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Deformation-Related Volcanism in the Pacific Ocean Linked To LETTERS PUBLISHED ONLINE: 27 APRIL 2015 | DOI: 10.1038/NGEO2416 Deformation-related volcanism in the Pacific Ocean linked to the Hawaiian–Emperor bend John M. O’Connor1,2,3*, Kaj Hoernle4, R. Dietmar Müller5, Jason P. Morgan6, Nathaniel P. Butterworth5, Folkmar Hau4, David T. Sandwell7, Wilfried Jokat1,8, Jan R. Wijbrans3 and Peter Stoers9 Ocean islands, seamounts and volcanic ridges are thought to reconstructions connecting the Indo-Atlantic realm to the Pacific form above mantle plumes. Yet,this mechanism cannot explain for Late Cretaceous predict a negligible bend13. many volcanic features on the Pacific Ocean floor1 and some Although diverse lines of evidence record a rough correlation might instead be caused by cracks in the oceanic crust linked to between other circum-Pacific tectonic changes (Supplementary the reorganization of plate motions1–3. A distinctive bend in the Note 2) and formation of the HEB (refs5 ,11,14), their timing has Hawaiian–Emperor volcanic chain has been linked to changes been too protracted to establish a connection. Here we report the in the direction of motion of the Pacific Plate4,5, movement of unexpected discovery of the long-sought-after independent tem- the Hawaiian plume6–8, or a combination of both9. However, poral record of circum-Pacific tectonic events while investigating these links are uncertain because there is no independent a new type of linear structure on the Pacific seafloor detected in record that precisely dates tectonic events that aected the recent years by improvements in satellite altimetry2. This new type of Pacific Plate. Here we analyse the geochemical characteristics structure consists of groups of linear en échelon volcanic ridges, first of lava samples collected from the Musicians Ridges, lines described in 1987 for the `Crossgrain' ridges located in the central of volcanic seamounts formed close to the Hawaiian–Emperor Pacific2. Mechanisms explaining these linear ridge groups include bend. We find that the geochemical signature of these lavas hotspot-spreading ridge interaction15 and tensional cracking of the is unlike typical ocean island basalts and instead resembles Pacific Plate2,3 (see Supplementary Note 3). mid-ocean ridge basalts. We infer that the seamounts are To investigate the origin of these enigmatic structures, we carried unrelated to mantle plume activity and instead formed in an out seismic surveys and dredge sampled the en échelon linear ridges, extensional setting, due to deformation of the Pacific Plate. extending eastward in clusters, from the northern and southern ends 40Ar/39Ar dating reveals that the Musicians Ridges formed of the Musicians Seamount Chain and the Murray Fracture Zone during two time windows that bracket the time of formation (FZ) on RV Sonne cruise SO142 (Fig.1 and Supplementary Fig. 1 of the Hawaiian–Emperor bend, 53–52 and 48–47 million years and Supplementary Table 1). The Musicians Seamounts form a NW ago. We conclude that the Hawaiian–Emperor bend was formed trending age-progressive Cretaceous hotspot track, located several by plate–mantle reorganization, potentially triggered by a hundred kilometres northwest of the Hawaiian Seamounts, best series of subduction events at the Pacific Plate margins. explained by plate motion over a now extinct Musicians hotspot15,16. Both changes in mantle flow6–8 and in the direction of The cluster of ridges extending from the southern end of the Pacific Plate motion4,5 have been proposed to explain the Musicians Seamount Chain is bounded to the north by the Murray Hawaiian–Emperor bend (HEB). Decreasing palaeolatitudes FZ, which consists of a ∼100 km band of linear ridges and troughs during the formation of the Emperor Seamounts6,8, and combined that stretch from the Musicians to the Hawaiian Seamount Chain16. global mantle flow and plate motion models5, support mantle flow as We dredge sampled one of these volcanic ridges in the Murray the dominant mechanism for creating the HEB. A palaeomagnetic FZ (Fig.1 ). pole for the Pacific Plate (based on the skewness of vector Seismic profiles collected during the SO142 expedition show that aeromagnetic profiles of magnetic anomalies due to seafloor the Musicians Ridges were formed by volcanism15. The volcanism is spreading) has been interpreted as evidence that 5◦ ± 3◦ of the interpreted to have been generated by flow of mantle along channels southward motion of the Hawaiian hotspot occurred after 32 Myr in the base of the lithosphere from the Musicians hotspot to the ago (ref. 10), thus post-dating the formation of the Emperor Pacific–Farallon spreading centre in the Cretaceous15. Although Seamounts, but the robustness of this type of analysis has been this is consistent with the ∼94–92 Myr 40Ar/39Ar ages for two questioned (Supplementary Note 1). An alternative hypothesis samples dredged from the volcanic ridge located furthest away from notes the broad coincidence of the HEB with major circum-Pacific the northern end of the Musicians Chain (Fig.1 ), most of the Plate tectonic events and favours HEB formation by the resulting 40Ar/39Ar ages for the southern Musicians Ridges are unexpectedly change in the direction of Pacific Plate motion4,5,11,12. But plate 52–53 Myr. A few younger ages show that volcanism might have 1Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Alten Hafen 26, 27568 Bremerhaven, Germany. 2GeoZentrum Nordbayern, University Erlangen-Nürnberg, Schlossgarten 5, 91054 Erlangen, Germany. 3Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands. 4GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany. 5EarthByte Group, School of Geosciences, The University of Sydney, New South Wales 2006, Australia. 6Department of Earth Sciences, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK. 7Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, California 92093-0225, USA. 8University of Bremen, Fachbereich 5, 330440 Bremen, Germany. 9Institute for Geosciences, Christian-Albrechts-University, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany. *e-mail: [email protected] NATURE GEOSCIENCE | VOL 8 | MAY 2015 | www.nature.com/naturegeoscience 393 © 2015 Macmillan Publishers Limited. All rights reserved LETTERS NATURE GEOSCIENCE DOI: 10.1038/NGEO2416 Longitude Bach Ridge ° ° 100 0.30 165 W 160 W 06MY102 SO142 9DR-1 90 plagioclase 80 39Ar fraction = 96% 70 0.20 96 60 K/Ca Musicians Seamounts 5 4 50 94 52.4 ± 0.6 Myr 40 Age (Myr) Age 0.10 91 30 90 20 Latitude 10 30° N 6 0 0.00 84 0102030405060708090100 86 Murray FZ Beethoven Ridge 100 0.10 04MY378 83 SO142 13DR-2 90 plagioclase Hawaiian Chain 39Ar fraction = 91% 8 9 10 12 80 0.08 75 70 75 13 60 0.06 K/Ca 79 82 83 50 52.7 ± 0.6 Myr 25° N 40 0.04 Age (Myr) Age 30 20 0.02 50° N 10 Emperor Chain 0 0.00 0 10 20 30 40 50 60 70 80 90 100 Murray FZ 0.20 140 02M0239 SO142 6DR-1 rock chips 39 120 Ar fraction = 70% 0.16 40° N Latitude 100 HEB K/Ca 80 0.12 Musicians 48.5 ± 0.9 Myr 60 Age (Myr) Age 0.08 40 30° N 20 0.04 Haw 0 aiian Chain 0102030405060708090100 Murray FZ ° 20 N 140 02M0240 SO142 6DR-4 rock chips 0.16 120 39Ar fraction = 71% 170° E 180° 170° W 160° W 100 Longitude 0.12 K/Ca 80 Figure 1 | Locations of sample sites on the Musicians volcanic ridges. 47.0 ± 1.2 Myr 60 Yellow circles in the top panel indicate the locations of SO142 expedition (Myr) Age 0.08 dredge sites and adjacent numbers give the station numbers 40 (see Supplementary Table 1 for sample information). Sample ages are 20 0.04 shown also on high-resolution bathymetric maps in Supplementary Fig. 1. 0 The base map is marine gravity from radar altimetry at a contour interval of 0 10 20 30 40 50 60 70 80 90 100 20 mGal (ref. 31). White numbers are for published ages measured in the Cumulative 39Ar released (%) 1990s and white boxes show sample locations16. The box around the HEB marks the position of an enlarged map with age information in Figure 2 | Examples of high-resolution incremental heating 40Ar/39Ar age Supplementary Fig. 3. spectra for the Musicians volcanic ridges. Pink lines are 40Ar/39Ar ages, and grey lines are K/Ca ratios. The reported 40Ar/39Ar age ages are continued until 47–48 Myr ago, or that a second event occurred weighted age estimates with errors reported on the 95% confidence level, roughly 6 Myr later. Surprisingly, the samples from the Murray FZ including 0.3%–0.4% s.d. in the J-value. All samples where monitored also yielded ages of 47–48 Myr. 40Ar/39Ar plateau ages are shown against Taylor Creek rhyolite (TCR) monitor (28.34±0.014 Myr, 1σ /. For in Fig.2 and Supplementary Fig. 2. For complete information see complete information see Methods, Supplementary Table 2, Methods, Supplementary Table 2 and Supplementary Methods. The Supplementary Fig. 2 and Supplementary Methods. most striking facet of these unexpectedly young lava ages is they bracket the formation of the HEB (50–47 Myr ago; refs5 ,9; see also (or post-erosional) volcanism found on intraplate volcanoes, Supplementary Fig. 3). such as the Hawaiian Island volcanoes, because they are tholeiitic The geochemistry of this late-stage volcanism can help and are depleted in both incompatible element and isotopic constrain its origin (Fig.3 and Supplementary Fig. 4 and composition, whereas rejuvenated volcanism is alkalic and shows Supplementary Table 2). The dated samples are unlike rejuvenated incompatible element enrichment (see also Supplementary Note 4). 394 NATURE GEOSCIENCE | VOL 8 | MAY 2015 | www.nature.com/naturegeoscience © 2015 Macmillan Publishers Limited.
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