摘要
管店岩体位于扬子地块东部,沿郯庐断裂带南段主断裂带侵位,其岩石组成为石英二长岩和二长岩。精确的SHRIMP锆石U-Pb定年给出岩体的形成时代为(131.5±1.6)Ma。该岩体为一中酸性侵入体(SiO254.84%～67.83%),属于高钾钙碱性系列,并具有与埃达克(质)岩类似的地球化学特征,如高Al2O3(14.12%～15.14%)、Sr(612～976μg/g)含量及Sr/Y(31～77)、La/Yb(18～42)比值,但低Y(8.20～21.4μg/g)和Yb(0.90～1.70μg/g)含量,无明显Eu异常至Eu正异常。管店侵入岩的87Sr/86Sr初始比值为0.7058～0.7061,εNd(t)为-17.03～-15.11,锆石的εHf(t)(-26.3～-22.6)较低但相对均匀,说明其不可能由俯冲洋壳熔融形成。管店埃达克(质)侵入岩具有较高的MgO(2.21%～6.75%)含量和Mg#(56～62)值及相容元素(Cr85.4～356μg/g,Ni40.8～144μg/g)含量。管店侵入岩可能由拆沉下地壳熔融形成,岩浆在上升过程中与地幔橄榄岩发生了反应。早白垩纪郯庐断裂带的活动、扬子地块东部在扬子-华北两块体碰撞后的地壳拆离作用可能导致增厚下地壳的拆沉与埃达克质岩浆活动。
The Guandian pluton, which is located in the eastern Yangtze block, occurs along the southern segment of Tan-Lu fault belt. It mainly consists of quartz monzonite and monzonite. New zircon SHRIMP U-Pb age data suggest that it intruded in （131.5 ± 1.6） Ma. The rocks of this pluton are intermediate-felsic （SiO2 54. 84% 67.83% ） and high-K calc-alkaline. They are geochemically characterized by relatively high Al2O3 （14. 12% - 15.14% ）, Sr （612 - 976 μg/g） and Sr/Y （31 - 77）, La/Yb （18 - 42） values, but low Y （8.20 - 21.4 μg/g） and Yb （0.90 - 1.70 μg/g） contents with negligible to positive Eu anomalies （ δEu 0. 73 - 1.58）, similar to adakites. The Guandian intrusive rocks exhibit homogeneous initial ^87Sr/^86Sr ratios （0.7058 - 0. 7061） but low εNd（t） values （ - 17.03 ～ - 15. 11 ）, as well as relatively homogeneous and low zircon εHf（t） （ - 26.3 ～- 22.6）, indicating that they were impossibly derived by partial melting of subducting oceanic crust. They also have relatively high MgO （2. 21% - 6.75% ）, Mg^# （56 - 62） and compatible elements （Cr 85.4 - 356 μg/g, Ni 40.8-144 μg/g）, suggesting that they should contain some mantle components. Taking into account geochronologic, geochemical, Sr-Nd and zircon Hf isotopic data, we suggest the Guandian adakitic magmas were most likely derived by partial melting of delaminated lower crust, and laterly contaminated at different percentage by mantle peridotites. In Early Cretaceous, the activities of the Tan - Lu fault and the crustal detachment of eastern Yangtze block after the collision between Yangtze and North China blocks possibly resulted in lower crustal delamination and associated adakitic magmatism.
出处
《地球化学》
CAS
CSCD
北大核心
2008年第5期462-480,共19页
Geochimica
基金
中国科学院知识创新工程重要方向项目(KZCX2-YW-128)
国家自然科学基金(40572042,40673037)
关键词
埃达克岩
下地壳拆沉
地壳拆离
郯庐断裂
管店
扬子地块
adakite
lower crustal delamination
crustal detachment
Tan-Lu fault
Guandian
Yangtze block
