浙中地区晚侏罗世花岗斑岩LA-ICP-MS锆石U-Pb年龄、地球化学特征及其地质意义  

LA-ICP-MS zircon U-Pb geochronology, petrochemistry of the Late Jurassic granite porphyry in central Zhejiang Province and their geological significance

作　　者：王对兴[1] 高万里[2] 李春麟[2] 王宗秀[2] 赵志丹[3] 

机构地区：[1]石家庄经济学院资源学院,河北石家庄050031 [2]中国地质科学院地质力学研究所,中国地质科学院页岩油气调查评价重点实验室,北京100081 [3]中国地质大学地质过程与矿产资源国家重点实验室,中国地质大学地球科学与资源学院,北京100083

出　　处：《中国地质》2015年第6期1684-1699,共16页Geology in China

基　　金：中国地质调查局地质调查项目(1212011121068);国家自然科学基金面上项目(41271344);国家自然科学基金面上项目(41172118);国家自然科学基金重点支持项目(90914010);石家庄经济学院博士科研启动基金(BQ201517)联合资助

摘　　要：在华南大陆东北缘浙中地区后山店及曹娥地区零星分布有小规模的花岗斑岩体,其LA-MC-ICP-MS技术测得的锆石U-Pb年龄分别为(149.1±1.1)Ma和(150.3±1.6)Ma,表明其均为中生代晚侏罗世岩浆活动的产物,属于燕山早期晚阶段形成。两个岩体均为高钾钙碱性系列,A/CNK值介于0.96~1.28,多小于1.1,属准铝质-弱过铝质花岗岩类;稀土含量中等,具明显的轻重稀土分馏,中等至强的Eu亏损(0.10~0.40),总体表现出略呈右倾的"海鸥型"稀土配分曲线,富集Rb、Th、U等大离子亲石元素(LILE)和Nd、Hf、Y等高场强元素(HFSE),而明显亏损Ba、Sr、P、Ti等元素。后山店岩体为高分异的S型花岗岩,曹娥岩体为A型花岗岩。锆石Hf同位素的εHf(t)值变化范围主要集中于-9.5^-2.9之间,均为负值,二阶段模式年龄tDMC变化范围主要集中于1364~1783 Ma,反映其物质来源可能为中元古代上地壳基底物质。结合前人成果,本文认为浙中晚侏罗世花岗斑岩形成于后碰撞环境下的后造山板内拉张阶段,其形成年龄可能代表了古特提斯构造域向古太平洋构造域转换的晚阶段。There are a few small granite porphyry plutons scattered in Houshandian and Cao＇e area of central Zhejiang Province on the northeastern margin of South China block. The LA-MC-ICP-MS zircon U-Pb dating shows that they were both generated in Late Jurassic of the Mesozoic simultaneously（149.1±1.1 Ma and 150.3±1.6 Ma respectively）, indicating that they both formed at the late stage of Early Yanshanian. The compositions of these two granite porphyry plutons fall into the high-K calc-alkaline category,with the A/CNK ratios being 0.96- 1.28（mostly less than 1.1）. They are of metaluminous and weakly peraluminous series. They have moderate REE and strong light- heavy REE fractionation and strong Eu depletion with a slightly right inclined＂sea- gull＂shaped REE pattern. The spider diagrams of trace elements show that the granite porphyry samples are enriched in LILEs（e.g., Rb,Th and U） and HFSEs（e.g., Nb, Hf and Y）, but depleted in Ba, Sr, P and Ti significantly. The Houshandian granite porphyries belong to S-type granite and Cao＇e granite porphyries are of A-type granite. Zircon εHf（t） values of the granites all are negative（-9.5 to-2.9）, and two-stage Hf model ages（tHf2） range from 1364 Ma to 1783 Ma, suggesting that these granites originated from remelting of the Mesoproterozoic upper- crustal materials. Combined with the previous results, the authors infer that the Late Jurassic granite porphyries in central Zhejiang Province on the northeastern margin of South China block were formed in a postorogenic extension environment. The formation age may represent a late stage of conversion from the Paleo-Tethys tectonic domain to the Paleo-Pacific tectonic domain.

关 键 词：锆石U-PB年龄 元素地球化学 锆石Hf同位素组成 晚侏罗世 浙中地区 

分 类 号：P597.3[天文地球—地球化学] P595[天文地球—地质学]