Mineralogy and geochemistry of lateritic soil profiles in Kerala, India

Lateritic soils near Calicut, Kerala, contain halloysite of intermediate hydration, kaolinite, goethite, gibbsite and quartz. The presence of halloysite is responsible for relatively high plasticity and cation-exchange capacity. Fe-hydroxide colloids along with halloysite contribute to significant phosphate uptake by this soil. Composition of local groundwater is consistent with weathering of sodic plagioclase to gibbsite, kaolinite and metastable halloysite.     

Shoreline change along Kerala,south-west coast of India,using geo-spatial techniques and field measurement

Natural Hazards - Coastal zone is a central attraction for coastal engineers, scientists and coastal community due to economic and developmental activities of the coast. Kerala has 593 km...     

Sediment geochemistry of coastal environments,southern Kerala,India: implication for provenance

Late Quaternary sediments representing the floodplain, estuary and offshore environments of southern Kerala were investigated to infer provenance. The grain size reveals the dominance of sand to silty clay, clay to clayey silt and clayey silt in the floodplain, estuary and offshore sediments, respectively. The chemical index of alteration (CIA) values and A-CN-K plot attributes to high, moderate and low weathering in floodplain, estuary and offshore regions, respectively. The SiO₂/Al₂O₃ values lesser than Post-Archean Australian Shale indicate low to moderate maturity for the estuarine and offshore sediments. The geochemical immaturity indicates its derivation from low to moderately weathered source rocks. The major and trace elemental ratios and discriminant function diagrams attribute that the sediments were derived from intermediate to felsic source rocks. The enrichment of Cr and Ni concentration in the sediments compared to the upper continental crust, related to the contribution of orthopyroxenes, weathered from charnockite and garnets from the granulite terrain, respectively.     

Radioelement variation in the Levang granite-gneiss,Bamble region,south Norway

An investigation of the distribution of thorium, uranium and potassium across the Levang granite-gneiss shows a significant increase in thorium and uranium from north to south. Although the mean thorium and uranium concentrations are comparable to average granitic values quoted in the literature, potassium is lower. The relative enrichment of thorium and uranium thus appears to be related to Sveconorwegian metamorphism recorded in the rocks of the adjacent Portør Peninsula to the south. The Levang granite-gneiss has recorded only the Svecofennian metamorphic event of approximately 1616 m.y.     

大兴安岭伊勒呼里山早白垩世碱长花岗岩年龄、地球化学特征及其地质意义

对大兴安岭伊勒呼里山早白垩世碱长花岗岩进行了岩相学、地球化学、LA-ICP-MS锆石U-Pb定年研究。伊勒呼里山地区碱长花岗岩主量元素具有富Si、富碱,贫Mg、Ca的特征;微量元素亏损Sr、P、Eu、Ti,富集K、Rb、Th等不相容元素,元素地球化学特征表明,岩体为铝质A型花岗岩(A/CNK=0.88~1.21,A/NK=0.94~1.49)。测年结果显示,粗中粒碱长花岗岩的锆石年龄为140.3±1.0Ma,细中粒碱长花岗岩锆石年龄为137.9±0.8Ma,均形成于早白垩世。结合区域研究资料,伊勒呼里山地区碱长花岗岩岩体的形成与蒙古-鄂霍茨克洋闭合后的岩石圈伸展密切相关,其岩浆源区可能为地壳物质的部分熔融。     

湘南多金属矿集区燕山期成矿花岗岩的主元素地球化学特征和成因探讨

湘南地区燕山期成矿花岗岩的主元素地球化学特征可划分为3种类型,不同成矿花岗岩形成的岩浆演化机理有明显差异:(1)成矿花岗岩的K_2O/Na_2O比值较高,均显示高钾钙碱性-钾玄岩系列特征。(2)MC型与CM型早期次单元花岗岩相对贫硅、碱.富钙、镁、铁,铝质指数(A/KNC)较低,碱度指数(KN/A)都不高,属镁质-铁质准铝质的高钾钙碱性系列花岗岩类,总体显示出I型花岗岩的特征。C型和CM型晚期次单元花岗岩相对富硅碱、贫镁钙,属铁质弱过铝质-过铝质钾玄岩系列-高钾钙碱性系列花岗岩类:岩石的FeO~T/MgO值明显高于一般I型和M型花岗岩.较高的FeO~T值又与高分异的I型花岗岩相区别,总体显示出S型花岗岩的特征。(3)成矿花岗岩的F或Cl含量高.岩浆向过铝质方向或过碱性方向演化,晚期岩浆中的高场强元素浓度增大,导致MC型与CM型的花岗岩的早期次单元多有Cu、Pb、Zn、Sb等多金属化,C型和CM型的晚期次单元花岗岩则常有大型Sn、W、Pb、Zn、Nb、Ta和稀土等矿化。(4)成矿花岗岩的形成与壳幔岩浆混合作用有关.形成MC型和CM型早期次单元花岗岩的岩浆演化主要是岩浆混合作用.而CM型花岗岩晚期次的花岗岩类和C型花岗岩类的岩浆演化可能还存在分离结晶作用。     

Coastal zone management programme in Kerala,India

The physiographic setting of Kerala State, India, is unique. A narrow strip of the state contains a chain of lagoons and estuaries with a very high population density. The strip is subjected to severe coastal erosion during the monsoon season. A number of other problems are also associated with the coastal zone of Kerala, such as irregular dredging of black sands from the beaches, coastal flooding, hazards due to developmental activities, etc. A Coastal Zone Management Programme was developed and administered by the Centre for Earth Science Studies, Trivandrum, to provide efficient coastal management and solve some of these problems. Various programmes included under the Coastal Zone Management are the following: (1) Sedimentological, bathymetric, and geochemical studies of lagoons and estuaries; (2) monitoring of planimetric changes of beaches by profiling beaches during different seasons all along the coast; (3) studies of the nature, distribution, and provenance of black sand deposits from beaches; (4) studies of the peculiar occurrence of patchy, calm, turbid areas of water in the offshore containing high suspended sediment concentrate known as mud banks; (5) wave studies involving continuous monitoring of wave data all along the coast in order to understand wave climate and erosion; (6) sediment movement studies using fluorescent tracer to aid in the development of ports and harbors; (7) studies on various aspects of offshore. The outlines of the various programmes discussed in this article will help other states and countries to develop a coastal zone management programme according to the needs of the state or country and the nature of the problem occurring in the coastal zone.     

Correct nomenclature for the Angadimogar pluton, Kerala, southwestern India

The proper usage of modal composition and geochemical classification of granitoids is discussed for assigning a proper nomenclature for the Angadimogar pluton, Kerala, southwestern India. This discussion is mainly aimed at addressing questions concerning the nomenclature of Angadimogar pluton (syenitevs. granite). Modal composition and whole-rock XRD data clearly show that the pluton exposed near Angadimogar is a quartz-syenite and its geochemistry is typical of a ferroan, metaluminous, alkali (A-type) granitoid     

新疆北部卡拉麦里地区黄羊山碱性花岗岩的岩石成因

北疆地区晚古生代后碰撞岩浆活动以大面积分布碱性花岗岩为特征。侵位于晚石炭世的黄羊山碱性花岗岩体是北疆地区产于300Ma左右后碰撞伸展环境中的典型的花岗岩体之一,以正εNd(t)值(+5.06～+6.67)和年轻的tDM(501～878Ma)为特征。黄羊山碱性花岗岩包括钠铁闪石碱性花岗岩和角闪石碱长花岗岩,为过碱质到弱过铝质,岩石化学属钾玄岩系列和高钾钙碱性系列;稀土元素配分曲线为典型的"V"字形,具明显的负Eu异常;富集大离子亲石元素和高场强元素,显著亏损Ba、Sr、P2O5、TiO2。根据这种碱性花岗岩高εNd(t)值和tDM与区域内洋壳年龄吻合度较好的特征,推测其可能源岩应为洋盆闭合时洋壳残片转化而来的年轻地壳。模拟计算得出,黄羊山碱性花岗岩中幔源组分的比例可达88%～92%。在维宪末期-谢尔普霍夫末期的萨吾尔运动之后,软流圈物质上涌所携带的巨大热能加热了区域范围内的地壳,先期抵达的幔源岩浆所携带的热能进一步加热并熔融了下地壳镁铁质物质,形成北疆地区～300Ma的碱性花岗岩。同时,本文也说明了洋壳残片通过构造运动归并到陆壳当中亦可能是某些地区在某些地质时期大陆地壳增生的重要方式之一。     

诸广山岩体南部区域地球化学特征

诸广山岩体南部是我国主要铀产地之一,找到并为国家提交了一大批可供利用的铀矿床。文章通过分析诸广山岩体南部以往区域化探资料及最新铀矿化探工作成果,总结了区域地球化学特征,提出了诸广山岩体南部地球化学元素存在空间分布组合关系,蚀变存在垂直分带,岩体内地球化学元素在空间上存在垂直分带,区内热液型铀矿床地球化学定位的三个标志等认识。     

Generation of leucogranites in the Kerala Khondalite belt,Southern India

Psammitic and pelitic gneisses of the Kerala Khondalite belt in southern India were subjected to granulite-facies metamorphism and migmatisation through fluid-absent biotite dehydration-melting which led to the generation of garnet-bearing leucogranites. Geochemical investigations provide support that the leucogranites were generated from gneisses compositionally similar to those into which they were emplaced.The intrusion of apatite-rich granites subsequent to the garnet-bearing leucogranites is recognized predominantly in leptynitic gneisses. A comparison of the chemical composition of both garnet- and apatite-bearing varieties displays a systematic shift to intermediate compositions (increase in CaO, FeO, LREE, Zr, Y; decrease in SiO₂ and δ¹⁸O) which coincides with higher modal abundances of apatite, garnet and biotite and decreasing contents of quartz and alkalifeldspar. The observation that apatite occurs in aggregates together with biotite and/or garnet as well as the extreme concentrations of FeO, LREE and Zr in some of the apatite-beraing granites which clearly exceed the maximum solubility values for these elements in granitic melts indicates that dehydration-melting alone, as it has been proposed for the generation of garnet-bearing leucogranites, cannot have been responsable for generation of apatite-rich leucogranites but that additional processes like crystal entrainment and accumulation or liquid removal must also have played a role.     

西藏八宿花岗岩岩石学、地球化学特征及其构造意义

西藏八宿地区大地构造位置为冈底斯-念青唐古拉板块北东缘,紧邻班公湖-怒江结合带。区内出露有花岗岩体,包括花岗闪长岩和黑云母二长花岗岩,侵位于朱村组火山岩中。区域主要完成了1:25万区域地质调查,研究程度相对较低,有关花岗岩的报道较少。本次工作在详细野外调研的基础上,研究了花岗岩类的岩石学,地球化学和年代学特征来确定岩体的构造意义。在该地区获得花岗闪长岩和石英闪长岩LA-ICP-MS锆石U-Pb年龄分别为119.7±1.2Ma和120.6±1.8Ma。岩体锆石ε_Hf(t)值为-10.42~-7.00,对应的地壳模式年龄为1624~1841Ma。地球化学特征反映壳源部分熔融成因,有地幔物质及热流参与,形成于板块俯冲构造环境。岩体北东侧的朱村组火山岩所获得的角闪英安岩锆石SHRIMP U-Pb年龄为128±2Ma,较岩体早9Myr,属于同一岩浆事件产物,因此,八宿花岗岩与火山岩一样,属于伯舒拉岭火山岩浆弧的一部分,形成于怒江洋壳向冈底斯-念青唐古拉板块俯冲、消减的火山弧环境。八宿岩体很可能是在班公湖-怒江洋岩石圈向南俯冲的地球动力学背景下形成的。     

The geochemistry of the Bushveld granites in the Potgietersrus tin-field

An area of 324 km² was selected for a pilot-study of the geochemical characteristics of the Bushveld granites in the Potgietersrus tin-field. Two hundred and sixty nine samples were collected from a regular grid of stations. Additional samples collected from selected sample stations provide data on “about station” variance to test the validity of conclusions based on regional variation. The samples were analysed for Ba, Ce, Co, La, Li, Nb, Ni, Rb, Sc, Sn, Sr, Ti, Y, Zn and Zr together with the major elements Ca, Na and K.The stratiform Bushveld granites have mean concentrations for these elements that compare closely with those in low Ca-granites. Ce, La, Rb, Y, Zn and Zr are enriched relative to low Ca-granites while Sr is markedly impoverished. The stanniferous Bobbejaankop granite stock is distinguished from the stratiform granites with respect to Ba, Sr, Ti and Zn. The median tin concentration in the stratiform granites is 6.5 ppm and in the Bobbejaankop granite it is 9 ppm. Economically viable deposits of tin disseminated through the upper 120 m of the Bobbejaankop granite stock have been exploited for over 70 years.It is concluded that the Bobbejaankop granite crystallized at low temperatures from a hydrous residual melt that had collected beneath a roof of felsite and early crystallization products of the original granitic magma. The presence of this concentration of volatile-rich, hydrous liquid depressed the melting temperatures of the quasi-solid, granitic crystal much below the ambient temperature initiating re-mobilization. The enrichment in Sn of the stratiform granites in the Potgietersrus area is compared with the “normal” (i.e., ± 3 ppm) Sn-content of the Bushveld stratiform granites building the Sekukuni Plateau in the eastern lobe of the Bushveld Complex where no tin mineralization has been reported.     

Gold in the beach placer sands of Chavakkad-Ponnani,Kerala Coast,India

Although sporadic mining of placer gold from river beds is not uncommon in India, there is no documented literature on the occurrence of gold in the beach placer sand deposits of the country. While characterizing the heavy minerals of the Chavakkad-Ponnani (CP) beach placer sands along the North Kerala coast, the association of gold with the pyriboles in these sands has been observed. A native gold grain of about 25 μm was seen to occur as an inclusion within an amphibole of hornblendic composition. The pyriboles of the CP deposit are angular to sub-angular indicating a nearby provenance that may be in the upstream reaches of the Ponnani River in the districts of Malappuram and Palakkad or further north in the auriferous tracts of the Wynad-Nilambur or Attapadi regions. It is argued that the occurrence of native gold in CP deposit is not a freak occurrence and that it warrants thorough investigation of all the pyribole-ilmenite-rich placers to examine the possible presence of gold and its abundance in the beach placers of northern Kerala coast.     

Geochemistry and petrogenetic evolution of the diatexites of Central Kerala,India

The hornblende-biotite gneisses of Central Kerala which cover approximately 490km² exhibit schlieric and nebulitic structures, tending towards a homophanous nature and are classified here as diatexites. Mafic protoliths and restite biotite, each representing the refractory residuum of two independent partial melting episodes are widely present in the gneisses. The general mineral assemblage of the gneisses comprise quartz, K-feldspar, oligoclase, biotite and hornblende. Chemically, they are dominantly adamellitic and the behaviour of major and trace elements is consistent with a magmatic parentage. Based on petrochemical criteria, a two-stage evolution model is proposed here, which involves (i) partial melting of mafic granulites under high Archean geothermal gradients and generation of tonalite/trondhjemite through amphibole and plagioclase fractionation and (ii) partial melting and subsequent quartz-alkali feldspar fractionation of the tonalite/trondhjemite under amphibolite facies conditions with synchronous K-enrichment resulting in the diatectic adamellites.     

Sphene coronites from Hyderabad granites,Andhra Pradesh,India

Sphene coronites around magnetite are recorded in the granodiorite of Hyderabad. The metamorphic origin of the corona is discussed.     

Flood 2018 and the status of reservoir-induced seismicity in Kerala,India

Natural Hazards - Floods in India, which were once mostly confined to southern part of the Himalayan region, have now started spreading over to many regions of India, including the urban...     

Ignimbritic cauldrons,alkali granites,and mineral deposits in fault-block mountains

The term fault-block mountains refers to an orogen, formed in an ensialic back arc by extension. The voluminous magmatism due to underplating of hot oceanic lithosphere, extrem thinning of the continental lithosphere and partial melting as well as mantle diapirs will be examplified by three ore provinces:

1. Southwestern North America (Middle Tertiary peralkaline ignimbrites and resurgent cauldrons)
2. Central Iran (Infracambrian ignimbrites and riebeckitegranite)
3. Arabian Shield (Infracambrian alkaligranites and rhyolites, 625-570 m.y.).

An overview of mineral deposits related to resurgent cauldrons will be given, encompassing disseminated deposits (Cu, Mo, Sn), skarns, massive magnetite ores, beryl pegmatites, sedimentary deposits (Pb-Zn; Hg, U, Li; Mn, borates, zeolites), mineralized vents (Au, U, apatite), vein type deposits (Au, Ag, Te, fluorite, U) and hydrothermal replacements (alunite). The value of several deposits exceeds 10 billion German Marks at current prices. The exploration concept based on resurgent cauldrons may also be applied successfully in other provinces.     

Late Pleistocene-Holocene Paleoclimatic History of the Southern Kerala Basin, Southwest India

The South Kerala Sedimentary Basin (SKSB) constitutes one of the most significant landward extensions of the southwest offshore sedimentary basins of India, and is situated between 8^o45^' and 10^o15^' N latitudes. With a maximum width of about 20 km and incorporating a 700 m thick sedimentary succession ranging in age from Early Miocene to Holocene, this belt lies almost entirely under water or alluvium-covered coastal plains. In this study, we use two continuously cored bore holes at Eruva (7.25m deep) and Muthukulam (3m deep) separated by a distance of about 7km to investigate the depositional environment as well as paleo ecology of the depocentre and climatic aspects during the Late Pleistocene and Holocene. Results from C¹⁴ dating of shell fragments from Eruva (depth zone: 2.10–6.64m) yielded ages in the range of 36.2 to 42.5 kyBP corresponding to the late Pleistocene. Wood fragments in the Muthukulam core sample (depth zone: 1.27–3.00m) gave C¹⁴ ages in the range of 3.7 to 7.2 kyBP indicating a Holocene history. The lower half of the Eruva bore hole indicates a marginal marine environment with an abundant supply of terrestrial carbonaceous debris probably corresponding to a period of abnormally high rainfall recorded in many parts of the globe covered by the Asian summer monsoon. The sediments in the upper part of this bore hole indicate a continuation of this environment but with much less input of terrestrial organic carbon. The lower part of the bore hole from this locality, corresponding to the Holocene transgression, is similar to the lower part of Eruva bore hole in the case of TOC. Deposition took place in water bodies with considerable marine influence but receiving high amounts of terrestrial plant debris-mostly in the form of finely divided particles mixed with mud. This transgressive sequence was also deposited during a time when the Asian summer monsoon was abnormally high in intensity as indicated by many examples in India, Africa, Madagascar and elsewhere. It is significant that during the deposition of this part, the sea level was probably the same as present or higher suggesting possible lowering of the stream velocities and resultant deposition of only muddy sediments laden with terrestrial organic material along the coast. The upper part of the section shows a progressively reduced rainfall pattern culminating in a period of very low precipitation with the development of a paleosol, which is traceable all over the SKSB where Late Holocene sediments are available. This period also witnessed aeolian activity modifying the sand ridges in the ridge-runnel systems formed by the Holocene regression.