magmatic epidote and its petrologic significance epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the mesozoic accreted terranes between northern california and southeastern alaska textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase the observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure plutonic rocks bearing magmatic epidote must have formed under moderately high pressures corresponding to lower crustal depths under fairly oxidizing conditions

paludal environments of the mary lee coal zone pottsville formation alabama stacked clastic swamps and peat mires abstract the blue creek and mary lee coals in the lower part of the mary lee coal zone upper pottsville formation northwestern alabama record deposition in peat accumulating environments or mires intervening strata contain a series of stacked clastic swamps forested wetlands which grew on a classtic sediment substrate rather than a peat soil these clastic swamp horizons are identified on the basis of 1 autochthonous erect lycophyte and calamites trunks 2 mud cast prostrate hypoautochthonous lycophyte and calamites trunks 3 compression impression assemblages of autochthonous to hypoautochthonous pteridosperm and lycophyte foliage branches and reproductive structures 4 autochthonous axes and appendages of stigmaria and pinnularia and 5 siderite nodules associated with rooting structures and other plant material sedimentological and biostratinomic features of the mary lee coal to blue creek coal interval are used as the basis for the interpretation that sediment loading and compaction of buried peat controlled the alternation between peat mires and clastic swamps and the stacking of the clastic swamps

development of inverted metamorphic isograds in the western metamorphic belt juneau alaska an inverted metamorphic gradient is preserved in the western metamorphic belt near juneau alaska the western metamorphic belt is part of the coast plutonic metamorphic complex of western canada and southeastern alaska that developed as a result of tectonic overlap and or compressional thickening of crustal rocks during collision of the alexander and stikine terranes detailed mapping of pelitic single mineral isograds systematic changes in mineral assemblages and silicate geothermometry indicate that thermal peak metamorphic conditions increase structurally upward over a distance of about 8 km peak temperatures of metamorphism increase progressively from about 530 c for the garnet zone to about 705 c for the upper kyanite biotite zone silicate geobarometry suggests that the thermal peak metamorphism occurred under pressures of 9 11 kbar the metamorphic isograds are in general parallel to the tonalite sill that is regionally continuous along the east side of the western metamorphic belt although truncation of the isograds north of juneau indicates that the sill intrusion continued after the isograds were established our preferred interpretation of the cause of the inverted gradient is that it formed during compression of a thickened wedge of relatively wet and cool rocks in response to heat flow associated with the formation and emplacement of the tonalite sill magma garnet rim compositions and widespread growth of chlorite suggest partial re equilibration of the schists under pressures of 5 6 kbar during uplift in response to final emplacement and crystallization of the tonalite sill the combined results of this study with previous studies elsewhere in the western metamorphic belt indicate that high t high p metamorphism associated with the collision of the alexander and stikine terranes was a long lived event extending from about 98 ma to about 67 ma

geology of southern prince of wales island southeastern alaska geologic mapping on southern prince of wales island combined with u pb zircon geochronologic geochemical and conodont studies yield new information about the early paleozoic geologic framework and evolution of the southern alexander terrane the oldest rocks recognized consist of arc type meta volcanic and metasedimentary rocks wales metamorphic suite which were derived from late proterozoic cambrian protoliths these rocks were deformed metamorphosed and uplifted during the middle cambrian early ordovician wales orogeny beginning soon after this orogenic event and continuing into early silurian time basaltic to rhyolitic rocks and marine clastic strata descon formation were deposited and dioritic to granitic plutons were emplaced a variety of geochemical data suggest that these ordovician early silurian rocks formed in a volcanic arc environment the middle silurian earliest devonian klakas orogeny marked the end of arc type magmatism it is manifest on southern prince of wales island by regional imbrication on southwest vergent thrust faults penetrative brecciation and pervasive hydrothermal alteration of pre devonian rocks in some areas and at least several kilometres of structural uplift lower devonian strata karheen formation record the waning stages of this event conglomeratic redbeds low in the section were deposited in topographically rugged subaerial to shallow marine environments whereas strata high in the section were deposited in more distal marine environments post devonian rocks on southern prince of wales island include the bokan mountain granite jurassic basaltic to dacitic dike swarms and mid cretaceous granodiorite and diorite bodies prior to emplacement of the mid cretaceous plutons the devonian and older rocks were offset along several sets of strike slip faults and then downdropped along the keete inlet fault

u pb zircon geochronology from the alexander terrane southeast alaska implications for the greens creek massive sulphide deposit this paper presents results of a laser ablation inductively coupled plasma quadrapole mass spectrometer la icp qms u pb dating study of small in situ zircon grains from samples collected in the vicinity of the greens creek massive sulphide deposit on northern admiralty island southeast alaska the greens creek mine is a volcanogenic massive sulphide deposit in the central portion of the alexander triassic metallogenic belt atmb and is one of the top global silver producers despite having a dominantly mafic metavolcanic stratigraphic footwall the stratigraphic footwall is a mississippian mafic metavolcanic sequence with a protolith age of approximately 340 330 ma the first u pb zircon constrained chronostratigraphy for the area places the deposit near or at the base of the host late triassic stratigraphy just above an approximately 100 million year old unconformity and probably 10 15 million years older than mineralization at the palmer and windy craggy deposits in the northern portion of the

stratigraphy and depositional environments of the kanawha formation middle pennsylvanian southern west virginia u s a abstract the kanawha formation of southern west virginia consists of up to 620 m of lithic sandstone and mudrocks with subordinate coal and impure limestone that accumulated in a subsiding foreland basin the formation contains 26 of the state s 62 minable coal seams it accounts for about 43 of the coal currently produced in west virginia component sedimentary facies from 46 outcrop localities reflect alluvial paludal lacustrine paralic and shallow marine environments internal and architectural facies attributes indicate more evidence for coastal and tidal estuarine deposition than traditional deltaic models evidence for tidal processes includes bipolar paleocurrents rhythmic textures and structures and associated biogenic structures a new two part model is presented that relates facies to changing coastal morphology during transgressive regressive cycles eustatic sea level changes played a major role in basin wide development of major coal zones and marine units lowstandss of sea level caused incisement of fluvial channels whereas rising sea level led to expansion of tidal plains and estuaries shoreface retreat produced ravinement surfaces and transgressive lags that now separate coastal plain and marginal marine facies from shallow subtidal facies coastal progradation began during highstands after estuarine sediment sinks had filled and may have been intensified during falling sea level

origin of the pennsylvanian coal bearing cyclothems of north america past controversy about the tectonic or eustatic origin of pennsylvanian cyclothems is resolved by regional basin subsidence analysis global paleoclimate paleogeography and plate tectonic evolution differences between marine carbonate kansas type cyclothems of the northern midcontinent and nonmarine clastic appalachian type cyclothems of the eastern united states are controlled by laterally changing flexural deformation during plate accretion into a supercontinent coupled with superposed glacial eustasy kansas type cyclothems accumulated on a relatively stable platform affected only moderately by collision tectonics of north american margins these cycles are eustatic characterized by a periodicity comparable to milankovitch orbital parameters appalachian type cyclothems accumulated in response to episodic thrust loading during plate collisions that developed a series of flexurally deformed wide and shallow resurgent foreland basins this resurgent foreland basin evolution during paleozoic time increased crustal rigidity in the appalachians thus yoking the appalachian and illinois basins during pennsylvanian time with each thrust load foreland basin deepening favored transgressive cyclothem facies which changed to a regressive facies because sediment yield increased as denudation rates increased off uplifted orogens illinois type cyclothems are intermediate between the two end member processes of flexural tectonics and glacial eustasy characterizing appalachian type and kansas type cyclothems respectively thus the pennsylvanian coal bearing cyclothems of north america owe their origin to the remarkable coincidence of supercontinent development concomitant glaciation and eustatic sea level change and associated episodic thrust loading and foreland basin subsidence of small magnitude on progressively more rigid crust

typhoon induced ground deformation geodetic instruments now offer compelling sensitivity allowing to investigate how solid earth and surface processes interact by combining surface air pressure data nontidal sea level variations model and rainfall data we systematically analyze the volumetric deformation of the shallow crust at seven borehole strainmeters in taiwan induced by 31 tropical cyclones typhoons that made landfall to the island from 2004 to 2013 the typhoon s signature consists in a ground dilatation due to air pressure drop generally followed by a larger ground compression we show that this compression phase can be mostly explained by the mass loading of rainwater that falls on the ground and concentrates in the valleys towards the strainmeter sensitivity zone further our analysis shows that borehole strainmeters can help quantifying the amount of rainwater accumulating and flowing over a watershed during heavy rainfalls which is a useful constraint for building hydrological models

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

detrital zircon geochronology and regional correlation of metasedimentary rocks in the coast mountains southeastern alaska u pb ages have been determined for 55 detrital zircon grains from a metasedimentary sequence along the west flank of the coast mountains in southeastern alaska these rocks belong to the port houghton assemblage which consists of upper paleozoic pelitic and psammitic schist metaconglomerate metabasalt and marble the port houghton assemblage rests unconformably on metamorphosed and deformed mid paleozoic arc type volcanics endicott arm assemblage which gradationally overlie upper proterozoic lower paleozoic continental margin strata tracy arm assemblage three main clusters of ages are present 330 365 ma 19 grains 1710 2000 ma 27 grains and 2450 2680 ma 6 grains additional grains are approximately 2334 2364 and 3324 ma comparison of these ages with detrital zircon ages in other cordilleran assemblages supports previous interpretations that metasedimentary rocks in the coast mountains i form a southwestern continuation of the yukon tanana terrane of eastern alaska and yukon

paleoclimate controls on late paleozoic sedimentation and peat formation in the central appalachian basin u s a abstract in the central appalachian basin at least two major climate changes affected sedimentation during the late paleozoic stratigraphically these two changes are indicated by the distribution of coal beds the variation in coal quality and the variation in rock lithologies in latest mississippian or earliest pennsylvanian time the climate changed from dry seasonal tropical to ever wet equable tropical the equable climate prevailed into the middle pennsylvanian influencing the morphology and geochemistry in peat forming environments many of the peat deposits which formed under the equable climate were probably domed raised bogs low concentrations of dissolved solids in peat formation water resulted in low buffering capacity organic acids caused acidic ph another climate change occurred in late middle pennsylvanian time when evapopation periodically exceeded rainfall resulting in an increase of both dissolved solids and ph 4 to 7 in surface and near surface water throughout the remainder of the pennsylvanian the surfaces of peat deposits were probably planar not domed water in peat forming and other depositional environments became more nearly neutral the coal beds derived from these peats are highly variable in both ash and sulfur contents drier or more seasonal climates are also indicated by sequences of 1 calcareous sandstone and shale 2 nonmarine limestone that shows shallow water and subaerial exposure features and 3 calcareous paleosols that have caliche characteristics our data and observations indicate that physical depositional environment models for the origin of coal do not adequately explain variations in mineral matter content and composition in commercial quality coal beds in the central appalachian basin stratigraphic variation in mineral matter in coal beds and in syngenetic and early diagenetic minerals in rocks associated with the coal beds appears to be better explained by changes in geochemical conditions of nonmarine sedimentation paleoclimate was a principle control on these geochemical conditions

paleogene metamorphism of an accretionary flysch terrane eastern gulf of alaska reconnaissance field studies have identified a regional metamorphic complex at least 200 km long and 25 to 50 km wide in the eastern chugach mountains southern alaska the metamorphic complex was developed within the cretaceous valdez group a flysch sequence that was accreted to the continental margin during the late cretaceous or early tertiary the metamorphic complex shows the progressive development from subgreenschist and green schist facies slate phyllite and semischist that is regionally characteristic of the valdez group to biotite plagioclase quartz schist muscovite cordierite andalusite staurolite garnet and sillimanite in an intermediate zone and amphibolite facies muscovite biotite plagioclase quartz schist and gneiss sillimanite and garnet in a higher grade central zone k feldspar is characteristically absent in the amphibolite facies schists but it is present in migmatitic rocks that are common to the central zone the mineral assemblages and petrographic relations indicate that metamorphism took place under low pressure intermediate facies series conditions partial melting took place at the highest grade of metamorphism melting produced granodioritic magmas in migma titic rocks of the central zone that were emplaced as discrete plutons in both the intermediate zone and peripheral rocks of the complex the timing of metamorphism as indicated by field relations and k ar data is about 50 to 65 m y ago and overlaps or is coeval with the emplacement throughout the gulf of alaska region of early tertiary plutons that are thought to be anatectic in origin the distribution of these plutons suggests that a high temperature low pressure metamorphic belt about 1 800 km long developed along the leading edge of the continental margin in late paleocene to early eocene time

sedimentology of pennsylvanian quartzose sandstones of the lee formation central appalachian basin fluvial interpretation based on lateral profile analysis abstract lateral profiling including bounding surface and architectural element analyses are utilized to demonstrate a fluvial origin for the quartzose sandstones of the lee formation internal architecture of the sandstones consists primarily of multistorey and multilateral channel bodies individual channel elements up to 20 m thick contain a complex hierarchy of bedform deposits the primary depositional elements within the channels were downstream accreting mid channel macroforms channel elements frequently contain deposits of more than one macroform reconstruction of the macroforms reveals accretion primarily by superposed bedforms that migrated down a low angle front steeper giant foresets transitional along flow with the low angle facies indicate that the macroform episodically developed a steep slipface the uppermost channels within the rockcastle member contain macroform elements with components of lateral accretion interpreted as deposits of alternate bank attached macroforms other depositional elements recognized within channel fill deposits are minor channel sandy bedform gravity flow attributed to bank slumping and channel bottom elements the latter element is contained within a facies sequence that suggests rising to flood to waning stage deposition in general deposition probably occurred during relatively high stage little evidence of low stage flow was recognized subordinate fine grained facies are interpreted as levee and overbank deposits the greater part of the lee formation was deposited in deep low sinuosity bedload dominated fluvial channels strongly unimodal paleocurrents lack of facies that suggest low stage reworking and paucity of lateral accretion features indicate deposition in a single channel system i e a low braiding index

the tatshenshini shear zone new in southwestern yukon canada comparison with the coast shear zone in british columbia and southeastern alaska and implications regarding the shakwak suture the tatshenshini shear zone extends from klukshu lake in southwestern yukon southward to the yukon british columbia border deformation in the shear zone ranges from hundreds of meters to a few kilometers in width and is characterized by protomylonitic and mylonitic turbidites belonging to the dezadeash formation jurassic cretaceous that are overlain by protomylonitic granodiorite of the ruby range batholith late cretaceous tertiary the dezadeash formation ruby range batholith contact bedding and deformation and magmatic fabrics within the tatshenshini shear zone are all coplanar striking northwest southeast and dipping moderately to the northeast kinematic indicators from the dezadeash formation and ruby range batholith record a top to the southwest sense of shear collision of the insular superterrane with the intermontane superterrane by the mid cretaceous resulted in the eastward directed underplating of yukon tanana terrane equivalent rocks by the dezadeash formation and the formation of the tatshenshini shear zone the tatshenshini shear zone preceded and controlled emplacement of the ruby range batholith but magmatism ending 58 56 myr ago outlasted deformation the results of this work support the correlation of the ruby range batholith with the adjacent great tonalite sill in southeastern alaska it also suggests a linkage between the tatshenshini shear zone and the coast shear zone in southeastern alaska and along which the great tonalite sill was emplaced the tatshenshini shear zone and the coast shear zone represent the coda of long lived tectonism along the shakwak suture the accretionary boundary between the insular and intermontane superterranes

silicate and sulphide thermobarometry of low to medium grade metamorphic rocks from holkham bay south east alaska the western metamorphic belt of the coast plutonic complex south east alaska and adjacent british columbia contains strongly deformed rocks and a prominent topographic low the coast range megalineament near holkham bay south east alaska the lineament separates the western metamorphic belt into a western low grade greenschist facies terrane and an eastern medium grade amphibolite facies terrane sphalerite compositions of grains in direct contact with pyrite and pyrrhotite in chlorite muscovite zone rocks in the low grade terrane give pressures of about 8 kbar compatible with pressures of 8 10 kbar at 500 c calculated from plagioclase biotite garnet muscovite assemblages adjacent to the windham bay pluton about 15 km away a pressure of 4 8 0 7 kbar was calculated from sphalerite compositions in staurolite zone rocks east of the coast range megalineament this is indistinguishable from pressures of 4 8 1 kbar at 585 c and 5 1 1 kbar at 680 c plagioclase garnet aluminum silicate quartz equilibria and 4 1 1 kbar at 585 c plagioclase biotite garnet muscovite equilibrium determined for the medium grade terrane an identical pressure of 4 8 0 7 kbar was calculated from sphalerite compositions in biotite zone rocks adjacent to the lineament this is considerably higher than a pressure of 3 1 1 kbar at 525 c obtained using plagioclase biotite garnet muscovite geobarometry from shear zones within the lineament the discrepancy may be explained by later equilibration of mineral phases within the shear zones the geothermobarometry suggests relatively low temperatures and high pressures for the low grade terrane 6 10 kbar and intermediate temperatures and pressures for the medium grade terrane to the east 4 6 kbar comparison of the barometers indicate that sphalerite can be used to estimate metamorphic pressures similar to those estimated from silicate mineral chemistry when pyrrhotite sphalerite pyrite assemblages are used

ancient continental margin assemblage in the northern coast mountains southeast alaska and northwest canada geologic relations indicate that quartz rich metasedimentary rocks in the northern coast mountains separate strata to the east that belong to the stikine terrane from strata to the west of the alexander wrangellia and taku terranes the quartz rich rocks structurally overlie western terranes along a mid cretaceous thrust fault and are overlain structurally originally stratigraphically by strata of the stikine terrace these rocks are interpreted to be a continental margin assemblage that belongs to the yukon crystalline terrane u pb and nd isotopic data indicate that the metasedimentary rocks were shed from a source terrane consisting at least in part of proterozoic rocks

interplay of plutonism and regional deformation in an obliquely convergent arc southern coast belt british columbia the coast plutonic complex is an extensive zone of continental growth that formed along the mesozoic convergent margin of northwestern north america the orogeny creating this belt involved terrane accretion and assembly massive upward transfer and emplacement of sial in the form of batholiths constituting a magmatic arc and transformation of broad tracts of sedimentary and volcanic rocks into crystalline continental crust all operating in more or less the same space and time the mechanisms and interplay of these orogenic processes are well displayed in the harrison lake area of the southern coast belt british columbia great structural relief across the area exhibits a present day architecture defined by thin thrust stacked terrane sheets and early concordant pluton sheets folded on a macroscopic scale all truncated by oblique dextral reverse faults and overlain by later floored plutons construction of this complex began with terrane assembly on orogen normal thrusts during a lull in plutonism in the early cretaceous low grade metamorphism during this event indicates only modest crustal thickening subsequent plutons intruded into the assembled terranes appear to be composites of sheets early pluton sheets are now steeply dipping due to folding but were likely intruded as horizontal bodies large ovoid post folding plutons are mostly subhorizontal floored bodies at least in part sheeted these plutons are underlain by barrovian mineralogic aureoles that indicate downward vertical displacement of 10 km or more during plutonism suggesting pluton emplacement by vertical inflation magmatic fabrics in these bodies and the discordant relation of plutons to regional structures preclude emplacement in active fault zones penetrative strain aureoles flanking plutons are mostly limited to zones a few hundred meters wide and regional tectonic structures are widely preserved tectonic deformation of the arc is characterized by contraction and strike slip not orogen normal extension plutons played a greater role than terrane accretion in causing crustal thickening and high grade metamorphism

pennsylvanian deposystems and paleoclimates of the appalachians abstract central appalachian basin rocks indicate major changes in source areas base level and climate for late mississipian through late pennsylvanian time through time dominant source areas change from craton and northeastern orogen to southeastern orogenic mountains the mississipian pennsylvanian uncomformity correlates with a worldwide eustatic event early pennsylvanian rocks contrast markedly with underlying mississippian mauch chunk redbeds in composition and texture yet the source areas and alluvial plain setting were similar seas transgressed northeastward during middle and earliest late pennsylvanian time along axes of the pocahontas and dunkard basins while fluvial dominant deltas prograded northwestward this progradation 1 progressively extended the coastal plain 2 provided coastal swamp environments for peat accumulation and 3 eventually cut off the narrow seaway of dunkard basin from the central interior by late pennsylvanian and transformed it into a large shallow freshwater lake redbeds calcium carbonate concretions and gilgai paleosol structures of late mississippian and late pennsylvanian rocks suggest seasonally dry tropical climate whereas the lithologies of the earlier pennsylvanian rocks are indications of everwet tropical climates with their quartz rich fluvial sandstones high quality coals and aluminum rich clay deposits streams change from predominantly bedload to suspended load generally from early to late pennsylvanian in response to changes in paleoslope gradient distance from source area unvegetated highland and change from everwet to intermittently dry tropical climate greater dryness is suggested for increased alkaline conditions observed in paleosols carbonates and coal beds of late pennsylvanian time but sufficiently wet to prevent evaporite deposition

correlation of carboniferous strata using a hierarchy of transgressive regressive units carboniferous strata can be described interpreted and correlated using six scales of allocyclic transgressive regressive t r units these t r units are inferred to be the net result of deposition during cycles of sea level change all pennsylvanian and lower permian strata constitute one second order t r unit or synthem the pennsylvanian system contains third fourth fifth and sixth order t r units that can be correlated across both marine and nonmarine facies in the appalachian basin this permits differentiation of allocyclic t r units from autocyclic t r units or fluvial autocyclic units the hierarchical approach is also useful for predicting the location of marine horizons coals claystones and various types of stratigraphic breaks a hierarchical scheme of allocyclic t r units could be combined with biostratigraphic radiometric and magnetostratigraphic data to form a practical chronostratigraphic framework for the carboniferous

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

p t t evidence for mechanisms of vertical tectonic motion in a contractional orogen north western us and canadian cordillera the 1800 km long coast mountains north cascades orogen of the canadian cordillera and north western us developed as a continental magmatic arc metamorphic rocks in the orogen contain widespread evidence for burial of supracrustal rocks to depths of c 40 km followed by nearly isothermal decompression to depths of 10 km near many shallowly emplaced mid cretaceous plutons low pressure contact metamorphic effects were overprinted by high pressure regional metamorphic minerals and textures as evidenced by kyanite staurolite pseudomorphs after andalusite in metapelitic rocks therefore near pluton rocks record the loading history of the orogen metapelitic rocks not associated with plutons only preserve evidence for high pressure conditions and or high temperature decompression as indicated for example by sillimanite and cordierite after kyanite and garnet respectively petrological evidence for burial and decompression is therefore recorded in different rocks various regions of the orogen differ in timing of metamorphism the overall shape of p t paths and the relative timing and regional extent of the high pressure event but most of these data and observations are consistent with thrusting and or pure shear thickening as primary loading mechanisms throughout the orogen as opposed to magma dominated loading this interpretation is further supported by comparison with thermal models which demonstrate that the p t paths are consistent with simultaneous thrusting and folding at a high initial geothermal gradient 35 40 c km 1 in much of the orogen a high geothermal gradient supports tectonic models invoking intra arc contraction and suggests that magmatism played an important role in regional temperature time paths this tectonic thermal history may be typical of other contractional orogens and illustrates the importance of large vertical displacement of crust in magmatic arcs

a northern cordilleran ocean continent transect sitka sound alaska to atlin lake british columbia the 155 km wide 310 km long sitka sound atlin lake continent ocean transect includes almost all the geologic geophysical and geotectonic elements of the canadian cordillera it crosses the chugach wrangellia alexander stikine and cache creek terranes the gravina and laberge overlap assemblages intrusive and metamorphic belts and neotectonic faults that bound major blocks linear belts of magnetic highs are associated with jurassic and cretaceous granitic belts in wrangellia and the western and central parts of the alexander terrane and with the granitic rocks of the coast plutonic metamorphic complex cpmc the border ranges fault may be expressed at depth on either side of the peril strait fault an enigmatic northeast trending gradient in the cpmc and adjacent rocks separates a regional magnetic low to the northwest from a 300 nt high field to the southeast the bouguer gravity field decreases in broad steps from pacific crust high values to lows at the international boundary with pronounc

two phase evolution of accretionary margins examples from the north american cordillera abstract the coast mountains orogen southeastern alaska and the salmon river suture zone western idaho record the accretion of oceanic crustal fragments to the north american cordilleran margin structural elements associated with these boundaries include a western accretion related thrust belt and steeply dipping post accretionary shear zone the shear zones the coast shear zone southeastern alaska and western idaho shear zone idaho are steeply dipping crustal scale structures characterized by steep isotopic and geophysical gradients the presence of syndeformational tabular calc alkaline tonalitic plutons concordant with shear zone fabrics locally preserved dextral strike slip indicators and pervasive down dip mineral and elongation lineations are consistent with an intra arc transpressional origin for both structures in addition to strike slip translation the structures accommodated exhumation of high pressure moderate temperature metamorphic rocks within the thrust belt to the west and moderate pressure high temperature batholithic rocks to the east similarities between the structures in alaska and idaho suggest that the observed two stage history of underthrusting of accreting crustal fragments followed by modification by intra arc transpressional shear zones is a common tectonic process our analysis implies that recognition of processes active during the accretion of crustal fragments to continental or cratonal margins is commonly inhibited by post accretion deformation and provides insight into lower crustal processes presently operative under modern strike slip accretionary boundaries in addition the intra arc transpressional shear zones e g the coast and western idaho shear zones are structures that could have accommodated paleomagnetically determined large magnitude transcurrent displacements

an appalachian sourced deltaic sequence northeastern alabama usa biofacies lithofacies relationships and interpreted community patterns abstract the thin sequence of lower pennsylvania rocks along sand mountain plateau coal field northeastern alabama u s a records the deposition in a deltaic coastal plain paleoenvironment along the ancient appalachian seaway the section is laterally continuous well exposed and preserves a rich macrobiota identified coexisting paleodepositional environments contain distinctive biofacies specific paleoenvironments of deposition contain unique biofacies in this late carboniferous westphalian a sequence the criteria established for the recognition of these biofacies can be utilized to assist in refined interpretations of deltaic sites in carboniferous coastal paleoenvironments identifiable biofacies include those preserved under a variety of forested wetland swamp conditions distributary and crevasse splay channels coastal bays interdistributary and lagoonal barrier sands and distal storm deposits fig 1 gastaldo et al 1989 vegetation in forested wetlands grew either in clastic substrates or peat substrates the principal biofacies preserved in clastic substrate swamps were lycophyte dominated and can be recognized by either a predominance of canopy litter or subterranean stigmarian appendages gastaldo 1986 the canopy litter that has accumulated on the forest floor was preserved under unique sedimentological conditions and reflects the ecological gradient associated with the distribution of lycophyte genera in the swamp gastaldo 1987 a monotypic assemblage of lycophytes characterized edaphically stressed sites in sites proximal to the levee a mixed assemblage of lycophytes calamiteans pteridophytes and pteridosperms is common in the absence of compressed canopy macrodetritus subterranean axes with helically arranged appendages rootlets crosscutting the bedding may be preserved macro invertebrates are restricted to traces and trails reflecting behavioral traits when conditions were conducive for their movement into these sites peat colonizing vegetation parallels that of the clastic swamp deep distributary channels contain sandstone cast and compressed aerial trunks of lycophytes and spenophytes these occur in bedload deposits along with quartz and quartzose pebbles and cobble size phyllite clasts degradation of external morphology usually precludes assignment of logs to a systematic position lower than order in shallower en echelon stacked crevasse sands occur a mixture of lycophyte calamitean and pteridosperm woody parts additionally scoriaceous fern like foliage may be found little evidence exists for macro invertebrate communities in these unstable settings coastal bays preserve in situ macro invertebrate communities as well as allochthonous macrodetritus that was derived principally from levee vegetation four phases of biofacies development can be delineated gibson and gastaldo 1987 stress tolerant inarticulate brachiopods dominate the initial transgressive phase individuals are found isolated in the siltstone commonly preserved by authigenic cementation in siderite concretions rarely are patches or clusters of individual encountered where clustering does occur it is associated with the colonization of woody plant parts transition to the molluscan dominated phase is accompanied by the establishment of a rich ichnofauna continued transgression and the development of more normal salinities under lagoonal conditions are paralleled by an increase in species richness and abundance the third biofacies phase remains molluscan dominated but the assemblages at any particular point in time are represented by monospecific genera plant macrodetritus was utilized by the macro invertebrate communities and that which is preserved is restricted to highly fragmentary unindentifiable remains the fourth biofacies phase reflects the development of lagoonal conditions this change can be recognized by macro invertebrate body and ichnofossil fauna seilacher s cruziana ichnofacies diversification an increase in the abundance of brachiopods and other invertebrates is considered to represent more open marine conditions barrier sandstone and distal storm deposits contain disarticulated epifaunal brachiopods bivalves gastropods and trilobites these stenohaline forms are concentrated in a shell lag at the base of migrating barrier sand bodies the overlying sandstone is devoid of macro invertebrate body fossils and plant macrodetritus but is characterized by the colonization of zoophycos traces

transgressive channel filling in the breathitt formation upper carboniferous eastern kentucky coal field usa abstract carbonaceous shales of brackish or marine origin in the breathitt formation may exhibit sharp bases with local channel form scours minor channels at the bases of these shales exhibit three general types of fill 1 shale 2 bioturbated heterolithic strata and 3 coal overlain by shale or bioturbated heterolithic strata most of the scours at the bases of the channels were formed during a depositional hiatus that preceded transgression some may also have been formed by transgressive reworking of underlying estuarine and deltaic siliciclastics the channel fills are bioturbated and may contain crudely cyclical rhythmites subordinate and dominant siltstone laminae couplets wave ripples and bimodal current ripple trends the fills are interpreted to represent estuarine sedimentation during marine transgression channels are capped by sideritic bioturbated sandstones that separate the fills from the overlying dark shales deposited under brackish to marine water conditions some of these sandstones may represent local transgressive surfaces the occurrence of these types of channels in different parts of the coal bearing breathitt formation supports the hypothesis of multiple transgressions during the late carboniferous in the central appalachian basin

heat capacities and entropies of andalusite and sillimanite the influence of fibrolitization on the phase diagram of the al 2 sio 5 polymorphs

evolution of some depositional models in late carboniferous rocks of the appalachian coal fields abstract models for carboniferous coal bearing strata developed early in this century and consisted of vertical columns that described commonly occurring sequences of coal beds and associated rocks these were followed by other models that expressed patterns of both vertical and lateral variation but in those as well as earlier models depositional interpretation did not extend much beyond a basic marine nonmarine dichotomy subsequently depositional processes were linked to lithic components and showed that the areal distribution of these components formed a lateral geomorphically controlled continuum ranging from alluvial plains seaward to barrier islands evaluation of this model within a tectonic setting of rapid and differential subsidence produced by growth faulting in the southern part of the appalachian coal fields has shown that while depositional processes are substantially the same as those suggested by the model the form and spatial distribution of resulting lithic components are profoundly affected by movements on contemporaneously active subsurface structures this leads to the conclusion that previous models are a product of depositional processes strongly controlled by their tectonic setting and that further attempts at model generation will require careful assessment of the relationships of lithic distribution to subsurface structures and amounts of data necessary to recognize them

distribution and characteristics of metamorphic belts in the south eastern alaska part of the north american cordillera the cordilleran orogen in south eastern alaska includes 14 distinct metamorphic belts that make up three major metamorphic complexes from east to west the coast plutonic metamorphic complex in the coast mountains the glacier bay chichagof plutonic metamorphic complex in the central part of the alexander archipelago and the chugach plutonic metamorphic complex in the northern outer islands each of these complexes is related to a major subduction event the metamorphic history of the coast plutonic metamorphic complex is lengthy and is related to the late cretaceous collision of the alexander and wrangellia terranes and the gravina overlap assemblage to the west against the stikine terrane to the east the metamorphic history of the glacier bay chichagof plutonic metamorphic complex is relatively simple and is related to the roots of a late jurassic to late early cretaceous island arc the metamorphic history of the chugach plutonic metamorphic complex is complicated and developed during and after the late cretaceous collision of the chugach terrane with the wrangellia and alexander terranes the coast plutonic metamorphic complex records both dynamothermal and regional contact metamorphic events related to widespread plutonism within several juxtaposed terranes widespread moderate p t dynamothermal metamorphism affected most of this complex during the early late cretaceous and local high p t metamorphism affected some parts during the middle late cretaceous these events were contemporaneous with low to moderate p high t metamorphism elsewhere in the complex finally widespread high p t conditions affected most of the western part of the complex in a culminating late late cretaceous event the eastern part of the complex contains an older pre late triassic metamorphic belt that has been locally overprinted by a widespread middle tertiary thermal event the glacier bay chichagof plutonic metamorphic complex records dominantly regional contact metamorphic events that affected rocks of the alexander and wrangellia terranes widespread low p high t assemblages occur adjacent to regionally extensive foliated granitic dioritic and gabbroic rocks two closely related plutonic events are recognized one of late jurassic age and another of late early and early late cretaceous age the associated metamorphic events are indistinguishable a small late devonian or early mississippian dynamothermal belt occurs just north east of the complex two older low grade regional metamorphic belts on strike with the complex to the south are related to a cambrian to ordovician orogeny and to a widespread middle silurian to early devonian orogeny the chugach plutonic metamorphic complex records a widespread late late cretaceous low to medium high p moderate t metamorphic event and a local transitional or superposed early tertiary low p high t regional metamorphic event associated with mesozonal granitic intrusions that affected regionally deformed and metamorphosed rocks of the chugach terrane the chugach complex also includes a post late triassic to pre late jurassic belt with uncertain relations to the younger belts

comment and reply on tectonic accretion and the origin of the two major metamorphic and plutonic welts in the canadian cordillera comment

paleoclimate controls on stratigraphic repetition of chemical and siliciclastic rocks climate is a primary control on sediment flux from continental sources into sedimentary systems in warm climates siliciclastic input is greatest under highly seasonal rainfall nonseasonal conditions favor formation of end member chemical rocks perennially wet climates are conducive to coal formation whereas dry climates produce carbonates and or evaporites stratigraphic repetition of siliciclastic and chemical rocks therefore appears to be related to paleoclimate cycles as well as to transgressive regressive events and tectonics