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doi:10.2204/iodp.pr.340.2012

Background and objectives

Background

The Lesser Antilles arc

The Lesser Antilles arc results from the subduction of the Atlantic oceanic plate beneath the Caribbean plate (Fig. F1). Recent plate convergence rates are relatively slow (2–4 cm/y; Feuillet et al., 2002), and magma productivity has been low relative to other arcs; estimates vary between 3 and 5 km³/m.y./km (Sigurdsson et al., 1980; Wadge, 1984; MacDonald et al., 2000). Volcanic activity along the arc started at ~40 Ma (Martin-Kaye, 1969; Bouysse et al., 1990).

North of Dominica, the arc is divided into two island chains and is built on an extinct ocean island arc from the Cretaceous period (Bouysse and Guennoc, 1983; Wadge, 1986). The eastern chain corresponds to an older although extinct arc, the volcanic basement of which is now covered by a thick carbonate platform. The western chain is the site of active volcanism since 20 Ma (Briden et al., 1979). South of Dominica, the older and more recent arcs merge, forming one chain of islands bordered to the west by the 2900 m deep backarc Grenada Basin. The Grenada Basin is a major depocenter for large debris avalanche deposits (Fig. F1), volcanogenic turbidites, large pyroclastic flow deposits, and hemipelagic sediment (Sigurdsson et al., 1980; Deplus et al., 2001; Picard et al., 2006; Boudon et al., 2007). Rates of background hemipelagic sedimentation vary from 1–2 cm/k.y. west of the northern islands to 10–20 cm/k.y. in the Grenada Basin to the south (Reid et al., 1996; Duchoiselle, 2003). In the absence of any deep drilling projects in the region, knowledge of the volcanic history of the arc, based on the marine record, is largely limited to the last 300 k.y. (in most places <<100 k.y.).

Eruptive history along the Lesser Antilles arc

The Volcanic Hazard Atlas of the Lesser Antilles (Lindsay et al., 2005a) provides a good synthesis of available information on the volcanoes of the arc. One characteristic of Lesser Antilles arc volcanism is that many of the volcanic centers overlap in both space and time (Lindsay et al., 2005a). Volcanic activity is observed to migrate from north to south (e.g., Montserrat; Harford et al., 2002) or south to north (e.g., Martinique; Boudon et al., 2005) or to cluster in contemporaneous centers (Dominica; Lindsay et al., 2005b). In each case discrete volcanic centers develop and appear to remain active for 5 × 10⁵ to 5 × 10⁶ y, although these inferred timescales are not well constrained. The onset of volcanic activity is generally unknown because the earliest products are not easily accessible through standard geological investigations.

It is often difficult to constrain the eruptive history of a volcano beyond the start of written historical records or beyond ages that are greater than those of well-preserved subaerial tephra deposits. Deciphering a complete eruption record from onshore geology alone can be problematic because of burial by subsequent deposits, growth of dense vegetation obscuring deposits, erosion, and remobilization of deposits by flank-collapse events. Marine sediment typically preserves a much more complete record of volcanic activity.

In the past decade, several studies of the magmatic history of a number of Lesser Antilles volcanoes have been carried out based on tephra deposits retrieved from piston coring of marine sediment during the 2002 Caraval cruise (Duchoiselle, 2003; Vennat, 2004; Le Friant et al., 2008; Machault, 2008). Correlations have been found between tephra sampled in a piston core off one island and pyroclastic deposits from volcanoes on different islands. In the case of the Montagne Pelée Volcano on Martinique, piston cores (7 m in length) extended the eruptive record for >25,000 y. In addition, 25 eruptive events have been identified within marine deposits between 5,000 and 15,000 y compared to only 10 magmatic events previously recognized onshore for the Montagne Pelée Volcano. For the Soufrière Hills Volcano (Montserrat), the record has been extended to ~250 ka in a 5.8 m piston core in an area of low sedimentation rate. The marine core also recorded several Plinian explosive eruptions that were not identified on land (Le Friant et al., 2008). Each volcanic island has a distinctive mineralogy and geochemistry (Sigurdsson et al., 1980; Lindsay et al., 2005a) owing to changes in magma types along the arc. Distinguishing the sources for tephra layers in cores is therefore straightforward.

Long-term magmatic evolution of the volcanic arc

Volcanism varies markedly along the Lesser Antilles arc (MacDonald et al., 2000; Lindsay et al., 2005a). Generally, magma becomes enriched in incompatible elements (notably K) and radiogenic isotopes southward along the arc. This enrichment may be related to the increasing influence of subducted Orinoco sediment from the South American continent that is supplied into the forearc region from the south. In addition, it may be a consequence of variations in the subduction rate and subduction geometry normal to the arc. In the south, St. Vincent, Grenada, and the Grenadine Islands are dominated by basaltic to basaltic andesitic magma. Soufrière on St. Vincent and the submarine Kick’em Jenny are the two historically active centers in this area. In the central Lesser Antilles, St. Lucia, Dominica, and Martinique are large islands dominated by silicic magma with subsidiary mafic magma. Relatively high rates of volcanism can be inferred from the regional inventory of marine tephra layers from these islands (Sigurdsson et al., 1980), as well as the size of the volcanic centers. Duchoiselle (2003) estimated a recurrence rate of 2.6 magmatic eruptions/k.y. for Montagne Pelée on Martinique. Volcanism on all the central islands has produced several large Plinian-style explosive eruptions with associated ignimbrites in the recent geological past. In the north, the small volcanoes of Soufrière Hills on Montserrat and Soufrière on Guadeloupe have produced dominantly andesitic magma, whereas Nevis, St. Kitts, St. Eustatius, and Saba have erupted substantial volumes of basaltic and andesitic magma. However, their magma production rates and eruption frequency are comparatively low (e.g., 0.5 magmatic eruptions/k.y., Soufrière on Guadeloupe; Komorowski et al., 2005). The areas studied during this project correspond to the central transition zone. Alternating periods of longer intervals of constant magma compositions with shorter intervals of varying magmatic compositions are typically observed on timescales of ~1 m.y. across this transition zone.

Much of the compositional variability observed in single volcanoes on the arc can be related to magma formation and evolutionary processes within the crust. Annen et al. (2006, 2008) provide a conceptual framework for understanding the dynamics of magma generation, magma differentiation, and transport. Magma flux rates are considered to be the major control of the formation of shallow magma chambers containing eruptible magma and of their compositions. Understanding the igneous processes of volcanic arcs and the subduction zone engine is fundamental because they provide a viable mechanism to generate continental crust and are key components of global-scale geochemical cycling.

Flank-collapse events

Volcano flank collapses are increasingly recognized as a normal process in the destruction of volcanic edifices (Ida and Voight, 1995; McGuire, 1996; Voight, 2000). They play a significant role not only in the evolution of volcanic edifices but also in the dynamics of subsequent eruptions. In addition, these collapses are a significant volcanic hazard. The recognition of flank-collapse events is based on mapping debris avalanche deposits that can be traced to a generally horseshoe-shaped collapse depression on the volcano (Voight, 1981). The most voluminous events (volumes from tens to hundreds or even thousands of cubic kilometers) have been recognized off oceanic islands such as Hawaii (Lipman et al., 1988; Moore et al., 1989) and La Réunion (Labazuy, 1996; Oehler et al., 2004, 2008), as well as on the Canary archipelago (Holcomb and Searle, 1991; Watts and Masson, 1995; Urgeles et al., 1997; Krastel et al., 2001).

At least 52 flank-collapse events, 15 of which have occurred within the last 12,000 years (Boudon et al., 2007), have been identified in volcanoes of the Lesser Antilles arc (Fig. F1) (Deplus et al., 2001; Le Friant, 2001; Le Friant et al., 2002, 2003a, 2003b, 2004; Lebas et al., 2011; Boudon et al., 2007). Edifice collapses are a major concern on the small Caribbean Islands, as a large portion of the debris avalanches flow into the sea, generating potentially destructive tsunamis. In the northern part of the arc, flank collapses are repetitive, can occur in all directions, and are promoted by intense hydrothermal alteration and well-developed fracturing of the summit of the edifices. For example, several prehistoric flank collapses have been recognized on the Soufrière Hills Volcano (Fig. F2) (Le Friant et al., 2004; Lebas et al. 2011). The English’s Crater event occurred ~2000 y ago, producing part of Deposit 1 (volume = ~1.8 km³). Debris avalanche Deposit 2 probably resulted from a combined subaerial flank collapse and submarine sediment failure of the eastern flank of the volcano (Le Friant et al., 2004; Lebas et al., 2011; Watt et al., 2012). In the southern part of the arc, flank collapses are larger (with volumes as large as tens of cubic kilometers), always directed to the west, and related to the higher overall slopes of the leeward side of the islands. The evolution of the active Montagne Pelée Volcano has been marked by three major flank collapses (~0.1 m.y., ~25,000 y, and ~9000 y ago) that systematically destroyed the western flank of the volcano (Fig. F3) (Le Friant et al., 2003a; Boudon et al., 2005, 2007). Collapse volumes varied from 2 to 25 km³, and debris avalanches flowed into the Grenada Basin. The Pitons du Carbet Volcano on Martinique experienced a sector collapse 0.3 m.y. ago (Boudon et al., 1992, 2007; Samper et al., 2007). Dominica has experienced at least three flank collapses and was the site for the generation of the most voluminous mass wasting deposits in this area, with submarine deposits that cover 3500 km² (Fig. F4). The proximal debris avalanche deposit consists of megablocks (as much as 2.8 km long and 240 m tall) that reflect the predominance of lava flows and lava domes, as observed in the source Plat Pays volcanic complex and in terrestrial relict debris avalanche material. Megablocks have been successfully mapped using marine geophysical data. In addition, different morphologies and deposit geometries have been observed for Antillean debris avalanche deposits. Large hummocks (as large as 2 km) characterize debris avalanches off Dominica, whereas the morphology of several debris avalanches off Martinique is smooth. These differences are probably related to the lithologies of the volcanic products (dominantly pyroclastic deposits versus massive lavas; Boudon et al., 2007). Northern island volcanoes collapse repeatedly, in contrast with southern island volcanoes where collapses are infrequent. Such variations in size and frequency along a volcanic arc have not been previously documented.

Areas of intraplate active volcanism associated with large submarine volcanic landslides have been drilled by the Ocean Drilling Program (ODP), such as Hawaii (ODP Leg 136: e.g., Garcia, 1993; Garcia and Hull, 1994; ODP Leg 200: e.g., Garcia et al., 2006) and the Canary Islands (ODP Leg 157: e.g., Schneider et al., 1997; Goldstrand, 1998; Schmincke and Sumita, 1998). However, all of these drill sites targeted distal turbidites away from proximal debris avalanche deposits and at water depths of ~4000 m or greater. Seismic surveys around the Canary Islands and the Hawaiian Islands have not penetrated volcanic debris avalanche deposits. In contrast, 2-D seismic surveys around Montserrat, Martinique, and Dominica have provided excellent images of debris avalanche deposits, including the basal surfaces of these deposits (e.g., Deplus et al., 2001; Le Friant et al., 2003a). Collapse deposits around Montserrat were emplaced in shallow water, whereas offshore Martinique and Dominica, debris avalanches flow into the Grenada Basin. The depositional successions provide good seismic reflectors. Study of these debris avalanche deposits will allow a better understanding of the emplacement processes for these huge collapses.

Sedimentation processes

The majority of detrital material resulting from the erosion of the islands of the arc is transported into the surrounding ocean (e.g., Sigurdsson et al., 1980; Le Friant et al., 2004; Picard et al., 2006). Studies of offshore deposits from the 1902 eruption of St. Vincent (Carey and Sigurdsson, 1982), from the recent eruption of the Soufrière Hills Volcano (Le Friant et al., 2004; Hart et al., 2004; Trofimovs et al., 2006), and from prehistoric eruptions on Dominica (Sigurdsson et al., 1980; Whitham, 1989) demonstrate that most of the erupted material also reaches the ocean (Le Friant et al., 2010; Wadge et al., 2010). Volcanogenic sediment is channeled by debris flows, turbidity currents, and persistent ocean currents through deep submarine canyons located west of the volcanoes, which, for Guadeloupe and Dominica, lead into the northern part of the Grenada Basin (Fig. F1).

Around Montserrat there are examples of single and multiple stacked carbonate turbidites that contain reworked shallow-water sediment and fauna. These turbidites are likely sourced from large carbonate platforms associated with islands such as Antigua and Redonda (Trofimovs et al., 2012). Understanding the origin of these bioclastic turbidites is particularly important because the deposit volume exceeds that of volcaniclastic deposits associated with the more recent (<100 k.y.) eruptions of the Soufrière Hills Volcano. Shallow vibrocores have only recorded bioclastic turbidites associated with the late glacial period. One possibility is that these turbidites are caused by the instability of carbonate platforms during rapid sea level rise at the end of major glaciations. Alternatively, major regional earthquakes may trigger them, in which case the occurrence of such events may be unrelated to climatic cycles.

Submarine alteration of volcanic material

The nature and timing of submarine alteration of volcanic material likely varies as a function of the chemical species of interest (e.g., high–field strength elements such as Hf and Zr appear to be largely unaffected, whereas alkali elements can be very mobile), the nature of the volcanic material (e.g., basaltic versus silicic volcanic products and the effect of grain size), and the physical emplacement mechanism (e.g., thin air fall deposits versus thick debris flows). Although there have been sporadic studies of tephra layers at individual Integrated Ocean Drilling Program (IODP) and ODP sites (e.g., Gardner et al., 1986; Gérard and Person, 1994; Martin, 1994; Utzmann et al., 2002), there has been no systematic attempt to study this process as a function of the variables outlined here. Machault (2008) shows that in a piston core sample taken west of Guadeloupe, several tephra layers are correlated with large Plinian eruptions that originated from volcanoes on Dominica (e.g., the Roseau tuff eruption). Chemical analysis (trace and major, incompatible, and immobile elements during the initial alteration stage) of glass from tephra in the cores and from pumiceous deposits on land, combined with mineral assemblages, allows correlation between marine and subaerial pyroclastic deposits. Machault (2008) and Sigurdsson et al. (1980) show that glass shards in marine sediment in the Caribbean region are not significantly altered.

Site survey data

Previous work has involved on-land geological, geochemical, petrological, geochronological, and geophysical studies and offshore marine studies. Much of the information is summarized in MacDonald et al. (2000) and in the Volcanic Hazards Atlas of the Lesser Antilles (Lindsay et al., 2005a).

• Drilling at Deep Sea Drilling Project (DSDP) Site 30 during Leg 4 took place in 1969 to investigate the geologic history of Aves Ridge (west of the Grenada Basin). DSDP Site 48 (Leg 15) was located north of Site 30, and was also drilled to investigate the Aves Ridge. However, no DSDP, ODP, or IODP sites have been drilled in the Grenada Basin or close to the Lesser Antilles Islands.

• A regional collection of piston cores was gathered during the Endeavour cruise of 1979, allowing assessments of rates of volcanism and sedimentation, dating of major explosive eruptions, recognition of submarine pyroclastic flow deposits, and establishment of a biostratigraphic framework for the eastern Caribbean (Sigurdsson et al., 1980; Sparks et al., 1980a, 1980b; Reid et al., 1996). Westbrook and McCann (1986) analyzed large-scale seismic experimental data on the overall arc crust and show that the history of subduction has been episodic (e.g., a shift of the axis of volcanism in the Lesser Antilles at the beginning of the Pliocene).

• Marine geophysical data were gathered during two cruises of the R/V L’Atalante—Aguadomar (December 1998–January 1999) and Caraval (March 2002)—and one cruise on the RRS James Clark Ross—JCR123 (May 2005). During the first two cruises (Principal Investigators [PIs]: C. Deplus and G. Boudon), Simrad EM12D swath bathymetry and backscatter, 3.5 kHz echo sounder, gravity, magnetic, and six-channel seismic reflection data were collected from Montserrat to St. Vincent (Deplus et al., 2001). During the Caraval cruise, seismic profiles using a 24-channel streamer (Deplus et al., 2002), sediment piston cores, and dredge samples were collected. During the JCR123 cruise (PI: R.S.J. Sparks), sediment cores were collected from around Montserrat to study submarine pyroclastic deposits from the recent eruption (Trofimovs et al., 2006).

• Two U.K. Natural Environment Research Council (NERC)-funded cruises took place in December 2007. The first cruise (PI: M. Palmer) collected box cores and shallow gravity cores at ~34 sites around Montserrat to constrain how diagenesis of tephra from the recent eruptions influenced seawater geochemistry. The second cruise, a component of the SEA-CALIPSO seismic experiment sponsored by the U.S. National Science Foundation (NSF), NERC, and collaborating agencies (PIs: S. Sparks and B. Voight), aimed at imaging the interior of Montserrat and the Soufrière Hills Volcano, using source seismic techniques in combination with ~240 onshore seismometers and offshore ocean-bottom seismometers (Voight et al., 2008; Sparks et al., 2008).

• The Gwadaseis cruise (PI: N. Feuillet) of the R/V Suroit (February–March 2009) collected high-resolution seismic data and piston cores.

• The JC45/46 cruise (PI: P. Talling) of the RRS James Cook in April–May 2010 collected high-resolution 2-D and 3-D seismic data around Montserrat.

Scientific objectives

Study of volcaniclastic sediment and volcanic landslide deposits drilled in the Lesser Antilles arc will significantly advance our understanding of eruptive history, magmatic evolution in volcanic arcs, and the timing and emplacement processes of large debris avalanches. Major advances will result from, for example, recovering the first cores through large-scale volcanic debris avalanches and analyzing the relative timing of eruptions.

We plan to achieve the major objectives of the project by documenting the evolution of three volcanic centers that represent the range of behaviors and eruptive styles in the Lesser Antilles arc: Montserrat in the north, where the Soufrière Hills Volcano has been erupting, resulting in serious hazards and social disruption since 1995; Martinique, with the sadly famous Montagne Pelée Volcano; and Dominica, where several large silicic eruptive centers are considered active, posing serious potential regional hazards because of the occurrence of large-magnitude ignimbrite-forming eruptions. Below, we identify five topics that are linked to the themes of understanding arc volcanic systems and the effects of volcanism on the environment.

1. Understand the timing and emplacement processes of potentially tsunamigenic large debris avalanche emplacements.

Volcano flank collapses are increasingly recognized as a normal process in the construction and destruction of volcanic edifices (Ida and Voight, 1995; McGuire, 1996; Voight, 2000). However, several questions regarding the mechanism controlling the processes and timing of debris avalanche emplacement are still unresolved. This project was designed to study the architecture of debris avalanche deposits and to specifically try to answer the following questions.

What factors control the timing of large flank failures (Voight, 2000; Voight and Elsworth, 1997)?

Are flank collapses associated with magmatic intrusions or major volcanic eruptions? Are failures triggered by processes such as more rapid volcano edifice construction, strength reduction by hydrothermal processes, or rapid sea level change (Quidelleur et al., 2008) as might occur in the future? Do flank collapses lead to changes in magmatic evolution by depressurizing the magma system (Voight, 1981; Pinel and Jaupart, 2000)?

Does significant erosion occur during the flow of the debris avalanche?

Are bulking, erosion, and sediment incorporation the same for subaerial and submarine landslides (Glicken, 1991; Komorowski et al., 1991; Voight, 1978; Voight and Sousa, 1994; Schneider et al., 2004)? How large is the volume of reworked sediment? What is the dynamic role of the undrained loading of overridden compressible marine sediment (Voight and Elsworth, 1997)? Is the sedimentary substratum deformed with the emplacement of the debris avalanche (Schneider et al., 2004)? Are the matrix facies of the debris avalanche more abundant in the bottom part (Gee et al., 1999)?

How might the collapse evolve?

The collapse might evolve in singular failure or retrogressively with several closely spaced failures leading to multiple debris avalanches (Wynn and Masson, 2003; Mattioli et al., 2007) and proportionately less severe consequences. For instance, large-scale flank-collapse events on the Canary and Hawaiian Islands have generated turbidites that comprise multiple fining-upward subunits (Wynn and Masson, 2003; Garcia and Hull, 1994), which suggest that flank collapse occurred in a number of stages separated by days to weeks.

2. Document the long-term eruptive history of the arc to assess volcano evolution (cycles of construction and destruction) and major volcanic hazards.

It is often difficult to precisely constrain the eruptive history of a volcano beyond the start of written historical records or beyond ages that are greater than those of young well-preserved subaerial tephra fall deposits (commonly only a few thousand years). Marine tephra records in sediment cores collected by piston, gravity, or vibrocoring extend volcanic histories of the Caribbean by several tens of thousands of years (Sigurdsson et al., 1980; Le Friant et al., 2008). However, this improvement is still not sufficient to characterize the evolution of volcanic systems that can extend a few million years or to diagnose the return periods of very large magnitude volcanic events (e.g., explosive eruptions and major flank collapses). This project was designed to answer the following questions: Are the volcanoes as discrete as onshore studies suggest? What are the characteristics of products erupted at the onset of activity from a specific center, particularly those that initially develop below sea level? What processes control migration from one volcanic center to another? Is the end of activity at one center and the onset at another center synchronous, or are there eruptive hiatuses? What is the nature of volcanism during the construction of a volcanic complex? Are there systematic patterns in the time series of volcanic eruptions in terms of eruptive style, eruption magnitude, and repose periods? If so, can these systematic patterns be linked to major processes of volcano construction and destruction (e.g., flank collapse), external factors (e.g, climate and sea level), or deeper magmatic processes?

3. Characterize the magmatic cycles and long-term magmatic evolution of the arc.

The third objective shares common objectives with those aimed at elucidating volcanic history and behavior. We will use time series and spatial records of variation in magma composition (mineralogy, major and trace element composition, and isotopic signature) and volume to characterize the processes governing magma composition, associated eruption mechanisms, and eruption frequencies. This project was designed to answer the following questions: Why do some magma systems remain steady state for long periods of time generating very similar magma (e.g., Montserrat and Montagne Pelée)? Why do others show much more variability in composition? Why are there marked excursions from mafic to silicic magmatism or vice versa? Are switches in composition sudden or gradual? Can change in composition be linked to major explosive eruptions or flank collapses that perturb the crystal magma systems, or do these changes reflect internal dynamics of crustal magma systems, such as buoyancy instabilities related to accumulation of regions of partial melt?

4. Document dispersal of sediment into the deep ocean.

The majority of detrital material resulting from the erosion of the islands of the arc is transported into the surrounding ocean (e.g., Sigurdsson et al., 1980; Le Friant et al., 2004; Picard et al., 2006). Our objectives are to contribute to the understanding of sedimentary facies on the submarine flanks and in the basins that surround arc volcanoes, characterize the sedimentation processes, and estimate local sedimentation rates in the northern and southern parts of the arc. This project was designed to answer the following questions: Do debris avalanches have the potential to generate turbidity currents? Are most turbidite units linked to volcanic eruptions? Can some (or many) be linked to nonvolcanic processes such as submarine slope failures triggered by regional earthquakes or gravitational instabilities? What is the proportion of volcanogenic sediment versus hemipelagic carbonate sediment? What are the differences between the north and the south in terms of sedimentation processes?

5. Determine the processes and element fluxes associated with submarine alteration of volcanic material.

The processes associated with submarine alteration of magmatic material are of fundamental importance on a global and a regional scale. Drilling will allow the investigation of the little explored issue of the diagenesis of volcanic deposits. This project was designed to answer the following questions: To what extent is volcanic material altered as it is buried and the processes of compaction and diagenesis take place? How does the timing and style of alteration vary as a function of the nature and thickness of the deposit? How does the process of submarine alteration change as a function of parent material composition (basalt, basaltic andesite, andesite, or dacite)?

Answering these questions is not only relevant to furthering our understanding of global biogeochemical cycles but also has implications for the use of geochemical and isotopic systems in dating individual volcanic layers in marine sediment and in correlating volcanic layers between sites.

Coring and drilling strategy

The main aim of Expedition 340 was the thorough characterization of volcanic and marine sediments at nine primary sites along the backarc region of the Lesser Antilles arc. Generally, these objectives involved logging and coring as much of the sedimentary sequences as possible in the specified time window, and thus drilling operations were adjusted accordingly.

The originally proposed drilling strategy determined at the precruise meeting in College Station, Texas (USA), in May 2011 was to begin by drilling at proposed Site CARI-02C (U1393) and end by drilling at proposed Site CARI-09B (U1398) following the sequence laid out in the operations plan (see table T2 in Le Friant et al., 2011). Two holes were planned at each site, with the exception of Site CARI-01C. Site CARI-01C was planned as a single hole, piston cored to a depth of ~132 mbsf. At all sites, holes would be cored with the advanced piston corer (APC) to refusal. The coring system would then be changed to the extended core barrel (XCB) to core to the total depth as determined by the scientific objectives. However, if coring of the first hole fulfilled all scientific objectives, the second hole would not be drilled. In detail, the first and second holes at each site (Holes A and B) would be cored with the APC/XCB to the planned depth. After reaching the planned depth, all Hole Bs would be conditioned, displaced with logging mud, and logged, as per the logging plan. While coring, a number of advanced piston coring temperature tool (APCT-3) measurements were also planned, formation conditions permitting. Core orientation with the FlexIt tool would also be measured during the APC-cored sections at each site. If depth objectives could not be achieved with APC/XCB coring, the rotary core barrel (RCB) would be deployed.

The downhole logging program of Expedition 340 was designed to complement the coring program, measuring continuous in situ profiles of physical properties such as bulk density, porosity, resistivity, and natural gamma radiation. Wireline logging was planned for eight of the nine primary sites. Two standard tool strings would be deployed at each logged hole. The first run would be the triple combination (triple combo) tool string, which records resistivity, neutron porosity, bulk density, and natural and spectral gamma radiation. The second run would be the Formation MicroScanner (FMS)-sonic tool string, which records gamma radiation, sonic velocity (compressional and shear waves), and oriented high-resolution electrical resistivity images. A third logging run was planned at three sites (CARI-03C, CARI-07C, and CARI-10B) using the Versatile Seismic Imager (VSI) to acquire a zero-offset vertical seismic profile (VSP) for calibrating the integration of borehole and seismic data. At three of the sites (CARI-02C, CARI-03C, and CARI-04C), deployment of the Magnetic Susceptibility Sonde (MSS) was planned. The MSS, which measures magnetic susceptibility, would be used to identify flank collapse deposits from the island of Montserrat, where the volcanic material has a high magnetite content compared to background sediment. During the expedition it was determined that magnetic susceptibility data were valuable for all sites, so the MSS was incorporated into the triple combo tool string for each deployment.

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