geochemical and mineralogical impacts of h2so4 on clays between ph 5 0 and 3 0 natural and constructed clay liners are routinely used to contain waste and wastewater the impact of acidic solutions on the geochemistry and mineralogy of clays has been widely investigated in relation to acid mine drainage systems at ph 1 0 the impact of h2so4 leachate characterized by ph 1 0 and potentially negative ph values on the geochemistry and mineralogy of clays is however not clear thus laboratory batch experiments were conducted on three natural clay samples with different mass ratios of smectite illite and kaolinite to investigate the impact of h2so4 on the geochemistry and mineralogy of aluminosilicates from ph 5 0 to 3 0 batch testing was conducted at seven ph treatments 5 0 3 0 1 0 0 0 1 0 2 0 and 3 0 using standardized h2so4 solutions for four exposure periods 14 90 180 and 365 d aqueous geochemical and xrd analyses showed increased dissolution of aluminosilicates with decreasing ph and increasing exposure period that smectite was more susceptible to dissolution than illite and kaolinite precipitation of an amorphous silica phase occurred at ph 0 0 and anhydrite precipitated in ca rich clays at ph 1 0 in addition global dissolution rates were calculated for the clays and showed good agreement to literature smectite illite and kaolinite dissolution rates which suggests global dissolution rates for complex clays could be determined from monomineralic studies a stepwise conceptual model of the impact of h2so4 on aluminosilicate geochemistry and mineralogy between ph 5 0 and 3 0 is proposed

the miocene roof mapping using microtremor recording and electrical survey method in blida city algeria bedrock depths in the mitidja basin in general and in the blida region in particular are still poorly known despite the existence of some relatively deep hydraulic boreholes that intersect only superficial alluvial formations to assess the seismic risk of blida town knowledge of soil amplification requires the thickness and properties of sedimentary formations that cover the substratum for the purposes of our study the thicknesses obtained by the vertical electric soundings carried out in the hydrogeological study of the basin were combined with horizontal to vertical spectral ratio hvsr microtremor recordings this combination made it possible to determine an empirical relationship between frequency and thickness specific to the blida site area which enabled the roof of the miocene to be mapped and shows slight undulations with directions compatible with the tectonic constraints of the region the boundaries between the low and high frequencies obtained by hvsr are well materialized at south by sidi el kebir river at west by chiffa river and in the central part by a line of direction se nw corresponding to the old passage of sidi el kebir river the presence of low frequencies attributed to the old alluvial deposits with significant thicknesses that originate just after sidi el kebir river confirms that the south mitidjian contact is subvertical

the gophu la and western lunana granites miocene muscovite leucogranites of the bhutan himalaya abstract petrographical mineralogical and geochemical data are given for the gophu la leucogranite the second largest leucogranite body of the bhutan himalaya and for the smaller western lunana leucogranite both leucogranites were emplaced in the amphibolite facies gneisses of the high himalaya basement nappes during the miocene the gophu la leucogranite is about 300 km 2 in outcrop surface and is homogeneous showing only moderate variations in chemical and modal composition the western lunana leucogranite has a far smaller outcrop surface about 40 km 2 and is less homogeneous than the gophu la leucogranite both are fine to medium grained hololeucocratic granites with white mica biotite and minor tourmaline significant accessories are andalusite and sillimanite the muscovites are phengitic being notably high in fe and mg and the biotites are fe rich the average chemical compositions are similar to that of other himalayan leucogranites and are typical for minimum melts both granites preserve geochemical features recording the heterogeneity of the parent material and were probably produced during the uplift of tectonically thickened continental crust

age and cooling history of the manaslu granite implications for himalayan tectonics abstract the manaslu granite is one of the high himalayan leucogranites which are believed to be derived by partial melting of quartzofeldspathic gneissess of the high himalayan crystallines hhc and emplaced at the contact between the hhc and the tethyan sedimentary series we have analyzed a suite of muscovite 15 biotite 3 and alkali feldspar 10 by the 40 ar 39 ar method to help constrain the age and cooling history of the granite 40 ar 39 ar ages ranges are 18 4 to 13 3 ma 17 0 to 14 7 and 16 4 to 3 4 for muscovite biotite and k feldspar respectively based on the muscovite analyses and a re interpretation of a previously published u pb monazite age we conclude that the crystallization age of the manaslu granite is everywhere 20 ma the postcrystallization cooling history given by the micas and the feldspars suggests the presently exposed parts of the pluton were emplaced at depths of 8 to 15 km these data place a minimum age of movement on the mct in this area of 20 ma we estimate the time of magma segregation and transport to be no more than 5 ma

new relationships between vs thickness of sediments and resonance frequency calculated by the h v ratio of seismic noise for the cologne area germany noise measurements were carried out in the cologne area germany and the resonance frequency of each site was estimated from the main peak in the spectral ratio between the horizontal and vertical component for 32 of these sites the thickness of the sedimentary cover was known from boreholes and a clear correlation between resonance frequency and sediment thickness was observed a formula that correlates cover thickness with frequency of the main peak in the horizontal to vertical spectral ratio was derived in addition a best fitting shear wave velocity distribution with depth vs z as well as a relationship between average shear wave velocity vs and thickness of the sedimentary cover was calculated by using all of the noise measurements and applying the derived relationships we obtained a subsoil classification for the cologne area

contact metamorphism and depth of emplacement of the manaslu granite central nepal implications for himalayan orogenesis abstract the manaslu massif central nepal provides a well exposed example of a deeply eroded pluton its contact aureole can be followed from the base to the top along medium to low grade mesozonal to anchizonal tethyan metasediments contact metamorphic mineral assemblages and thermobarometric estimations suggest that the granite was emplaced at 18 21 km for the base and 9 13 km for the roof calculated temperatures within the aureole at 550 40 c are compatible with the intrusion temperature of a leucogranitic magma microstructural evidence shows that the temperature remained high 500 c at the base of the massif during and after granite emplacement whereas towards the top of the granite deformation proceeded rapidly at lower temperature heating of the abundant calcareous rocks in the contact aureole released a local co2 rich fluid whereas a h2o and boron rich fluid seems to have pervaded the whole zone this fluid is probably exsolved from the granitic melt during its crystallization the depth of emplacement of the massif has an important implication for the reconstruction of the himalayan geodynamic evolution implying a burial of the tethyan metasediments by a major refolding of the sedimentary cover or more probably by extensive development of the north himalayan nappes towards the south for more than 70 km before granite emplacement i e before the miocene the young age of the granite and its depth of emplacement suggest a rapid tectonic denudation in the order of 1 mm a 1 probably by normal faulting north of the massif during its cooling

trace element modelling of pelite derived granites the presence or absence of a vapour phase during incongruent melt reactions of muscovite and biotite together with the composition of the protolith determines the trace element characteristics of the resulting melt provided that equilibrium melting occurs for those phases that host the tracc elements of interest for granitic melts rb sr and ba provide critical constraints on the conditions that prevailed during melting whereas ree are primarily controlled by accessory phase behaviour mass balance constraints for eutectic granites that are formed by the incongruent melting of muscovite in pelites indicate that melting in the presence of a vapour phase will result in a large melt fraction and deplete the restite in feldspar hence the melt will be characterized by low rb sr and high sr ba ratios in contrast vapour absent melting will result in a smaller melt fraction and an increase in the restitic feldspar consequently high rb sr and low sr ba ratios are predicted vapour absent melting will also enhance the negative eu anomaly in the melt granites that result from the incongruent melting of biotite in the source will be characterized by higher rb concentrations than those that result from the incongruent melting of muscovite the himalayan leucogranites provide an example of unfractionated crustally derived eutectic melts that are enriched in rb but depleted in sr and ba relative to their metasedimentary protoliths these compositions may be generated by the incongruent melting of muscovite as a low melt fraction f 0 1 from a pelitic source under vapour absent conditions

the behavior of trace elements during schwertmannite precipitation and subsequent transformation into goethite and jarosite schwertmannite is a ubiquitous mineral formed from acid rock drainage ard and plays a major role in controlling the water chemistry of many acid streams the formation of schwertmannite was investigated in the acid discharge of the monte romero abandoned mine iberian pyrite belt sw spain schwertmannite precipitated from supersaturated solutions mainly owing to the oxidation of fe ii to fe iii and transformed with time into goethite and jarosite in a few hours schwertmannite precipitation removed more than half of the arsenic load from solution whereas the concentration of divalent trace metals zn cu pb cd ni and co remained almost unchanged in the laboratory natural schwertmannite was kept in contact with its coexisting acid water in a flask with a solid liquid mass ratio of 1 5 for 353 days during this time the ph of the solution dropped from 3 07 to 1 74 and the concentrations of sulfate and fe increased during the first 164 days schwertmannite transformed into goethite plus h3o jarosite but subsequently goethite was the only mineral to form some of the trace elements such as al cu pb and as were depleted in solution during the first stage as schwertmannite transformed into goethite plus h3o jarosite on the contrary the transformation of schwertmannite to goethite with no jarosite during the second stage released al cu and as to the solution despite the variation in their concentrations in solution approximately 80 of the total al and cu inventories and more than 99 as and pb remained in the solid phase throughout the entire aging process

ascent of a granitoid diapir in a temperature varying medium a relationship for the ascent velocity of a granitoid diapir is derived and used in conjunction with a crustal heat flow model which incorporates a depth dependent temperature to predict emplacement histories ascent rate is strongly dependent on the width of a deformation layer of variable viscosity that is formed by the transfer of heat to the country rock and on the buoyancy force which propels the diapir through it ascent velocity is described by the expression u 2 gd3z 0r where is the density contrast between diapir and country rock g is gravitational acceleration d is the deformation zone width z is a parameter which describes the increase in viscosity across the zone 0 is the country rock viscosity at the contact and r is the diapir radius the width of the deformation zone as dictated by the temperature distribution and rheological function is the point at which the viscosity increases by a factor f from the contact value although ascent rates vary with choice of this parameter ascent distances are not strongly dependent on f results of simulations which incorporate a spectrum of input parameters reveal that ascent distance is strongly dependent on both the rheology and ambient temperature of the encompassing rock but only weakly dependent on the initial diapir temperature ascent velocity varies with the diapir size with larger bodies moving more slowly and ascending for longer periods relative to smaller plutons as a result of the proportionately larger amount of thermal energy available for ascent larger bodies will rise greater distances than smaller diapirs however the additional ascent appears nominal relative to the contrast in available energy modeling diapirs using a no slip boundary condition decreases ascent velocity by a factor of about 3 relative to results incorporating a stress free boundary condition the time scale of granitoid diapirism over crustal distances cannot be less than 104 years due to the rate limiting effect of thermal conduction above the body and not greater than 105 years reflecting solidification times of kilometer sized plutons a consequence of ascent by a deformation zone mechanism is the generation following emplacement of a mechanically weakened crust which extends from beneath the diapir to near the source perhaps explaining the relatively common occurrence of synmagmatic to postmagmatic mafic dikes within granites believed to be derived from interaction of basalt with the lower crust

phase equilibrium constraints on the viscosity of silicic magmas 1 volcanic plutonic comparison by using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at 104 5 pa s irrespective of their temperature and level of emplacement magmas crystallizing as granitic plutons are not water poor and thus not more viscous than their extrusive equivalents instead comparison between pre eruption magma viscosities of extrusive silicic intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous given the typical strain rates in silicic magma chambers magma rheological behavior is expected to be dominantly newtonian bubbles having a minor rheological influence at depth although exceptions can exist thus whether a silicic intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors but not on the rheology of the magma itself however preemptive viscosities of extrusive magmas rarely exceed 106 pa s which suggests that crystal melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes the narrow range of viscosities displayed by silicic intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas considerations of the relationships between magma crystallinities bulk sio2 and preemptive melt h2o contents show that the higher the melt h2o content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted an empirical correlation is proposed that enables us to estimate preemptive melt h2o contents of erupted magmas by knowing their crystallinity and bulk sio2

viscosity of himalayan leucogranites implications for mechanisms of granitic magma ascent the viscosity of the gangotri himalayan leucogranite has been experimentally determined between 80 o and 1100oc 300 and 800 mpa for meltwater contents of 3 98 and 6 66 wt the melt viscosity is independent of pressure and shows an arrhenian behavior relative to temperature within the range of conditions investigated we present an empirical relation that can be used to determine leucogranite magma viscosities knowing their meltwater content and temperature this relation together with phase equilibria experiments constrain the viscosity of the itimalayan leucogranit s to be around 104 5 pas during their eraplacement these viscosities and the widths of dikes belonging to the feeder system are consistent with the theoretical relationship relating these two parameters and show that the precursor magma of the leucogranite was at near liquidus conditions when emplaced within host rocks with preintmsion temperatures around 350oc calculated terminal asa nt rates for the magma in the dikes are around 1 m s magma cmber assembly time is on ths basis estimated to be less than 100 years for a volume of 150 icm3 in addition the dynamical regime of the magma flow in the dikes was essentially laminar thus allowing preservation of any chemical heterogeneity acquired in the source these results constrain the viscosity of melts f rmed during the first steps of crustal anatexis those involving muscovite breakdown to be alsoround 104 5 pas thus compaction may not be the only mechanism of melt segregation in partially melted crustal rocks in view of the very short timescale inferred for magma ascent and emplacement

microtremors as a geophysical exploration tool applications and limitations the usefulness of microtremors as a geophysical exploration tool has been analyzed this application is possible due to the relationship between the main resonance frequency of a given soil obtained from the h v spectral ratios of microtremors its thickness and average shear velocity we first measured the ambient noise at 33 sites and determined their main resonance frequency detailed geotechnical information was available for 23 of the sites thereby allowing us to establish a quantitative relationship between the resonance frequency and the thickness of the soil and indirectly between either of them and the shear velocity of the soil the practical application of this relationship has revealed its usefulness in determining the surface structure of a valley with excellent accuracy with an error of only 15 in the depths calculated these errors are due to the simplification of the problem that this method implies it requires that the shear velocity vary constantly with depth throughout the study region which is evidently not always so and that the input data themselves intrinsically have a certain degree of uncertainty this method is therefore not valid when there is no mechanical contrast between the study soil and the underlying layer or when the shear velocity varies irregularly with depth in the study area

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

the pangong injection complex indian karakoram a case of pervasive granite flowthrough hot viscous crust in the karakoram range of nw india the tangtse gorge cuts across deep crustal rock sexhumed by transpression along two strands of the dextral karakoram fault crustal leucogranitic magmas pervasively intruded amphibolites and migmatites in the form of sheets that locally coalesced and expanded to form kilometre scale plutons sheets resulted from slow seeping of granite into foliation planes magma wedging rather than from dyking driven by magma buoyancy and possibly syn intrusive tectonic deformation high temperature of the country rocks at the time of intrusion is inferred from similar crystallization ages of the intrusive leucogranite and in situ partial melt in the migmatites and reflected in the ductile structures developed whereas low country rock viscosity inhibited dyking high temperature freed the magma from the constraints of freezing and permitted pervasive intrusion the injection complex exposed along the tangtse gorge rather than representing the final emplacement structures represent transient structures of the granite pathways on their upward journey to build the karakoram batholith which crops out a few kilometres north at structurally shallower levels we suggest that pervasive magma flow is a transitional step between magma segregation at the source and later rise through cold crust and it may be one of several factors controlling whether dyking or diapirism becomes dominant during late ascent

incremental emplacement of the late jurassic midcrustal lopolith like qitianling pluton south china revealed by ams and bouguer gravity data modes of magma emplacement may provide key information on geodynamic tectonic settings of magmatism when the threshold of magma volume and duration of emplacement process is crossed brittle ductile crustal deformation behavior and volumes and rates of magma transfer in the crust the majority of upper crustal granitic intrusions are incrementally emplaced as laccoliths or sills while midcrustal or deeper level granitic intrusions appear to be predominantly emplaced as sills or lopoliths but relatively few examples have been studied we present a case study on the jurassic qitianling pluton from south china which was constructed in the upper part of the middle crust at a depth of 10 15 km to characterize its emplacement mechanism and evolution we have combined field and microscopic observations anisotropy of magnetic susceptibility measurements and bouguer gravity anomaly modeling the main findings are 1 the generally undeformed granite country rock contacts with a narrow thermal aureole 2 irregularly wavy and gradational contacts between the main granite facies 3 dominant subhorizontal magnetic fabrics in the granites with a scattered magnetic foliation 4 rare occurrence of dykes and 5 a subcircular surface and lopolith like pluton geometry accordingly we suggest that the qitianling pluton forms an 25 km wide and 5 km thick lopolith that was incrementally emplaced during a period of tectonic quiescence most likely by under accretion of multiple magma sheets deflected from magma pulses that ascended through pipe like channels the mineralogical and compositional variation of the pluton may be the result of in situ fractionation fractionation at deeper crustal level or variation in source derived melt compositions

heat sources for tertiary metamorphism and anatexis in the annapurna manaslu region central nepal following the collision of india with southern tibet crustal rocks of the leading edge of india 1 underwent regional metamorphism to upper amphibolite grade 2 melted locally to produce anatectic granitoids and 3 were sheared and thrust onto lower grade rock along the main central thrust yielding an inverted metamorphic sequence this sequence is exemplified in the annapurna manaslu region we use simple physical calculations to examine the heat sources involved in the different phases of metamorphism the regional metamorphism apparently is due to the burial of the northern edge of india beneath the accretionary prism along the southern edge of tibet the observed temperatures and pressures of this first phase of metamorphism are consistent with the thermal relaxation during the 10 30 m y before slip on the main central thrust began of thickened continental lithosphere whose original surface heat flux was between 50 and 70 mw m 2 the release of water from the footwall of the main central thrust apparently facilitated melting of the overlying crust in the second phase such melting could have occurred in the first million years or so of thrusting if warm 550 650 c crust in the footwall contained the necessary water if melting did not occur in the earliest stages of slip on the main central thrust dissipative heating with shear stresses of 10 to 100 mpa is required for temperatures near the main central thrust to have remained high enough to generate melting above the fault during the underthrusting of cold material the thickness 6 8 km of the zone of inverted isograds associated with the fault if undisrupted and due solely to thermal diffusion implies that the time required to carry the rocks preserving the inverted metamorphism from the surface to depths of 30 40 km was 4 8 m y the apparent inverted temperature gradients about 10 25 c km in this zone can be understood as the combined result of two processes diffusion of heat from hot rock thrust over cold rock expunged the original temperature gradient near the fault and could have created an inverse gradient of 10 20 c km the peak temperatures in such a zone however would not have exceeded about 350 c without an additional source of heat dissipative heating at shear stresses of about 100 mpa can account for peak temperatures in excess of 600 c during slip on the fault and would have contributed as much as 13 c km to the inverse gradient although inversion of metamorphic isograds could have occurred as a result of deformation within the main central thrust zone the high temperatures during slip on this zone still require dissipative heating unless the duration of slip exceeded 25 m y

ambient noise measurements for preliminary site effects characterization in the urban area of florence italy abstract environmental noise measurements and borehole data were used for a preliminary seismic characterization of the plio quaternary sedimentary basin underlying the city of florence italy an extensive survey of ambient vibrations was conducted by using the seismic noise horizontal to vertical h v spectral ratio technique hvsr to map the fundamental resonance frequency of the sedimentary cover in order to use this information to infer main features of the basin subsurface geometry an estimate of the s wave velocity profile in the sediment layer was obtained from array noise recordings along with information on resonance frequency and direct measurements of the sediment thickness available at 23 borehole sites a first order reconstruction of the seismic bedrock topography in the area was provided which shows a good consistency with available geological log data from these pieces of information a preliminary soil classification of the whole area was attempted in order to identify situations where possible seismic amplification effects are expected during future earthquakes and where more accurate investigations are needed to parameterize the local seismic response

badrinath gangotri plutons garhwal india petrological and geochemical evidence for fractionation processes in a high himalayan leucogranite the gangotri leucogranite is the western end of the badrinath granite one of the largest bodies of the high himalayan leucogranite belt hhl it is a typical fine grained tourmaline muscovite biotite leucogranite the petrography shows a lack of restitic phases the inferred crystallization sequence is characterized by the early appearance of plagioclase quartz and biotite and by the late crystallization of the k feldspar this suggests that in spite of being of near minimum melt composition the granite probably had long crystallization or melting interval in agreement with previous experimental studies tourmaline and muscovite have a mainly magmatic origin even though the major element composition is homogeneous there are several geochemical trends when cao decreases there is an increase in na2o rb sn u b f and a decrease in k2o fe2o3 tio2 sr ba zr ree th which are best explained by a fractionation process with early crystallizing phases experimental solubility models for zircon and monazite in felsic melt support a magmatic origin for these two accessory phases as well rb sr isotope data show this granite to have like other hhl heterogeneous isotopic values for sr initial 87sr 86sr ratios calculated at 20 ma range between 0 765 and 0 785 therefore no mixing i e no convection occurred between the different batches of magma in contrast 18o data show little variation 13 04 0 25 implying a source with homogeneous 18o values differences in timing between fluid infiltration and the onset of melting related to differences in temperature of the source could explain why source homogenization occurred for the gangotri and not for the manaslu granite the use of experimental results for solubility and the position of the accessory minerals during melting predict a low viscosity for the melt during its extraction this in turn explains the lack of restitic phases major and accessory in the granite as well as some field features lensoid shape pronounced magmatic layering based on the petrographic and isotopic studies it is suggested that the mechanism of ascent was not diapiric but rather that the melt ascended along several fractures and the level of emplacement was partialy controlled by the density contrast between the melt and host rocks

microtremor recordings in northern mississippi abstract this paper presents the results of 305 single point microtremor recordings covering northern mississippi that is situated within the upper mississippi embayment area both long and short term recordings were obtained by a le 3d 20s seismometer over a large network of points where the unconsolidated sediment thickness ust varies from zero to 1400 m applying the nakamura method the recordings were processed to determine predominant frequency f0 and its relation to ust initial results of wind influence on the frequency spectra particularly in low frequency band 0 05 0 2 hz and dominant vibration direction are also presented it is shown that analysis of systematic microtremor recordings can provide a stable and reliable estimation of the predominant frequency from which estimates of average shear wave velocity of overall sediment profile can be derived predominant frequency and average shear wave velocity is reasonably well correlated with ust wind and human activities are found to produce peaks over the low frequency band

mineralogical evidence for fractionation processes in the himalayan leucogranites of the ramba dome southern tibet abstract himalayan leucogranites provide some of the best examples in the world of highly felsic and strongly peraluminous granites and they have been paid special attention with regard to investigating the evolution of continental crust here we describe our mineralogical investigations of a late miocene leucogranite complex within the ramba dome of the tethyan himalaya belt that have helped us decipher the petrogenesis of these high silica peraluminous granites the ramba leucogranites range from two mica granites biotite muscovite to muscovite leucogranites muscovite garnet tourmaline with the two mica granites constituting the main part of the pluton and the muscovite leucogranites commonly occurring as late stage dikes that are located within the pluton or invaded the country rocks variations in the mineral assemblages of the two types of leucogranite are associated with systematic changes in bulk rock geochemistry and the distinctive mineralogical features demonstrate a genetic relationship between the two types of leucogranite that involved fractional crystallization with the muscovite leucogranites being more evolved than the two mica granites chemical data for the minerals in the two mica granites record a long period of differentiation during which a normal granitic melt developed into a highly evolved magmatic system with high flux components e g h2o f b in contrast the mineralogical data for the muscovite leucogranites record the crystallization of a very late residual melt i e a volatile rich highly fluid melt according to recent studies of differentiation processes in silicic magma reservoirs we can interpret the ramba leucogranites as having undergone a high degree of differentiation by in situ fractional crystallization in a crystal mush environment the two mica granites represent a congealed crystal mush that was composed of cumulate crystals and a trapped interstitial liquid and the muscovite leucogranites represent the almost pure liquid that was extracted from the crystal mush modeling using the trace elements sr and ba shows that the extraction probably occurred when the crystallinity of the mush was 59 64 at least for the most evolved muscovite leucogranite sample the two mica granite corresponds to a residual crystal mush that had a terminal porosity of 20 26 filled with a trapped interstitial liquid collectively fractional crystallization can account for the geological mineralogical petrological and geochemical variations between the two types of leucogranite this work highlights the important role of crystal fractionation in the generation of himalayan leucogranites

generation of leucogranites via fractional crystallization a case from the late triassic luoza batholith in the lhasa terrane southern tibet abstract leucogranites are important in understanding intracrustal differentiation and regional tectonic evolution but how these rocks form remains a matter of much debate the luoza batholith in the central lhasa subterrane provides an important opportunity to address these issues as this batholith consists of normal calc alkaline s type granodiorites group 1 and highly fractionated s type leucogranites group 2 laser ablation inductively coupled plasma mass spectrometry zircon u pb dating indicates that these rocks were emplaced at ca 221 205 ma the group 1 samples ca 205 ma have low sio2 content 64 67 wt and low differentiation index values di 75 76 and are slightly depleted in ba p sr and ti compared to the group 2 samples ca 221 ma and 213 ma which have high sio2 content 74 75 wt high differentiation index values 91 94 and are significantly depleted in ba p sr and ti samples from group 1 and group 2 exhibit similar zircon ehf t values 15 6 to 1 4 both of which are significantly higher than melts from the pure ancient basement in the central lhasa subterrane 20 5 to 10 6 the group 1 samples can be interpreted as having been derived from the partial melting of metagreywacke within the ancient basement in the central lhasa subterrane with contributions from mantle or juvenile crust derived components whereas the group 2 samples may have formed via varying degrees of fractional crystallization of different minerals e g plagioclase k feldspar biotite zircon allanite monazite titanite and apatite from the parental magmas represented by the granodioritic samples in group 1 in shallow crustal magma chambers in combination with sedimentary records the high temperature and low pressure conditions indicated by the group 1 samples can be geodynamically linked to a back arc extensional setting in response to the southward subduction of the bangong nujiang tethys ocean seafloor our work implies that fractional crystallization is likely a feasible mechanism for the development of leucogranites and for explaining the compositional diversity of the granite during intracrustal differentiation

himalayan leucogranites and migmatites nature timing and duration of anatexis widespread anatexis was a regional response to the evolution of the himalayan tibetan orogen that occurred some 30 ma after collision between asia and india this paper reviews the nature timing duration and conditions of anatexis and leucogranite formation in the greater himalayan sequence ghs and compares them to contemporaneous granites in the karakoram mountains himalayan leucogranites and associated migmatites generally share a number of features along the length of the mountain front such as similar timing and duration of magmatism common source rocks and clockwise p t paths despite commonalities most papers emphasize deviations from this general pattern indicating a fine tuned local response to the dominant evolution there are significant differences in p t xh2o conditions during anatexis and timing in relation to regional decompression further to that some regions underwent a second event recording melting at low pressures zircon and monazite ages of anatectic rocks range between c 25 and 15 ma suggesting prolonged crustal melting typically a single sample may have ages covering most of this 10 ma period suggesting recycling of accessory phases from metamorphic rocks and early formed magmas recent studies linking monazite and zircon ages with their composition have determined the timing of prograde melting and retrograde melt crystallization thus constraining the duration of the anatectic cycle in some areas this cycle becomes younger down section towards the leading front of the himalayas whereas the opposite is true in other areas the relationship between granites and movement on the south tibetan detachment std reveals that fault motion took place at different times and over different durations requiring complex internal strain distribution along the himalayas the nature and fate of magmas in the ghs contrast with those in the karakoram mountains ghs leucogranites have a strong crustal isotopic signature and migration is controlled by low angle foliation leading to diffuse injection complexes concentrated below the std in contrast the steep attitude of the karakoram shear zone focused magma transfer feeding the large karakoram baltoro batholith anatexis in the karakoram involved a cretaceous calcalkaline batholith that provided leucogranites with more juvenile isotopic signatures the impact of melting on the evolution of the himalayas has been widely debated melting has been used to explain subsequent decompression or conversely decompression has been used to explain melting weakening due to melting has also been used to support channel flow models for extrusion of the ghs or alternatively to suggest it triggered a change in its critical taper in view of the variable nature of anatexis and of motion on the std it is likely that anatexis had only a second order effect in modulating strain distribution with little effect on the general history of deformation thus despite all kinds of local differences strain distribution over time was such that it maintained the well defined arc that characterizes this orogen this was likely the result of a self organized forward motion of the arc controlled by the imposed convergence history and energy conservation balancing accumulation of potential energy and dissipation independent of the presence or absence of melt

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

thermal constraints on the emplacement rate of a large intrusive complex the manaslu leucogranite nepal himalaya the emplacement of the manaslu leucogranite body nepal himalaya has been modelled as the accretion of successive sills the leucogranite is characterized by isotopic heterogeneities suggesting limited magma convection and by a thin 100 m upper thermal aureole these characteristics were used to constrain the maximum magma emplacement rate models were tested with sills injected regularly over the whole duration of emplacement and with two emplacement sequences separated by a repose period additionally the hypothesis of a tectonic top contact with unroofing limiting heat transfer during magma emplacement was evaluated in this latter case the upper limit for the emplacement rate was estimated at 3 4 mm year or 1 5 myr for 5 km of granite geological and thermobarometric data however argue against a major role of fault activity in magma cooling during the leucogranite emplacement the best model in agreement with available geochronological data suggests an emplacement rate of 1 mm year for a relatively shallow level of emplacement granite top at 10 km uninterrupted by a long repose period the thermal aureole temperature and thickness and the isotopic heterogeneities within the leucogranite can be explained by the accretion of 20 60 m thick sills intruded every 20 000 60 000 years over a period of 5 myr under such conditions the thermal effects of granite intrusion on the underlying rocks appear limited and cannot be invoked as a cause for the formation of migmatites

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

manaslu leucogranite a collision signature of the himalaya a model for its genesis and emplacement the manaslu pluton is one of 10 leucogranites that formed in the overthrusted higher himalaya after the indo eurasian collision field and analytical data indicate that the underlying migmatites of the tibetan slab may be where the leucogranitic melts were generated the himalayan crustal thrusting of a hot slab over a rather cold volcano sedimentary pile le fort 1975a provides the necessary release of fluids these fluids cross the main central thrust mct induce the partial anatexis of the overheated tibetan slab and produce a leucogranitic magma the emplacement of the magma at first is located along the main disharmonic plane above the mct between the infrastructure and the superstructure there it generates a convective hydrothermal system extending very far laterally according to the stratification of permeabilities progressive emplacement of the granite proceeds as the convected fluids including the fluids released by the saturated magma dissolve the mainly calcareous host rocks of tibetan sedimentaries a frozen image of this caving out progression is given by the extensive network of granitic dikes outside the pluton the two quite independant fluid cycles of the generation and of the emplacement were triggered or guided by the tectonics due to collision this two fold model dominated by fluid activity may be of importance for other leucogranites and granites

diapiric ascent of magmas through power law crust and mantle there has never been a convincing explanation of the way in which diapirs of molten granite can effectively rise through mantle and crust we argue here that this is mainly because the country rocks have previously been assumed to be newtonian and we show that granitoid diapirs rising through thermally graded power law crust may indeed rise to shallow crustal levels while still molten the ascent velocity of diapirs is calculated through an equation with the form of the hadamard rybczynski equation for the rise of spheres through newtonian ambient fluids this well known equation is corrected by factors dependent on the power law exponent n of the ambient fluid and the viscosity contrast between the drop and the ambient fluid these correction factors were derived from results reported in the fluid mechanical and chemical engineering literature for the ascent of newtonian drops through power law fluids the equation allows calculation of the ascent rates of diapirs by direct application of rheological parameters of rocks the velocity equation is numerically integrated for the ascent of diapirs through a lithosphere in which the temperature increases with depth the depth of solidification of the diapir is systematically studied as a function of the geothermal gradient buoyancy of the body solidus temperature of the magma and rheological parameters of the wall rock the results show that when the wall rock behaves as a power law fluid the diapir s ascent rate increases without a similar increase in the rate of heat loss in this way diapirs rising at 10 to 102 m yr can ascend into the middle or upper crust before solidification strain rate softening rather than thermal softening is the mechanism that allows diapirism to occur at such rates the thermal energy of the diapir is used to soften the country rock only at late stages of ascent the transport of magmas through the lower crust and mantle as diapirs is shown to be as effective as magmatic ascent through fractures

getting granite dikes out of the source region whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow various formulations are developed for a viscous fluid at temperature t sub m intruding a growing crack in an elastic solid the initial solid temperature equals t sub m at the source and decreases linearly with distance from the source if t sub m is the unique freezing temperature of the fluid dike growth is initially self similar and an essentially exact solution is obtained if t sub m is above the solidus temperature the solution is approximate but is designed to overestimate the distance the dike may propagate the ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness perhaps more intuitively one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus necessary for dikes to propagate far into subsolidus rock it is concluded that for reasonable material properties and source conditions most basalt dikes will have little difficulty leaving the source region but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus while these results can explain why granitic dikes are common near granitic plutons but rare elsewhere the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes nonetheless these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies

crustal generation of the himalayan leucogranites abstract detailed studies of the himalayan two mica leucogranites such as the manaslu pluton indicate that they have very uniform mineralogical petrological and structural characteristics one can relate their occurrence to the thickest zones of the underlying tibetan slab in these zones migmatization attains its greatest development and vertical extension the granite is emplaced at first along the main disharmonic plane above the main central thrust mct at the top of the tibetan slab infrastructure ductile deformation of the granite is variable the granite being syn to late kinematic with regard to the functioning of the mct major elements are very homogeneous except for na and k implying that p t conditions of melting were relatively uniform the melted material was of a similar composition over a vast volume and the percentage of melting was small 10 15 trace elements are highly variable some are characteristic for very evolved material ta rb cs u or show the link with the tibetan slab ba sr whilst others are problematic th ree ree and th abundances being much less in the granite than in the tibetan slab imply that they have been extracted during one of the main stages of formation possibly by monazite radiogenic pb sr nd and stable o isotopes are consistent with the origin of the granite from the tibetan slab however the heterogeneous sr isotopic ratios make age dating difficult and imply poor mixing or little fluid interaction during its evolution h isotope data indicate that magmatic compositions of the main body of the manaslu granite have been preserved late or post magmatic alterations are extremely local in the main pluton to the north another belt of two mica granites occurs whose characteristics are very similar to the high himalaya belt they were probably generated in a similar way during this recent intracontinental evolution

mechanisms of pluton emplacement and structural evolution of a 2 1 ga juvenile continental crust the birimian of southwestern niger abstract the 2 1 ga birimian terranes of southwestern niger consist of a granite greenstone association the structures of the greenstone belts result from the interference between pluton emplacement and regional transcurrent deformation sinistral n s strike slip faults ne sw trending schistosity the regional cleavage trend is observed to change in the vicinity of elliptical plutons cleavage trajectories bend around their contacts resulting in triple junctions at the pluton extremities and narrow aureoles of intense penetrative schistosity and high grade amphibolitefacies metamorphism are developed around them structural features of plutons suggest syntectonic emplacement and age data indicate that all plutons were emplaced between 2 16 and 2 10 ga the plutons are assembled in two distinct types of batholith elongated either parallel or perpendicular to the inferred regional shortening direction a batholith parallel to the inferred regional shortening direction dolbel batholith consists of km sized subcircular alkali granite plutons except for the southernmost one which is of a larger size and exhibits an elliptical shape with a nw se short axis parallel to the shortening direction crosscutting relationships indicate a progressively northward emplacement trend for those plutons internal fabrics generally correspond to layering and magmatic flow fabrics and accessorily to schistosity and shear zones which represent late stage plastic deformation restricted to the pluton margin batholiths which are perpendicular to the inferred regional shortening direction are composed of large elliptical plutons 500 to 5000 km 2 in area consisting mainly of granodiorite and covering 70 of the region the plutons never show crosscutting relationships but are moulded against each other their internal fabric corresponds to a solid state foliation it either dips towards the centre of the pluton funnel or teardrop shaped intrusions or is subhorizontal in the centre and vertical at the margin dome shaped intrusions the foliation and the geometry of the largest pluton tera pluton were acquired during pluton ascent and inflation whereas the geometry of later shear zones indicates that deformation in the pluton was then passively acquired at the final emplacement level due to regional deformation the contrast in both the orientation and structural features of the batholiths reflects distinct emplacement mechanisms the small alkali granite plutons resulted from magma injection within nw se fractures parallel to the inferred regional shortening direction whereas the granodiorite plutons are assumed to be emplaced as diapirs forceful intrusions with long axes perpendicular to the shortening direction these two intrusion mechanisms for plutons emplaced during the same deformation event and at the same crustal level are considered to reflect a local change in the rheological behaviour of the crustal segment studied in connection with the thermal effect induced by the large granodioritic plutons this vertical tectonic regime appears to be typical of palaeoproterozoic juvenile continental crust areas and related to an interplay between emplacement of tremendous volumes of granodioritic magma and a regional transcurrent deformation

experimental generation of volcanic pseudotachylytes constraining rheology volcanic systems are highly dynamic environments that comprise rocks and magmas which in the process of strain localisation e g in catastrophic flank collapse or dome building events are candidate materials for the occurrence of frictional melting and the formation of pseudotachylytes we evaluate the frictional behaviour of a plagioclase two pyroxene and glass bearing andesite and introduce an approach to constrain the rheology of frictional melts frictional slip at a rate of 1 3 m s under an axial stress of 1 5 mpa induces heating at a rate approximating 130 c per meter of slip and frictional melting of the andesite occurs at 1000 c which corresponds to a peak in shear stress with continuing displacement the shear stress decreases by 25 from the peak strength and stabilises while the temperature equilibrates to 1230 1290 c the shear stress for the system is congruent with a non arrhenian temperature dependent frictional melt rheology exhibiting a non newtonian viscosity evolving from approximately 104 2 to 103 4 pa s post experiment analysis show a gradation from 1 the host rock to 2 an extraordinary zone of unmelted yet viscously deformed material to 3 a thin outer region of chemically heterogeneous protomelts and to 4 an inner region of chemically homogeneous frictionally generated modified melt in the core of the slip zone we discuss the role and identification of frictional melting in volcanic systems and the implication of viscous remobilisation of magmatic plugs during frictional slip of glass bearing volcanic materials

the a type mount scott granite sheet importance of crystal magma traps the presence of rapakivi feldspar and of distinctive porphyritic texture of mount scott granite indicates a period of crystallization prior to final emplacement beneath an extensive penecontemporaneous rhyolite volcanic pile final crystallization conditions are interpreted to have been 50 mpa at depths 1 4 km based on stratigraphic constraints however geobarometry based on the al content of amphibole phenocrysts and comparison of granite compositions with phase relations in the sio2 naalsi3o8 kalsi3o8 ternary system both yield pressure estimates of 200 mpa these pressure estimates are interpreted as plumbing the depth of a temporary storage chamber at 7 8 km this depth coincides in this case both with the probable proterozoic basement cover contact and with the calculated brittle ductile transition at time of ascent of mount scott magma although rising magma that fed the preceeding voluminous carlton rhyolite apparently rose unimpeded past these horizontal anisotropies rising magma that formed mount scott granite temporarily paused at this depth based on magmastatic calculations we suggest that horizontal anisotropies e g brittle ductile transition become crustal magma traps where the magma driving pressure exceeds the lithostatic load when the anisotropy is encountered during rifting initial large influxes of magma may proceed passed crustal anisotropies but have the effect of increasing the relative magma driving pressure through reducing horizontal stress thus magma driving pressure may eventually exceed the lithostatic load at the depth of the brittle ductile transition thereby activating this crustal magma trap ponding of magma at the brittle ductile transition chokes the eruption such a pause in magma supply rate may permit a return to initial stress conditions and deactivate the crustal magma trap once again magma will rise to the surface initiating a new magmatic cycle

structural reconstruction and zonation of a tilted mid crustal magma chamber the felsic chemehuevi mountains plutonic suite structural relief resulting from middle tertiary extensional deformation in the chemehuevi mountains of california exposes a unique cross section through an extensive 280 km 2 calc alkalic compositionally zoned sill like granitic intrusion of late cretaceous age minimum estimates for emplacement pressure 4 to 6 kbar imply that the chemehuevi mountains plutonic suite was initially intruded at mid crustal depths and has undergone 10 to 15 of postemplacement tilting tectonic denudation and erosion reconstruction of the pre tertiary pre tilt configuration suggests that this metaluminous to peraluminous granitic suite exhibits crude normal vertical and temporal zonation from granodiorite to granite the zonation involves a decrease in age and an increase in silica away from the walls and roof the youngest and most evolved members being concentrated toward the center and floor of the intrusion the lower part of the intrusion had a flat floor which was penetrated by at least three feeder dikes providing magma to the chamber the chamber grew laterally in stages each pulse being more evolved than the preceding one structural reconstruction indicates that the roof is less than 1 km above the exposed top of the intrusion suggesting a tabular geometry with an aspect ratio of about 5 1 the magma apparently ponded along the contact between undeformed proterozoic basement above and subhorizontally foliated mylonitic gneisses below and was therefore structurally controlled this reconstruction provides information on the geometry of mesozonal intermediate to silicic magma chambers in addition the restoration provides a rare opportunity to observe crosscutting relations between different types of mid crustal structures thick mylonitic shear zones granitic intrusions and temporally unrelated detachment faults the geometry of which emphasizes the need for careful evaluation of seismic reflection profiles across complexly deformed and intruded continental crust

impact of isostatic land uplift and artificial drainage on oxidation of brackish water sediments rich in metastable iron sulfide this study examines the dynamics of sulfur and trace elements as co mo ni ti and zn when brackish water sediments unusually rich in metastable iron sulfide probably a mixture of mackinawite

water fluxed melting of the continental crust a review abstract water fluxed melting also known as fluid or water present melting is a fundamental process in the differentiation of continents but its importance has been underestimated in the past 20 years during which research efforts focused mostly on dehydration melting reactions involving hydrate phases in the absence of a separate aqueous phase the presence of a free aqueous phase in anatectic terranes influences all major physical and chemical aspects of the melting process from melt volumes viscosity and ability to segregate from rock pores to melt chemical and isotopic composition a review of the literature shows that melting due to the fluxing of aqueous fluids is a widespread process that can take place in diverse tectonic environments active tectono magmatic processes create conditions for the release of aqueous fluids and deformation driven transient high permeability channels capable of fluxing high temperature regions of the crust where they trigger voluminous melting water fluxed melting can be either congruent in regions at the water saturated solidus or incongruent at suprasolidus p t conditions incongruent melting reactions can give rise to peritectic hornblende or to nominally anhydrous minerals such as garnet sillimanite or orthopyroxene in this case the presence of an aqueous phase is indicated by a mismatch between the large melt fraction generated and the much smaller fractions predicted in its absence the relatively small volumes of aqueous fluids compared to that of rocks imply that melting reactions are generally rock buffered fluids tend to move upwards and down temperature however there are cases in which pressure gradients drive fluids up temperature potentially fluxing suprasolidus terranes crustal regions at conditions equivalent to the water saturated solidus represent a natural impediment to the up temperature migration of aqueous fluids because they are consumed in melting reactions in this case continued migration into supra solidus terranes take place through the migration of water rich melts thus melts become the transport agent of water into supra solidus terranes and responsible for water fluxed melting other processes such as the relatively rapid fluid migration through fractures also allow regional aqueous fluids to by pass the water saturated solidus fluid trap and trigger melting above solidus conditions when aqueous fluids or hydrous melts flux rocks at supra solidus conditions they equilibrate with the surroundings through further melting decreasing water activity and giving rise to undersaturated melts it is in these conditions that hornblende or anhydrous peritectic phases are stabilized unlike dehydration melting the melt fraction generated in this case is not limited by the water contained in hydrous minerals but by the volume of water added to the system unlike melting at the water saturated solidus these melts are capable of rising without freezing and do give rise to upper crustal granitic bodies

characteristics of long period microtremors and their applicability in exploration of deep sedimentary layers abstract applicability of long period microtremors in inferring subsurface structure is examined using measurements of microtremors in the northwestern part of the kanto plain in japan short term continuous measurements of long period microtremors at both sediment and basement sites were taken a spectral peak at a period of 4 to 5 sec is stable with time while peaks at periods less than 2 sec are time variant suggesting a variation of microtremor sources however it was found that the spectral ratio between vertical and horizontal microtremors ellipticity at each site is stable with time good agreement was found between ellipticities of microtremors at the sediment site and those computed for rayleigh waves in which the structure of the sediments beneath the site was taken into account we also found that the ellipticities of rayleigh waves in earthquake ground motions were consistent with those of the microtremors these comparisons provide strong evidence that long period microtremors in the area studied consist mainly of rayleigh waves the ellipticity of microtremors was investigated by observing microtremors at temporary observation sites in the kanto plain where the sediment thickness varied from 0 to 1 km the subsurface structures were deduced by trial and error fitting of observed ellipticities with theoretical ellipticities that were calculated assuming rayleigh waves these results show that ellipticity of long period microtremors is effective for deducing structure from microtremor data at a single site

seismotectonics of the lower cheliff basin structural background of the el asnam algeria earthquake the 1980 el asnam earthquake should be understood within its tectonic environment a seismotectonic map of the lower cheliff basin scale 1 500 000 has been synthesized from known geologic tectonic and seismological work on the region and from satellite photos the data set was integrated by a computer in order to handle different scales and projections several important tectonic features divide the region into 5 domains active faults and recent folds are consistent with a nnw sse direction of compression the cheliff basin is limited to the south by the relizane fault the basin is also crossed by three broken folds the eastern one being the one associated with the el asnam fault historical and instrumental seisinicity seems to be located at both ends of relizane fault it is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk a simple tectonic model is proposed

a world perspective on acid sulphate soils abstract generalizations about the morphology and genesis of acid sulphate soils at a regional scale are derived from a review of extensive though patchy soil survey data a general sequence of sedimentation accumulation of sulphides and burial of sulphitic material by peat or alluvium of low sulphide content and a parallel sequence of soil profile development are illustrated by examples of unripe sulphitic soils under a natural tidal regime artificially drained raw acid sulphate soils and ripe acid sulphate soils at various stages of development the world pattern has been driven mainly by postglacial sea level change but each regional pattern is determined by its unique sedimentary and geomorphological history distinctive patterns occur in deltas and estuaries and in humid and seasonally dry climates very extensive areas of ripe acid sulphate soils in areas that are not known to have experienced falls in relative sea level are ascribed to human activity forest clearance and soil erosion in catchments causing lower dry season river flows and piecemeal clearance of peat over the floodplains permitting the dry season water table to fall the implications for further agricultural development in other comparable areas include the absolute necessity to know the extent of potential acid sulphate soils and to maintain their water table above the sulphide datum most effective systems of management have been developed by farmers themselves but the sustainability of these systems is often doubtful due to their detrimental effects on the aquatic ecosystem

the gangotri granite garhwal himalaya laccolithic emplacement in an extending collisional belt the gangotri miocene leucogranite is composed of several laccoliths 6 7 km long 1 5 2 km thick which can be divided into two sets of lenses the southern lenses intruded in the lower part of the high himalaya sedimentary cover and the northern lenses intruded in an older porphyritic biotite bearing granite in both cases the magmatic fabric is commonly weak with no dominant stretching direction although a rough e w trend is present in the northern lenses the magnetic fabric is characterized by the fact that drastic changes in the direction in the magnitude of the magnetic parameters or in the fabric type planar or linear may take place over very short distances measurements of preferred orientations in thin sections indicate that the strain regime was largely dominated by a coaxial component for both sets of lenses in agreement with the large dispersion observed in both the field and magnetic lineations the comparison of the granite and host rock structures shows that the leucogranite emplacement dates the onset of the extensional tectonism in the high himalaya range and is not related to a southward directed thrust event associated with the main central thrust this is exemplified by the vertical attitude of the feeder dikes that intrude the metasedimentary rocks beneath die southern lenses the presence of these dikes indicates in turn that magma ascent occurred by fracture propagation the spatial disposition of the southern lenses could have resulted either from the disruption of a single laccolithic intrusion by crustal scale boudinage due to a northern gravity backslide of the top of the tibetan slab or from the intrusion of independent laccoliths the use of the elastic bending theory of pollard and johnson 1973 shows that in both hypotheses the current laccolith sizes are compatible with a laccolithic mode of magma emplacement however neither the density contrast between the magma and its enclosing rocks nor the lithological boundary between the tibetan slab and the overlying tibetan metasedimentary series controlled the level of magma emplacement rather flat lying collapse structures which intersected the upward propagating magma dikes are the most likely causes of magma arrest such a mechanism was favored by the schist rich lithology of the metasedimentary host rocks in addition field relationships indicate that the melt supply through the dike system was a continuous rather than pulsed process existing numerical treatments on the rates of magma transport through fractures show that in such a case the laccoliths could have been built in less than 100 years this short time of emplacement the small size of the laccoliths and their peripheral disposition relative to the badrinath granite suggest that the gangotri lenses may represent the initial stage of pluton accretion in the high himalaya which ultimately gave rise to a much larger massif such as the manaslu granite

viscosity of andesite melts and its implication for magma mixing prior to unzen 1991 1995 eruption abstract the viscosity of an iron bearing melt with composition similar to unzen andesite was determined experimentally in the high 10 9 10 10 5 pa s and low 5 1000 pa s viscosity range using a parallel plate viscometer and the falling sphere method respectively falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 k and 200 to 2000 mpa creep experiments were performed in the temperature range of 747 845 k at 300 mpa the water content of the melt varies from nominally dry to 6 2 wt h 2 o the fe 2 fe tot ratio was determined for each sample in the quenched glass using a colorimetric method pressure has minor influence on the viscosity compared with the effect of temperature water content main compositional parameter controlling the viscosity or with the fe 2 fe tot ratio especially important at low water content of the melt based on our new viscosity data and literature data with measured fe 2 fe tot ratio we propose a new empirical equation to estimate the viscosity in pa s of andesitic melts as a function of temperature t in k water content w in wt and fe 2 fe tot ratio the derived relationship reproduces the experimental data 87 in total in the viscosity range from 10 0 5 to 10 13 pa s with a 1 standard deviation of 0 17 log units however application of this calculation model is limited to fe 2 fe tot fe tot 0 3 and to temperatures above t g moreover in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements the viscosity data are used to interpret mixing processes in the unzen magma chamber prior to 1991 1995 eruption we demonstrate that the viscosities of the rhyolite and andesite melts from the two end member magmas are nearly identical prior and during mixing enabling efficient magma mixing

introduction to special section mechanisms and consequences of melt segregation from crustal protoliths much of petrological effort has been concentrated on attempts to discern define and interpret regularly recurring patterns of igneous and metamorphic petrogenesis i do not wish to deny the existence of discernable order in petrological phenomena but every geological event is unique if we concentrate too heavily on discernment of order and pattern may we perhaps overlook or underrate the unique quality of each igneous or metamorphic episode possibly uniqueness may have as great significance as conformity to pattern when we attempt to fit the phenomena of petrology into the broad framework of geology francis j turner presidential address to the mineralogical society of america november 11 1969

importance of late magmatic and hydrothermal fluids on the sm nd isotope mineral systematics of hypersolvus granites abstract despite the significant impact of the sm nd radiometric system in various fields of isotope geochemistry very few attempts have been made to use it at the mineral scale in granite studies this approach has been used on two granites from the anorogenic province of corsica se france two statistically acceptable alignments were obtained in an isochron diagram for the hypersolvus fayalite bearing granite of mantelluccio alkali feldspar amphibole inclusion free zircon fluorite and fergusonite give an age of 331 10 ma whereas allanite whole rock amphibole and inclusion free zircon yield a significantly younger age at 291 13 ma the latter is validated by a zircon u pb age of 283 1 ma as the magmatic emplacement date of the granite the other alignment giving a 50 ma older age can be interpreted either as being inherited or more likely as the result of hydrothermal convection interacting with the country rocks at the end of granite crystallization the sm nd systematics of epidote records a second fluid rock event which probably occurred at least 200 ma after the emplacement of the granite extremely low 143 nd 144 nd ratio indicates that the epidote crystallized from a fluid that carried lanthanides in the crust over a distance of at least 1 km zircons with inclusions have a lower initial 143 nd 144 nd ratio than inclusion free zircons this feature is attributed to apatite and or zircon core inheritance through contamination during the ascent of the granitic melt in the crust two isochrons have been also obtained for the hypersolvus peralkaline granite of evisa amphibole fluorite sphene and fergusonite yield an age of 259 6 ma whereas the whole rock alkali feldspar and metamict zircon give an age at 209 14 ma in this case the former value is roughly in agreement with a possibly slightly rejuvenated whole rock rb sr date of 249 3 ma suggesting that it documents the magmatic crystallization age of the granite sm nd isotope systematics of the alkali feldspar metamict zircon and possibly allanite were re equilibrated during an important hydrothermal event that affected western europe in early jurassic times in both examples however it appears that the whole rock nd isotopic signatures were not strongly affected by the various fluid rock events indicating that they can still be used for petrogenetic investigations in contrast these results show that like k ar and rb sr the sm nd systematics of minerals with weak resistance to post magmatic processes can be used to trace and date hydrothermal events

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

mesoscale pervasive felsic magma migration alternatives to dyking abstract this paper reviews the literature on dyking as a mechanism of felsic magma extraction from a source and transport to shallower crustal levels and review the recent literature suggesting a range of alternative mechanisms of magma migration in hot crustal zones which produce mesoscale pervasive granite sheet intrusions recent papers have strongly favoured dyking as the main mechanism controlling magma migration however the initiation of dykes from a felsic magma source is fraught with difficulties even when magma is immediately available for transportation as in magma chambers within a partially molten source magma may reside in a range of structures with a wide range of shapes sizes and degrees of connectivity whereas the growth of individual dykes within a partially molten zone and the self propagation of large dykes into subsolidus crust have both been studied in some detail little attention has been given to the crucial intermediate step of the growth of a dyke network capable of producing wide crustal scale dykes the rarity of granite dyke swarms suggests that if dyking is the preferred mechanism of magma transport felsic magma sources produce only few major transporting dykes during their lifetime alternatively dyking is not an important mechanism the parameters controlling the volume of the catchment drained by one such dyke as well as other basic geometrical parameters controlling the structure of the dyke network within the source are unknown the ability of dyking to drain a partially molten source depends crucially on these variables and particularly on the horizontal permeability of the source the slow velocity of viscous felsic magmas traveling in rock pores implies that magma drained during dyking is mostly that previously extracted from the pores and resident in irregular magma bodies or dyke networks the observation that large volumes of buoyant magma are commonly present in migmatite zones and that dyking in these zones plays a secondary role suggest that dyking is inefficient and is able to extract only a fraction of the total melt available in the source in support of this conclusion recent detailed studies of exhumed hot crustal zones have revealed a range of alternative migration mechanisms characterized by mesoscale pervasive magma flow outcrop scale as opposed to porous flow pervasive migration gives rise to magma sheets preferentially emplaced parallel to high permeability zones such as foliation or bedding planes apart from local dyking three alternative mechanisms have been proposed to account for pervasive migration of magmas namely tectonic pumping magma wedging into low viscosity rocks and volatile driven intrusion because of their unfocused pervasive character these mechanisms are restricted to hot crust where magmas are not exposed to rapid freezing a model is proposed whereby heat advected with the magma pushes crustal geotherms upwards allowing pervasive magma migration to shallower depths

sedimentary iron geochemistry in acidic waterways associated with coastal lowland acid sulfate soils abstract we examined the solubility mineralogy and geochemical transformations of sedimentary fe in waterways associated with coastal lowland acid sulfate soils class the waterways contained acidic ph 3 26 3 54 fe iii rich 27 138 m surface water with low molar cl so 4 ratios 0 086 5 73 the surficial benthic sediments had high concentrations of oxalate extractable fe iii due to schwertmannite precipitation kinetically favoured by 28 30 of aqueous surface water fe being present as the fe iii so 4 species subsurface sediments contained abundant pore water hco 3 6 20 mm and were reducing eh ii concentrations were high 2 mm and were constrained by precipitation dissolution of siderite the near neutral reducing conditions also promoted so 4 reduction and the formation of acid volatile sulfide avs the results show for the first time for class associated waterways that sedimentary avs consisted mainly of disordered mackinawite in the presence of abundant pore water fe ii precipitation dissolution of disordered mackinawite maintained very low i e ii concentrations such low concentrations of s ii caused slow rates for conversion of disordered mackinawite to pyrite thereby resulting in relatively low concentrations of pyrite 1 as fe compared to disordered mackinawite up to 590 mol g 1 as fe this study shows that interactions between schwertmannite goethite siderite disordered mackinawite and pyrite control the geochemical behaviour of sedimentary fe in class associated waterways

iron and aluminum hydroxysulfates from acid sulfate waters acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite chalcopyrite pyrrhotite and marcasite in rocks soils sediments and industrial wastes this spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits the formation of acid sulfate soils and the mobilization and release of acidity and metals to surface and ground waters the purely natural process of acid rock drainage is often intensified by human activities related to mining mineral processing construction soil drainage and dredging geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water and to microbes that catalyze the reaction process large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation hydrolysis and neutralization the objective of this chapter is to describe the formation properties fate and environmental implications of the nano to microphase hydroxy sulfates of fe and al that are precipitated from acid sulfate waters these minerals are commonly of poor crystallinity and difficult to characterize much remains to be learned about their occurrence formation and properties mine drainage the best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited ash et al 1951 barton 1978 nordstrom 1982a rose and cravotta 1998 nordstrom and alpers 1999 there may be as many as 500 000 inactive or abandoned mine sites in the united states alone lyon et al 1993 although most of these pose no immediate water quality problem kleinmann 1989 estimated that about 19 300 km of streams and more than 72 000 ha of lakes and reservoirs have been

on the relationship between dike width and magma viscosity on the basis of measurements of bulk rock and phenocryst chemical compositions phenocryst content and estimation of water content and magma temperature the magma viscosity of 44 dikes from oki dozen and tango southwest japan and ocros peruvian andes was estimated to examine a relationship between viscosity and dike width the results show that magma viscosity increases with dike width mafic magmas with viscosities of 101 102 pa s form dikes l m wide while felsic magmas with viscosities of 106 107 pa s form dikes 100 m wide this indicates that magma viscosity as well as magma driving pressure and host rock stiffness are important factors in explaining the variation of dike width because magma viscosity is a measure of internal friction the magmatic force required to widen the fracture during hydrofracturing is proportional to viscosity on the basis of the range of chemical composition of the studied samples dike widths formed by highly viscous felsic magma should be of the order of 100 m maximum furthermore the observed basaltic dike width variations from various tectonic settings indicate that the effective factor on driving pressure of dike magma may be not magma pressure but compressive stress on the other hand dikes derived from low viscosity basaltic magma and exceeding 100 m width may be formed by extremely high magma pressure associated with flood basalt volcanism this is supported by 1 the observation that a rifting event with decreased compressive stress was not always associated with the volcanism and 2 the inferred effusion rates for this type of volcanism are anomalously high suggesting increased magma pressure in addition the active magma generation and the decreased host rock stiffness by locally anomalous thermal conditions like a hotspot phenomenon may assist flood basalt volcanism or emplacement of anomalously wide mafic dikes

the geochemistry during management of lake acidification caused by the rewetting of sulfuric ph 4 acid sulfate soils abstract understanding the geochemistry and kinetics of acidification events arising from acid sulfate soils is important to enable effective management and risk assessment large scale exposure and oxidation of acid sulfate soils occurred during a drought in the lower lakes murray darling basin of south australia we examined the geochemical changes that occurred in one region boggy lake that experienced surface water acidification and was subsequently neutralised via aerial limestone caco3 dosing and dilution via natural lake refill very low ph

secondary sulfate minerals associated with acid drainage in the eastern us recycling of metals and acidity in surficial environments weathering of metal sulfide minerals produces suites of variably soluble efflorescent sulfate salts at a number of localities in the eastern united states the salts which are present on mine wastes tailings piles and outcrops include minerals that incorporate heavy metals in solid solution primarily the highly soluble members of the melanterite rozenite epsomite halotrichite and copiapite groups the minerals were identified by a combination of powder x ray diffraction xrd scanning electron microscopy sem and electron microprobe base metal salts are rare at these localities and cu zn and co are commonly sequestered as solid solutions within fe and fe al sulfate minerals salt dissolution affects the surfacewater chemistry at abandoned mines that exploited the massive sulfide deposits in the vermont copper belt the mineral district of central virginia the copper basin ducktown mining district of tennessee and where sulfide bearing metamorphic rocks undisturbed by mining are exposed in great smoky mountains national park in north carolina and tennessee dissolution experiments on composite salt samples from three minesites and two outcrops of metamorphic rock showed that in all cases the ph of the leachates rapidly declined from 6 9 to b3 7 and specific conductance increased gradually over 24 h leachates analyzed after 24 h dissolution experiments indicated that all of the salts provided ready sources of dissolved al n30 mg l 1 fe n47 mg l 1 sulfate n1000 mg l 1 and base metals n1000 mg l 1 for minesites and 2 mg l 1 for other sites geochemical modeling of surface waters mine waste leachates and salt leachates using phreeqc software predicted saturation in the observed ochre minerals but significant concentration by evaporation would be needed to reach saturation in most of the sulfate salts periodic surface water monitoring at vermont minesites indicated peak annual metal loads during spring runoff at the virginia site where no winter long snowpack develops metal loads were highest during summer months when salts were dissolved periodically by rainstorms following sustained evaporation during dry spells despite the relatively humid climate of the eastern united states where precipitation typically exceeds evaporation salts form intermittently in open

impact of acid sulfate soils on the geochemistry of rivers in south western finland large areas of acid sulfate as soils are located along the coastal plains of finland and previous studies have shown that after reclamation they release extreme quantities of metals to watercourses in mid western and northern finland in this study on streams of south western finland where little information about as soils is available these soils were found to exhibit the same pattern of elevated metal and sulfate concentrations as in the notorious as soil landscapes of mid western finland meteorologically hydrologically driven temporal variations of these elements were great in the most affected streams there were also significant positive implications regarding future environmental work as soils in the highlighted region were found to cause sudden temporal influxes of acidic water only in the most affected streams indicating that the overburden and soils of the area discharge well buffered water moreover it was indicated that the high less toxic metal concentrations are largely caused by erosion of suspended phyllosilicates 0 45 m from farmland rather than by as soils

oxygenation of acid sulfate soils stimulates co2 emission roles of acidic dissolution and hydroxyl radical oxidation abstract emission of co2 from acid sulfate soil regions has received great attention in recent years production of co2 due to microbial respiration has been documented by previous studies but the abiotic mechanisms are poorly understood in this study co2 production was measured from oxygenation of 60 acid sulfate soil samples that were collected from a typical acid sulfate soil region the soil samples were characterized by low ph 3 3 5 8 and high sulfate content 0 51 5 03 mg g the cumulative concentrations of co2 were 0 76 54 54 mol per g dry soil upon oxygenation for 24 h when 0 1 hgcl2 was added into soil suspension to kill microbes the yield of co2 decreased by 8 7 41 1 which suggests that both microbial respiration and abiotic pathways contributed to co2 production and abiotic pathway played a major role both acidic dissolution and hydroxyl radical oh oxidation were identified to be the abiotic mechanisms for co2 production for acidic dissolution co2 was produced from the decomposition of carbonate by h generated production of co2 from acidic dissolution was dependent on the content of carbonate and the generation of h a combination of fe speciation sequential extraction and kinetic model shows that h was mainly generated from the oxidation of both fe2 and pyrite by o2 for oh oxidation co2 was produced from the oxidation of organic carbon by oh produced and its relative importance for co2 production was estimated to be 14 6 27 6 oh was mainly produced from exchangeable fe ii oxidation in sulfuric horizon but from pyrite oxidation in potential acid sulfate soils this study presents the overlooked abiotic mechanisms acidic dissolution and oh oxidation for co2 emission in acid sulfate soils when perturbed by o2 our findings implicate that contribution of microbial respiration for co2 production is not as large as previously thought to be in acid sulfate soils and instead abiotic mechanisms contribute largely particularly for oxygenation of potential acid sulfate soils

wetting behavior of partial melts during crustal anatexis the distribution of hydrous silicic melts in polycrystalline aggregates of quartz the equilibrium distribution of hydrous silicic melts in polycrystalline aggregates of quartz was characterized in a series of partial melting and melt distribution experiments in the systems quartz albite orthoclase h2o and quartz anorthite h2o at 650 to 1000 mpa and 800 to 900 c near equilibrium textures in these experiments are characterized by very low quartz quartz melt wetting angles and by a substantial number of thin melt films along grain boundaries wetting angles in the h2o saturated experiments are as follows 18 at 800 c 1000 mpa and 12 at 900 c 1000 mpa in the granitic system 18 at 850 c 650 mpa 15 at 900 c 650 mpa and 15 at 900 c 1000 mpa in the quartzanorthite system in the granitic system at 900 c 1000 mpa a decrease of h2o content in melt from 17 wt at saturation to 6 wt results in a slight increase of wetting angle from 12 to 16 these low wetting angles and the observation that many grain boundaries are wetted by melt films indicate that the ratio of quartz quartz to quartz melt interfacial energies ss s1 is high 2 secondary electron imaging of fracture surfaces of melt poor samples provided a three dimensional insight into the geometry of melt at low melt fraction melt forms an interconnected network of channels along grain edges as predicted for isotropic systems with wetting angles below 60 this high permeability geometry suggests that the segregation of granitic melts is not as sluggish as previously anticipated simple compaction calculations for a permeability range of 10 12 to 10 9 m2 indicate that segregation may operate at low to moderate melt fractions below 30 vol within relatively short time scales i e 105 to 106 years quartzmelt textures show significant deviations from the equilibrium geometries predicted for isotropic partially molten systems the most consistent deviation is the pervasive development of crystallographically controlled planar faces of quartz these faces provide definitive evidence for non isotropic quartz melt surface energy for most silicates other than quartz the grain scale distribution of partial melts deviates even more significantly from equilibrium distributions in isotropic systems accordingly in order to describe adequately melt distributions in most natural source regions the equilibrium model should be modified to account for anisotropy of solid liquid interfacial energy

isotopic study of the manaslu granite himalaya nepal inferences on the age and source of himalayan leucogranites a detailed isotopic study of the manaslu leucogranite was carried out a u pb age of 25 ma and a whole rock rb sr age isochron of 18 ma were obtained suggesting that the magmatic activity lasted at least 7 ma initial sr isotopic ratios are very high 0 740 to 0 760 and initial nd isotopic ratios are low nd in 13 to 16 and they show the existence of large isotopic variations even at the metre scale these are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes e g fusion mixing by convection these results also support the crustal origin of this leucogranite the tibetan slab paragneisses whose sr and nd isotopic ratios are very similar to those of the granite at an age of 20 ma are the most probable parental material nd model ages for both the leucogranite and the gneisses are in the range 1 5 2 ga a model of formation of the manaslu granite by coalescence of different batches of magma is in agreement with the present data

basement topography of the kathmandu basin using microtremor observation abstract kathmandu valley an intermontane basin of the himalaya has experienced many destructive earthquakes in the past the observations of the damage pattern during the 1934 earthquake m w 8 1 in particular suggest that the spectral ground amplification due to fluvio lacustrine sediments plays a major role in intensifying the ground motion in the basin it is therefore imperative to conduct a detailed study about the floor variation of sediments in the basin in this paper a preliminary attempt was made to estimate the thickness of soft sediment in the kathmandu basin using microtremor observations the measurements of microtremors were carried out at 172 sites spaced at a grid interval of 1 km the results showed that the predominant frequency varies from 0 488 hz to 8 9 hz a non linear regression relationship between resonance frequency and sediment depth was proposed for the kathmandu basin the thickness of lacustrine sediments at various points in the basin was estimated using the proposed equation and then the estimated thickness was used to plot a digital elevation model of the basement topography and cross profiles of the sediment distribution in the basin the results were validated by correlating the estimated sediment thickness with geology and geomorphology of the study area

kinematic implications of regional 40ar 39ar ages east central nepal abstract this study presents new 40ar 39ar ages from across the himalaya in east central nepal 40ar 39ar ages from the mahabharat region the southernmost and structurally lowest part of the study area range between 27 5 and 17 3 ma while those from the high himalaya the northernmost and structurally highest part of the study area range from 17 7 to 17 4 ma these two areas bracket a middle portion characterized by younger ages that range between 8 6 and 14 3 ma and cluster around 10 ma these new dates outline a u shaped pattern across the region that is interpreted to reflect cooling facilitated by out of sequence motion across the upper tama kosi thrust in agreement with previous work in the area the results presented herein are also consistent with published model cooling predictions and highlight the potential importance of late lower temperature deformation on the present geometries of the exhumed former metamorphic core exposed mountain belts around the globe

characterization of the sedimentary cover of the zafarraya basin southern spain by means of ambient noise the sedimentary structure in the zafarraya basin located in the south of spain is studied by using the horizontal to vertical spectral ratio hvsr for ambient noise to improve the reliability of the results the stability of the hvsr measurement was checked by using a time dependent analysis of the noise records taking into account only clear peaks the resonant frequency varies through the basin and does not ever coincide with the maximum of the horizontal power spectrum several fits between the frequency of the main peak in the hvsr for microtremors and the depth to the bedrock are obtained for data from 17 sites where geotechnical information was available the relation derived using a scheme based on surface waves was considered to be the most reliable one thus a function describing the average velocity versus depth for the sedimentary cover of the basin is also derived under assumptions of lateral homogeneity and smooth vertical variations of velocity due to age and or confining pressure the measurement of microtremors at 86 uniformly distributed points provides a map of the sedimentary thickness based on the previously calculated relationships showing values greater than 200 m at the deeper zones

emplacement of himalayan leucogranites by magma injection along giant sill complexes examples from the cho oyu gyachung kang and everest leucogranites nepal himalaya abstract the upper part of the high himalayan slab in north central nepal is comprised of a thick layer parallel sheet of biotite muscovite tourmaline garnet sillimanite cordierite leucogranite up to 3 4 km thick and dipping north at 5 20 these strongly peraluminous magmas were emplaced into high temperature low pressure sillimanite and cordierite bearing gneisses calc silicates and rare amphibolites which were metamorphosed at temperatures of 600 650 c some time during the oligocene early miocene parallel stringers of black xenolithic gneisses within the leucogranites suggest passive magmatic intrusion along fractures parallel to the schistosity in the country rocks in the mountains of cho oyu gyachung kang pumori lingtren and the base of the everest massif these leucogranites form part of a single structural horizon bounded at the top by the lhotse detachment the lower of two n dipping normal faults of the south tibetan detachment std system and below by the khumbu thrust kt an out of sequence fault which was partly responsible for the uplift erosion and exhumation of the leucogranites a model for the emplacement of these leucogranites is proposed where they represent viscous minimum melts produced by melting of a pelitic protolith similar to the underlying sillimanite grade gneisses through muscovite breakdown either during fluid absent melting at

profiling of late tertiary early quaternary surface in the lower reaches of narmada valley using microtremors abstract in this paper we propose the first approximation for thickness of quaternary sediment and late quaternary early tertiary topography for the part of lower reaches of narmada valley in a systematic way using the shallow seismic method that records both horizontal and vertical components of the microtremor ambient noise caused by natural processes the measurements of microtremors were carried out at 31 sites spaced at a grid interval of 5 km s using lennartz seismometer 5 s period and city shark ii data acquisition system the signals recorded were analysed for horizontal to the vertical h v spectral ratio using geopsy software for the present study we concentrate on frequency range between 0 2 hz and 10 hz the thickness of unconsolidated sediments at various sites is calculated based on non linear regression equations proposed by ibs von seht and wohlenberg 1999 and parolai et al 2002 the estimated thickness is used to plot digital elevation model and cross profiles correlating with geomorphology and geology of the study area

the metamorphism in the central himalaya all along the himalayan chain an axis of crystalline rocks has been preserved made of the higher himalaya crystalline and the crystalline nappes of the lesser himalaya the salient points of the metamorphism as deduced from data collected in central himalaya central nepal and kumaun are 1 the higher himalaya crystalline also called the tibetan slab displays a polymetamorphic history with a first stage of barrovian type overprinted by a lower pressure and or higher temperature type metamorphism the metamorphism is due to quick and quasi adiabatic uplift of the tibetan slab by transport along an mct ramp accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover the resulting metamorphic pattern is an apparent diachronic inverse zonation with the sillimanite zone above the kyanite zone 2 conversely the famous inverted zonation of the lesser himalaya is basically a primary pattern acquired during a one stage prograde metamorphism its origin must be related to the thrusting along the mct with heat supplied from the overlying hot tibetan slab as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust 3 thermal equilibrium is reached between units above and below the mct far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the tibetan slab during the second metamorphic stage but closer to the mct front the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the tibetan slab

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

high resistant sand injected marl and low resistant damaged marl to locate and characterize the thenia fault zone in boumerdes city north central algeria the purpose of this study was to locate and characterize the thenia fault zone tfz in the urban area of boumerdes city geological and electrical resistivity tomography surveys have targeted the plaisancian marl and its quaternary cover as a whole data indicate a complex near vertical fault zone with an asymmetric and zoned internal structure of at least 150 m wide and with a straight n120 overall trending the fault zone is traversed with two elongated parallel fault branches fb1 and fb2 generally 70 m distant from each other these fault branches locate two intense damage zones idzs of 10 15 m thick each situated at the margin of two damage zones each having a thickness of several tens of meters downward sand injections into idzs during pleistocene epoch possible pulverization of plaisancian marl rocks systematic deflection of actual stream channels and vertical displacement of at least 30 m affecting quaternary alluvial deposits show that the area would have undergone active tectonic driven by the tfz

microtremor measurements used to map thickness of soft sediments the observations about the behavior of microtremor spectra presented here show that noise measurements can be used as a powerful tool to determine the thickness of soft cover layers the most suitable method for this determination is nakamura s technique which is the ratio of the horizontal component noise spectrum and that of the vertical component i i v spectrum the frequency of the main peak in these spectral ratios correlates well with the sediment thickness at the site using an extensive database of microtremor measurements carried out in the western lower rhine embayment germany it was possible to show that this correlation is clearly valid for a wide range of thickness namely from tens of meters to more than 1000 m a simple formula was derived that for the sediments to be found in the area investigated directly calculates the cover thickness from the frequency of the main peak in the h v spectrum a comparison with calculated resonant frequencies sug gests the relation derived from the noise measurements depending on the velocity depth function of the shear wave classical spectral ratios are shown to be strongly influenced by the noise level and are therefore less reliable in determining the res onant frequency of the subsoil the practical relevance of the investigation is illus trated by means of cross sections constructed from results of the microtremor anal yses which provide a convincing image of the surficial structure of the areas investigated

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses

characterization of limestone reacted with acid mine drainage in a pulsed limestone bed treatment system at the friendship hill national historical site pennsylvania usa abstract armoring of limestone is a common cause of failure in limestone based acid mine drainage amd treatment systems limestone is the least expensive material available for acid neutralization but is not typically recommended for highly acidic fe rich waters due to armoring with fe iii oxyhydroxide coatings a new amd treatment technology that uses co2 in a pulsed limestone bed reactor minimizes armor formation and enhances limestone reaction with amd limestone was characterized before and after treatment with constant flow and with the new pulsed limestone bed process using amd from an inactive coal mine in pennsylvania ph 2 9 fe 150 mg l acidity 1000 mg l caco3 in constant flow experiments limestone is completely armored with reddish colored ochre within 48 h of contact in a fluidized bed reactor effluent ph initially increased from the inflow ph of 2 9 to over 7 but then decreased to 6 during operation limestone removed from a pulsed bed pilot plant is a mixture of unarmored rounded and etched limestone grains and partially armored limestone and refractory mineral grains dolomite pyrite the 30 of the residual grains in the pulsed flow reactor that are armored have thicker 50 to 100 m more aluminous coatings and lack the gypsum rind that develops in the constant flow experiment aluminium rich zones developed in the interior parts of armor rims in both the constant flow and pulsed limestone bed experiments in response to ph changes at the solid solution interface