藏北高原金顶山第四纪火山岩特征及构造环境  

Characteristics and tectonic environments of Quaternary volcanic rocks in Jindingshan, North Tibet Plateau

作　　者：陈必河 刘耀荣[1] 肖冬贵 彭学军[1] 

机构地区：[1]湖南省地质调查院,湖南湘潭411100

出　　处：《岩石矿物学杂志》2003年第2期125-130,共6页Acta Petrologica et Mineralogica

基　　金：中国地质调查局资助项目 (199913 0 0 0 0 90 5 1)

摘　　要：金顶山火山岩位于藏北高原西昆仑东段华北板块与华南板块结合带南缘 ,为典型的陆相中心式喷发产物 ,存在 3次以上火山活动 ,呈平缓的被状熔岩覆盖于陡倾斜的古近纪阿克塔什组 (E3 a)之上 ,轻微剥蚀 ,K -Ar同位素年龄为 0 .4 5～ 1.93Ma。主要岩石类型为安粗岩 ,属亚碱性系列中的钙碱性系列。SiO2 5 7.88%～ 6 0 .82 % ,MgO1.95 %～ 2 .2 % ,Na2 O +K2 O 6 .93%～ 7.2 7% ,δ值 2 .73～ 3.1,DI值 6 3.5～ 6 4 .6。大离子亲石元素强烈富集 ,高场强元素富集相对较弱 ,REE 6 5 0× 10 -6～ 76 6× 10 -6,LREE/HREE 14 .9～ 15 .7,为LREE强富集型 ,δEu 0 .75～ 0 .89。( 87Sr/86Sr) i为 0 .70 970 ,δ18O为 10 .4‰。综合研究表明 ,岩浆来源于下地壳或壳幔过渡带部分熔融的同源岩浆 。Jingdingshan volcanic rocks occur in the eastern part of West Kunlun Mountain in North Tibet Plateau, geotectonically on the southern margin of the suture zone between North China plate and South China plate. The rocks originated from typical continental central eruption characterized by more than three times of volcanic activities. They overlie abruptly declining Palaeogene Aletars Formation (E 3 a ) in the form of gentle lava sheet and have been subjected to slight erosion. K_Ar isotopic age is 0.45～1.93 Ma. Latite, the main volcanic rock, is of calc_alkaline series in the sub_alkaline series: SiO 2 57.88%～60.82%, MgO 1.95%～2.2%, Na 2O+K 2O 6.93%～7.27%,δ 2.73～3.1, and DI 63.5～64.6. The large_ion lithophile elements are highly concentrated, while the high_field intensity elements are comparatively less concentrated. REE 650×10 -6 ～766×10 -6 and LREE/HREE 14.9～15.7 point to intensely_concentrated LREE. δEu values are 0.75～0.89, ( 87 Sr / 86 Sr) is 0.70970 and δ 18 O is 10.4‰. A comprehensive study shows that the magma came from partly melting magma in the lower crust or the transitional zone between the crust and the mantle, whereas the volcanic rocks were formed in a post_collision uplifted extensional setting.

关 键 词：火山岩 第四纪 构造环境 K—Ar同位素年龄 藏北高原 金顶山 

分 类 号：P588.14[天文地球—岩石学] P584[天文地球—地质学]