摘要
采用 Rb-Sr.u—Pb 和 Sm-Nd 法测定了黄陵花岗岩类岩基南部各岩体的形成年龄。它们是:镁铁—超镁铁质岩体1368Ma;由闪长岩、石英闪长岩和英云闪长岩组成的三斗坪岩体为832±12Ma;主体期似斑状黑云母花岗闪长岩体为819±7Ma;细粒花岗岩脉769±1Ma。根据岩体的 Sr-Nd 同位素组成特征,认为岩基的形成是深源的,与亏损地慢和地壳组分的混合,以及岩浆分离结晶的联合作用有关。
By using Rb—Sr,U—Pb and Sm—Nd methods the formation ages of various mas- sives in the south of Huangling batholith have been measured.The average Nd model age T_(Dm) of the mafic —ultramafic massives is 1368 Ma Which may be considered as the for- mation age.The Sandouping massif composed of diorite,quartz diorite and tronalite was formed at 832±12 Ma B.P.The time for the closure of Rb—Sr system of the rock— forming minerals(i.e.,regional cooling to the temperature lower than 300℃)was 805 ±5 Ma B.P.The biotite trondhjemite and porphyritic biotite granodiorite Which is the principal portion of the batholith were formed later at 819±7 Ma B.P.and closed at 800 ±2 Ma B.P.;the fine-graincd granite veins and stocks widely intruded into the mas- sives mentioned above were formed at 769±1 Ma.B.P.According to the Sr and Nd iso- topic characteristics it is considered that the genesis model of Huangling batholith is the mixing of the two components of lower crust and depleted mantle combined with magma fractional crystallization.
