辽西早白垩世义县组砖城子层湖相碳酸盐岩地球化学特征及古湖泊学沉积意义

辽西义县盆地早白垩世义县组陆相湖盆沉积中常发育多个薄层碳酸盐岩沉积层,碳酸盐岩地球化学的研究对揭示湖盆沉积古环境具有重要理论意义。义县组砖城子层英窝山剖面湖相碳酸盐岩分析结果显示,岩石δ¹³C值为-3.44×10^-3~0.27×10^-3,均值为-1.21×10^-3;δ¹⁸O值为-15.73×10^-3~-9.93×10^-3,均值为-10.88×10^-3。盐度Z值变化范围114.78~122.39。碳酸盐岩主量元素分析表明,w（CaO+MgO+LOI）=53.38%~97.04%,均值71.15%;陆源组分w（Al₂O₃+SiO₂+Fe₂O₃）=2.19%~44.87%,均值为27.77%;x（Mg）/x（Ca）摩尔比介于0.92~1.01。碳酸盐岩微量元素地球化学提供了古湖泊学的古盐度、氧化还原和古气候证据。w（Sr）=110.4×10^-6~1360.2×10^-6,w（Ga）=0.152×10^-6~14.13×10^-6,w（Sr）/w（Ba）=0.34~131.49（多数>1）,指示沉积湖泊水体为咸水环境;氧化-还原指标w（V）/w（V+Ni）＝0.51~0.83,w（V）/w（Cr）＝1.59~8.28（多数>2.0）,w（U）/w（Th）=0.39~10.24,且变化范围较大,指示为半封闭—封闭的缺氧还原强分层水体沉积环境;w（Sr）/w（Cu）=54.94~1260.71,均值为213.79,反映炎热干旱气候类型。义县组砖城子层沉积期湖泊为干旱古气候背景下的半咸水—咸水、缺氧还原强分层的半封闭—封闭型。     

吕梁地区古元古代花岗片麻岩成因及变质时代:锆石和独居石U-Pb年龄及锆石Hf同位素证据

吕梁地区在华北克拉通前寒武纪研究中具有重要位置,出露大量的古元古代变质表壳岩和花岗质岩石,对研究华北克拉通古元古代地质演化历史具有重要意义。本次研究选择吕梁地区白家滩花岗片麻岩进行锆石和独居石U-Pb年代学以及锆石Hf同位素研究,2个花岗片麻岩的岩浆锆石U-Pb年龄分别为2182±16Ma和2185±24Ma,代表了其侵位时代。独居石U-Pb年龄分别为1898±7Ma和1899±14Ma,明显比锆石增生边的谐和²⁰⁷Pb/²⁰⁶Pb年龄（2180~2032Ma）年轻,说明独居石对后期变质作用的响应程度比锆石强,其U-Pb年龄更能反映白家滩花岗片麻岩经历了~1900Ma的退变质作用,与华北克拉通中部造山带的变质作用时间一致。花岗片麻岩的锆石Hf同位素亏损地幔模式年龄（t_DM）为2473~2598Ma,两阶段亏损地幔模式年龄（t_DM^C）分别为2646~2839Ma,ε_Hf（t）值分布于-1.3~+1.8之间,未显示同期幔源物质的加入,而是新太古代地壳物质部分熔融的产物,结合已有的古元古代中期（2.2~2.1Ga）的岩浆岩锆石Hf同位素数据,华北克拉通新太古代地壳在2.2~2.1Ga期间发生了广泛的重熔作用,这期岩浆活动在华北克拉通吕梁、中条、五台以及胶-辽-吉等地区广泛发育,可能形成于陆内裂谷环境。     

五台地区滹沱群时代与地层划分新认识:地质学与锆石年代学证据

本文从五台地区滹沱群豆村亚群四集庄组、东冶亚群纹山组和郭家寨亚群西河里组地层中共采集了5件浅变质砂岩样品,并对其进行了La-MC-ICPMS锆石U-Pb年龄测定。分析结果显示,四集庄组2件砂岩样品碎屑锆石²⁰⁷Pb/²⁰⁶Pb年龄主要集中于~2.5Ga和2.1~2.2Ga两个峰值,其中~2.5Ga碎屑锆石来自新太古代五台群和五台地区花岗质杂岩;2.1~2.2Ga碎屑锆石获得²⁰⁷Pb/²⁰⁶Pb加权平均年龄2134±5Ma,限定了四集庄组砂岩沉积下限为2134Ma。结合四集庄组火山岩形成时代(2140±10Ma)和四集庄组底部发育厚层砾岩,我们认为滹沱群初始形成时代为~2.2Ga,即早元古代中期。东冶亚群纹山组底部砂岩中碎屑锆石²⁰⁷Pb/²⁰⁶Pb年龄主要集中于2050~2122Ma之间,其中64粒相对年轻的锆石获得²⁰⁷Pb/²⁰⁶Pb加权平均年龄2068±3Ma,代表了东冶亚群形成时代下限为2070Ma左右。综合豆村亚群青石村组火山岩形成时代2087±9Ma,我们认为东冶亚群初始形成于2070Ma左右。郭家寨亚群中最年轻碎屑锆石²⁰⁷Pb/²⁰⁶Pb年龄为1958±10Ma,表明郭家寨亚群开始沉积时代小于1.95Ga,为早元古代晚期/末期。区域上,早元古代末期是华北最终克拉通阶段,而郭家寨亚群与东冶亚群呈明显的角度不整合接触关系,两者记录了明显不同的地质过程。因此,我们建议郭家寨亚群应从滹沱群中解体出来并独立命名为郭家寨群,且郭家寨群可能沉积于华北克拉通化过程中/之后,开始沉积的时代为1.9~1.8Ga。     

塔里木盆地东北缘敦煌群的形成和演化:锆石U-Pb年代学和Lu-Hf同位素证据

采用LA-MC-ICP-MS手段对敦煌地块中敦煌群的白云母石英片岩、石榴斜长角闪岩、石榴黑云斜长片麻岩和长英质伟晶岩脉中的锆石进行了U-Pb 和Lu-Hf同位素分析,获得白云母石英片岩碎屑岩浆锆石的²⁰⁷Pb/²⁰⁶Pb表面年龄为1545~756Ma,主要集中在1200~1000Ma,表明地层的最大沉积时代为756Ma,蚀源区存在中、新元古代的岩浆事件。白云母石英片岩锆石的ε_Hf(t)分为两组,一组为正值,ε_Hf(t)=1.2~10.1,单阶段模式年龄为t_DM=1.09~1.66Ga;一组为负值,ε_Hf(t)=-1~-16,两阶段模式年龄为t_DM2=1.91~2.42Ga。表明蚀源区存在古元古代、中元古代的再造地壳。石榴斜长角闪岩的两粒捕获锆石的年龄为2272Ma 和1208Ma,ε_Hf(t)为-3和14,t_DM2和t_DM为2.82Ga和1.1Ga,暗示捕获区存在太古代再造地壳和中元古代晚期新生地壳。石榴斜长角闪岩碎屑锆石的Th/U比值为0.02~0.42,²⁰⁶Pb/²³⁸U年龄为441±5Ma,代表了岩石遭受变质作用的时代。石榴黑云斜长片麻岩中的碎屑锆石与长英质伟晶岩脉中的继承锆石特征相同,锆石年龄集中在3个峰值区间:2.2~2.1Ga,1.8~1.6Ga,1.2~0.8Ga,相应的的ε_Hf(t)分别为-9~4,-5.4~15,-27~20,相应锆石的模式年龄分别为3.1~2.4Ga,2.6~1.4Ga,3.1~1.7Ga,均大于其形成年龄,表明蚀源区锆石来自于再循环的新太古代、古元古代和中元古代地壳,样品代表的地层的最大沉积时代为新元古代早期。岩石中检测出早古生代的变质锆石, ²⁰⁶Pb/²³⁸U年龄为464~422Ma,可能代表了沉积岩的变质时代。敦煌群锆石U-Pb和Lu-Hf同位素表明蚀源区岩石类型和时代的多样性,也表明部分敦煌群不是前寒武纪的变质基底,而是塔里木盆地变质基底之上新元古代的沉积盖层,后卷入了我国西北部早古生代的造山事件。     

大氧化事件在山西滹沱群中的记录:碳酸盐岩碳同位素资料分析

古元古代早期爆发了全球性大氧化事件（GOE）,诱发了休伦冰川事件（Huronian Glaciation Event,HGE）和2.3~2.06Ga的拉玛岗地-瓦图里碳酸盐碳同位素正漂移事件（Lomagundi-Jatuli Event,LJE）。滹沱群是华北克拉通最具代表性的古元古代沉积地层,变质程度最低,地层学研究程度高,是探索GOE以及HGE和LJE的理想研究对象。通过总结和分析滹沱群碳酸盐岩碳同位素研究结果,我们发现：（1）滹沱群主体未显示δ¹³C_carb正漂移现象,但下部大石岭组有高达3.5‰的δ¹³C_carb正异常;（2）显示δ¹³C_carb正异常的大石岭组可能形成于2.08Ga之前,未显示δ¹³C_carb正异常的东冶亚群可能形成于2.06Ga之后;（3）五台地区记录休伦冰川事件的冰碛岩应发育在大石岭组之下,即四集庄组砾岩。总之,滹沱群形成于2.3Ga之后,下部豆村亚群沉积于HGE或LJE期间,可能保留了更显著的δ¹³C_carb正漂移信息及冰川沉积记录,中部的东冶亚群沉积于LJE之后,不存在δ¹³C_carb正漂移。     

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

【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。     

江西省黄坑黑色岩系钒矿床微量元素地球化学特征及成矿背景分析

江西修武盆地寒武纪早期黑色岩系中富含多种稀散、稀土及放射性等元素,不乏赋存大型、超大型矿床。本文基于黄坑地区下寒武统荷塘组黑色岩系中富钒矿石（21件样品w（V）>4500×10^-6,且连续厚度大于2 m）测试分析研究,探讨其微量元素地球化学特征及沉积成矿环境。研究结果表明：①矿样中V、As、Mo、Cd、Sb、U等元素的富集系数在10倍以上,其中Cd最大富集系数达822倍;w（V）=4954.64×10^-6~13041.21×10^-6,相对于上地壳的富集系数达35~93倍;相对亏损Sc、Co、Ga、Nb、Ta、Sn、Zr、Hf、Th等元素。②矿样w（ΣREE）值介于67.75×10^-6~210.80×10^-6之间,w（LREE）/w（HREE）=2.14~5.55,w（Eu）/w（Eu^*）=1.11~2.42,w（Ce）/w（Ce^*）=0.45~0.64。③矿样的w（Ni）/w（Co）=10.80~54.71,w（V）/w（V+Ni）=0.96~0.99,w（V）/w（Cr）=6.91~41.80,w（U）/w（Th）值3.14~31.86,皆表明其形成于缺氧还原环境,且存在较强的海底热水沉积作用-热水喷流沉积型钒矿床。     

辽北西丰地区晚侏罗世营厂岩体LA-ICP-MS锆石U-Pb年龄及岩石地球化学特征

营厂岩体分布于辽北西丰县和隆镇境内，研究结果表明，该岩体主要为似斑状二长花岗岩，锆石²⁰⁶Pb/²³⁸U年龄加权平均值为156.1 Ma±1.5 Ma，形成时代为晚侏罗世。营厂岩体w（Na₂O）/w（K₂O）平均值为1.07，属高钾钙碱性系列；里特曼指数σ平均值为2.15，属钙碱系列；铝饱和指数A/CNK平均值为1.16，A/CN平均值为1.99，属过铝型；Rb、Sr、Ba、Th、Hf含量偏高，Cr、Ni、Co、V、Rb、Zr、Nb等元素含量低，为"S"型花岗岩特征。稀土元素总量平均值为w（ΣREE）＝82.80×10^-6，w（LREE）/w（HREE）=15.76，w（La）_N/w（Yb）_N=24.32，表明其轻稀土相对富集，重稀土相对亏损，稀土配分曲线右倾。δEu=0.80，铕弱负异常，说明成因与板块运动有关，w（Sm）/w（Nd）=0.20，w（Ba）/w（Sr）=1.60，w（K）/w（Rb）=249.15，表明具有壳源性质。营厂岩体具有埃达克岩的特点，其属于受太平洋板块向欧亚板块俯冲作用的影响，在挤压环境下加厚下地壳部分熔融，从而形成活动陆缘型花岗岩。     

川西松林口岩体锆石U-Pb定年及其地球化学特征

松林口岩体位于松潘—甘孜造山带中东部,为确定岩体的侵位时代和地球化学特征,通过镜下薄片观察、主微量元素分析以及锆石U-Pb测年,对松林口岩体进行了研究。结果表明,松林口岩体由二长花岗岩体和花岗闪长岩体组成,花岗闪长岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（212.4±0.9） Ma （MSWD=0.66）,二长花岗岩锆石²⁰⁶Pb/²³⁸U年龄加权平均值为（222.4±1.1） Ma （MSWD=0.39）,形成于晚三叠世,由两期次岩浆作用形成;岩石的SiO₂含量56.56%~61.97%;铝饱和指数A/CNK=0.93~1.05,全碱含量3.78~5.38,K₂O/Na₂O=1.02~1.68,里特曼指数σ=1.194~1.612,样品属于准铝质中—高钾钙碱性岩系列。岩石轻重稀土比值LREE/HREE=5.22~7.13,La_N/Yb_N比值为6.93~8.96,轻、重稀土分异较明显,具较强的负Eu异常。岩石Mg^#值较高（50.97~61.27）,w（Rb）/w（Sr）为0.12~0.25,Rb-（Y+Nb）图解显示为后碰撞环境。因此,松林口二长花岗岩—花岗闪长岩属后碰撞准铝质中—高钾钙碱性I型花岗岩类。     

云南省镇雄县羊场磷矿地球化学特征及其沉积环境分析

羊场磷矿是近年来在云南评价确认的沉积大型磷矿床,磷矿体赋存于下寒武统梅树村组碳酸盐岩-泥质碎屑岩沉积中部的一套含磷岩系中,呈层状、似层状展布于羊场背斜两翼,其产状与地层产状基本一致,含矿岩性为含磷白云岩、磷质岩、磷块岩、硅质岩建造。通过分析该矿床矿体特征和梅树村组磷块岩的主微量元素组成,研究了羊场磷矿的地球化学特征及其沉积环境。结果表明,羊场磷矿磷块岩具有富钙（w（CaO）=42.07%~45.01%）、磷（w（P₂O₅）=27.66%~39.25%）和贫硅（w（SiO₂）=8.27%~15.40%）的特征;w（P₂O₅）与w（CaO）呈较好的正相关关系,与w（MgO）呈负相关关系,与w（Al₂O₃）呈较明显的负相关关系。矿石的w（Th）/w（U）值小于1、Pb （亲硫元素）和Sr富集（Pb平均富集系数16.66,Sr平均富集系数1.17）特征表明,羊场磷矿可能是热水沉积成矿与生物成矿双重作用的结果;微量元素特征值反映,羊场磷矿形成于深海到浅海的变化环境,为海相沉积型磷块岩,沉积时水体呈还原环境。     

Discovery of rhyolitic tuffaceous slate in the southwestern margin of Yangtze Craton: Zircon U-Pb ages (2491 Ma) and tectonic-thermal events

The Mesoproterozoic Dongchuan Group that is widely exposed in Yimen area, central Yunnan Province is a series of sedimentary sort of low-grade metamorphic rocks interbedded with volcanic rocks, which are closely related to the early tectonic evolution of the Earth. However, its formation era, sedimentary filling sequence, and geotectonic characteristics have always been in dispute. In this study, several rhyolitic tuffaceous slate interlayers with a centimeter-level thickness were found in the previously determined Heishan Formation of the Dongchuan Group located to the western part of Yimen-Luoci fault zone. This paper focuses on the study of the rhyolitic tuffaceous slate in Qifulangqing Village, Tongchang Township, Yimen County. LA-ICP-MS zircon dating was conducted, achieving the crystallization age of magma of 2491 ± 15 Ma and the metamorphic ages of about 2.3 Ga, 2.0 Ga, and 1.8 Ga for the first time. Meanwhile, according to in-situ Hf isotope analysis, the zircon ε_Hf(t) values were determined to range from −3.0 to 7.6, with an average of 2.7. Furthermore, the first-stage Hf model age (T_DM1) was determined to be 2513−2916 Ma, indicating that the provenance of the rhyolitic tuffaceous slate is the depleted mantle or juvenile crust between the Middle Mesoarchean and the Late Neoarchean. Therefore, it is believed that the strata of the slate were deposited in the Late Neoarchean, instead of the Mesoproterozoic as determined by previous researchers. Accordingly, it is not appropriate to group the strata into the Mesoproterozoic Dongchuan Group. Instead, they should be classified as the Maolu Formation of the Neoarchean Puduhe Group given the lithologic association and regional information. Furthermore, the magma ages of 2491 ± 15 Ma are highly consistent with the eras of the large-scale Late Neoarchean orogenic magmatic activities on the northern margin of the Yangtze Craton, and thus reflect the orogenic process consisting of subduction and collision from Late Neoarchean to Early Paleoproterozoic. The magmatic activities during this period were possibly caused by the convergence of the supercontinent Kenorland. Meanwhile, the metamorphic ages of 2.3 Ga, 2.0 Ga, and 1.8 Ga are highly consistent with three metamorphic ages of 2.36 Ga, 1.95 Ga, and 1.85 Ga of the northern margin of the Yangtze Craton, indicating that the strata experienced Paleoproterozoic tectonic-thermal events. The study area is located on the eastern margin of Qinghai-Tibet Plateau, and thus was possibly re-transformed by magmatism subjected to the subduction of the Meso-Tethys Ocean during the Early Cretaceous. The discoveries made in this study will provide strong petrological and chronological evidence for analyzing the early crustal evolution of the Yangtze block.©2021 China Geology Editorial Office.     

鄂东北地区沉积变质型锰矿矿物学特征和地球化学特征

扬子陆块北缘的鄂东北地区是湖北省沉积变质型锰矿集中区,发育了广水—黄陂—蕲春SEE-NWW向元古代沉积变质锰矿带,锰矿赋存于新元古界红安岩群中。本文以鹰咀山锰矿床、四方山锰矿床及孙冲锰矿床为例,分析研究其矿物学特征和地球化学特征,以便为总结该区锰矿床成矿环境及成矿物质来源提供帮助。研究表明,锰矿石矿物主要为菱锰矿、软锰矿、硬锰矿、黑锰矿、锰铝榴石等;矿石化学组分多样,Co、Ni、Zn、Sr、Ba、U等元素相对富集。锰矿石的w(Th)/w(U)、w(V)/w(Cr)值反映锰矿形成于弱氧化-还原的沉积环境;w(SiO2)/w(Al2O3)、w(Fe+Mn)/w(Ti)、w(Fe)/w(Ti)、w(Al)/w(Fe+Mn+Al)、w(Y)/w(Ho)、w(La)/w(Ce)特征值,以及w(SiO2)—w(Al2O3)图解、w(Fe)/w(Ti)—w(Al)/w(Fe+Mn+Al)图解,均反映其成矿过程中有热水物质参与。因此,鄂东北地区的沉积变质型锰矿形成于弱氧化-还原性沉积环境,有热水(液)活动参与成矿作用并提供了丰富的物质来源。     

Zircon U–Pb Ages and Lu–Hf Isotope of the Dongchuan Group in Central Yunnan, China, and their Geological Significance

On the southwestern margin of the Yangtze Block, the Dongchuan Group consists of slightly metamorphosed sedimentary rocks, including silty slate, argillaceous slate, clayey slate, arkose, dolomite, and minor volcanic rocks. To date, it is still a controversy over the depositional age and stratigraphic sequence of the Dongchuan Group. In this study, we analyzed five samples of meta-sedimentary rocks and one sample of meta-tuff from the Yinmin, Luoxue and Etouchang Formations of the Dongchuan Group in the Yuxi region for detrital zircon U-Pb ages and Lu-Hf isotope. The detrital zircon ages of the meta-sediments vary from 3073 to 1703 Ma, mainly clustered at three periods, from 1889 to 1840, 2490 to 2008 and 2878 to 2844 Ma. The youngest age peak of all the samples is ～1859 Ma, with the εHf(t) values of the zircons ranging from-20.3 to +4.3 and more than 90% being negative, indicating that the Paleoproterozoic crustal accretion on the southwestern margin of the Yangtze Block was dominated by reworking of the ancient crustal materials involved in the assembly and breakup of the Columbia supercontinent. Another important age range is between 2490 Ma and 2008 Ma, with εHf(t) values from-14.7 to +8.9 and 70% of them are negative, suggesting that the magmatism in the source area was also dominated by reworking and recycling of the ancient crustal materials, with minor juvenile mantle substances added. The detritus was probably derived from the Paleoproterozoic crystalline basement in the southern Yuxi region. The oldest peak age is ～2847 Ma and the εHf(t) values are from-7.7 to +7.0 with 50% of both positive and negative values, demonstrating a possible ～2.85 Ga ancient continental nucleus on the southwestern margin of the Yangtze Block and substantial growth in juvenile crust materials during this period. Besides, the weighted average age of the zircons from the meta-tuff of the Etouchang Formation is 1677 ± 14 Ma. Combining the previous research data and this study, we can constrain the depositional age of the Dongchuan Group in central Yunnan Province to the period from the late Paleoproterozoic to early Mesoproterozoic, slightly earlier than that of the Dongchuan Group in the Dongchuan area near to the southwestern Sichuan Province. The depositional age of the Dongchuan Group is older than that of the Kunyang Group.     

粤北大瑶山地区前泥盆纪地层中的火山岩特征及LA-ICP-MS锆石U-Pb年龄

通过1︰5万地质填图及剖面测制,作者在粤北大瑶山地区的震旦-寒武纪地层中首次发现多层火山岩,岩性主要为火山-沉积碎屑岩类的变质凝灰质不等粒岩屑石英砂岩、变质凝灰质不等粒长石石英砂岩、沉凝灰岩等,局部见变流纹质熔结凝灰岩。对变流纹质熔结凝灰岩、变质凝灰质砂岩用LA-ICP-MS法测定锆石U-Pb年龄,206Pb/238U年龄介于614~2869 Ma之间,年龄值较为分散,说明碎屑锆石是多来源的。火山岩年龄数据与地层时代归属矛盾,粤北大瑶山地区前泥盆纪地层的时代归属值得进一步探讨。     

Nd isotopic stratigraphy of Paleoproterozoic to late Paleozoic sedimentary strata of the southwestern Yangtze Block and implications for its tectonic evolution

ABSTRACT

A systematic Sm-Nd isotopic study is reported for Paleoproterozoic to Late Paleozoic strata from the Dongchuan area in the southwestern Yangtze Block. The results, combined with the available detrital zircon U-Pb ages and Hf isotope data, constrain the provenances of these sedimentary rocks and further identify three important tectono-magmatic activities. Most of the Paleo-Mesoproterozoic samples (Dongchuan Group) display a wide T_DM2 range of 1.92–2.52 Ga with corresponding ε_Nd(t) values of +4.0 to ?3.5, suggesting Paleoproterozoic-dominated provenances mixed with mantle-derived materials. This corresponds to the ~1.7–1.5 Ga mafic magmatic activities commonly occurred in the southwestern Yangtze Block, which are related to the early breakup of the Columbia supercontinent. The obvious vale of T_DM2 and apex of ε_Nd(t) occurred in the Neoproterozoic strata (~0.8 Ga) of the southwestern margin over the whole Yangtze Block. This is consistent with the widely recognized mantle-derived magmatism around the Yangtze Block related to the breakup of Rodinia. However, the decreases in Nd model ages are different among various regions, indicating that the Neoproterozoic mantle inputs are more profound in the southwestern and central Yangtze Block than the southeastern Yangtze and the Jiangnan orogenic belt. The late Ediacaran to early Cambrian strata from the southwestern Yangtze exhibit a decrease in T_DM2 (from 2.00 to 1.67 Ga) and increase in ε_Nd(t) (from ?9.0 to ?5.2). This is in accordance with the coeval juvenile crustal materials discovered in the northwestern Yangtze, which were probably derived from the assembly of the Gondwana continent. Thus, a Gondwanan affinity is suggested for the southwestern Yangtze Block. Overall, the Nd isotopic studies of the Paleoproterozoic to Late Paleozoic sedimentary strata from the southwestern Yangtze Block identified three major episodes of magmatic activities, late Paleoproterozoic (~1.7 Ga), Neoproterozoic (~0.8 Ga) and late Neoproterozoic-early Cambrian (~0.55 Ga) in the context of Columbia, Rodinia and the subsequent Gondwana supercontinents.     

福建李家坊金矿区火成岩岩体锆石U-Pb年龄、地球化学特征及其地质意义

福建李家坊金矿为何宝山矿田近年新发现的中型金矿床,矿区内广泛发育火成岩岩体,然而,由于缺少对其岩浆活动时限及地球化学特征的研究,各类岩体与金矿化的关系尚不明确.针对这一问题,文章通过全岩主微量元素分析和LA-ICP-MS锆石U-Pb定年及微量元素测试,约束李家坊金矿床内火成岩岩体成岩年龄,并讨论了其地球化学特征.研究表...     

Sediment provenance,sediment-dispersal systems,and major arc-magmatic events recorded in the Mexican foreland basin,North-Central and Northeastern Mexico

ABSTRACT

The Late Cretaceous-Paleogene Mexican foreland basin (MFB), defined herein, represents the southern continuation of the late Mesozoic Cordilleran foreland basin. Sandstone petrography, new detrital-zircon (DZ) U-Pb geochronology, and paleocurrent data indicate that much of the sedimentary fill of the basin was derived from an active Late Cretaceous-Paleogene magmatic arc, termed here the Mexican Cordilleran arc, on the western continental margin of Mexico. The oldest known strata of the proximal foreland basin in the Mesa Central consist of Cenomanian-Turonian turbidites. Sampled sandstones are compositional volcanic litharenites with abundant neovolcanic grains and a dominant, approximately syndepositional DZ age group ranging ~98–92 Ma that records a major magmatic event in the Mexican Cordilleran arc. Santonian-Campanian strata in the distal MFB consist of carbonate pelagites with abundant interbedded tuffs and tuffaceous sandstones. Represented by the Caracol and San Felipe formations deposited in the forebulge and back-bulge depozones, respectively, these strata form an arcuate outcrop belt ~700 km in length. DZ ages ranging ~85–74 Ma in the arc-derived tuffaceous strata record a second prominent magmatic event.

Two principal transport mechanisms delivered volcanogenic sediment to the MFB from multiple, simultaneously active arc sources during Late Cretaceous time: (1) Cenomanian-Turonian east-directed transverse fluvial systems transported volcanic-lithic sand rich in young zircon grains; and (2) airborne ash clouds transported Santonian-Campanian zircon grains to the distal foreland basin in prevailing Late Cretaceous northwesterly winds. Axial transport of sediment derived from active arc sources, Proterozoic basement and derivative sedimentary rocks in northwestern Mexico, in addition to transverse transport from the thrust orogen itself, represents a younger sediment-routing system, modified by advance of the foreland fold-thrust belt, to the Maastrichtian-Paleogene foreland of northeastern Mexico.     

滇中易门地区新元古代澄江组凝灰岩锆石U-Pb年龄及其地质意义

扬子西缘广泛出露的新元古代澄江组是一套与晋宁运动密切相关的沉积岩夹火山岩系,其形成时限对华南新元古代区域地层格架、地层划分对比及古大陆再造具有重要意义。出露于滇中易门地区的新元古代澄江组底部发育有厚数米的凝灰岩夹层,本次采集凝灰岩进行LA-ICP-MS锆石U-Pb定年研究,结果表明,锆石206Pb/238U年龄加权平均值为812±5. 5Ma(n=17,MSWD=0.46),可以代表滇中澄江组的底界年龄,从而进一步确定澄江组底界年龄为812Ma左右。此外,凝灰岩中捕获的锆石年龄信息指示扬子西缘可能存在2. 5Ga、1. 8～1. 6Ga、1. 5Ga、1. 3Ga及1.0Ga等数期重要的区域构造-热事件。     

柴达木盆地东部扎布萨尕秀组的时代归属讨论

柴达木盆地石炭系是中国北方新区新层系油气勘探调查研究的热点,盆地东部地区石炭系出露较全,但多数学者认为柴东地区不存在二叠系。针对扎布萨尕秀组归属于石炭纪还是二叠纪的争议,采集扎布萨尕秀组的砂岩碎屑锆石开展了U-Pb LA-ICP-MS同位素测年,获得40个和谐年龄分布在2488±34 Ma至288±3 Ma之间,最年轻的一组碎屑锆石的加权平均年龄288.0±2.0 Ma（MSWD=0.112,n=21）。这意味着该扎布萨尕秀组中的砂岩沉积于288 Ma之后,晚于国际石炭—二叠纪界限（299 Ma）。依据野外调查和已有研究成果,扎布萨尕秀组中赋存丰富的虫筳科化石,其中膨胀型虫筳属Pseudoschwagerina或Sphaeroschwagerina的出现是进入二叠纪的重要标志。结合碎屑锆石年代学和虫筳属化石特征,扎布萨尕秀组应归属早二叠世,说明柴达木东部地区存在二叠纪沉积记录。该认识为深化柴达木盆地晚古生代—中生代沉积建造和构造演化提供了重要的地层学证据。