河北阜平平阳片麻状奥长花岗岩的地质和岩相学特征

Geology and petrography of the Pingyang gneissic trondhjemite,Fuping,Hebei

平阳片麻状奥长花岗岩位于河北阜平县平阳镇一带,围岩为包括混合岩和片麻岩在内的变质表壳岩,层位上相当于阜平群的下部。研究表明平阳地区空间上存在高级变质作用、混合岩化作用和深熔作用的“三位一体”,因而由变质岩到花岗岩显示了系统的岩石学、岩相学以及产出关系上的渐变过渡特点。花岗岩中的变质表壳岩以及部分包体不仅在岩性上可和外围的同类岩石对比,而且也显示了明显的深熔作用改造的痕迹。有较为充分的证据表明平阳片麻状花岗岩总体上是原地深熔的奥长花岗岩,局部发生了一定尺度的位移。平阳地区变质表壳岩的深熔作用经历了以流体活动占主导地位、以矿物的溶解和重结晶为主要特点的早期阶段,演变为以部分矿物的熔融占主导地位的高级阶段。平阳片麻状奥长花岗岩的形成代表了阜平岩群变质表壳岩深熔作用的高级演化阶段,对于客观认识阜平岩群的组成和地质演化具有重大意义。

The Pingyang gneissic trondhjemite is located in the vicinity of Pingyang Township,Fuping County,Hebei Province.Its country rocks are supracrustal rocks including migmatites and gneisses,stratigraphically equivalent to the lower part of the Fuping Group.The high-grade metamorphism,migmatization and anatexis have close spatial relationships in the Pingyang area,showing the'trinity';thus the change from metamorphic rocks to granites show the gradational features with respect to systematic petrology,petrography and occurrence relationships.The metamorphosed supracrustal rocks and some inclusions in granites can not only be correlated with their equivalents in the surrounding areas but also show signs of modification by anatexis.Ample evidence indicates that the Pingyang gneissic trondhjemite is generally autochthonous anatectic trondhjemite,which has been displaced to some extent locally.The anatexis of metamorphosed supracrustal rocks in the Pingyang area progressed through the early stage characterized mainly by dissolution and recrystallization of minerals and the late stage when melting of some minerals predominated.The formation of the Pingyang gneissic trondhjemite represents the higher evolutionary stage of anatexis of metamorphosed supracrustal rocks of the Fuping Group-complex,which has great significance for the objective understanding of the composition and geological evolution of the Fuping Group-complex.