青藏高原东北缘海原断裂带新生代构造演化

海原断裂带作为青藏高原东北缘构造变形最显著断裂带之一,记录了青藏高原向北东扩展的构造信息。在详细的构造测量基础上,初步提出海原断裂带新生代以来的古构造应力场序列,反演了其新生代构造演化历史。详细构造解析表明,海原断裂带新生代以来主要经历了5个构造演化历史阶段,即始新世-中新世NWSE向构造伸展与沉积盆地发育、中新世晚期-上新世NNESSW向构造挤压与海原断裂带右行走滑活动、上新世末-早更新世NESW向构造挤压与强烈褶皱逆冲活动、晚更新世晚期以来ENEWSW向构造伸展与断陷盆地发育、全新世以来NESW向构造挤压作用与断裂带强烈左行走滑活动。变形分析表明海原断裂带现今地貌格局主要缘于上新世末-早更新世NESW向强烈逆冲活动,后期ENEWSW向构造挤压作用导致断裂走滑活动,并改造了局部地貌,主要表现为沿断裂带发育一系列第四纪小型拉分盆地。该带新生代构造演化研究,为探讨青藏高原东北缘新构造演化提供了具体构造证据。     

青藏高原古大湖与夷平面的关系及高原面形成演化过程

青藏高原经过古近纪挤压缩短和增厚地壳均衡隆升,晚新生代形成了以走滑和伸展为主的相对稳定构造环境。中新世早期与晚更新世分别发育巨型古大湖,上新世-早更新世发育很多规模较大的古湖泊,古大湖对夷平面形成演化具有重要的控制作用。中新世早期(（24.1±0.6） ~（14.5±0.5）Ma)以古大湖的湖面为侵蚀基准面,经过隆起区剥蚀夷平和长期湖相沉积,在高海拔环境下形成早期夷平面。中新世晚期-第四纪以湖面与五道梁群湖相沉积顶面为基准,在高海拔环境下继续发生剥蚀夷平和准平原化,逐步形成主夷平面或高原面。第四纪河流溯源侵蚀导致内外流水系分界线自东向西迁移,在青藏高原东部形成高山峡谷地貌。     

塔里木盆地西缘晚新生代岩石磁学特征及其对区域构造活动的响应

本文在前人研究基础上,选择中国西部塔里木盆地、南天山及西昆仑3个重要大地构造单元交界部位的塔里木盆地西北缘喀什凹陷地区,通过对乌恰黑孜苇剖面晚新生代巨厚陆相沉积物岩石磁学特征的分析,结合岩性、古水流和物源变化等的研究,揭示了晚新生代以来区域存在5次构造活动事件,它们分别发生于渐新世末—中新世初、中中新世初、晚中新世初、晚中新世末—上新世初和上新世末—更新世。其中渐新世末—中新世初和上新世末—更新世的构造活动是该区两次重大事件,并与青藏高原构造隆升有关,前者造成西昆仑和南天山强烈上升使塔里木盆地西缘喀什凹陷地区中断了与古地中海的连通进入了陆盆沉积环境演化阶段,后者进一步造成西昆仑和南天山强烈上升、帕米尔—天山之间地壳强烈缩短以及该区现今地貌格局的形成。     

四川攀西地区晚新生代构造变形历史与隆升过程初步研究

基于TM遥感图像解译和野外调研，分析了攀西地区大渡河、安宁河深切河谷地貌特征和断裂带构造变形特征，建立了安宁河断裂带晚新生代5阶段变形历史。研究表明，中新世晚期—上新世早期，安宁河断裂以挤压走滑活动为主；上新世晚期至早更新世时期，断裂以斜张走滑活动为主，活动强度较弱；早中更新世之间发生的元谋运动使昔格达组湖相地层褶皱变形；中晚更新世时期发生断陷作用，形成安宁河两堑夹—垒的构造格局；晚更新世—全新世时期又以左旋走滑活动为主。综合安宁河、大渡河河谷地貌和晚新生代地层记录和变形特征，提出了攀西高原晚新生代4阶段隆升模式：中新世早中期(12Ma之前)以缓慢隆升与区域夷平化作用为主，中新世晚期—上新世早期(12～3．4Ma)是高原快速隆升与河流强烈下切的时期，上新世晚期—早更新世(3．4～1.1Ma)为昔格达湖盆发育时期，中晚更新世—全新世(1．1Ma以来)是高原快速隆升与河谷阶地发育时期。最后指出，至上新世晚期(3．4Ma以前)，攀西高原海拔高度可能超过了3000m。     

天水盆地晚新生代构造演化——对青藏高原北东向扩展的指示意义

天水盆地是一个位于青藏高原东北缘的晚新生代盆地,西秦岭北缘断裂穿盆而过。盆地内充填了较为完整的晚新生代地层,记录了该区晚新生代以来的构造变形历史,对研究青藏高原北东向扩展的构造响应具有重要意义。本文基于详细的野外构造变形分析与测量,结合已有的年代学与沉积学研究,初步提出天水盆地晚新生代以来构造变形序列与构造应力场,重建其晚新生代构造演化历史。详细研究表明,天水盆地晚新生代以来主要经历了3期构造演化:即中新世早-晚期NW-SE向构造伸展,沉积盆地发育,并伴随碱性超基性火山岩喷发和金刚石矿床形成;中新世晚期-早、中更新世NE-SW向挤压,盆地发生构造反转,其动力学背景可能源于晚新生代青藏高原的北东向扩展,指示高原物质扩散开始显著影响到西秦岭地区;晚更新世以来受近N-S向伸展作用控制,盆地发生向东有限挤出并伴随顺时针旋转,主要由于青藏高原向北东扩展过程中,区域构造挤压应力方向发生顺时针偏转所致。     

伊洛瓦底江上游水系形成时代研究——以滇西龙川江为例

研究伊洛瓦底江水系的发育历史对理解青藏高原东南缘的生长具有重要意义,但是长期以来对其形成时代的研究一直比较薄弱。通过研究伊洛瓦底江上游支流的演化可为认识其水系的发育提供重要线索。龙川江是伊洛瓦底江的一级支流,发源于高黎贡山,流经腾冲芒棒盆地。研究表明在上新世时期芒棒盆地曾被一中型湖泊所占据,现代意义上的龙川江并不存在。龙川江在芒棒盆地内同时切割了上新世中晚期和早更新世的火山岩,腾冲地区早更新世火山岩的K-Ar年龄为0.84~1.4 Ma,说明现代龙川江的出现可能不会早于0.80 Ma,由此推测伊洛瓦底江上游水系可能也是0.80 Ma以来形成的。晚新生代以来东喜马拉雅构造结的强烈构造活动可能是其水系形成与演化的动力来源。     

藏北西部鲁玛江冬错地区新构造运动特征

从地貌（断块山地及水系特征）、活动断裂和地震标志3个方面新构造运动的表现形式,阐述了西藏鲁玛江冬错地区新构造运动活动特征,并对晚新生代以来（尤其是早更新世以来）青藏高原地形的演化趋势进行了论述。晚新生代,尤其是早更新世以来,高原南北两侧的陆内俯冲仍然继续强烈进行,主夷平面瓦解,大型断陷盆地形成,高原整体继续强烈上升。高原主体正是经历了由此开始的新构造运动,才逐渐形成目前的地貌特征。     

贵州晚新生代构造运动的主要特征

贵州晚新生代构造运动以隆升活动为主。它是贵州地壳自中—晚三叠世开始的大面积、大幅度的由海变陆,并经由中生代末燕山运动进一步强化的隆升过程的继续和发展,是形成现代贵州高原(山原)地貌的主要动力。从沉积物组成的演变、沉积物变形、剥夷面变形,以及多层状地貌的形成等方面剖析,它的发展过程可以划分出四个时期,即:①中新—上新世时期;②早更新世早期;③早更新世中晚期;④早更新世末至全新世时期。发生于早更新世中晚期的碧痕运动,是贵州地区晚新生代时期最激烈的构造运动。     

羌塘盆地新构造活动与环境地质效应

本文将羌塘盆地新生代构造运动划分为三个阶段:古近纪为剥蚀、夷平和地壳加厚阶段;中新世为强烈挤压、褶皱阶段;上新世—全新世为高原缓慢整体抬升阶段。羌塘盆地的环境变迁和地质灾害与新生代构造活动密切相关。本区的强烈隆起、半荒漠化、沙尘暴、山洪、泥石流、冰川崩塌和雪崩、地震等均受新构造活动控制。     

青藏高原东部晚新生代重大构造事件与挤出造山构造体系

文章系统梳理了青藏高原东部地区晚新生代重大构造事件的沉积记录、岩浆记录和构造变形响应,重新厘定了青藏运动或横断事件的起始时限,建立了青藏高原东部晚新生代构造演化序列与挤出造山构造体系。研究认为,发生在上新世之前的青藏运动是青藏高原东部最重要的构造作用阶段,起始于距今12~8 Ma,并持续到上新世早期,持续时间达6~8 Ma。在这个构造运动阶段,青藏高原东部地块(川滇地块、川青地块、西秦岭构造带和陇中地块等)有序地向东挤出,受到鲜水河、东昆仑、海原等WNW-ESE向大型断裂左旋走滑运动调节,构造挤出同时伴随地块内部逆冲褶皱变形,导致地壳增厚和高原东缘山脉快速崛起;构造挤出也超越了现今东缘地貌边界,向东扩展导致扬子地块盖层滑脱褶皱,形成龙泉山、大凉山等褶皱构造带。上新世出现的砾石层(东缘前陆地带的大邑砾石层、临夏盆地的积石砾石层、兰州盆地的五泉砾石层等)标志了青藏高原东部差异性构造地貌的形成。上新世晚期至早更新世时期(3.6~1.0 Ma)对应一个构造松弛阶段,青藏高原东部整体进入冰冻时期,沿其东缘发育一系列受正断层控制的南北向伸展断陷盆地,如安宁河谷地、元谋盆地、盐源盆地、滇西北盆地群等,其中加积了以昔格达组为代表的稳定河湖相沉积。发生在早、中更新世之交(距今1.0~0.6 Ma)的昆—黄运动或元谋事件使青藏高原东部地块进一步向东挤出、东缘地壳逆冲增厚和年轻山系加速隆升。晚更新世以来的构造运动称为共和运动或最新构造变动阶段,起始于距今约120 ka,青藏高原东缘构造变形系统出现重大分化,南段川滇菱形地块发生绕喜玛拉雅东构造结的顺时针旋转运动,形成川滇双弧形旋扭构造体系;而中段川青地块的挤出伴随东缘龙门山断裂带的右旋走滑运动和秦岭山系的向东挤出。在这个最新构造变动阶段,青藏高原东部下地壳通道流可能是重要的深部构造驱动因素。     

Great Barrier Island silver-gold deposits,Hauraki Province,New Zealand

The Great Barrier Island subvolcanic silver-gold deposits comprise a number of essentially east striking, quartz filled, mineralized fissures, which transect andesitic volcanics and an unconformably overlying, bedded sinter deposit of upper Tertiary to Quaternary age. Wall rock alteration is characterized by a propylitic assemblage in the least altered andesite, with argillic assemblages and silicification developed in close proximity to the veins. Some twentyfive hypogene and supergene ore minerals have been recognized, of which pyrite is the most common and finely disseminated pyrargyrite constitutes the main source of silver. The mineral assemblage is dominantly hypogene with minor supergene alteration occurring at surface exposures, and includes mainly sulfides, selenides and native metals. Fineness of electrum derived from two electron microprobe analyses is approximately 500, while total silver to gold ratio from a number of bulk chemical analyses is 30:1. Maximum depth of deposition is estimated to be in the order of 500 m and for some surface exposures 100 m. The mineralization is regarded as subvolcanic and along with other hydrothermal fissure deposits of Hauraki Province is considered to be of Pliocene-Pleistocene age, and hence is believed to be associated with the late phase extrusions and intrusions of acid magma in the volcanic belt.     

Volcanic highlands in the South Atlantic rift zone

The morphostructure of the segment between the Cardno and St. Helen transform fracture zones is studied in the rift zone of the South Atlantic slow-spreading mid-oceanic ridge (SAMOR). It was found that it is atypical of similar ridges because of the absence of an evolved rift valley. The rift zone in the transverse section is a cupola with flat slopes, whose surface is divided by volcanic massifs, plateau-like valleys, and unclear ridges and valleys. The entire morphostructure (a cupola-like regional pedestal and the listed relief forms of the second order) indicates its volcanic origin, and the rift zone in this segment is a volcanic high-land. This conclusion is supported by seismic and magnetic data. Because other (not all) SAMOR segments contain the rift valley, the results of this study indicate alternation of the tectonic and magmatic morphostructures along the entire rift zone and identification of its scales is the most important task of the morphostructural study of the SAMOR rift zone. Determination of geodynamic regimes on the basis of the results of morphostructural studies of the rift zone will arise from the solution of this task.     

西藏北部永珠地区石炭系永珠组岩石地层和古生物特征

永珠地区位于申扎古生代盆地,区内发育连续的早奥陶世—中二叠世海相沉积序列。石炭系永珠组岩石组合特征为细粒石英砂岩、页岩、粉砂岩,夹多层生物碎屑灰岩,含丰富的生物化石,主要有腕足类、双壳类、牙形刺、珊瑚、苔藓虫、菊石、三叶虫。牙形刺Gnathodusgirtyi—Gnathodustexanus为早石炭世晚期组合;腕足类Productus—Rhipidomellatibetena为早石炭世晚期组合,Choristites—Spirigerella为晚石炭世早期下部组合,Trigonatretacf.paucicostulata—Elivellabaschkirica为晚石炭世早期上部组合。Uncinunellina是典型的冷水习性腕足类,Cyathaxonia是典型的冷水习性珊瑚,表明了全球石炭纪冰期已影响到本区。确定了永珠组的时代为早石炭世晚期—晚石炭世早期,且早石炭世与晚石炭世分界线在第11层与第12层之间。     

云南沾益泥盆系龙华山组、西冲组孢子生物地层研究

云南沾益龙华山剖面泥盆系龙华山组和西冲组上段含丰富的孢子化石,按某些重要孢子类群的数量变化关系和重要分子的发生、发展和消失情况,分为下部龙华山组的RP孢子组合带和西冲组上段的VM孢子组合带。RP组合带含有早泥盆世典型分子,VM组合带含有吉维期(Givetian)晚期才在国内外出现的典型分子。结合其他门类化石研究,认为龙华山组的地质时代为泥盆纪布拉格期(Pragian)中期至埃姆斯期(Emsian)早期,西冲组上段为吉维期(Givetian)晚期,可能包括弗拉斯期(Frasnian)早期。当前研究还揭示,滇东在吉维期(Givetian)晚期Cyr-tospora cristifer已经丰富,较国内外其他地区该类孢子出现的时代(最早为弗拉斯期晚期)明显要早,据此提出了滇东可能是Cyrtospora cristifer的发源地。     

Radiolarians from Upper Jurassic (Middle Oxfordian and Upper Kimmeridgian) deposits of Yaroslavl oblast

The middle Oxfordian and late Kimmeridgian radiolarian assemblages from Upper Jurassic deposits of Yaroslavl oblast are studied for the first time. The middle Oxfordian assemblage is dominated by stauraxonic morphotypes of genera Paronaella and Pseudocrucella occurring in association with discoid forms. Nassellarian radiolarians are very rare in this assemblage of extremely low taxonomic diversity, which is lacking spheroidal morphotypes. The late Kimmeridgian assemblage is more diverse in morphological and taxonomic aspects. It includes spheroidal forms, those of the family Pantanelliidae Pessagno inclusive, and more frequent nassellarian species, but stauraxonic radiolarians are less abundant in its composition. This assemblage is comparable to a considerable extent with the Kimmeridgian radiolarians from Moscow oblast, being of the South Boreal type according to its composition.     

安徽南部地区浅变质地层孢子化石的发现及其地质意义

皖南地区广泛分布着溪口群浅变质岩地层,尽管对其进行了大量的研究,但关于地层时代的归属问题仍存在很大争议。在皖南溪口群采集的43件样品中发现较丰富的陆生植物孢子(Spoers)20余属,50余种,其中具有地层意义的孢子有15属25种。这些孢子组合可与中国华南、西南、西北地区及新疆塔里木盆地巴楚地区晚泥盆世晚期孢子带相比较,也可与西欧、东欧和北美地区晚泥盆世法门阶(Famennian)孢子带对比,其时代为晚泥盆世晚期,相当于西欧晚盆世晚期法门阶(Famennian)。     

Pleistocene deposits at Stoke Goldington,in the valley of the Great Ouse,UK

At Stoke Goldington in the valley of the Great Ouse in Buckinghamshire a river terrace at a height of about 7 m above the floodplain is underlain by fluvial sediments representing climatic fluctuations in the late Middle Pleistocene. Near the base of the succession, at a level only 1 m above the modern floodplain, a fossil assemblage, including pollen, plant macrofossils, molluscs, insects and ostracods, provides evidence for the local development of herb-rich grassland under temperate climatic conditions. The fossil record, amino-acid racemisation ratios and uranium disequilibrium dating all suggest deposition of this material during Oxygen Isotope Stage 7. The deposits containing the temperate assemblage are immediately overlain by typical cold-climate gravels of the Great Ouse. These have been subjected to a later cut-and-fill episode, with the fill accumulating in cool climatic conditions. The cut-and-fill episode was succeeded by aggradation, forming the overlying terrace surface. Amino-acid racemisation ratios indicate that the fill was emplaced, and the terrace surface created, during or after Oxygen Isotope Stage 5. © 1996 John Wiley & Sons, Ltd.     

西藏定结高喜马拉雅石榴辉石岩-镁铁质麻粒岩的岩石特征及其地质意义

在高喜马拉雅带的定日县曲当—扎乡一带出露的高喜马拉雅结晶岩系中, 发现了高压变质的石榴辉石岩及其降压变质的镁铁质麻粒岩组合, 早期高压条件下形成的石榴辉石岩矿物组合为Grt+Cpx (富铝) +Ru+Q, 斜长石已完全消失, 形成温度为845~896℃, 压力大于1.2GPa, 已达到榴辉岩相的压力条件.中期的麻粒岩相组合为Opx+Pl±Cpx±Ga, 其中Opx、Cpx和Pl为石榴石的后成合晶, 形成温度为993~776℃, 压力为0.90~1.21GPa, 为中压麻粒岩相产物, 晚期矿物仅见普通角闪石、斜长石和石英, 是角闪岩相退变质的产物, 表明HHC经历了降压升温-降压降温的快速抬升过程, 证明其抬升作用与地幔热源的参与有关.      

新疆拜城阿合组、阳霞组及克孜勒努尔组的孢粉组合

拜城地区中生代陆相地层非常发育.作者在阿合组、阳霞组和克孜勒努尔组中获得了不少的孢粉化石,共鉴定有58属,93种,其中2新种和2新联合种.     

Agglutinated foraminifera from the Campanian-Maastrichtian Kiseiba Formation in the Kurkur area,Egypt

The upper Campanian to upper Maastrichtian sedimentary sequence of the Kiseiba Formation in south Western Desert is sampled and described in two surface sections (Sinn El Kaddab and Wadi Abu Siyal). Forty-four agglutinated foraminiferal species are identified from 42 samples in the studied succession. The benthic foraminiferal assemblages are dominated by agglutinated foraminifera which comprise more than 90% of the assemblage. The agglutinated foraminifera are subdivided into five morphogroups (A, B, C, D, E) according to shell architecture, integrated with the supposed microhabitat and feeding strategy. The foraminiferal assemblage is assigned to mixohaline shallow water environments. These assemblages with Ammoastuta megacribrostomoides and Ammotium bartheli suggest lagoonal environments with considerably reduced salinity in warm climates and high runoff for the late Campanian-Maastrichtian interval.