摘要
长江中下游地区发育多个中生代火山盆地,自西向东依次为金牛、怀宁、庐枞、繁昌、宁芜、溧水和溧阳盆地。繁昌盆地自下而上发育中分村组、赤沙组和蝌蚪山组火山岩。中分村组下段和上段流纹岩的LA-ICPMS锆石U-Pb定年结果分别为131.2±1.1Ma和129.1±1.3Ma,和蝌蚪山组流纹岩的形成时代(130.7±1.1Ma)在误差范围内一致,表明繁昌盆地火山岩喷发持续时间较短。中分村组发育英安岩和流纹岩,赤沙组以粗安岩为主,并有少量的流纹岩,两者的SiO2含量分别为64.36%～75.45%和63.08%～69.75%。中分村组和赤沙组火山岩的稀土和微量元素特征基本一致,均富集轻稀土和大离子亲石元素,亏损Nd、P和Ti,其中,流纹岩表现为Eu的负异常。中分村组样品的87Sr/86Sr(t)为0.7060～0.7074,εNd(t)为-7.91～-8.11,赤沙组样品的87Sr/86Sr(t)为0.7073,εNd(t)为-6.62～-6.71,和蝌蚪山组玄武岩的Sr-Nd同位素组成很相似。综合分析表明,中分村组火山岩为岩石圈地幔部分熔融的岩浆底侵形成的下地壳再次部分熔融的产物,并经过辉石、角闪石、斜长石和磷灰石的结晶分异。赤沙组粗安岩为岩石圈地幔部分熔融形成的玄武岩浆,经过橄榄石、辉石、斜长石和钛铁氧化物结晶分异形成。岩石圈地幔的部分熔融在长江中下游地区中生代火山岩中表现的最为集中,表明～130Ma时期为本地区的拉张峰期。
A few Mesozoic volcanic basins distribute along the Middle-Lower Yangtze River. From west to east, they are subsequently Jinniu, Huaining, Luzong, Fanchang, Ningwu, Lishui and Liyang basins. From bottom to up, the volcanic rocks in Fanchang basin are compartmentalized to Zhongfencun, Chisha and Kedoushan formations. Zircon LA-ICPMS U-Pb dating on the lower and upper parts of rhyolite from Zhongfencun Formation are 131.2 ± 1.1Ma and 129. 1 ±1.3Ma, respectively, consistent with erupted age （130. 7 ± 1.1Ma） of the Kedoushan Formation in error, suggesting a brief erupted duration of volcanism in Fanchang basin. Zhongfencun Formation is predominated by dacite and rhyolite and Chisha Formation is predominated by trachyandesite, with minor rhyolite. SiO2 contents of volcanic rocks from Zhongfencun and Chisha formations are from 64. 36% to 75.45% and 63.08% to 69. 75%, respectively. Characteristics of trace element distributed patterns are similar for the volcanic rocks of two formations, showing enrichment of LREE and LILE and depletion of Nb, P and Ti. Eu negative anomalies can be observed in the rhyolite samples. 87Sr/86Sr（t） ratios are from 0. 7060 to 0. 7074, 0. 7073 and εNa（t） values are from -7. 91 to -8.11, -6. 62 to -6. 71 for samples of Zhongfencun and Chisha formation, respectively, similar to that of basalts from Kedoushan Formation. Integrated studies suggest that the volcanic rocks from Zhongfencun Formation were derived from partial melting of the lower crust, which was formed by underplating of the volcanic rocks from Zhongfencun Formation were derived from partial melting of the lithospheric mantle, undergoing crystallized fractionation of pyroxene, amphibole, plagioclase and apatite. The volcanic rocks from Chisha Formation were formed by basaltic magma which derived from partial melting of the lithospheric mantle and underwent crystallized fractionation of olivine, pyroxene, plagioclase and Ti-Fe oxide. It was the most dominant that the material from partial melting of the lithospheric mantle contributed in the Mesozoic volcanic rocks from the Lower Yangtze region, suggesting that ～ 130Ma was the summit period of lithospheric extension.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第10期3228-3240,共13页
Acta Petrologica Sinica
基金
国家自然科学基金项目(40972052)
安徽省公益性地质研究项目(2008-g-5)联合资助
关键词
火山岩
锆石定年
地球化学
中生代
繁昌
长江中下游
Volcanic rock
Zircon dating
Geochemistry
Mesozoic
Fanehang
The Middle-Lower Yangtze River
