Tectonophysics, 131 (1986) 1-21
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
1
TECTONIC DEVELOPMENT OF THE NEW MADRID RIFT COMPLEX,
MISSISSIPPI EMBAYMENT, NORTH AMERICA
LAWRENCE W. BRAILE I, WILLIAM J. HINZE ‘. G. RANDY KELLER r, EDWARD G. LIDIAK s
and JOHN L. SEXTON 4
’ Depurtment of Geosciences, Purdue iJniversi[v, West Lafuyette, IN 47907 (U.S.A.)
’ Department oj Geologicul Sciences, University of Texas at El Puso, El Puso, TX 79968 (U.S.A.)
’ Depurtment of Ceologv and Pkmetury Sciences, University of Pittsburgh, Pittsburgh, PA 15260 (U.S.A.)
’ Department of Ceoiogx So~hern flfinois ~njue~~~~, ~or~nd~~e, 1z 62901 (U.S.A.)
(Received February 21,1986; revised version accepted March 24,1986)
ABSTRACT
Rraile, L.W., Hinze, W.J., Keller, G.R., Lid&k, E.G. and Sexton, J.L., 19%. Tectonic development of the
New Madrid Rift Complex, Mississippi Embayment, North America. Tectonop~~~ia, 131: l-21.
Geological and geophysical studies of the New Madrid Seismic Zone have revealed a buried late
Precambrian rift beneath the upper Mississippi Embayment area. The rift has influenced the tectonics
and geologic history of the area since late Precambrian time and is presently associated with the
contemporary earthquake activity of the New Madrid %kismic Zone. The rift formed during late
Precambrian to earliest Cambrian time as a result of continental breakup and has been reactivated by
compressional or tensional stresses related to plate tectonic interactions. The configuration of the buried
rift is interpreted from gravity, magnetic, seismic refraction, seismic reflection and stratigraphic studies.
The increased mass of the crust in the rift zone, which is reflected by regional positive gravity anomalies
over the upper Mississippi Embayment area, has resulted in periodic subsidence and control of
sedimentation and river drainage in this cratonic region since formation of the rift complex. The
correlation of the buried rift with contemporary earthquake activity suggests that the earthquakes result
from slippage along zones of weakness associated with the ancient rift structures. The slippage is due to
reactivation of the structure by the contemporary, nearly E-W regional compressive stress which is the
result of plate motions.
INTRODUCTION
The New Madrid Seismic Zone has been the subject of increasing interest and a
large number of geological and geophysical studies in the past several years. This
interest has followed the recognition of the earthquake hazard in the New Madrid
area as evidenced by the lgll-1812
series of earthquakes near New Madrid,
Missouri (Nuttli, 1973,1982) and of the significance of the New Madrid area as an
example of intraplate seismicity. As the geological and geophysical data base in the
@ 1986 Elsevier Science Publishers B.V.
New
Madrid
subsurface
paper,
Seismic
structure
Zone
has improved;
and geologic
we review the tectonic
its earliest
known
history
geologic evolution
The interpretation
that
upper
activity
of the eastern
an ancient
(Ervin
crustal
feature
which
that
the New
Reelfoot
Recent
drilling
to underlay
gneiss
from basement
uplift
Zone
of the
models
of the crust. as well
craton.
lay beneath
with
the
Seismic zone. Subsequently,
gravity
Reelfoot
(Denison,
the upper
Rift
Hildenbrand
and magnetic
and
infer
near
of a
contemporary
a thick
the center
rock distributions
Although
et al. (1982a,
(1981) described
interpretation
section
of
they noted
of the buried
sediments.
a detailed
Arkansas
of arkosic
the
was
in addition,
the well bottomed
rhyolites
which can be inferred
the area, have been removed
analysis
local
is needed,
gravity
Rift to the northwest
the subsurface
adjacent
the arkosic
and
magnetic
and northeast,
structure
to the northern
in
by
sediments
Mississippi
“New
Rift Complex”
Embayment
of the Rough
which
(Fig. 1). The rift complex
gravity
and magnetic
with the edges of the rift. However,
the regional
maps
Creek
Graben
Seismic Zone and adjacent
in
that a failed rift system
was delineated
termed
the
primarily
on
which are associated
data
of Cordell
(1977),
illustrated in Fig. 1, also show a clear correlation with the rift complex.
The historical seismicity of the New Madrid Seismic Zone was described
Nuttli (1973, 1979, 1982) and microearthquake
by Stauder et al. (1977) and Stauder (1982).
and
Rift. An integrated
these authors
anomalies
gravity
to infer
and Soderberg
end of the Reelfoot
of these studies (Braile et al., 1982b) indicates
the basis of short-wavelength
confirm
sediments
at least in part from these rhyolites.
the upper
Madrid
700 m) section
to have covered
b) utilized
of the Reelfoot
Kentucky
1984) in northeastern
the late Precambrian
exists beneath
Madrid
et
data to better
with the rift. In addition,
was located
the lower Paleozoic
to have been derived
Braile
Keller
Rift)
since
1975) was the first suggestion
utilized
in that a thick (-
suggesting
and erosion.
extensions
western
results
interpretation
a granitic
appear
Seismic
interpretations
American
is correlative
associated
In this
Rift.
graben
found
Madrid
The
of the
possible.
Seismic Zone
structure
rift (Reelfoot
of the buried
rocks filling the graben
interpretations
data and geophysical
North
and McGinnis.
of the New Madrid
the location
sedimentary
time.
rocks and underlying
al. (1977, 1982) and Kane et al. (l981)
delineate
detailed
of the New Madrid
in late Precambrian
activities
Embayment
earthquake
development
sedimentary
as related plate tectonic
recognizable
more
of the area have become
of this area are based on geological
of the Phanerozoic
Mississippi
history
by
activity since 1974 has been reported
Earthquake
activity within the New
area is generally
correlative
with the configura-
tion of the New Madrid Rift Complex (Braile et al., 1982b, c) as illustrated in Fig. 1.
Additional
seismicity adjacent to the complex is possibly derived from reactivation
of adjacent
minor faults that are related but secondary
to the faulting of the
principal rift. Alternatively
they may be related to release of strain concentrated
by
Iocal variations
in the strength of the crustal rocks. Important
information
from
NEW
^
M A D F ?lD
i
d
.o
O_
INnmA
Fig. 1. Index map of the New Madrid Seismic Zone and surrounding regions. The outline of the New
Madrid Rift Complex is from Braile et al. (1982b). Major fauits (pre-Cenozoic) are shown from the work
of Hey1 (1972); Hey1 and McKeown (1978); Bristol and Treworgy (1979); and Autt et al. (19X0). Circles
are earthquake epicenters from the data file provided by Otto W. Nuttli. Locations of epicenters have
been “randomized” by adding a random number uniformly distributed between iO.2” to the latitude
and longitude. This randomization prevents an artificial alignment of epicenters along even lines of
latitude and longitude caused by round-off of the original epicenter locations to the nearest 0.1’. The
solid line in the vicinity of New Madrid indicates the location of the linear trend of microearthquake
epicenters reported by Stauder et al. (1977) and Stauder (1982). The arrows indicating strike-siip and
thrust fault mechanisms along these linear trends of epicenters are inferred from the focal mechanisms of
Herrmann and Canas (197X). The contours show the Bouguer gravity anomaly (in mGa1) from the
geologic corrected regional gravity map presented by Cordell (1977).
earthquake studies have been provided by Herrmann and Canas (1978) who have
shown that focal mechanisms of earthquakes within the New Madrid Seismic Zone
are consistent with right-lateral strike-slip faulting along the primarily northeasterly
trend of the microearthquake seismicity southwest of the town of New Madrid (Fig.
1).
A variety of models have been proposed to explain the occurrence of earthquake
activity in the intraplate region of ~dcontinent North America. Hinze et al. (1980)
reviewed the various models and grouped them into five different types. More
recently, these authors (Hinze et al., 1986) have suggested that only two of these
4
mechanisms
midcontinent
provide
North
model”
the “local
and
viable models for explaining
the intraplate
earthquakes
in
America. These models are termed the “zone of weakness
model was proposed
by Zoback
and
earthquake
activity
porary
(1981)
activity
the nearly
associated
Kane
(1977);
to be related
ens near
rifting
during
McKeown
definition
(1978).
regional
region
activity
by pronounced
America
are
in the
appears
to
to be
gravity
suggested
may be the mechanism
North
focal
Rift,
can be shown
originally
the
and
by Long
for a small
which do not
RIFT COMPLEX
can be broadly
roughly
crust
caused
correlated
northeastward
extends
gravity
the outline
in western
anomaly
Rift Complex.
this anomaly
associated
Rift. From
anomaly,
of the inferred
Kentucky
(Schwalb,
maps as presented
are correlative positive gravity and magnetic
circular) which are approximately
coincident
with late
rift complex.
written
Ervin
and
Precambrian
splits into lobes
The geometry
of
in light of recent deep
commun..
is provided
by Hildenbrand
anomalies
and broad-
Fig. 1, it can be seen that
of the rift complex
and Braile et al. (1982a, b). The characteristic
positive
to be due to a mass
the anomaly
has been slightly modified
of the configuration
with a linear
along the axis of the upper
north of the Embayment
by intrusion
of the Reelfoot
end of the linear
and magnetic
within
model
which
evidenced
(1977) interpreted
arm of the rift complex
results
inhomogeneity
activity
of
contem-
oriented
for the earthquake
of the arms of the New Madrid
following
detailed
faults
field of the New Madrid
in midcontinent
The anomaly
the formation
drilling
stress
inhomogeneities
Rift Complex
in the lower
the eastern
of ancient
et al., 1986). This model,
(1975) and Cordell
approximately
to be the cause
to this model,
to an appropriately
of earthquake
earthquakes
Embayment.
near the northern
According
The local basement
(Fig. 1) trending
excess
gravity
and
the junction
McGinnis
of weakness
to zones of weakness.
The New Madrid
Mississippi
subjected
OF THE NEW MADRID
anomaly
et al. (1982bc)
region.
as an explanation
zones
(Hinze
of intraplate
IDENTIFICATION
gravity
Zone.
some small
anomalies
percentage
Braile
compressive
with local crustal
magnetic
appear
east-west
Seismic
best explain
The zone
of the New Madrid Seismic Zone, the earthquake
of the trend of seismicity with the buried Reelfoot
with this hypothesis
New Madrid
model”.
is due to a reactivation
crust which are presently
consistent
(1976);
and
in the New Madrid
stress field. The orientation
mechanisms,
the correlation
and
inhomogeneity
by Sbar and Sykes (1973) and Sykes (1978) and was suggested
Zoback
earthquake
crystalline
basement
defining
1984).
More
by detailed
et al. (1977, 1982)
the Rift Complex
anomalies (many of which are nearly
with the edges of the rift complex. In
some locations,
strong linear gradients in the gravity or magnetic field are also
related to the edge of the buried rift. Within the rift complex, the gravity and
magnetic
basement
anomaly expression is generally more subdued reflecting a deeper depth to
(Hildenbrand
et al., 1982). Examples of gravity and magnetic anomalies
92*
BOUGUER
GRAVITY
(MGAL)
88"
90"
SP
n
e-50
cl
-5010-30
_,F,O
-I0t010
>I0
Fig. 2. Simple Bouguer gravity anomaly map of the upper Mississippi Embayment area. Contour interval
is 5 mGal. Shading interval is 20 m&l. Heavy lines are faults associated with the Cottage Grove and St.
Genevieve fault zones. Short-wavelength positive anomalies and high-gradient zones delineate the
approximate edge of the St. Louis arm of the New Madrid Rift Complex. The gravity data are from
Keller et al. (1980). Figure from Braile et al. (1982b).
6
920
go*
91*
89*
880
38*
37’
TOTAL
cl
FIELD
<400
VERTICAL
FIELD
(GAMMAS)
<o
100
400

0’
- 600
O-200
600 - 800
600
- 1000
200-400
400
- 600
>I000
> 600
km
O,,,,‘p
Fig. 3. Magnetic
River
(border
anomaly
between
(1980). Data in Missouri
map of the upper
Illinois
are averaged
from Buehler (1943). Contour
faults associated
anomalies,
and Missouri)
interval
with the Cottage
approximately
Mississippi
are total
Embayment
(over a ten by ten km grid), vertical
is 100 nT (gammas).
Grove and St. Genevieve
Shading
Rift Complex.
Figure
interval
east of the Mississippi
values
from Johnson
field, ground
data
lines are
short-wavelength
River, mark the approximate
from Braile et al. (1982b).
et al.
magnetic
is 200 nT. Heavy
fault zones. The prominent
100 km on either side of the Mississippi
the St. Louis arm of the New Madrid
area. Data
field aeromagnetic
edge of
associated with a portion of the New Madrid Rift Complex are shown in Fig. 2 and
The depth to magnetic basement interpretation of Hildenbrand et al. (1982)
suggested the presence of boundary faults associated with the edges of the Reelfoot
Rift. Seismic reflection data in the Reelfoot area (Zoback et al., 1980; Hamilton and
Zoback, 1982; Sexton et al., 1982) have also been used to identify faults within the
rift.
Recently, a seismic reflection profiling experiment conducted in the Wabash
River Valley in southern Illinois and southern Indiana (Fig. 4)near the margin of the
inferred southern Indiana arm of the New Madrid Rift Complex (Fig. 1) has
provided clear evidence for late Precambrian to early Paleozoic faulting associated
with the New Madrid Rift Complex. An example of these data is shown in Fig. 5
from Sexton et al. (1986) for portions of two seismic reflection record sections
centered on the Wabash River (Fig. 4). The seismic sections (Fig. 5) show good
reflections from Paleozoic stratigraphic units and allow identification of the smalloffset (20-50 m) Wabash River Valley faults. In addition, the record sections
provide evidence for a thick section of pre-Mt. Simon (i.e., pre-Late Cambrian)
layered rocks existing within a fault-bounded graben beneath the Illinois Basin. A
schematic cross-section based on the seismic reflection data of Sexton et al. (1986)
as well as gravity and magnetic interpretations, across the southern Indiana arm of
the New Madrid Rift Complex is shown in Fig. 6. Two stages of normal fault
activity are indicated by these data. Major graben-bounding faults formed in late
Precambrian to early Cambrian time. The grabens are filled with pre-Mt. Simon
layered rocks. A generally conformable sequence of Paleozoic sedimentary rocks
ILLINOIS
INDIANA
,
ot
NEW
Fig. 4. Index map of the southern
the seismic reflection
record
Illinois and southern
sections
illustrated
solid lines with small dots every 100 source-point
sections
HARMONY
which are shown in Fig. 5.
5 Miles
‘I
‘I
’ I’ : ,
0
Indiana
area surrounding
in Fig. 5. The seismic reflection
locations.
IO
km
the Wabash
River for
lines are shown
The heavy lines indicate
the locations
by the
of the
record
of the Wabash
Valley
section
faults
(Sexton
but is approximately
1.2.
rocks approximately
line across
5.2 to 6.2 km, Dashed
lines are interpreted
and
Illinois
New Harmony
River in southern
Island.
positons
of stratigraphic
units. Vertical
exaseration
and
The
varies,
reflector
Bristol
Indiana.
faulted
is from
and southern
faults)
3.6 km beIow sea level and to the prominent
Ribeyre
the Wabash
is approximately
Harold-Phillipstown.
et al., lY86j for an east-west
(Albion-Ridgway.
(1979) and Ault et al.(lY~~f. The depth to the Eau Claire reflector
location
below the pre-Milt. Simon layered
Treworgy
surface
Fig. 5. Seismic reflection
EISMIC REFLECTION
0
40
80
DISTANCE
120
( KM 1
Fig. 6. Schematic diagram illustrating the geologically and geophysically determined configuration of
Phanerozoic sedimentary rocks and crystalline basement beneath the southern Indian arm of the New
Madrid Rift Complex (Sexton et al., 1986). The cross-section is along a NW-SE profile which includes
the area shown in Fig. 4.
follows with the upper boundary of the sequence being a post-Pennsylvanian
unconformity. Relatively minor faulting evidenced by the Wabash Valley Fault
System followed. Although we do not have equivalent, detailed seismic reflection
data in other areas, the representation of one of the arms of the New Madrid Rift
Complex, as illustrated in Fig. 6, is consistent with the interpretations in the
Reelfoot area and we expect that other sections of the rift complex will have a
similar configuration.
Seismic refraction data are also available which support the interpretation of a
buried rift complex beneath the northern Missisippi Emba~ent
area. McCamy and
Meyer (1966) discovered that an anomalous, basal high-velocity (7.4 km/set P-wave
velocity) layer existed in the crust beneath the upper Mississippi Embayment.
Recent refraction (Mooney et al., 1983) and surface wave (Austin and Keller, 1982)
studies have better defined the extent of this high-velocity layer and correlated it
with the excess mass in the crust required to explain the regional gravity data.
Mooney et al. (1983) also have interpreted a low-velocity layer beneath the Paleozoic carbonates in the Reelfoot Rift area which they suggest is due to late
Precambrian to early Paleozoic graben-filling sedimentary rocks. Baldwin (1980)
10
utilized refraction data in southern Indiana to suggest a similar increased thickness
of sedimentary rocks in the southern Indiana arm of the rift complex. He also found
that the basement beneath one of the rift margin gravity and magnetic anomalies
exhibited an anomalously high seismic velocity.
TECTONIC
EVOLUTION
OF THE NEW MADRID
SEISMIC
ZONE
Hinze et al. (1980), Kane et al. (1981) and Braile et al. (1982b) argued that the
New Madrid Seismic Zone is related to a late Precambrian rift and that the origin of
this rift and its subsequent tectonic evolution has been intimately related to plate
tectonic processes. This view has provided a plate tectonic framework for the
contemporary intraplate seismicity of the New Madrid Seismic Zone, as well as, the
basis for understanding the geologic history of the region. Although the basic
conclusions of these studies are not changed here, much additional evidence in
regard this tectonic evolution has been gathered in the past few years (e.g., Kane et
al., 1981; Schwalb, 1982; Van der Voo, 1982; Howe and Thompson, 1984; Sexton et
al., 1986). Thus, a more detailed picture of the geological history of the midcontinent region of the North American craton and its relationship to plate interactions
along the eastern and southern margins of the continent is now available. These
data indicate a causal relationship between plate-tectonic events and tectonism and
sedimentation in the New Mad~d area within the interior of the craton. The New
Madrid Rift Complex, a failed rift, has influenced the geologic history of this region
since late Precambrian time. It has controlled younger structures, sedimentation,
drainage of major river systems, and contemporary earthquake activity, as well as
possibly localizing ore deposits. This control appears to have been exercised by two
properties of the rift complex which were produced at its formation. Firstly, a mass
excess, probably due to intrusion of mafic rocks, exists within the crust along the
rift zone (McGinnis, 1970). This mass excess is clearly reflected in the regional
positive gravity anomaly (Fig. 1) described by Cordell (1977). Under appropriate
thermal and stress conditions, this mass excess has resulted in periodic subsidence
of the craton in the New Madrid region, thus in~uencing sedimentation and the
drainage of major river systems. Secondly. the deep-seated normal faults associated
with the initiat rifting of the New Madrid Rift Complex have served as zones of
weakness which have been reactivated and have localized intrusive activity in late
Paleozoic and Mesozoic times. Hey1 (1972) showed that intrusives and ore bodies in
the midcontinent area are related to structures which we now associate with buried
rifts (Keller et al., 1983). Faults within the rift complex have been reactivated in
later phases of faulting, such as in the Wabash Valley Fault System in post-Pennsylvanian time. They may also be the fault planes related to the contemporary
earthquake activity in the New Madrid Seismic Zone.
The stratigraphy of Paieozoic rocks in the Illinois basin and Mississippi Embayment and interpretation of deep seismic reflection results (such as those shown in
Fig. 5) indicate that the rifting of the New Madrid Rift Complex occurred prior to
deposition of the basal elastic sedimentary rock unit that is characteristic of
midcontinent North America (the Mt. Simon formation of late Cambrian age).
Thus, the initial rifting event was either latest Precambrian or earliest Paleozoic.
Pre-Mt. Simon rocks are largely confined to the area within or immediately adjacent
to the rift complex and are interpreted to be contemporaneous with rifting of the
New Madrid Rift Complex. Adjacent areas were largely topographic highs as
evidenced by the fact that Mt. Simon sedimentary rocks typically rest on crystalline
92’
40’
90’
64’
860
68’
00
ILLINOIS
38’
t
I,
0
400
0
ONLf
STE
-Y--_._____________-_
TENNESSEE
ISOPACHS OF EARLY PALEOZOIC
SEDIMENTARY
UNITS
MT.
SIMON (UPPER
APPROXIMATE
‘/
CAMBRIAN)
OF BURIED
OUTLINE
RIFT
COMPLEX
‘/
EAU CLAIRE AND BONNETERRE
(UPPER CAMBRIAN)
EVERTON - KNOX
(CAMBRIAN
- ORDOVICIAN)
Fig. 7. Index map of the New Madrid
Schwalb
(1982). Additional
features
/THICKNESS
,pP”
(IBOPACH
area showing
are as described
isopachs
OF SEDIMENTARY
UNITS
IN METERS
DATA
FROM
of early Paleozoic
in Fig. 1.
SCHWALB.
sedimentary
1982)
rocks, after
basement in areas far from the rift complex (Schwalb,
excess in the crust beneath
Paleozoic
the New Madrid
time which resulted
SEDIMENTARY
’
40
100
in the formation
BASINS,
ANOMALY
POSITIVEGRAVITY
1982). Subsequently,
Rift Complex
caused subsidence
of sedimentary
basins
MAJOR RIVER SYSTEMS,
AND THE NEW MADRID
the mass
during
above the rift
REGIONAL
RIFT COMPLEX
\
+
\200KM
38
36
Fig. 8. Map of the
upper Mississippi Embayment area showing Paleozoic sedimentary basins (contours
are depth
to basement
Cretaceous
sediments
ment).
the geologic
river systems
pattern.
for the Paleozoic
corrected
Bouguer
Embayment;
gravity
which have been structurally
Rift Complex.
Cretaceous
in kilometers
for the Mississippi
The sedimentary
to present
Stratigraphic
anomaly
controhed
basins containing
sedimentary
sedimentary
data
of Cord41
Paleozoic
and
marks
(1977).
and the approximate
rocks in the Mississippi
data are from Schwalb
rocks
the zero contour
depth
to base of the
the edge of the embaythe locations
outline
of major
of the New Madrid
rocks are shown with the small dot pattern.
Embayment
(1982) and Buschbach
(1983).
are shown
with the large dot
13
complex.
Figure
indicate
7 shows isopach
a significant
portions
of the New
persisted
throughout
basin
data for early Paleozoic
thickening
of the formations
Madrid
Rift
Paleozoic
and the Reelfoot
Complex.
Subsidence
time with thickened
Basin,
a trough
sedimentary
approximately
which
with
of the
sedimentary
between
units
coincident
area
the Arkoma
and Warrior
underlying what is presently the Mississippi Embayment
(Fig. 8).
After a period of uplift and erosion in Mesozoic time, subsidence
part of the New Madrid
coastal
plain resulting
subsidence
served
has continued
in the formation
and structural
to control
millions
Rift Complex
control
of the faults
the drainage
of major
of years. As illustrated
adjacent
of the Mississippi
within
river
basins,
of the southern
to the downwarping
Embayment
(Fig. 8). The
the rift complex
systems
generally
units in the Illinois
for tens
in Fig. 8 and demonstrated
have also
to hundreds
by Potter
(1978)
of
the
lower Mississippi
River has been nearly in its present position;
approximately
coincident
with the Reelfoot section of the New Madrid Rift Complex, since early
Mesozoic
time. Potter
which he called
down
the center
Complex
(1978) also showed
the Michigan
of the inferred
southern
due to disruption
been interpreted
approximately
arm of the New
The tectonic
Madrid
Rift
adjacent
plates
sponding
evolution
updated
of a portion
which have influenced
cross-sections
Complex
has
and approximately
in
Rift Complex
and its relationship
to
structural
is based
Thompson,
1984)
geophysical
data
its history
are illustrated
evolution
primarily
and
on
the interpretation
as described
on paleomagnetic
previously.
(LeFort
Rift
data
of the rift
The
plate
development
(ap-
and McGinnis
the New
(Schwalb,
complex
and
et al. 1983). The
by Ervin
Madrid
1982;
Howe
determined
reconstructions
are
Rift
and
from
based
and Van der Voo, 1981; Van der Voo, 1982)
and geological and geophysical data (Keller and Cebull, 1973; Morris,
1980; Cook et al., 1980; Lillie et al., 1983) related to the plate-tectonic
the North American craton during the past 600 m.y.
The tectonic
Complex
(Fig. 9) are modified
surrounding
and
of the New Madrid
et al. (1980) and Keller
stratigraphic
craton
in Fig. 9, and corre-
Madrid
from interpretations
of the area
in Figs. 9
American
are shown
the New
time and the plate reconstructions
of Hinze
which
controlled
of the North
through
(Fig. 10) are modified
River,
Rift Complex,
are shown in Fig. 10. The configuration
from the presentations
The
Mississippi
since the late Precambrian
reconstructions
through
cross-sections
for
are
time.
of the New Madrid
activity
NW-SE)
Rift Complex
course
Rivers
The upper
since at least mid-Tertiary
schematic
proximately
glaciation.
its present
Ohio and Wabash
of the St. Louis arm of the New Madrid
plate margin
10. Plate
followed
upper
by Flint (1941) to be structurally
the same position
adjacent
of the present
by Pleistocene
flows down the center
primarily
Indiana
has approximately
the last 250 m.y. The locations
(1975).
to the Ohio River,
flowed southwestward
(Fig. 8). The lower part of the Ohio River was part of this river system,
which like the lower Mississippi,
and
that the predecessor
River System,
of the New Madrid
Rift Complex
1974; Burke,
evolution of
(Figs.
9 and 10)
AND AULACOGENS.
\
L SEPARATION.
I
\
IGNEOUS INTRUSIONS
AND REACTIVATION
OF FAULTS
IN AULACOGENS.
"I /
MPRESSIONAL
Fig. 9. Schematic
interactions
diagrams
with adjacent
illustrating
the plate
plates and geologic
600 million years. The outline
reconstruction
activity
of the State of Missouri
of the North
of the New Madrid
is shown for location
American
Rift Complex
craton
during
and approximate
and
the last
scale.
indicates the control
portion of the North
the rift complex has exerted on the geologic history of this
American craton, as wefl as the connection
between cratonic
tectonism
margin
and plate
interaction
through
time. After
formation
of the rift
15
PRECAMBRAN:
INCIPIENT RIFTINS
A LATE
LATE PALEOIOIC
c3
:
SUBS!OENCE, LOCALIZED OEFORMATION
EXTENSION
OwRESSlON
0
B
LATE PRECAMBRfANCAM8RiAAN: Rlf TING
C
PALEOZOIC:
EARLY
EARLY I”0 MIDDLE
SUBSIDENCE
E
.‘%t&ioe?i%c:
F LATE
UPLIFT, REACTlVATION
MESOZOIC
TO PRESGVF
SUBSIOENCE, COMPRESSION
Fig. 10. Schematic cross-sections for a NW-SE profile through the New Madrid Rift Complex
illustrating the evolution of the rift complex and associated cratonic basins through time. Stages of
development shown in parts A-F are related approximately to the map views illustrated in the
corresponding diagrams in Fig. 9.
during continental breakup (Figs. 9A, B, and lOA, B), the rift complex underwent
subsidence during times of regional compression associated with either subduction
or collision along the eastern and southern margins of the North American craton.
During early Mesozoic rifting of the continents (Figs. 9E and HOE), the craton was
undergoing uplift and erosion resulting in the broad unconfo~ty
which is observed
in the cratonic basins of North America. Erosion of considerable thicknesses of
sedimentary rocks occurred over intracontinental arches such as the Pascola Arch
centered near southeastern Missouri. Reactivation of faults associated with the New
Madrid Rift Complex caused structural uplifts and intrusion of plutons near the
margins of the rift complex (Fig. 1OE). Since Cretaceous time (Figs. 9F and lOF),
the eastern margin of the North American craton has been the trailing edge of a
rifted continental margin and the continent has been under a regional compressive
stress. The New Madrid Rift Complex has continued to exert control on depositional patterns as evidenced by the subsidence of the Missi~ippi Embayme~t and
the location of major river drainage systems (Fig. 11). The co~e~ation of earth~u~e
Michigan
RIVER SYSTEM
MRE-GLACIALI
Af
/
ARKI
REGlCNiiL
COMPRESSlVE
STRESS
/
‘LOWER
Fig. 11 Block diagram
The structurally
Embayment,
illustrating
controlled
all associated
near the edge of the buried
the present
rivers. Paleozotc
with the buried
rift. An uplifted
the cause of the linear positive
gravity
CRUST
configuration
rocks
rift complex.
and possibly
anomaly
of the buried
in cratonic
associated
sedimentary
are also shown.
anomalously
New Madrid
basins.
Rift Complex.
and the Mississippi
Dark areas indicate
intrusions
dense lower crust is suggested
with the upper
Mississippi
as
Embayment.
epicenters with the location of the buried rift complex suggests that the earthquakes
in the New Madrid Seismic Zone are the result of slippage along pre-existing zones
of weakness inherited from the late Precambrian rift. The fault planes are reactivated by the contempora~ stress field which is approximately east-west compression in the New Madrid area (Haimson, 1976; Zoback and Zoback, 1980, 1981).
The correlation of cratonic basin subsidence with continental margin subduction
has been pointed out by Johnson (1971), Sloss and Speed (1974) and Bally (1980).
However, acceptable explanations for the origin of cratonic basins, their association
with plate-tectonic regimes, and their synchroneity remain elusive. Recently, DeRito
et al. (1983) suggested a possible mechanism for cratonic subsidence that relates to
plate-tectonic processes. They point out that many cratonic basins are developed
over ancient rift zones with related excess crustal masses, and thus the driving force
for subsidence of these basins is the isostatically uncompensated mass excesses.
Under conditions of continental stability, these masses are supported by the
strength of the lithosphere, but during periods of sea-floor spreading they may not
be fully supported and may be reactivated. DeRito et al. (1983) believe that geologic
17
constraints
indicate
only two possible
force, either a regional
increase
regional
stress.
decrease
in the viscosity
A global
uncompensated
increase
in the geothermal
of the lithosphere
suggest that the horizontal
may
component
for reactivation
of the lithosphere
and
mass in the crust which remains
They further
processes
mechanisms
in temperature
activate
subsidence
by the curvature
regional
would
activate
lead
stress
to a
of an
as a vestige of the rifting
process.
with plate tectonic
is resolved
or (2) the viscosity
in the
downwarp
stress associated
as (1) the
of the basin,
gradient
thus
of this driving
or a change
into
a vertical
of the lithosphere
is
lowered leading to subsidence of the uncompensated
load. DeRito et al. (1983) favor
a combination
of the two methods of utilizing a horizontal
regional compressive
stress to cause subsidence
models
favored
observations
by
Although
through
Precambrian
basins
and Dewey,
appear
underlain
cratonic
(Ammerman
basins
Basin (Hinze
et al., 1975; Brown
Basin and midcontinent
geophysical
to that
displayed
influence
history
cratonic
et al.,
Basin (Burke
Basin (Shurbet
had a continued
tectonic
Each has certainly
et al., 1983).
in southern
and Keller, 1979), the Anadarko
have
of the associated
influence
have been identified
1973; Wold and Hinze,
similar
the
fit the
as contemporary
by rifts (DeRito
1973; Brewer et al., 1983), the Delaware
1980), and the Lake Superior
had
unsolved,
the continued
and Zietz, 1971; Ocola and Meyer,
Complex.
remains
to qualitatively
rifts are reactivated
are commonly
1968), the Michigan
1982) the Rome Trough
the problem
area and help to explain
intracontinental
rifts beneath
(Kanasewich,
Although
his colleagues
time.
not all ancient
seismic zones, cratonic
Alberta
and
for the New Madrid
of the rift complex
Other
of paleorifts.
DeRito
and Cebull,
anomaly
(King
1982). These rifts may
in the
New
Madrid
on the geological
Rift
evolution
basin.
CONCLUSIONS
The New Madrid
tectonism
time.
Rift Complex
of the North
It has controlled
influenced
the location
reactivation
activity.
correlated
American
geologic
with events
craton
sedimentation
of major
of rift structures,
The
has had a significant
and
since its formation
by causing
river systems,
and is probably
tectonic
at the margins
history
Rift Complex
through
for understanding
the formation
of cratonic
seismicity
intrusive
of this
activity
intracratonic
American
basins
basins,
during
erathquake
region
is also
plate. The history
a plate-tectonic
associated
on
Precambrian
in cratonic
the cause of contemporary
time provides
of the New Madrid
influence
in latest
subsidence
localized
of the North
the New Madrid
and intraplate
and continued
of
framework
with the rift complex
Seismic Zone. Thus, the New Madrid
Rift Complex, formed about 600 m.y. ago, has influenced
the response of the
midcontinent
region to events occurring at the margin of the North American plate.
It is also plate motions which are presently producing the compressive stress within
the North American craton (Zoback and Zoback, 1980) which is in turn probably
causing
the reactivation
of faults within
the New Madrid
Seismic Zone.
ACKNOWLEDGEMENTS
This research
Contracts
was supported
by the U.S. Nuclear
No. NRC-04-81-195-01
graduate
students
Regulatory
and NRC-04-80-224.
We are grateful
who have assisted in the collection,
compilation
data upon which many of the interpretations
contained
thank
comments.
Paul Morgan
the many
useful
concerning
for a number
discussions
of helpful
with colleagues
the seismotectonics
Commission
to our many
and processing
of
in this paper are based. We
We also greatly
of the “New
of the New Madrid
under
Madrid
appreciate
Study
Group”
area.
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