【作者】 张西平；

【导师】 程裕淇；

【作者基本信息】 中国地质科学院 ， 岩石学， 2002， 博士

【摘要】 平阳片麻状花岗岩位于阜平复式穹状构造猴石顶倒转背斜的东部，出露面积大于40平方公里，为奥长花岗岩。岩体的西部似一穹状背斜，向东逐渐转变为两个向南倒转的次级背斜，总体上为向南倒转的复式背斜的核部，其产状及其面理构造与区域构造线完全一致。花岗岩在中北部与围岩呈侵入接触，其他部分主要由混合岩或混合质黑云斜长片麻岩过渡到变质表壳岩。平阳岩体岩性不很均匀，长英质集结体及团块、长英质“无根”脉很发育，暗色矿物（黑云母、角闪石、磁铁矿）分布不均匀，在岩体边缘及附近围岩中伟晶岩脉较为多见。平阳片麻状花岗岩之中存在以片麻岩为主的变质表壳岩残留层（体），片麻理与岩体的片麻理协调一致，其产状继承了原岩的产状，尤其是在岩体的东部，使花岗岩的原地特征表现十分清楚。岩体中还广泛分布着各种类型的变质基性岩石包体（角闪质岩石和麻粒岩）和岩片，在东部具有明显的“成群成带”分布特点，边缘地带也较为多见。平阳片麻状花岗岩主要由奥长石，石英和黑云母组成，含少量微斜长石，局部含少量角闪石，极少量白云母。具有典型的波状一齿状花岗变晶结构，补片状的反条纹长石多见，常见绢云母化、缝合线结构、乳滴状石英的交代穿孔结构。石英外形弯曲多变，波状消光明显。黑云母常见暗化边并有细粒磁铁矿析出等的深熔初期的岩相学现象。总体显示了交代、重熔成因的岩相学特点。平阳片麻状花岗岩的化学成分是在区域混合岩化对岩石成分总体改造趋势的背景下，在黑云斜长片麻岩成分的基础上，通过黑云斜长片麻岩的深熔以及可能的变质脱水反应流体和深部流体的加入演变而成，富SiO₂、Na₂O以及Sr和Ba。花岗岩的不相容元素、REE和Sm-Nd同位素与片麻岩、变粒岩显示了系统性的演变，并具一定互补性。片麻岩等的深熔还使Sm／Nd发生轻微分馏，进而使花岗岩Nd同位素组成随Sm／Nd一起表现了明显的区域性变化。花岗岩Sm-Nd同位素模式年龄比片麻岩等要小约200Ma。根据副矿物和锆石，以及矿物温压计估算，并结合已有同位素测年数据，认为平阳片麻状花岗岩是在25亿年稍后，在造山作用中，伴随构造减压作用，与阜平群中一系列倒转褶皱形成的同时，由片麻岩等深熔而成。更多还原

【Abstract】 Occurs to the eastern Houshiding overturned anticline of Fuping complex domal uplift, Pingyanggneissic granite, a trondhjemite looks like a domal anticline in the west part and becomes twosub-anticlines overturned to south in the east part. It is just the core of a multiple anticline aswhole and parallels including its gneissosity to the regional tectonic line. The granite has a belt oftransition composed of migmatite and migmatitic biotite gneiss between its body andmetamorphosed supracrustal rocks, but it exhibits magmatic features in center-north part andshows intrusive contact with wall rocks in some parts of its northern. Lithologic inhomogeneity ofgranite can be observed by the truth such as commonly occurred quartz-feldspathic lumps andblind ending Veins, uneven distributed dark minerals as well as pegmatite veins in its border.Within the granite particularly its eastern part, it is frequently met that gneiss which has itsoriginal occurrence, and granulite and amphibolite enclaves as well.Pingyang gneissic granite which has wavy-hackly granoblastic texture mainly comprisesoligoclase, quartz and biotite, and also some microcline,hornblende and little muscovite.Characteristics of the metasomatic and re-melting petrography has been shown by metasomaticstructures of varieties, antiperthite of small sheets, quartz of various shapes with stronly wavyextinction and biotite with dark rim and fine magnetite presents along the rim..The chemical composition of Pingyang gneissic granite with high contents of SiO₂,Na₂O,Sr andBa was inherited and developed from that of mainly biotite gneiss through anatexis under thebackground of regional migmatisation, it might also be introduced the fluid material from deep.Thus the comparatively and systematically variations of incompatible elements, REE and Sm-Ndisotopic ratios can be seen among granoblasite-gneiss-granite. Anatexis of gneisses resulted in aslightly fractionation of Sm/Nd and this in turn caused areal variation of Sm-Nd isotopic ratioswithin the granite. A deduction has been made that explains the gneissic granite was formed byanatexis of mainly gneisses in the time of overturned folding during the tectonic depressurizationperiod of the orogeny, these were happened at about 2.5Ga or later.更多还原