EPSC 201 Lecture Notes - Lecture 11: Mid-Ocean Ridge, Gabbro, Oceanic Basin

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Evidence%of%SeaNfloor%Spreading%
!Magnetism%in%seaNfloor%rocks%varies%farther%from%MOR%
o!Stripes%of%positive%(stronger)%and%negative%(weaker)%magnetic%intensity%
o!Recorded%in%seaNfloor%basalts%
!Magnetic%anomaly:%
o!Difference%between%the%expected%strength%of%the%Earth’s%magnetic%field%at%a%
certain%location%and%the%actual%measured%strength%at%that%location%
Magnetic%Reversals:%
!Reversals%in%Earth’s%magnetic%field%are%recorded%in%ironNrich%rocks,%such%as%basalts%
SeaNfloor%Spreading:%
!Predicts%that%magnetic%anomalies%should%be%mirror%images%across%the%midNocean%ridge%
!%
!Sea%floor%spreading%explains%the%stripes%
o!Magnetic%polarity%reversals%are%imprinted%in%seaNfloor%rock%as%the%sea%floor%
continues%to%spread%
!The%width%of%the%magnetic%anomaly%stripes%is%related%to%the%spreading%rate%%
o!Faster%spreading%"%wide%stripes%
o!Slower%spreading%"%narrow%stripes%
Magnetic%Stratigraphy%N%dating%magnetic%reversals%%
!Chrons%of%epochs%%
o!Periods%of%predominantly%normal%or%reversed%polarity%
!Subchrons%or%events%%
o!Short%term%magnetic%reversal%%
o!1000%"%200,000%years%
!whereas%the%cause%of%reversals%remains%to%be%elucidated%
%
%
%%
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