Download Continental Drift, IV: The Caribbean "Plate"

CONTINENTAL DRIFT, IV: THE CARIBBEAN "PLATE"1
A. A. MEYERHOFFAND HOWARDA. MEYERHOFF
American Association of Petroleum Geologists and GeoSurveys, Tulsa, Oklahoma 74101
ABSTRACT
According to "the new global tectonics," the Caribbean Sea and the marginal lands surrounding it comprise one "lithosphere plate." Its eastern margin includes the Barbados Ridge, Lesser Antilles arc, and Aves
Ridge; the western margin is composed of Central America and the Middle America Trench. These two
margins are interpreted as subduction zones by "new global tectonics" advocates. The northern and southern margins are the alleged North Caribbean and South Caribbean faults, respectively. According to recent
JOIDES drilling data, the Caribbean "plate" may be underlain by Late Cretaceous (75-85 m.y.) basaltic
crust, and therefore is younger than both the Americas plate on the north, east, and south and the Cocos
plate on the west. From this, some workers have inferred that the Caribbean formed by sea-floor spreading
which separated North and South America. However, there is no spreading center in the Caribbean. Moreover, geologic and seismic data prove that the proposed North Caribbean and South Caribbean faults do
not exist. La Desirade is a Jurassic or older island east of the Lesser Antilles. Barbados Ridge is an aseismic,
pre-Late Jurassic salient of South America (that is, part of the so-called Americas plate) that parallels and
lies just east of the alleged Lesser Antilles subduction zone. The stratigraphic units of Barbados are correlatable with those of northern South America. Structural trends on Barbados strike east-northeast, are Late
Cretaceous-early Eocene, and parallel those of South America. These facts show that the position of Barbados with respect to that of South America has not changed for more than 140 m.y. Yet "the new global
tectonics" require that La Desirade and the Barbados Ridge must have been subducted more than 70 m.y.
ago. On the basis of the facts presented here, the so-called Caribbean plate and the regions surrounding it
have held the same positions relative to one another since pre-Jurassic (probably pre-Paleozoic) time. "The
new global tectonics," therefore, are not applicable in the Caribbean area.
new ad hoc concept tends to outrun the
The problem.-For more than 60 years available evidence and too commonly seems
geologists have tried their hand at inter- oblivious of the geology exposed on land.
preting the Caribbean region as a whole. We have no illusions about the finality of
Their greatest handicap was ignorance of our views, but several recent papers show
the geology of the vast expanses covered by the dire need of some accord between land
and sea geology-geophysics, particularly in
water-a
cover that made extrapolation
from mainland to island, and island to is- the eastern Caribbean. It is our purpose to
land, extremely speculative. Much more bring the facts together and to offer an inrecently, the research vessel has brought terpretation of their meaning.
A principal key in the tectonics of the
geophysicists into the scene and, as knowleastern
Antilles-in fact, of the entire Caedge of the sea floor has been revealed, new
ribbean-is
the Barbados Ridge (fig. 1).
interpretations have been ventured. AlSuess
(1908,
p. 700-708) appears to have
though there are not quite as many interfirst to recognize this fact.
been
the
among
are
workers
the
region
pretations as there
in
He observed that the position of the Barba(H. A. Meyerhoff 1954, p. 149), confusion
is compounded by the constantly recurring dos Ridge with respect to the Lesser Antilneed that confronts advocates of "the new les is nearly identical with that of the Baglobal tectonics" to change their interpreta- hamas-Turks and Caicos Islands with retions as new dredge hauls, new cores, new spect to the Greater Antilles. Both the
seismic-refractiondata, and new gravimet- Barbados Ridge and the Bahamas-Turks
ric profiles belie yesterday's concepts. Each and Caicos are salients from a continent on
the outer, or Atlantic sides, of the two AnManuscript
received
1
April 20, 1971; revised tillean arcs. Suess noted further that the
June 7, 1971.
older formations of Barbados are related
genetically to correlative units on Trinidad.
[JOURNAL
1972, Vol. 80, p. 34-60]
OF GEOLOGY,
Suess's is the first geologic synthesis of
© 1972. The University of Chicago. All rights reserved.
INTRODUCTION
34
CONTINENTAL DRIFT, IV
35
FIG. 1.-Index map, eastern Caribbean Sea. Modified from Hess (1966) and Bunce et al. (1971). Locations
of figs. 4, 8, 9, 10, 11, 12, 13, 17, 18, 19, and 20 are shown.
the Caribbean. Since his day, many summaries and syntheses of Caribbean geology
have been published, but only a few have
succeeded in explaining any part of the complex tectonics and stratigraphy of the area.
Among the most important works are those
of Woodring (1928, 1954), Rutten (1935),
Schuchert (1935), Hess (1938, 1966), Waters and Hedberg (1939), H. A. Meyerhoff
(1946, 1954), Bucher (1947), Hess and
Maxwell (1953), Eardley (1954), Butterlin
(1956), Barr (1958), Weyl (1961, 1966),
North (1965), Judoley and Furrazola (1967)
A. A. Meyerhoff (1967), Tijomirov (1967),
Ball and Harrison (1969), Dengo (1969),
Molnar and Sykes (1969), Stainforth (1969),
and MacGillavry (1970).
Most syntheses have treated the Carib-
bean Sea as a foundered landmass (Woodring, Schuchert, Bucher, Eardley, Butterlin, Judoley and Furrazola, Tijomirov) or
a permanent oceanic basin surrounded by
island arcs and geosynclines (Hess, Waters
and Hedberg, H. A. Meyerhoff, Hess and
Maxwell, Barr, Weyl, North, A. A. Meyerhoff, Dengo, Molnar and Sykes, MacGillavry). Among the former group, two hypotheses are favored: (1) foundering (Woodring, Schuchert, Bucher, Eardley, Butterlin), and (2) oceanization (Judoley and
Furrazola, Tijomirov). Among the latter,
three hypotheses have been advanced: (1)
contraction (Waters and Hedberg, H. A.
Meyerhoff, A. A. Meyerhoff), (2) convection (tectogene of Hess 1938; Hess and
Maxwell, Barr), and (3) some form of con-
36
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
tinental drift-generally sea-floor spreading
(Hess 1966; North, Ball and Harrison, Dengo, Molnar and Sykes, Stainforth, MacGillavry).
Sea-floor spreading and plate tectonics.A major question during recent years is the
age of the Caribbean floor. Most sea-floor
spreaders ("mobilists") and nondrifters
("fixists") have regarded the floor as ancient oceanic crust. However, the mobilists
generally have maintained that the Caribbean floor predates the present Atlantic
and Pacific crusts. To explain the presence
and preservation of this ancient Caribbean
crust, Mattson (1969), Edgar et al. (1971a),
and Malfait and Dinkelman (1971) proposed that the Caribbean is a remnant of
pre-Mesozoic sea floor which once flanked
the ancient Darwin Rise of the Pacific
basin. After the Darwin Rise ceased to be
a spreading center, the East Pacific Rise
formed, and all ancient ocean floor was destroyed, except (1) the Darwin Rise itself
(which ultimately is to be consumed in the
trenches of the western Pacific as the sea
floor plods steadfastly west-southwestward);
and (2) the Caribbean "child" of the Darwin Rise which, caught between North and
South America as they wended their way
westward, was sealed off on the west by the
newly formed Middle America Trench and
its subduction zone and on the east by the
Lesser Antilles Trench and its so-called
subduction zone (fig. 2).
This mobilist concept has been modified
radically by the 1970-1971 drilling results
of JOIDES Leg 15 (Purrett 1971). A 762-m
hole reached basalt 746 m below the ocean
bottom at 14°47'11" N, 69019'36" W. Only
18 m of basalt was drilled. The oldest faunas
above the basalt are middle Late Cretaceous
(Edgar et al. 1971b). Edgar and his col-
FIG. 2.--Index map, Caribbean "plate." Shows locations of figs. 6, 7, and 14, plus major elements of
Greater Antilles orthogeosyncline. Note absence of through-going faults.
CONTINENTAL DRIFT, IV
leagues (in Purrett 1971) then did an
abrupt about-face, concluded that the Caribbean Sea is a young ocean basin (younger
than the Atlantic and Pacific), and declared that it is the product of the tearing
apart of North and South America during
Late Cretaceous time.
According to mobilists, the Caribbean is
one of the many "lithosphere plates"
(Isacks et al. 1968; Morgan 1968) which
comprise the earth's crust (fig. 3). The Caribbean was first shown as a discrete lithosphere plate by Morgan (1968), although,
ironically-and for very different reasonsone of us (H. A. Meyerhoff 1946, 1954)
first expressed in print the concept of the
Caribbean plate as an independent tectonic
unit.
Both the mobilists and we agree on one
point: the so-called Caribbean plate is moving eastward relative to the Atlantic, North
America, and South America; but on the
following points we differ: (1) the mobilists
FIG. 3.-"Lithosphere plates" of Caribbean and
surrounding areas. From Morgan (1968). Published
with permission of W. J. Morgan and American
Geophysical Union.
37
also move the Caribbean plate relatively
westward, at a somewhat slower rate than
that of the two American continents, as the
new Pacific floor descends down the Middle
America Trench; (2) the mobilists require
that unbroken transform faults bound the
Caribbean plate on the north (North Caribbean fault) and on the south (South
Caribbean fault); and (3) they believe that
the Western Atlantic (Americas) plate is
being subducted on the east beneath the
Lesser Antilles arc. These mobilist speculations conflict with the geological and geophysical facts.
EASTERN CARIBBEAN MARGIN
The eastern margin of the Caribbean
basin includes a geomorphically and geologically complex system of subparallel
ridges which range from slightly to markedly convex toward the Atlantic Ocean (fig. 1).
From west to east, these are: Aves Ridge,
Lesser Antilles, and Barbados Ridge. H. A.
Meyerhoff (1946, 1954) termed this ridge
complex the "Lesser Antilles anticlinorium."
Except for Aves Island, 215 km west of
Dominica, the Aves Ridge is submerged
through its entire north-south length of
550 km. It is approximately 100 km wide
at the 2,000-m isobath. It joins the South
American continent just northeast of La
Blanquilla Island and converges northward
toward the Lesser Antilles arc which it joins
near Saba Island.
The Aves Ridge is separated from the
Lesser Antilles arc by the Grenada Trough,
which has an average width of 150 km at
the 2,000-m isobath. The width of the
trough from the crest of the Aves Ridge to
the axis of the Lesser Antilles volcanic arc
is about 215 km.
The Lesser Antilles arc is about 750 km
long, and includes the Leeward Islands on
the north and the Windward Islands on the
south. The arc is only 25-40 km wide in the
south, but north of Dominica it bifurcates
into two island groups which comprise a
ridge system more than 100 km wide. The
two groups consist of an outer chain of
38
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
limestone islands (Limestone Caribbees)
and an inner chain of volcanic islands (Volcanic Caribbees). The volcanic chain extends from Grenada, about 150 km north
of the Paria Peninsula, Venezuela, to Saba,
due east of St. Croix. The limestone islands
are limited to the northern half of the island
arc-from Marie Galante, north of Dominica, to Sombrero Island, east of Anegada.
The Tobago Trough, about 150 km wide,
separates the volcanic islands of the Lesser
Antilles from the Barbados Ridge. At the
2,000-m isobath, the Trough is only 80 km
wide.
The island of Barbados is 160 km due
east of St. Vincent in the Volcanic Caribbees. The island is almost precisely in the
center of the Barbados Ridge, which parallels the Volcanic Caribbees, and extends
nearly 500 km northward from Tobago to
its northern end. The northern end of the
Ridge is almost 170 km due east of Marie
Galante, the southernmost of the Limestone Caribbees.
PRINCIPAL TECTONIC PROBLEMS
The principal tectonic problems in the
eastern Antilles (fig. 1) are (1) the origin
and age of the Aves Ridge, (2) the origin
and age of the Lesser Antilles arc, (3) the
abrupt southern termination of the Limestone Caribbees at Marie Galante Island,
(4) the origin and age of the Barbados
Ridge, (5) the abrupt northern termination
of the Barbados Ridge east of Marie Galante Island, (6) the nature(s) of the junctions of the three ridges with the Greater
Antilles on the north and with South America on the south, and (7) the position of La
D6sirade Island in the Lesser Antilles arc.
Solution of these problems must take into
account the facts that Aves Island, the
southern terminus of the Limestone Caribbees, and the northern terminus of the
Barbados Ridge are at the same latitudeabout 15°42' N.
We believe that a successful solution to
the problem of the Lesser Antilles's origin
hinges on the establishment of their position in the framework of the entire Caribbean.
DESCRIPTION OF EASTERN CARIBBEAN
RIDGE SYSTEM
theories, and
Numerous hypotheses,
factual observations have been recorded
for the Caribbean region and for the landmasses that surround it. The Lesser Antilles alone generally are interpreted as a compressional feature. The Volcanic and Limestone Caribbees have been described as a
"typical" island arc system belonging to the
circum-Pacific belt, even though they face
the Atlantic Ocean (Benioff 1954; Gutenberg and Richter 1954). However, earthquake hypocenters generally are above a
depth of 200 km, in contrast to those of
some Pacific-facing arcs where hypocenters
locally reach depths as great as 720 km.
H. A. Meyerhoff (1954) interpreted the
Lesser Antilles as a series of crustal "waves"
pushed upward by eastward rotation of the
Caribbean plate as it was caught in a viselike movement between North and South
America. The underlying cause of Caribbean deformation was attributed by Meyerhoff to contraction.
Hess (1938) interpreted the Lesser Antilles complex to be part of a tectogene formed
by downbuckling between two converging
convection currents. When seismic and
gravity studies showed that the huge "roots"
required by the tectogene concept are not
present beneath arcs, convection currents
still were invoked as the mechanism which
provided the compressive stresses needed
to create the island arc.
When the sea-floor spreading hypothesis
of Holmes (1931) was revived by Hess
(1960, 1962), the Lesser Antilles logically
was interpreted as a zone where the westward-spreading Americas "plate" plunged
beneath the Caribbean "plate." Evidence
purporting to show that part of the socalled Americas plate actually does plunge
into a Benioff (subduction) zone beneath
the Lesser Antilles island arc was published
by Chase and Bunce (1969) (fig. 4). Today
the sea-floor spreading, or mobile plate,
model for the origin of the Lesser Antilles
is widely accepted. The purposes of this
paper are to show that the geological and
CONTINENTAL DRIFT, IV
SW
SECTION A
LESSER ANTILLESTRENCH
NE
FAULTS
SEDIMENTS
MANTLE
CFROMCHASE AND BUNCE, 1969; BUNCE ET AL,1971)
FIG. 4.-Southwest-northeast seismic-reflection
profile A. Location shown on fig. 1. From Chase
and Bunce (1969) and Bunce et al. (1971). Published with permissionof authors, AmericanGeophysicalUnion, and Wiley-Interscience.
geophysical facts contradict the sea-floor
spreading-mobile plate model in this area,
and that North America, South America,
and the Caribbean region have held relatively permanent positions through time
with respect to one another.
BARBADOS RIDGE
Nature and origin.--The only exposed
part of this ridge is Barbados island, 275 km
north of Trinidad, and 225 km south of the
northern terminus of the ridge. South of
Barbados, the ridge is divided in two
branches (fig. 1) separated by the Barbados
Basin (Lattimore et al. 1971; Weeks et al.
1971).
Sedimentary rocks exposed on Barbados
island range in age from Paleocene through
Pleistocene (Senn 1940, 1947; Beckmann
1953; Baadsgaard 1960; Kugler 1961). The
oldest strata, the Scotland Formation
which ranges in age from Paleocene through
early middle Eocene, are strongly deformed.
They are mainly terrigenous marine turbidites and synorogenic flysch (sensu Tercier 1947). The beds contain a heavy mineral suite consisting of abundant opaque
minerals (mainly ilmenite); common leucoxene, zircon, epidote, zoisite-clinozoisite,
chloritoid, hypersthene, garnet, and augite;
and scarce tourmaline, staurolite, sillimanite, andalusite, topaz, glaucophane, rutile,
anatase, brookite, titanite, and corundum
(H. D. Hedberg, in Senn 1940, p. 15601561). Pyroclastic pyroxenes are present,
as are milky white pebbles of vein quartz.
The source of the mineral suite listed is
a mixed terrane of low- to high-grade meta-
39
morphosed acidic rocks, and basic volcanic
rocks cut by diorite and veins of milky
quartz. A low-grade metamorphosed terrane is present below the Late Jurassic on
the Araya-Paria Peninsulas of northeastern
Venezuela (Gonzilez de Juana et al. 1968),
but medium- to high-grade metamorphic
rocks are not exposed. The grade of metamorphism on the two peninsulas increases
northward. Consequently, medium- to highgrade metamorphic rocks may underlie the
offshore area. Basic to silicic volcanic rocks
cut by dioritic intrusives and by milky
quartz veins comprise much of Tobago,
Margarita, and the remaining VenezuelanNetherlands Antilles. A fresh diorite from
Tobago yielded a K-Ar date of 113 + 6
m.y.2 The Paleocene-Eocene section thickens toward the south-southeast (a fact
which indicates southern provenance), and
contains numerous, large exotic blocks of
Albian limestone bearing faunas identical
with those of Trinidad and the Eastern
Venezuelan basin (Vaughan and Wells 1945;
Douglass 1961). Additional outcrops of the
Scotland Formation have been dredged
from the Barbados Ridge north of Barbados island (Hurley 1966).
The inference to be drawn is sufficiently
plain, as Senn (1940, 1947), Barr (1958),
and Baadsgaard (1960) have noted. The
pre-Late Jurassic basement of the ArayaParia Peninsulas area, and the Cretaceous
volcanic sequence of the Venezuelan-Netherlands Antilles and Tobago underlie the
Barbados Ridge. Therefore, the Barbados
Ridge is a part of the North VenezuelaTrinidad fold belt of South America that
projects north-northeastward from Trinidad and Tobago. The seismic data of Bassinger et al. (1971), Lattimore et al. (1971),
and Weeks et al. (1971) also show clearly
the geological and geophysical continuity
between Trinidad-northern Venezuela and
the Barbados Ridge.
Hurley (1966) emphasized the fact that
2 Age determinationwas carried out by the
Isotope GeologyUnit of the Institute of Geological
Sciences,London,and is quoted by permissionof
the director of the IGS. We thank Norman J.
Snellingand John F. Tomblinfor this information.
40
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
the east-northeast-trending structures of
Trinidad and Barbados and the great distance separating the two islands preclude a
simple relation between them. Hurley's
observation is correct, but he overlooked the
fact that the low- to high-grade metamorphic clasts of the Scotland Formation require the presence, between Trinidad and
Barbados, of a broad area of metamorphic
rocks of higher grade than any that are exposed on Trinidad or in northeastern Venezuela.
A fact which is well known to some Caribbean geologists, but which seems to be
unknown to most geophysical-geological
oceanographers, is that the pre-middle
Eocene structural trends of Barbados
strike east-northeast-west-southwest, parallel with the structures of Tobago (200 km
south), Trinidad (275-350 km south), and
northern South America (Senn 1940, 1947;
Baadsgaard 1960). In middle and late Eocene times, strong folding, directed toward
the north-northwest, affected the entire
early Eocene and older sequence. Overturned sections, thrusts, isoclinal and recumbent folds, and large gravity-glided
olistoliths and olistostromes are abundant
(Baadsgaard 1960). Baadsgaard (1960)
suggested that the mass of pre-late Eocene
sediments on the island was emplaced by
gravity gliding from a ridge in the southsoutheast. If this interpretation is correct,
bathymetric data suggest that the distance
of gliding did not exceed 50-75 km (fig. 1).
The important facts to keep in mind are
that (1) the east-northeast strike of the
older formations requires a north-northwestsouth-southeast compressive stress field in
early and middle Eocene times, when the
Lesser Antilles arc supposedly was being
formed by a west-to-east stress field; and
(2) the Barbados Ridge geologically is not
a part of the Caribbean or Lesser Antilles,
but a part of the South American continent.
Therefore, the Barbados Ridge most
certainly does not take "the place of the
Puerto Rico [Antilles] trench east of the
southern end of the Antilles arc," as Chase
and Bunce (1969, p. 1419) claimed; nor is
it "a mass of sedimentary material that
fills the southern part of the Antilles [Lesser
Antilles] trench." According to these authors, "The thickening of the sediments
overlying the oceanic basement is due to the
increasing proximity of South America, the
source for the material of the sedimentary
wedge that constitutes the continental
rise" (p. 1419). Chase and Bunce wrote
further: "That there is no basic change in
the major subsurface structural elements is
shown by the southward continuation of
the negative gravity anomaly, which characterizes the [Puerto Rico] trench, through
Barbados to Trinidad (Talwani, 1966)."
Chase and Bunce's statements require
comment.
1. Talwani (1966, p. 177) wrote that
"Eastwards [from Puerto Rico], the negative free-air anomaly belt of the Puerto
Rico Trench departs from the topographic
trench and continues into Trinidad and
Venezuela." Talwani neither stated nor implied that "there is no basic change in the
major subsurface structural elements . . .."
The gravity trends of the eastern Caribbean
are shown in figure 5.
2. A large negative free-air gravity anomaly will be produced by either a deep, sediment-filled oceanic trench or by a thick
prism of continental crust. The fact that a
broad negative anomaly band strikes from
east of the Virgin Islands to the Barbados
Ridge is not proof of a common origin for
the Lesser Antilles Trench and the Barbados Ridge. We regard the Puerto Rico
Trench, Lesser Antilles Trench, and Barbados Ridge as three distinct structural
features. The Puerto Rico Trench is an
east-west-trending graben, characterized by
strike-slip and dip-slip movements. It continues eastward from Puerto Rico to a location north of the Barracuda fracture
zone (fig. 1; see Hess 1966). The Lesser
Antilles Trench intersects the Puerto Rico
Trench northeast of the Virgin Islands.
Molnar and Sykes (1969, p. 1655) recognized that the large gravity anomalies
and the presence of intermediate-depth
earthquakes beneath Puerto Rico suggest
41
CONTINENTAL DRIFT, IV
POSITIVE
VALUES
(MGAL)
ONEGATIVE
VALUES
(MGAL)
FIG. 5.-Pratt-Hayford isostatic gravity map of eastern Caribbean. From Bush and Bush (1969). Black
dots are control points. Published with permission of authors and Gulf Coast Association of Geological Societies.
that an island-arc structure extends eastwest, parallel with the Puerto Rico Trench.
However, in the absence of volcanism in
this region since the Eocene (Monroe 1968),
Molnar and Sykes (1969, p. 1658) concluded that "the present tectonics of the
Puerto Rico trench should not be regarded
as typical of island arcs."
3. Khudoley and Meyerhoff (1971) were
able to corroborate the conclusion of Molnar and Sykes that the Puerto Rico Trench
is not an island-arc-type trench. They analyzed the earthquake epicenters reported
by Sykes and Ewing (1965, p. 5071), who
erroneously had combined the hypocenter
data from the Dominican Republic with
those from Puerto Rico, and thereby portrayed a hypocenter distribution beneath
Puerto Rico and the eastern Dominican
Republic similar to that of a typical island
arc. If the hypocenters beneath the eastern
Dominican Republic and the Puerto Rico
Trench are plotted separately (figs. 6, 7),
patterns result which are totally unlike
that of an island-arc hypocenter distribution and resemble most closely those associated with actively subsiding grabens
and broad strike-slip zones.
4. The gravity data from east of the
Lesser Antilles are sparse. Bush and Bush
(1969) showed that the Lesser Antilles
Trench axis passes through Barbados (fig.
5). Hess (1966, p. 2) showed that the main
part of the Lesser Antilles negative anomaly
belt passes along the western side of the
Barbados Ridge. Masson-Smith and Andrew (1965, in Hurley 1966) showed one
negative trend to strike from southwestern
Barbados island to a point midway between
Grenadaand Tobago, and another negative
trend to pass east of Tobago toward central
Trinidad.
5. The facts have been mentioned that
the pre-late Eocene structural trends of
Barbados island are east-northeast-westsouthwest, and that the stresses which de-
42
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
N
A
OUTER
RIDGE
PUFRTO RICO
TRENCH
PUERTO
RI
CARIBBEAN
SEA
NAVIDAD
3BANK
PUERTO RICO
TRENCH
DOMINICAN
REPUBLIC
CARIBBEAN SEA
S
A
LOWER LIMIT OR EPICENTERS,
(AFTER SYKES AND
1950-1964
EWING, 195)
100 KMG
VERT.
ExAC.=
2x
A
B
of eastern Dominican
FIG. 6.-Hypocenters of Puerto Rico. From
FIG. 7.-Hypocenters
Khudoley and Meyerhoff(1971). Location shown Republic. From Khudoley and Meyerhoff (1971).
on fig. 2. Publishedwith permissionof The Geolog- Location shown on fig. 2. Published with permisical Society of America.
sion of The Geological Society of America.
formed the island were directed toward the
Geophysical data colnorth-northwest.
lected by Bassinger et al. (1971) between
Barbados and Tobago, and between Tobago and Trinidad, show that (a) structures
become progressively steeper and more
complex with increasing depth; (b) magnetically and seismically determined structural trends of the submarine part of the
Barbados Ridge strike east-northeast; (c)
the structural similarity across the entire
area from Trinidad to Barbados shows that
the Ridge has been deformed as a single
tectonic unit; (d) the Cretaceous basic igneous rocks of Tobago can be traced northeast toward a point not far from Barbados;
and (e) the whole area from Trinidad to
Barbados belongs structurally and stratigraphically to northern South America and
the Venezuelan-Netherlands Antilles. These
statements are borne out in full by Collette
et al. (1969; see fig. 8). Figure 8 shows the
basement rising to near the surface at 110 N.
This basement is interpreted to be the premiddle Eocene, and more probably is preLate Jurassic medium- to high-grade metamorphic rocks equivalent to those exposed
on the Paria-Araya Peninsulas.
The present north-south strike of the
Barbados Ridge, paralleling the trend of
the Volcanic Caribbees, apparently was
acquired by the compressive stresses which
formed Aves Ridge and the Lesser Antilles.
Its earlier structural history, however, was
an integral part of the development of the
Caribbean orthogeosyncline of northern
South America. A pre-Jurassic metamorphic terrane presumably extended from the
Paria-Araya Peninsulas on the mainland
northward to within a few tens of kilometers
of the island of Barbados. Deformation before Paleocene time, probably in Late Cretaceous time, raised the Caribbean orthogeosyncline, and its Late Jurassic rocks
were shed north-northwestward into a foredeep much like the trenches on the ocean-
43
CONTINENTAL DRIFT, IV
FIG. 8.--South-north seismic-reflection profile B, Barbados Ridge, and Lesser Antilles Trench. Location
shown on fig. 1. South American shelf at 90; basement approaches surface at 110; junction of Lesser Antilles and Puerto Rico Trenches between 180 and 190. From Collette et al. (1969). Published with permission
of B. J. Collette and Elsevier Publishing Company.
ward side of modern volcanic arcs, as Hurley (1966) concluded.
The Paleozoic-early Eocene deep-water
turbidites and flysch deposits of the Scotland Formation that accumulated in the
foredeep were themselves deformed prior
to the deposition of the middle Eocene to
early Miocene Oceanic Formation (Beckmann 1953; Kugler 1961). The latter is
bathyal marl which overlies the Scotland
Formation with marked angular unconformity on Barbados. Cores recovered from
the Barbados Ridge between Barbados and
Tobago, although of late Miocene or Quaternary sediments, contain reworked faunas
and detritus from shallow-water strata as
old as middle Eocene (Ramsay 1968). The
cores show that the Eocene was raised and
eroded from 11040' N at least as far as 130 N.
The Oceanic Formation shows the first
link with the Lesser Antilles. It was deposited in at least 1,000-1,500 m of water
(Beckmann 1953), and its late Eocene beds
contain volcanic ash of the same composition as the ash of the modern Lesser Antillean volcanoes (Senn 1940, 1947). The water depth in which the Oceanic accumulated contrasts with the evidence of concurrent shallow-water deposition south of Barbados (Ramsay 1968).
Conclusions.--The Barbados Ridge is a
north-northeastward salient of the Caribbean orthogeosyncline of northern South
America that extends 550 km along the
eastern side of the Lesser Antilles arc. The
Barbados Ridge basement is pre-Late Jurassic-possibly
Paleozoic or older. The close
similarity between the stratigraphy of Barbados and that of Trinidad and the identity
of their faunal zones indicate that the two
islands belong to the same geologic province. Geophysical data and structures
mapped in the field also show the geologic
unity of the area between the mainland and
Barbados island. The Barbados Ridge may
have been part of an outer deep-sea trench
during the development of the Late Jurassic-early Eocene Caribbean orthogeosyncline of northern South America.
LESSER
ANTILLES
Origin.-The
Volcanic Caribbees and,
from Marie Galante Island northward, the
Limestone Caribbees have been discussed
briefly. The oldest paleontologically dated
beds are middle Eocene-a limestone interbedded with volcanigenic beds on the island
of St. Barthelemy in the northeastern part
of the Lesser Antilles (Christman 1953).
Late Eocene fossils have been collected by
Robinson and Jung (1972) from Carriacou
Island, north of Grenada.
On the basis of the dated middle-Eocene
rocks, almost all workers in the region have
assumed that the Lesser Antilles formed
during latest Cretaceous through middle
Eocene time, and that this volcanic arc has
remained active ever since.
Fink's data.-In 1970, L. K. Fink (1970a,
1970b) provided a major surprise for students of Lesser Antilles geology. On the island of La Desirade, east of Grand Terre,
Guadeloupe (fig. 1), Fink discovered an igneous assemblage which to date is unique in
44
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
the Lesser Antilles. The main volcanic islands of the Lesser Antilles consist mainly
of andesite and dacite, with lesser amounts
of basalt, basic (basaltic) andesite, bandaite,
and rhyolite. In contrast, La D6sirade is underlain by a "basement" of easterly striking pillowed spilite, quartz keratophyre, and
bedded chert of unknown ages that are intruded by a rock very similar to trondhjemite (Fink, written communication, January
11, 1971). Greenschists and related rocks
have been dredged from an escarpment
north of La Desirade (Johnston et al. 1971).
Similar eugeosynclinal rocks are common
in the Greater Antilles (Khudoley and
Meyerhoff 1971) and also are known from
the Barracuda fracture zone (Bonatti 1967,
p. 481-482) east of La D6sirade. Several KAr and U-Pb ages for the La Desirade
trondhjemite range from 139 to 143 m.y.
(Tithonian, Late Jurassic). Fink (written
communication, January 11, 1971) stated
that, "The fundamental question at this
point is whether the igneous rocks on La
Desirade are the only known exposures of
nascent island arc products or relict seafloor crust."
Fink (1970b) suggested that the ancestral
Lesser Antilles arc began to form in Late
Jurassic time and was active until EoceneOligocene time. At this time, according to
Fink, crustal subduction ceased, a new arc
formed on the west (the present Lesser Antilles arc), and sea-floor spreading and
subduction began anew (see Fink 1971, and
in press). Fink proposed that the renewed
sea-floor spreading caused the rise and emergence of the Barbados Ridge. Thus Fink
(1970b, 1971, and in press) interpreted the
development of the entire Lesser Antilles
arc and the Barbados Ridge in terms of
"the new global tectonics."
Problems.-If the term may be stretched
a little farther than it has been already, La
Desirade may be labeled a "maverick island." It is east of the Limestone Caribbees,
and its structural trend is east-west. Its
keratophyre and spilite match none of the
volcanic products found among the Volcanic Caribbees, but are much more closely
linked with rocks of unknown age dredged
from the Barracuda fracture zone on the
east (fig. 1, and Bonatti 1967). Northwest
of La D6sirade the rocks also can be
matched, not only in type but also in approximate age, by keratophyre and spilite
in the Greater Antilles (Khudoley and
Meyerhoff 1971). The island of La Desirade
surfaces above a salient which protrudes 50
km east of the scarp that separates the
Limestone Caribbees from the Lesser Antilles Trench (Hess 1966, bathymetric
chart). The salient lies north of a structural
zone of weakness (possibly a transverse
fault, as proposed by Fink 1970b), along
which the north end of Barbados Ridge,
the southern end of the Limestone Caribbees, and Aves Island are aligned. In figure
9 this zone is shown as the southern edge of
the Greater Antilles orthogeosyncline, and
we suggest the term "Dominica fault" for
this transverse feature. Although long-distance projection has its hazards, there is
much more logic in extending the eastsoutheast trend of the Greater Antillean
Jurassic-through-Eocene structures as far
as La Desirade than there is in erecting
this single island into a nascent island arc,
halting sea-floor spreading, and restarting
it to form the younger Lesser Antilles arc,
as Fink (1970b) has proposed.
In addition to the Greater Antilles structural trend, there are sound tectonic reasons
for our proposal that La D6sirade is the
easternmost outpost of the Greater Antilles orthogeosyncline. The latter, like the
Caribbean orthogeosyncline of northern
South America, was compressed between
the North and South American continents
against the rigid Caribbean basin, which we
interpret to be an ancient oceanic plate
fixed in position, except for a small eastward rotation, between North and South
America. The major stress components were
from south-southwest for the northern orthogeosyncline and from north-northwest
for the southern orthogeosyncline. A secondary component was directed toward the
east and is believed to have caused the initial development of Aves Ridge. Both the
CONTINENTAL DRIFT, IV
45
FIG. 9.-Interpretation of relative geologic ages of Greater Antilles and Caribbean orthogeosynclines
(Late Jurassic-middle Eocene), Aves Ridge (Late Cretaceous-middle Eocene), and Lesser Antilles arc
(middle Eocene-present). Location shown on fig. 1.
northern and southern orthogeosynclines
originated during Late Jurassic or earlier
time, and the compressive stresses were
operative through middle Eocene time. On
both the north and south, Caribbean-facing
volcanic chains or arcs were formed during
part or all of this time span. Donnelly's
(1964) contention that the Greater Antilles
orthogeosyncline faced the Atlantic, rather
than the Caribbean, is unfounded, as demonstrated by Khudoley and Meyerhoff
(1971).
Since post-middle Eocene time the major
stress component has been eastward. Aves
Ridge, intruded by granodioritic and related plutons, became part of the competent Caribbean crust, and compression has
been exerted against and through the par-
tial closure effected by the converging Barbados Ridge extension of the Caribbean
orthogeosyncline and the La Desirade extension of the Greater Antilles orthogeosyncline. The result of continued compression is the Caribbean-facing Volcanic Caribbees arc on the west, and the raised marginal ridge supporting the Limestone Caribbees on the east, which is overriding the
Lesser Antilles Trench. This new arc is
superposed on salients of the older Greater
Antilles and Caribbean orthogeosynclines
(fig. 9). The rigid La Desirade salient has
been raised sufficiently for part of it to surface and to elevate the Oceanic Formation
of Barbados to its present position. It is difficult, if not impossible, to visualize the process by which the Oceanic Formation was
46
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
raised to its present position if subduction
ridge, Aves Island, shows some evidence of
by the so-called Americas plate was the east-northeast-striking structure (Maloney
body producing the operative stress. If et al. 1968; Weeks et al. 1971). If this obsubduction is taking place, it must be far servation is confirmed, the Aves Ridge
out (somewhere in the Atlantic?).
must have been in existence when the CaScholl et al. (1968, 1970) arrived at sim- ribbean orthogeosyncline, including Barbailar conclusions regarding the Peru-Chile
dos, was folded. Recent dredge hauls have
Trench. However, Scholl and his colleagues
confirmed that the rocks which comprise
did not have the benefit of a dated ridge, the Ridge did exist during the latest Cresuch as the Barbados Ridge, west of the taceous-early Eocene folding of the CaribPeru-Chile Trench, to be able to establish
bean geosyncline, and the nature of the redefinitely that underthrusting has not oc- covered rocks led Fox et al. (1972) to concurred.
clude that Aves Ridge is underlain by
A collateral effect has been to superim- granitic rocks.
pose on the original east-northeast strucWeeks et al. (1971) reported that the
ture of the Barbados Ridge its present dredge hauls recovered basalt at some lonorth-south trend, its dual ridge structure calities, and that at 50 localities, granitic
with the intervening Barbados Basin, as intrusive rocks were recovered. Fox et al.
well as the Tobago Trough separating the (1969, 1972) reported the dredging of graRidge from the southern Volcanic Carib- nitic rocks, unconsolidated Quaternary
bees. It is possible that we are witnessing
sediments, and shallow-water, lithified carthe formation of a new eastern Antillean
bonates of late Eocene and early to middle
orthogeosyncline.
Miocene ages. Late Miocene and PlioD&sirade, as inter- Pleistocene samples which were recovered
Conclusions.-La
preted by us, is genetically a part of the indicate deep-water deposition.
Greater Antilles orthogeosyncline, as the
The granites have been dated, but none
Barbados Ridge is genetically a part of the of the dates has been widely publicized.
Caribbean orthogeosyncline. The modern Joseph R. Curray (written communication,
Lesser Antilles are younger than the Aves September 3, 1970; Curray et al., in prepRidge, and it is likely that they formed dur- aration) wrote that, "Neil Maloney and I
ing Paleocene and early Eocene times. did succeed in dredging some granitic rocks
off the southern part of the Aves Ridge...
AVES RIDGE
and have, with some of our colleagues, been
Description.-Aves
Ridge (fig. 10) long slowly working away at that rock ever
has puzzled geologists. Most students of since. We . .. now do have some information and are preparing to publish a short
the eastern Caribbean have interpreted
the Aves Ridge to be an anticlinorium
note. The data... have been worked up
which formed by compression in an east- in collaboration with Manuel Bass,...
west stress field. The only island on the J. Hawkins, and ... D. Macdougall....
We
0
50
KM
FIG. 10.-West-east seismic-reflection profile C, Aves Ridge. Location shown on fig. 1. From Bunce et al.
(1971). Published with permission of authors and Wiley-Interscience.
47
CONTINENTAL DRIFT, IV
have dates both by K-Ar and by fission
track. These dates range from 46 to 66
million years [late Eocene to earliest Paleocene] with some consistent variation by
technique, and are a bit younger than those
obtained by Heezen and his associates.3
Most of our samples are relatively rich in
K-feldspar and merge on granodiorite."
Thus a partial history of the Aves Ridge
can be deduced. A sequence of strata of unknown lithology and age-probably
Cretaceous and earliest Tertiary-was deposited and deformed. H. A. Meyerhoff (1954, p.
153) suggested that the Late Cretaceous
volcanogenic section (mainly pyroclastic
rocks) of St. Croix may belong to the Aves
Ridge structural province and, if so, the St.
Croix section may typify the sequence underlying the late Eocene carbonates of the
Aves Ridge.
During and after deformation, granodioritic rocks of latest Cretaceous to Eocene age intruded the Aves Ridge. The
ridge was uplifted and eroded, and a shallow-water late Eocene through middle Miocene carbonate platform formed. During
late Miocene time, the ridge began to sink,
and a deeper water regime has since characterized much of the ridge.
Relation to Lesser Antilles arc.-The relations between the Aves Ridge and the
Lesser Antilles arc are unknown. We believe that the Aves Ridge probably is a volcanic-arc precursor to the Lesser Antilles
arc. A. A. Meyerhoff (1966) compared the
Lesser Antilles-Aves system with the ridgetrough-ridge systems of the Bartlett Trough
and the Marianas-Bonin arc. In both examples, two ridges are separated by 180220 km of deep water. However, the Bartlett system is associated with an active
fault zone; hence, a comparison with the
double ridge systems of the western Pacific
seems more appropriate (Dietz 1954; Karig
1971).
As stated, we prefer to interpret the Aves
3 Dates rangingfrom 57 to 89 m.y. have been
determined at Columbia University (Fox et al.
1972). Sample collections were made by B. C.
Heezen and his colleaguesfrom aboard the R/V
Eastward.
Ridge as a precursor to the Lesser Antilles
arc. As the Caribbean plate was thrust
eastward between the Greater Antilles orthogeosyncline on the north and the Caribbean orthogeosyncline on the south, the
first volcanic arc to form (in middle Cretaceous time) was the Aves Ridge. After it
was deformed and intruded during the early
part of the "Laramide" orogeny, a new arc
-the present Lesser Antilles arc-formed
east of the Aves Ridge during PaleoceneEocene time. The Lesser Antilles arc involved a segment of the inactive Greater
Antilles orthogeosyncline (for example, La
Desirade Island). Thus, as postulated by
H. A. Meyerhoff (1954, p. 155), the Lesser
Antilles anticlinorium forms "a transverse
range which can be simply explained as a
product of compression resulting from rotation of the Caribbean basin." One major
difference between our interpretation and
that of H. A. Meyerhoff in 1954 is that the
Barbados Ridge is now known to be a salient of northern South America, which was
uplifted anew during the Tertiary as a result of eastward movement of the Caribbean "plate."
PRINCIPAL BASINS
GRENADA
TROUGH
The Grenada Trough is between the
Aves Ridge and the Lesser Antilles arc. In
the south, the bottom of the Trough is
nearly flat (fig. 11), and the beds dip gently toward the south and west (Bunce et al.
1971). A turbidite sequence characterizes
the upper part of the section and overlies
unconformably an older section of rocks.
The total thickness to acoustical "basement" is about 1,500-2,000 m, although
older sediments may underlie the acoustical
"basement." Northward the turbidite section wedges out, and west of Guadeloupe
Island, the Tobago Trough section and the
acoustical "basement" are disturbed by
faults, gentle folds, and slumps (Bunce et al.
1971).
TOBAGO TROUGH
The Tobago Trough separates the Lesser Antilles arc from the Barbados Ridge.
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
48
50
0
KM
FIG. 11.-West-east seismic-reflection profile D, Grenada Trough. Location shown on fig. I. From Bunce
et al. (1971). Published with permission of authors and Wiley-Interscience.
In contrast to the Grenada Trough, the
floor of the Tobago Trough is bowed upward on the eastern and western flanks
(fig. 12), and there is considerable evidence
for large-scale slumping on both of its
flanks. Although the ages of the sediments
in the Grenada and Tobago Troughs have
not been determined, the upturn of the
strata on both margins of the Tobago
Trough, in contrast to their horizontal position in the Grenada Trough, lends strong
support to the earlier origin which we assign to the Aves Ridge.
Several unconformities are present in the
section, particularly along the basin margins. At least 2,000-3,000 m of section is
present above acoustical "basement."
North of the Trough, the section is tilted
eastward, and there is much evidence for
gravity sliding from west to east (Bunce et
al. 1971).
LESSER
ANTILLES
TRENCH
The Lesser Antilles Trench extends north
from the Tobago Trough along the eastern
margin of the Lesser Antilles arc. The oceanic basement and overlying rocks dip westward beneath the volcanic arc (Bunce et al.
1971). Our figure 4, taken from Chase and
Bunce (1969), was interpreted by them as
evidence for underthrusting of the Caribbean "plate" by the so-called Americas
plate. In sections farther south along the
eastern side of the Barbados Ridge, Chase
and Bunce (1969) and Bunce et al. (1971)
also postulated underthrusting (fig. 13).
Chase and Bunce used the steep-angle reverse faults shown on figure 13 as further
support for their underthrusting interpretation. However, the seismic sections they
have presented also support west-to-east
overthrusting of the Caribbean "plate,"
accompanied by slumping of unconsolidated
sediment masses from the Lesser Antilles
arc and the Barbados Ridge. The Ridge
was broken into hundreds of fault slices
during latest Cretaceous-early Eocene orogeny, and many of the faults seen on figure
13 may be of Eocene age. Regardless of
50
0
KM
FIG. 12.-West-east seismic-reflection profile E, Tobago Trough. Location shown on fig. 1. From Bunce
et al. (1971). Published with permission of authors and Wiley-Interscience.
49
CONTINENTAL DRIFT, IV
50
o
KM
profileF, East Ridgeof BarbadosRidge.Locationshownon fig. 1.
FIG.13.-West-east seismic-reflection
FromBunce et al. (1971).Publishedwith permissionof authorsand Wiley-Interscience.
their age, they show a remarkable resemblance to the imbricate faults along the
Lewis and Clark overthrust in Montana.
Relations between Puerto Rico Trench and
have menLesser Antilles Trench.-We
tioned the fact that, on the basis of Hess's
(1966) bathymetric map, the Puerto Rico
Trench is separate from the Lesser Antilles
Trench. The latter strikes southward, on
the western side of the Barbados Ridge (fig. 1).
The main point is that the two trenches are
just that-two
trenches, the Puerto Rico
Trench striking far eastward into the Atlantic and intersecting the Lesser Antilles
Trench at an angle of nearly 600°.
ALLEGED PLATE TECTONICS
DATING
The sea-floor spreaders' struggle to insert a Caribbean plate between the North
and South American continents has been
negated by the emergence of implacable
facts. Emplacement from the Pacific Ocean
had to take place in Jurassic time, or certainly not later than very Early Cretaceous
time, because the most recent dating of the
North Central American orogen (fig. 2) indicates that the Middle America Trench
would have become a subduction zone in
pre-Late Cretaceous time (Barr and Escalante 1969). This fact precludes Mattson's
(1969) and Malfait and Dinkelman's (1971)
postulated early Tertiary date of insertion.
The Pacific origin further assumed an ancient floor for the Caribbean plate (Edgar
et al. 1971a), for it was supposedly a drifted
relict from the inactive Darwin Rise. However, JOIDES Leg 15 drilling found Late
Cretaceous diabase beneath 746 m of sediments, the oldest of which contained a middle Late Cretaceous fauna. Thereupon,
Edgar et al. (in Purrett 1971) abandoned
their earlier insertion hypothesis and postulated that the Caribbean plate formed in
situ with the north-south separation of
North and South America.
A weak case might have been made for
the retention of the Pacific origin of the
plate because sediments at the diabase
contact are baked, and the diabase obviously is an intrusion younger than the sediments;4 hence the drill, which penetrated
only 18 m of diabase, did not reach the base
of the sedimentary section. This straw at
which some mobilists have grasped would
be more attractive if only there were a midCaribbean ridge to serve as a spreading
center, or if, somewhere, there were a linear
pattern of magnetic anomalies. Neither is
present (fig. 14). It also would help if the
southern, western, and northern margins
of the Caribbean were not flanked by sedimentary sequences that thin toward the
center of the basin from marginal thicknesses of 6,000-8,000 m (Edgar et al. 1971a).
The presence of these thick marginal sedimentary basins is devastating to any concept of insertion or in situ origin.
JOIDESsite 10, leg 2, western Atlantic, also
supposedlyreached basaltic "basement"in Campanian (80-m.y.-old) sediments. Dating of the
"basement" (which also has baked contacts)
revealed the "basement" to be 15.9 m.y. old
(Macdougall1971), as predictedby Kamen-Kaye
(1970) for most JOIDESbasaltic "basements," the
majorityof whichhave bakedcontacts.
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
50
FIG. 14.-South-north seismic-refraction profile across Caribbean Sea. From Officer et al. (1959). Note
total absence of evidence for midocean ridge spreading center. Location shown on fig. 2. Reprinted with
permission from authors and Pergamon Press Ltd. (@ 1959).
PRESUMED
NORTH CARIBBEAN
FAULT
Figure 3 shows the "lithosphere plates"
required by the sea-floor spreading hypothesis. The presumed Caribbean plate is
bounded on the west and east by subduction
zones, and it is bounded on the north and
south by through-going faults. On the
north is the so-called North Caribbean
fault, which is supposed to consist of the
Bartlett fault on the west, the Cibao graben
in the center, and the Puerto Rico Trench
on the east.
Figure 2 shows the fault systems of the
northern Caribbean.
Earthquake data show that the faults
are not connected (fig. 15; Molnar and
Sykes 1969, p. 1655); bathymetric data support this thesis; and geologic data are even
more conclusive.
The Bartlett fault system lies along a
Paleozoic zone of structural weakness
(Suess 1909, p. 524-525; A. A. Meyerhoff
1966; Anderson 1969; Bonis 1969). Although strike-slip movements take place
along the fault system, dip-slip movement
has predominated from early in the fault
zone's history (Anderson 1969; Bonis 1969)
This statement is substantiated not only by
field studies of the fault in Guatemala (Anderson 1969; Bonis 1969), but also by extrapolation of Cretaceous structural trends
between Cuba and Hispafiola (A. A. Meyerhoff 1966). On the west the fault dies out in
central Guatemala (Anderson 1969), and on
the east it ends due south of Oriente Province, Cuba (A. A. Meyerhoff 1966). It never
reaches the Cibao graben.
The Cibao graben is isolated and does
not join either the Bartlett fault system on
the west or another fault zone on the east
(A. A. Meyerhoff 1966; Khudoley and Meyerhoff 1971). Dip-slip movement has char-
FIG. 15.-Earthquake epicenters of Caribbean. From Sykes and Ewing (1965) and Molnar and Sykes
(1969). Published with permission of authors, American Geophysical Union, and The Geological Society of
America.
CONTINENTAL DRIFT, IV
acterized most of its history. There is no
measurable strike-slip component in excess
of a few kilometers. The fault probably originated during the Paleocene-early Eocene,
much later than the Bartlett fault system
(Khudoley and Meyerhoff 1971).
The age of the Puerto Rico Trench is
post-early Eocene (Van Voorhis and Davis
1964; Monroe 1968). The fault system dies
out on the western and eastern ends. The
system forms a graben, and predominant
movement is dip-slip (Sykes and Ewing
1965; Molnar and Sykes 1969, p. 16571658). The Puerto Rico Trench abruptly
cuts the west-northwest-east-southeast early Eocene-Cretaceous trends of Puerto Rico
and the Virgin Islands. These trends strike
obliquely across the Puerto Rico Trench
and have been mapped with the magnetometer (Van Voorhis and Davis 1964).
Thus, the northern Caribbean is characterized by three unconnected fault systems
of different ages.
To circumvent the fact that the Bartlett,
51
Cibao, and Puerto Rico fault systems are
separate, Donnelly (1967)-following
Barr
(1958)-postulated
that the so-called North
Caribbean fault crosses the Virgin Islands
via the Anegada Trough, passes south of
Puerto Rico to the Enriquillo graben of
Hispaiola, and joins the Bartlett fault zone
west of Haiti. This postulate encounters
even more serious problems. Not only are
the ages of the Bartlett and Enriquillo
faults very different, but also there is no
earthquake activity or fault zone south of
the Dominican Republic and Puerto Rico
(Sykes and Ewing 1965; Molnar and Sykes
1969). Ball and Harrison (1969) also have
reviewed some of the difficulties in postulating a North Caribbean fault.
PRESUMED
SOUTH CARIBBEAN
FAULT
The so-called Caribbean plate also has to
be bounded on the south by a through-going fault. Figure 16 shows the general structure of the Trinidad-Barbados Ridge area
of the southeastern Caribbean. The El Pilar
CONTOURS
IN FM.
4-ANTICLINE OR ARCH
SYNCLINE
OR TROUGH
FAULT OR FAULT ZONE
D
PROMINENT UNCONFORMITY
(EDGE OF BASIN
60
\0
40
20
(FROM
BASSINGER
ET AL.,19711
FIG. 16.-Major structural elements of southeastern Caribbean. Locations of figs. 17, 18, 19, and 20
are shown. From Bassinger et al. (1971). Published with permission of authors and The American Association of Petroleum Geologists.
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
52
fault truncates the east-northeast regional
strike of Trinidad and Venezuela, and it
may extend beneath the CariacoTrench, to
continue its east-west strike on the mainland as far as Valencia. West of Valencia,
most sea-floorspreadersconnect the El Pilar
fault with the Oca fault north of the Gulf of
Maracaibo (fig. 15), but there is no evidence
of a connection across the 350-km stretch
between the Gulf of Maracaibo and Valencia. Apart from its discordanttrend relative
to the El Pilar fault, the Oca fault is supposed to pass westward through northwestern Colombia and/or Panama into the Pacific. No surface faults and no epicentral
zones exist in this area. The Oca fault dies
out just west of the Guajira Peninsula of
northeastern Colombia (fig. 15). The problems were summarized briefly by Ball and
Harrison (1969), but were expressed very
nicely by Molnar and Sykes (1969, p. 16601661), in what may be described as classic
understatement: "Hence, in northwestern
South America, the present data do not ap-
o
(0
KM
--SEDIMENTS
(FROM
BASSINGER
ETAL197,1
+--I"BASEMENT"
FIG. 17.-North-south seismic-reflection profile
G, east of Tobago, across El Pilar block and fault.
Location shown on figs. 1 and 16. From Bassinger
et al. (1971). Published with permission of authors
and The American Association of Petroleum Geologists.
N
SECTION
pear to define a consistent pattern. There is
some suggestion of underthrusting of the
Pacific under South America from the seismicity, but other complexities are present.
Moreover, the present mechanism solutions
do not seem to clarify the tectonic pattern
very much."
Surfaceand geophysical data from Trinidad, northeasternVenezuela, and the areas
offshore show that the El Pilar and Oca
faults are characterized by minor strikeslip and large-scale dip-slip movements.
Figure 17 depicts the south end of the Barbados Ridge far east of Tobago at the eastern end of the El Pilar fault, close to the
point where it cannot be traced farther east
by geophysical methods or by epicenter
patterns. The gentle drag resulting from
dip-slip movement and the total absence of
evidence for strike-slip movement are noteworthy.
Figure 18 shows a section just east of
Tobago, which also crosses the El Pilar
fault. The evidence for dip-slip motion is
clear, but evidence for strike-slip movement
is negative. Figure 19, of the Dragon's
Mouth between the Northern Range of
Trinidad and the Paria Peninsula of Venezuela, shows the same type of evidence.
North of the line of section of figure 19, the
section is flat-lying and almost undisturbed
-a typical post-early Eocene section of the
Venezuelan continental shelf. The absence
of any evidence for an east-west, throughgoing strike-slip fault on the shelf or across
the southern part of the Lesser Antilles arc
(fig. 20) eliminates Barr's (1958) suggestion
that the South Caribbean fault passed
south of Grenadaand north of the shelf off
H
S
FIG. 18.-North-south seismic-reflection profile H, east of Tobago, across El Pilar block and fault.
Location shown on figs. 1 and 16. From Bassinger et al. (1971). Published with permission of authors and
The American Association of Petroleum Geologists.
CONTINENTAL DRIFT, IV
FIG. 19.-North-south seismic-reflection profile
I, between Paria Peninsula and Northern Range
of Trinidad. Crosses El Pilar block and fault. Location shown on figs. 1 and 16. From Bassinger et al.
(1971). Published with permission of authors and
The American Association of Petroleum Geologists.
Venezuela. Geophysical data published by
Lattimore et al. (1971) and Peter and Lattimore (1971) also eliminate the possibility of
a South Caribbean fault. Therefore, as is
true of the so-called "North Caribbean
fault," there is no evidence for a throughgoing "South Caribbeanfault."
EPICENTERS
AND STRUCTURE OF
EASTERN CARIBBEAN
It is difficult to resist putting frosting on
a cake, and in the eastern Caribbean, the
frosting is available. Therefore, it should
not be wasted.
Figure 4 shows the Chase and Bunce
(1969) interpretation of a lithosphere plate
sliding under the Lesser Antilles arc and the
Barbados Ridge, which is east of the Lesser
Antilles arc. If Chase and Bunce are correct, the epicenters in this area should be
distributed east of and beneath the Barbados Ridge on the south. Figure 21 shows
clearly that the epicenters are uniformly
just west of, beneath, and just east of the
Lesser Antilles arc, but do not underlie, or
fall east of Barbados and the eastern Barbados Ridge. Moreover, because the epicenters do not underlie the Ridge or fall
53
east of the Ridge, the Chase and Bunce
hypothesis, if correct, would record the only
exception to island-arc epicenter distributions in the world. In short, figure 21 shows
that the Barbados Ridge is aseismic.
The importance of figure 21 cannot be
overstated. This figure shows that, if subduction of the Caribbean by the so-called
Americas plate is taking place, the Barbados Ridge (which is part of the South American continent and of the alleged Americas
plate) is not affected. This clearly is not
possible. Nor can it be argued that the Barbados Ridge has been rotated into its present position, because the structures underlying the Ridge and exposed on Barbados
island parallel those of Tobago, Trinidad,
and northern South America.
A very similar situation exists in the
southwestern Pacific, from Tonga-Kermadec on the north, onto North Island (New
Zealand) on the south (Hatherton 1970,
1971). According to the seismic data (on
the assumption that the sea-floor spreading
hypothesis is correct), the eastern part of
North Island is being subducted under the
rest of North Island, a concept which, as in
the Lesser Antilles, is ruled out by the geology and geophysics; eastern North Island
is Permian or older.
In the Caribbean, other problems also
arise.
1. The concept that the so-called Caribbean plate was inserted from the Darwin
Rise of the Pacific is invalidated by the
facts that (a) the North and South Central
American orogens (fig. 2) were in existence
by Early to middle Cretaceous time (A. A.
Meyerhoff 1967; Barr and Escalante 1969)
FIG. 20.-South-north seismic-reflection profile J, west of Grenada. Location shown on figs. 1 and 16.
From Hurley (1966). No through-going faults are present. Hence, so-called South Caribbean fault does not
pass north of Venezuelan shelf, as suggested by Barr (1958).
54
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
FIG. 21.-Distribution of epicenters in eastern Antilles. From Molnar and Sykes (1969). Published with
permission of authors and The Geological Society of America.
and (b) the sediments in the Middle America Trench are fiat-lying (Ross 1971).
2. The latest hypothesis-that
the Caribbean plate formed by sea-floor spreading
during Late Cretaceous-early Tertiary time
(Edgar et al., in Purrett 1971)-is negated
by the fact that (a) there is no spreading
center in the Caribbean; (b) the Cretaceous
and younger strata are flat-lying adjacent
to the Greater Antilles and Caribbean orthogeosynclines; (c) the Barbados Ridge,
550 km long, fronts two-thirds of the Lesser
Antilles arc (thus, 550 km of the width of
the Caribbean plate had to be in existence
since pre-Late Jurassic time); and (d) the
Aves Ridge does extend the full width of the
Caribbean Sea and has existed since prelatest Cretaceous time. These points also
eliminate the Ball and Harrison (1969)
"extension" hypothesis. Edgar et al. (in
Purrett 1971) brushed aside the absence of
a spreading center and attributed the origin
of the Caribbean ocean basin to the tearing
of North America from South America. In
effect, Edgar et al. had to propose another
hypothesis of ocean-basin formation.
3. La Desirade Island also is of pre-Late
Jurassic origin, but maintains its east-west
structural grain and its position east of the
postulated Lesser Antilles subduction zone.
4. According to all pre-drift reconstructions (see Bullard et al. 1965), the area of
the Lesser Antilles was adjacent to West
Africa. Some credence might be given to this
concept if there were correlative orthogeosynclines in West Africa, but there are none.
CONTINENTAL DRIFT, IV
5. According to the sea-floor spreaders,
the alleged Americas plate had moved more
than 500 km between Late Jurassic and
Paleocene times. This amount of movement
means that La Desirade and the Barbados
Ridge should have been subducted by Paleocene time. No hypothesis of sea-floor
spreading explains the presence of these two
ancient segments of older rocks east of the
alleged subduction zone. According to the
measurements of all sea-floor spreaders
(the half rate of spreading is 1-1.5 cm per
year), Barbados Ridge and La D6sirade
Island now should be subducted, without
trace, 200-400 km beneath the Lesser Antilles arc.
The amount of supposed subduction
which must have taken place, the aseismic
nature of the Barbados Ridge, the necessity
for a medium- to high-grade metamorphic
terrane between the Araya-Paria Peninsulas, the Collette et al. (1969) and Bassinger et al. (1971) geophysical data from
the Barbados Ridge, and the time-sequence
implications of the structural trends on
Barbados were not taken into account by
Daviess (1971). Daviess' failure to consider
these facts in his reconstruction negates his
interpretation of Barbados in terms of seafloor spreading.
6. If the presumed Americas plate is
descending beneath the Caribbean, that
part of the plate which is east of the Lesser
Antilles has to be moving at a faster rate
than the rest of the plate.
7. Finally, the Mohoroviid6 discontinu-
55
ity is 14 km below sea level east of the Barbados Ridge and west of the Aves Ridge,
as shown on figure 22. The same is true for
the eastern Pacific and the western Caribbean. These facts make no sense at all if the
alleged Americas plate is moving westward
beneath the Caribbean and if the presumed
Cocos (part of the Eastern Pacific) plate is
moving northeastward beneath the Caribbean (L. Austin Weeks, oral communication, December 9, 1970).
SUMMARY AND CONCLUSIONS
All current efforts to fit the Caribbean
rim and basin into "the new global tectonics" mold fail every geologic test and have
meager, if any, geophysical support.
1. Insertion of a Caribbean "plate" between the North and South American continents from the Pacific Ocean, as proposed
by Mattson (1969), Edgar et al. (1971a),
and Malfait and Dinkelman (1971), is an
untenable hypothesis unless the "plate"
was inserted before Late Cretaceous time.
2. Although the JOIDES Leg 15 boreholes were not drilled to the base of the
sedimentary section, Mattson's (1969) and
Malfait and Dinkelman's (1971) early Tertiary date of insertion is precluded by closure of the postulated zone of entry in Central America by the pre-Late Cretaceous
age of the Middle America Trench and associated orogenic belt.
3. The mobile plate concept requires
through-going boundary faults on the north
E
w
0
0
KM
5
5
IN 10
10
15
15
DEPTH
20
W
(FROM
BUNCE ET AL., 1971 )
0
100
200 KM
E
20
VELOCITIES IN KM/SEC
VERT. EYAG.= 14: I
FIG. 22.-West-east cross section of Aves Ridge-Lesser Antilles arc-Barbados Ridge, from Bunce et al.
(1971). Note that Mohorovcid discontinuity is at same depth beneath the so-called Caribbean plate on
west and Americas plate on east. Published with permission of authors and Wiley-Interscience.
56
A. A. MEYERHOFF AND HOWARD A. MEYERHOFF
and south of the Caribbean,but such faults
do not exist.
4. The conclusive geophysical and geological evidence that movement along the
several discontinuousfaults on the northern
and southern margins of the Caribbean
basin has been vertical, with only minor
strike-slip displacement,precludesthe longdistance lateral shifts postulated by the
mobilists.
5. The alternative idea of in situ origin
by Caribbean sea-floor spreading (Edgar
et al., in Purrett 1971) fails to produce an
active or dormant midocean ridge, a corresponding epicenter belt, or linear magnetic
pattern.
6. The claim that the so-called Americas
plate is underriding and subducting the
eastern margin of the Caribbean basin
along the Barbados Ridge-Lesser Antilles
arc is vitiated (a) by the presence of preLate Jurassic structural elements (Barbados Ridge and La Desirade), which, according to the requirements of the concept, should have been subducted at least
70 m.y. ago; (b) by the extension of the Lesser Antilles Trench west, instead of east, of
the Barbados Ridge; and (c) by the aseismic nature of the Barbados Ridge.
In contrast to the shifting hypotheses of
the mobilists, the cumulative geophysical
and geologic evidence combines to provide
an integrated, if incomplete, interpretation
of Caribbean history, at least since Late
Jurassic time.
1. The presence of Jurassic (or older)
orthogeosynclines on the north (Greater
Antilles) and south (Caribbean) shows
that the Caribbean basin had its present
east-westlength since the Jurassic Period.
2. The Jurassic date, the character of the
rocks on La Desirade, and the east-west
structural trend indicate that this island is
the eastern outpost of the Greater Antilles
orthogeosyncline,raised to its present elevation by overthrust at the edge of the Lesser
Antilles Trench.
3. The Aves Ridge, interpreted to be a
product of compression directed from west
to east, and antedating the formation of
the Lesser Antilles arc, proves that the Caribbean basin had its present north-south
width in pre-Late Cretaceous time.
4. Barbados Ridge is a pre-Late Jurassic
feature, genetically (stratigraphically and
structurally) related to, and an integral
part of, the Caribbean orthogeosyncline,
whose tectonic history it has shared, at
least into early Tertiary time. The eastnortheast strike of the pre-middle Eocene
structures and stratigraphictrends parallels
those of Trinidad and Venezuela, and demonstrates that the Barbados Ridge has not
changed position since Mesozoic time.
5. The Lesser Antilles arc probably is an
early Tertiary feature, a successor to the
Aves Ridge.
6. Continued compressive stresses from
the west have given the Lesser Antilles arc
its north-south orientation and have superimposed a younger north-south geomorphic
pattern on the older (Late Cretaceous-early
Eocene) east-northeast structures of the
Barbados Ridge.
7. The west-to-east compression, caused
by compression against, and rotation of,
the Caribbeanbasin, apparently caused the
overthrust that has exposed the Oceanic
Formation on Barbados and brought La
D6sirade to the surface.
8. Overthrust of the eastern margin of
Caribbean basin, rather than underthrust
of the alleged Americasplate, is favored by
the structures shown in Barbados Ridge by
Chase and Bunce (1969) and Bunce et al.
(1971), as well as by the salients in the
Lesser Antilles arc and the elevation of the
Limestone Caribbees, La Desirade, and
Barbados island.
Few, if any, of the known geological features of the Caribbean are adequately accounted for, or even considered, by the adherents of "the new global tectonics." The
geophysical data on which they depend are,
at best, equivocal, and some interpretations
even lack that support (e.g., the in situ
origin of the Caribbean). The "instant reinterpretations" of Caribbean history advanced as new data become available make
mobilist dicta about other island arcs sus-
CONTINENTAL DRIFT, IV
pect. The data published by Scholl et al.
(1968, 1970) in the southeasternPacific, and
by Hatherton (1970, 1971) in New Zealand,
also challenge "the new global tectonics"
concept.
We believe that our interpretation of the
Caribbean presented here will not have to
be changed after the next dredge haul or
core is taken from the ocean floor.
ACKNOWLEDGMENTS.-Typing was done by
Miss Amy Lee Brown, Mrs. Carol Thompson,
and Miss Ernestine R. Voyles. Drafting was
done by Mrs. Kathryn L. Meyerhoff.
We are grateful to scores of colleagues who
have encouraged and aided us in this work.
Among them are Elizabeth T. Bunce, S. A.
Bush, Joseph R. Curray, John I. Ewing, L. K.
Fink, Jr., Bruce C. Heezen, Norman J. Snelling,
John F. Tomblin, and L. Austin Weeks, who
supplied the writers with valuable data for
57
this paper. L. K. Fink, Jr., was particularly
generous in supplying us with radiometric
dates from La D6sirade. We also thank Dr.
Fink's co-workers, J. Mattinson, C. A. Hopson,
C. T. Harper, and J. J. Stipp. Norman J.
Snelling and John F. Tomblin were most kind
to provide us with the radiometric dates from
Tobago. We are grateful to M. E. Bickford,
Meade Cadot, H. A. Ireland, J. A. Peoples,
and Curt Teichert for valuable suggestions and
criticisms when this paper first was presented
orally on February 18, 1971, at The University
of Kansas, Lawrence, Kansas. We particularly
appreciate the thorough reviews by Jules
Braunstein, Peter Misch, and Benjamin A.
Tator-reviews which strengthened this paper,
a version of which was presented at the Sixth
Caribbean Geological Conference, Margarita,
Venezuela, in July 1971 under the title, "Tectonics of the Eastern Caribbean." These acknowledgments in no way imply agreement
with our opinions and conclusions.
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