柴达木盆地一里坪凹陷新近系混积岩岩石磁学特征

Rock magnetic characteristics of Neogene mixed rock in Yiliping depression,Qaidam Basin

柴达木盆地腹地因其沉积地层厚度较大,开展古地磁研究对还原青藏高原隆升过程、揭示全球气候变化规律等具有更为重要的意义,但发育于盆地内部的细粒混积岩沉积具有何种岩石磁学特征,是否可用于磁性地层学测试尚无相关研究.本研究通过X-衍射、κ-T曲线、饱和等温剩磁及反向场退磁和三轴等温剩磁系统热退磁实验对柴达木盆地一里坪凹陷内部钻井获得的新近纪细粒混积岩矿物学、岩石磁学特征展开研究,结果表明:细粒混积岩样品中以单畴或假单畴为主的低矫顽力的磁铁矿作为主要载磁矿物,含有少量高矫顽力的赤铁矿;黄铁矿与绿泥石在地层中的普遍存在使得与温度相关的实验结果均受影响,从而导致热退磁失效.利用交变退磁和低温混合退磁方法对地层中占主导地位的混积岩开展古地磁学相关工作,可获得理想结果.

Due to the large thickness of the sedimentary strata in the hinterland of Qaidam Basin,it is more important to study paleomagnetism for reducing the uplift process of the Tibet Plateau and revealing the global climate change.However,there is no relevant research on the rock magnetic characteristics of the fine-grained mixed rock and whether it can be used for magnetic stratigraphic testing.Through X-ray diffraction,κ-T curve test,saturated isothermal remanence and reverse field demagnetization test,three-axis isothermal thermal demagnetization test,the mineralogy and rock magnetism characteristics of Neogene fine-grained mixed rock obtained from drilling in Yiliping depression of Qaidam Basin are studied in this paper.The results show that the magnetic minerals are dominated by low coercive magnetite with single domain or pseudo single domain in fine-grained mixed rock,and contain a small amount of hematite with high coercivity.The widespread existence of pyrite and chlorite in the strata affects the results of temperature related experiments,resulting in thermal demagnetization failure.In addition,we can get ideal results by using alternating demagnetization and low temperature mixed demagnetization methods to carry out paleomagnetism related work on the dominant mixed rocks.