imaging subduction from the trench to 300 km depth beneath the central north island new zealand with vp and vp vs summary recent dense deployments of portable digital seismographs have provided excellent control on earthquakes beneath the central north island of new zealand here we use a subset of the best recorded earthquakes in an inversion for the 3 d vp and vp vs structure the data set includes 39 123 p observations and 18 331 s observations from 1239 earthquakes and nine explosions the subducted plate is imaged as a high vp low vp vs feature vp within the mantle of the subducted slab is almost always 8 5 km s 1 which requires the ca 120 myr slab to be unusually cold the low vp vs within the subducted plate closely parallels the lower plane of the dipping seismic zone it most likely indicates fluid resulting from dehydration of serpentine in the slab mantle and the earthquakes themselves are likely to be promoted by dehydration embrittlement we identify a region with vp 8 0 km s 1 directly above the dipping seismic zone can be interpreted as sinking entrained with the motion of the subducted slab and forming a viscous blanket that insulates the slab from the high temperature mantle wedge material in the overlying low vp region can be interpreted as rising within a return flow within the wedge the volcanic front appears to be controlled by where this dipping low vp region meets the base of the crust the thickness of the backarc crust also shows significant variation along strike in the central taupo volcanic zone tvz the crust is ca 35 km thick while southwest of mt ruapehu the crust thickens by ca 10 km there is no significant low vp zone in the mantle wedge in this southwestern region suggesting that this thicker crust has choked off mantle return flow the seismic tomography results when combined with constraints on mantle flow from previous shear wave splitting results provide a plausible model for both the distribution of volcanism in the central north island and the exceptional magmatic productivity of the central tvz

first report of wiwaxia from the cambrian chengjiang lagerstatte research was supported by the chinese academy of sciences kzzd ew 02 2 the national basic research program of china 2013cb835006 the national natural science foundation of china 41472012 the natural science foundation of jiangsu province bk2012893 and clare college cambridge

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

effect of stress fields on magma chamber stability and the formation of collapse calderas 1 the summits of many of the earth s and other planets larger volcanoes are occupied by calderas that formed by collapse into an evacuating underlying magma chamber these collapse calderas are typically several tens of square kilometers in area and are commonly elliptical in shape we show that the long axes of late quaternary collapse calderas in the kenya rift valley the western basin and range province the snake river yellowstone plateau and the iceland rift zone are parallel to the upper crustal minimum horizontal stress direction sh as determined by independent criteria we suggest that circular magma chambers beneath these volcanoes became elliptical by stress induced spalling of their chamber walls by a mechanism that is analogous to the formation of breakouts in boreholes and tunnels in breakouts the hole becomes elongate parallel to the far field minimum stress in the kenya rift late pleistocene caldera collapse was accompanied by a 45 rotation of sh and an increase in the magnitude of the maximum horizontal stress sh the breakout model predicts increasingly unstable caldera walls under these conditions a possible explanation for the sudden appearance of so many collapse events in a volcanic setting that had never experienced them before this mechanism of stress change induced collapse may have played a role in other caldera settings

new wiwaxia material from the tsinghsutung formation cambrian series 2 of eastern guizhou china wiwaxia is an extinct early metazoan with uncertain affinities which is well represented in strata of cambrian series 2 3 age well preserved representatives of wiwaxia are known from the burgess shale biota and the kaili biota here new material of wiwaxia corrugata matthew 1899 is reported from the upper part of the tsinghsutung formation cambrian series 2 near balang village guizhou province china these specimens have a close evolutionary relationship to wiwaxia taijiangensis zhao qian lee 1994 from the overlying kaili formation new wiwaxia material from the tsinghsutung formation and observations of specimens with articulated individuals from the kaili formation suggest that wiwaxia taijiangensis should be a junior synonym of w corrugata a new study indicates that w corrugata has a wide geographic distribution a short geological history and evolutionary uniqueness and provides new data on taphonomy of this genus

quaternary temporal stability of a regional strike slip and rift fault intersection abstract intersecting strike slip and normal fault systems form either two or three plate configurations in circumstances where they intersect to form a triple junction internal block deformation produces a quasi stable 3 d configuration permitting maintenance of both the regional geometry and kinematics of the intersection this paper examines the temporal stability of such a triple junction in new zealand over a range of timescales from individual earthquakes to millions of years and discusses the factors that impact its stability using seismic reflection gravity drill hole and outcrop data the accumulation of vertical displacements is examined both on individual faults and across the intersection zone between the strike slip north island fault system nifs and the taupo rift fault throws and throw rates for the nifs and taupo rift suggest that despite a three fold increase in throw rates in both fault systems at about 0 3 ma which may have modified the orientation of the slip vectors and therefore the contemporary kinematics of the triple junction the intersection of the two fault systems has functioned coherently for the last 0 6 1 5 myr accumulating vertical displacements interdependently since the early stages of rifting the apparent arrest of a large magnitude earthquake on the rift bounding fault adjacent to the intersection suggests that the short term dynamic behaviour of the system is relatively complex compared to the more coherent long term kinematics

fossilization modes in the chengjiang lagerstatte cambrian of china testing the roles of organic preservation and diagenetic alteration in exceptional preservation abstract one important and poorly understood issue concerning the taphonomy of nonmineralizing organisms in cambrian burgess shale type deposits is the diagenetic pathways by which organisms have become exceptionally preserved scanning electron microscopy sem analyses of exceptionally preserved fossils from the lower cambrian chengjiang deposit of china demonstrate that nonmineralized tissue is preserved in a variety of ways and further suggest that there was some taxonomic control over the precipitation of authigenic minerals during early diagenesis organic preservation is limited to certain decay resistant structures such as heavily sclerotized spines on the claws of anomalocaridids labile organic tissues of nearly all nonmineralizing animals however are preserved by thin films of diagenetic minerals microstructural studies energy dispersive x ray edx analyses and elemental mapping of these minerals indicate that mineral films include apatite pyrite and fe rich aluminosilicates the results support the assumption that early diagenetic mineralization such as phosphatization and pyritization played a key role in the preservation of nonmineralized organisms pyritization seems to be the most important process by which nonmineralizing chengjiang organisms are preserved in exceptional condition precipitation of fe rich aluminosilicates which occurred following pyritization also played a role in the preservation of some chengjiang fossils phosphatization in the chengjiang lagerstatte was evidently rare and limited taxonomically or to animals having large masses of organic material

crystallisation ages in coeval silicic magma bodies 238u 230th disequilibrium evidence from the rotoiti and earthquake flat eruption deposits taupo volcanic zone new zealand abstract the timescales over which moderate to large bodies of silicic magma are generated and stored are addressed here by studies of two geographically adjacent successive eruption deposits in the taupo volcanic zone new zealand the earlier caldera forming rotoiti eruption 100 km3 magma at okataina volcano was followed within months at most by the earthquake flat eruption 10 km3 magma from nearby kapenga volcano both generated non welded ignimbrite and coeval widespread fall deposits the rotoiti and earthquake flat deposits are both crystal rich high silica rhyolites with sparse glass bearing granitoid fragments also occurring in rotoiti lag breccias generated during caldera collapse here we report 238u 230th disequilibrium data on whole rocks and mineral separates from representative rotoiti and earthquake flat pumices and the co eruptive rotoiti granitoid fragments using tims and in situ zircon analyses by sims multiple grain zircon controlled crystallisation ages measured by tims from the rotoiti pumice range from 69 3 ka 350 ka with a pronounced peak at 70 90 ka the weighted mean of isochrons is 83 14 ka in accord with the tims data one glass bearing rotoiti granitoid clast yielded an age of 57 8 ka by tims controlled by th rich phases that however are not apparently present in the juvenile pumices another glass bearing rotoiti granitoid yielded sims zircon model ages peaking at 60 90 ka having a similar age distribution to the pumice age data from pumices are consistent with a published 64 4 ka eruptive age now modified to 62 2 ka but chemical and or mineralogical data imply that the granitoid lithics are not largely crystalline rotoiti rhyolite but instead represent contemporaneous partly molten intrusions reflecting different sources in their chemistries and mineralogies similarly although the earthquake flat eruption immediately followed and probably was triggered by the rotoiti event age data from juvenile material are significantly different a multiple grain zircon controlled crystallisation age measured by tims from a representative pumice is 173 5 ka while sims model ages range from 70 26 34 ka to 350 ka with a peak at 105 ka these age data coupled with previously published geochemical and isotopic data show that the rotoiti and earthquake flat deposits were erupted from independent unconnected magma bodies

small carbonaceous fossils scfs a new measure of early paleozoic paleobiology use of a low manipulation hydrofluoric acid extraction procedure on cambrian mudstones reveals an unexpectedly abundant and diverse range of small carbonaceous fossils scfs primarily the disarticulated sclerites and cuticular fragments of animals relatively recalcitrant forms such as wiwaxia sclerites and priapulid like scalids are sufficiently common to yield a reasonably reliable biostratigraphic signal unlike their rare macroscopic counterparts molluscan radulae crustacean appendages and the carbonaceous components of originally mineralized metazoan sclerites provide further insights into the histology diversity and distribution of early metazoans the widespread occurrence of scfs is due in part to their enhanced biostratinomic potential for transport burial and preservation particularly in well aerated epicratonic settings not represented by burgess shale type macrofossils more generally the scf record represents a largely untapped measure of ecological and evolutionary dynamics through the early paleozoic

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

multiple rhyolite magmas and basalt injection in the 17 7 ka rerewhakaaitu eruption episode from tarawera volcanic complex new zealand abstract the 17 7 ka rerewhakaaitu eruption episode volume 5 km3 dre rhyolite magma was the second of five major episodes that have built the tarawera volcanic complex in the okataina volcanic centre over the past 22 kyr the rerewhakaaitu episode produced a widespread tephra fall deposit associated proximal pyroclastic flow deposits and voluminous rhyolite lava extrusions two different rhyolite magmas t1 and t2 were simultaneously erupted from the main vent area throughout much of the eruption episode t1 magma was a crystal poor orthopyroxene hornblende rhyolite that is highly evolved whole rock sio2 77 wt with a moderate temperature 760 c based on fe ti oxides t2 is a crystal rich biotite hornblende rhyolite that is less evolved sio2 75 wt with a fe ti oxide temperature of 700 c ejecta from the simultaneous and sequential eruption of these two magmas include some pumice clasts with mixed hybrid and mingled glass compositions and crystal populations a third rhyolite magma t3 was extruded from another vent 3 km distant to form an apparently contemporaneous lava dome t3 was the least evolved sio2 74 wt and hottest 820 c of the three magmas saturation pressures calculated using dissolved h2o and co2 contents of melt inclusions in quartz crystals indicate that t2 magma stagnated and crystallised at about 12 km depth while small quartz crystals in t1 magma grew during ascent through 8 km depths some t1 and t2 rhyolite clasts contain vesicular brown blebs with widely variable andesite to rhyolite glass compositions accompanied by olivine clinopyroxene and calcic plagioclase crystals that are interpreted as xenocrysts derived from injected basalt temperatures over 1000 c estimated from pyroxene phase equilibria in these clasts reflect intrusion of the more mafic magma which is now identified as the priming and triggering mechanism for three of the four post 22 ka tarawera rhyolite eruption episodes however the rhyolite magma bodies and conduits modelled for each episode have considerable differences in characteristics and geometry our preferred model for the rerewhakaaitu episode is that eruptions occurred from three laterally and vertically isolated rhyolite magma bodies that were initially primed and triggered by basalt intrusion during a regional rifting event the ascending hotter and less viscous t1 rhyolite magma intersected and further invigorated a stagnant pond of cooler denser and more viscous t2 magma and lubricated its transport to the surface

oblique back arc rifting of taupo volcanic zone new zealand taupo volcanic zone tvz is a back arc rift innorth island new zealand its geometry andkinematics are investigated using shaded reliefimages field examination of faults and offset streamchannels the results show that tvz trends nne is 250 km long by hikurangi margin in the north island of new zealand 20 km wide and consists of fivesegments extension is principally manifest as steeplydipping 60 90 normal faults parallel to tvz these in the last 300 kyr have experienced acomponent of dextral shear tvz is therefore anoblique back arc rift the dextral shear is 37 of thetotal displacement which for previously estimatedspreadingrates 7mm yr correspondsto 2 6mm yr thisvalueissimilartopreviousestimatesofthedextralshear from the back arc to the forearc domains in thenorthisland distributeddextralshearacrosstvzthussuggests that strain partitioning across the plateboundary at latitudes of tvz is less significant thanpreviously thought

magma induced strain localization in centrifuge models of transfer zones abstract scaled centrifuge experiments have been used to investigate the dynamic relations between deformation and magma distribution in rift related transfer zones the physical models were built using suitable analogue materials such as sand to represent the brittle upper crust various kinds of silicone mixtures to simulate the lower crust and upper mantle and glycerol to reproduce magma models simulated the development of transfer zones across pre existing glycerol reservoirs placed at the base of the analogue continental crust in plan view different geometries dimensions and positions of subcrustal reservoirs were reproduced in three different sets of experiments to compare results models were also performed without magma simulating glycerol set 1 experiments incorporating a narrow rectangular glycerol reservoir show that the low viscosity material is able to localise deformation into the overlying crust giving rise to discrete transfer zones this concentrated surface deformation corresponds at depth to major magma accumulation set 2 experiments with an initial wide squared glycerol reservoir show instead that deformation is distributed across the whole model surface corresponding at depth to relatively minor magma accumulation set 3 experiments explored various positions of a small squared reservoir that invariably localised faulting in the overlying analogue brittle crust at the onset of model deformation the overall model behaviour suggests that magma distribution at depth can effectively control the strain distribution in the overlying crust and the deformative pattern of transfer zones strain distribution in turn may control magma emplacement as localized deformation would favour major accumulation of magma at transfer zones coupled to a strong thermal weakening of the country rocks this process may ultimately lead to a positive feedback interaction between magma and deformation

vent migration and changing eruptive style during the 1800a taupo eruption new evidence from the hatepe and rotongaio phreatoplinian ashes the 1800a taupo eruption was one of the most complex silicic eruptions worldwide within the past 5000 years new work on phases 3 and 4 the hatepe and rotongaio ashes has identified a mappable internal stratigraphy for each enabling detailed isopach and isopleth measurements for subunits within the deposits the new data indicate that the vent configuration for the taupo eruption was more complex than previously thought and involved at least three sources on a ne sw fissure centred on horomatangi reefs phases 1 3 of the eruption were from a southwestern vent s phase 4 from a northeastern source and phases 5 and 6 probably from the horomatangi reefs area a separate source for the rotongaio ash phase 4 helps explain the contrast between the pumice rich phases of the eruption and the dense juvenile clasts of the rotongaio ash the rotongaio magma resided in a separate initially blind conduit and was degassing prior to and during earlier phases of the taupo eruption this new work on the hatepe and rotongaio ashes underscores the importance of a detailed stratigraphic framework in deciphering extremely fine grained fall units of largescale sustained eruptions

continental rift architecture and patterns of magma migration a dynamic analysis based on centrifuge models 1 small scale centrifuge models were used to investigate the role of continental rift structure in controlling patterns of magma migration and emplacement experiments considered the reactivation of weakness zones in the lower crust and the presence of magma at moho depths results suggest that surface deformation which reflects the weakness zone geometry exerts a major control on patterns of magma migration in the case of a single rift segment the experimental lower crust and magma were both transferred in an extension parallel direction toward the rift flanks this lateral migration reflected the dominance of far field stresses over extension induced buoyancy forces local pressure gradients favored the raise of experimental magma in correspondence of marginal grabens the lateral migration gave rise to major accumulations below the footwall of major boundary faults providing the magma source able to feed off axis volcanoes in nature as inferred for the main ethiopian rift in the case of two offset rift segments a major transfer zone developed this transfer zone was characterized by prominent experimental lower crust doming and strong magma accumulation dynamic analysis showed that the transfer zone development caused a strong pressure difference in a rift parallel direction which dominated over the far field thinning owing to this pressure gradient almost all the underplated experimental magma collected below the lower crust dome suggesting a rift parallel extension orthogonal migration this process has a direct relevance for the localization of magmatic activity at transfer zones in natural continental rifts such as in the western branch of the east african rift system

spatial variation in the diversity and composition of the lower cambrian series 2 stage 3 chengjiang biota southwest china abstract strata hosting the lower cambrian series 2 stage 3 chengjiang biota maotianshan shale member yu anshan formation occur throughout the eastern part of yunnan province southwest china in this study literature based faunal inventories from 10 areas representing 34 localities together with 22 038 new specimens collected at three localities from three of the 10 areas were analyzed quantitatively to assess large scale spatial variation in taxonomic diversity and composition our analyses show substantial co variation between local paleoenvironmental settings and species diversity and suggest the presence of three general taphofacies in the maotianshan shale member from west to east low diversity 26 species characterizes the wuding area where fossiliferous strata have undergone extensive bioturbation high diversity 215 species characterizes the chengjiang haikou anning areas where fossiliferous strata consist of stacked couplets of thin event and background mudstone layers moderate diversity 55 species characterizes the malong area where fossiliferous strata consist of indistinctly bedded shale showing fewer single event layers but abundant background layers in spite of variations in sampling effort between sites spatial patterns in species diversity and community composition were controlled primarily by variation in depositional environments along a proximal offshore to lower shoreface gradient which influenced both ecological and taphonomic factors the offshore settings haikou chengjiang anning areas show relatively high species diversity and exceptional preservation of soft bodied fossils reflecting rapid burial in distal tempestites relatively high degrees of bioturbation time averaging and hydrodynamic disturbance caused a substantial decrease in the quality of preservation and number of soft bodied species in the wuding and malong areas arthropods are the most diverse group in most localities followed by priapulids poriferans brachiopods lobopods and hyoliths this study shows that the chengjiang biota lends itself very well to high resolution characterization of spatial variation in taxonomic diversity faunal composition and fossil preservation furthermore the chengjiang biota may provide a unique opportunity to assess the roles of environmental factors taphonomy and ecological controls on species diversity at local to regional spatial scales

devonian permian magmatic pulses in the northern vosges mountains ne france result of continuous subduction of the rhenohercynian ocean and avalonian passive margin

a geophysical geological transect of the silent canyon caldera complex pahute mesa nevada revision of lithological logs for boreholes penetrating the volcanic center at pahute mesa nevada has led to a thorough review of the volcanic stratigraphy and geologic structure we have combined this review with a compilation of old and newly acquired gravity and seismic travel time data producing a unified interpretation along a northwest to southeast profile the analysis supports a new interpretation of the silent canyon caldera complex the caldera is found to be more asymmetric than previously suggested with the southeastern boundary formed by linear high angle normal faults and a more gently sloping northwestern boundary the total thickness of volcanic units within the caldera complex does not appear to exceed 5 km the shallow structure at pahute mesa could have a profound effect on the seismic response for regional and teleseismic signals from this nuclear test site the silent canyon caldera complex is actually a set of nested calderas first filled by thick 1 km postcaldera lavas and subsequently buried by outflow sheets of the timber mountain caldera to the south thick postcaldera lavas filled a half graben structure formed west of the west greeley fault dropping the tops of the youngest caldera forming units to depths in excess of 2 km therefore the western boundary of the caldera complex is poorly defined east of the west greeley fault two overlapping calderas are defined and stratigraphic data suggest the presence of even older calderas the youngest caldera the calc alkaline area 20 caldera is well defined from drill hole data the area 20 caldera overlaps the 13 6 ma peralkaline grouse canyon caldera which is less well defined but apparently collapsed in trap door style along the almendro fault for both these calderas collapse continued after the main caldera forming eruption concurrent with the accumulation of thick 1 km lavas within the peripheral collapse zones the geophysical interpretation indicates that the major structural boundary of the caldera complex corresponds to the nne trending scrugham peak and almendro faults which offset the pre tertiary contact more than 1 km but have less than 200 m offset in rocks of 11 ma age drill hole data show that offsets along these faults increase systematically within older up to 15 ma units which are commonly rotated eastward in a style similar to units at the surface abrupt changes in the subsurface thickness of the caldera forming units occur across the faults indicating that these linear features served as caldera boundaries

asymmetric multiple block collapse at rotorua caldera taupo volcanic zone new zealand calderas worldwide have been classified according to their dominant collapse styles although there is a good deal of speculation about the processes involved recent laboratory experiments have tried to constrain these processes by modelling magma withdrawal and observing the effects on overlying materials however many other factors also contribute to final caldera morphology rotorua caldera formed during the eruption of the mamaku ignimbrite collapse structure and evolution of rotorua caldera is interpreted based its geophysical response geology and geomorphology and the stratigraphy of the mamaku ignimbrite rotorua caldera is situated at the edge of the extensional taupo volcanic zone in which major faults strike ne sw a second less dominant fault set strikes nw se these two fault sets have a strong influence on the morphology of rotorua caldera no one style of collapse can be applied to rotorua caldera it was formed during a single eruption but subsided as many blocks and shows features of trapdoor piecemeal and downsag types of collapse here rotorua caldera is described according to its composition activity and geometry as a rhyolitic single event asymmetric multiple block single locus collapse structure the mamaku ignimbrite is the only ignimbrite to have erupted from rotorua caldera extracaldera thickness of the mamaku ignimbrite is up to 145 m whereas inside the caldera it may be greater than 1 km thick the mamaku ignimbrite can be separated into a basal tephra sequence and main ignimbrite sequence the main ignimbrite sequence contains no observable flow unit boundaries but can be split into lower middle and upper parts lmi mmi umi respectively based on crystal content welding jointing devitrification and vapour phase alteration juvenile clasts within the ignimbrite comprise three consanguineous silicic pumice types and andesitic fragments only the most evolved pumice type occurs in the basal tephra sequence all three pumice types occur together throughout the main ignimbrite sequence whereas the andesitic fragments are only present in umi lithic lag breccias in umi indicate a late stage of caldera collapse concentration of lithic fragments increases towards the middle of the ignimbrite and may also reflect increased subsidence rate during an earlier stage collapse of rotorua caldera is thought to have occurred throughout the eruption of the main ignimbrite sequence of the mamaku ignimbrite allowing simultaneous eruption of all the different pumice types and causing the abrupt transition from deposition of the basal tephra sequence to the main ignimbrite sequence

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

intracaldera volcanic activity toledo caldera and embayment jemez mountains new mexico the toledo caldera was formed at 1 47 0 06 ma during the catastrophic eruption of the lower member bandelier tuff the caldera was obscured at 1 12 0 03 ma during eruption of the equally voluminous upper member of the bandelier tuff that led to formation of the valles caldera earlier workers interpreted a 9 km diameter embayment located ne of the valles caldera toledo embayment to be a remnant of the toledo caldera drill hole data and new k ar dates of toledo intracaldera domes redefine the position of toledo caldera nearly coincident with and of the same dimensions as the younger valles caldera the toledo embayment may be of tectonic origin or a small tschicoma volcanic center caldera this interpretation is consistent with distribution of the lower member of the bandelier tuff and with several other field and drilling related observations explosive activity associated with cerro toledo rhyolite domes is recorded in tuff deposits located between the lower and upper members of the bandelier tuff on the northeast flank of the jemez mountains recorded in the tuff deposits are seven cycles of explosive activity most cycles consist of phreatomagmatic tuffs that grade upward into plinian pumice beds a separate deposit of the same age and consisting of pyroclastic surges and flows is associated with rabbit mountain located on the southeast rim of the valles toledo caldera complex these are the surface expression of what may be a thicker more voluminous intracaldera tuff sequence the combined deposits of the lower and upper members of the bandelier tuff toledo and valles intracaldera sediments tuffs and dome lavas form what we interpret to be a wedge shaped caldera fill this sequence is confirmed by deep drill holes and gravity surveys this fill accumulated in depressions formed during precaldera rifting and episodes of caldera collapse we interpret the toledo valles caldera complex to be a pair of nearly coincident trapdoor calderas with the hinge on the west side and thick caldera fill in the east

the phlegraean fields structural evolution volcanic history and eruptive mechanisms abstract the main event within the volcanic history of the phlegraean fields was the eruption about 35 000 years ago of a huge alkali trachytic ignimbrite 80 km 3 dre followed by caldera collapse the pre caldera activity evidence from geothermal wells and surface outcrops changed from submarine to subaerial shortly before the ignimbrite eruption the caldera was subsequently invaded by the sea and became progressively filled with tuffites and subordinate submarine flows in its northern half the last submarine explosive activity dates back to 12000 10500 yr with the eruption of mostly hydroplinian yellow tuffs recent mostly subaerial activity consists of a series of explosive eruptions whose volume decreases with time until the last eruption of mt nuovo in 1538 a d two peaks in recent activity occur at 10000 8000 and 4700 3000 years ago during post caldera activity eruptive vents migrated from the caldera rim toward the center where there are two distinct zones of recent vents minor collapses occurred within the caldera after the main eruptions often they are eccentric to the vent and displaced toward the caldera center phlegraean explosive activity is characterized by water magma interaction eruptive events without a hydromagmatic component are extremely rare in most cases the evolved trachytic magmas interacted with surface water either the sea or intracaldera lakes however there is evidence of interaction of magma with deep seated aquifers for some plinian events explosivity i e the efficiency of the transformation of thermal into kinetic energy during magma water interaction is largely controlled by the primary fragmentation of the magmatic melt

the reporoa caldera taupo volcanic zone source of the kaingaroa ignimbrites the reporoa caldera occupies the northern end of the reporoa depression previously described as a tectonic fault angle depression earlier confirmation of the topographic basin as a caldera had been hindered by the lack of an associated young pyroclastic flow deposit of large enough volume to have caused caldera collapse new exposures on the eastern margin of the reporoa basin reveal thick lithic lag breccias 30 m interbedded within the 0 24 ma kaingaroa ignimbrites these ignimbrites were previously attributed to the adjacent okataina volcanic centre lag breccia thicknesses and maximum clast sizes decrease rapidly outward from the caldera rim and discrete breccias are absent from ignimbrite sections more than 3 km from the rim the lithic lag breccias together with structural and geophysical evidence confirm reporoa caldera as the source of the c 100 km3 kaingaroa ignimbrites adding another major rhyolitic volcanic centre to the seven previously recognized in the taupo volcanic zone other older calderas may also be present in the reporoa depression

volcanic and structural evolution of the okataina volcanic centre dominantly silicic volcanism associated with the taupo rift new zealand article the okataina volcanic centre ovc contains the northeasternmost caldera complex in onshore taupo volcanic zone tvz new zealand sited largely within the taupo rift pyroclastic fall deposits and ignimbrites deposited in the bay of plenty coast area between 420 and 625 ka were probably erupted from ovc and these provide a maximum age for the centre the earliest ignimbrite for which there is good evidence for eruption from ovc is the c 550 ka quartz biotite ignimbrite exposed to the west of lake okataina and to se of ovc this ignimbrite probably correlates with one of the early ignimbrites found in the kawerau geothermal wells and is large enough to have been accompanied by caldera collapse it was followed by extensive rhyolitic explosive eruptions of the murupara subgroup culminating with eruption of the matahina ignimbrite at c 325 ka this c 160 km 3 magma volume eruption was accompanied by caldera collapse to form the southern part of the present day okataina caldera complex a long duration sequence of rhyolite lavas and pyroclastics was then erupted on the southern and western sides of ovc before eruption of the 100 km

displacement transfer between intersecting regional strike slip and extensional fault systems interaction and displacement transfer between active intersecting strike slip or transform and extensional fault systems are examined outcrop data from a well preserved strike slip fault and rift intersection in new zealand are compared to a global data set of 13 such intersections in both continental and oceanic crust displacement transfer between strike slip and normal faults is typically accomplished by gradual changes of fault orientations and slip vectors close to the intersection zone for two and three plate configurations these changes result in sub parallelism of the slip vectors of the component faults with their line of intersection the dimensions of the area over which fault strike and slip vectors change are principally controlled by the extent to which displacements on the dominant of the two intersecting fault systems are confined to a single slip surface or distributed across a zone where slip is spatially distributed the region in which the two displacement fields are superimposed produces transtension and associated oblique slip this distributed off fault deformation facilitates the development of a quasi stable configuration of the fault intersection region maintaining both the regional geometry and kinematics of the intersection zone which in many cases would not be possible for rigid block translations the dimensions of the transition zone are larger for continental crust than for oceanic crust because oceanic crust is thinner fault geometries in oceanic crust are simpler two plate configurations and the slip vectors of the component intersecting fault systems are sub parallel

a new burgess shale type assemblage from the thin stephen formation of the southern canadian rockies a new burgess shale type assemblage from the stephen formation of the southern canadian rocky mountains is described herein it occurs near stanley glacier in kootenay national park 40 km southeast of the type area near field british columbia while at least a dozen burgess shale localities are known from the thick stephen formation the stanley glacier locality represents the first discovery of burgess shale type fossils from the thin stephen formation the cathedral escarpment an important regional paleotopographic feature has been considered important to the paleoecologic set ting and the preservation of the burgess shale biota however the stanley glacier assemblage was preserved in a distal ramp setting in a region where no evidence of an escarpment is present the low diversity assemblage contains eight new soft bodied taxa including the anomalocaridid stanleycaris hirpex n gen n sp new genus new species pelagic or nektobenthic predators represent the most diverse group whereas in relative abundance the assemblage is dominated by typical cambrian shelly benthic taxa the low diversity of both the benthic taxa and the ichnofauna which includes diminutive trace fossils associated with carapaces of soft bodied arthropods suggests a paleoenvironment with restrictive conditions the stanley glacier assemblage expands the temporal and geographic range of the burgess shale biota in the southern canadian rockies and suggests that burgess shale type assemblages may be common in the thin ste phen formation which is regionally widespread

stratigraphy chronology styles and dynamics of late quaternary eruptions from taupo volcano new zealand taupo volcano is the southerly of two dormant caldera volcanoes in the rhyolite dominated central portion of the taupo volcanic zone in the north island of new zealand taupo has an average magma output rate of 0 2 m 3 s 1 over the past 65 000 years and is one of the most frequently active and productive rhyolite volcanoes known the structure of the modern inverse volcano was formed largely by caldera collapse associated with the voluminous 22 600 14 c years bp oruanui eruption and has been little modified since except for collapse following the 1850 14 c years bp eruption the products of 28 eruptions labelled psi omega a ldots z all of which post date the oruanui eruption are defined and described here twenty seven of these eruptions are represented by pyroclastic deposits of which three were accompanied by a mappable lava extrusion and one eruption z solely by evidence for a lava extrusion the deposits of seven eruptions b c e s v x and y largely correspond to previously defined tephra formations karapiti poronui opepe waimihia whakaipo mapara and taupo respectively the previously defined motutere and hinemaiaia tephras are reinterpreted to represent the products of 12 eruptions g to r while the remaining eight deposits and one eruption are newly recognized eruption psi occurred at ca 17 200 14 c or 20 500 calibrated years bp and eruption z about 1740 calibrated years bp eruption volumes vary by more than three orders of magnitude between 0 01 and more than 44 km 3 and repose periods by more than two orders of magnitude from ca 20 to 6000 years the eruption deposits reflect great variations in parameters such as volume the dispersal characteristics of the fall deposits the presence or absence of intraeruptive time breaks the formation of pyroclastic flows the degree of magma water interaction the vesiculation state of the magma on fragmentation and the relative proportions of juvenile obsidian versus foreign lithologies in the lithic fractions all but seven fall deposits are plinian in dispersal two y1 and probably w are sub plinian one y5 has been termed ultraplinian while psi and a are too poorly preserved for their dispersal to be assessed the lengths of repose periods in the post oruanui sequence range are not randomly distributed but show self similar properties fractal dimensionality repose intervals r in years of not more than 350 years follow n 53 5r 0 21 and those of not less than 350 years follow n 2096r 0 83 where n is the number of eruptions the shorter repose periods may reflect triggering processes such as regional extension affecting magma bodies during their viable lifetimes while longer repose intervals i e not less than 350 years may reflect an episodicity of major rifting events or the production of magma bodies below the volcano bulk volumes v in km 3 of the eruption products also show self similar properties fractal dimensionality with n 6 17v 0 46 however there are then apparently random relationships between eruption volumes and the preceding or succeeding repose period such that prediction of the time and size of the next eruption is impossible the post oruanui activity at taupo represents noise superimposed on the more uniform longer term activity in the central taupo volcanic zone where large greater than 100 km 3 eruptions such as the oruanui occur at more evenly spaced intervals of one per 40 60 000 years

middle late pleistocene tephrostratigraphy of the eastern bay of plenty new zealand abstract up to fifty tephras ranging in age from ca 500 to 50 ka are recorded in a terrestrial sequence of loess and paleosols in the eastern bay of plenty north island new zealand tephra correlations are based on the distinctive physical characteristics of the airfall beds and confirmed by microprobe analysis of glass shards the deposits are divided into six subgroups with their boundaries marked by either major tephras or significant changes in the paleo climate indicator deposits such as loess and paleosols age control on these tephras has been provided by fitting the paleoclimatic data seen in the field to the specmap oxygen isotope curve with correlations to a few well dated tephras and ignimbrites providing key time planes within this record

tectonic influences in piecemeal caldera collapse at glencoe volcano scotland glencoe volcano is renowned as the archetype for caldera collapse that results from piston like subsidence of a coherent crustal block on a ring fault however the caldera floor rocks and the geometry of seven intracaldera units that record large volume explosive eruptions show that the collapse involved incremental and haphazard subsidence of numerous crustal blocks before development of the ring fault some subsidence involved flexure downsag with associated development of extensional crevasses hundreds of metres deep a system of orthogonal faults and related grabens records the influence of two intersecting basement discontinuities one of which is inferred to have linked with the active great glen fault substantial extensional and or transtensional faulting with distinct related sedimentary responses occurred without eruptions the tectonic framework substantially controlled the magmatic plumbing and the locations of vents caldera depocentres and through going rivers the related sediments influenced contrasting eruption styles e g transitions between phreatomagmatic and magmatic and the shallow level emplacement of sills

a geophysical study of the taupo volcanic zone new zealand the taupo volcanic zone is a region of intense volcanic activity from which over 16 000 km3 of lavas and pyroclastics have been erupted since the late pliocene analysis of gravity and magnetic anomalies over the zone has revealed the presence of five major centers each associated with an approximately circular negative gravity anomaly and a positive pseudogravity anomaly these centers are interpreted as collapse features resulting from large scale withdrawal of magma from the upper crust four of the depressions occur beneath recognized volcanic centers or calderas the fifth kapenga is inferred to underlie an extinct hidden volcanic center three dimensional models of the thicknesses of low density and magnetized rocks in the taupo volcanic zone have been determined by inversion of gravity and magnetic anomalies beneath three of the centers the thicknesses of low density and magnetized rocks are approximately equal 2 3 km that is the collapse structures are infilled by magnetized volcanics however there is a significant discrepancy between the thicknesses of the gravity 5 km and magnetic models 1 5 km in the region of the okataina volcanic centre it is therefore suggested that a significant volume of low density nonmagnetic rock possibly acidic magma underlies okataina

burgess shale type fossils from a lower cambrian shallow shelf sequence in northwestern canada fossil lagerstatten comparable to that of the burgess shale potentially provide the detail necessary to resolve and assess the so called cambrian explosion of multicellular life1 2 distributional and taphonomic biases however often limit the generalizations that can be drawn here i report widespread occurrences of burgess shale type fossils in shallow shelf sediments of the lower cambrian mount cap formation district of mackenzie northwest territories canada these borehole assemblages significantly expand the known geographical and ecological range of such fossil biotas and document the early appearance of both wiwaxiid polychaetes and filter feeding crustaceans the ability of this latter group to exploit microplanktic primary productivity marks a fundamental shift in trophic structuring and may distinguish phanerozoic from pre phanerozoic ecosystems

silicic recharge of multiple rhyolite magmas by basaltic intrusion during the 22 6 ka okareka eruption episode new zealand abstract deposits of the 22 6 ka okareka eruption episode from tarawera volcanic complex record the sequential and simultaneous eruption of three discrete rhyolite magmas following a silicic recharge event related to basaltic intrusion the episode started with basaltic eruption 0 01 km3 magma and rapidly changed to a plinian eruption involving a moderate temperature 750 c cummingtonite bearing rhyolite magma t1 with a volume of 0 3 km3 hybrid basalt rhyolite clasts demonstrate direct basaltic intrusion that helped trigger the eruption crystals shards and lapilli of two other rhyolite magmas then joined the eruption sequence they comprise a cooler 720 c crystal rich biotite hornblende rhyolite magma t2 0 3 km3 and a hotter 780 c crystal poor pyroxene hornblende rhyolite magma t3 4 5 km3 all mid to late stage ash units contain various mixtures of t1 t2 and t3 components with a general increase in abundance of t3 and rapid decline of t1 with time about 4 km3 of t3 magma was extruded as lavas at the end of the episode contrasts in melt composition crystal and volatile contents and temperatures influenced viscosity and miscibility and thus limited pre eruption mixing of the rhyolite magmas the eruption sequence and the restricted direct basaltic intrusion into only one magma t1 is consistent with the rhyolites occupying separate melt pods within a large crystal mush zone melt crystal equilibria and volatile contents in melt inclusions indicate temporary magma storage depths of

fingerprints and age models for widespread new zealand tephra marker beds erupted since 30 000 years ago a framework for nz intimate abstract the role of tephras in the nz intimate project is a critical one because most high resolution palaeoclimatic records are linked and dated by one or more tephra layers in this review first we document eruptive distributional and compositional fingerprinting data both mineralogical and geochemical for 22 key marker tephras erupted since 30 000 years ago to facilitate their identification and correlation we include new glass compositional data the selected marker tephras comprise 10 from taupo and nine from okataina volcanoes rhyolitic one from tuhua volcano peralkaline rhyolitic and one each from tongariro and egmont volcanoes andesitic second we use four approaches to develop 2 age models for the tephras youngest to oldest 1 calendar ages for kaharoa and taupo y were obtained by wiggle matching log derived tree ring sequences dated by 14c 2 whakaipo v was dated using an age depth model from peat 3 14 tephras in the montane kaipo peat sequence waimihia s unit k whakatane tuhua mamaku rotoma opepe e poronui c karapiti b okupata konini waiohau rotorua rerewhakaaitu were dated by simultaneously wiggle matching stratigraphic position and 51 independent 14c age points against intcal04 using bayesian probability methods via both oxcal and bpeat and 4 the five oldest tephras erupted before ca 18 000 cal yr bp were dated by calibrating limited numbers of 14c ages using intcal04 okareka or comparison curves of the expanded cariaco basin sequence te rere kawakawa oruanui poihipi okaia kawakawa oruanui tephra the most widely distributed marker tephra was erupted probably ca 27 097 957 cal yr bp potential dating approaches for the older tephras include their identification in antarctic ice cores if present or annually laminated sediments for which robust calendar age models have been constructed high precision ams 14c dating on appropriate material from environmentally stable sites systematic luminescence dating or new radiometric techniques e g u th he if suitable minerals are available and errors markedly reduced further application of bayesian age modelling to stratigraphic sequences of 14c ages possibly augmented with luminescence ages may help refine age models for pre holocene tephras with the largest errors finally we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the new zealand region which is a key objective of australasian and southern hemisphere intimate projects