William I. Manton

Cytoarchitectonic distribution of zinc in the hippocampus of man and the rat

Zinc was measured in whole hippocampus and in hippocampal sub-regions by stable-isotope dilution mass spectrometry. In both man and the rat, the most zinc (102-145 ppm, dry weight) was found in the hilar region, the least (27-35) in the fimbria. The amount of zinc directly associated with mossy-fiber axons was estimated to be approximately 8% of the total zinc in the hippocampus, and the concentration of mossy-fiber zinc was estimated at 220-300 microM. Methodological and theoretical implications of the quantitative findings were discussed.

A new correlation of sapphirine granulites in the indo-antarctic metamorphic terrain: Late proterozoic dates from the eastern ghats province of India

Abstract Uranium-lead and thorium-lead ages were obtained from perrierite and zircons in two samples from the Eastern Ghats Province of South India, a sapphirine-bearing granulite from Anakapalle and a charnockite from Visakhapatnam. The isotopic data are concordant or close to concordant at 1 Ga, which is interpreted to be the age of granulite-facies metamorphism and charnockite plutonism in the vicinity of Anakapalle and Visakhapatnam, and provides the first report of a late Proterozoic granulite-facies event in the Eastern Ghats Province. In reassemblies of Gondwanaland based on DuToits original proposal, the Eastern Ghats Province is juxtaposed against a high-grade terrain in East Antarctica affected by a granulite-facies event and charnockitic plutonic activity 800–1100 Ma ago. The ages reported here suggest that a portion of the Eastern Ghats Province represents an extension of the late Proterozoic terrain from Antarctica into India. The radiometric results on the Anakapalle rocks are the first evidence in South India for sapphirine formation during the late Proterozoic; other South Indian sapphirine localities appear to be Archaean in age. A review of sapphirine localities in the Indo-Antarctic metamorphic terrain indicates that sapphirine developed under a range of pressure-temperature conditions during the Archaean and Proterozoic. Evidence for a systematic change in peak metamorphic conditions with time is obscured by these regional variations. Characterization of the entire pressure-temperature path, in addition to estimates for the peak conditions, is needed to distinguish the Archaean and Proterozoic metamorphic regimes.

Release of lead from bone in pregnancy and lactation

Concentrations and isotope ratios of lead in blood, urine, 24-h duplicate diets, and hand wipes were measured for 12 women from the second trimester of pregnancy until at least 8 months after delivery. Six bottle fed and six breast fed their infants. One bottle feeder fell pregnant for a second time, as did a breast feeder, and each was followed semicontinuously for totals of 44 and 54 months, respectively. Bone resorption rather than dietary absorption controls changes in blood lead, but in pregnancy the resorption of trabecular and cortical bone are decoupled. In early pregnancy, only trabecular bone (presumably of low lead content) is resorbed, causing blood leads to fall more than expected from hemodilution alone. In late pregnancy, the sites of resorption move to cortical bone of higher lead content and blood leads rise. In bottle feeders, the cortical bone contribution ceases immediately after delivery, but any tendency for blood leads to fall may be compensated by the effect of hemoconcentration produced by the postpartum loss of plasma volume. In lactation, the whole skeleton undergoes resorption and the blood leads of nursing mothers continue to rise, reaching a maximum 6-8 months after delivery. Blood leads fall from pregnancy to pregnancy, implying that the greatest risk of lead toxicity lies with first pregnancies.

Age of Feiran basement rocks, Sinai: implications for late Precambrian crustal evolution in the northern Arabian–Nubian Shield

Basement exposed on the perimeter of the Red Sea was created during the Pan-African event at the end of the Precambrian. Pre-Pan-African crust in the northern part of this region has not yet been identified. This paper reports the results of Rb–Sr whole-rock and U–Pb zircon dating of gneisses and related basement units from the Wadi Feiran area in the Sinai peninsula, where the existence of such older basement has previously been suggested. A post-tectonic extensional dyke gives a Rb–Sr age of 591 ± 9 Ma with an initial 87Sr/86Sr ratio of 0.7034 ± 0.0002. Rb–Sr whole-rock and thin slab dating of paragneisses gives ages of c. 610 Ma with an initial 87Sr/86Sr ratio of 0.7035. A U–Pb zircon age of 632 ± 3 Ma is interpreted as either the time of formation of these gneisses or the age of the crust sampled by protolith sediments. Granodiorite to the east gives a U–Pb zircon age of 782 ± 7 Ma and is interpreted as representing the westernmost extent of a 780 ± 50 Ma terrane that extends across Sinai into Jordan. Uplift and erosion of the 780 ± 50 Ma terrane supplied detritus to flanking terranes in N and SE Sinai. This region thus acted as a foreland to the younger accretionary and extensional units to the south and west that were active later in the Pan-African event. There is still no evidence for pre-Pan-African basement in the Precambrian units around the northern Red Sea east of the Nile.

Geochronology of the late Precambrian Hamisana shear zone, Red Sea Hills, Sudan and Egypt

The Hamisana shear zone (HSZ) is a broad zone of deformation, approximately 50 km wide and at least 300 km long, making it one of the largest basement structures in NE Africa. It has been interpreted as a Precambrian suture, as a zone of strike-slip displacement, or as a zone of crustal shortening. The results of new Rb-Sr and U-Pb zircon geochronological studies indicate that the northern HSZ was thermally active during the Pan-African event until c. 550 Mg ago; initiation of the structure may have begun 40–110 Ma earlier. All units have low initial 87Sr/86Sr ratios, indicating juvenile derivation. The timing of activity in the HSZ is 50–150 Ma younger than collisional suturing and terrane assembly in the Arabian-Nubian Shield but is similar to the 655–540 Ma Najd fault system of Egypt and Arabia. Deformation and metamorphism along the HSZ clearly post-date terrane accretion and probably are closely related to the Najd tectonic cycle. The most important deformation of the HSZ is unrelated to suturing, and at least one late Precambrian suture must extend west from Arabia into the interior of N. Africa.

Archean rocks in antarctica: 2.5-billion-year uranium-lead ages of pegmatites in enderby land.

Uranium-lead isotopic data indicate that the granulite-facies Napier complex of Enderby Land, Antarctica, was cut by charnockitic pegmatites 2.5 billion years ago and by pegmatites lacking hypersthene 0.52 billion years ago. The 4-bil-lion-years lead-lead ages (whole rock) reported for the Napier complex are rejected since these leads developed in three stages. Reconstructions of Gondwanaland suggest that the Napier complex may be a continuation of the Archean granulitic terrain of southern India.

Stable-isotope dilution measurement of zinc and lead in rat hippocampus and spinal cord

Abstract Zinc and lead concentrations in hippocampus and spinal cord of rats were measured using the highly-accurate method of stable isotope dilution mass-spectrometry. In hippocampus, average zinc concentration was 72.7 ppm (dry weight), average lead, 0.053 ppm; in spinal cord, zinc averaged 26.1 ppm, lead, 0.018 ppm. Possible explanations for apparent overestimations of rat CNS metal content in previously publisjed work were discussed.

Some Pb and Sr isotopic measurements on eclogites from the Roberts Victor mine, South Africa

Abstract Five nodules of eclogite, one nodule of garnet peridotite and one sample of kimberlite from the Roberts Victor mine were analyzed for concentrations of U, Th, Pb, Rb and Sr and isotopic compositions of Pb and Sr. In the eclogites, U content ranges from 0.09 to 0.26 ppm, Th from 0.35 to 1.1 ppm, Pb from 0.79 to 5.5 ppm, Rb from 2.1 to 28 ppm and Sr from 133 to 346 ppm; 206 Pb/ 204 Pb ratios range from 14.8 to 18.5, 207 Pb/ 204 Pb from 14.9 to 15.7, 208 Pb/ 204 Pb from 35.2 to 38.5. The garnet peridotite contains 0.22 ppm U, 0.97 ppm Th, 1.05 ppm Pb, 6.9 ppm Rb and 108 ppm Sr and the kimberlite contains 2.5 ppm U, 30 ppm Th, 37 ppm Pb, 113 ppm Rb and 2040 ppm Sr. The lead in the eclogites has two components, a lead pyroextractable at 1100–1200° and a non-pyroextractable residual lead. In three of the eclogites, which are to some extent altered, a proportion of the pyroextractable lead may be contaminating lead from the kimberlite, but an altered kyanite eclogite does not appear to be contaminated by this same kimberlite. The pyroextractable lead from a less altered eclogite contains a much larger proportion of 206 Pb. Compositions calculated for the residual leads vary greatly. In many of the pyroextraction runs the primary eclogitic phases disappeared and the new phases plagioclase, clinopyroxene and a magnetic iron compound were formed. Why part of the lead should have been retained by these new phases is not understood.

U-Pb data on granulite facies rocks from fold island, Kemp Coast, East Antarctica

Abstract The northern tip of Fold Island (67°16′S; 59°20′E) on the Kemp Coast is composed largely of quartzofeldspathic gneisses (charnockitic and enderbitic) and pyroxene granulite. Garnet-biotite-sillimanite gneiss, garnet-clinopyroxene-plagioclase-calc-silicate rock, magnetite-bearing rocks, and ultramafic rocks are very subordinate. The gneisses were deformed by the two phases of isoclinal folding and were subsequently intruded by mafic dikes. A second stage of deformation involving tight, ductile folding post-dates the dikes. This deformation culminated with the emplacement of hypersthene-bearing pegmatites in discordant planar veins and irregular masses, and with the hornblende-granulite facies metamorphism that resulted in the present-day mineral assemblages. U-Pb isotope data on zircon and monazite from two pegmatites define a chord intersecting concordia at 0.94 ± 0.08 Ga and 0.21 ± 0.21 Ga. The 0.94 Ga age dates deformation, granulite facies metamorphism, and the pegmatite emplacement of Stage II. U-Pb data on a total of five fractions of highly rounded zircons from two quartzofeldspathic gneisses define a chord with intersections at 3.08 ± 0.17 Ga and 0.82 ± 0.48 Ga. Our results suggest that the gneiss zircons are xenocrysts and do not provide any direct indication of the age of the host gneisses. The Fold Island gneisses are interpreted to be older (Napier Complex?) rocks that were reworked during the Late Proterozoic (∼ 1000 Ma) Rayner event. A similar sequence of events has been reported for a coastal portion of the Eastern Ghats Province of South India, suggesting that these two areas were part of the same metamorphic complex in Gondwanaland.

Stable isotope identification of lead sources in preschool children--the Omaha Study.

The objective was to determine, from analysis of the naturally occurring stable isotopes of lead, the relative contribution of food, handdust, housedust, soil and air lead to the absorbed (urinary) lead and the blood lead of children living in a former smelter city. A longitudinal 12 month study was conducted of 21 children, 2 - 3 years of age, living in central Omaha, balanced for race, gender and socioeconomic status. Field clean samples were collected monthly of 24 hour duplicate diet, handwipe and urine, with quarterly blood lead, annual environmental lead, weekly air for total lead and 206Pb, 207Pb and 208Pb by thermal ionization/mass spectrometry with a 205Pb spike in a Class II laboratory. Despite residence in a smelter city each child had a unique isotopic ratio of handwipe, blood and urine lead, the latter being identical. There was no correlation of handwipe isotopic ratio with proximity to a lead emission source or to the decade of the housing stock. The isotopic ratio of the annual mean handwipe lead predicted 43% of the variance of the annual mean blood and urine lead ratio (r2 = .43; p = .001). Handwipe lead ratios correlated (p < or = .05) with those of the windowsills and air ducts. The mean isotopic ratios of blood and urine lead were lower than those of handwipe and food, consistent with a contribution by endogenous bone lead. Clean catch urine provides a noninvasive index of blood lead isotopic ratio in children, as in adults.