Major- and Trace-Element Chemistry of Hole 504B Basalts and Their Alteration Products (Costa Rica Rift, Deep Sea Drilling Project Leg 70)

Sharaskin, A.Ya.; Migdisov, A. A.; Rostschina, I.A.; Miklishansky, A.Z.

doi:10.2973/dsdp.proc.69.151.1983

Cited by 9 publications

(3 citation statements)

References 12 publications

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“…Again, Sample 111-504B-159R-1, 52-56 cm (Piece 9), lies at the far end of this trend although at a slightly higher Zr/Y ratio than that of the experimental sample. The low ratios are similar to those found for La/Sm (0.3-0.5 CH ; Autio and Rhodes, 1983;Etoubleau et al, 1983;Sharaskin et al, 1983;Emmermann, 1985;Thai et al, 1985) and suggest a greater degree of depletion in highly incompatible elements (Zr, La, and Ce) than in moderately incompatible elements (Y, Ti, and Sm).…”

Section: Resultssupporting

confidence: 79%

“…A number of preliminary studies of igneous basalt compositions from the upper part of Hole 504B have been published on major element microprobe analyses of fresh glasses (Natland et al, 1983;, major and trace element whole-rock compositions (Autio and Rhodes, 1983;Marsh et al, 1983;Etoubleau et al, 1983;Sharaskin et al, 1983;Hubberton et al, 1983;Emmermann, 1985;Tual et al, 1985), rare earth element analyses (Autio and Rhodes, 1983;Etoubleau et al, 1983;Sharaskin et al, 1983;Tual et al, 1985;Emmermann, 1985), and isotopic analyses (Barrett and Friedrichsen, 1982;Barrett, 1983;Friedrichsen, 1985). Although all of these studies show an unusual depletion in incompatible elements (Ti, Zr, Nb, La, Ce, etc.…”

Section: Introductionmentioning

confidence: 99%

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Geochemistry of Leg 111 Basalts: Intrusive Feeders for Highly Depleted Pillows and Flows

Autio¹,

Sparks²,

Rhodes³

1989

Proceedings of the Ocean Drilling Program

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Fifty samples of basalt recovered during ODP Leg 111 from the dikes (Layer 2C) of Hole 504B (1350.0-1562.3 m below seafloor) were analyzed by X-ray-fluorescence techniques. All of the samples are highly depleted in magmaphile elements relative to other mid-ocean ridge basalts, with Ti0 2 = 0.75-1.24 wt%, Na 2 0 = 1.59-2.22 wt%, Zr = 38-64 ppm, Nb = 0.3-1.5 ppm, and Y = 20-30 ppm (for samples containing 0%-2% phenocrysts), but have ratios of highly incompatible elements similar to normal Type I mid-ocean ridge basalts (e.g., Zr/Nb > 30). Abundances of compatible elements are similar to those of typical mid-ocean ridge basalts, with MgO = 7.2-9.2 wt%, Fe 2 0 3 * = 9.3-12.5 wt%, Ni = 55-164 ppm, and Cr = 26-388 ppm. Approximately 2% of the samples recovered from the top part of Hole 504B are similar to normal Type I or Type II ocean floor basalts. However, all of the analyzed Leg 111 samples from Hole 504B are depleted basalts. Aphyric dike rocks from Leg 111 are virtually identical to the depleted aphyric samples recovered from the pillow lavas and dikes in the upper 1075 m of Hole 504B during DSDP Legs 69, 70, and 83, with the exception of elements readily altered by seawater (Sr, Rb, and K). These elements reach a maximum in both abundance and variability in the pillow lavas of the upper 571.5 m of Hole 504B and decline to more constant values in the dike system sampled on Legs 83 and 111, apparently as a result of a decrease in porosity and increase in alteration temperatures relative to the pillow lavas. Based on compositional similarities to the vast majority of the pillows and flows, the dikes sampled on Leg 111 appear to be the feeder system for the pillow lavas in the upper part of Hole 504B. The incompatible-element-depleted compositions of the Costa Rica Rift Zone basalts are consistent with multistage melting of a normal mid-ocean ridge source.

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Section: Resultssupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Geochemistry of Leg 111 Basalts: Intrusive Feeders for Highly Depleted Pillows and Flows

Autio¹,

Sparks²,

Rhodes³

1989

Proceedings of the Ocean Drilling Program

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“…To summarize, smectites are the main water bearing alteration mineral down to approximately 580 mbsf, while chlorite and chlorite-smectite mixtures are dominant in the rest of the hole, with amphiboles becoming very common below 900 mbsf. The H2 O+ weight fraction measured by different authors [Hubberten et al, 1983;Sharaskin et al, 1983;Emmermann, 1985;Alt and Emmermann, 1985] is low down to approximately 836 mbsf, thus suggesting a low degree of alteration, and then increases in the lower part of the hole. As a consequence, this trend is reflected by the apparent porosity curve computed from the oxide measurements (Figure 8).…”

Section: Sitesmentioning

confidence: 94%

Effect of alteration, formation absorption, and standoff on the response of the thermal neutron porosity log in gabbros and basalts: Examples from Deep Sea Drilling Project‐Ocean Drilling Program Sites

Broglia¹,

Ellis²

1990

J. Geophys. Res.

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DARWIN ELLIS Schlumberger-Doll Research, Ridgefield, ConnecticutThis study focuses on the effects of hydrous alteration minerals, formation absorption, and standoff on the response of the thermal neutron porosity log in the basaltic and gabbroic rocks logged at sites 395,418,504, 642, and 735 during the Ocean Drilling Program. The concentration of hydrogen present in the rocks in the form of free water (pore space) and bound water (hydrous minerals) is the primary factor controlling the neutron elastic scattering process, while the presence of other elements, such as chlorine, gadolinium, boron, lithium, and samarium in the fluids and in the rock matrix can largely affect the thermal diffusion phase. These neutron absorbers cause an increase of the capture cross section, and in turn of the apparent thermal porosity. Further perturbations occur when the recording conditions depart from those under which the tool has been calibrated; a large and irregular hole diameter and a lack of eccentralization both produce erroneous porosity readings. The effect of hydrous alteration minerals on the thermal neutron porosity log has been estimated from 922 core oxide measurements using an analysis program that calculates the slowing-down length and converts it into apparent porosity. The results show that the computed apparent porosity ranges from less than 1% in fresh basalts and gabbros to about 30% in highly altered units. Depending on the alteration mineral assemblage, natural gamma ray, capture cross section, or hydrogen logs have been used to continuously predict the effect of bound hydrogen at each site. Corrected porosities generally show excellent agreement with core data for massive units, whereas they are higher for pillow basalts and fractured zones. The discrepancy is interpreted as the result of (1) difference in the volume of rock investigated (core specimens do not sample large vugs and fractures) and (2) frequent variations in the hole size and lack of tool contact with the borehole wall (standoff), not completely accounted for in the corrections. High capture cross section values measured on selected basalt samples seem to be associated with more altered basalts, suggesting a larger concentration of strong neutron absorbers in secondary minerals. The concentrations of elements with large capture cross section (E) measured at three of the five sites studied yield a maximum increase of 1% in the apparent neutron porosity. This is too low to explain the porosity values, some greater than 7%, observed in some of the fresh and unfractured massive units. A 1-to 2-inch standoff due to the lack of eccentralization of the tool string used in the Ocean Drilling Program is considered the most probable cause of such discrepancy. This interpretation is confirmed by the neutron porosity values recorded at site 735, where the nuclear string was for the first time fully eccentralized, and only a correction for borehole size and the presence of hydrous minerals has been applied. and Chiaromonte, 1983; Gilchrist et al.scientif...

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Redistribution of Cu, Zn, Pb and Ba in the Bollibokka Group, East Shasta, California, U.S.A.: Implications for metallogeny and geochemical balances

Eastoe

1992

Chemical Geology

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Major- and Trace-Element Chemistry of Hole 504B Basalts and Their Alteration Products (Costa Rica Rift, Deep Sea Drilling Project Leg 70)

Cited by 9 publications

References 12 publications

Geochemistry of Leg 111 Basalts: Intrusive Feeders for Highly Depleted Pillows and Flows

Geochemistry of Leg 111 Basalts: Intrusive Feeders for Highly Depleted Pillows and Flows

Effect of alteration, formation absorption, and standoff on the response of the thermal neutron porosity log in gabbros and basalts: Examples from Deep Sea Drilling Project‐Ocean Drilling Program Sites

Redistribution of Cu, Zn, Pb and Ba in the Bollibokka Group, East Shasta, California, U.S.A.: Implications for metallogeny and geochemical balances

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