云南思茅盆地早白垩世扒沙河组地层地球化学特征及其物源制约

摘要

思茅盆地晚白垩世勐野井组地层是我国唯一的古代固体钾盐发育地层,由于盆地内部断层纵横,地层横向对比困难,急需有效的标志性地层以完善区域对比及后续研究的深入.在确认早白垩世扒沙河组地层良好的区域可对比性基础上,通过对比思茅盆地江城地区两个典型地质露头剖面及勐野井钾盐矿床钻孔岩芯的元素地球化学特征,探讨了江城地区含盐系地层及其下伏扒沙河组地层的化学风化、构造背景及物源属性特征.结果表明,1)思茅盆地江城地区勐野井组与扒沙河组地层在形成过程中,其物源区均经历了中至强的化学风化作用过程;2)尽管这两套地层间呈不整合接触关系,但在物源属性上二者却均具有混和物源的特性(活动大陆边缘或大陆岛弧背景的长英质物源与被动大陆边缘背景的古老沉积物物源的混合),扒沙河组地层在沉积过程中可能还受到了少量基性岩物源的影响;3)云南江城勐野井组及其下伏扒沙河组地层的主要物源区可能为哀牢山隆起带和扬子古陆块.%The Late Cretaceous Mengyejing Formation in Simao Basin is the only strata with ancient solid potash deposits in China.Because of the developed faults in the basin, horizontal stratigraphic correlation is difficult.It is urgent for effective marker strata to improve regional comparison and follow-up research.On the basis of identification for the good marker strata of the early Cretaceous Pashahe Fm., we compared the geochemical characteristics of two geological sections, which located in the Jiangcheng area of Simao Basin and core samples from the Mengyejing Potash Deposit.The results show that 1) Both the Mengyejing Fm.and Pashahe Fm.of Simao Basin have experienced moderate to strong chemical weathering process during their formation;2) Despite the unconformity between the two sets of strata, both of them have the mixed provenances (mixture of feldspathic source on the background of active continental margin or island arc and ancient sediments from passive continental margin), while the Pashahe Fm.may also be affected by minor mafic source in the process of deposition;3) The major source areas of Mengyejing Fm.and Pashahe Fm.may be the Ailaoshan uplift and Yangtze block.