中祁连西段黑沟梁子花岗岩的锆石U-Pb同位素年龄及成因

INTRUSION IN THE WESTERN SEGMENT OF THE MIDDLE QILIAN MOUNTAINS

黑沟梁子花岗岩岩体为中祁连山带两段野马南山巨量花岗岩的一部分,出露于野马山南北缘,岩性为黑云母二长花岗岩。δ值、NK/A值、A/NCK值、Eu负异常、δEu值、ACF图解、87Sr/86Sr比值、εSr、147Sm/144Nd比值、207Pb/204Pb比值、εNd值等岩石化学和同位素特征表明黑沟梁子花岗岩属钙碱性过铝质岩系,浆来源于地壳物质的重熔,具S型花岗岩特点。通过对黑沟梁子花岗岩的颗粒级锆石U Pb同位素测年,获得206Pb/238U表面年龄统计权重平均值为(444±17)Ma。w(Nb) w(Y)和w(Rb) w(Y+Nd)图和R1-R2图解上两个样点均落入同碰撞花岗岩区,结合前人研究成果可以确定该岩体形成于板块碰撞阶段。该岩体的锆石U Pb年龄的确定和成因的探讨对于深入研究祁连造山带的构造演化提供了一条重要的地质信息。

Heigouliangzi pluton is a part of Yema'nanshan, a huge of granites in the west segement of middle Qilian Mountains, the pluton located north margin of Yema'nanshan and their mineral assemblages belong to biotite monzogranite. Based on the new data from some recent studies, single-grained zircon U-Pb dating and genesis of the Heigouliangzi pluton were introduced in this paper.δ,NK/A,A/NCK,δEu,(()^(87)Sr/^(86)Sr,) (()^(207)Pb/)^(204)Pb,^(147)Sm/^(144)Nd,εSr,εNd and ACF-diagram et al. petrochemical and isotopic features all indicated that Hegouliangzi granite is calc-alkaline and extra-aluminium S-type granite and the magma derived from the earth's crustal remelting. By the U-Pb zircons dating from the Heigouliangzi biotite monzogranite acquired an average weighted ()^(206)Pb/()^(238)U age is(444 ±17)Ma. In the Nb-Y vs. Rb-(Y+Nb)diagram and R_1-R_2 diagram, the geochemical data all plotted into collision scales, combining the former researches, we can ensure that the granite was intruded during the stage of collision of Calidonian Qilian orogen. The U-Pb zircon dating and genesis discussion provided an important geological information for lucubrating geodynamic environment and evolvement of the Qilian orogen.