pb isotopic evidence for an early enriched crust on mars abstract martian meteorite nwa 7533 is a regolith breccia that compositionally resembles the martian surface measured by orbiters and landers nwa 7533 contains monzonitic clasts that have zircon with u pb ages of 4 428 ga the pb isotopic compositions of plagioclase and alkali feldspars as well as u pb isotopic compositions of chlorapatite in the monzonitic clasts of nwa 7533 have been measured by secondary ion mass spectrometry sims the u pb isotopic compositions measured from the chlorapatite in nwa 7533 yield an age of 1 357 81 ga 2 the least radiogenic pb isotopic compositions measured in plagioclase and k feldspar lie within error of the 4 428 ga geochron these data indicate that the monzonitic clasts in nwa 7533 are a product of a differentiation history that includes residence in a reservoir that formed prior to 4 428 ga with a value 238 u 204 pb of at least 13 4 1 7 2 and a value 232 th 238 u of 4 3 this value is more than three times higher than any other documented martian reservoir these results indicate either the martian mantle is significantly more heterogeneous than previously thought value of 1 14 vs 1 5 and or the monzonitic clasts formed by the melting of martian crust with a value of at least 13 4 therefore nwa 7533 may contain the first isotopic evidence for an enriched differentiated crust on mars

application of high resolution x ray computed tomography to mineral deposit origin evaluation and processing abstract high resolution x ray computed tomography ct is the industrial equivalent of medical cat scanning and provides a mechanism for non destructive studies of the three dimensional nature of geological materials hrxct produces two dimensional images slices that reveal the interior of an object as if it had been sliced open along the image plane for viewing a ct image is generated by differences in x ray attenuation that arise from differences in density and composition within the object by acquiring a contiguous set of slices volumetric data for all or part of a sample can be obtained allowing three dimensional inspection and measurement of features of interest ct is particularly effective in the study of metallic ores that commonly contain minerals spanning the range of densities of natural materials available software can produce grain shape size and orientation data from the scanned volume which can be particularly useful for oriented samples ct is particularly useful for studies of gold and other precious metal bearing minerals that typically have significant contrast even with common metallic mineral phases ct precisely defines the in situ location of mineral grains of interest within a sample which then can be studied in conventional petrographic sections and other forms of data collected e g isotope or trace element geochemistry another area of application is fluid inclusions which can be discerned even in opaque phases and fluid and vapor volumes measured for sufficiently large occurrences we summarize ct principles and review available instrumentation as well as scanning and data reduction protocols that provide unique three dimensional information for diverse ore types and applications in mineral deposits geology ct applications for economic geology and other fields will continue to expand as instruments continue to evolve and as scanning protocols and applications are extended for more precise quantification of three dimensional relationships particularly for fine grained particles and small fluid inclusions in larger volumes and for separation of minerals with limited contrast

shedding light on ore deposits a review of synchrotron x ray radiation use in ore geology research abstract geology researchers commonly confront critical research questions that require microscopic and sub microscopic level observations e g distribution of chemical elements of economic interest nature of mineralising fluid in order to explain the macroscale phenomena related to the characterisation of and controls on ore mineralisation the emergence and technological evolution of fourth generation synchrotron radiation light sources render these facilities as important but still largely under utilised tools for advancing the frontiers of ore related research to this end the present contribution seeks to critically review and highlight the power and affordances of synchrotron x ray techniques specifically to the fields of fundamental and applied ore geology the review introduces a range of commonly applied synchrotron x ray techniques before comprehensively highlighting past applications of synchrotron x rays to a range of commodities and ore deposits types a synthesis of this information highlights the historical importance of synchrotron x ray techniques towards 1 understanding ore textures and chemical relationships at high m spatial resolutions 2 understanding coordination chemistry of metals in aqueous fluids at geologically relevant p t conditions 3 in situ evaluation of the chemistry and speciation of fluid inclusions 4 evaluating the coordination environment of deleterious and economic trace metal substitutions in major mineral structures and 5 understanding the biogeochemical behaviour and transformations of metals in the low temperature supergene mineralising environment these applications as well as recommendations for future work are described in the hope that a greater diversity of ore geology researchers will incorporate synchrotron x ray tools into their existing suite of analytical and experimental techniques

synthetic normal faulting of the 9 january 2008 nima tibet earthquake from conventional and along track sar interferometry 1 we use synthetic aperture radar interferometry insar to derive the coseismic deformation field of the 9 january 2008 nima tibet earthquake the results show an asymmetric deformation pattern consistent with normal faulting on a nw dipping fault plane the complex line of sight los fringe pattern suggests that a second synthetic fault in the hanging wall of the mainshock rupture slipped during the event most likely during the largest aftershock we use conventional and along track insar data to invert for the geometry and the slip distribution on the two fault planes the focal mechanisms of the mainshock and its largest aftershock show normal faulting with a small left lateral strike slip component near the ne trending riganpei cuo fault which is consistent with our insar observation and inversion result this event suggests that normal faulting in addition to previously established conjugate strike slip deformation in the region contributes to the internal deformation of central tibet

laser ablation u th sm he dating of detrital apatite abstract laser ablation u th sm he dating of apatite la ahe is an emerging technique that presents a number of advantages over conventional whole grain methods increased analytical efficiency through the elimination of he re extractions and acid digestion increases sample throughput and facilitates larger datasets the spatially resolved selection of helium extraction locations eliminates the need for alpha ejection corrections and allows for imperfect grains with inclusions fractures unusual morphologies rounding and surface frosting or coatings to be measured these advantages allow the effective analysis of detrital samples which opens new avenues for geologic applications time resolved parent isotope concentration data collected by la icp ms enables the screening of grains for chemical zonation a commonly cited cause of over dispersion in u th sm he dates simultaneous collection of other chemical e g anion or trace element compositions or isotopic u pb age information for the grain may enhance provenance interpretations we demonstrate the accuracy and uncertainty of the measurement method using two measurement sessions we determine the age of the fish canyon tuff apatite reference material to be 27 9 0 6 ma n 45 mswd 1 5 which is in agreement with previous determinations our data reveal that zonation is a common feature in fish canyon tuff apatite and can be resolved by la ahe methods to reduce dispersion la ahe methods are ideally suited to detrital studies where a large number of measurements and a reduction in grain selection bias compared to whole grain methods should result in the sample better reproducing the source population the utility of the method is demonstrated using a modern sand from the wenatchee river washington usa previously characterized by conventional whole grain ahe methods our la ahe dataset n 74 better reproduces the ahe ages of bedrock samples within the drainage in comparison to the age distribution derived from conventional ahe dating

estimation of arctic glacier motion with satellite l band sar data offset fields between pairs of jers 1 satellite sar data acquired in winter with 44 days time interval were employed for the estimation of arctic glacier motion over svalbard novaya zemlya and franz josef land the displacement maps show that the ice caps are divided into a number of clearly defined fast flowing units with displacement larger than about 6 m in 44 days i e 50 m year the estimated error of the jers 1 offset tracking derived displacement is on the order of 20 m year occasionally azimuth streaks related to auroral zone ionospheric disturbances were detected and dedicated processing steps were applied to minimize their influence on the estimated motion pattern our analysis demonstrated that offset tracking of l band sar images is a robust and direct estimation technique of glacier motion the method is particularly useful when differential sar interferometry is limited by loss of coherence i e for rapid and incoherent flow and large acquisition time intervals between the two sar images the jers 1 results obtained using sar data acquired by a satellite operated until 1998 raise expectations of l band sar data from the alos satellite launched in early 2006

radiation enhanced fission track annealing revisited and consequences for apatite thermochronometry apatite fission track aft analyses for granitoid and metamorphic bedrock samples from the western superior province ontario the churchill rae province melville peninsula and southampton islan

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

coseismic slip distribution of the 24 march 2011 tarlay myanmar mw 6 8 earthquake from alos palsar interferometry abstract we investigate coseismic deformation of the 24 march 2011 m w 6 8 tarlay myanmar earthquake using alos palsar data from both descending and ascending passes using high quality synthetic aperture radar interferograms and amplitude offset images the nearly linear surface rupture is well traced along the western end of the nam ma fault and strikes 69 from both descending and ascending pass interferometric synthetic aperture radar data and a rigorous maximum a posteriori probabilistic inversion method we infer that the event involved mostly a pure left lateral strike slip rupture with near vertical geometry our one segment model shows that the maximum slip of 4 1 m occurred at 4 km depth much larger than the slip at the surface both interferograms also reveal a small segment to the east of the main rupture in a densely populated farming area our inversion of a two segment model shows a similar slip distribution on the main fault in addition to 0 1 0 3 m left lateral slip with normal component on a 58 north dipping segment the total seismic moment from the two segment model is 1 95 10 19 n m equivalent to an m w 6 79 earthquake which is comparable to the u s geological survey seismic inversion estimate of 2 10 10 19 n m m w 6 84 the earthquake occurred within a group of east northeast striking left lateral strike slip faults near the myanmar laos border which are seismically active and reflect a system of actively clockwise rotating blocks online material figures of insar observations amplitude offset maps insar deformation decomposition one segment model inversion residuals single data set inversion results and tectonic setting

statistics for la icp ms based fission track dating abstract despite the conceptual elegance and simplicity of the external detector method edm for fission track dating an increasing number of laboratories are switching to la icp ms as a means of measuring the uranium content of apatite zircon and sphene la icp ms based fission track laft dating offers shorter turnaround times removes the need to handle radioactive materials and hydrofluoric acid and facilitates double dating with the u pb method this paper aims to bring the statistical treatment of laft data on an equal footing with the edm by formulating four different analytical protocols depending on the accuracy and reproducibility of the uranium measurements under the absolute dating approach the spontaneous track densities and uranium concentrations are directly plugged into the fundamental fission track age equation assuming that both of these measured quantities have been determined accurately and that the fission decay constant and equivalent isotopic track length are known the zeta calibration approach avoids making these assumptions by normalisation to a reference material of known age uranium zoning has a detrimental effect on the accuracy of laft ages this effect can be removed by counting only those fission tracks located within the laser ablation pit alternatively the uranium heterogeneity may be quantified by fitting multiple ablation spots in some or all the analysed grains using a lognormal distributional assumption for the uranium concentration laft dating is arguably less well suited than the edm to young and u poor samples that lack sufficient spontaneous fission tracks to reveal visual evidence for uranium zoning such samples occasionally contain no fission tracks at all resulting in infinite analytical uncertainties this paper introduces a pragmatic solution to this problem in which the uranium measurement are converted to virtual induced fission track counts to produce strictly positive ages with finite standard errors with the age equation and zero track strategy in place laft ages can be subjected to more sophisticated statistical analysis using a logarithmic transformation these ages can be visualised on radial plots and deconvolved into finite and continuous mixtures the methods introduced in this paper have been implemented in a software package called isoplotr that is available free of charge at http isoplotr london geochron com

earthquakes and slip rate of the southern sagaing fault insights from an offset ancient fort wall lower burma myanmar field investigations of an ancient fortress wall in southern myanmar reveal an offset of 6 m across the sagaing fault the major right lateral fault between the sunda and burma plates the fault slip rate implied by offset of this 16th century fortress is between 11 and 18 cm yr 1 a palaeoseismological excavation within the fortress reveals at least two major fault ruptures since its construction the slip rate we obtained is comparable to geodetic and geological estimates farther north but is only 50 per cent of the spreading rate 38 mm yr 1 at the andaman sea spreading centre this disparity suggests that other structures may be accommodating deformation within the burma plate we propose two fault slip scenarios to explain the earthquake rupture history of the southern sagaing fault using both small offset features along the fault trace and historical records we speculate that the southern sagaing fault exhibits a uniform fault slip behaviour and that one section of the fault could generate a m7 earthquake within the next few decades

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

global compilation of interferometric synthetic aperture radar earthquake source models 1 comparisons with seismic catalogs 1 while many earthquakes have now been studied using interferometric synthetic aperture radar insar data a full assessment of the quality and additional value of insar source parameters compared to seismological techniques is still lacking we compile a catalog of source models obtained using insar and estimate the corresponding centroid moment tensor cmt parameters we refer to this compilation as the icmt archive we compare source parameters from over 70 insar studies of 57 global earthquakes with those in the global cmt gcmt international seismological centre isc and engdahl hilst buland ehb seismic catalogs we find an overall good agreement between fault strike dip and rake values in the gcmt and icmt archives likewise the differences in seismic moment between these two archives are relatively small and we do not find support for previously suggested trends of insar leading to larger moments than seismic data however epicentral locations show substantial discrepancies which are larger for the gcmt median differences of 21 km than for the ehb and isc catalogs median differences of 10 km since insar data have a high spatial resolution and thus should map epicentral locations accurately this allows us to obtain a first independent estimate of epicentral location errors in the seismic catalogs earthquake depths from insar are systematically shallower than those in the ehb catalog with a median of differences of 5 km while this trend may be partly due to unmodeled crustal complexity it is also compatible with the observation that the rupture of crustal earthquakes tends to propagate upward in the seismogenic layer

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

coseismic and postseismic slip of the 2004 parkfield earthquake from space geodetic data we invert interferometric synthetic aperture radar insar data jointly with campaign and continuous global positioning system gps data for slip in the coseismic and postseismic periods of the 2004 parkfield earthquake the insar dataset consists of eight interferograms from data collected by the envisat and radarsat satellites spanning the time of the earthquake and variable amounts of the postseismic period the two datasets complement each other with the insar providing dense sampling of motion in the range direction of the satellite and the gps providing more sparse but three dimensional measurements of ground motion the model assumes exponential decay of the postseismic slip with a decay time constant of 0 087 years determined from time series modeling of continuous gps and creepmeter data we find a geodetic moment magnitude of m 6 2 for a 1 day coseismic model and m w 6 1 for the entire postseismic period the coseismic rupture occurred mainly in two slip asperities one near the hypocenter and the other 15 20 km north postseismic slip occurred on the shallow portions of the fault and near the rupture areas of two m 5 0 aftershocks a comparison of the geodetic slip models with seismic moment estimates suggests that the coseismic moment release of the parkfield earthquake is as little as 25 of the total this underlines the importance of aseismic slip in the slip budget for the parkfield segment online material complete data tables and supplemental tables

high resolution x ray computed microtomography a holistic approach to metamorphic fabric analyses an intrinsic limitation of studying microstructures in thin section is that their spatial three dimensional 3 d distribution shape and orientation have to be inferred by combining 2 d data from different sections this procedure always involves some degree of interpretation that in some cases can be ambiguous recent advances in high resolution x ray computed microtomography have made possible the direct imaging in 3 d of volumes of rock to centimeter scale this rapidly evolving technology is nondestructive and provides a holistic approach of microstructural analysis that eliminates interpretative procedures associated with 2 d methods spatial images can be generated through any part of the rock sample and used as virtual petrographic sections our application of this technique to an oriented drill core sample from the classic orijarvi metamorphic region of southern finland reveals a number of in situ 3 d aspects including 1 the spatial distribution and shape of andalusite porphyroblasts 2 the geometry of a matrix foliation anastomosing around the porphyroblasts 3 a millimeter scale compositional layering that controlled the oscillation of porphyroblasts and sulfide mineralization and 4 distinct inclusion trail patterns characterizing porphyroblast core versus rim zones the combined data indicate that the steeply dipping bedding subparallel foliation that characterizes the orijarvi area formed by bulk north south crustal shortening and associated vertical stretching

depth segmentation of the seismogenic continental crust the 2008 and 2009 qaidam earthquakes 1 the seismic hazard in the immediate vicinity of an earthquake is usually assumed to be reduced after rupture of a continental fault with along strike portions being brought closer to failure and aftershocks being significantly smaller this period of reduced hazard will persist as strain re accumulates over decades or centuries however this is only realised if the entire seismogenic layer ruptured in the event here we use satellite radar measurements to show the ruptures of two mw 6 3 earthquakes occurring in almost the same epicentral location ten months apart in the qaidam region china were nearly coplanar the 2008 earthquake ruptured the lower half of the seismogenic layer the 2009 event the upper half fault segmentation with depth allows a significant seismic hazard to remain even after a moderate and potentially devastating earthquake this depth segmentation possibly exists in the case of the 2003 bam earthquake where satellite radar and aftershock measurements showed that it ruptured only the upper half of the 15 20 km deep seismogenic region jackson et al 2006 and that the lower unruptured part may remain as a continuing seismic hazard

a succession of near orthogonal horizontal tectonic shortenings in the paleoproterozoic central lapland greenstone belt of fennoscandia constraints from the world class suurikuusikko gold deposit the relative and absolute timing of orogenic gold deposits in complex structural settings are active and challenging topics of research especially in precambrian greenstone belts the suurikuusikko gold deposit in central lapland greenstone belt is currently the largest primary gold producing deposit in europe located on a slight bend of the strike slip kiistala shear zone kisz gold is refractory and locked inside arsenopyrite and pyrite in this study different structural features were investigated along the kisz from the recently stripped etela pit which is the southern extension of the suurikuusikko ore body our data source ranges from aeromagnetic to high resolution aerial images x ray computed tomography scans of selected rock samples and regional geological and geophysical datasets the kisz has recorded five discrete deformation phases spanning between ca 1 92 and 1 76 ga the refractory gold at the suurikuusikko deposit formed during e w contraction related to the d1 thrusting phase this was followed by a n s shortening event d2 where most of the strain was taken up by the northern and southern thrusts tectonic vectors then switched from n s to ne sw and as a result dextral strike slip regime d3 commenced along the kisz this event exsolved invisible gold from the sulfides and remobilized it along with fractures a near orthogonal switch of the regional stress regime from ne sw to nw se flipped the kinematics of the kisz from dextral to sinistral d4 the last deformation phase d5 produced widespread veining under e w contraction and secured gold mineralization at the iso kuotko gold deposit within the kisz

calibration of ga1550 biotite standard for k ar and 40ar 39ar dating abstract the mineral separate ga1550 biotite has become an international standard for k ar and 40 ar 39 ar dating studies although it was prepared as an intralaboratory standard at anu to monitor tracer depletion from a gas pipette it is one of a small number of samples that has been calibrated against 38 ar tracers some of which had been mixed with known amounts of atmospheric argon so that a so called primary calibration has been performed by measuring ga1550 biotite against additional tracers from the same batch we have determined the radiogenic argon content of this sample as 1 342 0 007 10 9 mol g and together with the measured k content of 7 645 0 050 weight percent we derive a best estimate for the k ar age as 98 5 0 5 ma where the error is derived from averaging the ages determined relative to the 38 ar tracer

tectonic deformation of the indochina peninsula recorded in the mesozoic palaeomagnetic results summary in order to describe features of tectonic deformation in the indochina peninsula early jurassic to early cretaceous red sandstones were sampled at three localities in the shan thai and indochina blocks stepwise thermal treatment of most samples revealed the presence of characteristic remanent magnetization which is generally unblocked by 680 c this component from phong saly 21 6 n 101 9 e and borikhanxay 18 5 n 103 8 e localities yield positive fold tests with late jurassic early cretaceous directions of dec inc 28 8 32 1 ks 15 4 95 8 8 n 22 and dec inc 42 1 46 9 ks 20 1 95 7 9 n 18 respectively additionally a syn folding mid cretaceous characteristic magnetization is observed in the samples of muang phin locality 16 5 n 106 1 e which gave a mean direction of dec inc 30 8 39 9 k 102 6 95 3 0 n 23 this reliable late jurassic to mid cretaceous palaeomagnetic directions from three different localities are incorporated into a palaeomagnetic database for shan thai and indochina blocks based on these compilations tectonic deformation of the shan thai and indochina blocks is summarized as follows 1 the shan thai and indochina blocks experienced a clockwise rotation of about 10 as a composite unit in the early stage of india asia collision and 2 following this the shan thai block underwent an internal tectonic deformation whereas the indochina block behaved as a rigid tectonic unit during the same period comparison of our palaeomagnetic results with seismic tomographic images suggests that the strength of continental lithosphere beneath these blocks played an important role in the process of deformation rather than any other tectonic regime in contrast to the shan thai block an existence of continental roots beneath the indochina block prevented its internal deformation

right lateral shear along the northwest pacific margin and the india eurasia collision right lateral shear along the eastern margin of asia from the eocene to the present has led to the opening of pull apart basins intracontinental such as the bohai basin or oceanic such as the japan sea we suggest in this paper that this right lateral shear is a consequence of indentation of asia by india as in small scale analog experiments we conclude that antithetic wrench faults accommodate the counterclockwise rotation of large domino blocks between two major left lateral shear zones tien shan baikal stanovoy for the northern one and qin ling for the southern one we discuss the compatibility of this mechanism which involves a rather small amount of extrusion with the fast eastward expulsion described for southeast asia we re emphasize the role played in the opening of marginal basins by the pacific subduction as a free boundary to the east

hairpin river loops and slip sense inversion on southeast asian strike slip faults in the golden triangle region of southeast asia northern thailand laos and burma southern yunnan the mekong salween and neighboring rivers show hairpin geometries where they cross active strike slip faults restoration of young left lateral offsets of these rivers leaves residual right lateral bends of many kilometers we interpret these hairpins as evidence of late cenozoic slip sense inversion on these faults about 5 to 20 ma near the red river fault stress field and slip sense inversion occurred ca 5 ma this implies that the present course of these large rivers has existed for at least several million years pliocene quaternary slip rates possibly on the order of 1 mm yr are inferred on each of the strike slip faults of the golden triangle

accuracy and resolution of alos interferometry vector deformation maps of the father s day intrusion at kilauea we assess the spatial resolution and phase noise of interferograms made from l band advanced land observing satellite alos synthetic aperture radar sar data and compare these results with corresponding c band measurements from european space agency remote sensing satellite ers based on cross spectral analysis of phase gradients we find that the spatial resolution of alos interferograms is 1 3times better than ers interferograms the phase noise of alos i e line of sight precision in the 100 5000 m wavelength band is 1 6times worse than ers 3 3 mm versus 2 1 mm in both cases the largest source of error is tropospheric phase delay vector deformation maps associated with the june 17 2007 father s day intrusion along the east rift zone of the kilauea volcano were recovered using just four alos sar images from two look directions comparisons with deformation vectors from 19 continuous gps sites show rms line of site precision of 14 mm and rms azimuth precision flight direction of 71 mm this azimuth precision is at least 4times better than the corresponding measurements made at c band phase coherence is high even in heavily vegetated areas in agreement with previous results this improved coherence combined with similar or better accuracy and resolution suggests that l band alos will outperform c band ers in the recovery of slow crustal deformation

arsenopyrite pyrite association in an orogenic gold ore tracing mineralization history from textures and trace elements laser ablation inductively coupled plasma mass spectrometry la icp ms spot analysis and element mapping coupled with high resolution focused ion beam scanning electron microscopy fib sem imaging has been performed on au hosting sulfides from a proterozoic orogenic gold deposit tanami gold province north central australia gold distribution patterns in the arsenopyrite pyrite assemblage which probably crystallized toward the end of the au forming event suggest a process of initial scavenging of au into arsenopyrite and subsequent remobilization of that au following brittle fracture gold expelled from the sulfide lattice during the remobilization event is reconcentrated around the margins of the same arsenopyrite grains and within swarms of crosscutting microfractures the distribution of pb bi and ag closely mimic au indicating that these elements were also reconcentrated preservation of oscillatory zonation patterns for co ni sb se and te in arsenopyrite imply however that no significant degree of sulfide recrystallization took place residual concentrations of invisible gold in grain centers are 5 ppm in arsenopyrite and 1 ppm in coexisting pyrite the presence of submicron sized pores is suggestive of a fluid driven process rather than solid state diffusion micron scale 2 10 m remobilized gold is accompanied by fine particles 200 nm 2 m and nanoparticles 200 nm of gold the extensive variation of au concentrations within single arsenopyrite grains underlines the significance of textures when using trace element data to understand how gold ores evolved

advances in 3d imaging and volumetric reconstruction of fluid and melt inclusions by high resolution x ray computed tomography abstract fluid and melt inclusions are tiny pockets of fluid and melt trapped in natural and synthetic minerals characterizing the 3d distribution of fluid and melt inclusions within minerals their shape and the volume fraction of their different phases is crucial for determining the conditions of crystal growth and paleostress analysis however their relatively small size typically 5 to 100 m complex shape heterogeneous content the opaque nature of some host minerals and projection bias frequently hamper accurate imaging and volumetric reconstruction using conventional microscopic techniques high resolution x ray computed tomography hrxct is a non destructive method which uses contrasts of x ray attenuation in a series of contiguous radiographs with different view angles to reconstruct the 3d distribution of areas of different densities within a large variety of materials in this work we show the capabilities of hrxct for i imaging the 3d distribution of aqueous and hydrocarbon bearing fluid inclusions and silicate melt inclusions in a crystal ii characterizing the shape of fluid and melt inclusions and iii reconstructing the total volume and the volume of the different phases liquid glass crystal vapor of fluid and melt inclusions we have used a variety of hand specimens and chips of transparent and opaque minerals olivine quartz feldspar garnet emerald wolframite that we analyzed using three different hrxct setups when a resolution of 1 m3 voxel is achieved hrxct allows identifying 5 m fluid inclusions and the identification and volumetric reconstruction of the different phases can be carried out with reasonable confidence for relatively large 25 m inclusions density contrasts are high enough to properly identify i a silicate melt inclusion and its different phases glass vapor and crystals such as clinopyroxene and spinel in an olivine crystal ii aqueous monophase liquid and two phase liquid vapor fluid inclusions in transparent and opaque minerals quartz garnet emerald wolframite in the case of hydrocarbon bearing fluid inclusions containing a vapor phase and two liquid phases oil and aqueous solution the two liquid phases could not be distinguished from each other volumetric reconstruction of liquid and vapor phases of aqueous and hydrocarbon bearing fluid inclusions show compatible results with independent calculations using known pressure temperature molar volume and composition p t v x conditions of trapping or imaging using confocal laser scanning microscopy respectively collectively our results show that hrxct is a promising tool for non destructive characterization of fluid and melt inclusions

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

bimodal distribution of gold in pyrite and arsenopyrite examples from the archean boorara and bardoc shear systems yilgarn craton western australia this study investigates the microstructures geochemistry and hydrothermal evolution of gold bearing pyrite and arsenopyrite from six orogenic gold deposits in the archean eastern goldfields province western australia scanning electron microscope sem electron microprobe emp and laser ablation inductively coupled plasma mass spectroscopy la icp ms analyses show that the gold bearing minerals possess a number of similar textural features including the occurrence of invisible gold within initial phases of growth and later stage visible gold associated with alteration rims the alteration rims are characterized by a higher than average atomic mass mainly owing to arsenic enrichment and are preferentially located along fractures and grain boundaries in the pyrite and arsenopyrite these observations suggest that visible gold formation is associated with hydrothermal alteration of preexisting pyrite and arsenopyrite textural observations and la icp ms data suggest that some invisible gold was remobilized from early formed pyrite and arsenopyrite to form visible gold during development of these alteration rims gold may also have been added by hydrothermal fluids during a later stage of mineralization in situ geochemistry and phase relationships of alteration rims are used to further constrain the hydrothermal process responsible for formation of alteration rims and visible gold in fractures based on sulfide stability relations our data indicate that development of arsenopyrite alteration rims associated with late stage visible gold formation was related to an increase in temperature maximum increase from 310 to 415 c and up to of sic orders of magnitude increase in sulfur fugacity whereas changes in oxygen fugacity were less important la icp ms analyses show that the relative and absolute variations in selected trace element au ag sb bi ba te pb co and mo concentrations can also be used to distinguish between unaltered and altered pyrite and arsenopyrite in general trace elements within pyrite and arsenopyrite have a relatively uniform distribution whereas later stage alteration rims have more variable trace element distributions although the observed textures are typical of prograde metamorphic coronae we suggest that they are the consequence of variations in fluid conditions and chemistry and that mineralization occurred in response to syn and or postpeak metamorphic fluid infiltration

post breakup tectonics in southeast brazil from thermochronological data and combined inverse forward thermal history modeling the continental margin of southeast brazil is elevated onshore tertiary basins and late cretaceous paleogene intrusions are good evidence for post breakup tectono magmatic activity to constrain the impact of post rift reactivation on the geological history of the area we carried out a new thermochronological study apatite fission track ages range from 60 7 1 9 ma to 129 3 4 3 ma mean track lengths from 11 41 0 23 mm to 14 31 0 24 mm and a subset of the u th he ages range from 45 1 1 5 to 122 4 2 5 ma results of inverse thermal history modeling generally support the conclusions from an earlier study for a late cretaceous phase of cooling around the onshore taubate basin for a limited number of samples the first detectable period of cooling occurred during the early tertiary the inferred thermal histories for many samples also imply subsequent reheating followed by neogene cooling given the uncertainty of the inversion results we did deterministic forward modeling to assess the range of possibilities of this tertiary part of the thermal history the evidence for reheating seems to be robust around the taubate basin but elsewhere the data cannot discriminate between this and a less complex thermal history however forward modeling results and geological information support the conclusion that the whole area underwent cooling during the neogene the synchronicity of the cooling phases with andean tectonics and those in ne brazil leads us to assume a plate wide compressional stress that reactivated inherited structures the present day topographic relief of the margin reflects a contribution from post breakup reactivation and uplift

orthogonal switching of ams axes during type 2 fold interference insights from integrated x ray computed tomography ams and 3d petrography abstract we applied x ray computed microtomography ct in combination with anisotropy of magnetic susceptibility ams analysis to study metamorphic rock fabrics in an oriented drill core sample of pyrite pyrrhotite quartz mica schist the sample is extracted from the paleoproterozoic martimo metasedimentary belt of northern finland the ct resolves the spatial distribution shape and orientation of 25 920 pyrrhotite and 153 pyrite grains localized in mm thick metapelitic laminae together with microstructural analysis the ct allows us to interpret the prolate symmetry of the ams ellipsoid and its relationship to the deformation history ams of the sample is controlled by pyrrhotite porphyroblasts that grew syntectonically during d1 in subhorizontal microlithons the short and intermediate axes k3 and k2 of the ams ellipsoid interchanged positions during a subsequent deformation d2 that intensely crenulated s1 and deformed pyrrhotite while the long axes k1 maintained a constant position parallel to the maximum stretching direction however it is likely that all the three ams axes switched similar to the three principal axes of the shape ellipsoid of pyrite porphyroblasts from d1 to d2 the superposition of d1 and d2 produced a type 2 fold interference pattern

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

cenozoic deformation in western yunnan china myanmar border in the present paper we describe ductile and brittle deformation styles in western yunnan and ne myanmar using field data and landsat 7 imagery we show that this complex area located at the northern termination of sunda plate three rivers area was wedged during the tertiary between the left lateral ailao shan chong shan metamorphic belts to the east and the right lateral shan scarp gaoligong metamorphic belt in west this triangular region therefore underwent the effects of these continental size ductile strike slip faults separating major blocks with a dominant ew to ene compression since the late miocene date of the reversal of motion along the rrf the incipient eastward motion of the sunda block and the persisting right lateral motion along its western boundary sagaing fault created n s compression and e w to wnw extension underlined by left lateral transtension along the wanding nanting fault zones at the same time the diangcan shan situated along strike the ailao shan metamorphic belt was slightly impinged by the blocks extruded from the syntaxis and exhumed again from the early pliocene in accordance with this late and still active state of stress q 2004 elsevier ltd all rights reserved

surface ruptures of the mw 6 8 march 2011 tarlay earthquake eastern myanmar abstract field observations indicate the m w 6 8 tarlay myanmar earthquake of 24 march 2011 resulted from the rupture of a short section of the left lateral nam ma fault we document coseismic left lateral offsets that range from approximately 10 cm to about 2 m along a 19 km long section of the fault based upon both field investigations and the interpretation of high resolution satellite imagery comparison of these early field and later remote measurements suggests that most of the paddy field offsets became obscured within a year or two our measurements indicate the magnitude of sinistral offset decreases gradually eastward from the epicentral area to the rupture terminus within the tarlay basin along the southern edge of a 2 3 km wide transtensional stepover our measurements confirm that the earthquake resulted from rupture of a structurally distinct segment of the nam ma fault bounded on the west by the fault s terminus and on the east by the tarlay basin stepover if the 215 km nam ma fault were to rupture entirely in a single event the magnitude of the resulting earthquake would likely be about m w 7 7 online material field observations and photos after the 2011 tarlay earthquake table of offset and maps with location and offset

apatite fission track chronometry using laser ablation icp ms abstract comparison is made of apatite fission track ft ages measured by using conventional thermal neutron irradiation and laser ablation inductively coupled plasma mass spectrometry la icp ms to determine sample uranium content spontaneous track densities were determined on specified apatite grains from the durango fish canyon tuff and mount dromedary complex age standards neutron induced track densities and icp ms uranium values were determined for the same specified grains ages determined using the two approaches show reasonable consistency indicating the possibility of routine fission track analysis using la icp ms uncertainties and assumptions in the la icp ms approach include the laser ablation of chemically etched mineral surfaces the suitability of reference materials for calibration and the derivation of ft ages using the alternatives of selection of a f value or a revised zeta comparative approach the use of la icp ms in ft chronometry would dramatically increase the speed of analysis and hence sample throughput as well as avoiding the need for neutron irradiation and the production transport and handling of radioactive samples with the acknowledged dependency of ft annealing in apatite on composition such grain by grain multi element analysis could provide a more robust definition of the specific track annealing characteristics of each apatite crystal

three dimensional textural and quantitative analyses of orogenic gold at the nanoscale ore textures provide direct clues for tracking ore forming processes in this regard most of our knowledge is generally based on two dimensional 2 d image analyses leaving a considerable gap in comprehending three dimensional 3 d in situ textural settings recent advances in lab based and synchrotron radiation based x ray computed microtomography and nanotomography have made it possible to visualize and quantify rock volumes in a 3 d space in this study we first analyzed microscale textures in oriented drill cores from the world class suurikuusikko orogenic gold deposit of northern finland using lab based x ray computed microtomography the technique revealed a kinematic history and a number of in situ 3 d quantitative aspects including size shape spatial distribution and geometrical orientation of arsenopyrite and pyrite in a highly altered host rock matrix for 3 d nanotomography the experimental procedure known as holotomography was adopted individual arsenopyrite crystals were separated and scanned with voxel sizes ranging from 50 nm to 150 nm using the x ray nanoprobe beamline id16b at the european synchrotron radiation facility france this ultrahigh resolution technique illustrated the 3 d distribution of micron to nanoscale gold inclusions mostly associated with primary rutile or along secondary microfractures inside arsenopyrite the workflow from micro to nanotomography outlined in this study offers an indispensable new technique in quantifying and characterizing 3 d textural settings of ores which is otherwise impossible with conventional 2 d imaging devices the method can also be highly useful in evaluating the amenability of ores to treatment with different processing options

a precise 40ar 39ar reference age for the durango apatite u th he and fission track dating standard the distinctive durango apatite is widely distributed as a reference material for mineralogy geochemistry and thermochronology the apatite occurs within the cerro de mercado open pit iron mine located in the northern portion of durango city mexico it is largely confined to vugs and open fractures within the lower portion of the ore deposit apatite and iron ore formed in situ and concurrently along with emplacement of small felsic intrusions along the southern margin of the chupaderos caldera complex this activity occurred between eruptions of two major ignimbrites from the caldera complex four single crystal sanidine anorthoclase 40 ar 39 ar ages from these ignimbrites and from a conformable older unit have been used to compute a reference age of 31 44 0 18 ma 2 for the apatite itself four additional multi crystal measurements are in general agreement with this age also in agreement are a set of 24 u th sm he ages recently determined directly on the apatite which have a mean of 31 02 1 01 ma 1 with a standard error s e of 0 22 ma

magmatic history of central myanmar and implications for the evolution of the burma terrane the burma terrane is a microplate at the eastern edge of the himalayan tibetan orogen the origin of which remains poorly understood its basement comprises metamorphic and igneous rocks forming the wuntho popa arc wpa and has been correlated with tibetan gondwana or transtethyan rocks yet little is known about the magmatic history of the wpa we report elemental and sr nd isotopic compositions of magmatic rocks crystallization zircon and apatite u pb and exhumation apatite fission track ages from rocks and river sands and structural measurements from the wuntho ranges central myanmar where the wpa is best exposed we show that the wpa in the wuntho ranges is characterized by two magmatic events at 108 90 ma and 46 32 ma magmatism is subduction related for both events characterized by depleted nd and sr isotopic compositions with more enriched values with time apatite fission track data suggest arc exhumation during the 39 22 ma time interval partly overlapping with the last magmatic event structural data indicate nw se striking tilting folding and thrusting that we associate with at least two phases of deformation in the cretaceous and the late paleogene correlating the wpa with tibetan gondwana or transtethyan rocks based on its magmatic history remains ambiguous however models arguing for a transtethyan origin for the wpa are most compatible with our results combined with available burmese geological data

a three step maximum a posteriori probability method for insar data inversion of coseismic rupture with application to the 14 april 2010 mw 6 9 yushu china earthquake 1 we develop a three step maximum a posteriori probability method for coseismic rupture inversion which aims at maximizing the a posterior probability density function pdf of elastic deformation solutions of earthquake rupture the method originates from the fully bayesian inversion and mixed linear nonlinear bayesian inversion methods and shares the same posterior pdf with them while overcoming difficulties with convergence when large numbers of low quality data are used and greatly improving the convergence rate using optimization procedures a highly efficient global optimization algorithm adaptive simulated annealing is used to search for the maximum of a posterior pdf mode in statistics in the first step the second step inversion approaches the true solution further using the monte carlo inversion technique with positivity constraints with all parameters obtained from the first step as the initial solution then slip artifacts are eliminated from slip models in the third step using the same procedure of the second step with fixed fault geometry parameters we first design a fault model with 45 dip angle and oblique slip and produce corresponding synthetic interferometric synthetic aperture radar insar data sets to validate the reliability and efficiency of the new method we then apply this method to insar data inversion for the coseismic slip distribution of the 14 april 2010 mw 6 9 yushu china earthquake our preferred slip model is composed of three segments with most of the slip occurring within 15 km depth and the maximum slip reaches 1 38 m at the surface the seismic moment released is estimated to be 2 32e 19 nm consistent with the seismic estimate of 2 50e 19 nm

la icp ms apatite fission track dating a practical zeta based approach abstract the la icp ms method is becoming increasingly popular for uranium determinations in fission track dating of apatite zircon or titanite this is because the approach has several advantages over the classical external detector method edm including faster sample throughput simultaneous acquisition of additional data such as u pb age information and trace element abundances while removing the need for neutron irradiation two different approaches are used to determine u contents in la icp ms fission track dating an absolute dating approach or a zeta based determination analogous to the classical edm absolute age dating by la icp ms potentially suffers from small but systematic deviations in apatite u contents which in turn propagate through to minor systematic deviations in the accuracy of absolute fission track age determinations a zeta based approach typically requires time consuming counting of large numbers of zeta standard grains usually durango apatite so as to yield a precise zeta factor for every la icp ms session containing unknowns the modification of the zeta based approach proposed here has two major advantages firstly it employs just one large primary la icp ms session to determine a precise primary zeta factor on a large number of counted durango primary zeta grains during subsequent secondary la icp ms sessions with unknowns no further fission track counting of the primary zeta standard is required this is because we reanalyse a subset of the primary zeta grains to calculate a session specific zeta fractionation factor which is related to variations in the instrumental operating conditions primarily plasma tuning between primary and secondary la icp ms sessions this enables us to reuse the primary zeta factor and thus avail of its precision derived from the large spontaneous track count the second advantage is that reusing the primary zeta grains by applying a session specific zeta fractionation factor allows us to verify that background and drift corrections applied during the secondary la icp ms session were fully appropriate this method has been successfully tested by dating samples of known apatite fission track age by comparing edm and la icp ms data from the same sample and by participating in a round robin test between international fission track laboratories where blind fission track dating of two unknown samples was undertaken our la icp ms apatite fission track dating approach is also easily modifiable for fission track dating of zircon or titanite if suitable age standards are employed

an integrated method based on dinsar mai and displacement gradient tensor for mapping the 3d coseismic deformation field related to the 2011 tarlay earthquake myanmar abstract the satellite differential interferometric synthetic aperture radar dinsar technology has been widely applied for mapping the ground deformation associated with the geophysical events such as earthquakes however the conventional dinsar can measure only the one dimensional 1d ground displacement along the radar line of sight los and the crucial displacement measurements e g near the epicenter and along the surface ruptures are usually not available or degraded in quality due to the significant deformation gradients with availability of satellite sar images acquired along ascending and descending orbits this paper proposes an integrated method to map the three dimensional 3d coseismic deformation field by combining dinsar for detecting los displacements the multiple aperture interferometry mai for detecting along track displacements and the displacement gradient tensor dgt model for characterizing spatial correlation of ground displacements the proposed method termed as insar dgt was first tested through an experiment of recovering 3d displacements from a simulated coseismic deformation field we then applied the proposed method to map the 3d coseismic deformation field related to the 2011 tarlay earthquake myanmar by using the ascending and descending alos palsar images both the results derived for the simulated experiment and the 2011 tarlay earthquake show that the quality of the 3d coseismic displacements can be raised efficiently by the insar dgt method and the precisions in the east west e w north south n s and up down u d displacements for the 2011 tarlay earthquake are increased 22 36 and 24 respectively the validation indicates that the improved coseismic deformation field for the 2011 tarlay earthquake is in good agreement with the deformation field simulated from the existing optimized fault model the number of the missing data points in the 3d coseismic deformation field can be reduced significantly by the insar dgt method it is revealed that the causative fault i e the west part of the nam ma fault for the tarlay earthquake generated a left lateral slip that was accompanied by a minor normal dip slip component the careful interpretation demonstrates that the causative fault structures include the determined main fault segment and the two suspected branched segments at east of the tarlay town

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods

high resolution la icp ms trace element mapping of igneous minerals in search of magma histories we report experiments on optimisation of la icp ms mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals the experimental design was refined with maps on clinopyroxene and amphibole macrocrysts mainly antecrysts from a porphyritic lamprophyre in ne spain as well as on a high precision metal wire grid in terms of spatial resolution we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0 4 and 0 7 mu m of material depending on ablation parameters maps were produced with square laser beam spots of 12 and 24 mu m it was found that complexities can be resolved in the sample even though they are smaller than the beam diameter e g 7 10 mu m discontinuities using 12 mu m laser beam resolution in x and y was found to be identical probably reflecting the fast washout of the two volume ablation cell and the short total dwell time of the analyte menu selected due to the excellent stage reproducibility and the limited ablation depth it is feasible to re ablate the identical map area many times employing different instrument parameters or analyte menus on the magmatic crystals la icp ms maps define very sharp compositional zoning in trace elements highlighting complex crystallisation histories where normal magmatic fractionation is not the only process events of mafic recharge are easily recognised as zones enriched in compatible metals such as cr ni or sc further trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data these include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones therefore la icp ms mapping opens a new window of opportunity for analysis of magmatic histories the wide combination of instrumental parameters such as laser beam size scan speed and repetition rate make it possible to carry out experiments at different levels of detail we recommend a two step approach to mapping the initial step involves rapid maps to gain an overview of potential complexities in the sample this enhances representativeness of the analysed materials as a large number of crystals and trace elements can be tested in little time subsequently detailed maps can be carried out on areas of interest an additional functionality is to create 1d profiles from 2d maps the potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond c 2015 elsevier b v all rights reserved