早古生代古亚洲洋俯冲记录:来自东天山卡拉塔格高镁安山岩的年代学、地球化学证据  

Early Paleozoic subduction of the Paleo-Asian Ocean: Zircon U-Pb geochronological and geochemical evidence from the Kalatag high-Mg andesites,East Tianshan

作　　者：李玮[1] 陈隽璐[2] 董云鹏[1] 徐学义[2] 李智佩[2] 柳小明[1] 何登峰[1] 

机构地区：[1]大陆动力学国家重点实验室西北大学地质学系,西安710069 [2]中国地质调查局西安地质调查中心,西安710054

出　　处：《岩石学报》2016年第2期505-521,共17页Acta Petrologica Sinica

基　　金：国土资源部地质矿产调查评价专项(1212011085009;1212011085475);国家自然科学基金项目(41372204;41190074;41225008)联合资助

摘　　要：吐哈盆地南缘荒草坡群大柳沟组火山岩出露于大草滩断裂以北的彩霞山、土屋铜矿北和卡拉塔格地区。该组火山岩主要为基性、中酸性熔岩及火山碎屑岩组合。LA-ICP MS锆石U-Pb分析获得安山岩和英安岩的年龄分别为434.8±3.8Ma和438.4±4.9Ma,表明大柳沟组火山岩形成于早志留世。安山岩Si O2含量为54.35%~60.70%;Al2O3含量为11.8%~16.3%,Mg O含量为4.94%~8.27%,Ti O2含量为0.38%~0.52%,Na2O和K2O的含量分别为0.50%~3.83%和0.08%~1.26%,铝饱和指数（A/CNK）为0.77~1.37,低ΣREE（43×10-6~70×10-6）,为具有亏损源区特征的高镁安山岩。英安岩较安山岩Si O2含量高（63.74%~75.35%）,具有相似的Al2O3（12.3%~16.0%%）和Ti O2（0.32%~0.52%）含量;Na2O和K2O含量分别为2.01%~5.53%和0.16%~2.19%,ΣREE含量较安山岩略高（61×10-6~84×10-6）,铝饱和指数（A/CNK）为0.77~5.74。安山岩和英安岩均轻重稀土分异明显,具有中等的Eu负异常;富集大离子亲石元素（LILE）,亏损高场强元素（HFSE）,具有明显的Nb-Ta-Ti负异常。相似的岩石地球化学特征表明安山岩和英安岩可能为同源岩浆,英安岩是安山质岩浆经过角闪石等矿物结晶分异作用形成的,安山岩的母岩岩浆很可能来自亏损大洋岩石圈地幔。基于该组岩石组合、地球化学特征和区域地质资料,推测研究区高镁安山岩可能形成于洋内弧环境,这表明东天山吐哈盆地南缘卡拉塔格地区在早古生代已经存在古亚洲洋的俯冲。The Kalatag area is located on the southern margin of the Turpan-Hami Basin,northern Xinjiang,Northwest China. The Early Paleozoic Daliugou Formation volcanic rocks in this area are widely distributed in Caixia mountains,Tuwu ore and Kalatag districts,which are located to the north of the Dacaotan fault. They consist of basic,intermediate,acidic lavas,and pyroclastic rock.LA-ICP-MS zircon U-Pb dating yield dacite and andesite age of 434. 8 ± 3. 8Ma and 438. 4 ± 4. 9Ma,respectively,which show that the Daliugou Formation volcanic rocks formed in the Early Silurian. Andesite have contents of Si O2（ 54. 35% ~ 60. 70%）,Al2O3（ 11. 8%~ 16. 3%） with A / CNK of 0. 77 ~ 1. 37,Mg O（ 4. 94% ~ 8. 27%）,Ti O2（ 0. 38% ~ 0. 52%）,Na2O（ 0. 50% ~ 3. 83%） and K2O（ 0. 08% ~ 1. 26%） with high Na2 O / K2 O ratios of 3. 63 ~ 38. 3（ except one samples）,and lower ΣREE（ 43 × 10- 6~ 70 × 10- 6）.These samples are high-Mg andesites which have the characteristics of depleted source. Dacite have higher contents of Si O2（ 63. 74%~ 75. 35%） than andesite,and similar contents of Al2O3（ 12. 3% ~ 16. 0%） with A/CNK of 0. 77 ~ 5. 74,Ti O2（ 0. 32% ~ 0. 52%）,Na2O（ 2. 01% ~ 35. 53%） and K2O（ 0. 16% ~ 2. 19%）,and higher ΣREE（ 61 × 10- 6~ 84 × 10- 6）. Both andesites and dacites have an obvious differentiation between the light rare earth element（ LREE） and heavy rare earth element（ HREE）,Eu negative anomaly with medium. They are all enriched with large-ion lithophile elements（ LILE）,but are relatively depleted in high field strength elements（ HFSE）,and have an obvious negative Nb-Ta-Ti anomaly. These andesite and dacite are likely to come from the same magma chamber based on similar geochemical characteristics. Dacite is likely to be formed after andesitic magma underwent minerals such as hornblende crystallization differentiation. Andesitic magmas were most probably derived from a depleted ocean lithosphere mantle. Based on the volcanic assemblage,geochemical characteristics a

关 键 词：卡拉塔格 高镁安山岩 大南湖岛弧带 古亚洲洋俯冲 东天山 

分 类 号：P588.144[天文地球—岩石学] P597.3[天文地球—地质学]