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Geological Society of America Bulletin

doi: 10.1130/0016-7606(1959)70[1459:GASOTN]2.0.CO;2 1959;70;1459-1478Geological Society of America Bulletin

PATRICK ARTHUR HILL GEOLOGY AND STRUCTURE OF THE NORTHWEST TRINIDAD MOUNTAINS, LAS VILLAS PROVINCE, CUBA

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BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICAVOL. 70. PP. 1459-1478. 3 FIGS.. 4 PLS. NOVEMBER 1959

GEOLOGY AND STRUCTURE OF THE NORTHWEST TRINIDADMOUNTAINS, LAS VILLAS PROVINCE, CUBA

BY PATRICK ARTHUR HILL

ABSTRACT

The major rock types of the Trinidad Mountains of central Cuba are carbonate rocksand schists of presumable Mesozoic age. Both are carbonaceous, yet devoid of fossils.The carbonate rocks comprise limestones (about 90 per cent), brucite limestone, anddolomites.

The brucite limestone contains chloritic mica (sheridanite). The dolomites, despitelenticulation, might serve as marker horizons. Two varieties are noted, one with crystalsof black euhedral gypsum, the other without them.

Most widespread of the schists is a carbonaceous chloritic mica schist which alternateswith quartz-garnet-mica schist or less commonly grades into epidote or talc schists.

Serpentinites are of two types: a nodular type derived from peridotites, and a fine-grained type (greenstone) derived from microgabbro. The greenstone is older and hasbeen affected by movement of two periods; one (preserpentinization) formed actinolite,the other (postserpentinization) locally developed magnetite-chlorite schist. Other chlo-ritic derivatives include a goethite-chlorite schist and an albite-lawsonite-chlorite schist.The predominant chlorite is clinochlore.

All rocks are isoclinally folded. Cleavage or jointing that might serve to establish over-turning is absent. Strike faults are prominent. Transverse faults, because of the lack oftraceable units, are difficult to recognize.

The mountains appear to form a gigantic anticlinorium. A continuous band of amphib-olite averaging 1200 feet in thickness separates the carbonate rocks and schists of themountains from diorite and granodiorite to the north. Although thrusting may existwithin the mountains, the large northerly directed thrust formerly postulated for thenorthern boundary is disproved.

CONTENTSTEXT Page

Faulting ............................... 1476Page Structure of the Trinidad Mountains ...... 1476

Introduction ............................. 1460 References cited .......................... 1477Acknowledgments ........................ 1460Previous regional investigations ............ 1460 ILLUSTRATIONSGeomorphology .......................... 1461 Fi«<"e PageCarbonate rocks .......................... 1461 1. Location of the Trinidad Mountains ...... 1460

General statement ...................... 1461 2. Postulated Tertiary thrusts in the struc-Limestpnes proper ...................... 1462 tural highs of Cuba ................... 1474Dolomite .............................. 1463 3. Fault systems of the northwestern Trini-Brucite limestone ....................... 1463 dad Mountains ...................... 1475Halloysite ............................. 1464 Platc Facing page

Schists. • • • • • • ---- _ . . . . . . . . . . . . . . . . . . . . . . 1465 j Geologic map and section of the north-General statement . . . . . . . . . . ..... 465 w^em Tr\nidad Mountains, Las VillasCarbonaceous chloritic mica schist ........ 1465 Province, Cuba ............ ....... 1459

uartz-mica-garnet schist ................ 1465 2 Panoramas 1464lack argillite. . . . . . . . . . . . . . . . . . . . 1467 3; photomicrographs \ [ \ [ ' '.'.'".'.'.'. . . . . . . . . H65

„»Epidote-quartz-mica schist ............... 1468 .................Age of the carbonate rocks and schists ...... 1468 TABLESIgneous rocks ............................ 1468 Table Page

General statement ................. 1468 l- x-ray powder lines of sheridanite ........ 1466Fine-grained serpentinites ................ 1468 2' Standard x-raX powder lines for sherida-Schistose serpentinites and chloritic schists. 1469 7 ,, mte ..... . Y. ..... , , • „ • • • • .: .........Nodular serp'entinites and olivine rocks. . 1471 J ̂ ^jT,£££ff analysisAmphibolites . . . . . . . . . . . . . . . . . . . . . . . . 42 Of halloysite .... . P . . . . g . P .... . . . . . . . 1467Problems of the serpentinites ............. 1474 5. Semiquantitative spectrographic analyses

Structural geology ........................ 1476 of igneous rocks ...................... 1473Folding ................................ 1476 6. Azimuths and tentative ages of faults. . . . 1476

1459



1460 P. A. HILL—NORTHWEST TRINIDAD MOUNTAINS, CUBA

INTRODUCTION

The Trinidad Mountains of central Cuba(Fig. 1) lie almost wholly within La VillasProvince and include the sierras of Trinidad,San Juan, and Sancti Spiritus. They rise to a

Thanks are due the Alonso family of Cuba fortheir hospitality and also to Mr. RichardColligan, the Diaz de Villegas Company, andthe late George Sicklick.

Technical help was rendered by Mr. Walter

FIGURE 1.—LOCATION OF THE TRINIDAD MOUNTAINS

maximum height of 3792 feet (Pico Potrerillo)and consist of isoclinally folded limestones andschists, which in the area of Plate 1 dip steeplynorth and northwest. The rocks lack fossils andare of unknown age. However they are olderthan the dioritic intrusions to the north and theCretaceous sediments to the west (Thiadens,1937).

In some areas, serpentinites associated withthe limestones are accompanied by pyrite. Thelargest pyrite deposit is at Minas Carlota (Hill,1958b).

Field work was conducted by the author aloneduring July and August 1951 and with theassistance of Mr. Edward Lewko of UraniumCity, Saskatchewan, from December to Febru-ary 1952-1953.

Laboratory work comprised examination ofthin sections and mineral separations, togetherwith X-ray and spectrographic analyses. ADebye-Scherrer-type camera was used for theX-ray work. A 3-meter Baird grating-typespectrograph with 300-volt, 6-ampere D.C. arcwas used for spectrographic analyses.

ACKNOWLEDGMENTS

The study was sponsored by the FreeportSulphur Company and the Department ofGeology, Columbia University; both weregenerous with financial assistance and equip-ment.

Sutcliffe of the University of Nottingham,England, and Mr. John Stewart of the MinesBranch, Ottawa. Professor W. D. Gill madeavailable laboratory facilities at Trinity College,Dublin. Mr. F. W. Dunning of the GeologicalSurvey of Great Britain painstakingly identifiedor confirmed many minerals in thin sections or inseparations.

A special debt is owed Prof. Charles H.Behre, Jr., for advice and encouragement.Profs. Paul E. Kerr, Ralph Holmes, and SidneyPaige read parts of the manuscript. Dr. D. R.de Vletter and Dr. Charles W. Hatten suppliededitorial criticism.

PREVIOUS REGIONAL INVESTIGATIONS

Thiadens (1937) noted that "A rather largeamount of literature concerning Cuban geologyexists. Notwithstanding, the geologic knowledgeof the island in general and also of the southernSanta Clara province is very poor." In the firstgeological map of Cuba, de Castro (1881)represents the schists of the TrinidadMountains as Silurian-to-Carboniferous sedi-mentary rocks, bounded on the north bygranite, serpentine, and basalt.

Spencer (1896, p. 71) notes that although deCastro assigns the formations of the TrinidadMountains to the Paleozoic

"... there appears to be no certainty as to theirage. They are composed of a semicrystalline lime-



PREVIOUS REGIONAL INVESTIGATIONS 1461

stone of fine texture and blue colour, resemblingexternally some Ordovician rocks, so also do theassociated black slates . . . but in their internalstructure the Trinidad mountains constitute theoldest rocks of central Cuba."

Hayes, Vaughan, and Spencer (1901) regardthe schists as basement rocks. Wright (1916, p.58) mentions that the town of Trinidad wasfounded in 1513 because gold was discovered inthe Rio Arimao. Calvache (1925) reports thatlarge pyrite deposits were found in the sixteenthcentury south of Cumanayagua; presumablythese are the Minas Carlota (PL 1). Allende(1928) describes these as ellipsoidal ore bodiesconformable in "Precambrian" schists.

Thiadens (1937) summarized a survey under-taken 4 years previously by Dutch students.This paper contains an excellent descriptivebibliography and reconnaissance map. De-scribing the rocks of the Trinidad Mountains,Thiadens writes:

"Geologic history begins with the genesis of thoserocks which furnished by metamorphism theschists and marbles of the Schist Formation.The age of these rocks cannot be stated withcertainty, as fossils if formerly present, entirelydisappeared in consequence of the metamor-phism. By comparison of these rocks with othersfound elsewhere on Cuba and on surroundingislands, it may be deduced that the age is veryprobably Lower Cretaceous and Upper Jurassic.This age, however, has not been proven and therocks may be very well older. They are at leastof pre-Middle Cretaceous age."

Other writers also speak of a Schist for-mation. In this study the "schists" are dividedinto carbonate rocks and schists. The termSchist formation is not used hereafter.

GEOMORPHOLOGY

The serrated sky line (PI. 2) suggests that theTrinidad Mountains consist predominantly oflimestone. Field work within and without thearea of Plate 1 confirms this.

The limestone forms high ground. Theprominent northerly dip gives hills a distinctivesilhouette with a gentle northern slope and asteep southern one. Karst features are common,including dry valleys, caves, sink holes, and, ona lesser scale, solution cavities. Many valleysend abruptly in steep walls, and many arecrossed at right angles by rock buttresses.

Carribbean karst lands are described byLehmann, Krommelbein, and Lotschert (1956)and Sweeting (1958).

Soil is red, especially where the adjacentlimestone is schistose and rich in hematite. Soil

creep is rapid; thus the best exposures oflimestone are usually on high ground.

The original drainage of the northwestTrinidad Mountains was probably to the northand west, governed by the dome structure ofthe mountains. The next stage, superimpositionupon underlying bedrock, is indicated by windgaps along the Gorro-Chivo ridge which arealigned with streams draining off El Puerco.

The third and present stage of drainage wasthe rapid development of subsequent streamsalong strike faults or easily eroded belts ofschists. The Navarro River (PI. 1) which hascaptured many consequent streams is anexample.

River terraces are rare. They are locallydeveloped at Charco Azul. Higher-level terracesthat cut directly across bedrock are morecommon and are found at 1400 feet at StationB (PL 1), at 1250 and 1600 feet on La Barona(PL 2, fig. 2), and at various levels between1300 and 1500 feet on Honeymoon Hill.

Upraised and tilted peneplains of unknowndate are indicated by concordant summit levels(PL 2, figs. 1,3).

CARBONATE ROCKS

General Statement

The carbonate rocks are dynamically meta-morphosed, devoid of fossils, and are believedto be pre-Middle Cretaceous (Thiadens, 1937).They are crystalline, foliated, or schistose. Allare graphitic; all are steeply and isoclinallyfolded. They include limestones (comprisingabout 90 per cent of the carbonate rocks),dolomite, and brucite limestone.

An attempt was made to locate fold axes.Because of the absence of fossils, lithology wasused for correlation. Each natural, unbrokenoutcrop along the Cumanayagua-Carlota roadwas studied (PL 4). The following limestonevarieties were found:

(1) Light-blue densely compressed limestone(2) Medium-blue massive-weathering platy and

foliated limestone(3) Medium-blue massive-weathering foliated

limestone(4) Limestone weathering light blue, foliated,

and containing black calcite crystals up to an inchin diameter

(5) Flaggy limestone with bluish-white patina(6) Similar to 5 but with schist bands(7) Tightly folded limestone ranging from white

to blue; may be equivalent to (1)(8) Schistose limestone with whitish patina




(9) Dolomite, buff to light gray, with kneadedand sculptured appearance. One band with smallblack gypsum crystals

(10) Brucite limestone resembling weatheredlamprophyre in color and appearance

Although these lithostratigraphic subdi-visions confirmed isoclinal folding, only one foldaxis (the northern axis through Chivo) wasdiscovered. Attempts to discover other axeswere unsuccessful because (1) only the dolomiteand brucite limestone, which together form lessthan 10 per cent of the carbonate rocks, aredistinctive enough to be recognized in anyoutcrop; (2) the limestones proper are sub-divided by subtle shades of color that are notsharp enough for stratigraphic distinction; (3)isoclinal folding is so intense that different rocktypes alternate abruptly; (4) rock flowagealong strike is extreme, so that some units thinto disappearance; (5) cleavage and jointing arevirtually absent and cannot be used to de-termine overturning.

The most reliable exposures are on hillsideswhere runoff is rapid and rock faces dry. Whererunoff is slow or continuous, water seepingthrough the overlying mantle coats outcropswith a buff-pink patina, or it may depositlayers of gray tufa several inches thick. Conse-quently exposures in many stream beds, par-ticularly where the stream is small or inter-mittent, are useless for mapping, becausebedrock and loose rock fragments are cementedtogether and coated with thick sheets oftravertine.

Limestones Proper

The outcrops of rocks of lithologies 1-8 are,in hand specimen, composed of equigranularrelatively massive limestone and laminatedlimestone. These, perhaps, are equivalent to thecrystalline and the quartz-bearing limestonesof Thiadens (1937). Each b divisible intosubtypes, between which every gradation existsas a result of (1) change in proportion ofminerals, (2) change in grain size, and (3)flowage, injection, and mingling of units. Theequigranular and laminated limestones aresubdivided macroscopically as follows:

Equigranular limestones

El Black dense limestone with "diabasic"texture; grain size less than 1 mm

E2 Speckled limestone intermediate betweenEl and E3

E3 Mottled blue-gray and white limestone with

augen of blue limestone averaging J-£ to 1inch in length, engulfed by white calcite

Laminated limestonesLI Silvery micaceous and schistose limestone

containing white calcite in many casesstained yellow with iron, hematite cubespseudomorphic after pyrite, and sideriteveinlets commonly less than 1 inch thick

L2 Gray schistose limestone of chloritic ap-pearance; graphite content stains fingers;visible pyrite

L3 Red schistose limestone, slightly harderthan LI or L2, with abundant red hematitepowder along laminae, micaceous lusterpresent but not prominent

In general the equigranular limestones yieldmassive outcrops. Flaggy outcrops are developedwhere equigranular and laminated limestonesalternate.

Both the equigranular and laminated types areveined by calcite. Siderite is rare. In hand specimen,quartz veinlets are inconspicuous, but some out-crops are cut by quartz veins up to 2J^ feet thick.

Microscopically the difference between equi-granular and laminated limestone as seen inabout 50 slides is one of degree only; each gradesimperceptibly into the other. The subtypesappear to depend upon the varying proportionsof the constituents.

EQUIGRANULAR COMPONENT: Sections show agranoblastic mosaic consisting of:

(1) Calcite, comprising at least 85 per cent of therock and showing twin lamellae, usually two setsfor each crystal, commonly bent. The lamellaegenerally incline at 30°-50° to any foliation present.Much of the calcite is slightly biaxial and cloudy-gray to yellow owing to a high proportion of graph-itic or ferruginous inclusions. In places the inclusionsare concentrated into rectangular or six-sidedpatches indicative of a pyrite or epidote crystalpartly or wholly replaced.

(2) Quartz, averaging 5 per cent and invariablypresent either as rounded, elongated, or subangulargrains or as irregular patches or fractured veinletsin places crenulated and indicating introduced orrecrystallized quartz. Under low magnification nogas or liquid inclusions are visible, but extremehigh-power magnification shows glassy pink in-clusions of indeterminate composition.

(3) Muscovite, averaging 3 per cent, as clearlaths of varying length scattered through thesections. No alignment is recognizable.

(4) Hematite, translucent and blood red, pseu-domorphic after rectangular pyrite.

(5) Pyrite, surrounded by hematite.(6) Magnetite, found in separations although

not distinguished in microsection.(7) Graphite which, although suspected as

inclusions in calcite, is recognizable only in sepa-rations.



CARBONATE ROCKS 1463

(8) Apatite, occasional, commonly broken andshredded.

(9) Epidote or clinozoisite in columnar ag-gregates associated with iron-rich bands. Polar-ization colors are low-order dark grays; the opticalsign is biaxial negative; the interference figure ispoor; and two cleavages are in some cases presentat 70°-90° angles with one another. The possibilityof plagioclase cannot be ruled out.

(10) Sphene and chlorite as occasional constit-uents of the iron-rich bands.

The different varieties of equigranular limestoneresult from variations in size of the calcite andvariations in amount and distribution of inclusions.The mottled subtype is an injection phenomenonwith light calcite surrounding and veining blue-graycalcite. Vein calcite is everywhere white, suggestingthat in recrystallization and injection it has beencleared of inclusions.

LAMINATED COMPONENT: The textures of sectionsexamined range from gneissic-granoblastic tointensely crumpled, swirled, and microfaulted. Thesections contain:

(1) Calcite, composing at least 85 per cent of thematerial seen in the slides. Individual grains aremore elongated than in the equigranular variety;some grain boundaries are "fused" together anddifficult to recognize. Twin lamellae are wavy andmultiple.

(2) Quartz, poikiloblastic in calcite or as angularveinlets or lenticles along definite folia. No detritalquartz was seen, and this may be diagnostic of thelaminated variety. There is more quartz in subtypeL3, and it is arranged in lenticles.

(3) Hematite and goethite compose most of theabundant red and brown powdery or mossy aggre-gates scattered throughout the calcite. Replace-ment of pyrite is especially noticeable in subtype L3.

(4) Muscovite, everywhere present in amountsof about S per cent. It may be arranged sporadicallyor in parallel or subparallel folia. In many placesit is corrugated and associated with dark graphiticpowder, and it may occur in swirl aggregates withquartz and calcite (as a pseudomorph after garnet?).

(5) Chlorite, of two types. One is colorless,twinned, with lamellae at right angles to schistosity,and commonly occurs in the same folia as quartz.Polarization colors are dark gray (slightly yellow)to black. No anomalous blues are seen. The secondvariety is pale green, nonpleochroic, scaly, withcleavage at high angles to schistosity. Its extinctionis parallel; it is length slow and uniaxially negativewith no rings or colors; its polarization color is lowand blotchy. The laminated varieties of limestonecontain more chlorite-serpentine than the equigran-ular varieties.

Accessory minerals are apparently not so nu-merous as in the equigranular varieties, but thismay not be diagnostic.

Dolomite

Dolomite outcrops arc buff to light gray andappear kneaded and sculptured. Their thicknessranges from 2 to 20 feet and averages 5 to 10feet. Although lenticular dolomite was foundonly at Wilson Ridge, three-quarters of a milewest of Charco Azul, the Carlota variety, likemany others, may be highly lenticular. Theaccompanying maps show only the actualoutcrops; many of these undoubtedly connectunder cover.

In hand specimen this rock is gray, fine-grained, and has a dense gritty texture. Veinletsof quartz less than 1 mm thick are common.Pyrite cubes occupy some of the graphite-chlorite folia in drill-core samples. Micro-scopically the rock consists of a sugary mosaicof anhedral calcite and euhedral to subhedraldolomite. Muscovite is scattered throughoutthe slides. Hematite occurs either as dust orpseudomorphic after cubes and possible inter-grown pyritohedra of pyrite.

Perfect euhedral crystals of black gypsumup to 5 mm long are scattered throughout oneband of dolomite 6 feet thick on a road bendnorth of Charco Azul. This is at least locally auseful marker bed.

Unfortunately the small gypsum crystals pullout when slides are made. However, thinsections show that the groundmass of thegypsiferous rock consists of cloudy fine-grainedpatches of calcite, rare muscovite, and abundantgraphite surrounded by euhedral to subhedraldolomite with interstitial quartz and sporadicthin muscovite laths, all with a slight graphiticcontent. No hematite was seen.

Approximately 45 gms of the rock was dis-solved in warm dilute HC1. The residue onfiltration amounted to 5.8 per cent and, asconfirmed by F. W. Dunning, consisted ofblack euhedral gypsum 1-5 mm long, containingclouds of dark inclusions, biaxially positive with2V = 60° and n7l approximately 1.530, andchloritic mica with nz approximately 1.57 andcontaining dark inclusions. No anhydrite wasdetected in either of these two subtypes.

Brucite Limestone

An interesting brucitic limestone is exposednear limestone-schist contacts. Because of soilcover, outcrops could be traced only a few feetalong the strike. This unit appears to be 1-4feet thick. The rock is brownish black, highlygraphitic and dusty, and laminated and




speckled with laths (up to 10 mm long) oflustrous black brucite. This, too, is a usefulhorizon marker.

Microscopic sections (PI. 3, fig. 1) reveal amurky fine-grained aggregate consisting ofbrownish-black graphitic powder, poorly de-nned calcite granules, minute calcite veinlets,and very rare muscovite in small broken laths.The graphitic powder is arranged in parallel orsubparallel lines and may occur in fuzzy rodsat an angle of 25° with each other. The detailin the calcite is not clear, even under highpower.

Irregularly inset in the calcite-graphitegroundmass are elongated subhedral porphyro-blasts of brucite, uniaxial and optically positive,with zoned extinction and anomalous blue-grayinterference colors. Smaller, usually clearer,crystals show good longitudinal cleavage with asuggestion of another cleavage at 75° to this.Graphitic inclusions are prominent parallel tocrystal outlines, especially to the longer di-mensions. Generally the inclusions are a con-tinuation of the graphitic lines of the ground-mass. The brucite appears to have grown afterthe foliation of the rock developed.

To supplement the thin sections the followingstudies were conducted. Samples averaging 6gms were dissolved in acid. The percentages ofnitrate obtained from localities w, x, y, and z(PL 1) were respectively 17.8, 8.78, 28.8, and15.4. The residues revealed (1) abundant blackflakes closely resembling graphite but identifiedby F. W. Dunning as chloritic mica (biaxial,optically positive, 2V very small, nz 1.57)containing hosts of minute dark inclusions,some of which may be carbonaceous, othersferruginous; (2) brownish fragments of hydra tediron oxide, possibly gocthite, together withsome finely divided micaceous material; and(3) minor amounts of magnetite, hematite re-

placing pyrite, muscovite, irregular grains ofquartz, and possible undissolved brucite.

As a check on optical identification thechloritic mica was X-rayed. Two runs weremade, the first, copper radiation with a nickelfilter, for identification; the second, cobaltradiation and an iron filter, for photographic-reproduction purposes. The chlorite was found(Tables 1; 2) to be sheridanite (McMurchy,1934). The sheridanite was also spectrographi-cally analyzed. Carbon, suspected from theoptical analyses, was confirmed as a minorconstitutent.

Halloysite

Although the limestones of the TrinidadMountains are subjected to tropical weathering,aluminous residual products are absent. Heavyrainfall and high relief, which result in heavyslope wash, are responsible. Pockets of bauxitemay exist, but only where very unusual circum-stances favor their preservation.

The only aluminous product discovered wasa chalky white powder which encrusts an out-crop of limestone along the road leading to ElCapitan (PI. 1). Microscopic examination indi-cates it is halloysite, extremely fine-grained andwith a refractive index slightly greater thanbalsam.

The material was X-rayed. Three runs weremade, the first, iron radiation for identification;the second, iron radiation and manganese filter,for visual intensity determination; and thethird, cobalt radiation and an iron filter, forphotographic reproduction (Table 3).

The clarity of the X-ray pattern is good.Although several lines appear that are notrecorded by at least 6 authors, the extra linesagree closely with those of the Mines Branch,Ottawa, Canada.

PLATE 2.—PANORAMAS

FIGURF. 1.—Serrated limestone topography. Panorama looking west from Sallo del Hanabanilla about10 miles east of Minas Carlota. Note northerly slope of the dissected upraised peneplain which forms thesky line (cf. Fig. 3).

FIGURE 2.—View from dolomite knob three-quarters of a mile west of Charco Azul, looking eastwardstoward Chivo (Peak 9) and La Barona (Peak 16). Two high-level terraces with elevations are shown.

FIGURE 3.—Panorama from Peak 5 looking southwest toward Guaos Hill (Peak 1) and the coastal plain.On the left, an upraised peneplain surface slopes gently toward the right. Banding is visible in the Guaos Hillserpentinite.

FIGURE 4.—A panorama, complementary to Figure 3 of this plate (building X is common to both photo-graphs) from the saddle south of Gorro looking northwest across open, hummocky, schist country towardPeako (Peak 3).



I

--------- -- -- --------- - --

--------- - -- --------- - --

PANORAMAS



--------- - -- --------- - --

wOa

--------- - -- --------- - --

PHOTOMICROGRAPHS

--------- - -- p

f



CARBONATE ROCKS 1465

The material was also analyzed spectro-graphically. Semiquantitative comparisons weremade against standard calibration powders.The results are listed in Table 4.

The possible significance of the halloysitecannot be considered here. No alunite or endel-lite were detected. The halloysite appears tohave been deposited by ground water issuingbetween red clay and limestone. Its purity mayindicate selective leaching or selective precipi-tation.

SCHISTS

General Statement

Schists of sedimentary origin occur withinthe map area (PL 1) and to the east and south.As with the limestones they lack fossils, aretightly isoclinally folded, and usually possesssteep northerly dips.

Schist topography is smooth and gentlyrolling (PL 2, fig. 4). Soil is gray or silveryfrom the carbonaceous or micaceous constitu-ents. Thiadens (1937) mentions quartz-micaschists with accessory garnet. At least sevenvarieties of schists exist.

Carbonaceous Chloritic Mica Schist

These schists are soft, soil the fingers, andweather to form gray soil. Fresh specimenssuitable for thin sectioning are difficult to findMineral separations show that the chloriticmica of these schists resembles that of thelimestones in containing minute dark inclusions,some of which may be carbonaceous, othersferruginous. This is the commonest schist. Itmay grade into, or with isoclinal foldingalternate with, quartz-mica-garnet schist.

Quartz-Mica-Garnet Schist

Where carbonaceous and associated withchloride-mica schist, this schist is easilyweathered. By itself, it may form high ground;it occurs high up the north and south sides ofPeak 4 (PL 1). The rock is corrugated andlustrous with silvery muscovite. The garnetsvary in amount and size, are red, and give therock a spotted appearance.

Two varieties exist: variety 1 occursthroughout the area; variety 2 is restricted tothe Marafion River north of Flattop (PL 1).

Variety 1 consists of lenticular sheared andsliced quartz, albite, and muscovite laths with

PLATE 3.—PHOTOMICROGRAPHS

FIGURE 1.—(X30) Brucite limestone. Brucite laths in a groundmass of graphitic dust and calcite granules.Note clear strips in brucite parallel to groundmass. Locality Y, Plate 1

FIGURE 2.—(X9) Garnet in graphitic quartzite. The euhedral garnets follow rock lamination. Cross-bedding is suggested by merging V at top left

FIGURE 3.—(X12) Magnetite skeleton in felted chlorite (clinochlore), cut by shear. Locality: WilsonRidge, half a mile north of Gorro

FIGURE 4.—(X40) Goethite-chlorite schist. Biotite with cleavage at high angle to lamination, replacedby chlorite; quartz with inclusions (Q); apatite showing cross fracture. Locality: Charco Azul

FIGURE 5.—(X12) Albite-lawsonite-chlorite schist. Albite (Ab) and lawsonite in a chloritic groundmass.The sphenes (black) of the groundmass pass through the lawsonite crystal. Locality: gossan approximately10 miles east of Charco Azul

FIGURE 6.—(X12) Serpentinite; antigorite with magnetite. Note relict of pyroxene outlined by finer-grained matted antigorite and outlines of tubby lath-shaped mineral ophitically contained in the upperright of relict of pyroxene. Locality: Guaos Hill

FIGURE 7.—(X24) Olivine-pyroxene rock. Cross-polarized light. Large first-generation (?) pyroxeneembayed and surrounded by olivine, pyroxene, and amphibole with lines of included magnetite and greenspinel in the large pyroxene. Locality: Terminal Hill

FIGURE 8.—(X18) Amphibolite showing incipient alteration. Granulation in hornblende and plagioclase(Anw-eo) with sheaves of anthophyllite developed along zones of microshearing. Locality 4, Cumanayagua-Minas Carlota road (PI. 4)

FIGURE 9.—(XSO) Amphibolite showing more advanced alteration than Figure 8. Sheared porphyro-blasts of clinozoisite are set in a groundmass of nephrite, sericite, and altered plagioclase (lower left). Lo-cality 5, Cumanayagua-Minas Carlota road (PI. 4)




occasional porphyroblasts of garnet. Rockdeformation is indicated by curvature of thealbite and swirl structure in the muscovite.

TABLE 1.—X-RAY POWDER LINES OF SHERJDANITE

TABLE 2.—STANDARD X-RAY POWDER LINESFOR SHERIDANITE

(From McMurchy, 1934, p. 423-424; maximumintensity—10; camera radius 57.3 mm.

CuKa 1.537)Cobalt radiation: iron niter)

I..... .

610541924586451932

Xy2i482

y2i332

d(kXA)

' " '13.79*

7.074.744.163.703.533.35 (graphite)2.842.592.552.442.382.252.062.001.881.811.741.711.661.561.531.501.461.411.391.321.29

* Obtainable only on long film (camera diameter114.3 mm)

The fabric suggests some postcrystallizationdeformation.

The albite is generally corroded and sub-hedral, in some cases euhedral. Subhedralcrystals contain quartz and other constituentsof the groundmass. Euhedral crystals formstraight or curved blades and may containdusty inclusions (graphite?) arranged in bandsparallel to their length. Simple Baveno twinningand rare lamellar twinning are present. Thegarnet has developed in and includes thegroundmass, the rotation and distortion ofwhich it faithfully reproduces. Hematite formsmetallic granules and spangles. No magnetitewas identified.

Variety 2 consists of garnet porphyroblasts in

7

78292

1017

H75634

y*17644332

1010223

10

44

y*7/

Vz34

cjco2o34

d

13.6787.0405.2504.6803.9223.5093.1292.8282.7122.5782.5422.4302.3702.2472.2152.0642.0211.9981.8811.8251.7311.7061.6591.5621.5341.5021.4601.4171.3901 7 CA.JjO1.3191.2831.2511 91 ftI . Zlo1.1911 1811 . lol1.1311.0941 r\Af\i . U4U1 nini . u<suI n i "?.Ulo1.001

no7~ . 70 1

a groundmass of lenticular calcite. In thegroundmass, muscovite laths follow laminaeand wrap around garnets; quartz shows wavyextinction, angular outlines, and is older than



SCHISTS 1467

the calcitc. Minor apatite in columnar aggre-gates, scattered sphene granules, and possiblerounded dolomite follow the rock lamination.

Inset in the groundmass are: porphyroblastsof large euhedral garnet containing quartz

TABLE 3.—X-RAY POWDER LIKESOF HALLOYSITE

(Cobalt radiation: iron filter)

Graphitic Quartzile with Garnet

Loose slabs of tough laminated quartzite,averaging 5 by 5 by 3 feet, lie apparentlyhorizontally at plane-table station L,Weathered surfaces exhibit a dull-black ribbingof manganese oxide along the laminae whichrange in width from a fraction of a mm to 2 or3 mm. Fresh surfaces are siliceous and showthat the laminae are actually stratificationplanes with such features as cross-bedding.

Thin sections reveal predominant quartz,garnet, and manganese oxide. The quartz formsa mosaic of elongated grains, some of which aresurrounded by a greenish film; others lack thisfilm and show mortar structure. Small scatteredrounded grains suggest that the original detritalshape of the quartz grains may be preserved.

The garnets are minute, yellow, and euhedral(PI. 3, fig. 2) and contain inclusions. They arealigned along certain laminae and appear tohave developed in an impure sandstone.

The manganese is black, in many casescolloform with brown translucent edges, andmay be associated with carbonaceous material.

TABLE 4.—SEMIQUANTITATIVE SPECTROGKAPHIC ANALYSIS or HALLOYSITE(Analyses by Mines Branch, Ottawa, Canada)

/

109821221511

d(kXA)

7.334.444.123.723.602.552.341.671.481.281.23

Elements—per cent

White chalky powder encrustinglimestone on roadside near ElCapitafi, Minas Carlota

Fe

0 1

Si

?s

Al

1S

Mg

0 07

Mn

lessthan0 005

Pb

0 0?

Cr

lessthan0 002

Sn

lessthan0 01

Ni

0 OS

V

lessthan0 01

Ca

lessthan0 01

Cu

lessthan0 005

Zn

lessthan0 OS

Ti

lessthan0 002

inclusions reproducing the swirl structure ofthe groundmass; large augen of pale-green non-pleochroic diopside (2V about 50°) alteredalong the margins to calcite and to yellowish-green chloritic glass; and scattered laths ofpleochroic (colorless to pale-blue) glaucophanewhich appear to replace shredded ends ofdiopside crystals and to be associated withmuscovite.

Black Argillite

By increase in carbon content, the carbona-ceous chloritic-mica schist grades into blackargillite. Good exposures are at Charco Azuland southwest of La Barona (PI. 1). North ofFlattop the argillite is dark brown and yieldsreactions for manganese. All argillites areextremely weathered; most are soft, crumbly,and damp and could not be sectioned.

It appears to be a late introduction, as it cross-cuts rock lamination and coats and replacesgarnet.

Siliceous Graphitic Schist

These are silver-gray to grayish-black schiststhat soil the fingers. Unweathered specimensare rare and have a gritty feel. The rock hasrough, slabby, jointing parallel to and cuttingacross the schistosity. Steep crosscutting jointsare reported from similar (?) rocks in the Isle ofPines (Page and McAllister, 1944). Lineation ispresent along planes of schistosity and iscaused by alignment of muscovite laths.

The rock is the only one in which pyriteweathers out instead of being replaced by ironoxides. Weathered outcrops are rusty, withyellow streaks and holes representing leachedpyrite. The rock occurs in an area up to 1 mile




away from the graphitic quartzite into whichit grades by increase in silica.

Thin sections show quartz (40-45 per cent),carbonaceous and ferruginous dust (30-35 percent), muscovite (10-15 per cent), garnet, andpyrite pits (10 per cent). The texture is highlyplicated, with slippage along the limbs of theplications. The garnets are small and colorless,generally decomposed, and, apart from amarginal dusty layer, do not affect the sur-rounding minerals. With higher magnificationthe dusty material proves to be brownish red.

Epidolc-Quarts-Mica Schist

These schists are interbedded with argillitesand serpentinite schists. The association and"purple" color—common to many tuffs else-where—may indicate a tuffaceous origin.

Under the microscope the rock consists ofpatchy and recrystallized quartz followingschistosity; muscovite in wisps and laths;epidote in knots and augen, cloudy with dustyhematite and carbonaceous material andforming granular aggregates or crude six-sidedporphyroblasts; hematite in red lenticles, thecorners filled with yellowish-green isotropicglass; and light-green pennine (?) in veinletswith fibers at high angles to walls of veinlets.The pennine is crosscut by muscovite andappears to be older.

AGE OF THE CARBONATE ROCKS AND SCHISTS

The limestones and schists of the TrinidadMountains are of unknown age. Allende (1928)believed them to be Precambrian. Thiadens(1937) correlated them lithologically withschists in the Isle of Pines and in the lower SanAndres formation of Pinar del Rio. As theupper San Andres was supposedly UpperJurassic-Lower Cretaceous (Vermunt, 1937),he regarded them as pre-Upper Jurassic.

The lower San Andres formation (Cayento)has recently been dated as late Dogger(Krommelbein, 1956). To assume that the rocksof the Trinidad Mountains are necessarily ofthe same age would be unwise. More than 50per cent of the Cayento formation rocks aresandstones, which on metamorphism wouldform quartzites—common on the Isle of Pines(Rutten, 1934; Page and McAllister, 1944) butrare in the Trinidad Mountains.

Within the mountains the age relationshipbetween limestone and schist is unknown. Thelimestone is depicted as older (PL 1), becauselimestone ridges as indicated by fold noses areanticlinal, and schist lies directly underneath

younger amphibolite. However the ridges maybe antiforms (Bailey and McCallien 1937), andthe juxtaposition of schist and amphibolitemay be fortuitous.

Faulting, isoclinal folding, and overburdenprevent an immediate solution to the problems.For the present, the limestones and schists areregarded simply as "Mesozoic".

IGNEOUS ROCKS

General Statement

Igneous rocks of the Caribbean region arediscussed by Schtirmann (1935), Weyl (1950),Mitchell (1955), and Butterlin (1956). Analysesand descriptions of rocks from southern LasVillas are given by Schiirmann (1936) andThiadens (1937).

The igneous rocks here discussed are im-mediately adjacent to, or within, the TrinidadMountains. The diorite to the north is notdescribed.

Although with one exception contact effectsare lacking, the igneous rocks are consideredyounger than the enclosing limestone andschist. Nothing indicates that the sedimentsnow represented by limestone and schist weredeposited unconformably on an igneous base-ment.

The igneous rocks are divided into (1) fine-grained serpentinites and their schistose andchloritic derivatives, (2) nodular serpentinitesand olivine rocks, and (3) amphibolites.

For the present, two groups of serpentinizedrock are distinguished, based on field, mega-scopic, and microscopic characteristics. Eachgroup may include rocks different in age, origin,or degree of serpentinization. In particular thesecond group is broad and includes rocks whichcontain olivine or relicts of olivine.

All the igneous rocks contain much magnetiteas dust or, less usually, as granules andstringers. Because of the fine particle size,separation is difficult. Approximate estimatesrange from 7 per cent for the amphibolites to25 per cent for veins in the Guaos Hill serpen-tinite.

Fine-Grained Serpentinites

Rocks of this category correspond to theserpentine schists of Thiadens (1937) and thegreenstones of earlier reports. They stretcheastward from Honeymoon Hill through themain Carlota Valley and comprise greenishfine-grained felted rocks which originally mayhave been different but are now serpentinizedand chloritized. Where massive these serpen-



IGNEOUS ROCKS 1469

tinites form high ground, but where schistosethey form depressions. Contact metamorphismand jointing are absent.

Serpentinization of the fine-grained type mayvary vertically, laterally, or in part accordingto the proximity of faults. Drill cores from thegossan area north of Gorro (PI. 1) show thatalthough outcrops appear completely serpen-tinized, the rock below may be only partiallyso and may contain unserpentinized actinolite.Accordingly, on the basis of surface information,Serpentinization is described as incipient,partial, or complete.

INCIPIENT SERPENTINIZATION : IncipientSerpentinization is found only at HoneymoonHill where actinolitic serpentinite forms thecore of the mountain. The contact on the northindicates a northerly dip of 30°; the southerncontact is steeper, but the exact dip is unknown.The body appears to be a pluglike intrusionwith an elliptical outcrop.

Macroscopically the serpentinite is a tough,dark-green rock with rusty phenocrysts.Polished sections are green and white withpolygonal iron stains and are of igneous ap-pearance with diabasic texture. Relicts of alarger mineral (plagioclase of pyroxene?) areapparent.

Thin sections confirm the relict structure andshow rectangular areas composed of actinolite,zoisite, garnet, calcite, plagioclase, and rutile.

The actinolite is pale green with brownishtriangular cross sections. The mineral outlinesrectangular areas as border laths but also mayfill them. The border laths are commonlytalcose.

The zoisite forms brownish aggregates. Indi-viduals are too small for positive identificationand may include some idocrase. Antigorite andchlorite are present in places as part of thezoisite aggregates.

The garnets form euhedral crystals scatteredthrough the zoisite areas. They may be arrangedconcentrically or clotted into polygons, theoutlines of which may replace the cleavage of aformer mineral, possibly pyroxene or amphibole.

The calcite and plagioclase (An^^s) occur inminor amounts and are usually associated withactinolite. Former lamellar twinning in plagio-clase is suggested by lines of inclusions and clearlanes in the brown zoisite areas.

Rutile and possible perovskite are found inscattered murky-brown areas associated withiron staining.

The relationship between actinolite andserpentine is confused. Thin sections suggestthat Serpentinization followed actinolitization.However, (1) elsewhere, i.e., in the faulted

amphibolite, actinolite is the latest mineral and(2) movement appears to have been repeatedalong the east-west faults, so that actinolitemay be of different ages.

PARTIAL SERPENTINIZATION: IncreasedSerpentinization is shown by the rock im-mediately south of Gorro. The north contact isfaulted; the fault plane dips 70° north. Othercontacts are covered. On Peak 8 the rock is softand light green, shows a glassy felted texture,and contains reddish-brown streaks.

Thin sections reveal that pennine andscrpophite have increased in amount. Talc alsohas increased but is erratically distributed.Plagioclase (Anio) and sphene are associated withirregular patches of murky-brown rutile.

COMPLETE SERPENTINIZATION: Serpentini-zation is complete on Wilson Ridge and nearGossan 2 and is also indicated at Gossan 1 and3 by loose float. The differences between theserocks are best considered by describing the twoextremes—samples from Gossan 2 (one quarterof a mile north of El Puerco) and WilsonRidge (half a mile west of Charco Azul).

Hand specimens of gossan 2 serpentiniteresemble those from south of Gorro, but theycontain more blue-green patches (averaging 5mm in diameter) of structureless serpophite.

Microscopically the rock is a meshwork offibrous antigorite, clear patches of serpophite,occasional lenticles and bursts of minutelyfelted talc needles, veinlets of magnetite dust,and scattered spangles of red hematite. Darkercloudy yellowish-green areas show finer-grainantigorite pseudomorphic after actinolite. Thesquare outlines with truncated corners of theserelict areas suggest that the actinolite was itselfreplacing an earlier mineral, probably a pyrox-ene.

At Wilson Ridge, development of fine-grainedserpentinite, as indicated by surface outcrops,reaches its maximum. The rock is soft, applegreen, and minutely felted with thin veinlets(maximum width, 1 mm) of magnetite dust.Picrolitc, confirmed by X-ray analysis, is foundat one locality associated with magnetite (Hill,1958b, p. 969).

Thin sections reveal a uniform crisscrossedantigorite. Isolated relicts of former mineralsare outlined by finer-grained, darker antigorite.Magnetite is ubiquitous as dust, stringers, andaggregates.

Schistose Serpenlinites and Chloritic Schists

Schistose and chloritic derivatives exist (1)along sheared margins of large serpentinitebodies, e.g., south of Gorro (Pl.l), (2) where




serpentinite is thin and sheared, and (3) whereserpentinite grades into carbonaceous schist.

TALC-CHLORITE SCHISTS: These are partlyequivalent to the chlorite schists of Thiadens(1937). They are soft, of greasy feel, with redferruginous laminae, and contain minute mattedfibers of tremolite. Drill cores reveal that theyare commoner than surface outcrops wouldindicate. Some may have developed alonghorizons of sheared dolomite.

MAGNETITE-CHLORITE SCHIST: Greenish chlo-rite rocks with octahedra (up to 7 mm long) ofblack, shiny magnetite occur along the marginsof many serpentinites. The largest outcrop ison Wilson Ridge. It may be traced laterallyfor 150 feet. Ferruginous laminae indicateschistosity dipping 40°-60° north; this is ap-proximately the same dip as that of the sur-rounding rocks.

Thin sections show intermeshed tufts of palepleochroic yellow to green chlorite, biaxiallypositive (2V = S°-10°) with good cleavage,parallel extinction, and occasional anomalouspolarization. X-ray powder lines for thischlorite are fuzzy but agree with those forclinochlore.

The chloritic groundmass contains largecuhedral magnetites and magnetite skeletons(PL 3, fig. 3), occasional columnar apatites,rare idocrase (?), slightly bluish with extinctionup to 10° and biaxially negative, and minutegrains of broken epidote. Rectangular relictareas are discernible under crossed nicols.Minor antigorite fills the ferruginous laminaenoted in hand specimens and may replacetremolite-actinolite.

GOETHITE-CHLORITE SCHIST: A waxy, yel-lowish rock with goethite pseudomorphousafter striated pyrite cubes (up to 1 cm long),quartz lenticles, and reddish hematite laminaeis exposed in Charco Azul (PL 4).

Thin sections show that the yellow color isderived from chlorite after biotite, films ofserpentine (PI. 3, fig. 4), and rare talc. Thevariety of chlorite could not be identified;X-ray powder lines are too fuzzy.

The chlorite infiltrates the biotite, which ispleochroic from colorless to yellow green.Cleavage in the biotite is at high angles to thatin adjoining laminae; thus if oriented specimenscould be collected, it might be possible todetermine the relative direction of rock move-ment.

The quartz is lined with solid inclusions, ismargined with apatite, and contains colloformgoethite. It appears to have been introducedafter the pyrite. Also present are colorless,

idioblastic garnets, euhedral zircons, aggregatesof dark-brown sphene and yellow rutile, andsporadic talc.

The goethite is translucent reddish brownand was identified by X-ray analysis. Ljunggren(1958, p. 23) describes schists where the chlo-rite formed probably "as a result of the de-composition of biotite by the action of sulphuricacid formed from the partial decomposition ofpyrite".

The schist and the amphibolite (to the north)both have a high visible titanium content andmuch introduced quartz. However, the possiblerelationship between these two rock typescannot be settled on the basis of one smalloutcrop, for TiC>2 and Si02 are both mobileconstituents.

ALBITE-LAWSONITE-CHLORITE SCHIST: Chlo-rite schists with porphyroblasts of albite andlawsonite occur approximately 10 miles east ofCharco Azul. The schist is exposed about 200feet south of a pyritic gossan, strikes in thesame direction (east-west), and appears to dipsteeply northwards. It is at least 8 feet thick.The rock is green with crystals of whitehexagonal albite and gray rectangular lawsonite.

Chloritic tufts parallel or at high angles tothe over-all schistosity (PL 3, fig. 5) constitutethe groundmass. Relicts of amphibole areoutlined by tufts at 120° angles. The chlorite ispale green, weakly pleochroic, and extinguishesobliquely at 2°-5°. Refractive indices are dif-ficult to obtain; the chlorite was identified byX-ray analysis as clinochlore.

Irregular granules of sphene follow thecrumpled rock laminae and run through bothlawsonite and albite. Small crystals of apatite,needles of actinolite, and clean and minutegarnets and bluish anatase (?) arc scatteredthroughout the groundmass.

Albite porphyroblasts are colorless, euhedral,and riddled with needles of actinolite. Theporphyroblasts show simple and lamellar twin-ning and have 2V = 80° (approximately).The lawsonite is gray and usually rectangular.No actinolite is seen in the lawsonite, whichappears to have formed before the albite.Incipient albite is possibly represented bypatches of the groundmass that show uniformpolarization.

Lawsonite-chlorite schists occur northeast ofSanta Clara (Schurmann, 1936). The formulafor this lawsonite is given as 2H2O-2SiO2-Al2O3-(Ca, Mg, Fe, Na2, K2)O. Barker (1950)suggests that lawsonite is perhaps the firststep in the formation of zoisite or epidotefrom anorthite.



IGNEOUS ROCKS 1471

Nodular Serpenlinites and Olivine Rocks

Members of this group contain olivine orserpentinized relicts of olivine. The groupincludes rocks different in age and perhaps inorigin, including (1) the Guaos Hill serpentinite,(2) the amphibolite serpentinites, and (3) theolivine pyroxenite north of Wilson Ridge.

GUAOS HILL SERPENTINLTE: At a distance, thisserpentinite body (PI. 1, PL 2, fig. 3) shows alayered structure dipping approximately 30°west. At close range this layering is not ap-parent, and only a rough sheeting, broken byjoints at right angles, is visible. Neverthelessstereoscopic study of aerial photographsstrongly suggests that the apparent dip is morethan an illusion. Schiirmann (1935, p. 345) andWassal (1956) report layered gabbro-serpen-tinite elsewhere in Las Villas Province.

Weathered surfaces are nodular, appear some-what waxy, and show variegated coloring.Freshly broken surfaces expose pinkish-yellownodules (1 cm maximum length) set in a gray-green matrix. The rock is highly magnetic.With a lens, thin veinlets (1 cm maximumthickness) of dusty magnetite are visible.

Veins up to 18 inches thick of a smoothyellow serpentinite cut the nodular serpentinite.In these veins magnetite is conspicuous (up to25 per cent) in wavy stringers. Many veinsare concealed; limited exposures prevent accu-rate mapping.

Contact metamorphism of the surroundingrock appears absent, for although the actualcontact is concealed, limestone and schist about50 feet from the inferred contact show nometamorphism.

Thin sections show aggregates of serpophiteand antigorite. The serpophite is yellow,occupies patches within the antigorite, andcontains cores of magnetite. It appears toreplace olivine.

Antigorite (2V = 85°) occurs predominantlyas a mesh aggregate but also as veinlets.Former minerals are outlined by a finer-mattedantigorite (PL 3, fig. 6). Many of the pseudo-morphic areas show uniform and parallel ex-tinction and may represent rhombic pyroxenes.Other nonmatted areas of antigorite showonly traces of amphibole and pyroxene cleavage.

Rare pleochroic tufts of yellowish-greenbiotite occur with the antigorite. Magnetite ispresent both in serpophite and as dust inveinlets and grids.

Yellow vein serpentinite proves in thin sectionto consist of fine-grained felted antigorite withscattered strains of magnetite dust. Bastite,

with typical texture after rhombic pyroxene,is well developed. Large areas of magnetiteare ophitic toward antigorite, and larger clotssurround brown chromite. No picotite wasdetected.

AMPHIBOLITE SERPENTINITE: Amphibolite ser-pentinite is the name here given to partially orcompletely serpentinized igneous rocks croppingout along hilltops in areas of amphibolite. Theoriginal rocks appear to have been olivinepyroxenites. These have been serpentinized.The problem is which came first—serpentiniza-tion or amphibolitization?

Although contacts between the serpentinizedpyroxenites and the surrounding amphiboliteare hidden, the unaltered condition and themagmatic texture of the amphibolite stronglyindicate that it is younger and engulfs ser-pentinized remnants of older rocks. Thin sec-tions suggest that the green amphibole in theseremnants is a late introduction.

Under the microscope the partially ser-pentinized pyroxenite consists of large pyroxenesembayed and surrounded by olivine, smallerpyroxenes (second generation?), and an amphi-bole.

The large pyroxene crystals (PL 3, fig. 7) aregray and nonpleochroic (2V = 60°). Theycontain plates and rods of magnetite and greenspinel in planes parallel and at right angles tothe longitudinal cleavage of the pyroxene.

The olivine, with low first-order polarization,forms rounded subhedral crystals and broadveinlike clusters. Wide twin bands parallelcrystal length. The smaller pyroxenes formshort subhedral crystals and show weak pleo-chroism from colorless to pale green. Theamphibole is pale green and weakly pleochroic;it is length slow with a large 2V angle and has amaximum extinction of 15°-20°. It is anhedraland interstitial. Veinlets of yellow serpophite,granules of magnetite, and green spinel composethe remainder of the groundmass.

The more highly serpentinized rock isvariegated yellow green with black veinlets.Thin sections show colloform serpophite andrippled magnetite infiltrating and surroundingmineral components. Fine, parallel-tufted anti-gorite occupies distinct areas; hematite hasincreased in amount.

OLIVINE PYROXENITE: Olivine pyroxenitecrops out approximately 1 mile north of Gorro(PL 1). It is overlain by limestone which dips40° north. Although the contact is partlycovered, metamorphism of the limestone is




apparent—the only example of contact meta-morphism discovered.

The pyroxenite is a tough, dark-green rockwith salmon-colored ellipsoidal olivines (maxi-mum dimension 2 by 5 mm). Weatheredsurfaces are brownish.

Microscopically the rock is hypidomorphic-granular with 35 per cent augite, 35 per centhornblende, and 25 per cent olivine. Despitethe lack of serpentinization, microsections re-semble in many respects those from the ser-pentinized pyroxenites of the amphiboliteareas.

The augite, 2V = 4S°(?), is pale gray andcontains included rods and plates of greenspinel and magnetite. These appear to bisectthe rectangular cleavage intersections and tomake a 70° angle with many of the longitudinalcleavage traces. The olivine is subhedral andstained reddish yellow. Minor antigorite andchlorite are grouped together at augite in-terfacial angles. The hornblende is anhedral,shows schiller structure, and is pleochroic frompale yellow (a) to light green (7). It appears tohave been the last mineral to crystallize.

Above and grading into the pyroxenite is agarnet-pyroxene rock at least 4 feet thick. Thegarnets are euhedral, in part rimmed withveinlets of magnetite, and contain older laminaeof a dark unidentifiable powder; crystals,needles, and grains of pleochroic yellow tobrown piedmontite; and angular, fractured(?) quartz. The pyroxene (hedenbergite ?) ispale green, nonpleochroic, occasionally twinned;it surrounds the garnets. It is columnar withsquat cross sections and contains lines of dust-gray powder. Muscovite occupies shears in thegarnets. Sphene and calcite are ubiquitous.Quartz crosscuts all other minerals. Mineralpercentages are: pyroxene, 50; garnet 40; theremainder, 10.

Sheafing through the garnet-pyroxene rockare veins composed of columnar zoisite (2Vapproximately 30°) with slightly oblique extinc-tion, minor epidote, and clinozoisite.

For 30 feet above the contact, the limestonecontains scattered garnet, sphene, chlorite, andmuscovite. Clinozoisite (2V = 80°) wraps thegarnets. Minor irregular quartz is also present;some detrital grains are suggested by theiroutlines. No wollastonite was detected.

Amphiboliles

Immediately adjacent to the mountains,amphibolite separates diorite from limestone

and schist (Hill, 1958a). The northern contactof the amphibolite, although poorly exposed,shows intermingling of amphibolite and diorite.The southern contact is faulted and dips steeplynorthward, with amphibolite resting abovecarbonaceous graphitic schist.

No extensions of the diorite and amphibolitewere found within the mountains. To investigatethe possibility that the amphibolite and theserpentinites might have a common magmaticsource, seven samples were analyzed spectro-graphically for chromium, cobalt, and nickel.Semiquantitative comparisons were made withstandard calibration powders (Table 5). Moresampling and greater sensitivity are requiredbefore any significance can be attached to thesimilarity between results.

The origin of the amphibolite thereforeremains uncertain. It may represent (1) anintrusion earlier than the diorite, (2) a basicborder phase of the diorite (Thiadens, 1937),(3) limestone assimilation by a dioritic magma,(4) an intrusion later than the diorite, (5)metamorphosed diorite, or (6) metasomatizeddolomitic limestone.

Deep weathering and soil cover prevent anydefinite solution to the problem. The meageroutcrops that exist reveal gneissic amphiboliteand diorite so intimately mingled that it isimpossible to decide which is the intrusivebody. A tentative explanation might involvetheories 2 and 3. Later faulting has causeddynamic metamorphism of the amphibolitenear the contact, but this does not explain theorigin of the amphibolite, which averages1200 feet in thickness.

The gneissosity and the apparent intrusivenature of the amphibolite, if not wholly de-veloped when the diorite came into place, mayhave formed subsequently when the mountainfront was flexed.

UNALTERED AMPHIBOLITE: The amphibolitewhere unaffected by cataclastic or dynamicmetamorphism is a gneissic green and whiterock. Its grain size approximates 1 by 5 mm.All samples are noticeably magnetic.

A hypidiomorphic-granular texture formedby hornblende, andesine (An^.^), and accessoryiron ores shows up under the microscope. Thehornblende (2V = 65°) is strongly pleochroicfrom yellowish green (a) to blue green (7).It is usually anhedral, but cross sections aresubhedral.

The andesine forms large tabular crystalsand smaller rounded ones. Both show lamellaralbite and pericline twining.



IGNEOUS ROCKS 1473

The iron minerals are magnetite, ilmenite, appear. These include epidote (2V = 70°and rare flakes of hematite. The ilmenite is plus) wrapped by actinolite; pale-pink, brokenpartially altered to leucoxene. garnets with separated fragments; quartz show-

ALTERED AMPHiBOLiTE: Although the am- ing mortar structure or, where squeezed betweenphibolite appears to rest undisturbed on the amphibole and epidote, rare strain shadows;

TABLE 5.—SEMIQUANTITATJVE SPECTROGRAPHIC ANALYSES or IGNEOUS ROCKS(Analyses by Mines Branch, Ottawa, Canada)

No.

1

2

3

4

5

6

7

Locality

Guaos Hill nodu-ular serpenti-nitc

Fine-grainedserpentiniteWilson Ridge

Fine-grainedserpentinitesouth of Gorro

Lawsonite-chlo-rite schist, gos-san, 10 mileseast of CharcoAzul

Amphibolite, 1mile northwestof TerminalHill

Amphibolite,Locality 1(PI. 4)

Sheared amphib-olite, Locality 9(PI. 4)

Co

0.01

0.025

0.007

0.015

0.006

0.006

0.006

Cr

0.4

0.13

0.03

0.02

0.01

0.07

0 OS

Ni

0.5

0.38

0.04

0.05

0.01

0.06

0 OS

Nb (?)

0.03

B

0.004

Si

10

Mn

0.2

Mg

15

Fe

5

Al

1

V

0.01

Ca

0.03

Cu

0.007

Ag

0.01

Ti

0.03

underlying schist, locally it has been disturbedby fault movement. Dynamic metamorphismis exhibited in specimens 3-9 collected along theCumanayagua-Minas Carlota road (PI. 4).

Local metamorphism appears related tomovement along several minor faults andshears. Therefore the degree of metamorphism,as seen in hand specimens, varies from sampleto sample; altered but massive rock alternateswith sheared schist. As expected, more ad-vanced dynamic metamorphism is shown bythe schistose varieties.

Thin sections of the massive rock revealmany changes. The hornblende has lost itspleochroism, and anthophyllite has developedsporadically along microshears (PI. 3, fig. 8).The amount and crystal size of the andesinehas decreased.

With advancing metamorphism new minerals

irregular stringers of sphene, surroundingilmenite, which in turn surrounds deep-yellowrutile; and scattered, slightly biaxial apatite.Many sections of epidote, dark under crossednicols, do not show cleavage and in ordinarylight might be mistaken for olivine or diopside.

More advanced alteration in the massiverock has led to the disappearance of hornblendeand andesine. Thin sections reveal porphyro-blasts of clinozoisite set in a disturbed andcloudy groundmass (PL 3, fig. 9).

The clinozoisite (optically positive, 2V =70°) is sheared and embayed by a groundmassof nephrite composed of fine antigorite andactinolite, nebulous and cloudy oligoclase-andesine (A^o-ss), and sericite and chloritereplacing plagioclase. Sphene and larger lathsof actinolite are scattered throughout.

The most disturbed rocks are the schistose




varieties. In thin section, laminae of fibrousactinolite are cut and coated by chlorite, talc,and possible nephrite; albite is riddled withneedles of actinolite; individuals or masses of

grained variety (see gossans of PI. 1) mayperhaps be relicts of contact metamorphism.The fine-grained type has been folded andfaulted, whereas the nodular serpentinite ap-

FIGURE 2.—POSTULATED TERTIARY THRUSTS IN THE STRUCTURAL HIGHS OF CUBA(After M. T. Kozary, 1954, unpub. PhD thesis, Columbia Univ.)

zoisite, epidote, decomposed ilmenite, calcite,and sphene are ubiquitous. Quartz showingmosaic structure is a late introduction.

Problems of the Serpentinites

The division of serpentinites into fine-grainedand nodular types is convenient for fielddistinction. The question arises, whether thetwo types are of the same origin, with differenttextures merely representing different tectonicenvironments.

Spectrographically, although the Guaos Hillnodular serpentinite and the Wilson Ridgefine-grained type show higher percentages ofCo, Cr, and Ni than the other rocks analyzed(Table 5), the results are not conclusive inview of the small number of samples.

Microscopically the fine-grained serpentinites,compared with the nodular types, show grada-tion into, or association with, an actinolitic"greenschist" rock; occasional relicts of py-roxene; and, except for Honeymoon Hill, anabsence of olivine pseudomorphs.

In the field, differences show up when thetwo types are compared. The nodular type,judging by its crosscutting outcrops (PL 1), isintrusive, and large masses of the fine-grainedvariety may also be intrusive. Smaller bodiesof the fine-grained type apparently grade intoepidote schists, suggesting that they mayrepresent altered flows or tuffs. Although bothtypes lack evidence of contact metamorphism,the pyrite deposits which surround the fine-

pears to have come into place after folding(e.g., Guaos Hill) and may thus be intrusiveand younger.

Therefore mostly on field evidence, thefine-grained serpentinites are considered olderthan the nodular ones.

The origin of serpentinites is beyond thescope of this paper. Many hypotheses havebeen advanced to account for their genesis andmode of emplacement (Hugh Gabrielse, 1955,unpub. Ph.D thesis, Columbia Univ.). Therelative ages of West Indian serpentinites aresummarized by Mitchell (1955).

Although late faults are parallel to the con-tacts between serpentinites and limestones,no evidence exists that the serpentinites repre-sent cold intrusions (Taliaferro, 1943; Kozary,1956). In addition nothing indicates thatmagnesian serpentinizing solutions were leachedfrom dolomitic horizons. However shearingalong possible tuffaceous horizons (B and Dfaults, Fig. 3) may have formed chlorite schistsby the addition of A1203 in the form of hydrousaluminum silicates or hydrous alkali aluminumsilicates.

The concordant "bedded" nature of many ofthe serpentinites here described raises thepossibility of a sedimentary origin. This pos-sibility may be eliminated, at least for themajority of the serpentinites, because thinsections show that igneous rocks have beenserpentinized, and the concentration of nickel,chromium, and cobalt is too great (Faust,Murata, and Fahey, 1956).



FAULT DIP IN DEGREES

0/P OBSERVED Off CALCULATEDDIP

PRINCIPALGOSSAN L

O

§n

FIGURE 3.—FAULT SYSTEMS or THE NORTHWESTERN TRINIDAD MOUNTAINSAge decreases alphabetically, i.e., A is the oldest system




STRUCTURAL GEOLOGY

Folding

Many of the isoclinal folds are bent. Thebending may have been contemporaneous with

banding of which indicates that the underlyingore bodies occupy tension cavities, no structuresare preserved in the soluble limestone. Noschistosity, slickensiding, shearing, or jointingwere found along any fault.

TABLE 6.—AZIMUTHS* AND TENTATIVE AGES OF FAULTS

S.W. of Barona

E-W (B)NE-SW (C)N-S (E)NW-SE (F)E-W (G)NW-SE (H)

Minas Carlota

E-W (B)NE-SW (C)N-S (E)E-W (G)NW-SE (H)

North of Chivo

NE-SW (A)E-W (B)NE-SW (C)E-W (D)N-S (E)

Amphibole Hill

E-W (G)NW-SE (H)E-W (I)

South of Hon-eymoon Hill

E-W (G)NW-SE (H)E-W (I)N-S (J)

PeakS

E-W (G)NW-SE (H)E-W (I)

* Azimuths are approximate; units vary up to 10° either side. Letters in parentheses correlate sys-tems; "A" is the oldest system.

isoclinal folding. However as three orogeniesafter the formation of the Trinidad Mountainsare reported (Thiadens, 1937), the bending orcross folding may well have been later.

Faulting

Relief from isoclinal-folding pressure appearsto have been predominantly "upward"; reversefaulting, much of it contemporaneous withisoclinal folding, is prominent. Most of thesefaults follow bedding and are difficult torecognize.

Tranverse faults, because of the lack oftraceable units, are also difficult to recognize.Although the surface displacement of some ofthese faults is conjecturable, relative move-ment, whether normal, reverse, or tear (strike-slip), is unknown. So far as dcterminable, theintensity of folding on either side of thesetransverse faults is the same.

Interpretation of any faulted area consistsof grouping the faults according to strike,noting whether one system offsets or is offset byanother, and critically examining associatedstructures.

Difficulties in applying these criteria wereat once apparent. Many faults change strikeor may dip in opposite directions at differentplaces. Many fault intersections are covered.Also, because one fault ends at, or is offset byanother, it is not necessarily older—the twomay be of the same age. Apart from the hardlimonites of Gossans 2 and 3a (Fig. 3), the

Despite the limitations and difficulties in-volved, fault intersections and strikes wereanalyzed in certain localities to ascertain generalrelationships (Fig. 3; Table 6).

Some generalizations appear tenable: (1)movement along the east-west faults was re-peated; (2) system E may be used tentativelyto divide the faults into younger and olderfaults; (3) the oldest systems are in the interiorof the mountains; (4) the northeast-southwestsystems (A and C) are among the oldest;(5) along the northern boundary of the moun-tains, the majority of the H faults appear tobe late extension faults of "Appalachian"type, diagonal to folding.

Structure of the Trinidad Mountains

The outer boundary of the Trinidad Moun-tains—the contact between amphibolite andschist (or limestone)—appears to lack contactmetamorphism. Thiadens (1937, p. 22) repre-sented the contact as steeply faulted because ofthe " . . . vertical and overturned position of theschists" and the ". . . strong cataclastic structureof the dioritic rocks".

Subsequently anomalies of Cuban structurehave been explained as resulting from large-scale thrusts from north or south (Palmer,1945; Thayer and Guild, 1947; Flint, Albear,and Guild, 1948; Kozary, 1954, unpub. Ph.Dthesis, Columbia Univ.; 1956; Wassal, 1956)(Fig. 2).

Although the actual contact is not exposed,the demarcation is believed sharp. Gneissosity



STRUCTURAL GEOLOGY 1477

in the amphibolite parallels schistosity in theschist, and each rock was traced to within 15feet of the other. Apart from large and sporadicactinolite crystals (along calcareous horizons ?)300-400 feet from the contact, the schist issingularly undisturbed.

The present work therefore does not supportnortherly thrusting (Palmer, 1945). In the areastudied the contact appears to be a high-anglereverse fault.

Later transverse faults displace the contact.Some, e.g., west of Terminal Hill, form scarpsbetween rocks normally of equal resistance totropical weathering. These may be recent.Keijzer (1944) describes Pleistocene faultingfrom other parts of the island.

The extent to which thrusting exists withinthe mountains is debatable. Field conditionsare not good. The proportion of cover to rockis 8:1. Critical outcrops may be hidden byforest and overburden. However Charles Hatten(1958, personal communication) writes:

"To my knowledge, the best area within themain Sierra de Trinidad where thrusting isevidenced is in the eastern end of the mountains(Sierra de Sancti Spiritus). East of the RioBafiao the general attitude of the metamorphics(quartz mica schists with minor interheddedcalcareous schists) is north-south with a 60-80°east dip. Minor drag folds and poorly developedfracture cleavage indicate that the sequence isright-side up. To the west of Rio Banao a se-quence, obviously different lithologically fromthe above, with calcareous schists predominating,also strikes north-south but dips steeply to thewest. Near the base of this latter sequence,cataclastites are well developed. Minor recumbentisoclinal folds are present, which I believe, plungeto the northwest. The structural discordancebetween these two units is interpreted as awestward dipping thrust fault; however it couldbe an unconformity. More work should be donein this area to determine the relationship."

To summarize; in the area studied, themountains are not overthrust from the south.As suggested by Thiadens (1937) they appearto form a gigantic anticlinorium.

REFERENCES CITED

Allende, Roque, 1928. Yacimientos piritosos de laSierra de Trinidad, Mina Carlota, Cuba:Direc. Monies y Minas Bol. de Minas, v. 12,p. 50-57

Bailey, E. B., and McCallien, W. J., 1937, Perth-shire tectonics; Schiehallion to Glen Lyon:Royal Soc. Edinburgh Trans., v. 1, p. 79-117

Butterlin, Jacques, 1956, La constitution geologiqueet la structure des Antilles: Centre Natl. de laRecherche Sci., Paris, p. 1-64

Calvache, Antonio, 1925, Resumen de historia de lamineria de Cuba: Bol. de Minas, Habana,v. 8, p. 23-35

Castro, Manual Fernando de, 1881, Pruebaspaleontologicas de que la Isla de Cuba haestade unido al continente Americano y breveidea de su constitucion geologica: Espana Com.Geol. Bol., v. 8, p. 357-372

Faust, George T., Murata, K. J., and Fahey,Joseph J., 1956, Relation of minor-elementcontent of serpentines to their geologicalorigin: Geochim. Cosmochim. Acta, v. 10,p. 316-320

Flint, Delos E., Albear, J. Francisco de., and Guild,Philip W., 1948, Geology and chromite de-posits of the Camagiiey district, CamagiieyProvince, Cuba: U. S. Geol. Survey Bull.954-B, p. 39-63

Barker, Alfred, 1950, Metamorphism: 3d ed.,London, Methuen and Co. Ltd., 362 p.

Hayes, C. W., Vaughan, T. W., and Spencer, A. C.,1901, Report on a geological reconnaissance inCuba: 123 p., also in civil report of BrigadierGeneral Leonard Wood, Military Governor ofCuba, v. 1

Hill, Patrick Arthur, 1958a, Guaos area, Las Villas,Cuba: Carleton Univ., Geol. Paper 58-1, 8 p.1958b, Banded pyrite deposits of MinasCarlota, Cuba: Econ. Geology, v. 53, p. 966-1003

Keijzer, F. G., 1944, Outline of the geology of theeastern part of the Province of Oriente, Cuba:Reeks ser. 2, no. 6, Univ. of Utrecht, 239 p.

Kozary, Myron T., 1956, Ultramafics in the thrust-zones in northwestern Oriente, Cuba: 20thInternal. Geol. Cong. (Mexico), Resumenes,p. 138-139

Krommelbein, K., 1956, Die ersten marinen Fos-silien (Trigoniidae, Lamellibr.) aus der Cayen-tano-Formation West-Cubas: Senck. leth.,Frankfurt, bd. 37, nr. 3-4, p. 331-335

Lehmann, H., Krommelbein, K., and Lotschert, W.,1956, Karstmorphologische, geologische undbotanische studien in der Sierra de los Organosauf Cuba: Erkunde, bd. 10, h. 5, p. 185-204

Ljunggren, Pontus, 1958, Basic metamorphic rocksfrom the region of Holjes in northern Verm-land: Geol. Fciren. i Stockholm, Forh. bd. 80,h. 1, p. 23

McMurchy, R. C., 1934, The crystal structure of thechlorite minerals: Zeitschr. Kristall., v. 88,p. 420-432

Mitchell, R. C., 1955, The ages of the serpentinizedperidodites of the West Indies: Koninkl.Nederlandse Akad. Wetensch. Proc., v. 58,ser. B, p. 194-212

Page, Lincoln R., and McAllister, James F., 1944,Tungsten deposits, Isla de Pinos, Cuba: U. S.Geol. Survey Bull. 935-D, p. 177-246

Palmer, R. H., 1945, Outline of the geology of Cuba:Jour. Geology, v. 53, p. 1-34

Rutten, L., 1934, Geology of Isla de Pinos, Cuba:Koninkl. Nederlandse Akad. Wetensch. Proc.,v. 37, nos. 6-10, p. 401-406

Schurmann, H. M. E., 1935, Massengesteine ausCuba: Neues Jahrbuch f. Miner. Abh., Beil.Bd. 70A, p. 335-3551936, Lawsonite aus Cuba: Zentralbl. f. Miner.Abh., no. 8, p. 245-251

Spencer, J. W., 1896, Geographical evolution ofCuba: Geol. Soc. America Bull., v. 7, p. 67-94




Sweeting, M. M., 1958, The karstlands of Jamaica:Geog. Jour., v. 124, p. 184-199

Taliaferro, N. L., 1943, Franciscan Knoxvilleproblem: Am. Assoc. Petroleum GeologistsBull., v. 27, p. 109-219

Thayer, T. P., and Guild, Philip W., 19^rThrustfaults and related structures in eastern Cuba:Am. Geophys. Union Trans., v. 28, no. 6,p. 919-930

Thiadens, A. A., 1937, Geology of the southern partof the Province Santa Clara, Cuba: Physiog.-Geol. Reeks, no. 12, Utrecht, Holland, 69 p.

Vermunt, L. W. J., 1937, The geology of Pinar delRio province, Cuba: Physiog.-Geol. Reeks,no. 13, Utrecht, Holland, 60 p.

Wassal, Harry, 1956, The relationship of oil andserpentine in Cuba: 20th Internat. Geol. Cong.(Mexico), Resumenes, p. 45

Weyl, R., 1950, Die geologische Geschichte desAntillenbogens: Neues Jahrbuch f. Miner.Abh., Beil-Bd. 92, h. 2-3, p. 137-241

Wright, I. A., 1916, The early history of Cuba,1492-1586: N. Y., Macmillan Co., 390 p.

DEPARTMENT or GEOLOGY, UNIVERSITY OF TAS-MANIA, HOBART, TASMANIA, AUSTRALIA

MANUSCRIPT RECEIVED BY THE SECRETARY or THESOCIETY, JANUARY 27, 1958



Bull. Geol. Soc. Am., vol. 70 Hill, PI. 4

&ALTERED

AVCA SCH/STlnl~3"luntk with

thin layers of blackgillite

QUARTZ-MICA SCHISTWith garnet* and thin sea,to 3'thick, of black argillite

SEkPENTINIZED.'PYROXZNITE

CARBONACEOUS MICA SCHIST

With thin bands up to IB"thickof quartz-mica schist

CARBONACEOUSMICA SCHIST

Greenstone (fine-grained serpentiniie)

Light-blue densely compressed limestone

Medium-blue platy and foliated limestone;massive weathering

Medium-blue foliated limestone; massive weathering

Limestone weathering light blue, foliated; containingblack calcite crystals up to an inch m diameter

S.F/aggy limestone with bluish-white patina

to 5 with intercalated schist

Tightly-foliated white to blue limestone; may beequivalent to I

8. Schistose gray limestone with whitish patina

9. Dolomite, buff to light gray- with small hlack gypsum crystals

\O.Brucite limestone *

Quartz veins ..... qz - --- Specimen locality ____

Fault ............... A/\A>/W Thickness in feet .....

Approx. contact ..... ..... . Road

LIMESTONE (7ufti-encrujrtJ

GOETHITE-CHLOtflTE SCHIST

QUARTZ-MICA SCHIST

Deeply weathered with red5oil

GEOLOGIC TRAVERSE ALONG THE CUMANAYAGUA-MINAS CARLOTA ROADFrom Terminal Hill to Charco Azul



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