middle jurassic rhyolite volcanism of eastern graham land antarctic peninsula age correlations and stratigraphic relationships silicic volcanism at c 168 ma has been identified previously on the antarctic peninsula and the mapple formation which includes those volcanic rocks has been defined and documented from one area of the east coast of graham land based on age and geochemical criteria correlations have been made to the extensive chon aike province of south america which has been demonstrated to be one of the largest silicic volcanic provinces in the world rhyolitic and intermediate composition volcanic successions from six separate localities on the east coast of the antarctic peninsula are described here and are confirmed as correlatives of the mapple formation based on newly acquired geochronology and field observations they are dominantly rhyolitic crystal tuffs and or ignimbrites with ages in the interval 162 168 ma overlapping with the age of the mapple formation 167 171 ma at the type locality andesitic agglomerates are also described which are included in the same event and demonstrate the occurrence of rare intermediate volcanism which is also seen in the chon aike province a new group the graham land volcanic group is defined here and criteria are established which allow the separation of some volcanic successions out of the previously defined antarctic peninsula volcanic group which takes no account of tectonic setting eruption age or geochemistry

sandstone matrix olistostrome deposited on intra subduction complex serpentinite franciscan complex western marin county california abstract detailed field mapping in the franciscan complex in western marin county california offers insight into the origins and development of melanges as well as accretionary complex architecture from structurally high to low the study area units comprise a structurally high sandstone matrix olistostrome serpentinite a structurally intermediate sandstone matrix olistostrome early cretaceous nicasio reservoir terrane greenstone and coherent cretaceous greywacke all exhibiting prehnite pumpellyite burial metamorphism the structurally high sandstone matrix olistostrome includes volcanic blocks up to 700 m in diameter and chert blocks up to 100 m in diameter whereas the structurally intermediate olistostrome unit comprises a lithic rich sandstone matrix enclosing volcanic blocks 1 20 m in diameter the youngest detrital zircons in the high olistostrome and the coherent greywacke have u pb ages of 20 m y older than the inferred depositional ages of the units themselves suggesting that the bulk of the detritus comprising these units was derived by exposure and sedimentary recycling of significantly older previously accreted sediments the matrix of both olistostrome units exhibits minimal strain with weak local development of pressure solution cleavage these findings demonstrate introduction of franciscan exotic blocks and development of franciscan block in matrix fabrics through sedimentary sliding and support sedimentary interpretations for more highly strained shale and serpentinite matrix melanges additionally these data suggest that sandstone matrix olistostromes melange may constitute a larger part of the franciscan and other accretionary complexes than previously believed the structurally high olistostrome preserves a depositional contact on serpentinite verifying an intra subduction complex origin for the serpentinite the serpentinite lacks block in matrix structure and likely represents a tectonically emplaced unit derived from the subducting plate as a coherent nappe rather than a sedimentary serpentinite deposit multi kilometer scale west vergent overturned folds with subhorizontal fold axes deform the nappes of the field area and a later generation of open northeast trending folds overprints the earlier folds

diagnostic features and field criteria in recognition of tectonic sedimentary and diapiric melanges in orogenic belts and exhumed subduction accretion complexes abstract multiple episodes of deformation during the tectonic evolution of orogenic belts and ancient subduction accretion complexes cause obfuscation of primary block in matrix fabric of melanges and thereby making the recognition of their tectonic sedimentary or diapiric origin difficult here we present a comprehensive overview and synthesis of a diverse set of field based stratigraphic and structural criteria which are at the base of geological mapping rules to differentiate between various melange types developed by disparate geological processes and mechanisms we first define the current concepts of melange and melange nomenclature and describe the most diagnostic features of tectonic sedimentary and diapiric melanges at different scales we discuss some of the main issues complicating the application of these diagnostic criteria such as i similarities between the block in matrix fabric of different melange types formed in partially lithified sediments at shallow structural levels ii transformation of fabric elements with increased depth due to tectonic reworking and recrystallization processes iii significance of exotic versus native blocks in melange matrix and iv age relationships between blocks and matrix in a melange we introduce two additional criteria in approaching these complexities and in recognizing different processes of polygenetic melanges formation in the field when primary diagnostic fabrics were reworked by multiple deformational events these new criteria are based on i the coherence between lithological compositions of melange components blocks and matrix and characteristics and tectonic evolution of the geodynamic setting of their formation tectonic environment criterion and ii specificity and kinematic coherence in the distribution of deformation between blocks and the matrix deformation criterion the discussed diagnostic criteria can be applied to all field based investigations of melanges and broken formations in orogenic belts and exhumed subduction accretion complexes around the world regardless of their location age and tectonic history

the notion of climate driven strath terrace production assessed via dissimilar stream process response to late quaternary climate abstract previous research results from the gabilan mesa are combined with new optically stimulated luminescence osl age estimates and sedimentological analyses with the aim of identifying factors that inhibit climate driven strath terrace production and factors that make possible strath terrace production independent of climate forcing the factors are revealed by comparing the morphostratigraphy and osl age estimates of terraces in the adjacent san lorenzo creek and pancho rico creek drainage basins of the central california coast ranges osl age estimates on san lorenzo creek fill terrace alluvium overlying bedrock at two paleofluvial levels range between 50 5 and 41 3 ka and between 33 4 and 18 2 ka these osl age estimates indicate that although the channel of pancho rico creek was degrading at these times san lorenzo creek aggradation was synchronous with previously documented regional climatically driven aggradation that elsewhere in southern california led to strath production and alluvial deposition the regional scale climate forcing events had different effects on san lorenzo and pancho rico creeks because of the influences of drainage basin lithology on bedload size and tectonic tilting direction on base level fall the holocene history of channel denudation and strath production of pancho rico creek is also different from that of san lorenzo creek and different from that of many other streams in southern california after pancho rico creek captured the upper part of the drainage basin of san lorenzo creek sometime after 15 5 to 11 7 ka pancho rico creek has been producing unpaired erosional strath terraces the weak clay rich fine grained sedimentary rock underlying pancho rico valley is an ideal substrate in which to form straths the meandering channel of pancho rico creek produces straths and weathering resistant relatively hard bedload introduced by stream capture ensures their preservation as strath terraces

franciscan complex olistostrome at crescent city northern california an olistostrome and bounding turbidites are exposed within the late mesozoic franciscan complex along the crescent city california coastline facies grade in character from mutti ricci lucchi 1978 mixed facies b c and d to f the olistostrome to mixed a b and e progressing upwards within the franciscan stratigraphic section the facies f unit outcrop is up to 600 m thick and extends 12 km along strike it consists of oblate to tabular blocks up to 200 m in maximum dimension of greenstone tonalite radiolarian chert limestone phyllite and greywacke dispersed in a scaly argillite matrix the olistostromal origin of the unit is indicated by depositional contacts with bounding turbidites by the presence of abundant recycled sedimentary clasts within the unit and by the presence of sedimentary breccias and associated dismembered slump folded turbidites both within the olistostrome and among subjacent turbidites sandstones are chiefly feldspathic litharenites that were very likely derived from the partially dissected late mesozoic sierran klamath magmatic are franciscan rocks record an early pervasive layer parallel flattening strain in such features as extensional faults necking and pinch and swell structures several scales of extensional faulting account for the juxtaposition of turbidites of different facies and or with varying degrees of stratal disruption the formation of sandstone lozenges and the formation of scaly foliation in the olistostrome matrix the latter resulted from the juxtaposition of lenticles with varying concentrations of silt and clay these were ultimately derived from the finer divisions of turbidite beds that were incorporated into the olistostrome the presence of gradational contacts between some sandstone olistoliths and the olistostrome matrix and of sandstone dykes that intrude fractures and associated drag folded turbidite beds indicate that franciscan sediments were not lithified during their early deformation these sediments were deposited in either a trench or trench slope basin and were first deformed either by gravity collapse of the trench slope cover or less likely by vertical loading beneath the toe of the accretionary wedge they later were folded during internal shortening of the growing franciscan accretionary prism

chemical weathering in antarctica an example of igneous rock particles in big lachman lake sediments james ross island jezerni sedimenty velkeho lachmanova jezera ostrov jamese rosse antarktida dominuji jilovite a prachovite castice r zneho petrografickeho slo eni ty jsou sopecneho p vodu a jsou odvozeni p eva n z mendelova souvrstvi intenzita chemickeho zv travani vulkanick ch castic v sedimentech byla vyjad ena chemick m indexem alterace cia kter popisuje p em nu ivc na jilove mineraly pozorovane mineralni asociace montmorillonitu illitu a kaolinitu pravd podobn pochazela z p em ny sopecneho skla a ivc na jilove mineraly mira zv travani vyjad ena pomoci cia z lakustrialnich sediment je podobna jako u spodnojursk ch na ti bohatach vulkanick ch hornin souvrstvi mount poster a st ednojursk ch na ti bohat ch vulkanick ch hornin ze souvrstvi mapple z antarktickeho poloostrova nami studovane sedimenty ukazuji dobrou shodu se slo enim st ednojursk ch ryolit ze souvrstvi mapple a naopak se castecn lisi od slo eni kenozoick ch bazalt vulkanicke skupiny ostrova jamese rosse zdrojov material z jezernich sediment pochazi z antarktickeho poloostrova a byl pravd podobn transportovan p es kanal prince gustava mal mi ledovci v pr b hu neogenu a kvarteru

the origin of the upper palaeozoic chanaral melange of n chile the fragmented and mixed strata of the chanaral melange extend for some 220 km from n to s in the coastal ranges of n chile 26 20 to 28 20 s the melange was produced in an accretionary wedge resulting from the ne subduction of the ancestral pacific oceanic plate beneath the gondwana land margin during carboniferous times the melange consists essentially of blocks of sandstone in a pelitic matrix these sediments were deposited as deep sea basin plain turbidites prior to their fragmentation other blocks in the melange include mafic volcanic rocks with the geochemical characteristics of oceanic island basalts and rare shallow marine limestones structures in the melange suggest an origin by two distinct deformation processes involving unlithified sediments initial boudinage and break up of the strata was apparently accomplished by intrastratal movement resulting from imbricate thrusting within the accretionary wedge the second process produced cross cutting zones of breccia which are interpreted as fluid escape conduits resulting from the high pore pressures produced during underthrusting

melange diapirs into the cambria slab a franciscan trench slope basin near cambria california near cambria california a franciscan trench slope basin of late cretaceous age is intruded by two diapirs of blueschist block bearing mud matrix melange the rise of the diapirs caused major upturning of the bedded strata within a few hundred meters of the contact and complex interfingering of mud matrix melange with basin sediments near the contacts at one locality a fragment of basin sandstone is observed partially detached from the wall rock the mud matrix melange is highly mobile and the intrusive character during diapirism is clearly analogous to that of magma in igneous intrusions diapirism may be responsible for large scale intercalation of slope and slope basin sediments with subduction generated melange at actively convergent plate margins

paleothermal structure of the point san luis slab of central california effects of late cretaceous underplating out of sequence thrusting and late cenozoic dextral offset late cretaceous shale and sandstone turbidites of the point san luis slab are isoclinally folded locally sheared and faulted but their severity of stratal disruption is relatively mild when compared to adjacent polymictic melange of the franciscan complex we tested the interpretation of a trench slope basin origin for these strata by documenting their paleothermal structure including contacts between turbidites and melange values of mean random vitrinite reflectance rm from turbidites are 0 9 1 7 estimates of maximum paleotemperature are 135 200 c melange matrix samples yield rm values of 1 1 2 5 with an average of 1 5 and peak temperatures between 160 and 240 c the turbidite over melange contact is locally cooler over warmer and was folded after peak heating the relatively high paleotemperatures cast doubt on a shallow slope basin model i e 1 2 km burial depth we suggest instead that thermal maturation of the point san luis slab occurred much deeper in an accretionary prism 10 15 km where offscraped trench wedge deposits were faulted against underplated melange the paleothermal structure was offset and tilted after peak heating by two out of sequence faults late oligocene to pliocene strata rest unconformably above the franciscan and there is a significant gap in thermal maturity across this unconformity with no evidence to show that franciscan rocks were reset thermally following the main episode of uplift and erosion three dimensional orientations of isoreflectance surfaces on opposite sides of the san gregorio san simeon hosgri fault system also can be used to test interpretations of strike slip neotectonics the failure to match these geometries among suspected piercing points at point san luis cambria and point sur favors a suggestion that differential post thermal peak dextral offset of franciscan basement has not exceeded 10 15 km

nappes tectonics of oblique plate convergence and metamorphic evolution related to 140 million years of continuous subduction franciscan complex california this paper presents a new synthesis of franciscan complex tectonics with the emphasis on the pre san andreas fault history of these rocks field relations suggest that the franciscan is characterized by nappe structures that formed during sequential accretion at the trench the presence of these structures along with other field relations including the lack of evidence for large offset of conglomerate suites indicates that strike slip fault systems of large displacement 500 km did not cut the franciscan complex during subduction regional geology and comparisons to modern arc trench systems suggest that strike slip faulting associated with oblique subduction took place inboard east of the franciscan in the vicinity of the magmatic arc the franciscan varies along strike because individual accreted elements packets of trench sediment seamounts etc did not extend the full length of the trench different depths of underplating distribution of post metamorphic faulting and level of erosion pro

the 2010 ash emissions at the summit craters of mt etna relationship with seismo acoustic signals 1 mt etna volcano italy typically generates lava fountains and strombolian eruptions from the summit craters producing significant emissions of tephra which may cause moderate to high impact both in the atmosphere and on the ground however we have also witnessed a number of minor ash emissions that although far less powerful may pose considerable volcanic hazards in this paper we deal with three ash emissions occurring in 2010 8 april at southeast crater 25 august at bocca nuova and 14 15 november at northeast crater correlating their volcanological features with the associated seismo acoustic signals we provide details regarding the chronology eruption column dispersal of the deposit and texture grain size componentry and morphology of the emitted ash each eruptive episode has also been characterized by means of seismo acoustic analyses evaluating the volcanic acoustic seismic ratio vasr furthermore the source of volcanic tremor recorded from march to december 2010 was localized the joint volcanological and seismo acoustic analyses allowed distinguishing two main kinds of ash emissions types a 8 april and 25 august and b 14 15 november regarding the former the accumulation of gas below a dense cap rock obstructing the conduit vent giving rise with the uncorking to impulsive explosivity was hypothesized the latter type instead is characterized by a longer lasting and less explosivity likely due to the existence of open conduit conditions therefore type b ash emissions are less hazardous than type a this simple model regarding minor explosive activity may constitute a starting point to assess the volcanic risk from unexpected explosions

major effusive eruptions and recent lava fountains balance between expected and erupted magma volumes at etna volcano 1 over the last four decades etna has shown a high output rate through numerous eruptions the volcano has displayed two eruptive behaviors the first is characterized by effusive eruptions that efficiently drained the storage system and emitted large volumes of magma the second behavior is related to lava fountains erupting small magma batches which are normally with high frequency and have been considered as precursors of major effusive eruptions in this paper we present an updated estimation of emitted volumes from etna eruptions which include the 38 lava fountain episodes that occurred from january 2011 to april 2013 these recent explosive episodes have been frequent discharging significant magma volumes observing the steady trend of magma output over time we present insights on expected erupted volumes we highlight that the january 2011 to april 2013 lava fountains efficiently drained the intermediate shallow storage system and favored a balance between the incoming and outgoing magma

eruptive processes leading to the most explosive lava fountain at etna volcano the 23 november 2013 episode the 23 november 2013 lava fountain at etna volcano was the most explosive of the last 44 episodes that have occurred at etna in 2011 2013 we infer the total magma volume erupted by thermal images analysis and show that it was characterized by a very high time averaged discharge rate tadr of 360 m3 s 1 having erupted 1 6 106 m3 of dense rock equivalent magma volume in just 45 min which is more than 3 times the tadr observed during previous episodes two borehole dilatometers confirmed the eruption dynamics inferred from the thermal images when compared to the other lava fountains this episode can be considered as the explosive end member however the erupted volume was still comparable to the other lava fountain events we interpret that the 23 november explosive end member event was caused by more primitive and gas rich magma entering the system as demonstrated by the exceptional height reached by the lava fountain

large volume silicic volcanism along the proto pacific margin of gondwana lithological and stratigraphical investigations from the antarctic peninsula jurassic magmatism in western gondwana produced the most voluminous episode of continental volcanism in the phanerozoic era during the early to middle jurassic some 2 5 3 million km3 of dominantly basalt and to a lesser extent rhyolite were erupted onto a supercontinent in the early stages of break up the major silicic portion of the gondwana magmatic province is exposed in patagonian south america the volcanic rocks of patagonia have been collectively termed the chon aike province and constitute one of the world s most voluminous silicic provinces the volcanic rocks are predominantly pyroclastic dominated by ignimbrite units of rhyolite composition volcanic rocks crop out sporadically across much of the once contiguous antarctic peninsula and are considered to form an extension of the chon aike province a continuation of the province to include the antarctic peninsula would extend its strike length along the active pacific margin by c 2000 km volcanic rocks exposed along the east coast of the antarctic peninsula defined here as the mapple formation are also dominated by rhyolitic ignimbrite flows with individual units up to 80 m in thickness and a total thickness of c 1 km the ignimbrites vary in degree of welding from high grade rheomorphic ignimbrites with parataxitic textures to unwelded lithic rich ignimbrites rhyolite lava flows air fall horizons debris flow deposits and epiclastic deposits are volumetrically minor occurring as interbedded units within the ignimbrite succession the lithology and stratigraphy of the jurassic volcanic rocks of the mapple formation are presented and comparisons are made to the chon aike province a consistent stratigraphy of permo triassic metasedimentary rocks unconformably overlain by terrestrial mudstone siltstone sequences which are in turn conformably overlain by largely silicic subaerial volcanic rocks is present at several localities along the antarctic peninsula and at localities in the chon aike province precise zircon u pb middle jurassic ages exist for two volcanic formations from the antarctic peninsula and a middle lower jurassic age has been suggested for the underlying sedimentary formations based on fossil flora analysis the antarctic peninsula chronostratigraphy coupled with lithological similarities indicate a close relationship to those sequences of the chon aike province

autochthonous v accreted terrane development of continental margins a revised in situ tectonic history of the antarctic peninsula the allochthonous terrane accretion model previously proposed for the geological development of the antarctic peninsula continental margin arc is reviewed in light of recent data and the geology is reinterpreted as having evolved as an in situ continental arc this is based upon the following factors 1 the presence of early palaeozoic basement and stratigraphic correlation of sequences between the autochthonous and previously proposed allochthonous terranes 2 isotopic evidence for similar deep crustal structure across the different terranes 3 ocean island basalt magmas and deep marine sedimentary rocks formed during continental margin extension within the previously proposed accretionary wedge sequence i e not formed against an active oceanic arc 4 the distribution of magnetic susceptibility measurements and aeromagnetic data locating the palaeo subduction zone along the west of the peninsula 5 a lack of clear palaeomagnetic distinction between the terranes the following alternative tectonic history is proposed 1 amalgamation and persistence of gondwana 2 subsequent silicic large igneous province magmatism and extension 3 development and history of andean subduction until its cessation in the cenozoic a number of features in the antarctic peninsula correlate with those of other circum pacific margins supporting a global evaluation of allochthonous v autochthonous margin development to aid our understanding of crustal growth mechanisms

the continuing story of etna s new southeast crater 2012 2014 evolution and volume calculations based on field surveys and aerophotogrammetry abstract during the years 2013 2014 the new southeast crater nsec at the summit of mount etna produced frequent episodes of lava fountaining paroxysms and its cone continued to grow at unprecedented rates many of the episodes were of rather brief duration and violently explosive producing mostly pyroclastic material and minor volumes of lava other episodes especially those since mid december 2013 were characterized by violent strombolian activity without producing sustained lava fountains and significant amounts of tephra but emitting more voluminous lava flows one episode of intense strombolian and effusive activity that was possibly fed from the nsec conduit occurred from vents located approximately 1 km north of the crater on the east flank of the northeast crater in july august 2014 the evolution of the nsec cone between 2012 and 2014 was documented by repeated gps surveys carried out both from a distance and on the cone itself by the acquisition of comparison photographs and by two aerophotogrammetric surveys from these surveys the highest point of the nsec results to have grown from 190 m may 2012 to 215 m october 2014 above the pre cone surface reaching an elevation of 3290 m and its volume more than doubled to 50 0 6 5 10 6 m 3 representing the 40 of the total bulk volume of the volcanic products including pyroclastic fallout erupted in 2011 2014 which is 147 2 10 6 m 3 101 3 10 6 m 3 dense rock equivalent the whole of the 2011 2014 nsec activity marks an unusually high frequency of rather explosive tephra rich eruptive episodes compared to etna s activity in past decades and centuries although the average magma production rate in this interval is close to the supposed long term output rate of the volcano the latest eruptive episodes show a tendency of the nsec coalescing with the old southeast crater cone which therefore represents a miniature example of a growing compound volcano at the summit of etna

new paleomagnetic data from the antarctic peninsula and their tectonic implications new paleomagnetic data presented here further constrain the relative motion of the antarctic peninsula relative to east antarctica during the mesozoic development of the southern ocean basins the antarctic peninsula ap is one of four crustal blocks that define west antarctica the others being the ellsworth whitmore mountains ewm thurston island eights coast ti and marie byrd land mbl a jurassic pole 155ma 124 e 64 s a95 7 1 n 10 vgps was obtained from the ap block which suggests that the ap block rotated clockwise between 175 and 155 ma due to significant early opening in the weddell sea basin a new early cretaceous paleomagnetic pole 182 e 74s a95 5 9 n 6 site mean vgps indicates that the ap block was in or near to its present day position with respect to east antarctica by 130 ma between 155 and 130 ma counterclockwise rotation of the ap ti blocks together with the southward motion of east gondwanaland probably resulted in subduction of weddell sea ocean floor beneath the southern ap block and initiated the palmer land deformational event a 130 ma pole from the ti block requires clockwise rotation of the ti and possibly the ewm blocks between 130 and 110 ma producing sinsistral strike slip motion between the ewm block and east antarctica and dextral transpressional motion between the ti ewm blocks and the ap block new ap block 110 ma and 85 ma poles from this study 199 e 74 s a95 6 9 n 13 vgps 152 e 86 s a95 7 5 n 6 vgps respectively are similar to equivalent age poles from east antarctica and suggest little or no relative motion between the antarctic peninsula and east antarctica northern and southern antarctic peninsula mid cretaceous poles are very much alike suggesting that the s shape of the antarctic peninsula is not due to oroclinal bending since 110 ma

very shallow dyke intrusion and potential slope failure imaged by ground deformation the 28 december 2014 eruption on mount etna on 28 december 2014 eruptive activity resumed at mount etna with fire fountain activity feeding two lava flows on the eastern and southwestern upper flanks of the volcano unlike all previous summit activity this eruption produced clear deformation at the summit of the volcano gps displacements and sentinel 1a ascending interferograms were calculated in order to image the ground deformation pattern accompanying the eruption the displacements observed by gps depict a local ground deformation pattern affecting only the upper part of the volcano despite snow cover on the summit differential interferometry synthetic aperture radar dinsar data allowed obtaining more detail on the ground deformation pattern on the upper eastern side of the volcano three dimensional gps displacements inversion located a very shallow ne sw intrusion just beneath the new southeast crater however this model cannot justify all the deformation observed by dinsar thus revealing a gravitational failure of the lava flow field

perspectives on the roles of melanges in subduction accretionary complexes a review abstract melanges play three principal overlapping roles in the architecture of subduction accretionary complexes sacs during and after sac formation first tectonic melanges serve as zones of concentrated deformation within and below the accreted rocks that are assembled during the subduction accretion process these melanges facilitate preservation of inter melange less deformed accretionary units aus beneath the trench side of the sac the initial deformation zone along the decollement at the top of the down going plate is marked by non melange tectonically dismembered formations or thinner units of scaly rock and breccia that separate accreted rocks above from the subducting rocks below olistostromal rocks may be incorporated into the decollement here in the mid arc to inner arc areas of the sac exotic block bearing melanges develop in zones of tectonic fragmentation and mixing of accreting ocean plate stratigraphy in mud diapirs and along out of sequence faults some of which facilitate uplift of high pressure rocks and serpentinite matrix melanges second after accretion the sedimentary tectonic diapiric and polygenetic melange units serve as single block or sheet architectural aus or subunits within larger accreted aus of the sac diapiric melanges and sedimentary olistostromal melanges formed in and above sac fault blocks respectively may become incorporated into the sac during ongoing deformation and become architectural units as well third melanges serve as post subduction stress guides that focus shear strain during continuing and post accretion deformation of sacs allowing ongoing modification of the sac during progressive deformation of the orogen examples of each type of role reveal the importance of all three processes in the current architecture of outer orogenic belts

origins of large volume rhyolitic volcanism in the antarctic peninsula and patagonia by crustal melting voluminous rhyolitic volcanism along the palaeo pacific margin of gondwana was marked by three principal episodes of magmatism the first of these v1 is essentially coincident with the main episode of karoo ferrar magmatism at 184 ma a younger v2 episode occurred at 168 ma and a third episode v3 occurred in the interval 157 153 ma we evaluate the origin of v1 and v2 rhyolites from the antarctic peninsula using major and trace element and isotopic sr nd o data an isotopically uniform 87sr 86sri 0 707 endi 3 andesite dacite magma was generated as a result of anatexis of grenvillian age hydrous mafic lower crust linked to earlier arc related underplating the lower crustal partial melts would have mixed with fractionated components of the mafic underplate followed by subsequent storage and homogenization early jurassic v1 rocks of the southern antarctic peninsula are interpreted as melts of upper crustal paragneiss which have mixed with the isotopically uniform magma in upper crustal magma chambers the v2 rhyolites are the result of assimilation fractional crystallization of the isotopically uniform magma this occurred in upper crustal magma chambers involving assimilants with similar isotopic composition to that of the magma a continental margin setting was crucial in developing hydrous readily fusible lower crust lower crustal anatexis was in response to mafic underplating associated with the discovery shona bouvet group of plumes thought to be responsible for the karoo magmatic province the progression old to young of volcanism from ne to sw in patagonia and south to north in the antarctic peninsula is consistent with migration away from the mantle plumes towards the proto pacific margin of gondwana during rifting and break up

a preliminary assessment of the hydrocarbon potential of the larsen basin antarctica abstract the larsen basin on the northwest margin of the weddell sea formed as a mesozoic ensialic basin during gondwana breakup deposition was either in half grabens on the extending weddell sea margin or in a restricted back arc basin at the northern end of this basin 5 6 km of sedimentary rock crop out on james ross island exposing elements of a large potential hydrocarbon system aeromagnetic and outcrop data suggest that the basin structure inferred from james ross island can be recognised at least as far south as 70 s upper jurassic anoxic marine strata deposited prior to the main phase of arc development form a rich potential source t o c up to 3 5 with both marine and terrestrial kerogens arc derived volcaniclastic sediments of barremian oligocene age form a regressive megasequence basal strata represent slope apron and rudaceous submarine fan deposits proximal to the margin fan conglomerates form lenticular bodies hundreds of metres thick and tens of kilometres across enveloped in slope apron mudstones late cretaceous fault reactivation and uplift led to dramatic shallowing of the basin with deposition of shelf facies although there are many potentially attractive reservoir targets there may be problems of pore occlusion due to the abundant labile volcanic grains however there is evidence of more quartzose sandstone towards the top of the section and inferentially toward the basin centre in the larsen basin there is moderate potential for oil generated from upper jurassic source rocks and reservoired in cretaceous and tertiary sandstones and conglomerates in large stratigraphic or structural traps caused by partial basin inversion during deposition

the influence of upper crust lithology on topographic development in the central coast ranges of california abstract a fundamental geological tenet is that as landscapes evolve over graded to geologic time geologic structures control patterns of topographic distribution in mountainous areas such that terrain underlain by competent rock will be higher than terrain underlain by incompetent rock this paper shows that in active orogens where markedly weak and markedly strong rocks are juxtaposed along contacts that parallel regional structures relatively high topography can form where strain is localized in the weak rock such a relationship is illustrated by the topography of the central coast ranges between the pacific coastline and the san andreas fault zone safz and along the length of the gabilan mesa the gabilan mesa segment of the central coast ranges within the gabilan mesa segment the granitic upper crust of the salinian terrane is in contact with the accretionary prism melange upper crust of the nacimiento terrane along the inactive nacimiento fault zone a prominent topographic lineament is present along most of this lithologic boundary approximately 50 to 65 km southwest of the safz with the higher topography formed in the melange on the southwest side of the nacimiento fault this paper investigates factors influencing the pattern of topographic development in the gabilan mesa segment of the central coast ranges by correlating shortening magnitude with the upper crust compositions of the salinian and nacimiento terranes the fluvial geomorphology of two valleys in the gabilan mesa which is within the salinian terrane and alluvial geochronology based on optically stimulated luminescence osl age estimates reveal that the magnitude of shortening accommodated by down to the southwest tilting of the mesa since 400 ka is less than 1 to 2 m our results combined with those of previous studies indicate that at least 63 to 78 of late cenozoic northeast southwest directed upper crustal shortening across the gabilan mesa segment has been accommodated within the nacimiento terrane this is significant because perpendicular to orogenic strike the nacimiento terrane constitutes less than of the distance between the coast and the safz and the other or greater of the distance between the coast and the safz is underlain by the granitic upper crust of the salinian terrane we propose that strain and mountain building are localized within the nacimiento terrane because it consists predominantly of the relatively weak franciscan complex melange and because the upper crust of the salinian terrane is composed of relatively strong granitic rocks our hypothesis is supported by the distribution of post seismic surface uplift associated with the 2003 6 5 m w san simeon earthquake which mimics the topography of the southwestern part of the gabilan mesa segment of the central coast ranges

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

continental rift to back arc basin jurassic cretaceous stratigraphical and structural evolution of the larsen basin antarctic peninsula the larsen basin developed in jurassic times as a result of continental rifting during the early stages of gondwana break up lower upper jurassic non marine sedimentary and volcanic rocks constitute a syn rift megasequence recording initial largely amagmatic extension and subsequent widespread extension related silicic volcanism a succeeding kimmeridgian early berriasian transgressive megasequence consisting largely of anoxic dysoxic hemipelagic mudstones is thought to have been deposited during a thermal subsidence phase when relative magmatic quiescence and peak jurassic eustatic sea levels served to maximize sediment starvation the fragmentary record for late berriasian barremian times suggests that a regressive megasequence may have developed in the earlier part of this period recording increased sediment yield to the larsen basin from the increasingly emergent antarctic peninsula arc subsequently strata in the southern but not the northern part of the basin underwent relatively intense eastward verging deformation possibly during the formation of a retro arc fold thrust belt where exposed the lower part of the succeeding aptian eocene megasequence consists of a deep marine clastic wedge deposited along the fault bounded western basin margin during a phase of arc uplift and related differential subsidence following partial basin inversion in late cretaceous times regression took place as reduced basinal subsidence rates allowed shallow marine facies to prograde basinward

tectonic significance of low temperature blueschist blocks in the franciscan melange at san simeon california abstract the blueschist bearing franciscan melange exposed near san simeon is very similar to the melange terrane forming the central belt north of san francisco epidote bearing low t blueschist blocks at san simeon n 3 are the same age as high t garnet bearing blocks in the northern and diablo range melange terranes 155 150 ma this age approximates the time of initiation of franciscan subduction during the initial stages of franciscan subduction part of the top volcanic sequence from the subducting oceanic plate and small volumes of overlying sediments were imbricated at the bottom of the overriding plate and metamorphosed under high p conditions this underplated material was variably retrograded as subduction refrigerated the forearc blocks actinolitic rinds formed at the contacts between blueschists and intercalated mantle under relatively static conditions as the base of the overriding plate became serpentinized a model is proposed in which exhumation was facilitated by gravity driven seaward oriented extensional thinning of the forearc prism caused by the decrease in subducting plate dip starting around 80 ma that caused the laramide orogeny as this occurred blueschist and graphite schist blocks were plucked from the bottom of the hanging wall incorporated into the shale and water rich shear zone at the plate interface subduction channel shear zone and exhumed during the upward flow of melange driven by the movement of the downgoing plate while subduction was still active

barbados architecture and implications for accretion the island of barbados exposes the crestal zone of the remarkably broad accretionary prism of the lesser antilles foreacrc the architecture of barbados is three tiered an upper arched cap of pleistocene reefs that record rapid and differential uplift of the island an intermediate zone of nappes of mainly abyssal or deep bathyal pelagic rocks and a basal complex whose lithotypes extend to substantial depth and may be representative of the bulk of the western or inner accretionary prism the exposed basal complex consists of generally steeply dipping ene to ne striking fault bounded packets which contain rocks of one of three lithic suites terrigenous quartzose turbidite and mudstone debris flow and hemipelagic chiefly radiolarite present but imcomplete rock dating indicates that the terrigenous and hemipelagic suites and the pelagic rocks of the intermediate zone are age overlapping in early and middle eocene time deformation within packets of the basal complex is systematic pre or synfault and indicative of shortening that is generally normal to packet boundaries a unit of terrigenous materials that probably underwent local resedimentation in the miocene is recognized in wells but its relationship to exposed rocks is uncertain the packet bounding faults of the basal complex are interpreted to have been primary accretionary surfaces which may have been reactivated by later intraprism movements exposed sedimentary rocks of barbados can be successfully assigned to contemporaneous depositional sites associated with an accretionary prism terrigenous beds to a trench wedge that was connected to south american sediment sources debris flow to trench floor or slope basin accumulations of material derived from the lower slope hemipelagic to atlantic plain strata and pelagic rocks of the intermediate zone to deep outer forearc basin sites the decollement at the base of the intermediate zone is probably due to uplift and arcward motion of the crestal zone of the accretionary prism with respect to the forearc basin during progressive prism growth principal uplift of the prism seems to have started apparently abruptly in the miocene quaternary uplift of barbados may be due partly to local diapirism paleogene subduction that created the arcward region of the prism probably occurred in a differently configured zone from the present one

volcanoes on borders a scientific and geo political challenge while the scientific community readily collaborates across international borders the boundaries of administrative units particularly the nation state can be critical in defining the availability of scientific resources the management of crises and the use of land managing border eruptions can be particularly challenging when international relations between the relevant nation states are strained or complex or when political agendas become involved given that over 700 volcanoes lie within 100 km of an international border and over 1300 are within 250 km the potential for cross border eruption impacts is significant this paper aims to provide an overview of the topic it presents results from a global study of volcanoes on or near borders and uses five case studies to highlight key issues that arise in the management of risk at such volcanoes while volcano monitoring provides critical support for hazard assessment and decision making its availability depends on the policies of particular governments and institutions furthermore the complexity and diversity of volcanic hazards activity and impacts can exacerbate existing cross border inequalities in vulnerabilities in scientific resources in disaster management and mitigation capacity and indeed public awareness we suggest that pre crisis planning and communication resource sharing and international agreements can help to mitigate the challenges of cross border eruptions

a new stratigraphy for the latady basin antarctic peninsula part 1 ellsworth land volcanic group the jurassic mount poster formation of eastern ellsworth land southern antarctic peninsula comprises silicic ignimbrites related to intracontinental rifting of gondwana the identification of less voluminous basaltic and sedimentary facies marginal to the silicic deposits has led to a reclassification of the volcanic units into the ellsworth land volcanic group this is formally subdivided into two formations the mount poster formation silicic ignimbrites and the sweeney formation basaltic and sedimentary facies the mount poster formation rhyolites are an intracaldera sequence greater than 1 km in thickness the basaltic and sedimentary facies of the sweeney formation are consistent with deposition in a terrestrial setting into or close to water the geochemistry of the mount poster formation is consistent with derivation of the intracaldera rhyolites from a long lived upper crustal magma chamber the basalts of the sweeney formation are intermediate between asthenosphere and lithosphere derived magmas with little or no subduction modified component the basalt could represent a rare erupted part of the basaltic underplate that acted as the heat source for local generation of the rhyolites u pb ion microprobe zircon geochronology of samples from the mount poster formation yield an average eruption age of 183 4 1 4 ma analysis of detrital zircons from a sweeney formation sandstone suggest a maximum age of deposition of 183 4 ma and the two formations are considered coeval in addition these ages are coincident with eruption of the karoo ferrar igneous province in southern africa and east antarctica our interpretation of the ellsworth land volcanic group is consistent with the model that the jurassic volcanism of patagonia and the antarctic peninsula took place in response to intracontinental extension driven by arrival of a plume in that area

near real time forecasting of lava flow hazards during the 12 13 january 2011 etna eruption we are grateful to eumetsat for seviri data to nasa for modis data and tonoaafor avhrr data the authors thank one anonymous reviewer and v acocella for their helpful and constructive comments this study was performed with the financial support from the v3 lava project ingv dpc 2007 2009 contract

permo carboniferous conglomerates in the trinity peninsula group at view point antarctic peninsula sedimentology geochronology and isotope evidence for provenance and tectonic setting in gondwana field observations from the trinity peninsula group at view point on the antarctic peninsula indicate that thick southward younging and overturned clastic sedimentary rocks comprising unusually coarse conglomeratic lenses within a succession of fine grained sandstone mudstone couplets are the deposits of debris and turbidity flows on or at the foot of a submarine slope three detrital zircons from the sandstone mudstone couplets date deposition at 302 3 ma at or shortly after the carboniferous permian boundary conglomerates predominantly consist of quartzite and granite and contain boulders exceeding 500 mm in diameter zircons from granitoid clasts and a silicic volcanic clast yield u pb ages of 466 3 ma 373 5 ma and 487 4 ma respectively and have corresponding average ehft values between 0 3 and 7 6 a quartzite clast conglomerate matrix and sandstone interbedded with the conglomerate units have broadly similar detrital zircon age distributions and hf isotope compositions the clast and detrital zircon ages match well with sources within patagonia however the age of one granite clast and the ehf characteristics of some detrital zircons point to a lesser south africa or ellsworth mountain like contribution and the quartzite and granite dominated composition of the conglomerates is similar to upper palaeozoic diamictites in the ellsworth mountains unlike detrital zircons large conglomerate clasts limit possible transport distance and suggest sedimentation took place on or near the edge of continental crust comparison with other upper palaeozoic to mesozoic sediments in the antarctic peninsula and patagonia including detrital zircon composition and the style of deformation suggests deposition of the trinity peninsula group in an upper plate basin on an active margin rather than a subduction related accretionary setting with slow extension and rifting punctuated by short periods of compression

continental margin tectonics submarine accretionary prisms submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted deformed and ultimately transformed to continental crust accretionary prisms develop at sites of lithospheric convergence that is subduction zones commonly accretionary prisms form along continental margins although accretionary prisms may also occur adjacent to island arcs which are ultimately coalesced into continental landmasses here we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the united states

geodynamic evolution of the antarctic peninsula during mesozoic times and its bearing on weddell sea history this review of the tectonic evolution of the antarctic peninsula during mesozoic times highlights four main events 1 late triassic late jurassic extension 2 late jurassic early cretaceous dextral transpression 3 early cretaceous extension and 4 mid cretaceous compression magmatism was virtually continuous during much of this period with the exception of possible breaks in the known record in early jurassic and late jurassic early cretaceous times the second of these breaks corresponded to the first compressional event there was no apparent hiatus in the magmatic record during the mid cretaceous compressional event although there was a significant change in the pattern of sedimentation in the larsen basin on the eastern margin of the weddell sea at about that time the tectonic evolution of the peninsula is compared to and puts some constraints on existing weddell sea models the late triassic late jurassic arc extension correlates with initial rifting in the weddell sea region during sinistral motion between east and west gondwana however there is no known record of large scale pre mid jurassic transcurrent deformation in the antarctic peninsula that would have been consistent with rotation of west antarctic crustal blocks in the initial rifting period the peninsula wide late jurassic early cretaceous compressional event may correlate with the major change in gondwana plate motions from e w to n s african reference frame separation of east and west gondwana this change probably resulted in formation of an ocean continent boundary along the northern margin of the weddell sea embayment and initial seafloor spreading geological data do not seem to support subduction of southwestern proto weddell sea oceanic lithosphere beneath the eastern margin of the peninsula at that time cretaceous arc extension was coeval with the initial seafloor spreading phase in the weddell sea mid cretaceous arc compression linked to a global increase in ocean floor spreading rates and a superplume event correlates with a change from ne sw to nw se spreading in the weddell sea

gondwana breakup via double saloon door rifting and seafloor spreading in a backarc basin during subduction rollback abstract a model has been developed where two arc parallel rifts propagate in opposite directions from an initial central location during backarc seafloor spreading and subduction rollback the resultant geometry causes pairs of terranes to simultaneously rotate clockwise and counterclockwise like the motion of double saloon doors about their hinges as movement proceeds and the two terranes rotate a gap begins to extend between them where a third rift initiates and propagates in the opposite direction to subduction rollback observations from the oligocene to recent western mediterranean the miocene to recent carpathians the miocene to recent aegean and the oligocene to recent caribbean point to a two stage process initially pairs of terranes comprising a pre existing retro arc fold thrust belt and magmatic arc rotate about poles and accrete to adjacent continents terrane docking reduces the width of the subduction zone leading to a second phase during which subduction to strike slip transitions initiate the clockwise rotated terrane is caught up in a dextral strike slip zone whereas the counterclockwise rotated terrane is entrained in a sinistral strike slip fault system the likely driving force is a pair of rotational torques caused by slab sinking and rollback of a curved subduction hingeline by analogy with the above model a revised five stage early jurassic to early cretaceous gondwana dispersal model is proposed in which three plates always separate about a single triple rift or triple junction in the weddell sea area seven features are considered diagnostic of double saloon door rifting and seafloor spreading i earliest movement involves clockwise and counterclockwise rotations of the falkland islands block and the ellsworth whitmore terrane respectively ii terranes comprise areas of a pre existing retro arc fold thrust belt the permo triassic gondwanide orogeny attached to an accretionary wedge magmatic arc the falklands islands block is initially attached to southern patagonia west antarctic peninsula while the ellsworth whitmore terrane is combined with the thurston island block iii paleogeographies demonstrate rifting and extension in a backarc environment relative to a pacific margin subduction zone accretionary wedge where simultaneous crustal shortening occurs iv a ridge jump towards the subduction zone from east of the falkland islands to the rocas verdes basin evinces subduction rollback v this ridge jump combined with backarc extension isolated an area of thicker continental crust the falkland islands block vi well documented ew oriented seafloor spreading anomalies in the weddell sea are perpendicular to the subduction zone and propagate in the opposite direction to rollback vii the dextral strike slip gastre and sub parallel faults form one boundary of the gondwana subduction rollback whereas the other boundary may be formed by inferred sinistral strike slip motion between a combined thurston island ellsworth whitmore terrane and marie byrd land east antarctica

seismo tectonic behavior of the pernicana fault system mt etna a gauge for volcano flank instability 1 flank instability at basaltic volcanoes is often related to repeated dike intrusions along rift zones and accompanied by surface fracturing and seismicity these processes have been mostly studied during specific events and the lack of longer term observations hinders their better understanding here we analyze 20 years of deformation of the pernicana fault system pfs the key structure controlling the instability of the eastern flank of mt etna we exploit east west and vertical components of mean deformation velocity as well as corresponding time series computed from ers envisat 1992 2010 and cosmo skymed 2009 2011 satellite radar sensors via synthetic aperture radar interferometry techniques we then integrate and compare this information with field seismic and leveling data collected between 1980 and 2012 we observe transient displacements accompanied by seismicity overprinted on a long term background eastward motion 2 cm yr in the last decades these transient events were preceded by a constant amount of accumulated strain near the pfs the time of strain accumulation varies between a few years and a few decades also depending on magma emplacement within the nearby north east rift which may increase the strain along the pfs these results suggest that the amount of deformation near the pfs may be used as a gauge to forecast the occurrence of instability transients on the eastern flank of etna in this context the pfs may provide an ideal small scale structure to test the relations between strain accumulation stress loading and seismic energy release

monitoring the december 2015 summit eruptions of mt etna italy implications on eruptive dynamics abstract a lengthy period of eruptive activity from the summit craters of mt etna started in january 2011 it culminated in early december 2015 with a spectacular sequence of intense eruptive events involving all four summit craters voragine bocca nuova new southeast crater and northeast crater the activity consisted of high eruption columns strombolian explosions lava flows and widespread ash falls that repeatedly interfered with air traffic the most powerful episode occurred on 3 december 2015 from the voragine after three further potent episodes from the voragine activity shifted to the new southeast crater on 6 december 2015 where strombolian activity and lava flow emission lasted for two days and were fed by the most primitive magma of the study period activity once more shifted to the northeast crater where ash emission and weak strombolian activity took place for several days sporadic ash emissions from all craters continued until 18 december when all activity ceased although resembling the summit eruptions of 1998 1999 which also involved all four summit craters this multifaceted eruptive sequence occurred in an exceptionally short time window of less than three days unprecedented in the recent activity of mt etna it also produced important morphostructural changes of the summit area with the coalescence of voragine and bocca nuova in a single large crater the central crater reproducing the morphological setting of the summit cone before the formation of bocca nuova in 1968 the december 2015 volcanic crisis was followed closely by the staff of the etna observatory to monitor the on going activity and forecast its evolution in accordance with protocols agreed with the italian civil protection department

mid jurassic age for the botany bay group implications for weddell sea basin creation and southern hemisphere biostratigraphy new u pb zircon ion microprobe ages from the alluvial conglomerates and flood plain sediments of the botany bay group demonstrate that sedimentation occurred at c 167 ma coeval with rift related silicic volcanism in the northern antarctic peninsula in contrast rift related volcanism and sedimentation in the southern antarctic peninsula latady basin occurred at c 183 ma the new data indicate that syn rift sedimentation and volcanism was diachronous from south to north consistent with early opening of the weddell sea embayment by anti clockwise rotation of the antarctic peninsula in the mid jurassic a definitive date for the botany bay group floras has important implications for southern hemisphere biostratigraphic correlations

splendid and seldom isolated the paleobiogeography of patagonia the idea that south america was an island continent over most of the cenozoic during which its unusual mammalian faunas evolved in isolation is outstandingly influential in biogeography although large numbers of recent fossil discoveries and related advances require that the original isolation concept be significantly modified it is still repeated in much current literature the persistence of the idea inspired us to present here an integrated paleobiogeographic account of mammals reptiles and plants from the jurassic to the paleogene of patagonia which has by far the richest fossil record on the continent all three groups show distribution patterns that are broadly consistent with south america s long separation history first from laurasia by the late jurassic then from africa and india madagascar during the late early cretaceous and finally from antarctica and australia during the early middle eocene after which isolation finally commenced we highlight areas of promising future research a

magmatism of the weddell sea rift system in antarctica implications for the age and mechanism of rifting and early stage gondwana breakup abstract thick 800 m basaltic successions from the eastern antarctic peninsula have been dated in the interval 180 177 ma and preserve a transition from a continental margin arc to a back arc extensional setting amygdaloidal basalts from the black coast region of the eastern margin of the antarctic peninsula represent a rare onshore example of magmatism associated with back arc extension that defines the early phase of weddell sea rifting and magmatism and gondwana breakup the early phase of extension in the weddell sea rift system has previously been interpreted to be related to back arc basin development with associated magnetic anomalies attributed to mafic intermediate magmatism but with no clearly defined evidence of back arc magmatism the analysis provided here identifies the first geochemical evidence of a transition from arc like basalts to the development of depleted back arc basin basalts in the interval 180 177 ma the exposed black coast basaltic successions are interpreted to form a minor component of magmatism that is also defined by onshore sub ice magnetic anomalies as well as the extensive magnetic anomalies of the southern weddell sea back arc magmatism is also preserved on the falkland plateau where intrusions postdating 180 ma are associated with early phase rifting in the weddell sea rift system back arc extension was probably short lived and had ceased by the time the northern weddell sea magmatism was emplaced

actinolitic rinds on low t mafic blueschist blocks in the franciscan shale matrix melange near san simeon implications for metasomatism and tectonic history abstract in the melange terrane of the franciscan accretionary prism mg rich actinolite tremolite rinds have long been known to be present on many high t garnet epidote bearing mafic blueschist and eclogite blocks but they were thought to be absent on low t lawsonite chlorite blueschist blocks by analogy with rinds on high t blocks these rinds on low t blocks must have been produced by metasomatic reaction with ultramafic rock the rinds on high t blocks have led to the speculation that the high t franciscan blueschists were uplifted to the surface in serpentinite diapirs while other processes exhumed the volumetrically more numerous low t blocks this paper reports the discovery of actinolitic rinds on the margins of nine low t lawsonite epidote franciscan blueschists that are or were clearly encased in the shale matrix melange exposed in seacliffs and wavecut benches near san simeon california petrographic and geochemical analyses show these mg rich rinds are similar to those found on high t garnet bearing blocks the bulk composition indicates the protolith of the blueschist blocks was mafic oceanic crust the high fe3 fe contents indicate it was probably the uppermost hydrated volcanic part of the crust the block ultramafic rock association was created by faulting during subduction initiation as fragments from the top of the subducting ocean crust were imbricated with mantle materials at the base of the ophiolitic leading edge of the north american plate the chemistry of a block margin altered to actinolitic rind indicates si na pb cu and sr were lost from the blocks while k rb cs and ba were added most pieces of actinolitic rind are mg and ni rich because they are metasomatized ultramafic material that was enriched in si k rb cs and ba these metasomatic changes indicate the fluids that hydrated the mantle and altered the mafic blocks ascended from subducting and or underplated sediments both high t and low t blueschists that have actinolitic rinds were uplifted to near the surface after they sank or were plucked from the base of the overriding plate by subduction generated melange that upwelled from depths of 15 km

a new stratigraphy for the latady basin antarctic peninsula part 2 latady group and basin evolution recent detailed mapping section logging and an improved understanding of the geological evolution of the antarctic peninsula provide a robust framework for an improved lithostratigraphic subdivision of the latady basin eastern ellsworth land within the latady basin we recognize two main groups ellsworth land volcanic group and latady group the focus of this paper is the latady group which is formally subdivided into five formations anderson formation witte formation hauberg mountains formation cape zumberge formation and nordsim formation middle jurassic shallow marine deposits of the anderson formation are overlain by quiet anoxic deposits assigned to the witte formation the start of the late jurassic is marked by the deposition of higher energy deposits of the hauberg mountains formation subdivided into three members long ridge mount hirman and novocin members that reflect varying lithological and environmental characteristics thermal subsidence during the latest jurassic led to deposition of the basinal cape zumberge formation while uplift of an active continental arc along the antarctic peninsula led to deposition of the terrestrial nordsim formation in the latest jurassic to earliest cretaceous the evolution of the latady basin reflects early extension during gondwana break up from the early jurassic to earliest cretaceous and is consistent with a shift in the underlying forces driving extension in the weddell sea area from intracontinental rifting related to a mantle plume to active margin forces in response to subduction

cataclastic deformation and metasomatism in the subduction zone of mafic blocks in melange san simeon california abstract the primary origin of shale matrix melange forming the central belt of the franciscan complex is still debated the seacliff exposures near san simeon display numerous lensoidal blocks of graywacke greenstone lesser layered chert and blueschist that are encased in a matrix of scaly shale the boudinaging of mafic greenstone and blueschist blocks was accommodated by cataclasis and varied amounts of metamorphic reconstitution that is particularly intense along block margins zones of necking and intra block shear zones cataclastic zones in blueschists are greenish where chlorite and pumpellyite have formed the mineralogic assemblage produced during cataclasis in greenstones is the same as that replacing the interior of the block albite chlorite pumpellyite the cataclastic margins of many 7 of 12 greenstones gained k rb cs and ba in contrast the cataclastic margins of all blueschist blocks lost na several 3 of 9 with substantial decreases and some 3 of 9 had significant increases in k rb cs and ba this metasomatic alteration is indicative of fluid rock interaction between mafic blocks and sediments alteration of the mafic rocks with the growth of pumpellyite and chlorite occurred when blocks were encased in the shale matrix of the melange which was dynamically deforming and heated to temperatures of 150 c as synsubduction temperature depth gradients were 10 c km burial of mafic blocks while encased in the melange matrix to depths approaching 15 km is apparent surficial olistostromal movements alone do not account for the incorporation deformation and retrograde metasomatic alteration of the exotic blueschist blocks and the metamorphism of the shale matrix at such inferred depths these attributes indicate chemical exchange with shale and smearing displacement of the margins of mafic blocks occurred in the subduction zone as the shale matrix flowed and exerted shear tractions

late cenozoic glacier volcano interaction on james ross island and adjacent areas antarctic peninsula region hambrey m j smellie john l nelson anna e johnson joanne s 2008 late cenozoic glacier volcano interaction on james ross island and adjacent areas geoantarctic peninsula region geological society of america bulletin 120 5 6 709 731