modeling mountain building and the seismic cycle in the himalaya of nepal a host of information is now available regarding the geological and thermal structure as well as deformation rate across the himalaya of central nepal these data are reconciled in a two dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes over geological timescale 5 ma the 20 mm yr estimated shortening rate across the range is accommodated by localized thrust faulting along the main himalayan thrust fault mht the mht reaches the surface along the foothills where it is called the main frontal thrust fault mft the mht flattens beneath the lesser himalaya and forms a midcrustal ramp at the front of the higher himalaya consistent with the river incision and the anticlinal structure of the lesser himalaya farther northward the mht roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust increasing the coulomb stress beneath the front of the higher himalaya where most of the microseismic activity clusters negligible deformation of the hanging wall requires a low apparent friction coefficient less than 0 3 on the flat portion of the mht on the ramp might be as high as 0 6 sensitivity tests show that a rather compliant quartz rich rheology and a high radioactive heat production in the upper crust of 2 5 w m 3 is required erosion affects the thermal structure and interplays with crustal deformation a dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure topography and deformation field using a linear diffusion model of erosion we constrain the value of the mass diffusivity coefficient to 0 5 1 6 l0 4 m 2 yr this study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period

occurrence of low stress drop earthquakes in the garhwal himalaya region abstract the digital seismic data recorded by a telemetered seismic array has been used to compute seismic moments and stress drops of local earthquakes in the garhwal himalaya region based on brune s model of the earthquake source the seismic moments for 18 shallow focus earthquakes range from 7 10 18 dyn cm to 6 23 10 21 dyn cm these earthquakes are found to have very low stress drops less than 1 bar for seven events and between 1 bar and 10 bars for another seven events the maximum stress drop is found to be 38 bars for an earthquake of magnitude 4 2 with focal depth 15 km the shallow focus events having low stress drops in this region indicate that the crust has low strength to withstand the accumulated strain energy

inversion of complex body waves we have developed a method that inverts seismic body waves to determine the mechanism and rupture pattern of earthquakes the rupture pattern is represented as a sequence of subevents distributed on the fault plane this method is an extension of our earlier method in which the subevent mechanisms were fixed in the new method the subevent mechanisms are determined from the data and are allowed to vary during the sequence when subevent mechanisms are allowed to vary however the inversion often becomes unstable because of the complex trade offs between the mechanism the timing and the location of the subevents many different subevent sequences can explain the same data equally well and it is important to determine the range of allowable solutions some constraints must be imposed on the solution to stabilize the inversion we have developed a procedure to explore the range of allowable solutions and appropriate constraints in this procedure a network of grid points is constructed on the i plane where and i are respectively the onset time and the distance from the epicenter of a subevent the best fit subevent is determined at all grid points then the correlation is computed between the synthetic waveform for each subevent and the observed waveform the correlation as a function of and i and the best fit mechanisms computed at each i grid point depict the character of allowable solutions and facilitate a decision on the appropriate constraints to be imposed on the solution the method is illustrated using the data for the 1976 guatemala earthquake

estimation and applicability of attenuation characteristics for source parameters and scaling relations in the garhwal kumaun himalaya region india abstract source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region in this study the source parameters were determined for 58 small to moderate size earthquakes 3 0 m w 5 0 occurred during 2007 2015 in the garhwal kumaun region the estimated shear wave quality factor q f values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters the q f values have been estimated by using coda wave normalization method in the frequency range 1 5 16 hz a frequency dependent s wave quality factor relation is obtained as q f 152 9 7 f 0 82 0 005 by fitting a power law frequency dependence model for the estimated values over the whole study region the spectral low frequency spectral level and corner frequency and source static stress drop seismic moment apparent stress and radiated energy parameters are obtained assuming 2 source model the displacement spectra are corrected for estimated frequency dependent attenuation site effect using spectral decay parameter kappa the frequency resolution limit was resolved by quantifying the bias in corner frequencies stress drop and radiated energy estimates due to finite bandwidth effect the data of the region shows shallow focused earthquakes with low stress drop the estimation of zuniga parameter e suggests the partial stress drop mechanism in the region the observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region however the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth attenuation and site corrections although the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach

upper crustal stress and seismotectonics of the garhwal himalaya using small to moderate earthquakes implications to the local structures and free fluids abstract the work presents new focal mechanism data of small to moderate 3 0 ml 5 0 upper crustal earthquakes for the garhwal himalaya from a local seismic network installed in july 2007 majority of the epicenters of these earthquakes are located close to the main central thrust mct zone we retrieved moment tensor mt solutions of 26 earthquakes by waveform inversion the mt results and 11 small to moderate earthquakes from the published records are used for stress inversions the mt solutions reveal dominatingly thrust mechanisms with few strike slip earthquakes near chamoli the seismic cross sections illustrate that these earthquakes are located around the mid crustal ramp mcr in the detachment the optimally oriented faults from stress inversions suggest that the seismogenic fault in this region is similar to a fault plane having dip angle between 12 and 25 degrees which is compatible with the dip angle of the mcr 16 in this region p axes and the maximum horizontal compressive stress are ne sw oriented the direction of the relative motion of indian plate with respect to the eurasian plate the friction coefficient estimated from stress inversions show that the chamoli region having low friction in comparison to the overall values the free fluids trapped beneath the detachment are penetrating into the local faults hence decreasing the frictional strength and altering the prevailing stress conditions of the surroundings the present study reveals that the mcr structure is seismogenically active and producing the small moderate earthquakes in the region while the mct is probably dormant at present

influence of fluorine on the solubility of manganotantalite mnta2o6 and manganocolumbite mnnb2o6 in granitic melts an experimental study abstract solubility experiments of manganotantalite mnta 2 o 6 and manganocolumbite mnnb 2 o 6 were conducted under nearly fluid saturated conditions in synthetic haplogranitic hpg and natural granitic ng melts containing different amounts of fluorine at 800 to 1000 c and 200 mpa the experiments were carried out in cold seal pressure vessels at 800 c with water or ar as a pressure medium and in internally heated pressure vessels 1000 c with ar as a pressure medium the f contents vary from 0 to 11 43 wt in experiments using hpg melts and from 0 61 to 3 78 wt in experiments using ng melts additionally the ng melt contains minor amounts of p 2 o 5 0 44 to 0 64 wt in hpg melts alumina saturation index including mn asi mn 0 88 to 0 99 the solubility product values at 800 c yield log k sp ta and log k sp nb ranging from 3 36 0 10 to 2 92 0 10 mol kg and from 3 01 0 11 to 2 87 0 06 mol kg respectively in ng melts the log k sp ta and log k sp nb vary from 3 00 0 04 to 2 35 0 13 mol kg and from 2 83 0 06 to 2 67 0 18 mol kg at 800 c respectively the solubility products of both mnta 2 o 6 k sp ta and mnnb 2 o 6 k sp nb are not significantly affected by the f content for a given melt composition data are virtually identical within error the variation of the solubility products observed in this study is rather attributed to the changes in melt structure e g polymerization and in particular to the alumina saturation index by contrast there is no evidence for the formation of complexes associating f and nb and or ta our results also indicate that the structural changes caused by the incorporation of f in natural water rich silicate melts are not expected to significantly influence the maximum concentrations of nb and ta in granitic or pegmatitic melts coexisting with manganotantalite and manganocolumbite

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

seismotectonic model of the kangra chamba sector of northwest himalaya constraints from joint hypocenter determination and focal mechanism the existing seismological network in the kangra chamba sector has been upgraded with 12 three component digital seismometers to obtain new insight on the nature and sources of continued clustered seismicity in this part of northwest himalaya a combination of travel time distance plots and travel time inversion of p and s phases have been used to derive a 1d velocity model for the region the mini mum 1d velocity model divides the average 44 km thick crust into four layers the top 10 km thick layer represents the metamorphosed sediments of the chamba nappe that dominates the surface geology of the study area suggestion of a thin low velocity layer at 15 km depth possibly marks the detachment zone separating the downgoing indian plate from the overriding wedge the improved locations of epicenters show close clustering of seismic events immediately northeast of the epicenter of the 1905 kangra earthquake while away from this zone the seismicity in the chamba sector has more even distribution in the later sector space depth distribution of hypocenters suggests that strain resulting from the ongoing collision of the indian plate with asia is being consumed by reverse fault movement on the chamba thrust the clustered seismicity in the kangra sector has three distinct source regions and mechanisms 1 southward displacement of the thick chamba nappe sheet over the panjal imbricate zone along the panjal thrust accounts for the seismicity at shallow depths of less than 7 km 2 the nucleation of strains where the northeast dipping main boundary thrust mbt merges with the detachment plane produces focused seismicity near this junc tion and 3 the seismicity in a small pocket below the plane of detachment appears to be a consequence of stresses generated at the base of the northeast dipping detachment plane by the transverse structure

fluid generation and pathways beneath an active compressional orogen the new zealand southern alps inferred from magnetotelluric data 1 forty one wideband magnetotelluric mt soundings were collected in a 150 km long transect across the southern alps of the central south island of new zealand an active compressional orogen decomposed mt impedance tensors vertical magnetic field relations and reconnaissance soundings at two locations off line imply an approximately two dimensional geometry here with average regional geoelectric strike of n40 e similar to surface geologic trends two independent two dimensional inversion algorithms were applied to the mt data and both imply a concave upward u shaped middle to lower crustal conductive zone beneath the west central portion of the island the average conductivity of this zone in the strike direction appears to be much higher than that required across strike and may represent anisotropy or along strike conductive strands narrower than the transverse magnetic cross strike mode mt data can resolve the deep crustal conductor under the southern alps is interpreted to represent mainly a volume of fluids arising from prograde metamorphism within a thickening crust fluid interconnection and electrical conduction are promoted by shear deformation the conductor rises northwestward toward the trace of the alpine fault but attains a near vertical configuration at a depth of 10 km and reaches close to the surface 5 10 km inland of the fault trace itself the transition to vertical orientation at this depth is interpreted to occur as fluids ascend across the brittle ductile transition in uplifting schist and approach the surface through induced hydrofractures the high grade schist becomes resistive after depletion of fluids and continues to extrude toward the alpine fault shallow extensions of the deep high conductivity are coincident with modern hydrothermal veining and gold mineralization interpreted to be of deep crustal provenance to the southeast high conductivity also reaches the surface coincident with a major back thrust fault zone of the doubly vergent southern alps orogen which also exhibits evidence for expulsion of high temperature fluids the higher conductivity inferred along strike possible anisotropy could reflect more efficient fluid interconnection in this higher strain direction as well as possible contributions by sheared fluid deposited graphite conductivity of the uppermost mantle of the south island is low consistent with advection of cold mantle lithosphere into the underlying asthenosphere as suggested by p wave delay studies

seismogenesis of clustered seismicity beneath the kangra chamba sector of northwest himalaya constraints from 3d local earthquake tomography abstract to investigate subsurface structure and seismogenic layers 3d velocity inversion was carried out in the source zone of 1905 kangra earthquake m8 0 in the northwestern himalaya p wave and s wave phase data of 159 earthquakes recorded by a network of 21 stations were used for this purpose inverted velocity tomograms up to a depth range of 18 km show significant variations of 14 in vp and vs and 6 in the vp vs across the major tectonic zones in the region synthesis of seismicity pattern velocity structure distinctive focal mechanisms coupled with nature of stress distribution allows mapping of three different source regions that control regional seismotectonics accumulating strains are partly consumed by sliding of chamba nappe to the southwest through reverse fault movements along chamba panjal main boundary thrusts this coupled with normal fault type displacements along chenab normal fault in the north account for low magnitude widespread seismicity in upper 8 10 km of the crust at intermediate depths from 8 to 15 km adjusting to residual compressive stresses the detachment or lower end of the mbt slips to produce thrust dominated seismicity nucleation of secondary stresses in local ne sw oriented structure interacts in complex manner with regional stresses to generate normal type earthquakes below the plane of detachment and therefore three seismic regimes at different depths produce intense seismicity in a block of 30 30 km 2 centered ne to the epicenter of kangra earthquake

tracking magmatic and hydrothermal nb ta w sn fractionation using mineral textures and composition a case study from the late cretaceous jiepailing ore district in the nanling range in south china abstract the jiepailing mining district in the nanling range in south china is well known for its granite related sn be f mineralization recently drill holes have exposed an nb ta w sn mineralized granitic porphyry and topaz bearing granite greisen at depth which we have studied here using mineral columbite rutile wolframite cassiterite zircon and mica major and trace element compositional data mineral textures and zircon and columbite u pb geochronology our age data shows that the porphyry and the granite and their mineralization formed at 91 89 1 ma in the late cretaceous and thus subsequent to the main ore forming events of the region continuous mineral compositional trends indicate that the studied granitoids are related by progressive fractionation we propose that 1 subhedral euhedral low ta columbite crystallized from melt 2 euhedral subhedral rutile and wolframite and subhedral and subhedral cassiterite up to 30 m in size formed at the magmatic hydrothermal transition of the system and 3 high ta columbite and subhedral cassiterite up to 10 m in size formed from subsolidus hydrothermal fluids in combination with the nb ta w and sn compositions of zircon and mica their textures and compositional variation allow us to track the magmatic to hydrothermal rare metal fractionation concentration mobilization and deposition of the system in detail despite our limited access to it through only two exploration drill cores using the nb ta w and sn concentrations in zircon refractory early crystallized and in micas late equilibrated respectively was particularly useful for tracing the partial loss of sn and w ore components from the intrusion and to constrain the information which is crucial for any rigorous ore exploration

recent earthquake swarms in garhwal himalaya a precursor to moderate to great earthquakes in the region abstract himalayas one of the most seismically active belts have been formed due to continent continent collision and are probable locations for future moderate to great earthquakes it is of paramount importance to recognize precursory swarm activity considered to be long predictors of main events recently two earthquake swarms occurred across main central thrust mct in garhwal himalayan region in a time interval of nearly one month the first swarm of april 2009 had epicentral locations lying north of mct on hanging wall side which has shown less seismic activity in recent times while the second swarm occurred in may 2009 near gopeshwar having epicenters on active seismic zone located south of mct the approximate distance between the two swarms is about 50 km in present study preparation zone of 100 100 km 2 has been demarcated recognizing these swarms as precursors to moderate to great earthquake in the garhwal himalaya

zoning in columbite tantalite crystals from the granitic pegmatites of the erajarvi area southern finland abstract electron microprobe analyses of zoned columbite tantalite crystals from the granitic pegmatites of the erajarvi area in orivesi southern finland indicate wide compositional variation within the series fenb2o6 feta2o6 mnnb2o6 mnta2o6 especially in specimens from thin pegmatite dikes most crystals show gentle progressive zoning characterized by small scale variations in the major elements where the compositional variation is large backscattered electron images indicate oscillatory or patchy zoning or various replacement textures the zones in oscillatory zoned crystals are usually 1 50 m in width exceptions reaching 50 120 m the wider zones often consist of a group of very narrow subzones of only slightly different composition zoning is due mainly to the compositional variation in ta and nb in two of these crystals the oscillations in mn follow the strongest oscillations in nb content patchy zoned crystals exhibit corroded cores of early columbite tantalite surrounded by later zones enriched in ta the mottled appearance of such crystals results from two or more successive replacements replacement tongues or network like replacement textures are typical in the rims of some crystals the zoning of the columbite tantalite is related to the complex crystallization history of the pegmatite dikes the main factors controlling oscillatory zoning are considered to be the growth dynamics of the crystals the concentration and diffusion of the main elements and the successive flows of the magma in an intrusion channel the generation of a corrosive supercritical vapor phase at the end of magmatic crystallization caused resorption patchy zoning and the replacement of the columbite tantalite

relative seismic moment tensor determination for vrancea intermediate depth earthquakes the method of relative seismic moment tensor determination proposed bystrelitz 1980 is extended a from an interactive time domain analysis to an automated frequency domain procedure and b from an analysis of subevents of complex deep focus earthquakes to the study of individual source mechanism of small events recorded at few stations

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

tetrad effect in rare earth element distribution patterns a method of quantification with application to rock and mineral samples from granite related rare metal deposits abstract in some geological environments the tetrad effect can be observed as a split of rare earth element ree patterns into four rounded segments a new method is proposed to quantify the sizes of the individual segments and for the first time the significance of observed tetrad effects is evaluated by taking analytical errors into account the outlined method was applied to lanthanide patterns of whole rock and fluorite samples collected from granite related rare metal deposits the ree patterns of the granite and greisen samples investigated exhibit significant tetrad effects that may not be accounted for by analytical uncertainties it is shown that the study of whole rock samples is insufficient to determine whether this effect is developed during fractional crystallization or is due to other processes such as fluid rock interaction a concave tetrad effect mirroring the pattern of the whole rock samples was not observed in the ree patterns of related vein fluorite samples therefore it is unlikely that the convex tetrad effect in the samples from the magmatic environment can be explained by removal of a respective complementary ree pattern by a coexisting hydrothermal fluid as previously suggested it is proposed that the tetrad effect formed within the magma fluid system before emplacement in the subvolcanic environment where phase separation caused a split of this system into fluid and magma subsystems alternatively the tetrad effect may also be inherited from an external fluid influencing the system during or after the emplacement of the magma on the basis of the fluorite data it is shown that the behavior of eu in the fluids is not related to the tetrad effect consequently different physico chemical factors control the occurrence of both phenomena y was found to be strongly enriched in samples precipitating from hydrothermal fluids that experienced prolonged interaction with the wall rocks whereas the tetrad effect in the fluids vanished with time and increasing distance from the ore bearing granite thus these different geochemical parameters can be used to reconstruct different aspects of the fluid evolution within this type of deposit

granite pegmatite connection and mineralization age of the giant renli tanb deposit in south china constraints from u th pb geochronology of coltan monazite and zircon abstract the recently discovered renli ta nb deposit in northeastern hunan province is the largest known pegmatite ta nb deposit in south china previous research has shown that biotite monzogranite is locally spatially associated with the pegmatites and could be the parental granite of the nb ta mineralization in this study we determine that muscovite monzogranite also has a close spatial relationship with the nb ta pegmatites we present new u th pb ages for coltan monazite and zircon that constrain the timing of nb ta mineralization and related magmatism laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of coltan from the nb ta pegmatite yielded a weighted mean 206pb 238u age of 140 2 2 3 ma zircon grains from the biotite monzogranite and muscovite monzogranite yielded weighted mean 206pb 238u ages of 154 1 2 5 ma and 141 0 2 4 ma respectively and monazite grains from the muscovite monzogranite yielded a weighted mean th pb age of 140 7 2 2 ma rare earth element contents of the coltan suggest that the nb ta mineralization is related to highly evolved granite the muscovite monzogranite shows highly evolved features with higher contents of sio2 and al2o3 and lower contents of fe2o3t k2o tio2 cao mgo and p2o5 than the biotite monzogranite the obtained ages and the close spatial relationship between the pegmatite type mineralization and the muscovite monzogranite together with the major and trace element compositions indicate that the nb ta mineralization is genetically related to the early cretaceous muscovite monzogranite rather than the late jurassic biotite monzogranite muscovite monzogranite that formed during the early cretaceous should be considered a target for nb ta exploration in south china

mineralogical constraints on the magmatic hydrothermal evolution of rare elements deposits in the bailongshan granitic pegmatites xinjiang nw china abstract the bailongshan pegmatite district in south xinjiang province nw china is a newly discovered area of rare element pegmatites it is a superlarge li rb reserve that includes an estimated 3 45 million tons of li2o and 176 000 tons of rb2o on the basis of a detailed characterization of textures and minerals in the bailongshan 2 and 5 pegmatites six zones are identified a saccharoidal albite zone zone i a graphic pegmatite zone zone ii a blocky microcline zone zone iii a muscovite quartz zone zone iv a cleavelandite spodumene zone zone v and a quartz spodumene zone zone vi the detailed mineralogical characteristic is performed by epma for illustrating both the existent state of rare elements and the magmatic hydrothermal evolution of the bailongshan pegmatite lithium be rb nb ta and sn are major economic rare elements which are concentrated in zones v and vi the rare elements are hosted by minerals including spodumene montebrasite eucryptite lepidolite beryl rb enriched k feldspar columbite group minerals cassiterite and tourmaline which formed from the fractional crystallization of pegmatitic magma the bailongshan pegmatites show lower degrees of fractional crystallization than many other li cs ta lct family pegmatites worldwide as evidenced by the relatively low nb ta zr hf and k rb fractional degree in the carrier minerals in zones v and vi the primary minerals record intense interaction with hydrothermal fluids which caused the alteration of spodumene and mica the development of cs or na enriched veinlets in beryl and the formation of mn and ta enriched veinlets coupled with micropores within columbite group minerals the hydrothermal fluids were composed predominantly of li f cs and ta which conformed to the evolved trend of pegmatitic melt these late hydrothermal fluids exsolved from the magma as it differentiated and may have the benefit with rare elements metallogeny

la icp ms u pb zircon columbite tantalite and 40ar 39ar muscovite age constraints for the rare element pegmatite dykes in the altai orogenic belt nw china the chinese altai is renowned for its rich rare element resources nine representative rare element rel pegmatites were dated using la icp ms and 40ar 39ar methods the columbite grains yield a weighted mean 206pb 238u age of 239 6 3 8 ma for the dakalasu be nb ta pegmatite and concordia u pb ages of 258 1 3 1 ma and 262 3 2 5 ma for the xiaokalasu li nb ta pegmatite the zircons display a weighted mean 206pb 238u age of 198 5 2 5 ma for the husite be pegmatite and concordia u pb ages of 194 3 1 6 ma and 248 2 2 2 ma for the qunkuer be and taerlang barren pegmatites the muscovite 40ar 39ar dating gives plateau ages of 286 4 1 6 ma 297 0 2 6 ma 265 2 1 5 ma 178 8 1 0 ma 162 2 0 9 ma 237 7 1 3 ma 237 4 1 2 ma and 231 9 1 2 ma for the talate li be nb ta baicheng nb ta kangmunagong barren husite be qunkuer be nb ta xiaokalasu li nb ta weizigou be and taerlang barren pegmatites respectively these new ages coupled with previous geochronological work suggest that the rel pegmatites in the chinese altai formed during early permain late jurassic time the rel pegmatites located in the central altaishan terrane are younger than those in the qiongkuer abagong terrane showing a correlation with the coeval and adjacent granites the formation of the rel pegmatites and these granites indicates frequent and strong magmatic activity in the post orogenic and anorogenic setting the spatial and temporal distribution of pegmatites and granites reveals a magmatism path from the se of age early middle permian to the nw middle permian middle triassic and finally to the central part middle triassic jurassic of the chinese altai

seismic tomography structure of the 1999 chamoli earthquake source area in the garhwal himalaya simultaneous inversion of about 5000 seismic phase data of 391 aftershocks of the 29 march 1999 chamoli earthquake m b 6 3 recorded by 28 closely spaced temporary and permanent seismic stations sheds new light on understanding the seismogenic structure of the source area the best located 160 aftershocks m d 2 0 4 0 with root mean square error less than 0 2 sec and epicentral and depth error less than 1 km are clustered at a depth range of 8 16 km above the plane of detachment the interface between the himalayan sedimentary wedge and the indian shield the mainshock nucleated by thrust faulting at the fault end where the alakananda fault meets the plane of detachment at a depth of 15 km and the aftershocks occurred by shear adjustment at the alakananda fault the 3d p and s wave velocity structures of the source area show an east west trending low velocity zone lvz the lvz is comparable with the north dipping or near vertical alakananda fault on the surface it extends from the surface down to 15 km depth it broadens in the north south direction at shallower 0 10 km depth and narrows at deeper depth 10 15 km the p wave tomography shows a high velocity zone hvz at the eastern margin of the lvz the mainshock and the aftershocks occurred at the contact of these two zones and within the hvz the s wave velocity structure resembles that of the p wave but it shows an lvz at the mainshock source area at a depth of 15 km where the higher p wave velocity structure hvz is observed the seismogenic source area is thus characterized by a higher v p v s or higher poisson s ratio at the fault end this anomaly may be due to fluid filled fractured rock matrix which might have contributed to the nucleation of the mainshock manuscript received 17 june 2002

resolution of non double couple components in the seismic moment tensor using regional networks i a synthetic case study summary we perform a detailed synthetic study on the resolution of non double couple non dc com ponents in the seismic moment tensors from short period data observed at regional networks designed typically for monitoring aftershock sequences of large earthquakes in addition we test two different inversion approaches a linear full moment tensor inversion and a non linear moment tensor inversion constrained to a shear tensile source model the inversions are applied to synthetic first motion p and s wave amplitudes which mimic seismic observa tions of aftershocks of the 1999 mw 7 4 izmit earthquake in northwestern turkey adopting a shear tensile source model to analyse the resolution capability for the obtained non dc components inverted we contaminate synthetic amplitudes with random noise and incorporate realistic uncertainties in the velocity model as well as in the hypocentre locations we find that the constrained moment tensor inversion yields significantly smaller errors in the non dc components than the full moment tensor inversion in particular the errors in the compensated linear vector dipole clvd component are reduced if the constrained inversion is applied furthermore we show that including the s wave amplitudes in addition to p wave amplitudes into the inversion helps to obtain reliable non dc components for the studied station config urations the resolution remains limited due to the lack of stations with epicentral distances less than 15km assuming realistic noise in waveform data and uncertainties in the velocity model the errors in the non dc components are as high as 15 percent for the isotropic and clvd components respectively thus being non negligible in most applications however the orientation of p and t axes is well determined even when errors in the modelling procedure are high

southward extrusion of tibetan crust and its effect on himalayan tectonics the tibetan plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during india asia collision and the contrast in potential energy between the plateau and its surroundings strongly influences the modern tectonics of south asia the distribution of potential energy anomalies across the region derived from geopotential models indicates that the himalayan front is the optimal location for focused dissipation of excess energy stored in the plateau the modern pattern of deformation and erosion in the himalaya provides an efficient mechanism for such dissipation and a review of the neogene geological evolution of southern tibet and the himalaya shows that this mechanism has been operational for at least the past 20 million years this persistence of deformational and erosional style suggests to us that orogens like other complex systems can evolve toward steady state configurations maintained by the continuous flow of energy the capacity of erogenic systems to self organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far field plate interactions

mineral chemistry of columbite tantalite from spodumene pegmatites of kolmozero kola peninsula russia abstract compositional variation results of electron microprobe analyses and mass spectrometry analyses of columbite group minerals cgm from fully differentiated albite spodumene pegmatites at kolmozero in the kola peninsula is evaluated concentric zoning typical of rare metal pegmatites was not observed in the kolmozero pegmatites columbite group minerals occur in all main parageneses of the pegmatites and form four generations reflecting the sequence of pegmatite formation these minerals demonstrate wide variations in the content of major and trace elements the composition of cgm ranges from columbite fe to tantalite mn fractionation trends were observed in mn mn fe versus ta ta nb diagrams and trace element abundances plotted versus xta and xmn the early cgm paragenesis is characterized by homogeneous oscillatory and progressive oscillatory zoning and corresponds to a primary magmatic type late generation cgm show patchy irregular internal textures replacing earlier regular patterns of zoning the irregular zoning points to metasomatic replacement processes for the first time it is shown that distributions of rare earth elements ree in cgm reflect the evolution of a pegmatite forming system at kolmozero the main trend of ree variation from early to late generations of cgm involves decreasing total ree contents due to a decrease in heavy ree and y decreasing negative eu anomaly and decreasing magnitude of m shape tetrad effect between gd and ho these changes are accompanied by gradual flattening of the bird like patterns of chondrite normalized ree distribution all these features are typical for late differentiates of granitic volatile rich magma late metasomatic tantalite mn is characterized by sharp changes in its ree distribution pattern decreasing total ree contents changing shape of the ree distribution pattern the absence of eu anomaly and tetrad effects and the appearance of a negative ce anomaly the textural characteristics and mineral chemistry of cgm indicate that the pegmatite forming system underwent several stages of evolution the earliest magmatic stage can be divided into two sub stages involving direct crystallization and collective recrystallization respectively and was succeeded by a late hydrothermal metasomatic post magmatic stage variations in chemical composition among the different generations of cgm are explained by the interplay of several processes fractional crystallization competitive crystallization of main rock forming feldspar muscovite spodumene and accessory triphylyte lithiophilite spessartine fluorapatite zircon microlite minerals and evolution of the mineral forming environment from a melt to a hydrothermal metasomatic fluid

seismotectonics of the nepal himalaya from a local seismic network the national seismological network of nepal consists of 17 short period seismic stations operated since 1994 it provides an exceptional view of the microseismic activity over nearly one third of the himalayan arc including the only segment between longitudes 78 e and 85 e that has not produced any m 8 earthquakes over the last century it shows a belt of seismicity that follows approximately the front of the higher himalaya with most of the seismic moment being released at depths between 10 and 20 km this belt of seismicity is interpreted to reflect interseismic stress accumulation in the upper crust associated with creep in the lower crust beneath the higher himalaya the seismic activity is more intense around 82 e in far western nepal and around 87 e in eastern nepal western nepal between 82 5 and 85 e is characterized by a particularly low level of seismic activity we propose that these lateral variations are related to segmentation of the main himalayan thrust fault the major junctions between the different segments would thus lie at about 87 e and 82 e with possibly an intermediate one at about 85 e these junctions seem to coincide with some of the active normal faults in southern tibet lateral variation of seismic activity is also found to correlate with lateral variations of geological structures suggesting that segmentation is a long lived feature we infer four 250 400 km long segments that could produce earthquakes comparable to the m 8 4 bihar nepal earthquake that struck eastern nepal in 1934 assuming the model of the characteristic earthquake the recurrence interval between two such earthquakes on a given segment is between 130 and 260 years

spatial distribution of earthquake potential along the himalayan arc abstract to determine the spatial distribution of earthquake potential along the active himalayan arc we utilize gps measurements and earthquake data we derive horizontal velocity field and 2 d strain rates from a new set of 41 regional gps stations along with 446 published velocities we convert these strain rate tensors to geodetic moment rate build up within 24 contiguous segments and compare to the seismic moment rate release derived from a reassessed earthquake catalog of 900 years the geodetic to seismic moment rate ratio an indicator of stored strain energy varies from below unity to more than 50 in different segments the estimated geodetic moment rate ranges from 1 7 1018 nm yr to 10 2 1018 nm yr whereas the seismic moment rate ranges from 3 7 1016 nm yr to 5 1 1019 nm yr this variation between the geodetic and seismic moment rate corresponds to a moment deficit rate of 1 15 1017 nm yr to 7 97 1018 nm yr along various segments of the study region the above moment deficit rate provides an equivalent earthquake potential of magnitude 5 7 8 2 in different segments specifically the higher earthquake potential mw 8 0 corresponds to the segments in the central seismic gap and the northeast part of himalaya whereas the lower earthquake potential mw

thrust geometries and deep structure of the outer and lesser himalaya kumaon and garhwal india implications for evolution of the himalayan fold and thrust belt the kumaon garhwal region of the himalaya lies near the center of the himalayan fold and thrust belt we have drawn two balanced cross sections 100 km apart through the outer and lesser himalaya the cross sections incorporate all the surface well log and earthquake seismic data currently available from the region two branch line maps showing trailing and leading branch lines and cutoff lines of the major thrusts in the region are also drawn the three dimensional deep structure of the outer and lesser himalaya is interpreted based on the balanced cross sections and the branch line maps deep structure of the higher and tethyan himalaya is extrapolated based on surface geology and is subject to revision as more surface and seismic data become available from these areas a sequential evolutionary model for the kumaon himalaya along the eastern pindari section is proposed according to this model the kumaon himalaya evolved by an overall forelandward progression of thrusting with some reactivation along the munsiari thrust mt the main boundary thrust mbt and the main central thrust mct we use structural stratigraphic and radiometric criteria to place time constraints on the motion of these thrusts earliest motion along the mbt may have occurred in early middle paleocene but the main episode probably started in late eocene and may still be continuing emplacement of the mt had occurred by middle late eocene whereas the mct shows activity around 20 ma thus exhibiting break back thrusting with respect to the mt shortening estimates are obtained from the pindari section minimum shortening in the sedimentary thrust sheets of the outer and lesser himalaya is 161 km or 65 as a first approximation we have also restored the crystalline sheets in order to obtain shortening estimates for the entire himalaya minimum shortening for the himalaya after restoring the mct sheet varies from 354 76 to 421 km 79 these estimates were further combined with published data from the area between the mct sheet and the indus tsangpo suture zone itsz minimum shortening between the indo ganga foreland and the itsz thus obtained lies in the range 687 754 km or 69 72 we compare our shortening estimates with those available from the pakistan and nepal himalaya

mw 4 9 earthquake of 21 august 2014 in kangra region northwest himalaya seismotectonics implications abstract a moderate earthquake m l 5 0 m w 4 9 occurred in the kangra region of himachal pradesh on 21 august 2014 08 11 ut the earthquake attains significance as it occurred immediately northeast of the source zone of the large kangra earthquake of 1905 m w 7 8 the source mechanism of the later earthquake remains a subject of debate further the seismic event is nucleated in a narrow block where intense clustering of small and moderate events has been indicated by earlier campaign mode surveys taking advantage that recent earthquake is well recorded by a regional bbs network the source parameters are estimated and interpreted to provide fresh constraint on the elements of seismotectonic model the earthquake with its epicenter at 32 34 n and 76 52 e is seated on the panjal thrust boundary between panjal imbricate zone and the chamba nappe the travel time inversion and wave form inversion technique suggest focal depth no more than 5 km a stress drop of 92 bars and a source radius of 1 1 km the moment magnitude m w for this event is calculated as 4 9 the anomalous high value of stress drop compared to the generally low values prevailing over much of the kangra chamba region indicates that the earthquake of 21 august 2014 is rooted in crustal blocks characterised by strong material strength to support accumulation of high strain during the earthquake building cycle fault plane solution of the event under study suggested that source fault is striking 323 with dip of 34 the rake value of 105 indicated thrust movement with a very negligible right lateral movement synthesis of source parameters especially the shallow focal depth strike paralleling the panjal thrust mbt with steep dip favour the seismotectonic model where moderate magnitude earthquake of 21st august 2014 is a typical example caused by the reverse fault displacement on the panjal thrust fault in the compressive regime of the kangra himalaya such movements are facilitated by the stresses resulting in response to the southward sliding of the chamba nappe and thus activating the contact zone between the nappe and panjal imbricate zone

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

li nb ta mineralization in the jurassic yifeng granite aplite intrusion within the neoproterozoic jiuling batholith south china a fluid rich and quenching ore forming process abstract the neoproterozoic jiuling batholith in northwestern jiangxi province south china is one of the largest batholiths in the nanling range and it is intruded by mesozoic granitic intrusions associated with mineralization the jurassic yifeng granitic pluton intrudes to the southern part of the jiuling batholith and comprises li rich muscovite li mus granite trilithionite tri granite and aplite dikes the granitic rocks are enriched in rare metals li rb cs nb ta we conducted whole rock geochemical analyses undertook columbite u pb dating and examined the textures and chemistry of feldspars micas and the accessory minerals montebrasite columbite group minerals cgms microlite cassiterite and zircon all three granitic rock types have high li contents up to 6200 ppm and the 7li values of the li mus granite and aplite are 3 55 0 14 and 5 34 0 04 respectively the isolated grains of cgms and cassiterite in the aplite are magmatic products but intense fluid activity in the later stages and quenching resulted in unique mineral aggregates of cassiterite cgms zircon the nb ta mineralization of the li mus granite took place at 144 5 ma according to columbite u pb dating and this age is similar to that of the neighbouring yichun granitic pluton to the south moreover both the yifeng and yichun plutons contain p rich rare metal bearing li f granitic rocks that contain p rich feldspars montebrasites amblygonites cs rich lepidolites cgms close to the mn endmember and hf rich zircons it is inferred that a metallogenic district characterized by li nb ta mineralization exists in northwestern jiangxi province thus providing a reliable guide for further exploration

earthquake swarm of himachal pradesh in northwest himalaya and its seismotectonic implications abstract on the 27th of august 2016 a seismic swarm activity consisting of 58 earthquakes 1 5 ml 4 4 which occurred in rampur area of the kullu rampur tectonic window of himachal pradesh in northwest himalaya the epicenters of these events are located at the northern front of the berinag thrust in its hanging wall to better understand the seismotectonics of this region we analyzed the spectral source parameters and source mechanism of this swam activity spectral analysis shows the low stress drop values from 0 05 to 28 9 bars suggesting that the upper crust has low strength to withstand accumulated strain energy in this region the moment tensor solutions of 12 earthquakes 2 7ml obtained by waveform inversion yield the shallow centroid depths between 5 and 10 km all these events are of dominantly thrust fault mechanism having an average dip angle of 30 the p axes and the maximum horizontal compressive stresses are ne sw oriented the relative motion of the indian plate the present study reveals that the swarm activity in the himachal region of nw himalaya is related to the out of sequence thrusting or the lesser himalayan duplex system

melt composition control of zr hf fractionation in magmatic processes zircon zrsio4 and hafnon hfsio4 solubilities in water saturated granitic melts have been determined as a function of melt composition at 800 and 1035 c at 200 mpa the solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt moreover the molar ratio of zircon and hafnon solubility is a function of melt composition although the solubilities are nearly identical in peralkaline melts zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts accordingly calculated partition coefficients of zr and hf between zircon and melt are nearly equal for the peralkaline melts whereas for metaluminous and peraluminous melts dhf dzr for zircon is 0 5 to 0 2 consequently zircon fractionation will strongly decrease zr hf in some granites whereas it has little effect on the zr hf ratio in alkaline melts or similar depolymerized melt compositions the ratio of the molar solubilities of zircon and hafnon for a given melt composition temperature and pressure is proportional to the hf zr activity coefficient ratio in the melt the data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts however it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached for most ferromagnesian minerals in equilibrium with a depolymerized melt dhf dzr typical values of dhf dzr range from 1 5 to 2 5 for clinopyroxene amphibole and titanite because of the change in the hf zr activity ratio in the melt the relative fractionation of zr and hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite it is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in zr hf whereas fractional crystallization of depolymerized melts tends to increase zr hf there is no need to invoke fluid metasomatism to explain these effects results demonstrate that for ions with identical charge and nearly identical radius crystal chemistry does not alone determine relative compatibilities rather the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice

the kumaun and garwhal lesser himalaya india part 1 structure and stratigraphy our understanding of the geologic evolution of the himalaya remains incomplete particularly in regard to structural and geochronologic details of the proterozoic paleozoic lesser himalayan sequence we conducted an integrated field mapping geochronological study and geochemical analysis of the lesser himalayan sequence strata in the kumaun and garwhal himalaya of nw india 78 00 80 30 e structural observations reveal a systematic change in deformation styles from lower to higher structural levels in the main central thrust footwall in the south and at lower structural levels the main central thrust footwall is characterized by parallel folding and sparse development of axial cleavage quartz microstructures indicate that deformation occurred at temperatures below 350 c in contrast in the north and at higher structural levels close to the main central thrust deformation is characterized by replacement of original bedding the development of penetrative cleavage and schistosity locally folds are tight in places isoclinal and overturned the corresponding quartz microstructures indicate that deformation occurred above 350 c dating of detrital zircons from lesser himalayan sequence metasedimentary units and igneous zircons from schistose gneisses throughout the lesser himalayan sequence allow refinements to the stratigraphic framework first unlike has been observed in western nepal immediately west of our study area u pb zircon dating suggests the absence of paleoproterozoic strata in the ramgarh thrust hanging wall this suggests that the thrust cuts upsection laterally along strike second u pb detrital zircon dating suggests that metasedimentary strata in the ramgarh thrust hanging wall are correlative with basal units of the outer lesser himalayan sequence removing the necessity that the ramgarh thrust hanging wall was allochthonous with respect to its footwall lesser himalayan sequence units schistose gneisses with u pb ages of ca 1850 ma are older than lesser himalayan sequence units in the area suggesting that they are thrust emplaced lesser himalayan sequence basement we conclude that the ramgarh thrust is an out of sequence thrust postdating a folding event in its footwall the earlier proposal that neoproterozoic cambrian lesser himalayan sequence strata are the southern extension of the tethyan himalayan sequence requires that the tons thrust which separates the distal and proximal facies of the lesser himalayan sequence be a major south directed structure with a slip magnitude of 50 100 km

textural features and chemical evolution in tantalum oxides magmatic versus hydrothermal origins for ta mineralization in the tanco lower pegmatite manitoba canada tantalum a key element in the electronics industry is produced mainly from rare element granitic pegmatites although their internal structure mineralogy and petrogenesis have been extensively investigated the processes that control tantalum mineralization remain poorly understood in particular the role of fluids in the crystallization of tantalum ore one of the major problems arises from the difficulty in distinguishing primary magmatic from secondary hydrothermal textures in such complex rocks in the tanco pegmatite manitoba canada tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite eight different families of tantalum oxides occur in various associations and compositions the tanco lower pegmatite is an isolated body beneath the main pegmatite body that contains abundant tantalum associated with mica alteration tantalum mineralization in the tanco lower pegmatite occurs as three different styles facies 1 is hosted by the wall zone and hosts primary magmatic ta oxides with simple textures progressive and oscillatory zoning facies 2 is hosted by the lower and upper intermediate zones where most mineralization occurs with dendritic amblygonite facies 3 is hosted by the central zone which is affected by mica alteration in this latter facies the oxides show particularly complex textures evident from x ray mapping by combining information obtained from textural observations and chemical analyses we are able to determine the paragenesis for each ta oxide bearing mineral assemblage and hence to evaluate the relative contributions of magmatic versus hydrothermal processes in complex associations we observe relics of primary ta phases that are replaced or overgrown by secondary ta phases we propose the paragenetic sequence columbite group minerals microlite early primary magmatic columbite wodginite group minerals microlite late primary magmatic wodginite group minerals microlite secondary magmatic ferrotapiolite secondary magmatic in addition chemical variations were identified in the columbite and wodginite group minerals both at the crystal scale and at the pegmatite scale columbite and wodginite group minerals show the typical ta ta ta nb and mn mn mn fe atomic ratios increase from earlier to later zones at the crystal scale the increase in ta and mn with fractionation in the columbite group is explained by the higher solubility of the ta end member relative to the nb end member and the crystallization of other minerals that shift the melt composition toward mn enrichment the fractionation trend in the wodginite group shows fe enrichment which is consistent with experimental results that show a higher solubility of the fe end member relative to the mn end member in columbite group minerals considering the available experimental data as well as the intimate association of ta oxides with zircon observed in this study we conclude that tantalum mineralization is a product of direct crystallization from the melt rather than hydrothermal in origin fluids are attributed an indirect role only as they could have brought minor elements fe mn or ca into the melt which resulted in the crystallization of secondary ta phases textural evidence shows that the late secondary phases were formed at the same time as mica alteration we suggest that mica alteration was due to a late melt rather than a hydrothermal fluid that reacted with the blocky k feldspar of the central zone during the alteration event tantalum was remobilized from primary phases and incorporated in new secondary ta oxide species

automated moment tensor inversion to estimate source mechanisms of hydraulically induced micro seismicity in salt rock abstract two methods for an automated moment tensor inversion are investigated the first is a single source inversion using amplitude spectra of observed body wave phases and theoretical green functions and the second a relative moment tensor inversion using spectral moments of body wave phases an optional general dislocation source constraint is introduced to stabilize the inversions for sparse data both methods are successfully tested on synthetic data and are applied to hydraulically induced micro seismicity in salt rock the estimated moment tensors of 187 events show similar radiation patterns with a major double couple component and a small or zero isotropic component we explain the double couple component with failure on horizontal preexisting planes of weakness within the process zone of circular tension fractures

tin tantalum niobium mineralization in the penouta deposit nw spain textural features and mineral chemistry to unravel the genesis and evolution of cassiterite and columbite group minerals in a peraluminous system abstract the sn ta nb penouta granite is a highly evolved rare metal post kinematic leucogranite located in north western spain which was intermittently mined from roman times until 1985 when falling metal prices led to the closure of most mines in the country mineralization consists mainly of cassiterite cassiterite i and columbite group minerals cgm disseminated in the leucogranite that increase in abundance and crystal size towards the upper part of the granitic cupola especially in banded pegmatite like dikes upwards quartz veins and greisen zones associated with the wall rock mainly augen gneisses were developed containing coarse grained cassiterite cassiterite ii in contrast to nearly homogenous cassiterite chemistry cgm may show complex compositional zonation patterns in relation with compositional variations of the leucogranite taking into account the mineral chemistry and textural features of cgm two main groups were distinguished i the first one group i follows a general main trend from columbite fe to columbite mn and finally to tantalite mn which is in accordance with the evolution of the magma observed from the less to the more evolved zones of the leucogranite and from bottom to top of the body and responds to common fractionation patterns of decreasing nb ta ratios in the melt and ii a second group group ii with intermediate values of mn mn fe and ta ta nb due to local supersaturation effects of the melt during crystallization resulting in complex oscillatory zoned cgm crystals textural and chemical features of cassiterite and cgm support the magmatic origin for both minerals although cassiterite crystallized later in the sequence in both generations mineral chemistry evolution of cgm is in good agreement with a greater solubility of tantalite in the melt at the upper levels where besides the fluorine contents of apatite and muscovite were increased and the onset of fluorite crystallization occurred so the fluorine enrichment in the upper levels seems likely to be an important component to explain the mineral chemistry of the penouta granite although the same mineral chemistry scheme could also be explained in terms of white mica fractionation upwards furthermore the absence of typical textures originated by fluids in the cgm as well as the lack of these minerals in the quartz veins point to a low influence of the hydrothermal fluids in dissolution and recrystallization processes of the primary oxides

mineralogical constraints on the genesis of w nb ta mineralization in the laiziling granite xianghualing district south china abstract the laiziling granitic pluton located in the xianghualing district hunan province china comprises typical rare metal granites with a pronounced vertical lithological zonation this pluton includes three granitic phases comprising from base to top medium grained mg alkali feldspar granite fine grained fg alkali feldspar granite and albite granite here we report the results of textural and chemical analyses of w nb ta oxide minerals from the laiziling granitic pluton the chemical compositions of whole rock samples rock forming minerals and zircon have allowed us to identify the magmatic hydrothermal processes that operated during the formation and rare metal mineralization of the laiziling pluton the granites are slightly peraluminous to peraluminous highly evolved and fractionated as inferred from whole rock geochemical and mineralogical micas and zircon signatures all the micas in different granitic phases are classified into the zinnwaldite group li concentration in the primary micas 2 6 4 wt li 2 o and hf concentration 1 8 wt hfo 2 in the zircon increase for the base to the top granitic phases both alkali feldspar granites contain oxide mineral aggregates including columbite group minerals wolframoixiolite qitianlingite wolframite and cassiterite the columbite group minerals wolframite and cassiterite also occur as isolated grains within the albite granite the presence of the oxide minerals suggests that the w nb ta mineralization developed during the latter stages of the magmatic evolution related to fluids that were compositionally evolved from the granites the composition of the fluids controls the aggregate of the oxide minerals the wolframite and cassiterite that precipitated within the laiziling skarn type deposit are chemically different from those within the granite indicating a hydrothermal origin for the oxide minerals that formed as a result of pervasive alteration

structural control on along strike variation in the seismicity of the northwest himalaya an overview of seismicity along the northwest himalaya exhibit along strike segmentation intricately controlled by the subsurface topographic ridges on the underthrusting indian plate as well by rift and nappe structures in the overriding wedge of the himalaya the segmentation exists for thrust dominated large magnitude earthquakes m 6 seated on the active detachment beneath the outer and lesser himalaya segmentation also prevails for moderate and small magnitude earthquakes concentrated in a narrow himalaya seismic belt hsb straddling northern lesser himalaya and southern higher himalaya numerical calculations of stress distribution favour that the degree of seismicity in the hsb is a good proxy to the presence of mid crustal ramp connecting the locked section of active detachment to aseismically slipping detachment beneath higher himalaya further gap or diffused pattern in the concentrated seismicity in the hsb in agreement with mapped high electrical conductive structure suggests ramp structure may be absent where underthrusting delhi hardwar ridge interacts with the himalaya arc in the nappe dominated tectonics the accommodation of the accumulating strains on the listric thrust faults produces increased frequency of moderate magnitude earthquakes and thereby possibly influences stress level on the detachment this may explain relatively less frequent occurrences of large earthquake in the kangra chamba region compared to that in the garhwal himalaya the low level seismicity in the simla region may also be influenced by the active kaurik chango rift in the higher himalaya as the former casts a stress shadow on the latter

miocene to holocene exhumation of metamorphic crustal wedges in the nw himalaya evidence for tectonic extrusion coupled to fluvial erosion the himalayan crystalline core zone exposed along the sutlej valley india is composed of two high grade metamorphic gneiss sheets that were successively underthrusted and tectonically extruded as a consequence of the foreland directed propagation of crustal deformation in the indian plate margin the high himalayan crystalline sequence hhcs is composed of amphibolite facies to migmatitic paragneisses metamorphosed at temperatures up to 750 c at 30 km depth between eocene and early miocene during early miocene combined thrusting along the main central thrust mct and extension along the sangla detachment induced the rapid exhumation and cooling of the hhcs whereas exhumation was mainly controlled by erosion since middle miocene the lesser himalayan crystalline sequence lhcs is composed of amphibolite facies para and orthogneisses metamorphosed at temperatures up to 700 c during underthrusting down to 30 km depth beneath the mct the lhcs cooled very rapidly since late miocene as a consequence of exhumation controlled by thrusting along the munsiari thrust and extension in the mct hanging wall this renewed phase of tectonic extrusion at the himalayan front is still active as indicated by the present day regional seismicity and by hydrothermal circulation linked to elevated near surface geothermal gradients in the lhcs as recently evidenced in the himalayan syntaxes active exhumation of deep crustal rocks along the sutlej valley is spatially correlated with the high erosional potential of this major trans himalayan river this correlation supports the emerging view of a positive feedback during continental collision between crustal scale tectono thermal reworking and efficient erosion along major river systems

columbite solubility in granitic melts consequences for the enrichment and fractionation of nb and ta in the earth s crust the behaviour of niobium and tantalum in magmatic processes has been investigated by conducting mnnb2o6 and mnta2o6 solubility experiments in nominally dry to water saturated peralkaline aluminium saturation index a s i 0 64 to peraluminous a s i 1 22 granitic melts at 800 to 1035 c and 800 to 5000 bars the attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution crystallization mn doped and nb or ta doped experiments at the same pressure and temperature the solubility products of mnnb2o6 ksp nb and mnta2o6 ksp ta at 800 c and 2 kbar both increase dramatically with alkali contents in water saturated peralkaline melts they range from 1 2 10 4 and 2 6 10 4 mol2 kg2 respectively in subaluminous melt a s i 1 02 to 202 10 4 and 255 10 4 mol2 kg2 respectively in peralkaline melt a s i 0 64 this increase from the subaluminous composition can be explained by five non bridging oxygens being required for each excess atom of nb5 or ta5 that is dissolved into the melt the ksp nb and ksp ta also increase weakly with al content in peraluminous melts ranging up to 1 7 10 4 and 4 6 10 4 mol2 kg2 respectively in the a s i 1 22 composition columbite tantalite solubilities in subaluminous and peraluminous melts a s i 1 02 and 1 22 are strongly temperature dependent increasing by a factor of 10 to 20 from 800 to 1035 c by contrast columbite tantalite solubility in the peralkaline composition a s i 0 64 is only weakly temperature dependent increasing by a factor of less than 3 over the same temperature range similarly ksp nb and ksp ta increase by more than two orders of magnitude with the first 3 wt h2o added to the a s i 1 02 and 1 22 compositions whereas there is no detectable change in solubility for the a s i 0 64 composition over the same range of water contents solubilities are only slightly dependent on pressure over the range 800 to 5000 bars the data for water saturated sub and peraluminous granites have been extrapolated to 600 c conditions at which pegmatites and highly evolved granites may crystallize using a melt concentration of 0 05 wt mno 70 to 100 ppm nb or 500 to 1400 ppm ta are required for manganocolumbite and manganotantalite saturation respectively the solubility data are also used to model the fractionation of nb and ta between rutile and silicate melts predicted rutile melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions it is demonstrated that the nb2o5 ta2o5 activity coefficient ratio in the melt phase depends on melt composition this ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions accordingly all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate nb preferentially over ta this explains the enrichment of ta over nb observed in highly fractionated granitic rocks and in the continental crust in general

material transfer and its influence on the formation of slope basins along the south central chilean convergent margin insights from scaled sandbox experiments abstract material transfer along and across a subduction zone determines not only the morphology of an accretionary prism but also the architecture and tectono sedimentary development of their forearc basins however the nature of these processes is not fully resolved yet we investigated through analog simulations the relationship among parameters influencing material transfer along the south central chilean margin and the marine basin evolution seismic lines revealed half graben basins controlled by subvertical faults governing differential uplift and subsidence through the slope the identified sedimentary pattern evidenced three main seismic sequences which have been linked to major climatic fluctuations and episodes of accretion non accretion or tectonic erosion which operate since the pliocene our experimental set up was motivated by the coupled tectonic climatic history of the chile peru trench fill i e climatic episodes represent variations in sediment supply and also in frictional properties of the materials entering in a convergent margin by using three key sandbox experiments we tested two main parameters i variable trench sediment thickness and ii basal frictional properties we highlight that by changing frictional conditions of sediments along the plate interface and the length of adjacent weak and strong segments we modified the evolution of the wedge from frontal to basal accretion in addition we obtained sub vertical faults with potential reactivation such as the observed geometry in seismic lines the change from a long segment of low basal friction to one of high basal friction offered an efficient mechanism to transport a long sand layer similar to a subduction channel this controlled the activation of thrust faults towards the backstop driving shortening and differential uplift with small individual extensional basins forming along the top of the wedge during further underplating the total volume of accommodation space in slope basins decreased whereas the volume of shelf basins tended to increase

electrical resistivity cross section across the garhwal himalaya proxy to fluid seismicity linkage abstract magnetotelluric mt measurements along a profile cutting across the garhwal himalaya of india are inverted to obtain 2 d electrical resistivity structures of the himalayan wedge and of the underthrusting indian plate the imaged resistivity cross section is dominated by a low angle north east dipping intra crustal high conducting layer ic hcl with an average thickness of 5 km at transition from the lesser himalaya to the higher himalaya the ic hcl is marked by a ramp structure across which its top jumps from a depth of 8 km to 13 km high conductivity of the layer is caused by pounding of upward propagating metamorphic fluids trapped by tectonically induced neutral buoyancy in compression regime of the himalaya the mechanical weakening effects of the fluids counteract the fault normal stresses thereby facilitating thrust type earthquakes on a plane imaged as the top of the ic hcl it is suggested that in the himalaya collision belt like the active subduction zone the active seismic plane forming seat of large and great earthquakes is located a few kilometers above the top of the down going plate in this tectonic setting the high conductance ramp symbolizes a block of low shear strength and high strain which under the deviatoric stresses release accentuated stresses into the brittle crust thereby generating small but more frequent earthquakes in the narrow himalayan seismic belt in response to either the co seismic pumping or the stress transfer during inter seismic period the upward infiltration of fluid fluxes into the over pressurized zones sufficiently reduces the shear strength of local thrusts and shear zones turning these into locales of concentrated seismicity

high frequency seismic wave radiation from antiplane cohesive zone model and fmax as source effect while a high frequency cutoff fmax is widely observed in strongmotion seismic data there is no consensus on whether it is due to source processes or to attenuation and scattering of high frequency radiation in the crust or near the surface to investigate the ability of source processes to control fmax we use a standard antiplane crack propagation formalism to numerically model the effect of rupture nucleation and arrest on high frequency radiation based on a simple physical hypothesis a slip weakening model we model rupture arrest due to three types of inhomogeneity 1 a strong portion of rupture medium barrier 2 a drop in the pre existing stress distribution of rupture medium and 3 a finite length of unruptured medium asperity lying between previous ruptures for cases 2 and 3 high frequencies fall off more steeply than 2 and fmax cannot be properly defined for case 1 we find that fmax vflfllj 2 where vf is the final crack velocity lf is the final rupture length and l i is the initial crack size we extrapolate this result to the rupture for a three dimensional model and try to explain observed fm x if we assume that an earthquake is a single crack li is large for a large earthquake however if we assume that an earthquake is made up of set of cracks and asperities fmax will be determined by the interaction of small cracks and barriers if the distribution of these cracks and asperities is independent of source size then fmax will be nearly constant for all earthquakes

characterizing the main himalayan thrust in the garhwal himalaya india with receiver function ccp stacking abstract we use common conversion point ccp stacking of ps receiver functions to image the crustal structure and moho of the garhwal himalaya of india our seismic array of 21 broadband seismometers spanned the himalayan thrust wedge at 79 80 e between the main frontal thrust and the south tibet detachment in 2005 2006 our ccp image shows the main himalayan thrust mht the detachment at the base of the himalayan thrust wedge with a flat ramp flat geometry seismic impedance contrasts inferred from geologic cross sections in garhwal imply a negative impedance contrast velocity decreasing downward for the upper flat located beneath the lower himalaya and a positive impedance contrast velocity increasing downward for the ramp located beneath the surface trace of the munsiari thrust or mct i at the lower flat located beneath the higher himalaya spatially coincident measurements of very high electrical conductivities require the presence of free fluids and we infer a negative impedance contrast on the mht caused by ponding of these fluids beneath the detachment our seismic image indicates that the upper flat of the mht is 10 km below sea level and dips north at 2 connecting to a mid crustal ramp which is 10 km high and dips at 16 the lower flat is 20 25 km below sea level and dips at 4 the main central thrust mct appears as a negative impedance contrast dipping at 16 the moho is nearly horizontal at 35 45 km depth beneath the sub himalaya and lower himalaya deepening to 50 km or more beneath the higher himalaya this depth is 10 25 km shallower than in the nw indian himalaya and 5 10 km shallower than in central nepal requiring significant along strike variations in crustal thickness the observed thickness of subducted indian crust in garwhal is 20 28 km

exhumation history of a shear zone constrained by microstructural and fluid inclusion techniques an example from the satluj valley nw himalaya india abstract the regional structures rock microstructures and fluid inclusion trail patterns have been employed to determine the evolution of the jakhri thrust zone jtz the jtz is a break back thrust cutting across the folded lesser himalayan crystalline nappe and is best exposed in the kulu rampur window zone of the nw himalaya the microstructures in the jtz suggest sw directed ductile shearing and a progressively decreasing finite strain away from the thrust in the footwall the quartz recrystallization microstructures and presence of chlorite in the thrust zone indicate lower greenschist facies p t conditions during deformation the microstructures and fluid inclusion trails secondary show analogous patterns suggesting that the latter would have formed by the healing of microfractures during shearing in the footwall the microthermic studies on these fluid inclusions suggest that the co2 h2o inclusions have been emplaced and reequilibrated during peak deformation whereas the h2o nacl inclusions reequilibrated during footwall exhumation the density and salinity of fluid inclusions were also reset during the same exhumation the isochores of co2 h2o and h2o nacl inclusions in the greenschist facies suggest an isothermal exhumation path from a depth of 15 to 17 km assuming lithostatic pressure conditions these results in the jtz emphasize the utility of fluid inclusions in tectonic studies

long term seismogenic process for major earthquakes in subduction zones abstract a qualitative physical process for the long term seismogenesis of major earthquakes in subduction zones is proposed on the basis of quantitative empirical evidence that swarms mainshocks and aftershocks are closely related phenomena the relations which have been identified in the comprehensive long term catalogues of new zealand and japan represent swarms as predictors of mainshocks with respect to location time and magnitude clustering of swarms and of mainshock aftershock events is allowed for with a database of 15 sequences of swarms mainshocks and aftershocks tests are being conducted with the object of refining the relations and evaluating them as a possible means of practical synoptic forecasting three sequences have culminated in major earthquakes since the tests began and the systematic study now relates a total of 36 swarms with 29 mainshock aftershock events these empirical results strengthen and quantify the connection between swarms and major earthquakes which several authors have demonstrated by means of numerical physical modelling the proposed seismogenic process includes swarms mainshocks and aftershocks as separate event stages which are related by predictability interevent conditions are specified according to the mogi criteria for the medium cracks at which fractures subsequently occur constitute nonuniformity in the mogi sense and post earthquake healing restores uniformity where the gutenberg richter relation occurs it is accepted as possible evidence of deterministic chaos and unpredictability as a corollary the process is noncyclical the principle of scaling is held to apply except when modified by large scale boundaries in the medium subduction zones and some other localities where water is abundant are indicated by the main empirical studies as favourable to the occurrence of swarms fluid overpressuring is therefore proposed as a mechanism for the self triggering of swarms and this is supported by additional examples of the predictive relations occurring in conditions of high fluid pressure including the vicinity of large man made reservoirs the process can be tested by systematic studies in other subduction regions given adequate catalogues for quantifying the algorithm it also has implications for other tectonic environments with swarms replaced by cognate more protracted seismicity precursors

geochemistry of oxide minerals of nb ta sn and sb in the varutrask granitic pegmatite sweden the case of an anomalous columbite tantalite trend the complex petalite subtype varutrask pegmatite in the proterozoic rocks of northern sweden is as a whole rather poor in nb and ta the pegmatite consolidated in eight units but the nb ta oxide minerals attained saturation levels only in a late albite lepidolite bearing unit under conditions of high activity of alkali fluorides consequently the compositional trends of columbite group minerals and cassiterite mimic those typically displayed in pegmatites of the lepidolite subtype from ferroan manganocolumbite with mn mn fe at of 0 35 and ta ta nb of 0 08 through near end member manganocolumbite 0 95 and 0 20 respectively to fe depleted manganotantalite 0 99 and 0 55 respectively and from fe mn nb ta bearing to mn fe ta nb enriched cassiterite to date rare occurrences of cassiterite with mn fe are restricted solely to the lepidolite enriched granitic pegmatites the degree of cation order in the varutrask columbite group minerals increases from early to late phases and with decreasing amounts of heterovalent substitutions slower cooling of initially disordered structures in late phases or their diminished compositional complexity may be responsible for the higher degree of order rare primary microinclusions of cassiterite in columbite group minerals show consistent and systematic preference for ta and fe suggesting an approach to chemical equilibrium but columbite group inclusions in cassiterite show in part a compositional scatter in contrast rare inclusions of ferrotapiolite and wodginite closely reflect the fe mn ta nb compositional features of the host cassiterite stibiotantalite shows high values of ta ta nb and mere traces of bi reflecting the relative abundance of native antimony and stibarsen in the pegmatite and the absence of bi bearing minerals rare primary microlite is ta and f rich whereas the more widespread pyrochlore microlite metasomatic after columbite group minerals reflects the ta ta nb values of the precursors as does the stibiomicrolite replacing stibiotantalite cesium is elevated in several grains of primary and metasomatic pyrochlore group phases that also are enriched in sb but not in stibiomicrolite the array of large cations in pyrochlore microlite metasomatic after columbite group minerals is quite different from that typical of stibiomicrolite suggestive of differences in the nature of the parent fluids the lepidolite subtype signature of the columbite group minerals and cassiterite in the petalite subtype varutrask pegmatite emphasizes the importance of specific conditions controlling stabilization of these minerals the restriction of the columbite group minerals to a very late lepidoliterich unit imposes a lepidolite subtype signature on the whole petalite subtype pegmatite a signature grossly different from the characteristics typical of petalite subtype pegmatites elsewhere

fractionation trends of the nb and ta bearing oxide minerals in the greer lake pegmatitic granite and its pegmatite aureole southeastern manitoba

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

earthquakes in the garhwal himalaya of the central seismic gap a study of historical and present seismicity and their implications to the seismotectonics the historical and the present seismicity catalogues of the garhwal himalaya have been studied for their spatio temporal variations and their implications on the seismotectonics of the region the micro seismicity fractal dimensions dc and frequency magnitude distribution b value coupled with the available literature on geology geomorphology and geophysics have been used to derive the seismotectonics and stress level changes in the region the seismic cross sections for the relocated micro seismicity focal mechanisms and the swath profiles for the presence of physiographic transition 2 pt2 at the foothill of the higher himalaya indicate the constant presence of the mid crustal ramp mcr in the detachment plane and its active seismogenic nature the comparison of this scenario suggests the constant presence of seismogenically active mcr structure throughout the central seismic gap the seismic cross sections further reveal that the sensu stricto main central thrust munsiari thrust is also a site of generation of the micro seismicity in few segments due to its reactivation by thrusting along the mcr the high fractal dimension value dc 1 47 suggests the heterogeneous nature of the region owing to the presence of local faults and transverse tectonics the high stress accumulation in the garhwal himalaya with low b value b 0 70 suggests the high probability of occurrence of a larger or greater earthquake in the near future further the study also reveals that the 2011 chamoli earthquake of m 5 0 preceded by a quiescence period of nearly a year shows different stress levels before and after its occurrence which is well constrained with the increased moderate earthquake activity around the chamoli region this increased seismic activity and stress conditions in the chamoli region suggest the high possibility of the occurrence of major earthquakes hence the study recommend for a detailed seismic hazard evaluation of the region

extrusion vs duplexing models of himalayan mountain building 1 discovery of the pabbar thrust confirms duplex dominated growth of the northwestern indian himalaya since mid miocene ongoing himalayan growth is generally thought to be dominated by duplexing and or extrusion processes these models may be tested by reconstructing himalayan fold thrust belt growth since the middle miocene however our knowledge of basic structural geometry remains too fragmentary to resolve the issue even in areas with rich stratigraphic diversity such as the northwestern indian himalaya in this region a primary outstanding question involves the uncertain relationship of the berinag thrust and the tons thrust structures with displacements of 80 km and 40 km respectively the uncertain geometry and kinematics allow for the complete range of duplexing or extrusion processes for the integrated kinematic history since the middle miocene to address this issue field mapping and kinematic analysis were performed to reconstruct the deformation of the lesser himalayan sequence in the northwest indian himalaya our results reveal a new discovery a 450 m thick top to southwest shear zone termed the pabbar thrust the pabbar thrust placed the outer lesser himalayan sequence the tons thrust hanging wall directly on the berinag group the berinag thrust hanging wall this discovery requires that the berinag thrust and tons thrust are in fact the same structure and discrete duplexing processes dominated growth of the northwest indian himalaya for the past 10 15 million years along strike extension of these kinematics and corresponding geometries is consistent with the observed orogenic framework and resolves a stratigraphic continuity problem across the india west nepal border where prior work suggests that structures are continuous but stratigraphy does not match

possible influence of subducting ridges on the himalayan arc and on the ruptures of great and major himalayan earthquakes abstract subduction of bathymetric features such as ridges seamounts fractures etc on the subducting plate influences the arc morphology and earthquake ruptures we analyse their effect on the development of the arcuate shape of the himalayan arc and on the ruptures of great and major himalayan earthquakes besides the two most prominent ridges in the indian ocean namely the chagos laccadive deccan ridge and the 90 e ridge which are assumed to extend up to the himalayan arc at least three major subsurface ridges have been mapped on the underthrusting indian plate under the indo gangetic plains it appears that the subduction of the two most prominent ridges contributed to the development of the arcuate shape of the himalayan arc the interaction and subduction of the other subsurface ridges probably influenced the himalayan arc morphology by causing a localised cusp in the frontal topography also these ridges probably acted as barriers to the ruptures of the major and great himalayan earthquakes

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

fluid driven earthquakes in the chamoli region garhwal himalaya evidence from local earthquake tomography summary the chamoli region within the 700 km seismic gap of the seismically active region of the central himalaya has been site of moderate sized earthquakes in recent past viz 1999 march 29 mb 6 3 2005 december 14 mb 5 3 and very recently 2011 june 20 m 4 6 to understand the process of earthquake generation in the region we constrain earthquake distribution pattern and determine the crustal seismic wave velocity variation using local earthquake data recorded by the kumaon garhwal himalaya seismic network that was operated during 2005 2008 also we included aftershocks data from the 1999 chamoli earthquake we infer that the earthquakes are mainly clustered near the munsiary thrust marking the southern part of the main central thrust zone and in depth above the main himalayan thrust the chamoli earthquake source region is characterized by low p wave velocity vp and high vp vs this could be expression of possible presence of fluids because of metamorphic dehydration reaction by the underthrusting indian crust the released fluid percolates upwards into the brittle portion of the crust reducing the fault zone friction leading to generation of crustal earthquakes

structure of the chamba nappe and position of the main central thrust in kashmir himalaya abstract the chamba nappe composed of an approximately 8 km thick sequence of late precambrian to jurassic age rocks is located between the higher himalaya crystallines hhc and the lesser himalayan lh formations of panjal imbricate zone piz in the kashmir himalaya to the south the panjal thrust demarcating the base brings the chamba nappe rocks over the panjal imbricate zone to the north the chamba nappe rocks lie over the metamorphic hhc along the south dipping chenab normal fault cnb a pervasive stretching lineation defined by a mineral lineation stretched pebbles and felspar phenocrysts plunges ne nne and occurs on the foliation cleavage surface this lineation is related to southward displacement of the chamba nappe the chamba nappe is folded by regional scale fold viz the chamba tandi and bharmor synclines and the tisa anticline these nw se trending folds structures were developed synchronously with southward thrusting of the chamba nappe the chamba nappe results from southwestward sliding of cover rocks from their basement hhc due to topographic uplift the main central thrust mct in kashmir himalaya is different from that of the kumaun and nepal himalaya the mct vaikrita thrust does not extend west of the beas river but it is exposed in the rampur window and the kishtwar window separating the hhc from the underlying lh rocks southward propagation of the mct from the window zone up cutting the overlying hhc is transferred to the panjal thrust which transports the chamba nappe to the south over the lesser himalayan formations

magmatic hydrothermal evolution of rare metal pegmatites from the mesoproterozoic orange river pegmatite belt namaqualand south africa abstract the 450 km long orange river pegmatite belt intruded the namaqua sector of the mesoproterozoic namaqua natal province southern africa at ca 1 ga the western part of the belt is characterized by the occurrence of lct pegmatites locally mineralized in li ta nb be and bi most of these mineralized pegmatites display zonation with a quartz feldspar muscovite garnet beryl bearing aplite border and wall zone a quartz feldspar spodumene lepidolite bearing intermediate zone and a quartz k feldspar core the pegmatites and their granodioritic country rocks commonly show evidence of albitization and greisenization i e secondary muscovitization in this study detailed petrographic observations and the compositions of mica feldspar spodumene and nb ta oxide minerals are reported this information is combined with bulk country rock compositions and new u pb zircon and monazite ages plus sm nd isotope compositions of monazite to constrain the origin and magmatic hydrothermal evolution of weakly and strongly mineralized lct pegmatites the li ta be kokerboomrand i pegmatite emplaced at ca 985 ma during the main stage of pegmatite emplacement in the orange river belt and regional strike slip deformation it has end t monazite 14 3 and potentially formed by partial melting of paleoproterozoic rocks from the richtersveld magmatic arc alternatively mesoproterozoic sediments of the bushmanland subprovince may also provide a suitable magma source for the kokerboomrand i pegmatite the rare metal contents of muscovite and columbite group minerals cgm increase from the weakly mineralized to strongly mineralized pegmatites suggesting early stage fractional crystallization or variable partial melting conditions mica nb ta values of rare metal bearing minerals crystallized throughout the magmatic hydrothermal evolution of mineralized pegmatites during the magmatic dominated stage i constitutional zone refining likely induced a decrease of spodumene fe contents and increase of cgm ta contents toward the pegmatite core stage ii marks the pervasive circulation of an immiscible hydrosaline melt this stage is characterized by the replacement of the primary mineral assemblage by lamellar albite cleavelandite fluor calciomicrolite and cs ta rich li muscovite and zinnwaldite stage iii represents the progressive transition from a magmatic hydrothermal system dominated by a li cs ta rich hydrosaline melt toward a system mainly involving li cs ta bi rich aqueous fluids this stage is characterized by the crystallization of lepidolite and zero valence dominant pyrochlore as well as strong localized greisenization and bi mineralization magmatic hydrothermal alteration of the immediate country rock of the mineralized pegmatites is marked by the crystallization of albite li ta cs rich mica various nb ta oxide minerals and led to a strong decrease of the whole rock nb ta ratio plus significant rare metal enrichment our findings from the orange river belt demonstrate that an important role can be ascribed to melt melt and melt fluid immiscibility and metasomatism in the formation of pegmatite related rare metal deposits greisens and albitites associated with pegmatites and their immediate country rocks can be considered as favorable targets for li ta mineral exploration strong and pervasive metasomatism across the mineralized pegmatites and their country rocks suggests involvement of a parental medium that was highly enriched in water

crustal velocity structure and earthquake processes of garhwal kumaun himalaya constraints from regional waveform inversion and array beam modeling abstract in order to understand present day earthquake kinematics at the indian plate boundary we analyse seismic broadband data recorded between 2007 and 2015 by the regional network in the garhwal kumaun region northwest himalaya we first estimate a local 1 d velocity model for the computation of reliable green s functions based on 2837 p wave and 2680 s wave arrivals from 251 well located earthquakes the resulting 1 d crustal structure yields a 4 layer velocity model down to the depths of 20 km a fifth homogeneous layer extends down to 46 km constraining the moho using travel time distance curve method we then employ a multistep moment tensor mt inversion algorithm to infer seismic moment tensors of 11 moderate earthquakes with m w magnitude in the range 4 0 5 0 the method provides a fast mt inversion for future monitoring of local seismicity since green s functions database has been prepared to further support the moment tensor solutions we additionally model p phase beams at seismic arrays at teleseismic distances the mt inversion result reveals the presence of dominant thrust fault kinematics persisting along the himalayan belt shallow low and high angle thrust faulting is the dominating mechanism in the garhwal kumaun himalaya the centroid depths for these moderate earthquakes are shallow between 1 and 12 km the beam modeling result confirm hypocentral depth estimates between 1 and 7 km the updated seismicity constrained source mechanism and depth results indicate typical setting of duplexes above the mid crustal ramp where slip is confirmed along out of sequence thrusting the involvement of tons thrust sheet in out of sequence thrusting indicate tons thrust to be the principal active thrust at shallow depth in the himalayan region our results thus support the critical taper wedge theory where we infer the microseismicity cluster as a result of intense activity within the lesser himalayan duplex lhd system

geochronology geochemistry mineralogy and metallogenic implications of the zhaojinggou nb ta deposit in the northern margin of the north china craton china abstract the large zhaojinggou nb ta deposit is located in the northern margin of the north china craton ncc inner mongolia china the deposit is mainly hosted in the mineralized dikes around the hutoushan pluton and the residual pegmatite shell at the top of the pluton samples from the pluton and the mineralized dikes are characterized by high contents of sio2 73 3 84 3 total alkalis 5 24 9 60 and al2o3 7 94 13 8 and moderate a cnk values with an average of 1 04 indicating a weakly peraluminous affinity the trace element patterns are characterized by rb nb ta zr and hf enrichment and markedly negative ba sr p eu and ti anomalies zircon u pb dating suggests that the emplacement of the pluton and the nb ta mineralization occurred coevally in the early cretaceous 126 1 ma and 127 2 ma respectively variations in both bulk rock geochemistry k rb zr hf nb ta and mineral composition mica and columbite consistently unveil a magmatic evolutionary trend from the hutoushan alkali feldspar granite through the hutoushan pegmatite shell to the mineralized dikes typical a type characteristics of the granite and ancient hf isotopic features ehf t ranging from 6 80 to 12 95 and crust model ages from 1 61 to 2 00 ga indicate that the parental magma was derived from the partial melting of palaeoproterozoic crust with insignificant mantle material involved considering the significantly higher bulk contents of nb ta and f in the pegmatite shell and the mineralized dikes than that in the alkali feldspar granite as well as the similar composition in the biotite from the pegmatite shell and the alkali feldspar granite we propose that a residual nb ta enriched brine melt phase segregated from the crystal mush at the late stage of crystallization the progressive concentration of f in the melt was conducive to the solubility of nb and ta in granitic melts and decreased the viscosity by depolymerizing the melt and thus contributed to the high magma differentiation and nb ta concentration the post magmatic fluid triggered the fluid rock interaction resulting in the extensive albitization m type tetrad effect extremely low nb ta ratio

nb ta ti sn oxide mineral chemistry as tracer of rare element granitic pegmatite fractionation in the borborema province northeastern brazil the borborema pegmatitic province bpp northeastern brazil is historically important for tantalum mining and also famous for top quality specimens of exotic nb ta oxides and more recently for the production of gem quality turquoise blue paraiba elbaite with more than 750 registered mineralized rare element granitic pegmatites the bpp extends over an area of about 75 by 150 km in the eastern part of the neoproterozoic serido belt the late cambrian pegmatites are mostly hosted by a sequence of neoproterozoic cordierite sillimanite biotite schists of the serido formation and quartzites and metaconglomerates of the equador formation the trace element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl columbite phosphate subtype electron microprobe analyses empa of columbite tapiolite niobian tantalian rutile ixiolite and wodginite group minerals from 28 pegmatites in the bpp are used to evaluate the effectiveness of nb ta oxide chemistry as a possible exploration tool to trace the degree of pegmatite fractionation and to classify the pegmatites the columbite group mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite this trend is typical of complex spodumene and or lepidolite subtype pegmatites it clearly contrasts with another trend from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions typical of pegmatites of the beryl columbite phosphate subtype large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns this indicates that a large representative data set of heavy mineral concentrate samples collected systematically along cross sections would be necessary to predict the metallogenetic potential of individual pegmatites other mineral species e g garnets and or tourmaline with a more regular distribution than nb ta oxides would be more appropriate and less expensive for routine exploration purposes the currently available nb ta oxide chemistry data suggest the potential for highly fractionated ta li cs pegmatites in the bpp so far undiscovered and encourages further more detailed research

statistical characteristics and origin of oscillatory zoning in crystals complex intracrystalline zoning patterns in hydrothermal garnet and vesuvianite and magmatic plagioclase were analyzed by statistical methods to test for fractal behavior the zoning data were collected by electron and proton microprobe and backscattered electron images and polarized micrographs were digitized the analysis shows that self affine fractal geometry can be used to characterize the zoning patterns of vesuvianite and some garnet patterns the range of power law scaling extended up to two decades the results from the plagioclase samples were not sufficient to determine whether or not the zoning patterns were self affine the measured hurst exponents are mostly in the range 0 25 0 45 indicating fractal scaling and anti persistent behavior this means that an increasing compositional trend in the past favors a decreasing trend in the future and vice versa no distinct periodic components of the zoning patterns were found the influence of environmental changes external fluctuations on a simple crystal growth model was investigated by numerical simulations the concentration at the boundary of a diffusion layer was allowed to vary as a brownian motion curve and the effect of the external fluctuation on diffusion and local growth kinetics was investigated we conclude that factors operating on scales much larger than the local interface processes are most important in controlling the zonation

resolution of non double couple components in the seismic moment tensor using regional networks ii application to aftershocks of the 1999 mw 7 4 izmit earthquake summary we study potential non double couple non dc components in aftershocks of the 1999 izmit earthquake the izmit earthquake ruptured a 140 km long segment of the north anatolian fault zone in northwestern turkey and was followed by the mw 7 1 d uzce earthquake that extended the rupture further to the east focal mechanisms of izmit aftershocks clearly indicate a segmentation of the rupture into several segments one of which is the akyazi plain a pull apart structure where significant non dc components might be observed the analysedearthquakecataloguecontainswaveformsofmorethan4000accuratelylocatedevents observedat35three componentshort periodseismicstations toensurehigh qualitydatawith good focal coverage we apply strict quality criteria to the aftershock catalogue reducing the number of events to only 33 aftershocks for which stable moment tensors were calculated using p and s wave amplitudes the moment tensors of the 33 analysed aftershocks display significant differences in the percentage of the non dc components for the three distinct fault segments the izmit sapanca karadere d uzce and the akyazi segments events located in the izmit sapanca and karadere d uzce segments exhibit only small percentages of the non dc components and if existent they are mainly positive this correlates well with the predominant strike slip stress regime along these segment and also with the main shock rupture being rightlateral strike slip in contrary we found a substantial percentage of non dc components for events below the akyazi plain where the sapanca fault splits into the mudurnu and karadere faults there the observed non dc components are entirely positive indicating a tensional regime and ranging from 20 to 48 percent clearly exceeding the defined error bounds found in a synthetic study this observation is in accordance with the post seismic setting following the izmit main shock that left a remarkable slip deficit of 3 5 m below the akyazi bend

determination of near surface attenuation with κ parameter to obtain the seismic moment stress drop source dimension and seismic energy for microearthquakes in the granada basin southern spain abstract a set of 43 microearthquakes of the granada basin with magnitude duration m d from 1 4 to 3 5 have been spectrally analysed the digital data used in this study was recorded by two short period digital seismic network five permanent stations using andalusian seismic network red sismica de andalucia rsa and three stations of a portable digital seismic network red sismica portatil rsp the displacement spectra for p and s waves were analysed with brune s j geophys res 75 1970 4997 j geophys res 76 1971 5002 source model and the spectra parameters were determined by snoke s model to correct spectra from path attenuation coda q was used for the spectra correction from near surface attenuation parameter was calculated obtaining it from acceleration spectra the values of parameter range from 0 01 to 0 04 s for p waves and from 0 006 to 0 04 s to s waves once the spectra of these attenuation effects was corrected we obtained the seismic moments that range from 5 45 10 17 dyne cm to 1 53 10 20 dyne cm the source radii are between 0 13 and 0 39 km the seismic energy ranges from 7 17 10 3 j to 1 13 10 8 j the stress drop values were below 4 bars the scaling relations between seismic moment and stress drop indicated decreasing stress drop with decreasing seismic moment