preliminary model for an early transform history in central atlantic rifting dextral and sinistral shear along an arcuate intracontinental transform system parallel to the present coastlines of eastern north america and western africa is believed to have played a significant role in the decoupling of continental blocks during the extremely complex tectonic history of central atlantic rifting near pole small circle transform systems are developed as wide zones of shear during counterclockwise and clockwise rotations of africa and south america relative to north america about a pole of rotation in the sahara transform and rifting histories are combined in a model proposed for atlantic rifting that includes the following phases of rotation interacting with the linear belt of pre existing appalachian structural grain 1 late permian to middle triassic counterclockwise rotation of africa with dextral shear localizing an initial thermal arch and early sedimentation in southern appalachian grabens along a reactivated structural grain 2 dominant late triassic to early jurassic extensional reactivation in a northwest southeast direction with minor plate separation producing the main phase of graben sedimentation and a major 190 m y b p basalt sill and flow event 3 middle jurassic clockwise rotation of africa with sinistral shear resulting in the folding and faulting of graben sediments and the injection of basalt dikes 175 m y b p along a distinctive fan shaped distribution of extensional structures and 4 separation of the north american and african continents parallel to early atlantic fracture zone trends with the onset of plate accretion

paleomagnetism of the triassic red beds of the lower fundy group and mesozoic tectonism of the nova scotia platform canada the lower fundy group red beds of the wolfville and lower blomidon formations in nova scotia and of wolfville equivalent units in new brunswick are exposed around the bay of fundy these red beds were sampled at twenty six shoreline sites for paleomagnetic analysis primarily by thermal step demagnetization methods samples from four sites proved too fragile to core however coating many of the rest of these poorly indurated samples and cores with waterglass enabled them to withstand the rigours of coring measurement and thermal cleaning a stable hematite remanence was found in all twenty one coherent sites with normal reversed and mixed polarities conglomerate and fold tests indicate the remanence is either primary or very early diagenetic its mean direction is d 196 5 i 3 8 95 7 2 which converts to a pole position of 45 3 n 97 1 e dp 3 6 dm 7 2 this pole indicates that the lower fundy group was likely deposited in the early triassic rather than in the middle and late triassic as currently thought it also indicates that the nova scotia platform was rotated about 8 clockwise after deposition of the lower fundy group and before extrusion of the north mountain basalts the consequences are briefly discussed for two alternative tectonic models of mesozoic motion on the minas geofracture that led to formation of the bay of fundy rift as the atlantic ocean basin started to open in early rather than middle triassic time the fundy group pole is similar to those from granitic plutons in maine thereby increasing the probability that there is a significant error in the mid triassic portion of the apparent polar wander path for north america finally magnetostratigraphic methods appear to be a promising way to subdivide and correlate between these red beds

u pb geochronology of devonian granites in the meguma terrane of nova scotia canada evidence for hotspot melting of a neoproterozoic source abstract u pb isotopic analyses of monazite and zircon from six granitic plutons in the meguma terrane yield nearly concordant ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 373 pm 3 end document ma interpreted as the time of intrusion u pb analyses of euhedral zircons with thick rims overgrowing cores which were abraded to remove all or most of the rim plot on chords between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage p

individual lava flow thicknesses in oceanus procellarum and mare serenitatis determined from clementine multispectral data abstract we use multispectral reflectance data from the lunar clementine mission to investigate the impact ejecta deposits of simple craters in two separate lunar mare basalt regions one in oceanus procellarum and one in mare serenitatis over 100 impact craters are studied and for a number of these we observe differences between the tio 2 and feo contents of their ejecta deposits and the lava flow units in which they are located we demonstrate that in the majority of cases these differences cannot plausibly be attributed to uncorrected maturity effects these observations coupled with morphometric crater relationships that provide maximum crater excavation depths allow the investigation of sub surface lava flow stratigraphy we provide estimated average thicknesses for a number of lava flow units in the two study regions ranging from 80 m to 600 m in the case of the serenitatis study area our results are consistent with the presence of sub surface horizons inferred from recent radar sounding measurements from the jaxa kaguya spacecraft the average lava flow thicknesses we obtain are used to make estimates of the average flux of volcanic material in these regions these are in broad agreement with previous studies suggesting that the variation in mare basalt types we observe with depth is similar to the lateral variations identified at the surface

magnetic fabric of the barrington passage pluton meguma terrane nova scotia a two stage fabric history of syntectonic emplacement abstract structural analysis and the anisotropy of magnetic susceptibility ams are used to document the internal magmatic to high temperature subsolidus fabrics of the tonalitic late devonian barrington passage pluton the ams fabric orientations compare favorably with mesoscopic scale fabrics in general the k1 k2 principal plane of the ams is close to the observed mineral foliation defined by biotite and plagioclase and the k1 axis is aligned parallel to a mineral lineation defined by the same minerals and to a locally developed weak extension lineation defined by quartz measurement of the anisotropy of anhysteretic remanence aar and image analysis of biotite preferred orientations confirm that the orientation of the ams is principally controlled by biotite locally anomalous ams orientations are attributed to the influence of fine grained magnetite crystals the presence of which is revealed by measurements of hysteresis and coercivity properties a two stage fabric history is revealed first horizontal fabrics were formed foliation compositional banding during emplacement of a laccolith like pluton the second stage involved synmagmatic folding of the horizontal foliation and banding in response to regional contraction associated with the acadian orogeny with development of a lineation that records stretching parallel to the fold axis the results demonstrate that the barrington passage pluton was emplaced during the main phase of the acadian orogeny a model is proposed that depicts the barrington passage pluton as the folded base of a larger syntectonic pluton that is now largely eroded off

40ar 39ar ages from the botwood mount peyton region newfoundland possible paleomagnetic implications hornblende and biotite from the freshest available sample of the gabbroic early phase of the mount peyton batholith have both yielded 40ar 39ar apparent age plateaus an age of 420 8 ma is sugg

geochemical behavior of sulfur in granitoids during intrusion of the south mountain batholith nova scotia canada abstract a detailed stable isotope s o and elemental major trace s content study of peraluminous s type granites and granodiorites of the south mountain batholith and the meguma group metasediments into which the batholith was intruded has been conducted on a regional and local scale near mt uniacke sulfur contents of the metasediments range from 5 to 2440 ppm and 34 s ranges from 3 7 to 26 3 sulfur contents of the igneous rocks range from 6 to 570 ppm with the granites 20 ppm having lower sulfur contents than the granodiorites 300 ppm approximately 30 to 60 of the sulfur in the granodiorites is present as pyrrhotite a late phase with most of the remainder being present as sulfur substituted into biotite an early phase 18 oq quartz values of the mt uniacke granodiorites are heavy a 12 2 indicating formation of the magmas by partial melting of sedimentary rocks major element variations suggest that the granites are related to the granodiorites by fractional crystallization of plagioclase quartz and biotite comparison of the sulfur contents of the granodiorites with experimental determinations of sulfur solubility suggest that the distribution coefficient of sulfur d s between the cumulate and the magma during fractional crystallization 4 the regional granodiorites have a relatively restricted range of 34 s values 5 4 to 8 4 while the regional granites have a wide range of 34 s values 1 6 to 15 0 granodiorites at mt uniacke with normal magmatic values 0 76 to 1 42 for 18 o quartz feldspar have 34 s values between 6 6 and 12 3 and show good negative correlations between 34 s and s feo and mgo contents some granodiorites at mt uniacke have anomalously low sulfur contents for their major element composition and 18 o quartz feldspar values 0 45 to 0 67 indicate that these samples have undergone hydrothermal alteration and this alteration event is probably responsible for the low sulfur contents a number of processes have been considered in order to understand the variations of 34 s partial melting of inhomogeneous source rocks may be responsible for some of the regional 34 s variations but this implies that the granites are not genetically related to the granodiorites inhomogeneous source rocks are an unlikely explanation for the systematic variations of 34 s observed over only a few kilometres at mt uniacke rayleigh fractionation accompanying the fractional crystallization of biotite 34 s pyrrhotites silicate s 0 5 to 1 0 can account for only a small component of the observed 34 s variations the assimilation of isotopically variable sulfur derived from the meguma group metasediments during fractional crystallization combined assimilation fractional crystallization or afc provides the best explanation for the 34 s variations transfer of sulfur from the country rock may have been possible by either bulk afc where all of the country rock material is incorporated into the magma or by selective afc where sulfur and other volatile elements only are transferred from the country rock into the magma selective afc could have been effected by a sloping mechanism of intrusion followed by the heating of country rock xenoliths to the point where extensive desulfidation reactions took place with sulfur being transferred from the country rock to the magma by a fluid phase

lunar volcanism produced a transient atmosphere around the ancient moon abstract studies of the lunar atmosphere have shown it to be a stable low density surface boundary exosphere for the last 3 billion years however substantial volcanic activity on the moon prior to 3 ga may have released sufficient volatiles to form a transient more prominent atmosphere here we calculate the volume of mare basalt emplaced as a function of time then estimate the corresponding production of volatiles released during the mare basalt forming eruptions results indicate that during peak mare emplacement and volatile release 3 5 ga the maximum atmospheric pressure at the lunar surface could have reached 1 kpa or 1 5 times higher than mars current atmospheric surface pressure this lunar atmosphere may have taken 70 million years to fully dissipate most of the volatiles released by mare basalts would have been lost to space but some may have been sequestered in permanently shadowed regions on the lunar surface if only 0 1 of the mare water vented during these eruptions remains in the polar regions of the moon volcanically derived volatiles could account for all hydrogen deposits suspected to be water currently observed in the moon s permanently shadowed regions future missions to such locations may encounter evidence of not only asteroidal cometary and solar wind derived volatiles but also volatiles vented from the interior of the moon

volcanic gas composition metal dispersion and deposition during explosive volcanic eruptions on the moon abstract the transport of metals in volcanic gases on the moon differs greatly from their transport on the earth because metal speciation depends largely on gas composition temperature pressure and oxidation state we present a new thermochemical model for the major and trace element composition of lunar volcanic gas during pyroclastic eruptions of picritic magmas calculated at 200 1500 c and over 10 9 10 3 bar using published volatile component concentrations in picritic lunar glasses we have calculated the speciation of major elements h o c cl s and f in the coexisting volcanic gas as the eruption proceeds the most abundant gases are co h 2 h 2 s cos and s 2 with a transition from predominantly triatomic gases to diatomic gases with increasing temperatures and decreasing pressures hydrogen occurs as h 2 h 2 s h 2 s 2 hcl and hf with h 2 making up 0 5 0 8 mol fractions of the total h water h 2 o concentrations are at trace levels which implies that h species other than h 2 o need to be considered in lunar melts and estimates of the bulk lunar composition the cl and s contents of the gas control metal chloride gas species and sulfide gas and precipitated solid species we calculate the speciation of trace metals zn ga cu pb ni fe in the gas phase and also the pressure and temperature conditions at which solids form from the gas during initial stages of the eruption elemental gases are the dominant metal species as the gas loses heat chloride and sulfide species become more abundant our chemical speciation model is applied to a lunar pyroclastic eruption model with isentropic gas decompression the relative abundances of the deposited metal bearing solids with distance from the vent are predicted for slow cooling rates 2 o co 2 and cl rich volcanic gas from erta ale volcano ethiopia as an analogy for more oxidized planetary eruptions in the terrestrial cl rich gas the metals are predominantly transported as chlorides as opposed to metallic vapors and sulfides in the lunar gas due to the presence of cl species metal transport is more efficient in the volcanic gas from erta ale compared to the moon

early carboniferous deformation and mineralization in the cobequid shear zone nova scotia an 40ar 39ar geochronology study latest devonian to early carboniferous igneous rocks along the cobequid shear zone of central nova scotia record a complex history of intrusion volcanism deformation and hydrothermal alteration twenty new 40ar 39ar age determinations have been made on biotite and hornblende separates from rocks that constrain these events the mafic plutons of the cobequid shear zone are synchronous with the previously dated granitoid plutons 363 355 4 ma with the exception of the younger folly lake gabbro 355 350 4 ma high temperature shear deformation continued along the cobequid shear zone during this entire period of pluton emplacement several samples from mylonitic and hydrothermally altered rocks with dates ca 340 ma indicate renewed movement along the cobequid shear zone at this time accompanied by minor magmatism younger 330 320 ma ages reflect final movement along the rockland brook fault resulting in mid namurian uplift of the cobequid highlands following this regional alleghenian event ther

subsidence in late paleozoic basins in the northern appalachians during the interval between continental collision in the devonian and continental breakup in the triassic the northern appalachians became the site of a wide plate boundary zone of dominantly right lateral strike slip as is typical of intracontinental transforms tectonism was both diachronous and rapidly variable along strike through regimes of pure strike slip transpressional deformation and rapid subsidence of extensional basins up to 9 km of mainly nonmarine clastic sediments accumulated in these local depocenters which subsided episodically in two stages 1 an initial phase of stretching and thinning of the lithosphere when subsidence was rapid fault controlled and often accompanied by volcanism and 2 a subsequent phase of gradual thermal subsidence during which the depositional basins expanded to bury the earlier border faults and progressively younger sedimentary units onlapped basement the largest depocenter the magdalen basin opened as a pull apart between strike slip faults in newfoundland and new brunswick from late devonian to early carboniferous subsequent thermal subsidence affected a large area during medial and late carboniferous a phenomenon that is well recorded to the north and west where no later tectonism occurred in areas to the south and east of the basin strike slip on other faults continued into the time of thermal subsidence introducing complications such as localized transpressional deformation and rapid subsidence in smaller pull aparts

a review of the mesothermal gold deposits of the meguma group nova scotia canada abstract the gold province of the meguma terrane in nova scotia contains several classic examples of turbidite hosted mesothermal gold deposits there are over 300 gold occurrences and deposits hosted by the cambro ordovician meguma group rocks in southern nova scotia canada the meguma group consists of two formations 1 a lower sand dominated flysch goldenville formation and 2 an upper shaley flysch halifax formation subdivision of the goldenville formation into several map units is leading to a better understanding of the stratigraphic constraints on the gold mineralization although detailed stratigraphic investigations in all of the major gold producing areas is still ongoing it is evident that the steve s road beaverbank and the mt uniacke stratigraphic intervals contain most of the major past gold producers in the province the meguma group rocks are variably deformed into upright gently to moderately doubly plunging folds with multiple cleavages the strata are metamorphosed from greenschist to amphibolite facies and are subsequently intruded by ca 370 ma peraluminous granites and minor mafic intrusions the gold deposits can be divided into three main types 1 high grade approximately 15 g t au narrow gold bearing quartz veins 2 low grade 0 5 4 g t au slate argillite hosted and 3 low grade meta sandstone hosted a combination of two or more of the above can also occur almost all of the historic production 47 million g au has come from the high grade veins within 200 m of surface a variety of vein types occur although most of the gold produced came from bedding concordant stockwork and fissure veins isotopic investigations and dating of the vein minerals indicate that the mineralization was related to migration of metamorphic fluids from multiple reservoirs in the waning stages of the acadian orogeny disseminated low grade gold with minor electrum and associated intermetallic compounds and metal alloys have recently been recognized in host rocks at several of the former gold mining areas in nova scotia the presence of disseminated gold in combination with high grade vein mineralization greatly enhances the economic viability of gold deposits in the meguma group the association of disseminated gold and narrow vein hosted deposits has important exploration implications for similar mesothermal gold districts elsewhere

interaction among upper crustal lower crustal and mantle materials in the port mouton pluton meguma lithotectonic zone southwest nova scotia the port mouton pluton is unique among the late devonian peraluminous granitoid bodies in the meguma lithotectonic zone of southwestern nova scotia in its lithological heterogeneity extensive physical and chemical interac tion with the country rocks clear evidence for mingling and mixing with mafic magmas and highly abundant pegmatites new u pb age determinations on monazite establish an intrusion age of 373 1 ma similar to the ages of other meguma lithotectonic zone granitoid plutons and mafic intrusions field relations petrology and geochemistry define three stages of intrusion of the port mouton pluton i early stage discontinuously exposed around the outer margin of the pluton dominated by coarse grained tonalite granodiorite and with rb sr 0 40 and gdn lun 0 55 eu eu 2 and iii late stage consisting of abundant minor sheets throughout the pluton dominated by fine grained tonalite granodiorite and leucogranite that are similar to rocks of the early and middle stages the port mouton pluton shows a wider range of 87 sr 86 sri 0 7036 0 7154 and a wider range and generally higher endi 3 72 to 2 12 than other granitoid rocks in the meguma lithotectonic zone potentially reflecting a com plex partially equilibrated interaction among mantle lower crust and upper crust field petrological and chemical evi dence for the involvement of mantle derived magmas and melting of upper crust permit modelling of the port mouton pluton granitoid compositions by three simultaneous mixing equations these mixing model results suggest that the early stage granitoid rocks can form from simple three component mixing relationships when the bulk distribution coefficients between residuum and melt for sr and nd range from 1 05 to 1 18 or two component mixing combined with fraction ation of material like the known felsic lower crust the middle stage granitoid rocks only yield solutions involving two component mixing and fractionation of material unlike the known felsic lower crust we conclude that the late devonian mafic magmas played a major role in the formation of granitoid magmas in the meguma lithotectonic zone by supplying heat and material to cause partial fusion of the avalon lower crust

the weekend dykes a newly recognized mafic dyke swarm on the eastern shore of nova scotia canada a group of related mafic dykes is present along the eastern shore of nova scotia from halifax to country harbour the dykes are generally vertical strike about 150 and have an abundance of carbo

40ar 39ar dating of micas from the east kemptville tin deposit yarmouth county nova scotia the east kemptville tin deposit in nova scotia the largest known tin deposit in north america lies in a greisen zone within the davis lake pluton generally considered to be part of the devonian south mountain batholith our dating of micas from within the deposit suggests that the greisenization process that accompanied mineralization took place about 295 5 ma ago that is ca 60 ma after the emplacement of the batholith hydrothermal alteration mineralization activity in southern nova scotia coincided with extensive shearing and tectonism throughout the hercynian orogen the east kemptville deposit appears to be approximately coeval with similar mineralization in southwest england the iberian peninsula and northwest africa and much younger than the devonian acadian orogeny

the geology and tectonics of central bhutan lithotectonic mapping metamorphic observations and u pb zircon ages underpin a substantial revision of central bhutan geology notably a more extensive and continuous outcrop of the tethyan sedimentary series tss than previously mapped metamorphic grade in the tss increases downward towards a basal north vergent tectonic contact with the underlying greater himalayan series ghs interpreted as a southward continuation of the south tibetan detachment std miocene c 17 20 ma leucogranite sheets are associated with the std in this region but appear to diminish southwards two leucogranite dykes that cross cut tss structures yield ages of 17 8 0 2 and 17 9 0 5 ma a 500 4 ma u pb zircon metamorphosed ash bed in the pele la group within the psammite dominated lower tss yields the first direct isotopic age for the tss in the eastern himalaya confirming existing age constraints from detrital zircon and fossil studies a continuation of the paro metasedimentary unit underlying the ghs was mapped near wangdue phodrang our observations notably the exposure of a wholly ductile std so far south and the significance of large nappe like structures in the tss prompt a major revision to the geological map of the bhutan himalaya and require a reassessment of tectonic interpretations of the bhutan himalaya supplementary materials zircon u pb geochronological data sample locations and descriptions features of analysed zircons sample processing method and detailed analytical conditions are available at http www geolsoc org uk sup18876

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

progressive hybridisation between late devonian mafic intermediate and felsic magmas in the meguma zone of nova scotia canada two felsic plutons of late devonian 385 370 ma age in the meguma zone of southwestern nova scotia contain three circa 376 ma synplutonic mafic intermediate intrusions that collectively record progressive stages of in situ hybridisation a 5 m wide spessartite dyke in the port mouton pluton probably underwent rapid cooling and crystallisation immediately after intrusion which heated and coarsened the adjacent tonalite an 85 m long sheet of pillowed kersantite also in tonalite of the port mouton pluton presumably contained residual magma after quenching and obtained k p ba rb more radiogenic sr zr nb and light ree from the tonalite during magma mingling the third synplutonic body a 100 m wide diorite sheet intrudes granodiorite of the adjacent shelburne pluton and has a circa 45 m wide gradational contact of metaluminous hornblende tonalite this tonalite dominantly records magma mixing by the transfer of ti mg fe ca and v in hornblende biotite plagioclase and at least in part apatite xenocrysts derived from dioritic pillows that were originally disaggregated in the granodiorite probably in response to convection scattered data points unusual concave down variation trends for al2o3 p2o5 and sr and non hyperbolic sr nd isotopic characteristics in the tonalite apparently reflect syn or post mixing fractionation and accumulation of xenocrysts from residual magma phosphorus may have assisted diffusion of sr zr nb and light ree and caused premature quenching of the hybrids at mcleods cove and birchtown during magma mingling and mixing

a petrological and geochronological study of a 360 ma metallogenic event in maritime canada with implications for lithophile metal mineralization in the canadian appalachians the occurrence of ca 360 ma greisen related molybdenite mineralization in the clayton hill biotite muscovite leucomonzongranite 1 km2 is unusual for the southwestern meguma terrane of the maritime appalachians where 380 ma granite related sn mineralization dominates the presence of extensive hornfelsing and occurrence of mineralized sn w cu zn skarns in the area suggests a larger intrusion occurs at depth the intrusion and mineralization are constrained to 361 ma based on concordant re os molybdenite and 40ar 39ar muscovite ages which equates to other ca 360 ma granites in the area hence magmatism of this age is more widespread than previously considered the intrusion is highly evolved 74 wt sio2 metaluminous a cnk 1 1 05 a cnk molar ratio al2o3 cao na2o k2o and depleted in cafemic and transition elements rare earth elements ree 106 23 ppm are strongly fractionated with light rare earth elements lree enriched la lun 10 and negative eu anomalies biotite is

age constraints of mercury s polar deposits suggest recent delivery of ice abstract surface ice at the poles of mercury appears as several m thick deposits that are composed of nearly pure water we provide new age estimates of the surfaces of mercury s polar deposits from combined analyses of poisson statistics and direct observations of crater densities within permanently shadowed radar bright regions imaged by the messenger spacecraft these age estimates conservatively suggest that ice was delivered to mercury within the last 330 myr the geologically young ages suggest that the surfaces have been recently refreshed and this may be accomplished by the delivery of ice in a young impactor or impactors a single recent impactor is more consistent with the relative purity of the ice as suggested by the earth based radar observations in contrast to ice on mercury observations of the lunar poles are suggestive of a highly patchy distribution of surface frost the patchiness of lunar polar deposits is consistent with long exposure times to the space weathering environment given enough time the polar deposits on mercury may age into a more heterogeneous spatial distribution similar to that on the moon

thermal history of the southwestern meguma zone nova scotia from an 40ar 39ar and fission track dating study of intrusive rocks two geologically distinct regions within the meguma terrane have been studied in detail and are shown to have contrasting thermal histories this conclusion is based on 31 new 40ar 39ar age spectra on micas k feldspars and hornblendes from several of the plutons in southern nova scotia which are satellites to the much larger south mountain batholith smb in addition we report four k feldspar age spectra from a locality in the northeastern part of the smb and seven fission track ages from both the southern and northern areas the complex age spectrum of hornblende from a mafic phase associated with the bamngton passage pluton suggests a minimum intrusive age of 385 ma a result consistent with geologic evidence that this pluton represents an early less evolved magmatic pulse later intrusive activity appears to have been coeval with the intrusion of the smb at ca 370 ma ago in the southern region argon clocks in feldspars were completely reset and mica clocks variably reset by a later thermal event the cumulative geochronologic and geologic evidence constrains this event to 300 320 ma ago in the smb this alleghanianl hercynian thermal disturbance is much less pronounced and appears to be localized to small areas that are often associated with economic mineralization k feldspars from the southern plutons record an episode of argon loss 220 230 ma ago which is less evident in the smb to the north upper triassic dike injection in the southern region associated with the initial rifting phase of the canadian atlantic margin accompanied this milder thermal pulse apatites in the two regions record a mean fission track age of ca 180 ma which we attribute to the final cooling of the terrane below about 100 c the timing of this event coincides with regional uplift recorded in sedimentary sequences along much of the maritime continental shelf deux kgions gtologiques distinctes inttgkes au terrane de meguma ont ctt ctudites en dctai1 et leurs histoires thermales

the touquoy zone deposit an example of unusual orogenic gold mineralisation in the meguma terrane nova scotia canada the touquoy zone deposit is host to disseminated gold mineralisation in metasiltstones of lower palaeozoic age from the close correlation between ore grades and the intersection of favourable stratigraphy and bounding faults it is apparent that mineralisation is controlled by both structural and lithological influences within the ore zone disseminated gold arsenopyrite pyrite and rare base metal sulphides are associated with a network of widely spaced millimetre scale quartz carbonate veinlets quasi pervasive fluid flow and prolonged interaction with the host rocks resulted in a diffuse but pronounced halo of wall rock alteration that is characterized by the breakdown of detrital feldspar and metamorphic chlorite and the development of hydrothermal carbonate phases k mica and disseminated sulphides these mineralogical changes are accompanied by enrichment in co2 k au as and s and depletion in na across the ore zone vein formation occurred at between 250 and 350 c and pressures of less than 1 2 kbar 1 kbar 100 mpa corresponding to an estimated depth of between 2 8 and 6 km mineralisation resulted from the unmixing of an overpressured low salinity co2 rich fluid in response to decreasing pressure during its ascent and penetration into permeable host rocks geological and geochemical features of mineralisation in the touquoy zone deposit are seen as convincing evidence for a close genetic association between disseminated style and lode gold mineralisation in orogenic terrains with the resulting style of mineralisation largely controlled by the overall structural geometry of the mineralising site rheological properties permeability and chemical receptiveness of the host rock and structural level of emplacement

sediment sources and dispersion as revealed by single grain 40ar 39ar ages of detrital muscovite from carboniferous and cretaceous rocks in mainland nova scotiageological survey of canada contribution 20090289 single grain ages of detrital muscovite from 15 sand stone samples from the lower carboniferous horton group and the lower cretaceous chaswood formation of central nova scotia were used to infer the nature of the early carboniferous unroofing of the meguma terrane and the reworking of carboniferous rocks in the early cretaceous in the western windsor basin a sample from the oldest horton group rocks yielded ages principally between ca 400 and 380 ma suggesting that most of the muscovite present came from the metamorphic rocks of the meguma terrane but was variably reset by the intrusion of the south mountain batholith at ca 380 ma other samples in this part of the basin show partial post depositional resetting younger horton group metamorphic rocks in the eastern windsor basin contain many grains with ages of ca 370 360 ma suggesting derivation from the central core of the south mountain batholith or the musquodoboit pluton horton group sandstones from the western part of the st marys basin co

derivation of the early carboniferous wedgeport pluton by crystal fractionation of a mafic parental magma a rare case of an a type granite within the meguma terrane nova scotia canada the cambrian ordovician metasedimentary rocks of the meguma terrane canadian appalachians were extensively intruded by silicic plutons during middle devonian to early carboniferous times syn plutonic but volumetrically minor mafic ultramafic intrusions were also emplaced in most localities the silicic plutons and mafic ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources the attwoods brook gabbronorite of sw nova scotia yielded an in situ zircon weighted mean 206pb 238u age of 357 9 3 3 ma that is within the uncertainty of the age of the neighbouring wedgeport pluton 357 1 ma the wedgeport pluton is a rare example of a mantle derived peraluminous a type granite within the meguma terrane the similar ages and nd isotopes of the attwoods brook gabbronorite end t 1 1 to 4 0 and wedgeport pluton end t 2 1 to 3 3 suggest the two intrusions are petrogenetically related fractional crystallization modelling demonstrates that a parental magma similar to the attwoods brook gabbronorite can produce residual silicic liquids that resemble the granites of the wedgeport pluton indicating that they could be members of the same intrusive complex the emplacement of the gabbronorite and wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the maritimes basin that produced the fountain lake continental flood basalts and a type granites of the cobequid highlands within the avalon terrane it is possible that the early carboniferous rocks of sw nova scotia are related to the rifted related magmatism within the maritimes basin

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

thermochronologic constraints on ore formation at the gays river pb zn deposit nova scotia canada from apatite fission track analysis fission tracks in detrital apatites from the cambro ordovician metasedimentary basement in the vicinity of the carboniferous hosted gays river pb zn deposit nova scotia provide a record of final

geologic fluid inclusion and stable isotope studies of the gays river lead zinc deposit nova scotia canada the gays river deposit is the largest carbonate hosted lead zinc deposit known in the mississippian windsor group of atlantic canada the orebody mainly occupies one flank of a porous dolomitized carbonate bank that unconformably overlies a basement ridge of the metasedimentary lower paleozoic megurea group the orebody consists of stratiform disseminated sulfides as open space fillings in primary and secondary pores of the dolomite and fault controlled veinlike bodies of high grade massive sphalerite and galena the carbonate bank is overlain by evaporite deposits of mississippian age underground mapping and laboratory studies suggest four main stages of evolution for gays river 1 deposition of the visean carbonate bank preore evaporite deposition pervasive dolomitization and growth of diagenetic marcasite 2 deposition of sphalerite galena chalcopyrite and calcite as a result of influx of hydrothermal metal rich saline brines into fractures and porous dolomite 3 postore deposition of calcite fluorite barite marcasite pyrite and selenite and 4 uplift localized dedolomitization of the mineralized carbonates and exposure by erosion in cretaceous times microthermometry of fluid inclusions yields the following mean homogenization temperatures sphalerite 215oc ore stage calcite 173oc postore calcite 142oc fluorite 142oc and barite 137oc pressure corrections should be minimal for these temperatures no evidence of boiling was observed in the inclusions salinity determinations from the ice melting temperatures of inclusions in postore fluorite and calcite yield a value of ca 20 4 equivalent wt percent naci for the hydrothermal fluid during the waning stages of mineralization isotopic analyses indicate that anhydrite and gypsum in the overlying evaporites and barite within the orebody are enriched in heavy sulfur t 34s 13 1 16 5 0 suggesting a mississippian seawater source ore stage sphalerite galena and chalcopyrite probably derived their sulfur b34s 8 0 13 65 0 from sulfates or possibly a homogenized basement source postore marcasite and pyrite are characterized by light probably biogenic sulfur ba4s 9 7 to 46 0 mineralized carbonates are significantly depleted in the heavier isotopes of oxygen and carbon with respect to their unmineralized equivalents preliminary lead isotope data for galena suggest that the metasedimentary basement was a source of lead this study disputes an earlier interpretation that the stratiform lead zinc ores are an early low temperature diagenetic cement of the carbonate bank the high grade zones are not residual concentrations related to sinkholes as originally thought instead both disseminated and massive ores are probably the result of the same mineralizing episode involving deeply convecting brines or brines expelled during basin dewatering under high geothermal gradients in the late paleozoic

k ar and 40ar 39ar geochronology of granitoid rocks from southern nova scotia its bearing on the geological evolution of the meguma zone of the appalachians k ar and or 40ar 39ar apparent ages are reported for 28 samples of biotite and muscovite from nova scotia s south mountain batholith and associated northern satellite stocks in addition 14 mica samples from the southern satellite stocks were dated previous workers using primarily k ar and rb sr techniques have reported a spread of apparent ages ranging from 240 420 ma for these intrusive rocks the present data set is internally consistent and has been calibrated against accepted interlaboratory standards a mean age of 367 ma was obtained for the south mountain batholith and the northern stocks a value consistent with results recently obtained in an rb sr study by clarke and halliday no differences in apparent age among the various phases or clear geographic age distribution patterns were evident satellite stocks in the southern part of the province have in general younger apparent ages clustered in the range 300 320 ma we suggest that in southern areas mica argon systems record the effect

dating mineralization using several isotopic methods an example from the south mountain batholith nova scotia canada abstract granitic plutons in the meguma terrane may be broadly divided into two suites 1 an areally predominant cogenetic suite of peraluminous granitoid rocks tonalite leucogranite and 2 an areally subordinate paraintrusive suite specialized in sn w mo cu f u p zn as which appears to have been produced by fluid interaction with either residual magma or crystallized rock granite related mineralization is generally considered to have developed during terminal stages of magmatic crystallization that lead to metasomatism and hydrothermal alteration previous geochronological data have suggested that the main cogenetic suite was emplaced at 350 375 ma whereas some of the paraintrusive suite is markedly younger 250 350 ma the apparently large time interval between the intrusion of the cogenetic suite and some of the mineralization suggests that they are not coeval and has led to the conclusions that the younger mineralization may be related to later magmatism and or tectonothermal events rocks associated with two mineral occurrences in the south mountain batholith that had previously yielded anomalously young isotopic ages millet brook and westfield have been analyzed for u pb and ar isotopes in an attempt to resolve this dilemma new geochronological data from the millet brook area indicate that intrusion of granodiorite at 377 5 3 ma nearly concordant monazite age was closely followed by intrusion of most other phases all of which had cooled through 375 c closure temperature for ar in muscovite by 377 373 6 ma 40 ar 39 ar plateau ages new data from westfield indicate that a paraintrusive porphyry was intruded at 385 2 ma upper intercept of a chord through four nearly concordant zircon fractions and that greisen muscovite cooled through the closure temperature by 368 2 6 ma 40 ar 39 ar plateau age these data indicate that a previously reported rb sr whole rock isochron age of 270 ma at westfield reflect isotopic resetting that occurred below the blocking temperature for 40 ar 39 ar in muscovite 375 c clearly further rb sr analysis is required to document this process other 250 300 ma ages in the meguma terrane are recorded along the tobeatic fault zone away from the fault ages increase upto 370 ma suggesting that the fault may have acted as an important pathway for fluids and heat that facilitated isotopic resetting rb sr whole rock and mineral systems may be affected after formation of an alteration assemblage associated with mineralization by the migration of rb and its concentration in secondary minerals

the petrology geochemistry and economic potential of the musquodoboit batholith nova scotia the musquodoboit batholith of southwestern nova scotia is a massive post tectonic granitoid intrusion that was emplaced into the regionally deformed and metamorphosed meguma group metasedimentary rocks the batholith is composed primarily of medium to coarse grained monzogranites into which two small 1 km2 porphyries and numerous dykes have been injected all rocks contain quartz alkali feldspar plagioclase muscovite and biotite with the exception of some leucocratic dykes cordierite is a major constituent in most monzogranitic rocks and also occurs in some leucocratic dykes andalusite and garnet 0are also present as accessory phases in some rocks major element chemical analyses indicate that all rock types in the musquodoboit batholith are peraluminous compositions resemble those of the eastern part south mountain batholith however slightly higher concentrations of al2o3 and p2o5 distinguish the musquodoboit batholith from the central part of the south mountain batholith major and trace

remagnetization of the rush springs formation cement oklahoma implications for dating hydrocarbon migration and aeromagnetic exploration the permian rush springs formation above the cement anticline in oklahoma contains a late permian early triassic chemical remanent magnetization crm that is interpreted to reside in authigenic magnetite the crm is found in bleached carbonate cemented sandstones that were altered by hydrocarbons and contain authigenic magnetite the magnetite presumably precipitated in the late permian early triassic as a result of chemical conditions created by hydrocarbons or associated fluids that migrated from underlying reservoir units red sandstones around cement that were not altered by hydrocarbons contain a permian crm that resides in hematite the red and bleached sandstones have similar magnetization intensities and susceptibilities this raises questions about the use of aeromagnetic surveys in hydrocarbon exploration

40ar 39ar age spectrum analysis of detrital microclines from the southern san joaquin basin california an approach to determining the thermal evolution of sedimentary basins abstract detrital microcline grains from sedimentary strata preserve a record of thermal evolution in the temperature range 100 to 200 c which can be revealed by40ar 39ar age spectrum analysis microcline separates from deep drill hole intersections with eocene to miocene sediments in the basin and tejon blocks of the southern san joaquin valley california analysed by the age spectrum approach show radiogenic40ar 40ar gradients that record both the slow cooling of the uplifting sediment source 65 ma ago and a recent thermal event this information in conjunction with the observation of fission track annealing in the coexisting apatites allows estimation of the temperature time conditions of this thermal event at about 140 c for 200 ka present and paleotemperature data is in accord with heating related to several kilometers of pleistocene sediment deposition heat flow calculations suggest that this recent subsidence has depressed the thermal gradient from about 30 c km 1 to the present apparent gradient of 24 c km 1 40ar 39ar analysis of detrital microcline crystals yields thermochronological information in the temperature time range of petroleum maturation and provides this technique with potential as both a useful exploration tool and as a means of probing the fundamental geodynamic processes of basin evolution

controls on lunar basaltic volcanic eruption structure and morphology gas release patterns in sequential eruption phases assessment of mare basalt gas release patterns during individual eruptions provides the basis for predicting the effect of vesiculation processes on the structure and morphology of associated features we subdivide typical lunar eruptions into four phases phase 1 dike penetrates to the surface transient gas release phase phase 2 dike base still rising high flux hawaiian eruptive phase phase 3 dike equilibration lower flux hawaiian to strombolian transition phase phase 4 dike closing strombolian vesicular flow phase we show how these four phases of mare basalt volatile release together with total dike volumes initial magma volatile content vent configuration and magma discharge rate can help relate the wide range of apparently disparate lunar volcanic features pyroclastic mantles small shield volcanoes compound flow fields sinuous rilles long lava flows pyroclastic cones summit pit craters irregular mare patches imps and ring moat dome structures rmdss to a common set of eruption processes

origin of basalt fire fountain eruptions on earth versus the moon fire fountain eruptions of basaltic magma occur on earth at centers such as kilauea hawaii and deposits from apparently similar eruptions have been found on the lunar surface the driving force for terrestrial fire fountain eruptions is the exsolution of dissolved co 2 based on gases dissolved in melt inclusions trapped in olivine phenocrysts and the relatively high oxidation state of these magmas gases released at the vent show that so 2 and eventually h 2 o are partitioned into the co 2 rich gas adding to the gas volume in contrast analytical and experimental studies of lunar samples indicate that the gas phase responsible for driving the lunar eruptions was co rich and produced by the oxidation of c graphite carried in the slowly ascending low f o 2 basalt the graphite oxidation occurs when the pressure in the ascending lunar magma reaches that of the graphite gas reaction surface 40 1 mpa or 8 km depth for the apollo 17 orange glass magma as graphite is oxidized some feo is reduced potentially forming a fe rich metal phase and fe rich metal spherules are present in beads in lunar glass deposits other gas species such as s cl and f partitioned variously into co rich lunar volcanic gas and appear in surface coatings on the glass spherules modeling of the magma flow from 8 km depth to the lunar surface shows that the gas bubble volume fraction assuming initial c at 50 500 ppm levels ranges from 0 5 to 0 8 at the surface the exit velocity ranges from 15 to 35 m s and the low viscosity magma fragments only as it erupts at the lunar surface

sulphur in pennsylvania coals of atlantic canada geologic and isotopic evidence for a bedrock evaporite source abstract higher sulphur contents in coals are commonly explained by the proximity of the original peat to marine waters during deposition as the sulphate ions in seawater provide an abundant source of sulphur however pennsylvanian coals of the maritimes basin which commonly contain 5 8 sulphur are associated with a predominantly freshwater biota and alluvial sedimentary features and evidence for marine beds is scare several workers have suggested that the sulphur was derived from dissolution of thick sulphate evaporites in the underlying mississippian windsor group rather than from pennsylvanian seawater we set out to test this hypothesis using a biogeochemical model derived from studies of sulphur isotopes in modern peat swamps during the bacterial decomposition of plant material the h 2 s generated from groundwater sulphate is fixed as metal sulphides which are enriched in the lighter 32 s isotope by 15 or more sulphides formed chemically during burial will be much less fractionated isotope ratios of sulphur bearing products can thus be used to trace the original source of the sulphur by comparison with a source of known isotopic composition eight evaporite samples from the upper windsor group in the sydney basin have a mean 34 s value of 15 sixteen pyrite samples from five coal seams in the overlying morien group range from 14 8 to 5 34 s the pyrite values follow the pattern predicted for derivation from windsor sulphates disseminated pyrite generally contains more highly fractionated sulphur than nodular pyrite suggesting that much of the former was generated by bacterial action whereas the latter was produced during later burial isotopic ratios for soluble sulphate in the coal correspond closely to those for the associated pyrite because mississippian and pennsylvanian seawaters showed a similar range of 34 s values the test does not preclude a pennsylvanian marine source of sulphate both geological and isotopic data however are consistent with a windsor evaporite source

a comparative 40ar 39ar conventional and laserprobe study of muscovite from the port mouton pluton southwest nova scotia we report 40ar 39ar age spectrum and laserprobe data for primary magmatic or fluido magmatic muscovite minerals from the port mouton pluton one of several weakly peraluminous peripheral plutons in the meguma terrane southwestern nova scotia laserprobe data from the cores of thin grain fragments suggest that this pluton cooled rapidly following intrusion at 373 1 ma the u pb monazite age the rims of thicker more complete grains record ages of 315 325 ma even in cases where there have been no apparent changes in grain rim chemistry and where deformation is minimal the observed age gradients may be the result of prolonged reheating during the late carboniferous alleghanian orogeny or alternatively the result of rapid cooling at this time to temperatures below the closure value for muscovite rims conventional age spectra obtained from muscovite separates record neither the older intrusion age nor the younger reset cooling age instead these intermediate ages appear to reflect the averaging of int

consonorm_lg new normative minerals and alteration indexes for low grade metamorphic rocks the consonorm lg method provides a standardized solution for approximating metamorphic parageneses as well as indexes for estimating chemical and mineralogical changes caused by hydrothermal alteration consonorm lg is designed for rocks dominated by silicates fe ti oxides and or carbonates and it approximates the main parageneses of greenschist and lower amphibolite grade metamorphic rocks for three sets of temperature and pressure conditions 350 c and 2 5 kbars 450 c and 2 5 kbars 575 c and 2 kbars for each model the norm calculates the main paragenesis using an acfmnk tetrahedron a convenient way of representing a large number of silicate assemblages in addition to silicate minerals consonorm lg calculates fe ti oxides and other accessory minerals from minor elements as well as sulfides from analyzed s or from analyzed metals and carbonates from analyzed co2 or from normative co2 estimated from loss on ignition loi consonorm lg also calculates several alteration indexes to estimate fe mg e g chloritization ca e g propylitic alteration na and k acid alterations e g sericitization phyllic alterations and al gain e g argillization carbonatation indexes are also calculated using the amount of normative minerals formed by this type of alteration i e carbonates chlorite and muscovite the normative calculation is validated using published whole rock analyses and petrographic descriptions alteration indexes are validated using several natural samples of alteration halos around base metal and gold deposits

detrital muscovite geochronology and the cretaceous tectonics of the inner scotian shelf southeastern canada1 2 geochronology of detrital muscovite from the lower cretaceous of the central scotian basin has shown predominant supply of meguma terrane detritus including muscovite with alleghanian mid carboniferous to permian ages from the inner scotian shelf in this study 87 detrital muscovite grains from five wells in the eastern scotian basin representing depositional ages from tithonian to early albian were dated by single grain 40ar 39ar techniques previous work shows that the provenance of this sediment was different from wells in the central scotian basin compared with the central scotian basin the muscovite age populations from the eastern scotian basin have more 20 versus 7 pre devonian ages derived from inboard terranes of the appalachians in both the central and eastern scotian basin most old grains are found in the tithonian and the aptian albian with fewer in the valanginian and almost none in the kimmeridgian and the hauterivian barremian these data suggest rapid unroofing of the megum

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

deep generation of magmatic gas on the moon and implications for pyroclastic eruptions 1 lunar pyroclastic beads are interpreted to represent primitive magmas derived from great depths and rapidly erupted to the surface in explosive events however a detailed mechanism for gas generation at great depth and rapid magma transport to the surface has not yet been described furthermore the pyroclastic beads are not petrogenetically related to basalts erupted near the sampling sites we propose a model in which these conundrums are resolved through gas build up in a low pressure micro environment near the tip of a magma filled crack dike propagating rapidly from the magma source depth to the surface the gas rich region consists of a free gas cavity overlying a foam extending vertically for 20 km eruption of the foam results in the widespread emplacement of unfractionated pyroclastic beads subsequent ascent of the underlying gas free picritic magma is unlikely to occur perhaps accounting for the lack of sampled eruptive equivalents

precise u pb dating of meguma basement xenoliths new evidence for avalonian underthrusting u pb zircon and monazite dates for granulite facies basement xenoliths from the popes harbour dyke on the eastern shore of nova scotia provide strong evidence that the meguma terrane overlies avalo

lunar mare volcanism stratigraphy eruption conditions and the evolution of secondary crusts abstract lunar mare basalt deposits cover 17 of the lunar surface occur preferentially in topographic lows on the nearside and have a total volume estimated at 1 107 km3 analysis of returned samples and photogeologic and remote sensing studies shows that mare volcanism began prior to the end of heavy bombardment the period of cryptomare formation in pre nectarian times and continued until the copernican period a total duration approaching 3 5 4 ga stratigraphic analyses show that the flux was not constant but peaked in early lunar history during the imbrian period which spans the period 3 85 3 2 ga average volcanic output rate during this peak period was about 10 2 km 3 a very low relative to the present global terrestrial volcanic output rate and comparable to the present local output rates for individual volcanoes such as vesuvius and kilauea hawaii volcanic landforms indicate that many eruptions were of high volume and long duration some eruptions associated with sinuous rules may have lasted of the order of a year and emplaced 103 km3 of lava representing the equivalent in one year of about 70 000 years at the average flux shallow magma chambers were uncommon the nearsidefarside mare deposit asymmetry can be readily explained by differences in crustal thickness magma ascending from the mantle or from a buoyancy trap at the base of the crust should preferentially extrude to the surface on the nearside but should generally stall and cool in dikes in the farside crust extruding only in the deepest basins the occurrence of farside maria within craters whose diameter is generally near to or less than the thickness of the crust may be accounted for by the difference between local and regional compensation dikes that establish pathways to the surface on the nearside should have very high volumes comparable to the volumes associated with many observed flows and sinuous rilles an abundance of dikes should exist in the lower crust of the moon many more than those feeding surface eruptions the upper limit is 37 50 of the crust by volume the presence and abundance of such dike swarms have important implications for the interpretation of the average composition of the lunar crust and the composition of basin and crater ejecta the interplay between thermal contraction and differentiation leads to net cooling and ultimate contraction of the outer portions of the moon resulting in a regional horizontal compressive stress acting on the lunar crust in addition overall cooling and deepening of sources require the production of ever larger volumes of magma in order to reach the surface with time stresses became high enough so that few dikes could open to the surface causing eruptive activity to be severely diminished in the eratosthenian and perhaps to cease in the copernican period lower stress levels are required to terminate eruptive activity on the lunar farside consistent with the imbrian age of the farside maria and the nearside location of the youngest maria lunar mare deposits provide an example of the transition from primary crusts to secondary crusts and illustrate the significance of several factors in the evolution of secondary crusts such as crustal density variations in crustal thickness presence of impact basins state and magnitude of stress in the lithosphere and general thermal evolution these factors are also responsible for the extremely low volcanic flux even during periods of peak extrusion

brines in the carboniferous sydney coalfield atlantic canada abstract formation waters within upper carboniferous sandstones in the sub sea prince and phalen coal mines nova scotia originated as residual evaporative fluids probably during the precipitation of windsor group lower carboniferous salts which underlie the coal measures salinity varies from 7800 to 176 000 mg l and the waters are na ca cl brines enriched in ca sr and br and depleted in na k mg and so4 relative to the seawater evaporation curve br cl and na cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30 the brines lie close to the meteoric line on h o isotopic plots but with a compositional range of 18o from 4 18 to 6 99 and of d from 42 4 to 23 5 distant from modern meteoric or ocean water mine water composition contrasts with that of nearby salt spring brines which are inferred to have originated through dissolution of windsor group evaporites by modern meteoric waters however a contribution to the mine waters from halite dissolution and from br in organic matter cannot be ruled out present concentrations of several elements in the brines can be explained by water rock interaction the original windsor brines probably moved up into the overlying coal measure sandstones along faults prior to the late triassic the high salinity and irregular salinity distribution in the phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile in contrast prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters basinal brines from which these modern formation fluids were derived may have been important agents in base metal and ba mineralisation from the mid carboniferous onwards as saline fluid inclusions are common in zn pb sulphide deposits in the region

occurrence of secondary magnetite within biodegraded oil samples of solid bitumen from the thornton quarry illinois and the cynthia quarry mississippi were found to be strongly magnetic and to have rock magnetic properties suggesting that the magnetizable grains present are magnetite studies of magnetic isolates revealed that magnetite is present primarily as spherical crystal aggregates that appear identical to magnetite spherules isolated from re magnetized paleozoic carbonate units from other localities organic geochemical analyses of the solid bitumen suggest an origin by microbial attack on what once was liquid crude oil the occurrence of secondary magnetite as inclusions within solid bitumen suggests a relationship between crude oil biodegradation and development of that mineral in our samples we infer that secondary magnetite in other geologic environments may be related to the presence of hydrocarbons the discovery of a natural association of secondary magnetite and hydrocarbons has important implications for paleomagnetism and for petroleum exploration

late carboniferous and early permian drainage patterns in atlantic canada paleoflow data have been compiled for late carboniferous late westphalian a to early permian alluvial deposits over a large area of atlantic canada the data which include more than 36 000 measurements of large scale trough cross strata indicate a predominantly northeasterly paleoflow and suggest that a major source area lay to the southwest of the region throughout the 30 ma period represented uplands within the basin deflected paleoflow and probably formed important local drainage and sediment sources tectonostratigraphic analysis suggests that the drainage originated in the fold and thrust belt of the central appalachians and parts of the northern appalachians rivers probably followed northeast oriented structural lineaments through the older acadian mountains of the northern appalachians a considerable proportion of the rising orogen s drainage and probably detritus may have traversed basins along the strike of the mountain belt a situation analogous to that of the modern himalayas

temperature and age constraints on the metamorphism of the tethyan himalaya in central nepal a multidisciplinary approach abstract metasediments of devonian to triassic age of the tethyan himalaya th from several areas in central and western nepal between western dolpo and marsyandi valley were sampled for thermo metamorphic studies illite and chlorite crystallinity vitrinite reflectance calcite dolomite and chlorite chloritoid geothermometers k ar dating on illite rich fractions and zircon fission track thermochronology this paper reports for the first time the occurrence of chloritoid in the th out of the range of granite contact aureoles it also presents the first zircon fission track dating performed on th metasediments the peak temperatures of metamorphism have been around 250 300 c 320 350 c 330 370 c and 400 450 c in the western dolpo hidden valley manang and marpha areas respectively in the manang and hidden valley areas illite k ar data are interpreted as ages of recrystallized k white micas newly formed during metamorphism at around 25 30 ma in the marpha area illite k ar and zircon fission track ages 12 15 ma are consistent representing cooling ages after metamorphic overprinting of higher grade than in the other areas the joint investigation of the organic maturation and zircon ft chronology yields insight on the thermal calibration of zircon reset the rmax of 5 7 to 8 0 indicates a temperature range of ca 315 325 c which is in the partial annealing zone of the zircon ft thermochronometer our results might be explained by the presence of a thick thrust sheet once existing above the study area

cation study of fluid inclusion decrepitates in the jubilee and gays river canada zn pb deposits characterization of ore forming brines an sem eds instrument sensitive to c and o is used to measure cation ratios in individual fluid inclusion decrepitates of main paragenetic phases from two nova scotian mississippi valley type deposits the technique confirms that the analyses obtained for the carbonate hosts are not contaminated by substrate and permits measurements of small amounts of decrepitates the technique has been used to investigate fluid compositions in inclusions of presulfide stage dolomite and calcite sulfide stage sphalerite and calcites and postsulfide calcite at the gays river and jubilee zn pb deposits in nova scotia the results indicate that na and ca are the two major cations minor amounts of k and mg are also detected nacl and cacl 2 ranges for decrepitates from the two deposits are as broad as for modem mixed brines and thereby suggest that solution mixing partly controlled the paleobrine compositions when compared to other mississippi valley type deposits the gays river and jubilee deposits are similar in nacl cacl 2 kcl composition to a group of mississippi valley type districts including deposits from the ozark region that are associated with large volume clastic sequences or paleoaquifers higher proportions of kcl at gays river and higher proportions of cacl 2 at jubilee indicate that the mineralizing brines interacted with horton group clastic aquifers of different mineral compositions the brines in the two areas might have originated from evaporation of seawater but they were later modified by interaction with clastic rocks of different compositions

a comparison of orogenic gold mineralisation in central victoria aus western south island nz and nova scotia can implications for variations in the endowment of palaeozoic metamorphic terrains abstract the palaeozoic western lachlan orogen in victoria se australia the buller terrane western south island new zealand and the meguma terrane nova scotia canada are remarkably similar in regard to their geological age and history structural make up and the setting and formation of orogenic lode and disseminated style gold deposits within these fold belts a comprehensive review of the principal characteristics of orogenic gold deposits in each of the three historically important gold provinces illustrates the many similarities but it also reveals several major geological structural tectonic geochemical and geochronological differences that may account for the disparity in contained gold and overall endowment between the three fold belts aspects that stand out as potentially playing a critical role in the generation of a phanerozoic world class orogenic gold province include 1 the presence of a hydrated oceanic character substrate that can provide a fertile source rock for both fluids and metals 2 asthenospheric thermal input to trigger and sustain crustal devolatilisation and melting 3 the existence of a number of near vertical deep seated faults 4 substantial transcurrent movement and 5 evolution of an accretionary subduction system that promotes development of an extensive fore arc system with prolonged fluid generation and circulation quantification of these controlling factors provide a significantly improved understanding of the processes that control the genesis of orogenic gold deposits and also have the potential to enable discrimination between more and less gold favourable orogens and parts of orogens

the east kemptville tin deposit yarmouth county nova scotia a pb isotope study of the leucogranite and mineralized greisens evidence for a 366 ma metallogenic event pb isotopic data for whole rock leucogranite and mineral separates variably mineralized greisen and galena from the east kemptville sn cu zn ag deposit yarmouth county southwestern nova scoti

lunar cryptomaria physical characteristics distribution and implications for ancient volcanism cryptomaria lunar volcanic deposits obscured by crater and basin impact ejecta can provide important information about the thermal and volcanic history of the moon the timing of cryptomare deposition has implications for the duration and flux of mare basalt volcanism in addition knowing the distribution of cryptomaria can provide information about mantle convection and lunar magma ocean solidification here we use multiple datasets e g m3 lola lroc diviner to undertake a global analysis to identify the general characteristics e g topography surface roughness rock abundance albedo etc of lunar light plains in order to better distinguish between ancient volcanic deposits cryptomaria and impact basin and crater ejecta deposits we find 20 discrete regions of cryptomaria covering approximately 2 of the moon which increase the total area covered by mare volcanism to 18 of the lunar surface comparisons of light plains deposits indicate that the two deposit types volcanic and impact produced are best distinguished by mineralogic data on the basis of cryptomaria locations the distribution of mare volcanism does not appear to have changed in the time prior to its exposed mare basalt distribution there are several hypotheses explaining the distribution of mare basalts which include the influence of crustal thickness mantle convection patterns asymmetric distribution of source regions kreep distribution and the influence of a proposed procellarum impact basin the paucity of farside mare basalts means that multiple factors such as crustal thickness variations and mantle convection are likely to play a role in mare basalt emplacement

remanence in authigenic magnetite testing the hydrocarbon magnetite hypothesis paleomagnetic rock magnetic petrographic and geochemical studies of hydrocarbon saturated speleothems in southern oklahoma indicate there is a relation between hydrocarbons and a chemical magnetization that resides in magnetite the speleothems which are composed of light and dark calcite bands occur in caves of karst origin in the ordovician kindblade formation vertebrate fossils interbedded with the deposits indicate they are permian in age the dark bands contain primary hydrocarbon filled fluid inclusions the dark calcites possess over an order of magnitude stronger natural remanent magnetization than the lighter bands which do not yield stable decay during demagnetization alternating field af and thermal demagnetization of specimens of the dark bands reveal a permian direction of magnetization declination 160 inclination 3 k 17 95 5 n 56 the results of rock magnetic experiments and the fact that most maximum unblocking temperatures are below 580 c suggest that the dominant component resides in magnetite in some specimens stable decay to 640 c suggests the presence of a weak component residing in hematite the presence of authigenic magnetite spheres in magnetic extracts of the dark calcites supports a chemical origin for the magnetization shallow burial depths probably eliminate the possibility of a thermoviscous magnetization the occurrence of primary hydrocarbon inclusions suggests that hydrocarbons seeped into the caves during precipitation of the speleothems and were trapped in the calcite crystals the relationship between intensity of magnetization and hydrocarbon abundance leads us to propose that chemical conditions created by the hydrocarbons caused precipitation of authigenic magnetite and acquisition of the associated chemical remanence

volcanically induced transient atmospheres on the moon assessment of duration significance and contributions to polar volatile traps a transient lunar atmosphere formed during a peak period of volcanic outgassing and lasting up to about 70 ma was recently proposed we utilize forward modeling of individual lunar basaltic eruptions and the observed geologic record to predict eruption frequency magma volumes and rates of volcanic volatile release typical lunar mare basalt eruptions have volumes of 102 103 km3 last less than a year and have a rapidly decreasing volatile release rate the total volume of lunar mare basalts erupted is small and the repose period between individual eruptions is predicted to range from 20 000 to 60 000 years only under very exceptional circumstances could sufficient volatiles be released in a single eruption to create a transient atmosphere with a pressure as large as 0 5 pa the frequency of eruptions was likely too low to sustain any such atmosphere for more than a few thousand years transient volcanically induced atmospheres were probably inefficient sources for volatile delivery to permanently shadowed lunar polar regions 2020 american geophysical union all rights reserved

small scale lunar farside volcanism abstract we identified and mapped 28 mare basalt occurrences between the australe and south pole aitken basins on the southern lunar farside and determined their absolute model ages amas by performing crater size frequency distribution csfd measurements our study area can be subdivided into seven major mare basalt occurrences in and around bolyai roche v rosseland pauli and roche craters south of both rosseland and coblentz craters as well as mare patches between eotvos and roche craters the amas of the mare basalts in and around bolyai crater range from 2 1 ga to 3 5 ga two units varying drastically within short distances the mare patches south of coblentz crater contain nine units that have amas ranging from 2 1 ga to 3 8 ga the mare basalts in roche v crater show an ama of 2 2 ga we mapped seven volcanic units in rosseland crater and derived amas for five of these units the mare basalts in rosseland crater show the youngest amas found in our study area ranging from 1 5 ga to 2 9 ga the mare basalt occurrence south of rosseland crater shows significantly older ages with an ama of 3 3 ga the mare basalts in pauli and roche craters show amas from 1 7 ga to 3 1 ga the mare patches between eotvos and roche craters show a similar range of amas from 1 9 ga to 3 1 ga the amas of the mare basalts in our study show that the lunar farside was volcanically active for nearly as long as the lunar nearside 1 2 ga ago or at least longer than previously thought 2 5 ga ago and predicted by models of the ascent and eruption of lunar basalts in addition we calculated thicknesses and volumes of the investigated mare basalts with thicknesses between 21 m and 172 m and volumes from 0 1 km3 to 379 km3 the mare basalts in our study area show a wide range of dimensions similar to other mare basalts of the lunar near and farsides

the scotian basin offshore nova scotia thermal history and provenance of sandstones from apatite fission track and 40ar 39ar data apatite fission track and 40ar 39ar age spectrum data from sandstone drill core minerals taken from depths of 2 5 km in nine wells from the scotian basin are presented and interpreted in terms of the thermal history of the basin and the provenance of its sediments the focus of the study is a comparison of the data from these thermochronometers with each other and with previously published vitrinite reflectance and aromatization isomerization a i reactions in biomarker compounds from the same or nearby wells apatite fission track ages are generally in agreement with expectations in that they trend to zero at a depth of 4 km corrected bottom hole temperature 120 c shallower lower present temperature samples are partially annealed the degree of partial annealing correlates closely with the degree of a i reactions both thermal indicators are activated over the temperature range 60 120 c samples from two wells mic mac j 77 and erie d 26 are anomalous they are more annealed than present formati

a theoretical model for the formation of ring moat dome structures products of second boiling in lunar basaltic lava flows abstract newly documented ring moat dome structures rmdss low mounds typically several hundred meters across with a median height of 3 5 m and surrounded by moats occur in the lunar maria they appear to have formed synchronously with the surrounding mare basalt deposits it has been hypothesized that they formed on the surfaces of lava flows by the extrusion of magmatic foams generated in the flow interiors as the last stage of the eruption and flow emplacement process we develop a theoretical model for the emplacement and cooling of mare basalts in which the molten cores of cooling flows are inflated during the late stages of eruptions by injection of additional hot lava containing dissolved volatiles crystallization of this lava causes second boiling an increase in vapor pressure to the point of supersaturation due to crystallization of the melt generating copious quantities of vesicles magmatic foam layers at the top and bottom of the central core of the flow flow inflation of many meters is predicted to accompany the formation of the foam layers flexing the cooled upper crustal layer and forming fractures that permit extrusions of the magmatic foams onto the surface to form domes with subsidence of the subjacent and surrounding surface forming the moats by modeling the evolution of the internal flow structure we predict the properties of rmdss and the conditions in which they are most likely to form we outline several tests of this hypothesis

late devonian lamprophyric dykes in the meguma zone of nova scotia hornblende rich lamprophyric dykes from southeastern nova scotia are contemporaneous with the large peraluminous granitic batholiths ca 370 ma of the meguma zone and may be closely associated with their origin

characteristics of ree and other trace elements in response to successive and superimposed metasomatism within a portion of the south mountain batholith nova scotia canada abstract successive and superimposed periods of late to post magmatic metasomatism have resulted in mineralogical and textural modification within leuco monzogranitic rocks of the big indian lake polyphase intrusive suite bipis the alteration and associated mineralization exhibit a transition from an early pervasive style to a later fracture controlled style and can be defined by diagnostic ree and other trace element behavior while the anomalous behavior of some elements mno ta u k rb hree is attributed to metasomatic hydrothermal activity the compatible behavior of b f li w and rb appears to have been governed by predominately magmatic processes all elements including al can be mobilized during repeated fluid rock interaction the behavior of ree during evolution of the bipis indicates that they also were affected by both magmatic lree depletion eu depletion and metasomatic hree lree enrichment eu enrichment depletion processes the remobilization and subsequent redeposition of trace elements is dependent upon the nature and stability of the metasomatic mineral assemblages in this respect a metasomatized granitic rock could reflect a ree pattern similar to that of an unaltered equivalent

application of bingham statistics to a paleopole data set towards a better definition of apwp trends abstract bingham statistical analyses were applied to paleomagnetic data from 50 published studies from north america of carboniferous through early jurassic age in an attempt to test whether the azimuths of the long axes of the bingham ellipses lie tangent to the apparent polar wander path the underlying assumption is that paleomagnetic directions will form a fisherian circular distribution if no apparent polar wander has taken place during magnetization acquisition however the distribution should appear elongated elliptical if magnetization acquisition occurred over a significant amount of time involving apparent polar wander the long axes in direction space yield corresponding azimuths in paleopole space which can be compared to the north american apwp we find that generally these azimuths are indeed sub parallel to the apwp validating the methods and the hypothesis plotting a pole as an azimuthal cord representing the long axis of the ellipse will provide additional robustness or definition to an apwp based upon temporally sparse paleomagnetic studies

thermal and magmatic evolution of the moon as with all science our continually developing concepts of lunar evolution are firmly tied to both new types of observations and the integration of these observations to the known pool of data this process invigorates the intellectual foundation on which old models are tested and new concepts are built just as the application of new observational tools to lunar science in 1610 galileo s telescope and 1840 photography yielded breakthroughs concerning the true nature of the lunar surface the computational and technological advances highlighted by the apollo and post apollo missions and associated scientific investigations provided a new view of the thermal and magmatic evolution of the moon 1 1 pre apollo view of the thermal and magmatic evolution of the moon many of the early views of the moon manifested in mythology and art throughout the world were primarily tied to lunar and terrestrial cycles and the relationships between the sun and the moon prophetically myths involving the lunar deities mwuetsi from zimbabwe and coyolxauhqui from mexico told of rather violent or catastrophic events in which the moon was expunged from the earth numerous ancient scientific observations were made about the nature of the moon ranging from those uncovered in early neolithic sites that correctly identified mare crisium and mare humorum to the insights made by greek philosophers such as anaxagoras ca 500 428 b c and democritus ca 460 370 b c who attached terrestrial analogues to its character stone mountains with the advent of the telescope 1610 and photography 1840 as scientific tools for lunar exploration semiquantitative data could be collected that would provide an intellectual foundation for scientific interpretation initially modern terrestrial geological analogs were extended to the moon lunar highlands volcanic craters seas combined with the rigors of computational modeling these observational data were extended to predict the original thermal state of the moon and its thermal and magmatic history its proximity to the earth

metalliferous coals of the westphalian a joggins formation cumberland basin nova scotia canada petrology geochemistry and palynology abstract five coals of westphalian a early middle pennsylvanian age were sampled from the joggins formation section exposed along chignecto bay at joggins nova scotia coal beds along the bay were mined beginning in the early 17th century yet there have been few detailed published investigation of the coal beds of this classic section the lowermost coal the upper coal 28 upper fundy is a high vitrinite coal with a spore assemblage dominated by arboreous lycopsid spores with tree ferns subdominant the upper portions of the coal bed have the highest ratio of well preserved to poorly preserved telinite of any of the coals investigated coal 19 clam coal has 88 total vitrinite but unlike the fundy coal bed the telinite has a poor preservation ratio and half the total vitrinite population comprises gelocollinite and vitrodetrinite the latter coal bed is directly overlain by a basin wide limestone bed the lower kimberly coal shows good preservation of vitrinite with relatively abundant telinite among the total vitrinite the middle kimberly coal which underlies the tetrapod bearing lycopsid trees found by lyell and dawson in 1852 exhibits an upward decrease in arboreous lycopod spores and an upward increase in the tree fern spore punctatisporites minutus telinite preservation increases upwards in the middle kimberly but overall is well below the preservation ratio of the upper fundy coal bed the coals all have high sulfur contents yielding up to 13 7 total sulfur for the lower lithotype of the upper fundy coal bed the kimberly coals are not only high in total and pyritic sulfur but also have high concentrations of chalcophile elements zinc ranging up to 15 000 ppm ash basis is present as sphalerite in fusain lumens arsenic and lead each exceed 6000 ppm ash basis in separate lithotypes of the kimberly coals together these data are consistent with elevated ph in planar mires the source of the elemental enrichment in this presumed continental section is enigmatic

some observations on the interpretation of 40ar 39ar age spectra several recent applications of the 40ar 39ar age spectrum technique have utilized the ability of this technique to resolve the internal ar isotope distribution in crystals for the purpose of placing constraints on the timing of thermal events additionally a few of these studies have attempted to use certain properties of the age spectrum to estimate the temperature and duration of heating experienced by the sample during the disturbance although these successful applications are encouraging the interpretation of age spectra of disturbed samples is in many ways still an art form with the beholder apparently relatively free of constraints that might limit an assessment in fact there are a number of restrictions on interpretation imposed by 1 multiple episodic loss 2 slow cooling 3 mixed phases 4 resolution of the age spectrum 5 excess 40ar 6 recoil artifacts 7 grain distribution and size and 8 phase changes while in the vacuum extraction system these effects are discussed with a view to understanding possible ambiguities in ar release patterns in most cases only with independent geochronological knowledge an understanding of the release systematics and complete sample characterization can these constraints be successfully dealt with in a quantitative framework

paleomagnetism of the gays river zinc lead deposit nova scotia pennsylvanian ore genesis the gays river zinc lead deposit is the largest known mississippi valley type deposit in the mississippian windsor group of atlantic canada thermal and af demagnetization show that both ore and host rock have very similar magnetic characteristics stability tests constrain the magnetization to be mid mississippian to late pennsylvanian the pole position from the ore and host rock sites falls next to the pennsylvanian apw path suggesting an 8 clockwise rotation of the meguma platform relative to the craton regional thermal history and geochemical evidence suggest that the zinc lead ore magnetization and host rock remagnetization are coeval

model for the origin ascent and eruption of lunar picritic magmas a model for the origin ascent and eruption of the lunar a17 orange glass magma has been constructed using petrological constraints from gas solubility experiments and from analyses of the lunar sample 74220 to better determine the nature and origin of this unique explosive eruption three stages of the eruption have been identified stage 1 of the eruption model extends from 550 km the a17 orange glass magma source region based on phase equilibria studies to 50 km depth in the moon stage 2 extends from 50 km to 500 m where a c o h s gas phase formed and grew in volume based on melt inclusion analyses and measurements the volume of the gas phase at 500 m depth below the surface is calculated to be 7 to 15 vol of the magma closed system using the minimum and maximum estimates of co h2o and s loss from the melt in stage 3 depths shallower than 450 m the rising magma exsolved an additional 800 900 ppm h2o and 300 ppm s increasing the moles in the gas by a factor of 3 to 4 the closed system gas phase is calculated to reach 70 vol at 130 m depth enough to fragment the magma and form pyroclastic beads however fragmentation bead formation is interpreted to have occurred at depths ranging from 600 to 300 m below the lunar surface based on the pressure necessary to explain the c content of the orange glass beads the gas volume 70 required to fragment the ascending magma at this depth is a factor of 5 greater than the volume determined for closed system degassing of an orange glass magma at 500 m strongly implying that the gas was produced by open system degassing as the magma ascended from greater depths formation of the dike carrying the magma up from the 550 km deep source is considered to occur by a crack propagation mechanism wilson and head 2003 2017 the rapid dike propagation process facilitates gas collection by open system degassing in the upper part of the dike this is necessary to achieve the gas volumes required for magma fragmentation at 600 m depths and the magma ascent velocities to explain the wide areal distribution of the bead deposit the explosive nature of the picritic orange glass eruption and the homogeneity of the bead compositions are consistent with this gas assisted eruption scenario as is the evidence of a fe metal forming reduction event during stage 2 followed by a stage 3 oxidation event in the ascending magma

offshore continuation of meguma terrane southwestern nova scotia eight short drill cores have been examined from the continental shelf southwest of nova scotia four cores recovered granitoid rocks of two types ilmenite bearing granitoid rocks petrographically and geochemically resemble granodiorites of the south mountain batholith and granites of the seal island pluton magnetite bearing granitoid rocks are also peraluminous but have no exact analogues onshore in nova scotia two cores recovered metamorphic rocks in a small area 50 km south of seal island one consits of chlorite muscovite quartz schist geochemically similar to rocks of the halifax formation the second sampled epidote chlorite quartz schist similar to metavolcanic rocks of the white rock formation one further core sampled quartzite and another sampled a metavolcanic rock possibly erratic the regional extent of these lithotypes can be inferred from gravity and aeromagnetic data regional gravity data suggest the presence of a large granite body off southwestern nova scotia in this area magneti

the evolution of illite to muscovite mineralogical and isotopic data from the glarus alps switzerland thirty five illite and muscovite concentrates were extracted from triassic and permian claystones shales slates and phyllites along a cross section from the diagenetic alpine foreland tabular jura and borehole samples beneath the molasse basin to the anchi and epimetamorphic helvetic zone of the central alps concentrates and thin sections were investigated by microscopic x ray infrared mossbauer thermal dta and tg wet chemical electron microprobe k ar rb sr 40ar 39ar and stable isotope methods with increasing metamorphic grade based on illite crystallinity data xrd and ir the following continuous changes are observed i the 1md 2m1 polymorph transformation is completed in the higher grade anchizone ii k2o increases from 6 8 wt diagenetic zone to 8 5 10 anchizone to 10 11 5 epizone reflecting an increase in the total negative layer charge from 1 2 to 2 0 iii a decrease of the chemical variation of the mica population with detrital muscovite surviving up to the anchizone epizone boundary iv a shift of an endothermic peak in differential thermal curves from 500 to 750 c v k ar and rb sr apparent ages of the fraction 2 m decrease from the diagenetic zone to the epizone k ar ages being generally lower than rb sr ages the critical temperature for total ar resetting is estimated to be 260 30 c k ar and rb sr ages become concordant when the anchizone epizone boundary is approached the stable isotope data on the other hand show no change with metamorphic grade but are dependent on stratigraphic age these results suggest that the prograde evolution from 1 md illite to 2m1 muscovite involves a continuous lattice restructuration without rupture of the tetrahedral and octahedral bonds and change of the hydroxyl radicals however this is not a recrystallization process this restructuration is completed approximately at the anchizone epizone boundary the isotopic data indicate significant diffusive loss of 40ar and 87sr prior to any observable lattice reorganization the restructuration progressively introduces a consistent repartition of ar and k in the mineral lattices and is outlined by the 40ar 39ar age spectra concordant k ar and rb sr ages of around 35 30 ma with concomitant concordant 40ar 39ar release spectra are representative for the main phase of alpine metamorphism calanda phase in the glarus alps a second age group between 25 and 20 ma can probably be attributed to movements along the glarus thrust ruchi phase while values down to 9 ma in regions with higher metamorphic conditions suggest thermal conditions persisting at least until the middle tortonian

formation of carboniferous pb zn and barite mineralization from basin derived fluids nova scotia canada lead zinc and barite deposits in central nova scotia generally occur at the tournaisian visean mississippian clastic carbonate evaporite disconformity overlying cambrian to devonian metasedimentary and granitic rocks the deposits are located at the southern margin of the 10 km deep carboniferous maritimes fundy magdalen basin fluid inclusion homogenization temperatures of ore stage to postore minerals range from 230 degrees to 130 degrees c and fluid salinity is or 24 equiv wt percent nacl a mineralization age of ca 300 to 330 ma is suggested by 1 fission track dates on zircon from clastic host rock at gays river 2 k ar dates on clays from altered clastic rock in close proximity to mineralization and 3 rb sr data on illite from samples collected over a 10 m section of tournaisian sandstone far away from mineralization lead and strontium isotope data indicate that tournaisian rock of the horton group could have been a source at ca 300 ma of lead and radiogenic strontium in the ore stage minerals at the larger deposits visean carbonate carbon and sulfate were the dominant sources of carbon and sulfur respectively hydrogen and oxygen isotope data suggest that the mineralizing fluids were basinal brines nonbiogenic sulfate reduction at the deposits is the likely sulfide precipitation mechanism the ore forming fluids may have originated at a 5 km depth under visean evaporites in the magdalen basin and migrated rapidly through tournaisian clastic rocks and the immediately overlying pembroke breccia to the basin margins a pulse of regional tectonism may have set off at least one massive hydrofracturing compaction driven fluid expulsion event by about 300 ma

paleomagnetic reconnaissance of early mesozoic carbonates from williston lake northeastern british columbia canada evidence for late mesozoic remagnetization three classic sections of middle and late triassic fossiliferous limestones cropping out around williston lake in british columbia canada were sampled for paleomagnetic study the objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference triassic geomagnetic polarity time scale the williston lake characteristic magnetizations differ however from any triassic north america cratonic reference directions a satisfactory agreement is found instead with cretaceous early cenozoic north america cratonic reference directions the exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the cretaceous long normal superchron remagnetizations may have been triggered by connate brines which moved along aquifers of porous sandstones and carbonates in the early stages of laramide folding resume trois sections fossiliferes classiques de calcaires trias moyen et tardif affleurant autour du lac williston en colombie britannique ont ete echantillonnees pour une etude paleomagnetique l objectif etait de s assurer de la pertinence de ces unites pour une etude magneto bio stratigraphique detaillee visant a ameliorer l echelle referentielle de temps de la polarite geomagnetique au trias les magnetisations caracteristiques du lac williston different toutefois de toute direction cratonique referentielle au trias en amerique du nord toutefois une correlation satisfaisante est etablie avec les directions cratoniques referentielles du cretace cenozoique precoce en amerique du nord l occurrence exclusive d une polarite normale suggere qu il y eut probablement une remagnetisation au cours du long superchron normal du cretace les remagnetisations peuvent avoir ete declenchees par des saumures connees qui se sont deplacees le long d aquiferes de gres et de carbonates poreux dans les premieres phases du plissement laramide

late paleozoic collision delamination short lived magmatism and rapid denudation in the meguma terrane nova scotia canada constraints from 40ar 39ar isotopic data the meguma terrane consists of 8 15 km of early paleozoic stratified rocks deposited on a continental basement that were deformed and metamorphosed during the late paleozoic as a result of lithospheric plate collision the oldest cleavage previously published whole rock 40ar 39ar plateau ages of 415 395 ma dates the onset of crustal thickening which was followed by voluminous but short lived late devonian granitic and minor mafic magmatism 380 370 ma this magmatism may have been the product of delamination of the lower lithosphere and upwelling of asthenosphere which effected melting above the new moho and resulted in intrusion at depths of 5 12 km 40ar 39ar plateau ages of hornblende muscovite and biotite indicate that at the present erosion level most of the meguma terrane cooled through 300 c by 368 360 ma slightly earlier than for the southwestern meguma terrane ca 345 ma the present erosion level was exhumed by the latest devonian early carboniferous visean the age of the

geochronological evidence for multiple tectono thermal overprinting events in the east kemptville muscovite topaz leucogranite yarmouth county nova scotia canada the east kemptville muscovite topaz leucogranite located in yarmouth county nova scotia canada is host rock to the only producing primary tin deposit in north america 56 mt 0 165 sn previous geochronological studies include i rb sr whole rock analyses of the quartz topaz greisens which indicated a date of 337 5 ma and ii 40ar 39ar analyses of greisen muscovite which indicated apparent plateau dates of ca 300 ma however the pervasive development of deformational fabrics at east kemptville suggests that both the rb sr whole rock and 40ar 39ar muscovite ages are at best minimum estimates for the inferred time of mineralization in the present study rb sr whole rock and mineral muscovite plagioclase k feldspar analyses and 40ar 39ar incremental step heating of a muscovite separate indicate the following i diffusion of sr on the whole rock scale terminated at 344 5 ma 11 point isochron date coincident with closure of muscovite to intracrystalline diffusion of ar apparent plat

the german bank pluton offshore sw nova scotia age petrology and regional significance for alleghanian plutonism permian plutonism is widespread in the u s appalachians but not in the canadian sector of the appalachians the german bank pluton sampled in two boreholes offshore southwestern nova scotia gave a u pb age of 300 1 ma determined by isotope dilution thermal ionization mass spectrometry id tims on thermally annealed and chemically etched zircon grains electron microprobe dating of monazite yielded an age of 308 13 ma late paleozoic plutonism in the canadian appalachians was dominated by northwestward subduction of the rheic ocean whereas the rheic ocean in the u s appalachians closed by southeasterly subduction a slab tear therefore developed at the southwestern margin of the rheic ocean slab beneath the canadian appalachians the high sr and ba metaluminous magnetite granite of the german bank pluton resulted from melting of underplated lower crust and or lithospheric mantle by a rising asthenospheric diapir related to this slab tear geochemically the german bank pluton is similar to most 300 265 ma plutons of the southern appalachians except in its strongly negative nd isotopic composition that results from the underthrusting of a ca 2 ga lower crustal block of saharan craton

isotopic constraints on the genesis of zn pb mineralization at gays river nova scotia canada the gays river zn pb deposit is hosted in a carboniferous carbonate bank on the southern marginal platform of the major 8 km deep fundy magdalen basin fluid inclusion homogenization temperatures 130 degrees 215 degrees c and structural control of the mineralization determined in our previous study of the immediate mine area suggest affinities with both mississippi valley type and irish type deposits new isotopic work extending to within a 2 km radius of the mine area significantly constrains genetic hypotheses for the deposit preliminary hydrogen isotope measurements of inclusion fluids together with calculated oxygen isotope compositions suggest that the mineralizing fluids were basinal brines delta d 39ppm delta 18 o 3 3ppm strontium isotope composition of ore stage calcite 87 sr 86 sr 0 7117 indicates that components of the strontium and calcium had a source considerably more radiogenic than mississippian carbonate or evaporite 87 sr 86 sr 0 7085 0 7090 these and limited lead isotope data suggest that the fluids had a strontium and metal source in cambro ordovician basement rocks or their immediate clastic derivatives sulfur probably derived from the voluminous mississippian evaporites delta 34 s 14 or 1ppm was probably carried as sulfate in a fluid with neutral ph to the depositional site where complete nonbiogenic reduction at asymp 200 degrees c occurred this is supported by the lack of extensive dissolution and brecciation and the close similarity of the delta 34 s sub sigma s value for the mineralizing fluids and the delta 34 s value of the evaporites the carbon budget of the ore forming fluids was dominated by oxidized carbon from a carbonate source with delta 13 c value near 2 per mil locally influenced by organic carbon with low delta 13 c values which is abundant in the gays river carbonate bank a basinal brine expulsion model is favored the hot mineralizing fluid must have originated at a 4 km depth and interacted with elastic carbonate and evaporite sedimentary rocks on its way to the depositional site the likely age for this mineralizing event is approximately 300 m y

identification of buried lunar impact craters from grail data and implications for the nearside maria gravity observations from the dual gravity recovery and interior laboratory grail spacecraft have revealed more than 100 quasi circular mass anomalies 26 300 km in diameter on the lunar nearside these anomalies are interpreted to be impact craters filled primarily by mare deposits and their characteristics are consistent with those of impact structures that formed prior to and during intervals of flooding of feldspathic terrane by mare basalt lavas we determine that mare deposits have an average density contrast of 850 200 300 kg m 3 relative to the surrounding crust the presence of a large population of volcanically buried craters with minimal topographic expression and diameters up to 300 km requires an average nearside mare thickness of at least 1 5 km and local lenses of mare basalt as thick as 7 km

petrogenesis and regional tectonic significance of late devonian mafic intrusions in the meguma zone nova scotia late devonian 377 368 ma 40ar 39ar 376 ma u pb mafic intrusions in the meguma zone crop out as dykes plugs and synplutonic bodies of gabbro diorite or lamprophyre all of the intrusions have similar lithologie characteristics and hydrous ferromagnesian mineral assemblages and they appear to represent a genetically related series of mafic bodies with similar petrogenetic histories in the crust of the meguma zone the intrusions show wide chemical variation of sio2 45 7 65 7 wt al2o3 8 9 26 5 wt mgo 2 8 26 5 wt cao 1 2 11 2 wt and k2o 0 1 4 4 wt and they have calc alkaline high k calc alkaline and shoshonitic characteristics large ion lithophile elements lile are present at variable but high concentrations e g ba 62 1920 ppm sr 176 2567 ppm relative to most high field strength element hfse abundances e g y 10 37 ppm zr 8 421 ppm and light rare earth elements lree have much higher concentrations than heavy rare earth elements hree la lu 24 3

extreme variations in strontium initial ratios in ore related fluids magmato hydrothermal cassiterite topaz ore at the carboniferous east kemptville ek greisenhosted tin deposit nova scotia canada is cross cut by veins containing apatite triplite vivianite and fluorite initial 87sr 86sr ratios of these minerals have an extreme range 0 7135 to 0 8284 the initial ratios of the host rocks ek quartz topaz rock and davis lake biotite monzogranite 0 729 0 001 0 727 0 004 are also high the adjacent meguma group metasedimentary rocks are more typical of crustal material 0 712 0 719 at 330 ma rb and sr contents of ek fluorite max 13 0 1420 ppm and apatite max 88 1 6660 ppm are unusually high and variable unexpectedly high sr contents correlate positively with the high initial 87sr 86sr ratios fluorite and phosphate minerals from the first set of post greisen veins at east kemptville reflect the unusual chemistry of a high 87sr 86sr fluid present in the deposit after ore formation the most extreme composition of this fluid was characterized by 87sr 86sr 0 8284 high rb sr high p rb cu zn and fe contents but low abundances of ca pb and sn with respect to the davis lake monzogranite such a fluid could have been derived from the greisen fluid and modified by reaction with the overlying meguma metawacke a second alternative which cannot be well constrained at present is that an extremely radiogenic fluid entered the deposit after ore formation and mixed with the postore fluid in either case the modified fluid subsequently mixed with meteoric water and precipitated the minerals with much lower 87sr 86sr ratios and rb and sr contents