摘要
同位素地质年代学研究证实了恒山地区古老大陆壳的存在,斜长角闪岩包体的Sm-Nd等时线,13个点构成两条平行线,年龄为2.8Ga,∈_(Nd(t))分别为2.27Ga和5.52Ga.A组包体与年龄为2.23Ga的五台群火山岩的∈_(Nd(t))值几乎一样(2.14Ga),表明两套幔源岩派生于同一源区,华北地区新生代火山岩和元古代基性,超基性岩的∈_(Nd(t))也在这一范围,因此,认为该区的地幔源自3.5Ga以来∈_(Nd)值几乎没有明显的改变。B组包体∈_(Nd(t))值较高可能是由于五台群火山活动对早期包体混染的结果。
Isotope geochronological studies indicate the existence of an old continental crust in the Henshan area. The Sm-Nd isochrons for xenoliths in plagioclasse amphibolites, with 13 data points constituting two parallel arrays, give ages around 2800 Ma, with Nd(t) = 2.27 and 5.52, respectively. The Nd(t) value for the xenoliths of group A is almost the same as that for the Wutai Group volcanic rocks (2230Ma) (2.14), indicating that the two suites of mafic rocks were derived from the same.source region within the mantle. The Nd(t) values for the Proterozoic mafic and ultra-mafic rocks as well as for the Cenozoic volcanics in North China also fall within the same region. Therefore, there has been no remarkable change in Nd(t) for the mantle source in North China since 3500Ma. Higher Nd(t) values for the xenoliths of group B seem to be attributed to the contamination of primary xenoliths by the Wutai Group volcanic materials.
出处
《地球化学》
CAS
CSCD
北大核心
1992年第3期255-264,共10页
Geochimica
