内蒙古温都尔庙群变质基性火山岩Sm-Nd、Rb-Sr同位素年代研究

温都尔庙群主要分布在内蒙古温都尔庙地区,该套地层是白乃庙-温都尔庙构造岩浆带的重要组成部分。长期以来,由于缺少古生物化石和可信的年龄数据,一般认为温都尔庙群属早古生代。本文对温都尔庙群变基性火山岩进行了Sm-Nd和Rb-Sr同位素研究,5件变基性火山岩全岩样品Sm-Nd和Rb-Sr等时线年龄分别为961±66Ma和624±110Ma,并对其形成时代和成因提出了一些新看法。

Sm-Nd, Rb-Sr ISOTOPIC ISOCHRON OF METAMORPHIC VOLCANIC ROCKS OF ONDOR SUM GROUP, INNER MONGOLIA

The Ondor Sum Group is over the Ondor Sum area,Inner Mongolia,which is an important composition in Boin Sum-Ondor Sum tectono-magmatic belt.Being lacking in fossil and other dependable data of isotopic age,the Ondor Sum Group was recognized as early Paleozoic for a long time.This paper is a study on the Sm-Nd,Rb-Sr isotopic isochron of metamorphic volcanic rocks of Ondor Sum Group.The isotopic ages got form five basic volcanic rock samples of Sm-Nd and Rb-Sr are 961±66(2σ)Ma and 624±110Ma(2σ).The Sm-Nd age data provides the first evidence of the Late Proterozoic rather than the early Paleozoic as was deduced before.∈_Nd(t)=8.8 reveals that there would be a depleted mantle.Sedimentary facies analysis suggests that the series formed in a intercontinental small sea basin with volcanic materials and distal fragmenes which belongs to the Proterozoic passive volcanic continental margin.Rb-Sr age data provides the metamorphic-deformed time which finished Proterozoic passive continental margin evolution and into the early Paleozoic active continental margin evolution.