Isotopic evidence for Late Cretaceous plume-ridge interaction at the Hawaiian hotspot

When a mantle plume interacts with a mid-ocean ridge, both are noticeably affected. The mid-ocean ridge can display anomalously shallow bathymetry, excess volcanism, thickened crust, asymmetric sea-floor spreading and a plume component in the composition of the ridge basalts. The hotspot-related volcanism can be drawn closer to the ridge, and its geochemical composition can also be affected. Here we present Sr-Nd-Pb isotopic analyses of samples from the next-to-oldest seamount in the Hawaiian hotspot track, the Detroit seamount at 51 degrees N, which show that, 81 Myr ago, the Hawaiian hotspot produced volcanism with an isotopic signature indistinguishable from mid-ocean ridge basalt. This composition is unprecedented in the known volcanism from the Hawaiian hotspot, but is consistent with the interpretation from plate reconstructions that the hotspot was located close to a mid-ocean ridge about 80 Myr ago. As the rising mantle plume encountered the hot, low-viscosity asthenosphere and hot, thin lithosphere near the spreading centre, it appears to have entrained enough of the isotopically depleted upper mantle to overwhelm the chemical characteristics of the plume itself. The Hawaiian hotspot thus joins the growing list of hotspots that have interacted with a rift early in their history.     

Peripheral vascular effects of histamine administered into the cerebral ventricles of anaesthetized cats

Zusammenfassung An narkotisierten Katzen wurden der arterielle Blutdruck und der venöse Ausfluss aus der Vorderpfote oder aus dem Hinterbein registriert. Injektionen von Histamin in die Hirnventrikel bewirkten Erhöhung des Blutdruckes und Vasokonstriktion in der Vorderpfote. Im Hinterbein war die Vasokonstriktion weniger ausgesprochen. Auch nach Entfernung der Nebennieren war der Pressoreffekt vorhanden, woraus folgt, dass die periphere Vasokonstriktion für den durch intraventrikuläres Histamin hervorgerufenen Pressoreffekt verantwortlich ist.

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This work was supported by the Swedish Medical Research Council (Project No. W 349). Rheomacrodex was kindly supplied by Pharmacia, Uppsala (Sweden).     

Isolation of sodium-complexing polypeptides from mammalian blood and cardiac muscle

Summary Two distinct polypeptides have been isolated from rat heart and ox blood. They are both found to be effective in forming complexes with sodium ions, and it is suggested that they may have a function in stabilizing sodium ion activity.Acknowledgments. We are indebted to ProfessorG. A. Gilbert, F.R.S. and to Dr.C. J. Lote for helpful discussion, and to the Royal Society for a Grant-in-aid which in part supported the investigation.