西藏北冈底斯扎独顶A型花岗岩锆石U-Pb年代学、地球化学及其地质意义  

Zircon U-Pb geochronology, geochemistry and geological significance of the Zhaduding A-type granites in northern Gangdise, Tibet

作　　者：解龙[1] 顿都 朱利东[3] 尼玛次仁 杨文光 陶刚[1] 李超[1] 何碧[1] 和源[1] 

机构地区：[1]成都理工大学沉积地质研究院,四川成都610059 [2]西藏地勘局区域地质调查大队,西藏拉萨851400 [3]成都理工大学地质调查研究院,四川成都610059

出　　处：《中国地质》2015年第5期1214-1227,共14页Geology in China

基　　金：国家自然科学基金(41002055);高等学校博士学科点专项科研基金(20125122110010);中国地质调查局项目(1212011121232)联合资助

摘　　要：西藏北冈底斯早白垩世花岗岩分布广泛;扎独顶岩体作为其中的一个典型代表,其分布广泛,呈岩基型式产出,在岩性上属二长花岗岩。在岩石化学上扎独顶岩体具有富Si O2（70.05%~74.97%）和K2O（4.09%~5.35%）,贫Ca O（0.93%~2.19%）、Ti O2（0.22%~0.52%）和Al2O3（12.81%~14.24%）的特征;属于准铝质-弱过铝质（A/CNK=0.99~1.0）高钾钙碱性系列。岩体稀土元素总量偏高（∑REE=199.36×10-6~247.91×10-6）,相对富集轻稀土元素（LREE/HREE=5.82~6.88）,Eu负异常明显（δEu=0.30~0.45）,球粒陨石标准化分布模式呈向右缓倾的V型。微量元素显示其富集Rb、Th、K、Zr和Hf,亏损Nb、Ta、Sr、Ba、P和Ti,（Zr＋Nb＋Ce＋Y）平均值为427.63。全岩锆石饱和温度（828~838°C）表明岩浆形成温度高。上述岩石地球化学特征表明扎独顶岩体为A型花岗岩。扎独顶岩体LA-ICP-MS锆石U-Pb年龄为（103.8±1.0）Ma,表明其形成于早白垩世晚期;在构造判别图解上位于碰撞后的A2型花岗岩区,是在碰撞后岩石圈伸展背景下,由于软流圈物质上涌导致岩石圈地幔与壳源熔体部分熔融并经历过一定程度的混合作用而形成的。Early Cretaceous granites are widely distributed in northern Gangdise, Tibet. The Zhaduding intrusive body, which belongs to monzogranite in lithology, is widely distributed and occurs in the form of batholith, being a typical case of the granites.Petrogeochemically it is characterized by high Si O2（70.05%- 74.97%） and K2O（4.09%- 5.35%）, low Ca O（0.93%- 2.19%）, Ti O2（0.22%- 0.52%） and Al2O3（12.81%- 14.24%）. Moreover, it belongs to metaluminous or weak peraluminous（A/CNK=0.99- 1.06）high- K calc- alkaline series. The rocks are characterized by high REE content（ ∑ REE=199.36 × 10- 6-247.91×10- 6）, rich LREE relative to HREE（LREE/HREE=5.82-6.88）, and significant negative Eu anomalies（δEu=0.30-0.45）. Chondrite-normalized REE patterns exhibit V-type with slight right-oblique feature. Trace elements show that the rocks are enriched in Rb, Th, K, Zr and Hf and depleted in Nb, Ta, Sr, Ba, P and Ti, with average（Zr＋Nb＋Ce＋Y） 427.63. Bulk-rock zircon saturation temperature（828-838°C）shows that the temperature of magma formation was pretty high. The petrogeochemical characteristics show that the Zhaduding rock body is A-type granite. The LA-ICP-MS zircon U-Pb age of 103.8±1.0Ma indicates that Zhaduding rock body was formed in late Early Cretaceous, and is located in the post-collisional A2-type granite area in discrimination diagrams. It was formed by a certain degree of mixing of the lithosphere mantle and the crustal partial melts, resulting from asthenosphere material upwelling in the postcollision extensional setting.

关 键 词：西藏 北冈底斯 A型花岗岩 锆石U-PB年龄 地球化学 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]