摘要
根据天山地区(4244°N,8189°E)1∶20万化探采集的900余个岩石样品的分析结果,基于全样本统计和迭代剔除方法,得到新疆天山地区表壳(出露地壳)的39种元素丰度值;对其中的SiO2、TiO2、Al2O3、TFe2O3、MgO、MnO、CaO、Na2O、K2O、P2O510种常量元素,按氧化物之和为100%进行归算。与全球大陆上地壳元素丰度值相比,天山地区表壳元素丰度富集SiO2、MnO和Ag、As、Bi、Sb元素,明显亏损CaO和Be、Co、Cr、Ni、Mo、Sn、V、W等元素。从元素比值来看,该区表壳的Ba/La、K/La、K/Th、Nb/La、Th/La、Y/La值与全球大陆上地壳相应元素值相当;而K/Na、La/As、La/Sb值明显低于全球大陆上地壳。该区表壳化学成分相当于花岗闪长岩,同时表现出相对富钠和As、Sb元素的特征;这一地球化学特征与区内出露的表壳岩石主要是加里东期和海西期岛弧造山作用的产物有关,相对富钠的成分特征与岛弧岩浆活动中的Adakite质岩浆作用有关。
On the basis of the analysis results of more than 900 rock samples that were evenly colleted during the (geochemical) exploration of 1∶200 000 scale that covered Tianshan region (42 ~ 44°N, 81~89°E), the average abundances of 39 elements were obtained for the supra-crust (exposed crust) of Tianshan region. For calculating the element contents, the total sample statistics and iteration pick-out method were used; meanwhile, the abundances of ten oxides, SiO_2, TiO_2, Al_2O_3, TFe_2O_3, MgO, MnO, CaO, Na_2O, K_2O and P_2O_5, were normalized to 100%. In comparison with the average abundances of elements in the upper crust of global continent, the supra-crust of Tianshan region exhibits the enrichment of SiO_2, MnO, Ag, As, Bi and Sb, and the depletion in CaO, Be, Co, Cr, Ni, Mo, Sn, V and W. In the view of element ratios, the ratios of Ba/La, K/La, K/Th, Nb/La, Th/La and Y/La of the supra-crust of Tianshan region are identical to those of upper crust of global continent, but the ratios of K/Na, La/As and La/Sb are significantly smaller than those of continental upper crust. The whole rock chemistry of supra-crust of Tianshan corresponds to granodiorite composition. Meanwhile, the supra-crust geochemistry of Chinese Tianshan region is characterized by its relative enrichment of Na, As and Sb. This geochemical characteristic is originated to arc lithologies dominantly exposed in Tianshan region, which was mainly formed during Caledonian and Hercynian orogenesis. Especially, the Na-rich characteristic of supra-crust may be related to Adakite (or Adakite-like) magmatism accompanied with arc orogenesis.
出处
《矿物岩石地球化学通报》
CAS
CSCD
2004年第1期5-9,共5页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
中国博士后科学基金
中国科学院王宽诚博士后奖励基金
中国科学院南海海洋研究所边缘海地质与古环境开放室基金课题(BYH02A03)资助
关键词
元素丰度
地球化学
表壳
天山
新疆
geochemistry
element abundance
supra-crust
Tianshan
Xinjiang
