tectonic history of the lunksoos composite terrane in the maine appalachians several ordovician volcanic terranes are preserved between the paleozoic north american margin and the avalon terrane in the northern appalachians of maine they have been interpreted as remnants of an island arc on the basis of their current position in the appalachians or as ocean islands near the margin of avalon on the basis of paleontologic data a study of one of these terranes the lunksoos terrane in northern maine was undertaken through a combination of paleomagnetic and structural analyses in order to understand its tectonic evolution paleomagnetic study of the pre caradoeian pre late ordovician stacyville volcanics revealed three components of magnetization the final magnetization removed d 90 i 36 95 11 8 is interpreted to be primary and yields a paleolatitude of approximately 20 s however a late ordovician remagnetization cannot be excluded the stacyville volcanics now overlie a cambrian and lower ordovician sequence the grand pitch and shin brook formations that is believed to have been deposited at the southern side of iapetus possibly near the margin of avalon during the middle and late ordovieian avalon was at paleolatitude s higher than 40 s while the volcanics were either formed or remagnetized at a paleolatitude of 20 s the pre caradocian stacyville volcanics therefore could not have been deposited directly on the grand pitch shin brook sequence but must have been tectonically emplaced the rockabema diorite which intrudes the entire cambro ordovician sequence constrains the timing of this emplacement to be pre late early silurian these relationships indicate that the lunksoos area is a composite terrane within the maine appalachians the tectonic emplacement scenario is unnecessary if the grand pitch and shin brook formations were not located on the south side of iapetus during the ordovician this alternative however poses conflicts with the interpretation of faunal affinities

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

aftershocks of the 2010 mw 7 2 el mayor cucapah earthquake reveal complex faulting in the yuha desert california 1 we detect and precisely locate over 9500 aftershocks that occurred in the yuha desert region during a 2 month period following the 4 april 2010 mw 7 2 el mayor cucapah emc earthquake events are relocated using a series of absolute and relative relocation procedures that include hypoinverse velest and hypodd location errors are reduced to 40 m horizontally and 120 m vertically aftershock locations reveal a complex pattern of faulting with en echelon fault segments trending toward the northwest approximately parallel to the north american pacific plate boundary and en echelon conjugate features trending to the northeast the relocated seismicity is highly correlated with published surface mapping of faults that experienced triggered surface slip in response to the emc main shock aftershocks occurred between 2 km and 11 km depths consistent with previous studies of seismogenic thickness in the region three dimensional analysis reveals individual and intersecting fault planes that are limited in their along strike length these fault planes remain distinct structures at depth indicative of conjugate faulting and do not appear to coalesce onto a throughgoing fault segment we observe a complex spatiotemporal migration of aftershocks with seismicity that jumps between individual fault segments that are active for only a few days to weeks aftershock rates are roughly consistent with the expected earthquake production rates of dieterich 1994 the conjugate pattern of faulting and nonuniform aftershock migration patterns suggest that strain in the yuha desert is being accommodated in a complex manner

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

pre folding magnetization reconfirmed for the late ordovician early silurian dunn point volcanics nova scotia johnson r j e and van der voo r 1990 pre folding magnetization reconfirmed for the late ordovician early silurian dunn point volcanics nova scotia tectonophysics 178 193 205 paleomagnetic results have been obtained for three new sites in steeply inclined subarea1 volcanic flows of the dunn point formation from the avalon terrane of nova scotia demagnetization analysis reveals a characteristic magnetization carried by hematite which is similar to that reported in previous studies of this unit a new and improved fold test for the characteristic component combining paleomagnetic and structural data from the present study with paleomagnetic data for vertically dipping flows and laterites studied previously by the authors is significantly positive the new fold test reconfirms the prefolding age of the characteristic component a primary age of magnetization is inferred based on field evidence for early oxidation of the flows the overall mean direction for the characteristic component of d 344o i 60 k 68 6 ass 4 1 paleopole at 2on 130 e corresponds to a late ordovician earliest silurian paleolatitude for avalon of 41 s the latter is much higher than that predicted for the area on the basis of the cratonic north america apparent polar wander path implying a substantial post ordovician displacement 1700 km of avalon with respect to the craton the dunn point result supports previous paleogeographic reconstructions that show avalon together with the continental blocks of hercynian europe and northwestern gondwana

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

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

thrust sheet rotation and out of plane strains associated with oblique ramps an example from the wyoming salient u s a abstract movement over oblique thrust ramps results in local thrust sheet rotation and principal strains which deviate from the transport plane resulting folds faults and deformation fabrics are superposed on those associated with displacement on frontal ramps the south fork thrust a hangingwall imbricate of the absaroka thrust sheet sw wyoming has a steeply dipping 70 small displacement 300 m oblique ramp in the hangingwall and footwall which makes an angle of 25 to the regional transport direction two penetrative deformation events are recorded by folding stylolitic cleavage and calcite twinning strains in the deformed hangingwall and footwall the first is e to se directed layer parallel shortening prior to or during motion of the absaroka thrust sheet the second event indicates ne directed shortening unique to the oblique ramp at a high angle to ramp strike at the trailing frontal ramp oblique ramp intersection folds in the footwall and normal faults in the hangingwall reflect local strike parallel shortening and extension due to out of plane deflection of the wallrock during displacement the out of plane strains arc consistent with those predicted by kinematic and mechanical models in the hangingwall of the oblique ramp cross strike fractures and bedding are rotated 30 counterclockwise about a vertical axis with respect to structural domains to the north and south due to differential displacement on the south fork thrust stylolitic cleavage and caleite strains unique to the oblique ramp show a similar change in attitude indicating the rotation was the latest recorded stage of deformation in general if an oblique ramp is shallowly dipping the hangingwall may move from the lower flat up the ramp and onto the upper hat if an oblique ramp has a steep dip as in the case of the south fork thrust relatively greater sliding and bending resistance may impede displacement up the ramp and upper flat further transport of the thrust sheet is then accommodated by footwall deformation and hangingwall rotation

application of paleomagnetism to accretionary tectonics and structural geology the use of paleomagnetism to determine translations and rotations of geologic terranes has contributed to a better understanding of deformation within accretionary complexes shear zones and rifts in this report to the i u g g we review the progress resulting from paleomagnetic studies during the last four years in the cordillera of north america the appalachian orogen and the circum pacific region

middle cambrian paleomagnetism of the avalon terrane in cape breton island nova scotia interbedded volcanics and sediments of the bourinot group mid cambrian in central cape breton island were studied as part of a paleomagnetic investigation to quantify the geologically plausible displacements of the avalon terrane with respect to the north american craton both volcanics and sediments reveal prefolding magnetizations with steep to intermediate inclinations dual polarity magnetizations in different volcanic flows are probably primary and they yield a mean direction of d 293 i 66 n 9 k 41 8 95 8 1 the sediments reveal upon detailed thermal demagnetization complex multivectorial remanences however a few samples show characteristic components and a large number of samples 38 have intersecting great circle remagnetization trajectories when combined this yields a mean direction of d 267 i 65 k 16 mean radius of error ellipse is 8 5 the mean directions for the bourinot rocks correspond to a paleolatitude of 49 s 11 which is different from the range of possible values for the predicted mid cambrian paleolatitudes for nova scotia 29 s to 18 n inferred from the north american apparent polar wander path this discrepancy between predicted paleolatitudes and the observed paleolatitude implies that nova scotia was not part of north america during the mid cambrian but rather they were separated by an ocean with a minimum width of 1000 km 20 10 this interpretation of the relative positions of nova scotia and north america based on paleomagnetism is consistent with the geological record in the northern appalachians and supports previous interpretations of the dissimilar early paleozoic faunas in avalon and north america it is paleomagnetically quite plausible that the avalon terrane formed part of a larger continent comprising africa gondwana and armorica during the cambrian

cambro ordovician paleogeography of the southeastern new england avalon zone implications for gondwana breakup paleomagnetic measurements and u pb geochronology of alkalic igneous rocks intruding the ediacaran cambridge argillite and the lower cambrian weymouth formation north of boston at nahant massachusetts yield a well constrained paleopole the oldest intrusive phases are a syenodiorite sill and a granite dike with 206 pb 238 u crystallization ages of 490 19 0 90 ma and 489 03 0 82 ma respectively this sequence along with undated mafic sills penetrating both the argillite and weymouth strata are cut by 488 53 0 81 ma gabbro locally associated with 488 48 0 79 ma syenite forming a steep sided intrusive plug ten paleomagnetic sampling sites within the mafic sills and the gabbro contain a stable a magnetic component with a mean direction of d 278 5 i 76 7 a 95 3 9 n 10 this is considered to be the primary magnetization direction because it passes both fold and reversals tests the corresponding paleopole at 320le 34 n a 95 7 2 n 10 places the southeastern new england avalon zone at a southerly paleolatitude of 65 slightly removed from the african margin of gondwana and suggests that bimodal nahant magmatism is linked with latest cambrian early ordovician rifting of west avalonia to form the rheic ocean stable b and c magnetic components in nahant syenodiorite and syenite give rise to virtual geomagnetic poles that track late silurian through carboniferous segments of the north american apparent polar wander path indicating docking of west avalonia by mid paleozoic time

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

the arc lavas of the shirahama group japan sr and nd isotopic data indicate mantle derived bimodal magmatism new sr and nd isotopic data are presented and integrated with previous data for the shirahama group mio pliocene mediumk volcanic arc suite of south central honshu japan main results are 1 the shirahama lavas range in sr sr from 0 70315 to 0 70337 and in mnd 144nd from 0 51298 to 0 51306 the sr and nd isotopic data cluster tightly within the mantle array and all lie within an overlapping field of midocean ridge basalt and ocean island basalt 2 small differences exist among the shirahama tholeiitic series calc alkaline series and mixed lavas the present isotopic data are consistent with a previously published model which proposes that chemical variations in magmas of coexisting tholeiitic and calc alkaline series are produced through crystal fractionation from mantlederived magmas of basalt and magnesian andesite respectively moreover the tholeiitic series and the calc alkaline series are isotopically identical thus both magma series can be derived from a source mantle with the same isotopic composition supporting the hypothesis of simultaneous generation of basalt and magnesian andesite magmas from a single diapir rising through the mantle wedge above the subduction zone the differences of water content and temperature within the diapir are again thought to have been produced through dehydration and heating of an isotopically homogeneous hydrous diapir the isotopic data show that the high sio lavas have the same isotopic compositions as more mafic lavas these data and liquid lines of descent of the shirahama magmas suggest that even rhyolites can be produced by differentiation from mantle derived magmas without crustal contamination analyses from 38 other arc volcanoes have been compiled to investigate the intravolcano variability of sr sr twelve of these display no intravolcano strontium isotopic variability as is the case with the shirahama group but others show greater variation of sr 86sr from individual volcanic centers presumably reflecting crustal contamination most of the latter volcanoes are underlain by thick continental crust it is noteworthy however that the greater variations of sr sr correlate with sio2 content andesites or dacites not basalts from the same volcano have the lowest sr sr and these rocks are calc alkaline in terms of feo mgo and sio theoretically assimilation of continental crust by the isotopically uniform shirahama magmas could produce these relationships given that mantle derived basalt and magnesian andesite both encounter continental crust on their ascent to the surface the hotter basalt magma would assimilate more crustal wallrocks than the cooler andesite resulting in the basalt being more radiogenic fractional crystallization magma mixing and or assimilation fractional crystallization of these magmas in crustal magma chambers could produce large compositional variations but the derivatives of the hotter basaltic magmas tholeiitic series in the broad sense would display greater contamination than those derived from the cooler andesitic magmas calc alkaline series

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

continental tectonics selected topics cause and effect relations between plate boundary processes and orogeny were investigated using new and refined plate models for the mesozoic and cenozoic terrane accretion and large components of horizontal shear were shown to be fundamental aspects of orogen evolution deep crustal thrust systems with large lateral transport and vertical stacking of slices of crystalline basement were documented in the cordillera and appalachians new geomechanical models of crystalline thrust sheets and foreland thrust belts emphasized the dominance of tectonic rather than gravitational stresses lithospheric thickening was shown to cause buoyancy forces that control the lateral spread of deformation outward from the interior of an orogen and may modify regional stresses in the vicinity of topographic fronts resulting in extension within the upper part of the lithosphere coeval with shortening at depth

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

passive roof duplexes under the rocky mountain foreland basin alberta seismic reflection data in the central alberta foothills near edson reveal the presence of small passive roof duplexes in upper cretaceous rocks within the otherwise undeformed foreland basin as much as 40 km northeast of the mountain front monocline the tops and bottoms of the duplexes are defined by backthrusts and sole thrusts which follow bedding planes within upper cretaceous strata overlying the structures is an essentially uncontracted 1 8 km thick section of upper cretaceous and tertiary rocks which is passively uplifted over the thickened duplexes the underlying autochthonous sequence of mesozoic and paleozoic rocks exhibits some minor folding but is also uncontracted our interpretation extends both the upper and lower detachments of the widely accepted triangle zone model more than 30 km farther under the foreland basin than has previously been supposed the seismic data illustrate relatively clearly the form of the leading edge of the last phase of rocky mountain thrusting we expect that similar features will be observed elsewhere in the rocky mountain foothills and probably at other mountain fronts worldwide

the evolution of volcanic systems following sector collapse abstract sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass comparable in scale to the largest magmatic eruptions the eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage which imply that collapse driven unloading may lead to changes in eruption rate and erupted magma compositions large sector collapses are infrequent events globally with all historical examples being relatively small in comparison to many of the events documented in the geological record as a result exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses but this is often hindered by poorly resolved stratigraphic relationships and dating uncertainties nevertheless observations from a number of volcanoes indicate sharp changes in activity following sector collapse here a global synthesis of studies from individual volcanoes in both arc and intraplate settings is used to demonstrate a number of common processes in post collapse volcanism multiple examples from large 5 km3 sector collapses in arc settings show that collapse may be followed by compositionally anomalous large volume and often effusive eruptions interpreted to originate via disruption of a previously stable upper crustal reservoir these anomalous eruptions highlight that magma compositions erupted during periods of typical i e unperturbed by sector collapse volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir if eruptible magma is not present upper crustal reservoirs may rapidly solidify following collapse without further eruption allowing more mafic compositions to ascend to the surface with only limited upper crustal modification resulting in edifice regrowth at temporarily elevated eruption rates subsequent re establishment of an upper crustal reservoir further supports a relationship between surface loading and crustal storage but long term chemical and mineralogical differences between pre and post collapse evolved magmas imply that a newly developed reservoir can overprint the influence of a preceding reservoir forming a spatially and compositionally distinct plumbing system these broad patterns are replicated in intraplate settings despite differences in scale and melting processes current evidence suggests that post collapse evolution of intraplate volcanoes can be explained by unloading induced destabilisation of the magma plumbing system rather than increased melt production what emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent storage and pressurisation eruption rates erupted compositions and the style of volcanism at any particular system may thus be modulated from the surface and long term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems observations of sharp post collapse changes in erupted compositions including the ascent of primitive mafic magmas also require a crystal dominated mid to upper crustal reservoir consistent with recent models of crustal magmatic systems

paleomagnetism of the callander complex and the cambrian apparent polar wander path for north america the 7 km2 circular callander alkaline complex was emplaced into anorthositic and granitic gneisses of the grenville province in the canadian shield about 575 5 ma ago at the start of the cambrian the complex has not been subsequently metamorphosed or tilted detailed alternating field and thermal step demagnetization of 252 specimens from 29 sites led to the identification of a characteristic a magnetization component with a direction of d 82 2 i 82 7 95 3 1 k 83 n 26 sites in 5 sites of mesocratic to leucocratic syenite from the core of the complex in 5 sites of fenitized host rock from its aureole and in 16 sites of lamprophyre from radiating dikes isothermal remanent magnetization tests show that the a component is retained by both magnetite and hematite in a complete spectrum of domain sizes a reversals test suggests and a contact test shows the a component to be primary its pole position at 46 3 s 121 4 e dp 5 9 dm 6 1 does not fall on published but poorly defined

role of cryptic amphibole crystallization in magma differentiation at hudson volcano southern volcanic zone chile hudson volcano chile is the southern most stratovolcano of the andean southern volcanic zone and has produced some of the largest holocene eruptions in south america there have been at least 12 recorded holocene explosive events at hudson with the 6700 years bp 3600 years bp and 1991 eruptions the largest of these hudson volcano has consistently discharged magmas of similar trachyandesitic and trachydacitic composition with comparable anhydrous phenocryst assemblages and pre eruptive temperatures and oxygen fugacities pre eruptive storage conditions for the three largest holocene events have been estimated using mineral geothermometry melt inclusion volatile contents and comparisons to analogous high pressure experiments throughout the holocene storage of the trachyandesitic magmas occurred at depths between 0 2 and 2 7 km at approximately 972 c 25 and log fo2 10 33 10 24 0 2 one log unit above the nno buffer with between 1 and 3 wt h2o in the melt pre eruptive storage of the trachydacitic magma occurred between 1 1 and 2 0 km at 942 c 26 and log fo2 10 68 0 2 with 2 5 wt h2o in the melt the evolved trachyandesitic and trachydacitic magmas can be derived from a basaltic parent primarily via fractional crystallization entrapment pressures estimated from plagioclase hosted melt inclusions suggest relatively shallow levels of crystallization however trace element data e g dy yb ratio trends suggests amphibole played an important role in the differentiation of the hudson magmas and this fractionation is likely to have occurred at depths 6 km the absence of a garnet signal in the hudson trace element data the potential staging point for differentiation of parental mafic magmas i e 20 km e g annen et al in j petrol 47 3 505 539 2006 and the inferred amphibolite facies 24 km e g rudnick and fountain in rev geophys 33 267 309 1995 combine to place some constraint on the lower limit of depth of differentiation i e 20 24 km these constraints suggest that differentiation of mantle derived magmas occurred at upper mid to lower crustal levels and involved a hydrous mineral assemblage that included amphibole and generated a basaltic to basaltic andesitic composition similar to the magma discharged during the first phase of the 1991 eruption continued fractionation at this depth resulted in the formation of the trachyandesitic and trachydacitic compositions these more evolved magmas ascended and stalled in the shallow crust as suggested by the pressures of entrapment obtained from the melt inclusions the decrease in pressure that accompanied ascent combined with the potential heating of the magma body through decompression induced crystallization would cause the magma to cross out of the amphibole stability field further shallow crystallization involved an anhydrous mineral assemblage and may explain the lack of phenocrystic amphibole in the hudson suite

aspects of the three dimensional structure of the alberta foothills and front ranges ever more detailed subsurface images of the alberta foothills and front ranges obtained from improving seismic techniques coupled with an ever expanding base of information from deep wells and improved structural analysis techniques have produced an understanding of fold thrust deformation that is probably applicable to other fold thrust belts comprehensive subsurface data obtained by the petroleum industry are used to outline and analyze the three dimensional configuration of fold thrust deformation of paleozoic carbonate strata these data indicate that displacement changes smoothly along individual thrusts but displacement changes along strike may be large marked by considerable horizontal rotation 20 30 or more of hanging wall stratigraphic cutoffs relative to the footwalls stacking of thrusts with varying displacements has produced summed horizontal rotations of hanging wall cutoffs of as much as 45 50 the three dimensional trajectories of the thrusts through the stratigraphy are smooth for large distances interrupted by abrupt offsets at lateral and oblique ramps these are more common than previously realized the intersections of these ramps with other thrusts produce complex three dimensional links between thrusts with concomitant abrupt displacement changes some simple examples of these linkages are examined with a three dimensional geometric analysis the predictions of the analysis are consistent with structural geometries observed in two case studies of subsurface structures the links at lateral ramps imply simultaneous displacement on parts of the thrusts connected by the ramps since the ramps extend downdip 20 km or more displacement occurred simultaneously on structures occupying relatively interior and exterior positions in the thrust belt the smooth and long radius of curvature folding of many upper detachments indicated by reflection seismic data also is consistent with simultaneous or overlapping periods of motion on groups of thrusts distributed along regional dip most major alberta foothills thrust sheets terminate southward at lateral ramps at the paleozoic level the abrupt southwest northeast offsets at these features are most clearly apparent on a palinspastic reconstruction these offsets cause the paleozoic deformation front to step out east and northeast around the southern and eastern margins of the main arc of the foothills in contrast northward thrust terminations at the paleozoic level commonly occur at both tip lines and lateral ramps subsurface data reveal that there have been some misconceptions regarding large scale structural relationships for example the mcconnell and livingstone sheets are actually portions of the same thrust sheet as are the bighorn and nikanassin sheets when corrected for these misconceptions the data from the alberta foothills suggest that maximum displacement has a nonlinear relationship to thrust length although a linear relationship cannot be ruled out

remagnetized cratonic cambrian strata from southern nevada stratigraphic sections of cambrian strata in southeastern nevada are akin to thin cratonic facies exposed in the grand canyon their structural setting is much more complicated however from mesozoic and cenozoic tectonism paleomagnetic samples from two sections through these strata appear to have been completely remagnetized coarse grained lightcolored sandstone from the tapeats sandstone yields scattered magnetizations residing in hematite that appear to reflect protracted diagenetic acquisition of remanence a hematitic sandstone in the bright angel shale yields relatively consistent paleozoic directions of magnetization but petrographic study shows that the hematite results from diagenetic oxidation and stratigraphic arguments suggest that the oxidation was not penecontemporaneous gray limestones of the jangle and muav limestones yield a magnetization residing in magnetite that may reflect late tertiary remagnetization being imposed during uplift related to the onset of basin and range deformation in any case this magnetization differs greatly in direction from a hematite magnetization reported from slightly younger muav limestone in the grand canyon both the sampling sites also appear to have been tectonically rotated but whether this rotation is true or a geometric artifact of the tilt correction cannot be determined from the present data these results suggest that paleomagnetic data from rocks as old as cambrian must be scrutinized very carefully before their magnetizations can be accepted as penecontemporaneous and such scrutiny must include geologic data

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

a review of paleomagnetic results from the carboniferous of north america the concept of carboniferous geomagnetic field horizon markers results from the east coast carboniferous basin contain an important time stratigraphic horizon of possible global significance late carboniferous units are found to have mostly reversed magnetizations while older carboniferous units may have normal reverse or most frequently dual polarity magnetizations this feature records the change in geomagnetic field from a period of common polarity changes to a period of mainly reversed polarity the kiaman magnetic interval recognition of the stratigraphic position of this polarity feature provides a time line for correlation of units within and among carboniferous basins in the east coast carboniferous basin of atlantic canada this horizon has now been located at the riversdale group level early pennsylvanian namurian westphalian boundary since remanence acquisition of red sediments is often a lengthy process possibly spanning field reversal time scales red bed units pre dating and post dating this time line can in most instances be readily distinguished the former generally recording both polarities and the latter just one reverse polarity a polar displacement of at least 16 is recorded in the results from the east coast carboniferous basin paleolatitude maps show that the area was located near the equator and was displaced northwards by about 8 during the pennsylvanian it cannot be ascertained if those observations are representative of the whole of north america or merely the atlantic seaboard poles derived from other areas of north america do not all fit the regular pattern observed on the atlantic coast using the horizon marker as a tool it is suggested that those poles are post time line in age so that none of them is representative of the position of north america prior to the time line

polar wander and paleomagnetic reference pole controversies the purpose of this paper is to review the progress made over the past four years in studies of phanerozoic and precambrian polar wander with an emphasis on the contributions made by u s scientists we perceive a general theme embracing the notion that the accuracy of cratonic reference poles and therefore of apparent polar wander apw paths is not as good as was generally believed four years ago a renewed interest in research concerning cratonic reference poles is largely the result of paleomagnetic studies in orogenic belts namely the western cordillera and appalachians of north america the andes of south america and elsewhere which seek to document the existence or non existence of displacements of suspect terranes i e rotation and or translation with respect to their presently associated cratons some of the results of this research are reviewed in this volume by hillhouse and mcwilliams an important realization of which paleomagnetists have long been aware but which was demonstrated recently by a number of sobering examples for both the paleozoic and mesozoic apw paths for north america is that the reliability of concordance discordance parameters that define terrane displacement is dependent not only on the precision and accuracy of the individual paleomagnetic study but also on the precision and accuracy of the appropriate cratonic reference pole

paleomagnetism of lower cambrian volcanics and a cross cutting cambro ordovician diabase dyke from buckingham quebec the buckingham area quebec is characterized by cambrian volcanic flows 573 32 ma cut by a cambro ordovician diabase dyke which is dated at 497 14 ma by k ar method the volcanics yield multicomponent magnetizations a hard characteristic magnetization and a relatively soft one these components could be separated easily and the intensity decay curves of the different components could also be obtained separately using zijderveld s method three different groups of site mean characteristic magnetizations can be distinguished each representing a different stratigraphic level the paleopoles derived from these magnetizations are from oldest to youngest 186 e 10 s 173 e 01 n and 154 e 06 n this is interpreted as a rapid motion of the paleopole for the north american craton during the early cambrian the paleopole derived from the hard characteristic dyke direction is 123 e 03 s this magnetization direction was also found at one of the sites in the volcanics this means that the contact test

possible effects of pre existing basement topography on thrust fault ramping finite element models show that one way in which thrust ramps may arise is through the mechanical interaction between basement and overlying sediments in the simplest case shear coupling between a planar basement sediment causes the differential stresses in the sediments to die out with depth and distance from the applied load for such cases curved thrust faults may result if the strength of the rock is exceeded basement topography may also affect the location and shape of ramps by acting as a stress concentrator by producing a stress shadow and by changing principal stress orientations modeling suggests that whether or not these basement topographic features cause ramping will depend on the height and angularity of the feature as well as the rock types that overlie it under the assumption of linear elasticity and for given boundary conditions the poisson s ratio plays an important role in determining the orientation and magnitude of the principal stresses calculations using experimentally measured poisson s ratios predict that the earliest maximum compressive stress directions should be nearly vertical in the more cratonward portions of thrust belts however the stress directions which are inferred to have occurred earliest in this part of thrust belts are nearly horizontal this suggests that non elastic or ductile processes have an effect on the propagation of thrust faults

forced folds and fractures this volume is concerned with defining the major similarities and difference between forced folds and buckle folds in order that these differences can be used to recognize the type of folding and therefore the expected fracture pattern present in regions of poor exposure or where the geologist has to rely on seismic images an understanding of the differences between the two fold types their 3d geometry spatial organization fracture patterns etc provides an invaluable tool for earth scientists concerned with assessing the possible role of folds and their associated fracture patterns in controlling fluid migration and concentration within the crust the papers presented here are grouped into 4 sections contributions in the first section describe the use of numerical analyses to investigate the formation of fractures in forced folds including compaction folds and the section contains a description of large scale compaction folding in which the associated fracturing has given rise to the development of large sandstone dykes the papers in the second section deal with the formation of forced folds as a result of normal faulting in various geological environments including along a classical graben margin and around a resurgent caldera the third section contains papers relating to forced folding in compressional and strike slip regimes the final section considers the temporal and spatial relationships between forced folds and buckle folds the formation of crustal scale folds and a method of determining the distribution of strain on any folded surface a key parameter controlling the distribution of fractures

effects of irregular basement structure on the geometry and emplacement of frontal thrusts and duplexes in the quebec appalachians interpretations from well and seismic reflection data abstract irregular basement geometry may affect thrust propagation in foreland fold thrust belts creating a perturbation in structural continuity of hydrocarbon fields here we investigate how the irregular pattern of normal faults along with the presence of uplifts and transverse faults in the grenvillian basement has influenced the geometry and emplacement of frontal thrusts and duplexes in the parautochthonous domain of the southern quebec appalachians during the middle late ordovician taconian orogeny integration of data from surface geology wells and 2d and 3d seismic reflection surveys into a regional scale structural model is used to reconstruct the 3d geometry and emplacement history of one and two horse duplexes in the joly saint flavien gas storage area the normal hinterland to foreland sequence of thrusting in this area is complicated by the differential emplacement of tectonic slices along strike of the orogenic front starting in the sw and developing subsequently to the ne within each structural level the shortening related to duplex emplacement decreases laterally over the distance of 20 km from 49 in the sw joly area to 31 in the ne saint flavien area duplex emplacement resulted from the differential forward propagation deflexion and vertical axis rotation of the roof thrust logan s line which in turn has been induced by the presence of frontal uplift and transverse faults in the basement the structural lithological analysis of tectonic slices and restoration of their initial location allows us to consider the lower slice of the joly duplex as a structural trap comparable to the fractured reservoir in lower ordovician dolomites of the saint flavien duplex

dual polarity early carboniferous remagnetization of the fisset brook formation cape breton island nova scotia summary red siltstones and volcanic flows of the fisset brook formation of cape breton island nova scotia were folded or tilted in two phases one of late tournaisian and the other of mid namurian age upon thermal demagnetization both rock types yield three components of magnetization herein denoted as l i and h the l component has low unblocking temperatures and a direction conforming to that of the present day geomagnetic field l is inferred to be of recent origin the intermediate i component carried by haematite is of synfolding origin directions could be obtained through vector subtraction for the demagnetization interval of 300 550 c and yield a mean of d i 160 38 k 90 8 ag5 s lo after 39 per cent of the tilt correction is applied the h component has even higher unblocking temperatures which overlap to a large degree with those of the i component but analysis of intersecting great circles appears to yield a best fit direction for h which is nearly antipodal to that of the i component h is also synfolding and yields a mean direction of d i 342 38 k 120 9 ag5 6 9 after 60 per cent of tilt correction both components are interpreted as secondary chemical remanent magnetizations of late tournaisian to early namurian age a comparison of all available carboniferous results from the craton and the northern appalachians indicates that palaeolatitudes for nova scotia changed from about 20 s to about 10 s in the interval between the early and late namurian and that they changed again from about 10 s to 0 between the late namurian and the stephanian declinations show good agreement between newfoundland nova scotia new brunswick and the craton with the exception of the meguma terrain which underwent a counterclockwise rotation with respect to the mainland in the late carboniferous as noted previously by spariosu kent keppie 1984

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

geoelectromagnetic measurements across the moine thrust and the great glen in northern scotland summary results are presented for a magnetotelluric and magnetovariational study in northern scotland for nine of the 20 sites at which observations were made the results of the analysis are presented fully together with one dimensional 1 d monte carlo inversions for representative sites from the lewisian foreland the north west highlands the great glen region and the grampian highlands for the remaining sites the results are summarized the 1 d models of all sites situated in a traverse extending from the lewisian foreland to the neighbourhood of the highland boundary fault have been used as the basis for preliminary 2 d modelling maps of magnetic field induction vectors and transfer functions for an inducing field perpendicular to the average geological strike are presented for periods of 23 819s the 2 d conductivity models were constrained by both the magnetotelluric and magnetovariational responses the period range of observation in this study was too limited to resolve structural differences in the upper crust but adequate to reveal a moderately good conductor at upper mantle lower crustal depths in the caledonian metamorphic zone in contrast the whole of the crust in the lewisian foreland is highly resistive and there is no evidence of an intermediate conducting layer between the crust and mantle in this region

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

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

palaeomagnetism of late precambrian cambrian volcanics and intrusives from the armorican massif france samples of the keratophyre tuffs of treguier 640 12 myr of the upper brioverian series and the microgranite dykes of loguivy 548 24 myr have been collected from the north coast of brittany france the samples were progressively demagnetized with af and predominantly thermal methods blocking temperatures coercivities and acquisition of isothermal remanent magnetization irm indicate that the keratophyre remanence is variably carried in magnetite hematite or occasionally in both after removal of a soft viscous component two stable palaeomagnetic directions were found one in magnetite the other in hematite the characteristic magnetite direction tb 300 580 c is a pre folding primary thermoremanent magnetization trm which after structural correction has a mean declination inclination of 217 9 30 4 the younger hematite component has a mean in situ direction of 320 4 20 3 the microgranite natural remanent magnetization nrm intensity distribution is distinctly bimodal forming high and low 1 6 a m 1 intensity groups upon demagnetization a single stable remanence in magnetite was removed between 300 and 580 c or 20 and 100 mt two characteristic directions were found to be statistically related to the intensity groups at the 99 per cent confidence level low intensity samples have a mean direction of 201 9 2 3 and probably resulted from a late devonian early carboniferous local magnetization high intensity microgranites have a mean direction of 200 50 8 and this remanence is shown to be a primary trm palaeopoles obtained from the two keratophyre magnetizations magnetite 44 7 n 116 4 e hematite 39 5 n 233 6 e as well as the high intensity microgranite remanence 5 8 s 339 9 e show good agreement with similar age poles from the apparent polar wander path for the armorican massif comparison of these data to recent palaeomagnetic data from southern england and wales gives additional evidence to link that region with the armorica plate as proposed by van der voo and hagstrum et al

triangle zone and displacement transfer structures in the eastern front ranges southern canadian rocky mountains the geometry of a relict triangle zone at the boundary of the foothills and front ranges in the southern canadian rocky mountains is constrained by detailed surface mapping over 700 m of relief and by seismic reflection data the geometry and progressive development of the triangle zone along a strike length of 15 20 km in the displacement transfer zone between the coleman and misty thrusts is illustrated using closely spaced balanced cross sections palinspastic restorations and a sequentially restored cross section structural geometries show that a northeast foreland verging mainly carbonate wedge of mississippian to triassic rock was inserted along a major upper detachment zone in shale near the base of the jurassic cretaceous clastic package this was accompanied by southwest hinterland verging displacements along the upper detachment zone tectonic thickening of the clastic package exceeding 200 and backthrusting later northeast verging deformation slightly modified the triangle zone by steepening structures tightening folds and minor thrusting recognition of relict triangle zones within the fold and thrust belt may document important changes in the rate of thrust front advancement and aid in the delineation of potential hydrocarbon traps similar to those discovered along th present day thrust belt margin in the southern canadian rocky mountains

role of transverse faulting in along strike termination of limestone mountain culmination rocky mountain thrust and fold belt alberta canada abstract surface geology well data and 100 km of 2d seismic reflection data delineate the 3d geometry of limestone mountain culmination lmc the lower lithotectonic package of the culmination is a se plunging antiformal stack of four thrust sheets of paleozoic platform carbonates that is detached from and folds the upper package of ne verging thrust sheets of mesozoic siliciclastics tilting these imbricates toward the foreland lmc abruptly loses 1 5 km of structural relief along strike in less than 2 km across a ne striking blind transverse fault that changes from a nw dipping lateral ramp in the southwest to a steep tear fault in the northeast it soles into the brazeau thrust and merges upward into the roof thrust of lmc an extension fault that soles into the steepest portion of the transverse fault cuts moderately sw dipping mesozoic rocks that drape over the tear fault thereby juxtaposing mesozoic siliciclastics against paleozoic carbonates of the brazeau sheet synchronous thrusting is suggested by preferential imbrication over the forelimb of the antiformal stack by offset of the roof thrust and by folded and unfolded thrust segments in the stack a precambrian basement structure beneath this transverse fault may have acted as a buttress during the laramide orogeny

palaeomagnetism of early cambrian brigus red shale eastern newfoundland abstract studies of the early cambrian brigus br red shale exposed in conception bay yielded a single stable mean remanence direction of d 265 i 58 reverse polarity before tilt correction and d 279 i 48 k 47 95 6 9 forn 7 sites 25 samples after correction for gentle tilt the corresponding north pole palaeopole position is 27 s 51 e dp dm 6 9 this magnetization is characterized by a linear vector trajectory at higher unblocking temperature t ub spectra 400 680 c the magnetization directions at the low t ub range 400 c are more variable from sample to sample although they typically have steep downward inclinations with no evidence of kiaman overprinting marginal but not statistically significant improvement k 44 77 in the grouping of site means after tilt correction suggests that the predominant univectorial westerly remanance was probably acquired after deposition based on both geological and magnetic evidence the brigus shale formation appears to be remagnetized during siluro devonian times the position of the far sided antipole br 27 n 129 w located in the vicinity of the pole for the cambrian morrison river formation mr at 20 n 146 w which is discordant from the younger palaeozoic late ordovician carboniferous poles reported for the avalon zone is fortuitous since the magnetization of br is most likely secondary the magnetization is younger than the iapetus closure date determined geologically late ordovician consequently the displacement of the avalon zone with respect to the north american craton cannot be estimated the width of the proto atlantic ocean cannot be calculated

seismic reflection and potential field studies of the vulcan structure western canada a paleoproterozoic pyrenees the vulcan structure is a major tectonic boundary between the medicine hat and loverna blocks archean crustal domains that are buried beneath the western canada sedimentary basin it is characterized by prominent east trending gravity and magnetic anomalies more than 350 km in length which cut across the potential field fabric of southern alberta at a high angle three decades ago the vulcan structure was the target of one of the first deep crustal seismic profiles and it has since been variously interpreted as a failed proterozoic rift an intraplate collisional zone and or a largely amagmatic proterozoic suture several recent lithoprobe seismic reflection profiles coupled with new coincident high resolution gravity data regional gravity data and updated aeromag netic coverage provide the basis for a revised model of the crustal architecture in this region we interpret the vulcan structure to be a relatively narrow 40 70 km axial zone of a continental collisional belt the seismic images imply crustal delamination and south directed subduction of the lower crust of the loverna block the axial gravity low and corresponding magnetic anomaly are interpreted to originate from a large granitic pluton while prominent gravity highs on the flanks of the structure are modeled as thrust slices of lower crustal and or mantle material brought up during the collision cross cutting relationships inferred from aeromagnetic data indicate that the timing of collision postdated formation of archean fabrics in the medicine hat block but predated terminal collision in the adjacent transhudson orogen the geographic extent inferred net shortening and tectonic setting of the vulcan structure appear to resemble the modern pyrenees belt although the deep structure appears to be more akin to the scandinavian caledonides either scenario is consistent with an interpretation of the vulcan structure as the proterozoic collisional suture between the wyoming and hearne provinces of the laurentian craton

a paleomagnetic investigation of the lower ordovician st george group port au port peninsula newfoundland implications for the iapetus ocean and evidence for late paleozoic remagnetization abstract to obtain an early ordovician paleomagnetic pole position for north america and to determine the paleolatitude of its margin of the lapetus ocean prior to the taconic orogeny a study of the lower st george group tremadocian arenigian of western newfoundland was undertaken analysis of 84 oriented core samples from six localities on port au port peninsula indicates that the nrm of the st george rocks is the resultant of three distinct paleomagnetic directions the first is a steep downward component commonly observed in the low temperature range of demagnetization room temperature 250 c in virtually all samples that roughly corresponds to the present day axial dipole field direction in situ d 350 i 68 the second is a stable component with southerly declinations and shallow intermediate negative inclinations d i in situ 176 20 d i tilt corrected 173 5 respectively usually seen in the range of 450 600 c and found in approximately 46 of the specimens the third is a stable southeasterly shallow intermediate positive component d i insitu 161 16 d i tilt correcied 163 34 respectively generally unblocked within the 350 550 c or 450 600 c range which was observed in 40 of the specimens these components of remanence are herein referred to as the type 1 type 2 and type 3 components respectively the remaining 14 of the specimens were found to be either directionally unstable to thermal demagnetization or totally overprinted by the type 1 component the type 2 component is interpreted to represent a post folding late paleozoic remagnetization possibly associated with the alleghanian orogeny on the other hand the type 3 component is interpreted as an early ordovician possibly pre taconic remanence and in tilt corrected coordinates yields a paleolatitude for this region of the north american craton of 19 s 6

eocambrian paleomagnetism of the boston basin evidence for displaced terrane a paleomagnetic study of the late precambrian roxbury formation consisting of extrusives and clastic sediments has yielded a steeply downward directed and pre folding characteristic magnetization d i 219 71 95 5 k 311 paleopole at 13 n 267 e n 4 sites which indicates a significantly higher paleolatitude 55 than would be expected if the boston basin were part of the equatorial north american craton in the latest precambrian and earliest paleozoic this characteristic magnetization reveals dual polarities and is further supported by a positive conglomerate test a ubiquitous post folding late paleozoic overprint is present in nine sites d i 183 14 95 8 k 42 with a paleopole at 41 s 285 e the pre folding magnetization resides in hematite which is inferred to have formed during early oxidation of the rocks the high stability of this hematite may have prevented its magnetization from being reset during the late paleozoic chemical event responsible for the magnetic overprint the boston basin has a marked geological similarity to the avalon basement terranes in nova scotia and newfoundland as well as the armorican massif in france and the high paleolatitudes observed for all these terranes suggest a common paleogeographical affinity a likely paleolocation is near the northwestern margin of gondwana which was located at the southpole in the latest precambrian and early cambrian

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

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

a cambrian pole for the moroccan coastal meseta summary middle cambrian volcanics of sidi said maachou east of el jadida western morocco 158 cores 23 sites sampled in two localities north of sidi said maachou were subjected to progressive alternating field and thermal demagnetization thermomagnetic cycles isothermal remanent magnetization acquisition experiments as well as microscopic observations the magnetic mineralogy of these volcanic rocks is dominated by magnetite and titanomagnetites the palaeomagnetic analysis has revealed two characteristic components of magnetization the first direction d 300 i 31 95 6 pole position at 14 n 231 e p 4 m 7 palaeolatitude 16 7 s is carried by magnetite and yields a positive fold test it is interpreted using the results of a baked contact test as the original magnetization of middle cambrian age 520 ma the second direction d 121 i 20 95 6 pole position at 18 s 55 e p 3 m 6 is nearly anti parallel to the first magnetization but the fold test is not conclusive and it is interpreted as an overprint that occurred a short time after this volcanism this study provides the first detailed palaeomagnetic result from cambrian rocks in the moroccan meseta

the evolution of the avalonian plate abstract the avalon platform of newfoundland is the type locality of the avalonian plate that is characterized by late precambrian volcanic and clastic rocks marine at the bottom and terrestrial at the top all are intruded by 650 550 ma granites late precambrian rocks in the southern british isles are similar in both areas northeastern parts of the belt are affected by deformation and metamorphism that have orogenic aspects the orogeny is referred to as the avalonian in newfoundland and monian in britain to the southeast of the avalonian rocks in europe lies another late precambrian cadomian orogenic belt of rocks as a part of the pan african orogenic belt the cadomian and avalonian belts extend into north africa morocco since these belts are ophiolite bearing it is suggested that the plate was bordered by oceanic domains it is therefore proposed that a microcontinental volcanic arc that was generated in the late precambrian was orogenically deformed by collision with north america europe and africa and survived as a coherent terrain until the late carboniferous

tectonic wedging beneath the rocky mountain foreland basin alberta canada high quality seismic reflection data reveal the geometry of a blind thinly tapered wedge of allochthonous rocks inserted into autochthonous foreland basin strata for 8 km east of the previously recognized deformation front triangle zone of the canadian rocky mountain foothills west of calgary alberta upper and lower detachment surfaces have been identified as boundaries between continuous and discontinuous reflection patterns over the length of the wedge coherent reflections above the upper and below the lower detachment show that strata outside the wedge are essentially undeformed the upper detachment is parallel to bedding for at least 7 km with a dip that decreases gradually from west to east at its distal limit the upper detachment lies 350 m above the lower detachment and does not merge with it the internal reflection geometry of the wedge changes with position we interpret the thickest part of the wedge to be dominated by thrust slices up to 500 m thick whereas the toe of the wedge is folded and faulted internally

thrust wedges with decollement levels and syntectonic erosion a view from analog models abstract analog sandbox models have been set up to study the impact of syntectonic erosion on thrust wedges with one and two decollement levels different accretion mechanisms are activated depending on interactions between surface processes and wedge mechanics frontal accretion backthrusting underthrusting and underplating due to decollement induced duplex formation at depth these mechanisms may function simultaneously being located at different parts across the wedge for all the experiments a high friction is imposed at the base of models and the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during the shortening erosion limits the forward propagation of thrust wedges and favors the underthrusting of basal layers allowing duplex formation erosion promotes development of major backthrusts in the thrust wedges without or with one decollement but no backthrusts was formed in the wedges with two decollements slow erosion allows lower extent of basal underthrusting in comparison with regular rate erosion variations in the erosion taper lead to changes in duplex geometry and exhumation rate in thrust wedges with one or two decollements the 6 erosion taper promotes formation of antiformal stack at the rear part of thrust wedge high rate of basal underthrusting and high extent of erosional removal the cover layers are nearly completely eroded above the antiformal stack and form the synformal klippe in frontal part of thrust wedges the 8 erosion taper allows development of individual ramp anticlines and active forward thrusting of cover layers above the decollement and low rate of basal underplating below it with consequent low extent of erosional removal the results of our experiments support the observations on structural evolution and erosion in the alberta foothills of the canadian rockies

a pennsylvanian paleomagnetic pole from the mineralized late cambrian bonneterre formation southeast missouri one hundred eighty eight oriented samples of the late cambrian bonneterre carbonates of southeastern missouri were taken from viburnum trend mines and local surface outcrops initial natural remanent magnetization directions have south southeasterly declinations and downward inclinations progressive demagnetizations using thermal and af techniques give two directions one is a viscous present day field direction and the other is of reversed polarity with south southeasterly declinations and very shallow inclinations the resulting paleopole at 43 n 126 e is located near the pennsylvanian to early permian segment of the north american apparent polar wander path a negative conglomerate test supports this assignment for the magnetization age magnetic extracts from the mineralized as well as unmineralized zones of the bonneterre contain spherical crystal aggregates of pure magnetite of late diagenetic origin the secondary magnetization resides in the magnetite spheroids and we infer that the spheroids formed prior to sulfide mineralization

provenance and tectonic evolution of ganderia constraints on the evolution of the iapetus and rheic oceans we provide estimates for the width timing and rates of opening and closing of the iapetus and rheic oceans the evolution of which profoundly infl uenced paleozoic global paleogeography these estimates are primarily derived from the transfer of ganderia and avalonia from gondwana to laurentia which led to closure of the iapetus ocean and opening of the rheic ocean ganderia a long lived arc terrane separated from the paleo caribbean margin of amazonia at 505 ma with a latitudinal speed of 9 cm a northward initiating the rheic ocean as a backarc basin ganderia s trailing edge was reduced to 5 cm a following opening of a 600 800 km wide backarc basin within ganderia at 475 ma opening and closing of the iapetus ocean was largely driven by far fi eld stresses slab pull in some places and slab rollback in others

a plate tectonic scenario for the iapetus and rheic oceans abstract the tectonics dynamics and biogeographic landscape of the early paleozoic were dominated by the opening and expansion of one large ocean the rheic and the diminution to terminal closure of another iapetus an understanding of the evolution of these oceans is thus central to an understanding of the early paleozoic but their chronicle also presents a rich temporal profile of the wilson cycle illustrating continental scale rifting microcontinent formation ocean basin development arc accretion and continent continent collision nevertheless contemporary paleogeographic models of the iapetus and rheic oceans remain mostly schematic or spatiotemporally disjointed which limits their utility and hinders their testing moreover many of the important kinematic and dynamic aspects of the evolution of these oceans are impossible to unambiguously resolve from a conceptual perspective and the existing models unsurprisingly present a host of contradictory scenarios with the specific aim to resolve some of the uncertainties in the evolution of this early paleozoic domain and a broader aim to instigate the application of quantitative kinematic models to the early paleozoic i present a new plate tectonic model for the iapetus and rheic oceans the model has realistic tectonic plates which include oceanic lithosphere that are defined by explicit and rigorously managed plate boundaries the nature and kinematics of which are derived from geological evidence and plate tectonic principles accompanying the presentation and discussion of the plate model an extensive review of the underlying geological and paleogeographic data is also presented

faunal evidence for oceanic separations in the palaeozoic of britain the faunal criteria for the recognition of the relative separation of old continents are 1 the contrast between shallow not deep water faunas off opposite shorelines 2 the recognition of deeper water facies surrounding the edges of continents and 3 the recognition of the disposition of ancient climatic belts these criteria are defined and used to assess the relative position of the various parts of what is now britain in the palaeozoic the iapetus ocean is well characterized by faunal differences from the cambrian until the lower ordovician but from caradoc times onwards these differences dwindle until by the latest silurian only the distribution of the ostracods separates the two sides of the ocean on faunal grounds in the early ordovician s british faunas are comparable with those from bohemia france and elsewhere to the s indicating connection with gondwanaland and these faunas differ from those in the baltic area a distribution which we attribute to a true ocean tornquist9s sea between n and s europe tornquist9s sea probably closed in the upper ordovician and from ashgill times onwards the s british and baltic faunas remained similar during the middle and late silurian there is evidence of increasing faunal distinction between britain the baltic area and north america on the one hand and southern europe and gondwanaland on the other indicating an opening rheic ocean which appears to have persisted until late carboniferous times

avalonian proximity of the ordovician miramichi terrane northern new brunswick northern appalachians paleomagnetic evidence for rifting and back arc basin formation at the southern margin of iapetus a paleomagnetic investigation of the middle ordovician tetagouche group in northern new brunswick was undertaken to determine the paleogeo aphi position of the miramichi terrane stepwise thermal demagnetization of pillow basahs reveals a high temperature characteristic gnet tion with a mean direction of b w z 69 k 22 aas 13 tih corrected n 7 sites 73 samples a positive fold test and the presence of antipodal normal and reversed polarity directions indicate that this ancient direction is ordovician in age with a paleopole position of 52 n 352 e the corresponding pateolatitude of 535 places these vokanic rocks near the southern margin of the iapetus ocean at paleolatitudes similar to those revealed by avalon for the middle to late ordovician the mafic and felsic volcanic rocks and marine sedimentary rocks of the tetagouche and fournier groups have been interpreted to be remnants of a rifted continental margin and a middle ordovician back arc basin our results show that the process of rifting and back arc basin formation occurred at the avalonian margin of iapetus which implies that ordovician subduction was not restricted to the laurentian margin but also marks the southern margin of japetus

palaeomagnetism of palaeozoic rocks from the cabo de penas asturia spain summary ordovician volcanic samples of the cabo de penas area yielded a primary remanent magnetization d 202 i 78 95 6 which is partially or entirely overprinted by a late palaeozoic remagnetization late devonian early carboniferous sedimentary samples reveal a pre or syntectonic carboniferous remanent magnetization similar to the secondary one of the volcanic samples a soft post tectonic component appears also in few samples for which a late carboniferous age is inferred comparison of the carboniferous remanent magnetizations and structural parameters suggests that in a late stage of the deformation the sites have undergone minor rotations around a vertical axis a strike correction is therefore proposed to take such an effect into account the average of the corrected mean site directions d 178 i 19 95 9 is considered to be a good approximation of the early or middle carboniferous palaeomagnetic direction in asturia

implied basement tectonic control on deposition of lower carboniferous carbonate ramp southern cordillera canada cambrian kanasevich et al 1969 and prethe mount head embayment is a regional downwarp along the west coast of lower middle devonian norris and price 1966 carboniferous western canada that developed by differential subsidence which we recog benvenuto and price 1979 nize from lithostratigraphic and biostratigraphic patterns palinspastic restoration of the mount head embayment illustrates that subsidence domains are geometrically coincident with previously identified tectonic elements of the autochthonous basement thus it ap methods pears that basement tectonic elements controlled sediment accommodation and accumu geologic observations were recorded on lation within the mount head embayment the overall shape of this embayment is probably palinspastically restored maps and cross setinherited from the arcuate shape of the late proterozoic cratonic rift margin within the tions and to basement tectonic mount head embayment several northeast southwest trending archean and proterozoic domains defined on aeromagnetic and gravbasement tectonic elements intersect the autochthonous cratonic margin at high angles ity maps brandley 1993 the palinspastic carboniferous piano key like structural reactivation of these tectonic elements produced base map is modified from gibson s 1985 oriented trends of differential subsidence that partitioned the mount head embayment into map of displacement vectors for jurassic two subbasins crowsnest and kananaskis depocenters separated by a more positive area rocks the magnitudes of the vectors were highwood high moreover our data imply that precambrian basement structure noted by others under the plains and rocky mountain fold and thrust belt continued across the altered to reflect displacements at the misrocky mountain trench to the west and that tectonic control on sedimentation noted by sissippian level documented by bally et al others for precambrian and pre middle devonian rocks extends clearly into overlying 1966 price 1981 and price and fermor carboniferous deposits 1985 university theses and geological survey of canada maps and sections across

eruptive stratigraphy of the tatara san pedro complex 36 s southern volcanic zone chilean andes reconstruction method and implications for magma evolution at long lived arc volcanic centers

substratum transverse faults in kuqa foreland basin northwest china and their significance in petroleum geology abstract the importance of transverse faults in basin evolution and petroleum geology has been often emphasized however the transverse faults in the kuqa foreland basin the most important gas producing area in china have rarely been studied interpreted seismic sections and earthquake focal mechanism solutions as well as other geological and geophysical data allow us to identify a few widely spaced approximately ns trending transverse strike slip faults separating major structural units and to clarify the geometry and kinematics of these transverse faults hidden below thrust faults in the kuqa foreland basin two major structural domains can be distinguished transverse faults in the northern kuqa foreland basin are mainly nne trending sinistral indicating clockwise rotation of fault bounded blocks in contrast the predominant nw trending dextral faults in the southern kuqa foreland basin imply counterclockwise rotation of fault bounded blocks we propose a tectonic model in which crustal blocks are bounded by strike slip faults in a zone of simple shear rotation about vertical axis the strike slip faulting and thrust faulting in the kuqa foreland basin suggest that some of the convergence between south tianshan and tarim blocks may have been accommodated not only by obvious crustal shortening and thickening along thrust faults but also by rotation and possible lateral movement of the crust along transverse faults controlled by the remote collision of indian block with eurasian block since the miocene these reactivated substratum faults which may inherit from paleozoic deformation control various elements relevant to gas accumulation in the kuqa foreland basin which should expect to be paid more attention in the future these elements include maturity of tertiary and jurassic source rocks a difference in the regional cap of kumugelimu salt beds from east to west reservoir bed properties gas migration channels and traps formation in addition the strike slip faulting of the transverse faults may affect deformation of the sedimentary cover including making the western qiulitag structural belt to form an arcuated structure curved to the ssw

paleomagnetism of siluro devonian and cambrian granitic rocks from the avalon zone in cape breton island nova scotia as part of a major study of the avalon zone in cape breton island we describe the paleomagnetism of radiometrically well studied granitic rocks of two generations representing the acadian 350 45

oxygen isotope geochemistry of the lassen volcanic center california resolving crustal and mantle contributions to continental arc magmatism this study reports oxygen isotope ratios determined by laser fluorination of mineral separates mainly plagioclase from basaltic andesitic to rhyolitic composition volcanic rocks erupted from the lassen volcanic center lvc northern california plagioclase separates from nearly all rocks have o values 6 1 8 4o higher than expected for production of the magmas by partial melting of little evolved basaltic lavas erupted in the arc front and back arc regions of the southernmost cascades during the late cenozoic most lvc magmas must therefore contain high o crustal material in this regard the o values of the volcanic rocks show strong spatial patterns particularly for young rhyodacitic rocks that best represent unmodified partial melts of the continental crust rhyodacitic magmas erupted from vents located within 3 5 km of the inferred center of the lvc have consistently lower o values average 6 3o 0 1o at given sio2 contents relative to rocks erupted from distal vents 47 0 km average 7 1o 0 1o further magmas erupted from vents situated at transitional distances have intermediate values and span a larger range average 6 8o 0 2o basaltic andesitic to andesitic composition rocks show similar spatial variations although as a group the o values of these rocks are more variable and extend to higher values than the rhyodacitic rocks these features are interpreted to reflect assimilation of heterogeneous lower continental crust by mafic magmas followed by mixing or mingling with silicic magmas formed by partial melting of initially high o continental crust 9 0o increasingly hybridized by lower o 6 0o mantle derived basaltic magmas toward the center of the system mixing calculations using estimated endmember source o values imply that lvc magmas contain on a molar oxygen basis approximately 42 to 4 isotopically heavy continental crust with proportions declining in a broadly regular fashion toward the center of the lvc conversely the o values of the rhyodacitic rocks suggest that the continental crust in the melt generation zones beneath the lvc has been substantially modified by intrusion of mantlederived basaltic magmas with the degree of hybridization ranging on a molar oxygen basis from approximately 60 at distances up to 12 km from the center of the system to 97 directly beneath the focus region these results demonstrate on a relatively small scale the strong influence that intrusion of mantle derived mafic magmas can have on modifying the composition of pre existing continental crust in regions of melt production given this result similar but larger scale regional trends in magma compositions may reflect an analogous but more extensive process wherein the continental crust becomes progressively hybridized beneath frontal arc localities as a result of protracted intrusion of subduction related basaltic magmas

paleomagnetism of the cambro ordovician mcclure mountain alkalic complex colorado the middle to late cambrian loop in the north american apparent polar wander path apwp has been variously attributed to tectonic rotations remagnetizations and primary magnetizations although no primary thermal remanent magnetizations or primary detrital remanent magnetizations have as yet been demonstrated the temporally self consistent nature of the loop has been used as an argument for primary magnetizations we have studied 535 5 ma nepheline syenites and syenites of the mcclure mountain alkalic complex as well as 495 10 ma red trachyte dikes which intruded the complex in an effort to find a primary trm because zijderveld analysis yielded consistent results for only one trachyte dike remagnetization great circle analysis was employed giving a pole for the trachyte dikes at the tip of the loop 43 n l14 e while the syenites and nepheline synenites gave a pole at the base of the loop 18 n 142 e the magnetic carrier in the trachytes is hematite which apparently formed during a pervasive hydrothermal alteration k ar whole rock dating of the trachytes suggests a pennsylvanian age for the alteration and thus a late paleozoic remagnetization of the trachytes thus the low latitude cambrian pole is confirmed but we find no evidence in this study to support the primary nature of the cambrian apwp

lateral variations in tectonic style across cross strike discontinuities an example from the central apennines belt italy in foreland thrust belts abrupt lateral changes in tectonic style structural stratigraphic features and topography usually occur across cross strike faults the central apennines of italy offer an exceptional scenario of lateral variations in tectonic setting here the sangro volturno oblique thrust ramp svotr represents the outer thrust front of the pliocene quaternary foreland thrust system confining southward the axial culmination of the orogen that occurs in the central apennines we present an interpretation of the pliocene quaternary evolution of this cross strike fault through an integrated dataset including structural geological mapping and subsurface onshore seismic reflection profiles the interpretation of the structural framework is augmented by the analysis of low temperature thermochronometers from 32 new sites extending across the subsurface transverse structure as evidenced by seismic line interpretation the localization and development of the svotr have been influenced by inherited extensional faults within a positive inversion tectonics context the regional distribution of the maximum paleotemperature values across the svotr constrains the original extent of the allochthonous thrust sheet over all its hanging wall and footwall blocks the pliocene quaternary thrusting and inversion of svotr caused the strong hanging wall uplift which brought to the complete erosion of the allochthonous units and the exhumation of the adria units the integrated analysis of low temperature thermochronometers and structural evidence as applied in the study case can define the role of major cross strike discontinuities in foreland thrust belts by constraining and verifying their tectonics inversion significance and the amount of related exhumation

andesite petrogenesis in the ordovician borrowdale volcanic group of the english lake district by fractionation assimilation and mixing a suite of composite basalt andesite dykes in the ordovician borrowdale volcanic group of the english lake district records magmatic evolution from basalt to andesite although altered the rocks preserve textures that indicate magma mixing primitive basalts were derived from a fertile subduction modified mantle source evolution by fractional crystallization is suggested by rapid decrease of compatible trace element concentrations and similar incompatible trace element and ree profiles throughout the sample range recharge of the evolving magma with fresh batches of basaltic composition is indicated by some samples that have compatible trace element concentrations much higher than expected from their otherwise evolved compositions geochemical evidence of magma mixing is provided by linear trends between pairs of incompatible trace elements not at constant ratio e nd values indicate addition of a crustal component but samples do not conform to a simple mixing equation the combined evidence points to magma evolution by assimilation of wallrock during fractional crystallization afc with periodic recharge we have modelled an afc process using a skiddaw group metasediment contaminant that can explain trace element and isotopic variation through variable amounts of assimilation crystal fractionation and recharge to produce a spectrum of compositions that was sampled periodically by the dykes there is evidence from other parts of the borrowdale volcanic group that similar processes operated throughout its history

lateral variations and linkages in thrust geometry the traligill transverse zone assynt culmination moine thrust belt nw scotland abrupt lateral changes in thrust geometry occur in many fold and thrust belts along so called transverse zones commonly related to pre existing basement faults however the causative structures are usually concealed we analyse here the traligill transverse zone in the assynt culmination of the caledonian moine thrust belt nw scotland this transverse zone trends sub parallel to the wnw transport direction and is associated with en echelon faults cutting thrusts discontinuity of thrust architecture and oblique fold and thrust structures thick thrust sheets north of the transverse zone contain thick basement slices thrust sheets to the south are thin and involve a thin bedded sequence the traligill transverse zone developed above the loch assynt fault a basement cross fault and reactivated proterozoic ductile shearzone piercing point analysis shows that the cross fault was active both before and after thrusting thrusting thus affected strata that were already disrupted by steep faults the amplitude of the disturbance in fold and thrust architecture along the traligill transverse zone is much greater than the vertical displacement along the fault this is attributed to localised transpressional thrust stacking other basement cross faults and their relationship with lateral variations within the moine thrust belt and in other thrust belts are discussed

volatile sulphur and chlorine major and trace element geochemistry of mafic to intermediate tephras from the chilean southern volcanic zone 33 43 s here we present the first systematic investigation of volatile geochemistry along the southern volcanic zone svz of chile holocene olivine hosted melt inclusions in the most mafic tephras sampled from 16 volcanoes along the volcanic front of the svz between 33 s and 43 s were analysed for pre eruptive sulphur chlorine and major element contents these results are combined with trace element compositions of the host whole rocks the highest fractionation corrected gas contents occur in the least degassed melt inclusions from small monogenetic cones of los hornitos cabeza de vaca and apagado from both the transitional and the southern central svz reaching 3 000 g g s and 1 400 g g cl while the lowest abundances of 1 100 g g s and 600 g g cl were found in the central svz at volcan lonquimay volcan llaima and volcan villarrica chlorine co varies with trace element indicators for the degree of melting and or source enrichment such that the lowest cl contents are found in high degree melts from the most depleted mantle sources the size of the volcanic edifices correlates inversely with cl abundances in the melt this could reflect more extensive degassing during ascent through the complex magma plumbing systems beneath the stratovolcanoes or greater dilution during larger degrees of melting of more depleted sources or a combination of these factors compared to other subduction zones the svz melt inclusions exhibit cl and s abundances in the same range as most of those from the central american and those from the marianas arcs