Page 184 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

under-
uncon-
of
that
167
wedge-shaped,
that
Costain
in
in
with
crust
dipping
consistent
basement
“sea-
fluid
to
that
the
are
convex
was
regions
(Fig. 6.30b).
some pas-
The
inher-
Reflections
a
Isles,
subsidence
contrasts
sediments
used
sequences
as
strata
ridge”
basement
reveals
basin,
6.28b).
2;
oceanic
these
expression
the
reflectivity
postrift
Settings
layer
British
a
1979:
faults
shelf
be
have
The
of
On
from
half-grabens
ocean
of
“mid-ocean
therefore
Strong
Moho
6.27;
Greenland,
sediments
postrift
oceanic
al.,
top
to
and
true
parts
normal
The
continental
reflections
the
of Tectonic
overall
basement). The
sediments
Boundary
prior
Crust
et
seismic
The
the
ridges (Figs.
crustal
slope
Crust,
and
Around
display
land.
Grow
upper
beneath
from
of
eroded
can
with
Continental
are
crust
show
Crust
the
development
postrift
continental
on
east
margins show
same
Lower
al., 1976;
sections
Continent/Ocean
and
the
postrift
Expression
individual
volcanics)
away
indicate
portrayed
6.24).
erupted
when
continental
were
and
however,
Oceanic
observed
of
sediments; crystalline
mid-ocean
the
basin
the
Reflective
or
Drilling
Norway
6.23,
the
kilometers,
reveals
blocks
et
unmigrated
Extended
toward
thus
was
ocean
beneath
time;
beneath
6.30a; Schlee
Seismic
often
initial
with
separates
of
passive
(Figs.
profiles,
events
that
areas
extended
Top
1982).
horst
at
commonly
of
travel
Crust;
intercalated
the
either
are
at
the
formed
stage
Defining
basalt
coasts
crust
from
of
some
Defining
1984).
“Seaward-Dipping Wedges”
toward
shelf
Wedge-shaped
on
that
unconformity
margins
reflection
during
al.,
tens
two-way
Upper
dipping
(Fig.
events
rifting
between
oceanic
reflections
et
entirely
flat, suggesting
from
the
synrift
continental
2
areas
al.,
over
(Mutter
dip
Wedges
layer
during rifting
formed
level.
(sediments
Events
off
Passive
et
Nonreflective
continental
hyperbolic
profiles
faults
always
of
seaward;
rise
(Mutter
laterally
and
true
wedges,”
direction.
zone
almost
oceanic
s
below sea
breakup)
impedance.
Graben
two
continental
appearance
prominent
have
Hyperbolic
(prerift
normal
of
1989).
and
reflections
reflection
the
about
often
grabens
extent
are
level
predominately
spread
block-faulted,
to
characteristic,
extended
ward-dipping
margins,
the
plain
dominate
Rift
8.
Coruh,
6.30c).
(or
wedges
interpreted
rocks
margin
major
sea
is
7,
from
spanning
the
acoustic
beneath
displays
formity
upward
postrift
3.
Seismic
4.
5.
coastal
6,
basalts
rift
above
Those
lying
(Fig.
with
map
was
and
sive
the
ited
the
no
fill
crust, reflective upper nonreflective reflections Moho and crust, lower especially are (continued) 6.30 FIGURE the northwest, down to 3.5 s on 2s on 0.2 to about the southeast. The postrift unconformity separates those sediments from older rocks, including crystalline basement and a prominent rift graben. The major
Southeast Fasi ete a F——— — sediments lie from
D
ees Each profile shows of the continental shelf off the east
a SLA - sediment- basalt interface sedimentary section. Deeper reflection patterns wedge indicating continental crust extended
=
Crust km 10 Boundary km 10 See ro = as <r Cod, part Cape water layer is above 0.2 s. Postrift
Continental = = = Crust Seismic reflection profiles from passive continental margins. the postrift reflections from basement. a) Rift graben Offshore 25 from transparent
Extended Northwest Continent/Ocean Wasi = E Oceanic Northwest 6.30 horizontal the type of crystalline line during rifting. U.S.G.S. United States. The
N
©
©
N
a
a) 0 (Ss) Uy JOABLL ABAA-OML b) " (5) euly JOABLL ABAA-OML c) {(s) ew, JOABsLL ABAA-OML gQ FIGURE prominent suggest coast of the