Petrology, geochemistry and Ar-Ar geochronology of eclogites in Jinshajiang orogenic belt, Gonjo area, eastern Tibet and restriction on Paleo-Tethyan evolution

As one of the important Paleo-Tethys suture zones in eastern Tibet,the Jinshajiang orogenic belt is of great significance to study the tectonic evolution of the main suture zone of Paleo-Tethys.In this paper,eclogites developed in the Jinshajiang suture zone in Gonjo area,eastern Tibet,are selected as specific research objects,and petrological,geochemical and Ar-Ar geochronological analyses are carried out.The major element data of the whole rock reveals that the eclogite samples have the characteristics of picritic basalt-basalt and belong to the oceanic low potassium tholeiites.The results of rare earth elements and trace elements of the samples show that the protoliths of eclogites have characteristics similar to oceanic island basalt(OIB)or normal mid ocean ridge basalt(N-MORB).Muscovite(phengite)from two eclogite samples yield the Ar-Ar plateau ages of 247±2 Ma and 248±2 Ma respectively,representing the peak metamorphic age of eclogite facies and the timing of complete closure of the Jinshajiang Paleo-Tethys Ocean.Muscovite and biotite selected from the hosting rocks of eclogite yield the Ar-Ar plateau ages are 238±2 Ma and 225±2 Ma respectively,reflecting the exhumation age of eclogites and their hosting rocks.Combined with the zircon U-Pb dating data(244 Ma)of eclogites obtained in previous work,it can be concluded that the Jinshajiang Paleo-Tethys ocean was completely closed and arc-continent collision was initiated at about 248-244 Ma(T21).Subsequently,due to the large-scale arc(continent)-collision orogeney between Deqin-Weixi continental margin arc and Zhongza block(T31-T32),the eclogites were rapidly uplifted to the shallow crust.

Early Permian–Late Triassic Magmatism in the Tuotuohe Region of the Qinghai–Tibet Plateau: Constraints on the Tectonic evolution of the Western Segment of the Jinshajiang Suture

In this paper we present new zircon U-Pb ages,whole-rock major and trace element analyses,and zircon Hf isotopic data for magmatic rocks in the Tuotuohe region of the western segment of the Jinshajiang suture.Our aim is to constrain the Early Permian-Late Triassic tectonic evolution of the region.Zircons from the magmatic rocks of the Tuotuohe region are euhedralsubhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios （0.4-4.6）,indicating a magmatic origin.The zircon U-Pb ages obtained using LA-ICP-MS are 281 ± 1 Ma,258 ± 1 Ma,244 ± 1 Ma,and 216 ± 1 Ma,which indicate magmatism in the Early Permian-Late Triassic.A diorite from Bashihubei （BSHN） has SiO2 =57.18-59.97 wt％,Al2O3=15.70-16.53 wt％,and total alkalis （Na2O ＋ K2O） =4.46-6.34 wt％,typical of calc-alkaline and metaluminous series.A gabbro from Bashibadaoban （BSBDB） belongs to the alkaline series,and is poor in SiO2 （45.46-54.03 wt％） but rich in Al2O3 （16.19-17.39 wt％） and total alkalis （Na2O ＋ K2O =5.48-6.26 wt％）.The BSHN diorite and the BSBDB gabbro both display an enrichment of LREEs and LILEs and depletion of HFSEs,and they have no obvious Eu anomaly; they have relatively low MgO contents （2.54-4.93 wt％）,Mg# values of 43 to 52,and low Cr and Ni contents （8.07-33.6 ppm and 4.41-14.2 ppm,respectively）,indicating they differentiated from primitive mantle magmas.They have low Nb/U,Ta/ U,and Ce/Pb ratios （1.3-9.6,0.2-0.8,and 0.1-18.1,respectively）,and their initial Hf isotopic ratios range from ＋9.6 to ＋16.9 （BSHN diorite） and ＋6.5 to ＋12.6 （BSBDB gabbro）,suggesting their primary magmas were derived mainly from the partial melting of a mantle wedge that had been metasomatized by subduction fluids.Taking all the new data together,we conclude that the western and eastern segment of the Jinshajiang suture regions underwent identical processes of evolution in the Early Permian-Late Triassic：oceanic crust subduction before the Early Permian,continental collision during the Early-Middle Triassic,and post-collisional extension from the Late Triassic.

Timing of formation of the Western Jinshajiang and Ganze–Litang sutures:evidence from the Duocai Granite in the Zhiduo region,West China

The timing of the closure of the Paleo-Tethys Ocean in West China remains debated.To investigate this problem,we examined the geochemical characteristics,zircon U-Pb chronology,and Hf isotopes of monzogranites and quartz diorites from the Duocai granite in the Zhiduo region,at the intersection of the Jinshajiang and GanzeLitangsutures.The monzogranites have the chemical characteristics of calc-alkalineⅠ-type granites and yield a weighted mean zircon U-Pb age of 234.6±0.9 Ma[mean square weighted deviation(MSWD)=0.36].InitialεHf(-t)values are high and positive,ranging from+7.9 to+13.6 with a mean of+10.7,corresponding to two-stage Hf isotope model ages(TDM2)of 762-395 Ma.Geochemical and isotopic data indicate that the source magma of the monzogranites formed from mantle-derived magmas mixed with the overlying crustal materials.The quartz diorites,which also have compositional characteristics of calcalkaline I-type granites,yield a weighted mean zircon UPb age of 209.1±0.7 Ma(MSWD=0.29).InitialεHf(-t)values range from-2.5 to+0.6 with a mean of-1.5,with the corresponding TDM2 of 1402-1210 Ma.Geochemical and isotopic data indicate that the primary magma of the quartz diorites was derived mainly from partial melting of the mafic lower crust and small amount mantle-derived magma involved.Combining these results with regional data,the studied granites are inferred to have formed as a result of continuous subduction of plates underlying the Western Jinshajiang Ocean-Ganze-Litang Ocean from 234 to 209 Ma,and were unrelated to subduction of the South Jinshajiang oceanic plate.We suggest that the Western Jinshajiang Ocean-Ganze-Litang Ocean closed by the end of Late Triassic.

GEOCHEMISTRY OF VOLCANIC ROCKS IN WESTERN PART OF JINSHAJIANG STRUCTURAL BELT AND ITS TECTONIC SETTING

The volcanic rocks in western part of Jinshajiang structural belt are zonally distributed between Qiangtang and Kunlun landmasses. It is bounded on the north by Yanghu\|Hoh Xil deep fault and on the south by Bairabu Co\|Ruolagangri deep fault. As component part of ophiolites in this belt, volcanic rocks consist of basalts, dorgalites, picrites, basaltic\|andesites, andesites and a few pyroclastic rocks. They mainly occur within low\|grade metamorphic and thick flysch deposits of Lower Permian and Late Triassic and are associated with gabbro, diabase, ultramafites, radiolarian silicalites and limestones. This suit of volcanics\|bearing flysch deposits had been considered as Triassic or Late Triassic stratum and also called as “Ruolagangri Group”.

THE ROCK ASSOCIATION IN JINSHAJIANG MELANGE BELT

Jinshajiang melange belt locates between Jianda\|Weixi island arc and Zhongzha massif. The melange belt and island arc makes up Jinshajiang plate junction. Although subsequent tectonic movements had complexed the structural form of Jinshajiang melange belt, there are still a lots of structural block remained which carried amount of information about the tectonic evolution of the belt. Recent researches have identified several kinds of rock association in the structural blocks.(1) Ophiolite:The ophiolite consists of serpentinization ultramafite, ultramafic cumulus crystal rock (pyroxenite, dunite), gabbro, diabase cluster, ocean\|ridge type basalt, plagiogranite and radiolarian silicalite. The isotopic age shows that the ultramafite and basalt formed during Upper Carboniferous and Lower Permian. The silicalite is high in radiolaria of Lower Permian.(2) Rock association of oceanic island\|arc:The liptocoenosis of oceanic island\|arc scatter in melange belt, it mainly consists of sandy slate, pyroclastic rock, silicalite, basalt and andesite. A part of volcanic rock belongs to calc\|alkaline volcanic suite and the other is tholeiite. The petrochemistry, REE and microelement of volcanic rock have the feature of the rock in ocean\|island arc. The isotopic age of basalt shows that the ocean\|island arc formed in Lower Permian.

THE PERMIAN SYSTEM OF THE NUJIANG—LANCANGJIANG—JINSHAJIANG AREA, SOUTHWESTERN CHINA

Permian system is one of the best developed systems in Sanjiang area. In Yidun\|Zhongdian and in Zhiso\|Muli, The Lower Permian is clastics\|carbonates\|volcanics with interbeds of siliceous sediments, Whereas the Upper Permian is composed of lower part of basic volcanics and upper part of clastics\|carbonates with a total thickness of 1000～4000 meters .In Zhongzha (Batang)\|Jingping region, It is mainly carbonates of 217～1320 meters thick, But in Jingping proper, there occur about 5000 meters thick basalts of early late Permian . From Batang to Benzinan along the Jinshajiang river , the lower Permian is clastics\|volcanics\|carbonates formation with interbeds of siliceous sediments and spilite formation; Whereas the Upper Permian is clastics with volcanic interbeds; The total thickness being 3700 to 7100 meters. In Jiangda—Mangco (Mangkang), It is clastic\|carbonate\|volcanic formation of 1100 to 2400 meters . In Tuoba (Qamdo)—Haitong (Mankang)—Ximi (Mujiang ), It is mainly clastics\|carbonates formation , the Upper Permian being coal\|bearing clastics sequence and the total thickness being 700～2500 meters ,In Zhado—Zhasuosuo (Mangkang)—Deqing—Qinggu—Qinghong, It is clastic\|carbonate\|volcanic formation, locally with coal\|bearing clastics of Upper Permian and the total thickness of mainly carbonate formation and clastic formation with coal\|bearing clastic formation of Uppermian, is 800 to 2000 meters. In the whole area , the Permian strata were slightly metamorphosed, locally more intensively metamorphosed up to amphibolite facies. The fossils found belong to fusulinids, coral, brachiopods,ammonite,bivalve, gastropods, bryozoa,foraminifera, trilobite, algae ,porifera (sponge), and continental plant . Besides the Gondwana cold\|water type components of brachiopods found in Baoshan, the fossils belong mainly to Cathaysian biota, especially to South China type. In some places such as Mangkang, Guxue (Dewong), to South China type. In some places such as Mangkang, Guxue (Dewong), and Wachang (Muli), the resedimented Late Carboniferous fusulinid fossils can be found in the clastic limestone of Lower Permian, and the Early Permian or even Middle to Late Carboniferous fusulinid fossils found in Upper Permian classic limestone. All these suggest the resedimentation of biolimestone blocks or fragments related to fault\|volcanism .On the section of Tongba (Muli), the permian is continuous graded upwards into the Triassic, with a transitional zone of fossil.

Stratigraphic Sequence and Tectonic Evolution of Passive Continental Margin of Jinshajiang Belt in Northwestern Yunnan, China

The Jinshajiang belt, located between the Zhongzan and Qamdo massifs, preserves varied sediments representing different tectonic background. Those sediments outcrop in stratigraphic slices,not in continuous stratigrapky. The stratigraphic slices of the passive continental margin are investigated by geologic mapping in Tuediug-Xiaruo, Northwestern Yunnan Province, and each of these slices is researched in age and sedimeutary environment. The stratigraphic successions of the passive continental margin are reconstructed. On the basis or new sequence, the evolutional history of the passive continental margin is divided into four stages: rift basin (D,-C,), complex continental margin basin (P1 ), residual hasin (P2-T2) and synorogenic basin (T3).

Compositional Variation and Mineral Chemistry of the Jinshajiang and Lancangjiang Serpentinites, Yunnan Province, SW China

We present the whole rock and the mineral chemical data for upper mantle peridotites from the San-Jiang region in Yunnan, SW China. These peridotites are a part of a Paleo-Tethyan ophiolite belt occurring along the Jinshajiang and Lancangjiang suture zones. All samples of the Jinshajiang and Lancangjiang ultramafic rocks are completely serpentinized. The Jinshajiang serpentinites are characterized by no relict of olivine and pyroxene, and the Cr# content of spinels is 0.32–0.49. The Lancangjiang serpentinites were collected from two different locations; the northern location which has some relict of Opx（Al2O3 is 0.13–2.2 wt%, TiO 2 is 0.004–0.057 wt% and Mg# content is 0.895–0.933） and the Cr# content of spinel is 0.26-0.55; the southern location, which has some relict of Olivine（Fo = 90–92.5 and NiO = 0.12–0.26 wt%）, and spinel Cr# ranging from 0.41 to 0.57. The whole rock geochemical and the mineral chemistry data imply that the Jinshajiang and Lancangjiang serpentinites represent abyssal peridotites residues after ~15–20% partial melting for the Jinshajiang and Lancangjiang serpentinites（south location）, and ~11–19% partial melting for the Lancangjiang serpentinites（north location）. In addition, the compositional trends of the spinel analyses of the Lancangjiang serpentinites imply that the MORB melt-peridotite interaction process played a significant role during their evolution. These processes are evidenced by an increase in Cr# with an increase in TiO 2, whereas the spinel analyses of the Jinshajiang serpentinites display an increase in Cr# with a decrease in Ti O2, indicating that the Jinshajiang serpentinites were subjected to a simple partial melting process.

Cause Analysis of Gully Erosion in Yuanmou Basin of Jinshajiang Valley

Some factors （i.e. lithology, topography, climate, the change of population as well as land use during the past 50 years） that could have great influence on the development of gully in the arid-hot basin of Jinshajiang valley were investigated. The results show that the factors leading to the strong gully erosion in this area include： the widely distributed Yuanmou group stratum, which promotes the development of gully erosion; the unique geomorphologic configuration that is prone to rock fall and gully erosion; the strong and time-concentrated rainfall; the arid-humid alternate climate characteristics that prepares the ground for the development of fissures in soils; the arid-hot climate that goes against the growth and recovery of vegetation; and the unreasonable and abusive human activities.

Oceanic lithosphere heterogeneity in the eastern Paleo-Tethys revealed by PGE and Re-Os isotopes of mantle peridotites in the Jinshajiang ophiolite

Platinum group elements(PGE)and Re-Os isotopes of mantle peridotites in the Jinshajiang ophiolite(SW China)were investigated in this study,in order to constrain the evolution of the lithospheric mantle beneath the Jinshajiang-Ailaoshan Ocean,which was a branch of the eastern Paleo-Tethys.The Jinshajiang peridotites have whole-rock compositions(e.g.,MgO=32.7-38.1 wt.%;Al_(2)O_(3)=0.67-1.30 wt.%)and spinels with moderate Cr#values(0.4-0.6)similar to those of abyssal peridotites,which indicate moderate degrees of partial melting(15%-20%).These peridotites exhibit U-shaped chondrite-normalized REE patterns that could be caused by hydrothermal alteration or melt-rock interaction after mantle melting.In addition,Pd concentrations and(Pd/Ir)_(N)ratios of the Jinshajiang peridotites increases with decreasing Al_(2)O_(3) concentrations.These negative correlations cannot be explained by simple partial melting but record a melt-rock reaction event after mantle melting.This study therefore demonstrates the efficiency of PGE in detecting the melt-rock reaction process relative to whole-rock major and trace elements.The suprachondritic^(187)Os/^(188)Os ratios(0.1272-0.1374)further indicate that the later percolating melt derived from a mantle domain with distinct^(187)Os-enriched isotopic compositions.In comparison with peridotites in the Ailaoshan ophiolite belt,which were not significantly affected by melt percolation,this study further highlights that the lithospheric mantle compositions beneath different segments of the same ocean basin are highly variable and might be controlled by distinct mantle processes in response to different rifting mechanisms.

Engineering geological conditions and features of geologic hazards in Wudongde reservoir of Jinshajiang River valley

There is a great difference between the distribution and evolvement characteristics of slope geological hazard in the same geographical location and climatic conditions,taking the similar structural-genetic connection in Wudongde reservoir area of Jinshajiang River valley for example. In all engineering geological conditions,the chronologic age and attitude of strata,and the lithologic association factors control the distributions and evolvement characteristics of slope geological hazard in the studied area. The study shows that the slopes in geological evolution are in different stages. The conclusion helps to understand the types and the intensity of geological disasters.

滇西剑川始新世粗面岩及其包体成因:印度-欧亚大陆碰撞过程的约束和大地构造意义

新生代以来,印度-欧亚大陆碰撞导致青藏高原发生大规模隆升和岩石圈挤出,这一过程引发了金沙江-哀牢山-红河构造带等深大断裂带的大规模剪切走滑,并沿该构造带发生强烈的碱性岩浆作用。这些始新世碱性岩记录了印度-欧亚大陆的早期碰撞过程,因而可以作为研究青藏高原早期隆升和岩石圈挤出过程及其深部动力学机制的重要“探针”。本文针对剑川盆地甸南地区始新世粗面岩及其二长岩包体和辉长岩包体开展了系统的锆石U-Pb年代学、Lu-Hf同位素和全岩主-微量元素和Sr-Nd同位素组成研究。锆石U-Pb定年结果显示,剑川盆地甸南粗面岩形成时代为36Ma;其内部包含的两件二长岩包体的形成年龄分别为41.6±3.4 Ma和35.7±0.3 Ma,一件辉长岩包体的形成时代为35.8±0.2 Ma。地球化学研究结果显示,粗面岩与二长岩包体K_(2)O含量均较高,属于钾玄质系列岩石,且富集轻稀土元素(LREE)和大离子亲石元素(LILE),亏损高场强元素(HFSE)。结合锆石Hf同位素和全岩Sr-Nd同位素组成,表明甸南地区寄主粗面岩和二长岩包体来自相同的交代富集岩石圈地幔的部分熔融,并经历了不同程度的橄榄石和辉石分离结晶作用。包体研究显示,~41Ma二长岩包体为寄主粗面岩岩浆上升过程中捕获自早期围岩,而~36Ma二长岩包体为同源岩浆房内与围岩接触淬冷的早期结晶产物,它们被寄主粗面岩岩浆裹挟而存在其内部。堆晶辉长岩包体较寄主粗面岩和二长岩包体具明显低的K2O、稀土和微量元素含量,其全岩Nd同位素组成与剑川盆地二龙山橄榄玄武岩相似,但高于寄主粗面岩,表明其源自弱富集地幔的部分熔融,并在壳-幔过渡带堆晶形成。此外,~41 Ma碱性岩包体和碱性岩内46~38 Ma捕获锆石年龄,以及剑川盆地内近源沉积岩内碎屑锆石的同期年龄记录,均表明金沙江-哀牢山-红河碱性岩带的岩浆作用并非存在从高原内部向东南方向的滇西地区逐渐变年轻的趋势,而是印度-欧亚大陆碰撞过程中,岩石圈向东南向挤出导致兰坪-思茅地块和印支地块旋转挤出的响应。

The Jinshajiang suture zone: tectono-stratigraphic subdivision and revision of age

Integrated study of rock assemblage, tectonic setting, geochemical feature, fossil contained and isotopic geochronology on the metamorphic mixed bodies, exposed in the Jinshajiang suture zone, suggests that one informal lithostratigraphic unit, the Eaqing Complex, and three tec-tono-stratigraphic units, the Jinshajiang ophiolitic melange, the Gajinxueshan Group and the Zhongxinrong Group, can be recognized there. It is first pointed out that the redefined Eaqing Complex might represent the Meso- to Neo-Proterozoic remnant metamorphic basement or mi-crocontinental fragment in the Jinshajiang area. The original rocks of it should be older than (1627 ±192) Ma based on the geochronological study. The zircon U-Pb age of plagiogranites within the Jinshajiang ophiolitic assemblage is dated for the first time at (294±3) Ma and (340±3) Ma respectively. The Jinshajiang ophiolite is approximately equivalent to the Ailaoshan ophiolite in the formation age, covering the interval from the Late Devonian to the

云南高原金沙江干支流水沙相关性分析

云南省境内的金沙江流域覆盖全省主要的经济、政治地域,金沙江虎跳峡河段是正在开工建设的滇中引水工程的水源区,分析云南高原金沙江干支流水沙相关性对揭示区域水沙规律、保障水源安全具有重要意义。为此,基于云南省境内金沙江流域干流及典型支流上的控制站点的流量和悬移质含沙量等观测资料,依托随机水文、趋势分析、Copula函数等方法系统地分析了水沙年际年内分布、时空遭遇、协同变化等规律和特性。结果表明,云南省境内金沙江干、支流流量和悬移质含沙量的年内分配不均,流量和悬移质含沙量正相关变化不完全同步;流域发生连续丰水/多沙事件的概率大于连续枯水/少沙事件的概率,但前者的持续影响弱于后者;水沙遭遇异步概率大于同步概率,丰水多沙组合的同现重现期最大、联合重现期次之、条件重现期最小。

金沙江—红河走滑构造与富碱斑岩铜金多金属成矿作用的关系

【研究目的】金沙江—红河富碱斑岩及铜金多金属成矿带展布于青藏高原东南缘,北部产有玉龙超大型铜钼矿床,中部发育北衙超大型金多金属矿床,在南部的金平(铜厂)地区,铜钼(金)多金属成矿亦显现潜力,是中国西南地区最重要的铜金矿集区之一,已成为东特提斯成矿域内的研究热点。【研究方法】本文在该富碱岩浆成矿带内长期工作的基础上,结合已有的研究,概述了该带内典型富碱斑岩和矿床特征。【研究结果】富碱斑岩总体上以二长花岗斑岩和石英正长斑岩为主,显示富集碱质(K_(2)O+Na_(2)O含量高)、铝、轻稀土元素及亏损重稀土元素和高场强元素的特性,相似的Sr-Nd同位素组成显示源区主要为下地壳物质;同时在野外调查工作的基础上,讨论了区域走滑构造之次一级构造的发育特征及其对本区成岩成矿的制约,并进一步总结了东特提斯成矿域内受控于金沙江—红河区域走滑深大断裂及其次级构造活动的“区域构造-富碱岩浆-铜金多金属”成矿作用。【结论】通过上述三地(玉龙、北衙、铜厂)主要矿区内主控岩断裂构造野外特征观察研究,提出金沙江—红河深大断裂的次一级近北西向构造控制了本区富碱岩浆活动及铜金多金属成矿的认识。

金沙江流域水库消落带优势植物生态位及种间关系

近年来水库消落带植被恢复愈发引起关注,消落带植被在固岸护坡、水土保持和截污过滤等方面发挥着重要作用。然而金沙江流域作为我国最大的水电基地,由于地处偏远,现有研究较少,因而对其水库消落带适生植物及其种间关系尚未明确。通过结合生态位理论和种间关系分析方法,包括生态位测定、方差比率法、χ^(2)检验、联结强度系数A C、种间关联指数O I、Pearson相关检验和Spearman秩相关检验等,揭示金沙江水库消落带优势植物的生态适应性、种间内在联系以及群落演替现状,并在此基础上,将优势植物划分了3种生态种组,为本区域消落带适生植物的筛选及其科学配置提供参考。结果表明:1)金沙江流域水库消落带共记录植物19科36属37种,频度≥20%的优势物种为狗牙根(Cynodon dactylon)、酸模叶蓼(Polygonum lapathifolium)、钻叶紫菀(Symphyotrichum subulatum)、牛筋草(Eleusine indica)、莲子草(Alternanthera sessilis)、苘麻(Abutilon theophrasti)、土荆芥(Chenopodium ambrosioides)和苍耳(Xanthium sibiricum)。其中,狗牙根的重要值和生态位宽度最大,占绝对竞争优势。2)整体来看,消落带优势植物的生态位相似性和重叠度较小,对资源利用的相似程度低,优势植物生态位分化程度较高。3)优势植物的总体联结性表现为不显著负联结,χ^(2)检验、Pearson相关检验和Spearman秩相关检验结果均显示负联结比例大于正联结,种间联结性较弱,群落整体稳定性较差。结合生态位和种间关系研究结果,推荐以上8种优势植物为先锋物种,根据划分的3种生态种组沿水位梯度进行配置试验,使植物种间关系向着更协调的方向发展,促进消落带植被自然修复进程。

金沙江矮子沟巨型古滑坡形成机制及运动过程研究

通过详细的野外调查,并结合遥感解译、室内试验以及数值模拟等手段,对矮子沟巨型古滑坡的基本特征、形成机制及运动演化过程进行了深入研究。矮子沟古滑坡的形成条件为:滑坡剪出口与坡脚之间存在巨大的高差,为滑坡的形成创造了良好的临空条件;顺向岸坡结构以及坡体内发育的多组控制性结构面是滑坡发生的结构基础;玄武岩系中的凝灰岩软弱夹层削弱了岩体的完整性,地表水及地下水长期入渗,水的软化作用降低了软弱夹层的抗剪强度;地震作用是造成岩体最终滑动失稳的关键因素。该滑坡的动力学过程可划分为四个阶段:①启程活动阶段。斜坡地形效应使得地震波在斜坡上部表现出异常放大现象,当短时间内积聚的振动能量超过岩土体的强度时,易形成高位滑坡,滑坡的变形破坏机制为拉裂-滑移;②近程活动阶段。近3.82×108 m3的滑坡物质高位高速下滑,与矮子沟右岸坡体发生猛烈碰撞后进一步碎裂解体;③高速远程碎屑流阶段。碎屑流继续沿矮子沟高速运动约3 km;④堆积堵江阶段。滑坡物质最终形成体积为2.73×108 m3的巨型堰塞坝,堵塞金沙江并形成堰塞湖,其回水区域向上游延续75 km至格勒一带。对金沙江矮子沟口上游河段采集到的堰塞湖沉积物进行光释光测年,结果指示该古滑坡发生于距今2.5万年左右。

滇西吉义独蛇绿混杂岩的岩石地球化学特征、成因和构造环境探讨

滇西吉义独蛇绿混杂岩位于金沙江缝合带的南端,岩石组合出露较齐全,包括堆晶橄榄岩、堆晶辉石岩、堆晶辉长岩以及玄武岩等,它们呈构造岩片的形式产出并与外来岩块组成蛇绿混杂岩。堆晶橄榄岩和辉石岩具低Al_2O_3,低TiO_2,而高Mg~#值(Mg~#=0.88～0.92),富集Cr和Ni,稀土总量偏低(∑REE=14.82×10^(-6)～27.75×10^(-6)),倒"U"型的稀土元素分布特征。堆晶辉长岩和玄武岩的Mg~#值较低,分别为0.70～0.79和0.51～0.66,具拉斑系列的演化趋势。玄武岩可以细分为2组:第一组玄武岩以平坦型稀土配分模式,低Mg~#(Mg~#=0.44～0.46),低稀土总量(∑REE=52.29×10^(-6)～60.26×10^(-6))为特征;第二组玄武岩则为LREE弱富集型的稀土配分模式,其Mg~#较高(Mg~#=0.54～0.68),稀土总量也较高(ΣREE=62.13×10^(-6)～101.87×10^(-6))。在原始地幔标准化的微量元素配分图解中,两组玄武岩均相对富集大离子亲石元素而亏损Nb、Ta和Ti,与岛弧岩浆岩类似,明显不同于N-MORB。岩石的Sr-Nd同位素组成较为均一和稳定,堆晶橄榄岩和辉石岩的(^(87)Sr/^(86)Sr);=0.7051～0.7056,ε_(Nd)(t)=2.8～4.1,玄武岩的(^(87)Sr/^(86)Sr)_i=0.7050～0.7056,ε_(Nd)(t)=5.1～5.8,且显示出原始地幔的同位素组成特征,暗示这些岩石为同源岩浆分异演化而成的岩浆产物。岩浆演化的主要方式为分离结晶作用,受地壳混染不明显。岩浆结晶形成岩石的顺序为:堆晶橄榄岩→堆晶辉石岩→堆晶辉长岩→玄武岩2组→玄武岩1组。岩石地球化学特征表明,吉义独蛇绿岩的形成与俯冲作用有关,且形成于金沙江洋内俯冲的消减环境。

滇川西部金沙江石炭纪蛇绿岩SHRIMP测年:古特提斯洋壳演化的同位素年代学制约

本文应用SHRIMP方法精确测定了金沙江蛇绿岩带中蛇绿岩的辉长岩和斜长岩、呈脉状产于辉长岩和变质橄橄岩中的斜长花岗岩、以及呈岩株状侵入蛇绿岩中的花岗闪长岩的锆石U-Pb年龄,提供了古特提斯洋壳演化的年代学制约。滇西之用层状角闪辉长岩的年龄为328±8Ma,书松斜长岩为329±7Ma,白马雪山辉长岩为282～285Ma,它们可能反映了海底扩张不同阶段的时代。研究还表明,在这些辉长岩和斜长岩中,部分锆石记录了375～352Ma的略老的年龄,暗示蛇绿岩浆活动可能始于晚泥盆世。在金沙江蛇绿岩中,滇西娘九丁斜长花岗岩和川西雪堆斜长花岗岩,具有高硅低钾的成分特征。但是,这些岩石的REE总量高,LREE富集;Sr初始值高,达0.7058～0.7070;在其锆石组成中,存在继承锆石。这些证据表明斜长花岗岩中存在陆壳物质的混染,可能与洋壳俯冲消减有关。娘九丁斜长花岗岩的年龄为285±6Ma,雪堆斜长花岗岩为300±5Ma,记录了古特提斯洋壳俯冲消减事件。滇西吉义独花岗闪长岩,呈岩株状侵入蛇绿岩中,年龄为263±6Ma,限定了蛇绿混杂岩的年代上限。

人为活动干扰对纳帕海湿地环境影响的研究

纳帕海是金沙江流域云南西北高原低纬度高海拔的季节性沼泽湿地,有着若尔盖高原湿地和我国北方湿地所不具备的特点,为我国湿地的独特类型。由于其发育于生态脆弱的横断山石灰岩地区,地处长江上游,承接和调节着高原山区的冰雪融水、地表径流和河流水量,控制着土壤侵蚀,对长江下游水位和水量均衡有着重要作用,但长期以来不合理开发利用,使该区生态环境退化问题十分严重。探讨了人为活动干扰对纳帕海湿地环境的影响,结果表明:排水垦殖造田、过牧超载等人类活动的强烈干预对纳帕海湿地发生发展产生显著影响,40年间湖面积减少了9/10,高原特有水生植物消失或减少,草场资源与牲畜放牧关系严重失调,超载率132.5%,土壤养分衰减下降,湿地严重退化。