北秦岭二郎坪岩群~(40)Ar/~(39)Ar坪年龄特征及其地质意义

对来自二郎坪岩群的白云母、角闪石用阶段升温法进行了~(40)Ar/~(39)Ar年龄谱研究，结合二郎坪岩群地质特征，认为白云母近似直线年龄港的评年龄（111．2Ma）及角闪石稳定评年龄（121．5Ma）代表了二郎坪岩群最后一次热事件的时代；角闪石与白云母封闭温度的不同以及角门石的成分与结构环带导致二者坪年龄的差异，二郎坪岩群在121．5～111．2Ma曾发生区域变质作用，整个秦岭造山带在此期间仍处于构造活动期。

~(40)Ar/~(39)Ar PLATEAU AGE SPECTRA OF ERLANGPING GROUP,NORTH QINLING AND THEIR GEOLOGICAL IMPLICATIONS

To gain a better understanding of the thermal history of the Erlangping Group,~(40)Ar/~(39)Arplateau age analysis was made on muscovite from garnet-bearing mica quartz schist and hornblendefrom amphibolite. The ~(40)Ar/~(39)Ar plateau age spectra of muscovite are represented by nearly astraight line. An age of 111. 2Ma stands for the age of last regional thermal event the ErlangpingGroup has experienced because muscovites arrange along the regiona1 schistosity plane.The~(40)Ar/~(39)Ar age spectra of hornblende are more complex than those of muscovite - The ages of horn -blende in the range of low temperatures are of no geological signification. The ~(40)Ar/~(39)Ar plateauage of hornblende is 121. 5Ma. The ~(40)Ar/~(39)Ar plateau ages (111. 2Ma and 121. 5Ma ) of muscoviteand hornblende represent the last metamorphic thermal event the Erlangping Group has experi-enced. It is evidenced that a regional metamorphism occurred during this period(121.5~111.2Ma).The whole Qinling orogenic belt was still in the active state.