silurian turbidite provenance on the northern avalonian margin the windermere supergroup of nw england was deposited in a foreland basin on the northern margin of eastern avalonia and preserves an almost complete ashgill to poidoli sequence it was ideally positioned to record provenance changes associated with the closure of the iapetus ocean petrographic geochemical and nd isotopic parameters show distinct and concordant temporal trends the late ashgill to early llandovery is characterized by progressive hemipelagic dilution of material derived from the underlying borrowdale volcanic group from the llandovery onward petrographic and geochemical data indicate supply from a recycled orogen source input from the scandian orogen may be inferred no conclusive evidence is recorded of laurentian input into the basin by the late wenlock a unified sedimentary system probably spanned the iapetus ocean an abrupt reversal in provenance trends towards the end of the ludlow records basin inversion the occlusion of the iapetus seaway and concomitant cannibalization of older foreland basin sediments provenance data derived from upper wenlock to poidoli sediments aid the characterization of marine foreland basins

infrasonic tremor in the diffraction zone 1 volcanic tremor signals recorded by an infrasound array 12 5 km from the active vent of k lauea volcano show clear diurnal amplitude variations and originate from a well defined direction pointing to the active pu u crater complex spectral amplitudes between 0 02 0 3 hz a proxy for wind speed increase when the wind speeds increase during the daytime spectral amplitudes between 0 5 3 hz where infrasonic tremor is concentrated increase when the wind speeds decrease at night power spectrum analysis shows that when ambient noise levels drop infrasonic tremor amplitudes rise array processing confirms this relationship and reveals tremor detections and amplitudes decrease during the day these changes in infrasonic tremor spectral amplitude and coherence are most likely due to diurnal variations in atmospheric boundary layers affecting infrasonic propagation within the diffraction zone recognition of these regional atmospheric patterns is necessary to permit robust infrasonic remote sensing of volcanic processes

franciscan complex olistostrome at crescent city northern california an olistostrome and bounding turbidites are exposed within the late mesozoic franciscan complex along the crescent city california coastline facies grade in character from mutti ricci lucchi 1978 mixed facies b c and d to f the olistostrome to mixed a b and e progressing upwards within the franciscan stratigraphic section the facies f unit outcrop is up to 600 m thick and extends 12 km along strike it consists of oblate to tabular blocks up to 200 m in maximum dimension of greenstone tonalite radiolarian chert limestone phyllite and greywacke dispersed in a scaly argillite matrix the olistostromal origin of the unit is indicated by depositional contacts with bounding turbidites by the presence of abundant recycled sedimentary clasts within the unit and by the presence of sedimentary breccias and associated dismembered slump folded turbidites both within the olistostrome and among subjacent turbidites sandstones are chiefly feldspathic litharenites that were very likely derived from the partially dissected late mesozoic sierran klamath magmatic are franciscan rocks record an early pervasive layer parallel flattening strain in such features as extensional faults necking and pinch and swell structures several scales of extensional faulting account for the juxtaposition of turbidites of different facies and or with varying degrees of stratal disruption the formation of sandstone lozenges and the formation of scaly foliation in the olistostrome matrix the latter resulted from the juxtaposition of lenticles with varying concentrations of silt and clay these were ultimately derived from the finer divisions of turbidite beds that were incorporated into the olistostrome the presence of gradational contacts between some sandstone olistoliths and the olistostrome matrix and of sandstone dykes that intrude fractures and associated drag folded turbidite beds indicate that franciscan sediments were not lithified during their early deformation these sediments were deposited in either a trench or trench slope basin and were first deformed either by gravity collapse of the trench slope cover or less likely by vertical loading beneath the toe of the accretionary wedge they later were folded during internal shortening of the growing franciscan accretionary prism

thermal evolution of convergent plate margins thermal modeling and reevaluation of isotopic ar ages for blueschists in the franciscan complex of california modeling of heat flow through a wedge shaped accretionary complex emplaced beneath the overriding plate at a convergent plate margin provides insight into the tectonic significance of ar isotopic ages and metamorphic progressions across blueschist belts if convergence rates are maintained at rates of a few centimeters per year or more material recrystallized at depth where the accretionary wedge is narrow can be rapidly heated to high temperatures and then rapidly cooled to the low temperatures where ar loss by diffusion and recrystallization effectively ceases maximum temperatures are lower and the periods of heating and cooling are longer at shallower levels where the wedge is wider because of this difference in thermal history k ar and 40ar 39ar ages from blueschists recrystallized in the upper part of the accretionary wedge can be younger by several tens of million years than ages from material initially recrystallized at the same time but at greater depth application of this thermal modeling to the franciscan subduction complex of northern california indicates that the coherent blueschists in the eastern belt typically with 115 to 125 m y ar isotopic ages and the high grade blueschist blocks in the mud matrix melanges of the western portion of the central belt typically with 140 to 150 m y ar isotopic ages could both have formed during a single prolonged period of continuous convergence

nappes tectonics of oblique plate convergence and metamorphic evolution related to 140 million years of continuous subduction franciscan complex california this paper presents a new synthesis of franciscan complex tectonics with the emphasis on the pre san andreas fault history of these rocks field relations suggest that the franciscan is characterized by nappe structures that formed during sequential accretion at the trench the presence of these structures along with other field relations including the lack of evidence for large offset of conglomerate suites indicates that strike slip fault systems of large displacement 500 km did not cut the franciscan complex during subduction regional geology and comparisons to modern arc trench systems suggest that strike slip faulting associated with oblique subduction took place inboard east of the franciscan in the vicinity of the magmatic arc the franciscan varies along strike because individual accreted elements packets of trench sediment seamounts etc did not extend the full length of the trench different depths of underplating distribution of post metamorphic faulting and level of erosion pro

u pb ages of detrital zircons in pacheco pass metagraywackes sierran klamath source of mid cretaceous and late cretaceous franciscan deposition and underplating 1 using laser ablation icp ms techniques u pb ages are reported for 338 detrital zircons separated from four franciscan metagraywacke samples from imbricate thrust sheets cropping out in the pacheco pass area east central california coast ranges structurally higher slabs are clastic quartz albite bearing rocks typified by neoblastic lawsonite jadeitic pyroxene the lowest exposed slab lacks jadeitic pyroxene but contains traces of newly grown pumpellyite and lawsonite in addition to abundant quartz albite studied specimens contain moderate amounts of phengite titanite chlorite stilpnomelane carbonate iron oxides rock fragments and carbonaceous matter these diablo range clastic sediments were deposited in mid cretaceous and late cretaceous time the highest allochthon unit i was deposited after 102 ma unit iv was deposited after 90 102 ma and unit v was deposited after 86 ma metagraywacke depositional accretionary ages within slab iv young upward but ages of the slabs decrease progressively downward in the four sample aggregate most zircons have igneous ages falling in the 135 170 ma range with a smaller population at 85 120 ma the rocks contain rare zircons of middle proterozoic late archean ages a minor source in northern california and nw nevada seems likely for the pacheco pass metagraywackes but the sierran klamath calcalkaline arc provided most of the clastic debris judging by the volcanic nature of lithic clasts in these eastern belt metagraywackes and because massive sierran plutonism occurred at 85 120 ma the abundant 135 170 ma zircons probably were derived chiefly from the eroding comagmatic volcanic arc rather than from the less voluminous jurassic arc plutons

provenance of franciscan graywackes in coastal california a systematic comparison of available detrital modes for graywacke sandstones of the franciscan subduction complex and for coeval sandstones of the great valley sequence in the california coast ranges indicates that both were apparently derived from the same general sources the inferred provenance terrane was the ancestral sierran klamath magmatic arc from which mixed volcanic and plutonic detritus readily entered the adjacent great valley forearc basin at intervals along the trend of the arc trench system arc derived detritus also bypassed the forearc region through submarine canyons that fed the franciscan trench longitudinal flow along both the great valley trough and the franciscan trench achieved wide dispersal of the turbidite sediment suites of both franciscan and great valley samples include an array of subquartzose compositions ranging from feldspatholithic to lithofeldspathic mean framework modes of 17 franciscan suites comprising 203 individual samples and of 23 great valley suites comprising 410 individual samples range from 14 to 44 quartz grains 15 to 54 feldspar grains and 7 to 71 total lithic fragments the ratio of quartz to feldspar remains relatively constant as the proportion of lithic fragments changes the compositional variations reflect differences mainly in the admixture of lithic fragments derived principally from volcanic cover with quartz and feldspar derived principally from erosion of underlying plutons despite major overlap in the compositions of the two sets of samples some franciscan sandstones are somewhat more feldspathic and less lithic than any known great valley counterparts and were probably derived from segments of the arc terrane where exposures of plutons were more extensive than within typical great valley sources higher proportions of non volcanic to volcanic lithic fragments in some franciscan sandstones probably reflect complex recycling processes on the trench slope diagenetic effects in many franciscan suites include apparent wholesale replacement of k feldspar by albite present age control is inadequate to test fully for time dependent trends in the compositions of franciscan sandstones analogous to the known stratigraphic variations in the composition of great valley sandstones this question ought to be investigated in future studies

a palaeoclimate model for the kimmeridgian abstract most attempts at using numerical general circulation model gcm to simulate mesozoic climates have studied the late cretaceous and have focused on the enigmaof apparently equable global climates however this climate regime lasted throughout the mesozoic and it is of interest to examine other periods we present the results of an integration for the late jurassic using a relatively detailed and high resolution model there is generally good agreement between the model climate and the existing geological data in particular the simulation predicts no permanent ice cover near either pole arid conditions over the southwestern usa seasonally arid climate over southern europe and winter storminess over europe and australia however the surface temperatures over siberia and southeastern gondwanaland drop below zero for a significant part of the winter

a cryptic caledonian flysch terrane in scotland a substantial part of the lower old red sandstone crawton group in the north east midland valley of scotland has a first cycle provenance from the south and east i e from a source block within the midland valley from the clast assemblages in proximal conglomerates it is clear that this provenance comprised a flysch terrane cut by granodioritic and tonalitic plutons angular clasts of lithic arenite and metagreywacke derived from this cryptic flysch sequence show it to be distinct from a metasedimentary sequence which flanked the lower old red sandstone basin to the north and north east the basin must overlie or lie adjacent to a boundary between two quite different sedimentary assemblages petrographic examination and chemical analysis of the clasts show that the southerly cryptic succession includes an important mafic ultramanc provenance implying that ophiolitic source rocks may have originally contributed to it sr and nd isotopic compositions for the clasts establish that the midland valley flysch is isotopically unrelated to either southern uplands shales and greywackes or dalradian metasedimentary rocks the clasts have lower sr contents than either suite and sr isotopic compositions 87 sr 86 sr in the range 0 7099 0 7176 at 450 ma which are more radiogenic than the southern uplands but less radiogenic than the dalradian crustal residence ages t dm have a narrow range of 1 76 1 94 ga the mean of 1 87 0 06 ga compares with a mean residence age of 1 49 0 21 ga for southern uplands greywackes and shales mixing calculations demonstrate that the incorporation of young ophiolite derived basaltic detritus into the caledonian sedimentary mass can explain properties of the nd data previously attributed to a bimodal proterozoic provenance the distinct compositions of the southern uplands and midland valley flysch sediments suggest they originally tapped different parts of the laurentian margin and have subsequently been brought together structurally as displaced fore arc slivers the diverse isotopic compositions of outboard flysch terranes has implications for the nature of the sedimentary component incorporated in inboard magma suites

mesozoic transpression transtension subduction and metallogenesis in northern and central california middle paleozoic to middle jurassic terrane assemblies in the klamaths and sierran foothills consist of mafic ultramafic complexes fine grained terrigenous strata derived from previously accreted continental margin belts sutured oceanic terranes reflect c 230 myr of margin parallel slip involving chiefly transtension and transpression quartzofeldspathic clastic rocks and blueschists eclogites are very rare little devolatilization occurred at magmagenic depths hence coeval hydrothermal ore deposits and granitoids are uncommon in contrast nearly head on cretaceous subduction of the farallon plate generated the massive klamath sierra nevada volcanic plutonic arc reflecting dewatering of the eastward descending oceanic lithosphere in the magmagenic zone immature great valley forearc and franciscan trench deposits shed from the arc record c 70 myr of rapid crustal growth au bearing solutions rising from magmagenic depths exsolved from plutons and expelled from heated wall rocks were mobilized attending arc construction precipitation of gold bearing quartz veins occurred where h2o co2 bearing fluids encountered major geochemical discontinuities in the wall rocks

sediment provenance within subduction complexes an example from the aleutian forearc abstract the ultimate composition of any sandstone is affected by a host of primary and secondary factors including the lithologies present in source terranes climate depositional environment and diagenesis in the case of a subduction complex however unequivocal identification of detrital provenance may be impossible because of the cumulative effects of tectonic and sedimentary transport long distance sedimentary transport 1000 km is common within trenches and abyssal plain turbidites can be tectonically transported for long distances as the underlying oceanic basement drifts towards a subduction front post accretionary displacement can occur as a consequence of strike slip faulting and the total distance of tectonic dislocation may reach several thousand kilometers the present day aleutian forearc region north pacific ocean illustrates many of the problems which typify subduction zones several petrologic suites can be identified and there are significant variations in detrital modes in both time and space the aleutian region serves as a sobering modern analog for accreted rock units such as the franciscan complex of california where intercalations of discrete sandstone suites have been noted in the absence of paleomagnetic control interpretations of sediment provenance within ancient subduction complexes probably should be restricted to the generic level

phanerozoic continental accretion and the metamorphic evolution of northern and central california abstract the late paleozoic and younger tectonic fabric of california north of the transverse ranges consists of accreted exotic and parautochthonous lithic belts which extend north south and northwest southeast separated from one another by subvertical strike slip faults and gently to steeply east dipping thrust faults where recognizable folds in general verge to the west and stratigraphic tops face east a rough but systematic westward decrease in geologic age and metamorphic intensity may also be recognized exotic terranes of uncertain provenance include the central metamorphic belt of the klamath mountains and the salina sur obispo composite block of the central coast ranges pre permian sections of the eastern klamath terrane and portions of the sierran calaveras melones complex may also represent far traveled crustal entities allochthonous oceanic basement seamounts and pelagic sediments are additional transported materials widespread in most of the parautochthonous lithotectonic belts that make up much of the rest of northern and central california ophiolitic assemblages are especially abundant along the fault zones which mark boundaries between these units the parautochthonous lithotectonic belts appear to have been constructed in the vicinity of the continental margin and or an offshore arc judging from the nature and provenance of their constituent igneous and sedimentary rocks intimately associated tholeiitic calc alkaline complexes indicate that at least locally ophiolite generation occurred nearby the salinia sur obispo amalgamated terrane exhibits the effects of fragmentation and removal of crust now represented by the suture juxtaposing the two blocks other areas may have been subjected to similar truncations but relationships are not as clear far traveled terranes are characterized by ages of formation and recrystallization foreign to surrounding units the nature of the protoliths and grades of metamorphism developed within them contrast with those of juxtaposed lithotectonic belts on the other hand essentially in situ growth of many californian lithotectonic belts is suggested by a gradually decreasing age of formation and both monotonically decreasing times and grades of metamorphism proceeding towards the pacific basin some parautochthonous units as well as exotic terranes are locally bounded by discontinuous blueschist belts the latter attesting to at least episodic preservation of the effects of subduction metamorphism and offloading into the accreting continental margin phanerozoic evolution of northern and central california thus apparently consisted of a more or less in situ seaward encroachment of the continental margin relative to the craton involving occasional truncation and loss of section with a concomitant semi continuous or episodic incorporation of allochthonous seamounts oceanic crust and deep sea sediments and the less frequent arrival and juxtaposition of exotic microcontinental fragments of problematic but distant source

petrofacies and provenance of late mesozoic forearc basin northern and central california data from the great valley group sequence represent the most complete information regarding sandstone petrology of sediment derived from a magmatic arc this information is useful in documenting tectonic and magmatic events within the arc and related terranes and forms the basis for the establishment of petrostratigraphic units for mapping and correlation sandstone and conglomerate compositions are controlled by changes in provenance many of which were basinwide and synchronous clay mineral composition is controlled primarily by burial metamorphism careful attention to sample collection sample preparation and petrographic techniques is essential for uniform results seven petrographic parameters p f lv l m qp q q f and l listed in decreasing importance to petrofacies discrimination define eight petrofacies stony creek platina lodoga grabast boxer cortina los gatos and rumsey listed in approximate order of decreasing age the upper jurassic lower cretaceous petrofacies stony creek platina and lodoga contain higher lithic contents supracrustal sources whereas the upper cretaceous petrofacies especially the rumsey contain higher proportions of plutoniclastic components quartz feldspar and micas the proportion of potassium feldspar increases from near zero in the upper jurassic to nearly 50 of all feldspars in the uppermost cretaceous the lower part of the great valley group upper jurassic and lower cretaceous contains significant quantities of sedimentaclastic and metamorphiclastic material eroded from accreted and deformed terranes tectonic highlands formed by the arc arc collision nevadan orogeny that occurred prior to initiation of the franciscan great valley sierra nevada arc trench system the klamath mountains area provided a major proportion of this detritus ophiolite and serpentinite detritus was deposited locally near the base of the great valley group as a result of deformation along the east side of the growing franciscan subduction complex volcaniclastic detritus was fed into the entire forearc basin as magmatism increased in the sierra nevada area during the cretaceous as the volcanic cover was stripped off plutoniclastic and metamorphiclastic detritus from the underlying batholithic terranes was provided in abundance to the forearc basin crustal components were more continental in the southern sierra nevada and more oceanic in the northern sierra nevada as demonstrated by the higher proportions of metamorphiclastic detritus and by the more felsic nature of volcaniclastic detritus to the south by the middle of the late cretaceous extensive batholithic terranes provided potassium feldspar rich arkosic detritus to the entire forearc basin by the paleogene arc magmatism had migrated eastward sufficiently that deeper levels of the california part of the arc were exposed by erosion tectonic activity decreased in the forearc basin and the basin was filled to sea leve in most parts

deformation history of the yolla bolly terrane at leech lake mountain eastern belt franciscan subduction complex california coast ranges the roles of volume loss coaxial versus noncoaxial flow and blueschist exhumation in subduction related accretionary wedges are still poorly understood in our study at leech lake mountain in the eastern belt of the franciscan subduction complex we focus on these subjects in the specific example of the franciscan the tectonic significance of the boundary between the eastern and central belts remains controversial the leech lake mountain area in northern california is situated immediately above this boundary and therefore appears to be of crucial importance for understanding aspects of the tectonic evolution of the franciscan the structural development at leech lake mountain is characterized by three deformational events d2 produced the regional cleavage s2 during blueschist facies metamorphism d2 is the only entirely ductile deformation event and was associated with accretion related internal stacking within the yolla bolly terrane the s2 cleavage is folded by f3 folds which are overturned to the west spacing of a related s3 cleavage is generally at the decimeter scale but locally is spaced at the centimeter scale the s2 and s3 cleavages and f3 folds are overprinted by tight to open f4 folds at the decimeter to map scale map scale f4 folds are largely upright whereas small scale f4 folds are either upright or overturned to the east our finite strain analysis relates deformed lengths to original lengths in the rock and thus provides an absolute reference frame which allows us to detect deformation related volume changes absolute finite strain data from 20 samples support earlier studies indicating that the development of the moderately dipping s2 cleavage was accompanied by pronounced volume loss averaging 36 the directions of the principal finite strain axes are scattered therefore we calculated a tensor average of the data the principal stretches of the tensor average are s x s y s z 1 06 0 91 0 66 indicating that the accumulation of ductile strain was characterized by subvertical shortening which was largely compensated for by volume loss and not by orthogonal extension evidence for noncoaxial deformation in our samples is limited indicating that the accumulation of ductile strain was largely coaxial our preferred tectonic interpretation is that accretion and blueschist facies metamorphism of the yolla bolly terrane at leech lake mountain occurred during d2 under an almost coaxial deformation regime during and after d2 the rocks were considerably exhumed and were telescoped by d3 top to the west out of sequence thrusts at shallow crustal levels in the leech lake mountain area d3 thrusting juxtaposed the eastern and central belts along the red mountain fault and cut out the lower tectonic units of the eastern belt the difference in the degree of peak metamorphism between the eastern and central belts is modest indicating that displacement at the red mountain fault was not large we propose that d3 out of sequence thrusts attenuated the metamorphic and stratigraphic section across the entire franciscan and overlying great valley forearc the final d4 event produced large scale folds all three events resulted from horizontal shortening there is no evidence for a major phase of horizontal extension which might have aided exhumation of the eastern belt blueschists modest tectonic exhumation was due to vertical ductile shortening during d2

late cretaceous protolith age and provenance of the pelona and orocopia schists southern california implications for evolution of the cordilleran margin the pelona and orocopia schists are southern members of a eugeoclinal terrane that structurally underlies a large part of southwestern north america ion microprobe u pb ages of 100 detrital zircons from three widely spaced samples of these two units indicate that deposition occurred after 70 80 ma moreover the distribution of zircon ages including a significant peak centered ca 1 7 ga implies a major contribution f detritus from the mojave desert and transverse ranges of southern california recrystallization of the schists at depths of 20 35 km occurred within 10 15 m y of deposition which requires underthrusting at minimum rates of approximately 4 12 mm yr for reasonable thrust dips considering that similar processes formed the more northern rand schist at somewhat earlier times results indicate a southward progression in timing of deformation for the schists protoliths this result is at odds with northward migration of deformation implied by the baja british columbia hypothesis the age and provenance of the schist s protoliths are consistent with models that derive the schists from either the franciscan complex or great valley group

mesozoic evolution of exotic terranes and marginal seas western north america abstract regional terrane analysis has been combined with a global evaluation of plate kinematics to produce a new tectonic model for the mesozoic evolution of western north america and its associated marginal seas the model employs a two tiered data reliability ranking system to resolve conflicts within data sets the lower tier of the ranking system involves the assignment of a numerical rank to paleomagnetic and or paleobiogeographic data based on each data set s reliability the upper tier of the ranking system places the paleomagnetic and paleobiogeographic data in perspective by assigning a relative order of importance to different types of data the most reliable data are considered to be departure rift and arrival collision times that are tightly constrained by independent data sets evidence of subduction and or strike slip motion also ranks high in the master ranking system paleomagnetic and vertebrate paleobiogeographic data come next in the hierarchy followed by invertebrate and floral paleobiogeographic data application of this approach to a case study the baja british columbia controversy has resulted in a coherent model for the entire region results derived from the application of this modelling approach to the problem of the mesozoic assembly of western north america suggest that its evolution may be modeled using a minimum of 57 large terranes oblique convergence may have been the dominant tectonic process along the western north american margin during the mesozoic causing large scale latitudinal transport of many exotic terranes the motions of the terranes produced a number of marginal seas yukonia etc that were short lived but important components of western margin tectonics a combination of collision events side swiping episodes and changes in plate kinematics led to the initiation of several regional tectonic upheavals including the nevadan and sevier orogenies

provenance and thermal history of the franciscan accretionary complex constraints from zircon fission track thermochronology the franciscan accretionary complex of california contains large belts of sediments that were subducted to depths of 10 to 30 km metamorphosed under high pressure and low temperature conditions and later returned to the surface reconnaissance zircon fission track ft data 21 samples place constraints on the sedimentary provenance thermal history and or exhumation history of various franciscan units in a transect across the northern coast ranges through mendocino pass metagraywacke samples from the valantine springs formation of the franciscan eastern belt experienced maximum temperatures tmax ranging from 250 to 310 c zircon ft and previously reported apatite ft data indicate that parts of the western eastern and eastern central belts cooled at about 100 70 ma from 300 c to 100 c considering the low paleogeothermal gradient of roughly 9 c km during franciscan subduction these rocks were apparently uplifted and exhumed from 30 to 10 km depth at this time one sample from the eyler mountain sequence in the northwestern diablo range similarly shows tmax 310 c and major cooling at 100 70 ma this uplift and exhumation may have reflected accelerated accretion at the base as well as the front of the franciscan wedge accompanied by extensional thinning at shallower levels as a result of massive sediment influx into the franciscan trench from the sierra nevada magmatic arc in the northern coast ranges the western part of the central belt and the coastal belt experienced lower tmax probably 200 c and retain source area detrital zircon ft ages burnt hills terrane samples in the diablo range also experienced tmax 230 c and retain detrital ages the detrital single grain age patterns from these areas are compatible with those expected from the sierra nevada magmatic arc and its country rocks this is consistent with derivation of franciscan sediments from arc terranes in california and provides no particular suggestion that these parts of the franciscan are highly allochthonous paleogene coastal belt sandstones also yield detrital ages compatible with derivation from the sierra nevada but also include early tertiary zircon populations compatible with reconstructions suggesting these sandstones were sourced partly from the idaho batholith

the northern belt of the longford down inlier ireland and southern uplands scotland an ordovician back arc basin the northern belt of the southern uplands longford down zone contains two compositionally distinct clastic petrofacies suites each ranging from mid to late ordovician age they extend throughout the length of the belt and are generally separated by a strike fault the northwestern metaclast petrofacies suite is characterized by felsic igneous and metamorphic detritus derived from a continental source to the nw whereas the southeastern basic clast petrofacies suite contains abundant calc alkaline detritus derived from an island arc and plutonic metamorphic root zone complex to the s or se a similar source but located to the north is indicated for younger clastic sequences of similar composition in the northern part of the central belt immediately south of a major sinistral shear zone which defines the boundary between the northern and central belts it is concluded in light of other facets of regional geology and possible palaeogeographic configurations that this pattern reflects a back arc basin in the northern belt margined by a volcanic arc massif which once occupied the space now represented by the shear zone and a fore arc basin to the se central and southern belts the northern belt back arc basin is postulated to have been closed and deformed at the end ordovician and subsequently overthrust northwestward by the allochthonous thrust stack imbricated central and southern belts fore arc sequence at the end silurian this in the northern belt resulted in the development of a major recumbent structure downward facing on regional end silurian cleavage

geology geochemistry and tectonic setting of archaean greywackes from karnataka nucleus india more than 80 of the area covered by the chitradurga and shimoga schist belts 3 0 2 6 ga of karnataka nucleus india is made up of greywackes feldspathic lithic and quartzose greywackes are deposited respectively along the western northern and the eastern margin of the chitradurga schist belt greywackes of the shimoga schist belt show a large compositional scatter between feldspathic and lithic types compositional differences indicate variable provenance for the different localities tonalite trondhjemite gneisses ttg mafic ultramafic schists basic intermediate acid volcanic rocks sedimentary rocks like banded iron formation quartzites and cherts and k granites in minor quantity were exposed in the source area volcanic debris was also contributed from contemporaneous volcanism in the basin greywackes in this region are invariably interbedded with fine grained biotite rich phyllites and schists marked compositional differences are observed between the greywackes and the interbedded phyllites the greywackes have k2o na2o 1 whereas phyllites show large variation in k2o na2o ratios ranging from 1 5 to 15 0 high cr ni content of the greywackes and phyllites of the chitradurga belt are indicative of an important contribution from ultramafic rocks light ree enrichment and negative eu anomalies are particularly pronounced in the mudpacks of the greywackes represented by phyllite the ree and other chemical data such as la th ti zr and k2 mgo ratios indicate that these greywackes were supplied from a juvenile continental nucleus and were laid down on a simatic and converging active continental margin an archaean miniplate model with low angle subduction and sedimentary basins of moderate size is proposed to explain the geochemical and tectonic features of the schist belts

geochemical and isotopic studies of the sedimentary and granitic rocks of the altai orogen of northwest china and their tectonic implications the altai orogen northwest china represents the southwestern margin of the central asian orogenic belt geochemical and nd sr isotope analyses were carried out on the palaeozoic sedimentary and granitic rocks in order to trace their sources and to evaluate the pattern of continental growth of the orogen nd isotopic data for both the granites and sediments suggest a significant proportion of middle proterozoic crust beneath the altai orogen however addition of juvenile material arc back arc oceanic crust during palaeozoic times is also significant trace elements and isotopic data of sediments suggest their sources were immature they represent mixtures between a palaeozoic juvenile component and an evolved continental crust the early palaeozoic sediments show e nd t 3 4 to 5 0 t dm 1 5 1 8 ga and i sr 0 710 0 712 they represent a passive margin setting with a predominance of evolved crustal material in the source the devonian sequences however might have been deposited in a back arc basin setting produced by subduction of the junggar oceanic crust along the irtysh fault a significant addition of arc material into the sedimentary basin is responsible for the highly variable e nd values 6 to 0 and i sr 0 711 0 706 the carboniferous rocks were also deposited in a back arc basin setting but with predominantly arc material in the source as suggested by an abrupt increase in e nd t 6 to 3 and decrease in i sr 0 7045 0 7051 voluminous syn orogenic granitoids have e nd t 2 1 to 4 3 i sr 0 705 0 714 and t dm 0 7 1 6 ga they were not derived by melting of local metasedimentary rocks as suggested by previous workers but by melting of a more juvenile source at depth post orogenic granites have higher e nd t 4 4 than the syn orogenic granitoids indicating their derivation from a deeper crustal level where juvenile crust may predominate

mesozoic subduction accretion history in central tibet constrained from provenance analysis of the mugagangri subduction complex in the bangong nujiang suture zone

diverse sources for igneous blocks in franciscan melanges california coast ranges igneous blocks in franciscan melanges are of three chemical petrologic types 1 tholeiitic basalts of both arc and spreading center origin with depletions in light relative to heavy rare earth elements 3 tio 2 1 high y zr and y ti ratios and relict augites that generally have low al and ti and well defined iron enrichment trends 2 basalts of probable seamount origin with marked enrichments in light relative to heavy rare earth elements 5 tio 2 1 lower y zr and y ti than 1 and ti al rich augites showing little if any iron enrichment trends and 3 hypabyssal intrusives having sio 2 52 tio 2 1 flat or only slightly fractionated rare earth abundance patterns and diopsidic augites that are very low in ti and al and show no iron enrichment trends all of the blocks are metamorphosed most are undeformed pumpellyite bearing greenstones and a few contain sodic amphibole lawsonite sodic pyroxene the melanges are probably olistostromal in origin deriving the

a plate tectonic model for late jurassic ophiolite genesis nevadan orogeny and forearc initiation northern california recently published age and structural data allow the reconciliation of previously conflicting models for late jurassic genesis of the josephine smartville and coast range ophiolites and the nevadan orogeny in the klamath mountains and sierra nevada the resulting model is consistent with the mode of initiation location and geometry of the great valley forearc basin and with the lack of a significant forearc basin west of the klamath mountains the coast range ophiolite formed by backarc spreading west of an east facing intraoceanic arc soon thereafter a remnant arc was calved off the west side of this arc and the smartville ophiolite formed by backarc interarc spreading during this time the sierran phase of the nevadan orogeny began as the intraoceanic arc encountered the west facing continental margin arc of north america an east west trending calcalkaline dike swarm in the sierra nevada foothills may mark the trajectory of the colliding arcs at the initiation of the collision simultaneously a new subduction zone was initiated west of the collision suture zone and this new trench propagated southward thus trapping the coast range ophiolite in the new forearc area south of the klamath area intense deformation in the sierran region resulted from this collision and both magmatic arcs became inactive as the last remnant of intervening oceanic crust was subducted continued westward relative movement of the north american arc was permitted north of the sierra nevada owing to the lack of a colliding intraoceanic arc the result was the westward rifting of the continental margin arc by intraarc spreading which formed the josephine ophiolite in the klamath area the klamath phase of the nevadan orogeny resulted from contraction of the west facing intraoceanic arc and josephine backarc basin beneath the continental margin basal sediments of the great valley forearc basin were derived primarily from the sutured arc ophiolite terranes and were deposited on top of the coast range ophiolite the southern edge of the klamaths and the western side of the sierra nevada a new late mesozoic magmatic arc was superposed across the previously accreted terranes and formed the primary sediment source for the cretaceous forearc basin

infrasonic propagation from the 2010 eyjafjallajokull eruption investigating the influence of stratospheric solar tides 1 the stratospheric infrasound duct formed between earth s surface and altitudes of 50 km is sensitive to spatiotemporal variations in stratospheric wind speed and temperature infrasound recorded at long range from the 2010 summit eruption of eyjafjallajokull volcano iceland exhibits temporal variability correlated with diurnal stratospheric solar tidal wind speed variations between 18 and 28 april 2010 signal observations at stations bkni u k range 1745 km and is18 greenland range 2285 km exhibit prominent diurnal variations in infrasonic amplitude bandwidth back azimuth and apparent speed which we identify using the clean spectral analysis algorithm for unevenly sampled time series results of 3 d acoustic ray tracing through operational atmospheric specifications indicate that tidal wind speed variations with amplitudes of 20 m s can generate diurnal variations in the proportion of the acoustic wavefield propagating within the stratospheric acoustic duct range dependent meteorology is required propagation modeling using averaged meteorological profiles fails to predict the leakage of acoustic energy out of the stratospheric acoustic duct at times of low observed signal amplitudes ray tracing correctly predicts the phase of the observed signal amplitude and apparent speed variations diurnal variability in ducting combined with diurnal variations in ambient noise at the sensors can explain the observed signal bandwidth variations back azimuth variations observed only along the eyjafjallajokull to bkni path are not predicted by 3 d ray tracing tidal variations have implications for models of infrasound array network detection capability and for studies that utilize amplitude and bandwidth measurements to make inferences about the acoustic source

accretion of the franciscan complex attending jurassic cretaceous geotectonic development of northern and central california scattered igneous activity marks the triassic margin of california but an andean volcanic plutonic arc began to form in the sierra nevada white inyo range and klamath mountains at ca 170 ma during underflow of the oceanic lithosphere this calc alkaline belt supplied volcanogenic erosional debris to the mariposa galice proximal overlap sequence by ca 165 160 ma transpression also generated high pressure low temperature basaltic eclogites garnet blueschists and amphibolites along the middle and late jurassic convergent plate junction at ca 170 155 ma most of these returned surfaceward as tectonic blocks only during the mid cretaceous the high grade metamafic metamorphosed mafic blocks that formed during construction of the emergent arc and derived mariposa galice strata predate the onset of franciscan trench deposition near the end of jurassic time the klamath salient evidently migrated 200 km westward an earliest cretaceous westward stepout of the convergent junction apparently formed directly offshore from the klamath imbricate orogen but to the south preexisting oceanic crust capped lithosphere was trapped landward as the coast range ophiolite andean arc detritus began to accumulate on this ophiolitic basement within the great valley forearc and outboard franciscan oceanic trench at ca 145 140 ma because earliest cretaceous relatively continuous great valley strata were deposited on the stable north american plate protected from both surface and subcrustal erosion forearc terrigenous sedimentation also signaled coeval deposition in the outboard trench 10 25 m y after middle and late jurassic initiation of the continental margin calc alkaline arc voluminous sedimentation and the accretion of franciscan and san joaquin sections of great valley rocks took place during mid and late cretaceous time after a flare up in igneous arc activity at 125 120 ma the youngest sierran granites have ca 85 ma ages reflecting extinction of the magmagenic zone beneath northern and central california and presumably reflecting subhorizontal oceanic plate underflow attending the laramide orogeny feebly zeolitized upper cretaceous and lower tertiary franciscan coastal belt rocks derived from the now inactive arc underwent only low pressure burial metamorphism reflecting shallow offloading and or large scale transpression they were not appreciably subducted although coastal belt units are members of the franciscan lithotectonic assemblage their origin contrasts with the rest of the subduction complex

compositions of sandstones in circum pacific subduction complexes and fore arc basins arc trench systems of the circum pacific orogenic belt contain voluminous sandstones within fore arc terranes that include complexly deformed subduction complexes and relatively undeformed fore arc basins of several types turbidites incorporated within subduction complexes include not only axially transported trench fill but also abyssal plain sediments deposited on the sea floor beyond the trench and slope basin deposits perched on the accretionary trench slope mean framework modes of circum pacific sandstone suites can be expressed adequately by the use of qfl and qmflt plots supplementary qmpk and qplvls plots depict partial modes of mineral grains alone and polycrystalline lithic fragments respectively source rocks were mainly volcanic and plutonic terranes of he circum pacific magmatic arcs although some recycled sedimentary and metasedimentary debris is also present analysis of point counts for 2 587 rocks grouped into 104 suites from california the pacific northwest southern alaska southwest japan and new zealand indicates that the characteristic fore arc sandstones display similar compositional ranges everywhere and can be termed the circum pacific volcano plutonic graywacke suite knowledge of their petrology may aid the recognition of analogous tectonic settings in the geologic past frameworks vary across a compositional spectrum that ranges chiefly from feldspatholithic sands derived mainly from volcanic cover in undissected magmatic arcs to lithofeldspathic sands derived largely from plutonic batholiths in dissected magmatic arcs quartz contents are typically intermediate and the feldspar to quartz ratio is semiconstant plagioclas is the dominant feldspar and volcanic rock fragments are commonly the most abundant lithic fragments interpretations of compositional trends within subduction complexes and adjacent fore arc basins imply that simple transverse delivery of sediment from the arc orogene to the fore arc region is not the rule instead sand evidently is distributed along subduction zones by longitudinal turbidity currents initiated at widely spaced sediment delivery points where sediment derived from tectonic culminations along the arc trench system can bypass the sediment traps of fore arc basins moreover turbidites shed from dormant or transform segments of arc orogenes are locally spread far into the ocean basin as abyssal plains which are later rafted bodily into the subduction zone finally no sedimentologic explanations of compositional contrasts across fore arc graywacke terranes can be acce ted without considering the alternative of postdepositional tectonic transport by strike slip

normal faulting at convergent plate boundaries mylonitic extensional fabrics in the franciscan subduction complex in del puerto canyon california revisited 1 using a strain and rotation analysis we tested the hypotheses that top east mylonitic extensional structures in the uppermost franciscan subduction complex in del puerto canyon california accomplished exhumation of the franciscan blueschists we found no evidence of strongly noncoaxial deformation instead our data indicate overall coaxial deformation in the proposed zone of mylonitic extensional deformation there are no extensional strains moderate vertical shortening occurred without horizontal extension and was compensated by modest deformation related volume loss there is also no strain gradient toward and within the proposed shear zone therefore the results of our work indicate that mylonitic extensional structures in del puerto canyon do not exist overall we conclude that there is no currently identifiable structure adjacent to or within the franciscan in california that could have accommodated large scale horizontal extension exhumation of the franciscan blueschists was mainly achieved by erosion of an emergent forearc high our strain results and published data are also inconsistent with the development of a supercritically tapered franciscan wedge that ultimately should have triggered normal faulting strain magnitudes are low despite the relatively long residence time of the rocks in the accretionary wedge from this we infer that strain rates were low and that the wedge material flowed with a relatively high viscosity therefore ductile flow probably was not fast enough to form a supercritically tapered franciscan wedge

a note on the use of statistics in reporting detrital clastic compositions error polygons and error bars are commonly used graphical methods for showing the precision associated with means on triangular diagrams and orthogonal plots respectively if the error or precision associated with a mean based either upon counts of individual components or upon count ratios is to be defined using basic statistics the confidence interval method should be used standard deviation alone which has been frequently in the literature is not an appropriate statistic to use for this purpose the graphical use of confidence intervals permits a rapid visualization of statistically significant differences between means and thus more quantitative description of detrital clastic composition previous investigators using the standard deviation method have underestimated the precision of their data when sample sizes are large and overestimated precision with small samples

remagnetization and northward coastwise transport of franciscan complex rocks northern california a reinterpretation of the paleomagnetic data previous paleomagnetic studies of accreted oceanic rocks within the franciscan complex of northern california have concluded that these rocks originated far to the south of their present positions with respect to the north american continent based on positive fold tests the characteristic remanent magnetizations were inferred to predate accretion related deformation and metamorphism and to have been acquired during or soon after deposition of these rocks thus the paleomagnetic data were thought to provide direct information on ancient oceanic plate motions however the plate motions implied by some of these paleomagnetic data are problematic e g exceptional plate velocities and uniform polarity magnetizations in almost all of these rocks indicate the possibility of remagnetization recent work on oceanic rocks in similar subduction complexes of japan and mexico have shown that they were most likely chemically remagnetized during accretion prior to disruption of the original stratigraphic sequences modern analogs indicate that the oceanic rocks in mexico were probably remagnetized while still part of a shallow dipping subducting slab 10 at the base of an accretionary prism assuming these rocks were near horizontal at the time of remagnetization paleolatitudes at which these rocks were subducted and subsequent arc parallel displacements along the western margin of north america can be inferred in this paper franciscan rocks in northern california are reinterpreted as also having been remagnetized prior to accretion related deformation this scenario satisfies both geologic and paleomagnetic constraints for these rocks and resolves conflicts between data indicating both remagnetization and tectonic displacement transport of the laytonville limestone from the southern hemisphere is not required paleolatitudes of subduction and remagnetization in the northern hemisphere 12 to 33 appear to be inversely proportional to age of accretion middle cretaceous to oligocene for the franciscan rocks subsequent northward diplacements 800 to 3700 km and clockwise rotations 56 and 154 of these rocks inferred from the paleomagnetic data are consistent with potential displacements along the western margin of north america during late mesozoic and cenozoic time calculated using examples of modern subduction zones and current plate reconstruction models

compositional trends in the permian sandstones from the denison trough bowen basin queensland reflect changing provenance and tectonics abstract point count data of sandstone samples collected from six sedimentary formations encountered in boreholes in the permian sequence of the denison trough an australian backare retroarc foreland basin provide information about the tectonic evolution of their source areas and the depositional sites plots of the detrital compositions of these permian sandstones against borehole depths indicate that the reids dome beds sandstones containing highly abundant lithic volcanolithic grains mark the onset of intense compressional tectonics and arc volcanic activities to the east accompanied by extensional tectonics and subsidence in the trough folding and thrusting owing to intense compressional tectonics in the new england fold belt and arc volcanism in the camboon volcanic arc region to the east generated a great supply of recycled sediment and volcanic detritus that led to a rapid infilling of the subsiding denison trough during formation of the reids dome beds sandstones in early permian time the detrital composition of the sandstones of the overlying cattle creek formation aldebaran sandstone and the freitag formation indicate gradually decreasing compressional tectonics and arc volcanism accompanied by increasingly dominant sediment supply from the stable continental craton to the west the freitag formation sandstone compositions mark the quietest tectonic and volcanic episode in the region accompanied by subsidence of the denison trough owing to thermal cooling during the middle permian the peawaddy formation and the bandanna formation sandstone compositions represent a late permian renewal of compressional tectonics and arc volcanism to the east accompanied by uplift and folding of the sedimentary strata resulting in the formation of largely fluvial depositional environments in the denison trough modal compositions of the bandanna formation sandstones indicate that renewed arc volcanism and compressional tectonic activity attained maximum intensities during the late permian

tectonic versus chemical weathering controls on the composition of fluvial sands in tropical environments the compositions of fluvial sands collected in mountainous regions along the volcanic front in central america and along the andean front in venezuela and colombia correlate with the tectonic setting of their source terrains the sands derived from the central american volcanic arc are compositionally distinct from those derived from the andean terrains and minor variations in tectonic style can also be discriminated subtle differences in tectonic setting and source rock composition are recognizable only when modification by chemical weathering is slight they are strongest in sands from low order streams draining mountainous areas with modest alluvial plain development sands that have been exposed to weathering for extended periods during alluvial storage are progressively enriched in chemically stable phases with increased weathering sands from continental terrains converge toward a supermature quartz arenite end member and the imprint left by source rock composition and tectonic setting is obscured in intraoceanic terrains a similar but much less pronounced enrichment in stable phases relative to less stable phases is observed similarly overprinting the tectonic signal although detailed tectonic information is easily lost sands derived from intraoceanic terrains are distinguishable from those derived from continental terrains even after long exposure to intense chemical weathering conditions

franciscan geologic history constrained by tectonic olistostromal high grade metamafic blocks in the iconic california mesozoic cenozoic accretionary complex figure 1 subduction generated a nw trending andean arc along the californian margin beginning at 175 ma coeval high pressure hp transformation of oceanic crust in an east dipping subduction zone probably accompanied plate convergence but recovered franciscan eclogite and garnet blueschist blocks chiefly possess younger recrystallization ages of 165 150 ma these jurassic hp metamafic rocks were sequestered in a low temperature environment well into cretaceous time fragments of actinolitic rinds partially surround many such high grade blocks only slightly younger than the hp metamorphism these rinds reflect metasomatic exchange between metabasalt and serpentinized harzburgite along the dynamic oceanic crust mantle hanging wall during storage of the mafic rocks at moderate depth high grade tectonic blocks later were brought toward the surface in circulating low density sheared mud matrix melange and or in buoyant serpentinite bodies most exotic hp metamafic blocks occur in melanges of the franciscan central belt reflecting tectonic insertion within the subduction zone not near surface additions to the clastic section however rare high grade clasts in feebly recrystallized franciscan conglomerates suggest erosion and sedimentary deposition for some hp blocks the addition of dense metabasaltic olistoliths to the mid and upper cretaceous section requires that these hp material were carried surfaceward first as tectonic fragments perhaps immersed in low density serpentinite or mud matrix melange then eroded and transported into the trench hp rocks are conspicuously lacking in coeval great valley strata whatever the origin of particular high grade rocks widespread post depositional shearing has largely obliterated their original natures but all dense metamafic blocks of jurassic recrystallization age must have been supplied to the cretaceous franciscan accretionary complex by entrainment in a low density circulating muddy matrix or serpentinite body the vast majority of exotic hp blocks resides in central belt melanges and appears to be tectonic rather than olistostromal in origin 1 pending yes

implications of franciscan complex graywacke geochemistry for sediment transport provenance determination burial exposure duration and fluid exchange with cosubducted metabasites 1 interpretation of graywacke provenance has long been used to evaluate the record of tectonic process in orogenic belts our geochemical data from graywackes of the franciscan subduction complex california show that the connection between sedimentary record and geologic processes may be more complex than previously believed trace elements and nd sr pb isotopes of franciscan graywackes indicate two sources types one group lacking negative eu anomaly eu eu 0 9 shows slightly concave up heavy rare earth elements arc like trace element patterns and western pacific island arc like pb isotopes reflecting derivation from older accreted oceanic arc terranes in the sierra nevada klamath mountains the other group displays small negative eu anomalies with trace element patterns resembling post archean australian shale and pb isotopes similar to jurassic cretaceous sierran batholith there is no systematic separation of these two groups by depositional ages thus geochemistry of the graywackes may partly reflect variation in location of sediment delivery systems rather than solely reflecting evolution of the neighboring arc variation of nd sr isotopes with stratigraphic age for the graywackes mimics the trends of the coeval great valley group clastic rocks suggesting that 1 they share the same sediment sources 2 there are no exotic sediment sources that fed the franciscan trench and 3 burial exposure cycles for franciscan clastic rocks were comparatively brief comparison of franciscan graywacke and metabasite geochemistry corroborates earlier conclusions that metabasites had little or no chemical exchange with fluids from cosubducted graywacke detrital zircon age populations major element chemistry and detrital framework modes when compared to our data suggest that the former three parameters underrepresent the mafic component of clastic sediment provenance

mineral parageneses regional architecture and tectonic evolution of franciscan metagraywackes cape mendocino garberville covelo 30 60 quadrangles northwest california 1 the franciscan complex is a classic subduction zone assemblage in northwest california it comprises a stack of west vergent thrust sheets westernmost eastern belt outliers central belt melange coastal belt yager terrane coastal belt coastal terrane coastal belt king range false cape terranes we collected samples and determined p t conditions of recrystallization for 88 medium fine grained metasandstones to assess their subduction exhumation histories and assembly of the host allochthons feebly recrystallized yager coastal and king range strata retain clear detrital features scattered neoblastic prehnite occurs in several coastal terrane metasandstones traces of possible pumpellyite are present in three yager metaclastic rocks pumpellyite lawsonite aragonite bearing central belt metasandstones are moderately deformed and reconstituted intensely contorted thoroughly recrystallized eastern belt affinity quartzose metagraywackes contain lawsonite jadeitic pyroxene aragonite glaucophane we microprobed neoblastic phases in 23 rocks documenting mineral parageneses that constrain the tectonic accretion and metamorphic p t evolution of these sheets quasi stable mineral assemblages typify eastern belt metasandstones but mm sized domains in the central and coastal belt rocks failed to achieve chemical equilibrium eastern belt slabs rose from subduction depths approaching 25 30 km whereas structurally lower central belt melanges returned from 15 18 km coastal belt assemblages suggest burial depths less than 5 8 km eastern and central belt allochthons sequentially decoupled from the downgoing oceanic lithosphere and ascended into the accretionary margin k feldspar rich coastal belt rocks were stranded along the continental edge without undergoing appreciable subduction probably during paleogene unroofing of the older deeply subducted units of the franciscan complex in east vergent crustal wedges

cretaceous sinistral strike slip along nacimiento fault in coastal california the san andreas and nacimiento faults of coastal california both separate granitic and metamorphic basement rocks of the salinian block from partly coeval but contrasting mesozoic terranes underlain by the franciscan subduction complex by analogy with neogene dextral strike slip along the san andreas fault cretaceous sinistral strike slip can be inferred along the nacimiento fault in preference to hypotheses for tectonic erosion during subduction or for dextral strike slip of unspecified amount following restoration of known san andreas and inferred proto san andreas dextral displacements reversal of about 560 km 350 mi of postulated sinistral slip on the nacimiento fault brings four major mesozoic lithotectonic belts of california and baja california into simple al gnment as subparallel terranes related to mesozoic subduction along the continental margin neogene deformation within the san andreas transform system involved a elongation of the salinian block by dextral slip along subsidiary faults that branch from the san andreas fault and b dextral rotation of crustal panels within the transverse ranges latest cretaceous and or earliest paleogene dextral slip along a proto san andreas fault followed the san andreas course in central california but diverged westward in southern california nacimiento sinistral displacements occurred in mid cretaceous to early or medial late cretaceous time after cretaceous emplacement of plutons now within the salinian block but prior to deposition of uppermost cretaceous sedimentary sequences in central california available data on mesozoic relative and absolute plate motions in the mesoameric n region support the likelihood of cretaceous sinistral strike slip subparallel to the california continental margin paleotectonic reconstruction of crustal blocks in california and baja california to their inferred mid cretaceous relative positions shows the salinian block inserted on a bias between the flanking mojave and peninsular ranges blocks salinian granitic rocks thus formed an interior part of the mesozoic batholith belt and their initial strontium isotopic ratios are compatible with the gradients displayed by values from the adjoining blocks the similar mesozoic terranes that now lie east and west of the salinian block were then adjacent to one another west of the sierra nevada block available paleomagnetic data neither support nor preclude the reconstruction but additional work together with future detailed lithotectonic comparisons potentially can confirm or refute the hypothesis i represents a correct interpretation of the nacimiento fault is important for understanding the overall tectonic framework of petroliferous basins both onshore and offshore in coastal california

detrital record of neoproterozoic arc magmatism along the nw margin of the yangtze block china u pb geochronology and petrography of sandstones abstract neoproterozoic conglomerate sandstone successions with abundant volcanic components ranging from 750 to 2200 m in thickness occur along the northwestern margin of the yangtze block they were previously regarded as sinian tillites and typical platform sediments or the fills of a passive margin rifted basin or arc related basin in chinese literature crude ripple parallel normal and inverse grading structures suggest together that these conglomerate sandstones were deposited by subaqueous debris flows and high density turbidity currents new shrimp zircon u pb results from a tuffaceous interlayer with syn sedimentary deformation indicate deposition at 797 ma sandstone detrital clasts and conglomerate composition analysis suggest that volcanic sedimentary and granitoid rocks were exposed to erosion in their source area in terms of primary components these conglomerate sandstone successions with tuffaceous interlayers along the northern margin of the yangtze block are similar in composition to other sandstones from the magmatic arc detrital modal analysis indicates that they were derived from a continental arc hannan complex and accumulated in a forearc basin

paleoecology of the quarry 9 vertebrate assemblage from como bluff wyoming morrison formation late jurassic abstract quarry 9 is among the richest microvertebrate localities in the morrison formation having thus far produced the remains of dozens of late jurassic taxa because this lenticular claystone deposit records such a high diversity of contemporaneous species it provides an exceptionally detailed view of their paleoecology and local paleoenvironment in this study we reexamined the entire quarry 9 collection totaling more than 3700 specimens and developed a revised faunal list that was used to determine taxonomic and ecological diversities comprehensive abundance data were collected as well revealing significant discrepancies between the most diverse and most abundant groups amphibious taxa crocodilians and turtles were very abundant and seemed to fill an important ecological role as connectors between the terrestrial and aquatic food webs in contrast small terrestrial taxa small theropods mammals and small reptiles were very diverse highlighting their central placement within the terrestrial food web lithologically and sedimentologically the deposition of quarry 9 occurred in a low energy pond or swamp an interpretation supported by the available taphonomic data

provenance diversification within an arc trench system induced by batholith development the cretaceous japan case by comparing detrital zircon u pb age spectra of coeval fore arc and back intra arc basin sandstones we identified the overall distributary pattern of terrigenous clastic material within the cretaceous arc system of sw japan abundant proterozoic c 1500 2500 ma detrital grains from the interior of east asia are present in the cretaceous intra arc basin however after a barrier mountain range formed during batholith emplacement proterozoic clastics were rarely transported into the fore arc domain episodic batholith formation in pacific type orogens likely played a major role in controlling terrigenous supply routes between coeval back arc and fore arc domains the cretaceous orogen in japan thus provides a good template for analysing the tectono sedimentary development of other arc related basins

contrasting early and late mesozoic petrotectonic evolution of northern california devonian middle jurassic terrane assemblies in the klamath mountains and sierra nevada foothills consist chiefly of ophiolite chert argillite sequences mafic ultramafic complexes are oceanic whereas associated fine grained deep water terrigenous sediments were derived mainly from adjacent previously docked klamath sierran terranes coeval calc alkaline arc rocks are volumetrically rare geologic and petrochemical relations suggest a rifted arc origin for klamath mafic metavolcanic units inter layered with distal turbidites in the 170 200 ma north fork terrane detrital zircon u pb ages indicate that the clastic debris had a regional eastern klamath source the eastern hayfork cherty melange contains ophiolitic scraps and distinctive olistostromal sandstone blocks evidently derived from the nearby eastern klamath antelope mountain quartzite the seaward 200 ma rattlesnake creek terrane is an ophiolitic melange with north fork petrotectonic affinities the north fork eastern hayfork rattlesnake creek amalgam correlates with the calaveras complex and the outboard jura triassic arc belt in the sierran foothills geochemical bulk rock and zircon u pb age data support interpretation of the 200 ma jura triassic arc as an adjacent offshore mafic belt overlying a 300 ma ophiolitic basement these oceanic complexes were sutured against the central metamorphic belt eastern klamath feather river northern sierra terrane backstop before deposition and deformation of the outboard upper jurassic galice and mariposa formations klamath sierran terrane assemblies reflect 230 m y of transpression transtension involving only minor episodes of subduction producing ubiquitous ophiolite chert argillite lithologies and rare felsic arc rocks in contrast the late jurassic to largely cretaceous klamath sierra nevada quartzo feldspathic volcanic plutonic arc attests to massive calc alkaline magmatism attending a strong eastward component of underflow by the farallon plate the coeval galice mariposa formations followed by the cretaceous great valley forearc and franciscan trench deposits are first cycle felsic debris shed mainly from the klamath sierran arc these units record 70 m y of rapid sialic crustal growth attending major periods of approximately margin normal convergence this profound transition in northern california included devonian middle jurassic rifting drifting and stranding of ophiolite chert argillite terranes along an adjacent curvilinear continental margin then nearly head on cretaceous subduction that resulted in massive calc alkaline igneous activity the erosion of which generated the felsic great valley group forearc basin and franciscan complex trench clastic sedimentary units

the impact of the atmosphere on the eyjafjallajokull 2010 eruption plume 1 the eruption of eyjafjallajokull volcano in 2010 lasted 39 days 14 april 23 may the eruption had two explosive phases separated by a phase with lava formation and reduced explosive activity during the explosive phases there were episodes of strong winds that advected ash to the south and southeast leading to widespread disruptions in air traffic the height of the eruption plume was monitored with a weather radar and with web cameras mounted with a view of the volcano three different types of the impact of the ambient atmosphere on the eruption plume are described first the weather situation throughout the eruption has been analyzed the frequency of northerly wind component is found to be unusually high or 71 in comparison to 49 on average in spring secondly during the effusive phase of the eruption diurnal variation was observed in the plume altitude and there is evidence that suggest that nocturnal inversions may have played a role limiting the rise of the weak plume thirdly images from a web camera were analyzed and the rise of individual cloud heads associated with explosions at the volcano vent mapped the velocity profiles obtained largely agree with conceptual models of volcanic plumes

effect of interarray elevation differences on infrasound beamforming summary the international monitoring system infrasound network will upon completion contain 60 microbarometer arrays with apertures of between 1 and 4 km these arrays are located within a variety of terrains leading to large ratios of interelement elevation differences to array aperture for those arrays situated in areas of significant topography systematic errors in beamforming estimates caused by neglecting the vertical extent of the arrays are quantified for both signal backazimuth and apparent velocity of the 43 arrays certified as of 2011 january i14cl on juan fernandez island has the greatest topography across an array with a least squares fitted plane through the array elements having an 8 1 slope from the horizontal compared to a network mean of 1 6 beamforming errors both backazimuth and apparent velocity are a function of the arrival azimuth and become increasingly large for steeply inclined arrivals such that systematic errors will be significantly larger for signals returned from the thermosphere compared to those from the stratosphere at several arrays azimuthal errors due to array topography are comparable in magnitude to deviations often associated with atmospheric propagation these findings are illustrated using signals recorded in greenland at i18dk where differences between results processed using both full 3 d array geometry and the 2 d topography neglected approximation exhibit good correspondence to theoretical predictions

palaeoceanography and tectonic setting of the jurassic coast range ophiolite central california evidence from the extrusive rocks and the volcaniclastic sediment cover abstract the primary thesis of this paper is that the character of sedimentary rocks within or directly on top of an ophiolite complex can be used to constrain tectonic models of oceanic crustal genesis late jurassic c 169 161 ma coast range ophiolite remnants are exposed e and w of the san andreas fault in central california ophiolite volcanic rocks are mainly sub alkaline tholeiitic basalts but include subordinate intermediate and silicic flows and breccias available immobile major and trace element data indicate that the coast range ophiolite formed above a subduction zone possibly in a fore arc setting as suggested by the presence of high magnesian andesites and boninites the ophiolite extrusives mainly comprise pillow lava and lava breccia formed on a rugged fault controlled ocean floor interlava pelagic sediment is restricted to very small amounts of interstitial red chert and nannoplankton limestone widespread occurrence of vesicular lavas probably reflects high primary volatile contents rather than eruption in shallow water local interbeds of arc derived silicic tephra in the uppermost extrusives suggest that the ophiolite and cover sediments formed together in a single tectonic setting depositionally overlying deep water successions up to 600 m thick comprise radiolarian rich tuffaceous and volcaniclastic sediments of callovian mid tithonian age 165 148 ma depositional processes included airfall turbidity currents mass flow and current reworking small si fe mn lenses along the lava sediment contact formed by hydrothermal replacement of basal siliceous tuffaceous sediments or by direct chemical precipitation at one locality llanada the ophiolite is overlain by up to 1 8 km of younger tithonian basic intermed and acid lava flows submarine lahars and mainly silicic pyroclastic sediments of inferred volcanic arc origin the volcaniclastic cover passes conformably upwards into late tithonian and younger terrigenous deep water clastic sediments of the great valley group deposited in a fore arc setting the coast range ophiolite and its cover are interpreted as an incipient intraoceanic volcanic arc possibly developed above an eastward continent ward dipping subduction zone within the equatorial pacific ocean in this scenario short lived 5 8 ma supra subduction zone spreading to form the ophiolite was followed by callovian tithonian arc volcanism shedding tuffaceous debris onto the adjacent fore arc subduction was active separately along the western american continental margin with the result that the coast range arc ophiolite complex eventually collided with north america triggering the late jurassic nevadan orogeny and initiating franciscan subduction accretion the coast range ophiolite remnants at least those west of the san andreas fault were apparently translated northwards to their present positions after late cretaceous

characterization of the 2008 kasatochi and okmok eruptions using remote infrasound arrays 1 the 2008 plinian eruptions of kasatochi and okmok volcanoes were recorded by six remote international monitoring system infrasound arrays high amplitude infrasound at these stations combined with remote sensing permits insight into important volcanic source parameters such as origin times durations and source characteristics infrasound from the 7 8 august kasatochi eruption consists of three well defined eruption pulses with the first two steam rich and the last ash rich pulse 2 is the most energetic and impulsive okmok produced over 9 h of continuous infrasound on 12 13 july acoustic propagation modeling for the okmok eruption and first kasatochi pulse predict thermospheric ducting and origin times consistent with seismic and satellite observations however theoretical acoustic origin times of pulses 2 3 are predicted to occur 15 min earlier than the seismic stratospheric ducting for these later pulses provides more consistent origin times although both volcanoes ejected ash into the stratosphere 15 km kasatochi produced higher amplitude infrasound than okmok previous studies have shown sustained infrasound with frequencies 2000 km and does not seem to be appreciably affected by changes in ash content between the eruption pulses

geologic implications of new zircon u pb ages from the white mountain peak metavolcanic complex eastern california 1 the nnw trending white inyo range includes intrusive and volcanic rocks on the eastern flank of the sierran volcano plutonic arc the ne striking steeply se dipping barcroft reverse fault separates folded metamorphosed mesozoic white mountain peak mafic and felsic volcanic flows volcanogenic sedimentary rocks and minor hypabyssal plugs on the north from folded well bedded neoproterozoic cambrian marble and siliciclastic strata on the south the 163 2 ma barcroft granodiorite rose along this fault and thermally recrystallized its wall rocks however new shrimp rg ages of magmatic zircons from three white mountain peak volcanogenic metasedimentary rocks and a metafelsite document stages of effusion at 115 120 ma as well as at 155 170 ma the u pb data confirm the interpretation by hanson et al 1987 that part of the metasedimentary metavolcanic pile was laid down after late jurassic intrusion of the barcroft pluton the lower cretaceous largely volcanogenic metasedimentary section lies beneath a low angle thrust fault the upper plate of which includes interlayered late jurassic mafic and felsic metavolcanic rocks and the roughly coeval barcroft pluton late jurassic and early cretaceous volcanism in this sector of the californian continental margin combined with earlier petrologic structural and geochronologic studies indicates that there was no gap in igneous activity at this latitude of the north american continental margin

early cretaceous transition from nonaccretionary behavior to strongly accretionary behavior within the franciscan subduction complex 1 during subduction at the franciscan trench beginning at 170 160 ma and continuing to the present marine sedimentary and lesser volcanic rocks have been underthrust accreted and metamorphosed to form the franciscan accretionary wedge the south fork mountain schist sfms forms the eastern margin and structural top of the wedge and so was apparently the first unit of substantial size to accrete into the franciscan new u pb ages of detrital zircons and 40ar 39ar ages of metamorphic white micas indicate that the sfms accreted surprisingly late in the time span of franciscan subduction probably at ca 123 ma at least parts of the valentine spring formation and yolla bolly terrane accreted soon thereafter therefore accretion of the sfms apparently marks a fundamental transition from virtually nonaccretionary behavior to strongly accretionary behavior in the franciscan forearc about 75 of modern forearcs are nonaccretionary so recognition of an early nonaccretionary period is consistent with modern examples the franciscan mafic high grade exotic blocks and related very small slabs which yield ca 132 to 169 ma metamorphic ages are the only well documented rock record of the early 40 m y long nonaccretionary period and represent very sparse accretion during that interval the transition into an accretionary regime at ca 123 ma was essentially synchronous with the end of the late jurassic early cretaceous magmatic lull in the sierra nevada magmatic arc with the waning of early cretaceous faulting and warping within the great valley forearc basin and possibly with changes in motion vectors of the pacific and farallon plates

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

a global study of volcanic infrasound characteristics and the potential for long range monitoring abstract volcanic infrasound from explosive eruptions is detectable at distances up to 1000 s of km and is often recorded on the international monitoring system ims infrasound network though infrasound produced by individual volcanoes has previously been studied more general relationships between infrasound characteristics and eruption parameters remain unclear therefore using a dataset comprising 110 events at 39 globally distributed volcanoes we assess the ability of the ims to monitor remote volcanoes and investigate whether volcanic infrasound exhibits consistent trends across a range of eruption styles and intensities acoustic pressure amplitude and frequency content of the volcanic infrasound were measured and acoustic energy was also calculated these were compared along with the maximum distance of detection for each event to the maximum plume height reported for the event which was used as a proxy for event intensity of the events investigated 62 were detected by at least one infrasound station the maximum distance at which an event was detected generally increased with the plume height and infrasound produced during the eruption of manam png in january 2005 which produced a plume which rose over 20 km above the summit was detected at a distance of 10 671 km total acoustic energy and acoustic pressure amplitude corrected for geometrical spreading increased with plume height whilst the lowest frequency present in the volcanic infrasound decreased additionally relationships seen between infrasound characteristics and eruption plume height indicate that analyses of this data alone could constrain vital estimates of plume heights for otherwise un observed eruptions taken together these findings indicate that if made available for this purpose in the future the ims infrasound network could complement existing monitoring techniques by detecting and characterising eruptions at remote volcanoes which often have no local monitoring networks