Ian L. Gibson

NINETYEAST RIDGE (INDIAN-OCEAN) - A 5000 KM RECORD OF A DUPAL MANTLE PLUME

Data and observation from Drifting Program Leg 121 and plate-tectonic reconstructions indicate that the Ninetyeast Ridge (Indian Ocean) was derived from the interaction of a deep-seated Dupal hotspot and a nearby spreading-ridge axis. The 5000-km-long ridge, from lat 34°S to Rat 10°N, was drilled at three sites during Leg 121. About 178 m of basalt, >38 to >80 Ma, were recovered from a total penetration of ∼310 m. Shipboard petrographic and geochemical studies showed that each site has distinctive characteristics. Most of the cored lavas have a tholeiitic basalt composition. Incompatible-element abundanes and ratios show systematic trends, consistent with an origin for the Ninetyeast Ridge lavas by mixing between a depleted component-Indian Ocean mid-ocean ridge basalt-and an enriched component-oceanic-island basalt similar to that observed in the youngest alkalic basalts from the Kerguelen archipelago. Preliminary shore-based trace element abundance and isotopic data are compatible with this hypothesis, although Pb isotopes indicate the involvement of another component. The long-lasting and more or less continuous activity of the Kerguelen-Heard plume (ca. 115 Ma), now located under Heard Island, south of the Southeast Indian Ridge, provides evidence that the source of the Dupal anomaly is deep seated.

Crustal flexures and flood basalts

Abstract Five major flexures or downwarps in the earths crust are described. Each appears to be related to the extrusion of thick sequences of flood basalts extruded from long linear fissure systems. The flexures and associated volcanicity are perhaps related to large scale crustal deformation.

The interpretation of human hair trace element concentrations

Scalp hair samples collected from 86 Canadian elderly, non-institutionalized women (mean age 66.6 +/- 6.2 y) on two separate occasions ten weeks apart, were analyzed for Zn, Cu and Mn content. Fasting blood samples were also collected and serum Zn, Cu and albumin content determined. Median hair Zn, Cu and Mn and mean serum Zn and albumin concentrations were not significantly different at the pre- and post-study periods. Furthermore, hair Zn concentrations at the two sampling times were positively and significantly correlated as were hair Cu, hair Mn, serum Zn and serum albumin values. In contrast no significant correlation related the hair and serum Zn values and hair and serum Cu values at any time. The constancy of the hair Zn, Cu and Mn concentrations at the two sampling periods may reflect the homeostatic regulation which controls absorption and hence body trace element content. In addition, results indicate that, after careful laboratory washing, the effects of adventitious contamination on hair trace element content are small, and can be effectively ignored.

A study of inter- and intrasubject variability in seven-day weighed dietary intakes with particular emphasis on trace elements

In this study of inter- and intrasubject variance of trace element (TE) dietary intake data, 14 female university students recorded weighed, self-selected food intakes for seven consecutive days, starting on a randomly selected day of the week. Daily intakes of energy, dietary fiber, macronutrients, 7 vitamins, and Fe, Zn, Cu, Mn, and Se were calculated using food composition tables and literature values. Analysis of variance showed a significant weekend effect for energy and TE intakes that was reduced when data were expressed on the basis of nutrient densities. No day of the working week or training effect was noted for energy or any nutrient. The ratios of the inter- to intrasubject coefficient of variation for all the nutrients were surprisingly constant. However, the overall coefficients of variation—Fe, 36.5%; Zn, 45.7%; Cu, 43.7%; Mn, 58.2%, and Se, 52.7%—were markedly lower than for vitamin A (109.0%), Vitamin D (117.1%), and linoleic acid (82.2%), but slightly higher than those for energy (27.2%) and carbohydrate (30.1%). The widespread distribution of TE in the diets results in comparable reliability for dietary studies of TE and macronutrients. The 95% confidence intervals for mean individual TE intakes ranged from 25% (Zn) to 40% (Se). These relatively large uncertainties make it essential that any assessment of the significance of correlations between dietary TE intakes and biochemical indices takes into account the intra-individual variation associated with both variables.

An extensional fault model for the early development of greenstone belts, with reference to a portion of the Abitibi belt, Ontario, Canada

Abstract Detailed geological mapping of a small part of the Archaean Abitibi greenstone belt, northwestern Ontario, suggests that the mafic and ultra-mafic lavas were extruded in a submarine environment in which the volcanism was intimately associated with deformation of the growing volcanic pile. The deformation led to the subsidence and progressive tilting of the lavas and to the development of discontinuities. A review of selected areas of Quaternary volcanism suggests that subsidence of the lava pile during volcanism is not unusual and that activity is frequently also associated with normal faulting. In both volcanic and non-volcanic extensional regimes deformation is dominated by the development of listric faults. We argue that greenstone belts, such as the Abitibi, were formed in extensional regimes and we show that a simple geometric model involving fissure volcanism and synvolcanic rotation of the lavas on listric faults, accounts for the major primary features of greenstone belts and for some associated geophysical properties.

An improved multi-element measurement of mineral absorption in the piglet utilizing the fecal monitoring technique.

The fecal monitoring technique for measuring the absorption of Zn, Mn, Se, and Fe was studied in eight male piglets (mean±SEM birthweight (bw)=1695±50 g) using high resolution gamma spectrometry. Four d old piglets were fed a complete liquid milk diet for five d prior to the orogastric administration of an isotope dose (75Se,54Mn,59Fe, and65Zn) equilibrated with the liquid milk diet.51CrCl3 was used as a fecal marker but was found to be partially absorbed. Stool samples were collected daily for 15 d, counted, and then the daily fecal excretion was calculated. Results indicate that endogenous excretion for each of the isotopes was not constant but decreased exponentially with time. The pattern of endogenous excretion varied between elements. An improved method for calculating the endogenous excretion was therefore developed. This method is based on the pattern of endogenous excretion in three-four d old male piglets (mean±SEM bw=2060±75 g) injected intravenously with the same isotopes and on the level of endogenous excretion in orally fed animals in the postabsorptive phase of excretion. These findings have important implications for the estimation of endogenous excretion in future fecal monitoring absorption studies in order to minimize underestimation of true absorption.