Page 54 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

are
by
evo-
bound-
depths
boundaries
three-dimensional
upper
composition
volcanic
are
observa-
different
rifts
continental
oceanic
has
continental
They
seismic
the
The
char-
therefore
first
sepa-
(“post-
geophysi-
37
the
textbook
of
setting
mantle
grabens
processes.
and
continental
and
was
2.18).
are
interfaces
brittle
Observations
inter-relationship
younger
the
gross
fundamental
within
structure
and
of
constraints,
that
(Moho)
2.24a),
can
to
A.
one
constraining
at
upper
application
at
(Fig.
subsurface
rift
detail
a
the
this
method
features
as
Appendix
sedimentary
crust
shallow
reveal
associated
(Fig. 2.14b).
layering
in
flat
at
beneath
continental
well
on
ranges
(Fig.
the
with
boundary
the
crustal
and
developed
thin
oceanic
Geophysical
relatively
constraints
often
as
potential
Moho. The
third
on
that
structural
boundaries.
is
form
sequence
two
conjunction
the
is
in
in
the
characteristic
region
grabens
mountain
asthenosphere
the
as
crust
and
profiles
outlined
suggest
from
margins
a
useful
present
thinner
OBSERVATIONS
well
the
illustrates
example,
overall
on
crust/mantle
features
with
resolving
structure
the
by
the
a
sea),
as
potential
Research
and
the
reflections
“ophiolite”
rift
in
particularly
offered
reflection
fundamental
Together
setting,
at
surveys
that
chapters
to
continental
Assignment”
including
its
changes
in
stratigraphic
like
mantle.
suggest
at
thick
For
continental
some
of
8)
The
done
reveal
hot
in
bathymetry
tectonic
velocity,
Chapter
much
below.
Constraints
another.
offers
useful
given
Refraction
2.13).
the
where
6)
and
remaining
boundary.
of
settings;
zones, seismic
uppermost
CONSTRAINTS
reflections
thickness
an
be
tectonics,
often
are
and
owes
passive
boundaries:
zones
three
a
2.14),
technique
to
Writing
outlined
is
can
(Fig.
seismic
of’plate
image
thicker
in
GEOPHYSICAL
in
observations
velocities
at
method
correspond
5
studies.
(discussed
and
4)
materials
observations
framework
Tectonic
tectonic
feature
the
subsurface
2.16b).
(Chapters
wedge-shaped
(Fig.
on
ridges
region. The
crustal
(Chapter
lithosphere/asthenosphere
Similar
to
and
profiles
“Sequenced
in
land
from
of
interpretations
strata
understanding
rift
techniques
increases
Each
refraction
ridges
depths
crust
refraction
seismic
fundamental
Plate
tectonic
Atcontinental
2.14c,
mid-ocean
on
certain
of
of
transition
isostasy
sedimentary
2.14a).
reflection
Geophysical
tectonic
to
state
TECTONIC
observations.
the
(topography
the
pattern
Refraction
Reflection
Refraction
the
mid-ocean
thought
and
(Figs.
low
abrupt
for
the
in
by
physical
of
seismic
by
BY
geophysical
of
a
(Fig.
of
elevations
identified
tions, and
relatively
velocities
following
acteristic
of
the
plate
structure
revealed
and
revealed
facilitate
the
margins
concept
Seismic
two
OFFERED
rating
strata
crust,
lution
show
rift”)
map
rifts
The
and
and
The
Seismic
ary
Seismic
PLATE
cal
to
head of zone deeper A crust. lower layered, ductile a overlying nonreflective, is that crust Moho. the of nature and depth the interpret to used be mas- can reflections horizontal beneath observed also is Moho and crust continental the North of signature reflection This margins. stem continental passive som
broad in the As This in

. ee to 1995) cloud.” The ago, resulting 2.26a). remained. enriched upward. The ee
\ 1 _—~- Plateau movement of the (Fig. magma
i : \ i { Plateau to Yellowstone Plateau/Snake River Plain/Yellowstone the Columbia the westward within the deeper mantle. “mushroom million years Plateau “stem” thin the of migrated magma O between
Columbia from (from A. Grunder, personal communication hotspot of a 18 Columbia the portion larger the as stream
Kdaho shape and Washington hotspot,
Oregon Numbers show age of volcanism the in forming the the with a crust steady (Fig. 2.26b).
Tectonics Volcanic Rocks from Interpretation of Columbia Park Observed ages of volcanism are consistent with lithospheric plate over a mantle Oregon basalt over volcanism, continental a narrow, westward
Plate ene, aS National deep struck in of moved of in
ee £3 2.26 North American the Plate far less melting erupted moved
2 ~~, Se eos, FIGURE volcanism. a) Yellowstone from cloud outpourings in the
Chapter b) upward the sive American resulted to due lavas ing plate the
36 of