Site U1372 | Site U1373 | Site U1374 | Site U1375 | Site U1376
IODP Expedition 330:
Louisville Seamount Trail
Site U1377 Summary
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Background and Objectives
Site U1377 (Prospectus Primary Site LOUI-4B) on Hadar
Guyot (168.6°W Guyot) was the sixth and last site completed during Integrated Ocean Drilling Program (IODP) Expedition 330. This is also the youngest seamount targeted during Expedition 330 with a measured 40Ar/39Ar
age of 50.1 Ma similar to Koko Seamount in the Hawaiian-Emperor Seamount Trail.
Hadar Guyot belongs to a cluster of three seamounts that is located in close
proximity to the Wishbone Scarp fault zone. Hadar Guyot is the smallest
seamount cored during Expedition 330, consisting of a single volcanic center
with a base diameter of ~25 km, and like all Louisville seamounts drilled, it
has a flat summit plane, defining it as a guyot that at some point must have
emerged above sea level as a volcanic island. Site U1377 was placed near the
middle of this small edifice, away from its shelf edges and away from any
packages of dipping volcaniclastics on its flanks. Sidescan sonar reflectivity
survey and 3.5 kHz sub-bottom profiling data indicate that Site U1377 is
covered with less than 8 m of pelagic sediment, and seismic reflection profiles
show that this site is characterized by a 52 m thick section of dipping
volcaniclastics and 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
material and 350 m into igneous basement. A full downhole logging series was
planned including the standard Triple Combo and FMS-Sonic tool strings, the
Ultrasonic Borehole Imaging (UBI) tool, and the third-party Göttingen Borehole
Magnetometer (GBM) tool. Similar to drilling at Site U1375 on Achernar Guyot,
drilling at Site U1377 became difficult after instabilities were met in the
uppermost part of the seamount formation, likely due to the presence of loose
clast-rich volcanic breccias, which were only rarely recovered due to the low
16% and 39% recovery in Holes U1377A and U1377B. Drilling reached 53.3 mbsf in
Hole U1377A and 37 mbsf in Hole U1377B, but due to time constraints no logging
was carried out.
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.
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).
However, since Site U1377 is located in close proximity to the Wishbone Scarp,
it was speculated whether the recovered rocks would have a slightly different
geochemical composition as a result of a possible step in lithosphere thickness
across this scarp (Beier et al., 2011). 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. In addition, incremental heating 40Ar/39Ar
age dating will allow us to establish age histories within each drill core
delineating any transitions from the shield-building phase to the post-shield
capping and post-erosional stages.
basalts and sediments cored at Site U1377 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. We also planned to determine 3He/4He
and 186Os/187Os signatures of the Louisville mantle plume
to evaluate its potential deep mantle origin, to use oxygen and strontium
isotope measurements on carbonates and zeolites to assess the magnitude of
carbonate vein formation in aging seamounts and its role as a global CO2
sink, to age date celadonite alteration minerals for estimating the total
duration of low-temperature alteration following seamount emplacement, and to
determine the hydrogeological and seismological character of the seamount
The vessel arrived on Site U1377 (Prospectus
Site LOUI-4B) at 0930 hr on 5 February. A 3-stand rotary core barrel (RCB)
drilling assembly was made up and seafloor was tagged at a depth of 1262.0 mbrf
(2050.8 mbsl). The vibration-isolated television (VIT) showed a seabed that
appeared to be mostly covered by a fine layer of sediment with a few rocks
scattered about and didnÕt generate any anxiety regarding the spudding of the
hole. Hole U1377A was spudded at 1510 hr. Rotary coring advanced with
increasingly difficult hole conditions and overall poor recovery. Finally after
coring to a depth of 53.3 mbsf, the hole became too unstable and had to be
abandoned. The bit cleared the seafloor at 1815 hr on 6 February and was picked
up to 1103 mbrf. The average recovery for Hole U1377A was 16.4%. The time
expended at Hole U1377A was 12.5 hours.
It was decided to offset the vessel
500 m south of Hole U1377A and attempt to spud another hole at this site. After
a 30 minute vessel offset with the bit 159 m above the seafloor, the vessel was
on position. The VIT was deployed and a seafloor covered with soft sediment was
observed. The driller tagged seafloor at 1262.0 mbsl. Hole U1377B was spudded
with the RCB at 2325 hr on 6 February. Rotary coring advanced the hole to a
final depth of 37.0 mbsf with an average recovery of 14.5% when time on site
expired. After the drill string was recovered, and the beacon retrieved, the
vessel departed Site U1377 for Auckland at 0730 hr on 8 February. The time on
Hole U1377B was 57.5 hours and the total time on site was 70.0 hours (2.9
days). Because of concerns of moderate headwinds and rough seas on the transit
to Auckland, the vessel departed the location approximately 18 hours earlier
than originally planned.
Although the characterization of the
stratigraphy at Site U1377 has been limited by a very poor recovery,
observations define a consistent sedimentary pattern on top of Hadar Guyot. Two
units were recognized based on macroscopic and microscopic observations of the
sediment. Unit I represents the uppermost sediment of Hadar Guyot and was
recovered at Holes U1377A and U1377B. The sediment is composed of nannofossil
foraminiferal ooze, which strongly resembles the soft sediment recovered in the
uppermost part of Sites U1372 on Canopus Guyot, U1374 on Rigil Guyot, and U1375
on Achernar Guyot, and is considered to reflect recent pelagic sedimentation on
top of the drilled seamount. Unit II corresponds to few cuttings recovered in
Section U1377A-3R-CC, and ten small-sized (<20 cm-thick) pieces recovered by
drilling of in situ sediment (Holes
U1377A and U1377A B) and out of sequence material due to partial collapse of
Hole U1377B during drilling of Core U1377-3R. Unit II includes (1) a
middle-late Eocene foraminiferal limestone with abundant planktonic
foraminifers, a few ferromanganese encrustations, and rare shallow-marine
bioclasts (e.g., echinoderm fragments); and (2) a latest Paleocene-early Eocene
(see below), heterolithic multicolor basalt conglomerate with a few
ferromanganese encrustations. The matrix of the conglomerate is composed of
foraminiferal limestone with abundant plantkonic foraminifers and a few shallow
marine fossils (e.g., echinoderm fragments, larger foraminifera, shell
fragments, and gastropod). Faunal assemblages and sedimentary textures indicate
that Unit II at Site U1377 represents a (or several) condensed section(s)
likely to have deposited in a shallow marine to hemipelagic-pelagic environment
on top of Hadar Guyot.
The foraminiferal ooze of Unit I from Holes U1377A and U1377B
contained mixed assemblages of calcareous microfossils that displayed a range from Pliocene to Holocene,
though Pleistocene to Holocene species are the dominant component. Planktonic foraminifers observed in thin
sections, prepared from the limestone of Unit II from Holes U1377A and U1377B,
indicate a preliminary age of middle-late Eocene and late Paleocene-early
Eocene, respectively. This discrepancy may indicate the presence of diachronous
limestones in Holes U1377A and U1377B. On the basis of these preliminary age
estimates, an unconformity representing approximately 30 million years exists
penetrated a total of 38.2 m of igneous rocks after entering the igneous
basement at 15.1 mbsf. Hole U1377B penetrated a total of 27.9 m of igneous
rocks after entering the igneous basement at 9.1 mbsf. The igneous sequences
have been divided into six lithologic units in Hole U1377A and 18 in Hole
U1377B. The similarity of the rocks throughout both sequences led to the
definition of one stratigraphic unit in each hole (Unit III in both cases). The
lithology in the two holes is broadly similar, consisting largely of aphyric
trachybasalt with occasional olivine-rich bands, and in Hole U1377B intervals
containing plagioclase-augite glomerocrysts. Throughout Hole U1377A and in the
upper part of Hole U1377B the trachybasalt units exhibit intervals of
pronounced flow banding, suggesting that these parts of the successions formed
as massive lava flows or smaller lobate flows. There is no evidence in these
flows that allows us to determine whether they erupted in a submarine or
subaerial environment. The lower part of the succession in Hole U1377B,
however, consists of much smaller (7 cm to 2.08 m) individual cooling units
with well-preserved, curved glassy margins,
diagnostic of small lobate flows or pillows, and emplacement in a submarine
environment. A curious feature of these margins is that, in several instances,
the volcanic glass between adjacent pillows is seen to connect with the more
massive interior of the unit below. It appears that lava in the still molten
interior of a pillow has broken out as a protrusion that filled the space between
overlying pillows. Alternatively, magma may have been injected into a stack of
pillows, but the similarity in appearance between injected and pillow
trachybasalt suggests that, in either case, both were part of the same eruptive
event. The presence of glassy pillow margins that are distinct from the glass
in the protrusions shows that the pillows must already have had glassy crusts
when lava from below protruded into the space between them. In one case,
fragments of the pillows are incorporated into the protrusion.
Time constraints limited the shipboard
petrographic and geochemical investigation of the lithologic units at Site
U1377 and so we have to infer the rock composition from visual inspection of
the core. However, it seems likely that the magma represented by the rocks
recovered at this site was generally alkalic and intermediate in composition.
If post-cruise petrographic and analytical studies confirm this, then the rocks
recovered at Site U1377 will have the most evolved composition of all rocks
drilled during Expedition 330.
The rocks recovered from Holes U1377A and U1377B have undergone
secondary alteration by low temperature water-rock interactions and/or
weathering. The overall alteration of the volcanic rocks from Hole U1377A
ranges from slight to high (between 10% to 75%), whereas the rocks from Hole U1377B vary from moderately to
completely altered (between 30% to 100%). Brown to reddish brown alteration
indicates the prevalence of oxidizing conditions at both sites. Olivine is
typically completely altered to white clay minerals in rocks in Hole U1377A,
and iddingsite, and Fe-oxyhydroxides in Hole U1377B. Plagioclase generally is
well preserved, as phenocrysts and in the groundmass, in several lithologic
units in Hole U1377B. A few sparse bands of relatively fresh glass are also
present in margins of pillows or lava lobes toward the bottom of Hole U1377B. Alteration
phases for both holes are primarily carbonates (Mg-calcite, siderite, ankerite), white clay minerals, and Fe-oxyhydroxide (e.g., goethite). Fe-oxyhydroxide is particularly abundant in veins in the rocks from both holes.
Structural features at Site U1377 are dominated by veins, vein networks,
and vesicle bands. The highest vein density in Hole U1377A is at 15.1-16.6 mbsf
(Lithological Unit 1), with 34 veins/meter, while most of the recovered
intervals have between 5-25 veins/meter. In Hole U1377B the maximum vein
density is 26 veins/meter, which occurs from 20-21 mbsf (Lithological Unit 2),
while other recovered intervals typically have between 10-24 veins/meter. The
veins in both holes have moderate to steep dips. A single horizontal geopetal
structure at 0.85 mbsf in U1377B is evidence that this part of Hadar Guyot has
not been tilted since deposition of the geopetal infilling material. Vesicle
bands and chilled contacts in Hole U1377B are moderate to steep, with dips
ranging from 45 to 90¼. Vesicle bands (but not chilled contacts) were recovered
in Hole U1377A, with either moderate or sub-horizontal dips.
Major and trace element concentrations were
measured for one altered (3.0 wt% loss on ignition) igneous sample from Unit
III of Hole U1377A. It is the most siliceous rock analyzed during Expedition
330, with 55.00 wt% SiO2.
It also has the highest Al2O3, lowest Fe2O3T
(total iron as Fe2O3), and second-lowest MgO and CaO
concentrations. In a total alkalis (Na2O + K2O)
vs. SiO2 diagram, data for the sample fall in the field of basaltic
trachyandesite, very near the dividing line between alkalic and tholeiitic
compositions. However, alteration may have modified the rockÕs K2O,
and perhaps Na2O, concentration. Concentrations of incompatible
elements less susceptible to alteration are near the high end of values
measured for other Expedition 330 rocks, suggesting the sample represents a
highly differentiated transitional to alkalic magma that could have evolved
from a composition rather similar to those of many of the Expedition 330
basalts. However, other characteristics of the sample complicate any simple
explanation of its origin. In particular, concentrations of the compatible
trace elements Cr, Ni, and Co are anomalously high (686, 421, 122 ppm,
respectively). The unusual combination of characteristics suggests the sample
may represent an evolved magma that was contaminated by a small amount of
olivine-rich material from a mush zone or ultramafic wall rock during ascent.
Characterization of physical
properties was conducted for material recovered at Site U1377. The data sets
are mutually consistent and fall within the ranges expected based on the
identified lithologies. Several distinct intervals of high magnetic
susceptibility in excess of 2.5 x 10-2 SI are observed within the
aphyric trachybasalt. In addition, the level of natural gamma ray radiation is
higher in both Holes U1377A and U1377B than has been observed at earlier sites
on Expedition 330; this is likely due to a combination of the increased
alteration and more evolved magma composition at this site. This increased
alteration is also seen in the strongly red and yellow color reflectance
spectrum seen in Hole U1377B. Density and p-wave velocity are consistently
lower than has been observed in lavas at earlier sites, possibly reflecting the
more evolved composition.
The natural remanent magnetization intensity of archive half-core samples from Site U1377 is typically less than 1 A/m,
notably lower than for other guyots sampled during Expedition 330. This lower
value presumably reflects the higher degree of alteration observed. Holes U1377A and U1377B had only shallow penetration
and, particularly for Hole U1377A, poor core recovery. Nonetheless, samples
from both holes appear to have moderate to steep positive inclinations,
indicating southern hemisphere reversed polarity. Shipboard sampling at these
holes was limited because of the short time remaining for shipboard analysis
during the expedition.
Two whole-round samples (8-11 cm
long) were collected for microbiological analysis, a moderately olivine-phyric
trachybasalt from Hole U1377A and an aphyric trachybasalt from Hole U1377B.
Both samples were preserved for shore-based cell counting, deoxyribonucleic
acid (DNA) analyses and δ34S and δ13C analyses.
The sample from Hole U1377A was used to inoculate culturing experiments with
nine different types of cultivation media targeting sulfur and iron cycling
microbes and general heterotrophic bacteria. Both samples were used to set up
stable isotope addition bioassays to determine rates of carbon and nitrogen
utilization by subsurface microbes at Hadar Guyot.
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