Left-lateral shear deformation found in southern part of the Gaoligong range in west Yunnan and its tectonic implications

LocatedinthesouthwestborderareaofChina ,theGaoligongrangeisauniquegeologicandgeomor phologicfeature ,withitssnow cappedsummitele vatedupto 35 88mabovesealevel.ItgoesupnorthalongtheNuRivertoeasternTibet ,joiningupwiththeBoshulalingrange ,anddownsouthtotheareaofLongling ,whereitdescendsrapidlyandsplitsupintoseverallowandlinearridges .RespectivelytothewestandeastoftherangearetheTengchongandBaoshanblocks ,themainpartofwhich ,anarrowbeltofin tensivelydeformedmetamorphicrocksnamedGaoligongGroup …     

Sinistral shear and extension of the northern section of Lijiang Basin in northwest Yunnan in quaternary

The northern section of Lijiang Basin (NSLB) has the features of a zigzag fault, a kind of “tracing extension” in the shape. Fault slip is characterized by both extension and sinistral shear. Average sinistral-shear and extensional displacements are respectively 1950 and 1730 m. This kind of movement began in middle Pleistocene, which is about 800 ka ago. Average sinistral and extensional slip-rates can be acquired, which are 2.44 and 2.16 mm/a. Geological evidence at different segments of the NSLB demonstrates results of geomorphic analysis, and is consistent with our knowledge about the zigzag fault. Realization of sinistral shear and extension of the NSLB provides direct evidence for the model of clockwise rotation of northwest Sichuan active block and the understanding of dynamic features of the Red River fault zone.     

高黎贡山南段种子植物区系科属的两种不同排序方法及其意义

高黎贡山南段迄今计有种子植物192科,887属,2 807种。将其科属按所含种的绝对数目和区系存在度两种不同排序,以提供完整的高黎贡山南段种子植物区系的区系组成,反映本区系的独特特点和各科属在区系建成中的相对重要性。     

Magnetostratigraphy of the Zanda basin in southwest Tibet Plateau and its tectonic implications

The Zanda basin is one of the very important basins at the north slope of the Himalaya Range. Thus the study of the basin strata will provide critical information about the tectonic evolution of the Himalayan Orogenic Belt. 268 oriented block samples were collected in the 750-m-thick sections of the Zanda basin. The characteristic remanent magnetization （ChRM） was isolated that decays linearly to the origin between 500℃ and 690℃for most studied samples. An age range of 9.5-2.6 Ma was estimated from the correlation between our observed polarity column and the Geomagnetic Polarity Time Scale （GPTS）. The age of the Zanda basin does not support the models that the South Tibetan Detach system （STDS） is one of the basin controlling faults. Given the sedimentological features in the basin and the tectonic features at the north edge of the basin, the Zanda basin was a half graben that was possibly controlled by the Karakorum fault on the northeast.     

Evolution of the Xiaotian-Mozitan fault and its implications for exhumation of Dabie HP-UHP rocks

The Xiaotian-Mozitan fault （XMF） located north of the Dabie orogenic belt separates the North Dabie complex to the south from the Beihuaiyang low-grade metamorphic rocks to the north. It comprises several NW-striking ductile shear zones and brittle faults. The brittle faults obviously overprinted on the ductile shear zones and promoted the development of the volcanic basins in early Cretaceous to the north, which suggests that the brittle faults were normal faults formed in early Cretaceous during doming of the Dabie orogenic belt. The ductile shear zone superposed on the north Dabie gray gneiss, and it is an important channel where the Dabie HP-UHP rocks exhumed. For obtaining new structural constraint on exhumation of the HP-UHP rocks, we present here experimental results on the microstructure, quartz C-axis fabrics and the microprobe analyses of phengite. The ductile shear zone was determined to be formed at a temperature of 600-650 ℃ and pressure of 1.1 GPa by the mineral deformation, microprobe analyses and geobarometry of Si-in-phengite of the mylonite, the results suggest that the mylonite now exposed on the surface experienced an upper amphibolite-facies metamorphism in the lower crust. The mineral stretching lineation varies from horizontal in the east segment to sub-dip in the west. Shear sense indicators from outcrop and thin sections of orientated specimen and quartz C-axis fabrics suggest that the XMF is a sinistral normal fault. The kinematics analysis of the ductile shear zone indicates that the exhumation of Dabie HP-UHP rocks is the results of a SE-directed extrusion and an anticlockwise rotation around its eastern pivot simultaneously.     

Evolution of the Xiaotian-Mozitan fault and its implications for exhumation of Dabie HP-UHP rocks

The Xiaotian-Mozitan fault (XMF) located north of Dabie orogenic belt separates the North Dabie complex to the south from the Beihuaiyang low-grade metamorphic rocks to the north. It comprises several NW-striking ductile shear zones and brittle faults. The brittle faults obviously overprinted on the ductile shear zones and promoted the development of the volcanic basins in early Cretaceous to the north, which suggests that the brittle faults were normal faults formed in early Cretaceous during doming of Dabie orogenic belt. The ductile shear zone superposed on the north Dabie grey gneiss, and it is an important channel where the Dabie HP-UHP rocks exhumed. For obtaining new structural constraint on exhumation of the HP-UHP rocks, we present here experimental results on the microstructure, quartz C-axis fabrics and the microprobe analyses of phengite. The ductile shear zone was determined to be formed at temperature of 600-650℃ and pressure of 1.1 GPa by the mineral deformation, microprobe analyses and geobarometry of Si-in-phengite of the mylonite, the results suggest that the mylonite now exposed on the surface experienced an upper amphibolite-facies metamorphism in the lower crust. The mineral stretching lineation varies from horizontal in the east segment to sub-dip in the west. Shear sense indicators from outcrop and thin sections of orientated specimen and quartz C-axis fabrics suggest that the XMF is a sinistral normal fault. The kinematics analysis of the ductile shear zone indicates that the exhumation of Dabie HP-UHP rocks is the results of a SE-directed extrusion and an anticlockwise rotation around its eastern pivot simultaneously.     

Early Paleozoic granite in Nujiang River of northwest Yunnan in southwestern China and its tectonic implications

The Nujiang region along the China-Burma border in the western Yunnan has received a great deal of attention and has been considered to be the important channel of southeastward escape of the Tibetan Plateau[1-4]. This channel is bordered by the Red River-Ailao Mountain left-literal strick-slip fault in the east and Gaoligong- Sagaing right-literal strick-slip fault in the west[5-7]. Within this channel, it is still not clear to which tectonic     

龙门山中段推覆构造的变形特征

论述了龙门山三大推覆体和推覆面的构造变形特征 ,认为耿达 -汶川推覆体为褶皱冲断推覆体 ,映秀 -白水河推覆体为冲断推覆体 ,彭灌推覆体为冲断褶皱推覆体 ,并将其划分为两个次级推覆体 ,而相应的推覆面分别为韧性变形为主叠加后期脆性变形 ;脆 -韧性变形以脆性为主及脆性变形的特征。其形成次序由北西向南东 ,即前展式扩张方式。主要活动时期为印支期和喜马拉雅期     

Near-field postseismic deformation along the rupture of 2008 Wenchuan earthquake and its implications

At first time, we observed the postseismic deformation, which actually is a kind of creep after slip, along the intra-plate active fault associated with the Wenchuan earthquake. To understand the near-field postseismic deformation following 2008 Wenchuan earthquake in Sichuan Province of China, we compared the fault scarp or flexure scarp profiles measured in different campaigns. Our result shows that among total 19 observation sites, on 13 sites (68% of 19) fault scarps fall back with an average about 9.7% decrease; on 5 sites (26% of 19) fault scarps present no change; and on one site (6% of 19) fault scarp continues to uplift with 12.8% increase. The variety of fault scarp we observed results mainly from near-field postseismic deformation, after slip occurred in shallow. Based on our observations, the following are demonstrated: except for the southwestern end near Yingxiu Town where coseismic slip deficit and some elastic energy residue exist there, fall back (68%) or non-changing (26%) of fault scarp shows energy balance or energy deficit due to overthrust, implying that the likelihood of occurrence of strong aftershocks of ≥ M7 becomes very small in these energy-released areas. Moreover, we suggest that a minimum of 10% error due to near-field postseismic deformation should be considered when evaluating the magnitude of historic and paleoearthquake or slip rate based on the fault scarp dis-placement, even though the error caused by erosion has been accounted already.     

基于多参数翘曲位移函数的箱梁剪力滞和剪切效应分析解析法

用多参数翘曲位移函数考虑箱梁截面底板、顶板、悬臂板剪滞翘曲幅度一般各不相同的影响,计入箱梁剪切变形,导出了箱梁剪滞效应分析的控制微分方程组、边界条件及相应的闭合解。给出了算例结果,表明此方法用于求解薄壁宽箱梁的应力和挠度能大幅度提高计算精度。此方法蜕化后可广泛用于多种常见桥梁结构剪力滞效应的高精度分析。     

川西北断块东部区域活动构造体系及其对地震活动的控制作用

川西北倒三角形断块东部区域地处青藏高原东部边缘地带,跨川西北高原及其与四川盆地过渡带的高山峡谷区.由其南东侧边界活动断裂即龙门山北东向活动断裂带,北侧边界活动断裂即西秦岭近东西向构造带的南缘活动断裂带,断块内部近南北向岷山隆起断裂带的岷江与虎牙断裂等活动断裂带组合,构成了本区由西向东逐渐收敛的平卧"A"字形活动构造体系.在该活动构造体系的控制和强大的近东西向构造应力场的驱动下,川西北断块沿两侧边界活动断裂向东强力楔入,于武都、文县-平武、青川"构造急剧收口带"之西侧,沿东经104°线附近形成了一个近南北向展布、地跨三大构造单元的统一强震活动带.而在该带的东、西两侧地区,地震活动则明显减弱.强震沿该带有规律地南、北往返迁移和重复发生.     

Characteristics of the island-arc pillow lavas from southeast Yunnan Province, and its tectonic implications for Paleo-Tethys in South China

Based on the geological mapping, it is suggested that the pillow lavas exposed in Jianshui area in southeastern Yunnan Province are emplaced into the western part of Shizong-Mile faults, the boundary between the Yangtze and Cathaysian blocks, and mainly composed of tectonic massive of basalts and basaltic andsites. The geological and geochemical studies show that these lavas erupted in an island arc tectonic setting, which suggests that there existed the subduction of oceanic crust between the Yangtze and Cathaysian blocks. The paleontological fossils in the sedimentary interlayers between the volcanic rocks indicate that these pillow lavas erupted during Carboniferous-Permian. The geologic and geochemical evidence suggested that there existed an eastern branch of Paleo-Tethys between the Yangtze and Cathaysian blocks in southeastern Yunnan, South China.     

山脉地形对云南冷锋切变型强降水的影响

利用多种资料对2014年6月2829日云南省冷锋切变型强降水进行诊断分析,并利用WRF中尺度模式,对此次过程进行地形敏感性数值试验.结果表明去除山脉地形后,全省区域降水量明显减弱,大雨、暴雨的落区急剧缩减;降水量的变化差异主要由降水强度的变化引起.山脉对低层冷空气的引导和阻挡作用最为显著,四川东部到贵州一带的东北气流经乌蒙山加速进入到滇中地区,受哀牢山、无量山和横断山脉的阻挡,与青藏高原东南侧沿横断山脉南下的冷平流汇合,在滇中及以东、以北地区盘踞;夏季来自南海的东南气流及来自孟加拉湾的偏西气流均具有高温高湿性质,在山脉的引导和阻挡作用下,与南下受阻的冷空气交汇,形成锋面降水;山脉的强迫抬升机制迫使其周边出现显著的垂直上升运动,强度约0.4~0.7m/s;在山谷相间的区域,特别是山脉的迎风坡处,水汽通量辐合,其增量可达(0.02~0.07)10-6gs-1cm-2hPa-1,有利于当地大雨、暴雨的发生.     

准噶尔南缘磷灰石裂变径迹定年及其构造意义

目的 确定准噶尔南缘伊林哈比尔尕山的隆升时限.方法 测定磷灰石样品的裂变径迹年龄,并进行热史模拟.结果 磷灰石的裂变径迹中心年龄变化于78～51 Ma之间,记录了构造隆升活动的时间.结论 伊连哈比尔尕山自白垩纪以来经历了3期冷却剥露,分别是晚白垩世(97.1～68.8 Ma),视隆升速率为0.062 mm·a-1;新生代早中期(59～30 Ma),视隆升速率为0.023 mm·a1;新生代晚期(13～5 Ma)为山体隆升的峰期,其隆升速率为0.127 mm·a1.白垩纪以来的北天山变形作用与亚洲南缘多期的地体碰撞增生有关.     

大别山东缘郯庐断裂带早期韧性剪切带的形成温度

年龄的解释强烈依靠于构造热事件的发生温度和矿物的封闭温度,在缺少构造热事件的温度资料的情况下,很难对年龄数据做出正确合理的解释。文章利用白云母-绿泥石地质温度计,计算了大别山东缘郯庐早期左旋走滑韧性剪切带的形成温度,获得了350～450℃的温度区间,并且多数温度值位于430～450℃之间。该温度值大于40Ar/39Ar法中白云母的封闭温度,从而由主要以残斑形式存在的白云母获得的年龄值记录了郯庐断裂带的活动时间,190Ma左右的白云母年龄值为接近于韧性剪切带变形年龄的冷却年龄。并由此年龄和温度数据得出郯庐断裂带形成于大别造山带造山作用后期。该韧性剪切带形成温度明显低于所叠加的造山带高角闪岩相变质岩,也指示为造山后期走滑运动的结果。     

Zircon U-Pb SHRIMP ages of high-pressure granulite in Yushugou ophiolitic terrane in southern Tianshan and their tectonic implications

Zircons from two high-pressure granulite samples from the Yushugou ophiolitic terrane, southern Tian shan have been investigated by cathodoluminescence, LA ICPMS and ion microprobe (SHRIMP) for their internal textures, trace elemental compositions and in situ dating. The weighted mean ages of these two samples are 392±7 and 390±11 Ma, respectively, representing the granulite-facies meta morphic age of the ophiolitic terrane, and indicating that the southern Tianshan ocean initiated its northward subduction since the early Devonian.     

The age of the plant fossil assemblage in the Liuqu Conglomerate of southern Tibet and its tectonic significance

The Liuqu Conglomerate, situated to the south of Yarlung Tsangbo Suture Zone (YTSZ), is a suit of molasse formed in a foreland basin of the Himalayan orogenic belt after the collision between the two plates of the Indian and Eurasion. It is of great significance in constraining the younger limit time of the collision of the two plates and providing stratigraphic evidence to reveal the post?collisional tectonic evolution and uplifting history of the Tibet plateau. However, the age of this molasse suit and its correlation to other synchronous strata distributed in southern Tibet have been in great disputes for a long time. Especially in recent years, argues on its ages are growing violently with the recognition of the great sedimentary tectonic significances of this molasse. During the field work carried out recently on this molasse suit, a lot of plant fossils were found preserved in fairly good conditions in the upper part of this strata, which is of great help in determining its age. By identification, the assemblage of the plant fossils belongs to a tropic to subtropic flora developed in the southern margin of the Northern Hemisphere supercontinent during the Middle to Later Eocene, which can provide good constraint on its formation age. This paper is to give a brief introduction of the plant assemblage and its age, and to discuss their tectonic significances.     

黄河三角洲沉积物含盐量与其临界剪切应力的关系研究

黄河入海径流量变化引起河口区盐度场的改变,从而影响沉积物的动力学行为和工程性质。在黄河三角洲4个不同沉积年代的叶瓣采集柱状样,采用统计和相关性分析的方法对不同深度原状沉积物的含盐量、临界剪切应力以及其他物理力学性质进行分析。结果表明:黄河三角洲不同沉积年代、不同深度沉积物含盐量变化范围是0.2‰~2.0‰,整体剖面定义为"均匀型";在研究区范围内,沉积物临界剪切应力呈现空间不均匀分布,并随沉积物含盐量的增大而增大。表层沉积物临界剪切应力偏小,高容重、低含水率的沉积物偏大。研究对于黄河口冲淤研究具有重要意义。     

40Ar-39Ar ages of the Louzidian-Dachengzi ductile shear zone near Chifeng,Inner Mongolia and their tectonic significance

The Louzidian normal fault occurs as the eastern detachment fault of the Kalaqin metamorphic core complex. Field observations and microstructural analyses reveal that the Louzidian-Dachengzi ductile shear zone developed in its lower-plate was genetically related to sinistral strike-slips and extensional faulting. Two samples from this ductile shear zone yield 40Ar-39Ar plateau ages of 133 Ma (Bi) and 126 Ma (Kp), which are concordant with their isochron ages. The plateau age of 133 Ma (Bi) records the formation age of the ductile shear zone. The inconsistent relationship between the earlier strike-slip ductile shear zone and the later normal fault makes the Kalaqin Quasi-metamorphic core complex distinctive from Cordilleran metamorphic core complex. These ages provide important geochronological data for putting constraints on the formation age and genesis of such ductile shear zones.     

紫木凼金矿控矿断层带的变形特征及其与成矿作用关系的讨论

紫木凼金矿的控矿断层是一条低角度逆断层断层的变形特征为低温变形,断层岩的变形主要为碎裂岩类,有温度在２００℃左右,断层岩在平面上分带特征明显,可划分为碎裂岩－节理密集带,磨砾岩－剪切旋转带和断层泥－局部压溶带等三个带,随着变形程度的增加,金元素有明显的富集趋势,峰值区位于断层泥－局部压溶带内,即金元素的富集与岩石变形过程中的压溶作用有关。