upper crust beneath the central illinois basin united states newly available industry seismic reflection data provide critical information for understanding the structure and origin of the upper crust 0 12 km depth beneath the central illinois basin and the seismic tectonic framework north of the new madrid seismic zone in the central mississippi valley mapping of reflector sequences furnishes the first broad three dimensional perspective of the structure of precambrian basement beneath the central united states midcontinent the highly coherent basement reflectivity is expressed as a synformal wedge of dipping and subhorizontal reflections situated beneath the center of the illinois basin that thickens and deepens to the northeast e g 0 to 3 km thickness along a 123 km south to north line the thickening trend of the wedge qualitatively mimics the northward thickening of the late cambrian mt simon sandstone however other paleozoic units in the illinois basin generally thicken southward into the basin center the seismic data also reveal an anomalous subsequence defined by a spoon shaped distribution of disrupted reflections located along the southern margin of the wedge the boundaries of this subsequence are marked by distinct steeply dipping reflections possible thrust faults that continue or project up to antiformal disruptions of lower paleozoic marker reflectors suggesting paleozoic or possibly later tectonic reactivation of precambrian structure the areal extent of the subsequence appears to roughly correspond to an anomalous concentration of larger magnitude upper to middle crustal earthquakes there are multiple hypotheses for the origin of the precambrian reflectivity including basaltic flows or sills interlayered with clastic sediments and or emplaced within felsic igneous rocks such explanations are analogous to nearby keweenawan rift related volcanism and sedimentation which initiated during proterozoic rifting and were followed eventually by reverse faulting along the rift margins caused by grenville compression

stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

geology and geochemistry of the sangamner mafic dike swarm western deccan volcanic province india implications for regional stratigraphy abstract numerous large ne sw to e w trending mafic dikes outcrop around sangamner in the western deccan volcanic province this area is part of a broader region postulated to be a shieldlike feature and a major eruption center a combination of field geochemical and isotopic sr and nd characteristics is used here to understand the relationship of this dike swarm with the associated lava flows and their position in the established deccan stratigraphy many dikes are compositionally similar to the khandala and poladpur formations belonging to the lonavala and wai subgroups respectively while one dike is similar to the ambenali formation one dike has a composition distinct from all other dikes in this area as well as from most stratigraphic units although there are many similarities in composition with the bushe formation as well as the boyhare member of the khandala formation while several dikes are geochemically similar to specific flows members within certain formations their isotopic composi

geochemistry of sediments of the peninsular rivers of the ganga basin and its implication to weathering sedimentary processes and provenance abstract geochemistry of the himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate among the himalayan rivers the ganga and its himalayan catchment have been studied extensively however the peninsular rivers constituting a significant part of the ganga basin have not received much attention heretofore in the present geochemical study of the peninsular river s sediments we have found that the initial chemical weathering of rocks in the catchment produces texturally mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine grained suspended sediments the overbank sediments possess an intermediate texture and geochemistry but more towards the suspended sediments the sediment geochemistry data indicates that the peninsular river s sediments show an increase in the weathering intensity from the west banas river to the east son river along the climate gradient i e from the arid semiarid to the sub tropical condition the higher chemical index of alteration cia values of the peninsular river s sediments than the yamuna and ganga river sediments reflect the control of weatherable lithology in the tectonically stable low relief and subtropical climate condition the yamuna and ganga river sediments with lower cia values show more physical weathering in the tectonically active himalaya the suspended and overbank sediments of the yamuna and ganga rivers show an increase in their cia values after the confluence of the peninsular rivers indicating the contribution of more weathered materials by the peninsular rivers it has been found that there is a geochemical split between the channel and suspended sediments of the peninsular rivers for sharing different sources i e the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments the weathering geochemistry trace element systematics and ree patterns suggest that the dominant sources of the channel sediments of the peninsular rivers are the felsic crystallines and sedimentary lithologies of the aravalli range bundelkhand and chhotanagpur granite and gneisses and vindhyan sandstones whereas the mafic lithologies such as the deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments within the range of intermediate composition the overbank sediment chemistry reflects more contribution of the mafic sources except for the ken which shows a higher contribution of the felsic sources the geochemical split between the channel and suspended sediments of the peninsular river s sediments for the different provenances indicates differential weathering of the deccan basalts bundelkhand crystalline and vindhyan sedimentary rocks and also the hydrodynamic control of the peninsular rivers during erosion transport and deposition however the himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the himalayan catchment

uplift and erosional history of the deccan traps india evidence from laterites and drainage patterns of the western ghats and konkan coast abstract the western ghats escarpment in the western coastal region of peninsular india is locally capped by plateau remnants on which a regional high level laterite carapace is preserved geochemical fingerprinting studies show that the laterite has been developed from a protolith of panhala formation basalts the youngest known formation of the deccan sequence the high level laterite is in detail structurally concordant with its underlying basalts and hence it is concluded that it represents the original top of the lava pile a younger low level laterite carapace is developed on the konkan plain below the escarpment where it lies discordantly on basalts of the ambenali and poladpur formations from which it developed in situ the low level laterite rises topographically northwards in response to differential uplift probably at a maximum in the nasik region the main structures of the ghats region excluding the coastal monocline are the nasik dome and the mahabaleshwar anticline these have no effect on regional drainage patterns and it is argued that they are largely secondary features developing in response to post volcanic uplift

a ā lava flows in the deccan volcanic province india and their significance for the nature of continental flood basalt eruptions newly identified a lava flows outcrop intermittently over an area of 110 km2 in the western deccan volcanic province dvp india they occur in the upper thakurvadi formation in the region south of sangamner the flows one of which is compound are 15 25 m thick and exhibit well developed basal and flow top breccias the lavas have microcrystalline groundmasses and are porphyritic or glomerocrystic and contain phenocrysts of olivine clinopyroxene or plagioclase feldspar they are chemically similar to compound p hoehoe flows at a similar stratigraphic horizon along the western ghats petrographic and geochemical differences between a flows at widely spaced outcrops at the same stratigraphic horizon suggest that they are the product of several eruptions potentially from different sources their presence in the dvp could suggest relative proximity to vents this discovery is significant because a lavas are generally scarce in large continental flood basalt provinces which typically consist of numerous inflated compound p hoehoe lobes and sheet lobes their scarcity is intriguing and may relate to either their occurrence only in poorly preserved or exposed proximal areas or to the flat plateau like topography of flood basalt provinces that may inhibit channelization and a formation or both in this context the a flow fields described here are inferred to be the products of eruptions that produced unusually high effusion rate lavas compared to typical flood basalt eruptions whether these phases were transitional to lower intensity sustained eruptions that fed extensive low effusion rate p hoehoe flow fields remains unclear

geochemistry of the palitana flood basalt sequence and the eastern saurashtra dykes deccan traps clues to petrogenesis dyke flow relationships and regional lava stratigraphy recent studies of large mafic dyke swarms in the deccan traps flood basalt province india indicate that some of the correlative lava flows reached several hundred kilometers in length here we present field petrographic mineral chemical and whole rock geochemical including sr nd isotopic data on the palitana lava sequence and nearby dykes in the saurashtra region of the northwestern deccan traps these rocks are moderately evolved many with low ti nb characteristics we infer that most dykes are notably and systematically less contaminated by ancient continental crust than the palitana flows but four dykes are equally or significantly more contaminated with some of the most extreme sr nd isotopic compositions seen in the entire deccan traps initial end is as low as 18 0 a bhimashankar type and a poladpur type dyke are present several hundred kilometers from the type section of these magma types in the western ghats escarpment we find no geochemical correlations between the palitana sequence and three subsurface sequences in ne saurashtra containing abundant picritic rocks surface lavas previously studied from saurashtra or the western ghats sequence intriguingly the eastern saurashtra dykes cannot have been feeders to any of these lava sequences feeder dykes of these sequences may be located in southwestern or central saurashtra or in the dhule nandurbar dediapada areas across the gulf of cambay 200 300 km east of palitana our results indicate polycentric flood basalt eruptions not only on the scale of the deccan traps province but also within the saurashtra region itself

elemental and nd sr pb isotope geochemistry of flows and dikes from the tapi rift deccan flood basalt province india abstract the deccan traps are a large rift associated continental flood basalt province in india parts of which have been studied extensively in terms of geochemistry palaeomagnetism and stratigraphy however the basalts of the tapi rift in the central part of the province have been little studied thus far two ene wsw trending tectonic inliers of the deccan basalts in this region forming ridges rising from younger alluvium are made up of basalt flows profusely intruded by basaltic dikes both of these ridges lie along a single lineament although they are not physically continuous the flows are aphyric plagioclase phyric and giant plagioclase basalts and the dikes are aphyric or plagioclase phyric we consider the two inliers to have been originally continuous from the presence of bouldery remnants of a major dioritic gabbro dike along both samples of this dike from both ridges have previously yielded typical deccan ages of 65 6 0 5 ma and 65 6 0 6 ma by the 40 ar 39 ar incremental heating technique initial 87 sr 86 sr ratios and end t values and present day pb isotopic ratios of most dikes indicate that they are isotopically similar to lavas of the mahabaleshwar and panhala formations of the western ghats about 450 km to the south their mantle normalized trace element patterns have small pb and ba peaks one dike has a strong bushe formation affinity and a nd sr isotopic composition more extreme than that of any other deccan rock yet sampled with end t 20 2 and 87 sr 86 sr t 0 72315 its mantle normalized element pattern shows large pb th and u peaks and large nb ta troughs its elemental and isotopic chemistry reflects substantial continental contamination the flows cut by the mahabaleshwar type dikes are isotopically similar to the poladpur formation lavas of the western ghats their mantle normalized element patterns show modest peaks at rb ba and pb and rather low nb and ta relative to la indicating that they have been contaminated to intermediate degrees the mantle normalized element patterns of all the flows and dikes show enrichment in the light rare earth elements with small or no eu anomalies the entire flow dike sequence is similar to the wai subgroup of the western ghats in terms of its elemental and isotopic chemistry and stratigraphic relationships wai subgroup like lavas i e some of the younger magma types originally identified from the southern part of the western ghats are previously known from the central northern and northeastern deccan and many have been thought to be far travelled flows erupted in the southwestern deccan although at least the dikes and probably the giant plagioclase basalt flows of our study area are locally generated and emplaced our new data extend the known outcrop area of these widespread magma types substantially and these magma types indeed appear to have a nearly province wide distribution

iron titanium oxide geothermometry and petrogenesis of lava flows and dykes from mandla lobe of the eastern deccan volcanic province india abstract compositional studies on different forms of magnetite ulvospinel ilmenite and hematite mineral phases occurring in 37 lava flows and 6 dykes of the mandla lobe are presented in this paper ilmenite 0001 in equilibrium with titanomanetite show high values of temperature of equilibration ranging from 1172 974 c for high alumina quartz normative tholeiitic lava flows of chemical type a 1129 1229 c for low alumina quartz normative tholeiitic lava flows of chemical type b 1283 1124 c for tholeiitic lava flows of chemical type f and 1243 c and 99o c for two diopside olivine normative tholeiite flows of chemical type d high olivine normative flows of chemical type g and h show 1095 c and 1092 c respectively whereas high hypersthene normative tholeiite flow of chemical me c shows temperature of 1187 c data plots disposition over iron titanium oxide equilibration temperature vs logfo 2 diagram for mandla lava flows and other parts of the deccan igatpuri mahabaleshwer nagpur and sagar areas revealed that tholeiitic evolved basalt of the eastern deccan volcanic province formed at high temperatures whereas picritic primitive lavas of igatpuri and tholeiitic basalt of mahabaleshwar areas were formed at low temperatures mahabaleshwer basalts follow fmq fayalite magnetite quartz buffer curve but plots of the mandla basalts lie above this curve indicating higher temperatures of crystallisation of ilmenite titanomagnetite than that of the lava flows from other parts of deccan raps the eastern deccan traps are most evolved types of lava as characterised by its low mg number and ni content whereas igatpuri lava flows are picritic primitive having high mg number and ni contents temperature vs feo fe 2 o 3 feo fe 2 o 3 mgo ratio data plots for mandla and other deccan lava flows and liquidus data for hawaiian tholeiites indicated that igatpuri basalts lie parallel to the liquidus line of hawaiian tholeiite but at lower temperatures large data plots of mandla lava flows lie along the liquidus line of the hawaiian lava the highly vesicular nature of compound lava flows having large amount of volatile is responsible for low temperature values whereas lava flows represented by high temperatures show high modal values of glass and opaque minerals

seismic velocity model of the central united states version 1 description and simulation of the 18 april 2008 mt carmel illinois earthquake abstract we have developed a new three dimensional seismic velocity model of the central united states cusvm that includes the new madrid seismic zone nmsz and covers parts of arkansas mississippi alabama illinois missouri kentucky and tennessee the model represents a compilation of decades of crustal research consisting of seismic aeromagnetic and gravity profiles geologic mapping geophysical and geological borehole logs and inversions of the regional seismic properties the density p and s wave velocities are synthesized in a stand alone spatial database that can be queried to generate the required input for numerical seismic wave propagation simulations we test and calibrate the cusvm by simulating ground motions of the 18 april 2008 m w 5 4 mt carmel illinois earthquake and comparing the results with observed records within the model area the selected stations in the comparisons reflect different geological site conditions and cover distances ranging from 10 to 430 km from the epicenter the results based on a qualitative and quantitative goodness of fit gof characterization indicate that both within and outside the mississippi embayment the cusvm reasonably reproduces 1 the body and surface wave arrival times and 2 the observed regional variations in ground motion amplitude cumulative energy duration and frequency content up to a frequency of 1 0 hz in addition we discuss the probable structural causes for the ground motion patterns in the central united states that we observed in the recorded motions of the 18 april mt carmel earthquake online material simulated and observed waveforms and response spectral acceleration ground motion prediction equation comparison

sr and nd isotopes in river sediments from the ganga basin sediment provenance and spatial variability in physical erosion 1 sr and nd concentrations and isotope compositions in sediment of the ganga river from gangotri to rajmahal and its tributaries have been measured to determine provenance and the spatial variability in physical erosion among the ganga subbasins sr and nd in silicates range from 37 to 138 and from 10 to 36 g g with 87sr 86sr and nd of 0 7474 0 8428 and 25 5 to 15 5 respectively the results suggest that 65 of ganga mainstream sediments are derived from the higher himalayan crystallines highlighting intense physical erosion in this region the 87sr 86sr values of sediments in the gangetic plain show nearly identical trends during two seasons with a sharp and significant decrease at barauni downstream of gandak confluence this brings out the major impact of the sediment contribution from the gandak to the ganga mainstream model calculation suggests that about half of the ganga sediment at rajmahal is sourced from the gandak the erosion rates in the himalayan subbasins of the ganga range between 0 5 and 6 mm a where a is years with the gandak having the highest erosion rate high relief and intense precipitation over the headwater basins of the gandak appear to drive the rapid and focused erosion of this basin the results of this study and those in literature suggest that the eastern syntaxis brahmaputra the western syntaxis indus and the gandak have much higher physical erosion rates than the other himalayan basins focused erosion in the hot spots of these river basins contributes significantly to the global riverine sediment budget and influence regional tectonics

stratigraphy structure and volcanology of the se deccan continental flood basalt province implications for eruptive extent and volumes the deccan volcanic province is one of the world9s largest continental flood basalt provinces and derives additional importance because its eruptions 64 67 ma straddle the cretaceous tertiary boundary to better assess the environmental impact of deccan volcanism and its possible effect upon cretaceous tertiary boundary biota it is necessary to document the stratigraphy chronology and volume of the eruptions new chemostratigraphical data permit mapping of the se deccan these data strengthen the likelihood that the rajahmundry traps of eastern india were originally fed by long distance flows and are an extension of the main deccan volcanic province an east west cross section reveals a depression or moat around the se periphery of the deccan volcanic province this provided a site in which shallow lakes initially formed and along which later lava eruptions became channelled and confined published palaeomagnetic data indicate that the lavas of the se deccan were erupted during chron 29r coeval with the cretaceous tertiary boundary and the chemostratigraphic data place the associated lake sediments i e lameta group beneath and within lavas of the wai subgroup finally these new map data are combined with previous work to provide a quantitative estimate for the original deccan volcanic province eruptive volume of c 1 3 10 6 km 3

origin of the deccan trap flows at mahabaleshwar inferred from nd and sr isotopic and chemical evidence abstract the deccan flows at mahabaleshwar are divisible into a lower and an upper group based on nd and sr isotopic ratios which define two correlated trends this distinction is supported by incompatible element ratios and bulk compositions the data reflect contamination in a dynamic system of magmas from an lil depleted e juv 8 mantle by two different negative e juv endmembers one undoubtedly continental crust the other either continental crust or enriched mantle the depleted mantle source anomalously high in 87 sr 86 sr may have been in the subcontinental lithosphere or a region of rising indian ocean morb mantle

tectonomagmatic setting of lava packages in the mandla lobe of the eastern deccan volcanic province india palaeomagnetism and magnetostratigraphic evidence

application of a textural geospeedometer to the late stage magmatic history of mil 03346 dynamic crystallization experiments performed on fe rich al poor basalt are employed as a textural calibration set to quantify the late stage igneous history of nakhlite miller range mil 03346 the ratio of crystal melt surface area to volume typifying morphologically distinct populations of ca pyroxene has been shown to vary as a strong function of cooling rate hammer 2006 furthermore a texture of phenocrysts surrounded by finer grained groundmass crystals arises by sequential nucleation events during constant rate cooling but multiple populations nucleate only if the cooling rate is 72 c h 1 textural analysis of meteorite mil 03346 reveals at least two distinct populations the ca pyroxene phenocryst and microphenocryst three dimensional 3d aspect ratios are 112 8 3 and 1530 160 mm 1 respectively by comparison with the calibration set the range of cooling rates consistent with 3d aspect ratios of both populations in mil 03346 is 20 c h 1 an additional experiment was performed approximating a conductive heat transfer profile in order to interpret and apply results of constant rate cooling experiments to the natural cooling of magma results suggest that the textures of constant rate experiments parallel the initial period of rapid cooling in natural magma initial cooling rates of 20 c h 1 in the lava hosting mil 03346 occur in conductively solidifying lava at depths of 0 4 m constraining the minimum total thickness to 0 8 m crystal accumulation beginning in a subsurface reservoir and continuing after lava emplacement as an inflated pahoehoe sheet satisfies all textural constraints on the late stage igneous history of mil 03346

volcanological and tectonic control of stratigraphy and structure in the western deccan traps many of the world s flood basalt provinces form elevated plateaux at the margins of continents although in most cases their present large elevation is not the result of mountain building processes several explanations have recently been put forward to explain such occurrences of epeirogeny the deccan trap basalt province forms one such elevated plateau and results are presented here showing how the epeirogenic uplift in this region combined with crustal subsidence probably associated with the rifting of the indian continental margin has affected the structure of the basalt sequence trace element analytical data are used for samples from numerous vertical sections through the deccan traps lava series along and around the western ghats ridge in india the results reinforce the previously defined stratigraphy of the mahabaleshwar area and extend it over a region covering some 36 000 km2 reaching as far south as belgaum and the trap basement contact these results show that the lava pile is not flat lying but forms a very low amplitude anticlinal fold structure plunging southwards by up to 0 3 over most of the area although in the south there is evidence of a reversal of this plunge the fold is interpreted as being the result of two tilting processes 1 westward tilting near the coast due to the foundering of the passive continental margin and 2 epeirogenic uplift along the whole west coast of india producing the observed topography and the peninsula wide drainage patterns and also the easterly component of dip variations in the magnitude of the latter effect along the western continental margin may also be important in generating the plunge of the fold although the possibility of some component of depositional dip may also be important this latter possibility can be modelled using a simple computer program the results of this modelling show that a migrating linear volcanic edifice fits the observations best

magnetostratigraphy and 40ar 39ar geochronology of the malwa plateau region northern deccan traps central western india significance and correlation with the main deccan large igneous province sequences abstract basaltic lava flows of malwa plateau together with the mandla area and the toranmal section constitute the northern deccan province in central western india with the present outcrop area of 80 000 km2 the malwa flows form an extensive but relatively thin sequence we sampled deccan basalts along two 100 km each n s and e w transects along the western and southern rims of the malwa plateau the 67 12 0 44 ma 40ar 39ar age obtained in the present study clearly shows that the eruption of the malwa flows started during the magnetochron c30n by mapping the magnetic c30n c29r transition on the western and southern edge of the plateau the total volume and eruption rate can be calculated 42 000 km3 0 03 km3 a furthermore the results point towards the narmada tapi rift zone as the possible source area for the malwa lava flows the malwa sequence is older and partly synchronous with the thick sequences of the western ghats since their eruption centers are spatially independent they should not be correlated with younger although geochemically similar formations of the western ghats other northern deccan flows show clear similarities with the malwa flows and can be magnetostratigraphically and geochemically correlated we therefore suggest a new subgroup for the northern deccan province the narmada subgroup defined on the geochemical and magnetic characteristics of the malwa mandla and toranmal flows the introduction of this new subgroup clarifies the position of the northern deccan province in the deccan stratigraphy and is a step towards a better understanding of the deccan eruption history

elemental geochemistry of river sediments from the deccan traps india implications to sources of elements and their mobility during basalt water interaction abstract the abundances of several major na ca mg k al ti fe and minor elements sr ba mn p v cr ni cu and zn have been measured in twenty eight sediment samples from seventeen rivers belonging to the krishna headwaters and west flowing western ghat rivers all of which drain the deccan trap basalts these results particularly those of na ca mg and sr coupled with those reported for these elements in the dissolved phase of the same rivers provide an assessment of their relative mobility and insight into the nature of chemical weathering of deccan basalts the sediments are heavily depleted in na ca mg and sr relative to parent basalts by 60 the abundance ratios of these elements in sediments are roughly the same as those in basalts and in dissolved phases of these rivers das a krishnaswami s sarin m m pande k 2005a chemical weathering in the krishna basin and the western ghats of the deccan traps rates of basalt weathering and their controls geochim cosmochim acta 69 2067 2084 suggesting their near congruent release from basalts to water during chemical weathering both at present and over the residence time of particles in the basin k and ba show limited mobility relative to the above four elements the abundances of k and ba are strongly correlated most likely due to their association in rock forming minerals al fe and ti are generally enriched in the sediments resulting from the loss of more mobile elements from basalts and their association with secondary minerals formed during weathering the data also provide evidence for the fractionation of fe and al during chemical weathering and erosion fe and ti exhibit significant correlation attributable either to their co occurrence in weathering resistant minerals and or due to scavenging of ti by fe oxy hydroxides formed during weathering of basalts the abundance of minor elements mn p v cr ni cu and zn and their ratios with al show significant scatter by and large bracketing the range reported for deccan basalts the wide and overlapping ranges in the concentration of these elements and their ratios relative to al between sediments and basalts place severe constraints in assessing their mobility during weathering and erosion and in judging the role of anthropogenic sources in contributing to their abundances among the minor elements there is a hint that zn concentration may have been influenced by anthropogenic inputs mn v and ni analogous to ti show significant correlation with fe either due to their association with fe ti minerals or their sequestration by fe oxy hydroxides the mobility of elements during weathering and erosion of deccan basalts follows the trend na ca mg sr k ba al fe ti there is considerable spatial variability in the intensity of chemical weathering of deccan basalts the cia chemical index of alteration values for the sediment range between 42 and 92 compared to 37 for the deccan basalts the lower cia values are in sediments richer in caco 3 this may be a result of semi arid climate of the region which facilitate caco 3 precipitation and restrict chemical weathering erosion higher cia values are generally associated with sediments from basins with higher runoff modeling the major element composition of sediment and water yields estimates of particulate abundances in water these estimates agree with the measured values within a factor of 2 for some of the rivers whereas in some others they differ by more than a factor of 3 4 the use of sediment composition instead of that of the suspended matter spatial and temporal variations in sediment flux and non steady state erosion all can contribute to this discrepancy these factors also seem to be contributing to difference in co 2 consumption estimated from sediment composition and that reported based on dissolved phase data

geology and geochemistry of pachmarhi dykes and sills satpura gondwana basin central india problems of dyke sill flow correlations in the deccan traps many tholeiitic dyke sill intrusions of the late cretaceous deccan traps continental flood basalt province are exposed in the satpura gondwana basin around pachmarhi central india we present field petrographic major and trace element and sr nd pb isotope data on these intrusions and identify individual dykes and sills that chemically closely match several stratigraphically defined formations in the southwestern deccan western ghats some of these formations have also been identified more recently in the northern and northeastern deccan however the pachmarhi intrusions are significantly more evolved lower mg numbers and higher tio2 contents than many deccan basalts with isotopic signatures generally different from those of the chemically similar lava formations indicating that most are not feeders to previously characterized flows they appear to be products of mixing between deccan basalt magmas and partial melts of precambrian indian amphibolites as proposed previously for several deccan basalt lavas of the lower western ghats stratigraphy broad chemical and isotopic similarities of several pachmarhi intrusions to the northern and northeastern deccan lavas indicate petrogenetic relationships distances these lava flows would have had to cover if they originated in the pachmarhi area range from 150 to 350 km the pachmarhi data enlarge the hitherto known chemical and isotopic range of the deccan flood basalt magmas this study highlights the problems and ambiguities in dyke sill flow correlations even with extensive geochemical fingerprinting

palaeomagnetism of the upper carboniferous strzegom and karkonosze granites and the kudowa granitoid from the sudet mountains poland abstract carboniferous granites and granitoids varying in age from 305 to 281 ma from the sudet mountains latitude 51n longitude 16e poland carry dual polarity magnetic components consisting of an inferred primary high temperature a component found in the strzegom granite the karkonosze granite with the bordering karpacz hornfels and the kudowa granitoid and scattered low stability components of mesozoic tertiary age present in all rocks except the strzegom granite the group a component defines a palaeomagnetic pole position d 202 i 12 95 13 0 n 4 calculated palaeomagnetic pole position 42 s 346 e which is in good agreement with palaeomagnetic results from rocks of similar age in western europe thus implying that no major tectonic movement has taken place in the sudets relative to stable europe since upper carboniferous times

geochemical stratigraphy of deccan flood basalts of the bijasan ghat section satpura range india abstract the 240 m thick bijasan ghat section exposes deccan basalt flows and dykes that have major and trace element compositions suggestive of variable amounts of contamination by continental material most flows and a dyke are chemically similar to lavas of the poladpur formation in the southwestern deccan one flow and one dyke are similar to lavas of the bushe formation in the southwest and one dyke is similar to lavas of the mahabaleshwar formation in the southwest the type sections of these formations are located 350 km to the south of bijasan ghat but many poladpur type lavas a few mahabaleshwar like lavas and dykes and a few broadly bushe like lavas and dykes have recently been identified in the satpura region lavas resembling the thick ambenali fm of the southwest are absent from bijasan ghat and nearby areas our data further extend the known outcrop area of poladpur like flows estimated at 3 105 km2 one of the most widespread deccan magma types seven giant plagioclase basalt flows encountered in seven different sections in this region cannot unambiguously be correlated at present either physically or chemically and therefore are of little use in deciphering the complicated stratigraphic and structural make up of the regional lava pile

temporal variations in 87sr 86sr and ɛnd in sediments of the southeastern arabian sea impact of monsoon and surface water circulation sr and nd isotopic composition of silicate fractions of sediments have been measured in two well dated gravity cores from the eastern arabian sea archiving a depositional history of 29 and 40 ka the 87 sr 86 sr and e nd in the northern core ss 3104g 12 8 n 71 7 e ranges from 0 71416 to 0 71840 and 8 8 to 12 8 these variations are limited compared to those in the southeastern core ss 3101g 6 0 n 74 0 e in which they vary from 0 71412 to 0 72069 and 9 0 to 15 2 respectively this suggests that the variation in the relative proportions of sediments supplied from different sources to the core ss 3104g are limited compared to core ss 3101g the 87 sr 86 sr and e nd profiles of ss 3101g exhibit two major excursions ca 9 ka and 20 ka coinciding with periods of holocene intensified monsoon phase imp and the last glacial maximum lgm respectively with more radiogenic 87 sr 86 sr and lower e nd during these periods these excursions have been explained in terms of changes in the erosion patterns in the source regions and surface circulation of the northern indian ocean resulting from monsoon intensity variations the intensification of north east ne monsoon and associated strengthening of the east indian coastal current in southwest direction during lgm transported sediments with higher 87 sr 86 sr and lower e nd from the western bay of bengal to the arabian sea in contrast enhanced south west sw monsoon at 9 ka facilitated the transport of sediments from the northern arabian sea particularly indus derived to the southeastern arabian sea this study thus highlights the impact of monsoon variability on erosion patterns and ocean surface currents on the dispersal of sediments in determining the sr and nd isotopic composition of sediments deposited in the eastern arabian sea during the last 40 ka

deep faulting and structural reactivation beneath the southern illinois basin abstract the investigation of deep fault structure and seismogenesis within stable continental interiors has been hindered by the paucity of detailed subsurface information and by low levels of seismicity outstanding seismotectonic questions for these areas include whether pre existing structures govern the release of seismic energy as earthquakes can reactivation of such structures be recognized and to what extent have precambrian basement structures exerted long lived controls on the development of overlying phanerozoic features the southern portion of the illinois basin provides a premier area in which to study the relation between contemporary seismicity and pre existing structures due to the frequency of seismic events the concentration of available geophysical data and the wealth of borehole information we have integrated the study of this information in order to create a 2 5 dimensional picture of the earth for local seismogenic depths 0 15 km for a study area of moderate 20th century earthquake activity the area is located along the western flanks of two of the major structures within the illinois basin the wabash valley fault system wvfs and the la salle anticlinal belt lsa the results of reprocessing seismic reflection profiles combined with earthquake hypocenter parameters suggest three distinct seismotectonic environments in the upper crust first we have delineated a fault pattern that appears to correspond to the steep nodal plane of a strike slip mechanism event 1974 04 03 mb 4 7 the fault pattern is interpreted to be a deeply buried rift zone or zone of intense normal faulting underpinning a major paleozoic depocenter of the illinois basin fairfield basin second a similar event 1987 06 10 mb 5 2 and its well located aftershocks define a narrow zone of deformation that occurs along and parallel to the frontal thrust of the lsa third the hypocenter of the largest event in the study area 1968 11 09 mb 5 5 may be spatially associated with a prominent zone of dipping middle crustal reflections just west of the wvfs which have been interpreted as a deeply buried blind thrust the proposed correlation of pre existing structures with earthquakes having consistently oriented structural parameters supports the reactivation of old deformation zones by contemporary stresses as previously proposed by earlier workers however the degree to which deformation has propagated upward from precambrian basement into the paleozoic rocks varied significantly even over a small study area the societal value of associating an earthquake with a specific pre existing deformation zone in the seismogenic crust is to improve the assessment of seismic hazard or to assess the integrity of a stratigraphic formation being considered as a target for natural gas storage or carbon sequestration

the timing of crustal extension and the eruption of continental flood basalts the association between mantle plumes continental flood basalt eruption and the extension and rifting of the crust is well recognized1 3 but there has always been controversy as to whether the plume or the rifting was the initiating factor4 5 was rifting triggered by doming above the thermal plume2 3 6 or was rifting the driving force preceding the associated volcanicity7 8 here i show that recent flow by flow mapping of two continental flood basalt provinces the columbia river basalt group and the deccan basalt group allows one to infer the relative timing of volcanicity and crustal extension in both provinces eruption of the main tholeiitic phase preceded significant extension and crustal thinning this suggests that the primary event in the formation of these provinces was the upwelling of a mantle plume and that the subsequent crustal extension rifting and decompression was in part a consequence of the initiation of that plume

intracanyon flows in the deccan province india case history of the rajahmundry traps the rajahmundry traps form small exposures of basaltic flows on either side of the godavari river near the east coast of india and they are thought to be late cretaceous early paleocene in age because they lie 400 km from the nearest surface exposures of the deccan traps their mode of formation remains unknown furthermore the rajahmundry traps show normal magnetic polarity indicating that they cannot be exact time equivalents of the large volumes of the deccan traps which show reversed magnetic polarity geochemical analyses reveal that the rajahmundry traps are of very uniform composition geochronological studies suggest an age of 64 ma marginally younger than the main sections western ghats of the deccan traps the only section of the main deccan province that may be stratigraphically equivalent on the basis of age geochemical signatures and magnetic polarity is the kolhapur formation at the southern end of the deccan province near the west coast 800 km from the rajahmundry traps we suggest that the rajahmundry traps and other basaltic material found near the mouth of the godavari river represent remnants of intracanyon flows that flowed eastward down the ancestral river systems of peninsular india away from the domed structure caused by the plume that led to the formation of the deccan traps similar intracanyon flows that have traveled 600 km from their source to the pacific coastline are well documented in association with the columbia river basalt province united states in the case of the rajahmundry traps the distance traveled would appear to be 1000 km

investigations of the spatial and temporal variations of sr and nd isotopes in sediments from two indian rivers implications to source identification radiogenic isotopes of sr and nd provide crucial information on chemical and physical erosion processes therefore used as tracers for fingerprinting the sources of fluvial sediments moreover elemental geochemistry 87sr 86sr and 143nd 144nd signatures in silicate fractions of sediments primarily reflect intricate controls of characteristics and provenance of sediment a suite of sediment samples collected from two rivers of india narmada large and netravati small were analyzed for elemental concentrations 87sr 86sr and 143nd 144nd in silicate as well as acid leachable fractions 87sr 86sr in acid leachable sediment fractions from both the rivers 0 7094 0 0002 for narmada and 0 7158 0 003 for netravati showed more radiogenic 87sr 86sr in netravati compared to narmada indicating influence of source rocks in their watersheds weak correlation of sedimentary 87sr 86sr and 143nd 144nd with al and chemical index of alteration cia in silicate fraction indicate that isotopic compositions are primarily controlled by their sources and not by chemical weathering in both the rivers provenance of sediments in narmada is dominated by their supply from deccan deposits with secondary supply from mid late proterozoic vindhyan along with mesoproterozoic to mesoarchean tdmnd ages sediments from netravati reflected signatures of peninsular gneisses dominant with gneisses schists and granodiorite along with paleoarchean tdmnd ages based on variability of 87sr 86sr and 143nd 144nd present study highlight that sediment supplies from tributaries to the mainstream in narmada is inadequate as compared to that in netravati 87sr 86sr and 143nd 144nd signatures in narmada and netravati are comparable with global rivers this article is protected by copyright all rights reserved

correlation of the deccan and rajahmundry trap lavas are these the longest and largest lava flows on earth abstract we propose that the rajahmundry trap lavas found near the east coast of peninsular india are remnants of the longest lava flows yet recognized on earth 1000 km long these outlying deccan like lavas are shown to belong to the main deccan traps several previous studies have already suggested this correlation but have not demonstrated it categorically the exposed rajahmundry lavas are interpreted to be the distal parts of two very large volume p hoehoe flow fields one each from the ambenali and mahabaleshwar formations of the wai sub group in the deccan basalt group eruptive conditions required to emplace such long flows are met by plausible values for cooling and eruption rates and this is shown by applying a model for the formation of inflated p hoehoe sheet flow lobes the model predicts flow lobe thicknesses similar to those observed in the rajahmundry lavas for the last 400 km of flow the lava flows were confined to the pre existing krishna valley drainage system that existed in the basement beyond the edge of the gradually expanding deccan lava field allowing the flows to extend across the subcontinent to the eastern margin where they were emplaced into a littoral and or shallow marine environment these lavas and other individual flow fields in the wai sub group may exceed eruptive volumes of 5000 km3 which would place them amongst the largest magnitude effusive eruptive units yet known we suggest that the length of flood basalt lava flows on earth is restricted mainly by the size of land masses and topography in the case of the rajahmundry lavas the flows reached estuaries and the sea where their advance was perhaps effectively terminated by cooling and or disruption however it is only during large igneous province basaltic volcanism that such huge volumes of lava are erupted in single events and when the magma supply rate is sufficiently high and maintained to allow the formation of very long lava flows the rajahmundry lava fields were emplaced around 65 ma during the later times of deccan volcanism probably just after the k t environmental crisis however many lava forming eruptions of similar magnitude and style straddled the k t boundary

fossil flat slab subduction beneath the illinois basin usa abstract the illinois basin is one of several well studied intracratonic sedimentary basins within the north american craton whose formational mechanisms and subcrustal structure are not well understood we study the s velocity structure of the upper mantle beneath the illinois basin and its surrounding area through seismic tomography we utilize continental scale waveform data of seismic s and surface waves enhanced by regional earthquakes located near the illinois basin our 3d tomographic model il05 confirms the existence of a slow s velocity structure in the uppermost mantle beneath the illinois basin region this anomalously slow region exists from the base of the crust to depths of 90 km and is slower than the north american cratonic average by about 200 m s this anomalous uppermost mantle beneath the illinois basin is underlain by a faster lithosphere typical of the surrounding craton to depths of 200 km excluding the formation of the reelfoot rift this area of north american has been stable for over 1 0 gy thus we do not expect thermal anomalies from before that time to persist into present day s velocity anomalies and we consider a delamination origin as an explanation of illinois basin subsidence unlikely we cannot rule out that the slow mid lithosphere beneath the illinois basin is caused by an uppermost mantle enriched by a deep but weak plume we attribute the slow mid lithosphere to the presence of either oceanic hydrous crust or a relatively cool mantle wedge with preserved hydrous minerals in the illinois basin s uppermost mantle related to a fossilized flat subduction zone

geophysical constraints on understanding the origin of the illinois basin and its underlying crust abstract interpretation of reprocessed seismic reflection profiles reveals three highly coherent layered unconformity bounded sequences that overlie or are incorporated within the proterozoic granite rhyolite province beneath the paleozoic illinois basin and extend down into middle crustal depths the sequences which are situated in east central illinois and west central indiana are bounded by strong laterally continuous reflectors that are mappable over distances in excess of 200 km and are expressed as broad basinal packages that become areally more restricted with depth normal fault reflector offsets progressively disrupt the sequences with depth along their outer margins we interpret these sequences as being remnants of a proterozoic rhyolitic caldera complex and or rift episode related to the original thermal event that produced the granite rhyolite province the overall thickness and distribution of the sequences mimic closely those of the overlying mt simon late cambrian clastic sediments and indicate that an episode of localized subsidence was underway before deposition of the post cambrian illinois basin stratigraphic succession which is centered farther south over the new madrid rift system i e reelfoot rift and rough creek graben the present configuration of the illinois basin was therefore shaped by the cumulative effects of subsidence in two separate regions the proterozoic caldera complex and or rift in east central illinois and west central indiana and the new madrid rift system to the south filtered isostatic gravity and magnetic intensity data preclude a large mafic igneous component to the crust so that any proterozoic volcanic or rift episode must not have tapped deeply or significantly into the lower crust or upper mantle during the heating event responsible for the granite rhyolite

the deccan tholeiite lavas and dykes of ghatkopar powai area mumbai panvel flexure zone geochemistry stratigraphic status and tectonic significance abstract mumbai city situated on the western indian coast is well known for exposures of late stage deccan pillow basalts and spilites pyroclastic rocks rhyolite lavas and trachyte intrusions these rock units and a little studied sequence of tholeiitic flows and dykes in the eastern part of mumbai city constitute the west dipping limb of a regional tectonic structure called the panvel flexure here we present field petrographic major and trace element and sr nd isotopic data on these tholeiitic flows and dykes best exposed in the ghatkopar powai area the flows closely resemble the mahabaleshwar formation of the thick western ghats sequence to the east in sr nd isotopic ratios and multielement patterns but have other geochemical characteristics e g incompatible trace element ratios unlike the mahabaleshwar or any other formation the flows may have originated from a nearby eruptive center possibly offshore of mumbai two dykes resemble the ambenali formation of the western ghats in all geochemical characteristics though they may not represent feeders of the ambenali formation lavas most dykes are distinct from any of the western ghats stratigraphic units some show partial e g sr nd isotopic similarities to the mahabaleshwar formation and these include several dykes with unusual concave downward ree patterns suggesting residual amphibole and thus a lithospheric source the flows and dykes are inferred to have undergone little or no contamination by lower continental crust most dykes are almost vertical suggesting emplacement after the formation of the panvel flexure and indicate considerable east west lithospheric extension during this late but magmatically vigorous stage of deccan volcanism

an anomalous high velocity layer at shallow crustal depths in the narmada zone india summary the narmada zone in central india is a zone of weakness that separates the region of vindhyan meso neoproterozoic deposition to the north from gondwana permo carboniferous lower cretaceous deposits to the south the reinterpretation of analogue seismic refraction data acquired during the early 1980s using 2 d raytracing techniques reveals a basement velocity 5 8 6 0 km s 1 topography suggesting that the narmada zone bounded by the narmada north and narmada south faults is a region of basement uplift a layer of anomalously high velocity 6 5 6 7 km s 1 at depths between 1 5 and 9 0 km appears to be present in the entire region within the narmada zone this layer occurs at shallower depths than outside the narmada zone at two places within the narmada zone this layer is at a depth of about 1 5 km this layer cannot be considered as the top of the lower crust because in this case it should have produced large positive gravity anomalies at the shallowest parts instead these parts correspond to bouguer gravity lows furthermore lower crust at such shallow depths has not been reported from any other part of the indian shield therefore this layer is likely to represent the top of a high velocity mafic body that has different thicknesses in different places

chemical weathering outputs from the flood plain of the ganga abstract transport of sediment across riverine flood plains contributes a significant but poorly constrained fraction of the total chemical weathering fluxes from rapidly eroding mountain belts which has important implications for chemical fluxes to the oceans and the impact of orogens on long term climate we report water and bedload chemical analyses from the ganges flood plain a major transit reservoir of sediment from the himalayan orogen our data comprise six major southern tributaries to the ganga 31 additional analyses of major rivers from the himalayan front in nepal 79 samples of the ganga collected close to the mouth below the farakka barrage every two weeks over three years and 67 water and 8 bedload samples from tributaries confined to the ganga flood plain the flood plain tributaries are characterised by a shallow 18o d array compared to the meteoric water line with a low dexcess from evaporative loss from the flood plain which is mirrored in the higher dexcess of the mountain rivers in nepal the stable isotope data confirms that the waters in the flood plain tributaries are dominantly derived from flood plain rainfall and not by redistribution of waters from the mountains the flood plain tributaries are chemically distinct from the major himalayan rivers they can be divided into two groups tributaries from a small area around the kosi river have 87sr 86sr ratios 0 75 and molar na ca ratios as high as 6 tributaries from the rest of the flood plain have 87sr 86sr ratios 0 74 and most have na ca ratios

constraints on the mantle sources of the deccan traps from the petrology and geochemistry of the basalts of gujarat state western india the late cretaceous early tertiary flood basalts in the gujarat area of the northwestern deccan traps kathiawar peninsula pavagadh hills and rajpipla exhibit a wide range of compositions from picrite basalts to rhyolites moreover the basaltic rocks have clearly distinct tio2 contents at any given degree of differentiation and strongly resemble the low titanium and hightitanium basalts found in most of the gondwana continental flood basalt cfb suites four magma groups are petrologically and geochemically distinguished 1 a low ti group characterized by rocks with varying sio2 saturation and with tio2 1 8 wt in picrites nb 19 p p m zr av 6 5 and tt v av 47 3 an intermediate ti group with tio2 contents slightly lower than the high ti rocks at the same degree of evolution and with correspondingly lower incompatible trace element contents and ratios in particular k2o nb ba and zr y av 5 2 4 a potassium rich group kt broadly similar in geochemical character to the high ti group but showing more extreme k rb and ba enrichment av k20 na20 l ba y 20 the most primitive low ti and high ti picrites when corrected for low pressure olivine fractionation show distinct major and trace element geochemistry in particular for cao ai2o3 cao tio2 and al2o3 tio2 and moderate but significant variations in their sio2 and fe2ost contents these characteristics strongly suggest the involvement of different mantle sources more depleted for the low ti picrites and richer in cpxfor the high ti picrites but with broadly the same pressures of equilibration 27 14 kbar this in turn suggests a strong lateral heterogeneity in the gujarat trap mantle low ti picrites and related differentiates in kathiawar are reported systematically for the first time here and suggest the existence of hfse depleted mantle in the northwestern deccan traps with extension at least to the seychelles islands and to the area of the bushe formation near bombay in the pre drift position before the development of the carlsberg ridge the absence of correlations between lile hfse ratios and sio2 argues against crustal contamination processes acting on the low ti picrites possibly owing to their probably rapid uprise to the surface consequently the mantle region of this rock group was probably re enriched by small amounts of ule rich materials the substantially higher trace element enrichment of the least differentiated high ti picrites relative to the basalts of the ambe noli and mahableshwar formations of the western ghats testifies also to the presence of more incompatible element rich oib4ike mantle sources in northern and northwestern gujarat these sources were geochemicaily similar to the present day reunion mantle sources

geochemistry of flood basalts of the toranmal section northern deccan traps india implications for regional deccan stratigraphy unpublished data 1998 andthe southeastern deccan particularly the poladpur andambenali formations mitchell widdowson 1991 bilgrami 1999 for as much as 350 km from their south western type sections in addition lavas isotopically andchemicallyequivalenttothoseoftheambenaliformation fm arepresentinthenortheastern sectoroftheprovinceas far as 900 km from their southwesternmost counter parts mahoney 1988 deshmukh

deep seismic reflectivity beneath an intracratonic basin insights into the behavior of the uppermost mantle beneath the illinois basin abstract reflectivity images of the lower crust and uppermost mantle beneath the paleozoic illinois basin have been derived from reprocessing of several hundred kilometers of industry seismic reflection data using extended vibroseis recorrelation the recorrelation was based on extending an originally 4 s correlated record acquired with a 16 s sweep from 14 to 126 hz to the absolute limit of the full 20 s 70 km listening traveltime sub moho reflections are recorded to 18 s two way traveltime unmigrated and are observed on intersecting profiles apparently dipping to the southwest and striking northwest southeast occasional moho reflections are also observed across the profiles 12 s or 38 km while reflectivity in the lower crust is generally marked by intermittent horizontal packages and short gently dipping reflections and diffraction segments the presence of newly observed mantle reflectivity beneath the illinois basin indicates significant uppermost mantle heterogeneity relative to other parts of the usa studied using reflection methods the mantle reflectivity effectively defines an area of anomalous mantle that rests beneath the depocenter of the early paleozoic illinois basin which is itself superimposed over a deeper proterozoic basinal depocenter filtering and inversion of geopotential field data reveal that this anomalous mantle also partially correlates with a positive density anomaly in the upper mantle these correlations suggest that the anomalous mantle zone exerted an influence on the early paleozoic subsidence of the basin perhaps as a buried load due to eclogitization of former lower crust the relatively isolated occurrence of sub moho reflections beneath the basin makes it difficult to uniquely infer their origin however available geologic and geophysical constraints especially from geochemical and geochronological studies of drilled and exposed basement rocks limit the possibilities to 1 remnants or scars of sub crustal processes associated with lithospheric extension or delamination related to the melting of the proterozoic crust that led to the emplacement of the granite rhyolite province that underlies much of usa midcontinent or 2 deformation caused by plate subduction associated with the hypothetical accretion of a juvenile island arc to the pre 1 6 ga southern margin of the laurentian continent

from trash to treasure three dimensional basement imaging with excess data from oil and gas explorations modern oil and gas seismic surveys commonly use areal arrays that record continuously and thus routinely collect excess data that are not needed for the conventional common reflection point imaging that is the primary goal of exploration these excess data have recently been recognized to have utility not only in resource exploration but also for addressing a diverse range of scientific issues here we report processing of such discarded data from recent exploration surveys carried out in southeastern new mexico these have been used to produce new three dimensional 3 d seismic reflection imagery of a layered complex within the crystalline basement as well as elements of the underlying crust this enigmatic basement layering is similar to that found on industry and academic seismic reflection surveys at many sites in the central united states correlation of these reflectors with similar features encountered by drilling in northwestern texas suggest that they may be part of an extensive continental scale network of tabular mafic intrusions linked to keweenawan rifting of the igneous eastcentral unites states during the late proterozoic more importantly this analysis clearly demonstrates that the new generation of continuously recorded 3 d exploration datasets represent a valuable source of fresh information on basement structure that should be examined rather than discarded such basement information is not only important to understanding crustal evolution it is directly relevant to assessing risks associated with fossil fuel extractions such as induced seismicity related to waste water injection

source and differentiation of deccan trap lavas implications of geochemical and mineral chemical variations the basalt stratigraphy of the deccan trap between mahabaleshwar ghat and belgaum over steps the basement from north to south sr isotope and zr nb ratios and sr rb and ba concentrations correlate portions of the post poladpur stratigraphy over 250 km along the western ghats thereby confirming a southerly component of dip of 0 06 at the southwestern margin the stratigraphy extends upwards from the compositionally uniform ambenali formation cox hawkesworth 1984 into a sequence of grossly heterogeneous flow units which have been allocated to the mahabaleshwar and panhala formations lightfoot hawkesworth 1988 the mahabaleshwar formation is represented only by a sequence of highly fractionated flows termed the kolhapur unit with similar 87sr 86sr0 to the mahabaleshwar 0 7045 but with sr 2 25 succeeding the kolhapur unit are a series of flows with high 87sr 86sr0 0 7045 0 705 zr nb 13 and low sr 230 but trace element concentrations similar to the mahabaleshwar formation these have been allocated to the desur unit of the panhala geochemical variations in flows overlying the ambenali define two distinct trends one is attributed to gabbro fractionation and the other to variations in the compositions of the parental magmas and arguably their source regions there is little evidence for significant crustal contamination in these flows and the degree of fractionation and the composition of the phase extract are shown to vary along strike within the mahabaleshwar formation the high tio2 content of kolhapur unit flows is shown to be the result of shallow level gabbro fractionation rather than the presence of a primitive high ti magma mahabaleshwar formation basalts exhibit a broad negative correlation between the degree of fractionation and sr isotopic composition the endmember with lower 87sr 86sr0 has different zr y from the ambenali basalts and would appear to have been generated by lower degrees of melting of a similar source the other endmember has more radiogenic sr lower zr nb similar zr y but higher mg number the simplest interpretation is that these magmas were more primitive and hence hotter and more able to interact with the lithosphere en route to the surface and that they then mixed to produce the mahabaleshwar array the panhala formation basalts plot on the sr nd array defined by the mahabaleshwar formation and the desur unit basalts plot on an extension of this array this suggests that the source characteristics are also lithospheric the absolute elemental abundances may then be a function of melting and fractionation we are impressed by the apparent switch from crustal lithospheric contributions to mantle lithospheric contributions through the stratigraphy and suggest that this together with the more protracted fractionation of the magma reflects a change in the availability of the lithospheric components accompanying the southerly migration of the volcanic edifice

k t transition in deccan traps of central india marks major marine seaway across india deccan intertrappean sediments in central india are generally considered as terrestrial deposits of maastrichtian age but the cretaceous tertiary k t position is still unknown here we report the discovery of the k t transition a marine incursion and environmental changes preserved within the intertrappean sediments at jhilmili chhindwara district madhya pradesh integrative biostratigraphic sedimentologic mineralogic and chemostratigraphic analyses reveal the basal danian in the intertrappean sediments between lower and upper trap basalts that regionally correspond to c29r and the c29r c29n transition respectively intertrappean deposition occurred in predominantly terrestrial semi humid to arid environments but a short aquatic interval of fresh water ponds and lakes followed by shallow coastal marine conditions with brackish marine ostracods and early danian zone p1a planktic foraminifera mark this interval very close to the k t boundary this marine incursion marks the existence of a nearby seaway probably extending inland from the west through the narmada and tapti rift valleys the jhilmili results thus identify the k t boundary near the end of the main phase of deccan eruptions and indicate that a major seaway extended at least 800 km across india

trace element and isotopic evidence for archean basement in the lonar crater impact breccia deccan volcanic province abstract the lonar impact crater in the deccan traps of the indian peninsula provides unique opportunities to study physical and chemical processes of impact cratering on basaltic targets because terrestrial impact craters on basalts are extremely rare such studies are needed for determining provenance and other parameters of the excavated rocks and the cratering phenomenon that may have implications for similar crater formations in lunar martian and other basaltic targets in the solar system considering some of these objectives we analyzed trace elements and nd sr pb isotopes of impact breccia rocks and target basalts collected from the lonar crater chondrite normalized rare earth element ree patterns in the target basalts and breccia rocks show similar light ree enriched patterns although in detail the impact breccia are more fractionated in la sm compared to the target basalts the target basalts also show much lower concentrations of rb ba th u and pb compared to the breccia and are characterized by rb ba and pb depletions with respect to the primitive mantle normalized th u nb ta and the ree contents the breccia rocks are significantly enriched in rb ba and pb and to a lesser extent in th and u compared to the target rocks the nd sr and pb isotopic compositions of the lonar target basalts can be correlated with those of the poladpur suite one of the mid section volcano stratigraphic units of the deccan traps in contrast to the host basalts the impact breccia rocks show more radiogenic sr less radiogenic nd and higher rb sr and lower sm nd ratios indicating an additional component other than the target basalt that must have been derived from beneath the basaltic target rocks at the impact site the deccan traps in western india are underlain by archean to mid proterozoic cratonic rocks the overall geochemical signatures of the impact breccia rocks specifically the trace element concentrations negative end values radiogenic sr isotopic composition as well as the high 207pb 204pb at low 206pb 204pb indicate that a major component of the lonar impact breccia was derived from melting of archean basement rocks we argue that the archean component in the breccia cannot be from the incorporation of paleosols that are weathering products of the target basalts or from the inter trappean sediments that are most commonly cherts and limestones of mesozoic age similarly the possible role of eolian sediments in causing the archean pb isotopic signature identical to those of the deccan basement in the breccia rocks can be excluded the basement beneath the lonar region is believed to be similar to the dharwar craton of peninsular india based on their similar pb isotopic compositions with the breccia rocks we suggest the archean chitradurga group of rocks of this craton to be present in the basement beneath the deccan lavas of the lonar region the thickness of the basaltic target rocks at the crater site 400 m and the inferred crater depth 350 m 610 m based on depth to diameter ratios in simple planetary craters 0 2 0 33 are consistent with our conclusion regarding melting and incorporation of these ancient basement rocks in the impact breccia of the lonar crater using pi group scaling relations the observed crater diameter and density of the basaltic target rocks we have estimated with reasonable approximation the diameter of the lonar impactor to be either 70 m 86 m or 120 m assuming the bolide to be an iron meteorite stony iron meteorite or an ordinary chondrite respectively

tholeiitic dykes in the seychelles and the original spatial extent of the deccan we report geochemical data from c deccan age tholeiitic dykes from praslin island in the seychelles a continental fragment which lay adjacent to the coast of india before sea floor spreading started in the arabian sea at 64 ma the dykes have compositions very similar to the distinctive bushe magma type from the deccan and hence constitute the first traces of deccan activity recognized on the seychelles fitting the seychelles and india back together to reconstruct the original extent of the deccan we find that the present estimate of 1 million km 2 needs to be revised upwards by c 25 to account for the deccan magmatism in the seychelles if dipping reflectors found on seismic lines to the northwest of the seychelles are also deccan age flows this would increase still further the area and volume estimates

paleomagnetic constraints on the structure of the deccan traps abstract new paleomagnetic results from two widely separated areas of the deccan traps allow one to test the simple normal reversed normal nrn magnetostratigraphic model previously proposed the new data from the mandla region to the northeast of the main outcrop of the deccan traps together with earlier apparently conflicting results are all compatible with the nrn stratigraphy provided the flows are not strictly horizontal but have a synform antiform structure with 500 m amplitude and 150 km wavelength the structure parallels the paleozoic narmada son rift system with slopes never exceeding 0 5 sampling in rajahmundry a remote southeastern outlier of the deccan with well constrained age allowed identification of the rn boundary in an area where only normal polarities had been reported it has also been possible to correlate the detailed geochemical stratigraphy in the western ghats with the nrn magnetic stratigraphy a compilation of 35 magnetic studies together with the above findings confirms the general applicability of the nrn model and reveals the large scale topography of the rn boundary which is an isochron over most of the deccan the rn isochron surface displays a boomerang shape with topography ranging from sea level to above 1600 m this observed topography is consistent with a simple model in which doming and renewed rifting and dyke intrusion resulted from impingement 70 65 ma ago of the reunion plume under the indian lithosphere the narmada son rift was rejuvenated and a continental rift system with minor extension with a triple junction in the cambay graben resulted and was subsequently covered by the deccan flows although in places tectonic faulting and volcanism continued to interfere the rajahmundry outcrops constrain the original extent and southeastward dip away from the triple junction of much of the traps a significant part of which has now been removed by erosion and rifting away of the seychelles

sr nd and pb isotopic and chemical compositions of central deccan traps lavas and relation to southwestern deccan stratigraphy abstract sr nd and pb isotopic compositions and major and trace element abundances of lavas in five central deccan traps sections are generally very similar to those of lavas in the southwestern deccan western ghats escarpment the combination of strong isotopic and chemical similarities between lavas of the two regions indicates that they shared a closely similar petrogenesis our results indicate that unlike many lavas in the northeastern deccan most of the lavas studied in the central deccan sections can be grouped into different stratigraphic members and chemical types cts belonging to four formations thakurvadi bhimashankar khandala and poladpur present in the type sections of the western ghats bhimashankar and thakurvadi type lavas are found in a section near outram whereas only khandala type lavas make up the mhaishmal ellora and ajanta sections to the east and only poladpur type lavas are present in the easternmost section at lonar this west east sequence is the same as that seen going upward in the western ghats stratigraphy except that bushe type lavas which are located stratigraphically between the khandala and poladpur formations in the western ghats have not been found in this study overall our results indicate that the khandala and poladpur formations extend over west east distances of more than 300 km and some individual members e g the dhak dongar may extend over as much as 500 km the regional dip from igatpuri in the southwest to lonar in the east central deccan is less than 0 5 to the east which is similar to the southward regional dip in the southwestern deccan near horizontal flows in the central and southwestern deccan areas suggest that post deccan tectonic activity has had limited effects on the studied area large volumes of basaltic lavas derived from eruptive centers in the western deccan may have covered both the central and southwestern deccan areas

a geological map of the southern deccan traps india and its structural implications a geological map of an area of over 125 000 km 2 within the southern deccan traps india is presented which is based upon variations in the basalt geochemistry it represents a synthesis of new data and earlier work the use of large data sets has allowed stratigraphic boundaries to be established with greater accuracy over a much larger area than before the geochemical sections demonstrate that the southward overstepping stratigraphic style encountered along the ghats ridge has an essentially north to south polarity and that there appears to be detectable overstep in an east to west sense however the stratigraphy defines a pronounced coastward dipping monoclinal flexure across the western ghats ridge between 16 n and 18 n the data are consistent with two models of eruption the first considers the deccan eruptive focus to have been fixed throughout the volcanic episode producing an essentially annular flow pattern the second considers the flow pattern to have been generated from a southerly migrating eruptive centre resulting from the northerly drift of india over a fixed hotspot both hypotheses are consistent with recent quantitative models which suggest that rapid and voluminous flood basalt eruptions are the result of continental rifting events associated with plume generated thermal 9highs9 until a causal link between established plume hotspot trails and impact sites can be satisfactorily demonstrated we find it unnecessary to invoke a cataclysmic impact event as an explanation for the deccan eruptions

the mount pavagadh volcanic suite deccan traps geochemical stratigraphy and magmatic evolution abstract the patterns of eruption and dispersal of flood basalt lavas on the surface or as magmas in dykes and sills within the crust determine the volcanological and stratigraphic development of flood basalt provinces this is a geochemical and sr isotopic study of lavas of varied compositions that outcrop around mount pavagadh 829 m deccan traps an important outlier north of the main basalt outcrop most of the 550 m thick exposed section at pavagadh is made up of subalkalic basalts rich in the incompatible elements particularly nb ba and sr picrite and rhyolite dacite flows also occur the latter capping the sequence the relatively high initial 87sr 86sr ratios up to 0 7083 and chemical characteristics of the rhyolitic rocks of pavagadh are consistent with a small but significant involvement of the granitic basement crust in their genesis an assimilation fractional crystallization afc model involving the picrite lava and either a southern indian or a western indian granite as the contaminant explains the geochemical and sr isotopic variation in the basalts and the rhyolites quite well a systematic comparison of the basaltic lavas with binary plots normalized multielement patterns and discriminant function analysis to the well established lava stratigraphy of the western ghats 400 500 km to the south precludes any chemical genetic relationships between the two basalts exposed in sections closer to pavagadh 150 200 km in the toranmal navagam and barwani mhow areas have several flows with some similar chemical characteristics however the pavagadh sequence is significantly different from all of these sequences geochemically petrogenetically and in magnetic polarity to be considered independently built this result is significant in terms of eruptive models for the deccan traps as it is increasingly apparent that there were separate but possibly coeval eruptive centers with their own distinctive chemistries developed in various areas of this vast province

basalts of the eastern deccan volcanic province india abstract the mandla lobe in the eastern part of the deccan volcanic province represents an isolated lava pile having a thickness of 900 m the large thickness of this lava pile and its spatial detachment from the western deccan outcrop points to a plausible second source the stratigraphic configuration of the central and eastern deccan lava sequences and their possible stratigraphic correlation are primarily based on geology and chemical signatures of the lava flows based on variations in the incompatible element ratios the lava sequences of chindwara jabalpur seoni and jabalpur piparia sections were classified into four informal formations showing similarity with the southwestern formations major and trace element abundances in fifteen lava flows of jabalpur area are similar to that of the southwestern deccan lava flows it has been found that the ambenali fm and a few khandala and bushe fm flows are present in the northeastern deccan the regional mapping and detailed petrographic studies coupled with the lateral tracing have enabled the recognition of thirty seven physically distinct lava flows and is justified by their major elemental chemistry the intraflow variations studied in some of the flows is very low for most of the major oxides these thirty seven lava flows are grouped into eight chemical types the order of superposition in this sequence reflects that the older flows occur in the west of the outlier at the seoni jabalpur sahapura sector whereas the younger flows are confined to the dindori amarkantak sector in the east the spatial disposition of the lava flows suggests that the structural complexity in the lava flow sequence in the mandla lobe lies between jabalpur and dindori the juxtaposition of distinct groups of lava flows are observed near deori flows 1 to 4 abeted aginst flows 5 to 14 and dindori areas at dindori and towards its south the distinct lava packages flows 15 to 27 and flows 28 to 37 are juxtaposed along the course of narmada river the possible explanation for this could be the presence of four post deccan faults at nagapahar kundam deori and dindori areas the vertical shift of chemically distinct lava packages at different sectors in the outlier contravenes the idea of small regional dip and favours the presence of four ne sw trending post deccan faults major geochemical breaks when traced out from section to section exhibit shifting in heights by approximately 150 m near nagapahar and 300 m near deori and dindori areas the field petrographic and major oxide data sets considered in conjuction with the magnetic chron reversal heights support the inference that four faults trending ne sw are present in the mandla lobe a commonality in the mineralo chemical attributes of the infra lametas inter trappean as well as weathered deccan basalt further favours their derivation from deccan basalt implying the availability of deccan basalt during the maastrichtian lameta sedimentation this observation does not match with the models suggesting an extremely short duration of deccan volcanism

chemical discrimination of columbia river basalt flows 1 the homogeneity and distinctive chemical composition of individual columbia river basalt flows are illustrated in a series of chemical plots and the procedure for flow identification is outlined the unique characterization of many individual eruptions permits units to be mapped from feeder dike to flow margins across the columbia plateau for hundreds of kilometers and so provides critical constraints on the physical and chemical evolution of this continental flood basalt province

the cottage grove fault system illinois basin late paleozoic transpression along a precambrian crustal boundary the cottage grove fault system in southern illinois has long been interpreted as an intracratonic dextral strike slip fault system we investigated its structural geometry and kinematics in detail using 1 outcrop data 2 extensive exposures in underground coal mines 3 abundant borehole data and 4 a network of industry seismic reflection profiles including data reprocessed by us structural contour mapping delineates distinct monoclines broad anticlines and synclines that express paleozoic age deformation associated with strike slip along the fault system as shown on seismic reflection profiles prominent near vertical faults that cut the entire paleozoic section and basement cover contact branch upward into outward splaying high angle reverse faults the master fault sinuous along strike is characterized along its length by an elongate anticline 3 km wide that parallels the southern side of the master fault these features signify that the overall kinematic regime was transpressional due to the absence of suitable piercing points the amount of slip cannot be measured but is constrained at less than 300 m near the ground surface the cottage grove fault system apparently follows a precambrian terrane boundary as suggested by magnetic intensity data the distribution of ultramafic igneous intrusions and patterns of earthquake activity the fault system was primarily active during the alleghanian orogeny of late pennsylvanian and early permian time when ultramafic igneous magma intruded along en echelon tensional fractures

origin of deccan trap lavas evidence from combined trace element and sr nd and pb isotope studies abstract geochemical and isotope results are presented from a new study of the most southern basalts in the deccan trap india three chemical formations are recognised two of which can be correlated with the established stratigraphy in mahabaleshwar and imply a regional southerly dip of 0 06 over a distance of 250 km in detail sr isotope variations within the ambenali and mahabaleshwar formations can be shown to reflect three distinct end members which provide new constraints for petrogenetic models pb isotope data for selected basalts exhibit a wide range with 206 pb 204 pb 16 87 22 45 and a linear correlation on a pb pb diagram the least contaminated ambenali basalts plot within the pb array and interaction with mantle lithosphere involves a shift to less radiogenic pb whereas contamination with crust is characterised by more radiogenic pb unlike the karoo and parana continental flood basalt provinces only four flow units within the southern deccan appear to contain a significant contribution from mantle lithosphere the mahabaleshwar and ambenali formation basalts exhibit a striking negative pb sr isotope trend which is presently regarded as one of the features of interaction with shallow level lithospheric mantle it further suggests that basalts from the walvis ridge kerguelen and ninetyeast ridge all remobilised such shallow level material and that the deccan basalts which were not affected by crustal contamination reflect interaction between asthenospheric material similar to t type morb but related to the reunion hotspot and continental mantle lithosphere of the indian plate

a post k t boundary early palaeocene age for deccan type feeder dykes goa india basaltic dykes exposed along the coast of goa represent the youngest phase of a number of different mafic suites intruding the complex precambrian terrain that forms the pre deccan basement of peninsular india these dykes crop out 50 80 km beyond the southern limits of the deccan continental flood basalt cfb province four of seven sampled dykes were dated using the whole rock 40ar 39ar step heating technique three 40ar 39ar determinations yield palaeocene plateau and isochron ages that clearly indicate an early post cretaceous i e danian age and as a weighted mean average of all four samples yields an age of 62 8 0 2 ma these intrusions are clearly significantly younger than the current estimates for the age range of deccan traps volcanism 65 69 ma the trace element signatures rare earth element patterns and 87sr 86sr ratios of these dykes are consistent with those of the nearby deccan basalts more specifically their geochemical signatures are similar to those of the basalt flows composing the volumetrically important ambenali mahabaleshwar formations which form the uppermost succession wai subgroup of the sw deccan these geochemical and age data demonstrate that deccan type magmatism continued to affect western india for at least 1 2 my after the k t boundary 65 0 0 1 ma and therefore their emplacement places important constraints upon the timing duration and evolution of this much debated cfb province the importance of these dykes is examined within the context of the deccan eruptions and the associated rifting of the western indian margin

basalts of the northeastern deccan traps india isotopic and elemental geochemistry and relation to southwestern deccan stratigraphy the northeastern deccan traps include flows with strong isotopic and elemental affinities to lavas in the southwest as far as 900 km away however many of the northeastern flows show a negative correlation of 206pb 204pb with end t and positive correlation of 206pb 204pb with 87sr 86sr t distinct from any of the isotopic fields for the southwestern formations this array from end t 5 87sr 86sr t 0 7041 206pb 204pb 17 9 to end t 0 87sr 86sr 0 7068 206pb 204pb 20 5 overlaps the ambenali formation fm field and runs toward that of the common signature peng et al 1994 that appears to have been an important magma type in several of the lower formations of the southwest this array appears to represent mixing between an ambenali type and 1 a common signature end member or 2 an end member with even higher 206pb 204pb and 87sr 86sr and lower end than the common signature such mixing has been postulated but not documented previously for the deccan lavas isotopically and chemically indistinguishable from the ambenali fm form the tops of sections near jabalpur and chikaldara beneath them are flows that chemically resemble the poladpur fm which sits immediately below the ambenali in the southwest and several lavas similar to the khandala fm beneath the poladpur and intervening bushe fm in the southwest given the general stratigraphic correspondence with the southwestern sequence many of these northeastern flows may be petrogenetically related to the respective southwestern formations lavas with broadly poladpurand khandala like elemental compositions are also abundant in a thick section south of mhow several other mhow area flows resemble the distinctive bushe fm however nearly all of the poladpur and khandala like northeastern deccan lavas analyzed have higher 206pb 204pb man any southwestern poladpur or khandala fm basalts if they indeed are related petrogenetically to these formations many of the northeastern magmas interacted less with low 206pb 204pb continental material and thus must have erupted from different feeder systems