origin of fine scale sheeted granites by incremental injection of magma into active shear zones examples from the pilbara craton nw australia in the archaean pilbara craton of western australia three zones of heterogeneous centimetre to metre scale sheeted granites are interpreted to represent high level syn magmatic shear zones evidence for the syn magmatic nature of the shear zones include imbricated and asymmetrically rotated metre scale orthogneiss xenoliths that are enveloped by leucogranite sheets that show no significant internal strain at another locality granite sheets have a strong shape preferred alignment of k feldspar suggesting magmatic flow while the asymmetric recrystallisation of the grain boundaries indicates that non coaxial deformation continued acting upon the sheets under sub solidus conditions elsewhere randomly oriented centimetre wide leucogranite dykes are realigned at a shear zone boundary to form semi continuous layer parallel sheets within a magma dominated dextral shear zone it is proposed that the granite sheets formed by the incremental injection of magmas into active shear zones magma was sheared during laminar flow to produce the sheets that are aligned sub parallel to the shear zone boundary individual sheets are fed by individual dykes with up to 1000s of discrete injections in an individual shear zone the sheets often lack microstructural evidence for magmatic flow either because the crystal content of the magma was too low to record internal strain or because of later recrystallisation

mafic and felsic magma interaction in granites the hercynian karkonosze pluton sudetes bohemian massif the hercynian post collisional karkonosze pluton contains several lithologies equigranular and porphyritic granites hybrid quartz diorites and granodiorites microgranular magmatic enclaves and composite and lamprophyre dykes field relationships mineralogy and majorand trace element geochemistry show that 1 the equigranular granite is differentiated and evolved by small degrees of fractional crystallization and that it is free of contamination by mafic magma 2 all other components are affected by mixing the end members of the mixing process were a porphyritic granite and a mafic lamprophyre the degree of mixing varied widely depending on both place and time all of the processes involved are assessed quantitatively with the following conclusions most of the pluton was affected by mixing implying that huge volumes 475 km of mafic magma were available this mafic magma probably supplied the additional heat necessary to initiate crustal melting part of this heat could have also been released as latent heat of crystallization only a very small part of the karkonosze granite escaped interaction with mafic magma specifically the equigranular granite and a subordinate part of the porphyritic granite minerals from these facies are compositionally homogeneous and or normally zoned which together with geochemical modelling indicates that they evolved by small degrees of fractional crystallization 520 accessory minerals played an important role during magmatic differentiation and thus the fractional crystallization history is better recorded by trace rather than by major elements the interactions between mafic and felsic magmas reflect their viscosity contrast with increasing viscosity contrast the magmatic relationships change from homogeneous hybrid quartz diorites granodiorites to rounded magmatic enclaves to composite dykes and finally to dykes with chilled margins these relationships indicate that injection of mafic magma into the granite took place over the whole crystallization history consequently a long lived mafic source coexisted together with the granite magma mafic magmas were derived either directly from the mantle or via one or more crustal storage reservoirs compatible element abundances e g ni show that the mafic magmas that interacted with the granite were progressively poorer in ni in the order hybrid quartz dioritescgranodioritescenclavesccomposite dykes this indicates that the felsic and mafic magmas evolved independently which in the case of the karkonosze granite favours a deep seated magma chamber rather than a continuous flux from mantle two magma sources mantle and crust coexisted and melted almost contemporaneously the two reservoirs evolved independently by fractional crystallization however mafic magma was continuously being intruded into the crystallizing granite with more or less complete mixing several lines of evidence e g magmatic flux structures incorporation of granite feldspars into mafic magma feldspar zoning with fluctuating trace element patterns reflecting rapid changes in magma composition indicate that during its emplacement and crystallization the granite body was affected by strong internal movements these would favour more complete and efficient mixing the systematic spatial temporal association of lamprophyres with crustal magmas is interpreted as indicating that their mantle source is a fertile peridotite possibly enriched metasomatized by earlier subduction processes

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

curie point depths in northeast china and their geothermal implications for the songliao basin abstract this work integrates processing and interpretation of the combined geomagnetic anomaly model of ngdc 720 v3 1 to better constrain thermal structures of the northeast china lithosphere which shows intensive extension and active volcanism during the mesozoic and cenozoic numerical tests demonstrate that magnetic anomalies calculated at 20 km altitude can be used for accurate curie depth estimation averaged curie depths using a 3d fractal exponent of 3 0 vary from 13 2 0 to 33 4 1 km with a mean of 22 2 4 km in northeast china with temperature dependent thermal conductivity models constrained by incorporated surface heat flow and curie depths in different geological blocks the thermal lithospheric thicknesses are estimated mostly between 45 and 90 km based on 1d steady state thermal conduction equation beneath the songliao basin the moho temperatures are abnormally high ranging from ca 700 to 1000 c and the mantle contributes about 65 of the total surface heat flow the shallow curie points and thermal lithosphere asthenosphere boundary together with high moho temperatures and mantle heat flow support abnormally high geotherms in the songliao basin originated from hot upper mantle upwelling triggered likely by lithospheric delamination

shrimp u pb zircon geochronology and thermal modeling of multilayer granitoid intrusions implications for the building and thermal evolution of the central system batholith iberian massif spain abstract this work shows the results of a u pb shrimp zircon geochronological study of the central part of the gredos massif spanish central system batholith the studied batholith is composed of several granodiorite and monzogranite tabular bodies around 1 km thick each intruded into partially molten pelitic metasediments granodiorites and monzogranites belonging to three distinct intrusive bodies and samples of anatectic leucogranites have been selected for shrimp u pb zircon geochronology distinct age groups separated by up to 20 ma have been distinguished in each sample important age differences have also been determined among the most representative age groups of the three analyzed granitoid bodies 312 6 2 8 ma for the circo de gredos bt granodiorites floor intrusive layer 306 9 1 5 ma for the barbellido plataforma granitoids top intrusive layer and 303 5 2 8 ma for las pozas crd monzogranites middle intrusive layer these age differences are interpreted in terms of sequential emplacement of the three intrusive bodies contemporary with the late paleozoic d3 deformation phase the anatectic leucogranites are coeval to slightly younger than the adjacent intrusive granodiorites and monzogranites 305 4 1 6 ma for refugio del rey leucogranites and 303 2 ma for migmatitic hornfelses it is suggested that these anatectic magmas were generated in response to the thermal effects of granodiorite intrusions thermal modeling with comsol multiphysics reveals that sequential emplacement was able to keep the thermal conditions of the batholith around the temperature of zircon crystallization in granitic melts around 750 c for several million of years favoring the partial melting of host rocks and the existence of large magma chambers composed of crystal mush prone to be rejuvenated after new intrusions

crustal magnetic anomaly in the ordos region and its tectonic implications abstract in this paper the ngdc 720 v3 model is utilized to investigate the distribution of crustal magnetic anomaly and curie surface in the ordos block and its surrounding areas the curie surface is compared with the regional heat flow bouguer anomalies moho and seismicity the interior block has strong wide distributed magnetic anomalies well corresponding to the basement lithofacies the surrounding areas have weak anomalies of various strikes and intensities the magnetic anomaly confirms the geological finding that the yabulai and bayanhot basins are small blocks detached from the northern ordos block the magnetic anomalies at the satellite altitude reveal that deep materials flow northward from the northeast margin of tibet plateau to the qilian fold belt the depth of curie surface ranges from 24 to 42 km and the ordos block is dominated by curie surface depth over 32 km and average heat flow value of 44 mw m2 the distribution of bouguer anomalies is consistent with that of magnetic anomalies the well correlation between the curie surface and the seismicity is also explained

seismic signature of the mantle transition zone beneath eastern tibet and sichuan basin abstract the strong interaction between the eastward flow escaping from tibet and the rigid sichuan basin resulted in the rise of the longmenshan however the detailed dynamics in the mantle remains controversial in this study the structure of the mantle transition zone mtz beneath eastern tibet and sichuan basin is investigated using 5080 receiver functions from 51 broadband stations the depth of the 410 km discontinuity is close to the global average except for the longmenshan where the 410 and 660 km discontinuities are found to be depressed by up to 10 25 km and 5 10 km respectively the observed simultaneous depressions of the 410 and 660 km discontinuities distributed along the lms together with proofs from tomography and regional tectonics suggest that asthenospheric flow sinks into the mtz resulting in a high velocity zone as well as variation in the mtz thickness the depressions are not from the traditional clapeyron slopes or temperature variation also the depression of the 410 km discontinuity and the dehydration of wadsleyite are syngenetic both of which originate from the dry mantle flow traveling across the old 410 km interface

palaeozoic amalgamation of central europe new results from recent geological and geophysical investigations abstract multidisciplinary studies of geotransects across the north european plain and southern north sea and geological reexamination of the variscides of the north bohemian massif permit a new 3 d reassessment of the relationships between the principal crustal blocks abutting baltica along the trans european suture zone tesz accretion was in three stages cambrian accretion of the bruno silesian lysogory and malopolska terranes end ordovician early silurian accretion of avalonia and early carboniferous accretion of the armorican terrane assemblage ata palaeozoic plume influenced metabasite geochemistry in the bohemian massif explains the progressive rifting away of peri gondwanan crustal blocks before their accretion to baltica geophysical data faunal and provenance information from boreholes and dated small inliers and cores confirm that avalonian crust extends beyond the anglo brabant deformation belt eastwards to northwest poland the location and dip of reflectors along the tesz and beneath the north european plain suggest that avalonian crust overrode the baltica passive margin marked by a high velocity lower crustal layer on shallowly southwest dipping thrust planes forming the heligoland pomerania deformation belt the variscan orocline of southwest poland masks two junctions between the armorican terrane assemblage ata and previously accreted crustal blocks to the east is a dextrally transpressive contact with the bruno silesian and malopolska blocks accreted in the cambrian while to the north is a thrust contact with easternmost avalonia deeply buried beneath younger sedimentary cover in the northeast bohemian and rhenohercynian massifs devonian early variscide deformation dominated by wnw and nw directed thrusting records closure of ordovician devonian seaways between detached islands of the ata and avalonia

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

multiple injections of magmas along a hercynian mid crustal shear zone sila massif calabria italy abstract syn tectonic late hercynian granitoids emplaced at mid crustal level through multiple dyke injections are well exposed in a 1 km long section in the southern sila massif calabria italy the fieldwork study permitted us to reconstruct the following order of emplacement i granodiorites with euhedral kfs megacrystals grd1 in the main text and heterogranular granodiorites with coarse rounded pl and kfs in a fine grained biotite rich matrix grd2 ii granodiorites with a nearly homogeneous grain size grd3 iii tonalite and iv granite both in the wall rock represented by migmatitic paragneisses and in the deformed granitoids the foliation attitude is substantially homogeneous striking about n140 with a dip of 50 60 to the ne the magmatic lineation is defined by the preferred alignment of euhedral feldspars parallel to the mineral lineation observed in the host rocks micro and meso structural analyses indicate that foliation evolved from melt present to solid state conditions feldspar tiling s c structures type structures c axis quartz orientations commonly suggest a top to the west sense of shear during magma injection and deformation under decreasing temperatures age of magma emplacement is constrained by u pb datings at 304 300 ma coeval with the regional metamorphic peak foliated granitoids and wall rock are intruded by poorly foliated hbl gabbro and finally by undeformed leucogranite pegmatite and felsic porphyritic dykes new u pb datings of the last intrusion event indicate an age of emplacement of 281 8 ma providing a minimum estimate for the end of the shear strain at mid crustal level

a review on active tectonics and deep crustal processes of the western sichuan region eastern margin of the tibetan plateau abstract one of remarkable geological and geomorphological features in continental china is the presence of a north south trending tectonic zone which separates the seismically active tibetan plateau to the west from the tectonically stable south china and ordos blocks to the east the zone also owns a name of north south seismic belt as a large number of great historical earthquakes occur on it the most recent one the 2008 wenchuan earthquake attests its recent tectonic activity in this review i take the western sichuan region as an example to probe the structural styles and kinematic pattern as well as deep geological process associated with tectonic deformation of the north south trending zone through integrated studies on active faults gps crustal deformation and geophysical structure we show that deformation in the western sichuan is governed by interactions among three crustal blocks songpan chuandian and south china of distinctive rheological properties under the tectonic framework that eastward growth of the soft eastern tibet is blocked by the hard lithosphere of the south china block the left lateral xianshuihe fault continues to the north south trending fault system without crustal shortening to form a bounding fault to limit the northern extend of the magnificent clockwise rotation of crustal material around the eastern himalaya syntax upper crust of the three blocks is dominated by brittle deformation whereas the ductile flow of lower crust would drag the brittle upper crustal blocks to move with respect to each other the relative motions among the brittle upper crustal blocks cause strain accumulations among their bounding faults to generate large earthquakes deformation of the western sichuan region can thus be described in terms of combined model of rigid block movement and continuous deformation we suggest this combined model can be applied to entire continental china

origin of rare earth element signatures in groundwaters of circumneutral ph from southern nevada and eastern california usa concentrations of the rare earth elements ree were measured in circumneutral ph groundwaters from southern nevada and death valley ca groundwaters from the regional lower paleozoic carbonate rock aquifer cambrian devonian have flat shale normalized patterns that closely resemble the shale normalized patterns of the aquifer rock samples principally cambrian groundwaters associated with younger carbonate rocks chiefly permian in the study region exhibit heavy ree hree enriched shale normalized ree patterns with substantial negative ce anomalies that also mimic these carbonate rocks in addition groundwaters from the felsic volcanic rock aquifers have the same flat to light ree lree enriched shale normalized patterns with large negative eu anomalies as the felsic volcanic rocks the similar ree patterns of all the groundwaters and associated aquifer rocks studied suggest that the groundwaters inherited ree signatures from the host rocks through which they flow because negative ce anomalies are not an uncommon feature of carbonate rocks of marine origin the negative ce anomalies reported here for these groundwaters may reflect a permian marine ce signature previously we demonstrated that carbonate complexes dominate ree speciation in southern nevada and death valley groundwaters moreover solid liquid partitioning coefficients kd indicate that the affinity of lrees to sorb to aquifer surface sites is substantially greater than for the hrees in the southern nevada carbonate and felsic volcanic rock alluvial aquifers consequently the hrees enrichments reported here for groundwaters associated with younger paleozoic carbonate rocks compared to these source rocks is consistent with ree carbonate complexation and preferential removal of lrees to aquifer surface sites

from valley to marginal glaciation in alpine type relief lateglacial glacier advances in the piec stawow polskich roztoka valley high tatra mountains poland abstract the piec stawow polskich roztoka valley in the high tatras western carpathians features typical alpine type relief with a deeply incised glacial trough and large compound trough head cirque the prominent hypsographic maximum in the valley 1680 2000 m along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms specifically the most recent lateglacial advances the valley has been intensively studied before in the context of glacial chronology in this paper we re establish the post last glacial maximum lgm glacial chronology of the valley via detailed geomorphologic mapping equilibrium line altitude ela reconstruction and schmidt hammer sh dating along with a critical review of previously published cosmogenic exposure age data 36 cl and lacustrine sediment chronology our results indicate that the first four of the five distinguished lateglacial stages roztoka i iii pusta i occurred before the bolling allerod b a interstadial thus virtually the entire valley became deglaciated in course of the oldest dryas cold phase a distinct reorganization of deglacial patterns from valley type to marginal type occurred before b a warming when the ela increased above the valley hypsographic maximum concentrated at the cirque bottom elevation it shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing this points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions we infer that glaciers vanished in the tatra mountains during the b a interstadial later a renewed advance during the younger dryas pusta ii formed a nearly continuous festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls furthermore we discus some paleoenvironmental significance of the geomorphological record in the valley as well the applicability of sh dating in constructing glacial chronology

crustal thickness and lithospheric thermal state beneath the junggar basin and adjacent mountain ranges northwest china abstract in this paper data of gravimetry aeromagnetic survey and surface heat flow are utilized in a combined manner to investigate the crustal thickness curie surface and lithospheric thermal state beneath the junggar basin and adjacent mountain ranges the moho depth curie depth and thermal lithospheric thickness are found to be 38 52 km 32 50 km and 120 260 km respectively the moho and curie surface present a rough inverse correspondence between each other in the tianshan and altai mountain ranges moho interface is deep but curie surface is shallow in the junggar basin turpan basin and yili basin the situation is in reverse the uppermost mantle in the central depression and eastern uplift of the junggar basin the turpan basin the yili basin as well as the north west area off fuhai is investigated to have been magnetized the aeromagnetic anomalies and the curie surface in the junggar basin surprisingly reveal that the northward subduction of the north tarim block slab under the junggar basin accompanied by the uplift of the tianshan mountain range also in response to the northward movement the rigid central depression of the junggar basin extruded from its east and west sides the westward extrusion is manifested by the west uplift of the western junggar mountain range

s receiver function analysis of the crustal and lithospheric structures beneath eastern tibet abstract s receiver functions from 51 permanent broad band stations are used to investigate the structures of the crust and lithosphere beneath eastern tibet and sichuan basin by stacking the s receiver functions the sp converted phases from the moho and the lithosphere asthenosphere boundary lab are clearly visible the moho depth ranges from 40 to 50 km beneath sichuan basin and from 55 to 60 km on the west side of the longmenshan lms fault the largest depth is 70 km occurring at the northern sichuan yunnan terrane the lab depth beneath sichuan basin ranges from 130 to 170 km while that on the west side of lms ranges from 100 to 120 km from the east to the west across lms there is a sudden rise of the lab followed by a gradual dip western sichuan basin is found to be surrounded by thinner lithosphere extending northeastward along the lms and southward to indochina the thinner lithosphere may indicate that the lower part of eastern tibet lithosphere is heated and delaminated by the underlying hot asthenospheric flow thus reflecting the size and direction of the flow it appears that asthenospheric flow from tibet is resisted by the cold rigid sichuan basin thus branching into northeastward and southeastward parts the complicated topography of the lithosphere likely results from this dynamic process

petrogenetic interpretation of granitoid rock series using multicationic parameters abstract granitoid rock compositions from a range of tectonic environments are plotted on a multicationic diagram devised by de la roche and his coworkers this shows that there is a systematic change through an orogenic cycle which leads progressively to the ultimate development of alkaline magmas possible source materials and mechanisms of magma generation are considered from analysis of mineral compositional vectors these suggest that most granitoid series result from a two stage process first fractional crystallisation of clinopyroxene olivine and calcic plagioclase from a basic source with tholeiitic affinities produces a magma of intermediate composition this magma then undergoes periodic mixing with a felsic magma followed by in situ fractionation to generate individual intrusions within granitoid series

overview of calcite opal deposits at or near the proposed high level nuclear waste site yucca mountain nevada usa pedogenic hypogene or both calcite opal deposits cod at yucca mountain were studied with respect to their regional and field geology petrology and petrography chemistry and isotopic geochemistry and fluid inclusions they were also compared with true pedogenic deposits tpd groundwater spring deposits gsd and calcite vein deposits cvd in the subsurface some of the data are equivocal and can support either a hypogene or pedogenic origin for these deposits however sr c and o isotope fluid inclusion and other data favor a hypogene interpretation a hypothesis that may account for all currently available data is that the cod precipitated from warm co2 rich water that episodically upwelled along faults during the pleistocene and which upon reaching the surface flowed downslope within existing alluvial colluvial eluvial or soil deposits being formed near or on the topographic surface the cod acquired characteristics of pedogenic deposits this subject relates to the suitability of yucca mountain as a high level nuclear waste site

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

are strongly peraluminous magmas derived from pelitic sedimentary sources igneous compositions that require the presence of a phase more aluminous than biotite are here designated as strongly peraluminous ps such compositions are common but subordinate in felsic rocks and exceedingly rare in more mafic rocks the term s type has been applied to many igneous rocks based largely or even solely upon their ps compositions neglecting or placing less emphasis on other criteria for sedimentary parentage in chappell and white s i and s type classification system the s type designation was in fact initially restricted to granites which were thought to have been derived from a chemically mature strongly weathered pelitic shaly source application of chappell s and white s criteria together with others based upon isotopic and phase equilibria considerations leads to the following conclusions about ps igneous rocks worldwide 1 very few ps rocks are derived entirely from pelitic sources 2 a majority are derived largely from intermediate to felsic crustal sources including

distribution of the crustal magnetic anomaly and geological structure in xinjiang china based on the high order crustal magnetic field model ngdc 720 v3 we investigate the distribution of crustal magnetic anomaly the decay characteristics of the anomaly and the relationship between the magnetic anomaly and geological structure in xinjiang china topography of the magnetic layer basement is studied through curie isothermal surface using the power spectrum method it is found that south tarim basin junggar basin and turpan hami basin have strong positive magnetic anomaly whereas west kunlun mountain altun mountain tianshan mountain and altai mountain have weak or negative anomaly the magnetic anomaly well reflects the regional tectonic structure i e three alternating mountains intervened by two basins the magnetic anomaly on the ground surface in tarim basin is well corresponding to the mafic dykes the decay of the magnetic anomaly with altitude indicates that xinjiang is a large massif composed of several magnetic blocks with different sizes in different directions the curie surface presents a feature of being shallow under mountains whereas being deep under basins roughly having an anti mirror correspondence with the moho depth

propagation of surface uplift lower crustal flow and cenozoic tectonics of the southeast margin of the tibetan plateau surface uplift of the southeast margin of the tibetan plateau is interpreted to have progressed from the northwest near the tibetan border to the southeast in the red river region of the central yunnan province china this interpretation is based on existing thermochronologic data and new mapping and sedimentologic and paleobotanic data demonstrating incision in the headwaters of the red river in pliocene time or later together with previously published data demonstrating surface uplift and a gradient in crustal thickness in the absence of upper crustal shortening this is strong evidence for growth of the southeast margin of the tibetan plateau through lower crustal flow displacement along the ailao shan red river shear zone slowed or ceased in early pliocene time and the xianshuihe xiaojiang fault system initiated accommodating diffuse deformation and rotation around the eastern himalayan syntaxis we suggest a kinematic link between the change in mode of deformation and the introduction of a weak crustal layer through lower crustal flow

differential reduction of magnetic anomalies to the pole on a massively parallel computer a finite impulse response filter was implemented on a computer with massively parallel processors to reduce a magnetic anomaly map to the magnetic pole allowing each grid node to have a different inclination and declination differential reduction to the pole drtp the dramatic speed improvement of such an implementation for the filter design and application via space domain convolution makes drtp a practical tool for hydrocarbon and mineral exploration application of this tool to magnetic anomalies in east china reveals that the northward shift in position of the anomaly maximum generated by drtp is 6 km for anomalies with dominant wavelengths of approximately 25 km in the northernmost part of the study area the shift increases as the anomaly wavelength increases shifts for all anomaly wavelengths are even larger in the southern part of the study area where the magnetic inclination is lower the shift in position of the anomaly maximum for anomalies of wavelengths 25 km in the northernmost area pro

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

geodynamic evolution and palaeogeography of the polish carpathians and adjacent areas during neo cimmerian and preceding events latest triassic earliest cretaceous

heterogeneous extrusion and exhumation of deep crustal variscan assembly geochronology of the western tatra mountains northern slovakia abstract the nature and style of mid crustal assembly and exhumation during continental collision has been investigated in the tatra mountains of the western carpathians the pre alpine basement of the western carpathians represents the easternmost exposure of the variscan orogen in europe which marks the collision of laurasia with gondwanian affiliated terranes during the palaeozoic the tatric crystalline unit of the western tatra in northern slovakia displays an inverted metamorphic sequence where a high grade unit comprising migmatites with relicts of eclogite has been thrust over a lower grade mica schist unit new geochronological and thermochronological data together with published thermobarometry illuminate the metamorphic history of the western tatra the upper unit eclogites with occasionally preserved omphacite record near isothermal decompression from 1 6 gpa to 1 0 1 2 gpa at 750 800 c which lead to intensive re equilibration at high pressure granulite facies conditions comparable to the peak metamorphic conditions of the host migmatite both eclogite and migmatite shared a retrograde p t path following the insertion of the eclogite assemblage into the migmatites the metamorphic evolution of the lower unit mica schist is constrained to peak p t conditions of 0 6 0 8 gpa and 640 and 660 c followed by retrogression this suggests that different rock types of the western tatra metamorphic core shared only their exhumation path from mid crustal levels id tims sm nd dating of garnet from eclogite yields a whole rock garnet isochron age of 337 10 ma with an initial e nd isotopic composition of 8 3 in situ u pb dating of monazite from a migmatite surrounding the eclogite shows one age population of c 380 ma whereas monazite from a migmatite away from the eclogite preserves a robust 340 11 ma age which is indistinguishable from sm nd garnet age and u pb age of zircons in the anatectic leucosome of the migmatite 347 7 ma a younger monazite age population from the migmatite of 300 16 ma is consistent with 40 ar 39 ar mica ages of c 310 ma this argues for a contemporaneous and likely shared exhumation path of the assemblage pair in situ monazite total pb analyses from the lower unit mica schists yields xenocrystic and c 370 ma ages but no geochronologic evidence for peak variscan tectonism exhumation of the deep crustal root occurred most probably in a two stage process the timing of the high pressure eclogite facies metamorphism before the onset of exhumation into the mid crust was likely between c 380 ma and 360 ma subsequent exhumation into the middle crust was coeval with migmatite generation at c 340 ma and garnet diffusion modeling suggest 30 c ma cooling rates the exhumation was likely tectonically forced by the action of a rigid indentor which prompted the weak lower crust to be heterogeneously extruded to mid crustal levels at a time coeval with anatexis and subsequently extruded with mid crustal material to the upper crust

geochemical and c o sr and u series isotopic evidence for the meteoric origin of calcrete at solitario wash crater flat nevada usa calcite rich soils calcrete in alluvium and colluvium at solitario wash crater flat nevada usa contain pedogenic calcite and opaline silica similar to soils present elsewhere in the semi arid southwestern united states nevertheless a ground water discharge origin for the solitario wash soil deposits was proposed in a series of publications proposing elevation dependent variations of carbon and oxygen isotopes in calcrete samples discharge of ground water in the past would raise the possibility of future flooding in the unsaturated zone at yucca mountain nevada site of a proposed high level nuclear waste repository new geochemical and carbon oxygen strontium and uranium series isotopic data disprove the presence of systematic elevation isotopic composition relations which are the main justification given for a proposed ground water discharge origin of the calcrete deposits at solitario wash values of 13c 4 1 to 7 8 per mil 18o 23 8 17 2 87sr 86sr 0 71270 0 71146 and initial 234u 238u activity ratios of about 1 6 in the new calcrete samples are within ranges previously observed in pedogenic carbonate deposits at yucca mountain and are incompatible with a ground water origin for the calcrete variations in carbon and oxygen isotopes in solitario wash calcrete likely are caused by pedogenic deposition from meteoric water under varying quaternary climatic conditions over hundreds of thousands of years

shear influenced partial melting in the western tatra metamorphic complex geochemistry and geochronology abstract the geochemical and isotopic characteristics as well as the age relationship between the migmatites and leucogranites present in the metamorphic basement of the western tatra mts tatric superunit central western carpathians were studied the suggested process for their formation was the progressive melting of the same metapelitic source under differing p t a h2o conditions during shearing the migmatitic leucosomes started to form by vapour present partial melting as the melting developed with increasing temperature and stress muscovite dehydration melting under both vapour present and vapour absent conditions was continued giving rise to the formation of leucogranite melt pockets of different size coupled feldspar governed fractionation and restite removal influenced the chemical and mineralogical zonation in leucogranite bodies accumulated in the pressure shadows no fractionation was observed in migmatitic leucosomes u pb tims and la mc icp ms zircon and monazite ages obtained from anatectic leucosome and leucogranite indicate that the partial melts crystallized at ca 360 365 ma the zircon u pb ages reflect the span of time encompassing partial melting melt separation and crystallization the effect of the incipient crystallization of the partial melt is recorded by the inner part of the isometric zircons th u their growth continued until the metamorphic climax at ca 750 c and 8 kbar elongate zircons th u 0 1 yielding an age of 360 5 1 9 ma 2 crystallized during initial cooling accompanied by melt crystallization the two zircon populations bracket the time interval during which the analyzed monazite ce crystallized ca 365 360 ma the u pb age of the leucogranite zircons 359 1 1 2 ma supports the thesis that the leucogranites crystallized from melt expelled from the migmatised metapelites

why no anomaly is visible over most of the continent ocean boundary in the global crustal magnetic field abstract it is generally believed that an anomaly should be expected over the continent ocean c o boundary in the global magnetic anomaly maps however such maps prepared at satellite altitude do not show an anomaly over most of the c o boundary we address this issue by a forward modelling technique we use a geographic information system gis technique to integrate information of the various geological units of continents and oceans the seismic crustal structure and standard susceptibility values of the rock types and compute a global vertically integrated susceptibility vis model in addition a remanent magnetisation model is used for the oceanic crust combining the induced and remanent magnetisation models the crustal field anomaly is predicted at a satellite altitude of 400 km for spherical harmonic degrees 16 80 the results show that an anomaly is indeed not predicted over the c o boundaries where the oceanic crust is flanked by continental regions phanerozoic in age we demonstrate that largely a c o anomaly over these regions is not even expected in the global magnetic anomaly map for degrees 1 80 confirming that it is not a long wavelength feature masked by the core field an anomaly however is predicted over some parts of the c o boundary where the flanking geological provinces over the continents are precambrian in age we argue that the vis values for the continents and oceans are largely comparable and therefore no anomaly is expected over most of the c o boundary

crustal structure of yunnan province people s republic of china from seismic refraction profiles seismic refraction profiles in yunnan province southwestern china define the crustal structure in an area of active tectonics on the southern end of the himalaya burma arc the crustal thickness ranges from 38 to 46 kilometers and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta sedimentary and silicic intrusive rocks with little mafic or ultramafic component this composition suggests a crustal evolution involving sedimentary processes on the flank of the yangtze platform rather than the accretion of oceanic island arcs as has been proposed an anomalously low upper mantle velocity observed on one profile but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy

curie isotherm map of indian subcontinent from satellite and aeromagnetic data abstract estimating depth to the bottom of the magnetic crust synonymously called the curie isotherm on a regional scale from long wavelength magnetic anomalies requires that large areas of survey data be used for the calculations there is still no consensus on the minimum survey area required to arrive at a reliable estimate of the curie isotherm depth from the available aeromagnetic data over india depth to the curie isotherm is estimated using spectral techniques we found that the significant spectral maxima required to calculate the depth to the curie isotherm existed only for 4 4 blocks in southern peninsular india up to 18 n latitude and for 5 5 blocks for the rest of the region in central india as aeromagnetic data coverage over india is incomplete we also calculate the magnetic crustal thickness from the lithospheric model of the champ satellite data for the whole country using an iterative forward modeling approach the calculated curie isotherm is shallow in the mobile belts and deeper in the cratons in both the derivations as the curie isotherms calculated from the two data sets collected at very different altitudes using totally different techniques match reasonably well it lends credence to the methodology adopted the derived curie isotherm depth map is in accordance with the basic structural trend of the major tectonic units within the indian subcontinent a comparison is made of the calculated curie isotherm depth with moho depths along available dss profiles over india and it is found that the curie depth is generally shallower than the moho depth implying that it possibly represents a thermal boundary rather than a compositional change further we find that high magnitude earthquakes are associated with high gradients in curie depth

response of yunnan crustal structure to eastward growth of the tibet plateau and subduction of the india plate in cenozoic abstract most previous studies advocate that crustal weakening in the yunnan area is predominantly the result of eastward growth of the tibetan plateau here we observe regional variations in the yunnan crustal structure from the waveform characteristic variations of receiver functions at 342 seismic stations furthermore receiver function imaging along three seismic sections reveals the response of crustal structure to different tectonic evolution our results show that northwestern yunnan is characterized by 49 64 km thick crust with multi layer low velocity materials and local lower crustal doublet these low velocity structures may reflect partial melting caused by crustal thickening associated with the eastward growth of the plateau however in southern and eastern parts of yunnan the topography of the moho varies relatively gently with crustal thicknesses of 26 42 km and widespread low velocity zones are located above the crust mantle boundary we speculate that these features might favor the action of partial melting of crust triggered by asthenospheric upwelling related to the subduction of the india plate

a plume modified lithospheric barrier to the southeastward flow of partially molten tibetan crust inferred from magnetotelluric data abstract broadband and long period magnetotelluric mt data were used to obtain a continuous image of the lithospheric electrical conductivity structure across the southeastern tibetan plateau margin where long wavelength crustal thickening and surface uplift have been attributed to the influx of weak crustal material from tibet into the adjacent yangtze block the resulting resistivity model reveals two major conductive features in the middle lower crust beneath southeastern tibet and the chuxiong basin both of which are consistent with the presence of fluids and likely enhanced by shear deformation along large faults the horizontally extensive conductor beneath southeastern tibet could be interpreted as a partially molten layer that represents topography driven crustal flow from central tibet whereas the anomalously high conductivities observed beneath the chuxiong basin require the addition of substantial amounts of saline aqueous fluids these two conductors are separated by a lithospheric scale high resistivity body that situated beneath the geologically inferred core of the emeishan large igneous province elip together with other geophysical and geological evidence we interpret this anomaly as remnants of a plume modified lithosphere that originally formed during the permian emeishan volcanism and speculate it acts as an obstruction to the southeastward crustal flow from tibet since late cenozoic these results indicate that topography driven crustal flow may contribute to crustal thickening and uplift in southeastern tibet but not in the adjacent foreland instead magmatic underplating associated with the permian plume activity could account for both the elevated topography and thickened crust of the adjacent yangtze block without the need for crustal flow

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

sequential granite emplacement a structural study of the late variscan strzelin intrusion sw poland the strzelin massif in sw poland central european variscides records a protracted igneous evolution with three main magmatic stages 1 tonalitic i 2 granodioritic and 3 tonalitic ii granitic in the northern part of this massif the strzelin intrusion proper comprises three successively emplaced rock types a medium grained biotite granite 303 2 ma a fine grained biotite granite 283 8 ma and a fine grained biotite muscovite granite based on field evidence the third variety postdates both types of the biotite granites the structural data from the three granites including their parallel approximately e w striking and steeply dipping lithological contacts and ene wsw trending subhorizontal magmatic lineations suggest that the emplacement of all three successive granite varieties was controlled by an active long lived strike slip fault striking ese wnw with a dextral sense of movement after the emplacement of the youngest biotite muscovite granite the intrusion underwent brittle extension which produced q joints striking nnw sse to n s and dipping at 55 70 wsw to w and showing evidence of broadly n s directed sinistral displacements the structural observations supported by new geochronological data indicate that the internal structure of the composite granitoid intrusion including the faint magmatic foliation and lineation formed in a long lived strike slip setting different from the subsequent post emplacement extensional tectonics that controlled the development of brittle structures

a study of spectral methods of estimating the depth to the bottom of magnetic sources from near surface magnetic anomaly data summary based on a critical evaluation of several different spectral magnetic depth determination techniques on areally large synthetic layered and random magnetization models we recommend the following considerations in the usage of the methods as necessary prerequisites to successful bottom depth determinations 1 using windows with sufficient width to ascertain that the response of the deepest magnetic layer is captured and by verifying the spectra and computing the depth estimates with the largest possible windows 300 500 km 2 avoiding filtering to remove arbitrary regional fields accomplished by compiling magnetic anomalies derived from modern spherical harmonic degree 13 earth s main field models e g recent international geomagnetic reference field models igrf or comprehensive models cm 3 ascertaining the near circularity of the autocorrelation function to avoid analysing biased spectra containing strong anomaly trends and 4 avoid determining the slopes from the exponential low wavenumber part of the spectra in the cases of layered magnetization we also describe the details of the new spectral peak forward modelling method and discuss the conditions under which the method can lead to useful results we found that despite all these precautions in some cases the results can still be erroneous and therefore we recommend a critical evaluation of the results by modelling heat flow and taking into account seismic information on the crustal and lithospheric thicknesses and seismic velocities wherever possible in the southcentral us east of the rockies where the surface heat flow ranges between 40 and 65 mw m 2 w e obtained the magnetic bottom depth of 40 10 km using the approach of the forward modelling of the spectral peak this range is similar to the seismically derived crustal thickness of 45 50 km suggesting therefore that the entire crust may be magnetic in this region because of the uncertainties in the various heat flow contributing parameters such as the variations in thermal conductivity radiogenic heat and hydraulic regime we could not constrain the lithospheric thickness beyond an estimate ranging approximately from 100 to 200 km

characteristics of the active xiaojiang fault zone in yunnan china a slip boundary for the southeastward escaping sichuan yunnan block of the tibetan plateau abstract the xiaojiang fault zone within the yunnan province china is one of the most active fault zones of the southeastern edge of the tibetan plateau this n s trending 400 km long fault zone defines the southern part of the eastern boundary of the sichuan yunnan block which is escaping southeastward from the tibet plateau and rotating around the eastern himalayan syntaxis the middle section of the fault zone splits into two branches each branch fault consists of several en echelon faults basins of various ages have developed on the step overs between the secondary faults the left lateral strike slip rate along the eastern branch is up to 9 mm a and that on the western branch is 7 mm a more than 10 m 6 historic earthquakes have occurred along the fault zone the largest was the 1833 songming earthquake of m 8 four earthquake rupture zones were discovered along the fault zone 15 trenches have been excavated along every major segment of the fault zone and 4 5 paleoearthquakes have been distinguished along the xiaojiang fault zone the average strong earthquake recurrence interval is 2000 2500 years

devonian mississippian i type granitoids in the western carpathians a subduction related hybrid magmatism abstract sims zircon u pb dating of i type granitoids from four variscan crystalline basement outcrops in the western carpathians tribec nizke tatry cierna hora and slovenske rudohorie mts implies that they originated between 367 and 353 ma therefore they belong to the earliest variscan i type granitoids the oldest devonian age at ca 367 364 ma is obtained from an enclave bearing tonalite and associated dikes of the tribec mts several granodiorites from the nizke tatry vepor and cierna hora mts 353 357 ma show younger early carboniferous ages these data require a re assessment of older models that explained the genesis of i type granitoids in the western carpathians based on the assumption of younger middle to upper carboniferous ages the i type granite massifs of the western carpathians most probably originated in an arc related environment within the galatian superterrane an assemblage of gondwana derived fragments the early age of i type magmatism in the western carpathians marks the beginning of a north dipping subduction of the paleotethys ocean under ibero ligerian and intra alpine terranes we suggest a term proto tatricum for that part of the galatian superterrane where devonian mississippian i type granitoids were emplaced now the granitoids are incorporated as a part of crystalline basement into the alpine tatric and veporic units within present west carpathian mountain chain

metamorphic evolution and fluid composition of garnet clinopyroxene amphibolites from the tatra mountains western carpathians relics suggesting an early high pressure eclogite facies stage have been identified in the garnet and clinopyroxene bearing amphibolites of the tatra mountains in the variscan basement of the western carpathians slovakia in these rocks primary omphacite cpx i has been wholly converted to symplectites of diopside cpx ii and plagioclase apart from minor inclusions in the garnet cores amphibole and plagioclase are secondary minerals formed in the kelyphitic rims between garnet and clinopyroxene several generations of amphibole pargasite hornblende cummingtonite actinolite are evidence of a transformation down to greenschist facies conditions thermobarometric calculations from mineral inclusions in the garnet cores yield 670 700 c and 10 15 kbar recording the initial path from upper amphibolite to eclogite facies conditions the attainment of the eclogite facies stability field is inferred from the composition of a reconstructed omphacite jd36 implying a minimum peak pressure of 15 16 kbar conditions of around 650 c and 8 10 kbar record the post eclogite breakdown and partial re equilibration in the amphibolite facies region the earliest fluid inclusions contain high density nitrogen dominated water absent fluid younger are polyphase brines and two phase h2o n2 ch4 inclusions with signs of heterogeneous entrapment of coexisting gas rich and water rich immiscible phases pure nitrogen 0 5 mol ch4 is considered to have been the major component during the high pressure metamorphism in contrast the later aqueous inclusions are interpreted to represent retrogression related fluids the brines have originated by leaching and re entrapment of saline melt inclusions observed in tonalitic trondhjemitic layers of the amphibolite enclosing the eclogitic relics a similar mechanism is assumed for the origin of the h2o n2 ch4 inclusions these represent relics of the primary eclogite facies related n2 inclusions re equilibrated and re entrapped during retrogression under increasing water activity a possible source of n2 and cl rich fluids was primary amphibole which decomposed during the prograde metamorphism from the amphibolite to the eclogite facies the metamorphic pt path is generally clockwise reflecting a steep increase in pressure and temperature during burial followed by decompression and cooling the retrograded eclogites occur in boudins within an allochthonous unit of an inverted metamorphic sequence their exhumation was facilitated by tectonic transport along a ductile shear zone during the variscan orogeny

crustal magnetic anomaly and curie surface beneath tarim basin china and its adjacent area based on the geomagnetic field model ngdc 720 v3 national geophysical data center the distribution of crustal magnetic anomalies and the curie surface beneath tarim basin china and its adjacent area were investigated the results show that the spatial distribution of the magnetic anomalies in tarim basin coincides with the regional tectonic structure i e a basin sandwiched between mountain ranges shallow parts of the curie surface are located in uplifted zones of the basin and correspond well to high values of heat flow in contrast deep parts of the curie surface having low values of heat flow are distributed along the depression zones of the basin the curie point depth is consistent with the measured heat flow value with a correlation coefficient of 0 65

latest pleistocene glacier advances and post younger dryas rock glacier stabilization in the mt krivaň group high tatra mountains slovakia abstract the timing of glacier disappearance and rock glacier stabilization in the highest massifs of the carpathians is still poorly documented in this paper we establish the extent and chronology of the final stages of glaciation and timing of stabilization of the uppermost rock glaciers in the tatra mountains which are the highest 2654 m a s l northernmost n 49 12 and coldest range in the carpathians on the base of morphostratigraphic principles schmidt hammer tests and glacier equilibrium line altitude ela estimation we assigned moraines and rock glaciers in the mt kriva massif sw part of high tatras to a threefold stratigraphic sequence with glacial stages advances from older to younger popradske pleso pp sucha va ecka i sv i and sucha va ecka ii sv ii landforms attributed to two younger advances sv i and sv ii were sampled for the purpose of cosmogenic 10be surface exposure dating our data show that pp and sv i glacial advances occurred during the oldest dryas climatic downturn the younger advance sv i occurred just before the bolling allerod b a warming at 14 9 0 4 ka at this time small glaciers occupied lower glacial cirques in the study area the youngest sv ii advance was characterized by rock glaciers and small debris covered glaciers confined to the highest cirques the mean exposure age of four relict rock glaciers of this stage is 11 1 0 9 ka but individual rock glacier mean ages spanned between 11 8 and 10 4 ka our research results show that the youngest moraines and rock glaciers in the tatra mountains were formed during the younger dryas yd but the final permafrost melting and rock glacier stabilization period was delayed until the early holocene but no later than 10 4 ka in high elevation cirque bottoms up to 2120 m a s l the yd glaciers and rock glaciers readvanced across land which was ice free as early as 14 8 14 2 ka thus it is likely that during the b a interphase glaciers completely disappeared in the tatra mountains the yd was the last period of glacial periglacial activity in the massif as we investigated one of the highest situated rock glaciers in the tatras up to 2220 m a s l we conclude that all rock glaciers in this massif are relict landforms which developed in response to severe lateglacial climate conditions the lateglacial climate of the tatra mountains is discussed herein on the basis of glacier equilibrium line altitude ela estimation and the vertical distribution of rock glacier belts we argue that paleoclimate significance of the presented geomorphological record may match paleobotanical proxy reconstructions and the results of climate simulations but only if the impact of enhanced temperature seasonality on glacier mass balance and rock glacier activity is taken into account

emag2 a 2 arc min resolution earth magnetic anomaly grid compiled from satellite airborne and marine magnetic measurements 1 a global earth magnetic anomaly grid emag2 has been compiled from satellite ship and airborne magnetic measurements emag2 is a significant update of our previous candidate grid for the world digital magnetic anomaly map the resolution has been improved from 3 arc min to 2 arc min and the altitude has been reduced from 5 km to 4 km above the geoid additional grid and track line data have been included both over land and the oceans wherever available the original shipborne and airborne data were used instead of precompiled oceanic magnetic grids interpolation between sparse track lines in the oceans was improved by directional gridding and extrapolation based on an oceanic crustal age model the longest wavelengths 330 km were replaced with the latest champ satellite magnetic field model mf6 emag2 is available at http geomag org models emag2 and for permanent archive at http earthref org cgi bin er cgi s erda cgi n 970

geodynamic evolution of the european variscan fold belt palaeomagnetic and geological constraints the variscan fold belt of europe resulted from the collision of africa baltica laurentia and the intervening microplates in early paleozoic times over the past few years many geological palaeobiogeographic and palaeomagnetic studies have led to significant improvements in our understanding of this orogenic belt whereas it is now fairly well established that avalonia drifted from the northern margin of gondwana in early ordovician times and collided with baltica in the late ordovician early silurian the nature of the gondwana derived armorican microplate is more enigmatic geological and new palaeomagnetic data suggest armorica comprises an assemblage of terranes or microblocks palaeobiogeographic data indicate that these terranes had similar drift histories and the rheic ocean separating avalonia from the armorican terrane assemblage closed in late silurian early devonian times an early to mid devonian phase of extensional tectonics along this suture zone resulted in formation of the relatively narrow rhenohercynian basin which closed progressively between the late devonian and early carboniferous in this contribution we review the constraints provided by palaeomagnetic data compare these with geological and palaeobiogeographic evidence and present a sequence of palaeogeographic reconstructions for these circum atlantic plates and microplates from ordovician through to devonian times

depths to the magnetic layer bottom in the south china sea area and their tectonic implications p the depths to the magnetic layer bottom z b in the south china sea scs area are estimated by computing radially averaged amplitude spectra of total field magnetic anomalies we test different sizes of moving windows in which the spectra are calculated to better understand how window sizes affect the depth estimations apart from lowering the resolutions of estimated z b larger windows do not necessarily incur presumable increases in z b in the scs area although the centroid method is taken as our primary technique for estimating z b for cross check the spectral peak and the non linear inversion methods are also applied to those windows where spectral peaks do appear in a single window we may find discrepancy in z b estimated from different techniques but for all windows showing spectral peaks the estimated z b from one technique are grossly correlated with those from another our results show that most parts of the central scs ocean basin and the northern continent ocean transition cot zone have significantly smaller z b than the surrounding continental blocks in the surrounding continental regions z b are averaged at about 34 km a depth close to the moho depth the average z b is about 22 km in the central basin but this value is much larger than the moho depth signifying that the uppermost 10 km or so of the mantle beneath the central basin is also magnetized the strong faulting and recent magmatism within the cot zone can account for the small z b near the northern continental margin the estimated z b are also found very correlative to surface heat flow this observation verifies dominant contributions to surface heat flow from incoming mantle heat flow due to thermal conduction the positive correlations observed among z b from different techniques as well as the good correlation between surface heat flow and z b support the reasoning that our estimated z b are within an acceptable range of accuracy

weakly magnetic crust in the canadian cordillera abstract current models of continental crust favor an increase in magnetization with depth here we report a counter example from the canadian cordillera where almost a full thickness of non magnetic continental crust is suggested by joint interpretation of magnetic and seismic data the magnetic field over the cordillera is characterized by complex short wavelength 100 km portion of the cordilleran field is subdued and mainly featureless and suggests a lack of magnetic sources at greater depths seismic reflection and refraction data from three major transects in the yukon and british columbia canada support this interpretation and indicate that sedimentary like formations make up the majority of the crust the dominance of shallow upper crustal magnetization in the canadian cordillera contrasts with the generally held view that the lower continental crust is the primary source for long wavelength magnetic anomalies sources for these anomalies are often assumed to be located in the lower crust when surface magnetizations are insufficient to produce such anomalies or no correlation exists between the magnetic field and the mapped surface geology the canadian cordillera appears to be an example of a non magnetic lower crust overlain by a more magnetic upper crust that is however not magnetized strongly enough to produce significant long wavelength magnetic anomalies

formation of igneous layering in granodiorite by gravity flow a field microstructure and geochemical study of the tuolumne intrusive suite at sawmill canyon california layered granites and granodiorites occur in many plutons they occur together with non layered granodiorites at the margin of the tuolumne intrusive suite one of the largest late cretaceous intrusions in the sierra nevada results from field observations quantitative microstructural analysis and whole rock compositions from the non layered kuna crest half dome and cathedral peak granodiorites and layered granodiorites from the sawmill canyon area are compared to determine which processes contributed to the formation of the layering the non layered granodiorites have foliated but homogeneous microstructures which are attributed to the orientation of crystals with high aspect ratios when the magma flowed before solidification their compositions are consistent with magma mixing and fractional crystallization the microstructure in the layered granodiorite is heterogeneous and shows normal gradation of the dense primocryst minerals magnetite hornblende and titanite at the base and inverse size gradation with large crystals of the less dense primocryst phases plagioclase and biotite at the top and a systematic change in the preferred orientation of minerals from base to top macroscopic structures in the layers indicate erosion and the action of traction currents when the layers formed and the sinking of the dense minerals and rise of interstitial melt immediately afterwards the layered rocks have similar grain size and mineral compositions to the non layered granodiorites and thus could be derived from the same magmas as the kuna crest half dome and cathedral peak non layered granodiorites the major and trace element variations in the layered rocks are very different from those in the non layered rocks and indicate a strong segregation of crystals during formation of the layers however the separation process did not fractionate the main rare earth element bearing phases from one another the macrostructure and microstructural features in the layers resemble those from hyper concentrated sediment gravity flows the layering is interpreted to have formed from gravity flows of melt and crystals initiated by syn magmatic tectonic deformation and seismic shaking two types of layering are identified one called normal layering represents material derived from a single granodiorite magma and deposited from a relatively low energy gravity flow whereas the other called melanocratic layering incorporated mafic minerals eroded from the substrate had the felsic tops of layers eroded off by subsequent flows incorporated crystals from more than one magma source and formed from gravity flows that had higher energy

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

overview of calcite opal deposits at or near the proposed high level nuclear waste site yucca mountain nevada usa pedogenic hypogene or both by c a hill y v dublyansky r s harmon c m schluter

episodic construction of the tatra granitoid intrusion central western carpathians poland slovakia consequences for the geodynamics of variscan collision and rheic ocean closure the tatra granitoid pluton central western carpathians poland slovakia is an example of composite polygenetic intrusion comprising many magmatic pulses varying compositionally from diorite to granite the u pb la mc icp ms zircon dating of successive magma batches indicates the presence of magmatic episodes at 370 368 365 360 355 and 350 340 ma all together covering a time span of 30 ma of magmatic activity the partial resorption and recycling of former granitoid material petrological cannibalism was a result of the incremental growth of the pluton and temperature in the range of 750 850 c the long lasting granitoid magmatism was connected to the prolonged subduction of oceanic crust and collision of the proto carpathian terrane with a volcanic arc and finally with laurussia closing the rheic ocean the differences in granitoid composition are the results of different depths of crustal melting more felsic magmas were generated in the outer zone of the volcanic arc whilst more mafic magmas were formed in the inner part of the supra subduction zone the source rocks of the granitoid magmas covered the compositional range of metapelite amphibolite and were from both lower and upper crust the presence of the inherited zircon cores suggests that the collision and granitoid magmatism involved crust of cadomian consolidation age c 530 and 518 ma forming the proto carpathian terrane crust of avalonian affinity 462 426 ma and melted metasedimentary rocks of volcanic arc provenance

study on crustal magnetic anomalies and curie surface in southeast tibet abstract in this paper the potsdam model pomme 6 2 is used to investigate the distributions of crustal magnetic anomalies and curie surface in southeast tibet the curie surface is compared with the regional heat flow bouguer anomaly moho depth and seismicity the results show that the magnetic anomalies and curie surface are both consistent with the geological structure sichuan basin exhibits a high positive anomaly while orogenic belts such as the longmenshan northwestern sichuan and western yunnan exhibit weak positive or negative anomalies the distribution of magnetic anomaly confirms that escape flow from east tibet branches into northeastward part and southward part on west sichuan basin due to resistance by the rigid basin the depth of curie surface ranges from 20 to 34 km the curie surface beneath the longmenshan xiaojiang and lijiang xiaojinhe faults is shallow with the uplift strike consistent with the faults the curie surface beneath sichuan basin and the central bayan har massif is deep with sheet like depressions strong earthquakes primarily occurred in the areas with the uplift of curie surface the heat flow values near tengchong lijiang dali and kunming are high and the curie surface there is shallow

third generation of the potsdam magnetic model of the earth pomme the potsdam magnetic model of the earth pomme is a geomagnetic field model providing an estimate of the earth s core crustal magnetospheric and induced magnetic fields the internal field is represented to spherical harmonic sh degree 90 while the secular variation and acceleration are given to sh degree 16 static and time varying magnetospheric fields are parameterized in geocentric solar magnetospheric gsm and solar magnetic sm coordinates and include disturbance storm time dst index and interplanetary magnetic field imf by dependent contributions the model was estimated from five years of champ satellite magnetic data all measurements were corrected for ocean tidal induction and night side ionospheric f region currents the model is validated using an independent model from a combined data set of orsted and sac c satellite measurements for the core field to sh degree 13 the root mean square rms vector difference between the two models at the center of the model period is smaller than 4 nt at the earth s surface the rms uncertainty increases to about 100 nt for the predicted field in 2010 as inferred from the difference between the two models

laser microprobe 40ar 39ar analysis of pseudotachylyte and host rocks from the tatra mountains slovakia evidence for late palaeogene seismic tectonic activity laserprobe 40ar 39ar data from fault related pseudotachylytes and granitic host rocks from the tatra mountains central western carpathians resolve the controversy over the age of propagation of the sub tatra detachment fault this major structure has resulted in exhumation of crystalline basement to the north west and subsidence and sediment deposition in the palaeogene central carpathians basin to the south east host rock biotite ages range from 331 ma to 322 ma and pseudotachylyte spot ages range from 164 ma to 28 ma of these the youngest group identify the maximum timing of the early stages of tatra mountains uplift which continued in the miocene 20 10 ma and culminated during the quaternary the wide ranging older ages are an artefact of an unsupported 40ar component that is most likely a combination of both inherited and excess argon

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation