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为更好认识聂荣微陆块上的泛非-早古生代构造热事件并约束其构造演化,本文报道了聂荣微陆块中安多片麻岩锆石LA-ICP-MS U-Pb定年结果及其地球化学特征.安多片麻岩出露于藏北安多县城以南约30 km,4件片麻岩的野外产状、矿物组成、结构特征以及全岩地球化学特征均表明片麻岩的原岩为中酸性侵入岩;片麻岩中锆石微量元素示踪、成因分析研究表明锆石具有岩浆锆石的典型特征,锆石206Pb/238U谐和年龄在505～517 Ma,为中-晚寒武世,代表了片麻岩原岩的时代.样品具显著高硅,富碱的特征,碱度率AR=1.73～3.7,分异指数DI=70.78～90.28,岩石铝饱和指数在1.02～1.05,FeO*/MgO介于2.63～4.50,10000×Ga/Al在2.12～2.41,P2O5和Al2O3含量随SiO2增加而降低,Th,Y与Rb含量具有非常好的正相关关系,片麻岩类原岩的成因类型属于分异的亚碱性过铝质I型花岗岩.结合区域资料,安多片麻岩原岩形成的大地构造背景与碰撞造山过程密切相关,初步认为微陆块上发育的中晚寒武纪岩浆事件可能是泛非造山作用结束之后,沿冈瓦纳超大陆边缘安第斯型造山作用的产物.
In order to better understand the tectonic thermal events of the Pan-African Paleozoic in the Nierong micro-block and to constrain the tectonic evolution, this paper reports the zircon LA-ICP-MS zircon U-Pb dating of the Anduo gneiss in the Nie Rongwei block and its geochemistry Characteristics: The adventitious gneisses were exposed at about 30 km south of Anduo County, northern Tibet. The field-like characteristics, mineralogical composition, structural features and geochemical characteristics of four gneiss show that the original rock of gneiss is In silicic acid intrusive rocks; Traces and trace elements of zircon trace elements in gneisses indicate that zircons have the typical characteristics of magmatic zircons. The 206Pb / 238U zircons have a harmonic age of 505-517 Ma and are medium-late Cambrian The age of the original gneiss represents the epoch of the gneissic protolith, and the samples are characterized by high silicon and alkali-rich. The alkalinity ratios (AR) are 1.73 ~ 3.7, differentiation index DI = 70.78 ~ 90.28, rock aluminum saturation index 1.02 ~ 1.05, FeO * / MgO ranged from 2.63 to 4.50, and 10000 × Ga / Al ranged from 2.12 to 2.41. P2O5 and Al2O3 contents decreased with the increase of SiO2 content. Th, Y and Rb contents had a very good positive correlation. The genetic type belongs to the differentiated subaltern peraluminous type I granite. Combined with the regional data, the earth formed by the Anduo gneiss protolith Made background closely related to the collision orogeny, the preliminary view that the development of micro landmass in the late Precambrian magmatic events may be made after the end of the Pan-African orogeny along the continental margin of Gondwana super product Andean orogeny.