摘要
川西南简阳地区TF2井钻井发现上二叠统龙潭组凝灰岩,其岩浆属性和沉积大地构造背景仍缺乏研究。该凝灰岩具有高TiO_(2)(分别为3.86%,5.21%)、低Al_(2)O_(3)/TiO_(2)(分别为5.72、4.84)的特征,属于中-基性凝灰岩。其富集轻稀土及Rb, Th, Nd等元素,并具有Eu明显负异常,表明与峨眉山高钛玄武岩特征相似,暗示其形成于地幔柱作用下的板内环境。锆石U-Pb测年显示,岩石含有大量新元古代捕获锆石(800~1 100 Ma)和两组较为集中的显生宙锆石U-Pb年龄谱系(245~265 Ma和410~465 Ma),而最年轻锆石谱系的加权平均年龄为259.8±2.3 Ma,与峨眉山玄武岩主相喷发时间相吻合。Hf同位素分析结果显示,~260 Ma的锆石εHf(t)值具有两组特征(-3.6~1.5和9.6~12.6),指示该组锆石起源于亏损地幔源区并遭受了地壳物质的混染;410~465 Ma的锆石具有较低的εHf(t)值(-13.3~-5.6),其锆石微量元素具典型长英质弧岩浆特征,表明该组锆石起源于俯冲弧背景下的古老大陆地壳源区。结合区域资料研究,本次研究认为简阳地区龙潭组凝灰岩为中晚二叠世峨眉山大火成岩省的产物,其大量早古生代锆石表明扬子板块深部可能发育与原特提斯洋俯冲消减相关的岩浆记录,新元古代-古元古代锆石则可能来源于扬子板块的结晶基底。
The magmatic properties and sedimentary tectonic setting of the Upper Permian Longtan Formation tuff discovered in well TF2,Jianyang area,southwest Sichuan province,are studied in this paper.Geochemical analysis shows that the tuff is characterized by high TiO_(2)(3.86%,5.21%)and low Al_(2)O_(3)/TiO_(2)(5.72,4.84),belonging to medium-basic volcanic tuff.The rocks are enriched with light rare earth and Rb,Th,Nd and other elements,and show obvious negative Eu anomalies,which is similar to the characteristics of the high titanium basalt in Emei Mountain,suggesting that it was formed in the intraplate environment under the action of mantle plumes.Zircon U-Pb dating shows that the Longtan Formation tuff contains a large number of Neoproterozoic captured zircons(800 to 1100 Ma)and two concentrated groups of Phanerozoic zircon U-Pb age lineages(245 to 265 Ma and 410 to 465 Ma).The weighted average age of the youngest zircon lineages is 259.8±2.3 Ma,which coincides with the eruption time of the main facies of the basalt in Emei Mountain.The Hf isotope analysis results show that the εHf(t)values of~260 Ma zircons have two sets of characteristics(-3.6 to 1.5 and 9.6 to 12.6),indicating that the zircons originated from the depleted mantle source region and were contaminated by crustal materials.Zircons from 410 to 465 Ma have low εHf(t)values(-13.3 to-5.6),and the trace elements of these zircons have typical felsic arc magmatic characteristics,suggesting that the zircons originated in the ancient continental crust source region under the subduction arc background.Combined with the regional data,it is considered that the Longtan Formation tuff in Jianyang area is the product of the Emei Mountain igneous province in the Middle and late Permian,and its large number of early Paleozoic zircons developed in the depth of the Yangtze Plate may present the magmatic records related to the subduction of the Proto-Tethys Ocean.While the Neoproterozoic-Paleoproterozoic zircons may have originated from the crystalline basement of the
作者
孙娜
杨帅
张玺华
孙豪飞
陈延贵
李天军
龚婷婷
熊富浩
SUN Na;YANG Shuai;ZHANG Xihua;SUN Haofei;CHEN Yangui;LI Tianjun;GONG Tingting;XIONG Fuhaol(College of Earth Sciences,Chengdu University of Technology,Chengdu,Sichuan,610059,China;Institute of Sedimentary Geology,Chengdu University of Technology,Chengdu,Sichuan 610059,China;Eaploration and Development Research Institute,PetroChina Southwest Oil&Gasfield Com pany,Chengdu,Sichuan 610041,China)
出处
《矿物岩石》
CAS
CSCD
北大核心
2023年第3期20-33,共14页
Mineralogy and Petrology
基金
国家自然科学基金面上项目(批准号:42172132)。
