摘要
本文通过岩石地球化学研究和讨论 ,认为桐柏—大别造山带燕山晚期存在过碱性( peralkaline)和铝质 (aluminous)A型花岗岩。过碱性花岗岩的岩石类型为碱长花岗岩和石英正长岩 ,其ACNK =0 .72～ 0 .97,NKA =1.0 2。铝质A型花岗岩是本文研究的重点 ,岩石类型也为碱长花岗岩和石英正长岩 ;其SiO2 含量为 67.73%～ 77.60 % ,富碱 (Na2 O +K2 O含量为 7.97%～9.76% ) ,ACNK =0 .72～ 1.0 3,NKA =0 .84～ 0 .97,属于偏铝质 -微过铝质岩石 ;轻稀土元素富集 ,负铕异常明显 (δEu =0 .12～ 0 .57) ,Zr、Nb、Ga、Y富集。与高分异的I型花岗岩相比 ,研究区高硅 (SiO2 >72 % )的铝质A型花岗岩富Fe(FeOT>1.50 % ) ,高Zr +Nb +Ce +Y和Ga/Al,具有较高的Zr饱和温度 ( 84 5～ 880℃ )。研究区A型花岗岩形成于造山期后环境 ,标志着桐柏—大别造山带在晚白垩世进入了伸展塌陷阶段及碰撞 -叠覆造山的结束。
The study and discussion of petrology and geochemistry have revealed that there exists two kinds of A_type granites in Tongbai_Dabie orogenic belt: peralkaline and aluminous granites. The peralkaline A_type granites include alkaline feldspar granite and quartz syenites, characterized by ACNK=0.72～0.97 and NKA=1.02. The aluminous A_type granites also include alkaline feldspar granite and quartz syenites, characterized by SiO 2=67.73%～77.60%, rich alkali, Na 2O+K 2O=7.97%～9.60%, ACNK=0.72～1.03, NKA=0.84～0.97, rich REE, δEu=0.12～0.57 and rich Zr, Nb, Ga and Y. Compared with high fractionated I_type granites, the high Si(SiO 2>72%) aluminous A_type granites show rich Fe (FeO T>1.50%), high Zr+Nb+Ce+Y and Ga/Al as well as high zircon saturation temperature (845～880℃). The A_type granites were formed in a post_orogenic environment. It is suggested that Tongbai-Dabie orogenic belt entered the phase of extension and collapse in Late Cretaceous, during which the orogenic movement ended.
出处
《岩石矿物学杂志》
CAS
CSCD
北大核心
2000年第4期297-306,315,共11页
Acta Petrologica et Mineralogica
基金
国家攀登计划预选(95 -预 - 2 5 )
国家重点基础研究发展规划 (G19990 432 0 2 )
广东省自然科学基金博士启动(9945 88)
国家博
关键词
A型花岗岩
桐柏-大别造山带
岩石地球化学
A_type granite
high fractionated I_type granite
tectonic environment
Tongbai-Dabie orogenic bx
