Now showing items 51-60 of 82
Indirect crustal contamination: evidence from isotopic and chemical disequilibria in minerals from alkali basalts and nephelinites from northern Tanzania
(Springer-Verlag; Springer-Verlag Berlin Heidelberg, 1996-11)
Alkali basalts and nephelinites from the volcanic province of northern Tanzania contain pyroxene and nepheline that show evidence for chemical and/or isotopic disequilibria with their host magmas. Olivine, pyroxene, ...
Petrology, isotope characteristics, and K-Ar ages of the Maranhão, northern Brazil, Mesozoic basalt province
(Springer-Verlag, 1990-04)
Northern Brazil contains remnants of Mesozoic flood basalts and hypabyssal rocks that were apparently emplaced during tectonism related to opening of the Atlantic Ocean. Analyses and new K-Ar ages reveal that this ∼700x250 ...
Mobility and fractionation of rare earth elements in argillaceous sediments: Implications for dating diagenesis and low-grade metamorphism
(Elsevier, 1994-01)
We report Sm-Nd and Rb-Sr data for the fine fractions of Lower Paleozoic argillaceous rocks from Wales, UK and New York, USA, spanning the range of low-grade metamorphic conditions from the diagenetic zone (zeolite facies) ...
A strontium and neodymium isotopic study of Apollo 17 high-Ti mare basalts: Resolution of ages, evolution of magmas, and origins of source heterogeneities
(Elsevier, 1991-07)
A combined Sr and Nd isotopic study of 15 Apollo 17 high-Ti mare basalts was undertaken to investigate geochronological and compositional differences between previously identified magma types (A, B1, B2, and C). Whole-rock ...
Evolution of the upper mantle of the Earth's Moon: Neodymium and strontium isotopic constraints from high-Ti mare basalts
(Elsevier, 1994-11)
Isotopic studies of mare basalts have led workers to conclude that their sources are heterogeneous on both large and small scales. Furthermore, these studies have led workers to postulate that depletion within the lunar ...
Thermochronology of the Cornubian batholith in southwest England: Implications for pluton emplacement and protracted hydrothermal mineralization
(Elsevier, 1993-04)
The metalliferous ore deposits of southwest England are associated with biotite-muscovite granites that intruded upper Paleozoic sediments and volcanic rocks at the end of the Hercynian Orogeny. The hydrothermal mineralization ...
[delta]18O values, 87Sr/86Sr and Sr/Mg ratios of Late Devonian abiotic marine calcite: Implications for the composition of ancient seawater
(Elsevier, 1991-07)
Late Devonian (Frasnian) abiotic marine calcite has been microsampled and analyzed for 87Sr/86Sr ratios, [delta]18O and [delta]13C values, and minor element concentrations. Portions of marine cement crystals from the Alberta ...
Isotope and chemical microsampling: Constraints on the history of an S-type rhyolite, San Vincenzo, Tuscany, Italy
(Elsevier, 1994-01)
Fine scale heterogeneities in strontium isotope ratios, 40Ar-39Ar ages, and chemical composition have been determined for individual mineral grains and enclaves in the rhyolites of San Vincenzo, Italy. The rhyolites are ...
Modelling the petrogenesis of high Rb/Sr silicic magmas
(Elsevier, 1991-09-25)
Rhyolites can be highly evolved with Sr contents as low as 0.1 ppm and Rb/Sr > 2,000. In contrast, granite batholiths are commonly comprised of rocks with Rb/Sr 100. Mass-balance modelling of source compositions, ...
Origin and evolution of formation waters, Alberta Basin, Western Canada Sedimentary Basin. II. Isotope systematics and water mixing
(Elsevier, 1990)
Isotopic measurements (Sr, O, D) on formation waters from the Alberta Basin have been made, covering a stratigraphic range from Devonian to Upper Cretaceous. These measurements, combined with chemical compositional trends, ...