diagnostic features and field criteria in recognition of tectonic sedimentary and diapiric melanges in orogenic belts and exhumed subduction accretion complexes abstract multiple episodes of deformation during the tectonic evolution of orogenic belts and ancient subduction accretion complexes cause obfuscation of primary block in matrix fabric of melanges and thereby making the recognition of their tectonic sedimentary or diapiric origin difficult here we present a comprehensive overview and synthesis of a diverse set of field based stratigraphic and structural criteria which are at the base of geological mapping rules to differentiate between various melange types developed by disparate geological processes and mechanisms we first define the current concepts of melange and melange nomenclature and describe the most diagnostic features of tectonic sedimentary and diapiric melanges at different scales we discuss some of the main issues complicating the application of these diagnostic criteria such as i similarities between the block in matrix fabric of different melange types formed in partially lithified sediments at shallow structural levels ii transformation of fabric elements with increased depth due to tectonic reworking and recrystallization processes iii significance of exotic versus native blocks in melange matrix and iv age relationships between blocks and matrix in a melange we introduce two additional criteria in approaching these complexities and in recognizing different processes of polygenetic melanges formation in the field when primary diagnostic fabrics were reworked by multiple deformational events these new criteria are based on i the coherence between lithological compositions of melange components blocks and matrix and characteristics and tectonic evolution of the geodynamic setting of their formation tectonic environment criterion and ii specificity and kinematic coherence in the distribution of deformation between blocks and the matrix deformation criterion the discussed diagnostic criteria can be applied to all field based investigations of melanges and broken formations in orogenic belts and exhumed subduction accretion complexes around the world regardless of their location age and tectonic history

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

case studies of developing east pacific easterly waves this paper contains a study of developing east pacific easterly waves observed during the summer of 1991 with aircraft in situ and radar data and geosynchronous infrared satellite imagery the circulation and divergence profiles surface momentum and entropy fluxes as well as 700 mb and 975 mb saturated and actual equivalent potential temperatures were measured repeatedly for three disturbances that evolved into east pacific hurricanes as the disturbances develop the level of maximum updraught mass flux decreases which leads to increased convergence at low levels this process appears to be coupled to an increase in the mid level relative humidity which in turn suppresses the development of convective downdraughts comparison of the respective tendencies of convergence and surface friction to spin up and spin down a developing disturbance suggests that friction is unimportant in the early stages of development however as the surface circulation develops the two effects become comparable in magnitude if surface friction is deposited through a fairly deep layer of the troposphere the observations appear to rule out boundary layer ekman balance in these developing systems though more accurate observations of the eddy fluxes of absolute vorticity into such systems are needed to answer this question with certainty

inner core structure of hurricane alicia from airborne doppler radar observations abstract airborne doppler radar measurements are used to determine the horizontal winds vertical air motions radar reflectivity and hydrometer fallspeeds over much of the inner core region within 40 km of the eye of hurricane alicia 1983 the reconstructed flow field is more complete and detailed than any obtained previously the data show both the primary azimuthal and secondary radial height circulations the primary circulation was characterized by an outward sloping maximum of tangential wind the secondary circulation was characterized by a deep layer of radial inflow in the lower troposphere and a layer of intense outflow above 10 km altitude the rising branch of the secondary circulation was located in the eyewall and sloped radially outward discrete convective scale bubbles of more intense upward motion were superimposed on this mean rising current and convective scale downdrafts were located throughout and below the core of maximum precipitation in the eyewall precipitation particle

large pressure gap between the coastal and central franciscan belts northern and central california abstract the nature of the metamorphism of the central belt of the franciscan complex has long been debated did the whole central belt or its melange matrix undergo high p t metamorphism to solve this problem we have investigated the regional distribution of aragonite in these rocks in northern and central california we have discovered more than 300 new localities of aragonite using the staining method by friedman 1959 aragonite occurs as network veins or pods in both metagraywacke and matrix forming metashale and is invariably partially replaced by calcite on its rim thus we conclude that aragonite is stable in all parts of the franciscan central belt from the lower boundary between the coastal and central belts to the topmost part of the central belt and that both the matrix forming melange shale and exotic blocks of the central belt suffered high p t metamorphism we traced the boundary between the central and coastal belts in northern california using the staining method along the gently eastward dipping thrust plane between the underlying coastal and overlying central belts more than 2 5 kbar pressure break is obtained through the lawsonite laumontite aragonite quartz relations such an observed large pressure gap was formed during the exhumation process of the central belt of the franciscan complex

an analysis of the environmental moisture impacts of western north pacific tropical cyclones abstractthe present study examines the environmental moisture anomalies present during western north pacific tropical cyclone tc passage using storm relative composites composited precipitable water anomalies reveal asymmetric anomalies with dry anomalies to the northwest and southwest of the tc and moist anomalies to the east of the tc precipitable water anomalies filtered in space and time suggest that the moisture anomalies in the northwest southwest and east regions nwr swr and er respectively are partially due to the tc while the anomalies in the swr are also forced by a convectively suppressed madden julian oscillation mjo and equatorial rossby wave erw composited vertically integrated moisture budgets and backward parcel trajectories reveal that the moisture anomalies in the nwr swr and er are primarily due to the convergence of climatological mean moisture by the anomalous meridional wind this convergence is induced by the secondary circulation of the tc in the nwr and er and b

the east anatolian fault an oblique collisional belt abstract the tectonic setting for the area around the arabia africa anatolia triple junction is described from combined landsat spot satellite image analysis and field observations since the late miocene the motion along the east anatolian fault generated major structures corresponding to shortening with a sinistral slip component the 150 km wide area of the triple junction is highly deformed by folding and thrusting distributed mainly on the border of the anatolian block in addition kinematic reconstructions confirm that the arabia anatolia relative motion is both sinistral and convergent the sinistral strike slip faults of the east anatolian fault zone are of second order and local consequences of the n s arabia anatolia collision

magmatic origin of low t mafic blueschist and greenstone blocks from the franciscan melange san simeon california abstract the franciscan melange exposure near san simeon contains abundant greenstone and minor blueschist blocks that were tectonically boudinaged while encased in the shale matrix tectonic deformation of the blueschists is evident from variable amounts of cataclastic flow along their margins and in pinched tails major trace and rare earth elemental analyses indicate that blueschist and greenstone blocks in this area of the melange were derived from sources with morb like composition along with some having trace element and ree patterns similar to oib compositions most blocks are low lree basalts that probably formed in an open ocean ridge setting but some blocks have high lree contents similar to off axis seamounts linear trends of incompatible elements for both blueschist and greenstone blocks indicate that both lithologies were probably derived from a similar variably fractionated tholeiitic magma blueschist blocks with sodic amphibole lawsonite epidote were pervasively recrystallized at 300 350 c and foliated during ductile deformation that included folding their protolith can only be identified as mafic a few blocks contain very small amounts of metasedimentary materials indicating some were probably seafloor basalts but some may have been diabase or even gabbro where interlayered sediment was present the mafic protolith was enriched in k rb and na greenstones on the other hand contain abundant pseudomorphic evidence of magmatic textures alteration to albite chlorite and pumpellyite at temperatures of 100 200 c is intense especially in cataclastic margins and pinched tails some of the basaltic greenstones have attached radiolarian chert and a few have relict diabasic textures the mafic blueschists and greenstones in the melange near san simeon are probably fragments from the uppermost part of the farallon plate the blueschists may be mostly mafic slabs uprooted from the subducting crust underplated to the base of the north american plate and later detached and carried back towards the surface in upwelling melange the greenstones are most likely fragments detached from seamounts subducted during times of melange upwelling

tropical cyclone environments over the northeastern and northwestern pacific based on era 15 analyses abstract this study uses a 1 1 lat long dataset extracted from ecmwf reanalyses for the 15 yr period 1979 93 era 15 to composite environmental characteristics and flow features in the vicinity of named tropical cyclones tcs in the eastern and western north pacific ocean basins tropical cyclones are partitioned into one of four classifications as they pass by selected locations along the axes of maximum frequency and tc tracks weak w strong s intensifying i or dissipating d results of this study show that peak values of rising motion within the same classification are greater for tc composites in the western pacific than for those in the eastern pacific the level of maximum rising motion was at or above the 500 hpa level for all locations and classifications except for the ss at our northernmost point 25 n 130 e in the western pacific their maximum upward motion occurred at 700 hpa it is also found that the latter systems contrary to all other points were located in a reg

optical determination of topotactic aragonite calcite growth kinetics metamorphic implications textures produced by the partial recrystallization of aragonite to calcite in the blueschist facies show that heterogeneous topotactic nucleation is rapid enough to permit growth kinetics to dominate the overall geologic rate of transformation both grain boundary velocities measured microscopically between 375 c and 455 c and analysis of topotactic relations predict a growth mechanism involving only small atomic displacements near a highly coherent boundary between the two phases the kinetic equation of turnbull for interface controlled growth based on that mechanism accurately describes the experimental results when calculated rates are integrated over geologically plausible pressure temperature time paths for convergent plate margins even the most extreme values lead to the conclusion that aragonite bearing rocks enroute to the surface must enter the calcite stability field between 125 c and 175 c the widespread occurrence of aragonite along the pacific margin of north america and by contrast

mesoscale and convective scale characteristics of mature hurricanes part i general observations by research aircraft abstract the analysis of instrumented aircraft data from four recent mature hurricanes reveals common mesoscale and convective scale features the structure and organization of the convection precipitation and wind flow are studied by combining the airborne observations using basic instrumentation with quantitative radar measurements three predominant precipitation features seen are 1 the eyewall 2 a stratiform rain region adjacent to and outside the eyewall and 3 rainbands that contain both convective and stratiform regions the eyewall is so named because it surrounds the rain free eye but several additional features distinguish it from other convective bands in the hurricane in particular the updraft tangential wind maximum and highest rainfall have preferred locations relative to each other with the updraft being radially inward from the rain and wind maxima the 10 dbz radar reflectivity contour indicative of the inner edge slopes substantially outward with height and there is evide

kinematic evidence for extensional unroofing of the franciscan complex along the coast range fault northern diablo range california franciscan metagraywacke immediately below the del puerto ophiolite an outlier of the coast range ophiolite in the northern diablo range was sheared during top to the east displacement on the coast range fault this represents normal faulting and extensional offset it was accompanied by attenuation of the coast range ophiolite and great valley sequence in the hanging wall along layer parallel normal faults that sole into the coast range fault extension occurred as the franciscan complex moved relatively west out from under north american lithosphere and across the subducting ocean plate below this effected a lengthening and thinning in the wedge of material above the down going plate presumably in response to instability brought about by subduction shallowing krueger and jones 1989 and accretion of the franciscan central belt in the latest cretaceous to early paleocene as a result blueschist facies terranes of the uppermost part of the franciscan complex are now juxtaposed directly against hanging wall units that bear only low grade metamorphism

evolution of the structure of precipitation in hurricane allen 1980 abstract reflectivity data from the airborne radar systems on board the three noaa aircraft were gathered during six consecutive days in hurricane allen of 1980 the data have been used to specify the horizontal and vertical precipitation distribution within 111 km radius of the hurricane center the evolution of the structure and intensity of the precipitation in the storm is described from representative time composite radar maps for seven research flights made during the 6 day period the eyewall was characterized by a narrow ring 12 15 km wide of intense reflectivity 42 47 dbz surrounding the center of the storm at a radius that varied in time from 12 40 km the eyewall had steep radial gradients of reflectivity 4 5 db km 1 and tilted radially outward in height the rainbands were characterized by areas of enhanced reflectivity embedded in a region of stratiform rainfall that contained a distinct bright band at the height of the 0 c isotherm the most striking changes in structure during the 6 d

aluminous titanite sphene from the eclogite zone south central tauern window austria abstract highly aluminous titanite with al 2 o 3 contents up to 14 wt 50 of the caalsio 4 f oh end member occurs in siliceous dolomites from the eclogite zone south central tauern window austria 140 chemical analyses of titanites from 13 samples from the eclogite zone and adjacent tectonic units reveal that al is incorporated into titanite primarily by the mechanism ti o al f oh there is also a strong positive correlation between al and f content of these titanites indicating that the combined substitution is enhanced by the presence of f al contents of titanite vary between tectonic units with the most aluminous varieties occurring in the high pressure eclogite zone variations also occur from sample to sample within a single tectonic unit and both between and within individual grains in a single sample complex zoning with sharp chemical and optical discontinuities is observed with al 2 o 3 variations of up to 6 wt within a single sample individual grains generally have low al cores mantled by high al zones and rimmed by low al edges it is suggested that the incorporation of al into titanite is favoured by high p low t and high f activity

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

large scale influences on tropical cyclogenesis in the western north pacific abstract objectively analyzed data from the european centre for medium range weather forecasts are used to examine the large scale aspects of the formation of tropical cyclones it is hypothesized that tropical cyclogenesis occurs when external atmospheric forcing on the synoptic or larger scale provides uplift through a deep layer enhancing convection in a region with environmental conditions favorable for genesis emphasis is placed on the roles of upper level troughs low level wind surges preexisting tropical cyclones and propagating wave disturbances in triggering tropical cyclogenesis composites of the 200 hpa and 850 hpa flows reveal the presence of both upper level troughs and low level wind surges respectively prior to genesis in the composites the wind surges also appear to be related to the presence of a prior circulation located approximately 2000 km to the west of the genesis location an examination of the individual cases demonstrates that approximately 85 of all storms had either

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

geochemistry and petrology of mafic volcanic rocks from olistostromes in the basal great valley group northern california coast ranges the mysterious valley formation mvf is a 1 km thick accumulation of chaotic olistostromes consisting of ophiolitic blocks set in a mudstone and serpentinous mudstone matrix in the basal great valley group of the northern california coast ranges the mvf overlies serpentinite of the middle jurassic coast range ophiolite cro most igneous blocks from the mvf are mid ocean ridge type tholeiitic basalts morb9s with moderate tio 2 contents 1 0 2 5 and depletions in light relative to heavy rare earth elements ree9s relict clinopyroxenes in these blocks are low ti augites rare blocks that are light ree enriched and contain titanaugite probably represent ocean island type basalts coarse grained plutonic blocks have not been found however abundant blocks of mafic breccia similar to breccia overlying intact cro elsewhere in the northern coast ranges contain clasts of ultramafic rock and both cumulus and noncumulus gabbro diabase intrusions into the underlying cro serpentinite are chemically identical to mvf basalts suggesting a possible relationship between cro igneous rocks and mvf blocks because most mvf basalt blocks are more ti rich and in general more morb like than are cro extrusive basalts however the mvf olistostromes are not easily explained as being derived from the uplift and erosion of the ancient cro our chemical data indicate that either 1 mvf basalt blocks were not derived from the cro 2 our samples which are from a geographically limited area are not representative of the mvf or 3 the mvf was derived from a more morb like part of the cro that is not well represented in the few analyses presently available from the northern cro

tectonic significance of low temperature blueschist blocks in the franciscan melange at san simeon california abstract the blueschist bearing franciscan melange exposed near san simeon is very similar to the melange terrane forming the central belt north of san francisco epidote bearing low t blueschist blocks at san simeon n 3 are the same age as high t garnet bearing blocks in the northern and diablo range melange terranes 155 150 ma this age approximates the time of initiation of franciscan subduction during the initial stages of franciscan subduction part of the top volcanic sequence from the subducting oceanic plate and small volumes of overlying sediments were imbricated at the bottom of the overriding plate and metamorphosed under high p conditions this underplated material was variably retrograded as subduction refrigerated the forearc blocks actinolitic rinds formed at the contacts between blueschists and intercalated mantle under relatively static conditions as the base of the overriding plate became serpentinized a model is proposed in which exhumation was facilitated by gravity driven seaward oriented extensional thinning of the forearc prism caused by the decrease in subducting plate dip starting around 80 ma that caused the laramide orogeny as this occurred blueschist and graphite schist blocks were plucked from the bottom of the hanging wall incorporated into the shale and water rich shear zone at the plate interface subduction channel shear zone and exhumed during the upward flow of melange driven by the movement of the downgoing plate while subduction was still active

hydrothermal alteration in oceanic ridge volcanics a detailed study at the galapagos fossil hydrothermal field abstract the galapagos fossil hydrothermal field is composed of altered oceanic crust and extinct hydrothermal vents within the eastern galapagos rift between 85 49 w and 85 55 w the discharge zone of the hydrothermal system is revealed along scarps thus providing an opportunity to examine the uppermost mineralized and highly altered interior parts of the crust altered rocks collected in situ by the submersible alvin show complex concentric alteration zones microsamples of individual zones have been analysed for major minor trace elements and strontium isotopes in order to describe the complex compositional details of the hydrothermal alteration interlayered chlorite smectite and chlorite with disequilibrium compositions dominate the secondary mineralogy as replacement phases of primary glass and acicular pyroxene phenocrysts and matrix grains of plagioclase are unaffected during alteration using a modification of the gresens equation we demonstrate that the trivalent rare earth elements rees are relatively immobile and calculate degrees of enrichment and depletion in other elements strontium isotopic ratios increase as sr concentrations decrease from least altered cores to most altered rims and cross cutting veins in individual samples and can be modeled by open system behaviour under low fluid rock ratio

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

metamorphic evolution of two different eclogites in the franciscan complex california u s a the eclogites in california u s a have been regarded as tectonic blocks which formed 150 160 ma ago and have been tectonically incorporated into younger rocks of the franciscan complex of 90 130 ma however in ward creek northern california two different types of eclogites were identified type i is a typical tectonic block and type ii is a possible in situ eclogite formed during the franciscan metamorphism most eclogites in the franciscan complex are type i eclogites type i eclogites in ward creek consist of garnet omphacite epidote glaucophane phengite rutile barroisite quartz and have coarse grained gneissic texture they have precursors of the epidote amphibolite facies and are overprinted in various degrees by blueschist facies retrograde metamorphism remnants of metamorphic rinds which consist of actinolite talc chlorite and formed during metasomatic interaction with serpentinizing peridotite occur at the margins of type i eclogite blocks type ii eclogites are medium grained and consist of garnet chloromelaniticclinopyroxene epidote glaucophane paragonite phengite rutile quartz petrochemical characters of type ii eclogites are similar to those of in situ eclogitic schists in the ward creek metabasite sequence epidote amphibolite f facies precursors metamorphic rinds and overprint of retrogressive blueschist facies metamorphism are not found in type ii eclogites garnets in type ii eclogites are medium grained unaltered and idioblastic and have higher spessartine contents sp14 25 whereas garnets in type i eclogites are coarse grained and chloritized and have lower spessartine contents sp2 7 the pt conditions of peak metamorphism for type ii eclogites are 380 10 11 5 kb type i eclogites follow a counter clockwise pt path from the epidote amphibolite through eclogite to blueschist facies whereas the presumable in situ type ii eclogites follow a clockwise pt path from the blueschist to eclogite facies

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

polyphase and anticlockwise p t evolution for franciscan eclogites and blueschists from jenner california usa high grade exotic blocks in the franciscan complex at jenner california show evidence for polydeformation metamorphism with eight distinct stages two parallel sets of mineral assemblages e eclogite and bs laminated blueschist representing different bulk chemistry were identified stage 1 recorded by parallel aligned inclusions s1 of crossite omphacite epidote ilmenite titanite quartz e and glaucophane actinolite epidote titanite bs in the central parts of zoned garnets represents the epidote blueschist facies the onset of a second stage stage 2 is represented by a weak crenulation of s1 and growth of garnet this stage develops a well defined s2 foliation of orientated barroisite epidote titanite e or subcalcic actinolite epidote titanite bs at c 90d to s1 with syntectonic growth of garnet defining the albite epidote amphibolite facies a third stage with aligned inclusions of glaucophane subcalcic actinolite phengite parallel to s2 in the outermost rims of large garnet grains is assigned to the transitional albite epidote amphibolite garnet bearing epidote blueschist facies the fourth stage represents the peak metamorphism and was identified by unorientated matrix minerals in the least retrograded samples in this stage the mineral assemblages garnet omphacite glaucophane phengite e and garnet winchite phengite epidote bs both represent the eclogite facies stage 5 is represented by the retrogression of eclogite facies assemblages to the epidote blueschist facies assemblages crossite glaucophane garnet omphacite epidote phengite e and glaucophane actinolite epidote phengite bs with the development of an s5 foliation subparallel to s2 stage 6 represents a crenulation of s5 with the development of a well defined s6 crenulation cleavage wrapping around relics of the eclogite facies assemblages this crenulation cleavage is further weakly crenulated during a d7 event post d7 stage 8 is recorded by the growth of lawsonite chlorite actinolite replacing garnet and by veins of lawsonite pumpellyite aragonite and phengite apatite the different yet coeval mineral parageneses observed in rock types e and bs are probably due to differences in bulk chemistry the metamorphic evolution from stage 1 to stage 8 seems to have been broadly continuous following an anticlockwise p tpath 1 epidote blueschist garnet free to 2 albite epidote amphibolite to 3 transitional epidote blueschist garnet bearing albite epidote amphibolite to 4 eclogite to 5 epidote blueschist garnet bearing to 6 7 epidote blueschist garnet free facies to 8 lawsonite pumpellyite aragonite bearing assemblages this anticlockwise p t path may have resulted from a decreasing geothermal gradient with time in the mesozoic subduction zone of california at early or pre franciscan metamorphism

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

radar characteristics of precipitation features in the epic and tepps regions of the east pacific abstract ship based radar data are used to compare the structure of precipitation features in two regions of the east pacific where recent field campaigns were conducted the east pacific investigation of climate processes in the coupled ocean atmosphere system epic 2001 10 n 95 w in september 2001 and the tropical eastern pacific process study tepps 8 n 125 w in august 1997 corresponding july september 1998 2004 tropical rainfall measuring mission trmm precipitation radar pr data are also used to provide context for the field campaign data an objective technique is developed to identify precipitation features in the ship and trmm pr data and to develop statistics on horizontal and vertical structure and precipitation characteristics precipitation features were segregated into mesoscale convective system mcs and sub mcs categories based on a contiguous area threshold of 1000 km2 these features were required to have at least one convective pixel as well as an other nc category com

the snow mountain volcanic complex an on land seamount in the franciscan terrain california the snow mountain volcanic complex in the franciscan terrain of northern california is a 1 1 2 to 2 km thick sequence of altered submarine pillow lavas pillow breccias diabase and interbedded sediments forming a klippe that structurally overlies nearby rocks of the franciscan assemblage the coast range ophiolite and great valley sequence all of the snow mountain rocks bear a weak overprint of blue schist facies metamorphism the volcanic rocks were deposited on top of 200 300 m of interbedded turbiditic greywacke shale and radiolarian chert which are interpreted as an interfingering abyssal fan and pelagic sequence the volcanic pile is therefore supracrustal and is not an ophiolitic fragment formed at a mid ocean spreading center rather it is probably the remnant of a former seamount the lavas are mostly titanium rich transitional basalts minor associated rocks include rhyolite and peralkaline rhyolite relict clinopyroxenes in the basaltic rocks are all titanium aluminum rich augites thes

geochemical evidence for a subducted infant arc in franciscan high grade metamorphic tectonic blocks some of the evidence of tectonic and chemical processes that occur in subduction zones is preserved in blueschists and eclogites as validated by the geochemical data presented from high grade metamorphic tectonic blocks from the franciscan complex in central california combining major elements compatible and incompatible trace element concentrations and ratios and sr nd pb isotopic data we conclude that the protoliths of these high grade franciscan blocks were arc lavas with no continental crust derived components although the protoliths underwent high grade metamorphism at the inception of subduction the tectonic affi nity of the protoliths can be distinguished by our geochemical study our geochemical data are signifi cant in that 1 the protoliths of these high grade blocks have a different mode of origin than the protoliths of the lower grade franciscan basalts that were incorporated later in the subduction complex as the latter generally are considered to be oceanic island basalts oib and derived from mid oceanicridge basalt morb and 2 the protoliths of the high grade blocks were formed over a pre franciscan subduction zone based on the geochemical evidence for an arc origin and the available geochronological data we suggest that protoliths of the highgrade tectonic blocks of the franciscan complex and the coast range ophiolite formed in the same infant arc setting initiation of franciscan subduction in this arc crust led to the formation of the high grade blocks beneath the young coast range ophiolite continued subduction resulted in subduction of older oceanic crust of morb and oib origin some of which was scraped off to form lower grade metabasites within the franciscan complex

clustering of eastern north pacific tropical cyclone tracks enso and mjo effects 1 a probabilistic clustering technique is used to describe tropical cyclone tracks in the eastern north pacific on the basis of their shape and location the best track data set is decomposed in terms of three clusters these clusters are analyzed in terms of genesis location trajectory landfall intensity seasonality and their relationships with the el nino southern oscillation enso and madden julian oscillation mjo longitudinal track location plays a strong discriminating role in the regression mixture model s solution with the average track orientation becoming more zonal toward the west this progression encapsulates well the relationship between tropical cyclones over the eastern tropical pacific and the mjo or enso two of the clusters describe tropical cyclones tcs with tracks that lie near the coast of mexico and central america the most frequent cluster contains tracks that trend west northwestward while the second most frequent one has genesis locations that lie slightly to the southeast of those in the most frequent cluster and tracks that run typically parallel to the central american coast this second cluster is shown to be significantly associated with the westerly phase of the mjo the third least frequent cluster contains tcs with westward trajectories over the central and eastern equatorial pacific some of these tcs have an impact on hawaii and other islands as far as the central and western north pacific regions the least frequent cluster is strongly related to enso while the others are not it occurs significantly more frequently during el nino conditions examination of the large scale patterns of atmospheric circulation and sea surface temperature associated with each of our three clusters are consistent with previous studies anomalous low level westerly zonal winds from the monsoon trough and mjo meet anomalous easterlies near the region of genesis in each cluster

new evidence for polyphase metamorphism of glaucophane schist and eclogite exotic blocks in the franciscan complex california and oregon abstract the early metamorphic history of high grade exotic blocks in the franciscan complex may be more complicated than previously supposed the different assemblages of high grade glaucophane schist eclogite amphibolite and hornblende schist are commonly considered to have formed at the same time from essentially unmetamorphosed oceanic crust however new textural and mineralogical data presented here suggest that high grade glaucophane schist and eclogite have replaced an earlier epidote amphibolite facies assemblage that is identical to the primary assemblages in many of the hornblende rich blocks at least some of the hornblende rich blocks may therefore be well preserved remnants of the earlier metamorphism comparison of the mineral assemblages and element partitioning in the mixed assemblage blocks suggests that the glaucophane schist and eclogite metamorphism took place at slightly lower temperatures but at the same or higher pressures than the earlier hornblende forming stage

metamorphism of franciscan tectonostratigraphic assemblage pacheco pass area east central diablo range california coast ranges the pacheco pass area well known for the relatively high pressure low temperature mineral assemblages developed in a well ordered section of chiefly metaclastic strata was restudied in order to elucidate the geologic paragenetic and textural relationships among the various lithologic units the mapped 7 minute quadrangle extends from 4 km west of the range crest eastward to the ortigalita fault tectonic contact of the franciscan assemblage with coeval great valley strata semicontinuous metachert beds underlain by scraps of na cpx and or na amphibole bearing metabasaltic rock mark the base of terrigenous tectonostratigraphic units evidently decoupled from the downgoing oceanic crust capped plate underplating along newly recognized bedding plane faults has juxtaposed members of an apparently conformable franciscan sedimentary sequence four depositional units each consisting of monotonous metagraywacke and interlayered metashale are stacked within the accretionary section from top down these are tectonostratigraphic members a b c and d unit d differs from overlying members in possessing a greater abundance of bluestone greenstone pods minor serpentinite bodies and rare metaconglomerate lenses varying degrees of stratal disruption indicate that it has been arrested in the transformation to broken formation the ortigalita fault is nearly vertical strikes north northwest and exhibits apparent dextral offset it truncates the east west striking gonzaga fault and other franciscan structures the topographic low occupied by san luis reservoir is a cenozoic tectonic depression sited at a releasing bend on the ortigalita fault newly acquired textural chemical mineralogic and areal relations of albitic and jadeitic pyroxene bearing franciscan metagraywacke near pacheco pass demonstrate that 1 na cpx and na amphibole are metamorphic minerals not clastic materials 2 pumpellyite is a minor neoblastic phase in albite bearing metagraywacke west of pacheco pass and in the north western corner of the quadrangle but it does not occur in jadeitic pyroxene bearing metaclastic rocks 3 higher textural grade metagraywacke specimens generally contain higher modal proportions of jd 4 abundance textural grade and chemistry of na cpx are not related to tectonostratigraphic units and 5 because of sluggish reaction rates albite persisted metastably into the higher pressure jadeitic pyroxene quartz p t field production of na cpx resulted from a reaction of the sort ab chl jd iws qtz gln h 2 o irregular oscillatory zoning within single jadeitic pyroxene prisms and variable jd ab modes for rocks of the same bulk composition reflect growth governed by diffusion rather than recrystallization within a p t transition zone high pressure overstepping of the phase boundary explains variable modal proportions of ab and jd as well as chemical heterogeneity of the jd elevated p attended metamorphism of na cpx bearing rocks exposed in the pacheco pass area as indicated by the wide spread coexistence of quartz and naalsi 2 o 6 rich pyroxene inferred physical conditions of prograde metamorphism were 150 50 c at 7 8 kbar or more franciscan rocks in the east central diablo range underwent subduction zone metamorphism accompanying paleo pacific lithospheric plate descent during mid cretaceous convergence underplating contraction and sequestering of the tectonostratigraphic assembly at depths of 25 30 km during underflow followed by gradual rise took place under conditions of refrigeration due to protracted descent of the oceanic slab paleogene diapiric uplift and extension followed indicating more complete decoupling of the buoyant trench complex from the downgoing plate finally passage of the east pacific rise triple junction in neogene time initiated the present dextral slip regime in the california coast ranges

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

embaluh group turbidites in kalimantan evolution of a remnant oceanic basin in borneo during the late cretaceous to palaeogene turbidites crop out in large parts of nw borneo including kalimantan and sarawak the strata predominantly comprise the embaluh group in kalimantan and lateral equivalents the rajang group in sarawak collectively known as the rajang embaluh group previous interpretation of these rocks as the product of deep marine deposition and deformation as part of an accretionary prism during late cretaceous to palaeogene subduction implies south dipping thrusts northward stratigraphic younging the existence of a complete arc to trench system and significant deformation and metamorphism of the turbidites however new fieldwork described here established consistent southward stratigraphic younging in kalimantan no evidence for southward dipping thrusts and a lack of metamorphism and associated accretionary complex related deformation features furthermore all available palaeontological and radiometric age data indicate that deposition of the bulk of the rajang embaluh group postdates in board subduction related magmatism and thus a complete arc trench system cannot be demonstrated consequently the rajang embaluh group turbidites are re interpreted as having formed in either a post collisional foreland basin or a remnant ocean basin the lack of a identifiable mountain belt and linked thrust system and probable oceanic aynity of crust beneath the rajang embaluh group basin favour the latter interpretation borneo occupies a pivotal position within southeast asia this new model of a remnant oceanic basin setting for extensive turbidite units of borneo therefore has far reaching implications for the tectonic evolution of borneo the south china sea and se asia the new model is compared with older palaeozoic orogenic belts which also contain thick turbidites sequences

an examination of the thermodynamic impacts of western north pacific tropical cyclones on their tropical tropospheric environment abstractthe present study examines the tropospheric thermodynamic anomalies induced by western north pacific tropical cyclone tc passage using storm relative composites negative moist static energy mse anomalies containing embedded westward propagating anomalies generally occur only following larger tcs for two months following tc passage in a region extending from the domain center to 3000 km to its west larger tcs force negative mse anomalies likely because of feedbacks from stronger broader tc induced negative sea surface temperature sst anomalies and the excitation of tc induced rossby waves to the southeast of the tc the negative mse anomalies are composed of lower and midtropospheric negative latent energy anomalies with smaller contributions from boundary layer and upper tropospheric negative sensible heat anomalies the lower and midtropospheric negative mse anomalies are forced by the tc whereas the upper tropospheric negative mse anomalies are forced by the madden julian oscillatio

vertical motion characteristics of tropical cyclones determined with airborne doppler radial velocities abstract vertical motions in seven atlantic hurricanes are determined from data recorded by doppler radars on research aircraft the database consists of doppler velocities and reflectivities from vertically pointing radar rays collected along radial flight legs through the hurricane centers the vertical motions are estimated throughout the depth of the troposphere from the doppler velocities and bulk estimates of particle fallspeeds portions of the flight tracks are subjectively divided into eyewall rainband stratiform and other regions characteristics of the vertical velocity and radar structure are described as a function of altitude for the entire dataset and each of the four regions in all of the regions more than 70 of the vertical velocities range from 2 to 2 m s 1 the broadest distribution of vertical motion is in the eyewall region where 5 of the vertical motions are 5 m s 1 averaged over the entire dataset the mean vertical velocity is upward at all altitudes mean downward mot

first 40ar 39ar ages from low t mafic blueschist blocks in a franciscan melange near san simeon implications for initiation of subduction abstractthe franciscan complex of california is a type example of an accretionary prism with widespread high p t subduction zone metamorphism low t fine grained lawsonite bearing mafic blueschists encased in a shale matrix melange near san simeon have been dated for the first time 40ar 39ar ages were obtained for phengite separated from four blocks and from an actinolitic rind on the margin of one of the blocks the three blocks with lawsonite epidote yield ages of between 154 and ma while the actinolitic rind yields an age of ma these ages are from the part of the franciscan complex west of the san andreas fault that moved northward at least 300 km with respect to the extensive franciscan exposures east of the fault the ages obtained in this study show that some fine grained low t lawsonite epidote franciscan blueschist blocks formed at the same time as coarse grained high t garnet epidote franciscan blueschist blocks these dated rocks indicate that both high and low t mafic blueschi

low temperature eclogites and eclogitic schists in mn rich metabasites in ward creek california mn and fe effects on the transition between blueschist and eclogite

neogene arc continent collision in sabah northern borneo malaysia abstract the neogene evolution of sabah can be interpreted in terms of an arc continent collision initiated during early middle miocene time and followed by intraplate shortening the latter being active in this area at the present day the volcanic arc of late oligocene middle miocene age is imbricated with melanges and thrust northwestward on a polyphase deformed turbiditic sequence of late cretaceous middle miocene age crocker range intraplate shortening is seen in the thrusting and folding offshore sabah along the palawan north borneo trench and also by broad open folds and strike slip faulting in the previously sutured terranes this collision can either be interpreted as the final stage of southward subduction of the hypothetical proto south china sea or the result of back thrusting of the sulu volcanic arc resulting from the subduction of the celebes sea toward the north

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

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

geochemical evidence for the tectonic setting of the coast range ophiolite a composite island arc oceanic crust terrane in western california the middle to late jurassic age coast range ophiolite cro of california contains two geochemically distinct volcanic rock associations that formed in different tectonic settings volcanic rocks from the southern cro point sal cuesta ridge stanley mountain llanada quinto creek and del puerto and parts of the northern cro healdsburg elder creek are similar to low k tholeiites and calc alkaline rocks of the island arc suite the thin volcanic sections of these ophiolite remnants suggest formation by intra arc rifting in contrast volcanic rocks from stonyford seamount and paskenta in the northern cro are transitional subalkaline metabasalts with geochemical characteristics similar to enriched mid ocean ridge basalts or ocean island tholeiites these rocks are associated with tithonian radiolarian cherts and may be part of the franciscan complex alternatively they may represent a change in tectonic setting within the cro during the late jurassic regardless the cro as currently conceived cannot be considered a single terrane with one mode of origin

actinolitic rinds on low t mafic blueschist blocks in the franciscan shale matrix melange near san simeon implications for metasomatism and tectonic history abstract in the melange terrane of the franciscan accretionary prism mg rich actinolite tremolite rinds have long been known to be present on many high t garnet epidote bearing mafic blueschist and eclogite blocks but they were thought to be absent on low t lawsonite chlorite blueschist blocks by analogy with rinds on high t blocks these rinds on low t blocks must have been produced by metasomatic reaction with ultramafic rock the rinds on high t blocks have led to the speculation that the high t franciscan blueschists were uplifted to the surface in serpentinite diapirs while other processes exhumed the volumetrically more numerous low t blocks this paper reports the discovery of actinolitic rinds on the margins of nine low t lawsonite epidote franciscan blueschists that are or were clearly encased in the shale matrix melange exposed in seacliffs and wavecut benches near san simeon california petrographic and geochemical analyses show these mg rich rinds are similar to those found on high t garnet bearing blocks the bulk composition indicates the protolith of the blueschist blocks was mafic oceanic crust the high fe3 fe contents indicate it was probably the uppermost hydrated volcanic part of the crust the block ultramafic rock association was created by faulting during subduction initiation as fragments from the top of the subducting ocean crust were imbricated with mantle materials at the base of the ophiolitic leading edge of the north american plate the chemistry of a block margin altered to actinolitic rind indicates si na pb cu and sr were lost from the blocks while k rb cs and ba were added most pieces of actinolitic rind are mg and ni rich because they are metasomatized ultramafic material that was enriched in si k rb cs and ba these metasomatic changes indicate the fluids that hydrated the mantle and altered the mafic blocks ascended from subducting and or underplated sediments both high t and low t blueschists that have actinolitic rinds were uplifted to near the surface after they sank or were plucked from the base of the overriding plate by subduction generated melange that upwelled from depths of 15 km

the geology of northern sabah malaysia its relationship to the opening of the south china sea basin abstract the northern part of sabah consisting of sedimentary and igneous rocks of early cretaceous to pliocene age has experienced three major episodes of deformation associated with nw se and n s oriented compressions the earliest episode deformed and uplifted an oceanic basement chert spilite formation to form an elongate basin trending approximately ne sw during the late cretaceous to early eocene this elongate basin became the site for the deposition of middle eocene to early miocene quartzose sediments of the crocker and kudat formations sourced from continental basement towards the southwest and north respectively these sediments were subsequently deformed by a second episode of deformation associated with nw se and n s oriented compressions during the latter part of the late oligocene and the early middle miocene to form a series of imbricate thrust slices the n s trending compressive direction controlled the development of approximately e w trending basins during the deposition of the upper miocene sediments of the south banggi and bongaya formations the continuation of n s compression which represents the third episode of deformation gently deformed these sediments the three episodes of deformation were related to the differential southward movements of continental blocks separated from the southern margin of china during the intermittent opening of the south china sea subbasins the first episode was related to the opening of the southwest subbasin while the second episode was related to both the opening of the southwest and east subbasins the third episode was related to continued opening in the east subbasins

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

cataclastic deformation and metasomatism in the subduction zone of mafic blocks in melange san simeon california abstract the primary origin of shale matrix melange forming the central belt of the franciscan complex is still debated the seacliff exposures near san simeon display numerous lensoidal blocks of graywacke greenstone lesser layered chert and blueschist that are encased in a matrix of scaly shale the boudinaging of mafic greenstone and blueschist blocks was accommodated by cataclasis and varied amounts of metamorphic reconstitution that is particularly intense along block margins zones of necking and intra block shear zones cataclastic zones in blueschists are greenish where chlorite and pumpellyite have formed the mineralogic assemblage produced during cataclasis in greenstones is the same as that replacing the interior of the block albite chlorite pumpellyite the cataclastic margins of many 7 of 12 greenstones gained k rb cs and ba in contrast the cataclastic margins of all blueschist blocks lost na several 3 of 9 with substantial decreases and some 3 of 9 had significant increases in k rb cs and ba this metasomatic alteration is indicative of fluid rock interaction between mafic blocks and sediments alteration of the mafic rocks with the growth of pumpellyite and chlorite occurred when blocks were encased in the shale matrix of the melange which was dynamically deforming and heated to temperatures of 150 c as synsubduction temperature depth gradients were 10 c km burial of mafic blocks while encased in the melange matrix to depths approaching 15 km is apparent surficial olistostromal movements alone do not account for the incorporation deformation and retrograde metasomatic alteration of the exotic blueschist blocks and the metamorphism of the shale matrix at such inferred depths these attributes indicate chemical exchange with shale and smearing displacement of the margins of mafic blocks occurred in the subduction zone as the shale matrix flowed and exerted shear tractions

tectonic implications of diverse igneous blocks in franciscan melange northern california and southwestern oregon more than 50 of the igneous blocks from melanges of the franciscan subduction complex in northernmost california and from the equivalent dothan formation of southwestern oregon are more silica rich than basalt and some contain supra subduction zone geochemical signatures such as elevated th ta ratios in contrast blocks from more southerly parts of the franciscan melange belt are more commonly mid ocean ridge and ocean island seamount basalts the data indicate a north south variation in the block population due to differences in source terrane or in the processes that provided the blocks and transported them into the melange or both we suggest that in the northern franciscan a relatively greater fraction of igneous melange blocks was emplaced by block slumping from the forearc crust into the trench than was the case to the south