K-Ar ages and Pb,Sr isotopic characteristics of Cenozoic volcanic rocks in Shandong Province,China

28 samples of Cenozoic volcanic rocks collected from Shandong Province have been dated by K-Ar method. They are mainly Neogene with an age range of 4–19 m. y. The basalts from Linqu and Yishui in west Shandong Province are Miocene and those from Penglai and Qixia in east Shandong Province are Miocene and Pliocene in age. The basalts from Wudi in north Shandong Province are Middle-Early Pleistocene in age. In each area the duration of volcanic eruption was estimated at about 2–3 m. y. Pb and Sr isotopic compositions and U, Th, Pb, Rb, Sr, and major elements in most of the samples were determined. The isotopic compositions are:²⁰⁶Pb/²⁰⁴Pb—16.92-18.48,²⁰⁷Pb/²⁰⁴Pb—15.30-15.59,²⁰⁸Pb/²⁰⁴Pb—37.83-38.54, and (⁸⁷Sr/⁸⁶Sr)_i—0.70327-0.70632. There are some positive or negative linear correlations between²⁰⁶Pb/²⁰⁴Pb and²⁰⁷Pb/²⁰⁴Pb, Pb isotopes and Pb content, Pb isotopes and Sr isotopes, and Sr isotopes and other elements. The basaltic rocks from east and west Shandong Province have somewhat differences in isotopic composition and element content. The basalts probably are products of multi-stage evolution of the mantle. They have preserved the primary features of the source, although they were influenced, to some extent, by the contamination of crustal materials.     

青藏高原北部新生代火山岩的成因机制

Based on the electron probeanalyses result of the minerals and the bulk rock composition of the Cenozoic volcanicrocks from Yumen and Hoh Xil lithodistricts on the Qinghai-Tibet Plateau, the formingconditions including temperature and pressure of those rocks are studied.According to thethermodynamics calculation result of the mineral-melt equilibrium,the depth of theasthenosphere superface (about 75～130km) for the northern part of the Qinghai-TibetPlateau during Cenozoic era is suggested. Finally, this paper indicates that the Cenozoicvolcanic rocks in the northern part of the Qinghai-Tibet Plateau mainly consist ofshoshonite series.Their forming temperature is 630～1039℃ and forming pressure isbetween 2.3～4.0 GPa and formed in the intracontinental orogenic belt,where the primarymagma was originated from a particular enriched upmantle and accreted crust-mantle belt ordirectly originated from asthenosphere superface by partial melting of pyrolite.     

First data on U-Pb SHRIMP-II isotopic dating based on zircons of ash sediments from Cenozoic depressions in Southwest of Primorie

U-Pb (SHRIMP-II) isotopic dating has been conducted for zircons of the ash sediments of the Ust’-Suifun Suite, which was the final stage of Late Cenozoic explosive volcanism in Southwest Primorskii krai. These pyroclastic units are widespread within sediments that fill in Cenozoic depressions including large coalfields. The concordant dates (23.7–24.6 Ma) are in line with the results of the K-Ar determinations for volcanic tephra (23.6–27.1 Ma) and correspond to the beginning of the active phase of spreading and taphrogenesis in the neighboring Trench of the Sea of Japan. These processes started as early as the Eocene and are reflected in the continental vicinity with the formation of riftogenic depressions and the occurrence of a peculiar gas volcanism.     

青藏高原及邻区新生代火山岩Sr-Nd-Pb同位素特征

笔者在综合分析最近十多年来的Sr、Nd、Pb同位素资料基础上,重点研究了青藏高原及邻区新生代火山岩岩浆源区在时空上的变化规律。结果表明:①冈底斯中段火山岩的岩浆源区逐渐从普通地幔向EMⅡ方向演化;西段晚期火山岩源区的演化方向为俯冲带壳幔混合源→造山带上地壳源→下地壳源。②西羌塘岩浆源区主要为不具富集或亏损的幔源物质;囊谦盆地、大理海东火山岩源区较深,为大洋型软流圈地幔+消减组分混合源;藏北羊湖、雄鹰台鲸鱼湖、西昆仑以及北羌塘巴毛穷宗火山岩的岩浆源区为EMⅡ;鱼鳞山超钾质火山岩为经历了大陆地壳物质强烈交代作用的EMⅡ型岩浆源区;西秦岭火山岩源于亏损地幔,腾冲新生代火山岩源区为受到地壳物质交代的EMⅡ。③西羌塘、可可西里、西昆仑和腾冲新生代火山岩具两种演化趋势——鱼鳞山、普鲁、雄鹰台鲸鱼湖岩区和腾冲火山群向EMⅡ方向演化,而泉水沟、黑石北湖、阿什库勒则分别沿0Ma的地幔上地壳混合线方向演化。④青藏高原及邻区新生代火山岩至少存在4种不同的岩浆源区。     

青藏高原北部黑石北湖新生代钾质火山岩的成因

昆仑岩带新生代钾质火山活动是青藏高原北缘深部动力学过程的重要记录。有关岩浆源区的性质和岩浆产生的机制一直存在较大的认识分歧。阐述了昆仑岩带黑石北湖钾质火山岩的岩石学和地球化学特征,并与西昆仑康西瓦和泉水沟新生代火山岩进行了成因对比分析。研究表明,昆仑火山岩带玄武质岩石的K2O和Na2O含量变化较大,从钠质过渡到钾质,硅碱图显示玄武质初始岩浆向钾质安粗岩方向演化。黑石北湖火山岩的高场强元素和Sr、Nd同位素组成显示岩浆源区具有EMⅡ的性质。岩石LREE的强烈富集和HREE的强烈分馏指示岩浆来自富集型含石榴子石地幔源区。不相容元素K/Nb、Ba/La等比值具有岛弧火山岩与OIB型玄武岩的过渡特征,指示源区为曾遭受软流圈流（熔）体交代的古俯冲地幔楔。     

青藏高原北部黑石北湖新生代钾质火山岩的成因

昆仑岩带新生代钾质火山活动是青藏高原北缘深部动力学过程的重要记录。有关岩浆源区的性质和岩浆产生的机制一直存在较大的认识分歧。阐述了昆仑岩带黑石北湖钾质火山岩的岩石学和地球化学特征,并与西昆仑康西瓦和泉水沟新生代火山岩进行了成因对比分析。研究表明,昆仑火山岩带玄武质岩石的K2O和Na2O含量变化较大,从钠质过渡到钾质,硅碱图显示玄武质初始岩浆向钾质安粗岩方向演化。黑石北湖火山岩的高场强元素和Sr、Nd同位素组成显示岩浆源区具有EMⅡ的性质。岩石LREE的强烈富集和HREE的强烈分馏指示岩浆来自富集型含石榴子石地幔源区。不相容元素K/Nb、Ba/La等比值具有岛弧火山岩与OIB型玄武岩的过渡特征,指示源区为曾遭受软流圈流（熔）体交代的古俯冲地幔楔。     

Petrogenesis of the Cenozoic volcanic rocks from the northern part of Qinhai-Xizang (Tibet) plateau

Based on electron probe analyses of the minerals and bulk composition of the Cenozoic volcanic rocks from Yumen and Hoh Xil lithodistricts, Qinghai-Xizang plateau, the forming conditions including the temperature and pressure of those rocks are studied in this paper. According to the thermodynamic calculation results of mineral-melt equilibrium, the depth of the asthenosphere superface (about 75 – 130 km) for the northern part of the Qinghai-Xizang plateau during the Cenozoic is suggested. Finally, this paper indicates that the Cenozoic volcanic rocks in the northern part of the Qinghai-Xizang plateau mainly consist of shoshonite series. Their forming temperature is 630 – 1039°C and forming pressure is between 2.3 – 4.0 GPa. The rocks were formed in the intracontinental orogenic belt, of which the primary magma was originated from a particular enrichment upper mantle and accreted crust-mantle belt or directly from asthenospheric superface as a result of partial melting of pyrolite. The project was supported by the National Natural Science Foundation of China (No. 49234080), the Geological Sectional Foundation of MGMR (No. 8506201, 8506207) and the Science Foundation of Northwest University (97NW23).     

Permian biostratigraphy of the northern Okhotsk region (Northeast Asia)

Fossil biota and detailed biostratigraphy of the Permian northeastern Okhotsk and Ayan-Yuryakh sedimentary basins located in the northern Okhotsk region are characterized. The biota core is represented by bivalves associated with gastropods, brachiopods, and other faunal groups. It is shown that a new regional stratigraphic scale of northeastern Russia based on brachiopods and bivalves may be used for subdivision of Permian sections in these basins. Fossil assemblages have many features in common with their counterparts from the Verkhoyansk region; at the same time, there are endemic species and the big group of species characteristic of the Omolon basin. The upper part of the Khivach regional horizon is subdivided into subzones based on the evolutionary lineages of the Maitaia and Intomodesma genera. Changes in the taxonomic composition of coeval communities in different basins are shown to be largely controlled by the basin depths and facies environments. Impoverished fauna of the Ayan-Yuryakh basin was less diverse in taxonomic aspect, represented almost entirely by bivalves (mostly Inoceramus-like) accompanied by rare gastropods. The discovered taxa are figured in majority, and table of their stratigraphic distribution is presented.     

晚新生代以来天山北缘沉积记录及其稳定同位素变化的环境意义

晚新生代以来,天山北缘的沉积记录与天山的隆升密切相关.研究表明:始-渐新世安集海河组主要沉积发育水平层理的绿色、灰绿色湖泊相泥岩;晚渐新世沙湾组中上部岩石组合特征为紫红色曲流河相砂岩、粉砂岩和砾岩夹层;早中新世塔西河组下部主要为灰绿色、褐红色砂、泥岩互层,上部主要为土黄色砂岩和粉砂岩夹层;晚中新世-早上新世独山子组为辫状河相灰色砾岩和砂砾岩沉积;晚上新世-早更新世西域组主要为厚层砾岩堆积.土壤碳酸盐中稳定同位素数据表明:安集海河组δ13C平均值为-3.9‰,δ18O平均值为-5.0‰;沙湾组中上部δ13C平均值为-8.1‰,δ18O平均值为-11.0‰;塔西河组δ13C平均值为-5.9‰;δ18O平均值为-7.7‰;独山子组δ13C平均值为-8.5‰,δ18O平均值为-10.3‰;西域组δ13C平均值为-6.0‰,δ18O平均值为-10.4‰.同位素结果和沉积记录共同表明,始-渐新世为湿润温暖气候;晚渐新世为干旱寒冷气候;早中新世早期为半湿润、半温暖气候,晚期为干旱、寒冷气候;晚中新世.早上新世为干旱寒冷气候;晚上新世-下更新世为干旱、半温暖气候.结合古地磁数据和全球气候变化,天山北缘晚新生代以来发生五次主要气候变化事件,即晚渐新世(沙湾组时期中上部)气候转换,约24Ma(沙湾组时期顶部)气候突变,早中新世内部(约24～19Ma)气候转换事件,晚中新世(约7Ma)C4植被迅速扩张和约3.17Ma以来气候的剧烈震荡.     

藏北羌塘地块新生代火山岩中麻粒岩捕虏体的岩石学和地球化学研究:对青藏高原新生代火山岩成因及下地壳性质的约束

青藏高原北部羌塘地块的新生代高钾钙碱性火山岩中含有很多下地壳捕虏体,这些捕虏体的主要岩石类型为二辉石麻粒岩和单斜辉石麻粒岩.本文对乌兰乌拉湖南侧枕头崖地区新生代高钾钙碱性火山岩中的9个麻粒岩样(6个基性麻粒岩和3个酸性麻粒岩)进行了系统的岩石学,矿物化学,地球化学和Sr-Nd-Pb同位素地球化学研究.其中,紫苏辉石具有高Mgo FeO,低Al2O3的特征,单斜辉石具有低Al2O3和TiO2的特征,黑云母具有高TiO2的特征,这些特征都表明这些矿物为变质成因.矿物温压计算表明二辉石麻粒岩形成的平衡温度为783℃～818℃.单斜辉石麻粒岩形成压力在0.845～0.858GPa之间,来源深度约28km.表明它们可能是来自青藏高原加厚陆壳中部的岩石样品.基性麻粒岩的SiO2=48.76%～58.61%,Al2O3=18.34%～24.50%,Na2O=3.16%～5.41%,K2O=1.58%～3.01%,低Mg#(30～67),富集轻稀土(LREE)和大离子亲石元素(LILE),其具有较高的Rb/Sr(0.09～0.21)和(La/Yb)N(17.32～49.35),具有较低的Nb/Ta(9.76～14.92),其Eu异常变化于0.19～0.89之间.基性麻粒岩的Sr-Nd-Pb同位素地球化学表现为87Sr/86Sr=0.710812～0.713241,εSr=169.13～203.88,143Nd/144 Nd=0.512113～0.512397;εNd=-4.70～-10.05,206Ph/204Pb=18.7000～-18.9565,207Pb/204Pb=15.7135～-15.7662,208pb/204Pb=39.1090～39.4733.和基性麻粒岩类似,酸性麻粒岩也表现出富集轻稀土(LREE)和大离子亲石元素(LILE)的特征,它们的87Sr/86Sr=0.712041～0.729088,εNd=180.71～430.59,143Nd/144Nd=0.512230～-0.512388;εNd=-4.74～-7.96,206Ph/204Pb=18.9250～-19.1717,207Pb/204Pb:15.7662～-15.7720,208Pb/204Pb=39.2109～39.6467.上述地球化学特征表明这些基性麻粒岩的源岩是下地壳岩石,而非地幔岩或玄武质堆晶岩,而酸性麻粒岩的源岩极有可能是准铝质的花岗质岩石.这就表明青藏高原新生代下地壳的地温梯度很高,并含有部分沉积岩,而非典型的辉长质下地壳.而且,详细的研究表明,这种特殊的下地壳可能对青藏高原新生代高钾钙碱性和橄榄粗安质岩浆的起源有重要作用.因此目前所认为的超钾质-橄榄粗-安质岩浆源于富集岩石圈地幔在对流减薄作用下发生部分熔融的观点值得重新考虑.     

藏北羌塘戈木错北部新生代钾质火山岩40Ar/39Ar定年

1∶25万玛依岗日幅区域地质调查期间,在藏北戈木错北部发现了一套新生代钾质火山岩。对保存较好的3处火山岩的样品进行40Ar/39Ar年代学研究,获得了30.6Ma±0.4Ma、30.0Ma±0.2Ma和29.8Ma±0.3Ma三个坪年龄,代表该地区火山岩的喷溢时代。戈木错北部火山岩的地球化学特征与钾质火山岩的类似,它与鱼鳞山、走构由茶错、多格错仁等地区的新生代火山岩共同构成了羌塘地区钾质—超钾质火山岩带,它们的形成与印度大陆同亚洲大陆的碰撞和青藏高原的隆升密不可分。     

藏北羌塘戈木错北部新生代钾质火山岩40Ar/39Ar定年

1∶25万玛依岗日幅区域地质调查期间,在藏北戈木错北部发现了一套新生代钾质火山岩。对保存较好的3处火山岩的样品进行40Ar/39Ar年代学研究,获得了30.6Ma±0.4Ma、30.0Ma±0.2Ma和29.8Ma±0.3Ma三个坪年龄,代表该地区火山岩的喷溢时代。戈木错北部火山岩的地球化学特征与钾质火山岩的类似,它与鱼鳞山、走构由茶错、多格错仁等地区的新生代火山岩共同构成了羌塘地区钾质—超钾质火山岩带,它们的形成与印度大陆同亚洲大陆的碰撞和青藏高原的隆升密不可分。     

First U-Pb and Sm-Nd isotopic data on granitoids from the Devonian volcanic belt of Kazakhstan

First U-Pb zircon isotopic dates were obtained for rocks from the Devonian volcanic belt in Kazakhstan. The granodiorites of the Zhabden Massif (Karamendinskii Complex) were dated at 391 ± 1 Ma. The Sm-Nd isotopic system of a whole-rock granodiorite sample (?_Nd = 2.5) suggests a high percentage of mantle material in the initial granite melt, which is in good agreement with known data on granitoids in neighboring territories in Kazakhstan. With regard for the isotopic dates obtained for the granodiorites, the material of their source was separated from the mantle at 946 Ma.     

长江源区新生代火山岩的年代学研究

长江源区的火山岩包含了青藏高原北部新生代火山岩形成及演化的全部信息，其年代学研究对查明青藏高原北部新生代火山活动时空演化具有重要意义。通过K—Ar同位素年代学研究，将长江源区新生代的火山活动划分为3期：第Ⅰ期(40．1-35．1Ma)火山喷发较弱，形成小范围分布的细粒安粗岩和斑状粗面岩；第Ⅱ期(26．5～17．6Ma)火山喷溢最为强烈，形成大面积厚层黑色气孔状安粗岩；第Ⅲ期(5．5-4．61Ma)由潜火山作用形成球粒状、斑状粗面岩岩丘。长江源区3个期次的火山喷发与青藏高原北部火山活动的阶段性相对应。长江源区新生代火山岩的演化特征为：从早到晚，岩石系列由高钾钙碱性系列→钾玄岩系列演化；岩性由安粗岩→粗面岩演化。     

华北克拉通中、新生代典型火山岩的岩石成因：Hf同位素新证据

本文首次报道了华北克拉通中、新生代典型火山岩（碱性玄武岩、拉斑玄武岩和高镁安山岩）的高精度Hf同位素数据。结果表明，这些中、新生代火山岩具有完全不同的Hf同位素组成，即具有很宽的εHf（t）（-18．4～9．6）变化范围，并和Nd同住素有很好的正相关性。其中新生代昌乐-临朐地区和晚白垩世碱锅（～105Ma）地区的碱性玄武岩具有高Hf同位素（εHf（t）=6．8～9．6）和高Nd同位素组成（εd（t）=0．4～4．9），表明其来源于亏损的软流圈，代表未分异无混染的原始岩浆组成；早白垩世方城（125Ma）碱性玄武岩和拉斑玄武岩具有极低的Hf同位素（εNd（t）=-15．6～-18．4）和低Nd同住素组成（εNd（t）=-12．8--4．4），代表了富集的大陆岩石圈地幔的Hf同位素组成；乌拉哈达（142Ma）地区的高镁安山岩具有较低的Hf同位素（εHf（t）=-2．1～-2．6）和低的Nd同位素组成，代表古老难熔的岩石圈地幔橄榄岩与俯冲的地壳物质相互作用的结果。玄武岩中较大的Hf同位素组成范围（εHf（t）／εNd（t）〉1）说明Hf同位素比Nd同位素具有更好的源区示踪结果。     

辽东凸起北段新生代隆升时间的确定:来自裂变径迹的证据

对取自辽东凸起北段凸起带和陡坡带的6个岩芯样品进行了磷灰石裂变径迹(AFT)测试并分析了裂变径迹特征,选定其中2个样品在约束条件下进行热史模拟。结果表明,辽东凸起北段新生代经历了距今50 Ma±孔店组沉积期末及距今24 Ma±的东营组沉积期末的2次构造隆升。通过对辽东湾坳陷东西部的沉积结构和控凹断裂对比可知,辽东湾坳陷一系列NE向隆起具有相似的发育机制。结合渤海湾盆地区域构造背景,推断辽东湾坳陷辽东凸起的形成是古近纪地幔热活动引起的伸展作用在孔店组沉积期末的构造响应,形式为拆离性质的翘倾断块;而辽东凸起的第二次抬升是受东营组沉积期末发生的区域性构造抬升运动影响的结果。     

A revised stratigraphic framework for later Cenozoic sequences in the northeastern Mediterranean region

This study describes the lithostratigraphic character of mid-Cenozoic (Oligocene-Pliocene) sequences in different parts of the northeastern Mediterranean area and offers a detailed stratigraphic correlation for this region. The sequences concerned are drawn from the Camardi area (south-central Anatolia), the Adana Basin, the Misis Mountains and the Kyrenia Range (northern Cyprus) and the submerged Florence Rise (west of Cyprus). The stratigraphic relationships identified here indicate the following: (a) Following the middle Eocene (Lutetian) regression there was uplift throughout the entire region; (b) Episodes of fluvial and lacustrine deposition in intramontane settings ensued in most of this region during the late Eocene/early Miocene interval; (c) Following a regionally extensive phase of tectonic compression, major marine transgression commenced in the late Oligocene in northern Cyprus and in the early Miocene in adjacent southern Turkey, with the exception of the Ecemi§ Fault Zone where continental deposition continued; (d) These Oligo-Miocene transgressive sequences comprise a broadly diachronous complex of both shallow and deeper marine facies, including reefal carbonates, littoral clastics, basinal shales and fan-turbidites; (e) Deeper marine Miocene facies persisted longer in the Misis area and in northern Cyprus; (f) A regional regression occurred throughout most of the area during the late Serravallian to Tortonian interval and is marked by the abrupt, locally discordant appearance of extensive shallow marine, deltaic and fluvial deposits; (g) Continued regression in the Messinian led to the formation of significant evaporite deposits in the western and southern parts of the region, but localized uplift of the Misis area is attested by the initial deformation of the Neogene rocks there and the absence of Messinian sediments from this area; (h) In the Pliocene there was extensive emergence of the northern parts of the region interrupted by brief marine incursions. The present-day drainage pattern was established at this time; (i) Marine conditions persisted longer in northern Cyprus, where emergence occurred only in the latest Pliocene.     

松辽盆地林深3 井火山岩的锆石U——Pb 年龄与Hf 同位素组成

根据松辽盆地北部林深3 井火山岩的岩相、全岩主微量元素、锆石U--Pb 同位素和锆石Hf 同位素特征的分析结果,探讨了该火山岩的形成时代和岩浆源区。锆石LA--MC--ICPMS U--Pb 研究结果表明: 林深3 井火山岩形成时代约为120 Ma,处于早白垩世中晚期,属于营城组火山岩。锆石的LA-- MC--ICPMS Hf 同位素研究显示,本区火山岩的锆石εHf ( t) 全部为较高的正值,二阶段Hf 模式年龄为789 ～ 1 494 Ma,表明其主要起源于中--新元古代增生的地壳物质,暗示中--新元古代时期兴蒙造山带东段存在地壳增生事件。