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TECTONIC LINEAMENTS IN THE CENOZOIC VOLCANICS

Or" SOUTHERN GUATEMALA:

EVIDENCE FOR A BROAD CONTINENTAL PLATE BOUNDARY ZONE

(NASA-Ch-17545b) ZICTCNIC llbkAhINTS IN Tb! tiE5-15499

CYNUZOIC YGLCAHICZ GF SGUTfkFK GU172rAli:

XvIDENCB FCB a EfCAL CCN11t 1611L FLAIR

LCUNLARY 20ht (JEt Frcpulsicr Lab.) 23 F Unclas

HC 11021LIF A01 -SCL C8b G3/43 14306

k/

M. Baltuck

Department Geology

Tulane University

New Orleans, LA 70118

'^ _i ^► Q1a, J^O

T. H. Dixon

Jet Prcpulsion Laboratory

Mail Code 183-701

4800 Oak Grove Drive

Pasadena, CA 91109

Submitted to Geology

October, 1984

This report was prepared for the Jet Pripulsior Laboratory,

California Institute of Technology, ,nonsored by the 'National

Aeronautics and Space Administration.
ABSTRACT

The northern Caribbean plate boundary has been undergoing left-lateral

strike slip motion since middle Tertiary time. Current rates are

estimated between 2 and 3.7 cm/yr. The western part of the boundary

occurs in a complex tectonic zone in the continental crust of Guatemala

and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly

Jocotan-Chamelecon faults. Previously mapped offsets along these faults

do not appear to be capable of accommodating the required cumulative

displacement.

We have mapped prominent lineaments visible in radar imagery in the

Neogene volcanic belt of southern Guatemala and western E1 Salvador and

interpret them to suggest southwest extensions of this already broad plate

boundary zone. Because these extensions can be traced beneath Quaternary

volcanic cover, we suggest that this newly mapped fault zone is active and

is accommodating some of the strain related to motion between the North

American and Caribbean plates. Onshore exposures of the MotoquaPolochic fault systems are characterized by abundant, tectonically

emplaced ultramafic rocks. Because several Leg 84 sites that recovered

ultramafic rocks occur within our postulated fault zone, we suggest a

similar mode o.f emplacement for these off-shore ultramafics.
INTRODUCTION

Geological studies of the northern Caribbean plate boundary can reveal

the history of interaction betweer; the North American and Caribbean

plates. Such studies may also yield insight into broader tectonic

questions, such as the opening history of the Atlantic Ocean (e.g.,

Anderson & Schmidt, 1983). The Northern Caribbean plate boundary has

undergone left-lateral strike-slip motion since at least middle Tertiary

time. Current rates of strike-slip motion are estimated between about 2

cm/yr (MacDonald and Holcombe, 1978) to nearly 4 cm/yr (Sykes et al,

1982). The western part of the boundary occurs in a complex tectonic zone

in the continental crust of Guatemala, southernmost Mexico, and western

Honduras along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon

faults (figure 1). The Chixoy-Polochic fault system may currently be the

most active fault (Muehlberger and Ritchie, 1975) but the actual amount of

offset along this and the other related faults is contentious.

Previous interpretations of regional structure in Northern Central

America have emphasized the influence of the subducting Cocos plate and

associated compressional tectonism on the overlying lithosphere. For

example, Carr (1976) related transverse breaks in the subducted Cocos

plate to northeasterly lineaments in the overlying Caribbean plate.

Associated northerly and northwesterly lineaments were interpreted as

normal and right-lateral faults respectively.

Recent results from site surveys and drilling during Leg 84 of the

Deep Sea Drilling Project (DSDP) strongly suggest a lack of mechanical

coupling between the subducted and overriding plate along the Middle

America trench, because there is no evidence for an an accretionary wedge

(e.g. Aubouin et al, 1982; Von Huene et al, In Press; Aubouin and Von

Huene, In Press).

-1-
If coupling between the Cocos and Caribbean plates is not a major factor

in deformation of the overriding Caribbean plate, then regional Neogene

and Quaternary structures may be largely controlled by the strike-slip

boundary between the Caribbean and North American plates.

In this paper, we interpret lineaments visible in radar imagery of

Southern Guatemala to suggest southwest extensions of this already broad 

fault zone. Because these lineaments can be traced beneath Quaternary 

volcanic cover, we suggest that this remapped plate boundary zone is

active and is accommodating some of the strain related to motion between

the North American and Caribbean plates. The existence of this fault zone

also suggests another interpretation of the affinity of ultramafic rocks

recovered offshore during DSDP Leg 84. These rocks are currently thought

to be related to ultramafic material exposed to the southeast in the

Nicoya complex of Costa Rica. To reach their present location from a

position near the Nico;a complex would necessitate large amounts ( N500 km)

of right-lateral strike-slip motion along major faults parallel to the

middle America Trench, for which there is little physical evidence.

GEOLOGIC SETTING OF NORTHERN CENTRAL AMERICA

The geology and physiography of Guatemala (fig. 1) are dominated by

the left-lateral strike-slip boundary between the North American and

Caribbean Plates, and the Middle America Trench off the Pacific Guatemala

coast where the Cocos Plate is subducted beneath Central America. The

former feature is expressed in the Central Cordillera (Dengo, 1973), a

geologically complex region exposed along the Motagua River valley and

mountains to the north and south. Several large serpentinized ultramafic

bodies occur in this fault zone and were emplaced during the Cretaceous

(Dengo, 1972). The serpentinites of the Central Cordillera are associated

with metavolvanic and metasedimentary rocks of the E1 Tambor Formation

-2-
GEOLOGIC SETTING (Continued)

(McBirney and Bass, 1967) including phyllites and recrystallized

limestone. Near Sansare south of the Motagua fault, limestone occurs with

pillow basalts and radiolarian . p ert (Wilson, 1974). The entire sequence

is considered Mesozoic and possibly as young as Campanian, deformed and

emplaced during or after Campanian time. Structural features indicate

thrusting to the north over the Maya Block and to the south over the

Chortis Block, the main crustal block in the western part of the Caribbean

Plate (Dengo, 1973). Thus, the ultramafics rocks were tectonically

emplaced, probably as a result of convergence between the North American

and Caribbean plates (Malfait and Dinkelman, 1972).

South of the Motagua Fault several stratigraphic assemblages have been

described. Between the Motagua and Jocotan-Chamelecon Faults are

high-grade (garnet-staurolite) metamorphic sediments and igneous rocks, as

well as silica-rich schists, gneisses, amphibolite, and marble. In the

area of Sierra de Omoa in Western Honduras, Horne et al (1976) describe a

northern low-grade metavolcanic assemblage, a central medium-grade

metamorphic assemblage and a southern assemblage of low-grade

metasediments intruded by granitic rocks of various ages, but mainly

Jurassic or older.

Overlying the tectonized metabasalts of the Chortis block is a thick

sequence of Mesozoic sediments. Late Triassic to Early Jurassic

sandstones and shales are overlain by a continental sandstone of probable

Late Jurassic to Early Cretaceous age. Above this a thick early

Cretaceous limestone extends from southern Guatemala to northern Nicaragua.

Post-Albian rocks are predominantly continental redbeds with

intercalations of limestone and gypsum. These beds are locally disrupted

by mid-Cretaceous to early Tertiary intrusive rocks. The Tertiary

section contains Eocene or older red beds, restricted marine sedimentary

I

deposits on the Caribbean side of the Chortis Block and Tertiary basalts

and andesites which form the basal part of the Volcanic Highlands of

Guatemala.

-3-
()

The Volcanic Highlands are the product of subduction of the Cocos

Plate under Central America at the Middle America Trench. The oldest

volcanics are thick, extensive flow basalts and andesites of probable

Oligocene age. These are overlain by Miocene to Pliocene rhyodacitic

ignimbrites and a discontinuous chain of high relief Quaternary volcanos

parallelling the Pacific coast. Smaller Quaternary cones are associated

with north-south trending faults and grabens in western El Salvador,

southeastern Guatemala and Central Honduras (Williams and McBirney, 1969).

METHODS

In order to investigate possible tectonic movement south of the

presently defined strike-slip fault zone between the North American and

Caribbean plates, synthetic aperture radar (SAR) imagery was examined to

map lineaments in the Tertiary and Quaternary Volcanic Highlands. The

image data were obtained in November 1981 during the second flight of the

Space Shuttle, which carried the Shuttle Imaging Radar Experiment

(SIR-A). A description of the SIR-A experiment is given in Elachi et al

(1982). Image resolution of the SIR-A imagery is about 40 m. The

incidence angle (off nadir) is 50 0 , +30.

Imaging radar has been used extensively in geological reconnaisance of

tropical regions (e.g. Wing, 1971). The sensitivity of radar backscatter

to surface slope means that it is an excellent tool for investigating

t *tonic problems where individual structural elements are likely to have

topographic expression. Structural interpretations from radar imaging

must take into account the direction of radar illumination, since scarps

perpendicular to this direction are more strongly enhanced than those

parallel to it (MacDonald, 1969; Ford, 1980). The available SIR-A imagery

has only one illumination direction (from the northwest); consequently

structural elements trending northeast-southwest will be enhanced, while

-4-
METHODS (Continued)

those trending northwest-southeast will be less apparent.

Analysis of radar imagery in high relief terrain must also take into

account "fold-over" distortion, or apparent fore-shortening of slopes

facing the radar illumination vector. The effect is large for steep

incidence angle systems (e.g. NASA's Seasat Satellite) but is much less

apparent for the SIR-A system with its more shallow incidence angle.

For convenient comparison of radar features to geological features the

imagery was printed at the same scale (1:500,000) as the geologic map.

Lineaments of probable tectonic origin 5 km or more in length were

considered for SIR-A. The lineaments were recorded on an overlay and

compared to trends of faults mapped on the Geologic Map of Guatemala

(Bonis et al., 1970). Linear features with no obvious tectonic

association such as short drainages were not considered. The following

discussion refers only to the trends of lineations in the Volcanic

Highlands in order to separate younger tectonism from pre-Tertiary

deformation.

RESULTS & DISCUSSION

Figure 2 shows the image data and interpreted lineaments. Figure 3

shows the Rose Diagram indicating trends of lineaments in the Volcanic

Highlands. Two major groups of lineament orientations stand out: a

north-northwest trend and an east-northeast trend. The stippled wedges in

the figure indicate the trends of faults in the Central Cordillera

compiled from the Geologic Map of Guatemala. The larger stipple

(north-northwest trend) corresponds to extensional faulting while the

smaller stipple (east-northeast) indicates the range of left-lateral

strike-slip fault trends. Quaternary volcanic cover is cut by both groups

of lineations, suggesting tectonic activity in this area since Pleistocene

time.

_5_
The Rose diagram illustrates a strong correspondence of lineaments in

young Tertiary and Quaternary volcanics to older but still active

structural features of the Central Cordillera, i.e, to the exposed fault

zone that marks the plate boundary between North America and the

Caribbean. The lineaments most probably reflect accommodation in the

volcanic cover of movement along underlying faults. A similar

accommodation was suggested by Erdlac and Anderson (1982) in the cental

Cordillera of Western Guatemala. The simplest explanation for the

correspondence between lineaments in the volcanic cover and the exposed

plate boundary fault zone is that the lineaments mapped in the volcanic

cover mark southward extensions of the active Motogua-Polochic fault

system . Thus, the plate boundary fault zone may be considerably wider

and more complex than previously recognized.

Comparison of on-land structural cross sections with those developed

offshore reveals a structural similarity which implies that the offshore

margin is a continuation of a broad plate boundary. Dengo (1973)

presented a generalized north-south cross-section through Central America

showing a series of high angle strike slip faults in the Central

Cordillera trending east-west which continues through the Volcanic 

Highlands. Dip-slip motion also occurs on these faults, and the mapped or

estimated vertical offset along them may be as much as 500m with the

down-dropped block generally to the south (Sanchez-Barreda, 1981).

Seismic profiles of the Guatemalan margin (Ladd et al., 1982) reveal a

series of landward-dipping reflectors. Based on DSDP Leg 84 results

(Aubouin et al., 1982) these have been interpreted as the tops of normally

faulted and tilted blocks of continental margin material, with the faults

striking nearly east-west and dipping south. We therefore suggest that

the plate boundary fault zone exposed in Guatemala may extend to the south

and west to include the continental margin of Guatemala (Figure 4a)

similar to the plate boundary originally proposed by Molnar & Sykes (1969).

-6-
RESULTS & DISCUSSION (Continued)

The possibility that the zone of deformation associated with the

present boundary between the North American and Caribbean plate in Central

America is much broader than previously suggested has a number of

important implications. We will address two; (1) the origin of

ultramafic rocks discovered offshore near the Middle America Trench during

Deep Sea Drilling Project (DSOP) Leg 84, and (2) the controversy

surrounding mappable offsets along the Motogua and Chixoy-Polochic fault

zones.

1. The recovery of ultramafic rocks during drilling of DSDP Leg 84 off

the coast of Guatemala gave rise to the controversial problem of their

provenance. In all of the sites on Leg 84 where basement was reached

(566, 567, 569, 570; fig. 1) mafic and/or ultramafic rocks were

recovered. Primarily consisting of serpentinite with minor vestiges of

the original peridotite, metadiabase, metagabbro and metabasalt, the rocks

were generally similar to the ophiolitic assemblages described on land in

Costa Rica (the Nicoya Complex; Dengo, 1962) and in Guatemala (Williams,

1960; Rosenfeld, 1980).

The serpentinized ultramafic rocks of the El Tambor formation outcrop

along the exposed length of the Motagua-Polochic-Chamelecon fault system

(geologic map of Guatemala, 1970; fig. 1), the left-lateral strike-slip

boundary between the North American and Caribbean plates. These rocks are

related to a pre-Tertiary history of convergence along this plate boundary

(e.g., Malfait and Dinkelman, 1972). The full extent of this plate

boundary is obscured by a broad belt of Tertiary to Quaterary volcanoes,

the product of offshore subduction along the Middle America Trench. Thus

the southern and western edges of the plate boundary are unknown.

The shipboard scientific party (Aubouin et al, 1981) suggested that

the ultramafics recovered on Leg 84 were related to the Santa Elena

peridotites of the Nicoya Complex, requiring strike-slip displacements of

-7-
RESULTS & DISCUSSION (Continued)

about 500 km. While faults subparallel to the required trend exist (see

Dengo 1973) these are mapped a, normal faults with very limited lateral

offset. To our knowledge theve is no offshore or onshore expression of a

major strike-slip fault subparalleling the middle America coast between

Costa Rica and Guatemala. However, Von Huene et al (in press) suggest

transcurrent faulting along an ancestial offshore Polochic-Motugua system

as an explanation of bench topography and basement deformation in the

Guatemalan continental slope.

We suggest that the ultramafics of the Guatemalan continental slope

are related to those exposed on land in outcrops of the E1 Tambor

Formation (McBirney and Bass, 1969). Figure 1 shows the known extent of

ultramafics in Central America including those drilled on Leg 84. The

Leg 84 material was recovered south of the exposed trend of the Guatemalan

ultramafics along the Motogua-Polochic fault zone, but can be directly

related to the broad tectonic zone we infer on the basis of the radar

imagery.

i

2. MacDonald and Holcombe (1978) used magnetic lineations in the Cayman

Trough to estimate the relative motion of the North American and Carib an

plates at 2 cm/yr from 0-2.4 Ma, and 4 cm!yr from 2.4-8.3 Ma. More

r

recently, Sykes et al (1982) argued that a rate of 3.7 cm/yr must

characterize the easterly motion of the Caribbean with respect to NC'jth

America for at least the last 7 Ma and possibly since 38 Ma (late Eocene)

implying displacements of 1400 km since the inception of spreading in the

Cayman Trough (late Eocene) and more than 250 km of displacement since 7 Ma

(Pliocene time).

The active faulting accommodating motion across this plate boundary is

believed to be concentrated along the Chixoy-Polochic (CP) fault (e.g.

Muehlberger and Ritchie, 1975). However, mapped offsets along this fault

are much less than the total estimated motion across the plate boundary.

Kesler (1971) suggested that the CP fault has accommodated less than

-8-
RESULTS & DISCUSSION (Continued)

150 km of displacement during the entire Cenozoic. Burkhart (1978)

suggested that 132+ 5 km of motion on the CP fault has occurred since

middle Pliocene (7 Ma) or possibly as early ar middle Miocene (15 Ma).

Erdiac'and Anderson (1982) suggested that no more than a few kilometers of

displacement has occurred along the CP fault since the ernplacemer,t of

young volcanic rock; of probable Miocene to Pliocene age.

All of the above workers recognized the possibility that motion

between the North American and Caribbean plates was likely accommodated nn

other faults besides the CP fault. The topographically distinct Motogua

fault zone is a major candidate. The great earthquake of 1976 in

Guatemala occurred along this fault and caused meter-scale left-lateral

displacements over hundreds of kilor.eters (Plafker, 1976; Kanamori and

Stewart, 1978). The Jocotan-Chamelocon fault (fig. 1) is another

candidate to accommodate strain across the North American Caribbean plate

boundary (e.g., Schwarz et al, 1979). Schwarz et al (1979) mapped

Quaternary offsets along the Motogua fault zone to derive slip rates of

.15 to .60 cm/yr. They assumed equivalent slip rates would characterize

the CP and Jocotan-Chamelocon fault zones and estimated a cumulative

displacement of 170 to 685 km between the North American and Caribbean

plate since late Eocene time. This is still significantly less than

} displacements expected if present rates of motion (Sykes et al, 1982) are

1 

extrapolated to late Eocene time.

Based on our observations of recent tectonism within the Tertiary and

Quaternary volcanic belt, we agree with the suggestion of Carr and Stoiber

(1977) that subsididary faults south of the Motogua and Jocotan-Chamelecon

fault zones also take up some of the strain related to motion between the

Caribbean and North American plates. Thus, mappable offsets within the

better exposed northern fault system (Chixoy-Polochic and Motogua) cannot

be expected to equal cumulative displacements inferred from rates based on

magnetic lineations in the Cayman Trough (MacDonald and Holcombe, (1978)

-9-
RESULTS & DISCUSSION (Continued)

or plate motion solutions derived from earthquake slip vectors and

fracture cone azimuths (Sykes et al., 1982).

REFERENCES

Anderson, T H. and Schmidt, V.A., 1983, The evolution of Middle

America and the Gulf of Mexico - Caribbean Sea region during Mesozoic

time: Geological Society of America Bulletin, vol. 94, pp. 941-966.

Aubouin, J., Von Huene, R., Saltuck, M., Arnott, R., Bourgois, J. et

al., 1982, Leg 84 of the Deep Sea Drilling Project. subduction

without accretion: Middle America Trench off Guatemala. Nature,

vol. 297, pp. 458-460.

Bonis, S., Bohnenberger, 0. H., and Dengo, G., 1970, Mapa Geologico de

la Republica de Guatemala City, Guatemala. 1:500000, National

Institute of Geography, Guatemala City, Guatemala.

Bowin, C., 1971, Caribbean gravity field and plate tectonics:

Geological Society of America Special Paper 169, 77 p.

Burkhart, B., 1978, Offset across the Polochic Fault and Guatemala and

Chiopas, Mexico: Geology, vol. 6, pp. 328-332.

Carr, M. J., 1976, Underthrusting and Quaternary faulting in northern

Central America: Geological Society of America Bulletin, vol. 87, pp.

825-829.

Carr, M.J. and Stoiber, R.E., 1977, Geologic setting of some

destructive earthquakes in Central America: Geological Society of

America Bulletin, ol.v 88, pp. 151-156.

Case, J.E. and Holcombe, T.L., 1980, Geologic-Tectonic Map of the

Caribbean Region: U.S. Geological Survey, scale 1:1,250,000.

Dengo, G., 1962, Tectonic-igneous

A.E.J., James, H.L., and Leonard,

volume to honor A, F. Buddington:

pp. 133-161.

sequence in Costa Rica: Engel,

B.F. (eds). Petrologic Studies: a

Geological Society of America,

Dengo, G., 1972, Review of Caribbean serpentinites and their tectonic

implications: Geological Society of America Memoir 130, pp. 303-312.

Dengo, G., 1973. Estructura geologica, historia tectonica y

morfologia de America Central; Centro regional de Ayuda Tecnica

Mexico/Buenos Aires, 52 p.

-10-
Dengo, G., 1984, Mid

America: tectonic setting for the Pacific margin

from southern Mexico to northwestern Columbia, (in review).

Erdlac, R. J. Jr., and Anderson, T. H., 1982, The Chixoy-Polochic

fault and its associated fractures in Western Guatemala: Geo;ogira'i

Society of American Bulletin, vol. 93, pp. 57-67.

Elachi, C., P.rown, W.E., Cimino, J.B., Dixon, T.H., Evans, D.L., Ford,

J.P., Saunders, R. S., Breed, C., Masursky, H., McCauley, J.F.,

Schaber, G., Dellwig, L., England, A., MacDonald, H., Martin-Kaye, P.,

Sabina, F. 1982, Shuttle Imaging Radar experiment, Science, vol. 218,

pp. 996-1003.

Ford, J. P., 1980, Seasat orbital radar imagery for geologic mapping:

Tennessee - Kentucky - Virginia. American Association of Petroleum

Geologists Bulletin, vol. 64, pp. 2064-2094.

Horne, G.S., Clark, G.S., and Pushkar, P., 1976, Pre-Cretaceous rocks

in northwestern Honduras: basement terrane in Sierra de Omoa: American

Association of Petroleum Geologists Bulletin, vol. 60, pp. 566-583.

Kanamori, H. and Stewart, G. S.,1978, Seismological aspects of the

Guatemala earthquake of February 4, 1976: Journal of Geophysical

Research, vol. 83, p: 3427.

Kesler, S. E., 1971, Nature of the ancestral orogenic zone in nuclear

Central America: American Association of Petroleum Geologists

Bulletin, vol. 55, pp, 2116-2129.

Ladd, J.W., Ibrahim, A.K., McMillen, V.J., Latham, G.V., and Von

Naene, R., 1982, Interpretation of seismic reflection data of the

Middle America trench offshore Guatemala. In: Von Huene, R., Aubouin,

J, et al, 1982, Initial Reports of the Deep Sea Drilling Project, vol.

67, pp. 675-690. U.S. Government Printing Office, Washington, D. C.

Macdonald, H. C., 1969, Geologic evaluation of radar imagery from

Darien Province, Panama: Modern Geology, vol. 1, pp. 1-63.

MacDonald, K. C. and Holcombe, T. L., 1978, Inversion of magnetic

amomalies and sea-floor spreading in the Cayman Trough: Earth &

Planetary Science Letters, vol. 40, pp. 407-414.

Malfait, B.T., and Dinkelman, R.G., 1972, Circum-Caribbean tectonic

and igneous activity and the evolution of the Caribbean plate.

Geological Society of America Bulletin: vol. 83, pp. 251-272.

McBirney, A.R., and Bass, M.N., 1967. Structural relations of

pre-Mesozoic rocks in Central America: American Association of

Petroleum Geologists Memoir 11, pp. 229-243.

Minster, J. B. and Jordan, T. H., 1978, Present day plate motions:

Journal of Geophysical Research, vol. 83, pp. 5331-5354.

-11
Middle America regions from focal mechanisms and seismicity,

Geological Society of America Bulletin: vol. 80, pp. 1639-1684.

Muehlberger, W. R. and Ritchie, A. W., 1975, Caribbean-Americas plate

boundary in Guatemala and southern Mexico as seen on Skylab IV orbital

photography: Geology, vol. 3, pp. 232-235.

Piafker, G., 1976, Tectonic aspects of the Guatemalan earthquake of

4 February, 1976: Science, vol. 193, pp. 1201-1208.

Rosenfeld, J.H., 1981: Geology of the Western Sierra Santa Cruz,

Guatemala, Central America; an ophiolite sequence: Ph.D Thesis, State

University of New York, Binghampton, 313 p.

Sanchez-Barreda, L.A., 1981, Geologic evolution of the continental

margin of the Gulf of Tehuantepec in Southwestern Mexico: Ph.D.

Thesis, University of Texas, Austin, 191 p.

Schwartz, D. P., Cluff, L. S. and Donnelly, T. W., 1979, Quaternary

faulting along the Caribbean-North American plate boundary in Central

America: Tectonophysics, vol. 52, pp. 431-445.

Sykes, L. R., McCann, W. R. and Kafka, A. C., 1982, Motion of

Caribbean plate during the last 7 million years and implications for

earlier Cenozoic movements: Journal of Geophysical Research, vol. 87,

pp. 10656-10676.

Von Huene, R., Miller, J., Taylor, D., and Blackman, D., In Press, A

study of geophysical data along the IPOO active margin transect off

Guatemala: In Von Huene, R., Aubouin, J., et al., Initial Reports of

the Deep Sea Drilling Project, vol. 84, U. S. Government Printing

Office, Washington, D.C. 

Williams, H., 1960. Volcanic iiistory of the Guatemalan highlands:

Univeristy of California Publications in Geological Science, vol. 32,

pp. 1-64.

Williams, H., and McBirney, A.R., 1969. Volcanic history of Honduras:

University of California Publication in Geological Science, vol. 85,

pp. 1-101.

Wilson, H.H., 1974, Cretaceous sedimentation and orogeny in nuclear

Central America: American Association of Petroleum Geologists, vol. 58

pp. 1348-1396.

Wing, R. S., 1971, Structural analysis for radar imagery of the

eastern Panamanian isthnus, Parts i and 2: Modern Geology, vol. 2,

pp. 1-21; pp. 75-127.

-12-
Figure 1: Geological sketch map of Central America with major plate

boundaries. Location of ultramafic rocks exposed on the

surface and discovered offshore during Deep Sea Drilling

Project Leg 84 as well as the Nicoya ultramafic complex in

Costa Rica, are also shown. Modified from Dengo (1973).

Figure 2a: Portion of the Geological Map of Guatemala covering the area of

available SIR-A imagery (After Bonis et al, 1970, and

2b: Imagery from Shuttle Imaging Radar (SIR-A) data take 18

2c: Lineations over 5 km in length mapped from SIR-A data take 18

Figure 3: Rose diagram of lineament azimuth from Fig. 2c, scaled to

lineament length.

Figure 4: Comparison of existing plate boundary interpretations: a)

Molnar and Sykes, 1969; b) Bowin, 1976; c) Case and Holcombe,

1980. From Dengo (1984).

-13-
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