terrain influences in sar backscatter and attempts to their correction synthetic aperture radar sar images reveal radiometric image distortions that are caused by terrain undulations the authors present the results of a study extracting and investigating the various components of these terrain influences an imaging model is set up for the geometric rectification of the sar image and for a reconstruction of the imaging geometry a prerequisite for the setup of this model is the use of a digital elevation model eight different geometric parameters are derived and investigated for their influence on grey value variations in the geocoded sar image image grey value variations of three major land use classes forest agricultural land and urban suburban areas are examined empirical models of the sar backscatter variations are used to describe the relations between image grey values and various geometric parameters

radiometric slope correction of synthetic aperture radar images the brightness in a sar image is affected by topographic height variations due to 1 the projection between ground and image coordinates and 2 variations in backscattering coefficient with the local scattering geometry this paper derives a new equation for 1 i e the radiometric slope correction based on a calibration equation which is invariant under a coordinate transformation an algorithm is described to obtain the slope correction from a sar interferogram which also enables retrieval of the full scattering geometry since the sar image and interferogram are derived from the same data set there is no need to match the image with the calibration data there is also no need for phase unwrapping since the algorithm only uses the fringe frequencies a maximum likelihood estimator for the fringe frequency is analyzed and the algorithm is illustrated by processing ers 1 sar data the example demonstrates that the spatial resolution and calibration error are adequate for most applications

provenance and tectonic setting of middle upper devonian sandstones in the qinling orogen shanyang area new insights from geochemistry heavy minerals and tourmaline chemistry abstract devonian sandstones in the shanyang area crop out in the southern part of the qinling orogenic belt geochemical analyses show that the sandstones are enriched in zr and have high th u and rb sr ratios indicating the sandstones underwent repeated recycling zircon tourmaline apatite rutile and anatase are the predominant heavy minerals while minor minerals include spinel pyroxene ilmenite and magnetite the mineral compositions of detrital tourmaline grains indicate that the alkali compositional subgroup dominates schorl and dravite are the main tourmaline species a tourmaline composition environment discrimination diagram shows that about 70 grains are consistent with metapelite metapsammite and calc silicates sources and about 30 of grains are from granitoids and associated pegmatites and aplites metamorphic and granitic rocks in the qinling complex area are potential provenance overall data from geochemistry heavy minerals and tourmaline chemistry suggests the devonian sandstones were extensively recycled in a foreland basin setting rather than at a passive continental margin

multi model radiometric slope correction of sar images of complex terrain using a two stage semi empirical approach practical approaches for the implementation of terrain type dependent radiometric slope correction for sar data are introduced radiometric slope effects are modelled as the products of two models the first is a simple physical model based on the assumption of a uniform opaque layer of isotropic scatterers which is independent of terrain type frequency and polarization it accounts for the slope induced variation in the number of scatterers per resolution cell the second is a semi empirical model which accounts for the variation in scattering mechanisms dependent on terrain type frequency and polarization palsar fbd l band hh and hv polarization data are used at two test sites in brazil and fiji results for the brazilian area which has slopes up to 25 show that remaining slope effects for the multi model case are much smaller than 0 1 db for all land cover types this is much better than the best single model approach where remaining slope effects can be very small for forests but be as large as 1 77 db for woodland in hh polarization results for the fiji area which has different vegetation types are very similar the potential large improvement using this multi model approach in the accuracy of biomass estimation for transparent or open canopies is discussed it is also shown that biomass change on slopes can be systematically under or overestimated because of associated change in scattering mechanism

grain size effect on multi element concentrations in sediments from the intertidal flats of bohai bay china abstract in the intertidal flats of bohai bay china the spatial distribution of the grain size of sediments becomes coarser from landward to seaward to study the grain size effect on multi element concentrations in sediments samples along the coastline and 3 horizontal cross sections were collected from the intertidal flats of bohai bay china in 1998 total concentrations of 49 elements including alkali alkaline earth trace metal rare and rare earth elements were measured by icp aes icp ms and inaa the results show that sediment texture plays a controlling role on the concentrations and their spatial distribution principal component analysis and cluster analysis were carried out based on the grain sizes of the sediments and the samples were classified into 3 groups mud silt mud and silt significant differences among the element concentrations in the 3 groups were observed and the concentrations of the elements in each group are reported in this study most of the elements have their highest concentrations in the fine grained mud samples in comparison with the silt and silt mud samples with clay minerals possibly playing an important role in contrast concentrations of ba sr hf and zr are elevated in the coarse silt samples ba and sr may reside in feldspars while zr and hf are present in zircons landward to seaward spatial variation of element concentrations in the sediments is observed which is in line with the spatial distribution of the grain size and is related to the seawater hydrological dynamics in the intertidal flats

inferring tectonic provenance of siliciclastic rocks from their chemical compositions a dissent abstract chemical compositions of siliciclastic sedimentary rocks are commonly used to infer their tectonic provenance we have tested the universal applicability of the underlying principle in a small but controlled study expecting 100 confirmation of the practice a comparison is made between the chemical composition of the 1480 ma butler hill granite in an uplifted cratonic block of the st francois mountain igneous complex and that of a small 1 m thick regolith body a weathered granite sample and the basal quartz arenites of the 520 ma lamotte formation immediately above the regolith the results show that in plots of k 2 o na 2 o vs sio 2 al 2 o 3 the regolith and sandstone samples correctly plot in the passive margin field although the weathered granite plots in the arc field in plots of th sc zr 10 and la th sc the results plot in the passive and active continental margins and their extensions in other common plots to discriminate tectonic provenance e g sio 2 vs k 2 o na 2 o fe 2 o 3 mgo vs al 2 o 3 sio 2 fe 2 o 3 mgo vs tio 2 sc cr vs la y a few points plot in the passive margin field but scatter into and outside of other fields of tectonic provenances the chondrite normalized ree distributions show variable degrees of negative eu anomalies with flat hree conforming to a felsic source the lree distributions show both positive and negative ce anomalies that can be ascribed to the variability of redox conditions during weathering and diagenesis of the original siliciclastic sediments the variability of the eu anomaly was likely affected by post erosion processes in addition to whatever was inherited from the parent rocks we conclude that chemical compositions can provide good clues but are neither strong indicators nor unique identifiers of their tectonic provenance rather they indicate a dominantly felsic or dominantly mafic or a mixed set of source rocks

sar observations and modeling of the c band backscatter variability due to multiscale geometry and soil moisture the effect of the multiscale surface geometry on the sensitivity of c band synthetic aperture radar sar data to soil moisture is studied the experimental data consist of c band sar images of an agricultural site including fields with various combinations of three distinct roughness components from small to large scale the backscatter variability due to surface roughness has been analyzed the effect of random roughness associated with soil clods is never less than 2 db and the effect of a row pattern can be as strong as 10 db in addition the periodic drainage topography induces a backscatter variability due to soil moisture variation and drainage relief the results indicate that airborne c band sar data cannot be easily inverted into soil moisture data however with ers 1 or radarsat data at an incidence angle of about 20 degrees the effect of random and periodic roughness can be reduced to about 2 db if the look angle is less than 50 degrees

the north american midcontinent rift beneath lake superior from glimpce seismic reflection profiling the midcontinent rift system is a 1 1 b y old structure extending from kansas through the lake superior region and into southern michigan the rift is filled with thick sequences of basaltic volcanic rocks and clastic sediments for most of its extent it is buried beneath paleozoic rocks but can be traced by its strong gravity and magnetic anomalies the rocks of the rift system are exposed only in the lake superior region and comprise the keweenawan supergroup much of the geology of the keweenawan is beneath lake superior and has only been inferred from potential field studies and seismic refraction studies and extrapolation from on shore geology seismic reflection surveys by the great lakes international multidisciplinary program on crustal evolution in 1986 imaged much of the deep structure of the rift beneath the lake in detail the reflection profiles across the rift reveal a deep asymmetrical central graben whose existence and magnitude was not previously documented they show that in addition to crustal sagging documented by previous investigations normal faulting played a major role in subsidence of the axial region of the rift a sequence of volcanic and sedimentary rocks in places greater than 30 km thick fills the graben thinner volcanic and sedimentary units lie on broad flanks of the rift outside of the graben near the axis the prerift crust is thinned to about one fourth of its original thickness apparently by a combination of low angle extensional faulting and ductile stretching or distributed shear the sense of asymmetry of the central graben changes along the trend of the rift documenting the segmented nature of the structure and suggesting the existence of accommodation zones between the segments the location of the accommodation zones is inferred from abrupt disruptions in the bouguer gravity signature of the rift uplift of the central graben occurred when the original graben bounding normal faults were reactivated as high angle reverse faults with throws of 5 km or more in places the midcontinent rift has some striking similarities to some younger passive continental margins we propose that it preserves a record of nearly complete continental separation which had it not been arrested would have created a middle proterozoic ocean basin

continental rifting and porphyry molybdenum occurrences in the oslo region norway abstract the overall structure of the oslo rift system can be viewed as the result of interference between a n s trending permian fault system and a regional ne sw trending precambrian shear zone the rift system comprises four mutually opposed horst and graben structures in a centrosymmetrical arrangement igneous activity occurred only in two en echelon segments both of which possess a notable symmetric distribution of rocks and structures around the central axis of the rift system the axial zone is occupied by cambro silurian sediments which have been intruded by major granite bodies extensive lava plateaus occur on each side of this axial zone the adjacent zones contain the most prominent cauldrons of province further away from the axis follows a zone of batholitic intrusions emplaced as composite diapirs and plutonic ring complexes hornfelsed sediments and volcanics in narrow bands occur at the lateral borders of the province possibly preserved as the result of marginal tectonics associated with batholith emplacement the formation of the oslo rift system apparently reflects a passive continental rifting which was gradually succeeded by considerable igneous activity important porphyry molybdenum mineralization in the oslo region is associated with shallow level magmatism in the glitrevann and hurdal areas the porphyry mo mineralization in these prospects have several evolutionary features in common 1 1 an initial period of effusive eruptions of pyroclastic flows followed by 2 2 the formation of large scale ring structures partly accompanied by peripheral syenite granite intrusions 3 3 the emplacement of a multiple intrusive central stock of sub alkaline granite composition which is terminated by 4 4 the injection of a highly differentiated aplogranite granophyre closely associated with the development of the mineralizing hydrothermal porphyry system molybdenum mineralization of the oslo province is closely associated with highly differentiated alkali granites which possess striking similarities to mo related granites of the colorado mo province and evolved rapakivi or a type granites usually considered to be typically associated with bimodal magmatism of crustal extension and continental rifts the discovery of significant porphyry mo mineralization in the oslo rift associated with permian igneous rocks draws attention to the possible economic potential of rift structures elsewhere

arkose subarkose quartz sand and associated muds derived from felsic plutonic rocks in glacial to tropical humid climates abstract in the range of climates from high latitude glacial to equatorial tropical the mineral and chemical compositions of over 600 modern nonmarine first cycle sands and muds produced from felsic crystalline basement provenance in various tectonic settings were studied under glacial conditions sediments are developed by mostly mechanical weathering and thus are mineralogically and chemically similar to their source rocks humid tropical climates yield quartz rich sands kaolinite rich muds along with si mg ca na and k in solution between these extremes a wide range of detrital sediment compositions are developed in arid to wet climates in arid climate and semi arid climate sands feldspar is commonly more abundant than quartz and plagioclase k feldspar except in the cases of granite source rocks the muds are feldspathic with smectite dominant in the clays with increasing temperature and moisture in temperate to subtropical climates mafic silicates and feldspars are destroyed so that the sands range from arkoses with plagioclase as the major feldspar to subarkoses with dominant k feldspar through this range of climate muds become more kaolinitic and thus more aluminous with increasingly severe weathering typically feldspathic sands are associated with feldspathic muds with decreasing feldspar in sands there is less feldspar in muds with increasingly intense chemical weathering rare earth elements ree are more fractionated into muds typically sands contain 150 ppm ree with much of the ree in heavy minerals abundance differences are greatest between humid tropical sands and muds in many samples the ree are mostly in monazite allanite sphene and apatite more intensely weathered samples contain more xenotime and zircon evidenced by yb enrichment

relations between sill intrusions and bedding parallel extensional shear zones in the mid continent rift system of the lake superior region abstract the mid continent rift system is a continuous u shaped feature extending from kansas north through the lake superior region and then south through michigan the logan sills on the northwest side of the lake were intruded during the rifting stage 1109 ma deformation features in the country rock adjacent to the logan sills indicate two episodes of shear strain the first consists of minor thrusts and mesoscopic shear bands both suggesting top to the south southwest movement parallel to the bedding the second rotates the previously formed shear bands in the opposite sense top to the north northeast and is localized at the basal contact between the sills and the country rock we attempt to explain the relations observed with a tectonic model in which sill intrusions take advantage of bedding parallel shear zones that are the surface expression of a south dipping detachment plane the detachment plane steps up in the layered proterozoic sedimentary sequence and allows extension during rifting in this scenario the first episode of shear strain might be related to bedding parallel extension and the second to shear stress induced by the intrusion of magma along the detachment from the south the polarity of both events is supported by small scale kinematic indicators such as veins fiber growths and foliation

the mesoproterozoic midcontinent rift system lake superior region usa abstract exposures in the lake superior region and associated geophysical evidence show that a 2000 km long rift system developed within the north american craton 1109 1087 ma the age span of most of the volcanic rocks this system is characterized by immense volumes of mafic igneous rocks mostly subaerial plateau basalts generated in two major pulses largely by a hot mantle plume a new ocean basin was nearly formed before rifting ceased perhaps due to the remote effect of the grenville continental collision to the east broad sagging subsidence combined with a system of axial half grabens separated along the length of the rift by accommodation zones provided conditions for the accumulation of as much as 20 km of volcanic rocks and as much as 10 km of post rift clastic sediments both along the rift axis and in basins flanking a central post volcanic horst pre rift mature quartzose sandstones imply little or no uplift prior to the onset of rift volcanism early post rift red bed sediments consist almost entirely of intrabasinally derived volcanic sediment deposited in alluvial fan to fluvial settings the exception is one gray to black carbon bearing lacustrine unit this early sedimentation phase was followed by broad crustal sagging and deposition of progressively more mature red bed fluvial sediments with an extra basinal provenance

geochemistry and provenance of the altendorf feldspathic sandstone in the middle bunter of the thuringian basin germany an integrated mineralogical and geochemical study of the altendorf feldspathic sandstone in the middle bunter of the thuringian basin germany was carried out to obtain more information on its provenance sedimentological history and geochemistry the fine to coarse grained sandstone has an average composition of 66 63 71 quartz 30 27 35 feldspar and a fine grained illitic matrix the heavy mineral assemblage consists mainly of tourmaline zircon rutile apatite and opaque fe ti minerals it is inferred that this terrigenous material was laid down at the margin of the bunter basin high abundances of igneous quartz grains determined by cathodoluminescence cl the lack of metamorphic heavy minerals as well as alkali feldspar with an average k2o na2o ratio of 14 9 point to material of mostly granitic origin regional geologic and paleogeographic observations suggest that granites of the older and younger intrusive complex of the western erzgebirge are possible source rocks of the feldspathic sandstone the geochemical signature of the alkali feldspar k2o na2o ratio bao content points to the bergen and kirchberg granites as possible parent rocks comparing the mineralogical and geochemical data of the presumed source granites with those of the altendorf sandstone provides information on the sedimentation processes weathering fluvial transport and sedimentation under arid climatic conditions have caused complete decomposition and removal of plagioclase and biotite lowered the bulk ree content and led to the development of a positive eu anomaly the immobile trace elements e g ta th zr sc co ti are best suited for provenance determination because of their relatively low mobility during sedimentary processes elemental ratios such as la sc th sc co th and th ta have inherited the signature of the parent rocks and thus may be particularly useful for provenance studies to evaluate the control of specific minerals and grain size fractions on the distribution of trace elements in the sandstone separated fractions of quartz feldspar the 20 m fraction and heavy minerals were additionally analyzed the concentration densities elemental concentration in the fraction fraction weight reveal that with exception of hf the influence of the heavy mineral fraction on the whole rock geochemistry is insignificant although this fraction generally plays the most important role as carrier of trace elements quartz feldspar and the 20 m fraction have similar concentration densities between 20 and 40 for the ree with exception of eu which is mainly hosted in feldspar strong positive eu anomaly the influence of the 20 m fraction on the distribution of the ree and the elements u th sc ta strongly depends on the abundance of this fraction in the sediment alkali feldspar contains most of the ba sr rb and cs in the samples concentration densities of up to 97 thus differences in the abundances of these elements in whole rock samples can be related to changes in the mineralogical composition quartz feldspar ratio of the sediment

chemical and mineralogical comparison of the pennsylvanian fountain formation colorado u s a an uplifted continental block to sedimentary rocks from other tectonic environments the mineralogic and chemical composition of composites of cobble and pebble sized rock clasts clay stones siltstones fine sandstones and size fractions of two sandstones of the fountain formation near beulah colorado were determined the sandstones are arkosic and most plot in the basement uplift or transitional continental fields of qfl diagrams the mineralogic composition of the sandstones is similar to that of the composite of rock clasts at a given location al mg fe ti mn sc th ree and cs are concentrated in the clay minerals or heavy minerals and are diluted by quartz or feldspar consequently they are inversely correlated with si cr hf k rb ba and sr are poorly correlated with si cr is concentrated in clay and in heavy minerals in the silts k rb ba and sr are correlated with k feldspar mica or clay mineral abundances sedimentary rocks from the fountain formed from an uplifted continental block the element concentrations plot in the fields of active or passive continental margins in many tectonic discrimination diagrams probably as a result of derivation from granitoid sources of similar composition the ree patterns eu anomaly size k and rb concentrations of the fine sandstones are mostly similar to those of the corresponding composite of rock clasts at a given location suggesting that these parameters might be the most reliable in distinguishing sources the most reliable discrimination diagram for uplifted tectonic blocks like the fountain may be a plot of k2o vs eu anomaly size since both of these parameters were very similar in concentration in both the sedimentary rocks and presumed source of the fountain most sedimentary rocks in this study have larger negative eu anomalies than those from the nasc north american shale composite or mcps midcontinent platform sediment this suggests a more evolved source for the fountain than that for average platform sediment

origin of loess deposits in the north tian shan piedmont central asia abstract loess deposits are widely distributed along the mountain piedmonts of central asia the transport processes and origins of central asian loess sediments remain poorly understood here we investigate the origin and formation of loess along the northern piedmont of the tian shan based on trace element including rare earth element ratios and multidimensional scaling analysis our results indicate that the loess has undergone weak chemical weathering using a selection of geochemical fingerprinting techniques based on pearson correlation and kruskal wallis h tests we establish a genetic link between alluvial proluvial fans plains deserts and loess along the tian shan piedmont in northern kyrgyzstan and southern kazakhstan the unsorted sediments on the piedmont slopes and alluvial proluvial plains are common sources for both deserts and loess to the north of the tian shan dune sediments are not the main source of the fine grained loess origin and formation of central asian loess is strongly dependent on local topographic context and wind dynamics only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made

paleomagnetism of the native copper mineralization keweenaw peninsula michigan the age and genesis of michigan s world class native copper deposits are poorly constrained the copper is hosted by basaltic flow tops and conglomeratic interbeds of the 1095 2 ma keweenawan por

removal of terrain effects from sar satellite imagery of arctic tundra synthetic aperture radar sar images of the earth s terrestrial surface contain geometric and radiometric image effects which are caused by varying terrain elevation and slope the radiometric effects tend to mask signal variations caused by other physical variables such as soil moisture and surface vegetation type which are known to influence sar backscatter signals as a result raw sar images are of limited use in classifying surface vegetation type or quantifying the spatial distribution of soil moisture in regions of terrain relief the authors present a technique for removing radiometric terrain effects from sar images image correction was carried out in two steps first an existing modeling package was used in combination with digital elevation data in order to map the raw image pixels onto a geodetic coordinate system thereby removing the geometric portion of the image distortion radiometric effects were then removed with the aid of a backscatter model which treats the reflected radiation as a combination of diffuse lambertian and specular components parameters in the backscatter model were determined by comparing two c band sar images of a test area in a region of arctic tundra which were taken from ascending and descending orbit tracks of the ers 1 satellite the ascending and descending images displayed reductions in pixel value variance of 30 and 13 respectively after processing direct comparison of the two test area images reveals a dramatic improvement in image similarity after processing

quartz and zircon decoupling in sandstone petrography and quartz cathodoluminescence of the early triassic continental buntsandstein group in germany

a geological database for parameterization in numerical modeling of subsurface storage in northern germany underground land use can play a significant role in future concepts of energy and gas storage and requires an improved understanding of the parameters of potential storage formations saline aquifers for instance of porosity and permeability and also of mineralogical and gas compositions this study aims at providing data examples and calculating vertical spatial variations through variogram analyses of important north german geological reservoirs from dogger rhaetian middle buntsandstein and rotliegend sub groups and formations focusing on the western part of the north german basin vertical correlation lengths of porosity and permeability data range between 0 and 30 m while most results are calculated at approximately 2 4 m and do not show relevant differences among the evaluated formations in the majority of the regarded formations the kozeny carman relationship between porosity and permeability is supported as long as low porosity and permeability values are excluded from the evaluation mineral percentages varied significantly among the evaluated sediments besides quartz ankerite is the main compound in the dogger group while feldspars and clay minerals were more frequent in the rhaetian middle buntsandstein and rotliegend sediments methane was the main gas compound in the reservoirs followed by nitrogen ethane and carbon dioxide this study serves as preparatory work to allow for the parameterization of geological models and a subsequent simulation of fluid transport to evaluate long term safety and impacts of geothermal and gas storage projects

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

reversal asymmetry in mesoproterozoic overprinting of the 1 88 ga gunflint formation ontario canada non dipole effects or apparent polar wander abstract eighty two palaeomagnetic samples of calcareous and jaspilitic grainstones iron formation or taconite and chert carbonate were collected from the 1 88 ga gunflint formation at 22 sites in the thunder bay area ontario twenty clasts of gunflint taconite also were sampled from the basal conglomerate of the overlying mesoproterozoic sibley group anisotropy of magnetic susceptibility measurements indicate the gunflint formation in the sampling area has not experienced regional dynamic metamorphism analyses by variable field translation balance and x ray diffraction show that the predominant magnetic mineral is hematite but a small amount of magnetite also is present in some samples altogether 213 gunflint specimens and 59 sibley conglomerate specimens were subjected to stepwise thermal demagnetisation and 74 gunflint specimens to stepwise alternating frequency demagnetisation the following components were isolated for the taconites gunflint magnetite normal declination d 293 4 inclination i 30 8 95 7 2 n 21 reverse d 86 7 i 54 6 95 5 8 n 29 gunflint hematite normal d 243 6 i 23 6 95 6 0 n 11 reverse d 70 3 i 51 4 95 3 2 n 79 sibley clasts magnetite normal d 282 7 i 33 4 95 7 6 n 20 sibley clasts hematite normal d 254 5 i 56 2 95 8 4 n 13 reverse d 110 6 i 55 7 95 8 3 n 11 none of these sets passed the reversal test with the normal component generally being the shallower fold tests were negative or inconclusive and the conglomerate test also was negative chert carbonate at one other site appears to have acquired a remanence carried by magnetite d 97 3 i 78 2 95 6 3 n 18 prior to folding related to keweenawan 1 1 ga logan diabase sill emplacement most of the components we identified match components for keweenawan sills volcanic rocks intrusions and baked contact rocks in the thunder bay area indicating that keweenawan magmatism caused widespread chemical remagnetisation of the proterozoic country rock in our sampling area although others have argued that asymmetry was a feature of the keweenawan geomagnetic field the declinations of our gunflint and sibley hematite and magnetite components are different suggesting that the components were acquired at significantly different times we conclude that the reversal asymmetry shown by our gunflint and sibley data may best be ascribed to apparent polar wander during keweenawan times

diagenetic albitization in the tera group cameros basin ne spain recorded by trace elements and spectral cathodoluminescence abstract this paper deals with the diagenetic albitization of both plagioclases and k feldspars in the tithonian fluvial sandstones of a rift basin cameros basin the sandstones in the lower part of the rift record have not suffered this albitization process a clear relationship is observed between sodium contents as the main element of some feldspars and their cathodoluminescence cl color the higher the sodium content the lower is their cl intensity in conclusion albitization processes are detectable by decreased cl intensities and changes in the cl spectra in addition very different trace element compositions are obtained by laser ablation when comparing trace elements of non albitized feldspars in sandstones of the lower part of the rift record with those of albitized feldspars in sandstones of the infill top non albitized k feldspars show rb sr ba and pb contents of up to 1000 ppm in contrast very flat profiles of trace element contents cl spectra from non albitized and albitized k feldspars and plagioclases revealed marked differences non albitized k feldspars present blue main emission band at 460 nm and brownish cl colors 590 nm sometimes in the same grain brownish colors are related to weathering processes the primary blue emission is related to al o al centers enhanced probably by al incorporation due to the coupled substitution of ba2 al3 m si4 weathered k feldspars present 4 8 times lower ba content than fresh blue luminescent ones the brownish colors are related to the external border or fractured grain zones altered by weathering processes therefore the observed 590 nm emission is assumed to be caused by structural defects resulting from weathering and alteration albitized k feldspars are usually weak luminescent with a typical cl emission band at 620 nm sometimes relicts of the original blue luminescence 460 nm band are still present the leaching of probably both al and ba can be responsible for the decrease in the blue band the characteristic 620 nm band is also dominant in albitized weak luminescent plagioclases two additional emission bands at 440 nm al o al center and 565 nm mn2 occur when albitized plagioclases preserved their original cl characteristics green cl color another spectral peak at ca 720 nm can be explained by fe3 activation due to fe3 al3 substitution the spectral cl measurements indicate that changes in luminescence due to albitization 620 nm emission seem to be more related to structural defects than to trace element activation or quenching

geologic and geochemical evidence for the nature and development of the middle proterozoic keweenawan midcontinent rift of north america abstract general models of active continental rifting must take into account the large plateau basalt provinces many of which have been precursors of or associated with continental breakup the keweenawan middle proterozoic midcontinent rift mcr of north america 2300 km long is one such major continental rift but it aborted before significant crustal separation was achieved these plateau basalt rifts including the mcr differ from the east african type in being dominated by broad subsidence rather than rift valleys tholeiitic flood basalts rather than alkalic central volcanoes and large positive gravity anomalies geologic and geophysical evidence is reviewed which contradicts some recent models which have been proposed for the development of the mcr the basic causes of the pre rift subsidence the u shaped nature of the structure and the abrupt termination of its activity are obscure a triple junction in the usual sense does not appear to have been formed

late paleozoic tectonics of the solonker zone in the wuliji area inner mongolia china insights from stratigraphic sequence chronology and sandstone geochemistry abstract the geology in the wuliji area including the enger us and quagan qulu areas is important for understanding the late paleozoic tectonics of the solonker zone ultramafic mafic rocks in the enger us area previously interpreted as an ophiolitic suture are actually lava flows and sills in a permian turbiditic sequence and a small body of fault breccia containing serpentinite subduction zone features such as accretionary complexes magmatic arc volcanics or lp hp metamorphism are absent early permian n morb mafic rocks and late permian radiolarian cherts accompanied by turbidites and tuffeous rocks indicate a deep water setting in the quagan qulu area outcrops of the late carboniferous to permian amushan formation are composed of volcano sedimenary rocks and guyot like reef limestone along with a late permian volcano sedimentary unit a dacite lava in the late permian volcano sedimentary unit yields a zircon u pb age of 254 ma the gabbros in the quagan qulu area are intruded into the amushan formation and caused contact metamorphism of country rocks sandstones in the upper member of the amushan formation contain detrital clasts of volcanic fragments and mineral clasts of crystalline basement rocks i e biotite muscovite and garnet geochemical analysis of volcaniclastic sandstones shows a magmatic affinity to both continental island arc cia and active continental margin acm tectonic settings a late permian incipient rift setting is suggested by analyzing the lithostratigraphic sequence and related magmatism in the wuliji area the volcano sedimentary rocks in the wuliji area experienced a nearly n s shortening that was probably related to the early mesozoic nearly n s compression well developed in other areas close to the wuliji area

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

seismic identification of basement reflectors the bagdad reflection sequence in the basin and range province colorado plateau transition zone arizona although seismic reflection profiling has contributed greatly to our knowledge of the crust and upper mantle it is often difficult to unambiguously identify the geologic origin of reflections this is particularly true of intrabasement reflectors whose geometry and origin we need to know in order to understand tectonic processes operating in the crust we present synthetic seismogram modeling of recently collected p and s wave seismic reflection data which suggests that the intrabasement bagdad reflectors in west central arizona are intrusive mafic sheets the identification is based on the determination of the phase positive polarity and amplitudes of the reflected arrivals if the bagdad reflectors are cenozoic age mafic sheets they may be the product of rapid intrusion into an area of weak extension where the principal stresses are approximately equal

a preliminary survey of relict shoreface attached sand ridges in western lake superior abstract high resolution multibeam and seismic reflection surveying in western lake superior near the outflow of the amnicon river wisconsin has shown that the nearshore lake floor appears to consist of till with no recent sediment cover this surface is partially obscured 3 km offshore by a series of low relief elongate sand ridges that are arranged in an en echelon pattern at an oblique angle to the present day shoreline they are extensively gullied suggesting that they are not presently active two sets of elongate features can be identified the features in first group group i are over 0 5 km wide rise 3 5 m above the surrounding lake floor and are over 2 km long the features belonging to the second set group ii are not as well developed and are typically smaller than those in group i group ii features are typically 0 2 0 3 km wide 0 4 1 6 km long and rise 1 3 m above the surrounding lake floor the most striking difference between the groups is the difference in their orientation with respect to the shoreline the group i features run ne sw while the group ii features are directed approximately n s the shoreline runs approximately ene wsw so the features in both cases open northeast the group i features are believed to be relict drowned shoreface attached sand ridges that formed when the lake level lay over 10 m below its present day level these sand ridges formed as the result of currents associated with strong northeasterly gales moving the abundant sediment eroded off the shore the smaller group ii features are believed to be sub aqueous sand dunes that developed transverse to bottom currents produced by the northeasterly gales no dates have been obtained for the sand ridges based upon their depth and the lake level history curve for lake superior we suggest that the ridges formed either 6500 6000 bp prior to the nipissing highstand

interoceanic variation in the rare earth major and trace element depositional chemistry of chert perspectives gained from the dsdp and odp record rare earth element ree major and trace element abundances and relative fractionations in forty nodular cherts sampled by the deep sea drilling project dsdp and ocean drilling program odp indicate that the ree composition of chert records the interplay between terrigenous sources and scavenging from the local seawater major and non ree trace element ratios indicate that the aluminosilicate fraction within the chert is similar to nasc north american shale composite with average pacific chert including 7 nasc like particles indian chert 11 nasc atlantic chert 17 nasc and southern high latitude shl chert 53 nasc using la as a proxy for ree approximations of laex the amount of la in excess of that supplied by the detrital aluminosilicate fraction indicate that pacific chert contains the greatest laex 85 of latotal and shl chert the least 38 of latotal as shown by interelement associations this laex is most likely an adsorbed component onto aluminosilicate and phosphatic phases accordingly chert from the large pacific ocean where deposition occurs relatively removed from significant terrigenous input records a depositional ree signal dominated by adsorption of dissolved rees from seawater pacific chert cece 1 and lanybn 0 8 1 resulting from adsorption of local ce depleted seawater and preferential adsorption of lrees from seawater e g lanybn 0 4 which increases the lanybn ratio recorded in chert chert from the atlantic basin a moderately sized ocean basin lined by passive margins and with more terrigenous input than the pacific records a mix of adsorptive and terrigenous ree signals with moderately negative ce anomalies and lanybn ratios intermediate to those of the pacific and those of terrigenous input chert from the shl region is dominated by the large terrigenous input on the antarctic passive margin with inherited cece 1 and inherited lanybn values of 1 2 1 4 cece does not vary with age either throughout the entire data base or within a particular basin overall cece does not correlate with p2o5 concentrations even though phosphatic phases may be an important ree carrier this and previous studies of the large scale controlling parameters of sedimentary rees across ocean basins collectively indicate that ree indices of depositional regime e g cece lanybn laex are reproducible in a variety of sediment and rock lithologies ages and ocean basins and present a coherent tool for paleoceanographic and tectonic basin reconstructions

contrasts among bidirectional reflectance of leaves canopies and soils the apparent brightness of a natural surface depends on the characteristics and direction of incident radiation surface radiative properties and the direction from which the surface is viewed the bidirectional reflectance distribution functions brdf for soils vegetation canopies and individual leaves have common features that arise from an anisotropic diffuse scattered component as well as specular reflections from irregular surfaces the diffuse scattered component however tends to dominate canopy and soil brdf s where as specular reflection tends to dominate leaf brdf s in this paper simple models are presented for predicting soil and canopy brdf s and predicted results are compared with some measurements this effort represents an attempt to illustrate the important features that cause observed brdf s the results of the models are compared with a simple three coefficient empirical equation that may be easier to invert than the causitive models so that radiation measurements can be used to obtain surface features some brdf measurements from corn and soybean leaves provide a contrast for canopy and soil distributions and also provide needed leaf properties that are important to vegetation canopy models the knowledge of soil canopy and leaf brdf s is combined into a single model called cupid to predict the resultant brdf of complex natural surfaces

mantle temperature and lithospheric thinning beneath the midcontinent rift system evidence from magmatism and subsidence the tectono magmatic history of the midcontinent rift system can be explained by the presence of a mantle plume bringing elevated temperature mantle beneath the rift system at about 1110 ma huge volumes of extrusive and intrusive igneous rocks were generated as abnormally hot mantle decompressed beneath the lithospheric rift geochemical and isotopic data from the keweenawan volcanics show that the earliest melts were derived from small degree melting of primitive plume mantle coupled with enriched metasomatic melts derived from the continental lithosphere as rifting progressed the main bulk of the volcanics was generated primarily from the plume mantle with the melting starting at depths of about 120 km and extending to as shallow as the base of the stretched lithosphere at 45 km depth elevated mantle temperatures of 1500 1560 c approximately 150 200 c above normal are inferred from the rare earth element concentrations in the volcanic rocks further constraints on the mantle temperature come f

radiometric correction of c band imagery for topographic effects in regions of moderate relief the combined effects of topography slope look angle and aspect on c band synthetic aperture radar sar data on the radiometric quality of sar images in a region of moderate relief are examined a correction method was used to attenuate the change of illumination across the swath due to the antenna pattern ground data were integrated into the analysis using a digital terrain model dtm correction functions based on the cosine of the incidence angle were applied to the thematic classes and to the grouped classes in order to reduce the effects related to topography it was found that it is possible to eliminate part of the radiometric variations created by moderate topographic relief after the corrections were applied a reduction was noted of the variance in the radiometric values of the spectral signatures of the cover types which ranged between 3 03 and 9 47 depending on the correction function used

consortium for continental reflection profiling michigan surveys reprocessing and results reprocessing of consortium for continental reflection profiling data from central michigan with emphasis on deconvolution and velocity filtering before stack and more detailed velocity analysis has resulted in greatly improved imaging of a previously reported keweenawan rift buried beneath the paleozoic of the michigan basin the seismic stratigraphy of the sub paleozoic units can now be related to the basin filling middle keweenawan volcanic sequence and the upper keweenawan clastic assemblage in greater detail important structural and stratigraphic features can be seen for the first time for example reprocessing has imaged an unconformity within the upper keweenawan it is possible some of these newly imaged features are associated with a late keweenawan compressive episode furthermore reprocessing also reveals previously unrecognized sub keweenawan structures including a deeply penetrating reflection which may represent a major crustal fault and possible weak reflections from midcrustal 25 km and moho 43 km depths

geochemistry of shales of the upper cretaceous hayang group se korea implications for provenance and source weathering at an active continental margin abstract shales of the upper cretaceous hayang group in the yeongyang subbasin southeastern korea were deposited in fluvio lacustrine environments as the paleo pacific izanagi plate obliquely subducted beneath the asian continent major and trace element compositions derived from shales analyzed from the hayang group reveal geochemical signatures that are different from post archean average australian shale paas but are typical of igneous rocks found in the continental margin island arc settings for example most major element concentrations are depleted relative to paas among them mgo and mno depletions are most pronounced in all shales cao enrichment is notable in some formations due to the presence of secondary calcite as dispersed micro calcite nodules sc y and th concentrations are also slightly depleted relative to paas while chondrite normalized ree data for shales from the hayang group show moderate to large uniform lree enrichment but variable hree depletions in addition they are more fractionated than paas and have significant negative eu anomalies moreover the chemical index of alteration and a cn k relations comply that the source area was dominated by non steady state weathering regimes indicative of active uplift along an active continental margin these regions were punctuated by two periods of steady state weathering or alternatively by enhanced recycling of sediments the latter interpretation is in accord with the timing of exposure of a cherty sequence in the source area mixing calculations based on ree data suggest that the average shale in the hayang group was derived from sources composed of precambrian granitic gneiss arc basaltic rocks triassic yeongdeok granite in the subbasin and the mino accretionary complex of sw japan with ratios around 43 7 31 8 73 2 26 4 15 8 36 7 15 4 2 8 33 9 14 5 0 0 33 8 however these proportions change up sequence

flattening gamma radiometric terrain correction for sar imagery enabling intercomparison of synthetic aperture radar sar imagery acquired from different sensors or acquisition modes requires accurate modeling of not only the geometry of each scene but also of systematic influences on the radiometry of individual scenes terrain variations affect not only the position of a given point on the earth s surface but also the brightness of the radar return as expressed in radar geometry without treatment the hill slope modulations of the radiometry threaten to overwhelm weaker thematic land cover induced backscatter differences and comparison of backscatter from multiple satellites modes or tracks loses meaning the asar palsar sensors provide state vectors and timing with higher absolute accuracy than was previously available allowing them to directly support accurate tie point free geolocation and radiometric normalization of their imagery given accurate knowledge of the acquisition geometry of a sar image together with a digital height model dhm of the area imaged radiometric image simulation is applied to estimate the local illuminated area for each point in the image ellipsoid based or sigma naught 0 based incident angle approximations that fail to reproduce the effect of topographic variation in their sensor model are contrasted with a new method that integrates terrain variations with the concept of gamma naught 0 backscatter converting directly from beta naught 0 to a newly introduced terrain flattened 0 normalization convention the interpretability of imagery treated in this manner is improved in comparison to processing based on conventional ellipsoid or local incident angle based 0 normalization

correction of sar imagery for variation in pixel scattering area caused by topography the radiometric correction of synthetic aperture radar sar imagery for topographically induced changes in the pixel scattering area is examined the relative significance of ground slope in the range and azimuth directions is compared and a widely used correction factor based on the sin of the local radar incidence angle is shown to be sufficiently accurate the importance of performing this correction in slant range rather than ground range is demonstrated

seasonal and short term variability of multifrequency polarimetric radar backscatter of alpine terrain from sir c x sar and airsar data signatures of glaciated and ice free areas were analyzed from polarimetric sar data at c l and p band and single polarization x band data the data base includes an airsar scene from june 25 1991 and sir c x sar images from april and october 1994 srl 1 and srl 2 acquired over the high alpine test site o spl uml tztal in austria the environmental conditions were different at the time of the three experiments ground measurements meteorological observations and backscattering modeling are the basis for interpreting the backscattering signatures seasonal differences are due mainly to the presence or absence of snow and due to changes of its properties short term variations of snow conditions can be monitored at c and x band for unglaciated areas the surface roughness has a dominant influence on backscattering in all seasons the dependence of the mean backscattering and correlation coefficients on the incidence angle was analyzed spectral and depolarization ratios and the magnitude of the hhvv correlation coefficient were selected as components of the multidimensional feature vector for studying the target separability good separability was found between the accumulation and ablation areas on the glaciers whereas on ice free areas the dominance of surface roughness limits the discrimination of different surface types short term variations of backscattering have significant impact for the classification of accumulation and ablation areas on glaciers as verified by comparisons with field data

characterization of forests in western sayani mountains siberia from sir c sar data abstract this paper examines the use of space borne radar data to map forest types and logging in the mountainous western sayani area in central siberia l and c band hh hv and vv polarized images from the shuttle imaging radar c instrument were used in the study techniques to reduce topographic effects in the radar images were investigated these included radiometric correction using illumination angle inferred from a digital elevation model and reducing apparent effects of topography through band ratios forest classification was performed after terrain correction utilizing typical supervised techniques and principal component analyses an ancillary data set of local elevations was also used to improve the forest classification map accuracy for each technique was estimated for training sites based on russian forestry maps satellite imagery and field measurements the results indicate that it is necessary to correct for topography when attempting to classify forests in mountainous terrain radiometric correction based on a digital elevation model improved classification results but required reducing the synthetic aperture radar resolution to match the digital elevation model using ratios of synthetic aperture radar channels that include cross polarization improved classification and had the advantages of eliminating the need for a digital elevation model and preserving the full resolution of the synthetic aperture radar data

authigenic k feldspar in the bromsgrove sandstone formation triassic of ccntral england abstract authigenic k feldspar is a ubiquitous feature of the bromsgrove sandstone formation triassic in central england it occurs mainly as partially to completely developed euhedral overgrowths on detrital k feldspar cores the authigenic k feldspar is virtually pure kalsi3o8 potassian low sanidine and occurs as optically continuous overgrowths on detrital sanidine and optically discontinuous overgrowths on detrital orthoclase differences in structure and al si disorder thus control the degree of optical continuity of the overgrowths an important feature is the presence of optically and compositionally zoned overgrowths due to minor fluctuations in the bao and na2o content the formation of the overgrowths was dependent upon intrastratal dissolution of detrital grains for a supply of potassium aluminum and silicon precipitation took place within the k2o na2o al2o3 sio2 h2o system and in association with other phases in this system the diagenetic sequence 1 illite 2 quartz 3 k feldspar 4 illite 5 kaolinite is consistent with a progressive increase in k h ratio or h4sio4 activity followed by a general decrease so that the later interstitial fluids were much depleted in k ions and kaolinite was the final phase to precipitate

cratonic sedimentation during the proterozoic an anorogenic connection in wisconsin and the upper midwest certain proterozoic quartzites including baraboo barron and sioux and associated metasedimentary rocks in the upper midwest represent a distinct epicontinental depositional environment new data indicate that argillite chert iron formation micaceous conglomerate and rhyolite are much more abundant and significant in this sequence than previously reported the entire group of rocks was deposited during one period in a series of tectonic episodes magmatism and uplift related to epeirogeny none of these episodes included overt rifting sedimentation began on subsiding continental crust during the waning stages of anorogenic magmatism 1760 m y ago following deposition a regional event 1630 m y ago is interpreted as a time of uplift and mild deformation with no magmatic expression in the region epeirogenic tectonism was culminated in the widespread intrusion of 1500 m y old alkalic plutonism which metamorphosed and further deformed the sedimentary rocks and surroundings

the chemical signature of source rocks in size fractions of holocene stream sediment derived from metamorphic rocks in the wet mountains region colorado u s a eight stream sediments draining primarily mixed silica rich and silica poor metamorphic rocks in the wet mountains colorado were analyzed at their source for their mineralogic and selected elemental composition the low silica source rocks include amphibolite hornblende schist and muscovite biotite schist the high silica source rocks include granodioritic to leucocratic granitic gneisses the high silica source rocks tend to contain higher concentrations of ree th hf and ba lower concentrations of fe sc and cr higher la sc and thsc ratios and more negative eu anomalies than the low silica source rocks especially those low silica source rocks derived from basic sources rather than weathered silicic sources the stream sediments draining this mixed metamorphic rock terrain are dominated by sands and gravels and they are composed of feldspar quartz and 25 heavy minerals the silts contain more total biotite hornblende pyroxene and opaque minerals and less quartz and feldspar than the sands and gravels sediment especially the silts derived from mixed low and high silica sources tends to be intermediate in elemental composition between those of the end member sources so there is some hope that source rock signatures may be preserved in the sediment elemental ratios of la sc th sc la co th co and ba co and th la sc plots most clearly distinguish sediment derived from the most silicic and most basic source rocks in addition finer sediment near the source can potentially distinguish silicic sources higher ree and more negative eu anomalies from those of basic sources the clay and silt fractions contain negative eu anomalies normalized to the mcps north american mid continent platform sediment and the sands and gravels have positive eu anomalies normalized to the mcps most size fractions are similar to more enriched in la sc th sc la co and th co ratios than the mcps this suggests local sources in the wet mountains are on the average more silica rich than those that formed the mcps

chemical behavior of detrital feldspars in mudrocks versus sandstones frio formation oligocene south texas abstract in both sandstones and mudrocks dissolution and replacement can cause substantial modification of detrital feldspar assemblages over burial depths from 1 km to 5 5 km in the frio formation oligocene of south texas mudrocks lose most k feldspar and ca plagioclase both of these minerals however survive to greater depths in mudrocks than in associated sandstones and are not completely removed even in the deepest samples examined albite is the most abundant replacement phase calcite and al rich sphene are common sphalerite pyrite and tio2 also occur as replacements of detrital feldspar replacement phases are introduced subsequent to dissolution of the detrital grain and require transport of material over minimum distances of tens of microns from sources exter al to the detrital feldspar

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

the age of the latest thermal overprint of tin and polymetallic deposits in the erzgebirge germany constraints from fluorite u th sm he thermochronology the erzgebirge region of germany records two major episodes of hydrothermal activity which includes a late carboniferous to early permian event associated with significant sn w mineralization that is related to late variscan granite magmatism and a mesozoic episode of polymetallic vein mineralization in contrast to the first event the age of the younger hydrothermal activity is poorly constrained for the latter various geochronological methods yielded a wide age range from permian to early tertiary here we apply fluorite u th sm he thermochronology fhe on both types of mineralization with a twofold goal 1 to investigate the sensitivity and applicability of the new fhe method evans et al 2005 and 2 to constrain the thermal history of ore deposits in the erzgebirge region two hundred and thirty three aliquots from seven mineralization localities have been dated fluorite from six deposits yielded cretaceous fhe ages between 112 to 79 ma which are independent of their paragenesis in contrast fluorite from the sadisdorf sn w deposit yielded an age of 234 ma the younger ages are interpreted as cooling ages indicating the time of the last thermal overprint including possible hydrothermal activity in the erzgebirge the oldest triassic fhe ages at sadisdorf indicate that the mesozoic thermal overprint only partially reset the u th sm he system of the late variscan mineralization thermal modeling based on fhe ages and he diffusion parameters in fluorite results in thermal histories comparable to the results from the well established apatite based thermal modeling this study emphasizes the applicability of fluorite u th sm he thermochronology which is especially suited for ore deposits where apatite is lacking

distribution of ree and trace elements in size and mineral fractions of high purity quartz sands eight sample sets raw quartz sand quartz fraction 2 m clay fraction 2 20 m fraction and heavy minerals of the cretaceous quartz sand deposits of haltern and weferlingen central germany and the tertiary quartz sand of frechen western germany were studied to characterize the distribution of ree and trace elements and to get genetic information about provenance and sedimentologic history of the sediments the quartz sand samples from different localities have rather similar trace element distribution and ree patterns with enriched lree and negative eu anomalies however these relations can be modified by local changes in syn or postsedimentary geochemical conditions adsorption of ree and trace elements on humic substances under reducing conditions and postsedimentary weathering in the quartz sand of weferlingen resulted in significantly modified element abundances the concentration of trace elements is most important in the 2 m fraction and in the heavy mineral fraction where they may be enriched by a factor of up to 100 the chondrite normalized ree distribution of the 2 m fraction is quite similar to those in the north american shale nas with average eu sm ratios of 0 21 and layb cn of 6 1 low trace element abundances in the 2 and 2 20 m fractions were attributed to quartz dilution and quantified among the common minerals in the heavy mineral fractions especially zircon and the fe 1bti oxides rutile ilmenite magnetite influence the trace element distribution investigations concerning the provenance of the quartz sands illustrate that the host sediments have a rather homogeneous geochemical signature due to their sedimentological history taking into account th ta variations the quartz sands of weferlingen and haltern can be distinguished from the frechen quartz sand additionally discriminations based on element ratios within the quartz fraction th sc ba sc ba co cs sc or li sc seem to be promising

superposition of burial and hydrothermal events post variscan thermal evolution of the erzgebirge germany the post variscan thermal history of the erzgebirge germany is the result of periods of sedimentary burial exhumation and superimposed hydrothermal activity the timing and degree of thermal overprint have been analysed by zircon and apatite u th he and apatite fission track thermochronology the present day surface of the erzgebirge was exhumed to a near surface position after the variscan orogeny thermal modelling reveals permo mesozoic burial to temperatures of up to 80 100 c although the sedimentary cover thins out towards the north resulting in maximum burial temperatures of less than 40 c this thermal pattern was locally modified by cretaceous hydrothermal activity that reset the zircon u th he thermochronometer along ore veins the thermal models show no significant regional exhumation during cenozoic times indicating that the peneplain like morphology of the basement is a late cretaceous feature

geologic evidence for a mantle superplume event at 1 9 ga 1 both preserved and restored areal distributions of proterozoic marine intracratonic passive margin and platform sediments show a prominent peak at 1 9 ga indicating that shallow marine sediments were widespread on the continents and that sea level was high at this time the chemical index of alteration in shales deposited at this time was high suggesting warm climates possibly due to enhanced co2 levels in the atmosphere high sea level and warms climate may also explain an abundance of black shale banded iron formations and shallow marine phosphate deposits and an increase in the number of occurrences and diversity of stromatolites in general and microdigitate stromatolites at 1 9 ga all of these observations are consistent with a 1 9 ga superplume event the occurrence of only a minor positive carbon isotope shift in marine carbonates at 1 9 ga indicates that the relative rates of burial of organic and oxidized carbon remained about the same as at present slightly low 87sr 86sr isotopic ratios in seawater at 1 9 ga reflect increased mantle input of sr from the proposed superplume event whereas higher ratios at 1 85 1 75 ga may reflect increased input of continental sr from a growing supercontinent the first massive sulfate evaporites in the geologic record at 1 8 1 6 ga follow the possible 1 9 ga superplume event this may reflect an increase in both oxidation state and carbonate deposition in the oceans as plume related volcanism wanes

igneous emplacement in a shear zone termination the biotite granite at strontian scotland deformed xenolith strain data together with other structural information indicate that the biotite granite body 90 sq km of the strontian complex scotland was emplaced in the extensional termination of a dextral transcurrent shear zone this shear zone is a splay of the major great glen fault which lies along the southern boundary of the granite siting of the shear zone splay was probably controlled by a a slight releasing bend in the great glen fault in this area and b a large pre existing asymetric synform in proterozoic metasedimentary country rocks which intersects the great glen fault trace at a high angle a model is proposed in which moine thrust caledonian compression at ca 435 ma activated the great glen fault dextrally dextral movements around the releasing bend detached a flat segment from the inside fault wall and the biotite granite was emplaced side ways at depths of about 15 km as a sheet into this extensional listric fault bounded cavity

spatially heterogeneous strength in thrust fault zones deformation in the hanging wall of the lewis thrust fault at marias pass northwest montana is heterogeneous in space with regions dominated by either large scale contraction or extension faults the distribution of mesoscopic structures within the two regions also differs the density of fractures is highest in the extensional region whereas the density of solution seams is highest in the contractional regime this spatial heterogeneity of structures at the base of the lewis thrust sheet may result from spatially heterogeneous fault zone strength in analytical models of an elastic thrust sheet overlying a fault represented by spatial heterogeneity in shear traction or displacement stress magnitudes and principal directions vary with position within the model thrust sheet with the application of a mohr coulomb criterion contraction and extension faults initiate within localized regions at the base of the model thrust sheet spatial variations in mean stress at the base of the thrust sheet predicted by the models may explain both the greater density of solution seams in the contractional region than in the extensional region and the greater density of mesoscopic faults and veins in the extensional region than in the contractional region of the marias pass exposure the spatial heterogeneity of pressure solution and cataclasis in response to variable mean stress within a fault zone of heterogeneous strength may facilitate thrust sheet movement relative to movement over a fault zone of uniform strength because a decrease in mean stress enhances cataclasis and an increase in mean stress maintains a constant shear stress during pressure solution

quartz arenites review and interpretation abstract quartz arenites orthoquartzites are exceptional sands pettijohn et al 1972 that in the past have formed extensive and commonly thick formations they are somewhat enigmatic in that they do not appear to be forming at the present time this paper examines the origin of quartz rich sands documents the range of environments in which they are found and suggests a model for their genesis quartz sand is most commonly formed by tropical weathering of coarse grained quartz bearing rocks such as granite it may be deposited as texturally immature fluvial sandstones generally under a humid climate with drying of the climate quartz rich bauxitic soils and sandy alluvium can be a substantial source of poorly rounded dune sands for major deserts quartz sand when transported into shallow marine environments becomes very well rounded through reworking by tidal currents such sand may spill into deep oceanic environments and by sedimentary or tectonic transport may come to rest in both stable and active tectonic settings quartz rich sandstones can also be formed by diagenetic destruction of labile framework grains of immature sandstones precambrian orthoquartzites are commonly thick and widespread when compared to younger examples the thinness of post silurian quartz arenites may be largely due to the trapping effect of land vegetation and solution of quartz by organic acids in weathering profiles there is an abundance of shallow marine and fluvial quartz arenites in the early paleozoic and the cretaceous this is due to widespread continental flooding and a humid world climate following the disintegration of supercontinents the shallow marine examples are commonly associated with bituminous sometimes phosphatic shale glauconite and possibly chamositic ironstone there is an abundance of eolian quartz arenites in the permo triassic this is related to a widespread dry continental climate during assembly of the pangean supercontinent

the 1 1 ga midcontinent rift system central north america sedimentology of two deep boreholes lake superior region abstract the midcontinent rift system mrs of central north america is a 1 1 ga 2500 km long structural feature that has been interpreted as a triple junction rift developed over a mantle plume as much as 20 km of subaerial lava flows mainly flood basalts are overlain by as much as 10 km of sedimentary rocks that are mostly continental fluvial red beds this rock sequence known as the keweenawan supergroup has been penetrated by a few deep boreholes in the search for petroleum in this paper two deep boreholes in the upper peninsula of michigan are described in detail for the first time both the amoco production 1 29r test herein referred to as the st amour well and the nearby hickey creek well drilled by cleveland cliffs mining services were 100 cored the former is 7238 ft 2410 m deep and the latter is 5345 ft 1780 m deep the entirety of the stratigraphic succession of the hickey creek core correlates very well with the upper portion of the st amour core as determined by core description and point counting of 43 thin sections selected out of 100 studied thin sections two lower paleozoic units and two keweenawan red bed units the jacobsville sandstone and the underlying freda sandstone are described the jacobsville is largely a feldspatholithic sandstone and the freda is largely a lithofeldspathic sandstone below the freda the remaining footage of the st amour core consists of a thick quartzose sandstone unit that overlies a heterogenous unit of intercalated red bed units of conglomerate sandstone siltstone and shale black shale individual basalt flows and a basal ignimbritic rhyolite this lower portion of the st amour core presents an enigma as it correlates very poorly with other key boreholes located to the west and southwest while a black shale sequence is similar to the petroleum bearing nonesuch formation farther west there is no conglomerate unit to correlate with the copper harbor conglomerate other key boreholes are distributed over a 1300 km distance along the better known southwest arm of the triple junction mrs and can be correlated rather well with the units that are exposed in the lake superior region however a definitive explanation of the anomalous deeper st amour stratigraphy is elusive and any explanation is tenuous a possible explanation for this anomalous stratigraphy may be the geographic proximity of the st amour borehole to the keweenawan hot spot mantle plume the suggested thermal force behind the development of the mrs similarly a drastic change in structural architecture may be explained by this geographic relationship thus within the locale of this rifting center complexities of expansion tectonics may well be responsible for igneous and sedimentary sequences that differ considerably from those found farther west along the rift arm

geochemistry of agates a trace element and stable isotope study abstract agate samples of acidic intermediate and basic volcanics from 18 localities around the world and of different age precambrian to tertiary were studied by trace element and stable isotope analysis to provide information about the process of agate formation and the origin of mineral forming fluids trace element data are similar for agates from acidic and basic volcanics the general chondrite normalized ree distribution pattern is characterized by a slope from la to lu with enriched lree and a positive eu anomaly in some samples the similarity in the shape of the ree patterns between agates and the parent volcanic rocks suggests that the elements are mobilized by circulating fluids during syn and postvolcanic alteration of the volcanic wall rocks observed positive eu anomalies in agates probably originate from feldspar alteration deuterium and oxygen isotope analyses of agates and associated quartz incrustations d 44 to 130 18o 16 4 to 33 4 reveal variations in isotopic composition between samples of different localities but also within single agate samples up to 10 for 18o in general oxygen isotope compositions become heavier as volcanic host rocks grow more acidic furthermore agates have higher 18o values than associated quartz incrustations variations within single agate samples can be explained either by kinetic effects during isotope fractionation e g the formation of agate from a noncrystalline precursor or by mixing processes of meteoric and magmatic fluids remarkably high 18o values of the parent volcanic rocks up to 19 5 suggest that the circulation of 18o enriched hydrothermal fluids originated from heated meteoric water and or residual magmatic fluids this conclusion is supported by 13c and 18o data of paragenetic calcite the temperature of agate formation was calculated for different fluid compositions and they indicate a temperature range of ca 50 c to 250 c

radiometric correction of airborne radar images over forested terrain with topography radiometric correction of radar images is essential to produce accurate estimates of biophysical parameters related to forest structure and biomass we present a new algorithm to correct radiometry for 1 terrain topography and 2 variations of canopy reflectivity with viewing and tree terrain geometry this algorithm is applicable to radar images spanning a wide range of incidence angles over terrain with significant topography and can also take into account aircraft attitude antenna steering angle and target geometry the approach includes elements of both homomorphic and heteromorphic terrain corrections to correct for topographic effects and is followed by an additional radiometric correction to compensate for variations of canopy reflectivity with viewing and tree terrain geometry the latter correction is based on lookup tables and enables derivation of biophysical parameters irrespective of viewing geometry and terrain topography we evaluate the performance of the new algorithm with airborne radar data and show that it performs better than classical homomorphic methods followed by cosine based corrections

the midcontinent rift system one of the most prominent features on gravity and aeromagnetic maps of the united states is a series of major generally linear anomalies that extend from central kansas to lake superior and then turn southward into central michigan figures 1 2 this system of anomalies clearly reflects major geological features and as such it must represent a very significant episode in the history of the north american continental lithosphere the geologic features associated with these anomalies particularly axial basins filled with basalt and immature clastic rocks along with evidence of crustal extension indicate that the episode was probably one of incipient rifting