Model Calibration Techniques for Use with the Analytic Element Method

The combination of the analytic element method and a nonlinear parameter estimation technique forges a computationally efficient, information-rich, and cost-effective solution to the inverse ground-water flow problem. The recommended model calibration method uses a nonlinear least-squares objective, as quantified by misfitting the measured and modeled heads, and a modified Levenberg-Marquardt algorithm. As detailed and demonstrated by a steady-state regional aquifer model of Bemidji, Minnesota, automated calibration techniques make ground-water modeling feasible for a wider variety of projects where tight budgets and a lack of tools may have previously made such modeling inappropriate.     

Ti-rich komatiites from northern Norway

Komatiites of the Karasjok Greenstone Belt, northern Norway, show two unusual features: they have certain compositional differences compared with other komatiites, and they are largely volcaniclastic in origin. Their geological setting suggests that the komatiites were crupted into shallow water, thus permitting phreatomagmatic eruption, in a small ocean basin that opened in the Baltic Shield. The major oxides (except for TiO₂), the trace elements Y, Sc, V, heavy rare earth elements (HREE), Cr, Co, Ni and the platinum group elements (PGE) cover similar ranges to those observed in other komatiites, but TiO₂, Sm, Zr and Hf (Ti-associated elements, TAE) are enriched compared with abundances commonly reported for komatiites. Thus, the Karasjok komatiites have interelement ratios 2 to 3 times greater than chondritic between the TAE and the HREE, PGE, Sc, V, Y, Al (HRE-associated elements, HAE). The light rare earth elements (LREE), Ta and Th are enriched in some samples relative to Ti, Sm, Zr, and Hf, but are depleted in others. One group of rocks that is similar to the Karasjok komatiites both in terms of geological setting and geochemistry is the Baffin Bay picrites. The reason for the high concentrations of TAE in the Karasjok komatiites could be that they formed at lower degrees of partial melting than most komatiites. The greater-than-chondritic TAE/HAE ratios indicate that garnet was a residual phase during their formation, requiring that the melt formed at a pressure greater than 40 kb. A model involving decompression melting of a mantle plume rising in a rifting environment, can explain the main features of the Karasjok komatiites.     

Are Bushveld U-type parent magmas boninites or contaminated komatiites?

Three distinct categories of magmas — Bushveld U-type parent magmas, boninites, and siliceous high magnesium basalts from Archaean greenstone belts —share the distictive geochemical characteristics of high MgO (9%–19%), low TiO₂(less than 1%) and high SiO₂(greater than 52%). Boninites are generally thought to form by hydrous melting of metasomatized, previously depleted upper mantle, while siliceous high magnesium basalts (SHMB) in greenstone belts have recently been recognized as the products of combined fractionation and crustal contamination of komatiites. Both these mechanisms can apparently give rise to similar end products, and both mechanisms have been proposed for the petrogenesis of Bushveld U-type magmas.A detailed comparison of the three magma types, using data drawn from the literature, shows a broad area of overlap in major elements and most trace elements. U-type magmas are generally intermediate in composition between SHMB and boninites. U-type magmas differ significantly from boninites, and are more similar to SHMB, in three important respects: their relatively high abundances of rare earth elements and degree of light rare earth enrichment; higher FeO/MgO ratio for a given MgO content; and Sm/Nd isotopic systematics indicative of crustal contamination. BU magmas are therefore more likely to be extreme examples of contaminated komatiitic parents than primary boninitic mantle melts. The striking similarity in major element chemistry of the three groups may be due to the near-coincidence in compositional space of the mediumpressure, hydrous olivine-orthopyroxene phase boundary, which controls the composition of boninites, with the lowpressure anhydrous phase boundary which controls differentiated SHMB and U-type magmas.     

A review of kentriodontine dolphins (Cetacea; Deiphinoidea; Kentriodontidae): Systematics and biogeography

Abstract Fossil dolphins belonging to the extinct family Kentriodontidae are small to medium-sized toothed cetaceans, which probably include the ancestors of some living species. Kentriodontids are known from rocks of Late Oligocene to Late Miocene age in various parts of the world. Among kentriodontids, species in the subfamily Kentriodontinae (e.g. species of Kentriodon Kellogg, 1927) are the most ubiquitous and generalized; these are now known from latest Oligocene to earliest Miocene strata in New Zealand and Patagonia, and Middle Miocene deposits in Maryland, Virginia, California and Japan. The diversity, morphologies and distributions of Miocene species of Kentriodontinae seem to parallel those of the living species of mostly pelagic delphinids in the subfamily Delphininae, and the fossil group may have been an ecological or behavioral/functional counterpart of the latter. Kentriodontines are inferred to have been wide-ranging neritic to pelagic animals that ate small fish and other nectonic organisms; they were probably active echolocators, and might have formed large schools. They are relatively common as fossils and, therefore, are potentially useful for intercontinental correlations of marine deposits.