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Implications for Seamount Paleopoles Jeff Gee, Hubert Staudigel, Lisa Tauxe, Thomas Pick

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Implications for Seamount Paleopoles Jeff Gee, Hubert Staudigel, Lisa Tauxe, Thomas Pick Magnetization of the La Palma Seamount Series: Implications for Seamount Paleopoles Jeff Gee, Hubert Staudigel, Lisa Tauxe, Thomas Pick To cite this version: Jeff Gee, Hubert Staudigel, Lisa Tauxe, Thomas Pick. Magnetization of the La Palma Seamount Series: Implications for Seamount Paleopoles. Journal of Geophysical Research, American Geophysical Union, 1993, 98767, pp.11743-11754. 10.1029/93JB00932. insu-01864349 HAL Id: insu-01864349 https://hal-insu.archives-ouvertes.fr/insu-01864349 Submitted on 29 Aug 2018 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 98, NO. B7, PAGES 11,743-11,767, JULY 10, 1993 Magnetizationof the La Palma SeamountSeries: Implicationsfor SeamountPaleopoles JEFFGF_11,1 HtmERT STAUDIGI•L, 2 LISA TAUX•, 3 AND THOMAS PICK ScrippsImtitutlon of Oceanography,La Jolla, California YVES GALLET Institutde Physiquedu G?obede Paris Paleopolesdetermined from seamountmagnetic anomalies constitute the major data sourcefor the Pacific apparentpolar wander path, but relatively little is known about the processesof remanence acquisitionin seamounts.Since magneticanomalies reflect both natural remanence(NRM) and the inducedfield, it is importantfirst to assesswhether the NRM is likely to representan original field directionand secondto constrainthe magnitudeof the inducedcomponent. To this end, we present paleomagneticdata from an uplifted, subaeriallyexposed section through a seamounton La Palma, Canary Islands. The PlioceneSeamount Series of La Palma comprisesa >6 km sequenceof alkalic extrusivesand intrusives which includes all lithologieslikely to be volumetricallyimportant in seamounts. The structuraltilt of the SeamountSeries allows separation of early thermalor chemicalremanence from magnetizationcomponents acquired after tilting (e.g., viscousremanence). The NRM providesa poor indicationof the originalmagnetization direction, although the characteristicmagnetization of manyLa Palma samplesis compatiblewith the originalpretilt direction.Hydrothermal alteration has resultedin the productionof Ti-poormagnetite and an increasingcontribution of hematitewith increasingdegree of alteration.More importantly,well-defined magnetization directions which deviatefrom any reasonable geomagneticdirection at La Palmacan be attributedto hydrothermalalteration in a differentpolarity than prevalentduring the originalmagnetization. Based on a comparisonof the magnitudeof low-stability componentsof magnetizationand laboratory acquisition of viscousremanence and previousestimates of the inducedmagnetization, we concludethat viscousand inducedmagnetization probably account for 15-25% of the total magnetizationof seamounts.The resultingpaleopole bias is a functionof the polarityand paleolatitudeof the seamountand rangesfrom 4ø to 16ø for Cretaceousseamounts in the Pacific. INTRODUCTION plex anomaly patterns may be accommodatedby arbitrarily' subdividingthe seamountinto regionsof uniform magnetiza- Magnetic anomaliesassociated with seamountshave long tion [e.g., McNutt, 1986], the spatialcoherence of residuals been recognized as a source of tectonic information, and suggeststhe standardleast squaresinversion is based on an seamountpaleopoles have been particularlyuseful in r<on- improper statisticalmodel [Parker, 1988]. The seminorm structingthe history of the Pacific plate [e.g., Francheteau minimizationtechnique of Parker et al. [1987] incorporates et al., 1970] where traditional, land-basedpaleomagnetic both uniformand nonuniformcomponents, providing the most sampling is rarely possible. Although paleomagneticdata uniform model compatible with the observed anomaly and from drillcores, sedimentdistribution patterns, and skewness thereby estimatingthe minimum degreeof nonuniformityin of lineatedcrustal anomalies provide complementary tectonic the magnetizationof the seamountdemanded by the data. The information[Gordon and Cox, 1980], seamountpoles remain lognormal distributionof magnetizationintensities observed the principalsource for the Pacificapparent polar wanderpath in seamountrocks [e.g., Kono, 1980; Gee et al., 1989] and, indeed, are sometimesheld as the standardby which suggeststhat nonuniformityin intensity is probably the rule theseadditional data arejudged [e.g., Gordon,1990]. ratherthan the exception.In recognitionof this largeintensity The nonuniquenessinherent in the determination of variation,Parker [1991] developedan ideal body modeling seamount paleopoles requires that some assumptionsbe t•hnique for seamountmagnetization which constrainsthe madeconcerning the magnetizationsources (see Parker et al. solutionto have uniform directionwhile allowing intensityto [ 1987] for a review). Early modelsutilized the assumptionof vary. Directional informationcan still be recovereddespite uniform magnetizationto determinethe best fit magnetization relaxation of the intensity constraints,but the location of in a least squaressense [Vaquier, 1962]. Although com- seamountpaleopoles is much more poorly constrainedthan commonly assumed. Although these recent models have made significant •Nowat Lamont-Doherty Earth Observatory, Palisades, New York. 2Nowat Vrije UniversiteitAmsterdam, Faculteit der Aardweten- progress in addressingthe nonuniformityof seamountmag- schappen. netic sources,bias introducedby viscousand inducedcontri- 3Alsoat FortHoofddijk Paleomagnetic Lab, Utrecht. butionsis difficult to incorporatein the models.Comparison of modeling results from normal and reversely magnetized seamounts[Hildebrand and Staudigel,1986; Bryan and Gor- Copyright1993 by the AmericanGeophysical Union. don, 1991] suggestsa combinedcontribution of up to 25% Papernumber 93JB00932. for induced and viscous components. A similar bias from 0148-0227/93/93 JB-00932505.00. induced magnetization(~15% of total magnetization)has 11,743 11,744 GEEET AL.: MAGNErlZATION OF LA PALMASEAMOUNT SERIES beensuggested for large seamountswith a significantportion layeredsequence of entirely submarineextrusives and volcani- of intrusive material based on results from the La Palma clastics,three generationsof alkalic dikes/sills,and a basal SeamountSeries [Gee et al., 1989]. In addition,the presence plutonicsequence (Figure lb). Thesubmarine extrusive series of multiplepolarities is often difficultto assessfrom models. is consistentlybedded with a dip of 48o alongan azimuth For example,the ideal body solutionfor JasperSeamount of 230o [Staudigel,1981], which representsa tilt roughly doesnot requiremixed polarity [Parker, 1991] despitethe radial with respectto the presentcenter of intrusiveactivity demonstrablylong duration(>7 nay.) of volcanismwhich in the southeasternand centralportions of the caldera. The stronglysupports the presenceof both normaland reversed extrusiveseries consists predominantly of pillow lavas(50%), polarityrocks [Pringleet al., 1991]. Finally, the effects pillow fragmentbreccias, submarine scoriaceous breccias and of' progressivehydrothermal alteration (perhaps in different hyaloclastites(terminology of Fisherand Schmincke[1984]) polarity intervals)on the original magnetizationare poorly and ranges in compositionfrom alkalic basalt to mugearite understood. and rare trachyte. Three generationsof dikes and sills are In this paper we discussthe origin of the magnetization observedin the basementcomplex [Staudigel and Schmincke, in an uplifted, tilted sectionthrough a seamountexposed 1984; Staudigelet al., 1986]. The earliest generationof on La Palma, Canary Islands. The La Palma Seamount dikes (Group I) is orientedapproximately orthogonal to the Seriesprovides a uniqueopportunity to studythe magnetic bedding of the layered extrusive series. On the basis of propertiesand originof the magnetizationin seamounts.In their orientation and the similarity in both compositionand contrastto dredgingand drilling, which sample only the alteration history to the extrusive series, these dikes are outermostpart of the volcanic edifice, the exposuresof interpretedas feedersfor the extrusiveseries. Sills (Group11) the SeamountSeries provide about 4 km of stratigraphic occur within the layered extrusiveseries, parallel to bedding, relief and include a wide range of extrusivesand intrusives and also form a 2 km sheeted sill swarm which underlies the which encompassall lithologieslikely to be importantin extrusivesequence. Crosscuttingrelationships suggest that seamounts. Age constraintsfor the SeamountSeries and mostof the sillsare younger than the GroupI dikes[Staudigel the overlyingsubaerial flows allow generalcorrelation to the et al., 1986]. GroupIII dikes generallyhave steepdips, may geomagneticreversal time scale and facilitateevaluation of crosscutthe overlying Cobefta lavas and are typically less the role of multiple polarities in generatinginhomogeneous alteredthan the countryrock. These dikes are interpretedas magnetization.The tiltingof the seamountsequence (~50 ø) membersof a radial dike swarm feeding the Cobeftalavas. allows separationof pretilt thermalor chemicalcomponents Isotopicage dating suggests an agerange of 0.51
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