塔里木盆地前寒武地层岩石磁化率

Analysis of rock magnetic susceptibility on Precambrian strata in Tarim basin

在塔里木盆地前寒武结晶基底研究过程中,为了准确建立地层地磁模型,对库鲁克塔格地区岩浆岩、柯坪地区沉积岩、塔什库尔干地区变质岩地层进行系统取样及岩石薄片鉴定和准确命名,并测量岩石密度、磁化率。研究发现:①库鲁克塔格地区:基性、超基性岩蛇纹石化析出磁铁矿,磁化率剧烈变化,而中、酸性侵入岩磁化率随黑云母含量增加而增大;②柯坪地区:沉积岩中含黑云母长石石英砂岩、绢云母化长石砂岩及绿泥石化粉砂质泥岩的磁化率明显高于其他沉积岩,磁化率主要受沉积岩中少量的黑云母和绿泥石等强顺磁性矿物所影响;③塔什库尔干地区:副变质岩中含顺磁性物质和铁磁性物质较少,磁性一般较弱;正变质岩中黑云母、角闪石等强顺磁性矿物含量明显增加,磁化率较副变质岩高;弱磁性变质岩中黑云母、角闪石、绿泥石等在后期变质过程中蚀变,析出磁铁矿等铁磁性矿物,岩石磁化率明显增高。

During the research on Precambrian crystalline basement in Tarim basin,in order to build an accurate stratigraphic geomagnetic model,systematic sampling,accurate rock naming,and thin section identification have been carried out on strata of magmatic rocks from Kuruktag,sedimentary rocks from Kalpin,and metamorphic rocks from Taxkorgan;rock density and magnetic susceptibility have also been measured.The study found:①Kuruktag area:mafic,ultramafic rock is serpentinized,magnetite is precipitated,susceptibility changed violently;Intermediate,acidic intrusive rock’s susceptibility increased with biotite’s content;②In Kalpin area:sedimentary rocks such as biotite-bearing feldspathic quartz arenite,sericite arkose,chlorinated silty mudstone,whose susceptibility is higher than other sedimentary rocks,susceptibility is mainly affected by few high paramagnetic minerals such as biotite,chlorite in sedimentary rock;③In Taxkorgan area:parametamorphite’s susceptibility usually have lower values with few paramagnetic and ferromagnetic minerals;while orthometamorphite’s susceptibility is much higher than parametamorphite with the content of high paramagnetic minerals such as biotite,hornblende increased obviously;ferromagnetic minerals such as magnetite are altered from biotite,hornblende,chlorite on synantexis process in weak magnetic metamorphite,accordingly its rock susceptibility increased significantly.