鲁西七星台地区新太古代基性岩浆作用:变质辉长岩的时代和组成  

Neoarchean Mafic Magmatism in Qixingtai Area, West Shandong: Formation Ages and Compositions of Meta-Gabbros

作　　者：马铭株[1] 万渝生[1] 颉颃强[1] 刘守偈[1] 谢士稳[1] 董春艳[1] 白文倩[1] 李源[1] 王宇晴 Ma Mingzhu;Wan Yusheng;Xie Hangqiang;Liu Shoujie;Xie Shiwen;Dong Chunyan;Bai Wenqian;Li Yuan;Wang Yuqing(Beijing SHRIMP Center,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所北京离子探针中心,北京100037

出　　处：《地球科学》2020年第7期2610-2628,共19页Earth Science

基　　金：中国地质科学院地质研究所基本科研业务费项目(No.J2026);中国地质调查局工作项目(Nos.DD20190370,DD20190003,D20190009,DD20190358)。

摘　　要：通过研究鲁西七星台地区新太古代变质辉长岩及相关岩石的锆石SHRIMP U-Pb年龄和地球化学组成.它们侵入新太古代表壳岩和TTG岩体.根据12个样品SHRIMP U-Pb锆石定年,可把形成时代划分为3期:2662~>2711 Ma、2608~2618 Ma和2508~2526 Ma.其他样品(进行地球化学分析)的形成时代是根据岩石空间分布、野外特征及与定年样品所代表岩石的关系来确定的.>2.65 Ga变质辉长岩既有来自于富集地幔源区也有来自亏损地幔源区.~2.6 Ga变质辉长岩具平坦型稀土模式,大离子亲石元素富集,Nb、Ta、P亏损,来自亏损地幔源区,可能遭受陆壳物质影响,~2.6 Ga变质辉石岩显示中稀土富集,与单斜辉石堆晶作用有关.~2.5 Ga变质辉长岩存在平坦型-轻微亏损轻稀土和轻稀土富集型两种类型稀土模式.与~2.5 Ga变质辉长岩相比,~2.5 Ga变质辉长闪长岩稀土含量更高,轻重稀土分异程度更高,大离子亲石元素更为富集,Nb、Ta亏损更为明显,是~2.5 Ga辉长质岩浆进一步结晶分异产物.结合前人研究,可得出如下结论.(1)七星台地区存在>2.65 Ga、~2.6 Ga和~2.5 Ga 3期变质辉长岩,其中~2.6 Ga变质辉长岩规模最大;(2)不同时代变质辉长岩地球化学组成特征不同,反映了源区组成和形成过程的复杂性;(3)鲁西地区在新太古代早期(>2.7~2.6 Ga)存在长期连续的基性岩浆作用,可能与地幔岩浆板底垫托有关;(4)在七星台地区首次发现~2.5 Ga辉长岩-辉长闪长岩,为鲁西地区A带广泛存在的~2.5 Ga深熔作用提供了热源来自地幔的直接证据.This study reports SHRIMP U-Pb zircon ages and element compositions of meta-gabbros and related rocks from the Qixingtai area,western Shandong.They intrude the Neoarchean supracrustal and TTG rocks.The formation ages can be divided into three groups based on SHRIMP U-Pb dating on 12 samples:2662->2711 Ma,2608-2618 Ma and 2508-2526 Ma.The formation ages of other rock samples for element analyses are determined in terms of their spatial distribution,field features and the relationships with the samples dated.>2.65 Ga gabbros are derived from enriched and depleted mantles,respectively.~2.6 Ga gabbro has no enrichment of the LREE relative to the HREE,but shows LILE enrichment and weakly negative Nb,Ta and P anomalies.It is considered that the gabbro is derived from depleted mantle source,probably with continental contamination.~2.6 Ga meta-pyroxenite shows enrichment of middle REE,as a result of crystallization and accumulation of clinopyroxene.~2.5 Ga meta-gabbros are variations in REE composition from slight deplation of LREE to HREE,and flat REE pattern to enrichment of of LREE to HREE.~2.5 Ga meta-gabbroic diorite has higher REE contents and is more strongly enriched in LREE and LILE and depleted in Nb and Ta compared with^2.5 Ga meta-gabbro.Combined with early study,the conclusions can be drawn as follows:(1)In the Qixingtai area,meta-gabbros and related rocks of three periods have been identified,with the^2.6 Ga rocks being the largest in distribution scale;(2)the rocks of different ages are different in geochemical composition,showing complexities of source regions and formation processes;(3)In western Shandong,continuous mafic magmatism occurred in early Neoarchean from>2.7 Ga to 2.6 Ga,being probably related to mantle underplating;(4)~2.5 Ga mafic meta-gabbro-diorite rocks are discovered for the first time in the Qixintai area,providing a direct evidence that the heat source is from mantle for the widespread anatexis of^2.5 Ga in Belt A.

关 键 词：变质辉长岩 SHRIMP U-Pb锆石定年 地球化学 鲁西 新太古代 

分 类 号：P597[天文地球—地球化学]