“the most important ingredient in the formulation of the sea floor spreading and the later plate...
TRANSCRIPT
“The most important ingredient in the formulation of the sea floor spreading and the later plate tectonic theories was the knowledge of the existence of the mid-ocean ridge system.”
-L. Morley
Carrie WelkerMason Edwards
History of Mid-Ocean Ridges: Role in the Development of Plate Tectonics
Pre-Plate Tectonics
Questions driving the theories:• Why do continents like South America and Africa look like they fit
together?• Why are there corresponding rock formations and fossil assemblages
on the edges of continents?• How do mountains form?
Theories:• Contraction Theory
– Edward Suess (1831-1914)• Geosynclines
– James Hall (1811-1889)• Continental Drift
– Alfred Wegener (1880-1930)
No unifying theory of earth science!
1900 1950 2000
Mid-Ocean Ridges: Pre World War II
1620 –Francis Bacon notices how South America and Africa “fit” together
1855 – Bathymetry from U.S. Navy proves mountains in the mid-Atlantic
1912 – The Origins of Continents by Wegener suggests continental drift.
WWI –Development of sonar will aid in sea floor mapping
1920s-30s –Mechanism of continental drift hotly debated. What could cause lateral motion of continents?
WWII – Extensive mapping of sea floor magnetics
1954 – Benioff zones at continental margins
1956 – Magnetic field orientation rock record noted
1900 1950 2000
Mid-Ocean Ridges: World War II - 1960
(Benioff, 1954)(http://www.clas.ufl.edu)
1900 1950 2000
0 5 10 0
5
10
15
20
25
30
Per
cen
t o
f ci
rcu
mfe
ren
ceco
nn
ecte
d t
o s
ub
du
ctin
g s
lab
Plate Velocity(Centimeters per year)
Eu
rasi
anN
. A
mer
ican
S.
Am
eric
an
An
tarc
tic
Afr
ican
Car
ibb
ean
Ara
b
Ind
ian
Ph
ilip
pin
e
Naz
caP
acif
ic
Co
cos
1962 – Hess suggests sea floor spreading
1963 – Vine & Matthews correlate magnetic anomalies to sea floor age
1965 – Wilson differentiates between MOR transcurrent and transform faults
1975 – Uyeda correlates plate velocity with subducted slab “quantity”
Mid-Ocean Ridges: Post 1960 (Synthesis)
(Reproduced from Uyeda, 1978)