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世界地质 2022, 41(4) 675-688 DOI:
ISSN: 1004-5589 CN: 22-1111/P |
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| 基础地质 |
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吉林中部地区余富屯组形成时代及构造意义 |
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宋晨1，裴福萍1，魏敬洋1，王奕朋2 |
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1. 吉林大学 地球科学学院，长春 130061;
2. 中铁工程设计咨询集团有限公司，北京 100055 |
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摘要：
本文对吉林中部地区余富屯组中英安质凝灰岩和英安岩进行了岩石学、锆石 U--Pb 年代学及地球化学的研究，确定了余富屯组的形成时代和构造意义。英安质凝灰岩中锆石多呈半自形，发育振荡生长环带，具有较大的 Th /U 比值 ( 0. 52 ～ 1. 68) ，以及强烈的 Eu 负异常和明显的 Ce 正异常，表明其为岩浆成因。定年结果显示英安质凝灰岩中锆石206Pb / 238U 年龄有 4 组: ( 247 ± 1) Ma、 ( 262 ± 2)Ma、316 Ma 和 427 Ma。英安岩中锆石呈半自形，Th /U 比值为 0. 39 ～ 0. 90，锆石206 Pb / 238U 加权平均年龄为 ( 187 ± 1) Ma，即形成于早侏罗世。因此，余富屯组为不同时代岩片组成的构造混杂岩，此外，样品中锆石微量元素显示其源岩形成于弧/造山带环境。综合区域资料，认为余富屯组至少存在早石炭世、早三叠世和早侏罗世的岩石。其构造混杂的时代下限为早侏罗世。余富屯组杂岩反映了早侏罗世—早白垩世时期古太平洋板块俯冲背景之下区域构造改造作用的存在。
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关键词：
构造混杂岩
锆石 U--Pb 定年
余富屯组
吉林中部地区
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Geochronology and tectonic significance of Yufutun Formation in central Jilin Province |
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SONG Chen1，PEI Fuping1，WEI Jingyang1，WANG Yipeng2 |
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1. College of Earth Sciences，Jilin University，Changchun 130061，China;
2. China Ｒailway Engineering Design and Consulting Group Co. Ltd.，Beijing 100055，China |
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Abstract:
This study reports petrology，zircon U--Pb geochronological and geochemical analysis for dacite tuff
and dacite from Yufutun Formation in central Jilin Province，to reveal their geochronology and tectonic significance．Zircons from the dacite tuff are subhedral in shape and show oscillatory growth zoning，relatively high Th /U ratios ( 0. 52 ～ 1. 68) ，and strong negative Eu anomalies and obvious positive Ce anomalies，indicating a magmatic origin． U--Pb dating results of zircons from dacite tuff exhibit four groups of 206Pb / 238U ages: ( 247 ± 1) Ma，( 262 ±2) Ma，316 Ma and 427 Ma． Zircons from the dacite are subhedral，and Th /U ratios of are 0. 39 ～ 0. 90． The weighted mean 206Pb / 238U ages of zircons from the dacite is ( 187 ± 1) Ma，suggesting that it was formed in the Early Jurassic． Therefore，it can be concluded that the Yufutun Formation is a tectonic mélange composed of rock fragment of different ages． In addition，zircons trace elements indicate that the source rocks were formed in an arc / orogenic environment． Based on the regional data，the authors believe that there are Early Carboniferous，Early Triassic and Early Jurassic rocks in the Yufutun Formation． The lower limit of tectonic mélange is Early Jurassic．The Yufutun Formation may reflect the regional tectonic transformation under the subduction background of the Paleo--Pacific Ocean plate during the Early Jurassic--Early Cretaceous period． |
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Keywords:
tectonic mélange
zircon U--Pb dating
Yufutun Formation
central Jilin Province
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