| The north Qinling Orogen was the most intricated belt for its complex in petrology and tectonics. After suffering multi-phases tectonic movements since Phanerozoic, it is cropped out distributing as intermittent lenticulars. As strong compression and strike-slip distortion which lead to significant newborn foliation structures, most of geological structure have no stratigraphic indication, and it brings a lot of problems to the age determination relevant to the North Qinling Orogen. Based on the prevail distributing characterics of river in North Qinling Orogens and south margin of North China, as well as the metamorphic extent of North Qinling geological tectonic bodies which is not great enough to change the isotopic behavior in zircon, this paper will try to determine the age of varieties of complicated magma-tectonic events, by using U-Pb age dating to analyze large number of piedmont river detrital zircons. This is also the innovation of this study in technical way and research method.Based on comparison of the data about detrital zircons from Piedmont eight rivers in the north Qinling orogenic belt by U-Pb dating, we acquire some new ideas like this:Through previous practice, it is proved that it is feasible and a suitable way to study geological history which are cropped out along the river in the limited zone by analyzing modern river detrital zircon. And to the study relevant to some special tectonic belts, it is also useful and meaningful.In the Xiaoqinling zone, eastern part of Qingling, namely Tongguan-Huanyin, the age peaks mainly lie on Wutai and Lvliang period, which is highly consistent with geological evolution history in southwestern part of north China craton. From Neoproterozoic to late Mesozoic, the craton was stabile, so there was lack of zircon record. Though previous studies concluded that involvement of north China craton in Xiaoqinling into Qinling is not belong to orogenic belt, our study reflect that there is not leave any tectonic movement records of Jinning, Caledonian and Indosinian in Xiaoqinling of north China craton. That is to say, the basic characteristics of north China craton in Xiaoqinling have not been changed obviously. The age of Yanshanian zircon record (about 127Ma) is the reflect of granite and dike rock.In classic north Qinling valley, namely Chang'an-Huxian, the zircon record since Neoproterozoic is common, mainly about Jinning, Caledonian, Variscan and Indosinian. Compared with Xiaoqinling, the geological record in north Qinling tectonic belt has its unique evolution history. The Archean basement in north Qinling tectonic belt is proved not existed.Hybrid zone, namely Zhouzhi county. Because the ShangDan suture zone lies on the south of the Qinling watershed, the river detrital material records not only the geological information in north Qinling tectonic belt, but also Shannan, even detrital material information in souther zone. All of these make the source sophisticated, so we call it hybrid material source. The river detrital zircon here not only leave the message as same as before we clarified, but also little Neoproterozoic (2500Ma) and Mesoproterozoic (1600Ma) records. We presume that these record may come from the south Qinling basement which lies to the south of Shandan suture, and the material source will be the Foping complex or Changjiaoba complex near watershed in this area.
|
PDF Full Text Request