安徽金寨响洪甸碱性侵入岩年代学、岩石地球化学及其意义  

Geochronology and petrogeochemistry of Xianghongdian alkaline intrusion in Jinzhai County of Anhui Province and its significance

作　　者：周伟伟[1] 蔡剑辉[2] 阎国翰[3] 王亚莹[2] 闫星光[4] 闫志娇 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]中国地质科学院矿产资源研究所国土资源部成矿作用和资源评价重点实验室,北京100037 [3]北京大学地球科学与空间科学学院,北京大学造山带与地壳演化教育部重点实验室,北京100871 [4]中国地质大学科学研究院,北京100083

出　　处：《矿床地质》2014年第1期104-122,共19页Mineral Deposits

基　　金：国家自然科学基金项目(41073047)和(40773041)资助

摘　　要：金寨响洪甸碱性侵入岩体分布在大别造山带东北缘的北淮阳地区,侵位于上元古界青白口系佛子岭群中。主要岩石类型为正长岩(似斑状正长岩)、碱性正长岩和霞石正长岩。正长岩的主要矿物为碱性长石及少量黑云母、普通辉石、绿钙闪石;碱性正长岩包含钾长石、角闪石、辉石和少量黑云母;霞石正长岩主要由碱性长石、霞石及少量绿钙闪石、普通辉石、次透辉石等矿物组成。化学成分上均具有偏铝质、富碱、高钾、贫钛的特点。富集大离子亲石元素K、Rb、U、Nd和轻稀土元素La、Ce、Pr、Nd、Sm,亏损高场强元素Nb、Ta、P、Ti,轻、重稀土元素比值及La/Nb、Ba/Nb值较高,呈弱的负铕异常。根据高精度同位素年代学测试结果,响洪甸碱性侵入岩成岩期次分为2期:早期霞石正长岩,LA-ICP-MS锆石U-Pb年龄为(135.1±0.7)Ma;晚期正长岩,SHRIMP锆石U-Pb年龄为(125.0±1)Ma和碱性正长岩,颗粒锆石U-Pb年龄为122.3 Ma。主体岩石似斑状正长岩的Hf同位素分析结果表明,其初始176Hf/177Hf比值为0.282 243~0.282 404,εHf(t)为-10.376^-16.602,结合该岩体的Sr-Nd同位素地球化学特征,推测响洪甸碱性侵入岩是富集地幔部分熔融的产物,其源区可能有部分陆壳物质的参与。其形成的构造背景为后碰撞的伸展环境。Lying in Beihuaiyang area on the northeastern margin of the Dabie orogenic belt, the Xianghongdian alka- line intrusion in Jinzhai County of Anhui Province was emplaced in Upper Proterozoic strata of Foziling Group of Qingbaikou System. The complex mainly includes syenite, alkaline syenite and nepheline syenite, with the syenite （mainly porphyroid syenite） being the largest among them. Their mineral compositions are successivelyas follows： alkali feldspar-biotite-augite-hastingsite, potassium feldspar-hornblende-pyroxene- biotite and alkali feldspar-nepheline-hastingsite-augite-diopside. Chemically they are characterized by meta-aluminum nature and enrichment of alkaline, high K and low Ti. These alkaline rocks are also enriched in LILE elements （K, Rb, U, Nd） and LREE elements （La, Ce, Pr, Nd, Sm）, depletion of HFSE elements （Nb, Ta, P, Ti）, with high La/Nb, Ba/Nb ratios and slightly negative Eu anomalies. According to the isotope chronological data, the rock-forming process can be divided into two phases. The formation periods of the early nepheline syenite and the late syenite-alkaline syenite are about 135.1 Ma and 122.3 Ma～125.0 Ma respectively. Hf isotopic analy- sis data of the porphyroid syenite show initial 176Hf/177Hf ratios （0.282 243～ 0.282 404） and low EHf （t） （ -10. 376～-16. 602）. Based on their petrogeochemistry and Hf, Sr-Nd isotopic geochemistry, it is suggested that Xianghongdian alkaline intrusion was produced by partial melting of the enrichment mantle with the addi- tion of some crustal materials in the magma source region, and was formed in an extensional tectonic setting, mainly in the post-collision period.

关 键 词：地质学 响洪甸碱性侵入岩 正长岩 霞石正长岩 碱性正长岩 SHRIMP锆石U-PB测年 

分 类 号：P597[天文地球—地球化学] P588.15[天文地球—地质学]