early archean crust in bastar craton central india a geochemical and isotopic study abstract high a12o3 trondhjemitic gneisses occur in enclaves within granites at markampara in the bastar craton central india these gneisses exhibit a highly fractionated rare earth element ree pattern frsol la yb n 60 83 and may have been produced by partial melting of an amphibolitic protolith a zircon u pb age of 3509 14 7 ma dates primary crystallization of the trondhjemites a granite surrounding the gneissic enclaves yields a zircon u pb age of 2480 3ma rb sr wholerock data for the trondhjemitic gneisses are somewhat disturbed and indicate initial 87 sr 86 sr ratios of 0 7016 pb isotopic data are poorly correlated and suggest a three stage evolution with an early period of high u pb growth 9 5 10 5 after emplacement at 3 5 ga followed by isotopic disturbance and u depletion at 2 5 ga during widespread magmatism and metamorphism loss of rb and other mobile elements may also have occurred at this time

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

structural architecture of the northern composite terrane the eastern ghats mobile belt india implications for gondwana tectonics abstract new data from structural mapping and tectonic evaluation in the northern parts of the eastern ghats mobile belt egmb north involving the interpretation of satellite images field traverses critical outcrop mapping and kinematic studies of macro as well as microstructures of the shear zone rocks together with the geometry and disposition of gondwana basins led to for the first time the elucidation of post grenvillian structural architecture of the terrane this helps in assessing the sequence of successive tectonothermal events that were responsible for the origin and progressive evolution of the permo carboniferous coal bearing sediments along the mahanadi rift that forms significant in the reconstruction models of east gondwana the composite terrane of high grade metamorphic rocks egmb north strikes e w in contrast to the regional ne sw trend of the egmb the structural architecture obtained from this study is controlled by the boundary shear zones and associated link shear zones the dextral kinematic displacements along the northern boundary shear zone nbsz as well as the mahanadi shear zone msz and koraput sonapur rairakhol shear zone ksrsz were derived from multi scale field based structural observations a n s structural cross section presents a crustal scale flower structure across the composite terrane exposing different domains displaying distinctive internal structures with widely varying different geological evolution history and strain partitioning separated by crustal scale shear zones deep seismic imaging and gravity signatures support flower structure model the pervasive first formed gneissic fabrics were continuously reworked and partitioned into a series of e w crustal scale shear zones the neoproterozoic regional dextral transpressional tectonics along the shear zones and their repeated reactivation could be responsible for initiation and successive evolution of gondwana basins and different episodes of sedimentation available geochronological data shows that the structural architecture presented here is post grenvillian which has been repeatedly reactivated through long lived transpressional tectonics the composite terrane is characterized by all the typical features of an oblique convergent orogen with transpressional kinematics in the middle to lower crust the kinematic changes from transpression to transtensional stresses were found to be associated with global geodynamics related to the transformation from rodinia to gondwana configuration

an integrated study of anomalies observed before four major earthquakes 2004 sumatra m9 3 2006 pingtung m7 0 2007 chuetsu oki m6 8 and 2008 wenchuan m8 0 abstract in this paper we cross examine anomalies before four major earthquakes sumatra indonesia 2004 12 26 m9 3 pingtung taiwan 2006 12 26 m7 0 2 chuetsu oki japan 2007 7 16 m6 8 and wenchuan china 2008 5 12 m8 0 measurements of the crustal stress infrasonic wave and budgerigar jumping rate recorded at institute of earthquake prediction are used to monitor in the lithosphere and atmosphere while the total electron content over the four epicenters are employed to detect anomalies in the ionosphere these cross examinations allow us to have better understanding on the leading time of the four observed anomalies the earthquake preparation process and the lithosphere atmosphere ionosphere coupling before the earthquakes

a statistical investigation of preearthquake ionospheric anomaly 1 empirical evidence of the preearthquake ionospheric anomalies peias is reported by statistically investigating the relationship between variations of the plasma frequency at the ionospheric f2 peak fof2 and 184 earthquakes with magnitude m 5 0 during 1994 1999 in the taiwan area the peia defined as the abnormal decrease more than about 25 in the ionospheric fof2 during the afternoon period 1200 1800 lt significantly occurs within 5 days before the earthquakes moreover the odds of earthquakes with peia increase with the earthquake magnitude but decrease with the distance from the epicenter to the ionosonde station these results indicate that the peia is energy related

crustal evolution in south india constraints from nd isotopes nd isotope analyses from a range of lithologies including charnockites metasediments and granitoids that comprise the high grade terrain of south india define contrasting age provinces north of the palghat cauvery shear zone the karnataka craton and the granulite blocks of nilgiri and madras are characterized by model nd ages from 3 4 to 2 4 ga with significant crustal growth during the late archean south of the palghat cauvery shear zone a pan african granulite facies event resulted in sm nd fractionation as observed in several incipient charnockite localities model nd age calculations that allow for sm nd fractionation at 550 ma yield ages in the range of 2 9 to 1 3 ga this range compares closely with published model nd ages from the high grade terrain of sri lanka mid proterozoic crustal growth 1 1 ga observed in the vijayan complex of sri lanka may have provided source material for metasediments characterized by young model nd ages in southern peninsular india the palghat cauvery shear z

a differential equation for specific catchment area 1 analysis of the behavior of specific catchment area in a stream tube leads to a simple nonlinear differential equation describing the rate of change of specific catchment area along a flow path the differential equation can be integrated numerically along a flow path to calculate specific catchment area at any point on a digital elevation model without requiring the usual estimates of catchment area and width the method is more computationally intensive than most grid based methods for calculating specific catchment area so its main application is as a reference against which conventional methods can be tested this is the first method that provides a benchmark for more approximate methods in complex terrain with both convergent and divergent areas not just on simple surfaces for which analytical solutions are known preliminary evaluation of the d8 m8 digital elevation model networks demon and d methods indicate that the d method is the best of those methods for estimating specific catchment area but all methods overestimate in divergent terrain

late proterozoic charnockites in orissa india a u pb and rb sr isotopic study charnockite formation in the angul district of orissa took place between 1088 26 17 ma the u pb zircon upper intercept crystallization age of a leptynite neosome and 957 8 4 956 pm 4 ma the u pb zircon monazite upper intercept and u pb monazite crystallization ages of a granite confirmation of the proterozoic age of the charnockites is given by 1 a u pb zircon upper intercept 1159 h 59 30 ma age and a rb sr whole rock 1080 pm 65 ma age for an augen gneiss which pre dates the leptynite and 2 u pb monazite ages of 973 pm 5 964 pm 4 and 953 pm 4 ma for a gray quartzofeldspathic gneiss the augen gneiss and the leptynite respectively these late proterozoic dates are interpreted as representing ages recorded during charnockitization the ca 950 980 ma charnockite and granite forming events are related to the evolution of mantle derived co 2 bearing basic magma emplaced into the deeper levels of an extensional tectonic transcurrent fault regime the ca 1100 1150

growth of early archaean crust in the ancient gneiss complex of swaziland as revealed by single zircon dating abstract we present new single grain zircon ages derived from ion microprobe and evaporation analysis for rocks of the ancient gneiss complex agc of swaziland southern africa that enable us to document a more extended history of early archaean crustal growth in the eastern kaapvaal craton than previously documented the oldest rocks appear to be strongly flattened tonalitic trondhjemitic orthogneisses dated as 3644 4 ma compston and kroner 1988 which are in faulted contact with rocks of the barberton greenstone belt bgb in an agc enclave in northwest swaziland and which also record subsequent thermal metamorphic plutonic events at 3580 3500 3430 3200 and 3000 ma these rocks are tectonically interbanded with 3200 ma old granodiorites and k rich leucogranites thereby providing evidence for a severe and important post 3 2 ga deformation event that is also inferred for 3500 to 3200 ma old tonalitic to trondhjemitic gneisses in the agc of northeast swaziland in central swaziland zircons from the oldest tonalitic gneiss of the agc have an age of 3560 ma whereas younger additions of granitoid which also intrude the dwalile greenstone enclave in the agc record ages of 3450 3460 ma intense ductile deformation has repeatedly obliterated original intrusive contacts so that preserved field relationships often cannot resolve the above chronology chemical and whole rock isotopic data are consistent with derivation of some agc gneisses from mantle sources and thus imply very short crustal residence times for their granitoid precursors but this is not generally true for the entire agc we suggest that at least some gneisses resulted from intracrustal melting perhaps during crustal thickening events as recorded in granulite parageneses within the agc documentation of 3 5 ga or older granitoid crust in all major regions of the agc now exposed suggests the presence of continental terrains of up to at least 100 km in diameter before the barberton greenstone succession was deposited the combined geochronologic and structural metamorphic data for the agc and bgb reveal a complex history of growth and deformation for the eastern kaapvaal craton that lasted for at least 600 ma from 3 64 to about 3 ga ago the magmatic and tectonic evolution of the agc was broadly similar to that of the bgb and suggests that early archaean greenstone and gneiss terrains were coeval but formed and evolved in different settings and at different crustal levels our age data and the structural metamorphic evolution of the eastern kaapvaal craton are compatible with models suggesting crustal growth through vertical magmatic underplating and early crustal thickening uplift and erosion as a result of tectonic interleaving due to repeated horizontal shortening

high precision 207pb206pb zircon geochronology using a small ion microprobe abstract a small geometry ion microprobe cameca ims 4f has been successfully used for the routine measurement of 207 pb 206 pb ratios in individual zircons with a spatial resolution of 20 m in spite of the lower sensitivity of the small ion microprobe resulting from operating at high mass resolution m m 4600 in order to resolve isobaric molecular interferences we can discern archean components whose ages differ by 50 ma a single measurement requires 90 min of data acquisition thus a comprehensive study of a zircon population can be accomplished in a few days three sets of precambrian zircons analyzed earlier by other techniques yielded ages which are within 2 of their true values as our first unknown we analyzed zircons from a sample of orthogneiss collected from the aravalli craton of northwestern india for this sample we obtained a minimum age of 3281 3 ma 1 which we believe closely approximates the time of crystallization of the gneiss s igneous protolith

controls on gully formation following forest clearing in a humid temperate environment we have constructed a chronology of gully initiation forest clearing and rainfall events for gullies eroded into pine plantations near bombala southeastern australia over the last 15 years the chronology suggests that daily rainfall of 80 100 mm which has a recurrence interval of 1 4 2 years can initiate gully erosion on areas cleared of native forest within the previous year massive gully erosion was experienced from a daily rainfall of 200 mm with a recurrence of 10 15 years resistance to channel initiation effectively recovers within a year of disturbance allowing only a limited opportunity for erosion analysis of the spatial pattern of gully erosion using a digital elevation model shows that gullies were initiated across all landscape positions in contrast to previous studies there is no clear topographic threshold that limits the extent of the gully network we infer that the weak topographic threshold results from low resistance to scour allowing local flow convergence to dominate over topographic accumulation of flow although resistance to scour is low relative to previous studies a process threshold for gully initiation is still a useful simplification of the erosion processes for the soils that we studied the threshold for gully erosion relates to intense scour exposing erodible subsoils

high temperature crustal anatexis in a clockwise p t t path isotopic evidence from a granulite granitoid suite in the eastern ghats belt india the high grade metamorphic belt of the eastern ghats india displays polyphase deformation structures a complex metamorphic record and dehydration melting in different crustal protoliths high temperature melting in pelitic and greywacke like precursors in a clockwise p t path decompression and subsequent isobaric cooling have recently been described from the south central sector of this belt in this contribution high temperature melting has been dated at c 1162 ma by sm nd whole rock isotopic compositions of granitoids subsequent isobaric cooling could have occurred between 988 and 900 ma as indicated by u pb ages of zircon and monazite in pelitic granulites thus a prolonged orogenic cycle of at least 250 ma is envisaged additionally isotopic disequilibrium between whole rock and minerals in sapphirine granulites could have resulted from rapid melting and been further enhanced by a prolonged reaction history of the sapphirine granulite

hillslope runoff processes and models abstract hillslope hydrology is concerned with the partition of precipitation as it passes through the vegetation and soil between overland flow and subsurface flow flow follows routes which attenuate and delay the flow to different extents so that a knowledge of the relevant mechanisms is important in the 1960s and 1970s hillslope hydrology developed as a distinct topic through the application of new field observations to develop a generation of physically based forecasting models in its short history theory has continually been overturned by field observation thus the current tendency particularly among temperate zone hydrologists to dismiss all hortonian overland flow as a myth is now being corrected by a number of significant field studies which reveal the great range in both climatic and hillslope conditions some recent models have generally attempted to simplify the processes acting for example including only vertical unsaturated flow and lateral saturated flows others explicitly forecast partial or contributing areas with hindsight the most complete and distributed models have generally shown little forecasting advantage over simpler approaches perhaps trending towards reliable models which can run on desk top microcomputers the variety now being recognised in hillslope hydrological responses should also lead to models which take account of more complex interactions even if initially with a less secure physical and mathematical basis than the richards equation in particular there is a need to respond to the variety of climatic responses and to spatial variability on and beneath the surface including the role of seepage macropores and pipes which call into question whether the hillside can be treated as a darcian flow system

the structural setting of the chilka lake granulite migmatite anorthosite suite with emphasis on the time relation of charnockites abstract the granulites and anorthosites occurring around chilka lake in orissa display polyphase deformation structures which have been utilized to constrain the deformation history and the time relation between the rock units the granulites are represented by metapelitic khondalites and migmatitic charnockite leptynite complexes structural mapping complemented by examination of aerial photographs reveals imprints of three folding episodes the dominant ne sw tectonic trend was produced by the first folding f 1 with s 1 preserved in khondalites and charnockites the second episode of folding was tight coaxial with f 1 resulting in hook shaped folds described on the map scale by the khondalites in the leptynitic orthopyroxene free garnetiferous granite gneiss component of the migmatite complex s 1 is absent and the major structural grain is due to the gneissose banding s 2 the third folding affected the metapelites and the migmatite complex differently in the metapelites the f 3 folds which are asymmetric show a uniformly gentle plunge towards the ne nne and the dome basin patterns ascribed to f 3 by sarkar et al 1981 are not discernible in the migmatite complex these folds though nearly upright are disharmonic probably a consequence of a different rheology owing to the presence of melts the anorthosites register the imprint of f 3 only and are thus distinctly younger the retention of s 1 in the charnockite enderbite layers and lenses within composite charnockite leptynite exposures transposition of s 1 to the leptynitic foliation s 2 in several locales and the different orientation of s 1 in charnockite patches in the different limbs of f 3 folds are strong indications of the charnockites being older than the leptynites the charnockite measles occurring near the hinge regions of the f 3 structures cannot be construed as sites of in situ arrested charnockitization instead they are discontinuous relicts of charnockite layers which have been deformed torn and displaced we argue that separation of structures of different generations is necessary for a proper understanding of the field features taken to indicate arrested formation of charnockites in south india and elsewhere

seismoionospheric gps total electron content anomalies observed before the 12 may 2008 mw7 9 wenchuan earthquake 1 the global ionospheric map gim is used to observe variations in the total electron content tec of the global positioning system gps associated with 35 m 6 0 earthquakes that occurred in china during the 10 year period of 1 may 1998 to 30 april 2008 the statistical result indicates that the gps tec above the epicenter often pronouncedly decreases on day 3 5 before 17 m 6 3 earthquakes the gps tec of the gim and electron density profiles probed by six microsatellites of formosat3 cosmic f3 c are further employed to simultaneously observe seismoionospheric anomalies during an mw7 9 earthquake near wenchuan china on 12 may 2008 it is found that gps tec above the forthcoming epicenter anomalously decreases in the afternoon period of day 6 4 and in the late evening period of day 3 before the earthquake but enhances in the afternoon of day 3 before the earthquake the spatial distributions of the anomalous and extreme reductions and enhancements indicate that the earthquake preparation area is about 1650 km and 2850 km from the epicenter in the latitudinal and longitudinal directions respectively the f3 c results further show that the ionospheric f2 peak electron density nmf2 and height hmf2 significantly decreases approximately 40 and descends about 50 80 km respectively when the gps tec anomalously reduces

207pb 206pb zircon ages and the evolution of the singhbhum craton eastern india an ion microprobe study1this paper is dedicated to prof a k saha one of the senior co authors who passed away after submission of the paper 1 abstract we used an ion microprobe to measure 207 pb 206 pb ages of single zircons from four key lithologies from the singhbhum craton of eastern india detrital zircons from the oldest recognized sedimentary sequence of the craton the older metamorphic group yielded 3 5 3 6 ga ages indicating that crustal formation had already been initiated by 3 6 ga in this region this data also established an older limit of 3 5 ga for the age of sediment deposition the first appearance of extensive continental crust in the singhbhum region marked by the emplacement of the older metamorphic tonalite gneisses is dated at 3 44 ga our data from both of these units reveal that a 3 2 ga event induced overgrowths within each of these pre existing zircon populations we determine an age of 3328 7 ma for the singhbhum granite phase ii the most widespread of this granite s three phases the emplacement of the two phases of the mayurbhanj granite marking the youngest major episode of acid plutonism in this craton took place in rapid succession at 3 1 ga marking the broad scale stabilization of this terrain

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

early archaean continental crust in the eastern ghats granulite belt india isotopic evidence from a charnockite suite the eastern ghats granulite belt of india has traditionally been described as a proterozoic mobile belt with probable archaean protoliths however recent findings suggest that synkinematic development of granulites took place in a compressional tectonic regime and that granulite facies metamorphism resulted from crustal thickening the field petrological and geochemical studies of a charnockite massif of tonalitic to trondhjemitic composition and associated rocks document granulite facies metamorphism and dehydration partial melting of basic rocks at lower crustal depths with garnet granulite residues exposed as cognate xenoliths within the charnockite massif the melting and generation of the charnockite suite under granulite facies conditions have been dated c 3 0 ga by sm nd and rb sr whole rock systematics and pb pb zircon dating sm nd model dates between 3 4 and 3 5 ga and negative epsilon values provide evidence of early archaean continental crust in this high grade terrain

emplacement history of pasupugallu gabbro pluton eastern ghats belt india a structural study structural mapping of the pasupugallu pluton an elliptical intrusive gabbro anorthosite body emplaced into the western contact zone between the eastern ghats mobile belt and the archaean east dharwar craton along the east coast of india reveals concentric helicoidal and inward dipping magmatic and or tectonic foliations we identify a 1 km wide structural aureole characterized by pronounced deflection of regional structures into margin parallel direction mylonitic foliations with s c fabrics sigmoidal clasts moderately plunging stretching lineations non cylindrical intrafolial folds and stretched elliptical mafic enclaves in the aureole rocks our results suggest that the pluton emplacement is syn tectonic with respect to the regional ductile deformation associated with the terrane boundary shear zone at the western margin of the eastern ghats we present a tectonic model for the emplacement of the pluton invoking shear related ductile deformation rotation and a minor component of lateral expansion of magma the intrusive activity 1450 800 ma along the western margin of the eastern ghats can be correlated with the significant event of recurring mafic alkaline and granitic magmatism throughout the global grenvillian orogens associated with the continent continent collision tectonics possibly related to the amalgamation and the breakup of the supercontinent rodinia

a 2 5 ga porphyry cu mo au deposit at malanjkhand central india implications for late archean continental assembly abstract eight re os ages from six molybdenite samples representative of the cu mo au mineralization at the giant malanjkhand deposit in madhya pradesh were obtained using id ntims these data provide a clear late archean early paleoproterozoic age for this deposit and by implication for its calc alkaline granitoid host among other diverse models the origin of malanjkhand has been debated as orogenic lode style associated with development of a quartz reef in a shear zone or as porphyry style associated with a pink granitoid intrusion that is conspicuously present in the vicinity of the brittle ductile deformed quartz reef previous models included middle proterozoic ages for the cu mo au mineralization based on poorly constrained rb sr and k ar data direct dating of molybdenite shows that stringer mineralization in the quartz reef and disseminated and vein mineralization in the granite were contemporaneous at 2490 8 ma 2489 5 1 4 ma based on regression without uncertainty in the 187re decay constant mswd 0 5 n 5 additional molybdenite from the quartz reef dated at 2475 and 2450 ma represents at least two pulses of reworking that we suggest configured the elongate and arcuate quartz reef into its present position we suggest that the quartz reef is a high silica stockwork cap embedded in its primary potassic alteration halo and subsequently tilted so that it lies convex to the east with deeper levels exposed to the north petrographic evidence coupled with high re concentrations for molybdenites 400 650 ppm support this scenario and suggest that malanjkhand is a subduction related stockwork porphyry style cu mo au deposit involving mantle malanjkhand geology shares little affinity with three surrounding and tectonically juxtaposed terranes we suggest that the malanjkhand cu mo au deposit and the surrounding batholith containing multiple cu mo au prospects may be the vestiges of a microplate captured along the north margin of the nearly amalgamated southern indian craton at 2 5 ga as the southern craton began to converge with the northern indian craton or other protocontinents now embedded or consumed within the central indian tectonic zone citz this scenario could imply an early paleoproterozoic age for the earliest development of the citz at least in the region of the central indian shear suture cis whose marked ene trend imprints the northwestern part of the malanjkhand batholith and the cu mo au deposit based on a compilation of 2 5 ga events in both the southern and northern indian cratons we suggest that some units in the citz linked an extensive and continuous late archean early paleoproterozoic orogenic belt that may extend to the moyar bavali bhavani attur palghat and cauvery shear zones in southern india and include inboard units of the eastern ghats and the aravalli delhi orogenic belts robust geochronology that can be tied to the early history within these orogenic belts is scarce and extensive reworking during grenvillian and pan african time creates a pervasive overprint at some localities this late archean early paleoproterozoic belt preserves sutures within a coalesced late archean continent that included east antarctica napier and vestfold hills complexes at 2 5 ga

hornblende dehydration melting in mafic rocks and the link between massif type charnockite and associated granulites eastern ghats granulite belt india a massif type intrusive charnockite body in the eastern ghats granulite belt india is associated with hornblende bearing mafic granulite two pyroxene granulite and enderbitic granulite the charnockite is characterised by pervasive gneissic foliation s1 this is axial planar to the folded layers of hornblende bearing mafic granulite f1 folds indicating that the granulite protoliths were present before the development of s1 two pyroxene granulite and enderbitic granulite occur as lenticular patches disposed along the foliation and hence could be syngenetic to s1 the tonalitic to granodioritic metaluminous to weakly peraluminous compositions and relatively high sr rb of the charnockite are consistent with its derivation by partial melting of a mafic protolith strong y depletion lack of sr depletion and strongly fractionated ree patterns with high la yb n ratio but relatively lower hree gd lu fractionation with marked positive eu anomalies suggest major residual hornblende as well as garnet but not plagioclase consistent with the hornblende dehydration melting in the source rocks such a residual mineralogy is broadly similar to those of some of the hornblende bearing mafic granulite inclusions which have compositional features indicative of a restitic nature quantitative modelling supports an origin for the charnockite melts by partial melting of a hornblende rich mafic granulite source although source heterogeneity is very likely given the rather variable trace element contents of the charnockite the whole rock and mineral compositions of the two pyroxene granulites and enderbitic granulites are consistent with them representing peritectic phase segregations of hornblende dehydration melting a clockwise p t path implies that melting could have occurred in thickened continental crust undergoing decompression

a non conventional watershed partitioning method for semi distributed hydrological modelling the package aladhyn the extraction of the river network from a digital elevation model dem plays a fundamental role in modelling spatially distributed hydrological processes the present paper deals with a new two step procedure based on the preliminary identification of an ideal drainage network idn from contour lines through a variable mesh size and the further extraction of the actual drainage network and from the idn using land morphology the steepest downslope direction search is used to identify individual channels which are further merged into a network path draining to a given node of the idn the contributing area peaks and saddles are determined by means of a steepest upslope direction search the basin area is thus partitioned into physically based finite elements enclosed by irregular polygons different methods i e the constant and variable threshold area methods the contour line curvature method and a topologic method descending from the hortonian ordering scheme are used to extract the adn from the idn the contour line curvature method is shown to provide the most appropriate method from a comparison with field surveys using the adn one can model the hydrological response of any sub basin using a semi distributed approach the model presented here combines storm abstraction by the scs cn method with surface runoff routing as a geomorphological dispersion process this is modelled using the gamma instantaneous unit hydrograph as parameterized by river geomorphology the results are implemented using a project oriented software facility for the analysis of land digital hydrological networks aladhyn

a contour based topographic model for hydrological and ecological applications a digital model for discretizing three dimensional terrain into small irregularly shaped polygons or elements based on contour lines and their orthogonals is described from this subdivision the model estimates a number of topographic attributes for each element including the total upslope contributing area element area slope and aspect this form of discretization of a catchment produces natural units for problems involving water flow as either a surface or subsurface flow phenomenon the model therefore has wide potential application for representing the three dimensionality of natural terrain and water flow processes in the fields of hydrology sedimentology and geomorphology three example applications are presented and discussed they are the prediction of zones of surface saturation the prediction of the distribution of potential daily solar radiation and the prediction of zones of erosion and deposition in a catchment

gps detection of ionospheric perturbations following the january 17 1994 northridge earthquake sources such as atmospheric or buried explosions and shallow earthquakes producing strong vertical ground displacements are known to produce pressure waves that propagate at infrasonic speeds in the atmosphere at ionospheric altitudes low frequency acoustic waves are coupled to ionospheric gravity waves and induce variations in the ionospheric electron density using global positioning system gps data recorded by the permanent gps network operating in southern california we computed ionospheric electron content time series for several days preceding and following the january 17 1994 mw 6 7 northridge earthquake we observe an anomalous signal beginning several minutes after the earthquake with time delays that increase with distance from the epicenter the signal frequency and phase velocity are consistent with results from numerical models of atmospheric ionospheric acoustic gravity waves excited by seismic sources as well as previous electromagnetic sounding results we believe that these perturbations are caused by the ionospheric response to the strong ground displacement associated with the northridge earthquake

time resolved study of charge generation and propagation in igneous rocks electrical resistivity changes ground potentials electromagnetic em and luminous signals preceding or accompanying earthquakes have been reported many times in addition to ground uplift and tilt and other parameters however no concept exists that would tie these diverse phenomena together into a physically coherent model using low to medium velocity impacts to measure electrical signals with microsecond time resolution it is observed that when gabbro and diorite cores are impacted at relatively low velocities 100 m s highly mobile charge carriers are generated in a small volume near the impact point they spread through the rocks causing electric potentials exceeding 400 mv em and light emission as the charge cloud spreads the rock becomes momentarily conductive when a granite block is impacted at higher velocity 1 5 km s the propagation of the p and s waves is registered through the transient piezoelectric response of quartz after the sound waves have passed the surface of the granite block becomes positively charged suggesting the same charge carriers as observed during the low velocity impact experiments expanding from within the bulk during the next 2 3 ms the surface potential oscillates indicating pulses of electrons injected from ground and contact electrodes the observations are consistent with positive holes e g defect electrons in the o2 sublattice traveling via the o 2p dominated valence band of the silicate minerals the positive holes propagate as charge clouds rather than as classical em waves before activation they lay dormant in form of electrically inactive positive hole pairs php chemically equivalent to peroxy links o3x oo xo3 with x si4 al3 etc phps are introduced into the minerals by way of hydroxyl o3x oh which all nominally anhydrous minerals incorporate when crystallizing in h2o laden environments the fact that positive holes can be activated by low energy impacts and their attendant sound waves suggests that they can also be activated in the crust by microfractures during the dilatancy phase depending on where in the stressed rock volume the charge carriers are activated they will form rapidly moving or fluctuating charge clouds that can account for earthquake related electrical signals and em emission wherever such charge clouds intersect the surface high fields are expected causing electric discharges and earthquake lights

variations of ionospheric total electron content during the chi chi earthquake on 20 september1999 ut 21 septemberin local time lt a large earthquake mw 7 7 struck central taiwan nearthe small town of chi chi the greatest plasma frequency in the ionosphere fof2 observed by the chung li ionosonde 25 0 n 121 2 e reveals three clear precur sors at 1 3 and 4 days prior to the earthquake this paper examines the ionospheric total electron content tec ob served by a network of the global positioning system gps receivers in taiwan area it is found that variations in fof2 and overhead tec recorded at chung li have a similar ten dency combining the data of the network of 13 gps re ceivers time and spatial variations of tec prior to the chi chi earthquake are examined results show that the equa torial anomaly crest moves equatorward and its tec value significantly decreases 1 3 and 4 days before the earth quake a comparison between the disturbed and reference previous 15 day median days confirms that tec decreases significantly around the epicenter in the afternoons of these days finally possible mechanisms are proposed and dis cussed

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

neoarchean tectonothermal imprints in the rengali province eastern india and their implication on the growth of singhbhum craton evidence from zircon u pb shrimp data a detailed zircon u pb shrimp geochronological study of the amphibolite to granulite grade rocks of the rengali province of eastern india records the growth history of the southern margin of the singhbhum craton pelitic and mafic granulites from the gneissic belt exhibit contrasting styles of metamorphism zircon of the pelitic granulites from the eastern segment yields c 3528 3064 ma detrital ages charnockitic gneiss from the eastern segment has protolith age of 3058 15 ma while that from the central segment has protolith age of 2861 30 ma the latter rock records high grade metamorphism at 2818 15 ma hornblende gneiss from the central sector has a protolith age of 2828 9 ma deformed leucogranite in the central and undeformed granitoid in the eastern segment were emplaced at 2807 13 and 2809 13 ma respectively the protolith of felsic gneiss from the central sector was emplaced at 2776 24 ma most of the zircon samples contain overgrowths of c 2500 ma inferred to be the age of reworking of the gneissic belt our data suggest that the rengali province evolved as an orogenic belt in the neoarchean time c 2800 2500 ma during southward growth of the singhbhum craton these tectonothermal imprints at the margin of the singhbhum craton are possibly related to its inclusion within the supercontinent ur

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

proterozoic low pressure high temperature metamorphism and an anticlockwise p t t path for the hazeldene area mount isa inlier queensland australia in the hazeldene area situated in the mount isa inlier queensland the metamorphic grade changes from chlorite zone through biotite and cordierite zones to sillimanite k feldspar zone microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation s2 was replaced by biotite andalusite and sillimanite at the metamorphic peak late in s2 and in turn by kyanite chlorite adjacent to localized small post d2 shear zones although the anticlockwise p t t path is well defined the precise p t conditions are uncertain because of problems with experimental and thermodynamic data the best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600 c at 4 kbar the metamorphism has been dated at 1544 ma and was synchronous with a major crustal shortening event because proposed extensional events occurred more than 60 ma earlier their contribution to the peak metamorphic thermal perturbation would have been insignificant the syn metamorphic mica creek pegmatites the abundance of high heat producing elements in the nearby pre d2 sybella granite and advective heat by fluids which caused considerable metasomatism in the hazeldene area may have each contributed to the thermal budget however the metamorphic thermal gradient may be 80 c km 1 or higher strongly suggesting a local magmatic control as none are known in the area such syn metamorphic plutons would have to lie beneath the exposed high grade rocks

observation of abnormal thermal and infrasound signals prior to the earthquakes a study on bonin island earthquake m7 8 may 30 2015 scientists from all over the world try to incorporate multi disciplinary precursors to forecast the earthquake on a short term basis the authors here have analyzed outgoing longwave radiations acquired from polar orbiting national oceanic and atmospheric adminstration noaa satellites and long period infrasound waves recorded by the ground observatories in china prior to the recent bonin islands japan region earthquake which occurred on may 30 2015 with the magnitude of 7 8 the anomalous outgoing longwave radiation olr was observed on may 15 2015 and was recorded by noaa 18 satellite during its night pass similarly an abnormal infrasound spike was recorded at the beijing station on may 17 2015 the delay in observing anomalous infrasound waves compared to the olr anomaly is due to these low frequency waves traveling at low speed with the velocity range of 10 15 m s from the analysis of the results it can be inferred that there is a substantial relation between parameters like olr and infrasound waves hence the authors conclude that it is possible to forecast the earthquake on a short term basis with reasonable accuracy

proterozoic events in the eastern ghats granulite belt india evidence from rb sr sm nd systematics and shrimp dating metamorphic and protolith ages of five rock types mafic granulite orthopyroxene granulite leptynite sillimanite granite and metapelite from rayagada in the north central part of the eastern ghats granulite belt eggb india were determined from rb sr and sm nd whole rock and mineral isochrons in combination with shrimp u pb zircon data most of the whole rock isochron ages in both sm nd and rb sr systems point to either 1450 or 1000 ma and the mineral isochron ages are 1000 800 and 550 ma shrimp u pb zircon ages of 940 ma were obtained from metapelite which are in close agreement with the sm nd and rb sr isochron ages from all these data four age clusters 1450 1000 800 and 550 ma have been noted the 1450 ma ages are interpreted to represent igneous protolith formation of mafic granulite and leptynite the 1000 ma age cluster is regarded as the intrusion ages of sillimanite granite and charnockite and associated granulite facies metamorphism two other age clusters 800 a

archean proterozoic evolution of indian charnockites isotopic and geochemical evidence from granulites of the eastern ghats belt pyroxene granulites and charnockites are associated with metasedimentary khondalite garnet sillimanite gneiss and migmatites in the eastern ghats mobile belt various stages of in situ granulitization similar to those observed in southern india and sri lanka are present geochemically the granulite suite around visakhapatnam is bimodal with acid and mafic variants there is an increase in the concentration and fractionation of the rare earth elements ree from pyroxene granulites to charnockites and six sm nd models ages t dm range from 2 86 to 2 35 ga with 2 1 ga for a younger granite the charnockites a pyroxene granulite and granite define a pb pb isochron age of 1176 pm 201 ma u pb ages of zircons and monazites from a charnockite near phulbani orissa yield near concordant data with ages of 985 pm 5 ma and 965 pm 7 ma respectively the new isotopic data and the available ages from the northeastern part of the eastern ghats in orissa suggest a major charnockite formati

a multi stage pressure temperature record in the chilka lake granulites the epitome of the metamorphic evolution of eastern ghats india metapelitic and charnockitic granulites exposed around chilka lake in the northern sector of the eastern ghats india preserve a multi stage p t record a high t decompression from above 10 kbar to 8 kbar around 1100 c has been determined from mg rich metapelites xmg 0 60 with quartz cordierite orthopyroxene sillimanite and cordierite orthopyroxene sapphirine spinel assemblages between this and a second decompression to 6 0 kbar isobaric cooling from 830 to 670 c at 8 kbar is evident these changes are registered by the rim compositions of orthopyroxene and garnet in charnockites and metapelites with an orthopyroxene quartz garnet plagioclase cordierite assemblage and are further supported by the garnet quartz orthopyroxene cordierite and biotite producing reactions in sapphirine bearing metapelites another indication of isobaric cooling from 800 to 650 c at 6 0 kbar is evident from rim compositions of orthopyroxene and garnet in patchy charnockites two sets of p t values are obtained from metapelites with a quartz plagioclase garnet sillimanite cordierite assemblage garnet and plagioclase cores yield 6 2 kbar 700 c and the rims 5 kbar 650 c suggesting a third decompression the earliest deformation f1 structures are preserved in the larger charnockite bodies and the metapelites which retain the high p t record the effects of post crystalline f2 deformation are observed in garnet megacrysts formed during or prior to f1 in some metapelites fold styles indicate a compressional regime during f1 and an extensional regime during f2 these lines of evidence and two phases of cooling at different pressures point to a discontinuity after the first cooling and imply reworking two segments of the present p t path replicate parts of the p t paths suggested for four other granulite terranes in the eastern ghats and the sense of all the paths is the same this plus the signature of three phases of deformation identified in the eastern ghats suggests that the chilka lake granulites could epitomize the metamorphic evolution of the eastern ghats

mesoarchaean crustal history of the eastern indian craton smnd and upb isotopic evidence abstract a variety of xenoliths representing high al trondhjemites and supracrustal lithologies occur within mesoarchaean granitoid rocks of the eastern indian craton a trondhjemitic xenolith from the bonai pluton yields a u pb age of 3380 6 4 ma for magmatic zircon and a minimum age of 3448 ma for xenocrystic zircon grains this sample also shows an nd value of 4 2 and t dm of 3 9 ga whereas four other xenoliths yield nd values ranging from 0 3 to 1 8 and t dm of 3 54 to 3 37 which are consistent with published data from the region and suggest a derivation from protoliths with relatively short lived crustal residence times

saturation regions in catchments and their relations to soil and topographic properties abstract criteria are derived for the existence of saturated areas on draining hillslopes in natural catchments these are given in terms of soil transmissivity the hillslope gradient and its wetness state characterised by the baseflow discharge from the catchment analyses are made for idealised hillslopes with uniform soils to obtain expression for the width of the saturated zone the size of saturated zones on undulating hillslopes with gradiational soils is shown to depend strongly on topographic convergence or divergence the effects of soil transmissivity hillslope geometry and drainage flux density are lumped into a dimensionless parameter whose value determines the location of seepage boundaries on slopes of specified geometry scaling relations for seepage area in catchments of different size are shown to be generally nonlinear and depend primarily on local hillslope gradients relative predictions of seepage zone size are confirmed by observed hydrographs from three catchments with different physical characteristics

the significance of topology for modeling the surface hydrology of fluvial landscapes the realistic representation of terrain in hydrological models of fluvial landscapes poses problems particularly for representing convergence and divergence of lateral flows in this work we consider the topology of contour representation of surfaces the networks of ridge and drainage lines are linked at critical points peaks saddles confluences and simple ridge junctions the properties of these points are given and from these three topologic rules are derived these are used to develop an automatic procedure for generating a catchment boundary and a modified flow net use of the flow net increases speed by 2 orders of magnitude over earlier contour based topographic analyses and the use of topology increases speed accuracy and sophistication over a recent flow net technique topology is used to evaluate simplifications of natural surfaces and in particular shows the unsuitability of the common ridge to stream rectangular flow strip finally implications for the structure of distributed catchment models and for designing and interpreting field experiments are considered

anatexis of interlayered amphibolite and pelite at 10 kbar effect of diffusion of major components on phase relations and melt fraction we have conducted h2o undersaturated melting experiments on charges consisting of a layer of a sillimanite bearing metapelite and a layer of garnet bearing amphibolite with the goal of studying how layered metamorphic rocks interact during anatexis experiments with the layered charges were performed at 10 kbar 1 gpa at 900 c 334 h 925 c 341 h and 950 c 50 161 332 h dehydration melting of the amphibolite alone and of the pelite alone were studied at the same p t conditions when run alone at 900 c the pelite and the amphibolite yielded ca 40 vol and 15 vol melt respectively corresponding melt fractions at 950 c were ca 50 vol and 30 vol when run side by side melt abundance in the pelite is fairly uniform and ca 20 vol higher than in the solo runs at all temperatures studied in contrast complex zoning patterns parallel to the interface develop in the amphibolite layer far from the interface the melt fraction is 5 10 vol lower than in the amphibolite solo runs closer to the interface the melt fraction in the amphibolite layers are comparable to or somewhat higher than in the amphibolite solo runs and both clinopyroxene and plagioclase react out and are replaced by orthopyroxene and quartz melt fraction closest to the interface reaches 65 70 vol and the only crystalline phase present is garnet with hollow cores the increase in melt fraction in the pelite layers of the layered runs is caused by transfer of na from the amphibolite to the pelite which forces biotite to be eliminated at lower temperature along the biotite garnet reaction boundary k is transferred from the pelite to the amphibolite and the lower melt fraction in the distal end of the amphibolite layers is caused by faster diffusion of na compared to k which results in a net depletion of alkalies ca is transferred from the amphibolite to the pelite and the resulting changes in cao concentrations affect the stabilities of plagioclase pyroxenes garnet and quartz and cause the observed zoning in the amphibolite layer ca entering the pelite layer induces crystallization of large plagioclase neoblasts radiating from the interface into the pelite layer these results show that diffusion of components between contiguous lithologies undergoing anatexis can cause profound changes in phase relations melt fractions and restite compositions

can archean granulites be direct crystallization products from a sialic magma layer archean granulite terrains are generally dominated by charnockite enderbite suites these rocks are geochemically similar to the tonalite trondhjemite granodiorite ttg gneisses of archean cratons following an open system fractional crystallization model for formation of ttg crust through solidification from a shallow level tonalitic magma ocean we propose that such granulites could have formed by crystallization at depth at the base of the same magma layer which is undergoing convection increasing solubilities with depth of fluids in a magma mean that the base of a thick convecting magma layer will be undersaturated with respect to h 2 o and co 2 this allows the formation of charnockitic assemblages crystallization at depth can involve the reverse of dehydration melting reactions e g producing biotite and quartz at the expense of k feldspar orthopyroxene and liquid such reactions buffer the activity of water but not of co 2 during crystallization hence fluids exsolved during progressive solidification are likely to be co 2 rich

structural constraints on the proterozoic reworking of archaean crust in the rayner complex macrobertson and kemp land coast east antarctica abstract the high grade metamorphic rocks exposed along the macrobertson and east kemp land coasts consist of in the west archaean gneisses reworked during a ductile mid proterozoic deformation and in the east foliated proterozoic charnockite gneiss containing large remnants of gneiss of probable archaean age evidence for three folding events is recognized in the reworked gneisses an early recumbent terrain is deformed by two upright events possessing near vertical axial surfaces the charnockite gneiss preserves evidence of only the final event these three events comprise the rayner structural episode which was a consequence of the ductile thrusting of archaean gneiss westward toward a stable archaean block the napier complex kinematic indicators are consistent with formation of the proterozoic recumbent terrain by dominantly shear deformation dissection of both the rayner and napier complexes by retrograde shear zones and mylonite pseudotachylite zones was a consequence of the northward thrusting of the two complexes during the cambrian

high temperature dehydration melting and decompressive p t path in a granulite complex from the eastern ghats india the granulite complex of paderu in the south central sector of the eastern ghats belt india consists of closely related pelitic granulites and peraluminous granitoids which could be linked via dehydration melting in pelitic and greywacke like precursors the pelitic granulites including high mg al sapphirine granulites with early deformation microstructures also record a high temperature decompression from 10 to 8 kbar at 1 000 c preceding isobaric cooling from above 900 to 600 c at 8 kbar highly magnesian biotite in the pelitic granulites the presence of spinel in some of the granitoids and granitoids of two distinct compositions namely granite and quartz monzonite all suggest dehydration melting in highly magnesian pelitic and greywacke like precursors moreover high temperature melting in highly magnesian pelitic precursors is indicated by the migmatitic spinel bearing layers which besides having significant abundance of quartz and feldspar also contain aluminous orthopyroxene and cordierite these melting reactions occurring above 9 kbar may constrain the prograde arm of the p t trajectory this and the high temperature decompression constitute a clockwise p t path this clockwise p t path is consistent with the tectonic model in which crustal thickening and granulite metamorphism in the eastern ghats belt is interpreted as the result of homogeneous shortening in a compressional setting

multi stage deformation in the nallamalai fold belt cuddapah basin south india implications for mesoproterozoic tectonism along southeastern margin of india abstract the common occurrence of small scale refolded folds deformed lineations and overprinting of foliation in the northern nallamalai fold belt nfb within the intracratonic cuddapah basin south india suggest three phases of deformation d 1 d 2 and d 3 during the late paleoproterozoic to neoproterozoic d 1 structures are represented by tight to isoclinal folds a slaty cleavage and local development of mylonites d 2 structures include ne trending tight to open folds f 2 with variable plunge indicating control of large domal structures and a steep crenulation cleavage developed in phyllites and other schistose rocks the above structures are overprinted by e w trending d 3 folds and cleavage which affect mesoproterozoic rocks of the srisailam formation uppermost nallamalai group in the e w trending vami konda range and metasediments of the palnad area thought to be equivalent of the neoproterozoic kurnool group taking into account the ages of intrusive vellaturu granite 1575 ma which is post d 2 deformation in the nfb and the chelima lamproite 1400 ma which intrudes the folded nallamalai rocks we suggest that the earlier episodes of multiple deformation in the nfb represent either late paleoproterozoic or early mesoproterozoic nw se compression in this part of the east gondwana the e w fold thrust structures affecting the srisailam quartzite and adjacent metasediments in the palnad area represent late mesoproterozoic and or neoproterozoic event the granite gneisses and schists of the nellore schist belt bordering the nfb are affected by both early and later events and thrust over rocks of the nallamalai group we propose that early deformation in the nfb lying southwest of the eastern ghats and roughly parallel to the present southeastern coast of india was unrelated to and occurred prior to the main deformation in the eastern ghats which is generally correlated with the 1000 ma old grenville event alternatively in view of the complex protracted evolution of the eastern ghats and published geochronological data supporting pre grenvillian tectonism particularly in the western charnockite zone of the eastern ghats d 1 and d 2 deformation in the nfb may be linked to this older 1600 1400 ma tectonic disturbance in the eastern ghats

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

single zircon evaporation ages constraining the growth of the archaean aravalli craton northwestern indian shield single grain 207 pb 206 pb zircon ages were determined for granitoids and gneisses which constitute the archaean basement rocks of the aravalli craton of rajasthan northwestern indian shield the protolith ages for two gneisses collected from east of udaipur are 3230 ma and 2887 ma respectively the granitoids display an intrusive relationship with the gneisses and yielded ages ranging between 2666 ma and 2620 ma these ages provide the basis for a geochronological model of evolution of the oldest basement of the aravalli craton

earthquake prediction by animals evolution and sensory perception animals living within seismically active regions are subjected episod ically to intense ground shaking that can kill individuals through burrow collapse egg destruction and tsunami action although anecdotal and retrospective reports of animal behavior suggest that although many organisms may be able to detect an impending seismic event no plausible scenario has been presented yet through which accounts for the evolution of such behaviors the evolutionary mechanism of ex aptation can do this in a two step process the first step is to evolve a vibration triggered early warning response which would act in the short time interval between the arrival of p and s waves anecdotal evidence suggests this response already exists then if precursory stimuli also exist similar evolutionary processes can link an animal s perception of these stimuli to its p wave triggered response yielding an earthquake predictive behavior a population genetic model indicates that such a seismic escape response system can be maintained against random mutations as a result of episodic selection that operates with time scales comparable to that of strong seismic events hence additional understanding of possible earthquake precursors that are presently outside the realm of seismology might be gleaned from the study of animal behavior sensory physiology and genetics a brief review of possible seismic precursors suggests that tilt hygroreception humidity electric and mag netic sensory systems in animals could be linked into a seismic escape behavioral system several testable predictions of this analysis are discussed and it is recom mended that additional magnetic electrical tilt and hygro sensors be incorporated into dense monitoring networks in seismically active regions

evidence for isotopic equilibration of smnd whole rock systems in early archaean crust of enderby land antarctica smnd isotopic data indicate that differential ree mobility occurred on a whole rock scale during transitional amphibolite to granulite facies regional metamorphism 700 c 7 kbar in early archaean rocks 3930 ma of the napier complex of enderby land antarctica the degree of mobility is independent of metamorphic grade but correlates directly with development of tectonic fabric whole rock samples with d3 m3 internal fabrics lie along an array corresponding to an age of 2410 100ma whereas samples preserving only earlier fabrics preserve an older albeit imprecisely defined isochron age in contrast to a widely held belief such changes did not require the presence of a large hydrous fluid flux if the mechanism responsible for smnd resetting at this locality where tchur ages range from 1990 ma to 6090 ma is more widespread than is currently recognised isolated smnd model ages particularly in complex terrains should be treated with caution

continental thermal and tectonic regimes during the archaean metamorphic pressures estimated from mineral assemblages in archaean high grade terrains may be used to constrain geothermal regimes in the archaean continental crust in two ways first they may be combined with temperature estimates to yield bounds on the heat flux during the thickening events that produced the metamorphism the pressure temperature data do not require any greater supply of heat to the base of the continental crust in the archaean than is supplied at the present day second the pressures alone may be used to infer the height of archaean mountains these mountains appear to have had elevations comparable with those of present day mountain belts it seems probable that the elevation of present day belts is limited by the creep strength of the lithosphere and in view of the strong temperature dependence of creep in earth materials this second observation also implies that archaean continental thermal regimes were similar to present day ones these observations together with the common

vapor absent melting at 10 kbar of a biotite and amphibole bearing tonalitic gneiss implications for the generation of a type granites vapor absent melting experiments on a biotite and amphibole bearing archean tonalitic gneiss agc150 at 10 kbar and 875 to 1050 c show that amphibole breaks down from 900 to 950 c producing garnet orthopyroxene and granitic melt biotite dehydration melting produces 10 wt melt up to 950 c via incongruent melting reactions that produce garnet orthopyroxene and titanomagnetite widespread biotite dehydration melting occurs between 950 and 975 c and produces orthopyroxene magnetite titanomagnetite and 20 wt fluorine rich melt up to 0 31 wt f minor f rich 2 7 wt biotite is present even at 1000 c our experiments show that under vapor absent conditions intrusion of hot mantle derived magmas into the lower crust is necessary to initiate widespread biotite dehydration melting in rocks with compositions like agc150 we propose that the high thermal stability of biotite in agc150 suggests that this rock is residual after a previous episode of partial dehydroxylation that left behind somewhat f enriched biotite we show that dehydration melting of such f enriched biotite produces f rich granitic liquids with compositions within the range of a type granite and leaves behind a granulitic residue consisting of orthopyroxene plagioclase quartz titanomagnetite and magnetite

metasedimentary melting in the formation of charnockite petrological and zircon u pb hf o isotope evidence from the darongshan s type granitic complex in southern china abstract charnockites are opx bearing igneous rocks commonly found in high grade metamorphic terranes despite being volumetrically minor they show a wide range in both bulk geochemistry and intensive parameters they form a characteristic component of the amcg anorthosite mangerite charnockite granite suite but their association with typical s type granites is less well known the darongshan s type granitic complex dsgc in guangxi province southern china contains granites varying in mafic silicate mineral assemblages from bt crd darongshan suite to opx grt bt crd jiuzhou suite and opx crd bt taima suite corresponding to a geochemical transition from magnesian calc alkalic to ferroan calc alkalic however its genesis even the accurate age of intrusion remains highly contentious despite intensive research in order to understand the genesis of charnockite and its genetic relationship with s type granite here we first determined zircon u pb ages of each suite using a sims on the basis of a detailed petrological study zircon u pb ages show that all suites of the complex were emplaced contemporaneously at ca 249 ma monazite apparent u pb ages are indistinguishable from zircon u pb ages within analytical error further in situ zircon hf o isotope analyses reveal that the granitic complex was dominantly derived from reduced melting metasedimentary rocks 18ozircon ca 11 ehf t zircon ca 10 log fmq 0 mn in apatite oxybarometer with rare material input from the mantle the variation in 18o 7 8 12 9 is more likely a result of hybridization whereas that in ehf t 31 9 to 1 8 is a result of both hybridization and disequilibrium melting the variation in mineralogy and geochemistry may be interpreted as a result of entrainment of peritectic garnets from biotite dehydration melting nevertheless heat input from mantle through basaltic intrusion underplating is considered to play a major role in high temperature 850 c melting at mid crustal levels i e the cordierite stable field for generation of the granitic complex we interpret that the granites were intruded in a back arc setting and basaltic magmatism was directly associated with slab roll back and tearing during the latest permian and early triassic times

ionospheric total electron content response to solar eclipses on october 24 1995 and march 9 1997 two solar eclipse events occur it is therefore of interest to investigate how the ionosphere responded to the eclipses five global positioning system gps ground based receivers are specifically designed to observe large scale ionospheric variations over the geomagnetic equatorial equatorial anomaly crest and midlatitude regions two dimensional images of ionospheric total electron content tec during the two eclipse periods are constructed the deviations in the tec images on eclipse days from those on reference days show that during the eclipse days the ionosphere experienced some large scale changes four features of the tec deviations pre ascension pa major depression md sunset ascension sa and secondary depression sd have been observed a detailed study shows that in geomagnetic low latitudes pas are possibly related to the locations of the equatorial anomaly crest the latitudinal location amplitude and occurrence time of mds suggest that the fountain effect is essential sas and sds occurring in geomagnetic equatorial and low latitudes and appearing respectively before around and after local sunset indicate that the prereversal enhancement plays an important role

structure of the nagavali shear zone eastern ghats mobile belt india correlation in the east gondwana reconstruction abstract interpretation of satellite data in combination with regional field traverses delineating the major structural features such as the nagavali and vamsadhara shear zones and associated fold patterns provides a synoptic picture of the regional tectonic framework of the central part of the eastern ghats mobile belt the complex geology of the study area can broadly be grouped into three distinct deformational events d1 fabrics represented by near flat lying gneissic foliations paralleling the lithological banding are best preserved in low strain domains and are related to middle to late archaean thrusting 3000 2600 ma the second deformational event d2 is characterized by the development of shear zones and associated mylonitic fabrics and magmatism probably during 1450 850 ma the pan african thermal 500 550 ma overprint is restricted to shear zones in the form of reworking regionally the central part of the eastern ghats mobile belt can be divided into five distinct structural domains based on structural geometry of folds foliations and lineations a three dimensional block diagram of the nagavali and vamsadhara shear zones involving fold thrust tectonics associated with westward thrusting is presented here a correlation of pan african shear zones in adjacent continents wrapping around the archaean dharwar craton in the reconstruction of rodinia and east gondwana supercontinent suggests an east west convergence

a physically based catchment partitioning method for hydrological analysis we propose a partitioning method for the topographic surface which is particularly suitable for hydrological distributed modelling and shallow landslide distributed modelling the model provides variable mesh size and appears to be a natural evolution of contour based digital terrain models the proposed method allows the drainage network to be derived from the contour lines the single channels are calculated via a search for the steepest downslope lines then for each network node the contributing area is determined by means of a search for both steepest upslope and downslope lines this leads to the basin being partitioned into physically based finite elements delimited by irregular polygons in particular the distributed computation of local geomorphological parameters i e aspect average slope and elevation main stream length concentration time etc can be performed easily for each single element the contributing area system together with the information on the distribution of geomorphological parameters provide a useful tool for distributed hydrological modelling and simulation of environmental processes such as erosion sediment transport and shallow landslides copyright 2000 john wiley sons ltd

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

a new correlation of sapphirine granulites in the indo antarctic metamorphic terrain late proterozoic dates from the eastern ghats province of india abstract uranium lead and thorium lead ages were obtained from perrierite and zircons in two samples from the eastern ghats province of south india a sapphirine bearing granulite from anakapalle and a charnockite from visakhapatnam the isotopic data are concordant or close to concordant at 1 ga which is interpreted to be the age of granulite facies metamorphism and charnockite plutonism in the vicinity of anakapalle and visakhapatnam and provides the first report of a late proterozoic granulite facies event in the eastern ghats province in reassemblies of gondwanaland based on dutoit s original proposal the eastern ghats province is juxtaposed against a high grade terrain in east antarctica affected by a granulite facies event and charnockitic plutonic activity 800 1100 ma ago the ages reported here suggest that a portion of the eastern ghats province represents an extension of the late proterozoic terrain from antarctica into india the radiometric results on the anakapalle rocks are the first evidence in south india for sapphirine formation during the late proterozoic other south indian sapphirine localities appear to be archaean in age a review of sapphirine localities in the indo antarctic metamorphic terrain indicates that sapphirine developed under a range of pressure temperature conditions during the archaean and proterozoic evidence for a systematic change in peak metamorphic conditions with time is obscured by these regional variations characterization of the entire pressure temperature path in addition to estimates for the peak conditions is needed to distinguish the archaean and proterozoic metamorphic regimes

abnormal infrasound signals before 92 m 7 0 worldwide earthquakes during 2002 2008 abstract in this paper 240 abnormal infrasound signals observed at beijing 39 87 n 116 48 e and 92 m 7 0 worldwide earthquakes during 2002 2008 are investigated it is found that about 85 the earthquakes are preceded the signals by 1 30 days and the greater m 7 6 earthquakes are most likely leaded by 1 10 days the maximum amplitude of the abnormal infrasound signal generally exceeds 8 pa in sound pressure the statistical analyses further indicate that the amplitude of the abnormal signals is proportional to the magnitude the associated forthcoming earthquake but inversely to the distance from that earthquake to the observation station

high temperature crustal scale shear zone at the western margin of the eastern ghats granulite belt india implications for rapid exhumation abstract a mylonitic shear zone occurs along the western margin of the eastern ghats granulite belt india in the northern sector it separates metapelitic and mafic granulites from the granite gneisses of the bastar craton while in the southern sector it separates charnockitic gneisses and mafic granulites from the granite gneisses of the bastar craton this boundary shear zone is characterized by a mylonitic foliation and a stretching lineation microstructures characterize high grade conditions and quartz c axis patterns show strong point maxima close to the long axes of the strain ellipsoids indicating dominant prism c slip in quartz commonly interpreted in terms of ductile deformation at high temperatures quartz c axis patterns in the recrystallized and unrecrystallized domains also imply grain boundary migration as the principal mechanism of dynamic recrystallization at high temperature conditions a rapid exhumation during shearing in this marginal part of the convergent eastern ghats orogen is indicated by decompression reaction textures and retrograde hydration reactions presumably due to hydrous fluid ingress in the shear zone rocks

new constraints on current deformation in asia from continuous gps measurements at ulan baatar mongolia on the basis of 3 years of continuous gps measurements 1995 1998 show a velocity of 6 4 1 6 mm yr in a n125 30 azimuth with respect to eurasia at a permanent site in ulan baatar mongolia together with recent gps results in asia this result indicates motion of the amurian north china block at 6 10 mm yr to the east to southeast relative to eurasia 0 to 5mm yr slower than south china 10 11 mm yr eastward the small differential motion between these two blocks is in agreement with deformation models of asia where crustal thickening dominates lateral extrusion the fact that the velocity of the amurian north china block is significantly faster than the predictions of models based on the hypothesis that deformation in asia is enterely driven by the india eurasia collision suggests that other mechanisms such as far field effects of subduction processes and gravitational forces could significantly contribute to intracontinental deformation