The Nature of the Crust of the Earth, with Special Emphasis on the Role of Plagioclase

  1. John G. Heacock
  1. A. L. Boettcher

Published Online: 15 MAR 2013

DOI: 10.1029/GM014p0261

The Structure and Physical Properties of the Earth's Crust

The Structure and Physical Properties of the Earth's Crust

How to Cite

Boettcher, A. L. (1971) The Nature of the Crust of the Earth, with Special Emphasis on the Role of Plagioclase, in The Structure and Physical Properties of the Earth's Crust (ed J. G. Heacock), American Geophysical Union, Washington D. C.. doi: 10.1029/GM014p0261

Author Information

  1. Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802

Publication History

  1. Published Online: 15 MAR 2013
  2. Published Print: 1 JAN 1971

ISBN Information

Print ISBN: 9780875900148

Online ISBN: 9781118664049

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Keywords:

  • Amphibolite and anorthosite;
  • Basalt-eclogite transformation;
  • Continental crust;
  • Crust-mantle system;
  • Oceanic crust;
  • Phase transformations;
  • Plagioclase;
  • Pressure-temperature projection

Summary

This paper is primarily a discussion of the evolution, composition, and structure of the crust-mantle system of the earth; we attempt to determine the nature of any layers, including high electrical-resistance and low seismic-velocity zones, within upper levels. Our concepts regarding the composition and structure of the crust and mantle are significantly influenced by our prejudiced view of the mechanisms by which the earth formed and evolved. A ‘hot-earth’ model in which the earth accreted from silicate-rich dust appears to be most nearly consonant with available geochemical data. This model implies that the crust evolved by crystal-liquid differentiation of a partially or wholly molten silicate mantle. Estimates of the composition of the lower crust range from intermediate to basic. On the basis of available experimental data for such compositions, we can say that melting cannot be responsible for continuous layering within at least the upper 30 km, but compositional changes and phase transformations could provide geophysically detectable layers within the crust and upper mantle. Within the oceanic crust, zones of acidic rocks and the transformation of basalts to rocks including those in zeolite, greenschist, and amphibolite facies may create continuous layers. In continental areas, layers possibly result from zones of amphibolite or even anorthosite, but the major seismically detectable layers probably occur at the first appearance of garnet at 0–40-km depth and at the disappearance of plagioclase at depths as great as 70–90 km, based on the behavior of plagioclase and selected basic and intermediate rock compositions in the laboratory at high temperatures and pressures.