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Yehuda Ben-Zion 《Geophysical Journal International》1990,101(3):507-528
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Throughgoing fractures play a major role in subsurface fluid flow yet the kinematics of their formation, which directly impact rock flow properties, are often difficult to establish. We investigate throughgoing fractures in the Monterey Formation of California that developed by the coalescence of pre-existing joints. At Lompoc Landing, throughgoing fractures fall into three main groups: linked, linked with aperture, and breccia zones. The segmented nature of their walls provides numerous piercing points to firmly establish the sense of displacement. Analysis of displacement vectors derived from piercing points demonstrates that the NW–SE trending throughgoing fractures, often interpreted as strike–slip faults, are in fact extensional structures in origin. We suggest that this method may be applied to throughgoing fractures that form by the same mechanism in other geologic settings. Establishing kinematics of throughgoing fractures will lead to a better understanding of their contribution to subsurface fluid flow. 相似文献
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The migmatite complex of the Magrish area is part of a large crystalline massif south of Elat. The mineralogical composition of the migmatites is very uniform. The components of the melanosome are biotite, quartz and plagioclase, with small amounts of garnet and very rarely sillimanite and those of the leucosome — quartz and plagioclase. On the basis of chemical composition of the migmatites and possible premigmatitic parent rocks, absence of orthoclase in the leucosome, similar composition of plagioclase in the leucosome and in neighbouring melanosome, and Qz:Plag values which do not plot around a cotectic line, it is concluded that migmatisation occurred in a nearly closed system, without the presence of a melt phase. Thus, injection of granitic material, metasomatism or partial anatexis as possible main formation mechanisms are rejected and metamorphic differentiation is favoured. 相似文献
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Preferential release into solution of radionuclides that result from alpha decay is a contributor to natural isotopic disequilibrium. Such release is critical to geochemical understanding of alpha-decay products and would be an undesirable characteristic of solidified nuclear waste in deep geological formations. Spontaneous annealing of the radiation damage that is responsible for the preferential release is shown to diminish the effect in thorianite and uraninite which we have found to be 550 to 1000 M.y. old, respectively. Leaching experiments and measurements of the thorium and uranium isotopes show that there is strongly enhanced release of short-lived 228Th relative to 232Th, but only slight enhancement of long-lived 234U and 230Th relative to 238U and 232Th. These results are interpreted in terms of natural annealing of damage occurring on a time scale between the ~10 and 105 years of the alpha-decay products. With a simple assumption actual times for the survival of the enhanced leaching in these minerals are ~ 15,000 years. 相似文献
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