fluid absent melting of a layered crustal protolith implications for the generation of anatectic granites we report the result of h2o undersaturated melting experiments on charges consisting of a layer of powdered sillimanite bearing metapelite hq36 and a layer of powdered tonalitic gneiss agc150 experiments were conducted at 10 kbar at 900 925 and 950 c when run alone the pelite yielded 40 vol strongly peraluminous granitic melt at 900 c while the tonalite produced only 5 vol weakly peraluminous granitic melt at 950 c the pelite and the tonalite yielded 50 vol and 7 vol granitic melt respectively when run side by side the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone in the pelite the melt abundance increased by 25 vol when run alone biotite dehydration melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt when run side by side only garnet was produced in addition to granitic melt experiments of relatively short duration however also contained al rich orthopyroxene we suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of al2o3 in the melt which lowers the temperature of the biotite dehydration melting reaction in the pelite the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite layer to the pelite layer this has the effect of changing the bulk composition of this layer in the direction of minimum temperature granitic liquids our results show that rocks which are poor melt producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase s and facilitate dehydration melting because of this effect the continental crust may have an even greater potential for granitoid melt production than previously thought our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks which will be reflected in their isotopic and geochemical compositions

zircon u pb ages and hf isotope compositions of migmatite from the north dabie terrane in china constraints on partial melting migmatite gneisses are widespread in the dabie orogen but their formation ages are poorly constrained eight samples of migmatite including leucosome melanosome and banded gneiss were selected for u pb dating and hf isotope analysis most metamorphic zircon occurs as overgrowths around inherited igneous cores or as newly grown grains morphological and internal structure features suggest that their growth is associated with partial melting according to the hf isotope ratio relationships between metamorphic zircon and inherited cores three formation mechanisms for metamorphic zircon can be determined which are dissolution reprecipitation of pre existing zircon breakdown of zr bearing phase other than zircon in a closed system and crystallization from externally derived zr bearing melt four samples contain magmatic zircon cores yielding upper intercept u pb ages of 807 35 768 12 ma suggesting that the protoliths of the migmatites are neoproterozoic in age the migmatite zircon yields weighted mean two stage hf model ages of 2513 97 894 54 ma indicating reworking of both juvenile and ancient crustal materials at the time of their protolith formation the metamorphic zircons give u pb ages of 145 2 120 2 ma the oldest age indicates that partial melting commenced prior to 145 ma which also constrains the onset of extensional tectonism in this region to pre 145 ma the youngest age of 120 ma was obtained from an undeformed granitic vein indicating that deformation in this area was complete at this time two major episodes of partial melting were dated at 139 1 and 123 1ma the first episode of partial melting is obviously older than the timing of post collision magmatism corresponding to regional extension the second episode of partial melting is coeval with the widespread post collision magmatism indicating the gravitational collapse and delamination of the orogenic lithospheric keel of the dabie orogen which were possibly triggered by the uprising of the cretaceous mid pacific superplume

detecting volcanism on titan and venus with microwave radiometry the detection by spaceborne instrumentation of infrared thermal emission from volcanic eruptions is well established on earth but is challenged on venus and titan by their optically thick atmospheres microwave radiometry in principle offers the ability to detect emission from surface thermal anomalies on these worlds due to greater atmospheric transparency microwaves also offer the prospect of sensing the shallow subsurface and thus may detect warmth from lava flows for longer than surface infrared emission however satellite microwave instruments typically have low spatial resolution 10s of km so volcanic heat is diluted in the wide instrument footprint we examine the prospects for the detection of volcanic deposits by microwave given likely planetary eruption rates and lava flow deposit geometries using mt etna as a template nondetection of prominent hotspots in cassini data may imply that the resurfacing rate is lower than 2 km3 yr five times smaller than the expression of an earth like fraction of geothermal heat flow as latent heat in extrusive volcanism

simulation of igneous differentiation processes one of the primary goals of igneous petrology is the definition and evaluation of the roles of the processes responsible for chemical differentiation quantitative simulation of these processes not only requires an understanding of the systematics of mineral liquid equilibria in natural systems but also some understanding of how different processes interact the programs presented here consist of empirically calibrated expressions of mineral melt equilibria that are built around a thermodynamic framework the framework of the programs which are designed to model phase equilibria based igneous differentiation have been published in earlier works nielsen and dungan 1983 nielsen 1985 nielsen 1988 a b nielsen et al 1988 this presentation is to show how modeling can be used to gain otherwise unobtainable insights into the mechanics of igneous differentiation in particular for processes that are difficult to simulate in the laboratory in this chapter we will simulate the major differentiation processes that are characteristic of shallow igneous magma chambers these processes include crystallization recharge assimilation and eruption in each example we will examine how observations of natural systems can be converted into the mathematical constraints necessary for the construction of computer based models since our primary goal is to model natural igneous systems the examples show how phase equilibria modeling can be used to help solve problems related to interpretation of the chemical and mineralogic diversity of suites of natural lavas

trade off of elastic structure and q in interpretations of seismic attenuation the quality factor q is an important phenomenological parameter measured from seismic or laboratory seismic data and representing wave energy dissipation rate however depending on the types of measurements and models or assumptions about the elastic structure several types of qs exist such as intrinsic and scattering qs coda q and apparent qs observed from wavefield fluctuations we consider three general types of elastic structures that are commonly encountered in seismology 1 shapes and dimensions of rock specimens in laboratory studies 2 geometric spreading or scattering in body surface and coda wave studies and 3 reflectivity on fine layering in reflection seismic studies for each of these types the measured q strongly trades off with the inherently limited knowledge about the respective elastic structure for the third of the above types the trade off is examined quantitatively in this paper for a layered sequence of reflectors e g an oil or gas reservoir or a hydrothermal zone reflection amplitudes and phases vary with frequency which is analogous to a reflection from a contrast in attenuation we demonstrate a quantitative equivalence between phase shifted reflections from anelastic zones and reflections from elastic layering reflections from the top of an elastic layer followed by weaker reflections from its bottom can appear as resulting from a low q within or above this layer this apparent q can be frequency independent or dependent according to the pattern of thin layering due to the layering the interpreted q can be positive or negative and it can depend on source receiver offsets therefore estimating q values from frequency dependent or phase shifted reflection amplitudes always requires additional geologic or rock physics constraints such as sparseness and or randomness of reflectors the absence of attenuation in certain layers or specific physical mechanisms of attenuation similar conclusions about the necessity of extremely detailed models of the elastic structure apply to other types of q measurements

late mesozoic intrusive complexes in the coastal area of fujian se china the significance of the gabbro diorite granite association abstract the pingtan and daiqianshan igneous complexes southeastern china are typical of calc alkaline series developed at active continental margins these two complexes are dominated by granites or gabbros with minor diorites and granodiorites and these rock types closely coexisted both temporally and spatially the major and trace element signatures of gabbros indicate they were crystallised from high aluminium basaltic magmas which were generated from metasomatised upper mantle the typical metaluminous calc alkaline composition trace element patterns and sr nd isotopes indicate the granites in the complexes are i type granites which may have been generated from the deeper crust by a thermal contribution from the mantle field relationships petrography and geochemistry favour a mechanical mingling together with a limited chemical mixing between high aluminium basaltic magma and granitic magma resulting in the formation of diorites or granodiorites the essentially bimodal character of these complexes reflects the general character of back arc extensional magmatism which was induced by the subduction of the pacific plate beneath the eurasian continent in late mesozoic time

eclogite facies relics and inferred ultrahigh pressure metamorphism in the north dabie complex central eastern china mineral assemblages and microstructures of a newly identified retrogressed eclogite sensu lato in the north dabie complex ndc central eastern china indicate early very high pressure metamorphic relics preserved in a dominant amphibolite facies host where no eclogite sensu stricto has been positively identified before the investigated eclogitic rock shows distinct multistage recrystallization with granulite and amphibolite facies assemblages overprinting eclogite facies relics the minimum temperature for the eclogite facies metamorphism is estimated to be 800 820 c a spectacular microstructure of oriented quartz needles 2 20 m wide 5 200 m long in matrix ca na clinopyroxene implies the prior existence of a non stoichiometric supersilicic omphacite stabilized at ultrahigh pressure uhp 25 kbar conditions although no coesite or coesite pseudomorphs have been found in the samples the absence of coesite may be due to the lack of free silica at uhp conditions or the consumption of silica during retrograde reactions the inferred uhp conditions metamorphism is further supported by sm nd ages that are equivalent to triassic metamorphic ages from uhp eclogites in the southeastern dabie mountains this finding expands the uhp terrane northward about 50 km spatial distribution of subduction collision related uhp rocks includes parts of the ndc

ultra high pressure metamorphism of carbonate rocks in the dabie mountains central china abstract widespread ultra high p assemblages including coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite in marble gneiss and phengite schist are present in the dabie mountains eclogite terrane these assemblages indicate that the ultra high p metamorphic event occurred on a regional scale during triassic collision between the sino korean and yangtze cratons marble in the dabie mountains is interlayered with coesite bearing eclogite and gneiss and as blocks of various size within gneiss discontinuous boudins of eclogite occur within marble layers marble contains an ultra high p assemblage of calcite aragonite dolomite clinopyroxene garnet phengite epidote rutile and quartz coesite coesite quartz pseudomorphs after coesite aragonite and calcite pseudomorphs after aragonite occur as fine grained inclusions in garnet and omphacite phengites contain about 3 6 si atoms per formula unit based on 11 oxygens similar to the coesite bearing eclogite marble exhibits retrograde recrystallization under amphibolite greenschist facies conditions generated during uplift of the ultra high p metamorphic terrane retrograde minerals are fine grained and replace coarse grained peak metamorphic phases the most typical replacements are symplectic pargasitic hornblende epidote after garnet diopside plagioclase an18 after omphacite and fibrous phlogopite after phengite ferroan pargasite plagioclase and actinolite formed along grain boundaries between garnet and calcite and calcite and quartz respectively the estimated peak p t conditions for marble are comparable to those for eclogite garnet clinopyroxene geothermometry yields temperatures of 630 760 c the garnet phengite thermometer gives somewhat lower temperatures the minimum pressure of peak metamorphism is 27 kbar based on the occurrence of coesite such estimates of ultra high p conditions are consistent with the coexistence of grossular rich garnet rutile and the high jadeite content of omphacite in marble the fluid for the peak metamorphism was calculated to have a very low xco2 0 03 the p t conditions for retrograde metamorphism were estimated to be 475 550 c at 7 kbar

search for active lava flows with virtis on venus express there are several lines of evidence suggesting that effusive volcanism still shapes the surface of venus but the rate is not well constrained the preservation of impact craters is consistent with a rate of 1 km year comparable to earth intraplate volcanism as well as a rate several orders of magnitude less it has been proposed to search images of the venus nightside near 1 m for the excess thermal emission of active lava flows the scattering of photons in the optically thick cloud cover is similar in effect to a gaussian blur with a full width half maximum fwhm of 90 km this reduces the maximum intensity of the anomalies introduced by eruptions making detection more difficult than in a clear atmosphere but also provides larger targets for imaging the virtis instrument on venus express observed surface thermal emission at 1 02 m wavelength between april 2006 and october 2008 at a spatial resolution of typically a few tens of km we have searched the 1000 images for the signatures of active lava flows in form of transient excess emission measured in several adjacent pixels we estimate that eruptions with 1gw m sr total excess specific thermal emission would be clearly visible compared to the instrumental and atmospheric noise but no such anomalies were detected it has been shown that the total thermal emission of eruptions on earth can be related to the lava discharge rate we adjust this model to the venus surface environment by adjusting observed lava surface temperature distributions and estimate that a discharge rate on the order of 1000 m s is required to produce an anomaly clearly identifiable in virtis data this is a relatively high value for effusive volcanism but a few historical eruptions on earth surpassed it adopting a fit to the discharge rates of historical eruptions on hawaii as a model 4 to 10 of the eruptions in the field of view of virtis images would have been detectable in addition to the low detection probability the low surface coverage of on average 1 of the surface per day over a period of 800 days indicates that the probability of an eruption imaged by virtis was low to begin with therefore the virtis data set fails to provide a useful constraint on the rate of volcanism on venus venus express continues to observe surface thermal emission with the venus monitoring camera for future missions near infrared imaging would profit from more frequent images of the same area than is possible from the excentric 24h orbit of venus express the superrotation of the cloud cover allows to reduce atmospheric noise by averaging of images taken hours apart and the detection of eruptions with 100 m s lava or less might then be possible nevertheless searching for lava flows emplaced between two observations of the same surface by high resolution radar imaging altimetry or interferometry generally provides a better constraints than infrared imaging for the same observation duration and surface coverage however high resolution radar and low resolution infrared observations are highly complementary and could be accommodated on the same mission preferably with a low circular polar orbit

determining heights and slopes of fault scarps and other surfaces on venus using magellan stereo radar this report presents relationships and techniques for determining the heights and slopes of discretely dipping surfaces such as normal fault scarps on the surface of venus from measurements of their widths in magellan stereo synthetic aperture radar sar images these surfaces are clearly recognizable as distinct bands of increased or decreased radar backscatter relative to flat lying areas in the 120 to 280 m resolution magellan sar images but are not generally imaged in the 10 km resolution magellan altimetry our methods take into account radar distortion effects and allow one to determine whether a slope is foreshortened laid over elongated or in radar shadow the techniques make use of graphs constructed for the magellan incidence angle profiles so that investigators can determine the local height and slope of an individual surface in a straightforward manner but the techniques are applicable to any stereo radar data set if the radar incidence angles are known additionally the techniques can be used to improve digital elevation models constructed using radar stereoscopy in areas that have steep local terrain where stereoscopic fusion may be impossible due to the effects of layover or radar shadow using these techniques we show that there are normal fault scarps on venus with heights in the 700 m range that have remarkable topographic slopes of close to 60 something unheard of on earth and which suggests a high effective cohesive strength of the venusian crust

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

present day volcanism on venus evidence from microwave radiometry 1 we present new evidence for volcanic eruptions and lava flow emplacement on venus within the last several decades an integrated study of a radar dark lava flow unit in bereghinia planitia on venus 28 e 39 n based on magellan data obtained in 1993 reveals a significant apparent microwave thermal emission excess consistent with increased subsurface temperature due to very recent lava flow emplacement the flow unit occupies the stratigraphically youngest position in the area and in part is more than 15 years old because it was also observed in the radar map obtained by pioneer venus in 1978 analysis of lava flow cooling rates and geological characteristics point to flow material of mafic composition future missions can employ this microwave radiometry technique to search for and monitor active volcanism on venus

equivalent viscoelastic solids for heterogeneous fluid saturated porous rocks differenttheoreticalandlaboratorystudiesonthepropagation ofelasticwavesinrealrockshaveshownthatthepresenceofheterogeneities larger than the pore size but smaller than the predominant wavelengths mesoscopic scale heterogeneities may producesignificantattenuationandvelocitydispersioneffectson seismic waves such phenomena are known as mesoscopic effects and are caused by equilibration of wave induced fluid pressure gradients we propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluidsaturated rocks it consists in simulating oscillatory compressibility and shear tests in the space frequency domain which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample we assume that the behavior of the porous media obeys biot s equations and use a finiteelementproceduretoapproximatethesolutionsoftheassociated boundary value problems also because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature we propose applying the compressibility and sheartestsinamontecarlofashion thisfacilitatesthedefinition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution we analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples also theapplicationofthemontecarloprocedureallowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi fractal heterogeneities

hercynian late post tectonic granitic rocks from the fornos de algodres area northern central portugal abstract the fornos de algodres complex fac comprises several intrusions of late post tectonic hercynian granitic rocks ranging in composition from hornblende granodiorites and quartz monzodiorites through coarse porphyritic biotite granites and two mica granites coarse medium and fine grained to muscovite rich leucogranites field and regional constraints show that the emplacement of this large composite batholithic complex post dates the main variscan regional deformation phases d1 d2 d3 and associated metamorphic events field petrographic and geochemical data suggest a strong genetic relationship between most of the members of the fac however their rb sr and sm nd isotopic signatures appear to rule out any genetic process involving a single homogeneous source and or closed system fractional crystallization of the same parental magma a model involving hybridization of mantle derived basaltic liquids with crustal anatectic melts followed by further contamination and fractional crystallization is proposed to explain the isotopic and geochemical variation trends defined by the fac granitic rocks

active volcanism on venus in the ganiki chasma rift zone venus is known to have been volcanically resurfaced in the last third of solar system history and to have undergone a significant decrease in volcanic activity a few hundred million years ago however fundamental questions remain is venus still volcanically active today and if so where and in what geological and geodynamic environment here we show evidence from the venus express venus monitoring camera for transient bright spots that are consistent with the extrusion of lava flows that locally cause significantly elevated surface temperatures the very strong spatial correlation of the transient bright spots with the extremely young ganiki chasma their similarity to locations of rift associated volcanism on earth provide strong evidence for their volcanic origin and suggests that venus is currently geodynamically active

solid viscosity of fluid saturated porous rock with squirt flows at seismic frequencies abstractwe have developed a macroscopic model for a two phase medium solid porous rock frame plus saturating pore fluid with squirt flows based on lagrangian continuum mechanics the model focuses on improved physics of rock deformation including explicit differential equations in time domain causality linearity frequency independent parameters with clear physical meanings and an absence of mathematical internal or memory variables the approach shows that all existing squirt flow models can be viewed as microscopic models of viscosity for solid rock as in existing models the pore space is differentiated into compliant and relatively stiff pores at lower frequencies the effects of fluid flows within compliant pores are described by bulk and shear solid viscosities of the effective porous frame squirt flow effects are biot consistent which means that there exists a viscous coupling between the rock frame and the fluid in stiff pores biot s poroelastic effects associated with stiff porosity

development of lava tubes in the light of observations at mauna ulu kilauea volcano hawaii during the 1969 1974 mauna ulu eruption on kilauea s upper east rift zone lava tubes were observed to develop by four principal processes 1 flat rooted crusts grew across streams within confined channels 2 overflows and spatter accreted to levees to build arched roofs across streams 3 plates of solidified crust floating downstream coalesced to form a roof and 4 pahoehoe lobes progressively extended fed by networks of distributaries beneath a solidified crust still another tube forming process operated when pahoehoe entered the ocean large waves would abruptly chill a crust across the entire surface of a molten stream crossing through the surf zone these littoral lava tubes formed abruptly in contrast to subaerial tubes which formed gradually all tube forming processes were favored by low to moderate volume rates of flow for sustained periods of time tubes thereby became ubiquitous within the pahoehoe flows and distributed a very large proportionof the lava that was produced during this prolonged eruption tubes transport lava efficiently once formed the roofs of tubes insulate the active streams within allowing the lava to retain its fluidity for a longer time than if exposed directly to ambient air temperature thus the flows can travel greater distances and spread over wider areas even though supply rates during most of 1970 1974 were moderate ranging from 1 to 5 m3 s large tube systems conducted lava as far as the coast 12 13 km distant where they fed extensive pahoehoe fields on the coastal flats some flows entered the sea to build lava deltas and add new land to the island the largest and most efficient tubes developed during periods of sustained extrusion when new lava was being supplied at nearly constant rates tubes can play a major role in building volcanic edifices with gentle slopes because they can deliver a substantial fraction of lava erupted at low to moderate rates to sites far down the flank of a volcano we conclude therefore that the tendency of active pahoehoe flows to form lava tubes is a significant factor in producing the common shield morphology of basaltic volcanoes

petrogenesis and tectonic implications of a type granites in the dabie orogenic belt china geochronological and geochemical constraints the dabie orogenic belt is characterized by the presence of large volumes of intrusive and volcanic rocks that formed in late mesozoic times most of the intrusive bodies are i type granites but it is still unclear whether there are contemporary a type granites here we report the first unambiguous discovery of a type granite from baiyashan in the north dabie tectonic belt the crystallization age of the body has been fixed as 120 4 1 2 ma using u pb analysis of zircons by la icpms the baiyashan granite is enriched in si k na rb and ree has elevated feo tot feo tot mgo and ga al ratios and is depleted in mg ca mn ba sr p and ti the ree composition shows highly fractionated patterns with la yb n 6 95 16 68 and eu eu 0 33 0 59 its crystallization age field relationships petrographic and geochemical data show beyond doubt that the baiyashan granite is an early cretaceous a type granite sr nd isotope systematics are characterized by a high i sr of 0 708 0 714 and a low nd of 7 5 to 19 4 with t dm2 1 5 2 5 ga and these data indicate that the magmas were dominantly sourced from partial melting of middle to lower crustal intermediate felsic igneous rocks and mingling with mafic to intermediate magmas during rift related magmatism associated with subduction of the palaeo pacific plate beneath eastern china in early cretaceous times

ar ar geochronology of ultrahigh pressure metamorphism in central china the dabie shan of china contain the largest areal exposure of ultrahigh pressure regional metamorphic rock known on earth the thermal history of these unusual rocks is central to understanding the tectonic processes responsible for their creation preservation and exhumation published ages of ultrahigh pressure metamorphism and subsequent cooling range from archean to jurassic by analyzing 21 dabie hornblende phengite and biotite samples by the 40ar 39ar method we find that 1 cooling from peak metamorphic temperatures to 300 c occurred between about 206 and 178 ma 2 widespread cretaceous ages reflect reheating by a postultrahigh pressure magmatic extensional episode 3 40ar 39ar and k ar ages older than 230 ma and perhaps 210 ma are geologically meaningless due to the incorporation of excess 40ar and 4 dabie ultrahigh pressure metamorphic rocks are temporally related to blueschist facies rocks farther west in the suture zone

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

generation of sodium rich magmas from newly underplated basaltic crust sodium rich rocks of trondhjemite tonalite dacite ttd or granodiorite ttg suites form much of precambrian continental crust1 they are thought to have formed by partial melting of subducted oceanic crust2 3 a process that would have been much more widespread early in earth history than at present owing to the higher thermal gradients prevailing at that time4 phanerozoic ttd suites do exist however and seem also to relate to subduction zones5 defant and drummond6 proposed that these suites form where young 25 myr hot oceanic lithosphere is subducted and melts thus locally simulating the conditions that led to widespread crustal growth in the archaean here we describe plutonic and volcanic rocks from the cordillera blanca complex in peru which have characteristics of the high al ttd suite but which were produced above a subduction zone containing a 60 myr old slab we present evidence that the complex formed by partial melting of newly underplated basaltic crust and argue that this mechanism should be considered more generally as an additional way of generating sodium rich arc magmas

surface properties and surficial deposits on venus new results from magellan radar altimeter data analysis abstract microwave remote sensing data acquired with magellan venus orbiter are the main source of information about the surface of the planet we analyze variability of the backscattering function dependence of radar cross section on incidence angle for steep incidence angles 0 25 4 75 in the 75 n 55 s latitude zone with data from the magellan radar altimeter at 12 6 cm wavelength we show that all variability of the backscattering function can be described by three parameters describing 1 surface reflectivity 2 relative proportion of horizontal facets and 3 general roughness analysis of maps of these parameters revealed that surficial deposits for example microdune fields are abundant on venus even in places where they are not readily seen in the synthetic aperture radar images properties of surficial deposits rather than original volcanic flow roughness define the shape of the backscattering function on the majority of regional plains a large radar dark flow in bereghinia planitia has anomalously high proportion of horizontal facets which is consistent with it being formed by a relatively recent plain forming volcanic episode some crater associated radar dark diffuse features and splotches are also characterized by increased proportion of horizontal faces which indicate the presence of mantles deposited from fluidized granular material the backscattering functions of the anomalous radar bright material of mountaintops are more consistent with the strong internal scattering hypothesis rather than the exotic surficial material hypothesis obtained maps can be useful for planning future lander missions to sites with access to surface material with known provenance

sr and o isotope constraints on source and crustal contamination in the high k calc alkaline and shoshonitic neogene volcanic rocks of se spain the neogene volcanic province of se spain nvps is characterized by calc alkaline ca high k calc alkaline kca shoshonitic sh ultrapotassic up and alkaline basaltic ab volcanic series all these series except the ab have high lilerlree lilerhfse and brbe ratios and high but variable sr pb and o isotope compositions the kca and sh lavas contain metapelitic xenoliths whose mineralogical and chemical composition are typical of anatectic restites the geochemical characteristics of ca kca sh and up series suggest that they originated from the lithospheric mantle previously contaminated by fluids derived from pelagic sediments additionally the presence of restite xenoliths in the kca and sh lavas indicates some sort of interaction between the mantle derived magmas and the continental crust trace element and isotope modeling for the kca and sh lavas and the restites point towards the existence of two mixing stages during the first stage the lithospheric mantle was contaminated by 1 5 of fluids derived from pelagic sediments which produced

mesozoic high ba sr granitoids from north china geochemical characteristics and geological implications mesozoic magmatism occurred extensively in the north china block ncb and the dabie sulu orogen dso post dating the north south china collision resulting in abundant intrusive and volcanic rocks ranging from basic to acidic compositions the intermediate acidic intrusive rocks can be grouped into two types namely high ba sr granitoids and low ba sr granitoids that both have distinct geochemical characteristics the high ba sr granitoids are similar in most of the incompatible trace element systematics to the associated basic rocks which probably originated from melting of subcontinental lithospheric mantle indicating significant mantle contributions to them geochemical similarities are observed between the basic rocks from the ncb and dso implying a regional scale magma generating mechanism and that mantle enrichment beneath the dso was independent from the triassic deep continental subduction in the region we therefore interpret that the mesozoic magmatism resulted from delamination of the ancient lithospheric mantle beneath the eastern part of north china

genesis of granitoid batholiths of peninsular malaysia and implications for models of crustal evolution evidence from a ndsr isotopic and upb zircon study nd sr and u pb isotopic data for the late triassic west coast province batholiths and permian to triassic east coast province batholiths of peninsular malaysia allow estimates of the ages of the crustal fragments comprising the peninsula to be made initial nd and sr values for granitoids from the west coast province range from 6 to 10 and 160 0 716 to 660 0 751 respectively nd model ages calculated based on a depleted mantle evolution model tdmnd range from 1300 ma to 1800 ma and are in general agreement with the mid proterozoic upper intersection ages of u pb zircon reverse discordia 1500 1700 ma initial nd and sr values for granitoids from the east coast province range from 0 8 to 6 and 10 0 705 to 130 0 714 respectively calculated tdmnd ages of 900 1400 ma for these granitoids are comparable to two u pb zircon reverse discordia intercepts that yield 800 ma and 1350 ma the general agreement of u pb zircon inheritance ages and tdmnd ages are interpreted to correspond to the proterozoic crust formation ages of the continental fragments represented by the west coast and east coast batholithic provinces mid proterozoic 1300 1900 ma crust formation ages are commonly shown by other phanerozoic continental margin plutonic and volcanic belts the ubiquitous mid proterozoic crust formation ages and the absence of archaean signatures suggest voluminous juvenile additions to the continental crust in the mid proterozoic such ages at continental margins would imply that many continental blocks had achieved very much their present day extent by the mid proterozoic

cooling of lava flows on venus the coupling of radiative and convective heat transfer 1 a lava flow extruded on the surface of venus cools by radiating heat and by advecting heat upward by thermal convection unlike on other planetary bodies these processes are intimately coupled on venus because the dense co2 rich atmosphere has strong absorption bands in the infrared relative to a transparent atmosphere absorption and emission of radiation within short distances above a lava reduces the radiant heat loss and substantially diminishes the vigor of convection by dampening the thermal gradients within the boundary layer for these reasons lavas on venus cool significantly more slowly 30 40 than they would if the atmosphere were transparent in the infrared as assumed in previous calculations considering these effects indicates that lavas on venus cool more slowly than their equivalents on earth rather than more rapidly as previously estimated the reduction in cooling rate due to the suppression of convection by radiation extends our understanding of how some lavas on venus reach extraordinary lengths on the order of a thousand kilometers before solidifying

geomorphology and volcanology of maat mons venus abstract full resolution fmidr magellan radar backscatter images have been used to characterize the geology and volcanology of the volcano maat mons on venus this volcano has often been identified by remote sensing techniques as one of the volcanoes on the planet that could have been recently active and is the highest volcano on venus with a relief of 9 km the summit of maat mons is characterized by a caldera complex 26 30 km in diameter with at least six remnant pit craters 10 km in diameter preserved in the walls of the caldera suggesting that multiple small volume 1 km in diameter on the flanks these pits appear to have formed by collapse with no effusive activity associated with their formation no evidence for explosive volcanism can be identified despite the relatively low atmospheric pressure 55 bar near the summit there is also a lack of evidence for lava channels deformation features within the caldera and thrust faults on the flanks indicating that the physical volcanology of maat mons is simpler than that of typical martian and terrestrial shield volcanoes preservation of fine scale 3 4 pixels structures within the pit craters and summit pits is consistent with geologically very recent activity but no evidence for current activity can be identified

water saturated and undersaturated melting of metaluminous and peraluminous crustal compositions at 10 kb evidence for the origin of silicic magmas in the taupo volcanic zone new zealand and other occurrences

viscoelasticity of ells river bitumen sand and 4d monitoring of thermal enhanced oil recovery processes abstractsamples of ells river bitumen sand from alberta canada were measured at low frequencies 0 2 205 hz to determine the temperature and frequency dependence of velocities and attenuations the samples were first measured as received where the pore space is mostly filled with bitumen but also contains small amounts of air and water with residual air in the pores at 5 c there is strong dispersion in the p wave modulus and a peak in attenuation at seismic frequencies the frequency dependent moduli and attenuations shift by three orders of magnitude in frequency as temperature is increased from 5 c to 48 c consistent with the bitumen viscosity samples were then saturated so any empty pore space is filled with water after saturation at 1 hz increasing temperature from 5 c to 49 c causes a 30 reduction in the saturated p wave modulus a 34 reduction in the saturated bulk modulus and a 6 reduction in the shear modulus this behavior can only be explained by the temperature dependent bulk mo

petrogenesis of a high temperature metamorphic terrane a new tectonic interpretation for the north dabieshan central china the northern dabie terrane consists of a variety of metamorphic rocks with minor mafic ultramafic blocks and abundant jurassic cretaceous granitic plutons the metamorphic rocks include orthogneisses amphibolite migmatitic gneiss with minor granulite and metasediments no eclogite or other high pressure metamorphic rocks have been found granulites of various compositions occur either as lenses blocks or layers within clinopyroxene bearing amphibolite or gneiss the palaeosomes of most migmatitic gneisses contain clinopyroxene melanosomes and leucosomes are intimately intermingled tightly folded and may have formed in situ the granulites formed at about 800 830 c and 10 14 kbar and display near isothermal decompression p t paths that may have resulted from crust thickened by collision plagioclase amphibole coronae around garnets and matrix pi hbl assemblages from mafic and ultramafic granulites formed at about 750 800 c partial replacement of clinopyroxene by amphibole in gneiss marks amphibolite facies retrograde metamorphism amphibolite facies orthogneisses and interlayered amphibolites formed at 680 750 c and c 6 kbar formation of oligoclase orthoclase antiperthite after plagioclase took place in migmatitic gneisses at t 490 c in response to a final stage of retrograde recrystallization these p t estimates indicate that the northern dabie metamorphic granulite amphibolite facies terrane formed in a metamorphic field gradient of 20 35 c km 1 at intermediate to low pressures and may represent the sino korean hangingwall during triassic subduction for formation of the ultrahigh and high p units to the south post collisional intrusion of a mafic ultramafic cumulate complex occurred due to breakoff of the subducting slab

modeling magma flow and cooling in dikes implications for emplacement of columbia river flood basalts 1 the columbia river flood basalts include some of the world s largest individual lava flows most of which were fed by the chief joseph dike swarm the majority of dikes are chilled against their wall rock however rare dikes caused their wall rock to undergo partial melting these partial melt zones record the thermal history of magma flow and cooling in the dike and consequently the emplacement history of the flow it fed here we examine two dimensional thermal models of basalt injection flow and cooling in a 10 m thick dike constrained by the field example of the maxwell lake dike a likely feeder to the large volume wapshilla ridge unit of the grande ronde basalt two types of models were developed static conduction simulations and advective transport simulations static conduction simulation results confirm that instantaneous injection and stagnation of a single dike did not produce wall rock melt repeated injection generated wall rock melt zones comparable to those observed yet the regular texture across the dike and its wall rock is inconsistent with repeated brittle injection instead advective flow in the dike for 3 4 years best reproduced the field example using this result we estimate that maximum eruption rates for wapshilla ridge flows ranged from 3 to 5 km3 d 1 local eruption rates were likely lower minimum 0 1 0 8 km3 d 1 as advective modeling results suggest that other fissure segments as yet unidentified fed the same flow consequently the maxwell lake dike probably represents an upper crustal 2 km exposure of a long lived point source within the columbia river flood basalts

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

analysis of impact crater populations and the geochronology of planetary surfaces in the inner solar system analyzing the density of impact craters on planetary surfaces is the only known technique for learning their ages remotely as a result crater statistics have been widely analyzed on the terrestrial planets since the timing and rates of activity are critical to understanding geologic process and history on the moon the samples obtained by the apollo and luna missions provide critical calibration points for cratering chronology on mercury venus and mars there are no similarly firm anchors for cratering rates but chronology models have been established by extrapolating from the lunar record or by estimating their impactor fluxes in other ways this review provides a current perspective on crater population measurements and their chronological interpretation emphasis is placed on how ages derived from crater statistics may be contingent on assumptions that need to be considered critically in addition ages estimated from crater populations are somewhat different than ages from more familiar geochronology tools e g radiometric dating resurfacing processes that remove craters from the observed population are particularly challenging to account for since they can introduce geologic uncertainty into results or destroy information about the formation age of a surface regardless of these challenges crater statistics measurements have resulted in successful predictions later verified by other techniques including the age of the lunar maria the existence of a period of heavy bombardment in the moon s first billion years and young volcanism on mars

small volcanic edifices and volcanism in the plains of venus the most widespread terrain type on venus consists of volcanic lowland plains several styles of volcanism are represented in the plains the most extensive volcanic units consist of flood lavas the largest of which have volumes of the order of thousands of cubic kilometers as with terrestrial flood lavas they are inferred to have erupted at high effusion rates they show a range of radar backscatter characteristics indicating different surface textures and ages small edifices on the plains occur mainly in clusters associated with fracture belts the majority are shield volcanoes that may be up to a few tens of kilometers across but are generally 10 km or less in diameter volcanic cones have the same size range volcanic domes have diameters up to several tens of kilometers and volumes of the order of 100 km3 these are interpreted as being constructed of lava erupted with a relatively high effective viscosity and thus possibly composed of more silicic lava for many domes the flanks were unstable during and afte eruption and suffered gravity sliding that produced steep scalloped outer margins because of the high atmospheric pressures on venus explosive activity is less likely to occur than on earth however n a few plains areas there is evidence of pyroclastic deposits surrounding craters indicating that volatile contents in some of the magmas may be high in comparison to earth the clusters of small volcanic edifices are considered to be analogous to plains volcanism similar to that of the snake river plain of idaho there may also be analogues with terrestrial volcanic clusters associated with mid oceanic ridges

morphometry of wrinkle ridges on venus comparison with other planets the widths of wrinkle ridges on venus and the spacing of their network were measured at 30 randomly selected sites on the venusian plains at one of the sites heights of ridges were also estimated results of our measurements indicate that 1 wrinkle ridges on venus form a quasi periodic rather than chaotic network 2 there are regional variations of the typical spacing within the network with the mean for all 30 sites being 12 9 km and the standard deviation of the means of all sites being 5 8 km 3 there are regional variations of typical ridge width with the mean width being 1 25 km and the standard deviation of the means of all sites being 0 66 km 4 there is no site to site correlation between the mean ridge widths and spacings comparison with other terrestrial planets shows that wrinkle ridges on venus are generally narrower than on the other planets and the spacing of the ridge network on venus is smaller than on tharsis plateau mars global surface shortening due to formation of the wrinkle ridge network is estimated to be of order of 0 1

magma mixing the marsco suite isle of skye scotland magma mixing has been proposed as a major mechanism for the origin of a wide variety of rock suites in mid ocean basalts there are few obstacles to mixing because of the similarities in chemical and physical properties of the proposed end members however in calc alkaline rocks the proposed end members have disparate properties and these present obstacles to mixing

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

u pb zircon ages of granitoid rocks in the north dabie complex eastern dabie shan china the north dabie complex ndc comprises a high temperature metamorphic suite dominated by amphibolite facies granitoid orthogneiss intruded by voluminous granites u pb zircon dating on these rocks yields the following new results 1 two of the granitoid orthogneiss samples have early cretaceous protolith emplacement ages of 133 7 2 3 ma and 134 0 2 8 ma 2 an undeformed granodiorite intrusive into granitoid gneiss yields an emplacement age at 125 6 0 3 ma these early cretaceous ages entirely post date late triassic early jurassic continental subduction and exhumation evident in the neighboring ultrahigh and high pressure metamorphic terrains to the south in the dabie shan hence they do not support previous tectonic models that infer paleozoic or triassic protolith emplacement ages for these granitoid orthogneisses 3 a mylonitic granite from the northern boundary of the ndc yields a concordant age of 756 6 0 8 ma which is interpreted as magma emplacement age the concordance of this late

neodymium and strontium isotopic characteristics of new zealand granitoids and related rocks initial 87sr 86sr and 143nd 144nd ratios of phanerozoic granitoids and related intrusions of the new zealand block display a mixing type array indicative of the involvement in their sources of old continental crustal material most likely of proterozoic age sr t values range from 4 to 273 87sr 86sr 0 7041 0 7233 while nd t ranges from 2 7 to 11 0 preexisting metasedimentary rocks have generally higher sr and lower nd ranging to present day values of 646 and 15 0 respectively and particularly for the mesozoic intrusives are isotopically appropriate mixing end members the widespread early paleozoic greenland group graywackes which are derived from proterozoic sources are modeled as the source of the crustal end member mixing with mantle derived mafic magmas to produce the intrusive rocks four different types of models are applied to the isotopic and trace element rb sr ba ree data simple mixing mixing with a partial melt of the metasedimentary rock with or without isotopic equilibrium and assimilation fractional crystallization based on these models some constraints may be applied on petrogenesis e g the lack of high rb concentrations points to the presence of biotite and hree depletion points to the presence of garnet however the models fail to adequately explain all the data the new zealand granitoids show similarities in isotopic character not only to rocks from offshore islands on the new zealand block but also to similar aged granitoids in adjacent regions of antarctica and australia this points to similarities in crustal character between continental blocks formerly proximal in gondwanaland we note an overall increase in nd and decrease in sr in felsic magmas from the paleozoic to the mesozoic to the cenozoic in new zealand indicative of a decrease over time in the level of influence of recycled continental crust in subduction related magmatism

recent hotspot volcanism on venus from virtis emissivity data the questions of whether venus is geologically active and how the planet has resurfaced over the past billion years have major implications for interior dynamics and climate change nine hotspots areas analogous to hawaii with volcanism broad topographic rises and large positive gravity anomalies suggesting mantle plumes at depth have been identified as possibly active this study used variations in the thermal emissivity of the surface observed by the visible and infrared thermal imaging spectrometer on the european space agency s venus express spacecraft to identify compositional differences in lava flows at three hotspots the anomalies are interpreted as a lack of surface weathering we estimate the flows to be younger than 2 5 million years and probably much younger about 250 000 years or less indicating that venus is actively resurfacing

the 1919 1920 eruption of mauna iki kilauea chronology geologic mapping and magma transport mechanisms utilizing historical accounts field mapping and photogeology this paper presents a chronology of and an analysis of magma transport during the december 1919 to august 1920 satellitic shield eruption of mauna iki on the sw rift zone of kilauea volcano hawaii the eruption can be divided into four stages based on the nature of the eruptive activity stage 1 consisted of the shallow injection of a dike from the summit region to the eventual eruption site 10 km downrift during stage 2 a low ridge of pahoehoe formed in the vent area later a large a a flow broke out of this ridge and flowed 8 5 km sw at an average flow front velocity of 0 5 km day the eruption continued until mid august producing almost exclusively pahoehoe first as gas rich overflows from a lava pond stage 3 and later as denser tube fed lava stage 4 that reached almost 8 km from the vent at an average flow front velocity of 0 1 km day magma transport during the mauna iki eruption is examined using three criteria 1 eruption characteristics and volumetric flow rates 2 changes in the surface height of the halemaumau lava lake and 3 tilt measurements made at the summit of kilauea we find good correlation between halemaumau lake activity and the eruptive stages additionally the e w component of summit tilt tended to mimic the lake activity the n s component however did not multiple storage zones in the shallow summit region probably accounted for the decoupling of e w and n s tilt components analysis of these criteria shows that at different times during the eruption magma was either emplaced into the volcano without eruption hydraulically drained from halemaumau to mauna iki or fed at steady state conditions from summit storage to mauna iki volume calculations indicate that the supply rate to kilauea during the eruption was around 3 m3 s similar to that calculated during the mauna ulu and kupaianaha shield building eruptions and consistent with previously determined values of long term supply to kilauea

garnet tourmaline and muscovite bearing leucogranites gneisses and migmatites of the higher himalayas from zanskar kulu lahoul and kashmir

seismic attenuation effects of pore fluids and frictional sliding seismic wave attenuation in rocks was studied experimentally with particular attention focused on frictional sliding and fluid flow mechanisms sandstone bars were resonated at frequencies from 500 to 9000 hz and the effects of confining pressure pore pressure degree of saturation strain amplitude and frequency were studied observed changes in attenuation and velocity with strain amplitude are interpreted as evidence for frictional sliding at grain contacts since this amplitude dependence disappears at strains and confining pressures typical of seismic wave propagation in the earth we infer that frictional sliding is not a significant source of seismic attenuation in situ partial water saturation significantly increases the attenuation of both compressional p and shear s waves relative to that in dry rock resulting in greater p wave than s wave attenuation complete saturation maximizes s wave attenuation but causes a reduction in p wave attenuation these effects can be interpreted in term

impact crater related surficial deposits on venus multipolarization radar observations with arecibo 1 the distribution of surficial deposits in the vicinity of impact craters on venus was studied using measurements of the polarization properties of the reflected radar wave subsurface scattering of an incident circularly polarized radar signal results in a linearly polarized component in the radar echo due to the differing transmission coefficients at a smooth at wavelength scales atmosphere surface boundary for the horizontal h and vertical v linearly polarized components of the incident wave arecibo 12 6 cm wavelength radar observations in 1999 and 2001 provided images of the surface of venus in the full stokes polarization parameters of the reflected echo from which images in the degree of linear polarization were derived these images show that substantial areas of sedna guinevere and lavinia planitias return a radar echo with a significant degree of linear polarization indicating that mantling deposits may be relatively widespread on the plains of venus the areas showing linear polarization enhancements are strongly correlated with topographic features primarily impact craters dome fields and windblown deposits including dune fields a strong linearly polarized echo component 10 40 linear polarization is found from regions near 45 impact craters including 5 parabolas these linear polarization features typically correspond to diffuse higher backscatter cross section bright regions in magellan images the linearly polarized component in these regions is attributed to subsurface echoes from a mantled substrate or from buried rocks

venus topography and kilometer scale slopes during the first 8 months of the magellan mission the radar altimeter has made some three million measurements of the surface of venus covering the latitude range from 85 n to 80 s methods involving range correlation doppler filtering multi burst summation and range migration are used to focus the observations and to achieve high surface resolution results are presented as maps of the global distribution of topography meter scale roughness and power reflection coefficient the results are similar to those reported in previous experiments surface heights exhibit a unimodal distribution with more than 80 of the surface lying within 1 km of the 6051 84 km mean radius but the higher resolution of the magellan altimeter has disclosed several surprisingly steep features e g the southwest face of the maxwell montes the southern face of the danu montes and the chasmata to the east of thetis regio where average kilometer scale slopes of greater than 30 are not uncommon this conclusion is corroborated by close inspection of synthetic aperture radar imagery

cellular plagioclase intergrowths as a result of crystal magma mixing in the proterozoic aland rapakivi batholith sw finland finely cellular plagioclase intergrowths have been studied in xenocrystic andesine an32 and andesine mantled k feldspars within mafic magmatic enclaves in a quartz feldspar porphyry from the proterozoic subvolcanic hammarudda complex aland rapakivi batholith sw finland the cellular intergrowths usually occur as 0 2 2 0 mm mantles around xenocrysts but also as entirely cellular grains and are built up of a network of two distinct phases one relatively na rich an31 and one relatively ca rich an50 the grains are also covered by a thin 0 08 0 12 mm continuous normally zoned rim outside the cellular mantle small inclusions 0 01 0 05 mm of fe mg minerals are concentrated in the ca rich part of the network compositionally the na rich phase of the network is close to the inner non cellular andesine of the xenocrysts however it has a lower or and a slightly lower an content the ca rich phase has the same composition as the inner part of the normally zoned rim which outwards grades into lower an contents that overlap the an content of the matrix plagioclases the cellular network was developed after the andesine xenocrysts or andesine mantled k feldspars were engulfed in mafic magmatic enclaves during a mixing event the xenocrysts became heated to a temperature just below the liquidus of the mafic magma dissolution of the xenocrysts developed a spongy cellular texture which was penetrated by enclave magma ca rich plagioclase crystallized in the cells in equilibrium with the enclave magma trapping fe mg rich melt as the enclaves cooled the outermost thin rim and matrix plagioclases crystallized from the mafic melt these processes operated in fairly large enclaves as the one studied here which has a diameter of 70cm smaller enclaves on the other hand were cooled more rapidly to temperatures close to the solidus of the enclave magma and consequently had no time to dissolve the xenoxrysts

nature of local magma storage zones and geometry of conduit systems below basaltic eruption sites pu u o o kilauea east rift hawaii example the fluid dynamics of the well documented eruptive episodes at pu u o o kilauea wolfe et at 1987 are used to investigate quantitativeely the size and shape of the shallow conduit system beneath the vent cooling calculations are employed to study the long term survival of conduits and the consequences of multiple dike injection events we find that the subvent conduit must have a planar geometry at depths greater than a few tens to at most a few hundreds of meters with a width of less than a few meters a length of the order of 100 m and a height of the order of 1 kin this structure is clearly the residue of the preeruption dikes although such a feature can be widened somewhat by repeated dike emplacement events there is no evidence to suggest that a larger and much more equant magma reservoir should develop at shallow depth the extensive degassing often occurring after single eruptions or between repeated eruptions previously thought to imply the presence of a large equidimensional shallow magma chamber can be readily explained by the volume of magma in a dikelike subvent planar magma storage zone on the basis of these observations which we infer to apply commonly to basaltic eruption sites we suggest that the terms chamber or reservoir be used with caution because they most often connote a relatively large equant magma body distinct from the feeder dike lying just below the vent we find that the subvent region has the same basic geometric characteristics as the parental dike and we propose that it be referred to as a planar magma storage zone

a geochemical traverse across the north chilean andes evidence for crust generation from the mantle wedge major and trace element and sr and nd isotope analyses are presented on 186 0 ma magmatic rocks along an east west traverse across north chile at 22 s esr ranges from 25 to 100 and end from 6 to 9 but the low end and high esr values are in rocks generated in the last 15 ma it is argued that previous discussions of petrogenesis in north chile have been hampered because the changes in magma chemistry in this area of unusually thick crust reflect not one but two processes one results in a progressive shift of esr from 25 to 20 and end from 6 to 6 in jurassic to recent rocks which is accompanied by increasing ta sm and sr and decreasing th ta the second is largely confined to the younger rocks and it is characterised by esr increasing up to 100 with increasing sio2 and decreasing sr and it results in relatively shallow trends on an end esr diagram the preferred interpretation is that trend 1 is due to the mobilisation of old late proterozoic mantle lithosphere as magmatism migrated eastwards and that trend 2 is due to crustal melting and contamination with differentiation in this area of thickened continental crust it follows that the mantle wedge is the principal site of crust generation and it is argued that 20 of the sr in the recent northern chile rocks is derived from the subducted ocean crust

post solidification cooling and the age of io s lava flows abstract the modeling of thermal emission from active lava flows must account for the cooling of the lava after solidification models of lava cooling applied to data collected by the galileo spacecraft have until now not taken this into consideration this is a flaw as lava flows on io are thought to be relatively thin with a range in thickness from 1 to 13 m once a flow is completely solidified a rapid process on a geological time scale the surface cools faster than the surface of a partially molten flow cooling via the base of the lava flow is also important and accelerates the solidification of the flow compared to the rate for the semi infinite approximation which is only valid for very deep lava bodies we introduce a new model which incorporates the solidification and basal cooling features this model gives a superior reproduction of the cooling of the 1997 pillan lava flows on io observed by the galileo spacecraft we also use the new model to determine what observations are necessary to constrain lava emplacement style at loki patera flows exhibit different cooling profiles from that expected from a lava lake we model cooling with a finite element code and make quantitative predictions for the behavior of lava flows and other lava bodies that can be tested against observations both on io and earth for example a 10 m thick ultramafic flow like those emplaced at pillan patera in 1997 solidifies in 450 days at which point the surface temperature has cooled to 280 k and takes another 390 days to cool to 249 k observations over a sufficient period of time reveal divergent cooling trends for different lava bodies examples lava flows and lava lakes have different cooling trends after the flow has solidified flows cool faster thin flows solidify and cool faster than flows of greater thickness the model can therefore be used as a diagnostic tool for constraining possible emplacement mechanisms and compositions of bodies of lava in remote sensing data

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

geochemical investigations of the origin of the manaslu leucogranite himalaya nepal the himalayan orogeny is characterized by an intraplate subduction zone the thrusting of the tibetan slab over the foreland is probably responsible for the origin of the manaslu type leucogranites this geochemical study tries to examine the crustal origin of the granite to verify whether the paragneisses of the tibetan slab are the most probable parent material and to determine the subsequent petrogenetic processes the rb sr systematics suggest that 1 1 the scatter of data points in the 87sr86srvs 87rb86sr diagram may be due to the heterogeneity of the initial 87sr86sr ratios 2 2 the initial isotopic ratios are very high 0 730 0 760 and are in agreement with those of the gneisses of the tibetan slab at the time of the melting pb isotopic ratios are homogeneous they are also consistent with a crustal prehistory the ree and th contents are unexpectedly low in comparison with the much higher contents of the parent material monazite left in the residue of melting or more probably extracted in an early stage of the magmatic history may explain the observed ree and th abundances alternatively field observations show that the emplacement of the granite has been accompanied by a very strong hydrothermal activity in consequence the low ree and th contents of the granite could also be due to the loss by solution during prolonged fluid circulation throughout the granitic melt and the sr and pb isotope distribution to the effect of late to post magmatic fluids the isotopic character of which was determined by the underlying tibetan slab

early cretaceous low mg adakitic granites from the dabie orogen eastern china petrogenesis and implications for destruction of the over thickened lower continental crust it is generally accepted that the low mg adakitic rocks were derived from the partial melting of metabasalts eclogites in this study we demonstrate that the early cretaceous low mg adakitic granites in the north dabie complex ndc were generated by the partial melting of the ndc orthogneisses here we present in situ u pb and lu hf isotopes in zircon with whole rock geochemical and sr nd isotopic compositions were carried out for the tiantangzhai porphyritic monzogranites from the dabie orogen eastern china the monzogranites are characterized by high sr 576 988 ppm low y 7 3 19 0 ppm and depletion in hree yb 0 50 1 78 ppm thus resulting in high sr y 34 3 135 2 and la yb n 17 0 105 2 ratios without a negative eu anomaly they also exhibit high sio2 66 5 73 5 wt and k2o 2 7 4 7 wt and low mgo 0 4 1 6 wt or mg 28 2 45 3 mostly 40 values whole rock geochemical compositions suggest that the monzogranites represent low mg adakitic rock with high si and rich k features equilibrated with residues rich in garnet sr nd isotopic compositions end t 16 2 to 20 3 87sr 86sr i 0 707798 0 708804 tdm2 nd 2 3 2 6 ga of the monzogranites are distinct from that of the eclogites and amphibolites in the dabie orogen but similar to that of the neoproterozoic 700 800 ma gneisses in the ndc u pb dating of zircons gives a consistent age of 130 0 3 4 ma with discordia upper intercept age of 716 34 ma for inherited cores identified by cl imaging correspondingly in situ lu hf analyses of early cretaceous young age spots from zircons yield initial 176hf 177hf ratios from 0 281898 to 0 282361 ehf t values from 28 1 to 17 6 and two stage crust hf model ages tdm2 from 2293 89 to 2949 108 ma which are generally in agreement with values of 0 281891 to 0 282218 28 2 to 11 7 and 1927 87 to 2963 92 ma for the pre mesozoic inherited cores respectively as for individual core rim pairs in zircon th u ratios increase from the inherited cores to the young growth rims possibly due to variable degrees of partial melting whereas 176lu 177hf ratios greatly decrease because of the garnet effect in residues thus we suggest that the early cretaceous low mg adakitic granites were derived from the partial melting of the ndc neoproterozoic 700 800 ma gneisses and the foundering of the garnet bearing residues could have caused the destruction of the over thickened lower continental crust

petrogenesis of mesozoic granitoids in the dabie uhp complex central china trace element and nd sr isotope evidence post collisional magmatism in the dabie orogen is characterized by the near contemporaneous intrusion of voluminous granitoids and minor mafic magmas in the late mesozoic 135 110 ma the granitoids are represented by three major batholiths in northern dabie zhubuyuan baimajian and tiantangzhai the largest zhubuyuan batholith comprises hornblende bearing intermediate rocks penghe suite and hornblende free granitic rocks huangbai suite the huangbai granites show limited variation in chemical composition but are highly variable in textures ranging from medium to coarse grained they have rather homogeneous sr and nd isotopic compositions with 87sr 86sr i 0 708 0 709 and end t 19 to 24 the penghe intermediate suite covers a wide spectrum of rock types including diorite monzodiorite quartz monzonite to monzogranitic rocks and all of them contain hornblende and mafic enclaves the existence of compositional and textural disequilibrium e g calcic and resorbed cores of plagioclase and the nature of chemical variation in these rock types indicate that magma mixing between an evolved mafic and a granitic magma was involved in their genesis fractional crystallization fc could have coupled with the process of magma mixing but with minor contamination by the upper continental crust during magma ascent isotopically the intermediate rocks show a variation in end t values from 13 7 to 18 while their 87sr 86sr i ratios vary from 0 7074 to 0 7088 the genesis and evolution of the dabie post collisional magmatic rocks may be summarized as follows intrusion of mantle derived mafic ultramafic magmas into thickened continental crust induced dehydration melting of the lower crust rocks with intermediate compositions and subsequent production of large amounts of granitic melts huangbai suite extensive interaction between the crustal and mantle derived melts through mixing produced a hybrid parental magma which subsequently underwent a fc process en route to higher crustal levels producing a wide variety of rock types as shown by the penghe intermediate rock suite injection of successive pulses of basic magma into upward mobile magma chambers could have resulted in the formation of the mafic enclaves as well as mafic dykes

dynamic poroelasticity a unified model with the squirt and the biot mechanisms the velocities and attenuation of seismic and acoustic waves in rocks with fluids are affected by the two most important modes of fluid solid interaction 1 the biot mechanism where the fluid is forced to participate in the solid s motion by viscous friction and inertial coupling and 2 the squirt flow mechanism where the fluid is squeezed out of thin pores deformed by a passing wave traditionally both modes have been modeled separately with the biot mechanism treated in a macroscopic framework and the squirt flow examined at the individual pore level we offer a model which treats both mechanisms as coupled processes and relates p velocity and attenuation to macroscopic parameters the biot poroelastic constants porosity permeability fluid com pressibility and viscosity and a newly introduced microscale parameter a characteristic squirt flow length the latter is referred to as a fundamental rock property that can be determined experimentally we show that the squirt flow mechanism dominates the biot mechanism and is responsible for measured large velocity dispersion and attenuation values the model directly relates p velocity and attenuation to measurable rock and fluid properties therefore it allows one to realistically interpret velocity dispersion and or attenuation in terms of fluid properties changes e g viscosity during thermal enhanced oil recovery eor or to link seismic measurements to reservoir properties as an example of the latter transformation we relate permeability to attenuation and achieve good qualitative correlation with experimental data

squirt flow in fully saturated rocks we estimate velocity frequency dispersion and attenuation in fully saturated rocks by employing the squirt flow mechanism of solid fluid interaction in this model pore fluid is squeezed from thin soft cracks into the surrounding large pores information about the compliance of these soft cracks at low confining pressures is extracted from high pressure velocity data the frequency dependence of squirt induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space and the characteristic squirt flow length these unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency the appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity the low frequency velocity limits as given by our model are identical to those predicted by gassmann s formula the high frequency limits may sign

velocity and attenuation in sandstone at elevated temperatures and pressures new measurements of seismic velocity and attenuation have been made in the kilohertz frequency range to temperatures of 120 c confining and pore pressure to 200 bars in berea sandstone with increasing temperature shear velocity and attenuation decrease at all pressures in a fully saturated rock the data suggest that thermal relaxation is not a significant loss mechanism under these conditions we propose that dissipation is controlled by a viscous fluid flow mechanism in which a sharp frequency peak in attenuation is shifted from 2khz at room temperature to 8 khz at 120 c as the pore fluid viscosity is decreased with increasing temperature however the velocity decrease is too great to be accounted for by a change of relaxation times a non dispersive temperature softening in shear may control the velocities

element fluxes associated with subduction related magmatism destructive plate margin magmas may be subdivided into two groups on the basis of their rare earth element ree ratios most island arc suites have low ce yb and remarkably restricted isotope ratios of 87 sr 86 sr 0 7033 143 nd 144 nd 0 51302 206 pb 204 pb 18 76 207 pb 204 pb 15 57 and 208 pb 204 pb 38 4 however they also have rb sr 0 03 th u 2 2 and ce yb 8 5 ratios which are significantly less than accepted estimates for the bulk continental crust the high ce yb suites have higher incompatible element contents more restricted heavy ree and much more variable isotope ratios such rocks are found in the aeolian islands grenada indonesia and philippines and their isotope and trace element features have been attributed both to contributions from subducted sediment and or old trace element enriched material in the mantle wedge it is argued that for isotope and trace element models the slab component can usefully be taken to consist of subducted sediment and altered mid ocean ridge basalts since these may contain ca 80 of the water in the subducted slab and the distinctive trace element features of arc magmas are generally attributed to the movement of material in hydrous fluids the isotope data indicate that not more than 15 of the sr and th in an average arc magma were derived from subducted material and that the rest were derived from the mantle wedge the fluxes of elements which cannot be characterized isotopically are more difficult to constrain but for most minor and trace elements the slab derived contribution in arc magmas is too small to have a noticeable effect on the residual slab

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

multiple sources for the coastal batholith of central chile 31 34 s geochemical and sr nd isotopic evidence and tectonic implications abstract the coastal batholith of central chile between 31 and 34 s represents a locus of long lived c 200 ma plutonic activity it is composed of four plutonic complexes santo domingo limari papudo quintero and illapel these complexes which occur as north trending discontinuous belts that decrease in age eastward were emplaced during four major episodes of arc magmatism the santo domingo complex carboniferous comprises hornblende biotite bearing tonalites and granodiorites with abundant mafic enclaves and enclave free granites the association of enclave bearing granitoids and enclave free granites resulted from different degrees of mixing of crustal and mantle derived magmas the limari complex lower jurassic is a bimodal association of crustal leucogranites and mantle derived gabbros the lithology of the papudo quintero complex middle jurassic varies from hornblende pyroxene diorite to biotite granite the main rock types namely tonalites and granodiorites commonly contain mafic enclaves the granitoids and the enclaves have remarkably similar ree patterns and are similar in sr nd isotope composition which suggest that they represent a cogenetic suite of mantle origin the illapel complex cretaceous consists of hornblende bearing tonalites trondhjemites and granodiorites that resemble the rocks of ttg suites the end values and initial 87 sr 86 sr ratios sri for the mafic rocks of the carboniferous complex end 2 0 and 3 5 sri c 0 7057 differ markedly from those of the mesozoic mafic rocks end 1 9 to 5 4 sri 0 7033 to 0 7039 the cretaceous rocks being the most depleted with regard to sr nd a change from carboniferous lithosphere dominated sources to mesozoic asthenosphere dominated sources of the magmas that started in the early jurassic is recognized slab components can be recognized in the source of the cretaceous rocks the crustal source of the lower jurassic leucogranites was more isotopically depleted and refractory than that of the carboniferous granites on the other hand no crustal participation in the origin of the middle jurassic and cretaceous felsic granitoids is recognized they are differentiated from mantle derived magmas progressive removal of old lithospheric mantle during the mesozoic due to a process of lithospheric delamination would explain the profound change in the subcrustal source as well as the melting and modification towards a more refractory nature of the continental crust

geochemical age and isotopic constraints on the location of the sino korean yangtze suture and evolution of the northern dabie complex east central china the northern dabie complex in east central china lies between the sino korean plate to the north and the yangtze plate to the south the northern dabie complex has been variously proposed to represent a paleozoic magmatic arc on the sino korean plate an exhumed piece of subducted yangtze plate crust or crust produced almost entirely by cretaceous extension related magmatism trace element compositions of northern dabie complex orthogneisses and granites show arc signatures similar to those of ultra high pressure rocks in the central dabie but no mineralogical evidence of ultra high pressure metamorphism is present in the samples investigated here field relationships textures major and trace element compositions and ion microprobe u pb zircon protolith crystallization ages reveal three distinct types of gneiss diorite gneiss xenoliths 770 6 26 ma 95 confidence limit those within first genation highly deformed migmatitic grey gneisses 747 6 14 ma and those cross cut by secondgeneration cretaceous weakly foliated felsic gneisses 127 6 4 ma unfoliated cretaceous granites 117 6 11 ma monazite th pb age 5 117 6 1 ma intrude secondgeneration gneisses cretaceous second corresponding author e mail john c ayers vanderbilt edu generation gneisses and granites yield zircon inheritance ages of ca 2 ga 700 800 ma and rarely 227 271 ma indicating that the northern dabie complex is not simply a cretaceous extensional terrane the 700 800 ma zircon ages are similar to those of granitic gneisses from the central ultra highpressure zone 698 6 47 ma and are characteristic of the yangtze craton nd values suggest that cretaceous rocks in the northern dabie complex formed by partial melting of basement with very low nd and not by melting of first generation or diorite gneisses nd depleted mantle model ages are consistent with the time of formation of the yangtze craton at 1 4 2 5 ga the northern dabie complex is interpreted to be an extension of the yangtze craton that was unaffected by ultra high pressure metamorphism the sino korean yangtze suture must lie to the north of the northern dabie complex