热带对流层上空东风带扰动影响西太平洋副热带高压的个例分析

利用NCEP/NCAR1000—10hPa2.5°×2.5°日平均和每日4次再分析资料,分析了2003年6月19—25日热带对流层上空东风带扰动对西太平洋副热带高压东西向进退的影响。结果表明:热带对流层上空东风带扰动从对流层中低层伸展到50hPa高度附近,在200hPa上表现最为明显,在热力场上表现出“上暖强,下冷弱”的垂直分布特征。当西太平洋副热带高压南/北侧的东/西风带上的扰动在相向运动中抵达同一经度上时,对应于西太平洋副热带高压的异常东退。垂直涡度方程的诊断分析表明:在东风带扰动附近,涡度倾向效应贯穿于对流层整层到50hPa高度上,在200hPa高度附近表现最显著,当高层东风带扰动东/西侧的负/正变涡增强时,当东/西风带扰动在相向移动过程中,它们涡度倾向正值区在130°E南北打通时,西太平洋副热带高压出现突然东撤。涡度方程分析还表明,对于涡度倾向变化的贡献中,水平涡度平流的贡献最大、β效应的贡献最小;当东风带扰动附近的水平涡度平流和β效应增强时、且由β效应所引起的东/西风带扰动中的南、北风分量在130°E附近南北同相迭加出现“正压发展”时,有显著的正涡度增长,对应于西太平洋副热带高压的东撤。     

干旱气候背景下塔尔湖暴雨形成机理诊断分析

利用常规气象资料和自动站资料,对2009年8月18日发生在塔尔湖地区1次暴雨过程进行分析,结果表明：⑴整个前汛期副高位置偏西,是造成巴彦淖尔市干旱的直接原因。⑵副高东退,东高西低形势建立,是塔尔湖暴雨形成的必要条件。⑶500hPa短波槽前正涡度区与700hPa暖切变区、地面暖锋切变区在阴山山脉南麓罕乌拉沟喇叭口地形上空垂直叠置,是产生塔尔湖暴雨的动力抬升条件,也是其形成的触发机制。⑷700hPa贝湖冷涡维持,西南暖涡北抬,两涡在阴山南北相遇的辐合流场建立,为塔尔湖暴雨提供了水汽和冷空气条件,也是干旱年份巴彦淖尔市暴雨预报的重要着眼点。     

亚洲大陆逃逸构造与现今中国地震活动

2008年5月12日汶川地震让中国地学界强烈感受到深入研究地震地质与构造变形的重要性和肩负防震减灾巨大的社会责任。本文作者从构造地质学家的角度对中国大陆地震分布、成因规律以及发展趋势做了一些讨论。按地震分布,中国大陆可以粗分为两个区域,其交界是一条过渡带。该过渡带的东界是郯庐断裂及其和海南岛的连线,西界是齐齐哈尔—北京—邯郸—郑州—宜昌—贵阳—(越南)河内连成的线,后者其实就是松辽盆地的西界(大兴安岭的东界、太行山的东界、大娄山的东界）。我们不妨将上述两线所夹过渡带称之为“地震区分界线”。分界线以西的广大地区,活动断裂、活动褶皱、活动盆地都与印度板块楔入欧亚大陆造成的青藏高原隆升、快速侧向扩展、亚洲大陆逃逸构造活动有关。流变性较好的造山带(如青藏高原和天山)和流变性较差的古老地块(如塔里木、准噶尔、阿拉善、鄂尔多斯、四川盆地等)在其边界强烈对抗,形成强震。地震区分界线以东的中国沿海地区受太平洋和菲律宾海板块运动的影响也会发生地震,但其强度和频度与该线以西的青藏高原周边、天山、鄂尔多斯地块周缘以及张家口渤海断裂带上地震低得多。由太平洋板块在日本海沟向西深俯冲形成的地震在中国仅分布在吉林省珲春—汪清一带,这些深源地震对地面工程建筑破坏性不大。处于欧亚、菲律宾海和南海3个板块的交汇部位的我国台湾地震不断。受我国台湾地震的影响,闽粤沿海NW和NE向断裂往往被激活,形成地震。总之,虽然中国大陆的现代地震受太平洋、欧亚、印度和菲律宾海四大板块联合作用控制,但最主要、最直接、影响最大的还是印度板块楔入欧亚大陆造成的青藏高原隆升、快速侧向扩展和大陆逃逸。因此,对中国的地震研究不能仅局限于某区域或某条断裂,而应把整个亚洲大陆逃逸构造作为整体的、统一的“一盘棋”看待。     

柴达木北缘超高压变质带形成与折返的时限及机制

位于青藏高原北缘的祁连山加里东造山带的形成是阿拉善板块、祁连微板块及柴达木一东昆仑板块在加里东期间汇聚和碰撞的结果。祁连微板块和柴达木一东昆仑板块之间的柴(达木)北缘超高压变质带形成于495～440Ma,是继南祁连洋壳向北俯冲于祁连微板块下形成增生的柴北缘火山岛弧带之后,陆壳深俯冲的产物。柴北缘超高压变质带是在祁连微板块及柴达木一东昆仑板块之间的“正向陆内俯冲”向“斜向陆内俯冲”转化过程中“斜向挤出”机制下折返的,开始折返年龄为470～460Ma,最后的折返时间为400～406Ma。折返构造很好地保存在超高压变质岩石中,并且记录了广泛的退变质作用。     

造山带挤出构造

挤出构造模式已经从二维变形进入三维变形研究，在喜马拉雅造山带，高喜马拉雅结晶地体沿北倾的主中央逆冲断层和北倾 的绒布寺正断层，表现为相对刚性体之间的韧性体的楔状挤出。非连续介质大变形有限元数值模拟结果为这一模式提供了力学依据。在前人工作的基础上，提出了东阿尔卑斯三维管状挤出模式，将上部脆性层划分出北部左行平移带，南部右行平移带和中部挤出楔，中部韧性层在南阿尔卑斯和欧洲前陆碰撞过程中，既有垂向挤出，也有侧向挤出，在平行缩短方向的剖面上，由箱状背形隆起演化成逆－逆断层组合的楔状挤出，形成三角断面的管状，在垂直缩短方向的剖面上，中部韧性层呈不均匀流动，形成管状层流－韧性层中心为纯剪切，上部和侧部为简单剪切，在陕甘川邻接区，由于祁连山－北秦岭加里东喧向南的推挤和川西前陆的刚性阻挡，造成西秦岭和东松潘－甘孜复合造山体的三维滑脱挤出，以北西西向玛曲－略阳滑脱逆冲断裂和北东向青川一茂县滑脱逆冲断裂为界，将陕甘川邻接区的三维滑脱挤出复合造山体划分为西秦岭滑脱挤出带，摩天岭0若尔盖滑脱挤出楔和龙门山滑脱挤出逆冲椎覆带，以近南北向岷江滑脱逆冲断裂为界将滑脱挤出楔进一步划分成摩天岭滑脱挤出体和苦尔盖滑脱挤出体，除了不同构造单元的不均匀隆升外，摩天岭还表现出向西的侧向挤出。     

Late Cenozoic faulting in SW Bulgaria: Fault geometry,kinematics and driving stress regimes. Implications for late orogenic processes in the Hellenic hinterland

We investigate the geometry and kinematics of the faults exposed in basement rocks along the Strouma River in SW Bulgaria as well as the sequence of faulting events in order to place constraints on the Cenozoic kinematic evolution of this structurally complex domain. In order to decipher the successive stress fields that prevailed during the tectonic history, we additionally carried out an analysis of mesoscale striated faults in terms of paleostress with a novel approach. This approach is based on the P–T axes distribution of the fault-slip data, and separates the fault-slip data into different groups which are characterized by kinematic compatibility, i.e., their P and T axes have similar orientations. From these fault groups, stress tensors are resolved and in case these stress tensors define similar stress regimes (i.e., the orientations of the stress axes and the stress shape ratios are similar) then the fault groups are further unified. The merged fault groups after being filled out with those fault-slip data that have not been incorporated into the above described grouping, but which present similar geometric and kinematic features are used for defining the final stress regimes. In addition, the sequence of faulting events was constrained by available tectonostratigraphic data.Five faulting events named D1, D2, D3, D4 and D5 are distinguished since the Late Oligocene. D1 is a pure compression stress regime with σ₁ stress axis trending NNE-SSW that mainly activated the WNW-ESE to ENE-WSW faults as reverse to oblique reverse and the NNW-SSE striking as right-lateral oblique contractional faults during the Latest Oligocene-Earliest Miocene. D2 is a strike-slip − transpression stress regime with σ₁ stress axis trending NNE-SSW that mainly activated the NNW-SSE to N-S striking as right-lateral strike-slip faults and the ENE-WSW striking faults as left-lateral strike-slip ones during the Early-Middle Miocene. D3 extensional event is associated with a NW-SE to WNW-ESE extension causing the activation of mainly low-angle normal faults of NE-SW strike and NNE-SSW to NNW-SSE striking high-angle normal faults. D4 is an extensional event dated from Late Miocene to Late Pliocene. It activated NNW-SSE to NW-SE faults as normal faults and E-W to WNW-ESE faults as right-lateral oblique extensional faults. The latest D5 event is an N-S extensional stress regime that dominates the wider area of SW Bulgaria in Quaternary times. It mainly activated faults that generally strike E-W (ENE-WSW and WNW-ESE) normal faults, along which fault-bounded basins developed. The D1 and D2 events are interpreted as two progressive stages of transpressional tectonics related to the late stages of collision between Apulia and Eurasia plates. These processes gave rise to the lateral extrusion of the Rhodope and Balkan regions toward the SE along the Strouma Lineament. The D3 event is attributed to the latest stage of this collision, and represents the relaxation of the overthickened crust along the direction of the lateral extrusion. The D4 and D5 events are interpreted as post-orogenic extensional events related to the retreat of the Hellenic subduction zone since the Late Miocene and to the widespread back-arc Aegean extension still prevailing today.     

四川盆地西北部新生代构造变形模式讨论——对认识青藏高原东北缘新生代变形机制的意义

综合造山带内的构造热年代学及盆地内部进行的磷灰石裂变径迹研究,提出了四川盆地西北部的三个背斜（潼梓关背斜、九龙山背斜和南阳坝背斜）主要是新生代构造变形的产物。野外观察发现汉中盆地是一个第四纪的拉分盆地,其主控断层具左行走滑性质。新生代青藏高原东缘大型地块向东挤出,遭遇强硬的四川克拉通阻挡之后,沿着龙门山形成了一个右行的走滑挤压带,并且影响到邻近的四川盆地,形成北东向背斜。这期构造变形往北延伸进入米仓山,形成具有逆冲性质的北东向断层。四川盆地北面也存在向东的挤出作用,这和汉中盆地主控断层的左行走滑性质是匹配的。四川盆地北面的地块挤出影响了米仓山前缘的四川盆地,由于龙门山和米仓山构造变形的叠加,使得最东面的南阳坝背斜相对于其它两个背斜在褶皱轴上发生了偏转。     

再论“大陆深俯冲和折返动力学”: 来自中国大陆科学群钻及苏鲁超高压变质带的制约

通过CCSD-MH、卫星孔的岩性-构造剖面和苏鲁造山带中榴辉岩-超镁铁质岩的产出、深俯冲/折返过程的岩石的塑性流变特征和变形序次的分析、俯冲-折返过程中流体作用及变质化学地球动力学对流变学行为的制约,以及韧性剪切作用形成的折返年代学时限,提出苏鲁超高压变质地体为面型深俯冲/折返杂岩带组成的穹形挤出推覆岩片、叠置在扬子陆块之上; 根据岩石变形微构造及组构的分析,重塑超高压变质岩石深俯冲阶段、折返早期、折返主期和折返后期的塑性流变;提出深俯冲的物质沿板块汇聚边界的多层隧道呈多重/分片样式“挤出”的折返模式,并认为在折返初期开始（230~220Ma）和折返主期（220~200Ma）形成的透入性韧性剪切是俯冲岩片挤出的重要机制;提出郯庐走滑断裂的形成对苏鲁高压/超高压变质地体演化的影响。     

Rapid Exhumation in the Alpine Belt of the Betic-Rif (W Mediterranean): Tectonic Extrusion

—Extreme cooling rates (500 °C/m.y.) during the late stage, 22–18 Ma, orogenic evolution of the Alpine Betic-Rif belt are suggested to result from rapid exhumation caused by tectonic extrusion and concomitant extensional tectonics. The extrusional/extensional tectonic setting is controlled by the SW-NE trending break-off scar left in the lithosphere of the Alborán Sea and SE Spain after detachment of a lithospheric slab. The extruded material represents the collisional crustal nappe pile (together with fragments of underlying mantle, such as the Ronda peridotites) and the cause of the extrusion is the thermal softening within the crustal section during and after collision. The extrusion/extension took place under the influence of a NW-SE directed compressive regime, perpendicular to the collisional belt. At the same time the sub-lithospheric mantle still showed the E-W compressive regime of the collisional stage. The Alpine tectono-metamorphic evolution of the Betic-Rif belt in the W Mediterranean thus comprises two main stages: (1) continental collision with formation of primary nappes and high-pressure metamorphic parageneses, (2) tectonic extrusion with vertically directed tectonics (high pressure, very rapid decompression) and extensional tectonics with roughly horizontal, lateral transport and final emplacement of the extruded mélange in the form of a stack of detachment sheets (low pressure, very rapid cooling). This model for the Betic-Rif may offer important constraints to all rapidly exhumed convergent terranes.     

TOGA-COARE IOP部分观测资料初步分析

初步分析中国科学院南海海洋研究所《实验3号》科学考察船在TOGA—COARE IOP连续三个航次中部分CTD和ADCP原始观测资料指出:90-210m间大于35的盐度极值除存在准日周期变化外,在量值上还存在约73d的周期变化。但受资料长度的限制,目前尚无法确定上述周期是否属于稳定周期。在上述深度范围内亦存在较低盐度和温度水体侵入现象,其强度存在10—15d的周期变化。等温线和等密度线常出现振幅达10m以上,周期约3d的振荡,而且有时表现出次中尺度涡(submesoscale eddy)及涡旋链特征。比较风、SST、混合层深度间的关系时发现,风强度和大风维持时间对SST和混合层深度的影响很大,如西风暴发过程可使平均SST降低0.5℃左右,使平均混合层深度加深8m以上。分析西风暴发过程及西风暴发后洋流铅垂变化和洋流随时间变化发现,西风暴发过程导致79m以浅深度上的东向射流,且19m深处流动随时间顺时针改向,79m深处流动随时间逆时针方向改向。