【作者】 杨春霞；

【导师】 张铭杰； 龚全胜；

【作者基本信息】 兰州大学 ， 构造地质学， 2012， 硕士

【摘要】 祁连山是研究甘肃省主要的古生代碰撞型造山带的有利位置,也是中国地质构造最为复杂的地区之一,本文以板块理论为指导,构造-岩浆作用为主线,为祁连山构造演化的深入研究提供一些重要的科学依据,初步研究结果如下：(1)斜长花岗岩具有典型的O型埃达克岩特征,具有富Na贫K,高Sr低Y,富集LREE,相对亏损HREE,无Eu异常,高氧逸度等特征。与西湾型埃达克岩特征一致,熔体是在高压条件下由俯冲板片在角闪岩相-榴辉岩相条件下发生部分熔融形成的具有初始成分的埃达克岩。(2)闪长岩具有典型高Sr高Yb的广西型花岗岩类特征,具有高P、Ca、 Al及高Sr高Yb的特征,A/NKC<1.1,类似于典型I型花岗岩特征,和ATG花岗岩也很类似；石英闪长岩和花岗闪长岩具有典型低Sr低Yb的喜马拉雅型花岗岩类特征,有富Si、Al、Na贫K,低Sr、低Yb、低Y的特征,LREE富集且具有微弱的负Eu异常,REE呈平坦型,HREE亏损的特征,均类似于Jamalca岛弧型花岗岩特征,暗示残留相主要为麻粒岩(石榴子石及斜长石是主要组成矿物),源岩可能为岛弧型火山岩部分熔融形成或是与岛弧型火山岩同源的岩浆演化而成。(3)早古生代末期正常岛弧岩浆岩位于乌鸡山以南,暗示当时海沟位于乌鸡山埃达克岩以北,早志留纪由于中祁连陆块向北俯冲,在俯冲带以北形成较完整的沟—弧—盆体系,由于当时洋盆已经萎缩得很小,但仍存在洋壳向北俯冲作用,表明在洋壳晚期也可以形成典型的埃达克岩,并且代表了当时洋壳即将闭合的时限,志留纪末期-早泥盆纪,随着南北向挤压作用使得残余海盆封闭,两侧刚性大陆碰撞,形成碰撞造山带,大规模的南北向逆冲推覆造山活动,使中祁连陆块仰冲于北祁连造山带之上,碰撞结合带形成由南而北叠瓦状逆冲推覆,构成了现存的复合断裂构造混杂岩带。更多还原

【Abstract】 Qilianshan is not only the favorable position to study the major Paleozoic collisional orogenic belt in Gansu Province, but also one of the most complex geological structure in China. The article, based on plate tectonic theory and tectonic-magmatism, primarily provides some important scientific accordings as follow:(1) Plagiogranites has typical O-type adakite characteristics, which, with the same characteristics as xiwan’s adakite’s, is rich in Na and depleted in K, high Sr and low Y, rich in LREE and relatively depleted in HREE, with no Eu anomaly, high oxygen fugacity, etc. The melt, with with the initial composition of adakite, is formed by partial melting under high pressure by the subducted slab in the amphibolite facies.(2) The diorite has characteristics of Guangxidiorite:high-P, Ca, Al; high Sr and high Yb, A/NKC<1.1, which are typical I-type granite characteristics and also very similar with ATG granite. Quartz diorite and granodiorite have characteristics of Himalayan granitoid:low Sr and Yb; rich of Si, Al, Na and depleted of K; rich in LREE yet a weak negative Eu anomaly and flat REE ratios; HREE loss, all of which are similar to Jamalca island arc granites. All above imply that residual phase is mainly granulite (garnet and plagioclase is the major constituent minerals) and source rocks may be formed by partial melting of island arc volcanic rocks or island arc volcanic magmatic evolution from homology.(3)In the later of Early Paleozoic normal island arc magmatic rocks are located in the south of the Wuji Mountain, suggesting that the trench located in north of Wujishan, adakite during that time. Because of the northward subduction of Central Qilian during Early Silurian, a comparatively complete trench-arc-basin system was formed in the north of the subduction belt. As the ocean basin had been shrinked very small, there was still oceanic crust northward subduction, suggesting that in the later of the oceanic crust, typical adakites, which represents the closed time limitation of ocean crust, can also be formed of. During Late Silurian-Early Devonian, with the progression of north vs. south compression the residual basin closed, the rigid continental collision happened, and collisional orogenic belt was formed of. Large-scale of north-south thrusting orogeny made the Middle Qilian continental mass above the North Qilian orogenic belt. From south to North, imbricate thrust nappe constitutes the existing fracture tectonic combination melange belt in the collision zone.更多还原