Sea floor basalt alteration: Some chemical and Sr isotopic effects

Hart, Stanley R.; Erlank, A. J.; Kable, E.J.D.

doi:10.1007/bf00413167

Cited by 384 publications

(155 citation statements)

References 25 publications

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“…The low abundances of K, Rb, and Ba imply that the analyzed basalts have undergone little chemical modification during low-temperature secondary alteration. It is well documented that low-T exchange with seawater enriches these elements (e.g., Hart et al, 1974) and, although it is demonstrable that high-grade hydrothermal activity can leach K, Rb, and Ba from the ocean crust Stern and Elthon, 1979), none of the Nauru Basin basalts has attained a sufficiently high grade for this to have been an important process. If the basalts have indeed undergone minimal exchange with seawater or sediment pore water, the 87 Sr/ 86 Sr ratios reported by Fujii et al (1981) probably represent magmatic values.…”

Section: Geochemistrymentioning

confidence: 99%

Geochemistry of Basalts from the Nauru Basin, Deep Sea Drilling Project Legs 61 and 89: Implications for the Origin of Oceanic Flood Basalts

Saunders¹

1986

Initial Reports of the Deep Sea Drilling Project

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At Site 462 in the Nauru Basin, western Pacific Ocean, 56 lithologic units have been recovered from an extensive flood basalt province. Fossil evidence suggests that the lavas were emplaced during the interval 100-115 Ma, some 30 m.y. after formation of the underlying Jurassic ocean crust. The lithologic units can be broadly divided into three chemical units, the lowermost two of which are chemically monotonous, suggesting rapid eruption of basalt from a compositionally homogeneous magma chamber. All the basalts are hypersthene-(hy-) rich tholeiites, with approximately chondritic La/Sm, La/Yb, Zr/Nb, La/Ta, and Th/Hf ratios. Chemically they resemble, in part, "transitional" mid-ocean ridge basalts (MORB) from areas such as the Reykjanes Ridge, although Rb, Ba, and K contents are very low and similar to those of "normal" MORB. Their 87 Sr/ 86 Sr ratios are higher than in N-type MORB (Fujii et al., 1981). The chemistry of the Nauru basalts differs from that of continental flood basalts, which tend to be strongly enriched in large-ion lithophile (LIL) elements, although the extent to which the differences result from sialic contamination or source variability is not clear.

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Section: Geochemistrymentioning

confidence: 99%

Geochemistry of Basalts from the Nauru Basin, Deep Sea Drilling Project Legs 61 and 89: Implications for the Origin of Oceanic Flood Basalts

Saunders¹

1986

Initial Reports of the Deep Sea Drilling Project

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“…Previous work has stressed changes in bulk rock composition resulting from seawater-rock alteration (e.g., Hart et al, 1974); however, with a few exceptions (e.g., Bass et al, 1973;Bass, 1976), detailed studies of the mineralogical evidence for these changes have not been undertaken. A clear understanding of the alteration processes, and by implication the nature of the geochemical balance between seawater and the oceanic crust (e.g., Hart, 1970;Muehlenbachs and Clayton, 1976) depends on the mineralogical evidence.…”

Section: Introductionmentioning

confidence: 99%

Mineralogy and Chemistry of Secondary Phases in Some Basaltic Rocks from DSDP Leg 37

Scarfe¹,

Smith²

1977

Initial Reports of the Deep Sea Drilling Project

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“…2) suggests that K and Rb have been affected by secondary processes (cf. Hart et al, 1974). Ba and Sr, elements that have variable susceptibility to seawater interaction, have more constant abundances (Table 3) and have levels similar to those seen in N-type MORB.…”

Section: Chemistry Site 595mentioning

confidence: 89%

Geochemistry of Basalts from Mesozoic Pacific Ocean Crust: Deep Sea Drilling Project Leg 91

Saunders¹

1987

Initial Reports of the Deep Sea Drilling Project

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Basalts recovered from Sites 595 and 596 on Mesozoic crust in the southwest Pacific range from olivine-bearing tholeiites to ferrobasalts. Despite having undergone extensive low-grade alteration, which has raised K and Rb abundances, the basalts have consistent interelement ratios of Ti, Zr, Hf, rare-earth elements, Y, Th, Ik, and Nb. La/Ta (-18), La n / Yb n (0.6), Ti/Zr (115), Zr/Nb (20), and Th/Hf (0.08) ratios all fall within the range of N-type mid-ocean-ridge basalt. The basalts from Sites 595 and 596 indicate that the Mesozoic Pacific crust was derived from a mantle source by processes similar to those operating at the present-day East Pacific Rise. INTRODUCTIONMuch of the ocean crust on the Pacific and Atlantic ocean floors comprises tholeiitic basalts formed at spreading centers. Although far from constant in composition since they range from olivine-rich tholeiites to ferrobasalts, the majority of ocean-ridge basalts are depleted in light rare-earth elements (REE) and other highly incompatible elements, a feature considered to reflect the composition of their mantle source. Most ridge-derived basalts recovered from the eastern Pacific, the East Pacific Rise (EPR), and the Galapagos Spreading Center, are these depleted, or normal (N-type) mid-ocean-ridge basalts (MORB) (Sun et al., 1979;Rhodes et al., 1976;Thompson et al., 1976;Mattey and Muir, 1980;Humphris et al., 1980;Saunders, 1983;Marsh et al., 1983).Unfortunately, few data are available for pre-Cenozoic Pacific crust, and none for pre-Cretaceous crust. (Material recovered from the Jurassic sequences in the Nauru Basin probably represents off-axis volcanism that may not be typical of the Jurassic ocean basement as a whole; Larson, Schlanger, et al., 1981; Moberly, Schlanger, et al., in press.) This omission has, until the recovery of Mesozoic crust during Leg 91, prevented an objective chemical investigation of ancient Pacific crust; in particular, it has made it impossible to monitor secular variations in crustal accretion processes and mantle evolution.Leg 91 was the second of two legs primarily dedicated to the placing of a Defense Advanced Research Projects Agency (DARPA) seismometer package into oceanic basement. Following the unsuccessful deployment of a package during Leg 88 in the northeast Pacific, Leg 91 drilled a series of four holes (595, 595A, 595B, and 596) in the southwest Pacific on old ocean crust near the seismically active Tonga Trench (Fig. 1) Prior to Leg 91, the regional magnetic survey data indicated that the magnetic anomalies in the area of study were either subdued or too confused to resolve. From these data it was thought, however, that the crust at Site 595 formed by rapid spreading in high southern latitudes during Mesozoic times (Montgomery and Johnson, this volume). Studies of the sedimentary rocks recovered during Leg 91 so far have failed to ascertain a precise age for the succession, but a magnetic survey carried out during Leg 91 indicates that the sites possibly are located on Anomaly M29 (see Site 595 r...

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Sea floor basalt alteration: Some chemical and Sr isotopic effects

Cited by 384 publications

References 25 publications

Geochemistry of Basalts from the Nauru Basin, Deep Sea Drilling Project Legs 61 and 89: Implications for the Origin of Oceanic Flood Basalts

Geochemistry of Basalts from the Nauru Basin, Deep Sea Drilling Project Legs 61 and 89: Implications for the Origin of Oceanic Flood Basalts

Mineralogy and Chemistry of Secondary Phases in Some Basaltic Rocks from DSDP Leg 37

Geochemistry of Basalts from Mesozoic Pacific Ocean Crust: Deep Sea Drilling Project Leg 91

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