坦桑尼亚西部基戈马—姆藩达地区前寒武纪地质特征及锆石测年新资料

THE PRECAMBRIAN GEOLOGICAL CHARATERISTICS OF KIGOMA-MPANDA REGION,TANZANIA AND THE NEW DATA OF U-Pb AGE DETERMINATION ON ZIRCON

基戈马—姆藩达地区位于坦桑尼亚西部,前寒武纪地层分布广泛。近年来,在该区获得了一批新的同位素测年数据:Shanwe hill英云闪长岩的上交点年龄(2.64 Ga)说明岩体形成于新太古代,但下交点的年龄(0.7 Ga)可能为变质年龄,也有可能是继承锆石的年龄;Fili mult hill花岗岩(1893±3)Ma的年龄值表明岩体为古元古代晚阿宾迪纪产物;Gua花岗岩(1 889±40)Ma的测定结果说明是与Fili mult hill花岗岩同构造期的产物;Nyamahanga粒玄岩年龄(1337±47)Ma代表新元古代基性岩墙侵入的时代。

Kigoma-Mpanda region is located in the west Tanzania with Precambrian rocks spreading widely. In resent years a group of new isotopic age data has been obtained from the region. The upper cross point age of tonalite sample form Shanwe hill is 2.64 Ga indicating that the granite body is formed in Neo-archean Era. However, the lower cross point age is 0.7 Ga that may represent its metamorphic age or the age of inheriting zircon. Age of granite from Filimult hill is determined at 1. 893 ± 3 Ma suggesting that it is the product of Ubendian Period. Age of Gua granite is 1. 889±40 Ma showing that it is the product of syn-tectonic period of Filimult hill granite. Age of 1. 337±47 Ma for Nyanahanga dolerite represents the time when Neo-proterozoic basic dykes intruded.