testing the reliability of discrimination diagrams for determining the tectonic depositional environment of ancient sedimentary basins the lower palaeozoic rocks of the west of ireland caledonides provide a novel way to test the reliability of discrimination diagrams in sedimentary rocks a comparison between the geochemical signature of the tuff bands and the signature from the adjacent sedimentary rocks reveals that a combination of multi element diagrams and discrimination diagrams is best suited to identify the tectonic environment of deposition the tuff bands from the ordovician and silurian formations all carry an active continental margin signature only three of the sedimentary discrimination diagrams assigned more than 50 of the samples to this setting the results from the discrimination diagrams indicate an active margin setting for the ordovician mweelrea and rosroe formations and the silurian formations whilst the derrylea and sheeffry sedimentary samples have a passive margin signature overall the results show that in the case where felsic volcanism occurred on a quartz rich source region the active continental margin field on many established discrimination diagrams is not reliable in identifying this setting however the study highlights one of the key strengths of discrimination diagrams in their ability to be used as a lever to reveal significant information about the sediment source as in this case to identify sediment that has been transported from different tectonic settings and deposited in one sedimentary basin

curie point depth beneath the barramiya red sea coast area estimated from spectral analysis of aeromagnetic data abstract the geothermal regime beneath the barramiya red sea coast area of the central eastern desert of egypt has been determined by using the curie point depth which is temperature dependent this study is based on the analysis of aeromagnetic data the depth to the tops and centroid of the magnetic anomalies are calculated by power spectrum method for the whole area the result of this investigation indicates two new maps of the curie point depth cpd and the surface heat flow q maps of the study area the coastal regions are characterized by high heat flow 83 6 mw m2 due to the geothermic nature of the region and shallow curie depth 22 5 km where cpd depends on the tectonic regime and morphology in the eastern part of the area the western portion of the studied area has a lower heat flow

thermal structure of the crust in inner east anatolia from aeromagnetic and gravity data abstract inner east anatolia has many hot spring outcomes in this study the relationship between the thermal structure and hot spring outcomes is investigated the residual aeromagnetic and gravity anomalies of the inner east anatolia surveyed by the mineral research and exploration mta of turkey show complexities the magnetic data were analyzed to produce curie point depth estimates the depth of magnetic dipole was calculated by azimuthally averaged power spectrum method for the whole area the curie point depth cpd map covering the inner east anatolia has been produced the curie point depths of the region between sivas and malatya vary from 16 5 to 18 7 km values of heat flow were calculated according to continental geotherm from the model the heat flow values vary between 89 and 99 mw m 2 heat flow values are incorporated with surface heat flow values gravity anomalies were modeled by means of a three dimensional method the deepest part of the basin 12 14 km determined from the 3d model are located below the settlement of hafik and to the south of zara towns two dimensional cross sections produced from the basin depths curie values and moho depths based on the analysis of magnetic gravity anomalies thermal structures and geology it seems likely that the hot springs are not related to rising asthenosphere in the regions of shallow cpds 16 5 km and mostly hot springs are related to faulting systems in inner east anatolia

application of satellite magnetic anomaly data to curie isotherm mapping a boundary condition on temperature at depth in the continental crust can in principle be obtained by mapping of the curie isotherm where it forms the base of the magnetic crust an approach to mapping magnetic crustal thickness using satellite magnetic anomaly data is described because magnetic crustal thickness is small with respect to satellite altitude inversion of the anomaly data yields magnetization models expressing regional variations in the vertical integral of magnetization this parameter is inversely correlated with regional heat flow in the western united states suggesting that areas of low apparent magnetization are areas of thin magnetic crust resulting from a shallow curie isotherm for a simple model of a uniformly magnetized magnetic crust or intra crustal layer curie depth is linearly related to apparent magnetization if the relation can be calibrated by two or more curie depth estimates regional apparent curie isotherm configuration can be mapped in an alternative approach a family of curie depth models can be computed using assumed magnetization values in each case the curie depth configuration is used as a boundary condition in a thermal model that model is selected which gives a heat flow distribution best fitting observations conductive heat flow models for a traverse across the rio grande rift using a finite element technique and for a map grid using a one dimensional thermal model approximation are given as examples

curie point depth from spectral analysis of magnetic data in erciyes stratovolcano central turkey curie point depth and heat flow values of the erciyes region are determined to identify the thermal regime of the central anatolia by applying the spectral analysis method to the magnetic anomaly data to compute the spectrum of the data the magnetic anomaly of the region is transformed into 2 d fourier domain to attain the average curie depth this method is useful in determining the top boundary of magnetic anomaly sources and reveals the curie depth as 13 7 km in the study area the obtained results imply a high thermal gradient 42 3 c km 1 and corresponding heat flow values 88 8 mwm 2 in the research area using the temperature value measured at borehole drilled by the general directorate of mineral research and exploration of turkey mta the values for the thermal gradient and heat flow value were computed as 50 7 c km 1 106 5 mwm 2 from the heat flow value the curie point depth was determined as 11 4 km in this region it is concluded from the obtained values that the region has very high geothermal potential caused by partial melting of the lower crust

estimation of curie point temperature and geothermal structure of island arcs of japan abstract curie depth analysis from aeromagnetic data was performed in a nationwide project to assess the geothermal resources of japan creation of a curie depth map of japan was completed in 1984 and it agrees well with thermal structures such as the high temperature gradient regions of volcanic chains low temperature regions of the forearc basins and the intermediate temperature regions of the backarc basins measured temperature gradient t data were gathered in order to estimate the curie temperature from the t and the curie depths when t is assumed to be constant with respect to depth a remarkable difference is found in the estimated curie temperature t e c of the backarc and forearc side of the basins in the backarc side an average t e c of 450 c is reasonable for both the curie depth estimated from aeromagnetic data average depth of about 10 km in the backarc side and the temperature gradients average gradient of 4 5 c 100 m the average t e c on the forearc side was found to be low at about 300 c the difference in the curie temperatures between the two areas may be due to a regional difference in rock type e g granite as opposed to basalt in the case of the northeast japan arc as suggested by some authors the isotherms may suddenly fall between the volcanic front and the trench based on model studies we recognized that a curie depth map obtained by the algorithm we developed should include an averaging effect this suggests that the inferred curie depth curve across the line marking the sudden fall in the curie isotherm should gradually increase towards the trench therefore the low curie temperature that we estimated may indicate an apparent shallow curie depth caused by the averaging effect against an area bearing deep curie depths hence the reasons for the inconsistency of the estimated curie temperature between the forearc side and backarc side may be as follows 1 the averaging effect of the curie depth estimate which makes the curie depth apparently shallower in the forearc side and 2 the lower curie temperature of basaltic rocks which are assumed to be distributed along the east side of the aseismic front

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

curie point depths of bulgarian territory inferred from geomagnetic observations and its correlation with regional thermal structure and seismicity abstract the basal depth of the magnetic layer curie point depths of bulgarian territory was calculated using geomagnetic field observation and the variations of this border were mapped for the first time the adopted computational method transforms the spatial data into the frequency domain and provides a relationship between radially averaged power spectrum of the magnetic anomalies and the depths to the magnetic sources the magnetic layer bottom thus obtained has normal 28 32 km values in the moesian platform and central part of bulgaria which are the relatively most stable regions of the investigated territory in the moesian platform cpd and moho are very close but the magnetic layer s bottom is still marked as a thermal boundary in the southern part calculated depths gradually reach the minimal values of the derived curie isotherm up to 14 16 km with relatively high gradient according to the results from geothermal modeling and paleomagnetic investigations magnetic layer s bottom of the bulgarian territory corresponds to different curie temperatures they vary from 400 425 c in the regions of rila rhodope unit up to 550 600 c in the moesian platform west and east balkan unit the obtained results comprise useful information concerning regional estimates of the correlation between different geophysical and geological characteristics of the earth s crust of the bulgarian territory

geology and diagenetic history of overpressured sandstone reservoirs venture gas field offshore nova scotia canada deep exploratory wells in the scotian basin offshore nova scotia canada have encountered overpressured formations with pressures 1 9 x the normal hydrostatic gradient the overpressures occur over an area of approximately 10 000 sq km in the venture field the abnormal pressures are confined below a depth of 4500 m and are associated with upper jurassic lower cretaceous gas and condensate bearing sandstone reservoirs the overpressures occur within normally compacted shales containing numerous overpressured sandstone reservoir beds the development of overpressures seals and secondary reservoirs are all diagenetically driven the volumetric increase achieved by kerogen to petroleum gas conversion and hydrocarbon expulsion are believed to be the main driving forces or venture overpressures three secondary porosity depth levels which top at 2500 m 65 degrees c 3700 m 95 degrees c and 4600 m 130 degrees c correlate with major steps in the organic matter maturation in the basin secondary porosity is initially achieved by alumosilicate dissolution with ferroan sparry calcite cement dissolution dominating below 4000 m porosity enhancement and preservation is not the result of a single diagenetic event but instead the result of a series of diagenetic events that overlapped in time formation of dynamic diagenetic barriers within the zone of peak gas generation helps retard the diffusive migration of hydrocarbons and other fluids expelled during shale diagenesis resulting in pressure build up the preservation of up to 32 percent porosity under 500 1000 atm of pressure could not be achieved without simultaneous pressuring of developing voids thus the expansion of secondary reservoirs in the overpressured zone also had to be late 50 ma or younger and about synchronous with pressurizing of the reservoirs significant for hydrocarbon exploration is that venture type diagenetic overpressures are not associated with undercompacted sediments and hence they cannot be predicted from compaction trends during drilling petrographic diagenetic and lithofacies studies can be instrumental in predicting potential areas of deep subsurface secondary reservoirs development

thermal investigation in the cappadocia region central anatolia turkey analyzing curie point depth geothermal gradient and heat flow maps from the aeromagnetic data in this study curie point depth cpd heat flow geothermal gradient and radiogenic heat production maps of the cappadocian region in central anatolia are presented to reveal the thermal structure from the aeromagnetic data the large circular pattern in these maps matches with previously determined shallow 2 km in average depression estimated cpds in this depression filled with loose volcano clastics and ignimbrite sheets of continental neogene units vary from 7 to 12 km while the geothermal gradient increases from 50 to 68 c km heat flows were calculated using two different conductivity coefficients of 2 3 and 2 7 wm 1 k 1 the radiogenic heat production was also obtained between 0 45 and 0 70 w m 3 in this area heat flow maps were compared with the previous regional heat flow map of turkey and significant differences were observed in contrast to linear heat flow increment through the northeast in the previous map in the literature produced maps in this study include a large caldera like circular depression between nevsehir aksaray nigde and yesilhisar cities indicating high geothermal gradient and higher heat flow values in addition active deformation is evident with young magmatism in the neogene and quaternary times and a large volcanic cover on the surface boundaries of volcanic eruption centers and buried large intrusions are surrounded with the maxspots of the horizontal gradients of magnetic anomalies analytic signal as map pointing out exact locations of causative bodies is also presented in this study circular region in the combined map of as and maxspots apparently indicates a possible caldera

provenance of triassic cretaceous sandstones in the antarctic peninsula implications for terrane models during gondwana breakup abstract the antarctic peninsula is the largest of twelve micro continental fragments between southern south america east antarctica and new zealand their original positions and movement history following gondwana breakup are poorly constrained recent work on the antarctic peninsula fore arc arc back arc suggests it consists of two suspect terranes that originated elsewhere and collided with the pacific margin of gondwana in the cretaceous this study reviews provenance models for three laterally extensive kilometers thick sedimentary units in the antarctic peninsula using previous studies and new sandstone detrital modes and chemistry 1 the trinity peninsula group accretionary complex triassic was possibly derived from a glaciated continental margin and may consist of several accreted tracts the deformed quartzose view point and legoupil formations were eroded from a deeply eroded stable continental margin containing an old arc and mature quartzose sandstones with provenance ages suggesting sources in north patagonia and local antarctic peninsula basement the weakly deformed and more feldspathic hope bay formation was derived from an eroded arc possibly the early permian arc of the north patagonian massif 2 the lemay group accretionary complex middle triassic middle cretaceous is dominated by arkoses derived from an eroded continental margin of carboniferous and permian age possibly in the marie byrd land sector with several belts of volcanilithic sandstones representing episodes of arc magmatism the youngest part of the lemay group contains abundant metamorphic detritus derived from basement uplifted during mid cretaceous terrane docking 3 the latady formation in the southern antarctic peninsula has a completely different petrology comprising mature sublitharenites 190 ma of gondwanan provenance deposited in restricted rift basins younger volcanic litharenites 180 ma are dominated by ree enriched low eu eu rhyolitic material eroded from silicic calderas associated with gondwana breakup abundant dacitic to andesitic detritus in the youngest lf 160 145 ma was derived from a contemporaneous arc possibly on the thurston island block as the latady evolved into a back arc basin

composition and discrimination of sandstones a statistical evaluation of different analytical methods the discriminative power of four analytical approaches to sandstone composition is evaluated with respect to the separation of different formations and source areas the case study is cretaceous synorogenic sandstones litharenites from the eastern alps of europe which belong to four different formations and are derived from two source areas methods evaluated are light mineral analysis petrographic framework composition heavy mineral analysis major element xrf analysis and trace element xrf analysis the statistical parameters calculated percentages of well classified samples mahalanobis distance applying the logratio approach suggest that light mineral analysis has a significantly lower discriminative power than the other three methods taking into account the analytical expenditure for data acquisition trace element analysis appears to be the most efficient method for discrimination of at least the sandstone units examined although based on a single case study these results are interpreted to have a more general meaning with respect to sandstone discrimination based on composition concerning sandstone provenance trace element analysis provides a quick tool to estimate the discriminative potential of a sample suite i e the potential to discriminate between contrasting source areas if a provenance model already exists and discriminate functions between contrasting source areas are calculated trace element analysis is considered to be most efficient in correctly assigning an unknown sample to its source area these results cannot be extended to all kinds of sands and sandstones but they cast serious doubt on the belief that petrographic point count methods are the best approach to discriminate between sandstones

curie depth map for sinai peninsula egypt deduced from the analysis of magnetic data abstract sinai peninsula is considered as a unique region in the world due to its geographical location tectonic and thermal activities it is located geographically at the crossroads of europe asia and africa constituting a triple junction point between the three continents it is also characterized by thermal manifestations represented by several hot springs with varied temperatures 30 70 c most of these hot springs are located along the shoreline of the gulf of suez in this study we aim to map the curie depth isotherm surface for sinai peninsula based on the analysis of ground magnetic data spectral analysis technique will be used to estimate the boundaries top and bottom of the magnetized crust the depths obtained for the bottom of magnetized crust are assumed to correspond to curie point depths where the magnetic layer loss its magnetization results of this study indicate that the shallow curie depths 15 18 km are located at the southern part of sinai peninsula and along the shoreline of the gulf of suez and depths increase 22 25 km towards the central and north western portions of sinai peninsula the whole average curie depth point of sinai peninsula is about 20 km generally the shallow depths to curie isotherm indicate that sinai peninsula is a promising area for further geothermal exploration particularly near the eastern side of the gulf of suez

the provenance of middle jurassic sandstones in the scotian basin petrographic evidence of passive margin tectonics the tectonic and geomorphological evolution of the scotian margin and its hinterland is poorly known between late triassic rifting and the early cretaceous progradation of major deltas this study determined sedimentary provenance of middle jurassic mohican formation sandstones from three wells using heavy minerals and mineral chemistry indicator minerals such as xenotime altered ilmenite and varietal types of garnet and tourmaline are similar to those in hauterivian barremian sandstones in the western scotian basin which are almost exclusively derived from the meguma terrane the wells adjacent to the canso ridge have more zircon and less ilmenite indicating a greater contribution of polycyclic reworking but with an ultimate source in the meguma terrane zircon and ilmenite were likely derived in part from carboniferous sandstones in eastern mainland nova scotia and cape breton island any river drainage from the inboard terranes of the appalachians either was diverted through the fundy basin or entered the easternmost scotian basin where the mohican formation is 5 5 km thick along the linear continuation of the southwest grand banks transform such sediment did not reach the canso ridge suggesting that the cobequid chedabucto fault zone in orpheus graben was not a significant physiographic feature this tectonically controlled paleogeography in the middle jurassic is quite different from that during active rifting in the late triassic early jurassic middle jurassic quiescence was followed in the tithonian early cretaceous by renewed tectonic uplift associated with rifting of grand banks from iberia and labrador from greenland

the west indian road pit central nova scotia key to the early cretaceous chaswood formation the west indian road pit is the only large outcrop in nova scotia of the chaswood formation the terrestrial equivalent of the offshore missisauga and logan canyon formations it provides outcrop information on sedimentology gravel petrology and structures for a formation that is otherwise known from a few small overgrown pits and from boreholes the chaswood formation in the pit is 60 m thick and consists principally of sorted sand and gravel with three thinner clay units successions of sedimentary structures indicate deposition from a coarse bedload river flowing to the east southeast gravel consists principally of vein quartz quartz arenite and subarkose together with minor igneous lithologies that can be matched to sources in the cobequid highlands to the north quartz arenite and subarkose appear derived from carboniferous horton group single crystal 40 ar 39 ar dates of detrital muscovite are a little older than the muscovite ages for the south mountain batholith interpreted to mean that the muscovite is second cycle from the horton group which records the earliest unroofing of the batholith the chaswood formation accumulated during progressive tectonic deformation along nne trending strike slip faults in basement rocks resulting in syn sedimentary faulting and local unconformities sedimentation kept pace with the creation of accommodation unrelated younger deformation folded the chaswood formation at the pit into an east west trending syncline the early cretaceous paleogeography of the maritime provinces is interpreted to have consisted of fault bound horsts shedding coarse detritus surrounded by an interconnected series of basins that accumulated fluvial sands and gravels and overbank muds with well developed paleosols

interpretation of magnetic anomalies and estimation of depth of magnetic crust in slovakia the magnetic map of slovakia used in the paper was compiled as part of a project titled atlas of geophysical maps and profiles in 2001 the residual magnetic data were analyzed to produce curie point estimates to remove distortion of magnetic anomalies caused by the earth s magnetic field reduction to pole transformation was applied to the magnetic anomalies using the magnetization angle of the induced magnetization anomalies reduced to the pole tend to be better correlated with tectonic structures we applied a 3 km upward continuation to the residually compiled magnetic anomalies in order to remove effects of topography the depth of magnetic dipoles was calculated by an azimuthally averaged power spectrum method for the entire area such estimates can be indicative of temperatures in the crust since magnetic minerals lose their spontaneous magnetization according to curie temperature of the dominant magnetic minerals in the rocks the computed curie point depths in the slovakia region vary between 15 2 km and 20 9 km heat flow higher than 100 mwm 2 occurs at the central volcanics and eastern part of slovakia where the curie point depths values are shallow the correlation between curie point depths heat flow and crust depth was investigated for two e w cross sections heat flow and curie point depth values are correlated with each other however these values could not be correlated with crust depth the curie point isotherm which separates magnetic and non magnetic parts of the crust is represented in two cross sections

curie point depth of the island of crete greece the aeromagnetic data of the island of crete were inverted to produce curie point estimates the data were high pass filtered to remove components arising from topography and magnetic core fields which were not adequately modeled by igrf the depth to the centroid z 0 of the deepest distribution of the magnetic dipoles was obtained by computing a least squares fit to the lowest fre quency segment of the azimuthally averaged log power spectrum the depth to the top of the deepest crustal block was computed as the depth z t to the centroid of the second deepest distribution using the second lowest frequency segment of the spectrum the depth to the bottom of the deepest dipoles the inferred curie point depth is then z b 2z 0 z t the curie depth estimates range between 24 and 28 km this is in accordance with the depths inferred by extrapolating heat flow values measured in boreholes

provenance and tectonic setting of the proterozoic turbidites in hunan south china geochemical evidence the geochemical composition of the middle upper proterozoic turbidites in hunan south china is related to provenance and tectonic setting of the sedimentary basin the turbidites are characterized by moderate sio 2 contents al 2 o 3 sio 2 typically 0 1 0 3 and moderate k 2 o na 2 o ratios generally 0 1 0 3 but relatively high fe 2 o 3 mgo contents 5 10 wt and unusually low contents of cao typically 1 wt abundances of ferromagnesian trace elements and incompatible elements are moderate the ree patterns are uniform and similar to the upper continental crust and typical post archean shales with lree enrichment flat hree and significant negative eu anomalies in general the slates show higher contents of fe 2 o 3 mgo and ferromagnesian trace elements and lower ratios of la sc and th sc than the associated graywackes suggesting that more mafic materials were incorporated into the clay size fraction compared to the upper proterozoic banxi group the middle proterozoic lengjiaxi group has higher concentrations for most ferromagnesian trace elements and lower la sc ratios implying more mafic components in the provenance of the latter the relationship among alkali and alkaline earth elements the chemical index of alteration cia and the th u ratios indicate that the source area was affected by a moderate weathering history the main source was old continental crust the yangtze craton dominated by felsic rocks of magmatic origin with a variable admixture of mafic components from continental island arcs e g the fangjingshan dayong and the sibao yiyang island arc chains the flysch deposition took place in a back arc basin rather than a failed intracontinental rift as proposed by some workers we suggest that suturing between the yangtze and cathaysia blocks did not occur until late proterozoic time and that the final assembly of the supercontinent rodinia in south china was probably marked by the jingning orogeny at 0 8 ga

tertiary extension of continental crust and uplift of psiloritis metamorphic core complex in the central part of the hellenic arc crete greece kinematic analysis of the deformation in central crete suggests that the structural evolution and exhumation of the high pressure low temperature hp lt rocks outcropping at the mount psiloritis metamorphic core complex are associated with a regional miocene north south extension and thinning of the continental crust this tectonic regime developed under bulk coaxial strain conditions with ductile deformation in the lower and brittle deformation in the upper crust and followed on the decompressional path a north south compression associated with a hp lt metamorphism in the lower crust this compressional event took place during oligocene early miocene and led to overthickening of the accretionary wedge in the hellenic arc an east west directed compression accompanied in the final stages the miocene north south extension of the continental crust

geochemistry and tectonic setting of lewisian clastic metasediments from the early proterozoic loch maree group of gairloch nw scotland abstract the early proterozoic 2 0 ga loch maree group lmg of the lewisian complex consists of a supracrustal sequence of metasedimentary schists and associated tholeiitic metavolcanic amphibolites within the archaean basement the metasediments comprise three main mapped units the flowerdale schists kerrysdale schists and charlestown schists together with numerous narrower bands the dominant clastic metasediments within the schist units semipelites and psammites are chemically distinguished as a series of greywackes and lithic sandstones with variable lil and transition element abundances fractionated ree patterns and overall compositions similar to paas three chemical groups are recognized whose range of composition largely reflects the mixing between two main source components lewisian gneissose basement with an intermediate acid continental crust composition and local rift related amphibolites with a primitive tholeiitic composition which also incorporates components not preserved within the lmg the geochemistry of the clastic metasediments confirms a previous tectonic model for the lmg as an intracontinental extensional rift receiving clastic detritus from the adjacent uplifted basement as well as from internal volcanogenic sources

testing provenance diagrams lessons from the well constrained cariaco basin abstract the fine grained sediments of the cariaco basin venezuela of the last 130 ky whose deposition history is well characterized were analyzed geochemically in order to test the validity of sediment bulk geochemistry as an indicator of detrital provenance several binary and ternary diagrams as well as the chemical index of alteration cia were tested for their capacity to discriminate the poorly contrasted detrital sources to the cariaco basin and to describe the temporal evolution of the contributions of these different sources most of the diagrams tested did not allow a good discrimination of sources or when sources were well discriminated did not allow an interpretation of the temporal variations consistent with the known history a relatively good discrimination of sources and a consistent interpretation of temporal variations were however obtained using hf vs th and la yb vs gd yb binary diagrams as well as ti zr th ti zr la and lu hf th ternary diagrams compared to the previous studies of the detrital content of the cariaco basin sediments the geochemical approach permitted the recognition of a sediment contribution eroded from the unare platform and gulf of cariaco during rapid sea level oscillations and the contribution of saharan eolian particles during the younger dryas preboreal and mis6 5 transition the choice of plotted elements was determined after considering carrier minerals so that different elements may be informative in different sedimentary contexts overall mineral sorting during transport appears as a major limit to quantitative estimation of the different contributions in particular mineral sorting leads to the selective enrichment of elements associated with clays al rb th and lree in sediments deposited in the basin unless the geochemical effect of mineral sorting can be measured it appears that quantitative provenance analysis should be performed on fractions of similar grain size instead of bulk sediment

sedimentary fractionations between al ti and zr and the genesis of strongly peraluminous granites sedimentary sorting produces alternating shales and sandstones with complementary chemistries the preferential partitioning of quartz and zircon in the coarse grained fraction of the sediments results in a strong fractionation between sio 2 zr and other components al 2 o 3 tio 2 as a consequence shales may be defined chemically as having higher al 2 o 3 sio 2 and tio 2 zr ratios than their source rocks sandstones have the opposite characteristics and vary in composition according to the maturity of their source and the intensity of sorting processes most sedimentary suites display a good correlation between al 2 o 3 sio 2 and tio 2 zr this result is used to evaluate an average bulk composition for recent clastic materials and to model their composition on a ternary al ti zr diagram because the al 2 o 3 tio 2 ratio of igneous rocks is highly sensitive to magmatic differentiation igneous and sedimentary trends crosscut in the al ti zr di

geophysical investigation of the geothermal potential under the largest volcanic cover in anatolia kars plateau ne turkey in this study curie point depth cpd geothermal gradient radiogenic heat production and heat flow maps were constructed based on different thermal conductivity coefficients using magnetic anomaly data for the kars plateau which has the largest volcanic cover in turkey the bottom depths of the magnetic crust in the research area were revealed by the cpd map for the first time in this investigation there are two apparent magnetic anomaly trends in the study area the first is the horasan senkaya sarikamis selim arpacay trend in the ne sw direction and the other is the hanak ardahan arpacay trend in the nw se direction two other prominent elongations extend into the ardahan gole senkaya and kars digor axes all these trends represent mountain chains and or stratovolcanoes in the region and no anomalies are observed around the non volcanic outcrops curie depths are shallow up to 14 km between horasan and kagizman towns and 12 km in the northwestern part of the study area gradient values can reach 50 c km 1 in the northwestern sector together with the high heat flows represented by the 150 wm 1 k 1 contours the deepest cpd region lies between gole and susuz towns where the geothermal gradient decreases to 27 c km 1 heat flows decrease 60 wm 1 k 1 in the same area an apparent gap around the kars plateau was observed in previous regional heat flow maps of turkey by other authors who used the bottom hole temperatures of boreholes and hot springs temperatures this gap has been accurately filled from the results of this study and geothermal exploration areas and the geothermal potential of the kars plateau have thus been determined for future exploration activity on the basis of the tectonic elements and earthquake data

geochemical identification of clastic sediment provenance from known sources of similar geology the cretaceous scotian basin canada abstract this study tests the effectiveness of a geochemical approach in identifying provenance in a basin where different sources do not show strongly contrasting geology petrological studies indicate that at least three distinct rivers draining reactivated horsts of the appalachian orogen supplied sediment to the lower cretaceous deltaic sandstones and mudrocks in the offshore scotian basin ninety five samples mostly from conventional core were analyzed for 44 major and trace elements the data were first screened for variability unrelated to provenance including changes in elemental abundance due to weathering and diagenesis and the effects of grain size and sorting on element variation the effect of hydraulic sorting was distinguished from the effects of concentration of ultrastable heavy minerals from polycyclic sources multivariate statistical analysis by principal component analysis pca was used to test the hypothesis of three discrete sources suggested by the petrologic model major element pca on sandstones discriminated the sources but results from trace element pca required further investigation using element biplots to understand their significance only a few elements were found to be diagnostic of different sources namely k rb sr u th nb and ti with the latter two of value only for sandstones all of these are elements that are abundant in the granites of the appalachians most published geochemical discrimination diagrams did a poor job of distinguishing the three petrographically recognized sources in other basins with quite different hinterland geology other elements are known to be of value in discriminating provenance thus it is unlikely that a globally applicable set of elemental discriminants can identify terrigenous sediment sources rather systematic investigation is needed that evaluates processes such as diagenesis and sorting and then tests geographic and stratigraphic variability in bulk geochemistry informed by at least semiquantitative petrographic data

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

the effects of strike slip motion along the cobequid chedabucto southwest grand banks fault system on the cretaceous tertiary evolution of atlantic canada the newfoundland fracture zone the southwest grand banks transform and the cobequid chedabucto fault zone form a linked strike slip fault system from the atlantic ocean to southeastern canada this paper suggests that several large scale geological features in southeastern canada are the result of a small amount of strike slip motion on the system during the mid cretaceous and oligocene regional extension features developed in the releasing bend in the laurentian sub basin during the mid cretaceous but the same area experienced oligocene compression this tectonic model accounts for the distribution of mid cretaceous volcanism fault bounded basins and regional unconformities as well as mid to late cretaceous subsidence of the scotian basin and oligocene uplift of the eastern scotian shelf

the provenance of jurassic and lower cretaceous clastic sediments offshore southwestern nova scotia jurassic and cretaceous sandstones in the shelburne subbasin and fundy basin offshore nova scotia are poorly known but are of current interest for petroleum exploration the goal of this study is to determine the provenance of sandstones and shales which will contribute to a better understanding of regional tectonics and paleogeography in the study area mineral and lithic clast chemistry was determined from samples from conventional cores and cuttings from exploration wells using scanning electron microscopy and an electron microprobe whole rock geochemical composition of shales was used to test the hypotheses regarding provenance of mesozoic clastic sedimentary rocks in the sw scotian basin lower jurassic clastic sedimentary rocks in the fundy basin contain magnetite biotite and chlorite suggesting local supply from the north mountain basalt and meguma terrane whereas pyrope and anthophyllite suggest small supply from distant sources in the sw scotian basin detrital minerals lithic clasts and shale geochemistry from middle jurassic to early cretaceous indicate a predominant meguma terrane source and transport by local rivers rare spinel and garnet grains of meta ultramafic rocks only in the middle jurassic at the mohawk b 93 well suggest minor supply from the rising labrador rift via the same river that transported distant sediments to the fundy basin lower cretaceous sandstones from the mohican i 100 well contain minor garnet spinel and tourmaline from meta ultramafic rocks characteristic of sediment supplied to the central scotian basin at that time the dominant meguma terrane provenance precludes thick deep water sandstones in the eastern part of the shelburne subbasin but the evidence of middle jurassic distant river supply through the fundy basin is encouraging for deep water reservoir quality in the western part

beyond whole rock geochemistry of shales the importance of assessing mineralogic controls for revealing tectonic discriminants of multiple sediment sources for the ouachita mountain flysch deposits the origin of the ouachita mountains has been the focus of significant debate for decades considerable confusion also exists concerning the provenance of the carboniferous flysch of the ouachitas trace element geochemistry of shales from the stanley group delineates the provenance of the sediments and provides clues to the plate tectonic evolution of the southern continental margin during mississippian time th sc and cr th ratios indicate a cratonic source for the majority of the stanley group sedimentary rocks however in several samples low th sc ratios and high cr th ratios suggest a contribution from a mafic source using element ratio diagrams all of the samples plot along a curve consistent with a two component mixing model consisting of a dominant felsic and a subordinate mafic source the heavy mineral fraction of these shales sequester many of the trace elements used in whole rock studies monazite is ubiquitous in trace amounts and is the probable site for much of the rare earth elements in the whole rock the occurrence of monazite almost exclusively in sialic igneous rocks implies that sm nd isotopic signatures are not sensitive to sediment input from more mafic sources in some stanley shale samples chromite and mn oxides were identified and positively identify an oceanic crustal component as a source of stanley group sediment the results of this study emphasize the importance of determining the mineralogic sites of trace elements and realization of specific mineralogic contributions from mafic or sialic tectonic provenances

mantle flow induced crustal thinning in the area between the easternmost part of the anatolian plate and the arabian foreland e turkey deduced from the geological and geophysical data abstract eastern anatolia consisting of an amalgamation of fragments of oceanic and continental lithosphere is a current active intercontinental contractional zone that is still being squeezed and shortened between the arabian and eurasian plates this collisional and contractional zone is being accompanied by the tectonic escape of most of the anatolian plate to the west by major strike slip faulting on the right lateral north anatolian transform fault zone natfz and left lateral east anatolian transform fault zone eatfz which meet at karliova forming an east pointing cusp the present day crust in the area between the easternmost part of the anatolian plate and the arabian foreland gets thinner from north ca 44 km to south ca 36 km relative to its eastern eahp and western sides central anatolian region this thinner crustal area is characterized by shallow cpd 12 16 km very low pn velocities

curie point depths of the island of kyushu and surrounding areas japan as part of a comprehensive nationwide evaluation of geothermal resources for japan the first of the curie point depth maps covering the island of kyushu has been prepared the map was created by inverting gridded regional aeromagnetic data two satisfactory algorithms were developed to invert the gridded data based upon a distribution of point dipoles the first algorithm estimates x0 y0 and z0 the coordinates of the centroid of the distribution by computing a least squares fit to the radial frequency of the fourier transform the second algorithm estimates centroid depth only by computing a least squares fit to the squared amplitude of the frequency estimates the average depth to the top zt of the collection of point dipoles was estimated by a variation of the second algorithm the depth to the bottom of the dipoles inferred curie point depth is zb 2z0 zt the depth estimates are hand contoured to produce the final map the curie point depth map is then compared to regional geology and heat

deep structure investigations of the geothermal field of the north euboean gulf greece using 3 d local earthquake tomography and curie point depth analysis abstract new findings on the deep origin of the geothermal field and volcanic centres at the north euboean gulf or north evian gulf central greece were obtained by combining a three dimensional traveltime inversion of microseismic data recorded by an on offshore local seismic network with a curie point depth analysis based on aeromagnetic data a magma chamber was detected from low seismic p wave velocity values and high poisson ratios at depths below 8 km also coincident with a curie surface estimated at 7 8 km depth furthermore it was also observed that local geothermal anomalies are generated by hydrothermal flux facilitated by nw se and ne sw oriented faults microseismic activity is also associated with these fault systems

provenance of pliocene clay deposits from the iberian atlantic margin and compositional changes during recycling abstract the xrd mineralogy and geochemistry of recycled fine grained deposits from the west iberia atlantic margin are used to establish sediment provenance and evaluate the features that most closely reflect the nature of the source areas and the transformations during the last depositional cycle a set of pliocene sediment samples is organized according to grain size distribution geochemistry and mineralogy and their chemical composition is compared with the composition of possible source rocks most deposits located to the north of the mondego river were derived from the uplifted precambrian metapelites of the basin edge while to the south of the mondego river they result mainly from recycling of cretaceous and cenozoic clastic units which in turn were derived from precambrian paleozoic granitoids and metasedimentary rocks this differentiation is supported by several element ratios and biplots involving la sm gd sc th u y yb and zr for the specific grain size range of the deposits studied which are mainly made up of silt and clay particles composition is not substantially affected by the grain size distribution of the sediment multi element diagrams designed to discriminate the tectonic setting and the nature of source rocks are of little use in the interpretation of provenance but help to trace geochemical and mineralogical transformations during the last depositional cycles despite the evidence of element leaching during the pliocene depositional cycle the geochemical and mineralogical indicators of weathering intensities are largely determined by the nature of the previous cycle units

provenance analysis and tectonic setting of the ordovician clastic deposits in the southern puna basin nw argentina provenance studies on early to middle ordovician clastic formations of the southern puna basin in north western argentina indicate that the sedimentary detritus is generally composed of reworked crustal material tremadocquartzrich turbidites tolar chico formation mean composition q t 89 f7 l4 are followed by volcaniclastic rocks and greywackes tolillar formation mean q t 33 f42 l25 these are in turn overlain by volcaniclastic deposits mean qt24 f30 l46 of the diablo formation late arenig early llanvirn that are intercalated by lava flows all units were deformed in the ocloyic orogeny during the middle and late ordovician sandstones of the tolar chico formation are characterized by th sc ratios 1 la sc ratios 10 whereas associated fine grained wackes show slightly lower values for both ratios lree light rare earth elements enrichment of the arenites is 50 chondrite eu eu values are between 0 72 and 0 92 and flat hree heavy rare earth elements patterns indicate a derivation from mostly felsic rocks of typical upper crustal composition the e n d t s e d values scatter around 11 to 9 the calculated nd t d m residence ages vary between 1 8 and 2 0 ga indicating contribution by a palaeoproterozoic crustal component the th sc and la sc ratios of the tolillar formation are lower than those of the tolar chico formation normalized ree rare earth elements patterns display a similar shape to paas post archaean average australian shale but with higher abundances of hrees eu eu values range between 0 44 and 1 17 where the higher values reflect the abundance of plagioclase and feldspar bearing volcanic lithoclasts average e n d t s e d values are less negative at 5 1 and nd t d m are lower at 1 6 ga this is consistent with characteristics of regional rocks of upper continental crust composition which most probably represent the sources of the studied detritus the rocks of the diablo formation have the lowest th sc and la sc ratios lower lree abundances than the average continental crust and are slightly enriched in hrees eu eu values are between 0 63 and 1 17 the nd isotopes e n d t s e d 3 to 1 t d m 1 2 ga indicate that one source component was less fractionated than both the underlying early ordovician and the overlying middle ordovician units synsedimentary vulcanites in the diablo formation show the same isotopic composition our data indicate that the sedimentary detritus is generally composed of reworked crustal material but that the diablo formation appears to contain 80 of a less fractionated component derived from a contemporaneous continental volcanic arc there are no data indicating an exotic detrital source or the accretion of an exotic block at this part of the gondwana margin during the ordovician

geochemistry and provenance of metasedimentary rocks from the archean golden pond sequence casa berardi mining district abitibi subprovince the archean golden pond sequence is made up of deformed and metamorphosed conglomerates greywackes and mafic volcanic rocks and is overlain by ferrugineous metasedimentary rocks of the north iron formation the clastic rocks were derived mainly from a volcanic source that had undergone weak chemical weathering their source area was dominated by the presence of 60 80 high al2o3 felsic volcanics having strongly fractionated la sm n 3 7 0 3 and very low ta th ratios 0 09 0 02 with lesser proportions of basaltic 10 30 and ultramafic volcanic rocks 1 10 the ferrugineous metasedimentary rocks can be modelled by mixing 20 40 siliciclastic material of the composition of the average golden pond greywacke with an fe and si rich precipitate molecular fe si 0 6 0 2 the high al2o3 felsic source rocks were most likely produced by subduction processes within an oceanic arc environment but the mafic and ultramafic volcanic rocks were derived by different processes from an asthenosphe

eo alpine metamorphism in the uppermost unit of the cretan nappe system petrology and geochronology the uppermost unit of the cretan nappe system consists of ophiolites on the top and an ophiolitic melange at the base

authigenesis of titania minerals and the mobility of ti new evidence from pro deltaic sandstones cretaceous scotian basin canada titania tio2 minerals are minor diagenetic phases in many sandstone shale successions but the conditions of ti mobility and titania authigenesis are poorly known here new modes of occurrence of authigenic titania minerals filling pores and replacing phytodetritus are documented from lower cretaceous prodeltaic sandstones in the offshore scotian basin of southeastern canada textural relationships suggest that titania minerals formed at the same time as kaolinite most commonly below lowstand sequence boundaries related to flux of meteoric water such authigenic titania is most abundant in thin bedded sandstones interbedded with thick prodeltaic mudstone in which fine grained detrital ti rich minerals are concentrated textures in titania that has replaced uncompacted phytodetritus suggest microbial mediation in near surface eodiagenesis eogenetic titania is enriched in phosphorus 0 6 p2o5 and may co occur with authigenic fluorapatite and crandallite crystals such titania resulted from prolonged flow of meteoric water that dissolved p from apatite and feldspar thereby enhancing ti solubility in basins with supply of immature sediment from granitic terranes and important diagenesis by meteoric water the assumption that ti is an immobile element and that rutile or other titania minerals are exclusively of detrital origin may not be valid probable mesodiagenetic titania has low p content suggesting that ti mobility under these conditions was facilitated by some other agent probably organic acids the results of this study illustrate that even in cases where titania minerals are volumetrically insignificant their microtextures and trace element chemistry can provide important insights into the character of fluid flow during diagenesis of siliciclastic rocks

modelling the joint variability of grain size and chemical composition in sediments abstract the geochemical composition of siliciclastic sediments correlates strongly with grain size hence geochemical composition may serve as a grain size proxy in the absence of grain size variations geochemical data of siliciclastic sediments may be used to characterise size independent processes i e sediment provenance weathering mixing shape density sorting and diagenesis in general however geochemical data sets contain both types of information in order to formalise interpretation of geochemical data we propose a mathematical method to decompose the total geochemical variability of a series of genetically related specimens into a grain size dependent the shared signal and a grain size independent part the residual signal the former may serve as a proxy for grain size whereas the latter represents geochemical variability that would have been observed if all sediments would have had the same grain size distribution the two data sets are jointly decomposed by means of partial least squares pls and orthogonal projection subsequently the presence of significant grain size independent geochemical variability in the residual signal is determined in a statistically rigorous manner using a 2 test using a synthetic example we show that the residual record effectively reveals an imposed provenance signal which could not have been resolved from the geochemical or grain size data sets individually we analysed the relation between grain size and geochemical composition in three quaternary marine sediment cores located offshore west africa and south america geob7920 2 geob9508 5 and geob7139 2 both sites are characterised by biogenic sediment input in addition to fluvial and aeolian sediment input from the continent it was found that all cores show a strong but different correlation between the mean grain size and the bulk geochemical composition these results demonstrate that geochemical grain size proxies are empirical and site specific it was also found that the geochemical and grain size data in cores geob7920 2 and geob7139 2 do not contain unique information whereas in core geob9508 5 ti varies independently from the grain size this residual ti signal correlates with the transport mechanism as demonstrated by statistically different values of aeolian and fluvial dominated sediments however a unique interpretation of this residual signal in terms of the postulated grain size independent mechanisms could not be provided without additional information we conclude that the proposed model facilitates identification and validation of different element ratios as grain size proxies and more importantly as proxies for size independent processes for this reason the model paves the way for rigorous analysis of multi proxy data which are widely used in palaeoceanographic and palaeoclimatic research

investigations into the tectonic lineaments and thermal structure of kutahya denizli region western anatolia from using aeromagnetic gravity and seismological data abstract residual aeromagnetic map of western anatolia displays intense anomalies especially in the nw of the region curie point depth cpd map obtained from the residual aeromagnetic anomalies is indicative of larger area of shallow curie levels than previously defined two important shallow depth regions located at between kutahya and denizli are determined from cpd and thermal gradient tg map the intense aeromagnetic anomalies are located in the west of kutahya along the e w direction these anomalies are resulted from the metamorphic units of menderes massif the analytic signal as map produced from residual aeromagnetic data shows the e w trending geological bodies causing magnetic anomalies which become intense in the west and south of kutahya it is also observed from the as map that thermal structures or bodies are buried under the non magnetic surface geology the maxspot map derived from the location of the horizontal gradient of aeromagnetic anomalies can be well correlated with not only tectonic lineaments but also the distribution of earthquake data bouguer anomalies of the region can also be well correlated with the graben system and thus provide supportive information about the geothermal energy potential of the study area

critical evaluation of six tectonic setting discrimination diagrams using geochemical data of neogene sediments from known tectonic settings abstract an attempt is made to evaluate 6 tectonic setting discrimination diagrams 1 discriminant function and 5 bivariate diagrams frequently used by many researchers for this purpose an extensive database was established for major element geochemistry derived from miocene to recent sand and sandstone medium to fine grained samples collected from a variety of tectonic settings including 1 passive margin pm setting 2 active continental margin acm setting and 3 oceanic island arc oia setting our results suggest that the discrimination fields proposed to infer tectonic settings for six commonly used discrimination diagrams do not work properly for the analyzed miocene to recent sediments the success for these diagrams varies from 0 to about 62 we therefore recommend that these diagrams be used with prudence

factors controlling the trace element distribution in fine grained rocks the albian kaolinite rich deposits of the oliete basin ne spain abstract this paper combines mineralogical data x ray diffraction petrographic and scanning electron microscopy techniques and geochemical analyses in order to investigate the composition of a set of samples claystones siltstones and sandstones which belong to the albian deposits of the oliete basin in spain the aims of the study are to characterize the distribution of major and trace elements in kaolinite rich rocks to infer the role played by accessory phases and clay minerals on the trace element distribution and to assess the source area composition of these materials mineralogical analyses show that these rocks are mainly composed of different proportions of quartz and clay minerals kaolinite and illite with minor feldspar micron accessory minerals such as monazite zircon pyrite marcasite fe oxides and ti oxides have also been detected the sandstone framework implies that the source area of these sediments was probably a granitoid source which underwent low rank metamorphism the major element distribution reflects the mineralogy of the rocks plots in the a cn k diagram as well as their cia values indicate that these sediments were generated from an intensely weathered source area this produced the development of relatively cation poor clays such as kaolinite and claystones with large rare earth elements ree contents the fact that transition element contents in claystones are greater than in siltstones and sandstones suggests that they are preferentially linked to clay minerals probably by surficial sorption in comparison with other lithologies the high abundances of high field strength elements in siltstones imply that accessory minerals such as zircon and nb bearing phases are mainly concentrated in siltstones it should be noted that siltstones are also the lithology which displays the highest ree abundances the statistical analysis of the geochemical data suggests that ree are mainly controlled by ti and nb bearing phases such as titanite and nb and ti oxides although clay minerals are not the main phases in the ree control they probably also have some influence as the analyses show in addition other accessory phases such as monazite secondary phosphates and zircon also contribute to the ree contents although much less than amorphous fe oxides in some samples according to the ree patterns and elemental ratios such as la sc th sc th co etc the source area of the studied outcrops was probably felsic and with intermediate composition between granite and granodiorite

the lower cretaceous chaswood formation in southern new brunswick provenance and tectonics the most northwesterly outcrop of lower cretaceous chaswood formation is in a pit at vinegar hill south of sussex new brunswick new mapping and boreholes show thick fluvial loosely lithified conglomerates and lesser sandstones unconformably overlying 12 m of mudstone in a 1 km2 basin bounded to the northwest by the clover hill fault sparse paleocurrent indicators to the southwest parallel this fault the tectonic setting is similar to that of the chaswood formation in the fault bounded elmsvale basin in nova scotia in both cases a basal unit is paraconformable on underlying upper mississippian rocks was folded into a syncline within which a middle unit accumulated and was further deformed and is capped by thin flat lying sandstone and conglomerate the tectonic style of the chaswood formation at vinegar hill demonstrates that early cretaceous deformation was widespread in the southern maritimes gravel clasts consist overwhelmingly of vein quartz but sparse lithic clasts match source rocks in s

geothermal energy reconnaissance of southeastern nigeria from analysis of aeromagnetic and gravity data given the daunting energy challenges currently bedeviling nigeria with demand for electrical power exceeding availability alternative energy sources preferentially renewable are vigorously considered this is the first study to examine geothermal energy prospects in southeastern nigeria with the ultimate aim of locating and mapping regions of shallow curie point depths cpds crustal thickness and geologic structures supportive of a geothermal system we estimated cpd using the spectral analysis technique on magnetic field anomalies gravity anomalies were subjected to a series of procedures to assess geological structures result reveals deeper cpds within central and southern regions of okposi afikpo and biase towns in an approximate range of 18 4 to 19 3 km shallow cpds 9 8 17 4 km have also been obtained within obubra and abakaliki regions estimated crustal thickness moho ranges between 26 5 and 35 8 km part of the region with shallow cpd correlates with regions of shallow moho depths particularly in abakaliki and deeper moho depths coincide with deeper cpd estimates at the afikpo location the estimated geothermal gradient and heat flow values range between 29 0 and 45 0 oc and 52 2 101 5 mw m2 respectively and fall within values evaluated from deep wells drilled for oil exploration within the adjoining anambra basin region this study recommends the regions with shallow depths for possible geothermal power plant location gravity data evaluations also reveal significant subsurface intrusions within ugbodo obubra and abakaliki locations overall this study is a step forward toward a better evaluation of the geothermal energy resources potential of southeastern nigeria

curie point depths of macedonia and thrace n greece the aeromagnetic data of macedonia and thrace were used to produce curie point estimates the data were high pass filtered to remove components arising from topography and magnetic core fields which were not adequately modeled by a dgrf the depth to the centroid z 0 of the deepest distribution of the magnetic dipoles was obtained by computing a least squares fit to the lowest frequency segment of the azimuthally averaged log power spectrum the average depth to the top of the deepest crustal block was computed as the depth to the top z t of the second lowest frequency segment of the spectrum the depth to the bottom of the deepest magnetic dipoles the inferred curie point depth was then calculated from z b 2z 0 z t the curie depth estimates for macedonia and thrace range between 11 2 and 17 3 km these results are consistent with the depths inferred by extrapolating known geothermal gradient and heat flow values

curie point depth map of turkey summary a curie point isotherm map of the whole of turkey has been prepared from aeromagnetic data by means of a spectral analysis technique the most characteristic signature of this map is that the shallow depths generally correlated with the young volcanic rocks and the thinned crustal thicknesses in the west reveal geothermal fields and several hot springs the orogenic pontide belt of the black sea region in the north the western taurus belt in the south and some high plateaus in eastern turkey show that the deepest curie isotherm depths range between 20 and 29 km depth contour lines elongating in an almost e w direction are due to the overlapping percentage of adjacent data blocks of 50 per cent in the e w direction and to magnetic anomalies trending in the e w direction curie isotherm depths are in the range 6 to 10 km in the aegean region and are characterized by e w and ne sw trending graben structures as expected since the region has crustal thinning and many hot springs and geothermal fields these imply the existence of shallow heat sources that could be utilized for electricity heating of towns and cities greenhouse and health purposes

curie point depths in north china craton based on spectral analysis of magnetic anomalies magnetic anomaly analysis is an important method to study the structure of deep crust with the assumption of random magnetization sources the structure of a magnetic layer can be inverted via spectral analysis curie point depth cpd the depth at which rocks lose their ferromagnetic properties is the bottom of a magnetic layer in this study we estimate from the magnetic anomaly data of emag2 dataset the cpd and the top of the magnetic layer in north china with a moving window of 180 km 180 km we calculate the average top and centroid depth of the magnetic layer in each window and determine the regional cpd distribution across north china the cpd of north china varies from 18 to 32 km in addition the cpd in the western part of the north china craton is deeper than that in the eastern part the shallowest cpd is located near the bohai sea when compared to available heat flow data the estimated cpd values are consistent with thermal conductivity of 1 8 3 2 wm 1 k 1 and on heat production value of 0 4 1 3 wm 3

tectonic environment of the devonian gramscatho basin south cornwall framework mode and geochemical evidence from turbiditic sandstones the portscatho formation within the allochthonous unit of the middle and upper devonian gramscatho group is a thick sequence of deep water sandstones and interbedded slates deposited by southerly derived turbidity currents into the gramscatho basin of south cornwall throughout an approximately 3 5 km thick sequence the portscatho formation is petrographically and chemically coherent except that the upper section shows a higher proportion of metamorphic clasts high but variable cr and low uniform zr abundances complementary framework mode and bulk geochemistry indicate that the sandstones were derived from a dissected continental magmatic arc of predominantly acidic composition similar to average upper continental crust but with an admixture of minor intermediate basic material flysch deposition took place in a fore arc setting the presence of an arc to the south of cornwall during the devonian implies that there was subduction at the margin of the gramscatho basin whose ultimate closure was accommodated by the northward stacking of flysch ophiolite nappes

hidden cretaceous basins in nova scotia early cretaceous unconsolidated quartz sand and kaolinitic clay deposits in the lowlands of nova scotia are preserved in narrow half grabens obscured by glacial drift the chaswood formation sediments can be subdivided into three members upper and lower members dominated by cyclical sand mud facies of fluvial origin and the middle member with lignitic clay of lacustrine origin ferruginous oxisols are common in the fine grained facies of the upper and lower members seismic data indicate that chaswood formation strata in the elmsvale basin are deformed into steeply dipping faults and fault related folds rutherford road fault zone an aptian albian age for this tectonic event is inferred from synsedimentary deformation and from the angular unconformity spanning the late cretaceous and tertiary that truncates the chaswood formation exhumation of a thick cover of mesozoic sediment 1 2 km is needed to account for the preservation of chaswood formation outliers after 80 ma of erosion the half grabens that host the chaswood formation were formed in the mesozoic and were antecedent to the present day structurally controlled lowlands

curie point depths based on spectrum analysis of aeromagnetic data west anatolian extensional province turkey the curie point depth map of western anatolia was constituted from spectral analysis of the aeromagnetic data the curie point depth values from 53 overlapping blocks 90 90 km in size have been estimated from the band pass filtered data the slope of the longest wavelength part of the radially averaged log power spectrum divided by the radial frequency produced the depth to the centroid z0 for the deepest crustal block the depth to the top zt was obtained by the slope of the second longest wavelength part of the spectrum from these depths the curie point depth was then calculated by using zb 2z0 zt the curie point depth estimates for western anatolia range between 8 2 and 19 9 km

relationship of diagenetic chlorite rims to depositional facies in lower cretaceous reservoir sandstones of the scotian basin the relationship between diagenetic chlorite rims and depositional facies in deltaic strata of the lower cretaceous missisauga formation was investigated using a combination of electron microprobe bulk geochemistry and x ray diffraction data the succession studied comprises several stacked parasequences the delta progradational facies association includes i fluvial or distributary channel sandstones some with tidal influence ii thick bedded delta front graded beds of sandstone interpreted as resulting from fluvial hyperpycnal flow during floods and storms and iii more distal muddier delta front and prodeltaic facies the transgressive facies association includes lag conglomerate siderite cemented muddy sandstone and mudstone and bioclastic sandy limestone chlorite rims are absent in the fluvial facies and best developed in thick sandstones lacking mudstone baffles good quality chlorite rims are well correlated with ti in bulk geochemistry ti is a proxy for fe availability principally from the breakdown of abundant detrital ilmenite fetio3 under conditions of sea floor diagenesis the abrupt decrease in sedimentation rate at transgressive surfaces caused progressive shallowing of the sulphate depletion level and of the overlying eh controlled diagenetic zones resulting in conditions suitable for diagenetic formation of berthierine to migrate upwards through the packet of reservoir sandstones this early diagenetic berthierine suppressed silica cementation and later recrystallized to chlorite thick euhedral outer chlorite rims were precipitated from formation water in sandstone lacking muddy baffles on this chlorite substrate and inhibited late carbonate cementation this study thus shows that the preservation of porosity by chlorite rims is a two stage process rapidly deposited delta front turbidite facies create early diagenetic conditions that eventually lead to the formation of chlorite rims but the best quality chlorite rims are restricted to sandstones with high permeability during burial diagenesis

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

sr nd isotopic characteristics of the northeast sandy land china and their implications for tracing sources of regional dust abstract the sr nd isotopic study of the northeast sandy land nesl china is of great significance for a thorough understanding of the dust system in this area the 162 bulk

ground truthing chemostratigraphic correlations in fluvial systems changes in elemental chemistry have been used to define stratigraphic correlations between wellbores in petroleum basins few publications however relate defined chemical stratigraphy to physical correlations and none have been found that do so in fluvial systems here chemostratigraphy is applied to permian fluvial sediments within the beaufort group of the karoo basin in south africa and a correlation between three logged sections is defined this correlation is tested against physically determined chronostratigraphic correlations achieved using heli lidar data to provide a high resolution correlation between two sections 7 km 4 4 mi apart and mapping of strata using google earth to produce a correlation between sections 25 5 km 15 8 mi apart the chemostratigraphic characterization that is defined using data from fine grained lithologies resulted in the recognition of eight chemostratigraphic packages with thicknesses between 50 and 250 m 164 and 820 ft over a stratigraphic interval of approximately 900 m 2953 ft two distinctive changes in geochemical composition of the coarser lithologies fluvial channel belts were seen over this interval in the two sections that are 7 km 4 4 mi apart higher resolution subdivision of chemostratigraphic packages was achieved to produce four correlative geochemical units 30 60 m 98 197 ft in thickness that provide a high resolution correlation the chemostratigraphic and chronostratigraphic correlations are in close agreement in both the 7 km 4 4 mi and the 25 5 km 15 8 mi spaced sections the thickness of the study interval and spacing of sections is analogous to published chemostratigraphy studies on subsurface sequences thereby ground truthing the use of chemostratigraphy for correlation in subsurface fluvial systems that are to some degree analogous to the beaufort group sediments of this paper

curie surface of the alkaline provinces of goias gap and alto paranaiba apap central brazil abstract the study area includes the most important carbonatite and kimberlite complexes in brazil located in the brazilian states of goias and minas gerais the central portion of this area involves the azimuth 125 lineament az 125 that consists of an extensive set of faults oriented in the nw se direction that served as a conduit for magma ascent this lineament is the main structural feature associated with these complexes the goias gap and alto paranaiba apap alkaline provinces occur along the az 125 and include highly economically valuable mineralizations in this study we aim to map the depth to the curie isotherm or curie point depths cpd of the study area mainly the gap and apap regions based on spectral analysis of aeromagnetic data the cpd estimations were achieved from a spectral approach known as the centroid method providing the relationship between the spectra of magnetic anomalies and the depths of the magnetic source of a 2 d magnetic data the cpd estimates from approximately 500 overlapping blocks vary from 7 km to 40 km deep the shallower depths are related to the gap and apap regions and the deeper ones are related to the sao franciscana plate the curie depths related to the az 125 are between 30 km and 15 7 km deep according to the results the gap and apap intrusive bodies have shallower roots the major faults of the az 125

3d seismic analysis of the coast shear zone in se alaska and western british columbia broadside analysis of accrete wide angle data abstract the multidisciplinary accrete project addresses the question of continental assemblage in southeast alaska and western british columbia by terrane accretion and magmatic addition the previous studies of this project yielded important information for understanding the structures across the coast shear zone csz and the formation of the csz and the coast mountains batholith cmb the present study extends these interpretations into pseudo 3 d by using two additional wide angle accrete seismic lines by analyzing the broadside wide angle data using a series of laterally homogeneous 2 d models we derive a lower resolution 3 d velocity model of the outboard terranes and constrain variations in crustal thickness across and along the csz models of the broadside data confirms major structural and compositional trends extend along strike to the northwest the key features are a a steep moho ramp only 15 km wide is coincident with the csz and divides thin 25 1 km crust to the west below the west vergent thrust belt wtb from thicker 31 1 km crust to the east below the cmb b low velocity mantle 7 7 7 9 km s extends beneath the entire study region indicating high crustal and upper mantle temperatures below the wtb and cmb and c the alexander terrane is characterized by strong mid crustal reflectivity and high lower crustal velocities that are consistent with gabbroic composition this study extends the earlier interpretation and implies that the ramp is indeed likely associated with transpressional tectonics and magmatic crustal addition east of the csz

quantification of the effects of secondary matrix on the analysis of sandstone composition and a petrographic chemical technique for retrieving original framework grain modes of altered sandstones abstract most studies of sandstone provenance involve modal analysis of framework grains using techniques that exclude the fine grained breakdown products of labile mineral grains and rock fragments usually termed secondary matrix or pseudomatrix however the data presented here demonstrate that when the proportion of pseudomatrix in a sandstone exceeds 10 standard petrographic analysis can lead to incorrect provenance interpretation petrographic schemes for provenance analysis such as qfl and qfr should not therefore be applied to sandstones containing more than 10 secondary matrix pseudomatrix is commonly abundant in sandstones and this is therefore a problem for provenance analysis the difficulty can be alleviated by the use of whole rock chemistry in addition to petrographic analysis combination of chemical and point count data permits the construction of normative compositions that approximate original framework grain compositions provenance analysis is also complicated in many cases by fundamental compositional alteration during weathering and transport many sandstones particularly shallow marine deposits have undergone vigorous reworking which may destroy unstable mineral grains and rock fragments in such cases it may not be possible to retrieve provenance information by either petrographic or chemical means because of this pseudomatrix rich sandstones should be routinely included in chemical petrological provenance analysis because of the many factors both pre and post depositional that operate to increase the compositional maturity of sandstones petrologic studies must include a complete inventory of matrix proportions grain size and sorting parameters and an assessment of depositional setting

sedimentary environment and diagenesis of the lower cretaceous chaswood formation southeastern canada the origin of kaolin rich mudstones abstract the lower cretaceous fluvial sandstone mudstone succession of the chaswood formation is the proximal equivalent of offshore deltaic rocks of the scotian basin that are reservoirs for producing gas fields this study interprets the mineralogical consequences of cretaceous weathering and early diagenesis in a 130 m core from the chaswood formation in order to better understand detrital and diagenetic minerals in equivalent rocks offshore mineralogy was determined by x ray diffraction electron microprobe analysis and scanning electron microscopy the rocks can be divided into five facies associations light gray mudstone dark gray mudstone silty mudstone and muddy sandstone sorted sandstone and conglomerate and paleosols facies transitions in coarser facies are related to deposition in and near fluvial channels in the mudstones they indicate an evolutionary progression from the dark gray mudstone facies association swamps and floodplain soils to mottled paleosols well drained oxisols and ultisols following syntectonic uplift facies transitions and regional distribution indicate that the light gray mudstone facies association formed from early diagenetic oxidation and alteration of the dark gray mudstone facies association probably by meteoric water principal minerals in mudstones are illite muscovite kaolinite vermiculite and quartz illite muscovite is of detrital origin but variations in abundance show that it has altered to kaolinite in the light gray mudstone facies association and in oxisols vermiculite developed from the weathering of biotite and is present in ultisols the earliest phase of sandstone cementation in reducing conditions in swamps and ponds produced siderite nodules and framboidal pyrite which were corroded and oxidized during subsequent development of paleosols kaolinite is an early cement coating quartz grains and as well crystallized pore filling booklets that was probably synchronous with the formation of the light gray mudstone facies association later illite and barite cement indicate a source of abundant k and ba from formation water this late diagenesis of sandstone took place when the chaswood formation was in continuity with the main scotian basin prior to oligocene uplift of the eastern scotian shelf findings of this study are applicable to other mid latitude cretaceous weathering and early diagenetic environments

interpretation of low seismicity in the eastern anatolian collisional zone using geophysical seismicity and aeromagnetic and geological data the eastern anatolia is a continental collisional zone between the arabia eurasia plates and is currently being accompanied by the westward escape of the anatolian crustal block to the west southwest along two major strike slip fault zones the natf and the eatf although these major fault zones have experienced historical earthquakes with moderate to high magnitude notably there is a low seismicity zone on the active eatf between the bitlis and poturge massifs the low seismicity zone is characterized by thinner crustal structure relative to its environs the shallow curie point depth scpd ca 12 14 km in between 39 40 e and 38 5 39 n in the easternmost part of the anatolian plate and moderate to high b values more than 0 7 we consider that the shallow cpd and moderate to high b values in the low seismicity zone characterized by thinner crustal area are closely related with the higher thermal structure of the crust which most probably resulted from crust hot asthenospheric mantle interactions

provenance and tectonic setting of clastic deposits in the devonian xicheng basin qinling orogen central china abstract the qinling orogenic belt is one of world s great collisional orogenic belts which extends from the pamirs west kunlun to the korean peninsula and occupies a key position in understanding of the evolution and assembly of asia this belt separates the north china and south china blocks extensive thick devonian clastic rocks sandwiched between the shangdan and mianlue suture zones are mainly infills of the xicheng basin and provide the principal sedimentary record of tectonism in the qinling orogen devonian infills were subdivided into three subunits the upper devonian dacaotan group the middle upper devonian shujiaba group and the lower upper devonian xihanshui group their provenance and tectonic setting are critical to understanding not only the tectonic evolution of asia but also the global aspects of collisional regions compared with devonian strata in the eastern part of the qinling orogen the xicheng basin was not seriously modified by mesozoic tectonism petrologic studies demonstrate that the dacaotan group consists mainly of feldspathic litharenite with abundant volcanic fragments in contrast the shujiaba and xihanshui groups contain more metamorphic and sedimentary fragments and fewer magmatics than other lithic fragments these relations demonstrate that magmatic plutons were not extensively exposed at the time of deposition of these groups on q f l plots sandstones fall into the field of transitional arcs but on qm p k and lm lv ls diagrams they plot in the fields of continental arc and continental suture rocks the presence of volcanic lithic grains in the sandstones suggests they were derived mainly from a continental arc major element geochemistry of siltstones and mudstones demonstrate that most were derived from a continental arc but some from an oceanic island arc trace element geochemistry favors a continental arc provenance mostly from felsic rocks a high cr content of siltstones and mudstones demonstrates that some mafic or ultramafic rocks were exposed in the source area and provided some detritus rare earth element patterns are very similar to those of sandstones in modern continental arcs devonian paleocurrent indictors demonstrate that this continental arc was located at the northern edge of the basin this deduction demonstrates that the qinling arc in the southern margin of the north china block was the major source of clastic debris in the devonian xicheng basin these relationships suggest that the sediments were most probably deposited in a forearc basin