摘要
本文对湖北金山店大型矽卡岩型铁矿床的矽卡岩和钠长石化岩体中的热液榍石进行了LA-ICPMS微量元素和UPb同位素定年分析,结果表明,与方柱石和透辉石矽卡岩中的榍石相比,钠长石蚀变岩中的榍石具有明显偏低的稀土元素含量和明显的轻重稀土分异、更小的δEu值、较低的Th、U、Lu含量和Th/U、Lu/Hf比值,以及高的Hf含量,表明二者的形成环境有所差异。热液榍石中的Ti可能主要来自于蚀变过程中岩体含Ti副矿物榍石、钛铁矿和金红石等矿物的分解。热液榍石原位微区LA-ICPMS U-Pb定年结果表明,矽卡岩和钠长石蚀变岩中的榍石形成时代分别为129.5±1.1Ma^130.4±1.2Ma和127±12Ma,与前人所得的成岩成矿时代在误差范围内一致,代表了成矿阶段的热液活动时间。热液榍石的年龄与鄂东南地区铁-铜矿化类型时代相近,均形成于区域早白垩世岩石圈减薄的环境。研究结果表明热液榍石原位微区LA-ICPMS U-Pb定年是确定矽卡岩型铁矿矿床年代的一种有效方法。
U-Pb ages and trace element compositions of two types of hydrothermal titanite from the Jinshandian iron skarn deposit, southeastern Hubei Province, have been successfully analyzed by laser ablation inductively coupled plasma mass spectrometry （LA- ICPMS） . Compared to titanite from diopside and scapolite skarn, hydrothermal titanite from albite altered quartz diorite are characterized by lower REE, δEu values, Th/U, Lu/Hf ratios and higher Hf component and LREE/HREE, suggesting they formed under different environment. The amount of Ti in the hydrothermal titanite probably resulted from the decomposition of Ti-bearing accessory minerals such as titanite, ilmenite and rutile from magma during the alteration. In situ U-Pb dating of titanite by LA-ICPMS shows that titanite from diopside ＋ anhydrite ＋ magnenite and scapolite ＋ anhydrite ＋ magnenite skarn sample yield a weighted mean 206pb/238U ages of 129. 5 ± 1.1Ma and 130. 4±1.2Ma, respectively, while that of albite altered quartz diorite give 127 ±12Ma. These ages might be considered to be the age of mineralization, consistent with crystallization age of phlogopite got by previous researcher, suggesting that Jinshandian iron skarn deposit formed associate with lithospheric thinning, similar to other skarn Cu-Fe deposits in the southeastern Hubei Province. Our study shows that in situ U-Pb dating of hydrothermal titanite by LA-ICPMS is a robust method for getting precise formation age of skarn iron deposit.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2014年第5期1322-1338,共17页
Acta Petrologica Sinica
基金
国家重点基础研究计划973项目(2012CB416802)
国土资源部公益性行业科研专项(200911007-18
201311136)
中国地质调查局地质矿产调查项目(12123311035)联合资助
关键词
热液榍石
原位微区定年
矽卡岩型铁矿
鄂东南地区
Hydrothermal titanite
In situ U-Pb dating
Skarn iron deposit
Southeastern Hubei Province
