| 岩浆包裹体的成因和意义 |
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| ORIGIN AND SIGNIFICANCE OF MAGMATIC INCLUSIONS |
| The study of physico-chemical variations and thermodynamic conditions in the course of formation of magmatic rocks has become the basis of modern theoretical magmatic petrology. The magmatic inclusion in magmatic minerals is an ideal object of studying the crystallization evolution of natural magma. The magmatic inclusions have effectively conserved a lot of physico-chemical information: temperature, pressure, volatile components and chemical composition of magmatic media during the formation of their host minerals. The magmatic inclusions are the faithful recorders of the crystallization history of their host minerals.Magmatic inclusions are generally trapped within crystals growing in a magma as a result of some irregularity in growth conditions. According to the study of magmatic inclusions, the author proposed a new plan of genetic classification of magmatic inclusions: in the light of the evolution degree of the included silicate melt after closing of cavity, the magmatic inclusions canbe distinguished into two categories--non-slightly evolved and evolved. Fornonslightly evolved magmatic inclusions the crystallization of magma has taken place near the surface (depth<6 km, lithostatic pressure<2 kb) and cooling of their host minerals is very fast (explosive projections, pumices, hyaloclastites),and the trapped silicate melt could remain in equilibrium with host minerals and was congealed under form of glass. The evolved magmatic inclusions have formed either in depth (P>2 kb)or near the surface.In the first case, their host minerals have undergone a slow cooling and decompression with the ascension of magma; in the second case, their host mineral crystals were situated within a thick basic lava flow or an acidic dome and they have also undergone a slow cooling. In this sort of conditions, the trapped silicate melt could not remain in equilibrium with the host minerals, and there have occurred a series of evolutions within the magmatic inclusions after they have been closed. The evolutions after closing of cavity are translated by the crystallization of various "daughter minerals". There is a close relation between the characters of magmatic inclusions and the history and the conditions of formation of their host minerals.The homogenization temperature of magmatic inclusions may represent the crystallization temperature of their host minerals. At present the homogenization thermometry has already become a classic and indispensable method in the study of magmatic inclusions. In order to obtain the significant thermometric data, we have to pay attention to the following three problems. 1 ) It is necessary for us to choose the inclusions, which didn't take any form of "leakage", as the object of thermometry study. 2) The homogenization thermometry study of magmatic inclusions has to follow a thermometrical rule. For acidic lavas, the total time of an experiment is about 8-12 hours with a time of stabilizing the temperature of 1.5-2 hours (for realizing the homogenization equilibrium of magmatic inclusions); for intermediate lavas, the total time of an experiment is about 4-8 hours with a time of stabilizing the temperature of 20-25 minutes; for basic lavas, the total time of an experiment is about 2-4 hours with a time of stabilizing the temperature of 5-10 minutes; for ultrabasic lavas, the total time of an experiment is about 2 hours with a time of stabilizing the temperature of 2-5 minutes. 3 ) Pressure correction of the homogenization temperature. For the non-slightly evolved magmatic inclusions, the relative incompressibility of silicate melts and the generally low pressures of most of the igneous environments involved in this type of inclusion studies make such corrections negligible at this time. For the evolved magmatic inclusions which have formed in depth, a pressure correction should be added to the homogenization temperature to obtain the true trapping temperature.For the barometry study of magmatic inclusions there are generaly two methods:direct and indirect. |
| XIA Lin-qi.1985.ORIGIN AND SIGNIFICANCE OF MAGMATIC INCLUSIONS[J].Acta Geoscientica Sinica,7(1):55-77. |
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