青藏高原的隆起与海洋锶同位素组成的演化

近年来,随着构造隆升驱动气候变化假说的提出,青藏高原的隆起受到越来越多的关注,并将之与大陆化学风化速率及海洋锶同位素的演化紧密联系。围绕青藏高原的隆升及其环境与气候效应,对海洋锶同位素组成的演化特征及其影响因素的较为全面而详细的论述表明:将青藏高原的隆升与全球气候变化、大陆化学风化速率及海洋锶同位素组成的演化相联系,也许是解决目前关于海洋锶同位素组成的演化及其物源问题的重要手段,根据海洋锶同位素的演化历史来研究全球气候变化规律及青藏高原的构造演化历史将是本研究领域的重点。     

近50 年华南地区极端强降水频次的时空变化特征

利用华南地区110 个台站1961—2008 年逐日降水资料,采用百分位法定义各站极端强降水事件的阈值,运用线性回归、M-K 突变检验、正交函数分解(EOF)、旋转经验正交函数分解(REOF)等方法,对华南地区年极端强降水频次的时空变化特征进行分析。结果表明:在空间分布上,年极端强降水频次在华南中部较大、广东沿海和广西西部内陆较小;华南极端强降水频次有3 个主要的空间异常模态,一致性异常特征是华南极端强降水频次分布的最主要空间模态,而东、西反向和南、北反向变化模态也是比较重要的异常模态。在时间分布上,华南的极端强降水事件主要发生在夏半年,夏半年极端强降水频次占全年总频次的83.7%;1960 年代和1980 年代极端强降水频次较少,从1980 年代中后期起,极端强降水频次有由少变多的趋势。华南区域各站极端强降水频次气候倾向率不一致,除中部呈减少趋势外,其余大部呈上升趋势,华南区域各站极端强降水频次的平均序列也呈上升趋势,但上升趋势不显著。华南极端强降水频次从区域变化特征上可分为6 个主要区域,分别具有不同的年际变化趋势,其中有3 个区域的代表站先后发生了显著增多的突变现象。      

鄂尔多斯盆地中奥陶统马五6亚段高频旋回层序研究:论海平面升降与横山凸起沉积分异效应*

高频旋回分析有利于揭示浅水碳酸盐岩台地海平面升降、沉积物响应、古地理单元演化及对盆地内沉积分异影响等诸多沉积学信息。依据鄂尔多斯盆地横山地区丰富的钻井取心资料,通过岩石类型、典型五级旋回结构等分析,对中奥陶统马家沟组马五₆亚段开展了高频旋回研究。研究表明: (1)基于研究区内马五₆亚段碳酸盐岩与蒸发岩共生组合的9种岩石类型,识别出5种典型T-R单旋回,其中旋回Ⅰ、Ⅱ、Ⅲ为云质潟湖—颗粒滩—灰泥丘沉积,Ⅳ、Ⅴ为膏盐质潟湖沉积,并以5种单旋回为基本单元搭建骨架井五级高频旋回结构剖面;(2)依据五级高频旋回结构剖面建立的Fischer图解,认为马五₆亚段处于三级旋回晚期,内部发育“2个”四级旋回,具有初次海退—快速海侵—再次海退的相对海平面变化趋势;(3)结合五级旋回厚度统计,认为第1套四级旋回沉积期处于隆拗格局发育阶段,该时期横山凸起作为水下高地,对东西两侧海水封隔明显;至第2套四级旋回沉积阶段,填平补齐作用导致横山凸起影响减弱,海水循环得到改善,凸起东西两侧盐度明显下降。以马五₆亚段为例的高频旋回研究,在横山地区马五₆亚段地层学、沉积学研究中取得了较好的效果,以期在鄂尔多斯盆地马家沟组未来研究中得到进一步推广和实践。     

不同构造环境下的壳─幔过渡带结构

位于中国西北部的天山造山带与准噶尔盆地是典型的盆岭构造。通过对横跨天山造山带与准噶尔盆地的沙雅-布尔津地学断面地震宽角反射、折射资料进行小波分析,获得了天山造山带与准噶尔盆地壳-幔过渡带的详细结构。结果表明,天山造山带的壳-幔间是以多个薄层过渡的。这些薄层的层厚度2～3km不等,层速度高低相间,总厚度约20km,平均速度较低,接近塔里木盆地下地壳的速度。塔里木盆地北缘与准噶尔盆地的壳-幔间不具有这种特点,其壳-幔间主要表现为一级间断面。而位于中国东北部的间阳-海城-东沟深地震测深剖面所揭示的辽东台隆-辽河盆地-燕山台褶带壳-幔过渡带的结构似乎具有完全相反的特征：辽河盆地的壳-幔过渡带比较复杂,它由数个薄层叠合而成,总厚度达15km;辽东台隆与燕山台褶带壳-幔过渡带结构十分简单,皆以一级间断面过渡为主。研究认为,造成二者差异的主要原因是它们所处的构造环境不同：前者为挤压环境,而后者为伸展环境。在挤压环境下,复杂的壳-幔过渡带形成于造山带的下面;而在伸展环境下,复杂的壳-幔过渡带形成于盆地的下面。壳-幔过渡的复杂程度与构造活动性相联系,在一定程度上反映了岩石圈目前的构造活动水平。     

从地形变资料探讨丽江7.0级地震的前兆特征

讨论了地震孕育发生的物理机制是“拉疏隆起－压缩凹陷”模式的形成机理及其特征;根据这一理性认识,应用丽江７．０级地震之前滇西地区的地形变资料,较确切出得出了本区有强震发生,并且可以认为孕震体是在丽江至玉龙雪山东麓地区;根据发震前夕所观测到孕震体的“拉疏隆起－压缩凹陷”的区域大小与幅度值及岩层的弹性应变,可近似计算震级的大小。     

Palaeokarst and rauhwacke development,mountain uplift and subaerial sliding of tectonic sheets (northern Sierra de los Filabres,Betic Cordilleras,Spain)

The rauhwackes near Serón in the northern Sierra de los Filabres (S Spain), previously considered as true tectonic breccias, are reinterpreted on the basis of sedimentological, geomorphological and geometrical evidence as subaerial or nearly subaerial sedimentary deposits. Channel fills, parallel lamination, cross-lamination, graded bedding, sedimentary clastic dykes and other sedimentary structures and features occur in the rauhwacke body. These sedimentary rocks correspond to continental deposits of alluvial and karstic origin deposited over a karstified erosional surface of Nevado–Filabride marbles. Although no fossils have been found in the rauhwackes, a Tortonian age for these rocks is suggested on the basis of structural arguments and lithostratigraphic data from the nearby Almanzora basin. The rauhwackes were buried by slabs of Alpujarride rocks that gravitationally slid over them during the uplifting of the Sierra de los Filabres.     

A BRIEF REVIEW OF SEVERAL MODELS OF TOPOGRAPHIC EVOLUTION

With steady development of mathematical-physical models and computer technology, numerous methods of topographic simulation have emerged during the past decades. A major challenge in the modeling is how to accurately and efficiently describe processes of surface erosion at different spatial scales. This review focuses on the physical processes controlling surface erosion, including river erosion and hillslope erosion. Four popular models of topographic simulation (CASCADE, CHILD, FastScape and DAC models)and their applications are presented. Although these models have become more sophisticated in recent years, there are still some issues unsolved regarding the basics of the physical erosion processes. For example, some factors have not been taken into account, such as the impacts of changes in grain size and sediment budget during transportation on river erosion and the measurements of the rock erodibilities for various lithologies. Moreover, there is no topographic index that can be used to evaluate the modeling results. Therefore, it would be helpful to combine the models of topographic simulation with other numerical models, e.g. the low-temperature thermochronometric data modeling, to provide better constraints on the terrain modeling.     

青藏高原东缘的地壳流及动力过程

黏滞性地壳流对地壳及上地幔变形作用及动力机制,是大陆新生代造山带的一个重要研究内容.青藏高原中下地壳存在部分熔融或含水物质的黏滞性流体,已为一系列地球物理及岩石学研究所证实.为研究青藏高原东缘地壳流的动力作用,本文用密集的被动源宽频带地震台的观测数据,反演了地壳上地幔精细速度结构和泊松比.研究表明,川西及滇西北高原的中地壳内普遍存在低速层,而高泊松比的地壳只分布在川西北地区.位于中地壳的黏滞性地壳流从青藏高原腹地羌塘高原流出,自北西向南东流入青藏高原东缘.这些黏滞性地壳流带动了上地壳块体水平移动,当它们受到刚强的四川盆地及华南地块阻挡时将发生分层作用,地壳流将分为二或更多分支不同方向的分流,向上的一支地壳流将对上地壳产生挤压,引起地面隆升,向下的一支地壳流将使莫霍面下沉加厚下地壳·黏滞性地壳流的运动在地壳中产生应变破裂发生强烈地震活动,地震的空间分布与震源机制也受到地壳流动力作用控制.     

THE RESPONSE OF FLUVIAL GEOMORPHOLOGIC CHARACTERISTICS OF THE FUJIANG DRAINGE BASIN TO ACTIVITY OF THE HUYA FAULT ZONE

The Huya Fault, located in the steep topographic boundary of the Minshan Mountains in the eastern margin of the Tibetan plateau, has documented many major earthquakes such as the 1630(M=6 3/4), 1973 Huanglong(M_S=6.5) and the 1976 Songpan-Pingwu earthquake swarm(M_S=7.2, 6.7, 7.2). While its activity remains unclear because of lacking Quaternary sediments. In the past few decades, there have been significant advances in understanding the relationship between bedrock channel landscapes and active tectonics, indicating that the bedrock fluvial features can well record the tectonic activity. Many studies reveal that tectonism is the primary factor of landscape evolution in tectonically active regions, and the erosional landscapes can be used to reveal tectonic signals on timescales of 10³~10⁶ years. The Huya Fault crosses the Fujiang drainage basin, making it suitable for the study of bedrock rivers and tectonic uplift in the eastern margin of Minshan. In this study, we calculate the geomorphologic indeices(hillslope, local relief, normalized steepness indices and hypsometric integral) on the basis of the digital elevation model(DEM) SRTM-1. For better understanding the tectonic activity along this fault, we derive some small catchments on the two sides of the Huya fault to analyze the differences of average steepness indices and hypsometric integral. Combining with field observations, lithology, precipitation and modern erosion rates, this study suggests that tectonic activity is the controlling factor of geomorphology in the eastern margin of the Minshan Mountains. We use focal mechanism solutions, GPS data and geomorphic evidence to explore the relationship between the geomorphologic indices of the Fujiang drainage and activity characteristics of the Huya fault. Our results suggest that:(1) The Fujiang drainage basin is in a steady state. The characteristics of the knickpoints indicate that they are mainly controlled by the locally resistant substrate. (2) The suggested value of the geomorphologic index on the west side of the Huya fault is generally larger than on the east side, showing differential tectonic uplift rates across the fault. (3) The difference of the geomorphologic index of the small catchments on both sides of the Huya fault is gradually increasing from north to south along this fault, in accordance with that the north and south segments of the Huya fault are dominated by strike-and reverse-slip, respectively.     

海岸带海水入侵的研究进展

海岸带海水入侵问题一直是国际社会共同关注的焦点。海水入侵的影响因素很多,其中人为因素占较大比重。海水入侵的方式因地而异,孔隙水含水层海水入侵较为严重。在研究中突变界面模型和过渡带模型各有其实用性。其中过渡带模型更具有适用价值,是今后主要的研究方向。本文概述了海岸带海水入侵问题现状,系统地总结了海岸带海水入侵模型近40多年来的研究成果,分析了研究中存在的困难,为进一步的研究打下基础。