| 其他摘要 | Thorough researches on clinopyroxene megacrysts from the Huangyishan volcano, Kuandian, Lianning were carried out with respect to fundamental mineralogy, mineral spectroscopy, crystal structure and crystal chemistry, crystalization kinetics, and exsolution texture, etc. The mineral composition of clinopyroxene megacrysts is aluminian augite. Opaque sulfide inclusions, fracture minerals, and exsolved minerals can be found in them, while both compositions and structure of the major part of megacrysts were demonstrated by several experimental methods to be homogeneous, to certain degree. Crystal structure refinement showed the M2 splitting in the structure of megacryst. The fittings of Mossbauerspectra of Cpx megacrysts presented four doublets, namely the so-called "anomalous Mossbauer spectrum" of clinopyroxene. During explanation of the doublets, the CC' doublet was emphsized to be produced due to the next-nearest-neighbour effect of Fe~(2+) in M1. It was found that there seemed to be such relationship: M2 splitting-diversification of the next-nearest-neighbour configuration of M1→" anomalous Mossbauer spectrum". With this the problem of "anomalous Mossbauer spectrum", about which there have been several different explanations so far, may be settled satisfactorily. In addition, the structure state of Fe and the applicabilities of Mossbauer spectroscopy were analyzed. The crystallizing environment of Cpx megacrysts might be rather oxidative because they have high Fe~(3+)/ΣFe ratios. According to the kinetics theory of crystallization of mineral in igneous rock, author studied, for the first time, the crystallization kinetics of megacryst as well as its physical environment. Through synthetic theoretical analyses of the relations between P and viscousity(η) and diffusity(D) and that between η and nucleation rate(I) and growth rale(Y), it was demonstrated that higher crystallizing pressure will lead to smaller I and Y with greater η. But the differences of I and Y, in the interested range of pressure, are not beyond a order of magnitude. In sense of the nucleation theory of silicate mell, it was concluded that the sequence of nucleation of the major megacryst silicate phases should be as follows: Grt → Cpx → An. Moreover, the movement of melt and its effects on the crystallization of megacrysts were discussed, predicting that a relatively stable environment should be in favor of the crystallization of megacrysts. After careful investigation of some samples by means of optical microscopy, electron microprobe and TEM, author ascertained that, in some Cpx megacrysts, there may exist complex exsolution texture. On the basis of experimental there may exist complex exsolution texture. On the basis of experimental observation, explanations were given for the relative phenomena, such as concurrence of several exsolved phases, exsolution of augite (or diopside) from augite and the variable sizes of exsolved phases. Simultaneously, some relative improper previous considerations were evaluated. From either the composition or the size of exsolved phases it can be deduced that exsolution have lasted a fairly long period and have not deduced that exsolution have lasted a fairty long period and have not taken place within only one magma reservoir. According to the fact that most of Cpx megacrysts have coronae (or reaction rims), several pieces of information accounting for evolution of megacryst and the host magma were found. |
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