新疆准噶尔脉岩群地质及成因

GEOLOGY AND GENESIS OF VEIN ROCK GROUP IN WESTERN ZHUNGGAR, XINJIANG

脉岩群发育于薪疆准噶尔西部托里县境内,是海西中期的产物,Rb-Sr等时线年龄为277～283Ma。据国际火成岩分类有石英二长闪长玢岩和石英闪长玢岩等6种岩石。属于钙碱性岩系列,Ⅰ型花岗岩类。92个样品的平均(La/Sm)N=1.29,(La/Lu)_N=5.05,LREE/HREE=22。δEu变化范围0.84～1.49。温压条件:角闪石斑晶T=825～1044℃,P=3.37～7.39kPa,斜长石T=809～1070℃。锶同位素初始比值0.70379～0.70410。Sm-Nd同位素测得ε_(Nd)(t)=7.63～9.47,母岩浆源自亏损的上地幔。

Vein rock group in Teli, Western Zhunggar, Xinjiang was formed in middle Variscian, and its Rb-Sr isotopic ages are 277～283 Ma. Classification and nomenclature on vein rocks by IUGS are as follows: quartz monzodiorite(40％ of sample number), quartz diorite(30％), diorite(13％), monzodiorite(11％), granodiorite(5 samples) and monzonite(only 1 sample). The petrochemical characteristics are:MgO/(MgO+Fe_2O_3+FeO)=0.37～0.47,sodium is rich and potassium is lower,average Na_2O/K_2O=4.05(N=92,σ=0.2701). The A-F-M diagram shows that almost all of the points of vein rocks are distributed under average trend line of Hawaiian TH, so they belong to calc-alkali rock series. The diagrams of (Al-Na-K)-Ca-Fe^(2+)+Mg) (atomic ratios) and Na_2O-CaO-Al_2O_3(molar ratios) show that they are of Ⅰ-types. Chondrite-normalized REE distribution patterns of vein rocks in Western Zhunggar show gentle sloping, demonstrating that the rocks have Eu anomaly or have small negative to positive anomaly(Eu=0.84～1.49). The average values(N=92) : (La/Sm)_N=1.29, (La/Lu)_N=5.05, LREE/HREE=22.00. The similar patterns among various varieties and structures in vein rock group indicate that they possess common consanguinity and homologous series. The T and P condition for hornblende phenocrysts is T=825～1044℃,P=3.37～7. 39kPa; and for plagioclase phenocrysts, T=809～1070℃. The strontium isotopic initial ratios of vein rock group are 0.70379～0.70410, ∈_(Nd)(t)=7.63～9.47, so the source of parental magma is the depleted upper mantle.