origin of mesozoic and tertiary granite in the western united states and implications for pre mesozoic crustal structure 2 nd and sr isotopic studies of unmineralized and cu and mo mineralized granite in the precambrian craton in the cordilleran region of the western united states mesozoic and tertiary peraluminous granitic rocks display regional variations in initial 143nd 144nd end end 10 to 12 in southern arizona 17 to 19 in the northern great basin ngb and 30 in the northern rocky mountains initial 87sr 86sr values are between 0 710 and 0 721 and show no regional pattern metaluminous granitic rocks have a wider range of end values extending from values similar to those of the peraluminous granites to much higher values the 87sr 86sr values are mostly fairly low between 0 705 and 0 710 except in the ngb where values as high as 0 7157 are observed no systematic differences between the end or 87sr 86sr values of cu or mo mineralized and unmineralized granite were discerned except for cu mineralized granite in eastern nevada and mo mineralized granite in colorado which have end values higher 0 and lower 10 0 respectively than unmineralized granite in the same region comparison to end values of exposed precambrian rock suggests that the peraluminous granite and the mo granite in colorado were derived exclusively from felsic precambrian basement rocks and that the regional variations in the end values reflect the regional variation in the average crustal age the nd data confirm that the precambrian basement underlying the ngb and eastern california is isotopically distinct from precambrian crust in the remainder of the western united states the similarity between the end values of peraluminous granite and precambrian crust also suggests that the high 147sm 144nd 0 13 and the low total light rare earth element lree abundances characteristic of peraluminous granite in southern arizona were imposed during the chemical evolution of the magmas metaluminous granite are interpreted to have formed via mixing of mantle derived magma and large proportions of low 87sr 86sr granulite facies lower crust except in the eastern ngb where the mantle magmas mixed with a lower crustal source with a significantly higher 87sr 86sr ratio ree abundance patterns for metaluminous granite in the ngb are characterized by extreme lree enrichment which supports the proposed origin for these rocks by mantle crust mixing or by remelting of the lower crust alone no systematic difference exists between the sources of cu or mo mineralized and unmineralized metaluminous granite but the data suggest that the cu sources are in the mantle and the mo sources are in preexisting crust overall the nd data indicate that continental interior granite in the western united states was primarily derived from preexisting crust and although changes in the thermal structure of the continental mantle may have triggered magma formation the resulting granites do not represent significant juvenile additions to the continental crust

geochemistry and nd isotope systematics of archaean granites of the eastern goldfields yilgarn craton australia implications for crustal growth processes abstract the archaean granites and granitic gneisses of the eastern goldfields in the yilgarn craton western australia can be divided into two major groups high ca and low ca and three minor groups high hfse high field strength elements mafic and syenitic the high ca group 68 77 sio 2 with high al 2 o 3 na 2 o and sr and low y shares many features with typical archaean tonalite trondhjemite suites but has higher k 2 o rb and th contents the low ca group 70 76 sio 2 differs from the high ca group in having lower al 2 o 3 cao and na 2 o but higher k 2 o rb th zr y la and ce contents granites of the high hfse mafic and syenitic groups form a minor component 10 20 of the eastern goldfields granites the siliceous 74 77 sio 2 high hfse granites are restricted to a narrow nnw trending zone and are characterised by high tio 2 total feo mgo y zr and ce but only moderate rb th and pb contents the a type syenites 50 68 sio 2 are distinguished by their high total alkalies and mainly occur along tectonic lineaments the mafic group 55 70 sio 2 is lithologically diverse and exhibits a wide range of k 2 o rb th la and ce contents granite emplacement occurred between 2 69 and 2 60 ga contemporaneous with or post dating greenstone formation nd values for the high ca mafic and syenitic groups are similar mostly 0 0 to 2 5 whereas those for the low ca group show a pronounced polarity from 4 5 in the west to 2 0 in the east nd depleted mantle model ages for the low ca granites range from 3 2 ga in the west to 2 75 ga in the east model ages for the high ca group 2 75 2 9 ga overlap with ages for inherited zircons from these granites the high ca granites appear to have been derived at high pressures by partial melting of a mafic to intermediate source subducted oceanic crust crustal underplate or thickened crust or remelting of an older tonalitic source derived by such a process if the high ca granites were largely crust derived then their extensive source rocks must have formed less than 250 ma prior to granite formation the low ca granites appear to be the products of crustal reworking probably from a tonalitic to granodioritic protolith that was progressively younger towards the east perhaps in the order of several hundred million years younger or involved an additional younger component the localisation of the crustally derived high hfse granites suggests either geochemical zonation of the crust or specific tectonic processes such as rifting the mafic granites and possibly the syenites imply a significant mantle contribution and new crustal growth although the extent is equivocal the crust of the eastern goldfields appears to have been generated by both lateral and vertical accretion over a significant period from or before 3 0 ga until the time of granite emplacement

some aspects of the seismicity associated with the 1982 eruption of el chichon volcano chiapas mexico we review the different phases of the seismicity related to the 1982 eruption of el chichon volcano chiapas mexico the pre eruption seismicity was already anomalous by late 1980 became significant by late 1981 and increased towards 28 march 1982 when the first eruptive event occurred a noticeable feature within the 7 day period of unrest is the occurrence of three earthquake swarms before the devastating explosions of 3 and 4 april 1982 local time the periodicity and appearance of the swarms close to the time of maximum tidal strain suggests a large overpressure in the magmatic system and the triggering of the events by the earth tides the post eruption seismicity occurred mostly in a radius 5 km from the crater and a depth range 11 to 15 km suggesting that this region was a deeper reservoir of the erupted magma

some regularity in the process of re awakening of andesite and dacite volcanoes specific features of the 1982 el chichon volcano mexico reactivation el chichon volcano is an andesite stratovolcano in southern mexico it erupted in march 1982 after about 550 years of quiescence the 1982 eruption of el chichon has not been followed by the growth of a lava dome within the newly formed crater this is rather anomalous since the construction of a new dome after the destruction of an old one is a common process during the eruptions at andesite and dacite volcanoes to discuss this anomalous aspect of the el chichon eruption some regularity in the process of re awakening of dormant here defined as a period of quiescence of more than 100 years andesite and dacite volcanoes are studied based on the seismic activity recorded at the volcanoes bezymianny mount st helens el chichon unzen pinatubo and soufriere hills three stages were identified in the re awakening activity of these volcanoes 1 preliminary seismic activity leading up to the first phreatic explosion 2 activity between the first and the largest explosions 3 post explosion dome building process the eruptions were divided into two groups low vei volcanic explosivity index and the long duration stage 1 events unzen 1991 and soufriere hills volcano 1995 and high vei and the short duration stage 1 events bezymianny 1956 mount st helens 1980 el chichon 1982 and pinatubo 1992 the comparative analysis of the seismo eruptive activity of two eruptions of the second group the 1980 of mt st helens and the 1982 of el chichon produced an explanation the absence of new dome building during the 1982 eruption of el chichon volcano it may be explained in terms of the unusually rapid emission of gas and water from the magmatic and hydrothermal system beneath the volcano during a relatively short sequence of large explosions that could have sharply increased the viscosity of the magma making impossible its exit to the surface

major and trace element geochemistry of neutral and acidic thermal springs at el chichon volcano mexico implications for monitoring of the volcanic activity abstract four groups of thermal springs with temperatures from 50 to 80 c are located on the s sw w slopes of el chichon volcano a composite dome tephra edifice which exploded in 1982 with a 1 km wide 160 m deep crater left very dynamic thermal activity inside the crater variations in chemistry and migration of pools and fumaroles drastic changes in the crater lake volume and chemistry contrasts with the stable behavior of the flank hot springs during the time of observations 1974 2005 all known groups of hot springs are located on the contact of the basement and volcanic edifice and only on the w sw s slopes of the volcano at almost same elevations 600 650 m asl and less than 3 km of direct distance from the crater three groups of near neutral ph 6 springs at sw s slopes have the total thermal water outflow rate higher than 300 l s and are similar in composition the fourth and farthest group on the western slope discharges acidic ph 2 saline 10 g kg of cl water with a much lower outflow rate water rock interaction modeling of main types of the el chichon thermal waters using regular log q k graphs saturation indices vs temperature showed maximum equilibrium temperature slightly higher than 200 c acidic waters are equilibrated with some clay minerals at about 120 c three main sources of the salinity of thermal water are suggested on the basis of mixing plots and isotopic data a magmatic source for co2 boron sulfur and a limited part of cl volcanic rock source for the major cations and trace elements the oil bearing evaporitic basement source oil field brine for nacl br a part of ca and some trace elements all flank thermal springs end up in the river rio magdalena that has a variable seasonal flow rates from 4 to 20 m3 s any changes in the chemistry of springs must notably change the composition of the streams draining hot springs and eventually rio magdalena a monthly geochemical monitoring of rio magdalena and streams draining main hot springs would be a useful tool for surveying the activity of the volcano

interactions between axial and transverse drainage systems in the late cretaceous cordilleran foreland basin evidence from detrital zircons in the straight cliffs formation southern utah usa new detrital zircon geochronologic data from the straight cliffs formation of southern utah provide insight into the controls on stratigraphic architecture of the western interior basin during turonian early campanian time detrital zircon ages n 40 n 3650 derived from linked fluvial and shallow marine depositional systems of the kaiparowits plateau indicate the majority of zircons in fluvial strata were derived from the mogollon highlands 1 25 1 90 ga 67 of fluvial zircons with subordinate contributions delivered from the sevier fold and thrust belt 265 1250 ma 17 and cordilleran magmatic sources 81 265 ma 16 integration of these data with fluvial facies distributions petrography clast counts and evidence of magmatic arc sources from the mohave region of california implies the presence of a northeast flowing axial fluvial system this system was fed by rivers draining the mogollon highlands to the south and by transverse drainages from the sevier fold and thrust belt to the west compared to the fluvial deposits shallow marine sandstones have a greater proportion of sevier fold and thrust belt derived zircons 42 which were delivered via longshore currents from the north shallow marine samples also contain less mogollon input 44 compared to contemporaneous fluvial systems and similar input from the magmatic arc 14 although proterozoic zircons associated with the mogollon highlands are also present in the sevier fold and thrust belt several lines of evidence argue for a distinct southerly source for the straight cliffs formation these include 1 moderate proportions of feldspar and angular quartz grains in fluvial sandstones which favor a felsic intrusive source and 2 prominent 1 4 and 1 7 ga zircon populations the 1 4 and 1 7 ga peaks are the only dominant proterozoic peaks in samples from the straight cliffs formation whereas samples derived more directly from the sevier fold and thrust belt tend to have a broader distribution of proterozoic age peaks up section architectural trends in the straight cliffs formation are linked to trends in detrital zircon geochronologic data underscoring the likelihood of common drivers and controls the axial system depositing straight cliffs fluvial strata was primarily fed by drainages originating in the mogollon highlands during a pulse of tectonic activity in the maria fold and thrust belt and generally high subsidence rates in the foreland basin turonian santonian over time activation of the paxton duplex in the sevier fold and thrust belt early campanian exhumed proximal foreland basin strata and enabled drainage systems from the sevier fold and thrust belt to feed into the basin more prominently the results presented here underscore the potential significance of axial fluvial systems and their complex interplay with transverse drainage networks in foreland basins

intrusive reawakening of el chichon volcano prior to its holocene eruptive hyperactivity abstract el chichon volcano in southeastern mexico chiapas has produced compositionally homogeneous trachyandesite throughout its ca 372 kyr eruptive history but crystal scale heterogeneity reveals a complex interplay between magmas generated and stored at different crustal levels high sensitivity ion microprobe 238u 230th zircon dating from the last two eruptions of el chichon 1982 and 550 bp demonstrates that most zircon crystallized between 0 and ca 40 ka few zircon crystals date back to ca 130 kyr and none to the middle pleistocene phase of eruptions trace elements and oxygen isotope variations in zircon indicate fairly stable conditions in the magma chamber between ca 20 and 130 ka with average ti in zircon temperatures estimated at 712 c and 18o values of 6 6 however excursions to high ti in zircon temperatures and high 18o values in zircon occurred at ca 24 ka these excursions also mark the onset of subsequent progressive changes to occasionally higher ti in zircon temperatures lower 18o values and more primitive magma compositions e g high eu eu zr hf and th u systematic rim ward decrease in 18o is recorded by juvenile zircon domains which quasi continuously crystallized for up to 30 kyr prior to eruption textural relationships and o isotopic variations within single zircon crystals are thus evidence for magma recharge causing initial resorption of xenocrystic zircon rapid zircon re saturation driven by local supersaturation and effective magma mixing with sediment contaminated high 18o melts from a boundary layer at the contact of the magma reservoir to country rock initial thermal and compositional defrosting of an intermediate boundary layer and its crystal cargo may have been rapid due to the brief duration of high temperature recharge events as evidenced by the preservation of zircon xenocrysts the delay of at least 12 kyr between major recharge episodes recorded by zircon and the onset of holocene eruptions at brief recurrence intervals suggests that frequent eruptions only started when trachybasaltic magma recharge continued or intensified during the holocene

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

energy partition in the 1982 eruption of el chichon volcano chiapas mexico abstract the 1982 eruption of el chichon volcano chiapas mexico has been extensively investigated from various standpoints including seismicity tephra geology atmospheric effects and tectonic structure in this paper the six largest of a series of explosions are isolated considering various sources of information then the seismic energy released by volcanic earthquakes and tremor is estimated using seismograms of low magnification in order to avoid saturation of seismic wave amplitudes the explosion kinetic energy is evaluated by two methods one by the initial velocity of the ejecta and the other by the air wave data recorded at a distance both the results are roughly coincident the thermal energy is classified into two components that transferred by volcanic ejecta and that consumed by convective clouds the thermal energy released by the explosions is very large compared with that of mechanical energy such as the seismic energy and explosion kinetic energy after the last major explosion of april 4 a type volcanic earthquakes swarmed till the end of april their occurrence rate decreased with time in an aftershock like sequence these earthquake swarms may have been due to post eruptive readjustment of the stress field within and near the volcano such seismic activity contrasts with other examples of similar major eruptions which were followed by growth of lava domes in the new craters after the paroxysmal eruptions the 1982 eruption of el chichon volcano has not been followed by the growth of a lava dome within the newly formed crater

the geochemistry of potassic lavas from vulsini central italy and implications for mantle enrichment processes beneath the roman region major and trace element and 143nd 144nd 0 51209 0 51216 and 87sr 86sr 0 70879 0 71105 isotope analyses are presented on a representative group of lavas from the vulsini district of the roman magmatic province three distinct series are identified the high k and low k series are similar to those described from other italian volcanoes while the third is represented by a group of relative ly undifferentiated leucite basanites which are thought to be near primary mantle melts major and trace element variations within the high k series are consistent with fractional crystallisation from a parental magma similar to the most magnesian leucitites crustal contamination resulted in an increase in 87sr 86sr with increasing fractionation but it was superimposed on magmas which had already inherited a range of incompatible element and isotope ratios from enrichment processes in the sub continental mantle these are reviewed using the available results from vulsini roccamonfina and ernici transition element abundances and ta yb ratios indicate that the pre enrichment mantle was similar to that of e type morb and that these elements were not mobilised by the enrichment process mixing calculations suggest that three components were involved in the enrichment process mantle comparable with the source of morb and two other components rich in trace elements one the low k component had high sr nd th ta and ba nb and no europium anomaly while the second had lower sr nd a negative europium anomaly and very high th ta it was also characterised by low nb ba and high rb ba ratios similar to those reported from phlogopite rich peridotite xenoliths the trace element enrichment processes are therefore thought to have occurred in the mantle wedge above a subduction zone with the trace element characteristics of the high k end member reflecting the subduction of sediments and the stabilisation of mantle phlogopite

a 550 year old plinian eruption at el chichon volcano chiapas mexico explosive volcanism linked to reheating of the magma reservoir 1 some 550 years ago 1320 1433 a d a powerful plinian eruption at el chichon volcano in southern mexico produced a widespread pumice fall deposit we subdivided the deposit into three parts on the basis of structural and textural characteristics pumice lithology and density granulometry and petrologic geochemical attributes the deposit covers an area of 1500 km2 within the 1 cm isopach and has a minimum estimated bulk volume of 2 8 km3 1 1 km3 dense rock equivalent dre its eruptive column reached an altitude of 31 km consideration of field evidence the presence and nature of mafic enclaves and chemical data strongly suggest that the 550 year b p eruption is linked with the intrusion of a high temperature basaltic magma into preexisting but stagnated trachyandesitic magma beneath el chichon thorough mixing of the two magmas produced a compositionally uniform hybrid trachyandesite magma average sio2 55 3 wt which subsequently underwent crystal growth and gas exsolution ultimately overpressurizing the zoned magmatic system to erupt explosively on the basis of el chichon s known eruptive history the intrusion mixing event occurred sometime after the 900 year b p eruption the hybrid magma had a preeruption temperature of 820 830 c and was water undersaturated 5 6 wt h2o at pressures of 2 2 5 kbar

petrogenesis of cogenetic nepheline and quartz syenites and granites northern damara orogen namibia enriched mantle versus crustal contamination abstract geochemical and nd sr o whole rock isotope data and pb isotope data from leached feldspars for a suite of synorogenic ca 540 ma syenites and granites from the northern part of the proterozoic damara orogen namibia constrain their sources and petrogenesis major rock types are mildly potassic nepheline syenites and quartz syenites that were primarily generated by fractional crystallization from a mantle derived alkaline magma even the most primitive samples show pronounced depletion in nb ti sr and p on a primitive mantle normalized diagram indicating the involvement of a recycled crustal component in the source extrapolation of the sr nd pb o isotope composition of the syenites back to a hypothetical parental melt with 8 wt 10 wt mgo suggests derivation from a moderately enriched lithospheric upper mantle documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage t

40ar 39ar thermochronology and thermobarometry of metamorphism plutonism and tectonic denudation in the old woman mountains area california discrimination of individual tectonometamorphic events in polymetamorphosed terranes requires a comprehensive understanding of the relative timing and conditions of metamorphism and plutonism we have applied a combination of 40 ar 39 ar thermochronology petrology and thermobarometry to reconstruct the complex early proterozoic through early cenozoic tectonic and metamorphic evolution of continental crust in the old woman mountains area south eastern california strong mesozoic thermal events obscure the earlier history in much of the old woman mountains area in those areas where early proterozoic rocks underwent only lower greenschist facies metamorphism during the mesozoic thermobarometry of pelitic schists indicates that proterozoic metamorphism occurred at 9 to 11 kbar and 700 c 40 ar 39 ar ages of hornblende from samples of interbedded proterozoic amphibolite indicate that this high grade metamorphism took place before 1600 ma the relatively high pressure conditions of early proterozoic metamorphism in the old woman mountains area contrast with the low pressure granulite facies metamorphism that occurred elsewhere in the mojave desert at this time 40 ar 39 ar analyses of hornblende from proterozoic rocks within mesozoic shear zones and hornblende barometry from jurassic intrusive rocks suggest that tectonism and burial of paleozoic strata to 10 km began between 170 and 150 ma this tectonism resulted in regional greenschist facies metamorphism late stage mineral assemblages in proterozoic and paleozoic pelitic rocks in the old woman mountains area indicate an increase in metamorphic grade from greenschist to upper amphibolite facies toward late cretaceous plutons of the 73 ma old woman piute batholith metamorphic temperatures from garnet biotite thermometry increase from 650 c and 40 ar 39 ar ages of hornblende from proterozoic rocks decrease from 1600 to 73 ma toward these plutons barometric calculations from garnet bearing metamorphic rocks suggest that this cretaceous metamorphism took place at 3 5 to 5 0 kbar in the old woman mountains similar pressures are obtained from hornblende barometry of late cretaceous granodiorite 40 ar 39 ar and apatite fission track data from the 73 ma batholith indicate that the rocks exposed in the old woman mountains cooled rapidly to below 350 to 300 c by 70 1 ma and that moderately rapid cooling at rates of 10 to 30 c m y continued until after 60 ma the presence of maximum mesozoic temperatures on the borders of plutons hornblende ages of ca 73 ma and similar pressure estimates for plutons and country rocks indicate that the high temperatures needed to cause ductile deformation and amphibolite facies metamorphism were related to heating from the intrusion of the 73 ma old woman piute batholith amphibolite facies metamorphism along pluton contacts was superimposed on the regional greenschist facies metamorphism related to thrusting and crustal thickening the extremely rapid cooling in the old woman mountains between 73 and 71 ma was due largely to conduction of heat into the country rocks whereas protracted rapid cooling to temperatures below ambient temperatures estimated for the depth of emplacement was due to tectonic denudation at 1 to 2 km m y until about 68 to 65 ma

deposition temperature of some pdc deposits from the 1982 eruption of el chichon volcano chiapas mexico inferred from rock magnetic data abstract thermal remanent magnetization trm analyses were carried out on lithic fragments from two different typologies of pyroclastic density current pdc deposits of the 1982 eruption of el chichon volcano in order to estimate their equilibrium temperature tdep after deposition the estimated tdep range is 360 400 c which overlaps the direct measurements of temperature carried out four days after the eruption on the pdc deposits this overlap demonstrates the reliability of the trm method to estimate the tdep of pyroclastic deposits and to approximate their depositional temperature these results also constraint the time needed for reaching thermal equilibrium within four days for the studied pdc deposits in agreement with predictions of theoretical models sedimentological analysis demonstrates that different thickness of aggrading granular dominated pulses does not affect significantly the estimated tdep for the two studied pdcs the component analysis highlights how the entrapment of a significant amount of pre heated lithic fragments from the dome and the conduit walls reduced the cooling of the pyroclastic mixture

reappraisal of the 1982 eruptions of el chichon volcano chiapas mexico new data from proximal deposits additional data from proximal areas enable a reconstruction of the stratigraphy and the eruptive chronology of phases iii and iv of the 1982 eruption of el chichon volcano phase iii began on 4 april at 0135 gmt with a powerful hydromagmatic explosion that generated radially fast moving 100 ms 1 pyroclastic clouds that produced a surge deposit s1 due to the sudden reduction in the confining pressure the process continued by tapping of magma from a deeper source causing a new explosion the ejected juvenile material mixed with large amounts of fragmented dome and wall rock which were dispersed laterally in several pulses as lithic rich block and ash flow f1 partial evacuation of juvenile material from the magmatic system prompted the entrance of external water to generate a series of hydromagmatic explosions that dispersed moisture rich surge clouds and small volume block and ash flows iu up to distances of 3 km from the crater the eruption continued by further decompression of the magmatic system with the ensuing emission of smaller amounts of gas rich magma which with the strong erosion of the volcanic conduit formed a lithic rich plinian column that deposited fallout layer b associated with the widening of the vent an increase in the effective density of the uprising column took place causing its collapse block and ash flows arising from the column collapse traveled along valleys as a dense laminar flow f2 in some places flow regime changes due to topographic obstacles promoted transformation into a turbulent surge s2 which attained minimum velocities of approximately 77 ms 1 near the volcano the process continued with the formation of a new column on 4 april at 1135 gmt phase iv that emplaced fall deposit c and was followed by hydromagmatic explosions which produced pyroclastic surges s3

evolution of the seismic activity from the 1982 eruption of el chichon volcano chiapas mexico we analyzed more than 1700 earthquakes related to the 1982 eruption of el chichon volcano in southern mexico the data were recorded at specific periods throughout the whole eruptive interval of march to april 1982 by three different networks the seismic activity began several months before the first eruption on 28 march during this period the seismicity consisted of hybrid and long period shallow earthquakes most likely related to processes of faulting fracturing and fluid movement underneath the volcano the foci of events occurring before the eruption circumscribe an aseismic zone from approximately 7 to 13 km below the volcano after the eruption the seismic activity consisted of tectonic type earthquakes that peaked at 1200 events h this later activity occurred over a wide range of depths mostly between 5 and 20 km that includes the former aseismic zone and is roughly limited by the major tectonic faults in the area

the slow boiling of magma chambers and the dynamics of explosive eruptions abstract explosive eruptions are fed by shallow magma chambers and are mainly characterized by a water saturated magma a temporal increasing eruption rate and deep seismicity following the later stages of eruption we develop two simple physical models based on the decompression of a water saturated magma and the non equilibrium growth of bubbles that drives the magma out of the chamber the eruption ends when sufficient decompression is attained to cause magma chamber collapse and restoration of the initial pressure conditions the first model considers a single step decompression the second one a multi step decompression the models predict that the duration of the eruptive phase is mainly controlled by the bubble number densities and the initial decompression pressure decrease of the order 0 1 1 mpa results in eruption lasting days hours the erupted volume magnitude and eruption rate intensity are mainly controlled by the volume of the magma chamber by the strength of the rocks surrounding the reservoir and the physical properties of the magma water diffusivity and bubble density we simulated the eruptions at mt st helens 1980 and vesuvius 79 ad the models correctly predict the duration and evolution of the eruptions with the initial phases characterized by a slow eruption rate with the formation of a plinian column and the subsequent increase resulting eventually in pyroclastic flow activity

chronologic and isotopic framework for early proterozoic crustal evolution in the eastern mojave desert region se california the early proterozoic geologic evolution of the eastern mojave desert region as defined by characteristics of its supracrustal rocks granitoids metamorphism structural history and pb and nd isotopic signature contrasts sharply with other proterozoic provinces of the southwestern united states the oldest supracrustal rocks of the mojave desert region contain zircons over 2 0 ga corroborating nd isotopic evidence for a much older crust here than elsewhere in the southwestern united states granitoids widely emplaced within these supracrustal rocks range from 1 76 to 1 64 ga the earlier plutons and surrounding supracrustal rocks were metamorphosed to granulite and high amphibolite facies throughout the province at about 1705 ma in a migmatite producing event that we term informally the ivanpah orogeny subsequent granitoids emplaced from 1 69 to 1 67 ga were voluminous along a north trending belt in the middle of the mojave province younger plutons were emplaced at about 1 66 ga in several places and at about 1 64 ga along the extreme southern part of the province commonalities between the proterozoic evolutions of the mojave and arizona crustal provinces do not conclusively establish the time that the provinces were juxtaposed the data only suggest that the juxtaposition occurred between about 1 76 and 1 64 ga

petrogenesis of the highly potassic 1 42 ga barrel spring pluton southeastern california with implications for mid proterozoic magma genesis in the southwestern usa syenites from the barrel spring pluton were emplaced in the early proterozoic mojave crustal provine of southeastern california at 1 42 ga all rocks even the most mafic are highly enriched in incompatible elements e g k2o 4 12 wt rb 170 370 ppm th 12 120 ppm la 350 1500xchondrite la ybn 35 100 elemental compositions require an incompatible element rich but mafic or ultramafic source trace element models establish two plausible sources for barrel spring magmas 1 lree enriched garnet websterite with accessory apatite rutile enriched lithospheric mantle and 2 garnet amphibolite or garnet hornblende granulite with enriched alkali basalt composition also with accessory apatite rutile mafic lower crust nd and pb isotopic ratios do not distinguish a crust vs mantle source but eliminate local mojave province crust as the principal one and indicate that generation of the enriched source occurred several hundred million years before emplacement of the barrel spring pluton 1 40 1 44 ga potassic granites are common in southeastern california suggesting a genetic link between the barrel spring pluton and the granites however although the same thermal regime was probably responsible for producing both the granitic and syentic magmas elemental and isotopic compositions preclude a close relationship isotopic similarity of the barrel spring pluton to 1 40 1 44 ga granites emplaced in the central arizona crustal province to the east may imply that a common component was present in the lithosphere of these generally distinct regions

shear zone related syenites in the damara belt namibia the role of crustal contamination and source composition geochemical and nd sr pb o isotope data for a suite of syn collisional ca 520 ma syenites associated with a major shear zone in the proterozoic damara orogen namibia constrain their sources and petrogenesis major rock types from within and outside the shear zone range from highly potassic nepheline syenites to quartz syenites and were primarily generated by fractional crystallization from a mantle derived alkaline magma even the most primitive samples show pronounced depletion in nb ti sr and p on a primitive mantle normalized diagram indicating the involvement of a recycled crustal component in the source extrapolation of the sr nd pb o isotope composition of the syenites from within the shear zone back to a hypothetical parental melt with 10 wt mgo suggests derivation from a moderately enriched lithospheric upper mantle 87sr 86sr 0 705 e nd 2 18o 6 206pb 204pb 19 40 207pb 204pb 15 82 more evolved quartz syenites show increasing 87sr 86sr ratios increasing 18o values but less radiogenic e nd values and pb isotopes with decreasing mgo indicating assimilation of ca 10 archaean to proterozoic local lower crust with unradiogenic e nd high 87sr 86sr and low u pb for samples from outside the shear zone a hypothetical parental melt with 10 wt mgo has distinctly more radiogenic sr but less radiogenic nd isotopic composition 87sr 86sr 0 712 e nd 13 with strongly unradiogenic pb isotope ratios 206pb 204pb 17 40 207pb 204pb 15 50 suggesting another strongly enriched lithospheric mantle source for these rocks differentiated syenites from outside the shear zone show decreasing 87sr 86sr increasing 18o values more radiogenic e nd values and pb isotope ratios with decreasing mgo indicating interaction with a lithospheric component with low rb sr but high sm nd and u pb

the 1982 eruptions of el chichon volcano mexico stratigraphy of pyroclastic deposits abstract following a repose period of 500 to 600 years el chichon volcano in se mexico erupted explosively during the months of march and april 1982 three major eruptions involving trachyandesite magma injected ash into the stratosphere on 29 march at 0515 gmt and on 4 april at 0139 and 1110 gmt the first major eruption generated only tephra fall which was dispersed ene in the troposphere over the yucatan peninsula and wsw in the stratosphere towards the pacific ocean the second eruption produced tephra fall and pyroelastic surges and pyroclastic flows by repeated collapse of a lithicrich eruption column the surge and flow activity devastated a roughly circular area 153 km 2 around el chichon to a distance of about 6 km from the vent nine villages within the zone were either partially or completely destroyed and loss of human life was perhaps as high as 2000 pyroclastic flows and surges were also generated during the third eruption although ash fall was the primary activity as a result of both the second and third eruptions tephra was transported ene in the troposphere and wsw in the stratosphere the total volume of material ejected during the three major eruptions 0 50 km 3 d r e is represented by tephra fall 0 37 km 3 pyroclastic surges 0 09 km 3 and pyroclastic flows and debris flows 0 04 km 3 as a result of the eruptions a new 1 km wide and 300 m deep crater was formed by the disruption and excavation of a pre existing summit dome

mesoproterozoic trans laurentian magmatism a synthesis of continent wide age distributions new sims u pb ages zircon saturation temperatures and hf and nd isotopic compositions abstract the origin and tectonic setting of the mesoproterozoic 1 50 1 34 ga granite rhyolite provinces of the midcontinent region of the united states and the coeval a type granite plutons of the southwestern united states have been an enigma for decades in this paper we review the history of this problem examine the significance of a wealth of previously published u pb zircon and whole rock sm nd data and present new u pb zircon age and lu hf isotopic data from selected zircon samples our data show that the initiation of this magmatism spans the interval 1 50 1 40 ga across the continent but there is a general younging westward younger 1 39 1 34 ga magmatism also occurred across the continent but forms a major magmatic event only in the south central mid continent there is generally a good correlation between sm nd and lu hf isotopic compositions and inferred mantle derivation model ages except possibly in southeastern oklahoma the absence of older cores in zircons is compatible with calculated zircon saturation temperatures of ca 850 c and supports mantle driven basaltic underplating and resulting crustal partial melting as a petrogenetic model for the a type magmatism our new data compilation refines the existence of the nd line that extends from southwestern texas into southeastern michigan and the western grenville province in canada it marks an isotopic boundary between granites and rhyolites of cratonal origin to the northwest 1 8 1 6 ga model ages and those of more juvenile origin to the southeast 1 5 1 4 ga model ages our suggested tectonic model for the mesoproterozoic a type magmatism across eastern and southern laurentia involves the development of an active laurentian margin extending from eastern canada across what is now the midcontinent region of the united states and at least into the current southwestern united states magmatism along this margin was likely related to asthenosphere lithosphere interactions associated with the accretion of outboard arcs and possible exotic terranes that caused complex deformational and magmatic responses in the continental interior this activity evidently spread from northeast to southwest over a period of ca 70 million years the occurrence of the younger ca 1 39 1 34 ga event indicates that similar processes occurred some 130 million years later suggesting a long lived convergent plate margin and recurring basaltic underplating in some locations perhaps due to inboard lithospheric delamination and or mantle upwelling

minette lavas and associated leucitites from the western front of the mexican volcanic belt petrology chemistry and origin during the late pliocene k rich minette and leucitite lavas erupted in the western mexican volcanic belt near the town of los volcanes a region which is located much closer to the middle america trench than the main line of currently active andesite stratovolcanoes during this period the tectonic regime in western mexico was highly complex due to the simultaneous occurrence of active subduction of the young rivera plate and rifting caused by crustal extension most of these basic lavas contain phenocrysts of phlogopite augite and apatite along with microphenocrysts of leucite and fe ti oxide olivine is absent from all but two of the flows one an olivine leucitite and the other a felsic minette the phlogopite phenocrysts and high whole rock fe2o3 feo ratios which are characteristic of this suite record evidence of high magmatic water contents and oxygen fugacities all of these rock types are highly enriched in the large ion lithophile and light rare earth elements with sr 5100 ppm ba 4800 ppm and ce 330 ppm they are also mildly enriched in the high field strength elements e g zr 260 700 ppm and display the strong relative enrichment of the lile over the hfse that is characteristic of magmas erupted in convergent margins consideration of high pressure phase equilibria in the mg2sio4 camgsi2o6 kalsio4 sio2 system shows that the minettes from this region are not related through fractional crystallization to the more mgo rich olivinebearing minettes which have erupted in other parts of the western mexican volcanic belt during the quaternary this conclusion is consistent with both the trace element geochemistry of these lavas and with the results of fractional crystallization models instead the data suggests that these high k magmas were derived from a source region which consists predominantly of phlogopite clinopyroxene and apatite and which has formed through hydrous enrichment of the subarc mantle in response to subduction

apatite liquid partition coefficients for the rare earth elements and strontium abstract sixteen sets of apatite liquid partition coefficients dap liq for the rare earth elements ree la sm dy lu and six values for sr were experimentally determined in natural systems ranging from basanite to granite the apatite melt glass assemblages were obtained from starting glasses artificially enriched in ree sr and fluorapatite components these were run under dry and hydrous conditions of 7 5 20 kbar and 950 1120 c in a solid media piston cylinder apparatus an sem equipped electron microprobe was used for subsequent measurement of ree and sr concentrations in coexisting apatites and quenched glasses the resulting partition coefficient patterns resemble previously determined apatite phenocryst groundmass concentration ratios in the following respects 1 the rare earth patterns are uniformly concave downward i e the middle ree are more compatible in apatite than the light and heavy ree 2 dreeap liq is much higher for silicic melts than for basic ones and 3 strontium and therefore eu2 is less concentrated by apatite than are the trivalent ree the effects of both temperature and melt composition on dreeap liq are systematic and pronounced at 950 c for example a change in melt sio2 content from 50 to 68 wt causes the average ree partition coefficient to increase from 7 to 30 a 130 c increase in temperature on the other hand results in a two fold decrease in dreeap liq partitioning of sr is insenstitive to changes in melt composition and temperature and neither the sr nor the ree partition coefficients appear to be affected by variations in pressure or h2o content of the melt the experimentally determined partition coefficients can be used not only in trace element modelling but also to distinguish apatite phenocrysts from xenocrysts in rocks reported apatite megacryst host basalt ree concentration ratios 12 for example are considerably higher than the equilibrium partition coefficients which suggest that in this particular case the apatite is actually xenocrystic a reversal experiment incorporated in our study yielded diffusion profiles of ree in apatite from which we extracted a ree ca interdiffusion coefficient of 2 4 10 14 cm2 s at 1120 c extrapolated downward to crustal temperatures this low value suggests that complete ree equilibrium between felsic partial melts and residual apatite is rarely established

volcano tectonic earthquakes a new tool for estimating intrusive volumes and forecasting eruptions abstract we present data on 136 high frequency earthquakes and swarms termed volcano tectonic vt seismicity which preceded 111 eruptions at 83 volcanoes plus data on vt swarms that preceded intrusions at 21 other volcanoes we find that vt seismicity is usually the earliest reported seismic precursor for eruptions at volcanoes that have been dormant for decades or more and precedes eruptions of all magma types from basaltic to rhyolitic and all explosivities from vei 0 to ultraplinian vei 6 at such previously long dormant volcanoes because large eruptions occur most commonly during resumption of activity at long dormant volcanoes vt seismicity is an important precursor for the earth s most dangerous eruptions vt seismicity precedes all explosive eruptions of vei 5 and most if not all vei 4 eruptions in our data set surprisingly we find that the vt seismicity originates at distal locations on tectonic fault structures at distances of one or two to tens of kilometers laterally from the site of the eventual eruption and rarely if ever starts beneath the eruption site itself the distal vt swarms generally occur at depths almost equal to the horizontal distance of the swarm from the summit out to about 15 km distance beyond which hypocenter depths level out we summarize several important characteristics of this distal vt seismicity including swarm like nature onset days to years prior to the beginning of magmatic eruptions peaking of activity at the time of the initial eruption whether phreatic or magmatic and large non double couple component to focal mechanisms most importantly we show that the intruded magma volume can be simply estimated from the cumulative seismic moment of the vt seismicity from log10 v 0 77 log moment 5 32 with volume v in cubic meters and seismic moment in newton meters because the cumulative seismic moment can be approximated from the size of just the few largest events and is quite insensitive to precise locations the intruded magma volume can be quickly and easily estimated with few short period seismic stations notable cases in which distal vt events preceded eruptions at long dormant volcanoes include nevado del ruiz 1984 1985 pinatubo 1991 unzen 1989 1995 soufriere hills 1995 shishaldin 1989 1999 tacana 1985 1986 pacaya 1980 1984 rabaul 1994 and cotopaxi 2001 additional cases are recognized at frequently active volcanoes including popocateptl 2001 2003 and mauna loa 1984 we present four case studies pinatubo soufriere hills unzen and tacana in which we demonstrate the above mentioned vt characteristics prior to eruptions using regional data recorded by neic we recognized in near real time that a huge distal vt swarm was occurring deduced that a proportionately huge magmatic intrusion was taking place beneath the long dormant sulu range new britain island papua new guinea that it was likely to lead to eruptive activity and warned rabaul volcano observatory days before a phreatic eruption occurred this confirms the value of this technique for eruption forecasting we also present a counter example where we deduced that a vt swarm at volcan cosiguina nicaragua indicated a small intrusion insufficient to reach the surface and erupt finally we discuss limitations of the method and propose a mechanism by which this distal vt seismicity is triggered by magmatic intrusion

deposit temperature of pyroclastic density currents emplaced during the el chichon 1982 and colima 1913 eruptions new data on the pyroclastic density current pdc deposit temperature t dep are provided for two prominent eruptions of mexican volcanoes of the twentieth century the 1982 eruption of el chichon and the 1913 eruption of colima in spite of similar lithofacies magma composition and pre eruptive conditions the t dep of the pdcs from the 1982 el chichon and 1913 colima eruptions differ significantly with intervals of t dep of 360 420 c and 250 330 c respectively these new data emphasize that a full understanding of the physical mechanisms responsible for equilibrium temperature attainment within a pyroclastic deposit has not yet been realized the t dep measured for el chichon pdc deposits confirm the preliminary data published elsewhere while colima magnetic temperatures provide different values to those published previously

neo proterozoic rift related syenites northern damara belt namibia geochemical and nd sr pb o isotope constraints for mantle sources and petrogenesis abstract major element trace element and nd sr pb o isotope data for a suite of neo proterozic pre orogenic rift related syenites from the northern damara orogen namibia constrain their sources and petrogenesis new u pb ages obtained on euhdreal titanite of inferred magmatic origin constrain the age of intrusion of the lofdal and oas syenites to ca 750 ma compatible with previous high precision zircon analyses from the oas complex major rock types from lofdal and oas are mildly sodic nepheline normative and quartz normative syenites and were primarily generated by fractional crystallization from a mantle derived alkaline magma primitive samples from lofdal and oas show depletion of rb k and th relative to ba and nb together with variable negative anomalies of p and ti on a primitive mantle normalized diagram evolved samples from oas develop significant negative ba sr p and ti anomalies and positive u and th anomalies mainly as a function of crystal fractionation processes the lack of a pronounced negative nb anomaly in samples from lofdal suggests that involvement of a crustal component is negligible for the nepheline normative samples from lofdal the unradiogenic sr and radiogenic nd isotope composition and low 18 o values suggest derivation of these samples from a moderately depleted lithospheric upper mantle with crustal like u pb ratios 87 sr 86 sr 0 7031 0 7035 e nd ca 1 18 o 7 206 pb 204 pb ca 18 00 207 pb 204 pb 15 58 15 60 primitive samples of the oas quartz normative syenites have identical isotope characteristics 87 sr 86 sr 0 7034 e nd ca 1 18 o 6 5 206 pb 204 pb ca 18 00 207 pb 204 pb 15 59 whereas more differentiated samples have higher 87 sr 86 sr ratios 0 709 0 714 slightly higher 18 o values 7 0 7 1 less radiogenic e nd values 1 1 to 1 4 and more radiogenic 206 pb 204 pb ratios up to 18 27 these features together with model calculations using sr nd pb isotopes suggest modification of a primary syenite magma by combined afc processes involving ancient continental crust in this case high nb abundances of the parental syenite liquid prevent the development of significant negative nb anomalies that may be expected due to interaction with continental crust

mesoarchean and paleoproterozoic history of the nimrod complex central transantarctic mountains antarctica stratigraphic revisions and relation to the mawson continent in east gondwana abstract high grade metamorphic and igneous rocks originally mapped as the nimrod group represent the only known crystalline basement of the east antarctic shield exposed in the transantarctic mountains shrimp u pb age data from zircon show that this assemblage preserves multiple geologic events spanning 2 5 b y of archean to early paleozoic history culminating in thermomechanical reworking and active margin magmatism during the ross orogeny new age data from igneous and metamorphic rocks as well as from detrital zircons in metasedimentary quartzites refine the mesoarchean to paleoproterozoic history and indicate the need to abandon the stratigraphic term nimrod group and its five formations in its place we redefine only the igneous and high grade gneissic parts of the assemblage as the nimrod complex and all other metasedimentary rocks exposed in the miller and geologists ranges are included in a newly defined argosy schist within the nimrod complex the oldest layered gneisses represent magmatic mesoarchean crust formed between about 3150 and 3050 ma correspondence of u pb zircon crystallization ages with whole rock sm nd model ages indicates formation from juvenile mantle melts magmatism at ca 3100 ma was followed closely by high temperature metamorphism recorded by zircon crystallization at 2955 2900 ma likely due to high advective heat transfer and or thermal insulation of newly stabilized crust metaigneous units with ages of ca 2500 ma indicate a late neoarchean period of anatexis and or magmatism although the geologic context for these events is uncertain gneissic eclogitic and metaigneous rocks record an important period of deep crustal metamorphism thickening and magmatism between 1730 and 1700 ma referred to as the nimrod orogeny that may have played an early role in assembly of east gondwana cratons a new lithodemic unit argosy schist consists of interlayered mica schist quartzite amphibolite and calc silicate schist quartzites from the schist unit have two distinctive detrital zircon provenance characteristics one type has populations that correlate with dated gneissic and metaigneous units of the nimrod complex indicating a proximal provenance whereas a second type has detrital zircon ages resembling those from neoproterozoic beardmore group sandstones indicating a common broader east antarctic shield provenance their maximum depositional ages range widely from about 2000 to 900 ma leaving unresolved their age and geologic relationship to either the nimrod complex or beardmore group yet they comprise a metasedimentary assemblage that is distinctive from the nimrod complex recent findings of mesoarchean gneisses in the gawler craton geochronology from terre adelie and our new age data from the nimrod complex thus highlight the importance of ca 3 1 2 5 and 1 7 ga events in formation of the composite east antarctic shield adjacent to the modern transantarctic mountains correlative crustal units may extend to the southern prince charles mountains and shackleton range collectively this extensive crustal province referred to as the mawson continent represents an elongate belt of primary mesoarchean crust that experienced major reworking at ca 2 5 and 1 7 ga the latter period includes both high and low p t petrologic signatures providing evidence of crustal thickening and magmatism that may signify collisional processes related to paleoproterozoic cratonal amalgamation during formation of the nuna supercontinent

behavior of isotopic systematics during deformation and metamorphism a hf nd and sr isotopic study of mylonitized granite a combined compositional and hf nd and sr isotopic study was performed on a suite of samples of progressively deformed granite from a mylonite zone in the harquahala mountains western arizona to evaluate the effects of deformation and metamorphism on the isotopic systematics of typical continental crustal rocks the 1 4 ga harquahala granite was deformed during mesozoic thrusting along the harquahala thrust granite in the resulting 60 m wide shear zone ranges from protomylonite to ultramylonite in most of these mylonites the protolith is not megascopically recognizable and can be discerned only by the progressive transition to undeformed granite isotopic analyses of hf nd and sr from the shear zone document the immobility of the hf and nd isotopic systems relative to that of the sr isotopic system during deformation the rb sr isotopic data show considerable scatter on an isochron plot exhibiting both gains and losses of rb and sr from the whole rock systems in contrast the sm nd and lu hf isotopic systematics are mostly well behaved on isochron diagrams plotting mostly in tight clusters or along 1 4 ga isochrons these results show that while the sr isotopic system in crustal rocks is quite susceptible to later tectonic disturbance both hf and nd isotopic systems can provide reliable model age information in continental crustal terranes even when the rocks have been subjected to low to medium grades of deformation and metamorphism

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

origin and chemical evolution of the 1360 ma san isabel batholith wet mountains colorado a mid crustal granite of anorogenic affinities the 1360 ma san isabel batholith is a weakly foliated hornblende biotite sphene monzogranite consisting predominantly of two variants a coarse grained facies and a medium grained equigranular facies it is a deeper seated portion mid crustal 5 7 kbar of the extensive rhyolite and upper crustal granite terrane that occurs in parts of missouri oklahoma kansas and texas mafic minerals are abundant variable in amount to as high as 35 and segregated into mafic enriched zones the san isabel magma probably formed in an anorogenic setting as suggested by 1 high total alkali and high feo feo mgo ratios 2 relatively dry nature 3 trace element plots in tectonic discrimination diagrams 4 similar composition of its leucogranite differentiates to shallower a type granites and 5 contemporaneity with other a type granites compared to many granitic plutons the batholith contains small negative eu anomalies low sio 2 56 1 72 0 wt moderate sr and high fe ti k mn ba sc ree9s and feo feo mgo there are large and fairly linear ranges in the abundances of elements concentrated in mafic minerals for example fe ti mg and ca and smaller ranges more scatter in elements concentrated in the felsic minerals for example eu anomaly size and ba the san isabel magma is thus distinctly mafic in comparison with shallow a type magmas the san isabel magma could have formed by 20 aggregate melting of a tonalite andesite or by

sg06 a fully continuous and varved sediment core from lake suigetsu japan stratigraphy and potential for improving the radiocarbon calibration model and understanding of late quaternary climate changes abstract the high potential of the varved sediments of lake suigetsu central japan to provide a purely terrestrial radiocarbon calibration model and a chronology of palaeoclimatic changes has been widely recognised for the last two decades however this potential has not been fully realised since the only available long sediment core from the lake sg93 was extracted from a single bore hole and was therefore interrupted by gaps of unknown duration between successive core sections in the summer of 2006 a new sediment core sg06 was recovered from the lake four separate boreholes were drilled and the parallel sets of cores recovered were found to overlap completely without gaps between segments this new record provides the ability to test existing atmospheric radiocarbon calibration models as well as to assess the scale of inter regional leads and lags in palaeoclimatic changes over the last glacial interglacial cycle multi disciplinary analyses from sg06 are still ongoing but a reliable description of the sedimentary sequence needs to be provided to the wider science community before major outputs from the project are released thereby allowing fully informed critical evaluation of all subsequent releases of data based on the sg06 record in this paper we report key litho stratigraphic information concerning the sg06 sediment core highlighting changes in the clarity of annual laminations varves with depth and possible implications for the mechanism of the climate change we also discuss the potential of the sg06 record to meet the fundamental goals of the inqua intimate project