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1.
Geological and geochemical study has been carried out to investigate arsenic contamination in groundwater in Nawalparasi, the western Terai district of Nepal. The work carried out includes analyses of core sediments, provenance study by rare earth elements analyses, 14C dating, and water analyses. Results showed that distribution of the major and trace elements are not homogeneous in different grain size sediments. Geochemical characteristics and sediment assemblages of the arsenic contaminated (Nawalparasi) and uncontaminated (Bhairahawa) area have been compared. Geochemical compositions of sediments from both the areas are similar; however, water chemistry and sedimentary facies vary significantly. Extraction test of sediment samples showed significant leaching of arsenic and iron. Chemical reduction and contribution from organic matter could be a plausible explanation for the arsenic release in groundwater from the Terai sediments. 相似文献
2.
Pramod Singh 《Chemical Geology》2010,269(3-4):220-236
Major, trace and REE compositions of sediments from the upper Ganga River and its tributaries in the Himalaya have been examined to study the weathering in the Himalayan catchment region and to determine the dominant source rocks to the sediments in the Plains. The Ganga River rises in the Higher Himalaya from the Higher Himalayan Crystalline Series (HHCS) bedrocks and traverses over the Lesser Himalayan Series (LHS) and the Himalayan foreland basin (Siwaliks) rocks before entering into the Gangetic Plains. The major element compositions of sediments, reflected in their low CIA values (45.0–54.7), indicate that silicate weathering has not been an important process in the Himalayan catchment region of the Ganga River. Along the entire traverse, from the HHCS through LHS and the Siwaliks, the sediments from the tributaries and the mainstream Ganga River show higher Na2O, K2O, CaO and silica. This, and the higher ratios of La/Sc, Th/Sc and lower ratios of Co/Th, suggest that the source rocks are felsic. The fractionated REE patterns and the significant negative Eu anomalies (Eu/Eu? = 0.27–0.53) indicate highly differentiated source. Moreover, the comparison of the sediments with different source rock lithologies from the HHCS and the LHS for their major elements clearly suggests that the HHCS rocks were the dominant source. Further, comparison of their UCC (upper continental crust) normalized REE patterns suggests that, among the various HHCS rocks, the metasediments (para-gneiss and schist) and Cambro-Ordovician granites have formed the major source rocks. The Bhagirathi and Alaknanda River sediments are dominantly derived from metasediments and those in the Mandakini River from Cambro-Ordovician granites. The resulting composition of the sediments of the Ganga River is due to the mixing of sediments supplied by these tributaries after their confluence at Devprayag. No further change in major, trace and rare earth element compositions of the sediments of the Ganga River after Devprayag up to its exit point to the Plains at Haridwar, suggests little contribution of the Lesser Himalayan and Siwalik rocks to the Ganga River sediments. 相似文献
3.
Babar A. Shah 《Environmental Geology》2008,53(7):1553-1561
Late Quaternary stratigraphy and sedimentation in the Middle Ganga Plain (MGP) (Uttar Pradesh–Bihar) have influenced groundwater
arsenic contamination. Arsenic contaminated aquifers are pervasive within narrow entrenched channels and flood plains (T0-Surface) of fine-grained grey to black coloured argillaceous organic rich Holocene sediments (Newer Alluvium). Contaminated
aquifers are often located close to distribution of abandoned or existing channels and swamps. The Pleistocene Older Alluvium
upland terraces (T2-Surface) made up of oxidized yellowish brown sediments with calcareous and ferruginous concretions and the aquifers within
it are free of arsenic contamination. MGP sediments are mainly derived from the Himalaya with minor inputs from the Peninsular
India. The potential source of arsenic in MGP is mainly from the Himalaya. The contaminated aquifers in the Terai belt of
Nepal are closely comparable in nature and age to those of the MGP. Arsenic was transported from disseminated sources as adsorbed
on dispersed phases of hydrated-iron-oxidea and later on released to groundwater mainly by reductive dissolution of hydrated-iron-oxide
and corresponding oxidation of organic matter in aquifer. Strong reducing nature of groundwater is indicated by high concentration
of dissolved iron (11.06 mg/l). Even within the arsenic-affected areas, dugwells are found to be arsenic safe due to oxyginated
nature. 相似文献
4.
5.
Shilpa Vuba Sadia Farnaaz Netramani Sagar S. Masood Ahmad 《Journal of the Geological Society of India》2013,82(3):217-226
The major, trace and rare earth elements geochemistry and clay mineral compositions in the river bed sediments from lower reaches of Godavari river suggest that they are derived from weathering of felsic rocks. Trace and rare earth elemental compositions indicate evidence of sedimentary sorting during transportation and deposition. Lower concentrations of transition elements, such as V, Ni and Cr imply enrichment of felsic minerals in these bed sediments. The REE pattern in lower Godavari sediments is influenced by the degree of source rock weathering. The light rare earth elements (LREE) content are indicating greater fractionation compared to the heavy rare earth elements (HREE). A striking relationship is observed between TiO2 and gZREE content suggesting a strong control by LREE-enriched titaniferous minerals on REE chemistry. Shale-normalized REE pattern demonstrate a positive Eu anomaly, suggesting weathering of feldspar and their secondary products, which are enriched in Eu. Chondrite-normalised REE pattern is characteristic of felsic volcanic, granites and gnessic source rocks. Trace elemental compositions in sediments located near urban areas suggest influence of anthropogenic activity. Chemical Index of Alteration (CIA) is high (avg. 65.76), suggesting a moderate chemical weathering environment. X-ray diffraction analysis of clay fraction shows predominance of clay minerals that are formed because of the chemical weathering of felsic rocks. 相似文献
6.
《Journal of Asian Earth Sciences》1999,17(5-6):577-606
Nepal can be divided into the following five east–west trending major tectonic zones. (i) The Terai Tectonic Zone which consists of over one km of Recent alluvium concealing the Churia Group (Siwalik equivalents) and underlying rocks of northern Peninsular India. Recently active southward-propagating thrusts and folds beneath the Terai have affected both the underlying Churia and the younger sediments. (ii) The Churia Zone, which consists of Neogene to Quaternary foreland basin deposits and forms the Himalayan mountain front. The Churia Zone represents the most tectonically active part of the Himalaya. Recent sedimentologic, geochronologic and paleomagnetic studies have yielded a much better understanding of the provenance, paleoenvironment of deposition and the ages of these sediments. The Churia Group was deposited between ∼14 Ma and ∼1 Ma. Sedimentary rocks of the Churia Group form an archive of the final drama of Himalayan uplift. Involvement of the underlying northern Peninsular Indian rocks in the active tectonics of the Churia Zone has also been recognised. Unmetamorphosed Phanerozoic rocks of Peninsular India underlying the Churia Zone that are involved in the Himalayan orogeny may represent a transitional environment between the Peninsula and the Tethyan margin of the continent. (iii) The Lesser Himalayan Zone, in which mainly Precambrian rocks are involved, consists of sedimentary rocks that were deposited on the Indian continental margin and represent the southernmost facies of the Tethyan sea. Panafrican diastrophism interrupted the sedimentation in the Lesser Himalayan Zone during terminal Precambrian time causing a widespread unconformity. That unconformity separates over 12 km of unfossiliferous sedimentary rocks in the Lesser Himalaya from overlying fossiliferous rocks which are >3 km thick and range in age from Permo-Carboniferous to Lower to Middle Eocene. The deposition of the Upper Oligocene–Lower Miocene fluvial Dumri Formation records the emergence of the Himalayan mountains from under the sea. The Dumri represents the earliest foreland basin deposit of the Himalayan orogen in Nepal. Lesser Himalayan rocks are less metamorphosed than the rocks of the overlying Bhimphedis nappes and the crystalline rocks of the Higher Himalayan Zone. A broad anticline in the north and a corresponding syncline in the south along the Mahabharat range, as well as a number of thrusts and faults are the major structures of the Lesser Himalayan Zone which is thrust over the Churia Group along the Main Boundary Thrust (MBT). (iv) The crystalline high-grade metamorphic rocks of the Higher Himalayan Zone form the backbone of the Himalaya and give rise to its formidable high ranges. The Main Central Thrust (MCT) marks the base of this zone. Understanding the origin, timing of movement and associated metamorphism along the MCT holds the key to many questions about the evolution of the Himalaya. For example: the question of whether there is only one or whether there are two MCTs has been a subject of prolonged discussion without any conclusion having been reached. The well-known inverted metamorphism of the Himalaya and the late orogenic magmatism are generally attributed to movement along the MCT that brought a hot slab of High Himalayan Zone rocks over the cold Lesser Himalayan sequence. Harrison and his co-workers, as described in a paper in this volume, have lately proposed a detailed model of how this process operated. The rocks of the Higher Himalayan Zone are generally considered to be Middle Cambrian to Late Proterozoic in age. (v) The Tibetan Tethys Zone is represented by Cambrian to Cretaceous-Eocene fossiliferous sedimentary rocks overlying the crystalline rocks of the Higher Himalaya along the Southern Tibetan Detachment Fault System (STDFS) which is a north dipping normal fault system. The fault has dragged down to the north a huge pile of the Tethyan sedimentary rocks forming some of the largest folds on the Earth. Those sediments are generally considered to have been deposited in a more distal part of the Tethys than were the Lesser Himalayan sediments.The present tectonic architecture of the Himalaya is dominated by three master thrusts: the Main Central Thrust (MCT), the Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). The age of initiation of these thrusts becomes younger from north to south, with the MCT as the oldest and the MFT as the youngest. All these thrusts are considered to come together at depth in a flat-lying decollement called the Main Himalayan Thrust (MHT). The Mahabharat Thrust (MT), an intermediate thrust between the MCT and the MBT is interpreted as having brought the Bhimphedi Group out over the Lesser Himalayan rocks giving rise to Lesser Himalayan nappes containing crystalline rocks. The position of roots of these nappes is still debated. The Southern Tibetan Detachment Fault System (STDFS) has played an important role in unroofing the higher Himalayan crystalline rocks. 相似文献
7.
藏南定结淡色花岗岩--基底隆升降压熔融成因的地质证据 总被引：6，自引：0，他引：6
西藏南部定结地区高喜马拉雅结晶基底中淡色花岗岩体紧靠藏南拆离断层内部产出．野外地质和岩相学特征显示其为S型、分两期侵入的淡色花岗岩体——早期的黑云母淡色花岗岩和晚期的白云母淡色花岗岩。基底副变质岩中广泛分布淡色花岗岩脉体．在基底副变质岩中的淡色花岗岩脉体中发现紫苏辉石暗色麻粒岩残留体，这表明本区高喜马拉雅淡色花岗岩源岩为基底副变质岩，且基底副变质岩是在基底快速隆升降压的条件下发生缺水熔融生成的淡色花岗岩岩浆。 相似文献
8.
喜马拉雅淡色花岗岩世界瞩目,具有重要的理论研究和找矿意义,但是其成因争议较大。本文统计了两千余件样品的全岩主微量地球化学、Sr-Nd-Pb-Hf同位素、锆石/独居石/磷钇矿等副矿物原位U-Pb年龄和锆石Hf同位素等,试图全面地总结喜马拉雅淡色花岗岩的研究进展和现状。喜马拉雅淡色花岗岩分为南北两带,北带花岗岩主要出露于特提斯喜马拉雅和片麻岩穹隆中,而南带花岗岩主要发育在高喜马拉雅顶部和东-西构造结中。从北往南,成岩时代逐渐变新;南北两带均以二云母花岗岩和(石榴石-电气石)白云母花岗岩为主,两期(始新世和中新世)中-基性岩脉和埃达克质岩主要在北带中发育。新生代岩浆活动分为5个阶段：49~40 Ma、39~29 Ma、28~15 Ma、14~7 Ma、6~0.7 Ma,分别主要与新特提斯洋壳板片断离、印度陆壳板片的低角度俯冲、断离或回撤、南北向撕裂(裂谷)和东西构造结的快速隆升有关。喜马拉雅淡色花岗岩起源于高喜马拉雅杂岩系的不一致(不平衡)部分熔融,并经历了矿物分离结晶的高分异演化。淡色花岗岩属于强过铝质岩石,具有高Si、K、Na,低Ca、Fe、Mg、Ti、Mn,高的Rb/Sr、Y/Ho值,低的Th/U、Nb/Ta、Zr/Hf、K/Rb值,稀土元素总量较低,负Eu异常明显的地球化学特征。随着成岩时代变新,Sr-Nd-Pb-Hf等同位素都指示岩浆源区中古老地壳物质的占比逐步增加。喜马拉雅淡色花岗岩/伟晶岩中Li、Be、W、Sn、Ta、Cs和Rb等稀有元素的富集系数大于10,伟晶岩属于典型的LCT型伟晶岩。喜马拉雅新生代淡色花岗岩带有望成为一条新的世界级的Li-Be-Sn-W-Ta稀有金属成矿带。 相似文献
9.
Major and trace element and Rb-Sr isotope systematics of the Manaslu leucogranite, Central Nepal, have been examined to constrain the role of mineral fractionation and fluids in peraluminous granite petrogenesis. Biotite and tourmaline are, for the most part, mutually exclusive, with a predominance of two-mica leucogranites over tourmaline leucogranites. The 87Sr/86Sr initial isotopic ratios (Sri) indicate that leucogranitic melts were derived from two different sources, the two-mica leucogranites having a metagreywacke origin (with Sri < 0.752 and εNd < −15) and the tourmaline leucogranites a metapelitic one (Sri> 0.752; εNd > − 15). Such a bimodal nature of the source zone does not directly influence the magmatic evolution, except that probably the higher initial boron content in the metapelitic rocks may increase the Na2O/K2O ratio. In contrast, the amount of water present during melting principally controls in part anatectic processes and element behaviour. Water-saturated conditions probably occured during melting of metagreywackeous rocks and favoured crystallization of two-mica leucogranites whereas water-absent conditions prevailed during melting of metapelitic layers and favoured biotite, plagioclase and monazite fractionation in the source zone and tourmaline crystallization in the leucogranite. 相似文献
10.
《地学前缘(英文版)》2021,12(3)
More than 2.5 billion people on the globe rely on groundwater for drinking and providing high-quality drinking water has become one of the major challenges of human society.Although groundwater is considered as safe,high concentrations of heavy metals like arsenic(As) can pose potential human health concerns and hazards.In this paper, we present an overview of the current scenario of arsenic contamination of groundwater in various countries across the globe with an emphasis on the Indian Peninsula.With several newly affected regions reported during the last decade, a significant increase has been observed in the global scenario of arsenic contamination.It is estimated that nearly 108 countries are affected by arsenic contamination in groundwater(with concentration beyond maximum permissible limit of 10 ppb recommended by the World Health Organization.The highest among these are from Asia(32) and Europe(31), followed by regions like Africa(20), North America(11), South America(9) and Australia(4).More than 230 million people worldwide, which include 180 million from Asia, are at risk of arsenic poisoning.Southeast Asian countries, Bangladesh, India, Pakistan,China, Nepal, Vietnam, Burma, Thailand and Cambodia, are the most affected.In India, 20 states and 4 Union Territories have so far been affected by arsenic contamination in groundwater.An attempt to evaluate the correlation between arsenic poisoning and aquifer type shows that the groundwater extracted from unconsolidated sedimentary aquifers, particularly those which are located within the younger orogenic belts of the world, are the worst affected.More than 90% of arsenic pollution is inferred to be geogenic.We infer that alluvial sediments are the major source for arsenic contamination in groundwater and we postulate a strong relation with plate tectonic processes, mountain building, erosion and sedimentation.Prolonged consumption of arsenic-contaminated groundwater results in severe health issues like skin, lung, kidney and bladder cancer; coronary heart disease;bronchiectasis; hyperkeratosis and arsenicosis.Since the major source of arsenic in groundwater is of geogenic origin, the extend of pollution is complexly linked with aquifer geometry and aquifer properties of a region.Therefore, remedial measures are to be designed based on the source mineral, climatological and hydrogeological scenario of the affected region.The corrective measures available include removing arsenic from groundwater using filters, exploring deeper or alternative aquifers, treatment of the aquifer itself, dilution method by artificial recharge to groundwater, conjunctive use, and installation of nano-filter, among other procedures.The vast majority of people affected by arsenic contamination in the Asian countries are the poor who live in rural areas and are not aware of the arsenic poisoning and treatment protocols.Therefore, creating awareness and providing proper medical care to these people remain as a great challenge.Very few policy actions have been taken at international level over the past decade to reduce arsenic contamination in drinking water, with the goal of preventing toxic impacts on human health.We recommend that that United Nations Environment Programme(UNEP) and WHO should take stock of the global arsenic poisoning situation and launch a global drive to create awareness among people/medical professionals/health workers/administrators on this global concern. 相似文献
11.
选择江汉盆地中心位置的ZL钻孔,利用ICP-MS方法,对钻孔岩心微量元素组成进行了R因子分析,研究了新近纪以来江汉盆地沉积物物源的变化。结果表明：2.77~2.68 Ma B.P.期间,江汉盆地沉积物微量元素组成表达了一种近源为主的沉积过程;2.68~2.23 Ma B.P.期间,江汉盆地碎屑沉积受长英质类物源供给影响较为明显;2.23~1.25 Ma B.P.时期及1.25 Ma B.P.以来的沉积物微量元素特征都表现出受铁镁质岩体影响的特征,推测这一阶段有较大面积基性岩体分布的长江上游流域可能已经成为江汉盆地的物源供给者。 相似文献
12.
徽成盆地是西秦岭造山带内一个具有代表性的盆地,保留较完整的地层记录.早白垩世田家坝组、周家湾组和鸡山组为一套砂砾岩沉积组合序列.本文通过对早白垩世砂岩的古水流恢复、砾石成分与含量、重矿物和地球化学分析,对沉积岩物源区特征和原型盆地进行探讨.古水流恢复和砾石成分统计表明,沉积物主要是近源堆积,主要来自于盆地南缘和北部.重矿物研究结果表明,早白垩世砂岩母岩以岩浆岩为主,并有少量变质岩/沉积岩.地球化学分析表明,早白垩世砂岩为成熟度较低的硬砂岩和长石/岩屑砂屑岩.稀土元素标准化配分曲线呈现轻稀土富集、重稀土平坦和弱Eu负异常特征.砂岩物源区组成判别图研究表明,早白垩世砂岩的物源区主要出露长英质火山岩.砂岩源区构造环境判别图解及特征指数分析表明,早白垩世砂岩源区主要形成于大陆岛弧和活动大陆边缘.结合区域资料和前人研究,表明早白垩世徽成地区发育走滑拉分盆地. 相似文献
13.
High- and Low-Temperature I-type Granites 总被引：4，自引：0，他引：4
B. W. CHAPPELL C. J. BRYANT D. WYBORN A. J. R. WHITE I. S. WILLIAMS 《Resource Geology》1998,48(4):225-235
Abstract: I– and S-type granites differ in several distinctive ways, as a consequence of their derivation from contrasting source rocks. The more mafic granites, whose compositions are closest to those of the source rocks, are most readily classified as I– or S–type. As granites become more felsic, compositions of the two types converge towards those of lowest temperature silicate melts. While discrimination of the two is therefore more difficult for such felsic rocks, that in no way invalidates the twofold subdivision. If felsic granite melts undergo fractional crystallisation, the major element compositions are not affected to any significant extent, but the concentrations of trace elements can vary widely. For some trace elements, fractional crystallisation causes the trace element abundances to diverge, so the I– and S– type granites are again easily separated. Such fractionated S-type granites can be distinguished, for example, by high P and low Th and Ce, relative to their I-type analogues. Our observations in the Lachlan Fold Belt show that there is no genetic basis for subdividing peraluminous granites into more mafic and felsic varieties, as has been attempted elsewhere. The subdivision of felsic peraluminous granites into I– and S-types is more appropriate, and mafic peraluminous granites are always S–type. In a given area, associated mafic and felsic S-type granites are likely to be closely related in origin, with the former comprising both restite-rich magmas and cumulate rocks, and the felsic granites corresponding to melts that may have undergone fractional crystallisation after prior restite separation. We propose a subdivision of I-type granites into two groups, formed at high and low temperatures. The high-temperature I–type granites formed from a magma that was completely or largely molten, and in which crystals of zircon were not initially present because the melt was undersaturated in zircon. In comparison with low-temperature I–type granites, the compositions extend to lower SiO2 contents and the abundances of Ba, Zr and the rare earth elements initially increase with increasing SiO2 in the more mafic rocks. While the high-temperature I–type granite magmas were produced by the partial melting of mafic source rocks, their low-temperature analogues resulted from the partial melting of quartzofeldspathic rocks such as older tonalites. In that second case, the melt produced was felsic and the more mafic low-temperature I–type granites have that character because of the presence of entrained and magmatically equilibrated restite. High temperature granites are more prospective for mineralisation, both because of that higher temperature and because they have a greater capacity to undergo extended fractional crystallisation, with consequent concentration of incompatible components, including H2O. 相似文献
14.
藏南萨迦拉轨岗日淡色花岗岩特征及与变质核杂岩的关系 总被引：11，自引：1，他引：10
藏南拉轨岗日带展布着串珠状变质核杂岩, 其内出露的淡色花岗岩体构成北喜马拉雅淡色花岗岩带.岩体既有在变质核杂岩内核中分布的, 亦有在滑脱系分布的, 岩体均表现出强力主动侵位的特征.淡色花岗岩可分为两期: 早期黑云母淡色花岗岩和晚期白云母淡色花岗岩.岩石高硅富铝, 含白云母±电气石±石榴石特征富铝矿物, 为S型花岗岩.北喜马拉雅淡色花岗岩结晶年龄为17~10Ma, 源岩为MCT上部基底副变质岩.当挤压体制与伸展体制转换时, 降压作用导致了岩浆的生成, 同时, 由于压力骤减, 年轻造山带更为塑性的下地壳物质与软层隆起导致上地壳伸展, 从而形成变质核杂岩, 岩浆对内核的上隆起到促进作用. 相似文献
15.
莫尔道嘎地处额尔古纳地块中北段,该区发育一套中低级变质的佳疙瘩组变质岩,如千枚岩、云母片岩和变质砂岩;但是目前其原岩类型、物质来源以及沉积环境尚不明确.基于全岩主微量元素测试和LA-ICP-MS U-Pb定年,结果表明千枚岩类和云母片岩类总体富Al和K,变质砂岩类总体富Si.岩石轻稀土明显富集,具负铕异常特征,高场强元素相对富集,Sr强烈亏损,Nb、Ta、P、Ti相对亏损.原岩性质及构造环境分析表明,原岩类型主要是杂砂岩和粘土岩,物源以长英质成分为主,并混有少量古老沉积物.它们形成于活动大陆边缘,并存在较多大陆岛弧性质物质,成熟度不高,属于近源沉积.岩石样品中的碎屑锆石多为岩浆成因,且显示了较大的年龄变化,主要集中在新元古代（1.0~0.8 Ga）和古元古代（2.0~1.8 Ga）,说明佳疙瘩组的沉积物源时代主要为新元古代和古元古代. 相似文献
16.
鄂尔多斯盆地三叠系延长组长7段物源区分析 总被引：1，自引：0，他引：1
随着鄂尔多斯盆地长7段油藏勘探的不断突破,对其物源方向和母岩区性质的分析尤显重要.三叠世延长期鄂尔多斯盆地周缘存在多个古陆,包括北缘的阴山古陆、西北缘的阿拉善古陆、西南缘的陇西古陆及南缘的祁连-秦岭古陆等,它们都是盆地碎屑沉积物的主要供给源.通过碎屑组分、岩屑组分、重矿物、微量元素和稀土元素分析等研究,认为研究区长7段存在东北、西北、西及西南、南部4个方向的物源.轻、重矿物组合综合分析认为,盆地北部母岩主要为太古宙—古生代中—深变质岩和中基性火成岩,西南及南部母岩主要为元古宙—古生代浅变质岩、碳酸盐岩和碎屑岩.微量及稀土元素分析表明母岩以大陆上地壳的长英质岩石为主,并混有一定数量的含长石较高的中—基性岩浆岩如安山岩、碱性玄武岩,母岩中太古代古老地层占有相当大的比重. 相似文献
17.
P. K. Govil J. E. Sorlie D. Sujatha A. K. Krishna N. N. Murthy K. Rama Mohan 《Environmental Earth Sciences》2012,66(1):121-128
Spatial distribution and temporal trends studies were carried out at Katedan Industrial Development Area (KIDA) near Hyderabad,
capital of Andhra Pradesh state, India under Indo-Norwegian Institutional Cooperation Program, to find out the extent of contamination
in streams and lake sediments from the discharge of industrial effluents. Stream and lake sediment samples were collected
from the five lakes in the study area and connecting water streams. The samples were analyzed by XRF spectrometer for toxic
elements. The studies reveal that the stream sediments with in the KIDA and the impounded Noor Mohammed Lake down stream have
high concentration of some of the toxic elements like chromium, nickel, lead, arsenic, zinc etc. The geology of the area indicates
that the study area consists of residual soil of acidic rocks, which are predominantly of Archaean gneisses and granites having
low to medium concentrations of chromium and nickel. The source of these high concentration of elements like lead 2,300 mg/kg,
copper 1,500 mg/kg, arsenic 500 mg/kg, chromium 500 mg/kg etc. cannot be derived from the surrounding acidic rocks and may
be attributed to the industrial effluents released in the ditches and random dumping of hazardous solid waste. It was observed
that the metal concentrations increased in the streams during the dry season (pre-monsoon period). After the monsoon rains,
the metal concentrations in the streams were reduced by half which may be due to dilution. The eroded sediments are deposited
in the lake where very high concentrations were encountered. Overflowing of the lake will spread the contamination further
downstream. The lake sediments will remain as a major source of contamination by desorption to the water phase regardless
of what happens to the effluent discharge in the KIDA. However, some samples showed enrichment of lead, arsenic and nickel
during post-monsoon, which were collected near the dumpsite due to the leaching of toxic elements from the dump site to the
lakes. Some of the toxic elements like nickel and copper have not shown any dilution but have increased after the rains, which
could be due to the leaching of arsenic from the dumpsite to the lake along with rainwater. Geochemical maps showing the distribution
of heavy/trace elements in streams and lakes are prepared and presented in this paper. Effect of toxic elements on the health
of the residents in the surrounding residential areas is also discussed. 相似文献
18.
《Journal of Asian Earth Sciences》1999,17(5-6):607-628
At least seven different groups of felsic magmatic rocks have been observed in the Lesser and Higher Himalayan units of Nepal. Six of them are pre-Himalayan. The Ulleri Lower Proterozoic augen gneiss extends along most of the length of the Lesser Himalaya of Nepal and represents a Precambrian felsic volcanism or plutono-volcanism, mainly recycling continental crustal material; this volcanism has contributed sediment to the lower group of formations of the Lesser Himalaya. The Ampipal alkaline gneiss is a small elongated body appearing as a window at the base of the Lesser Himalayan formations of central Nepal; it originated as a Precambrian nepheline syenite pluton, contaminated by lower continental crust. The “Lesser Himalayan” granitic belt is well represented in Nepal by nine large granitic plutons; these Cambro-Ordovician peraluminous, generally porphyritic, granites, only occur in the crystaline nappes; they were probably produced by large-scale melting of the continental crust at the northern tip of the Indian craton, during a general episode of thinning of Gondwana continent with heating and mantle injection of the crust. The Formation III augen gneisses of the Higher Himalaya, such as the augen gneiss of the Higher Himalayan crystalline nappes (Gosainkund) are coeval to the “Lesser Himalayan” granites, and their more metamorphic (lower amphibolite grade) equivalents. Limited outcrops of Cretaceous trachytic volcanism lie along the southern limb of the Lesser Himalaya and are coeval with spilitic volcanism in the Higher Himalayan sedimentary series. This volcanism foreshadows the general uplift of the Indian margin before the Himalayan collision. The predominance of felsic over basic magmatism in the 2.5 Ga-long evolution of the Himalayan domain constitutes an unique example of recycling of continental material with very limited addition of juvenile mantle products. 相似文献
19.
Jaya K. Gurung Hiroaki Ishiga Mohan S. Khadka Nav R. Shrestha 《Environmental Geology》2007,52(3):503-517
The geochemical analyses of fluvial-lacustrine aquifer sediments of the Kathmandu Valley have been made as a step in assessing
the environment for the mobilization of arsenic in groundwater. Elements measured by X-ray fluorescence (XRF) include 4 major
oxides (Fe2O3, TiO2, CaO, P2O5) and 14 trace elements (As, Pb, Zn, Cu, Ni, Cr, V, Sr, Y, Nb, Zr, Th, Sc and TS). Elution tests of 15 selected core samples
were also carried out to determine the potential leaching of arsenic from the sediments. The XRF results show that average
bulk concentrations of the major oxides and trace elements are similar to modern unconsolidated sediments and average upper
continental crust. However, the abundance of elements varies with grain size, with higher concentrations in finer-size grades.
Variations in elemental abundances within the basin are strongly controlled by sediment facies. The elution tests show that
greater amounts of arsenic are generally eluted from the fine sediments, although the rates are variable. The results overall
suggest that As concentrations in the bulk sediments are not a controlling factor for elevated As in the Kathmandu Basin groundwater,
and the roles of other factors such as redox conditions and organic matter contents are likely to be more significant. 相似文献
20.
Iván Morales-Arredondo Ramiro Rodríguez Maria Aurora Armienta Ruth Esther Villanueva-Estrada 《Hydrogeology Journal》2016,24(4):1029-1044
A groundwater sampling campaign was carried out in the summer of 2013 in a low-temperature geothermal system located in Juventino Rosas (JR) municipality, Guanajuato State, Mexico. This groundwater presents high concentrations of As and F? and high Rn counts, mainly in wells with relatively higher temperature. The chemistry of major elements was interpreted with different methods, like Piper and D’Amore diagrams. These diagrams allowed for classification of four groundwater types located in three hydrogeological environments. The aquifers are hosted mainly in alluvial-lacustrine sediments and volcanic rocks in interaction with fault and fracture systems. The subsidence, faults and fractures observed in the study area can act as preferential channels for recharge and also for the transport of deep fluids to the surface, especially in the basin plain. The formation of a piezometric dome and the observed hydrochemical behavior of groundwater suggest a possible origin of the As and F?. Geochemical processes occurring during water–rock interaction are related to high concentrations of As and F?. High temperatures and alteration processes (like rock weathering) induce dissolution of As and F?-bearing minerals, increasing the content of these elements in groundwater. 相似文献