Hisao Tanaka, Chung Huang, Youichi Nakamura, E. Kurokawa, Masahiro Nobusaka
{"title":"Petrology of an epizonal gabbroic suite: the Batow pluton, Yamizo Mountains, Central Japan","authors":"Hisao Tanaka, Chung Huang, Youichi Nakamura, E. Kurokawa, Masahiro Nobusaka","doi":"10.2465/GANKO1941.82.419","DOIUrl":null,"url":null,"abstract":"The Batow pluton, an epizonal gabbroic body, Central Japan, was studied to delineate its geologic, petrographic and geochemical characteristics. Though the pluton is small, it exhibits a wide compositional range from melagabbro to granodiorite and varies from 42.8 to 62.7 wt.% SiO2. The Batow rocks have similar features to calc-alkaline, magnetite-series and I-type plutonic rocks and are characterized by high abundances of lithophile elements, comparable to those in a shoshonite rock association. Crystallization path calculations and petrographic observations suggest that the wide compositional variation was brought mainly by amphibole- and plagioclase-dominated fractionation of a gabbroic magma with minor fractionation of clinopyroxene, biotite and potash feldspar. This fractionation occurred at a comparatively shallow crustal level, deeper than 2kb, before upward migration. The granitic rocks characterized by an abundance of amphibole (up to 39%) and a scarcity of biotite (less than 4%) were formed at a higher P H2O and lower temperature than early-crystallized gabbros. The close association of clinopyroxene- and biotite-rich gabbro, whose clinopyroxene and plagioclase often show reverse zoning in the Mg/(Mg+Fe*) ratio and An content, with amphibole-rich gabbro suggests that P H2O had increased rapidly during crystallization of the gabbroic melt. The intrusion of H2O-saturated granodioritic melt to the gabbroic melt may have caused the rapid increase of P H2O.","PeriodicalId":22709,"journal":{"name":"The Journal of the Japanese Association of Mineralogists,Petrologists and Economic Geologists","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"1987-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"2","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"The Journal of the Japanese Association of Mineralogists,Petrologists and Economic Geologists","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.2465/GANKO1941.82.419","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 2
Abstract
The Batow pluton, an epizonal gabbroic body, Central Japan, was studied to delineate its geologic, petrographic and geochemical characteristics. Though the pluton is small, it exhibits a wide compositional range from melagabbro to granodiorite and varies from 42.8 to 62.7 wt.% SiO2. The Batow rocks have similar features to calc-alkaline, magnetite-series and I-type plutonic rocks and are characterized by high abundances of lithophile elements, comparable to those in a shoshonite rock association. Crystallization path calculations and petrographic observations suggest that the wide compositional variation was brought mainly by amphibole- and plagioclase-dominated fractionation of a gabbroic magma with minor fractionation of clinopyroxene, biotite and potash feldspar. This fractionation occurred at a comparatively shallow crustal level, deeper than 2kb, before upward migration. The granitic rocks characterized by an abundance of amphibole (up to 39%) and a scarcity of biotite (less than 4%) were formed at a higher P H2O and lower temperature than early-crystallized gabbros. The close association of clinopyroxene- and biotite-rich gabbro, whose clinopyroxene and plagioclase often show reverse zoning in the Mg/(Mg+Fe*) ratio and An content, with amphibole-rich gabbro suggests that P H2O had increased rapidly during crystallization of the gabbroic melt. The intrusion of H2O-saturated granodioritic melt to the gabbroic melt may have caused the rapid increase of P H2O.