摘要
在内蒙古扎兰屯东侧出露一群中性岩脉,产在晚石炭世扎兰屯花岗岩体中,脉岩岩性为闪长玢岩,似斑状结构,斑晶为斜长石、碱性长石、角闪石、辉石和石英,基质为细粒状的上述矿物及玻璃质。其锆石 U-Ph LA-ICP-MS 谐和年龄为120.6±4.7Ma,基质^(40)Ar/^(39)Ar 坪年龄为122.2±0.6Ma,侵位时代可确定为早白垩世。脉岩的 SiO_2含量为56.88%～61.69%,Al_2O_3含量为15.83%～19.29%,全碱含量较高,为5.32%～8.37%。稀土元素总量为121.4×10^(-6)～144.1×10^(-6),轻重稀土分馏系数较大,(La/Yh)_N 值为6.24～10.40。富集大离子亲石元素(LILE),亏损重稀土元素(HREE)。δEu 表现为弱的负异常(0.92～0.79)。在同位素地球化学方面,具有正的ε_(Nd)(t)值(+3.06)和较低的初始^(87)Sr/56 Sr 值(0.7047～0.7053);岩石铅同位素均一,具幔源特征。综合考虑脉岩年代学和地球化学研究结果,本文认为研究的脉岩形成于伸展背景下重熔的新底侵玄武质下地壳的岩浆侵入作用。
Zhalantun dyke swarm was emplaced in a late Carboniferous Zhalantun granitic pluton, Inner Mongolia. The dyke swarm consists of diorite porphyrite in lithology. The samples all have porphyraceous texture. Phenocrysts are plagioclase, alkalic feldspar, hornblende,pyroxene and quartz, matrixes are fine-grained minerals above mentioned and glass. Zircon U-Pb determination yields a concordant age of 120.6 ±4.7Ma and ^40Ar-^39Ar dating of the matrix gives a plateau age of 122.2 ±0.6Ma, indicating intrusive time of the dyke swarm is the early Cretaceous. The chemical analyses of the dyke swarm show that SiO2 contents have a range of 56.88% - 61.69%, Al2O3 contents range from 15.83% to 19.29%, and total alkali is high （5.32% -8.37% ）. The total REE contents have a large variation, ranging from 121.4 ×10^-6 to 144. 1 ×10^-6. The samples have high （La/Yb） N Values （6.24 - 10.40） and little negative Eu anomaly （0.92 -0.79）. The samples are enriched in LILE and depleted in HFSE. Isotopic geochemistry shows that the dykes have high εNa （ t ） of ± 3.06 and low （ ^87 Sr/^86 Sr） i of 0. 7047 - 0. 7053 and Pb characteristics similar to those of mantle. According to the geochemistry and geochronology of the dyke swarm and compared to the contemporary volcanic rocks, we concluded that the dykes originated from the remehing of the underplating basaltic juvenile lower crust.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2006年第11期2733-2742,共10页
Acta Petrologica Sinica
基金
国家自然科学基金重点项目40334043资助.
关键词
扎兰屯脉岩
岩石地球化学
下地壳熔融
大兴安岭
Zhalantun dyke swarm, Petrogeochemistry, Remehing of the lower crust, Da Hinggan Mountain.
