incremental 40ar 39ar thermochronology of mylonitic rocks from the northern snake range nevada a 40ar 39ar thermochronologic study of muscovite biotite and potassium feldspar from footwall rocks of the northern snake range decollement nevada was undertaken in order to constrain the timing and temperatures of mylonitic deformation during extension and the subsequent cooling uplift history of these mylonitic rocks mylonitic deformation has been bracketed between 37 ma and about 24 ma and minimum temperatures during ductile thinning were about 300 c mineral cooling ages along the east flank of the range suggest a minimum tmax gradient of about 55 c ma this steep thermal gradient is the result of a localized heat source and or shearing of colder rocks with older cooling histories over hotter rocks with younger cooling histories although mylonitic deformation may have spanned a 13 m y period 37 ma to 24 ma deformation was not synchronous throughout the range on the west flank of the range age spectra from muscovite and microcline samples indicate that rocks were at temperatures well below 325 c and deformation had ceased by 30 ma while on the east flank of the range lower plate rocks were at temperatures above 325 c and ductile deformation was still ongoing this is also reflected in chrontours of published k ar muscovite ages along with 40ar 39ar ages which monotonically decrease in age from west to east these data provide evidence for a temperature difference across the range within the same structural horizon from about 30 to 24 ma these relations suggest a lateral thermal gradient the east flank of the range cooling more slowly than the west flank alternatively the data suggest either an eastward dip of lower plate units prior to the onset of tertiary mylonitic deformation or that layering dipped eastward due to deformation in an east dipping top to the east shear zone both cases result in differential cooling of lower plate units as they pass through a series of subhorizontal isotherms the 40ar 39ar data along with published finite strain structural and quartz petrofabric data provide constraints on the formation and geometric evolution of metamorphic core complex detachment faults

unroofing of active metamorphic core complexes in the d entrecasteaux islands papua new guinea metamorphic core complexes in the d9entrecasteaux islands are forming as a result of active extension at the western end of the woodlark basin spreading center high grade metamorphic rocks exist in the cores of gneissic domes including eclogites formed at minimum depths of 45 75 km i e 13 21 kbar high temperatures were maintained during uplift of basement rocks from 13 21 kbar t 730 900 c through 7 11 kbar t 570 730 c to 5 6 kbar t 730 c subsequent rapid cooling 100 c m y of the basement occurred between 1 and 2 ma on the basis of 40 ar 39 ar geochronology the core zone rocks were transected by kilometre scale amphibolite facies ductile shear zones active at depths of 25 35 km extensive intrusion of granodiorite plutons occurred and the age of granodiorite intrusions constrains late stage shear zone activity to 2 ma and younger unroofing was accomplished by faults and shear zones bounding the gneiss domes juxtaposing them against ultramafic rocks and sedimentary deposits surface uplift continues today and has led to topographic elevations of up to 2 5 km

mapping the buraburi granite in the himalaya of western nepal remote sensing analysis in a collisional belt with vegetation cover and extreme variation of topography abstract the aim of the present study is to define the most suitable methodologies for aster data pre processing and analysis in order to enhance peraluminous granitoid rocks in rugged and vegetated areas the research started with raw image data pre processing and continued with a comparison of satellite field and laboratory data the masking technique adopted to isolate rocky pixels was of fundamental importance to perform further analysis an integration of density sliced images and false colour composite images of band ratio relative absorption band depth and principal component analysis allowed us to generate a geological map that highlights a new granitoid body buraburi granite and the surrounding host rocks in the dolpo region western nepal the buraburi granite was mapped and sampled integrating remotely sensed aster data with analysis of rocks and minerals spectral signatures the innovative approach that we have adopted considers the absorption features of particular lichen species acidophilic the results highlight the importance of considering acidophilic lichen means of detecting granitoid rocks furthermore since peraluminous granitoids i e buraburi granite have a considerable al2o3 bulk rock content the muscovite al oh absorption peaks centred in the 6th aster band were also considered an important parameter for their detection field observations confirm the results of remote sensing analysis showing the intrusive relationship between the newly discovered 110 km 2 granitoid body and the wall rocks of the higher himalayan crystalline and the tibetan sedimentary sequence in conclusion the proposed methods have great potential for granitoid mapping in vegetated and rough terrains particularly those with climatic and geological conditions similar to the ones of the southern himalayan belt

thermal infrared multispectral remote sensing of lithology and mineralogy based on spectral properties of materials abstract the major minerals forming the earth s crust exhibit characteristic spectral properties in the thermal infrared tir 7 14 m region of the spectrum although most of them have few features in the visible and near infrared 0 4 2 5 m region as there exists a good atmospheric window in the tir spectral region a number of multispectral tir remote sensors have been developed by various agencies the world over for geological applications this paper reviews such type of remote sensing systems and especially focuses attention on the advanced spaceborne thermal emission and reflection radiometer aster the spectroscopic basis in analyzing and interpreting the multispectral tir remote sensing data is discussed it includes a review of the historical studies methodology of spectral measurements and comparison of spectra measured in laboratory field with that derived from the remotely sensed data subsequently the studies of lithology and mineralogy using tir multispectral remote sensing data by various workers are reviewed the various spectral indices proposed by the authors for extracting information on the mineralogy or chemistry of the target geological materials are summarized

core complex geometries and regional scale flow in the lower crust a simple flexural model that treats the lithosphere as a thin elastic plate overlying a fluid asthenosphere produces an excellent fit to the domal detachment fault geometries observed in typical core complexes of the basin and range province however this mode of isostatic compensation requires an unacceptably large reduction in local topographic elevation 3 5 km above core complex structures because topographic lows of this magnitude are not observed above core complexes today it requires mountain ranges 3 5 km higher than the surrounding areas to have existed at the site of each future core complex and requires these mountain ranges to have had large crustal roots that were subsequently uplifted to form a flat moho as the core complexes developed an alternate mode of isostatic compensation whereby compensation occurs primarily by regional scale flow of material within the lower crust beneath an elastic midcrust provides an equally good fit to the observed detachment fault geometries while requiring little reduction in local topographic elevation above developing core complex structures and providing an obvious means of maintaining a flat moho beneath these zones of upper crustal doming if this interpretation is correct then the effective elastic plate thickness below the basin and range province probably cannot exceed a maximum of about 4 km with a best guess estimate of about 0 5 to 1 km computation of the temperature structure associated with crustal flow during doming shows that an increase in temperature at the moho of about 100 c follows doming by several million years perhaps explaining the observed coincidence of core complexes with crustally derived igneous rocks subsequent cooling of the mid to lower crust beneath the core complex could result in freezing of the initially ductile lower crust within the core of the dome effectively locking the domal shape into the crust even after the detachment surface is cut by younger faults

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

the mesozoic cenozoic tectonothermal evolution of the ruby mountains east humboldt range nevada a cordilleran metamorphic core complex a combined k ar and 40ar 39ar geochronological study of the ruby mountains east humboldt range nevada a cordilleran metamorphic core complex has revealed a complex tectonothermal history the three structural subdivisions of the core complex migmatitic core mylonitic zone and cover share magmatic and deformational histories in part but also display important contrasts in structural style metamorphic paragenesis and thermal history during the late jurassic ca 160 ma miogeoclinal rocks were polyphase deformed metamorphosed under amphibolite facies conditions and pervasively intruded by peraluminous granitic magmas thereby forming an igneous and metamorphic complex late jurassic muscovite granite porphyry plugs also intruded unmetamorphosed cover rocks late cretaceous cooling of the igneous and metamorphic complex is locally suggested by poorly resolved cretaceous incremental release 40ar 39ar hornblende spectra and by u pb monazite ages from pelitic schist exposed in the northern ruby mountains between ca 45 ma and 20 ma the igneous and metamorphic rocks experienced an episode of complex extensional tectonism which involved the development of low angle normal sense simple shear zones as a result rocks metamorphosed at depth in the mesozoic were translated to higher crustal levels which resulted in cooling through temperatures required for the intracrystalline retention of argon within minerals near concordance of hornblende and biotite plateau ages from the migmatitic core of the complex suggest relatively rapid exhumation however it is not certain if this cooling followed a prolonged maintenance at elevated temperatures after the ca 160 ma metamorphism or if distinct locally superposed late mesozoic and or middle tertiary thermal overprints had affected the cooling history a major extensional simple shear zone is marked by an approximately 1 kilometer thick mylonite zone that experienced late kinematic superposed brittle deformation a geometric consequence of the development of low angle extensional fault zones is the eventual translation of colder rocks over hotter rocks such a history is supported by the 40ar 39ar data for example mylonitic mafic orthogneisses from a major allochthon record 40ar 39ar hornblende plateau ages between 44 and 48 ma and biotite plateau ages between 32 and 33 ma and are structurally positioned above mylonitic rocks of the northern ruby mountains which record biotite cooling ages of ca 22 24 ma such relations suggest either multiple episodes of tertiary mylonitization or a protracted multiphase history of mylonitization however after ca 20 ma all of the presently exposed mylonitic rocks were maintained below 100 c and have only experienced upper crustal brittle deformation this article contains supplementary material

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

correlation of plate motions with continental tectonics laramide to basin range some of the major tectonic and magmatic events of the last 150 ma in the western cordillera can be correlated with a new model for the displacement histories between western north america and adjacent oceanic plates sierra nevada plutonism ended and laramide compression began during increasingly rapid convergence of the farallon plate with north america and during a moderate increase in the westward motion of north america in the hotspot reference frame the end of the laramide and beginning of widespread arc magmatism and extension correlates with slowing of both of these motions the spectacular slowing of faralion north america convergence is attributed to the decreasing age of the farallon plate entering the trench and thus to a change from negative to positive buoyancy the transition from widespread arc related magmatism and rapid extension to basaltic volcanism and moderate extension in the basin and range province finds no ready explanation in the plate motions of the pacific basin a change to oblique spreading in the basin and range province accompanied growth in length of the san andreas fault as the mendocino triple junction progressed northward

cross hole seismic surveys applications for studying subsurface fracture systems at a hot dry rock geothermal site the use of cross hole seismic surveys for delineating the location and size of subsurface fracture systems is investigated the radiation pattern for p and s waves emitted by a seismic source in a borehole is derived experimental work in relatively homogeneous granite suggests that the derived relationship adequately describes the radiation pattern for both explosive sources and acoustic transducers placed in fluid filled boreholes using the above functional expressions for the s and p wave amplitudes we have developed a technique to estimate q and locate discrete fractures in crystalline rock that compose the hot dry rock geothermal reservoir at fenton hill new mexico to calculate q we measure the p and s wave amplitudes as a function of distance from the source compensate for the radiation pattern and geometrical spreading effects and match the relative attenuation to a function of the form exp fr qv using a least squares regression technique for undisturbed parts of the reservoir we obta

miocene nne directed extensional unroofing in the menderes massif southwestern turkey structural investigations in the central part of the menderes massif odemio kiraz submas sif reveal the presence of a large scale low angle extensional shear zone with a top to the n ne shear sense regional ductile deformation was accompanied by the intrusion of two syntectonic granodiorites that have been dated with the 40 ar 39 ar method one hornblende isochron age of 19 5 1 4 ma and two biotite plateau ages of 13 1 0 2 and 12 2 0 4 ma respectively constrain that extension was already active in the early miocene successive tectonic denudation of the odemio kiraz submassif resulted in the formation of a n dipping detachment fault in which ductile fabrics were severely reworked by cataclasis under decreasing temperature syntectonic neogene sediments currently exposed along the southern margin of the gediz graben were deposited in the hanging wall of the extensional fault system and were tectonically emplaced onto the cataclasites during progressive exhumation minor rotation c 15 caused southward tilting of the sediments ongoing nne directed extension created a steep normal fault that truncates the detachment fault and constitutes the southern boundary fault of the gediz graben

regional correlation of extension directions in cordilleran metamorphic core complexes cordilleran metamorphic core complexes exhibit tertiary extensional deformation expressed either as detachment faults or detachment faults plus ductile mylonitic shear zones extension directions as indicated by stretching lineations within mylonite and striations along detachment faults fall into regional groups in which the directions are similar in trend throughout each group asymmetric fabrics on both small and large scale give a sense of shear and indicate that tectonic vergence within groups is directed outward from a central axis the regional consistency of extension directions implies a regional control of extension in metamorphic core complexes

folding of mylonitic zones in cordilleran metamorphic core complexes evidence from near the mylonitic front metamorphic core complexes of north america are asymmetric when viewed perpendicular to the direction of tectonic transport on one side mylonitic fabrics and the overlying detachment fault dip gently in the direction of upper plate transport and the mylonitic rocks have a down dip sense of shear on the opposite side the mylonitic zone rolls over to a dip opposed to the direction of upper plate transport diverges downward from the detachment fault and dies out upward across a mylonitic front new kinematic data show that the backdipping mylonitic zone in most complexes is a downfolded continuation of the main mylonitic zone folding of the mylonitic zone was accompanied by the formation of antithetic shear zones and occurred during the late stages of mylonitization

using dual well seismic measurements to infer the mechanical properties of a hot dry rock geothermal system high frequency 8 15 khz seismic waves that travel between two boreholes are used to probe the detailed structure of rock in the los alamos national laboratory fenton hill hot dry rock geothermal energy reservoir we study travel times of direct p waves and spectral characteristics of waveforms in an effort to determine whether or not large fluid filled fractures are present in the rock between the two boreholes data from two experiments separated in time by 1 year are studied we find dramatic differences between the two experiments in p wave velocity and in spectral characteristics of waveforms that traversed the same region we also find variations in p wave velocity and spectra as a function of location during one experiment loss of high frequency content of direct arriving p waves during the second dual well seismic experiment is compared with q found by using the coda wave technique aki and chouet 1975 and also with theoretical results on frequency dependence of transmission through a water filled fracture to determine the minimum number of large fractures in the system two to four fractures with thickness about 4 mm and vertical extent of as much as 200 m are required to explain observations during the second experiment efficient transmission of high frequencies observed during the first experiment is interpreted as meaning that fracture thickness was less than 1 mm at that time increased fracture thickness during the second experiment is probably due to a 75 day period of heat extraction during which in situ temperature dropped by as much as 100 below the virgin temperature since the coefficient of linear thermal expansion of granite is approximately 10 5 c a decrease in temperature of 100 c in a region on the order of 1 m around the fracture is required to explain the increased fracture thickness

flux of4he from carnmenellis granite modelling of an hdr geothermal reservoir abstract the diffusion coefficient d of he in the carnmenellis granite recovered from the rosemanowes hot dry rock hdr geothermal reservoir is experimentally determined in the laboratory in a temperature range of 100 300 c temperature variation of d fits an arrhenius plot but yields an activation energy for he release from rock significantly lower than the value for feldspar or quartz suggesting that most of the he in the reservoir granite resides within grain boundaries and jointing cement and may be easily released the reservoir surface area s is estimated based on the laboratory determined value of d from granite and the measured4he contents of circulation fluids from rh 15 well in the first year of reservoir circulation 4he based reservoir surface area was about twice that based on222rn it increased and stabilized at about 6 times after 2 a the excess he release from newly opened up fracture surfaces within the reservoir during its expansion is shown to be responsible for the temporal increase in the he based reservoir surface area over that of rn

changes in compressional and shear wave velocities and dynamic moduli during operation of a hot dry rock geothermal system compressional and shear wave velocities measured during cross well seismic surveys are found to decrease during operation of a hot dry rock geothermal system the relative p and s wave velocity decrease is very close to values predicted by o connell and budiansky 1974 who modeled velocities in rocks containing fluid saturated and dry cracks because our data fit their model quite well we attribute the velocity decrease to an increased density of fluid filled fractures in the reservoir fracture density parameters of o connell and budiansky range as high as 0 365 near the main heat transfer areas of the geothermal reservoir the dynamic shear and young s modulus are significantly lower near the principal heat transfer surfaces but the bulk modulus is largely unaffected these observations suggest that the velocity differences are caused by fully saturated fractures we demonstrate that the fractures inferred by this survey may have lengths as large as 70 cm these fractures may have been caused by shear failure microcracking associated with thermal drawdown or thermal stress cracking

magmatism as an essential driving force for formation of active metamorphic core complexes in eastern papua new guinea the d entrecasteaux islands in eastern papua new guinea are composed of a number of active metamorphic core complexes which have been intruded by granodiorite plutons during their formation the plutons do not appear to have been intruded by diapiric processes as previously suggested late relatively undeformed plutons form flat lying bodies which crosscut structural boundaries and are strongly discordant to core complex shear zones granodiorite magmatism and the development of the metamorphic core complexes have occurred in a linear zone which coincides with a zone of thick crust and rugged topography it is proposed that plutonism facilitated deformation in ductile extensional shear zones which resulted in tectonic exhumation of deep crustal rocks and formation of the metamorphic core complexes the source of the plutons is thought to be related to a linear zone of mantle upwelling beneath the islands related to the propagation of the woodlark seafloor spreading center into continental crust it is suggested that a localized heat source of this type which can provide heat and magmatic material to the crust is essential for the development of metamorphic core complexes

mid crustal cretaceous roots of cordilleran metamorphic core complexes thermobarometry for cretaceous to mid tertiary plutonism and deformation in the lower plate of whipple and santa catalina metamorphic core complexes shows that both crystalline terranes originated in the middle crust moreover they are characterized by a striking acceleration of tectonic decompression coincident with middle tertiary low angle detachment faulting leading to erosional and tectonic unroofing by mid miocene time depth estimates for emplacement of five intrusive suites within the whipple complex include 1 33 4 km for the peraluminous 89 ma whipple wash plutonic suite 2 29 1 km for the 73 ma axtel quartz diorite 3 16 5 km for mylonitization and synkinematic plutonism at 26 ma 4 6 2 1 9 km for the postkinematic 19 ma war eagle gabbro quartz diorite complex and 5 5 2 2 3 km for a 17 ma postkinematic granodiorite decompression initially occurred at a low rate of 0 3 mm yr from 89 to 26 ma and increased to approximately 2 mm yr during the late oligocene to middle miocene estimated depths for four pluton emplacement or deformational events in the santa catalina mountains include 1 21 1 km for the magmatic epidote bearing 68 ma leatherwood quartz diorite 2 15 3 km for the garnet two mica 47 ma wilderness granite 3 9 3 1 9 km for post wilderness mylonitzation and 4 6 3 2 6 km for the 27 ma catalina monzogranite post laramide decompression estimated at 0 3 mm yr accelerated to 1 3 mm yr prior to the cessation of detachment faulting whereas most batholithic terranes of the north american cordillera are representative of an upper crustal setting core complexes provide as a consequence of their tectonic evolution a petrological and structural view into middle crustal processes

natural long term annealing of the zircon fission track system in vienna basin deep borehole samples constraints upon the partial annealing zone and closure temperature abstract fission track ft analysis of zircon from cretaceous and tertiary sandstone samples in vienna basin boreholes has provided constraints for the thermal stability of the zircon ft system over a geological timescale confined track lengths and ages were measured for samples from depths of 1 5 7 5 km the deepest with a present environmental temperature of 200 c mean track lengths range from 10 3 to 10 8 m indistinguishable within error from the unannealed reference length of 10 7 0 1 m 1 standard error thus showing no sign of systematic downhole reduction central zircon ages are consistently older than stratigraphic ages of parent rocks with no single grain ages significantly younger than their respective stratigraphic ages such ft age and length evidence strongly suggests that the tracks have not been significantly annealed since sediment deposition because the present geothermal regime as well as sample burial depths have been near constant for at least the past 5 m y the lower temperature limit of the zircon ft partial annealing zone is 200 c for a heating duration of the order of 5 10 m y such evidence from long term natural annealing is compatible with a zircon ft partial annealing zone cf 200 350 c derived by the extrapolation of laboratory annealing results based on onfined track length measurements but cannot alone discriminate between different annealing models for the zircon ft closure temperature a perhaps over simplified concept these results are consistent with the oft quoted temperature of 250 c for cooling rates of 10 100 c m y

coupled hydromechanical thermochemical processes in rock fractures the behavior of rock fractures under various coupled processes is reviewed under seven broad categories 1 hydromechanical processes 2 thermohydrologic processes 3 hydrochemical processes 4 thermohydromechanical processes 5 thermohydrochemical processes 6 hydromechanical chemical processes and 7 thermomechanical hydrochemical processes the state of the art and possible directions of further research in these coupled processes are discussed rock fracture behaviors considered include not only dilation closure shear and joint propagation but also changes in flow permeability and chemical sorption and retardation capabilities these properties are of critical concern in practical considerations of the rock mass as a medium to store and isolate chemical and radioactive wastes investigations of coupled processes in two fracture systems and multifracture systems are identified as important areas for future research the need to consider coupled processes in borehole testing procedures involving rock fractures is emphasized

quartzose mafic spectral feature space model a methodology for extracting felsic rocks with aster thermal infrared radiance data abstract the original spectral features of felsic rocks are often intermingled with other surface objects which results in difficulty of detecting felsic rocks using remote sensing techniques few felsic rock indices were proposed and visual interpretation with rgb false color composition is widely used to detect felsic rocks this paper aims to construct a two dimensional spectral feature space model to extract felsic rocks using aster thermal infrared radiance data the study area is located in northern qinghai province western china with average altitude of approximately 4200 m a large number of training pixels of mafic ultramafic rock quartz rich rock felsic rock carbonate rock and vegetation were selected from the aster images as samples of these surface objects then we used a quartz rich rock index qi qi band14 0 844 band12 1 897 and a mafic ultramafic rock index mi mi 0 915 band10 band13 1 437 to generate a two dimensional scatter plot the plot was named after quartzose mafic spectral feature space qmfs the samples show an approximate triangular shape in the qmfs mafic ultramafic rock quartz rich rock and carbonate rock are located in separate locations in the three vertex regions respectively while felsic rock is located in the central region of the triangle next we calculated a linear belt of silicate rocks in which silicate rocks vary regularly by using a linear regression analysis in the qmfs statistical characteristics of the felsic rock samples are analyzed afterwards a polygon which delineates the distribution of felsic rock samples was constructed from the linear belt of silicate rocks then we generated a system of inequalities based on the equations of the edges of the polygon the application of the inequalities to the aser images shows a good performance of the qmfs for extracting felsic rocks

rock water interactions in hot dry rock geothermal systems field investigations of in situ geochemical behavior abstract two hot dry rock hdr geothermal energy reservoirs have been created by hydraulic fracturing of precambrian granitic rock between two wells on the west flank of the valles caldera in the jemez mountains of northern new mexico heat is extracted by injecting water into one well flowing it through the fractured region and recovering the heated water from the second well the produced fluid is cooled on the surface and reinjected into the system the first reservoir was formed by fracturing the injection well at a depth of 2 75 km where the initial rock temperature was 185 c a heat extraction experiment conducted in this reservoir was run from january 27 to april 13 1978 a second larger reservoir was created after cementing the fracture to wellbore connections at 2 75 km in the injection well and refracturing 180 m deeper this second reservoir was tested from october 23 to november 16 1979 during each of these experiments samples of the geothermal fluids and gases were collected at regular intervals from the injection wellhead the production wellhead and at the make up pump which provided the water from storage ponds to replace the water lost downhole by permeation into the reservoir walls changes in the composition of the produced fluid provide a means for studying the reservoir behaviour under normal recirculating operating conditions certain of the dissolved species appear to be derived by displacement of an indigenous pore fluid while others appear to be derived by dissolving minerals known to be present in the reservoir rock in this paper we describe the results of the chemical analysis of the geothermal fluids and relate the fluid and gas chemistry to geochemical processes that result from the heat extraction experiments in particular the implications of the silica and na k ca geothermometers and the pore fluid displacement theory are examined for insight about the long term effects of fluid geochemistry on heat extraction from hdr reservoirs

extensional deformation with northwest vergence pioneer core complex central idaho the pioneer mountains of idaho contain a detachment fault that separates a lower plate core of precambrian and ordovician metasedimentary rocks and cretaceous and eocene plutonic bodies from a surrounding upper plate of paleozoic sedimentary and tertiary sedimentary and volcanic units the detachment system developed during tertiary extension and it overprinted paleozoic and mesozoic east directed compressional features beneath the detachment both brittle and ductile mylonitic deformation can be observed trends of stretching lineations in the mylonite and striations along the detachment surface both cluster around n65 w composite planar fabrics s and c surfaces in the mylonite and development of the mylonite zone on the northwest side of the core both suggest a top to the west sense of shear both brittle and ductile deformation affect the eocene pluton of the core therefore the deformation must be eocene or younger displacement is estimated at about 17 km the extension direction in the pioneer complex correlates with that of other core complexes in the region north and south of the snake river plain this suggests that the direction of extension in core complexes was controlled by an inherited structural framework which was crustal in scale

denudation of metamorphic core complexes and the reconstruction of the transition zone west central arizona constraints from apatite fission track thermochronology apatite fission track thermochronologic results from transects across the basin and range and transition zone provinces in west central arizona provide constraints on the denudational history and structural framework of the region apatite fission track ages decrease from 21 to 14 ma in the harcuvar mountains and from 16 to 13 ma in the buckskin rawhide mountains in the slip direction sw ne of detachment faults in the lower plates of the metamorphic core complexes mean lengths of confined fission tracks from the core complexes are all 14 m indicating that the apparent apatite ages record rapid cooling through the apatite partial annealing zone 40 c m y for lower plate rocks apparent apatite ages in the transition zone province generally increase from 25 ma to 100 ma away from the basin and range province this trend of increasing apatite age is disrupted by faulting as many as seven times at the fronts of major mountain ranges and within valleys between the weaver mountains and the colorado plateau gradients of apatite fission track age and confined track length with elevation in the mountain ranges and in the phillips kirkland drill hole reveal parts of denuded mesozoic and cenozoic apatite partial annealing zones these paleopartial annealing zone profiles provide a reference datum for preextension reconstructions of fault blocks the reconstructions indicate that the major faults in the transition zone province have relative displacements of 1 km and that offset on them occurred mostly after 25 ma these data also indicate that most of the rocks now exposed in the transition zone of west central arizona were not exposed until miocene time

geological mapping of the francistown area in northeastern botswana by surface temperature and spectral emissivity information derived from advanced spaceborne thermal emission and reflection radiometer aster thermal infrared data abstract we identified geological units in the francistown area in northeastern botswana by using advanced spaceborne thermal emission and reflection radiometer aster thermal infrared tir data which contains both surface temperature and spectral emissivity information a scatter plot of aster l1b daytime tir digital values and l2 daytime temperature indicates that in the aster l1b daytime tir data bands 10 11 and 12 contain spectral emissivity and temperature information whereas surface temperature dominates the spectral emissivity information in bands 13 and 14 visual interpretation of the aster tir false color composite fcc images generated by assigning red green and blue to band 14 band 12 band 10 using l1b daytime data allowed us to identify mafic to ultramafic units and quartz rich felsic units mafic to ultramafic units such as gabbro dolerite and dunite appear white in aster l1b daytime tir fcc images due to their high spectral emissivities in the 8 9 m region bands 10 and 12 and high surface temperatures mafic to ultramafic units have higher surface temperatures than other geological units because they absorb more solar radiation due to their lower albedos and they have a lower thermal inertia quartz rich felsic units such as granite and dry river sand appear reddish in the aster l1b daytime tir fcc image because the spectral emissivity of quartz is lower in the 8 9 m region bands 10 and 12 than in the 10 12 m region band 14 mafic to ultramafic and granitic units are important targets for mineral exploration because they are potential geological units to host or accompany mineralization the proposed aster l1b daytime tir fcc images can be prepared very simply and they provide valuable information for geological mapping and mineral exploration

detecting lithology with advanced spaceborne thermal emission and reflection radiometer aster multispectral thermal infrared radiance at sensor data abstract the advanced spaceborne thermal emission and reflection radiometer aster aboard nasa s terra satellite measures multispectral thermal infrared tir emission from the earth s surface to space based on analysis of tir spectral properties of typical rocks on the earth several mineralogic indices including the quartz index qi carbonate index ci and mafic index mi for detecting mineralogic or chemical composition of quartzose carbonate and silicate rocks with aster tir data are proposed these indices are applied to the aster tir data scenes for selected study areas in china and australia the results show that aster tir can discriminate quartz and carbonate rocks as well as mafic ultramafic rocks even with atmospherically uncorrected radiance at sensor data lithologic interpretations agree well with published geologic data and field observations the mineralogic indices applied to aster tir provide one unified approach for lithologic mapping in arid and semi arid regions of the earth

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

tertiary extension in the old woman mountains area california evidence from apatite fission track analysis apatite fission track ages and confined track length distributions from the old woman mountains area southeastern california record evidence for periods of rapid cooling during the late cretaceous following mesozoic orogenesis and during miocene crustal extension apatites from the clipper marble and turtle mountains give fission track ages between 62 and 69 ma as a result of cooling of these upper crustal rocks after regional late cretaceous plutonism and metamorphism in the piute mountains apatite fission track ages decrease from 70 ma with mean track lengths of 13 5 m to 14 m from west to east intermediate aged samples from the piute mountains have mean track lengths between 11 and 13 m due to their extended residence in the apatite annealing zone during the early tertiary this pattern is the result of 20 30 of westward tilting of the piute mountains block as indicated by the dip of tertiary strata the apatite data indicate that tilting occurred after 18 ma and caused rapid cooling of rocks exposed on the eastern side of the mountain range knowing the amount of tilting and the apparent paleotemperatures across the piute mountains allows us to estimate that the synextensional geothermal gradient was 50 20 c km apatites from the northeastern old woman mountains yield fission track ages of 68 ma with mean track lengths of 13 8 m these samples record cooling after batholith emplacement at 73 ma in the northwestern old woman mountains apatite fission track ages decrease to 20 ma and have mean track lengths 15 m indicating very rapid cooling we interpret this age pattern to be the result of minor eastward tilting of the old woman mountains block after 18 19 ma or flexural unroofing of the northwestern old woman mountains due to movement on the ship mountains fault extension in the old woman mountains area occurred between 19 and 16 ma which is coincident with extension in the colorado river extensional corridor and later than major extension in the mojave extensional belt

direct evidence for a steep geotherm under conditions of rapid denudation western himalaya pakistan recent fluid inclusion and 40 ar 39 ar cooling age data show that currently exposed basement rocks in the raikhot glacier valley of the nanga parbat haramosh massif pakistan himalaya were at temperatures of 350 50 c at depths of 6 2 km hydrostatic pressure correction these data imply the presence of a steep thermal gradient in the upper crust at 1 ma 29 100 c km and denudation rates over the past 1 0 m y of 3 6 mm yr providing independent corroboration of previous estimates of rapid denudation at nanga parbat 4 5 mm yr over 3 3 m y our data provide direct documentation of near surface compaction of isotherms under conditions of rapid denudation a result that has long been supported by thermal modeling

granite related ore deposits an introduction a symposium on mineralization associated with granitic magmatism was held within the framework of the 33rd igc in oslo norway in august 2008 while our initial idea was to bring together field experimental and theoretical studies in order to review and summarize the current ideas and recent progress on granite related mineralization systems we were caught by surprise realizing that participants were inclined to focus more on ore deposits related to granitic magmatism this spontaneous shift from granites the major intended focus of the symposium to mineralization associated with them spawned the idea for a special issue on this theme and ultimately to the nine papers assembled here chosen from about 60 scientific contributions at the symposium around twenty oral presentations were given and forty posters were presented at the meeting the 60 papers were grouped according to the current main granite related ore systems as follows granite pegmatite skarn and greisen veins porphyry orogenic gold intrusion related epithermal and porphyry related gold and base metal iron oxide copper gold iocg and special case studies importance of granite related mineralization systems diversity of mineralization styles and related

energy extraction from fractured geothermal reservoirs in low permeability crystalline rock two hot dry rock geothermal energy reservoirs were created by hydraulic fracturing of precambrian granitic rock on the west flank of the valles caldera a dormant volcanic complex in the jemez mountains of northern new mexico heat was extracted in a closed loop mode of operation injecting water into one well and extracting the heated water from a separate production well the first reservoir was produced by fracturing the injection well at a depth of 2 75 km where the indigenous rock temperature was 185 c the relatively rapid decline in temperature of the water produced from the first reservoir 100 c in 74 days indicated an effective fracture radius of about 60 m with an average thermal power extracted of 4 mw a second larger reservoir was created by refracturing the injection well 180 m deeper downhole measurements of water temperature at the reservoir outlet as well as temperatures inferred from chemical geothermometry showed that the thermal decline of this reservoir was negligible the effective heat transfer area of the new reservoir must be at least 45 000 m2 nearly 6 times larger than the first reservoir in addition reservoir residence time studies employing visible dye tracers indicated that the mean volume of the second reservoir is 9 times larger other measurements showed that flow impedances were low and that downhole water losses from these reservoirs should be manageable the geochemistry of the produced water was essentially benign with no scaling problems apparent moreover the level of induced seismic activity was insignificantly small

metamorphic and stratigraphic constraints on the evolution of the santa catalina mountains metamorphic core complex arizona contact metamorphic mineral assemblages in the santa catalina mountains metamorphic core complex constrain the emplacement depth of the metaluminous late cretaceous leatherwood quartz diorite to between 7 5 and 14 km 2 3 8 kbar the peraluminous eocene wilderness granite is constrained to have been emplaced at depths of less than 14 km stratigraphic and tectonic considerations are consistent with emplacement of both the leatherwood quartz diorite and wilderness granite at upper crustal levels published igneous thermobarometry anderson et al 1988 although in approximate agreement with the metamorphic and tectonostratigraphic estimates for the depth of emplacement of the wilderness granite suggests that the leatherwood quartz diortite was emplaced at depths of 21 km 5 6 kbar or greater the discrepancy between the different emplacement estimates may reflect ambiguities associated with interpretations of the results from each technique igneous barometric assemblages may reflect conditions experienced during a period of crystallization during ascent of the magma through the crust i e ponding of the magma alternatively emplacement of the voluminous wilderness granite and associated plutons may have entirely overprinted earlier leatherwood related contact metamorphism the proposed upper crustal emplacement of the leatherwood quartz diorite is consistent with the observation that lararrade age crustal thickening in southeast arizona probably did not exceed 8 km

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

mafic ultramafic and quartz rich rock indices deduced from aster thermal infrared data using a linear approximation to the planck function abstract aster thermal infrared tir data are widely used to detect mafic ultramafic rock and quartz rich rock and several rock indices have been proposed based on emissivity features however aster tir bands of radiance data correlate highly with each other which indicates that the independent information derived from different bands may be limited what s more aster tir radiance at sensor data contain atmospheric effect and temperature information thus interfering with the availability of these previously proposed indices in this study we aim to explain the correlation using a linear approximation of the planck function and deduce a linear equation that represents the relationship of the radiance between two tir bands theoretical difference indices were deduced based on the linear equation and regression residual characteristics for any two aster tir radiance bands the study area is located in qinghai province china and belongs to the qinghai tibet plateau where the average elevation is approximately 4200 m a scatter plot of radiance derived from the aster image that overlaps the study area indicates that mafic ultramafic rock and quartz rich rock can be distinguished from other surface objects well two mafic ultramafic rock indices mi1 b13 0 9147 b10 1 4366 and mi2 b13 0 8945 b11 1 2404 and two quartz rich rock indices qi1 b13 0 9261 b12 1 4623 and qi2 b14 0 844 b12 1 8971 were proposed they satisfactorily map these rock units the atmospheric effect on the indices is weak in arid or high elevation region so it will not interfere with the indices obviously in these regions one way variance analysis was performed to discuss the stability of the indices with respect to temperature the mafic ultramafic rock indices are found to be independent of temperature whereas the values of quartz rich rock indices increase with the rising of temperature we thus conclude that the quartz rich rock indices are suitable for the high elevation region only while the mafic ultramafic rock indices may be capable of detecting these rocks in regions with different natural conditions

evidence for a local crustal root beneath the santa catalina metamorphic core complex arizona we used data from the tucson arizona broad band seismic station to analyze crustal and mantle structure under and adjacent to the catalina metamorphic core complex the data can be modeled with a simple two layer crust having an average moho depth of 30 km and seismic velocities consistent with a felsic composition the lower crust thickens under the catalina mountains depressing the moho by 4 2 km the crustal root can isostatically compensate the average topography of the catalina mountains indicating that the depth of isostatic compensation is at or below the moho and that the catatina mountains act as a coherent block bounded by high angle normal faults the presence of the crustal root is not consistent with models that predict upward bowing of the moho under the catalina metamorphic core complex the presence of the root cannot rule out models of lower crustal flow during the formation of the core complex however the presence of a root favors a model of metamorphic core complex development described by crustal thickening in shortening episodes crustal welt model followed by collapse of the crustal welt through extension

cocorp arizona transect strong crustal reflections and offset moho beneath the transition zone the consortium for continental reflection profiling cocorp transect across the southwest margin of the colorado plateau in arizona reveals prominent subhorizontal zones of reflections here termed the bagdad reflection sequence brs which dominate the upper and middle crust in the transition zone tz between the colorado plateau and the basin and range province a cenozoic origin for the brs is considered most likely it may represent fragmented or sheared zones related to detachment faulting or a series of intrusions possibly emplaced along preexisting zones of weakness moho reflections observed beneath the tz and the basin and range province contrast with the nonreflective moho beneath the colorado plateau suggesting that extension and its associated igneous processes probably played a key role in the development of reflectors at the moho the moho and a prominent midcrustal reflector are offset by about 3 km in a normal sense in at least one place this is the best example of offset moho yet found by cocorp and contrasts sharply with cocorp observations of a smooth moho elsewhere this offset is probably a late tectonic expression of crustal extension and thinning across the tz

plutonism and the origin of metamorphic core complexes the formation of metamorphic core complexes may be triggered by plutonic activity during episodes of continental extension pulses of ductile deformation have taken place during short lived thermal events initiated by the heat input from intruded plutons sills or dikes such intrusions may be the underlying cause for differential uplift of the footwall during tectonic denudation of metamorphic core complexes fast cooling inferred from 40 ar 39 ar apparent ages may have taken place after periods of magma arrival and need not be the result of rapid erosional or tectonic denudation heterogeneity of 40 ar 39 ar apparent ages can be explained by rapid cooling of deforming mylonites formed at shallow crustal levels in the thermal aureoles of intruded sills or sill swarms under such circumstances apparently isothermal decompression paths may actually link pressure temperature points set during periods of transient mineral growth during and after periods of igneous activity

interpretation of seismic data from hydraulic fracturing experiments at the fenton hill new mexico hot dry rock geothermal site an attempt was made to synthesize the results of active seismic experiments carried out by the los alamos national laboratory s hot dry rock project staff for determining the geometrical and physical properties of the fracture system produced by hydraulic fracturing in a hot low permeability rock interpretation of data from several reflection transmission and attenuation experiments using seismic probes in the frequency range from a few hundred to more than 10 sup 4 hz led us to postulate the existence of a highly complex fracture system consisting of major discrete vertical cracks intersected by several inclined joints which are surrounded by a large volume of rock containing small scale cracks we found an interesting coincidence between the mean square fluctuation of p arrival time and q sup 1 of coda waves both are increased by nearly the same amount 35approx 40 when fluid pressure in the reservoir is increased another coincidence is the scale length of the inhomogeneity of roughly 3 m obtained from the frequency dependence of attenuation and also from the spatial variation of p arrival time these results suggest that the seismic attenuation in the fractured region is caused primarily by scattering

implications of low temperature cooling history on a transect across the colorado plateau basin and range boundary west central arizona fission track ages of apatite and zircon from metamorphic plutonic and sedimentary rocks along a 80 km transect across the colorado plateau basin and range boundary in west central arizona show differences in the low temperature cooling histories between the provinces the transect extends from cypress mountain in the colorado plateau transition zone to the eastern buckskin mountains in the basin and range along the northeast margin of the basin and range province metamorphic rocks exposed in the footwall of a major detachment fault system yield zircon and apatite fission track ages of 16 10 ma these ages are similar to k ar fusion ages of biotite and age minima of k feldspar on 40ar 39ar age spectra and collectively indicate rapid cooling one k feldspar age spectrum has an age maximum of about 22 8 ma an age minimum of 11 8 ma and a spectrum whose shape is suggestive of reheating possibly in middle miocene time the heating event was probably related to hydrothermal activity during emplacement of cu and mn deposits in and above the detachment fault zone effects of this heating are only locally detected in rocks above the detachment fault in the poachie range fission track ages of apatite and zircon are 60 50 and 80 70 ma respectively the disparity between the apatite and zircon ages indicates that the rocks cooled slowly in late cretaceous and early tertiary time probably due to gradual uplift and erosion total uplift and denudation in the area of the poachie range since cretaceous time is 6 km or more to the northeast of the range fission track ages of apatite and zircon increase and diverge indicating that apparent uplift decreased in that direction the apatite ages from the poachie range are concordant with early tertiary hornblende ages determined in other studies of lower plate rocks near the southwest end of the transect the ages represent cooling of crystalline rocks after cretaceous regional metamorphism and magmatism near bagdad 20 km northeast of the poachie range 2 km or less of erosion has occurred since intrusion of high level plutons and dikes and caldera formation in late cretaceous time remnants of an erosion surface that developed in middle tertiary time are preserved in the transition zone volcanic and sedimentary rocks at least as old as early miocene were deposited on the erosion surface and filled valleys cut into it dissection of these deposits began about 8 ma we interpret these data combined with those from other studies to indicate that in cretaceous time southward thrusting and later extensive magmatism in the middle crust led to thickening and heating of the crust the cretaceous igneous rocks at bagdad are high level manifestations of this magmatism uplift and slow cooling occurred in late cretaceous and early tertiary time in late oligocene and early miocene time during northeast southwest extension middle crustal rocks moved southwest put from beneath the southwest margin of the transition zone tectonic denudation rapidly exposed the crust that had been brought up from a depth of 10 km or more and rapidly cooled in the eastern buckskin and harcuvar mountains middle miocene reheating occurred locally in the lower plate along the detachment and in nearby parts of the upper plate

emissivity of terrestrial materials in the 3 5 μm atmospheric window remotely sensed infrared radiance emitted by a surface is a function both of its kinetic temperature and its spectral emissivity consequently assumptions are usually made about the emissivity of earth surface materials to allow their temperatures to be determined or vice versa to increase the accuracy of these assumptions the directional hemispherical spectral reflectance of a wide range of natural earth surface materials has been measured and is summarized here these include igneous metamorphic and sedimentary rocks desert varnish soils vegetation water and ice kirchhoff s law can be used to predict directional spectral emissivity from these data

new aster derived thermal indices to delineate mineralogy of different granitoids of an archaean craton and analysis of their potentials with reference to ninomiya s indices for delineating quartz and mafic minerals of granitoids an analysis in dharwar craton india abstract we processed five thermal infrared tir bands of advanced spaceborne thermal emission and reflection radiometer aster at sensor radiance level 1b data to derive few new indices to delineate variation in quartz feldspar and mafic minerals in three different variants of granitoid commonly occurring quartz bearing intrusive rock group in this regard three indices named as quartz bearing rock index qri feldspar bearing rock index fri and mafic bearing rock index mri were proposed qri index was derived using band 10 band 12 and band 13 band 10 band 12 band 13 band 12 of aster radiance image mri index was derived using band 12 band 13 and band 14 band 12 band 13 band 13 band 14 of aster radiance bands while band 10 band 11 were combined to derive fri band 10 band 11 index three indices were combined in false colour composite image fcc and three dimensional scatter plot to delineate granite alkali granite and mafic rich granodioritic gneiss from each other as these granitoids had variable abundances of quartz feldspar and mafic minerals qri and mri were compared with the corresponding quartz and mafic indices proposed by ninomiya 2005 it was observed from the respective ratio images and their regression plots that mri and ninomiya s mafic index nmi were complementary to each other on the other hand qri image was better in enhancing quartz enrichment in alkali granites than ninomiya s quartz index nqi however qri index was comparable with the quartz index proposed by rockwall and hofstra 2008 in terms of delineating quartz enrichment in alkali granite mutual exclusive nature of mafic minerals and quartz in granitoids was also evident from the negative correlation between mri and qri indices of the granitoids on the other hand fri and qri were negatively correlated with low regression value this was resulted due to the combined effect of inverse relation of abundance of two dominant feldspars with quartz in different granitoids in granitoids abundance of plagioclase is known to increase with decreasing quartz content in granodiorite and tonalite although alkali feldspar bearing granites are characterised with high silica content results of discrimination of granitoids using proposed indices were validated based on deriving emissivity spectra of rocks and comparing them with aster tir band resampled laboratory spectra of respective granitoids in addition to use geological map of the study area emissivity spectra of granitoids were derived from emissivity image derived using emissivity normalisation method after geospatially tagging it with qri fri mri image composite which was used to delineate exposures of granitoids further we also found that the qri mri and fri indices had poor temperature dependence when these indices were compared with relative surface temperature image derived from radiance bands using emissivity normalisation algorithm therefore proposed indices can be implemented for delineating mineralogical variations of granitoids irrespective of surface temperature condition hence proposed indices may be used successfully to delineate different granitic intrusions and relating their mineralogical variations with metallogeny

regional mineral mapping of island arc terranes in southeastern mongolia using multi spectral remote sensing data abstract over the last few decades many porphyry cu deposits have been discovered in southeastern se mongolia in particular the gurvansayhan and mandalovoo island arc terranes have high potential for ore deposits regional mineral mapping of these terranes using data from the landsat enhanced thematic mapper plus etm and the advanced spaceborne thermal emission and reflection radiometer aster have provided new geological information on the metallogenic province revealing potential mineral deposits for future explorations iron oxides hydroxides with high etm band 1 3 ratio values occur extensively in quaternary deposits located at the boundary between the gurvansayhan and mandalovoo island arcs terranes and basins the high average band ratios 1 35 registered for the porphyry cu and au deposits and their occurrences are associated with iron oxidation which originates from the erosion and weathering of ore zones regional mapping of the island arc terranes using the aster shortwave infrared swir logical operators showed circular or semicircular alteration patterns which usually cluster along faults the mineral assemblages mapped by the aster swir analysis in five major porphyry cu districts can be divided into two types the first type includes argillic phyllic and propylitic mineral assemblages as exemplified by the shuteen ikh shankhai and oyu tolgoi deposits the second type of assemblage includes phyllic and propylitic mineral assemblages as exemplified by the kharmagtai and tsagaan suvarga deposits within the deposits of the first type quartz was also mapped using the aster thermal infrared tir mineral index the difference between the two types may be related to the presence of a lithocap the results of a field survey including spectral reflectance measurements in the ikh shankhai porphyry cu district showed a good correlation with the image analysis results

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

thermal infrared 2 5 13 5 μm spectroscopic remote sensing of igneous rock types on particulate planetary surfaces fundamental molecular vibration bands are significantly diminished by scattering thus such bands in spectra of fine particulate regoliths i e dominated by 5 m particles or regoliths displaying a similar scale of porosity are difficult to use for mineralogical or rock type identification consequently other spectral features have been sought that may be more useful in spectroscopic remote sensing of composition we find that mineralogical information is retained in overtones and combination tones of the fundamental molecular vibrations in the 3 0 to 7 0 m region but that relatively few minerals have a sufficiently distinctive band structure to be unambiguously identified with currently available techniques more significantly identification of general rock type as defined by the scfm chemical index scfm sio2 sio2 cao feo mgo is possible using spectral features associated with the principal christiansen frequency and with a region of relative transparency between the si o stretching and bending bands however environmental factors may affect the appearance and wavelengths of these features finally prominent absorption bands may result from the presence of relatively small amounts of water hydroxyl or carbonate because absorption bands exhibited by these materials in the 2 7 to 4 0 m region where silicate spectra are otherwise featureless increase strongly in spectral contrast with decreasing particle size such materials are thus detectable in very small amounts in a particulate regolith composed predominantly of silicate minerals

tectonothermal evolution of the pinaleno jackson mountain core complex southeast arizona petrologic data u pb analyses of zircon and 40 ar 39 ar analyses were used to document the tectonothermal history of two mylonite zones and the temporal relationship of mylonite formation to movement on detachment faults in the pinaleno jackson mountain metamorphic core complex of southeastern arizona mylonite formation in the pinaleno mountains is dated at ca 29 and ca 19 ma the later event possibly is synchronous with and structurally related to the most recent movement on the black rock detachment fault at

lithologic mapping of the mordor nt australia ultramafic complex by using the advanced spaceborne thermal emission and reflection radiometer aster abstract spectral measurements made in the mordor pound nt australia study area using the advanced spaceborne thermal emission and reflection radiometer aster in the laboratory and in situ show dominantly al oh and ferric iron vnir swir absorption features in felsic rock spectra and ferrous iron and fe mg oh features in the mafic ultramafic rock spectra aster ratio images matched filter and spectral angle mapper processing sam were evaluated for mapping the lithologies matched filter processing in which vnir swir image spectra were used for reference resulted in 4 felsic classes and 4 mafic ultramafic classes based on al oh or fe mg oh absorption features and in some subtle reflectance differences related to differential weathering and vegetation these results were similar to those obtained by match filter analysis of hymap data from a previous study but the units were more clearly demarcated in the hymap image aster tir spectral emittance data and laboratory emissivity measurements document a wide wavelength range of si o spectral features which reflect the lithological diversity of the mordor ultramafic complex and adjacent rocks sam processing of the spectral emittance data distinguished 2 classes representing the mafic ultramafic rocks and 4 classes comprising the quartzose to intermediate composition rocks utilization of the complementary attributes of the spectral reflectance and spectral emittance data resulted in discrimination of 4 mafic ultramafic categories 3 categories of alluvial colluvial deposits and a significantly more completely mapped quartzite unit than could be accomplished by using either data set alone

fission track analysis of the footwall of the catalina detachment fault arizona tectonic denudation magmatism and erosion new apatite and zircon fission track ages obtained from the footwall of the catalina metamorphic core complex record a complicated cooling history associated with mid tertiary extension zircon fission track ages record the progressive unroofing of the catalina metamorphic core complex along the catalina detachment fault zircon fission track ages range from 31 9 to 19 4 ma generally decrease in the hanging wall slip direction and yield slip rates along the catalina detachment fault ranging from 1 2 to 12 km myr 1 in contrast apatite fission track ages increase in the hanging wall slip direction samples from the main range of the santa catalina mountains yield apatite fission track ages of 20 5 to 14 6 ma samples from the santa catalina mountain forerange located closer to the detachment fault yield apatite fission track ages of 21 4 to 18 8 ma rapid cooling 40 to 60 c myr 1 related to detachment faulting is best recorded by zircon fission track ages and higher temperature thermochronometers in the main range and by nearly concordant zircon and apatite fission track ages in the forerange slower cooling 3 7 c myr 1 of the footwall is recorded by shortened mean confined fission track lengths 14 m and is related to erosional unroofing approximately 2 km of late tertiary erosion played a significant role in the unroofing of the footwall of the catalina metamorphic core complex in contrast to metamorphic core complexes in western arizona where detachment faulting is the dominant unroofing mechanism

rapid extension recorded by cooling age patterns and brittle deformation naxos greece the metamorphic core complex exposed as the island of naxos in the aegean sea records an unusually complete sequence of structures developed as a result of continental extension the structures formed during miocene rise and cooling from ductile upper amphibolite facies and anatectic conditions to brittle near surface conditions beneath the naxos detachment fault top to the north ductile fabrics in the footwall which initially developed during amphibolite facies prograde metamorphism were overprinted by a succession of north directed normal sense lower temperature brittle structures as the footwall was tectonically unloaded and unroofed pseudotachylite and cataclasite formation brittle faulting alteration and erosion of the footwall occurred during continued slip and tectonic denudation neogene conglomerate and megabreccia in part derived from exhumation of this footwall lie structurally above the peripheral naxos fault published k ar and 40ar 39ar ages for hornblende white mica and biotite in the footwall decrease northwestward apparent ages 17 50 ma in the southeast correspond to areas of low metamorphic grade where preextension argon was partially retained published ages 16 10 ma in higher grade rocks of the domal core in the north are cooling ages that for each of the three minerals show a component of younging in the nne direction of extension assuming this is the direction of unroofing we interpret the rate of this younging as the fault slip rate as the footwall rocks moved 20 km ssw relative to their hanging wall along the base of the naxos detachment fault the calculated rates of slip average 5 8 mm yr comparable to maximum rates reported in the basin and range province

precambrian tectonics and crustal evolution in south india about 3 4 ga ago voluminous calc alkaline magmas represented by the granitoid gneisses of southern india were emplaced into a now poorly preserved non continental crust unstable ensialic basins initiated at about 3 0 ga were filled with volcanic and sedimentary rocks up to about 2 6 ga this basement cover sequence was deformed at the close of the archaean first by northward accretion and thickening of several crustal slabs formerly separated by prisms of stable shelf sediments structures produced by this episode were refolded and dislocated by large n s strike slip shear belts to impart intense steep planar fabrics to large volumes of the crust fluids rich in co possibly derived from sedimentary material driven beneath the crustal slabs by the thickening mechanism purged the deep crust of h o to form granulites upward migration of hot h o rich fluids encouraged partial melting at intermediate crustal levels these late archaean tectonic and thermal events began soon after the close of basin f

cenozoic crustal extension in southeastern arizona and implications for models of core complex development abstract in conventional models of cordilleran style metamorphic core complex development initial extension occurs along a breakaway fault which subsequently is deformed into a synform and abandoned in response to isostatic rebound and new faults breaking forward in the dominant transport direction the catalina core complex and associated geology in southeastern arizona have been pointed to as a type example of this model from southwest to northeast the region is characterized by the nw se trending tucson basin the catalina core complex the san pedro trough and the galiuro mountains the catalina core complex is bounded by the top to the southwest catalina detachment fault along its southwestern flank and the low angle northeast dipping san pedro fault along its northeastern flank the galiuro mountains expose non mylonitic rocks and are separated from the san pedro trough to the southwest by a system of low to moderate angle southwest dipping normal faults this galiuro fault system is widely interpreted to be the breakaway zone for the catalina core complex it is inferred to be folded into a synform beneath the san pedro trough to resurface to the southwest as the san pedro fault and to have been abandoned during slip along the younger catalina detachment this study aimed to test this model through analysis of field relations and geochronological age constraints and reprocessing and interpretation of 2 d seismic reflection data from the catalina core complex and san pedro trough in contrast to predictions of the conventional breakaway zone model we raise the possibility of a moderate angle southwest dipping detachment fault beneath the san pedro trough that could extend to mid crustal depths beneath the eastern flank of the catalina mountains we present an alternative kinematic model in which extension was accommodated by a pair of top to the southwest normal fault systems the catalina and galiuro detachment faults with the only major difference between the two being the magnitude of displacement which was greater for the catalina detachment

some theoretical and field aspects of reinjection in geothermal reservoirs theoretical and field aspects of reinjection into geothermal reservoirs is discussed using examples from various geothermal fields reinjection effects can be observed in terms of pressure maintenance changes in chemical concentrations and temperature decline pressure support due to injection is observed in many liquid dominated fields and in two phase field pressure effects are often felt through mobility changes in most geothermal fields where injection is employed changes in chemical concentrations of the produced fluids have been observed due to the higher salinity of the injected fluids in some cases the returns of the injected fluids observed through chemical changes have resulted in temperature declines at the producing wells in those cases the fluid flow is probably concentrated through a few fractures or faults with insufficient surface area for heat exchange with the host rock

effects of plate convergence obliquity on timing and mechanisms of exhumation of a mid crustal terrain the central anatolian crystalline complex abstract apatite fission track ft ages from the central anatolian crystalline complex cacc a microcontinent within the turkish segment of the alpine himalayan orogen vary dramatically from north to south this variation correlates with differences in the obliquity of convergence of the continental fragment relative to the pontide belt for the northern cacc and the tauride belt for the southern cacc the northern cacc was deformed and metamorphosed during late cretaceous orogen normal collision and was exhumed from the mid crust to shallow crustal levels 50 ma to the present in contrast the southern cacc nigde massif was initially deformed and metamorphosed during late cretaceous contraction but subsequently developed as a metamorphic core complex in a wrench dominated regime and was exhumed to

thermochronologic constraints on the tectonic evolution of active metamorphic core complexes d entrecasteaux islands papua new guinea metamorphic core complexes in the d entrecasteaux islands papua new guinea formed as the result of active extension at the western end of the propagating woodlark basin spreading center domes of high grade metamorphic rocks i e amphibolites eclogites and migmatites intruded by large granodiorite bodies comprise the lower plate of the d entrecasteaux metamorphic core complexes the domes are transected by kilometer scale shear zones a thermochronologic study of the d entrecasteaux islands utilizing k ar 40ar 39ar and fission track techniques has documented the unroofing history of these active metamorphic core complexes gneisses in the cores of the domes cooled rapidly 100 c m y as indicated by hornblende and biotite 40ar 39ar apparent ages of 2 7 to 3 0 ma and 1 6 to 1 7 ma respectively and apatite fission track ages of 0 4 to 0 9 ma 40ar 39ar apparent ages on white mica biotite and potassium feldspar and fission track ages on apatites from shear zone gneisses indicate extremely rapid cooling in some cases 500 c m y and suggest shear zones were active from 4 0 to 3 5 ma and 1 9 to 1 4 ma in general 40ar 39ar mineral ages for retrogressed core zone gneisses shear zone gneisses and granodiorites are 2 0 to 3 0 ma amphiboles 1 5 to 1 7 ma muscovites and 1 4 to 1 8 ma biotites and 1 0 to 2 0 ma k feldspars apatite fission track ages from core zone gneisses shear zone gneisses and granodiorites range from 0 4 to 1 0 ma thermochronologic results indicate that emplacement of granodiorites closely coincided with retrogression of the metamorphic basement and movement on the outer shear zones bounding the gneiss domes the granodiorite bodies associated with the d entrecasteaux islands domes represent syn kinematically emplaced granitoids intruded into an area of active continental extension

dispersed fluid flow in fractured reservoirs an analysis of tracer determined residence time distributions a methodology for analyzing the internal flow characteristics of a fractured geothermal reservoir using tracer determined residence time distribution curves is outlined emphasis is placed on comparison of the statistical quantities obtained from the tracer curves of different reservoirs or of the same reservoir under different conditions in this way model independent information may be used unambiguously to construct empirical reservoir performance correlations downhole measurements of the tracer response exiting from discrete fracture zones permit further characterization of reservoir fluid flow behavior tracer experiments conducted in prototype hot dry rock geothermal reservoirs in fractured rock are examined using these statistically based data analysis methods

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

experimental and geologic evaluation of monazite u th he thermochronometry catnip sill catalina core complex tucson az abstract monazite is a petrologically important and analytically promising target for u th he thermochronology previous studies have reported highly variable he diffusion results from monazite from a single sample and demonstrated that composition can significantly affect he diffusion parameters in this study we performed incremental heating of single monazite grains to experimentally determine the 4he diffusion properties of reference monazite 554 that occurs within a peraluminous two mica granite from the catnip sill within the catalina core complex arizona assuming that the grain size defines the diffusion geometry the six experiments yielded e a values of 212 to 238 5 kj mol 1 1 and d o values of 15 7 to 103 cm 2 s 1 with one value of 784 cm 2 s 1 monazite u th he data from five grains yielded closure temperatures of 291 to 262 c c 15 c and ages of 23 8 20 3 1 2 2 ma the weighted mean age is 21 8 0 73 mswd 1 83 n 5 and the weighted mean closure temperature is 282 6 c mswd 0 96 n 5 1 we tested the accuracy of these results by comparing our monazite thermochronology data with monazite th pb depth profiling results the 40ar 39ar thermal history for the catnip sill constrained using coexisting muscovite biotite and k feldspar and published regional zircon and apatite fission track results the monazite th pb data indicate emplacement of the catnip sill at 45 ma the 40ar 39ar muscovite and biotite data indicate cooling from 460 to 350 c from 27 to 26 ma k feldspar mdd modeling suggests cooling from 360 to 240 c from 26 to 24 ma zircon fission track data indicate cooling through 250 c between 29 and 20 ma additional cooling through 110 c is recorded by apatite fission track ages of 19 16 ma because the monazite thermochronology results are reproducible and consistent with the thermal history constrained by the other chronometers our results 1 confirm the accuracy of the 4he diffusion kinetics from monazite 554 and 2 demonstrate that monazite can be an effective u th he thermochronometer provided that he diffusion properties are either measured or reasonably assumed for each sample

thermochronologic evidence of major tectonic denudation associated with detachment faulting northern ruby mountains east humboldt range nevada fission track ft thermochronology studies on igneous and metamorphic rocks from the ruby mountains east humboldt range metamorphic core complex provide important constraints on the timing and nature of major mid tertiary extension in northeast nevada rocks from within the ruby east humboldt detachment brittle ductile normal sense shear zone were analyzed the dominant lithology studied was variably mylonitic mafic orthogneiss nonmylonitic amphibolite from the top of the structurally lower migmatitic core and porphyritic biotite granodiorite from the oligocene circa 36 ma harrison pass pluton were also studied ft ages on apatite zircon and sphene except one 18 4 ma apatite from the basal portion of the detachment zone are concordant and range in age from 26 5 ma to 23 6 ma all ages overlap at 1 between 25 4 ma and 23 4 ma these data suggest that rocks of the upper and middle portions of the detachment zone cooled rapidly from temperatures above 285 c sphene closure temperature to below 70 c lower temperature limit of track stability in apatite near the beginning of the miocene minimum cooling rate of 40 c ma the length distribution of confined fission tracks in apatites from these exhumed middle crustal rocks is strikingly similar to those of rocks known to have cooled rapidly fish canyon ash flow tuff the lower part of the detachment zone as well as the underlying migmatitic core also cooled through sphene and zircon closure temperatures during this time interval but apparently only cooled to a temperature within the zone of partial annealing of apatite 70 130 c residence of these rocks in this zone led to a partial retention of fission tracks thus resulting in a reduced age confined track length distributions from apatite provide independent evidence of very rapid cooling but also indicate that the rocks of the lower detachment zone experienced a more protracted cooling history remained hotter longer than structurally higher levels of the zone ft data firmly establish the lower limit on the timing of mylonitization during detachment faulting in this area as 23 4 ma rapid cooling of the region is considered to reflect large scale tectonic denudation intracrustal thinning the vertical complement to crustal extension rocks originating in the middle crust 10 15 km were quickly brought near the surface along the ruby east humboldt detachment fault brittle ductile simple shear zone and juxtaposed against brittlely extended rocks deformed under upper crustal conditions

along strike upper plate deformation in response to metamorphic core complex emplacement se arizona abstract metamorphic core complexes represent concentrated zones of crustal extension universally the hanging walls of these systems are extensively fractured attesting to the significant horizontal extension above the evolving detachment zone recent analysis of a large grid of 2 d seismic reflection lines within the tucson basin of southeastern arizona has facilitated a nearly three dimensional interpretation of subsurface features related to cenozoic crustal extension within the northern tucson basin the catalina detachment fault dips 23 35 to the southwest from the western flank of the catalina rincon metamorphic core complex in the southern portion of the basin the ne trending santa rita normal fault dips 15 20 to the northwest from the western flank of the santa rita mountains and is cut by the catalina detachment beneath the central tucson basin the orientation of the santa rita fault is problematical in that its orientation is nearly perpendicular to extension directions in the region while geologic and seismic reflection evidence indicates that the catalina detachment and santa rita fault were active synchronously one possible explanation is that the santa rita fault is accommodating along strike upper plate deformation in response to core complex emplacement to test this we employed a finite element modeling approach a two dimensional model consisting of a homogenous elastic material undergoing uniform extension is used to study changes in stresses and displacements in proximity to a zone of weakness representing a detachment fault in the upper crust away from the detachment fault primary principal stresses are oriented parallel to the regional extension direction as expected near the detachment extension in the system produces a rotation of the primary principal stresses of nearly 60 with respect to the regional stress field around the end of the fault additionally the model predicts mechanical failure of the upper plate of the detachment system to the south of the catalina core complex this model supports our interpretation that the orientation and early displacement noted on the santa rita fault is the result of a perturbation in the regional stress field caused by the catalina detachment and the associated brittle failure of the upper plate from the extreme crustal extension associated with core complex emplacement

discrimination of iron ore deposits of granulite terrain of southern peninsular india using aster data abstract this work describes a new image processing technique for discriminating iron ores magnetite quartzite deposits and associated lithology in high grade granulite region of salem southern peninsular india using visible near infrared and short wave infrared reflectance data of advanced spaceborne thermal emission and reflection radiometer aster image spectra show that the magnetite quartzite and associated lithology of garnetiferrous pyroxene granulite hornblende biotite gneiss amphibolite dunite and pegmatite have absorption features around spectral bands 1 3 5 and 7 aster band ratios 1 3 2 3 5 4 5 7 6 in rgb are constructed by summing the bands representing the shoulders of absorption features as a numerator and the band located nearest the absorption feature as a denominator to map iron ores and band ratios 2 4 3 5 7 6 7 9 8 in rgb for associated lithology the results show that aster band ratios 1 3 2 3 5 4 5 7 6 in a red green blue rgb color combination identifies the iron ores much better than previously published aster band ratios analysis a principal component analysis pca is applied to reduce redundant information in highly correlated bands pca 3 2 and 1 for iron ores and 5 4 2 for granulite rock in rgb enabled the discrimination between the iron ores and garnetiferrous pyroxene granulite rock thus this image processing technique is very much suitable for discriminating the different types of rocks of granulite region as outcome of the present work the geology map of salem region is provided based on the interpretation of aster image results and field verification work it is recommended that the proposed methods have great potential for mapping of iron ores and associated lithology of granulite region with similar rock units of granulite regions of southern peninsular india this work also demonstrates the ability of aster s to provide information on iron ores which is valuable for mineral prospecting and exploration activities

hot dry rock geothermal reservoir testing 1978 to 1980 abstract the phase i hot dry rock geothermal energy reservoirs at the fenton hill field site grew continuously during run segments 2 through 5 january 1978 to december 1980 reservoir growth was caused not only by pressurization and hydraulic fracturing but also by heat extraction and thermal contraction effects reservoir heat transfer area grew from 8000 to 50 000 m2 and reservoir fracture volume grew from 11 to 266 m3 despite this reservoir growth the water loss rate increased only 30 under similar pressure environments for comparable temperature and pressure conditions the flow impedance a measure of the resistance to circulation of water through the reservoir remained essentially unchanged and if reproduced in the phase ii reservoir under development could result in self pumping geochemical and seismic hazards have been nonexistent in the phase i reservoirs the produced water is relatively low in total dissolved solids and shows little tendency for corrosion or scaling the largest microearthquake associated with heat extraction measures less than minus one on the extrapolated richter scale

crustal structure from three dimensional gravity modeling of a metamorphic core complex a model for uplift santa catalina rincon mountains arizona gravity modeling shows that the observed fluctuations in gravity over the catalina rincon metamorphic core complex of southeastern arizona are caused primarily by shallow crustal density contrasts the wilderness suite granites the probable source of a 20 mgal low over the central part of the core complex may extend to depths of 7 12 km below the surface seismic refraction information is consistent with the existence of a deep crustal root under the catalina rincon core complex we hypothesize that the voluminous wilderness suite granites are related to a crustal thickening event that built the root in early tertiary time modeling of flexural isostatic uplift resulting from an excess crustal root predicts two episodes of uplift for the catalina rincon metamorphic core complex 1 low relief flexural uplift in the middle tertiary and 2 complete uplift precipitated by high angle basin and range faulting at 10 15 ma the uplift and exposure of core complexes therefore can be an isostatically driven process that occurs in regions of locally thickened crust

unroofing history of a suture zone in the himalaya of pakistan by means of fission track annealing ages abstract the uplift history of the swat valley and hazara region of northwestern pakistan has been established using 22 fission track dates on apatite zircon and sphene a major fault the main mantle thrust mmt strikes east west across the swat valley separates regions of markedly differing fission track age regimesm and may be a suture zone separating an extinct island arc terrane on the north from the indian plate to the south fission track ages ranging from about 55 to 58 m y for sphene 18 to 53 m y for zircon and 9 to 17 m y for apatite were obtained from the region north of the mmt to the south the fission track age ranges are 20 to 25 m y for sphene 17 to 26 m y for zircon and 16 to 23 m y for apatite disparate zircon and sphene ages on each side of the mmt imply different cooling histories for each side of the fault prior to 15 m y similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m y this may indicate that faulting ceased by 15 m y mean uplift rates have been derived from the fission track data using mainly the mineral pair method uplift rates in the region north of the mmt increased from 0 07 to 0 20 mm yr during the period 55 to 15 m y south of the fault uplift rates averaged in excess of 0 70 mm yr for the period 25 to 15 m y during the past 15 m y uplift across the mmt in the swat valley showsno discontinuities ranging from 0 16 mm yr in the south to 0 39 mm yr in the north a plausible interpretation for the fission track uplift data has the mmt verging to the south with overthrusting taking place at a depth between 3 5 and 6 0 km juxtaposing two terranes that were originally separated by a substantial but unknown distance in this model regional uplift followed cessation of faulting just prior to 15 m y

thermal constraints on the tectonic evolution of a metamorphic core complex santa catalina mountains arizona abstract we present an analysis of the thermal evolution of the metamorphic core complex of the santa catalina rincon and tortolita mountains in south arizona the structural and kinematic data are briefly reviewed granite mylonites result from three successive shearing events respectively compressional top west during paleocene and top ne during mid eocene and extensional top sw after eocene in a preliminary part of the paper available radiometric data are reviewed in detail for both deformed and undeformed granites with closing temperatures from 565 to 105 c these data are then used to constrain the temperature history for three intrusions which were emplaced respectively during paleocene eocene and miocene times the general temperature time curve shows 1 rapid cooling for the three intrusions just after emplacement and 2 a large and rapid cooling of the entire complex between 35 and 22 ma from 530 to 100 c in the final part this thermal history is used to constrain the tectonic history of the metamorphic core complex the thermal effects of erosion tectonic denudation homogeneous and heterogeneous thinning are computed using a finite difference scheme in one dimension an analysis of the parameters involved in the models shows that the crust of the santa catalina metamorphic core complex has undergone mainly a thinning of its upper part of at least 15 km and more reasonably 20 25 km in less than 10 ma this estimation is discussed considering thermal effects of magmatism