suitability of open ocean instrumentation for use in near field tsunami early warning along seismically active subduction zones over the past decade the number of open ocean gauges capable of parsing information about a passing tsunami has steadily increased particularly through national cable networks and international buoyed efforts such as the deep ocean assessment and reporting of tsunami dart this information is analyzed to disseminate tsunami warnings to affected regions however most current warnings that incorporate tsunami are directed at mid and far field localities in this study we analyze the region surrounding four seismically active subduction zones cascadia japan chile and java for their potential to facilitate local tsunami early warning using such systems we assess which locations currently have instrumentation in the right locations for direct tsunami observations with enough time to provide useful warning to the nearest affected coastline and which are poorly suited for such systems our primary findings are that while some regions are ill suited for this type of early warning such as the coastlines of chile other localities like java indonesia could incorporate direct tsunami observations into their hazard forecasts with enough lead time to be effective for coastal community emergency response we take into account the effect of tsunami propagation with regard to shallow bathymetry on the fore arc as well as the effect of earthquake source placement while it is impossible to account for every type of off shore tsunamigenic event in these locales this study aims to characterize a typical large tsunamigenic event occurring in the shallow part of the megathrust as a guide in what is feasible with early tsunami warning

mechanisms of crustal anatexis a geochemical study of partially melted metapelitic enclaves and host dacite se spain to shed light on the mechanisms of crustal anatexis a detailed geochemical study has been conducted on minerals and glasses of quenched anatectic metapelitic enclaves and their host peraluminous dacites at el hoyazo se spain anatectic enclaves composed of plagioclase biotite sillimanite garnet glass k feldspar cordierite graphite formed during the rapid heating and overstepped melting of a greenschist facies metapelite and finally equilibrated at 850 508c and 5 7 kbar glass appears as melt inclusions within all mineral phases and in the matrix of the enclaves and has a major element composition similar to that of peraluminous leucogranites melt inclusions and matrix glasses have normative quartz orthoclase albite compositions that plot in the vicinity of h2o undersaturated haplogranite eutectics melt inclusions show some compositional variability with high li cs and b low y first row transition elements frte and rare earth elements ree and zircon and monazite saturation temperatures of 665 7508c they are interpreted as melts produced by muscovitebreakdown melting reactions at the onset of the process of rapid melting and mostly under h2o undersaturated conditions compared with melt inclusions matrix glasses show less compositional variability lower large ion lithophile element contents higher y frte and ree and higher zircon and monazite saturation temperatures 695 8158c they are interpreted as former melts recording the onset of biotite dehydration melting matrix glasses in the dacite are compositionally different from glasses in the enclaves hence the genetic connection between metasedimentary enclaves and dacite is not as straightforward as previous petrographic and bulk major element data suggest this opens the possibility for some alternative interpretation this study shows the following 1 melt inclusions provide a window of information into the prograde evolution of anatexis in the enclaves 2 melting occurred for the most part under h2o undersaturated conditions even if because of the rapid heating the protolith preserved most of the structurally bound h2o contained at greenschist facies up to the beginning of anatexis such that the excess h2o maximized the amount of h2o undersaturated melt generated during anatexis 3 although a large proportion of accessory minerals are currently shielded within major mineral phases they have progressively dissolved to a considerable extent into the melt phase along the prograde anatectic path as indicated by the relative clustering of accessory mineral saturation temperatures and closeness of these temperatures to those of potential melting reactions 4 the dacite magma was probably produced by coalescence of melts

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

rupture kinematics of the 2005 mw 8 6 nias simeulue earthquake from the joint inversion of seismic and geodetic data the 2005 mw 8 6 nias simeulue earthquake was caused by rupture of a portion of the sunda megathrust offshore northern sumatra this event occurred within an array of continuous global positioning system gps stations and produced measurable vertical displacement of the fringing coral reefs above the fault rupture thus this earthquake provides a unique opportunity to assess the source character istics of a megathrust event from the joint analysis of seismic data and near field static co seismic displacements based on the excitation of the normal mode data and geodetic data we put relatively tight constraints on the seismic moment and the fault dip where the dip is determined to be 8 to 10 with corresponding moments of 1 24 10 22 to 1 00 10 22 n m respectively the geodetic constraints on slip distribution help to eliminate the trade off between rupture velocity and slip kine matics source models obtained from the inversion of various combinations of the teleseismic body waves and geodetic data are evaluated by comparing predicted and observed long period seismic waveforms 100 500 sec our results indicate a rela tively slow average rupture velocity of 1 5 to 2 5 km sec and long average rise time of up to 20 sec the earthquake nucleated between two separate slip patches one beneath nias and the other beneath simeulue island the gap between the two patches and the hypocentral location appears to be coincident with a local geological disrup tion of the forearc coseismic slip clearly tapers to zero before it reaches the trench probably because the rupture propagation was inhibited when it reached the accre tionary prism using the models from joint inversions we estimate the peak ground velocity on nias island to be about 30 cm sec an order of magnitude slower than for thrust events in continental areas this study emphasizes the importance of util izing multiple datasets in imaging seismic ruptures

andalusite and na and li rich cordierite in the la costa pluton sierras pampeanas argentina textural and chemical evidence for a magmatic origin the la costa pluton in the sierra de velasco nw argentina consists of s type granitoids that can be grouped into three igneous facies the alkali rich santa cruz facies scf sio2 67 wt distinguished by the presence of andalusite and na and li rich cordierite na2o 1 55 1 77 wt and li2o 0 14 0 66 wt the anillaco facies sio2 74 wt with a significant proportion of mn rich garnet and the anjullon facies sio2 75 wt with abundant albitic plagioclase the petrography mineral chemistry and whole rock geochemistry of the scf are compatible with magmatic crystallization of na and li rich cordierite andalusite and muscovite from the peraluminous magma under moderate p t conditions 1 9 kbar and ca 735 c the high li content of cordierite in the scf is unusual for granitic rocks of intermediate composition

miocene andalusite leucogranite in central east himalaya everest masang kang area low pressure melting during heating abstract the studied miocene andalusite bearing leucogranites intrude the upper part of the high himalayan crystallines hhc and the north himalayan domes and outcrop in an area stretching from mt everest to the kula khangri massif bhutan towards the east the leucogranites constitute both dykes as well as sills and parts of larger andalusite free leucogranite plutons e g makalu they represent mainly of two mica muscovite biotite tourmaline cordierite andalusite sillimanite dumortierite leucogranite and tourmaline muscovite tourmaline biotite andalusite sillimanite garnet kyanite spinel corundum leucogranites microstructures reveal several generations of andalusite from residual peritectic early magmatic to cotectic late magmatic even in the same sample the occurrence of residual and or peritectic andalusite together with inclusions of sillimanite biotite in cordierite indicates that melts formed by dehydration melting of biotite at t 660 700 c during prograde heating at low pressure conditions p according to current models leucogranites are produced by dehydration melting of muscovite and or biotite during exhumation of the hhc in this case micas are consumed in the sillimanite stability field as a consequence these models cannot explain the occurrence of residual and or peritectic magmatic andalusite conditions for anatexis in the andalusite field may have been achieved by heat transfer within the exhuming extruding hhc from structurally lower and hotter rocks towards upper and colder fertile lithologies

dissolution of corundum and andalusite in h2o saturated haplogranitic melts at 800 c and 200 mpa constraints on diffusivities and the generation of peraluminous melts of h2o in the aluminum alkali eigenvector could not be obtained the mechanisms and kinetics of equilibration between peraluminous from our results we propose that some h2o may provide charge minerals and granitic melt were investigated experimentally by balance for excess aluminum multicomponent diffusion models the dissolution of corundum and andalusite into h2o saturated yield eigenvalues for the corresponding aluminum alkali eigenvector metaluminous haplogranitic melt at 800 c and 200 mpa mineral of 0 3 10 to 1 9 10 cm s calculated effective and haplogranitic glass rods were juxtaposed inside platinum binary diffusion coefficients for al2o3 are higher 1 0 10 to capsules and then subjected to experimental conditions for times 3 6 10 cm s these diffusion coefficients are used to ranging from 12 to 2900 h upon melting the mineral melt calculate equilibration times between peraluminous minerals and interface retreats with the square root of time the composition of granitic melts in a model system in which two grains of corundum the melt at the interface changes with time but its asi aluminum or andalusite 1 cm apart are connected via a narrow melt column saturation index molar al2o3 cao na2o k2o at the conditions of the experiments diffusive equilibrium through remains constant at 1 20 after 480 h this value is close to initially metaluminous h2o saturated melt would be attained within the asi of an h2o saturated haplogranitic melt in equilibrium with 10 10 years at h2o activity well below saturation of the corundum or andalusite which may indicate that the composition of melt lower diffusivity of all components may increase the time to the melt at the interface follows the liquidus of these minerals in equilibration to 10 10 years approaching possible time frames the system sodium and potassium diffuse rapidly uphill across the for the generation and extraction of crustal melts entire length of the charge towards the interface resulting in a rapid and uniform increase in asi throughout the entire melt column this uphill diffusion of alkalis is due to coupling with excess aluminum entering the melt at the interface and involves long range

carboniferous inherited grain and age zoning of monazite and xenotime from leucogranites in far eastern nepal constraints from electron probe microanalysis chemical th u total pb isochron method chime of monazite and xenotime from three leucogranites in far eastern nepal revealed the presence of carboniferous inherited grains of monazite and intense intrusion of leucogranites around 18 16 ma in the high himalaya in garnet bearing sillimanite muscovite biotite leucogranite most monazite grains have inherited cores with the chemical dates of 504 418 and 342 272 ma which were overgrown by early miocene mantles and rims of 17 9 1 5 ma early ordoviciain and carboniferous ages are rarely found in the same euhedral subhedral cores in addition to the previously recognized early paleozoic magmatism monazite cores with carboniferous ages in early miocene leucogranites provide evidence for two periods of magmatism at the base of the high himalaya prior to the cenozoic himalayan orogeny in muscovite biotite leucogranite no inherited domains were observed in monazite and xenotime grains they yielded the chime monazite and xenotime dates of 16 1 2 0 and 19 8 6 5 ma respectively monazite grains adjacent to xenotime have significantly lower concentrations of uo 2 and y 2 o 3 compared to those isolated from xenotime these results imply that xenotime influences y and u contents in monazite reflecting local equilibrium system in aplitic leucogranite monazite grains yielded the mean of apparent chemical date of 18 0 2 2 ma the chime monazite ages of 18 16 ma in three leucogranites reflect the timing of melt crystallization

metamorphic zonation migmatization and leucogranites along the everest transect of eastern nepal and tibet record of an exhumation history

out of sequence deformation and expansion of the himalayan orogenic wedge insight from the changgo culmination south central tibet 1 the changgo culmination one of the north himalayan domes in south central tibet consists of a multiphase granite core surrounded by a deformed metasedimentary carapace the granitic core records general non coaxial shear with a top to the south sense shear component the contact between the core and the carapace is a shear zone characterized by general non coaxial shear with a top to the north shear sense interpreted to be the northern continuation of the south tibetan detachment system stds the shear zone contains lenses of leucogranite dated at 35 4 ma this is interpreted to reflect eocene crustal thickening coeval with the earliest shortening event recorded in the carapace the main phase of the changgo granite crystallized at 23 5 ma while undeformed aplite dikes the youngest phase observed in the granite were intruded at 22 1 ma aplite dikes crosscut the main deformation fabric within the changgo granite therefore that deformation and associated south directed shearing must have ended between 23 5 ma and 22 1 ma the dikes are strained within the stds indicating that final displacement along the stds must post date 22 ma yet be older than 18 4 ma the cooling age of muscovite in the shear zone it is proposed that the exhumation of the changgo culmination is related to tectonically driven erosion in response to crustal thickening and rebuilding of the orogenic critical taper wedge subsequently deformation in the wedge migrated toward the foreland expanding the orogenic wedge laterally and moving the locus of displacement from the main central thrust structurally downward to the main boundary thrust

contrasting behaviour of boron during crustal anatexis the study of volatile elements in crustal anatectic terranes may provide information about the role of fluid flow and fluid pathways during high temperature metamorphism we have studied the distribution of li and b in two migmatitic areas the pena negra anatectic complex central spain and the migmatites and leucogranites associated with the ronda peridotites southern spain they represent two contrasting cases in the behaviour of volatiles particularly b during anatexis the pena negra migmatites are dominated by diatexites where it is possible to distinguish granitic leucosomes melanosomes metric to decimetric leucogranitic segregates and decimetric to metric sillimanite rich restitic enclaves all lithologies are characterized by low b concentrations mean values 30 ppm and b is enriched in melanosomesrrestites with respect to leucosomesrleucogranites this may be due to the fact that a notable proportion of b can reside in restitic sillimanite b concentrations in leucosomes and leucogranites can be explained by closed system anatexis at ronda metatexitic and diatexitic migmatites underlie the ronda peridotites and diatexite and leucogranite dikes intrude the peridotites diatexites underlying the peridotites are characterized by cordierite q biotite garnet as ferromagne sian phases with rare or absent tourmaline low b contents 10 ppm and cordierite garnet leucosomes leucogranite dikes have high b concentrations mean valuef 400 ppm with tourmaline being a common and sometimes the most abundant ferromagnesian phase a genetic relationship between diatexites and leucogranites is strongly suggested by the presence of dikes of diatexites intruding the bottom of the peridotites we conclude that b in the leucogranites may stem from the dissolution of tourmaline originally present in the metasediments or infiltration of b rich aqueous fluids into the anatectic zone according to recent experimental work textures in some tourmaline rich ronda leucogranites suggest initial b o 23 contents in the melt higher than the present measured concentrations preliminary experimental results presented in this paper propose that this difference is not due to water activities in the melt rapid crystallization of the melts following undercooling may explain the existence of abundant euhedral tourmaline in leucogranites with low aluminium saturation index asis molar al o r caoq na oq k o and relatively low b contents q 2001 elsevier science b v all rights 23 2 2 reserved

tsunami inundation modeling for western sumatra a long section of the sunda megathrust south of the great tsunamigenic earthquakes of 2004 and 2005 is well advanced in its seismic cycle and a plausible candidate for rupture in the next few decades our computations of tsunami propagation and inundation yield model flow depths and inundations consistent with sparse historical accounts for the last great earthquakes there in 1797 and 1833 numerical model results from plausible future ruptures produce flow depths of several meters and inundation up to several kilometers inland near the most populous coastal cities our models of historical and future tsunamis confirm a substantial exposure of coastal sumatran communities to tsunami surges potential losses could be as great as those that occurred in aceh in 2004

the not so simple relationship between seismicity and oil production in the permian basin west texas we have relocated seismicity occurring in the permian basin of west texas between 1975 and 1979 using three dimensional velocity models constructed from well log information and compared the locations to detailed geological and geophysical models of specific oil fields the seismicity appears to be related to a variety of causes including migration of naturally occurring overpressured fluids tectonic activity reservoir production and enhanced recovery operations many earthquakes may represent a combination of these effects although the permian basin is the site of numerous oil and gas fields only a limited number of fields appears to be associated with seismicity we find that there are similarities in the structural setting in the fields associated with seismicity furthermore fields within the delaware basin that are associated with seismicity are located in regions of high vertical and lateral fluid pressure gradients related to an overpressured zone within the delaware basin

timescales of melt generation and the thermal evolution of the himalayan metamorphic core everest region eastern nepal in the everest region of the nepalese himalaya 40ar 39ar and u pb geochronology provide evidence for a complex thermal history marked by multiple episodes of granite intrusion the oldest mobilized melt formed syn deformational granitic sills that have u pb crystallization ages of 21 33 0 03 and 21 80 0 05 ma preserved in these same granites is a record of earlier magmatic crystallization of xenotime zircon and monazite between ca 26 ma and ca 23 ma this pattern of accessory phase crystallization is interpreted to reflect incremental melting and crystallization in the source region of the sills before ultimate melt migration and provides the earliest evidence for anatexis in the everest region the beginning of crustal melting in the everest region predates the earliest known movement on both the main central thrust and the south tibetan fault systems but is temporally associated with the implied pressure decrease between eohimalayan and neohimalayan metamorphism

an experimental study of element partitioning among biotite muscovite and coexisting peraluminous silicic melt at 200 mpa h2o

andalusite sillimanite quartz veins as indicators of low pressure high temperature deformation during late stage unroofing of a metamorphic core complex turkey ductilely deformed veins consisting of quartz andalusite in which the andalusite is partially replaced by fibrous sillimanite locally occur in garnet sillimanite schist near a margin of the nigde metamorphic core complex in south central turkey mineral assemblages reaction textures and structural features of the veins record low pressure high temperature deformation during exhumation of mid crustal rocks the partial replacement of andalusite by sillimanite may indicate a late stage increase in temperature and or fluid pressure possibly related to miocene magmatism during extensional unroofing of the core complex aluminosilicate bearing veins are observed at the eastern margin of the massif where metapelitic rocks were deformed during unroofing of the core complex veins formed in aluminous rocks where deformation enhanced permeability allowed fluid flow during extensional shear the cm scale veins are typically boudinaged and form asymmetric lenses concordant with the host rock foliation and are parallel to the down dip lineation defined by sillimanite and stretched biotite aluminosilicate bearing boudins record top to the east shear sense which is compatible with the extensional shear sense displayed by structures in the host rock

the tsunami of 2007 september 12 bengkulu province sumatra indonesia post tsunami field survey and numerical modelling summary the m w 8 4 earthquake on 2007 september 12 offshore of the bengkulu province of sumatra indonesia generated a moderate tsunami with run up heights of up to 4 m as measured by indonesian and international researchers in the days following the earthquake the tsunami was observed along 250 km of coastline and caused damage at several locations the largest wave heights and most severe inundation were observed about 50 km to the northwest of bengkulu elsewhere the effects were less severe with the exception of substantial inundation at a site 150 km to the south in addition to presenting the field data we conduct a modelling study and compare the run up heights and water level predictions from four different seismic deformation models used to initialize a tsunami propagation and inundation model our comparative results suggest that for this event the estimates of fault parameters available immediately after determination of the earthquake size and location predicted the near field run up heights and distribution and far field wave equally well as estimates obtained using more detailed descriptions of the seafloor deformation as typically available hours or days after an event we conclude that while detailed slip patterns can be important to the near field run up distribution simple fault models can be used to rapidly assess the likely near and far field tsunami effects of a particular earthquake

experiments on the kinetics of partial melting of a leucogranite at 200 mpa h 2 o and 690 800 c compositional variability of melts during the onset of h 2 o saturated crustal anatexis we have experimentally investigated the kinetics of melting of an aplitic leucogranite quartz sodic plagioclase of ab90 k feldspar traces of biotite at 690 740 and 800 c all at 200 mpa h2o leucogranite cylinders 3 5 mm in diameter and 7 mm in length were run in the presence of excess h2o using cold seal pressure vessels for 11 2 925 h at 690 and 740 c and any experimental time and 800 c and short run times silicate glass melt at run conditions occurs as interconnected films along most of the mineral boundaries and in fractures with the predominant volume occurring along quartz feldspars boundaries and quartz plagioclase k feldspar triple junctions glass film thickness is roughly constant throughout a given experimental charge and increases with experimental temperature and run duration the results indicate that h2o saturated partial melting of a quartzo feldspathic protolith will produce an interconnected melt phase even at very low degrees 5 vol of partial melting crystal grain boundaries are therefore completely occluded with melt films even at the lowest degrees of partial melting resulting in a change in the mechanism of mass transport through the rock from advection of aqueous vapor to diffusion through silicate melt at 690 and 740 c the compositions of glasses are homogeneous and at both temperatures close to but not on the h2o saturated 200 mpa haplogranite eutectic glass compositions do not change with run duration at 800 c glasses are heterogeneous and plot away from the minimum although their molar ratios asi mol al2o3 cao na2o k2o and al na are constant throughout the entire charge at any experimental time glass compositions within individual 800 c experiments form linear trends in wt normative quartz albite orthoclase space the linear trends are oriented perpendicular to the 200 mpa h2o haplogranite cotectic line reflecting nearly constant albite orthoclase ratio versus variable quartz feldspar ratio and have endpoints between the 800 c isotherms on the quartz and feldspar liquidus surfaces with increasing experimental duration the trends migrate from the potassic side of the minimum toward the bulk rock composition located on the sodic side due to more rapid and complete dissolution of k feldspar relative to plagioclase the results indicate that partial melting at or slightly above the solidus 690 740 c is interface reaction controlled and produces disequilibrium melts of near minimum composition that persist metastably for up to at least 3 months relict feldspars show no change in composition or texture and equilibration between melt and feldspars might take from a few to tens of millions of years partial melting at temperatures well above the solidus 800 c produces heterogeneous disequilibrium liquids whose compositions are determined by the diffusive transport properties of the melt and local equilibrium with neighboring mineral phases feldspars recrystallize and change composition rapidly partial melting and equilibration between liquids and feldspars might take from a few to tens of years h2o saturated conditions at these temperatures well above the solidus

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

calculation of partial melting equilibria in the system na2o cao k2o feo mgo al2o3 sio2 h2o nckfmash a thermodynamic model for haplogranitic melts in the system na2o cao k2o al2o3 sio2 h2o nckash is extended by the addition of feo and mgo with the data for the additional end members of the liquid incorporated in the holland powell 1998 internally consistent thermodynamic dataset the resulting dataset with the software thermocalc is then used to calculate melting relationships for metapelitic rock compositions the main forms for this are p t and t x pseudosections calculated for particular rock compositions and composition ranges the relationships in these full system pseudosections are controlled by the low variance equilibria in subsystems of nckfmash in particular the solidus relationships are controlled by the solidus relationships in nkash and the ferromagnesian mineral relationships are controlled by those in kfmash however calculations in nckfmash allow the relationships between the common metapelitic minerals and silicate melt to be determined in particular the production of silicate melt and melt loss from such rocks allow observations to be made about the processes involved in producing granulite facies rocks particularly relating to open system behaviour of rocks under high grade conditions

phase relations of peraluminous granitic rocks and their petrogenetic implications peraluminous granitic rocks are magmatic rocks that contain quartz po tassic feldspar and or sodic plagioclase and one or more aluminum rich minerals thus these rocks contain more aluminum than could be accom modated by feldspar in a cipw normative calculation and show normative corundum peraluminous granites are defined by their chemical nature but their recognition is often based on petrography this discrepancy thus may lead to inconsistency although peraluminous granitic rocks are com monly true granite streckeisen 1973 they range from tonalite to granite of special interest are strongly peraluminous as defi ned below granite granodiorite or in rare instances trondhjemite these rocks contain alumi nous minerals almandinic garnet cordierite tourmaline muscovite that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous the origin of peraluminous granite and related intrusive rocks is of much current interest many of these form shallow level intrusions and they can reach enormous sizes examples are the batholiths in the lachlan fold belt in southeastern australia white chappell 1983 the cornub ian batholith in england exley stone 1966 the south mountain batholith in nova scotia mckenzie clarke 1975 the manaslu batho lith in the himalayas lefort 1981 much of the idaho batholith

stability of andalusite and sillimanite and the al_ 2 sio_ 5 triple point constraints from the ballachulish aureole scotland andalusite and and sillimanite sil occur in well defined zones in the ballachulish aureole in most of the aureole s sillimanite bearing rocks sillimanite grain diameters range from 2 m to 10 m the boundary between prograde andalusite and prograde sillimanite is constrained to a zone of max 30 m width upgrade of the muscovite quartz andalusite k feldspar h 2 o reaction isograd this boundary is interpreted to correspond to the and sil equilibrium the common occurrence of andalusite well upgrade of the first occurrence of sillimanite is ascribed to sluggish kinetics of the polymorphic inversion the p t position of the and sil equilibrium in the aureole is estimated as 645 20 c and 3 0 0 4 kbar based on a combination of 1 location of the ms qtz and kfs h 2 o reaction corrected for non end member fluid and mineral compositions and 2 independent pressure estimates obtained from equilibria in metapelites marbles calcsilcates and granitoids all in exce

oligocene miocene middle crustal flow in southern tibet geochronology of mabja dome new u pb zircon monazite 40 ar 39 ar and apatite fission track ages provide constraints on the timing of formation and exhumation of the mabja dome southern tibet shed light on how this gneiss dome formed and provide important clues on the tectonic evolution of middle crustal rocks in southern tibet zircons from a deformed leucocratic dyke swarm yield a u pb age of 23 1 0 8 ma providing the first age constraint on the timing of middle crustal ductile horizontal extension in the north himalayan gneiss domes zircons and monazite from a post tectonic two mica granite yield ages of 14 2 0 2 ma and 14 5 0 1 respectively indicating that vertical thinning and subhorizontal stretching had ceased by the middle miocene mica 40 ar 39 ar ages from schists and orthogneisses increase structurally down section from 12 85 0 13 ma to 17 0 0 19 ma and then decrease at the deepest structural levels to 13 29 0 09 ma micas from the leucocratic dyke swarm and post tectonic two mica granites yield similar 40 ar 39 ar cooling ages of 13 48 0 13 to 12 84 0 08 ma the low temperature steps of potassium feldspar 40 ar 39 ar spectra yield ages of c 11 0 12 5 ma and apatite fission track analyses indicate the dome uniformly cooled below c 115 c at 9 5 0 6 ma based on these data calculated average cooling rates across the dome range from c 40 60 c million years in schist and orthogneiss and following emplacement of the leucocratic dyke swarm to c 350 c million years following emplacement of the two mica granites the mylonitic foliation peak metamorphic isograds and mica 40 ar 39 ar chrontours are domed whereas the low temperature step potassium feldspar 40 ar 39 ar and apatite fission track chrontours are not suggesting that doming occurred between 13 0 and 12 5 ma and at temperatures between 370 and 200 c our new ages along with field structural and metamorphic data indicate that the domal geometry observed at mabja developed by middle miocene southward directed thrust faulting upward and southward along a north dipping ramp above cold tethyan sediments the structural metamorphic and geochronologic histories documented at mabja dome are similar to those of kangmar dome suggesting a common mode of occurrence of these events throughout southern tibet vertical thinning and horizontal stretching metamorphism generation of migmatites and emplacement of leucogranites in the domes of southern tibet are synchronous with similar events in the greater himalayan sequence that underlie the high himalaya these relations are consistent with previously proposed models for a ductile middle crustal channel bounded above by the south tibetan detachment system and below by the main central thrust in the high himalaya that extended northward beneath southern tibet

the four plutonic belts of the transhimalaya himalaya a chemical mineralogical isotopic and chronological synthesis along a tibet nepal section

probabilistic assessment of potential fault slip related to injection induced earthquakes application to north central oklahoma usa we utilize quantitative risk assessment qra to calculate the conditional probability of slip on mapped faults in response to injection related increases in pore pressure in north central oklahoma usa where widespread injection of produced saltwater has triggered thousands of small to medium sized earthquakes in the past 7 yr the conditional probability incorporates the uncertainty in each mohr coulomb parameter stress tensor pore pressure coefficient of friction and fault orientation through qra the result is a cumulative distribution function of the pore pressure required to cause slip on each fault segment the results can be used to assess the probability of induced slip on a known fault from a given injection related pore pressure increase after dividing north central oklahoma into six study areas we invert earthquake focal plane mechanisms in each area to constrain the orientation and relative magnitude of the principal stresses the qra identifies the potential for slip on the fault that produced the m 5 6 prague earthquake in 2011 and the northeastern extension of a mapped fault associated with the m 5 1 fairview earthquake sequence that occurred in early 2016 and had the 289 striking fault of the september 2016 m 5 8 pawnee event been mapped it would have been identified as potentially active

source process of the september 12 2007 mw 8 4 southern sumatra earthquake from tsunami tide gauge record inversion 1 we infer the slip distribution and average rupture velocity of the magnitude mw 8 4 september 12 2007 southern sumatra earthquake from available tide gauge records of the ensuing tsunami we select 9 waveforms recorded along the west coast of sumatra and in the indian ocean slip distribution and rupture velocity are determined simultaneously by means of a non linear inversion method we find high slip values 10 m into a patch 100 km long and 50 km large between 20 and 30 km of depth about 100 km north west from the epicenter we conclude this earthquake did not rupture the whole area of the 1833 event indicating some slip has still to occur our estimate of rupture velocity is of 2 1 0 4 km sec the relatively large depth of the main slip patch is the likely explanation for the low damaging observed tsunami

u th pb systematics and ages of himalayan leucogranites south tibet abstract the age and origin of five leucogranites from the high and tethys himalaya and two country rock gneisses were investigated by u pb dating of zircon fractions and single grains and fractions of monazite additionally th u concentrations in whole rock powders and isotopic compositions of pb in leached k feldspars were determined monazites yield ages of 16 8 0 6 m y for the nialam migmatite granite 15 1 0 5 m y for the lhagoi kangri granite 14 3 0 6 m y for a granite from mt everest and 9 8 0 7 m y and 9 2 0 9 m y for two varieties of the maja granite these data together with monazite ages of 21 9 0 2 and 24 0 0 4 m y determined earlier on the makalu granite 1 substantiate a period of intracontinental granite emplacements from 24 to 9 m y ago i e from uppermost oligocene to late miocene times such a period of plutonic activity is consistent with the view that all these granites result from intracrustal melting following the collision of india with eurasia furthermore the individual ages together with structural relationships between granites and country rocks suggest that granite formation and tectono metamorphism occurred as alternating and strongly related processes with a periodicity of 7 to 9 m y inherited lead components present in all granite zircons point to large proportions of precambrian material in the magma source regions up to 2200 m y old th u systematics between monazite and country rocks indicate that u has been leached from most of the granites after crystallisation of monazite zircon dating of the kangmar granite gneiss which occurs in a window through the tethys himalayan sediments shows that this pluton transformed to a gneiss during the alpine orogeny crystallised in lowermost palaeozoic times 562 4 m y ago

the 2016 mw5 1 fairview oklahoma earthquakes evidence for long range poroelastic triggering at 40 km from fluid disposal wells abstract wastewater disposal in the central u s is likely responsible for an unprecedented surge in earthquake activity much of this activity is thought to be driven by induced pore pressure changes and slip on pre stressed faults which requires a hydraulic connection between faults and injection wells however direct pressure effects and hydraulic connectivity are questionable for earthquakes located at large distances and depths from the injectors here we examine triggering mechanisms of induced earthquakes which occurred at more than 40 km from wastewater disposal wells in the greater fairview region northwest oklahoma employing numerical and semi analytical poroelastic models the region exhibited few earthquakes before 2013 when background seismicity started to accelerate rapidly culminating in the mw5 1 fairview earthquake in february 2016 injection rates in the 2 2 5 km deep arbuckle formation started to increase rapidly in 2012 about two years before the start of seismicity increase most of the injection activity was concentrated toward the northeast of the study region generating a relatively cohesive zone of pressure perturbations between 0 1 and 1 mpa much of the near injection seismicity was likely triggered by pressure effects and fault assisted pressure diffusion to seismogenic depth outside of the high pressure zone we observed two remarkably detached linear seismicity clusters which occurred at 20 to 50 km distance from the initial seismicity and 10 to 40 km from the nearest high rate injector semi analytical models reveal that poroelastically induced coulomb stress changes surpass pore pressure changes at these distances providing a plausible triggering mechanism in the far field of injection wells these results indicate that both pore pressures and poroelastic stresses can play a significant role in triggering deep and distant earthquakes by fluid injection and should be considered for seismic hazard assessment beyond the targeted reservoir

two mica and tourmaline leucogranites from the everest makalu region nepal tibet himalayan leucogranite genesis by isobaric heating in the higher himalaya of the region from cho oyu to the arun valley northeast of makalu the miocene leucogranites are not hosted only in the upper high himalayan crystallines hhc a network of dykes also cuts the lower hhc and the lesser himalayan crystallines lhc the plutons and dykes are mainly composed of two mica muscovite biotite tourmaline cordierite andalusite sillimanite leucogranite with tourmaline 2 6 and biotite 1 5 modal and tourmaline muscovite tourmaline biotite sillimanite garnet kyanite andalusite spinel corundum leucogranite with tourmaline 2 2 and biotite 1 5 modal both leucogranite types were produced by partial melting in the andalusite sillimanite facies series under lp ht conditions constrained by the occurrence of peritectic andalusite and cordierite the geochemical features of the leucogranites suggest that tourmaline leucogranite was produced by muscovite dehydration melting in muscovite rich metapelites at p 350 mpa and t 640 c whereas two mica leucogranite was produced by biotite dehydration melting in biotite rich metapelites at p 300 mpa and t 660 710 c melting in fertile muscovite rich metapelites of the top of both the hhc and lhc produced magmas which were emplaced at the same structural level in which they had been generated melting in the biotite rich gneiss of both the hhc and lhc produced hotter magmas which were transported upwards by dyking and eventually coalesced in the plutons of the upper hhc a similar process also produced a network of two mica granite at the top of the lhc in the ama drime nyonno ri range northeast of makalu the prograde character of leucogranite melt producing reactions in the everest makalu area suggests that here the generation of miocene leucogranites took place in a regime of nearly isobaric heating following nearly adiabatic decompression

extensional flow produces recumbent folds in syn orogenic granitoids padron migmatitic dome nw iberian massif this contribution provides a case example on the generation of large scale recumbent folds in syn orogenic granitoids we analyze the progressive reworking of extension related structures into later ones after a period of crustal thickening the padron migmatitic dome formed after the climax of the gondwana laurussia collision in the late paleozoic petrostructural analysis carried out in the eastern flank of this dome reveals that extensional flow resulted in progressive exhumation of mainland gondwana which rested under peri gondwanan allochthonous terranes and a suture zone during maximum crustal thickening exhumation proceeded up to upper crust levels andalusite stability field along with partial melting of the middle lower crust and with the generation of granitoid laccoliths during an early extensional stage newly formed lithological and mechanical anisotropies such as the presence of variably sized sheet shaped bodies of syn orogenic granitoids provided a favorable rheological setting for fold nucleation during the intermediate stages of extension in extending orogenic crust whether recumbent folds occur after significant melt production depends on the lateral vertical flow ratio and on the orientation of deforming bodies with regard to kinematic strain axes we suggest that subhorizontal extensional flow dominated over vertical flow during the early and intermediate stages of the evolution of the padron dome a component of vertical diapiric flow caused progressive tilting of the sheet like bodies and obliquity respect to strain axes this resulted in the development of regional scale folds at the expense of syn orogenic granitoids such as in the case of the portomouro recumbent synform extensional ductile flow was oblique to the trend of the orogen during the whole process and directed to the nnw during the formation of recumbent folds non coaxial shearing favored an nnw sse elongate shape for the syn kinematic granitic massifs as well as the subsequent nucleation of recumbent folds deformation concentrated along discrete detachments during the late stages of extension

causes and consequences of protracted melting of the mid crust exposed in the north himalayan antiform gneiss domes exposed by the north himalayan antiform in southern tibet provide evidence for protracted melting of the mid crust during convergent tectonics anatexis was initiated during underthrusting and recurred during the southwards extrusion of a low viscosity crustal sheet sr nd isotope systematics establish that the cores of the domes dominated by cambrian gneiss form a window of the high himalayan crystalline series hhcs indian plate combined trace element and isotopic analyses from 4 two mica granites that intrude both core and the metasedimentary mantle of the domes indicate an origin from melting of the high himalayan crystalline series by the incongruent breakdown of muscovite and to a lesser extent biotite at temperatures from 680 to 760 c u pb dating of accessory phases extends the known period of granite magmatism from the late oligocene to mid miocene a ca rich garnet bearing leucogranite of oligocene age 27 5 ma provides a rare insight into the pre miocene history of the underthrust indian plate reflecting prograde melting at greater depths during a period of crustal thickening the origin of the miocene granites 15 10 ma can be modeled from the exhumation of an extruding channel at a rate of ca 1 mm year constrained by ar isotope data melting over a protracted time scale along the leading edge of the indian plate less than 50 km from the suture accelerated horizontal shortening within the collision zone and provided a positive feedback mechanism between magmagenesis and deformation

the south tibetan detachment system facilitates ultra rapid cooling of granulite facies rocks in sikkim himalaya 1 the eastern himalaya is characterized by a region of granulites and local granulitized eclogites that have been exhumed via isothermal decompression from lower crustal depths during the india asia collision spatially most of these regions are proximal to the south tibetan detachment system an orogen parallel normal sense detachment system that operated during the miocene suggesting that it played a role in their exhumation here we use geo and thermochronological methods to study the deformation and cooling history of footwall rocks of the south tibetan detachment system in northern sikkim india these data demonstrate that the south tibetan detachment system was active in sikkim between 23 6 and 13 ma and that footwall rocks cooled rapidly from 700 to 120 c between 15 13 ma while active the south tibetan detachment system exhumed rocks from mid crustal depths but an additional heat source such as strain heating advected melt and or crustal thinning is required to explain the observed isothermal decompression cessation of movement on the south tibetan detachment system produced rapid cooling of the footwall as isotherms relaxed a regional comparison of temperature time data for the eastern south tibetan detachment system indicates a lack of synchronicity between the sa er sikkim yadong section and the nw bhutan section to accommodate this requires either strike slip tear faulting or local out of sequence thrusting in the younger segment of the orogen

sillimanite bearing shear zones in syntectonic leucogranite fluid assisted brittle ductile deformation under amphibolite facies conditions abstract in the imja kola valley eastern nepal miocene peraluminous leucogranite dykes were emplaced within transtensional shear zones synchronously with regional amphibolite facies metamorphism in the metamorphic host rocks within the dykes the magmatic foliations parallel to the metamorphic schistosity are cross cut by thin millimetre to centimetre size shear zones which are made up of prismatic and or fibrolitic sillimanite with a minor amount of white mica these structures have a heterogeneous distribution and form networks of strongly deformed and foliated layers wrapping around poorly deformed granitic pods the textural and strain features are consistent with development of sillimanite shear zones as a result of heterogeneous deformation and fluid action which allowed the replacement of strained magmatic minerals such as feldspar and biotite by means of incongruent pressure solution the described example illustrates that nucleation and development of heterogeneous shear zones under amphibolite facies conditions is also strongly favoured by brittle fracturing and fluid action at the grain scale along pre existing planes of weakness the growth of cracks and fractures can be regarded as a sequence of short lived brittle events due to work hardening which punctuate a history of plastic deformation

evolution of north himalayan gneiss domes structural and metamorphic studies in mabja dome southern tibet field structural and metamorphic petrology investigations of mabja gneiss dome southern tibet suggest that contractional extensional and diapiric processes contributed to the structural evolution and formation of the domal geometry the dome is cored by migmatites overlain by sillimanite zone metasedimentary rocks and orthogneiss metamorphic grade diminishes upsection and is defined by a series of concentric isograds evidence for three major deformational events two older penetrative contractional and extensional events and a younger doming event is preserved metamorphism migmitization and emplacement of a leucocratic dike swarm were syntectonic with the extensional event at mid crustal levels metamorphic temperatures and pressures range from 500 8c and 150 450 mpa in chloritoid zone rocks to 705 65 8c and 820 100 mpa in sillimanite zone rocks we suggest that adiabatic decompression during extensional collapse contributed to development of migmatites diapiric rise of low density migmatites was the driving force at least in part for the development of the domal geometry the structural and metamorphic histories documented in mabja dome are similar to kangmar dome suggesting widespread occurrence of these events throughout southern tibet q 2004 elsevier ltd all rights reserved

the 16 august 1931 valentine texas earthquake evidence for normal faulting in west texas the 1931 valentine texas earthquake occurred in a region near the transition from the southern basin and range rio grande rift physiographic province to the southern great plains province previous studies of this earthquake have presented focal mechanisms from first motion data supporting either pure normal or strike slip faulting with extension oriented in a southwest northeast direction nearly perpendicular to the physiographic boundary between the provinces this study presents the results of an inversion of regional and teleseismic body wave phases to determine earthquake source parameters results of the inversion suggest that the earthquake occurred at a depth of 10 km along a fault dipping 54 to the east with a strike of 10 to 20 and a rake of 155 the strike is similar to that of the southern segment of the nearby mayfield fault a fault that shows evidence for repeated movement during the quaternary seismic and geodetic information suggest unilateral rupture toward the south during the earthquake the t axis for the earthquake shows extension oriented in a northwest southeast direction a direction in agreement with the direction given by geologic stress indicators

highly fractionated himalayan leucogranites and associated rare metal mineralization abstract the formation of the himalaya was associated with the exhumation of high grade metamorphosed rocks of the higher himalayan sequence hhs complex which underwent amphibolite granulite to eclogite facies metamorphism and anatexis occurring along the himalayan mountain crest in the south and the lhagoi kangri mountain in the north the himalayan leucogranites contain varying proportions of biotite

solubility of excess alumina in hydrous granitic melts in equilibrium with peraluminous minerals at 700 800 c and 200 mpa and applications of the aluminum saturation index we have studied the controls on the alumi num saturation index asi molec al2o3 cao na2o k2o and the concentration of normative corundum of granitic liquids saturated in alumina by equilibrating peraluminous minerals with initially meta luminous haplogranitic minimum composition liquids at 700 800 c and 200 mpa at and below h2o saturation the asi and normative corundum increase with increasing h2o concentration in the melt 0 04 to 0 10 moles excess al2o3 per mole of h2o temperature and with addition of the non haplogranitic components fe mg and b the asi parameter and concentration of normative corundum cannot be used to monitor aal2o3 between different mineral assemblages and melt because other components that affect the solubility of alumina including h2o fe mg and b do not appear in their formulations asi and normative corundum however provide petrogenetic information about magmas gener ated by partial melting of strongly peraluminous proto liths by virtue of their regular and predictable variation with melt composition e g h2o concentration and temperature for the application of these data to natural rocks it is necessary to choose as an analogue system the asi solubility or normative corundum solubility relations of the most chemically complex peraluminous mineral present in the rock comparison of asi values of anatectic leucosomes and allochthonous leucogranites with experimentally predicted values suggests low h2o concentrations in melt during crustal partial melting rapid melt segregation before equilibration with restitic peraluminous phases is also suggested in some cases

early paleozoic granitic rocks of the south qiangtang terrane northern tibetan plateau implications for subduction of the proto paleo tethys ocean abstract knowledge of the early paleozoic tectonic framework of the northern margin of gondwana continent is critical for reconstructions of the gondwana supercontinent early paleozoic leucogranite and gneissic granite units within the south qiangtang terrane northern tibetan plateau can constrain the timing and geological processes that occurred along the northern margin of gondwana continent at this time here we present new field petrological zircon geochronological geochemical and nd hf isotopic data for this suite of granitic rocks and use these data to provide insights into the evolution of this gondwanan margin zircon u pb dating yielded two groups of ages at 469 453 and 486 473 ma all of the granitic rocks in the gemuri area are high k calc alkaline and peraluminous and record the fractionation of variable amounts of plagioclase k feldspar and biotite these leucogranites formed from magmas generated by the dehydration melting of muscovite within paleoproterozoic mesoproterozoic metapelites under relatively low temperature conditions tzr 616 c 695 c in contrast the protoliths of the duguer gneissic granite formed from magmas generated by the partial melting of paleoproterozoic mesoproterozoic metapelites contaminated by mantle derived material under relatively high temperature conditions tzr 730 c 884 c the coeval nature and linear distribution of the igneous rocks within the northern gondwanan margin and the fact that the granites in the gemuri area are enriched in large ion lithophile elements liles e g rb and k and depleted in high field strength elements hfses e g zr nb ta and ti suggest that this magmatism occurred in an active continental margin setting involving the formation of arc type rocks the presence of an early paleozoic suprasubduction zone type ophiolite within the south qiangtang terrane provides evidence of the southward subduction in the paleo tethyan ocean at this time suggesting that the two stages i e the gemuri leucogranites and duguer gneissic granites of arc type magmatism in the gemuri area may both be related to this subduction event

geochemical constraints on the bimodal origin of high himalayan leucogranites major and trace element and rb sr isotope systematics of the manaslu leucogranite central nepal have been examined to constrain the role of mineral fractionation and fluids in peraluminous granite petrogenesis biotite and tourmaline are for the most part mutually exclusive with a predominance of two mica leucogranites over tourmaline leucogranites the 87sr86sr initial isotopic ratios sri indicate that leucogranitic melts were derived from two different sources the two mica leucogranites having a metagreywacke origin with sri 0 752 nd 15 such a bimodal nature of the source zone does not directly influence the magmatic evolution except that probably the higher initial boron content in the metapelitic rocks may increase the na2ok2o ratio in contrast the amount of water present during melting principally controls in part anatectic processes and element behaviour water saturated conditions probably occured during melting of metagreywackeous rocks and favoured crystallization of two mica leucogranites whereas water absent conditions prevailed during melting of metapelitic layers and favoured biotite plagioclase and monazite fractionation in the source zone and tourmaline crystallization in the leucogranite

dating protracted fault activities microstructures microchemistry and geochronology of the vaikrita thrust main central thrust zone garhwal himalaya nw india

pressure temperature deformation time constraints on the south tibetan detachment system in the garhwal himalaya nw india a peculiar feature of the himalaya is the occurrence of a system of low angle normal faults and shear zones the south tibetan detachment system stds at the mountain crests the stds was active during syn convergent tectonics we describe the stds related sheared rocks along the dhauli ganga valley in the garhwal himalaya nw india where the malari granite reported as an undeformed igneous body cross cutting the stds occurs a detailed multidisciplinary study integrating field based microstructural petrographic and geochronological analyses was carried out on rocks along this valley we demonstrate how the non coaxial ductile portion of the stds affected the upper part of the greater himalaya sequence migmatite which experienced peak pressure p temperature t conditions of 0 9 1 1 gpa and 750 c at 24 ma this migmatite has been reworked structurally upwards leading to the formation of high t sillimanite bearing mylonites further upward medium t shearing deformed the malari granite and leucogranite dykes forming medium t mylonites ductile shearing was temporally constrained based on new in situ monazite datings and previously published ar ar geochronology between 20 15 ma we demonstrate that a preserved ductile to brittle spatial and temporal transition of the stds deformation exists with the brittle features overprinting ductile ones our data shed new light on the geological evolution of the stds in the nw himalaya with implications for the relationship and relative timing of partial melting granite emplacement and deformation along low angle normal faults

crystal chemistry of al rich biotites coexisting with muscovites in peraluminous granites a comparison was made between single crystal structure refinements electron microprobe analyses and octahedral site populations of seven biotite crystals and data obtained previously for coexisting muscovite in peraluminous granites using the same methods both micas from several plutons of northern victoria land antarctica and sardinia italy show significant octahedral substitutions biotite has a composition characterized by relatively high 6 al content 0 32 6 al 0 59 apfu whereas muscovite is characterized by phengite like substitutions 0 12 6 mg fe ti mn 0 35 mean bond lengths and electron count data for six biotites 1 m space group c 2 m agreement factor 2 7 r obs 3 6 and a biotite 2 m 1 space group c 2 c r obs 2 8 show that al substitutes for divalent cations in the octahedral m2 site and that the fe and mg distribution is disordered the mean tetrahedral bond lengths determined for biotite 2 m 1 reflect al si disorder in coexisting muscovite 2 m 1 crystals small positive electron density residuals close to m1 site position as well as the increase in m2 mean atomic number is in agreement with the presence of a significant phengitic component reduction in biotite unit cell dimensions with the increase of al follows a pattern similar to that of associated muscovites and the octahedral site volumes of both micas are influenced by the al saturation index asi of the rock these results and the calculated partition coefficients between biotite and muscovite for elements in m sites are consistent with continuous reaction and re equilibration of biotite and muscovite during crystallization of peraluminous granitic melts

depositional and tectonic setting of the paleoproterozoic lower aillik group makkovik province canada evolution of a passive margin foredeep sequence based on petrochemistry and u pb tims and lam icp ms geochronology abstract the paleoproterozoic lower aillik group is a deformed metasedimentary metavolcanic succession located in the makkovik province of labrador eastern canada the group is situated near the boundary between reworked archaean gneiss of the nain north atlantic craton and juvenile paleoproterozoic crust that was both tectonically accreted and formed on or adjacent to this craton during the ca 1 9 1 78 ma makkovikian orogeny the lower aillik group is structurally underlain by archaean gneiss and structurally overlain by ca 1860 1807 ma bimodal dominantly felsic volcanic and volcaniclastic rocks of the upper aillik group we present geochemical data from metavolcanic rocks and u pb geochronological data from several units of the lower aillik group in order to address the depositional and tectonic history of this group u pb data were obtained using both thermal ionization mass spectrometry tims and laser ablation microprobe inductively coupled plasma mass spectrometry lam icp ms two quartzite units near the structural base of the lower aillik group contain detrital zircons only of archaean age and are interpreted to have been deposited on the nain craton during post 2235 ma rifting and initiation of a passive continental margin overlying mafic metavolcanic rocks contain thin horizons of intermediate tuff one of which is dated at 2178 4 ma this relatively old age and an inferred stratigraphic relationship with underlying sedimentary units suggest that the volcanic rocks represent transitional oceanic crust consistent with their geochemical similarity to tholeiitic rifted margin sequences of mesozoic age in eastern north america a package of interlayered psammitic and semipelitic metasedimentary rocks that appears to stratigraphically overlie the mafic volcanic unit is dominated by paleoproterozoic detrital zircons but also contains archaean grains this package was deposited after 2013 ma the age of the youngest concordant zircon the u pb data imply a minimum 165 m y time gap between mafic volcanism and sedimentation and are consistent with deposition of the psammite semipelite unit in an evolving foredeep that heralded the approach of a paleoproterozoic arc terrane accretion of this terrane to the nain cratonic margin at ca 1 9 ga initiated the makkovikian orogeny although the lower aillik group is highly deformed and may contain internal tectonic boundaries or be incomplete the u pb and geochemical data allow quantitative assessment of a prolonged rift drift basin closure cycle that characterized the early paleoproterozoic evolution of the southern nain cratonic margin

partial rupture of a locked patch of the sumatra megathrust during the 2007 earthquake sequence the great sumatra andaman earthquake and tsunami of 2004 was a dramatic reminder of the importance of understanding the seismic and tsunami hazards of subduction zones 1 2 3 4 in march 2005 the sunda megathrust ruptured again producing an event 5 of moment magnitude mw 8 6 south of the 2004 rupture area which was the site of a similar event in 1861 ref 6 concern was then focused on the mentawai area where large earthquakes had occurred in 1797 mw 8 8 and 1833 mw 9 0 6 7 two earthquakes one of mw 8 4 and twelve hours later one of mw 7 9 indeed occurred there on 12 september 2007 here we show that these earthquakes ruptured only a fraction of the area ruptured in 1833 and consist of distinct asperities within a patch of the megathrust that had remained locked in the interseismic period this indicates that the same portion of a megathrust can rupture in different patterns depending on whether asperities break as isolated seismic events or cooperate to produce a larger rupture this variability probably arises from the influence of non permanent barriers zones with locally lower pre stress due to the past earthquakes the stress state of the portion of the sunda megathrust that had ruptured in 1833 and 1797 was probably not adequate for the development of a single large rupture in 2007 the moment released in 2007 amounts to only a fraction both of that released in 1833 and of the deficit of moment that had accumulated as a result of interseismic strain since 1833 the potential for a large megathrust event in the mentawai area thus remains large

twenty five years of progress in the science of geological tsunamis following the 1992 nicaragua and flores events we review a set of 47 tsunamis of geological origin triggered by earthquakes landslides or volcanoes which have occurred over the past 25 years and provided significant new insight into theoretical experimental field or societal aspects of tsunami science among the principal developments in our command of various aspects of tsunamis we earmark the development of the w phase inversion for the low frequency moment tensor of the parent earthquake the abandonment of the concept of a maximum earthquake magnitude for a given subduction zone controlled by simple plate properties the development and implementation of computer codes simulating the interaction of tsunamis with initially dry land at beaches thus introducing a quantitative component to realistic tsunami warning procedures and the recent in situ investigation of current velocities in addition to the field of surface displacements during the interaction of tsunamis with harbors continued research remains warranted notably in the field of the real time identification of tsunami earthquakes whose tsunamis are larger than expected from their seismic magnitudes especially conventional ones the recent tragedy during the 2018 krakatau flank collapse along a scenario which had been quantitatively forecast also emphasizes the need for a continued effort in the education of the populations at risk

the 17 may 2012 m4 8 earthquake near timpson east texas an event possibly triggered by fluid injection this study summarizes our investigation of the 17 may 2012 mw rmt4 8 earthquake near timpson texas the largest earthquake recorded historically in eastern texas to identify preshocks and aftershocks of the 17 may event we examined the arrivals recorded at nacogdoches natx 30 km from the 17 may epicenter at nearby usarray transportable array stations and at eight temporary stations deployed between 26 may 2012 and mid 2013 at natx we identified seven preshocks the earliest occurring in april 2008 reliably located aftershocks recorded by the temporary stations lie along a 6 km long nw se linear trend corresponding to a previously mapped basement fault that extends across the highest intensity mmi vii region of the 17 may main shock earthquakes in this sequence are relatively shallow with focal depths ranging from 1 6 to 4 6 km evidence supporting these depths include hypocentral locations of exceptionally well recorded aftershocks s p intervals at the nearest stations and comparisons of synthetics and observed seismograms within 3 km of the linear trend of aftershock activity there are two class ii injection disposal wells injecting at 1 9 km depth beginning in august 2006 and february 2007 with injection rates averaging 42 750 m3 mo and 15 600 m3 mo respectively several observations support the hypothesis that fluid injection triggered the timpson sequence well located epicenters are situated near a mapped basement fault and near high volume injection wells focal depths are at or below the depths of injection and the earliest preshock april 2008 occurred after the onset of injection in 2006

deformation and slip along the sunda megathrust in the great 2005 nias simeulue earthquake seismic rupture produced spectacular tectonic deformation above a 400 kilometer strip of the sunda megathrust offshore northern sumatra in march 2005 measurements from coral microatolls and global positioning system stations reveal trench parallel belts of uplift up to 3 meters high on the outer arc islands above the rupture and a 1 meter deep subsidence trough farther from the trench surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward a saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 sumatra andaman rupture the southeastern edge abuts a predominantly aseismic section of the megathrust near the equator

insights on the source of the 28 september 2018 sulawesi tsunami indonesia based on spectral analyses and numerical simulations the 28 september 2018 sulawesi tsunami has been a puzzle because extreme deadly tsunami waves were generated following an mw 7 5 strike slip earthquake while such earthquakes are not usually considered to produce large tsunamis here we obtained processed and analyzed two sea level records of the tsunami in the near field pantoloan located inside the palu bay and far field mamuju located outside the palu bay and conducted numerical simulations to shed light on the tsunami source the two tide gauges recorded maximum tsunami trough to crest heights of 380 and 24 cm respectively with respective dominating wave periods of 3 6 4 4 and 10 min and respective high energy wave duration of 5 5 and 14 h the two observed waveforms were significantly different with wave amplitude and period ratios of 16 and 3 respectively we infer tsunamigenic source dimensions of 3 4 4 1 km and 32 5 km for inside and outside of the palu bay respectively our numerical simulations fairly well reproduced both tsunami observations in pantoloan and mamuju except for the arrival time in mamuju however it was incapable of reproducing the maximum reported coastal amplitudes of 6 11 m it is possible that these two sources are different parts of the same tectonic source a bay oscillation mode of 85 min was revealed for the palu bay through numerical modeling actual sea surface disturbances and landslide generated waves were captured by two video recordings from inside the palu bay shortly after the earthquake it is possible that a large submarine landslide contributed to and intensified the sulawesi tsunami we identify the southern part of the palu bay around the latitude of 0 82os as the most likely location of a potential landslide based on our backward tsunami ray tracing analysis however marine geological data from the palu bay are required to confirm such hypothesis

upb geochronology of gangdese transhimalaya plutonism in the lhasa xigaze region tibet abstract a series of different plutons from the lhasa xigaze segment of the gangdese transhimalaya belt has been studied by high resolution u pb analyses of zircon using zircon fractions of 5 100 grains each selected upon specific grain characteristics for two diorites located east of xigaze dazhuka the zircons yield concordant ages of 93 4 1 0 and 94 2 1 0 m y respectively also concordant ages of 41 1 0 4 and 41 7 0 4 m y have been obtained for two granodiorites collected southwest of lhasa qushui the precision on the ages of two granites from the xigaze and lhasa area is limited by two factors the presence of inherited radiogenic lead and the occurrence of subsequent lead loss however some concordant zircons detected in both granites define approximate ages of about 67 and 53 m y respectively the inherited lead components show that melting of precambrian material was involved in magma genesis the u pb ages substantiate a magmatic activity lasting from mid cretceous cenomanian to eocene lutetian time such a period of plutonism at the southern margin of eurasia as well as the occurrence of magma generation from continental crust suggest that the gangdese range results from the subduction of tethys oceanic lithosphere indian plate underneath eurasia eurasian plate if this model is true the collision of india with eurasia along the lhasa xigaze sector postdates the emplacement of the 41 m y old gangdese granodiorites i e the collision occurred after lutetian time

eocene partial melting recorded in peritectic garnets from kyanite gneiss greater himalayan sequence central nepal the himalayan mountain belt is characterized by the impressive continuity over 2500 km of tectonic units thrusts and normal faults as well as large volumes of high grade metamorphic rocks and granite exposed at the surface visona et al 2012 although there are many studies on metamorphism melt generation and deformation concentrated in the same time span as activity on the mct and std 23 17 ma godin et al 2006 much fewer data on deformation metamorphism melt generation and geochronology in the greater himalayan sequence ghs is available for the large time span 30 m y between collision at 55 ma and mct std activities carosi et al 2010 2013 montomoli et al 2013 melt generation and granite emplacement have been mainly related to the exhumation stage of the ghs during early miocene harris and massey 1994 very few evidences of partial melting during prograde metamorphism have been reported until now in the southern part of the belt godin et al 2001 imayama et al 2012 the ghs of eastern nepal and sikkim india shows the occurrence of melting at the bottom of the ghs barun gneiss at nearly 33 27 ma imayama et al 2012 ferrero et al 2012 rubatto et al 2012 anatectic melt inclusions nanogranites and nanotonalites have been found in garnet of kyanite gneiss at the bottom of the greater himalayan sequence fig 1 along kali gandaki valley central nepal nearly 1 km structurally above the main central thrust in situ u th pb dating of monazite included in garnets in the same structural positions as melt inclusions allowed to constrain partial melting starting at 36 41 ma carosi et al in press

himalayan metamorphic sequence as an orogenic channel insight from bhutan the bhutan himalayas differ from the rest of the himalayas in two major ways i low grade sedimentary rocks lie above the greater himalayan sequence as klippen i e erosional remains of the south tibetan detachment and ii an out of sequence thrust the kakhtang thrust lies structurally above the klippen and it doubles the exposed thickness of the greater himalayan sequence our field observations and geochronological data constrain the main kinematic events in the bhutan himalayas crystallisation ages of leucogranite dykes deformed by the main central thrust and the south tibetan detachment indicate that these two structures operated together between 16 and 22 ma the out of sequence kakhtang thrust was active at 10 14 ma and was concurrent with reactivation of the south tibetan detachment restoration of the bhutan himalayas prior to the out of sequence thrusting shows that the greater himalayan sequence was the core of a long low viscosity crustal channel extending under the tibetan plateau we propose that the gravity driven southward extrusion of the channel material from underneath the tibetan plateau caused the inverted metamorphic sequence in the lesser himalayan sequence and in the greater himalayan sequence this process also led to occurrences of present day surface rocks that were derived from variable distances down dip but from similar crustal depths such an exhumation pattern can explain the similar peak pressures for the greater himalayan sequence along the length of the himalayas

structural insights into the early stages of exhumation along an orogen scale detachment the south tibetan detachment system dzakaa chu section eastern himalaya abstract structural transects through the south tibetan detachment system stds in the dzakaa chu valley tibet reveal a 1000 m thick low angle

spodumene pegmatites from the pusila pluton in the higher himalaya south tibet lithium mineralization in a highly fractionated leucogranite batholith abstract the himalayan leucogranite belt is evaluated as a prospect for rare metal mineralization the pusila pluton is located 44 km northwest of mount everest and consists of two mica granite muscovite granite albite granite and pegmatites numerous pegmatite dikes have intruded the higher himalayan crystalline sequence and the granites oligocene pegmatites in the chomogu and cuore areas which we constrain to have formed at ca 25 23 ma were investigated in this study because they are strongly enriched in li up to 8460 ppm and contain abundant spodumene petalite lithium was progressively enriched from the two mica granite to the muscovite granite and finally li mineralization occurred in the highly fractionated pegmatites the chomogu no 1 pegmatite is a well zoned dike that hosts beryl columbite cassiterite and li minerals which are concentrated in the inner parts of the dike scanning electron microscopy and cathodoluminescence images reveal two stages of li mineralization primary spodumene spd 1 crystallized in the magmatic stage whereas secondary spodumene spd 2 and petalite formed later in the hydrothermal stage the pusila pluton is thus an important site of li mineralization in the himalayan leucogranite belt

uplift and subsidence associated with the great aceh andaman earthquake of 2004 rupture of the sunda megathrust on 26 december 2004 produced broad regions of uplift and subsidence we define the pivot line separating these regions as a first step in defining the lateral extent and the downdip limit of rupture during that great m w 9 2 earthquake in the region of the andaman and nicobar islands we rely exclusively on the interpretation of satellite imagery and a tidal model at the southern limit of the great rupture we rely principally on field measurements of emerged coral microatolls uplift extends from the middle of simeulue island sumatra at 2 5 n to preparis island myanmar burma at 14 9 n thus the rupture is 1600 km long the distance from the pivot line to the trench varies appreciably the northern and western andaman islands rose whereas the southern and eastern portion of the islands subsided the nicobar islands and the west coast of aceh province sumatra subsided tilt at the southern end of the rupture is steep the distance from 1 5 m of uplift to the pivot line is just 60 km our method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions

onset of mid crustal extensional flow in southern tibet evidence from u pb zircon ages new ion microprobe u pb dates from zircon in deformed orthogneiss and migmatite and an undeformed granite in mabja dome are the first to constrain the timing of peak metamorphism and onset and duration of mid crustal ductile extension in southern tibet at 35 0 0 8 ma and 12 19 million years the structural metamorphic and intrusive his tories in mid crustal rocks exposed in these north himalayan gneiss domes are similar to those recorded in the greater himalayan sequence suggesting that middle crust was continuous from beneath southern tibet southward to the high himalaya strain compatibility indicates that 35 ma ductile extension in mid crustal rocks of southern tibet was accommodated to the south at shallow crustal levels via normal slip along the southern tibetan detachment system the oldest age estimate for slip along this normal fault zone and extrusion of its footwall if gravitational collapse is an additional important process driving extension then southernmost tibet may have been at or near maximum elevation by late eocene early oligocene time

himalayan tectonics explained by extrusion of a low viscosity crustal channel coupled to focused surface denudation recent interpretations of himalayan tibetan tectonics have proposed that channel flow in the middle to lower crust can explain outward growth of the tibetan plateau1 2 3 and that ductile extrusion of high grade metamorphic rocks between coeval normal and thrust sense shear zones can explain exhumation of the greater himalayan sequence4 5 6 7 here we use coupled thermal mechanical numerical models to show that these two processes channel flow and ductile extrusion may be dynamically linked through the effects of surface denudation focused at the edge of a plateau that is underlain by low viscosity material our models provide an internally self consistent explanation for many observed features of the himalayan tibetan system8 9 10

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

field survey of the march 28 2005 nias simeulue earthquake and tsunami on the evening of march 28 2005 at 11 09 p m local time 16 09 utc a large earthquake occurred offshore of west sumatra indonesia with a moment magnitude mw of 8 6 the event caused substantial shaking damage and land level changes between simeulue island in the north and the batu islands in the south the earthquake also generated a tsunami which was observed throughout the source region as well as on distant tide gauges while the tsunami was not as extreme as the tsunami of december 26th 2004 it did cause significant flooding and damage at some locations the spatial and temporal proximity of the two events led to a unique set of observational data from the earthquake and tsunami as well as insights relevant to tsunami hazard planning and education efforts

a decade of induced slip on the causative fault of the 2015 mw 4 0 venus earthquake northeast johnson county texas on 7 may 2015 a mw 4 0 earthquake occurred near venus northeast johnson county texas in an area of the bend arch fort worth basin that reports long term high volume wastewater disposal and that has hosted felt earthquakes since 2009 in the weeks following the mw 4 0 earthquake we deployed a local seismic network and purchased nearby active source seismic reflection data to capture additional events characterize the causative fault and explore potential links between ongoing industry activity and seismicity hypocenter relocations of the resulting local earthquake catalog span 4 6 km depth and indicate a fault striking 230 dipping to the west consistent with a nodal plane of the mw 4 0 regional moment tensor fault plane solutions indicate normal faulting with b axes striking parallel to maximum horizontal compressive stress seismic reflection data image the reactivated basement fault penetrating the ordovician disposal layer and mississippian production layer but not displacing post lower pennsylvanian units template matching at regional seismic stations indicates that low magnitude earthquakes with similar waveforms began in april 2008 with increasing magnitude over time pressure data from five saltwater disposal wells within 5 km of the active fault indicate a disposal formation that is 0 9 4 8 mpa above hydrostatic we suggest that the injection of 28 000 000 m3 of wastewater between 2006 and 2015 at these wells led to an increase in subsurface pore fluid pressure that contributed to inducing this long lived earthquake sequence the 2015 mw 4 0 event represents the largest event in the continuing evolution of slip on the causative fault

a structural transect in the lower dolpo insights on the tectonic evolution of western nepal abstract we present the results of a structural transect in lower dolpo cross cutting the upper part of the lesser himalaya lh the higher himalayan crystallines hhc and the lower part of the tibetan sedimentary sequence tss the mct zone affects the upper part of the lh as well as the lower part of the hhc and shows a later brittle reactivation mean vorticity in the mct points to non coaxial deformation these data together with available kinematic data along the belt on the south tibetan detachment system stds and in the core of the hhc point to increasing simple shear toward the tectonic boundaries a top to the sw high temperature shear zone toijem shear zone is recognized in the middle part of the hhc at the boundary between units 1 and 2 it developed during the earlier stages of exhumation of the hhc enhancing the decompression of the hanging wall and the emplacement of leucogranite dykes and sills its development could be explained by a change in the velocity profile during the extrusion of the hhc triggered by first order changes in rock types of the tectonic unit the stds is marked by a wide zone of high strain and by a metamorphic jump from amphibolite facies in the carbonate rocks of the upper part of the hhc to greenschist facies marbles in the lower part of the tss the development of a pervasive foliation towards the bottom of the tss indicates increasing strain related to top down to the ne tectonic transport a low p metamorphic event marked by the growth of post d1 biotite porphyroblasts at the base of the tss is related to the conductive heating from the underlying hhc

occurrence and origin of andalusite in peraluminous felsic igneous rocks andalusite occurs as an accessory mineral in many types of peraluminous felsic igneous rocks including rhyolites aplites granites pegmatites and anatectic migmatites some published stability curves for and sil and the water saturated granite solidus permit a small stability field for andalusite in equilibrium with felsic melts we examine 108 samples of andalusite bearing felsic rocks from more than 40 localities world wide our purpose is to determine the origin of andalusite including the t p x controls on andalusite formation using eight textural and chemical criteria size compatibility with grain sizes of igneous minerals in the same rock shape ranging from euhedral to anhedral with no simple correlation with origin state of aggregation single grains or clusters of grains association with muscovite with or without rims of monocrystalline or polycrystalline muscovite inclusions rare mineral inclusions and melt inclusions chemical composition andalusite with little significant chemical variation except in iron content 008 171 wt feo compositional zoning concentric sector patchy oscillatory zoning cryptically reflect growth conditions compositions of coexisting phases biotites with high siderophyllite eastonite contents aliv 268 007 atoms per formula unit muscovites with 057 401 wt feo and 002 285 wt tio2 and apatites with 353 018 wt f coexisting muscovite biotite pairs have a wide range of f contents and fbt 1612fms 0015 most coexisting minerals have compositions consistent with equilibration at magmatic conditions the three principal genetic types of andalusite in felsic igneous rocks are type 1 metamorphic a prograde metamorphic in thermally metamorphosed peraluminous granites b retrograde metamorphic inversion from sillimanite of unspecified origin c xenocrystic derivation from local country rocks and d restitic derivation from source regions type 2 magmatic a peritectic water undersaturated t associated with leucosomes in migmatites b peritectic water undersaturated t as reaction rims on garnet or cordierite c cotectic water undersaturated t direct crystallization from a silicate melt and d pegmatitic watersaturated t associated with aplite pegmatite contacts or pegmatitic portion alone type 3 metasomatic water saturated magma absent spatially related to structural discontinuities in host replacement of feldspar and or biotite intergrowths with quartz the great majority of our andalusite samples show one or more textural or chemical criteria suggesting a magmatic origin of the many possible controls on the formation of andalusite excess al2o3 water concentration and fluid evolution high be b li p high f high fe mn ti and kinetic considerations the two most important factors appear to be excess al2o3 and the effect of releasing water either to strip alkalis from the melt or to reduce alumina solubility in the melt of particular importance is the evidence for magmatic andalusite in granites showing no significant depression of the solidus suggesting that the and sil equilibrium must cross the granite solidus rather than lie below it magmatic andalusite however formed is susceptible to supra or sub solidus reaction to produce muscovite in many cases textural evidence of this reaction remains but in other cases muscovite may completely replace andalusite leaving little or no evidence of its former existence

channel flow ductile extrusion and exhumation in continental collision zones this collection of 27 review and research papers provides an overview of the geodynamic concepts of channel flow and ductile extrusion in continental collision zones the focal point for this volume is the proposal that the middle or lower crust acts as a ductile partially molten channel flowing out from beneath areas of over thickened crust such as the tibetan plateau towards the topographic surface at plateau margins this controversial proposal explains many features related to the geodynamic evolution of the plateau and for example extrusion and exhumation of the crystalline core of the himalayan mountain chain to the south in this volume thermal mechanical models for channel flow extrusion and exhumation are presented and geological and geophysical evidence both for and against the applicability of such models to the himalayan tibetan plateau system as well as older continental collision zones such as the hellenides the appalachians and the canadian cordillera are discussed

the mongol okhotsk ocean subduction related permian peraluminous granites in northeastern mongolia constraints from zircon u pb ages whole rock elemental and sr nd hf isotopic compositions abstract northeastern mongolia represents a unique area that experienced evolution of both the mongol okhotsk ocean moo and the central asian orogenic belt caob in order to better understand the evolution of moo and its effect on the caob we performed zircon u pb dating and hf isotope and whole rock elemental and sr nd isotopic analyses on three permian peraluminous granitic plutons in northeastern mongolia zircon dating result revealed that granitoids of east monhhaan south monhhaan and tuvshinshiree plutons were emplaced at 254 3 265 5 and 273 3 ma respectively the result provides permian ages for the permian triassic volcanic plutonic belt in northeastern mongolia geochemical analysis suggests that all the granitoids are of peraluminous s type granites elemental and sr nd hf isotopic data indicate that these s type granites were generated from mainly clay poor greywacke with some contribution of juvenile mantle component the permian s type granites emplaced likely in an active margin related to the subduction of the mongol okhotsk ocean the protracted intermittent extension during the long lived compression was considered as a likely geodynamic mechanism for the upwelling of mantle derived basaltic magma and melting of crustal materials