摘要
为了研究西秦岭地区早古生代岩浆活动的构造环境及动力学背景,选择西秦岭凤县地区靠近商丹断裂带的龙王沟岩体的花岗岩和闪长岩、唐藏岩体闪长岩进行了地球化学测试和LA-ICP-MS锆石U-Pb年代学测试,并对龙王沟岩体的花岗岩和闪长岩进行了LA-MC-ICP-MS锆石Hf同位素分析.龙王沟岩体花岗岩锆石U-Pb年龄为433±4 Ma和439±5 Ma,闪长岩年龄为453±3 Ma,早于花岗岩侵位.龙王沟岩体的闪长岩和唐藏花岗闪长岩ΣREE分别为(107~181)×10^(-6)和(209~321)×10^(-6),稀土配分曲线特征相似,都明显右倾,轻、重稀土分馏强烈((La/Yb)_(N)分别为7~13和31~57),都没有明显的负Eu异常(δEu分别为0.88~1.00和0.79~0.87),唐藏花岗闪长岩相对于龙王沟闪长岩,具有高的SiO_(2)和Na_(2)O含量,较低的TiO2和CaO含量,较高的ΣREE,Ba和Th相对更富集,轻重稀土分馏更强烈,负Eu异常稍明显.龙王沟闪长岩与唐藏岩体其侵位时代一致,认为他们都来源于下地壳,在上升过程中与幔源基性岩浆发生一定程度的混合,唐藏花岗闪长岩经历的岩浆演化相对较为充分.龙王沟花岗岩的样品Hf同位素显示出了较大的差异,虽然ε_(Hf)(t)全部为正值,但峰值分别为0~3和7~10,对应的两阶段模式年龄(t_(DM2))分别为1.1~1.4 Ga和0.8~1.0 Ga,结合其地球化学特征,认为它们形成于活动大陆边缘(岛弧)的构造环境,来源于秦岭群的部分熔融,同时有俯冲作用带来大量的洋壳中的基性岩的加入,在上升侵位过程中经历了较为强烈的结晶分异作用,但没有发生明显的岩浆混合作用.龙王沟岩体是一个由不同性质、不同时代的岩浆侵位形成的复合杂岩体,经历了板块俯冲到碰撞挤压的构造体制转换过程,记录了秦岭洋从俯冲到闭合各阶段的构造演化信息,秦岭洋在古生代的俯冲造山作用持续时间较长,伴随的岩浆活动从早古生代一直持续到中古生代.
In order to study the tectonic environment and dynamic background of the magmatic activity in the West Qinling orogenic belt in Early Paleozoic,it chooses the granite and diorite in Longwanggou rock mass and granodiorite in Tangzang rock mass,which near the Shang-Dan fault zone,for study.Geochemistry and LA-ICP-MS zircon U-Pb chronology were tested for all type of rocks and Hf isotope analysis for granite and diorite in Longwanggou rock mass.The dating results show that the age of Longwanggou granite is 433±4 Ma and 439±5 Ma,the diorite emplacement time is later than granite with the U-Pb age of 453±3 Ma.ΣREEs of Longwanggou diorite and Tangzang granodiorite are(107-181)×10^(-6)and(209-321)×10^(-6),respectively.Rare earth element distribution curve characteristics are similar,both showing clearly to the right-inclined pattern,strong light and heavy rare earth element fractionation strongly((La/Yb)_(N) at 7-13 and 31-57,respectively),and no obvious negative Eu anomaly(δEu are 0.88-1.00 and 0.79-0.87,respectively).Relative to the Longwanggou diorite,Tangzang granodiorites have highΣREE,light and heavy rare earth element fractionation is more intense,less negative Eu anomaly.The emplacement times of Longwanggou diorite and Tangzang rock mass are consistent,both of originate and granodiorites are from the lower crust,mixed with mantle-based magma to a certain extent during the rising process.The Tangzang granodiorite experienced relatively sufficient magma evolution.Hf isotopic compositions have distinct differences between the two Longwanggou granite samples.Although theε_(Hf)(t)values are all positive,they concentrated on the values of 0-3 and 7-10 respectively,with corresponding two-stage model ages(t_(DM2))1.1-1.4 Ga and 0.8-1.0 Ga.Combined with geochemical characteristics,the granite formed in the active continental margin tectonic environment(island arc)and derived from the partial melting of Qinling Group.At the same time,much of basic rocks from oceanic crust were brought into the melt during the pla
作者
王永
石永红
陈柏林
谭人文
高允
申景辉
Wang Yong;Shi Yonghong;Chen Bailin;Tan Renwen;Gao Yun;Shen Jinghui(Key Laboratory of Paleomagnetism and Paleotectonic Reconstruction,Ministry of Natural Resources,Institute of Geomechanics,CAGS,Beijing 100081,China;School of Earth Sciences and Resources,China University of Geosciences,Beijing 100083,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,China)
出处
《地球科学》
EI
CAS
CSCD
北大核心
2021年第6期2016-2036,共21页
Earth Science
基金
中央财政地质调查项目(Nos.DD20190161,DD20160053)
中国地质科学院中央级公益性科研院所基本科研业务费(Nos.JYY-WF20183702,JYYWF20180602).
