Geochronology and geochemistry of lithium-rich tuffs in the Sichuan basin,western Yangtze: Implication for the magmatic origin and final closure of eastern Paleo-Tethys     

《地学前缘(英文版)》2023,14(1):101480

The felsic volcanogenic tuffs named “green-bean rocks” (GBRs), characterized by a green or yellowish green color, are widely distributed in the western Yangtze platform and have a high lithium content (286–957 ppm). This paper studies the ages, origin and tectonic setting of the GBRs in the Sichuan basin on the western margin of the Yangtze platform through the whole-rock geochemistry and zircon trace elements by using U–Pb dating and Hf–O isotopes. The GBR samples from the Quxian and Beibei sections yielded zircon U–Pb ages of 245.5 ± 1.8 Ma and 244.8 ± 2.2 Ma. These samples can be used as the isochronous stratigraphic marker of the Early–Middle Triassic boundary (EMTB) for regional correlation. The whole-rock and zircon geochemistry, and zircon Hf–O isotopes exhibited S-type geochemical affinities with high positive δ¹⁸O values (9.28‰–11.98‰), low negative ε_Hf(t) values (?13.87 to ? 6.79), and T_DM² ages of 2150–1703 Ma, indicating that the lithium-rich GBRs were generated by the remelting of the pre-existing ancient Paleoproterozoic layer without mantle source contamination in the arc-related/orogenic tectonic setting. The results of this study demonstrate that the lithium-rich GBRs in the western Yangtze platform were derived from arc volcanic eruptions along the Sanjiang orogen, triggered by the closure of the eastern Paleo-Tethys Ocean and the syn-collision between the continental Indochina and Yangtze blocks at ca. 247 Ma. This was marked by a major shift from I-type magmas with intermediate ε_Hf(t) values to S-type magmas with low negative ε_Hf(t) values. Collectively, our results provide new insights into the origin of the GBRs and decodes the closure of the eastern Paleo-Tethys.  相似文献   

西拉木伦构造带克德河砂砾岩的时代及构造意义     

郑月娟  张德军  张海华  张健  陈树旺  甄甄 《地质学报》2023,97(8):2459-2475

西拉木伦构造带北部双井地区发育一套巨厚的、成熟度低的快速堆积的粗碎屑沉积建造,为同造山磨拉石沉积,前人称其为克德河砂砾岩带并将其时代分别划为中二叠世(哲斯组)、晚二叠世(林西组)。本次工作对该套地层进行了大比例尺剖面测量,对取自剖面第下、中、上(1、25、86层)三个部分的砂岩样品进行LA-ICP-MS U-Pb年代学研究,结果显示：3个样品具有相似的主要年龄区间,依次为405-485Ma、401-463Ma、363-520Ma,其峰值年龄分别为427Ma、445Ma、440Ma,锆石数量分别占总量的48％、52.5％和38.75％;其次为大于1000Ma的年龄,锆石数量分别占30.7%、22.5%、45%,且均具有1800Ma和2500Ma左右的峰值年龄,明显具有华北板块基底年龄信息;自下而上3个测年样品最年轻峰值年龄分别为312Ma、376Ma,282Ma,最年轻的锆石年龄分别为304Ma、244Ma和245Ma。在第85层杂色复成分砾岩的灰岩砾石中发现晚石炭－早二叠世阿木山组的蜓和珊瑚化石,在41及43层发现中生代孢粉化石。综合碎屑锆石测年及生物化石研究结果,克德河砂砾岩带的时代应为中三叠世。推测西拉木伦构造带经历了一个较长的演化过程,中二叠世开始华北板块和西伯利亚板块进入碰撞造山阶段, 同造山磨拉石建造(克德河砂砾岩带)标志着中亚造山带演化的终止,华北板块和西伯利亚板块的碰撞拼合造山一直延续到中三叠世才结束。  相似文献   

广西柳东地区火山岩锆石U-Pb-Hf同位素特征及其对岩浆源区的限定          下载免费PDF全文

魏春夏  陆刚  杨锋  李巍  钟锋运  金靖杰  潘艺文  梁力杰  白晓 《中国地质》2022,49(4):1309-1322

【研究目的】柳东地区位于右江盆地东缘,近年来该地区早三叠世石炮组中首次发现一套火山岩夹层,为研究盆地东缘的构造演化特征提供了重要依据。【研究方法】本文以新发现的柳东地区火山岩为研究对象,通过LAICP-MS锆石U-Pb年龄及Hf同位素分析,研究右江盆地东缘火山岩的形成时代及岩浆源区特征。【研究结果】结果表明,火山岩的岩性为凝灰岩-凝灰质熔岩-凝灰质火山角砾岩组合,指示了典型的火山岩特征。其2件凝灰岩样品中锆石LA-ICP-MS U-Pb加权平均年龄分别为（244.0±1.9） Ma和（247.1±0.9） Ma,锆石微量元素（U、Th、Hf、Nb）表现出大陆岩浆弧属性特征。锆石Hf同位素结果显示ε_Hf （t）为-13.2~-1.2,二阶段模式年龄（T_DM^C）为1.35~2.06 Ga,其岩浆源区主要为地壳物质,平均地壳存留年龄为1.7~2.06 Ga。【结论】该火山岩夹层与其所出露的地层时代基本相符,属于早三叠世末期—中三叠世早期火山喷发产物,火山岩形成于火山弧-同碰撞的构造环境,代表了弧后盆地的沉积环境,与印支期古特提斯洋的闭合相关。该成果为古特提斯构造域的演化研究提供了新的基础资料,具有重要意义。创新点：柳东地区火山岩属于早三叠世末期—中三叠世早期火山喷发产物,形成于印支期古特提斯洋的闭合条件下的火山弧-同碰撞构造环境。  相似文献   

桂西南那坡盆地河口组沉凝灰岩的时代与来源及其大地构造意义SCIEI北大核心CSCD     

夏磊  闫全人  向忠金  郑洪波  牛睿 《岩石学报》2022,38(3):883-900

桂西南那坡盆地位于八布-Song Hien构造带,发育早-中三叠世岩浆岩和巨厚海相碎屑岩系,是研究华南地块南缘古特提斯造山过程的关键地区。本文对那坡盆地中三叠统河口组中-上部的两套沉凝灰岩开展了详细的岩石学、地球化学和锆石U-Pb-Hf同位素分析研究。两件沉凝灰岩样品LA-ICP-MS锆石U-Pb定年结果分别为240.6±1.0Ma和236.3±0.8Ma,指示河口组碎屑岩沉积时代为中三叠世拉丁期,部分为晚三叠世卡尼期早期。全岩地球化学结果显示,该沉凝灰岩属于亚碱性英安质,富集轻稀土(LREEs)和大离子亲石元素(LILEs)、Rb、Th和U,亏损高场强元素(HFSEs),具有显著的Nb、Ta和Ti负异常。沉凝灰岩锆石具有较低的ε_(Hf)(t)值(-18.6~-6.3)和较老的地壳模式年龄(t_(DM)^(C)=1664~2434Ma),结合锆石微量元素特征认为其形成于俯冲环境。整体上,那坡盆地河口组沉凝灰岩表现出俯冲作用形成的岛弧火山岩地球化学特征,推断其来源于桂西南凭祥地区的中-晚三叠世酸性火山岩。结合已有区域地质调查成果,认为华南地块南缘八布-Cao Bang古特提斯分支洋盆于晚二叠世至晚三叠世早期向北俯冲,随后自西向东呈“剪刀”式逐渐闭合。华南地块与北越地块完全碰撞拼合的时间发生在晚三叠世中晚期。  相似文献   

西藏改则洞错地区白垩纪火山岩锆石U-Pb年代学、Hf同位素组成及对班公-怒江洋俯冲闭合的制约   总被引：1，自引：0，他引：1       下载免费PDF全文

付佳俊  丁林  许强  蔡福龙  岳雅慧  郭钰 《地质科学》2015,50(1):182-202

班公湖—怒江缝合带是青藏高原内一条重要的缝合带,其俯冲极性和闭合时限一直存在着争议,这无疑限制了我们对青藏高原演化历史的认识。本文对仲岗安山玄武岩和一套新发现的晚白垩世安山岩进行研究,获得了其锆石U-Pb年龄分别为123.75±0.92 Ma和74.23±0.76 Ma。仲岗安山玄武岩锆石的ε_(Hf)(t)值为-7.3~+4.4,具有岛弧玄武岩特征,指示班公湖—怒江洋盆在该地区仍然继续向北俯冲;晚白垩世安山岩锆石的ε_(Hf)(t)值为+3.1~+11.1,其可能是亏损地幔混熔了部分的陆壳物质而形成的,且不整合在蛇绿岩之上。结合区域资料本文认为班公湖—怒江洋盆在改则地区的闭合时限在100~75 Ma之间。  相似文献   

Zircon U-Pb Geochronology and Hf Isotopic ConstraintsOn Petrogenesis of Plagiogranite from the Cuomuqu Ophiolite, Bangong Lake Area, North Tibet     

YIN Zhengxin  YUAN Yajuan  Lü Baofeng  CAI Zhourong  ZHENG Hao  HUANG Qiangtai  XIA Bin  ZHONG Yun  XIA Zhongyu  SHI Xiaolong  GUAN Yao 《《地质学报》英文版》2015,89(2):418-440

Field observation,geochemical signatures and zircon Hf isotope data indicate that Cuomuqu ophiolite in the Bangonghu area was formed in a back-arc basin(BAB) above a suprasubduction zone(SSZ). Zircon U-Pb dating of the diabase from the Cuomuqu massif yielded an age of 164.3±1.9 Ma,thus indicating that the ophiolite complex was formed in the Middle Jurassic during back-arc extension of the mature Bangonghu-Nujiang Ocean. The zircon εHf(t) and TDMC values of the plagiogranite are similar to the εHf(t) and TDM of the diabase,respectively. The mode of occurrence of plagiogranites and their bulk-rock and Hf isotope characteristics indicate that they were derived from the mantle,associated with the surrounding gabbro and diabase,and were formed by partial melting of altered and hydrated mafic rocks under shear conditions during lateral drifting of the oceanic crust. The zircon U-Pb age of the plagiogranite is 156.4±1.4 Ma,and it is 7.9 Ma younger than the hosting diabase. In this study,zircon chronological and Hf isotopic data were tentatively analyzed to determine the genesis of plagiogranites in the Cuomuqu ophiolite complex.  相似文献   

新特提斯缝合带中段豆荚状铬铁矿成矿规律对比研究     

洪俊  姚文光  张晶  张辉善  吕鹏瑞  杨博 《地质学报》2015,89(9):1618-1628

新特提斯缝合带中的铬铁矿带是全球最重要的豆荚状铬铁矿成矿带之一,尤其是新特提斯缝合带中段,即穆斯林巴赫-科希斯坦-雅鲁藏布江一带,自东向西发育罗布莎、马拉坎德、穆斯林巴赫等若干大型铬铁矿床。本文系统总结和梳理新特提斯缝合带中段蛇绿岩的时空分布特征以及典型豆荚状铬铁矿的矿床特征、赋存规律和控矿因素。研究表明,蛇绿岩形成时代主体为中侏罗世—晚白垩世,自东向西大致呈逐渐变新的趋势,构造侵位的时代相近,为古新世—始新世;马拉坎德、瓦济里斯坦、穆斯林巴赫及贝拉铬铁矿,与罗布莎矿床相似,均属于富铬型铬铁矿,产于SSZ相关构造背景下,显示良好的岩相分带,具有良好的成矿条件;提出下一步找矿方向是针对成矿条件优越的蛇绿岩,解析层序剖面,识别纯橄岩与方辉橄榄岩的岩相分带,确定有利赋矿岩相。  相似文献   

南秦岭勉略蛇绿构造混杂带辉长辉绿岩类微量-稀土元素地球化学   总被引：2，自引：0，他引：2  

赖绍聪 《地球科学与环境学报》2005,27(3):5-9

应用元素地球化学方法．研究了勉略带中辉长辉绿岩的相关特征．结果表明．勉略蛇绿构造混杂带内的辉长岩属高铝强碱质辉长岩类，是地幔橄榄岩部分熔融的产物。辉绿岩墙群属强碱铝质基性岩类，过渡族元素蛛网图与辉长岩类几乎完全相同，其不相容元素与辉长岩类总体趋势相一致．反映了一种递进岩浆演化趋势。因此，本区辉长岩与辉绿岩墙群具同源岩浆分异演化的地球化学特征．其均为勉略蛇绿岩的重要组成端元。  相似文献   

横断山区地质构造分区     

潘裕生 《山地学报》1989,(1)

位于青藏高原东南部的横断山区,是我国东部环太平洋区与西部古地中海区间的交接过渡地带,也是我国地质结构最为复杂的一个区域。作者根据1981—1985年在当地考察资料,将本区分出5条具洋壳性质的强变形构造带,2块具陆壳性质的地块,它们相间并列。文章论述了各条块的发育特征及区域演化历史。  相似文献   

Silurian A-type granitoids in the southern margin of the Tongbai-Dabieshan: Evidence from SHRIMP zircon geochronology and geochemistry     

MA Changqian  SHE Zhenbing  XU Pin & WANG Lingyan State Key Laboratory of Geological Processes  Mineral Resources  and Faculty of Earth Sciences  China University of Geosciences  Wuhan  China 《中国科学D辑(英文版)》2005,48(8):1134-1145

The Dabieshan Orogenic belt is well known for the exhumation of early Mesozoic ultrahigh-pressure (UHP) metamorphic rocks and Jurassic–Cretaceous emplacement of voluminous granitoids. However, the tectonic evolution in the orogen during the Paleozoic, especially its magmatic response to tectonism has not received much attention. As indicated by published data, the Dabieshan orogenic belt contains different records of Paleozoic magmatic-tectonic association in different tectonic units. Occ…  相似文献