贺兰山群变质杂岩中假玄武玻璃的成因

贺兰山群变质杂岩是晚太古代的一套孔龙岩系，在其中发育了一条东西向延伸的假玄武玻璃岩带。其产状特征、碎斑的熔蚀结构、基质的长石微晶和球粒结构表明，它是由岩浆结晶而成。这种岩浆形成于古地震带中，与滑动面高速运动摩擦生热有关。岩浆成分是安山质的，熔融是过热非平衡状态下进行的，深融温度可达１４００℃以上，深度可能不足１ｋｍ。

CHARACTERISTICS AND GENESIS OF THEPSEUDOTACHYLITE IN THE METAMORPHICCOMPLEX OF THE HELANSHAN GROUP

A zone of well-preserved pseudotachylite was found in the metamorphic complex of the HelanshanGroup. From the attitUdes and the configUrations of the pseudotachylite injection veins, the resorption borderof the porphyroclasts, feltspat microlites, the now texture and the spherulitec structures, it can be inferredthat the pseudotachylite was the cooling substances formed from the fused mass which had been producedfrom a part of the melted rocks on the ancient seismic fault planes due to the frictional heat caused by therapid movement along the slip surfaces. Chemicaly the pseudotachylite appears similar to the andestic magma.The melting process was a rapid, overheating and unbalaced process. The highest melting temperature wasprobably above 1400C,and the depth under which it formed was aoproximately Ibm. The ancient earthquakestook place later than the early Woterozoic era but earlier tham the formation of the S--N trending fold beltsof the Helanshan mountains, concerning the basement uplifting during the formation of the middle Proterozoicbasin structures.