PETROLOGIC STUDY OF THE RYOKE METAMORPHIC ROCKS IN THE TAKATO SHIOJIRI AREA, CENTRAL JAPAN
PETROLOGIC STUDY OF THE RYOKE METAMORPHIC ROCKS IN THE TAKATO SHIOJIRI AREA, CENTRAL JAPAN
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日本中部高远盐尻地区Ryoke变质岩的岩石学研究
DOI：
10.2465/ganko1941.72.453
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发表时间：
1977
期刊：
影响因子：
--
通讯作者：
A. Ono
中科院分区：
文献类型：
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作者：
A. Ono
根据泥质岩的矿物组合，调查区域分为六个区域，即 I 区至 VI 区。区域边界分别由黑云母、中长石、堇青石或红柱石、硅线石和铁铝榴石的首次出现确定。利用电子探针显微分析仪对矿物的化学成分进行了分析。黑云母中TiO2和Al2O3的含量随着品位的增加而增加。 II区绿泥石中Al2O3含量低于III区。 I区和II区常见富含青瓷石成分的碎屑白云母。 III 区上方不存在。 III区和IV区大部分地区的白云母化学成分相似。与低品位白云母相比，V 区白云母的 FeO 和 MgO 含量稍差。钠长石与中长石 (An30-34) 或寡长石共存于 III 区。斜长石中K2O含量随着变质温度的升高而增加。钾长石的 Ab % 从 IV 区到 VI 区显着增加。钛铁矿中MnO含量从II区到VI区逐渐增加。 Fe 和 Mg 在黑云母、绿泥石和白云母之间的分配系数不随品位变化。 Ab组分在钾长石和斜长石之间的分配系数随品位变化。根据Stormer的双长石地温计，如果压力约为4000巴，则硅线石等梯度处的温度为500°C，铁铝榴石等梯度处的温度略高于550°C_600°C。黑云母大部分是由中长石等梯度附近的白云母、绿泥石和白云母反应生成的。然而，黑云母的形成发生在黑云母等梯度以上和III区中温部分以下。堇青石是通过与 V 区和 VI 区的黑云母、硅线石和石英反应形成的。白云母与石英的反应主要发生在硅线石等梯度稍上方。钾长石和硅线石几乎共存于 V 区的所有泥岩中。铁铝榴石和钾长石的伴生仅出现在 VI 区。分区斜长石常见于 V 区和 VI 区。与斜长石的核心相比，边缘的 K2O 含量较低。分区斜长石是在退行变质作用过程中产生的。 V区和VI区的许多白云母都有微小的硅线石和石墨包裹体，表明这些白云母是在退变质作用过程中形成的。将岩石学结果与现有的实验研究进行比较，以估计 Ryoke 变质作用的地温梯度。在PH2O_??_1/4 PTotal 条件下，估计地温梯度约为6.5 bar/deg。
The area surveyed was divided into six zones, Zone I to Zone VI, based on mineral assemblages of pelitic rocks. Zone boundaries were determined by the first appearance of biotite, andesine, cordierite or andalusite, sillimanite and almandine, respectively. Chemical compositions of minerals have been analyzed by means of electron probe microanalyzer. TiO2 and Al2O3 contents of biotite increase with increasing grade. Al2O3 content of chlorite is lower in Zone II than in Zone III. Detrital white mica rich in celadonite component is common in Zones I and II. It is absent above Zone III. Muscovite from most of Zone III and Zone IV are similar in chemical composition. Muscovite in Zone V is slightly poorer in FeO and MgO contents as compared with lower-grade muscovite. Albite coexists with andesine (An30-34) or oligoclase in Zone III. K2O content in plagioclase increases with increasing metamorphic temperature. Ab % of K-feldspar remarkably increases from Zone IV to Zone VI. MnO content in ilmenite increases from Zone II to Zone VI. Partition coefficients of Fe and Mg between biotite, chlorite, and muscovite do not change with grade. Partition coefficient of Ab component between K-feldspar and plagioclase change with grade. According to Stormer's two-feldspar geothermometer, it is 500°C and 550_??_600°C at the sillimanite isograd and slightly above the almandine isograd, respectively, if pressure is about 4000 bars. Most of biotite are produced from the reaction of white mica, chlorite and muscovite near the andesine isograd. However, formation of biotite occurs above biotite isograd and below medium temperature part of Zone III. Cordierite was formed by the reaction with biotite, sillimanite and quartz in Zones V and VI. The reaction of muscovite plus quartz mainly took place slightly above the sillimanite isograd. K-feldspar and sillimanite coexist in almost all pelites in Zone V. Association of almandine and K-feldspar occurs only in Zone VI. Zoned plagioclases are common in Zones V and VI. The rims are poor in K2O content as compared with cores of plagioclases. Zoned plagioclases were produced during retrogressive metamorphism. Many muscovite in Zones V and VI have tiny inclusions of sillimanite and graphite, suggesting that these muscovite were formed during retrogressive metamorphism. The petrological results were compared with available experimental investigations in order to estimate geothermal gradient of the Ryoke metamorphism. The geothermal gradient estimated is about 6.5 bar/deg under the condition of PH2O_??_1/4 PTotal.