LA-ICP-MS U-Pb Zircon Geochronology of Basic Dikes within Maxianshan Rock Group in the Central Qilian Orogenic Belt and Its Tectonic Implications

• 责任者：He Shiping ( Xi’an Institute of Geology and Mineral Resources ; Chinese Acdemy of Geological Sciences ; Xi’an 710054 ; China) ; Wang Hongliang
• 刊名：Journal of China University of Geosciences
• 出版年：2007
• 卷期：18(1)
• 页码：p.19-29
• 图表：illus., tables, refs.
• issnNo：ISSN1002-0705
• isbnNo：CN42-1279/P

A large number of basic dikes, which indicate an important tectonic-magmatic event in the eastern part of the Central Qilian  orogenic belt, were found from Maxianshan rock  group, Yongjing county, Gansu Province, China. According to the research on the characteristics of geology and petrology, the basic dike swarms, widely intruded in Maxianshan rock group, are   divided   into   two   phases   by   the   authors.   U-Pb  isotope   of   zircons   from   the   basic   dikes   above   two phases   is   separately   determined   by   LA-ICP-MS   in  the   Key   Laboratory   of   Continental   Dynamics   of Northwest University, China and the causes of formation of the zircons are studied using CL images. The formation age of the earlier phase of metagabbro dikes is (441.1±1.4) Ma (corresponding to the

early stage of Early Silurian), and the age of the main metamorphic period is (414.3±1.2) Ma (corresponding to the early stage of Early Devonian). The formation age of the later phase of diabase dike swarms   is   (434±1.0)   Ma   (corresponding   to   the   late   stage of   Early   Silurian).   The   cap-tured-zircons from diabase dike swarms saved some information of material interfusion by Maxianshan rock group ²⁰⁷Pb/²⁰⁶Pb apparent ages are (2 325±3)–(2 573 (±6)   Ma),   and   some   zircons   from   diabase   dike swarms also saved impacted information by tectonic   thermal  event  during   the  late  period  of Caledonian movement (206Pb/238U apparent ages are   (400±2)–(429±2)     Ma).   By  combining   the results   of  the  related  studies,  the  basic  dikes within Maxianshan rock group were considered to be formed in the transfer period, from subductional orogeny   towards   collisional orogeny, which represents   geological   records of   NW-SE   extension   during  regional NE-SW towards intense compression in the Central Qilian block.