taking mylonites temperatures we measured titanium in quartz titaniq temperatures by ion microprobe for three deformed rocks having different quartz microstructure to assess the possibility of constrain ing the temperature of mylonitization directly from dynamically recrystallized quartz grains calibration via ion microprobe indicates analytical precisions and accuracies of 2 c and 10 c respectively 2 high versus low temperature mylonites yield high versus low ti concentrations and temperatures that are consistent with other fi eld studies of mylonites that have similar microstructures these observations imply that titaniq accurately measures dynamic recrystallization temperatures variations in temperature in a single domain exceed analytical errors implying that one microstructure in a rock can refl ect different tempera tures and presumably strain rates combined with paleopiezometric and phase equilibrium estimates of differential stress and water fugacity strain rates may be estimated

role of plutonism in low pressure metamorphic belt formation wickham and oxburgh1 recently proposed that low pressure high temperature low p high t metamorphism in the eastern pyrenees and possibly all low p high t metamorphic belts resulted from anomalously high mantle heat flow brought about by rifting their model is largely constrained by the presence of nearby synmetamorphic rift related sedimentary rocks and the interpretation that the migmatites and granites are the product of in situ melting in the presence of an anomalously steep geotherm here we present an alternative model in which low p high t metamorphism pro grade reactions at pressures near or below the al2sio5 triple point results from contact effects near sill like igneous intrusions at intermediate crustal levels low p high t conditions can be achieved through this process in regions of continent continent collision with normal mantle heat flux as well as in zones of extension our model is based on studies of the low p high t metamorphic terrane in the new england appalachians

transpression and extensional collapse steep belts and flat belts in the appalachian central mobile belt northern new brunswick canada models of the appalachian caledonian orogen infer oblique collision and an enigmatic reversal from sinistral silurian to dextral devonian transpression the miramichi highlands in canada are relevant to such models because 1 they are a subductional thrust complex in which the inferred reversal coincided with recumbent folding and 2 its kinematic indicators include rotated thrust structures and conjugate sets of coeval structures both are easily mistaken as evidence for sinistral and dextral transpression the thrust complex is part of the appalachian central mobile belt and is partitioned into steep belts and flat belts according to the attitude of the schistosity we argue that the steep belts are coeval with late silurian plutonism and low pressure metamorphism representing transpressional zones d 2 in which the extension lineation of d 1 thrusting was tilted twice first from gentle to steep then back to a gentle plunge the transpression was synchronous with exhumation as well as sedimentation flat belts represent a later flattening d 3 that probably resulted from extensional collapse and preceded early devonian dextral transpression d 4 along the central mobile belt our model for the flat belts differs principally from models proposed for equivalent flat belts in newfoundland

serpentinization of the martian crust during noachian abstract this paper proposes a model of serpentinization of the southern martian crust that may explain the topographic dichotomy the absence of an associated free air gravity anomaly and the presence of strong magnetic anomalies in the southern hemisphere the thermodynamical conditions for serpentinization were likely met in the lithosphere during the noachian period this process may have decreased the density in the southern crust and created the topographic dichotomy different reactions of serpentinization that can form magnetite have been considered assuming an intense magnetic field core dynamo we obtain chemical remanent magnetizations that are in the order of the estimates deduced from martian magnetic anomaly studies the pertinence and the implications of our model concerning the early thermal evolution of mars are discussed with emphasis on the intensity of the paleo magnetic field

evidence for basin restriction during syn collisional basin formation in the silurian arisaig group nova scotia the arisaig basin in nova scotia canada provides a regional sedimentary record of an early silurian basin subsidence on the microcontinent of avalon the lower members of the arisaig group beechill cove and lower ross brook formations are likely to be deposited in a basin formed during syn to post collisional rifting subsidence driven by the collision of avalon and baltica the evolution of this constricted basin can be tracked by examining the geochemistry of the sedimentary rocks deposited within the basin here we report on the chemostratigraphy of the arisaig group a series of siliciclastics with a focus on understanding the redox chemistry during sedimentation the trace and major element geochemistry of this group provides insight into the oceanographic and geological processes that were influencing its depositional environment in particular concentrations of u v mo ni cd and pb indicate regional shifts in ocean redox state which serve as a proxy for changes in ocean circulation and regional tectonic activity we find evidence for anoxic conditions near the base of ross brook formation and attribute this anomaly in redox status to a significant change in physical mixing in the region trace element concentrations indicate that this anoxic event was associated with poor circulation rather than elevated productivity and organic matter burial based on these data we confirm that these sediments are deposited in a tectonically formed basin during a period of limited ocean circulation

a method for evaluating basement exhumation histories from closure age distributions of detrital minerals we have developed a two dimensional thermokinetic model that predicts the closure age distributions of detrital minerals from pervasively intruded and differentially exhumed basement using this model we outline a method to determine the denudation history of orogenic regions on the basis of closure age distributions in synorogenic to postorogenic forearc strata at relatively high mean denudation rates of 0 5 km m y 1 sustained over millions of years magmatic heating events have minimal influence upon the age distributions of detrital minerals such as k feldspar that are moderately retentive of radiogenic ar at lower rates however the effects of batholith emplacement may be substantial we have applied the approach to detrital k feldspars from forearc strata derived from the deeply denuded peninsular ranges batholith prb agreement of the denudation history deduced from the detrital k feldspar data with thermochronologic constraints from exposed prb basement lead us to conclude that exhumation histories of magmatic arcs should be decipherable solely from closure age distributions of detrital minerals whose depositional age is known c 1999 american geophysical union

silurian tectonics of western avalonia strain corrected subsidence history of the arisaig group nova scotia the arisaig group is a silurian succession of predominantly shallow marine clastic sediments overlying volcanics exposed in northern mainland nova scotia sediment accumulation provides a record of the subsidence of western avalonia during the interval when terranes were being accreted within the canadian appalachians to calculate the amount of subsidence one must correct the measured thicknesses for the effects of tectonic strain deformed fossils on bedding surfaces indicate strain ratios mainly between 1 2 and 1 6 an empirical porosity depth relationship is used to correct for compaction the subsidence curves are then adjusted to allow for variations in water depth and eustatic sea level the resulting curves show significant variations in subsidence rate regardless of which version of the silurian time scale is used an initial episode of rapid subsidence followed eruption of llandoverian volcanics slower subsidence took place in wenlockian and ludlovian time with deeper water sedimentation dur

dating transcurrent terrane accretion an example from the meguma and avalon composite terranes in the northern appalachians the polygenetic minas geofracture separates the meguma and avalon composite terranes of the maritime appalachians dynamically recrystallized muscovite and biotite occur within d3 shear zones which developed during dextral movement along the geofracture these record 40ar 39ar plateau ages between circa 360 and 370 ma comparable plateau ages are recorded by micas within undeformed portions of granitic plutons and their low pressure contact metamorphic aureoles these are similar to u pb ages previously reported for igneous monazite therefore indicating relatively rapid postmagmatic cooling at shallow crustal levels the d3 fabrics were superimposed on earlier s1 structures which formed during initial amalgamation of the meguma and avalon composite terranes whole rock slate phyllite samples collected outside high temperature portions of the plutonic contact aureoles yield 40ar 39ar plateau ages which correspond to groupings of circa 400 395 ma 390 385 ma and 380 375 ma these are interpreted to date diachronous formation of the s1 fabrics and concomitant low grade regional metamorphism in the circa 25 ma between initial amalgamation and granitic plutonism it is inferred that there was a slow rise of isotherms through the crust as a result of overthrust tectonic thickening this led to crustal melting and the production of widespread granitic magmas which were emplaced immediately prior to d3 dextral shearing

synthesis of palaeozoic deformational events and terrane accretion in the canadian appalachians plate tectonic theory predicts that most deformation is associated with subduction and terrane accretion with some deformation associated with transform transcurrent movements deformation associated with subduction varies between two end members 1 where the tectonic regime is dominated by subduction of oceanic lithosphere containing small terranes a narrow surface zone of accretionary deformation along the subduction zone starts diachronously on the subducting plate at the trench as material is transferred from the subducting plate to the over riding plate and 2 where continent continent collision is occurring a wide surface zone of accretionary deformation starts synchronously or with limited diachronism palaeozoic deformational events in the canadian appalachians correspond to narrow diachronous events in the ordovician and silurian whereas devonian carboniferous and permian deformational events are widespread and broadly synchronous along the western side of the canadian appalachians the taconian deformational event starts diachronously throughout the ordovician and corresponds to the north north west accretion of the notre dame ascot weedon st victor and various ophiolitic massifs volcanic arc and peri arc terranes over cratonic north america within the eastern half of the central mobile belt the late cambrian early ordovician penobscotian deformational event corresponds to the south easterly accretion of the exploits subzone various volcanic are and peri arc terranes over the gander zone continental rise in the centre of the orogen the late ordovician silurian beothukan deformational event corresponds to the south easterly accretion of the notre dame over the exploits gander subzones along the south eastern side of the central mobile belt the silurian ganderian deformational event corresponds to the north north east sinistral transcurrent accretion of the avalon composite terrane microcontinent over the gander exploits zones along the south eastern half of the orogen the late silurian middle devonian acadian deformation event corresponds to the westerly accretion of the meguma terrane intradeep or continental rise over the avalon composite terrane affecting the entire orogen the late devonian carboniferous and permian acadian alleghanian deformational events correspond to the east west convergence between laurentia and gondwana continent continent collision

major late cretaceous cooling events in the eastern peninsular ranges california and their implications for cordilleran tectonics fission track ages from the peninsular ranges batholith in the san jacinto mountains near palm springs california indicate two major late cretaceous cooling events concordant sphene and zircon fission track ages of plutonic rocks tonalite and low k granodiorite range from ca 85 ma to 98 ma with a mean of 92 ma the concordance of these ages over 2 5 km of exposed vertical section coupled with previous u pb zircon dating 94 93 ma implies major cooling from crystallization temperatures to below 235 c between 94 ma and ca 92 ma cooling is attributed to initial intrusion of the tonalite and granodiorite into an evolving brittle ductile normal fault zone detachment followed by 10 14 5 km of exhumation during continued crustal extension along the santa rosa mylonite belt field relationships microstructural fabrics and amphibole thermobarometry from the mylonite belt support the notion that extensional faulting was preceded by west directed thrusting this sequence of tectonic thickening followed by extension is similar to other areas in the southwestern cordillera and may represent the creation and failure of an unstable regional crustal welt in late cretaceous time a second event is evident from concordant fission track ages and indistinguishable tracklength distributions from apatite at all elevations these data indicate very rapid cooling of the tonalitic plutons through the apatite partial annealing zone 130 70 c between ca 74 ma and 80 ma mean age of 76 ma the occurrence of late cretaceous age regional unconformities throughout baja and southern california suggests that this cooling event was the result of surface uplift and erosion by using a reasonable range of geothermal gradients 20 40 c km the cooling data imply a minimum of 4 5 km of exhumation in conjunction with the ca 76 ma event surface uplift coincided with several important changes in the north american and farallon or kula plate motions these include an increase in convergence rate an increase in the absolute velocity of the north american plate and a change in the direction of convergence between the plates the changes in plate motions are thought to have initiated low angle or flat slab subduction that in turn was responsible for the laramide deformation of the cordilleran foreland surface uplift erosion and associated cooling during exhumation of the eastern peninsular ranges are considered to be an initial expression of laramide tectonism phenomena documented here are consistent with uplift brought on by tectonic erosion of the north american lithospheric mantle due to low angle subduction and by subsequent underplating of lower crustal rocks

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

timing of peak metamorphism and deformation along the appalachian margin of laurentia in newfoundland silurian not ordovician u pb and ar ar isotopic age data from the corner brook lake region of the eastern appalachian humber zone in western newfoundland indicate that regional deformation and peak amphibolite facies metamorphism are early silurian a lower limit on deformation is provided by a u pb zircon age of 434 2 3 ma for a pegmatite that is affected by the regional foliation and is interpreted to be syntectonic monazite and rutile from a garnet kyanite staurolite schist which records peak metamorphic conditions and in which porphyroblasts have overgrown the regional foliation gave u pb ages of 430 2 ma and 437 6 ma respectively ar ar cooling ages for hornblende from amphibolites and muscovite from psammitic and pelitic schists range from 430 to 420 ma a silurian age for deformation and metamorphism of the laurentian margin is coincident with the timing of similar events along the newfound land gondwana margin and suggests that the silurian was a period of major continent continent collision

sedimentary fades depositional environments and faunal associations of the lower llandovery silurian beechill cove formation arisaig nova scotia six facies are recognised in the beechill cove formation these are 1 conglomerate facies deposited as a transgressive beach lag 2 red shale facies deposited in shoreface environments 3 mottled mudstone facies extensively bioturbated sediments indicative of shallow subtidal areas influenced by low sedimentation rates 4 regular layered facies shelf turbidites generated by storm activity and superimposed on quiescent subtidal environments 5 lenticular facies including a thinner bedded more persistent and a thicker bedded lenticular subfacies induced by storm activity and deposited in shallow subtidal environments and 6 laminated shale facies produced by sediment fallout from suspension in a low energy environment where the oxygen minimum layer intersected the sediment water interface three faunal associations occur which have distinct distributional patterns the lingula clintoni association which is characterized by l clintoni in life position and a moderately diverse but abundan

40 ar 39 ar amphibole ages from the kingston complex new brunswick evidence for silurian devonian tectonothermal activity and implications for the accretion of the avalon composite terrane the kingston complex of southern new brunswick canada is a regional ne trending belt of mafic and felsic dikes bordered by dextral ductile shear zones the complex separates two contrasting late precambrian early paleozoic tectonostratigraphic assemblages near the nw margin of the avalon composite terrane rhyolitic dikes within the complex record an early silurian crystallization age dike orientations suggest that emplacement of the complex accompanied sinistral movement interpreted to reflect accretion of the avalon composite terrane to cratonic north america mafic dikes within the complex display greenschist to epidote amphibolite facies metamorphic assemblages that developed during dextral transpression amphibole concentrates from seven metamorphosed mafic dikes record late silurian to early devonian ca 416 390 ma 36 ar 40 ar vs 39 ar 40 ar isotope correlation ages interpreted to date closely the dextral transpressive deformation together with other recent age data the 40 a

determination of finite strain in bedding surfaces using sedimentary structures and trace fossils a comparison of techniques abstract determination of the two dimensional finite strain in turbidite bedding surfaces is important in both structural and sedimentological investigations of deformed sediments the meguma group of nova scotia is one such sequence in which the directional distribution of paleocurrent markers has been modified by strain previous strain determinations have used sand volcanoes as strain markers which do not deform homogeneously with their matrix and hence may underestimate the true strain ratio intraclasts and concretions also suffer inhomogeneous deformation and are of limited use as strain markers hexagonal trace fossil networks can provide more reliable strain estimates but are rare widths of burrows exposed on bedding surfaces provide a new straightforward means of measuring strain each burrow is represented by a pair of parallel lines the separation of the lines is proportional to the burrow width and their direction represents burrow orientation the lines are tangential to the strain ellipse which can be discerned despite initial scatter in burrow widths

tectonic significance of late ordovician silicic magmatism avalon terrane northern antigonish highlands nova scotia12 1 this article is one of a series of papers published in cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology 2 contribution to international geological correlation programme igcp project 497 avalonia was a microcontinent during most of the ordovician separating the iapetus ocean to the north from the rheic ocean to the south in the northern antigonish highlands nova scotia volcanic rocks dunn point and mcgillivray brook formations underlie early silurian early devonian strata arisaig group and were thought to represent extension that heralded the development of the basin into which arisaig group strata were deposited however recent u pb zircon thermal ionization mass spectrometry data from rhyolite in the dunn point formation dpf yielded an age of 460 0 3 4 ma and here we report a concordant age of 454 5 0 7 ma for an ignimbrite in the overlying mcgillivray brook formation mbf these data confirm a ca 10 million year gap between volcanism and onset of arisaig group deposition which occurred after accretion of avalonia to baltica the dpf and mbf both resemble a type sio2 rich magmas the mbf has very high concentrations of zr 745 1965 ppm y 65 213 ppm nb 57

growth conditions of symplectic muscovite quartz implications for quantifying retrograde metamorphism in exhumed magmatic arcs symplectic intergrowths are important markers of incomplete retrograde metamorphism because they represent arrested reactions that were limited by diffusion these textures provide constraints on how pressure and temperature varied following peak grade metamorphism for example symplectic intergrowths of muscovite quartz that formed in upper amphibolite facies sillimanite k feldspar wall rocks permit assessment of the thermal history of a magmatic arc post intrusion wall rocks surrounding the last plutons to be emplaced within the peninsular ranges batholith southern california usa to baja california mexico present an ideal setting to investigate retrograde textures that elucidate arc evolution during intrusion wall rocks reached 625 25 c and exceeded muscovite quartz stability post intrusion muscovite quartz symplectites grew at the expense of k feldspar in response to falling temperature ti in quartz measurements reveal that symplectic quartz grew at 375 c which reflects temperatures as much as 250 c lower than peak grade metamorphism this result has significant implications for the mechanical and thermal evolution of peninsular ranges batholith arc crust

tio2 activity in metamorphosed pelitic and basic rocks principles and applications to metamorphism in southeastern canadian cordillera the activity of tio2 can be precisely defined as a function of pressure temperature and activities of other components for common mineral assemblages in metapelites ilmenite quartz garnet plagioclase al2sio5 and in metabasites plagioclase sphene ilmenite quartzgarnet these mineral assemblages can be modelled by the equilibria 1 3ilmenite al2sio5 2quartz almandine 3tio2 2 anorthite 2sphene grossular 2tio2 quartz 3 3anorthite 3quartz 6ilmenite grossular 6tio2 2almandine these mineral assemblages can be used at a text tio text 2 1 rutile saturation and a given t to get maximum pressure limits of some metapelites and metabasites when electron microprobe analyses of mineral grains adjacent to ti bearing phases are made these data give maximum pressure estimates in reasonable agreement with other geobarometers the activity of tio2 in many metapelites is very near rutile saturation but for metabasites the activity of tio2 in some sillimanite zone rocks is as low as 0 6 the solubility of tio2 in biotite hornblende and garnet is a complex function of t p the activities of components in coexisting minerals and crystal chemical constraints in these minerals at a given p and t the solubility of tio2 in biotite and hornblende does not appear to be strongly dependent upon a text tio text 2 1 for sphene and ilmenite versus rutile bearing assemblages

promontory promontory collision in the canadian appalachians in cape breton island and southwestern newfoundland the appalachian orogen is extremely narrow the rocks were strongly deformed and underwent high grade barrovian type metamorphism in silurian time and the orogen parallel silurian thrusts are dominantly west vergent antithetic to the westward subduction this area is bounded by two transverse dextral wrench faults the canso fault to the southwest and the gunflap hills fault to the northeast these tectono stratigraphic structural and metamorphic features are explained by silurian collision between the st lawrence promontory on the laurentian margin and the cabot promontory on the avalon margin during the final closure of the iapetus ocean the west vergent antithetic thrusting is interpreted to be related to tectonic wedging while the two transverse wrench faults accommodated differential movement from promontories to reentrants during the collision promontory promontory collision should be a common process and probably played a significant role in shaping the tectonic framework of many orogenic belts

palaeozoic to early jurassic history of the northwestern corner of gondwana and implications for the evolution of the iapetus rheic and pacific oceans abstract the palaeozoic to mesozoic igneous and metamorphic basement rocks exposed in the merida andes of venezuela and the santander massif of colombia are generally considered to define allochthonous terranes that accreted to the margin of gondwana during the ordovician and the carboniferous however terrane sutures have not been identified and there are no published isotopic data that support the existence of separate crustal domains a general paucity of geochronological data led to published tectonic reconstructions for the evolution of the northwestern corner of gondwana that do not account for the magmatic and metamorphic histories of the basement rocks of the merida andes and the santander massif we present new zircon u pb icp ms data from 52 igneous and metamorphic rocks which we combine with whole rock geochemical and pb isotopic data to constrain the tectonic history of the precambrian to mesozoic basement of the merida andes and the santander massif these data show that the basement rocks of these massifs are autochthonous to gondwana and share a similar tectono magmatic history with the gondwanan margin of peru chile and argentina which evolved during the subduction of oceanic lithosphere of the iapetus ocean the oldest palaeozoic arc magmatism is recorded at 500 ma and was followed shortly by barrovian metamorphism peak metamorphic conditions at upper amphibolite facies are recorded by anatexis at 477 ma and the intrusion of synkinematic granitoids until 472 ma subsequent retrogression resulted from localised back arc or intra arc extension at 453 ma when volcanic tuffs and interfingered sedimentary rocks were deposited over the amphibolite facies basement continental arc magmatism dwindled after 430 ma and terminated at 415 ma coevally with most of the western margin of gondwana after pangaea amalgamation in the late carboniferous to early permian a magmatic arc developed on its western margin at 294 ma as a result of subduction of oceanic crust of the palaeo pacific ocean intermittent arc magmatism recorded between 294 and 225 ma was followed by the onset of the andean subduction cycle at 213 ma in an extensional regime extension was accompanied by slab roll back which led to the migration of the arc axis into the central cordillera of colombia in the early jurassic

evidence for silurian sinistral accretion of avalon composite terrane in canada the kingston dyke complex forms a regionally developed belt of sheeted bimodal dykes within the avalon composite terrane of southern new brunswick canada dyke orientation relative to the belt suggests their injection accompanied sinistral movement and the belt has previously been attributed to transform activity within the late precambrian magmatic arc regime typical of the avalon composite terrane in the northern appalachians however rhyolite dykes of the sheeted complex yield a u pb age of 435 5 1 5 ma that is interpreted to date their emplacement the complex therefore provides evidence of early silurian sinistral displacement in the northern appalachians such movement is suggested by palaeomagnetic data and may record the accretion of the avalon composite terrane to cratonic north america

using microstructures and titaniq thermobarometry of quartz sheared around garnet porphyroclasts to evaluate microstructural evolution and constrain an alpine fault zone geotherm abstract interpretations of deformation processes within ductile shear zones are often based on the characterisation of microstructures preserved in exhumed rocks however exhumed microstructures provide only a snapshot of the closing stages of deformation and we need ways of understanding how microstructures change through time and at what rate this occurs to address this problem we study optical microstructures and electron backscatter diffraction ebsd data from samples of quartz layers deflected around garnet porphyroclasts which generate local stress and strain rate perturbations during mylonitic deformation in the alpine fault zone of new zealand during shearing around rigid garnet porphyroclasts quartz undergoes grain size reduction in response to locally increased stresses while c axes reveal increasing components of rhomb and prism slip reflecting a local increase in shear strain and strain rate titaniq thermobarometry and quartz microstructures suggest a rather narrow range of recorded quartz deformation temperatures around 450 500 c which we propose reflects the cessation of grain boundary migration driven deformation given that temperatures well above the brittle ductile transition for quartz 350 c are preserved we anticipate that rapid cooling and exhumation must have occurred from the 500 c isotherm ultimately we propose a modified geotherm for the central alpine fault zone hanging wall which raises the 500 c isotherm to 11 km depth near the brittle ductile transition our updated alpine fault zone geotherm implies a hotter and weaker middle to lower crust than previously proposed

rates of processes in magmatic arcs implications for the timing and nature of pluton emplacement and wall rock deformation abstract the construction of arcs and in many cases the emplacement of plutons occur in tectonically active regions it is critical therefore to evaluate the rates of structural and magmatic processes when trying to understand the evolution of arcs and the associated pluton wall rock systems our best estimates of average rates or durations of processes in shallow to moderate level arc environments are the following 1 crystal growth rates in magma of 10 4 cm year 1 2 growth rates of metamorphic porphyroblasts between 10 5 and 10 2 cm year 1 3 long term magma supply rates of 10 1 km 3 year 1 and short term rates of up to 350 km 3 year 1 4 diapiric ascent rates for mafic plutons of 1 3 m year 1 5 cooling of plutons to ambient wall rock temperatures in 10 5 10 6 years 6 final crystallization of plutons in a small fraction of the time needed for complete cooling 7 fault displacements of 3 cm year 1 8 development of cleavages in fault zones in less than 10 6 years at strain rates of 10 13 s 1 or higher and 9 the development of regional cleavages in 10 6 years at strain rates of 10 14 s 1 these rates indicate that processes operating in magmatic arcs are relatively rapid pluton emplacement cleavage development etc occur over time spans of tens of thousands to no more than a few million years however the rate of ascent and crystallization of plutons at shallow levels is generally shorter than that needed to get large displacements on faults or widespread cleavages developed at deeper levels or in zones undergoing faster strain rates the time spans of the various processes approach one another thus plutons with otherwise similar characteristics emplaced in regions undergoing fast strain rates or at deeper crustal levels may appear quite different structurally from those emplaced at shallow levels or in regions undergoing slower strain rates comparison of these data also suggests that the rate at which wall rock deforms is the limiting factor controlling the rates of other structural processes during emplacement of plutons unless fast strain rates or multiple deformation mechanisms are considered thus emplacement mechanisms that rely on the transport of magma over 10 5 to 10 6 years are favored and need further consideration finally we argue that the structural and other characteristics of pluton wall rock systems will depend on rates of various processes involved and that these rates at the very least influence and sometimes invalidate the timing criteria previously published by us and others