integrated interpretation of 3d seismic data to enhance the detection of the gold bearing reef mponeng gold mine witwatersrand basin south africa we present an integrated approach to the seismic interpretation of one of the world s deepest gold ore body carbon leader reef using three dimensional seismic data ultrasonic velocity measurements at elevated stresses and modified instantaneous attribute analysis seismic wave velocities of the drill core samples quartzite shale and conglomeratic reef from the mine are sensitive to uniaxial stress changes i e they slowly increase with increasing pressure until they reach maximum value at 25 mpa for all the samples seismic velocities are constant above 25 mpa indicating a possible closure of microcracks at stress corresponding to 1 0 km 1 5 km a reflection coefficient of 0 02 computed between hanging wall and footwall quartzites of the carbon leader reef ore body suggests that it may be difficult to obtain a strong seismic reflection at their interface our modified seismic attribute algorithm on the other hand shows that the detection of the lateral continuity of the carbon leader reef reflector can significantly be improved by sharpening the seismic traces three dimensional seismic data reveal that faults with throws greater than 25 m that offset the carbon leader reef can clearly be seen faults with throws less than 25 m but greater than 2 m throw were identified through horizon based attribute analysis while most dykes and sills with thickness less than 25 m were invisible the detection of the lateral continuity of the carbon leader reef reflector and its depth position is greatly improved by integrating the modified instantaneous attributes with controls from borehole observations the three dimensional visualization and effective interpretation of the carbon leader reef horizon shows a host of structurally complex ore body blocks that may impact future shaft positioning and reduce its associated risks

seismic and geoelectric evidence for collisional and extensional events in the fennoscandian shield implications for precambrian crustal evolution extensive deep seismic and electromagnetic sounding programs have resulted in tens of deep refraction seismic profiles normal incidence reflection profiles several hundred magnetotelluric soundings and several magnetovariational array observations results are compiled into four maps 1 moho depth 2 thickness of the lower crustal high velocity layer vp 7 km s 3 depth to the upper interface of the high velocity layer and 4 distribution of upper and middle crustal electrical conductors the moho depth is approximately 40 km in the archaean domain and varies between 40 and 65 km in the svecofennian domain most of the thickness variation 0 24 km is concentrated in the lower crustal high velocity layer electrically the crust is formed of several rather homogeneous either resistive or conductive blocks that are bounded by upper and middle crustal conductive zones the cratonized archaean crust experienced an extensional phase during which a thin mafic lower crustal high velocity layer was produced in association with mafic dykes 2 2 2 1 ga and well conducting volcanogenic and metasedimentary belts 2 5 2 0 ga the moho of the archaean domain was consequently reformed in the early proterozoic major thickening of the crust 50 65 km occurred when a svecofennian island arc and the archaean craton collided the svecofennian orogeny 1 76 1 9 ga resulted in a collage of metasedimentary rocks squeezed between crustal blocks of the island arc the internal terrane boundaries are seen as good reflectors and or inclined or vertical conductors that extend at least to the middle crust the thick high velocity 7 km s lower crust is a combination of mafic lower crust of the island arc crustal blocks and mafic additions from either delamination of the lithosphere after the collision or from a period of late svecofennian subduction the collisional boundary is also preserved as a discontinuous conductive zone between the archaean and svecofennian domains the thickened crust was subsequently thinned to 42 km along e w striking zones during an extensional period characterized by the intrusion of anorogenic rapakivi granitoid batholiths coeval mafic dykes and gabbro anorthosite bodies 1 6 1 5 ga the crust of the central part of the shield has since remained virtually intact

delamination of eclogitized lower crust control on the crust mantle boundary in the central fennoscandian shield abstract the crustal structure of the central part of the fennoscandian shield is dominated by a high velocity lower crust hvlc vp 7 3 7 5 km s at the depth of 40 63 km in an area of ca 400 km 600 km formed in the palaeoproterozoic svecofennian orogen at 1 91 1 87 ga in the area of the hvlc the moho is deeper than 50 km and attains depths of up to 63 km in eastern finland at the archaean proterozoic boundary zone we suggest that the present moho dates back to late svecofennian time and was determined by delamination of high density eclogitized lower crust after tectonic collisional thickening of crust densities deduced from seismic and gravity data suggest a very small or completely lacking density contrast between lower crust and uppermost mantle new geological evidence from kimberlite hosted garnet xenocrysts supports the presence of a garnet population with compositions in agreement with crustal eclogitic garnets in addition small clinopyroxene garnet mineral aggregates microxenoliths show omphacitic clinopyroxene compositions therefore the presence of eclogites in the high velocity lower crust is implied although the eclogite proportion as estimated from seismic velocity data is only a few percent in the present hvlc with results on near incidence and wide angle seismic studies and geological and geochemical data on heat producing elements we modeled the svecofennian collision and the thermal evolution of the crust to provide temperature constraints for the delamination model the constructed thermal model simulates the genesis of svecofennian synkinematic at 1 89 1 88 ga and postkinematic 1 88 1 87 ga granitoids as well as the general metamorphic grade of the surface rocks and lower crustal xenoliths moreover the narrow distribution of the ages of the svecofennian mafic ultramafic magmatism ca 1 89 1 87 ga dispersed around the hvlc area is explained by the homogeneous warming of the lithosphere the conditions of lower crustal delamination were estimated with a rayleigh taylor convective instability model constrained with lower crustal and upper mantle rheological data delamination of a lower crustal eclogite layer 5 30 km thick takes place in about 7 50 ma if the rock dynamic viscosity is 1 1021 pa s it requires temperatures of 1000 c in the lower crust and upper mantle in the svecofennian crust such temperatures were attained at about 1860 1850 ma i e after the orogenic peak we conclude that the moho of the hvlc area was controlled by delamination of a ca 5 10 km thick layer of high density lowermost crust into the mantle such a density controlled process may have controlled the moho depth also in other proterozoic shield areas

permo triassic tectonism in volcanic arc sequences of the western u s cordillera and implications for the sonoma orogeny the permo triassic sonoma orogeny western u s cordillera involved tight folding and imbricate thrust faulting of basinal strata of the golconda allochthon this event is generally interpreted in terms of accretion of upper paleozoic volcanic arc rocks of the western u s cordillera mccloud arc to the north american continent either via back arc basin closure or arc continent collision the structural history of the mccloud arc during the sonoma orogeny is poorly understood however as are the implications of this history for tectonic models this paper presents a synthesis of the permian to triassic stratigraphic and structural evolution of the mccloud arc incorporating new data from the pine forest range northwest nevada the synthesis indicates that on a regional scale the arc was affected by widespread uplift but only local tilting folding and faulting in the late permian to early triassic the timing of permo triassic tectonic activity in the mccloud arc is thus similar to the middle permian to early triassic age of deformation in the golconda allochthon but the structures produced in the two groups of rocks differ markedly the significance of this contrasting structural response to sonoma age tectonism can be evaluated by comparison with other better understood examples of arc continent accretion back arc basin closure in the southern andes compressional arc continent collision in new guinea and extensional arc continent collision in the mediterranean this comparison indicates that the contrasting structural history of the mccloud arc and golconda allochthon is entirely compatible with an arc continent accretion model for the sonoma orogeny and cannot be used as a basis for concluding that the mccloud arc was not involved in the orogenic event the comparison further indicates that either back arc basin closure or compressional arc continent collision are the most likely settings for the sonoma orogeny in contrast an extensional mediterranean style arc continent collision as has been recently proposed for the earlier middle paleozoic antler orogeny is probably not an appropriate analogue for the sonoma orogeny the weak structural response of the mccloud arc during sonoman compression also provides new constraints on the specific processes involved in arc accretion either via arc continent collision or back arc basin closure these constraints suggest that there may be few fundamental differences between the two models during the final stages of arc accretion regardless of tectonic setting permo triassic uplift and associated deformation in the mccloud arc should be considered as much a response to the sonoma orogeny as is tight folding and imbricate faulting in the golconda allochthon

late paleozoic radiolarian ages from the gwydir terrane new england orogen eastern australia discoveries of late devonian early mississippian radiolaria in the gwydir terrane eastern australia indicate that much of the terrane is younger than previously thought radiolaria provide valuable constraints on the timing of the development of the gwydir terrane moreover this new biostratigraphic data indicate that previously published models detailing the development of the new england orogen need to be reappraised

a chemo mechanical insight into the failure mechanism of frequently occurred landslides in the loess plateau gansu province china abstract thick loess deposits are considered problematic soils due to their susceptibility to collapse suddenly and in large volumes upon increase of water content in the past decades a large number of landslides occurred in the loess plateau in gansu province north western china triggered by the extensive irrigation the increase of water content has been identified as a key factor controlling the loess strength however the role of long term saturation and pore fluid chemistry changes has not been investigated systematically this paper reports on an experimental study on loess samples from heitai loess terrace yongjing gansu carried out through chemical analyses oedometer and ring shear tests the natural pore fluid was found to be a concentrated saline solution in unsaturated soil condition upon saturation the pore ion concentration drop can contribute to shear strength loss in the clay component and volume decrease a prolonged exposure to the irrigation water might facilitate cement dissolution which could result in further weakening

crustal structure and composition of the oslo graben norway abstract although more than 250 my old the oslo graben has retained a distinctive distribution of p wave velocities associated with rifting intrusion and underplating of the thinned crustal section we calculate poisson s ratio values from crustal p and s wave velocities along an 400 km long profile across the southern scandinavian peninsula with a focus on the oslo graben plutonic rocks are now exposed at the surface in the graben due to post rifting erosion and the corresponding low 5 5 km s p wave velocities extend to depths of 3 km the p wave velocity and poisson s ratio between depths of 6 and 34 km are 5 higher inside than outside the rift boundaries which together with thickening of the 7 km s lower crust beneath the rift indicate magmatic intrusions poisson s ratio of 0 27 and high 7 1 7 4 km s velocities indicate a heterogeneous composition lower crust the thickened high velocity lower crust is 1 5 times wider than the surface expression of the rift and extends to both the east and west of the main rift axis depth dependant extension may have occurred within the rift and may account for the significant volumes of volcanic output despite the small surface extension observed the added volume of intrusive material may explain why the moho up warp is small as little as 2 km at the rift based on the new p wave velocities poisson s ratio measurements and the thickness of the magmatic underplate apparent values for the rift are estimated to be 1 5 but when intrusion within the crust is included could be as high at 2 3

modelling the thermal evolution of a collisional precambrian orogen high heat production migmatitic granites of southern finland abstract we present results of thermal and geochemical modelling of paleoproterozoic southern finland which is characterized by formation of high heat production migmatitic granites post orogenic granitoids and high temperature low pressure metamorphism at 1 85 1 78 ga during late svecofennian time metamorphic grade is mostly amphibolite facies 4 5 kbar 650 700 c but also granulite facies 6 kbar up to 800 c occurs our results suggest that the thermal evolution of the area can be modelled as a process of rapid crustal thickening up to 70 km in a plate collision at ca 1870 1860 ma ago followed by conductive heating of the crust simultaneous exhumation and partial melting of middle crust and emplacement of the melts in the upper crust as late orogenic high heat production granites at about 1825 ma ago the upper crust collapsed gravitationally at about 1820 ma but the crust was still thick 57 km when the main orogenic era terminated about 1800 ma ago in modelling the thermal evolution we applied crustal heat production values constrained by geochemical data and a conservative estimate i e relatively low value for mantle heat flow density the modeled temperatures at 30 50 km depths in the thickened crustal stack exceed the dehydration melting temperatures of micas at 40 km 750 c for muscovite and 800 c for biotite respectively 25 35 ma after the collision and thickening of crust the results explain the high temperature low pressure metamorphism in southern finland as an inevitable consequence of crustal thicknening leading to an increase of the total heat production of the crust crustal thicknening is the main heat source for melting and metamorphism of the orogeny advective and latent heat brought by the melts further increased the temperatures at the emplacement depth and contributed to the granulite facies metamorphism that is spatially related to the migmatitic granites geochemical models suggest that the high concentrations of u and th in the migmatitic granites can be attributed to about 20 vol partial melting of deeply buried sediments and volcanic rocks about 36 71 of the original u 18 54 of th and 34 46 of k respectively in the source rock types entered the melt phase no anomalous concentrations of these elements in the source rock are required in addition to explaining the migmatitic late orogenic granite and post orogenic granitoid genesis the collision model implies that the middle lower crust and the upper mantle continued warming until the mesoproterozoic times which suggests a causal link between the svecofennian thermal evolution and the extensive bimodal rapakivi granite and anorthosite magmatism in the fennoscandian shield about 200 250 ma later

deep crustal mineral assemblages and potential for crustal rocks below the moho in the scottish caledonides summary the scottish caledonian lower crust is strongly seismically reflective beneath the moho at about 30km very few reflections are seen on seismic records with the exception of a strong reflector at about 50km depth the rocks between the moho and this strong reflector have been interpreted as crustal but with mantle velocities and densities we report tests of this in which the densities and seismic velocities of likely crustal precursors are assessed through determination of the stable mineral assemblages along geotherms appropriate to the region likely crustal precursors were selected from suites of exhumed deep crustal rocks and deep crustal xenoliths and from a variety of basaltic rocks mineral assemblages were estimated using a variant of the lowest free energy search procedure of wood 1987 with account taken of nonideal mixing in solid solutions geotherms were calculated from the heatdow heatproduction relationship for the scottish caledonides using the methods of pollack chapman 1977 seismic velocities were estimated from empirical density velocity relationships and from the velocities of individual mineral species weighted for modal proportions

full scale crustal interpretation of kokkola kymi kokky seismic profile fennoscandian shield the kokkola kymi deep seismic sounding profile crosses the fennoscandian shield in northwest southeast nw se direction from bothnian belt to wiborg rapakivi batholith through central finland granitoid complex cfgc the 490 km refraction seismic line is perpendicular to the orogenic strike in central finland and entirely based on data from quarry blasts and road construction sites in years 2012 and 2013 the campaign resulted in 63 usable seismic record sections the average perpendicular distance between these and the profile was 14 km tomographic velocity models were computed with jive3d program the velocity fields of the tomographic models were used as starting points in the ray tracing modelling based on collected seismic sections a layer cake model was prepared with the ray tracing package seis83 along the profile upper crust has an average thickness of 22 km average and p wave velocities vp of 5 9 6 2 km s near the surface increasing downward to 6 25 6 40 km s the thickness of middle crust is 14 km below cfgc 20 km in se and 25 km in nw but vp ranges from 6 6 to 6 9 km s in all parts lower crust has vp values of 7 35 7 4 km s and lithospheric mantle 8 2 8 25 km s moho depth is 54 km in nw part 63 km in the middle and 43 km in sw yet a 55 km long section in the middle does not reveal an obvious moho reflection s wave velocities vary from 3 4 km s near the surface to 4 85 km s in upper mantle consistently with p wave velocity variations results confirm the previously assumed high velocity lower crust and depression of moho in central finland

seismic structure and composition of the crust beneath the southern scandes norway abstract new results on p and s wave seismic velocity structure in southern norway indicate that the crust has an average poisson s ratio of 0 25 is predominantly of felsic intermediate composition and lacks a significant mafic lower crust a crustal scale refraction seismic study magnus rex mantle investigations of norwegian uplift structure refraction experiment acquired data along three 300 to 400 km long active source seismic profiles across the southwest scandinavian domain in southern norway the youngest section of the fennoscandian shield moho depths in the domain are 36 40 km thinning towards the continental shelf and oslo graben the high vp lower crust beneath the southwest scandinavian domain vp 7 km s is around 4 km thick crustal structure in the adjacent svecofennian domain differs significantly moho depths reach 50 km and an up to 24 km thick high vp lower crust is present strong p and s wave arrivals are recorded from magnus rex from which poisson s ratio for the crust is calculated the unusually strong s wave arrivals allow rare insight into crustal poisson s ratio structure that is not commonly available from active source data the thinness of the mafic lower crust in southern norway is in significant contrast to other parts of the fennoscandian shield and delamination or convective removal of the lower crust is proposed tectonic events that may have triggered detachment of the lower crust include extensional collapse after the caledonian orogeny and permian extension

age constraints on jerritt canyon and other carlin type gold deposits in the western united states relationship to mid tertiary extension and magmatism carlin type gold deposits are difficult to date and a wide range of ages has been reported for individual deposits therefore several methods were employed to constrain the age of the gold deposits in the jerritt canyon district dated igneous rocks with well documented crosscutting relationships to ore provided the most reliable constraints k ar and 40 ar 39 ar dates on igneous rocks are as follows andesite dikes 324 ma sericitic alteration in andesite dikes 118 ma basalt dikes 40 8 ma quartz monzonite dikes 39 2 ma and calc alkaline ignimbrites 43 1 to 40 1 ma of these only the andesite and basalt dikes are clearly altered and mineralized the gold deposits are therefore younger than the 40 8 ma basalt dikes the sericitic alteration in the andesite dikes is unrelated to the gold deposits a number of dating techniques did not work k ar and 40 ar 39 ar dates on mica from mineralized ordovician to devonian sedimentary rocks gave misleading results the youngest date of 149 ma from the smallest 187 os 188 os initial 0 9 3 6 but did not yield a meaningful isochron due to very low re and os concentrations and large analytical uncertainties paleomagnetic dating techniques failed because the hydrothermal fluids sulfidized nearly all of the iron in the host rocks leaving no remnant magnetism when published isotopic dates from other carlin type deposits in nevada and utah are subject to the rigorous evaluation developed for the jerritt canyon study most deposits can be shown to have formed between 42 and 30 ma k ar and 40 ar 39 ar dates on the youngest preore igneous rocks range from 41 to 32 ma whereas the oldest postore igneous rocks range from 35 to 33 ma hydrothermal adularia from the twin creeks deposit yields similar 40 ar 39 ar dates of 42 ma k ar dates on supergene alunite range from 4 to 30 ma k ar and 40 ar 39 ar dates on micas separated from sedimentary 395 43 ma and igneous 145 38 ma rocks are usually much older than the gold deposits and most are suspect because they are from incompletely reset preore micas or from mixtures of preore and ore stage mica fission track dates on zircons are also generally older than the deposits 169 35 ma and are not completely reset by mineralization apatites are likley to be reset by the hydrothermal systems and by younger thermal events and yield dates 83 22 ma that are younger than those from zircon independent support of a mid tertiary age is provided by the low delta d sub h 2 o values of hydrothermal fluids from 10 widely separated carlin type deposits 134 or 23ppm the low delta d sub h 2 o values are consistent with a mid tertiary age when the climate was cool but are inconsistent with the cretaceous and jurassic ages favored by some workers when the climate was warm the age and distribution of carlin type deposits coincides with areas that underwent extension and calc alkaline magmatism over the same time period despite this relationship the deposits lack clear spatial or genetic relationships to mid tertiary epizonal plutons rather many deposits are localized along preexisting crustal fault zones in the getchell trend structures tapped deep sourced metamorphic or magmatic fluids and subsequently variably exchanged meteoric water in the other trends and districts only variably exchanged meteoric water has been detected these relationships suggest either that all of the deposits formed from deep sourced fluids and were subsequently flooded by meteoric water or that fluids from different sources evolved to produce deposits with similar charateristics

the crustal structure along the polar profile from seismic refraction investigations abstract seismic refraction investigations along a 440 km long profije on the northern baltic shield have resolved the crustal structure in this area of archaean to early proterozoic lithosphere formation the profile called the polar profile extends approximately along a sw ne oriented line from the karelian province in northern finland across the lapland granulite belt and the kola peninsula province to the varanger peninsula in northeastern norway at six shotpoints large explosions 200 1680 kg and at three shotpoints small explosions 80 kg were detonated and recorded at an average station spacing of 2 km providing high quality record sections a two dimensional cross section of the crust was obtained by forward modelling using ray tracing techniques high velocity bodies are found in the upper crust related to the karasjok kittila greenstone belt and the lapland granulite belt they extend to a depth of 6 13 km in the karelian province in the southwest a low velocity zone was found between the depths of 8 and 14 km the middle crust shows a slight increase in the average velocities from the southwest to the northeast and a small velocity jump is found along a mid crustal boundary between 18 and 21 km the thickness of the middle crust varies between 16 and 18 km the lower crust and the crust mantle boundary moho show considerable lateral variation the top of the lower crust lies between 26 and 33 km while its thickness decreases from 21 km in the southwest to 10 14 km beneath the lapland granulite belt and the inari terrain reaching 20 km again in the extreme northeast the velocities also change laterally the thin lower crust is characterized by rather low velocities 6 8 6 9 km s whereas in the southwest and northeast the velocities 6 9 7 3 km s resemble more typical shield structures the moho is found at 47 km in the karelian province rises to 40 km beneath the lapland granulite belt and descends to 46 km in the northeastern part of the kola peninsula province the upper mantle velocities at the moho range from 8 1 km s in the region of the thin crust to 8 5 km s and more beneath the karelian province it is tempting to suggest that the anomalous lower crust underlying the lapland granulite belt and the inari terrain may represent the remnants of an early proterozoic back arc basin that was active prior to the 2 0 to 1 9 ga plate convergence event during which the lapland granulite belt was thrust onto the archaean basement of the karelian province another explanation is to assume that the velocity reduction in the anomalous lower crust was caused by a rather pronounced uplift of this region following the 1 9 ga collision event

does the golden spike still glitter a modus operandi for precambrian stratigraphy is suggested which combines the geochronometrical scale and late proterozoic chronostratigraphy the development of phanerozoic stratigraphical classification is followed from the pioneering days of murchison through the growing understanding of fossils in relation to time and the later distinction of rock and time rock to the advent of the golden spike criticisms of chronostratigraphy global standard stratigraphy are assessed and its value upheld stratigraphical procedures such as those of event stratigraphy are useful in particular situations but correlative methods in the phanerozoic are dominated by biostratigraphy examples are taken of its use and potential in north american cordilleran palaeozoic stratigraphy in the triassic system as a whole and in the caledonides of britain and ireland

stratigraphy and structure of the schoonover sequence northeastern nevada implications for paleozoic plate margin tectonics radiolarian biostratigraphy and detailed geologic mapping have been used to resolve the complex structure and stratigraphy of part of the golconda allochthon in the independence mountains nevada here the schoonover sequence is latest devonian to early permian in age spanning the time interval from the emplacement of the roberts mountains allochthon onto the shelf in the earliest mississippian antler orogeny to the inception of the sonoma orogeny the history of the schoonover basin is tied to that of the adjacent shelf in nevada and provides important insights into the upper paleozoic paleogeographic framework of the continental margin in the schoonover sequence latest devonian famennian chert overlies basaltic and andesitic greenstone and is in turn overlain by early mississippian kinderhookian chert interbedded with tuff and volcaniclastic rocks derived from an island arc the kinderhookian volcaniclastic rocks grade upward with no obvious depositional break into siliciclastic turbidites and pebbly mudstones that contain debris derived primarily from erosion of the antler orogenic belt although in some beds volcanic rock fragments and greenschist grade metasedimentary clasts are also common the age of underlying kinderhookian and interbedded and overlying osagian to meramecian chert sequences indicates that the siliciclastic turbidites are synchronous with the early deposits of the autochthonous foredeep basin of the antler orogenic belt the dual or composite source terranes represented by the schoonover siliciclastic rocks place the basin between an arc and the antler orogen on the edge of the shelf meramecian age basalt flows in the schoonover are coeval with subsidence and basaltic volcanism in autochthonous shelf sequences in northern nevada suggesting that a rifting event may have occasioned the end of antler age compression in nevada the onset of limestone turbidite deposition in the schoonover corresponds to the reestablishment of carbonate shelf conditions on the continental margin in latest mississippian earliest pennsylvanian time the late devonian earliest mississippian part of the schoonover depositional history has not yet been documented elsewhere in the golconda allochthon but late mississippian to permian rocks in the schoonover sequence are analogous to those of the havallah sequence suggesting deposition in the same basin thrust faults in the schoonover repeat the late devonian to permian section detaching the basinal sequence from its depositional basement thrust faults extend along strike for at least 10 km but thrust plates are the stratigraphic relations documented in the schoonover sequence are compatible with a back arc thrusting model for the formation of both the roberts mountains and golconda allochthons but they are more difficult to reconcile with models that interpret the allochthons as accretionary prisms developed in front of farther traveled arcs that collided with a passive margin in a broader context the stratigraphy of upper paleozoic allochthonous rocks in nevada records short lived episodes of crustal shortening along the continental margin separated by longer episodes of extensional and or transcurrent tectonics this data suggest that the western united states was a southwest pacific style active margin at least as far back as the devonian

the collapse behavior of a compacted soil during inundation the collapse behavior of a compacted uncemented soil is studied within a theoretical context consistent with the concepts of unsaturated soil mechanics experimental data are presented relating the initial matric suction of a compacted soil to its volume decrease during inundation the laboratory results indicate a unique relationship between the changes in matric suction i e ua uw where ua is the pore air pressure and uw is the pore water pressure of the compacted soil and the resulting volume reduction during inundation changes in the matric suction and total volume with respect to time were modelled using the theory of transient flow through an unsaturated soil the predicted results show reasonable agreement with the experimental observations the comparisons between the simulated results and the experimental data indicate that the coefficient of consolidation of the soil varies linearly with matric suction during the inundation process key words unsaturated soil matric suction collaps

highly varying radiogenic heat production in finland fennoscandian shield abstract radiogenic heat production in finland has been previously studied using airborne gamma ray surveys and glacial till measurements alike for the first time this paper presents a detailed survey on the spatial variation in radiogenic heat production determined using outcrop samples obtained from all important lithologies of the country the dataset of 6465 samples represents mostly mesoarchean about 2 7 ga paleoproterozoic ca 2 2 1 8 ga and mesoproterozoic ca 1 6 1 3 ga rocks nearly all data are from precambrian fennoscandian shield area but heat production appears to be highly variable and above global archean and proterozoic averages spot readings show an arithmetic average of 1 34 1 19 wm 3 and a range from 0 02 to 19 4 wm 3 the interpolated areal average of the whole area is 1 42 1 41 wm 3 the high standard deviation of data is related to the geochemical characteristics of uranium u thorium th and potassium k resulting in a skewed distribution of heat production mesoproterozoic anorogenic rapakivi granites and late paleoproterozoic svecofennian granitoids show the highest heat production values in the range of 3 5 wm 3 the results show no distinct dependencies of heat production with geological age metamorphic grade nor seismic p wave velocity but an increasing trend of heat production with sio2 content and decreasing trends of heat production with fe2o3 content and with rock density are evident surface heat flow 44 borehole data values correlates weakly with heat production r 0 35 the general heterogeneity of heat production calls for supporting information from other geophysical methods for better understanding of the thermal state of the lithosphere in finland and beyond

petrology and geochemistry of mafic granulite xenoliths from the lahtojoki kimberlite pipe eastern finland abstract the lahtojoki kimberlite pipe in kaavi eastern finland contains lower crustal mafic granulite xenoliths with a mineral assemblage cpx amph pl grt opx bt the tweequ thermobarometry indicates crystallization at ca 800 900 c and 0 75 1 25 gpa which corresponds with crustal depths of ca 22 38 km reaction textures and results of thermobarometry in some xenoliths indicate post peak decompression with cooling chemical composition of the xenoliths suggest that their protoliths crystallized from basaltic melts with some k enrichment their ree patterns are slightly lree enriched some xenoliths having small negative eu anomalies the u pb ion probe dating of zircons from two samples yielded variable ages for zircons even in the same xenolith between ca 2 6 and 1 7 ga these ages correspond with main late archaean and palaeoproterozoic orogenic events in the fennoscandian shield the sm nd garnet clinopyroxene isochron age from one dated sample is 1 6 ga which represents either a cooling or reheating of the lower crust by rapakivi magmatism because the petrology geochemistry and ages of xenoliths do not correlate well with the nearest exposed archaean mafic granulites it is evident that the present lower crust underlying the archaean rocks has a considerable palaeoproterozoic component

multi stage origin of the lower crust of the karelian craton from 3 5 to 1 7ga based on isotopic ages of kimberlite derived mafic granulite xenoliths abstract mafic garnet granulite xenoliths recovered from 500 to 600 ma old eastern finland kimberlites provide direct information on the petrology and physical properties of the lower cust below the archean karelian craton mineral thermobarometry together with isotopic petrological and seismic velocity constraints imply that the xenolith suite is derived from a geophysically determined dense high velocity layer at the base of the crust 40 58 km depth single grain zircon u pb dates and nd model ages t dm imply that this is a hybrid layer consisting of both archean and proterozoic mafic granulites zircon ages of up to 3 5 ga and nd t dm model ages 3 7 ga of the xenoliths are equivalent to those of the oldest upper crustal assemblages during the proterozoic transient heating of these archean granulites by voluminous basic magmatic intrusions resulted in multiple younger zircon generations within individual xenoliths the most important post archean lower crust growth took place during 1 9 ga accretion of the svecofennian arc complex to the craton margin when underplating proterozoic basaltic magmas became mingled with pre existing archean mafic granulites later post orogenic 1 80 1 73 ga transient heating of the lower crust occurred as a response to magmas ponded at the uppermost lithospheric mantle in conclusion karelian lower crust records the geological evolution of the craton margin environment through a period of nearly 4 billion years our data add a new piece to the emerging picture that emphasises the global importance of the 3 5 ga crustal growth episode we suggest that it represents a major mantle plume event more widespread than previously recognized when a significant fraction of paleoarchean continental crust was formed

geologic and geophysical evidence for the influence of deep crustal structures on paleozoic tectonics and the alignment of world class gold deposits north central nevada usa abstract geologic data concur with geophysical and isotopic data that suggest the presence of deep crustal fault zones along the battle mountain eureka bme trend and elsewhere in nevada the fault zones may have originated during proterozoic rifting of the continent and were likely substantially reactivated and modified during paleozoic tectonism five distinct paleozoic structural and stratigraphic domains are defined that demonstrate the complexity of paleozoic tectonic events and also lead to hypotheses about ways in which the margin could have been modified the current locations of these domains adjacent to the geophysically and isotopically defined indicators of the buried continent edge corroborate their interactions with the continental margin during the tertiary preexisting crustal fault zones were intersected and reopened during episodes of extension and served as the conduits for deep sourced gold rich fluids which were disseminated into paleozoic slope facies sedimentary rocks forming sediment hosted carlin type and other deposits multiple factors including the locations of these deep seated structures the original configuration of the lower paleozoic continental margin of nevada and its subsequent reactivation during the paleozoic all were fundamental controls on the location of younger mineral deposits a clearer understanding of the original configuration of the margin and of the effects of subsequent paleozoic and mesozoic tectonic events on the margin would provide insight into the locations of these and other prospective mineral belts

a mid permian chert event widespread deposition of biogenic siliceous sediments in coastal island arc and oceanic basins abstract radiolarian and conodont of permian siliceous rocks from twenty three areas in teh the circum pacific and mediterranean regions reveal a widespread permian chert event during the middle leonardian to wordian radiolarian and or sponge spicule rich siliceous sediments accumulated beneath high productivity zones in coastal island arc and oceanic basins most of these deposits now crop out in fault bounded accreted terranes biogenic siliceous sediments did not accumulate in terranes lying beneath infertile waters including the marine sequences in terranes of northern and central alaska the permian chert event is coeval with major phosphorite deposition along the western margin of pangea phosphoria formation and related deposits a well known analogue for this event is middle miocene deposition of biogenic siliceous sediments beneath high productivity zones in many parts of the pacific and concurrent deposition of phosphatic as well as siliceous sediments in basins along the coast of california interrelated factors associated with both the miocene and permian depositional events include plate reorientations small sea level rises and cool polar waters

an experimental investigation of the mechanical behavior and microstructural features of a volcanic soil isparta turkey and stability of cut slopes in this soil abstract volcanic soils are widely distributed group of soils which cover significant parts of the world s surface and include areas occupied by urban settlements structures and infrastructures and may create geo engineering problems these soils exhibit a distinctive behaviour that is a consequence of their formation history mineralogy and structure some part of the subsoil of a large area surrounding the city of isparta western turkey mainly consists of volcaniclastic deposits this paper presents the results of the part of a research programme aiming at geotechnically characterizing the uppermost layer of this volcaniclastic sequence particularly focusing on its collapse potential shear behaviour and the influence of microstructure on these behaviours in addition its main futures were compared with those of some similar volcanic soils at different parts of the world and the stability of sub vertical cuts in this soil was also assessed the experimental investigation mainly consisted of index and classification tests double oedometer and direct shear box tests to assess the collapse potential and shear behaviour of the soil respectively matric suction of the samples was also determined for preliminary evaluation of the influence of suction on collapse and shear behaviours of the soil in addition thin section studies and x ray diffraction xrd and scanning electron microscopy sem analyses were also conducted to determine mineralogical and microstructural features and to evaluate their influences on the mechanical behaviour of the volcanic soil the deposit is composed of weakly bonded firm silty sand with an open structure low unit weight and high porosity generally unsaturated in situ the results of the double oedometer tests suggest that the volcanic soil generally falls in the category of slight collapse potential at normal stresses ranging between 5 and 100 kpa while at normal stresses greater than 100 kpa its collapse potential increases and ranges between moderate and moderately severe collapse potential classes at normal stresses lower than 100 kpa matric suction may have an effect on collapse behaviour the direct shear box test results indicated that the volcanic soil has two different types of shear strength behaviour represented by bi linear failure envelopes in other words the shear strength parameters of the volcanic soil within a low normal stress range generally between about 6 and 200 kpa exceed those of determined at higher normal stresses since no matric suction was measured during the direct shear box tests it could not be possible to evaluate the effect of suction on the bi linear failure envelopes however some differences between the suction and degree of bonding of the samples taken from different locations might probably have been contributed to the separation of the bi linear behaviour at different normal stress levels the destruction of the bonding cementation between the particles is probably more responsible from the bi linear form of the failure envelope comparisons between the sem micrographs taken from natural and tested specimens revealed that the mechanical behaviour of the volcanic soil is strongly influenced by the bonding material the results of the stability analyses showed a good agreement with the current situation of the cut slopes observed in the study site and suggested that vertical cut slopes with a height of 14 15 m will maintain their stability based on a reasonable factor of safety such as 1 5

lithological interpretation of crustal composition in the fennoscandian shield with seismic velocity data abstract in this study we report the results of an investigation of lithological interpretation of the crust in the central fennoscandian shield in finland using seismic wide angle velocity models and laboratory measurements on p and s wave velocities of different rock types the velocities adopted from wide angle velocity models were compared with laboratory velocities of different rock types corrected for the crustal pt conditions in the study area the wide angle velocity models indicate that the p wave velocity does not only increase step wise at boundaries of major crustal layers but there is also gradual increase of velocity within the layers on the other hand the laboratory measurements of velocities indicate that no single rock type is able to provide the gradual downward increasing trends thus there must be gradual vertical changes in rock composition the downward increase of velocities indicates that the composition of the crust becomes gradually more mafic with increasing depth we have calculated vertical velocity profiles for a range of possible crustal lithological compositions the finnish crustal velocity profiles require a more mafic composition than an average global continental model would suggest for instance on the sveka 81 transect the calculated models suggest that the crustal velocity profiles can be simulated with rock type mixtures where the upper crust consists of felsic gneisses and granitic granodioritic rocks with a minor contribution of amphibolite and diabase in the middle crust the amphibolite proportion increases the lower crust consists of tonalitic gneiss mafic garnet granulite hornblendite pyroxenite and minor mafic eclogite assuming that these rock types are present in sufficiently extensive and thick layers they would also have sufficiently high acoustic reflection coefficients for generating the generally well developed reflectivity in the crust in the central part of the shield density profiles calculated from the lithological models suggest that there is practically no density contrast at moho in areas of the high velocity lower crust comparison of reflectors from fire 1 and fire 3 transects and the velocity model from sveka 81 wide angle transect indicated that the reflectors correlate with velocity layering but the three dimensional structures of the crust complicate such comparisons

crust and upper mantle structure along the dss baltic profile in se finland summary the 430 km long dss baltic profile in se finland runs through the rapakivi intrusion the svecokarelian geosynclinal complex including the ladoga bothnian bay zone and the archean basement complex a brief description of field operations in 1982 is presented record sections of p and s waves were used for the interpretations a starting model was constructed by inverse methods and improved by dynamic ray tracing modelling three blocks are indentified on the cross section from sw to ne these are the southern associated with the rapakivi massif depth to moho m about 40 km the central ladoga bothnian bay zone with m of approximately 55 60 km and the northern archean crystalline basement with m about 40 45 km the average crustal velocity is 6 6 6 7 kms the crustal structure along the baltic profile is compared with the surrounding dss profiles finnish sveka and soviet kern tulos and ladoga profiles the eastern border of the ladoga bothnian bay zone was located and specific features of the crust and uppermost mantle along the profile area are discussed

a sequence stratigraphic framework for the upper devonian woodford shale permian basin west texas criteria for recognizing stratigraphic sequences are well established on continental margins but more challenging to apply in basinal settings we report an investigation of the upper devonian woodford shale permian basin west texas based on a set of four long cores identifying sea level cycles and stratigraphic sequences in an organic rich shale the woodford shale is dominated by organic rich mudstone sharply overlain by a bioturbated organic poor mudstone that is consistent with a second order eustatic sea level fall interbedded with the organic rich mudstone are carbonate beds chert beds and radiolarian laminae all interpreted as sediment gravity flow deposits bundles of interbedded mudstone and carbonate beds alternate with intervals of organic rich mudstone and thin radiolaria rich laminae defining a 5 10 m 16 33 ft thick third order cyclicity the former are interpreted to represent highstand systems tracts whereas the latter are interpreted as representing falling stage lowstand and transgressive systems tracts carbonate beds predominate in the lower woodford section associated with highstand shedding at a second order scale chert beds predominate in the upper woodford section responding to the second order lowstand additional variability is introduced by geographic position wells nearest the western margin of the basin have the greatest concentration of carbonate beds caused by proximity to a carbonate platform a well near the southern margin has the greatest concentration of chert beds resulting from shedding of biogenic silica from a southern source a well in the basin center has little chert and carbonate here third order sea level cycles were primarily reflected in the stratigraphic distribution of radiolarian rich laminae

biostratigraphy of the caballos novaculite tesnus formation boundary marathon basin texas abstract the caballos novaculite is a radiolarian sponge spicule chert and siliceous mudstone which represents the final episode of a 200 ma span of dominantly biogenous hemipelagic sedimentation in marathon basin it is overlain by the tesnus formation an upward coarsening flysch sequence produced during the ouachita orogeny by the collision of laurasia and gondwana detailed radiolarian biostratigraphy of the boundary between these two units has provided greater age control as to the onset of flysch deposition and provides a greater understanding of the sedimentary patterns produced in ouachita basinal facies when switching modes of sedimentation from a passive to an active regime radiolarians and conodonts recovered from this interval show a hiatus equivalent to much of the early mississippian occurring in the vicinity of the boundary between the caballos and tesnus formations in three sections late mississippian meramecian radiolarians overlie earliest mississippian early kinderhookian radiolarians in an apparently conformable sequence of siliceous shale in a fourth section meramecian radiolarians overlie late devonian famennian radiolarians and conodonts separated by a conglomerate layer these data indicate that a hiatus equivalent to the late kinderhookian to osagean time period is present and that local erosion into the famennian part of the section occurred lithostratigraphically this hiatus is coincident with the caballos novaculite tesnus formation boundary in the central part of the basin while at the western margin it occurs 8 m above the base of the tesnus formation immediately above a clastic zone containing olistoliths results from this investigation show that localized deposition of olistoliths occurred in the western basin margin during the famennian late devonian followed by an interval of non deposition in the early mississippian finally basin wide flysch deposition in the meramecian

composition of the crust in the grenville and appalachian provinces of north america inferred from v p v s ratios we use the ratios between p and s wave velocities vp vs derived from seismic refraction data to infer the composition of the crust in the grenville and the appalachian provinces of north america the crust exhibits vp vs increasing with depth from 1 64 to 1 84 there is a clear distinction between the grenville province average vp vs 1 81 and the appalachian province average vp vs 1 73 which persists at all depths the boundary between these provinces is east dipping extending for 100 km east of the champlain thrust in the appalachian province the increase in vp vs ratios with depth from 1 67 to 1 74 0 02 may reflect a normal decrease of silica content in the continental crust in the grenville province beneath the central granulite terrane an anomalous vp vs ratio of 1 82 0 02 is observed extending to a depth of 10 km this correlates with the abundance of ca plagioclase in the marcy anorthosite at greater depth 15 20 km where seismic lamination and high electrical conductivity is observed vp vs is 1 84 0 02 and correlates with the tahawus complex a layered mafic intrusion within the 25 km thick lower crust of the grenville province the vp vs is 1 84 0 02 and p velocity is 7 0 0 1 km s which are typical for plagioclase bearing rocks gabbro norite the high vp vs ratio in the grenville province has not been reported in crust of any other age since the grenville province contains 75 of the world s known anorthosites high vp vs ratio is related to high plagioclase we suggest that the composition of the grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid proterozoic

nina creek group and lay range assemblage north central british columbia remnants of late paleozoic oceanic and arc terranes in north central british columbia a belt of upper paleozoic volcanic and sedimentary rocks lies between mesozoic arc rocks of quesnellia and ancestral north america these rocks belong to two distinct terranes the nina creek group of the slide mountain terrane and the lay range assemblage of the quesnel terrane the nina creek group is composed of mississippian to late permian argillite chert and mid ocean ridge tholeiitic basalt formed in an ocean floor setting the sedimentary and volcanic rocks the mount howell and pillow ridge successions respectively form discrete generally coeval sequences interpreted as facies equivalents that have been interleaved by thrusting the entire assemblage has been faulted against the cassiar terrane of the north american miogeocline west of the nina creek group is the lay range assemblage correlated with the harper ranch subterrane of quesnellia it includes a lower division of mississippian to early pennsylvanian sedimentary and volcanic rocks some with con

composition of the uralide crust from seismic velocity v p v s heat flow gravity and magnetic data abstract p wave velocity vp s wave velocity vs poisson s ratio heat flow potential field and surface geological data are integrated to constrain a model for the composition of the uralide crust along the urseis transect the model is constructed using published laboratory measurements of vp vs and density for a variety of crustal rock types these laboratory data have been corrected for depth pressure and the uralides temperature depth function the model shows clear differences between the composition of the old continental crustal nucleus of the east european craton and the newly added crust of the accreted arc terranes to the east the crust of the east european craton is more felsic than that of the magnitogorsk and east uralian zones and the latter two have a lowermost crust whose characteristics indicate a high garnet content mafic garnet granulite and or the presence of hornblendite the overall composition of the arc terranes is basaltic physical properties suggest that eclogite is not present in the arc terranes or if present it exists in small amounts that are below the resolution of the data set the lack of eclogite in the lower crust favours an intracrustal differentiation model for the evolution of the bulk composition of the continental crust nevertheless the absence of surface uplift the lack of metamorphism and late orogenic mantle melts and the current crustal thickness indicate that crustal thinning did not affect the bulk composition of the uralide crust

analog modeling of one way gravitational spreading of hot orogens a case study from the svecofennian orogen fennoscandian shield abstract geodynamic models offer insight into deformation styles of syn and post collisional extensional processes such models often ignore the effect of lateral viscosity contrast between accreted terranes and inherited tectonic boundaries this paper presents a set of crustal scale analog experiments of one way post collisional gravitational spreading testing the effect of crustal heterogeneity by using two mechanically contrasting blocks pre existing cuts with varying dips and three layers with contrasting rheologies two blocks represent strong mature and weak juvenile crustal parts both blocks have three horizontal crustal layers brittle upper weak partially molten middle and dry strong lower layer cuts represent pre existing crustal scale shear zones and tectonic boundaries the experiments indicated that tectonic boundaries may facilitate exhumation and increase extensional strain when the boundaries dip opposite to the flow direction the tectonic boundaries may also split and divide the crust into separate blocks with independent deformation signatures shortening elongation or rotation the tectonic boundaries rotated along vertical axes toward the flow direction the modeling results suggest that in areas with inherited tectonic boundaries and compositional differences the amount of extension is unevenly distributed between the different parts during the widespread unilateral gravitational spreading and that the flow has different effects on the contrasting crustal units in both lateral and vertical directions to validate the modeling the results are compared to geophysical and geological data from the paleoproterozoic svecofennian orogen in the fennoscandian shield the comparison suggests that the orogen underwent 50 extension and was thinned by maximum of 20 via westward gravitational spreading this spreading rotated the crustal scale blocks shear zones and tectonic contacts it also brought exhumed high grade middle crustal blocks into contact with subsided low grade upper crustal blocks we suggest that results of the analog models can be used as proxies in both ancient and modern hot accreted orogens which have undergone post convergence continental mid crustal weakening and have comprised of juxtaposed terranes with varying rheological compositions

three stages to form a large batholith after terrane accretion an example from the svecofennian orogen abstract the magmatic history of batholiths formed as the result of tectonic accretion mirrors the evolution of the underlying crust from island arcs to accretion and collapse chemical composition age and structure give information about the magma source and emplacement depths the target of this study is the central finland batholith cfgc that provides a magmatic record after terrane accretion during the svecofennian orogeny followed by orogenic collapse the crustal source of partial melting has changed during the crustal evolution and differentiation after the terrane accretion and when the stress regime has changed from contraction to extension here we present a three stage magmatic evolution model for accretional batholith in the svecofennian orogen in the first stage the lower crust of the accreted crust melts partially and produces calcic tonalitic melts that are emplaced above the upper middle crustal detachment zone group 1 1887 3 ma in the second stage the middle crust begins to melt producing calc alkalic granodioritic melts that are emplaced close to the surface group 2 1890 1886 ma and at both sides of the upper middle crustal detachment zone group 2 1884 1883 ma in the third stage the lower crust remelts and produces bimodal calc alkalic gabbroic and alkali calcic to alkalic granitic melts group 3 1881 1880 ma which are emplaced above the upper middle crustal detachment zone this kind of crustal differentiation produces a mafic lower an intermediate middle and a felsic upper crust the third stage represents the last magmatic event of the svecofennian accretional orogeny where the high velocity lowermost crust is formed during this stage crustal thickening and widespread mid crustal partial melting have inititated lateral flow after or concurrently with the emplacement of the group 2 granodiorite the lateral flow has reactivated large scale shear zones allowing the transportation of the group 3 rocks from the lower crust to the upper middle crustal detachment zone the change in the degree of deformation at the exposed parts from undeformed through local to pervasive is attributed to differences in the exhumation level

timing of exhumation wheeler pass thrust sheet southern nevada and california late jurassic to middle cretaceous evolution of the southern sevier fold and thrust belt zircon u th he zhe thermochronologic data for 46 samples from the wheeler pass thrust sheet which carries thick passive margin strata and is discontinuously exposed across the southern part of the sevier fold and thrust belt record late jurassic cooling related to exhumation during early thrust slip and local middle cretaceous cooling related to footwall basement imbrication within the frontal part of the wheeler pass sheet exposed in the northwest spring mountains zhe ages decrease from ca 160 to 140 ma over a paleodepth interval of 6 to 9 km in devonian to lower cambrian strata interpreted to record exhumation and enhanced cooling above a frontal ramp followed by slow cooling a similar pattern of zhe ages occurs over a more limited paleodepth range exposed within the resting spring range to the south in the nopah range zhe ages of ca 140 ma in lower cambrian strata record early cooling followed by slow cooling until ca 100 ma zhe ages in underlying paleoproterozoic basement rocks decrease from ca 100 to 85 ma over a paleodepth interval of 9 to 12 km interpreted to record uplift exhumation and cooling during footwall basement imbrication as slip was transferred eastward onto the keystone thrust system late jurassic slip on the wheeler pass thrust overlapped with deformation along the nw trending east sierran thrust system early hinterland crustal thickening and growth of the sierra magmatic arc and may have been correlative with early deformation in the central nevada thrust belt slip on the wheeler pass thrust preceded major slip on other thrust sheets that carried thick passive margin strata in more northern parts of the sevier belt probably reflecting the influence of different initial widths and tapers of the passive margin sedimentary wedge

experimental investigation of foundation on collapsible soils abstractgeotechnical engineers face serious problems when building on collapsible soils these types of soil show considerable strength when dry and experience excessive and sudden settlement when

speculative reconstruction of the mojave snow lake fault implications for paleozoic and mesozoic orogenesis in the western united states available evidence suggests that the mojave snow lake fault a major early cretaceous dextral fault with up to 400 km displacement formerly existed in what is now the axial part of the sierra nevada batholith regional relations suggest that the fault formerly continued in western nevada the mojave desert and in rocks now exposed in the salinian block restoration of 400 km of early cretaceous dextral displacement on the mojave snow lake fault leads to speculative but testable reconstructions of mesozoic and paleozoic tectonic features of california and nevada insights derived from these reconstructions include the following 1 two regionally extensive jurassic thrust belts of opposed vergence appear to have intersected in the northern sierra nevada the eastern east vergent thrust belt which includes the fencemaker and liming thrusts in western nevada and several east vergent thrusts in the northern sierra may be a contractional belt along which an early jurassic interarc or marginal basin was closed in middle to late jurassic time the western west vergent thrust belt is part of the classic nevadan orogen of the western klamath mountains and the western sierra metamorphic belt in which collisions and or thrusting of various island arc terranes occurred during middle and late jurassic time 2 the early mesozoic continental arc included paired belts of triassic jurassic blueschist and melange and igneous rocks including late triassic and younger plutons and volcanic rocks this conclusion is not new but the reconstruction provides a slightly different geometry than previously thought 3 sonomia the late paleozoic island arc terrane of the western u s may have formed a relatively narrow belt extending from northwestern nevada to the latitude of the western mojave desert the geologic development of the paleozoic basement complex of sonomia was very different from that of the cordilleran miogeocline in death valley and the mojave desert requiring that a continuation of the sonoma suture belt or golconda thrust must have extended southward through the sierra nevada batholith to the mojave region 4 a heterogeneous belt of permian to triassic or triassic deformation in the mojave and eastern sierra nevada together with the golconda allochthon in nevada may represent the protracted response to the collision of sonomia with the western margin of north america the contractional deformation continued during the evolution of the early mesozoic continental arc 5 several predictions can be made about the nature of concealed basement within the sierra nevada batholith and within western nevada the reconstruction suggests that elements of the antler and sonoma orogenic belts should underlie areas of the batholith and western nevada as a result of northward displacement along the mojave snow lake fault from the western mojave and southern sierra nevada

laboratory measurements of the seismic velocities and other petrophysical properties of the outokumpu deep drill core samples eastern finland summary petrophysical in particular seismic velocity measurements of the outokumpu deep drill core depth 2 5 km have been carried out to characterize the geophysical nature of the paleoproterozoic crustal section of eastern finland and to find lithological and geophysical interpretations to the distinct crustal reflectors as observed in seismic surveys the results show that different lithological units can be identified based on the petrophysical data the density of the samples remained nearly constant throughout the drilled section only diopside tremolite skarns and black schists exhibit higher densities the samples are dominated by the paramagnetic behaviour with occasional ferromagnetic signature caused by serpentinitic rocks large variations in seismic velocities both at ambient pressure and under in situ crustal conditions are observed the porosity of the samples which is extremely low is either intrinsic by nature or caused by decompaction related to fracturing during the core retrieval it is noteworthy that these microfractures have dramatically lowered the vp and vs values from the measured velocities and density data we have calculated the seismic impedances young s modulus and poisson s ratios for the lithological units of the outokumpu section and from these data the reflection coefficients for the major lithological boundaries evident in the surveyed section were determined the data show that the strong and distinct reflections visible in wide angle seismic surveys are caused by interfaces between diopside tremolite skarn and either serpentinites mica schist or black schist

the lower cretaceous king lear formation northwest nevada implications for mesozoic orogenesis in the western u s cordillera cretaceous paleogeography of the u s cordillera west of the sevier fold and thrust belt is poorly known due to the scarcity of cretaceous supracrustal rocks in the arc and backarc regions the lower cretaceous king lear formation exposed in the jackson mountains and the krum hills of northwest nevada provides a rare and important record of early cretaceous tectonism and paleogeography our work shows that the king lear formation everywhere overlies deformed and metamorphosed triassic jurassic rocks across a major unconformity the king lear formation is dominated by conglomerates and sandstones deposited in subaerial alluvial fan and gravelly braided river systems and it can be divided into three new members based on differences in clast provenance a lower member derived from local arc and backarc rocks a middle member dominated by externally derived quartzite and chert clasts and an upper member derived largely from an intrabasinal volcanic complex sedimentary features and provenance analysis indicate that clasts in the middle member were derived from nearby exposures of paleozoic rocks such as the roberts mountains and golconda allochthons which must have formed a topographically elevated area in central nevada during the early cretaceous the stratigraphic record provides evidence of deposition in a tectonically active basin in contrast with some prior studies inferring that deposition was synchronous with contractional deformation our new field observations structural data and a shallow seismic reflection profile confirm that the king lear formation was deposited in an active half graben in the jackson mountains these results provide new upper age constraints on the timing of shortening deformation in the arc and backarc regions shortening must have been complete not only before deposition of the king lear formation in the middle early cretaceous but also prior to several kilometers of exhumation of its depositional basement possible driving forces for extension leading to development of the king lear basin include relaxation of thick crust in the hinterland of thrust belts to the east stresses associated with regional tilting and development of dynamic topography and stresses related to dextral strike slip deformation to the west

receiver function analysis of the crust and upper mantle in fennoscandia isostatic implications abstract the mountains across southern norway and other margins of the north atlantic ocean appear conspicuously high in the absence of recent convergent tectonics we investigate this phenomenon with receiver functions calculated for seismometers deployed across southern fennoscandia these are used to constrain the structure and seismic properties of the lithosphere and primarily to measure the thickness and infer the bulk composition of the crust such parameters are key to understanding crustal isostasy and assessing its role or lack thereof in supporting the observed elevations our study focuses on the southern scandes mountain range that has an average elevation 1 0 km above mean sea level the crust mantle boundary moho is ubiquitously imaged and we occasionally observe structures that may represent the base of the continental lithosphere or other thermal chemical or viscous boundaries in the upper mantle the moho resides at 25 30 km depth below mean sea level in southeastern coastal norway and parts of denmark 35 45 km across the southern scandes and 50 60 km near the norwegian swedish border that section of thickest crust coincides with much of the transscandinavian igneous belt and often exhibits a diffuse conversion at the moho which probably results from the presence of a high wave speed mafic lower crust across inner fennoscandia a zone of thinned crust

pds receiver function evidence for crustal scale thrusting relic subduction and mafic underplating in the trans hudson orogen and yavapai province a b s t r a c t article history the trans hudson orogen tho in the north central united states represents a major suturing event between the wyoming and superior archean provinces it is bounded to the south by the ne sw striking yavapai province which was accreted along the southeastern margin of north america between 1 71 and 1 68 ga and was one of a series of major collisional events responsible for the assembly of laurentia in this study pds teleseismic receiver functions were used to investigate the deep crustal structure associated with these collisions using data from over 800 broadband seismic stations distributed throughout the great plains midcontinent region we calculated 0 5 hz receiver functions using 245 m 6 0 teleseismic events the receiver functions were then ccp common conversion point stacked to create a 3d image volume profiles through this image volume show evidence of crustal scale thrusting of the wyoming province in the west over the superior province in the east and a relic subduction zone associated with the yavapai superior boundary we also performed a density analysis of the region using relative amplitude of the 2p1s and 0p1s receiver function phases from 233 stations these data indicate a relatively low moho density contrast throughout the tho and northern yavapai province associated with a region of thickened crust 50 km which we interpret to be evidence of a dense lower crustal layer that is the result of mafic underplating