贺兰山古元古代花岗岩年代学及地球化学特征:对华北克拉通西部孔兹岩带形成和演化的制约  

Geochronology and geochemistry of the Paleoproterozoic granites from the Helanshan region: Contrains on the formation and evolution of khodalite belt in the western North China Craton

作　　者：甘保平 第五春荣[1] 王伯隆 王庭怡 GAN BaoPing;DIWU ChunRong;WANG BoLong;WANG TingYi(State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China)

机构地区：[1]西北大学大陆动力学国家重点实验室西北大学地质学系

出　　处：《岩石学报》2019年第8期2325-2343,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41421002、41672188、41272004);西北大学大陆动力学国家重点实验室科技部专项联合资助

摘　　要：华北克拉通西部贺兰山地区基底岩石以古元古代孔兹岩系和S型花岗岩为主,该区的S型花岗岩是探索华北克拉通西部陆块孔兹岩带地质演化的关键研究对象之一。本文主要以贺兰山北部的片麻状含石榴黑云母花岗岩和似斑状石榴黑云母花岗岩为研究对象,通过详细的岩石学、锆石U-Pb年代学、Hf同位素以及全岩地球化学等方法来讨论其岩石成因和地质意义。结果表明,片麻状含石榴黑云母花岗岩和似斑状石榴黑云母花岗岩侵位年龄分别为~2. 0Ga和~1. 97Ga,属于古元古代时期不同阶段岩浆作用的产物。片麻状含石榴黑云母花岗岩具有较低SiO2(60. 88%~65. 42%),高Al2O3(16. 84%~19. 35%)、Fe2O3T(5. 94%~6. 14%)、K2O (3. 25%~5. 10%)、A/CNK (1. 75~2. 34)和Mg#(47~51),低Na2O (1. 14%~2. 45%),以及较高的稀土元素含量(∑REE=262×10-6~290×10-6)和明显的Eu负异常(δEu=0. 30~0. 55)。似斑状石榴黑云母花岗岩具有高SiO2(71. 93%~74. 98%)、K2O (4. 58%~6. 98%)、Al2O3(13. 25%~14. 79%)和Na2O (3. 13%~3. 94%),低Fe2OT3(0. 69%~1. 39%),A/CNK值为1. 08~1. 14,且具有相对较低的Mg#值(17~43)和稀土元素总量(∑REE=35. 3×10-6~127×10-6),Eu负异常和正异常(δEu=0. 07~3. 58),二者均属于过铝质S型花岗岩。贺兰山两期花岗岩明显富集大离子亲石元素(如Rb、U等),亏损高场强元素(如Nb、Ta等)。早期片麻状含榴黑云母花岗岩和晚期似斑状石榴黑云母花岗岩的εHf(t)值分别为-1. 1^+2. 6和-2. 1^+3. 8,对应的两阶段Hf同位素模式年龄(tDM2)分别为2. 45~2. 68Ga和2. 36~2. 73Ga,远大于其锆石的结晶年龄。此外,贺兰山花岗岩具有相对高的Al2O3/TiO2和低的CaO/Na2O、Rb/Sr、Rb/Ba比值,表明其原岩可能主要以变沉积岩为主。上述结果表明贺兰山地区古元古代S型花岗岩的岩浆起源于古老地壳变沉积岩物质,可能有少量新生地壳物质的加入。综合区域地质资料,本文研究认为贺兰山地区在古元古代晚期�The basement rocks of Helanshan area in the Western Block of the North China Craton( NCC) are dominated by the Paleoproterozoic khondalites series and S-type granites,among which the S-type granites are one of the key objects to explore the geological evolution history of the khondalites belt in the western part of the NCC. In this paper,the detailed petrology,zircon U-Pb geochronology,Hf isotopes and whole-rock geochemistry studies were done on the gneissic garnet-bearing biotite granite and porphyritic garnet biotite granite from the north of the Helanshan region,to discuss their petrogenesis and geological significance. Zircon U-Pb dating yields emplacement ages for the gneissic garnet-bearing biotite granite and porphyritic garnet biotite granite of ~ 2. 0 Ga and~ 1. 97 Ga,respectively, which represent the products of different stages of magmatism in the Helanshan region during the Paleoproterozoic. The gneissic garnet-bearing biotite granites have low SiO2( 60. 88%~ 65. 42%),high Al2O3( 16. 84%~ 19. 35%),FeT2O3( 5. 94%~ 6. 14%),K2O( 3. 25%~ 5. 10%),A/CNK values of 1. 75 ~ 2. 34 and Mg#values of 47 ~ 51,and low Na2O( 1. 14%~ 2. 45%),which have relatively high total rare earth elements(∑REE = 262 × 10-6~ 290 × 10-6) with evidently negative Eu anomalies(δEu = 0. 30 ~ 0. 55). Whereas,the porphyritic garnet biotite granites have relatively high SiO2( 71. 93%~ 74. 98%),KT2O( 4. 58%~ 6. 98%),Al2O3( 13. 25%~ 14. 79%) and Na2O( 3. 13%~ 3. 94%),low Fe2O3( 0. 69%~ 1. 39%),A/CNK values of 1. 08 ~ 1. 14 and relatively low Mg#values of 17 ~ 43,which have relatively low total rare earth elements(∑REE = 35. 3 ×10-6~ 127 × 10-6),and negative or positive Eu anomalies(δEu = 0. 07 ~ 3. 58). The Helanshan granites belong to the peraluminous S-type granites. Additionally,two-period granites of the Helanshan region were enriched in large-ion lithophile elements( LILEs)( e. g. Rb,U),but depleted in high-field-strength elements( HFSEs)( e. g. Nb,Ta). Zircon Hf isotope composition shows that theεHf( t) values for the early

关 键 词：S型花岗岩 孔兹岩 古元古代 贺兰山 华北克拉通 

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