Whole rock analytical techniques and glas analytical techniques of silicic magmas from the South East Rift, Manus Basin

There has been much recent interest in the origin of silicic magmas at spreading centres away from any possible influence of continental crust. Here we present major and trace element data for 29 glasses (and 55 whole-rocks) sampled from a 40 km segment of the South East Rift in the Manus Basin that span the full compositional continuum from basalt to rhyolite (50-75 wt % SiO2). The glass data are accompanied by Sr-Nd-Pb, O and U-Th-Ra isotope data for selected samples. These overlap the ranges for published data from this part of the Manus Basin. Limited increases in Cl/K ratios with increasing SiO2, La-SiO2 and Yb-SiO2 relationships, and the oxygen isotope data rule out models in which the more silicic lavas result from partial melting of altered oceanic crust or altered oceanic gabbros. Rather, the data form a coherent array that is suggestive of closed-system fractional crystallization and this is well simulated by MELTS models run at 0.2 GPa and QFM (quartz-fayalite-magnetite buffer) with 1 wt % H2O, using a parental magma chosen from the basaltic glasses. Although some assimilation of altered oceanic crust or gabbro cannot be completely ruled out, there is no evidence that this plays an important role in the origin of the silicic lavas. The U-series disequilibria are dominated by 238U and 226Ra excesses that limit the timescale of differentiation to less than a few millennia. Overall, the data point to rapid evolution in relatively small magma lenses located near the base of thick oceanic crust; we speculate that this was coupled with relatively low rates of basaltic recharge. A similar model may be applicable to the generation of silicic magmas elsewhere in the ocean basins.

SHRIMP Pb/U zircon ages of plutonic rocks from Southwest Indian Ridge

Absolute ages of plutonic rocks from mid-ocean ridges provide important constraints on the scale, timing and rates of oceanic crustal accretion, yet few such rocks have been absolutely dated. We present 206Pb/238U SHRIMP zircon ages from two ODP Drill Holes and a surface sample from Atlantis Bank on the Southwest Indian Ridge. We report ten new sample ages from 26-1430 m in ODP Hole 735B, and one from 57 m in ODP Hole 1105A. Including a previously published age, eleven samples from Hole 735B yield 206Pb/238U zircon crystallization ages that are the same, within error, overlap with the estimated magnetic age and are inferred to date the main period of crustal growth, the average age of analyses is 11.99 ± 0.12 Ma. Any differences in the ages of magmatic series and/or tectonic blocks within Hole 735B are unresolvable and eight well-constrained ages vary from 11.86 ± 0.20 Ma to 12.13 ± 0.21 Ma, a range of 0.27 ± 0.29 Ma, consistent with the duration of crustal accretion observed at the Mid-Atlantic Ridge. An age of 11.87 ± 0.23 Ma from Hole 1105A is within error of ages from Hole 735B and permits previous correlations made between zones of oxide-rich gabbros in each hole. Pb/U zircon ages > 0.5 Ma younger than the magnetic age are recorded in at least three samples from Atlantis Bank, one from Hole 735B and two collected along a fault scarp to the East. These young ages may date one or more off-axis events previously suggested from thermochronologic data and support the interpretation of a complex geological history following crustal accretion at Atlantis Bank. Together with results from the surface of Atlantis Bank, dating has shown that while the majority of Pb/U SHRIMP zircon ages record the short-lived (< 0.5 Ma) phase of crustal accretion on-axis, results from several samples precede and post-date this period by > 1 Ma suggesting a complex and prolonged magmatic/tectonic history for the crust at Atlantis Bank.

Sedimentology and geochemistry of ODP Site 184-1144

We analyzed sediment from Ocean Drilling Program (ODP) Site 1144 in the northern South China Sea to examine the weathering response of SE Asia to the strengthening of the East Asian Monsoon (EAM) since 14 ka. Our high-resolution record highlights the decoupling between continental chemical weathering, physical erosion and summer monsoon intensity. Mass accumulation rates, Ti/Ca, K/Rb, hematite/goethite and 87Sr/86Sr show sharp excursions from 11 to 8 ka, peaking at 10 ka. Clay minerals show a shorter-lived response with a higher kaolinite/(illite + chlorite) ratio at 10.7-9.5 ka. However, not all proxies show a clear response to environmental changes. Magnetic susceptibility rises sharply between 12 and 11 ka. Grain-size becomes finer from 14 to 10 ka and then coarsens until ~7 ka, but is probably controlled by bottom current flow and sealevel. Sr and Nd isotopes show that material is dominantly eroded from Taiwan with a lesser flux from Luzon, while clay mineralogy suggests that the primary sources during the Early Holocene were reworked via the shelf in the Taiwan Strait, rather than directly from Taiwan. Erosion was enhanced during monsoon strengthening and caused reworking of chemically weathered Pleistocene sediment largely from the now flooded Taiwan Strait, which was transgressed by ~8 ka, cutting off supply to the deep-water slope. None of the proxies shows an erosional response lasting until ~6 ka, when speleothem oxygen isotope records indicate the start of monsoon weakening. Although more weathered sediments were deposited from 11 to 8 ka when the monsoon was strong these are reworked and represent more weathering during the last glacial maximum (LGM) when the summer monsoon was weaker but the shelves were exposed.

Description of, and 238U, 234U, 232Th and 230Th measurements on a nodule from R/V Sonne station SO79_62KD, Central East Pacific Ocean

Two diagenetic manganese nodules from the Peru Basin were investigated by thermal ionization mass spectrometry and high resolution alpha spectrometry for uranium and thorium. The TIMS concentrations for nodule 62KD (63KG) vary as follows: 0.12-1.01 ppb (0.06-0.59) 230Th, 0.51-1.98 ppm (0.43-1.40) 232Th, 0.13-0.80 ppb (0.09-0.49) 234U, and 1.95-13.47 ppm (1.66-8.24) 238U. Both nodules have average growth rates of ~110 mm per million years. However, from the variations of excess 230Th with depth we estimate partial accumulation rates which range from 50 to 400 mm per million years. The 234U dating method cannot be applied due to remobilization of U from the sediment and subsequent incorporation into the nodules' crystal lattice, reflected by decay corrected 234U values far above the ocean water value. Sections of fast nodule growth are related to those layers having high Mn/Fe ratios (up to 200) and higher densities. As a possible explanation we develop a scenario that describes similar glacial/interglacial trends in both nodules as a record of regional changes of sediment and/or deep water chemistry.

Absolute abundances of benthic foraminifers and stable isotopes from the Alvin dives 3709-3712

The presence of gas hydrates on the Blake Ridge diapir, northeastern Atlantic Ocean, offers an opportunity to study the impact of methane seepage on the ecology and geochemistry of benthic foraminifera in the late Holocene. Three push cores, covering a time span of ~ 1000 yrs, were retrieved from three distinct microhabitats at the top of the diapir at a water depth of ~ 2150 m: (i) sediments away from seepage (control core), (ii) sediments overlain by clusters of methanotrophic and thiotrophic bivalves, and (iii) chemoautotrophic microbial mats. The foraminiferal assemblages at the two seep sites are marked by a reduction in benthic foraminiferal species diversity, coupled with a near-absence of agglutinated species. However, an opportunistic population rise in CH4- or H2S-tolerant calcareous species (e.g., Globocassidulina subglobosa and Cassidulina laevigata) that utilize the abundant trophic resources at the seeps has led to an increase in the overall assemblage density there. The delta18O and delta13C values of three species of benthic foraminifera - Gyroidinoides laevigatus, Globocassidulina subglobosa, and Uvigerina peregrina - and the planktonic species Globorotalia menardii were acquired from all three cores. The benthic species from methane seeps yield delta13C values of 0.1 to - 4.2 (per mil VPDB), that are distinctly more 13C-depleted relative to the delta13C of 0.4 to - 1.0 (per mil VPDB) at the control (off seep) site. The species from a mussel-bed site exhibit more negative delta13C values than those from microbial mats, possibly reflecting different food sources and higher rate of anaerobic oxidation of methane. The positive delta13C values in the paired planktonic species suggest that authigenic carbonate precipitation did not overprint the observed 13C depletions. Hence the probable cause of negative delta13C of benthic foraminifera is primary calcification from Dissolved Inorganic Carbon (DIC) containing mixed carbon fractions from (a) highly 13C-depleted, microbially-oxidized methane and (b) a seawater source.

(Table 8.2, Page 178) Annotated record of the detailed examination of Mn deposits from submarine photographs acquired by the R/V Vityaz in the Pacific Ocean

Prof. H. H. W. Menard has brought together nearly all that was known of the Pacific geology in the early 1960s. His book contains a particular chapter on manganese nodules giving a stimulating review of the features and processes known to govern their distribution and chemical composition.

Biological Atlas of the Arctic Seas 2000: Physical oceanography, hydrochemistry, meteorology, and plankton of the Barents and Kara Seas

Presented are physical and biological data for the region extending from the Barents Sea to the Kara Sea during 158 scientific cruises for the period 1913-1999. Maps with the temporal distribution of physical and biological variables of the Barents and Kara Seas are presented, with proposed quality control criteria for phytoplankton and zooplankton data. Changes in the plankton community structure between the 1930s, 1950s, and 1990s are discussed. Multiple tables of Arctic Seas phytoplankton and zooplankton species are presented, containing ecological and geographic characteristics for each species, and images of live cells for the dominant phytoplankton species.

(Table 1) Depth and revised depth from ODP Sites 169-1033 and 169-1034

The Holocene section in Saanich Inlet, Vancouver Island, British Columbia, is 50-70 m thick. Cores from Saanich Inlet obtained during Leg 169S of the Ocean Drilling Program afford an excellent opportunity to obtain an ultrahigh-resolution paleomagnetic and environmental magnetic record for the Holocene and Late Pleistocene of western Canada. We have used an automated, long-core cryogenic magnetometer to study over 380 m of continuous u-channel samples from ODP Sites 1033 and 1034, the two sites that constitute Leg 169S. Holocene records of paleomagnetic inclination and intensity show excellent intra-site correlation and can be used to fine-tune the lithologic correlation among cores from each site. The Late Pleistocene magnetic records provide a means of intra-site correlation of the otherwise featureless marine clay. Near the Holocene/Late Pleistocene boundary, both sites contain a magnetic intensity feature that is interpreted as a Missoula-type flood event on the Fraser River. The composite Holocene inclination records from the two sites are quite similar and provide a means of comparing current age-models that are based on radiocarbon dating of material from each site. This comparison shows only minor differences in the available age-models. It also provides strong evidence that the sediments of Saanich Inlet represent a reliable record of geomagnetic field behavior.

Chemical composition of ODP Leg 138 sediments

A major oceanographic event preserved in the Cocos plate sedimentary column survived subduction and is recorded in the changing composition of Nicaraguan magmas. A uranium increase in these magmas since the latest Miocene (after 7 Ma) resulted from the 'carbonate crash' at 10 Ma and the ensuing high organic carbon burial in the sediments. The response of the arc to this paleoceanographic event requires near steady-state sediment recycling at this margin since 20 Ma. This relative stability in sediment subduction invites one of the first attempts to balance sedimentary input and arc output across a subduction zone. Calculations based on Th indicate that as much as 75% of the sedimentary column was subducted beneath the arc. The Nicaraguan margin is one of the few places to observe such strong links between the oceans and the solid earth.

Annotated record of the detailed examination of Mn deposits from the VERMILION SEA Expedition stations

On Vermilion Sea Expedition two research vessels among which the R/V Spencer F. Baird conducted a geological and geophysical exploration of the Gulf of California from February to May, 1959. Support was obtained from the Office of Naval Research and the Bureau of Ships of the U. S. Navy and from a grant of the American Petroleum Institute. Study of the canyons was one feature of the first part of the expedition. Submarine canyon studies were directed by Francis P. Shepard, Professor of Submarine Geology, aboard the research vessel Spencer F. Baird. The expedition found that the narrow channel between Angel de la Guarda Island, toward the head of the Gulf, and the peninsula is scoured almost free of sediments by strong currents. On the other side of Angel de la Guarda Island, between it and the mainland, one of the dredge hauls brought up a manganese nodule. It came from a depth of approximately 1500 feet. This is the shallowest water in which the nodules have been found. Studies have been under way some time on the feasibility of mining such nodules from the sea floor. They contain cobalt, nickel, copper and other valuable metals. (also in, Scripps Institution of Oceanography Vermilion Sea Expedition to the Gulf of California, http://library.ucsd.edu/dc/object/bb34484017)

Geological map of Heimefrontfjella, Dronning Maud Land, Antarctica (Scale 1:250,000)

The geological overview map was compiled from 15 geological maps (1 : 25,000) and is based on Jacobs et al. 1996. The topographic basemaps were adapted from unpublished 1:250,000 provisional topographic maps, Institut f. Angewandte Geodäsie, Frankfurt, 1983. Part of the contour lines are from Radarsat (Liu et al. 2001).

Annotated record of the detailed examination of Mn deposits from DEEPSONDE Expedition stations near the East Pacific Rise

Basalts from the base of a small seamount on ~1.5-m.y.-old crust west of the East Pacific Rise (EPR) at 9°N are intermediate in chemical and isotopic composition between light-rare-earth-element-depleted tholeiite (normal midocean ridge basalt (MORB)) and alkali basalt. Like oceanic alkali basalt, these rocks contain significantly more Ba, K, P, Sr, Ti, U, and Zr than normal MORB. Since the absolute abundances of these elements are still well below alkali basalt levels, the label transitional is adopted for these basalts. A series of fractionated MORB also occurs in this area, northwest of the Siqueiros Fracture Zone - Transform Fault. The normal tholeiites are either olivine-plagioclase or plagioclase-clinopyroxene phyric, while the transitional basalts are spinel-olivine phyric. Fractional crystallization quantitatively accounts for the chemical variability of the tholeiitic series but not for the transitional basalts. The tholeiitic series probably evolved in a crustal magma chamber ~4 km below the crest of the East Pacific Rise. 143Nd/144Nd and other chemical data suggest that the large-ion-lithophile-enriched transitional basalts may represent a hybrid of normal MORB and Siqueiros area alkali basalt. Incompatible element plots of K, P, and U indicate possible derivation of the transitional basalts by magma mixing. Magma mixing of unfractionated normal MORB and Siqueiros alkali basalt has been quantified. Derivation of the transitional basalts from a 1:1 mixture is supported by all available chemical data, including Cr, Cu, Nd, Ni, Sm, Sr, U, and V. This magma mixing apparently occurred at ?<~30 km depth within a few tens of kilometers from the EPR axis. These Siqueiros area EPR transitional basalts are compared with Mid-Atlantic Ridge (MAR) transitional basalts from the Iceland and Azores areas. The Siqueiros area basalts reflect a profound chemical and isotopic heterogeneity in the upper mantle, similar to that found along the MAR. Unlike the MAR, the EPR shows no evidence of plumelike bulges and associated large-scale outpourings of nonnormal MORB resulting from these mantle heterogeneities. Siqueiros alkali basalt and MORB, as well as transitional basalt and MORB, were recovered from single dredge hauls. Such close spatial and temporal proximity of the inferred mantle sources places severe constraints on geometric and physicochemical upper mantle models.

Age and isotopes in bottom sediments from Core VER-99-1-St2, Baikal Lake

A simple, reliable, and efficient method has been elaborated for direct determination of isotopic composition of authigenic uranium in siliceous lacustrine sediments. The method is based on studying kinetics of selective extraction of authigenic uranium from sediments by weak solutions of ammonium hydrocarbonate followed by ICP-MS analysis of nuclides. To estimate contamination of authigenic uranium by terrigenous one contents of 232Th and some other clastogenic elements in the extracts were measured simultaneously. Selectivity of extraction of authigenic uranium from the sediments treated with 1% NH4HCO3 solution appeared to be no worse than 99%. The method was applied to analysis of isotopic composition of authigenic uranium at several key horizons of the earlier dated core from the Baikal Lake. Measurements directly show that 234U/238U values in Baikal water varied depending on climate, which contradicts existing hypotheses. Measured 234U/238U ratios in water of the paleo-Baikal match corresponding values reconstructed from isotopic data for total uranium in the sediments on supposition that U/Th ratio is constant in terrigenous fraction of the sediments. Direct experimental determination of total and authigenic nuclides in sediments enhances potentiality of the method for 234U-230Th dating of non-carbonate lacustrine sediments including those from the Baikal Lake within intervals corresponding to periods of glaciation, when sediments were rich in terrigenous components. Portions of terrigenous and authigenic uranium are well separated and we can study variability of sources of terrigenous matter and refine the earlier model for reconstructing climate humidity in the East Siberia.

Annotated record of the detailed examination of Mn deposits from R/V Ryofu Maru Cruise JEDS-4 stations

Manganese nodules and manganese-coated pumice fragments were recovered at Station E6 at the middle of the flat Northwest Pacific Basin, during the Japanese Deep Sea Expedition of 1961 undertaken aboard R/V Ryofu Maru.

Stable isotope record and composition of planktonic foraminifera from ODP Site 172-1056

The stable isotopic composition of two planktonic foraminifer species (Globigerinoides sacculifer and Neogloboquadrina dutertrei) and two benthic foraminifer species (Cibicidoides wuellerstorfi and Uvigerina peregrina) was measured at sub-orbital resolution through the marine isotope stages (MISs) 10, 11, and 12 (345-460 ka) at Site 1056 on the Blake-Bahama Outer Ridge. Planktonic foraminifers were counted for the interval 405-450 ka at 2-4-kyr resolution. Site 1056 (32°29'N, 76°20'W) is located on the continental slope (water depth: 2167 m) beneath the Gulf Stream. The average rate of sediment accumulation through the interval is 11.4 cm/kyr, but sediment accumulation is much more rapid during glacial intervals (15-17 cm/kyr). The decline in percent carbonate during glacial intervals, and its rise during interglacials, indicates that the increased sediment supply is of terrigenous origin. Low carbonate values and low benthic delta13C, which are both associated with a weak Western Boundary Undercurrent and low North Atlantic Deep Water production, persist for 6 kyr after the benthic delta18O record indicates that ice volume has begun to decrease. Recovery of carbonate and benthic delta13C values is abrupt and rapid. Millennial-scale variation (~3-4 kyr) is apparent in the glacial intervals of the planktonic delta18O records and is more pronounced in a Delta delta18O record, which represents the temperature range in the photic zone. Semi-precessional (10-12-kyr) cycles are apparent in the planktonic deltadelta13C record. The millennial-scale cycles are largely caused by an increase in G. sacculifer delta18O and represent surface warming. They are interpreted as representing periodic increases in westward intensification of the gyre. The semi-precessional cycles are driven by changes in the N. dutertrei delta13C and represent fluctuations in the Gulf Stream itself and therefore likely have a tropical origin. Planktonic foraminifer census counts did not show an expected response to one of the largest glacial/interglacial transitions of the late Pleistocene. The most obvious change was an increase in faunal diversity during MIS 12.2, the interval of maximum delta18O values. This suggests that cool slope water and warm subtropical gyre water penetrated a more sluggish Gulf Stream with greater frequency at this time. The millennial-scale maxima in the Delta delta18O record are accompanied by decreases in diversity, which is consistent with the interpretation of surface warming during these events.