Anthropogenic Eutrophication and Red Tide Outbreak in Lacustrine Systems of the Kashmir Himalaya     

M. A. Kahn 《洁净——土壤、空气、水》2000,28(2):95-101

Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate.  相似文献   

喜马拉雅淡色花岗岩结晶分异机制概述   总被引：8，自引：5，他引：3  

刘志超  吴福元  刘小驰  王建刚 《岩石学报》2020,36(12):3551-3571

近年来,喜马拉雅淡色花岗岩的高分异成因得到了学术界的高度关注。另外,有调研工作发现,喜马拉雅淡色花岗岩具有良好的稀有金属成矿潜力,是未来矿产勘探的重点靶区。稀有金属元素的富集过程应与岩浆的结晶分异作用密切相关。但是,目前我们对喜马拉雅淡色花岗岩的岩浆分异演化过程缺乏深入的了解,因而也难以对其成矿效应进行有效评估。针对该问题,本文选择喜马拉雅带中两个颇具代表性的、明显发生稀有金属矿化现象的岩体（特提斯喜马拉雅带中的然巴淡色花岗岩和高喜马拉雅带中的告乌淡色花岗岩）开展系统野外地质、岩相学、矿物学、岩石学和地球化学调查研究,就喜马拉雅淡色花岗岩的结晶分异机制进行初步探讨。综合近年来有关花岗岩结晶分异作用的研究进展,我们认为喜马拉雅淡色花岗岩的结晶分异过程可以划分为原地结晶分异和岩浆侵位运移过程中流动分异两种主要机制,大部分的喜马拉雅淡色花岗岩应是两种机制共同作用的产物。  相似文献   

藏南错那洞铍稀有多金属成矿时代:来自热液白云母Ar-Ar年龄的约束   总被引：2，自引：0，他引：2       下载免费PDF全文

梁维  李光明  张林奎  付建刚  黄勇  张志 《沉积与特提斯地质》2020,40(1):76-81

特提斯喜马拉雅是继华南和新疆阿尔泰之后又一条新发现的大型稀有金属成矿带,其成矿时代受到广泛的关注。本文以代表性矿床错那洞铍稀有多金属矿床为研究对象,挑选出矽卡岩型矿化体中的热液白云母,利用Ar-Ar同位素定年的方式测定热液活动时间,以此限制成矿时代。结果显示错那洞穹窿矽卡岩型矿体中白云母Ar-Ar同位素坪年龄为14.21±0.22Ma,对应的~(40)Ar/~(36)Ar-~(39)Ar/~(36)Ar的等时线年龄为14.21±0.27Ma,与错那洞穹窿中具有高分异特征的白云母花岗岩浆侵位时间(～14Ma)一致,表明错那洞矽卡岩型铍稀有多金属矿床的成矿年龄为～14Ma,而与穹窿内高分异白云母花岗岩一致的年龄暗示了该高分异花岗岩为该期矽卡岩型稀有金属矿化的成矿母岩浆。  相似文献   

Genetic implications of Zn‐ and Mn‐rich Cr‐spinels in serpentinites of the Tidding Suture Zone,eastern Himalaya,NE India     

Athokpam K. Singh  Rajkumar B. Singh 《Geological Journal》2013,48(1):22-38

Metamorphosed serpentinites of the Tidding Suture Zone (TSZ), eastern Himalaya, contain variably altered Cr‐spinels that are concentrically zoned from high‐Cr, low‐Fe³⁺ spinel at the core to Cr‐magnetite at the rim. Two types of Cr‐spinel have been recognized, based on back‐scattered electron imaging in conjunction with microprobe analytical profiles. Cr‐spinel type‐I is present in the least metamorphosed serpentinite (Cr# = 0.78–0.85, Mg# = 0.38–0.45) and Cr‐spinel type‐II is present in the most highly metamorphosed serpentinite (Cr# = 0.86–0.94, Mg# = 0.10–0.34). Primary igneous compositions are preserved in the type‐I chromites whereas these compositions have been partly or completely obscured by metamorphism and alteration in type‐II grains. The enrichment of Mn and Zn increases from the type‐I (MnO = 1.86–2.42 wt.%, ZnO = 0.77–1.67 wt.%) to type‐II (MnO = 2.72–4.04 wt.%, ZnO = 1.33–3.22 wt.%) and the strong similarity in their distribution patterns implies that these elements were introduced during low‐grade metamorphism and serpentinization. The abundance of Mg‐rich chlorite and serpentine minerals suggest that olivine was the predominant silicate phase before serpentinization. Zn and Mn enrichment in the core zone of the Cr‐spinel is due to the substitution of Mg²⁺ and in part of Fe²⁺, by Zn and Mn. These elements were probably supplied from olivine upon serpentinization during and after obduction of the ophiolitic mélange along the Tidding Suture Zone in the eastern Himalaya, NE India. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献