摘要
阿拉善北缘造山带位于中亚造山带最南端,前人鲜有报道的尚丹岩体是认识其构造演化的关键。尚丹岩体中花岗闪长岩的LA-ICP-MS锆石U-Pb年龄为331. 7±0. 9Ma,是在宗乃山-沙拉扎山构造带中获得的最早的晚古生代年龄,指示了早石炭世的岩浆事件。尚丹花岗闪长岩体具有中等硅含量(SiO_2=66. 07%～68. 15%)、高Na_2O(Na_2O/K_2O> 1. 6),并相对高CaO(CaO/Na_2O> 1),属于准铝质(A/CNK <1,A/NK> 1)和中钾钙碱性系列(σ=1. 21～1. 40,K_2O=1. 55%～2. 21%),其岩石薄片中可见角闪石,地球化学和岩相学上都显示出I型花岗岩的特征。岩石的稀土元素含量中等,轻重稀土分异较明显((La/Yb)N=5. 30～6. 62),富集Rb、Th、K、Zr、Hf等元素,亏损Ba、Nb、Ta、P、Ti等元素。样品未出现明显Eu负异常,表明其可能形成于中下地壳的部分熔融。同时,2件全岩样品具有弱负的εNd(t)值(-1. 02、-0. 91),Nd模式年龄tDM1为1. 30～1. 28Ga,1件样品的锆石εHf(t)值为+0. 30～+5. 27,Hf模式年龄tDM2为1. 32～1. 00Ga。结合地球化学分析,尚丹岩体很可能形成于中新元古代地壳的再循环。总的来说,尚丹岩体具有岛弧相关特征,构造判别图解显示其形成于俯冲相关环境,表明阿拉善北缘在早中古生代造山停歇后,晚古生代的俯冲作用至少开始于早石炭世。
The Northern Alxa Orogenic Belt is the southernmost segment of the Central Asian Orogenic Belt. The less investigated Shangdan pluton is a key point to understanding its tectonic evolution. The granodiorites from this pluton yield zircon LA-ICP-MS U-Pb ages of 331. 7 ± 0. 9 Ma,which is the earliest age obtained for the Late Paleozoic plutons in the Zongnaishan-Shalazhashan tectonic zone and indicates an Early Carboniferous magmatic event. The granodiorites from the Shangdan pluton have moderate silicon contents（ SiO_2= 66. 07% ～ 68. 15%）,high Na_2O contents（ Na_2O/K_2O 1. 6） and relatively high CaO contents（ CaO/Na_2O 1）,and belong chemically to metaluminous series（ A/CNK 1,A/NK 1） with medium-K and calc-alkaline（ σ = 1. 21 ～ 1. 40,K_2O = 1. 55% ～2. 21%） characteristics. The hornblendes are also found in the rock slices. Both the geochemistry and petrography show affinity to the I-type granites. The granodiorites have moderate REE contents and moderate to strong LREE to HREE differentiation（（ La/Yb）N=5. 30 ～ 6. 62）. They are enriched in Rb,Th,K,Zr,Hf and depleted in Ba,Nb,Ta,P,Ti. No negative Eu anomalies have been found in the samples,suggesting that they might be derived from partial melting of middle-lower crust. Meanwhile,two whole-rock samples have slightly negative εNd（ t） values of-1. 02 and-0. 91 with Nd model age tDM1 of 1. 30 ～ 1. 28 Ga. One sample yields zircon εHf（ t） values between ＋ 0. 30 and ＋ 5. 27 with Hf model age tDM2 of 1. 32 ～ 1. 00 Ga. Combined with geochemical analysis,the Shangdan pluton was likely recycled from the Meso-Neoproterozoic crust. In conclusion,the Shangdan pluton with arc characteristics has been discriminated to be formed in a subduction-related setting,suggesting that after the termination of the Early-Middle Paleozoic orogenesis in the northern Alxa,the Late Paleozoic subduction occurred at least in the Early Carboniferous.
作者
甘立胜
吴泰然
陈彦
张文
张昭昱
GAN LiSheng;WU TaiRan;CHEN Yan;ZHANG Wen;ZHANG ZhaoYu(MOE Key Laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Space Sciences,Peking University,Beijing 100871,China;Research School of Earth Sciences,Australian National University,ACT 0200,Australia;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Department of Civil Engineering,Technical University of Denmark,2800 Kongens Lyngby,Denmark)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第11期3359-3374,共16页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41372225)资助
