PETROLOGICAL STUDY OF THE THERMALLY METAMORPHOSED ROCKS SURROUNDING THE TANOHATA GRANITIC MASS, NORTHERM KITAKAMI MOUNTAINLAND, NORTHEASTERN JAPAN (II)
PETROLOGICAL STUDY OF THE THERMALLY METAMORPHOSED ROCKS SURROUNDING THE TANOHATA GRANITIC MASS, NORTHERM KITAKAMI MOUNTAINLAND, NORTHEASTERN JAPAN (II)
复制标题
日本东北部北上山区田畠花岗岩体周围热变质岩的岩石学研究（二）
DOI：
10.2465/ganko1941.48.167
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发表时间：
1962
期刊：
影响因子：
--
通讯作者：
M. Shimazu
中科院分区：
文献类型：
--
作者：
M. Shimazu
摘要：该区广泛出露古生界、侏罗系、下、上白垩系、古近系和花岗岩。地质序列和火成岩活动见表1。花岗岩体分为两组。第一组由花岗岩岩体组成，如太郎岩体、胡美旗岩体、上府森岩体和小尻岩体，第二组由花岗岩岩体组成，如田野畑岩体、桥上岩体和宫古岩体。 Tanohata 花岗岩体分为两种岩相，即 Otomo 型和 Moichi 型。大友型由粗粒辉长岩和花岗闪长岩组成，茂市型由中粒花岗闪长岩、石英二长岩和石英闪长岩组成。本文提到的热变质岩发育在第二组田野畑花岗岩体周围，主要来源于古生界和下白垩统地层的沉积物。该花岗质体周围的接触光环分为以下三个区域：黑云母板岩带........西侧和东侧堇青石斑板岩带....西侧和东侧以及部分顶板垂高品位带........西侧和顶板垂黑云板岩带和堇青石斑板岩带分别以黑云母和堇青石的存在为特征。在堇青石斑板岩带中，堇青石先于红柱石出现。高品位区的特征是堇青石和红柱石和/或硅线石和钾长石共存。高品位带的大部分岩石，尤其是层状和带状角岩，在特征和矿物共生方面与 Ryoke 变质地形的岩石相似。硅线石很罕见，在花岗岩体西侧的角岩中，在黑云母和红柱石晶体周围形成纤维状针状结构。相反，在屋顶吊坠的一些角岩中，硅线石针取代了红柱石。红柱石-硅线石转变（第一等线硅线石）似乎发生在该光环的角岩中，其中还发现了钾长石和硅线石（第二等线线石）的共存。从这种关系看来，在这个接触光环中，第一硅线石等线与第二硅线石等线重合。这与 Ryoke 变质地形有明显的区别，这可能是由于两个地区的岩石压力不同所致。与北上山地的远野和仙马屋接触光环相比，该光环的岩石中硅线石、红柱石和石榴石的含量很少。另一方面，该光环的岩石中通常大量存在钾长石。其接触环之间的变质矿物及其共生矿物含量的差异可能不是由于物理条件造成的，而是由于原岩的化学成分造成的。通过光学和 X 射线方法研究了钾长石。高品位带岩石中的钾长石呈单斜对称性。钾长石的结晶温度也通过巴特法进行了测定。高品位带黑云母的铁-亚铁比（Fe2O3/Fe2O3+FeO）为0.05～0.07，与仙马屋光环和Ryoke变质带相似，但小于阿武隈变质带。最后从主、微量元素的组成变化角度讨论了交代作用。在高品位带的一些岩石中，钾似乎可能是从花岗岩中引入的。
Abstract: Paleozoic formation, Jurassic formation, lower and upper Cretaceous formation, Paleogene formation and granitic rocks are widely exposed in this district. The geological succession and the igneous activity are shown in Table 1. Granitic masses are divided into two groups. The first group consists of granitic stocks such as the Taro, Kurumihata, Jofutsumori and Ojiri masses, and the second group consists of granitic masses such as the Tanohata, Hashikami and Miyako masses. The Tanohata granitic mass is divided into two rock facies, i.e., the Otomo and Moichi types. The Otomo type is composed of coarse-grained trondjhemite and granodiorite, and the Moichi type is composed of medium-grained granodiorite, quartz monzonite and quartz diorite. The thermal metamorphosed rocks mentioned in this paper develope around the Tanohata granitic mass of the second group and are derived mainly from sediments of the Paleozoic and lower Cretaceous formations. The contact aureole around this granitic mass is divided into the following three zones: biotite slate zone........western and eastern sides cordierite spotted slate zone....western and eastern sides, and a part of the roof-pendant high grade zone........western side and roof-pendant The biotite slate and cordierite spotted slate zones are characterized by the existence of biotite and cordierite respectively. In the cordierite spotted slate zone, cordierite begins to occur prior to andalusite. The high grade zone is characterized by the coexistence of cordierite and andalusite and/or sillimanite with potash feldspar. Most of the rocks of the high grade zone, especially laminated and banded hornfelses, resemble the rocks of the Ryoke metamorphic terrain in feature and mineral paragenesis. Sillimanite is rare, and forms fibrolitic needles around biotite and andalusite crystals in the hornfelses of the western side of the granitic mass. On the contrary, sillimanite needle replaces andalusite in some hornfelses of the roof-pendant. It seems that andalusite-sillimanite transition (the first sillimanite isograd) takes place in the hornfelses of this aureoles, where the coexistence of potash feldspar and sillimanite (the second sillimanite isograd) is also found. From such relation, it seems that the first sillimanite isograd coincides with the second sillimanite isograd in this contact aureole. This is a distinct difference from the Ryoke metamorphic terrain, and this may be due to the difference in the rock pressures of the two areas. The rocks of this aureole contain few sillimanites, andalusites and garnets compared with those of the Tono and Senmaya contact aureoles in the Kitakami Mountainland. On the other hand, potash feldspar are present generally in large amount in the rocks of this aureole. Difference of contents of metamorphic minerals and mineral paragenesis among their contact aureoles may be due not to the physical condition, but to the chemical composition of original rocks. Potash feldspars were studied optically and by X-ray method. Potash feldspars in the rocks of the high grade zone show monoclinic symmetry. The crystallization temperatures of potash feldspars were also examined by Barth´s method. Ferric-ferrous ratios (Fe2O3/Fe2O3+FeO) of biotites in the high grade zone are 0.05 to 0.07 and resemble those of the Senmaya aureole and the Ryoke metamorphic terrain, but they are smaller than those of the Abukuma metamorphic terrain. Lastly, metasomatism was discussed from the compositional variation of major and minor elements. In some rocks of the high grade zone, it seems probable that potassium was introduced from granitic rock.