volcanic markers of the post subduction evolution of baja california and sonora mexico slab tearing versus lithospheric rupture of the gulf of california the study of the geochemical compositions and k ar or ar ar ages of ca 350 neogene and quaternary lavas from baja california the gulf of california and sonora allows us to discuss the nature of their mantle or crustal sources the conditions of their melting and the tectonic regime prevailing during their genesis and emplacement nine petrographic geochemical groups are distinguished regular calc alkaline lavas adakites magnesian andesites and related basalts and basaltic andesites niobium enriched basalts alkali basalts and trachybasalts oceanic morb type basalts tholeiitic transitional basalts and basaltic andesites peralkaline rhyolites comendites and icelandites we show that the spatial and temporal distribution of these lava types provides constraints on their sources and the geodynamic setting controlling their partial melting three successive stages are distinguished between 23 and 13 ma calc alkaline lavas linked to the subduction of the pacific farallon plate formed the comondu and central coast of the sonora volcanic arc in the extensional domain of western sonora lithospheric mantle derived tholeiitic to transitional basalts and basaltic andesites were emplaced within the southern extension of the basin and range province the end of the farallon subduction was marked by the emplacement of much more complex middle to late miocene volcanic associations between 13 and 7 ma calc alkaline activity became sporadic and was replaced by unusual post subduction magma types including adakites niobium enriched basalts magnesian andesites comendites and icelandites the spatial and temporal distribution of these lavas is consistent with the development of a slab tear evolving into a 200 km wide slab window sub parallel to the trench and extending from the pacific coast of baja california to coastal sonora tholeiitic transitional and alkali basalts of subslab origin ascended through this window and adakites derived from the partial melting of its upper lip relatively close to the trench calc alkaline lavas magnesian andesites and niobium enriched basalts formed from hydrous melting of the supraslab mantle triggered by the uprise of hot pacific asthenosphere through the window during the plio quaternary the no slab regime following the sinking of the old part of the farallon plate within the deep mantle allowed the emplacement of alkali and tholeiitic transitional basalts of deep asthenospheric origin in baja california and sonora the lithospheric rupture connected with the opening of the gulf of california generated a high thermal regime associated to asthenospheric uprise and emplaced quaternary depleted morb type tholeiites this thermal regime also induced partial melting of the thinned lithospheric mantle of the gulf area generating calc alkaline lavas as well as adakites derived from slivers of oceanic crust incorporated within this mantle

orographic clouds in terrain blocked flows an idealized modeling study abstract idealized numerical simulations of moist strongly stratified flow over topography are used to study the processes that control orographic clouds in terrain blocked flows as a joint function of the nondimensional flow parameter nh u the horizontal topographic aspect ratio and the rossby radius of deformation nh f the simulations show the competition between enhanced upstream condensation in the secondary vertically propagating gravity wave and the reduction of condensation owing to enhanced low level flow deflection as nh u increases above about 1 5 the tendency for flow to be deflected around the barrier reduces cloud formation in the primary gravity wave over the ridge while increasing expands low level clouds over a broader upstream area ice clouds may form aloft in the secondary vertically propagating gravity wave and extend upstream for several hundred kilometers in terrain blocked flows more than half of the condensate mass develops upstream of the barrier in the secondary gravi

the neglected indo gangetic plains low level jet and its importance for moisture transport and precipitation during the peak summer monsoon accurately simulating the indo asian monsoon iam using atmospheric general circulation models agcms is challenging but crucial this study uses reanalysis products erai jra55 and har to highlight an easterly low level barrier jet along the indo gangetic plain referred from here as ig llj which we identify as the primary moisture transport mechanism for the northeastern branch of the iam we show that the ncar family of agcms cam does not capture this circulation until 1 2 degree or greater spatial horizontal resolution is used the ig llj develops due to a persistent low pressure system centered over the ganges basin and is enhanced by the himalayas using diabatic heating rates and the moist froude number as diagnostics we find that in cam this branch of the iam displays two different dynamical regimes as a function of resolution at low resolution the atmosphere near the himalayas is statically unstable diabatic heating is strong and the moisture flow is southwesterly from the arabian sea and moves over the terrain unblocked at high resolution the moist static stability near the hm is stable diabatic heating is weak and the flow primarily enters easterly from the bay of bengal and moves parallel to the terrain blocked during the summer season the low resolution cam is locked into the unblocked mode which has serious implications for interpreting topography monsoon interactions for a broader context we demonstrate that more than half of the cmip5 models do not capture the ig llj which further highlights model data mismatch across the iam region

proto avalonia a 1 2 1 0 ga tectonothermal event and constraints for the evolution of rodinia the neoproterozoic evolution of avalonia is thought to have been geodynamically linked to the amalgamation and dispersal of rodinia similar sm nd isotopic signatures for different periods of arc activity suggest that avalonian basement or proto avalonia was generated in a series of primitive oceanic island arcs between 1 2 and 1 0 ga because this interval coincides with the amalgamation of rodinia proto avalonia is inferred to have been located in a panthalassa like peri rodinian ocean an early 760 660 ma phase of avalonian arc activity is attributed to renewed subduction in the peri rodinian ocean following the breakup of rodinia which caused the accretion of avalonian terranes to the gondwanan margin by ca 650 ma further subduction along the margin occurred outboard of these terranes and resulted in the onset of main phase avalonian volcanism at 630 ma the diachronous cessation of arc magmatism is attributed to ridge trench collision and the generation of a continental transform the geodynamic link between avalonia and rodinia is analogous to that between the mesozoic dispersal of pangea and the tectonothermal evolution of western north america this event also resulted in the accretion of outboard terranes and in arc related magmatism that is currently being terminated in a diachronous manner by ridge collision and the generation of the san andreas transform the model implies that the neoproterozoic evolution of avalonia and other peri gondwanan terranes provide important constraints on the tectonic history of a large portion of the rodinian continental margin

influences of the sierra nevada on intermountain cold front evolution abstractrecent studies indicate that strong cold fronts develop frequently downstream of the sierra nevada over the intermountain west to help ascertain why this paper examines the influence of the sierra nevada on the rapidly developing intermountain cold front of 25 march 2006 comparison of a weather research and forecasting wrf model control simulation with a simulation in which the height of the sierra nevada is restricted to 1500 m roughly the elevation of the valleys and basins of the intermountain west shows that the interaction of southwesterly prefrontal flow with the formidable southern high sierra produces a leeward orographic warm anomaly that enhances the cross front temperature contrast several processes generate this orographic warm anomaly including flow modification by the sierra nevada i e windward blocking of low level pacific air leeward subsidence and increased southerly flow from the mojave desert and lower colorado river basin into the intermountain west diabatic hea

the archean to late paleozoic architecture of the oulad dlim massif the main gondwanan indenter during the collision with laurentia abstract the oulad dlim massif located west of the archean part of the reguibat rise of the west african craton has an areal extent close to 36 000 km2 despite its tectonic importance as it may have been the main indenter during the late paleozoic laurentia gondwana collision that formed supercontinent pangea this region has remained unstudied for a long time based on previous research done by spanish geologists before 1965 the pioneering work done by rjimati and zemmouri 2002 and personal communication between 2000 and 2010 and new fieldwork conducted after 2010 in collaboration with moroccan exploration geologists we carried out a massif wide study that includes sensitive high resolution ion mass spectrometry shrimp zircon u pb geochronology modern petrography geochemistry and isotope geology here we present these results and discuss their interpretation in the context of other circum atlantic orogens and terranes the oulad dlim massifs is composed of an archean terrain divided by an nne ssw trending ediacaran pan african intracontinental rift marked by a voluminous bimodal mafic felsic magmatism and a silurian devonian belt in the west the massif is affected by an intense shear deformation that likely marks its main assembly deformed and undeformed silurian devonian granites indicate that such deformation was active at 420 ma declined at 410 ma and ended at 404 ma the whole massif is metamorphosed the metamorphism is especially intense in the ediacaran adrar suttuf metamafic complex i e the rift related mafic magmatic rocks which have a crystallization age of 603 1 ma and probable metamorphic age of 570 ma to 550 ma there is also evidence of a later thermal event likely related to the formation of the silurian devonian belt that reset the rb sr system of the ediacaran leucogranites to 420 ma and metamorphosed them in the greenschist facies we have also found an enigmatic strip of late carboniferous rocks in the silurian devonian belt and evidence indicating that the latest structures and low grade metamorphism affecting the silurian devonian granites likely were of this age therefore we suggest that off shore and west of the silurian devonian belt underneath the cenozoic cover and on the continental shelf there may be more evidence for late carboniferous deformation equivalent to the eastern north america alleghanian orogen which like this would have resulted from the laurentia gondwana collision during the late carboniferous

p t t conditions nd and pb isotopic compositions and detrital zircon geochronology of the massabesic gneiss complex new hampshire isotopic and metamorphic evidence for the identification of gander basement central new england

a comparative analysis of pre silurian crustal building blocks of the northern and the southern appalachian orogen the new york promontory serves as the divide between the northern and southern segments of the appalachian orogen antiquated subdivisions distinct for each segment implied that they had lithotectonic histories that were independent of each other using new lithotectonic subdivisions we compare first order features of the pre silurian orogenic building blocks in order to test the validity of the implication of independent lithotectonic histories for the two segments three lithotectonic divisions termed here the laurentian iapetan and the peri gondwanan realms characterize the entire orogen the laurentian realm composed of native north american rocks is remarkably uniform for the length of the orogen it records the multistage neoproterozoic early paleozoic rift drift history of the appalachian passive margin formation of a taconic seaway and the ultimate demise of both in the middle ordovician the iapetan realm encompasses mainly oceanic and magmatic arc tracts that once lay within the iapetus ocean between laurentia and gondwana in the northern segment the realm is divisible on the basis of stratigraphy and faunal provinciality into peri laurentian and peri gondwanan tracts that were amalgamated in the late ordovician south of new york stratigraphic and faunal controls decrease markedly rock associations are not inconsistent with those of the northern appalachians although second order differences exist exposed exotic crustal blocks of the peri gondwanan realm include ganderia avalonia and meguma in the north and carolinia in the south carolinia most closely resembles ganderia both in early evolution and late ordovician silurian docking to laurentia our comparison indicates that to a first order the pre silurian appalachian orogen developed uniformly starting with complex rifting and a subsequent drift phase to form the appalachian margin followed by the consolidation of iapetan components and ending with accretion of the peri gonwanan ganderia and carolinia this deduction implies that any first order differences between northern and southern segments post date late ordovician consolidation of a large portion of the orogen

brunswick subduction complex in the canadian appalachians record of the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick subduction complex in the new brunswick part of the canadian appalachians records the late ordovician to late silurian collision between laurentia and the gander margin of avalon the brunswick complex is anomalously well preserved compared with equivalent rocks and structures elsewhere owing to its unique position in the deepest part of the quebec reentrant of the laurentian margin this part of the margin experienced less underthrusting and exhumation and overprinting by orogen parallel faulting than the adjacent promontories where collision started earlier the early southeast to east vergent thrust related structures represent a progressive d1 deformation that formed in response to northwestward subduction of the previously extended gander margin and subsequent tectonic unroofing of the subduction complex the original shallow northwestward dipping envelope to s1 was deformed in the late silurian by d2 upright folds and associated shear zones into a steep belt during terminal collision the d2 structures probably formed in response to sinistral transpression together d1 and d2 indicate that convergence was oblique and sinistral most rocks incorporated in the subduction complex formed in the tetagouche back arc basin that evolved from rifting of an arenig magmatic arc built on the gander margin into a wide marginal basin subduction was initiated in the late ordovician 455 ma in the back arc basin following collision of the middle ordovician popelogan arc with laurentia in the caradoc shortly after its opening in the late arenig 473 ma the closure history of the iapetus ocean involved more than one subduction zone and arc continent collision and rivals the southwestern pacific ocean in its complexities

origin of the rheic ocean rifting along a neoproterozoic suture the rheic ocean is widely believed to have formed in the late cambrian early ordovician as a result of the drift of peri gondwanan terranes such as avalonia and carolina from the northern margin of gondwana and to have been consumed in the devonian carboniferous by continent continent collision during the formation of pangea other peri gondwanan terranes e g armorica ossa morena northwest iberia saxo thuringia moldanubia remained along the gondwanan margin at the time of rheic ocean formation differences in the neoproterozoic histories of these peri gondwanan terranes suggest the location of the rheic ocean rift may have been inherited from neoproterozoic lithospheric structures formed by the accretion and dispersal of peri gondwanan terranes along the northern gondwanan margin prior to rheic ocean opening avalonia and carolina have sm nd isotopic characteristics indicative of recycling of a juvenile ca 1 ga source and they were accreted to the northern gondwanan margin prior to voluminous late neoproterozoic arc magmatism in contrast sm nd isotopic characteristics of most other peri gondwanan terranes closely match those of eburnian basement suggesting they reflect recycling of ancient 2 ga west african crust the basements of terranes initially rifted from gondwana to form the rheic ocean were those that had previously accreted during neoproterozoic orogenesis suggesting the rift was located near the suture between the accreted terranes and cratonic northern gondwana opening of the rheic ocean coincided with the onset of subduction beneath the laurentian margin in its predecessor the iapetus ocean suggesting geodynamic linkages between the destruction of the iapetus ocean and the creation of the rheic ocean

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

latest cretaceous early paleogene boom of porphyry cu mineralization associated with the laramide magmatic arc of mexico abstract porphyry copper and associated deposits are widespread through most northwestern mexico particularly in sonora and sinaloa in the northwestern part of the country these deposits belong to a nw se trending copper belt that extends from southwestern usa to southern mexico the copper mineralization is clearly linked to subduction related calc alkaline plutons formed during the eastward migration of the cordilleran magmatic arc largely coincident in time and space with the laramide orogeny 80 40 ma the economically most important porphyry copper deposits were emplaced in the southwest margin of the north american craton the porphyry copper mineralization was formed during the latest cretaceous to early paleogene between 75 and 52 4 ma but it was particularly fertile between 69 and 54 ma when the larger copper concentrations were deposited to form the famous copper cluster of arizona new mexico and sonora during this time more than half of the total porphyry copper related metals of the entire cordillera was deposited this large copper accumulation developed south of the classical flat slab laramide province characterized by uplift of large crustal blocks and mostly amagmatic conditions an inferred slab tear zone separated this zone from a slab segment above which asthenospheric magma flux favored copper concentration the mexican porphyry copper belt accounts for 30 deposits out of which the buenavista del cobre 30 mt cu and the la caridad 8 mt cu are the most relevant more to the south close to the boundary between sonora and sinaloa the porphyry copper deposits are smaller

granite petrogenesis in the gander zone ne newfoundland mixing of melts from multiple sources and the role of lithospheric delamination silurian to devonian granites within the gander zone of the appalachian central mobile belt in northeastern newfoundland formed adjacent to the former gondwanan continental margin following terminal closure of the iapetus ocean comparison of geochemical and isotopic characteristics of the granites with their host migmatites and metasediments amphibolite and orthogneiss constrain their potential source nd and sr isotopic compositions indicate that no single source or binary mixing product could have produced the granites instead we show that they result from multicomponent mixing involving a contribution from unexposed crystalline basement mantle or underplate and variable contamination by supracrustal host rocks the timing and composition of granite magmatism do not exhibit collisional orogenic subduction related or continental rifting characteristics hence we relate magmatism to lithospheric melting following delamination of an orogenic keel this process provides the influx of mantle derived magma into fertile crust and hence promotes lower crustal melting and primary magma mixing

polycyclic evolution of the late neoproterozoic basement in the hermitage flexure region southwest newfoundland appalachians new evidence from the cinq cerf gneiss abstract the cinq cerf gneiss represents one of the oldest tectonic elements yet documented within the avalonian basement complex of the hermitage flexure region of the newfoundland appalachians this gneiss is a composite unit that includes both supra crustal and granitic gneisses the latter having an igneous crystallization age of 675 12 11 ma the timing of the gneiss forming event d1 polyphase deformation is constrained by the protolith age of the orthogneiss and the 584 7 6 ma crystallization age of granodiorite intrusive into gneiss the emplacement of the granodiorite is coeval with the previously dated 585 ma eruption of felsic tuff within nearby low grade stratified elements of the pre silurian basement north of the grand bruit fault zone gbfz adding support to models of a late neoproterozoic basement cover relationship between the gneiss and the low grade volcano sedimentary sequence younger neoproterozoic magmatism in the gneissic basement is recorded by emplacement of 557 14 5 ma gabbro and the intrusion of 547 2 7 ma diorite dykes the latter have a recrystallized tectonic fabric that hosts 448 9 3 ma titanite peak appalachian cycle overprinting of the cinq cerf gneiss occurred in mid to late silurian time and commenced with high temperature deformation d2 of the gneiss associated with synkinematic intrusion of western head granite at 431 5 1 ma mafic dyke swarms that intrude the gneiss and the granite contain 420 3 ma titanite this age reflects new growth during silurian retrogression and mylonitization of the mafic dykes the d3 mylonitization is widespread and linked to thrusting of the cinq cerf gneiss along the gbfz during the 420 418 ma closure of the northerly adjacent silurian volcano sedimentary cover basin new data bearing on the late neoproterozoic record of the basement block of the western hermitage flexure further demonstrates similarities in magmatic stratigraphic and metallogenic record documented in avalonian rocks of east newfoundland s connaigre burin and avalon peninsulas pointing to a neoproterozoic linkage with the rocks in these areas the early to mid paleozoic history of the hermitage flexure basement indicates that during that time the basement block evolved as a terrane separate from the avalon zone sensu stricto

nd isotopic characteristics of terranes within the avalon zone southern new brunswick nd isotopic data are presented for rock units in four terranes within the traditional avalon zone of southern new brunswick initial end values for igneous rocks within the caledonia terrane range from 1 6 to 4 6 whereas values for sedimentary rocks range from 8 4 to 3 6 a granite within the kingston terrane has end 438 ma 4 0 nd isotopic compositions for the kingston and caledonia terranes are similar to those of the mira terrane in cape breton island the antigonish highlands of nova scotia and plutonic rocks of eastern newfoundland each of these regions may be a dismembered part of a single terrane the avalon terrane sensu stricto initial end values for rocks from the brookville terrane range from 1 3 to 2 8 the coverdale anorthosite within the brookville terrane has a present day end value of 12 1 and a depleted mantle model age of 1 3 ga similar to mesoproterozoic anorthosites in laurentia clastic sedimentary rocks in the green head group have end 750 ma values of 2 0 and 10 9

the effects of a mountain on the propagation of a preexisting convective system for blocked and unblocked flow regimes abstract observations and previous research of squall lines impinging on mountain ranges have revealed that the squall lines sometimes stall upstream of the mountains for several hours leading to copious accumulations of precipitation it has been hypothesized that squall line stagnation may be more prone to occur in flows where the froude number f u nh where u is the basic state wind n is the brunt vaisala frequency and h is the mountain height is low this hypothesis is tested herein through a series of idealized two dimensional experiments where a convective system was triggered upstream of a mesoscale mountain in conditionally unstable flow for simulations with relatively low froude numbers stagnation of the preexisting convective system was not observed in the simulations with high values of f squall lines were noted to stagnate between 100 and 200 km upstream of the mountain this result indicates that squall line stagnation may be more favored for moderate to large values of f for condi

sm nd isotopic systematics as tectonic tracers an example from west avalonia in the canadian appalachians abstract the tectonothermal evolution of west avalonia in mainland nova scotia appalachian orogen provides an excellent example of the application of sm nd isotopic analyses to tectonic studies regional syntheses indicate that west avalonia originated in the neoproterozoic as one of a number of terranes collectively known as peri gondwanan terranes along the gondwanan margin these terranes are characterized by late neoproterozoic voluminous arc related magmatism west avalonia became detached from gondwana in the early ordovician was accreted to laurentia by the silurian and was deformed by post accretionary strike slip tectonics in the late devonian and carboniferous associated with the amalgamation of pangea all stages of this evolution can be recognized in the sm nd isotopic signature in various neoproterozoic and paleozoic volcanic and sedimentary successions in mainland nova scotia crustally derived felsic volcanic rocks of late neoproterozoic ca 615 ma early cambrian and early silurian ages define an envelope that provides gross constraints on the sm nd isotopic composition of the underlying basement source e nd values range from 0 78 to 2 92 in the neoproterozoic rocks from 2 0 to 5 0 in the cambrian rocks and from 0 1 to 2 5 in the silurian rocks t dm model ages for each of these suites are remarkably similar they typically range from 0 9 to 1 2 ga suggesting that the sm nd isotopic composition of these suites was profoundly influenced by repeated melting of the same basement source this sm nd envelope provides a reference by which other suites may be compared and interpreted for example turbidites in a late neoproterozoic volcanic arc basin have sm nd compositions that lie within this envelope suggesting that they are derived from the coeval volcanic rocks that flank the basin the genetic significance of the model ages can be investigated by the analysis of felsic and metasedimentary rocks that pre date the main arc phase two felsic complexes have compositions that lie within the envelope and have similar model ages the presence of this signature in early avalonian rocks suggests that the model ages represent a genuine tectonothermal event at ca 1 0 to 1 2 ga that formed juvenile proto avalonian crust by implication the main arc phase in avalonia recycled this crust sm nd isotopic analyses of the metasedimentary sequences are incompatible with previous interpretations of deposition in a passive margin setting that pre dated avalonian arc activity instead the data indicate derivation from two distinct sources ancient gondwanan basement and juvenile avalonian arc suggesting deposition in a western pacific type back arc environment this re interpretation has important implications for neoproterozoic reconstructions the sm nd isotopic composition of west avalonian basement contrasts with that of other peri gondwanan terranes for example similarly aged felsic rocks in the cadomian terrane of nw france are characterized by more negative e nd values and older t dm model ages 1 0 1 9 ga these data together with detrital u pb data suggest that west avalonia was developed along the amazonian margin whereas cadomia was developed along the west african margin of gondwana sm nd isotopic analyses of early silurian clastic rocks in mainland nova scotia show fundamental differences with unconformably underlying neoproterozoic and early paleozoic avalonian successions these data have e nd values ranging from 5 7 to 6 1 with t dm model ages of about 1 4 to 1 7 ga indicating that the clastic rocks cannot have been derived from underlying successions a variety of geologic data and regional constraints suggests that they may have been derived from the caledonide orogen of western europe thereby providing a minimum age for the accretion of west avalonia to laurentia baltica sm nd isotopic analyses from late devonian early carboniferous continental clastic rocks deposited along the southern flank of avalonia in mainland nova scotia also show little influence from avalonian rocks and are compatible with derivation from the meguma terrane immediately to the south these data are consistent with regional synthesis which indicate uplift of the meguma terrane relative to west avalonia during dextral transpression

orographic precipitation isotopic ratios in stratified atmospheric flows implications for paleoelevation studies an idealized fully nonlinear atmospheric model was used to evaluate the effects of stratified atmospheric flows on orographic precipitation isotopic ratios with the aim of improving the foundation for interpreting proxy records used for paleoelevation studies orographic precipitation isotopic ratios can be understood in terms of two nondimensional parameters the flow parameter nh u where n is the moist brunt vaisala frequency a measure of atmospheric stratification h is the large scale relief and u is the upstream horizontal wind speed perpendicular to the orogen and the horizontal aspect ratio the ratio of the along strike length of the orogen to its across strike width existing rayleigh condensation models for paleoaltimetry studies are only strictly applicable when nh u 0 much of the time high values of both nh u and favor precipitation upstream of the terrain leading to isotopic ratios that are more depleted than predicted by the rayleigh model high nh u and low favor low level deflection of winds around the terrain which substantially reduces lifting and condensation leading to precipitation isotopic ratios in that are less depleted than predicted by the simple rayleigh model changes in climate or the horizontal terrain aspect ratio can change precipitation isotopic ratios at least as much as changes in surface elevation and surface uplift need not always affect precipitation isotopic ratios suggesting that proxy records must be interpreted within a broad context of climate variability and landscape evolution

u pb ages geochemistry and tectonomagmatic history of the cambro ordovician annidale group a remnant of the penobscot arc system in southern new brunswick 1this article is one of a series of papers published in this cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology the penobscot arc system of the northeastern appalachians is an early cambrian to early tremadocian ca 514 485 ma ensialic to ensimatic arc back arc complex that developed along the margin of the peri gondwanan microcontinent ganderia remnants of this paleozoic arc system are best preserved in the exploits subzone of central newfoundland cor relative rocks in southern new brunswick are thought to occur in the ca 514 ma mosquito lake road formation of the ellsworth group and ca 497 493 ma annidale group however in the past the work that has been conducted on the latter has been of a preliminary nature new data bearing on the age and tectonic setting of the annidale group provides more conclusive evidence for this correlation the annidale group contains subalkaline tholeiitic to transitional basalts to basal tic andesites picritic tuffs and calc alkaline to tholeiitic felsic dome complexes that have geochemical signatures consistent with suprasubduction zone magmatism that was likely generated in a back arc basin new u pb ages establish that the late cambrian to early tremadocian annidale group and adjacent ca 541 ma volcanic rocks of the belleisle bay group in the new river belt were affected by a period of younger magmatism ranging in age from ca 479 467 ma this provides im portant constraints on the timing of tectonism in the area a ca 479 ma age for the stewarton gabbro that stitches the faulted contact between the annidale and belleisle bay groups demonstrates that structural interleaving and juxtaposition occurred during early tremadocian time which closely coincides with the timing of obduction of penobscottian back arc ophiolites onto the ganderian margin in newfoundland resume le systeme d arc penobscot du nord est des appalaches est un complexe d arc d arriere arc ensialique a ensima tique datant du cambrien precoce au tremadocien precoce 514 485 ma qui s est developpe le long de la bordure peri gondwannienne du microcontinent ganderia des lambeaux de ce systeme d arc paleozoique sont le mieux conserves dans la sous zone exploits du centre de terre neuve des roches correlatives dans le sud du nouveau brunswick seraient presen tes dans la formation de mosquito lake road 514 ma du groupe d ellsworth et dans le groupe d annidale 497 493 ma toutefois par le passe le travail effectue sur ce dernier groupe n a ete que preliminaire de nouvelles donnees sur l ge et l environnement tectonique du groupe d annidale fournissent des evidences plus concluantes de cette correlation le groupe d annidale contient des basaltes a des andesites basaltiques subalcalins tholeiitiques a intermediaires des tufs picritiques et des complexes de domes felsiques calco alcalins a tholeiitiques possedant des signatures geochimiques qui concordent avec un magmatisme de zone de suprasubduction probablement generee dans un bassin d arriere arc de nou veaux ges u pb ont etabli que le groupe d annidale cambrien tardif a tremadocien precoce et les roches volcaniques ad jacentes du groupe de belleisle bay 541 ma dans la ceinture de new river ont ete affectes par une periode de magmatisme plus jeune datant d environ 479 a 467 ma ces donnees fournissent des contraintes importantes sur le moment du tectonisme dans la region un ge d environ 479 ma pour le gabbro de stewarton qui reunit le contact de faille entre les groupes d annidale et de belleisle bay demontre que l imbrication et la juxtaposition structurales ont eu lieu au debut du tremadocien ce qui coincide de pres avec le moment de l obduction des ophiolites d arriere arc de penobscot par dessus la bordure de ganderia a terre neuve traduit par la redaction

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

tropical convection and precipitation regimes in the western united states abstract the authors have documented the relationship between tropical convection and precipitation regimes in the western united states circulation patterns associated with precipitation regimes are described and physical mechanisms are proposed contributions from intraseasonal and interannual bands are examined when enhanced convection is located in the western pacific dry conditions in the southwest sw and wet conditions in the pacific northwest pnw are observed fluctuations in both intraseasonal and interannual bands contribute to the rainfall variability enhanced convection in the western pacific is accompanied by suppressed convection in the central pacific the associated rossby wave vorticity source s anomalies keep the pacific jet west of 150 w a westward shift of the storm track to the north pacific also contributes to dry conditions in the sw and wetness in the pnw when enhanced tropical convection is located near 150 e substantial contributions to outgoing longwave radiation ano

moist dynamics and orographic precipitation in northern and central california during the new year s flood of 1997 abstract the dynamics of moist orographic flows during the january 1997 floods in northern and central california are investigated using numerical simulations computed with the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 early in the event 31 december 1996 1 january 1997 the low level winds offshore of california s central coast were blocked by the topography of the santa lucia range and the low level winds in the central valley were blocked by the topography of the central sierra nevada range in contrast moisture laden winds along the northern coast ranges and the northern sierra nevada flowed over topographic barriers as the core of humid air migrated to the south over 24 h the low level barrier jets weakened as the atmospheric stability decreased bringing heavy rainfall to the central and southern sierra nevada at the end of the event the heavy precipitation during this event was largely controlled by the interactio

multiple precipitation mechanisms over mountains observed by airborne doppler radar during map iop5 abstract this study uses airborne doppler radar measurements from the special observing period of the mesoscale alpine programme map to document the detailed airflow and precipitation structure over the mountainous regions near the border of northeastern italy and slovenia as a cold frontal system moved eastward and encountered the eastern alps on 4 october 1999 during map iop5 in contrast to previously documented map cases the environmental conditions associated with this case are characterized by a deep layer of strong convective instability in the lower troposphere and by a cold northeasterly continental flow coming down from the mountains the so called bora wind along the southeastern alps over the study region there are two primary mountain barriers the julian alps oriented roughly west east with a peak mountain height of 2500 m and a significant variation in terrain height along its length and the other the dinaric alps a relatively lower mountain range oriented northwest southeast

a theoretical study of cold air damming abstract the dynamics of cold air damming are examined analytically with a two layer steady state model the upper layer is a warm and saturated cross mountain easterly or southeasterly onshore flow the lower layer is a cold mountain parallel northerly jet trapped on the windward eastern side of the mountain the interface between the two layers represents a coastal front a sloping inversion layer coupling the trapped cold dome with the warm onshore flow above through pressure continuity an analytical expression is obtained for the inviscid upper layer flow with hydrostatic and moist adiabatic approximations blackadar s pbl parameterization of eddy viscosity is used in the lower layer equations solutions for the mountain parallel jet and its associated secondary transverse circulation are obtained by expanding asymptotically upon a small parameter proportional to the square root of the inertial aspect ratio the ratio between the mountain height and the radius of inertial oscillation the geometr

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

geological correlations between cape breton island and newfoundland northern appalachian orogen geological correlations between cape breton island and newfoundland are apparent both in surface geology and at deeper crustal levels based on similarities in sm nd isotopic signatures the mira terrane of southeastern cape breton island is part of the avalon terrane sensu stricto and is composed of neoproterozoic volcanic sedimentary plutonic belts and overlying cambrian rocks directly comparable to those in the western part of the newfoundland avalon terrane the bras d or terrane is also mainly of neoproterozoic age but shows lithological and isotopic contrasts with the mira terrane small areas of similar neoproterozoic rocks occur in southern newfoundland and to the north as inliers in the exploits terrane the bras d or terrane and similar rocks in newfoundland are interpreted to represent a peri gondwanan terrane where rocks of the gander terrane were later formed hence this area is part of the central mobile belt and distinct from avalon terrane sensu stricto the aspy terrane is a complex area

neoproterozoic and cambrian arc magmatism along the eastern margin of the victoria lake supergroup a remnant of ganderian basement in central newfoundland abstract the eastern margin of the composite and structurally complex victoria lake supergroup has previously been mapped where the silurian rogerson lake conglomeratic rocks unconformably overlie cambrian tally pond volcanic rocks however the recognition that the form of this contact changes between an unconformity and a brittle ductile fault in conjunction with the neoproterozoic age of the crippleback intrusive suite dictate that the above interpretation of the nature of this margin requires revision these discrepancies are resolved by the recognition of a neoproterozoic largely bimodal volcanic sequence sandy brook group which is unconformably overlain by rogerson lake rocks to the east with these combined units in fault contact with the tally pond group to the west the sandy brook group and crippleback intrusive suite form a terrane of ca 563 ma rocks with continental arc like geochemical signatures the distinctly negative nd 563 values for the felsic rocks mean 3 of this terrane imply derivation from a crystalline basement older than the largely pan african crust that underlies contemporaneous volcanic rocks in west avalonia but similar to that inferred for the gander zone thus this terrane is likely to be the leading edge of the peri gondwanan microcontinent ganderia the ca 511 ma tally pond group arc magmatism represent some of the oldest products of iapetean subduction in newfoundland although the tally pond group are only observed to be in fault contact with the ca 50 million year older sandy brook group the high proportion of felsic volcanic rocks sandy brook crippleback age inherited zircons and pb isotopic data all support the inference that the tally pond group was formed on sandy brook crippleback continental crust

geochemical criteria for a refined tectonic discrimination of orogenic andesites abstract minor trace element and sr isotope data are compiled for tertiary recent orogenic andesites of three tectonic settings 1 oceanic island arcs divided into low k and other andesites 2 continental island arcs and thin continental margins and 3 thick continental margins andean from 1 to 3 there is a steady overlapping increase in la ce ree la yb la y th th u zr y hf yb and ni co and a decrease in k la p la sc cr and sc ni optimum discriminationis achieved with a plots of la yb vs th and la yb vs sc ni and b cluster analysis using the critical parameters listed above shoshonitic andesites and high mg andesites boninites are considered separately orogenic andesites are distinguished from non orogenic andesites by high contents of al low contents of ti zr ree y nb ta and ga and the absence of pronounced negative eu anomalies

hydroclimate of the western united states based on observations and regional climate simulation of 1981 2000 part ii mesoscale enso anomalies abstract the hydroclimate of the western united states is influenced by strong interannual variability of atmospheric circulation much of which is associated with the el nino southern oscillation enso precipitation anomalies during enso often show opposite and spatially coherent dry and wet patterns in the northwest and california or vice versa the role of orography in establishing mesoscale enso anomalies in the western united states is examined based on observed precipitation and temperature data at 1 8 spatial resolution and a regional climate simulation at 40 km spatial resolution results show that during el nino or la nina winters strong precipitation anomalies are found in northern california along the southern california coast and in the northwest mountains such as the olympic mountains the cascades and the northern rockies these spatial features which are strongly affected by topography are surprisingly well reproduced by the regional climate simulation a spatial feature investigat

late cenozoic surface uplift of the southern sierra nevada california usa a paleoclimate perspective on lee side stable isotope paleoaltimetry late cenozoic surface uplift of the southern sierra nevada sierra california united states is widely debated recent interpretations of lee side isotope records from the southern sierra suggest that the elevation of the southern sierra has been sufficiently high to induce atmospheric flow patterns similar to modern patterns since the mid miocene at ca 12 ma the tendency for flow to deflect around a topographic barrier can be determined by the atmospheric stability barrier height and incoming wind speed we test the sensitivity of flow deflection to elevation to determine what elevation would have been sufficiently high to establish modern flow patterns in the mid miocene using global paleoclimate models and idealized regional weather models we find that the miocene atmosphere was more stable than modern we suggest that in a miocene climate flow patterns similar to modern pat terns could have been achieved for elevations as low as 2 km and that while miocene lee side isotope records from the southern sierra may indicate that the southern sierra has been a longstanding topographic feature they may not have changed significantly in response to proposed late cenozoic surface uplift of the southern sierra

numerical simulations of the 2013 alberta flood dynamics thermodynamics and the role of orography abstractthe 19 21 june 2013 alberta flood was the second costliest 6 billion cad natural disaster in canadian history trailing only the 2016 fort mcmurray alberta canada wildfires one of the primary drivers was an extreme rainfall event that resulted in 75 150 mm of precipitation in the foothills west of calgary canada here the mesoscale dynamics and thermodynamics that contributed to the extreme rainfall event are elucidated through high resolution numerical model simulations in addition terrain reduction model sensitivity experiments using gaussian smoothing techniques quantify the importance of orography in producing the extreme rainfall event it is suggested that the extreme rainfall event was initially characterized by the formation of a surface cyclone on the eastern side of the canadian rockies due to quasigeostrophic qg mechanisms orographic processes and diabatic heating feedbacks maintained the surface cyclone throughout the event extending the duration of both easterly upslope

appalachian cold air damming abstract appalachian cold air damming is investigated by means of 1 a 50 yr monthly climatology 2 a synoptic case study of the event of 21 23 march 1985 and 3 an investigation of the flow structure and force balance within the cold dome the climatology reveals cold air damming is a year round phenomenon in the southern appalachians with the most frequent prolonged and intense events occurring in winter particularly december and march when three five events per month can be expected cold air damming is least frequent and intense in july the synoptic case study reveals that cold air damming is critically dependent upon the configuration of the synoptic scale flow the cold dome can be identified by a u shaped ridge trough in the sea level isobar thermal patterns and the 930 mb height temperature fields representative of conditions at the base of the inversion overlying the cold dome differential horizontal and vertical thermal advection as well as adiabatic and evaporative cooling are r

the ellsworth terrane coastal maine geochronology geochemistry and nd pb isotopic composition implications for the rifting of ganderia the ellsworth terrane is one of a number of fault bounded blocks that occur along the eastern margin of ganderia the westernmost of the peri gondwanan domains in the northern appalachians that were accreted to laurentia in the paleozoic geologic relations detrital zircon ages and basalt geochemistry suggest that the ellsworth terrane is part of ganderia and not an exotic terrane in the penobscot bay area of coastal maine the ellsworth terrane is dominantly composed of bimodal basalt rhyolite volcanic sequences of the ellsworth schist and unconformably overlying castine volcanics we use new u pb zircon geochronology geochemistry and nd and pb isotopes for these volcanic sequences to constrain the petrogenetic history and paleotectonic setting of the ellsworth terrane and its relationship with ganderia u pb zircon geochronology for rhyolites indicates that both the ellsworth schist 508 6 0 8 ma and overlying castine volcanics 503 5 2 5 ma are middle cambrian in age two tholeiitic basalt types are recognized type tb 1 basalt present as pillowed and massive lava fl ows and as sills in both units has depleted la and ce la nd n 0 53 0 87 values fl at heavy rare earth element ree values and no positive th or negative ta anomalies on primitive mantle normalized diagrams in contrast type tb 2 basalt present only in the castine volcanics has slightly enriched lree la yb n 1 42 2 92 values and no th or ta anomalies both basalt types have strongly positive e nd 500 values tb 1 7 9 8 6 tb 2 5 6 7 0 and relatively enriched pb isotopic compositions 206

late cretaceous to early eocene magmatic evolution of the laramide arc in the nacozari quadrangle northeastern sonora mexico and its regional implications abstract late cretaceous to early eocene volcanic and plutonic rocks that crop out in the nacozari quadrangle compose the laramide magmatic arc in northeastern sonora northwestern mexico the purpose of this work is to characterize the arc rocks based on new cartography stratigraphy u pb and k ar geochronology and major trace and isotope geochemical data and interpret them in the regional context of evolution of the arc the study area lies within the proterozoic mazatzal crustal block which is limited to the south by the caborca block the volcanic rocks regionally correlate with the tarahumara formation and consist of volcanic flows breccias tuffs and volcaniclastic sandstones with an estimated thickness of 4 km they range in composition from andesite to rhyolite and have isotopic ages from 76 8 0 4 to 57 1 0 4 ma the granitic plutons and rhyolitic domes that intrude them yielded ages from 59 3 0 8 to 53 3 1 6 ma initial 87 sr 86 sr and epsilon nd values for these rocks vary from 0 70553 to 0 70841 and 3 7 to 8 5 respectively and have 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb isotope ratios that range from 18 05 to 19 05 15 52 to 15 63 and 38 25 to 39 07 respectively regional integration of our u pb ages suggests that the volcanic activity lasted between ca 81 and 57 ma with two main peaks of activity at 74 5 and 61 ma similarly regional magmatic activity indicated by dated plutons initiated at ca 91 and ended by 50 ma after main peaks of activity at 71 and 60 55 ma the plutonism between 91 and 80 ma was subordinate and regionally restricted to coastal and central sonora and might represent an older event unrelated to the laramide arc two k ar cooling ages of 55 4 0 7 and 48 5 0 7 ma obtained from la purica granite dated at ca 59 ma u pb in the study area correlate regionally with a possible event of rapid uplift between 68 and 50 ma the geochemical composition of the studied rocks indicate high k calc alkaline metaluminous to weakly peraluminous compositions typical of subduction arc related magmas which characterize the laramide magmatic belt in northwestern mexico the nd sr and pb isotope compositions of these and other samples documented for northeastern sonora closely correlate with isotope signatures of the mazatzal crustal block in southeastern arizona and differ from those in the caborca block which display affinity with the mojave yavapai province the data also allow to best constrain the location of the boundary between the mazatzal and caborca crustal blocks in east central sonora

sierra barrier jets atmospheric rivers and precipitation characteristics in northern california a composite perspective based on a network of wind profilers abstractfive 915 mhz wind profilers and gps receivers across california s northern central valley cv and adjacent sierra foothills and coastal zone in tandem with a 6 km resolution gridded reanalysis dataset generated from the weather research and forecasting model document key spatiotemporal characteristics of sierra barrier jets sbjs landfalling atmospheric rivers ars and their interactions composite kinematic and thermodynamic analyses are based on the 13 strongest sbj cases observed by the sloughhouse profiler between 2009 and 2011 the analyses show shallow cool south southeasterly i e sierra parallel flow and associated water vapor transport strengthening with time early in the 24 h compositing period culminating in an sbj core at 1 km above ground over the eastern cv the sbj core increases in altitude up the sierra s windward slope and poleward toward the north end of the cv but it does not reach the westernmost cv above the developing sbj strengthening southwesterly flow des

the influence of mesoscale orography on a coastal jet and rainband abstract the role of mesoscale orography along the central california coast in the development and evolution of a coastal jet and rainband is investigated using a high resolution triply nested nonhydrostatic numerical model comparison of the model simulations which use horizontal grid increments of 5 and 2 km on the inner computational meshes with a coastal mesoscale observation network indicates that the finescale structure of the jet and rainband dynamics are adequately simulated although phase and orientation errors occur the observed and simulated near surface winds have maximum speeds that exceed 22 m s 1 and a direction nearly parallel to the coastline and topography force balance analysis indicates that blocking in the lowest 500 m and flow over the coastal range above this layer contribute to mesoscale pressure perturbations including pressure ridging upstream of the coastal mountains which forces the ageostrophic dynamics of the coastal jet pressure perturbations associated with the to

neoproterozoic early devonian magmatism in the antigonish highlands avalon terrane nova scotia tracking the evolution of the mantle and crustal sources during the evolution of the rheic ocean abstract the antigonish highlands lies in the avalon terrane avalonia in the canadian appalachians and records four episodes of continental rift related bimodal magmatism ranging in age from late neoproterozoic to middle devonian the oldest episode ca 615 ma clydesdale formation was emplaced in a local rift setting in an andean style arc when avalonia resided along the northern gondwanan margin early cambrian magmatism arbuckle brook formation occurred in a local transtensional setting after arc magmatism had given way to a san andreas type transform environment middle ordovician dunn point and bears brook formations magmatism occurred in a local rift in an ensialic island arc setting analogous to the modern taupo volcanic zone in northern new zealand after avalonia had separated from gondwana middle devonian mcarras brook formation and correlatives occurred after avalonia had collided with laurentia in each episode mafic rocks are characterized by high feot feot mgo tio2 zr y and ti y typical of differentiated within plate mafic magmas multi element spider diagrams indicate that all four episodes were generated in an enriched sub continental lithospheric mantle lil hfs and ree patterns indicate that the clydesdale dunn point bears brook and mcarras brook formations were sourced in the shallow spinel lherzolite mantle and that the arbuckle brook formation was generated in the deeper garnet lherzolite mantle in each episode coeval felsic rocks were generated by crustal anatexis taken together the sm nd isotopic data for the mafic rocks form an envelope that defines the evolution of the mantle source beneath the antigonish highlands that was enriched between 0 8 and 1 1 ga and has an average sm nd ratio of ca 0 24 a value that is typical of an enriched mantle source sm nd isotopic data for the felsic rocks are characterized by a recurrence of tdm ages between 0 95 and 1 0 ga interpreted to reflect repeated melting of the lower crust that was itself derived from a depleted mantle source between 0 95 and 1 1 ga the remarkable geochemical and isotopic similarity of the neoproterozoic to middle devonian mafic and felsic magmas indicate that the crust and sub continental lithospheric mantle beneath the antigonish highlands were coupled during the rift and drift of avalonia from the gondwanan margin during the formation of the rheic ocean in the ordovician its accretion to baltica and to laurentia in the silurian and post accretionary strike slip movement of avalon along the laurentian margin although the sm nd isotopic data suggest that avalonian basement and lithospheric mantle formed over the same time interval 0 8 to 1 1 ga the divergence of their respective envelopes with time reflects their differing end values and sm nd ratios we suggest that avalonian crustal basement and its enriched mantle were both formed between 0 8 and 1 1 ga in a panthalassa type ocean that surrounded the supercontinent rodinia and were accreted to the northern gondwanan margin at about 650 ma prior to the oldest magmatic event in the antigonish highlands

laramide porphyry cu mo mineralization in northern mexico age constraints from re os geochronology in molybdenite twenty five new re os molybdenite ages for nine porphyry copper molybdenum deposits from northern mexico constrain the timing of mineralization and the longevity of porphyry systems in this region the ages of all the deposits are between 50 and 61 ma i e paleocene to early eocene and are associated with the laramide orogeny the oldest deposits are those from the cananea district and include the el alacran prospect 61 ma the maria deposit 60 ma the current cananea mine and la colorada breccia 59 ma the age of mineralization at cumobabi also is 59 ma and it was followed by the emplacement of deposits at suaqui verde and cuatro hermanos at about 57 to 56 ma the malpica prospect the southernmost porphyry copper prospect in western mexico was emplaced at 54 ma the la caridad deposit in nacozari and the el creston prospect both have re os molybdenite ages of 54 ma the tameapa prospect has a protracted hydrothermal mineralization history with multiple molybdenite mineralization events at 57 52 to 53 and 50 ma total re and 187 os concentrations for molybdenites range from 10 424 to 26 ppm and from 6 641 to 14 ppb respectively the deposit with the highest re and os concentrations is el alacran and the lowest concentrations are found in el creston the ages determined support the formation of porphyry copper deposits in northern mexico during the laramide orogeny in general the ages of porphyry copper deposits in the north american province range from 76 ma at bagdad arizona to 50 ma at tameapa sinaloa the ages also show that porphyry copper mineralization occurred continuously between these two dates with two main episodes at 60 ma cananea district mexico and sierrita and copper creek united states and at 54 ma la caridad el creston malpica in mexico and morenci united states

kinematic and thermodynamic structures of sierra barrier jets and overrunning atmospheric rivers during a landfalling winter storm in northern california abstractthis study characterizes kinematic and thermodynamic structures of sierra barrier jets sbjs atmospheric rivers ars and their interaction over the period 14 16 february 2011 when a winter storm made landfall in northern california a suite of scanning and profiling doppler radars rawinsondes and gps receivers is used to document these structures across the central valley and up the western sierra slope to the crest along an 200 km segment of the sierra the winter storm is grouped into two episodes each having an ar that made landfall low level winds in the sbj observed during episode 1 were southeasterly and embedded in a stably stratified air mass along barrier wind speeds u340 reached maximum values of 25 30 m s 1 as low as 0 2 km msl over the central valley and as high as 1 5 km msl over the western sierra slope southwesterly winds associated with the ar overlaid the sbj along an interface that sloped upward from southwest to northeast with a southwestern extent at the western

distinct taconic salinic and acadian deformation along the iapetus suture zone newfoundland appalachians structural mapping in central newfoundland has identified seven distinct phases of deformation d 1 to d 7 the most significant of which are d 1 d 2 and d 4 d 1 involved the formation of a middle and late ordovician southsoutheast directed thrust belt and concomitant development of mylonite and phyllonite a late ordovician to early silurian d 2 thrust and fold belt overprints d 1 mylonitic deformation and is the most distinctive deformation event in the study area late silurian to devonian d 4 is responsible for folds and north northwest directed dextral thrust and reverse faults that overprint d 1 to d 3 structures d 4 structures in central newfoundland include the exploits gander boundary subsequent deformation is generally of local significance only the arc back arc complexes making up the various terranes in central newfoundland are predominantly juxtaposed along d 1 shear zones which include the red indian line our data indicate that terrane boundaries initiated during d 1 may have protracted deformation histories spanning several deformation events this has important implications for the interpretation of terrane boundaries in newfoundland as d 1 terrane boundaries may be interpreted as d 2 or d 4 shear zones depending on the intensity of overprinting or reactivation the deformation history proposed in this paper corresponds closely to that of established appalachian orogenic cycles d 1 is correlated with the ordovician taconic orogeny and involved accretion of arc back arc complexes to the laurentian margin d 2 and d 4 are correlated with the ordovician silurian salinic and silurian devonian acadian orogenies which involved the subsequent accretion of the ganderia and avalonia microcontinents to the laurentian margin respectively

factors controlling rain on small tropical islands diurnal cycle large scale wind speed and topography abstracta set of idealized cloud permitting simulations is performed to explore the influence of small islands on precipitating convection as a function of large scale wind speed the islands are situated in a long narrow ocean domain that is in radiative convective equilibrium rce as a whole constraining the domain average precipitation the island occupies a small part of the domain so that significant precipitation variations over the island can occur compensated by smaller variations over the larger surrounding oceanic area while the prevailing wind speeds vary over flat islands three distinct flow regimes occur rainfall is greatly enhanced and a local symmetric circulation is formed in the time mean around the island when the prevailing large scale wind speed is small the rainfall enhancement over the island is much reduced when the wind speed is increased to a moderate value this difference is characterized by a change in the mechanisms by which convection is forced a thermally forced se

the influence of coastal orography the yakutat storm abstract an unforecast windstorm in the vicinity of yakutat alaska on 14 march 1979 illustrates the importance of ageostrophic dynamics within a coastal zone proximal to significant terrain large pressure rises greater than 4 mb 3 h 1 were observed along the southeastern alaska coast after passage of a cold front when the low level geostrophic flow was directed onshore these pressure rises did not occur simultaneously along the coast but rather propagated northward along the coast as a coherent pulse or surge strong surface winds approximately 25 30 m s 1 were observed in the region of laid sea level pressure gradient at the leading edge of the surge and occurred after the passage of the synoptic front although the sparseness of the observations prevent definite conclusions this feature resembles a kelvin wave more than a density current omega dropwindsonde observations collected along the coast of alaska during two other less dramatic situations suggest damming and downslope flow structu

the evolution of the avalonian plate abstract the avalon platform of newfoundland is the type locality of the avalonian plate that is characterized by late precambrian volcanic and clastic rocks marine at the bottom and terrestrial at the top all are intruded by 650 550 ma granites late precambrian rocks in the southern british isles are similar in both areas northeastern parts of the belt are affected by deformation and metamorphism that have orogenic aspects the orogeny is referred to as the avalonian in newfoundland and monian in britain to the southeast of the avalonian rocks in europe lies another late precambrian cadomian orogenic belt of rocks as a part of the pan african orogenic belt the cadomian and avalonian belts extend into north africa morocco since these belts are ophiolite bearing it is suggested that the plate was bordered by oceanic domains it is therefore proposed that a microcontinental volcanic arc that was generated in the late precambrian was orogenically deformed by collision with north america europe and africa and survived as a coherent terrain until the late carboniferous

mid late ordovician magmatism and metamorphism along the gander margin in central newfoundland fieldwork coupled with u pb dating has clarified the relationships between the exploits and gander derived rocks in central newfoundland during the mid ordovician opening of the exploits back arc basin reinforcing correlation across the peri gondwanan segments of the appalachian caledonian orogen we have separated a new back arc related unit the red cross group from the arc related victoria lake supergroup this group includes 466 3 ma felsic volcanic rock interlayered with alkali basalt enriched mid ocean ridge basalt 457 6 ma gabbro llanvirn caradoc normal mid ocean ridge basalt island arc tholeite limestone black shale and melange locally the red cross group is in parautochthonous contact with low grade gander psammite this contact was overrun by the meelpaeg metamorphic nappe during the devonian the nappe contains gander metapsammite meelpaeg subzone and the coticule bearing howley waters complex exploits which hosts 467 3 ma felsic porphyry the gander and exploits metasediments in the nappe are stitched by arenig llanvirn granite 467 6 ma and 468 3 5 3 ma and caradoc intrusions 458 3 ma and 454 2 ma metamorphic monazite 462 1 ma and titanite 460 3 ma from the nearby mount cormack subzone gander indicate the coeval formation of a low pressure high temperature metamorphic dome the widespread presence of caradoc magmatism suggests that the width of the back arc basin remained relatively narrow

provenance and tectonic evolution of ganderia constraints on the evolution of the iapetus and rheic oceans we provide estimates for the width timing and rates of opening and closing of the iapetus and rheic oceans the evolution of which profoundly infl uenced paleozoic global paleogeography these estimates are primarily derived from the transfer of ganderia and avalonia from gondwana to laurentia which led to closure of the iapetus ocean and opening of the rheic ocean ganderia a long lived arc terrane separated from the paleo caribbean margin of amazonia at 505 ma with a latitudinal speed of 9 cm a northward initiating the rheic ocean as a backarc basin ganderia s trailing edge was reduced to 5 cm a following opening of a 600 800 km wide backarc basin within ganderia at 475 ma opening and closing of the iapetus ocean was largely driven by far fi eld stresses slab pull in some places and slab rollback in others

skarn manto and breccia pipe formation in sedimentary rocks of the cananea mining district sonora mexico skarns mantos and breccia pipes occur at cananea in a 2 by 4 km horst of paleozoic carbonate rock and minor quartzite surface mapping and core logging reveal a sequence of events beginning with early metamorphism that converted impure carbonate lithologies to iron poor garnet pyroxene or idocrase hornfels subsequent metasomatism formed garnet py roxene skarn along the pre cretaceous elisa fault contact between carbonate rock and mesozoic volcanic rock skarn is zoned from an andradite rich center through a zone containing both andraditic garnet and salitic pyroxene to a mineralogic sequence near the marble front which is largely a function of the sedimentary protolith chert nodules are rimmed by wollastonite dolomite is converted to massive phlogopite magnetite skarn calc silicate hornfels is over printed by veins of skarn garnet and relatively pure marble is replaced by coarse blades of iron and manganese rich pyroxene multiple generations of garnet and pyroxene can be distinguished by subtle variations in color and texture age classification on the basis of crosscutting vein and overgrowth relationships indicates that late pyroxenes are more iron and manganese rich than the early generations garnets show a less regular iron enrichment with time the spatial distribution of the different garnet and pyroxene generations is irregular garnet and pyroxene in late veins have iron rich compositions both near the skarn center and near the marble front pyrite and minor chalcopyrite are the only sulfides associated with this stage of metasomatism following the main stages of garnet and pyroxene formation veins and orbicular patches of amphibole or quartz or calcite occur replacing pyroxene and in some cases garnet most of the amphibole is actinolitic in composition and is associated with pyrite and minor amounts of chalcopyrite about 20 percent of the amphibole is subcalcic and is associated with or replaced by massive calcite the alteration of prograde skarn to amphibole or quartz or calcite can be best explained by a general temperature decline the destruction of skarn by alteration related to brecciation and breccia pipe formation and the replacement of previously unaltered carbonate rocks by stratiform blankets mantos of iron oxides and sulfides resulted in some of the highest grade orebodies breccia pipe and manto formation appears to have been largely contemporaneous with emplacement and subsequent sericitic alteration of a series of quartz monzonite porphyry stocks where breccia pipes crosscut skarn garnet pyroxene and amphibole are converted to mixtures of calcite quartz chlorite hematite siderite and sulfides where breccia pipes or porphyries crosscut previously unaltered carbonate rock mixtures of magnetite sulfides chlorite siderite calcite quartz and serpentine form massive mantos veinlets of chlorite and magnetite or pyrite or serpentine extend tens of meters beyond the zones of massive replacement there is a rough vertical and lateral zonation of sulfide minerals with respect to the democrata breccia pipe from chalcopyrite or bornite or pyrite in the core and at depth to sphalerite pyrite chalcopyrite to pyrite sphalerite galena distal to the center of mineralization mineral stability relations suggest that brecciation and mineralization took place at lower temperatures 275 degrees 25 degrees c and possibly under lower x sub co 2 conditions than the earlier skarn formation the high zn cu ratios in skarn the zonation of most hypogene mineralization relative to the breccia pipes which crosscut skarn and the lack of skarn spatially associated with the quartz monzonite porphyry stocks which intrude carbonate rock all suggest that unlike skarn in most porphyry copper districts skarn at cananea is not related to the quartz monzonite porphyry stocks that are mined elsewhere in the district for disseminated supergene enriched sulfide mineralization rather the skarn may be related to a deeper magmatic system which has not yet been encountered in subsurface exposures

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

geochronology of the porphyry copper deposits and related mineralization of mexico k ar dating demonstrates that all but eight of 41 dated porphyry copper and related ore deposits of mexico were emplaced during the laramide episode of maximum plate convergence one older deposit is related to the jurassic volcanic arc of western north america one is pre laramide cretaceous four are oligocene in age and two late cenozoic deposits are within the modern trans mexican chiapenecan volcanic arc thirty three of the deposits lie within a long narrow belt that continues into arizona and new mexico and widens from 100 km to over 300 km in the region of maximum extension in the southern basin and range province eighty five percent of the deposits were emplaced during the eastward transgression of the cordilleran volcanic arc in middle cretaceous through eocene time the occurrence of the porphyry copper deposits of mexico appears to be independent of the terrane intruded and the copper content of the wall rocks where the wall rocks predate the volcanic arc which is syngenetic with the porphy

tectonic setting and regional correlation of ordovician metavolcanic rocks of the casco bay group maine evidence from trace element and isotope geochemistry ordovician metamorphic rocks of the casco bay group are exposed in an approximately 170 km long ne trending belt liberty orrington belt in southern and south central maine geochemical analysis of rocks within the spring point formation 469 3 ma of the casco bay group indicate that it is an assemblage of metamorphosed bimodal volcanic rocks the mafic rocks originally basalts have trace element and nd isotopic characteristics consistent with derivation from a mantle source enriched by a crustal and or subduction component the felsic rocks originally rhyolites and dacites were likely generated through partial melting of continental crust in response to intrusion of the mafic magma relatively low initial e nd values for both the mafic 1 3 to 0 6 and felsic 4 1 to 3 8 rocks suggest interactions with gander zone continental crust and support a correlation between the casco bay group and the bathurst supergroup in the miramichi belt of new brunswick this correlation suggests that elements of the early to middle ordovician tetagouche exploits back arc basin can be traced well into southern maine a possible tectonic model for the evolution of the casco bay group involves the initiation of arc volcanism in early ordovician time along the gander continental margin on the eastern side of the iapetus ocean basin slab rollback and trenchward migration of arc magmatism initiated crustal thinning and rifting of the volcanic arc around 470 ma and resulted in the eruption of the spring point volcanic rocks in a back arc tectonic setting

porphyry copper deposit density estimating numbers of undiscovered mineral deposits has been a source of unease among economic geologists yet is a fundamental task in considering future supplies of resources estimates can be based on frequencies of deposits per unit of permissive area in control areas around the world in the same way that grade and tonnage frequencies are models of sizes and qualities of undiscovered deposits to prevent biased estimates it is critical that for a particular deposit type these deposit density models be internally consistent with descriptive and grade and tonnage models of the same type in this analysis only deposits and prospects that are likely to be included in future grade and tonnage models are employed and deposits that have mineralization or alteration separated by less than an arbitrary but consistent distance 2 km for porphyry copper deposits are combined into one deposit only 286 deposits and prospects that have more than half of the deposit not covered by postmineral rocks sediments or ice were counted nineteen control areas were selected and outlined along borders of hosting magmatic arc terranes based on three main features 1 extensive exploration for porphyry copper deposits 2 definable geologic settings of the porphyry copper deposits in island and continental volcanic arc subduction boundary zones and 3 diversity of epochs of porphyry copper deposit formation porphyry copper deposit densities vary from 2 to 128 deposits per 100 000 km2 of exposed permissive rock and the density histogram is skewed to high values ninety percent of the control areas have densities of four or more deposits 50 percent have densities of 15 or more deposits and 10 percent have densities of 35 or more deposits per 100 000 km2 deposit density is not related to age or depth of emplacement porphyry copper deposit density is inversely related to the exposed area of permissive rock the linear regression line and confidence limits constructed with the 19 control areas can be used to estimate the number of undiscovered deposits given the size of a permissive area in an example of the use of the equations we estimate a 90 percent chance of at least four a 50 percent chance of at least 11 and a 10 percent chance of at least 34 undiscovered porphyry copper deposits in the exposed parts of the andean belt of antarctica which has no known deposits in a permissive area of about 76 000 km2 measures of densities of deposits presented here allow rather simple yet robust estimation of the number of undiscovered porphyry copper deposits in exposed or covered permissive terranes

a re os study of sulfide minerals from the bagdad porphyry cu mo deposit northern arizona usa rhenium and osmium isotopes in sulfide minerals from the bagdad porphyry cu mo deposit have been used to determine timing of mineralization and the source of osmium and by inference ore metals molybdenite chalcopyrite and pyrite were analyzed mainly from the quartz monzonite and porphyritic quartz monzonite units which are characterized by moderate to strong potassic alteration secondary biotite and k feldspar rhenium concentrations in molybdenite are between 330 and 642 ppm four re os analyses of two molybdenite samples from the quartz monzonite and porphyritic quartz monzonite yield a weighted average age of 71 8 0 2 ma 2 analyses of a third sample from a molybdenite vein in precambrian rocks outside of the main ore zone yield a weighted average age of 75 9 0 2 ma 2 and provide evidence of two separate mineralization episodes chalcopyrite samples contain 6 to 12 ppt os and 1 7 to 4 1 ppb re 187os 188os initial ratios are between 0 1 and 0 8 pyrite samples have osmium and rhenium concentrations varying in the range 8 17 ppt and 3 9 6 8 ppb respectively analyses from these pyrite samples yield an eight point isochron with an age of 77 15 ma 2 and an initial 187os 188os ratio of 2 1 0 8 mswd 0 90 the results presented here add to the growing body of work indicating that porphyry type mineralization is produced by long term multiple episodes of magmatism and associated mineralization the data also support the hypothesis that a significant part of the metals and magmas may have a crustal source as has been suggested for other copper deposits and districts in arizona

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

late proterozoic and silurian alkaline plutons within the southeastern new england avalon zone distinct pulses of quartz bearing alkaline plutonism and volcanism are known to have occurred in the avalon zone of southeastern new england during the late ordovician early silurian devonian and carboniferous zircon separates from the franklin and dartmouth plutons demonstrate that two additional previously unrecognized periods of alkaline magmatism occurred the franklin pluton yields an age of 417 plus minus 6 ma late silurian whereas the dartmouth pluton is late proterozoic 595 plus minus 5 ma and markedly older than the other plutons of alkaline affinity the new ages further emphasize the episodic nature and long term duration of such alkaline igneous events within the southeastern new england avalon zone the dartmouth pluton may represent a post collisional alkaline granite emplaced in the late proterozoic almost immediately after a major period of calcalkaline igneous activity that accompanied plate convergence and continental accretion the abrupt change from orogenic calcalkaline igneous activity to post collisional alkaline granite followed by younger episodes of anorogenic emplacement is remarkably similar to igneous events reported from pan african mobile belts widespread throughout africa in addition parts of the dartmouth pluton exhibit features indicative of mixing and commingling of felsic and mafic melts that are associated with coevally formed mylonitic fabrics becausemore these fabrics are conformable to those in adjacent gneisses but discordant with alleghanian fabrics in the nearby carboniferous narragansett basin they represent some of the best candidates for pre alleghanian structures thus far identified in the southeastern new england avalon zone less

extension of laramide magmatism in southwestern north america into trans pecos texas the red hills intrusion hosts the easternmost porphyry copper molybdenum system in southwestern north america and consists of quartz sulfide stockwork veins in sericitized porphyritic quartz monzonite zircon u pb and molybdenite re os analyses yield ages of 64 2 0 2 ma and 60 2 0 3 ma respectively indicating that the red hills intrusion and mineralization are distinctly older than all other tertiary magmatism 48 17 ma in the trans pecos region of texas including the nearby 32 ma chinati mountains caldera the red hills intrusive system is contemporaneous with and genetically related to other laramide magmatic systems 75 54 ma that host porphyry copper deposits in arizona southwestern new mexico and northern mexico these results significantly extend the laramide magmatic province eastward and suggest that laramide subduction related magmatism and deformation are coextensive over a broad area of southwestern north america

upper cambrian to upper ordovician peri gondwanan island arc activity in the victoria lake supergroup central newfoundland tectonic development of the northern ganderian margin the exploits subzone of the newfoundland appalachians comprises remnants of cambro ordovician peri gondwanan arc and back arc complexes that formed within the iapetus ocean the exploits subzone experienced at least two accretionary events as a result of the rapid closure of the main portion of the iapetus tract the penobscot orogeny c 480 ma which juxtaposed the penobscot arc c 513 486 ma with the gander margin and c 450 ma collision of the victoria arc c 473 454 ma with the annieopsquotch accretionary tract that juxtaposed the peri laurentian and peri gondwanan elements along the red indian line the newly recognized pats pond group forms a temporal equivalent to other lower ordovician intra oceanic complexes of the penobscot arc the pats pond group c 487 ma has a geochemical stratigraphy that is consistent with rifting of a volcanic arc an ensialic setting is indicated by low end values end 0 3 to 0 5 near the stratigraphic base and its abundant zircon inheritance c 560 ma and 0 9 1 2 ga the spatial distribution of tremadocian arc back arc complexes indicates that the penobscot arc is best explained in terms of a single east dipping subduction zone this model is favored over west dipping models in that it explains the distribution of the penobscot arc elements continental arc magmatism and the obduction of back arc penobscot ophiolites without requiring subduction of the gander margin or subduction reversal the newly recognized wigwam brook group c 454 ma disconformably overlies the pats pond group and records the youngest known phase of ensialic arc volcanism end 4 1 in the victoria arc which is also related to east dipping subduction thus the penobscot and the overlying victoria arc are reinterpreted in terms of a single relatively long lived east dipping subduction zone beneath the peri gondwanan microcontinent of ganderia the cessation of arc volcanism towards the top of the wigwam brook group and the subsequent syn tectonic sedimentation in the badger group constrain the arrival of the leading edge of ganderia with the ensialic arc complexes to the laurentian margin to c 454 ma

large magnitude oligo miocene extension in southern sonora implications for the tectonic evolution of northwest mexico new structural and 40ar 39ar data from the santa rosa area southeastern sonora shed light on the magnitude and timing of extensional tectonism episodic magmatic activity from the late cretaceous to the miocene is recorded by a 3 4 km thick structural stratigraphic section that includes a composite laramide granodiorite batholith and its andesitic wall rocks early to middle tertiary rhyolite ignimbrites and silicic domes and late oligocene to middle miocene mafic lavas interbedded with tuffaceous sediment and fanglomerate the older units are complexly faulted and steeply tilted by several generations of normal faults palinspastic reconstructions indicate cumulative extension of 90 early gently dipping nw striking normal faults document major extension oriented n50 e angular unconformities and growth fault relations within oligo miocene sequences bracket this extension between 26 and 20 ma younger widely spaced ns to nnw trending high angle normal faults cut the previously faulted and tilted sections and produced modest 10 15 e w extension that is largely bracketed between 20 and 17 ma the magnitude of neogene extension in this region is greater and the timing is older than previously recognized reconnaissance of other areas between the sierra madre occidental and the coast at this latitude suggests that most extension in sonora occurred between 27 and 12 ma while remnants of the farallon plate were still being subducted plate tectonic models that predict substantial extension in sonora during proto gulf 10 5 ma transtensional deformation may need to be reevaluated an alternative model presented here is that baja california began moving with pacific plate motion shortly after the 11 ma termination of subduction and that northwest motion of baja relative to mainland mexico might total 500 km distributed across the previously extended oligo miocene magmatic arc

rain shadow development during the growth of mountain ranges an atmospheric dynamics perspective 1 an idealized atmospheric model is used to explore the links between climate and topography in the development of orographic rain shadows during orogenesis the atmospheric dynamics theory of density stratified fluid flow over topography is used to interpret the results the controlling nondimensional parameter is nh u where n is the brunt vaisala frequency a measure of atmospheric stability h is the terrain relief and u is the initial horizontal wind speed rain shadow development is found to be a nonlinear and nonunique function of both topography and atmospheric state indicating that geological records of orographic aridity cannot be interpreted in terms of relief alone when upstream topography exceeds nh u 1 during surface uplift downstream orographic precipitation vanishes and downstream orographic cloud mass decreases by as much as 90 upstream blocking of air flow can generate a forward projecting rain shadow in which a relatively low ridge nh u 1 may be decoupled from the atmospheric flow by a zone of flow stagnation extending upstream of the high terrain such an effect may occur if the valley separating the two ranges is narrower than the length scale of flow stagnation in the model configuration used here lateral widening of a relatively low nh u 1 range increases downstream cloud mass by up to a factor of 3 these results help to refine interpretations of climate tectonic interactions in shaping the geological record of the sierra nevada and andes

crustal affinities of metallogenesis in the american southwest the source of metals in many lands of ores and ore deposit styles remains uncertain notwithstanding more than a century of field studies scientific advances in concepts and enhancement of analytical capability however numerous geologic research efforts that have addressed many relevant themes in southern arizona have resulted in different kinds of data supporting and consistent with the interpretation of significant association of some ore metals of this region with cratonic crust these themes range in scale from studies of regional geology geophysical interpretations and precious metal production through petrology to trace element and isotope geochemistry the notion of a crustal source for metals contrasts with many long standing ideas of direct mantle sources for this metal province or more recently direct derivation of metals from subducted materials a hundred years of recorded silver and gold production reveal a two fold separation of mining districts in arizona and new mexico on the basis of ranges of produced ag au ratio that correspond in turn with a separation of two distinct geologic domains of the southern cordilleran metal province the produced ag au ratio in districts of different ages ore styles tectonic setting and metal habit are not affected by deposit style or ore control or igneous rock type or vertical zoning and weathering studies of the isotopes and trace element chemistry of related igneous rocks reveal that ore related intrusions have a significant crustal progenitor studies of pb and os isotopes have discovered strong signals of crustal parentage in ore minerals the regional geology metallization history production and chemical and isotopic data strongly support a hypothesis of crustal sources of some of the metal in this large and complex province

late cretaceous porphyry copper mineralization in sonora mexico implications for the evolution of the southwest north america porphyry copper province two porphyry cu mo prospects in northern sonora mexico fortuna del cobre and los humos located within the southwestern north american porphyry province have been dated in order to constrain the timing of crystallization and mineralization of these ore deposits in fortuna del cobre the pre mineralization granodiorite porphyry yielded an u pb zircon age of 76 5 2 3 ma whereas two samples from the ore bearing quartz feldespathic porphyry were dated at 74 6 1 3 and 75 0 1 4 ma four molybdenite samples from los humos porphyry cu prospect yielded a weighted average re os age of 73 5 0 2 ma whereas two samples from the ore bearing quartz monzonite porphyry gave u pb zircon ages of 74 4 1 1 and 74 5 1 3 ma showing a late cretaceous age for the emplacement of this ore deposit the results indicate that laramide porphyry cu mineralization of late cretaceous age is not restricted to northern arizona as previously thought and provide evidence for the definition of ns trending metallogenic belts that are parallel to the paleo trench porphyry copper mineralization follows the inland migration trend of the magmatic arc as a result of the farallon slab flattening during the laramide orogeny

interaction of an intense extratropical cyclone with coastal orography abstract observational analyses and numerical simulations are used to investigate the interaction of an intense extra tropical cyclone with the coastal orography of the pacific northwest known as the inauguration day cyclone the system made landfall upon the washington state coast on 20 january 1993 producing one of the most damaging wind storms in pacific northwest history the strongest winds accompanying the storm were associated with an intense low level pressure gradient that was concentrated along a bent back front mesoscale pressure perturbations produced by the time dependent interaction of the cyclone and bent back front with the coastal orography were isolated using numerical simulations the simulations showed that during the period of peak winds over puget sound there was only a minor enhancement of the local pressure gradient by troughing to the lee east of the olympic mountains gradual amplification of this olympic mountain lee trough over a period of 2 3 h extended the period of s

low froude number flow past three dimensional obstacles part ii upwind flow reversal zone abstract the present paper contains a continuation of our study of the flow of a density stratified fluid past three dimensional obstacles for froude number o 1 linear theory large froude number and potential flow type theory small froude number are both invalid in this range which is of particular relevance to natural atmospheric flows past large mesoscale mountains the present study was conceived to provide a systematic investigation of the basic aspects of this flow thus we have excluded the effects of friction rotation nonuniform ambient flow and the complexity of realistic terrain in part i of this study we focused on the pair of vertically oriented vortices forming on the lee side when the froude number decreases below 0 5 approximately and argued that their formation may be understood in terms of nonlinear aspects of inviscid gravity waves i e without invoking traditional arguments on the separation of the friction boundary layer herein we examine the zone of flow reversal on

blocking and deflection of airflow by the alps abstract a method of computing low level trajectories from observed sea level pressure is shown to be capable of distinguishing cases of blocked and non blocked flow around the alps a flow splitting parameter s derived from the trajectories is found to be a reasonable criterion for distinguishing blocked from nonblocked cases with a value of s 1 5 serving as a useful threshold for classification in considering eight cases of postfrontal cold flow against the alps only a few can be clearly identified as blocking or noblocking and even these identifications may not pertain to all levels and all segments of the alpine chain the trajectory based classification scheme compares well with sounding and flight level data from the noaa p 3 research aircraft the degree of blocking is shown to be related to the upstream froude number and the strength of the upstream pressure nose a remarkable result is that the observed surface wind patterns appear blocked in all cases considered here we refer to this

a comparison between mid paleozoic new england usa and the modern western usa subduction of an oceanic ridge transform fault system abstract a detailed comparison is made between the mid paleozoic norumbega fault system nfs in maine usa and the san andreas fault system safs of coastal california usa and their tectonic settings the safs formed following subduction of an oceanic ridge transform system and the nfs is interpreted as having formed the same way the parallel evaluation of mid crustal processes associated with the nfs and surface processes associated with the safs gives a unique perspective on modern and inactive crustal scale strike slip fault systems the safs is separated from the cascadia subduction zone by the mendocino triple junction similarly the mid paleozoic nfs is interpreted as having been separated from a convergent zone to the southwest by the interpreted norumbega triple junction the safs cuts a subduction complex the franciscan complex that formed when the margin was still convergent no equivalent subduction complex associated with the nfs has been recognized perhaps because it was eroded away or displaced or because it never formed the safs experienced periods of transpression and transtension whereas the nfs shows transpressive structures only slab window magmatic rocks exist along the safs devonian to earliest carboniferous plutonic rocks along the nfs may in part be slab window magmatic rocks although the effects of the acadian and prior orogenies in the appalachians complicate their identification magmatic rocks along the safs are offset due to the high rate of displacement 20 40 mm yr magmatic rocks along the nfs show little offset consistent with the low rate of displacement 3 mm yr in the model transverse structures are associated with both the safs and nfs other mendocino type triple junctions may have existed in the past but may be difficult to recognize where a past crustal scale intracontinental strike slip fault system terminates on an along strike contemporaneous convergent system such a fault fault trench triple junction may be considered

mineralization at cananea sonora and the paragenesis and zoning of breccia pipes in quartzofeldspathic rock correlative early and late deposit types in the cananea district correspond to similarly classified deposit types in other porphyry copper districts potassic alteration massive silicates in the colorada orebody and prograde skarn were produced by early probably predominantly magmatic hydrothermal fluids from a limited number of porphyry stocks later stockwork disseminated deposits associated with sericitic alteration were contemporaneous with breccia pipes retrograde alteration of skarn and limestone replacement deposits fluids associated with the relatively late deposits were probably predominantly meteoric hydrothermal but geologic relations suggest that the earliest fluids in some of these deposits may have included fluid exsolved from porphyry mineralization in both early and late deposits precipitated in the sequence silicates followed by sulfides except for early molybdenite in some pipes many pipes in the district appear to have formed by collapse into open space at depth consistent paragenetic sequences structures and textures shared by these pipes suggest that collapse occurred into space formed at the same time relative to emplacement of the responsible porphyry phases and evolution of the associated hydrothermal systems a possible analogue of the space into which collapse took place is abreccia at the outer contact of a large porphyry stock small outlying structures containing sulfide mineralization and breccia or intensely fractured rock appear to be associated with the upper terminations of pipes late mineralization has high overall pyrite cu fe sulfides ratios greater than 1 wherever the sulfide sequence could be established it is 1 pyrite 2 cu fe sulfides and 3 sphalerite galena tetrahedrite except for small amounts of second stage sulfides zoning of these numbered sulfide stages in breccia pipes in quartzofeldspathic rock and also in limestone replacement deposits is inferred to be 1 1 2 1 2 3 and 1 3 from the proximal to the distal ends of the deposits pipes within disseminated deposits contain the lower portion of the pattern textures indicative of local replacement of wall rock and early gangue minerals by later phases e g sulfides are common the common occurrence of late paragenetic stages in a pipe indicates that the pipe remained open during precipitation of the main stage of economic sulfides garnet in pipes in quartzofeldspathic rock is diagnostic of limestone at depth nearby early adularia and quartz adularia alteration of wall rock fragments in the cananea duluth pipe persist to much greater distances above limestone than garnet does and might prove to be similarly diagnostic