Page 280 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

of
of
This
for
rift
then
the
simplifying
(Am),
starting
com-
topo-
density
the
in
263
series
depth
change
at
used
(continental
of
range).
(lithosphere/asthenosphere
ridge),
then
that,
the
mass
sum
Expressions
significant
the
depth. The
a
commonly
for
at
the
is
so
these
in
the
for
mid-ocean
therefore:
(mountain
anomaly
is
chosen
model
/ateral changes
to
Moho
was
therefore
apart
constructed-with
due
of
2.18.
Gravity
it
km
those
effects:
contrasts
each
Zones
as
the
air
craton
gravity
boundaries, are
180
fragments
to
and
same
g/cm’.
g/cm’.
free
level; 2)
g/cm’.
is
in
their
g/cm’.
as
2.14
at
anomaly
bathymetric
(Ap).
depth
margins
same
to
the
The
the
is
Density
to
Figs.
due
and
g/em3
(bathymetry):
1.64
+2.67
boundary
(topography):
+0.4
ripping
s
—0.04
contributions
of lithosphere
is
sea
craton,
boundaries
change
calculated.
continental
the
Settings
are
in
pressure
Bouguer
at
(continental
3.3
=
contributions.
exactly
portrayed
fundamental
=
=
effects
=
is
and
(Pc),
of
Pg
(peu
continental
=
Pm
craton
boundaries
g/cm?
lithosphere/asthenosphere
g/em*
progression
Tectonic
—
g/em?
of Lithosphere: p,,
topographic
—
the
are
(p.)y
—
across
the
are
the
upper crust
—
modeling, important
(Moho):
air
models,
mantle part
py
pm
py
km),
Cycle,”
the
3.26
2.67
boundaries
8.12):
vs.
effects
colliding
=
basin
2.9
=
=
=
three
of
contrasts
level
three
Ap
Ap
a
=
fundamental
Ap
(180
Ap
=
=
with
surface
lower crust
a
p,
five
“Wilson
(p,)y
(Fig.
ocean
(p,),
the
as
the
bathymetric
vs.
Mass above sea
the
Asthenosphere:
vs.
compensation
start
and
viewed
the
water
without
by
effects:
the
corrections
Asthenosphere
crust:
crust:
density
of
part
the
an
bounded
ocean
of
the
models
sum
boundary):
of
Ocean
opening
1)
vs.
gravity
three
Mantle
be
each
Lower
Upper
each
is
Shallow
contributions
the
assumptions:
Mantle
the
and
by
progression
can
the
The
The
For
3)
reflected
as
of
Bouguer
to
contrast,
b)
graphic
a)
In
models
closing
km;
zone),
depth
depth
puted
“
3.
2.
1.
33
craton. bound- three the of depth in changes from result gravity to Contributions composite craton. A the for zero to equal contribution each to relative aries, model , grav- Bouguer and air of free forms and amplitudes the of comparison a shows then tectonic settings. different the in an
characteristic litho- entire nor- of continental and crust the and crust con- can basin ocean sides the on lithosphere, a as crust simi- are expressions significant conti- a for compensation illus- to grav- ridges). the on relief than dense column lithosphere of part mantle crustal and boundary example. for to 1994). al.. et excess mass equi- isostatic compen-
has and crust lithosphere lithosphere. thicker oceanic the rifting b) an forming margins oceanic the of 8.40) (Fig. gravity no be may said be sufficient settings. mid-ocean considering less is asthenosphere the of the lithosphere/asthenosphere topography the Alps. balance, contributing 30 Lillie a comprises of due settings.
Equilibrium setting Each the of and crust thin and from ocean; thin apart rips 2.13); (Fig. created, continental the of thickening model the respective there old, can same isostasy. where often is 8.20). three those rifts: without asthenosphere the 1) part mantle and the to due lithosphere/asthenosphere In anomalies. 1983: al., et models as well 1975). anomalies
Isostatic settings. thicknesses Jevel; sea crust transition normal than crust. thick craton a as zone rift is lithosphere passive subduction and margins on range 8.32, 8.36). Their are features boundary. The Airy normal (Fig. Moho in anomalies (continental adequately the that that: so the to asthenosphere the on relief excesses 3 the gravity of isostatic (Kissling downgo
Local tectonic and near topography; thin topography; water topography; a) that: continental and center through continental mountain those assuming deepest Bouguer divergence Note lithosphere, relative between large mass settings, modeling component anomalies the of gravity and (Grow contributions (bathymetry),
lsostasy in five (bathymetry) Topography in Drop Shallower in a forming oceanic the close 2.18). and (Figs. models when the and explained boundary. the of (—Am), contrast that so compensate plate in important gravity mantle in for flexure show simplified g/cm*
and Regions comprise Craton: Uplifted Margin: crust. High related, new in can basin the of (Fig, margin lithosphere/asthenosphere modeling of plate be part small, to considered an the accounted below topography for 1.03
Gravity for below topography thickness. Rift: oceanic Ridge: lithosphere. Range: are settings thin. where point ridge the collision forms continental previous because Gravity depth the of free-air active of cannot mantle deficit mass density is required convergent be is root observed zones, be lithosphere models in depth, are: 0 = = p,
8 Anomalies models of Continental mal Continental Continental thinner Mid-Ocean thin Mountain The lithosphere the mid-ocean c) 2.14); in range The in those similar, the craton. at forms areas anomalies lithosphere/asthenosphere overlying, the 2) lithosphere is active to needs lithosphere the to subduction to needs and The changes boundary p, Air: Water:
Chapter The heights sphere. 1. ai od to 4. 5. entire to tinue a with (Fig. resulting mountain to lar also are on relief nental achieved is the trate In ity the represents (+Am); the boundary thinning. In also a mGal 50 At that librium satory sphere assumptions
262 Gravity