PROSPECTING FOR COPPER (GOLD )-POLYMETAL ORES FROM THE LANCANGJIANG TECTONIC ZONE IN WESTERN YUNNAN

The Lancangjiang tectonic zone in Western Yunnan is an important magmatic,metamorphic and tectonic mobile zone of Southwestern China,whose geotectonic location is very unique.It is characterized by complex geological structures,perfectly developed strata,frequent magmatic activities,,various degrees of metamorphism,rich ore resources and lots of metal deposits,thus formed a centralized zone of mineralization and also constituted one of the important metallogenic belts of noble and nonferrous metal deposits.     

Geochemistry and Geochronology of the Jinghong Ophiolites: Implications for the Tectonic Evolution of the Eastern Paleo-Tethys

The Jinghong mafic–ultramafic complex, exposed in the eastern margin of the Lancangjiang tectonic belt, is related to the subduction of the Paleo-Tethys Ocean. Its petrogenesis plays a key role in constraining the tectonic evolution of the eastern Paleo-Tethys Ocean in southwestern China. In this study, we present petrological, geochemical and geochronological results of the Jinghong complex rocks, in order to decipher their origin and tectonic significance. The Jinghong mafic–ultramafic complex was composed of peridotite, gabbro, basalt and minor plagiogranite. Whole-rock geochemical data of the mafic rocks indicate that they have both MORB and IAB affinities and plot in the back-arc basin basalt (BABB) field in the FeO*/MgO vs. TiO2 diagram. Combined with their trace element characteristics, it can be concluded that the Jinghong mafic–ultramafic complex represents an ophiolite suite that was formed in a back-arc ocean basin. Precise LA-ICP-MS zircon U-Pb dating yielded weighted mean 206Pb/238U ages of 298.4 ± 1.7 Ma, 294.3 ± 1.6 Ma, and 292.8 ± 2.0 Ma for gabbroic rocks from this complex, which indicates that the Jinghong ophiolites were formed during the early Permian (298–293 Ma). We propose that during subduction of the main Paleo-Tethys Ocean, a back-arc ocean basin was formed at the east of the Lancangjiang tectonic belt.     

滇西南南澜沧江构造岩浆岩带早侏罗世火山岩的发现——兼论云南省境内印支构造旋回的上限

采用锆石激光剥蚀法(LA-ICP-MS)对滇西南南澜沧江火山岩带普洱市江桥—那澜一带的流纹岩进行了年代测定,获得了(196.7±2.3)Ma、(198.1±3.5)Ma的同位素年龄;表明该地区的流纹岩形成于早侏罗世,而非前人划分的晚三叠世,填补了该地区早侏罗世的火山-沉积记录。从岩石的主元素、稀土元素及微量元素资料分析,南澜沧江构造岩浆岩带早侏罗世的火山岩形成于碰撞后的伸展构造背景,可能与西侧昌宁—孟连古特提斯洋盆关闭后,俯冲岩石圈板片或造山带山根的拆沉作用相关,属后碰撞—后造山阶段岩浆活动的产物。具有典型后造山花岗岩或"A"型花岗岩的特征,其指示了印支构造旋回在滇西南地区最终结束的时间上限。     

三江地区澜沧江带南段半坡杂岩体锆石U-Pb年龄、岩石地球化学特征及板块构造环境

半坡杂岩体位于滇西澜沧江构造岩浆带南段,岩体主要由橄榄岩、辉石岩、辉长岩和辉长闪长岩等镁铁 超镁铁质岩组成。通过ID-TIMS锆石U-Pb年代学方法对半坡杂岩体中辉长闪长岩进行精确定年,获得其结晶年龄为(294.9±2.6) Ma,表明半坡杂岩体的形成时代为早二叠世。半坡杂岩体中不同类型岩石微量元素、稀土元素和同位素组成相似,均呈现轻稀土元素(LREEs)相对于重稀土元素(HREEs)弱到中等富集,高场强元素Nb、Ta、Zr和Hf相对亏损的特征,εNd(t=295 Ma)为正值,在+3.4~+6.6,接近亏损地幔值,这些特征与典型的大洋岛弧玄武岩的特征相似。混合计算表明,半坡杂岩体母岩浆为地幔楔部分熔融,加上约2%~7%源于大洋俯冲沉积物的富硅熔浆和蚀变洋壳流体形成的岛弧玄武质岩浆。上述年龄和同位素数据提供了早二叠世早期南澜沧江地区洋内俯冲的可靠证据。     

大瑞铁路澜沧江大桥工程边坡稳定性三维数值模拟分析

采用现场调查、工程地质分析和三维数值模拟方法,对在建大瑞铁路工程澜沧江大桥边坡稳定性进行了综合分析研究。澜沧江大桥是在建大瑞铁路的控制性工程之一,由于多种因素的综合作用,桥址岸坡发育延伸较长的顺坡向节理和近垂直的陡倾节理。右岸桥位工程开挖区位于一组较大型顺坡结构面的下方,岸坡稳定性直接关系到桥位的适宜性。综合研究表明,工程开挖后,右岸桥位上部岩体极易在顺坡向结构面的控制下发生滑移–拉裂式破坏,沿外倾结构面产生较大的位移,甚至可能失稳,需要进行专门的工程治理。左岸边坡岩体结构相对稳定,工程开挖后,位移将主要集中在开挖面附近的浅表层部位,不仅变形较小,影响范围也相对较小。      

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.     

澜沧江梯级筑坝下水体氮磷分布特征及其形成机制

水库建设改变了河流水文情势及物质迁移转化过程,从而影响水环境质量。为探究梯级筑坝影响下河流氮、磷的空间分布特征及其形成机制,以澜沧江为研究对象,于2016年和2021年分别开展了沿程水环境监测,对比分析水体中氮、磷及其形态浓度在水库建成前后的变化及沿程分布特征,探究氮、磷变化及其沿程分布的主控因子和影响机制。结果表明：由于河流建库蓄水淹没的土地释放大量土壤有机氮,新建水库段(2021年)水体总氮(TN)浓度相比于建库前(2016年)显著上升;由于建库后水流流速减缓而促进颗粒态磷沉降,水体总磷(TP)浓度显著下降。此外,河流建库蓄水后原自然河道的水环境特征改变且利于沉积物磷的释放,筑坝后水体磷酸盐(PO₄^3--P)占生物可利用磷(Bio-P)的比例显著上升。受沿程土地利用的影响,从上游到下游水体TN浓度总体上逐渐升高,而水体TP浓度由于水库的截留效应逐渐降低。筑坝增加的水力停留时间为水库氮、磷转化提供了有利条件,主要表现为溶解性无机氮以硝态氮为主转变为以氨氮为主;同时,Bio-P中PO₄^3--P的占比...     

2005年雨季"三江源"地区对流云的特征分析

利用2005年6~9月逐日逐时FY-2C气象卫星数值云图资料,计算和分析了青藏高原三江源区域的对流云和中尺度对流系统(s-MCS)的发生频率。结果表明,该区域主要以对流云为主,对流云占总云量的80%以上,利用TBB值得出该区域对流云发生源地主要集中在两大区域,其中以32°~35°N,93°~98°E为主要多发区(称为第一高发区),以35°~37°N,91°~95°E为次多发区(称为第二高发区);该区域对流云存在着明显的日变化,22:00(世界时,下同)~06:00(上半夜)对流云旺盛,06:00~14:00(下半夜)及清晨对流云很少。最后结合地面观测资料给出了云顶亮温与地面降水的关系。     

澜沧江铁矿带惠民式-疆峰式铁矿床特征与含铁建造

通过对惠民式和疆峰式铁矿的研究,认为它们都是受变质中基性火山岩建造控制的海相火山-沉积型铁矿床,前者兼有条带状含铁建造(BIF)和粒状含铁建造(GIF)的特征,而后者则为条带状含铁建造.它们均具备元古代条带状铁硅建造铁矿的特征,满足形成前寒武纪大型条带状含铁建造的“大型海洋热液供应系统、作为沉积仓储的大陆架体貌及有能力...     

三江地区澜沧江带南段南林山基性岩体锆石U-Pb年龄及岩石地球化学特征

南林山基性岩体位于西南三江地区,岩体主要由辉长岩和闪长岩组成。通过ID-TIMS锆石U-Pb年代学方法对南林山岩体中闪长岩进行精确定年,获得其结晶年龄为（298.44±0.33）Ma,表明南林山基性岩体的形成时代为早二叠世。全岩主量、微量元素与稀土元素等研究表明,辉长岩和闪长岩总体上均呈现轻稀土元素（LREEs）相对于...