nd sr isotopic geochemical and petrographic stratigraphy and paleotectonic analysis mesozoic great valley forearc sedimentary rocks of california measurements of nd sr isotopes major and trace elements and model mineralogy were made on upper jurassic and cretaceous great valley forearc sedimentary rocks to test models for the temporal and spatial evolution of sierra nevada arc sources isotopes and major and trace elements are sensitive provenance indicators because of the large west east isotopic geochemical and age gradients in the plutonic rocks of the sierra nevada batholith and because petrographic models indicate that source areas moved east during the cretaceous isotopic and chemical variations are correlated in the forearc sandstone as nd decreases th u la nb zr hf pb rb sio2 and k2o concentrations increase and feo mgo tio2 ni and cr concentrations decrease this relation is the same as that observed in the plutonic rocks and indicates that the arc was the primary source of sediment and that the sandstone chemistry was not disturbed by sedimentary processes the nd sr relation of san joaquin valley sandstone is the same as the plutonic rocks but sacramento valley sandstone is elevated in sr because of seawater exchange weathering and diagenesis whole rock sandstone decreases in nd from 7 to 5 and increases in 87sr 86sr from 0 7045 to 0 7073 with decreasing stratigraphic age the nd sr isotopic composition is correlative with the plagioclase to feldspar ratio and indicates that source areas moved inland during the cretaceous upper cretaceous san joaquin valley shale is similar in nd to the sandstone indicating that sandstone and shale were derived from the same source and that the nd isotopic composition is independent of grain size the shale is higher in 87sr 86sr than the sandstone possibly due to concentration of biotite in the fine fraction during transport and subsequent rb loss during diagenesis nd sr isotopes were used to construct models to locate source areas parameters include lithology drainage basin geometry and erosion rate the age and isotopic compositions of the calculated igneous component of the sandstone correspond to the age and isotopic compositions of the plutonic rocks of the batholith this correspondence indicates that 1 the isotopic composition of the plutonic rocks and the coeval volcanic cover were similar 2 the volcanic front was denuded within a few million years and 3 the sediment was derived from the head of the drainage basin located at the migrating volcanic front

deformation resulting from regional extension during pluton ascent and emplacement central sierra nevada california solid state foliation lineation small scale folds and domainal shear zones have developed in preexisting granitic and minor metasedimentary wallrock during a combined deformation involving a regional extensional strain and ascent and emplacement of the mt givens pluton mgp mylonite is common throughout much of the 1 2 km wide 10 km long shear zone with ultramylonite best developed near the contact with the mgp which itself lacks significant solid state deformation migmatization accompanies ultramylonite formation in the northern half of the zone but both these features are poorly developed or absent in its southern half where the shear zone is distributed over a wider area strain estimates across the shear zone using microgranitic enclaves as markers show a positive gradient and an increasing ratio of simple shear pure shear towards the mgp microprobe analyses on hornblende and plagioclase yield pressure and temperature estimates of 3 5 kb and 680 c respectively during shear zone formation at least at its late stages of development zircon pb u and 40 ar 39 ar ages constrain timing of the high temperature movement on the shear zone to 90 ma essentially the age of the mgp although movement immediately prior to that time appears likely we speculate that a regional extensional shear zone was developing prior to the emplacement of the mgp which as it ascended heated the wallrock facilitating both further strain in the zone as well as buoyant rise of the pluton along the zone the mgp was near its critical melt fraction during the last several kilometers of its ascent and could have possessed sufficient viscosity strength to impose a weak shear strain on the shear zone rocks although most of the foliation and extensional features in the zone are probably related to the regional strain field late stage folding of the foliation is attributed to shouldering aside of the wallrock by the mgp during the last increment of its ascent and final emplacement

mesozoic ash flow caldera fragments in southeastern arizona and their relation to porphyry copper deposits jurassic and upper cretaceous volcanic and associated granitic rocks in southeast arizona are remnants of large composite silicic volcanic fields characterized by voluminous ash flow tuffs and associated calderas presence of 10 15 large caldera fragments is inferred primarily from 1 ash flow deposits more than 1 km thick having features of intracaldera ponding 2 exotic block breccias within a tuff matrix interpreted as caldera collapse megabreccias and 3 local granitic intrusions along arcuate structural boundaries of the thick volcanic sequences several porphyry copper deposits are associated with late granitic intrusions within the calderas or along their margins

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

petrology and geochronology of metamorphosed volcanic rocks and a middle cretaceous volcanic neck in the east central sierra nevada california metamorphosed mesozoic volcanic rocks from the east central sierra nevada range in composition from basalt to rhyolite and have ages based on whole rock rb sr and u pb zircon dating of about 237 224 185 163 134 and 100 m y the major plutons of the batholith in this area are of triassic 215 200 m y and cretaceous 94 80 m y ages initial 87sr 86sr values for the metamorphosed volcanic rocks of the area are in the range from 0 7042 to 0 7058 and are generally different from the values for the surrounding batholithic rocks 0 7056 0 7066 a circular zoned granitic pluton with an outcrop area of 2 5 km2 similar in appearance to a ring dike complex was apparently a conduit for some or possibly all of the middle cretaceous metamorphosed volcanic rocks exposed about 5 km to the south in the western part of the ritter range samples from the metamorphosed volcanic rocks and the pluton yield a rb sr whole rock isochron age of 99 9 2 2 m y with an initial 87sr 86sr of 0 7048 0 0001 major element variation diagrams of the pluton and volcanic rocks define coincident compositional trends the pluton intruded into early jurassic metamorphosed volcanic rocks rb sr whole rock isochron age of 185 6 m y initial 87 86sr 0 70474 0 00009 is composed of a central body of granite that is intruded into and almost completely surrounded by a crescent shaped outer rim of quartz monzodiorite contact relations between the granitic rocks intrusive in some places and completely gradational at other places indicate that the quartz monzodiorite was not completely crystallized prior to the intrusion of the granite modal minerology within the pluton is also consistent with this inferred crystallization history the granitic rock textures are cataclastic characterized by a groundmass of feldspar and quartz that surrounds larger grains of feldspar hornblende and biotite widely spaced aplite dikes from the granite intrude the quartz monzodiorite along the contact between the granitic rocks the aplite dikes and interstitial alkali feldspar associated with myrmekite in the pluton being undeformed indicate crystallization of a small amount of silicate liquid after cataclasis aplite compositions suggest a minimum crystallization pressure of 0 5 kb 1 2 km this depth is consistent with crystallization near the base of a large stratovolcano the pluton is characterized by steep linear features defined by mineral clots and inclusions that probably formed during the upward movement of the nearly crystallized magma in the volcanic conduit the ages of volcanic events relative to the ages of the major intrusive epochs and the major element and isotopic compositions of the volcanic rocks relative to the major plutons indicate that the volcanic rocks are not simply or directly related to the major plutons in the sierra nevada

fabric analysis using the intercept method abstract the intercept method is a convenient yet powerful method for the numerical analysis of fabrics for geological applications it can be used when a set of objects e g pores grains or aggregates of a specific mineral lineaments etc with unique characteristics can be identified in an image the intercept method analyses boundaries of objects as a population of lines how intercepts are definined is therefore important in order to establish the significance of the intercept counts when the method is applied to digital images the subdivision of the information into square pixels must also be considered we apply a linear filter which minimizes the effects of grid anisotropy on the counting of intercepts analysis of the resulting rose of intercept counts by a fourier series considerably facilitates the interpretation of the data a rose of directions can readily be derived for the phase boundaries if a population of objects can be assumed to have started with an originally isotropic orientation and to have been deformed passively the fourier components of the rose of intercepts also give the sectional strain the fourier components also permit an objective test of the validity of describing a fabric as resulting from a homogeneous strain on an initially isotropic section two computer programs for the counting and analysis of intercepts on digital images are presented and applied in four examples which illustrate the usefulness of the intercept method for magmatic fabric measurement strain analysis and lineament analysis we also illustrate the importance of fourier series decomposition of rose of intercept counts for fabric interpretations intercept results are also shown to be compatible with those derived by other methods eigenvector surfor inertia tensor autocorrelation methods

geologic and geophysical investigation of two fine grained granites sierra nevada batholith california evidence for structural controls on emplacement and volcanism the johnson granite porphyry and the silver pass porphyry are two late stage porphyritic intrusions in the cretaceous sierra nevada batholith california both intrusions are characterized by fine grained textures miarolitic cavities pegmatite veins and abundant xenoliths microstructures in the johnson granite porphyry record magmatic flow magnetic fabrics in the johnson granite porphyry determined by anisotropy of magnetic susceptibility show that the poles to magnetic foliations define a nne ssw girdle and magnetic lineations plunge shallowly to moderately to the wnw and ese a gravity survey and three dimensional inversion indicate that the johnson granite porphyry is shallow and tabular extending to 1 5 km depth beneath the southwestern margin a second gravity anomaly was delineated southeast of the johnson granite porphyry suggesting the intrusion continues to depth the silver pass porphyry is deformed by the dextral rosy finch shear zone and records a gradient of high to low temperature solid state fabrics field and magnetic foliations in the silver pass porphyry are subvertical and lineations are shallowly plunging we propose that regional shear zones controlled the emplacement of these intrusions the johnson granite porphyry was emplaced in a three dimensional tension gash associated with the termination of the bench canyon shear zone the rosy finch shear zone facilitated the emplacement of the silver pass porphyry probably as a tension fracture associated with the shear zone the field observations and magnetic fabrics suggest that the johnson granite porphyry may record an extrusive event suggesting that volcanism may be related to deformation along active shear zones

the gem lake shear zone cretaceous dextral transpression in the northern ritter range pendant eastern sierra nevada california the gem lake shear zone is a northwest striking steeply dipping dextral transpressional shear zone that provides the first direct evidence for dextral deformation in wall rock pendants in the central part of the sierra nevada batholith the gem lake shear zone is a minimum of 30 km in length and extends at least from the north end of the northern ritter range pendant to the southeast edge of the ritter range pendant the amount of displacement on the zone is uncertain but matching fault slivers of pennsylvanian marble in the northern ritter range pendant to similar exposures north of the mount morrison pendant suggests a minimum dextral offset of 20 km the gem lake shear zone was active in early late cretaceous time from before 91 ma the age of the syntectonic granodiorite of kuna crest to at least 80 ma 40ar 39ar age of syndeformational mica from the shear zone in the ritter range pendant deformation in the gem lake shear zone is characterized by combined dextral simple shear and subvertical stretching which are variably partitioned in anastomosing high strain zones in the shear zone at gem lake predominantly dextral deformation is indicated by porphyroclast asymmetries s c fabric and asymmetric crenulations a component of subvertical stretching is indicated by a moderately to steeply plunging stretching lineation in a segment of the shear zone at kuna crest a strongly developed stretching lineation indicates predominantly subvertical stretching with a lesser component of dextral strike slip the gem lake shear zone is considered to be part of a proposed regional system of shear zones in the eastern sierra nevada the sierra crest shear zone system this dextral transpressional system was active prior to and synchronous with intrusion of the late cretaceous sierra nevada batholiths deformation ceased shortly after pluton emplacement the sierra crest shear zone system includes possibly related shear zones as far north as saddlebag lake pendant and at least as far south as oak creek pendant and the owens valley indicating a possible strike length greater than 150 km

structural pattern and ascent model in the central extremadura batholith hercynian belt spain abstract the central extremadura batholith constitutes an important alignment of plutonic rocks occupying part of the internal zones of the iberian hercynian belt it comprises 13 plutons and numerous minor intrusions and covers a wide compositional range from quartz diorites to alkali feldspar granites structural study of the individual plutons reveals that their internal structural patterns may be correlated correlation between the different structural patterns in the plutons and interpretation of the superimposed deformation in the metasedimentary host rocks indicate that the plutons were emplaced and deformed in an e w dextral intracontinental shear zone developed during the second deformation phase 302 320 ma a qualitative ascent model has been established as follows 1 development of extensional fractures at 45 to the e w dextral shear zone 2 intrusion of granitic magmas along these fractures and 3 rotation of the earlier intrusions in a dextral sense inducing antithetic shear zones n s sinistral and a transverse shortening perpendicular to the major axis of the earlier deformed plutons as well as the forced emplacement of the later plutons

fracture controlled magma conduits in an obliquely convergent continental magmatic arc magnetic fabric patterns of two mid cretaceous nested plutons 102 1 and 96 3 ma in the central sierra nevada batholith provide evidence that felsic magma emplacement and ascent occurred via north trending steeply dipping planar fracture conduits oriented obliquely to the arc u pb geochronology data indicate that emplacement of the plutons was separated by 2 to 10 m y and that they were emplaced in part via the same conduit magnetic fabrics in the younger pluton are related to its final emplacement which was strongly influenced by a system of host rock joints formation of the north trending conduits at 100 ma can be related to a small arc parallel dextral shear component that produced tension fractures and that was associated with high angle oblique convergence by 90 ma convergence had become sufficiently oblique for the development of nearly arc parallel structures which were then favored as magma conduits

middle cretaceous ash flow tuff and caldera collapse deposit in the minarets caldera east central sierra nevada california a 2 3 km section of ash flow tuff and associated caldera collapse deposit representing the extrusive facies of part of the sierra nevada batholith is totally exposed from its floor to its top in the minarets caldera east central sierra nevada rapid burial and subsequent hornblende hornfels facies metamorphism resulted in remarkable preservation of primary textures and structures despite the development of cleavage domains in parts of the caldera fill late tertiary uplift and quaternary erosion have produced a rugged terrain where every meter of section is available for study large scale caldera filling eruption of ash flow tuff was interrupted by emplacement of a wedge shaped mass of caldera collapse deposit as much as 2 km thick whose volume exceeded 70 km 3 individual clasts in the caldera collapse deposit range to as much as 1 8 km across and include a wide variety of andesitic to rhyoliic lavas and related volcaniclastic rocks remnants of a precaldera volcanic field that was probably much more extensive than the caldera itself the caldera fill sequence rests with angular unconformity on a rugged surface eroded into older volcanic rocks the sequence is capped by bedded volcaniclastic rocks including delicately laminated tuffs of probable caldera lake origin the total aerial extent of the minarets caldera is not known but the area studied plus scattered pendants of ash flow tuff and associated volcaniclastic rocks to the west defines a 30 x 22 km elliptical area that may approximate its original shape the caldera fill is invaded by a body of quartz monzonite porphyry locally miarolitic that was probably emplaced during an episode of caldera resurgence

simulation of synoptic and subsynoptic scale phenomena associated with the east asian summer monsoon using a high resolution gcm abstract a 20 yr simulation using a global atmospheric general circulation model with a resolution of 0 5 latitude 0 625 longitude is compared with observational findings the primary goal of this survey is to assess the model performance in reproducing various summertime phenomena related to the continental scale asian monsoon in general and the regional scale east asian monsoon in particular in both model and observed atmospheres the seasonal march of the precipitation centers associated with the asian summer monsoon is characterized by onsets occurring earliest over the southeastern bay of bengal followed by rapid northeastward advances over indochina the south china sea philippine sea and the western pacific northward evolution in the east asian sector as well as northwestward development over the bay of bengal the indian subcontinent and the arabian sea this onset sequence is accompanied by southwesterly low level flows over the rainy regions as well as northwestward migration of the 2

relationship between tectonism and volcanism along the great sumatran fault zone deduced by spot image analyses abstract satellite images provide evidence for numerous stepovers pull apart grabens and volcanic structures along the nw trending right lateral great sumatran fault zone high resolution spot images permit us to analyze the relationship between volcanic and tectonic structures this analysis reveals that releasing stepovers and pull aparts are ephemeral structures along the great sumatran fault zone and that the geometry of the strike slip fault evolves permanently through time the interpretative structural maps obtained from spot image analysis reveal that the formation of huge peculiarly shaped volcanic calderas has occurred in large releasing stepover fault zones and that the bounding faults of rectangular pull apart basins are analogous to the circular ring faults of calderas in particular detailed study of the segments at the southernmost 150 km long termination of the great sumatran fault zone from northwest of ranau lake to semangka bay allows us to describe the development of the ranau collapse caldera this caldera is located within a pull apart basin bounded by a stepover its peculiar rectangular shape and its relatively large size about 200 km 2 are controlled by the evolution of the extinct ranau releasing stepover similarly the toba elliptical caldera one of the largest volcanic caldera in the world is elongated parallel to the present trace of the great sumatran fault and appears to be related to a releasing stepover associated with a wide pull apart basin that is not active at present

isotopic variation in the tuolumne intrusive suite central sierra nevada california granitoid rocks of the compositionally zoned late cretaceous toulumne intrusive suite in the central sierra nevada california have initial87sr 86sr values sri and143nd 144nd values ndi that vary from 0 7057 to 0 7067 and from 0 51239 to 0 51211 respectively the observed variation of both sri and ndi and of chemical composition in rocks of the suite cannot be due to crystal fractionation of magma solely under closed system conditons the largest variation in chemistry ndi and sri is present in the outer most equigranular units of the tuolumne intrusive suite sri varies positively with sio2 na2o k2o and rb concentrations and negatively with ndi al2o3 fe2o3 mgo feo cao mno p2o5 tio2 and sr concentrations this covariation of sri ndi and chemistry can be modeled by a process of simple mixing of basaltic and granitic magmas having weight percent sio2 of 48 0 and 73 3 respectively isotopic characteristic of the mafic magma are sri 0 7047 ndi 0 51269 and 18o 6 0 and of the felsic magma are sri 0 7068 ndi 0 51212 and 18o 8 9 the rocks sampled contain from 50 to 80 of the felsic component an aplite in the outer equigranular unit of the tuolumne intrusive suite apparently was derived by fractional crystallization of plagioclase and hornblende from magma with granudiorite composition that was a product of mixing of the magmas described above siliceous magmas derived from the lower crust having a maximum of 15 percent mantle derived mafic component are represented by the inner prophyritic units of the tuolumne intrusive suite

granite emplacement in an extensional setting an ams study of the magmatic structures of monte capanne elba italy abstract monte capanne elba is an excellent example of a granite pluton 42 km 2 emplaced 6 m y ago in a well known extensional environment that of the tyrrhenian sea its internal fabric has been studied using the magnitude of magnetic susceptibility and anisotropy measurements at 74 regularly distributed stations susceptibility magnitudes reveal a normal and asymmetrical petrographical zoning in the pluton the magnetic lineations are remarkably well organized mostly of nw se azimuth with slight plunges and always normal to the walls of the late aplitic dykes these lineations are also parallel to the stretching lineations of the immediate country rocks of the pluton in the western and probably deepest part of the pluton a ne sw trending magnetic magmatic lineation is also imprinted the following scenario is proposed for the emplacement of monte capanne during the opening of the tyrrhenian sea an approximately e w trending sinistral transform fault is taken as being responsible for the creation of a pull apart void that permitted upwelling of the magma orientations of the magmatic structures at depth are parallel to the elongation of the feeding zone of this void i e ne sw the very top part of the pluton was sheared parallel to the granite country rock interface i e nw se parallel to the local stretching of the tyrrhenian sea at the time of emplacement

transpressional shearing and strike slip partitioning in the late cretaceous sierra nevada magmatic arc california the rosy finch shear zone rfsz represents an example of synmagmatic strike slip tectonics in the east central sierra nevada and provides information on transpressional tectonics within magmatic arcs the rfsz 1 4 km wide and 80 km long is contained in late cretaceous granitoids 92 83 ma of the mono pass intrusive suite dextral strike slip deformation is indicated by a continuous band of orthogneiss mylonitic and cataclastic deformation characterized by subvertical foliations with subhorizontal lineations the style of dextral shearing in the rosy finch shear varies along strike from wide zones of ductile deformation in the youngest plutons to narrow zones of cataclastic deformation in the older plutons deformation of the youngest granitoids is synmagmatic as constrained by both field observations and isotopic studies dextral shearing occurs concurrently in contemporaneous intrusive suites to the north and south tuolumne and mount whitney suggesting strike slip movement along the axis of active plutonism field studies also suggest that contraction across the arc acted concurrently with strike slip movement consistent with a transpressional setting for the late cretaceous sierra nevada magmatic arc comparison of the field data with strain models of oblique plate convergence suggests that the rfsz is a preserved ductile signature of transcurrent motion of strike slip partitioning within a transpressional orogenic system recent plate reconstructions indicate a switch from sinistral to dextral oblique convergence at 95 ma which is consistent with the timing constraints on the dextral movement on the rfsz

the effect of glacier wastage on the flow of the bow river at banff alberta 1951 1993 a surface area volume relationship was used to estimate total glacier volumes for the highly glacierized hector lake basin 281 km 2 in the canadian rockies in the years 1951 and 1993 the change in volume was calculated and this value then extrapolated up to the bow basin at banff 2230 km 2 based on relative proportions of glacier cover the mean net glacier volume loss estimate of 934 10 6 m 3 was divided into annual proportions of glacier wastage and storage using a local mass balance record collected at peyto glacier in the mistaya valley contiguous to the bow basin unfortunately the record began in 1966 and a hind cast to 1952 hydrological year was necessary banff maximum summer temperature and lake louise snow course data were used as surrogates for summer and winter glacier mass balance respectively monthly wastage proportions were estimated for 1967 1974 by using modelled values of glacial melt as a template glacier wastage inputs to and storage held back from the bow river hydrograph at banff were compared with known basin yields to assess the hydrological effects of glacier volume change for 1952 1993 the average annual wastage basin yield ratio was found to be around 1 8 for the extremely low flow year of 1970 this ratio increased to 13 the proportion of flow derived from glacier wastage in august of this year was estimated to be around 56 although the results tend to confirm the regulatory effect of glaciers on stream flow it was found that in some years of low flow this situation has been aggravated by water being held in glacial storage

petrofacies and provenance of late mesozoic forearc basin northern and central california data from the great valley group sequence represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc this information is useful in documenting tectonic and magmatic events within the arc and related terranes and forms the basis for the establishment of petrostratigraphic units for mapping and correlation sandstone and conglomerate compositions are controlled by changes in provenance many of which were basinwide and synchronous clay mineral composition is controlled primarily by burial metamorphism careful attention to sample collection sample preparation and petrographic techniques is essential for uniform results seven petrographic parameters p f lv l m qp q q f and l listed in decreasing importance to petrofacies discrimination define eight petrofacies stony creek platina lodoga grabast boxer cortina los gatos and rumsey listed in approximate order of decreasing age the upper jurassic lower cretaceous petrofacies stony creek platina and lodoga contain higher lithic contents supracrustal sources whereas the upper cretaceous petrofacies especially the rumsey contain higher proportions of plutoniclastic components quartz feldspar and micas the proportion of potassium feldspar increases from near zero in the upper jurassic to nearly 50 of all feldspars in the uppermost cretaceous the lower part of the great valley group upper jurassic and lower cretaceous contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes tectonic highlands formed by the arc arc collision nevadan orogeny that occurred prior to initiation of the franciscan great valley sierra nevada arc trench system the klamath mountains area provided a major proportion of this detritus ophiolite and serpentinite detritus was deposited locally near the base of the great valley group as a result of deformation along the east side of the growing franciscan subduction complex volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the sierra nevada area during the cretaceous as the volcanic cover was stripped off plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin crustal components were more continental in the southern sierra nevada and more oceanic in the northern sierra nevada as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south by the middle of the late cretaceous extensive batholithic terranes provided potassium feldspar rich arkosic detritus to the entire forearc basin by the paleogene arc magmatism had migrated eastward sufficiently that deeper levels of the california part of the arc were exposed by erosion tectonic activity decreased in the forearc basin and the basin was filled to sea leve in most parts

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

local crustal extension at mount st helens washington seismicity and the orientation of fault planes from focal mechanisms indicate that mount st helens is located at a dextral offset along the st helens seismic zone shz earthquake swarms occurring in this offset are related to volcanic eruptions because motion on the shz is in a right lateral strike slip sense this dextral offset creates extension within a volume of the crust between the offset fault segments this offset geometry is similar to that of geothermal areas along the san andreas fault system we apply a model derived from these geothermal areas to mount st helens and find that the major differences between mount st helens and the geothermal areas can be related to the ratio of the width of the offset between fault segments l to the seismogenic depth h at mount st helens this ratio is 1 whereas in the geothermal areas the ratio is 1 we propose that when l h 1 as at mount st helens the regional minimum principal stress does not completely dominate the small volume under extension and as a consequence the opening geometry is poory established compared to the oblique crustal spreading that characterizes the geothermal areas where l h 1 late quaternary volcanic vents near mount st helens strike northeast similar to the strike of a set of pre quaternary faults and intrusive rocks that are mapped north of the volcano in addition the deepest earthquakes occurring within the extensional volume are aligned along a northeast striking fault since these northeast striking features are aligned approximately prependicular to the regional minimum principal stress we infer that the spatial position of mount st helens is controlled by the junction of the right stepping offset of the shz with the older set of fractures and that these fractures are favorably aligned with respect to the contemporary regional tectonic stress directions for the transport of magma through the brittle crust the sense of fault motions predicted by our model for local crustal extension is consistent with an apparent component of right lateral shear measured from geodetic lines around mount st helens during june and july 1980

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

origin damping and pattern of development of faults in granite observations of brittle fractures in the granite of the massif de la borne as well as in other rocks allow us to discuss the different hypotheses regarding the origin of faults it seems that all faults originate by shear along a preexisting plane which can be an important fracture joint former fault or a microflaw pore grain boundary the shear on the plane gives rise to an array of en echelon cracks that makes the rock less resistant and permits the lengthening of the fault we also found an arrangement of horsetail fractures damping the movements on the faults we then propose a pattern for the development of the faults they originate on preexisting plane and propagate by initiating en echelon cracks the movements are damped by horsetails which permit by faults connection in relays the creation of larger faults

simulation of the east asian summer monsoon using a variable resolution atmospheric gcm the east asia summer monsoon easm is simulated with a variable resolution global atmospheric general circulation model gcm developed at the laboratoire de meteorologie dynamique france the version used has a local zoom centered on china this study validates the model s capability in reproducing the fundamental features of the easm the monsoon behaviors over east asia revealed by the ecmwf reanalysis data are also addressed systematically providing as observational evidence the mean state of the easm is generally portrayed well in the model including the large scale monsoon airflows the monsoonal meridional circulation the cross equatorial low level jets the monsoon trough in the south china sea the surface cold high in australia and the upper level northeasterly return flow while the performance of simulating large scale monsoonal climate is encouraging the model s main deficiency lies in the rainfall the marked rainbelt observed along the yangtze river valley is missed in the simulation this is due to the weakly reproduced monsoonal components in essence and is directly related to the weak western pacific subtropical high which leads to a fragile subtropical southwest monsoon on its western flank and results in a weaker convergence of the southwest monsoon flow with the midlatitude westerlies the excessively westward extension of the high together with the distorted indian low also makes the contribution of the tropical southwest monsoon to the moisture convergence over the yangtze river valley too weak in the model the insufficient plateau heating and the resulting weak land sea thermal contrast are responsible for the weakly reproduced monsoon it is the deficiency of the model in handling the low level cloud cover over the plateau rather than the horizontal resolution and the associated depiction of plateau topography that results in the insufficient plateau heating comparison with the simulation employing regular coarser mesh model reveals that the local zoom technique improves in a general manner the easm simulation

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

magnetic susceptibility of the mont louis andorra ilmenite type granite pyrenees a new tool for the petrographic characterization and regional mapping of zoned granite plutons we have observed remarkably consistent patterns of concentric zonation in the values of low field magnetic susceptibility measurements over the variscan age mont louis andorra granite pluton of the eastern pyrenees of andorra spain and france this zonation is a function of the rock petrology since a close correlation is shown between the petrographic nature as defined by chemical analysis and the magnetic susceptibility magnitude of the rocks it reflects the dominantly paramagnetic nature of the granite carried by fe bearing silicates and this is demonstrated by the fact that low field susceptibilities of representative specimens are almost equal to 1 their high field susceptibilities and 2 their calculated susceptibilities using fe contents assuming a null ferromagnetic contribution we conclude that this technique accurately reflects the modal abundances of ferromagnesian phases in rocks of the ilmenite series and that it represents a powerful and efficient tool for the reconnaissance surveying of petrological variations in granitoid plutons

laccolith like emplacement model for the papoose flat pluton based on porphyroblast matrix analysis detailed porphyroblast matrix analysis within the concordant metasedimentary aureole rocks surrounding the papoose flat pluton of eastern california indicates that inclusion trails within porphyroblasts can be used as strain markers to restore the aureole rocks to their prepluton emplacement position using porphyroblast matrix relationships in combination with measurement of stratigraphic sections and whole rock geochemical analyses we have determined the kinematics of rotation the change in thickness and volume and the amount of translation of the metasedimentary formations within the aureole these data are consistent with initial emplacement of the magma as an inclined sill and subsequent inflation into a pluton or laccolith the combination of structural and porphyroblast matrix analysis leads to a three dimensional kinematic history of the wall rocks wherein vertical upward translation represents a significant part of the pluton emplacement related strain history

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

assembly of a dike fed magma chamber the jackass lakes pluton central sierra nevada california the mechanisms of ascent assembly and emplacement of granitic magma in the crust are critical to understanding the dynamics of continental margin growth yet these mechanisms remain controversial and poorly understood detailed study of structural and petrologic fabrics in the middle cretaceous jackass lakes pluton wall rock system central sierra nevada california coupled with u pb geochronology indicates that the pluton formed via sheet like assembly of a dike fed magma chamber final emplacement of the pluton was facilitated by multiple brittle and ductile mechanisms that were active at different times and places within the system this supports hybrid viscoelastic emplacement models as realistic alternatives to end member models i e dike versus diapir fracture propagation which initiated 40 of the space required for emplacement may have been facilitated by a small component of arc parallel dextral shear that produced north northwest striking tension gashes a combination of ductile wall rock shortening during lateral expansion of sheets and return flow of elongate strongly deformed wall rock septa produced an additional 25 of the space required other mechanisms including coeval formation of the overlying minarets caldera and stoping in the subvolcanic part of the magma chamber must account for the remaining 35 space implying that vertical transfer of material is an important emplacement mechanism at shallow crustal levels

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

the association of folds and veins in shear zones abstract paired hook shaped asymmetric folds with shared limbs cut by axial planar veins dikes or fractures are common in glaciers and rocks the sense of offset across the vein or fracture is characteristically opposite to that expected from the sense of fold asymmetry the kinematics of development of the folds and the relationship of the folds to the fractures or veins can be understood by considering the nature of glacial flow and by utilizing simple clay experiments in zones of simple shear dilational fractures may form at about 45 to the shear zone boundaries the perturbation of strain around such a fracture during its development and subsequent rotation and closure under continued deformation causes layers or pre existing foliation cut by the fracture to become folded thus folding is a consequence of the fracturing and not vice versa the precise shape of the fold depends on the nature of the perturbation and particularly whether or not the fracture remains for a time open or fluid filled and thus has walls unable to sustain a shear stress during vein rotation paired hook folds provide evidence for non coaxial strain and are good sense of shear indicators however not all folds with veins parallel to their axial surfaces form in the way described in this paper in some cases vein emplacement occurs late during fold development or post dates folding in these cases offsets along the veins are consistent with fold asymmetry

pseudotachylyte generated in the semi brittle and brittle regimes bench canyon shear zone central sierra nevada pseudotachylyte cuts cretaceous plutonic and volcanic rocks in the bench canyon shear zone central sierra nevada california as documented by optical and scanning electron microscopy the pseudotachylyte displays evidence for a friction melt origin including vesicles amygdules crystallites flow fabrics and embayed crystal fragments based on fault related rock association vein morphology and inferred crustal level of generation two distinct types of pseudotachylyte are documented in the shear zone pseudotachylyte associated with cataclasite was generated at shallow crustal levels 1 10 km via unstable velocity weakening abrasive wear friction pseudotachylyte associated and interlayered with mylonite was generated at deeper crustal levels 10 15 km most likely via stable velocity strengthening adhesive wear friction this pseudotachylyte underwent ductile deformation in the solid state interlayered pseudotachylyte and mylonite records cyclic aseismic seismic slip at a transitional crustal level between the semi brittle field of quartzofeldspathic rocks and the base of the seismogenic zone the cyclicity is attributed to strain rate fluctuation effected by strain resistant phacoids pore fluid pressure variation ductile instabilities or downward fault propagation the mode of deformation within the shear zone progressed from i production of mylonite during amphibolite to greenschist facies conditions to ii generation of pseudotachylyte by intermittent seismic faulting within a background of aseismic shear in the upper realm of the semi brittle field 300 400 c to iii generation of pseudotachylyte through seismic events in the brittle 300 c during uplift exhumation and cooling some of the latter may have been generated at shallow enough crustal levels 4 km to allow vesicle formation the exhumation of a crustal level exposing such an assemblage provides a rare opportunity to study the enigmatic nature of the transitional change from semi brittle flow to seismogenic rupturing

quantification of fracture networks in non layered massive rock using synthetic and natural data sets abstract two quantitative measures correlation dimension and maximum lyapunov exponent are investigated for quantifying fracture spacing in massive non layered rock the correlation dimension a measure of fractal dimension characterizes some aspects of fracture distribution relative to other fractal methods used in structural geology the correlation dimension provides a more rigorous mathematical calculation of the fractal dimension and is particularly robust in cases where data is limited the maximum lyapunov exponent calculation also provides quantification of observed distributions of fracture spacing emphasizing variations in adjacent spacing measurements the two methods are tested on two different synthetic data sets to elucidate their usefulness in distinguishing between different distributions and their sensitivity to population size average fracture spacing and standard deviation both methods provide accurate results for small population sizes and for a range of average fracture spacings these methods are then used together to quantify two different fracture sets in the granitoids of the sierra nevada batholith the results indicate that the different fracture sets inferred to form from different tectonic processes have distinctive and quantifiable differences in patterns of fracture spacing

crustal scale en echelon p shear tensional bridges a possible solution to the batholithic room problem the apparent paradox of voluminous granitoid emplacement in an overall compressional magmatic are has been somewhat alleviated by the idea of pluton emplacement in tension cracks and dilational jogs within arc parallel strike slip fault systems as an alternative hypothesis we propose that an en echelon p shear array provides a continuous batholith scale zone of dilation along the trend of active magmatism and that it is favored by transpressional tectonics in the sierra nevada california the late cretaceous granitoids of the cathedral range intrusive epoch are consistent with emplacement into bridges between p shears because 1 they are elongated oblique to the magmatic trend consistent with p shear orientation within a dextral system 2 they were all emplaced within 5 10 m y along a 300 km trend resulting in a displacement rate of 1 cm yr across the arc and 3 syn to late magmatic dextral shear zones bound and crosscut the plutons as in a p shear tensional bridge

structural eruptive and intrusive evolution of the grizzly peak caldera sawatch range colorado volcanic and shallow intrusive features of the deeply dissected 34 ma grizzly peak caldera in west central colorado record evolution of the magmatic center from pre caldera through post resurgent stages pre caldera dikes zones of hydrothermally altered rocks and lava flows formed along a circular swarm of cone sheet fractures around the site of the future caldera early largely rhyolitic uppercrustal magmatism culminated in the caldera forming eruption of the grizzly peak tuff intracaldera tuff is zoned from high silica rhyolite at the base to low silica rhyolite at the eroded top and further contains dacite to mafic latite pumice lumps in two heterogeneous tuff layers in the upper third of the preserved section half of the erupted tuff ponded in the 17 by 23 km 600 km 3 caldera filling the asymmetric depression to a compacted thickness locally 2 7 km including intercalated rock avalanche megabreccias shed from ring fault scarps the asymmetric caldera has an inner ring fracture zone that separates two structural segments that collapsed to different depths caldera fill buried collapse structures as they formed the inner ring fracture zone is a growth or syn depositional fault in the single cooling unit tuff welded tuff ring dikes are locally exposed at erosion levels below the caldera fill these dikes are remnants of fissure vents in the outer ring fracture zone following collapse the grizzly peak caldera was uplifted forming a complexly faulted resurgent dome resurgence resulted partly from emplacement of a composite granodiorite laccolith now exposed in the eroded core of the dome a belt of mafic latite to rhyolite porphyry dikes and small stocks formed across the center of the domed caldera during the waning of the magmatic center latite intrusions in this suite represent the penetration of relatively mafic magma to the surface following solidification of the felsic subcaldera batholith

interannual variability of summer monsoon onset over the western north pacific and the underlying processes climatological summer monsoon onset over the south china sea scs and the western north pacific wnp defined as the region of 108 208n 1208 1608e displays three distinct stages around mid may monsoon rain commences in the scs and the philippines in early to mid june the monsoon rain extends to the southwestern philippine sea after mid july the rainy season starts in the northeastern part of the wnp the onset anomaly however displays an in phase interannual variation across the entire wnp domain the standard deviation of the onset date increases eastward from 3 pentads in the scs to 5 pentads in the northeastern part of the domain the large onset variability in the wnp is mainly attributed to large year to year changes of the seasonal cycle

importance of the resolution of surface topography in indian monsoon simulation abstractthe influence of surface topography resolution in indian summer monsoon simulation is investigated three sets of six member ensemble simulations with climatological sea surface temperature are conducted with the community atmospheric model version 5 1 cam5 1 coarse simulation at 1 9 2 5 latitude longitude resolution fine simulation at 0 47 0 63 resolution and hybrid simulation that is using coarse surface topography imposed on the fine configuration with regard to the representation of the surface topography substantial differences occur at the regional scales between the simulations especially over the foothills and steep flanks of the mountains in the coarse and hybrid simulations the orographic height of the foothills is overestimated whereas that of the steep flanks adjacent to the foothills is underestimated the biases are severe up to 1 km over the himalayas and tibet and have detrimental effects on regional climate through barrier effects on the low level flow and

variations in deformation fields during development of a large volume magmatic arc central sierra nevada california mid to late cretaceous plutons in the central sierra nevada magmatic arc show widely preserved magmatic foliation whereas regionally developed solid state foliation is absent relatively slow cooling of these plutons and expected strain rates 10 14 suggest that the plutons were emplaced in a neutral or weakly extensional deformation regime domains of solid state ductile shear of only slightly younger age than the plutons on the other hand indicate a contractional regime timing of pluton emplacement and movement on the shear zones have been constrained using pb u zircon and 40 ar 39 ar hornblende and biotite geochronology both plutons and ductile shear zones become younger toward the east the four more westerly shear zones which were active between ca 100 and 90 ma show steeply plunging stretching lineations whereas the most easterly and or youngest zones active between ca 88 and 78 ma show mostly oblique and or subhorizontal stretching lineations indicating a change in kinematics at ca 90 ma the above events define a complex deformation pattern in which strain regimes fluctuated in time and space between neutral or weak extensional and contractional we propose a tectonic model in which thenospheric mantle corner flow produced eddy pairs in the mantle corner that transmitted a neutral or weak extensional regime to the overlying crust and facilitated the movement of granitic magma to mid and upper levels probably as dikes via fractures slab flattening caused the neutral or weak extensional regime to move eastward away from the trench increased coupling between upper and lower plates induced by the slab flattening promoted contractional strain in the cooling plutons and domains of ductile shear formed in progressively younger plutons to the east the above events were accompanied by an oblique convergence vector between north america and farallon plates engebretson et al 1985 which imposed a relatively small component of right lateral shear onto the arc that increased with time we estimate that at ca 100 ma the convergence vector made an angle obl 20 to the arc normal and we suggest that around ca 90 ma obl passed through a critical value conceivably 20 oblcrit 30 at this juncture the component of right lateral shear became sufficiently large to induce significant arc parallel strike slip movement on the most easterly shear zones these kinematics continued as the dominant scheme possibly as late as ca 78 ma

apatite in felsic rocks a model for the estimation of initial halogen concentrations in the bishop tuff long valley and tuolumne intrusive suite sierra nevada batholith magmas

coupled model simulations of boreal summer intraseasonal 30 50 day variability part 1 systematic errors and caution on use of metrics boreal summer intraseasonal 30 50 day variability bsisv over the asian monsoon region is more complex than its boreal winter counterpart the madden julian oscillation mjo since it also exhibits northward and northwestward propagating convective components near india and over the west pacific here we analyze the bsisv in the cmip3 and two cmip2 coupled ocean atmosphere models though most models exhibit eastward propagation of convective anomalies over the indian ocean difficulty remains in simulating the life cycle of the bsisv as few represent its eastward extension into the western central pacific as such few models produce statistically significant anomalies that comprise the northwest to southeast tilted convection which results from the forced rossby waves that are excited by the near equatorial convective anomalies our results indicate that it is a necessary but not sufficient condition that the locations the time mean monsoon heat sources and the easterly wind shear be simulated correctly in order for the life cycle of the bsisv to be represented realistically extreme caution is needed when using metrics such as the pattern correlation for assessing the fidelity of model performance as models with the most physically realistic bsisv do not necessarily exhibit the highest pattern correlations with observations furthermore diagnostic latitude time plots to evaluate the northward propagation of convection from the equator to india and the bay of bengal also need to be used with caution here incorrectly representing extratropical tropical interactions can give rise to apparent northward propagation when none exists in association with the eastward propagating equatorial convection despite these cautions the use of multiple cross checking diagnostics enables the fidelity of the simulation of the bsisv to be meaningfully assessed

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

comparison of the structure of the itcz in the west pacific during the boreal summers of 1989 93 using amip simulations and ecmwf reanalysis the dynamic structure and interannual variability of the itcz in the western north pacific and east asia during the boreal summers of 1989 93 are investigated european centre for medium range weather forecasts ecmwf reanalyses are used to characterize the dynamical structure of the itcz the itcz structure in the national center for atmospheric research ncar community climate model 3 ccm3 6 and the national aeronautics and space administration nasa goddard institute of space studies giss si2000 gcm is also explored the itcz axis can be partitioned into three sections in the western north pacific and east asia the continental monsoon trough cmt in india the bay of bengal and indo china the oceanic monsoon trough omt in the pacific warm pool and the trade wind trough twt in the central pacific the confluence point cp is defined as an area where the broad cyclonic flow in omt changes to the easterly trades of the twt east of the cp both gcms simulate a weaker easterly trade wind regime with a broader itcz due to the dislocation of the pacific high to the west of the cp both gcms simulate a weaker cross equatorial flow and omt both models show skill in simulating the interannual variability of the location of the cp however for the peak enso warm phase years 1992 93 the spread among ensemble members of the cp longitude is comparable to the shift of ensemble mean cp location relative to 1989 that is the internal variability of each gcm is on the same order as the simulated interannual variability in this region

is this magnetic fabric normal a review and case studies in volcanic formations abstract when studying weakly anisotropic rocks non standard relationships between magnetic and expected petrofabric axes are sometimes observed in particular the so called inverse or intermediate fabrics a review of possible explanations for these effects is presented and leads to the conclusion that a majority of abnormal magnetic fabrics often encountered in magnetite rich volcanic rocks are due to abnormal preferred orientations or distributions of magnetite grains through case studies in dikes from skye island yemen and the iberian peninsula and magma and ash flows from the ethiopian traps and southern corsica the various possible origins of such fabrics are examined it is possible to retrieve reliable magma flow directions from these sites provided proper data selection is performed leading to non unique interpretations

a tectonic model for the emplacement of the main donegal granite nw ireland the main donegal granite is shown to lie in a major late stage ne sw trending transcurrent sinistral shear zone in the caledonides of nw ireland the zone which is bent both laterally and upwards around the pluton has displacements which diminish sw along its length from a maximum of approximately 20 km at the ne end of the pluton the granite has also been deformed by this sinistral shear but it has a strain component of its own the nature and development of which indicate that the pluton was accommodated rather than forcefully emplaced in the shear zone strain variations between granite and wall rock and an early plagioclase fabric associated with the petrographic banding of the granite suggest that intrusion and deformation were more or less synchronous at around 400 ma it is suggested that unconsolidated granite in the shear zone locally created high strain rates and instability which caused the zone to bend split lengthwise and progressively create an internal low pressure zone into which the main granite was emplaced the wide variety of emplacement styles of the other radiometrically synchronous plutons of the batholith can be attributed to the progressive development of the shear zone thorr and fanad in tension between the zone and a complimentary structure to the n ardara and toories in local compression at the shear zone termination rosses in tension on the outer arc of the bending zone and trawenagh bay as displaced main granite magma in a similar tensional setting during the final stages of deformation

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

fractional crystallization in granites of the sierra nevada how important is it although compositional variation in zoned calc alkalic plutons is often ascribed to crystal fractionation diagnostic large scale field evidence of crystal accumulation in these slowly cooled bodies is generally missing in many plutons however small scale crystal cumulates have been preserved as layered schlieren and in microcosm may allow an assessment of the importance of crystal fractionation in their host pluton9s development small widely separated patches of schlieren in the tuolumne intrusive series yosemite national park california formed as cumulates their darkest layers show high concentrations of magnetite sphene biotite horn blende and zircon and have unusually fractionated major and trace element compositions feo 33 al 2 o 3 in chondrites 750 zr 2000 ppm the layers define smooth trends on major and trace element al 2 o 3 variation diagrams that diverge strongly from patterns for the main sequence rocks of the tuolumne series and granitoids throughout the sierra nevada removal of such cumulates from any main sequence magma would produce al rich evolved rocks not the al poor felsic rocks of the pluton the findings suggest that fractional crystallization did not produce the dominant chemical patterns seen in the tuolumne and similar sierra nevada granites

magmatic tectonic interaction during early rio grande rift extension at questa new mexico pre caldera and caldera related igneous rocks near questa new mexico provide a well constrained example of upper crustal extension over a magma chamber extensional strain exceeding 200 occurred over many square kilometers in a region now underlain by a batholith the most intense deformation followed emplacement of intrusions related to formation of questa caldera at 25 7 ma and preceded the cooling of 24 6 ma plutons detailed mapping of the southern part of questa caldera indicates the sequence 1 extension concurrent with plutonism resulting in an overlying carapace of highly tilted blocks bounded by low angle faults 2 renewed intrusion into overlying units with the orientation of pluton tops dikes and molybdenum bearing alteration zones controlled by previously formed low angle faults 3 reactivation or continued motion of low angle normal faults possibly aided by hydrothermal fluids and 4 high angle normal faults that formed after the magmatic system waned early high angle faults remained active again possibly aided by fluids during their rotation to low angles at upper crustal levels the magma chamber is believed to have provided a zone of ductility into which overlying brittle normal structures were rooted at mid levels in the crust regional magmatism thermally softened the crust and allowed it to deform in a ductile manner regional extension appears to have been focused in a thermally and mechanically weakened area during the period of maximum plutonic activity the features at questa provide insights into processes that may have occurred in similar systems in the basin and range province and elsewhere

shear zone development during magmatic arc construction the bench canyon shear zone central sierra nevada california the bench canyon shear zone is a 20 km long moderately to steeply dipping zone of ductile to brittle strain that cuts cretaceous plutonic and volcanogenic rocks located in the central sierra nevada california this zone is one of several cretaceous age ductile shear zones that record fluctuating strain fields associated with the tectonic magmatic evolution of the central sierra nevadan magmatic arc as determined by field relations fabric analysis and u pb and 40 ar 39 ar geochronology the bench canyon shear zone underwent an episodic deformation history involving both contractional and extensional strain over a period of 17 m y or longer deformation is divided into early ca 101 95 ma main ca 95 90 ma and late ca 90 78 ma phases temperature during main phase deformation followed a retrograde t t path of 600 300 c after emplacement of multiple plutons main phase deformation involved ductile thrust movement in both the 95 1 ma red devil lake pluton and lower to mid cretaceous volcanic rocks where thrusting was facilitated by heat and fluids associated with plutonism fingerlike sills associated with the red devil lake pluton were emplaced syntectonically with respect to main phase deformation but cooled rapidly undergoing heterogeneous strain more typical of pre tectonic emplacement the ca 90 ma mount givens pluton cuts the shear zone fabric in the wall rock limiting the bulk of deformation to have occurred prior to that time domainal and diachronous late phase reactivation s along the zone involved weak fluid enhanced ductile 500 t 300 c deformation and generation of abundant cataclasite and pseudotachylyte the long lived episodic and diachronous deformation history of the bench canyon shear zone illustrates the complexities to be expected within shear zones during continental magmatic arc evolution

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

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

jurassic ash flow sheets calderas and related intrusions of the cordilleran volcanic arc in southeastern arizona implications for regional tectonics and ore deposits volcanologic petrologic and paleomagnetic studies of widespread jurassic ash flow sheets in the huachuca southern dragoon mountains area have led to identification of four large source calderas and associated comagmatic intracaldera intrusions stratigraphic facies and contact features of the caldera related tuffs also provide constraints on the locations lateral displacements and very existence for some major northwest trending faults and inferred regional thrusts in south eastern arizona for example the intricate cochise thrust system as mapped by others in the southern dragoon mountains consists instead of primary depositional contacts within caldera fill megabreccia and the inferred regional thrusts do not exist at least as previously interpreted silicic alkalic compositions of the jurassic caldera related ash flow tuffs bimodal associated mafic magmatism and interstratified coarse sedimentary deposits provide evidence for synvolcanic extension and rifting within the cordilleran magmatic arc gold copper mineralization is associated with subvolcanic intrusions at several of the jurassic calderas

simulation of the northern summer monsoon in the ecmwf model sensitivity to horizontal resolution abstract the ability of the ecmwf model cycle 33 to simulate the indian and east asian summer monsoons is evaluated at four different horizontal resolutions t21 t42 t63 and t1o6 generally with respect to the large scale features of the circulation the largest differences among the simulations occur at t42 relative to t21 however on regional scales important differences among the high frequency temporal variability serve as a further critical rest of the model s ability to simulate the monsoon t106 best captures both the spatial and temporal characteristics of the indian and east asian monsoons whereas t42 fails to correctly simulate the sequence and development of synoptic scale milestones that characterize the monsoon flow in particular t106 is superior at simulating the development and migration of the monsoon trough over the bay of bengal in the t42 simulation the development of the monsoon occurs one month earlier than typically observed at this time the trough is incorrectly locate

the effect of horizontal resolution on indian monsoon depressions in the met office nwp model monsoon depressions are synoptic scale features that are responsible for a significant fraction of the rain over northern india during the summer monsoon season and as such it is important to quantify their structure and behaviour in numerical weather prediction models it is known that increasing model resolution is strongly correlated with improved forecasts in the short term and global circulation in the longer term as well as better representation of tropical cyclones here we explore the sensitivity of depressions to changes in resolution using the met office unified model seven nwp case studies of depressions from 2013 15 were run at eight resolutions corresponding to equatorial grid spacing of between 16 and 208 km and compared with data for the same events from trmm and era interim reanalysis we found that at the low resolution end of the spectrum increases in resolution led to improvements in the composite structure but with diminishing returns the model also persistently overestimated the depression intensity in particular the wind speed and the warm core aloft with the source appearing to originate in the mid troposphere the sensitivity of the diurnal cycle to resolution was also explored the stratiform component was found to be very well represented by the model whereas the convective component was described quite poorly improvement in most components of structure with increasing model resolution were marginal beyond n320 63 km and n512 39 km for dynamic and thermodynamic fields respectively

igneous emplacement in a transpressive shear zone ox mountains igneous complex the central and southwestern ox mountains inlier in western ireland comprises amphibolite facies metasediments and metavolcanic rocks which have been deformed by a major sinistral shear zone granitoid emplacement occurred in two distinct styles in the ox mountains shear zone the older pluton the ox mountains granodiorite was emplaced syn kinematically with respect to the main sinistral transpressional events in its wall rocks it was emplaced as a series of compositionally distinct sheets in the central part of the shear zone system thus suggesting the formation of transient dilational sites occurred in response to the transpressive deformation the younger lough talt and easky lough adamellites were emplaced as individual intrusions in dilational cavities produced by reactivated movements on a discrete zone within the ox mountains inlier the different intrusive styles are considered to be a product of the tectonic regimes operating during emplacement intrusion into transient dilational cavities may be one method by which granitoid magmas are emplaced into fault zones undergoing active contractional deformation

interannual and intraseasonal variations in monsoon depressions and their westward propagating predecessors abstract the majority of monsoon depressions develop from the regenesis of westward propagating residual lows from the east most of these residual lows can be traced to weather disturbances in the south china sea including tropical cyclones and 12 24 day monsoon lows hypothetically any mechanism causing a variation in the occurrence frequency of these two types of weather disturbances in the western tropical pacific south china sea wtp scs region may result in a corresponding change in the formation frequency of monsoon depressions over the bay of bengal two such possible mechanisms are interannual and intraseasonal variations of large scale summer circulation in the wtp scs region induced by 1 the interannual variation of the sea surface temperature sst in the eastern tropical pacific and 2 the northward migration of the 30 60 day monsoon trough ridge the national centers for environmental prediction national center for atmospheric research reanalysis data and the 6 hourly tropical cyclone tr

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

synkinematic granite emplacement in a shear zone the pleasant hills pluton canadian appalachians the 361 356 ma late devonian pleasant hills pluton comprises a series of sheets of mafic felsic and hybrid intermediate plutonic rocks that were emplaced along a positive flower structure associated with the crustal scale cobequid fault zone this dextral strike slip fault zone forms the boundary of the meguma and avalon terranes the sequence of emplacement is inferred from crosscutting structures radiometric dating shows that the pluton was crystallized within a few million years gabbroic magma was probably derived from partial melting of the mantle beneath the extensional magdalen basin and successive batches of mafic magma were progressively richer in h 2 o ti zr and nb felsic magmas were probably derived by partial melting of the lower crust small batches of felsic magma show differing trace element evolution that reflects changes in magma temperature and type of volatiles younger magmas being generally richer in high field strength elements and fluorine rapakivi textured granite is common heat transfer and mass transfer along the fault zone resulted in thermal softening and lubrication of all branches of the flower structure so that there was repeated magma flow through each branch the presence of magma controlled the localization of strain which is expressed as synmagmatic deformational structures and deformation continued under solid state conditions to produce mylonitic fabrics each branch of the flower structure acted as a pathway for many magma batches and only small volumes of magma reached the highest structural levels the pluton was emplaced by progressive widening of and magma emplacement along branches of the flower structure as a result of country rock translation this translation involved both lateral and upward movement of blocks within the cobequid fault zone dextral slip is recognized on the southern margin of the escaping block and reverse oblique sinistral slip on its northern margin the pleasant hills pluton shows progressive creation of space for magma along branches of the flower structure and gradual expansion of the pluton from a series of dike like bodies to a larger composite pluton through the emplacement of numerous small geochemically distinct magma batches

batholith emplacement at mid crustal levels and its exhumation within an obliquely convergent margin abstract emplacement of the central part of the coast mountains batholith of northern coastal british columbia occurred within a regime characterized by oblique convergence between the farallon kula and north american plates we use new structural kinematic and u pb isotopic data to show that the locations geometry and mechanisms of pluton emplacement within this batholith were controlled by displacements within a network of normal faults and transtensional shear zones these data also show that the most active period of pluton emplacement from 67 to 51 ma coincided with a change in style of deformation within the batholith prior to 67 ma plutons were emplaced within an arc dominated by regional scale contractional shear zones in contrast emplacement of 67 51 ma plutons occurred in an arc increasingly dominated by normal faults with arc parallel to oblique displacement and by sinistral transtensional shear zones we have identified and mapped the structure of three plutonic complexes composed of 67 to 51 ma plutons the khyex sill complex arden lake plutonic complex and quottoon plutonic complex shear zone controlled emplacement of plutons within the batholith accounts for the widely different orientations and structural features that characterize plutons within these three complexes during and after this latest cretaceous paleogene period of intense plutonic activity and accompanying deformation the deep roots of the batholith were rapidly unroofed by ductile normal faulting prior to 50 ma

viscosity determinations of some frictionally generated silicate melts implications for fault zone rheology at high strain rates analytical scanning electron microscopy has been used to determine the major element compositions of some natural and artificial silicate glasses and their microcrystalline equivalents derived by the frictional melting of intermediate to acid protoliths the data show that the matrices of the friction melts which cool to form pseudotachylytes are relatively basic and hydrous even when their protoliths are intermediate to acid this is because frictional fusion involves the selective comminution and nonequilibrium melting of minerals based on their individual mechanical properties and melting points not the formation of minimum melts through equilibrium mineral interaction this means that hydrous ferromagnesian minerals e g micas and amphiboles melt preferentially to form the liquid matrix while feldspars and especially quartz more readily survive as clasts pseudotachylytes generated by frictional melting are therefore not bulk melts and as clast melt suspensions they cannot be considered as simple newtonian fluids the calculated viscosities of the friction melts are low for example at 1200 c most friction melts possess zero shear suspension viscosities of 102 104 dpa s 1 dpa s 1 p this is equivalent to the viscosities of tholeiitic and alkaline basaltic magmas at the same temperature these viscosities are maximum determinations because as clast melt suspensions friction melts may undergo shear thinning and exhibit pseudoplasticity at high shear rates i e during slip on a fault surface contrary to earlier suggestions where the bulk melting of intermediate to acid protoliths was believed to result in the generation of viscous friction melts that could act to inhibit continued sliding this work shows that most pseudotachylytes are partial melts possessing low viscosities the formation of highly fluid suspensions during slip may have profound effects on the dissipation of stored strain energy in the rocks surrounding a fault interface lubrication could facilitate an increase in the slip rate and the rate of energy dissipation this would be manifest as an increase in high frequency seismic wave radiation and vibrational

what controls gold distribution in archean terranes despite intensive efforts determination of a predictable pattern of gold distribution to enhance process understanding and simplify exploration has remained elusive the pattern of gold distribution along the archean boulder lefroy shear zone in the yilgarn craton of western australia provides insights into gold distribution in one of the world s richest provinces four world class gold deposits including the giant golden mile at kalgoorlie are regularly spaced along the shear zone providing a window into understanding large scale archean hydrothermal systems relationships among gold endowment shear zone trend and geologic complexity as measured by fractal dimensions indicate that 1 ore fluids were focused into those parts of the shear zone with greatest misorientation from the regional trend which define dilational sites during shearing and became the sites of world class gold deposits and 2 the degree of complexity contrast along the shear zone modulated gold endowment

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation

multi scale temporal spatial variability of the east asian summer monsoon frontal system observation versus its representation in the gfdl hiram this study examines the representation of the multi scale temporospatial variability of the east asian summer monsoon stationary front msf in the high resolution atmospheric model hiram of the national oceanic and atmospheric administration noaa geophysical fluid dynamics laboratory compared with the observed variability of the msf in the european center for medium range weather forecasts reanalysis interim era interim hiram reproduces reasonably well the seasonal mean precipitation pattern and the seasonal migration of msf however wet biases are found over the northern and eastern china and northern japan and dry biases extend from the southern china to the western north pacific these rainfall biases are directly tied to a northwestward bias in the model simulated seasonal mean location of msf and this location bias is most pronounced in the month of may in general the msf in hiram is more intense located more northwestward and more stationary with weaker interannual variations compared to the observed a pronounced positive bias in the ocean land sea level pressure contrast over east asia largely manifested as the westward expansion of the western north pacific subtropical high is hypothesized to be the main cause of the northwestward location bias of msf in hiram this bias in sea level pressure contrast likely results from the missing of realistic air sea interactions in the hiram simulations