吉林省新生代龙岗火山群期次划分及火山喷发类型特点

吉林省龙岗地区龙岗火山群,新生代火山活动可划分为5个火山喷发期次,由老至新为：船底山期、小椅子山期、大椅子山期、金龙顶子期、四海期。根据对各期火山岩相的研究,确定了它们的火山喷发类型。     

龙岗火山喷发特征与火山岩化学初步研究

龙岗火山是中国少数几个近代仍有喷发的活动火山区之一,在1700多平方千米火山区内形成100多个玄武质岩浆爆炸成因的火山锥和低平火口湖(龙湾),并有约1600 a BP喷发的金龙顶子活火山。龙岗火山岩是单一的粗面玄武岩,具有一致的化学成分,表明岩浆上升过程中很少演化,推测龙岗火山岩来自同源地幔岩浆。     

吉林龙岗火山群火山碎屑基浪堆积特征与成因机理

吉林龙岗火山群火山碎屑基浪堆积是中国少数保存较好的、近代喷发的低平火山区之一。基于岩性、岩相与相序的识别与分析,火山碎屑基浪堆积序列由分选性和磨圆度较差的玄武质砂、砾和火山灰构成的毫米级-厘米级厚高频率韵律有序叠置而成,堆积物中发育大量的块状层理、似丘状层理、低角度板状交错层理、槽泊层理、平行层理、冲蚀槽等堆积构造。横向上低平火山由内至外其碎屑粒度、堆积构造、厚度存在着一定规律变化,与易混淆的火山岩区地面流水沉积和火山碎屑流堆积物存在明显的差别。岩浆射汽喷发晚期往往伴随斯通博利式喷发和夏威夷式熔岩流,三者构成一个完整火山活动旋回。     

吉林龙冈火山群金龙顶子火山喷发物中幔源包体的基本特征及其地质意义

龙冈火山群金龙顶子火山喷发发生在距今1500年前,其火山喷发物中所含的幔源橄榄岩包体是我国在最新火山喷发物中所发现的幔源包体。这些包体以普遍含有韭闪石为特征。包体的结构和位错构造反映这些包体在上地幔条件下经历过一定程度的变形作用。包体的平衡温度大多数集中在800～950℃之间,只有个别样品温度达到1050℃;平衡压力大多数集中在1.0～1.5 GPa之间。由包体平衡温度、压力得到的上地幔地温线稍低于中国东部由新第三纪包体得到的上地幔地温线,但接近第四纪包体得到的地温线。包体在上地幔条件下变形时的差异应力在30～44MPa,应变速率为10-18s-110-15s-1。角闪石的出现反映上地幔流体的渗透及交代作用。金龙顶子火山发的玄武岩浆直接来自35～50km的上地幔顶部。     

吉林大椅子山火山年代学、地球化学特征及其排气量的估算

利用铀系组分法测得龙岗大椅子山火山喷发时间为距今71±9 ka,属于晚更新世.各类喷发物的岩石化学、地球化学特征表明,它们形成于同一岩浆源.根据岩石学方法,结合Thordarson (1996)等人的排气模型,估算此次喷发向大气层输送的HCl、HF总量分别为7.36 Mt和5.21 Mt.     

吉林东南部晚中生代中酸性火山作用成因的地球化学制约

详细的主、微量元素和Sr-Nd-Pb同位素研究结果显示,延吉地区晚中生代(早白垩世)中酸性火山岩具有岛弧型微量元素特征(富集轻稀土(LREE)、大离子亲石元素(LILE)和亏损高场强元素(HFSE)),和中等放射成因Sr、Pb及类似于硅质地球的Nd同位素组成(~(87)Sr/~(86)Sr(i)=0.70437～0.70525;~(206)Pb/~(204)Pb(i)=18.19～18.37,~(207)Pb/~(204)Pb(i)=15.54～15.57,~(208)Pb/~(204)Pb(i)=38.13～38.22;ε_(Nd)(t)=-2.75～+1.61)。其Sr-Nd-Pb同位素组成特征类似于区域同期基性火山岩和大兴安岭地区同时代火山岩。这些广泛分布于吉林南部的晚中生代中酸性火山岩是岩石圈地幔来源岩浆经分离结晶或地壳物质混染/AFC过程的产物。吉林省东南部晚中生代不同区域火山岩的Sr-Nd-Pb同位素对比结果显示,辽源-延吉与通化地区分属不同构造单元,其中辽源-延吉一带则为中亚造山带的东段,而通化地区为华北克拉通的一部分,夹皮沟-松江断裂可能是华北克拉通东北缘的边界。     

甘肃临洮晚更新世黄土环境变迁

对甘肃临洮县塔湾乡晚更新世黄土-古土壤序列的粒度、磁化率两个环境代用指标进行综合分析, 可划分出以下7个气候阶段: (1) 距底18.5m (92.478.8ka), 平均粒径24.42μm, 平均磁化率716.8×10-6SI, 年均温度7.8℃, 年均降水量500mm, 气候温暖较湿; (2) 距底8.514.8m (78.865.3ka), 平均粒径26.83μm, 平均磁化率为442.3×10-6SI, 年均温度5.2℃, 年均降水量370mm, 气候温干; (3) 距底14.820.3m (65.357.3ka), 平均粒径25.94μm, 平均磁化率320.7×10-6SI, 年均温度3.5℃, 年均降水量280mm, 气候温干偏凉; (4) 距底20.324.9m (57.347.7ka), 平均粒径25.23μm, 平均磁化率516.4×10-6SI, 年均温度6.0℃, 年均降水量410mm, 气候温干偏湿; (5) 距底24.929.4m (47.740.9ka), 平均粒径25.46μm, 平均磁化率299.4×10-6SI, 年均温度在3.1℃, 年均降水量270mm, 气候温干偏凉; (6) 距底29.434.2m (40.932.4ka), 平均粒径21.46μm, 平均磁化率405.5×10-6SI, 年均温度4.7℃, 年均降水量350mm, 气候温干偏湿; (7) 距底34.239m (32.4ka以后), 平均粒径188.89μm, 平均磁化率381.1×10-6SI, 年均温度4.4℃, 年均降水量330mm, 气候温干.这些环境变迁阶段与区域环境变迁具有较好的可对比性, 其中Ⅰ阶段相当于MIS5温暖期; Ⅱ阶段和Ⅲ阶段相当于MIS4降温期; Ⅳ阶段、Ⅴ阶段和Ⅵ阶段相当于MIS3的气候温暖期; Ⅶ阶段相当于MIS2降温期.但与邻区兰州九洲台和若尔盖RM孔相比, 同时期临夏地区气候明显偏温偏湿.      

吉林中部小蜂蜜顶子组火山岩的形成时代及其地质意义:锆石U-Pb年代学和Hf同位素组成证据

本文对出露于吉林省中部地区的小蜂蜜顶子组标准剖面的流纹岩（样品号：JH21-1）和非标准剖面小蜂蜜顶子组的安山岩（样品号：JX1-1）进行了锆石LA-ICP-MS U-Pb年代学以及Hf同位素组成研究。2个样品中的锆石均呈自形-半自形,CL图像上显示条痕状吸收或典型的岩浆振荡生长环带,结合其Th/U比值（0.27~0.81）,均暗示了它们的岩浆成因。定年结果表明：流纹岩（JH21-1）中锆石²⁰⁶Pb/²³⁸U加权平均年龄为（192±2）Ma （MSWD=4.8）,其形成于早侏罗世;安山岩（JX1-1）中锆石²⁰⁶Pb/²³⁸U加权平均年龄为（172±1）Ma （MSWD=0.27）,表明其形成于中侏罗世。前者与标准剖面时代一致,后者与小蜂蜜顶子组并非同一套火山岩。而2个样品中锆石的Hf同位素组成较为均一,ε_Hf（t）值为+5.25~+9.37,二阶省模式年龄为803~1 177 Ma,暗示它们起源于中-新元古代新增生陆壳物质的部分熔融。综上所述,吉林中部地区侏罗纪岩浆事件至少可以划分为两期--早侏罗世和中侏罗世,结合区域构造演化历史,可以认为吉林省中部地区早-中侏罗世火山岩的形成应与古太平洋板块俯冲于欧亚大陆之下的地质作用相联系。     

Cretaceous Volcanic Events in Southeastern Jilin Province, China: Evidence from Single Zircon U-Pb Ages

Mesozoic volcanic rocks in southeastern Jilin Province are an important component of the huge Mesozoic volcanic belt in the northeastern area.Study of the age of their formation is of great significance to recognize Mesozoic volcanic rule in northeastern China.Along with the research of rare Mesozoic biota and extensive Mesozoic mineralization in western Liaoning,a number of researchers have focused on Mesozoic volcanic events.The authors studied the ages of the Cretaceous volcanic rocks in southeastern Jilin Province using single Zircon U-Pb.The result shows that the Sankeyushu Formation volcanic rocks in the Tonghua area are 119.2 Ma in age,the Yingcheng Formation in the Jiutai area 113.4±3.1 Ma,the Jinjiatun Formation in Pinggang Town of Liaoyuan City and the Wufeng volcanic rocks in the Yanji area 103.2±4.7 Ma and 103.6±1 Ma,respectively. Combined with the data of recent publication on volcanic rocks ages;the Cretaceous volcanic events in southeastern Jilin Province can be tentatively subdivided into three eruption periods:119 Ma,113 Ma and 103 Ma.The result not only provides important chronology data for subdividing Mesozoic strata in southeastern Jilin Province,establishing Mesozoic volcanic event sequence,discussing geological tectonic background,and surveying the relation between noble metals to the Cretaceous volcanic rocks,but also offers important information of Mesozoic volcanism in northeastern China.     

Cretaceous Volcanic Events in Southeastern Jilin Province, China: Evidence from Single Zircon U-Pb Ages

Mesozoic volcanic rocks in southeastern Jilin Province are an important component of the huge Mesozoic volcanic belt in the northeastern area. Study of the age of their formation is of great significance to recognize Mesozoic volcanic rule in northeastern China. Along with the research of rare Mesozoic biota and extensive Mesozoic mineralization in western Liaoning, a number of researchers have focused on Mesozoic volcanic events. The authors studied the ages of the Cretaceous volcanic rocks in southeastern Jilin Province using single Zircon U-Pb. The result shows that the Sankeyushu Formation volcanic rocks in the Tonghua area are 119.2 Ma in age, the Yingcheng Formation in the Jiutai area 113.4±3.1 Ma, the Jinjiatun Formation in Pinggang Town of Liaoyuan City and the Wufeng volcanic rocks in the Yanji area 103.2±4.7 Ma and 103.6±1 Ma, respectively. Combined with the data of recent publication on volcanic rocks ages; the Cretaceous volcanic events in southeastern Jilin Province can be tentatively subdivided into three eruption periods： 119 Ma, 113 Ma and 103 Ma. The result not only provides important chronology data for subdividing Mesozoic strata in southeastern Jilin Province, establishing Mesozoic volcanic event sequence, discussing geological tectonic background, and surveying the relation between noble metals to the Cretaceous volcanic rocks, but also offers important information of Mesozoic volcanism in northeastern China.     

吉林中部中—上志留统三叶虫动物群

描述了吉林中部永吉县中—上志留统张家屯组与二道沟组的三叶虫群6科的10属、12种及2未定种,其中新属3个、新种8个,并简要讨论了华北板块北缘三叶虫群的生物古地理特征。     

吉林磐石三道岗含铜镍硫化物矿床岩体群年代学意义

吉林省中南部产出系列铜镍硫化物矿床,形成于中生代早期的含矿镁铁-超镁铁质岩体在含矿岩体空间上受断裂构造控制,并且在一定范围内集中出现,构成具有成因联系的含矿岩体群。三道岗含矿岩体主要岩石类型为闪长岩、辉长岩、角闪辉石岩-辉石岩、含长角闪橄榄岩等组合,侵位于下二叠统范家屯组浅变质岩系中。辉长岩中LA-ICP-MS锆石原位定年得到(232.75±0.95)Ma(MSWD=0.87)的岩体结晶年龄,同时,角闪石单矿物40Ar-39Ar法测年得到(121.45±2.52)Ma的蚀变年龄,暗示三道岗含矿岩体群与红旗岭一样形成于印支中亚造山晚期,燕山期岩浆活动产生的热液叠加蚀变对矿床形成产生重要影响。     

西藏中部扎西错布晚更新世晚期微体古生物与环境变化初步研究

西藏中部扎西错布东岸T1剖面厚639cm,含6属11种介形类和1属2种以上轮藻类。据其在地层中的分布特征划分出8个生物组合,各组合间的差异表现在介形类动物群的丰度、分异度和每个种的丰度变化,根据生物属种生态特征和组合变化探讨湖区大约18653～13144aBP生态环境及气候变化情况如下:①约18653～17239aBP,湖区气候较干(冷),湖面收缩下降,湖水有一定含盐度(可能达中盐水18‰),其间有波动:18309～17809aBP,气候曾一度暖湿,湖面扩大,水质淡化;②约17239～13920aBP,气候较暖湿,水质含盐度降低,其间有气候波动,分别在16506～15213aBP和15213～13963aBP时段偏干(冷)和偏湿冷,相应地其水质含盐度增加或减小;③13920～13144aBP,气候突变,湖泊环境突然恶化,介形类灭绝,仅剩下对气候环境反应滞后的轮藻类低等植物。     

Chronology of Late Pleistocene environmental changes in the lower Mahi basin,western India

Sediments exposed in the lower Mahi basin at the southern fringe of the Thar Desert, Rajasthan, India, provide evidence of three distinct depositional environments, namely marine, aeolian and fluvial. These have been used to reconstruct Late Pleistocene environmental and tectonic history of the region. Infrared stimulated luminescence (IRSL) chronology of the fluvial and aeolian litho‐units provides evidence of two major fluvial aggradation phases in the region corresponding to Oxygen Isotopic Stages 5 and 3. The basal marine clay is inferred to represent the last interglacial stage and its present elevation at +20 m a.s.l. is attributed to post‐depositional tectonism. Comparison of fluvial records from other regions indicates interhemispherically documented wetter phases during Oxygen Isotope Stages 5 and 3. Copyright © 2000 John Wiley & Sons, Ltd.     

吉林临江迎门岔铜(钼)矿花岗闪长斑岩年代学和地球化学特征

LA-ICP-MS锆石U-Pb测年得出花岗闪长斑岩的成岩年龄为(168±1)Ma(中侏罗世),属燕山期岩浆活动产物。岩石地球化学特征显示岩石为准铝质-弱过铝质高钾钙碱性系列,富集Ba、K、Sr,亏损Nb、Ta、P、Ti,δEu异常不明显,属Ⅰ型花岗岩,岩浆来源于地壳部分熔融。综合区域同时代火成岩构造演化背景,认为该矿床形成于古太平洋板块向欧亚大陆俯冲下的火山弧环境。     

河北三河晚更新世地层粒度特征分析

本文通过详细测量河北三河齐心庄一带第四纪剖面、采集光释光测年样品和粒度样品,分析该区地层形成年龄、沉积速率、各粒度样品粒度参数、频率分布曲线及概率累积曲线,进而推断其沉积环境。实测剖面显示地层可以分为20层,沉积物以细砂、粉砂和黏土为主。第2层光释光地质年龄为12.23±1.32ka,第19层光释光地质年龄为19.35±2.10ka,故实测剖面为晚更新世末期堆积,根据地层厚度及年龄测定结果测算出该区平均沉积速率为0.071cm/a。12个粒度样品频率分布曲线均为不对称的单峰态,表明沉积物成分单一,为相对稳定条件下形成。概率累积曲线分为两段式和三段式,滚动组分较少,总体为能量相对不高的沉积环境。地层自下而上呈现明显的旋回性沉积特征,存在两种韵律沉积模式:"中砂-细砂-粉砂"和"粉砂-黏土"。结合区域地质特征,综合分析结果显示河北三河晚更新世地层形成于相对稳定的低水能条件下的河流环境,进一步可细分为河流砂坝和泛滥平原沉积。本文研究结果对于探讨华北北部平原的形成与发展过程、潮白河下游的变迁历史、晚更新世末期的沉积速率提供了重要的基础资料和数据。实测剖面位于新夏垫断裂的下盘,本文测试结果对于研究新夏垫活断裂两盘的差异性活动和断裂性质提供了重要的资料。     

Chronology and Geochemistry of Mesozoic Volcanic Rocks in the Linjiang Area, Jilin Province and their Tectonic Implications

Zircon U-Pb ages and geochemical analytical results are presented for the volcanic rocks of the Naozhigou, Ergulazi, and Sidaogou Formations in the Linjiang area, southeastern Jilin Province to constrain the nature of magma source and their tectonic settings. The Naozhigou Formation is composed mainly of andesite and rhyolite and its weighted mean 206Pb/238U age for 13 zircon grains is 2224±1 Ma. The Ergulazi Formation consists of basaltic andesite, basaltic trachyandesite, and andesite, and six grains give a weighted mean 206Pb/238U age of 131±4 Ma. The Sidaogou Formation consists mainly of trachyandesite and rhyolite, and six zircon grains yield a weighted mean 206Pb/238U age of113±4 Ma. The volcanic rocks have SiO2=60.24%-77.46%, MgO=0.36%-1.29% (Mg#=0.32-0.40) for the Naozhigou Formation, SiO2=51.60%-59.32 %, MgO=3.70 %-5.54% (Mg#=0.50-0.60) for the Ergulazi Formation, and SiO2=58.28%-76.32%, MgO=0.07%-1.20% (Mg#=0.14-0.46) for the Sidaogou Formation. The trace element analytical results indicate that these volcanic rocks are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), relative depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs, Nb, Ta, and Ti), and negative Eu anomalies. Compared with the primitive mantle, the Mesozoic volcanic rocks in the Linjiang area have relatively high initial 87Sr/86Sr ratios (0.7053-0.7083) and low eNd(t) values (-8.38 to -2.43), and display an EMII trend. The late Triassic magma for the Naozhigou Formation could be derived from partial melting of a newly accretional crust with the minor involvement of the North China Craton basement and formed under an extensional environment after the collision of the Yangtze Craton and the North China Craton. The Early Cretaceous volcanic rocks for the Ergulazi and Sidaogou Formations could be formed under the tectonic setting of an active continental margin related to the westward snbduction of the Izanagi plate.     

吉南龙岗岩群四道砬子河岩组泥质片麻岩变质作用

吉南新太古代泥质片麻岩出露于龙岗岩群四道砬子河岩组中,本文通过系统的岩相学、矿物化学、激光拉曼和锆石U Pb同位素年代学等分析,研究其变质演化特点、变质作用时代及构造意义.结果表明:龙岗岩群四道砬子河岩组泥质片麻岩记录了３个变质演化阶段,其中峰前期进变质阶段(M１)的矿物组合为石榴石＋黑云母＋斜长石＋石英＋白云母;峰期变质阶段(M２)的矿物组合为石榴石＋矽线石＋钾长石＋黑云母＋斜长石＋石英,达到麻粒岩相;峰后期退变质阶段(M３)以矽线石转变为蓝晶石为特征标 志,矿物组合为蓝晶石＋石榴石＋黑云母＋斜长石＋石英＋白云母.变质矿物地质温压计限定其变质作用,峰前期(M１)T 为４６８~５１５ ℃,p 为(３．８~４．３)×１０５ kPa;峰期(M２)T 为７０３~７６０ ℃,p 为(６．６~７．１)×１０５kPa;峰后期(M３)T 为５５２~５９１℃,p 为(５．５~６．０)×１０５kPa;具有典型的近等压冷却型逆时针变质作用p T 演化轨迹特征,可能是在地幔柱与岩石圈相互作用的环境中变质作用与大量的幔源岩浆底侵作用有关.LA ICP MS锆石U Pb定年结果显示麻粒岩相变质作用时代为２４９５~２４４２Ma,属于新太古代变质热事件产物.     

Late Pleistocene loess‐palaeosol sequences in the Vojvodina region,north Serbia

Late Pleistocene loess‐palaeosol sequences are widespread in the Vojvodina region, with thicknesses reaching a maximum of about 20 m. Our investigations include more than 40 of these loess sections. Geochronology of the last glacial loess‐palaeosol sequences, based on luminescence dating and amino acid racemisation, provides correlations between Upper Pleistocene loess‐palaeosol sediments in Vojvodina and comparable deposits at other European localities. Sedimentary logs of magnetic susceptibility, grain‐size measurements and carbonate content, combined with malacological evidence, indicate two main relatively cold and arid phases during the last glacial period, related to intensive accumulation of loess units L1L1 and L1L2, as well as many brief episodes of dry and windy climatic conditions, suggesting a possible relationship with cold events recorded in the North Atlantic region. Generally, late Pleistocene climate in the region was dry and relatively warm, compared with glacial period sites in central Europe, and was characterised by sharp differences between glacial and interglacial modes. New data and interpretations presented in this study emphasise the significance of loess‐palaeosol sequences in Vojvodina for the reconstruction of the temporal and spatial evolution of late Pleistocene palaeoclimate in this part of Europe. Copyright © 2007 John Wiley & Sons, Ltd.