天镇──怀安地区早前寒武纪钾质花岗岩地球化学特征及构造环境

Geochemistry and Tectonic significance of Early Precambrian Potassic Granite from Tianzhen-Huai’an Area

晋冀内蒙古交界地区太古宙怀安杂岩以南发育一条花岗岩带，和怀安杂岩以高压麻粒岩混杂岩带相隔，是该区一个单独的岩石构造单元，规模较大，宽２０多ｋｍ。从山西繁峙白马石经天镇南部向北东一直到宣化西葛峪和二道岭，断续相连。北东东向延伸近２００ｋｍ，延伸方向与区域片麻理和主构造线方向一致。该花岗岩带由众多中小规模花岗岩侵入体和其间残留体组成。大部分花岗岩呈肉红色，以富钾质和含有高压基性麻粒岩包体为特征，许多花岗岩发育片麻构造。岩石学研究表明，大多数花岗岩经历了变质作用，一些花岗岩经历了麻粒岩相变质作用，具有麻粒岩相矿物组合Ｑ＋Ｐｅｒ＋Ｐｌ±Ｇｔ＋Ｂｉ（棕）±Ｈｂ＋Ｍｔ，石榴石、黑云母等矿物的成分显示出麻粒岩相变质的特征。大部分花岗岩都是近低熔花岗岩的组分，并显示某些钙碱性岩系的演化趋势。微量元素组成表现出较大的变化范围，多数花岗岩富Ｋ，Ｒｂ，Ｂａ，贫Ｚｒ，Ｙ，Ｙｂ，部分样品还亏损Ｔｈ，Ｔａ和Ｎｂ，稀土元素从低到高有４种不同的配分型式。这些花岗岩由许多不同类型源岩的部分熔融形成，具有与碰撞型花岗岩相似的常量和微量元素地球化学性质。锆石Ｕ－Ｐｂ一致线年龄为２３７０Ｍａ，指示出这些花岗岩形成于太古宙末期。这条花岗岩带有可能是?

The south of Archaean Huai'an Complex along the frontier of the Shanxi and Hebeiprovince a granite belt is occurred and separated with the Huai'an Complex by a high-pres-sure granulite complex.The belt is demonstrated by multiple small-scale intrusive bodies,characterized mainly by red-colored potassic granite. Their zircon U-Pb data give a uniformage of 2370Ma, which means that they were formed in Archaean. Potassic granites had beeninfluenced by high-grade metamorphism,and the granulite mineral assemblage Gt-per para-genesis were developed in them. The compositions of the granite are on the range of the low-est melting point on the Or-Ab-An phase diagram and can be plotted in the calc-alkaline se-ries domain. Trace element geochemistry of granites suggests that they are riched in Rb andTh related Ta and Nb and Rb/Zr ratio is lower,which indicate that the granites here may bebelonged to post-collisional granites.