塔里木地块上石炭统的古地磁研究

本文对塔里木地块西北缘柯坪地区的3条上石炭统康克林组剖面进行了古地磁研究。95个定向岩心样品的逐步热退磁和交变退磁揭示出3个磁性组分,第一个是具有低解阻温度谱或低矫顽力谱在现代地磁场作用下形成的粘滞剩磁A(D=10°;I=56°,α95=4°);第二个是红色石英砂岩的具有反极性的高温组分B(D=217°,I=-43°,λ=56°,Φ=184°E;A25=6°详细研究表明,该分量受附近晚二叠世脉岩侵入的重磁化;第三个是灰岩高矫顽力谱的反极性组分C（D=241°、I=-51°,λ=41°N,Φ=160°E,A（?）=4°）。这一分量通讨倾斜检验,在95%概率水平上明显不同于塔里木地块目前已有的石炭纪以后的古地磁方向,它代表了原生剩磁。研究结果表明:（1）晚石炭世塔里木地块已和哈萨克斯坦地块、苏联西天山地块以及西伯利亚地块发生碰撞:（2）苏联西天山地块相对塔里木地块曾逆时针旋转了70°（欧拉极位置λ=8°N,Φ=69°E）,而塔里木地块则相对西伯利亚地块逆时计旋转了21°（欧拉极位置λ=20°N,Φ=34°E）。从该区已有的晚古生代至早三叠世占地磁数据看,这些地块之间的相对旋转运动发生于早三叠世之后。

A STUDY OF UPPER CARBONIFEROUS PALEOMAGNETISM FOR THE TARIM BLOCK

We present here a new paleomagnetic result of Upper Carboniferous Kankelin Formation from three sampling sections in Keping area, the north-west margin of the Tarim Block.Both alternating field and thermal stepwise demagnetizations of 95 specimens reveal two stable and one sof t~components of magnetization. A postfold-ing,low temperature or low coercivity component A with the direction near the recent geomagnetic dipole field in situ (D = 10? 1 = 56? 085=4? is represented as a viscous remanent magnetization acquared after Tertiary. A stable, high-temperature component B w-ith reversed polarity (D =217? I =-43? A. = 56, = 184, A95 = 6? is from red quartzose sandstones. A detailed study shows that this component is contaminated by the Upper Permian dikes near the sampling section.The second stable, high coercivity component C also with reversed polarity (D=241? I =-51? A = 11, = 160, A95 = 4? is from limestones. The successful tilt test and the fact that this component is distinct at 95%conf idence from the post Carboniferous paleomagetic directions in this area, strongly suggest that the component C is primary.The paleomagnetic result indicates that 1) the Tarim Block has collided with the Kahazakestan Block, the west Tianshan Block of U.S.S.R and the Siberian Block by Middle to Late Carboniferous; 2) the west Tianshan Block of U.S.S.R. hasrotated 70 anticlockwise about an Euler pole of 8, 69 with respect to the Tarim Block and the Tarim Block has rotated 21?anti clockwise about an Euler pole of 20?N. 34 with respect to the Sibsrian Block. The time of the rotations is not well constrained, but the detailed analysis of Late Paleozoic to Early Triassic paleomagnetic poles of the Tarim Block suggests that it seems to be a post Early Triassic in age.