广东莲花山花岗岩体锆石U-Pb年龄、地球化学特征及地质意义
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引用本文:杨航,辛宇佳,李建华,张培星.2022.广东莲花山花岗岩体锆石U-Pb年龄、地球化学特征及地质意义[J].地球学报,43(2):211-223.
DOI:10.3975/cagsb.2021.020801
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作者单位E-mail
杨航 中国地质科学院地质力学研究所
西北大学地质学系 
Hyang960509@163.com 
辛宇佳 中国地质科学院地质力学研究所 xyjasd123@163.com 
李建华 中国地质科学院地质力学研究所  
张培星 中国地质科学院地质力学研究所  
基金项目:国家自然科学基金项目(编号: 41822205; 42072239);中国地质科学院基本科研业务费项目(编号: DZLXJK202005);中国地质调查局项目(编号: DD20190306)
中文摘要:广东莲花山岩体位于莲花山断裂带北部, 由规模巨大的侏罗—白垩纪花岗岩组成。本文对莲花山岩体中部进行了系统的岩石学、地球化学、锆石U-Pb同位素和Lu-Hf同位素研究, 获得片麻状花岗岩、细粒黑云母花岗岩和细-中粒黑云母花岗岩的锆石206Pb/238U年龄分别为(142.5±1.5) Ma(MWSD=3.5, N=30)、(138.9±0.6) Ma(MWSD=1.4, N=30)和(145.5±0.7) Ma(MWSD=1.2, N=28), 表明岩体为晚侏罗至早白垩世岩浆活动的产物。地球化学特征显示岩体为偏铝质-弱过铝质(A/CNK=0.97~1.1)、富碱(K2O+Na2O=6.1 wt%~ 8.1 wt%)、富钾(K2O/Na2O=1.4~1.8), 富集Rb、Th、U、K、Pb, 亏损Ba、Ta、Nb、Sr、P、Ti, 与壳源岩浆特征类似。岩体SiO2含量差异较大(69.5 wt%~80.1 wt%), 高硅样品明显经历一定程度的结晶分异, 属于分异的I型花岗岩。所有样品锆石εHf(t)值均为负值(–4.5 ~ –2.0), 在年龄-εHf(t)图中, 均落入球粒陨石演化线和华夏基底演化线之间, 暗示源岩主要为古老壳源基底物质。在此基础上, 结合区域构造-岩浆记录, 本文认为莲花山花岗岩体的形成与古太平洋板片俯冲后撤(roll back)诱发的弧后扩张作用相关。
中文关键词:早白垩世  莲花山岩体  I型花岗岩  地壳伸展  锆石U-Pb  LA-ICP-MS  Lu-Hf同位素
 
Zircon U-Pb Ages and Geochemical Constraints of the Lianhuashan Granitoids in Guangdong Province and Their Geological Implications
Abstract:The Lianhuashan granitoids, located in the north of the Lianhuashan fault zone, are composed of massive Jurassic–Cretaceous granites. This paper presents a synthetical petrologic, geochemical and geochronological study and Lu-Hf isotopic analysis of the granitoids. LA-ICP-MS zircon U-Pb dating yielded ages of 146~139 Ma, indicating that the granitoids were mainly generated in Late Jurassic to Early Cretaceous period. The granitoids are metaluminous to weakly peraluminous (A/CNK=0.97~1.1), and have the data K2O+Na2O=6.1 wt%~8.1 wt% and K2O/Na2O=1.4~1.8. They are all depleted in Ba, Ta, Nb, Sr, P and Ti, and enriched in Rb, Th, U, K and Pb. All these features point to a major crustal source. The Lianhuashan granitoids show large variation in the SiO2 content (69.5 wt%~80.1 wt%), and the high SiO2 samples underwent strong fractional crystallization, exhibiting characteristics of highly fractionated I-type granites. All zircons from these samples show negative εHf(t) values from –4.5 to –2.0, recording a predominant contribution of partial melting of ancient crustal rocks. However, on the ages versus εHf(t) diagram, all the samples are plotted on the field between the evolution curve of chondrite and Cathaysia basement, indicating minor mantle contributions to the source of the Lianhuashan granitoids. Integrating regional tectono-magmatic records, the authors infer that the Lianhuashan granitoids were formed in a back-arc extension environment, which was associated with roll-back of the subducting Paleo-Pacific plate in the Late Jurassic to Early Cretaceous period.
keywords:Early Cretaceous  Lianhuashan granitoids  I-type granite  crustal extension  zircon U-Pb  LA-ICP-MS  Lu-Hf isotopes
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