field relations geochemistry and origin of the upper cretaceous volcaniclastic kannaviou formation in western cyprus evidence of a southerly neotethyan volcanic arc

influence of partial consolidation during cone penetration on estimated soil behavior type and pore pressure dissipation measurements estimation of soil behavior type from cone penetration testing and the interpretation of dissipation tests is complicated in in termediate soil types such as silty sands sandy silts etc where partial consolidation occurs during penetration this issue is investigated in this paper using results from cavity expansion and finite element analyses as well as field and centrifuge piezocone data the implications for soil classification are examined using analytical expressions to explore the effect of normalized shear strength rigidity index and over consolidation ratio relative to the influence of partial consolidation and viscous effects under fully undrained conditions it is shown that partial drainage conditions can affect where data plots on soil behavior charts thus complicating soil classification the effect on dissipation tests following partial consolidation during cone penetration is shown to create errors in interpretation using experimental and numerical data a new approach is developed based in part on manipulation of solutions for pore pressure dissipation following undrained penetration to account for these errors when interpreting dissipation tests errors can become significant during standard cone penetration testing when the t50 dissipation time is less than about 50 s guidelines including equations and a chart are presented for practical use finally imple mentation of this approach is demonstrated in a brief case study doi 10 1061 asce gt 1943 5606 0000646 2012 american society of civil engineers ce database subject headings soil consolidation cone penetration tests soil properties pore pressure sand soil type silts author keywords cone penetration test cpt cone penetrometer penetration rate consolidation dissipation test soil behavior type coefficient of consolidation intermediate soils

modeling the stress dilatancy relationship of unsaturated silica sand in triaxial compression tests abstractit is well known that partial saturation increases the shear strength and dilatancy of unsaturated sand however little research has been carried out on the actual stress dilatancy relationship this paper shows that the increase in peak shear strength caused by partial saturation is consistent with an increase in dilatancy and that conventional stress dilatancy theories are still valid for unsaturated sand the use of state indexes as a proxy for dilatancy were investigated and extended to unsaturated sands additionally these indexes can be used to establish a critical state line that is based on material properties only the validity of the stress dilatancy theories and the use of state indexes offer simplicity in modeling the shear behavior of unsaturated sand this will be demonstrated in this paper with the nor sand model with which the wetting collapse can be explained as a consequence of a loss of dilatancy characteristics

delamination of eclogitized lower crust control on the crust mantle boundary in the central fennoscandian shield abstract the crustal structure of the central part of the fennoscandian shield is dominated by a high velocity lower crust hvlc vp 7 3 7 5 km s at the depth of 40 63 km in an area of ca 400 km 600 km formed in the palaeoproterozoic svecofennian orogen at 1 91 1 87 ga in the area of the hvlc the moho is deeper than 50 km and attains depths of up to 63 km in eastern finland at the archaean proterozoic boundary zone we suggest that the present moho dates back to late svecofennian time and was determined by delamination of high density eclogitized lower crust after tectonic collisional thickening of crust densities deduced from seismic and gravity data suggest a very small or completely lacking density contrast between lower crust and uppermost mantle new geological evidence from kimberlite hosted garnet xenocrysts supports the presence of a garnet population with compositions in agreement with crustal eclogitic garnets in addition small clinopyroxene garnet mineral aggregates microxenoliths show omphacitic clinopyroxene compositions therefore the presence of eclogites in the high velocity lower crust is implied although the eclogite proportion as estimated from seismic velocity data is only a few percent in the present hvlc with results on near incidence and wide angle seismic studies and geological and geochemical data on heat producing elements we modeled the svecofennian collision and the thermal evolution of the crust to provide temperature constraints for the delamination model the constructed thermal model simulates the genesis of svecofennian synkinematic at 1 89 1 88 ga and postkinematic 1 88 1 87 ga granitoids as well as the general metamorphic grade of the surface rocks and lower crustal xenoliths moreover the narrow distribution of the ages of the svecofennian mafic ultramafic magmatism ca 1 89 1 87 ga dispersed around the hvlc area is explained by the homogeneous warming of the lithosphere the conditions of lower crustal delamination were estimated with a rayleigh taylor convective instability model constrained with lower crustal and upper mantle rheological data delamination of a lower crustal eclogite layer 5 30 km thick takes place in about 7 50 ma if the rock dynamic viscosity is 1 1021 pa s it requires temperatures of 1000 c in the lower crust and upper mantle in the svecofennian crust such temperatures were attained at about 1860 1850 ma i e after the orogenic peak we conclude that the moho of the hvlc area was controlled by delamination of a ca 5 10 km thick layer of high density lowermost crust into the mantle such a density controlled process may have controlled the moho depth also in other proterozoic shield areas

diffusion gradients in an eclogite xenolith from the roberts victor kimberlite pipe 1 mechanism and evolution of garnet exsolution in al2o3 rich clinopyroxene

tholeiitic and calc alkaline magma series at adatara volcano northeast japan 1 geochemical constraints on their origin abstract low alkali island arc by jakes and gill 1970 or low k by gill 1978 tholeiitic rocks are closely associated with calc alkaline rocks in the outer volcanic zone called the nasu volcanic zone of northeast japan major element trace element ni cr co sc v zr nb zn rb cs ba sr ce and y and sr isotope compositions are presented for 9 low alkali tholeiitic and 16 calc alkaline samples of adatara volcano belonging to the nasu volcanic zone in the trace elements vs sio 2 diagram the tholeiitic series and calc alkaline series show different trends to each other for co sc v zr rb sc ba and sr as expected from k 2 o contents the calc alkaline samples are enriched in incompatible elements such as rb cs ba ce and zr compared with the tholeiitic samples on the other hand contents of nb in the calc alkaline samples are somewhat lower than those in the tholeiitic samples plots of ni and cr contents vs sio 2 for the tholeiitic samples come near smooth trend lines whereas those for the calc alkaline samples are scattered sr isotopic ratios in the tholeiitic series lie within the range between 0 7056 and 0 7058 and between 0 7048 and 0 7052 in the calc alkaline series smooth major and trace element compositional trends in the tholeiitic series are successfully modelled by simple fractional crystallization of plagioclase hypersthene augite titanomagnetite and minor olivine similarly crystal fractionation models can closely reproduce major and most of the trace element variations in the calc alkaline series but failed to account for irregular variations of ni and cr the scattering of ni and cr probably reflects simultaneous crystal fractionation and subordinate magma mixing in the subvolcanic chamber the inferred fractionated phases for the calc alkaline series are richer in augite and titanomagnetite and slightly poorer in plagioclase than those for the tholeiitic series the tholeiitic magma and calc alkaline magma are not derived from a common parental tholeiitic magma and the calc alkaline parental magma is richer in sio 2 and incompatible elements in particular rb and zr poorer in radiogenic sr and possibly more oxidized than the tholeiitic parental magma

moho vs crust mantle boundary evolution of an idea abstract the concept that the mohorovicic discontinuity moho does not necessarily coincide with the base of the continental crust as defined by rock type compositions was introduced in the early 1980s this had an important impact on understanding the nature of the crust mantle boundary using information from seismology and from deep seated samples brought to the surface as xenoliths in magmas or as tectonic terranes the use of empirically constrained p t estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment the xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere and revealed that the crust mantle boundary in off craton regions commonly is transitional over a depth range of about 5 20 km early seismic reflection data showed common layering near the moho correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust mantle boundary developments in seismology petrophysics and experimental petrology have refined interpretation of lithospheric domains the expansion of in situ geochronology especially zircon u pb ages and hf isotopes os isotopes of mantle sulfides has defined tectonic events that affected whole crust mantle sections and revealed that the crust mantle boundary can change in depth through time however the nature of the crust mantle boundary in cratonic regions remains enigmatic mainly due to lack of key xenoliths or exposed sections the observation that the moho may lie significantly deeper than the crust mantle boundary has important implications for modeling the volume of the crust mapping the crust using seismic techniques alone without consideration of the petrological problems may lead to an overestimation of crustal thickness by 15 30 this will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust formation processes and the composition of the convecting mantle

shear wave velocity to evaluate in situ state of cohesionless soils shear wave velocity vs measurements were carried out in a triaxial testing program on three different cohesionless soils the vs was measured using bender elements during consolidation and at ultimate steady state after consolidation the soil samples were loaded in shear under constant strain rate triaxial compression either drained or undrained to determine their ultimate steady or critical state uss at large strains the vs measurements were used to develop relationships between the void ratio e mean normal effective stress p and vs the shear loading results were expressed within the framework of critical state soil mechanics the results of the vs and uss information were combined with the state parameter concept to develop an equation to use field measured vs to estimate the in situ consolidation state within a soil thus the contractive dilative boundary with respect to vertical effective stress for large strain loading can be determined from in situ measurements of vs these can then b

volcano tectonic interactions during rapid plate boundary evolution in the kyushu region sw japan evolution of the local plate tectonic and volcanic system relationship at kyushu island is defined by major changes in tectonics and volcanic style at ca 15 10 6 and 2 ma plate reconstructions presented here suggest that prior to 15 ma the pacific plate subduction dominated kyushu tectonics from 15 to 6 ma the evolving relative plate motions shifted the triple junction between the pacific plate philippine sea plate and southwest japan northwards so that the philippine sea plate was subducted beneath kyushu we suggest that a lack of subduction related volcanism from 10 to 6 ma is due to shallow subduction of the young shikoku basin lithosphere by 6 5 ma changes in the philippine sea plate motion led to more rapid nearly trench normal subduction of the eocene west philippine basin crust beneath kyushu this model is supported by an increase in arc like geochemistry of lavas since ca 6 5 ma subduction of fluid rich features such as the kyushu palau ridge introduced large volumes of fluids into the kyushu arc system leading to voluminous volcanism across kyushu focused particularly in areas where the ridge subduction occurs in tandem with local extensional tectonics key issues such as the timing of izu arc collision with central japan and the history of motion of the philippine sea plate are reassessed here resulting in a model that favors izu arc central japan collision at ca 8 6 ma rather than the more widely accepted date of ca 15 ma

aleutian tholeiitic and calc alkaline magma series i the mafic phenocrysts diagnostic mafic silicate assemblages in a continuous spectrum of aleutian volcanic rocks provide evidence for contrasts in magmatic processes in the aleutian arc crust tectonic segmentation of the arc exerts a primary control on the variable mixing fractional crystallization and possible assimilation undergone by the magmas end members of the continuum are termed calc alkaline ca and tholeiitic th ca volcanic rocks e g buldir and moffett volcanoes have low feo mgo ratios and contain compositionally diverse phenocryst populations indicating magma mixing their ni and cr rich magnesian olivine and clinopyroxene come from mantle derived mafic olivine basalts that have mixed with more fractionated magmas at mid to lower crustal levels immediately preceding eruption high al amphibole is associated with the mafic end member in contrast th lavas e g okmok and westdahl volcanoes have high feo mgo ratios and contain little evidence for mixing evolved lavas represent advanced stages of low pressure crystallization from a basaltic magma these lavas contain groundmass olivine fo 40 50 and lack ca poor pyroxene aleutian volcanic rocks with intermediate feo mgo ratios are termed transitional tholeiitic tth and calc alkaline tca tca magmas are common e g moffett adagdak great sitkin and kasatochi volcanoes and have resulted from mixing of high al basalt with more evolved magmas they contain amphibole high and low al or orthopyroxene or both and are similar to the japanese hypersthene series tth magmas e g okmok and westdahl contain orthopyroxene or pigeonite or both and show some indication of upper crustal mixing they are mineralogically similar to the japanese pigeonite series high al basalt lacks mg rich mafic phases and is a derivative magma produced by high pressure fractionation of an olivine tholeiite the low pressure mineral assemblage of high al basalt results from crystallization at higher crustal levels

zircon u pb geochronology and hf isotope of felsic volcanics from attappadi southern india implications for neoarchean convergent margin tectonics abstract the attappadi area on the south western flanks of the archean dharwar craton in southern india is located along the e w trending bhavani shear zone which marks the trace of a neoarchean suture zone the dominant rock types in the area include meta ultramafics amphibolites ttg tonalite trondhjemite granodiorite gneisses metapelites and sulphidic banded iron formation bif here we report the occurrence of felsic volcanic rocks preserving primary textures from the anaikatti area in eastern attappadi the felsic volcanics are interbanded with the bif amphibolite metapelite metapyroxenite and hornblende gneisses the felsic volcanics are divided into two types based on their textures the type 1 rock is medium grained with gneissic texture and lack unequivocal primary volcanic textures type 2 felsic volcanics are thinly laminated fine grained and at places preserve relict soft sediment deformation structures they also contain relict volcanic clasts or lapilli and are interpreted as felsic tuff geochemically the attappadi felsic volcanics are rhyolitic in composition and have arc related trace element signatures they also possess a calc alkaline volcanic affinity we report la icpms u pb ages from zircons in four samples of the felsic tuffs which show weighted mean ages of 2567 18 ma and mswd 1 4 2499 19 ma mswd 0 57 2555 24 ma mswd 1 7 and 2576 64 ma mswd 5 8 the late neoarchean early paleoproterozoic ages obtained in our study correlate well with the zircon u pb ages reported in recent studies from ophiolites and other suprasubduction suites from attappadi and surrounding regions the zircon ehf values range from 11 1 to 7 6 suggesting heterogeneous source material involving both juvenile and older reworked components we build a tectonic model for the sw margin of the dharwar craton with an oceanic realm characterized by island arcs and widespread submarine tholeiitic as well as komatiitic ultramafic and mafic volcanism during the neoarchean this predominantly mafic volcanism on the ocean floor is represented by primitive komatiitic lavas oxide and sulphide facies bif the birth of volcanic arc at the convergent margin is marked by felsic volcanism and the deposition of felsic volcanics and volcano sedimentary successions in the final stage of ocean closure the ocean plate and continental arc assemblages were brought in juxtaposition including the accretion of the ophiolitic fragments our study confirms the recent models of arc arc and arc continental accretion to the southern margin of the dharwar craton and major continental growth at the end of the archean

degassing of stratified magma by compositional convection abstract a new model is proposed for passive degassing from sub volcanic magma chambers the water content in stably stratified shallow magma chamber will be equated to its solubility at the upper boundary by convection water from a lower layer high in water content can enrich the contact zone of the upper layer and lead to further convective overturn of this boundary layer a complete set of equations describing convection with bubble formation and dissolution is reduced to a simplified form by assuming a small bubble content the development and pattern of flow driven by vesiculation is modeled numerically in a 2d magma chamber for relatively low raleigh numbers 5 105 bubbles rising from the magma will collect near the roof in a layer of 8 10 vol and then escape upward to fumaroles the stokes flux of bubbles escaping from an andesitic magma with viscosity 104 p and a top surface of about 500 500 m corresponds with observed total magmatic water fluxes of 35 kg s pressure within the chamber is buffered by elastic and local visco elastic deformations in the solid rocks bounding the chamber to the range between ambient and close to lithostatic values in a chamber closed to fresh magma inputs the decrease in volume due to such gentle volatile escape lowers the reference pressure bubbles flux from the lower layer induced by variation of the saturation level around stratification boundary may be efficient mechanism for the water transport between layers

andesites from northeastern kanaga island aleutians kanaga island is located in the central aleutian island arc northeastern kanaga is a currently active late tertiary to recent calc alkaline volcanic complex basaltic andesite to andesite lavas record three episodes series of volcanic activity series i and series ii lavas are all andesite while series iii lavas are basaltic andesite to andesite four series ii andesites contain abundant quenched magmatic inclusions ranging in composition from high mgo low alumina basalt to low mgo highalumina basalt the spectrum of lava compositions is due primarily to fractional crystallization of a parental low mgo high alumina basalt but with variable degrees of crustal contamination and magma mixing the earliest series i lavas represent mixing between high alumina basalt and silicic andesite with maximum sio2 contents of 65 67 wt later series i and all series ii lavas are due to mixing of andesite magmas of similar composition the maximum sio2 content of the pre mixed andesites magmas is estimated at 60 63 wt the youngest lavas series iii are all non mixed and have maximum estimated sio2 contents of 59 wt the earliest series i lavas contain a significant crustal component while all later lavas do not it is concluded that the maximum sio2 contents of silicic magmas the contribution of crustal material to silicic magma generation and the role of magma mixing all decrease with time furthermore silicic magmas generated by fractional crystallization at this volcanic center have a maximum sio2 content of 63 wt all of these features have also been documented at the central aleutian cold bay volcanic center brophy 1987 based on data from these two centers a model of aleutian calc alkaline magma chamber development is proposed the main features are 1 a single low pressure magma chamber is continuously supplied by primitive low alumina basalt 2 non primary high alumina basalt is formed along the chamber margins by selective gravitational settling of olivine and clinopyroxene and retention of plagioclase 3 sidewall crystallization accompanied by crustal melting produces buoyant silicic 63 wt sio2 liquids that pond at the top of the chamber and 4 continued sidewall crystallization now isolated from the chamber wall produces silicic liquids with 63 wt sio2 that increase the thickness and lowers the overall sio2 content of the upper silicic zone it is suggested that the maximum sio2 content of 63 imposed on fractionation generated magmas is due to a rheological barrier that prohibits the extraction of more silicic liquids from a crystal liquid mush along the chamber wall

the significance of u pb zircon dates in lower crustal xenoliths from the southwestern margin of the kaapvaal craton southern africa the combination of high precision id tims u pb geochronology with cathodoluminescence cl imaging and spatially resolved microsampling of zircon provides a high fidelity record of the temporal evolution of samples of the middle and lower crust a suite of xenoliths exhumed in cretaceous kimberlites at the southwestern margin of the kaapvaal craton including eclogite granulite amphibolite and greenschist facies plutonic rocks are the subject of these detailed zircon studies cl imaging demonstrates the complexity of chemical and growth structure in single zircons and highlights the importance of sampling on an intragrain scale to extract end member ages for zircon growth events for these diverse metamorphic rocks linking the zircon chronology to geologic events and processes requires an understanding of the kinetics and thermodynamics of zircon stability during metamorphism using an empirical approach we attempt to relate zircon crystallization dissolution and regrowth to metamorphic conditions through a detailed analysis of zircon chemical zonation patterns mineral inclusions and petrography these lines of evidence indicate the crystallization of zircon under p t conditions ranging from eclogite through greenschist facies we discuss four examples of this approach 1 at the lowest grade of metamorphism examined primary igneous zircon 1900 ma in a syenite xenolith from the klipfontein 08 kimberlite underwent two episodes 1015 and 964 ma of probable fluid mediated resorption and reprecipitation in the greenschist facies 2 an upper amphibolite facies xenolith from the markt kimberlite contains two distinct populations of blocky and fir tree sector zoned zircon which are suggested to date prograde hornblende breakdown reactions 1107 ma and melt infiltration under retrograde metamorphic conditions 1092 ma respectively 3 at granulite facies metamorphic zircon crystallized at 1114 ma during prograde reactions involving hornblende breakdown in a granulite xenolith also from the markt kimberlite later 960 ma zircon resorption followed by minor secondary crystallization occurred in both the amphibolite and granulite xenoliths during retrograde greenschist facies reactions possibly enhanced by fluids 4 in a much older episode of eclogite facies metamorphism recorded in a xenolith from the lovedale kimberlite zircon crystallized with the peak metamorphic mineral assemblage or possibly early on the cooling path in the late archean 2630 ma each of these examples provides unique information regarding the evolution of the kaapvaal craton while the links to metamorphic reactions and p t conditions clarify the interpretation of zircon dates obtained from these samples of the middle to lower crust

proterozoic age and cumulate origin for granulite xenoliths lesotho rare earth element ree 143nd 144nd and 87sr 86sr analyses on a range of granulite xenoliths from kimberlite pipes in lesotho demonstrate that useful whole rock ages can be obtained from such lower crustal material the characteristic positive eu anomalies relatively low ree abundances and large variation in sr contents suggest that many of the xenoliths are crystal cumulates rather than residua after partial melting they yield an sm nd whole rock age of 1 400 100 myr and are unrelated to the younger magmatic rocks of the karoo

geochemical and isotopic characteristics of different types of anorthosite in the namaqua mobile belt south africa abstract anorthosite genesis in the proterozoic namaqua mobile belt of south africa encompasses a range of intrusive histories including massif type as in the occurrences of plat sjambok and possibly koperberg suite and layered type as at oranjekom different compositional ranges at all levels of analytical resolution mineralogical geochemical and isotopical are revealed there is a spectrum from orthopyroxene dominance and extremely high lree koperberg suite to clinopyroxene horn blende dominance with normal ree patterns oranjekom plat sjambok and low iron oranjekom isotopic data for the various complexes rb sr sm nd indicate differences in magma evolution the oranjekom complex represents a depleted mantle origin with low to moderate contamination sr 6 to 9 nd 7 to 9 while the plat sjambok complex reflects a depleted mantle origin with a noticeable contribution from a crustal component sr 40 to 150 nd 5 to 1 in contrast the koperberg suite sr 300 nd 9 if derived from the mantle would require mixing between a highly enriched mantle source and an extremely enriched crustal contaminant high sr 700 to 800 nd 2 resulting in an unusual isotopic trend with a positive slope the waterkop pluton that has in the past been regarded as related to the plat sjambok complex represents a quite different syenitic magma from a slightly enriched mantle source with very little contamination and is not a cogenetic with the latter collectively the analytical data support original magma generation from different mantle sources followed by various intrusive histories ranging from rapid transit between source and emplacement in the upper crust oranjekom to prolonged travel and differentiation involving considerable crustal contamination koperberg suite the fact that the different intrusive types occur in different suspect terranes of the mobile belt may reflect originally contrasting tectonic settings during a late proterozoic continental collision that played a role during the assembly of rodinia

partial melting of mantle wedge and evolution of island arc crust evolution of the crust in the northeast honshu arc is discussed on the basis of the melting experiments of a peridotite under hydrous conditions and the crustal compositions estimated from deep crustal xenoliths and seismic velocity data the chemical compositions of melts formed by partial melting of a hydrous peridotite within the pressure temperature conditions for shallow parts of the mantle wedge 1 2 2 0 gpa have been experimentally determined with the sandwich experiment technique the melts range from olivine tholeiitic to magnesian andesitic compositions sio2 48 56 wt mgo 9 14 wt beneath the volcanic front in the northeast honshu arc and are slightly less silicic beneath the coast of the sea of japan the crustal compositions of the volcanic zone in the northeast honshu arc estimated from deep seated crustal inclusions in volcanic rocks and the velocity structures of the crust are andesitic in the central zone and high alumina basaltic near the coast of the sea of japan the compositions of possible primary melts formed in the mantle wedge are significantly more mafic than these crustal compositions consequently if the major part of the crustal materials in the volcanic zone was formed by magmas generated in the mantle wedge thick up to 30 km ultramafic cumulates including olivine pyroxenite must have been formed beneath moho during fractional crystallization and would constitute the upper part of the mantle wedge the volume of the mantle wedge consisting entirely of even fertile peridotite was not sufficient to produce crustal materials and cumulates in the volcanic zone by such processes in the northeast honshu arc a static mantle wedge model is therefore not satisfactory for the growth of the crust in northeast honshu arc a dynamic model is suggested in which the mantle materials have been supplied into the mantle wedge from the back arc side by a convective flow

environmental and climatic changes during the pleistocene holocene in the bor plain central anatolia turkey abstract the bor plain lies in a round shaped flat basin in the southern part of the central anatolia it is located at the southeastern end of the tuzgolu fault zone which is the nw trending active normal fault zone and extends between the north of the tuzgolu lake tuz at nw and at kemerhisar nigde se according to geomorphologic and geologic studies this plain was occupied by lake during the pleistocene the first high lake level terrace and the latest high lake level terrace were determined at 1170 1150 m and 1110 1100 m respectively pleistocene and holocene alluvial and lacustrine deposits are composed of claystone sandstone mudstone limestone and paleosol units these units contain mostly calcite and clay minerals palygorskite smectites illite and chlorite and lesser amounts of quartz phillipsite cristobalite feldspar plagioclase goethite and muscovite the results of this study are compared with the results of sedimentologic and dating obtained from konya eregli plain according to this comparison 1 the latest high lake terraces were dated 23 000 to 17 000 yr bp the high lake level was changed 2 sandy level with carbonate determined in stratigraphy indicates that a dry phase dominated after 17 000 yr bp and 3 black and brown muds indicate that the shallow freshwater lacustrine phases and sandy levels were formed between 12 500 and 1100 yr bp during late glacial stage paleosols muddy levels and shallow lake deposits were formed in the environment of the holocene during 6000 5000 yr bp carbonate rich sandstone and mudstone deposits show that this period was interrupted by the second drought in the latest stage temperatures have increased due to hot climate conditions and salinization has begun and been still ongoing

magma plumbing system of the aso 3 large pyroclastic eruption cycle at aso volcano southwest japan petrological constraint on the formation of a compositionally stratified magma chamber abstract aso volcano has the largest caldera 18 25 km in diameter in the southwestern japan island arc and it formed as the result of four large vei 6 7 pyroclastic eruption cycles we study the penultimate large eruption cycle the aso 3 cycle which occurred 123 ka with an ejecta volume of more than 150 km 3 the processes in the pre eruptive magma chamber and the magma genesis of the aso 3 cycle were inferred from geological data phenocryst chemistry and whole rock chemical and sr nd and pb isotopic analyses of juvenile clasts the geological and petrological data indicate that the pre eruptive magma chamber was stratified compositionally into three layers from top to bottom silicic intermediate and mafic magma layers the three magma layers had a uniform isotope composition suggesting that all the magmas were generated from a single source the silicic and intermediate magmas were not generated from the mafic magma by fractional crystallization the silicic magma has higher ni content compatible element than the mafic magma this suggests that these magmas were produced by partial melting of the same mafic crust but with differing amounts of partial melting the silicic magma was produced by a low degree of partial melting of the source rock without fractional crystallization and the mafic magma was produced by a large degree of partial melting followed by fractional crystallization the intermediate magma compositions plot on the tie line between the silicic magma and the melt of the mafic magma in variation diagrams and the intermediate magma has phenocrysts whose compositions are identical with those in the silicic magma this observation indicates that before the aso 3 eruption cycle a two layer stratified magma chamber of the silicic and mafic magmas was formed as a result of melting of the mafic crust which was followed by formation of the intermediate layer as a result of interfacial mixing between the silicic magma and the melt of mafic magma during the eruption the three layer stratified magma chamber was tapped from the top to the bottom

the crust mantle boundary beneath cratons and craton margins a transect across the south west margin of the kaapvaal craton lower crustal suite xenoliths occur in on craton and off craton kimberlites located across the south western margin of the kaapvaal craton southern africa rock types include mafic granulite plagioclase bearing assemblages eclogite plagioclase absent assemblages with omphacitic clinopyroxene and garnet pyroxenite orthopyroxene bearing eclogite the mafic granulites are subdivided into three groups garnet granulites cpx grt plag qtz two pyroxene garnet granulites cpx opx grt plag kyanite granulites cpx grt ky plag qtz reaction microstructures preserved in many of the granulite xenoliths involve the breakdown of plagioclase by a combination of reactions 1 cpx plag grt qtz 2 plag grt ky qtz 3 plag cpx jd rich qtz compositional zoning in minerals associated with these reactions records the continuous transition from granulite facies mineral assemblages and pressure p temperature t conditions to those of eclogite facies two distinct p t arrays are produced 1 off craton granulites away from the craton margin define a trend from 680 c 7 5 kbar to 850 c 12 kbar 2 granulite xenoliths from kimberlites near the craton margin and on craton granulites produce a trend with similar geothermal gradient but displaced to lower t by 100 c both p t fields define higher geothermal gradients than the model steady state conductive continental geotherm 40 mwm2 and are not consistent with the paleogeotherm constructed from mantle derived garnet peridotite xenoliths a model involving intrusion of basic magmas around the crust mantle boundary followed by isobaric cooling is proposed to explain the thermal history of the lower crust beneath the craton margin the model is consistent with the thermal evolution of the exposed namaqua natal mobile belt low pressure granulites and the addition of material from the mantle during the namaqua thermal event c 1150 ma the xenolith p t arrays are not interpreted as representing paleogeotherms at the time of entrainment in the host kimberlite they most likely record p t conditions frozen in during various stages of the tectonic juxtaposition of the namaqua mobile belt with the kaapvaal craton

petrogenesis of neoarchean metavolcanic rocks in changyukou northwestern hebei implications for the transition stage from a compressional to an extensional regime for the north china craton abstract the 2 5 ga metavolcanic rocks in changyukou northwestern hebei can be classified into three groups based on major and trace elements high mg basalts tholeiitic basalts and the calc alkaline series basaltic andesites andesites and dacites rhyolites both high mg basalts and tholeiitic basalts have negative anomalies of nb zr ti and heavy rare earth elements hree as well as enrichments of sr k pb ba and light rare earth elements lree and show typical subduction zone affinities the petrogenesis of high mg basalts can be ascribed to high degree partial melting of an enriched mantle source in the spinel stability field that was previously enriched in large ion lithophile elements lile and lree by slab derived hydrous fluids melts supercritical fluids as well as the subsequent magma mixing processes of different sources at different source depths with little or no influence of polybaric fractional crystallization the flat hree of tholeiitic basalts indicates they may also originate from the spinel stability field but from obviously shallower depths than the source of high mg basalts they may form at a later stage of the subduction process when rapid slab rollback leads to extension and seafloor spreading in the upper plate we obtain the compositions of the archean lower crust of the north china craton based on the archean wutai jining section by compiling the average tonalite trondhjemite granodiorite ttg components average mafic granulite components and average sedimentary rock components the modeling results show that the generation of high al basalts basaltic andesites and andesites can be attributed to assimilation by high mg basalts primary basalts of relatively high al 2 o 3 thickened lower crust and the subsequent crystallization of prevailing mafic mineral phases while al 2 o 3 rich plagioclase crystallization is suppressed under high pressure and nearly water saturated conditions dacites and rhyolites may be the result of further fractional crystallization of basaltic andesites high al basalts and andesites mixing of magmas at various stages along the fractionation course of basaltic andesites high al basalts toward rhyolites promotes the trend of the calc alkaline series to reconcile the 2 55 to 2 5 ga ttgs derived from overthickened crust the 2 51 to 2 50 ga calc alkaline volcanic rocks derived from thickened crust tholeiitic basalts representing low pressure and an extensional tectonic setting 2493 ma leucosyenogranites derived from overthickened crust 2437 ma biotite monzogranites derived from slightly thinner crust than leucosyenogranites but still thickened as well as the clockwise hybrid itd and ibc p t paths of the hp granulites and widespread extension and rifting setting within the ncc from 2300 ma we propose a model of an evolving subduction process among them the composition of the 2 5 ga changyukou volcanic rocks and potassic granites as well as the clockwise hybrid itd and ibc p t paths of the hp granulites may reveal that the tectonic setting in northwest hebei was in a transition stage from a subduction related compressional regime to an extensional regime related to plate rollback

archean magmatism and deformation were not products of plate tectonics abstract the granite and greenstone terrains that dominate upper crust formed from about 3 6 to about 2 6 ga and record magmatic and tectonic processes very different from those of a younger time they indicate heat loss by the archean earth primarily by voluminous magmatism from a mantle much hotter than that of the present plate tectonic processes were not then operating the distinctive array of petrologic structural and stratigraphic features that characterize phanerozoic convergent plate systems ophiolites magmatic arcs accretionary wedges fore arc basins etc have no viable analogues in archean terrains purported archean plate tectonic indicators consist merely of rock types that even superficially resemble actual phanerozoic indicators only when considered in isolation from their association and structure archean ultramafic and mafic volcanic rocks neither resemble ophiolitic rocks in petrology nor occur in ophiolite type successions they often depositionally overlie felsic basement rocks and often overlie and are intercalated with sedimentary and felsic volcanic rocks and they require a mantle about 200 c hotter than now archean graywackes are coherent strata derived from nearby volcanic rocks late in the histories of their regions and they lack the setting and disruption that characterize modern accretionary wedges the lithologic structural and stratigraphic assemblages that typify proterozoic and phanerozoic rifted and reassembled margins also lack archean analogues and no evidence has been found for archean rifting rotation and reassembly of continental plates conversely characteristic archean assemblages lack modern equivalents in any tectonic setting ultramafic lavas erupted at liquidus temperatures are voluminous granite and greenstone terrains have no modern analogues greenstone belts are typically anastomosing networks of upright synforms formed by crowding aside by and sinking between large rising diapiric elliptical composite batholiths the batholiths include both the products of new crustal melts and variably remobilized mid crustal gneisses the greenstone belts are defined by late deformation of regionally semiconcordant volcanic and sedimentary successions and are not relics of successively formed volcanic chains little deformation generally preceded the diapirism and metamorphism was primarily of contact type the regionally uniform areal density and accordant crustal level of the diapiric batholiths their contacts primarily against the oldest strata of the synforms their general age 10 20 million years younger than most of the flanking stratiform rocks and considerations of high archean radiogenic heat productivity all fit the explanation that the batholiths were mobilized by partial melting of hydrous lower crust by radiogenic heating diapirism was accompanied by modest regional orthogonal shortening and extension of the hot upper crust producing the orientations of the batholiths rise of the batholiths greatly increased the petrologic fractionation of the crust and the concentration of radionuclides high in it resulting in cooling of the deeper crust and subjacent mantle and thus cratonization the upper crust containing the granite and greenstone aggregates was decoupled from the gneissic middle crust which underwent flattening and extension subparallel to the elongation of the shallow batholiths this deep deformation may have been driven by flow of dense restites toward delamination loci from which they sank into the mantle the early earth was probably wholly molten the surface of the earth like that of the moon must have been wholly recycled by impacts before 3 9 ga and heavily modified by them until 3 8 ga zircons as old as 4 2 ga have been found as clastic grains in much younger archean quartzites and polycyclic migmatites last partly melted and reconstituted under hydrous conditions only after 3 6 ga contain relict zircons as old as 4 0 ga the lithologies of the early earth protoliths in which these zircons formed have not been established but impact melts and breccias must be represented and magma ocean fractionates may be the nature of the transition in tectonic style into the granite and greenstone mode is unknown plate tectonic rifting and convergence were operating by about 2 0 ga and were in an essentially modern mode by about 0 8 ga the nature of the transition from the granite and greenstone mode at about 2 6 ga to plate mode by about 2 0 ga has yet to be defined the change may have been facilitated by the increasing content of water and carbon dioxide in the mantle as dense but hydrated delaminated archean crust sank into it

regional geological setting of the limpopo belt abstract the 2 7 ga limpopo belt granulite terrane is situated between two lower grade granite greenstone cratons the kaapvaal craton in the south and the zimbabwe craton in the north this granulite facies terrane is subdivided into three zones each with a distinctive geological signature and separated from each other and from the adjacent cratons by well defined shear zones 1 the southern marginal zone composed of granite greenstone material very similar to that of the kaapvaal craton has retrogressed granulites on its southern margin in the hanging wall of the northward dipping terrane boundary hout river shear zone separating the granulite terrane from the adjacent kaapvaal craton 2 the northern marginal zone a granite greenstone terrane at granulite grade which is separated from the zimbabwe craton by a southward dipping terrane boundary and 3 the central zone a unique crustal element with distinctive carbonate platform lithologies and a metagabbroic layered complex which intruded before or at 3250 ma this zone cannot be related to the kaapvaal craton or to the zimbabwe craton it is separated from the two marginal zones by mylonitic shear zones with horizontal stretching lineations the entire limpopo belt is characterized by a distinctive deformational and metamorphic style which contrasts markedly from that of the adjacent granite greenstone terranes of the kaapvaal and zimbabwe cratons this distinctive pattern developed during the limpopo orogeny probably as a consequence of continental collision during the late archaean

a seismic refraction investigation of the namaqualand metamorphic complex south africa the namaqualand metamorphic complex forms part of the precambrian shield of southern africa and hosts several major base metal deposits a long line seismic refraction experiment traversing the complex was conducted in order to complement geological and geophysical studies of the structure and evolution of this region seismograms were obtained at approximately 10 km intervals along the 290 km profile seismic ray tracing techniques were used to model the travel time and amplitude data it was found that the namaqualand lower crust is comprised of a substantial proportion of intermediate velocity 6 2 to 6 9 km s rocks these intermediate velocity rocks approach the surface near the midpoint of the profile moho was found to be at a depth of 42 km no correlation was found between the seismic and electrical resistivity models of the crust when the seismic velocity structure of the middle proterozoic namaqualand metamorphic complex is compared with that of adjacent geological provinces it is found to differ significantly from the archaean kaapvaal province but resemble the late proterozoic damara province these differences might be attributed to variations in the principal mechanisms of crustal growth between archaean and proterozoic times

shear velocity structure and azimuthal anisotropy beneath eastern north america from rayleigh wave inversion 1 we have obtained shear velocity structure beneath the northeastern united states and southeastern canada using rayleigh wave phases and amplitudes thin crust 36 42 km is observed along the atlantic coast and in the eastern appalachian orogen and thick crust 42 46 km is imaged in the western appalachians and in the western new york portion of the grenville province the variation of crustal thickness correlates well with the observed bouguer gravity anomalies in the upper mantle the high velocity continental keel of cratonic north america is present in the western part of the study area while a broad low velocity region is imaged in new england from the hudson river valley to the white mountains this low velocity anomaly is probably the consequence of past heating of the lithospheric mantle associated with the monteregian hotspot and may represent intrusion of asthenosphere into the edge of the keel in addition to lateral variations in velocity we estimate the azimuthal dependence of phase velocity strong and relatively uniform shear wave splitting is observed in the study region but at periods of 100 s or less the average azimuthal anisotropy of rayleigh waves is less than 1 and is not significantly different from zero at any individual period this small degree of azimuthal anisotropy is not consistent with a substantial contribution to shear wave splitting from fossil anisotropy in the lithosphere much of the source of the shear wave splitting must lie deeper than 200 km

repeated large scale eruptions from a single compositionally stratified magma chamber an example from aso volcano southwest japan abstract aso volcano has the largest caldera 18 25 km in the southwestern japan island arc which was formed as a result of four gigantic pyroclastic eruption cycles the latest eruption cycle aso 4 cycle 90 ka produced the most voluminous deposits 600 km3 among the four eruption cycles we investigated pre eruptive magma chamber configurations and processes in compositionally stratified aso 4 pyroclastic eruptions based on whole rock chemical phenocryst mineralogical and sr isotope analyses of juvenile clasts previous stratigraphical studies have suggested that the aso 4 cycle is divided into two subcycles in both of which eruption of voluminous silicic is followed by eruption of mafic magma geochemical and mineralogical results indicate that the pre eruptive magma chamber was composed of three layers silicic hybrid and mafic magma layers from the top to the bottom the silicic magma layer was relatively homogenous whereas the mafic magma layer was compositionally zoned where magma became more silicic with height the hybrid magma was generated by mixing the silicic magma and the silicic end of the zoned mafic magma layer i e the uppermost part of the mafic magma layer the first subcycle began with evacuation of the upper silicic magma and successively proceeded to tap the lower hybrid and mafic magmas the eruption of the first subcycle stopped before the whole magma chamber evacuated during this subcycle the hybrid magma and the upper part of the mafic magmas layer were selectively withdrawn and mixed with the overlying silicic magma the second subcycle eruption started with the new hybrid magma and followed by eruption of the mafic magma

tectonic controls on tholeiitic and calc alkaline magmatism in the aleutian arc the tectonic position of aleutian arc volcanic centers and their magmatic differentiation trends calc alkaline or tholeiitic appear to correlate from 160 w to 175 e the volcanoes form four major arc segments that coincide with earthquake aftershock zones and major geographic features on both the upper and lower plates the tholeiitic volcanoes are large primarily basaltic centers that occur between or at the end of segments where magmas can more easily reach the surface and undergo shallow closed system differentiation the calc alkaline volcanoes are smaller more andesitic centers that occur in the middle of segments where transit through the upper plate is apparently more difficult differentiation is deeper and the intrusive to extrusive ratios are higher than in the tholeiitic centers the chemistry of the least differentiated basalts at both types of centers is similar and suggests a common parent magma probably derived from mantle peridotite conditions for the derivation of the two trends through crystal fractionation support the proposed model the tholeiitic magmas show characteristics i e no hydrous phenocrysts fe enrichment trend parallel ree patterns vitrophyric and esites and dacites consistent with low pressure high temperature crystallization in large shallow magma chambers the calc alkaline magmas show characteristics i e some hydrous phenocrysts no fe enrichment trend nonparallel rare earth patterns porphyritic lavas consistent with higher pressure and lower temperature of crystallization than the tholeiitic series tertiary plutons also show both calc alkaline and tholeiitic trends and appear to be chemically similar to the quaternary volcanoes the larger plutons are calc alkaline and probably represent the extensive 1002 km magma chambers of the small calc alkaline volcanoes the small shallow tholeiitic plutons complement the large tholeiitic volcanoes and reflect the greater percent of extrusive rocks in the tholeiitic series

rifting of kyushu japan based on the fault controlled concurrent eruption of oceanic island basalt type and island arc type lavas the tectonic environment of kyushu japan is affected both by the subduction of the philippine sea plate and by the extensional tectonics related to rifting of okinawa trough at the eastern margin of the eurasia plate we found that the sendai fault zone acts as a channel for concurrent eruption of oceanic island basalt oib type and island arc ia type basaltic rocks propagating west to east in the sendai region of southern kyushu the location of the sendai fault zone is likely to correspond to the left lateral shear zone in southern kyushu as inferred by gps earth observation network a similar magmatic association is present in the beppu shimabara bs graben system in central kyushu the associate magmas of oib type rocks in kyushu can be classified into typical em ii like and their intermediate oib type magmas in addition to morb like oib type magma in 87sr 86sr nb y systematics typical oib type and intermediate oib type magmas are erupted within the sendai fault zone and bs graben system respectively the former is characterized by highest nb y but low 87sr 86sr similar to morb like oib type magma erupted in northern kyushu and the latter has intermediate nb y and 87sr 86sr between typical and em ii like oib type magmas almost all the ia type rocks within the sendai fault zone are generated from parental ia type magma in kyushu and characterized by weak crustal assimilation having the lowest 87sr 86sr similar to typical oib type magma but the highest 143nd 144nd of arc magmas in kyushu the ages of both types of basaltic rocks within the sendai fault zone range from 1 6 to 0 01 ma clearly younger than those of andesitic rocks on northern and southern outsides of the fault zone and become younger from west to east initial formation of the fault zone has been induced by the counterclockwise rotation of southern kyushu during the last 2 ma as well as the bs graben system kyushu has continued to be split into three parts by the sendai fault zone and bs graben during the quaternary northern central and southern zones their initial formation ages are likely to be linked to the initial rifting age of the middle okinawa trough back arc basin

characterization of unsaturated mine waste a case history it is becoming increasingly common in the mining industry for either crushed ore or filtered mine waste to be stacked to a significant height 100 m in a moist state with little compaction resul

tectonothermal evolution of the continental crust beneath the yakutian diamondiferous province siberian craton u pb and hf isotopic evidence on zircons from crustal xenoliths of kimberlite pipes abstract u pb age and hf isotope data were collected on zircons from crustal xenoliths from the late devonian kimberlite pipes of markha terrane the xenoliths include mafic garnet granulites gt pl cpx opx amp bt scp and garnet biotite gneisses grt bt pl kfs qtz scp the data from this study demonstrate that the crust of the markha terrane experienced several tectonothermal events zircons with archean hf model ages tdm 3 13 2 5 ga are predominant in all xenoliths with one exception these data imply that most of the lower and middle crust beneath the markha terrane was produced in the archean time later this paleoarchean crust was significantly reworked in several tectonothermal events including a neoarchean stage 2 9 2 5 ga and several paleoproterozoic metamorphic stages 1 98 1 9 and 1 8 ga there is very little evidence for generation of juvenile crust associated with these metamorphic events importantly crustal xenoliths from kimberlite pipes of the markha terrane record all the same events that occurred in the adjacent daldyn and magan terranes

lateral magma intrusion from a caldera forming magma chamber constraints from geochronology and geochemistry of volcanic products from lateral cones around the aso caldera sw japan abstract we investigated the k ar ages and the petrological and geochemical features of lava units from lateral cones and lava distributed around the aso caldera in central kyushu japan in order to constrain the spatial range of lateral magma intrusion during the caldera forming stage the results of the k ar age determination showed that most of the analyzed lava units erupted almost simultaneously with the aso caldera forming pyroclastic eruptions 266 to 89 ka in addition the petrography major and trace element compositions and sr isotope ratios of these lava units are indistinguishable from the caldera forming pyroclastic products the contemporaneous activities of compositionally similar magmas inside and outside of the caldera presumably indicate the occurrence of a lateral intrusion of caldera forming magma which had accumulated in a huge magma chamber beneath the caldera system our results suggest that a total of 6 3 vol of caldera forming magma in the aso volcano migrated more than 20 km along the faults from the center of the caldera

geochemistry of basalts from central and southern new hebrides arc implication for their source rock composition abstract the basaltic rocks from the central and southern islands of the new hebrides aneityum tanna erromango efate emae tongoa and epi have geochemical features typical of island arc volcanics they are enriched in lile and depleted in zr hf nb and ta compared to n type morb the rocks were derived from a similar upper mantle source as n type morb but with a higher degree of partial melting in addition their source was enriched in lile k rb sr ba and lree probably by migrating hydrous fluids released during the dehydration of the subducted oceanic slab the basalts from futuna island which is located farther from the trench display characteristics typical of calc alkaline rocks the futuna basalts were generated from a different lile enriched upper mantle source it seems that this upper mantle source was modified by interaction with partial melts from the subducted oceanic lithosphere

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

phase relations on the diopside jadeite hedenbergite join up to 24 gpa and stability of na bearing majoritic garnet abstract phase relations on the diopside di hedenbergite hd jadeite jd system modeling mineral associations of natural eclogites were studied for the compositions mol di70jd30 di50jd50 di30jd70 di20hd80 and di40hd10jd50 using a toroidal anvil with hole 7 gpa and a kawai type 6 8 multianvil apparatus 12 24 gpa we established that di hd and jd form complete series of solid solutions at 7 gpa and melting temperatures of pure di 1980 c and jd 1870 c for that pressure were estimated experimentally the melting temperature for the di50jd50 composition at 15 5 gpa is 2270 c the appearance of garnet is clearly dependent on initial clinopyroxene composition at 1600 c the first garnet crystals are observed at 13 5 gpa in the jadeite rich part of the system di30jd70 whereas diopside rich starting material di70jd30 produces garnet only above 17 gpa the proportion of garnet increases rapidly above 18 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites are produced from diopside rich starting materials in all experiments garnet coexists with stishovite st at a pressure above 18 gpa pyroxene is completely replaced by an assemblage of majorite maj st casio3 perovskite ca pv in ca rich systems whereas maj is associated with almost pure jd up to a pressure of 21 5 gpa above 22 gpa maj and st are associated with naalsio4 with calcium ferrite structure cf we established that an hd component also spreads the range of pyroxene stability up to 20 gpa in the di70jd30 system at 24 gpa an assemblage of maj ca pv mgsio3 with ilmenite structure mg il was obtained the experimentally established correlation between na si and al contents in maj and pressure in grt maj pyroxene assemblages may be the basis for a majorite geobarometer the results of our experiments are applicable to the upper mantle and the transition zone of the earth 400 670 km and demonstrate a wide range of transformations from eclogite to perovskite bearing garnetite in addition the mineral associations obtained from the experiments allowed us to simulate parageneses of inclusions in diamonds formed under the conditions of the transition zone and the lower mantle

real time and in situ assessment of conduit permeability through diverse long period tremors beneath aso volcano japan abstract long period signal lps 0 2 2 s and very long period signal vlp 2 100 s observed in the shallow volcanic plumbing system are typically repetitive and time invariant in their location and source mechanism offering in situ probes of hot fluid transport over the eruption cycles while the amplitude and activity of volcanic tectonic earthquakes and lp events have been commonly used to infer overpressure within their source region one missing link is an observable that may permit inference on the change in the permeability of the conduit plug wall which can regulate the degree of pressurization affect the mechanical strength of the surrounding rock and consequently the likelihood of an upcoming eruption here we show that during the 2011 2016 eruption cycle at aso volcano in japan long period tremor events a vlp of 15 s period with opposite waveform polarity can be systematically detected and categorized as pressurization and depressurization events in the same crack like conduit we suggest that depending on the strength of the surrounding rock and the permeability of the crack like conduit wall plug pressurization due to magmatic heat and vaporization is more likely to occur when a less permeable conduit plug wall can effectively keep the gas inside the crack like conduit on the other hand depressurization is prone to occur if the conduit wall plug permeability is sufficiently high to allow gas to escape from the conduit considering the amplitude of lpt proportional to the conduit overpressure contrasting energetics of these diverse lpt events allows us to define whether the conduit is prone to pressurization or depressurization providing a framework to infer how the permeability of the conduit wall plug may evolve over an eruption cycle

determination of the rare earth element abundances in 29 international rock standards by instrumental neutron activation analysis a critical appraisal of calibration errors abstract a standard additions method has been used to calibrate an in house multi element rock standard for the analysis of the rare earth elements ree and th ta hf and co by instrumental neutron activation analysis this preliminary calibration with a precision of typically better than 7 1 has been refined by comparing our analyses of the four u s g s standard rocks agv 1 bcr 1 g 2 and gsp 1 with compiled analyses obtained by a critical survey of over 70 published references our standard calibration was adjusted by the average discrepancy between our analyses and published analyses for each element for all four u s g s standards the accuracy of this final calibration is estimated to be better than 5 absolute and it has been used to determine the above elemental abundances in 29 international rock standards five of the ree have been determined by interpolation from chondrite normalised plots

thermobarometry and p t t paths the granulite to eclogite transition in lower crustal xenoliths from eastern australia lower crustal suite xenoliths in basaltic and kimberlitic magmas are dominated by mafic granulites and may also include eclogites and garnet pyroxenites pressures of up to 25 kbar obtained from such xenoliths are well in excess of an upper value of c 12 kbar for exposed granulite terranes palaeogeotherms constructed from xenoliths for the lower crust beneath the phanerozoic fold belts of eastern australia sea and beneath the eastern margin of the australian craton emac indicate two distinct thermal regimes the two geotherms have similar form with the emac curve displaced c 150 c to lower temperatures reaction microstructures show the partial re equilibration of primary igneous assemblages to granulite and eclogite assemblages and are interpreted to reflect the cooling from magmatic temperatures variations in mineral compositions and zoning are used to constrain further the history of several emac xenoliths to near isobaric trajectories detailed graphical models are constructed to predict compositional changes for isobaric p t paths at 7 14 21 kbar to transform an sea type geotherm to a cratonic geotherm the models show that for the assemblage grt cpx ky plag qtz the changes associated with falling temperature in xgr xjd increase and xan decrease will be greater at higher pressures these results indicate that discernible zoning is more likely to be preserved in the higher pressure xenoliths the zoning recorded in clinopyroxene from mafic granulite xenoliths over the pressure range c 12 22 kbar suggests isobaric cooling of a large crustal thickness 30 35 km an isobaric cooling path is consistent with magma accretion models for the transition of a crust mantle boundary from an sea type geotherm to a cratonic geotherm the coexistence of granulite and eclogite over the depth range 35 75 km beneath the emac indicates that the granulite to eclogite transition in the lower crust is controlled by p t conditions bulk chemistry and kinetic factors at shallower crustal levels typified by exposed granulite terranes isobaric cooling may not result in the transition to eclogite

subduction style magmatism in a non subduction setting the colville igneous complex ne washington state usa of the klondike mountain formation which show no decoupling the colville igneous complex is located within the eocene magof the lile and hfse i e no subduction signature precluding matic belt of the north american cordilleran interior it straddles the presence of a subduction slab beneath this part of the north the us canadian border in northeast washington and southern american cordillera during the eocene we propose the alternative british columbia the complex consists of three intrusive and two model that the colville igneous complex formed as a result of extrusive phases the first extrusive phase being contemporaneous decompression melting of crust and mantle during post laramide with the latter two intrusive phases as a consequence of suborogenic collapse of an overthickened crust solidus re equilibration in the plutonic rocks this study concentrates on the two extrusive phases the sanpoil volcanic formation and the klondike mountain formation the sanpoil volcanic formation consists of andesites dacites and rare trachyandesites sio2

primary magmas at the volcanic front of the ne japan arc coeval eruption of crustal low k tholeiitic and mantle derived medium k calc alkaline basalts at azuma volcano it has long been thought that the low k tholeiitic th and medium k calc alkaline ca lavas in the nejapan arc were produced by fractional crystallization from mantle derived basalt magmas and that the latter formed from mixing of mafic and felsic magmas both derived from a common primaryth basalt through fractionation an alternative view was recently proposed on the basis of sr isotope microanalysis of plagioclase phenocrysts from the zao volcano suggesting that 1 the low k th basaltic andesites formed by melting of lower crustal amphibolite and that 2 the medium k ca basalts to andesites formed by mixing of mantle derived basalt and crustal th melts to investigate further the origin of the primary low k th and medium k ca basalts we investigated basalts and andesites from azuma volcano azuma is a quaternary eruption center at the volcanic front in the ne japan arc that has erupted two types of basalt 1 radiogenic sr sr sr1 4 0 7058 0 7062 low k th basalt lavas without evidence of magma mixing and assimilation 2 unradiogenic sr sr sr1 4 0 7039 0 7041 medium k ca basalt lavas with subtle evidence for magma mixing associated intermediate lavas are voluminous and are all 3 mildly radiogenic sr sr sr1 4 0 7044 0 7055 medium k andesites all of which have ca affinities with evidence for rigorous magma mixing but no crustal assimilation the low k th basalt has an isotopic composition similar to that of crustal granitoids beneath azuma and has a composition indicating that it potentially formed from a high degree lower crustal amphibolite melt the medium kca basalt has a basaltic groundmass with mg rich olivine fo89 and calcic plagioclase phenocrysts an90 and the most unradiogenic sr sr sr1 4 0 7037 0 7038 suggesting that it originated from a primary mantle melt major and trace element microanalysis of the basaltic groundmass indicates that the primary magma composition is close to high k we conclude that the mantle derived basalt at azuma is the result of a highto medium k magma that was later mixed with a low k th basalt melt from the amphibolitic lower crust to form medium k ca basalts and andesites this supports the view of a lower crustal origin of the low kth basalts and simultaneously requires a reappraisal of the origin of the across arc variation in k contents of the mantle derived primary arc basalts as the highto medium k ca basalt is geochemically fairly similar to the high k rear arc basalt in the ne japan arc

koolau shield basalt as xenoliths entrained during rejuvenated stage eruptions perspectives on magma mixing rejuvenated stage tuff cones honolulu volcanics on koolau volcano oahu hawaii contain xenoliths of koolau shield basalt because koolau subaerial shield lavas represent a hawaiian geochemical end member and submarine shield lavas have compositions with some affinities to mauna loa and kilauea we analyzed 28 xenolithic basalts from salt lake and koko head cones to determine how these seemingly random samplings of the koolau profile compare to established koolau geochemistry analyses reveal that 24 are shield tholeiitic basalt the focus of this study and 4 are rejuvenated stage basaltic rocks the tholeiitic xenoliths represent largely upper koolau shield lavas as these samples 8 3 to 5 8 wt mgo have with one exception overall major and trace element compositions that overlap those of koolau subaerial shield lavas secondary processes however created some distinctions namely enrichments depletions in k ba sr sio2 and feo and due to zeolitization chabazite with attending okenite and apophyllite elevated cao one xenolithic basalt with 8 2 wt mgo has higher ti zr nb and sc and lower zr nb than subaerial lavas and appears to represent relatively early deeper shield thereby reinforcing that the koolau shield source varied temporally olivine orthopyroxene and plagioclase are the phenocrysts clinopyroxene is rare and their core compositions range widely across the suite fo87 8 72 orthopyroxene mg s 85 72 and an74 60 several xenolithic basalts have both normally and reversely zoned orthopyroxene and plagioclase with a variety of core compositions e g orthopyroxene core mg s 82 77 and 72 all in one sample these compositions and zonations record evidence for wide compositional ranges of replenishment mgo 13 8 wt and reservoir mgo 7 to 5 wt magmas mixing in varying proportions however extreme mgo lavas 13 and 5 wt are not observed as either subaerial or xenolithic basalt but are indicated by phenocryst cores of fo87 8 and orthopyroxene mg 72 the koolau magma mixing history resembles that of kilauea and is unlike the steady state mixing known for mauna loa finally these basalt samples show that any xenolithic occurrence of koolau lava is subject to the zeolitization prevalent in the tuff cone hosts

the meta igneous granulite xenoliths from kerguelen archipelago evidence of a continent nucleation in an oceanic setting xenoliths of meta igneous origin occur as one of the two main types of ultramafic and mafic xenoliths entrained by alkaline lavas of the kerguelen islands these are designated type ii xenoliths and are subdivided into three mineralogical groups subtype iia and iic xenoliths are interpreted as crystallisation products of basaltic melts that were emplaced near the crust mantle boundary during the early tholeiitic transitional magmatic activity of the kerguelen islands younger magmatism became more alkaline and subtype iib xenoliths were formed as high pressure alkaline cumulates related to the last alkaline volcanic stage subsequently the plagioclase bearing type ii rocks have been re equilibrated under granulite facies conditions this addition of mafic material around the crust mantle boundary is consistent with seismic evidence for crustal thickening to 14 20 km calculated compressional seismic velocities vp for the basic granulites are consistent with the range of observed vp in the low velocity region underlying the oceanic crust such growth in the thickness of the oceanic crust may be caused by intrusion of basalts at different levels in the lithosphere and may provide the heat responsible for granulitic metamorphism in the oceanic setting this study suggests that basic granulites can account for the observed seismic characteristics of oceanic plateaux and can be important components of kerguelen oceanic lithosphere where there has been large scale magma production moreover we speculate that the kerguelen islands and perhaps the surrounding plateau represent a continental nucleation process

intracrustal controls on the coexistence of tholeiitic and calc alkaline magma series at aso volcano sw japan aso caldera sw japan was formed incrementally over a period of 300 kyr by the eruption of four basaltic to dacitic pyroclastic flow and fall deposits aso 1 4 these units are collectively referred to as the aso pyroclastic flow deposit apfd in which tholeiitic and calc alkaline magmas have been erupted in close temporal and spatial proximity detailed petrological and geochemical studies indicate that a major shift in magmatic composition occurred between aso 1 and 4 as the caldera forming stage evolved changing from a predominantly tholeiitic to a calc alkaline signature the mineralogical and geochemical characteristics of aso 1 4 suggest that magmatic evolution within each unit is controlled by fractional crystallization associated with magma mixing crustal assimilation by altering the fractional crystallization mineral assemblage as well as the relative amounts of fractional crystallization magma mixing and crustal assimilation the systematic shifts in differentiation trends and magmatic series observed between the four eruptive units can be reproduced this suggests that the coexistence of tholeiitic and calc alkaline magma series can be attributed to shallow level intracrustal processes

formation of an archaean continent about 30 of the earth is covered by continents but only about 10 small kernels of these continentsae known as archaean cratonsae are continental fragments formed before 2 5 gyr ago the kaapvaal craton of south africa which formed and stabilized between 3 7 and 2 7 gyr ago is one of the oldest reasonably sized examples of these continental fragments it consists of a mosaic of subdomains that have been welded together by processes similar to those of modern day plate tectonics the earliest subdomains may have owed their origin to the onset of efficient recycling from the earth s hydrosphere into the mantle

on the lateral variations in chemical composition and volume of quaternary volcanic rocks across japanese arcs the fe mg fe ratios xfe of the quaternary basalts sio2 53 wt in the japanese arcs were examined the xxfe of relatively magnesian basalts decreases from the volcanic front toward the japan sea across the arcs based on the partition coefficient of mg fe2 between olivine and liquid it is suggested that all the basalts near the volcanic front which are mostly tholeiitic basalts are significantly fractionated whereas many basalts near the japan sea which are mostly alkali basalts are little fractionated the k2 o content in the primary basalt magmas increases toward the japan sea combining the xfe and k2 o data it is suggested that relatively large amounts of tholeiitic magmas are produced near the volcanic front but they fractionate during their ascent whereas smaller amounts of alkali basalt magmas are formed near the japan sea but they can ascend with less fractionation the density of primary tholeiite magma is significantly larger than that of primary alkali basalt magmas it is most likely that primary tholeiite magmas cannot ascend beyond the upper crust and would fractionate to produce less dense tholeiitic magmas near the volcanic front whereas primary alkali basalt magmas can ascend through the upper crust without fractionation as far as buoyancy is the principal ascending force in the japanese arcs the stress field may be less compressional near the japan sea than near the volcanic front so that magmas can ascend more rapidly in the latter region than in the former these two factors may be responsible for the above mentioned chemical variations of basalt magmas across the arcs the variation in volume of the quaternary volcanic rocks across the arcs can be explained by the presence of a melt rich zone above but nearly parallel to the subducted slab

pressure temperature time paths and a tectonic model for the evolution of granulites petrologic studies and application of well calibrated mineralogic thermometers and barometers reveal several important features common to many granulite terrains 1 peak metamorphic pressure and temperature conditions cluster around values of 7 5 pm 1 kbar and 800 pm 50 c implying average geothermal gradients of 30 35 c km 2 in comparison with upper amphibolite facies rocks especially in paired amphibolite granulite terrains it is evident that granulites are distinguished from amphibolites by the former s higher metamorphic temperatures but not higher pressure 3 initial cooling of granulite terrains from peak conditions is nearly isobaric for garnet closure temperatures of 600 pm 50 c the dp dt retrograde paths inferred from compositionally zoned garnet rims are 2 8 b c in most granulites 4 primary coarse sillimanite is found in most granulites and retrograde kyanite is known in a few these data suggest that granulites form as a result of anomalous thermal gradients

tectonic model for the evolution of the limpopo belt abstract constraints on which any model for the tectonic evolution of the limpopo belt must be based include the following data crustal thickening to at least 65 km between 2700 and 2650 ma ago was responsible for the formation of the granulite terrane exposed in the limpopo belt today this crustal thickening probably resulted from the thrusting of the kaapvaal craton over the zimbabwe craton along the south dipping triangle tuli sabi shear zone other northwardverging thrusts related to this event occur in the kaapvaal craton south of the limpopo belt in the central and southern marginal zones and the kaapvaal craton this shortening is directed to the southwest while in the northern marginal zone it was directed to the north northwest peak metamorphism was superimposed on the thickened crust and then nearly isothermal decompression of several kbars occurred throughout the belt during this decompression rocks moved upward and spread outward onto the adjacent cratons from the zone of thickened crust along several inward directed shear zones creating a regional pop up high grade rocks were thrust over low grade rocks on the cratons producing along the terrane boundary retrograde metamorphism in the limpopo belt and prograde metamorphism on the cratons

cyclic liquefaction of loose gassy sand gas can be found in many soils but none more common than in seabed soils gas charged sediments are known to be widely distributed throughout the world s oceans numerous research programs have studied saturated soil response to cyclic loading however little is known about the behavior of gassy soils subjected to cyclic loading the response of loose gassy specimens subjected to cyclic loading was studied in a laboratory program triaxial tests were performed on specimens of reconstituted ottawa sand prepared to various gas contents and densities the specimens were consolidated and then sheared under undrained cyclic loading gas content was measured at the beginning and end of each test using time domain reflectometry the response of the gassy specimens has been shown to be influenced by the soil state and grain characteristics and the intensity duration and frequency of the cyclic loading the propensity of a soil to liquefy is represented by a cyclic resistance ratio defined as the cyclic stres

isotopic characteristics of neogene quaternary tephra from iodp site u1438 a record of explosive volcanic activity in the kyushu ryukyu arc a m acknowledges support from the swiss national science foundation grant 200020 135511 to othmar muntener and grant p2lap2 171819 to a m and swiss iodp this work was also supported by grants to g m y and m b from nsf oce 1537135 and iodp

shear wave velocity based probabilistic and deterministic assessment of seismic soil liquefaction potential abstractshear wave velocity vs offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property this paper presents the results of an 11 year international project to gather new vs site data and develop probabilistic correlations for seismic soil liquefaction occurrence toward that objective shear wave velocity test sites were identified and measurements made for 301 new liquefaction field case histories in china japan taiwan greece and the united states over a decade the majority of these new case histories reoccupy those previously investigated by penetration testing these new data are combined with previously published case histories to build a global catalog of 422 case histories of vs liquefaction performance bayesian regression and structural reliability methods facilitate a probabilistic treatment of the vs catalog for performance based engineering applications where possible uncertainties of the variables comprising both the seismic demand an

melting experiments on a high magnesian andesite abstract melting experiments were conducted on a high magnesian bronzite olivine andesite teraga ike andesite which is considered to be a primary andesite the high magnesian andesite magma is in equilibrium with both olivine and orthopyroxene at about 15 5 kbar and 1080 c under h2o saturated conditions and at lower pressure and higher temperature under h2o undersaturated conditions this suggests that high magnesian andesites could be generated by the partial melting of upper mantle peridotite containing a small amount of h2o

calculation and application of clinopyroxene garnet plagioclase quartz geobarometers recently published thermodynamic and experimental data in a variety of chemical systems have been evaluated to derive gibbs free energies for hedenbergite and pyrope these were used to calculate the geobarometric equilibria

interaction of arc magmas with subvolcanic hydrothermal systems insights from compositions and metasomatic textures of olivine crystals in fresh basalts of daisen and mengameyama western honshu japan