Structure and Tectonics of the Yucatan Basin, Caribbean Sea, As Determined from Seismic Reflection Studies

T}•;CTONI(iS, VOIJ. 9, NO. 5, PA(iF.S 1037-1059, {)('TOBI'JR 19L)0

STRUCTURE AND TECTONICS OF THE YUCATAN BASIN, CARIBBEAN SEA, AS DETERMINED FROM SEISMIC REFLECTION STUDIES

Eric Rosencrantz

Universityof Texas Institutefor Geophysics,Austin, Texas

Abstract. The YucatanBasin preserves a recordof the Late continues onland in Cuba as La Trocha fault. This Cretaceousto PaleogeneCaribbean-North American conver- reconstructionis consistentwith knownEocene regional genthistory that is largelyunaffected by Neogenestrike-slip tectonics,but the timing of regionalevents raises questions tectonicsof the currentplate boundary. An examinationof aboutpresent interpretations of plategeometry in the seismicbasement within the YucatanBasin, based upon northwestern Caribbean. availableseismic reflection data includingextensive multichanneldata, shows that the basementcomprises nine INTRODUCTION domainsdistinguished on the basisof internalreflection characterand surface topography. These domains encompass The YucatanBasin occupies a significantposition with threedistinct crustal types or blocks. The first underliesthe respectto northernCaribbean plate boundariesbecause it lies westernflank of the basinand represents the offshorecontinu- adjacentto the Late Cretaceousto Middle Eoceneconvergent ation of the adjacentYucatan platform. The secondincludes boundarytransecting Cuba, Hispaniola and Puerto Rico, but the topographicallyheterogeneous domains of the eastern outsidethe younger,present-day transform plate boundary two-thirdsof the basin,and is dominatedby a subsided extendingfrom Hondurasto PuertoRico (Figure 1). Because volcanicrise or arc (Caymanrise) restingupon probable thisyounger boundary has dissected and overprinted much of oceaniccrust of pre-Tertiaryage. The easternedge of the rise the older convergentboundary, the basinshould contain a and adjacentbasins dips northeast beneath the Cubanmargin recordof the convergenthistory of the Caribbeanplate that is alonga sedimentfilled trench. The thirdtype of crust unaffectedby later events,and so shouldprovide insight as to occupiesa rectangulardeep within the westernthird of the the natureand timing of the transitionfrom convergentto basin. Available evidence indicates that this crust is oceanic transformplate motion. in character,and representsa large,mature pull-apart basin set Unfortunately,the geologyof the basinhas been sparsely within a wide paleo-transformzone between the western sampledand the record of geologicaland tectonic events is platformand easternoceanic basin. This zonedefines the unclear,especially as to the compositionand ageof the crust. northwesternportion of the Caribbean-NorthAmerican Seismicrefraction profiles and regional gravity interpretations convergentplate boundary. Paleoceneto Middle Eocene suggestthat crust beneath the deepnorth-central and western transformmotion was left-lateralalong north-south to NNE- partsof thebasin is oceanic,but thatthe crust thickens SSW trends,with a displacementof about350 km. A long southwardto more than 20 km beneaththe Caymanridge Middle Eocene transcurrent fault of about 50 km left-lateral [Ewing et al., 1960;Dillon et al., 1972;Dillon andVedder, displacementcuts the basindiagonally from SW to NE and 1973; Bowin, 1968; 1976]. Rocksdredged from the southern wall of the Caymanridge include volcanics and metavolcanics as well as granodioriteswith K/Ar coolingages of 59 to 69 Copyright1990 Ma (Maastrichtianto Paleocene),which suggeststhat this by the AmericanGeophysical Union. thickercrust represents a buriedLate Cretaceousisland arc restingon Late Cretaceousor oldercrust [Perfit and Heezen, Papernumber 90TC00475. 1978]. Inferredocean crust beneath the deepwestern part of 0278-7407/90! 90T C-00475 $10.00 the basinappears younger, however, Late Paleoceneto Middle 1038 Rosencrantz'Structure and Tectonics of theYucatan Basin

Plate BoundaryZone • Eocene-Present Gulfof . • PlateBoundary f Mexico %' AtlanticOcean /•,C u.•ba,'I•d -•';•'o•.•.•'•His•'•nio•-I, , ß

'%•ol•ombian;;•Ven•sUienlan; )•t 85 ø 80 ø OL GULF OF MEXICO

CUBA GOLFO DE BA TABANO

I. de Cozumel 11sleofPines

Pickle Bank

I MisteriosaBank

Banco Chinchorro GrandCayman I o Cayman Ridge

Rosario Bank cAYMANTROUGH N

LighthouseReef YUCATAN BASIN

TurneffeI. I 0 100 250 GloverReef J DISTANCE IN KILOMETERS 85 ø

Fig.1. Tectonicsketch map of the northern Caribbean (upper panel), and simplified bathymetric map of theYucatan Basin (lower panel). The location of thebathymetric map is shownby therectangle outlinedon thetectonic map. Isobathsare in kilometers.

Eoceneon the basisof heat flow [Epp et al., 1970; Ericksonet withmetamorphic textures similar to thoseidentified as Late al., 1972] and depthto basementmeasurements [Rosencrantz Cretaceousin agein centraland western Cuba [Baie, 1970; et al., 1989]. In contrast,samples dredged and drilled along Pyleet al., 1973;Vedder et al., 1973;Hatten et al., 1988]. the western flank of the basin include metasediments Seismicreflection surveys of the westernflank andadjacent lithologicallysimilar to Paleozoicrocks found at depthacross deepbasin by Dillon andVedder [1973] and Uchupi [1973] the Yucatanplatform [Dillon et al., 1972;Dillon andVedder, leadboth to interpretthis margin as representing an old 1973; Deal, 1983; R. P. Rao, personalcommunication, 1988], passiverift margin. Rosencrantz:Structure and Tectonicsof the YucatanBasin 1039

This paperexamines available seismic reflection data from with datacollected using airgun and sparker sources. The the YucatanBasin to determinebasin tectonics as revealedby majorityof thesealso remain unpublished, except for several the distribution of basement seismic character and structure. presentedby Dillon et al. [ 1972],Vedder [ 1972],Uchupi The approachused here differsfrom previouswork [e.g., [1973] and Dillon and Vedder [1973]. Table 1 listsdata Dillon et al., 1972;Dillon andVedder, 1973;Uchupi, 1973; sourceand type. Figure 2 showsprofile locations. Tinkle, 1981] in that it examinesthe whole of the basinrather Althoughthe amountof availableseismic reflection thanjust its westernpart, and incorporatesand correlatesall materialappears extensive, these data are in fact limited in availableseismic data, including the largevolume of unpub- severalrespects. The overallcoverage of thebasin is sparsein lishedUniversity of TexasInstitute for Geophysics(UTIG) view of the morphologicaland structural complexity of the multichannelseismic (MCS) data. This largerset of infor- region. Matchingreflector sequences between profiles of mationshows a basinunderlain by crustof complicated differentvintages is oftendifficult owing to differencesof internalstructure, composed of oceaniccrust of two different scaleand resolution. Older profiles are commonly not well originsplus continental crusts, distributed across two plates. navigated.Variations of sourcesignature produce significant differencesin reflection character,and differencesin source SEISMIC REFLECTION DATA strengthresult in varyingdegrees of bottompenetration. Becausethe multichannelseismic lines show the deepest Seismicreflection profiles used in this synthesisinclude penetrationand have the mostconsistent source signatures, both singleand multichanneldata. The multichannelseismic descriptionsare basedprimarily on the the MCS lines, (MCS) datawere acquiredby UTIG duringfive separate supplementedby singlechannel data. acquisitionprograms between 1975 and 1980. Thesedata were collectedusing large-volume, low-pressure airguns or BASEMENT STRUCTURE explosivesources, shot to 24 or 48 channelstreamers of 2 to 4.5 km length,and were digitallyprocessed at UTIG with Basementis definedas the seismicunit belowthe deepest standardtechniques. These profiles are previously continuousseismic horizon, defined as the basementhorizon. unpublished,except for onepresented by Tinkle [1981] and Thishorizon is almostalways marked by a distinct,high anotherincluded in Rosencrantzet al. [ 1989]. The single amplitudereflection or groupof reflections.It occupiesthe channelseismic (SCS) datawere acquiredbetween 1961 and sameposition relative to overlyingsediments as the Late 1973 on thirteenseparate cruises by a numberof institutions, CretaceousB" horizonin the VenezuelanBasin [Edgar et al.,

TABLE 1. Seismic Reflection Data Project Year Agency Ship-Cruise SoundSource

MULTICHANNEL YB 1975 UTIG R,/VIda Green-IG 1506 Airgun, 1500-3000in 3, 350-450psi GT2 1977 UTIG R/V Ida Green-IG2401 Airgun, 3000 in3, 350-450 psi CT1 1978 UTIG R,/VIda Green-IG2901, 04 Airgun, 6000 in3, 350-450 psi CAR 1979 UTIG R,/VFred H. Moore-FMO 107 Maxipulse©, 5/8 lbs CT2 1980 UTIG R,/VFred H. Moore-FM0501, 02 Airgun, 6000 in3, 450-500 psi

SINGLE CHANNEL Verna 17 1961 LDGO R/VVema-V1704 Airgun ? Conrad9 1964 LDGO R,/VConrad-C0902 Airgun,20 in3, 2000 psi Conrad10 1966 LDGO R/V Conrad-ClO03,12 Airgun,20 in3, 2000 psi Verna 24 1967 LDGO R/V Verna-V2402 Airgun ? Conrad12 1968 LDGO R/V Conrad-C1201 Airgun,20 in3 SanPablo 1968 USCGS USSSan Pablo-SP939003 Sparker? Trident1 1969 URI R,/VTrident-TR067 Airgun,10 in3 Verna26 1969 LDGO R/V Verna-V2608 Airgun ? IDOE a 1971 USGS UnitedGeoI Sparker,220 kJ Chain100 b 1971 WHOI R/V Chain-CHlOO12 Sparker,90 kJ LosAlaminos c ? TAMU R/V LosAlaminos Airgun Wilkes73 1973 NAVOCEANO USNSWilkes-WI933008 Airgun

Projects:YB, YucatanBasin survey; GT2, Gulf(of Mexico) Tectonics-Phase2; CT1, CaribbeanTectonics-Phase 1; CT2, CaribbeanTectonics-Phase 2; CAR, Caribbeanphase of IPOD sitesurveying. Agencies: UTIG, Universityof TexasInstitute for Geophysics;LDGO, Lamont-DohertyGeological Observatory; WHOI, WoodsHole OceanographicInstitute; USCGS, UnitedStates Coast and Geodetic Survey; URI, Universityof RhodeIsland; USGS, United States Geological Survey; TAMU, TexasA&M University;NAVOcEANO, (UnitedStates) Naval OceanographicOffice. Publishedsources: aVedder [1972]; Dillon andVedder [1973]; bUchupi[1973]; CTinkle [1981]. 1040 Rosencrantz:Structure and Tectonicsof the Yucatan Basin

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1973], but is apparentlynot equivalentin ageor origin slopeexceeds 18 ø. A line extendingWNW from the offsetto becausethe Yucatanbasin horizon records events younger the northernedge of BancoChinchorro marks a boundary than thoseassociated with the B" reflector (seebelow). betweenshallow southern ridge tops and deeper northern The basementunit showsfour distinguishing ones,and may tracethe line of a cross-marginfault. characteristics:(1) largescale (> 1 km), basin-widerelief of Basementbeneath the centraltrough contains numerous the basementhorizon, mapped in Figure3; (2) largescale internalreflections that lie subparallelto the basement basementstructure, consisting predominantly of reflectorand horizon. Thesehave a discontinuoushummocky appearance, topographicoffset, interpreted as representing faults, mapped and includelocal high angleoffsets. The basementhorizon in Figure4; (3) distinctivesmall scaletopography and/or consistsof a distinctbut discontinuousreflector of hummocky distributionsof reflectionsat the basementhorizon; and (4) appearancedescribing a surfaceof low relief (<250 m). The distinctive distributions of reflections internal to basement. unit is apparentlycontinuous with units(and rocks) The dominant characteristic of basement is its surface underlyingthe Yucatanplatform to the west. To the east, topography,which controls the overallmorphology of the reflectionscannot be tracedbeyond the easternedge of the basin. Differences of small scale basement seismic structure centraltrough (Figure 6, kilometers70 to 72). Whetherthis is correlatewith largescale basement relief, indicatingthat due to basementunit truncation,or is simply an artifactof basement relief reflects variation in crustal structure. On the sourceenergy scattering by the roughbasement of the outer basisof thesedifferences, the basementunderlying the basin ridge, cannotbe determinedfrom the seismicdata. can be divided into 9 crustal domains. These are outlined in Figure 5, and are describedbelow. Domain B: Southwest Horst and Graben

Domain A: The Yucatan Borderland The southwesthorst and grabendomain is locatedat the southwestend of the Yucatan basin, between the Yucatan The Yucatan borderland underlies the western flank of the borderlandand the westernCayman ridge (Figure5). It is YucatanBasin, from Cubato Honduras(Figure 5). Basement boundedby the Yucatanborderland escarpment to the west includesthree linear topographic elements extending the andby the NE-SW trending,west-facing escarpment lengthof the domain:a troughaligned along the domainaxis, truncatingthe westernend of the Caymanridge to the east. an outertopographic high parallel to andeast of thetrough, Basementis pervasivelybroken by a seriesof NNE-SSW andan outerescarpment which slopes eastward from the outer trendinghorsts and grabens.The geometryof the basement ridges(see Figures 3 and4). surfacesuggests that blockshave tilted androtated, although The centraltrough, known as the Dangriatrough in Belize the blocksare internallyfeatureless, and their topscommonly [Rao andRamanathan, 1988], lies between35 and 65 km east indistinctwhere buried beneath thick sediments(Figure 7). of the Yucatancoastline. It is composedof a seriesof con- Fault spacingperpendicular to trendaverages about 10 km, nected,elongate deeps distributed en echelon,with right- andrelief of fault scarpsranges from a few hundredmeters to handedsense, on a NNE-SSW trend. Individualdeeps range over 2 km. The averagedepth of basementis about5 km. in lengthfrom 40 to 80 km, in width from 15 to 30 km, and havemaximum depths of between3.5 and4.5 km. They Domain C: WesternDeep Basin commonlyshow asymmetrical cross sections, wherein western,east-dipping basement slopes have shallower dips The westerndeep basin domain covers a rectangulararea, thaneastern, west-dipping slopes. Basin axes and eastern 140 to 170 km wide and 330 km long, orientedNNE-SSW, slopesare characterized by westvergent (down-dropped to the adjacentto and eastof the Yucatanborderland (Figure 5). west)normal and reverseoffsets trending subparallel to basin The domainis borderedon all sidesby basementscarps or length(Figure 6). offsets(Figure 4). Basementis relativelyfiat, with depths The topographichigh east of the centraltrough contains two rangingfrom 5 to 7 km, with an averageof about6 km linesof discontinuous,steep-sided, linear ridges which trend (Figure 3). The basementhorizon consists of nested,high NNE-SSW. Theseridges range in lengthfrom 20 to 60 km, amplitudediffraction hyperbola describing a surfaceof andhave an averagewidth of about12 km (Figures3 and4). moderate(200 to 500 m) relief. The basementcomplex North of ChinchorroBank (aboutlatitude 19ø N) the ridges containsno persistentinternal reflectors, except at depthon reachminimum depths of about1 km, but southof this profilesshot with high energysources [Rosencrantz et al., latitudethey approach the surfaceand emerge at Chinchorro 1989] (Figure 8). Bank, Turneffe Island, and Glover Reef. To the souththe The westerndeep is separatedfrom the Caymanrise (see ridge linesare separatedby about40 km, but convergeto below)to the eastby severalNNE-SSW trendingbasement about20 km in the north. Individual ridgesalong each line scarpsand lineaments,interpreted to representfault lines showa slight,dextral en echelonplacement. (Figure 8, kilometers180 to 200). Both the northernand The easternside of the borderlandis definedby a major southernboundaries are characterizedby WNW-ESE trending escarpmentwith an averagerelief of about3.5 km. Maximum basementscarps which may includefaults (Figure 9, kilo- crestto baserelief is over 5 km. The escarpmentextends meters20 to 30). The westernedge of the domainlies along essentiallyunbroken from Cubasouthward to latitude18 ø N, the baseof the Yucatanborderland escarpment. Adjacent to whereit is offset 15 km to the east. Southwardpast the offset the escarpmentbetween latitudes 19 ø and 20ø N, a small it againcontinues unbroken along the eastside of GloverReef wedge-shapedarea contains a NE-SW trendingtrough of 7 (Figure3). North of the offset,the escarpmentslopes to the km depthand an adjacentparallel ridge of about4.5 km depth eastwith an averagedip of about10 ø. Southof the offsetthis (Figure 3). The basementhorizon within the area is 1042 Rosencrantz: Structure and Tectonics of the Yucatan Basin Rosencrantz: Structure and Tectonics of the Yucatan Basin 1043

i i i i i •00 2• 85 ø DISTANCE IN KILOMETERS 80ø84/'/4/!//48 t:'L4 7.P O

CAUTO DEPRESSION

20 o

BANCO CHINCHORRO ORIENTE TRANSFORM TROUGH FAULT cAYMAN

YUCATAN BASIN BASEMENT STRUCTURE

ß SEAMCUNT BASEMENTRIDGE 2000• BASEMENTCONTOUR GLOVERREEF SHOWBASEMENT FACINGSCARP DIRECTION)(TICS • THRUSTFAULT DANGRIA TROUGH 85 ø

Fig. 4. Basementstructure of the YucatanBasin (contoursin meters).

characterizedby a discontinuousreflector of moderaterelief irregularsurface characterized by commonnested hyperbolas, (250-750 m). Internal reflectorsare discontinuous,hum- as shownin Figure 10 (kilometers60 to 105). Basement mocky,and dip relativeto, andare truncatedby, thebasement topographicoffsets suggest that the domainis cut by several horizon. NE-SW trendingfaults (Figure 4), but the basementcomplex showsno obviousstructural break with deepercrust to the Domain D: Northwesten• Rise northeast and southwest.

The northwesternrise lies to the northof thewestern deep Domain F: Eastenz Basin basin,south of Cubaand west of the Isle of Pines(Figure 5). Basementrises northward across a seriesof topographicsteps The easternbasin domain occupies the northeasterncomer to a minimumdepth of 4 km, thendrops across a north-facing of the YucatanBasin, between the Caymanrise (seebelow) scarpjust southof the Cubanmargin to a depthof over5 km and steepescarpments of the Cubanmargin (Figure6). (Figure3). Basementrelief is probablygenerated by faulting Basementdepths range from 5 to to slightlyover 6 km, but of unknownstrike. The basementcomplex contains no dis- reach6.5 to 7 km alonga north-southtrending linear deep tinctinternal reflections. The basementhorizon is definedby locatedsouth of the Isle of Pines(see Figure 3). Basement a strongreflection, smooth along the lower,southern part of westof this lineamentis flat with a slightsouthward slope, the rise (seeFigure 9, kilometers30 to 45, andFigure 10, kilo- whereasbasement to the eastshows some relief, increasing meters15 to 60), but characterizedby high amplitudediffrac- eastward(Figure 4). The basementhorizon consists of a tion hyperbolaacross the higher, northern parts of the domain strongdiscontinuous reflector with low to moderaterelief, (Figure 9). with minorfault disruptionsand diffraction hyperbola (see Domain E: Central Seamounts Figure 11). The basementcomplex shows uncommon indistinct and discontinuous internal reflectors.

This small domainis locatedcentral to the YucatanBasin, betweenthe westerndeep basin and eastern basin (see below) Domain G: Cayman Rise (Figure5). It containsisolated, irregular basement highs and deepsof morethan 2 km maximumrelief (Figure3). Base- The Caymanrise domainoccupies the triangulararea mentwithin the areais internallyfeatureless, but hasan betweenthe deepsof the westernand northern Yucatan Basin 1044 Rosencrantz:Structure and Tectonicsof the YucatanBasin

, i i i i 8øø I

CAUTO DEPRESSION

20,• o.

-' 2000

BANCO CHINCHORRO GRAND CAYMAN TRANSFORM I ORIENTEFAULT TROUGH TURNEFFE I. cAYMAN YUCATAN BASIN BASEMENT DOMAINS

0 100 250

DISTANCE IN KILOMETERS

DANGRIA TROUGH GLOVERREEF I 85ø i

Fig. 5. The distributionof crustaldomains within the YucatanBasin, identified as A throughI. Seethe text for descriptions.The heavy lineslocate the MCS profilesshown in Figures6 through13.

andthe Caymanridge (Figure5). The domainis faultswithin the zoneof grabenslocally disrupt and displace characterizedby a broadtopographic rise across the southern the deepestof the seismicfacies units. At longitude82.5 ø W, partof thebasin. The linearcrest of therise lies at depthsof this zone intersectsa linear, fault boundedtopographic deep greaterthan 2.6 to 2.8 km, andcontains several individual which cutsacross the rise with a north-southtrend at depths peaksor seamountswhich rise to lessthan 2 km. A carbonate exceeding5 km (Figure 3). The structureis similar in size pinnacleknown as Pickle Bank caps the easternmost of these and orientationto the one cuttingthe easternbasin to the peaks(Figure 3). To thewest the rise takes on thecharacter north. of an irregularplateau lying at a meandepth of about3.5 km The Caymanrise is separatedfrom domainsto the westand (Figure 10). northby a seriesof northwestfacing slopes and escarpments The basementhorizon is characterizedby a strongdiscon- that definea topographiclineament extending from the tinuousreflector of hummockyappearance, with uncommon, westernend of the Caymanridge northeastto centralCuba subdueddiffraction hyperbola, except along the crestof the (Figure4). This lineamentis mostextreme at the westernend rise,where the basementreflection becomes diffuse and of the rise (and westernend of the adjacentCayman ridge) mergeswith overlyingsediments (Figure 12, kilometers 58 to whereit consistsof a singleescarpment up to 2.5 km high. 88). The surfaceshows moderate small scale relief of Adjacentto the westerndeep basin the lineamentis definedby apparentconstructional origin. Uncommon reflectors internal a seriesof scarpsand linear valleys along the base of a rugged to the basementunit rangein appearancefrom chaoticto NW dippingslope. Southof the centralseamount domain, discontinuousparallel. Basement offsets are uncommon and basementalong and to the southof the lineamentshows do not directlydisrupt overlying sediments. evidenceof block faulting,with overlyingsediments both Basementsouth of the rise crest, between the crest and the offsetand deformed(Figure 11, kilometers122 to 132). Caymanridge, is cut by a seriesof ENE-WSW trendinghorsts Farther northeastward,the lineament follows a ENE-WSW and grabens. These extendfrom longitude79øW west to trending,north facing scarp separating the rise from the 83øW in a zone about50 km wide (Figure4). Individual easternbasin (Figure 11, kilometer95). Along the northeast- grabensrange in width from 10 to 20 km, andhave a ern part of the rise,however, the lineamentis expressedonly maximumrelief of up to 2 km (Figures10 and 12). Basement as a zone of anomalouslyrough basement (Figure 12, kilome- Rosencrantz: Structure and Tectonics of the Yucatan Basin 1045

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0 10 20 30 40 50 60 70 80 90 100 110 120 •130

DISTANCE IN KILOMETERS

Fig. 6. Multichannelseismic reflection profile (UTIG profileCT1-40) acrossthe Yucatanborderland. Seethe insetmap andFigure 5 for profilelocation. The upperpanel shows the uninterpretedprofile, processedwith standardtechniques, including automatic gaining of tracesduring profile plotting. The middlepanel contains an interpretativeline tracingof the profileshowing features discussed in the text. The basementhorizon is designatedB, the waterbottom WB. The WesternDeep Basinis identifiedas WDB. Major seismicunit horizonswithin the sedimentsare drawnwith light lines. The vertical exaggerationof thisand the upperpanel is about8:1 at the waterbottom. The bottompanel displays a simpleline drawingof a profiledepth section drawn without vertical exaggeration.

ters 173 to 180), and the rise slopestoward the easternbasin Domain I: Camagiiey Trench without apparentstructural break. The easternedge of the Caymanrise intersectsand dips Domain H: Cayman Ridge beneaththe southwesternCuban margin along a NE dipping thrustzone (Figure 13). The basementhorizon describes a The Caymanridge, located between the Caymanrise and trench,designated the CamagQeytrench, which extendsfrom the Caymantrough (Figure 5), is a ENE-WSW trendingcrest latitude 20 ø N in a curve south and east toward the Cauto definedby the 2000 m basement(and bathymetric) contour Depression(Figures 3,4). Basementdepths within the trench (Figure3). The geometryand reflectioncharacter of the reacha maximumof about6.5 km alongthe axis. The basementsurface suggests that basementblocks are faulted deepestof the sedimentarydeposits filling the trenchdisplay and tilted, althoughbasement underlying the ridge shows west-vergentthrusts and folds (Figure 13). either chaotic internal reflectors or no internal reflectors. Individualblocks defining the crestof the ridgelie parallelto DISCUSSION AND INTERPRETATION the ridge trend,except at the easternend where individual blocksshow a slight dextralen echelondistribution relative to Distribution, Composition,and Age of Basement the ridge trend (Figure 4). The westernextension of the Sierra Maestramountain range in southernCuba is not topographi- The reflectioncharacter of the basementunit, includingthe cally continuouswith the ridge but lies to the southof the relief of the basementhorizon, plus the geometryof faults easternridge crest(Figure 4). To the westthe ridge is cuttingthe basementunit, indicatethat the YucatanBasin truncatedby the 2.5 km high, NE-SW trendingscarp that includesthree distinctand separateblocks of crust. The first definesthe easternboundary of the southwesternhorst and block includesthe Yucatanborderland domain, plus the south- grabendomain. west horstand grabensdomain. The secondincludes the GULF OF MEXICO 0 SL

Z 0 0

SL- N'W SE SOUTHWEST HORST AND GRABEN GLOVERREEFBANK SLUMPEDAND uJ •k FOLDED• SEDIMENTS• SLUMPED AND •.,j• /•, •.•-- FOLDEDSEDIMENTS t '-.¾.L_.• .•.•%

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Fig.7. Multichannelseismic reflection profile (UTIG profileCT1-35) across the southwest horst and grabendomain. Diagram elements are the same as in Figure 6. Seethe inset map and Figure 5 for profile location. Rosencrantz: Structure and Tectonics of the Yucatan Basin 104 7

GULFMEXICOOF o, lO, 20, • ,-OlD , •,0 ,,00 ,10 ,f0 ,,•0 ,10 ,•0 ,•0 ,•0 ,•0 ,•0 •70 •I 0 •0 •0 3 4 • 5 .....•.•m•••5:½• ' ß .....

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Fig. 8. Multichannelseismic reflection profile (UTIG profile CAR-72) acrossthe westerndeep basin domain.The reflection suspected asrepresenting theMohorovi[i•. Discontinuity islabeled M?; other diagramelements are the sameas in Figure6. Seethe insetmap and Figure5 for profile location.

westerndeep basin domain. The third block comprisesthe compositionof basementrocks dredged and drilled alongthe remainingdomains underlying the easternbasin, the Cayman outerridge of the borderlandshow that crystallinerocks lying rise, Caymanridge, Camagfieytrench and centralseamcunts at depthbeneath the platformextend to the borderland domains,plus the northwesternrise. Theseare described escarpment.The GloversReef #1 well penetratesPaleozoic below. shalesimilar to that of the Maya Mountains[Dillon and The Yucatanborderland block. Seismicprofiles across the Vedder, 1973]. Baie [ 1970], Dillon et al. [ 1972], Dillon and Yucatanmargin (Figure 6) indicatethat the stratigraphyof the Vedder [ 1973] and Vedder et al. [ 1973] all observethat Yucatan platform [Bateson,1972; Batesonand Hall, 1977; alteredbasic extrusives, deformed metamorphosed (low Lopez-Ramos,1975; Weidie et al., 1979;Viniegra-O., 1981] grade)shale, siltstone and quartzite,metamorphosed (green- extends offshore beneath the borderland. The Basil Jones #1 schistfacies) phyllites, and foliated marbles dredged from the well, locatedon the Belizecoastline and on the easternedge outerescarpment at depthsbetween 4200 and 2700 m are of the CorozalBasin (see Figure 2 for location),includes equivalentto YucatanPaleozoic rocks. Pyle et al. [1973], on about 100 m of Tertiary limestones,1900 metersof Mesozoic the otherhand, suggest that these,on the basisof their shallowwater carbonatesand evaporites,a thin Jurassicred metamorphiccharacter, correlate to the Middle JurassicSan bed, andabout 100 m of Paleozoicshale resting on schist CayetanoFormation of westernCuba. [Lopez-Ramos,1975]. Rao andRamanathan [1988] show The lack of dredgedcarbonate and evaporitesamples that the offshorestratigraphic section measured at the probablyreflects the smallnumbers of rockscollected, but Turneffe #1 well section correlates with well sections in the couldalso mean that theselithologies either were not Corozal Basin. depositedon, or have sincebeen eroded from, the outer The Turneffesection, located on the outerridges of the bor- margin. A schistpebble conglomerate with a Late Eocene- derland,demonstrates that the platformsection extends across Early Miocenematrix dredgedfrom the northernescarpment the centraltrough beneath the southernouter ridges, and the [Vedder et al., 1973] hints that the northernouter ridges may 1048 Rosencrantz: Structure and Tectonics of the Yucatan Basin

I GULFOF •_. I

OL• o 4,13i 50I 6•0 70I 80I e•o 100I 110i 120I 130i 140I I

SOUTH CUBA BASIN • '•' NORTH

--WB

o RIFTED CRUST ß SMOOTH BASEMENT RIFT 8- •BOUNDARYZONE OCEANIC CRUST

210 310 40I 50I 610 70I 80I 910 100I 110I 120I 130I 140i I DISTANCE IN KILOMETERS

Fig. 9. Multichannelseismic reflection profile (UTIG profileCT2-1) acrossthe northwesternrise domain.Diagram elements are the same as in Figure6. Seethe inset map and Figure 5 for profile location.

haveincluded crystalline basement exposed during the Miocene. This wouldsuggest that lithologies above and Eocene. below the basementhorizon respectively represent the Belize The ageof thebasement horizon across the borderland is andToledo-Campur formations. However, Rao and not knownfor certain,but is likely to be Eocene. The Ramanathan[ 1988] also show (in crosssection) that both the synclinalcross section of the layeredbasement and onlapping Belize andunderlying Camput Formations thin or pinchout to of overlyingsediments (Figure 6) impliesthat the horizon the west at the coastlinealong north-south faults which define marks a tectonic event. The distinct difference in reflection the westernedge of the Dangriatrough. As the Campur characters of sediments above and the basement unit below formationalso rests with distinctunconformity upon Late the horizonimply a distinctchange in lithologyacross the Cretaceousdolomites and evaporites of the Cobanformation, horizon. The Late Eoceneand younger schist pebble con- the basementhorizon might also be reasonablyinterpreted as glomeratenoted above is consistentwith an Eoceneor older a Late Cretaceoussurface between the Belize-Campurand tectonicage for the horizon. The Turneffe#1 andSpanish Coban units. Lookout#1 wells penetrateMiddle Eoceneand younger reef East-westfree air gravityprofiles across the southwesthorst carbonates,lagoonal carbonate muds and terrigenous andgraben domain show that underlying crust thins eastward, sediments(Belize Formation),which restunconformably on from about 20 km beneath Glovers Reef Bank to about 8 km Paleogene-LateCretaceous deep water clastics (Toledo beneaththe westernend of the Caymantrough [Dillon and Formation)in the Turneffe well and massivebiomicrites Vedder, 1973]. The compositionof the crustis not known (CampurFormation) in the SpanishLookout well [Raoand directly,but the thinningand block faulting suggest that it Ramanathan,1988; R. P. Rao, personalcommunication, 1988]. may be stretchedcontinental crust. The hiatusbetween the Belize formationand underlyingunits The easternblock. Crustunderlying the areaeast of the becomesmore pronounced southward, extending into the westerndeep basin, including the easternbasin, central sea- Rosencrantz:Structure and Tectonicsof the Yucatan Basin 1049

GULFMEXICOOF 'C.L/SA'•J • 150 200 250 ,,ooi i I , I I , , I i • , , I I 0 ' • GRANDCAYMAN • 1- GT2-52.AMA,CA

• 5 •

oj NNW NW SSEI-

-- 321 CAYMANRIDGE "• F (•i5 ' •'RISE.--CENTRAL SEAMOUNTS'*'- ' CAYMANRISE ' .

0 50 100 150 200 250 I i I I I I i i • I I I I I I I ! i I I I I I I I I I I DISTANCE IN KILOMETERS

Fig. 10. Multichannelseismic reflection profile (UTIG profile GT2-52) across the central Yucatan Basin.Diagram elements are the same as in Figure6. Seethe inset map and Figure 5 for profile location.

mounts,Cayman rise, Cayman ridge and Camagiiey trench ridge. Theyfurther argue that the underlying 6.5 km s-• domains,is likely contiguousand of commonorigin. No velocitylayer consists of Cretaceousamphibolites and Late obvious structural break is observed between the central sea- Cretaceousto Paleoceneplutonics, volcanics and volcanoclas- mountsand the easternbasin, nor between the Cayman rise tics. andCamagiiey trench. The Bouguergravity field [Bowin, The Caymanridge undoubtedly includes Cayman rise crust, 1976]and free air gravityprofile models [Bowin, 1968] both upliftedin responseto platemotion along the Oriente trans- indicatethat crust beneath the rise is laterallycontinuous with form fault to the south.The two structuresintersect, and thatbeneath the easterndeep basin. The Caymanrise inter- apparentlyhave a commonlithology [Perfit and Heezen, sectsand topographically merges with theCayman ridge west 1978]. A single,shallow seismic refraction profile near Grand of longitude83 ø W. The reflectiveand small scale CaymanIsland shows crustal velocities broadly similar to topographiccharacters of the basementhorizon within the thoseof therise to thenorth [Ewing et al., 1960]. Seismic easternbasin are similar to thoseof theCayman rise, and the reflectionprofiles across the ridge show that it is separated basementcomplexes of bothdomains show uncommon fromthe rise by a lineof ENE-WSWfaults along its north internalseismic layering. side,particularly along the eastern half of theridge. Crustal The irregulartopography of basement,the presence of sea- blockswithin the ridge are apparently tilted (Figures 10 and mountsalong a lineartopographic crest, and likely presence 12). TheMiddle Eocene opening of theCayman Trough of volcanoclasticdeposits on the rise crest[Perfit andHeezen, [Rosencrantzet al., 1988]implies that the ridge had formed at 1978]all implythat the Cayman rise has a volcanicorigin. leastby Eocenetime. The earliestrecord of crustalmovement Seismicrefraction profiles show that the crustal thickness of alongthe ridgeis oneof subsidence,however, in thatthe therise is at least14 km [Ewinget al., 1960],and gravity distributionof datedcarbonate rocks dredged from the ridge modelingsuggests that it exceeds18 km, thinningto thenorth showthe western ridge subsiding by Miocenetime. [Bowin,1968]. Thebasement horizon corresponds to the top Oligoceneand older carbonates have shallow water origins, of a 2.6 km thick 4.8 km s-• seismic refraction interval whereasyounger carbonates include both deep and shallow [Ewing,et al., 1960](Figure 12). Perfitand Heezen [1978] watervarieties [Perfit and Heezen, 1978]. arguethat this seismicunit representsvolcanics, clastics and Crustbeneath the eastern deep basin is probablyoceanic, metasediments,plus carbonates, of Paleoceneto Eoceneage, butmay not be typical oceanic crust. A singlerefraction assampled at the westernend of thesouth wall of theCayman profilesouth of theIsle of Pines(Figure 2) showsan 8 km 1050 Rosencrantz:Structure and Tectonicsof the Yucatan Basin

MEXICO ,,• iiiiiiii Iiiiiii I iiiiiiiii ii .oø - ._t_.llOO ,.• ß GRANDCAYMAN

07-

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i 07- _ -

Z 8- O

u• 9 TRANSBASINFAULT

..i VlO:

0 10 20 30 40 50 60 70 80 90 100 !,•,•,•,•l,,t,,•, •tl,,,,,,,, •1,,,,,,,,,1,,,,, , •,1•,•,,,•,,1• • ,,,,,•,1,,, ...... ! .... ,,,,,! ...... ! DISTANCE IN KILOMETERS

Fig. 11. Multichannelseismic reflection profile (UTIG profile CT2-4) acrossthe easterndeep basin domain. Otherdiagram elements are the sameas in Figure6. Seethe insetmap and Figure 3 for profile location.

thick crustwith an oceanicvelocity structure [Ewing et al., GravityAnomaly Map of NorthAmerica, 1988] (Figure 14). 1960]. Oceaniccrust is consistentwith the regionalgravity Theseobservations suggest that the easterncrust is both signature[Bowin, 1968; 1976]} but the basement does not thickerand/or less dense than that of the westerndeep basin. showthe roughtopography and nestedhyperbolas charac- A possibleexplanation for thisapparent anomaly is that teristicof oceaniccrust, as evidentwithin the westerndeep easternbasin crust includes an upperlayer of volcanicsresting basin. The basementblock faultingseen in the easternbasin on the oceanicbasement. This would explain the semi- is alsoatypical. Mean depthsto basement(with the loading continuous character of the basement horizon across both the effectsof sedimentsremoved) are lessthan those of the appar- rise and basin, as well as small scale similarities of basement ently youngerwestern deep basin, about 5100 m versusabout relief betweenthe easternpart of the riseand adjacent basin. 5300 m. This differenceis alsoreflected in the regionalfree The layer neednot showa distinctinternal reflection air gravityanomaly field, whichshows a smallmean negative signature.The westwarddeepening of the easternbasin may

valueof 15 milligalsover the easternbasin, in contrastto the reflecta westwardthinning of this layer. _ meanpositive value of about15 to 20 milligalsover the The irregularrelief of the centralseamount domain suggests deeperwestern deep basin [Bowin, 1976; Committeefor the that the topographyhas a volcanicorigin. Theseseamounts Rosencrantz: Structure and Tectonics of the Yucatan Basin 1051

GULFMEXICOOF 'C, •U8 • ß 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 • 220 I I I I I I I I I I I I I I I I •D :2 CT1-30 1-2

:Z•4 ' O•

NN• i::: 2- CAYMAN RISE , • EASTERN BASIN

i_4- w•5- u•6 - 0 •:7-

o lO 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 i i I I I I I I I I ,l I I I I I I I I I I I I l DISTANCE IN KILOMETERS

Fig. 12. Multichannelseismic reflection profile (U'I'IG profile CT1-30) across the eastern Yucatan Basin.Measured crustal seismic refraction velocities [Ewing et al., 1960]are shown at kilometer40. Otherdiagram elements are the same as in Figure6. Seethe inset map and Figure 3 forprofile location.

alignwith the lineamentdefining the easternwall of the Vinentand Morales, 1988]. On theother hand, if a major westerndeep basin, and may reflect"leakage" along faults convergencezone lay betweenthe Zaza rocksand the Yucatan duringthe openingof thewestern deep basin. Basin,as implied by theCamagiley trench, then the maximum The nature of crust beneath the northwestern rise is crustalage of the easternYucatan Basin is unconstrained. unknown,as is its relationshipto the adjacenteastern basin. Westerndeep basin crust. A varietyof evidenceshows that The crosssectional pattern of basementfaults on the south the westerndeep basin is underlainby oceaniccrust. The slopeof the rise (Figure9) suggeststhat this crust is rifted and Bouguergravity field over the basinis oceanicin character thinned, but the strikes of these faults cannot be determined [Bowin, 1976]. Modelsof freeair gravityprofiles across the with presentdata. This basementmay be a rifted western basinindicate that crust underlying the deep basin has oceanic extensionof the continental(?)crystalline crust underlying the thickness(6 to 8 km) anddensity [Bowin, 1968;Dillon et al., Isle of Pines[Somin and Millan 1977;Millan, 1981],which 1972]. Seismicreflection profiles shot with highenergy would imply that the Isle of Pinesand relatedrocks of south- explosivesources show a persistentreflector at depthsconsis- westernCuba have a Caribbeanorigin rather than the North tentwith oceanicMoho (Figure8). Depthsof basement Americanorigin proposed by Pardo[ 1975]and Gealey acrossthe deepbasins are oceanic[Rosencrantz et al., 1989] [1980]. andthe nested hyperbolic reflection patterns of thetop of The age of oldestcrust within the easterndomains is a basementin the westerndeep basin are typical of oceancrust matterof conjecture.The minimumage is Late Cretaceous, reflectorpatterns (Figure 8). Basinheat flow measurements astonalites and granodiorites intruding the Caymanrise and [Eppet al., 1970;Erickson et al., 1972]are typical oceanic ridgeyield Late Cretaceous and Paleocene K/Ar coolingages values.The basincontains magnetic lineations, although the [Perfitand Heezen, 1978]. If thecrust is contiguouswith that NE-SW trendingpattern of anomaliesas mapped by Hall and of the Zaza terranein Cuba, then it would be at leastof Yeung [ 1980] and Yeung [ 1981] is inconsistentwith Aptian-Albianage [Pardo,1975; C.W. Hatten,O.E. Schooler, underlyingbasement topography and structure and shows a N. Giedtand A.A. Meyerhoff,Geology of centralCuba, poormatch with knownmarine magnetics reversals easternLas Villas andwestern Camagiley province, Cuba, sequences. unpublishedreport, 1958, hereinafter referred to as Hattenet The deepbasin is distinctin thatit is rectangularin shape al., 1958], andpossibly as old as Late Jurassic[Iturralde- andin thatthe basementhorizon is deeperthan that of sur- 1052 Rosencrantz: Structure and Tectonics of the Yucatan Basin

GULFMEXICOOF 'O0•,•'•• ' 0 10 20 30 40 50 60 .oO\• '/x/•/-7 .. 100 , ...... ,...... ,...... , ...... , ...... ,,,, ...... ,..... ,,,, ......

"'t CAYMANRISE . , TRENCH h- I'-- >.- •: 5- 6

• 6- Z O u.I 7- GRABENS'- ACCRETIONARY PRiSM••• o3 SL

¾1

,oi i i i I I I i i:,o, I I I i i I i I I I I i i i i I i I i I I I I i I j?i i I I I I I • ,soi i I I I I I I ,figi I i i I i i i ?, I i i i i I i I I I i i i I i i ??,i i i I i i i :ooi I i i i i i i i DISTANCE IN KILOMETERS

Fig. 13. Multichannelseismic reflection profile (UTIG profile CT2-10) acrossthe easternCayman rise and CamagiieyTrench domains. Diagram elements are the sameas in Figure6. Seethe insetmap and Figure 5 for profile location.

roundingcrust. The easternand westernboundaries of the depthto basementmeasurements indicate that the basin basinare definedby faults,as evidentboth from basement formed between 42 and 60 Ma 0VliddleEocene to Late offsetalong the boundariesand the abruptincreases of crustal Paleocene)[Rosencrantz et al., 1989], as determinedfrom the thicknessboth to thewest and east. Freeair andBouguer small basincooling curves of Boernetand Sclater[ 1989]. If gravitymodels across the westernboundary show that the the basinsimply represents a portionof a largerpiece of pronouncedgravity low alongthe baseof the borderland typicalocean crust, then its heatflow andbasement depth escarpmentmarks an abruptwestward thickening of crust yield an oldercalculated age of between55 and75 Ma from about7 to 23 km [Dillon et al., 1972; Bowin, 1976; (Paleoceneto Maastrichtian),based upon the crustalcooling Alvarado-Omana,1986]. Modelingof a similarbut less curvesof Parsonsand Sclater [ 1977]. pronouncedlow alongthe easternboundary shows an increase of crustalthickness to 12 to 18 km beneaththe Caymanrise Basement Structure: Faults, Thrusts,and Sutures andridge [Dillon et al., 1972;Dillon andVedder, 1973]. Gravitymodeling also suggests that crust thickens southward The majoroffsets, lineaments and faults cutting the base- towardthe southwestrift domain[Dillon and Vedder, 1973]. ment unit and horizon of the Yucatan Basin constitute three The rectangularshape, faulted boundaries and deep oceanic majortectonic structures. These are (1) the buriedCamagiiey basementof thewestern deep basin suggest that it formedas a trenchlocated on the easternboundary of the basin,(2) a smallrift basinwithin older surrounding crust. Heat flow and broad,structurally complex paleo-transform fault zone Rosencrantz: Structure and Tectonics of the Yucatan Basin 1053

Gulf of Mexico CU BA TRANSFORMLOW

o TRENCHLOW I o

Trodgh CAYMAN RIDGE HIGH

Gayman -50 0 +50

mgals

Fig. 14. Simplifiedgravity anomaly map of theYucatan Basin, adapted from the Gravity Anomaly Map of NorthAmerica [ 1988]. Notethat the gravity anomaly field everywherereflects basement topography (Figure3), exceptfor thegravity low alongthe base of theborderland escarpment (transform low) and the broadgravity high over the westerndeep basin. between the Yucatan borderland and easterncrustal blocks, similarin shape,size and internalstructure to the present-day and(3) a longtranscurrent fault thatextends diagonally SW- Caymanridge and escarpmentbordering the Caymantrough, NE across the eastern block. andis interpretedas being of similarorigin. As the baseof The Camagiieytrench. In crosssection the Camagiiey the southernflank of the Caymanridge defines the location trench shows all the characteristics of a trench associated with and trend of the Oriente transformfault, so the base of the a subductionzone (Figure 13). Basementclearly dips borderlandscarp defines the locationand trend of the paleo- northeastbeneath the Cubanmargin. To the norththe trench transformfault. This is supportedby free air and Bouguer hasbeen either truncated by, or truncatedand offset along, La gravitymodels of the pronounced,linear gravity low alongthe Trocha fault zone. To the south,it curvessoutheast toward baseof the slope,which showan abruptwestward thickening theCuban margin and Cauto depression. Whether it continues of crust(7 to 23 km) acrossthe escarpment[Dillon et al., southeastbeneath the margincannot be determined.There is 1973; Bowin, 1976, Alvarado-Omana, 1986] Seismic no directevidence on the ageor originof the trench,and the profilesacross the baseof the escarpmentshow little evidence tectonicsof Cuba are not knownwell enoughto fully for the presenceof this fault, but this is expectedin view of constraina mode of origin (seebelow). the roughnessand dip of the basementhorizon. The transformzone. The patternsof basementtopography North of latitude 19.5ø N, the westernfault systemincludes and structurewithin and adjacentto the Yucatanborderland two major,subparallel strands which mergenorthward as the andwestern deep basin indicate that this area includes a Pinar Fault. Between latitudes 19.5ø and 20 ø N, these two broad,north-south trending paleo-transform zone, or suture, strandsbracket a small pull-apartor rift basin. To the south, between the Yucatan borderland and eastern crustal blocks. between latitudes 18ø and 19.5 ø N, the fault zone in all The zone extends from the southwestern comer of the basin likelihoodincludes the faulted and acousticallylayered crust northwardto and includingthe Pinarfault of westernCuba, within the westerndeep basin adjacent to the escarpment, where it intersects the Cuban thrust belt. This transform which might representan exoticsliver of oldercrust emplaced definesthe northwesternsegment of the Late Cretaceous- within the transform zone. Paleogene("Laramide") suture along the Caribbean-North The fault zonedefining the easternboundary of the western Americanplate boundary (Figure 1). deepbasin is not aswell definedtopographically, and shows The basementtopography of the Yucatanborderland outer no distinctgravity signature. The presenceof multiplefault ridge and escarpment,as seenin crosssection (Figure 6) is strandsare likely, but not obvious. The zoneextends north- 1054 Rosencrantz:Structure and Tectonics of the Yucatan Basin wardinto the roughtopography of thecentral seamounts The north-southtrending topographic lineaments which cut domain,which may representvolcanics "leaked" along the the easternbasin and Caymanrise at longitude82.5 ø W fault zoneduring the earlystages of its development.To the probablyrepresent a narrowgraben of pre-MiddleEocene south,the easternboundary appears confined to a narrowzone age. Whetherit formedin responseto transbasinfaulting or alongthe baseof the low, lineartopographic rise flanking the to another earlier event is unknown. basin(see Figure 3), beyondwhich it disappearswithin the The basementfault blockscharacterizing the southwest block faultingthe southwesthorst and grabendomain. horstand graben domain may havedeveloped during Cayman The age of faulting,crustal rifting andbasement troughopening. However, the block faults could also reflect deformationis Paleogene.As notedabove, the probableage local crustal extension related to movement on the transbasin of westerndeep basin crust is Late Paleoceneto Middle fault,or representa wide zone of north-southtrending strike Eocene [Rosencrantzet al., 1989]. Late Cretaceousto slipfaulting related to transformdisplacements. Oligoceneradiometric ages of basementmetamorphic rocks Sedimentsthat fill the Yucatanbasin are largely dredgedfrom the Yucatanborderland escarpment represent undisturbed,indicating that the basinhas undergone little minimumages [Pyle et al., 1973;Vedder et al., 1973], deformationsince its formation. Exceptionsinclude the probablyreset by an Eocenethermal event [Vedder et al., foldingof deepsediments along the Camagiieytrench, the 1973]. Wells drilledin westernCuba penetrate series of faultingof deepsediments along the line of grabenssouth of platformsequence duplexes emplaced during Late Paleocene the Caymanrise, both noted above, and minor faulting and to EarlyEocene time, and dated melange rocks in centraland tilting of sedimentsalong the southernedge of the basin, western Cuban indicate that the arc rocks of the Zaza terrane adjacentto the Caymantrough. Seismicreflection profiles thrustover, and deformed, underlying sediments between acrossthe easternmostCayman ridge show small graben-like Early andMiddle Eocene time [Piotrowska,1978; structureswithin sedimentscapping the ridge. Much of the Pszczolkowski,1978; Mossakovskiy and Albear, 1978; Caymanridge has been displaced vertically during the Pszczolkowskiand Flores, 1986]. Neogene[e.g., Perfit andHeezen, 1978], although this is not Transbasinfault. The longtopographic lineament defined discernableon seismicprofiles. To thewest, faulting and by theseries of valleys,north facing escarpments, and slumpingof sedimentsand tilting of reefs[Stoddart, 1962] structural discontinuities that extends SW to NE across the alongthe southernYucatan borderland indicate that this part Yucatanbasin marks the locationof a largetranscurrent fault. of the marginis tectonicallyunstable at present[Dillon and To the northeastthis fault mergeswith andcontinues as La Vedder,1973]. Elsewhere,sediments overlying the Trocha fault of centralCuba. To the west, the fault cannotbe transcurrentfault southof the centralseamounts (Figure 10, reliablytraced beyond the point where it truncatesthe kilometers105 and 130) exhibitevidence of tilting and Caymanridge. faulting;these probably reflect local andlimited reactivation The orientationsof secondary(or splay)faults adjacent to of the transbasin fault. themain fault (seethe scarps at 20ø N, 82ø W, Figures4 and 15), andoffset of La Trochafault [Pardo,1975] both indicate Regional Iml)lications thatthe senseof displacementis left-lateral.The amountof offsetis small,probably less than 50 km, assuggested by the Preservedbasement structures of the present-dayYucatan probableoffset of La Trochafault and the apparent offset of Basin(Figure 15) providea snapshotof Eocenetectonic the north-southtrending graben-like structure located at conditions in the northwestern Caribbean. Plate motions longitude82.5 ø W. inferred from fault and rift orientations are consistent with The ageof thetransbasin fault relative to transformfaulting knownstructure of the Cubanthrust belts [e.g., Pardo, 1975]. to the westis not clear. Displacementalong La Trochafault is The timing of rift basinopening [Rosencrantz, et al., 1989] commonlythought to haveoccurred during the Middle correlateswith that of Cubanthrusting [e.g., Pszczolkowski Eocene[Pardo, 1975]. Thereis evidencefor northeast and Flores, 1986], and the amountof openingof the rift directedthrusting east of thefault duringthe Middle Eocene basin(s),about 350 km, providesa minimumestimate of the [Pszczolkowskiand Flores, 1986]. This is youngerthan the amountof Eocenethrusting in Cuba. ages(Paleocene, Early Eocene) attributed to faultingand This 350 km representsonly thefinal phaseof thetotal thrustingin westernCuba, and would imply that the northward movement of the Yucatan-Cuban blocks relative to transbasin-LaTrocha fault is younger.If so,this fault would the Bahamasplatform. Reconstructingthe basinby closing supportthe argument of Malfait andDinkiernan [ 1972] that therifts (Figure16) placesthe Zaza terrane adjacent to the the Caribbeanplate, during its transitionfrom northward to Yucatanplatform. Becausethe historyof the easternYucatan east-westmovement, was attachedto the North American platformrecords no (or insignificant)volcanics [e.g., Lopez- platethrough a processof "handing-off"pieces of Caribbean Ramos, 1975], the Zaza terranemust have moved from a lithosphere.On theother hand, the apparent small offset locationfurther south. Assuming that the SantaCruz ophio- acrossthe fault wouldsuggest that this process was limited lite in Guatemala[Rosenfeld, 1980] represents a fragment of and of short duration. the western continuationof the Zaza terrane, then the total Otherstructures. The originof the line of grabensbetween minimumdisplacement of the terranesince the emplacement the Caymanridge and the Cayman rise crest is unknown. of the SantaCruz ophiolitein Campaniantime hasbeen about They offsetbasement and lowest overlying sediments, so 1100 km. postdatethe rise, but are apparently truncated by theCayman Both the locationand structureof the pre-Eoceneplate ridge. Their developmentmay reflecttectonic movement boundarybetween the basinand Yucatanplatform are un- duringthe earlystages of Caymantrough development. knownat present,as is the questionof why the boundary Rosencrantz:Structure and Tectonics of theYucatan Basin 1055

rrrrrr

rrrrrrr 0 z -- -- w_ • • z• z zz•

r r • 0o O• r r r

r r r r r

r r r r

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r r r r r r r

r r r r r r r r

r r r r r

r r r r r r r

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r r r r

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i i i i I i i i i i i i 1056 Rosencrantz: Structure and Tectonics of the Yucatan Basin

111

BANCO CHINCHORRO DEPRESSIONCAUTO

TURNEFFE I.

I !i• PLATFORM • THRUST z ZAZA O TERRANE O ß***• """"'TRANS-BASINFAULTTRACE •LU i.?'• OCEANICCRUST EOCENE RECONSTRUCTION • SCARPSHOWBASEMENTFACING(TICS I "•:'" OCEANICRISE ß DIRECTION) 0 1co 250 RIFT DISTANCE IN KILOMETERS O SEAMCUNT• EOCENE

Fig. 16. Eoceneplate reconstructionof the YucatanBasin.

developedpull-apart or rift structuresduring the Late Caymantrough spreading represents a maturephase of pull- Paleoceneor Early Eocene. One possibleanswer is that as the apartrifting. If so, then the Yucatanbasin-Cuban block was leadingedge of the northwardmoving Yucatan basin-Cuban detachedfrom the Caribbean plate before the block had fully lithosphericblock "felt" the approachingBahamas platform, it convergedon the Bahamasplatform. The relative was nudgedeastward so as to rotatethe blocksin a clockwise displacementsrecorded by the basintransforms and rifts sense. This would reorientand "open"the strike-slip representthe displacementsof that blockrelative to the North boundaryalong the westernedge of the block. As new faults Americanplate, not thoseof the Caribbeanplate (as developedto accommodatethe new motion,the fault zone representedby the NicaraguaRise, ColombianBasin and would widen and existingfaults would extend so asto initiate VenezuelanBasin) relative to the NorthAmerican plate. "leaky" volcanism. This would be consistentwith the Additionalquestions about the Cretaceousplate bbean litho- volcanicsproposed for the northeasterncomer of the western sphere.On the otherhand, the apparentsmall offset across deepbasin. the fault wouldsuggest that this process was limited and of The apparentlack of a time gap betweenthe Middle Eocene short duration. cessationof Caribbean-NorthAmerican convergence, as Otherstructures. The originof the line of grabensbetween recordedby Cubanthrusting [e.g., Pardo,1975; the Caymanridge and the Caymanrise crest is unknown. Pszczolkowskiand Flores, 1986] and the Middle Eocene They offsetbasement and lowest overlying sediments, so openingof the Caymantrough [Rosencrantz et a1.,1988]raises postdatethe rise, but are apparently truncated by theCayman the possibilitythat east-weststrike-slip displacement between ridge. Their developmentmay reflect tectonic movement the Caribbeanand North Americanplates began before or duringthe early stages of Caymantrough development. duringCuban-Bahamas thrusting, rather than after. East-west The north-southtrending topographic lineaments which cut displacementmust have startedprior to the Middle Eoceneif the easternbasin and Cayman rise at longitude82.5 ø W Rosencrantz: Structure and Tectonics of the Yucatan Basin 1057

probablyrepresent a narrowgraben of pre-MiddleEocene Caribbean-NorthAmerican convergent plate boundary. This age. Whetherit formedin responseto transbasinfaulting or zoneincludes a largepull-apart basin, floored with oceanic to another earlier event is unknown. crust. The orientations of this basin and related fault trends The basementfault blockscharacterizing the southwest showthat displacementacross the transformwas left-lateral, horstand grabendomain may have developedduring Cayman with the eastern Yucatan basin and attached Cuban section troughopening. However, the block faultscould also reflect movingN to NNE relativeto a fixed Yucatanplatform. The local crustal extension related to movement on the transbasin amountof offset,as estimatedfrom the lengthof the pull- fault, or representa wide zoneof north-southtrending strike apartbasin, is about350 kin, notincluding displacement ac- slip faultingrelated to transformdisplacements. commodatedby crustalstretching and thinning. The best Sedimentsthat fill the Yucatanbasin are largely estimateof ageof displacementis Late Paleoceneto Middle undisturbed,indicating that the basinhas undergone little Eocene. deformationsince its formation. Exceptionsinclude the The easternedge of the Yucatanbasin has been thrust foldingof deepsediments along the Camagfieytrench, the beneaththe Cubanmargin along a now-buriedtrench, called faultingof deepsediments along the line of grabenssouth of the Camagiieytrench. This structuremay haveformed as an the Caymanrise, both noted above, and minor faultingand Eocenebackthrust behind the Cubanarc, or it may representa tilting of sedimentsalong the southernedge of the basin, remnantof the Cretaceoussubduction system associated with adjacentto the gencezone is the upliftedand exposed the Cuban arc (Zaza terrane). The trench is truncatedat its Trinidad thrustfault in south-centralCuba [Hatten et al., north end by a long, left-lateralfault which extendsSW-NE 1958; Hatten et al., 1988]. The right-lateraloffset of the zone diagonallyacross the basinand continues onland in central acrossLa Trochafault is apparentand due to crustaluplift Cuba as La Trocha fault. westof La Trochafault. To the southeastthe convergence The basementtopography of the Yucatanbasin gives a zone lies buriedbeneath the youngersediments and volcanics pictureof theEocene tectonics of thebasin and permits a of the Cautodepression and SierraMaestra. reasonablereconstruction of basementstructure during Late Paleoceneor Early Eocenetime, but yieldslittle information SUMMARY as to the pre-Eocenetectonics of the westernCaribbean. However,the closetiming betweenthe finish of Yucatan The distributionof basementtypes and the patternof basin-Cubannorthward motion and the start of Cayman faultingshown by YucatanBasin seismic reflection profiles trougheast-west strike-slip motion suggests that the two indicate that the basin includes crusts of three different eventsmay have overlapped. compositionsand origins: 1. Crustunderlying the westernedge of the basin(Yucatan Acknowledgments.James Pindell, Robert Speed, borderlanddomain) represents the eastern,offshore continua- ChristopherBowland, andJ. G. Vedder all commented tion of the adjacentYucatan platform section. Basement extensivelyon versionsof thispaper. Their insights, rocksprobably include Cretaceous carbonates and evaporites, correctionsand recommendations definitely helped improve Jurassicredbeds and Paleozoic crystalline rocks similar to thispaper, and I appreciatethe time and effort they put into thosesampled on the platform. Sedimentsfilling the troughs theirreviews. This work wassupported by NationalScience andbasins of the borderlandlikely representfacies Foundationgrant OCE 8308139and by theUniversity of equivalentsof platformcarbonates of middleand late Tertiary Texas. Universityof TexasInstitute for Geophysics age. Basementbeneath the southwesterncomer of the basin contribution number 804. (southwesternhorst and graben domain) may include stretchedplatform crust. 2. Topographicallyheterogeneous crust underlying the REFERENCES easterntwo-thirds of the basin(eastern basin, Cayman rise, Caymanridge, and CamagiieyTrench domains) includes a Alvarado-Omana,M. A., Gravityand crustal structure of the thicksequence of volcanicsand plutonics in the form of the south-centralGulf of Mexico, the YucatanPeninsula, and Caymanrise. With the exceptionof the Caymanridge, the adjacentareas, from 17ø30'N to 26øN and from 84øW to basementtopography predates basin formation. 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