四川攀西红格矿区辉长岩和正长岩的SHRIMP U-Pb和Sm-Nd定年及其地质意义

用SHRIMP U-Pb和Sm-Nd定年技术,对攀西红格矿区含矿层状辉长岩、碱性正长岩进行了年龄测定。获得红格辉长岩中3种不同晶形锆石的U-Pb年龄分别为258.4±4.1Ma、1841±34Ma、2487±12Ma,由辉长岩、辉石和磷灰石所构成的Sm-Nd等时线年龄为253±14Ma;碱性正长岩中锆石的U-Pb年龄为257.2±1.5Ma。结果表明,红格辉长岩中具有典型基性岩锆石特征的锆石U-Pb年龄(258Ma)与同一地质样品的Sm-Nd年龄(全岩+矿物内部等时线年龄),以及同一矿区的正长岩锆石U-Pb年龄在测定误差范围内一致。鉴于层状辉长岩和碱性正长岩在空间上密切共生,在形成时间上一致,可以认为它们都属于晚二叠世末岩浆活动的产物;而1841Ma和2487Ma的锆石,可能是在基性-超基性岩浆的上侵过程中,从基底所捕获的岩浆锆石和继承锆石,其年龄信息,揭示了康滇地轴岩浆岩带的下部或结晶基底存在元古代甚至新太古代末期的岩石或物质。

SHRIMP U-Pb and Sm-Nd dating of the gabbro and syenite from the Hongge ore district in western Panzhihua and its geological significance

Adopting the SHRIMP U-Pb and Sm-Nd method,this paper reported the dating results of the bedded ore-bearing gab-bros and alkaline syenites from the Hongge ore district in western Panzhihua area.The results show that the zircons from gabbro in Hongge have ages of 258.4±4.1Ma,1841±34Ma and 2487±12Ma,the Sm-Nd isochron age of the gabbro,pyroxene and apatite sam-ples is 253±14Ma,while the zircon U-Pb age of alkaline syenite is 257.2±1.5Ma.These data show that the zircon U-Pb age (258Ma) of the typical mafic rock is similar to the Sm-Nd isochron age of the same samples,and also similar to the zircon U-Pb age of syenite.Considering the close relationship between layered gabbro and alkaline syenite rock in space and in time,it is suggested that both of them resulted from Permian Magmatism,but 1841Ma and 2487Ma zircon might have been magmatic zircon and inherit-ed zircons,which originated from the basement.These data imply the existence of Paleo-Petrozoic or even Archean materials in the lower part of Kangdian axis magmatic rock belt or the crystalline basement.