安徽金寨响洪甸碱性杂岩体中碳酸盐脉成因初探

A preliminary study on the genesis of carbonate veins in the Xianghongdian alkaline complex,Jinzhai,Anhui

响洪甸碳酸盐脉呈脉状穿插于碱性杂岩侵入体中,与霞石正长岩和霓辉正长岩密切共生,富SiO_(2)、Na_(2)O,稀土含量明显高于壳源的沉积成因碳酸盐岩。岩脉与围岩霞石正长岩和霓辉正长岩有类似的稀土元素含量、稀土分配模式,轻稀土富集,Eu、Ce负异常,二者具有同源性;稀土和微量元素具有岩浆碳酸岩特征。微量元素相对富集大离子亲石元素Sr、K、LREE,强烈亏损高场强元素Nb、Ta、Ti、Zr、P。初步认为响洪甸碳酸盐脉是以岩浆成因为主的火成碳酸岩,其来源于地幔源的部分熔融作用,后期可能有残余岩浆热液叠加改造。

The Xianghongdian carbonate veins are interspersed in alkaline complex intrusions,and are closely associated with nepheline syenite and aegirine-augite syenite.They are rich in SiO_(2) and Na_(2)O,and have significantly higher content of REEs than crustal-sourced sedimentary carbonate rocks.Both the veins and the wall rocks of nepheline syenite and aegirine-augite syenite are similar in REE contents and distribution patterns,with light REE enrichment,and Eu and Ce negative anomaly,indicating their same origin.The REEs and trace elements have the characteristics of magmatic carbonatite.The trace elements are relatively enriched in large ion lithophile elements of Sr,K and LREE,and very depleted in high field-strength elements of Nb,Ta,Ti,Zr and P.It is suggested that the Xianghongdian carbonate veins are igneous carbonatite mainly of magmatic origin,which originate from partial melting of the mantle,and may have been superposed and reworked by later residual magmatic hydrothermal fluid.