Discovery of a large 2.4 Ma Plinian eruption of Basse-Terre, Guadeloupe, from the marine sediment record Martin R. Palmer1, Stuart J. Hatter1, Thomas M. Gernon1, Rex N. Taylor1, Michael Cassidy2, Peter Johnson1, Anne Le Friant3, and Osamu Ishizuka4 1School of Ocean and Earth Science, University of Southampton, European Way, Southampton SO14 3ZH, UK 2Institute for Geosciences, Johannes Gutenberg University Mainz, J.-J.-Becher-Weg 21, D-55128 Mainz, Germany 3Institut de Physique du Globe de Paris, UMR 7154, CNRS, Paris, France 4Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Central 7, 1-1-1, Higashi, Ibaraki, Tsukuba 305-8567, Japan ABSTRACT Figure 1. Northern Lesser St. Kitts Outer arc Large volcanic eruptions are major geo- Antilles (Caribbean Sea) map with Integrated hazards, so identifying their frequency in Nevis Antigua upper layer Ocean Drilling Program the geologic record is critical for making 6 cm 17oN Expedition 340 Site predictions and hazard assessments. Follow- Montserrat U1396 location. Inset shows image of tephra ing the discovery of a thick (18 cm) tephra lower layer layer T2.36. Also shown layer in marine sediments from Integrated 12 cm are Guadeloupe volca- Ocean Drilling Program (IODP) Site U1396 U1396 BC nic centers: Basal Com- between Montserrat and Guadeloupe in the SC plex (BC), Septentrional Caribbean Sea, we document here how high- Guadeloupe AC Chain (SC), Axial Chain 16oN (AC), Grande Découverte precision Pb isotopes, trace elements, and GD LS U1396A U1396C (GD), and Les Saintes grain morphological analyses of the tephra 6H4 6H2 (LS) (Samper et al., 2007, can be used, together with volcanological 2009). White circles indi- Dominica models, to identify a large (Volcanic Explo- Atlantic cate sampling locations Ocean for grain-size analyses sivity Index ~6) Plinian eruption from Basse- Inner arc (Hole U1396A) and geo- Terre, Guadeloupe, at ca. 2.36 Ma. This pre- 62oW 61oW 60oW chemistry and grain mor- viously unrecognized eruption is believed to phology (Hole U1396C). be the largest documented volcanic event in this region since this time. We hypothesize that this large eruption was associated with nism in the northern Lesser Antilles, Integrated et al., 2007), but there is a clear north-south gra- the final stage in the evolution of an individ- Ocean Drilling Program (IODP) Expedition dation in the Pb isotope ratio of volcanic rocks ual volcanic center, which has implications 340 occupied four sites in A.D. 2012 offshore in the Lesser Antilles that has been present for for prediction of geohazards in this setting. the currently active island of Montserrat. Site ~5 m.y. (Lindsay et al., 2005; Labanieh et al., U1396 is located on a topographic high (water 2010), and Pb isotope analyses of Montserrat INTRODUCTION depth of ~780 m), ~30 km southwest of Mont- (Cassidy et al., 2012) and Guadeloupe lavas Reconstructing the history of island arc vol- serrat and ~75 km west of Guadeloupe (Fig. 1). (White and Dupré, 1986) show that the two cen- canoes is critical for determining their petro- Of the three holes cored at the site with the ad- ters are distinguishable (Fig. 2A; see the GSA logical evolution and potential geohazards, but vanced piston corer, two produced continuous Data Repository1). The one Dominican Pb iso- such studies are difficult because erosion and (Hole U1396A, 140.5 m; Hole U1396C, 145.9 tope datum that lies in the Guadeloupe field is later eruptions destroy and obscure the subaerial m) records that extend back ~4.5 m.y. (Hatfield, from the <40 ka Morne Anglais center (Lindsay record of volcanoes, with much of the erupted 2015). The sediments comprise hemipelagic et al., 2005). Of 29 samples of visible tephras material rapidly transported to the oceans (Le (largely carbonate) sediment and volcaniclastic analyzed from Site U1396 and shown in Figure Friant et al., 2015). While marine sediment mud, with more than 150 visible (>0.5 cm thick) 1, 17 fall in the Montserrat Pb isotope field and cores can provide more complete histories of arc tephra layers intercalated in hemipelagic back- 12 in the Guadeloupe field. Of the latter, five volcanism, this approach requires identification ground sediments (Le Friant et al., 2015). The come from an ~18-cm-thick tephra layer (sub- of the depositional mode of marine tephra layers present study uses geochemical, grain morphol- cores 6H4-U1396A and 6H2-U1396C). The and their precise origin from closely spaced and ogy, and volcanological techniques to identify other samples with a Guadeloupe origin come compositionally similar volcanoes. the origin and magnitude of the eruption that from tephra layers <5 cm thick. This problem is exemplified in the Lesser generated the thickest tephra layer from Site The sedimentary interval of the tephra layer Antilles, Caribbean Sea, where volcanism has U1396. (Fig. 1) is bracketed by the base of the C2r.1n been active since ca. 40 Ma. To the north of (B) Reunion polarity zone (2.148 Ma) and the Martinique, the arc is divided into two chains. SEDIMENT CORE OBSERVATIONS base of the C2r.2r (B) Gauss/Matuyama polar- The eastern, inactive chain is older, with carbon- Tephra was likely delivered to Site U1396 ity zone (2.581 Ma) (Hatfield, 2015) and has an ate platforms covering volcanic basement. Tec- from different sources, but prevailing wind di- tonic adjustments during the Miocene modified rections and seafloor topography suggest, how- 1 GSA Data Repository item 2016031, T2.36 geo- the orientation of the subducting slab, causing ever, that these layers were predominantly from chemical data tables, figure of tephra grain morpho- westward migration of the volcanic front and volcanoes on Montserrat and Guadeloupe. The logical characteristics, and age assignment details, is available online at www.geosociety.org/pubs/ft2016 initiation of a new arc that includes all the ac- erupted material on both islands consists mainly .htm, or on request from [email protected] or tive volcanoes (Pindell and Barrett, 1990). In of andesites, with lesser amounts of basalts and Documents Secretary, GSA, P.O. Box 9140, Boulder, order to reconstruct a long-term record of volca- basaltic andesites (Harford et al., 2002; Samper CO 80301, USA. GEOLOGY, February 2016; v. 44; no. 2; p. 123–126 | Data Repository item 2016031 | doi:10.1130/G37193.1 | Published online 22 December 2015 GEOLOGY© 2015 The Authors.| Volume Gold 44 |Open Number Access: 2 | www.gsapubs.orgThis paper is published under the terms of the CC-BY license. 123 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/44/2/123/3549285/123.pdf by guest on 01 October 2021 16 Axial Chain (1.02–0.44 Ma) and the Grande ) 40 A Découverte volcanic complex (314 ka to pres- Upper 77/78 ent) (Samper et al., 2007, 2009) (Fig. 1). K-Ar 30 Layer 79/80 12 ages show a north-south migration of volcanic 81/82 4 Montserrat activity, with a relatively large age gap between 20 7/ ∆ Guadeloupe the youngest dates for the Basal Complex (2.68 8 Dominica ± 0.04 Ma) and the oldest age for the Septentri- 10 U1396 onal Chain (1.81 ± 0.03 Ma). In addition, there T 2.36 0 are K-Ar dates for the two volcanic islands— -0.5 1.5 3.5 5.5 7.59.5 4 Les Saintes (Terre-de-Bas, 0.92–0.88 Ma; and 18.8 19.0 19.2 19.4 40 Terre-de-Haut, 2.98–2.00 Ma)—that lie ~10 km Lower 206Pb/204Pb 83/84 south of Basse-Terre (Zami et al., 2014). 30 Layer 86/87 The latitude of the source of T is uncer- 3 2.36 90/91 Terre-de-Haut tain, but is likely south of the older Basal Com- 20 Basal Complex B N plex (~16°19′N). The depositional age of T2.36 ) Septentrional T2.36 lies within the age range of activity on Terre-de- 10 2 Haut, but the La/Sm ratio of samples from T2.36 fall on the Basse-Terre trend that is distinct from 0 Fraction of particles in sample (% -0.5 1.5 3.5 5.5 7.59.5 (La/Sm that of Terre-de-Haut lavas (Fig. 2B). Hence geochemical and age data suggest that T Bin size φ 1 2.36 likely derived from Basse-Terre, with equivalent Figure 3. Grain-size analyses of tephra deposits of this source now buried beneath the samples from Integrated Ocean Drilling Pro- 123 Septentrional and Axial Chain centers. gram Hole U1396A, northern Lesser Antilles (77/78, etc., refer to depth intervals [in cm] Age (Ma) The five sampled layers from T2.36 have MgO and SiO concentrations that range from 1.12 to shown in Fig. 1). Figure 2. Pb isotope and geochemistry data 2 of tephra and volcanic samples, northern 2.75 wt% and 59.4 to 64.6 wt%, respectively Lesser Antilles. A: D7/4 (relative to North- (see the Data Repository for methods), which ern Hemisphere reference line; Hart, 1984) are typical of andesites from Basse-Terre (Sam- wind direction reverses from east to west in the versus 206Pb/204Pb. Pb isotope data are for per et al., 2007, 2009). wet season, to west to east in the dry season (Ko- islands from Dominica (Lindsay et al., 2005), morowski et al., 2008). Stratospheric circulation Montserrat (Cassidy et al., 2012), and Gua- deloupe (White and Dupré, 1986; C. Chauvel, ERUPTION RECONSTRUCTION at this latitude is controlled by Brewer-Dobson 2015, personal commun.). Green symbols It is difficult to unequivocally determine circulation (Andrews et al., 1987), so there is no are for Integrated Ocean Drilling Program whether more than one eruption was responsible a priori reason to expect that stratospheric wind Site U1396, and red symbols are for tephra for deposition of T .