摘要
以U-Pb和Sm-Nd年代学的基本原理为基础,对东准噶尔荒草坡群下部的肉红色黑云母花岗片麻岩、1:25万纸房幅区域调查报告中划出的“新元古代”塔黑尔巴斯套糜棱杂岩和鲍尔羌吉糜棱杂岩等锆石U-Pb年龄数据作了分析研究;进一步明确了东准噶尔下马崖南小石头泉花岗片麻岩的Sm-Nd等时线年龄数据的地质意义,并结合准噶尔造山带变质岩和花岗岩类Nd模式的统计结果,得到初步结论是:至今还没有任何可靠的年龄数据指出准噶尔盆地的基底岩石具有前寒武纪年龄.目前的资料确定了东、西准噶尔的基底具有年轻岛弧组合的特征.
Understanding ages of basement rocks of Junggar basin is significant to study continental crustal evolution and mineralization in Xinjiang. Minor amounts of granitic gneisses occur in East and West Junggar, but none of them have been precisely dated yet. In this paper, we discussed brief principles of U-Pb and Sm-Nd geochronology, and commented the former 'Precambrian ages' in this area. A zircon Pb evaporation age of 1908 Ma was reported by Zhang et al. (1989) for the granitic gneiss from Xiaoliugou of Barkol region in the East Junggar, but the age has not been confirmed by accurate zircon U-Pb age and subsequent works. Using U-Pb 207Pb/206Pb ages of 830 and 933 Ma for zircons, those have t6/8 and t7/5 from ca. 250 to 340 Ma, and Pb evaporation age of 1105 and 605 Ma (t76) for granitic rocks from Baoerqangji and Taheierbasitao mylonite complex, Xinjiang Institute of geological survey (2000) would confirm existence of Meso-Neo-Proterozoic basement rocks (metamorphic complex and super .units ) in the report of the regional geological survey of Zhifang area (1:250000) in the East Junggar[20]. The above 'Precambrian ages' are uncertainty, because of very discordia U-Pb ages and t76 insignificant. [20] The above 'Precambrian ages' are uncertainty, because of very discordia U-Pb ages and t76 insignificant. Sm-Nd isotope analysis on five granitic gneisses from Xiaoshitouquan to south Xiamayan in East Junggar yielded an imprecise Sm-Nd isochron age of 668±140 Ma(26) with aNd(T) =+3.6 ±0.2 (MSWD=0.6)[4]. All above uncertainty Precambrian ages could not be used to estimate the existence of Precambrian basement rocks in the East Junggar. In addition, the granitic gneisses and metasediment (schists and phyllites) from the East and West Junggar have very young TDM ages of 0.7-1.4 Ga, which is very different from those of Tarim, Tianshan and Altai[26]. According to above discussing, the conclusions are as presence of a minor Precambrian crustal component is possible as inferred from the model ages, but no data have shown Precambrian ages for the Junggar basement anywhere. The present data thus confirm the East and West Junggar with the features of young island arc assemblages.
出处
《新疆地质》
CAS
CSCD
2003年第4期398-406,共9页
Xinjiang Geology
基金
国家重点基础研究发展规划项目(2001CB409805)
国家自然基金项目(40173026)共同资助
