摘要
为了深入探讨闽西南地区晚古生代以来的伸展构造演化特征,在岩石地球化学研究基础上,利用LA-ICP-MS锆石U-Pb定年方法对闽西南龙岩一带中基性岩墙群进行年龄测定。地球化学特征表明,该岩墙群属于钙碱性系列,主量元素以低TiO2（0.99%~1.73%）、高Al2O3（13.80%~15.76%）、高K2O（0.59%~4.42%）、K2O〉Na2O为特征；富集轻稀土元素（LREE）及大离子亲石元素（LILE,如Rb, Ba, Th, K等）,亏损高场强元素（HFSE,如Nb, Ta, Zr等）。锆石U-Pb测年结果表明,两期代表性岩墙分别形成于316 Ma和141 Ma,属于晚古生代中晚期和中生代晚期。本文运用构造环境判别方法,并结合沉积古地理特征,认为早期辉绿岩（316 Ma）可能形成于被动大陆边缘的板内拉张环境,晚期辉绿岩（141 Ma）可能形成于板块俯冲之后的火山弧？伸展的过渡环境。在以上研究基础上,讨论了闽西南地区晚古生代以来经历的构造演化阶段,即晚泥盆世？早三叠世伸展,中？晚三叠世印支运动挤压,早？中侏罗世古特提斯构造域向燕山期太平洋构造域转换,以及晚侏罗世末？早白垩世大规模伸展等主要阶段。
In order to discuss the tectonic evolution of southwestern Fujian since Neopaleozoic, the LA-ICP-MS zircons U-Pb dating method was employed to assess the ages of the basic-intermediate dykes, preceded by their petrological and geochemical studies. The zircons U-Pb dating of two representative samples yielded that they were emplaced at two different ages, 316 Ma and 141 Ma, belonging to the Late-Middle Neopaleozoic and Late Mesozoic respectively. Geochemical results attributed these dyke swamps to calcalkaline series, the major elements of the diabase dykes are characterized by low TiO2 （0.99%-1.73%）, high Al2O3 （13.80%-15.76%）, high K2O （0.59%-4.42%） and K2O〉Na2O. All these samples are enriched in LREE and LILE （Rb, Ba, Th, K）, but depleted in HFSE （Nb, Ta, Zr）. Combining these results, coupled with the tectonic discriminant analysis method and a comprehensive analysis of sedimentary palaeogeographic features, it is held that the early dykes might had been formed in an extensional passive continental margin in a sedimentary environment, while the late dykes might indicate a back arc spreading setting. Based on the above results, the authors think that since the Neopaleozoic, the southwestern Fujian has experienced the following main stages of tectonic events：Late Devonian-Early Triassic extension;Middle-Late Triassic compression orogenic tectonics;Early-Middle Jurassic tectonic transformation and Late Jurassic-Early Cretaceous extension.
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2015年第5期889-902,共14页
Geotectonica et Metallogenia
基金
中国地质调查局地质调查工作项目(12120113089600,12120114028701,1212011085472,1212010813064)
国家自然科学基金重点项目(41530321)联合资助
关键词
闽西南
辉绿岩
晚古生代
伸展构造
southwestern Fujian
diabase
Neopaleozoic
extensional tectonic
