黔东南苍蒲塘钾镁煌斑岩含铬尖晶石地球化学特征及其对金刚石含矿性的指示  

Geochemistry of Chrome Spinel from Cangputang Lamproite in Southeast Guizhou and its Implication for Diamond Potential

作　　者：邓小芹 黄远成[2] 丘志力 陆太进[3] 李志翔 张健[3] 饶红娟[2] 张跃峰 DENG Xiaoqin;HUANG Yuancheng;QIU Zhili;LU Taijin;LI Zhixiang;ZHANG Jian;RAO Hongjuan;ZHANG Yuefeng(School of Earth Sciences and Engineering,Sun Yat-Sen University/Guangdong Provincial Key Laboratory of Geodynamic and Geological Hazards/Guangdong Provincial Key Laboratory of Geological Process and Mineral Resource Exploration,Guangzhou 510275,Guangdong,China;No. 101 Geological Brigade,Guizhou Bureau of Geology and Mineral Exploration and Development,Kaili 556000,Guizhou,China;Beijing Institute of Gemology,National Gems and Jewelry Technology Administrative Center,Beijing 100013,China)

机构地区：[1]中山大学地球科学与工程学院,广东省地球动力作用与地质灾害重点实验室,广东省地质过程与矿产资源探查重点实验室,广东广州510275 [2]贵州省地矿局101地质大队,贵州凯里556000 [3]国土资源部珠宝玉石首饰管理中心,北京100013

出　　处：《大地构造与成矿学》2019年第5期1023-1035,共13页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(41703028、41473030);高校青年教师培育项目(19lgpy74);中国博士后基金项目(2017M610563)联合资助

摘　　要：钾镁煌斑岩是将原生金刚石从地幔带至地表的主要岩石类型之一,携带了岩石圈地幔金刚石源区和基底岩石丰富的地球化学信息。由于风化作用影响,出露地表的钾镁煌斑岩岩石结构和化学成分均发生明显变化,岩石组成和成因的原始信息很难保存。但是钾镁煌斑岩携带的锆石和尖晶石等副矿物/捕掳晶,可成为研究地幔深部岩浆–构造作用过程、钾镁煌斑岩金刚石含矿性等重要科学问题的探针。本文对黔东南苍蒲塘钾镁煌斑岩中的锆石和铬尖晶石分别进行了SHRIMPU-Pb定年和主量、微量元素分析。定年结果显示,苍蒲塘钾镁煌斑岩携带有古老的基底物质,较为年轻的岩浆锆石暗示其侵位年龄为451±7Ma,与黔东南其他钾镁煌斑岩的形成时代基本一致。苍蒲塘钾镁煌斑岩中铬尖晶石表面具有明显的溶蚀现象,具有高Cr(Cr#>0.6)、Ni(300~1026μg/g)和低Ti(TiO2<0.13%)、Ga(12.9~33.4μg/g)的特征,与全球金伯利岩/钾镁煌斑岩橄榄石捕虏体中的铬尖晶石特征相似;元素地球化学分析显示,铬尖晶石与受俯冲作用改造的地幔橄榄岩有关。依据铬尖晶石Cr#值(0.56~0.87)及其存在条件,推测其原始岩浆的压力范围为(30~53)×10^2MPa,对应于99~175km的深度,部分达到了金刚石稳定区的上限,暗示苍蒲塘地区具有较好的金刚石找矿前景。Lamproite is one of the important carriers that bring the primary diamonds from the mantle to the Earth’s surface, which bears abundant geological information on the lithospheric mantle and basement rocks. Exposed lamproites are vulnerable to weathering and thus the primary geochemical characteristics of the rocks are easily smeared. Fortunately, the zircon and spinel in the lamproite may provide vital constraints on magma-tectonism process of deep mantle, mantle-crust interaction, and the diamond potential. In this paper, we present SHRIMP U-Pb dating results of the zircon and major-trace elements of spinels hosted in the Cangputang lamproite from Southeast Guizhou. The dating results show that the lamproite contains old basement materials, and age of the youngest magmatic zircon indicates that the lamproite was emplaced at ca. 451±7 Ma, which is consistent with the other lamproites outcropped in Southeast Guizhou. The chrome spinels in the lamproite have high Cr (Cr#>0.6), Ni (300 to 1026 μg/g) and low Ti (TiO2 <0.13%), Ga (12.9 to 33.4 μg/g) contents, similar to those in peridotitic xenoliths from kimberlite/lamproites worldwide. Meanwhile, the major and trace element geochemistry of the chrome spinels also indicate a genetic link with peridotites fertilized by dehydration of subducting slab. Based on the Cr# values (0.56 to 0.87) of spinels, we speculate that lamproitic magmas were generated at (30–53)×10^2 MPa, corresponding to a 99 to 175 km depth, which reaches the upper limit of stable zone of diamond. Therefore, the Cangputang lamproite has the potential of diamond prospecting.

关 键 词：苍蒲塘钾镁煌斑岩 锆石U-PB年龄 铬尖晶石 金刚石找矿 扬子克拉通 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]