北秦岭褶皱带岩浆活动时代特征及地质意义

本文通过展示截止１９９４年北秦岭地区岩浆岩的Ｋ－Ａｒ、（４０）Ａｒ－（３９）Ａｒ、Ｒｂ－Ｓｒ、Ｓｉｎ－Ｎｄ、Ｕ－Ｐｂ谐和图、单颗粒锆石逐级蒸发（２０７）Ｐｂ－（２０６）Ｐｂ等方法同位素年龄结果，进行综合对比讨论，从而确定这一地区岩浆活动，在早元古末期以后多次发生，直至中生代。它们包括大约２０００Ｍａ、１２１０～９２０Ｍａ、８２２～７９４Ｍａ、４６４～３６０Ｍａ（奥陶纪－早石炭世）、１９５～１０５Ｍａ（早侏罗世－白垩纪）等五个地质时期。另外，根据北秦岭地区岩浆活动对确定变质岩层分层时限的制约的观点，提出该地区变质岩层划分的五个岩群的时序，首先是秦岭群（大于１７００Ｍａ）、然后是宽坪群（１１００Ｍａ前后）、二郎坪群（８００Ｍａ前后）、草滩沟群或丹凤群（４５０Ｍａ前后）、中生代岩群（２００Ｍａ前后）等等。它们是在不同时期，伴随着某一构造运动旋回形成的变质岩层。所展示的年龄资料同时为读者了解各种同位素年代测定方法的适应性，以及了解在复杂地质构造区域，如何有效开展同位素年代学研究，提供有益经验。

The Ages of Magmatism in North Qinling Fold Belt and Their Geol ogleal Significance

The ages of igneous rocks from North Qinling Fold Belt, measured by the methods of K-Ar, Rb-Sr, U-Ph, (40)Ar-(39)Ar and Sin-Nd, reveal that the magmatism in this region took place in the following five geological periods: about 2000 Ma, 1210~920 Ma, 822~794 Ma, 464~ 360 Ma (O-C1), 195~105Ma(J1-K). In addition, there five groups of metavolcanic-metasadimentary rock s in this region were appropriately distinquished, these are Qinling Group (> about 1700Ma),Kuangpin Group (about 1100Ma),Elangping Group (about 800Ma), Caotangou or Danfen Group (about 450Ma), the Group of Mesozoic age (abount 200Ma ).