three dimensional geometry of concentric intrusive sheet swarms in the geitafell and the dyrfjoll volcanoes eastern iceland sheet intrusions inclined sheets and dykes in the deeply eroded volcanoes of geitafell and dyrfjoll eastern iceland were studied at the surface to identify the location depth and size of their magmatic source s for this purpose the measured orientations of inclined sheets were projected in three dimensions to produce models of sheet swarm geometries for the geitafell volcano the majority of sheets converge toward a common focal area with a diameter of at least 4 to 7 km the location of which coincides with several gabbro bodies exposed at the surface assuming that these gabbros represent part of the magma chamber feeding the inclined sheets a source depth of 2 to 4 km below the paleoland surface is derived a second younger swarm of steeply dipping sheets crosscuts this gabbro and members of the first swarm the source of this second swarm is estimated to be located to the se of the source of swarm 1 below the present day level of exposure and deeper than the source of the first swarm for the dyrfjoll volcano we show that the sheets can be divided into seven different subsets three of which can be interpreted as swarms the most prominent swarm the njardvik sheet swarm converges toward a several kilometers wide area in the njardvik valley at a depth of 1 5 to 4 km below the paleoland surface two additional magmatic sources are postulated to be located to the northeast and southwest of the main source crosscutting relationships indicate contemporaneous as well as successive activity of different magma chambers but without a resolvable spatial trend the dyrfjoll volcano is thus part of a complex volcanic cluster that extends far beyond the study area and can serve as fossil analog for nested volcanoes such as askja whereas in geitafell the sheet swarms seem to have originated from a single focus at one time thus defining a single central volcanic complex such as krafla volcano

petrogenesis of coarse grained intrusives from tahiti nui and raiatea society islands french polynesia this study is based on a set of coarse grained igneous rocks collected from two zoned plutons located in the central part of tahiti nui and raiatea the ahititera pluton central depression of tahiti nui comprises a great diversity of rocks ranging from ultrabasic to felsic in composition it shows a concentric zonation with nepheline free rocks in its periphery and nepheline bearing rocks in its central part the faaroa pluton central depression of raiatea is entirely mafic and includes only gabbros and theralites the two plutons have variable nd sr isotopic signatures especially the ahititera rocks which are subdivided into three groups based on their mineralogy geochemistry and isotope composition the isotopic variability probably reflects local heterogeneities in the society mantle plume petrographic and isotopic data have been used to define two magmatic suites in ahititera identifiable from their degree of si undersaturation the evolution of the mildly si undersaturated suite is controlled by simple fractional crystallization whereas the strongly si undersaturated suite requires additional h2o influx the third isotopic group includes only theralites the rare earth element ree compositions of the mafic rocks from both plutons do not correlate with their isotopic signature the ree patterns of the most si undersaturated rocks are systematically characterized by steeper slopes such features are also observed in lavas from seamounts located within the present day hotspot area it appears that ree concentrations in society lavas and intrusives are probably mainly governed by variable degrees of partial melting of a garnet free mantle source and are independent of their isotopic signature

cone sheet formation and intrusive growth of an oceanic island the miocene tejeda complex on gran canaria canary islands more than 500 trachytic to phonolitic cone sheet dikes hypabyssal syenite stocks and subordinate radial dikes form a 20 km diameter intrusive complex in the volcaniclastic fill of the miocene tejeda caldera 20 35 km on gran canaria canary islands the dikes intruded concentrically around a central axis of radial symmetry and dip uniformly an average of 41 toward the center single crystal 40ar 39ar ages of dikes and syenite stocks ranging from 12 3 0 1 to 7 32 0 05 ma suggest more or less continuous intrusive activity during both volcanically active and inactive phases intrusions were emplaced at average intervals of 5 10 k y while explosive eruptions took place at 50 k y intervals the estimated aggregate volume of evolved cone sheet magma added at shallow level 2000 m below sea level amounts to 250 km3 compared to 500 km3 of evolved extrusive volcanics erupted during the same period formation of the tejeda cone sheets most likely resulted from deformation processes due to resurgent doming initiated by the recurrent replenishment of a flat laccolith like shallow magma chamber magma supply exceeding the volume that could be compensated for by updoming of the overlying caldera fill resulted in the formation of cone shaped fractures

structure and emplacement of the pliocene roque nublo debris avalanche deposit gran canaria spain abstract collapse of the flanks of the pliocene roque nublo stratocone on gran canaria lead to large debris avalanches that traveled far beyond the coastline with velocities that may have exceeded 100 m s the deposits comprised at least 14 km 3 of debris and covered an area of about 180 km 2 in the southern half of the island the debris filled deep canyons are largely exhumed at present incomplete disintegration poor fluidization and a good preservation of megablocks are thought to be mainly due to the confinement of the debris avalanche within deep canyons the rheological behavior of lithologic domains varies with their size internal strength and relative position within the deposit the deformation structures indicate that distinct components flowed whereas others slid throughout the transport in a relatively dense mode the following factors are believed to have been important in generating the roque nublo debris avalanche deposit 1 unusual abundance of pyroclastic flow and other volcaniclastic deposits making up the upper roque nublo cone 2 highly asymmetric basement beneath the cone with a very high southern ridge and a steep erosional southern slope leading to major instabilities 3 intrusion of dikes and cryptodomes as well as hydrothermal alteration in the crater area further weakening the volcano

ring complexes in the peninsular ranges batholith mexico and the usa magma plumbing systems in the middle and upper crust subvolcanic ring complexes are unusual in that they preserve a rapidly frozen record of intrusive events this sequential history is generally lost or complicated in plutons owing to mixing and mingling in a dynamic state thus subvolcanic ring complexes are more like erupted rocks in their preservation of instantaneous events but the self contained nature of the complexes allows detailed structural and chemical work to be conducted in environments where the relative timing between individual magmatic events is commonly well preserved we suggest that development of subvolcanic ring complexes in the western peninsular ranges batholith prb involved the following three stage generalized sequence 1 fracturing of the roof above a buoyant or overpressured magma chamber which resulted in moderately inward dipping conical fractures that locally hosted cone sheets 2 subsequent loss of magma from the chamber combined with degassing of the melt which facilitated collapse of the roof along near vertical ring faults that locally hosted ring dikes and 3 resurgence of the chamber and or intrusion of a broadly cogenetic nested pluton which locally destroyed evidence for the earlier history of the system this sequence has been repeated twice in one of the ring complexes that we have identified which resulted in nested intrusive centers calderas subvolcanic ring complexes and plutons may represent progressively deeper sections through linked magma plumbing systems and the systematic occurrences of these features in the western prb are consistent with progressively deeper along strike exposures of the batholith from south to north over a distance greater than 250 km in addition to subvolcanic complexes in the western prb deeper crustal levels exposed in the transition zone between eastern and western parts of the batholith preserve ring complexes emplaced at depths of up to 18 km occurrence of these deeper level complexes suggests either that caldera subsidence can extend to mid crustal levels or that other processes can produce ring complexes d 2002 elsevier science b v all rights reserved

a review on natural and human induced geohazards and impacts in karst karst environments are characterized by distinctive landforms related to dissolution and a dominant subsurface drainage the direct connection between the surface and the underlying high permeability aquifers makes karst aquifers extremely vulnerable to pollution a high percentage of the world population depends on these water resources moreover karst terrains frequently underlain by cavernous carbonate and or evaporite rocks may be affected by severe ground instability problems impacts and hazards associated with karst are rapidly increasing as development expands upon these areas without proper planning taking into account the peculiarities of these environments this has led to an escalation of karst related environmental and engineering problems such as sinkholes floods involving highly transmissive aquifers and landslides developed on rocks weakened by karstification the environmental fragility of karst settings together with their endemic hazardous processes have received an increasing attention from the scientific community in the last decades concurrently the interest of planners and decision makers on a safe and sustainable management of karst lands is also growing this work reviews the main natural and human induced hazards characteristic of karst environments with specific focus on sinkholes floods and slope movements and summarizes the main outcomes reached by karst scientists regarding the assessment of environmental impacts and their mitigation

cracking the lid sill fed dikes are the likely feeders of flood basalt eruptions although subparallel swarms of dikes are thought to be the primary feeders to voluminous volcanic eruptions increasing recognition of volumetrically significant sill complexes suggests that they too play an important role in magma ascent through the shallow crust however the extent to which sills and interconnected sill fed dikes actually transport magma to the earth s surface in many large igneous provinces lip is presently unclear by analyzing field relationships and dimensions of intrusions of the ferrar lip in south victoria land antarctica we show that sill fed dikes were the likely feeders for voluminous flood basalt eruptions these intrusions are small but numerous with cumulative dimensions equivalent to a feeder network 308 000 km long and 1 8 m wide due to the tremendous aerial extent of this intrusive network each individual dike feeder segment would only be required to actively feed magma for 2 to 3 days on average to erupt the 70 000 km3 of flood lavas represented by the kirkpatrick basalts the ferrar intrusions form a broadly distributed array of small moderately dipping dikes 2 km long 1 8 m wide 56 mean dip exhibiting almost any orientation this sill fed dike network contrasts with dike swarms conventionally depicted to feed flood basalt provinces and has the appearance of a variably cracked lid atop a sill complex the cracked lid model may apply to a range of shallow feeder systems 4 km depth intruding sedimentary basins where the effects of far field tectonic stresses are negligible and sill intrusions exert the dominant control on dike orientations we conclude that sill inflation and resulting deformation of surrounding host rock plays a critical role in the ascent of magma in shallow volcanic systems that span the full spectrum of eruptive volumes

geological constraints on the dynamic emplacement of cone sheets the ardnamurchan cone sheet swarm nw scotland cone sheets are a significant constituent of many central volcanoes where they contribute to volcano growth by intrusion and through flank eruptions although the exact emplacement mechanisms are still controversially discussed in particular it is not yet fully resolved whether cone sheets propagate as magma driven opening mode fractures or as shear fractures and to what extent pre existing host rock structures and different stress fields influence cone sheet emplacement to shed further light on the role of these parameters in cone sheet emplacement we use detailed field and remote sensing data of the classic ardnamurchan cone sheet swarm in nw scotland and we show that the cone sheets primarily propagated as opening mode fractures in the 1 2 plane of the volcanic stress field in addition more than one third of the ardnamurchan cone sheet segments are parallel to lineaments that form a conjugate set of nnw and wnw striking fractures and probably reflect the regional nw se orientation of 1 during emplacement in the palaeogene cone sheets exploit these lineaments within the ne and sw sectors of the ardnamurchan central complex which indicates that the local volcanic stress field dominated during sheet propagation and only allowed exploitation of host rock discontinuities that were approximately parallel to the sheet propagation path in addition outcrop scale deflections of cone sheets into sills and back into cone sheets also referred to as staircase geometry are explained by the interaction of stresses at the propagating sheet tip with variations in host rock strength as well as the influence of sheet induced strain as a consequence cone sheets associated with sill like segments propagate as mixed mode i ii fractures hence cone sheet emplacement requires a dynamic model that takes into account stress fields at various scales and the way propagating magma interacts with the host rock and its inherent variations in rock strength

volcanic and morphological evolution of la gomera canary islands based on new k ar ages and magnetic stratigraphy implications for oceanic island evolution the spatial and chronological evolution of canary islands volcanism is due to eastward progression of the slow moving african plate over a mantle plume la gomera is located between the western shield stage islands 12 ma with 23 k ar ages and palaeomagnetic data we can constrain the timing of the main subaerial volcanic phases of la gomera the shield volcano c 9 4 8 0 ma the postshield peripheral lava flows c 7 4 5 0 ma the postshield horizontal lava flows c 5 4 4 3 ma and late intra canyon lava flows c 1 9 ma the horizontal lava flows fill a 10 km wide depression formed by a giant landslide garajonay the entire structure of la gomera is in relief inversion declining volcanic construction rates from the shield to the postshield stages are correlated with increasing erosion rates whereas the period of volcanic quiescence hiatus has low erosion rates the succession and duration of the hotspot volcanic stages in the canary islands are compared with those in the hawaiian islands thus underlining differences between slow moving and fast moving plate settings

the earliest late paleolithic in north china site formation processes at shuidonggou locality 7 abstract shuidonggou sdg has long been recognized as the type site complex for the chinese late paleolithic as defined by the presence of blade technology and by its chronology recent field and laboratory research conducted in the past decade has revealed the presence of paleolithic ornaments and two different technological components of an industry equivalent to the early upper paleolithic levallois like blades and simple core and flakes which appear at sdg localities although clearly important for paleolithic research in china and broader old world prehistoric studies relatively little is known about the sdg site formation processes and the specifics of site context here we explore the various formation processes and sedimentary context associated with the stone artifact assemblage from one key site shuidonggou locality 7 sdg7 contrary to earlier suggestions that the sdg7 lithic accumulations are the result of secondary deposition our study indicates that sdg7 has been preserved in near primary context features that were previously argued to reflect fluvial disturbance are in fact localized collapse features caused by saturated sediment load in loess deposits in a lakeshore context multiple lines of evidence support the argument that the site preserves the original foraging behavior of the sdg hunter gatherers this evidence consists of the sedimentary matrix and the distribution patterns of archaeological materials particularly the artifact assemblage composition debitage size distribution artifact conditions orientation analysis inclination and spatial patterning the sdg7 archaeological deposits were buried rapidly in shallow lake margin deposits of fine sands silts and clays that were minimally disturbed and subjected only to relatively low energy hydraulic forces this indicates that the sdg7 occurrences are suitable for early hominin behavioral studies in north china at the start of the late paleolithic

tl dates of burnt flints from jelinek s excavations at tabun and their implications abstract a selection of 37 burnt flints from jelinek s excavations at tabun were dated by thermoluminescence the results indicate that the bottom of unit i garrod s layer c should be given an age of 171 17 ky bp transition from oxygen isotope stage 7 to 6 and that units xiii to ii layers ed to d were deposited between c 330 and 210 ky bp i e during the oxygen isotope stages 9 8 and the beginning of 7 these dates raise the possibility that a a pre wurmian neanderthal population may have settled in the levant during the oxygen isotope stage 6 and that b the transition from mugharan acheuleo yabrudian yabrudian and amudian to levallois mousterian type lithic industries occurred at the end of stage 8 more than 200 ky ago these early dates whose reliability was consistent with isochron analysis of the data are not that different from those now accepted for the development of the levallois mousterian industries in europe

paleocave carbonate reservoirs origins burial depth modifications spatial complexity and reservoir implications paleocave systems form an important class of carbonate reservoirs that are products of near surface karst processes and later burial compaction and diagenesis features and origins of fractures breccias and sediment fills associated with paleocave reservoirs have been studied in modern and ancient cave systems information about such cave systems is used in this paper to reconstruct the general evolution of paleocave reservoirs and their associated scale pore networks and spatial complexities spatial complexities in paleocave reservoirs result from near surface and burial processes near surface processes include dissolutional excavation clastic sedimentation chemical precipitation and localized fracturing brecciation and collapse of cave walls and ceilings burial processes begin as cave systems subside into the subsurface remaining cave passages commonly collapse and early formed breccia clasts are rebrecciated differential compaction of strata around and over collapsed passages produces fractures crackle breccias and mosaic breccias near surface and burial processes combine to produce typically complex reservoirs with several scales of heterogeneity hydrocarbon reservoirs of paleocave origin are commonly the product of coalesced collapsed paleocave systems the coalescing of passages in a cave system into larger connected porosity zones results from a combination of multiple cave forming episodes at composite unconformities and from the collapse of cave systems during burial where surrounding host strata are brecciated and fractured this combination of processes creates spatially complex reservoirs that can be hundreds to several thousands of meters across commonly forming large exploration targets final size pore network types and spatial complexities of coalesced collapsed paleocave systems are products of their evolution from near surface development through burial into the deeper subsurface the coalesced collapsed paleocave reservoir hypothesis explains the scale of reservoirs observed and the spatial complexities involved

cross platform architecture of a sequence boundary in mixed siliciclastic carbonate lithofacies middle cambrian southern great basin usa stratigraphic analysis of mixed siliciclastic carbonate lithofacies within the middle cambrian bonanza king formation of the southern great basin reveals three distinct facies associations that record a range of depositional environments from semi arid tidal flats to deeper subtidal restricted lagoons stratigraphic trends cross platform facies variations and correlation of individual surfaces across 250 km of the study area suggest that these mixed lithofacies were deposited in three temporally distinct phases 1 extensive progradation of mixed peritidal environments culminated in a prolonged episode of subaerial exposure marked by an areally extensive intraclast breccia 0 5 1 2 m thick that we interpret to be a major type 1 sequence bounding disconformity 2 abrupt flooding of the exposed platform resulted in the deposition of mixed deeper subtidal lithofacies including a condensed interval of fissile fossiliferous shale 3 progressive shallowing and aggradational accumulation was accompanied by a decrease in siliciclastics and a shift to pure carbonate deposition deep water siliciclastics and megabreccias record deposition along the base of slope off the middle cambrian shelf edge and are interpreted to represent lowstand deposits emplaced during the prolonged episode of subaerial exposure of the shallow shelf the presence of fine siliciclastics in both peritidal facies and sharply overlying deeper subtidal facies of the study interval within the bonanza king suggests a variable but relatively continuous influx of terrigenous material throughout an extended period of accommodation change apparently asynchronous with respect to the predictive model of reciprocal sedimentation we suggest that the primary siliciclastic source changed with relative sea level position during lowered sea level aeolian processes acting upon the unvegetated cambrian craton transported fine siliciclastics onto peritidal and shallow subtidal environments during higher sea level coastal siliciclastic reservoirs supplied sediment that was transported for long distances by geostrophic currents flowing along the submerged platform as opposed to many cambro ordovician grand cycles that are commonly interpreted to consist of a transgressive shaly half cycle grading upward into a regressive carbonate half cycle the sequence boundary within this middle cambrian succession occurs within siliciclastic rich mixed lithofacies rather than in adjoining purer carbonates implying that some grand cycles should not be considered synonymous with sequences interbasinal correlations of the type 1 sequence boundary within the mixed unit are speculative primarily because of the inherent imprecision of available trilobite biostratigraphy however there is evidence that an extended episode of subaerial exposure may have been continent wide during the ehmaniella trilobite biochron

blade production of shuidonggou locality1 northwest china a technological perspective abstract shuidonggou locality 1 sdg1 contains one of the most important early blade assemblages in east asia and has been excavated and studied in detail since its discovery in 1923 however most studies focus on typology and qualitative analysis along with contextual problems such as chronology and stratigraphy this article outlines current debates on its chronology and stratigraphy and supports a conservative wide temporal range for the sdg1 lower cultural layer of 40 000 25 000 bp using a combined chaine operatoire and attribute analytical approach we provide a quantitative technological analysis of the sdg1 lithic assemblage our analysis indicates that blade production was applied using two different strategies 1 the main reduction sequence produced standard blades elongated flakes and bladelets from broad faced cores and mostly from bidirectional knapping on some broad faced cores the flaking surface expands to the narrow facets in this case the strategy shifts from a broad faced to sub prismatic core approach 2 the second and less common reduction system produced blades and bladelets from prismatic and narrow faced cores our results also indicate that sdg1 blade production was based exclusively on direct percussion and not on pressure or indirect percussion flaking though marginal percussion was sometimes used comparing sdg1 with other initial upper paleolithic and early upper paleolithic eup in northeast asia we suggest the sdg1 assemblages are typologically and technologically similar to the iup assemblage in the altai region of siberia and mongolia given the wide chronological range of sdg1 with some eup technological features in sdg1 assemblage we cannot exclude the possibility of incursion of eup technology

submarine landslides around the canary islands the morphology and structure of the submarine flanks of the canary islands were mapped using the gloria long range side scan sonar system bathymetric multibeam systems and sediment echosounders twelve young 2 ma giant landslides have been identified on the submarine flanks of the canary islands up to now older landslide events are long buried under a thick sediment cover due to high sedimentation rates around the canary islands most slides were found on the flanks of the youngest and most active islands of la palma el hierro and tenerife but young giant landslides were also identified on the flanks of the older 15 20 ma but still active eastern islands large scale mass wasting is an important process during all periods of major magmatic activity the long lived volcanic constructive history of the islands of the canary archipelago is balanced by a correspondingly long history of destruction resulting in a higher landslide frequency for the canary islands compared to the hawaiian islands where giant landslides only occur late in the period of active shield growth the lower stability of the flanks of the canaries is probably due to the much steeper slopes of the islands a result of the abundance of highly evolved intrusive and extrusive rocks another reason for the enhanced slope instability is the abundance of pyroclastic deposits on canary islands resulting from frequent explosive eruptions due to the elevated volatile contents in the highly alkalic magmas dike induced rifting is most likely the main trigger mechanism for destabilization of the flanks flank collapses are a major geological hazard for the canary islands due to the sector collapses themselves as well as triggering of tsunamis in at least one case a giant lateral blast occurred when an active magmatic or hydrothermal system became unroofed during flank collapse

the channel between gran canaria and tenerife constructive processes and destructive events during the evolution of volcanic islands seismic sidescan sonar bathymetric multibeam and odp ocean drilling program data obtained in the submarine channel between the volcanic islands of gran canaria and tenerife allow to identify constructive features and destructive events during the evolution of both islands the most prominent constructive features are the submarine island flanks being the acoustic basement of the seismic images the build up of tenerife started following the submarine stage of gran canaria because the submarine island flank of tenerife onlaps the steeper flank of gran canaria the overlying sediments in the channel between gran canaria and tenerife are chaotic consisting of slumps debris flow deposits syn ignimbrite turbidites ash layers and other volcaniclastic rocks generated by eruptions erosion and flank collapse of the volcanoes volcanic cones on the submarine island flanks reflect ongoing submarine volcanic activity the construction of the islands is interrupted by large destructive events especially by flank collapses resulting in giant landslides several miocene flank collapses e g the formation of the horgazales basin were identified by combining seismic and drilling data whereas young giant landslides e g the guimar debris avalanche are documented by sidescan bathymetric and drilling data sediments are also transported through numerous submarine canyons from the islands into the volcaniclastic apron seismic profiles across the channel do not show a major offset of reflectors the existence of a repeatedly postulated major ne sw trending fault zone between gran canaria and tenerife is thus in doubt the sporadic earthquake activity in this area may be related to the regional stress field or the submarine volcanic activity in this area seismic reflectors cannot be correlated through the channel between the sedimentary basins north and south of gran canaria because the channel acts as sediment barrier the sedimentary basins to the north and south evolved differently following the submarine growth of gran canaria and tenerife in the miocene

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

low temperature hydrothermal alteration of intra caldera tuffs miocene tejeda caldera gran canaria canary islands article i nfo the miocene tejeda caldera on gran canaria erupted 20 rhyolite trachyte ignimbrites mogan group 14 13 3 ma followed by 20 phonolitic lava flows and ignimbrites fataga group 13 8 5 ma upper mogan tuffs have been severelyaltered immediately within the caldera margin whereas extra caldera mogan ignimbrites and overlying fataga units are apparently unaltered the altered intra caldera samples contain minerals characteristic of secondary fluid rock interaction clays zeolites adularia and relics of the primary mineral assemblage identified in unaltered ignimbrites k feldspar plagioclase pyroxene amphibole and groundmass quartz major and trace element data indicate that si na k pb sr and rb were strongly mobilized during fluid rock interaction whereas ti zr and nb behaved in a more refractory manner experiencing only minor mobilization the 18 o values of the altered intra caldera tuffs are significantly higher than in unaltered extra caldera ignimbrites consistent with an overall low temperature alteration environment unaltered extra caldera ignimbrites have d values between 110 and 173 which may reflect rayleigh type magma degassing and or post depositional vapour release the d values of the altered intra caldera tuffs range from 52 to 131 with ambient meteoric water at the alteration site estimated at ca 15 interaction and equilibration of the intra caldera tuffs with ambient meteoric water at low temperature can only account for whole rock d values of around 45 given that dclay water is ca 30 at 100 c and decreases in

tsunami deposits related to flank collapse in oceanic volcanoes the agaete valley evidence gran canaria canary islands abstract enigmatic marine conglomerates are attached at 41 188 m asl to the walls of the valley of agaete on the northwest coast of gran canaria canary islands they are formed by heterogeneous angular to rounded heterometric volcanic clasts roundness and maximal size decreasing with altitude and fossils rhodolites and marine shells never found in growth position and often broken the deposits are internally stratified into several layers most of them showing very poor sorting matrix supported and reverse grading they present lenticular morphologies with poor lateral continuity in transversal and longitudinal sections slopes show values and orientations similar to those of the relief of the substratum to which they seem to adapt although they show clear evidence of erosive contact with the substratum rip up clasts they do not tend to form horizontal terraces soft materials soils and colluviums are preserved in the contact with the substratum in outcrops with deposit slopes of up to 15 the age of the deposits is constrained between 1 75 ma and 32 ka their altitude and slope distributions are not related to pleistocene interglacial sea level changes storm deposits or isostatic movements all the above suggests that the agaete marine deposits were generated by tsunami waves the most probable source being a flank failure at least nine major such events having occurred in the canary islands during the pleistocene the guimar sector collapse east coast of tenerife 30 km 3 is the closest possible source for the tsunami and the sole flank failure that is directed towards another island in the canaries

deep intrusions lateral magma transport and related uplift at ocean island volcanoes abstract oceanic intraplate volcanoes grow by accumulation of erupted material as well as by coeval or discrete magmatic intrusions dykes and other intrusive bodies within volcanic edifices are comparatively well studied but intrusive processes deep beneath the volcanoes remain elusive although there is geological evidence for deep magmatic intrusions contributing to volcano growth through uplift this has rarely been demonstrated by real time monitoring here we use geophysical and petrological data from el hierro canary islands to show that intrusions from the mantle and subhorizontal transport of magma within the oceanic crust result in rapid endogenous island growth seismicity and ground deformation associated with a submarine eruption in 2011 2012 reveal deep subhorizontal intrusive sheets sills which have caused island scale uplift of tens of centimetres the pre eruptive intrusions migrated 15 20 km laterally within the lower oceanic crust opening pathways that were subsequently used by the erupted magmas to ascend from the mantle to the surface during six post eruptive episodes between 2012 and 2014 further sill intrusions into the lower crust and upper mantle have caused magma to migrate up to 20 km laterally resulting in magma accumulation exceeding that of the pre eruptive phase a comparison of geobarometric data for the 2011 2012 el hierro eruption with data for other atlantic intraplate volcanoes shows similar bimodal pressure distributions suggesting that eruptive phases are commonly accompanied by deep intrusions of sills and lateral magma transport these processes add significant material to the oceanic crust cause uplift and are thus fundamentally important for the growth and evolution of volcanic islands we suggest that the development of such a magma accumulation zone in the lower oceanic crust begins early during volcano evolution and is a consequence of increasing size and complexity of the mantle reservoir system and potentially the lithospheric stresses imposed by increasing edifice load

new insights into the cone sheet structure of the cuillin complex isle of skye scotland abstract structural data were collected on 1100 cone sheets and dykes with the aim of reconstructing the geometry of the complex recognizing emplacement phases and contributing to understanding this classical area and the evolution of cone sheets in general mean sheet dip angles are 40 43 47 and 50 in four sections transecting the complex sheet thickness ranges from a few centimetres to 5 m with a dominant thickness of

low temperature hydrothermal alteration of intra caldera tuffs miocene tejeda caldera gran canaria canary islands abstract the miocene tejeda caldera on gran canaria erupted 20 rhyolite trachyte ignimbrites mogan group 14 13 3 ma followed by 20 phonolitic lava flows and ignimbrites fataga group 13 8 5 ma upper mogan tuffs have been severely altered immediately within the caldera margin whereas extra caldera mogan ignimbrites and overlying fataga units are apparently unaltered the altered intra caldera samples contain minerals characteristic of secondary fluid rock interaction clays zeolites adularia and relics of the primary mineral assemblage identified in unaltered ignimbrites k feldspar plagioclase pyroxene amphibole and groundmass quartz major and trace element data indicate that si na k pb sr and rb were strongly mobilized during fluid rock interaction whereas ti zr and nb behaved in a more refractory manner experiencing only minor mobilization the 18o values of the altered intra caldera tuffs are significantly higher than in unaltered extra caldera ignimbrites consistent with an overall low temperature alteration environment unaltered extra caldera ignimbrites have d values between 110 and 173 which may reflect rayleigh type magma degassing and or post depositional vapour release the d values of the altered intra caldera tuffs range from 52 to 131 with ambient meteoric water at the alteration site estimated at ca 15 interaction and equilibration of the intra caldera tuffs with ambient meteoric water at low temperature can only account for whole rock d values of around 45 given that dclay water is ca 30 at 100 c and decreases in magnitude at higher temperatures all altered tuff samples have d values that are substantially lower than 45 indicating interaction with a meteoric water source with a d value more negative than 15 which may have been produced in low temperature steam fumaroles supported by numerical modeling our gran canaria data reflect the near surface epithermal part of a larger fault controlled hydrothermal system associated with the emplacement of the high level fataga magma chamber system in this near surface environment fluid temperatures probably did not exceed 200 250 c

the early appearance of shuidonggou core and blade technology in north china implications for the spread of anatomically modern humans in northeast asia abstract the identification and dating of south temple canyon 1 stc 1 an early upper paleolihic eup site in north central china near shuidonggou sdg helps confirm that sdg is one of the earliest eup sites in northern asia materials from stc 1 bear a strong resemblance to the early sdg core and blade lithic technology that includes flat faced cores and elongate blades we obtained a 14c age estimate of 41 070 890 14c yr bp on the innermost lamina of a calcium carbonate pendant attached to one of the quartzite flakes from the site the purity of the micrite lamina the care taken in obtaining the carbonate sample for processing and dating and the geomorphological setting from which the flake came suggest the age estimate represents a reasonable assessment of an accurate minimum age for stc 1 together with recently derived age estimates of 35 14c ka for the initial eup occupations at sdg 1 and 2 it appears that the eup in the sdg area is as old as any of the handful of eup sites in mongolia and siberia dating to about 40 14c ka and brings into question a postulated north to south spread of the eup lithic technology present at sdg whether or not the dispersal of this technology is associated with the spread of anatomically modern humans remains unknown

dike swarms key to the reconstruction of major volcanic edifices the basic dikes of la gomera canary islands the detailed study of the age and distribution of the basic dikes of la gomera canary islands has allowed us to reconstruct the evolution of its main volcanic edifice the dikes of the oldest unit the basal complex have a n70 80 dominant direction at regional scale on the other hand the dikes of the post basal complex subaerial units are the result of local stress fields the oldest swarm is composed of sills dated at 10 2 9 3 ma four younger radial dike swarms have been identified s1 s2 s3 and s4 with ages of 9 1 8 4 ma 8 2 6 7 ma 5 5 4 4 ma and 5 3 4 0 ma respectively the reconstruction of the magmatic focus location using these swarms shows a migration southwards with an average speed of 1 6 mm year this temporal sequence of parallel swarms sills and radial swarms is a pattern frequently repeated during the building of large insular volcanic edifices in the canary islands as well as in other archipelagos

structure and emplacement of the coastal deccan tholeiitic dyke swarm in goa on the western indian rifted margin mafic dyke swarms when controlled by a regional stress field are emplaced perpendicular to the minimum principal compressive stress direction however mafic dyke swarms may also exploit pre existing structural fabric in their host rocks distinguishing between the two scenarios is important for correct geodynamic understanding of magmatic events continental flood basalt provinces such as the deccan traps of india represent huge fissure eruptions produced by swarms of mafic dykes the coastal dyke swarm of the deccan along the western indian rifted margin is one of its three major dyke swarms we present a field study of the goa dykes part of the coastal swarm the dykes are typical dolerites and basalts exposed in proterozoic age basement lava flows which these dykes may have once fed have been stripped away by erosion though exposed in the western ghats escarpment 100 km to the east the goa dyke swarm contains 60 dykes some of which form larger multiple injection dykes the dykes are short compared to typical kilometers or tens of kilometers long dykes in flood basalt provinces such as the deccan or iceland and range in length from 15 to 220 m and in thickness from 3 cm to 20 m most dykes are vertical and the others dip steeply in various directions their structural attributes and internal features such as vesicular zones and columnar jointing provide clues to the processes of magma flow and solidification in the dykes field measurements yield an average crustal dilation of 8 due to dyke emplacement calculations of magmatic overpressures and magma chamber depths generally yield unrealistic values owing to the low aspect ratios of the dykes based on comparisons between the dyke trends and the host rock joint trends we consider that a few of the goa dykes were emplaced along pre existing fractures but the orientations of the great majority of the dykes reflect contemporaneous stress fields based on crosscutting relationships we infer that the regional minimum horizontal compressive stress 3 changed over time from a e w orientation to a ne sw orientation and finally to a n s direction

the felsic complex of the vallehermoso caldera interior of an ancient volcanic system la gomera canary islands abstract a mid to upper miocene felsic cone sheet dike complex caldera collapse and dome intrusion located around the vallehermoso and tamargada areas north of la gomera island is described it constitutes one of the less known volcanic episodes in the canary archipelago and especially in la gomera island based on detailed field and structural evidence it is suggested that the cone sheet shows at the surface an almost circular geometry truncated to the nw sector after the cone sheet dike complex formed decompression of the interior of an assumed shallow magma chamber occurred due to the subsequent migration of felsic magma throughout the dikes of the cone sheet this last event caused the roof of the magma chamber to collapse leading to the formation of a 3 to 4 km wide caldera a breccia deposit formed during the collapse and filled a depressed central area which finally was affected by an episode of magmatic resurgence leading to a later almost circular dome intrusion the association of cone sheet breccia deposits and domes constitutes the so called trachytic phonolitic complex tpc and should be viewed as the root of an ancient intensely eroded volcanic edifice made of trachytes nepheline phonolites and minor hauyne phonolites as the dominant materials a description of the structural petrological and geochemical features of the trachytic phonolitic complex and a discussion about their origin are considered in this paper we also consider the correlation between another felsic intrusion of alkali gabbros and syenites called tamargada syenites that also crops out in the vallehermoso tamargada area with respect to the trachytic phonolitic complex our data suggest that this alkaline intrusion of alkali gabbros and syenites belongs to an earlier intrusive episode on the basis of petrological geochemical and detailed field studies both trachytes and nepheline phonolites included in the trachytic phonolitic complex most likely evolved from alkali mafic magmas from the upper old basalt formation through a dominant fractional crystallization process additionally hauyne phonolites could develop from local and later magmatic processes such as gas transfer that altered and changed a small part of the previously mentioned nepheline phonolites to hauyne phonolites

evidence for intrusive activity on mercury from the first messenger flyby images from messenger s first flyby of mercury have shown convincing evidence for surface volcanism here we report on evidence in the new data for several features that are characterized by fractures and graben rare features on a planet dominated by contractional deformation that may be linked to intrusive activity these features include 1 a floor fractured crater interpreted to have been the site of laccolith like sill intrusions the feature is similar to some floor fractured craters on the moon and shows evidence for individual fractured dome like uplifts on the floor 2 a concentric complex of graben observed inside the peak ring on the floor of the 250 km diameter raditladi basin and associated with dark plains and possibly embayed by them the feature may represent an unusual type of floor fracturing associated with deeper intrusions and related ring dikes or cone sheets or the graben may instead be the product of non magmatic uplift of the basin floor 3 a large radial graben swarm pantheon fossae located near the center of the caloris basin thus far unique on mercury and characterized by hundreds of individual graben segments ranging from 5 km to 110 km in length in the nexus graben crosscut one another and produce a local polygonal pattern others curve away from the center as the nexus is approached two scales of graben length are observed the radius of the dense radially symmetric plexus of graben is 175 km and a few graben extend to greater radial distances to the north and southwest out to distances that intersect with a ring of generally concentric graben around the outer basin floor two width scales of graben are observed a large graben about 8 km wide emerges from the nexus and extends for 100 km most graben are less than half this width some graben walls appear cuspate with convex outward wall segments that resemble crater chain segments one crater chain with distinctive raised rims parallels nearby graben locally some graben appear in en echelon patterns and smaller graben sometimes show cross cutting superposition relationships abundant impact craters the most prominent being apollodorus and secondary crater clusters and chains are superposed on the graben system there is little evidence that craters greater than 5 km in diameter have been cut by a graben this relation implies that the graben swarm formed soon after the emplacement of the caloris floor plains these graben are interpreted to be the surface expression of a radial dike swarm emanating from a subsurface magma reservoir similar features in which the dikes contribute to a near surface stress field that favors radial graben are known on the earth venus and mars the location of pantheon fossae in the center of the caloris basin suggests that formation of the radial graben structure is linked to basin evolution

earlier history of the 70 ma old canary hotspot based on the temporal and geochemical evolution of the selvagen archipelago and neighboring seamounts in the eastern north atlantic major element trace element and sr nd pb isotope data combined with 40ar 39ar age determinations of volcanic rocks from the selvagen islands and neighboring seamounts in the eastern north atlantic reveal the earlier history of the 70 ma old canary hotspot a basanitic to phonolitic late shield stage intrusive complex 29 ma is exposed on selvagem pequena the evolution of selvagem grande can be divided into three magmatic phases a tephritic to phonolitic late shield stage intrusive complex 24 26 ma and two rejuvenated or post erosional stages 8 12 and 3 4 ma consisting of alkali basalt basanite and rare phonolite during the early to mid miocene volcanic hiatus 12 24 ma the top of the volcano was beneath sea level as evidenced by marine carbonate sediments 13 24 ma dated through correlation of 87sr 86sr with the seawater sr isotope curve the geochemistry of the shield stage lavas indicates that they derive from plume sources whereas the post erosional lavas are derived from metasomatized lithospheric sources five sampled seamounts to the east and northeast of the islands range in composition from alkali basalt and basanite to phonolite samples from dacia conception bank and lars were dated at 9 17 and 68 ma respectively geochemical data suggest that the dredged samples come from the post erosional stage of volcanism and therefore the dates represent minimum ages for the seamount volcanoes the elevation of erosional platforms formed at wave base decrease from selvagen grande 100 m above sea level to lars seamount 900 m below sea level suggesting a southwest to northwest age progression and that all of these seamounts are older than the selvagen islands trace element and sr nd pb isotopic composition of the selvagen islands and neighboring seamounts are consistent with their origin from the canary plume interaction of the weak canary mantle plume with a slow moving plate appears to be responsible for generating a 450 km wide irregular hotspot track extending 800 km from the youngest canary island of hierro in the southwest to lars seamount in the northeast

the interactions of sea level change terrigenous sediment influx and carbonate productivity as controls on upper cambrian grand cycles of western newfoundland canada the upper cambrian stratal record in western newfoundland is complex and reflects the interplay and feedback between 1 changes in third order sea level 2 episodic incursion of terrigenous fines onto the paleoshelf and 3 productivity levels of the ancient carbonate factory mixed carbonate and terrigenous clastic rocks of western newfoundland are configured in large scale third order stratal patterns called grand cycles such cycles are tens to hundreds of meters in stratigraphic thickness and appear to span millions of years grand cycles are divided here into ribbon half cycles composed principally of ribbon rock and oolitic half cycles dominated by oolite stratigraphic distribution of shale in these rocks however is not everywhere coincident with large and small scale patterns in carbonate lithofacies and it suggests that the incursion of terrigenous clay and silt onto the ancient platform must be evaluated separately in part from the dynamics of carbonate accumulation areal and stratigraphic distribution of rock cycles record shifts in facies belts on the ancient platform presumably in response to third order changes in accommodation potential meter scale cycles in carbonate lithofacies are of two types peritidal cycles that fine upward and shelf cycles that coarsen upward thick successions of shelf cycles composed of ribbon rock are interpreted as highstand deposits and are separated by a sequence boundary marked by peritidal cycles from lowstand deposits comprising thick successions of ootite shelf cycles the former mid grand cycle transitions of previous workers are thereby reinterpreted in this study as sequence boundaries the long term position of sea level and thus the degree of platform inundation influenced the health of the platform carbonate factory during times of low sea level the platform was bathed in water more saline than open ocean sea water and it had a robust non skeletal carbonate factory that was resilient to poisoning by episodic influx of terrigenous fines onto the shelf in contrast the carbonate factory during highstands was less resilient to terrigenous poisoning and was susceptible to localized drowning by the reduction in the rate of carbonate sediment production the thick shale units are therefore interpreted to represent the coincidence of and interaction between 1 incursion of terrigenous fines onto the ancient platform and 2 a weakened highstand carbonate factory unable to recover from this terrigenous poisoning

structure of regional dykes and local cone sheets in the midhyrna lysuskard area snaefellsnes peninsula nw iceland this paper provides the first detailed structural description of 48 vertical dykes 384 inclined sheets and two large intrusions and the geometry strike dip direction and dip of 1116 fractures in the central area of the snaefellsnes peninsula nw iceland our data show a more complex setting than that depicted by the wnw ese en echelon trend of the volcanic structures at the surface in the miocene basement lavas dykes dominantly strike n50 100 e whereas other directions are also present with a higher dispersion two main swarms of centrally dipping sheets have also been recognized focussing towards two areas sheet dips range from 2 to 75 with the higher frequency between 10 and 45 in section view there is no systematic variation of sheet dip with distance from the focus area gabbro and granophyre laccoliths are present in the studied area but cross cutting relations indicate that most of the inclined sheets are younger comparison with regional tectonics suggests that the n50 80 e striking dykes are coherent with emplacement under the stress field of the pre 6 ma snaefellsnes rift dominated by a nnw sse directed least principal stress 3 the n80 100 e dykes and the late quaternary wnw trending sub aerial volcanic features are instead consistent with the development of a more recent e w right lateral shear zone affecting the snaefellsnes peninsula coherent sets of fractures have also been found within the inclined sheet swarms the stress tensor rotated in response to an excess magma pressure linked to two underlying magma chambers of lobate shape located at an estimated depth of about 400 and 500 m below sea level this local magmatic stress also produced the centrally inclined fracture swarms that have been found in this area

cyclic caldera collapse piston or piecemeal subsidence field and experimental evidence many multicycle caldera volcanoes display a complex extracaldera fault system genetically linked to caldera evolution on gran canaria canary islands the miocene tejeda caldera was filled by ignimbrites and epiclastic sediments and intruded by syenites and a major cone sheet swarm obscuring intracaldera structural relations extracaldera radial and circumferential faults and dikes are well exposed we used field data and experiments scaled to the island of gran canaria to clarify the poorly understood structural temporal and genetic relationship of peripheral faults to the central caldera the experimental setup comprises a cone of medium grained sand in which a rubber balloon was repeatedly inflated and deflated balloon inflation resulted in updoming and a dominantly radial fault pattern whereas balloon deflation caused piecemeal caldera collapse and a concentric peripheral fault arrangement on the edifice flanks a complex interplay of repeated inflation and deflation cycles of the experimental magma chamber is found to explain the peripheral fault system of the tejeda caldera on gran canaria and offers insight into the structure of the caldera floor and the mechanisms acting in multicycle caldera volcanoes

reconstructing eroded paleovolcanoes on gran canaria canary islands using advanced geomorphometry abstract original volcanic edifices of two successive stages of gran canaria are reconstructed using a geomorphometric analysis of existent or restored paleosurfaces in the reconstruction surface fitting was applied preferably to planezes i e triangular facets of original volcano flanks and quasi planar surfaces qps those occurring on planezes or scattered slightly eroded portions derived from original cone surfaces with the help of red relief image map rrim analysis out of the long lasting mid miocene to holocene subaerial evolution of the island the late miocene fataga volcano and the subsequent pliocene roque nublo volcanoes were the largest and highest the eruptive center of fataga a composite edifice 12 2 8 8 ma that may have grown up excentrically with respect to the previous tejeda caldera is well defined by both two planezes named veneguera mogan and fataga tirajana and qps remnants its calculated original volume 1000 km3 is close to the largest stratovolcanoes on earth however its 3300 m elevation obtained by exponential fit may have been significantly lower due to the complex architecture of the summit region e g a caldera responsible for ignimbrite eruptions roque nublo a 3 7 2 9 ma stratovolcanic cone which was superimposed upon the fataga rocks 3 km west of the fataga center has left no considerable paleosurfaces behind due to heavy postvolcanic erosion yet its remnant formations preserved in a radial pattern unambiguously define its center moreover surface fitting of the outcropping rocks can be corrected taking the erosion rate for the past 3 ma into account such a corrected surface fit points to a regular shaped 3000 m high cone with a 25 km radius and ca 940 km3 original volume also comparable with the dimensions of the largest terrestrial stratovolcanoes

raw material procurement as a crucial factor determining knapping technology in the katta sai complex of middle palaeolithic sites in the western tian shan piedmonts of uzbekistan abstract this paper presents the results of the study of raw material procurement on two late middle paleolithic sites katta sai 1 and katta sai 2 located in the western tian shan piedmont the previous studies allowed to identify an unknown levallois variant of human cultural adaptation in the regional middle paleolithic predetermined flake technology focused on obtaining the thin triangular flakes or even blades at the same time the river pebbles of effusive rocks brought from the nearby river gorges were used for knapping the paper analyses the sources of the raw material collected and its knapping quality together with the technological features indicating how the manufacturing scheme was adjusted to the quality of used raw material

on the conditions of sheet injections and eruptions in stratovolcanoes nearly all eruptions in stratovolcanoes composite volcanoes central volcanoes are supplied with magma through fractures consequently a primary physical condition for an eruption to occur in a stratovolcano is that a magma driven fracture is able to propagate to the surface magma filled fractures frozen or fluid are referred to as sheet intrusions more specifically they are named dykes when subvertical and inclined or cone sheets when inclined field observations indicate that most sheet intrusions do not reach the surface to feed eruptions but rather become arrested at various crustal depths for this reason periods of volcanic unrest with sheet injections are much more common than volcanic eruptions whether a sheet intrusion becomes arrested or alternatively propagates to the surface depends primarily on the stress field in the stratovolcano a stratovolcano normally consists of layers of contrasting mechanical properties such as soft low young s modulus pyroclastic units and stiff high young s modulus lava flows we present numerical models indicating that volcanoes composed of such layers commonly develop stress fields encouraging sheet and dyke arrest the models indicate that a necessary condition for a sheet intrusion to reach the surface and feed a volcanic eruption is that the stress field along the sheet pathway becomes homogenised we propose that much of the activity in a stratovolcano during a volcanic cycle encourages stress field homogenisation field studies show that the sheet intrusions in individual stratovolcanoes have various dips some are vertical dykes others inclined sheets and still others horizontal sills analytical models indicate that the dip of a sheet reaching the surface can have great effects on the magma transport during an eruption this effect is normally greater for a flat volcano such as a collapse caldera than for a stratovolcano that forms a topographic high we conclude that the shallower the dip of a sheet intrusion the less will be its volumetric magma transport to the surface of a stratovolcano

an alternative emplacement model for the classic ardnamurchan cone sheet swarm nw scotland involving lateral magma supply via regional dykes abstract sub volcanic intrusive networks of which cone sheets are recognised as a major constituent partially control volcano growth and eruption style the accepted cone sheet model is that these confocally dipping intrusions originate from an unexposed central magma chamber through dip parallel magma flow however the emplacement mechanism of cone sheets remains poorly understood the 58 ma cone sheet swarm of ardnamurchan nw scotland offers an excellent opportunity to further resolve the emplacement dynamics of cone sheets through studying magma flow and their importance in volcanic edifice construction structural measurements and anisotropy of magnetic susceptibility ams analyses have constrained a lateral magma flow pattern consistently oriented nw se in the majority of the ardnamurchan cone sheets field observations also highlight the importance of host rock structure and interference between competing local and regional stress fields in controlling intrusion geometry our observations suggest cone sheet formation may be linked to laterally propagating nw se trending regional dykes sourced from laterally adjacent magmatic systems likely the palaeogene mull central complex which are deflected around the central complex by stress field interference implicitly edifice construction and potential eruption precursors observed at a volcano may instigate or result from magmatic activity in laterally adjacent volcanic systems

sequence stratigraphy in the middle ordovician carbonate successions yeongheung formation mid east korea paleogeographic implications for a land detached ramp type platform abstract this study reveals the origin of the stratigraphic discrepancy between the yeongweol and taebaek groups and reconstructs paleogeographic model for the taebaeksan basin on the sino korean craton skc the global sea level fall in the earliest middle ordovician would have subaerially extensively exposed the lower ordovician peritidal successions forming the solution collapsed breccia zones on the sauk tippecanoe bounding surface the successive rise in sea level generated the fine grained siliciclastic successions in the taebaek group during early transgression since the carbonate production of the group was hampered by the strong input of siliciclastic sediments from terrestrial sources however such successions are absent in the yeongweol group because the yeongweol platform was distant from the siliciclastic sources and sustained carbonate production due to isolation from terrestrial influences the yeongweol group is interpreted as a land detached isolated ramp type platform as it responded to sea level fluctuations with restricted terrestrial influence whereas the taebaek group can be described as a land attached ramp type platform affected by a large input of siliciclastic sediments during lowstand and early transgression based on the comparison of stratigraphic patterns and configurations of land attached and detached ramp type successions this study concludes that the yeongweol sequence would have been formed on a land detached isolated carbonate ramp type platform located at the skc along the northeastern gondwana margin

palaeokarst in the ordovician of the southern great basin usa implications for sea level history abundant and regionally unique dolostone lithoclast breccias occur throughout the shallow marine lower to middle ordovician pogonip group in the nopah range and adjacent ranges in eastern california and southern nevada breccia bodies display sharply cross cutting relationships with host dolostone bedrock stratigraphy they also show stratigraphic variability in size shape and dolostone clast composition but similarity in breccia matrix composition and framework texture and fabric these characteristics are consistent with a palaeokarst origin upsection changes in breccia clast lithology as well as multiple occurrences of associated quartz sand filled grikes solution widened fissures indicate multiple episodes of carbonate platform exposure and karstification repeated karstification is also indicated by stratiform bodies of quartz sand and thin terra rossa palaeosols that locally truncate breccias and grike systems thus bracketing karstified exposure surfaces facies successions and stacking patterns between recognized exposure surfaces are developed as transgressive regressive cycles and thus show depositional sequence architecture hence these breccias and other associated palaeokarst features are related to a succession of disconformities that provide a sequence stratigraphic framework for assessing ordovician relative sea level history of the south western cordilleran margin of laurentia

crustal structure of northern gran canaria canary islands deduced from active seismic tomography seismic p wave travel times collected during meteor cruise m24 are inverted to derive a three dimensional model of the p wave velocity structure of the northern part of gran canaria canary islands the data consist of 6689 p wave travel times from 1487 offshore air gun shots which were recorded by both land based seismometers and ocean bottom hydrophones the crustal structure is well imaged by the data set as demonstrated by analysis of the resolution and tests with synthetic data the volcanic island is characterized by generally high p wave velocities 5 5 km s and a heterogeneous structure with large lateral velocity variations high p wave velocities are found around the centers of the miocene shield volcanoes in the vicinity of aguimes san nicolas and agaete as well as the center of the pliocene roque nublo volcano the velocity structure suggests a high percentage of dense intrusive rocks some of the intrusive rocks were emplaced during the eruption of 1000 km3 of miocene felsic magmas following the basaltic shield phase the velocity structure beneath la isleta peninsula and its submarine continuation is interpreted as a volcanic rift zone with abundant dikes the velocities decrease to 5 km s north of the coastline a high velocity zone thinning away from the central edifice is interpreted as the massive island flank extending up to 50 km off the coast which is underlain by prevolcanic neogene jurassic sediments the igneous part of the oceanic crust exhibits an anomalous structure with a relatively small thickness 3 km layer 3 and a 2 4 km thick layer 2 probably reflecting a modification of the crust due to long lasting magmatic intrusive activity during the evolution of the canary islands the moho north of gran canaria is found at a depth of 15 km the structure of gran canaria and the adjacent ocean basin is thought to be the result of a diffuse mantle upwelling under a slowly moving plate

the ree ti mineral chevkinite in comenditic magmas from gran canaria spain a syxrf probe study the ree ti silicate chevkinite has been recognised previously in miocene ignimbrites from gran canaria and in correlative offshore syn ignimbrite turbidites we have estimated the partition coefficients of ree y zr and nb for chevkinite and co existing peralkaline rhyolitic comendite glass using synchrotron xrf probe analyses syxrf in order to evaluate the role of this mineral in the ree budget of felsic peralkaline magmas the zr nb ratio of the chevkinite is 1 55 1 7 strongly contrasting with zr nb of 6 5 in the associated glass zr shows a three fold enrichment in chevkinite relative to the residual melt whereas nb is enriched by a factor 10 the enrichment of ce and la in chevkinite is even more significant namely 19 wt ce and 12 wt la compared to 236 ppm ce and 119 ppm la in the glass chevkinite glass ratios are 988 30 for la 806 30 for ce 626 30 for pr 615 40 for nd 392 50 for sm 225 30 for eu 142 25 for gd 72 20 for dy for trace elements we derived kdte of 74 25 for y 8 for hf 50 for th 15 5 for nb and 3 55 0 4 for zr mineral glass ratios for co existing titanite are 28 10 for la 86 20 for ce 98 30 for pr 134 35 for nd 240 50 for sm 50 20 for eu 96 25 for gd 82 25 for dy 99 30 for y 45 10 for nb and 3 0 5 for zr based on these data the removal of only 0 05 wt of chevkinite from a magma with initially 300 ppm ce would deplete the melt by 93 ppm to yield 207 ppm ce in the residual liquid chevkinite thus appears when present to be the controlling mineral within the lree budget of evolved peralkaline magmas

late dinantian palaeokarst of england and wales implications for exposure surface development palaeokarst is an important feature of late dinantian exposure surfaces soil filled depressions are widely developed these are comparable to modern day solution dolines and were probably interspersed by areas of relatively bare limestone pavement the palaeokarst primarily exhibits a smooth mamillated to potholed surface form consistent with its formation beneath a soil cover areas between the depressions have been extensively stylolitised and would likely have originally been characterized by small scale fretted and sculpted karren forms typical of subaerial karstification palaeokarst pits making up the depressions are thought to have been initiated through stem flow drainage from trees rain water intercepted by the crown of the tree was concentrated at specific sites on the emergent surface and dissolution beneath the trunk produced cylindrical pits that propagated vertically downwards trees responsible for concentrating drainage may also have enhanced the acidic nature of the rain water through leaching of organic acids from foliar and woody tissues downward propagation of the pits was limited to the uppermost 1 2 m and enlargement primarily occurred through lateral amalgamation of adjacent pits once initiated continued development of the depressions would have been self perpetuating the preferential accumulation of volcanic ash and organic matter enhancing water retention and encouraging further vegetation growth in contrast intervening areas would have been characterized by slow vertical denudation only karstification likely took of the order of a few hundred years in the case of potholed palaeokarstic surfaces formed solely by stem flow drainage to a few tens of thousands of years where the palaeokarst is more mature

transition from circular to stellate forms of submarine volcanoes large volcanic islands and guyots have stellate forms that reflect the relief of radiating volcanic rift zones multiple volcanic centers and embayments due to giant flank failures small mid ocean ridge volcanoes in contrast are commonly subcircular in plan view and show only embryonic rift zones in order to characterize the transition between these two end members the morphology of 141 seamounts and guyots was studied using the shape of the depth contour at half the height of each edifice irregularity was characterized by measuring perimeter distance elongation and moment of inertia of the contours assuming an ideal edifice is circular the analysis reveals a general transition over 2 4 km edifice height best transition estimate 3 km while some large edifices 4 5 km high show no major embayments or ridges suggesting considerable variation in the effectiveness of mechanisms that cause flank instability and growth of rift zones the various origins of the transition are discussed and the upper limit of magma chambers many of which lie above the basement of the larger edifices is proposed to affect the morphologic complexity via a number of mechanisms and is an important factor affecting the mode of growth the origins of the truncated cone shape of mid ocean ridge volcanoes are also discussed of the eruption mechanisms that have been proposed to explain their flat summits the most likely mechanisms involve eruption from small ephemeral magma bodies lying within the low density upper oceanic crust the discussion includes speculations on factors affecting the depths of magma chambers beneath oceanic volcanoes supporting table is available via web browser or via anonymous ftp from ftp kosmos agu org directory append username anonymous password guest subdirectories in the ftp site are arranged by paper number information on searching and submitting electronic supplements is found at http www agu org pubs csupp about html

strike slip fault tectonics and the emplacement of sheet laccolith systems the thverfell case study sw iceland fault geometry and kinematics indicate that two different tectonic regimes affected the late pliocene volcanic succession around the thverfell magmatic complex esja peninsula sw iceland the older phase is characterized by sets of left lateral strike slip e w to ese striking faults and right lateral strike slip n s to ne striking faults the younger phase produced normal dip slip nne striking faults stress tensor calculation for the older regime provides a horizontal ne to e w trending greatest principal stress 1 and a horizontal nw to n s trending least principal stress 3 followed by a stress regime change with a vertical 1 and a wnw trending 3 structural stratigraphic analyses of the eroded thverfell magmatic complex indicate three main systems namely i a centrally dipping sheet swarm e w elongated in plan view ii a sill composed laccolith fed by e w striking dikes and iii nne to ne striking dikes offsetting the previous intrusions these data allow unravelling of a multiphase history of magma tectonics interaction first an excess magma pressure from an underlying magma chamber induced the emplacement of the centrally dipping sheets this was accompanied by magma upwelling along dikes that bent to propagate as sills under the influence of stress and rheological barriers induced by the lava overburden finally regional dikes linked to the wnw trending rift extension were emplaced

stresses and displacements in layered rocks induced by inclined cone sheets abstract currently the sheet intrusion paths and geometries including the sheet opening thickness as well as the depth to sheet tip are commonly determined from geodetic surface data using elastic dislocation models these models assume the volcanic zone central volcano to be an elastic half space of uniform mechanical properties field observations however show that volcanic zones volcanoes are composed of numerous layers whose mechanical properties primarily young s modulus vary widely here we provide new numerical models on the effects of a typical variation in young s modulus in an active volcanic zone central volcano on the internal and surface stresses and displacements induced by a sheet intrusion whose tip is arrested at a depth below the surface of 100 m the sheet has a dip dimension height of 2 km its opening thickness depends on the magmatic overpressure sheet dimension and host rock young s modulus for the values used here sheet thickness would be in the range of 0 5 1 4 m similar to commonly measured sheet thicknesses in the field the only loading is internal magmatic overpressure in the sheet of 5 mpa the modelled crustal segment volcano consists of 5 layers all with the same poisson s ratio 0 25 each of the 4 uppermost layers is 10 m thick layer 1 the top or surface layer has a young s modulus of 3 gpa layer 2 a modulus of 20 gpa layer 3 a modulus of 30 gpa and layer or unit 5 a modulus of 40 gpa we vary the young s modulus or stiffness of the fourth layer from 10 gpa to 0 01 gpa while the dip of the sheet takes the following values 30 45 60 for an inclined sheet and 90 for a dike the resulting displacement and stresses are highly asymmetric across the sheet tip except for the dike with the main surface stresses and displacements being above the dipping sheet and highest for the 30 dipping sheet for comparison three elastic half space models of the same sheet configuration and loading but uniform young s modulus in each model 40gpa 20gpa and 10 gpa all yield much higher surface stresses and displacements than any of the layered models as the stiffness of layer 4 decreases the surface stresses gradually decrease while changes in vertical displacements are comparatively small but greater in horizontal displacements in particular as the stiffness of layer 4 decreases from 10 gpa to 0 01 gpa for the 30 dipping sheet the maximum surface shear stress decreases from about 6 6 mpa to 2 2 mpa and the maximum tensile stress from about 6 9 mpa to about 2 3 mpa thus even a single comparatively thin 10 m soft layer close to the surface of a central volcano volcanic zone where such layers are almost universal may cause a great change in the maximum sheet induced stresses at the surface and thereby in any sheet induced fracture pattern furthermore the stress peaks in the layered models do not coincide with the displacement peaks fracture formation is most likely at the location of the stress peaks the results have important implications for the correct interpretation of geodetic data and fracturing during unrest periods with magma chamber rupture and sheet injection

sedimentary and volcano tectonic processes in the british paleocene igneous province a review research on the british paleocene igneous province bpip has historically focused on the emplacement chemistry and chronology of its elaborate central intrusive complexes and lava fields however the bpip has also been dramatically shaped by numerous erosion sedimentation and volcano tectonic events the significance of which becomes ever clearer as localities in the bpip are re investigated and our understanding of volcano sedimentary processes advances the resultant deposits provide important palaeo environmental palaeo geographical and stratigraphical information and highlight the wide range of processes and events that occur in ancient volcanic settings such as the bpip in this paper we review the sedimentary and volcano tectonic processes that can be distinguished in the bpip and conceptualize them within a generalized framework model we identify and describe the sedimentary responses to four broadly chronological stages in the history of the bpip volcanoes 1 the development of the lava fields 2 early intrusion induced uplift 3 caldera collapse and 4 post volcano denudation and exhumation of central complexes we highlight and illustrate the range of sedimentary processes that were active in the bpip these operated on and helped shape a dynamic landscape of uplands and lowlands of alluvial fans braided rivers lakes and swamps and of volcanoes torn apart by catastrophic mass wasting events and or caldera collapse

karst controlled reservoir heterogeneity in ellenburger group carbonates of west texas petroleum production from restricted shelf carbonates of the lower ordovician ellenburger group is commonly considered to have been a result of a pervasive relatively homogeneous tectonic fracture system within the reservoir rock however regional facies and diagenetic paleokarst studies of ellenburger strata based on cores and wireline logs have demonstrated that significant reservoir compartmentalization was caused by karst modification in the upper part of the unit ellenburger group carbonates which attain a thickness of over 1 700 ft 520 m record sedimentation on a shallow water restricted shelf occupying most of west texas logging of over 10 000 ft 3 050 m of core from 63 wells has allowed recognition of six facies assemblages 1 lithic arenite 2 mixed siliciclastic carbonate packstone grainstone 3 ooid peloid grainstone 4 mottled mudstone 5 laminated mudstone and 6 gastropod intraclast packstone grainstone these facies assemblages record initial transgression and subsequent progradation and aggradation paleoslope was generally south and east from the texas arch toward the ouachita and marathon orogenic belts all facies assemblages with the local exception of the ooid peloid grainstone assemblage are characterized y very low intergranular and intercrystalline porosity porosity development in ellenburger group carbonates is directly related to a prolonged period of subaerial exposure that coincided with a middle ordovician eustatic lowstand prior to transgression of simpson group siliciclastics during this episode a widespread system of caves sinkholes joint controlled solution features and collapse breccias developed of particular importance to reservoir development was the formation of a regionally extensive cave system between 100 and 300 ft 30 and 90 m beneath the exposed ellenburger surface infill of this cave system by simpson group sand and clay segmented the upper ellenburger into three karst facies which are in descending order 1 cave roof dolomites fracture and mosaic breccias 2 laterally persistent cave fill facies siliciclastic matrix supported and carbonate matrix supported breccias and 3 lower collapse facies chaotic clast supported breccias of the cave floor pronounced vertical segregation of permeable zones defined by the three karst facies is evident in the emma andector martin block 13 and several other major ellenburger reservoirs lateral reservoir heterogeneities formed by localized laterally extensive collapse structures such as in the shafter lake reservoir also contribute to compartmentalization of producing zones within the upper ellenburger group secondary and tertiary recovery programs in these ellenburger reservoirs can be optimized by integrating concepts of lateral and vertical heterogeneity predicted by the karst model

late ordovician mass extinction a new perspective from stratigraphic sections in central nevada integrated sequence stratigraphic biostratigraphic and chemostratigraphic analyses of three stratigraphic sections in central nevada indicate that late ordovician glaciation induced sea level fall produced diachronous stepwise faunal turnover in graptolites conodonts chitinozoans and radiolarians and also triggered a strong but transient positive 13c excursion this pattern is very different from that described for most mass extinction events

isotopic approach to soil carbonate dynamics and implications for paleoclimatic interpretations the radiocarbon content and stable isotope composition of soil carbonate are best described by a dynamic system in which isotopic reequilibration occurs as a result of recurrent dissolution and reprecipitation depth of water penetration into the soil profile as well as soil age determines the degree of carbonate isotope reequilibration we measured 13c 18o and radiocarbon content of gravel rinds and fine 2 mm carbonate in soils of 3 different ages 1000 3800 and 6300 14 c yr b p to assess the degree to which they record and preserve a climatic signal in soils developing in deposits independently dated at 3800 and 6300 radiocarbon yr b p carbonate radiocarbon content above 40 cm depth suggests continual dissolution and reprecipitation presumably due to frequent wetting events between 40 and 90 cm depth fine carbonate is dissolved and precipitated as rinds that are not redissolved subsequently below 90 cm depth in these soils radiocarbon content indicates that inherited fine carbonate undergoes little dissolution and reprecipitation in the 3800 and 6300 yr old soils 13c in rind and fine carbonate follows a decreasing trend with depth apparently in equilibrium with modern soil gas as predicted by a diffusive model for soil co2 18o also decreases with depth due to greater evaporative enrichment above 50 cm depth in contrast carbonate isotopes in a 1000 yr old deposit do not reflect modern conditions even in surficial horizons this soil has not undergone significant pedogenesis there appears to be a lag of at least 1000 but less than 3800 yr before carbonate inherited with parent material is modified by ambient climatic conditions although small amounts of carbonate are inherited with the parent material the rate of pedogenic carbonate accumulation indicates that ca is derived primarily from eolian and rainfall sources a model describing carbonate input and radiocarbon decay suggests that fine carbonate below 90 cm is mostly detrital inherited and that carbonate rinds have been forming pedogenically at a constant rate since alluvial fans were deposited

upper ordovician sequences of western estonia abstract the upper ordovician uppermost caradoc ashgill section of western estonia consists of a series of seven open shelf carbonate sequences depositional facies grade laterally through a series of shelf to basin facies belts grain supported facies shallow shelf mixed facies middle shelf mud supported facies deep shelf and slope and black shale facies basin locally a stromatactis mud mound occurs in a middle to deep shelf position shallow to deep shelf facies occur widely across the estonian shelf and grade laterally through a transitional slope belt into the basinal deposits of the livonian basin each sequence consists of a shallowing upward prograding facies succession sequences 1 upper nabala stage and 2 vormsi stage record step wise drowning of underlying shelf units lower nabala that culminated in the deposition of the most basinal facies fjacka shale in the livonian basin sequences 3 6 comprise the overlying pirgu stage and record the gradual expansion of shallow and middle shelf facies across the estonian shelf the porkuni stage sequence 7 is bracketed by erosional surfaces and contains the shallowest water facies of the preserved strata the uppermost part of the section normalograptus persculptus biozone is restricted to the livonian basin and includes redeposited carbonate and siliciclastic grains it is the lowstand systems tract of the lowest silurian sequence 8 sequence 7 and the overlying basinal redeposited material i e the lowstand of sequence 8 correspond to the latest ordovician hirnantian glacial interval and the bracketing unconformities are interpreted as the widely recognized early and late hirnantian glacial maximums the sequences appear correlative to upper ordovician sequences in laurentia graptolite biozones indicated that the estonian sequences are equivalent to carbonate ramp sequences in the western united states great basin and mixed carbonate siliciclastic sequences in the eastern united states appalachian basin cincinnati arch region these correlations indicate a strong eustatic control over sequence development despite the contrasting tectonic settings of these basins

the felsic dikes of la gomera canary islands identification of cone sheet and radial dike swarms on the northern part of la gomera there exists a great abundance of trachytic phonolitic dikes showing a broad diversity in dip and strike several methods have been applied in order to separate these dikes in different sets localise the area from where they derive and reconstruct the geometry of the swarms the oldest dikes correspond to a radial swarm dated at 8 ma the felsic activity migrated then southwestwards and a second radial swarm and a cone sheet complex were developed between 7 5 and 6 4 ma ago the cone sheet complex is 10 km in diameter and shared its centre with that of the second radial structure the cone sheets exhibit an outward decrease of dip angle whilst every individual sheet maintains a constant inclination this geometry reflects the existence of an ancient single dome shaped shallow magma chamber situated some 1650 m below present sea level the eastern radial swarm represents a felsic episode that could mark the ending of the lower old basalts the earlier subaerial activity of la gomera the two other dike swarms represent a younger episode coeval with the upper old basalts

structure of a sheet laccolith system revealing the interplay between tectonic and magma stresses at stardalur volcano iceland abstract this paper provides detailed structural data on the faults and intrusions of the eroded stardalur volcano in the esja peninsula at the sw margin of the icelandic rift and new lithostratigraphic data on the host rocks a swarm of centrally dipping sheets emplaced with a fan shaped geometry in section view depicts an ellipse in plan view with an about e w major axis sheet intensity reaches 80 in one 100 m transect near the central portion of the swarm where sheets strike e w with sub vertical dip a 200 m thick multiply intrusive body forms a laccolith in the middle of the centrally dipping sheet swarm at a higher altitude individual intrusive units within this laccolith are sub vertical and strike e w in the center acquiring a sill like geometry outwards and were emplaced in a stress field locally dominated by a n s directed least principal stress 3 within the inclined sheet swarm the stress tensor rotated in response to an excess magma pressure probably linked to an underlying magma chamber which interacted with the tectonic stresses crosscutting relationships between the various intrusions and with the host rock indicate that the activity in the central zone of the stardalur volcano ended with the emplacement of the laccolith later eruptions if they occurred at all were fed by centrally dipping sheets in the final stage nne striking regional vertical dykes and normal faults cut the previous structures in response to dominant regional plate tectonic stresses with a wnw ese directed 3 and a nne ssw directed intermediate principal stress 2

estimating palaeo water depth from the physical rock record abstract palaeo water depth and its change with time is a key factor in environmental analysis and in sedimentology in general the literature published on this topic and on related subjects however is substantial albeit scattered within and between different communities geologists oceanographers engineers physicists etc here i focus on proxies for palaeo bathymetry as obtained from the physical rock record floral faunal and chemical evidence for palaeo water depth being equally important must be dealt with elsewhere an assessment of the main depth related parameters in actualistic settings is presented and their applicability to the fossil sedimentary record discussed the outcome reveals the full complexity of this topic there is for example no such thing as an average wave base depth applicable to a wide range of fossil case settings this because wave and current climates in general and particularly so in neritic and coastal settings are intriguingly complex furthermore observations from modern oceans are not a priori applicable to fossil ones acknowledging these problems and limitations critically evaluated quantitative proposals for depth indicative facies and features in the sedimentary record are presented and error bars discussed

fluid rock interaction in the miocene post caldera tejeda intrusive complex gran canaria canary islands insights from mineralogy and o and h isotope geochemistry the intra caldera volcaniclastic deposits of the miocene tejeda caldera on gran canaria host an similar to 12 km diameter intrusive complex comprising a peralkaline trachytic to phonolitic cone sheet swarm surrounding a central core of hypabyssal syenite stocks both intrusive rock types display textural and mineralogical features indicative of secondary fluid rock interaction including 1 deuteric mineral phases e g aegirine alkali amphibole analcime 2 turbid alkali feldspars and 3 hydrothermal mineral phases phyllosilicates fe ti oxides mn oxides and quartz altered cone sheets have whole rock delta o 18 values ranging from 0 center dot 1 to 10 center dot 0 parts per thousand n 22 and whole rock delta d values between 62 and 149 parts per thousand n 28 three altered syenite samples have whole rock delta o 18 values of 2 center dot 5 1 center dot 5 and 0 center dot 9 parts per thousand and corresponding delta d values of 91 99 and 121 parts per thousand the h2o concentrations of the altered cone sheets range from 0 center dot 4 to 0 center dot 8 wt n 28 and the altered syenites have h2o concentrations of 0 center dot 5 0 center dot 5 and 0 center dot 6 wt respectively the majority of altered samples are depleted in o 18 relative to the typical delta o 18 range for unaltered trachytes and syenites delta o 18 6 8 parts per thousand indicative of interaction with local meteoric water delta o 18 c 8 parts per thousand at temperatures epsilon 150 degrees c only one cone sheet sample appears petrographically unaltered and has a typical igneous isotopic composition delta o 18 7 center dot 1 parts per thousand delta d 48 parts per thousand and a relatively high h2o concentration 2 center dot 2 wt a weak correlation r 0 center dot 55 between delta d and h2o is observed in the cone sheets reflecting the combined effects of magmatic h2o exsolution and subsequent deuteric and hydrothermal alteration no systematic variation in delta o 18 or delta d was detected across the cone sheet swarm most likely reflecting overprinting of isotopic compositions during successive intrusive events however the highest delta o 18 values 8 center dot 2 10 center dot 0 parts per thousand occur in clay bearing cone sheets from the central part of the intrusive complex suggesting enhanced infiltration of relatively cool meteoric water in this area overall at least three phases of fluid rock interaction can be distinguished 1 deuteric alteration c 300 500 degrees c by late magmatic fluids expelled from a solidifying crystal mush 2 hydrothermal alteration epsilon 150 300 degrees c by meteoric water during the final stages of crystallization and or immediately following solidification of the intrusive complex 3 retrograde alteration related to the influx of relatively cool 150 degrees c meteoric waters

a functional approach to the use of the earliest blade technology in upper paleolithic hokkaido northern japan abstract to understand the behavioral significance of the emergence and proliferation of blade technology in the northeastern asian upper paleolithic this paper explores the function of the earliest blade technology in hokkaido northern japan through an integrated analysis of edge morphology and use wears on blade tools from the last glacial maximum lgm assemblage of kawanishi c although varied edge morphologies i e straight convex concave denticulate have been distinguished the results of use wear analysis suggest that morphological differences of edges are not related to specific functions straight and convex edges experienced different use lives and use trajectories both straight and convex edges were principally served for cutting sawing and whittling while some edges changed their functions to scraping as edge resharpening blunted the edges the results of use wear analysis also suggest that lgm blades were intensively used for performing a narrow range of activities e g skin and meat stripping because this blade technology differs from the dominant flake technology in lgm hokkaido lgm foragers were able to employ it to perform intensive processing activity to exploit critical faunal resources that may have been sporadically clumped in the landscape

magma mixing and crustal recycling recorded in ternary feldspar from compositionally zoned peralkaline ignimbrite a gran canaria canary islands miocene ignimbrite a on gran canaria contains three compositional endmember fiamme types two rhyolites and one trachyte each of which crystallized distinct feldspar various textural and compositional criteria are interpreted as reflecting a complex scenario within the magma chamber in which the crystals formed about 25 30 of the feldspar phenocrysts contain evidence for magma mixing in the form of 1 partial to severe dissolution resorption rims 2 distinct zones of drastically different compositions and 3 overgrowth textures on formerly resorbed crystals four major types of zoning in the oligoclase to anorthoclase feldspars of ignimbrite a include a normal and a reversely zoned type and two complexly zoned types the feldspars with normal and reverse zonation show only minor compositional amplitudes between individual zones ab or 4 whereas the complexly zoned types show compositional differences between zones of up to 18 mol ab and 20 mol or and are commonly associated with an internal dissolution surface complex zoning with large compositional amplitudes and dissolution textures is taken as evidence of crystal movements within the magma and across compositional boundaries between magma batches a multiple step cycle model involving growth and transport of a crystal into another magma batch and its return to the original host magma is suggested by the data moreover feldspars from one rhyolite compositional group are found to be substantially elevated in 18o suggesting an input of a high 18o component to this rhyolite the other endmember rhyolite appears to be related to the endmember trachyte by mainly crystal fractionation of anorthoclase feldspar this observation is consistent with trace element and rare earth element concentrations for the magma endmembers and their feldspars where contamination led to a depletion in incompatible trace elements and light rare earth elements in the contaminated rhyolite and its feldspar phenocrysts we suggest that the combination of textural and compositional variation in ternary feldspar of peralkaline rhyolitic systems is well suited to reconstruct dynamic processes such as magma mixing and contamination in evolving rhyolitic magma chambers

dynamics of dikes versus cone sheets in volcanic systems igneous sheet intrusions of various shapes such as dikes and cone sheets coexist as parts of complex volcanic plumbing systems likely fed by common sources how they form is fundamental regarding volcanic hazards yet no dynamic model simulates and predicts satisfactorily their diversity here we present scaled laboratory experiments that reproduced dikes and cone sheets under controlled conditions our models show that their formation is governed by a dimensionless ratio 1 which describes the geometry of the magma source and a dynamic dimensionless ratio 2 which compares the viscous stresses in the flowing magma to the host rock strength plotting our experiments against these two numbers results in a phase diagram evidencing a dike and a cone sheet field separated by a sharp transition that fits a power law this result shows that dikes and cone sheets correspond to distinct physical regimes of magma emplacement in the crust for a given host rock strength cone sheets preferentially form when the source is shallow relative to its lateral extent orwhen the magma influx velocity or viscosity is high conversely dikes form when the source is deep compared to its size or when magma influx rate or viscosity is low both dikes and cone sheets may form fromthe same source the shift fromone regime to the other being then controlled by magma dynamics i e different values of 2 the extrapolated empirical dike to cone sheet transition is in good agreement with the occurrence of dikes and cone sheets in various natural volcanic settings

middle pleistocene hominin occupation in the danjiangkou reservoir region central china studies of formation processes and stone technology of maling 2a site abstract danjiangkou reservoir region drr is one of the areas where acheulean like stone technology mode 2 was reported in central and south china it is located at the end of the upper reaches of the hanshui river the largest tributary of the yangtze river systematic field investigations documented more than ninety paleolithic sites along the fluvial terraces of the hanshui and danjiang rivers the latter a tributary of the upper reach of the hanshui river subsequent excavations at more than 30 sites led to the discovery of a large number of paleolithic stone artifacts in the past decade showing that early hominins lived in the region at least by the early part of the middle pleistocene however little is known from the archaeological record about the context of the sites and their formation processes the technological characteristics of the stone artifact assemblages and whether they truly belong to mode 2 technology or just to core and flake technology and the overall hominin behavioral patterns and adaptation during the middle to late pleistocene maling locality 2a ml2a is buried in the front edge of the third alluvial terrace of the danjiang river archaeological excavations undertaken at the site in 2011 recovered 1026 stone artifacts from a red clay deposit preliminary osl dating and geomorphological comparisons between the terraces in the hanshui river system suggest that the site is dated to the late middle pleistocene patterns of artifact concentration suggest that the site was buried in secondary context where the stone artifacts were transported by water from a relatively higher location nearby the artifacts primarily made on quartzite and quartz cobbles include cores whole flakes various fragments retouched pieces two bifaces and a hammerstone all flaking is by direct hard hammer without core preparation the majority of flakes in the early stages of core reduction indicate that the cores are not extensively reduced choppers are the predominant core category together with discoids polyhedrons and core scrapers it should be noted that two bifacially flaked cobbles can classed as mode 2 implements eleven retouched pieces are recognized and they were casually modified by direct hammer percussion although only two bifaces were excavated from this site many more are recorded in the larger study area the ml2a artifact assemblage may be considered as a chinese variant of an acheulean like mode 2 industry it can be deduced that homo erectus was likely the responsible for manufacturing the stone artifacts

a new felsic cone sheet swarm in the central atlantic islands the cone sheet swarm of boa vista cape verde abstract the island of boa vista is one of the oceanic islands with the largest amount of felsic rocks reported in the world 50 of the total outcropping igneous rocks of boa vista the felsic rocks are trachytes and phonolites generated within the second main stage of the volcanic activity that lasted about four million years three consecutive felsic episodes are distinguished the first occurred between 14 5 ma and 13 5 ma the second between 13 6 ma and 12 0 ma and the third and last between 12 0 ma and 10 4 ma their geochemical composition reveals the presence of crystal fractionation processes with participation of feldspars and amphibole as well as different accessory phases involved in each episode the boa vista felsic cone sheet swarm the youngest third episode is formed by several hundreds of peralkaline ne phonolitic sheets distributed within a circular surface about 11 km in radius the cone sheets conform a single general pattern characterized by a decreasing dip outward the structure together with a constant dip of each individual sheet the average inclination of sheets is around 40 in the sectors next to the centre of the structure whereas it is only about 30 next to its periphery the magmatic focus of the sheets is located over 3 km deep almost coinciding with the convergence centre of a contemporary basic radial dike swarm

an atmospheric pco2 threshold for glaciation in the late ordovician the late ordovician glaciation differs from other major phanerozoic glaciations because of its short duration 1 m y a satisfactory explanation for this glaciation must be able to account for its sudden initiation short duration and rapid termination mechanisms operating on tectonic time scales appear to be precluded given recent studies of a major perturbation in the carbon cycle during the glaciation a climate model investigation of the sensitivity of the late ordovician climate to changes in atmospheric p co2 was undertaken under the condition of a 4 5 reduction in solar luminosity permanent snow cover taken as a key indicator of potential for glaciation is dramatically different between five experiments the range of 18x present atmospheric level co2 ice free to 8x runaway icehouse lies within the uncertainty of previous geochemical estimates of late ordovician atmospheric p co2 the strong sensitivity to the modest direct forcing from p co2 changes is due to the ice albedo feedback a plausible increase in organic carbon burial could have drawn down enough atmospheric co2 to have briefly lowered the climate system below a critical glacial inception threshold at the end of the ordovician conversely a high p co2 is required for the rest of the early paleozoic which was essentially ice free

caldera resurgence during magma replenishment and rejuvenation at valles and lake city calderas a key question in volcanology is the driving mechanisms of resurgence at active recently active and ancient calderas valles caldera in new mexico and lake city caldera in colorado are well studied resurgent structures which provide three crucial clues for understanding the resurgence process 1 within the limits of 40ar 39ar dating techniques resurgence and hydrothermal alteration at both calderas occurred very quickly after the caldera forming eruptions tens of thousands of years or less 2 immediately before and during resurgence dacite magma was intruded and or erupted into each system this magma is chemically distinct from rhyolite magma which was resident in each system 3 at least 1 km of structural uplift occurred along regional and subsidence faults which were closely associated with shallow intrusions or lava domes of dacite magma these observations demonstrate that resurgence at these two volcanoes is temporally linked to caldera subsidence with the upward migration of dacite magma as the driver of resurgence recharge of dacite magma occurs as a response to loss of lithostatic load during the caldera forming eruption flow of dacite into the shallow magmatic system is facilitated by regional fault systems which provide pathways for magma ascent once the dacite enters the system it is able to heat remobilize and mingle with residual crystal rich rhyolite remaining in the shallow magma chamber dacite and remobilized rhyolite rise buoyantly to form laccoliths by lifting the chamber roof and producing surface resurgent uplift the resurgent deformation caused by magma ascent fractures the chamber roof increasing its structural permeability and allowing both rhyolite and dacite magmas to intrude and or erupt together this sequence of events also promotes the development of magmatic hydrothermal systems and ore deposits injection of dacite magma into the shallow rhyolite magma chamber provides a source of heat and magmatic volatiles while resurgent deformation and fracturing increase the permeability of the system these changes allow magmatic volatiles to rise and meteoric fluids to percolate downward favouring the development of hydrothermal convection cells which are driven by hot magma the end result is a vigorous hydrothermal system which is driven by magma recharge

tectonic subsidence of the early paleozoic passive continental margin in eastern california and southern nevada quantitative analysis of tectonic subsidence in cambrian and ordovician platform carbonates and associated strata exposed in the spring mountains nevada and the nopah funeral and inyo ranges california indicates that subsidence associated with this segment of the early paleozoic passive continental margin is exponential in form consistent with thermal contraction of the lithosphere following extension as in other parts of the north american cordillera continental separation in the southern great basin appears to have taken place between 590 and 545 ma these results are not sensitive to uncertainties in stratigraphic thickness biostratigraphic age control or paleobathymetry uncertainties in the cambrian time scale lead to predictable variations in the inferred time of onset of thermal subsidence but they have no effect on the inferred stratigraphic position of the rift to post rift transition a younger age for the base of the middle cambrian results in a younger inferred age of onset of thermal subsidence accompanied by greater rates of subsidence during the cambrian whereas a significantly older estimate of the onset of thermal subsidence can be obtained only if the base of the middle cambrian is substantially older than 540 ma a possibility that is inconsistent with available data results of the subsidence analysis are particularly significant because this is one of the few regions along the length of the north american cordillera where they can be compared directly to the geologic evidence for syn rift and post rift deposition basement involved faulting associated with the amargosa basin aulacogen ceased during deposition of the noonday dolomite which is thought to be older than 700 680 ma on the basis of stromatolites of late riphean affinity the overlying johnnie formation contains supposed vendian stromatolites younger than 700 680 ma if it is assumed that our results indicate the timing of the final rift to post rift transition then either the ages inferred from stromatolites are incorrect or the lithosphere was thinned regionally after deposition of the noonday the latter possibility is supported by limited geologic evidence for extension in latest proterozoic and early cambrian time the lack of appreciable physical evidence for crustal extension after deposition of the noonday however may imply that 1 a uniform extension model for lithospheric thinning is inappropriate for this part of the margin or that 2 some or all of the localities studied are continentward of the hinge zone and that the observed subsidence is exaggerated by flexural loading in a deeper basin to the west

long lived glaciation in the late ordovician isotopic and sequence stratigraphic evidence from western laurentia the timing and causes of the transition to an icehouse climate in the late ordovician are controversial results of an integrated 13c and sequence stratigraphic analysis in nevada show that in the late ordovician chatfieldian stage mid caradoc a positive 13c excursion in the upper part of the copenhagen formation was closely followed by a regressive event evidenced within the prominent eureka quartzite the chatfieldian 13c excursion is known globally and interpreted to record enhanced organic carbon burial which lowered atmospheric p co2 to levels near the threshold for ice buildup in the ordovician greenhouse climate the subsequent regressive event in central nevada previously interpreted as part of a regional tectonic adjustment is here attributed in part to sea level drawdown from the initiation of continental glaciation on gondwana this drop in sea level which may have contributed to further cooling through a reduction in poleward heat transport and a lowering of p co2 by suppressing shelf carbonate production signals the transition to a late ordovician icehouse climate 10 m y before the widespread hirnantian glacial maximum at the end of the ordovician

recent discovery of a unique paleolithic industry from the yumidong cave site in the three gorges region of yangtze river southwest china the three gorges of yangtze river southwest china abundant in human and faunal fossils and lithic artifacts represents an important site complex for understanding hominin dispersion and adaptations during the pleistocene the yumidong cave is a newly discovered paleolithic site in this region which yielded a large number of animal fossils and lithic artifacts u th dating in conjunction with biostratigraphic analysis indicated that the archaeological remains were deposited during a long sequence from ca 400 to 8 ka middle pleistocene to holocene lithic technological analysis indicated an original material shaped on massive limestone blocks with chaine operatoire consisted of selection shaping and retouching the volumetric structures of selected blanks are regrouped into three categories structures with bevel s trihedral structure and convergent ones the outline of cutting edge is predonimated by denticulate ones followed by saw like ones rostrum convergent with a denticulate edge and beaked ones despite showing nothing in common with europe africa the near east and even the indian subcontinent and northern china the lithic assemblage of the yumidong cave exhibits a strong coherence and presents more similarity to mainland southeast asia with heavy angular and massive stone tools made on pebble cobble and without the levallois discoid and blade bladelet phenomenon the lithic assemblage of yumidong cave may represent material clues of a potential local technological center of origin in unique technical world of central south china and its uniqueness would be understandable as the result of a successful adaptation of hominids to a specific environment yumidong lithic material deconstructs the existing paradigm for a long period of time and presents new ideas and new facts for the technic evolution in south china

analogue models of collapse calderas and resurgent domes collapse calderas and resurgent domes are a common association related to inflation deflation processes in volcanic systems the structure of calderas and domes depends upon the permitted relative movements of crustal volumes at depth the so called space problem in order to study the structures of collapse calderas and resurgent domes and to take the space problem into account several analogue models were made dry quartz sand was used to simulate the rheology of the brittle crust while newtonian silicone putty located at the base of the sand pack simulated the ductile behaviour of the magma a piston moved the silicone putty downward or upward inducing collapse and doming within the sand three separate sets of experiments simulated 1 caldera collapse 2 resurgence and 3 superimposition of resurgence on collapse and vice versa collapse experiments are characterized by the development of two concentric depressions the first formed depression is bordered by outward dipping reverse ring faults the subsequent outer concentric depression is bordered by inward dipping normal ring faults the deformation pattern during resurgence is a function of the overburden thickness t and the dome diameter d for higher t d ratios a dome forms bordered by inward dipping high angle reverse ring faults outward dipping normal ring faults develop at late stages for lower t d ratios the dome shows at late stages a crestal depression accompanied by radial fractures subsequently an apical extrusion of silicone occurs the superimposition of resurgence over collapse and vice versa is characterized by the complete reactivation with opposite kinematics of all the pre existing ring faults during inversion both in caldera and resurgence reverse ring faults form in the early stages due to differential uplift extensional structures subsequently form to accommodate gravitational collapse during the activity of the reverse faults the experiments and the overall similarities with nature suggest that the activity of both reverse and normal faults constitutes a possible solution to the space problem during major collapses or resurgences

levallois and non levallois blade production at shuidonggou in ningxia north china the shuidonggou site is one of the most important for prehistoric research in china yielding evidence of ancient human colonisations in north china during the late upper pleistocene situated in the ordos desert it was first discovered and excavated by teilhard de chardin during the first half of the 20th century he noted the originality of the lithic assemblages produced on blades and flakes comparable to the upper palaeolithic in western europe this open air site in loess context dates from ca 17 000 to 25 000 bp and may be earlier than 30 000 bp the principal objective of this paper is to present the technical aspects of the shuidonggou lithic assemblages using a technological approach based on the dynamic analysis of blanks and cores in a global overview of the chaine operatoire concept the goal is to understand the knapping strategies used were both levallois and non levallois methods used the importance of shuidonggou is thus linked with the question of the use of the levallois method

three armed rifts or masked radial pattern of eruptive fissures the intriguing case of el hierro volcano canary islands abstract using new surface structural data as well as subsurface structural data obtained from seventeen water galleries we provide a comprehensive model of the volcano tectonic evolution of el hierro canary islands we have identified measured and analysed more than 1700 volcano structural elements including vents eruptive fissures dykes and faults the new data provide important information on the main structural patterns of the island and on its stress and strain fields all of which are crucial for reliable hazard assessments we conducted temporal and spatial analyses of the main structural elements focusing on their relative age and association with the three main cycles in the construction of the island the tinor edifice the el golfo las playas edifice and the rift volcanism a radial strike distribution which can be related to constructive episodes is observed in the on land structures a similar strike distribution is seen in the submarine eruptive fissures which are radial with respect to the centre of the island however the volcano structural elements identified onshore and reflecting the entire volcano tectonic evolution of the island also show a predominant ne sw strike which coincides with the main regional trend of the canary archipelago as a whole two other dominant directions of structural elements n s and wnw ese are evident from the establishment of the el golfo las playas edifice during the second constructive cycle we suggest that the radial striking structures reflect comparatively uniform stress fields during the constructive episodes mainly conditioned by the combination of overburden pressure gravitational spreading and magma induced stresses in each of the volcanic edifices by contrast in the shallower parts of the edifice the ne sw n s and wnw ese striking structures reflect local stress fields related to the formation of mega landslides and masking the general and regional radial patterns

interconnected sills and inclined sheet intrusions control shallow magma transport in the ferrar large igneous province antarctica field observations and structural data from intrusive complexes at allan hills and terra cotta mountain south victoria land antarctica demonstrate that interconnected sills and inclined sheets transported magma through the shallow subsurface these sills and sheets represent the upper crustal top 4 km plumbing system of the 183 ma ferrar large igneous province the sheets are short in length