Problems with radioactive dating methods
Although references throughout the text were updated to reflect recent literature, the modest amendments and refinements of archival methods and practices proposed during the past three years have not required me fundamentally to revise my premises.The first four essays address the four fundamental activities involved in the management of the physical record: selecting an appropriate record from the great volume of evidence, preserving that record against time, describing the record that has been retained, and providing for access and use.Intelligent artifices are presented as a tool for expanding intellectual control, and consequently, access and use.Chapter six returns to the themes in the introduction to consider the role of the archivist and the nature of the archival endeavor, and to propose new views of both based on the ideas in the intervening chapters.
At Rum, the chromitites formed at the melting front between newly injected magma and the magma chamber floor, an analogous process but one driven by thermal, rather than chemical, energy. Many cumulates in layered intrusions contain plagioclase crystals that are compositionally zoned in terms of their major elements, and, less commonly, in their 87Sr/86Sr isotopic ratios.Increasingly I have felt that this is irresponsible of me, and am glad to be bringing it out for public scrutiny at this time.In the process, the first four chapters have been substantially rewritten, but the underlying structure of the argument, and its conclusions, have not been affected.Here, we illustrate how bulk magnetic fabric data, particularly from intrusions with sparse silicate-hosted magnetite, may be used to extend direct crystallographic observations from thin sections.We also present a scheme for characterizing crystallographic foliation and lineation and use this to suggest that the strength of gabbro plagioclase foliations and lineations varies significantly with geodynamic environment. Northeastern Fennoscandia hosts a rich diversity of mafic–ultramafic intrusions of variable shape and size, emplaced in different tectonic regimes over a period spanning ~600 million years (between 1.88 Ga and 2.5 Ga).