Paleomagnetic Study Of The Permian Large Igneous Province In Tarim Block,China

The Carboniferous-Permian period is a very important transition stage during the process of the evolution of the Tarim block from the ancient tectonic-kinematics system to the new tectonic-kinematics system which has experienced large-scale magmatic activity and constitutes another large igneous province in China.In this paper,the paleomagnetic direction and paleomagnetic intensity of the Tarimian Permian igneous province are studied.The study of paleomagnetic direction can not only restore the relative position and the transformation of the Tarim block and its adjacent block during the Permian period,but also provide the paleomagnetic evidence to understand the tectonic evolution of both Paleo-Asian Ocean and Paleo-tethyan.The study of paleomagnetic intensity can provide the evidence for understand mechanism of the Carboniferous-Permian superchron period and for the establishment of reasonable geodynamics model during the superchron period.The samples were drilled from Early-Middle Permian Kupukuziman Formation and Kaipaizilieke Formation including the basalts and a small part of the sedimentary rock samples from Keping area,Tarim block.The results of rock magnetism show that main magnetic minerals of Kupukuziman formation is magnetite,magnetic mineral particles in the basalt is SD particles with a small amount of MD particles.The main magnetic minerals of Kaipaizilieke formation is magnetite,the magnetic mineral particle size is that of the mixing of the SD particles and the SP particles with the MD particles.Through the paleomagnetic study on the Kupukuziman Formation and Kaipailieke Formation from the Keping area,the Tarim block,the characteristic remanent component,passed fold test at both 95%and 99%confidence level,may represent the primary remanence.The paleomagnetic pole position of the Early-Middle Permian of Tarim block was obtained as ?=57.5°N,?=181.3 °E,A95 = 6.9,corresponding latitude is 27.9 °N.Our results combined with previously published indicate that:(1)the Tarim block,the Kazakhstan block and the Siberian block in the early Permian have been collided and amalgamate,and the ancient Asian ocean has been closed in or before the early Permian.(2)The Qaidam block,which is now on the southeastern margin of the Tarim block,collapses with the Tarim block in the Late Permian and becomes part of the Eurasian continent;(3)There are large distance between the Tarim block and North Qiangtang block in the early Permian period indicating that the Paleo-Tethys is still large-scale.The Paleo-Tethys began to subduction in early Permian,until the late Triassic Tarim block and the North Qiangtang block have been collided.The Paleo-Tethys,between the Tarim block and North Qiangtang block,closed in that period.Through the study on the paleomagnetic field intensity of the five eruption basalts of the large igneous province of Tarim block,most of the samples did not obtain reliable results,and a bit of samples that the age was the last stage of Middle Permian obtained reliable strength results.The average intensity value of the sample is 79.63± 8.87?T,and the corresponding virtual dipole magnetic moment(VDM)is(16.45±1.83)×1022Am2.Our results combined with previously published show that at the stage of the beginning and end of the superchron period,the dipole geomagnetic field is in a low-energy state,but the low-energy state of the dipole geomagnetic field is not always maintained during the whole superchron period.Our paleomagnetic intensity result of the last stage of Middle Permian was abnormal high,may indicated that an important geodynamics process happened in this period.