张广才岭燕山早期白石山岩体成因与壳幔相互作用

出露于东北地区张广才岭的白石山岩体,其全岩-矿物Rb-Sr等时线年龄为196士4 Ma,表明形成于中生代的燕山早期,而非传统认识上的印支期.岩体主岩和闪长质包体均具有低ISr(≈0.705)和正εNd(t)(+1.7～+2.2)值的特点,反映岩体成因与地幔具有密切的联系.地质学、岩石学和地球化学的详细研究表明该岩体具有壳幔混合成因,闪长质包体是较基性的地幔岩浆进入主岩浆中淬火结晶而成,花岗质岩浆的源区主要为新生的地壳物质.动力学分析表明,本区在华北板块和西伯利亚板块碰撞拼合后,由于东侧大洋板块的俯冲及后续的岩石圈拆沉效应,导致软流圈地幔上隆及幔源岩浆的板底垫托,并进而造成先存和新生地壳的部分熔融和不同源区岩浆的混合作用.底垫的新生地壳是兴蒙造山带造山后晚期形成的.因此,古生代-中生代是本区地壳生长的重要时期,且这种地壳生长是在垂向构造机制下进行的.     

海南岛早白垩世红层磁组构和古地磁新结果

海南岛白垩纪红层是迄今产出古地磁结果最多的地层,但古地磁结果难以在海南岛周边古地磁结果和地质限制条件下作出合理解释.为了更好地认识海南岛白垩纪红层古地磁方向的可靠性,我们对采自前人工作地区的14个采点132个样品开展了古地磁和磁组构的综合研究.磁化率各向异性测试显示14个采点样品平均各向异性度为1.018,线理度为1.014,面理度为1.004.各采点磁化率椭球体最小轴显著偏离地层法线,没有反映出沉积或压实特征.野外调查发现采点区域的节理组交线(代表中间应力轴)与磁化率椭球体中间轴一致,意味着采点磁性矿物的排列方位很可能因构造应力影响发生改变.逐步热退磁显示14个采点分离出的特征剩磁解阻温度高于660℃,方向区别于现代地磁场方向;褶皱检验表明在褶皱展平度为80.4%(95%置信范围内褶皱展平度为77%±12.2%)时精度参数达最大,对应方向为D=359.9°, I=43.4°,κ=70.2,α95=4.8°,与前人的古地磁方向一致.通过与华南地块参考极对比,以及综合分析海南岛围区古地磁和地质限制条件,表明该古地磁方向是不协调的.我们认为前人和本文采样红层剩磁很可能在沉积时获得,但在沉积后受到区域构造应力的影响,致使磁性矿物排列改变,从而导致古地磁方向也发生变化.因此,我们认为这些样品所记录的古地磁方向不能准确反映海南岛白垩纪古纬度.     

The Alleret maar (Massif Central, France): A new lacustrine sequence of the early Middle Pleistocene in western Europe

The Alleret maar (Massif Central, France) provides a long lacustrine sequence (40.6 m) attributed to the early Middle Pleistocene. Sediment, pollen and diatoms analysis of its upper part (AL2 core, 14.6 m) indicates two temperate phases marked by high lake levels, forest development and vegetation expansion. They are separated by a cold period during which lake level drops, coarse sediment input increases and steppic and xerophilous plants develop. Pollen data suggests that this sequence belongs to the upper part of the Cromerian complex. These results are in agreement with the 557 ± 3 ka (±12 ka, including all errors) ⁴⁰Ar/³⁹Ar age obtained from an interbedded tephra layer emitted by the Mont-Dore/Sancy strato-volcano and establish that this sequence probably covers the MIS 15 substages.     

Pseudofrenelopsis fossils from Cretaceous gypsum beds in Guixi,Jiangxi Province,China and their geological significance

Compressed fossil plants were found in the gypsum beds of the Zhoujiadian Formation in Guixi City, Jiangxi Province, China. The cuticular features of two species of Pseudofrenelopsis (Cheirolepidiaceae) were examined by scanning electron microscopy in this study: Pseudofrenelopsis papillosa Cao ex Zhou and Pseudofrenelopsis guixiensis Bainian Sun et Dai, sp. nov. A detailed analysis of the internode epidermis, and the adaxial and abaxial leaf cuticles of the two species, was performed, extending our knowledge of the morphological and anatomical characteristics of the extinct Pseudofrenelopsis. A new species, Pseudofrenelopsis guixiensis sp. nov., is proposed based upon comparison of its cuticular features. It differs from previously published species in that it has hairs on the abaxial surfaces of its leaves, sometimes shares subsidiary cells on the surfaces of internodes, lacks a hypodermis, and has no papillae on its epidermal cells. Because the distribution of fossil Pseudofrenelopsis is restricted to the Lower Cretaceous, the Early Cretaceous age of the Zhoujiadian Formation is affirmed. The fossils of Pseudofrenelopsis show obvious xeromorphic characteristics, such as apparent thickening of the cuticles, subsidiary cells with obvious papillae, and anticlinal walls with strong cutinization, and they are found associated with gypsum beds and close to red beds. All of these features indicate an arid climate.     

浙东南英安质火山岩早侏罗世锆石SHRIMP年龄的首获及其地质意义

浙江中生代晚期火山岩极为发育,而有无中生代早期火山岩,则向无定论。本文在确认浙东南松阳毛弄煤矿一带煤系沉积下部火山岩属中生界毛弄组的基础上,测得其SHRIMP锆石U-Pb年龄为180±4Ma,首次证明浙江存在早一中侏罗世火山岩,同时表明浙东南尚没有确切的中侏罗世晚期至晚侏罗世火山岩活动记录,而且也缺失晚侏罗世和大部分中侏罗世地层。     

Stratigraphy of the Lower Cretaceous Sediments from the Carpathian Bend Area, Romania

The Lower Cretaceous sediments of the Ceahl?u Nappe (from the bend region of the Romanian Carpathians) were investigated from lithological and micropaleontological (calcareous nannoplankton) points of view. Our investigations revealed that the studied deposits were sedimented within the latest Tithonian-Albian interval. The calcareous nannofossil assemblages of the turbidite calcareous successions (the Sinaia Formation) were assigned to the NJK-?NC5 calcareous nannofossil zones, which cover the Late Tithonian-Early Barremian interval. The sandy-shaly turbidites, which followed the calcareous turbidites of the Sinaia Formation, are Early Barremian-Early Albian in age (interval covered by the ?NC5-NC8 calcareous nannofossil zones). Because the studied deposited are mainly turbidites, many reworked nannofossils from older deposits are present in the calcareous nannofloras. Thus, some biozones (i.e., NC5), defined based on the last occurrences of nannofossils, could not be identified. The calcareous nannofossil assemblages are composed of Tethyan taxa (which dominate the nannofloras) and cosmopolitan taxa. During two intervals (the Late Valanginian and across the Barremian/Aptian boundary), Tethyan and cosmopolitan nannofossils, together with Boreal ones, were observed. This type of mixed calcareous nannoplankton assemblage is indicative for sea-level high-stand, which allows the nannofloral exchange between the Tethyan and Boreal realms, within the two-above mentioned intervals.     

新疆西准噶尔发现早泥盆世埃达克岩:大地构造及成矿意义

新疆西准噶尔博什库尔-成吉斯(Boshchekul-Chingiz)岩浆弧南缘,额敏县东南约100km的阿克乔克含铜花岗闪长岩和花岗闪长斑岩,其锆石U-Pb年龄为410.5±2.9Ma,形成于泥盆世早期.岩石具有埃达克岩的地球化学特征,表现为高钾钙碱性-钙碱性,SiO2含量在61％～66％之间,具高Al(Al2O3=15.67％ ～ 16.87％)、Sr(475×10-6 ～ 879×10-6)及高Sr/Y比值(36 ～77),低Y(9.87×10-6～14.46×10-6)、Yb(0.96×10-6～ 1.49×10-6),富钠贫钾(Na2O =4.25％ ～5.58％,K2O=2.26％ ～3.27％,Na2O/K2O=1.40～ 2.47),MgO=1.51％ ～2.58％,Mg#=41～48,并显示富集强不相容元素(Ba、Rb、Sr、Th、U)和LREE,(La/Yb)N=6.0～10.2,强烈亏损高场强元素(Nb-Ta、Ti),Y/Yb=10,无Eu异常(Eu/Eu*≈1.0)和HREE呈平坦型的配分特点,以及与环太平洋新生代埃达克岩相当的Rb/Sr(0.04 ～0.07)和La/Ce(0.42 ～0.51)比值,但偏低的Nb/U比值可能与俯冲沉积物加入有关.阿克乔克花岗闪长岩及花岗闪长斑岩是早泥盆世早期库吉拜-和布克赛尔(Kujibai-Hebukesaier)及洪古勒楞蛇绿岩带所代表的古大洋向南俯冲的玄武质洋壳部分熔融的产物,源区残留相主要为角闪石+辉石+石榴石,源岩应为石榴角闪岩;阿克乔克早泥盆世埃达克岩及谢米斯台-赛尔山晚志留世-早泥盆世A-型花岗岩(422～405 Ma,Chen et al.,2010)构造岩浆岩带可东延至扎河坝-阿尔曼太蛇绿岩带之北的岛弧带,构成一条贯穿东、西准噶尔北部的巨型构造带;阿克乔克埃达克岩伴有斑岩型Cu成矿作用,因此,在东、西准噶尔博什库尔-成吉斯-达拉特-巴依塔格巨型岩浆弧带有可能存在与埃达克岩有关的Cu-Au矿带.     

松科二井早白垩世早期玄武安山岩的发现及地质意义

松科二井超深钻探获取了松辽盆地连续沉积-火山岩心,为系统研究中生代松辽盆地形成机制、揭示中国东北地区构造演化历史提供了极好的研究材料。本文对取自松科二井井深-6035~-6084m的玄武安山岩开展了系统的锆石U-Pb定年、全岩主微量元素和Sr-Nd同位素分析测试。研究结果表明,松科二井玄武安山岩隶属于火石岭组底部,其形成时代为早白垩世早期（141.6±1.4Ma）。玄武安山岩样品富集大离子亲石元素,亏损高场强元素,具有弧岩浆的地球化学特征。这些样品显示了一定程度的轻重稀土元素分异（（La/Yb）_N=8.40~11.88）,具有轻微亏损的Sr-Nd同位素特征（（⁸⁷Sr/⁸⁶Sr）_i=0.70496~0.70478,ε_Nd（t）=1.05~1.61）,表明它们很可能源自于岩石圈地幔。早白垩世时期中国东北地区主要受控于蒙古-鄂霍茨克洋的南向俯冲和东侧古太平洋俯冲过程,目前研究揭示了前者影响了同期的大兴安岭地区的火山活动,但其影响范围是否延伸至松辽盆地内部尚不清楚。古太平洋岩石圈开始俯冲后很可能诱发了松辽盆地西侧晚中生代火山岩的形成。早白垩世松辽盆地演化主要受蒙古-鄂霍茨克洋还是古太平洋板块的活动影响仍存在较多争议。松科二井玄武安山岩具有与板内玄武岩相近的Th/Hf比值（1.10~2.87）及Zr/Y比值（10.1~18.7）,表明它们具有板内岩浆的地球化学特征,且松科二井样品比同时代盆地西部的大兴安岭地区玄武岩具有更高的Nb/Ta比值,更高的Zr、Hf与Ti含量,以及更亏损的Nd同位素特征,可能指示与大兴安岭地区玄武岩形成于不同的构造背景。松辽盆地内早白垩世火山岩很可能为古太平洋板片回转诱发形成,指示早白垩世古太平洋板片回转诱发的岩石圈伸展促进了松辽盆地的形成。

     

Holocene climate variability in Sicily from a discontinuous stalagmite record and the Mesolithic to Neolithic transition

Fabric and stable isotopic composition of a Holocene stalagmite (CR1) from a cave in northern Sicily record changes in paleorainfall in the early Holocene. High δ¹³C stable isotope values in the calcite deposited from ca. 8500 to ca. 7500 yr ago are interpreted as reflecting periods of high rainfall. The wet phase was interrupted by two periods of multi-century duration characterized by relatively cool and dry winters centered at ca. 8200 and ca. 7500 yr ago, highlighted by low δ¹³C and δ¹⁸O values. A high variability of δ¹³C values is recorded from ca. 7500 to ca. 6500 yr ago and indicates that the transition from a pluvial early Holocene to the present-day climate conditions was punctuated by decadal-scale periods of relatively dry winters. In northern Sicily, the traditional elements of the Neolithic appear at ca. 7700 yr ago. It is possible that changes in rainfall influenced the passage from hunter-gathering to farming and sheep-herding economies.     

北祁连山东部早石炭世早期腕足动物群落的古地理意义

北祁连山东部早石炭世早期经历了一次完整的海水进退旋回。此期该区腕足动物的演化明显受控于相对海平面变化。生存环境的稳定性似乎是群落演替过程能否持久进行的基础。在影响生物群落演替的诸多因素中,底质性质及其稳定性最为重要,其次是食物供应、海水盐度和水动力强度等。各群落在时间上相互取代的主要控制因素是海水深度,与海平面的变化直接相关。而造成这一时期腕足动物群落横向变化的主要因素除了海水深度外,陆源碎屑供应量、海水循环性以及含盐度都具有十分重要的影响。本区早石炭世早期腕足动物群落的生态位介于BA1和BA2之间,缺乏BA3－BA5较深水群落（BA－Benthic Assemblage,底栖组合）,说明此期该区早石炭世早期海水深度一般不超过10米。受沉积古地理环境的制约,本区早石炭世早期BA2生态域的主要分布范围局限于东部的景泰一带,向西水体明显变浅。