琼北儋州市洛基地区早白垩世火山岩的锆石U-Pb年龄、地球化学特征及其地质意义  

Zircon U-Pb Geochronology, Geochemistry of the Early Cretaceous Volcanics in Luoji Area, Danzhou, Northern Hainan Island and Its Geological Implications

作　　者：林义华[1,2] 吕昭英 袁勤敏[1,2] 官军 袁海军[1,2] 王超 胡在龙[1,2] LIN Yi-Hua;LYU Zhao-Ying;YUAN Qin-Min;GUAN Jun;YUAN Hai-Jun;WANG Chao;HU Zai-Long(Hainan Geological Survey,Haikou 570206,Hainan,China;Key Laboratory of Marine Geological Resources and Enviroment of Hainan Province,Haikou 570206,Hainan,China)

机构地区：[1]海南省地质调查院,海口570206 [2]海南省海洋地质资源与环境重点实验室,海口570206

出　　处：《华南地质与矿产》2019年第4期399-409,共11页Geology and Mineral Resources of South China

基　　金：中国地质调查局项目(1212011220524)

摘　　要：琼北儋州市洛基陆相火山盆地发育一套中基性火山岩系,主要岩性为安山岩-粗安岩。LA-ICP-MS锆石U-Pb测年结果显示其形成年龄为100.8 Ma,属早白垩世晚期。岩石具有SiO2、Al2O3、Na2O、K2O偏高,而CaO、MgO、TiO2等偏低的特点;岩石稀土配分模式均表现为右倾的轻稀土富集型,轻、重稀土分异较强;富集大离子亲石元素,亏损高场强元素;表明源岩可能受到了俯冲组分的影响。Sr-Nd-Pb同位素研究结果显示,Pb同位素初始比值为206Pb/204Pb=18.4715~18.5193、207Pb/204Pb=15.6124~15.6484、208Pb/204Pb=38.4444~38.6097,初始Sr比值为0.7071~0.7086,Nd初始比值为0.5122~0.5125,εNd (t)值为-4.3^-0.9,T2DM为980~1259 Ma。综合研究认为,中基性火山岩源自经俯冲流体交代作用的富集岩石圈地幔,并经历了明显的地壳物质混染作用,形成于太平洋板块俯冲体系引发的拉张伸展环境中。A set of intermediate-basic volcanic rocks has been found in the Luoji continental volcanic basin,Danzhou City, Northern Hainan Island, and the main lithology is andesite-rough rock. The LA-ICP-MS zircon U-Pb dating results show that it was formed at 100.8 Ma and belongs to the late Early Cretaceous. The rock has the characteristics of high SiO2, Al2O3, Na2O and K2O, and low CaO, MgO and TiO2. The REE distribution patterns of rocks are right-dip LREE enrichment type, and the LREE and HREE are highly differentiated. The enrichment of large ion lithophile elements and the depletion of high field strength elements indicate that the source may be affected by subduction components. The results of Sr-Nd-Pb isotope studies show that the initial ratios of Pb isotope are:206 Pb/204Pb values ranging from 18.4715 to 18.5193,207 Pb/204 Pb values ranging from 15.6124 to 15.6484,208 Pb/204 Pb values ranging from 38.4444 to 38.6097;the initial Sr ratios values of 0.7071 to 0.7086;the initial Nd ratios values of 0.5122 to 0.5125, εNd(t) values of-4.3 to-0.9, and T2DM values of 980 to 1259 Ma. According to the comprehensive study, the mesobasic volcanic rocks are derived from the enriched lithospheric mantle that had been metamorphosed by subductive fluids, and has experienced obvious crustal material contamination, forming in the extensional environment caused by subduction of the Pacific plate.

关 键 词：洛基安山岩 早白垩世 锆石U-PB测年 地球化学 琼北 

分 类 号：P588.144[天文地球—岩石学] P597.3[天文地球—地质学]