华北-扬子板块碰撞结构的识别:来自南黄海海域的证据

华北-扬子板块碰撞是中国东部中生代最重要的地质事件之一,碰撞形成了世界最大的超高压变质带秦岭-大别-苏鲁造山带。在苏鲁造山带向海域延伸部分,一直缺乏相关地球物理资料来约束碰撞造山带的深部特征。本文总结了华北-扬子板块碰撞的经典模型,根据南黄海海域最新二维地震反射资料和前人的研究成果,认为在造山带南缘南黄海盆地中,扬子板块上、下地壳发生拆离,形成类似"鳄鱼嘴式"形态,华北板块向南楔入到扬子板块之中。在区域重磁异常图中,千里岩隆起带与苏鲁造山带具有相似的重磁异常分布,认为千里岩隆起带为华北-扬子碰撞造山带在海域上的延伸;在南黄海盆地北缘二维地震剖面中,千里岩隆起与南黄海盆地具有完全不同的地震反射特征,南黄海盆地发育完整地层层序,而千里岩隆起内部反射杂乱,变形强烈。在南黄海盆地自西向东三条南北向地震剖面中,南黄海盆地与千里岩隆起带边界反射均具有南倾特征,表明扬子板块物质置于造山带之上;南黄海盆地北部烟台坳陷发育中侏罗统,约束华北-扬子碰撞所导致的挤压活动主要发生于晚三叠世。在千里岩隆起内部反射特征整体上具有背形形态,具有向北逆冲挤压特征,千里岩隆起内反射断续自南黄海盆地基底之下延伸至造山带近地表位置,形态类似于变质核杂岩从深部拆离到地表;千里岩隆起深部,在10 s深度附近可识别一系列近水平反射,具有莫霍面反射特征,莫霍面反射延伸至南黄海盆地北缘消失,推测千里岩隆起之下为华北板块地壳,而华北-扬子板块碰撞过程导致南黄海盆地之下莫霍面反射缺失。多方面的证据支持南黄海海域内扬子板块的"鳄鱼嘴式"地壳形态,以及华北板块地壳向南楔入到扬子板块地壳中。     

南黄海盆地盆山耦合作用与地质演化

对南黄海千里岩隆起区榴辉岩、仰口榴辉岩和海阳所榴辉岩的地球化学特征进行对比研究得出,千里岩榴辉岩原岩可能为古秦岭洋洋壳,海阳所榴辉岩原岩可能为扬子板块北缘的基性下地壳;而仰口榴辉岩原岩可能为受俯冲流体作用而发生分异的岩石类型。依据现有地球物理资料研究,对南黄海盆地的构造特征和构造样式进行了探究,进而阐述了南黄海盆山耦合作用的地质演化。     

青岛仰口榴辉岩及其围岩的岩石地球化学特征和成因机制

青岛仰口地区保存了完整的从变辉长岩到榴辉岩的超高压变质岩石组合。地球化学特征表明,榴辉岩、变辉长岩和片麻岩属钙碱性系列,超基性岩属拉斑系列;CIPW标准矿物计算显示榴辉岩和变辉长岩中长石以钠长石为主,超基性岩主要标准矿物为橄榄石、紫苏辉石和锥辉石,片麻岩中出现标准矿物刚玉;榴辉岩、变辉长岩和片麻岩富集大离子亲石元素,亏损高场强元素,超基性岩的微量元素相对于N-MORB亏损;榴辉岩和变辉长岩轻稀土明显富集,配分型式与岛弧玄武岩相似,片麻岩具明显的Eu的负异常,配分型式与后造山A型花岗岩相似,超基性岩稀土总量较球粒陨石偏高,具强烈的Ce的负异常。微量元素比值及地球化学图解表明榴辉岩与变辉长岩的原岩为辉长岩,片麻岩的原岩为造山后A型花岗岩,原岩的岩浆源区位于下地壳,超基性岩的岩浆源区位于上地幔,原岩均形成于岛弧环境。     

中国东部苏鲁造山带的印支期俯冲极性及其造山过程

中国东部的苏鲁造山带印支期先后经历了大洋消减俯冲、大陆碰撞、陆壳深俯冲、陆内造山等复杂过程。综合苏鲁造山带的构造地质学、岩石学、岩相古地理学、年代学进展,发现以下事实用传统的华南向华北俯冲难以解释:(1)徐淮地区形成了明显的朝北西拓展的逆冲构造变形,此外,苏鲁造山带中还存在大量的北西向逆冲推覆构造;(2)苏鲁造山带中出露的白垩纪花岗岩中来自古元古代的继承锆石,以及Sr、Nd、Pb同位素示踪结果都显示与华北地块南缘地质体更为相似;(3)苏鲁造山带北侧的胶莱盆地以及胶北隆起缺乏晚古生代到中生代的弧后火山岩证据;(4)华北南缘三叠纪时期的古地理环境更接近被动大陆边缘。基于这些事实,本文认为,晚古生代-早三叠世早期苏鲁段的商丹洋可能向南东俯冲,不同于秦岭-大别段的商丹洋向北俯冲,消减到秦岭-大别微陆块苏鲁段之下,发生华北地块与该微陆块的拼合,华北地块整体向南东楔入秦岭-大别微陆块,导致大别-苏鲁超高压岩石垂向折返剥露;中三叠世-晚三叠世,勉略洋自东向西的剪刀式闭合,华南地块向北秦岭-大别微陆块俯冲拼合,并逐渐将华南地块与华北地块之间的秦岭-大别微陆块向西、向北侧向挤出,到了中生代华北地块持续向南东俯冲并楔入华南地块,将苏鲁-大别造山带沿郯庐断裂错断并最终形成该区总体构造格局。     

中朝-扬子板块碰撞结合带东部边界及海域延伸

总结了中朝-扬子板块碰撞结合带的边界划分的各类观点,分析了存在争议的原因以及研究的不足之处。通过对苏鲁造山带及黄海海区的重磁资料、周缘断裂特征、典型地震剖面等最新研究成果的收集整理,研究认为华北扬子板块的碰撞结合带应为苏鲁超高压变质带-千里岩隆起,结合带在陆地的北边界可能为五莲-青岛-牟平断裂;南边界为连云港-黄梅断裂;千里岩南缘断裂在印支期是一条千里岩超高压变质带折返的边界断裂,白垩纪以来反转为一条控制南黄海北部坳陷的大型边界断裂,并指出加强黄海海域重磁震资料的精细研究及海陆结合带的构造关系研究是进一步研究重点。     

南黄海千里岩岛榴辉岩的矿物化学及成因探讨

南黄海千里岩岛地处中国华南板块与华北板块缝合线位置,其基底由强烈韧性变形的构造片麻岩组成,并出露具重要大地构造标型意义的超高压榴辉岩类岩石。本文通过对南黄海千里岩岛榴辉岩中主要造岩矿物石榴石的矿物化学研究,探讨了榴辉岩的成因。研究表明,千里岩地区高压变质岩是由于华北与华南两大陆块拼合时,处于其间的岛弧拉斑玄武岩沿碰撞带下插到华北陆块之下,从而使千里岩地区发生高压变质作用,形成了榴辉岩和片麻岩等,后期的构造折返使其上升到地壳上部。     

鲁苏榴辉岩的地球化学

以微量元素、稀土元素、Ｓｒ和Ｎｄ同位素变异特征为依据，确定鲁苏榴辉岩为多成因、多来源和多阶段，指出主要是在印支期扬子陆块与华北陆块碰撞造山作用过程中，挤入的上地幔碎片以及不同原岩类型的壳内高压变质岩碎块。燕山晚期的区域构造热事件使得某些榴辉岩的同位素体系再平衡。     

黄海海域盆地构造演化特征与中、古生界油气勘探前景探讨

黄海海域跨越扬子和华北两个板块构造单元 ,发育了北黄海和南黄海两个盆地构造单元。扬子和华北板块在这里沿五连—荣城—朝鲜的临津江断裂构造带于晚三叠至早中侏罗世碰撞缝合 ,形成了与秦岭 -大别超高压变质造山带成因意义完全相同的苏北张八岭 -朝鲜临津江超高压变质造山带。北黄海盆地就位于该变质造山带北侧的华北板块上 ,而南黄海盆地则位于该变质带南侧的扬子板块上。地震剖面和北朝鲜钻井资料证实北黄海盆地是晚中生代早期 ( J3 —K1)和新生代的叠合盆地 ,盆地基底为晚印支—早燕山期碰撞花岗岩和前寒武纪变质岩 ,局部可能残留有古…     

南黄海千里岩隆起区构造属性及地质演化

千里岩隆起位于南黄海的最北部,是一个长期裸露的基底隆起区.通过对南黄海重力异常的区域分析和异常分区以及与苏鲁隆起的地质对比研究,认为两者具有同一地质成因,前者是后者的东向延伸,皆成因于印支期华北板块和与扬子板块的碰撞.早白垩世,后期太平洋板块西向俯冲使千里岩断裂带反转变化为同生正断层.     

中国东部-朝鲜半岛中生代板块结合带划分——对嵌入模式的新认识

中国东部中朝与华南(或扬子)板块在晚二叠世—三叠纪期间碰撞形成大别-苏鲁超高压造山带,这一碰撞结合带过黄海在朝鲜半岛的延伸方式一直是国内外学者关注的焦点。通过梳理近年关于这一板块边界划分问题的最新研究成果,发现多数成果趋向于认为京畿地块及其以南地区仍属中朝板块,苏鲁造山带并未延伸至整个朝鲜半岛。结合郯庐断裂带中生代活动特征及下扬子区弧形构造的成因分析,支持板块碰撞的嵌入模式,并对嵌入模式的边界带进行了新的修订,即朝鲜半岛大多归属中朝板块,仅京畿地块西南局部归属扬子板块东延。郯庐断裂南段与朝鲜半岛Jooggaryeong断裂在黄海海域的延伸分别为下扬子向中朝板块嵌入的转换边界,两者具有相似的演化特征。印支期这两条断裂为碰撞的转换断裂,燕山期又发生了走滑活动,并向北延伸分叉。     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level.     

Flow Cytometric Analysis of Coastal Lagoon Bacterioplankton and Picophytoplankton: Fixation and Storage Effects

The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics.