glaucophane schists and ophiolites of the northern california coast ranges isotopic ages and their tectonic implications the geology of a strip of 15 quadrangles across the franciscan complex in the coast ranges of northern california is the basis for interpretation of the significance of potassium argon and fossil ages of glaucophane schists ophiolitic materials and associated sedimentary rocks whole rock and mineral separates of franciscan rocks were analyzed and 69 potassium argon ages were obtained white micas and actinolites from blueschist blocks in melange give apparent ages clustering about 142 and 153 m y but they probably represent a continuum blue amphibole ages from blocks range from 98 to 151 m y the younger ages are from the eastern portion of the central melange belt published u pb ages from the ophiolite belt give crystallization ages from 153 to 165 m y k ar ages extend from 143 to 166 m y whole rock ages from the south fork mountain schist range from 113 to 158 m y but cluster around 124 m y the association of older k ar ages with more coarsely crystalline schist suggests that metamorphism occurred prior to 124 m y ago fossil evidence indicates that the basal sediments of the great valley sequence were deposited upon the disrupted coast range ophiolite within 5 to 10 m y of the oldest crystallization ages for ophiolite fossils within melange units broken formations and unsubducted trench slope deposits provide evidence for melange development by the early cretaceous with youngest melange units generally lying to the west available chronologic evidence is compatible with a tectonic model involving melange formation in a restricted flow channel beneath the accretionary wedge of the subduction complex upflow of melange returned blocks of coarsely crystalline metamorphic rocks that were accreted during the initial stages of subduction when the hanging wall was still hot the viability of this and other proposed tectonic models can be assessed by continued careful field documentation of the nature of contacts between key lithotectonic units and by detailed application of temperature sensitive geochronologic tools

detrital zircon constraints on terrane ages and affinities and timing of orogenic events in the san juan islands and north cascades washington detrital zircon geochronology of this report pertains to cretaceous orogeny in northwest washington an event that involved blueschist metamorphism and emplacement of nappes in the san juan islands northwest cascades thrust system and continental arc magmatism and associated barrovian metamorphism in the neighboring coast plutonic complex structurally low in the thrust system quartzose gneiss of the yellow aster complex yields an entirely precambrian suite of detrital zircons with an age pattern that is similar to that of ordovician miogeoclinal rocks and the outboard yukon tanana yreka and shoo fly terranes elsewhere in the cordillera midway in the nappe pile of the northwest cascades sandstone in the bell pass melange has a zircon age population of 110 ma an age that together with the spectrum of exotic materials associated with the sandstone suggests the melange was a major zone of dislocation during mid cretaceous nappe emplacement at a high level in the thrust system are nappes of the fida

mineralogy and phase relations in the blueschist facies of the black butte and ball rock areas northern california coast ranges microprobe study of minerals in rocks of the blueschist facies from the black butte and ball rock areas of the south fork mountain schist northern california coast ranges is the basis in this report for analysis of reactions and phase relations among lawsonite pumpellyite epidote and associated minerals observed assemblages are intermediate in a progression from those observed elsewhere in high p low t schists of the franciscan e 9 panoche pass where lawsonite is present in nearly all lithologies to the relatively low phigh t assemblages of the shuksan blueschist washington where epidote is ubiquitous two successive reactions in this sequence in order of increasing temperature are l lawsonite na amphibole epidote quartz albite chlorite hzo 2 na amphibole pumpellyite quartz epidote ca amphibole albite chlorite h2o the pressure of metamorphism for the black butte and ball rock areas is estimated from the jadeite content of pyroxene and from the stability of aragonite to have been approximately 7 kbar temperature estimates are not tightly constrained by mineral equilibria but are suggested to be in the range of 250 to 300 c

cathodoluminescence petrography of syntectonic quartz fibres abstract the cathodoluminescence of low grade metamorphic quartz is reported in the literature to be uniformly brown this study describes an investigation of syntectonic quartz fibres from veins and pressure shadows contained in different carbonate units of the helvetic alps switzerland and of anglesey u k with the scanning electron microscope in the cathodoluminescence mode the cathodoluminescence spectra measured show systematic variations between older and younger parts of the same fibre and between fibres from different tectonic units these variations can be related first to variations in the temperature of formation of the quartz fibres and second to deformation induced differences in the microstructure of the earlier formed parts of fibres during later imposed strains

cathodoluminescence of quartz from sandstones interpretation of the uv range by determination of trace element distributions and fluid inclusion p t x properties in authigenic quartz quartz overgrowths from keuper sandstones of the paris basin were examined using cathodoluminescence cl microscopy and spectroscopy coupled with a scanning electron microscope sem with the use of standard cold cl equipment it was observed that the emission of authigenic quartz is much less intense than that of detrital quartz grains but a reversal of intensity was observed with scanned cl in the 200 800 nm range the main cl emission band of diagenetic quartz is at 330 340 nm in the uv range with other bands in the visible range the determination of trace element distributions in authigenic quartz by in situ analyses and by sims imagery reveals the correlation of the 330 340 nm emission band with the highest al and li contents the cathodoluminescence emission of diagenetic quartz in the uv range appears to be influenced by the coupled substitution of al and li into the crystal two explanations are suggested 1 ai li or both serve as activators and 2 the incorporation of al and li causes lattice defects that lead to an enhancement of the intrinsic luminescence trace element analyses and fluid inclusion studies revealed that quartz overgrowths precipitated from a fluid that partially originated from an li enriched primary brine derived from eastern triassic evaporites of the paris basin the specific cl emission band in the uv range can be linked to the diagenetic environment the chemistry of the fluids appears to be the essential parameter whereas precipitation temperatures do not influence the occurrence of such emissions

geochemistry of the shuksan greenschists and blueschists north cascades washington variably fractionated and altered metabasalts of oceanic affinity the shuksan schist comprises a structurally coherent metabasaltic member of the easton formation the uppermost allochthon shuksan thrust plate in the thrust system of the western north cascades of washington state late jurassic metamorphism at moderately high p t produced interlayering of actinolite bearing greenschist assemblages with blue amphibole bearing rocks major and trace element analyses of twelve greenschist and blueschist samples have been used to establish similarities between the basaltic protolith and moderately to strongly fractionated type i morb to distinguish the effects of seafloor alteration superimposed on the primary igneous chemistry and to evaluate the origin and nature of the chemical controls which produced the two mineral assemblages

luminescence properties of chert and some archaeological applications we have examined the cathodoluminescence cl and induced thermoluminescence tl properties of chert collected from the ozark mountains area of the central united states the cherts showed predominately orange cl with occasional blue cl x ray diffraction indicates that the amount of orange cl correlates closely with the abundance of carbonates within the chert previous studies have shown that macroquartz characteristically gives off a weak and transient blue cl thermoluminescence studies concentrated on the shape of the radiation induced tl glow curve the results seem to indicate all of the cherts sampled fall into one of four glow curve categories the tl categories correspond to quartz crystallinity as measured by x ray diffraction which is probably a reflection of quartz grain size application of these techniques is somewhat new to chert studies but may provide a useful criterion in establishing the number of chert varieties or sourcing chert provenience locations for artefacts collected from archaeological sites calcite and dolomite are expected to leach from chert surfaces upon exposure to weathering agents thus making cl a helpful tool for the detection of fake stone artefacts with fresh fracture surfaces quartz crystallinity is an important factor in determining chert cleavage characteristics and tl appears to be a useful measure of this property

petrologic structural and age relations of serpentinite amphibolite and blueschist in the shuksan suite of the iron mountain gee point area north cascades washington part of the shuksan blueschist terrane near iron mountain and gee point north cascades washington has associated serpentinite amphibolite barroisite schist blueschist rare eclogite and blackwall type metasomatic rock field petrographic and microprobe observations indicate that the amphibolite and barroisite schists were metamorphosed in contact with peridotite and suggest that the peridotite may have been a heat source the serpentinite and associated rocks are structurally concordant with the regional blueschists and have been overprinted by blueschist metamorphism isotopic dating gives metamorphic ages of 148 5 to 164 6 m y for the amphibolite and barroisite schist and 129 5 m y for nearby regional shuksan blueschists the origin of the serpentinite amphibolite blueschist assemblage is interpreted to be the result of sequential events in a subduction zone as subduction began oceanic crustal materials underwent high temperature metamorphism along the hot ultramafic hanging wall and were converted to amphibolites materials that were subducted later came in contact with a cooler hanging wall and recrystallized as blueschist this hypothesis may be applicable to the origin of similar rock associations in the franciscan terrane and other orogenic belts

structural and metamorphic history of the shuksan metamorphic suite in the mount watson and gee point areas north cascades washington the blueschist facies shuksan metamorphic suite of the north cascades has relict stratigraphy and sediment composition suggesting that it is of oceanic origin broadly defined the first metamorphic event affecting the rocks which probably occurred on the sea floor is a static epidote metasomatism of wide extent the earliest penetrative structures l 1 s 1 formed during latest jurassic early cretaceous blueschist facies metamorphism which is inferred to have occurred during subduction in this event recrystallization and intense penetrative strain were closely linked late metamorphic isoclinal fold axes f 2 and later crenulations l 3 formed at high angles to the l 1 lineation f 2 folds reflect extreme shortening perpendicular to the axis of the shuksan belt microscopic textural relations indicate that ca amphibole not na amphibole was stable during the development of f 2 and suggest that these structures record events related to uplift of the suite l 1 and f 2 structures can be interpreted to indicate either that uplift was the result of a distinct tectonic event or that metamorphism and uplift were part of a continuous tectonic process with no change in the stress field final emplacement of the shuksan suite occurred along a fault system which at least locally is high angle and includes zones of tectonic melange

geochronology of blueschists from west central baja california and the timing of uplift in subduction complexes a geochronologic study of blueschists from west central baja california has provided constraints on the timing of high pressure low temperature metamorphism and the subsequent uplift of this subduction complex mineral separates from coherent blueschists and blueschist blocks enclosed in serpentinite melange were analyzed by 40 ar 39 ar fission track and rb sr methods 40 ar 39 ar age spectra for white mica separated from four blueschist blocks and an overprinted eclogite block in serpentinite matrix melange show slow cooling gradients between 115 95 ma rb sr apparent ages for one block are concordant with these results 40 ar 39 ar ages of blue amphibole are primarily the result of the degassing of white mica intergrowths as confirmed by microprobe analyses apatite fission track ages indicate a blueschist block and an eclogite block cooled to a temperature below 100 c at 22 ma and 32 ma respectively subduction related metamorphism of the coherent blueschists occurred in la

constraints on the thermal and mixing history of lunar surface materials and comparisons with basaltic meteorites we have measured the induced thermoluminescence tl properties of mare basalts highland rocks glasses regolith breccias soils and core samples we also performed a series of heating experiments and made cathodoluminescence cl observations of apollo 16 soils the data are readily interpreted in terms of feldspar being the dominant source of tl and cl the known luminescence properties of feldspar and history of the samples for example the tl sensitivity of the mare basalts is lower than that of the highland basalts by about an order of magnitude probably due to the differing feo content of their feldspars similarly the tl properties of regolith breccias can readily be explained in terms of thermal processes similar to those experienced by the soils and by mixing of highland and mare components our major new observations and interpretations include 1 that there are maturity dependent variations in the tl and cl properties of the core samples which reflect thermal annealing and melting during regolith working 2 that the most primitive material in lunar samples in terms of their thermal histories is located in the immature lunar soils and 3 that there is no tl evidence for widespread long term thermal metamorphism of lunar samples tl being particularly sensitive to low level metamorphism in extraterrestrial materials in this latter respect lunar samples differ from basaltic meteorites which otherwise have very similar properties and histories we argue that this reflects a greater tendency toward thick regoliths on asteroid sized bodies

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

structural geology and accretionary history of the northwest cascades system washington and british columbia pre tertiary rock units on the western flank of the cascades in washington and southern british columbia constitute the northwest cascades system nwcs this litho tectonic package is characterized by predominantly oceanic lithologies subjected to high p t metamorphism and structurally mixed to form a regional melange although the focus of this report is on rocks of the nwcs as originally defined survey of the regional geology suggests broadening of the limits of this system to include the san juan islands the pacific rim complex and pre tertiary rocks on the western flank of the central and southern washington cascades the shuksan metamorphic suite a relatively coherent and broadly exposed unit of the nwcs contains a regionally consistent stretching lineation which provides evidence of east northeast directed underthrusting subduction during the early cretaceous blue schist metamorphism metamorphic f2 folds are approximately normal to the stretching lineation and appear to have developed late in the same deformational event the melange structure postdates the high pressure regional metamorphism it is characterized by a tectonic assemblage of diverse and unrelated rock units occurring as fragments as much as 10 or more kilometres in breadth and separated by a network of low to high angle north northwest striking faults pre fault restoration is impossible argillaceous or serpentinitic material commonly occurs in deformation zones between more competent lithologies mylonite zones as much as several metres thick are widely developed and display stretched clast lineations indicating a north northwest south southeast transport direction for both low and high angle faults the high angle faults are therefore strike slip in nature shear sense indicators are mixed in thrust fault zones but many indicate dextral movement for the strike slip faults k ar whole rock ages of mylonites range from 20 127 ma but two late cretaceous ages of 87 and 91 3 ma are considered as best representing the time of faulting the inferred shift in direction of tectonic transport from east northeast west southwest during early cretaceous metamorphism to north northwest south southeast during late cretaceous faulting and melange formation is correlated with a mid cretaceous change in plate interaction between the north american and farallon kula plates from high to low angle convergence the nwcs melange is interpreted to have formed during large dextral transform motion along the continental margin and to have reached final emplacement by thrusting against the southern end of wrangellia and the coast plutonic complex

the 40ar 39ar geochronology of the pelona schist and related rocks southern california seventeen 40ar 39ar ages for hornblende celadonitic muscovite and biotite from the pelona orocopia rand and portal ridge por schists range from 39 to 85 ma the 85 ma is from portal ridge consistent with the proposed correlation of that body with the schist of sierra de salinas two muscovites and one hornblende from the rand schist have ages of 72 to 74 ma indistinguishable from the k ar age of 74 ma for hornblende from a posttectonic granodiorite that intrudes the schist but younger than the 79 ma u pb age of the intrusion four muscovite and two hornblende ages for schist and mylonite from the east fork area of the san gabriel mountains range from 55 to 61 ma similar to k ar ages from nearby upper plate rocks a third hornblende has an age of 73 ma but is not well constrained concordance of schist and upper plate ages confirms structural and metamorphic evidence that the vincent thrust in the san gabriel mountains has not undergone significant postmetamorphic disruption ages from the orocopia mountains are 75 ma for hornblende from nonmylonitic upper plate 52 ma for muscovite from structurally high orocopia schist that is mylonitic and 41 ma for muscovite from nonmylonitic orocopia schist these are consistent with field evidence that the orocopia thrust is a postmetamorphic normal fault muscovite and hornblende from the gavilan hills have ages of 48 to 50 ma younger than ages from the san gabriel mountains but similar to schist ages from the orocopia mountains the geochronologic and structural complexities of the vincent chocolate mountains orocopia and rand thrusts imply that previously cited northeastward vergence may not relate to prograde metamorphism subduction of the por schists the 40ar 39ar data indicate substantial uplift of the por schists prior to middle tertiary detachment faulting which confirms other geochronologic evidence of uplift in southern california and southern arizona during the late cretaceous early tertiary

oxygen isotope geothermometry and stability of lawsonite and pumpellyite in the shuksan suite north cascades washington metamorphic temperatures of 330 400 c are inferred for rocks from the shuksan blueschist terrane in the north cascades washington the temperatures are calculated from 18o fractionations between coexisting quartz and magnetite using the equations of bottinga and javoy 1973 pressures of approximately 7 kilobars are indicated by the jadeite content of clinopyroxene coexisting with quartz albite published experimental and theoretical studies of the stability of lawsonite and pumpellyite are consistent with the oxygen isotope temperatures and occurrence of these minerals in the shuksan suite

correlation of early cretaceous blueschists in washington oregon and northern california the protolith and metamorphic histories of early cretaceous blueschists that occur in washington oregon and california are remarkably similar these blueschists are the shuksan metamorphic suite of northwestern washington the condrey mountain schist of northern california and southern oregon and the pickett peak terrane of northern california and southwestern oregon we suggest that these bodies were coextensive during their formation dispersion of the blueschists occurred in late cretaceous time by lateral translation of up to 900 km along the continental margin in response to oblique plate convergence

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

arc parallel extension and fluid flow in an ancient accretionary wedge the san juan islands washington structural analysis of the lopez structural complex a major late cretaceous terrane bounding fault zone in the san juan thrust system reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics after formation of regional ductile flattening and shear related fabrics the area was crosscut by brittle structures including 1 southwest vergent thrusts 2 extension veins and normal faults related to northwest southeast extension and 3 conjugate strike slip structures that record northwest southeast extension and northeast southwest shortening aragonite bearing veins are associated with thrust and normal faults but only rarely with strike slip faults high pressure low temperature hp lt minerals constrain the conditions for brittle deformation to 20 km and

correlation of settler schist with darrington phyllite and shuksan greenschist and its tectonic implications coast and cascade mountains british columbia and washington amphibolite facies settler schist in the southeastern coast mountains of british columbia has long been correlated with chiwaukum schist of the cascade metamorphic core north cascade mountains no

imbricate low angle faulting in uppermost franciscan rocks south yolla bolly area northern california the south yolla bolly area of northern california contains the intersection of the franciscan complex the klamath mountains and the great valley sequence four distinct lithic units among them the south fork mountain schist as well as several subunits have been discerned in the franciscan rocks of this area these units are composed mostly of coherent or semi coherent layered sedimentary and mafic igneous rocks and their metamorphic equivalents rather than melange and are arranged in largely upright parallel imbricate fault slices four major low angle faults have been clearly recognized paleontologic data indicate that at least one fault places older material over younger lithic units exhibit various degrees of differences in metamorphic mineral assemblages textural grade and amount of internal deformation across the faults with more intensely deformed and metamorphosed material occupying successively higher structural positions these contrasts indicate that some of these faults served as surfaces by which deformed rocks were emplaced differentially upward during and or after metamorphism original bedding and compositional layering in all of the coherent units generally parallel the thrust faults two fault bounded units are each composed of a coherent sequence of basalt at the base overlain by bedded chert and further overlain by mudstone and graywacke or their metamorphic equivalents the faults which underlie these two sequences seem to have originated as decollements localized at or near a sedimentary rock mafic crust interface perhaps as discrete underthrust slices the distinct contrasts in original rock composition among these units plus the aforementioned characteristics seem to indicate that these faults had an early history in the accretionary prism apart from their later use as convenient surfaces for differential upward emplacement of metamorphosed material

a neogene structural dome in the klamath mountains california and oregon regional structural doming of neogene age has affected rocks of the klamath and cascade mountains near the california oregon border evidence for this is seen in 1 subannular outcrop patterns of pre cretaceous lithotectonic units 2 a crude pattern of radially oriented high angle faults 3 tilted jurassic plutons 4 tilted cretaceous to miocene strata and 5 various geomorphological features the age of doming is constrained by a major middle miocene to earliest pliocene angular unconformity within the cascade mountains and uplifted upper miocene marine beds on the western edge of the klamath mountains uplift and doming may be the result of shortening in the cascade fore arc region or more speculatively the recent accretion of subducted material to the north american plate beneath the klamath mountains

major right lateral faulting in the franciscan assemblage of northern california in late tertiary time a minimum of 75 km of right lateral fault displacement occurred within the franciscan assemblage of northern california most likely in late tertiary time this displacement is inferred from the present position of two geologically unrelated units the rocks near black lassie california and the redwood creek schist the black lassie rocks show at least 75 km of northward displacement from their source terrane within the coast range ophiolite although no conclusive evidence of northward transport for the redwood creek schist is available the geologic setting of the schist and the nature of the faults that bound it strongly suggest that the redwood creek schist has also been laterally transported many tens of kilometres northward we propose that both these units moved northward by means of one or a few major north northwest trending right lateral faults that were active in the forearc basin off the california coast during right oblique subduction of the farallon plate under the north american plate in late tertiary time

deformational history and regional tectonic significance of the redwood creek schist northwestern california structural petrologic and geochemical data support the correlation of the redwood creek schist of northwesternmost california with the south fork mountain schist of northern california and the colebrooke schist of southwestern oregon metamorphism to lawsonite albite chlorite facies and development of secondary structures recording two penetrative deformations are shared by all three units a later deformational event recorded by the redwood creek schist but absent in the south fork mountain schist consists of differential rotation of domains several kilometres in size within the schist belt this deformation is significant because it records an event that occurred after the separation of the schist bodies the rotation most probably occurred in conjunction with northward strike slip movement of the redwood creek schist

evidence of multiple thermokarst events in northeastern france and southern belgium during the two last glaciations a discussion on features caused by ground ice growth and decay in late pleistocene fluvial deposits paris basin france bertran et al 2018 abstract the past thermokarst activities in valleys of northern france and belgium covered the upper weichselian and the upper saalian periods to develop in western europe thermokarst first requires an accumulation of ground ice close to the surface progressively stored along the glacial time permafrost aggradation it is regionally uncommon during the early glacials especially on the plateau but frequent during the upper pleniglacials in valleys these features mostly relate to various frost mounds created by injection and segregated ices the role of ice wedges is really very limited in this zone of southern extent of the european palaeo permafrost on plateau and terraces thermokarst events are mostly susceptible to occur during the coldest part of the glacial with a more progressive warming or a retrogressive thermokarst triggered by erosion as in arctic today deformations are more gradual in direct relation with the rheological properties of the sediments and usually local drainage they are in concurrence with the vegetation dynamic that will limit its expression thermokarst events are in first order orbitally forced under control of a maximum insolation and a minimum in precession as well as during the weichselian and the saalian they are moreover associated with abrupt warming transmitted by dansgaerd oeschger events snowiness and mild winter temperatures are probably the main triggers for thermokarst activity as of today other events can be triggered by solar activity as at 20 ka or perhaps enhanced by major ash splay as during the mis 6b zeiffen interstadial thermokarst events are usually followed on the continent by a reorganization of the rivers from braided to meandering systems