interactions between axial and transverse drainage systems in the late cretaceous cordilleran foreland basin evidence from detrital zircons in the straight cliffs formation southern utah usa new detrital zircon geochronologic data from the straight cliffs formation of southern utah provide insight into the controls on stratigraphic architecture of the western interior basin during turonian early campanian time detrital zircon ages n 40 n 3650 derived from linked fluvial and shallow marine depositional systems of the kaiparowits plateau indicate the majority of zircons in fluvial strata were derived from the mogollon highlands 1 25 1 90 ga 67 of fluvial zircons with subordinate contributions delivered from the sevier fold and thrust belt 265 1250 ma 17 and cordilleran magmatic sources 81 265 ma 16 integration of these data with fluvial facies distributions petrography clast counts and evidence of magmatic arc sources from the mohave region of california implies the presence of a northeast flowing axial fluvial system this system was fed by rivers draining the mogollon highlands to the south and by transverse drainages from the sevier fold and thrust belt to the west compared to the fluvial deposits shallow marine sandstones have a greater proportion of sevier fold and thrust belt derived zircons 42 which were delivered via longshore currents from the north shallow marine samples also contain less mogollon input 44 compared to contemporaneous fluvial systems and similar input from the magmatic arc 14 although proterozoic zircons associated with the mogollon highlands are also present in the sevier fold and thrust belt several lines of evidence argue for a distinct southerly source for the straight cliffs formation these include 1 moderate proportions of feldspar and angular quartz grains in fluvial sandstones which favor a felsic intrusive source and 2 prominent 1 4 and 1 7 ga zircon populations the 1 4 and 1 7 ga peaks are the only dominant proterozoic peaks in samples from the straight cliffs formation whereas samples derived more directly from the sevier fold and thrust belt tend to have a broader distribution of proterozoic age peaks up section architectural trends in the straight cliffs formation are linked to trends in detrital zircon geochronologic data underscoring the likelihood of common drivers and controls the axial system depositing straight cliffs fluvial strata was primarily fed by drainages originating in the mogollon highlands during a pulse of tectonic activity in the maria fold and thrust belt and generally high subsidence rates in the foreland basin turonian santonian over time activation of the paxton duplex in the sevier fold and thrust belt early campanian exhumed proximal foreland basin strata and enabled drainage systems from the sevier fold and thrust belt to feed into the basin more prominently the results presented here underscore the potential significance of axial fluvial systems and their complex interplay with transverse drainage networks in foreland basins

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

facies control on sandstone composition and influence of statistical methods on interpretations in the john henry member straight cliffs formation southern utah usa abstract the upper cretaceous john henry member of the straight cliffs formation preserves regressive shoreface and channel facies and transgressive lagoonal tidal inlet facies that suggest distinct modal sandstone compositions detrital modes from six sandstone facies upper shoreface lower shoreface deflected mouth bars fluvial channels tidal inlets and washover fans and their spatial and temporal variations provide additional data regarding the depositional environments and setting of the john henry member three statistical methods were utilized univariate standard deviation and confidence interval and multivariate logratio transformations to assess the compositional difference between facies using estimation of means both univariate statistical methods have some inherent problems standard deviation does not account for sample size while the confidence interval method incorporates a t test to account for only some of the uncertainty of small sample size the results of the univariate methods differ slightly and both indicate statistically distinct sandstone compositions based on facies multivariate statistics are much more robust and suggest similar trends yet display different compositional means and have inconclusive confidence fields as they incorporate all of the uncertainty associated with small sampling sizes in general sandstone compositions become more quartz rich and compositionally mature as sediment is transported from proximal fluvial environments to distal upper shoreface environments this trend reflects the degree of preferential reworking or winnowing of unstable grains prior to lithification more complicated relationships are observed as facies distributions shift through space and time sandstone compositions support a deflected wave dominated deltaic interpretation for the john henry member in this area sandstone compositions become more lithic rich from north to south corresponding to the facies distribution of upper shoreface and deflected mouth bars respectively mouth bars occur at the intersection of the fluvial channel and the coastline where sand is deflected via longshore drift to the southern portion of the field area upper shoreface facies located further away from mouth bar facies are heavily reworked by wave processes and contain more mature quartz rich modal compositions additionally high feldspathic and lithic concentrations in tidal inlet facies suggest that this facies was sourced closer to mouth bars rather than updrift upper shoreface sediments a shift in sandstone composition occurs at the end of the second transgressive regressive cycle of the john henry member throughout the rogers canyon area this compositional change is concurrent with a relatively large basinward shift in facies which suggests that it reflects the transition from regressive to transgressive facies associated with the relative sea level fall rather than a change in the main sediment source area

u pb geochronology and geochemistry of the mccoy mountains formation southeastern california a cretaceous retroarc foreland basin the timing of deposition of fluvial sediments now forming the 7 km thick mccoy mountains formation is one of the key uncertainties in reconstructing the mesozoic paleogeography of southern california and western arizona ion microprobe u pb geochronologic data for individual zircons from nine sandstones from the mccoy mountains type section and six associated igneous rocks provide significant new constraints on the tectonic setting and the timing of deposition within the northwest trending mccoy basin u pb zircon data from a metavolcanic rock of the underlying dome rock sequence in the palen mountains confirm that the mccoy mountains formation was deposited after regional middle to late jurassic arc magmatism u pb zircon data from a late cretaceous granodiorite intruding the formation in the coxcomb mountains confirm that the formation was deformed and metamorphosed prior to 73 5 1 3 ma populations of detrital zircons vary systematically with both rock type and stratigraphic height lithic arkoses predominantly derived from the west have consistently more abundant younger zircons than do litharenite sandstones predominantly derived from the north and the youngest zircons yield maximum depositional ages that decrease from 116 ma near the base to 84 ma near the top of the section the detrital zircon data permit a late jurassic age for the basal comparatively quartz rich sandstone however the data further suggest that 90 of the formation was deposited between middle early and middle late cretaceous time these results are consistent with the hypothesis that most of the mccoy mountains formation represents a retroarc foreland basin deposited behind the active evolving cretaceous cordilleran continental margin magmatic arc that lay to the west and in the foreland of the actively deforming cretaceous maria fold and thrust belt

fiamme textures in volcanic successions flaming issues of definition and interpretation abstract fiamme are aligned flame like lenses found in welded ignimbrite fiamme also occur in welded pyroclastic fall deposits secondary welded pumice rich facies diagenetically altered and compacted non welded pumiceous volcaniclastic facies and lavas fiamme can be formed in a variety of ways the common genetic use of the term fiamme for pumice clasts that have undergone welding compaction is too narrow fiamme is best used as a descriptive term for elongate lenses or domains of the same mineralogy texture and composition which define a pre tectonic foliation and are separated by domains of different mineralogy texture or composition this descriptive term can be used regardless of the origin of the texture and remains appropriate for flattened pumice clasts in welded ignimbrite

ignimbrites of the eastern snake river plain evidence for major caldera forming eruptions the eastern snake river plain is a predominantly rhyolitic province analogous to the present day yellowstone plateau volcanic field but older and further evolved the widespread quaternary basaltic lavas that now blanket the eastern snake river plain appear to have erupted after major rhyolitic activity ceased and represent less than 20 of the total volume of volcanic rock near the north central margin of the plain the rhyolites show a general age progression that becomes younger northeastward toward yellowstone three major ignimbrite sheets comparable in magnitude to those of the yellowstone plateau field have been correlated on both sides of the eastern snake river plain from the arco and pocatello areas to margins of the yellowstone plateau these 4 3 to 6 5 ma old ignimbrites are referred to herein as the heise volcanic field studies of facies changes and lateral variations in the three major ignimbrites of the heise field permit identification of related calderas that are now buried beneath the plain petrologic studies suggest that although the ignimbrites overlap compositionaliy each was derived from an isotopicaliy distinct magma that contained a significant component of crustal material

in situ formation of welded tuff like textures in the carapace of a voluminous silicic lava flow owyhee county sw idaho the badlands rhyolite on the owyhee plateau of southwestern idaho can be demonstrated to be a large lava flow on the basis of its geometry of large and small flow lobes its well exposed near vent features and its response to pre existing topography however samples of the dense upper vitrophyre of the unit reveal a range of annealed fragmental textures including material which closely resembles the compressed welded glass shards which are characteristic of ignimbrites formation of these tuff like textures involved processes probably common to emplacement of most silicic lava flow units decompression upon extrusion causes inflation of pumice at the surface of the lava flow some of this pumice is subsequently comminuted producing loose bubble wall shards bits of pumice chips of dense glass and fragments of phenocrysts this debris sifts down around loose blocks and into open fractures deeper in the flow where it can be reheated compressed and annealed to varying degrees the end result is a dense vitrophyre layer beneath the true upper non welded carapace breccia which can be extremely texturally heterogeneous with areas of flow foliated lava occurring very near lava which in many aspects looks like welded ignimbrite complete with flattened pumices identical textures in other silicic units have been cited by previous workers as evidence that those units erupted as pyroclastic flows which then underwent sufficient rheomorphism to create a flow foliated rock which otherwise appears to be lava the textures described herein indicate that lava flows can come to mimic rheomorphic ignimbrites at least at scales ranging from thin sections to outcrops voluminous silicic units with scattered fragmental textures but with otherwise lava like features are probably true effusive lava flows

petrogenesis of the highly potassic 1 42 ga barrel spring pluton southeastern california with implications for mid proterozoic magma genesis in the southwestern usa syenites from the barrel spring pluton were emplaced in the early proterozoic mojave crustal provine of southeastern california at 1 42 ga all rocks even the most mafic are highly enriched in incompatible elements e g k2o 4 12 wt rb 170 370 ppm th 12 120 ppm la 350 1500xchondrite la ybn 35 100 elemental compositions require an incompatible element rich but mafic or ultramafic source trace element models establish two plausible sources for barrel spring magmas 1 lree enriched garnet websterite with accessory apatite rutile enriched lithospheric mantle and 2 garnet amphibolite or garnet hornblende granulite with enriched alkali basalt composition also with accessory apatite rutile mafic lower crust nd and pb isotopic ratios do not distinguish a crust vs mantle source but eliminate local mojave province crust as the principal one and indicate that generation of the enriched source occurred several hundred million years before emplacement of the barrel spring pluton 1 40 1 44 ga potassic granites are common in southeastern california suggesting a genetic link between the barrel spring pluton and the granites however although the same thermal regime was probably responsible for producing both the granitic and syentic magmas elemental and isotopic compositions preclude a close relationship isotopic similarity of the barrel spring pluton to 1 40 1 44 ga granites emplaced in the central arizona crustal province to the east may imply that a common component was present in the lithosphere of these generally distinct regions

evidence of uppermost proterozoic to lower cambrian miogeoclinal rocks and the mojave snow lake fault snow lake pendant central sierra nevada california this is the published version copyright 2010 american geophysical union all rights reserved

uranium lead isotopic ages from the sierra nevada batholith california this study provides new information on the timing and distribution of mesozoic magmatic events in the sierra nevada batholithic complex chiefly between 36 and 37 n latitude u pb ages have been determined for 133 zircon and 7 sphene separates from 82 samples of granitoid rocks granitoid rocks in this area range in age from 217 to 80 m y triassic intrusions are restricted to the east side of the batholith jurassic plutons occur south of the triassic plutons east of the sierra nevada as isolated masses within the cretaceous batholith and in the western foothills of the range cretaceous plutons form a continuous belt along the axis of the batholith and occur as isolated masses east of the sierra nevada no granitic intrusions were emplaced for 37 m y east of the sierra nevada following the end of jurassic plutonism however following emplacement of the eastern jurassic granitoids regional extension produced a fracture system at least 350 km long into which the dominantly mafic calc alkalic independence dike swarm was intruded 148 m y ago the dike fractures probably represents a period of regional crustal extension caused by a redistribution of the regional stress pattern accompanying the nevadan orogeny intrusion of cretaceous granitic plutons began in large volume about 120 m y ago in the western sierra nevada and migrated steadily eastward for 40 m y at a rate of 2 7 mm y this slow and constant migration indicates remarkably uniform conditions of subduction with perhaps downward migration of parent magma generation or a slight flattening of the subduction zone such steady conditions could be necessary for the production of large batholithic complexes such as the sierra nevada the abrupt termination of plutonism 80 m y ago may have resulted from an increased rate of convergence of the american and eastern pacific plates and dramatic flattening of the subduction zone u pb ages of the giant forest alaskite sequence in sequoia national park are all in the range 99 3 m y indicating a relatively short period of emplacement and cooling for this nested group of plutons u pb ages of a mafic inclusion and its host granodiorite indicate that both were derived from a common source or that the mafic inclusion was totally equilibrated with the granodioritic magma comparison of isotopic ages determined by different methods such as zircon u pb sphene u pb hornblende k ar and biotite k ar suggests that zircon u pb ages generally approximate the emplacement age of a pluton however some plutons probably contain inherited or entrained old zircons and the zircons of some samples are disturbed by younger thermal and metamorphic events the ages reported here are consistent with u pb age determinations previously made on granitic rocks to the north stern et al 1981 the age distribution of granitic belts determined here is in general agreement with those established by k ar dating evernden and kistler 1970 but does not differentiate the five epochs of plutonism determined in their study

subaqueous rhyolitic dome top tuff cones a model based on the devonian bunga beds southeastern australia and a modern analogue the relics of two late devonian subaqueous rhyolitic dome top tuff and pumice cone successions are preserved in the bunga beds outlier of the boyd volcanic complex southeastern australia these cone successions and other rhyolitic volcanics of the bunga beds are associated with turbidite and other deep water massflow sedimentary rocks the two cone successions have a generally similar stratigraphy at the base flow banded variably autobrecciated and quench fragmented rhyolite representing an intrusive to extrusive dome is overlain by rhyolitesediment breccia representing extrusion of the dome through the deep water sediment pile and resedimentation down its flanks in the northern cone succession an overlying succession of bedded pumiceous crystal rich to crystal poor tuffs represents the onset of pyroclastic activity and growth of a tuff cone an overyling debris flow deposit represents degradation of part of the cone the topmost unit a stratified pumice succession is thought to represent another cone building eruptive phase and is separated from the underlying strata by a major slide surface the southern cone succession contains less tuff and abundant pumice and is also terminated by a debris flow deposit indicating cone degradation a modern analogue for the inferred eruptive style and sequence is the 1953 1957 rhyolite eruption that formed the tuluman island lava tuff cone complex in the bismarck sea the eruptions were often cyclical consisting of an initial inferred submarine lava forming stage passing into a pumicecone forming stage in some cases a subaeriallava forming stage and a final stage following the cessation of volcanism during which the cones collapsed gravitationally or were destroyed by wave erosion using observations from both the tuluman island eruptions and the preserved stratigraphies of the devonian tuff cones a dynamic model is proposed for the formation of subaqueous rhyolitic dome top tuff and pumice cones

relationship between mesozoic and cenozoic tectonic features in west central arizona and adjacent southeastern california the maria fold and thrust belt mftb is a narrow belt of mesozoic crustal shortening that trends east west across west central arizona and adjacent southeastern california it is characterized by generally south vergent folds and thrusts that commonly displace proterozoic crystalline rocks over deformed and metamorphosed paleozoic and mesozoic strata the mftb is cut by a south to southeast trending belt of mid tertiary extensional deformation extension was characterized by large displacements on low angle normal faults known as detachment faults and by isostatic uplift of mylonitic midcrustal rocks now exposed in metamorphic core complexes the geometry and style of extensional deformation change along the extensional belt and reveal the influence of the mftb several extensional features are spatially coincident with the root zone of mftb thrusts 1 an areally extensive west northwest trending belt of denuded tertiary mylonitic fabrics in the whipple and harcuvar metamorphic core complexes 2 a style of extension characterized by minimum extensional dismemberment of the upper plate and maximum denudation and uplift of deep seated lower plate rocks 3 an abrupt bend in the belt of arched uplifted rocks below detachment faults and 4 an abrupt bend in the trend of the breakaway zone of the detachment faults and an associated lateral ramp in the detachment fault system the first two features may be the result of isostatic uplift of a crustal root downward protruding moho bulge inherited from crustal thickening within the mftb and the other two features may reflect at the time of detachment fault initiation the influence of stresses in the crust associated with flexural support of the buoyant mesozoic crustal root

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

thermal history of crystalline nappes of the maria fold and thrust belt west central arizona the thermal history of the crust in west central arizona as documented by 40ar 39ar step heating analysis of mineral suites from crystalline nappes of the maria fold and thrust belt is characterized by three distinct stages for late cretaceous and tertiary time regional heating of the crust occurred during basement involved folding and thrust faulting in middle late cretaceous time 80 90 ma and represents the earliest phase recorded by the 40ar 39ar data the second stage was dominated by uplift and slow cooling 5 10 c m y of the crust throughout latest cretaceous and early tertiary lime tectonic denudation in late oligocene to early miocene time resulted in rapid uplift and cooling of midcrastal rocks in the footwall of the whipple buckskin rawhide detachment system marking the final thermal signature in the region evidence for variable argon loss in the hornblende spectra implies exposure of differing structural levels within the thrust belt and or significant thermal heterogeneity in the crust during late cretaceous orogenesis partially outgassed hornblende in the northern granite wash mountains reflects temperatures of 450 c whereas complete resetting of hornblende at mesquite mountain suggests that this area attained temperatures in excess of 500 c in contrast data from the northern plomosa mountains indicate that this area did not attain temperatures sufficient to completely degas biotite or k feldspar 350 c during late cretaceous time the range of early tertiary muscovite and biotite ages in the region reflects slow cooling presumably associated with uplift and erosion following crustal thickening k feldspars yield saddle shaped age spectra with minimum apparent ages ranging from 22 28 ma and reflect quenching due to rapid exhumation of midcruslal to upper crustal rocks in the detachment terrain collectively the data are consistent with either of two models for the thermal evolution of the crust in middle to late tertiary time either 1 lower plate rocks were still sufficiently hot following late cretaceous heating that argon clocks were set simply due to rapid cooling or 2 the area experienced a renewed thermal input associated with extension causing argon loss from previously cool rocks based on consideration of diffusion domain behavior in k feldspars we infer that a renewed thermal pulse was associated with the early stages of extension and was related to the cause for crustal weakening

cainozoic evolution of the state of stress and style of tectonism of the basin and range province of the western united states cainozoic evolution of the modern plate boundary along the western united states from subduction to a predominantly transform boundary coincided with a change from compressional to extensional deformation in the western united states extensions tectonism responsible for the modern basin and range province appears to represent a unique late stage episode of a much longer period of extension initiated in an in tra arc setting contemporaneously with calc alkaline magmatism basin range extension is distinguished from early extension on the basis of angular unconformities differences in fault trends and spacing and associated magmatism basaltic prebasin range extension i e extension preceding the break up of the region into ranges resembling the modern ones was under way locally by at least 30 ma and is now recognized by faulted and highly tilted strata exposed in uplifted range blocks by large regions of the crust underlain by passively emplaced subvolcanic batholiths and by the thickness and distribution of stratigraphic units locally high strain rates that accompanied early extensions of as much as 50 100 are implied data on preferentially orientated dyke swarms and fault slip vectors indicate a strikingly uniform wsw ene least principal stress orientation in the period ca 20 10 ma during this early extension the change from early extension to basin range style faulting of the upper 15 km of crust which resulted in broadly spaced ranges 25 35 km crest crest spacing was time transgressive and probably not abrupt locally both types occurred concurrently southern basin and range block faulting occurred largely in the period 13 10 ma in response to a stress field orientated similarly to that responsible for the early extension in contrast northern basin and range block faulting developed after 10 ma and continues to the present in response to a stress field orientated approximately 45 clockwise to the earlier stress field this modern stress field with a wnw ese to e w directed least principal stress characterizes the entire modern basin and range province and rio grande rift region the 45 change in least principal stress orientation is consistent with superposition of dextral shear associated with the development of the san andreas transform fault inclusion of pre basin range extension may help resolve the discrepancy between estimates of 15 30 for basin range block faulting and total extension estimates of 100 300 for the basin and range province

detrital zircon evidence for non laurentian provenance mesoproterozoic ca 1490 1450 ma deposition and orogenesis in a reconstructed orogenic belt northern new mexico usa defining the picuris orogeny detrital zircon and igneous zircon u pb ages are reported from proterozoic metamorphic rocks in northern new mexico these data give new insight into the provenance and depositional age of a 3 km thick metasedimentary succession and help resolve the timing of orogenesis within an area of overlapping accretionary orogens and thermal events related to the proterozoic tectonic evolution of southwest laurentia three samples from the paleoproterozoic vadito group yield narrow unimodal detrital zircon age spectra with peak ages near 1710 ma igneous rocks that intrude the vadito group include the cerro alto metadacite the picuris pueblo granite and the penasco quartz monzonite and yield crystallization ages of 1710 10 ma 1699 3 ma and 1450 10 ma respectively within the overlying hondo group a metamorphosed tuff layer from the pilar formation yields an age of 1488 6 ma and represents the first direct depositional age constraint on any part of the proterozoic metasedimentary succession in northern new mexico detrital zircon from the overlying piedra lumbre formation yield a minimum age peak of 1475 ma and 60 grains 25 yield ages between 1500 ma and 1600 ma possibly representing non laurentian detritus originating from australia and or antarctica detrital zircons from the basal metaconglomerate and the middle quartzite member of the marquenas formation yield minimum age peaks of 1472 ma and 1471 ma consistent with earlier results we interpret the onset of ca 1490 1450 ma deposition followed by tectonic burial regional al 2 sio 5 triple point metamorphism and ductile deformation at depths of 12 18 km to reflect a mesoproterozoic contractional orogenic event possibly related to the final suturing of the mazatzal crustal province to the southern margin of laurentia we propose to call this event the picuris orogeny

element redistribution during hydrothermal alteration of rhyolite in an active geothermal system yellowstone drill cores y 7 and y 8 abstract hydrothermal alteration of the 0 54 ma biscuit basin rhyolite flow in yellowstone drill cores y 7 and y 8 has involved significant changes in ti normalized whole rock concentrations of li mg ca na k mn rb sr sb cs ba and u whereas such changes have generally not occurred for al fe sc co y zr ree hf ta and th the relatively mobile elements have been redistributed over distances from 2 5 cm to more than 10 100 m and are associated mainly with zeolites and clays in thoroughly altered samples average whole rock changes in ti normalized mass range from about 0 5 17 g kg 9 49 for major elements and 0 1 280 mg kg 19 4260 for minor and trace elements compositional changes correlate with hydrothermal mineralogy the relatively immobile elements have been redistributed over a distance of at least 10 100 m but less than 2 5 cm and are associated mainly with clays in thoroughly altered samples addition of sio2 ranges from 110 890 g kg in samples where porosity has been thoroughly sealed by silica deposition thermal water is not in oxygen isotopic equilibrium with any primary or secondary phases analyzed except calcite modest depletions of 18o 1 2 due to exchange with thermal water apparently have occurred in y 8 plagioclase and obsidian oxygen isotope ratios in obsidian replacing smectite and in veinlet celadonite and cristobalite suggest that these phases precipitated from water locally enriched in 18o up to 8 heavier than present thermal water the minimum integrated water rock mass ratio in y 7 and y 8 is 103 104 assuming advective transport

architecture and formation of transgressive regressive cycles in marginal marine strata of the john henry member straight cliffs formation upper cretaceous of southern utah usa marginal marine deposits of the john henry member upper cretaceous straight cliffs formation were deposited within a moderately high accommodation and high sediment supply setting that facilitated preservation of both transgressive and regressive marginal marine deposits complete transgressive regressive cycles comprising barrier island lagoonal transgressive deposits interfingered with regressive shoreface facies are distinguished based on their internal facies architecture and bounding surfaces two main types of boundaries occur between the transgressive and regressive portions of each cycle i surfaces that record the maximum regression and onset of transgression bounding surface a and ii surfaces that place deeper facies on top of shallower facies bounding surface b the base of a transgressive facies bounding surface a is defined by a process change from wave dominated to tide dominated facies or a coaly shelly interval indicating a shift from a regressive to a transgressive regime the surface recording such a process change can be erosional or non erosive and conformable a shift to deeper facies occurs at the base of regressive shoreface deposits along both flooding surfaces and wave ravinement surfaces bounding surface b these two main bounding surfaces and their subtypes generate three distinct transgressive regressive cycle architectures i tabular shoaling upward marine parasequences that are bounded by flooding surfaces ii transgressive and regressive unit wedges that thin basinward and landward respectively and iii tabular transgressive lagoonal shales with intervening regressive coaly intervals the preservation of transgressive facies under moderately high accommodation and sediment supply conditions greatly affects stratigraphic architecture of transgressive regressive cycles acknowledging variation in transgressive regressive cycles and recognizing transgressive successions that correlate to flooding surfaces basinward are both critical to achieving an accurate sequence stratigraphic interpretation of high frequency cycles

air sea interaction between tropical cyclone nari and kuroshio 1 the air sea interaction between tropical cyclone nari sep 6 16 2001 and kuroshio is studied using satellite observations and an ocean model nari crossed the kuroshio several times which caused variations in typhoon intensity nari weakened when it was over the shelf north of kuroshio where cooling took place due to mixing of the shallow thermocline the cyclonic circulation penetrated much deeper for the slowly moving storm regardless of nari s intensity near inertial oscillations are simulated by the model in terms of the vertical displacement of isotherms the sst cooling caused by upwelling and vertical mixing is effective in cooling the upper ocean several days after the storm had passed at certain locations surface chlorophyll a concentration increases significantly after nari s departure upwelling and mixing bring nutrient rich subsurface water to the sea surface causing enhancement of phytoplankton bloom

architecture and origin of an amalgamated fluvial sheet sand lower castlegate formation book cliffs utah abstract amalgamated fluvial sheet sandstones in the stratigraphic record are often interpreted as the deposits of braided rivers alluvial sequence stratigraphic models show these sheet sandstones overlying sequence boundaries and deposited during low rates of base level rise and fall since sequence stratigraphic models rely on the balance between creation destruction of accommodation and sediment supply is the sheet like nature of these units controlled by channel style by aggradation rates tied to base level changes or a combination of both the lower member of the castlegate formation in the book cliffs of eastern utah u s a was selected to answer these questions regarding the origin and architecture of amalgamated sheet sandstones the lower castlegate is 60 m thick and is underlain by a regional sequence boundary delineation of the alluvial architecture utilized a combination of outcrop photography measured sections and paleochannel dimension estimation at two outcrops in the type area architectural components within the outcrops were defined and include 1 basal thalweg fill units 2 inclined sandy or heterolithic barform deposits and 3 overbank siltstone and mudstone thalweg fill units represent deposition in the topographically lowest part of the channel and are preferentially preserved thalweg units exist as single units or as a composite of multiple thalweg units overlying thalweg units inclined barform deposits are in places preserved and genetically linked to an underlying thalweg fill unit bar accretion directions when combined with paleocurrent indicators show that lateral downstream and upstream accretion all occur in the lower castlegate overbank deposits are rarely preserved but where present they typically overlie bar deposits the architectural components stack to form a threefold cyclic hierarchy of 1 channel bar systems 2 12 m thick 2 channel belts 2 16 m thick and 3 stacked channel belt complexes 17 40 m thick complete channel bar systems are rarely preserved and occur locally as a succession of multiple stacked thalweg fill units the lack of barforms within a composite thalweg unit suggests that channel migration is the dominant process controlling preservation within channel bar systems possibly associated with a component of local avulsion channel belts are composed of stacked channel bar systems capped by a barform the barform is preserved due to a regional avulsion moving the active channel to another location within the floodplain isolating it from potential reworking stacked channel belt complexes are characterized by alternations of thalweg dominated and barform dominated channel belts the mechanism responsible for deposition at the stacked channel belt complex scale may be creation destruction of accommodation associated with base level changes paleochannel reconstructions show that channel flow depths using bar and underlying thalweg thickness were up to 7 6 m channel depth estimates utilizing a cross bed set thickness of 26 cm averaged 4 6 7 7 m these values were used to calculate channel widths which were estimated at 143 365 m up to a maximum of approximately 1 km regional paleoflow within the lower castlegate was dominantly southeast directed the architectural components paleochannel characteristics and paleocurrent data suggest the lower castlegate member was deposited in low to intermediate sinuosity rivers influenced by autocyclic processes at smaller scales and allocyclic processes at the larger outcrop scale

climatic control of fluvial lacustrine cyclicity in the cretaceous cordilleran foreland basin western united states tectono stratigraphic models of foredeep sedimentation have generally presumed a direct link between changing rates of tectonism and concomitant sedimentological response as manifested by change in thickness composition or depositional environment of sediment accumulating in adjacent basins lacustrine limestone units within the early cretaceous fluviamacustrine gannett group of western wyoming exhibit systematic variation in several geochemical proxies of relative rates of precipitation and evaporation indicating that lakewater chemistry was controlled by variation in regional climate change in proportion of allochthonous terrigenous clastic vs autochthonous carbonate deposition as well as carbonate mg ca ratio and stable isotopic composition occurs at two scales metre scale alternation of micritic limestone and argillaceous marl is accompanied by mineralogical and isotopic variation within individual beds indicating preferential carbonate accumulation during intervals of decreased regional meteoric precipitation relative to lake surface evaporation limestone deposition began during intervals of maximum aridity and decreased as increased meteoric precipitation driven flux of terrigenous clastic sediment overwhelmed sites of carbonate accumulation similar upsection variation in limestone mineralogy and isotopic composition at a scale of tens of metres reflects the multiple processes of long term increase in meteoric precipitation and lakewater freshening prior to influx of terrigenous sediment across basin fluvial deltaic progradation and renewed accumulation of riverine terrigenous units such trends suggest that formation scale alternation between fluvial clastic and lacustrine carbonate deposition was controlled by climate change

structures within large volume rhyolite lava flows of the devonian comerong volcanics southeastern australia and the pleistocene ngongotaha lava dome new zealand abstract many rhyolitic units within the late devonian comerong volcanics erupted as lava flows and domes some up to 18 km long and 350 m thick the textural and structural characteristics that distinguish the flows and domes as lava rather than rheomorphic ignimbrite include unbroken phenocrysts zones of autobrecciation and finely developed flow layering with individual layers continuous for several metres the flow layering is typically contorted into isoclinal folds with forms suggesting fluidal deformation and is interlayered with and gradational into restricted zones of pumice rich lapilli tuff and zones of lenticulite breccia the lenticulite breccia comprises discontinuous lenticular rhyolite fragments the long axes of which define a foliation parallel to flow layering lenticles in the breccia vary from elongate layers up to 1 m long and several millimetres thick to short fragments less than 10 cm long and several centimetres wide similar zones of lenticulite breccia consisting of glassy lenticular clasts in a devitrified spherulitic matrix of cristobalite and albite exist within the late pleistocene ngongotaha dome near rotorua new zealand the lenticulite breccia is considered to form by aqueous diffusion and selective devitrification of the rhyolite along anastomosing fluid paths and to be modified by mechanical fracturing of the lava in a zone of high shear stress geochemically the rhyolites are high si and a type with high zr and y contents indicating that they formed from high temperature relatively anhydrous f rich melts a type granitoids crop out intermittently along the length of and adjacent to the volcanic complex and are comagmatic with the rhyolite the high temperature low bubble and phenocryst content and a high eruptive rate of the rhyolite likely resulted in a low effective viscosity and extensive flow units

evolution of late cretaceous and early tertiary basins of southwest utah based on clastic petrology abstract upper cretaceous to eocene clastic rocks of southwest utah record active sevier style thrust deformation cessation of thrusting and sedimentation related to laramide style folding the formations which record these tectonic events include from oldest to youngest the iron springs kaiparowits canaan peak grapevine wash grand castle informal name pine hollow and claron formations two petrographically distinct upward coarsening petrofacies occur in the foreland basin and are herein named for the formations they comprise the kaiparowits canaan peak and iron springs grand castle petrofacies the kaiparowits canaan peak petrofacies consists of volcanic and radiolarian chert lithic fragments derived from sources in southeastern california and southern nevada the finer grained kaiparowits formation was deposited during active thrusting in the middle to upper campanian while the conglomeratic canaan peak formation was deposited during cessation of thrust activity between the upper campanian and lower paleocene the iron springs grand castle petrofacies contains quartzite and carbonate clasts and sandstone compositions that suggest derivation from the wah wah and blue mountain thrust sheets in southwestern utah the iron springs formation represents upper cretaceous syn thrusting deposition whereas the grand castle conglomerates were deposited during lower paleocene rebound of these thrust sheets the upper cretaceous to paleocene grapevine wash formation is an areally restricted conglomeratic alluvial fan sequence composed of carbonate and sandstone clasts derived from paleozoic rocks in the upper plate of the square top mountain thrust in southwestern utah the pine hollow formation received sediment during development of laramide style folding of the sevier foreland basin during early paleocene to middle eocene time jurassic and cretaceous sedimentary units tilted during deformation shed detritus to the east and southwest into an intermontane basin the clastic basal part of the claron formation paleocene to eocene also received sediment from exposed highlands related to laramide structures the abundance of silty carbonate lithic grains suggests that much of the sedimentation in the claron basin was intraformational

jurassic magmatism in the central mojave desert implications for arc paleogeography and preservation of continental volcanic sequences exposures of jurassic magmatic rocks in the west central mojave desert provide insight into the changing character of volcanism throughout jurassic time and the paleogeography of the continental arc middle jurassic explosive volcanism lower sidewinder volcanic series resulted in collapse of multiple calderas this was followed by north south extension broadly coeval with batholith emplacement late jurassic effusive volcanism upper sidewinder volcanic series appears to reflect transtension over a larger region during intrusion of the independence dike swarm the lower sidewinder volcanic series consists of a subaerial nested caldera complex with an aggregate thickness of 4 km the first caldera formed during the eruption of crystal poor rhyolite ignimbrite outflow and intracaldera facies are intercalated with quartzose sandstone of probable cratonal provenance the second caldera formed during the eruption of crystal rich rhyolite to dacite ignimbrite this ignimbrite exhibits complex mineralogical zoning and contains two units of probable collapse related mesobreccia within the 1 400 m thick intracaldera sequence a third caldera nested within the second is filled with crystal rich biotite dacite ignimbrite and tuff breccia a fourth caldera largely coincident with the second formed during eruption of lithic and pumice lapilli dacite ignimbrite eruption and collapse appear to have been multistage as several units of reworked tuff and fallout tuff occur within the 1 750 m thick intracaldera sequence and caldera collapse breccias occur at the base and near the middle of the sequence the top of this sequence contains reworked tuffs and epiclastic rocks suggesting that the fourth caldera provided a posteruptive depocenter for accumulation of sediment normal faulting tilting and erosion followed explosive volcanism and was broadly contemporaneous with intrusion of middle jurassic porphyritic quartz monzonite plutons plutons and tilted lower sidewinder volcanic series are intruded and unconformably over lain by latest jurassic volcanic rocks upper sidewinder volcanic series the upper sidewinder volcanic series is characterized by alkalic basalt to basaltic andesite and rhyolite lavas hypabyssal intrusions and dikes including the 148 ma independence dike swarm regional northeast southwest extension is suggested by the presence of the northwest striking dike swarm and by bimodal volcanism the absence of debris flow deposits and epiclastic rocks suggests an intra arc region of low relief although local caldera related subsidence was the principal control on accumulation of lower sidewinder volcanic rocks preservation was likely enhanced by middle jurassic extension late jurassic extension was of broader regional extent but lesser magnitude because it did not create basins or cause significant tilting of strata the geometry timing and regional setting of middle and late jurassic extension and magmatism suggest a sinistral oblique subduction regime for the jurassic arc of the southern u s cordillera

the middle to late devonian eden comerong yalwal volcanic zone of southeastern australia an ancient analogue of the yellowstone snake river plain region of the usa abstract the middle to late devonian yalwal volcanics comerong volcanics boyd volcanic complex and associated gabbroic and a type granitic plutons form part of a continental volcano tectonic belt the eden comerong yalwal volcanic zone evz located parallel to the coast of southeastern australia the evz is characterised by an elongate outcrop pattern bimodal basalt rhyolite volcanism and a paucity of sedimentary rocks volcanic centres were located along the length of the volcanic zone at positions indicated by subvolcanic plutons dykes rhyolite lavas and other proximal vent indicators including surge bedforms in tuff rings and hydrothermal alteration previous interpretations that suggested the volcanic zone was a fault bounded rift are rejected in favour of a volcano tectonic belt the yellowstone snake river plain region y srp in the usa is an appropriate analogue both regions have basalt lavas which range in composition from olivine tholeiite to ferrobasalt alkalic rhyolitic rocks enriched in y zr and th large rhyolite lava flows plains type basalt lava flows and a paucity of sedimentary rocks the y srp is inferred to have developed by migration of the american plate over a fixed hot spot leading to a northeast temporal progression of the focus of volcanic activity application of a similar hot spot model to the evz using a length of 300 km and a time range for volcanic activity of 5 10 ma suggests that during the middle to late devonian the australian plate was moving at a rate of between 3 and 6 cm yr relative to the hot spot and that the northern extent of the volcanic zone at any time was a topographically high region with rhyolitic activity similar to present day yellowstone as the focus of activity moved northward the high region subsided and the depression was flooded by basalt the evz was much wider up to 70 km and much longer than the belt defined by present day outcrop and was of comparable scale to the y srp the main difference between the two volcanic belts is the lack of large pyroclastic flows and identifiable caldera complexes in the evz

the snake river plain idaho representative of a new category of volcanism studies of the volcanic geology of the snake river plain idaho and comparison with other basaltic regions suggest a new category of volcanic activity termed basaltic plains volcanism typified by the snake river plain this style of volcanism is intermediate between basaltic flood or plateau eruptions and hawaiian volcanism characteristics that are common to both hawaiian and plains volcanism are multiple lava flow units which erupt primarily from point sources formation of low shields and frequent emplacement through lava tubes or channels characteristics that are common to both flood basalts and plains volcanism are high volume flows vents aligned along rift zones and planar surfaces the recognition of plains volcanism in other areas provides a means to interpret the style of eruption and volcanic history

evolution and architecture of a large felsic igneous province in western laurentia the 1 6 ga gawler range volcanics south australia the gawler range volcanics grv of south australia are an intracontinental subaerial large igneous province lip formed during supercontinent assembly in the mesoproterozoic like many lips the grv are intraplate were erupted over a geologically short time 2 million years and are dominated by voluminous lavas however the grv are overwhelmingly dominated by felsic units the grv are essentially undeformed and have not been deeply buried so that their original textures are exceptionally well preserved furthermore they are well exposed in very gently northward and eastward dipping sections up to 4 km thick allowing assessment of the facies architecture and evolution of this felsic volcanic lip the evolution of the grv can be clearly separated into two main stages initial eruptions at numerous volcanic centres produced small to moderate volume geochemically distinct felsic lavas and lava domes together with ignimbrites and minor mafic and intermediate lavas forming a sequence 0 5 to 3 km thick volcanic activity in this lower sequence varied from effusive to explosive and was not much different in style or products from phanerozoic felsic volcanic provinces however the second stage produced at least three voluminous felsic units each of which represents about 1000 3000 km3 of magma moreover the dominance of evenly porphyritic textures and lack of pyroclastic textures pumice shards broken crystal lithic clasts in these units suggests that they were erupted effusively and flowed as lavas each of these felsic lavas are generally dominated by a single uniform composition and commonly mingled with a subordinate and compositionally distinct lava

thrust timing growth of structural culminations and synorogenic sedimentation in the type sevier orogenic belt western united states most of the regional shortening in the type area of the sevier orogenic belt in central utah was accommodated by displacement on the canyon range neocomian aptian pavant aptian albian paxton cenomanian campanian and gunnison late campanian paleocene thrust systems inception of each thrust system generated synorogenic sediment associated with frontal thrust tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland the sevier culmination a large antiformal duplex cored by crystalline basement rocks developed during paxton and gunnison thrusting west of and structurally beneath the canyon range and pavant thrusts growth of the sevier culmination was coeval with reactivation of the canyon range and pavant thrust systems and produced a second culmination in proterozoic lower cambrian rocks in the canyon range these structural highs provided much of the sediment to the adjacent foreland basin from late cenomanian to late paleocene time and may have helped to maintain critical taper in the thrust belt