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对溧水盆地8件典型的中生代次火山岩-侵入岩进行了详细的锆石U-Pb年代学和Lu-Hf同位素研究.结果显示,老虎头角闪闪长玢岩年龄为130.5±1.6 Ma,大铜山角闪闪长玢岩年龄为136.0±3.4 Ma,大魏庄角闪闪长玢岩年龄为132.7±2.7 Ma,野山凹粗安斑岩年龄为127.0±1.9 Ma,砚瓦桥石英闪长玢岩年龄为129.4±1.7 Ma,西北山辉石闪长玢岩年龄为133.2±2.1 Ma,长山头黑云母安山玢岩年龄为131.1±2.3 Ma,尖山黑云母粗安斑岩年龄为127.4±1.8 Ma.所有岩浆岩均为早白垩世产物,指示了溧水盆地岩浆活动的峰期时代.岩浆岩的锆石?Hf(t)值变化于-3.54~-9.11,其中大多数变化于-3.54~-5.93,与长江中下游其他火山岩盆地中同时代火山岩和侵入岩的锆石Hf同位素组成相似,表明它们具有相似的源区组成.在分析长江中下游地区以及邻区同时代岩浆特征的基础上,提出俯冲太平洋板块后撤模式来解释中国东部晚中生代岩浆活动.侏罗纪中晚期-白垩纪早期(170~135 Ma),太平洋板块向欧亚大陆俯冲,总体处于挤压背景,岩浆活动呈现出由沿海向内陆年轻化的趋势,且多具壳源特征;白垩纪早期(~135 Ma)之后,太平洋板块的俯冲作用减弱,俯冲板片发生后撤,研究区总体转变为拉张背景,从而形成了一系列火山盆地,造成大量富集地幔和较少量古老地壳物质的熔融,形成大量中基性岩浆岩.
Detailed zircon U-Pb dating and Lu-Hf isotopic studies of eight typical Mesozoic secondary volcanic-intrusive rocks in the Lishui basin have been performed. The results show that the age of the dolomite headdrift is 130.5 ± 1.6 Ma, The age of the hornblende diorite rock is 136.0 ± 3.4 Ma, the age of the Dalangzhuang hornblende diorite rock is 132.7 ± 2.7 Ma, the age of the Yushan pluton rock is 127.0 ± 1.9 Ma, the age of the Yanwaqiao quartz diorite rock is 129.4 ± 1.7 Ma, the age of the northwestern palygorskite diorite porphyrite is 133.2 ± 2.1 Ma, the age of the ancrickite of the Changshan head biotite is 131.1 ± 2.3 Ma, and the age of the Jian’an biotite amphibolite is 127.4 ± 1.8 Ma. All The magmatic rocks are all products of the Early Cretaceous and indicate the peak age of magmatism in the Lishui Basin.The zircon Hf (t) values of magmatic rocks vary from -3.54 to -9.11, with most of them varying from -3.54 to -5.93, Similar to the Hf isotopic composition of zircons from contemporaneous volcanic rocks and intrusive rocks in other volcanic basins in the middle and lower reaches of the Yangtze River, they are similar in source area composition. Based on the analysis of contemporaneous magma characteristics in the middle and lower reaches of the Yangtze River and its adjacent areas, Pacific plate retreat mode to explain Late Mesozoic rocks in eastern China During the Late Jurassic-Early Cretaceous (170-135 Ma), the Pacific plate subducted toward the Eurasian continent with an extruded background on the whole, and the magmatic activity showed a tendency of becoming younger from the coast to the inland and more crust-source characteristics After the Early Cretaceous (~ 135 Ma), the subduction of the Pacific plate diminished and the subducting slab retreated. The study area generally changed to a tensioned background, resulting in a series of volcanic basins that resulted in large enrichment of the mantle and less The amount of ancient crustal material melts, forming a large number of basic rock magma.