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

isotopic systematics of pb u zircon and 40ar 39ar biotite hornblende from rocks of the central foothills terrane sierra nevada california pb u zircon and 40 ar 39 ar biotite horn blende studies in conjunction with detailed structural and textural studies clarify the age and structural relations of a unique cluster of plutons in the central sierra nevada western metamorphic belt the plutons range from gabbro to tonalite trondhjemite and include the guadalupe igneous complex magmatic emplacement ages for the plutons are for the most part between 150 and 145 m y as recorded in both the zircon and hornblende isotopic systems additional ages of 138 and 123 m y were determined on small plutons having key structural settings in general the pb u and 40 ar 39 ar isotopic systems are well behaved second order complications are locally present in the pb u systems owing to the entrainment of older zircon from wall rocks and in 40 ar 39 ar systems owing to minor compositional differences in mica and amphibole phases the age data and structural relations of the plutons in conjunction with 40 ar 39 ar metamorphic wall rock biotite and hornblende age data constrain regional ductile deformation in the study area to have occurred between 150 and 125 ma such deformation was accompanied by upper greenschist to lower amphibolite facies metamorphism and is at least in part closely related to pluton emplacement such deformation and metamorphism has in the past been attributed to the late jurassic nevadan orogeny this study shows clearly however that ductile deformation and metamorphism in the study area are post nevadan if modern concepts of the nevadan orogeny are strictly adopted

quick clay a case study of chemical perspective in southwest sweden quick clay a soil that changes from normal firm ground to a liquid mass when it is disturbed has been involved in most of the large and serious clay slides in sweden norway and canada the location time of occurrence and size of quick clay slides are difficult to predict and large slides may cause great devastation some geochemical studies of swedish quick clay were done in the 1960s and early 1970s but no systematic studies of the interrelationships of pore water chemistry mineralogy geotechnical properties and other parameters on quick clays in sweden have been published such studies are of national and general interest because of the many combinations of rock flour source areas and sedimentation conditions that occurred across central sweden and into the baltic sea area during deglaciation in this study geotechnical properties related to the in situ chemistry at one quick clay site were extensively studied and spot sampling was conducted at two other locations in southwest sweden in this area the clay minerals mainly are non expanding phyllosilicate minerals illite and primary minerals quartz feldspar which is consistent with previous studies of quick clay mineralogy extensive leaching has occurred at all three locations at the extensively studied site surte the lowest salinity was found at the greatest depth inferring that the leaching by fresh water was accomplished by water movement upward and laterally through the sediment from the underlying bedrock this is consistent with the local setting where bedrock hills rise sharply to over 100 m above the marine sediment surface an artesian pressure would also be anticipated at this location there is a correlation negative between sensitivity and salinity but there is an indication that the maximum salinity or electrical conductivity consistent with the quick clay behaviour is higher than reported elsewhere however for high sensitivities the salinity is about the same as reported elsewhere in the deepest part of the borehole there is a higher content of fe and al in the pore water indicating reduced state further work is needed to confirm the difference in salinity and to investigate the possible interplay of salinity and potential dispersing agents such as the role of anoxic conditions in this region further work is especially needed in the locations where the sediment accumulation occurred under lower salinity conditions at all three locations high remoulded shear strength and low sensitivity have been seen near the surface together with a decrease in pore water cation concentrations

determination of rapid deccan eruptions across the cretaceous tertiary boundary using paleomagnetic secular variation 2 constraints from analysis of eight new sections and synthesis for a 3500 m thick composite section 1 the present paper completes a restudy of the main lava pile in the deccan flood basalt province trap of india chenet et al 2008 reported results from the upper third and this paper reports the lower two thirds of the 3500 m thick composite section the methods employed are the same i e combined use of petrology volcanology chemostratigraphy morphology k ar absolute dating study of sedimentary alteration horizons and as the main correlation tool analysis of detailed paleomagnetic remanence directions the thickness and volume of the flood basalt province studied in this way are therefore tripled a total of 169 sites from eight new sections are reported in this paper together with the results of chenet et al 2008 these data represent in total 70 of the 3500 m combined section of the main deccan traps province this lava pile was erupted in some 30 major eruptive periods or single eruptive events see each with volumes ranging from 1000 to 20 000 km3 and 41 individual lava units with a typical volume of 1300 km3 paleomagnetic analysis shows that some sees with thicknesses attaining 200 m were emplaced over distances in excess of 100 km both likely underestimates due to outcrop conditions and up to 800 km the total time of emission of all combined sees could have been much less than 10 ka with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence so called big red boles the number of boles thickness of the pulses and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end on the basis of geochronologic results published by chenet et al 2007 and paleontological results from keller et al 2008 we propose that volcanism occurred in three rather short discrete phases or megapulses an early one at 67 5 1 ma near the c30r c30n transition and the two largest around 65 1 ma one entirely within c29r just before the k t boundary the other shortly afterward spanning the c29r c29n reversal we next estimate sulfur dioxide likely a major agent of environmental stress amounts and fluxes released by sees they would have ranged from 5 to 100 gt and 0 1 to 1 gt a respectively over durations possibly as short as 100 years for each see the chemical input of the chicxulub impact would have been on the same order as that of a very large single pulse the impact therefore appears as important but incremental neither the sole nor main cause of the cretaceous tertiary mass extinctions

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

40ar 39ar dating of mineral separates and whole rocks from the western ghats lava pile further constraints on duration and age of the deccan traps abstract there has been an ongoing debate for almost two decades on the age and duration of deccan trap volcanism some of the best available ages have been determined using the 40 ar 39 ar method but differences in sample location laboratory procedure type of analyzed material and ages of monitors may have been responsible for much of the apparent spread in the data we have collected and analyzed samples from close to the bottom and top of the main lava pile in the western ghats near bombay we confirm previous findings that alteration and ar recoil strongly affect these rocks particularly measurements made on whole rocks when mineral separates mostly plagioclase are analyzed the spread is much reduced we find a mean age of 65 4 0 7 ma for five flows near the base of the section jahwar and igatpuri formations and 65 2 0 4 ma for a dyke cross cutting the poladpur formation below the topmost mahabaleshwar formation this implies that at least 1800 m out of the 2500 m composite trap section were erupted in a short interval less than 1 ma long and close to 65 5 ma i e close to the cretaceous tertiary boundary we find that older ages near 67 ma found by several authors are essentially based on whole rock samples which display disturbed spectra when this can be checked i e when the spectra are published

relationship between electrical resistivity and basic geotechnical parameters for marine clays recently considerable efforts have been made in the attempt to map quick clay areas using electrical resistivity measurements however there is a lack of understanding regarding which soil parameters control the measured resistivity values to address this issue inverted resistivity values from 15 marine clay sites in norway have been compared with basic geotechnical index properties it was found that the resistivity value is strongly controlled by the salt content of the pore fluid resistivity decreases rapidly with increasing salt content there is also a relatively clear trend of decreasing resistivity with increasing clay content and plasticity index resistivity values become very low 5 m for high clay content 50 medium to high plasticity ip 20 materials with salt content values greater than about 8 g l or corresponding remoulded shear strength values greater than 4 kpa for the range of values studied there is poor correlation between resistivity and bulk density and between r

accretionary tectonics of the north american cordillera continental geology stands on the threshold of a change that is likely to be as fundamental as plate tectonic theory was for marine geology ongoing seismic reflection investigations into the deep crustal structure of north america are verifying that orogenic zones are underlain by low angle faults of regional extent brown et al 1981 the growing body of regional field relations is likewise delineating numerous orogenic sutures that bound discrete crustal fragments paleomagnetic and paleobiogeographic studies are revealing major latitudinal shifts and rotations within and between suture bounded fragments particularly within the north american cordillera such interdisciplinary studies are leading to a consensus that the cordillera has been built by progressive tectonic addition of crustal fragments along the continent edge in mesozoic and early cenozoic time such crustal growth is referred to as accretionary tectonics in this paper we review some of the important concepts in accretionary tectonics discuss the nature of the materials accreted between central alaska and southern california in jurassic and cretaceous time and consider the general relations between cordilleran accretion and the movement of lithospheric plates the concept of continents growing by peripheral accretion through geologic time has long been a topic of great interest with the advent of plate tectonics a number of different mechanisms for crustal accretion have arisen along with mechanisms for crustal attrition accretion mechanisms include the growth of imbricated sedimentary prisms along inner trench walls slicing off of submarine topographic irregularities within subducting plates and collision of continents and volcanic arcs by ocean basin closure tectonic attrition mechanisms include rifting transform faulting and strike slip or underthrust removal of inner trench wall materials coincident with or in place of accretionary prism growth growth of intraorogenic ocean basins by seafloor spreading is an additional important mechanism for creating accretionary materials as well as displacing crustal fragments an important implication of plate kinematic theory is the likelihood for accretionary and attritionary mechanics to operate in series both in time and space along continental margins since attrition by nature leaves little material evidence of having operated one of the major problems confronting cordilleran geologists lies in the recognition of such attrition within the ancient record particularly when interspersed with accretionary events the spectrum of accretion and attrition mechanisms viewed at cm yr 1 plate transport rates over time scales of 100 m y leads one to suspect a highly mobile history for continental margin orogens the serial arrangement of subducting transform and rifting links along the modern cordillera plate juncture system and both serial and parallel arrangements in the western pacific systems show the complex interplay of such mechanisms through space similar arrangements overprinted through time are suggested by the rock assemblages and structural patterns within the cordillera which presently resemble a collage of crustal fragments davis et al 1978 recognition of the structural state of this collage geologic field mapping and geophysical investigations will bring about a new level of understanding in the growth of continental crust and the reading of stratigraphic records within the fragments and future palinspastic restorations will lead to a new level of understanding in paleogeography and earth history the first problem to be considered is the recognition of native north american crust from exotic fragments that have been accreted to its edge

three dimensional resistivity tomography in extreme coastal terrain amidst dense cultural signals application to cliff stability assessment at the historic d day site summary pointe du hoc overlooking the english channel in normandy france was host to one of the most important military engagements of world war ii but is vulnerable to cliff collapses that threaten important german fortifications including the forward observation post op and rudder s command post the objective of this study is to apply advanced 3 d resistivity tomography towards a detailed site stability assessment with special attention to the two at risk buildings 3 d resistivity tomography data sets at pointe du hoc in the presence of extreme topography and dense cultural clutter have been successfully acquired inverted and interpreted a cliff stability hazard assessment scheme has been designed in which regions of high resistivity are interpreted as zones of open dry fractures with a moderate mass movement potential regions of low resistivity are zones of wet clay filled fractures with a high mass movement potential the op tomography results indicate that the highest mass movement hazard appears to be associated with the marine caverns at the base of the cliff that are positioned at the point of strongest wave attack these caverns likely occupy the future site of development of a sea arch that will threaten the op building the mass movement potential at the rudder s command post area is low to moderate the greatest risk there is associated with soil wedge failures at the top of the cliffs

observations and controls on the occurrence of inherited zircon in concord type granitoids new hampshire u pb analyses of zircons separated from two concord type plutons near sunapee and dixville notch new hampshire reveal differences in the pattern and magnitude of zircon inheritance which are related to differences in melt chemistry the sunapee pluton contains only slightly more zr than required to saturate the melt at the peak temperature of 700 30 sup 0 c traces of inherited zircon in this separate are inferred to be present as small largely resorbed grains in contrast the long mountain pluton near dixville notch contains about 240 more zr than required to saturate the melt thus more than half of the zr existed as stable inherited zircon crystals during the partial fusion event consistent with the observation of substantial inheritance in all grain size fractions ion probe intra grain analyses of zircon from the long mountain pluton indicate a complex pattern of inheritance with contributions from at least two proterozoic terranes and caution against simple interpretations of upper and lower intercepts of chords containing an inherited component ion probe analyses of zircons from the sunapee pluton reveal clear evidence of u loss which results in incorrect apparent conventional u pb ages ages of crystallization for the long mountain and sunapee pluton are approx more 350 and 354 5 ma respectively a sm nd measurement for the long mountain pluton yields a depleted mantle model age of 1 5 ga consistent with the observed inheritance pattern in contrast a sm nd model age for the sunapee pluton is improbably old due to minor monazite fractionation less

petrogenetic significance of ferro enstatite orthopyroxene in basaltic dikes from the tapi rift deccan flood basalt province india abstract some basaltic dikes from the tapi rift in the deccan flood basalt province india contain abundant clusters of prismatic quench crystals of ferro enstatite orthopyroxene fe 39 42 mg 53 57 ca 2 4 such profuse orthopyroxene clusters are not yet known from any other flood basalt province in the world based on petrography mineral chemistry and whole rock chemistry we conclude that these crystals are formed due to assimilation of shale by deccan basalt magma this interpretation is consistent with the known bedrock geology of the area these quench crystals constitute the first direct petrographic evidence for crustal contamination in the deccan province the liquidus temperature for the dikes is estimated at 1220 10 c with the crystallization temperature of the orthopyroxene at 1080 c or less

an intercalibration study of the fish canyon sanidine and biotite 40ar 39ar standards and some comments on the age of the fish canyon tuff the age of the fish canyon tuff fct has been the subject of intense study due to its potential significance as a geochronological test to establish age concordance between the k ar and u pb isotopic systems minerals from the fct notably sanidine and biotite are in widespread use as 40ar 39ar fluence monitors standards and have been employed as both primary and intercalibrated standards in attempting to constrain the true age of fct the distinction between primary vs intercalibrated ages is important as only the primary age determinations are valid an investigation of both fish canyon sanidine fcs and fish canyon biotite fct 3 was undertaken to assess the chemical and isotopic homogeneity of the minerals on a grain to grain scale electron microprobe results show that fcs is chemically homogeneous verifying previous studies although there are some very small zones of minor k depletion fct 3 biotite commonly contains numerous and small mineral inclusions 40ar 39ar experiments further show that fcs is remarkably homogeneous confirming previous observations whereas fct 3 shows much greater isotopic variability due to contamination from the mineral inclusions by setting the age of fcs equal to 27 98 0 15 ma 2 as intercalibrated to the u pb system by villeneuve et al 2000 the resultant intercalibration factor between fcs and fct 3 is 1 005 0 017 yielding an age of 28 13 0 47 ma 2 for fct 3 although the significant intragrain chemical and isotopic variability precludes its use as an effective 40ar 39ar fluence monitor the true age of the fct is problematic a survey of all primary ages for fct shows that mean k ar ages for plagioclase hornblende biotite and sanidine are consistently younger than mean u pb ages from titanite and zircon in conjunction with recently published petrological results which indicate that the fct contains material from multiple crystallization events this significant discrepancy between the k ar and u pb data sets demonstrates that the fish canyon tuff cannot serve as a golden standard between the k ar and u pb systems

integration of sh seismic reflection and love wave dispersion data for shear wave velocity determination over quick clays quick clay is a water saturated formation originally formed through flocculation and deposition in a marine to brackish environment it is subsequently leached to low salinity by freshwater flow if its strength decreases then the flocculated structure collapses leading to landslides of varying destructiveness leaching can result in a reduction of the undisturbed shear strength of these clays and suggestions exist that a reduction in shear wave velocities is also possible integration of sh seismic reflection and love wave dispersion data was undertaken in an area near the gota river in southwest sweden to evaluate the potential of shear wave velocity imaging for detecting quick clays seismic reflection processing evidenced several geologically interesting interfaces related to the probable presence of quick clays locally confirmed by boreholes and sand gravelly layers strongly contributing to water circulation within them dispersion data were extracted with a gaussian windowing approach and inverted with a laterally constrained inversion using a priori information from the seismic reflection imaging the inversion of dispersion curves has evidenced the presence of a low velocity layer lvl with a velocity reduction of ca 30 per cent probably associable to quick clays this velocity reduction is enough to produce detectable phase velocity differences in the field data and to achieve a better velocity resolution if compared to reflection seismic velocity analyses the proposed approach has the potential of a comprehensive determination of the shear wave velocity distribution in the shallow subsurface a sensitivity analysis of love wave dispersion data is also presented underlining that despite limited dispersion of the data set and the velocity reducing effect of quick clay leaching the proposed interpretation procedure arises as a valuable approach in quick clay and other lvl identification

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

influence of porefluid salinity on instability of sensitive marine clays a new approach to an old problem the geographic association between earthflow occurrence sensitivity of the sediment and salinity of the interstitial fluid has been examined in an area of exposed marine champlain sea deposits in the lachute region northwest of montreal quebec mapping of earth resistivity as a means of calculating porefluid salinity revealed that areas of large earthflows 20 ha coincided with sediment of very low porefluid salinity earthflow scars were absent from intervening areas of higher salinity 5 gl 1 mapping of the thickness of the clay deposit by seismic refraction showed furthermore that low porefluid salinity occurred only in areas of relatively thin 25 m deposits resting upon more permeable drift or rock finally laboratory tests confirmed that high sensitivity was restricted to areas of low porefluid salinity the study thus provides a geomorphological verification of the importance of salt depletion as a prerequisite for earthflow occurrence and by implication presents mapping of porefluid salinity as a method of delineating zones which should be safe from landslide retrogression in this type of sediment

ultrasonic p and s wave attenuation and petrophysical properties of deccan flood basalts india as revealed by borehole studies petrophysical properties and ultrasonic p and s wave attenuation measurements on 35 deccan basalt core specimens recovered from killari borehole site in western india provide unique reference data sets for a lesser studied deccan volcanic province these samples represent 338 m thick basaltic column consisting four lava flows each of ambenali and poladpur formations belonging to wai subgroup of the deccan volcanic sequence these basalt samples are found to be iron rich average feot 13 4 wt but relatively poor in silica content average sio2 47 8 wt the saturated massive basalt cores are characterized by a mean density of 2 91 g cm3 range 2 80 3 01 g cm3 and mean p and s wave velocities of 5 89 km s range 5 01 6 50 km s and 3 43 km s range 2 84 3 69 km s respectively in comparison saturated vesicular basalt cores show a wide range in density 2 40 2 79 g cm3 as well as p wave 3 28 4 78 km s and s wave 1 70 2 95 km s velocities based on the present study the deccan volcanic sequence can be assigned a weighted mean density of 2 74 g cm3 and a low vp and vs of 5 00 and 3 00 km s respectively such low velocities in deccan basalts can be attributed mainly to the presence of fine grained glassy material high iron contents and hydrothermally altered secondary mineral products besides higher porosity in vesicular samples the measured q values in saturated massive basalt cores vary enormously qp 33 1960 and qs 35 506 while saturated vesicular basalt samples exhibit somewhat lesser variation in qp 6 46 as well as qs 5 49 in general high porosity rocks exhibit high attenuation but we observed the high value of attenuation in some of the massive basalt core samples also in such cases energy loss is mainly due to the presence of fine grained glassy material as well as secondary alteration products like chlorophaeite that could contribute to intrinsic attenuation dominance of weekly bound secondary minerals might also be responsible for the generation of microcracks which may generate squirt flow in saturated samples hence we argue that the deccan basalts attenuate seismic energy significantly where its composition plays a major role

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

pluton emplacement by sheeting and vertical ballooning in part of the southeast coast plutonic complex british columbia batholiths of the coast plutonic complex in the area of harrison lake british columbia are interpreted to have formed by horizontal sheeting and vertical inflation zoned ovoid batholiths exhibit sheeted margins as thick as 3 km shallow floors are indicated by moderately to gently inward dipping magmatic foliations the observed trace of floor contacts across topography and a published deep seismic reflection transect mineralogic aureoles under the floors preserve a paragenetic record of increasing pressure during aureole crystallization initial pressures of

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

geochemistry of the siberian trap of the noril sk area ussr with implications for the relative contributions of crust and mantle to flood basalt magmatism the sequence investigated of the siberian trap at noril sk ussr consists of at least 45 flows that have been divided into six lava suites the lower three suites consist of alkalic to subalkalic basalts the ivakinsky suite overlain by nonporphyritic basalts the syverminsky suite and porphyritic and picritic basalts the gudchikhinsky suite the upper three suites are tholeiitic the uppermost 750 m of dominantly non porphyritic basalt belong to the mokulaevsky suite and are characterized by a nearly constant mg number 0 54 0 56 sio2 48 2 49 1 wt ce 12 18 ppm and ce yb 5 8 the underlying 1100 m of dominantly porphyritic basalt belong to the morongovsky and nadezhdinsky suites there is a continuous increase in sio2 48 1 55 2 wt ce 12 41 ppm and ce yb 5 18 from the top of the mokulaevsky to the base of the nadezhdinsky with little change in the mg number 0 53 0 59 mokulaevsky magmas have trace element signatures similar to slightly contaminated transitional type mid ocean ridge basalts the change in major and trace element geochemistry in the upper three suites is consistent with a decline in the degree of anatexis and assimilation of tonalitic upper crust by mokulaevsky magma the nadezhdinsky and underlaying lavas thicken within and thus appear to be related to an elongate basin centred on the noril sk talnakh mining camp the mokulaevsky and morongovsky lavas thicken to the east and appear to be related to a basin centred more than 100 km to the east of the noril sk region these magmas may have risen up out of a different conduit system

concordant sea floor spreading rates obtained from geochronology astrochronology and space geodesy reversals of the earth s magnetic field allied to sea floor spreading have left their imprint in the form of a magnetic tape recorder on the sea floor it is demonstrated that the geomagnetic polarity time scale for the past few million years derived utilizing a radiometric dates of magnetic field reversals trapped in subareal igneous rocks and b as derived from the milankovitch forcing frequencies and their imprint in the sedimentary environment are in good agreement further sea floor spreading rates calculated from these results are in substantial agreement with the rate of plate movement averaged over the last decade as obtained by space geodetic measurements since the principles underlying these dating techniques are entirely different it lends credence to the results obtained for sea floor spreading arguably the most fundamental process in plate tectonics

integrated approach for pavement deterioration assessments in a low latitude crystalline basement of south western nigeria an integrated approach involving electrical resistivity er technique and geotechnical analysis was employed to assess the deterioration of pavement along iwo osogbo road in south western nigeria underlain by quartzo syenite migmatite gneiss and pegmatite crystalline rocks the er involved the use of two dimensional 2d electrical resistivity tomography and one dimensional 1d vertical electrical sounding ves to provide an overview of the ground conditions and probe the subsurface profile respectively geotechnical analysis involving compaction atterberg limits grain size distribution gsd and california bearing ratio cbr were also carried out on the recovered samples from four test pits two pits each dug at the smooth and deteriorated pavement portion whilst moisture related distresses originating beneath the pavement were investigated through suction distribution determined from estimated soil water characteristic curves swcc employing physico empirical model approach at the deteriorated pavement segment the 2d pseudosection indicated the material at and near surface depth less than 2 49 m was of low resistivity values ranging between 69 and 153 m with upper bound values near surface the resistivity further decreases with depth indicating increase in proportion of clay and or water content the other half of the pseudosection is characterized by relatively high resistive material whose resistivity values ranged between 103 and 227 m at and near surface depth less than 1 27 m as well as alternating bands of low 20 to 70 m and relatively high resistivity 103 to 337 m materials of varied thickness at greater depths conversely the pseudosection obtained from the smooth pavement segment was characterised by high resistivity 212 m at and near surface depth 3 5 m over the entire length iterative interpretation of 1d ves data indicated three to four layers earth model without association or relationship between a particular apparent resistivity curve type and deteriorated or stable portion of the road the moisture content and atterberg limit parameters namely plastic limit and liquid limit plots against depth suggest the soil environment beneath the pavement as unsaturated the gsd curves indicate the soils are gap graded comprising sand sized and coarse particle and corroborated by gsd curve fitting the cbr under soaked condition ranged from 16 5 to 41 1 indicating that the subbase soil could not withstand much load the cbr varied between 20 8 and 72 0 indicating that the subgrade soils have a relatively medium strength whilst the subbase soil has a very high strength the swccs generally indicated that the moisture content decreases with increasing matric suction resulting in suction gradient capable of generating flow thus the pavement deterioration could be attributed to improper handling of the flow initiated by the suction gradient

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

multistage emplacement of the mount givens pluton central sierra nevada batholith california the ca 90 ma mount givens pluton is one of the largest granodioritic to granitic intrusions in the sierra nevada batholith of california emplacement of the pluton occurred during a critical time in the tectonic evolution of the central sierra nevada magmatic arc marked by a transition from regional contraction to dextral transcurrent shear a model for the emplacement of the intrusion is developed based on detailed mapping of the pluton and its wall rocks and characterization of its internal structure by measurements of the anisotropy of magnetic susceptibility ams at 351 stations one of the key results of the study is documentation of a strong correlation between petrologic and structural fabrics in the pluton and determination that these fabrics reflect internal magma chamber dynamics more than regional tectonic strain the 80 km long 15 30 km wide pluton crystallized from a multiphase three segment magma chamber marked by a bulbous northern lobe and linear central and southern segments the pluton is interpreted to be tabular in shape with a thickness of 5 km most of the space for the pluton was created by piecemeal block downdrop of the magma chamber floor along three principal fracture sets the most important of which were steeply dipping northwest trending fractures formed parallel to the structural grain of the arc and vertical north trending extension fractures formed in response to a component of arc parallel dextral shear some of these fractures acted as magma conduits episodically filling the pluton as source rocks became depleted in melt an initial voluminous intrusive event stage 1 quickly filled the southern chamber with granodiorite magma but only partially filled the northern and central chambers stage 2 magmatism involved underplating of megacrystic granite in the northern chamber and lateral flow of a large batch of this magma from the northern to the central chamber the latter delineated by a 20 km long belt of megacrystic granite containing subhorizontal magnetic lineations that connects the pluton segments floor downdrop eventually ceased to be an effective space making process in the northern lobe and renewed magmatism stage 3 led to expansion and doming of the chamber as the northern lobe cooled a ring fault ruptured within the viscoelastic stage 1 2 carapace allowing ring dike intrusion stage 4 and sinking of a central flap of consolidated material the temporal and spatial variations in emplacement mechanisms demonstrated for the mount givens pluton i e fracture generation floor downdrop underplating inflation ring diking suggest that end member models e g fracture vs diapir are oversimplifications of the pluton assembly process

resistivity measurements as a tool for outlining quick clay extent and valley fill stratigraphy a feasibility study from buvika central norway resistivity measurements as a tool for outlining quick clay extents and valley fill stratigraphy feasability study from buvika central norway

uranium lead isotopic ages from the sierra nevada batholith california this study provides new information on the timing and distribution of mesozoic magmatic events in the sierra nevada batholithic complex chiefly between 36 and 37 n latitude u pb ages have been determined for 133 zircon and 7 sphene separates from 82 samples of granitoid rocks granitoid rocks in this area range in age from 217 to 80 m y triassic intrusions are restricted to the east side of the batholith jurassic plutons occur south of the triassic plutons east of the sierra nevada as isolated masses within the cretaceous batholith and in the western foothills of the range cretaceous plutons form a continuous belt along the axis of the batholith and occur as isolated masses east of the sierra nevada no granitic intrusions were emplaced for 37 m y east of the sierra nevada following the end of jurassic plutonism however following emplacement of the eastern jurassic granitoids regional extension produced a fracture system at least 350 km long into which the dominantly mafic calc alkalic independence dike swarm was intruded 148 m y ago the dike fractures probably represents a period of regional crustal extension caused by a redistribution of the regional stress pattern accompanying the nevadan orogeny intrusion of cretaceous granitic plutons began in large volume about 120 m y ago in the western sierra nevada and migrated steadily eastward for 40 m y at a rate of 2 7 mm y this slow and constant migration indicates remarkably uniform conditions of subduction with perhaps downward migration of parent magma generation or a slight flattening of the subduction zone such steady conditions could be necessary for the production of large batholithic complexes such as the sierra nevada the abrupt termination of plutonism 80 m y ago may have resulted from an increased rate of convergence of the american and eastern pacific plates and dramatic flattening of the subduction zone u pb ages of the giant forest alaskite sequence in sequoia national park are all in the range 99 3 m y indicating a relatively short period of emplacement and cooling for this nested group of plutons u pb ages of a mafic inclusion and its host granodiorite indicate that both were derived from a common source or that the mafic inclusion was totally equilibrated with the granodioritic magma comparison of isotopic ages determined by different methods such as zircon u pb sphene u pb hornblende k ar and biotite k ar suggests that zircon u pb ages generally approximate the emplacement age of a pluton however some plutons probably contain inherited or entrained old zircons and the zircons of some samples are disturbed by younger thermal and metamorphic events the ages reported here are consistent with u pb age determinations previously made on granitic rocks to the north stern et al 1981 the age distribution of granitic belts determined here is in general agreement with those established by k ar dating evernden and kistler 1970 but does not differentiate the five epochs of plutonism determined in their study

40k 40ar dating of the main deccan large igneous province further evidence of ktb age and short duration most mass extinctions coincide in time with outpourings of continental flood basalts cfb some 20 years ago it was shown courtillot v besse j vandamme d montigny r jaeger j j cappetta h 1986 deccan flood basalts at the cretaceous tertiary boundary earth planet sci lett 80 361 374 courtillot v feraud g maluski h vandamme d moreau m g besse j 1988 deccan flood basalts and the cretaceous tertiary boundary nature 333 843 846 duncan r a pyle d g 1988 rapid eruption of the deccan flood basalts at the cretaceous tertiary boundary nature 333 841 843 that the age of the deccan traps was close to the cretaceous tertiary kt boundary and its duration under 1 myr we have undertaken a new geochronological study using the unconventional 40k 40ar cassignol gillot technique which is particularly well suited to the potassium poor deccan lavas the mean of 4 determinations from the topmost ambenali and mahabaleshwar formations is 64 5 0 6 ma they straddle the c29r c29n reversal boundary for which they provide a new constraint the mean age of 3 determinations from the oldest jawhar formation is 64 8 0 6 ma the difference in age between top and bottom of a 3500 m composite section probably comprising 80 of the total deccan volume is statistically insignificant with the overall mean age being 64 7 0 6 ma n 7 our results are consistent with the most recent 40ar 39ar determinations knight k b renne p r halkett a white n 2003 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps earth planet sci lett 208 85 99 knight k b renne p r baker j waight t white n 2005 reply to 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps discussion by a k baksi earth planet sci lett 239 374 382 confirming that there should be no systematic difference between the two methods when they are used in an optimal way an earlier smaller but significant pulse of volcanism between 68 and 67 ma extending over at least 500 km in latitude in the northern part of the deccan cfb has also been identified after 2 to 3 ma of quiescence the second major phase of volcanism occurred near 65 ma expanding over most of the area covered by the first pulse and another 500 km to the south consistent with drift of india by 300 to 450 km at not vert similar 150 mm yr during the quiescence period new paleontological data from the remote rajahmundry section keller g adatte t gardin s bartolini a bajpai s humler e in prep the cretaceous tertiary boundary in deccan traps of the krishna godavari basin of southeastern india epsl to be submitted suggest that this second pulse can itself be divided into two major pulses one starting in c29r and ending at the kt boundary the second starting in the upper part of c29r and ending within c29n

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

evidence from the lamarck granodiorite for rapid late cretaceous crust formation in california strontium and neodymium isotopic data for rocks from the voluminous 90 million year old lamarck intrusive suite in the sierra nevada batholith california show little variation across a compositional range from gabbro to granite data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source recognition of local involvement of enriched mantle during generation of the sierran batholith modifies estimates of crustal growth rates in the united states these data indicate that parts of the sierra nevada batholith may consist almost entirely of juvenile crust added during cretaceous magmatism

plume rift interaction in the deccan volcanic province abstract it is widely accepted that the grand volcanic episode of the deccan in india was a consequence of the passage of the northerly drifting indian subcontinent over the reunion starting plume in the late cretaceous this plume also produced the three rift cambay triple junction the three arms being the west coast graben belt the narmada tapi rift zone and the cambay rift deccan related alkalic magmatism both preceded and followed the main tholeiitic phase of 65 ma ago by about 3 my the uniformly tholeiitic thick basalt sequence of the western ghats was derived from direct melting of the plume head but the tholeiitic alkalic magmatism of the three rift belts was due to melting of the hydrous lithospheric mantle due to variable amounts of rifting any lithospheric loading mechanism for generating post tholeiite alkalic lavas does not seem feasible for the deccan nor can it explain the pre tholeiite alkaline magmatism in the deccan similarly conductive heating of the lithosphere by the plume cannot have generated the alkalic melts some amount of actual rifting did occur direct melt supply from the plume is not necessary for magmatism in the rifts though it seems to have occurred in some cases our documentation of indigenous magmatism for the three rift belts calls into question any attempts at inferring the size of the plume head from synchroneity in geochronologic data alone and we negate the possibility or necessity of large distance transport of magmas from the plume through the lithosphere to feed the rifts recent evidence indicates that alkalic magmatism north of the main deccan outcrop preceded the main tholeiite phase by 3 my the cambay graben was active 3 5 my before the main tholeiite phase as the alkalic complexes at the northern end of this graben are 68 5 ma in age so far the oldest well proven deccan related rocks they are the first expression of the reunion plume and the borehole picrites from the triple junction area until now conventionally regarded as the oldest can no longer be considered so accurate radiometric dating of these picrites is therefore much needed

the aurora volcanic field california nevada oxygen fugacity constraints on the development of andesitic magma the aurora volcanic field located along the northeastern margin of mono lake in the western great basin has erupted a diverse suite of high k and shoshonitic lava types with 48 to 76 wt sio2 o ver the last 3 6 million years there is no correlation between the age and composition of the lavas three quarters of the volcanic field consists of evolved 4 wt mgo basaltic andesite and andesite lava cones and flows the majority of which contain sparse euhedral phenocrysts that are normally zoned there is no evidence of mixed hybrid magmas the average eruption rate over this time period was 200 m 3 ykm 2 yyear which is typical of con tinental arcs and an order of magnitude lower than that for the slow spreading mid atlantic ridge all of the au rora lavas display a trace element signature common to subduction related magmas as exemplified by baynb ratios between 52 and 151 pre eruptive water contents ranged from 1 5 wt in plagioclase rich two pyroxene andesites to 6 wt in a single hornblende lamprophyre and several biotite hornblende andesites calculated oxygen fugacities fall within 0 4 and 12 4 log units of the ni nio buffer the aurora potassic suite follows a classic calc alkaline trend in a plot of feo t ymgo vs sio 2 and displays linear decreasing trends in feo t and tio2 with sio2 content suggesting a prominent role for fe ti oxides during differentiation however develop ment of the calc alkaline trend through fractional crys tallization of titanomagnetite would have caused the residual liquid to become so depleted in ferric iron that its oxygen fugacity would have fallen several log units below that of the ni nio buffer nor can fractionation of hornblende be invoked since it has the same effect as titanomagnetite in depleting the residual liquid in ferric iron together with a thermal stability limit that is lower than the eruption temperatures of several andesites 1040 10808c derived from two pyroxene ther mometry unless some progressive oxidation process occurs fractionation of titanomagnetite or hornblende cannot explain a calc alkaline trend in which all erupted lavas have oxygen fugacites the ni nio buffer in con trast to fractional crystallization closed system equi librium crystallization will produce residual liquids with an oxygen fugacity that is similar to that of the initial melt however the eruption of nearly aphryic lavas ar gues against tapping from a magma chamber during equilibrium crystallization a process that requires crys tals to remain in contact with the liquid a preferred model involves the accumulation of basaltic magmas at the mantle crust interface which solidify and are later remelted during repeated intrusion of basalt as an end member case closed system equilibrium crystallization of a basalt followed by equilibrium partial melting of the gabbro will produce a calc alkaline evolved liquid namely high sio 2 and low feo t ymgo with a relative fo2 corrected for the effect of changing temperature that is similar to that of the initial basalt differentiation of the aurora magmas by repeated partial melting of previous underplates in the lower crust rather than by crystal fractionation in large stable magma chambers is consistent with the low eruption rate at the aurora vol canic field

the eruptive tempo of deccan volcanism in relation to the cretaceous paleogene boundary late cretaceous records of environmental change suggest that deccan traps dt volcanism contributed to the cretaceous paleogene boundary kpb ecosystem crisis however testing this hypothesis requires identification of the kpb in the dt we constrain the location of the kpb with high precision argon 40 argon 39 data to be coincident with changes in the magmatic plumbing system we also found that the dt did not erupt in three discrete large pulses and that 90 of dt volume erupted in 1 million years with 75 emplaced post kpb late cretaceous records of climate change coincide temporally with the eruption of the smallest dt phases suggesting that either the release of climate modifying gases is not directly related to eruptive volume or dt volcanism was not the source of late cretaceous climate change

similarities in the mineralogical and geochemical attributes of detrital clays of maastrichtian lameta beds and weathered deccan basalt central india abstract mineralo chemical attributes of the maastrichtian late cretaceous lameta sediments intimately associated with the deccan traps in central india provide insight into the initiation of deccan volcanism x ray diffraction studies on the detrital clays of the lametas and weathered deccan basalt show identical mineral assemblages with the dominance of smectite and subordinate kaolinite illite ir spectra are also indicative of their common mineralogical attributes structural formulae of the smectites in lameta exhibit high octahedral mg and fe the immobile trace element concentrations in lameta clays resemble those in weathered deccan basalt ree plots of the lametas are subparellel with that of weathered deccan basalt and show negative ce anomalies documented in basalt weathering these findings suggest that smectite rich clays of the lametas are derivatives of the deccan basalt implying early activities of deccan volcanism either during or just prior to the maastrichtian lameta sedimentation

post k pb younger 40 ar 39 ar ages of the mandla lavas implications for the duration of the deccan volcanism abstract we present new age determinations derived from 40 ar 39 ar incremental heating experiments for basaltic lava flows from the mandla lobe located on the eastern margin of the main deccan volcanic province some 1000 km from the western ghats escarpment the most reliable estimates of crystallization ages come from 5 plateau ages from plagioclase separates from a stratigraphically controlled succession of 37 lava flows we detect no statistically significant age difference from bottom to top range 63 65 ma and calculate a weighted mean age for the section at 64 21 0 33 ma these lava flows are significantly younger than the majority of the main deccan volcanic activity documented from the western ghats 67 65 ma the new ages are consistent however with geochemical correlation of the mandla lobe lavas with the uppermost succession poladpur ambenali mahabaleshwar formations of the sw deccan and indicate that this post k pb youngest phase of flood basalt activity erupted over much of the province

exposure of a late cretaceous layered mafic felsic magma system in the central sierra nevada batholith california new u pb zircon ages for the lamarck granodiorite associated synplutonic gabbro and diorite plutons and two large mafic intrusive complexes that underlie them in the sierra nevada batholith are 92 1 ma these ages establish the late cretaceous as a period of extensive mafic felsic magmatism in the central part of the batholith and confirm the significance of mafic magmatism in the evolution of the voluminous silicic plutions in the sierran arc the lack of significant zircon inheritance in any of the units analyzed supports isotopic evidence that the lamarck and other late cretaceous sierran plutons were derived predominantly from young crust recognition of an extensive mafic felsic magma system in the sierra nevada batholith emphasizes the importance of basaltic liquids in the evolution of continental crust in arc settings

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

plutonism oblique subduction and continental growth an example from the mesozoic of california major episodes of mesozoic plutonism in california correlate with periods of oblique subduction and trench parallel transport of western california along intrabatholithic faults major episodes of plutonism occurred in the late jurassic during left oblique convergence and in the mid cretaceous during right oblique convergence in contrast a conspicuous lull in plutonism but continuation of volcanism in the earliest cretaceous coincides with a time when the north america farallon convergence vector although large in magnitude was oriented perpendicular to the trench this correlation suggests that plutonism is facilitated by strike slip faulting within the batholithic belt one explanation which helps to solve the plutonic room problem is that plutons are passively emplaced at releasing bends in the strike slip faults and volume is conserved by thrusting at the trench if this correlation is generally applicable then it implies that mid crustal plutonism is limited beneath areas in which the convergence vector is subperpendicular to the trench continental growth in such areas may occur dominantly by volcanism

natural glass from deccan volcanic province an analogue for radioactive waste form deccan basaltic glass is associated with the differentiation centres of the vast basaltic magmas erupted in a short time span its suitability as a radioactive waste containment chiefly depends on alteration behaviour however detailed work is needed on this glass therefore the basaltic glass was treated under hydrothermal like conditions and then studied to understand its alteration moreover comparison of these results with the naturally altered glass is also documented in this paper solutions as well as residue obtained after glass alteration experiments were analysed treated glass specimens show partial to complete release of all the ions during alteration however abundant release of si and na ions is noticed in case of almost all the specimens and the ionic release is of the order of na si k ca al mg fe mn ti scanning electron images of the altered residue show morphologies of smectite montmorillonite and illite inside as well as outside of the secondary layers and represent paragenesis of alteration minerals it has been noticed that the octahedral cation occupancies of smectite are consistent with the dioctahedral smectite the secondary layer composition indicates retention for si al and mg ions indicating their fixation in the alteration products but remarkably high retention of ti mn and fe ions suggests release of very small amount of these elements into the solution by evolution of the secondary layer and retention of less soluble ions the obstructive effect of the secondary layer increases and the initial constant release rate begins slowly to diminish with the proceeding time it has been found that devitrification of glass along the cracks formation of spherulite like structures and formation of yellowish brown palagonite chlorite calcite zeolite and finally white coloured clays yielded after experiments that largely correspond to altered obsidian that existed in the natural environment since inception 66 ma ago

chapter 14 middle cretaceous silicic metavolcanic rocks in the kings canyon area central sierra nevada california metamorphosed silicic volcanic and hypabyssal rocks of middle cretaceous 110 to 100 ma age occur in two roof pendants in the kings canyon area of the central sierra nevada the metavolcanic remnants are similar in age to or are only slightly older than the voluminous enclosing batholithic rocks thus high to surface levels of the batholith are implied for this region this is interesting considering that deep level 25 km batholithic rocks of the same age as the metavolcanic rocks occur at the southern end of the range apparent structural continuity between these two regions suggests that the southern half of the range offers an oblique section through young 100 ma sialic crust the middle cretaceous ages of the two volcanic sequences are indicated by u pb zircon and rb sr bulk rock isochron data the two isotopic systems agree very closely with one another some of the u pb systems within the boyden cave pendant are discordant due to the inheritance or entrainment of proterozoic zircon this is a common phenomenon in volcanic or plutonic rocks erupted or emplaced within the kings sequence metamorphic framework a belt of distinct pendants with abundant continent derived sedimentary protoliths in conjunction with other petrochemical parameters lavas and magmas of this framework domain are shown to be contaminated with sedimentary admixtures the contaminated domain of the batholith reflects the bounds of the kings sequence framework which along its eastern margin probably represents a major pre batholith to early batholith tectonic break the middle cretaceous metavolcanic sequences were apparently built on two distinctly different early mesozoic substrates separated by a major tectonic break in the boyden cave pendant the substrate may be represented by the shallow to deep marine kings sequence to the east in the oak creek pendant the substrate consists of a thick silicic ignimbrite sequence in both areas the middle cretaceous rocks and adjacent sequences share intense ductile deformation fabrics earlier views that considered these fabrics as an expression of jurassic orogenic deformation are in error structural and age relations indicate that the fabrics developed between 105 and 100 ma and during the medial phases of cretaceous composite batholith growth

magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of california effects of assimilation crustal thickness and depth of crystallization in order to better understand geologic fac tors controlling pronounced regional variations in whole rock chemistry mineralogy and mineral chemistry in the batholiths of california we calculate the magmatic intensive variables f hf f h 2 o f hf f hcl and f o 2 regional scale west to east increases in f oh in mafic silicates corresponding to the systematic i wc to i mc and i sc progression reflect orders of magnitude increase in f hf f h 2 o attending pluton crystallization low f hf f h 2 o of formation of western i wc types is consistent with their derivation from low fluorine source rocks in subducted oceanic slabs or the upper mantle in contrast higher f hf f h 2 o of crystallization of i mc and i sc types to the east implies the involvement of 1 progressively greater amounts of continental crustal source material such as biotite bearing metamorphic rocks their unweathered sedimentary derivatives retaining f rich mafic minerals or their fusion products and or 2 source materials which become more f rich toward the continental interior the regional distribution of i mc and i sc types suggests that the precambrian craton of western north america or derivative sediments may extend farther north in california and be morphologically more complex than previously thought from seemingly out of place occurrences of i wc plutons on the eastern slopes of the sierra nevada batholith we infer the existence of regions where precambrian basement was thin or absent in mesozoic time which prevented extensive cratonal contamination of subducted slab or upper mantle derived magmas new methods for estimating t f o 2 relations in the magmas demonstrate that i scr granites crystallize at oxygen fugacities as much as five orders of magnitude lower than those of i wc i mc and i sc types under conditions at or below the maximum stability limit of graphite in equilibrium with a c o h s gas phase the local scale formation of i scr granites in plutonic belts within specific wall rock terranes containing highly reducing sediments or metasediments may occur by contamination of i types with graphitic pelite or in some cases by the direct fusion of this reducing pelitic wall rock the spatial distribution of i scr granite provinces therefore is controlled simply by wall rock lithology amphibole geobarometry demonstrates a general west to east decrease in crystallization pressure across the sierra nevada batholith in contrast the peninsular ranges batholith displays a west to east crystallization pressure increase the bulk of the california batholiths crystallized at pressures less than 4 5 kb and depths less than about 15 19 km in the southern sierra nevada batholith the san gabriels and the eastern peninsular ranges however plutons crystallized at pressures exceeding 6 kb at deep crustal levels 23 km reconstruction of the pre erosion top of the batholith shows that in an east west cross section the central sierra nevada batholith was a horizontal tabular body with an aspect ratio of at least five to one

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

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

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

high resolution 3d reflection seismic investigation over a quick clay landslide scar in southwest sweden quick clay landslides often occur in the northern hemisphere in areas that were covered by pleistocene glaciation they are particularly common along the shorelines of the gota river in southwester

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

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

applications of lead and strontium isotopic relationships to the petrogenesis of granitoid rocks central sierra nevada batholith california pb isotope data are given on 80 whole rock and or feldspar samples from 51 dated samples covering a traverse across the central sierra nevada batholith largely between latitudes 36 and 37 n in addition sr isotope data were measured on 30 whole rock samples no correlation is observed between age and isotope ratios in agreement with previously published data 87 sr 86 sr ratios are low 0 704 along the western margin and increase to high values 0 707 at the eastern margin 206 pb 204 pb ratios increase from 18 6 at the western margin to 19 5 in the middle of the batholith then decrease regularly to 18 5 toward the eastern margin 2o8 pb 204 pb ratios mirror the 206 pb 204 pb data but do not exhibit the decrease in values toward the eastern margin pb and sr isotopic data from the western margin plutons plot within or close to the field of primitive island arc magmas indicating predominantly mantle sources the high 206 pb 204 pb ratios in the central batholith suggest assimilation of sediments derived from precambrian basement rocks the decrease in 206 pb 204 pb ratios in the eastern segment of the batholith without corresponding reduction in 208 pb 204 pb ratios is attributed to assimilation of lower crustal granulitic amphibolitic rocks by mafic magmas initial pb ratios for samples with 87 sr 86 sr 0 706 from the central and eastern segments of the batholith indicate components from recycled crustal rocks with a mean 207 pb 206 pb age of ca 1 8 ga nd and o isotopic data from the literature are consistent with the pb sr model obtained in this study very similar isotope patterns to the present model are reported across the salinian block

u pb zircon strontium and oxygen isotopic and geochronological study of the southernmost sierra nevada batholith california the southernmost sierra nevada offers a view into the deep levels of the mesozoic batholithic belt which constitutes much of the range to the north and represents one of the major tectonic features of western north america the main crystalline rocks of the study area are 1 the intrusive suite of bear valley a middle cretaceous tonalite batholith complex with coeval gabbroic intrusives and 2 the gneiss complex of the tehachapi mountains which consists of early cretaceous orthogneiss and subordinate paragneiss with local domains having granulite facies metamorphic assemblages the orthogneisses are dominantly tonalitic in composition with significant layers of granodioritic to granitic and lesser dioritic to gabbroic gneiss quartz rich and psammitic metasedimentary rocks with subordinate marble constitute the main framework assemblage into which the plutonic rocks were emplaced field relations demonstrate assimilation of metasedimentary material into the orthogneiss and tonalite batholith magmas and magma mixing between mafic tonalitic and granitic materials significant domains of both homogenization and inhomogenization are recognized isotopically within the mixed rocks u pb zircon studies have resolved two major igneous suites and a third suite of postdeformational intrusives all lying between 90 and 120 ma the first suite gneiss complex of the tehachapi mountains was emplaced at 115 ma and exhibits penetrative high temperature deformation developed at or near solidus conditions a number of discordance patterns along with the physical properties of the zircon suggest minor inheritance of proterozoic zircon and limited open system behavior in response to a major 100 ma plutonic event the 100 3 ma intrusive suite of bear valley crosscuts the older suite but also exhibits significant synplutonic deformation mainly concordant zircon ages indicate the igneous crystallization age but some discordances occur due to inheritance or entrainment of proterozoic zircon the high temperature deformation fabrics in these suites and within the metasedimentary framework rocks were crosscut by the granodiorite of claraville 90 ma and pegmatite dikes 95 ma the granodiorite of claraville shows strong inheritance of proterozoic zircon and high initial 87 sr 86 sr and 18 o zircon populations from paragneiss and quartzite samples are dominated by proterozoic detrital grains strontium and oxygen isotopic data on the zircon geochronology sample suite suggest simple twocomponent mixing of mantle derived gabbroic to tonalitic magmas with partial to complete melt products from the metasedimentary framework rocks sedimentary admixtures for some granitic rocks may be as high as 45 but for the tonalitic batholithic complex are no higher than about 15 modeled values of 10 20 metasediment are typical for the orthogneisses initial 87 sr 86 sr correlates directly with 18 o and generally correlates inversely with sr content some subtle complexities in the sr and o isotopic data suggest the involvement of a third cryptic component such a component could be early phanerozoic ensimatic accretionary terranes that were structurally beneath the observed metasedimentary sequence or altered oceanic crust and sediments introduced into the mantle magma source area by subduction one of the initial aims of this study was to seek out remnants of proterozoic sialic crystalline rocks within the gneiss complex of the tehachapi mountains no such remnants were found and our studies strongly suggest that sialic components within this link of the mesozoic batholithic belt were introduced into mantle derived magraatic systems by anatexis of continent derived sedimentary rocks

late stage mafic injection and thermal rejuvenation of the vinalhaven granite coastal maine the vinalhaven intrusive complex consists mainly of coarse grained granite inward dipping gabbro diorite sheets and a fine grained granite core small bodies of porphyry occur throughout the coarsegrained granite the largest porphyry body roughly 0 5 km by 2 5 km occurs with coeval gabbro hybrid rocks and minor finegrained granite in the vinal cove complex which formed during the waning stages of solidification of the coarse grained vinalhaven granite porphyry contacts with surrounding coarse grained granite are irregular and gradational compositions of whole rocks and minerals in the porphyry and the coarse grained granite are nearly identical neighboring phenocrysts in the porphyry vary greatly in degree of corrosion and reaction indicating that the porphyry was well stirred thermal rejuvenation of a silicic crystal mush by a basaltic influx can explain the composition and texture of the porphyry comparable rejuvenation events have been recognized in recent studies of erupted rocks weakly corroded biotite phenocrysts in the porphyry require that hydrous interstitial melt existed in the granite during remelting field relations along with thermal calculations suggest that cooling and crystallization of coeval mafic magma could have generated the porphyry by thermal rejuvenation of granite crystal mush containing about 20 melt field relations also suggest that some of the porphyrymatrix may represent new felsic magma that was emplaced during remelting

weathering characteristics of interflow volcanic boles from mandla lobe eastern deccan volcanic province abstract the deccan volcanism straddling the cretaceous paleogene boundary resulted into one of the most extensive continental flood basalts in the western and central peninsular india the interflow sedimentary units boles often cited as paleosols are the rare archives of paleoenvironmental conditions existed during successive lava flows a debate on the origin of boles as true paleosols exists therefore in order to trace out regional extent of such conditions pedogenic non pedogenic in the context of their paleoenvironmental significance during the deccan volcanism we studied here mineral magnetic characteristics of 36 color differentiated bole beds from the mandla lobe in the eastern deccan volcanic province edvp classified into four types gray yellow brown and red based on their munsell notations the gray yellow and brown boles show dominantly ferrimagnetic composition chiefly magnetite and titanomagnetite while red boles characterize mixed ferri and antiferromagnetic mainly hematite mineralogy the granulometric domain parameters suggest larger single domain sd and the multidomain md ferrimagnets in the majority of cases whereas superparamagnetic sp particles with frequency dependent susceptibility fd 2 6 to 20 3 10 8 m 3 kg 1 are limited to the few red and brown boles only the significant presence of primary parent magnetic minerals i e coarse sd md titanomagnetite and magnetite in the majority of boles depict incipient to moderate weathering owing to limited time intervals during successive eruptions the combination of hematite and sp particles present only in the few red and brown boles depicts baking effect rather than pedogenesis the comparison of magnetic properties of boles from edvp and western deccan volcanic province wdvp shows significant differences in the concentration of sp ferrimagnetic particles and hematite attributed to variable weathering intensity duration and heating related alterations from the upper flows both edvp and wdvp boles indicate similar first order paleoenvironmental conditions without any major pedogenesis that can be regionally correlated

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

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

early alkaline magmatism in the deccan traps implications for plume incubation and lithospheric rifting abstract significant lithospheric extension which usually accompanies continental flood volcanism has been generally thought to always follow the main volcanic episode however plume derived uncontaminated early alkaline magmas from the deccan traps india indicate considerable lithospheric extension 3 million yrs my before the main tholeiitic phase indeed such early alkaline magmatism known from many flood basalt provinces of the world seems a necessary and natural consequence of plume head incubation with lithospheric doming and rifting

geophysical and geotechnical studies of geology and sediment properties at a quick clay landslide site at esp trondheim norway abstract increased urbanisation and development in previous marginal areas have led to the need to protect the population the environment and infrastructure from hazards such as quick clay landslides in this paper the opportunity which was presented following the gathering of a large amount of data in the area of the quick clay landslide at esp trondheim norway in 2012 is explored the data is of particular interest given the availability of frequency domain helicopter borne electromagnetic data fhem and extensive lidar imaging as well as a full range of in situ geophysical and geotechnical soundings and samples the ground conditions in the area are shown to be complex and it is clear that a multi disciplinary type approach combining geophysical geomorphological and geotechnical investigations is necessary in order to understand the hazards posed by potential quick clay landslides the investigation shows that very good overview mapping of the area can be obtained from fhem and that the data obtained from local electrical resistivity tomography ert and resistivity cone rcptu are consistent with each other and with the fhem data use of ert immediately after the landslide was particularly useful in delineating further risk areas and as an aid for assessment of evacuation of the local population lidar data is particularly useful in understanding the landslide trigger mechanisms the depth of the landslide the form of the run out and the nature of the material in the run out geotechnical data collected in the area is characteristic of that of soft sensitive norwegian marine clays and the various geotechnical and geophysical parameters correlate well with one another and also follow well established patterns the data shows that no single investigative method is available to accurately define quick clay layers but that a number of complimentary in situ and laboratory techniques are necessary for that purpose

paleontological view of the ages of the deccan traps the cretaceous tertiary boundary and the india asia collision volcanism in the deccan traps of india occurred over at most three magnetic chrons centered on a main reversed chron paleontological data indicate that this reversed chron must coincide with 29r which contains the cretaceous tertiary k t boundary recent 40 ar 39 ar data may therefore provide one of the best estimates of the absolute age of the k t boundary 65 7 2 0 ma moreover the eurasian character of k t boundary terrestrial faunas in india suggests that this was also close to the time of india asia collision this is significantly earlier than generally recognized and implies about 4000 km of continental shortening in the collision zone probably absorbed jointly by crustal thickening and strike slip extrusion

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

petrology of the chilliwack batholith north cascades washington generation of calc alkaline granitoids by melting of mafic lower crust with variable water fugacity calc alkaline granitoid rocks of the oligocene pliocene chilliwack batholith north cascades range from quartz diorites to granites 57 78 sio2 and are coeval with small gabbroic stocks modeling of major element trace element and isotopic data for granitoid and mafic rocks suggests that 1 the granitoids were derived from amphibolitic lower crust having ree rare earth element and sr nd isotopic characteristics of the exposed gabbros 2 lithologic diversity among the granitoids is primarily the result of variable water fugacity during melting the main effect of fh 2 o variation is to change the relative proportions of plagioclase and amphibole in the residuum the ree data for intermediate granitoids quartz diorite granodiorite eu eu 0 84 0 50 are modeled by melting with fh 2 o 1 kbar leaving a plagioclase pyroxene residuum in contrast data for leucocratic granitoids leuco granodiorites and granites eu eu 1 0 0 54 require residual amphibole in the source and are modeled by melting with fh 2 o 2 3 kbar consistent with this model isotopic data for the granitoids show no systematic variation with rock type 87sr 86sri 0 7033 0 7043 end 0 3 3 to 5 5 and overlap significantly with data for the gabbroic rocks 87sr 86sri 0 7034 0 7040 end 0 3 3 to 6 9 the fh 2 o variations during melting may reflect additions of h2o to the lower crust from crystallizing basaltic magmas having a range of h2o contents chillwack gabbros document the existence of such basalts one dimensional conductive heat transfer calculations indicate that underplating of basaltic magmas can provide the heat required for large scale melting of amphibolitic lower crust provided that ambient wallrock temperatures exceed 800 c based on lithologic and geochemical similarities this model may be applicable to other cordilleran batholiths