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西藏切琼地区钾长花岗岩年代学、地球化学及地质意义
投稿时间:2019-06-02  修订日期:2019-08-08  点此下载全文
引用本文:
DOI:10.19762/j.cnki.dizhixuebao.2020202
摘要点击次数: 106
全文下载次数: 78
作者单位E-mail
高强 中国地质大学资源学院 gaoqgeo@163.com 
闫茂强 中国地质大学资源学院  
魏俊浩 中国地质大学资源学院 junhaow@163.com 
曾成 中国地质大学资源学院  
刘颜 中国地质大学资源学院  
秦波 中国地质大学资源学院  
姜维 中国地质大学资源学院  
基金项目:国家自然科学基金项目(编号 41772071)
中文摘要:拉萨地体经历了新特提斯洋的俯冲、消减以及陆陆碰撞等地质过程,伴随以上地质过程大面积出露有中酸性侵入岩,为研究地壳演化提供了有利条件。该区晚三叠世—早侏罗世岩浆活动的成因和动力学背景目前仍存在一定争议,为解决以上问题,本文以中部拉萨地体南缘的切琼钾长花岗岩为研究对象,对其进行岩相学、锆石U-Pb年代学、Hf同位素和全岩地球化学特征分析,探讨其岩石成因特征及大地构造意义。切琼钾长花岗岩主要由石英、钾长石、斜长石和黑云母组成。岩浆锆石U-Pb加权平均年龄为210.28±0.92Ma(MSWD=0.99),形成于晚三叠世。岩体具高SiO2(73.44%~75.76%)、高K2O(4.87%~5.15%)和高Al2O3(12.58%~13.40%)的特征,铝饱和指数(A/CNK)大于1.0,属于过铝质高钾钙碱性S型花岗岩。轻稀土较富集且具有中等程度的负铕异常,微量元素富集大离子亲石元素K、Rb和放射性元素U、Th,不同程度亏损Ba、Nb、Sr、Ti、Zr和Hf等元素。εHf(t)为较低的负值(-4.2~-2.6),二阶段模式年龄t2DM在1262~1347Ma之间。综合分析认为钾长花岗岩形成于后碰撞伸展构造环境,为地壳中泥质沉积物部分熔融的产物。中二叠世末期,在研究区内中部拉萨地体南缘与澳大利亚北部边缘发生碰撞造山作用,造成松多洋的闭合以及由此产生后碰撞岩浆活动,在拉萨地体30°N附近形成一条晚三叠世花岗岩带。
中文关键词:拉萨地体  晚三叠世花岗岩  锆石U-Pb年代学  Hf同位素  地球化学
 
Geochronology, geochemistry and geological significance of syenogranitic granites in Qieqiong area, Tibet
Author NameAffiliationE-mail
GAO Qiang Faculty of Earth Resources,China University of Geosciences gaoqgeo@163.com 
YAN Maoqiang Faculty of Earth Resources,China University of Geosciences  
WEI Junhao Faculty of Earth Resources,China University of Geosciences junhaow@163.com 
ZENG Cheng Faculty of Earth Resources,China University of Geosciences  
LIU Yan Faculty of Earth Resources,China University of Geosciences  
QIN Bo Faculty of Earth Resources,China University of Geosciences  
JIANG Wei Faculty of Earth Resources,China University of Geosciences  
Abstract:The Lhasa terrane has undergone subduction, subtraction and land-land collision of the New Tethys Ocean, and a large area of intermediate-acid intrusive rocks have emerged, which provides favorable conditions for the study of crustal evolution. The genesis and dynamic background of the Late Triassic-Early Jurassic magmatism in this area are still controversial. To solve the above problems, this paper takes the Qieqiong syenogranitic granite in the middle south region of Lhasa terrane as a study. The object is analyzed by petrography, zircon U-Pb geochronology, Hf isotope and whole-rock geochemical characteristics, and its petrogenic characteristics and tectonic significance are discussed. Qieqiong syenogranitic granites is mainly composed of quartz, potassium feldspar, plagioclase and biotite. The U-Pb weighted mean age of magmatic zircon is 210.28±0.92 Ma (MSWD=0.99), which was formed in the Late Triassic. The rock is characterized by high SiO2 (73.44%~75.76%), high K2O (4.87%~5.15%) and high Al2O3 (12.58%~13.40%). The Al saturation index (A/CNK) is more than 1.0 and belongs to peraluminous high K calc-alkaline S-type granite. Light rare earth elements are relatively enriched and have moderate negative europium anomalies. Trace elements enrich K, Rb and radioactive elements U and Th of large ion lithophile elements, and deplete elements Ba, Nb, Sr, Ti, Zr and Hf in varying degrees. The εHf(t) was a lower negative value (-4.2 to -2.6), and the Hf two stage mode age was between 1262 Ma and 1347 Ma. The syenogranitic granites was formed in a post-collisional extensional tectonic environment and was the product of partial melting of argillaceous sediments in the crust. At the end of Middle Permian, collision orogeny occurred between the southern margin of middle Lhasa terrane and the northern margin of Australia, which resulted in the closure of the Songdo Tethyan Ocean and subsequent post-collision magmatism, forming the Late Triassic granite belt near the north latitude of Lhasa terrane at 30 degrees.
keywords:Lhasa terrane  Late Triassic granite  zircon U-Pb chronology  Hf isotope  geochemistry
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