impact of volcanic processes on the cryospheric system of the peteroa volcano andes of southern mendoza argentina abstract soil temperatures of the active volcanic complex peteroa situated in the cordillera principal between chile and argentina at 35 15 s and 70 35 w approximately were monitored in the area and local geomorphology periglacial geomorphology presence of permafrost and cryoforms was studied the present contribution also resulted in a comparison of two consecutive analyses of the volcano peak carried out with special thermocameras agema tvh 550 fur p660 in order to study the thermal range of different hot and cold sites selected in 2009 the thermocameras were used ascending by foot and also during flights with a cessna 180 a night expedition to the volcanic avalanche caldera at up to 3900 m asl approximately completed the monitoring activity of 2010 hot zones were associated to present volcanism and cold zones to the presence of glacier ice and shadowy slopes with possible presence of permafrost identifying and mapping uncovered and covered ice was possible with the help of monitoring and geomorphological interpretation related to the upper englacement which is severely affected by volcanism glaciers are retreating toward the north or approaching the rims of the volcanic avalanche caldera leaving islands of ice associated with superficial permafrost the cryogenic area with slope permafrost was identified through active protalus and sedimentary cryogenic slopes craters have undergone considerable thermal changes in comparison to the year 2009 and new much more vigorous fumaroles have appeared in hot areas detected in 2009 following a tendency toward the west new subaquatic heat columns that appeared in crater 3 crater walls and glaciated areas vanished supplying cold water and thus contributing to the formation of a new lake in crater 4 a possible post seismic shift of the volcanic activity may provide geodynamical evidence of the changes registered in other areas after the earthquake of 27 february 2010

volcano ice interactions precursory to the 2009 eruption of redoubt volcano alaska abstract in late summer of 2008 after nearly 20 years of quiescence redoubt volcano began to show signs of abnormal heat flow in its summit crater in the months that followed the excess heat triggered melting and ablation of redoubt s glaciers beginning at the summit and propagating to lower elevations as the unrest accelerated a variety of morphological changes were observed including the creation of ice cauldrons areas of wide spread subsidence punctures in the ice carved out by steam and deposition from debris flows in this paper we use visual observations satellite data and a high resolution digital elevation model of the volcanic edifice to calculate ice loss at redoubt as a function of time our aim is to establish from this time series a proxy for heat flow that can be compared to other data sets collected along the same time interval our study area consists of the drift glacier which flows from the summit crater down the volcano s north slope and makes up about one quarter of redoubt s total ice volume of 4 km 3 the upper part of the drift glacier covers the area of recent volcanism making this part of ice mass most susceptible to the effect of volcanic heating moreover melt water and other flows are channeled down the drift glacier drainage by topography leaving the remainder of redoubt s ice mantle relatively unaffected the rate of ice loss averaged around 0 1 m 3 s over the last four months of 2008 accelerated to over twenty times this value by february 2009 and peaked at greater than 22 m 3 s just prior to the first major explosion on march 22 2009 we estimate a cumulative ice loss over this period of about 35 million cubic meters m m 3

shallow magma transport for the 2002 3 mt etna eruption inferred from thermal infrared surveys abstract the 26 october 2002 28 january 2003 eruption of mt etna volcano was characterised by lava effusion and by an uncommon explosivity along a 1 km long eruptive fissure on the southern upper flank of the volcano the intense activity promoted rapid growth of cinder cones and several effusive vents analysis of thermal images recorded throughout the eruption allowed investigation of the distribution of vents along the eruptive fissure and of the nature of explosive activity the spatial and temporal distribution of active vents revealed phases of dike intrusion expansion geometric stabilization and drainage these phases were characterised by different styles of explosive activity with a gradual transition from fire fountaining through transitional phases to mild strombolian activity and ending with non explosive lava effusion here we interpret the mechanisms of the dike emplacement and the eruptive dynamics according to changes in the eruptive style vent morphology and apparent temperature variations at vents detected through thermal imaging this is the first time that dike emplacement and eruptive activity have been tracked using a handheld thermal camera and we believe that its use was crucial to gain a detailed understanding of the eruptive event

birth growth and morphologic evolution of the laghetto cinder cone during the 2001 etna eruption we have undertaken detailed observations of the formation of the laghetto cinder cone a new cone that formed during a 2 week period of intense activity in piano del lago on the upper slopes of mount etna in summer 2001 we describe the events leading to the formation of a small graben the formation of pit craters on the base of the graben the onset of phreatomagmatic activity a transition to intense strombolian activity and a return to phreatomagmatic activity as the eruption came to an end we discuss the reasons for these transitions and describe the morphological development of the cone during these events arcuate cracks on the southern part of the cone were related to withdrawal of magma at the end of the eruption other slope instabilities that developed during the eruption include the formation of small radial grain flows on the outer flanks of the cone and the collapse into the crater of part of the crater rim some of the failure planes we observed were first identified using a flir tm 695 thermal infrared camera this is the first time that infrared thermography has been used to detect instability of volcanic structures results obtained during this test case demonstrate that thermal cameras are a very useful tool for studies of volcanic instability

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

geochemistry of the active azufre planchon peteroa volcanic complex chile 35 15 s evidence for multiple sources and processes in a cordilleran arc magmatic system

the significance of intergranular diffusion to the mechanisms and kinetics of porphyroblast crystallization the spatial disposition compositional zoning profiles and size distributions of garnet crystals in 11 specimens of pelitic schist from the picuris range of new mexico usa demonstrate that the kinetics of intergranular diffusion controlled the nucleation and growth mechanisms of porphyroblasts in these rocks an ordered disposition of garnet centers and a significant correlation between crystal radius and near neighbor distances manifest suppressed nucleation of new crystals in diffusionally depleted zones surrounding pre existing crystals compositional zoning profiles require diffusionally controlled growth the rate of which increases exponentially as temperature increases with time an acceleration factor for growth rate can be estimated from a comparison of compositional profiles for crystals of different sizes in each specimen crystal size distributions are interpreted as the result of nucleation rates that accelerate exponentially with increasing temperature early in the crystallization process but decline in the later stages because of suppression effects in the vicinity of earlier formed nuclei simulations of porphyroblast crystallization based upon thermally accelerated diffusionally influenced nucleation kinetics and diffusionally controlled growth kinetics quantitatively replicate textural relations in the rocks the simulations employ only two variable parameters which are evaluated by fitting of crystal size distributions both have physical significance the first is an acceleration factor for nucleation with a magnitude reflecting the prograde increase during the nucleation interval of the chemical affinity for the reaction in undepleted regions of the rock the second is a measure of the relative sizes of the porphyroblast and the diffusionally depleted zone surrounding it crystal size distributions for the picuris range garnets correspond very closely to those in the literature from a variety of other localities for garnet and other minerals the same kinetic model accounts quantitatively for crystal size distributions of porphyroblastic garnet phlogopite sphene and pyroxene in rocks from both regional and contact metamorphic occurrences these commonalities indicate that intergranular diffusion may be the dominant kinetic factor in the crystallization of porphyroblasts in a wide variety of metamorphic environments

combining ash analyses with remote sensing to identify juvenile magma involvement and fragmentation mechanisms during the 2018 19 small eruption of peteroa volcano southern andes abstract the planchon peteroa volcanic complex ppvc is located on the border of chile and argentina and is one of the most active volcanic systems in the andes holocene activity has included magma water interaction with an evolving series of crater lakes mainly sourced from peteroa volcano this study examines data from the 2018 19 eruption together with the volcanic history of the ppvc to elucidate the complex interplay between magmatic activity and summit water and ice from february 2016 to mid 2019 three seismic swarms occurred in the ppvc preceding the explosive eruption from september 2018 to april 2019 the activity originated from a small vent nested within the easternmost crater the most active portion of the complex peteroa the explosions interacted with a crater lake producing ash plumes up to 2 km above the crater and building a small tephra cone to investigate the eruption mechanisms we performed remote sensing analysis of plume dispersal thermal anomalies and ground deformation and characterized the volcanic products including grain size componentry morphology internal textures composition and mineralogy our results suggest that the precursory seismicity beginning in 2016 was related to the intrusion of a new magma batch that reached the surface during the 2018 19 eruption the eruption was also preceded by thermal anomalies geomorphic changes and increased hydrothermal activity at the surface though without any ground deformation recognized through radar interferometry insar the eruption initially produced predominantly recycled ash phreatic activity then evolved to increasing proportions of juvenile magma phreatomagmatic by april 2019 the juvenile clasts had a trachyandesite composition 59 wt sio2 with vesicular and dense scoria containing plagioclase and pyroxene the ash surfaces show external quenching cracks and step fractures consistent with phreatomagmatic fragmentation within the active crater lake textural characteristics also point to a slowly ascending batch of magma that was relatively viscous by the time it interacted with water in the crater lake notably these juvenile particles are distinctive from the pre 2018 products ash erupted from 2010 11 did not contain recognizable juvenile material and is inferred to have been a mainly phreatic eruption our findings suggest that the interplay between phreatic and phreatomagmatic eruptions fed by small magma batches intruding at shallow levels characterize much of the eruptive behavior of the ppvc during the last three decades multi parametric assessment is a powerful tool to discriminate between phreatic and phreatomagmatic eruptions

the little ice age glacier advance in the central andes 35 s argentina abstract this paper documents the occurrence of the little ice age lia in the el azufre and el penon glaciers at 35 s and in the las choicas and las damas glaciers at 34 55 s in the headwaters of the rio grande basin in the central andes of argentina moraine morphology stratigraphic relationships radiocarbon ages obtained from peat on these glacial deposits and the proximity to the active glaciers enabled us to reconstruct the lia advance in this area the lia maximum advance occurred between cal yr 1550 and 1720 ad and a readvance occurred around cal yr 1830 ad in addition glacier fluctuations of the las vacas and gussfeltd glaciers 33 s and el penon and el azufre glaciers were documented from the end of the 19th century to the present based on historical and aerial photographs and satellite images the glaciers showed a marked retreat during 1894 2007 minor readvances occurred in the 1980s and 1990s which could be related with strong warm enso events during these decades our results are consistent with observations made by other authors in the region

deflection of paleomagnetic directions due to magnetization of the underlying terrain in the summers of 1989 and 1991 we made 344 near ground level measurements of the ambient geomagnetic field above recent basalts on the island of hawaii using a three component fluxgate magnetometer we studied 12 surface features including a lava pond lava channels long tilted blocks smooth sloping surfaces two fissures and a deep u shaped road cut we observed substantial differences up to 20 between the observed and expected international geomagnetic reference field igrf magnetic field directions over these features except those composed of shelly pahoehoe and a flat horizontally thin lava pond we also observed inclinations that were systematically shallower than the igrf field by up to 5 we show that these shallower inclinations can be explained by the magnetization of the regionally sloping surface of the southern side of the island we found that all of the observed inclination deflections can be explained by simple two dimensional models which assume uniform induced and remanent magnetization parameters in the local terrain our observations imply that the inclination deflections cannot be corrected without a complete knowledge of the preexisting terrain and the remanence in the underlying flows upon which the lavas cooled since this information is rarely available it is difficult or impossible to discriminate between dispersion of paleomagnetic directions caused by the magnetic terrain effect and dispersion due to other factors such as paleosecular variation psv we therefore conclude that psv dispersion parameters cannot be accurately determined from paleomagnetic measurements on highly magnetic volcanic flows we also suggest that some of the geomagnetic excursions inferred from measurements on volcanic rocks may be at least in part due to the magnetic terrain effect it is unnecessary to invoke ad hoc mechanisms such as clastic block or crustal rotations distortion of the top crust or flow deformation to explain the large between site dispersions or inclination anomalies observed in many of the paleomagnetic data from volcanic rocks our observations also bring into question the general reliability of paleomagnetic pole positions inferred from volcanic rocks as a systematic inclination deflection due to local and regional slopes and irregular terrain such as those we observed would lead to a corresponding error in the inferred paleolatitude the magnetic terrain effects also offer alternative explanations for anomalous paleomagnetically inferred plate motions

geochemistry of fluid discharges from peteroa volcano argentina chile in 2010 2015 insights into compositional changes related to the fluid source region s abstract this study presents the first geochemical data of fluid discharges collected from february 2010 to march 2015 from the planchon peteroa azufre volcanic complex ppavc located in the transitional southern volcanic zone tsvz at the border between argentina and chile during the study period from january 2010 to july 2011 peteroa volcano experienced phreatic to phreatomagmatic eruption possibly related to the devastating maule earthquake occurred on february 27 2010 the compositional dataset includes low temperature from 43 2 to 102 c gas discharges from i the summit of peteroa volcano and ii the se flank of azufre volcano both marked by a significant magmatic fluid contribution as well as bubbling gases located at the foothill of the peteroa volcanic edifice which showed a chemical signature typical of hydrothermal fluids in 2012 strong compositional changes affected the peteroa gases from the summit area the acidic gas species especially so 2 increased suggesting an input of fluids from magma degassing nevertheless the r ra and 13 c co 2 values decreased which would imply an enhanced contribution from a meteoric hydrothermal source in 2014 2015 the chemical and isotopic compositions of the 2010 2011 gases were partially restored the anomalous decoupling between the chemical and the isotopic parameters was tentatively interpreted as produced by degassing activity from a small batch of dacitic magma that in 2012 masked the compositional signature of the magmatic fluids released from a basaltic magma that dominated the gas chemistry in 2010 2011 this explanation reliably justifies the observed geochemical data although the mechanisms leading to the change in time of the dominating magmatic fluid source are not clear at this regard a geophysical survey able to provide information on the location of the two magma batches could be useful to clarify the possible relationships between the compositional changes that affected the peteroa fluid discharges and the 2010 2011 eruptive activity

evidence for late paleozoic and mesozoic non dipole fields provides an explanation for the pangea reconstruction problems abstract paleomagnetic pole positions have long been calculated with the assumption that the ancient geomagnetic field was purely that of a geocentric dipole but in recent years it has become a concern that this assumption is not always valid because of long term contributions from non dipole fields in particular octupole fields we tested for the presence of a zonal octupole field in the late carboniferous permian mesozoic and early tertiary by comparing the observed paleomagnetic paleolatitude distributions for the laurentian north america and greenland and european landmasses with those predicted from the mean paleopoles such a test is possible for a good sized continent not subsequently deformed when numerous and reliable paleomagnetic results exist from sites that cover a wide range of paleolatitudes if the field were purely dipolar coeval results should form a coherent dataset such that a regression line through the individual points in an observed versus predicted paleolatitude plot has a slope of 1 if the slopes of regression lines are systematically different from 1 0 for successive time intervals and granted that the earth s radius stayed the same then it is likely that non dipole fields can be held responsible regression line slopes standard errors for three intervals analyzed are 0 78 0 04 200 300 ma 0 93 0 11 120 200 ma and 0 82 0 06 40 120 ma as might be expected with a non dipole contribution to the total geomagnetic field paleomagnetic results from the most northerly areas of laurentia and europe i e ellesmere greenland and svalbard show clearly anomalous paleolatitudes because of the agreement between the equatorial locations determined independently by paleomagnetism and equatorial rain forest occurrences d v kent p e olsen earth planet sci lett 179 2000 311 324 we argue that long term quadrupole fields are less likely than octupole fields to be the cause of the paleolatitude discrepancies estimates of the magnitude of the octupole dipole field ratio are not very precise but center around 0 1 which could cause errors in conventional paleopole determinations using the dipole formula of 7 5 because of the antisymmetry of octupole fields a comparison of paleomagnetic poles from mid northern and mid southern hemisphere locations could thus be off by as much as 15 the well known misfit between the paleomagnetic results from the laurentia european and gondwana continents in a classical pangea a configuration could be explained by such errors due to octupole fields this explanation would negate the need to seek tectonic pangea b type solutions for the misfit these solutions have generally remained unacceptable in terms of the geology of the gondwana laurussia borderzone

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

high resolution satellite and airborne thermal infrared imaging of precursory unrest and 2009 eruption at redoubt volcano alaska abstract a combination of satellite and airborne high resolution visible and thermal infrared tir image data detected and measured changes at redoubt volcano during the 2008 2009 unrest and eruption the tir sensors detected persistent elevated temperatures at summit ice melt holes as seismicity and gas emissions increased in late 2008 to march 2009 a phreatic explosion on 15 march was followed by more than 19 magmatic explosive events from 23 march to 4 april that produced high altitude ash clouds and large lahars two or three lava domes extruded and were destroyed between 23 march and 4 april after 4 april the eruption extruded a large lava dome that continued to grow until at least early july 2009

palaeomagnetic distortion modelling and possible recovery by inversion abstract a robust finite element technique is presented for computation of both the internal demagnetization effects and magnetic terrain effects in bodies with arbitrary shape and arbitrary susceptibility distribution this method facilitates a flexible analysis of the palaeomagnetic deflection problem tests on geologically realistic settings of highly magnetic rocks demonstrate that deflections of several degrees may occur even for relatively simple two dimensional models similarly the magnetic intensity may well be biased by 5 15 by demagnetization effects the present paper focuses on deflections and intensity variations inside the magnetized body where we find a systematic shallowing of inclination for bodies with a horizontal elongation because the bodies sampled at a typical palaeomagnetic site will have a dominant direction of elongation the magnetic deflection effect will tend to impose a systematic bias which doesn t average out an inversion based procedure for elimination of the deflection effect is presented it requires that the magnetic body is quite homogeneous and that its surface geometry is known as may be the case for historical lava flows tests demonstrate that in order to recover both ambient palaeofield direction and the effective susceptibility at blocking temperature it is necessary to sample near strong topographic elements in the magnetic body since the surface geometry rarely is known it is proposed as an alternative to inversion that an effective susceptibility is assessed and a horizontal slab correction is applied for samples taken far from topographical features when shape geometry is unknown and no correction applied palaeomagnetic conclusions must take into account the possible bias from internal demagnetization and magnetic terrain effects

coseismic slip distribution of the february 27 2010 mw 8 8 maule chile earthquake 1 static offsets produced by the february 27 2010 mw 8 8 maule chile earthquake as measured by gps and insar constrain coseismic slip along a section of the andean megathrust of dimensions 650 km in length 180 km in width gps data have been collected from both campaign and continuous sites sampling both the near field and far field alos palsar data from several ascending and descending tracks constrain the near field crustal deformation inversions of the geodetic data for distributed slip on the megathrust reveal a pronounced slip maximum of order 15 m at 15 25 km depth on the megathrust offshore lloca indicating that seismic slip was greatest north of the epicenter of the bilaterally propagating rupture a secondary slip maximum appears at depth 25 km on the megathrust just west of concepcion coseismic slip is negligible below 35 km depth estimates of the seismic moment based on different datasets and modeling approaches vary from 1 8 to 2 6 1022 n m our study is the first to model the static displacement field using a layered spherical earth model allowing us to incorporate both near field and far field static displacements in a consistent manner the obtained seismic moment of 1 97 1022 n m corresponding to a moment magnitude of 8 8 is similar to that obtained by previous seismic and geodetic inversions

structure of the carrizo mountain group southeastern carrizo mountains west texas a transpressional zone of the grenville orogen 1 the west texas segment of the grenville orogen includes an oblique dextral transpressive zone the orogen exposed near van horn texas displays a transition from the mid amphibolite facies metamorphic core to a foreland fold and thrust belt in this paper detailed structural mapping and analyses presented for key exposures of the metamorphic rocks the mesoproterozoic carrizo mountain group show a southeastward increase in number of deformational phases and intensity of deformation the central portion is dominated by oblique northwest convergence which produced two phases of northwest verging folds and synchronous oblique reverse and dextral shearing the thick parts of pre tectonic mafic plutons which had been emplaced as locally discordant sills control the spatial distribution of structures two dominant phases of folds form type 0 interference patterns essentially coaxial and coplanar i e fold tightening was dominant this central belt also contains en echelon reverse to oblique shear zones and comprises a transfer zone within the orogen between structurally higher and lower major shear zones overall the mapped part of the central carrizo mountains represents localized dextral transpression within a larger region dominated by reverse motion possibly indicating a change through time from orthogonal to oblique contraction further south in the bass canyon region the earlier fold generations are refolded into type 2 mushroom interference patterns these structures show a westward vergence and are kinematically linked to those further north across a zone of disharmonic folding and heterogeneous shear the structure and kinematics of the polyphase deformation and ductile shearing in the metamorphic portion of the orogen is compatible with that seen in the foreland fold thrust belt suggesting that in both foreland and hinterland transpression was a characteristic feature of the west texas grenville orogeny the timing and kinematics of deformation in the van horn exposures contrasts with that seen in the llano uplift but compares favorably with those of the natal belt south africa a relationship with implications for recently proposed reconstructions of rodinia

magnetic anomalies of lava fields in the canary islands possible consequences for paleomagnetic records abstract measurements of the total magnetic field have been performed above the surface of 12 lava flows in the canary islands of la palma and tenerife directions can differ by up to 15 and intensity changes reach 20 the mean flow directions do not coincide and the mean flow virtual dipole moments vdms differ by more than 10 the deviations are linked to topographic features at the surface of the flows and should persist during emplacement of the next overlying flow such effects can thus limit the resolution of paleomagnetic records of detailed geomagnetic features and the field intensity variations above the flows and between the mean flow values could explain a significant part of the scatter inherent to many paleointensity studies historical field variations have been recorded from the same flows and are in agreement with the european curve for the same period however there is also some correlation with the present field which suggest that the underlying magnetized bodies could have affected the paleomagnetic records biases induced by the crustal field would increase considerably during periods of reduced field intensity like during reversals and induce erroneous records samplings performed over large distances within each lava flow would provide the best way to average out the contribution of the anomalies in any case such effects should not be neglected in paleomagnetic studies

magnetic and compositional variations in proterozoic mafic dykes in finland northern fennoscandian shield proterozoic mafic dykes of both tholeiitic basaltic and more magnesian compositions from four areas in finland have been studied for their magnetic and compositional variations to explain the varia

a comparative study of diffusion profiles in himalayan and dalradian garnets constraints on diffusion data and the relative duration of the metamorphic events cation diffusion rates at 690 30 c have been calculated by inverse modelling of observed manganese mn zonation profiles in 40 garnets from two kyanite bearing metapelite samples from the high himalayan crystalline series zanskar northwest india knowledge of the initial growth profile of mn in garnet is a pre requisite for this technique following previous workers we model mn partitioning into growing garnet in terms of a rayleigh fractionation process and demonstrate that the mngarnet whole rock partition coefficient is 60 100 three dimensional zonation profiles were obtained by successively grinding and polishing 1 cm slabs of each sample at 0 1 0 2 mm intervals and analysing the garnets at each stage thus ensuring that core sections were measured the diffusion model assumes that garnet has a spherical geometry and behaves as a closed system and simulates diffusive modification of the hypothetical mn rayleigh growth profile for each garnet the derived measure of the time integrated diffusion history for each garnet is then combined with radiometric and field relation constraints for the duration of the himalayan metamorphic event to calculate cation diffusion rates the average cation interdiffusion rate calculated for garnets in the two samples examined is 6 3 2 10 23 m2s 1 this interdiffusion rate pertains to a temperature of 690 30 c which is 0 97 t peak the peak temperature conditions experienced by the samples estimated using standard thermobarometric techniques garnet compositions are py2 17alm65 77gro6 16sp1 17 these new diffusion data are consistent with and more precise than existing high temperature 1000 c experimentally determined diffusion data although some uncertainties remain difficult to constrain qualitative comparison between diffusively modified mn growth profiles in garnets from the scottish dalradian and the himalayan garnets suggests that the duration of metamorphism affecting the dalradian garnets was 10 20 times longer than that endured by the himalayan garnets

grenville age polyphase deformation of mid proterozoic basement nw van horn mountains trans pecos texas psammitic pelitic and mafic schists in a basement horst in the nw van horn mountains of west texas preserve evidence of a multiphase synmetamorphic grenville age ductile deformation three phases of progressive isoclinal folding followed by two later less intense nearly coaxial folding phases have been identified the second phase of deformation produced the dominant foliation and foliatipn intersection lineation observed throughout the area this deformation is inferred to have resulted from a regional scale folding possibly associated with nappe formation at or near peak metamorphic conditions mineral assemblages indicate amphibolite facies and fe mg exchange thermometry provide maximum temperatures of 640 pm 50 circ c corresponding to mid amphibolite facies conditions three subsequent fold generations f 3 f 5 formed under progressively lower metamorphic conditions f 3 produced a weakly developed foliation s 3 whereas neither of the two later folding phases fo

the time averaged paleomagnetic field 0 5 ma persistent departures from the geocentric axial dipole field model of the time averaged paleomagnetic field over the past 5 myr have been analyzed using oceanic data from deep sea cores and continental data from igneous rocks and sediments the data set comprises the equivalent of 9490 spot readings of the field 5831 normal and 3659 reverse from 930 groups of data variations in declination anomalies between groups of data strongly suggest the existence of second order tectonic effects small rotations that make it difficult if not impossible to identify any nonzonal terms that might exist inclination anomalies have therefore been modeled in terms of low degree zonal harmonics the calculated inclination anomalies within 10 latitude bands are widely scattered for both oceanic and continental data and do not appear to have been drawn from distributions with common means we attribute this large scatter to previously undetected or uncorrected second order tectonic effects in the continental data or in the oceanic data to small departures from the vertical in deep sea cores if it is assumed that these effects are random between groups of data and without a systematic bias they can be averaged out to a large extent if there are sufficient numbers of groups within each latitude band this method also has the major advantage that it maximizes time averaging of the field when this is done an acceptable fit to the inclination anomaly data is found using a zonal harmonic model although the point estimates for the reverse polarity zonal quadrupole term are consistently larger than those for the normal polarity zonal quadrupole term the difference is not significant and is likely due to contamination effects this finding is true for a combination of all the data or for separate combinations of continental igneous rocks and ocean sediments this conclusion differs from all previous analyses the major differences occur in model estimates of the zonal octupole term the estimates varying widely depending on the particular data combination we show that false octupole terms can be introduced by several factors including inclination errors in sediments and lavas the use of unit vectors in the analyses and incomplete magnetic cleaning particularly of reversely magnetized rocks thus we cannot impute a geomagnetic significance to the estimates of a zonal octupole term we suggest that the best estimates for the zonal quadrupole g2 g20 g10 are obtained from the combined brunhes age igneous rocks and oceanic normal data 0 033 0 019 and for the combined matuyama age igneous rocks and oceanic reverse data 0 042 0 022 when these two sets are combined the overall best estimate of g2 is 0 038 0 012

unbiased analysis of geomagnetic data sets and comparison of historical data with paleomagnetic and archeomagnetic records reconstructions of the past geomagnetic field provide fundamental constraints for understanding the dynamics of the earth s interior as well as serving as basis for magnetostratigraphic and archeomagnetic dating tools such reconstructions when extending over epochs that precede the advent of instrumental measurements rely exclusively on magnetic records from archeological artifacts and farther in the past from rocks and sediments the most critical component of such indirect records is field intensity because of possible biases introduced by material properties and by laboratory protocols which do not reproduce exactly the original field recording conditions large biases are usually avoided by the use of appropriate checking procedures however smaller ones can remain undetected in individual studies and might significantly affect field reconstructions we introduce a new general approach for analyzing geomagnetic databases in order to investigate the reliability of indirect records this approach is based on the comparison of historical records with archeomagnetic and volcanic data considering temporal and spatial mismatches with adequate weighting functions and error estimation a good overall agreement is found between indirect records and historical measurements while for several subsets systematic bias is detected e g inclination shallowing of lava records we also demonstrate that simple approaches to analyzing highly inhomogeneous and internally correlated paleomagnetic datasets can lead to incorrect conclusions about the efficiency of quality checks and corrections consistent criteria for selecting and weighting data are presented in this review and can be used to improve current geomagnetic field modeling techniques

volcano surveillance using infrared cameras abstract volcanic eruptions are commonly preceded accompanied and followed by variations of a number of detectable geophysical and geochemical manifestations many remote sensing techniques have been applied to tracking anomalies and eruptive precursors and monitoring ongoing volcanic eruptions offering obvious advantages over in situ techniques especially during hazardous activity whilst spaceborne instruments provide a distinct advantage for collecting data remotely in this regard they still cannot match the spatial detail or time resolution achievable using portable imagers on the ground or aircraft hand held infrared camera technology has advanced significantly over the last decade resulting in a proliferation of commercially available instruments such that volcano observatories are increasingly implementing them in monitoring efforts improved thermal surveillance of active volcanoes has not only enhanced hazard assessment but it has contributed substantially to understanding a variety of volcanic processes drawing on over a decade of operational volcano surveillance in italy we provide here a critical review of the application of infrared thermal cameras to volcano monitoring following a summary of key physical principles instrument capabilities and the practicalities and methods of data collection we discuss the types of information that can be retrieved from thermal imagery and what they have contributed to hazard assessment and risk management and to physical volcanology with continued developments in thermal imager technology and lower instrument costs there will be increasing opportunity to gather valuable observations of volcanoes it is thus timely to review the state of the art and we hope thereby to stimulate further research and innovation in this area

plate tectonics model for proterozoic continental accretion in the southwestern united states proterozoic crustal provinces in the southwestern united states decrease in age south from the archean wyoming province supracrustal rocks define three major age provinces from north to south 1 72 to 1 80 1 65 to 1 72 and 1 1 to 1 2 b y successions within each province are similar and define two assemblages a bimodal volcanic assemblage commonly overlain by a quartzite shale assemblage precambrian granitic plutons intrude all three provinces geochemical and sr isotope data indicate a variably depleted upper mantle source for basalts and a short lived these observations can be explained by a plate tectonics model involving successive marginal basin closures and andean type orogenies associated with southward migrating arcs the net result is to accrete 1 300 km of continental crust to the southwestern margin of north america between 1 8 and 1 1 b y ago

thermochronology of the grenville orogeny in west texas abstract the carrizo mountain group cmg comprises the westernmost exposures of the metamorphic core of the grenville orogen in texas unlike the correlative llano uplift 500 km to the east the cmg underwent one phase of medium p t metamorphism peak t was attained during d2 in all cmg exposures the peak metamorphic paleotemperatures decrease to the northwest in the overall direction of tectonic transport from staurolite to biotite grade garnet in the southeast carrizo mountains grew isothermally and probably during decompression i e part of a clockwise p t loop at ca 520 c in between biotite grade d1 and d3 events hornblende in this region cooled below closure t during d2 at 1057 6 ma within error of muscovite closure in the northwest carrizo mountains at 1059 2 ma hornblende in higher grade exposures to the southeast cooled through closure t as late as 1002 7 ma muscovite in the garnet grade and higher exposures closed to ar diffusion at 992 4 ma to 981 3 ma biotite and partially recrystallized hornblende from the northwest carrizo mountains cooled through closure in this same time period we interpret these data as signifying 1 ar loss due to peak metamorphism in hornblende southeast carrizo mountains and muscovite northwest carrizo mountains at ca 1059 ma 2 post tmax cooling through 500 c in the higher grade outcrops until ca 1000 ma and 3 cooling of all cmg exposures through 300 c due to uplift along the streeruwitz thrust and erosion from 1000 to 980 ma these ages significantly post date known tectonism in the llano uplift and extend the duration of grenville orogenesis in texas by ca 115 million years the 1000 980 ma time period is a time of thrusting in frontal regions of the grenville province of canada and the northeastern us and shearing in the natal province south africa suggesting ultimate closure of the grenville orogen and supporting recent rodinia reconstructions

the metamorphic architecture of a transpressional orogen the kaoko belt namibia s 64 61 goscombe b hand m 2001b metamorphic model for the inland branch of the damara orogen a paired metamorphic mountain belt pmmb geological society of australia specialist group in tectonics and structural geology conference ulverstone

seismic scattering in the upper crystalline crust based on evidence from sonic logs summary evidence from sonic logs indicates that velocity fluctuations in the upper crystalline crust are remarkably uniform this motivates a generic approach to classifying uppercrustal seismic heterogeneity and to studying implications for seismic wave propagation the resulting canonical model of upper crustal seismic structure is characterized by a spatially isotropic von karman autocovariance function with a z 100 m 0 15 and cj 300 m s small angle scattering theory is used to predict the transition from weak to strong scattering as well as phase fluctuations and scattering attenuation compared with exponential random media v 0 50 the high fractal dimension i e small values of v of upper crustal heterogeneity causes smaller phase fluctuations and transition from weak to strong scattering at lower frequencies and shorter path lengths acoustic finite difference modelling shows that seismic reflections from deterministic features surrounded by heterogeneities are severely degraded when they fall into the strong scattering regime conversely traveltime fluctuations of transmitted waves are found to be relatively insensitive to the transition from weak to strong scattering upper crustal scattering q is predicted to lie between 600 and 1500 which is one to two orders of magnitude higher than q values inferred from seismic data this suggests that seismic attenuation in the upper crystalline crust is dominated by anelastic effects rather than by scattering

statistical analysis of palaeomagnetic data from the last four centuries evidence of systematic inclination shallowing in lava flow records the main objective of this work is to compare directional declination and inclination volcanic and archaeomagnetic data for the last four centuries 1600 1990 with the historical geomagnetic predictions given by the gufm1 model which spans from 1590 to 1990 the results show statistical agreement between archaeomagnetic data and directions given by the geomagnetic field model however when comparing the volcanic data with the model predictions marked inclination shallowing is observed this systematically lower inclination has already been observed in local palaeomagnetic studies italy mexico and hawaii for the 20th century by comparing recent lava flows with the international reference geomagnetic field igrf model here we show how this inclination shallowing is statistically present at worldwide scale for the last 400 years with mean inclination deviation around 3 lower than the historical geomagnetic field model predictions

late mesoproterozoic deformation of sw amazonia rondonia brazil geochronological and structural evidence for collision with southern laurentia abstract proposed assembly of the rodinia supercontinent in the late mesoproterozoic involved the collision of the amazon craton with some portion of the southern or eastern margin of cratonic north america previously reported paleomagnetic data from the sw amazon craton suggest a paleogeographic link between grenvillian deformation of the sw amazon craton and late mesoproterozoic tectonometamorphism in southern laurentia a structural geochronological and petrological investigation of the western amazon basement rocks rondonia brazil was carried out in order to document evidence of a grenvillian collision connecting the amazon to laurentia integration of 40ar 39ar data and feldspar thermometry data from regionally extensive strike slip mylonitic shear zones ji parana shear zone network indicates that deformation took place at 450 550 c between 1 18 and 1 15 ga an older ca 1 35 ga event found exclusively in less deformed basement rocks is interpreted as recording cooling from an earlier met