Leg 1 Charles Langmuir (914) 365-8657 Lamont-Doherty Earth Observatory email: langmuir@ldeo.columbia.edu Palisades, NY 10964John Bender (704) 547-4251 University of North Carolina at Charlotte email: fgg00jfb@unccvm.uncc.edu Charlotte, NC 28233 San Diego - Acapulco 02 November - 11 December 1997
Leg 2 Nancy Kanjorski (619) 534-1827 University of California, San Diego email: nkanjors@ucsd.edu La Jolla, CA 92093 Acapulco - Callao 14 December - 29 December 1997
Leg 3 Lisa Levin (619) 534-3579 University of California, San Diego email: llevin@ucsd.edu La Jolla, CA 92093
Christina Massell (619) 534-5993 University of California, San Diego email: cmassell@mpl.ucsd.edu La Jolla, CA 92093 Callao - Valparaiso 31 December 1997 - 12 January 1998
Leg 4 Jill Karsten (808) 956-5033 University of Hawaii at Manoa email: karsten@soest.hawaii.edu 2525 Correa Road Honolulu, HI 96822
Emily Klein (808) 956-5033 Duke University email: klein@rogue.geo.duke.edu 103 Old Chemistry Bldg. Durham, NC 27708 Valparaiso - Easter Island 15 January - 02 March 1998
Leg 5 Richard N. Hey (808) 956-8972 Hawaii Institute of Geophysics & Planetology email: hey@soest.hawaii.edu 2525 Correa Road Honolulu, HI 96822 Easter Island - Papeete 05 March - 12 April 1998
Leg 6
Jeffrey Gee (619) 534-4707 University of California, San Diego email: jsgee@ucsd.edu Geosciences Research Division La Jolla, CA 92093 Papeete - Honolulu 17 April - 06 June 1998Leg 7 Ralph Stephen (508) 457-2000 x 2833 Woods Hole Oceanographic Institution email: rstephen@whoi.edu Woods Hole, Ma 02543 Honolulu - Honolulu 10 June - 19 June 1998
Robert A. Knox (619) 534-4729 Assoc. Director, Shipboard Operations and email: rknox@ucsd.edu Marine Technical Support Captain Tom Althouse (619) 534-1643 Marine Superintendent, Nimitz Marine Facility email: capt@mpl.ucsd.edu Christian de Moustier (619) 534-1784 Scientific Advisor to Shipboard email: cpm@mpl.ucsd.edu Technical Support Services SEA BEAM information contact Woody Sutherland (619) 534-4425 Manager, Shipboard Technical email: woodys@odf.ucsd.edu Support Services Stu Smith (619) 534-1898 Head, Geological Data Center email: ssmith@ucsd.edu Ron Moe (619) 534-6054 Head, Shipboard Computer Group email: rmoe@ucsd.edu Bob Wilson (619) 534-1632 Head, Resident Marine Technician Group email: restech@sdsioa.ucsd.edu Rose Dufour (619) 534-2841 Elizabeth Rios email: shipsked@ucsd.edu Ship Schedulers
Leg 1 Charles Langmuir Lamont Doherty Earth Observatory San Diego - Acapulco 02 November - 11 December 1997 The East Pacific Rise (EPR) north of the Orozco transform fault provides unique opportunities to further our understanding of two important classes of problems relating to the origin of the ocean crust nature of the upper mantle. First, in recent years it has become clear that the geochemical systematics of the EPR differ in fundamental ways from those of the Atlantic. Whereas in the Atlantic enriched basalts are associated with hot spots, and normal sections of ridge are relatively homogeneous and depleted, along most of the EPR enriched and depleted basalts commonly occur in close proximity, and with no apparent association with hot spots. In addition, the Òlocal vectorÓ of petrological variability contrasts between the fast-spreading EPR and slow-spreading ridges. One model to account for the intermixed occurrence of enriched and depleted magmas is that the sub-Pacific mantle possesses ambient and ubiquitous small-scale heterogeneities that are not related to hot spots, possibly resulting from recycled subducted materials. Alternatively, it has been suggested that small hot spots are the source of this heterogeneity, and are diluted and dispersed by the more active upper mantle circulation caused by rapid spreading. There are also computing models for the fast-spreading local vector. Some say it reflects small changes in mantle potential temperature, while others call upon changes in mantle composition associated with hot spot influence. To distinguish between these models we need a Òsmoking gunÓ - a small hot spot whose effects on the EPR can be calibrated. An ideal candidate occurs in the region north of Orozco. The EPR in this region is the shallowest of the northern EPR, contains a preponderance of enriched basalts and off-axis there is a possible hot spot trace. The chemical effects of the hot spot can be traced in space and time because basalts from this region have a distinctive esotopic composition that can be used as a chemical fingerprint. Mapping, dating and sampling the possible off-axis trace can test whether this region is influenced by a hot spot. Sampling the axis, abyssal hills and off-axis seamounts can investigate the systematics of the Orozco chemical anomaly in space and time, and test whether a small hot spot can cause the commonly observed intimate association of normal and enriched MORB. Together these results will substantially further our understanding of the origin of the characteristic petrological signature of the EPR, and of possible contrasts in the mantle beneath the Pacific and Atlantic ocean basins.
Second, the width of the active volcanic zone, the extent of off-axis volcanism and the petrologic changes that take place over short time intervals at the EPR axis are poorly known. Published results from 12¡N is "starved" while 9¡N is "robust" in terms of axial morphology. The EPR N. of Orozco extends the range of axial morphology that can be investigated by a factor of two, and recent multichannel seismic results confirm that the region has an exceptional magmatic budget. Investigating this region will clarify how basalt composition and volcanic activity change as the magmatic budget increases and will aid in the design and interpretation of investigation of the new frontier of temporal variability. We propose, in collaboration with Mexican colleagues, to sample the N. Orozco region both on and off-axis and carry out a comprehensive petrological and geochemical study of the recovered samples. Multibeam mapping will be essential to map the off-axis terrain and put the sampling in a rigorous context. A complete geochemical investigation of the samples will be undertaken, including major elements, trace elements, isotopes and collaborative dating of samples using Th-U-Pa and 40Ar/39Ar.
Ship Time Request-Front Ship Time Request-Back Cruise Track
Leg 2 Nancy Kanjorski University of California, San Diego Acapulco - Callao 14 December - 29 December 1997 SEA BEAM 2000 data will be acquired at the OBS sites, the Gulf of Tehuantepec, and along the flexurally bending Mid America Trench outer rise in order to supplement existing SIO data(Lonsdale, 1995, and unpublished data) which indicates a unique pattern of faulting. The effects of aging, varying subducting slab angle, possible influences of the nearby Cocos-NorthAmerican-Caribbean Triple Junction, and the subduction of large aseismic bathymetric feature, the Tehuantepec Fracture Zone, along a non-linear segment of the trench will also be quantified.
Ship Time Request-Front Cruise Map
Leg 3 Lisa Levin Christina Massell University of California, San Diego Callao - Valparaiso 31 December 1997 - 12 January 1998 The requested ship time (R/V Melville) is to conduct studies of benthic processes within and below the oxygen minimum zone on the Peru continental margin. The project will involve sediment coring (with boxcorer and multicorer) and hydrographic measurements (CTD, water sampling) at depths between 200 and 2000 m on the margin between 9¡ S and 15¡ S. This research is being done in collaboration with scientists at the Instituto del Mar del Peru (IMARPE) and at the Universidad de Concepcion, Chile. We have submitted a joint proposal planning letter to the Inter America Institute (ISP III) for support of collaborative research titled "Oxygen minimum zone control of benthic processes in the eastern Pacific Ocean." This research will involve cruises in 1998 and 1999 funded by Scripps Institution of Oceanography (the current request), and funding agencies in Peru (IMARPE) and Chile (CONICYT). During the Melville cruises we request that our Peruvian observers be Mr. Sergio Mayor of IMARPE (phone 51-14-429-9811; FAX 41-14-465-6023) and Mr. Dimitri Gutierrez (a Peruvian citizen) presently at the University de Concepcion in Chile; phone: 56 41 234985 x 3153; FAX: 56 41 220104). Both of these scientists are actively collaborating on this research. Ship Time Request
Cruise Plan Christina Massell R/V Melville We will collect a 20km-wide SEA BEAM 2000 swath along 2000km of Peru Chile Trench between 15S and 32S. These happen to be the best latitudes to study tectonic landforms, because this part of the trench is sediment-starved, so its structures are not obscured by mud. Existing data include a SeaMARC survey of the Nazca Rise intersection at 15S (Hagen and Moberly, 1994), a regional seismic reflection survey (Schweller et al, 1981), and a pair of Melville SEA BEAM 2000 swaths collected in 1994 at Dr. Peter Lonsdale's request along the axis 24-20S and 19-17S. From these observations, we see that the trench between Callao and Valparaiso is a good place to address two specific problems during 3 survey days. "Problem 1:" Effect of a higher outer rise at a trench concavity. The flexural outer rise is exaggerated alongside concavities in the trench plan. The Arica Bight is a major concavity in the plan of the Peru-Chile Trench, and has a higher-than-usual outer rise. We will spend 2 days mapping the entire 80km-wide landward slope of this outer rise (i.e. the seaward slope of the trench around the Arica Bight) to see how the higher rise affects the intensity of faulting and tilting on the seaward slope, and to see how the changing direction of the axis of flexure affects the style of faulting (eg. reactivation of old abyssal hill faults vs. creation of new extensional fractures)."Problem 2:" Compressional faulting on the lower part of the outer trench slope. The best understood process on the outer slopes of trenches is extensional normal faulting, but along several trenches, the Peru-Chile Trench in particular, there is evidence from earthquakes and seismic reflection profiles that compressional thrust faulting takes over as the oceanic crust approaches the trench axis. Presumably some of the compressional inter-plate stress is transmitted from the subduction zone into the exposed part of the oceanic plate. The 1994 Melville data show what appears (from their plan pattern and asymmetric profile) to be excellent examples of lower slope thrusts in the deepest part of the trench at 22S - 24S. To confirm this interpretation and study how these thrusts develop I need additional swath coverage from higher up the slope. A total of 3 new bathymetry and side-scan swaths will be collected between these latitudes, allowing coverage of the entire actively faulting part of the trench slope.
Leg 4 Jill Karsten University of Hawaii Emily Klein Duke University Valparaiso - Easter Island 15 January - 02 March 1998
1998 Karsten/Klein Northern Chile Ridge/Valdivia Fracture Zone Program R/V Melville Cruise Goals: This cruise represents two field programs with distinct goals that have been combined into a single expedition: Northern Chile Ridge Study (Karsten/Martinez). This part of the program will map and sample the northern Chile Ridge, between the Chile F.Z. (~36¡S) and the western end of the Valdivia F.Z. (~41¡S). The primary objective of this study is to document the thermal effects of large, long-lived transform offsets on the tectonic and magmatic processes operating at a "transform dominated", intermediate rate spreading center. Theoretical models of ridge axis thermal structure near transform offsets, where the ridge axis is juxtaposed against older, colder lithosphere, predict that systematic relationships should be observed between transform offset age and parameters such as axial depth, crustal thickness, and lava composition. Previous examination of these predictions, using global comparisons of a few well-characterized ridge-transform intersections, have demonstrated a qualitative relationship between axial depth and offset age. Variations in crustal thickness and magma composition associated with transform fault effects have been less systematic and more ambiguous. Part of the problem with these earlier studies is that it has been difficult to separate out the effects of transform faults from the influence of other tectonic variables (e.g., spreading rate, regional depth anomaly, mantle temperature gradients) changing in the system. We propose to re-examine the predicted relationship between axial depth and morphology and transform offset age by mapping ~550 km of the northern Chile Ridge, where the only tectonic variable changing is the segment length-transform offset geometry. In addition, we propose to extend the inquiry by obtaining shipboard gravity and magnetics data and dredged rock samples, which will allow us to investigate variations in axial depth, inferred crustal thickness and structure, tectonic fabric and magma chemistry as a function of offset age and ridge-transform geometry. The results of this study will ultimately contribute to the refinement of theoretical models relating axial morphology and crustal accretion variables, as well as contribute to on-going characterization of extensive unmapped regions of the mid-ocean ridge system. We will conduct a SEA BEAM 2000 bathymetry/side-scan, gravity and magnetics survey of the ridge axis out to the Brunhes-Matuyama boundary, followed by rock dredging/wax coring with 5-10 km spacing along axis. Sample spacing will be densest within 30 km of ridge-transform intersections, where the greatest thermal effect is expected. The northern Chile Ridge is an ideal site for investigating relationships between ridge axis structure and thermal effects of large transform offsets for the following reasons: 1) There are at least six first-order ridge segments in this poorly mapped region, bounded by long-lived transform offsets with ages ranging between ~2 Ma and ~6 Ma (plus one ~15 Ma offset). First-order ridge segment lengths vary between ~35 and ~150 km, providing an opportunity to investigate whether ridge axis behavior varies systematically as a function of offset/length ratio. 2) All other parameters which might affect the ridge axis thermal structure (e.g., variable spreading rate, regional thermal anomalies or gradients associated with mantle hot/cold spots) do not change over the study area, thereby allowing a very controlled investigation of the transform fault effect to be undertaken. 3) Theoretical models indicate that ridge morphology at intermediate spreading rate ridges, such as the Chile Ridge, is very sensitive to small changes in ridge axis thermal structure, so there is a high probability of observable changes. 4) Complications of mantle outcrops found at slow spreading ridges or "over-shooting" intrusions in the transform domain found at faster spreading ridges should be minimized at intermediate spreading rates. 5) The moderate latitudes (i.e., calmer seas) of the proposed study area will allow us to make the high quality shipboard gravity measurements necessary to resolve small gradients along short ridge segments. Valdivia Fracture Zone Study (Klein/Karsten). This study will map and sample the small, deep, stable, intra-transform spreading centers of the Valdivia Fracture Zone (VFZ). This proposed work is an outgrowth of our work on the Southern Chile Ridge near its intersection with the Chile Trench, south of the target. Our previous results showed that the southern Chile Ridge is erupting an unusually diverse and in many respects geochemically unique suite of lavas. One type of enrichment displays geochemical characteristics that are unlike MORB sampled previously, extending toward compositions more commonly associated with arc or back-arc lavas. It is tantalizing to consider that there is a relationship between this highly unusual lava chemistry and the peculiar tectonic setting of ridge subduction; that is, that the contaminant for this endmember may derive from the adjacent subduction zone. While previous studies have identified a recycled component in the sub-oceanic mantle, such contaminants are presumed to represent ancient subduction and deep recycling. In contrast, the Chile Ridge may represent an example of more recent and shallow contamination from the adjacent subduction zone. Thus, one of our goals is to determine whether the unique geochemical signature that we observed along two of the four ridge segments of the southern Chile Ridge is a spatially extensive phenomenon that persists to the central Chile Ridge or whether it occurs in close proximity to the site of ridge subduction. To explore this, we will focus on the short (~25 km), stable intra-transform spreading centers of the VFZ system because this setting is most likely to erupt a diversity of magma compositions representative of the diversity of mantle compositions. A second goal of our project is to determine the spatial extent of the Indian Ocean/Dupal isotopic signature we identified at several sites on the northern end of the Southern Chile Ridge. The Dupal anomaly has been described as a globe-encircling belt of anomalous ocean island and ocean ridge basalt compositions, centered at ~30-40¡S. It has long been recognized, however, that available data left a huge gap in that belt in the eastern Pacific, occupying several thousand kilometers between Dupal highs. Thus, the central Chile Ridge data will provide a valuable gap-closing data set. A third goal of this program is to extend the depth range of previously sampled MORB from the Pacific. Previous studies have shown marked distinctions in major element compositions between Atlantic and Pacific MORB; due to the limited depth range of most Pacific ridges, it is not known if this difference is independent of extents and pressures of melting, reflecting fundamental difference in major element source composition. Our sampling program will extend the Pacific ridge depth range to ~5000 m.
Ship Time Request Cruise Track
Leg 5 Richard Hey University of Hawaii Easter Island - Papeete 05 March - 12 April 1998
There are three general objectives of this proposed work. First, to understand the structural controls of hydrothermal venting at superfast spreading rates. Do boundaries of morphotectonic/structural 4th order segments correspond to the boundaries of hydrothermal activity on superfast- spreading ridge segments as proposed for the fast-spreading northern EPR and intermediate-spreading Juan de Fuca ridge? Does the degree of hydrothermal activity along individual tectonic segments of ridge crest correspond more closely to high-frequency variations in the rate of magma supply (e.g., cross-sectional inflation, axial depth) than to low-frequency variations (e.g., spreading rate)? Large-scale surveys of hydrothermal activity on intermediate- to superfast-spreading ridges indicate that the relative spatial frequency of hydrothermal plumes increases linearly with spreading rate. This correlation implies that variations in hydrothermal activity are a function of large-scale, and thus low-frequency, variations in the magma supply rate. However, plotting plume incidence against either axial depth or cross-sectional area also yields linear correlations. This is because in the three areas in the Pacific surveyed to date, the mean values of axial depth, inflation, and spreading rate are nearly perfectly correlated. To identify which parameter is dominant we need a large survey area with morphological trends much different than the previously surveyed areas. Our proposed study area offers an ideal laboratory for examining the effect of these three parameters on the distribution and composition of hydrothermal discharge. Is the degree of hydrothermal activity greater along a plate boundary undergoing rapid reorganization than along segments of similar morphology and spreading rate along a stable boundary as proposed based on DSDP results near 19'S? Our proposed study area is unique because of the large-scale reorganization of spreading center geometry presently occurring by dueling rift propagation that may be evolving toward microplate tectonics, and thus offers a unique opportunity to evaluate the effect of such structures on the development of hydrothermal circulation. Second, to understand the temporal controls of hydrothermal venting. Do high ratios of volatiles/heat and volatiles/metals in hydrothermal fluids and in the overlying water-column plumes indicate that the ridgecrest volcanic/hydrothermal system has been recently perturbed by input of magma, as proposed for the Juan de Fuca ridge and northern EPR? Third, to understand the relative importance of hydrothermal venting and deep ocean currents in forming far-field plumes. Is the absence of a far-field helium plume to the west of the EPR at ~30'S due to the pattern of deep ocean currents which carry the hydrothermal effluent eastward at this latitude, or to the absence of hydrothermal sources on the EPR axis south of the Easter Microplate? In order to test these hypotheses we propose an integrated geophysical/hydrothermal survey. We first propose to collect high-resolution deep-towed sidescan and bathymetry using the WHOI DSL-120 system to map the detailed patterns of faults, fissures, and recent volcanic eruptive sites. CTD/nephelometers mounted on the vehicle and wire will provide precise plume distributions in conjunction with the deep-tow geophysical measurements. We then propose continuous mapping of hydrothermal anomalies using the PMEL SUAVE system in the tow-yo technique, continual raisings and lowerings of the instrumentation through the plume interval while the ship slowly steams ahead, to determine two-dimensional anomalies of temperature, particle concentration (light scattering/attenuation), and the dissolved fraction of certain chemical species (e.g., Fe and Mn). Tow-yo surveys are powerful tools for both thorough reconnaissance mapping and high-resolution discharge location. Comparison of plume surveys with vent location by camera or submersible has shown close agreement. We then propose to collect discrete samples from tows and vertical casts to determine the first-order composition of the discharging hydrothermal fluids. The combination of high-resolution bathymetric, acoustic, and hydrothermal plume data we plan to acquire will allow us to make quantitative measurements of the distribution and composition of hydrothermal venting and its relation to specific geologic characteristics of the ridge at three spatial scales of progressively increasing size. This unique data set will be used to test a series of hypotheses that address fundamental questions about the relation of hydrothermal processes to the morphotectonic/structural environment in which they exist. This proposed work will result in significant advances in understanding the pattern of hydrothermal venting at the fastest present-day spreading rates.Ship Time Request-Front Ship Time Request-Back
Leg 6 Jeffery Gee University of California, San Diego Papeete - Honolulu 17 April - 06 June 1998
Leg 7 Ralph Stephen Woods Hole Oceanographic Institution Honolulu - Honolulu 10 June -19 June 1998
Prospectus for the Ocean Seismic Network Pilot Experiment on R/V Melville (June '98) The primary goal of the proposed research is to learn how to make high quality broadband seismic measurements on the deep ocean floor. We plan to deploy three (0.001-10Hz) seismic sensors: one in an ODP borehole drilled into oceanic basalt, one buried surficially in sediments beneath the seafloor and one resting on the seafloor. These will be emplaced in January-February 1998 from the R/V Thompson. All three will record continuously for three months. The specific goal of this cruise on Melville is to recover the two Ocean Bottom Seismometers, the borehole seismometers and their associated equipment from the seafloor. In addition, pore water sampling measurements will be made in the borehole after the equipment is removed. The development of this capability to record broadband data on the ocean floor will open substantial new opportunities in the study of the dynamics and structure of the EarthÕs interior. The emplacement of a small number of permanent ocean floor observatories (about 20) is necessary to complete the coverage of our planet in oceanic regions where suitably located islands do not exist. These observatories would provide unique data that would significantly advance studies of , for example, the nature of the core-mantle boundary, the scales of mantle heteorgeneity, anisotropy of the inner core, and the source mechanisms of events on the edges of continents. Similarly the development of portable broadband ocean bottom seismometers (B-BOBS) would permit the study of a wide range of regional problems, ranging from the detection of hotspot plumes in the mid-mantle and the depth of anomalies beneath mid-ocean ridges, to detailed studies of the nature of upper mantle anisotropy. The four major instrument systems that will be used to carry out the data acquisition required for this Pilot Experiment effort have been designed and built over the past 2-4 years largely with NSF funds. The Broadband Borehole Seismometer System (B3S2) is the downhole seismometer (teledyne Geotech 54000 sensor) with the control electronics and recording system (SEABASS-II). This will be emplaced downhole using the wireline reentry control vehicle (CV) that is fitted with the necessary thrusters and video systems to permit precise placement of instrument systems either on the ocean floor or down an ODP drill hole that is fitted with a reentry cone. The seafloor measurements will be made with one of two broad-band ocean bottom seismometers (B-BOBS) that are equipped with Guralp CMG3T sensors. A second, identical B-BOBS will have its sensor package buried surficially beneath the sediments of the seafloor using the sensor burial system (SBS) that will be powered and emplaced using the control vehicle. If progress is to be made towards the routine recording of broadband data on the ocean floor, then we must understand the trade-off between the cost of installing sensors below the seafloor (either within the sediments or in basaltic basement) and improved data quality that may result from lower noise levels and/or improved coupling to true ground motion. The data collected during this Pilot Experiment will be made available to the community via the IRIS Data Management Center and will allow us to address this issue in This is a complex technological undertaking. Although the primary instruments exist substantial work remains related to the integration of the systems. This is a cooperative project between the Woods Hole Oceanographic Institution and Scripps Institution of Oceanography.
Ship Time Request
