摘要
大兴安岭西坡北段得耳布尔地区广泛分布中侏罗世酸性火山岩-次火山岩类,岩石组合以流纹岩、流纹质岩屑晶屑凝灰岩和石英斑岩组合为主,有关它们的成岩时代、岩石成因以及成岩动力学机制尚未开展过系统的年代学与地球化学研究。本文对该区比利亚铅锌多金属矿区流纹岩进行了岩相学、LA-ICP-MS锆石U-Pb定年、元素地球化学及锆石Hf同位素研究。LA-ICP-MS单颗粒锆石U-Pb谐和年龄为(164.2±1.6) Ma(MSWD=7.7,n=14),成岩时间为中侏罗世。岩石中主量元素Si、K、Al质量分数较高,属高钾、钙碱性、过铝质岩石系列。微量元素显示它们富集大离子亲石元素,弱富集高场强元素,明显亏损Ba、Sr、Ti等元素,Nb/Ta、Zr/Hf和Th/U值分别为13.05~22.36、39.57~43.57和3.37~3.51。稀土元素存在明显负铕异常(δEu=0.69~0.76),La_(N)/Yb_(N)、La/Ce和La/Yb值分别为9.95~10.12、0.48~0.50和14.13~15.05。此外,它们的元素地球化学还呈现出低的10 000Ga/Al值(2.33~2.34)与(K_(2)O+Na_(2)O)/CaO值(9.54~9.96)。根据锆石中Ti元素计算获取的锆石饱和温度介于683~756℃之间。这些特征表明该区中侏罗世流纹岩具有Ⅰ型流纹岩属性,成岩岩浆均具有火山弧或者活动大陆边缘岩浆特征。锆石中^(176)Hf/^(177)Hf值为0.282 853~0.282 990,对应的εHf(t)为6.22~10.83,Hf二阶段模式年龄为734.2~474.0 Ma,与一阶段模式年龄(592.6~410.1 Ma)相近,指示了它们的成岩岩浆主要来源于新生下地壳部分熔融。岩浆上侵或成岩过程中受到了壳源物质混染,并与该区同时代中基性火山岩构成了“双峰式火山岩”特征。结合区域岩浆岩时空分布规律与地球物理资料证据,进一步认为区内中侏罗世酸性熔岩(流纹岩、流纹质岩屑晶屑凝灰岩和石英斑岩)成岩地球动力学背景适值古太平洋板块向欧亚大陆下行俯冲的大陆边缘环境。
The Middle Jurassic acidic volcanic-subvolcanic rocks are widely distributed in Derbur area of the northern part of the western slope of the Great Xing’an Range.The rock assemblages are mainly composed of rhyolite,rhyolitic lithic tuff and quartz porphyry,and no systematic chronological and geochemical studies have been carried out on their diagenetic age,petrogenesis and diagenetic dynamic mechanism.In this paper,petrography,LA-ICP-MS zircon U-Pb dating,geochemistry and zircon Hf isotope studies were carried out on the rhyolites in Biliya leal-zine polymetallic mining area.LA-ICP-MS single grain zircon U-Pb concordance age is(164.2±1.6)Ma(MSWD=7.7,n=14),belongs to Middle Jurassic.They have relatively high contents of major elements Si,K and Al,and belong to high-K,calc-alkaline and peraluminous rock series.Trace elements show that they are enriched in large ion lithophile elements,weakly enriched in high field strength elements,and obviously depleted in Ba,Sr,Ti and other elements.The ratios of Nb/Ta,Zr/Hf and Th/U are 13.05-22.36,39.57-43.57 and 3.37-3.51,respectively.There are negative Eu anomalies in REE(the values ofδEu are 0.69-0.76),the ratios of La_(N)/Yb_(N),La/Ce and La/Yb are 9.95-10.12,0.48-0.50 and 14.13-15.05,respectively.In addition,they also have low 10000Ga/Al(2.33-2.34)and(K_(2)O+Na_(2)O)/Cao(9.54-9.96)ratios.According to the calculation of Ti element in zircon,the saturation temperatures of zircon are between 683 and 756℃.These characteristics indicate that the Middle Jurassic rhyolite has the property of I-type rhyolite,and the diagenetic magma has the characteristics of volcanic arc or active continental margin magma.The ^(176)Hf/^(177)Hf ratios in zircons are 0.282853-0.282990,the correspondingεHf(t)values range from 6.22 to 10.83,and the two-stage Hf model ages range from 734.2 to 474.0 Ma,which are similar to the one-stage Hf model ages(592.6-410.1 Ma),indicating that their diagenetic magma is mainly derived from the partial melting of the juvenile lower crust.The magma was contaminated by crustal materials during the process of emplacement or diagenesis,and constituted the characteristics of“bimodal volcanic rocks”with the contemporaneous intermediate-basic volcanic rocks in this area.Combined with the temporal and spatial distribution of regional magmatic rocks and the evidence of geophysical data,it is further believed that the diagenetic geodynamic background of the Middle Jurassic acid lavas(rhyolite,rhyolitic lithic tuff and quartz porphyry)in this area is closely related to the passive continental margin which influenced by the subduction of the paleo-Pacific plate into Eurasia.
作者
徐智涛
李萌萌
孙景贵
孙立影
冯靖乔
梁小龙
Xu Zhitao;Li Mengmeng;Sun Jinggui;Sun Liying;Feng Jingqiao;Liang Xiaolong(Institute of Volcanology,China Earthquake Administration,Changchun 130117,China;College of Earth Sciences,Jilin University,Changchun 130061,China;Jilin Earthquake Agency,Changchun 130117,China;Baotou Research Institute of Rare Earths,Baotou 014010,Inner Mongolia,China)
出处
《吉林大学学报（地球科学版）》
CAS
CSCD
北大核心
2023年第3期866-886,共21页
Journal of Jilin University：Earth Science Edition
基金
中国工程院院地合作项目(JL2021-03-1)
吉林省地震局青年科技发展基金(JZQ-202308)
国家留学基金项目(202104190014)
