magmatic epidote and its petrologic significance epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the mesozoic accreted terranes between northern california and southeastern alaska textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase the observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure plutonic rocks bearing magmatic epidote must have formed under moderately high pressures corresponding to lower crustal depths under fairly oxidizing conditions

lightning associated with the 1992 eruptions of crater peak mount spurr volcano alaska abstract lightning occurred associated with the ash clouds of all three eruptions of mt spurr volcano in 1992 lightning was detected on seismograms as simultaneous spikes and simultaneous gain ranging a feature that normally lowers the gain at a station when the signal level begins to saturate spikes had typical durations of 0 04 0 05 s using uniform criteria we found 28 lightning flashes in the june 27th eruption 29 in the august 18th eruption and three in the september 17th eruption we measured peak voltages on station rso 94 km ssw to determine the relative strengths of lightning and found that the august lightning was strongest june weakest and september intermediate based on relative signal strengths at different stations we found evidence for different lightning geometries between the june and august eruptions during which prevailing winds blew the ash clouds to the north and east respectively for all three eruptions the first lightning was recorded 21 26 min after the onset of the eruption suggesting that charge separation occurred in the convecting cloud rather than at the vent data recorded by a bureau of land management lightning detection system for the august eruption showed negative polarities for the first 12 recorded flashes and a positive polarity for the last this suggests a charge separation based on particle size in which negative charge is found for larger particles which fall first and positive charge remains on smaller particles which remain suspended longer all three eruptions had similar durations of 3 5 4 h and tephra volumes of 44 56 million cubic meters the august eruption however produced stronger volcanic tremor 30 cm2 reduced displacement as compared with 16 cm2 for june and greater gas 400 120 kt so2 for august and 200 60 kt for june thus lightning strength correlates with both tremor amplitude and magmatic gas content the august eruption occurred during the lightest winds so the ash cloud and charge separation were vertically oriented and favored cloud to ground lightning the september eruption occurred during the coldest and driest atmospheric conditions which may explain the small amount of lightning in general volcanic lightning is important because it can help confirm that explosive eruptions are in progress although the value of the information may be limited by the long delay from eruption onset to first lightning and the variability of eruptive and atmospheric conditions

disequilibrium melting of granite at the contact with a basic plug a geochemical and petrographic study mantle derived intrusions are potentially an important source of heat for melting in the crust yet there are few studies of anatectic melts occurring at the contacts of such intrusions to provide natural analogs this is a study of anatectic melts developed in a cretaceous granite at the contact with a 12 ma trachyan desite plug in the sierra nevada batholith california where a detailed textural and geochemical study was possible because the melt is now represented as a glass that has undergone limited devitrification a rb sr isochron age of 11 8 pm 0 6 ma for glasses and granite whole rocks is in agreement with the k ar age of 11 7 pm 0 7 ma for a similar trachyandesite plug nearby confirming that the melting was associated with the trachyandesite intrusion melting occurred at about 900 c or higher and at less than 1 kb the restite minerals consist dominantly of zoned plagioclase and sanidine both have rims of anorthoclase of similar composition quartz and magnetite the whole rock major

water exsolution from quartz implications for the generation of retrograde metamorphic fluids available data from the literature suggest that the solubility of h2o in nominally anhydrous minerals such as quartz should increase with increasing metamorphic grade if this is the case water should precipitate from the host mineral during cooling and uplift of regionally metamorphosed terranes calculations indicate that this mechanism could result in the release of significant quantities of h2o which would then be available to participate in retrograde hydration reactions and the formation of fluid inclusions

tectonic implications of metamorphism and gravity field in the penokean orogen of northern michigan published geologic data together with new metamorphic pressure and temperature data and gravity data provide strong evidence for northward directed thrusting of lower proterozoic rocks in northern michigan and wisconsin metamorphic studies indicate pressures of 7 kbar at watersmeet node and 4 kbar at the peavy node the republic metamorphic node located 30 km to the north of peavy attained pressures of 2 3 kbar all three metamorphic highs reached temperatures in the range of 600 650 c and are correlated with areas of negative gravity anomalies relative to surrounding regions in the peavy high the center of the gravity anomaly lies on the sillimanite isograd and we suggest that the source of this negative anomaly may be remobilized underlying archean gneiss the highest grade rocks of the republic node lie well within a residual gravity anomaly which is interpreted to have a very shallow source and the watersmeet high lies above gneiss domes which show negative gravity anomalies a north south geologic cross section constructed from a two dimensional gravity model which extends northward from the dunbar dome in the magmatic arc terrane of wisconsin across a terrane boundary interpreted as a suture and marked by the niagara fault and across the peavy metamorphic node suggests that the dunbar dome was transported northward onto the continental foreland during the penokean orogenic event these north verging fold thrust sheets or nappes produced prominent tectonic thickening at the peavy and watersmeet as indicated by the relatively high metamorphic pressures there the thrust sheets evidently thinned to the north as suggested by the relatively low pressures at republic we suggest that the archean continental edge defined by the steep gradient in the regional northeast trending gravity high lies beneath the magmatic rocks of wisconsin and thus extends south of the niagara fault suture

the dunbar gneiss granitoid dome implications for early proterozoic tectonic evolution of northern wisconsin the dunbar dome in northeastern wisconsin is a critical structural feature in the early proterozoic penokean orogen it provides exposures of gneisses dunbar gneiss that structurally underlie the voluminous metavolcanic rocks of northeastern wisconsin and exposures of abundant granitoid rocks ranging from tonalite to granite the granitoid rocks cut both the gneisses in the core and the supracrustal cover metavolcanic rocks and were emplaced essentially along the core cover boundary the dunbar gneiss is calc alkaline and was derived from volcanic and intrusive rocks of intermediate composition the various intrusive rocks have calcic calc alkaline and alkali to alkali calcic compositions and they progress with time to more sio 2 and k 2 rich compositions u pb zircon ages indicate that accumulation of the layered rocks in the core and cover deformation and metamorphism and intrusion of the granitoid rocks spanned a relatively short time 1865 1835 ma we interpret the dome as being a large scale fold interference structure resulting from polydeformation modified by diapirism northeast oriented folds f 3 and a related mylonitic foliation s 3 nearly confined to the dome are superposed on northwest oriented folds f 2 that developed during regional deformation in the core cover boundary these structures are obliterated by a zone of intense deformation a mylonitic foliation and a steeply plunging stretching lineation as much as 500 m wide which we interpret as resulting from diapirism metamorphic zoning is concentric amphibolite facies in inner parts of the mantle and greenschist facies in the outer part of the mantle the wisconsin magmatic terrane as represented by the rocks in the dunbar dome differs from the epicratonic early proterozoic sedimentary volcanic sequence marquette range supergroup in michigan to the north in stratigraphy structure and volume and composition of igneous rocks whereas the basalts in northern michigan are compositionally similar to continental rift basalts the volcanic rocks in the dunbar dome have over all island arc compositional affinities the over all calc alkaline compositions of the intrusive rocks are similar to those in magmatic arcs formed at convergent plate margin settings accordingly we interpret the wisconsin magmatic terrane as an oceanic arc complex that was sutured to the north american continent during development of the penokean orogen similar interpretations based on broad regional observations have been proposed previously

resetting of rb sr whole rock isochrons during sveconorwegian low grade events in the gjerstad augen gneiss telemark southern norway abstract the gjerstad augen gneiss comprises a single igneous body that shows intrusive relationships to the surrounding older telemark gneisses the formation of the gneissic structure and augen texture was due to mylonitic deformation along a major shear zone the porsgrunn kristiansand fault zone the augen gneiss can be divided petro graphically into green grey both pyroxene bearing and pink types samples from three locations were analysed isotopically two distinct at 2 level groups of ages were obtained which are interpreted as a 1250 ma cooling after high temperature deformation and formation of retrogressive corona structures b 1080 ma resetting of whole rock systems during low grade mineral alteration by hydrous fluids at 900 ma there was further isotopic disturbance during low grade alteration related to the intrusion of pegmatite veins the significant age differences are not related to colour grade of samples and significantly different ages have been found in the same rock body within a single locality as the gjerstad augen gneiss was intruded before 1250 ma into a previously existing gneissic terrain the gneiss forming event and associated upper amphibolite facies metamorphism in the gjerstad region is constrained to be pre 1250 ma i e pre sveco norwegian

the goodman swell a lithospheric flexure caused by crustal loading along the midcontinent rift system rb sr biotite ages of archean and early to middle proterozoic crystalline rocks in northern wisconsin and adjacent upper peninsula of michigan describe a regionally systematic pattern related to differential uplift an age low occurs in northern wisconsin where values range from 1070 1172 ma for rocks with crystallization ages of 1760 to 1865 ma these values overlap with the main episode of mafic igneous activity 1090 to 1120 ma along the midcontinent rift system mrs we interpret these low biotite ages as registering closure due to cooling below the 300 c isotherm as a consequence of uplift and rapid erosion of an area that we are informally naming the goodman swell the position of the goodman swell is independent of the archean and early proterozoic regional geologic framework but closely linked with the curvilinear concave to the south mrs we interpret the swell to be a forebulge imposed on an elastic crust by loading of mafic igneous rocks along and within the axis of the mrs the southward concavity of load axes resulted in flexural interaction that localized the swell because of rapid uplift the swell may have been a source area for clastic sediments in the rift sequence

the 2010 eruption of eyjafjallajokull lightning and plume charge structure six lightning mapping array lma stations were deployed in april 2010 around eyjafjallajokull volcano in southern iceland single station lma observations were made during the first explosive period 14 18 april and three dimensional lma observations were made during the second explosive period 5 22 may the single station observations revealed that continuous rf electrical activity caused by high rates of small vent discharges occurred during the first explosive period but not the second indicating that the strength of vent charging varied between the first and second explosive periods during the second explosive period very little lightning was detected between 5 and 10 may while moderate rates of lightning were detected between 11 and 21 may signaling that another change occurred on 11 may that affected plume electrification the data do not make clear if it was changing eruptive activity or changing meteorological activity that resulted in the sudden onset of lightning the plume charge structure during the second explosive period was inferred from the three dimensional lightning data showing that the dominant charge structure varied between a positive monopole and a negative over positive dipole the predominance of a low altitude region of positive charge and the observation that electrical activity was concentrated near the vent indicate that net positive vent charging was dominating the electrification

on the origin of early proterozoic gneiss domes and metamorphic nodes northern michigan biotite 40 r 39 r cooling ages from medium pressure 500 600 mpa rocks in the watersmeet district northern michigan suggest significant cooling uplift and concomitant deformation during gneiss dome formation at 1755 ma well after the close of the 1870 1830 ma penokean orogeny however an 1822 ma hornblende plateau date indicates that the isograds surrounding the dome are penokean in age we attribute gneiss dome formation and doming of penokean aged isograds to an episode of orogenic collapse superimposed on an earlier history of crustal shortening this contrasts with the compressional origin for gneiss domes preserved in the low pressure 200 300 mpa republic district the different origins may reflect the fact that collapse was localized along the overthickened region of the orogenic belt in contrast to the watersmeet area hornblende and biotite 40ar 39ar ages obtained from the republic area are 1720 1680 ma given the relatively shallow depth of this region it is unlikely that temperatures re

using lightning observations as a volcanic eruption monitoring tool lightning commonly occurs in the eruption columns produced by explosive volcanic eruptions there are several different kinds of lightning detection instruments that could be employed to help monitor volcanoes each with their own advantages and disadvantages very low frequency vlf instruments have the ability to detect lightning at long ranges but tend to have low sensitivity due to network geometry and typically can provide only the time and 2 d location of a cloud to ground return stroke or similar high amplitude pulse produced by an intracloud discharge low frequency lf and medium frequency mf instruments typically have more sensitivity than a vlf network but can only be used for detection on a regional scale very high frequency vhf lightning mapping instruments also provide only regional coverage but detect all lightning within their range during the 2009 eruption of redoubt volcano alaska usa each of these types of instruments detected lightning from redoubt s ash plume the vhf system consistently detected lightning before the other two during each distinct explosive event and also detected more lightning than the others by one or two orders of magnitude lightning observations could be used to confirm and in some cases detect explosive volcanic activity the rapid response provided by lightning monitoring is a valuable tool for fast identification of potentially hazardous ash clouds

determining the extent and nature of mazatzal related overprinting of the penokean orogenic belt in the southern lake superior region north central usa abstract twenty one hornblende and mica 40ar 39ar dates from central and northwest wisconsin usa provide important information on the timing spatial extent and intensity of mazatzal age metamorphism and deformation which overprinted the paleoproterozoic 1870 1820 ma penokean orogenic belt in the southern lake superior region 1760 1750 ma mica plateau ages from bedrock beneath undeformed 1750 1630 ma quartzites are interpreted as the time of lower temperature 300 350 c cooling and crustal stabilization after the penokean orogeny six mica ages from bedrock underlying deformed paleoproterozoic quartzites cluster around 1600 ma 1576 1614 ma the complete absence of 1760 1750 ma mica ages beneath regions of deformed quartzites suggests widespread heating to temperatures above 300 350 c during mazatzal related deformation and metamorphism the 1600 ma mica ages are interpreted to date the cooling phase of this metamorphism two anomalously young biotite dates are interpreted to indicate partial resetting associated with mesoproterozoic rifting at 1100 ma ten hornblende 40ar 39ar dates obtained in this study address the higher temperature overprinting effects in the southern lake superior region one latest archean age of 2503 18 ma and two ages of 1853 and 1830 ma are interpreted as remnant evidence of archean and penokean age amphibolite metamorphic events respectively the majority of hornblende ages are younger than the penokean orogeny scattering between 1796 and 1638 ma microtextural analysis indicates that similar microstructures exist in samples yielding highly discordant hornblende ages this suggests that shearing and recrystallization did not play an important role in the retention or loss of argon the 1638 ma hornblende age is concordant with the mazatzal orogeny to the south and is interpreted as representing complete thermal or fluid related resetting associated with that event six other post penokean ages scatter over a 70 million year interval 1796 1723 ma and probably reflect variable retention of radiogenic argon they are interpreted to indicate variable degrees of partial intermediate temperature 350 500 c resetting of hornblende argon systematics at 1650 1630 ma collectively these data suggest that the effects of the mazatzal orogeny in the southern lake superior region involved 350 500 c metamorphism and penetrative deformation

paleoenvironmental and paleoclimatic records from permafrost deposits in the arctic region of northern siberia ice complexes extremely ice rich permafrost deposits with large ice wedges are widely distributed in the arctic region of northeast siberia they present excellent archives for the reconstruction of late quaternary paleoenvironmental conditions in nonglaciated areas in 1998 1999 and 2000 russian and german scientists worked together on the bykovsky peninsula southeast of the lena delta in order to investigate the ice complex and its associated sediments intensive cryolithological and sedimentological studies radiocarbon age determinations paleobotanical studies micropaleontological investigations studies of mammal and insect fossils and stable isotope analyses of ground ice were performed radiocarbon data have been obtained from the entire exposed sequence coveringapproximately the last 60 000 years the results indicate that compared with modern time the investig ated ice complex sequence was formed duringtwo cooler and more arid stages of the late pleistocene with relatively uniform environmental conditions separated by a stage with environmental variations and more intensive soil formation caused by climate amelioration the late pleistocene environmental changes were not as strong as those occurring during the pleistocene holocene transition where a sharp break is evident r 2002 elsevier science ltd and inqua all rights reserved

postcollisional cooling of the penokean orogen in east central minnesota new 40ar 39ar thermochronologic data from the internal zone of the penokean orogen in east central minnesota indicate rapid cooling from mid crustal temperatures early proterozoic metamorphosed cover rocks yield concordant hornblende and biotite plateau ages of 1755 ma underlying archean basement gneiss yields concordant muscovite and biotite plateau ages of 1705 ma these are some of the oldest cooling ages recorded in rocks buried during the 1830 1860 ma penokean collisional orogeny cooling was coeval with regional rhyolitic volcanism and granite emplacement suggesting a period of tectonic activity in this region during mid to late 1700 ma based on similarities with phanerozoic extensional regimes we suggest preliminarily that these data might be explained by a previously unrecognized major extensional episode in the lake superior region

tectono stratigraphic evolution of the early proterozoic wisconsin magmatic terranes of the penokean orogen the early proterozoic penokean orogen developed along the southern margin of the archean superior craton the orogen consists of a northern deformed continental margin prism overlying an archean basement and a southern assemblage of oceanic arcs the wisconsin magmatic terranes the south dipping niagara fault suture zone separates the south facing continental margin from the accreted arc terranes the suture zone contains a dismembered ophiolite the wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure the northern pembine wausau terrane contains a major succession of tholeiitic and calc alkaline volcanic rocks deposited in the interval 1860 1889 ma and a more restricted succession of calc alkaline volcanic rocks deposited about 1835 1845 ma granitoid rocks ranging in age from about 1870 to 1760 ma intrude the volcanic rocks the older succession was generated as island arcs and or closed back arc basins above the south dipping subducti

rb sr biotite and whole rock data from the kapuskasing uplift and their bearing on the cooling and exhumation history rb sr isotopic ratios were measured on biotite and whole rocks from a suite of 21 granitoid rocks from the southern kapuskasing uplift results of 18 of the whole rock analyses fall on an isochron with an age of 2 677 0 057 ga and sri 0 70080 biotite model ages range from 2 50 to 1 93 ga in a general spatial relationship of decreasing age with depth in the structural section as calibrated with the igneous hornblende barometer for tonalitic rocks and garnet pyroxene barometers for granulites near the michipicoten belt in the west biotite ages of 2 ga reflect disturbances also recorded by paleomagnetic and whole rock rb sr systems to the east in a 70 km long northwest southeast transect toward the ivanhoe lake fault zone ages decrease from 2 50 to 1 95 ga in a southern transect ages are in the range 2 30 2 38 ga to within 15 km of the fault reflecting consistent erosion levels corresponding to 0 53 mpa but decrease to 1 93 ga to the east in concert with paleopressures in the 0 7 1 0 gpa ra

age and significance of precambrian basement samples from northern illinois and adjacent states geochronologic results are reported for 12 localities where deep drilling has penetrated precambrian basement in iowa illinois indiana michigan and kentucky for the northern illinois deep drill holes uph 1 and uph 3 a zircon u pb age of 1463 10 m y was obtained rb sr data for these samples indicate mild disturbance of this system but are not interpreted in terms of any specific younger event u pb ages for other localities fall in the interval 1450 1510 m y and indicate that this was a major period of igneous activity throughout the southern great lakes region rb sr results indicate that alteration was ubiquitous and that most ages in the range 1100 1400 m y probably represent disturbed systems the results obtained so far tend to support interpretations in which kentucky indiana and illinois are primarily underlain by a rhyolite and epizonal granite terrane that is 1450 1500 m y old older proterozoic rocks may be absent or more deeply buried

a comprehensive upb smnd rbsr and 40ar39ar geochronological study on guidong granodiorite southeast china records of multiple tectonothermal events in a single pluton a complicated tectonothermal history of the guidong granodiorite from the huanan fold belt has been revealed by using combined dating techniques u pb single zircon and whole rock nd model ages suggest that the granodiorite was derived from an ancient crustal source which was probably composed of a mixture of 1 2 2 4 ga crustal materials with a nd model age of 1 6 ga the granodiorite emplacement age of 427 3 ma is defined by concordant u pb single zircon analysis plagioclase biotite hornblende apatite sphene and whole rock yield an internal sm nd isochron age of 428 12 ma consistent within the analytical errors with the u pb zircon age due to the presence of inherited zircon however the zircon data point deviates from the sm nd isochron four whole rocks and two mineral separates plagioclase and hornblende yield a rb sr isochron age of 422 14 ma which is coincident with zircon u pb and sm nd isochron ages hornblende 40ar 39ar step heating analysis gives a main plateau age of 371 4 1 3 ma which is considerably younger than the crystallization age this age is interpreted as recording a post crystallization folding event which produced the prominent unconformity between pre devonian and middle devonian strata and resulted in the deformation of all major minerals of the granodiorite since most deformed minerals have remained closed to sm nd and rb sr isotopic migration since emplacement of the granodiorite it can be suggested that this folding event took place without significant fluid circulation and contemporaneous metamorphism a low temperature heating step of hornblende yields an apparent 40ar 39ar age of 208 5 2 0 ma which may or may not have a connection to the minimum age of the huanan indosinian orogeny a biotite 40ar 39ar age spectrum yields much younger apparent ages of 145 and 92 ma which are coincident with two important yanshanian magmatic episodes

middle proterozoic uplift events in the dunbar dome of northeastern wisconsin usa isotopic ages of granitic and metamorphic rocks exposed in the dunbar structural dome of northeastern wisconsin identify a protracted series of tectonic and hydrothermal events that culminated in major regional uplift during middle proterozoic keweenawan ca 1 100 ma continental rifting and volcanism the major rock forming events and the structural development of the dome occurred during the interval 1 862 4 ma to 1 836 6 ma whole rock rb sr ages are partly reset in response to a widely recognized but cryptic event in wisconsin and michigan at about 1 630 ma the scale and systematic character of the whole rock resetting strongly suggests the presence of a fluid phase derived in situ from water dissolved in the silicates or externally from a subthrust plate of low grade metamorphic rocks the regional nature of the 1 630 ma disturbance possibly indicates that it is related to a major tectonic event such as an active plate margin far to the south rb sr biotite ages for the dunbar dome this study the southern complex of the marquette district van schmus and woolsey 1975 and the felch trough area aldrich and others 1965 provide a remarkably coherent pattern that reflects multiple episodes of differential uplift younger events superimposed on a regional 1 630 ma imprint are recorded at 1 330 ma and 1 140 ma the 1 330 ma disturbance could reflect stabilization following intrusion of the wolf river batholith at 1 485 ma the 1 140 ma uplift event occurred during keweenawan rifting and volcanism as a result of stresses imposed on a mosaic of fault bounded blocks with possible subcrustal influence the remarkably small variance in the 1 140 ma biotite age peak argues for rapid uplift and cooling and hence rapid erosion detritus from the uplift probably was being shed into nearby tectonic basins most of which did not survive subsequent uplift and erosion

magnetotelluric pulses generated by volcanic lightning at sakurajima volcano japan 1 continuous magnetotelluric mt measurements were conducted at sakurajima volcano japan revealing syn eruption electric pulses and sometimes accompanying geomagnetic pulses movies of the eruptions recorded with timing provided by a gps clock show a large number of volcanic lightning flashes some mt pulses occurred simultaneously with lightning flashes pulses were observed more than 10 seconds after the onset of the eruption and tend to occur during eruptions that emit volcanic ash to high altitudes pulses were more common during mild eruptions rather than during vulcanian eruptions the observations suggest that the dominant mechanism of volcanic lighting is similar to that of lightning in thunderstorms in that it requires the collision of particles and subsequent separation of positive and negative charge

characterization and applications of vlf lf source locations from lightning using the huntsville alabama marx meter array 1 arrays that detect and locate the four dimensional spacetime positions of radiation sources from lightning have largely utilized sensors sensitive to the very high frequency vhf regime with 15 km baselines or very low frequency low frequency vlf lf regime with 100 km baselines this paper details initial results from the newly developed huntsville alabama marx meter array hamma consisting of marx meters electric field change meters sensitive to a frequency band 1 hz to 400 khz the arrival time of hamma waveforms due to radiation sources from lightning are used to determine the spacetime position of these sources the locations are compared with two well documented and operational arrays the national lightning detection network nldn and the north alabama lightning mapping array nalma the standard deviation of the difference between hamma and nldn locations of return strokes is 305 and 266 m in x and y respectively while the standard deviation of the difference between hamma and nalma sources is 237 226 and 688 m in x y and z respectively we further show that nldn intracloud locations differ in horizontal distance from the corresponding hamma locations by a median value of 479 m in addition we use hamma source locations to map several lightning flashes in the vlf lf and show hamma sources largely map out the same electrical extent as vhf sources and provide unique insights to the properties of the discharges occurring finally we show that vlf lf sources can determine the leader polarity in several example flashes but not necessarily whether a flash comes to ground copyright 2013 american geophysical union all rights reserved

physical properties of volcanic lightning constraints from magnetotelluric and video observations at sakurajima volcano japan abstract the lightning generated by explosive volcanic eruptions is of interest not only as a promising technique for monitoring volcanic activity but also for its broader implications and possible role in the origin of life on earth and its impact on the atmosphere and biosphere of the planet however at present the genetic mechanisms and physical properties of volcanic lightning remain poorly understood as compared to our understanding of thundercloud lightning here we present joint magnetotelluric mt data and video imagery that were used to investigate the physical properties of electrical discharges generated during explosive activity at sakurajima volcano japan and we compare these data with the characteristics of thundercloud lightning using two weeks of high sensitivity high sample rate mt data recorded in 2013 we detected weak electromagnetic signals radiated by volcanic lightning close to the crater by carefully inspecting all mt waveforms that synchronized with visible flashes and comparing with high speed 3000 frame s and normal speed 30 frame s videos we identified two types of discharges the first type consists of impulses type a and is interpreted as cloud to ground cg lightning the second type is characterized by weak electromagnetic variations with multiple peaks type b and is interpreted as intra cloud ic lightning in addition we observed a hybrid mt event wherein a continuous weak current accompanied type a discharge the observed features of volcanic lightning are similar to thunderstorm lightning and the physical characteristics show that volcanic lightning can be treated as a miniature version of thunderstorm lightning in many respects the overall duration length inter stroke interval peak current and charge transfer all exhibit values 1 2 orders of magnitude smaller than those of thunderstorm lightning thus suggesting a scaling relation between volcanic and thunderstorm lightning parameters that is independent of the type of charged particles on the other hand the polarities which are estimated by long time 3 4 yrs mt 32 samples s and video 30 frame s observations are different than those of normal thunderstorm lightning these observations are consistent with the notion that charge structures in volcanic ash plumes are highly disordered and are characterized by numerous small charged regions with high charge density

geochemistry and evolution of the early proterozoic post penokean rhyolites granites and related rocks of south central wisconsin u s a

u th pb isotope chronology of sulfide ores and rocks in the early proterozoic metavolcanic belt of northern wisconsin lead was probably derived from 3 7 b y old source material about 1 8 to 1 9 b y ago data on metavolcanic and granitic rocks from the belt show that the u th pb systems in most were reset about 1 6 b y ago a time of shearing and retrogressive metamorphism a concordia plot of the whole rock lead data shows that many of the rocks lost lead relative to uranium and thorium during the interval 200 to 400 m y ago similar ores might be sought between the northern wisconsin metavolcanic belt and the upper mississippi valley because the lead lost from the basement there might be available for ore formation in overlying units the lead in the early proterozoic metavolcanic belt of northern wisconsin seems to have been derived from the same mantle parent as the late archean metavolcanic belts of northeastern minnesota and southern ontario modified journal abstract