Site U1372 | Site U1373 | Site U1374 | Site U1375 | Site U1377
IODP Expedition 330:
Louisville Seamount Trail
Site U1376 Summary
PDF file is available for download.
Background and Objectives
Site U1376 (Prospectus
Alternative Site LOUI-7A) on Burton Guyot was the fifth site drilled during
Integrated Ocean Drilling Program (IODP) Expedition 330. This site and seamount
have an estimated age of ~63-65 Ma, slightly older than Site U1375 on Achernar
Guyot. Similar to Site U1375, new age data from Burton Guyot will fill in an
important gap in the age vs.
distance relationship of the Louisville Seamount Trail, providing key
information in the reconstruction of past plate motions and the motion of the
Louisville hotspot. This seamount is one of the smallest volcanoes in the
Louisville Seamount Trail, with both Burton Guyot and Achernar Guyot having a
base diameter smaller than 30 km. Site U1376 was targeted in the middle of this
small edifice, away from its shelf edges and away from any packages of dipping
volcaniclastics on its flanks, the latter sequences which were targeted at
Sites U1372, U1373 and U1374. Sidescan sonar reflectivity survey and 3.5 kHz
sub-bottom profiling data indicated that Site U1375 is covered with less than
10 m of pelagic sediment and seismic reflection profiles indicate that this
central part of Burton Guyot is typified by a less than 110 m thick sequence of
volcaniclastics overlaying igneous basement.
The original drilling plan was
to recover the soft sediment using a gravity-push approach with little or no
rotation using a Rotary Core Barrel (RCB), followed by standard coring into the
volcaniclastic materials and down to 350 m into igneous basement. A short
downhole logging series was planned including the standard Triple Combo and
FMS-Sonic tool strings, and the third-party Göttingen Borehole Magnetometer
(GBM) tool. Drilling and logging were successfully accomplished after drilling
to 183 mbsf and carrying out the planned logging program. Coring was
particularly successful with an average recovery of 75.6% in igneous basement.
Drilling during ODP Leg 197 provided the first compelling evidence for the motion of mantle plumes by documenting a large ~15° shift in
paleolatitude for the Hawaiian hotspot (Tarduno et al., 2003; Duncan et al.,
2006). This lead to two geodynamical end-member models that are being tested
during Expedition 330, namely that the Louisville and Hawaiian hotspots moved
coherently over geological time (Wessel and Kroenke 1997; Courtillot et al.
2003) or, quite the opposite, that these hotspots show considerable inter-hotspot
motions, as predicted by mantle flow models (Steinberger, 2002; Steinberger et
al., 2004; Koppers et al., 2004; Steinberger and Antretter, 2006; Steinberger
and Calderwood, 2006). The most important objective of Expedition 330 therefore
was to core deep into the igneous basement of four Louisville seamounts in
order to sample a large number of in situ
lava flows ranging in age between 80 and 50 Ma. With a sufficiently large
number of these independent cooling units high-quality estimates of their paleolatitude
can be determined, and any recorded paleolatitude shift (or lack thereof) can
be compared with seamounts in the Hawaiian-Emperor seamount trail. For this
reason Expedition 330 mimicked the drilling strategy of ODP Leg 197 by drilling
Louisville guyots equivalent in age to Detroit (76-81 Ma), Suiko (61 Ma),
Nintoku (56 Ma) and Koko (49 Ma) in the Emperor seamounts, with Achernar Guyot
being equivalent to Suiko Seamount. Accurate paleomagnetic inclination data are
required for the drilled seamounts in order to establish a record of the past
motion of the Louisville hotspot, and together with high-resolution 40Ar/39Ar
age dating of the cored lava flows, these data will help us to constrain the
paleolatitudes of the Louisville hotspot between 80 and 50 Ma.
Expedition 330 also aimed to provide important insights into
the magmatic evolution and melting processes that produced and constructed
Louisville volcanoes while progressing from their shield to post-shield, and
maybe post-erosional, volcanic stages. Existing data from dredged lavas suggest
that the mantle source of the Louisville hotspot has been remarkably
homogeneous for as much as 80 m.y. (Cheng et al., 1987; Hawkins et al., 1987;
Vanderkluysen et al., 2011). In addition, all dredged basalts are predominantly
alkalic and possibly represent a mostly alkalic shield-building stage, which is
in contrast to the tholeiitic shield-building stage of volcanoes in the
Hawaiian-Emperor seamount trail (Hawkins et al., 1987; Vanderkluysen et al.,
2011). Therefore, the successions of lava flows cored during Expedition 330
will help us to characterize the Louisville seamount trail as the product of a primary hotspot and to test the long-lived homogeneous
geochemical character of its mantle source. Analyses of melt inclusions,
volcanic glass samples, primitive basalts, high-Mg olivines and clinopyroxene
phenocrysts will provide further constraints on the asserted homogeneity of the
Louisville plume source, its compositional evolution between 80 and 50 Ma, potential
mantle plume temperatures, and its magma genesis, volatile outgassing and
differentiation. Finally, basalts and sediments cored at Site U1376 were
planned to be used for a range of secondary objectives such as searching for
active microbial life in the old seamount basements and to find fossil traces
of these microbes left behind in volcanic glasses and biofilms on the rocks.
The vessel arrived at Site U1376
(Prospectus Alternate Site LOUI-7A) on Burton Guyot at 2300 hr on 26 January.
Prior to spudding, the vibration-isolated television (VIT) was launched to
observe the character of the seafloor and the tagging of the bit on the bottom.
A rocky seabed devoid of any appreciable sediment was observed. After a 2.3
hour survey, a spot with a very small sediment pond was found, but it was clear
that this would be essentially a hard rock entry, which would not support a
potential free fall funnel (FFF) installation.
The driller tagged the seafloor at
1514.3 mbrf (1503.3 mbsl) and spudded Hole U1376A with the rotary core barrel
(RCB) assembly at 0705 hr on 27 January. Coring was suspended on 30 January at
a depth of 86.8 mbsf to change the bit, which had accumulated 72.4 rotating
hours. Because of the absence of sediment cover needed to support an FFF
installation, a marker comprised of a single glass float was remotely released
from the VIT frame via an acoustic release. The bit cleared the seafloor at
1800 hr on 30 January. A new RCB bit was made up to the bottom hole assembly
(BHA) and deployed. The open hole was successfully reentered at 0435 hr on 31
January. Coring continued without incident until the allocated coring time for
this site expired at 1630 hr on 2 February leaving the hole at a final depth of
182.8 mbsf. The total average recovery for the hole was 74.5% with an excellent
average recovery in basement of 75.6%. The average rate of penetration in
basement was 1.8 m/hour.
Following a wiper trip, which included
displacing the borehole with 42 barrels of heavy (10.5 ppg) mud, the bit was
released at the bottom of the hole. The end of pipe was positioned at the
logging depth of 80.4 mbsf by 2115 hr on 2 February. The Triple Combo (TC) tool
string was deployed first. The tool was run into the hole at 2140 hr and
reached a target depth of 1696.6 m wireline below rig floor (WRF) at 0139 hr (3
February). The TC made two full passes of the hole, and the tool string run was
completed at 0511 hr (3 February). The second tool string deployed was the Göttingen
Borehole Magnetometer (GBM). The GBM begins its log during the orientation
(sighting) process on the rig floor and continuously collects data until its
return to the rig floor following a down- and up-log portion. The GBM run began
at 0531 hr, however, following a report that the pipe was stuck in the hole,
the logging run was aborted and the tool returned to the surface (0643 hr). The
tool was not totally rigged down and owing to its short length, was placed in one
of the core barrel shucks on the rig floor. Once the pipe was worked free, the
GBM tool was deployed again at 0726 hr. The tool ran perfectly with no
communication or signal errors. It reached its target depths at 183 mbsf at
0956 hr. The tool returned to the surface at 1145 hr, was successfully sighted
and rigged down by 1218 hr. The final tool deployed was the FMS-Sonic. The tool
string was run into the hole at 1338 hr and successfully reached a depth of 182
mbsf. Two full passes were measured with the FMS-Sonic. The tool was rigged
down by 1755 hr, and at this time logging operations concluded. All tool
strings were able to reach their target depth in Hole U1376A and none of the
tools encountered tight spots.
Once the logging was concluded, the
drill string was recovered with the end of the pipe clearing the sea floor at
1850 hr on 3 February. Once the
drill collars were set back in the derrick, the beacon recovered, and the
drilling equipment secured, the vessel departed at 2200 hr for the 391 nmi voyage to the final site U1377 (LOUI-4B). The total time on Hole U1376A was 191 hours or 8.0 days.
Sediment at Site U1376 on Burton Guyot
was restricted to the sedimentary cover only. Two stratigraphic units were
defined on the basis of compositional and textural characteristics of the
sediment at macroscopic and microscopic scales. Stratigraphic Unit I represents
a younger sedimentary cover that extends between the seafloor and 23.45 mbsf.
This cover is mostly composed of monolithic, juvenile volcaniclastic deposits,
which extend between 4.50 and 21.48 mbsf. These deposits are interpreted as a
possible record of a rejuvenated volcanic stage of Burton Guyot in a
hemipelagic or pelagic environment. Other deposits of Subunit IA include
layered volcanic breccias and sandstones, which are interpreted as turbidites
and possible hyperconcentrated flow deposits. Four thin (<3 cm-thick)
ferromanganese crusts occur in the uppermost part of the drilled sequence,
which also yielded a minor amount of nannofossil and foraminifer-bearing chalk.
Stratigraphic Unit II represents an older sedimentary cover of Burton Guyot
that extends between 23.45 and 41.93 mbsf. A 15.15 m-thick interval of limestone
(classified as boundstone-rudstone) occurs in the upper part of Unit II, which
is composed of abundant red algae and minor amounts of other shallow marine
fossils. This interval is interpreted to represent an algal reef that developed
in very shallow marine conditions during subsidence of the drilled seamount.
The base of Unit II between 38.60 and 41.93 mbsf is composed of a basalt
conglomerate with few shallow marine bioclasts. The conglomerate emplaced on
top of an erosional surface that marks the boundary between the sedimentary
cover and underlying volcanic basement of Burton Guyot.
Nannofossils found in the upper
part of stratigraphic Subunit IA indicate a preliminary age of middle to late
Miocene. No age diagnostic microfossils were identified in Subunit IB through
Unit IV, but molluscan fossils may indicate a late Cretaceous age for Subunit
The 140.9 m basement
section cored at Site U1376 on Burton Guyot comprises a succession of basaltic
breccia, pillow lava and massive lava flows. Two Units were defined on the
basis of phenocryst minerals: Unit IV with mostly olivine phenocrysts, overlain
by Unit III with olivine and augite phenocrysts. The bottom 13.1 m of the
succession comprises mostly olivine-phyric basalt breccia, but an interval of
highly vesicular aphyric basalt (166.5-167.2 mbsf) on top of this breccia
heralds the arrival of a second, aphyric magma type. The next 31.7 m of the succession comprise heterolithic
breccia with olivine-phyric and aphyric basalt clasts and thin flows of aphyric
basalt. This interval records a period when two types of magma were being
erupted in the area at the same time. The upper part of this interval
(Lithologic Unit 26) consists of a number of highly vesicular and oxidized
fragments of aphyric and olivine-phyric basalt, and may provide evidence for a
period of shallow water or subaerial volcanism. Two thin flows of aphyric
basalt separated by a 24 cm thick interval of olivine-phyric basalt breccia
(Lithologic Units 22-24) mark the highest occurrence of aphyric basalt in the
recovered eruptive succession (127.57 mbsf). The upper 17.35 m interval of Unit
IV is composed of olivine-phyric hyaloclastite breccia containing a high
proportion of fresh glass. Unit IV ends at an erosion surface that marks the
beginning of Unit III and a change from magma crystallizing olivine alone to a
slightly more evolved one that crystallized olivine and augite. Unit III
includes a 33.11 m thick massive lava flow (Lithologic Unit 15). The presence
of pillow lava high in the Unit III succession suggests that most, if not all,
of the basement section was erupted in a marine environment.
(dikes) cutting Unit IV represent the last magmatic event recorded in the
basement section of Burton Guyot. They were not seen in Unit III but may have
extended through it. There are no aphyric basalt units in Unit III, immediately
above the upper limit of the dikes, and therefore these dikes cannot be linked
directly to any of the recovered volcanic units. It is possible that the dikes
penetrated Unit III and fed lava flows that have since been removed by erosion.
Alternatively, they may have fed aphyric lava flows similar to those in Unit IV
and have been truncated at an erosion surface at the top of this unit. The
presence of what looks like a fragment of a dike at the postulated erosion
surface between Units IV and III supports this hypothesis.
A record of a
post-erosional or rejuvenation phase of magmatism at Site U1376 is provided by
the volcanic sands and breccias of sedimentary Unit I. Clasts in these
sediments imply at least two magma types. Firstly, some of the sand layers
contain fragments of hornblende and biotite, implying the eruption of magma
more evolved than those represented by the basement succession. Secondly, Unit
IC contains olivine-pyroxene aggregates that may be mantle xenoliths. This is
supported by the occurrence of partly resorbed orthopyroxene xenocrysts in
basalt clasts in Unit IC.
The presence of olivine and augite
phenocrysts in the basaltic basement section at Site U1376, and the complete
absence of plagioclase phenocrysts, suggests that the magmas were alkaline and
more basic than those represented by most of the volcanic rocks drilled at
Sites U1372, U1373 and U1374. Reaction coronae around orthopyroxene xenocrysts
in basaltic clasts in sedimentary Unit I suggest that the rejuvenated stage
magmas were strongly alkaline.
The majority of the succession recovered from Hole U1376A has undergone
some degree of secondary alteration by low temperature water-rock interactions
and/or weathering, but large intervals are only slightly altered. The
alteration of the volcanic rocks, consisting of basaltic flows, basaltic
breccias, and hyaloclastite deposits, ranges from slightly to highly altered
(between 2% and 95%). Several basaltic lava flows are relatively well preserved
(10% or less alteration).
Core descriptions and thin section observations show that rocks in Hole
U1376A are defined by a single overall alteration type typical for submarine
environments. From the top of Hole U1376A to the bottom, the sequence displays
a range in alteration, from slightly to highly altered, showing greenish colors
indicating reducing conditions related to a submarine emplacement environment.
Only minor and sporadic intervals in the upper 60 meters of the core show some
Augite is generally well-preserved, as phenocrysts and in the groundmass
throughout the entire igneous portion of the core. Some olivine is completely
altered to iddingsite, hematite, and Fe-oxyhydroxide near the top of the core,
but large portions of the core contain fresh to slightly altered olivine. Some
olivine in the greenish altered rocks is replaced by green clay and carbonates (calcite/magnesite).
Overall, three main groups of alteration phases could be distinguished.
These are dominated by carbonates (Mg-calcite, aragonite, siderite) and clay
minerals (saponite, nontronite). Other secondary phases (iddingsite, Fe
oxyhydroxydes, hematite, goethite) are present and zeolites constitute only a
minor amount of the alteration assemblage. Additionally numerous vesicles and
veins were observed that are mainly filled with carbonates and clay minerals.
Structural features at Site U1376 are dominated by veins (n=1190, with
1489 individual features) and vein networks (n=280, with 1995 individual
veinlets). This site has the highest vein density of all Louisville seamounts
drilled, with a maximum density of 39 veins/meter. Veins are also commonly
wider than previously observed, with numerous veins between 5-10 mm wide, up to
a maximum of 30 mm, indicating higher fluid flow than in previous sites. In
further contrast to previous Louisville sites, veins and vein networks are abundant
in breccias and hyaloclastites in addition to rheologically hard lava units,
with the highest vein density actually occurring in hyaloclastite units at ~62
and 170 mbsf. The veins are dominantly shallowly dipping and often have
sub-vertical fibrous mineral infills, both of which may indicate sub-vertical
tension within this part of the seamount. The few fractures that are unfilled
by veins (n = 55), are present mostly in the rheologically hard lava flows and
intrusive sheets. Geopetal structures (n = 26) are horizontal, indicating that
this part of the seamount has not been tilted since deposition of the geopetal
infill material. Structural measurements were also undertaken for intervals
with sedimentary bedding (n=153) and 7 igneous contacts.
Major and trace element
compositions of thirteen igneous samples from Site U1376 on Burton Guyot show
general similarities to those from Site U1372 on Canopus Guyot and, to a lesser
extent, Sites U1373 and U1374 on Rigil Guyot. However, as a group, the Site
U1376 rocks are less alkalic. Alteration is generally moderate, and on a total
alkalis (Na2O + K2O) vs. SiO2 diagram most of
the Site U1376 samples are classified as alkalic basalts, whereas four are
transitional basalts. Olivine appears to have been the principal control on
magmatic evolution. Seven highly olivine-phyric samples have high MgO (between
11.85 wt% and 16.79 wt%) and Ni contents and are likely to contain excess
olivine crystals. These high-MgO basalts are distinct from other high-MgO rocks
recovered during Expedition 330 in having somewhat lower Al2O3
concentrations. Downhole chemical variations indicate that three different
magma types are represented among the lava samples from Site U1376. These types
are generally consistent with the stratigraphic units defined petrographically.
However, the composition of the topmost lava sample from Unit IV more closely
resembles those of Unit III. One of the two aphyric dikes encountered in Unit
IV is chemically similar to samples of low-MgO olivine-phyric lavas from Unit
IV, but the other dike has a significantly higher Ba/Y ratio then other Site
Physical property characterization
was performed for material recovered from Site U1376. The different data sets
are mutually consistent and show clear contrasts between lithified volcanic
sandstone and conglomerate, carbonates, lava flows, and the pervasive volcanic
hyaloclastites and breccias. In particular, the boundstone of Subunit IIA is
characterized by very low magnetic susceptibility and natural gamma ray
radiation. These carbonate samples have higher p-wave velocity and lower porosity
than would be predicted based on their density, reflecting their different
chemical composition when compared to the other basaltic lithologies. The 33 m
thick lava flow in Unit III is characterized by an increase in magnetic
susceptibility, p-wave velocity, and density.
The natural remanent magnetization
intensity of archive half-core samples from Hole U1376A ranges from 10-4 A/m to ~10 A/m (geometric mean = 0.4 A/m). The
lowest values are associated with the sediments in Subunit IIA and the
hyaloclastite in Unit IV,
and the highest values are from the lava flows, intrusive sheets and basalt
clasts in the volcanic breccia of Units III and IV. Relatively
well-defined principal component directions were obtained for 1580 intervals
from archive half-core measurements (for pieces >9 cm in length). These
directions are generally consistent with stepwise alternating-field and thermal demagnetization results from 99 discrete samples. Both data sets
reveal consistent reversed polarity magnetization throughout the hole.
Downhole logging of
Hole U1376A took place between 2 February (2125 hrs NZDT) and 3 February (1755
hrs NZDT). We deployed three tool strings in Hole U1376A at Burton Guyot. Two
tool strings took measurements of natural gamma ray radioactivity, density,
neutron porosity, elastic wave velocity and collected borehole resistivity
images. The third tool string, containing the third-party Gšttingen Borehole
Magnetometer (GBM), measured the three-component magnetic field in the drilled
seamount formation. Measurement depths were adjusted to match across different
logging runs, obtaining a wireline matched below seafloor (WMSF) depth scale.
The logged depth interval for Hole U1376A was 80.4 – 182.3 m WMSF.
density, compressional velocity and neutron porosity derived from downhole
logging measurements were used to identify a total of thirteen Log Units in
Hole U1376A with three in the section covered by the bottom hole assembly (BHA)
and ten in the volcanic sequences in the open hole interval. These defined Log
Units correlated to changes from massive basalt flows (Stratigraphic Unit III)
to more brecciated units, and interlayered aphyric and olivine-phyric flow
units (Stratigraphic Unit IV).
The GBM was run
once in Hole U1376A and collected good quality magnetic data, which will be
reoriented postexpedition. The GBM data shows that the massive lava flow in
Stratigraphic Unit III is not as homogeneous as it appears in the
palaeomagnetic data obtained from the recovered cores from Hole U1376A.
Additionally, in the unrecovered section of the hole, between ~130 and 140
mbsf, the GBM data shows strong variations. Post-expedition work, which will
split the horizonal component into north and east components, should provide
further insight into these observed variations.
structural features are well imaged with the Formation MicroScanner (FMS), in
particular fractures, clast size, shape and distribution and areas of solid,
massive basalt versus brecciated material. Of particular importance is FMS
coverage over the unrecovered section between ~130 and 140 mbsf because it will
provide valuable information to reconstruct the lithology for this interval of
Eleven whole-round samples (5-13 cm
long) were collected for microbiological analysis. Lithologies of the samples
collected were volcanic sandstone (two), boundstone (two), volcanoclastic
breccia (three) and basaltic lava flows (four). All samples were preserved for shore-based cell counting,
deoxyribonucleic acid (DNA) analyses and δ34S and δ13C
analyses. Five samples were used to inoculate culturing experiments with up to
ten different types of cultivation media. Media targeting sulfur oxidizing
bacteria and general heterotrophic bacteria were the most successful, and
growth was detected in samples as deep as 174 mbsf. Two samples were used to
set up stable isotope addition bioassays to determine rates of carbon and
nitrogen utilization by subsurface microbes at Burton Guyot. One core was
seeded with fluorescent microspheres, from which samples were collected for
shipboard analysis of contamination via fluorescent microsphere counts. No
microspheres were detected on the outside or inside of the whole round sample,
indicating the likelihood for microbial contamination is low.
Cheng, Q., Park,
K.-H., MacDougall, J.D., Zindler, A., Lugmair, G.W., Hawkins, J., Lonsdale, P.,
Staudigel, H. (1987). Isotopic evidence for a hotspot origin of the Louisville
seamount chain. In: B.H. Keating, P. Fryer, R. Batiza, G.W. Boehlert
(Editors), Seamounts, islands and atolls. American Geophysical Union Monograph,
Washington, 43: 283-296.
Courtillot, V., Davaille, A., Besse, J., Stock, J. (2003).
Three distinct types of hotspots in the Earth's mantle. Earth
and Planetary Science Letters, 205: 295-308.
Duncan, R.A., Tarduno, J.A. and Scholl, D.W. (2006). Leg 197 Synthesis:
Southward motion and geochemical variability of the Hawaiian Hotspot. In:
Proceedings of the Ocean Drilling Program, Scientific Results. R.A. Duncan,
J.A. Tarduno, T.A. Davies and D.W. Scholl.
Hawkins, J.W., Lonsdale, P.F., Batiza, R. (1987). Petrologic evolution of the Louisville seamount chain. In: B.H. Keating, P. Fryer, R. Batiza (Editors), Seamounts, islands and atolls. American Geophysical Union Monograph, Washington, 43: 235-254.
Koppers, A.A.P., Duncan, R.A., Steinberger, B. (2004). Implications of a non-linear 40Ar/39Ar age progression along the Louisville seamount trail for models of fixed and moving hotspots. Geochemistry Geophysics Geosystems 5(1). Paper Number 2003GC000671. 22 pp.
Steinberger, B. (2002). Motion of the Easter Island hotspot relative to hotspots on the Pacific plate. Geochem. Geophys.
Geosyst. 3(11): 8503, doi:10.1029/2002GC000334.
Steinberger, B., Sutherland,
R., and O'Connell, R. J. (2004). Mantle flow models constrained by
revised global plate motions successfully predict the Emperor-Hawaii and other
hotspot-related seamount chains. Nature, 430, 167-173,
Steinberger, B. and Antretter, M. (2006). Conduit
diameter and buoyant rising speed of mantle plumes: Implications for the motion
of hotspots and shape of plume conduits. Geochemistry Geophysics Geosystems
7, Q11018, doi:10.1029/2006GC001409.
Steinberger, B. and Calderwood, A. (2006). Models
of large-scale viscous flow in the Earth's mantle with constraints from mineral
physics and surface observations. Geophysical Journal International, 167, 1461-1481, doi:10.1111/j.1365-246X.2006.03131.x.
Tarduno, J.A., Duncan, R.A., Scholl, D.W., Cottrell, R.D., Steinberger,
B., Thordarson, T., Kerr, B.C., Neal, C.R., Frey. F.A., Torii, M., Carvallo, C.
(2003). The Emperor Seamounts: Southward motion of the Hawaiian hotspot plume
in Earth's mantle, Science, 301, 1,064-1,069.
Vanderkluysen, L., Mahoney, J.J., Koppers, A.A.P. and Lonsdale, P. (2011).
Geochemical Evolution of the Louisville Seamount Chain. In Preparation.
Kroenke, L.W. (1997). A geometric technique for relocating hotspots and
refining absolute plate motions. Nature, 387: 365-369.