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 multi- channeldata, 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 with metamorphictextures 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,