Critical evaluation of segregation vesicles in mid-ocean ridge basalts as a rock orientation tool (palaeomagnatism)

Segregation vesicles in seafloor basalts generally are spherical in shape, and partly filled with a dark, cup-shaped meniscus of chilled residual melt. The orientation of the meniscus can be used as an indicator of the cooling orientation of the rock. Results of statistical tests on samples previously oriented by megascopic geopetal features indicate that the meniscuses in segregation vesicles of a given rock sample are preferentially oriented about the earth's gravity field, as indicated by the megascopic features. As well, the distributions of magnetic inclinations of rocks oriented by megascopic features and segregation vesicles are similar. The segregation vesicle technique can be used to orient dredge and submersible samples for paleomagnetic polarity studies and to determine the dip and predeformational magnetic inclination of rocks recovered in drill cores, which have a known, in-place vertical orientation, if care is taken to select samples properly. A simple method for application of this technique is presented. - from Author