A detailed analysis on the generation and alteration hysteresis of high temperature skams

在冈山县福贺县和广岛县久路县的高温夕卡岩中，闪锌矿和镁铝榴石是其特有的主要矿物。夕卡岩是二长闪长岩和石英二长岩侵入石灰岩形成的。这些火成岩似乎是同一岩浆起源的产物。火成岩浆的温度影响夕卡岩的类型。利用地质温度计测定形成细粒硅卡岩的火成岩的温度范围为690℃至930℃。大部分钙铝榴石和闪锌矿晶体被蚀变成逆行矿物。通过织构分析和化学分析，阐明了钙铝榴石晶体的蚀变过程。经详细分析，其蚀变过程依次为：(1)径向蚀变过程(从方解石到方解石、方解石、紫苏辉石、石榴石和泡沫石)。(2)Ti-Fe相的形成过程(方铅矿和钙钛矿的形成)。(3)白云母脉蚀变过程(蚀变到白云母)。(4)黑液矿脉蚀变过程(对不明矿物的蚀变)。(5)分带蚀变过程(变水蚀变)。

In the high-temperature skarns at Fuka, Okayama Prefecture and Kushiro, Hiroshima Prefecture, spurrite and gehlenite occur characteristically as primary minerals. The skarns were formed by the intrusion into limestone of monzodiorite and quartz-monzonite. The igneous rocks appear to be products of the same magmatic origin. The temperature of the igneous magma affects the type of skarns. The temperatures of the igneous rocks forming the gehlenite-spunite skarns range from 690℃ to 930℃, using the geothermometer. Most of the gehlenite and spurrite crystals were altered to retrograde minerals. In the present study, the alteration process of the gehlenite crystals was clarified by texture and chemical analysis. As a result of detailed analysis, there are five alteration processes in order of formation as follows : (1) Radial alteration process (alteration from gehlenite to calcite, amesite, garnet and vesuvianite). (2) Ti-Fe phases formation process (formation of schoiiomite and perovskite). (3) Leucocratic vein alteration process (alteration to vesuvianite). (4) Melanocratic vein alteration process (alteration to unidentified mineral). (5) Zoning alteration process (alteration to hydrogrossular).