Nd, Pb, and Sr isotope composition of juvenile magmatism in the Mesozoic large magmatic province of northern Chile (18–27°S): indications for a uniform subarc mantle

The Jurassic to Early Cretaceous magmatic arc of the Andes in northern Chile was a site of major additions of juvenile magmas from the subarc mantle to the continental crust. The combined effect of extension and a near stationary position of the Jurassic to lower Cretaceous arc favoured the emplacement and preservation of juvenile magmatic rocks on a large vertical and horizontal scale. Chemical and Sr, Nd, and Pb isotopic compositions of mainly mafic to intermediate volcanic and intrusive rock units coherently indicate the generation of the magmas in a subduction regime and the dominance of a depleted subarc mantle source over contributions of the ambient Palaeozoic crust. The isotopic composition of the Jurassic (²⁰⁶Pb/²⁰⁴Pb: ∼ 18.2; ²⁰⁷Pb/²⁰⁴Pb: ∼ 15.55; ¹⁴³Nd/¹⁴⁴Nd: ∼ 0.51277; ⁸⁷Sr/⁸⁶Sr: ∼ 0.703–0.704) and Present (²⁰⁶Pb/²⁰⁴Pb: ∼ 18.5; ²⁰⁷Pb/²⁰⁴Pb: ∼ 15.57; 143Nd/144Nd: ∼ 0.51288; ⁸⁷Sr/⁸⁶Sr: ∼ 0.703–0.704) depleted subarc mantle beneath the Central and Southern Andes (18°–40°S) was likely uniform over the entire region. Small differences of isotope ratios between Jurassic and Cenozoic to Recent of subarc mantle-derived could be explained by radiogenic growth in a still uniform mantle source.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Application of a circulation and transport model system to the dispersal of herring larvae in the North Sea

A model system consisting of a three-dimensional circulation and transport model is used to simulate the dispersal of herring larvae in the North Sea. The driving forces of the circulation model are theM₂-tide, time dependent wind stress and air pressure fields, as well as monthly climatological density fields interpolated on a daily basis. The transport model includes advection as well as diffusion and uses a tracer technique to pursue the larvae in the time and space domain. Furthermore, the transport model incorporates a simulation of active vertical movement of the larvae as vertical migration has a marked effect on the drift route of the larvae.Simulated North Sea currents are compared to observed currents gained during the Autumn Circulation Experiment (ACE) which took place from August 1987 to March 1988. The variability in observed currents at the location of the moorings is found to be larger than in the simulated currents. On a larger scale, the simulated circulation in the northern North Sea shows a close correspondence to the inferred circulation from a quasi-synoptic hydrographic survey. The quality of the predictions of larval transport and distribution patterns by the model system is tested using sequential larvae distributions observed during ACE. Common features and discrepancies of observed and simulated distributions are discussed and conclusions for further field investigations and modelling studies are drawn.     

Five new species of Halacaridae (Acari) from New Zealand

In the Cape Rodney to Okari Point Marine Reserve, Goat Island Bay, Auckland, New Zealand, several halacarids were collected on an intertidal flat. The mites were found associated with encrusting bryozoans, sponges, and lithothamnia. Five mites—Rhombognathus lacunosus n.sp., Rhombognathus fractus n.sp., Halacarus nitidus n.sp., Agauopsis similis n.sp., and Agaue insignata n.sp.—are described, illustrated, and compared with related species.     

The east-west asymmetry in the number of spot-groups in relation to their classification

It is shown that the east-west asymmetry is quite different for spot-groups of different classes of evolution and that there exists a conspicuous difference between the ascending and descending branches with regard to the east-west asymmetry and the asymmetry between corresponding lunes. Some results point to the existence of systematic errors in the classification of the spot-groups.