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中国东部A型花岗岩形成时代及物质来源的Nd—Sr—O同位素地球化学制约
引用本文:魏春生,郑永飞,赵子福.中国东部A型花岗岩形成时代及物质来源的Nd—Sr—O同位素地球化学制约[J].岩石学报,2001,17(1):95-111.
作者姓名:魏春生  郑永飞  赵子福
作者单位:中国科学技术大学地球与空间科学系化学地球动力学研究实验室,
基金项目:中国科学院知识创新工程项目(KZCX2-107)、国家自然科学基金(49603043和4003301 0)以及国土资源部壳幔物质组成、相互作用及动力学演化开放研究实验室联合资助成果.
摘    要:对中国东部A型花岗岩有代表性的碾子山、山海关、崂山、苏州以及魁岐岩体的Nd-Sr-O同位素地球化学组成进行了系统研究。经过筛选的全岩Rb-Sr等时线拟合结果表明,基本未遭受岩浆期后大气降水交换的苏州和魁岐Rb-Sr等时线年龄分别是108±10Ma和109±5Ma,它们代表岩浆冷却结晶时代。其它遭受热液蚀变较为显著的碾子山、山海关以及崂山岩体Rb-Sr等时线年龄的地质意义不明确。全岩εNd(t)、(87Sr/86Sr)0以及锆石δ18O综合示踪研究表明,中国东部A型花岗岩可能起源于曾经历过高温海水热液交换的再循环下部俯冲洋壳的部分熔融。模型计算结果表明,碾子山、山海关以及崂山等岩体所表现出的εNd(t)-δ18O脱耦变化与大洋沉积物析出流体与下覆辉长岩洋壳之间不同程度的交代有关。在此基础上,提出了中国东部A型花岗岩统一的成因模式,并对其地球动力学意义进行了讨论。

关 键 词:A型花岗岩  同位素地球化学  形成时代  物质来源  交代作用  大气降水  成因模式  岩浆
修稿时间:2000/9/20 0:00:00

Nd-Sr-O isotopic geochemistr y constraints on the age and origin of the A-type granites in eastern China
WEI ChunSheng,ZHENG YongFei and ZHAO ZiFu.Laboratory for Chemical Geodynamics.Nd-Sr-O isotopic geochemistr y constraints on the age and origin of the A-type granites in eastern China[J].Acta Petrologica Sinica,2001,17(1):95-111.
Authors:WEI ChunSheng  ZHENG YongFei and ZHAO ZiFuLaboratory for Chemical Geodynamics
Affiliation:WEI ChunSheng,ZHENG YongFei and ZHAO ZiFu.Laboratory for Chemical Geodynamics,Department of Earth and Space Sciences,University of Science and Technology of Chin,Hefei,China
Abstract:Nd-Sr-O isotope studies are systematically carried out for five representativ e massifs of A-type granites in eastern China. From the north to the south, the y are Nianzishan, Shanhaiguan, Laoshan, Suzhou and Kuiqi pluton, respectively . Fitting of whole-rock Rb-Sr isochrons for the Suzhou and Kuiqi plutons pro ceeds by screened isotopic data, obtaining the ages of 108±10Ma and 109±5Ma, respectively. It appears that the isochron ages were not significantly affecte d by post-magmatic meteoric-hydrothermal alteration and thus represent the cl osure time of Rb-Sr system in the granites. However, whole-rock Rb-Sr isoch rons for the Nianzishan, Shanhaiguan and Laoshan plutons were significantly di sturbed by hydrothermal alteration, resulting in geologically meaningfulless ag es. A combined study of whole-rock εNd(t), (87Sr/ 86Sr)0 and zircon δ18O suggests that the A-type granites in easter n China would be derived from partial melting of hydrothermally altered oceanic crust which would correspond to gabbro layer in lower oceanic crust and thus u nderwent oxygen isotope exchange with seawater at high temperatures prior to su bduction of oceanic plate. A calculation of binary mixing model shows that the decoupling of the εNd(t) and δ18O values for the Nianzishan, Shanhaiguan and Laoshan granites is probably caused by metasomatic processes of subducted sediment-derived fluid to the underlying oceanic crust of gabbro. A n unified model is proposed to account for petrogenesis of the A-type granite s in eastern China and its geodynamic implications.
Keywords:A-type granite  Isotope geochemistry  Formation age  Source rock
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