JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 95, NO. Bll, PAGES 17,555-17,569, OCTOBER 10, I990 Evidence for Age and Evolution of Comer Seamountsand Great Meteor SeamountChain From Multibeam B athymetry BRL• E. TUCHOLKE WoodsHole OceanographicInstitution, WoodsHole, Massachusetts N. CHRtSTtAN SMOOT U.S. Naval OceanographicOffice, StennisSpace Center, Mississippi The Comer seamounts in the western North Atlantic and Great Meteor seamount "chain" in the eastern North Atlantic are thoughtto progressin age from Late Cretaceousthrough late Cenozoic. They both presumablyformed by volcanismabove the New Englandhotspot when first the North Americanplate, and then the Mid-Atlantic Ridge axis and African plate, moved over the hotspot. High-resolution,multibeam bathymetryof the seamountsshows geomorphic features such as guyors,terraces, and a baselevel plateau (Cruiserplateau) that we interpretto have formedat sealevel. We have backtrackedthese features to sea level alongthe North Arianticcrustal age-depth curve in orderto estimatetheir ages. The derivedage patternof volcanismindicates formation of the Comerseamounts at ca. 80 Ma to 76 Ma, withmigration of the Mid-AtlanticRidge plateboundary over the hotspotand formationof the Cruiserplateau about 76 Ma. Seamountages suggest that subsequentvolcanism on the Africanplate movedfirst northward,in the Late Cretaceousto early Cenozoic(Plato, Tyro, and Atlantisseamount groups), then southwardto GreatMeteor Seamountin the late Cenozoic.Recurrent volcanism appears to haveoccurred at someseamounts up to 20- 30 m.y. after their initial passageover the hotspot. It wouldthus appear that intralithosphericconduits can link the hotspotto old seamountsseveral hundred kilometers away. INTRODUCTION It appearsto haveformed as the North American plate migrated We have known for more than 30 years that the floor of the west-northwestwardover the New Englandhotspot during the ArianticOcean exhibits numerous large seamounts[Heezen et Cretaceousperiod. Radiometricage dating of seamount aI., 1959](see Epp and Smoot [1988] for a recentsummary). samplesreported by Duncan [1984]suggests that a linear Most existing knowledge of these seamountsis based on migration rate of 47mm/yr best fits the seamountage scatteredecho sounding and seismiclines and, in a very few distributionand that the seamountsrange in age from about places,on detailed surveys. Sampling of the seamounts 103 Ma in the west(Bear Seamount)to about82 Ma at their likewiseis limited, but it has recovered both basaltic igneous southeasternterminus (Nashville Seamount). Although rocksand sedimentary samples from the sedimentarycaps that separatedfrom the New Englandseamounts, the Comer sometimesare present,particularly on flat-toppedguyors. seamountgroup farther east (Figure 1) alsois interpretedas Mostof the recoveredigneous rocks have been exposedto havingbeen formed above the New Englandhotspot. The Comer seamountshave beenthought to date to about75-70 seawaterfor long periods of time and are highly altered. Consequently,accurate radiometric age datingof the samples Ma, andthey would thus fall alongthe same age-distance trend is difficult, and the derived geochronometricages can be as the New Englandseamounts [Duncan, 1984]. Hotspot modelssuch as thoseof Duncan [1984] and of Morgan [1983] subjectto large uncertainties. Samplesof the sedimentary capsare useful in providingminimum ages for the seamounts, predictthat the westward migrating Mid-Atlantic Ridge axis overrodethe New Englandhotspot in Late Cretaceoustime; butit usuallyis difficult to estimatethe periodof time that thereafterthe hotspotvolcanism formed seamounts on the elapsedbetween emplacementof the igneousrock and accumulationof the sampledsedimentary record. Despitethe Africanplate. LateCretaceous to Recentabsolute motion of lackof detailed data on most seamounts,enough information theAfrican plate with respect to themanfie is thoughtto have been slow and in a generallynortherly and then easterly existsto suggestgeneral ages or agetrends; these data have direction [Morgan, 1983;Duncan, 1984]. The volcanic beenused to predictlarger-scale age relationshipsin the edificesof the Ariantis,Plato, Tyro, Cruiser,and GreatMeteor contextof specific models for the origin of seamounts, groupsof seamounts,which form the GreatMeteor "chain" particularlythose seamounts found in linearchains. A number (Figure1), presumablywere constructedabove the New ofmodels have been proposed for theorigin of NorthAtlantic Englandhotspot during this period. seamounts[Vogt and Tucholke,1979]; the mostsuccessful The above models imply that there should be an age models have been those that attribute formation of the progressiontoward younger volcanism from north to southon seamountchains to passageof the lithosphereover a manfie theAfrican plate, terminating in the vicinityof GreatMeteor plumeor hotspot[e.g., Morgan, 1972, 1981;Duncan, 1984]. Seamount.K-At ageson two volcanicsamples from Great The bestdeveloped and best known seamountchain in the Meteor have been reportedas 11 Ma and 16.3_+0.4Ma by NorthAtlantic is theNew Englandseamount chain (Figure 1). Wendtet al. [1976]. yon Rad [1974] deducedfrom studyof carbonatesands that the flat summit of Great Meteor Seamount Copyright1990 by the AmericanGeophysical Union. was in shallow water from late Miocene to early Pliocenetime Papernumber 90JB00863. (<11 Ma). Seamountsfarther north in the GreatMeteor 0148-0227/90/90JB.00863505.00 "chain"presently have no directage data, although an indirect 17,555 17,556 TUCHOLKEAND SMOOT: AGE AND EVOLUTION OFNORTH ATLANTIC SEAMOUNTS 40øN 30' 80øW 70' 60' 50ø 40' 30' 20' 10ow 20' Fig. 1. Sketchmap showing locations of majorseamounts and volcanic islands in theNorth Atlantic and the positions of the Comerseamounts and eastern Atlantic groups of seamountswith respectto the HayesFracture Zone. Smallboxes show the areasdepicted by detailedbathymetry in Figures2-4. age determination has been noted for Hyeres Seamount. positionsalong the Mid-Atlantic Ridge crest, based on the Fermont and Troelstra [1983] reportedlarger foraminiferaof platemotion studies of Klitgord and Schouten[1986]. Thetwo late Aquitanian/earlyBurdigalian age (ca. 23-19 Ma) in a seamountgroups lie in conjugatepositions along the Hayes turbiditc bed that was piston-cored 50 km west of the FractureZone. Althoughthe fracturezone consistedof a single seamount. It is likely that the foraminiferawere derived from fracture valley at the time that the Corner and Cruiser sedimentsdeposited in shallow water (<50 m) on Hyeres' seamounts were formed in Late Cretaceous time, it summit. subsequentlyevolved into a triplet of fracture valleys in Verhoef [1984] made indirect age estimatesof seamountsin responseto changesin relative plate motion (Figure 1; B.E. the Great Meteor "chain" based on the relations between age Tucholke and N.C. Smoot, manuscriptin preparation, 1990). and elasticthickness of the lithosphereas describedby Bodine In the ensuing discussion we briefly describe the et al. [1981]. His greatestestimated age was 65 Ma for the morphology of the Comer and Cruiser seamounts, and we Cruiser group of seamounts;estimated ages of most of the derive the apparent age (based on age-depth relations) of remaining seamounts,including Great Meteor, were in the seamountgeomorphic features that are thought to have formed rangeof 3847 Ma. Subsequently,Verhoef and Collette[1985, at sea level. From these data we examine the patternsof 1987] recognized that these ages probably are too large volcanismin the seamountgroups and considerthe questionof becausethey do not considereffects of lithospherethinning age-progressivevolcanism above the New England hotspot. and thermal rejuvenationat the time of seamountformation We concludethat the pattern of volcanism is consistentwith [Derrickand Crough,1978]. Verhoefand CoIlette[1985] also sequentialformation of the New England,Comer, and the Great used age-depthbacktracking to determinemaximum ages of Meteor "chain" seamountsabove the New England hotspot. several seamounts in the Great Meteor "chain", with derived However, Late Cretaceous and Cenozoic absolute motion of the agesranging from 37 to 23 Ma. There are largeuncertainties African plate over the hotspot differs significantly from in the ages derived in all these studies, so the presenceor predictionsof existing hotspot models. absenceof age-progressivevolcanism has been unresolved. SEAMOUNT MORPHOLOGY However, Verhoefand Collette [1987] preferredthe conceptof generally simultaneousvolcanism, possibly as a responseto Corner Seamounts changein plate stresspatterns, and they assumedan age of 22 Ma for the bulk of the seamountcomplex. The Cornerseamounts (Comer Rise) lie betweenabout 34øN It is possiblesignificantly to improveour understandingof to 37øN and 47ø00'W to 52ø30'W (Figure 1). The seamounts the origin and age of these seamount groups through are positionedmostly along the north side of the Hayes examination of their morphology, depths, and associations FractureZone, and in largepart they parallelthe fracturezone with one another in plate kinematic reconstructions. (Figure2). The main volcanicedifice in the eastcentral region Consequently,we have studieddetailed multibeam bathymetry is an east-westtrending ridge near 34ø45'N;it parallelsthe over the Comer, Plato, Tyro, Cruiser, and Great Meteor Late Cretaceousseafloor spreading direction and supportsa seamount groups (Figures 1-4), obtained through swath- seriesof four peaks (Figure 2). The two largest of these mappingsurveys of the U.S.