甘肃北山地区同位素定年与构造岩浆热事件

在面积约100000Km~2的甘肃北山地区,共搜集同位素年龄数据216个,其中22个是本次测定的。依据这些资料做了年龄频谱图和地质环境一岩浆热事件综合示意图,从这些结果中可以得出以下看法:1.哈萨克斯坦板块的东端前寒武纪褶皱基底以微大陆的形式延入了本区,即本区有两大构造单元—塔里木板块和哈萨克斯坦板块。2.虽然有30多属燕山期的表现年龄,但从年龄频谱的骤然下落和野外复查表明,这些是后期岩脉和矿脉的年龄,而不是大规模岩浆活动的记录,即本区没有燕山期的大规模的岩浆活动。3.从加里东到印支期的每一构造岩浆旋回中,岩浆活动似有滞后现象,甚至延至下一个旋回,很可能这种滞后具有普遍意义。4.在每一构造单元内,大陆边缘区、过渡壳区和海洋区的喷发、侵入及变质作用也不尽相同。海洋区内喷发作用强于侵入和变质作用,而大陆边缘区侵入作用强于变质和喷发作用。

The Isotope Age-Dating and Tectonics Thermal Events in the Beishan Region, Gansu Province

The Isotope age-dating of 216 were collected from an area of 100000 km2 where the Beishan region situated in, Gansu province. The twenty two datings are determined this time. An isotope age-histogram and a geological environment-magmatic thermal event comprehensive sketch map have been made on the data. Some views resulted from both the maps and the data would be given as follows: (1) The Precambrian fold-base which belongs to the east part of the Kazakhstan plate streched to the Beishan region as a micro-continental, that means there are two big tectonic units in this region-Tarim plate and Kazakhstan plate; (2) This region has no bigger scale magma activity of the Yanshan stage, although more than 30 datings belong to the Yanshan stage. Because an abrupt fall on the age-histogram since 175 Ma and the feild investigation suggest that these apparent ages are that age of some later vein and ore-veins rather than any record of big scale magma activity; (3) The magmatic activity would delay some in each structure-magma circle from the Caledonian stage to the Indo-Chinese stage. May be, the delay of the magma activity has a common significance; (4) The thermal events are different between the Tarim plate and the Kazakhstan plate in both starting time and complete level although their thermal events have identical climax and ending time; (5) The eruption, the intrusion and the metamorphism were different among a continental margin region, a trasitional region and an ocean region within every tectonic unit. The eruption was stronger than both intrusion and metamorphism in the ocean region while the intrusion was stronger than both eruption and metamorphism in the continental margin region.