东北三江盆地始新世花岗闪长岩的发现及其地质意义:锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素证据  

Discovery and geological significance of the Eocene granodiorites in the Sanjiang basin, NE China: Evidence from zircon U-Pb chronology, geochemistry and Sr-Nd-Hf isotopes

作　　者：王智慧[1] 杨浩[1] 葛文春[1] 毕君辉[1] 张彦龙[1] 许文良[1] 

机构地区：[1]吉林大学地球科学学院,长春130061

出　　处：《岩石学报》2016年第6期1823-1838,共16页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41472050;41330206)资助

摘　　要：本文报道了三江盆地富锦地区临山花岗质岩体的锆石LA-ICP-MS U-Pb年龄、全岩地球化学和Sr-Nd同位素与锆石Hf同位素资料,以确定其形成时代、岩石成因、源区性质及其构造属性。花岗闪长岩中的锆石均呈半自形-自形晶,震荡环带发育,Th/U比值=0.31~1.92,指示其岩浆成因。对岩浆锆石的定年结果显示,临山花岗闪长岩形成于~54Ma,这是目前东北地区报道的最年轻的花岗质岩浆作用。该期花岗闪长岩的SiO_2含量主要在68.71%~72.42%之间,Na_2O=3.29%~4.41%,K_2O=2.79%~3.47%,Na_2O/K_2O=0.95~1.58,A/CNK=0.99~1.12;该区花岗闪长岩富集轻稀土元素(LREEs)和大离子亲石元素(LILEs),亏损重稀土元素(HREEs)和高场强元素(HFSEs),且轻重稀土元素分馏较强[(La/Yb)N=21.8~34.1]。样品无明显Eu异常(δEu=0.84~1.19)。它们的(87Sr/86Sr)i=0.7068~0.7071,εNd(t)介于-2.4^-2.3之间;锆石εHf(t)值介于+1.7^+5.7之间,二阶段Hf模式年龄(tDM2)介于765~1020Ma之间。上述特征表明,该期花岗闪长岩属于弱过铝质高钾钙碱性I型花岗岩,其原始岩浆起源于中元古代末-新元古代期间增生的陆壳物质的部分熔融。对三江盆地与佳木斯地块东缘已发表锆石Hf同位素资料进行总结和时空对比发现,佳木斯地块东缘和三江盆地具有相似的地壳增生历史,暗示三江盆地之下的基底物质可能仍归属于佳木斯地块范畴。另外,新生代临山岩体的识别,限制了富锦隆起的时限为始新世之后,并非前人认为的中生代。This paper presents zircon LA-ICP-MS U-Pb ages,whole-rock geochemical,whole-rock Sr-Nd and zircon Hf isotopic data of the Linshan hornblende-bearing granodiorites at Fujin in the Sanjiang basin,NE China,to constrain their emplacement age,magmatic sources,petrogenesis and tectonic setting. Zircons grains from these granodiorites are euhedral-subhedral in shape,display fine-scale oscillatory growth zoning with high Th / U ratios of 0. 31 - 1. 92,indicating a magmatic origin. U-Pb dating results give the emplacement age of about 54 Ma for the granodiorites,which records the youngest granitic magmatic event in the NE China. The granodiorite have high SiO_2 contents of 68. 71% - 72. 42%,Na2 O concentrations of 3. 29% - 4. 41%,and K——2O abundances of 2. 79%- 3. 47%,with Na_2O/K_2O ratios of 0. 95 - 1. 58 and A / CNK values of 0. 99 - 1. 12. They are enriched in light rare earth elements（ LREEs） and large ion lithophile elements（ LILEs）,and depleted in heavy rare earth element（ HREEs） and high field strength elements（ HFSEs）,with（ La / Yb）Nratios of 21. 8 - 34. 1. No obvious negative Eu anomalies（ δEu = 0. 84 - 1. 19） have been identified. They have（87Sr /86Sr）iratios of 0. 7068 - 0. 7071 and εNd（ t） values of- 2. 4 to- 2. 3. Zircon εHf（ t） values range from＋ 1. 7 to ＋ 5. 7,with model ages（ tDM2） of 765 - 1020 Ma. Collectively,it is suggested that these granodiorites chemically belong to weak peraluminous and high-K calc-alkaline I-type ones,and their primary magma could be derived from partial melting of Late Mesoproterozoic to Neoproterozoic crustal material. The summary and spatio-temporal compare of zircon Hf isotope data in the Sanjiang basin and the east part of the Jiamusi Massif,suggest that the Sanjiang basin and the east part of Jiamusi Massif have similar history of crustal growth. Therefore,we argue that the basement of the Sanjiang basin may be one part of the Jiamusi Massif. In addition,the identification of the Cenozoic Linshan pluton constrains that the

关 键 词：始新世花岗闪长岩 锆石U-Pb年龄 地球化学 三江盆地基底 富锦隆起 

分 类 号：P588.122[天文地球—岩石学] P597.3[天文地球—地质学]