The Petrology, Geochemistry, and Mineralogy of North Atlantic Basalts: A Discussion Based on IPOD Leg 49

Wood, David A.; Varet, Jacques; Bougault, Henri; Corre, Olivier Le; Joron, Jean-Louis; Treuil, M.; Bizouard, H.; Norry, Michael J; Hawkesworth, C. J.; Roddick, J. C.

doi:10.2973/dsdp.proc.49.121.1979

Cited by 18 publications

(28 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…None of the Leg 81 basalts can be considered a primary melt; their concentrations in Cr and Ni should be significantly higher (Cr = 600 ppm, Ni = 250 ppm) than those found; these concentrations are characteristic of derived liquids resulting from fractional crystallization. The good positive correlation between Ni and Cr shown in Figure 7, and the lack of correlation between them and the K 2 O or LOI values allow us to ascribe the Cr and Ni variations to the fractionation of Cr-and Ni-bearing minerals (chromiferous spinel and olivine), as previously shown for many ocean-floor basalt sequences (Bougault et al, 1979).…”

Section: Trace-element Compositionssupporting

confidence: 63%

“…This Ta (and Nb) behavior is known as Ta, Nb anomaly (Bougault, 1980). In basalts from mid-oceanic ridges (North Atlantic, Leg 49, Wood et al, 1979;PacificCosta Rica Rift, Leg 69, Etoubleau et al, in press), the Th/Ta ratio is close to 1 while in subduction zones this ratio is very variable and higher than 10 (Joron and Treuil, 1977;Joron et al, 1978;Briqueu et al, 1983). In basalts from Hole 555, the Th/Ta ratio is close to 2-3 and significantly different from the values found in the deep-oceanic tholeiites and the other holes from Leg 81 (Fig.…”

Section: Trace-element Compositionsmentioning

confidence: 99%

“…3; Analyses 8, 11, 15, 18, 32, 33, 34, Table 3). Although they have already been found in ocean-floor basalts as the result of extreme Ca depletion of augite resulting from quench trends (e.g., in Leg 49 basalts; Wood et al, 1979), Figure 3 shows that, with the possible exception of Hole 554A, there is no continuous transition from augite or ferroaugite to pigeonite or ferropigeonite through subcalcic augite or ferroaugite compositions [contrast with Wood et al's (1979) figure 47]. Moreover, pigeonite occurs in Leg 81 basalts either as independent microlites (Analyses 8, 9, 15, 18, sen, 1968;Jensen, 1978) and from the Antrim Plateau basalts, Northern Ireland (quoted by Preston, 1982).…”

Section: Pyroxenesmentioning

confidence: 99%

“…Usually, the La/Ta ratio is 9 (1 when normalized to chondrite) for mid-ocean ridge basalts (MORBs) that present flat to enriched Coryell-Masuda patterns and the La/Ta ratio is 19 ( = 2 for normalized ratio) in the case of typically depleted MORBs; some intermediate values have been found (Bougault et al, 1979;Bougault, 1980). In the case of Leg 81 samples, Figure 10 clearly shows a La/Ta ratio close to 19 even if somewhat higher.…”

Section: Trace-element Compositionsmentioning

confidence: 99%

See 3 more Smart Citations

Strongly Depleted Tholeiites from the Rockall Plateau Margin, North Atlantic: Geochemistry and Mineralogy

Joron¹,

Bougault²,

Maury³

et al. 1984

Initial Reports of the Deep Sea Drilling Project

Self Cite

View full text Add to dashboard Cite

The Leg 81 basalts, drilled either from the margins ("dipping reflectors" sequence: Holes 552, 553A, and 554A) or from the "continental" side (Hole 555) of the Rockall Plateau microcontinent, are strongly light rare-earth element (LREE) depleted oceanic tholeiites. The basalts from the four holes are almost similar. Most of their primary characteristics have been preserved, although they have suffered alteration by seawater. From the petrological and mineralogical points of view, they resemble deep-ocean-floor basalts but show some peculiarities (occurrence of pigeonite and ilmenite as normal components of the groundmass differentiation sequences toward ferrobasalts). Their geochemical characteristics are dominated by their extreme depletion in the most hygromagmaphile elements (Th, Ta, La, and Nb), the concentrations of which are sometimes lower than the corresponding chondritic values. Leg 81 basalts are thus clearly different from continental tholeiites (flood basalts): Possible equivalents in the Thulean Tertiary Magmatic Province include the LREE-depleted tholeiites from the Upper Basaltic Series of the Faeroe Islands and the Preshal Mhor basalt type from the British Tertiary Province.

show abstract

Section: Trace-element Compositionssupporting

confidence: 63%

Section: Trace-element Compositionsmentioning

confidence: 99%

Section: Pyroxenesmentioning

confidence: 99%

Section: Trace-element Compositionsmentioning

confidence: 99%

See 2 more Smart Citations

Strongly Depleted Tholeiites from the Rockall Plateau Margin, North Atlantic: Geochemistry and Mineralogy

Joron¹,

Bougault²,

Maury³

et al. 1984

Initial Reports of the Deep Sea Drilling Project

Self Cite

View full text Add to dashboard Cite

show abstract

“…6, Table 2). They differ significantly from MORB (Sigurdsson and Schilling, 1976;Wood et al, 1979), having higher amounts of replacement of Cr + Al by Fe 3+ + Ti, and resemble those known from ocean-island tholeiitic (OIT) basalts (Evans and Wright, 1972).…”

Section: Magnesiochromitesmentioning

confidence: 63%

Primary Composition, Alteration, and Origin of Cretaceous Volcaniclastic Rocks, East Mariana Basin (Site 585, Leg 89)

Viereck¹,

Simon²,

Schminke³

1986

Initial Reports of the Deep Sea Drilling Project

View full text Add to dashboard Cite

An upper Aptian to middle Albian series of volcaniclastic rocks more than 300 m thick was drilled at Site 585 in the East Mariana Basin. On the basis of textural and compositional (bulk-rock chemistry, primary and secondary mineral phases) evidence, the volcaniclastic unit is subdivided into a lower (below 830 m sub-bottom) and an upper (about 670-760 m) sequence; the boundary in the interval between is uncertain owing to lack of samples.The rocks are dominantly former vitric basaltic tuffs and minor lapillistones with lesser amounts of crystals and basaltic lithic clasts. They are mixed with shallow-water carbonate debris (ooids, skeletal debris), and were transported by mass flows to their site of deposition.The lower sequence is mostly Plagioclase-and olivine-phyric with lesser amounts of Ti-poor clinopyroxene. Mineralogical and bulk-rock chemical data indicate a tholeiitic composition slightly more enriched than N-MORB (normal mid-ocean ridge basalt). Transport was by debris flows from shallow-water sites, as indicated by admixed ooids. Volcanogenic particles are chiefly moderately vesicular to nonvesicular blocky shards (former sideromelane) and less angular tachylite with quench Plagioclase and pyroxene, indicating generation of volcanic clasts predominantly by spalling and breakage of submarine pillow and/or sheet-flow lavas.The upper sequence is mainly clinopyroxene-and olivine-phyric with minor Plagioclase. The more Ti-rich clinopyroxene and the bulk-rock analyses show that the moderately alkali basaltic composition throughout is more mafic than the basal tholeiitic sequence. Transport was by turbidity currents. Rounded epiclasts of crystalline basalts are more common than in the lower sequence, and, together with the occurrence of oxidized olivine pseudomorphs and vesicular tachylite, are taken as evidence of derivation from eroded subaerially exposed volcanics. Former sideromelane shards are more vesicular than in the lower sequence; vesicularity exceeds 60 vol.% in some clasts. The dominant clastic process is interpreted to be by shallow-water explosive eruptions.All rocks have undergone low-temperature alteration; the dominant secondary phases are "palagonite," chlorite/ smectite mixed minerals, analcite, and chabazite. Smectite, chlorite, and natrolite occur in minor amounts. Phillipsite is recognized as an early alteration product, now replaced by other zeolites. During alteration, the rocks have lost up to 50% of their Ca, compared with a fresh shard and fresh glass inclusions in primary minerals, but have gained much less K, Rb, and Ba than expected, indicating rapid deposition prior to significant seafloor weathering.

show abstract

The role of seamount volcanism in crustal construction at the Mid‐Atlantic Ridge (24°–30°N)

Smith¹,

Cann²

1992

J. Geophys. Res.

187

109

View full text Add to dashboard Cite

An analysis of approximately 6000 km 2 of Sea Beam swaths indicates that the floor of the median valley of the Mid-Atlantic Ridge (MAR) between 24ø-30øN is strewn with near-circular volcanoes. We have identified 481 seamounts in the height range 50-650 m. Because many of the features which appear to be seamounts do not meet our criteria fully, they have not been counted, and our numbers are likely a minimum estimate of the population. The large abundance of seamounts on the median valley floor indicates that seamount volcanism plays an important role in the accretionary processes at this section of the MAR. The summit height distribution of the MAR seamount population is consistent with the exponential frequencysize distribution model for off-axis eastem Pacific seamounts (Jordan et al., 1983; Smith and Jordan, 1987). The model parameters for the MAR population yield an average of about 195 seamounts per one thousand square kilometers, and a characteristic height of about 60 m. Shape statistics compiled from the 481 seamounts give parameters that are exactly the same, or cover the same range in values as those obtained from a study of Pacific seamounts in the height range 140-3800 m (Smith, 1988) implying a universal control on seamount construction.Based on the volcanic morphology, we identify 18 spreading segments along the ridge. All except two contain a prominent axial volcanic ridge. Many of the seamounts identified are associated with the axial ridges. From the Sea Beam swaths, we infer that the ridges are composed of piled up seamounts and hummocky flows, and interpret them to be the primary sites of crustal construction. This style of volcanism contrasts strongly with that observed at the East Pacific Rise where seamounts are virtually absent at the spreading axis. The construction of seamounts and hummocky flows may be directly related to the fact that the MAR is fed by magma chambers that are limited in size and frequency. We suggest that small magma pockets with slow eruption rates produce seamounts either from pipes or initial fissure eruptions that collapse to construct a single edifice; small magma bodies with somewhat higher eruption rates produce hummocky fissure fed flows. Using buoyancy arguments, the heights of the MAR seamounts are related to the depth of the magma bodies. We hypothesize that small magma bodies rise buoyantly to the base of the hydrothermally cooled brittle lid where they are trapped, and then erupt. If this hypothesis is correct, the thickness of the brittle lid controls seamount height, and the exponential distribution of seamount summit heights implies that the thickness of the brittle lid follows an exponential distribution in time and space with characteristic thickness 1.4-1.9 km. If seamounts and hummocky flows are fed each from their own discrete magma body trapped at the brittle/ductile transition, then the lower crust of the MAR will be made up of the products of a multitude of small plutons. the map of the northern part of the French-American Mid-Ocean Undersea Stud...

show abstract

The Petrology, Geochemistry, and Mineralogy of North Atlantic Basalts: A Discussion Based on IPOD Leg 49

Cited by 18 publications

References 30 publications

Strongly Depleted Tholeiites from the Rockall Plateau Margin, North Atlantic: Geochemistry and Mineralogy

Strongly Depleted Tholeiites from the Rockall Plateau Margin, North Atlantic: Geochemistry and Mineralogy

Primary Composition, Alteration, and Origin of Cretaceous Volcaniclastic Rocks, East Mariana Basin (Site 585, Leg 89)

The role of seamount volcanism in crustal construction at the Mid‐Atlantic Ridge (24°–30°N)

Contact Info

Product

Resources

About