University of Rhode Island DigitalCommons@URI Graduate School of Oceanography Faculty Graduate School of Oceanography Publications 1988 Origin of the Louisville Ridge and its relationship to the Eltanin Fracture Zone System A. B. Watts J. K. Weissel See next page for additional authors Follow this and additional works at: https://digitalcommons.uri.edu/gsofacpubs Terms of Use All rights reserved under copyright. Citation/Publisher Attribution Watts, A. B., J. K. Weissel, R. A. Duncan, and R. L. Larson (1988), Origin of the Louisville Ridge and its relationship to the Eltanin Fracture Zone System, J. Geophys. Res., 93(B4), 3051–3077, doi: 10.1029/JB093iB04p03051. Available at: http://dx.doi.org/10.1029/JB093iB04p03051 This Article is brought to you for free and open access by the Graduate School of Oceanography at DigitalCommons@URI. It has been accepted for inclusion in Graduate School of Oceanography Faculty Publications by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. Authors A. B. Watts, .J K. Weissel, R. A. Duncan, and R. L. Larson This article is available at DigitalCommons@URI: https://digitalcommons.uri.edu/gsofacpubs/186 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 93, NO. B4, PAGES 3051-3077, APRIL 10, 1988 Origin of the Louisville Ridge and Its Relationship to the Eltanin Fracture Zone System A. B. WATTS 1 AND J. K. WEISSEL Lamont-Doherty GeologicalObservatory, Palisades, New York R. A. DUNCAN College of Oceanography,Oregon State University, Corvallis R. L. LARSON GraduateSchool of Oceano•traphy,University of Rhode Island, Kin•tston We have combinedshipboard and Seasataltimeter derived data in an intergratedgeological and geophysicalstudy of the Louisville Ridge; a 3500-km-longseamount chain extendingfrom the Tonga trench to the Eltanin Fracture Zone. A break in the smooth trend of the ridge at latitude 37.5øShas been recognizedin both bathymetricand altimetricdata. The '•øAr-39Ardating of rocksdredged either side of the break suggestthat it is analogousto the bend in the Hawaiian-Emperorseamount chain. Although the generaltrend of the ridge can be fit by small circlesabout Pacific absolutemotion poles determined from other seamountchains, the new bathymetric and age data allow us to refine Pacific absolute motion poles. The continuity in smooth trend of the ridge and the Eltanin Fracture Zone suggestssome relationship between them. However, a major offset developed on this transform between 60 and 80 Ma, prior to the oldest dated rocks from the ridge. Although magmatism was more or lesscontinuous on the ridge during 28-60 Ma, it probably occurredon crust with little or no offset.Thus magmatismappears to have been little influenced by the developing fracture zone. By 28 Ma, the distance between the magmatic sourceand the fracture zone had decreasedsufficiently for a portion of the ridge to have been emplacedon crust with an offset.After about 12 Ma, however,volcanic activity on the Louisville Ridge apparently waned, despitea possibleinfluence on the magmatism of the fracture zone. 1. INTRODUCTION and that it terminated on a ridge and trough feature at the The Louisville Ridge (Plate 1)is a prominent bathymetric western edge of the Phoenix lineations in the central Pacific feature in the southwestPacific Ocean basin. (Plate 1 can be basin. Larson and Chase [1972] showed that the Louisville found in the separatecolor sectionin this issue.)The ridge is Ridge, the Phoenix ridge and trough, and the Eltanin Fracture approximately 3500 km long and representsa volcanic lin- Zone system could all fit a small circle about a pole of rota- eament comprising a number of short ridges, isolated peaks, tion similar to that inferred by Hayes and Ewing [1971]. and flat-topped seamounts[e.g., Mammerickx et al., 1974]. Clague and darrard [1973] pointed out that the smooth The ridge rises 3-4 km above the average depth of the sea- trend of the Louisville Ridge is approximately copolar with floor. The ridge is aseismic,but apparently where it intersects the Emperor and Hawaiian seamounts chains. The Emperor at the Tonga-Kermadec trench it influencesthe pattern of seamounts had been shown in previous studies [e.g., Clague regional seismicity[e.g., Giardiniand Woodhouse,1986]. and Dalrymple, 1975] to have formed by motion of the Pacific Hayes and Ewing [1971] suggestedthat the LouisvilleRidge plate over the Hawaiian hot spot. Clague and darrard [1973] was an extensionof the Eltanin Fracture Zone system.They proposed that the Louisville Ridge was similar in age to the showedthat the ridge lies closeto a great circleconnecting the Emperor seamounts (42-70 Ma) and that it also formed by Tonga-Kermadec trench with the Eltanin Fracture Zone. motion of the Pacific plate over a hot spot. Implicit in this Hayes and Ewing [1971] argued that a break in the trend of suggestionis that during this time, the Louisville and Ha- the ridge at 40øS,166øW reflected the changein orientationof waiian hot spots remained fixed with respect to each other. seafloorspreading in the Pacific Ocean basin prior to forma- In a subsequentdiscussion, Molnar et al. [1975] pointed out tion of anomaly 32. They implied that the Louisville Ridge that the topography of the ridge more closely resembled that was a fracture zone ridge and that it was Late Cretaceous or of a linear seamount chain than a fracture zone. They also greater in age. argued that sinceAustralia and Antarctica separatedat anom- A similar view for the origin of the Louisville Ridge was aly 34 time [Christoffel and Falconer, 1972], it was unlikely held by Larson and Chase [1972]. They suggested,however, that the Eltanin Fracture Zone extended into oceanic crust that the Eltanin Fracture Zone systemextended farther north that formed at the Pacific/Antarctica plate boundary since then. Thus, in the view of Molnar et al. [1975], the Louisville Ridge formed by processessimilar to those that control the •Also at Departmentof GeologicalSciences, Columbia University, evolution of other linear seamount chains in the Pacific, such New York. as the Hawaiian-Emperor chain. Copyright 1988 by the American Geophysical Union. Epp [1978] reviewed the age data along the Hawaiian- Paper number 6B6165. Emperor seamount chain and the bathymetric trends of indi- 0148-0227/88/006B-6165 $05.00 vidual seamount chains in the Pacific Ocean. He concluded 3051 3052 WATTS ET AL..' LOUISVILLERIDGE AND ELTANIN FRACTUREZONE TABLE 1. Principal Sourcesof Data navigation. Prior to 1967, the shipboard data were collected with celestialnavigation. Since 1967, the U.S. Navy's satellite Institution Ship navigation system (TRANSIT) has been utilized. It is difficult Lamont-Doherty Geological Observatory Verna, Conrad, Eltanin to assessthe positional accuracyduring the various shipboard National Oceanic and Atmospheric Oceanographer surveys. It seems probable, however, that cruises which uti- Administration (NOAA) lized satellite navigation should be accurate to about 0.1 Deep Sea Drilling Project Glomar Challenger nautical mile. Institute of Oceanology Vityaz (Moscow, USSR) Bathymetry measurements were obtained with precision Hawaii Institute of Geophysics Kana Keoki depth recorders (PDR). Typically, the bathymetry is sampled Defense Scientific Establishment Tui every 6 min, corresponding to distances between individual (Auckland New Zealand) data points of about 2 km. In regions of high relief, however, Hydrographic Office of the Royal ocean sounding charts the bathymetry is often sampledmore frequently. New Zealand Navy (multiple ships) Scripps Institution of Washington The gravity measurementswere obtained with different in- Oceanography struments. The measurementsobtained by LDGO, the Insti- tute of Oceanology and SIO (since 1977) utilized a Graf- Askania Gss-2 sea gravimeter mounted on a gyrostabilized platform, while the measurementsobtained by NOAA, Hawaii Institute of Geophysics,and SIO (prior to 1977) utilized the that most of the seamount chains on the Pacific plate could be Lacosteair-sea gravimetermounted either in gimbals(prior to attributed to a hot spot origin and that such a model could be 1965) or on a gyrostabilizedplatform (since 1965). Studies of used to predict their ages.In the case of the Louisville Ridge, the discrepancyof gravity anomalies at intersection of ship Epp [1978] proposed that the break in trend at 40øS, 166øW, tracks in the region [Davey and Watts, 1983] suggestthat the first pointed out by Hayes and Ewing [1971], correspondedto gravity anomalies are accurate to about 5-10 mGal, depend- the Hawaiian-Emperor bend. Since the age of the latter bend ing on the type of navigation used.Typically, gravity anomaly is reasonablywell known, Epp [1978] used the hot spot model values are calculated at 10-min intervals, correspondingto to predict ages along the Louisville Ridge. He proposed that distancesbetween data points of about 3 km. the Louisville Ridge north of the trend break (which he identi- Magnetic measurements were obtained by using a direct fied at 39.2øS, 167.5øW) was coeval with the Emperor sea- reading proton magnetometer towed behind a vessel. The mounts (42-70 Ma), while the ridge to the south was similar in total magnetic field observations were reduced to magnetic age to the Hawaiian Ridge between Midway and the bend anomalies using the International Geomagnetic Reference (15-42 Ma). Field (1971) as the background field. Although the hot spot model has in the past been widely The seismicreflection profiles were obtained with a single-