active strike slip faulting in el salvador central america several major earthquakes have affected el salvador central america during the past 100 yr as a consequence of oblique subduction of the cocos plate under the caribbean plate which is partitioned between trench orthogonal compression and strike slip deformation parallel to the volcanic arc focal mechanisms and the distribution of the most destructive earthquakes together with geomorphologic evidence suggest that this transcurrent component of motion may be accommodated by a major strike slip fault el salvador fault zone we present field geological structural and geomorphological data collected in central el salvador that allow the constraint of the kinematics and the quaternary activity of this major seismogenic strike slip fault system data suggest that the el salvador fault zone consists of at least two main e w fault segments san vicente and berlin segments with associated secondary synthetic wnw ese and antithetic nnw sse riedel shears and nw se tensional structures the two main fault segments overlap in a dextral en echelon style with the formation of an intervening pull apart basin our original geological and geomorphologic data suggest a late pleistocene holocene slip rate of 11 mm yr along the berlin segment in contrast with low historical seismicity the kinematics and rates of deformation suggested by our new data are consistent with models involving slip partitioning during oblique subduction and support the notion that a trench parallel component of motion between the caribbean and cocos plates is concentrated along e w dextral strike slip faults parallel to the volcanic arc

was deep water formed in the north pacific during the late quaternary cadmium evidence from the northwest pacific abstract a benthic foraminifera cd ca record dating from the last glacial period to the holocene for a high sedimentation rate core recovered from the northwest pacific is reported it shows that the deep water water depth of 2700 m cadmium concentration was about 50 lower in the last glacial period than in the holocene at 15 kyr b p the beginning of deglaciation a minimum cd ca is recorded which is almost the same as that of the modern north atlantic considering previously obtained cadmium records from the northwesternmost and western equatorial pacific a steep gradient in the deep water cadmium concentration between the western equatorial pacific and the northwest pacific from the last glacial to deglacial periods has been estimated in contrast to cadmium records benthic foraminifera 13 c records in these regions showed similar increasing trends during this time span and no large difference in 13 c can be observed between these two regions this discordance between these two nutrient tracers may come from the change in the 13 c phosphate relationship in the ocean during the late quaternary although we cannot absolutely rule out other possibilities we suggest that there was a convection cell in the northwest pacific during the last glacial period and at the beginning of deglaciation period the turnover rate of this cell increased and cadmium concentration in the northwest pacific significantly decreased

estimates of modern arc parallel strain rates in fore arcs deflections of slip vectors of interplate thrust earthquakes from expected directions are used to estimate arc parallel strain rates within the overriding plates at the world9s major convergent plate margins arc parallel extension strain rates between 10 8 yr and 10 7 yr and significant at 2 standard deviations are observed in the fore arcs of the aegean aleutian mariana sumatran southern kuriles new hebrides scotia and southern central american lat 8 to 12 n subduction zones and the himalayas northern chile lat 17 to 31 s and central america lat 11 to 18 n show arc parallel compression available geologic and geodetic estimates of fore arc slip and strain rates agree within a factor of two with slip vector estimates arc parallel strain in fore arcs is rapid enough to produce geologically significant effects such as unroofing of high grade metamorphic rocks and disruption of transported fore arc terranes fore arcs deform even where convergence is perpendicular to curved margins demonstrating that head on subduction can produce a three dimensional strain field

zeolites in fissures of granites and gneisses of the central alps six different ca zeolite minerals are widespread in various assemblages in late fissures and fractures in granites and gneisses of the swiss alps the zeolites formed as a result of water rock interaction at relatively low temperatures 250 c in the continental upper crust the zeolites typically overgrow earlier minerals of the fissure assemblages but zeolites also occur as monomineralic fissure fillings they represent the youngest fissure minerals formed during uplift and exhumation of the alpine orogen a systematic study of zeolite samples showed that the majority of finds originate from three regions particularity rich in zeolite bearing fissures i in the central and eastern part of the aar and gotthard massifs 2 gibelsbach fiesch in a fissure breccia located at the boundary of aar massif and permian sedimentary rocks and 3 in penninic gneisses of the simano nappe at arvigo val calanca rail and road tunnel construction across the aar and gotthard massif provided excellent data on zeolite frequency in alpine fissures it was found that 32 gotthard neat rail base tunnel amsteg section and 18 gotthard road tunnel of all studied fissures are filled with zeolites the number of different zeolites is limited to six species laumontite stilbite and scolecite are abundant and common whereas heulandite chabazite and epistilbite occur occasionally calcium is the dominant extra framework cation with minor k and na heulandite and chabazite contain sr up to 29 and 10 mol extra framework cations respectively na and k contents in zeolites tend to increase during growth as a result of changes in fluid composition and or temperature the k enrichment of stilbite found in surface outcrops compared to subsurface samples may indicate late stage cation exchange with surface water texture data relative age sequences derived from fissure assemblages and equilibrium calculations show that the ca dominated zeolites precipitated from fluid with decreasing temperature in the order old to young hot to cold scolecite laumontite heulandite chabazite and stilbite the necessary components for zeolite formation are derived from dissolving primary granite and gneiss minerals the nature of these minerals depends among other factors on the metamorphic history of the host rock zeolites in the aar massif derived from the dissolution of epidote secondary calcite and albite that were originally formed during alpine greenschist metamorphism from primary granite and gneiss assemblages zeolite fissures occur in areas of h2o dominated fluids this is consistent with equilibrium calculations that predict a low co2 tolerance of zeolite assemblages particularly at low temperature

fracture controlled magma conduits in an obliquely convergent continental magmatic arc magnetic fabric patterns of two mid cretaceous nested plutons 102 1 and 96 3 ma in the central sierra nevada batholith provide evidence that felsic magma emplacement and ascent occurred via north trending steeply dipping planar fracture conduits oriented obliquely to the arc u pb geochronology data indicate that emplacement of the plutons was separated by 2 to 10 m y and that they were emplaced in part via the same conduit magnetic fabrics in the younger pluton are related to its final emplacement which was strongly influenced by a system of host rock joints formation of the north trending conduits at 100 ma can be related to a small arc parallel dextral shear component that produced tension fractures and that was associated with high angle oblique convergence by 90 ma convergence had become sufficiently oblique for the development of nearly arc parallel structures which were then favored as magma conduits

deglacial climatic oscillations in the gulf of california a high resolution accelerator radiocarbon dated climate record of the interval 8 000 18 000 years b p from deep sea drilling project site 480 guaymas basin gulf of california shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation nonlaminated sediments are associated with cooler climatic conditions during the late glacial up to 13 000 years b p and from 10 300 to 10 800 years b p equivalent to the younger dryas event of the north atlantic region we propose that the changes from laminated varved to nonlaminated sediments resulted from increased oxygen content in pacific intermediate waters during the glacial and the younger dryas episodes and that the forcing for the latter event was global in scope prominent events of low 18o are recorded in benthic foraminifera from 8 000 to 10 000 and at 12 000 years b p evidence for an earlier event between 13 500 and 15 000 years b p is weaker maximum 18o is found to have occurred 10 500 13 500 and 15 000 years ago and beyond oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of pacific waters of intermediate depth during deglaciation or environmental changes within the gulf of california region several lines of evidence suggest that during deglaciation the climate of the american southwest was marked by increased precipitation that could have lowered salinity in the gulf of california recent modelling studies show that cooling of the gulf of mexico due to glacial meltwater injection which is believed to have occurred at least twice during deglaciation would have resulted in increased precipitation with respect to evaporation in the american southwest during summertime the timing of deglacial events in the gulf of mexico and the gulf of california supports such an atmospheric teleconnection

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

neotectonic deformation within an extensional stepover in el salvador magmatic arc central america implication for the interaction of arc magmatism and deformation abstract dominantly westward movement of the el salvador forearc at rates of 11 mm yr is accommodated by a series of e w to wnw oriented dextral strike slip fault zones herein referred to as the el salvador fault system esfs the geometry of the esfs defines a series of extensional step overs along the arc basaltic volcanism in the stepovers is associated with nnw oriented normal faults whereas rhyolitic volcanism is associated with strike slip fault zones of the esfs on the esfs the san salvador extensional stepover sses is bound to the south by the san vicente fault zone where the rhyolitic ilopango caldera is located in the sses tephras from ilopango the tierra blanca tb sequence track long term elongation older tb units tb5 8 contain abundant normal faults lying unconformably above these older tb units younger tb members tbj tb2 4 are generally unfaulted analyses of faults in tb5 8 indicate ne to ene oriented elongation in the sses deformation occurred between deposition of the tb4 and tb5 units during quiescence of the ilopango eruptive center using this temporal constraint minimum elongation rates of 3 50 10 15 s 1 2 06 10 14 s 1 and 4 42 10 14 s 1 were calculated for three traverses from regional geodetic data and fault kinematics throughout el salvador we interpret the sses as part of a series of pull apart structures along the arc axis the calculated paleostress orientations are consistent with a pull apart geometry resulting from forearc movement the extensional deformation occurs during a 50 k y lull in rhyolitic activity suggesting an interplay between magmatism and deformation within the arc during significant rhyolitic volcanic activity only minor elongation is observed in the sses despite ongoing translation of the salvadoran forearc we speculate that rhyolitic magmatism along upper crustal faults may facilitate strike slip movement on the esfs rather than distributing deformation throughout the extensional stepover

fluid transfers at a basement cover interface part ii large scale introduction of chlorine into the basement by mesozoic basinal brines significant fracture and porosity sealing characterizes the sedimentary cover basement interface in the northwestern margin of the aquitaine basin france dolomite and calcite and sometimes fluorite barite and quartz constitute most of the fracture fillings they contain primary inclusions of brines having chlorinities in the range of 3 3 to 5 5 mol cl kg solution with total homogenization temperatures in between 65 and 130 c for quartz and slightly lower for dolomite barite fluorite and calcite crush leach analyses indicate that brines are characterized by na k ratios of 5 to 40 na li ratios of 20 to 530 and cl br ratios of 200 to 1000 which are rather typical of deep basinal brines the fluid 18o signature is estimated to be 6 6 1 8 smow for a crystallization temperature of 100 20 c between 80 and 120 c and the d value is 30 10 smow the fluid source for the fracture filling mineral is interpreted as a deep sedimentary brine expelled during a period of maximum subsidence in the aquitaine basin which migrated along the sediment cover basement interface which is characterized by high permeabilities below the toarcian shales the sealing is likely to be linked to the mixing of the brines with dilute ascending hot waters these dilute waters infiltrated from emerged zones convected and heated at depth reaching temperatures of 100 c up to 150 c on the basis of cation geothermometry extensional activity of probable cretaceous age related to the gascogne gulf rifting could be considered as the most likely cause of a significant fluid migration event at the basement cover interface all along the margins of the french massif central these processes are large scale as shown by the similarities of mineral sequences fluid types and general features of most of the f ba pb zn deposits located at the basement sedimentary cover interface the mass transfer of cl linked to this stage is significant and accounts for the early introduction of large amounts of chlorine in the granitoid microporosity this probably explains the significant chlorine concentrations of the present day fluids recovered in the granitoid aquifer

analysis of fault slip inversions do they constrain stress or strain rate fault slip data commonly are used to infer the orientations and relative magnitudes of either the principal stresses or the principal strain rates which are not necessarily parallel or equal at the local scale of an individual fault the shear plane and slip direction define the orientations of the local principal strain rate axes but not in general the local principal stress axes at a large scale the orientations of p and t axes maxima for sets of fault slip data do not provide accurate inversion solutions for either strain rate or stress the quantitative inversion of such fault slip data however provides direct constraints on the orientations and relative magnitudes of the global principal strain rates to interpret the inversion solution as constraining the global principal stresses requires that 1 the fault slip pattern must have a characteristic symmetry no lower than orthorhombic 2 the material must be mechanically isotropic and 3 there must be a linear constitutive relationship between the global stress and the global strain rate isotropic linear elastic constitutive equations are appropriate to describe the local deformation surrounding an individual slip discontinuity fault slip inversions however constrain the characteristics of a large scale cataclastic flow which is described by constitutive equations that are probably but to an unknown degree anisotropic and nonlinear such material behavior would not strictly satisfy the requirements for the stress interpretation thus at the present state of knowledge fault slip inversion solutions are most reliably interpreted as constraining the principal strain rates

paleoenvironmental changes in the japan sea during the last 85 000 years five distinct changes in the paleoenvironment of the japan sea within the last 85 000 years are revealed from the sedimentary record of a piston core recovered from the oki ridge changes in both surface and deepwater conditions are registered by changes in lithology calcium carbonate content organic carbon content oxygen and carbon isotope ratios and microfossil assemblages including calcareous nannoplankton diatoms radiolaria and foraminifera between 85 and 27 ka the warm tsushima current did not flow into the japan sea and cold surface water conditions prevailed environments at the seafloor fluctuated between dysaerobic to weakly oxic conditions between 27 and 20 ka freshwater input to the japan sea probably from the huang ho river in china stratified the water column and the severe anoxic conditions eliminated most benthic fauna between 20 and 10 ka the cold oyashio current flowed into the japan sea through the tsugaru strait reestablishing deepwater ventilation shallow water benthic assemblages of the north pacific ocean subsequently colonized the japan sea and occupied the vacant niches of the deep basins between 10 and 8 ka the foraminifer compensation level fcl gradually rose to a depth shallower than 1000 m and bottom conditions changed from dysaerobic to oxic at 10 ka the warm tsushima current started to flow into the japan sea through the tsushima strait to establish the modern oceanographic regime which has existed since 8 ka the eustatic sea level during the last glacial maximum was above the sill depths 130 m of the tsushima and tsugaru straits assuming that tectonic movements at these straits were negligible for the last 20 ka

pacific offshore record of plinian arc volcanism in central america 2 tephra volumes and erupted masses 1 sediment gravity cores collected from the pacific seafloor offshore central america contain numerous distal ash layers from plinian type eruptions at the central american volcanic arc dating back to more than 200 ka in part 1 of this contribution we have correlated many of those ash layers between cores and with 26 tephras on land the marine ash layers cover areas of up to 106 km2 in the pacific ocean and represent a major fraction 60 90 of the erupted tephra volumes because the pacific coast lies within a few tens of kilometers downwind from the volcanic arc combining our own mapping efforts on land and published mapping results with our marine data yields erupted volumes of all major tephras along the arc that range from 1 to 420 km3 recalculated to erupted magma mass the widespread tephras account for 65 of the total magma output at the arc complementing our tephra data with published volumes of the arc volcanic edifices and volcano ages we calculate the long term average magma eruption rates for each volcano moreover we use incompatible element variations to calculate the cumulate masses that were fractionated during variable degrees of differentiation this yields a minimum estimate of long term average magma production rate at each volcano because intrusives without surface expression and losses by erosion are not accounted for peak magma production rates increase from costa rica to guatemala but there is considerable scatter within each region and large differences even between neighboring volcanoes

fore arc motion and cocos ridge collision in central america 1 we present the first regional surface velocity field for central america showing crustal response to interaction of the cocos and caribbean plates elastic half space models for interseismic strain accumulation on the dipping subduction plate boundary fit the gps data well and show strain accumulation offshore and beneath the nicoya and osa peninsulas in costa rica but not in nicaragua since large subduction zone earthquakes occur in nicaragua we suggest that interseismic locking in nicaragua and some other parts of central america occurs but is mainly shallow 20 km depth too far offshore to be detected by our on land gps measurements our data also show significant trench parallel motion for most of the region generally interpreted as due to oblique convergence and strong mechanical coupling between subducting and overriding plates however trench parallel motion is also observed in central costa rica where plate convergence is normal to the trench and in the nicaraguan fore arc where trench parallel motion is fast up to 9 mm a 1 but mechanical coupling is low a finite element model of collision as opposed to subduction involving the aseismic cocos ridge also fits the gps surface velocity field most significantly reproducing the pattern of trench parallel motion we infer that buoyant thickened cns 2 cocos ridge crust resists normal subduction and instead acts as an indenter to the caribbean plate driving crustal shortening in southern costa rica and contributing to trench parallel fore arc motion in costa rica and perhaps nicaragua as a type of tectonic escape

magma assisted strain localization in an orogen parallel transcurrent shear zone of southern brazil in a lithospheric scale orogen parallel transcurrent shear zone of the pan african dom feliciano belt of southern brazil two successive generations of magmas an early calc alkaline and a late peraluminous have been emplaced during deformation microstructures show that these granitoids experienced a progressive deformation from magmatic to solid state under decreasing temperature conditions magmatic deformation is indicated by the coexistence of aligned k feldspar plagioclase micas and or tourmaline with undeformed quartz submagmatic deformation is characterized by strain features such as fractures lattice bending or replacement reactions affecting only the early crystallized phases high temperature solid state deformation is characterized by extensive grain boundary migration in quartz myrmekitic k feldspar replacement and dynamic recrystallization of both k feldspar and plagioclase decreasing temperature during solid state deformation is inferred from changes in quartz crystallographic fabrics decrease in grain size of recrystallized feldspars and lower ti amount in recrystallized biotites final low temperature deformation is characterized by feldspar replacement by micas the geochemical evolution of the synkinematic magmatism from calc alkaline metaluminous granodiorites with intermediate 87sr 86sr initial ratio to peraluminous granites with very high 87sr 86sr initial ratio suggests an early lower crustal source or a mixed mantle crustal source followed by a middle to upper crustal source for the melts shearing in lithospheric faults may induce partial melting in the lower crust by shear heating in the upper mantle but whatever the process initiating partial melting lithospheric transcurrent shear zones may collect melt at different depths because they enhance the vertical permeability of the crust these zones may then act as heat conductors by advection promoting an upward propagation of partial melting in the crust synkinematic granitoids localize most if not all deformation in the studied shear zone the regional continuity and the pervasive character of the magmatic fabric in the various synkinematic granitic bodies consistently displaying similar plane and direction of flow argue for accommodation of large amounts of orogen parallel movement by viscous deformation of these magmas moreover activation of high temperature deformation mechanisms probably allowed a much easier deformation of the hot synkinematic granites than of the colder country rock and consequently contributed significantly to the localization of deformation finally the small extent of the low temperature deformation suggests that the strike slip deformation ended approximately synchronously with the final cooling of the peraluminous granites the evolution of the deformation reflects the strong influence of synkinematic magma emplacement and subsequent cooling on the thermomechanical evolution of the shear zone magma intrusion in an orogen scale transcurrent shear zone deeply modifies the rheological behavior of the continental crust it triggers an efficient thermomechanical softening localized within the fault that may subsist long enough for large displacements to be accommodated therefore the close association of deformation and synkinematic magmatism probably represents an important factor controlling the mechanical response of continental plates in collisional environments

a younger dryas icecap in the equatorial andes abstract morphologic and stratigraphic evidence shows that a late glacial ice cap existed on part of the eastern cordillera of ecuador lat 0 20 s on ground with a mean elevation of 4200 m where none exists now an outlet glacier from an ca 800 km 2 ice cap terminated at 3850 m altitude in the papallacta valley on the eastern side of the plateau radiocarbon dates show that moraines formed by this advance were ice free by 13 200 14 c yr b p tephras and the age of organic deposits at the plateau edge indicate ice free conditions before 11 800 14 c yr b p this interval was followed by the expansion of an ca 140 km 2 ice cap that discharged glaciers into adjacent valleys where terminal moraines were built at 3950 m altitude ams and conventional radiocarbon dates from macrofossils peat and gyttja above and below till of the readvance indicate that the ice cap formed between ca 11 000 and 10 000 14 c yr b p and was thus coeval with the european younger dryas event the ice cap developed in response to a surface temperature cooling of at least 3 c in the tropical andes a finding that is consistent with a coupled equatorial high latitude north atlantic climate system operating at the late glacial holocene transition these results are further evidence that younger dryas cooling may have been a global event

evidence for a role of the downgoing slab in earthquake slip partitioning at oblique subduction zones a new model incorporating shear deformation within a subducting slab is proposed to explain slip partitioning for oblique plate motion at subduction zones on the basis of investigation of 450 interplate earthquakes at 24 subduction zone segments we find that the degree of slip partitioning is largely correlated with the calculated slab pull force such correlation suggests that other than the upper plate deformation the slab pull force plays an important role in controlling oblique subduction our model proposes that the force balance between the slab pull force the interplate coupling resistance and the viscous mantle drag the latter two are passive forces to the former one produces a lateral shear within the slab which causes the slab to deform and change its motion direction gradually toward trench normal as it subducts the amount of direction change which would be observed as the slip partitioning during earthquakes therefore is closely related to the major plate driving force at the subduction zone which is the slab pull force in our model

crustal scale en echelon p shear tensional bridges a possible solution to the batholithic room problem the apparent paradox of voluminous granitoid emplacement in an overall compressional magmatic are has been somewhat alleviated by the idea of pluton emplacement in tension cracks and dilational jogs within arc parallel strike slip fault systems as an alternative hypothesis we propose that an en echelon p shear array provides a continuous batholith scale zone of dilation along the trend of active magmatism and that it is favored by transpressional tectonics in the sierra nevada california the late cretaceous granitoids of the cathedral range intrusive epoch are consistent with emplacement into bridges between p shears because 1 they are elongated oblique to the magmatic trend consistent with p shear orientation within a dextral system 2 they were all emplaced within 5 10 m y along a 300 km trend resulting in a displacement rate of 1 cm yr across the arc and 3 syn to late magmatic dextral shear zones bound and crosscut the plutons as in a p shear tensional bridge

late variscan magmatism revisited new implications from pb evaporation zircon ages on the emplacement of redwitzites and granites in ne bavaria pb evaporation zircon analyses coupled with a detailed cathodoluminescence cl study on the complete series of granitoids from the northern oberpfalz ne bavaria provide new evidence for the commencement and timing of late variscan magmatism all granitoids analysed in this study were dated before by rb sr and or k ar methods investigated samples comprise medium grained i type dioritic rocks redwitzites i s type granites leuchtenberg marktredwitz g1 zainhammer and s type granites falkenberg liebenstein mitterteich friedenfels steinwald flossenburg barnau the zircon evaporation technique reveals three groups of 207pb 206pb ages which are interpreted to represent magmatic crystallisation 1 ages of 324 321 ma are found in all analysed redwitzites and in almost all i s type granites 2 the granites of falkenberg and liebenstein yield ages of 315 ma 3 ages between 312 and 310 ma are recorded in the mitterteich friedenfels steinwald and flossenburg granites titanite crystals from different redwitzite bodies yield conventional u pb ages of 325 322 ma identical to the pb evaporation zircon data of these rocks the s type granites of groups 2 and 3 contain zircons with relict cores but only a small number of them yield older ages indicating that some of the cores must have lost their radiogenic pb from the geochronological data we infer that metamorphic conditions of the variscan crust produced different granite types at different times the data support a model involving an early period of mantle related magmatism which postdates the final convergence stage of the variscan orogen this magmatic activity was at the same time as the thermal peak of regional metamorphism and is followed by a late period of crustal anatexis which is probably related to post collisional extension of the thickened variscan crust

secondary ca al silicates in plutonic rocks implications for their cooling history secondary ca al silicates are used to constrain the p t x conditions of the very early post magmatic stage of the intermediate to basic hercynian plutonic complexes of charroux civray nw massif central france and fichtelgebirge ne bavaria germany the secondary ca al silicates hydrogarnet prehnite pumpellyite epidote and laumontite form lenses within unaltered or only slightly chloritized biotite hydrogarnet as the first occurring ca al silicate phase crystallizes at temperatures above 340 c the common paragenesis prehnite pumpellyite post dates hydrogarnet and indicates rather narrow ranges of temperature 200 280 c and pressure 2 3 kbar laumontite is formed at the end of ca al silicate crystallization 180 260 c 1 3 kbar mostly in small fractures in association with prehnite and adularia the observed crystallization sequence of the ca al silicates and their stabilities define a retrograde alteration path for the plutonic rocks the ca al silicate assemblage results from an early pervasive alteration of the plutonic rocks by low xco2 fluids during post magmatic cooling subsolidus cooling starts at about 4 kbar at solidus temperatures as indicated by magmatic epidote stability hornblende barometry and fluid inclusion data and continues under slightly decreasing pressure uplift down to 2 3 kbar at 200 280 c prehnite pumpellyite paragenesis this shows that ca al silicate assemblages may be a unique tool to constrain the p t conditions of the subsolidus cooling of intermediate to basic plutonic bodies

dioritic intrusions of the slavkovský les kaiserwald western bohemia their origin and significance in late variscan granitoid magmatism mafic and intermediate intrusions occur in the slavkovsk les as dykes sills and minor tabular bodies emplaced in metamorphic rocks or enclosed in late variscan granites near the sw contact of the western krusne hory erzgebirge granite pluton they are similar in composition and textures to the redwitzites defined in ne bavaria single zircon pb evaporation analyses constrain the age of a quartz monzodiorite at 323 4 4 4 ma and of a granodiorite at 326 1 5 6 ma the p t range of magma crystallization is estimated at 1 4 2 2 kbar and 730 870 c and it accords with a shallow intrusion level of late variscan granites but provides lower crystallization temperatures compared to the bavarian redwitzites we explain the heterogeneous composition of dioritic intrusions in the slavkovsk les by mixing between mafic and felsic magmas with a minor effect of fractional crystallization increased k ba rb sr and ree contents compared to tholeiitic basalts suggest that the parental mafic magma was probably produced by melting of a metasomatised mantle the melts being close to lamprophyre or alkali basalt composition diorites and granodiorites originated from mixed magmas derived by addition of about 25 35 and 50 vol respectively of the acid end member granite to lamprophyre or alkali basalt magma our data stress an important role of mafic magmas in the origin of late variscan granitoids in nw bohemian massif and emphasize the effect of mantle metasomatism on the origin of k rich mafic igneous rocks

estimates of strain due to brittle faulting sampling of fault populations abstract the geometry of sampling domains is a first order consideration in the characterization of brittle fault populations in most cases descriptions of fault size distributions based on map cross section traverse or borehole data systematically underestimate the number of small faults present in a volume the geometry of sampling domains may be accounted for using an empirical proportionality between fault displacement and trace length estimates of strain in which the sampling geometry is considered suggest that small faults accommodate a significant portion of the total strain due to the brittle faulting process

the caribbean north america cocos triple junction and the dynamics of the polochic motagua fault systems pull up and zipper models the polochic motagua fault systems pmfs are part of the sinistral transform boundary between the north american and caribbean plates to the west these systems interact with the subduction zone of the cocos plate forming a subduction subduction transform triple junction the north american plate moves westward relative to the caribbean plate this movement does not affect the geometry of the subducted cocos plate which implies that deformation is accommodated entirely in the two overriding plates structural data fault kinematic analysis and geomorphic observations provide new elements that help to understand the late cenozoic evolution of this triple junction in the miocene extension and shortening occurred south and north of the motagua fault respectively this strain regime migrated northward to the polochic fault after the late miocene this shift is interpreted as a pull up of north american blocks into the caribbean realm to the west the pmfs interact with a trench parallel fault zone that links the tonala fault to the jalpatagua fault these faults bound a fore arc sliver that is shared by the two overriding plates we propose that the dextral jalpatagua fault merges with the sinistral pmfs leaving behind a suturing structure the tonala fault this tectonic zipper allows the migration of the triple junction as a result the fore arc sliver comes into contact with the north american plate and helps to maintain a linear subduction zone along the trailing edge of the caribbean plate all these processes currently make the triple junction increasingly diffuse as it propagates eastward and inland within both overriding plates

constraints from finite element modeling on the active tectonics of northern central america and the middle america trench 1 we have developed an elastic finite element model in order to study the role of the different forces acting on the northwestern part of the central american volcanic arc and the chortis block we present synthetic focal mechanisms maps of tectonic regime and strain crosses to analyze the results the models show that to achieve the observed state of stress on the volcanic arc the arc must be modeled as a lithospheric weak zone also the forces related to the eastward drift of the caribbean plate must be higher than those related to the subduction of the cocos plate the coupling on the subduction interface must be low with or without slip partitioning due to the obliquity of the subduction at the trench at guatemala the western edge of the chortis block is pinned against north america even with low trench normal forces making the triple junction between the cocos north american and caribbean plates a zone of diffuse deformation the extension in the western part of the chortis block from guatemala to the honduras depression is explained by the geometry of the north american caribbean plate boundary and the direction of motion of the caribbean plate with respect to north america the direction of extension in the chortis block is always e w regardless of the magnitude of the applied forces and the main part of the deformation is absorbed between the ipala graben and the honduras depression both features being consistent with our models

dating multistage paleofluid percolations a k ar and 18o 16o study of fracture illites from altered hercynian plutonites at the basement cover interface poitou high france isotopic age determination of fluid events in basement fractures is of prime importance for the reconstruction of paleo hydraulic regimes however material from fracture or wall rock is not generally easily dated in the case of fractures filled by minerals such as phyllosilicates it can be expected that subsequent fluid circulation may cause partial alteration or recrystallization of the previous phyllosilicates disturbing the isotope signature using a specific methodology including the extraction process without contamination of the finest 0 2 m authigenic fractions identification of clay fractions by x ray diffraction xrd scanning electron microscopy and electron microprobe analysis of stable isotope composition d h 18o and k ar dating fluid event ages can be estimated this methodology was applied to the northwestern margin of the french massif central where basinal brines have interacted with the sedimentary cover infra toarcian formations and the fractured hercynian crystalline basement during periods of unknown age precipitates from brines sealed most basement fractures as carbonates and a recrystallization of early hercynian phengite chlorite into illite and illite smectite minerals occurred in the earlier fractures xrd patterns show that the clay fraction is dominated by illite and ordered mixed layer minerals having a relatively high amount of illite i s r3 in the shallowest samples beneath the paleo surface a late assemblage is identified as a mixture of i s minerals a part of them being characterized by significant amounts of swelling layers i s r0 the d values of the clay fractions are fairly constant around 50 10 but 18o values of the same clay fractions display a wide range from 8 to 18 smow the study of the size fractions between 2 and 0 2 m reveals a correlation between k ar ages and 18o values which cannot be related to a change in the relative amounts of clay minerals deep fractures at depths of 570 and 923 m are characterized by 18o values around 10 3 0 4 smow and old ages ranging from 253 to 272 ma the finest fractions 0 2 m of clays located at shallow level 300 m beneath the paleo surface yield the highest 18o values 15 7 18 2 and the youngest k ar dates 188 to 198 ma these dates are likely to record the extensional episode and thermal anomaly related to the rifting of central atlantic ocean c 190 ma the other important thermal extensional episode which affected the aquitaine basin namely the opening of the gascogne gulf at c 120 ma is not detected by the k ar method on the clay fractions we believe that resetting of clay type k ar ages linked to recrystallization was favoured in the upper part of the basement where the ancient hercynian clay minerals were destabilized by subaerial low temperature alteration during permo triassic times from a methodologic point of view the analytical characterization of several size fractions of clays from reactivated fractures using both stable isotope geochemistry and k ar isotope geochemistry can be considered as a powerful tool for dating fluid events when no suitable material for conventional methods is available

constraints for the recent tectonics of the el salvador fault zone central america volcanic arc from morphotectonic analysis abstract we have used hypsometric analysis to improve our understanding of the current tectonic deformation and structure of el salvador fault zone a n90 e oriented strike slip fault zone that extends 150 km through el salvador central america our results indicate an important amount of transtensive strain along this fault zone providing new data to understand the tectonic evolution of the salvadorian volcanic arc we have defined kilometric scale tectonic blocks and its relative vertical movements length of segments with homogeneous vertical motions and lateral relay of active structures we have identified and quantified slip rate variations along strike of the el triunfo fault within el salvador fault zone ranging from 4 6 mm year in its central parts to 1 mm year towards the tips of the fault this study supports the hypothesis of a recent rotation in the maximum shortening direction and the accommodation of the current deformation through the reactivation of pre existing structures inherited from a previous tectonic regime

mass transfer and porosity evolution during low temperature water rock interaction in gneisses of the simano nappe arvigo val calanca swiss alps late alpine fissures and fractures in amphibolite facies basement gneisses at arvigo val calanca swiss alps show distinct cm sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high grade gneiss assemblages the process of selvage or reaction vein formation occurred in the brittle deformation regime and at temperatures characteristic of first the prehnite pumpellyite facies and then later of the zeolite facies the vein formation occurred during uplift and cooling at very late stages of the alpine orogeny the reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space the central zone of the arvigo veins contains an early assemblage with epidote prehnite and chlorite and a late succession sequence of various species of zeolite the veins of the arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate ca zeolite this is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of ca zeolite species vein formation during late uplift and cooling of the alps occurred at continuously decreasing t and at hydrostatic pressure 1 coexisting prehnite epidote records temperatures of 330 380 c 2 chlorite formation at temperature of 333 32 c and 3 formation of zeolites 250 c in the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss in addition to albitisation chloritisation of biotite is the second important reaction in the alteration process the reactions release components for the formation of ca al silicates the water rock interaction is associated with a depletion of al si ca fe and k in the altered wall rock the overall reaction is associated with an increase in porosity of up to 14 2 2 2 in the selvage zone altered wall rock caused by the volume decrease during albitisation and the removal of biotite the propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution reprecipitation mechanism zeolite formation is tied to the plagioclase alteration reaction in the rock matrix which releases components for zeolite formation to a co2 poor aqueous liquid

transpressional tectonics and carboniferous magmatism in the limousin massif central france structural and 40ar 39ar investigations new structural microstructural and 40ar 39ar data from the nw massif central france provide additional constraints on the timing and tectonic setting of late variscan granite magmatism previous studies had emphasized the role of late orogenic extension in the emplacement of granite plutons in the limousin region in contrast the new data set is consistent with syntectonic emplacement of magma in a dextral simple shear active from 350 to 300 ma in a transpressional regime as an alternative hypothesis to late orogenic extension we propose that magmas migrated into tensional bridges between active p shears associated with a lithospheric shear zone comparable to a pop up structure the galician region in the western end of the ibero armorican tectonic arc exhibits major left lateral ductile shear zones which can be interpreted as conjugate structures to the limousin and armorican shear zones citation ge belin a m brunel p monie m faure and n arnaud 2007 transpressional tectonics and carboniferous magmatism in the limousin massif central france structural and 40ar 39ar investigations

how much does slip on a reactivated fault plane constrain the stress tensor given a fault plane and its slip vector the stress tensor which caused the displacement is sought two constraints are considered first a geometrical constraint that the shear stress applied to the fault plane is parallel to the slip wallace 1951 bott 1959 second a frictional constraint that the shear to normal stress ratio equals tan 0 coulomb 1776 in a first step the stress tensors that satisfy the geometrical constraint are sought for tensors belonging to the vectorial space of solutions shear and normal stress magnitudes become a function of the orientation of the principal stresses and are mapped extending a study by mckenzie 1969 in a second step it is investigated which of these tensors also satisfy the frictional constraint within this more restricted vectorial space there is a relationship between the magnitudes 1 2 1 3 and s 1 3 1 and the orientations of the principal stresses both the range of s and the spatial distribution of are more restricted than when the geometrical constraint alone is considered as when the geometrical constraint is solely considered mckenzie 1969 the orientations of the principal stresses may lie significantly away from and up to right angle to the p b t axes however this can happen only in two cases 1 either the effective stress difference s has reached a high value which is unlikely to happen if enough preexisting fractures are available to release the stress or 2 2 becomes close to either 1 or 3 and therefore barely distinguishable from it in that case the delocalization of the orientations of the principal stresses is best described by a tendency for to exchange role with either or when the stress difference remains small and 2 reasonably away from 1 and 3 approach positions that we define as the pf b tf axes and that are obtained from the p b t axes by a rotation of angle 0 2 around b and toward the slip vector this explains why the p b t axes gives reasonable estimates of the orientations of the principal stresses scheidegger 1964 despite objections mckenzie 1969 however whenever the fault plane can be distinguished from the auxiliary plane pf b tf should give a better estimate raleigh et al 1972 in an area where many fault planes are available and a uniform tensor is assumed the scatter in the plane orientations contains information about both the relative position of 2 represented by and the relative stress difference s the higher s or the closer to either 0 or 1 the more scatter this information could then be extracted by inverse methods because a friction law would constrain these inverse method more tightly it may show the necessity of nonuniform tensor to explain scattered fault plane

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

lithospheric scale centrifuge models of pull apart basins abstract we present here the results of the first lithospheric scale centrifuge models of pull apart basins the experiments simulate relative displacement of two lithospheric blocks along two offset master faults with the presence of a weak zone in the offset area localising deformation during strike slip displacement reproducing the entire lithosphere asthenosphere system provides boundary conditions that are more realistic than the horizontal detachment in traditional 1 g experiments and thus provide a better approximation of the dynamic evolution of natural pull apart basins model results show that local extension in the pull apart basins is accommodated through development of oblique slip faulting at the basin margins and cross basin faults obliquely cutting the rift depression as observed in previous modelling studies our centrifuge experiments suggest that the angle of offset between the master fault segments is one of the most important parameters controlling the architecture of pull apart basins the basins are lozenge shaped in the case of underlapping master faults lazy z shaped in case of neutral offset and rhomboidal shaped for overlapping master faults model cross sections show significant along strike variations in basin morphology with transition from narrow v and u shaped grabens to a more symmetric boxlike geometry passing from the basin terminations to the basin centre a flip in the dominance of the sidewall faults from one end of the basin to the other is observed in all models these geometries are also typical of 1 g models and characterise several pull apart basins worldwide our models show that the complex faulting in the upper brittle layer corresponds at depth to strong thinning of the ductile layer in the weak zone a rise of the base of the lithosphere occurs beneath the basin and maximum lithospheric thinning roughly corresponds to the areas of maximum surface subsidence i e the basin depocentre

a 20 000 year record of ocean circulation and climate change from the santa barbara basin much of the evidence for climate driven fluctuations in ocean circulation during the past 20 000 years has come from studies of the north atlantic region1 6 the extent to which such interactions have occurred in other ocean basins and any associated teleconnec tions between basins is poorly understood here we present high resolution palaeoclimate and palaeoceanographic records from a 20 000 year sedimentary sequence from the santa barbara basin on the eastern margin of the north pacific ocean the sequence shows oscillations of the benthic environment between low oxygen conditions laminated sediments during periods of warm climate and higher oxygen conditions non laminated bioturbated sediments during cool intervals age differences between coexisting benthic and planktonic foraminifers indicate climate related changes in the age and source and hence oxygen content of basin bottom waters relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources conversely older bottom waters are associated with the warmer intervals and were derived from more distal sources these climate driven variations in ocean circulation appear to be synchronous with the main ocean climate fluctuations in the north atlantic region1 6 suggesting that a tight coupling mechanism operates between the two basins

glacial climate instability in the northeast pacific ocean recent climate records from greenland ice cores1 2 and north atlantic sediments3a 5 have challenged the long held notion that pleistocene climate fluctuates between two relatively stable states glacials and interglacials it has been appreciated for some time that the transitions from one state to another are not smooth6 but the new records indicate that the glacial and interglacial periods themselves appear to be punctuated by significant climate variability several short interstadial events punctuated the last glacial period for example but it has not been clear whether this climate instability is a global phenomenon or is peculiar to the north atlantic region here we present climate proxy records from sediment cores from the eastern margin of the north pacific ocean which indicate that climate in this region was also highly unstable during the last glaciation our observations suggest that glacial climate instability throughout the northern hemisphere might be linked to rapid changes in the size of the laurentide ice sheet and associated changes in atmospheric circulation

fluid transfers at the basement cover interface part i subsurface recycling of trace carbonate from granitoid basement rocks france basement rocks usually contain trace amounts of disseminated carbonate minerals and sometimes also fractures veins filled with carbonates which may have a variety of origins extensive drilling has been performed of a granitoid body vienne western part of the french massif central overlain by a carbonate sedimentary sequence a situation which is representative of most of the variscan basement in western europe these unique samples provide the opportunity to investigate the behaviour of basement trace carbonate across the basin basement interface and the mass transfers throughout a series of fluid migration ranging from high ca 450 c to low down to 50 c temperature conditions study of quartz and carbonate found in fracture infillings reveals three major stages of fluid circulation namely 1 high to medium temperature late hercynian fluids which circulated in fractures developed during basement uplift 2 medium temperature mesozoic basinal brines migration laterally along the basement cover contact 3 late infiltration of diagenetic marine waters in the upper part of the granitoid body a majority of analyzed vein carbonates from the three stages displayed a rather restricted range of c isotopic compositions 13c between 14 and 9 pdb whatever the stage in which they were deposited and despite large variations of o isotopic ratios 18o in the range 3 to 30 smow carbon in pervasively altered rocks displays the same features and is distributed among the two broad groups defined using o isotopic ratios in veins and fluid inclusions data namely the hercynian and the mesozoic carbonates isotopic data argue that carbon was introduced as carbonates in the early stages of the retrograde hercynian metamorphism and was systematically reworked by subsequent fluids without any significant carbon introduction from external sources the only exception corresponds to the stage iii calcite veins which are located in the upper sections of the cores at depths lower than 350 m beneath the basement cover boundary and are the only witnesses of element transfer from the sediments towards the basement the present data show that trapping of carbon by ca rich plutonic rocks during their cooling history confers on these rocks an efficient self sealing capacity during later fracturing and fluid flow because carbonates possess high solubility and rapid dissolution precipitation kinetics fluid circulation occurred not only in the macroscopic system of fractures but also within some volumes of the granitic matrix in order to scavenge and redistribute the early granitic trace carbonate in the event of poly cyclic carbonate redistribution the use of carbon isotopic composition to unravel the fluid origins must be exercised with caution as early c could be easily redistributed during later fluid migration episodes

data model comparison of the younger dryas event the younger dryas cooling event is well established in the north atlantic region through numerous climate proxy records although the climatological controls vary from site to site it is considered to have taken place between about 10 000 and 11 000 bp radiocarbon years 11 500 13 000 calendar years ago outside the north atlantic region climate proxy records and chronology commonly become problematic because of weaker signals and less dating control in addition to this evidence oceanic records reveal conflicting evidence for younger dryas forcing mechanisms and the timing of events we compare proxy evidence with the results from an ocean general circulation model coupled to the energy moisture balance atmospheric model the model results reveal a global pattern and regional magnitude which generally agree with temperature changes interpreted from paleoclimate reconstructions the model also supports the general duration of global cooling of the younger dryas although proxy data can be controversial outside of the north atlantic region the authors believe that there is enough evidence to support the younger dryas event on a global scale they also recognize however that more concrete evidence is needed before the question can be unequivocally answered

inter decadal signals during the last millennium ad 1117 1992 in the varve record of santa barbara basin california annual varve thickness ad 1117 1992 from santa barbara basin has been decomposed into orthogonal components using singular spectrum analysis ssa to identify and retrieve inter decadal oscillations after removing all variability with periods greater than 150 years leading ssa eigenfunctions eofs identify four oscillatory pairs with periods of 100 58 25 and 12 years respectively based on 2500 simulated series and on two sided confidence intervals eofs 1 7 are significant at the 99 level and eofs 8 9 are significant at the 90 level oscillatory signals retrieved from the marine varves show an abrupt change in frequency and amplitude near ad 1600 the largest contribution to this environmental shift is given by the interdecadal components especially the 25 and the 12 year oscillation the near ad 1600 change may be related to multi annual events reported in the stratigraphy of the nearby santa monica basin and in dendrochronological records of the american southwest

petrology of the renard igneous bodies host rocks for diamond in the northern otish mountains region quebec abstract the renard igneous bodies were discovered in late 2001 as part of a regional diamond exploration program launched by ashton mining of canada and soquem nine bodies have been discovered within a 2 km diameter area and are comprised of root zone to lower diatreme facies rocks including kimberlitic breccia olivine macrocrystic hypabyssal material and brecciated country rock with minor amounts of kimberlitic material many mineralogical and petrographic features are common to both kimberlite and melnoite and strict assignment of the rocks as kimberlite is not possible with these criteria alone whole rock trace element compositions suggest a closer affinity to group i kimberlite with derivation from a garnet bearing mantle exceptions to conventional classification of the rocks along petrographic or mineralogical lines may be due in part to assimilation of felsic country rock into the renard magmas at the time of emplacement the renard magmas were emplaced into northeastern laurentia at 630 ma when the supercontinent was undergoing a change from convergent margin magmatism to rifting the latter being associated ultimately with the opening of the iapetus ocean

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

timing of low temperature mineral formation during exhumation and cooling in the central alps switzerland abstract construction of the new gotthard rail base tunnel through the central alps provided a truly unique sample of a fissure assemblage formed during exhumation and cooling of the central alps the base of the tunnel is at 500 m a s l and the overburden at the sampling locality amounts to 2000 m the fissure assemblage apophyllite kf laumontite and quartz occurs within the southern aar granite it formed during exhumation and erosion of the alpine orogen apophyllite and laumontite mark very late fissure minerals in the central swiss alps only followed by stilbite hematite and calcite the data from a combined study of 40 ar 39 ar age dating of apophyllite apatite fission track analysis and the petrology of rock samples from tunnel and the from the mountains above the tunnel reflect the late stages of an aging orogen apatite fission track analysis yields an exhumation rate of 0 46 mm yr a cooling rate of 12 3 c m y and a geothermal gradient of 27 c km at the time of apophyllite formation combining these data with the 40 ar 39 ar plateau age of 2 ma for the formation of apophyllite a minimum formation temperature and depth of 68 c at 2550 m below the present day erosion surface follow at this time the position of the sample location was 550 m below the tunnel level assemblage stabilities and computed temperature time evolution of fissures in the aar massif indicate that laumontite formed between 11 and 2 ma ago at temperatures between 180 and 70 c chemical components for forming laumontite were provided from dissolution of minerals of the alpine greenschist facies variscan granitoid rocks of the aar massif basement systematic variations in the composition of laumontite are an effect of decreasing temperature