u pb and th pb dating of apatite by la icpms abstract apatite is a common u and th bearing accessory mineral in igneous and metamorphic rocks and a minor but widespread detrital component in clastic sedimentary rocks u pb and th pb dating of apatite has potential application in sedimentary provenance studies as it likely represents first cycle detritus compared to the polycyclic behavior of zircon however low u th and radiogenic pb concentrations elevated common pb and the lack of a u th pb apatite standard remain significant challenges in dating apatite by la icpms and consequently in developing the chronometer as a provenance tool this study has determined u pb and th pb ages for seven well known apatite occurrences durango emerald lake kovdor mineville mud tank otter lake and slyudyanka by la icpms analytical procedures involved rastering a 10 m spot over a 40 40 m square to a depth of 10 m using a geolas 193 nm arf excimer laser coupled to a thermo elementxr single collector icpms these raster conditions minimized laser induced inter element fractionation which was corrected for using the back calculated intercept of the time resolved signal a tl u bi np tracer solution was aspirated with the sample into the plasma to correct for instrument mass bias external standards plesovice and 91500 zircon nist srm 610 and 612 silicate glasses and stdp5 phosphate glass along with kovdor apatite were analyzed to monitor u pb th pb u th and pb pb ratios common pb correction employed the 207pb method and also a 208pb correction method for samples with low th u the 207pb and 208pb corrections employed either the initial pb isotopic composition or the stacey and kramers model and propagated conservative uncertainties in the initial pb isotopic composition common pb correction using the stacey and kramers 1975 model employed an initial pb isotopic composition calculated from either the estimated u pb age of the sample or an iterative approach the age difference between these two methods is typically less than 2 suggesting that the iterative approach works well for samples where there are no constraints on the initial pb composition such as a detrital sample no 204pb correction was undertaken because of low 204pb counts on single collector instruments and 204pb interference by 204hg in the argon gas supply age calculations employed between 11 and 33 analyses per sample and used a weighted average of the common pb corrected ages a tera wasserburg concordia intercept age and a tera wasserburg concordia intercept age anchored through common pb the samples in general yield ages consistent at the 2 level with independent estimates of the u pb apatite age which demonstrates the suitability of the analytical protocol employed weighted mean age uncertainties are as low as 1 2 for u and or th rich palaeozoic neoproterozoic samples the uncertainty on the youngest sample the cenozoic 31 44 ma durango apatite ranges from 3 7 7 6 according to the common pb correction method employed the accurate and relatively precise common pb corrected ages demonstrate the u pb and th pb apatite chronometers are suitable as sedimentary provenance tools the kovdor carbonatite apatite is recommended as a potential u pb and th pb apatite standard as it yields precise and reproducible 207pb corrected 232th 208pb and common pb anchored tera wasserburg concordia intercept ages

intercalibration of astronomical and radioisotopic time the 40ar 39ar radioisotopic dating technique is one of the most precise and versatile methods available for dating events in earth s history but the accuracy of this method is limited by the accuracy with which the ages of neutron fluence monitors dating standards are known calibrating the ages of standards by conventional means has proved difficult and contentious the emerging astronomically calibrated geomagnetic polarity time scale apts offers a means to calibrate the ages of 40ar 39ar dating standards that is independent of absolute isotopic abundance measurements seven published 40ar 39ar dates for polarity transitions nominally ranging from 0 78 to 3 40 ma are based on the fish canyon sanidine standard and can be compared with apts predictions solving the 40ar 39ar age equation for the age of the fish canyon sanidine that produces coincidence with the apts age for each of these seven reversals yields mutually indistinguishable estimates ranging from 27 78 to 28 09 ma with an inverse variance weighted mean of 27 95 0 18 ma normalized residuals are minimized at an age of 27 92 ma indicating the robustness of the solution

evidence for enhanced aridity in the tarim basin of china since 5 3 ma abstract thick cenozoic deposits formed from the erosion of the northern evolving edge of the tibetan plateau provide opportunities to study the exhumation history and climatic changes within the region such deposits are important because they are located in an actively deforming mountain belt as well as in a rain shadow of the tibetan plateau multi proxy studies indicate that hyperarid climate has prevailed since 5 3 ma ago within the basin this information together with the geometry analysis of syntectonic deposits of the sanju anticline which indicate tectonic deformation at 5 3 ma enable us to better understand the interlay between climatic changes and tectonic uplift our results suggest that the tectonic uplift of the kunlun mountains at 5 3 ma must have been one of the significant regional tectonic events and the uplifted elevation of the kunlun mountains more effectively blocks the penetration of moisture from the indian monsoon into the tarim basin and thus enhances the rain shadow effect this can account for the increasing aridity as well as the formation of the world s second largest active sand desert the taklimakan desert in the tarim basin initiated at 5 3 ma ago

fluid inclusion characteristics of intrusion related gold mineralization tombstone tungsten magmatic belt yukon territory canada intrusion hosted low sulfide sheeted vein systems are common within many plutons and stocks of the middle cretaceous tombstone tungsten magmatic belt yukon territory and host significant gold mineralization fluid inclusion characteristics of five such systems namely emerald lake dublin gulch scheelite dome mike lake and mactung constrain the vein forming fluid composition formation temperatures and pressures hydrothermal fluid processes and potential fluid sources the veins contain a wide range of fluid inclusion types ubiquitous type 1a and 1b inclusions are low salinity 1a xnacl 1 kbar at emerald lake and dublin gulch and 2 kbar at mactung and scheelite dome that potentially control fluid composition and evolution a variety of fluid processes may have been responsible for gold precipitation including immiscibility and or release of an evolving magmatic fluid

rock magnetism in loess from the middle tian shan implications for paleoenvironmental interpretations of magnetic properties of loess deposits in central asia 1 considerable attention has recently been paid to the magnetic properties of loess deposits in central asia however paleoenvironmental interpretations of magnetic properties of loess deposits in south tajikistan the ili basin and the tarim basin remain controversial current meteorological observations demonstrate that the mean annual precipitation in the junggar basin exceeds that in the tarim basin and falls below that in the ili basin and south tajikistan this study of rock magnetism in loess from the junggar basin improves our understanding of the complicated relationships between magnetic properties climate and source materials for loess deposits of central asia this study involved multiparameter investigations of rock magnetism in a 71 m loess section in the dongwan area on the northern slope of the middle tian shan in the junggar basin variations in concentration of coarse eolian ferrimagnetic minerals appear to provide the main control over the magnetic properties of loess in this area the contribution of ultrafine pedogenically produced magnetic grains to the magnetic susceptibility is minimal furthermore long term increasing trends in the and the saturation isothermal remanent magnetization sirm were found in the dongwan loess section these trends may be linked with intensified aridification of central asia in the mid pleistocene this study suggests that reduced precipitation of westerly moisture from tajikistan into the tarim basin might play a critical role in the paleoenvironmental interpretations of magnetic properties in the loess deposits of central asia

magnetostratigraphic and rock magnetic study of the neogene upper yaha section kuche depression tarim basin implications to formation of the xiyu conglomerate formation nw china 1 magnetostratigraphic study of 251 horizons through the younger yaha succession in the kuche depression of the tarim basin nw china lying beneath a massive regionally extensive xiyu conglomerate formation identifies nine reversed and eight normal polarity chrons correlating with the geomagnetic polarity time scale to show that deposition spanned the interval 5 3 to 1 7 ma sedimentation rates fell episodically from 49 to 24 cm kyr as neotectonic deformation in the southern tian shan thrust belt became focused on two major anticlines with the northern qiulitage anticline being initiated at 5 5 ma and developing a northern hinged limb that embraces the basal part of the studied section rock magnetic parameters show multiple signatures of lithologic change deformation burial diagenesis and climate with the latter identifying an early pliocene warm humid interval followed by cooling and desertification after 2 6 ma diachronous commencement of xiyu conglomerate deposition ranged from mid miocene in the north of the southern flank of the tian shan to pleistocene in the south advancing as a clastic wedge derived from the uplifted range front to the north this southward progradation was not climatically controlled although climatic effects may have modulated deposition during the pleistocene uplift in the tian shan at 16 15 ma correlates with rapid increase in sedimentation rate and episodic increases occurred subsequently until the initiation of the qiulitage anticline reduced rates since 5 0 ma contrast with increases more commonly recorded in foreland basins and have been controlled by accelerated growth of this regional structure counterbalancing uplift of the mountain front to the north

seasonal variability in the origin of recent atmospheric mineral dust at northgrip greenland abstract isotopic sr and nd and mineralogical analyses of dust extracted from snow deposits from the last decade at the northgrip greenland ice camp 75 1 n 042 3 w confirm the eastern asian source for greenland dust and extend it to the present day the 1998 and 1999 samples which represent a 2 4 month resolution of dust deposition show that there are at least two east asian sources for the greenland dust that vary seasonally the provenance of dust during the major spring summer deposition is the takla makan desert of northwest china

new insights into the magnetic variations of aeolian sands in the tarim basin and its paleoclimatic implications abstract the tarim basin where aeolian activity is widespread has been regarded as a major source for global dust production therefore knowledge about variation of magnetic parameters in aeolian sands from the tarim basin has a global significance systematic rock magnetic studies of aeolian sands from this region are still scarce because of the vast area and poor accessibility of the basin in this paper multi parameter rock magnetic investigations of a larger number of aeolian sand samples from a wide area in the tarim basin have been conducted we find that magnetic properties of aeolian sands are controlled by changes in the concentration of larger pseudo single domain and multidomain magnetite grains which are produced by weathering and erosional processes in the surrounding mountain regions in addition aeolian sands collected from different geographic regions of the tarim basin exhibit different magnetic properties suggesting that selective wind and river transport and low temperature oxidation might play a critical role for the magnetic properties of aeolian sands in the tarim basin our study also provides a better understanding of the complex relationships between magnetic properties and source materials for pliocene deposits in the basin

garnet geochemistry of tungsten mineralized xihuashan granites in south china abstract the xihuashan complex intrusion in south china which is emplaced at ca 154 ma mainly comprises medium grained porphyritic biotite granite medium grained biotite granite and fine grained two mica granite medium grained biotite and fine grained two mica granites are important tungsten bearing granites and contain an unusual amount of garnet garnets from this intrusion are dominated by almandine and spessartine which constitute 94 to 99 of the total molecular composition of the garnet these garnets display unusual compositional zoning the cores of these garnets are rich in heavy rare earth element hree y ca and contain abundant hree and y rich mineral inclusions their rims are free of mineral inclusions and have low of these elements two types of fluorite inclusions exist in garnet y fluorite and y poor fluorite garnet exhibits specific mn zoning with a relatively mn poor core but a relatively mn rich rim thus constituting a specific spessartine inverse bell shaped profile that belongs to typical magmatic garnets all analyzed garnets have high ree content and exhibit hree enriched and lree depleted patterns with strong negative eu anomalies the incorporation of ree into garnet is in part controlled by its crystal chemistry with ree3 following a coupled substitution of the type fe2 mn2 1viii ree3 1viii si4 1iv z3 1iv the texture and compositional zoning of garnet suggest that garnet growth is largely controlled by the pressure temperature composition condition of magmatic evolution internal crystal chemical parameters and kinetics during mineral growth the garnet core grows in near equilibrium with magmatic melt under a relatively high pressure temperature p t condition by contrast the garnet rim grows rapidly by the coexisting melt fluid phase and co2 rich volatile environment under a relatively low p t condition which is virtually unfavorable for the incorporation of ree into the magmatic garnet structure garnet fingerprints the magmatic hydrothermal transition during crystallization of these granites

internal structure and emplacement of the papoose flat pluton an integrated structural petrographic and magnetic susceptibility study the papoose flat pluton of eastern california is commonly cited in the geologic literature as a classic example of a forcibly emplaced pluton although the relative importance attributed to magmatic versus tectonic processes in controlling the structural evolution of the pluton has been controversial reexamination of this late cretaceous 83 ma pluton using a combination of new structural petrographic microstructural and anisotropy of magnetic susceptibility ams data on the pluton wall rock system has shown that the pluton is an inclined and internally zoned tabular structure assembled by forcible intrusion of successive pulses of magma at a crustal depth of 12 15 km initial pluton formation involved magma ascent in a vertical west northwest striking feeder dike which was arrested at a stratigraphically controlled mechanical discontinuity in the overlying cambrian metasedimentary rocks leading to formation of a southwest dipping sill subsequent sill inflation accompanied by horizontal infilling from the feeder dike at the base of the sill resulted in deformation and vertical translation of previously emplaced magma pulses and local raising of the sill roof facilitated by thermal weakening as the wall rock temperatures progressively rose during emplacement of successive magma pulses cooling from the roof of the pluton downward resulted in cessation of vertical inflation on the west side of the pluton and promoted lateral expansion toward the northeast and floor depression below the eastern part of the pluton we have been unable to document any regional scale structures e g of equivalence to similar age synplutonic strike slip shear zones in the sierra nevada batholith to the west that may have controlled emplacement of the papoose flat pluton however this fact does not preclude the likelihood that the country rocks were subjected to a regional deviatoric stress field at this time indeed tectonic overpressuring was probably essential for producing sufficiently high magma pressures for laccolith formation at this midcrustal level simple thermal modeling using microstructural and thermobarometric data indicates that the total duration of emplacement of the pluton did not exceed 30 000 yr this rapid emplacement rate may explain why the pluton appears to be anorogenic even though it was emplaced during a period of regional scale deformation

re os and u pb geochronology of the clear creek dublin gulch and mactung deposits tombstone gold belt yukon canada absolute timing relationships between plutonism and mineralization new re os molybdenite and u pb zircon dates from deposits of the tombstone gold belt provide direct timing constraints for sulphide mineralization and crystallization of spatially associated plutons at clear creek re os molybdenite dates 93 6 0 3 to 92 4 0 4 ma are in excellent agreement with the host intrusion u pb zircon age 92 3 0 3 ma consequently we propose the nominally younger existing 40 ar 39 ar hydrothermal mica ages 91 7 0 4 and 90 0 0 3 ma for clear creek are a result of slow cooling at dublin gulch the re os molybdenite date 93 2 0 3 ma for a late stage vein is nominally younger than the host intrusion u pb zircon age 94 0 0 3 ma in agreement with the deposits paragenesis the u pb zircon date 92 1 0 2 ma for the mactung pluton which lies adjacent to the w skarn has a younger age than the re os molybdenite dates 97 5 0 5 ma fluid inclusion geochemical data for ore fluid indicate a magmatic origin for the w skarn however the u pb and re os age data suggest that the exposed mactung stock is not the source of ore fluid for the w skarn and that the progenitor pluton for ore fluid is unknown the robust age constraints obtained for mineralization and magmatism in this study are in accord with the hypothesis that these deposits are intrusion related ore systems the results are also in agreement with previous studies demonstrating that the re os molybdenite chronometer can provide accurate and precise dates for the timing of metallic mineralization with rigorous sampling protocol

characteristics of near surface wind regimes in the taklimakan desert china abstract using wind data from 17 meteorological stations distributed throughout the taklimakan desert we described the characteristics of the desert s wind regimes and analyzed the spatial and temporal variations in wind direction and sand drift intensity the near surface wind regimes were closely related to general atmospheric circulation patterns and the surrounding topography there are two prevailing wind directions in the desert in general the eastern part of the desert is mainly affected by ne winds and the western part is affected by nw winds in the area towards the center of the desert but not around its edges the monthly mean wind velocity is strongly correlated with the monthly mean temperature with the exception of ruoqiang on the eastern edge of the desert the drift potential dp is less than 200 vu and the desert thus belongs to a low energy environment based on fryberger s classification in addition most parts of the desert have an rdp resultant dp dp value greater than 0 4 suggesting that the wind regimes have mainly unimodal or bimodal characteristics in contrast with the sand drift intensity which was highest in the north and east parts of the desert the highest frequency of sand dust storms occurred at the southwestern margin of the desert this results primarily from the differences of dust content on ground surfaces and land use types

magmatic petrogenesis and the evolution of f cl oh fluid composition in barren and tungsten skarn associated plutons using apatite and biotite compositions case studies from the northern canadian cordillera abstract a detailed study of apatite and biotite compositions in multiple intrusive phases from five composite plutons in the northern canadian cordillera was undertaken with the aim of determining the composition of magmatic fluids relative to f cl oh for several plutons both barren and mineralizing and for specific intrusive phases from each pluton that may be related to nearby tungsten skarns magmatic apatite and biotite compositions are consistent with a crustal source of magma either derived from predominantly supracrustal rocks and or derived from predominantly infracrustal rocks and fractionated to felsic compositions increasing mno feo and xf xcl with decreasing cao in apatite broadly correlates with an increasing degree of magmatic differentiation although fe vs total aluminum in biotite is a better indicator of inter and intra plutonic differentiation anomalously iron rich biotites occur in highly fractionated and or wallrock contaminated phases of plutons associated with tungsten skarns estimates of magmatic fluid composition calculated as the activity ratios log a hcl a hf and log a hoh a hf from apatite and biotite compositions show several trends with respect to magmatic differentiation two barren plutons demonstrate that fluids in silicic magmas become hf enriched relative to hcl with increasing differentiation although re equilibration with late stage sub solidus or hydrothermal fluids may obscure this trend the three intrusions with associated tungsten skarn mineralization including the world class cantung deposit also become hf enriched with magmatic evolution however magmatic apatite and biotite in individual intrusive phases that are the most closely associated with mineralization have equilibrated with compositionally distinct fluids in these particular intrusive phases apatite appears to have equilibrated with an earlier hcl and h 2 o rich magmatic fluid and biotite appears to have equilibrated with a later hcl and a particularly h 2 o rich magmatic fluid the fluid in these magmas apparently evolved to a h 2 o rich or less saline composition as the temperature of the magma decreased none of the other intrusive phases from either the barren or tungsten associated plutons have apatite and biotite activity ratios that are suggestive of equilibration with such an hcl hf and h 2 o hf rich fluid instead the activity ratios calculated from apatite and biotite in intrusive phases that are not as closely associated with mineralization are well coupled and unremarkable although small variations are common which would suggest that both minerals equilibrated with similar fluids these intrusive phases do not appear to have produced a large quantity of saline hydrous fluid capable of seggregating and transporting tungsten the identification of intrusive phases that did produce magmatic fluids that were anomalously enriched in hcl and h 2 o could therefore be a predictor of nearby tungsten skarn mineralization

scratching the surface a marine sediment provenance record from the continental slope of central wilkes land east antarctica the geology of wilkes land east antarctica is masked by kilometers of ice and remains largely unexplored defining the sediment provenance adjacent to this hidden region is important for distinguishing the proximal subglacial basement terranes and refining the dynamic regional glaciological history this study presents a detrital sediment provenance record spanning c 23 5 ka from the continental slope of central wilkes land sediment provenance was characterized using u pb geochronology and trace element geochemistry from detrital zircon titanite and apatite and pb isotopic signatures from detrital feldspar these data were compared with new feldspar pb isotopic signatures and existing u pb zircon datasets from rare nearby coastal outcrop a principally igneous source was revealed with dominant age populations between c 1360 1100 ma and c 1620 1490 ma characteristic of rocks of the proximal wilkes and banzare provinces respectively minor detritus was additionally sourced from the proximal nuyina province c 1450 1390 ma temporal variation in the climate and ice sheet configuration are likely responsible for subtle downcore changes observed in detrital sediment provenance high sedimentation rates during the glacial period suggest reworking of continental shelf sediments and downslope transport in debris flows during ice sheet advance glacial meltwater fluxes fed largely by the totten glacier were responsible for supplying detritus during deglaciation during interglacials detritus was derived from a broad coastal region and delivered to the slope via multiple glacial outlets these results present the first substantial offshore evidence to support recent interpretations that the subglacial crust of central wilkes land has a dominantly mesoproterozoic history

evolution of hf and hcl activity in magmatic volatiles of the gold mineralized emerald lake pluton yukon territory canada we examine the halogen contents of biotite amphibole and apatite from four magmatic phases of the emerald lake pluton to document the evolution in composition of magmatic volatiles in this system and to determine if this evolution is consistent with the nature and distribution of weak gold mineralization in the pluton in general the variations in halogen compositions of hydrous minerals are greater between magmatic phases than within single magma batches and the abundance of chlorine decreases and fluorine increases in hydrous minerals during the evolution of the emerald lake pluton by applying the internally consistent thermodynamic database and mineral activity composition relationships that account for coupled site substitution we further employ biotite and apatite compositions as independent monitors of fluid composition most analyzed biotite exhibits textural and or compositional features characteristic of late subsolidus halogen exchange with fluid however we have identified biotite that appears to retain halogen contents indicative of magmatic conditions fluorine contents of these biotites range from around 1 5 syenite and monzonite to greater than 2 2 wt in a late stage pegmatite dike chlorine by contrast shows a more restricted range of values and typically falls between 1 0 syenite and monzonite and 0 6 wt pegmatite apatite inclusions within anhydrous phenocrysts have fluorine contents of around 3 3 syenite to greater than 3 7 wt granite while chlorine contents fall from 0 5 to 0 1 wt with evolution from syenite to granite phases of the pluton the fluid a hcl a hf conditions recorded by biotite and apatite are in close agreement these two independent measures of hcl and hf both show a modest decrease in hcl hf as the system evolves the highest log a hcl a hf values 0 6 to 0 3 are associated with magmatic volatiles of syenite the first phase to intrude at emerald lake activity ratios recorded from the second phase monzonite show a slight fall to 0 4 to 0 1 a similar drop is recorded in the transition to hydrothermal activity recorded in biotite from a late pegmatite dike 0 1 to 0 1 a decrease in log a hcl a hf is consistent with a loss of chlorine and residual enrichment of fluorine in the magma due to progressive release of a chlorine bearing metalliferous fluid the relatively small variation in inferred fluid hcl and hf activity suggests that the magmatic volatiles present during crystallization were relatively homogeneous and argues against both the incursion of external fluids and of substantial temporal variation in fluid composition from the magma source furthermore if magmatic volatiles are the source of the gold mineralization found across all phases of the emerald lake pluton as advocated by other workers our data would suggest that the mineralizing fluids were remarkably homogeneous and distributed throughout the pluton the disseminated and low grade nature of mineralization may be at least in part a consequence

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

assessing the link between mantle source and sub volcanic plumbing in the petrology of basalts from the 2001 and 2002 2003 eruptions of mount etna sicily evidence from geochemical and helium isotope data abstract the 2001 and 2002 2003 flank eruptions of mt etna consisted of near continuous explosive activity and sporadic lava flows previous studies have suggested that distinct magmas were simultaneously tapped by fissures in different parts of the volcano indicating a complex plumbing system from textural and chemical data it has been suggested that eccentric eruptions on the south flank were fed by a deep seated reservoir that is not related to the central conduit in contrast materials erupted above 2600 m and from the northeast flank represent partially degassed more fractionated magma typical of that residing within the central vents a concern is that etna has entered a new phase of activity with magma supply from a deep reservoir that is capable of generating recurrent flank eruptions posing significant hazard to populated areas and air travel we have investigated materials that erupted from different vents during both the 2001 and 2002 3 eruptive episodes by means of petrology whole rock chemistry and helium isotopic methods here we show from trace element chemistry and the 3he 4he isotope record of melt inclusions in olivine that the mantle source for both magma batches is identical furthermore this magmatic source has not changed over the past 0 5 ma as such our data support the premise that the petrological variability exhibited by products that erupted from different parts of the volcano reflects storage fractionation and degassing at different levels within the crust

mechanisms and duration of non tectonically assisted magma emplacement in the upper crust the black mesa pluton henry mountains utah abstract a new study of black mesa pluton henry mountains colorado plateau utah usa indicates that it is a classic example of a small upper crustal pluton assembled over a few years by incremental amalgamation of discrete magma pulses the results of our petrostructural study of the pluton interior allow us to constrain the geometry kinematics and timing of the processes the symmetric internal fabric is interpreted as an evidence for a feeding by below and not laterally the observed rotation of the lineation from wnw ese on the very top to nne ssw below lead us to propose that the fabric at the base of the pluton is a record of magma infilling process and the fabric at the very top is a record of the strain due to the relative movement between magma and wallrocks a consequence is that except at the contact between pluton and wallrocks top and margins the stretching direction recorded by the lineation is not parallel to the flow direction of the magma i e displacement the black mesa pluton is a sheeted laccolith on its western edge and a bysmalith on its eastern edge this e w asymmetry in pluton geometry construction and the symmetrical internal fabric indicates that the apparently different west and east growth histories could have occurred simultaneously our field data indicate pluton growth through an asymmetric vertical stacking of sill like horizontal magma sheets one dimensional thermal models of the pluton provide maximum limits on the duration of its growth we have constrained the number the thickness and the frequency of magma pulses with our structural observations including 1 the emplacement of the pluton by under accretion of successive magma pulses 2 the absence of solid state deformation textures at internal contacts and 3 the apparent absence of significant recrystallization in the wallrocks our results suggest that the emplacement of the black mesa pluton was an extremely rapid event with a maximum duration on the order of 100 years which requires a minimum vertical displacement rate of the wallrocks immediately above the pluton greater than 2 m yr finally our data show that the rates of plutonic and volcanic processes could be similar a significant result for interpretation of magma transfer in arc systems

a rock magnetic study of loess from the west kunlun mountains west kunlun mountains have continuous loess deposits however very few papers have explored the rock magnetic characteristics of loess deposited there thus although kunlun mountains loess is one of the useful paleoclimate archives its importance has not been emphasized here we present detailed rock magnetic and bulk grain size studies on a 207 m loess core on the northern slope of the west kunlun mountains we find that magnetic susceptibility of loess from the northern slope of the west kunlun mountains is not controlled by changes in the concentration of ultrafine pedogenic magnetite and maghemite but instead controlled by changes in the concentration of aeolian multidomain magnetite and maghemite this is unsurprising given the low rainfall of the kunlun region and the lack of postdepositional weathering and soil formation in these aeolian sequences in addition we find that magnetic susceptibility values increase dramatically at 111 m corresponding to an age of similar to 0 5 ma the magnetic susceptibility increase is accompanied by coarsening of both bulk and magnetic grain size and softening of magnetic mineralogy we tentatively tie these changes in rock magnetic and grain size parameter records to an expansion of desert environment

links between magma tectonic rate balances plutonism and volcanism with smith s 1979 model of ash flow magmatism as the point of departure quantitative regimes of crustal magmatic evolution are outlined the average extrusive regime of ash flow magmatism operates at a rate of about 0 001 km3 yr progressively larger episodes of increasing repose times characterize the evolution of caldera forming eruptions the intrusive regime operates at an inferred average rate of about 0 01 km3 yr expressed in terms of the volumetric influx of mafic magma from the mantle based on the record of silicic rates of extrusion and a 10 1 intrusive to extrusive ratio derived from evidence of zoned silicic systems this rate is almost identical with the mean cumulative rate for the hawaiian emperor system of basaltic volcanism which is determined to be 0 015 km3 yr fluctuations about a mean rate of 10 2 km3 yr lead to a threefold classification of magmatic regimes in terms of source power depending on whether they are persistently greater than hher regime about equal to mher regime or lower than lher regime the mean hawaiian emperor rate ash flow magmatism correlates with the mher regime averaged over a sufficiently long time thus the conditions of hawaiian emperor magmatism are identified with a characteristic power of magma transfer rates that optimize mechanisms for creation of high level chambers of derivative and fractionated silicic magma terminology of smith 1979 within sufficiently localized regions of high residence times these conditions represent a balance point and a bifurcation in dynamic paths of magmatic evolution leading to widely divergent types of plutonic volcanic associations categorical examples of the principal types of igneous path are discussed relative to continental basalt silicic ash flow batholithic granite and intrusive porphyry systems the henry mountains utah are thought to represent an example of an intrusive porphyry generated in the lher regime of a mafic source system lacking sufficient power for volcanic expression or significant mineralization long valley california and possibly other systems along the eastern front of the sierra nevada is an example operating at the mean rate with transient excursions to higher and lower rates in regions of rapid extension and or volcanic propagation whether linear or areal these regimes give rise to basaltic eruptions ranging from isolated cinder cones to flood basalts

cassiterite u pb and muscovite40ar 39ar age constraints on the timing of mineralization in the xuebaoding sn w be deposit western china abstract the xuebaoding deposit in the songpan garze orogenic belt western china spatially associated with the xuebaoding granitic complex is a unique pegmatite type sn w be deposit within the giant songpan garze polymetallic belt a lack of precise geochronological constraints on the timing of mineralization for this deposit has precluded definitive statements relating to a genetic link between ore formation and granitoid intrusion up to now to address the temporal relationship between the emplacement of granite and the spatially associated sn w be polymetallic mineralization in the xuebaoding deposit systematic cassiterite u pb and muscovite ar ar dating were undertaken u pb data of cassiterite analyzed by in situ la mc icp ms provided an isochron age of 193 6 6 ma at 95 confidence level mswd 4 the 40 ar 39 ar dating on the muscovite intergrown with the cassiterite sample yielded a plateau age of 194 50 1 02 ma mswd 1 26 and an inverse isochron age of 194 53 1 05 ma mswd 1 34 both the ar ar dates overlap the u pb date within uncertainties placing the timing of tin mineralization at 193 194 ma this is consistent with field geological relationships that show veins cutting marble and granite and with previous sm nd dating within experimental error for scheelite and indicates that sn w polymetallic mineralization at the xuebaoding deposit occurred during the early jurassic combined with previous published trace element and ree data from the xuebaoding granites and other ore minerals as well as the timing of granite emplacement the temporal and genetic associations between granite intrusion events and sn w mineralization of this deposit have been discussed in this paper the results suggest that the pankou granite is genetically related to the polymetallic mineralization in xuebaoding sn w be deposit and further demonstrate that the latest phase of granitic intrusion is commonly favorable for sn and or w mineralization although the pukou granite also exhibits close relationships with the ore formation in its spatial distribution and element characteristics the possibility as a parent for this deposit is excluded duo to the time span from its emplacement to mineralization event that exceed the estimated life of modern geothermal systems

timing slip rate displacement and cooling history of the mykonos detachment footwall cyclades greece and implications for the opening of the aegean sea basin we constrain the slip and cooling history of the mykonos detachment footwall using thermochronometry a u pb zircon age of 13 5 0 3 ma dates intrusion of the mykonos monzogranite 40 ar 39 ar hornblende and biotite ages from the monzogranite are 12 7 0 6 ma and 10 9 0 6 ma whereas zircon and apatite fission track ages range from 13 0 8 ma to 10 7 0 8 ma and 12 5 2 2 ma to 10 5 1 8 ma u th he ages range from 13 6 0 6 ma to 9 0 0 7 ma for zircon and 11 1 0 5 ma to 8 9 0 4 ma for apatite the ages in part overlap within 2 errors and together with the long apatite fission track lengths 14 m support rapid cooling at rates 100 c ma 1 the low temperature thermochronometric ages decrease east northeastwards in the direction of hanging wall transport on the mykonos detachment age distance relationships show that the mykonos detachment slipped at an average rate of 6 0 9 2 2 4 km ma 1 causing c 30 km of offset and c 12 km of exhumation this result indicates that miocene low angle normal faulting was not important for the exhumation of the cycladic blueschist unit the opening of the aegean sea basin in the miocene was controlled by a few large magnitude low angle normal faults

mineral magnetic investigation of the talede loess palaeosol sequence since the last interglacial in the yili basin in the asian interior summary the loess palaeosol deposit in the asian interior is sensitive to the evolution of the westerlies thus providing a good opportunity to investigate regional palaeoenvironmental evolution and its relationship with global climatic changes multiparameter mineral magnetic investigations have been conducted on the talede section in the yili basin asian interior our study finds that 1 loess samples have higher concentration magnetic minerals than palaeosols though the magnetic mineral composition is similar ferrimagnetic magnetite antiferromagnetic hematite and lepidocrocite 2 large pseudo single domain psd and multidomain md like grains dominate both in loess and palaeosols however magnetic mineral grains in loess are much coarser than those in the palaeosols 3 palaeosols contain approx 30 per cent more amount of hematite than the loess samples the frequency dependent susceptibility of both loess and palaeosols is very low indicating the small amount of super paramagnetic grains and the higher fd per cent values of palaeosols also reveal that palaeosols have more amounts of ultrafine magnetic grains than loess the magnetic variations in part 1 and 2 can be well explained by the wind vigour model but the observed enrichment of hematite and ultrafine magnetic grains in palaeosols also reveals the first onset of pedogenic enhancement therefore the talede section could be seen as an end member of the classic chinese loess plateau clp magnetic enhancement model

assembly of a dike fed magma chamber the jackass lakes pluton central sierra nevada california the mechanisms of ascent assembly and emplacement of granitic magma in the crust are critical to understanding the dynamics of continental margin growth yet these mechanisms remain controversial and poorly understood detailed study of structural and petrologic fabrics in the middle cretaceous jackass lakes pluton wall rock system central sierra nevada california coupled with u pb geochronology indicates that the pluton formed via sheet like assembly of a dike fed magma chamber final emplacement of the pluton was facilitated by multiple brittle and ductile mechanisms that were active at different times and places within the system this supports hybrid viscoelastic emplacement models as realistic alternatives to end member models i e dike versus diapir fracture propagation which initiated 40 of the space required for emplacement may have been facilitated by a small component of arc parallel dextral shear that produced north northwest striking tension gashes a combination of ductile wall rock shortening during lateral expansion of sheets and return flow of elongate strongly deformed wall rock septa produced an additional 25 of the space required other mechanisms including coeval formation of the overlying minarets caldera and stoping in the subvolcanic part of the magma chamber must account for the remaining 35 space implying that vertical transfer of material is an important emplacement mechanism at shallow crustal levels

wind energy environments and dunefield activity in the chinese deserts there are few detailed analyses of the wind energy environments and dunefield activity in the chinese deserts on the basis of wind data and other climatic parameters collected at meteorological stations in and around the deserts this paper considers wind environments and dunefield activity in the chinese deserts in the 1990s the results show that dunes in most of the deserts were developed and controlled by low energy wind regimes although most dunes had the morphology of transverse and linear types which is consistent with wind regimes some deserts did not show close relations between dune morphology and regional wind directional distributions due to other controls although sand transport mainly occurs in spring and early summer there is strong sand transport activity in winter in some deserts dune activity in the chinese deserts has great spatial variations the regions with low dune activity are located in the chaidm mu us hobq horqin and nenjiang deserts due to much higher annual precipitation in these regions the areas with strong dune activity are located in the eastern taklimakan and northern badain jaran deserts due to arid conditions and much stronger winds

a pedogenic model for the magnetic enhancement of late miocene fluvial lacustrine sediments from the xining basin ne tibetan plateau

geothermometry from 40ar39ar dating experiments abstract we have selected a variety of minerals from three basic intrusions within the high grade metamorphic terrane near haliburton ontario for k ar dating by application of 40 ar 39 ar incremental heating experiments we conclude that the discordant k ar mineral dates can best be explained by a slow cooling history from the stepwise heating experiments we calculated isotopic closure temperatures using dodson s theory for slow cooling and from these constructed a cooling curve this curve was then compared to independent constraints to test the overall validity of our procedures and assumptions the results are geologically reasonable insofar as 1 a the maximum calculated temperatures from hornblendes of 700 c are consistent with independent approximate metamorphic grid arguments 2 b the ar closure temperatures for biotites 350 400 c are consistent with independent evidence and 3 c minerals with older k ar dates have higher calculated closure temperatures the resultant geological cooling curve implies that a maximum temperature of 700 c was reached before 1000 ma ago and thereafter the temperature decreased via changes in uplift and cooling rates to below 200 c by 700 ma ago we have discovered that plutonic plagioclases are very sensitive indicators comparable to k felds pars of ar loss and therefore can usefully extend the range of application of the 40 ar 39 ar stepwise heating method we also describe experiments in which we have tested the effects on the ar systematics of acid leaching of plagioclases

processes operating during the initial stage of magma chamber evolution insights from the marginal reversal of the imandra layered intrusion russia the 13 m thick marginal zone of the 3 5 km thick mafic imandra layered intrusion ili consists of fine grained pigeonite gabbros that are chilled against the underlying host andesitic basalts but reveals a non chilled highly irregular upper contact with orthopyroxenites of the overlying layered series the marginal zone shows pronounced reverse compositional trends from the bottom to the very top and can therefore be referred to as a marginal reversal in particular the mg number of pyroxenes and the an content of plagioclase as well as the whole rock mgo mg number and normative an content show a systematic upward increase whereas all incompatible components e g tio2 k2o p2o5 rb ba zr y ree reveal an upward decrease similar reverse compositional trends are characteristic of intratelluric phenocrysts of plagioclase and inverted pigeonite that occur throughout the entire marginal zone the marginal zone is abruptly terminated by the overlying coarse grained orthopyroxenites which are interlayered with massive chromitite of the layered series the boundary between these two major units of the ili represents a sharp break in terms of grain size chemical composition and crystallization sequence it is noteworthy that the fine grained pigeonite gabbros of the marginal zone are distinguished by much lower concentrations of all incompatible elements than the coarse grained orthopyroxenite of the layered series the data indicate that filling of the chamber started with evolved phenocryst bearing liquids that probably represent the leading fractionates of parental basaltic magma that crystallized against the sidewalls of a deep conduit system the formation of the marginal zone from these evolved liquids was interrupted by the emplacement of a large batch of parental magma that reached the chamber without much fractionation en route to crystallize into the layered series the origin of the marginal reversal is best explained by the three increase model which implies that rocks becomes more primitive inwards in response to 1 an inward increase in the extent of primitivity of successively intruding magma pulses 2 an inward increase in the degree of chemical equilibrium among the phases and 3 an inward increase in the proportion of crystallizing cumulus minerals the notable distinction in incompatible element abundances between the marginal zone and the layered series is attributed to fundamentally different regimes of magma flow during their formation the crystallization of the marginal zone was dominated by fast flowing 0 5 5 m s intruding magmas that favoured the effective removal of evolved liquids from in situ growing crystals and the generation of incompatible element depleted mesoto adcumulates fine grained pigeonite gabbro in contrast the formation of the layered series was associated with a slow flowing 0 5 5 km a thermally convecting magma that was much less effective in stripping evolved liquid from the crystallizing minerals and therefore gave rise to incompatible element enriched orthocumulates coarse grained orthopyroxenites the proposed sequence of magma replenishment and rock forming processes may be common during the initial stage of the development of basaltic magma chambers

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

evolution of the northern cordilleran foreland basin during the middle cretaceous a detailed study of the middle late cenomanian belle fourche formation in southern alberta helps to elucidate the evolution of the cordilleran foreland basin during the middle cretaceous by combining isopach data from the study area with previously published research on middle cretaceous stratigraphy in adjacent areas of northern alberta and montana it is possible to defi ne the position of the proximal foredeep forebulge and backbulge depozones from late albian to cenomanian time the foredeep probably lay to the west of the present fold thrust belt in western montana from the late albian to middle cenomanian with the forebulge extending northwestward through the northwest corner of wyoming and curving northeastward through the present day location of calgary thick dunvegan deposits middle cenomanian of northwestern alberta are interpreted as foredeep deposits palinspastic reconstruction of the southern rocky mountains of alberta is consistent with a location of the foredeep within the area of the present fold thrust belt at the end of the middle cenomanian the forebulge retreated westward within alberta defi ning a nearly straight northwest southeast trend through the present position of the foothills and front ranges of alberta and northwestern montana the change in trend of the foreland basin at the end of the middle cenomanian may refl ect the change of convergence vectors along the western margin of north america during the middle cretaceous

thermal effects of magma degassing abstract the thermodynamics of diffusive bubble growth is dominated by latent heat of water exsolution vaporization and the work of gas expansion p dv work a numerical assessment of the effects of these on cooling of bubbly magma water in albite indicates that a magma can exsolve volatiles at equilibrium or with varying degrees of oversaturation depending on decompression history and degassing kinetics heat of water exsolution vaporization from magmatic melts has not previously been experimentally or analytically determined and we have evaluated it from others thermodynamic functions known for the albite water system heat of exsolution is small for pressures over 100 mpa but can reach 20 kj mole at 1 2 mpa 10 20 bar oversaturation degassing at 10 20 bar can cause cooling of albite by 8 k wt of exsolved water the thermal effect of equilibrium degassing depends on the starting pressure of decompression because it follows the solubility curve for a saturated melt at 100 mpa 4 wt water it can cool a magma at least by 35 k before it disrupts into spray as gas volume fraction exceeds 0 8 although we do not specifically consider the dynamics of bubble interactions in this study our results suggest that the dynamic cooling rate could be significant at the vent of an erupting magma column and under extreme eruption conditions can lead to glass formation around fast growing bubbles of magmatic foam this could cause fragmentation into fine ash by brittle failure conversely bubble wall cooling even before glass formation can serve to reduce diffusive volatile flux into bubbles decreasing the overall cooling of the system and lead to solidification of oversaturated magmas as occasionally observed in eruption products

correlation of mid cretaceous granites with source terranes in the northern canadian cordillera this study presents a broad geochemical and isotopic synthesis of mid cretaceous granites in the southern yukon as well as a comparative data set for granites sourced from and hosted by accreted

the great glen fault a major vertical lithospheric boundary two lamprophyre suites are used to constrain sub continental lithospheric mantle domains in late caledonian northern britain at 400 ma a northern highlands and a southern domain are resolved the first has low nd 6 4 to 12 8 the latter has higher 3 9 to 3 4 the boundary between them is coincident with the surface expression of the great glen fault the two mantle domains tightly bracket the fault the lamprophyre magmas were generated at depths of at least 100 km at the end of the caledonian orogeny the great glen fault was a major vertical discontinuity that transected the sub continental lithospheric mantle

time scales of assembly and thermal history of a composite felsic pluton constraints from the emerald lake area northern canadian cordillera yukon knowledge of the time scales of emplacement and thermal history during assembly of composite felsic plutons in the shallow crust are critical to deciphering the processes of crustal growth and magma chamber development detailed petrological and chemical study of the mid cretaceous composite emerald lake pluton from the northern canadian cordillera yukon territory coupled with u pb and 40 ar 39 ar geochronology indicates that this pluton was intruded as a series of magmatic pulses intrusion of these pulses produced a strong petrological zonation from augite syenite hornblende quartz syenite and monzonite to biotite granite our data further indicate that multiple phases were emplaced and cooled to below the mineral closure temperatures over a time scale on the order of the resolution of the 40 ar 39 ar technique v1 myr and that emplacement occurred at 94 3 ma simple thermal modelling and heat conduction calculations were used to further constrain the temporal relationships within the intrusion these calculations are consistent with the geochronology and show that emplacement and cooling were complete in less than 100 kyr and probably 70 5 kyr these results demonstrate that production transport and emplacement of the different phases of the emerald lake pluton occurred essentially simultaneously and that these processes must also have been closely related in time and space by analogy these results provide insights into the assembly and petrogenesis of other complex intrusions and ultimately lead to an understanding of the processes involved in crustal development 2002 elsevier science b v all rights reserved

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

thermal history of the pan african brasiliano borborema province of northeast brazil deduced from 40ar 39ar analysis abstract detailed step heating 40 ar 39 ar analyses were performed on different minerals from magmatic and metamorphic rocks of the borborema province this region located in northeast brazil belongs to the pan african brasiliano belt which is about 1000 km wide and 600 km long twenty six single grains of amphibole muscovite and biotite were extracted from eighteen samples selected in an area of about 17 500 km 2 250 km by 70 km in the patos region this region has been affected by a continental scale shear zone system well defined 40 ar 39 ar plateau ages and an u pb analysis on zircon leterrier j jardim de sa e f bertrand j m and pin c 1994 ages u pb sur zircon de granitoides brasilianos de la ceinture du serido province borborema ne bresil c r acad sci paris 318 1505 1511 allow the definition of a homogeneous and unusual slow cooling history 3 4 c ma and suggest a rather slow uplift rate between 580 and 500 ma followed by a fast cooling of the whole studied area around 500 ma rapid cooling is suggested by concordant plateau ages on muscovite and biotite the existence of such an event at the end of the belt history is in agreement with data obtained on other major belts such as the alpine himalayan system or the hercynian belt

multiscale magmatic cyclicity duration of pluton construction and the paradoxical relationship between tectonism and plutonism in continental arcs abstract the close relationship between crustal magmatism an expression of heat dissipation and tectonics an expression of stress dissipation leads to the question of their mutual relationships indeed the low viscosity of magmas and the large viscosity contrast between magmas and surrounding rocks favor strain localization in magmas and then possible magmatic initiation of structures at a wide range of scales however new data about 3 d pluton shape and duration of pluton construction perturb this simple geological image and indicate some independence between magmatism and tectonics in some cases we observe a direct genetic link and strong arguments for physical interactions between magmas and tectonics in other cases we observe an absence of these interactions and it is unclear how magma transfer and emplacement are related to lithospheric plate dynamics a simple explanation of this complexity follows directly from the pulsed incremental assembly of plutons and its spatial and temporal characteristics the size of each pluton is related to a magmatic pulsation at a particular time scale and each of these coupled time space scales is related to a specific process in small plutons we can observe the incremental process the building block of plutons in larger plutons the incremental process is lost and the pulsation which consists of a cycle of injections at different timescales must be related to the composition and thermal regime of the source region itself driving magmatic processes melting segregation and transfer that interact with tectonic boundary conditions the dynamics of pulsed magmatism observed in plutonic systems is then a proxy for deep lithospheric and magmatic processes from our data and a review of published work we find a positive corelation between volume and duration of pluton construction the larger a pluton the longer its construction time large fast or small slow plutons have not been identified to date one consequence of this observation is that plutonic magmatic fluxes seem to be comparable from one geodynamic setting to another and also over various geologic time spans a second consequence of this correlation is that small plutons which are constructed in a geologically short length of time commonly record little about tectonic conditions and result only from the interference between magma dynamics and the local geologic setting the fast rate of magma transfer in the crust on the order of cm s relative to tectonic rates on the order of cm yr explain why the incremental process of pluton construction is independent of but not insensitive to the tectonic setting however in large plutonic bodies which correspond to longer duration magmatic events regional deformation has time to interact with the growing pluton and can be recorded within the pluton wall rock structure magma transfer operates at a very short timescale comparable to volcanic timescales which can be sustained over variable periods depending on the fertility of the magma source region and its ability to feed the system the fast operation of magmatic processes relative to crustal tectonic processes ensures that the former control the system from below

incremental growth of the patagonian torres del paine laccolith over 90 k y the miocene paine granite in the torres del paine intrusive complex southern chile is an extraordinary example of an upper crustal mafic and granitic intrusion the granite intruded as a series of three sheets each one underplating the previous sheet along the top of the basal paine mafic complex high precision u pb geochronology on single zircons using isotope dilution thermal ionization mass spectrometry yields distinct ages of 12 59 0 02 ma and 12 50 0 02 ma respectively for the first and last sheet of the laccolith this age relationship is consistent with field observations the zircon ages define a time frame of 90 40 k y for the emplacement of a 2000 m thick granite laccolith these precise u pb zircon ages permit identification of the pulses in a 20 k y range the data obtained for the paine granite fill the gap between 100 k y and 100 1000 yr pulses described in the literature for crustal magma chambers

paleoclimatic significance of the temperature dependent susceptibility of holocene loess along a nw se transect in the chinese loess plateau we have conducted mineral magnetic investigations of samples of modern dune sand pristine loess and present day loess along a nw se transect from the northern to the central loess plateau in china the methods used include the temperature dependence of susceptibility tds before and after citrate bicarbonate dithionite cbd treatment as well as x ray diffraction xrd analysis the xrd analyses demonstrate that magnetite and hematite both exist in the chinese loess paleosol sequence and its modem source area but the tds measurements show that magnetite is the predominant contributor to magnetic susceptibility maghemite is present in the pristine loess and the present day loess due to pedogenesis the pedogenic processes that produce the maghemite are closely linked to paleoclimate and for this transect precipitation appears to be the most important climatic variable we suggest that tds can be used as a useful method for the analysis of pedogenesis and climatic change

extensional faulting on tinos island aegean sea greece how many detachments zircon and apatite fission track zft and aft and u th he 40ar 39ar hornblende and u pb zircon ages from the granites of tinos island in the aegean sea greece suggest together with published zft data that there are three extensional detachments on tinos the tinos granites crosscut the tinos detachment cooling of the granites was controlled by the livadi detachment which occurs structurally above the tinos detachment our u pb zircon age is 14 6 0 2 ma and two 40ar 39ar hornblende ages are 14 4 0 4 and 13 7 0 4 ma zft and aft ages go from 14 4 1 2 to 12 2 1 0 ma and 12 8 2 4 to 11 9 2 0 ma u th he ages are from 10 4 0 2 to 9 9 0 2 ma zircon and 11 9 0 5 to 10 0 0 3 ma apatite all ages decrease northeastward in the direction of hanging wall transport on the livadi detachment and age distance relationships yield a slip rate of 2 6 3 3 1 0 km ma 1 this rate is smaller than a published slip rate of 6 5 km ma 1 for the vari detachment which is another detachment structurally above the tinos detachment because of the different rates and because published zft ages from the footwall of the vari detachment are 10 ma we propose that the vari detachment has to be distinguished from the older livadi detachment we discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the vari detachment cut down into the footwall of the livadi detachment successively exhuming deeper structural units the thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation

a review of shallow ore related granites textures volatiles and ore metals shallow texturally complex granites can be associated spatially introduction and temporally with hydrothermal alteration and mineralization granite related ore deposits include porphyry and skarn the formation of a granite related ore deposit represents the confluence type ores and other hydrothermal deposits that are of many chemical and physical geological factors including magma spatially and temporally associated with granitic sensu composition e g concentrations of ore metals chlorine and water lato rocks in this paper i emphasize characteristics magma oxidation state the relative timing of crystallization magma found in porphyry style cu mo au deposits and some ascent magmatic volatile phase exsolution and the depth of em related systems however my treatment here is not meant placement early magmatic crystallization of ore metal rich minerals to cover the full range of granitic rocks and mineralization coupled with late exsolution of the magmatic volatile phase is that make up the granite related ore systems the forpromoted by deeper emplacement levels and lower magmatic water mation of granite related ore deposits by orthomagmatic concentrations and leads to low eyciencies of removal of compatible hydrothermal processes is dependent upon many physical elements from melts into the magmatic volatile phase s water and chemical magmatic factors including but not limited concentrations in the melt and pressures of crystallization can be to the composition and evolution of the associated estimated from phase equilibria and textural relationships of horn magmas the rate of magma ascent the depth and blende in some felsic systems physical factors avect the dynamics geometry of magma emplacement and the local temof fluid magma melt and volatile phase movement which in turn perature and stress fields at the site of magma emavect the size of zones of alteration and mineralization granite placement detailed studies of the igneous rocks textures can record the partial history of some dynamic processes associated with ore deposits can therefore yield critical miarolitic cavities are good evidence for magmatic volatile phase information regarding the source of metals and ligands exsolution both miarolitic cavities and pegmatitic texture exhibit in the ore generative hydrothermal solutions that are evidence for external nucleation of crystals nucleation controlled operative in the formation of granite related ores in this phenomena expressed as variations in granite textures can result review i will present a series of narratives consistent in from a multiplicity of causes including undercooling of the melt my view with prevailing field and experimental data on textural elements such as pegmatite aplite skeletal crystals and the orthomagmatic hydrothermal theory for the genesis graphic textures can form as a result of undercooling interconnected of some granite related deposits volumes of the magmatic volatile phase allow for advection of some high level granites i e those that are emplaced hydrothermal ore fluids through the magma in shallow granitic at depths of 8 km or less represent the crystallized systems miarolitic cavities can be interconnected consistent with remains of magmas that were associated with subvolcanic this hypothesis ore generative hydrothermal systems therefore studies of shallow granites aimed at understanding magmatic evolution and volatile phase exsolution at shallow levels are necessary if we are to understand ore genesis and the deep inputs to present day geothermal systems as well as evaluate hazards associated with the volcanic

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

position by position cooling paths within the toki granite central japan constraints and the relation with fracture population in a pluton abstract understanding the locational differences of time temperature t t paths within the granite contributes to clarifying the detailed formation history especially the thermal evolution of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust the position by position t t paths of fifteen samples of the toki granitic pluton central japan are reconstructed from thermochronological data including zircon u pb biotite k ar zircon fission track zft and apatite fission track aft ages ft length characterization and ft inverse calculation in case of sample no 1 the t t path consists of zircon u pb ages 74 0 1 1 ma and 72 6 1 7 ma a biotite k ar age 73 0 1 8 ma a zft age 57 2 2 3 ma an aft age 41 5 2 7 ma and the ft inverse calculation the t t paths show position specific characteristics that reflect the history of the pluton after the incipient intrusion of the granitic magma into the shallow crust shallow parts of the western and northeastern margins of the pluton show rapid cooling from the intrusion stage to the zft partial annealing zone paz and thus represent position specific characteristics in relation to crustal assimilation in the intrusion emplacement processes the cooling behavior around the condition of aft paz was interpreted as a reflection of regional tectonic exhumation of the pluton this study also presents useful knowledge to evaluate fracture populations in a granitic pluton the relationship between the position specific t t path and fracture frequency fracture number per unit interval provides a criterion for evaluating the fracture population of the granitic pluton called thermochronological evaluation which is a key insight to investigating fluid flow and mass transfer in the rock mass the t t path shows whether cooling was slow or rapid from thermal conditions of solidification crystallization to the biotite k ar closure temperature parts of the pluton that cooled slowly correspond to parts with high frequencies of fractures and vice versa the absolute value for duration between the zircon u pb age evaluated from the oscillatory zoned area oz age and biotite k ar age shows high correlation with fracture frequency r2 0 89 and thus gives a quantitative indicator for evaluating fracture frequency longer duration accompanies higher frequency a combination of thermochronological evaluation the local cooling indicator and the lithofacies effect can be applied as potential diagnostic tools for detailed evaluation of the fracture population

a method for intercalibration of u th pb and 40ar 39ar ages in the phanerozoic the increasing analytical precision of 40ar 39ar geochronological data and its use in studies that combine u pb and 40ar 39ar data has necessitated derivation of a means to intercalibrate ages between the two isotopic systems the primary determinants inhibiting accurate cross calibration are uncertainty in decay constant values and uncertainty in 40ar 40k usually presented as apparent age for 40ar 39ar standards notably those derived from the fish canyon tuff by utilizing a monazite and biotite bearing oligocene ash flow tuff mac 83 as the primary standard material precise u th pb and 40ar 39ar ages can be derived because both isotopic systems should reflect closure during the instantaneous eruption event the 24 21 0 10 ma 207pb 235u age should match the age resulting from 40ar 39ar biotite analysis this forced equivalence will partly offset the effects of decay constant uncertainty furthermore by co irradiating fish canyon tuff sanidine with mac 83 biotite the apparent age for fish canyon tuff sanidine is back calculated to 27 98 0 15 ma relative to the mac 83 207pb 235u age hence intercalibration between the two isotopic systems in a relative sense can be accomplished allowing for a direct and valid comparison of ages it is also shown that forcing equivalence of the two isotopic systems minimizes the effect of decay constant uncertainty for samples of phanerozoic age

mineral magnetic variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling a high resolution mineral magnetic investigation has been carried out on the jingbian loess paleosol sequence at the northern extremity of the chinese loess plateau results show that the magnetic assemblage is dominated by large pseudo single domain and multidomain like magnetite with associated maghemite and hematite variations in the ratios of sirm100mt sirm sirm100mt sirm30mt and sirm100mt sirm60mt sirm is the saturation isothermal remanent magnetization sirmnmt represents the residual sirm after an n mt alternating field demagnetization have been used to document regional paleoclimate change in the asian interior by correlating the mineral magnetic record with the composite 18o record in deep sea sediments the long term up section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema respectively which reveals a long term decreasing trend in chemical weathering intensity in both glacial stage source region the gobi and deserts in northwestern china and interglacial stage depositional area the loess plateau region we further relate this long timescale variation to long term increasing aridification and cooling during both glacial extrema in the dust source region and interglacial extrema in the depositional area over the quaternary period changes in those ratios are most likely due to quaternary aridification and cooling driven by ongoing global cooling expansion of the arctic ice sheet and progressive uplift of the himalayan tibetan complex during this period

anatomy of garnets in a jurassic granite from the south eastern margin of the north china craton magma sources and tectonic implications abstract the late jurassic jingshan granite located at the south eastern margin of the north china craton contains abundant garnets which can be subdivided into three types based on texture and composition i euhedral garnet in mafic biotite and garnet rich enclave grt i ii coarse grained garnet grt ii in the host granite and iii small euhedral garnet in aplite grt iii in general grt i has higher feo cao and lower mno contents than grt ii grt iii has higher mn but lower ca contents than others grt i has lower mree and hree contents than grt ii grt iii has prominent and distinctly negative eu anomaly as well as higher mree composition compared to the others systematic variations in oxygen isotope compositions are observed among the three garnet types with 18 o values of 4 7 in grt iii some of the grt ii and grt iii display two distinct zonings with cores having similar major and trace element compositions to grt i cathodoluminescence cl images revealed that the zircons from different garnet bearing samples possess fine scale oscillatory zoned magmatic rims with inherited cores in situ zircon u pb dating and trace element analyses show that the dark luminescent magmatic rims all have jurassic concordia ages 160 ma and similar trace element patterns most of the inherited cores also display similar triassic ages of 210 236 ma which is similar to the ages of ultrahigh pressure uhp metamorphic rocks of the dabie sulu orogen 230 ma in addition jurassic concordia ages were also found in a zircon inclusion in grt i implying that the grt i was formed shortly before the main magmatic event the age data suggest that the three different garnet types may be genetically related and modified by cogenetic magmatic events based on the zircon u pb ages from different garnet bearing samples the major element trace element oxygen isotope and zoning textures of the three kinds of garnet we suggest that grt i may be peritectic garnet whereas grt ii and iii are probably the results of magmatic dissolution precipitation processes and re equilibration of garnets with changing magmatic conditions during melting differentiation crystallization and cooling within the granite we conclude from the oxygen isotopic character of the garnets and ages of the zircons that the source rocks for the jingshan granites are from dabie sulu orogen representing the south china craton

porphyry deposits of the northwestern cordillera of north america edited by t g schroeter special volume 46 canadian institute of mining metallurgy and petroleum montreal 1995 888 pp canadian 95 plus 15 handling isbn 0 919086 56 x

incipient magma chamber formation as a result of repetitive intrusions an analytical solution for periodic magma intrusions in conduits was developed to study the onset of shallow magma chamber formation the solution is based on determining when a repetitive series of intrusions can cause the wall rock of a conduit to reach its melt temperature the results show that magma chamber formation in conduits is a strong function of the volume rate of intrusion and that magma chamber formation is likely when the intrusion rate exceeds 10 3 km3 yr which agrees with observations by other investigators once this critical value of intrusion rate is reached magma chambers are likely to begin forming after only a few intrusive pulses less than ten results for both cylindrical conduits and dikes show cylindrical conduits are more favourable for the formation of shallow magma chambers

comparison of hysteresis thermomagnetic and low temperature magnetic properties of particle size fractions from loess and palaeosol samples in central asia and the chinese loess plateau

magnetic proxy climate results from the duanjiapo loess section southernmost extremity of the chinese loess plateau we report mineral magnetic results from a 7 5 m loess sequence 150 samples from the southernmost extremity of the chinese loess plateau which includes the last two glacial cycles in this area the loess sediments experienced particularly intense weathering processes the magnetic assemblage is dominated by a mixture of pseudo single domain psd and multidomain md magnetite with associated superparamagnetic sp grains of either magnetite or maghemite in the paleosols and weathered loess horizons all the rock magnetic parameters fluctuate in parallel with marine sediment 18o data over the last 150 kyr thus reflecting changing global paleoclimatic conditions this relationship is also supported by the evidence of milankovitch cycles in the magnetic susceptibility record paleorainfall estimates when compared with other studies from the chinese loess plateau underline the more humid character of this region during the last 130 kyr

thermal requirements for extensional emplacement of granitoids numerical models of magma emplacement during crustal extension show that shallow 10 km rhyolitic to andesitic magma chambers can form and be maintained at typical rates of extension of continental crust chambers at depths of 8 km form within 90 ka after emplacement of a total width of 4 km of magma at half extension rates of 2 cm yr once even a small 1 km wide shallow chamber has formed by any process it can be maintained by extension at a half rate of 1 cm yr high temperatures are maintained at a half rate of 0 5 cm yr continental rifts and dilational jogs along strike slip faults in arcs provide areas where extension rates are most appropriate large granitoids and batholiths can form by this process over millions of years actual chambers at any one time may be considerably smaller than preserved granitoids

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

fast strain rates during pluton emplacement magmatically folded leucocratic dikes in aureoles of the mount stuart batholith washington and the tuolumne intrusive suite california finite strain analysis and thermal modeling of magmatically folded leucocratic dikes in the mount stuart batholith washington and the tuolumne intrusive suite california yield strain rates in the range of 10 2 to 10 1 3 s 1 compared to published regional strain rates 10 1 3 to 10 1 5 s 1 wall rock strain rates associated with dike fed expansion 10 7 s 1 and rates resulting from numerical modeling of crystal plastic creep in aureoles 10 1 1 s 1 our fast rates are several orders of magnitude higher field and microstructural observations suggest that multiple material transfer processes including rigid rotation ductile flow cracking and potentially melt assisted granular flow operated in the aureoles to accommodate emplacement of these two plutons calculated durations of pluton construction and bulk shortening in the aureoles indicate that aureole deformation requires only slow long term strain rates of 10 1 4 s 1 thus our local fast strain rates indicate that aureoles may be characterized by pulsating high strain rate surges we suggest that magmatically folded dikes in these and other pluton aureoles around the world may be used as evidence for fast host rock strain rates during pluton emplacement

cretaceous reduced granitoids in the goodpaster mining district east central alaska the 5 moz 1 oz troy 31 103 g gold veins of the liese zone and nearby prospects in the goodpaster mining district of east central alaska are spatially and temporally associated with late early to late cretaceous reduced granitoids that are divided into a granite suite tonalite suite and diorite suite in decreasing age synkinematic to postkinematic biotite hornblende granite granodiorite pegmatite and two mica granite with accessory garnet compose the granite suite 109 107 ma the tonalite suite 107 103 ma forms small to large bodies of postkinematic hornblende biotite granodiorite to tonalite with rare granite intruding the granite and parts of the tonalite suites are aplite and pegmatite that grade through sugary pegmatoidal or aplitic quartz veins and finally into quartz veins along strike the diorite suite 95 4 93 7 ma consists of small stocks of diorite to tonalite that intrude the older suites and are inferred to in trude the shallowly dipping auriferous quartz veins limited data indicate granitoid emplacement at 5 9 km depths consis tent with formation of the auriferous quartz veins based upon published fluid inclusion data the weakly peraluminous granite and tonalite suites are distinguished by variable amounts of monazite and zircon whereas the diorite suite is metaluminous contains 5 magnetite and lacks monazite all suites are subalkalic calc alkaline and have low mag netic susceptibilities high large ion lithophile element high field strength element lile hfse and depleted nb and ti the granite suite has higher 206 pb 204 pb values 19 4 19 6 than the diorite 19 1 overall the granite and tonalite suites likely represent melts generated late during crustal thickening that intruded along shallowly dipping faults during exhuma tion whereas the diorite suite represents postdeformation melts that underwent less interaction with the old silicic crust

mineral magnetic study of the taklimakan desert sands and its relevance to the chinese loess summary we conducted a mineral magnetic study on sand samples from the taklimakan desert tarim basin in western china modern sands were collected at 19 sites in the central and western parts of the taklimakan desert we carried out low field susceptibility measurements arm and irm acquisitions high and low temperature measurements and hysteresis measurements on these samples nearly stoichiometric magnetite is the dominant magnetic mineral of these samples the presence of titanomagnetite is unlikely and contributions from a high coercivity mineral s are minor magnetic grain size is estimated to be that of larger pseudo single domain or even greater we compared the hysteresis data against loess samples from both pristine and weathered loess sections from the chinese loess plateau we found an apparent decreasing grain size trend from the taklimakan to the central loess plateau through the western loess plateau these lines of evidence favour the idea that the taklimakan desert is one of the potential dust source areas even though it is located more than 2000 km west of the central loess plateau

precise u pb ages of syn extensional miocene intrusions in the central menderes massif western turkey western turkey is an area which has experienced large scale extension of continental crust here we report precise crystallization ages of two intrusions in the central menderes massif the turgutlu and salihli granodiorites using u pb dating both intrusions occur in the southern footwall of the seismically active alasehir graben and were emplaced syntectonically in an extensional top to the nne shear zone which was active at retrograde greenschist facies conditions the u pb ages of 16 1 0 2 ma monazite turgutlu granodiorite and 15 0 0 3 ma allanite salihli granodiorite document that tectonic exhumation of middle crustal rocks in the central menderes massif was already underway at the early to middle miocene transition combined with published geochronological structural and sedimentological data the new u pb ages point to a continued extension since at least 16 ma there is no convincing evidence for a late miocene pliocene phase of tectonic shortening

new evidence on the age of the taklimakan desert the taklimakan desert is the world s second largest shifting sand desert located in the rain shadow of the tibetan plateau the initiation of desert formation in the asian interior is one of the most prominent climate changes in the northern hemisphere during the cenozoic era dating the earliest formation of this desert is important for understanding the climatic effects of the uplifted tibetan plateau here we report 1071 m thick neogene deposits with inter calated eolian dune sands from the only outcrop in the central taklimakan desert based on paleo magnetic measurements biostratigraphic age control and previous electron spin resonance dating results the oldest in situ eolian dune sands were confi rmed to be ca 7 ma much older than the previous reported wind blown siltstone from the southern edge of the taklimakan desert this new result indicates that desert conditions initiated ca 7 ma in the center of the tarim basin we attribute this event to the late cenozoic climatic deterioration and or to the rain shadow effect caused by late miocene uplift of the northern tibetan margin

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

iron mineralogy characteristics of the desert sediments of the tarim basin and its provenance implications the vast desert area of the tarim basin contains a large amount of loose sediment and consequently it is one of the most important sources of aeolian dust in the mid latitudes of the northern hem

emplacement of rapakivi granite and syenite by floor depression and roof uplift in the palaeoproterozoic ketilidian orogen south greenland in the palaeoproterozoic ketilidian orogen of south greenland tabular intrusions of the rapakivi granite suite exposed at graah fjelde lindenow fjord and qernertoq and a mesoproterozoic syenite of the gardar province exposed at paatusoq were emplaced by a combination of roof uplift and floor depression the strain associated with the emplacement of the intrusions mainly involved redistribution of mass vertically within the lithosphere space for the emplacement of the rapakivi plutons was not created during regional extension on low angle ductile shear zones as claimed by some previous workers and there is no evidence that emplacement of the intrusions coincided with extensional collapse of the orogen following crustal thickening the rapakivi granites post date peak metamorphism in the orogen by 35 46 ma and their contacts cross cut and clearly post date intense flat lying d1 d2 fabrics that formed by partitioning of deformation into arc normal and arc parallel components during oblique convergence

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses