Palaeomagnetic Studies of Miocene Ignimbrites from Nevada

Abstract

A detailed palaeomagnetic study of a single ignimbrite shows marked variations in intensity, susceptibility, Koenigsberger ratio Q, and direction of magnetization. The behaviour of the intensity and Q can in part be explained as a change in grain size. A second profile through part of the same flow agrees well in its scalar properties, but the directions are very different. Six to fourteen samples have been collected from each of six additional ignimbrites in the same sequence. Their magnetic stability has been established by a.c. demagnetization and by lateral consistency over a distance of 60 km. Of all flows four are normally magnetized while the remainder have reversed polarity. The palaeomagnetic poles of two of these ignimbrites lie at 33°N and 49°N, the others lie within 20° of the rotational pole. Six of these ignimbrites have K‐Ar ages between 29.7 and 17.8 My. Copyright © 1970, Wiley Blackwell. All rights reserved