摘要
1978年,作者在野外调查期间发现了一种特殊的变质岩。根据其中主要矿物组成为石英,铁铝榴石和易熔石(eulite)将它定名为英榴易熔岩。该英榴易熔岩作为整合的层产在我国河北省东部迁安县娄子山早太古代迁西群中,出露范围为长1—2公里和宽数十米。它的上、下围岩分别为黑云母-石榴片麻岩(局部含蓝晶石)和二辉石麻粒岩。这类岩石长期被误认为榴辉岩。
A particular metamorphic rock—quartz-almandine eulitite was identified by the authors in 1978 for the first time in the Louzi Mountain,Qianan,eastern Hebei Province.It is essentially composed of eulite,almandine and quartz and locally ferrifayalite,magnetite,clinopyroxene,biotite,graphite and plagioclase;massive or well-banded.In the banded type the individual layer ranges in thickness from several milimeters to over one centimeter,and the layering is caused by the varying proportions of the three main minerals:eulite,almandine and quartz,with eulite always predominant.As the rock underwent plastic deformation under high temperature,anomalous extinction,subgrainization and kink bands appear in eulite and quartz.This causes the main minerals to break up through strong shear stress,forming porphyroclasts(1—3mm)and newblasts(0.3mm).Triples formed by the newblasts are common.In this case,the rock shows a cataclastic texture.In petrography,the rock studied is similar to the eulysite.Its parent rock in terms of the bulk rock chemistry is probably a Fe-rich sediment.The mineral chemistry and the distribution coefficient of Fe^(2+)and Mg in coexisting ferromaganesian minerals are discussed.The mineral spectral investigation(both inferared and Mossbauer spectra)are carried out.By making use of the two-pyroxene geothermometers made by Wood and Banno(1973),Saxena(1976)and Wells(1977),the equilibrium crystallization temperature of the rock studied is calculated to be about 750℃,and pressure obtained by Wood’s method(1974)is about 13kb at such temperature.The above P-T data are in correspondence with the geothermal gradient of about 17℃/kin.This implies that quartz-almandine eulitite was subjected to the granulite facies of medium-pressure metamorphism.
作者
张儒瑗
从柏林
应育浦
Zhang Ruyuan;Cong Bolin;Ying Yupu(Institute of Geology,Academia Sinica)
出处
《地质学报》
1982年第1期70-80,共11页
Acta Geologica Sinica
