ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract At least sis or perhaps seven types of contact metamorphism may be distinguished in nature (see Table 1). They differ from each other by a set of metamorphic facies in the exocontact aureoles, also by thermodynamic conditions of metamorphism. The manifestation of some types of metamorphism depends chiefly on magma temperature and composition, on the initial temperature of the country rocks (prior to contact metamorphism) and on the depth of the intrusive formation. The movement of magma through the intrusive channel (chamber) and the kinetic peculiarities of metamorphism exert additional influence on metamorphic conditions. Since the temperature elevation with depth corresponds in a general way to the increase in the lithostatic pressure, the maximum temperature levels attained at the direct intrusive contact must differ for various pressure levels (or depths). The two series of contact metamorphic rooks may be distinguished by their pressure: 1. common hornfelsic rock low-pressure series (types of metamorphism 1–4, Table 1), and 2. thermal transformed gneissous rock series metamorphosed under moderately high pressure (types 5–6, Table 1). The initial temperature of the country rock is low in the first series. It may apparently be discounted in certain cases. The usual non-abyssal contact low-pressure metamorphism (the proper “ contact metamorphism”) depends essentially on magma temperature and composition, while in the second series, the initial temperature of the country rocks may be rather high. This and the effect of the intrusive heat and high lithostatic pressure results in rock transformation under conditions of the regional metamorphism of the facies (under moderately high pressure). Since superposition of the local temperature field on a regional high-temperature field in the neighbourhood of intrusives (in deep conditions) results in an increase in the thickness of the contact aureole, Ingersoll's criterion (the ratio of the thickness of the aureole to the thickness of the intrusive body) may be helpful for distinguishing abyssal from non-abyssal contact metamorphism. The values of this criterion cannot exceed 0.2–0.3 for the non-abyssal contact metamorphism.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00371278
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