parameterization of topographic effect on surface solar radiation 1 topographic impact on the surface solar shortwave sw radiation was investigated using a 40 m high resolution digital topographic data model and a radiative transfer model with applications to the complex terrain of taiwan we found that the spatial variation of the surface sw radiation has a strong diurnal cycle the standard deviation of the sw radiation f over taiwan is nearly constant for a given solar zenith angle sza the maximum f occurs at sza 55 corresponding to midmorning early morning and midafternoon late afternoon in winter summer for a spatial resolution of 40 m the f over taiwan attains a maximum value of 300 w m 2 which is 50 of the domain mean sw radiation the topographic impact on the spatial variation of sw radiation increases with decreasing grid box size x in mesoscale land and atmospheric models x is small and the topographic impact is strong over taiwan the standard deviation of the difference between the daily mean sw radiation computed with a spatial resolution of 40 m and that computed with degraded spatial resolution reaches 25 w m 2 for x 1 km and 8 w m 2 for x 10 km indicating the importance of topographic impact on the surface sw radiation in mesoscale land and atmospheric models we developed a parameterization of the topographic impact on the surface sw radiation that scales the sw radiation computed for a flat surface without shading by surrounding terrains the scaling is separately applied to the direct and diffuse radiation it is applicable to all clear aerosol laden and cloudy conditions and to all spatial resolutions with x 40 m

the age petrogeneis and tectonic significance of the frontenac formation basalts northern new hampshire and western maine within plate basalts are present across the connecticut valley gaspe trough in new england and canada proposed mechanisms for the extensional magmatism include back arc basin extension slab breakoff and extensional collapse the age and composition of the bimodal frontenac formation of northern new england and southern quebec has bearing on the topic we analyzed zircons from the meta felsic rocks of the formation and determined a silurian age of 432 8 ma we also analyzed the frontenac rocks for major and trace elements and compared their compositions to the other mafic rocks along strike in the connecticut valley gaspe trough these include the comerford intrusive suite and the standing pond volcanic member of the waits river formation of vermont the silurian chaleur group and the early devonian dalhousie group of new brunswick and the gaspe peninsula and to the piscataquis belt rocks of northern maine all these rocks are post taconic within plate tholeiites that span an age range from 432 ma frontenac formation to 419 ma comerford intrusive suite in spite of their similar tectonic setting subtle differences in trace element compositions are evident indicating a multiplicity of sources in the production of the siluro devonian magmas ce yb versus la ta values suggest that the frontenac magmas were derived from spinel peridotite sources in the asthenospheric mantle we suggest that slab rollback and back arc basin extension permitted asthenospheric mantle upwelling to the spinel peridotite stability field causing the frontenac partial melting event at depths as low as 35 km sediments of the frontenac formation were deposited as turbidite successions into a developing trough resulting from extension the coeval influx of sediment and intrusion of basalt produced a sediment sill complex because the upward migration of the basaltic magmas was hindered by the rapidly thickening sediment overburden subsequently slab breakoff may have opened an asthenospheric window generating the younger within plate magmas that occurred from 425 to 418 ma across the connecticut valley gaspe trough

rates timing and cyclicity of holocene eolian activity in north central united states evidence from varved lake sediments most of the sediment components that accumulated in elk lake northwestern minnesota during the holocene are autochthonous or biogenic delivered to the sediment water interface on a seasonal schedule preserved in distinct annual laminae varves the main allochthonous component is detrital clastic material as measured by bulk sediment concentrations of aluminum sodium potassium titanium and quartz that enters the lake mostly as eolian dust the eolian clastic influx to elk lake was considerably greater during the mid holocene 8 4 ka than it has been for the past 4000 yr when periods of increased eolian activity correspond to the time of the little ice age and the dust bowl geochemical records of eolian activity exhibit distinct cyclicities with dominant periodicities of 400 and 84 yr

rock magnetic criteria for the detection of biogenic magnetite abstract we report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron reducing bacteria magnetotactic bacterial mtb strains ms1 mv1 and mv2 and dissimilatory iron reducing bacterium strain gs 15 grown in pure cultures were used in this study our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain sd particles of magnetite from mtbs the most useful magnetic property measurements include 1 acquisition and demagnetization of isothermal remanent magnetization irm using static pulse and alternating fields 2 acquisition of anhysteretic remanent magnetization arm and 3 thermal dependence of low temperature 20 k saturation irm after cooling in zero field zfc or in a 2 5 t field fc from 300 k however potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero field and field cooled sirms on warming through the verwey transition t 100 k intact chains of unoxidized magnetite magnetosomes have ratios of fc zfc greater than 2 where the parameter is a measure of the amount of remanence lost by warming through the verwey transition disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the fc zfc ratio to around 1 similar to values observed for some inorganic magnetite maghemite greigite and gs 15 particles numerical simulations of fc zfc ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the fc zfc parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole sediment samples the strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made compared to techniques such as electron microscopy

three thousand years of extreme rainfall events recorded in stalagmites from spring valley caverns minnesota article i nfo annual layer analysis in two stalagmites collected from spring valley caverns southeastern minnesota reveals hydrological response of the cave to extreme rainfall events in the midwest usa cave flooding events are identified within the two samples by the presence of detrital layers composed of clay sized particles comparison with instrumental records of precipitation demonstrates a strong correlation between these cave flood events and extreme rainfall observed in the upper mississippi valley a simple model is developed to assess the nature of rainfall capable of flooding the cave the model is first calibrated to the last 50 yr 1950 1998 a d instrumental record of daily precipitation data for the town of spring valley and verified with the first 50 yr of record from 1900 to 1949 a d frequency analysis shows that these extreme flood events have increased from the last half of the nineteenth century comparison with other paleohydrological records shows increased occurrence of extreme rain events during periods of higher moisture availability our study implies that increased moisture availability in the midwestern region due to rise in temperature from global warming could lead to an increase in the occurrence of extreme rainfall events

paleogeography and tectono sedimentary history at the margin of laurentia during silurian to earliest devonian time the gaspe belt quebec the silurian lower devonian sequence of the gaspe belt at the laurentia margin south of the quebec reentrant and st lawrence promontory was deposited during the period between the two main orogenies that created the northern appalachians the late ordovician taconian and the middle devonian acadian orogenies although this sequence is traditionally considered to have been deposited during a period of quiescence between both orogenies significant tectonic activity attributed to the salinic disturbance began during late llandoverian telychian time and persisted until the acadian orogeny this tectonic activity has profoundly influenced the composition and distribution of the silurian earliest devonian sedimentary facies the shelf and shelf edge history at the laurentia margin along the quebec reentrant st lawrence promontory is summarized according to four broad phases phase 1 is a llandoverian wenlockian regressive phase r1 related to post taconian successor basin filling that culminated with extensive carbonate platform development phase 2 is a late wenlockian ludlovian transgressive phase t1 phase 3 corresponds to a later ludlovian pridolian second regressive phase r2 phases 2 and 3 were accompanied by extensional tectonics that produced shelf faulting and block tilting on top of which block reefs and reef complexes settled and built a reef tract all the way along the gaspe temiscouata shelf phase 4 is an early devonian phase of accelerated subsidence transgression t2 affecting the northwestern part of the segment quebec reentrant area while the southeastern part st lawrence promontory area was already uplifted due to the ongoing collision between laurentia and the western margin of gondwana related terranes to the south composition and distribution of sedimentary facies were controlled by the interaction of tectonics sediment influx and sea level fluctuations construction of a post taconian pre acadian palinspastic map to plot facies has proven to be basic to obtaining a realistic picture of the paleogeography of the shelf and shelf edge of the gaspe temiscouata segment at the margin of the laurentia craton during the silurian earliest devonian time interval

detection of noninteracting single domain particles using first order reversal curve diagrams we present a highly sensitive and accurate method for quantitative detection and characterization of noninteracting or weakly interacting uniaxial single domain particles unisd in rocks and sediments the method is based on high resolution measurements of first order reversal curves forcs unisd particles have a unique forc signature that can be used to isolate their contribution among other magnetic components this signature has a narrow ridge along the hc axis of the forc diagram called the central ridge which is proportional to the switching field distribution of the particles therefore the central ridge is directly comparable with other magnetic measurements such as remanent magnetization curves with the advantage of being fully selective to sd particles rather than other magnetic components this selectivity is unmatched by other magnetic unmixing methods and offers useful applications ranging from characterization of sd particles for paleointensity studies to detecting magnetofossils and ultrafine authigenically precipitated minerals in sediments

silurian extension in the upper connecticut valley united states and the origin of middle paleozoic basins in the quebec embayment pre silurian strata of the bronson hill arch bha in the upper connecticut valley nh vt are host to the latest ludlow comerford intrusive suite consisting east to west of a mafic dike swarm with sheeted dikes and an intrusive complex the rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite the suite is truncated on the west by the monroe fault a late acadian thrust that carries rocks of the bha westward over silurian devonian strata of the connecticut valley gaspetrough cvgt dikes intrude folded strata with a pre intrusion metamorphic fabric taconian but they experienced acadian deforma tion twenty fractions of zircon and baddeleyite from three sample sites of gabbro diorite spanning nearly 40 km yield a weighted 207 pb 206 pb age of 419 1m a greenschist facies dikes sampled over a strike distance of 35 km were tholeiitic basalts formed by partial melting of asthenospheric mantle with little or no influence from mantle or crustal lithosphere the dike chemistry is similar to mid ocean ridge within plate and back arc basin basalts parent magmas originated in the astheno sphere and were erupted through severely thinned lithosphere adjacent to the cvgt extensive middle paleozoic basins in the internides of the appalachian orogen are restricted to the quebec embayment of the laurentian rifted margin and include the cvgt and the central maine trough cmt separated from the bha by a silurian tectonic hinge the ne trending comerford intrusions parallel the cvgt cmt and the tectonic hinge and indicate nw se extension during post taconian convergence the irregular margins of composite laurentia and avalon permitted continued colli sion in newfoundland st lawrence promontory and coeval extension in the quebec embayment extension may be related to hinge retreat of the northwest directed brunswick subduction complex and rise of the asthenosphere following slab break off an alternative hypothesis is that the basins originated as pull apart basins between northwest trending left stepping sinistral strike slip faults along the southern flanks of the new york and st lawrence promontories

late neoproterozoic to permian tectonic evolution of the quebec appalachians canada abstract due to the unique location of the quebec appalachians in a re entrant of the paleo north american margin and to the fact that the area largely escaped late paleozoic deformation this segment of the orogen preserves evidence of the early orogenic stages that are partly obscured elsewhere despite diachronicity both along and across strike of the orogen five tectonic events of regional significance are recognized 1 the earliest event is mainly recorded by neoproterozoic to early ordovician normal faults associated with extension of the laurentian craton and the establishment of a passive continental margin 2 the second event the ordovician taconian orogeny is marked by foreland directed deformation and corresponds to the principal deformational and metamorphic events recorded by the laurentian margin 3 the third event early salinic is early silurian it is restricted to the southern part of the quebec appalachians and consists of hinterland se directed thrusts folds and retrograde metamorphism 4 the fourth event late salinic is recorded by regional scale late silurian to early devonian normal or transtensional faults and is associated with the formation of the connecticut valley gaspe trough and 5 the last event the devonian acadian orogeny affects with variable intensity all the pre carboniferous lithologies this tectonic synthesis implies that the subdivision of the peri laurentian oceanic tracts proposed in other segments of the appalachians should be applied with caution in quebec and that the structural style the number of oceanic domains and possibly the vergence of subduction change along the strike of the orogen in particular the similarities of the thetford mines and boil mountain ophiolitic complexes and sedimentary covers and the lack of evidence for a major intervening suture are consistent with the maximum allochtony hypothesis i e the assumption that the southern quebec ophiolites are rooted east of the chain lake massif a geodynamic model involving the taconian obduction of a large ophiolitic nappe s the docking of a peri gondwanan gander medial new england terrane in early salinic the formation of large sedimentary basins connecticut valley gaspe and merrimack troughs due to trench rollback and or delamination during the late salinic event and collision at the outer margin of composite laurentia during the acadian orogeny can account for the protracted structural and metamorphic history of the quebec appalachians

late silurian early devonian rifting during dextral transpression in the southern gaspe peninsula quebec petrogenesis of volcanic rocks the upper silurian lower devonian volcanic rocks in the southern gaspe peninsula of the quebec appalachians crop out at the northeast end of the connecticut valley gaspe synclinorium these shallow marine and subaerial sequences reach a thickness of up to at least 2000 m and comprise two groups 1 the late silurian volcanic rocks which are mainly transitional alkalic tholeiitic basalts with steeply sloping ree patterns 2 the early devonian volcanic rocks which include a significant proportion of intermediate rocks in addition to tholeiitic basalts compared with the silurian rocks the devonian basalts have lower abundances of strongly incompatible trace elements such as ba th ta nb and light ree and relatively flat heavy ree patterns basalts of both groups display negative nb and ta anomalies relative to th and la although the basalts of both sequences were derived from lithospheric mantle the silurian basalts were generated from garnet peridotite at 80 km depth while the devonian ba

gaspe belt subsurface geometry in the northern quebec appalachians as revealed by an integrated geophysical and geological study 1 potential field mapping abstract together recent gravity and high resolution aeromagnetic datasets are used to qualitatively investigate the upper and middle crustal geometry of the middle paleozoic gaspe belt in the northern appalachians long wavelength potential field anomalies define two sub basins that are divided by northeast trending gravity highs for each sub basins gravity lows correlate with the youngest rock units maps that highlight anomalies associated with near surface features at the expense of those related to deeper sources provide an important supplement to the spatially discrete observations derived from bedrock mapping analysis of such maps indicates that the sub basins are characterized by different structural patterns and that faults trending obliquely compared to the main structural grain have been previously underestimated the geometry of the gaspe belt as revealed by this integrated geophysical and geological study bears similarities with orogens exhibiting lateral extrusion this geometry is interpreted as the result of a heterogeneous strain regime in front of an indenter corresponding to the early paleozoic gander dunnage crustal block the indentation tectonic model is supported by 1 the various strike and kinematic of faults that suggest a strongly heterogeneous strain regime 2 the greater geological complexity and the occurrence of faults with a significant thrust component in front of the indenter 3 the predominance of dextral strike slip faults in the eastern gaspe peninsula that result in lateral material transport away from the indenter 4 the location of abundant devonian magmatic dykes sills and stocks in a fault bounded zone that experienced local extension 5 the occurrence of block rotation

petrogenetic evolution of felsic volcanic sequences associated with phanerozoic volcanic hosted massive sulphide systems the role of extensional geodynamics abstract felsic volcanic hosted massive sulphide deposits form in many different geotectonic environments usually associated with episodes of extension however empirical geochemical links between felsic volcanism geotectonic environment and extensional geodynamics have not been adequately documented so as to distill the fundamental relationships between these features and formation of volcanic hosted massive sulphide vhms mineralization which is important considering most vhms deposits are hosted in felsic volcanic bearing sequences using felsic geochemical data from six different vhms mineralized phanerozoic geotectonic settings it seems that the felsic geochemical data are consistent with the overall geotectonic interpretations for these areas which in turn helps in stratigraphic and geotectonic interpretations for detailed vhms exploration in extensional geodynamic settings bimodal volcanism is common compared to the continuum of compositions observed under compressional to neutral high stress regimes in calc alkaline arc building environments the empirical geochemical metallogenic vhms relationships evident in the archean felsic volcanic rocks in particular the low zr y n yb n 2 o conditions in different source areas and geotectonic environments they seem to be the predominant controls on the compositional evolution of felsic magmas in extensional settings because of the limited degree of assimilation and fractional crystallization afc affecting their compositions with rapid intrusion into the uppermost crust to positions were they achieve neutral buoyancy in the volcanic to subvolcanic environment within plate felsic or a type anorogenic type and anomalous ocean ridge or type felsic magmas that have tholeiitic affinities relatively low alkali elements are common within parts of the volcanic sequences hosting massive sulphide deposits reflecting in part a relationship to extension the high contents of high field strength elements zr ga lree hree y nb etc and other lines of evidence indicate they are relatively high temperature relatively reduced magmas probably derived from previously dehydrated granulitic or melted oceanic simatic or continental sialic crust low p granulites or amphibolites but also in some cases possibly mantle rocks such that they are significantly water undersaturated during melting i e a h 2 o 1 reduced viscosities typical of high temperature melts enable rapid intrusion to higher levels diking vs diapirism higher rates of heat advection from mantle mafic magmas into the thickened oceanic and or continental crust during lithospheric extension are needed to facilitate melting of these rock to form a type and or or type partial melts tholeiitic felsic this usually results in bimodal magmatism as magma mixing is not favored in extensional settings especially at high magma production intrusion and extrusion rates i e high heat flow this would inhibit ferromagnesian phase in particular hornblende and magnetite fractionation especially at low f o 2 in the felsic magmas that would deplete the melt in y hree as well as ore related elements particularly zn which is 2 to 3 times higher in a type and or type rocks compared to other magma types therefore the empirical felsic igneous geochemical metallogenic relationships observed by others low zr y n yb n

sediment magnetic evidence for last millennium drought conditions at the prairie forest ecotone of northern united states abstract droughts are recurrent features in sedimentary records at the prairie forest ecotone of northern u s a it is therefore important to understand the duration of such events as well as their severity and consequences beyond the century scale instrumental record the existing drought records can be complemented with additional proxies that clearly document the interactions between external factors and the depositional environment here we attempt to reconstruct the last millennium drought history of deming lake a small lake at minnesota s prairie forest ecotone using sediment magnetism in particular this approach allowed us to explore the interactions between lake and catchment and test the hypothesis that periods of moderate aridity result in decreased hydrologic sediment transport from the catchment to the lake as a consequence of reduced erosion and overland flow concordantly during dry episodes we find that the mass fractions of in lake produced organic matter and biogenic magnetic particles increase relative to allochthonous component fractions we identify several episodes of aridity at deming lake consistent with existing regional drought reconstructions the most prolonged dry event occurred at the end of the little ice age suggesting that the second half of this cold interval was drier in the region than previously thought

a rapid method for magnetic granulometry with applications to environmental studies we have developed a rapid method of characterizing the fine scale variation sub micron to hundreds of microns m in the grain size of magnetite in long sediment cores this method is a new rock magnetic tool and can be readily applied to the following disciplines 1 environmental studies 2 hydrology 3 petrology and 4 geomagnetism the method consists of a comparative plot of the depth variation of two magnetic parameters the first parameter low field less than 0 1 millitesla mt or 1 oe susceptibility in a steady field is plotted on the abscissa the second parameter anhysteretic remanent magnetization arm imparted by a smoothly decreasing af of peak value 100 mt 1 000 oe in the presence of a weak steady field 0 01 0 1 mt or 0 1 1 oe is plotted on the ordinate for a sediment column in which the magnetic mineral is magnetite a plot of the two magnetic parameters shows transitions in the average magnetic grain size with depth as clearly discernible changes in the slope of a regression line fit to the individual points arm

trace element indiscrimination diagrams abstract we tested the accuracy of trace element discrimination diagrams for basalts using new datasets from two petrological databases petdb and georoc both binary and ternary diagrams using zr ti v y th hf nb ta sm and sc do a poor job of discriminating between basalts generated in various tectonic environments continental flood basalt mid ocean ridge basalt ocean island basalt oceanic plateau basalt back arc basin basalt and various types of arc basalt the overlaps between the different types of basalt are too large for the confident application of such diagrams when used in the absence of geological and petrological constraints none of the diagrams we tested can clearly discriminate between back arc basin basalt and mid ocean ridge basalt between continental flood basalt and oceanic plateau basalt and between different types of arc basalt intra oceanic island and continental arcs only ocean island basalt and some mid ocean ridge basalt are generally distinguishable in the diagrams and even in this case mantle normalized trace element patterns offer a better solution for discriminating between the two types of basalt

a 900 year pollen inferred temperature and effective moisture record from varved lake mina west central minnesota usa abstract drought is endemic to the north american great plains causing severe economic consequences however instrumental climate data only exist from ca ad 1890 and limited tree ring paleolimnological archeological and eolian records document the last two millennia to address this lack of monitoring and paleoclimatic data the pollen preserved in the varved sediments of lake mina minnesota on the northeastern border of the great plains were analyzed may and february mean monthly temperatures and annual precipitation minus potential evapotranspiration were reconstructed at a 4 year resolution using a pre settlement pollen climate calibration set the period of the so called little ice age lia ad 1500 1870 was colder than the medieval climate anomaly mca ad 1100 1500 in west central minnesota winter temperatures in the lia declined more than summer ones the pollen record suggests that the lia occurred in three phases an initial cold phase from ad 1505 to ad 1575 a warmer phase and then a very cold phase from ad 1625 to ad 1775 there were severe droughts detected in the lake mina record from ad 1660 to ad 1710 and ad 1300 to ad 1400 suggesting that high resolution pollen records can detect events previously defined from the tree ring records this latter century scale drought is concurrent with the widely reported ad 1250 1400 mega drought which exceeds the severity of 20th century droughts

late silurian early devonian transpressional rift origin of the quebec reentrant northern appalachians constraints from geochemistry of volcanic rocks silurian devonian rocks in the northwestern mainland appalachians form part of an overstep sequence deposited across the vestiges of iapetus after the collision of laurentia and gondwana they occur in three synclinoria gasl connecticut valley merrimack aroostook and fredericton synclinoria separated by two anticlinoria munsungun pennington boundary mountain bronson hill and miramichi silurian rocks in gasp6 connecticut valley and merrimack aroostook synclinoria consist of shelf and trough sediments derived mainly from laurentia to the northwest with some local contributions from an ephemeral landmass appalaclfia and from the miramiclfi highlands in contrast early devonian rocks in all three synclinoria are mainly flysch derived froxn the southeast in avalonia interbedded volcanic rocks are predominantly late silurian early devonian in age they are generally bimodal with the mafic rocks exhibiting a change from transitional alkalic tholeiitic to tholeiitic around the siluro devonian boundary broadly coincident with the salinic disturbance in the gaspe peninsula the geochemical characteristics of the basalts indicate that they were erupted in a continental intraplate environment with melting migrating upward through time across the garnet to spinel phase boundary as stretclfing increased thermal uplift during rifting is inferred to have led to erosion associated with the salinic disturbance the start of the volcanism appears to coincide with a switch from sinistral to dextral transpression along the orogen that may be related to the change from clockwise to anticlockwise rotation of laurentia relative to gondwana the effects of dextral transpression vary with the trend of the orogen intense deformation and metamorplfism occurred in the central mobile belt opposite the new york and st lawrence promontories whereas rifting developed in the quebec reentrant leading to tlfinning of the crest up welling of the asthenosphere melting and magmatism

paleomagnetic constraints on siluro devonian laurentian margin tectonics from northern appalachian volcanics abstract paleomagnetic analyses of silurian mafic volcanics from the overstep sequence of sedimentary and volcanic rocks deposited over the central mobile belt of the northern appalachians provide insight into the mid paleozoic tectonic history of the laurentian margin stepwise thermal demagnetization of the subaerial mafic volcanics of the ludlovian fivemile brook formation of northwestern maine reveals two ancient high temperature dual polarity remanences a tilt corrected mean direction yields an inclination of 41 i 3 9 n 4 sites and the magnetization is interpreted as a near primary magnetization acquired well before the end of early devonian deformation an in situ mean direction d 165 i 35 95 6 k 65 n 10 entries from 8 sites is interpreted as a secondary overprint with a pole 22 s 306 e near the early carboniferous segment of the north american apparent polar wander path apwp conglomerate and fold tests of the high temperature characteristic remanence preserved in wenlockian subaerial mafic volcanics of the bryant point formation and a red bed of the south charlo formation both of the chaleur group of northeastern new brunswick constrain paleolatitude and deformational age the inclination only fold test peaks at 50 unfolding with a mean inclination of 35 i 8 5 n 148 synfolding acquisition of magnetization is wenlockian based on a negative conglomerate test at the base of the section and a positive conglomerate test at the top of the section clockwise streaking of site mean directions away from a predominantly northerly declination is consistent with post middle wenlockian dextral shear in the chaleur bay region comparison of a locus of paleomagnetic pole positions with the north american apwp supports a silurian age of the magnetization of the chaleur group the age and synfolding nature of this remanence furthermore requires that deformation associated with the acadian orogeny in new brunswick began by mid silurian times moreover inclinations from these units indicate that within paleomagnetic resolution there has been no significant latitudinal displacement with respect to stable north america since the silurian

volcanic red bed copper mineralisation related to submarine basalt alteration mont alexandre quebec appalachians canada two types of native copper occur in upper silurian basaltic rocks in the mont alexandre area quebec appalachians 1 type 1 forms micrometric inclusions in plagioclase and is possibly magmatic in origin whereas 2 type 2 occurs as coarse grained patches rimmed by cuprite in altered porphyritic basalt type 1 has higher contents of sulphur 2 000 20 263 ppm and arsenic 146 6 017 ppm and a broader range of silver abundances 65 2 186 ppm ag than type 2 149 1 288 ppm s 90 146 as 65 928 ppm ag no mineral inclusions of sulphide or arsenide in native copper were observed at the electron microprobe scale primary igneous fabrics are preserved but the basaltic flows are pervasively oxidised and plagioclase is albitised chlorite replaces plagioclase and forms interstitial aggregates in the groundmass and has fe fe mg ratios ranging from 0 29 to 0 36 with calculated temperatures between 155 c and 182 c copper sulphides in vacuoles and veinlets are associated with malachite fibro radiating albite and yarrowite cu9s8 with up to 0 3 wt ag bulk rock concentrations of thallium and lithium range from 70 to 310 ppb and 10 to 22 ppm respectively and thallium is positively correlated with fe2o3 such concentrations of thallium and lithium are typical of spilitisation during heated seawater basalt inter action spilitisation is consistent with the regional geolog ical setting of deepwater facies sedimentation but is different from current models for volcanic red bed copper which indicate subaerial oxidation of volcanic flows the volcanic red bed copper model should be re examined to account for native copper mineralisation in basalts altered by warm seawater

pre acadian magmatic suites of the southeastern gaspe peninsula there are two phases of post taconic pre acadian magmatism in the eastern gaspe peninsula of quebec a the middle to upper ordovician pabos suite and b widespread silurian devonian volcanics and hypabyssal intrusions the pabos suite forms two large intrusions composed of lree depleted n morb like gabbros and ferrogabbros evolution within this suite was controlled by fractional crystallization and the presence of the intrusions implies a tensional event between the taconic and acadian orogenies the silurian devonian volcanic and intrusive rocks are chemically variable tholeiitic to alkaline basaltic to rhyolitic and do not belong to a single fractionation series quartz xeno cryst bearing rocks are enriched in si k zr and lree9s providing evidence of disequilibrium contamination by a felsic melt similar to locally occurring rhyolites the lavas and dikes that do not carry felsic xenocrysts also show patterns of enrichment depletion of trace elements which suggest that felsic contamination hybridization was an important factor in their development but show little si enrichment this is interpreted to be due to maintenance of chemical equilibrium during contamination this would have forced the composition of the magma to remain on the plagioclase clinopyroxene olivine cotectic and would thus have inhibited si enrichment the xenocryst bearing rocks superficially resemble a calc alkaline series but most of the pre acadian silurian devonian volcanics of the gaspe peninsula do not appear to have been directly associated with subduction the preferred model is that of local tensional environments in an orogenic foreland

a lost arc back arc terrane of the dunnage oceanic tract recorded in clasts from the garin formation and mccrea melange in the gaspe appalachians of quebec upper ordovician garin conglomerates base of the gaspe belt quebec appalachians contain three igneous clast populations 1 calc alkaline intermediat felsic rocks resemble exploits new brunswick maine and notre dame quebec newfoundland subzone lavas clasts monzonite rhyodacite give u pb zircon ages between 465 and 466 ma precluding correlation with exploits rocks we suggest that the suite represents peri laurentian continental arc magmas coeval with the red indian lake group of newfoundland correlation of lavas from a gaspe well with the popelogan arc implies that the red indian line passes through southern gaspe 2 mafic tholeiitic to alkaline clasts resemble new brunswick and maine exploits subzone alkaline lavas we interpret them as magmas associated with initiation of a back arc basin possibly on the laurentian margin 3 mafic intermediate tholeiitic to calc alkaline clasts have an oceanic subduction component and correlate with notre dame subzone lavas quebec newfoundland they are interpreted as products of spreading and off axis magmatism of a peri laurentian back arc basin we correlate mccrea melange lavas to the calc alkaline intermediat felsic and mafic intermediate suites and interpret them as samples of a notre dame subzone terrane coeval with the red indian lake group of newfoundland during initiation of a successor arc back arc a terrane which is no longer preserved in new brunswick and maine but that provides some evidence for possible extensions of newfoundland9s geology into the gaspe appalachians of quebec a mid ocean ridge basalt like intrusion in the mccrea melange ar ar age 471 2 11 2 ma is coeval with peri laurentian ophiolites in newfoundland and may record a back arc opening event

lower paleozoic tholeiitic dykes from central new brunswick possible evidence for the early opening of an ensialic taconian back arc basin cambrian and early ordovician sedimentary rocks of the lower tetagouche group from the southern miramichi terrane in new brunswick were intruded by a series of mafic dykes the age of dykes is unknown but their stratigraphic context and state of deformation indicate that they were intruded during the taconian orogeny the geochemistry of the dykes shows that they are a cogenetic magmatic suite of basaltic composition 48 55 wt sio2 and tholeiitic affinity the dykes are low in silica and high in tio2 1 5 3 5 wt and feo 8 16 wt magmatic evolution of the suite resulted from processes involving both crystal fractionation and crustal contamination as indicated by depletion of compatible elements important enrichment in high field strength elements and the presence of inherited zircons of precambrian age the most primitive samples resemble mid ocean ridge basalts except for higher alkali contents or continental tholeiites depleted of light rare earth elements in comparison the most evolve