| 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 |
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| 引用本文： | 马铭株,万渝生,颉颃强,刘守偈,谢士稳,董春艳,白文倩,李源,王宇晴.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[J].地球科学,2020,45(7):2610-2628. |
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| 作者姓名： | 马铭株 万渝生 颉颃强 刘守偈 谢士稳 董春艳 白文倩 李源 王宇晴 |
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| 作者单位： | 中国地质科学院地质研究所北京离子探针中心, 北京, 100037 |
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| 基金项目： | 中国地质科学院地质研究所基本科研业务费项目J2026中国地质调查局工作项目DD20190370中国地质调查局工作项目DD20190003中国地质调查局工作项目D20190009中国地质调查局工作项目DD20190358 |
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| 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:2 662~>2 711 Ma、2 608~2 618 Ma和2 508~2 526 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.
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| 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 |
| 收稿时间： | 2020-07-06 |
Neoarchean Mafic Magmatism in Qixingtai Area,West Shandong: Formation Ages and Compositions of Meta-Gabbros |
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| Abstract: | 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:2 662- > 2 711 Ma, 2 608-2 618 Ma and 2 508-2 526 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. |
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