School of Earth Science and Resources, Chang’ an University
Sino Shaanxi Nuclear Industry Group No. 214 Party Co., Ltd.
The Third Geological Brigade of Jiangxi Geological Bureau

为研究江南造山带北缘双桥山枕状基性熔岩的成因,用基性熔岩岩性特征、地球化学方法分析枕状基性熔岩的成因及地质意义。结果表明:双桥山地区位于江南造山带中段北缘出露为新元古代双桥山群,岩枕成群分布;基性熔岩贫碱、富钠,Na2O/K2O比值较高,稀土元素的含量中等,轻重稀土分馏程度较弱,具微弱负铕异常,高场强元素钕和钽相对于镧微弱亏损,且大部分样品出现一定程度的锶负异常,属典型的细碧岩,与典型的洋中脊玄武岩具有一定差异;岩浆来源于亏损地幔,受到地壳流体的交代,形成环境并非典型的大洋环境,而是陆壳基础上形成的弧后小洋盆。研究认为向东可与赣北德安彭山出露的蛇绿混杂岩带、庐山垅中地区的细碧角斑岩组合、赣北都昌县程浪蛇绿混杂岩带及皖南的歙县含蛇绿岩的新元古代洋壳对比,向西可与湘北益阳冷家溪群中的基性枕状熔岩相连,指示江南造山带具有多岛弧拼接、多缝合的特点。

To explore the genesis and geological significance of the pillow-shaped basic lava in Shuan-gqiaoshan on the northern edge of the Jiangnan orogen, an analysis was made by using geochemicalmethods based on lithological characteristic. The findings show that Shuangqiaoshan is located on thenorthern edge of the middle section of the Jiangnan orogen, where the Neoproterozoic ShuangqiaoshanGroup is exposed, displaying a clustered distribution of pillows. The basic lava exhibits a low alkalicontent, high sodium content, and a high Na2O/ K2O ratio. The rare-earth element content is moderate,with a weak fractionation of light and heavy rare-earth elements, presenting a slight negative Eu anoma-ly. Comparatively, the high-field-strength elements( HFSE) , such as Nd and Ta, are weakly deficient toNa. Most samples show a certain degree of Sr-negative anomalies, with typical spilite exhibited, thusdistinguishing them from typical mid-ocean ridge basalts. Moreover, it is suggested that the magma orig-inates from the depleted mantle, influenced by crust fluids. The formation environment is not represent-ative of a typical oceanic setting but rather a small post-arc ocean basin that is developed on crustalfoundations. The results indicate that to the east, the orogen here can be compared with the ophioliticmelange belt emerging from Pengshan, Dean, northern Jiangxi Province, the fine biocorphoporphyry as-semblage in Lushan Longzhong area, the Chenglang ophiolitic melange belt in Duchang County, north-ern Jiangxi Province, and the Neoproterozoic oceanic crust containing ophiolitic rocks in She County,southern Anhui Province. Additionally, a connection can be made with the basic pillow mafics in theLengjiaxi Group in Yiyang, north of Hunan Province in the west. These findings confirm that the Jiang-nan orogen exhibits the characteristics of multiple island-arc splicing and suturing in its southern re-gion.

中国地质调查局矿产地质志项目(DD20190379,DD20160346),中陕核工业集团有限公司院士工作站科技项目(R-YS190101);陕西省自然科学基础计划项目(2021JQ-985)