Tectonophysics, 187 (1991) 117-134
Elsevier Science Publishers B.V., Amsterdam
117
Anatomy of North America: thematic geologic portrayals of the continent
Harold Williams a, Paul F. Hoffman b, John F. Lewry ‘, James W.H. Monger d and Toby Rivers e
a Department of Earth Sciences and Centre for Earth Resources Research, Memorial University of Newfoundland, St. John’s, Nfd., AIB 3X5, Canada
’ Geological Survey of Canada, 588 Booth St., Ottawa, Ont., KIA OE4, Canada
’ Department of Geology, University of Regina, Regina, Sask., S4S OA2, Canada d Geological Survey of Canada, 100 West Pender St., Vancouver, B.C., V6B lR8, Canada
e Department of Earth Sciences and Centre for Earth Resources Research, Memorial University of Newfoundland, St John’s, Nfld., AlB 3X5, Canada
(Submitted to editors September 17, 1987; received by publisher July 31, 1990)
ABSTRACT
Williams, H., Hoffman, P.F., Lewry, J.F., Monger, J.W.H. and Rivers, T., 1991. Anatomy of North America: thematic geologic portrayals of the continent. In: T.W.C. Hilde and R.L. Carlson (Editors), Silver Anniversary of Plate Tectonics.
Tectonophysics, 187: 117-134.
Six thematic tectonic maps are used to analyse the makeup of the North American continent. Themes are: (1) major
tectonic elements of the continent, (2) time of last major deformation, (3) time of first major deformation. (4) miogeoclines
and terranes by kindred, (5) suture zones and terrane boundaries by age, and (6) time of accretion. Features illustrated include
distribution of erogenic belts and their extensions beneath cover sequences to the continental edge, contrast between juvenile
and reworked crust in erogenic belts, geometry of ancient continental margins, distribution and classification of accreted
terranes, geometry of suture zones and courses of ancient oceans, and how the continent evolved from an assemblage of
Archean minicontinents to its present configuration. It is suggested that essentially similar plate tectonic processes controlled
continental breakup and assembly from the Archean onwards, albeit with gradual increase in size of continental lithospheric
plates and quantitative change in other parameters such as heatflow and character of the mantle.
Introduction
Ideas regarding the evolution of North America have changed radically since the advent of plate tectonics over 20 years ago. However, while new maps of some of the better known orogens have been produced (Williams, 1978; Howell et al., 1985; Wheeler and McFeely, 1987; Hoffman et al., in prep.), modem tectonic maps of the entire continent that reflect current thinking remain un- available. This paper briefly discusses six tectonic
portrayals of North America, presented in reduced format (pp. 123-128). The original compilations were made at 1 : 10 million scale, mainly as teach- ing aids; the reduced versions show the same
significant features and provide new insights into the makeup of the continent. They are intended as a focus for discussion and speculation on con- tinental-scale tectonics and, it is hoped, will pro- vide impetus for detailed tectonic map compila- tions at a more meaningful scale of 1 : 5 million. Themes for the six portrayals are as follows: (1) major tectonic elements, (2) time of last major deforma- tion, (3) time of first major deformation, (4) miogeoclines and terranes by kindred, (5) suture zones and terrane boundaries by age, and (6) time of accretion. For completeness, Greenland is in- cluded in all figures but is unrestored with respect to eastern North America. The illustrations used
0040-1951/91/$03.50 0 1991 - Elsevier Science Publishers B.V.
118 H WILLIAMS ET AL..
here are available now in postcard format, in
colour, and as 35 mm slides, thus facilitating com-
parisons. Copies are available from the first author.
All of the maps are greatly simplified, already
outdated in some areas, and somewhat speculative
in regions where the data base is weak. However,
such failings, and other inevitable inaccuracies, do
not significantly detract from the primary purpose
of the exercise. More important is the practicality
and usefulness of maps produced according to the
selected themes. Above all, the portrayals provide
a vehicle to take ones imagination “out for a run”
while focusing on the broader aspects of the
evolution of the entire North American continent.
Maps are the way in which earth scientists com-
municate best and are the most practical way to
express quick, profound messages on the evolution
of North America, or indeed any other continent.
The first three maps (Figs. 1-3) are objective
compilations. The last three (Figs. 4-6) are more
interpretive, and developed, without inhibition or
apology, in accord with plate tectonic concepts,
even for Archean rocks (at least in principle). In
the spirit of this volume, the exercise represents an
especially practical application of plate tectonics.
Discussion of thematic maps (Figs. 1-6, pp. 123-
128)
Figure 1. Major tectonic elements of North America
This map portrays the first order components
of the continent; the Canadian Shield, Interior
Platform, Phanerozoic orogens and modern con-
tinental margins. It is the starting point for any
meaningful analysis on this scale. The arrange-
ment of tectonic elements, in particular the loca-
tion of Phanerozoic orogens peripheral to the Pre-
cambrian craton, greatly influenced early thinking
on the evolution of the continent and its geologic
mountain belts. North America has a gross sym-
metry of Phanerozoic elements not shared by other
continents. In the fixist view of permanent conti-
nents and oceans, the pattern suggested outward
growth of the continent by addition of younger
erogenic belts (e.g. Kay, 1951). In plate-tectonic
terms, it simply indicates that the modem con-
tinental margins of North America almost every-
where follow, and lie outboard of, Phanerozoic
orogens. The pattern breaks down in eastern
Canada, where the spreading axis of the Atlantic
crosses both the Appalachian Orogen and older
orogens of the Canadian Shield (Williams, 1984).
Figure 2. Time of last major deformation
This figure highlights the traditional structural
provinces of the Canadian Shield (Stockwell et al.,
1970) and their subsurface extensions, as well as
the Phanerozoic orogens and their extensions to
the continental edge. Undeformed cover rocks are
omitted. Comparison with Fig. 1 emphasizes the
varying reliability of the data base, e.g. where the
deformed rocks are exposed in the Canadian Shield
and where they occur beneath the Interior Plat-
form cover rocks, and where the Phanerozoic
orogens are exposed or where extended in sub-
surface to the continental edge. The Superior,
Slave, Wyoming and North Atlantic provinces
(cratons) were last significantly deformed in the
Archean (more than 2.5 Ga) and the Churchill,
Bear, Southern and Makkovik provinces in the
early Proterozoic (1.9-1.8 Ga). Successively
younger Proterozoic events define provinces which
occur progressively outward in the southeast part
of the continent; Central Plains (1.7 Ga), Mazatzal
(1.6 Ga), Grenville (1.0 Ga). The indicated pattern
of Precambrian elements is highly asymmetric,
with older deformed belts clustered at high lati-
tudes and younger Precambrian deformed zones
occurring to the southeast. Typically, the Archean
provinces or cratons are completely surrounded by
early Proterozoic deformed belts. “Patterned”
orogeneses is seen in the southeast, where succes-
sive sequential Precambrian provinces are fol-
lowed by the Paleozoic Appalachian Orogen and
finally the Atlantic continental margin, each sub-
parallel to its predecessor.
Divisions within the Phanerozoic orogens show
important differences along the length of these
belts. Some elements of the Canadian Appa-
lachians were last deformed in the late Pre-
cambrian (Avalonian), others during the Ordovi-
cian (Taconian), while the largest area was last
deformed during the middle Paleozoic (Acadian).
In the U.S. Appalachians, correlative rocks and
tectonic elements were overprinted by late Paleo-
ANATOMY OF NORTH AMERICA 119
zoic deformation (Alleghanian). These differences
reflect contrasting accretionary histories of differ-
ent segments of the orogen, which in turn are a
function of the complex closure of the Paleozoic
Iapetus Ocean during assembly of Pangea (Wil-
liams and Hatcher, 1983).
Central parts of the Cordilleran Orogen, last
deformed in the Jurassic and Cretaceous (Sono-
man and Columbian), were largely unaffected by
Cretaceous to Tertiary (Laramide) deformation. It
involved both the more outboard western elements
and extreme landward parts of the miogeocline;
despite the fact that Mesozoic accretion pro-
gressed from the miogeocline outwards (Monger et
al. 1982).
Figure 3. Time of first major deformation
Both the Precambrian craton and Phanerozoic
orogens remain clearly defined in this thematic
map, but their internal patterns contrast markedly
with those of Fig. 2. Large parts of the craton that
were significantly deformed in the Proterozoic
(1.9-1.8 Ga) represent overprinted Archean-de-
formed (more than 2.5 Ga) continental crust. This
is clear in the case of the Trans Hudson Orogen.
Similarly large parts of the mid to late Proterozoic
Grenville Orogen (1.0 Ga) involve reworking of
predeformed Archaean early (1.9-1.8 Ga) and
especially middle (1.6 Ga) Proterozoic crust. Simi-
larly the Phanerozoic orogens (e.g. Southern Ap-
palachians) incorporate rocks already affected by
earlier thermotectonism, e.g. Grenville inliers.
Comparison of Figs. 2 and 3 thus provides some
insight into the extent of reworking of older con-
tinental crust by younger deformational events,
most obviously in the Precambrian craton. The
higher proportion of reworked rocks in Protero-
zoic orogens compared to their Phanerozoic coun-
terparts may reflect deeper levels of erosion with
obliteration of miogeoclinal cover sequences and
overthrust upper crustal elements of accreted
juvenile terranes. On the other hand, it may be a
function of a predicted higher geothermal gradient
during the Proterozoic which could have resulted
in broader zones of ductile deformation in base-
ment rocks.
Structural provinces of the Canadian Shield,
defined by time of last significant deformation
and isotopic resetting, are less obvious in this
portrayal, save for the cratonic Superior, Slave,
Wyoming and North Atlantic provinces that com-
prise Archean rocks little affected by later events.
The factors that control extensive Proterozoic re-
working of Archean rocks in some areas and the
lack of reworking in other areas are of obvious
concern. This may reflect polarity of subduction,
toward the reworked areas and away from the
unreworked cratonic elements, and/or the pres-
ence of major Proterozoic “cryptic” collisional
sutures within abnormally wide reworked areas of
Archean crust, as suggested by recent work in the
western Churchill Province (e.g., Lewry et al.,
1985; Hoffman, 1987; 1988). Archean sutures are
also possible within some Archean structural prov-
inces (Hoffman, 1986a). The bulky, equidimen-
sional form of some Precambrian provinces re-
flects original shapes of discrete Archean minicon-
tinents. In other cases, shapes are the result of
disruption of larger Precambrian continents,
whereby original elongate erogenic belts were dis-
persed by subsequent ocean opening-closing
cycles or affected by major transcurrent faults.
Phanerozoic orogens display few Precambrian
deformed elements at present erosional levels but
some seismic reflection experiments indicate wide
stretches of older deformed basement in the deep-
er crust (Cook et al. 1979).
Figure 3 also provides an upper limit to age of
rocks, and in conjunction with Fig. 2 indicates
broad areas where the age of rocks can be gleaned
from the lack of older deformations (Fig. 3) and
preponderance of later deformations (Fig. 2). For
example, the lack of Precambrian deformations in
the Appalachian Orogen, coupled with the
frequency of Paleozoic events, implies that its
rocks are mainly of Paleozoic age. Similarly in the
Cordilleran Orogen, a lack of Paleozoic deforma-
tion (Fig. 3) and preponderance of Mesozoic de-
formations (Figs. 2 and 3) imply mainly Mesozoic
rocks. In contrast, the Grenville Orogen is com-
posed almost entirely of previously deformed
rocks; those first deformed during the Grenvillian
orogeny occur in small, widely separated areas
and make up less than 20% of the exposed orogen.
As a general rule, time of first deformation
approximates the age of rocks in erogenic belts.
120 H. WILLIAMS I!T Al.
The map illustrating last deformation is objec-
tive, being based on stratigraphic ages of de-
formed rocks and ages of unconformable cover
sequences, augmented by isotopic ages of
plutonism and metamo~~sm synchronous with
deformation. The map illustrating first deforma-
tion is more interpretive, especially in areas of
repeated structural, plutonic and metamorphic
overprinting. The necessary data for this map come
largely in the form of isotopic ages obtained from
minerals not easily reset during subsequent meta-
morphic events, e.g. U-Pb zircon. Nevertheless,
both maps are conceptually meaningful, regardless
of tectonic controls or presently available infor-
mation. A further breakdown of the prolonged
Archean interval, a difficult task not attempted
here, is essential to unravel the important earliest
crustal events.
Figure 4. Miogeoclines and terranes by kindred
The Archean structural provinces (Superior,
Slave, Wyoming, North Atlantic, North Kee-
watin *, South Keewatin *, Figs. 2, 3 and 5) are
all shown in the same pattern in this portrayal as
there is no attempt to separate their internal ele-
ments.
The Superior Province appears to have been
almost completely fringed by lower Proterozoic
miogeoclines, now extensively preserved in the
Circum-Ungava belt, Labrador Trough, Otish
Mountains and Penokean belt, but poorly defined
or obliterated along the southwestern margins of
the province. This implies that the Superior craton
was a discrete island minicontinent during at least
part of the early Proterozoic. The Circum-Superior
miogeoclines are essentially similar to those of the
Phanerozoic in most respects; moreover, a klippe
of predo~nantly oceanic rocks thrust upon the
Superior craton near Cape Smith (Hoffman, 1985),
resembles Ordovician Taconic allochthons in the
Appalachian Orogen.
* The North Keewatin and South Keewatin provinces are
renamed the Rae and Heame, respectively, and their
boundary, the Snowbird Line (Hoffman, 1988).
Lower Proterozoic miogeoclinal relics are also
preserved on the northwestern side of the Trans-
Hudson Orogen, in the Cree Lake and Foxe zones.
Continuity between these zones, and their farther
continuation through Baffin Island into the
Rinkian belt of Greenland, are matters of debate
(Lewry et al., 1985; Hoffman, 1987, 1988). The
best known and best exposed example of an Early
Proterozoic miogeocline is the fold and thrust belt
of the Wopmay Orogen that developed along the
western margin of the Archean Slave Province
(Hoffman, 1984; Hoffman and Bowring, 1984).
The stratigraphic analysis of this rniogeocline, from
its initiation and rift phase, through its passive
margin development, to final destruction rivals the
best analyses of Phanerozoic miogeoclines, such as
those existing for the App~ac~an and Cordil-
leran orogens. In contrast to the prolonged histo-
ries for the Phanerozoic miogeoclines (100 m.y. or
more), the Wopmay miogeoclinal cycle was short-
lived, about 10 m.y. This may not be typical of all
Early Proterozoic continental margins.
Rocks and structures of the Central Plains
Orogen truncate subsurface extensions of the
Penokean and Trans-Hudson orogens, consistent
with the Snowy Pass Supergroup of southeastern
Wyo~ng being a remnant of a Central Plains
miogeocline (Duebendorfer and Houston, 1987).
The younger Mazatzal, Southwest Province,
Trans-Labrador and Grenviile orogens, to the
southeast, are essentially devoid of preserved
miogeoclines (Condie, 1982; Green et al., 1985;
Bickford et al., 1986; Wardle et al., 1986; Sims
and Peterman, 1986).
The sinuous, disrupted and intersecting Pro-
terozoic miogeoclines of the North American cra-
ton form a pattern much like that of the African
continent where older Pr~amb~an provinces are
locally truncated and linked by late Precambrian
Pan-African belts. It is noteworthy that some
Pan-African belts are well-documented as result-
ing from plate tectonic processes, implying similar
controls for early to middle Proterozoic belts in
North America. The present complex tectonic pat-
tern of southeast Asia may be an analogue of early
Proterozoic North America (Hoffman, 1988).
Phanerozoic miogeoclines occur all around
North America. The Cordilleran miogeocline in
ANATOMY OF NORTH AMERICA 121
western North America is continuous from Alaska
to Arizona, and the Appalachian miogeocline in
eastern North America is continuous from New-
foundland to Mexico. Along the northern margin
of North America, the Cordilleran and Innuitian
miogeoclines can be linked by restoring the Alas-
kan North Slope terrane between the two at the
Beaufort Sea, and the Innuitian miogeocline and
Caledonian miogeocline of east Greenland are
continuous in northeast Greenland. Furthermore,
the gap between East Greenland and the Canadian
Appalachians is bridged by restoring the North
Atlantic (Williams, 1984). To the southwest, the
Cordilleran and Appalachian miogeoclines are
both truncated by the Sonora Megashear (Shurbet
and Cebull, 1987) and their rocks are translated
northward, possibly to reappear as suspect ter-
ranes-of the northern Pacific margin. The periph-
eral pattern and continuity of Phanerozoic
miogeoclines indicates that the late Precambrian
continent, Laurentia, was a discrete island much
like present day North America, though somewhat
smaller. The analysis also indicates that Laurentia
formed by late Precambrian breakup of a contem-
porary supercontinent, just as North America
formed by Mesozoic breakup of Pangea.
Suspect terranes, comprising either juvenile
crustal elements penecontemporaneous with ad-
jacent miogeoclines, or unrelated, mainly crystal-
line older terranes, occur within both Proterozoic
and Phanerozic orogens. The present challenge is
to document similar elements within the Archean
structural provinces, and some progress has been
made already in this regard (Card and Ciesielski,
1986; Hoffman, 1986a). Early Proterozoic juvenile
terranes are defined within the Trans Hudson
(Lewry et al., 1985; Van Schmus et al., 1987;
Chauvel et al., 1987), Penokean (Larue and Ueng,
1985) Central Plains (Bickford et al., 1986), Keti-
lidian (Allaart, 1976; Patchett and Bridgwater,
1984) and Grenville (Davidson, 1986) orogens.
They are generally of more limited area1 extent
than those of the Phanerozoic orogens, and
ophiolitic or chaotic terranes are sparse or un-
documented.
Much of the buried U.S. midcontinent may
comprise juvenile early to middle Proterozoic ad-
ditions. A broad area of granite and rhyolite
(1.50-1.44 Ga) is exposed in the St. Franqois
Mountains of Missouri and occurs widely in the
subsurface of Illinois, Indiana, Missouri and
Kentucky. Nd isotopic ratios (Nelson and De
Paolo, 1985) indicate derivation from crust having
a rather uniform model age of crust-mantle sep-
aration ca. 1.9 Ga, suggesting little or no involve-
ment of Archean crust. In contrast, granites of the
Penokean Orogen have model ages of ca. 2.3-2.1
Ga and were probably derived from crustal sources
containing mixed Archean and early Proterozoic
components.
Some crystalline tectonic elements, mainly
Archean, can be regarded as suspect relative to the
nearest well-defined miogeoclines; for example,
crystalline rocks in the vicinity of southern Baffin
Island are suspect with respect to the Circum-Su-
perior miogeocline to the south and the Foxe
miogeocline to the north.
Appalachian suspect terranes, most of them
composite or superterranes, are large and few
compared to Cordilleran examples (Williams,
1985). The orogen built up from the miogeocline
outward by successively younger Paleozoic accre-
tionary events. Boundaries between the miogeoc-
line and terranes, which amalgamated or accreted
during the Ordovician (Taconian Orogeny), are
marked by ophiolites and melanges, suggesting
head-on collisions. Boundaries between outboard
terranes, accreted later, are steep mylonite zones
or brittle faults, suggesting transcurrent oblique
motions (Williams and Hatcher, 1983). Some
ophiolitic and volcanic terranes occur as thin
Taconic allochthons, transported across the Ap-
palachian miogeocline, and a two-layered crust is
recognized in eastern parts of the ophiolitic Dun-
nage zone (Colman-Sadd and Swinden, 1984). To
the east, the Avalon terrane is a microplate, as its
rocks are embedded in the mantle (Keen et al.,
1986).
The Cordilleran orogen was assembled during
the Mesozoic, mainly by amalgamation and even-
tual accretion of two superterranes (Monger et al.,
1982). The two major accretionary episodes, in the
Jurassic and Cretaceous, are proposed as controls
for the contemporaneous metamorphic and
plutonic Omineca and Coast Plutonic belts, re-
spectively, in Canada. The greater number and
122 H. WILLIAMS ET AL
complexity of Cordilleran terranes compared to
those of the Appalachian Orogen reflect; (a) the
much longer history of the ancient Pacific Ocean
and persistence of the Cordilleran miogeocline,
from its late Precambrian initiation to Jurassic
destruction; (b) consequent greater width of
Pacific ocean crust destroyed by subduction; and
(c) greater dismemberment and dispersion of ter-
ranes by post-accretionary transcurrent faulting
(Coney et al., 1980).
A small area of mixed volcanic and sedimen-
tary rocks at the northern end of Ellesmere Island
is interpreted as an Innuitian suspect terrane
(Trettin, 1987). It includes an Ordovician ophiolite
complex at M’Clintock Inlet, records Ordovician
deformation, and has Grenville basement rocks.
These features are all typical of the western flank
of the Appalachian Orogen.
The Caledonides of east Greenland represent a
deformed, intruded and metamorphosed miogeo-
cline only. Its suspect elements were presumably
removed by spreading of the North Atlantic along
an axis coincident with the Ipetus suture.
Figure 5. Sutures and terrane boundaries
This figure portrays both well-documented and
probable collisional sutures representing closure
of former oceans, and other major terrane
boundaries whose significance and evolutionary
history are less well established. Some terrane
boundaries mark collisional zones across former
oceanic tracts; others are intracontinental trans-
current faults. As with miogeoclines and terranes
(Fig. 4), Archean sutures and terrane boundaries
are not depicted, but their existence is likely,
because of documented orogenies in Archean pro-
vinces.
Early to middle Proterozoic sutures and ter-
rane-boundaries surround and separate the
Archean Superior, Slave, Wyoming and North
Atlantic cratons, following the courses of the
Trans-Hudson, Wopmay, Penokean and Central
Plains orogens. Some of these orogen, e.g. Trans-
Hudson, are two-sided or symmetrical with oppos-
ing contemporary miogeoclines preserved. Others
are one-sided, asymmetric with only one miogeo-
cline. The asymmetric Precambrian orogens are
viewed as either accretionary, without collision of
opposing miogeoclines (like the Cordilleran
Orogen), or more likely collisional orogens with
opposing miogeoclines removed by subsequent
breakup along former collisional zones (like the
Appalachian Orogen).
The Thelon Front, between the Slave Province
and North Keewatin Province is interpreted now
as a collisional suture and part of a much longer
intracontinental shear zone, the Great Slave Lake
shear zone (Hoffman, 1986b; 1989). The geometry
of the Slave province against the North Keewatin
resembles the indentation of southeast Asia by
India at the Indus Suture. The indentation of the
North Keewatin was accommodated by 600-700
km of dextral offset on the Great Slave Lake shear
zone. The shear zone is marked by a wide zone of
mylonite and it is traceable in subsurface from the
foothills of the Rocky Mountains 1300 km north-
ward to the Thelon Basin. Another feature of the
shear zone is an 80 km wide belt of granitic and
dioritic intrusions along an exposed length of 1000
km, interpreted as a pre-collisional composite
magmatic arc and post-collisional zone of anatectic
batholiths (Hoffman, 1989).
Another important crustal break, the Intra-
Keewatin or Snowbird Line (Hoffman, 1988) sep-
arates the variably reworked North Keewatin and
South Keewatin divisions of the former western
Churchill Province. It may represent either a colli-
sional suture between former minicontinents or a
major intracontinental transcurrent fault (Hoff-
man, 1987; 1988). A suture between the Makko-
vikian/Ketilidian and North Atlantic province of
Labrador and southern Greenland is implied be-
cause the Ketilidian contains early Proterozoic
juvenile rocks (Allaart, 1976; Gower and Ryan,
1986; Patchett and Bridgwater, 1984). Evidence
for other sutures crossing north Greenland and
Baffin Island is weak.
A middle Proterozoic Central Plains suture is
indicated by apparent truncation of the slightly
older Trans-Hudson Orogen (Sims and Peterman,
1986) and by documented relations across the
Cheyenne Lineament (e.g., Duebendorfer and
Houston, 1987). In eastern Labrador, in what is
now the Grenville Province, there must be a cryptic
suture separating the early Proterozoic Mak-
ANATOMY OF NORTH AMERICA
Fig. 1. Tectonic elements of the North American continent.
TERTIARY TO RECENT
0 (Eurekan, Cascadian)
CRETACEOUS TO TERTIARY
ilaramide)
JURASSIC TO CRETACEOUS
(Columbian)
JURASSIC
m (Sonoman)
PALEOZOIC
[ Late (Alleghanian, Antler)
0 Middle (Acadian, Ellesmerianl
Early (Wonian)
PROTEROZOIC
0 Late to Cambrian (Avalonian)
Middle to Late (Grenvillian)
Early to Middle (Central Plains)
m Early (Hudsonian)
ARCHEAN CRATONS
m (Kenoran)
(Major erogenic events)
Fig. 7. Time of last major deformation. North -\merican continent. undeformed cober rocks omitted.
pp. 123-128
CRETACEOUS TO TERTIARY
f--J Mekan, LaramW
TRIASSIC TO jURASSlC AND OLDER
(Coiumbian~
PALEOZOIC
Late W@anhn, Ant&r)
Middle (&cadiam, Ellesmerian~
m Early flaconian‘ M%rintcxk)
PROTEROZOIC
Late to Cambrian fivalonian)
Middle Gzntral P&ins, Labradoran)
Early IHttdsonian)
ARCHEAN CRATONS
m (Kenoran and o&r)
Mjof orqgenic ewnts)
Fig. 3. Time of first major deformation. North American continent. undeformed cover rocks omitted.
Fig. 4. ~iogcocli~e~ and terranes of the North Amcrica~ continent cl~~~~ed by minored, ~~defo~ed anwr rocks omitted.
MESOZOIC TO CENOZOiC
PALEOZOIC
PROTEROZOic ‘_ I . ’ Middle to Late
I Middle
- Early to Middle
Sutures and &wane boundaries iden- tify the courses of ancient oceans destroyed by colffsfonal and accre- tiOMF/ events. The intricate array, with some boundaries dating back to the early Proterozoic, indicates the corn.. piexity of successive assembly and breakup episodes recorded in North American rocks. Where the stratigraphic record of miogeoclines is obfilerated, sutures may be the only evidence of ancient oceans.
Fig. 5. Sutures and terrane houndarics of the North American continent. undeformed cover rocks omitted
TERTIARY &s&j
CRETACEOUS
PALEOZOIC
0 Late
Middle to Late
Middle
Early
PROTEROZOIC
Middle to Late
Middle
Early
ARCHEAN CRATONS
Fig. 5. Time ofaccretion for the North American continent. undeformed cover rocks omitted
ANATOMY OF NORTH AMERICA 129
kovikian and middle Proterozoic Labradorian
orogens (Ward et al., 1986). Similarly, middle to late Proterozoic sutures are implied in the Gren- ville Province and may occur as terrane boundaries around an island arc sequence of middle Protero- zoic age in Ontario (Brown et al., 1975; Davidson, 1986), and around middle Proterozoic ophiolite and melange in the Llano Uplift in Texas (Garri- son, 1981). The New York-Alabama Lineament (Zietz, 1981), defined by strong magnetic and Bouguer gravity anomalies, is a possible unex- posed suture or terrane boundary within sub- surface extensions of the Grenville Province.
Paleozoic sutures mark the course of the Iape- tus Ocean along the Appalachian Orogen. In Canada, wide vestiges of Iapetus crust and mantle occur as discrete, thin allochthons thrust upon the Paleozoic eastern margin of North America. A thicker oceanic vestige, the Dunnage terrane (Fig. 4), is 150 km wide in northeast Newfoundland and sits above a collisional zone between the miogeo- cline and the outboard Gander terrane (Keen et al., 1986).
The Avalon and Meguma terranes in the Canadian Appalachians and the Carolina, Bruns- wick and Tallahassee terranes in the U.S. Appal- achians (Fig. 4) have European and African affini- ties, and evidently travelled great distances to their present positions; thus they must lie out- board of a suture. In the Gulf Coast area, late Paleozoic sutures truncate early and middle Paleo- zoic sutures and terrane boundaries, indicating final accretion during Alleghanian Orogeny in the southernmost Appalachians and Ouachitas. One such suture, marked onshore by the Brunswick magnetic anomaly and traceable along the off- shore shelf-edge as the East Coast Magnetic Anomaly, is a major collisional zone (Nelson et al., 1985a). Along the Atlantic shelf-edge between Georgia and Nova Scotia, it was the locus for opening of the Atlantic Ocean (Nelson et al., 1985b).
Middle Paleozoic accretion in the Innuitian Orogen involved a number of small terranes (Tret- tin, 1987) that are unseparated in Figs. 4 and 5.
Mesozoic and Cenozoic sutures and terrane boundaries of the Cordilleran Orogen, only a few of which are shown in Fig. 5, reflect a complicated
pattern of accretion (Coney et al., 1980). They separate mainly volcanic juvenile terranes and chaotic terranes of ophiolites and melanges. Blueschists are preserved along some boundaries in the Canadian Omineca belt and occur as blocks in the Franciscan Melange of California. The high pressure-low temperature conditions required for blueschist metamorphism are exclusively related to a subduction environment. The geometry of modem subduction beneath Vancouver Island in Canada has been defined recently by onland deep seismic experiments (Yorath et al., 1985).
Phanerozoic sutures and terrane boundaries are subparallel to the modem continental margins along much of the Appalachian, Cordilleran and Innuitian orogens, but they are sharply truncated by the present margin northeast of Newfound- land. Early to late Proterozoic sutures of the Grenville, Makkovik and Ketilidian provinces are also truncated by the modem margin in this area.
The ages of sutures and terrane boundaries (Fig. 5) date rocks and structures of adjacent miogeoclines and terranes (Fig. 4). The patterns shown in the two figures are complimentary and provide insight into the controls and geometry of last and first deformations depicted in Figs. 2 and 3, respectively.
Figure 6. Time of accretion
This illustrates the way in which the North American continent grew by accretionary episodes to attain its present form and internal pattern of geologic mountain belts. The stable deformed rocks of ancient orogens are the frozen record of a mobile crust that changed continually to shape the present continent. Progressively younger accre- tionary events affected adjacent contemporary rniogeoclines through several sequential cycles of geologic mountain building.
In this analysis, there is a need for a systematic nomenclature that identifies the North American element (offspring) that resulted through the breakup of a preceding landmass, or parent super- continent. Just as present North America is the offspring of Pangea, and Paleozoic Laurentia the offspring of a late Precambrian landmass (Pan- Africaland), names are necessary to denote off-
130
spring and parent supercontinents for Pre-
cambrian breakup cycles. One such scheme, sum-
marized in Table 1, uses names of contemporary
Precambrian orogenies, modified by suffixes for
the various offspring-parent relationship. Thus,
Hudsoniu (a North American element of un-
known original shape and extent) is the offspring
of Hudsonland (a fictitious supercontinent.
The existence of Archean deformed belts and
their truncation by fringing Proterozoic orogens
implies that the Archean structural provinces, or
minicontinents, were previously part of a larger
landmass (Kenorland). Late Archean (Kenoran)
orogeny, recorded isotopically in most Archean
provinces, was probably temporally related to as-
sembly of such an Archean landmass.
There is no documentation that rocks and
structures in any particular Archean province were
ever continuous with those of another. The
Archean provinces are all mutually suspect with
respect to one another. Prior cycles of Archean
breakup and assembly are also possible.
The breakup of Kenorland led to the formation
of the North American minicontinents, the Super-
ior, Slave, Wyoming, North Atlantic, and possibly
the North Keewatin and South Keewatin. Some,
like the Superior, were discrete island continents,
with their early Proterozoic peripheral miogeo-
clines still preserved. Others, like the Wyoming
H WILLIAMS ET AL
and South Keewatin are truncated and of un-
known earlier geometry. Other parts of Kenor-
land, dispersed by rifting, now lie beyond the
confines of North America.
The Archean minicontinents were assembled
(or reassembled), together with intervening juvenile
terranes accreted to continental margins, in the
early Proterozoic ca. 1.95-1.85 Ga (Hoffman,
1988) during development of the Trans-Hudson,
Wopmay, Penokean and Makkovikian/ Ketilidian
orogens. Other orogens, now largely obliterated,
developed adjacent to the Thelon Front and
Snowbird Line (Fig. 5). This early Proterozoic
phase of assembly, although probably di-
achronous, was rather brief, about 100 m.y. It
produced what has recently been termed the Pan-
American system (Lewry, 1987). It resulted in
stabilization of the northern two thirds of the
North American craton, that has remained unaf-
fected by younger orogeneses, except for diminu-
tion through several episodes of breakup. The
name Hudsonia is proposed for the present North
American faction of the supercontinent (Hudson-
land) formed by the early Proterozoic Pan-
American event.
Evidence for at least three middle to late Pro-
terozoic accretionary episodes is found in the
southeastern one third of the North American
craton. The Central Plains Orogen, comprising
TABLE 1
Scheme to denote North American offspring elements that resulted through breakup of preceding parent supercontinents
Parent Time of North American Time of
supercontinent amalgamation offspring separation
(Ga) (Ga)
Kenorland 2.5 and older
Hudsonland 1.9-1.8
Central Plainsland 1.7
Labradorland (Mazatzaland) 1.6
Grenvilleland 1.0
Pan-Africaland 0.8-0.6
Pangea (Pangealand) OS-O.3
Superior, Slave, Wyoming, North Atlantic,
North and South Keewatin
Hudsonia
Central Plainsia
Labradoria (Mazatzia)
Grenvillia
Laurentia
North America
2.5-1.9
1.x-1.7
1.7-1.6
1.6-1.0
1 .O-0.6
0.6-0.5
0.3-0.0
ANATOMY OF NORTH AMERICA 131
mainly juvenile rocks, formed at about 1.7 Ga. This modified the southern part of Hudsonia. The Mazatzal (Condie, 1982) and newly defined Trans-Labrador (Thomas et al., 1986; Wardle et al., 1986) orogens further modified the same gen- eral area at about 1.6 Ga, and were followed by the Grenville Orogen formed at about 1.0 Ga. The southern margin of Hudsonia was affected there- fore by at least three mountain building episodes, each with extended periods of juvenile accretion and/or collisions at contemporary continental margins. Orogenesis was patterned with successive deformed zones subparallel and to some extent overlapping preceding ones.
Accretion onto the southern margin of the North Atlantic, Superior and Wyoming provinces, which began before or during their confluence into Hudsonland, continued for at least 200 m.y. after their unification. It is not yet certain if some additions are unique to individual Archean prov- inces or if they are separately exposed parts of single belts accreted after the unification of Hud- sonland. In general, igneous crystallization ages decrease southward: about 1.9-1.8 Ga for Penokean, Makkovikian and Ketilidian; 1.8-1.7 Ga for Central Plains; and 1.7-1.6 Ga for Mazatzal and Labradorian (Hoffman, 1988).
The full extent and geometry of these middle to late Proterozoic mountain belts are unknown; however Labradorian and/or Grenvillian events are recorded in deformed rocks of Scandinavia (Gower and Owen, 1984), East Greenland (Max, 1979), the United Kingdom and Ireland (Piasecki et al., 1981) and Northwest Africa.
Late Precambrian (Pan-African) deformed zones, so widespread in the African continent, are absent in North America, except for local late Precambrian orogeny recorded in the Appalachian Avalon terrane (Figs, 2, 3 and 4). The Pan-African event is equated with the assembly of a late Pre- cambrian supercontinent (Pan-Africaland). Con- tinuity of miogeoclines around the periphery of the North American (Laurentian) craton, all ini- tiated in late Precambrian to Cambrian time, indi- cates that the North American (Laurentian) cra- ton was an internal part of the Pan-Africaland supercontinent. Its breakup isolated Laurentia, the early Paleozoic predecessor of North America.
Laurentia remained an island continent until initial early Paleozoic accretionary events recorded in the Appalachian Orogen. Middle Paleozoic accretion further modified its eastern margin, and the adjacent Iapetus Ocean was eventually de- stroyed during late Paleozoic assembly of Pangea. At that time the Appalachian Orogen was in the heart of a supercontinent (and Newfoundland was the hub of the Pangean world).
Breakup of Pangea, mainly along former Paleozoic collisional zones, led to formation of Mesozoic North America. Opening of the Atlantic Ocean was approximately coeval with the onset of Cordilleran accretion on the opposite side of the continent. Greenland, which was part of North America (Hudsonia) since early Proterozoic Pan- American assembly, was isolated from the rest of the North American continent late in the opening history of the Atlantic.
The Paleozoic record of Laurentia and its evolution to North America serves as a useful model for considering the earlier Precambrian accretionary and breakup events implied in Table 1.
Discussion and summary
The thematic maps described above together provide a vehicle for discussion and broad analy- sis of most major aspects of North American architecture and evolution. Other important re- lated features not represented in these maps might legitimately be presented in a similar fashion. For example, the portrayal of dyke swarms and rift zones, by age, would facilitate analysis of im- portant extensional episodes and their spatial- temporal relation to other major tectonic events (Fahrig et al., 1986). Are dyke swarms and rifts everywhere a prelude to significant spreading epi- sodes? Age and lithology of other anorogenic in- trusions, age and lithology of major magmatic belts, and age of rocks in intracratonic basins are other worthwhile themes.
Our portrayal and analysis emphasizes the es- sential similarities in character, spatial distribution of lithotectonic elements, and geodynamic evolu- tion of Precambrian and Phanerozoic erogenic belts. We are impressed with the similarities, rather
132 H. WILLIAMS t-1 AI.
than differences, among rocks and structures of
orogens, regardless of age; implying persistence of
plate tectonic processes back to at least the latter
part of the Archean Era. We do not, however,
ignore or underestimate possibly significant
quantitative differences between the Phanerozoic
and earlier Precambrian periods. These seem to
reflect gradual changes in crust-mantle evolution
and inevitable progressive accretionary expansion
of continental lithosphere, rather than major
qualitative change in lithosphere-mantle geody-
namics.
It is quite evident, from analysis of the North
American and other continents, that both the total
area1 extent of continental lithosphere and average
size of individual contemporary continental masses
has gradually increased from the Archean on-
wards. It is this progressive change, rather than
fundamental differences in lithospheric geody-
namics and mantle processes, that is reflected in
most of the observed differences between Early
Proterozoic and Phanerozoic lithotectonic ele-
ments. By extrapolation, it may account for many
of the even greater differences in the nature of the
Archean-deformed cratons. Other significant fac-
tors may include progressively lower spreading
rates and total spreading ridge length (the latter to
some extent implicit in our discussion) over time,
consequences of gradual decrease in total heat
flow, and effects of changing lithospheric levels of
geologically significant geotherms. Such factors
may control extensive volcanism and emplacement
of mafic sills in some Proterozoic foredeeps, such
as those connected with the Wopmay Orogen and
the Circum-Superior miogeocline, and their ab-
sence in Phanerozoic continental margin evolu-
tion. Absence of documented Proterozoic blue-
schists may reflect more general subduction of
hotter, younger oceanic lithosphere at contem-
porary destructive plate boundaries or other dif-
ferences in thermal regime. Certainly, the greater
abundance of ultramafic lavas during the Archean
and, to a lesser extent, in the early Proterozoic
must reflect significant progressive changes in
thermal regimes within the mantle.
Other differences may be related to changes in
the atmosphere-hydrosphere-biosphere, as for
example the widespread spectacular development
of sedimentary iron formations in the Early Pro-
terozoic Circum-Superior miogeocline.
Compilation of good thematic maps of North
America, although time consuming, is a relatively
easy exercise. The geologic data base is strong and
rapidly expanding, and it is accessible to all in a
single language. Maps are beautiful, fun, informa-
tive, and even profitable in some cases. We offer
our full support, loud applause and deep respect
to those brave souls who may surface to attempt
this task.
Acknowledgements
Thanks are extended to H.P. Trettin and W.R.
Muehlberger, who supplied material relevant to
the compilatons and unselfishly shared their latest
thoughts and ideas. We also thank G.A.G. Nunn
and A.P. Nutman for discussion, C. Conway and
G. McManus for preparation of figures, the
Canadian Geological Foundation and D.F. Strong
through Memorial University for financial support
in producing the coloured figures, and the Natural
Sciences and Engineering Research Council of
Canada and the Department of Energy, Mines
and Resources for supporting our work in the
field.
References
Allaart. J.H.. 1976. Ketilidian mobile belt in South Greenland.
In: A. Escher and W.S. Watt (Editors). Geology of Green-
land. Geological Survey of Greenland, Copenhagen, pp.
120-151.
Bickford, M.E.. Van Schmus, W.R. and Zietz. I., 1986. Pro-
terozoic history of the midcontinent region of North
America. Geology, 14: 492-496.
Brown. R.L., Chappell. J.F., Moore. J.M.. Jr. and Thompson,
P.H., 1975. An ensimatic island arc and ocean closure in
the Grenville Province of southeastern Ontario, Canada.
Geosci. Can., 2: 141-144.
Card, K.D. and Ciesielski, A.. 1986. DNAG No. 1. Subdrvi-
sions of the Superior Province of the Canadian Shield.
Geosci. Can., 13(l): 5-13.
Chauvel, C., Arndt, N.T., Kielinzcuk. S. and Thorn. A.. 1987.
Formation of Canadian 1.9 Ga old continental crust. Can.
J. Earth Sci.. 23: 3966406.
Colman-Sadd, S.P. and Swinden, H.S.. 1984. A tectonic window
in central Newfoundland? Geological evidence that the
Appalachian Dunnage Zone may be allochthonous. Can. J.
Earth SCI.. 21: 1349-1367.
ANATOMY OF NORTH AMERICA 133
Condie, K.C., 1982. Plate-tectonic model for Proterozoic con-
tinental accretion in the southwestern United States. Geol-
ogy, 10: 37-42.
Coney, P.J., Jones, D.L. and Monger, J.W.H., 1980. Cordil-
leran suspect terranes. Nature, 288: 329-333.
Cook, F.A., Albaugh, D.S., Brown, L.D., Kaufman, S., Oliver,
J.E. and Hatcher, R.D., Jr., 1979. Thin-skinned tectonics in
the crystalline southern Appalachians; COCORP seismic-
reflection profiling of the Blue Ridge and Piedmont. Geol-
ogy, 7: 563-567.
Davidson, A., 1986. New interpretations in the southwestern
Grenville Province. In: J.M. Moore, A. Davidson and A.J.
Baer (Editors), The Grenville Province. Geol. Assoc. Can.,
Spec. Pap., 31: 61-74.
Duebendorfer, E.M. and Houston, R.S., 1987. Proterozoic
accretionary tectonics at the southern margin of the Archean
Wyoming craton. Geol. Sot. Am. Bull., 98: 554-568.
Fahrig, W.F., Christie, K.W., Chown, E.N., Janes, D. and
Machado, N., 1986. The tectonic significance of some basic
dyke swarms in the Canadian Superior Province with spe-
cial reference to the geochemistry and paleomagnetism of
the Mistassini swarm, Quebec, Canada. Can. J. Earth Sci.,
23: 238-253.
Garrison, J.R., Jr., 1981. Coal Creek serpentinite, Llano Uplift,
Texas: a fragment of an incomplete Precambrian ophiolite.
Geology, 9: 225-230.
Gower, C.F. and Owen, V., 1984. Pre-Grenvillian and Grenvil-
lian lithotectonic regions in eastern Labrador-correlations
with the Sveconotwegian Orogenic Belt in Sweden. Can. J.
Earth Sci., 21: 679-693.
Gower, C.F. and Ryan, A.B., 1986. Proterozoic evolution of
the Grenville Province and adjacent Makkovik Province in
eastern-central Labrador. In: J.M. Moore, A. Davidson and
A.J. Baer (Editors), me Grenville Province. Geological As-
soc. Can., Spec. Pap., 31: 281-296.
Green, A.G., Weber, W. and Hajnal, Z., 1985. Evolution of
Proterozoic terranes beneath the Williston Basin. Geology,
13: 624-628.
Hoffman, P.F., 1984. Geology, Northern Internides of Wopmay
Orogen, District of Mackenzie, Northwest Territories. Geol.,
Surv. Can., Map 1576A. scale 1: 250,000.
Hoffman, P.F., 1985. Is the Cape Smith Belt (northern Quebec)
a klippe? Can. J. Earth Sci., 22: 1361-1369.
Hoffman, P.F., 1986a. Crustal accretion in a 2.7-2.5 Ga
“Granite-Greenstone” Terrane, Slave Province, NWT: a
prograding trench-arc system? Geol. Assoc. Can., Progr.
Abstr., 11: 82.
Hoffman, P.F., 1986b. Is the Thelon Front (NWT) a suture?
Geol. Assoc. Can., Progr. Abstr., 11: 82.
Hoffman, P.F., 1987. Birth of a craton. Geol. Assoc. Can.,
Progr. Abstr., 12: 56.
Hoffman, P.F., 1988. United Plates of America, the birth of a
craton. Amm. Rev. Earth Planet. Sci., 16: 543-603.
Hoffman, P.F., 1989. Continental transform tectonics: Great
Slave Lake shear zone (ca. 1.9 Ga), northwest Canada.
Geology, 17: 135-138.
Hoffman, P.F. and Bowring, S.A., 1984. Short-lived 1.9 Ga
continental margin and its destruction, Wopmay orogen,
northwest Canada. Geology, 12: 68-72.
Hoffman, P.F. et al., in prep. Tectonic map of the Canadian
Shield. Geological Survey of Canada.
Howell, D.G., Schermer, E.R., Jones, D.L., Ben-Avraham, 2.
and Scheibner, E. (Compilers), 1985. Preliminary
tectonostratigraphic terrane map of the Circum-Pacific re-
gion. American Association of Petroleum Geologists, Tulsa,
Okla., scale 1 : 17.000,000.
Kay, M., 1951. North American Geosynclines. Geol. Sot. Am.,
Mem., 48: 143 pp.
Keen, C.E., Keen, M.J., Nichols, B., Reid, I., Stockmal, G.S.,
Coleman-Sadd, S.P., O’Brien, S.J., Miller, H., Quinlan, G..
Williams, H. and Wright, J., 1986. Deep seismic reflection
profile across the northern Appalachians. Geology, 14:
141-145.
Larue, D.K. and Ueng, W.L., 1985. Florence-Niagara terrane:
an early Proterozoic accretionary complex, Lake Superior
region, U.S.A. Geol. Sot. Am. Bull., 96: 1178-1187.
Lewry, J.F., 1987. The Trans-Hudson Orogen: extent, subdivi-
sion and problems. Geol. Assoc. Can., Progr. Abstr.. 12: 67.
Lewry, J.F., Sibbald, T.I.I. and Schledewitz, D.C.P., 1985.
Reworking of basement in the western Churchill Province
in northern Saskatchewan and its significance. In: L.D.
Ayres, P.C. Thurston, K.D. Card and W. Weber (Editors),
Archean Supracrustal Sequences. Geol. Assoc. Can., Spec.
Pap., 28: 239-261.
Max, M.D., 1979. Extent and disposition of Grenville tectonism
in the Precambrian continental crust adjacent to the North
Atlantic. Geology, 7: 76-78.
Monger, J.W.H., Price, R.A. and Tempelman-Kluit. D.J.. 1982.
Tectonic accretion and the origin of the two major meta-
morphic and plutonic welts in the Canadian Cordilleran.
Geology, 10: 70-75.
Nelson, B.K. and DePaolo, D.J. 1985. Rapid production of
continental crust 1.7-1.9 b.y. ago: Nd isotopic evidence
from the basement of the North American mid-continent.
Geol. Sot. Am. Bull., 96: 746-754.
Nelson, K.D., Amow, J.A., McBride, J.H., Willemin, J.H.,
Huang, J., Zheng, L., Oliver, J.E., Brown, L.D. and Kauf-
man, S., 1985a. New COCORP profiling in the southeast-
em United States. Part 1: Late Paleozoic suture and
Mesozoic rift basin. Geology, 13: 714-718.
Nelson, K.D., McBride, J.H., Amow, J.A., Oliver, J.E., Brown,
L.D. and Kaufman, S., 1985b. New COCORP profiling in
the southeastern United States. Part 11: Brunswick and
east coast magnetic anomalies, opening of the north-central
Atlantic Ocean. Geology, 13: 718-721.
Patchett, P.J. and Bridgwater, D., 1984. Origin of continental
crust of 1.9-1.7 Ga age defined by Nd isotopes in the
Ketilidian terrain of South Greenland. Contrib. Mineral.
Petrol., 87: 311-318.
Piasecki, M.A.J., Van Breemen, 0. and Wright, A.E., 1981.
Late Precambrian geology of Scotland, England and Wales.
In: J.W. Kerr and A.J. Fergusson (Editors). Geology of the
134 H. WILLIAMS ET AL.
North Atlantic Borderlands. Can. Sot. Pet. Geol., Mem., 7:
57-94.
Shurbet, D.H. and Cebull, S.E., 1987. Tectonic interpretation
of the westernmost part of the Ouachita-Marathon
(Hercynian) erogenic belt, west Texas-Mexico. Geology,
15: 458-461.
Sims, P.K. and Peterman, Z.E., 1986. Early Proterozoic Central
Plains orogen: a major buried structure in the north-central
United States. Geology, 14: 488-491.
Stockwell, C.H., McGlynn, J.C., Emslie, R.F., Sanford, B.V.,
Norris, A.W., Donaldson, J.A., Fahrig, W.F. and Currie,
K.L., 1970. Geology of the Canadian Shield. In: R.J.W.
Douglas (Editor), Geology and Economic Minerals of
Canada. Geol. Surv. Can., Econ. Geol. Rep., 1: 43-150.
Thomas, A., Nunn, G.A.G. and Krogh, T.E., 1986. The
Labradorian Orogeny: evidence for a newly identified 1600
to 1700 Ma erogenic event in Grenville Province rocks
from central Labrador. In: J.M. Moore, A. Davidson and
A.J. Baer (Editors), The Grenville Province. Geol. Assoc.
Can., Spec. Pap., 31: 175-189.
Trettin, H.P., 1987. Pearya: a composite terrane with
Caledonian affinities. Can. J. Earth Sci., 24: 224-245.
Van Schmus, W.R., Bickford, M.E., Lewry, J.F. and Mac-
donald, R., 1987. U-Pb geochronology in the Trans-Hud-
son Orogen, northern Saskatchewan, Canada. Can. J. Earth
Sci., 23: 407-424.
Wardle, R.J., Rivers, T., Gower, C.F., Nunn, G.A.G. and
Thomas, A., 1986. The Northeastern Grenville Province:
new insights. In: J.M. Moore, A. Davidson and A.J. Baer
(Editors), The Grenville Province. Geol. Assoc. Can., Spec.
Pap., 31: 13-29.
Wheeler, J.O. and McFeely, P., 1987. Tectonic assemblage map
of the Canadian Cordillera and adjacent parts of the United
States of America. Geol. Surv. Can., Open file 1565, scale
1: 2,ooo,ooo.
Williams, H., 1978. Tectonic lithofacies map of the Appa-
lachian Orogen. Memorial University of Newfoundland,
Map no. 1, scale 1: 1,OOO,OOO.
Williams, H., 1984. Miogeoclines and suspect terranes of the
Caledonian-Appalachian Orogen: tectonic patterns in the
North Atlantic region. Can. J. Earth Sci., 21: 887-901.
Williams, H., 1985. Paleozoic miogeoclines and suspect ter-
ranes of the North Atlantic Region: Cordilleran compati-
sons. In: D.G. Howell (Editor), Tectonostratigraphic ter-
ranes of the Circum-Pacific region, Circum-Pac. Count.
Ener. Miner. Resour., Earth Sci. Ser., 1: 71-75.
Williams, H. and Hatcher, R.D., Jr., 1983. Appalachian sus-
pect terranes. In: R.D. Harcher, Jr., H. Williams and 1.
Zietz (Editors), Contributions to the Tectonics and Geo-
physics of Mountain Chains. Geol. Sot. Am., Mem., 158:
33-53.
Yorath, C.J., Clowes, R.M., Green, A.G., Sutherland-Brown,
A., Brandon, M.T., Massey, M.W.D., Spencer, C.,
Kanasewich, E.R. and Hyndman, R.D., 1985. Lithoprobe-
Phase 1: Southern Vancouver Island: Preliminary analyses
of reflection seismic profiles and surface geological studies.
In: Current Research, Part A. Geol. Surv. Can., Pap. 85-IA:
543-554.
Zietz, I., 1981. Aeromagnetic coverage of the mid-continent
U.S.A. Geol. Sot. Am., Abstr. Progr., 13: 558.