Notes on Piezo-remanent Magnetization of Igneous Rocks II

Open Access

1 January 1969

journal article
Published by Society of Geomagnetism and Earth, Planetary and Space Sciences in Journal of geomagnetism and geoelectricity

Vol. 21 (1) , 427-445
https://doi.org/10.5636/jgg.21.427

Abstract

Various characteristics of piezo-remanent magnetization of igneous rocks are experimentally demonstrated in small magnetic fields, H=0-10Oe., and under uniaxial compression comparable to the earth's crust stress, 0-100kg/cm². The main characteristics observed are as follows: (a) “After-effect” of uniaxial compression: J_R(P₊P₀H₊H₀). After a rock sample is uniaxially compressed in a non-magnetic space by a pressure P larger than a certain critical value (P_c), its IRM, J_R(P₊P₀H₊H₀), becomes larger than the ordinary IRM, J_R(H₊H₀), without such a pressure treatment. This after-effect of pressure takes place in both cases of P//H and P⊥H. Here [d/dPJ_R(P₊P₀H₊H₀)]_H=const>0 for P>P_c. (b) “Pressure demagnetization” effect: J_R(H₊H₀P₊P₀). After uniaxially compressing a rock sample having IRM, J_R(H₊H₀), in a non-magnetic space, the residual magnetization, J_R(H₊H₀P₊P₀), becomes appreciably smaller than the original intensity of J_R(H₊H₀) in both cases of P//H and P⊥H. Here [d/dPJ_R(H₊H₀P₊P₀)]_H=const0. (c) “Non-commutativity” of P and H. An inequality relationship expressed as J_R(H₊P₊P₀H₀)≥J_R(P₊H₊P₀H₀)>J_R(H₊P₊H₀P₀)≥J_R(P₊H₊H₀P₀) holds for all samples. In a magnetic field larger than a certain critical value, H*, J_R(P₊H₊H₀P₀)<J_R(H₊H₀), but in H<H* J_R(P₊H₊H₀P₀)>J_R(H₊H₀). J_R(H₊P₊P₀H₀) and J_R(P₊H₊P₀H₀) are always larger than J_R(H+H₀). The above argument holds in both cases of P//H and P⊥H. (d) A linear dependence of PRM on H. J_R(H₊P₊P₀H₀) is defined as piezo-remanent magnetization. In a range of small magnetic fields, J_R(H₊P₊P₀H₀)∞H for P=constant, though J_R(H₊H₀)∞H² in the

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