possible role of superheated magma in the formation of orbicular granitoids orbicular structures in granitoid rocks generally occur in minor intrusions inside or at the edges of larger granitoid plutons some orbs are associated with comb layering at or near pluton margins the orbs typically consist of cores enclaves of various rock types around which are concentric shells of rhythmically precipitated felsic and mafic layers dominated by radial and tangential arrangements of elongate crystals the orbs therefore contrast strongly with the enclosing granitoid rock which has a typical granitoid microstructure with randomly distributed crystals orbicular shells and comb layering have similar features and both require the absence of nuclei in the magma which permits a significant degree of undercooling and forces crystallization to occur only on solid objects superheating is an effective way of destroying nuclei as has been shown experimentally and so orbicular granitoids may have crystallized from formerly superheated magma effective superheating could be caused by engulfment of hydrous felsic or intermediate magma by hot mafic magma or more probably by injection of water into a felsic or intermediate magma the rarity of orbicular granitoids implies that superheating situations are also rare most magmas carrying sufficient nuclei to permit normal crystallization

stable carbon and oxygen isotope evidence of cretaceous sea level fluctuations recorded in septarian concretions from pueblo colorado u s a abstract limestone concretions in the blue hill member of the carlile formation middle middle turonian exposed in the lake pueblo state park colorado u s a range in size from 20 cm diameter approximately spherical forms to flattened spheroids 2 m in width and 1 m in height the earliest matrix and septarian calcite cement with 13c and 18o values ranging mostly from 18o oo to 8o oo pdb and 3o oo to 8o oo pdb respectively precipitated from diluted seawater during shallow burial where sulfate reduction largely controlled pore water bicarbonate composition in contrast the latest septarian cements exhibit very depleted 18o values 16o oo with 13c values approaching values of 1o oo to 3o oo reflecting a strong meteoric water component to pore fluids overall 13c and 18o values are inversely covariant concretion matrix calcite and septarian cements precipitated from mixtures of modified marine and meteoric fluids pore water reversals resulted from sea level fluctuations leading up to and associated with the formation of a sequence boundary or possibly the development of parasequences near the top of the blue hill member relative sea level falls caused pore water freshening as the coastal mixing zone migrated seaward similarly modified marine derived pore waters replaced fresher pore fluids accompanying subsequent marine flooding carbonate cements precipitated during this active hydrologic history recorded the isotopic characteristics of their parent fluids negative 18o values of the meteoric end member calcite compositions suggest derivation from high altitude precipitation in the sevier highlands to the west septarian cements in concretions despite their enclosure in relatively impermeable host sediment can act as sensitive indicators of relative sea level fluctuations

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

petrology chemistry and diagenesis of calcite concretions in silurian shales from central sweden calcite concretions in the lower silurian rastrites shale from central sweden were formed within 1 m depth of the seafloor micrite 1 4 m was formed initially but recrystallized into microspar 4 50 m and subsequently transformed into pseudospar 50 150 m skeletal calcite in the concretions and in the host shale has been replaced by microspar which is chemically similar to that occurring in the concretion body the 13cpdb values mostly between 2 and 2 suggest that carbonates were mainly derived from seawater some of the carbon within calcite was derived from the oxidation of organic matter recrystallization has resulted in increasingly negative 18 opdb values 7 to 4 3 whereas the 13c was not changed significantly

a 1100 year paleoclimatic record from burton bay tarr inlet baffin island pollen studies were carried out in the upper frobisher bay area baffin island as part of joint paleoenvironmental archaeological investigations in the area pollen data from southern baffin island are rare and this paper expands this record a shallow peat section and several recent pollen records are presented they suggest a contrast between an earlier assemblage dated 2000 1650 bp which was characterized by a rich diverse flora especially birch shrubs and a subsequent pollen assemblage dominated by grass pollen and interpreted as representing colder and drier conditions to 900 bp

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

the lightning creek sill complex cloncurry district northwest queensland a source of fluids for fe oxide cu au mineralization and sodic calcic alteration the lightning creek cu au prospect is hosted by a cogenetic suite of plutonic i type granitoids the dominant rock type is a porphyritic quartz monzodiorite that is intruded by more fractionated rocks including monzogranite and alkali feldspar granite a series of flat lying sills are interpreted to be late stage differentiates based on their timing mineralogy and chemistry in parts of the prospect there is pervasive sodic calcic alteration pyroxene after amphibole albite after k feldspar and oligoclase of the plutonic rocks this alteration predates sill emplacement and is unrelated to veining or fracturing of any kind the presence of small amounts of carbonate in the altered rocks suggests that the fluids were co2 bearing quartz and feldspar separates from these altered rocks have oxygen isotope compositions similar to those from fresh quartz monzodiorite suggesting that the fluids were hot and of magmatic composition sodium and ca were added and k fe cl and cu were stripped during what is interpreted as an autometasomatic event the sills display considerable textural and mineralogical complexity and evolved from equigranular quartzofeldspathic rocks aplites with magmatic chemistry to unusual fe rich rocks albite magnetite quartz that exhibit a range of bizarre spherulitic textures some of the albite and magnetite in the sills is secondary albite forms pseudomorphs after k feldspar na fe ca alteration along sill margins and within sills at the contacts between different textural zones halos of disseminated magnetite clinopyroxene fe ca na alteration are developed adjacent to early magnetite veins fluid inclusion studies indicate that these rocks crystallized at temperatures in excess of 500 c and at pressures in excess of 1 5 kbar the range of spherulitic textures is taken to indicate crystallization under hydrous conditions with the episodic release of a fluid phase this magmatic fluid phase was dominated by h2o co2 and chlorine and underwent phase separation into a co2 rich vapor and a hypersaline brine 33 55 wt nacl equiv the hypersaline fluid was enriched in fe 10 wt and cu 1 wt pixe analysis in addition to na k and ca where this fluid was retained within fe rich portions of the sills it caused ca fe na alteration pyroxene albite magnetite growth at the expense of quartz where the fluid was expelled from the sills it produced quartz magnetite clinopyroxene albite veins broadly coeval with the early magnetite veins although rich in cu these granitoid derived magmatic fluids did not generate significant cu au mineralization perhaps because of the high temperatures involved and or a lack of reduced sulfur in the fluids or host rock however the amount of iron present is estimated from the aeromagnetic anomaly to be in excess of 2 000 million tonnes mt a later generation of calcite chlorite pyrite chalcopyrite veins contain traces of cu au mineralization fluid inclusion and stable isotope work indicate that these veins probably crystallized from cooler 200 c more dilute 15 28 wt nacl equiv fluids perhaps generated by the admixture of a meteoric component the conclusions reached in this study have implications for understanding the genesis of fe oxide cu au deposits and related sodic calcic alteration the study indicates the potential for co2 rich granitoid magmas to evolve hypersaline fe and cu rich fluids capable of causing intense magnetite veining and cu au mineralization autometasomatic sodic calcic alteration of the granitoids may be an important precursor to mineralization contributing fe k cu and cl to the magmatic fluids

carbon oxygen and sulphur isotope variations in concretions from the upper lias of n e england carbon oxygen and sulphur isotope data for transects across two pyrite bearmg carbonate concretions and their host sediments from the upper lias of n e england show symmetrical zonation 13cpdb values of the calcite cement 12 9 to 15 4 indicate that most of it originated from organic matter by bacterial reduction of sulphate augmented with marine and to a lesser extent fermentation derived carbonate organic carbon 13cpdb 26 1 to 37 0 reflects the admixture of allochtho nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation two phases of pyrite are present in each concretion the earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34scd values of 22 to 26 indicating formation by open system sulphate reduction the later euhedral phase is more abundant and reaches values of 2 5 to 5 5 at concretion margins this phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system the 13c and 34s data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface the 18o values of the calcite in one concretion 18opdb 2 3 to 4 8 indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater the other concretion is isotopically much lighter 18opdb 8 9 to 9 9 and large 18o differences between concretions in closely spaced horizons imply that local factors control the isotopic composition of pore waters

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

microgranular enclaves as evidence of rapid cooling in granitoid rocks the case of the los pedroches granodiorite iberian massif spain microgranular enclaves from the los pedroches granodiorite lpg los pedroches batholith iberian massif spain have sr nd isotopic and mineral chemical compositions close to those of their host this similarity is not related to restite unmixing as indicated by the igneous textures of the enclaves a number of other geological and geochemical lines of evidence including the high ree and hfse contents of the microgranular enclaves relative to the host granitoid strongly suggest that this similarity cannot be explained by magma mixing alternatively a crystallization process by rapid cooling within the host granitoid magma could explain the geochemical and textural characteristics of the microgranular enclaves including shape grain size mineralogy texture chemistry and sr nd isotopic composition such a crystallization occurred at the walls of the magma conduits through which the granitic magmas were emplaced in the upper crust this process should be considered as an alternative hypothesis to magma mixing for the generation of some microgranular enclaves especially where no direct evidence exists for the presence of basic magmas coeval with granitoids and where there is a lack of isotopic contrast between hosts and enclaves as the process is favoured by feeder dyke related emplacement we suggest that abundance of microgranular enclaves can be related to the mechanism of emplacement of granitoid bodies

mineralogy and geochemistry of microgranular enclaves in palaeoproterozoic malanjkhand granitoids central india evidence of magma mixing mingling and chemical equilibration palaeoproterozoic ca 2 480 ma felsic magmatism of malanjkhand region of central indian precambrian shield referred to as malanjkhand granitoids mg contain xenoliths of country rocks and mesocratic to melanocratic fine grained porphyritic microgranular enclaves me the shape of me is spheroidal ellipsoidal discoidal elongated and lenticular varying in size from a few centimeters to about 2 m across the contact of me with the host mg is commonly sharp crenulate and occasionally diffuse which we attribute to the undercooling and disaggregation of me globules within the cooler host mg the me as well as mg show hypidiomorphic texture with common mineral hbl bt kfs pl qtz assemblage but differ in modal proportions the variation in minerals composition presence of apatite needles elongated biotites resorbed plagiclase ocellar quartz and other mafic felsic xenocrysts strongly oppose the restite and cognate origins of me compositions of plagioclases an3 an29 amphiboles mg mg fe2 0 55 0 69 and biotites mg mg fe2 0 46 0 60 of me are slightly distinct or similar to those of mg which suggest partial to complete equilibration during mafic felsic magma interactions al in amphibole estimates the mg pluton emplacement at ca 3 4 0 5 kbar and therefore magma mixing and mingling must have occurred at or below this level the hbox fe rightleftharpoons hbox mg substitution in biotites of me and mg largely suggests subduction related calc alkaline metaluminous i type nature of felsic melts most major and trace elements against sio2 produce near linear variation trends for me and mg probably generated by the mixing of mafic and felsic magmas in various proportions trace including rare earth elements patterns of me mg pairs however show partial to complete equilibration most likely governed by different degrees of elemental diffusion the available evidence supports the model of me origin that coeval mafic enclave and felsic mg magmas produced a hybrid me magma layer which injected into cooler partly crystalline mg and dispersed mingled and undercooled as me globules in a convectively dynamic magma chamber

patterns and mechanisms of fluvial sediment flux and accumulation in two subarctic fjords nachvak and saglek fjords nunatsiavut canada recent marine sedimentary deposits and river discharge in two subarctic fjords in nunatsiavut northern labrador canada have been studied to elucidate patterns and mechanisms of fluvial sediment transfer and accumulation in the fjords to further our understanding of the longer term sedimentary record multibeam and sub bottom acoustic data and sediment cores were collected in nachvak and saglek fjords within canada s torngat mountains national park as part of the most extensive study of the park s marine resources to date cores were subsampled for x radiography grain size and 210pb 137cs geochronology muddy basin sediments within each fjord are bioturbated indicating circulation of oxygenated bottom water depositional fluxes and inventories of 210pb indicate efficient marine scavenging of 210pb by fine suspended sediments in nachvak fjord with small rivers and steep presently glaciated catchments postglacial and recent sediment accumulation rates are similar implying relatively constant se

new didactyl dinosaur footprints dromaeosauripus hamanensis ichnogen et ichnosp nov from the early cretaceous haman formation south coast of korea abstract didactyl dinosaur footprints in fine grained sandstone of the early cretaceous haman formation namhae area korea are herein described the tracks are 15 cm long and 9 0 cm wide and consist only of impressions of digits iii and iv which show well developed pad impressions digit impressions are narrow about 2 0 cm and terminate in sharp claw traces trackway width is very narrow about 10 0 cm step length is about 92 cm and stride is about 185 cm pace angulation is about 180 i e consecutive tracks are nearly in a straight line the tracks are thought to have been made by a dromaeosaurid characterized by a strongly recurved pes digit ii that did not register on the substrate the didactyl trackway is attributed to a small dromaeosaurid deinonychosauria running bipedally with a speed of 17 5 km h on a lake margin the didactyl tracks described herein as dromaeosauripus hamanensis ichnogen et ichnosp nov represent only the fourth convincing record of didactyl tracks attributable to a member of the deinonychosauria in the world and the first in korea the report also provides significant information about the hip height body size foot morphology walking or running speed paleoecology and paleogeography of dromaeosaurids that flourished during the early cretaceous in northeast asia

climatic and limnological changes associated with the younger dryas in atlantic canada pollen diatom and chironomid fossils from the sediments of a core from brier island bog lake nova scotia were studied in an attempt to relate changes in microfossil composition to a climatic cooling in atlantic canada correlative with the european younger dryas ca 10 to 11 ka our paleolimnological data were then compared to similar types of data from splan pond new brunswick to determine if there were any significant differences between a coastal and a more inland site nonarboreal pollen was dominant throughout the brier island core and the interval 10 0 11 0 ka did not show the typical decline in picea and increases in tundra like vegetation characteristic of many sites in atlantic canada however the limnological indicators did undergo marked changes in taxon composition the chironomid assemblage was initially dominated by shallow water warm adapted chironomid taxa followed by abundant sergentia a cold stenotherm during 10 11 ka sergentia disappeared in the post younger dryas interval and the warm adapted genera resumed dominance chironomid inferred paleotemperature reconstructions revealed that at both brier island bog lake and splan pond summer surface water temperatures dropped abruptly to between 13 and 17 c during the 10 11 ka interval suggesting that a cooler climate was present in atlantic canada correlative with the european younger dryas diatom assemblage changes during the same period corroborate the occurrence of limnological fluctuations

tectonic and sedimentary evolution of a cretaceous continental arc backarc system in the korean peninsula new view abstract this paper focuses on the tectonic and sedimentary evolution of the cretaceous volcanic rocks and nonmarine successions in the southeastern part of the korean peninsula which constitute an ancient continental arc system the arc system gyeongsang arc system comprising an arc platform gyeongsang volcanic arc and a backarc basin gyeongsang backarc basin was a southwestward extension of the japanese arc formed by oblique northward subduction of the proto pacific izanagi plate under the asian continent the backarc basin was initiated in the southeastern part of the korean peninsula in the early cretaceous as a narrow ns trending trough the basin was bounded by a major fault in the northern part of the basin from which sediments largely emanated sediments were deposited in streamflow dominated alluvial fans adjacent to the fault bounded basin margin in the north and low gradient fluvial systems of braided channels that extended southward and southeastward for tens of kilometers sediments were also derived from the western highland margin draining precambrian to jurassic basement rocks the initially narrow trough progressively expanded toward the east resulting in eastward migration of depocenters that eventually generated a broad fluvio lacustrine plain fringing the volcanic arc platform the arc platform played an important role for the derivation of volcanogenic materials and accreted sediments into the backarc basin via extensive fluvial network pyroclastic density currents and landslides which originated from the arc platform also entered the basin in addition extrusion of basaltic volcanic rocks was continual within the basin during basin expansion the resultant succession of mixed sedimentary and volcanogenic rocks is generally indicative of a temporal increase in volcanic activity in the arc platform and in subsidence rate of the basin in the late cretaceous andesitic to rhyolitic volcanism became climactic in the arc platform producing a number of calderas or volcanotectonic depressions volcaniclastic aprons fringing the arc platform encroached upon the basin fill intraarc basins produced by sinistral shearing of the arc platform received sediments from active volcanoes and footwalls of contemporaneous faults forming small scale streamflow dominated alluvial fans and floodplains with later development of a deep lake overall the gyeongsang arc system formed under an extensional or transtensional sinistral strike slip stress regime suggesting that the subducting and the overriding plates were not strongly coupled both the volcanic arc and the backarc basin ceased to develop as volcanic activities shifted progressively eastward in the paleogene accompanied with rollback of the subduction of the izanagi plate

the internal structure of carbonate concretions in mudrocks a critical evaluation of the conventional concentric model of concretion growth abstract carbonate concretions have traditionally been viewed as forming concentrically through the progressive addition of carbonate to the outer edge of the growing concretion this conventional model of concretion growth is based mainly upon center to edge textural and geochemical trends that are consistent with concentric growth however a number of recent studies of concretions in mudrocks have documented complex zonation that is not compatible with the conventional concentric model in some cases complexly zoned concretions contain late stage cements that precipitated throughout the concretion body none of the center to edge relationships used to support the conventional concentric model exclude more complex modes of origin as concretions that fit the conventional model may be the exception rather than the rule high resolution petrographic analysis of concretions should always be used to characterize internal structure and mode of growth prior to interpretation of geochemical and textural data

the diagenetic history of some septarian concretions from the kimmeridge clay england abstract large septarian concretions from the kimmeridge clay up to 1 2 m in diameter have centres comprising anhedral calcite microspar passing into margins of radiating fibrous calcite microspar with a pyrite rich zone at the transition septarian veins formed and were lined with brown calcite synchronously with fibrous matrix growth with white calcite precipitated in septarian cavities after concretion growth ceased septarian veins filled only with white calcite formed later at the same time as the outermost calcite microspar crystals were enlarged the concretions were buried in the late jurassic to about 130 m and in the late cretaceous to about 550 m with uplift between oxygen isotopes show that the concretion grew throughout the first burial with septarian veins forming from about 30 m depth onwards later septarian veins formed between about 200 and 500 m during the second burial carbon isotopes show that the compact inner matrix grew in the sulphate reduction zone the end of which is marked by the pyrite enriched zone dissolving shells and possibly minor methanogenic carbonate slowly diluted sulphate reduction zone carbonate during deeper burial during early concretion growth mg and sr were depleted in the pore water during later stages of the first burial mg sr mn and fe all increased especially after concretion growth ceased during the second burial fe mn and mg decreased as calcite precipitated implying relatively closed systems for these elements synchronous formation of septarian fractures and fibrous calcite matrix shows that the kimmeridge clay became overpressured during the later stages of both burials

tectonic and sedimentary evolution of the korean peninsula a review and new view abstract this review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts late proterozoic neogene in the korean peninsula the korean peninsula is part of the amuria plate and represents an important link between continental blocks of north and south china and the island arcs of japan the basement rocks exposed in the kyonggi and yongnam massifs consist of 2 7 to 1 1 ga high grade gneiss and schist these massifs are separated by the okchon fold belt which comprises metasedimentary rocks and bimodal meta volcanic rocks the stratigraphy of the okchon group is unclear at present the okchon basin was probably initiated as an intraplate rift prior to the late proterozoic the hwanggangri formation clast bearing phyllite most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin the stratigraphic relationship between the okchon group and the choson supergroup cambro ordovician of the taebaeksan basin is poorly constrained the choson supergroup unconformably overlies the yongnam massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments reflecting numerous sea level fluctuations the sequence is disconformably overlain by siliciclastic sequence of pyongan supergroup carboniferous triassic which formed most likely in shallow marine deltaic and fluvial environments the imjingang belt is an east trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics devonian carboniferous underlain unconformably by proterozoic basement rocks late proterozoic amphibolites of oceanic affinity were metamorphosed at about 8 13 kbar and 630 740 c during the late permian to the early triassic the south vergent contraction and top down to the north normal faulting are suggestive of a suture belt between the north china block sino korea craton and the south china block yangtze craton an extension of sulu belt across the yellow sea entire peninsula experienced strong deformation and metamorphism during the suturing event namely songrim orogeny during this orogenic event the kyonggi massif and the okchon basin accreted to the yongnam massif and taebaeksan basin along the south korean tectonic line running northeast southwest a series of northward trending thrust formed along the boundary zone to the east kaktong and kongsuwon thrusts and others piggyback basins locally developed along the thrust faults forming the taedong group the crustal deformation resumed in the early to late jurassic daebo event under contractional setting dextral ductile shearing associated with thrusting and folding continued in the mid southern part of the peninsula it was due to orthogonal northwestward subduction of the izanagi plate under the asian continent the yongnam massif experienced continuous dextral offset along the honam shear zone in the early cretaceous the izanagi plate began to subduct northward and caused formation of strike slip basins in retroarc setting i e kyongsang basin in the southeastern part and a number of small scale basins in the mid southwestern part of the peninsula small scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions extensive intrusion of granitoids occurred from triassic to early tertiary with a gap between 160 and 100 ma representing continental magmatic arc in the tertiary the southeastern margin of the korean peninsula experienced back arc opening pull apart basins formed in the miocene bounded by the yangsan and hupo faults the yonil group sedimentary fill of the pohang basin comprises more than 1 km thick siliciclastic sequence which represents deposition in fan delta systems on the hanging wall of the yangsan fault thick more than 10 km thick sediments in the ulleung basin margin were deformed in the late miocene due to the northward movement of kyushu block quarternary volcanic events in cheju island represent intraplate hot spots

microbial processes controls on the shape and composition of carbonate concretions abstract shape size and mineralogical chemical compositions of carbonate concretions vary considerably the questions to be answered are why do they form at all what processes are involved why do they so often form as regular spheroids why do they sometimes form laterally extensive bands what controls whether the mineral composition is calcite dolomite rhodochrosite or siderite or mixtures of them the questions are addressed and the answers illustrated by selected examples carbonate precipitation is the result of the sedimentary system exploiting the potential energy provided by juxtaposing oxidised detrital input with reducing agents organic matter microbes take advantage of the energy source and are believed to be involved in most of the various processes pore waters in steadily accumulated sediments show a depth related succession of chemical and carbon stable isotope compositions this results from degradation of organic matter proceeding via an orderly succession of processes during burial each mediated by a specific microbial group aerobic oxidation using dissolved oxygen occurs first followed by mn iv reduced to mn ii as the oxidant fe iii reduction and sulphate reduction are probably more significant methanogenesis is the final deepest microbial process the common product of all these reactions is co 2 or dissolved hco 3 which can result in carbonate supersaturation the specific process controls the chemical and isotopic compositions of pore water and leads to a characteristic mineralogy of any carbonate precipitated however the processes may not proceed successively and localised micro environments occur recent work on siderite concretions in very young salt marsh sediments norfolk u k has shown that microbial populations are not homogeneously distributed and that these localise and control concretionary growth concretions in ancient rocks can be described in terms of the same processes observed in modern sediments laterally extensive siderite bands in bullhouse quarry westphalian u k resulted from interaction of two sets of complementary processes shallow manganese and iron reduction coupled with deeper methanogenesis and decarboxylation the model is supported by a mass and charge balance calculation similar complementary processes formed spheroidal concretions gammon shale usa but there is evidence that the outer shell of the concretion formed before the inner core and in the absence of a core the shell was crushed by burial compaction the spheroidal form resulted from diffusion of reactive components controlled by the relative rates of the contributory processes calcite or dolomite analogues of the siderite concretions are formed by similar processes but inhibition of carbonate precipitation makes it impossible to use an equilibrium mass balance model kimmeridge bay uk dolomite ledges are marine analogues to the bullhouse examples for the pyrite rimmed calcite jet rock concretions early jurassic yorkshire u k the rate of production of sulphide from sulphate reduction locally exceeded availability of fe ii to precipitate pyrite outward diffusion of sulphide produced the characteristic spheroidal shape of the concretion because of their developmental pattern bedded concretions are more likely to preserve a sequence of diagenetic cements which record the history of pore water evolution however all represent an expression in ancient rocks of microbiological processes similar to those operating today

reconstructed ice flow patterns and ice limits using drift pebble lithology outer nachvak fiord northern labrador reply the geology of outer nachvak fiord provides an opportunity to differentiate lithologies originating in the churchill structural province central and inner fiord from those in the sedimentary ramah group and the nain structural province outer fiord as a result the distribution of glacial erratics from the central and inner fiord depicts the former presence of regional laurentide ice in the outer fiord whereas the distribution of glacial deposits characterized by locally derived lithologies delimits the area of local glacier expansion based upon these criteria the suggestion is made that regional ice at some time covered the deeply weathered mountain summits 900 m asl in outer nachvak fiord a later advance confined to the fiord and valleys deposited the highest moraines and till 180 115 m asl recorded in the area on the basis of geomorphic relationships this advance is considered a discrete glacial event separate from a later glaciation that was responsible for moraines and sediments at lo

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

distribution and compositions of magmatic inclusions in the mount helen dome lassen volcanic center california insights into magma chamber processes abstract variations in spatial abundances compositions and textures of undercooled magmatic inclusions were determined in a glaciated pleistocene lava dome mt helen 0 6 km3 at the lassen volcanic center lvc southernmost cascades spatial variations were determined by point counting at 86 locations separated by 100 m on the dome major and trace element compositions of host rocks and inclusions at 12 locations along the flow length of the dome were obtained important results include the following 1 inclusion abundances range from 3 19 vol with the highest values generally located along the little eroded northwestern margin and flow front of the dome 2 host rock compositions are markedly uniform across the dome 65 4 0 4 wt sio2 indicating that the degree of inclusion disaggregation was uniform despite large spatial variations in inclusion abundances 3 inclusion sizes range from a maximum of 1 m across to mm sized crystal clots of phenocrysts plus adhering ca rich plagioclase microphenocrysts 4 inclusions have variable macroscopic textures indicating that partial undercooling both prior to and following entrapment in cooler dacitic host magma were important processes 5 inclusions are variably fractionated magmas with large variations in ni 79 11 ppm and cr 87 7 ppm contents that are lower than presumed mantle derived melts furthermore large ranges in incompatible trace elements indicate that inclusion compositions also reflect deep processes involving either melting of variable mantle source rocks or assimilation fractional crystallization 6 inclusions are variably mixed magmas 56 61 wt sio2 that contain up to 50 host dacitic magma 7 correlations between ni and cr contents in hosts and inclusions from individual outcrops indicate that the effect of inclusion disaggregation and magma mingling on host dacitic magma was local e g these features are interpreted to reflect protracted recharge of diverse composition mafic magmas into the base of a shallow magma reservoir containing a lower layer of compositionally evolving hybrid mafic magma and an upper layer of rhyodacitic magma complex interactions among magmas in the upper and lower layers resulted in formation of mafic inclusions by both pre and post entrapment undercooling mechanisms followed by buoyant rise and accumulation near the roof of the reservoir the main stage of inclusion disaggregation probably occurred in the conduit during eruptive ascent and largely ceased upon surface eruption we infer that endogenous growth concentrated inclusions along the margins and top of the dome as more inclusion poor dacite was progressively tapped from deeper regions of the reservoir

upper cretaceous vernal delta of utah depositional or paleotectonic feature a conspicuous seaward bulge of the middle to late turonian shoreline of the cretaceous seaway in northeastern utah and southwestern wyoming has been identified by previous authors as the vernal delta strata of the frontier formation and the ferron sandstone member of the mancos shale that form the vernal delta consist largely of fluviodeltaic facies the delta however is not recognizable as a locus of turonian sedimentation there is no isopach thick associated with it the vernal data is a large feature encompassing an area of at least 6250 mi sup 2 16 187 km sup 2 a comparison between the depositional setting and paleogeography of northeastern utah during the late cretaceous and a present day area on the east flank of the andes in colombia indicates strong similarities further comparison suggests that feature the size of the vernal delta could not have been produced by a single river the vernal delta overlies the ancestral uinta mountain uplift an area where cenomanian marine shales were entirely removed by what appears to have been submarine erosion during early turonian time when the shoreline prograded eastward across this area during middle uronian time the sediment load caused the area to subside but at a rate slowermore than rates of subsidence to the north and south this differential subsidence is the cause of the shoreline bulge although it includes deltaic facies the vernal delta is not a delta per se but a feature produced as the result of interaction between sedimentation and gentle tectonic movement of the ancestral uinta mountain uplift less

latest pleistocene and holocene glaciation of baffin island arctic canada key patterns and chronologies abstract melting glaciers and ice caps on baffin island contribute roughly half of the sea level rise from all ice in arctic canada although they comprise only one fourth of the total ice in the region the uncertain future response of arctic glaciers and ice caps to climate change motivates the use of paleodata to evaluate the sensitivity of glaciers to past warm intervals and to constrain mechanisms that drive glacier change we review the key patterns and chronologies of latest pleistocene and holocene glaciation on baffin island the deglaciation by the laurentide ice sheet occurred generally slowly and steadily throughout the holocene to its present margin barnes ice cap except for two periods of rapid retreat an early interval 12 to 10 ka when outlet glaciers retreated rapidly through deep fiords and sounds and a later interval 7 ka when ice over foxe basin collapsed in coastal settings alpine glaciers were smaller during the younger dryas period than during the little ice age at least some alpine glaciers apparently survived the early holocene thermal maximum which was several degrees warmer than today although data on glacier extent during the early holocene is extremely sparse following the early holocene thermal maximum glaciers advanced during neoglaciation beginning in some places as early as 6 ka although most sites do not record near little ice age positions until 3 5 to 2 5 ka alpine glaciers reached their largest holocene extents during the little ice age when temperatures were 1 1 5 c cooler than during the late 20th century synchronous advances across baffin island throughout neoglaciation indicate sub milankovitch controls on glaciation that could involve major volcanic eruptions and solar variability future work should further elucidate the state of glaciers and ice caps during the early holocene thermal maximum and glacier response to climate forcing mechanisms

geochemistry and u pb shrimp zircon chronology of granitoids and microgranular enclaves from jhirgadandi pluton of mahakoshal belt central india tectonic zone india abstract the northern part of central india tectonic zone citz is delineated by an arc shaped supracrustal belt commonly referred to as mahakoshal belt which is considered as a product of intense rifting of sialic crust that occurred at ca 2400 2600 ma several granitoid plutons intrude the parsoi formation of mahakoshal belt among these an elliptical small stock like granitoid body trending e w is exposed in and around jhirgadandi region of mahakoshal belt referred herein as jhirgadandi pluton it is composed of minor amount of mafic rocks diorite and predominant granitoids country rock pelitic xenoliths and microgranular enclaves me are commonly hosted in granitoids but are absent in diorite the me exhibit typical magmatic texture with a bt cpx hbl pl kf qtz mag ap assemblage similar to that in host granitoids but with contrasting mineral proportions whole rock molar al 2 o 3 cao na 2 o k 2 o a cnk ratios of diorite 0 63 0 72 me 0 69 1 21 and granitoids 0 83 1 05 suggest their nature largely metaluminous i type to rarely peraluminous s type granitoids on most binary plots involving silica two distinct compositional paths can be recognized one formed by an array of differentiating diorite and me and another by fractionating granitoids gradually depleting in compatible elements it is most likely that me were generated by progressive and concurrent mixing of coeval pristine mafic diorite and granitoid magmas and fractionation processes however coherent and identical trace elements except for sr th y and ni and ree patterns for me granitoid pairs most likely suggest partial to near complete chemical equilibration through varying degrees of diffusion process across the me partly crystalline host granitoid boundary high precision u pb shrimp zircon 206 pb 238 u ages for me 1758 19 ma and host granitoid 1753 9 1 ma from jhirgadandi pluton further support the notion that they were coeval the obtained age 1750 ma of jhirgadandi pluton also points to the existence and role of super columbian continental component in the evolution of mahakoshal belt of the citz

soft sediment deformation structures in a lacustrine sedimentary succession induced by volcano tectonic activities an example from the cretaceous beolgeumri formation wido volcanics korea abstract the cretaceous beolgeumri formation is composed of laminated mudstones intercalated with sandstones chert and a bed of lapilli tuff that were deposited in a lacustrine environment at the terminal part of a regional strike slip fault systems on the southwestern korean peninsula the beolgeumri formation contains various types of soft sediment deformation ssd structures that are characterized by a wide extent

elemental and sr nd isotope geochemistry of microgranular enclaves from peralkaline a type granitic plutons of the emeishan large igneous province sw china abstract microgranular enclaves are common within intermediate to felsic granitic rocks that have i and s type affinity however they are rare within alkaline anorogenic granitoids of a type affinity the permian 260 ma emeishan large igneous province elip of southwest china contains two peralkaline silica saturated a type granitic plutons that host microgranular enclaves the enclaves from the baima pluton are intermediate in composition and have lower sio 2 and higher tio 2 cao and mg sio 2 57 2 to 63 0 wt tio 2 0 8 to 1 8 wt cao 1 7 to 3 3 wt mg 28 to 44 than their host sio 2 62 6 to 67 8 wt tio 2 0 5 to 1 4 wt cao 0 4 to 1 8 wt mg 15 to 31 the enclaves from the taihe pluton are more felsic sio 2 63 8 to 71 3 wt tio 2 0 3 to 0 6 wt cao 0 6 to 2 3 wt mg 8 to 22 but are still less evolved than their host sio 2 69 8 to 75 1 wt tio 2 0 2 to 0 6 wt cao 0 4 to 0 8 wt mg 3 to 12 in both cases the enclaves have very similar end t values baima end t 2 8 to 3 2 taihe end t 1 0 to 2 0 as their hosts baima end t 3 0 to 3 2 taihe end t 1 5 to 1 9 the major and trace element trends of the enclave host pairs suggest that fractional crystallization occurred and that element diffusion was likely minimal the enclaves are interpreted as entrained accumulations of early formed crystals of a silicic magma which was originally produced by fractional crystallization of a mafic magma

cosmogenic 10be and 26al ages for the last glacial maximum eastern baffin island arctic canada a chronology for the last glacial maximum based on cosmogenic exposure dating in the pangnirtung fjord area eastern baffin island arctic canada is at odds with many decades of land based glacial stratigraphic research most previous chronologies focused primarily on relative weathering criteria and suggested that ice extent was restricted during the late wisconsinan ca 24 8 ka in contrast by directly dating glacial features we conclude that late wisconsinan ice was far more extensive than previously believed there are 36 gneissic boulders and 8 samples of ice molded gneissic bedrock that yield late wisconsinan 10 be and 26 al exposure ages for the last glaciation of pangnirtung fjord the prominent duval moraines which were previously interpreted to represent a significant early wisconsinan 100 60 ka ice advance on southern cumberland peninsula were actually deposited between 24 and 9 ka two boulders from a raised glaciomarine delta stratigraphically related to the duval moraines date to about 10 ka two recessional moraines and striated bedrock along pangnirtung fjord as well as erratics on the floor of the kolik river valley a tributary to pangnirtung fjord indicate that deglaciation began between 12 and 9 ka in situ produced 10 be and 26 al abundances indicate that ice filled pangnirtung fjord for about 15 k y either continuously or intermittently prior to 10 ka which is compatible with 14 c chronologies for adjacent cumberland sound thus our data support other recent studies that suggest the northern and southern margins of the laurentide ice sheet were generally in phase during the latest wisconsinan contrary to earlier interpretations

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

wisconsinan late glacial environmental change on the southeast baffin shelf southeast baffin island and northern labrador the importance of the baffin labrador region is explained in terms of the channelling through this area of the mass flux of meltwater from the laurentide ice sheet and the probable effects of this on the thermohaline circulation of the north atlantic the chronology of glaciation and deglaciation in the region is summarised reference is made to recent marine records from the baffin shelf isotopic changes recorded in foraminiferal assemblages obtained from marine sediments in the baffin shelf labrador sea area indicate the timing and possible magnitude of meltwater fluxes during the period 14 0 11 0 ka bp

reconstructed ice flow patterns and ice limits using drift pebble lithology outer nachvak fiord northern labrador discussion on the basis of their analysis of pebble lithologies and age estimates of marine shells the authors presented an interpretation for late quaternary events in outer nachvak fiord that they sav is incom atible with the late wisconsinan ice model of f k k and osh josenhans et al 1986 clark 1988 we believe that much of their data when reinterpreted do not conflict with our reconstruction and in fact can be accommodated by our reconstruction in contrast our data from nachvak fiord and the adjacent continental shelf are not compatible with their hypotheses nor have they directly addressed these data in their hypotheses in this discussion we will evaluate the clast morphologic and chronologic data used by the authors to develop their hypotheses we also summarize our work related to the glacial history of nachvak fiord and the adjacent shelf for the purpose of discussion and comparison with their hypotheses

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

abrupt changes in marine conditions sunneshine fiord eastern baffin island nwt during the last deglacial transition younger dryas and h 0 events

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

glacial geomorphology and chronology in the selamiut range nachvak fiord area torngat mountains labrador the summits of the selamiut range are the highest in the torngat mountains of northern labrador and contain some of the only permanent ice bodies of the eastern canadian mainland as they may have constituted a physical barrier to ice moving eastward from the ungava ice dispersal centre their glacial history is elaborate in a regional context consequently a complex interaction of local and regional ice masses is manifest in the morphochronological record dating from the late quaternary through the holocene physiographically the selamiut range is a plateau dominated by deep cirques and cirque outlet valleys with precipitous bounding rock walls colluvial processes are extremely active and consequently many surficial units have been extensively remodelled in dynamic landscape systems the northern half of the field area contains a wealth of glacial and periglacial landform assemblages and former local and regional ice activity has been determined from the cross cutting relationships of certain morainic features within the mccornick river valley a sequence of shorelines documents the depths and extent of ice dammed lakes during glaciation a further 33 metre marine limit demarcates former sea level during the final glaciation of the area three glaciations or stillstands are suggested for the field area after consideration of the landform evidence and are named the ivitak nachvak and superguksoak glaciations the adoption of a 1 5 cm ka soil development rate dates the three glaciations or stillstands for the selamiut nachvak area the ivitak glaciation at 40 ka the nachvak glaciation at c 23 ka and the superguksoak i glaciation at 10 12 ka b p two further neoglacial events were restricted to the cirque basins and are correlated locally by a combination of pedology lichenometry and morphologic superimposition a number of chronocorrelative inferences are made for northern labrador based upon the existing empirical data glacial styles appear to differ quite considerably from fiord to fiord along the coastal section of the torngat mountains the solution of discrepancies within the general northern labrador chronology resides in the successful construction of an absolute dating framework for the marine limits of the region relative chronologies may then attain a significant applicability

felsic enclave swarms in the gouldsboro granite coastal maine a record of eruption through the roof of a silicic magma chamber prominent zones of large globular fine grained felsic enclaves occur at the highest exposed levels of the gouldsboro granite along the coast of maine the physical characteristics of these enclaves and their chemical relations to the host granite indicate that they represent globules of resident magma that were trapped probably during eruption in the crystal mush at the top of the magma chamber these zones can appropriately be termed eruption trails enclave compositions provide a record of magma compositions within the chamber at the time of eruption they fall into two groups high k and low k with similar wt sio2 suggesting that magma in the chamber consisted of discrete compositional batches the distribution of these two types of enclaves within the swarms is consistent with the low k source magma residing as a layer beneath the high k source magma chilled and vesiculated inclusions of basalt occur only in the low k enclaves their presence there suggests that basaltic magma was injected

glacial geology of the torngat mountains labrador two late quaternary alloformations are identifed throughout the torngat mountains by degree of soil profile development in till with a granitic composition morphologic expression of deposits and their relative areal distribution the two alloformations are interpreted to represent two successively limited glaciations of the torngat mountains by the laurentide ice sheet deposits of the shoal cove alloformation mantle hillslopes distal to deposits of the younger saglek alloformation deposits are primarily soliflucted till found around coastal regions soils developed in till of the shoal cove alloformation are characterized by well expressed bw horizons 19 cm thick deposits of the younger saglek alloformation are characterized by prominent well preserved moraines outwash fan surfaces and ice marginal channels soils described in till are poorly developed with a horizons directly overlying cox horizons or separated from cox horizons by thin transitional ac ca horizons or poorly expressed bw

diatom shifts as evidence for recent subarctic warming in a remote tundra lake nwt canada abstract changes in diatom assemblage composition were examined from the sediments of slipper lake an isolated tundra lake located 50 km north of current treeline in canada s northwest territories diatom shifts over the last ca 5600 years were related to the response of this ecosystem to climatic and environmental change during the late holocene with particular emphasis on the last few hundred years to date a detailed diatom analysis for this recent time frame has not been undertaken for the central canadian subarctic the first ca 5400 years of the sediment record was marked by modest shifts between benthic alkaliphilous diatom taxa e g fragilaria achnanthes and navicula species and heavily silicified tychoplanktonic aulacoseira species in the 19th century abrupt changes were delineated by a marked shift to a diatom assemblage characteristic of more planktonic habitats consisting of the cyclotella stelligera complex c stelligera c pseudostelligera which was absent in earlier sediments several possible mechanisms for these recent changes are examined including atmospheric deposition of acidifying compounds and anthropogenically derived nutrient enrichment however we conclude that climatically induced limnological changes associated with shorter duration of ice cover and a longer growing season can best explain the direction and magnitude of changes in our diatom record

paleolimnology of a shrub tundra lake and response of aquatic and terrestrial indicators to climatic change in arctic quebec canada to better understand past aquatic ecosystems and their development a 99 cm sediment core was extracted from a shrub tundra lake in northern quebec fossil chironomids diatoms and pollen were analysed at 1 0 cm intervals several inference models based on chironomids and diatoms were used to reconstruct lake water conditions surface water temperature dissolved organic carbon doc alkalinity and water colour for the last 6700 cal yr reconstructed water temperatures varied between 10 3 and 17 6 8c with a cooling trend since at least 1500 cal yr bp doc concentrations increased with the establishment of terrestrial vegetation in the lake s catchment and decreased with the onset of the late holocene cooling trend lake water alkalinity was higher during the lake s early history and decreased throughout its postglacial development whereas water colour remained at fairly low levels throughout the entire record our results suggest that aquatic organisms directly influenced by temperature chironomids reacted most rapidly to climatic changes whereas terrestrial vegetation pollen reacted with a slight lag the vegetation succession in the catchment had subsequent impacts on the composition of runoff waters and hence on other aquatic organisms diatoms d 2004 elsevier b v all rights reserved

early holocene glacial lake meltwater injections into the labrador sea and ungava bay 1 in this paper we analyze drainage routes and estimate fluxes of meltwater released from labrador ungava glacial lakes into the labrador sea ungava bay and hudson bay between 7 5 and 6 0 kyr bp 8 4 7 0 calendar cal years ka the analysis and estimates are based on landform based reconstructions of the laurentide ice sheet lis decay pattern and the associated glacial lake evolution geomorphological data constraining the spatial extent of glacial lakes are coupled to a digital terrain model for meltwater volume calculations the lis ice recession between 7 5 and 6 0 kyr bp led to the formation of a large number of glacial lakes which drained in approximately 30 meltwater pulses with fluxes exceeding 0 015 sv 1 sv 106 m3 s 1 into labrador sea ungava bay and hudson bay the inferred rapid ice margin retreat during late stages of deglaciation indicates that these drainage events were relatively short lived the early holocene glacial lakes of labrador ungava released meltwater resulting in a total inflow of 6000 km3 freshwater to the north atlantic the pulsed nature of meltwater release from the lakes is likely to have resulted in rapid repeated cooling of the labrador sea surface water

recent arctic marine diatom assemblages from bottom sediments in baffin bay and davis strait abstract this study investigates the present geographical boundaries and environmental limits of the diatom flora in the baffin bay and davis strait area seventy four sea floor surface samples were examined the raw data were analyzed with the cabfac factor analysis program five factor assemblages explaining 87 of the observed variance emerged from this test the statistically most important assemblage is the baffin current assemblage composed ofthalassiosira gravida spores the second assemblage is the summer pack ice assemblage consisting ofactinocyclus curvatulus with a lesser contribution ofthalassiosira trifulta a third assemblage dominated bythalassiosira hyalina is located along the southwest coast of greenland indicating low ice concentration the fourth assemblage consists ofporosira sp spores and indicates fast ice conditions the fifth assemblage is dominated bythalassionema nitzschioides andporosira glacialis vegetative cells and indicates the coastal environment diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses such as salinity and ice conditions these findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments

shape and microstructure of microgranitoid enclaves indicators of magma mingling and flow abstract at tarandore point 328 km south of sydney new south wales australia two tonalite phases are in contact with a gabbroic diorite all belonging to the moruya batholith lobate to crenulate contacts pillowing of the more mafic phase in the more felsic phase net veining of the more mafic phase by the more felsic local chilling of the more mafic phase against the more felsic and an abundance of rounded to elongate microgranitoid enclaves all suggest mingling of magmas at the site of emplacement therefore all phases were emplaced before the others solidified and an order of intrusion cannot be determined the variety of microgranitoid enclaves suggests that repeated magma mingling has occurred linear geochemical trends indicate either magma mixing or restite unmixing as a prime cause of variation in the members of the moruya suite of granitoids direct evidence of mixing is not present but evidence that the magmas were substantially liquid at the time of emplacement sugests that mixing is possible restite unmixing is unlikely to be the prime process because near minimum melts which would occur in all granitoid phases according to that model should mix easily rather than mingling in fact mingling has occurred between tonalite phases of very similar composition which would not be expected if the liquid parts of enclaves were minimum melts available experimental and theoretical data on mixing in both magma chambers and conduits cannot be applied directly to the occurrence at tarandore point owing to inadequately constrained parameters but mixing generally should be favoured by higher temperatures which is consistent with our inference that relatively high proportions of melt were present in the granitoid phases at the time of emplacement conduit mixing may be reflected in a local zone of strong to extreme elongation of enclaves in which the distortion has been accomplished by magmatic flow without solid state deformation as evidenced by strong dimensional preferred orientations coupled with a lack of microstructural evidence of intragranular plastic strain this suggests that elongate enclaves should not be used as indicators of solid state deformation or as tectonic strain markers without microstructural evidence that suitably strong intracrystalline plastic deformation has taken place

magma mixing and the production of compositional variation within granite suites evidence from the granites of southeastern australia granite suites are groups of plutons possessing characteristic features that are a result of their derivation from source material of a specific composition variation within suites has been ascribed to a variety of processes magma mixing or mingling is a popular hypothesis generally proposed in terms of blending between a crustal melt and mafic material from the mantle that caused that melting when the compositions of pain of suites from the bega batholith of southeastern australia are compared any differences seen at either end of the range in composition are also seen at the other limit so that both the most mafic and mostfelsic rocks show similar relative abundances of particular elements similar relationships are seen for other granites in the region these observations are not consistent with largescale magma mixing or mingling and although those processes may operate on a small scale they cannot have been responsible for the major compositional variations likewise assimilation of country rocks had no significant role in producing variation in the granites of southeastern australia the production of variation by differential separation of melt from residual solid source material or restite must be favoured for many of the granite suites of this region

application of the restite model to the deddick granodiorite and its enclaves a reinterpretation of the observations and data of maas et al 1997 mafic s type granites of the lachlan fold belt always contain a introduction distinctive suite of enclaves dominated by schists and gneisses of high maas et al 1997 have proposed complex models of metamorphic grade generally with lesser numbers of microgranular crustal melting and magma mixing to account for the enclaves maas et al 1997 journal of petrology 38 chemical and isotopic features of several kinds of enclaves 815 841 recently described enclaves from the s type deddick in the s type deddick granodiorite of the lachlan fold granodiorite they concluded that the metasedimentary enclaves belt lfb exposed at mckillops bridge that grancould be either source lithologies or accidental xenoliths and that odiorite is a member of the bullenbalong suite area the most common microgranular enclaves formed as globules of 3100 km white chappell 1988 itself part of the hybrid magma that mingled with the host magma all features of very extensive and slightly more diverse bullenbalong the metasedimentary enclaves are consistent with an origin as lithic supersuite total area 8750 km plus 4000 km of restite fragments from the source and their ubiquity in the mafic svolcanic rocks it occurs near the southern extremity of type granites and their rarity in both felsic varieties and in i type those granites these are the rocks that have been used granites conform with such an origin the argument that these as primary examples of restite and of the restite model enclaves are not in chemical equilibrium with the host granite in s type granites hine et al 1976 white chappell because they do not complement its composition is not valid as they 1977 chappell et al 1987 chappell 1996b and the represent less fertile parts of the source that did not melt to the point enclosed enclaves have been regarded by us as lithic of disaggregation unaltered cores of microgranular enclaves in the restite white chappell 1988 chen et al 1989 s type granites have compositions that do not match those of any chappell white 1991 white et al 1991 wyborn known igneous rock and an origin by metamorphism of a calcareous et al 1991 sediment is probable partial melting during that metamorphism maas et al 1997 mostly reject the presence of restite accounts for the pseudo igneous textures seen in these enclaves enclaves in the deddick granodiorite however the

late deglaciation of the central labrador coast and its implications for the age of glacial lakes naskaupi and mclean and for prehistory the age of the marine limit and associated deglaciation has been estimated from relative sea level curves for the hopedale and nain areas of the central labrador coast as approximately 7600 200 and 8500 200 yr ago respectively these ages indicate that the ice margin remained on the coast for up to 3000 yr longer than previously estimated because the central coast is due east of glacial lakes naskaupi and mclean the earliest the lakes could have formed was 8500 200 yr ago with their largest phases being fully established only after 7600 200 yr ago this suggests that the age of the lakes and associated deglaciation of the central labrador ungava region is younger by at least 1500 yr than previously estimated a late glacial marine based ice mass in ungava bay that dammed the lakes collapsed ca 7000 yr ago within this time frame therefore the glacial lakes only existed for 500 yr the persistence of the laurentide ice sheet margin on the central labrador coast until 7600 yr ago probably restricted the northward movement of early prehistoric people into northern labrador

low latitude sea surface temperatures for the mid cretaceous and the evolution of planktic foraminifera isotopic data from exceptionally well preserved foraminifera show that the subtropical north atlantic had sea surface temperatures ssts between 30 and 31 c during the late albian and early cenomanian these temperatures were warmer than average modern temperatures in the tropical western atlantic and support previous inferences based on diagenetically suspect material of albian tropical ssts of 30 c this finding is consistent with basic theories of oceanic thermal response in the tropics to the high atmospheric carbon dioxide levels during the middle cretaceous greenhouse however our data do not support the concept of a super tethyan region of hypersaline waters in the western north atlantic during late albian and early cenomanian time because seawater salinities substantially higher than modern ones would require significantly higher ssts than those reported here isotopic analysis of mid cretaceous planktic foraminifera shows that planomalina ticinella and biticinella grew in surface waters and provide isotopic proxies for sst whereas deeper growing species include hedbergella rotalipora and praeglobotruncana none of these taxa display isotopic indications of photosymbiosis suggesting that this ecology did not evolve in planktic foraminifera before the late cretaceous contrary to previous hypotheses none of these species increased their depth habitat during their life cycles unlike many extant planktic foraminifera the rotaliporids may have been preferentially susceptible to extinction during oceanic anoxic events because they lived within or below the thermocline for most of their life cycles

evolution of the late cretaceous dadaepo basin se korea in response to oblique subduction of the proto pacific izanagi kula or pacific plate abstract the dadaepo basin is a small late cretaceous sedimentary basin in se korea located on the eastern margin of asia the basin is an isolated extensional basin situated between the nne striking yangsan and dongnae faults the basin fill sediments named the dadaepo formation consist of channelized conglomerates and sandstones intercalated with dominantly purple mudstones in the lower part the upper part is dominated by fine to coarse grained tuffaceous sandstones and olive to dark gray mudstones with abundant volcanic interbeds the formation unconformably overlies dacitic rocks dated at ca 94 ma and is overlain by basaltic andesite dated at ca 69 ma ar ar ages the overall configuration of the strata of the dadaepo formation indicates syndepositional tilting of the basin floor to the north northeast a number of outcrop scale faults are observed in the basin fill sediments of which the majority are nw striking normal faults including syndepositional growth faults the orientations of mafic magmatic and clastic dikes interpreted as being approximately contemporaneous with the deposition of the dadaepo formation are also nearly parallel to the strikes of outcrop scale normal faults all these extensional structures consistently indicate ne sw extension of the basin and obliquely intersect the basin bounding yangsan and dongnae faults at angles of 40 60 it is thus concluded that the dadaepo formation was deposited in a pull apart basin that subsided as a result of nne striking sinistral strike slip faulting in the southeastern part of the korean peninsula during the campanian late cretaceous this strike slip faulting was related to north northwestward oblique subduction of the proto pacific izanagi kula or pacific plate under the eastern margin of the eurasian plate

late quaternary chronology and environments of square lake torngat mountains labrador sediment pollen and diatom records from square lake a small lake dammed by a segment of saglek moraine cover the period of deposition of and deglaciation from the saglek moraine the basal radiocarbon date 18 210 1900 years bp is on sediment contaminated by reworked pollen and is thus a maximum age however the date was measured on organic carbon recovered from glaciolacustrine couplets associated with deposition of the saglek moraine and thus establishes a late wisconsinan age for the saglek moraine vegetation on the ice free upland surrounding square lake at this time was a sparse tundra vegetation dominated by grasses and herbs the absence of diatoms indicates perennial lake ice cover a major transition is recorded by pollen and diatoms at 8 5 ka vegetation probably remained sparse tundra but birch and willow may have arrived in the area by 8 ka diatoms are first dominated by alkaliphil species reflecting continued influence of glaciolacustrine sedimentation an abrupt change in depos

occurrence and origin of the zoned microgranular enclaves mes within the cretaceous granite in taejongdae se korea abstract microgranular enclave me is a common feature in granitic intrusive rocks however the zoned me that developed in the outcrop of cretaceous granite in the taejongdae geopark busan represents an interesting phenomenon in formation of zoned mes providing useful petrogenetic information on the formation of enclaves in this study we define the zoned me as an enclave composed of several contrasting orbicular rock zones due to the importance of the enclaves in the evolution of igneous rocks this study aims to understand the formation mechanism of the zoned mes including the reasons for their diversity in the study area the investigated mes in the study area have trachi andesitic to dioritic composition mainly composed of amphibole plagioclase and quartz with minor orthoclase and opaque minerals to achieve the above objectives the relationship between the mes and the host granite and the difference between zones were investigated based on petrological and geochemical studies the mes can be classified into two main types simple type composed of a single rock type has an angular shape and sharp or sometimes crenulated contact with the host granite and zoned type composed of several zones has a circular to elliptical shape and shows two different cooling processes the mineral composition of the simple mes shows some similarity with the zones of the zoned mes these results imply that the zoned mes are formed by two different phases of mixing and mingling in two different magma chambers firstly in a deep dioritic magma chamber 7 1 7 7 km and then in a shallower depth granitic magma chamber 1 7 2 4 km in the other hand the simple mes mainly represent xenoliths but also possibly resulted from disruption of early formed zoned mes before they solidified this study is therefore could be useful in the understanding of the possible mechanisms for the formation of mes and the magmatic evolution in this area

early holocene glacial lakes and ice marginal retreat pattern in labrador ungava canada abstract the existence of glacial lakes naskaupi mclean minto melezes and wapussakatoo during the deglaciation of labrador ungava canada was recognized at the end of 1950s however glacial lakes have seldom been included in regional reconstructions to constrain the outline of successive ice margins during the glacial retreat in labrador ungava reconstruction of the ice flow succession in labrador ungava has often primarily focused on till lineation systems these reconstructions often depict a late glacial ice dispersal center situated over central labrador ungava more recent studies on glacial geomorphology including meltwater features however suggest that north central labrador ungava exhibited cold based conditions at least during the latest deglaciation cold based conditions inhibit basal sliding and formation of landforms except for meltwater traces such as meltwater channels glacial lake shorelines and deltas this situation implies that meltwater traces are the main source of information when reconstructing the spatial retreat pattern during a cold based deglaciation evidence presented in this study such as glacial lake shorelines fossil deltas and spillway and drainage channels in north central labrador ungava indicates the existence of numerous previously unmapped glacial lakes the mapped glacial lake features are synthesized to a reconstruction of several glacial lake stages which in turn are used to constrain the late glacial ice margin retreat pattern over the inferred cold based areas of north central labrador ungava a total of 26 glacial lakes 65 sub stages existed during the deglaciation of labrador ungava these lakes were impounded along the southern margin of the shrinking ice sheet the required damming ice margins indicate that the last ice remnant of the laurentide ice sheet in labrador ungava was situated over the southern ungava bay and the adjacent southern shore

cosmogenic 10be ages of the saglek moraines torngat mountains labrador cosmogenic 10 be ages on boulders from the saglek moraines of the torngat mountains labrador suggest that the moraines were deposited in their type area 13 4 6 1 5 ka the 10 be ages on boulders from similar moraines in a valley system 100 km north of the type area yield a mean age of 12 0 6 2 1 10 be ka these data support the hypothesis that the saglek moraines were deposited by a regional system of outlet glaciers that drained the laurentide ice sheet and left extensive areas of the torngat mountains ice free as nunataks weighted mean ages for erratic boulders and bedrock 5 50 m higher in elevation than the saglek moraines at both field areas are indistinguishable at 1s from the weighted mean ages of moraines in each area these data either indicate that thicker late wisconsinan ice receded to the level of the saglek moraines at 12 13 10 be ka or that the saglek ice margin represents the maximum late wisconsinan extent but the ice margin fluctuated sufficiently to create a vertical zone of 50 m with essentially the same exposure history

meltwater and deglaciation se baffin shelf ne margin laurentide ice sheet between 13 5 and 7 ka from o and c stable isotopic data stable isotopic values on planktonic foraminifera in a suite of cores from basins across the se baffin shelf are used to extract a record of meltwater events during termination i deglaciation resolution and hatton basins lie on the se baffin shelf at water depths 500 m seaward of major conduits for ice drainage from the eastern sector of the laurentide ice sheet lis accelerator mass spectrometry 14c dates are used to constrain our chronology of events in ten cores in resolution basin three cores have 14c ams dates on foraminifera of 20 ka at their bases whereas hatton basin cores terminate in sediments 13 kyr sedimentation rates varied between 0 1 to 4 5 m ka stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera neogloboquadrina pachyderma ehrenberg sinistral from seven of the ten cores no evidence was found to indicate that test morphology or size affected 18o between 7 and 13 5 ka the surface water on the shelf was on average 1 lower than the open ocean signal significant temporal variations were found in both 18o and 13c evidence for significant low 18o events occurred between 13 and 8 ka the 13c record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka with positive values between 10 8 and 13 0 ka negative values between 9 and 10 8 ka and positive values from 7 to 9 ka the 18o data suggest the presence of meltwater on the shelf some 3 000 years prior to the first late glacial dates on terrestrial deglaciation at circa 10 4 ka hudson strait must be the real key to the importance of the calving process during deglaciation because it is potentially the largest marine outlet for the laurentide ice sheet and because it leads into the very center of the ice sheet the rates of calving through hudson strait during the period of initial 18o rise unfortunately are unknown w f ruddiman 1987 p 151

amphiboles in the igneous environment the time is ripe for a fresh inventory of occurrences of amphibole group minerals in igneous rocks here i build on the available resources for example on the review of wones and gilbert 1982 in volume 9b of the rimg series they entitled their chapter amphiboles in the igneous environment i adopt the same title but intend to make the scope of my review somewhat broader by including non igneous rocks formed in the igneous environments much has been written about occurrences of amphibole group minerals over the last quarter of a century much of it ably summarized by deer et al 1997 and it is quite impossible to do more here than to summarize representative findings concerning the textural development and broad compositional features of minerals of the amphibole group that are important in igneous contexts amphibole group minerals are widespread in igneous rocks produced in zones undergoing extension as well as in rocks associated with subduction systems each setting may be associated with specific late stage metasomatic phenomena in which amphibole group minerals play a key role metasomatic overprints involving an amphibole also are widespread in the mantle and act as an essential step in the fertilization of sterile mantle if it is to produce alkali basaltic magmas by partial melting finally selected findings are summarized here on amphibole group minerals in igneous environments in other parts of the solar system amphibole group minerals have generally been underutilized in petrological studies reasons are not hard to find the full characterization of an amphibole presents serious challenges so much so that most investigators have been constrained to examine only those major elements that can be assessed in routine electron microprobe analyses as hawthorne and oberti 2006 pointed out in their essay on the future of schemes of classification it has become abundantly clear that progress is within