Geochemistry of bulk samples and various minerals of sediment core CRP-1 from the Ross Sea, Antarctica

Thirty-nine medium and fine grained sandstones from between 19,26 and 147,23 mbsf in the Cape Roberts-l core (CRP-1) were analysed for 10 major and 16 trace elements. Using whole-lock compositions, 9 samples were selected for analyses of mineral and glass grains by energy dispersive electron microscope. Laser-Ablation Mass-Spectrometry was used to determine rare earth elements and 14 additional trace elements in glass shards, pyroxenes and feldspars in order to examine their contribution to the bulk rock chemistry. Geochemical data reveal the major contribution played by the Granite Harbour Intrusives to the whole rock composition, even if a significant input is supplied by McMurdo volcanics and Ferrar dolerite pyroxenes McMurdo volcanics were studied in detail; they appeal to derive from a variety of litologies, and a dominant role of wind transpoitation from exposures of volcanic rocks may be inferred from the contemporary occurrence of different compositions at all depths. Only at 116.55 mbsf was a thin layer of tephra found, linked to an explosive eruption McMurdo volcanic rocks exhibit larger abundances at depths above 62 mbsf, in correspondence with the onset of volcanic activity in the McMurdo Sound area. From 62 mbsf to the bottom of the core, McMurdo volcanics are less abundant and probably issued from some centres in the McMurdo Sound region. However, available data do not allow the exclusion of wind transport from some eruptive centres active in north Victoria Land at the beginning of the Miocene Epoch.

(Table 1) Nd and Sr isotopic analyses of ODP Leg 127 basalts

Sr and Nd isotopic compositions are reported for basaltic rocks collected during ODP Leg 127 from the Yamato Basin, a rifted backarc basin in the Japan Sea. The basalts are classified into two groups in terms of Nd isotopic composition: the upper sills at Site 797 are characterized by higher 143Nd/144Nd ratios (0.513083-0.513158, epsilon-Nd = 8.68-10.14) and the basalts from Site 794 and the lower sills at Site 797 have lower 143Nd/144Nd ratios (0.512684-0.512862, epsilon-Nd = 0.90-4.37). All of the basalts show higher Sr isotopic compositions than those of the mantle array, which is attributed to seawater alteration. The basalts with lower Nd isotopic values ranging in age from 20.6 to 17.3 Ma have tapped an enriched subcontinental upper mantle (SCUM) with the minor involvement of a depleted asthenospheric mantle (AM). Subsequent change in composition through the physical replacement of SCUM by AM yielded the basalts of the upper sills of higher Nd isotopic compositions. This event within the upper mantle was associated with the breakup of the overlying lithosphere during the rifting of the Japan Sea backarc basin.

Major and trace element concentrations of sediments from the IODP Exp302 sites

We analyzed a suite of sediment samples recovered in the central Arctic Ocean for major, trace, and rare earth elements in order to assess changes in terrigenous source material throughout the Cenozoic. The terrigenous component consists of two end-members. Input from a shale-like composition dominates bulk sediments, especially those deposited during the Paleocene and since the Miocene, and may represent sediment supply from the eastern Laptev Sea. Therefore, even though the environment and transport mechanisms may have varied from ice free to ice dominated, sequences of the early Paleogene and later Neogene appear to have been influenced by a single major terrigenous source. This suggests similar transport capabilities and trajectories for both ocean and drift currents through significant parts of the Cenozoic. Influence from a more mafic source appears to be more important through the early Eocene to the middle Miocene and most likely represents material from the western Laptev Sea or Kara Sea. Thus, Eocene major changes in surface water productivity appear broadly synchronous with those in terrigenous provenance. A combination of regional sea level variations, local shelf processes, and transport mechanisms are among the more probable causes for the observed source changes. Although the assignment of sources using chemistry presently is constrained by a lack of data from certain regions (e.g., eastern Siberian Sea) our results generally agree with inferences based on mineralogy or radiogenic isotopes and shed further light on long-term reconstructions of the central Arctic Ocean.

Chemistry of minerals from amphibole-chlorite veins of ODP Site 209-1270

We examined small-scale shear zones in drillcore samples of abyssal peridotites from the Mid-Atlantic Ridge. These shear zones are associated with veins consisting of chlorite + actinolite/tremolite assemblages, with accessory phases zircon and apatite, and they are interpreted as altered plagiogranite melt impregnations, which originate from hydrous partial melting of gabbroic intrusion in an oceanic detachment fault. Ti-in-zircon thermometry yields temperatures around 820°C for the crystallization of the evolved melt. Reaction path modeling indicates that the alteration assemblage includes serpentine of the adjacent altered peridotites. Based on the model results, we propose that formation of chlorite occurred at higher temperatures than serpentinization, thus leading to strain localization around former plagiogranites during alteration. The detachment fault represents a major pathway for fluids through the oceanic crust, as evidenced by extremely low d18O of altered plagiogranite veins (+3.0-4.2 per mil) and adjacent serpentinites (+ 2.6-3.7 per mil). The uniform oxygen isotope data indicate that fluid flow in the detachment fault system affected veins and adjacent host serpentinites likewise.

Geochemistry of minerals in CRP sediment cores from the Ross Sea, Antarctica

Sixty-four volcanic chists, sandstones and tephras between 5.95 and 618.19 meters below sea floor (mbsf) in the Cape Roberts Project cores 2 and 2A cores (CRP-2/2A) were examined for Cenozoic and Mesozoic volcanic components, using optical and Scanning Electron Microscopy. Minerals and glass shards in a selection of samples were analysed by electron microprobe fined with an EDAX detector. Laser-Ablation ICP-Mass-Spectrometry (ICP-MS) was used to determine rare earth elements and 14 additional trace elements in glass shards, pyroxenes and feldspars in order to pin-point the onset of McMurdo Volcanic Group (MVG) activity in the stratigraphic column. Pumices in tephra layers of peralkaline phonolite composition in Unit 7.2 -between 108 and 114 mbsf - were also analysed for trace elements by ICP-MS. This tephra unit is not reworked and its isotopic age (21.44 ± 0.05 Ma) is the age of deposition. The height of the eruptive column responsible for the deposition of the tephra was probably less than 8 km; the source was local, probably within 30 km from the drill site. Phonolite of unit 7.2 of CRP-2/2A has no direct petrogenetic relation with the peralkaline trachyte in the tephra-enriched layer of CRP-1 at 116.55 mbsf. Volcanic clasts and sand grains (glass shards, aegirine-augite, anorthoclase) related to Cenozoic activity of MVG were observed only starting from Unit 9.8, where they are dated at 24.22 ± 0.06 Ma at c. 280 mbsf. In this unit the lowest- occurring basaltic glass shard is found at 297.54 mbsf. Sampled McMurdo volcanics are generally vesicular and vary in composition from alkali basalt to trachyte and peralkaline phonolite. By contrast, below 320 mbsf, aphyric or slightly-porphyritic volcanic clasts become more abundant but they are all non-vesiculated, pigeconite and ilmenite-bearing basalts and dolerite of tholeiitic affinity. These rocks are considered to be related to lava flows and associated intrusions of Jurassic age (Kirkpatrick basalts and Ferrar dolerite). As in CRP-1, McMurdo volcanics appear to derive from a variety of lithologics. Besides glaciers, a dominant role of wind transportation from exposed volcanic rocks may be inferred from the contemporary occurrence of glass shards of different compositions at depths above 297.54 mbsf. These data confirm that the onset of magmatic activity in southern Victoria Land is considerably delayed (by about 24 Ma) with respect to northern Victoria Land.

Rb, Sr, Sm and Nd concentrations and isotopic composition of basalts from DSDP Leg 74 (Table 1)

Basement intersected in DSDP holes 525A, 528 and 527 on the Walvis Ridge consists of submarine basalt flows and pillows with minor intercalated sediments. These holes are situated on the crest and mid and lower northwest flank of a NNW-SSE-trending ridge block which would have closely paralleled the paleo mid-ocean ridge (Rabinowitz and LaBrecque, 1979 doi:10.1029/JB084iB11p05973, Moore et al. (1983 doi:10.1130/0016-7606(1983)94<907:TWRTDS>2.0.CO;2). The basalts were erupted approximately 70 m.y. ago, an age equivalent to that of immediately adjacent oceanic crust in the Angola Basin and coraistent with formation at the paleo mid-ocean ridge (Moore et al., 1983). The basalt types vary from aphyric quartz tholeiites on the ridge crest to highly plagioclase phyric olivine tholeiites on the ridge flank. These show systematic differences in incompatible trace element and isotopic composition. Many element and isotope ratio pairs form systematic trends with the ridge crest basalts at one end and the highly phyric ridge flank basalts at the other. The low 143Nd/144Nd (0.51238), 206Pb/204Pb (17.54), 207Pb/204Pb (15.47), 208Pb/204Pb (38.14) and high 87Sr/86Sr (0.70512) ratios of the ridge crest basalts suggest derivation from an old Nd/Sm-, Rb/Sr- and Pb/U-enriched mantle source. This isotopic signature is similar to that of alkaline basalts on Tristan da Cunha but offset to significantly lower Nd and Pb isotopic ratios. The isotopic ratio trends may be extrapolated beyond the ridge flank basalts with higher 143Nd/144Nd (0.51270), 206Pb/204Pb (18.32), 207Pb/204Pb (15.52), 208Pb/204Pb (38.77) and lower 87Sr/86Sr (0.70417) ratios in the direction of increasingly Nd/Sm-, Rb/Sr- and Pb/U-depleted source compositions. These isotopic correlations are equally consistent with mixing of depleted and enriched end member melts or partial melting of an inhomogeneous, variably enriched mantle source. However, observed Zr-Ba-Nb-Y interelement relationships are inconsistent with any simple two-component model of magma mixing, as might result from the rise of a lower mantle plume through the upper mantle. Incompatible element and Pb isotopic systematics also preclude extensive involvement of depleted (N-type) MORB material or its mantle sources. In our preferred petrogenetic model the Walvis Ridge basalts were derived by partial melting of mantle similar to an enriched (E-type) MORB source which had become heterogeneous on a small scale due to the introduction of small-volume melts and metasomatic fluids.

Composition of sedimentary material from the bottom and the area surrounding the Lake Untersee, East Antarctica

This paper presents data on geographic and geologic conditions of modern sedimentation in the Lake Untersee, the largest lake in the East Antarctica. Geochemical and sedimentation data indicate that the leading mechanism supplying aluminosilicate sedimentary material to the surface layer of bottom sediments is seasonal melting of the Anuchin glacier and the mountain glacier on the southeastern part of the valley hosting the lake. Strongly reduced conditions in the lowermost 25 m of the water column in the smaller of two depressions of the lake bottom were favorable for enrichment of the bottom sediments in bacteriogenic organic matter, Mo, Au, and Pd. H2S-contaminated water results to significant enrichment of the sediments only in redox-sensitive elements that are able to migrate in anionic complexes and precipitate (co-precipitate) as sulfides.

Chemical analysis and argon geochronology from dive SAR_1 on Cornacya seamount of the Sardinia Channel

Sarcya 1 dive explored a previously unknown 12 My old submerged volcano, labelled Cornacya. A well developed fracturation is characterised by the following directions: N 170 to N-S, N 20 to N 40, N 90 to N 120, N 50 to N 70, which corresponds to the fracturation pattern of the Sardinian margin. The sampled lavas exhibit features of shoshonitic suites of intermediate composition and include amphibole-and mica-bearing lamprophyric xenoliths which are geochemically similar to Ti-poor lamproites. Mica compositions reflect chemical exchanges between the lamprophyre and its shoshonitic host rock suggesting their simultaneous emplacement. Nd compositions of the Cornacya K-rich suite indicate that continental crust was largely involved in the genesis of these rocks. The spatial association of the lamprophyre with the shoshonitic rocks is geochemically similar to K-rich and TiO2-poor igneous suites, emplaced in post-collisional settings. Among shoshonitic rocks, sample SAR 1-01 has been dated at 12.6±0.3 My using the 40Ar/39Ar method with a laser microprobe on single grains. The age of the Cornacya shoshonitic suite is similar to that of the Sisco lamprophyre from Corsica, which similarly is located on the western margin of the Tyrrhenian Sea. Thus, the Cornacya shoshonitic rocks and their lamprophyric xenolith and the Sisco lamprophyre could represent post-collisional suites emplaced during the lithospheric extension of the Corsica-Sardinia block, just after its rotation and before the Tyrrhenian sea opening. Drilling on the Sardinia margin (ODP Leg 107) shows that the upper levels of the present day margin (Hole 654) suffered tectonic subsidence before the lower part (Hole 652). The structure of this lower part is interpreted as the result of an eastward migration of the extension during Late Miocene and Early Pliocene times. Data of Cornacya volcano are in good agreement with this model and provide good chronological constraints for the beginning of the phenomenon.

Geochemistry of Cretaceous sills and lava flows of ODP Holes 129-800A and 129-802A

On the basis of their respective eruptive environments and chemical characteristics, alkalic dolerite sills from the northern Pigafetta Basin (Site 800) and tholeiitic pillow lavas from the Mariana Basin (Site 802) sampled during Ocean Drilling Program Leg 129 are considered to represent examples of the widespread mid-Cretaceous volcanic event in the western Pacific. Both groups of basic rocks feature mild, low-grade, anoxic smectite-celadonite-carbonate-pyrite alteration; late-stage oxidation is very limited in extent, with the exception of the uppermost sill unit at Site 800. The aphyric and nonvesicular Site 800 alkalic dolerite sills are all well-evolved mineralogically and chemically, being mainly of hawaiite composition, and are similar to ocean island basalts. They are characterized by high contents of incompatible elements (for example, 300-400 ppm Zr), well-fractionated rare earth element patterns ([La/Yb]N 18-21) and HIMU isotopic characters. They probably represent deep-sea, lateral, intrusive off-shoots from nearby seamounts of similar age. The olivine-plagioclase +/- clinopyroxene phyric tholeiitic pillow lavas and thin flows of Site 802 are nonvesicular and quench-textured throughout. Relative to normal-type mid-ocean ridge basalt, they are enriched in large-ion-lithophile elements, exhibit flat (unfractionated) rare earth element patterns and have distinctive (lower) Zr/Nb, Zr/Ta, La/Ta, and Hf/Th ratios. Overall they are compositionally and isotopically similar to the mid-Cretaceous tholeiites of the Nauru basin and the Ontong-Java and Manihiki plateaus. The Site 802 tholeiites differ from the thickened crustal segments of the oceanic plateaus, however, in apparently representing only a thin veneer over the local basement in an off-axis environment.

Appendix A. Whole-rock major, trace and rare earth element analyses of the Ulubey volcanics, Appendix B. Analytical standards and detection limits for analyses

Collisional and post-collisional volcanic rocks in the Ulubey (Ordu) area at the western edge of the Eastern Pontide Tertiary Volcanic Province (EPTVP) in NE Turkey are divided into four suites; Middle Eocene (49.4-44.6 Ma) aged Andesite-Trachyandesite (AT), Trachyandesite-Trachydacite-Rhyolite (TTR), Trachydacite-Dacite (TD) suites, and Middle Miocene (15.1 Ma) aged Trachybasalt (TB) suite. Local stratigraphy in the Ulubey area starts with shallow marine environment sediments of the Paleocene-Eocene time and then continues extensively with sub-aerial andesitic to rhyolitic and rare basaltic volcanism during Eocene and Miocene time, respectively. Petrographically, the volcanic rocks are composed primarily of andesites/trachyandesites, with minor trachydacites/rhyolites, basalts/trachybasalts and pyroclastics, and show porphyric, hyalo-microlitic porphyric and rarely glomeroporphyric, intersertal, intergranular, fluidal and sieve textures. The Ulubey (Ordu) volcanic rocks indicate magma evolution from tholeiitic-alkaline to calc-alkaline with medium-K contents. Primitive mantle normalized trace element and chondrite normalized rare earth element (REE) patterns show that the volcanic rocks have moderate light rare earth element (LREE)/heavy rare earth element (HREE) ratios relative to E-Type MORB and depletion in Nb, Ta and Ti. High Th/Yb ratios indicate parental magma(s) derived from an enriched source formed by mixing of slab and asthenospheric melts previously modified by fluids and sediments from a subduction zone. All of the volcanic rocks share similar incompatible element ratios (e.g., La/Sm, Zr/Nb, La/Nb) and chondrite-normalized REE patterns, indicating that the basic to acidic rocks originated from the same source. The volcanic rocks were produced by the slab dehydration-induced melting of an existing metasomatized mantle source, and the fluids from the slab dehydration introduced significant large ion lithophile element (LILE) and LREE to the source, masking its inherent HFSE-enriched characteristics. The initial 87Sr/86Sr (0.7044-0.7050) and eNd (-0.3 to +3.4) ratios of the volcanics suggest that they originated from an enriched lithospheric mantle source with low Sm/Nd ratios. Integration of the geochemical, petrological and isotopical with regional and local geological data suggest that the Tertiary volcanic rocks from the Ulubey (Ordu) area were derived from an enriched mantle, which had been previously metasomatized by fluids derived from subducted slab during Eocene to Miocene in collisional and post-collisional extension-related geodynamic setting following Late Mesozoic continental collision between the Eurasian plate and the Tauride-Anatolide platform.

(Table 1) Sr, Nd, and Pb isotopic composition of ODP Leg 129 basalts

Basaltic rocks recovered from three drill sites in the western Pacific during Ocean Drilling Program Leg 129 have fairly distinct Sr, Nd, and Pb isotopic compositions. The Cretaceous alkali olivine dolerites from Site 800 in the northern part of Pigafetta Basin have fairly low 87Sr/86Sri (0.70292-0.70320) and 143Nd/144Ndi (0.51277-0.51281) and high present-day Pb isotopic ratios (206Pb/204Pb = 20.53-21.45; 207Pb/204Pb = 15.70-15.77; 208Pb/204Pb = 40.02-40.68). The Middle Jurassic tholeiites from Site 801 in the southern part of the basin have low 87Sr/86Sri (0.70237-0.70248), high 143Nd/144Ndi (0.51298-0.51322), and moderate present-day Pb isotopic ratios (206Pb/204Pb = 18.20-19.12; 207Pb/204Pb = 15.47-15.60; 208Pb/204Pb = 37.56-38.18); isotopic compositions of the alkali olivine basalts overlying the tholeiites fall between those of the tholeiites and Site 800 dolerites. The Cretaceous tholeiites from Site 802 in the East Mariana Basin have high 87Sr/86Sri (0.70360-0.70372), fairly low 143Nd/144Ndi (0.51277-0.51280), and fairly low and homogeneous present-day Pb isotopic ratios (206Pb/204Pb = 18.37-18.39; 207Pb/204Pb = 15.49-15.51; 208Pb/204Pb = 38.34-38.39). Isotopic compositions of Site 801 tholeiites are indistinguishable from those of modern mid-ocean ridge basalts, consistent with the proposal that these tholeiites are a part of the oldest Pacific crust. The diverse isotopic compositions of the younger basalts appear to be the result of Jurassic Pacific plate migration over the geologically anomalous south-central Pacific region, wherein they acquired their distinct isotopic compositions. The anomalous region was volcanically more active during the Cretaceous than at present.