滇西户撒盆地芒棒组砂岩地球化学特征及物源区和构造背景分析
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中国地质科学院,成都地质调查中心,成都地质调查中心,北京大学,成都地质调查中心,成都地质调查中心

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基金项目:中国地质调查局项目“西南地区铀矿调查选区及含煤岩系放射性地质环境调查” ,编号:121201010000150006


Geochemical Characteristic of Sandstones from the Mangbang Formation in the Husa Basin, Western Yuannan, and Its Constraints on Provenances and Tectonic Setting
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Chinese Academy Of Geological Sciences Beijing,china,Chengdu Geological Survey Center,Chengdu Geological Survey Center,Peking University Beijing,Chengdu Geological Survey Center,Chengdu Geological Survey Center

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    摘要:

    滇西户撒盆地芒棒组砂岩地球化学分析结果表明:砂岩主要为长石砂岩和杂砂岩,少量为页岩;矿物成分主要为石英、钾长石、斜长石和伊利石等;REE配分模式曲线一致,LREE/HREE=9.75~15.91,平均13.24,(La/Yb)N=13.06~26.41,平均19.21,轻稀土元素相对重稀土元素明显富集,稀土元素分馏明显。SiO2/Al2O3=2.06~6.01,平均4.60,ICV=0.54~1.09,平均0.86,结合沉积特征表明样品为被动构造环境下沉积物的再循环而成,而非强烈风化作用过程中形成的第一次旋回沉积物。Th/U=544~1210,平均848,CIA矫正均值为69,反映了温暖、湿润条件下的中等化学风化作用。A-CN-K判别图说明交代作用降低了CIA值、且样品源岩钾长石比斜长石含量高。Th/Sc=4.43~25.35,平均8.18,Rb-K2O图解、Co/ThLa/Sc图解和La/Yb∑REE图解表明样品物源为花岗岩。TiO2(Fe2O3T+MgO)、Al2O3/(Cao+Na2O)(Fe2O3T+MgO)、La-Th-Sc以及(K2O/Na2O)SiO2构造判别图解表明:源岩形成于被动大陆边缘环境,与中特提斯洋在晚侏罗世—早白垩世已经打开且长期稳定相对应。户撒盆地为沿早期户撒走滑挤压断裂拉张沉积形成,接受周缘晚侏罗世—早白垩世花岗岩沉积。

    Abstract:

    Geochemical analysis was conducted in this study for sandstones samples from the Mangbang Formation in the Husa basin,western Yunnan. The analysis results show that sandstones from the Mangbang Formation mainly comprise of feldspar sandstone and greywacke sandstone as well as minor shale, and the mineral assemblage mainly contains quartz,K-feldspar,plagioclase and illite. The sandsontes have a consistent REE pattern, enrichment of LREE relative to HREE, with LREE/HREE of 9.75~15.91 (averaging 13.24) and (La/Yb)N of 13.06~26.41 (averaging 19.21). The SiO2/Al2O3 ratio of 2.06~6.01 and index of the chemistry variation (ICV) of 0.54~1.09 together with the features of sedimentation make it clear that these sandstones resulted from recycling deposition in the passive tectonic setting, rather than the first cycle of sediments due to the relatively strong weathering. Furthermore,the Th/U values of 5.44~12.10% and CIA of 59~76 reflect a chemical weathering environment of medium intensity in warm and moist climate. A/CNK discrimination diagram shows that the sandstone clastics have a higher content of K-feldspar relative to plagioclase and low CIA value due to metasomation. The Th/Sc ratio of 4.43~25.35 (averaging 8.18 ) and the diagrams of Co/Th versus La/Sc,K2O versus Re,and La/Yb versus ∑REE all suggest that sandstones in the study area were mainly derived from the previously formed granites. Besides, the tectonic discrimination diagrams of TiO2 versus Fe2O3T+MgO,Al2O3/(Cao+Na2O) versus Fe2O3T+MgO,K2O/Na2O versus SiO2,and La-Th-Sc all reflect that these granites were formed in the setting of passive continental margin and possibly corresponded to the long term steady state of the MesoTethys Ocean which has been open during the Late Jurassic to Early Cretaceous. The Husa basin was formed due to the extension along the previous Husa transpressional fault and started to deposition sourced from the peripheral granites during this period.

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张建军,牟传龙,周恳恳,冯丽霞,伍皓,陈小炜.2017.滇西户撒盆地芒棒组砂岩地球化学特征及物源区和构造背景分析[J].地质学报,91(5):1083-1096.
ZHANG Jianjun, MOU Chuanlong, ZHOU Kenken, FENG Lixia, WU Hao, CHEN Xiaowei.2017. Geochemical Characteristic of Sandstones from the Mangbang Formation in the Husa Basin, Western Yuannan, and Its Constraints on Provenances and Tectonic Setting[J]. Acta Geologica Sinica,91(5):1083-1096.

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  • 收稿日期:2016-08-18
  • 最后修改日期:2016-12-23
  • 录用日期:2016-12-24
  • 在线发布日期: 2017-05-16