Remanent magnetic directions of some dykes from southern West Greenland

During the summer of 1965 Survey geologists collected 57 oriented samples from 25 dykes for palaeomagnetic investigations. The main problem was to see if palaeomagnetic methods could be used to distinguish dyke swarms of different ages. Of the 25 dykes, two were thought to be "Trap Diabase" (TD) dykes of late Phanerozoic age and seven dykes were thought to be Gardar in age (ca. 1100 m.y.); the other dykes were all of uncertain age.</jats:p

Some outstanding assumptions in geophysical studies of the Earth

AbstractThree examples of incorrect or incomplete assumptions are considered. (1) The oceanic geothermal gradient was originally established using an assumed temperature at the boundary between the rigid lithospheric tectonic plate and the underlying plastically deforming asthenospheric mantle. Revising this invalid temperature assumption has major implications for the concentration of radio-active elements within the mantle, convective patterns and the rate of cooling of the Earth, etc. (2) The earliest 19th century spectral observations of the surface of the Sun identified meteoritic components. This was plausible as Sunspots were thought to be meteoritic impacts, but are now known to be of internal origin. The Sun has no meteoritic materials and its age and origin require major revision. (3) Astronomical changes in the position of objects in the solar system provide causative mechanisms for periodicities in many Earth processes – climate, sea-level, sea-floor spreading, volcanism, etc. Unexplained spectral features probably originate from effects due to the same bodies influencing the solar processes that then affect the magnitude and nature of solar radiation, solar wind, electromagnetic storms, etc., reaching the Earth’s upper atmosphere

Archaeomagnetic study of the Late Minoan Kiln 2, stratigraphical museum extension, Knossos

Analysis of 26 oriented samples shows a clear, distinct, stable magnetic remanence in 25 of them. The magnetic carrier is probably 1 mm diameter magnetite and the remanence has thermal characteristics. On this basis, the direction of the geomagnetic field was 355.2°, 60.9° α95 = 1.7° and its intensity was 67 + 8 μT at the time when the kiln was last fired in Late Minoan IB (LMIB) times. The directional parameters are identical to those of LMIB destruction levels in central Crete and with the Minoan Plinian ash layer on Thera, but the mean direction differs from those of LMIB destruction sites in eastern Crete and those of the base surge and higher Minoan volcanic ash deposits on Thera. It is considered that the kiln was last fired at an almost identical time to the LMIB destruction levels of central Crete which appears to have occurred several years before the LMIB destruction levels in eastern Crete.</jats:p