magnetic fabric in the malanjkhand granite central india implications for regional tectonics and proterozoic suturing of the indian shield abstract in this paper field microstructural and anisotropy of magnetic susceptibility ams data are presented from the 2 48 ga malanjkhand granite and adjacent gneiss with an aim to evaluate the time relationship between fabric development in the granite and regional tectonics the central indian suture cis that demarcates the southern margin of the ne sw to ene wsw trending central indian tectonic zone citz and is a consequence of the accretion between the northern and southern indian shields lies to the north of the granite the northern margin of the granite that has proximity to the cis is mylonitized and shows a dextral top to the ne sense of shear field and magnetic foliation in the gneiss are parallel to each other as well as to the field foliation in the western and northwestern margin of the granite also the field fabrics in the granite and gneiss curve clockwise into the cis the magnetic foliation trajectories curve from a ns orientation in areas remote from the cis to a ne sw orientation in parts that are proximal to the cis in the north the granite shows synmagmatic deformation fabrics such as preferentially oriented zoned feldspar phenocrysts as well as evidence of high t solid state deformation fabric such as chessboard pattern in quartz magnetic anisotropy increases towards the cis which is inferred to support synmagmatic deformation it is concluded that the tectonic evolution of the citz and emplacement fabric development in the malanjkhand granite were synchronous phenomena wnw ese directed convergence led to transpression which is inferred to be responsible for the emplacement of the granite it is concluded that in the malanjkhand granite the development of syndeformational emplacement fabrics to syntectonic cooling was a continuum and the suturing of the northern and southern indian shields along the cis took place during the palaeoproterozoic period thus the study provides an insight into the amalgamation and stabilization of the indian shield during the late archaean palaeoproterozoic time

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

strain partitioning in a pluton during emplacement in transpressional regime the example of the neouvielle granite pyrenees this microstructural and anisotropy of magnetic susceptibility study of the internal structures of the hercynian neouvielle granite pluton 100 km2 provides new data indicating that the pluton was emplaced during the main hercynian tectonic event recognized in the pyrenees it also provides new data about the later alpine deformation localized along narrow mylonitic bands these bands acted as reverse faults and have not rotated the hercynian structures that define the main part of the pluton the pluton is composed of two structural domains the northern half of the pluton displays a beak shape in map view with subhorizontal e w trending lineations of magmatic origin the southern half is semi circular and displays rather steeply northward plunging lineations corresponding to magmatic and high temperature ht solid state microstructures these features are associated with magma deformation during emplacement magma deformation corresponds in the northern half of the pluton to an e w strike slip deformation recognized in the enveloping pelitic metasediments of carboniferous age and in the southern half of the pluton to southward overthrusting recognized in the enveloping quartzites of devonian age juxtaposition in a single granite body of transcurrent and compressive domains is viewed as a strain partitioning in the magma this strain partitioning is linked to both the transpressive character of the main regional deformation event and the rheological contrast between the pelitic country rocks and quartzose country rocks

mechanism of small vulcanian eruptions at suwanosejima volcano japan as inferred from precursor inflations and tremor signals we examine precursory signals of vulcanian eruptions at suwanosejima volcano southwest of japan by deploying seismic and tilt stations close to the active crater to understand the shallow conduit processes just before explosions vulcanian eruptions at suwanosejima for the period from october 2009 to 2011 are often preceded by a sudden cessation of continuous tremor associated with continuous ash emissions the amplitude of continuous tremor decreases within about 10 s and tilt signal starts to show uplift of the active crater then the pause of continuous tremor and uplift continue for about 1 2 min and tilt amplitudes reach a few tens of nanoradians at a distance of 400 m from the active crater as the pause time of continuous tremor before explosion becomes longer the maximum amplitude of explosion earthquake and uplift signal become larger vulcanian eruptions are also observed during periods without continuous tremor in these cases tilt signals capture uplifts of the active crater for about 10 min before explosions and reach a few tens of nanoradians cessations of volcanic gas emissions are observed before some explosions during periods without continuous tremor mori et al 2011 these observations suggest that pressurization in the shallow conduit is caused by an accumulation of volcanic gases and ash through the formation of cap in the conduit possibly composed of stiffened magma due to degassing cooling rheological changes or other mechanisms

rift to collision transition recorded by tectono thermal evolution of the northern pyrenees the impact of rift related processes on tectonic and thermal evolution of collisional orogens is poorly documented here we study the northern pyrenees a region that has preserved a geological record of the transition from rifting to collision using modeling of new low temperature thermochronological data including fission track and u th he on apatite and zircon we propose a temporal reconstruction of the inversion of the european rifted margin our data confirm that rifting and related cooling started in the late paleozoic triassic throughout the jurassic and early cretaceous the european margin recorded slow heating during postrift subdsidence modeling of thermochronological data allows distinguishing subsidence and denudation controlled by south dipping normal faults in granitic massifs that reflect a second episode of crustal thinning at 130 110 ma following onset of convergence at 83 ma shortening accumulated into the weak and hot albian cenomanian rift basins floored by both hyperextended continental crust and exhumed subcontinental mantle the lack of cooling during this initial stage of convergence is explained by the persistence of a high geothermal gradient the onset of exhumation related cooling is recognized in the whole pyrenean region at 50 35 ma this timing reveals that the main phase of mountain building started when hyperextended rift basins closed and collision between proximal domains of the rifted margin occurred

monitoring volcanic activity using correlation patterns between infrasound and ground motion 1 this paper presents a simple method to distinguish infrasonic signals from wind noise using a cross correlation function of signals from a microphone and a collocated seismometer the method makes use of a particular feature of the cross correlation function of vertical ground motion generated by infrasound and the infrasound itself contribution of wind noise to the correlation function is effectively suppressed by separating the microphone and the seismometer by several meters because the correlation length of wind noise is much shorter than wavelengths of infrasound the method is applied to data from two recent eruptions of asama and shinmoe dake volcanoes japan and demonstrates that the method effectively detects not only the main eruptions but also minor activity generating weak infrasound hardly visible in the wave traces in addition the correlation function gives more information about volcanic activity than infrasound alone because it reflects both features of incident infrasonic and seismic waves therefore a graphical presentation of temporal variation in the cross correlation function enables one to see qualitative changes of eruptive activity at a glance this method is particularly useful when available sensors are limited and will extend the utility of a single microphone and seismometer in monitoring volcanic activity

relative partitioning of acoustic and seismic energy during strombolian eruptions the relative elastic energy partitioning during strombolian eruptions can be estimated from acoustic pressure and seismic velocity records we outline methods for determining acoustic and seismic energies for sensors deployed within several kilometers of erupting vents we use these energies to introduce the concept of the volcano acoustic seismic ratio g or vasr which is the ratio of elastic energy propagated through the atmosphere and into the earth eruption vasr is a physical diagnostic of explosive degassing that is appropriate for comparing eruption mechanisms at individual and between various volcanoes here we assess acoustic and seismic energies and corresponding vasr for discrete strombolian explosive events at karymsky and erebus volcanoes we attribute the relatively high and stable vasr at erebus g 8 standard deviation 41 to repeatable source conditions occurring at the surface of a persistent lava lake with accompanying strong coupling to the atmosphere lower and more variable vasr at karymsky g 0 18 in 1998 to g 1 51 in 1991 with standard deviations of 93 and 313 respectively is attributed to changing conditions within a narrow partially choked conduit variable seismoacoustic energy partitioning for karymsky as manifested by the large vasr standard deviation suggests that conduit conditions affecting vasr which include magma properties conduit obstruction or fragmentation depths can evolve both during the course of an explosion and between successive events d 2005 elsevier b v all rights reserved

structure and u pb dating of the saint arnac pluton and the ansignan charnockite agly massif a cross section from the upper to the middle crust of the variscan eastern pyrenees in the agly massif pyrenees two variscan plutons the saint arnac pluton and the ansignan charnockite intrude different levels of a c 10 km thick crustal section the saint arnac pluton intrudes through upper crustal rocks and the ansignan charnockite cuts mid crustal country rocks a structural study of these plutons based on the anisotropy of magnetic susceptibility technique combined with a kinematic study of the country rocks shows that the structures and emplacement modes of the plutons are compatible with those of the other plutons of the pyrenees emplaced during the d 2 transpressive phase u pb dating on zircons from the saint arnac pluton yields a 308 3 1 2 ma age for a diorite and a 303 6 4 7 ma age for a granodiorite the charnockite was previously dated at 315 ma the emplacement ages of these two intrusions are thus separated by at least 5 ma first numerous sills and laccoliths such as the ansignan laccolith were injected in the middle crust and this induced heating and thickening subsequently the large saint arnac pluton was injected in the upper crust at the beginning of formation of a gneissic dome

local regional and remote seismo acoustic observations of the april 2015 vei 4 eruption of calbuco volcano chile the two major explosive phases of the 22 23 april 2015 eruption of calbuco volcano chile produced powerful seismicity and infrasound the eruption was recorded on seismo acoustic stations out to 1 540 km and on 5 stations is02 is08 is09 is27 and is49 of the international monitoring system ims infrasound network at distances from 1 525 to 5 122 km the remote ims infrasound stations provide an accurate explosion chronology consistent with the regional and local seismo acoustic data and with previous studies of lightning and plume observations we use the ims network to detect and locate the eruption signals using a brute force grid search cross bearings approach after incorporating azimuth deviation corrections from stratospheric cross winds using 3d ray tracing the estimated source location is 172 km from true this case study highlights the significant capability of the ims infrasound network to provide automated detection characterization and timing estimates of global explosive volcanic activity augmenting the ims with regional seismo acoustic networks will dramatically enhance volcanic signal detection reduce latency and improve discrimination capability

some remarks on fabric overprints and constrictional ams fabrics in igneous rocks during the ascent emplacement and post emplacement deformation of igneous rocks two or more phases of deformation that overprint each other are often depicted these overprints when magnetic minerals are present are recorded in magnetic fabric in this contribution overprints are studied by means of numerical modeling following several basic scenarios common to igneous rocks biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic susceptibility modeling shows that 1 a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic rocks may result from a deformation overprint and not necessarily from an extensional transtensional regime and 2 that the constrictional ams fabrics originates from orthogonal superimposition of a deformation event on an ams fabric inherited from earlier magma emplacement history therefore the interpretation of a constrictional fabric must be performed with caution numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data

u pb age and lead isotopic characterization of au bearing skarn related to the andorra granite central pyrenees spain auriferous skarns are associated with post and late kinematic hercynian granites that intruded into cambro ordovician to devonian sediments of the central pyrenees we determined the age of the andorra granite and the associated skarn at 305 3 ma by u pb dating titanite from the endo skarn the sulfur isotopic composition from sulfides in the skarn cardellach et al 1992 shows a significant variation with isotopically light sulfur 34s 3 in the barren skarns and heavy sulfur 34s 11 in the gold bearing skarns outwards it increasingly resembles sulfur from arsenopyrite disseminations in the cambro ordovician sediments the lead isotopic composition from sulfides of the skarns is very homogeneous 206pb 204pb 18 410 207pb 204pb 15 699 208pb 204pb 38 574 in contrast to the one in gold bearing arsenopyrite veins and in arsenopyrite disseminations in the sediments e g 206pb 204pb varies from 18 54 to 30 36 combined sulfur and lead isotope data indicate that the lead in the skarn is dominantly derived from the granite whereas the sulfur is derived at variable portions from both the granite and the sediments

magnetic and structural study of the eaux chaudes intrusion understanding the variscan deformation in the western axial zone pyrenees the present study provides new magnetic and microstructural data for the eaux chaudes granodioritic massif western axial zone pyrenees and contributes to the understanding of its geometry internal structure and emplacement mechanism moreover the geological cross sections and field data allow to reconstruct the evolution of the whole area from variscan to alpine times and to integrate the emplacement of the igneous body in the context of the variscan orogeny the eaux chaudes pluton 301 9 ma is mainly composed by granodiorite describing a normal compositional zoning and an approx imately concentric arrangement that is consistent with the zonation of the low field magnetic susceptibility magnetic foliation is subhorizontal in the inner part of the intrusion and becomes parallel to the petrographical contacts along pluton margins roughly describing the geometry of the intrusion magnetic lineations are dominantly subhorizon tal with e w to ene wsw directional maximum the general parallelism between variscan structures of the host rock and the geometry and magmatic fabric of the intrusion reveals a late syn variscan emplacement the tectonic regime registered during magma emplacement is in agreement with an n s shortening and an e w stretching direction consistent with the transpressive regime deduced for other pyrenean intrusions alpine overprint produced a slight tilting in the southern part of the intrusion but it can be considered that the original variscan structure is basi cally unchanged

on the reliability of ams in ilmenite type granites an insight from the marimanha pluton central pyrenees this study has been financed by the research project cgl2009 08969 spanish ministry of science and innovation bou acknowledges financial support from the geotransfer group university of zaragoza dga and the jaedoc postdoctoral program csic reviews from d bilardello b almquist and editor e appel are warmly acknowledged for their help to improve the manuscript info eu repo grantagreement ec fp7

tectonic levels in the palaeozoic basement of the pyrenees a review and a new interpretation reply abstract two different structural domains developed during the main hercynian deformation events were recognized by de sitter zwart in the hercynian basement of the central pyrenees a deep seated level infrastructure made of medium to high grade metasediments and orthogneisses with dome shaped gently dipping foliations contrasts with a shallow level suprastructure of low to very low grade metasediments with rather steep foliations since the recognition of this structural zonation different interpretations have been proposed disagreements concern timing of deformation and tectonic regime considered to be prevalent of the structural development of each tectonic level the proposed interpretation regards the progressive development and differentiation of both structural domains and considers the following factors to be significant for the structural arrangement of the pyrenean segment of the hercynian belt an increase with depth of the horizontal shear component of deformation related to tangential and transcurrent tectonics a marked inhomogeneity of deformation and penetrability of related foliations and the gradual evolution from an earlier compressive crustal shortening event to a late transpressive event responsible for crustal shortening and trend parallel stretching

long range acoustic observations of the eyjafjallajokull eruption iceland april may 2010 1 the april may 2010 summit eruption of eyjafjallajokull iceland was recorded by 14 atmospheric infrasound sensor arrays at ranges between 1 700 and 3 700 km indicating that infrasound from modest size eruptions can propagate for thousands of kilometers in atmospheric waveguides although variations in both atmospheric propagation conditions and background noise levels at the sensors generate fluctuations in signal to noise ratios and signal detectability array processing techniques successfully discriminate between volcanic infrasound and ambient coherent and incoherent noise the current global infrasound network is significantly more dense and sensitive than any previously operated network and signals from large volcanic explosions are routinely recorded because volcanic infrasound is generated during the explosive release of fluid into the atmosphere it is a strong indicator that an eruption has occurred therefore long range infrasonic monitoring may aid volcanic explosion detection by complementing other monitoring technologies especially in remote regions with sparse ground based instrument networks

permian granites in the pyrenees the aya pluton basque country we show that the permian volcanism in the pyrenees was accompanied with emplacement of granite plutons with transitional chemistry reassessment of age structure and petrological characteristics of the aya pluton intrusive in the cinco villas massif basque country indicates that it was emplaced at 267 1 1 1 ma in a dextral transtensive context and that it marks a transition between the high k calcalkaline and the alkaline emissions of the first and second permian volcanic cycles respectively this age is close to that of c 267 ma reported for lamprophyres dykes of the pyrenean axial zone these data characterize a period of transition between the variscan orogeny and the subsequent alpine cycle in the pyrenees with an earlier extensive regime that became widespread in the pyrenees during the mesozoic times

sigmoidal structures featuring dextral shear during emplacement of the hercynian granite complex of cauterets panticosa pyrenees abstract the three plutons of the cauterets panticosa granite complex are studied by the anisotropy of magnetic susceptibility ams technique as expected from the dominantly paramagnetic nature of the rocks the magnetic susceptibility zonation accurately compares with the lithological zonation detailed examination of the linear and planar structural patterns of the plutons allows the difficult problem of their formation mechanisms to be explored the sigmoidal pattern of the linear structures only results from regional tectonics and points unequivocally to a dextral shear component for the responsible tectonic event the concentric planar structures while also affected by regional tectonics retain some imprint of magma emplacement the microstructures observed in the granitoids point to a continuous deformation from the magmatic state to the high temperature solid state in the country rocks structures and kinematic criteria underline the transpressive character of the d2 hercynian event of the pyrenees which resulted in a partitioning between zones where either compression or dextral strike slip were dominant all these data constrain a new model of d2 syn tectonic emplacement for the plutons of the cauterets panticosa complex and remarkably illustrate structural features resulting from a transpressive regime

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

volcanic tremor and plume height hysteresis from pavlof volcano alaska the march 2016 eruption of pavlof volcano alaska produced an ash plume that caused the cancellation of more than 100 flights in north america the eruption generated strong tremor that was recorded by seismic and remote low frequency acoustic infrasound stations including the earthscope transportable array the relationship between the tremor amplitudes and plume height changes considerably between the waxing and waning portions of the eruption similar hysteresis has been observed between seismic river noise and discharge during storms suggesting that flow and erosional processes in both rivers and volcanoes can produce irreversible structural changes that are detectable in geophysical data we propose that the time varying relationship at pavlof arose from changes in the tremor source related to volcanic vent erosion this relationship may improve estimates of volcanic emissions and characterization of eruption size and intensity

structure age and mode of emplacement of the hercynian borderes louron pluton central pyrenees france the hercynian borderes louron pluton 20 km2 in the central pyrenees intrudes devonian and carboniferous metasediments it shows a concentric zoning and consists of a significant proportion of quartz gabbros in its periphery and of granodiorites biotite monzogranites and biotite muscovite monzogranites in its core ams study shows that the pluton corresponds to an elongated dome with a n100 e trending axis the anisotropy intensity ppara is high in the south and in the core of the pluton whereas it is low in the north the shape parameter t indicates that the fabric is strongly planar in a large central band oriented nw se whereas it is strongly linear in the western and eastern tips of the pluton these characteristics suggest that the borderes louron pluton emplaced in two episodes 1 intrusion of mafic magmas along a n100 e sill parallel to the regional foliation of the host metasediments and 2 injection of three successive silicic batches granodiorite biotite monzogranite two micas monzogranite which pushed aside the early mafic injections in situ u pb dating of zircon grains indicates that the emplacement age of the biotite monzogranite is 309 4 ma synchronous with the d 2 dextral transpressive event and close to the ages of the eastern pyrenean plutons may be slightly older

progressive deformation of a zone of magma transfer in a transpressional regime the variscan merens shear zone pyrenees france the ew striking variscan merens shear zone msz located on the southern border of the aston dome pyrenees corresponds to variously mylonitized gneisses and plutonic rocks that are studied using the anisotropy of magnetic susceptibility ams technique the plutonic rocks form ew striking bands with from south to north gabbro diorites quartz diorites and granodiorites the msz underwent a mylonitic deformation with an intensity progressively increasing from the mafic to the more differentiated rocks the foliations are ew to nw se striking and subvertical a first set of lineations shows a moderate wnw plunge with a dextral reverse kinematics more recent subvertical lineations correspond to an uplift of the northern compartment to the east the msz was cut by a n120 e striking late shear band separating the msz from the querigut pluton the different stages of mylonitization relate to late variscan dextral transpression this regime allowed the ascent of magmas along tension gashes in the middle crust we interpret the msz as a zone of magma transfer which fed a pluton now eroded that was similar to the querigut and millas plutons located to the east we propose a model of emplacement of these plutons by successive pulses of magmas along en echelon transfer zones similar to the msz

early variscan visean granites in the core of central pyrenean gneiss domes implications from laser ablation u pb and th pb studies abstract laser ablation u pb and th pb single zircon and monazite geochronology was applied to seven samples from two variscan gneiss domes in the central pyrenean axial zone detrital zircon ages obtained from a paragneiss in the western aston dome range from neoarchean ca 2 57 ga to late neoproterozoic ca 560 ma suggesting that late ediacaran sediments were deposited along the northern margin of gondwana cadomian magmatism is recorded for the first time in the central pyrenees from a biotite metagranite ca 545 ma in the central aston dome a second sample of an orthogneiss from the aston dome yields a middle ordovician protolith age ca 467 ma similar in age to other dated orthogneisses of the axial zone three samples from granite stocks situated in the core of the aston and bossost domes have crystallization ages of ca 339 337 ma providing the first evidence of visean igneous activity in the axial zone in contrast to the larger and significantly younger ca 312 305 ma granite plutons along the margins of the gneiss domes visean magmatism caused lp ht contact metamorphism m 2 migmatization throughout the aston dome though less well constrained by overgrowth ages on zircon ca 331 ma and monazite ages ca 340 320 ma is likely to be related to visean intrusions the main s 2 schistosity in the aston and bossost domes is coeval with the visean intrusions inclusion trails in porphyroblasts nucleating in the contact aureoles document the continuous development of s 2 related to local extension crystal plastic deformation of the granites indicates that the d 2 deformation event continued after their crystallization visean magmatism played a crucial role in early stages of dome formation by thermally weakening the metasedimentary mantle and to a certain degree the orthogneiss as well enhancing the development of orogen parallel shear zones in an overall n s compressive setting

in situ u pb zircon ages for early ordovician magmatism in the eastern pyrenees france the canigou orthogneisses u pb age determinations with an ion probe on zircons within orthogneisses from the canigou massif eastern pyrenees give an emplacement age for their granitic protolith of 475 10 ma arenigian this invalidates the previous interpretation of basement cover relationships between the orthogneisses and the overlying lower cambrian canaveilles metasedimentary series and corroborates the intrusive character of the orthogneisses which is further supported by field evidence the data also define two groups of inherited zircons paleo meso proterozoic and cadomian in addition to partial lead loss during the hercynian late carboniferous high temperature low pressure metamorphic event these results are in agreement with ages reported from other orthogneissic bodies across the entire variscan chain of western europe and indicate the existence of a widespread cambro ordovician magmatic event

permian clockwise rotations of the ebro and corso sardinian blocks during iberian armorican oroclinal bending preliminary paleomagnetic data from the catalan coastal range ne spain abstract paleomagnetic investigations of early permian and triassic magmatic rocks from catalan coastal ranges provide three magnetic directions which are interpreted as primary magnetizations and partly as overprints the succession of magnetic directions is interpreted in terms of a succession of large scale clockwise rotations which bring the whole assembly of pyrenees catalonia corsica sardinia and maures esterel massifs from the southeast of the massif central to the west during permian this major movement is associated with clockwise rotation of northern limb of the iberian orocline during latest carboniferous and early permian 305 290 ma subsequently permian large scale dextral transtensional extensional shearing operated along aquitanian shear belt between the massif central in the northeast and the iberian variscan massifs in the southwest the latest phase of the rotation in the late permian early triassic is associated with alkaline magmatism probably linked to neo tethys opening activity in western europe

an overview of volcano infrasound from hawaiian to plinian local to global abstract volcano infrasound is an increasingly useful technique for detecting locating characterizing and quantifying eruptive activity and can be used to constrain eruption source parameters in recent years studies of infrasound data from active volcanoes have shown clear progress towards mitigating volcanic hazards and understanding volcanic source processes volcano acoustic sources are shallow or aerial thus volcano infrasound data provide valuable information on eruption dynamics and are readily combined with direct and remote observations of gas ash and other eruptive phenomena the infrasound signals produced by volcanoes are indicative of the eruption style and dynamics here we review the diversity of infrasound signals generated by a wide variety of volcanic eruptions from hawaiian to plinian and the physical processes inferred to produce them we place particular emphasis on regional 15 250 km distance and global 250 km distance volcano infrasound studies as recent work in this area has made significant advances in monitoring and characterizing remote and difficult to monitor eruptions long range infrasonic detection of explosive volcanic eruptions is possible due to the energetic source mechanisms involved minor atmospheric attenuation at low frequencies and the existence of waveguides in the atmosphere however accurate characterization of the atmosphere and its spatiotemporal variability is required for reliable long range sound propagation modeling and correct interpretation of global infrasound recordings conversely because volcanic explosions are energetic and sometimes repetitive infrasound sources they can be used to validate atmospheric and acoustic propagation models

thermal and metamorphic environment of subduction zone episodic tremor and slip 1 episodic tremor and slip ets have been detected in the cascadia and southwest japan subduction zones where the subducting crust is relatively warm because of the young incoming lithosphere 20 ma and modest plate convergence rates 40 60 mm a in the southwest japan subduction zone low frequency earthquakes occur on the plate interface at depths of 30 35 km beneath shikoku where finite element thermal models predict temperatures of 425 c in the subducting oceanic crust and at depths of 30 40 km beneath the kii peninsula where predicted temperatures are 325 c warmer temperatures of 575 c are predicted at ets depths beneath southern vancouver island in the cascadia subduction zone but here tremor also occurs within the overlying fore arc crust where temperatures are lower in the southwest japan and cascadia subduction zones subducting oceanic crust passes through the blueschist greenschist and amphibolite metamorphic facies where mineral dehydration reactions are complex the different temperatures predicted for the two subduction zones suggest that ets does not coincide with a specific temperature or metamorphic reaction several lines of evidence indicate that a free h2o rich fluid is present at least transiently in subducting oceanic crust and fluids released by prograde metamorphic dehydration reactions may help trigger or enable ets within the subducting plate less clear is the role h2o may play in tremor observed in the cascadia fore arc crust where free h2o may exist locally in faults and fractures but retrograde hydration reactions are expected to consume h2o

infrasonic tremor observed at kīlauea volcano hawai i 1 infrasonic array data collected at k lauea volcano hawai i during november 12 21 2002 indicate that the active vents and lava tube system near the pu u vent complex emit almost continuous infrasound in the 0 3 10 hz frequency band the spectral content of these infrasonic signals matches well that of synchronous seismic tremor in sites protected from wind noise significant signal to noise ratios were recorded as far as 13 km from the crater of pu u the infrasonic recordings suggest that one or more tremor sources may be close to the surface in addition these results demonstrate that adequate site and instrument selections for infrasonic arrays are essential in order to obtain consistent and reliable infrasonic detections

granite intrusion in a metamorphic core complex the example of the mykonos laccolith cyclades greece abstract the aegean domain is a well suited place to study the formation of metamorphic core complex mcc and to investigate the role of syn tectonic granites on their development in the northern cyclades the mykonos delos rhenia mcc is characterized by the intrusion of a kilometer scale late miocene pluton of i type granitoids within a migmatitic gneiss dome new combined ams anisotropy of magnetic susceptibility and microstructural studies on the mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers the mykonos granitoids form a laccolith like intrusion with a n70 e long axis the laccolith is strongly asymmetric with an outlying root zone to the sw and a major body mainly developed to the ne the laccolith construction is due to successive pulses of more or less differentiated magma that intruded the cycladic blueschist unit the attitude of stretching markers suggests an important about 60 vertical axis local rotation phenomenon in the cycladic upper crust during the exhumation of the mykonos mcc structural data suggest a four stage evolution of the mykonos mcc i a first stage characterized by flat shearing toward the n ne and by the formation of a domal structure in migmatitic paragneisses with multi scale generation of folds with axes either perpendicular or parallel to the regional stretching as a result of the interplay between regional n20 e directed extension and ew shortening ii a second stage marked by the emplacement of the mykonos laccolith at 13 5 0 3 ma at the top of the migmatitic paragneisses iii the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions and iv the late stage marked by an acceleration of the exhumation of the mykonos mcc this exhumation was accommodated by important rotations of upper crustal blocks during the end of the exhumation processes around 10 ma deformation localized at the top of the laccolith in semi ductile conditions and then in brittle conditions in the major detachment plane our study shows that the cycladic plutonism event had no role on the initiation of the mcc however the geometry of the mykonos intrusion supports that the magmas are sucked into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the mcc development this acceleration was marked by a very fast exhumation of the laccolith after its emplacement

high broadband seismoacoustic signature of vulcanian explosions at popocatepetl volcano mexico author s matoza robin samuel arciniega ceballos a sanderson r w mendo perez g rosado fuentes a chouet b a

provenance of quartz rich metamorphic tectonite pebbles from the black flysch w pyrenees n spain an ebsd and detrital zircon la icp ms study abstract metasandstone and quartz tectonite conglomerate pebbles from the albian black flysch encapsulate evidence of pre mesozoic igneous and metamorphic events quartz deformation microstructures and crystallographic fabrics characterize plastic flow under sub greenschists 250 300 c to high grade metamorphic conditions above 550 600 c detrital zircon grains from the pebbles provide concordant 206pb 238u radiometric ages ranging from 473 26 ma to 2261 59 ma with four major populations clustered in the intervals 1 96 1 80 ga paleoproterozoic 1 11 0 93 ga stenian tonian 765 571 ma neoproterozoic and 500 475 ma cambro ordovician the youngest zircons and the probability distribution of the studied population permit us to establish an early ordovician maximum depositional age for tectonite pebble protoliths and relate them with the armorican quartzite detrital zircon signature we identify the currently submerged landes massif of the armorican platform as the most likely candidate to being the source of black flysch metamorphic conglomerate pebbles

a dynamic model of the structural evolution of the hercynian pyrenees abstract the structural history of the hercynian pyrenees is considered with respect to the relationships between the metamorphism and the successive deformations the characteristics and mode of emplacement of the gneissic and anatectic cores of the metamorphic domes the migmatization and the intrusions of plutonic and basic and ultrabasic rocks the metamorphism can be shown to have progressed upwards with time attaining the presently exposed levels just before during and a short time after the major penetrative regional deformation the intrusion of major plutonic anatectic and gneissic massifs which has determined the metamorphic domes in country rocks was roughly synchronous with the progression of the metamorphism but seems to have continued later in the uppermost levels the basic and ultrabasic rocks uplifted by the intrusion of the anatectic cores of the metamorphic domes have been deformed and foliated by the major regional penetrative deformation thus showing that their intrusion predated this deformation in the lowermost levels these results together with the presently available sedimentological data lead us to propose a dynamic model of the tectonic evolution of the hercynian pyrenees the first step was a crustal extension and thinning attaining its maximum during frasnian time marked in the upper levels by a horst and graben controlled sedimentation and in the lower crust by intrusions of basic magmas and the onset of the very low pressure metamorphism and anatexis characteristic of the hercynian pyrenees the second step was a crustal shortening marked by large scale crustal thrusting followed by widespread regional penetrative deformation the flysch troughs formed in front of the progressing and emerging thrusts in lower levels the thrusts are believed to have controlled the progressive ascent of the plutonic and anatectic magmas which continued their uplift and emplacement during major penetrative regional deformation in the actual mesozone and probably after it in the uppermost levels

polyphase magmatic pulses along the northern gondwana margin u pb zircon geochronology from gneiss domes of the pyrenees abstract alkaline granitic dikes intruding the metasedimentary mantle and orthogneiss cores of the aston and hospitalet domes of the axial zone of the pyrenees are subjects of a laser ablation icp ms u pb zircon geochronology study the age spectra recorded by detrital magmatic xenocrystic and inherited zircons reveal a more complex nearly continuous paleozoic magmatic history of the variscan basement of the pyrenees than previously known inherited and detrital zircons of mesoarchean paleoproterozoic to ediacaran ages attest to the peri gondwana location of the cambrian sediments that later form the metamorphic core of the variscan pyrenees the youngest magmatic zircon ages fall into the late carboniferous and earliest permian ranging from ca 306 297 ma and represent the emplacement ages of the dikes and small granite intrusions the age spectra of magmatic xenocrystic zircons contain several maxima middle 475 465 ma and late ordovician 455 445 ma early 415 402 ma and late devonian 385 383 ma early 356 351 ma and middle carboniferous ca 328 ma middle ordovician and middle carboniferous ages are obtained from xenocrystic zircons that were assimilated from the rocks the dikes intruded the aston and hospitalet orthogneisses and the soulcem granite the presence of early mid carboniferous magmatic zircons in several samples lends further support to a wide spread early variscan magmatic activity in the central pyrenees the other age peaks do not have equivalent igneous or metaigneous rocks in the central axial zone but are thought to be present in the pyrenean crust not exposed and yet to be identified the diversity of ordovician devonian and carboniferous up to permian magmatic ages indicates polyphase emplacement of intrusive bodies during pre variscan and variscan orogenies the source of the heat for the devonian to early mid carboniferous magmatic activity remains elusive and may involve intracontinental subduction zone lithospheric scale shearing or a mantle plume tuzo

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

magnetic fabric interpretation complicated by inclusions in mafic silicates abstract the expected relationships between anisotropy of low field magnetic susceptibility ams and crystal symmetry of mafic silicates are disturbed by the presence of magnetite inclusions measurements of ams anisotropy of anhysteretic remanence aarm and theoretically predicted bulk susceptibilities from chemical composition all favour the exercise of great caution in the interpretation of preferred orientation distributions of silicates from a rock s ams these results pertain mainly to the mafic silicates of lower crustal rocks pyroxene orthopyroxene amphibole and some of their low grade metamorphic alterations serpentine epidote

the shir kuh pluton central iran magnetic fabric evidences for the coalescence of magma batches during emplacement abstract the 136 ma nw se elongate shir kuh pluton is one of the most poorly understood geological feature of central iran it is composed of peraluminous rocks corresponding to ilmenite bearing s type granites compositionally ranging from granodiorites to leucogranites these rocks show a continuum in their chemistry attributed to progressive differentiation this allows using the anisotropy of magnetic susceptibility technique to tempt establishing the relative chronology between emplacements of magma batches in the pluton the rather low susceptibility magnitudes km

is there a time lag between the metamorphism and emplacement of plutons in the axial zone of the pyrenees detailed petrographic and geochemical studies conducted on zircons from the lys caillaouas pluton reveal their igneous and metamorphic affinities the igneous zircons constrain the emplacement of the pluton to 300 2 ma by contrast the metamorphic zircons yield an older age of 307 3 ma which probably dates the thermal peak of the ht lp variscan metamorphism therefore a short time lag of c 7 ma emerges between the metamorphic climax and emplacement of the pluton in the axial zone pyrenees

timing of formation and exhumation of the montagne noire double dome french massif central new u pb monazite zircon and xenotime ages date the late carboniferous crystallization of the anatectic vialais granite in the montagne noire axial zone and the high temperature deformation and metamorphism of the augen gneiss ordovician granite protolith from which the granite was likely derived the u pb monazite ages obtained from the augen gneiss 308 3 ma late kinematic vialais granite 303 4 ma and post kinematic leucogranite 298 2 ma bracket the high temperature deformation and metamorphism at 310 300 ma clearly postdating regional contraction and nappe emplacement 320 ma the planar linear and locally linear fabrics in the augen gneiss outline a regional scale double dome structure caroux and espinouse sub domes containing smaller km scale upright folds compared to the caroux sub dome the larger migmatitic espinouse sub dome contains abundant leucosome leucogranite bodies and late kinematic intrusions vialais granite the vialais granite displays a weak magmatic foliation that defines the main layering of the espinouse migmatite ellipsoidal quartz sillimanite nodules concentrated above the roof of the granite recorded an increment of strain vertical shortening e ne elongation during granite emplacement and crystallization consistent with the extension event that exhumed the domes these new geochronological and structural data suggest that the montagne noire double dome formed in a pull apart structure within a dextral strike slip system upright folding in the sub domes has been traditionally assigned to a regional contraction event alternatively we propose that local contraction is associated with the convergence of low viscosity crust beneath the upper crust pull apart dynamic models of extension of hot crust indicate that contraction at depth is generated by flow of low viscosity orogenic crust converging and rising to fill the gap created by upper crust extension this interpretation solves the long standing problem of apparent coeval contraction and extension in the montagne noire double dome and establishes migmatite dome emplacement in strike slip corridors as a style of late variscan tectonics

structural and magnetic fabric study of the marimanha granite axial zone of the pyrenees the structural and magnetic fabric study of the marimanha granite axial zone of the pyrenees provides new data to characterize the zonation and the internal structure of the pluton the marimanha granite intrudes cambro ordovician clastic rocks and silurian devonian limestones and slates the zonation of the low field magnetic susceptibility consistent with the petrological zonation of the igneous body indicates a concentric arrangement of rock types with more basic compositions at the external areas this pluton is characterized by a low susceptibility and rock magnetic studies indicate a majority of paramagnetic samples magnetic foliations strike parallel to petrographic contacts and to contours of zonation of magnetic susceptibility and show a dominant ne sw strike steeply dipping towards the north locally in the northern border of the pluton foliation directions become perpendicular to petrographic contacts and depict sigmoidal trajectories magnetic lineations are characterized by the predominance of ne sw trends with shallow plunges to the ne and sw these foliations and lineations are parallel to the slight elongation of internal petrographic zonation magnetic fabric within the granitoid body and internal elliptical shape of petrographic zonation suggest an intrusion contemporary with a transpressional regime and nnw sse shortening syntectonic with the late stages of the variscan orogeny these results are in accordance with anisotropy of magnetic susceptibility studies of others plutons in the pyrenees to explain the origin of the marimanha granite we propose magma ascent through faults at depth and emplacement by ballooning in situ at the rheological boundary between cambro ordovician and siluro devonian metasediments

timing of granite emplacement crustal flow and gneiss dome formation in the variscan segment of the pyrenees the variscan segment of the pyrenees is well suited to study the timing of crustal scale deformations as crustal flow and gneiss dome formation this has been constrained from a synthesis of available structural and geochronological data of intrusive rocks as well as new zircon u pb age determinations via laser ablation inductively coupled plasma mass spectrometry la icp ms after a stage of moderate thickening by fold thrust belt development in the upper crust between 323 and 308 ma the variscan segment of the pyrenees experienced crustal flow at c 306 ma and then gneiss dome formation at c 304 ma localization of the deformation along reverse dextral shear zones occurred at c 300 ma the variscan segment of the pyrenees recorded a high temperature regime which allowed crustal flow of the middle crust but with limited amounts of heat which induced rapid cooling the development of this enigmatic orogenic segment of the variscan belt is closely contemporaneous with the formation of the cantabrian orocline and could correspond to a lithospheric scale shear zone that accommodated buckling of the orocline late variscan lithospheric delamination and asthenospheric upwelling associated with buckling in the core of the cantabrian orocline could explain the short period high temperature regime in the variscan segment of the pyrenees

a new approach to modeling perpendicular fabrics in porphyritic plutonic rocks using the finite element method a growing body of field evidence indicates that hypersolidus fabrics preserved in syntectonic plutons are likely to have formed in highly crystallized rigid sponge magma this paper demonstrates that such magma could be idealized as a rheological solid and that the development of non coaxial fabrics in plutonic rocks can very conveniently be modeled in the framework of solid mechanics using the finite element method fem we modeled two strain regimes of small magnitudes plane strain horizontal simple shear with the shear strain of up to 0 30 and plane strain pure shear of up to 15 shortening superposed onto vertically oriented and variously spaced elastic phenocrysts set in the viscoelastic matrix in the simple shear regime the phenocrysts slightly rotate toward the shear plane while the principal strain directions in the matrix are instantaneously oriented at an angle of about 45 or less to the phenocryst fabric simple shear thus can only lead to the formation of oblique phenocryst and matrix fabrics by contrast the vertical phenocryst fabric is maintained in the pure shear regime and a new horizontal fabric can develop almost instantaneously in the matrix even for small amounts of superposed shortening 5 shortening after 10 ky in our model we conclude that such a mechanism can easily produce perpendicular hypersolidus fabrics in plutonic rocks and that only a very short time span first thousands of years is required to develop magmatic fabric in a pluton for normal rates 10 15 to 10 13 s 1 of tectonic deformation

an infrasound array study of mount st helens the ongoing activity of mount st helens provides an opportunity to study the infrasonic wavefield produced by an active silica rich volcano in late october 2004 as a pilot experiment for the acoustic surveillance for hazardous eruptions ashe project we deployed two infrasound arrays each co located with a broadband seismometer and weather station to continuously record seismo acoustic signals from mount st helens the nearest array coldwater was deployed on the northern flank of the volcano 13 km from the summit the second array sacajawea was deployed 250 km east of the volcano at a distance where stratospherically ducted acoustic waves may be expected during the winter this paper presents an overview of the experimental setup and preliminary results from this unique data set eruptions on january 16th 2005 and march 9th 2005 produced strong infrasonic signals the aseismic january 16th eruption signal lasted 9 4 min beginning at 11 20 44 01 16 05 utc while the march 9th eruption signal lasted 52 8 min beginning at 01 26 17 03 09 05 utc with the main steam and ash venting stage probably lasting 7 2 min the march 9th signal was an order of magnitude larger than the january 16th signal and was clearly recorded 250 km east at the sacajawea array infrasonic expressions of long period lp seismic events drumbeats have also been intermittently observed and are recorded as acoustic waves mimicking the waveform and temporal sequence of their seismic counterparts these acoustic observations provide important constraints for source models of long period events and eruptions

effusive to explosive transition during the 2003 eruption of stromboli volcano the persistent explosive activity of stromboli volcano italy ceased in december 2002 and correlated with the onset of a seven month long effusive eruption on the volcano flank from new vents that opened just below the summit craters we intensively monitored this effusive event collecting and interpreting in real time an extensive multiparametric geophysical data set the resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical strombolian activity we present a direct link between gas flux magma volume flux and seismicity supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity this insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity

deciphering relative timing of fabric development in granitoids with similar absolute ages based on ams study dharwar craton south india abstract anisotropy of magnetic susceptibility ams data are presented from the koppal granitoid dharwar craton south india that has u pb zircon age of 2528 9 ma the magnetic fabric is oriented in nne ssw direction this is parallel to the planar structures that developed during regional d 3 deformation but oblique to the nnw sse oriented magnetic foliation as well as field foliation d 1 d 2 deformation recorded in the country rock peninsular gneiss variation in the intensity of fabric within the granitoid is mapped it is inferred that the emplacement of koppal granitoid took place by ballooning and fabric development within the pluton was syntectonic with regional d 3 these results are compared with the time relationship between emplacement fabric development and regional deformation reported from the mulgund granite 2555 6 ma u pb zircon which is also located in the dharwar craton and is equivalent to the koppal granitoid in age this granite is known to have emplaced syntectonically with regional d 1 d 2 deformation and is thus not related to the same deformation event as the koppal granitoid despite their similar absolute ages it is argued that in the study area d 3 is 2537 ma while d 1 d 2 is 2549 ma in age thus this study highlights the use of ams in a deciphering the relative timing of regional deformation and emplacement of granitoids of equivalent age and b constraining the timing of regional superposed deformation events

noncoaxial k feldspar and ams subfabrics in the land s end granite cornwall evidence of magmatic fabric decoupling during late deformation and matrix crystallization 1 a comparative study of the anisotropy of magnetic susceptibility ams and k feldspar phenocryst fabrics in the land s end granite demonstrates that the ams fabric predominantly reflects late magmatic deformation tensor analysis of the k feldspar fabric shows a complex pattern characterized by meter scale variations in orientation symmetry and intensity mainly related to heterogeneous flow of the phenocryst rich magma during emplacement in contrast the ams fabric is predominantly homogenous subhorizontal and oblate and is stable at the pluton scale quantitative microstructural analysis suggests that the ams fabric is controlled by deformation of the partially crystallized matrix resulting from the combined effects of late internal adjustment within the pluton and regional deformation a general model of fabric development associated with a vertical pure shear overprint on a variable vertical fabric is evaluated by numerical modeling the study demonstrates how the memory of different fabric elements may be dependent upon their grain size crystallization sequence and recorded previous strain