摘要
中亚造山带南缘晚古生代与早中生代之交的构造背景一直存在争议。本文以西乌旗罕乌拉地区发育的花岗闪长岩和黑云母二长花岗岩为研究对象,对其开展了野外地质、岩石学、锆石U- Pb同位素年代学、地球化学研究。LA- ICP- MS 锆石U- Pb测年获得花岗闪长岩的结晶年龄为253. 8±1. 2Ma和240. 5±0. 78Ma,黑云母二长花岗岩的结晶年龄为249. 6±1. 7Ma和240. 4±0. 59Ma,反映了晚二叠世晚期-早中三叠世的构造岩浆作用事件。岩石学和地球化学研究表明,花岗闪长岩铝饱和指数A/CNK为 0. 89~1. 13,属于钙碱性I型花岗岩;SiO 2介于65. 97%~70. 56%(>56%),MgO介于1. 33%~ 1. 70%(<3%),Al 2 O 3 介于14. 75%~15. 01%(≈15%),Sr介于483. 2×10 -6 ~541. 9×10 -6 (>400×10 -6 ),Y介于10. 46×10 -6 ~13. 35×10 -6 (<18×10 -6 ),Yb介于0. 77×10 -6 ~1. 45×10 -6 (<1. 9×10 -6 ),岩石轻重稀土分馏明显,(La/Yb) N 介于12. 07~33. 05,具Eu轻微负异常(δ Eu=0. 78~0. 89),显示了埃达克质岩石的地球化学特征。黑云母二长花岗岩铝饱和指数A/CNK为1. 05~1. 20,属于过铝质高钾钙碱性系列,具有高SiO 2 (72. 73%~77. 02%)、富碱(K 2 O+Na 2 O=7. 36%~8. 47%),低P 2 O 5 (0. 016%~0. 085%)和CaO(0. 38%~1. 67%),富集Th、U、K、Nd、Hf,亏损Ba、Nb、Ta、P、T和HREE等元素,明显负Eu异常(δ Eu=0. 08~0. 61),高度分异(DI=85. 78~95. 76),P 2 O 5 含量与SiO 2 呈明显的负相关关系,Y含量与Rb呈明显的正相关关系,属于高分异Ⅰ型花岗岩。岩石地球化学特征反映它们为来源于不同深度的加厚地壳部分熔融形成的熔体,经进一步演化及结晶分异后,不同批次上升就位的产物。结合岩体地质学及区域地质资料,本文认为晚二叠世晚期-早中三叠世花岗岩形成于碰撞环境,为晚二叠世末古亚洲洋闭合后,西伯利亚板块和华北板块碰撞事件的岩浆响应。
The tectonic settings of the southern Central Asia Orogenic Belt (CAOB) in the late Paleozoic to early Mesozoic have long been controversial. The study carried out an investigation for granodiorite and biotite adamellite in Hanwula of Xiwu Banner, Inner Mongolia using petrology, zircon U-Pb isotopic geochronology and geochemistry. LA-ICP-MS U-Pb dating yields two crystallization ages of about 253. 8 + 1. 2 Ma and 240. 5±0. 78 Ma for the granodiorite and two ages of 249. 6±1. 7 Ma and 240. 4±0. 59 Ma for biotite adamellite, representing the tectonic-magmatic event in the late Late Permian to Early-Middle Triassic. Petrological and geochemical study indicates that the granodiorite has the aluminum saturation index (A/CNK) of 0. 89 to 1. 13, suggesting that it belong to calk-alkaline I-type granite. Geochemical analysisshow sthattherockhasS iO2 of 65.97% 70.56%(〉56%), M g O o fl.33% 1.70%(<3%), A1203 of 14. 75% 15. 01%(义 15%), high Sr of 483.2 X 1(T6 541. 9 X 10-6 (>400 X 1(T 6), low Y of 10.46X10 6 13. 35X K T6,(<18 X1(T 6), and Yb of 0.77X10-6 1.45X10_6(<1.9 X10 6). Distinct fractionation between LREE and HREE and (La/Y b)N varying between 12. 07 ~ 33.05, along with unapparent negative Eu anomaly (^Eu = 0. 78^0. 89) in the chondrite-normalized REE pattern, all suggest that the granodiorite belong to adakite. The biotite adamellite has an A/CNK of 1. 05 1. 20, suggesting that it belongs to peraluminous and high-K calc-alkaline series. The rock is characterized by high silicon (Si02=72.73% 77.02%),highalkali(K20 + Na20=7.36% 8.47%),low P205(0.016% 0.085%) and CaO (0.38% 1.67%), enrichment of T h,U,K,Nd,H f, and depletion of Ba,N b,T a,P , T and HREE, significant negative Eu anomalies (5Eu = 0. 08 0 61), and high degree of differentiation (DI = 85. 78 95. 76). P205 is negatively correlated with Si02 while Y is positively correlated with Rb, indicating that biotite adamellite belongs to highly fractional I-type granite. Lithogeochemical characteristics above indicate that the Hanwula granites were probably the
作者
张晓飞
滕超
周毅
王必任
曹军
李树才
张华川
庞振山
刘俊来
ZHANG Xiaofei;TENG Chao;ZHOU Yi;WANG Biren;CAO Jun;LI Shucai;ZHANG Huachuan;PANG Zhenshan;LIU Junlai(Development and Research Centre,China Geological Survey,Beijing, 100037;School of Earth Sciences and Resources,China University of Geosciences,Beijing,100083;Mineral Exploration Technical Guidance Center,Ministry of Natural Resources,Beijing, 100083;Cores and Samples Center of Natural Resources,China Geological Survey,Yanjiao, Hebei, 065201)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2019年第8期1903-1927,共25页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号41802222)
中国地质调查局项目“内蒙古1∶5万呼格吉勒图、巴彦华、巴彦布拉格、彦吉嘎庙幅区域地质调查”(编号1212011220453)项目联合资助的成果
关键词
中亚造山带
西乌旗
晚二叠世-早中三叠世
埃达克岩
高分异Ⅰ型花岗岩
Central Asia Orogenic Belt (CAOB)
Xiwu Banner
Late Permian to Early-Middle Triassic
Adakite
high differentiation I-type granites
