain range associated with the spreading Mid-Atlantic ridge vs East Pacific Rise Convergent boundaries mark areas where plates move together and collide Associated physiographic ocean-floor feature is trench, where subduction occurs Three subtypes of 
(two plates; move; away from one) (plates; collide; Associated physiographic ocean-floor feature is trench; L:mark areas) Context(plates collide,List([1797, 1829))):(Associated physiographic ocean-floor feature; is; trench, where subduction occurs Three subtypes of) (Nearly all igneous rocks and some sedimentary rocks; contain; particles of magnetite (Fe-oxide, magnetic) (plates; move; together; L:mark areas) (ocean basin; created; ) (Divergent boundaries; occur; L:where two plates move away from one) Context(Divergent boundaries occur,List([1220, 1246))):(another Associated physiographic feature; is; a mid-ocean ridge Stages in the development of mid-ocean ridge) (s ancient magnetic field; used; ) (Upwarping Rifting Sea; invades; rift valley Sea floor spreading continues, ocean basin) Context(Upwarping Rifting Sea invades,List([1429, 1458))):(rift valley Sea floor; continues; ) (these variations; used; ) (the broader the mountain range; associated; with the spreading Mid-Atlantic ridge vs East Pacific Rise Convergent boundaries) (rift valley Sea floor; spreading; ) (Worldwide distribution of earthquakes and active volcanoes; LECTURE; 5)
plates collide,List([1797, 1829)) Divergent boundaries occur,List([1220, 1246)) Upwarping Rifting Sea invades,List([1429, 1458))
two plates plates Associated physiographic ocean-floor feature Nearly all igneous rocks and some sedimentary rocks plates ocean basin Divergent boundaries another Associated physiographic feature s ancient magnetic field Upwarping Rifting Sea rift valley Sea floor these variations the broader the mountain range rift valley Sea floor Worldwide distribution of earthquakes and active volcanoes
move collide is contain move created occur is used invades continues used associated spreading LECTURE
away from one
Associated physiographic ocean-floor feature is trench L:mark areas
trench, where subduction occurs Three subtypes of
particles of magnetite (Fe-oxide, magnetic
together L:mark areas
L:where two plates move away from one
a mid-ocean ridge Stages in the development of mid-ocean ridge
rift valley Sea floor spreading continues, ocean basin
with the spreading Mid-Atlantic ridge vs East Pacific Rise Convergent boundaries
5