Genetic Classification of Pyroclastic Ejecta Based on Physical Volcanology of Possible Large Cauldron in Bombay Volcanic Complex, Western Deccan Trap Province, India

Many Propositions are made about the mechanism of emplacement of volcanoclastic material in the Bombay volcanic complex. The present paper deals exclusively with the physical features of the deposits laid by a complex tectono-magmatic process by making detailed inventory of the different kind of volcanic ejecta exposed in the Bomay Volcanic Complex (BVC), and an attempt has been made to classify the deposits genetically. A subsidenace which was hinted at earlier, may be a possible cauldron in BVC has been proposed, which might be responsible for producing such a varied and complex lithology.

Performance characteristics of tunnel boring machine in basalt and pyroclastic rocks of Deccan traps–A case study

A12.24km long tunnel between Maroshi and Ruparel College is being excavated by tunnel boring machine(TBM)to improve the water supply system of Greater Mumbai,India.In this paper,attempt has been made to establish the relationship between various litho-units of Deccan traps,stability of tunnel and TBM performances during the construction of5.83km long tunnel between Maroshi and Vakola.The Maroshi–Vakola tunnel passes under the Mumbai Airport and crosses both runways with an overburden cover of around70m.The tunneling work was carried out without disturbance to the ground.The rock types encountered during excavation arefine compacted basalt,porphyritic basalt,amygdaloidal basalt pyroclastic rocks with layers of red boles and intertrappean beds consisting of various types of shales Relations between rock mass properties,physico-mechanical properties,TBM specifications and the cor responding TBM performance were established.A number of support systems installed in the tunne during excavation were also discussed.The aim of this paper is to establish,with appropriate accuracy the nature of subsurface rock mass condition and to study how it will react to or behave during under ground excavation by TBM.The experiences gained from this project will increase the ability to cope with unexpected ground conditions during tunneling using TBM.

First observation of microspherule from the infratrappean Gondwana sediments below Killari region of Deccan LIP,Maharashtra(India) and possible implications

A rare occurrence of a microspherule has been found in the infratrappean sediments,encountered below338 m thick Deccan volcanic cover in KLR-1 scientific borehole,drilled in the epicentral zone of the 1993 Killari earthquake(Maharashtra,India).Palynological studies of the sediments indicate their age as Early Permian(Asselian,298-295 Ma) for deposition.Transmission electron microscope studies reveal that the spherule from the infratrappeans,is having a similar composition to that of the Neoarchean amphibolite to granulite facies mid crustal basement.The spherule is non-spherical in nature,containing mostly FeO(10.70±0.20 wt.%),CaO(13.8±0.5 wt.%),Al203(7.78±0.30 wt.%),MgO(6.47±0.3 wt.%),Si02(47,46±0.50 wt.%),Ti02(2.47±0.3 wt.%).K20(1.89±0.20 wt.%).and Cl(0.33±0.05 wt.%).Since the Fe composition of the spherule is almost same as the basement rock(10.5 wt.%),and the chlorine content is also in the same range as the basement(0.04-0.24 wt.%),it would suggest possibility of an extraterrestrial impact over the Indian terrain during the erstwhile Gondwana sedimentation period that may be associated with the Permian-Triassic mass extinction,the most severe one in the Earth's history.

Tectonic significance of dykes in the Sarnu-Dandali alkaline complex,Rajasthan, northwestern Deccan Traps

Whether swarms of preferentially oriented dykes are controlled by regional stress fields, or passively exploit basement structural fabric, is a much debated question, with support for either scenario in individual case studies. The Sarnu-Dandali alkaline complex, near the northwestern limit of the Deccan Traps continental flood basalt province, contains mafic to felsic alkaline volcano-plutonic rocks and carbonatites. The complex is situated near the northern end of the 600 km long, NNWe SSE-trending Barmer-Cambay rift. Mafic enclave swarms in the syenites suggest synplutonic mafic dykes injected into a largely liquid felsic magma chamber. Later coherent dykes in the complex, of all compositions and sizes,dominantly strike NNWe SSE, parallel to the Barmer-Cambay rift. The rift formed during two distinct episodes of extension, NWe SE in the early Cretaceous and NEe SW in the late Cretaceous. Control of the southern Indian Dharwar structural fabric on the rift trend, as speculated previously, is untenable,whereas the regional Precambrian basement trends（Aravalli and Malani） run NEe SW and NNEe SSW.We therefore suggest that the small-scale Sarnu-Dandali dykes and the much larger-scale BarmerCambay rift were not controlled by basement structure, but related to contemporaneous, late Cretaceous regional ENEe WSW extension, for which there is varied independent evidence.

Cretaceous-Paleogene Transition of Reptilian Tetrapods across Deccan Volcanism in India

Eruptions of lava flows of Deccan large igneous province straddled the Cretaceous-Palaeogene boundary (K-Pg). Sediments associated at different stratigraphic levels within the lava piles of Deccan volcanic sequences (DVS) are mainly terrestrial. We studied the sediments of Eastern and Central Deccan Volcanic Province, and the Malwa Plateau for tracking changes in reptilian tetrapods across the volcanism. The reptiles are mainly represented by abelisaurid-titanosaurid dinosaurs, Alethinophidia madtsoiia snakes, Notosuchian crocodylomorph Simosuchus, bothremydid Kurmademydinae turtles and Anguimorph and Scincomorphs lizards. The evidences suggest that the non-avian dinosaurs were adversely affected by the arrival of the first volcanic flows locally in the province either within C30N or C29R Maastrichtian. The abelisaurid theropods became extinct whereas a single or two species of titanosauriforme dinosaurs survived but eventually became extinct at least 350 ky before the K-Pg boundary with increasing volcanism. The madtsooid snakes and crocodylimorphs were also adversely affected with decline in their diversity and abundance, whereas the Bothremydid turtles survived the initial onslaught of Deccan volcanism and continued across the K-Pg boundary.

Alkali feldspar syenites with shoshonitic affinities from Chhotaudepur area: Implication for mantle metasomatism in the Deccan large igneous province

Two petrologically distinct alkali feldspar syenite bodies （AFS-1 and AFS-2） from Chhotaudepur area, Deccan Large Igneous Province are reported in the present work. AFS-1 is characterized by hypidio-morphic texture and consists of feldspar （Or55Ab43 to Or25Ab71）, ferro-pargasite/ferro-pargasite horn-blende, hastingsite, pyroxene （Wo47, En5, Fs46）, magnetite and biotite. AFS-2 exhibits panidiomorphic texture with euhedral pyroxene （Wo47-50, En22-39, Fs12e31） set in a groundmass matrix of alkali feldspar （Or99Ab0.77 to Or1.33Ab98）, titanite and magnetite. In comparison to AFS-1, higher elemental concentra-tions of Ba, Sr and PREE are observed in AFS-2. The average peralkaline index of the alkali feldspar syenites is w1 indicating their alkaline nature. Variation discrimination diagrams involving major and trace elements and their ratios demonstrate that these alkali feldspar syenites have a shoshonite affinity but emplaced in a within-plate and rifting environment. No evidence of crustal contamination is perceptible in the multi-element primitive mantle normalized diagram as well as in terms of trace elemental ratios. The enrichment of incompatible elements in the alkali feldspar syenites suggests the involvement of mantle metasomatism in their genesis.

Feeder and post Deccan Trap dyke activities in the northern slope of the Satpura Mountain： Evidence from new 40Ar-39Ar ages

We present new 40Ar-39Ar plagioclase crystallization ages from the dykes exposed at the northern slope of the Satpura Mountain range near Betul-Jabalpur-Pachmarhi area, - 800 km NE of the Western Ghats escarpment. Among the two plateau ages, the first age of 66.56 ± 0.42 Ma from a dyke near Mohpani village represents its crystallization age which is either slightly older or contemporaneous with the nearby Mandla lava flows （63-65 Ma）. We suggest that the Mohpani dyke might be one of the feeders for the surrounding lava flows as these lavas are significantly younger than the majority of the main Deccan lavas of the Western Ghats （66.38-65.54 Ma）. The second age of 56.95 -- 1.08 Ma comes from a younger dyke near Olini village which cuts across the lava flows of the area. The age correlates well with the Mandla lavas which are chemically similar to the uppermost Poladpur, Ambenali and Mahabaleshwar Formation lavas of SW Deccan. Our study shows that the dyke activities occurred in two phases, with the second one representing the terminal stage.

Breccia-cored columnar rosettes in a rubbly pahoehoe lava flow,Elephanta Island,Deccan Traps,and a model for their origin

Rubbly pahoehoe lava flows are abundant in many continental flood basalts including the Deccan Traps.However,structures with radial joint columns surrounding cores of flow-top breccia(FTB),reported from some Deccan rubbly pahoehoe flows,are yet unknown from other basaltic provinces.A previous study of these Deccan "breccia-cored columnar rosettes" ruled out explanations such as volcanic vents and lava tubes,and showed that the radial joint columns had grown outwards from cold FTB inclusions incorporated into the hot molten interiors.How the highly vesicular(thus low-density)FTB blocks might have sunk into the flow interiors has remained a puzzle.Here we describe a new example of a Deccan rubbly pahoehoe flow with FTB-cored rosettes,from Elephanta Island in the Mumbai harbor.Noting that(1)thick rubbly pahoehoe flows probably form by rapid inflation(involving many lava injections into a largely molten advancing flow),and(2)such flows are transitional to 'a'a flows(which continuously shed their top clinker in front of them as they advance),we propose a model for the FTB-cored rosettes.We suggest that the Deccan flows under study were shedding some of their FTB in front of them as they advanced and,with high-eruption rate lava injection and inflation,frontal breakouts would incorporate this FTB rubble,with thickening of the flow carrying the rubble into the flow interior.This implies that,far from sinking into the molten interior,the FTB blocks may have been rising,until lava supply and inflation stopped,the flow began solidifying,and joint columns developed outward from each cold FTB inclusion as already inferred,forming the FTB-cored rosettes.Those rubbly pahoehoe flows which began recycling most of their FTB became the 'a'a flows of the Deccan.

Giant Plagioclase Basalts from Northeastern Deccan Volcanic Province, India: Implications for Their Origin and Petrogenetic Significance

The giant plagioclase basalts (GPBs) with plagioclase phenocrysts that reach up to 3 cm in length are found near Jabalpur in the northeastern part of the Deccan Volcanic Province (DVP). The thickness of the basalt flow (flow 6) that contains the GPBs is ~ 20 m. Plagioclase phenocysts (An58 - An64) in the GPBs display many features of magma mixing (e.g., resorption, reverse zoning). Of the nine flows in the Jabalpur section, the GPBs (flow 6) with lowest Mg#s (38 - 43) and MgO (4.16 - 5.08 wt%), Ni and Cr abundances are the most evolved compositions. In addition, these GPBs have highest abundances of incompatible elements (TiO2, P2O5, Nb, Zr, Sr and Ba). The GPBs are compositionally similar to the well-studied Mahabaleshwar lavas of the western DVP. This new occurrence of GPBs has implications for existence of local crustal magma chambers, feeders and vents in the northeastern part of the DVP.

Reptilian vertebrates from Deccan volcanic associated sediments of Malwa Plateau in context to reptiles across Maastrichtian-Paleogene volcanic eruptions in Main Deccan Volcanic Province,India

The enormous eruptive volume of India's Deccan continental flood basalts has been linked to global mass extinction at Cretaceous-Paleogene boundary and destablilisation of both marine and terrestrial ecosystems before and after the Chicxulub bolide impact. Deccan Volcanic Province(DVP) currently covers around 500 000 km^2 of land between latitude 15°10′-24°30′N and longitude 70°10′-82°10′E over central India towards the west coast. The pre-erosional volume is estimated at around 1.6 million km^3 which is one of the largest volcanic eruptions on the Earth. The Deccan lava flows in geographically separated areas in DVP are considered to have separate sources and sites of eruptions and were outpoured in different magnetochrons viz. C30 n to C28 n of Maastrichtian to Paleocene. The Deccan volcanic sequences(DVS) in different provinces are associated with(i) sediments deposited before the arrival(Ground Zero) of the first lava flows-designated as infratrappean or Lameta sediments and(ii) sediments between the lava flows deposited during the period of quiescence at different stratigraphic levels designated as intertrappean(interflow) sediments. The Ground Zero Lameta sediments are the major dinosaur bearing sediments deposited in six inland basins viz. 1. Balasinor-Jhabua;2. Sagar;3. Jabalpur;4. Ambikapur-Amarkantak;5. Salburdi;6. Nand-Dongargaon. The sediments represent mainly the terrestrial ecosystems destabilised by the volcanism and they record history of biotic and environmental changes impacted by the volcanism across the Deccan volcanic eruptions. The titanosaurs, crocodylimorphs and bothremydid turtles survived across the first flows in the region in the C30 n. The skeletal remains of the surviving reptiles are preserved in the Deccan volcanic associated intertrappean lake sediments at different stratigraphic levels higher-up in the sequence. Locally, in the Malwa region the Scincomorp and Anguimorph lizards make their first appearance during the earlier phase of volcanic eruptions in C30 n wherein their well preserved bones are found in the intertrappean/inter lsva lake sediments deposited between the lava flows. The lizard fauna is indicated to have better flourished after the initial Deccan eruptions possibly owing to increased humidity.

Surface geochemical data evaluation and integration with geophysical observations for hydrocarbon prospecting,Tapti graben,Deccan Syneclise,India

The Deccan Syneclise is considered to have significant hydrocarbon potential. However, significant hydrocarbon discoveries, particularly for Mesozoic sequences, have not been established through conventional exploration due to the thick basalt cover over Mesozoic sedimentary rocks. In this study, near-surface geochemical data are used to understand the petroleum system and also investigate type of source for hydrocarbons generation of the study area. Soil samples were collected from favorable areas identified by integrated geophysical studies. The compositional and isotopic signatures of adsorbed gaseous hydrocarbons （methane through butane） were used as surface indicators of pe- troleum micro-seepages. An analysis of 75 near-surface soil-gas samples was carried out for light hydrocarbons （C_1-C_4） and their carbon isotopes from the western part of Tapti graben, Deccan Syneclise, India. The geochemical results reveal sites or clusters of sites containing anomalously high concentrations of light hydrocarbon gases. High concentrations of adsorbed thermogenic methane （C1 518 ppb） and ethane plus higher hydrocarbons （∑C2＋ = 977 ppb） were observed. Statistical analysis shows that samples from 13% of the samples contain anomalously high concentrations of light hydrocarbons in the soil-gas constituents. This seepage suggests largest magnitude of soil gas anomalies might be generated/source from Mesozoic sedimentary rocks, beneath Deccan Traps. The carbon isotopic composition of methane, ethane and propane ranges are from 22.5‰to -30.2‰ PDB, -18.0‰ to 27.1‰,, PDB and 16.9‰-32.1‰ PDB respectively, which are in thermogenic source. Surface soil sample represents the intersection of a migration conduit from the deep subsurface to the surface connected to sub-trappean Mesozoic sedimentary rocks. Prominent hydrocarbon concentra- tions were associated with dykes, lineaments and presented on thinner basaltic cover in the study area, which probably acts as channel for the micro-seepage of hydrocarbons.

Dyke Emplacement in the Narmada Rift Zone and Implications for the Evolution of Deccan Traps

Dykes are primarily extensional fractures that form perpendicular to the minimum principal compressive stress,which have been extensively studied in the world during the past decades for various reasons including the

Tracking temporal palynofloral changes close to Cretaceous-Paleogene boundary in Deccan volcanic associated sediments of eastern part of central Deccan volcanic province

Deccan volcanic sequences( DVS) in the central Deccan volcanic province( CDVP) are designated as Sahyadri Group having ~ 500 m thick lava pile associated with multiple sedimentary beds at different stratigraphic levels. In the eastern part of CDVP between the latitude 19 °55 '--20 °25 ' N and the longitudes 78 °15 '--78 °30 ' E,palynological investigation of the intertrappean sedimentary beds at five stratigraphic levels was carried out. The study was basically aimed for tracking the floral and environmental changes across the Deccan transition. The resulting finds indicate that the intertrappean sediments at the lowest stratigraphic level between the earliest lava flows are characterized by presence of marker Maastrichtian palynomorphs- Gabonisporis vigourouxii,Aquilapollenites bengalensis,Azolla cretacea and Farabeipollis associated with triporate and tricolpate pollen grains,phytoliths of Oryzeae of Poaceae family and peridinoid dinoflagellate cysts. The increasing volcanism deteriorated the existing flora as evident by absence of pollen-spores and presence of only structured biodegraded organic matter,fungal spores,acritarchs and algal( Botryococcus) remains in the sediments of higher-up in the sequence. For chronostratigraphic constraints on the lava flows magnetic polarity of the flows bracketing the intertrappean beds was investigated. The results indicated presence of N-R-N-R magnetic polarity in the basal lava pile that are interpreted as representing the magnetochron C30 N to C28 R( Maastrichtian-Paleogene). The floral change begins with the onset of volcanism in the chron C30 N and floral deterioration is observed in C29 N with increasing volcanism and it is only in the chron C28 R( Danian) that some evidence of recovery of flora is recorded. The current study shows that in eastern part of CDVP the post Cretaceous-Paleogene boundary eruptions represent the main phase of eruptions that triggered deterioration of the flora.

The effect of intra-trappean heterogeneities on seismic data： A case study from the Deccan Traps

烃探索兴趣为开发新潜水艇暗岩成像技术更新了需要。今天遇到的最重要的问题之一是在暗岩下面的地震成像。在最近的年里，这个问题看起来被长使用部分克服了抵消地震数据。然而近的偏移量数据充分还有待于由于表面以及暗岩的内部异质引起的复杂波形被利用。近正常的发生数据，影响亚暗岩成像，是高度有用的在暗岩层以内理解内部结构。为如此的目标的变换波浪的使用在相当同类的暗岩层作为一种选择被建议了。与合成建模这里行使的一些，我们在处理更多的现实主义、异构的暗岩流动加亮实际困难。完整的波形震动图被计算在地震数据上理解 intra-trappean 沉积的效果。从印度的 Deccan 陷井的案例研究在这篇论文被介绍。首先，我们在全面地震图象上讨论设置的沉积的效果。后来，来自这个领域的声音的木头数据被用来用反射率方法并且与领域数据相比计算完整的波浪地反应。使用模式的可行性变换了波浪(在顶和底部暗岩接口的到 S 并且反过来的 P ) 因为在 Kutch 区域的亚暗岩成像通过一系列速度深度侧面被讨论。由与领域数据作比较，我们证明在暗岩罐头以内的多重薄 layering 的效果强烈败坏我们寻求解释并且利用的图象。

Untangling the biotic stress in the late Maastrichtian Deccan-benchmark interval of Bidart(France)

The late Maastrichtian witnessed substantial surges in Deccan volcanism,prompting the hypothesis that these voluminous pulses may have instigated repeated episodes of ocean acidification during this period.The Cretaceous-Palaeogene(K/Pg)boundary at Bidart(France)is preceded by a~0.5 m thick interval with geochemical and taphonomic vestiges of an ocean acidification event linked with Deccan volcanism.New planktic foraminifera census and morphometric data now confirm biotic stress conditions related to acidification in the Deccan benchmark interval.The absolute abundance data of larger(>150μm)heavily calcified planktic morphogroups show fluctuating populations throughout zone CF1(spanning the final~225 ky),lowest peaks within the Deccan benchmark,and a demographic collapse(>90%)at the K/Pg boundary.The analyzed species are generally reduced in size,with thinner test walls in this~0.5 m interval,indicating the likelihood of calcification stress as a contributor to the overall biotic stress.At the K/Pg boundary,maximum biotic stress is recorded in all the tested faunal proxies.A preliminary graphic correlation of zone CF1 at Bidart with the auxiliary GSSP at Elles(Tunisia)constrains the Deccan benchmark interval of high biotic stress to the final~58ky of the late Maastrichtian,culminating in the K/Pg mass extinction.The volcanogenic Hg peaks coincident with faunal and taphonomic evidence of ocean acidification strengthen the Deccan-related ocean acidification hypothesis.

白垩纪—古近纪界限时期的陆地气候重建进展

白垩纪—古近纪(K-Pg)界限时期发生了地质历史中最严重的生物大灭绝事件之一,重建该时期气候演化历史及其对生态系统的影响对理解深时气候演化规律和预测未来气候变化都具有重要意义。相比海相剖面而言,基于陆相剖面的白垩纪—古近纪界限时期古气候重建研究开展较晚,相关成果缺乏系统总结和集成。本文系统回顾了全球陆相白垩纪—古近纪界限剖面的分布情况和事件年代学新进展,总结了基于以上剖面重建的定量古气候记录和德干火山喷发记录,建立了界限时期中纬度陆地年平均温度和大气CO_(2)浓度时间演化序列。陆相剖面分布相对集中且数量较少,中国是该时期陆相剖面发育最多的国家之一,多个盆地已经建立了德干火山喷发记录,在重建该时期陆地气候上具有很大潜力。基于陆相沉积物汞元素地球化学记录表明,德干火山作用导致了晚马斯特里赫特期变暖事件并触发了白垩纪末期生物大灭绝。中纬度陆地年平均温度重建结果显示马斯特里赫特期中期全球经历了~10℃的降温,到马斯特里赫特期晚期德干火山初始喷发前显著升温至~20℃,并在白垩纪—古近纪界限前后发生多次快速波动。尽管65~63 Ma之间陆地温度记录相对缺失,69~65 Ma之间重建的大气CO_(2)浓度记录与陆地年平均温度记录之间具有良好的耦合性,表明白垩纪—古近纪界限时期大气CO_(2)浓度变化是全球温度变化的主要驱动因素。

亚洲3个大火成岩省(峨眉山、西伯利亚、德干)对比研究

峨眉山(～260Ma)、西伯利亚(～250Ma)和德干(～66Ma)大陆溢流玄武岩是世界上3个重要的大火成岩省。大火成岩省至少具有4个通常被用于识别古地幔柱的标志:(1)先于岩浆作用的地表隆升;(2)与大陆裂谷化和裂解事件相伴;(3)与生物灭绝事件联系密切;(4)地幔柱源玄武岩的化学特征。虽然这3个大火成岩省都是来源于原始地幔柱,但是它们的地球化学特征有本质上的差异,反映其地幔柱曾与不同的上地幔库相互作用。(1)峨眉山和西伯利亚大陆溢流玄武岩的母岩浆,在上升过程中经受了与地球化学上和古老克拉通岩石圈地幔相同的上地幔库(EM1型幔源)的相互作用;(2)而德干大火成岩省没有受到地壳(或岩石圈)混染的原生玄武岩则显示地幔柱和EM2之间的Sr-Nd同位素变化。这种差异有可能制约了3个大火成岩省的成矿潜力。峨眉山和西伯利亚大火成岩省含有世界级岩浆矿床,而德干大火成岩省则不含矿。

德干断裂系的特征、活动性与地震危险性评价

乌东德水电站场址附近走向NNE的德干断裂系主要由裸佐断裂、马店断裂、鹿鹤断裂等组成,全长约120km。该断裂系向北收敛,向南呈＂帚状＂撒开成多条分支近平行排列,展布宽约6km。断层构造岩均为脆性变形所产生的碎裂岩系,断裂带内各种次级组构表明,该断裂系在新构造时期存在多次构造活动,且活动强度由强逐渐变弱。断裂最新活动年代在中更新世,运动方式为粘滑兼有稳滑。地震危险性分析认为,倮佐断裂的最大地震震级为6.0级,马店断裂、鹿鹤断裂等在5～5.5级之间。

Implications for the lithospheric structure of Cambay rift zone,western India:Inferences from a magnetotelluric study

Broad-band and long-period magnetotelluric(MT)data were acquired along an east-west trending traverse of nearly 200 km across the Kachchh,Cambay rift basins,and Aravalli-Delhi fold belt(ADFB),western India.The regional strike analysis of MT data indicated an approximate N59°E geoelectric strike direction under the traverse and it is in fair agreement with the predominant geological strike in the study area.The decomposed transverse electric(TE)-and transverse magnetic(TM)-data modes were inverted using a nonlinear conjugate gradient algorithm to image the electrical lithospheric structure across the Cambay rift basin and its surrounding regions.These studies show a thick(~1-5 km)layer of conductive Tertiary-Mesozoic sediments beneath the Kachchh and Cambay rift basins.The resistive blocks indicate presence of basic/ultrabasic volcanic intrusives,depleted mantle lithosphere,and different Precambrian structural units.The crustal conductor delineated within the ADFB indicates the presence of fluids within the fault zones,sulfide mineralization within polyphase metamorphic rocks,and/or Aravalli-Delhi sediments/metasediments.The observed conductive anomalies beneath the Cambay rift basin indicate the presence of basaltic underplating,volatile(CO2,H2 O)enriched melts and channelization of melt fractions/fluids into crustal depths that occurred due to plume-lithosphere interactions.The variations in electrical resistivity observed across the profile indicate that the impact of Reunion plume on lithospheric structures of the Cambay rift basin is more dominant at western continental margin of India(WCMI)and thus support the hypothesis proposed by Campbell&Griffiths about the plume-lithosphere interactions.

Isotope hydrogeochemical models for assessing the hydrological processes in a part of the largest continental flood basalts province of India

Continental Flood Basalts(CFB)occupy one fourth of the world’s land area.Hence,it is important to discern the hydrological processes in this complex hydrogeological setup for the sustainable water resources development.A model assisted isotope,geochemical,geospatial and geophysical study was conducted to understand the monsoonal characteristics,recharge processes,renewability and geochemical evolution in one of the largest continental flood basalt provinces of India.HYSPLIT modelling and stable isotopes were used to assess the monsoonal characteristics.Rayleigh distillation model were used to understand the climatic conditions at the time of groundwater recharge.Lumped parameter models(LPM)were employed to quantify the mean transit time(MTT)of groundwater.Statistical and geochemical models were adopted to understand the geochemical evolution along the groundwater flow path.A geophysical model was used to understand the geometry of the aquifer.The back trajectory analysis confirms the isotopic finding that precipitation in this region is caused by orographic uplifting of air masses originating from the Arabian Sea.Stable isotopic data of groundwater showed its meteoric origin and two recharge processes were discerned;(i)quick and direct recharge by precipitation through fractured and weathered basalt,(ii)low infiltration through the clayey black cotton soil and subjected to evaporation prior to the recharge.Tritium data showed that the groundwater is a renewable source and have shorter transit times(from present day to<30 years).The hydrogeochemical study indicated multiple sources/processes such as:the minerals dissolution,silicate weathering,ion exchange,anthropogenic influences etc.control the chemistry of the groundwater.Based on the geo-electrical resistivity survey,the potential zones(weathered and fractured)were delineated for the groundwater development.Thus,the study highlights the usefulness of model assisted isotopic hydrogeochemical techniques for understanding the recharge and geochemical processes in a basaltic aquifer system.