摘要
下扬子繁昌地区出露的三个规模较大的侵入岩体分别是板石岭岩体、浮山岩体和滨江岩体,岩石类型分别以石英二长岩、钾长花岗岩以及花岗岩为主。三个岩体的锆石LA-ICPMSU-Pb定年给出了较为一致的形成年龄,分别为124.9±1.7Ma、126.4±1.7Ma和124.6±4.7Ma(滨江粗粒花岗岩)及123.0±1.8Ma(滨江花岗斑岩)。下扬子沿江地区中生代岩浆岩可以划分为三个阶段,这三个岩体的形成时代与下扬子沿江地区其它A型花岗岩一致,均属于第三阶段岩浆活动的产物。三个岩体均表现为轻稀土富集和不同程度的Eu负异常,以及A型花岗岩所特有的Ba和Sr选择性亏损特征。板石岭岩体的锆石εHf(t)值和δ18O值分别为-2.7～-6.3、6.7～7.4,其全岩87Sr/86Sr(t)比值和εNd(t)值分别为0.7072和-6.8。浮山岩体的锆石εHf(t)值和δ18O值分别为-1.6～-7.9和7.1～9.1,其全岩87Sr/86Sr(t)比值和εNd(t)值分别为0.7076和-7.7。滨江岩体的锆石εHf(t)值和δ18O值分别为0～-6.6和8.0～10.3,其全岩87Sr/86Sr(t)比值和εNd(t)值分别为0.7078和-3.4。综合分析表明,滨江岩体为新元古花岗岩形成的中上地壳深熔的产物,板石岭和浮山岩体的岩浆来源于形成滨江岩体的壳源岩浆和幔源岩浆不同比例的混合。下扬子沿江地区三个阶段岩浆岩的成因和岩浆物质来源指示了一个较为清晰在拉张强度逐渐增加背景下的深部地质作用演化过程。
Three relatively large intrusions locating in Fanchang district, the Lower Yangtze region, are Banshiling, Fushan and Binjiang plutons, rock types of which are dominantly quartz-monzonite, potassium feldspar granite and granite, respectively. Zircon LA-ICPMS U-Pb dating of three intrusions give quite accordant ages of 124. 9 ± 1.7Ma, 126.4± 1.7Ma, 124. 6 ±4. 7Ma （the coarse- grained phase of Binjiang pluton） and 123.0 ± 1.8Ma （the fine-grained phase of Binjiang pluton） , respectively. The Mesozoic magmatism occurred along the Lower Yangtze River can be divided into three stages. These plutons are formed simultaneously with other A-type granites along the Lower Yangtze River and belong to the third stage magmatism. Three intrusions are characterized by LREE-enrichment as well as varying degrees of negative Eu anomaly, with selective depleted characteristic of Ba and Sr depletion, an exclusive signature of A-type granite. The range of zircon εHf（t） and δ180 values of Banshiling intrusion is from -2. 7 to -6. 3, 6.7 to 7. 4 and that of Fushan and Binjiang intrusions are from -1. 6 to -7. 9, 7. 1 to 9. 1 and 0 to -6. 6, 8.0 to 10. 3. Whole rock 87Sr/86Sr（t） and εNd （t） ratios for Banshiling, Fushan and Binjiang intrusions are 0. 7072, - 6. 8, 0. 7076, - 7. 7 and 0. 7078, 3.4, respectively. Comprehensive analysis suggests that the Binjiang pluton formed by anatexis of the middle and upper crust represented by the Neoproterozoic granites. The magma formed Banshiling and Fushan plutons were underwent processes of magma mixing with different degrees which derived from mantle and crust, respectively. The petrogenesis and magmatic source of the three stage magmatism in the Lower Yangtze region reveal a clearly deep geological process of evolution under an extension setting with increasing intensity during three magmatic stages.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第10期3209-3227,共19页
Acta Petrologica Sinica
基金
国家自然科学基金项目(40972052)
中国地质调查局基础地质项目(1212011085420)
教育部博士点基金项目(20090111110010)联合资助
关键词
花岗岩
中生代
Hf-O
锆石
繁昌
下扬子
Granite
Mesozoic
Hf-O
Zircon
Fanchang
The Lower Yangtze region
